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Transition-metal imidazolate polymers : a new family of molecule-based magnets Sánchez, Víctor 2001

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TRANSITION-METAL IMIDAZOLATE POLYMERS: A NEW FAMILY OF MOLECULE-BASED MAGNETS by VICTOR SANCHEZ B.Sc, Universidad Autonoma del Estado de Mexico, 1986 M.Sc., Universidad Autonoma del Estado de Morelos, 1992 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES (Department of Chemistry) We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA July 2001 © Victor Sanchez, 2001  In  presenting this  degree at the  thesis  in  University of  partial  fulfilment  of  of  department  this thesis for or  by  his  or  requirements  British Columbia, I agree that the  freely available for reference and study. I further copying  the  representatives.  an advanced  Library shall make  it  agree that permission for extensive  scholarly purposes may be her  for  It  is  granted  by the  understood  that  head of copying  my or  publication of this thesis for financial gain shall not be allowed without my written permission.  Department The University of British Columbia Vancouver, Canada  Date  DE-6 (2/88)  ABSTRACT  One-, two- and three-dimensional transition-metal coordination polymers involving imidazolate-based  ligands  have  been  prepared and  characterized structurally and  magnetically. A 1-D material, [Fe(pz)2] (pz = pyrazolate), which exhibits weak antiferromagnetic x  exchange (short-range), was found to possess a chain type structure in which metal ions are doubly bridged by pyrazolate ligands. In contrast, when imidazolate-type ligands were utilized in the synthesis of binary metal-azolate complexes, 3-D extended systems were produced as a consequence of the single-bridging of metal ions characteristic of imidazolate ligands. Hence, [Fe(4-abimid)2]  (4-abimid = 4-azabenzimidazolate),  x  and its cobalt  analogue, both of which have a novel 3-D single diamondoid structure, were prepared. Both of these materials exhibit long-range ferromagnetic ordering at low  temperatures.  [Co(imid)2] , (imid = imidazolate); [Cu(2-meimid) ] (2-meimid = 2-methylimidazolate); x  2  x  [Co(benzimid)2] , [Ni(benzimid)2] and [Cu(benzimid)2] (benzimid = benzimidazolate); x  x  [Cu(4,5-dichloroimid)2]  x  (4,5-dichloroimid  x  =  4 5-dichloroimidazolate);  and  i  [Co3(imid)6(imidH)2] (imidH = imidazole), all exhibit magnetic behaviour that classifies x  them as molecule-based magnets. Indirect evidence suggests that these materials also have extended 3-D lattices. [Fe (imid) (bipy)] 2  4  x  (bipy  =  2,2'-bipyridine),  [Co2(imid)4(bipy)]  x  and  [Fe (imid)8(terpy)] (terpy = 2,2':6',2"-terpyridine), have 2-D structures, a structural motif 4  x  never before seen in polymetallic imidazolates. The 'pyridine' molecules act as chelating,  ii  capping, ligands which separate the extended sheets of imidazolate-bridged metal ions in these materials. [Fe2(imid)4(bipy)] is unique in exhibiting two structural phase transitions. x  Both [Fe (imid)4(bipy)] and [Co (imid) (bipy)] exhibit long-range ferromagnetic ordering 2  x  2  at low temperatures while  4  x  [Fe4(imid)8(terpy)] shows more complex x  magnetization  behaviour. A l l three of these materials can be considered molecule-based magnets. [Fe(l-Me-2-S-imid) 0.5Cp Fe] 2  2  x  (l-Me-2-S-imid =  l-methyl-2-thioirnidazolate;  Cp Fe = ferrocene), was obtained as a rare example of a 1-D chain polymer that exhibits 2  long-range magnetic ordering. Alternating F e N and FeS chromophores along the chains is 4  4  a unique structural feature of this material. The single-bridging imidazolate ligands involved in most of the compounds studied here are efficient mediators of magnetic exchange interaction between metal centres. The observation of antiferromagnetic behaviour above a critical temperature, T , and long-range c  ferromagnetic ordering below T  c  suggests canted spin structures for many of these  compounds. Importantly, long-range tJhree-dimensional ordering of the residual spins, arising from the canting, leads to net magnetization at zero applied field. These magnetic properties classify these novel materials as molecule-based magnets.  iii  T A B L E OF CONTENTS  ABSTRACT  ii  LIST OF T A B L E S  xii  LIST OF FIGURES  xiv  LIST OF ABBREVIATIONS A N D S Y M B O L S  xxvi  ACKNOWLEDGMENTS  xxx  Chapter 1 1.1  INTRODUCTION  1  MAGNETISM  2  1.1.1  INTRODUCTION  2  1.1.2  MAGNETIC EXCHANGE  14  1.1.3  MOLECULE-BASED MAGNETS  17  1.2  DIMENSIONALITY A N D CONNECTIVITY  19  1.3  COORDINATION P O L Y M E R S  22  1.4  DIAZOLES A N D DIAZOLATES  24  1.5  PHYSICAL M E T H O D S OF C H A R A C T E R I Z A T I O N  27  1.5.1  M A G N E T I C SUSCEPTIBILITY DETERMINATION.  27  1.5.2  X - R A Y DIFFRACTION  30  1.5.3  SPECTROSCOPIC M E T H O D S  .31  1.5.3.1 INFRARED  31  1.5.3.2 UV-VIS-NTR  32  1.5.3.3 N M R  32  iv  1.6  Chapter 2  1.5.3.4 M O S S B A U E R  32  1.5.4  T H E R M A L GRAVIMETRIC ANALYSIS (TGA)  34  1.5.5  E L E M E N T A L ANALYSIS  34  OBJECTIVES A N D ORGANIZATION OF THIS THESIS  35  REFERENCES  38  POLYBIS(PYRAZOLATO)IRON(Il). A ONE-DLMENSIONAL M A T E R I A L SHOWING W E A K ANTIFERROMAGNETIC EXCHANGE  44  2.1  INTRODUCTION  44  2.2  RESULTS A N D DISCUSSION  45  2.2.1  SYNTHESIS A N D PHYSICAL PROPERTIES  45  2.2.2  S I N G L E - C R Y S T A L X - R A Y DIFFRACTION  2.3  Chapter 3  CHARACTERIZATION  46  2.2.3  INFRARED SPECTROSCOPY  49  2.2.4  M A G N E T I C BEHAVIOR  49  S U M M A R Y A N D CONCLUSIONS  52  REFERENCES  54  POLYBIS(4-AZABENZIMIDAZOLATO) LRON(II) A N D COBALT(n). 3-D SINGLE DIAMONDOID M A T E R I A L S EXHIBITING W E A K F E R R O M A G N E T I C ORDERING  56  3.1  INTRODUCTION  56  3.2  RESULTS A N D DISCUSSION  59  V  3.2.1  3.3  Chapter 4  SYNTHESES, STRUCTURES A N D PHYSICAL MEASUREMENTS  59  3.2.2  M A G N E T I C PROPERTIES  70  3.2.3  M O S S B A U E R SPECTROSCOPY  83  S U M M A R Y A N D CONCLUSIONS  86  REFERENCES  88  BINARY IMLDAZOLATES OF COBALT(II), NICKEL(H), A N D COPPER(II)  91  4.1  INTRODUCTION  91  4.2  COBALT(U) IMIDAZOLATE P O L Y M E R S  91  4.2.1  INTRODUCTION  91  4.2.2  RESULTS A N D DISCUSSION  93  4.2.2.1 SYNTHESES, PHYSICAL, T H E R M A L A N D S T R U C T U R A L CHARACTERIZATION 4.2.2.2 M A G N E T I C PROPERTIES 4.3  93 104  A NICKEL(II) BENZIMIDAZOLATE P O L Y M E R  116  4.3.1  INTRODUCTION  116  4.3.2  RESULTS A N D DISCUSSION  117  4.3.2.1 SYNTHESIS, S T R U C T U R A L , T H E R M A L A N D PHYSICAL CHARACTERIZATION 4.3.2.2 M A G N E T I C PROPERTIES 4.4  COPPER(II) IMIDAZOLATE P O L Y M E R S  vi  117 120 126  4.4.1  INTRODUCTION  126  4.4.2  RESULTS AND DISCUSSION  127  4.4.2.1 SYNTHESES, STRUCTURAL, THERMAL AND PHYSICAL CHARACTERIZATION 4.4.2.2 MAGNETIC PROPERTIES 4.5  Chapter 5  127 137  SUMMARY AND CONCLUSIONS  150  REFERENCES  152  TWO-DIMENSIONAL IRON(n) A N D COBALT(II) IMIDAZOLATE POLYMERS EXHIBITING LONG-RANGE FERROMAGNETIC ORDERING  155  5.1  INTRODUCTION  155  5.2  POLY-2,2'-BIPYRIDrNETETRAKIS(IMIDAZOLATO) DHRON(n)  156  5.2.1  156  RESULTS A N D DISCUSSION 5.2.1.1 SYNTHESIS, PHYSYCAL AND THERMAL CHARACTERIZATION  157  5.2.1.2 X - R A Y DIFFRACTION STUDIES  158  5.2.1.3 MAGNETIC PROPERTIES  169  5.2.1.4 MOSSBAUER SPECTROSCOPY  188  vii  5.3  POLY-2,2'-BIPYPJDrNETETRAKIS(IMIDAZOLATO) DICOBALT(H)  194  5.3.1  194  RESULTS A N D DISCUSSION 5.3.1.1 SYNTHESIS, T H E R M A L A N D S T R U C T U R A L CHARACTERIZATION  194  5.3.1.2 M A G N E T I C PROPERTIES 5.4  Chapter 6  197  S U M M A R Y A N D CONCLUSIONS  204  REFERENCES  208  POLY-2,2':6\2''-TEPvPYRIDrNEOCTAKIS(rMIDAZOLATO)TETRArRON(II). A V E R Y SOFT 2-D M O L E C U L E - B A S E D MAGNET  210  6.1  INTRODUCTION  210  6.2  RESULTS A N D DISCUSSION  211  6.2.1  SYNTHESIS A N D PHYSICAL PROPERTIES  211  6.2.2  X - R A Y DIFFRACTION STUDIES  213  6.2.3  M O S S B A U E R SPECTROSCOPY  218  6.2.4  M A G N E T I C PROPERTIES  219  S U M M A R Y A N D CONCLUSIONS  229  6.3  REFERENCES Chapter 7  ,  POLYBIS( 1 -METHYL-2-THIOIMIDAZOLATO)jRON(n).  231 A ONE  DIMENSIONAL M A T E R I A L EXHIBITING L O N G - R A N G E M A G N E T I C ORDERING  232  viii  7.1  INTRODUCTION  232  7.2  RESULTS A N D DISCUSSION  233  7.2.1  SYNTHESIS, PHYSICAL A N D T H E R M A L PROPERTIES  233  7.2.2  X-RAY CRYSTALLOGRAPHY  235  7.2.3  M A G N E T I C PROPERTIES  238  7.2.4  M O S S B A U E R SPECTROSCOPY  247  7.3  Chapter 8  S U M M A R Y A N D CONCLUSIONS  252  REFERENCES  254  G E N E R A L S U M M A R Y A N D SUGGESTIONS FOR F U T U R E WORK  256  8.1  GENERAL SUMMARY  256  8.2  SUGGESTIONS FOR F U T U R E W O R K  262  EXPERIMENTAL  265  9.1  INTRODUCTION  265  9.2  SYNTHESES  265  9.2.1  267  Chapter 9  IRON(II) A Z O L A T E P O L Y M E R S 9.2.1.1 Polybis(pyrazolato)iron(II), [Fe(pz) ] 2  x  267  9.2.1.2 Poly-2,2'-bipyridinete1rakis(imidazolato)diiron(Il), [Fe2(imid)4(bipy)]  x  268  9.2.1.3 Polybis(4-azabenzimidazolato)iron(II), [Fe(4-abimid) ] 2  x  ix  268  9.2.1.4 Poly-2,2':6', 2"-terpyridine octakis(imidazolato) tetTairon(n),[Fe4(imid)8(terpy)]  269  x  9.2.1.5 Polybis( 1 -memyl-2-tJiioirnidazolato) iron(II)hemidicyclopentadienyliron (II), [Fe(l-Me-2-S-imid) -0.5 Cp Fe] 2  9.2.2  2  270  x  COBALT(II) IMIDAZOLATE P O L Y M E R S  271  9.2.2.1 Polybis(irnidazolato)cobalt(II), [Co(imid) ] 2  271  x  9.2.2.2 Polybis(2-methylimidazolato)cobalt(II), [Co(2-meimid) ] 2  271  x  9.2.2.3 Polybis(4-methylimidazolato)cobalt(II), [Co(4-meimid) ] 2  272  x  9.2.2.4 Polybis(benzimidazolato)cobalt(II), [Co(benzimid) ] 2  x  272  9.2.2.5 Polybis(irmdazole)hexa(irmdazolato)tricobalt(II), [Co (imid) (imidH) ] 3  6  2  273  x  9.2.2.6 Polybis(4-azabenzimidazolato)cobalt(II), [Co(4-abimid) ] 2  ....273  x  9.2.2.7 Poly-2,2 '-bipyridinetetjakis(imidazolato)dicobalt(n), [Co (irnid) (bipy)] 2  9.2.3  4  274  x  NICKEL(II) IMIDAZOLATE P O L Y M E R  274  9.2.3.1 Polybis(benzimidazolato)nickel(ir), [Ni(benzimid) ] 2  9.2.4  COPPER IMIDAZOLATE POLYMERS  274 275  9.2.4.1 Polybis(imidazolato)copper(II), [Cu(imid) ] 2  X  x  x  275  9.2.4.2 Polybis(2-methylimidazolato)copper(II), [Cu(2-meimid) ] 2  275  x  9.2.4.3 Polybis(4-memylimidazolato)copper(LT), [Cu(4-meimid)2]x  •  276  9.2.4.4 Polybis(benzimidazolato)copper(Il), [Cu(benzimid)2]  x  276  9.2.4.5 Polybis(4,5-dichloroimidazolato)copper(Il), [Cu(4,5-dichloroimid) ]x 2  9.3  277  PHYSICAL M E T H O D S  277  9.3.1  277  M A G N E T I C SUSCEPTIBILITY M E A S U R E M E N T S  9.3.2  SINGLE C R Y S T A L X - R A Y DIFFRACTION  279  9.3.3  POWDER X - R A Y DIFFRACTION  279  9.3.4  E L E M E N T A L ANALYSIS  280  9.3.5  M O S S B A U E R SPECTROSCOPY  280  9.3.6  ELECTRONIC SPECTROSCOPY  281  9.3.7  TGA  281  9.3.8  INFRARED SPECTROSCOPY  281  9.3.9  N M R SPECTROSCOPY  282  REFERENCES...  283  APPENDIX I SINGLE C R Y S T A L X - R A Y DIFFRACTION D A T A  xi  284  LIST OF T A B L E S  Number Table 1.1  Page Mechanisms for achieving ferro- or antiferromagnetic spin coupling  15  Table 4.1  Magnetic parameters for some cobalt(II) weak ferromagnets  112  Table 4.2  UV-Vis-NIR spectra of copper(II) imidazolates. Approximate wavelength values or regions (nm)  Table 5.1  131  Magnetic parameters for three pairs of analogous iron(II) and cobalt(II) weak ferromagnets  Table 9.1  206  Commercial source of most chemical reagents employed in this thesis  Table I-1 Table 1-2  266  Crystallographic data for [Fe(pz) ] 2  284  x  Selected bond lengths (A) and angles (°) for [Fe(pz) ] with 2  x  estimated standard deviations in parentheses  285  Table 1-3  Crystallographic data for [Fe(4-abimid) ]  285  Table 1-4  Selected bond lengths (A) and angles (°) for [Fe(4-abimid) ] with  2  x  2  x  estimated standard deviations in parentheses  287  Table 1-5  Crystallographic data for a- and y-[Fe (imid)4(bipy)]  Table 1-6  Selected bond lengths (A) for a- and y-[Fe (imid) (bipy)] , with  2  2  estimated standard deviations in parentheses  xii  4  288  x  x  289  Table 1-7  Selected bond angles (°) for a- and Y-[Fe (imid) (bipy)] , with 2  4  x  estimated standard deviations in parentheses  291  Table 1-8  Crystallographic data for P-[Fe (imid) (bipy)]  Table 1-9  Selected bond angles (°) for (3-[Fe (imid) (bipy)] , with estimated  2  4  2  294  x  4  x  standard deviations in parentheses  295  Table I-10  Crystallographic data for [Fe (imid) (terpy)]  Table 1-11  Selected bond lengths (A) and angles (°) for [Fe (imid) (terpy)]  Table 1-12  Crystallographic data for [Fe(l-Me-2-S-imid) 0.5Cp Fe]  Table I-13  Selected bond lengths (A) and angles (°) for  4  g  300  x  4  2  [Fe(l-Me-2-S-imid) 0.5Cp Fe] 2  2  x  xiii  8  2  x  x  301 303  304  LIST OF FIGURES  Number Figure 1.1 Figure 1.2  Page Schematic illustration of magnetic behaviors  4  The reciprocal susceptibility % extrapolated from the x  high-temperature region as a function of temperature for independent g = 2,S=Vi spins as well as ferromagnetically coupled (0 = 10 K) and antiferromagnetically coupled (9 =-10 K) spins Figure 1.3  Schematic illustration of the magnetization, M, as a function of applied magnetic field, H, for several types of commonly observed magnetic behavior  10  Figure 1.4  A typical magnetic hysteresis loop  12  Figure 1.5  Illustration of the two types of superexchange. (a) kinetic exchange, and (b) potential exchange  16  Figure 1.6  The three regular planar nets, (a) 3-, (b) 4- and (c) 6-connected  21  Figure 1.7  Structures of pyrazole (a), and imidazole (b)  24  Figure 1.8  Schematic representation of different bridging modes for pyrazolate (1,2-diazolate) (top) and imidazolate (1,3-diazolate) (bottom) metal complexes. Spin orientations (arrows) are also illustrated as expected for the two different structural motifs  xiv  26  Figure 2.1.  Section of the polymer chain of [Fe(pz)2] showing the atom x  numbering scheme. Hydrogen atoms are omitted. (50 % probability thermal ellipsoids shown) Figure 2.2.  47  View looking almost down the c axis in the structure of [Fe(pz)2] . x  (50 % probability thermal ellipsoids shown) Figure 2.3  x  48  Heff versus temperature plot at 10 000 G for [Fe(pz)2] . x  Lines are from theory as described in the text Figure 3.1  50  View of the repeat unit of [Fe(4-abimid) ] and atom numbering 2  x  scheme (33% probability thermal ellipsoids). Hydrogen atoms are omitted Figure 3.2  60  Stereoscopic view of a section of the diamond-like framework of [Fe(4-abimid)2] . For clarity only the iron ions and the bridging x  N - C - N atoms of the imidazolate rings are shown  61  Figure 3.3  Iron ion connectivity diagram for a section of [Fe(4-abimid)2]  Figure 3.4  View of [Fe(4-abimid)2] looking down the b axis. Notice the voids  x  x  being occupied by the 4-azabenzene part of the ligand Figure 3.5  x  64  X-ray powder diffractograms of [Co(4-abimid)2]  x  (top, experimental) and [Fe(4-abimid)2] (bottom, calculated) x  Figure 3.7  63  View of [Fe(4-abimid)2] looking down the b axis. For clarity only the iron ions and the bridging N - C - N are shown  Figure 3.6  62  67  Electronic spectra of [Co(4-abimid)2] at two different mull x  concentrations  68  \  XV  Figure 3.8  T G A plots for [Fe(4-abimid) ] and [Co(4-abimid) ]  Figure 3.9  % and %T versus T plots at 500 G for [Fe(4-abimid) ] (top)  2  x  2  69  x  2  x  and [Co(4-abimid) ] (bottom) 2  Figure 3.10  71  x  Magnetization versus applied field plots at different temperatures for [Fe(4-abimid) ] (top) and [Co(4-abimid) ] (bottom) 2  Figure 3.11  x  2  73  x  Magnetic hysteresis plots at 4.8 K for [Fe(4-abimid) ] (top) and 2  x  at 10 K for [Co(4 abimid) ] (bottom) 2  Figure 3.12  74  x  %sndyj versus T plots at 10 000 G for [Fe(4-abimid) ] (top) 2  x  and [Co(4-abimid) ] (bottom) 2  76  x  Figure 3.13  A C susceptibility of [Fe(4-abimid)2]x; H  Figure 3.14  % versus T plots for[Co(4-abimid) ] at 50, 100, 500 and 10 000 G  Figure 3.15  A C susceptibility for [Co(4-abimid) ] ; H  ac  2  78  x  2  and H  = 1 G , f = 125 Hz  x  AC  = 1 G, f = 125 Hz (top)  = 1 G, #DC = 20 G, f - 125 Hz (bottom)  AC  80  82  Figure 3.16  Mossbauer spectrum of [Fe(4-abimid) ] at 77.3 K  Figure 3.17  Selected Mossbauer spectra for [Fe(4-abimid) ] at various temperatures...85  Figure 4.1  2  84  x  2  x  Asymmetric unit of [Co(imid) ] . View looking down the c axis. 2  x  Hydrogen atoms are omitted Figure 4.2  94  T G A plots for compounds [Co(imid) ] , [Co(2-meimid) ] , 2  x  2  x  [Co(4-meimid) ] , [Co(benzimid) ] , and [Co3(imid)6(imidH) ] 2  Figure 4.3  x  2  x  2  x  96  UV-Vis-NIR spectra for compounds [Co(imid) ] , (a); 2  x  [Co(2-meimid) ] , (b); [Co(4-meimid) ] , (c); [Co(benzimid) ] , (d); 2  x  2  and [Co (imid) (imidH) ] , (e) 3  6  2  x  xvi  x  2  x  97  Figure 4.4  X-ray powder diffractograms of [Co(imid)2] (top, experimental; x  bottom, calculated) Figure 4.5  X-ray powder diffractograms of [Co(2-meimid)2] (a) and x  [Co(benzimid)2] (b) x  Figure 4.6  X-Ray powder diffractograms of [Co3(imid)6(imidH)2J  x  (top, experimental) and Fe3(imid)6(imidH)2 (bottom, calculated). Figure 4.7  % versus T plots at 10 000 G for compounds [Co(imid)2] , x  [Co(2-meimid) ] , [Co(4-meimid)2] , [Co(benzimid)2] , 2  x  x  and [Co3(imid)6(imidH)2] Figure 4.8  Lieff  x  x  versus T plots at 10 000 G for compounds [Co(imid)2] , x  [Co(2-meimid) ] , [Co(4-meimid) ] , [Co(benzimid) ] , 2  x  2  and [Co3(imid)6(imidH)2] Figure 4.9  Lieff  x  2  x  x  versus T plots at 500 G for compounds [Co(imid) ] , 2  x  [Co(2-meimid) ] , [Co(4-meimid) ] , [Co(benzimid) ] , 2  x  2  and [Co3(imid)6(imidH)2] Figure 4.10  x  2  x  x  x versus T plots at 500 G for compounds [Co(imid) ] , 2  x  [Co(2-meimid) ] , [Co(4-meimid) ] , [Co(benzimid) ] , 2  x  2  and [Co3(imid)6(imidH) ] 2  Figure 4.11  x  2  x  x  Magnetization versus applied field plots at different temperatures for compounds [Co(imid) ] , (a); [Co(2-meimid)2] , (b); 2  x  x  [Co(4-meimid)2]x, (c); [Co(benzimid) ] , (d); and 2  [Co (imid) (imidH)2] , (e) 3  6  x  xvii  x  Figure 4.12  Magnetic hysteresis plots at 4.8 K for compounds [Co(imid)2] , x  (top); [Co(benzimid) ] , (middle); [Co3(imid)6(imidH) ] , (bottom) 2  Figure 4.13  x  2  x  Magnetic hysteresis plots at 4.8 K for compounds [Co(2-meimid) ] , (top); and [Co(4-meimid) ] (bottom) 2  Figure 4.14  Ill  x  2  115  x  UV-visible-near-IR spectrum for [Ni(benzimid) ] . Insert plot 2  x  shows the two highest energy d-d transition bands  118  Figure 4.15  T G A plot for [Ni(benzimid) ]  119  Figure 4.16  Plots of % and Ueff versus T for [Ni(benzimid) ]  Figure 4.17  Magnetization versus applied field plots at different  2  x  2  temperatures for [Ni(benzimid) ] 2  Figure 4.18  121  x  122  x  Magnetic hysteresis plot at 2 K for [Ni(benzimid) ] . The insert plot 2  x  shows a magnification of the central part of the hysteresis curve Figure 4.19  123  Zero-field cooling (ZFC) and field-cooling (FC) magnetization plots for [Ni(benzimid) ] at 50 G 2  Figure 4.20  125  x  T G A plots for compounds [Cu(imid) ] , [Cu(2-meimid) ] , 2  x  2  x  [Cu(4-meimid) ] , [Cu(benzimid) ] and [Cu(4,5-dichloroimid) ] 2  Figure 4.21  x  2  x  2  x  129  UV-Vis-NIR spectra for [Cu(imid) ] , (a); [Cu(2-meimid) ] , 2  x  2  x  (b); [Cu(4-meimid) ] , (c); [Cu(benzimid) ] , (d); and 2  x  2  x  [Cu(4,5-dichloroimid) ] , (e) 2  Figure 4.22 Figure 4.23  130  x  Repeat unit of blue-[Cu(imid) ] . Hydrogen atoms are omitted 2  x  133  Stereoview of a section of blue-[Cu(imid) ] including the 2  x  unit cell. Projection (001). No hydrogen atoms shown  xviii  134  Figure 4.24  X-ray powder diffractograms of blue-[Cu(imid)2] (top, calculated) x  and [Cu(imid)2]x prepared here (bottom, experimental) Figure 4.25  135  X-ray powder diffraction patterns of [Cu(2-meimid)2] , (a); x  [Cu(4-meimid) ] ,(b); [Cu(benzimid)2] , (c); and 2  x  x  [Cu(4,5-dichloroimid) ] , (d) 2  Figure 4.26  136  x  % versus T plots at 10 000 G for [Cu(imid) ] , [Cu(2-meimid) ] , 2  x  2  x  [Cu(4-meimid) ] , [Cu(benzimid) ] and [Cu(4,5-dichloroimid) ] 2  Figure 4.27  x  2  x  2  x  LL^F versus T plots at 10 000 G for [Cu(imid) ] , [Cu(2-meimid) ] , 2  x  2  [Cu(4-meimid) ] , [Cu(benzimid) ] and [Cu(4,5-dichloroimid) ] 2  x  2  x  2  Figure 4.28  Plot of x versus T for [Cu(4-meimid) ] at 500 G  Figure 4.29  Zero-field cooling (ZFC) and field-cooling (FC) magnetization  2  x  plots for [Cu(benzimid) ] at 50 G 2  Figure 4.30  x  2  x  2  x  139 140  142  143  144  Zero-field cooling (ZFC) and field-cooling (FC) magnetization plots for [Cu(imid) ] at 50 G 2  Figure 4.33  x  Zero-field cooling (ZFC) and field-cooling (FC) magnetization plots for [Cu(4,5-dichloroimid) ] at 50 G  Figure 4.32  x  Zero-field cooling (ZFC) and field-cooling (FC) magnetization plots for [Cu(2-meimid) ] at 50 G  Figure 4.31  138  145  x  Zero-field cooling (ZFC) and field-cooling (FC) magnetization plots for [Cu(4-meimid) ] at 50 G 2  x  xix  146  Figure 4.34  Magnetic hysteresis plots at 4.8 K for [Cu(4,5 dicloroimid)2] , x  (top); [Cu(benzimid) ] , (middle); and [Cu(2-meimid)2] , (bottom). 2  x  x  The insert plots show magnifications of the central part of the hysteresis curves Figure 4.35  148  Magnetic hysteresis plots at 4.8 K for [Cu(imid)2] , (top), and x  [Cu(4-meimid)2] , (bottom). The insert plots show magnifications x  Figure 5.1 Figure 5.2  of the central part of the hysteresis curves  149  T G A plot for [Fe (imid) (bipy)]  158  2  4  x  View of the repeat unit of [Fe (imid) (bipy)] (a-phase, 294 K) 2  4  x  and atom numbering scheme (33% probability thermal ellipsoids) Figure 5.3  159  ORTEP diagrams of [Fe (imid) (bipy)] (a-phase) looking down 2  4  x  the c axis. In the bottom view, bipyridine ligands have been removed to reveal the double-layer sheet extended framework. (50 % probability thermal ellipsoids) Figure 5.4  161  Iron ion connectivity diagram of a section of two double-layer sheets for the a-phase of [Fe (imid) (bipy)] . Octahedral iron (red), tetrahedral 2  4  x  iron (green). View looking approximately down the c axis Figure 5.5  162  View of the asymmetric unit of [Fe2(imid) (bipy)] (y-phase, 113 K) 4  x  and atom numbering scheme (33% probability thermal ellipsoids)  XX  164  Figure 5.6  Iron ion connectivity diagram of a section of two double-layer sheets for the y-phase of [Fe2(imid)4(bipy)] . Octahedral iron x  v  (red or semi-filled), tetrahedral iron (green or non-filled). View looking approximately down the c axis Figure 5.7  166  View of the asymmetric unit of [Fe2(imid)4(bipy)]  x  (P-phase, 143 K) and atom numbering scheme Figure 5.8  167  Comparison of coordination sphere geometries by overlapping octahedral irons (red circle) in the a - (black bonds) and y- (green bonds) phases of [Fe (imid) bipy] 2  4  168  x  Figure 5.9  % and Lie versus T plots at 10 000 G for [Fe (imid) (bipy)]  Figure 5.10  %^  Figure 5.11  ff  2  2  Meff versus T plots at 500 G for Y-[Fe (imid) (bipy)] 2  2  170  x  171  x  Magnetization versus applied field plots at different temperatures for y-[Fe2(imid) (bipy)] 2  172  x  Figure 5.12  Magnetic hysteresis plot at 4.8 K for y- [Fe (imid)4(bipy)]  Figure 5.13  Plot of % versus temperature at 10 000 G for [Fe2(imid)4(bipy)]  Figure 5.14  Plots of Z F C M , F C M and R E M for y-[Fe (imid) (bipy)] at a D C  2  173  x  _1  x  2  4  x  field o f 5 0 G Figure 5.15  174  177  Temperature dependences of the in-phase,  and out-of-phase,  X " , A C magnetic susceptibilities for y-[Fe2(imid) (bipy)] at 4  x  f=125 H z a n d i / = 1 G Figure 5.16  178  %T versus T for [Fe (imid) (bipy)] . Hoc = 10 000 G. Cooling mode 2  4  x  xxi  179  Figure 5.17  Temperature dependence of the derivatives d(%T)/dT (DC) in the cooling mode and determination of the transition temperatures for [Fe (imid) (bipy)] . Hue = 10 000 G 2  Figure 5.18  4  180  x  Cooling and warming modes yj versus temperature plots for [Fe (imid) (bipy)] . / / D C 2  4  1 000 G . Insert plot shows an  =  x  augmentation of the a<-»(3 transition region Figure 5.19  181  Temperature dependence of the derivatives d(%T)/dT (DC) in the cooling and warming modes and determination of the transition temperatures for [Fe (imid) (bipy)] . Hoc = 1 000 G 2  Figure 5.20  4  183  x  A C % versus T plot for [Fe (imid) (bipy)] . Cooling mode. 2  4  x  f=500Hz,i/ c = 2.5G  184  A  Figure 5.21  A C % versus T plot for [Fe (imid) (bipy)] . Warming mode. 2  4  x  f=500 H z , / / c = 2.5 G  185  A  Figure 5.22  Temperature dependence of A C %T in the cooling and warming modes for [Fe (imid) (bipy)] . f = 500 Hz, H c - 2.5 G . Arrow 2  4  x  A  down refers to cooling mode, arrow up refers to warming mode Figure 5.23  186  Temperature dependence of the derivatives d(%T)/dT (AC) in the cooling and warming modes and determination of the transition temperatures for the Y-phase of [Fe (imid) (bipy)] . f = 500 Hz, H 2  Figure 5.24  4  x  AC  = 2.5 G  187  Cooling and warming mode A C % versus temperature plots for [Fe (imid) (bipy)] . f = 500 Hz, H 2  4  x  AC  xxii  = 2.5 G  188  Figure 5.25  Mossbauer spectrum of [Fe2(imid)4(bipy)] at 293 K  189  Figure 5.26  Mossbauer spectra in the warming mode for [Fe2(imid)4(bipy)]  191  Figure 5.27  Mossbauer spectra in the cooling mode for [Fe2(imid)4(bipy)]  193  Figure 5.28  X-Ray powder diffractograms of [Co2(imid) (bipy)] (top, experimental)  x  x  4  x  and [Fe2(imid)4(bipy)] (bottom, calculated)  195  Figure 5.29  T G A plot for [Co (imid) (bipy)]  196  Figure 5.30  % and ^  Figure 5.31  % and p^ versus T plots at 500 G for [Co (imid) (bipy)]  Figure 5.32  Magnetization versus applied field plots at different  x  2  4  x  versus T plots at 10 000 G for [Co (imid) (bipy)] 2  ff  4  2  4  198  x  199  x  temperatures for [Co2(imid)4(bipy)]  200  x  Figure 5.33  Magnetic hysteresis plots at 4.8 K for [Co2(imid)4(bipy)]  201  Figure 5.34  Plot of y£ versus temperature at 10 000 G for [Co2(imid)4(bipy)]  Figure 5.35  Plots of Z F C M , F C M and R E M for [Co (imid) (bipy)] using a  x  x  x  2  4  x  D C field of 50 G  204  Figure 6.1  T G A plot of [Fe (imid) (terpy)]  Figure 6.2  Repeat unit of [Fe (imid)8(terpy)] showing the atom numbering  4  8  212  x  4  x  scheme; 33 % probability thermal ellipsoids are shown Figure 6.3  202  214  View of a section of [Fe4(imid)8(terpy)] looking down the a axis. x  Terpy ligands and C-4 and C-5 of imidazolate ligands have been omitted in the bottom view for clarity. Hydrogen atoms are not shown  xxiii  215  Figure 6.4  View of a section of [Fe4(imid)8(terpy)] looking down the b axis. x  For clarity, terpy ligands and C-4 and C-5 of imidazolate ligands have been omitted in the bottom view. Hydrogen atoms are not shown Figure 6.5  216  Iron ion connectivity diagram for a section of [Fe4(imid)g(terpy)] . x  Four-coordinate ions (green and pink/black ellipsoids), six-coordinate ions (blue ellipsoids) andfive-coordinateions (red ellipsoids)  217  Figure 6.6  Mossbauer spectrum of [Fe4(imid)g(terpy)] at 293 K  218  Figure 6.7  D C % and L^ff versus T at 10 000 G for [Fe (imid) (terpy)]  Figure 6.8  D C % and LL-ff versus T at 500 G for [Fe4(imid) (terpy)]  Figure 6.9  A C magnetic susceptibility for [Fe (imid)g(terpy)] , H\c = 1 G ,  x  4  8  8  4  220  x  221  x  x  f = 125 Hz  222  Figure 6.10  Plots of Z F C M , F C M and R E M for [Fe (imid) (terpy)] . Hoc = 50 G  Figure 6.11  Plot of magnetization versus applied field at different temperatures  4  8  x  for [Fe4(imid)g(terpy)]  224  x  Figure 6.12  223  Field dependence of magnetization at 4.8 K for [Fe4(imid) (terpy)] . 8  x  Central portion of hysteresis loop shown. The data obtained on decreasing the applied field are shown as • while the data obtained on increasing the applied filed are shown as A Figure 6.13  Field dependence of magnetization at 4.8 K for [Fe4(imid)g(terpy)] . x  Central portion of hysteresis loop shown Figure 7.1  225  .227  T G A plot for [Fe(l-Me-2-S-imid) 0.5Cp Fe] 2  xxiv  2  x  234  Figure 7.2  Molecular structure of the polymer chain of [Fe(l-Me-2-S-imid)2-0.5Cp2Fe] showing the atom numbering x  scheme; 33 % probability thermal ellipsoids are shown. (Hydrogen atoms are omitted) Figure 7.3.  236  View of the crystal structure of [Fe(l -Me-2-S-imid) -0.5Cp2Fe]x 2  down the c axis. 50 % thermal ellipsoids are shown Figure 7.4  237  D C % and %T versus temperature plots at 500 G for [Fe(l-Me-2-S-imid)2-0.5Cp2Fe] The line is from theory x  as described in the text. Figure 7.5  x  AC  G , f = 125 Hz  240  Plot of magnetization versus applied field at three temperatures for [Fe(l-Me-2-S-imid) 0.5Cp Fe] 2  Figure 7.7  239  A C magnetic susceptibility for [Fe(l-Me-2-S-imid)2-0.5Cp2Fe] , H =l  Figure 7.6  ;  2  241  x  Field dependence of magnetization at 4.8 K for [Fe(l-Me-2-S-imid) 0.5Cp Fe] . Central portion of hysteresis 2  2  x  loop shown Figure 7.8  ...242  Plot of %T versus temperature at three values of applied field for [Fe(l-Me-2-S-imid) 0.5Cp Fe] 2  2  243  x  Figure 7.9  Mossbauer spectrum of [Fe( 1 -Me-2-S-imid) 0.5Cp Fe] at 293 K  Figure 7.10  Mossbauer spectrum of [Fe(l -Me-2-S-imid) 0.5Cp Fe] at 77 K  249  Figure 7.11  Mossbauer spectrum of [Fe( 1 -Me-2-S-imid) 0.5Cp Fe] at 4.2 K  .251  2  2  2  2  XXV  2  x  x  2  x  248  LIST OF ABBREVIATIONS A N D S Y M B O L S  ~  approximately  %  percent  X  magnetic susceptibility  %'  in-phase magnetic susceptibility  X"  out-of-phase magnetic susceptibility  ° or deg  degree(s)  r|  hapticity  8  isomer shift  °C  degree(s) Celsius  U.B  Bohr magneton  Lieff  effective magnetic moment  0  X-ray diffraction angle or Curie-Weiss law correction term  AE  quadrupole splitting  H  applied magnetic field  H  applied magnetic field static component  H\  applied magnetic field oscillating component  1- D  one-dimensional  2- D  two-dimensional  0  xxvi  3-D  three-dimensional  F  goodness-of-fit parameter  f  frequency  cm"  wavenumber(s)  S  length of the coil  V  strength of the induced voltage  1  permeability of a material CO  period of oscillation  <P  phase angle  Cp2Fe or FeCp2  ferrocene  o  A  Angstrom(s)  bipy  2,2'-bipyridine  C  Curie constant  cm  centimeter(s)  cos  cosine  coth  hyperbolic cotangent  FCM  field-cooled magnetization  fw  formula weight  g  Lande splitting factor  G  Gauss  g  gram(s)  Hz  hertz  xxvii  imidH  imidazole  imid  imidazolate  IR  infrared  J  magnetic exchange coupling constant  k  Boltzmann constant  K  Kelvin  Me or me  methyl  ml  mililiter(s)  mmol  milimole(s)  mol  mole(s)  M  magnetization  M  saturation magnetization  N  Avogadro's number  NIR  near infrared  nm  nanometer(s)  NMR  nuclear magnetic resonance  ORTEP  Oakridge thermal ellipsoid plot  P  relative proportion of paramagnetism impurity  pz  pyrazolate  Ref.  reference  R E M or A/rem  remnant magnetization  S  total spin  s  xxviii  sin  sine  SQUID  superconducting quantum interference device  t  time  T or T  temperature  tan  tangent  Tc  Curie temperature  T  critical temperature  c  terpy  2,2':6',2"-terpyiridine  T  Neel temperature  N  TGA  thermal gravimetric analysis  UV  ultraviolet  Vis or VIS  visible  VSM  vibrating sample magnetometer  ZFCM  zero-field-cooled magnetization  xx ix  ACKNOWLEDGMENTS  I would like to express my sincere gratitude to my research supervisors, Drs. Robert C. Thompson and Alan Storr, for their remarkable support, guidance and great professional commitment during the development of this thesis. I am grateful to Dr. William M . Reiff at Northeastern University for his valuable contribution to this work and for fruitful discussions on Mossbauer spectroscopy. I would like also to thank the members of my guidance committee, Drs. C. Orvig, M . Wolf and D. Douglas for their knowledgeable suggestions during the final preparation of this dissertation. My gratitude is also extended to Drs. S. J. Rettig and B. O. Patrick of this Department for their expert crystal structure determinations, to Mr. P. Borda of this Department for microanalytical services, and to Mr. Pinder Dosanjh of the Advanced Materials and Process Engineering Laboratory at U.B.C. for assistance on the SQUID magnetometer. Many thanks are also extended to the experts in the glassblowing, electronics and mechanical shops for their aid. I also thank my colleagues Dr. D. A . Summers, Dr. Z. X u , Ms. I. Sham and Ms. C. L. Stevens for their assistance and for making my time in this Department more enjoyable. I want to give special thanks to my parents, and dedicate this work in commemoration of their fiftieth wedding anniversary. Finally, I wish to offer my deepest gratitude to my wife Emma Veronica, for her love and endless encouragement throughout this endeavour.  xxx  Chapter 1  INTRODUCTION  The search for and study of new molecule-based magnets, molecular materials that show spontaneous magnetization below some critical temperature, has become an area of considerable interest and activity in recent years [1]. Coordination polymers of the transition metals exhibiting such properties constitute a sub-classification of molecule-based magnets. The structural diversity of these materials and the fact that many contain ligands that are amenable to systematic derivatization, raises the possibility of tailoring their properties to specific desired applications [2].  Molecular magnetism is a multidisciplinary area of investigation that requires the combined efforts of chemists, physicists and materials scientists to establish the necessary fundamentals. In magnetochemistry, a chemist must be able to explain the magneto-structural correlations in a material. This work requires the use of a variety of techniques for both structural and magnetic characterization. Also important is the ability  to  synthesize  multidimensional  extended  molecular  systems,  such  as  coordination polymers, with potentially interesting magnetic properties.  One of the aims in the current work was to synthesize coordination polymers of transition metals, with different dimensionality, capable of exhibiting long-range magnetic ordering. The ligands chosen to connect the transition metals in this study  l  were diazolates, mainly 1,3-diazolates. It was anticipated that, due to the positioning of the nitrogen coordinating atoms in 1,3-diazolates, the formation of 2-D or 3-D structures (involving single azolate bridges) could be achieved.  Fundamental concepts in (i) magnetism and molecule-based magnets, (ii) dimensionality and connectivity in extended systems (coordination polymers) and (iii) the azolates as bridging ligands of transition metals are outlined in this Chapter. The techniques employed in this work in the physical characterization of materials are also briefly described. The general objectives of the research and a description of the organization of this dissertation are also included at the end of this Chapter.  1.1  MAGNETISM  1.1.1  INTRODUCTION  Magnetism can be measured using two different techniques, by the response (attraction or repulsion) of a material to a magnetic field, which is the basis for the outdated force methods [3], or by state-of-the-art induction methods that determine directly the change in magnetic flux density resulting from placement of the material in a magnetic field [4]. Magnetism is a collective effect based on the coupling of the spin or internal angular momentum of unpaired electrons throughout an entire material [5]. To simplify the following discussion, the orbital angular momentum contribution to the bulk magnetization of materials will be ignored. In other words, a spin-only model will  2  be employed. Paramagnetism is typically a consequence of the spin associated with an unpaired electron (m = A T or m = -Vi I) [5]. If a molecule or ion has only paired l  s  s  electrons, it is diamagnetic and will be repelled slightly in an applied magnetic field. If a molecule has an odd number of electrons, there will be at least one unpaired electron, and the molecule would have a net spin. Such molecules or ions are usually sufficiently isolated so that their spin-spin coupling energy, / (as deduced from the Hamiltonian H= -2/SA  -  SR) is small compared to (coupling-breaking) thermal energy. Their spins do not  couple in the absence of an applied field; these are called simple paramagnets (Figure 1.1).  When two paramagnetic metal ions interact directly such that their magnetic orbitals (those that contain the unpaired electrons) overlap, direct spin coupling operates [6]. In contrast, when paramagnetic metal ions are bridged by ligands, as in many molecule-based magnets (vide infra), superexchange coupling [7] takes place as the main mechanism responsible for spin interactions. Hence, spin-spin interactions may be large enough to enable an effective parallel -called ferromagnetic (TT)- or antiparallel -called antiferromagnetic (-IT)- coupling (Figure 1.1).  It is important to describe at this point a distinction between short-range and long range magnetic ordering. Short-range order may be described as the tendency of the paramagnetic spins to orient themselves locally relative to one another when a  3  A A A A AA A A A A AA Ferromagnetic  A  A A  A A  V A  Antiferromagnetic  A X A XA Y A XA Y A Ferrimagnetic  Canted Antiferromagnetic Figure 1.1  Schematic illustration of magnetic behaviors.  material is cooled [8]. Magnetic interactions in clusters are an example of short-range order [9]. Long-range magnetic ordering, on the other hand, is the result of an extended and cooperative ordering of the spins throughout the lattice. Long-range order  accompanies  a change in the spin phase of a material [10].  Therefore, bulk  ferromagnetic behaviour occurs when the spins in a material undergo long-range alignment in the same direction, resulting in a net magnetic moment. Hence, ferromagnetism requires that the individual unpaired spins interact collectively with each other aligning themselves parallel and in the same direction. Ferrimagnetism occurs  when,  due  to  the  presence  of  magnetic  dipoles  of  different  size,  antiferromagnetic coupling does not lead to complete cancellation of moments and a net moment remains (Figure 1.1). It is important to note that potentially commercially useful ferro- or ferrimagnetic behavior is not a property of a single molecule or ion; it, like superconductivity, is a cooperative solid-state bulk property [11].  As mentioned previously, paramagnets are characterized by their response to an applied magnetic field, H. For ideal, non-interacting spins a net magnetic moment or magnetization, M, is induced in the material when exposed to an applied field, H; where M i s proportional to H,  M=%H  The proportionality constant is termed the molar magnetic susceptibility, %. A material is magnetically isotropic when both the magnitude and the direction of M do not depend on orientation. In this case the direction of M is coincident with that of H, regardless of  5  the specimen orientation. If, on the contrary, a material is magnetically anisotropic, the direction and magnitude of M depend on orientation [12].  The magnetic  susceptibility of a simple paramagnet has a temperature  dependence that is characterized by the Curie expression [13],  _ C  The Curie constant C in cm K mol" , is defined according to the following equation, 3  1  ^Ng n S(S 2  c  + l)  2  B  3k  in which S is the spin quantum number, N is Avogadro's number, g is the Lande factor, LIB is the Bohr magneton, and k is the Boltzmann constant. If the spins experience an effective parallel (or antiparallel) exchange field due to cooperative interactions with neighboring spins this will increase (or decrease) the measured susceptibility from that predicted for independent spins by the Curie law. In these instances, the hightemperature susceptibility data often can be fit to the Curie- Weiss law [14],  C  X=  T-Q  6  where for parallel (ferromagnetic) or antiparallel (antiferromagnetic) interactions, 9 is greater or less than zero, respectively. The value of 0 can be determined from the intercept obtained in the linear extrapolation of the plot of %' versus T at high temperature. The temperature dependencies of %~ are illustrated for independent spins l  (Curie law) and spins with ferro-, and antiferromagnetic interactions in Figure 1.2.  T(K) Figure 1.2  The reciprocal susceptibility % extrapolated from the highA  temperature region as a function of temperature for independent g = 2, S = A spins as l  well as ferromagnetically coupled (9 = 10 K) and antiferromagnetically coupled (9 = -10 K) spins.  7  Very frequently in magnetic studies of materials the effective moment, 10^, or simply %T, is reported [15]. The effective moment, in units of the Bohr magneton (u. ), B  is defined by the following equation,  For a simple system comprising one mole of non-interacting spins (i.e., 0 = 0), and where S is a valid spin quantum number, |ieff is temperature-independent [15],  H =Jg S(S  + l)  2  eff  At low temperatures and high magnetic fields, conditions under which the magnetic energy (gS[ief0) is comparable in magnitude to the thermal energy (kT), the magnetization no longer obeys the equation M = %H, but approaches the limiting value or saturation magnetization, M , s  M =[i NSg s  B  For a system with non-interacting spins (i.e., 0 = 0) the temperature dependence of M can be calculated from the Brillouin function [16],  M = \L NSgB B  8  where  B=  25 + 1 '25 + 1 coth 25 25  1  ( x \  coth — 25  \2S  j  and gSfi B B  kT  Because the response to an applied magnetic field varies depending on the type of magnetic coupling within the material, a plot of magnetization as a function of applied field produces a curve with a shape characteristic of the type of magnetic coupling occurring in the material [5] (Figure 1.3). In Figure 1.3 the line labelled paramagnetic represents a simple paramagnetic system where there is no spin coupling. In this case the initial slope of the observed M versus H data is as expected for the equation M = [isNSgB. Antiferromagnetic coupling is evident if the initial slope is less than this and ferromagnetic coupling is evident if the initial slope exceeds the value expected by this equation. The M versus H plot of a diamagnetic sample will contrast with that of a paramagnetic one by having a negative  slope  (Figure  1.3).  Metamagnetism is a transformation from an antiferromagnetic state to a high-moment ferromagnetic state; that is, the spin alignment changes from antiparallel to parallel by the occurrence of an applied magnetic field [17]. This generates an M versus H curve of the type shown in Figure 1.3.  9  Ferromagnet  / /  J  j  j  /  Paramagnetic  /F e r r o m a g n e t i c  M  /Metamagnetic  —-** " ~* Diamagnetic~  Antiferromagnetic '  . _ J  H —> Figure 1.3  Schematic illustration of the magnetization, M, as a function of  applied magnetic field, H, for several types of commonly observed magnetic behavior.  When long-range magnetic ordering is present in a material, the temperature at which the spins order is termed the critical temperature, T . If the spins align c  ferromagnetically, a spontaneous magnetization in zero applied field is present and below T the material is a ferromagnet and the M versus H plot (Figure 1.3) does not c  extrapolate to zero magnetization at zero applied field. The critical temperature in this case is sometimes referred to as the Curie temperature, Tc- If a long-range antiparallel  10  alignment of spins occurs, there is no net moment below T and the susceptibility is c  zero. In this situation the critical temperature is sometimes referred to as the Neel temperature, T^. When ferrimagnetism is present in the system, the critical temperature is also referred to as the Neel temperature, 7N, and below  the material is a  ferrimagnet and under these conditions the M versus H plot (Figure 1.3), like that of a ferromagnet, does not extrapolate to zero magnetization at zero applied field.  Below T the magnetic moments for ferro- and ferrimagnets align in small c  regions (domains). The direction of the magnetic moment of adjacent domains differs, but can be aligned by application of a minimal magnetic field. This leads to history dependent magnetic behavior (hysteresis) characteristic of ferri- and ferromagnets. Thus, applying an external magnetic field will cause the domains to coalesce and form a single domain aligned with the external field. At low temperatures and high applied magnetic field, the magnet can rapidly reach a maximum magnetization, which is limited by its saturation magnetization, M . When the applied field is decreased, the spin s  alignment of the domains relaxes, but more slowly than the original alignment occurred, so that when the external field reaches zero, some remnant magnetization, Mrem, remains. Reversing the direction of the external magnetic field will cause the spins within the magnet to reverse. At a large enough applied magnetic field, the magnetization reaches saturation again, but in the opposite direction. Increasing, then, the applied magnetic field to positive values results in an approximately syrnmetric closed loop termed a hysteresis loop. A typical hysteresis loop is shown in Figure 1.4.  11  The coercive field, H , c  is the reverse magnetic field required to reduce the  magnetization of a sample to zero starting from a saturation condition magnetization. "Hard" magnets have values of H > 100 G, whereas "soft" magnets have values of < 10 c  G. Medium to large values (hundreds of G) of H are necessary for permanent magnetic c  storage of data, while low values (mG) are required for ac motors, magnetic shielding, and in the recording heads necessary to write, read and erase the recording information [18]. Hence, the T , M , and H are key parameters in ascertaining the commercial utility c  s  c  of a magnet.  -400  Figure 1.4  -200  0  200  A typical magnetic hysteresis loop.  12  400  Canted antiferromagnetism, canted ferromagnetism, metamagnetism, and spinglass behaviors are examples of other possible magnetic phenomena. The canted antiferromagnetic behavior (Figure 1.1, page 4) results from the action of antisymmetric exchange in anisotropic materials in which the coupled magnetic dipoles are not related by an inversion center [19]. The weak ferromagnetism, produced in this type of spin coupling, is due to the fact the antiparallel alignment of spins on the two sublattices have orientations slightly canted to each other. This canting leads to a non-zero magnetization at zero-applied field [20]. A material exhibiting canted antiferromagnetic behavior is referred to as a weak ferromagnet [20]. It should be noted that canted antiferromagnetism is considered to be the primary mechanism accounting for the residual magnetization observed in the molecule-based magnets studied in this dissertation. A canted ferromagnet, on the other hand, results from the relative tilting of ferromagnetically coupled spins (Figure 1.1, page 4) such that, though the material is ferromagnetic, there is a reduction of the residual moment. Finally, a spin glass occurs when there are local spatial correlations in the directions of neighboring spins, but no long-range order. For a spin glass the spin alignment is as described for a paramagnet (Figure 1.1, page 4). However, unlike a paramagnet where the directions of the spins vary with time, the spins remain fixed in their orientations for a spin glass. Hence, a spin glass has spins pointing in similar directions for short distances, but no long-range order [17].  13  1.1.2  MAGNETIC EXCHANGE  The type of spin coupling, whether ferromagnetic or antiferromagnetic, and the magnitude, can be described by the coupling interaction energy, J. When J is positive, the coupling is ferromagnetic; when it is negative, the coupling is antiferromagnetic. The value of J cannot be measured directly, but can be deduced from a mathematical model fitted to the magnetic data. Different models can give different values of J even in systems with a well defined T . Three distinct mechanisms for spin coupling have c  been proposed to lead to ferro- or antiferromagnetism. (Table 1.1). It is difficult to predict in advance which mechanism may dominate in a particular system, and more than one mechanism may be operational.  The  most straightforward type of spin coupling occurs between unpaired  electrons in orthogonal orbitals in the same spatial region. These spins couple o  ferromagnetically, and the closer the orbitals are in space (less than 3 A), the stronger the coupling [21]. This mechanism can lead only to ferromagnetic coupling.  Ferromagnetic coupling can also occur between unpaired electrons that are nominally not in the same spatial region. The most important and powerful exchange mechanism of this type is the termed superexchange. In superexchange [7], nonmagnetic moieties (atoms or molecules) can function as mediators for spin coupling between spin carriers. Anderson's theory [22] established that superexchange occurs  14  Table 1.1  Mechanisms for achieving ferro- or antiferromagnetic spin coupling. Spin interaction  Spin coupling  1. Spins in Orthogonal Orbitals  Intramolecular  Ferromagnetic  Spin coupling via Superexchange  Intramolecular  Ferro- or antiferromagnetic  Intra- or intermolecular  Ferro- or antiferromagnetic  Mechanism  2.  3. Dipole-dipole (through-space interactions)  because the metal d-orbitals, where the unpaired spins originate, overlap with filled s or p orbitals of the mediator atom or atoms. Consequently, delocalized magnetic antibonding orbitals, which include the metal ion and the intermediary atom or atoms, are formed. The spins in two such delocalized magnetic orbitals can interact in two ways: kinetic and potential exchange. Kinetic exchange arises when there is a nonorthogonal orbital interaction pathway between the bridging ligand and two magnetic centres. This process, which is illustrated in Figure 1.5, yields antiferrromagnetic coupling. On the contrary, potential exchange (Figure 1.5) happens when there is orthogonality in the orbital interaction pathway, and ferromagnetic coupling results.  15  (a) Figure 1.5  (b)  Illustration o f the two types o f superexchange.  (a) kinetic  exchange, and (b) potential exchange.  The majority o f the compounds studied i n this work are paramagnetic transition metal ions separated by imidazolate or pyrazolate ligands, which yields distances between metal ions larger than 3 A . Hence, superexchange is the main mechanism involved i n the magnetic coupling exhibited by the compounds described in this work.  A third type o f spin coupling can occur through space between spins i n orbitals that do not overlap. These interactions, which occur v i a the magnetic fields generated with each spin, are very weak and only produce magnetic ordering at temperatures below a few degrees K e l v i n  [21].  16  1.1.3  MOLECULE-BASED MAGNETS  Traditional magnetic materials are atom-based, which means that they have d- or f- orbital spin sites, and posses extended network magnetic "bonding" in at least two dimensions. Furthermore, they are prepared by high temperature methodologies. In contrast, molecule-based magnets [23]  are materials prepared utilizing the low-  temperature synthetic procedures of organic, organometallic, or coordination metal chemistry. As a result, the organic fragment may (i) be an active component with spin sites (free radicals) contributing to both the high magnetic moment and the spin coupling, or (ii) can mediate the spin coupling interaction by derealization of the spins on the metal ions throughout the ligand molecules (superexchange) [24].  The first molecular ferromagnetic compound was reported by Wickman et al. in 1967  [25].  This  five-coordinate,  square-pyramidal  complex,  cMorobis(diemyldithiocarbamato)iron(III), orders ferromagnetically at 2.46 K and is rather unusual because it represents a true molecular solid. By definition, a true molecular solid consists of neutral species bonded intermolecularly only by van der Waals interactions and/or hydrogen bonds [26]. Other examples of true molecular ferromagnets that have been described include the purely organic ferromagnets such as P-(p-nitrophenyl)nitronylnitroxide, which has a Curie temperature of 0.6 K [27], and Rassat's dinitroxide [28], which has the highest reported ordering temperature for a purely organic compound with T = 1.48 K . In contrast, most of the recently reported c  17  ferromagnetic molecular solids are more accurately described as "molecule-based". Examples include the metallocene charge-transfer salts which consist of organic and organometallic anions and cations bound by Coulomb interactions [29] and the Prussian Blue analog magnets which are three-dimensional coordination polymers involving bridging of metal ions by cyanide anions [30]. The field of molecule-based magnets is a relatively new branch of chemistry [31]. The first compounds of this kind were reported in 1986 [32], and in the last few years an increasing number of research groups have started some activity along this line. The typical synthetic approach to design moleculebased magnets consists of starting from precursors bearing a spin, then assembling them in such a way that there is no compensation of the spins at the scale of the crystal lattice.  Several  chemical  features  can stabilize  long-range  ferromagnetic  coupling. These include having as many spins as possible in orbitals oriented so that the spins can couple strongly to form a magnet. As described, the interactions between spin carriers may occur through space or through bonds. In the former case, a genuine molecular lattice with molecules or molecular ions at the lattice points is involved. In the latter case, a polymeric or extended structure is involved and in this case the magnets are termed "molecule-based". Most often the interactions are much stronger when they occur through bonds (superexchange). This is particularly true when the bridging linkages (ligands) are conjugated [7]. Therefore, an efficient strategy to obtain a molecule-based magnet is to assemble the spin bearing precursors using conjugated  18  bridging ligands with the structural capability of forming extended structures. This fundamental strategy was followed in the preparation of the molecule-based magnets investigated in the present thesis  Many other important aspects of magnetism may have been left out of the brief account presented here. The interested reader is encouraged to explore further some of the many interesting books and reviews published about this fascinating subject [1,2, 33-42].  1.2  DIMENSIONALITY A N D CONNECTIVITY  Dimensionality plays a critical role in determining the properties of materials due to, for example, the different ways that electrons interact in three-dimensional (3-D), two-dimensional (2-D), and one-dimensional (1-D) structures [43]. The study of dimensionality has a long history in chemistry and physics, although this has been primarily with the prefix "quasi" added to the description of materials. That is, quasi-ID solids, such as square-planar platinum chain compounds [44], and quasi-2D layered solids, such as copper oxide superconductors [45].  The control of dimensionality is a major challenge within the metal coordination polymer field [46]. Even when polyfunctional ligands are used to obtain high dimensional polymers, ancillary ligation by water or other solvent ligands may result in  19  low dimensionality [47]. Hence, the relatively new field of metallo-organic polymers [48], although offering great potential for chemical and structural diversity, suffers from general difficulties in the control of polymer dimensionality or framework stability. Sometimes low-dimensional coordination polymers can lack framework integrity [49], in other cases the resulting coordination polymers are frequently plagued by lattice interpenetration [50] or a framework breakdown upon removal of absorbates [51].  Synthesis at relatively higher temperatures can promote the formation of polymer frameworks of higher dimensionality through the loss of terminal ancillary ligands. Thus, for example, Wood et al. [52] have found a condensed 3D structure for [Mn(TMA)] [ T M A = trimesate (benzene-1,3,5-tricarboxylate)],  whereas a discrete  molecular complex [Mn(TMA-H2)2(H20)4] is formed at room temperature [53]. Hence, the use of synthetic methods, such as the reaction of metallocenes with molten-ligands [54], and those involving solvothermal chemistry [55], have been used in attempts to form higher dimensionality frameworks.  Connectivity is an influential concept that describes the way a set of points connects to build a lattice that is infinite in one to three dimensions, like a crystal [56]. In two dimensions, there are only three regularly connected nets [57]. In this case "regular" means a network that not only has the same number of neighbours at each site, but where there is only one type of polyhedron in the net. For 3-connected planar nets, there is a hexagonal arrangement, while the 4-connected one corresponds to a net  20  made up of quadrilaterals (not necessarily squares) and regular 6-connected nets are an array of triangles (not necessarily equilateral). The most symmetrical forms of these three regular networks are shown in Figure 1.6.  (a)  (b)  (c) Figure 1.6  The three regular planar nets, (a) 3-, (b) 4- and (c) 6-connected.  It has become more evident that connectivity (i.e. the number and arrangement of interaction pathways between neighbouring centres with localized spins) is critical in generating long-range ordered systems. Since the interaction mechanism between spins  21  connected through a chemical bonding pathway is superexchange, it is not only the connectivity between atoms that should be considered, but also connectivity between orbitals. Throughout this thesis, the concept of connectivity has been utilized for a better understanding of the relationship between extended structures and magnetic properties in several compounds studied.  Ferromagnetic interactions do not necessarily lead to long-range ferromagnetic ordering. The central point is that such long-range magnetic ordering is rigorously impossible for a system consisting of isolated molecules (zero-dimensional), or of isolated chains (one-dimensional). It may occur for a system consisting of isolated layers (two-dimensional), provided that the spins are not strictly isotropic. On the contrary, long-range magnetic ordering is the normal behaviour of a three-dimensional spin network. Therefore, the design of a molecule-based magnet requires one to create spin interactions along the three directions of space. Furthermore, these interactions must be either ferromagnetic, antiferromagnetic between non-equivalent spin lattices (ferrimagnetism), or as determined in this work, canted antiferromagnetic leading to weak ferromagnetism.  1.3  COORDINATION P O L Y M E R S  A coordination polymer may be defined as a material consisting of metal ions linked by coordinate bonds by mono-atomic or poly-atomic species forming an  22  extended structure. About 30 years ago, the main interest in coordination polymers depended mainly on the expectation of increased thermal stability for the materials. Over the last 10 years or so, the properties of ordered infinite aggregates of metal ions, connected by bridging ligands, have come to the fore as a subject for synthetic study. As in classical coordination chemistry the local electronic structure at the metal ion remains important but the connectivity of the lattice and the nature of the bridging groups tuning the inter-metallic interactions are essential in determining the properties of the bulk material.  The increasing interest in the area of coordination polymers has been motivated by the ability of the metal-ligand coordination to provide a facile approach to the controlled assembly of one-, two- and three-dimensional extended solids. This strategy presents an excellent opportunity for the construction of functional materials with interesting properties such as, second-order non-linear optical [58], electronic [59], magnetic [60], inclusion [61], and catalytic properties [62].  A general problem in the characterization of coordination polymers arises because of the extreme intractability of many of these of materials, and the consequent lack of available structural information. In addition, owing to the difficulty of obtaining single crystals of these materials, relatively few X-ray structure determinations have been carried out on coordination polymers, necessitating the use of indirect methods of structural characterization.  23  1.4  DIAZOLES A N D DIAZOLATES  Diazoles are five-membered, aromatic, two nitrogen-containing heterocyclic molecules. Among the best known of these compounds are the 1,2-diazole, pyrazole, and the 1,3-diazole, imidazole, which are shown in Figure 1.7. The role of diazoles and their anions (diazolates) as ligands in coordination chemistry is well documented by several reviews published on this topic [63 -65].  (b)  (a)  Figure 1.7  Structures of pyrazole (a), and imidazole (b).  From the point of view of molecular architecture, the most important characteristic of the diazolates is the way they bridge metal centres. Both, 1,2-diazolates and 1,3-diazolates act as exo-bidentate ligands; however, while pyrazolates generally form double ligand bridges between metals, imidazolates form only single-ligand  24  bridges [66] (Figure 1.8). This difference in the coordination modes of these two diazolates can be explained by the steric hindrance imposed by the C H group in the 2position between the two nitrogens in the 1,3-diazolate (i.e., imidazolate). As a consequence,  binary transition-metal  imidazolate  compounds  are typically 3-D  coordination polymers, whereas binary transition-metal pyrazolates have linear chain 1-D extended structures [67, 68] (Figure 1.8). Another important property of diazolate polymers is the conjugation of electronic density throughout their structures, This is an important characteristic of these ligands in terms of their ability to mediate magnetic exchange between paramagnetic centers [68].  As a consequence of their structural characteristics, paramagnetic transition metal pyrazolate and imidazolate polymers exhibit different spin coupling behaviours. Thus, while metallic pyrazolate-bridged polymers generally exhibit antiferromagnetic coupling due to antiparallel alignment of their spins (Figure 1.8 (top)), metallic imidazolate-bridged polymers possess a canted-spin structure resulting from an imperfect antiparallel alignment of the spins (Figure 1.8 (bottom)). As previously mentioned, canted-spin antiferromagnetism leads to weak ferromagnetism at low temperatures [19]. Hence, the 3-D long-range magnetic ordering exhibited by several paramagnetic transition-metal imidazolate polymers studied in this thesis, classify them as molecule-based magnets.  25  Figure 1.8  Schematic representation of different bridging modes for  pyrazolate (1,2-diazolate)  (top) and imidazolate (1,3-diazolate) (bottom) metal  complexes. Spin orientations (arrows) are also illustrated as expected for the two different structural motifs.  26  1.5  PHYSICAL M E T H O D S OF C H A R A C T E R I Z A T I O N  This section is intended to give a brief description of the principles and general usefulness of the main methods of characterization utilized in this thesis. References to detailed reviews on these techniques are given in the appropriate sections.  DC  magnetic susceptibility, thermal gravimetric analysis, X-ray powder  diffraction, UV-Vis-NIR spectroscopy and IR spectroscopy studies were performed by the author. A C magnetic susceptibility and Mossbauer spectroscopy studies were performed by Prof. William M . Reiff at the Department of Chemistry of Northeastern University, Boston, Mass., U S A . X-ray single crystal diffraction studies were carried out by Dr. Steven J. Rettig and Dr. Brian O. Patrick of this Department. Mr. Peter Borda of this Department performed the elemental analyses. Experimental details for most of the physical methods of characterization employed in this work are given in Chapter 9, section 9.3.  1.5.1  M A G N E T I C SUSCEPTIBILITY DETERMINATION  The magnetic properties of the materials investigated here were mainly studied by  D C and A C magnetization measurements.  Classical  methods  to measure  magnetization are based on the force acting on a sample when it is placed into an  27  inhomogeneous magnetic field or on the total electromotive force induced in a pick-up coil when the sample is moved in a constant magnetic field.  When an isotropic paramagnetic material is placed in an inhomogeneous magnetic field, a displacement force is applied on the sample drawing it into a region of higher field. Since the displacement force depends on the both magnetization and field gradient, measurement of the force gives direct information on the magnetic susceptibility of a material. These are the fundamentals of the force methods, such as the Gouy method, [69] the Faraday method [70, 71], and the alternating force magnetometer [72, 73].  Alternatively, the change in magnetic flux density that results from placement of the material in a magnetic field may be examined by inductive methods. If a sample is inserted into an induction detection coil, then a change in the voltage is induced in this coil associated with the insertion of the sample into the detection coil. The strength of the induced voltage is given by the equation  uN Adi v=— S dt 2  where N is the number of turns of wire, A is the cross-sectional area, S is the length of the coil, and di/dt is the frequency of current oscillation. The quantity p: is the  28  permeability of the material within the coil and is related to the magnetic susceptibility by the equation  Lt = l + 47tx  The general inductive response described in the first equation is the basis of several techniques that measure magnetic susceptibility, such as the vibrating sample magnetometer [74], A C susceptometer [75, 76], and superconducting susceptometer (SQUID) [77 - 82].  In D C (direct current) measurements, a static field, Ho, is applied, which induces a magnetization, M. In A C (alternating current) measurements, an oscillating field, Hi, is applied. Thus, the applied magnetic field can be defined as consisting of a static component HQ and an oscillating component Hi, then the magnetic field at any time, t, can be written as  H(t) = H +H cos(ox) 0  l  where co is the period of oscillation. The resulting magnetization of a sample in the oscillating magnetic field may be written as  M(t) = M +M 0  t  29  cos(aX - <p)  where cp is the phase angle by which the magnetization lags the oscillating component of the magnetic field. It can be then written  M(t) = Xo#o +X'#> cos(a>t)+x ^ sin(cot) ,,  1  where  Xo  M cos((p) x  —  and x' and X" depend on the frequency and magnitude of the oscillating field. Hence, the A C magnetic susceptibility is determined from its two components, the in-phase (or real) component, x', and the out-of-phase susceptibility (or imaginary) component, The in-phase susceptibility is an initial susceptibility with the same phase as the oscillating field. The out-of-phase susceptibility is related to the phase delay with respect to the oscillating field in the magnetically ordered phase. The presence of a nonzero x" response is characteristic of a magnet [83].  1.5.2  X - R A Y DIFFRACTION  Currently the most important method for determining molecular structure is single crystal X-ray diffraction. A n X-ray diffraction experiment consists of placing a crystal in a monochromatic X-ray beam and then measuring the position and intensity  30  of the diffracted (scattered) rays [84]. This is also the most widely used method to obtain accurate structural information about bond lengths and angles. The necessity of a single crystal to apply this technique precluded the in-depth structural characterization of several coordination polymers obtained as microcrystalline powders in this study. Nonetheless, several key structures were, in fact, obtained here by this method.  X-ray powder diffraction [85]  is used to get structural information on  microcrystalline powders; however, the information that can be obtained from a powder diffractogram is much more limited than that from single crystal X-ray diffraction. In this work, the powder diffraction patterns obtained are used to determine isomorphism between analogous compounds, and this is particularly useful when the molecular structure of one of the compounds is known.  1.5.3 1.5.3.1  SPECTROSCOPIC M E T H O D S INFRARED  Infrared (IR) spectroscopy involves direct absorption of radiation that can only occur when the vibrational motion in a molecule involves some change in its dipole moment. If this happens, a vibration is said to be infrared active. This very useful technique [86] provides, among other structural characteristics in a material, immediate information on the different chemical moieties present. IR spectroscopy was useful for  31  determining the presence or absence of neutral azoles in the compounds prepared in this work.  1.5.3.2  UV-VIS-NIR  Electronic spectroscopy of transition metal complexes can provide useful information about the metal chromophore geometry [87]. This was helpful in the current work primarily when microcrystalline samples of the compounds were obtained. Hence, electronic spectroscopy was used as an indirect method for structural characterization of some of the compounds obtained here.  1.5.3.3 N M R  Due to the paramagnetic nature and solubility properties of the main compounds synthesized here, this very powerful structural characterization tool [88, 89] had limited use in the present research. N M R was utilized here primarily to confirm the structure, and purity, of some ligand precursors.  1.5.3.4  MOSSBAUER  The discovery of the Mossbauer effect (Nuclear Gamma Resonance (ngr) spectroscopy) in 1958 [90] has led to an elegant and welcome spectroscopic technique  32  for direct microscopic observation of single ion effects and cooperative magnetic behavior in solids. Information on the type of magnetism and the onset of magnetic ordering (T  c  or 7N), can be obtained with this technique. The Mossbauer effect  experiment is based on the recoil free emission and subsequent recoil free, resonant absorption of low energy gamma rays (Ey generally < 100 kev) in the solid state for identical isotopes of a given element. The Mossbauer spectra of magnetic materials frequently show interesting features in the critical region near magnetic ordering transitions [91]. Hence, the onset of nuclear Zeeman splitting resulting from the growth of internal hyperfine fields owing to exchange fields and long-range magnetic ordering can be observed directly in Mossbauer effect spectra of appropriate metal nuclides, e.g. Fe-57 [92].  All the iron(H) imidazolate polymers obtained in this thesis were evaluated by Mossbauer spectroscopy studies. These studies were performed in order to confirm the presence of a magnetic transition in the compounds as well as the determination of the critical temperature, T , at which their long-range magnetic ordering occurs. Also this c  spectroscopic technique was utilized to further identify the different coordination geometries found in the iron(II) imidazolate type compounds. In addition, evidence of structural phase transitions occurring in one of the compounds studied was obtained from Mossbauer spectroscopy studies.  33  1.5.4  T H E R M A L GRAVIMETRIC ANALYSIS (TGA)  By monitoring the thermal decomposition of a material, additional information about its composition, and the thermal stability of a particular component of the material can be determined. In a typical experiment, the sample is placed in a very sensitive microbalance and the weight of the sample is monitored as the temperature is increased [93]. The programming capabilities of modern instrumentation involving this technique were also used here for the preparation of a coordination polymer, by thermal elimination of neutral molecules from precursor (Chapter 4, section 4.2.2.1).  1.5.5  E L E M E N T A L ANALYSIS  As an essential tool this technique provides the relative percentages of analyzed elements from which an empirical formula can be determined [94]. Purity and the composition of all the compounds described in this thesis were assessed by this technique. This technique was particularly important in the initial characterization of microcrystalline coordination polymers since spectroscopic techniques, such as IR, did not provide enough composition/structural information.  34  1.6  OBJECTIVES A N D ORGANIZATION OF THIS THESIS  The synthesis and structural and magnetic characterization of several paramagnetic transition metal diazolate polymers was carried out in the present thesis with the main purpose of contributing to fundamental understanding in the growing field of moleculebased magnets. Previous studies of compounds having mainly pyrazolate as the bridging ligand, established the ability of diazolate bridging ligands to promote magnetic interaction between paramagnetic transition metal ions [68, 95 - 98]. In the current work, new transition metal diazolate polymers, mainly with imidazolate type bridging ligands, were synthesized and found to have structures with one-, two- and three-dimensional frameworks. Hence, one aim of this work was achieved by correlating the magnetic properties of the compounds studied with their different structural dimensionalities. In this regard, the iron(II) diazolate polymers prepared here were the most successfully studied of the different metal systems because they were formed as macroscopic crystalline materials in a form suitable for single crystal X-ray diffraction characterization. Nevertheless, related cobalt(LT), nickel(II) and copper(H) imidazolate systems, which were obtainable only as microcrystalline powders, were also studied extensively since they were found to have magnetic properties that also characterize them as molecule-based magnets.  Another pursued objective, the comparison of the magnetic properties of isostructural systems possessing different transition metal ions was also possible. Thus,  35  2-D and 3-D coordination polymers of iron(II) and cobalt(II) isostructural systems provided a unique opporrxrnity to study the influence of the d electronic configuration n  on the magnetic properties of molecule-based magnets.  This thesis is structured in nine Chapters and an Appendix. Chapter 1 has introduced concepts and provided general information about the different topics involved in this work. In addition, a brief description of the physical methods of characterization has been presented. Chapter 2 concerns the characterization of polybis(pyrazolato)iron(II),  a  one-dimensional  material  showing  weak  antiferromagnetic exchange and no long-range magnetic order. Chapters 3 to 7 describe the synthesis and structural and magnetic characterization of several new imidazolatebased magnetic materials most of which are shown to exhibit properties of moleculebased magnets at low temperature. A binary iron(II) imidazolate (and its cobalt(H) analogue) with a novel 3-D single diamondoid structure is reported in Chapter 3. Binary imidazolates of Co(LT), Ni(II) and Cu(II) are described in Chapter 4. Chapters 5 and 6 describe compounds which incorporate neutral "capping ligands" and which have 2-D extended structures, a motif never before seen for metal imidazolate polymers. A rare example of a 1-D chain polymer exhibiting long-range magnetic ordering is described in Chapter 7. In Chapter 8, a general summary of this work and suggestions for future work are provided. Lastly, Chapter 9 provides experimental details of the syntheses and the methods utilized in the physical characterizations of the compounds studied in this  36  dissertation. 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C. Thompson, and J. Trotter. Can. J. Chem. 68, 1494 (1990).  96.  M . K . Ehlert, S. J. Rettig, A . Storr, R. C. Thompson, and J. Trotter. Can. J. Chem. 69, 432(1991).  97.  M . K . Ehlert, S. J. Rettig, A . Storr, and R. C. Thompson. Can. J. Chem. 70, 1121 (1992).  98.  M . K . Ehlert, S. J. Rettig, A . Storr, and R. C. Thompson. Can. J. Chem. 71, 1412(1993).  Determination  43  X-ray  Crystallography.  and Coordination  Spectroscopy.  Chemistry and its Applications.  by  Compounds.  Cambridge  John Wiley & Sons.  Chapter 2  POLYBIS(PYRAZOLATO)IRON(II). SHOWING  2.1  A ONE-DIMENSIONAL  WEAK ANTIFERROMAGNETIC  MATERIAL  EXCHANGE  INTRODUCTION  Metal coordination complexes with one-dimensional structures have long been investigated  as  materials with unusual properties.  Molecule-based  electrical conductors, and nonlinear optical materials represent applications  of  one-dimensional  coordination  polymers.  ferromagnets,  several potential  Several  studies  have  demonstrated that it is possible to modify the bulk magnetic, electronic, and optical properties of such materials [1-3]. Compared with high-dimensional materials, onedimensional molecule-based magnetic materials sometimes have larger anisotropy favoring hard magnetic materials (stronger coercive field and larger hysteresis loop) [4].  Coordination compounds containing pyrazoles or pyrazolates as terminal or bridging ligands to transition metals have been extensively studied. Reviews such as those authored by Trofimenko [5, 6] and La Monica and Ardizzoia [7] give a good account of the development and importance of this field in coordination chemistry. The ability of pyrazolates to form double bridges between transition metal ions and 1-D extended chain structures in which the metal ions are antiferromagnetically coupled via  44  the ligands has been well documented in previous research on binary M(II) pyrazolates (M = Mn, Co, Ni, or Cu) [8-11].  While iron(n) pyrazolate complexes or polymers are relatively rare, the synthesis of iron pyrazolate polymers, [Fe(pz)2] and [Fe(pz)3] , appeared in 1968 [12]. The work x  x  involved reacting pyrazole with Fe(CO)s or [CpFe(CO)2]2 in benzene or toluene solvent. Only the elemental analysis of the polymeric compounds was reported without further characterization. The extensive characterization of the 1-D polymer, [Fe(pz)2] , described x  here, is important for further discussion of other azolate transition metal polymers studied in this thesis. This model compound, [Fe(pz)2] , has permitted the determination of the x  main structural differences between the 1,2 and 1,3-diazolate bridging motifs as well as permitted a better understanding of the influence of structure on the different magnetic behaviors observed.  2.2  RESULTS A N D DISCUSSION  2.2.1  SYNTHESIS A N D PHYSICAL PROPERTIES  Details of the synthesis employed for [Fe(pz) ] are given in Chapter 9, section 2  x  9.2.1.1. In this approach, which was used previously to obtain other iron(U) azolate polymers [13], ferrocene was reacted with an excess of pyrazole under inert atmosphere conditions. The product was isolated as red brown air-sensitive crystals. In this synthetic "metallocene" approach, the formation of the polymer involves an acid-base reaction in  45  which the pyrazole N H proton is transferred to a Cp ring of ferrocene. The resulting pyrazolate binds to the iron ion liberating cyclopentadiene, in the process:  x(FeCp ) + xs(pzH)  •  2  [Fe(pz) ] + 2x(CpH) 2  x  The reaction of metallocenes with molten imidazoles has been a successful method for the preparation of divalent transition metal imidazolate coordination polymers. Often, when ferrocene is involved in this type of reaction, single crystals of the coordination polymers are obtained [13, 14]. Here, the reaction of ferrocene with pyrazole produced the polymeric Fe(II) material, [Fe(pz) ] , in needle-like crystalline 2  x  form suitable for single crystal X-ray diffraction studies.  2.2.2  SINGLE-CRYSTAL X - R A Y DIFFRACTION CHARACTERIZATION  A section of the extended structure of [Fe(pz) ] is shown in Figure 2.1. Selected 2  x  crystallographic data, atom coordinates, bond lengths and bond angles appear in Appendix I, Tables 1-1 and 1-2. In this coordination polymer iron ions are linked by double  pyrazolate  bridges  in  the  structure  generating  tetrahedral  FeNj  metal  chromophores and extended 1-D chains. The double pyrazolate bridge between the Fe ions generates a linear chain structure (Figure 2.1). A projection of the structure down the c axis is shown in Figure 2.2. This type of structure has been determined by X-ray crystallography previously for [Cu(pz) ] [8]. 2  x  46  C2  Figure 2.1.  Section of the polymer chain of [Fe(pz)2]  x  showing the atom  numbering scheme. Hydrogen atoms are omitted. (50 % probability thermal ellipsoids shown).  The Fe(l)—N(l) bond distance of 2.07(1) A is normal for an iron(II) azolate system [13, 14]. The N(l)—Fe(l>—N(l) bond angles, which range from 108.93(9) to 110.27(9)° are remarkably close to the value for a regular tetrahedron. The corresponding angles for the copper(U) analogue, for example, lie in the range 94.3(1) to 139.5(1)° [8].  47  Figure 2.2.  View looking almost down the c axis in the structure of [Fe(pz)2]x.  (50 % probability thermal ellipsoids shown).  48  2.2.3  INFRARED SPECTROSCOPY  Infrared spectroscopy was utilized to ensure that no neutral pyrazole molecules were present in the polymeric structure of [Fe(pz)2] - The sharp and intense band at ~ x  3380 cm" , expected for neutral pyrazole (N-H stretch), was absent in the LR spectrum of 1  this compound. Assignments of the vibrational spectrum of the pyrazolate ion were made previously [15].  2.2.4  M A G N E T I C BEHAVIOR  D C magnetic susceptibility measurements were made on powdered samples of [Fe(pz)2] at an applied field of 10 000 G over the temperature range 2 to 300 K. Plots of x  X and p^ff against T are given in Figure 2.3. Although no maximum is observed in the susceptibility plot, the decrease in LLsff with decreasing temperature (4.8 U , B at 300 K; 1.75 U-B at 2 K), suggests antiferromagnetic coupling, albeit very weak.  In an attempt to quantify the magnitude of the antiferromagnetic exchange in this system the magnetic data were fitted to a model appropriate for a 1-D compound. Accordingly, fits of the susceptibility data to the isotropic Heisenberg model for antiferromagnetically coupled linear chains developed by Weng [16] and Hiller et al. [17] were examined. To obtain a satisfactory fit it was necessary to include a term in the  49  expression to accommodate a fraction P of the iron ions present as a structural paramagnetic impurity. The necessity of allowing for paramagnetic impurity in analyzing magnetic data of antiferromagnetically coupled systems is not uncommon, as was found  50  to be the case in analyzing the magnetic properties of the copper(II) analogue [8]. The modified expression used was:  2 + 71.938*  2  X  =  (l-P){Ng p /kT 2  2  + P(2Ng p 2  l + 10.482x + 955.56x  3  2  IkT)  where x = \J\fkT, J is the exchange coupling constant, and g is the Lande factor. In the least squares fitting procedure used, the function minimized, F, was:  2  X calc ~ 5C  -il/2  o b s  % obs  where n = the number of data points.  The value of F provides a measure of the goodness of fit. Employing g, J (the exchange coupling parameter) and P as variable parameters the best fit of experiment to theory was obtained for g = 2.01, -J= 0.591(5) cm" and P = 0.033(2) with F= 0.011. 1  The solid lines shown in Figure 2.3 were calculated from theory employing these best fit parameter values and provide a visual indication of the goodness of fit. Clearly the magnetic properties of [Fe(pz)2] are well described by the model used. x  51  The antiferromagnetic coupling in [Fe(pz)2] is judged to be weak, based on the x  absence of a detectable maximum in the % versus T plot above 2 K and on the small value of the exchange coupling constant. To put the magnitude of the exchange observed here in some perspective it is necessary to compare it with that recorded for linear chain pyrazolates of other metals. To compare the magnitude of coupling in systems of different spin, rather than comparing J values it is appropriate to compare hJS 1 values 2  [18]. For [Fe(pz)2] this is 9.4 cm" , a value significantly smaller than the 78 cm' of the 1  1  x  copper(II) analogue [8].  In an earlier summary of [US I values for Ni(H), Mn(II), Cu(LI) and Co(H) linear 2  chain pyrazolates it was observed that the strength of coupling appears related to the total number of d electrons in the system, suggesting that covalency of the metal - ligand bonds is an important factor [19]. Consistent with this, the HJS  2  I value of [Fe(pz)2]  x  is  close to the range 10 to 50 cm" observed in Mn(II) systems and clearly outside the range 1  58 to 105 cm" observed in Cu(II) systems [19]. 1  2.3  S U M M A R Y A N D CONCLUSIONS  Polybis(pyrazolato)iron(II), [Fe(pz)2] , has an extended chain 1-D structure in x  which iron ions are doubly bridged by pyrazolate ligands. The compound exhibits weak antiferromagnetic interactions. The magnetic susceptibility data were fit to a Heisenberg  52  model for chains of antiferromagnetically coupled S = 2 metal centers, yielding the magnetic parameters -J= 0.591(5) cm" andg= 2.01. 1  In characterizing polybis(pyrazolato)iron(II), [Fe(pz)2] , as a 1-D linear chain x  polymer which incorporates double azolate  bridges  and which exhibits  weak  antiferromagnetic exchange mediated by the bridging ligands, the work confirms that the structural motif and consequent magnetic properties, that characterize binary metal pyrazolates of other metals, extend to iron(II) systems.  As mentioned previously, the analysis made here for [Fe(pz)2] will be useful in x  establishing a better understanding of the different structures, structural dimensionalities, and magnetic properties of the other transition metal azolate polymers presented in the following Chapters of this thesis.  53  References  1.  C. T. Chen and K. S Suslick. Coord. Chem. Rev. 128, 293 (1993).  2.  O. Kahn. Molecular Magnetism. V C H . New York. 1993.  3.  J. S. Miller. Ed. Extended Linear Chain Compounds. Vol. 3.Plenum. New York, 1982.  4.  P. Delahes and M . Drillon. Eds. Organic and Inorganic Linear Dimensional Crystalline Materials. N A T O : New York, 1989.  5.  S. Trofimenko. Chem. Rev. 72, 497 (1972).  6.  S. Trofimenko. Prog. Inorg. Chem. 34, 115 (1986).  7.  G. La-Monica and G. A . Ardizzoia, Prog. Inorg. Chem. 46, 151 (1997).  8.  M . K . Ehlert, S. J.Rettig, A . Storr, R. C. Thompson, and J. Trotter. Can. J. Chem. 67, 1970(1989).  9.  M . K . Ehlert, S. J.Rettig, A . Storr, R. C. Thompson, and J. Trotter. Can. J. Chem. 69,432(1991).  10.  M . K . Ehlert, S. J.Rettig, A . Storr, R. C. Thompson, F. W. B. Einstein, and R. J. and Batchelor. Can. J. Chem. 71, 331 (1993).  11.  M . K . Ehlert, A . Storr, and R. C. Thompson. Can. J. Chem. 71, 331 (1993).  12.  F. Seel, and V . Sperber. Angew. Chem. Int. Ed. 7, 70 (1968).  13.  S. J. Rettig, A . Storr, D. A . Summers, R. C. Thompson, and J. Trotter. J. Amer. Chem. Soc. 119, 8675 (1997).  14.  S. J. Rettig, A . Storr, D. A . Summers, R. C. Thompson, and J. Trotter. Can. J. Chem. 77, 425(1999).  15.  J. G. Voss; and W. L . Groeneveld. Inorg. Chim. Acta. 24,173 (1978).  16  C. H . Weng, Doctor of Philosophy Thesis, Carnegie-Mellon University, 1968.  54  17.  W. Hiller, J. Strahle, A . Datz, M . Hanack, W. F. Hatfield, and P. Gutlich. J. Am. Chem. Soc. 106, 329. (1984).  18.  S. L. Lambert, and D. N . Hendrickson. Inorg. Chem. 18, 2683 (1979).  19.  A . Storr, D. A . Summers, and R. C Thompson. Can. J. Chem. 76,1130 (1998).  55  Chapter 3  POLYBIS(4-AZABENZIMIDAZOLATO) COBALT(II).  3-D  SINGLE  IRON(II)  AND  DIAMONDOID MATERIALS  EXHIBITING WEAK FERROMAGNETIC ORDERING  3.1  INTRODUCTION  As described in Chapter 1, the ability of diazolate ligands to bridge metal ions and to mediate magnetic interactions between paramagnetic centers has been well documented [1-3]. Studies on binary copper(II), cobalt(II) nickel(II) and manganese(ir) [4-9] and iron (IT) (Chapter 2) pyrazolates show that the 1,2 positioning of the nitrogen atoms in the ligands leads to polymeric 1-D linear chain structures with double azolate bridges and antiferromagnetically coupled metal centers. In contrast, it has been suggested that the 1,3 positioning of the donor nitrogens in imidazolate ligands results in steric constraints which prevent the formation of double azolate bridges between metal ions [10]. These imidazolate ligands characteristically singly bridge metals leading to higher dimensional, 2-D or 3-D, structures often possessing interesting longrange magnetic interactions. This structural motif is exhibited by [Fe3(imid)6(imidH)2]  x  (where imidH = imidazole), a compound in which iron(II) ions are singly bridged by imidazolate ligands in an extended 3-D lattice [10].  56  Magnetic studies on [Fe3(inud)6(inudH)2] revealed antiferromagnetic coupling x  at higher temperatures but long-range ordering and weak ferromagnetism at lower temperatures. The use of 2-methylimidazolate as the bridging ligand in an analogous reaction led to an entirely different 3-D material, [Fe(2-meimid)2* 0.13Cp2Fe] (2x  meimid = 2-methylimidazolate and Cp = cyclopentadienyl) [11], which again was found to exhibit properties characteristic of molecule-based magnets at low temperatures. In expanding these studies we decided to try to prepare a 3-D Fe(U) polymer using 4azabenzimidazole as a precursor of the 4-azabenzimidazolate ion. Compared to imidazolate or 2-methylimidazolate, this ligand has an extra nitrogen, the 4-aza nitrogen, with potential to be coordinated to a metal ion. We were curious to know if this nitrogen would get involved in the coordination of the metal ion. Another interesting  difference,  compared to  imidazolate or 2-methylimidazolate,  is the  additional bulkiness that the 4-azabenzimidazolate ligand provides. Hence we were also interested in what effect the steric hindrance in the ligand would have on the structural dimensionality of the polymeric product.  The direct reaction between ferrocene and excess molten 4-azabenzimidazole yields amber-green crystals of polybis(4-azabenzimidazolato)iron(II), [Fe(4-abimid)2] . x  Single crystal X-ray diffraction studies reveal that in [Fe(4-abimid) ] the 4-aza nitrogen 2  x  is not involved in coordination to the metal, the 4-azabenz-substituent serving instead to create sufficient steric bulk in the imidazolate moiety to generate a unique 3-D diamond-like (diamondoid) extended lattice. The diamond-like structure in coordination  57  polymers has attracted the attention of synthetic and materials chemists for some time now. They provide examples of 3-D "scaffolding-like materials" of potential practical importance [12, 13] and they are part of supramolecular chemistry and the emerging cross-disciplinary field of crystal engineering [14, 15]. Since the work of Kinoshita et al., [16] on bis(adiponitrilo)copper(I) nitrate, there have been a number of papers devoted to this particular molecular motif [17-25]. The title compound, [Fe(4abimid)2] , is the first to be reported with a totally covalent, non-interpenetrating x  (single)  diamond-like network,  exhibiting  spontaneous  magnetization  at  low  temperatures.  The need to explore factors affecting characteristic properties of molecule-based magnets, such as coercivity, has been recently addressed [26]. To explore the effects of altering  the  d  n  configuration,  polybis(4-azabenzimidazolato)cobalt(n),  [Co(4-  abimid) ] , has also been synthesized and characterized here. Evidence indicates that the 2  x  polymer [Co(4-abimid)2] is isomorphous, and probably isostructural, with the polymer x  [Fe(4-abimid) ] . Although [Co(4-abimid)2] also exhibits the properties of a molecule2  x  x  based magnet its critical temperature, as well as coercive field and remnant magnetization at 4.8 K are all distinctly different from those of [Fe(4-abimid) ] . 2  x  A n article regarding the structural and magnetic properties of the compounds described in this chapter has been published recently [27].  58  3.2  RESULTS A N D DISCUSSION  3.2.1  SYNTHESES, STRUCTURES A N D PHYSICAL M E A S U R E M E N T S  The reaction of metallocenes with molten azoles has been utilized as an effective method for preparing divalent metal azolate polymers, often in macroscopic crystalline form [10, 11]. In the present work the reaction between ferrocene and excess molten 4azabenzimidazole has afforded a polymeric Fe(II) material, [Fe(4-abimid)2] , in x  macroscopic crystalline form. While, the reaction of cobaltocene with the same molten ligand generated the Co(LT) material, [Co(4-abimid) ] , as a microcrystalline powder. 2  x  Details about these syntheses are in Chapter 9, sections 9.2.1.3 and 9.2.2.6, respectively.  [Fe(4-abimid)2] , was obtained in crystalline form suitable for single crystal X x  ray diffraction studies. Crystallographic data for [Fe(4-abimid) ] , appear in Appendix I, 2  x  Table 1-3. Selected bond lengths and bond angles are shown in Appendix I, Table 1-4. The repeat unit of [Fe(4-abimid)2] is shown in Figure 3.1 and a stereoscopic view of a x  segment of the structure is shown in Figure 3.2. The structure consists of  iron(n) ions  linked by single 4-azabenzimidazolate bridges bridging through the 1,3 nitrogens giving a 3-D extended array. Coordination of the 4-aza nitrogen is not observed. The bond distances between Fe and the four nitrogen atoms in the tetrahedral chromophore are: Fe(l)—N(l) = 2.030 A , Fe(l)—N(2) = 2.046 A, Fe(l)—N(4) = 2.044 A , and Fe(l)—N(5) = 2.034 A . These values are within the expected Fe—N bond distances for  59  tetrahedral iron(IT) imidazolate complexes [10, 11]. The N—Fe(l)—N bond angles range from 102.10° to 118.24°, which correspond to angles typically obtained for FeN chromophores having a distorted tetrahedral geometry [10, 11].  Figure 3.1  4  Fused rings of six  View of the repeat unit of [Fe(4-abimid)2] and atom numbering x  scheme (33% probability thermal ellipsoids). Hydrogen atoms are omitted.  60  Figure 3.2  Stereoscopic view of a section of the diamond-like framework of  [Fe(4-abimid)2] - For clarity only the iron ions and the bridging N - C - N atoms of the x  imidazolate rings are shown.  distorted-tetrahedral iron centers form a unique covalently bonded diamond-like framework. This framework can be viewed easily in the iron ion connectivity diagram shown in Figure 3.3. Further views of this structure looking down the b axis of the unit cell are shown in Figures 3.4 and 3.5.  61  Figure 3.3  Iron ion connectivity diagram for a section of [Fe(4-abimid)2] x  62  Figure 3.4  View of [Fe(4-abixnid)2] looking down the b axis. Notice the x  voids being occupied by the 4-azabenzene part of the ligand.  63  Figure 3.5  View of [Fe(4-abimid) ]x looking down the b axis. For clarity 2  only the iron ions and the bridging N - C - N are shown.  Although coordination polymers with diamond-like structures have been reported before [17-25, 28], none of them involve iron(LT). Moreover, most of these materials present different degrees of interpenetration in their diamond-like arrays. In contrast, [Fe(4-abimid)2]  x  consists of a single, non-mterpenetjating, diamond-like  framework.  64  There are few examples of molecular compounds showing a single diamond-like motif. One of the most interesting studies of such structures was done by Hoskins and Robson  [12],  who  employed  [N(CH )4][Cu Zn (CN)4], I  II  3  large  counter  and  BF " 4  ions,  such in  as  N(CHs)4  +  in  Cu ^^'^"^'"1  tetracyanotetraphenylmethane]BF4JcC6H N02, to block the adamantane-like cavities 5  and  prevent interpenetration. The latter compound also contains molecules  of  nitrobenzene occupying the cavities. Another example of a single diamond-like framework was obtained in this laboratory [29]. The compound poly-bis(/j-2,5dimethylpyrazine)copper(I) hexafluorophosphate has a cationic diamond-like lattice where the PF6  ions occupy positions in the lattice cavities. It should be noted that these  reported single diamond-like structures have ionic lattices with counter ions occupying positions within the extended lattice, thus preventing interpenetration. Therefore, [Fe(4abimid)2] is the first example of a totally covalent coordination complex having a x  single diamond-like framework.  Extended non-diamondoid 3-D networks in compounds incorporating iron(II) and bridging imidazolate ligands have been observed before [10,  11]. The 2-  methylimidazolate iron(LI) polymer has a complex 3-D network of linear channels in which ferrocene molecules, utilized in the synthesis of the material, are trapped [11]. This contrasts with the situation seen for [Fe(4-abimid)2]x in which there is a single noninterpenetrating diamond-like lattice with nothing trapped in the lattice cavities, a consequence, presumably, of the steric bulk of the 4-azabenz-substituent (Figure 3.5).  65  By employing cobaltocene instead of ferrocene, and following the same synthetic  procedure as described for [Fe(4-abimid)2] , x  an analogous  cobalt(U)  compound, [Co(4-abimid)2] , was obtained in microcrystalline form, and its X-ray x  diffraction powder pattern was determined. The powder pattern for [Fe(4-abimid)2]  x  was calculated, for comparison with the experimentally determined one for [Co(4abimid)2] , employing the program Powdercell [30]. The X-ray powder diffractogram of x  [Co(4-abimid)2] , corresponds well with that calculated from the single-crystal data of x  [Fe(4-abimid) ] (Figure 3.6) indicating the two materials are isomorphous. Indexing 2  x  the powder data [31] for [Co(4-abimid)2] gave an orthorhombic unit cell with lattice x  o  parameters a = 9.72, b = 10.37 and c = 12.45 A , in close agreement with those of [Fe(4abimid) ] (a = 9.65, b = 10.34 and c = 12.46 A) (Appendix I, Table 1-3.). 2  x  Evidence in support of the fact the iron and cobalt compounds are isostructural in addition to being isomorphous comes from spectroscopic studies. The electronic spectrum of [Co(4-abimid)2] shows two principal absorption regions at around 1125 x  (broad), and between 580 nm to 540 nm (Figure 3.7). These bands can be assigned to the A2 -> Ti(F) and - » Ti(P) transitions, respectively, for tetrahedral cobalt(H) [32, 4  4  4  33]. The latter band seems to consist of two bands, one of them split. This complexity may result from transitions to doublet excited states occurring in this region [34]. Hence, complex envelopes in the visible region are generally observed for tetrahedral Co(II) chromophores [34]. It is also important to notice that, due to the strong bands  66  u 20  10  30  40  —I  50  29 (deg)  Figure 3.6  X-ray  powder  diffractograms  of  [Co(4-abimid)2]  x  (top,  experimental) and [Fe(4-abimid) ] (bottom, calculated). 2  x  arising presumably from charge transfer in the lowest wavelength region of the spectrum, the bands in the 540 - 580 nm region are not as well defined as usual for tetrahedral Co(II) compounds (See Chapter 4, section 4.2.2.1). Interesting also is the presence of another band at around 1750 nm, which appears very weakly in the higherconcentration mull spectrum (Figure 3.7). This low energy band corresponds to the A 4  -» T 4  2  2  transition. This band typically appears in the 1000-2000 nm region in the  67  " - •  1  500  '  1  1  1000  1  1  1500  1 2000  Wavelength (nm)  Figure 3.7  Electronic spectra of [Co(4-abimid)2] at two different mull x  concentrations.  tetrahedral Co(II) compounds, but is often too weak to be observed [33]. Comparison of the spectral data with the corresponding Tanabe-Sugano diagram for d tetrahedral 7  systems [35], shows that these transitions are consistent with Dq and B values of 541 cm" and 731 cm" respectively. In summary, the electronic spectra of [Co(4-abimid)2] 1  1  x  is consistent with tetrahedrally coordinated cobalt centers, and a structure akin to that of the iron compound. Further support that the compounds are isomorphous comes from infrared spectroscopy. The infrared spectra of [Fe(4-abimid)2] and [Co(4-abimid)2] x  show very similar vibrational bands at almost identical frequencies.  68  x  The 3-D diamond-like structure seems to confer high thermal stability on both [Fe(4-abiniid)2] and [Co(4-abimid)2] , as shown by thermal gravimetric analysis (TGA) x  x  (Figure 3.8). [Fe(4-abimid) ] 2  x  is thermally stable to 402 °C. Decomposition with  continuous weight loss occurs from 402 to 476 °C with a total weight loss of 70% of the initial mass. No additional loss of mass was observed up to the maximum temperature reached of 800 °C. [Co(4-abimid) ] is thermally more robust than [Fe(4-abimid)2] , and 2  x  x  it does not show significant weight loss until the temperature exceeds ~ 600 °C. This material shows a gradual weight loss amounting to 50 % of the initial mass over the temperature range of - 600 °C to 800 °C.  110100V V \  s5  80-  cent  90-  70-  \  [Fe(4-abimid) ] 2  •a  [Co(4-abimid) ]  fib 60-=  3  \ i  2  j 1  i  \  \ \_ "s.  50-  \  403020- — i  1  100  1  1  200  1  1  300  1  1  1  1  400  500  '  1  600  •  1  1  700  800  Temperature ( ° C )  Figure 3.8  T G A plots for [Fe(4-abimid) ] and [Co(4-abimid)2] . 2  69  x  x  3.2.2  M A G N E T I C PROPERTIES  Magnetic susceptibilities  of a powdered sample of [Fe(4-abimid)2]  x  were  measured at a field of 500 G from 2 to 300 K. Figure 3.9 presents the % versus T and %T versus T data obtained below 150 K . The value of yT decreases smoothly with temperature from the value 3.38 cm Kmol" at 300 K (corresponding to p^ff = 5.20 LIB) 3  1  to a low of 1.60 cn^Kmol" just above a critical temperature, T , of 21 K. Below T , %T 1  c  c  increases abruptly to a maximum value of 32.8 cm KmoT at 14 K before decreasing 3  1  again with temperature to 6.10 cm KmoT at 2 K . The magnetic transition at T is also 3  1  c  observed in the % versus T plot (Figure 3.9). The magnetic susceptibility, which decreases smoothly with decreasing temperature below 300 K , rises abruptly (below T ), as the temperature decreases before leveling off and approaching a saturation value. c  This magnetic behavior exhibited by [Fe(4-abimid)2] is similar to that reported x  for [Fe (imid) (imidH)2] 3  6  x  [10]  and [Fe(2-meimid) 0.13Cp Fe] 2  2  x  [11].  It suggests  antiferromagnetic coupling in which perfect antiparallel alignment of spins on neighboring metal ions does not occur due to canting of spins. This leads to a residual spin on the metal centers as the temperature is lowered. Long-range ferromagnetic ordering of these spins below T generates a ferromagnetic transition. c  70  s u  J(K)  £  J(K)  Figure 3.9  % and %T versus T plots at 500 G for [Fe(4-abimid)2] (top) and x  [Co(4-abimid)2] (bottom). x  71  The magnetization versus field plots at three temperatures, shown in Figure 3.10, reflect this anomalous magnetic behavior. The plot is linear at 35 K and extrapolates to zero magnetization at zero applied field while at 10 and 4.8 K (below T ) c  the plots extrapolate to give a net magnetization at zero applied field. These results confirm that [Fe(4-abimid)2]  x  exhibits long-range ferromagnetic order below T . c  Cycling the applied field between +55 000 and -55 000 G at 4.8 K generates a hysteresis loop, the central portion of which is shown in Figure 3.11. From this is obtained a remnant magnetization of 2100 cm Gmol" and a coercive field of 80 G. This 3  1  hysteresis magnetization result provides conclusive evidence that [Fe(4-abimid)2]  x  behaves as a magnet at low temperatures.  A spin-canted structure for [Fe(4-abimid)2] is supported by the fact that the x  highest magnetization reached, 6690 cm Gmol" , (at 4.8 K and 55 000 G) is 3  1  significantly smaller than the theoretical saturation value of 22 300 cm Gmor 3  1  [36].  Further evidence for a canted spin structure comes from the structural data of [Fe(4abimid) ] which show a feature observed before in this type of system, that is a 2  x  systematic alternation of the relative orientation of neighboring metal chromophores [10, 11]. As a measure of this the dihedral angles between the N(l)-Fe(l)-N(5) planes on adjacent, symmetry related, iron centers was examined. On every iron center, the N(l)-Fe(l)-N(5) plane forms dihedral angles of 75.4° with the corresponding planes on two of its nearest neighbors and angles of 172.5° with the corresponding planes on the other two neighbors.  72  8000  • ^6000  A  4.8 K 10 K  •  35 K  o S  s  4000  2000  30000  60000  H (G) 4000  • 3000  •  4.8 K 10 K  •  35 K  ©  S  o 2000 i rn  S u  i  A  1000  § A  t 30000  60000  #(G)  Figure 3.10  Magnetization versus applied field plots at different temperatures  for [Fe(4-abimid)2] (top) and [Co(4-abimid)2] (bottom). x  x  73  -1000  -750  -500  -250  0  250  500  750  1000  H (G)  -10000  -5000  0  5000  10000  H (G)  Figure 3.11  Magnetic hysteresis plots at 4.8 K for [Fe(4-abimid)2] (top) and x  at 10 K for [Co(4-abimid) ] (bottom). 2  x  74  The extent of the spin canting can be estimated by extrapolating the plot of magnetization (M) versus applied field (H) obtained at 4.8 K (Figure 3.10) to H = 0. This extrapolation gives a saturated moment (M (0)) of ~ 2650 cm GmoT for [Fe(43  1  s  abimid)2] - From this, an estimation of the spin canting angle, y, can be obtained using x  the following equation [37]  7 = tan  Hence, the canting angle for [Fe(4-abimid)2] is calculated to be y ~ 7°. x  In the earlier study on the related [Fe(2-meimid)2-0.13Cp2Fe] , it was observed x  that the ferromagnetic ordering appears to be repressed by the applied field [11]. The same situation, arising presumably through saturation effects, pertains to [Fe(4abimid) ] . Plots of %T and % versus T (2 to 150 K range) obtained at 10 000 G are 2  x  shown in Figure 3.12. Although the ferromagnetic transition is still observed at this applied field, the maximum in yT and the saturation value of % are both smaller than observed at an applied field of 500 G .  75  Figure 3.12  % and %T versus T plots at 10 000 G for [Fe(4-abimid)2]x (top)  and [Co(4-abimid)2] (bottom). x  76  In addition to D C measurements, the magnetic susceptibility was deterauhed in an applied A C field of 1 G at 125 Hz for [Fe(4-abimid) ] and the resulting data are 2  x  consistent with long-range ferromagnetic order. A n extremely sharp peak in the real part of the A C susceptibility, %', at 17.27 K is further confirmation of the spontaneous magnetization exhibited by this compound (Figure 3.13). A n out-of-phase component (imaginary), %", characteristic of a non-compensated moment is present also with a peak at 17.23 K (Figure 3.13). These peak maxima in x' and %" provide more accurate measures of T [38] than D C magnetic susceptibility studies (vide supra) which indicate c  the critical temperature to be 21 K .  The magnetic properties of [Co(4-abimid)2] suggest that it too can be classified x  as a spin canted low temperature molecule-based magnet. As for [Fe(4-abimid)2] , %T x  measured at an applied field of 500 G decreases with decreasing temperature from 2.30 cn^Kmol" at 300 K (corresponding to p^ff = 4.29 LI ) to a critical temperature T = 11 1  b  c  K. Below 11 K it increases abruptly, signaling the onset of long-range ferromagnetic ordering (Figure 3.9). Because of the very small remnant magnetization present in [Co(4-abimid)2] the magnetization versus field plots shown in Figure 3.10 do not x  clearly display the net magnetization at zero applied field for the data obtained below T . The non-linearity of the plots obtained at 4.8 and 10 K is, however, evident. The c  highest magnetization measured for [Co(4-abimid)2] was 3469 cm Gmor at 10 K and 3  1  x  55 000 G. This is significantly lower than the theoretical saturation value of 16 766  77  8  1  -1  1  1  1-  • X' 6H  i  4  s w  2  0+ T  r  1  10  20  15  25  T(K) Figure 3.13  A C susceptibility of [Fe(4-abirnid)2]x;  = 1 G , f = 125 Hz  crn Gmor for a S = 3/2 system [36], again consistent with spin canting providing the 3  1  source of the residual spin at low temperatures. The canting angle for [Co(4-abimid)2]  x  was estimated to be very small (~ 0.1°) employing the method described above for the iron analogue.  The x versus T plot for [Co(4-abimid)2] is somewhat different from that x  observed for [Fe(4-abimid) ] 2  x  (Figure 3.9). For [Co(4-abimid)2] , the susceptibility x  shows an incipient maximum just above T and the expected abrupt rise below T ; c  78  c  however, as the temperature is lowered further, instead of showing saturation, as in [Fe(4-abimid)2] , % passes through a maximum at 9 K and then decreases in value as the x  temperature is lowered further to 2 K (Figure 3.9). This type of behavior, which suggests the loss of long-range ferromagnetic order at the lowest temperatures, was observed previously for another cobalt(II)  spin-canted molecule-based  magnet,  polybis(formamide)bis(jU-formato)cobalt(II) [39]. In this earlier study it was observed that for the formate compound this disruption of long-range order is not seen at lower applied fields. This prompted us to examine the susceptibility versus temperature behavior of [Co(4-abimid)2] at applied fields below and above 500 G. Plots of % versus x  T obtained at applied fields ranging from 50 to 10 000 G in the temperature range 2 25 K are shown in Figure 3.14. Above T the susceptibilities are essentially field c  independent. Below T , at fields of 50, 100 and 500 G there is an abrupt rise in % c  signaling ferromagnetic ordering. At all three of these fields the susceptibility on further cooling passes through a maximum, the magnitude of which increases with decreasing applied field strength, consistent with earlier observations that ferromagnetic ordering in such systems appears to be repressed by applied fields. At the largest field studied, 10 000 G , there is no evidence of long-range ferromagnetic ordering as the susceptibility simply passes through a single maximum at about  10 K , indicative of the  antiferromagnetic coupling. This is more clearly seen in Figure 3.12 which also shows that there is no magnetic anomaly in the %T plot for [Co(4-abimid)2] at 10 000 G . In x  Figure 3.12, the susceptibility for [Co(4-abimid) ] is seen to approach a constant value 2  x  of ~ 0^043 cn^mol" at the lowest temperatures, a consequence, presumably, of the spin 1  79  0.5  • # o  • 0.4  •  -  •  A  '-. O  100 G 500 G 10 000 G  03  •  2 « S  e  50 G  •  •  0.2  _ • 0.1  {  o  0  °  0  I ft ft  0.0 10  15  20  25  J(K) Figure 3.14  %  v  e  r  s  u  s  T  P  l o t s  f  o  r  [Co(4-abimid) ] at 50, 100, 500 and 10 000 G . 2  x  canting. A t 2 K this % value corresponds to an effective magnetic moment o f 0.83 \\%. At  the three lowest fields  studied, where ferromagnetic  ordering is seen,  the  susceptibilities decrease below 9 K and, i n all cases, approach at the lowest temperature studied the same value as that recorded at 10 000 G (Figure 3.14). There is no simple explanation for this apparent loss i n ferromagnetic order at l o w temperatures. The cause could be at the single-ion level. The A electronic ground state o f tetrahedral cobalt(D) 4  2  is subject to zero-field splitting and i f this is large enough significant changes i n the  80  population of zero-field split levels at low temperatures could affect the exchange. The significance of this factor will depend of course on the magnitude of the zero-field splitting. This may account for the fact that, although the E ground state of tetrahedral 5  iron(II) is also subject to zero-field splitting, loss in ferromagnetic ordering at low temperatures is not seen for the iron analogue, [Fe(4-abimid)2] . x  A consequence of the phenomenon just discussed for the cobalt compound, [Co(4-abimid)2]x,  is  that its  hysteresis  properties measured below  T  c  depend  significantly on temperature. Measured at 10 K the hysteresis plot (central portion shown in Figure 3.11) yields  = 22 cm Gmol" and H 3  1  c o e r  = 400 G while at 4.8 K  (the temperature at which the hysteresis behaviour was measured for [Fe(4-abimid) ] ) 2  Mrem = 6 cm^Gmol" and H 1  AC  c o e  x  r = 100 G .  magnetic susceptibility measurements determined for [Co(4-abimid)2]  x  show this compound has a non magnetic ground state (Figure 3.15). In contrast to the A C susceptibility behaviour of [Fe(4-abimid)2] (Figure 3.13), the cobalt analogue x  displays just a discontinuity on the real component of the susceptibility, x', at 11 K (Figure 3.15). The imaginary component,  does not show a maximum. This result is  not totally inconsistent with the D C susceptibility study which clearly indicated a loss in ferromagnetic order at low temperatures for [Co(4-abimid)2] - In order to further x  investigate  this behavior, the A C susceptibility measurements  were done with  application of a small D C field. It was expected that the presence of a low D C magnetic  81  • i  0.060  1  i • i  1  i • i • i  1  i • i • i  i  1  i  1  1  i  0.055 -  x'  0.050 0.045 0.040 |  0.035 H  'g  0.030 H  ^  0.0250.0200.015 0.010 -  A  0.005 0.000 3  4  5  6  • i 7  1  i • i i • i——r i i 8 9 10 11 12 13 14 15 16 1  1  1  T(K)  0.060 -  —  r  •  i  x'  .*  1  i  1  i  0.0550.050-  ••  0.045-  ©  s s w  :  0.0400.035-  -  0.030-  -  0.0250.020 -  -  0.0150.010-  x"  :  0.005-  -  0.000 - — 1  i  1  1  1  1  1  1  T(K) Figure 3.15 (top) and H  AC  A C susceptibility for [Co(4-abirnid) ] ; H 2  = 1 G, Hoc = 20 G, f = 125 Hz (bottom).  82  x  AC  = 1 G, f = 125 Hz  field (20 G) would help to reveal the magnetic transition in the A C susceptibility study of [Co(4-abimid)2] - As can be seen in Figure 3.15 the application of the small D C field x  had basically no effect on the A C susceptibility behaviour.  Hence, in concordance with the magnetic studies discussed above it was found that, although [Co(4-abimid) ] also exhibits the properties of a molecule-based magnet 2  x  its critical temperature, as well as coercive field and remnant magnetization at 4.8 K are all markedly different from those exhibited by [Fe(4-abimid)2] . x  3.2.3  M O S S B A U E R SPECTROSCOPY  The Mossbauer spectrum of [Fe(4-abimid)2] shows a single quadrupole split x  doublet at 77.3 K (Figure 3.16) corresponding to a single tetrahedral site, and consistent with the structure determined single crystal X-ray diffraction studies (Figure 3.1). The isomer shift of about 0.83 mm s" at 77.3 K is typical of a tetrahedral ferrous 1  chromophore [40] whereas the quadrupole splitting of 3.01 mm s" indicates a large low 1  symmetry ligand field component lifting the degeneracy of the nominal E ground state 5  of regular T j symmetry [41]. This single, sharp, narrow line-width doublet is maintained down to 18.5 K (Figure 3.17). At a temperature of about 18 K magnetic hyperfine splitting occurs signaling the onset of long-range magnetic order. This is consistent with the findings of the magnetization experiments discussed above and the  83  10  -2  V e l o c i t y R e l a t i v e to F e ( m m s ) Figure 3.16  Mossbauer spectrum of [Fe(4-abimid)2] at 77.3 K. x  temperature is in good agreement with the ones determined by the D C and A C susceptibility measurements (21 K and 17.27 K respectively). For a unique Fe(II) site the number of hyperfme lines should be six. Careful examination of the spectra, particularly the one at 4.3 K (Figure 3.17), reveals more than six lines suggesting the presence of at least two unique iron sites. This is not in agreement with the higher temperature X-ray diffraction structure and suggest a structural phase change at low temperatures. A low temperature X-ray diffraction structure determination for [Fe(4-abimid)2] (below 18 K) is needed to confirm this finding. x  84  Oj. 3-  »i.  mm i  77.3 K  6 9 -6  0  2  0  2  4  0 3  19 K  6 9^ 12  -  6  ^  -  2  18.5 K  s  6  "". f  e  '•G a  e -2  =  18 K  S  o  V -2 0  15 K  "V -2  4.3 K  \  /\  0  /V^ w -2  V e l o c i t y relative to F e / m m s" Figure 3.17  Selected Mossbauer spectra for [Fe(4-abimid)2] at various temperatures x  85  3.3  S U M M A R Y A N D CONCLUSIONS  [Fe(4-abimid)2]  x  and  [Co(4-abimid)2]  x  provide  the  first  examples  of  isomorphous and presumably isostructural molecule-based magnets of two different metals. The objective in comparing two such materials was to examine the effect on the magnetic properties of changing the d  configuration of the metal. In both  n  [Fe(4-abimid)2] and [Co(4-abimid)2] the metal is in a pseudo-tetrahedral geometry. In x  x  terms of single ion effects there is no first-order orbital contribution to the magnetic moment in either case [42] and the primary difference lies in the spin contributions, S = 2 for [Fe(4-abimid) ] and S = 3/2 for [Co(4-abimid) ] - This may, partly at least, 2  contribute to the  x  2  smaller remnant magnetization  x  observed for [Co(4-abimid)2]  x  (6 cn^Gmol" at 4.8 K and 22 cn^Gmol" at 10 K) compared to that for [Fe(4-abimid) ]x 1  1  2  (2100 c m G m o r at 4.8 K). It seems likely, however, that the degree of spin canting, 3  1  calculated and described above to be very small for the cobalt compound, would be much more important in this regard. The coercive fields are not as remarkably different in the two materials. This quantity, defined as the applied field required to return the magnetization of the sample to zero, is 80 G (at 4.8 K) for [Fe(4-abimid)2] and 100 G x  at 4.8 K (400 G at 10 K) for [Co(4-abimid) ] . In terms of hysteresis behavior another 2  x  characteristic property is the range o f applied fields over which the magnetization of the sample is dependent on the history of the field sweep (increasing or decreasing). In this regard the samples are quite different. For [Fe(4-abimid)2]  x  this field range is  approximately ±1 000G at 4.8 K while for [Co(4-abimid) ] it is about ± 1 0 000 Gat 2  86  x  10 K. At 4.8 K the magnetization of [Co(4-abimid)2] is dependent on the history of the x  field sweep over the entire range of fields studied. Finally it is noticeable that below T  c  ferromagnetic ordering persists at higher applied fields for [Fe(4-abimid)2] than for x  [Co(4-abimid)2] and that the apparent loss in order at low temperatures and all fields x  exhibited by [Co(4-abimid) ] is not observed for [Fe(4-abimid)2] . On the basis of this 2  x  x  single study it would be dangerous to draw general conclusions. To establish the generality of such findings investigation of other isomorphous pairs of iron and cobalt compounds is required. Also to better understand the detailed aspects of the magnetic properties of both compounds single crystal and powder X-ray diffraction studies at He temperatures are needed. Ideally, neutron diffraction experiments would also be very useful. The difficulty here is that larger single crystals of the iron(II) compound are required and, since presence of hydrogen atoms interfere in the neutron diffraction results, a deuterated [Fe(4-abimid)2] would need to be prepared [43,44]. x  87  R e f e r e n c e s  1 .  M .K .E h l e r t , S. J. R e t t i g , A. S t o r r ,R . C. T h o m p s o n ,a n d J. T r o t t e r . Can. J. Ch 67, 1 9 7 0 ( 1 9 8 9 ) .  2.  M . A. M a r t i n e z L o r e n t e , V. P e t r o u l e a s , R . P o i n s o t , J. P . T u c h a g u e s , J. M . S a v a r i a u l t ,a n dM . Drillon. Inorg. Chem. 30, 3 5 8 7( 1 9 9 1 ) .  3 .  M .K . 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Comm 3 6 7( 2 0 0 1 ) .  90  Chapter 4  BINARY IMIDAZOLATES OF COBALT(II), NICKEL(II), AND COPPER(II)  4 . 1 N IT R O D U C T O IN  A s p r e v i o u s l ys t a t e d ,t h en o n c e n t r o s y r n m e t r c i M-L-M  e x c h a n g e p a t h w a y  p r o v d ie d by s i n g l e b r i d g i n g 1 , 3 d i a z o l a t eg i la n d s( C h a p t e r 1, s e c t o i n 1.4) a p p e a r s to be a key f a c t o r in g e n e r a t n ig s p i nc a n t n i g and w e a kf e r r o m a g n e t s im in [Fe3(imid)6(imidH)2] x  [1], [ F e ( 2 m e i m i d ) - 0 . 1 3 C p F e ] [2], and [ F e ( 4 a b i m i d ) ]( C h a p t e r 3). The p h e n o m e n o n 2  2  x  2 x  s h o u d l not be r e s t r i c t e d to c o o r d n ia t o in p o y lm e r s of i r o n ( F l ) . T h i s fact, c o u p e ld w i t h the o b s e r v a t o in t h a t the i r o nc e n t e r si n v o l v e d in the p r m i a r ye x c h a n g ep a t h w a y s in the a b o v e s y s t e m s are t e t r a h e d r a l y c o o r d i n a t e d , ac o m m o n g e o m e t r y for c o b a l t ( H ) , p r o m p t e d i n t e r e s t in b r o a d e n n ig the i n v e s t i g a t i o n to i n c l u d e the m a g n e c t i p r o p e r t e is of r e l a t e d c o b a t l s y s t e m s . T h i s w o r k w a sl a t e r e x t e n d e d to the n i c k e l a n dc o p p e r i m i d a z o l a t e s y s t e m s .  4 . 2 4 . 2 . 1  C O B A L T ( I l )M I D IA Z O L A T EP O L Y M E R S N IT R O D U C T O IN  R e p o r t e dh e r e are the s y n t h e s i s , s t r u c t u r a ls t u d e is and m a g n e c t i p r o p e r t e is of five c o b a t ls y s t e m s : [Co(imid) ] ,[ C o ( 2 m e i m i d ) ] ,[ C o ( 4 m e i m i d ) ] , [ C o ( b e n z i m i d ) ] 2 x  2 x  91  2 x  2 x  ( b e n z m i d i =b e n z i m i d a z o l a t e ) ,a n d [Co3(imid)6(imidH)]. [Co(imid)2] h a sb e e nr e p o r t e d 2x  x  p r e v i o u s l ya n d its s t r u c t u r ed e t e r m n ie db ys i n g l ec r y s t a lX r a yd i f f r a c t i o ns t u d e is [ 3 ] .W e  h a d h o p e d t o d e t e r m n ie t h e m o e lc u a lr s t r u c t u r e s o f t h e o t h e r c o b a l t ( I ) m i d ia z o a lt e s  s t u d e id h e r e ; u n f o r t u n a t e l y , in s p i t e o f utilizing a s y n t h e t c i r o u t e w h c ih h a s b e e n v e  s u c c e s s f u l in o b t a i n i n g s i n g l e c r y s t a l s o fr e l a t e d i r o n ( I I ) i m i d a z o l a t e p o y lm e r s [ 1 , 2], it  w a sn o tp o s s b ie l t o o b t a i nm a c r o s c o p c i s i n g l ec r y s t a l so ft h e s eC o ( H ) c o m p o u n d s .I nt h  p r e s e n t w o r k w e w e r e , h o w e v e r , a b e l t o s h o wb yX r a yp o w d e rd i f f r a c t i o n s t u d e is t h [Co3(imid)6(imidH)2], is s io m o r p h o u s , a n d p r e s u m a b y l i s o s t r u c t u r a l , w i t h t h e i r o n x  a n a o lg u e . T h e l a t t e rh a s a n e x t e n d e d 3 D l a t t i c e s t r u c t u r e [ 1 ] . [Co(2-meimid)2] , [ C o ( 4 x  meimid)2] a n d [Co(benzimid)2] , h a v e b e e n r e p o r t e d p r e v i o u s l y [ 4 6 ] a n d a t l h o u g h x  x  d e f i n i t i v e s t r u c t u r e s o f t h e s e c o m p o u n d s r e m a n i e l u s i v e , s p e c t r o s c o p c i a n d t h e r m a l a n a y ls s i d a t ad e s c r b ie db e o lw a t t e s tt ot h e i rp o y lm e r c i n a t u r e .  [Co(imid)2] w a s c h o s e nt o b e i n v e s t i g a t e d , in p a r t i c u l a r , b e c a u s e its s t r u c t u r e is x  k n o w n a n d b e c a u s e p r e v o iu sm a g n e c t i m e a s u r e m e n s t w e r e c o n d u c t e d a t h g ih  t e m p e r a t u r e s o n l y [ 3 , 6]. O ft h e o t h e r f o u r c o m p o u n d s o n y l [ C o ( b e n z i m i d ) ]h a sb e e n 2 x  s u b e jc t e d t o m a g n e c t i s t u d e is p r e v i o u s l y , a g a n i o n y l a t h i g h t e m p e r a t u r e s [ 7 ] . N e w  m a g n e t z ia t o in s t u d e is t o c r y o g e n c i t e m p e r a t u r e s o n t h e f i v e c o b a t l s y s t e m s a r er e p o r t e d  h e r e . All f i v ec o m p o u n d s s h o wt h ep r e s e n c eo fa n t f i e r r o m a g n e t c i e x c h a n g e , a n dt h r e eo t h e m , [Co(imid)2], [Co(benzimid)2] a n d [Co3(imid)6(imidH)2] s h o w c l e a r t r a n s i t i o n s x  x  x  b e o lw critical t e m p e r a t u r e s , T, t oo lw t e m p e r a t u r eo ln g r a n g ef e r r o m a g n e t i c a l yo r d e r e d c  s t a t e s .  92  4 . 2 . 2 R E S U L T SA N DD S IC U S S O IN 4 . 2 . 2 . 1S Y N T H E S E S ,  P H Y S C IA L ,  T H E R M A L  A N D S T R U C T U R A L  C H A R A C T E R Z IA T O IN  [Co(imid)2], w a s p r e p a r e d b y r e a c t i n g c o b a l t ( I T ) n i t r a t e h e x a h y d r a t e w i t h a n x  e x c e s s o fi m i d a z o l e in w a t e r ( C h a p t e r 9, s e c t o i n 9 . 2 . 2 . 1 ) . T h i s m e t h o d y i e l d s ap u r p m i c r o c r y s t a l i n ep o w d e r . Am e t h o d i n v o l v i n g b a s c i c o n d t io n sa n d a n o t h e r , a n  e e lc t r o c h e m c ia lp r o c e d u r e ,h a v eb e e nr e p o r t e d in t h el i t e r a t u r e [3, 4 6 ] . [Co(imid)2] w a s x  a s lo p r o d u c e d in t h ep r e s e n ts t u d yb yt h e r m a ld e c o m p o s t o in o f [Co3(imid)6(imidH)2], a t x  ~ 3 2 5 °C, a tw h c ih t e m p e r a t u r et h el o s so ft h en e u t r a li m i d a z o l em o e lc u e ls o c c u r s  (v  infra).  T h em e h to d s d e s c r b ie d f o rt h e s y n t h e s s i o f [Co(2-meimid)2] , [Co(4-meimid)2] , x  x  a n d [ C o ( b e n z i m i d ) ] ( C h a p t e r 9, s e c t o in s 9 . 2 . 2 . 2 t h r o u g h 9 . 2 . 2 . 4 ) , a s lo l e d t o p u r p e l 2 x  m i c r o c r y s t a l i n em a t e r i a l sa n de f f o r t st op r o d u c es a m p e ls s u i t a b l ef o rs i n g l ec r y s t a lX r a y s t u d e is w e r eu n s u c c e s s f u . l T h e s t r u c t u r e o f [Co(imid) ] , w a s d e t e r m n ie dp r e v i o u s l yb y 2 x  X r a yc r y s t a o lg r a p h y [3]. T h i s c r y s t a li n e f o r m o ft h e c o m p o u n d d s ip a ly s t e t r a h e d r a l y  c o o r d n ia t e dc o b a l t ( I) ions. I t is a 3 Dp o y lm e rc o n s i s t i n go ff u s e dp u c k e r e dringso ff o u t e t r a h e d r a l y c o o r d n ia t e d c o b a l t ( l l ) o in s l i n k e d b y s i n g l e b r i d g i n g i m i d a z o l a t e s . A r e p r e s e n t a t o in o f t h e a s y m m e t r c i u n i t o f [Co(imid)2] is s h o w n in F g iu r e 4.1. T h i s x  i lu s t r a t i o n w a so b t a n ie de m p o ly n ig t h es o f t w a r e P o w d e r c e l [ 8 ]u s n ig c r y s t a l o g r a p h i cd a t ap r e v i o u s l yr e p o r t e d [3].  93  t h e  F g iu r e4 . 1  A s y m m e t r c i u n i t o f [Co(imid) ] . V e iw l o o k i n g d o w nt h e c a x i s . 2 x  H y d r o g e na o tm sa r eo m i t t e d .  A t l h o u g h t h e e x a c t s t r u c t u r e s o f[ C o ( 2 m e i m i d ) ] , [ C o ( 4 - meimid) ] , a n d 2 x  2 x  [ C o ( b e n z i m i d ) ]r e m a n i u n k n o w nt h ep o y lm e r c i n a t u r eo ft h em a t e r i a l s is i n d i c a t e db y 2 x  t h e i rp h y s i c a lp r o p e r t i e s , w h c ih t os o m e e x t e n t r e s e m b e l t h o s e d e t e r m n ie d f o r  [Co(imid) ] . All f o u r o ft h e s e c o m p o u n d s a r e s t a b l e b o t h in a i r a n d in c o n t a c t w 2 x  m o s it u r e .T h e ya r ei n s o l u b l e in w a t e ra n dc o m m o no r g a n c i s o l v e n t s ;t h e ya r en o n v o l a  a n dt h e r m a l yr o b u s t , a n dt h e yd e c o m p o s ew h e nt r e a t e dw i t hc o n c e n t r a t e dm n ie r a la c i d  T h e r m a l g r a v i m e t r i c a n a y ls e s o f t h e s e m a t e r i a l s s h o w n o m a s s o ls s d u e t o t h e r m  94  d e c o m p o s t o in o r s u b m i l a t o in b e o lw 2 0 0 ° C a n d a t h g ih e rt e m p e r a t u r e s t h e c o m p o u n d s p r e s e n t s i m i l a r t h e r m a l d e c o m p o s t o in b e h a v o ir s w i t h n o s i g n i f i c a n t w e g ih t l o s s till  t e m p e r a t u r e s a b o v e 4 0 0 ° C a r e r e a c h e d ( F i g u r e 4 . 2 ) . [Co(benzimid)2] is t h e m o s t x  t h e r m a l y r o b u s t o f t h e f o u r c o m p o u n d s in t h a t t h e r e is n o i n d i c a t i o n o f t h e r m a d e c o m p o s t o in b e o lw 6 0 0° Cf o rt h i sm a t e r i a l .  T h e e l e c t r o n i c s p e c t r a o f [Co(imid) ] , [ C o ( 2 m e i m i d ) ] , [ C o ( 4 m e i m i d ) ] , a n d 2 x  2 x  2 x  [ C o ( b e n z i m i d ) ] a r e v e r y s i m i l a r ( F i g u r e 4 . 3 ) . T h e y s h o w t w o n it e n s e d d t r a n s i t i o n 2 x  b a n d s , t h e first o n e c e n t e r e d ( d e t e r m n ie d v i s u a ly ) a r o u n d 1 1 1 0 - 1 1 3 0 n m ( b r o a d a  s t r u c t u r e d ) ,a n dt h es e c o n do n eo b s e r v e db e t w e e n5 7 0-5 9 0n m ,t h el a t t e rw i t has h  a ta b o u t5 2 05 4 0n m . T h e s ec a nb et e n t a t i v e l ya s s g in e dt ot h e A -» Ti(F) a n dA 4  4  4  2  Ti(P) t r a n s i t i o n s , r e s p e c t i v e l y , o f( d i s t o r t e d ) t e t r a h e d r a l c o b a l t ( H ) [ 9 ] . T h e a b s o r p t o in s  4  s e e n a t t h e o lw e s t w a v e e ln g t h s ( F i g u r e 4 . 3 ) a r i s e f r o m c h a r g e t r a n s f e r t r a n s i t i o n s . A  e x p e c t e dt h i r d d d b a n dd u et ot h e A —» Tt r a n s i t i o n ,e x p e c t e d in t h e 1 5 0 0-2 5 0 0 4  4  2  2  r e g i o n , is u s u a l yt o o w e a k a n db r o a d , t o b e c l e a r l yi d e n t i f i e d in s p e c t r ao fm u s l o t y p e s t u d e id h e r e . N e v e r t h e l e s s , t h i s t h i r d b a n d is j u s t a p p a r e n t in t h e s p e c t r a [Co(imid) ] , [ C o ( 4 m e i m i d ) ]a n d [ C o ( b e n z i m i d ) ]b e t w e e n 1 7 5 0 t o 2 0 2 0 n m . U s n ig 2 x  2 x  2 x  a v e r a g eb a n dw a v e e ln g t h so f5 8 0 n ma n d 1 1 2 0n m ,D qa n dBp a r a m e t e r so f5 2 5 c m 7 0 0 cm" , r e s p e c t i v e l y , w e r e c a l c u l a t e du s n ig t h e a p p r o p r a it eT a n a b e S u g a n o c o r r e l a t i o n 1  d a ig r a m [ 1 0 ] . T h e s e v a u le s o f D q a n d B a r e in c o ls e a g r e e m e n t w i t h t h o s e r e p o p r e v i o u s l y f o r o t h e r t e t r a h e d r a l C o ( I ) i m i d a z o l a t e a n dp y r a z o a lt e c o m p e lx e s [ 6 , 1 1 ] .  95  Ok  -  —  60  [Cotimid),],  o  [Co(2-meimid) ] 2  x  [Co(4-meimid) ]  40  2  I  [Co(benzimid) ] 2  x  [COjCimid^imidH),], 20 200  600  400  800  Temperature (°C)  F g iu r e 4.2  TGA  p l o t s for c o m p o u n d s [Co(imid)2], [ C o ( 2 m e i m i d ) ] , [ C o ( 4 -  meimid)2] , [ C o ( b e n z i m i d ) 2 ] , and x  x  [Co3(innd)6(imidH)2] . x  U s n ig t h e s e Dq and B v a u le s the A 4  2  cm" (~ 1904 1  nm),  2 x  x  — > ^2 t r a n s i t i o n is p r e d c it e d to a p p e a r at ~ 5 2 5 0  w h c ih is w i t h i n the w a v e e ln g t h r a n g e w h e r e the v e r yw e a k , b r o a d ,  a b s o r p t o i n was o b s e r v e d in s o m e of the s p e c t r a  (vide supra).  E l e c t r o n i cs p e c t r a ld a t a for  al f o u r of t h e s ec o m p o u n d sh a v eb e e nr e p o r t e dp r e v i o u s l y [6, 7, 12]. P r e v o iu ss t u d e is [6] on the d i f f u s e r e f l e c t a n c e s p e c t r a of [Co(imid)2] and [Co(4-meimid)2] r e p o r t e d the x  96  x  F g iu r e4 . 3  U V V s iN E Rs p e c t r a for c o m p o u n d s [Co(imid)2], (a); [ C o ( 2 x  meimid)2], (b); [Co(4-meimid)2] , (c); [Co(benzimid)2] , (d); a n d [Co3(imid)6(imidH)2], x  x  x  (e)-  97  x  p r e s e n c e o fb a n d s a t 1 8 4 0 a n d 2 2 9 0n m f o r [Co(imid) ] , a n d 1 8 6 0 , 1 9 9 0 a n d2 2 8 2 x  f o r[ C o ( 4 m e i m i d ) ] ) .T h e s ea r e likely c o m p o n e n s t o ft h eA — »T t r a n s i t i o ns e e no n y l 4  2 x  4  2  2  v e r yw e a k y l in t h e s p e c t r a s t u d e id h e r e . A n e a r l i e re l e c t r o n i c s p e c t r o s c o p y s t u d y [ 7 ] o  [ C o ( b e n z i m i d ) ] , u s n ig b o t hr e f l e c t a n c e a n dm u l m e t h o d s , r e p o r t e d t h e o b s e r v a t o in o f 2 x  o n y l t h et w om a o jr d dt r a n s i t i o n s , w i t ht h em u l s p e c t r u mb a n d s a t 1 1 5 0 a n d 5 9 5  s h o u d le r a t 5 4 0n m ) . H e n c e , t h e s p e c t r a s h o w n in F i g u r e4 . 3 a r e in g e n e r a l a g r e e m  w i t h t h e e a r l i e r w o r k w h c ih a s lo c o n c u ld e d t h a t t h e s e c o m p o u n d s h a v e s t r u c t u r e s i n c o r p o r a t i n g t e t r a h e d r a l yc o o r d n ia t e d c o b a l t ( I l )c e n t e r s . T h e a b s e n c e o f a VN-H  s t r e t c h i n g v i b r a t i o n in t h e s e e l e c t r o n i c s p e c t r a a n d in t h e i n f r a r e d s p e c t r a o f t h e s e  c o m p e lx e s ( s e e t h e d s ic u s s o in b e o lw c o n c e r n n ig t h e o b s e r v a t o in o f t h i s b a n d in [Co3(imid)6(imidH)]) is i n d i c a t i v eo ft h ea b s e n c eo fn e u t r a li m i d a z o l e in t h e s em a t e r i a l s 2x  [ 1 ] .  T h e X r a yp o w d e r d i f f f a c t o g r a m o fa s a m p e l o f [Co(imid) ]s y n t h e s z ie d in t h i s 2 x  w o r k a g r e e s w e l w i t h t h a t c a l c u l a t e d [ 8 ]froms i n g l e c r y s t a l X r a y d i f f r a c t i o n d a t a r e p o r t e d f o rt h e s a m e c o m p o u n d [ 3 ] ( F i g u r e 4 . 4 ) .n Id e x n ig t h e X r a y p o w d e r  d i f f r a c t o g r a m u s n ig t h e p r o g r a m C e l r e f[ 1 3 ] y i e l d sc a l c u l a t e d l a t t i c e p a r a m e t e r s o fa =  2 2 . 8 3 4 ,b=2 2 8 .3 4a n dc= 1 2 9 .8 3 A. T h e s ev a u le sa r ev e r ys i m i l a rt ot h o s er e p o  t h es a m ec o m p o u n d in t h ep r e v o iu ss t u d y( a=2 2 . 8 7 2 ,b=2 2 . 8 7 2 ,c= 1 2 9 .8 1 A  c o n c u ld e t h a t [Co(imid) ] s y n t h e s z ie d in t h e p r e s e n t w o r k is t h e s a m e a s t h a tr e p o r t e 2 x  e a r l i e r[ 3 ] .  98  5  10  15  20  25  30  35  40  45  50  26 (deg)  F i g u r e4 . 4  X r a y p o w d e r d f if r a c t o g r a m s o f [Co(imid) ] ( t o p , e x p e r m i e n t a ; l 2 x  b o t o m ,c a l c u l a t e d ) .  U n f o r t u n a t e l y , r e l a t i v e l y little s t r u c t u r a l i n f o r m a t i o n w a s o b t a n ie dfromt h e  p o w d e rX r a yd i f f r a c t i o ns t u d e is o ft h eo t h e rt h r e ec o b a t l c o m p o u n d s .T h eX r a yp o w d e r d i f f r a c t i o np a t e r n s f o r [Co(2-meimid)2] a n d [Co(benzimid)2] a r es h o w n in F g iu r e4 . 5 . x  x  F r o mt h e s ed f if r a c t o g r a m s it c a nb es e e nt h a tt h e s ec o m p o u n d sa r en o ts io m o r p h o u sw  e a c h o t h e r , n o r w i t h [Co(imid)2]. A v e r y p o o r d i f f r a c t i o n p a t t e r n w i t h n o d e t e c t a b e l x  p e a k s ,c h a r a c t e r i s t i co fa na m o r p h o u s solid, w a so b t a n ie df o r [Co(4-meimid)4] . x  99  20 (deg)  F i g u r e4 . 5  20 (deg)  X r a yp o w d e rd f i f r a c t o g r a m so f [Co(2-meimid)2] ( a ) x  a n d  [Co(benzimid)2]x ( b ) .  I n s u m m a r y , c o n c e r n n ig s t r u c t u r e s , t h e s i m i l a r i t i e s in s t o c ih o im e t r ya n dp h y s i c a l a n d s p e c t r o s c o p c i p r o p e r t e is o f [Co(imid)2], [Co(2-meimid)2] , [Co(4-meimid)2] , a n d x  x  x  [Co(benzimid)2] s t r o n g y l s u p p o r t t h e c o n c u ls o in t h a t , a s k n o w n d e f i n i t i v e l y f o r x  [Co(imid)2], all h a v e e x t e n d e d s t r u c t u r e s w i t h t e t r a h e d r a l y c o o r d n ia t e d m e t a l c e n t e r s x  a n ds i n g l yb r i d g i n ga z o l a t el i g a n d s .  100  In a n e a r l i e rs t u d y [1] the s y n t h e s s i of a n e w m o e lc u e lb a s e d m a g n e t , [Fe3(imid)6(imidH)2], b y the r e a c t i o n of f e r r o c e n e w i t h e x c e s s m o t l e n i m i d a z o l e , w a s x  r e p o r t e d . T h es a m e r e a c t i o n , e m p o ly n ig c o b a t l o c e n e in p a lc e of f e r r o c e n e , y i e l d s the a n a o lg o u s c o b a t lc o m p o u n d , [Co3(imid)6(imidH)2], a sam i c r o c r y s t a l i n e p o w d e r x  ( C h a p t e r 9, s e c t i o n 9 . 2 . 2 . 5 ) . T h eX r a yp o w d e r d i f f r a c t o g r a m of [Co3(imid)6(imidH)] 2x  c o n ic d ie s w e l w i t h t h a t c a l c u l a t e d ( e m p o ly n ig s i n g l e c r y s t a l X r a y d i f f r a c t i o n d a t a [1] a n dt h ep r o g r a mP o w d e r C e l , [8]), for [Fe (imid) (imidH) ]( F i g u r e 4.6). n Id e x n ig t h e X3  6  2 x  r a yp o w d e rd i f f r a c t o g r a m o f [Co3(imid)(imidH)] u s n ig t h ep r o g r a mC e l r e f [13] y i e l d s 6  2x  c a l c u l a t e dl a t t i c ep a r a m e t e r so fa = 1 0 . 5 6 8 ,b= 1 2 9 .6 4a n dc= 1 0 6 .3 4 A. T h e s e  s i m i l a r t o t h o s e of [Fe (imid) (imidH) ] (a = 1 0 . 5 9 1 , b = 1 2 . 9 5 8 , c = 1 0 6 .1 7 A) [1 3  6  2 x  A d d i t i o n a l e v d ie n c e s u p p o r t n i g the c o n c u ls o in t h a t the i r o n a n d c o b a t l c o m p o u n d s a r e i s o s t r u c t u r a l in a d d i t i o n to s io m o r p h o u sc o m e sfroms p e c t r o s c o p c i s t u d e is o n [Co3(imid)6(imidH)2]- T h eX r a yd e t e r m n ie d s t r u c t u r e o ft h ei r o nc o m p o u n d s h o w s t h e x  p r e s e n c e of b o t h t e t r a h e d r a l a n do c t a h e d r a l m e t a l c e n t e r s , the a d d i t i o n a l c o o r d n ia t o in s i t e so nt h el a t t e rb e n i g filled b yn e u t r a li m i d a z o l em o e lc u e ls .T h ee l e c t r o n i cs p e c t r u m [Co3(imid)6(imidH)2] ( F i g u r e 4.3) s h o w s the a b s o r p t o in b a n d s a s s g in a b e l t o t h e A -> 4  2  x  Ti(F) a n d A2 ->Ti(P) t r a n s i t i o n s o ft e t r a h e d r a l y c o o r d n ia t e d C o o in s ( s e e p r e v o iu s  4  4  4  d i s c u s s i o n ) . T r a n s i t i o n s a s s g in a b e l to o c t a h e d r a l c o b a l t ( I ) c e n t e r s are n o t o b s e r v a b e l;  h o w e v e r , t h i s is n o tt o o s u r p r i s i n g in v e iw o ft h e f a c t t h e yw o u d l b ee x p e c t e d t ob o r d e r o fm a g n t u id e o r m o r e w e a k e r t h a n the b a n d s a r i s i n gfromthe t e t r a h e d r a l c e n t e r s [14]. E v d ie n c e for n e u t r a l i m i d a z o l e m o e lc u e ls ( c o o r d i n a t e d , p r e s u m a b y l, t o o c t a h e d r a l c o b a t l c e n t e r s ) in [Co3(imid)6(imidH)] c o m e sfromthe o b s e r v a t o in o fa s h a r p p e a k a t 2x  101  2 9 5 0 nm in the e l e c t r o n i c s p e c t r u m ( F i g u r e 4.3) v i b r a t i o n of n e u t r a l i m i d a z o l e [1].  c o r r e s p o n d n ig to the VN-H s t r e t c h i n g  F i n a ly we n o t e t h a t the i n f r a r e d s p e c t r u m of  LU —I—  10  ^0  To"  40  ~50  20 (deg)  Figure 4.6  X-Ray powder diffractograms of [Co3(imid)6(imidH)2]  x  experimental) and Fe3(imid)6(imidH)2 (bottom, calculated).  102  (top,  [Co3(imid)6(imidH)2] a n d t h e i r o n a n a o lg u e a r e v i r t u a ly i d e n t i c a l e x h i b i t i n g t h e s a m e x  v i b r a t i o n a lb a n d sa ta m l o s tt h es a m e f r e q u e n c i e s .I tc a n b ec o n c u ld e d t h a t  [Co3(imid)6(imidH)2] h a s t h e s a m e s t r u c t u r e a s t h e i r o n a n a o lg u e [ 1 ] . I n t h i s s t r u c t u r e x  t e t r a h e d r a l y c o o r d n ia t e d m e t a l o in s a r e c o n n e c t e d in c h a n is b y s i n g l y b r i d g i n g i m i d a z o l a t e i o n s . T h e c h a n is a r e c r o s s l i n k e d b y o c t a h e d r a y l c o o r d n ia t e d m e t a l i o n s .  E a c h t e t r a h e d r a l c e n t e r is l i n k e d t o t w o o t h e r s in t h e s a m e c h a n i a n d v i a o c t a h c e n t e r s t o t w o a d d i t i o n a l c h a i n s . E a c h c h a n i is l i n k e d t o f o u r d i f f e r e n t c h a n is v i a o c t a h e d r a lc e n t e r s .  [Co3(imid)6(imidH)2]x is n o n v o l a t i l e a n d d o e s n o t m e t l u p t o t h e t e m p e r a t u r e a t  w h c ih its t h e r m a l d e c o m p o s t o in b e g n is ( 2 0 8 °C). T h e r m a l g r a v i m e t r i c a n a y ls s i o ft h e  c o m p o u n ds h o w st h a t it d e c o m p o s e s in s e v e r a ls t e p s( F i g u r e4 . 2 ) .A p p r o x m i a t e y l 1 5 %o  t h e initial w e g ih t is l o s tb e t w e e n2 0 8 a n d2 5 5 °C. T h en e x t4 % is l o s tb e t w e e n2  3 2 0 °C. T h i s t o t a l w e g ih t l o s s o f 1 9 % c o r r e s p o n d s t o t h a t e x p e c t e d f o r t h e o ls s o  n e u t r a l i m i d a z o l e l i g a n d s . T h e r e m a n in ig m a t e r i a l h a s t h e s a m e c o m p o s t o in a s  [Co(imid)2]x- T h i s is e v d ie n c e d b y t h e t h e r m o g r a v m i e t r c i d a t a a n d b y t h e e x p e r m i e n t d e s c r b ie d in t h e e x p e r m i e n t a l s e c t o i n in w h c ih a s a m p e l w a s r e t r i e v e d f r o m t h e  n is t r u m e n t , a f t e rh e a t n ig f o r 3 0 m n iu t e s a t 3 2 5 °C, a n d s u b e jc t e d t o e e lm e n t a l a n a l y  T h er e s to ft h et h e r m o y ls s i c u r v eo f [Co(imid)(imidH)2] a b o v e3 2 0° Cp a r a le l sc l o s e l y 3  6  x  t h a to ft h ea u t h e n t c i s a m p e l o f [Co(imid)2], a se x p e c t e d . x  103  4 . 2 . 2 . 2 M A G N E T C I P R O P E R T E IS  M a g n e t c i s u s c e p t i b i l i t y , %, and m a g n e c t i m o m e n t , j i ^ f f , v e r s u s T d a t a o v e r the t e m p e r a t u r e r a n g e 2 3 0 0 K on p o w d e r e d s a m p e ls of the f i v e c o b a t l c o m p o u n d s in an a p p l i e d field of 10 000 G are s h o w n in F g iu r e s 4.7 and 4.8, r e s p e c t i v e l y . For all f i v e  [Co(imid) ] 2  x  [Co(2-meimid) ] 2  I  [Co(4-meimid) ] 2  [Co(benzimid) ] 2  x  x  [Co (iimd) (iimdH) ] 3  50  100  150  200  6  2  250  x  300  T(K)  F i g u r e 4.7  %v e r s u s Tp l o t s at 10 000 G for c o m p o u n d s [Co(imid)2], [ C o ( 2 x  meimid)2]x, [Co(4-meimid)2] , [ C o ( b e n z i m i d ) ] , and [Co3(imid)6(hnidH)2]. 2 x  x  104  x  000006  • •••••• e ° 0 X  4  n  3 i  •  [Co(imid) ] 2 x  [ Co ( 2 m e i m i d ) ]  2B  5 0  1 0 0  •  [ C o ( 4 m e i m i d ) ]  •  | C o ( b e n z i m i d ) , ]  0  [ C O j C i m i d ^ C i m i d H ) , ] ,  2 x  x  1 5 0  2 0 0  2 5 0  3 0 0  T(K)  F g iu r e4 . 8  [i^s v e r s u sTp l o t sa t 1 00 0 0Gf o rc o m p o u n d s [Co(imid)2], [Co( x  m e i m i d ) ] , [ C o ( 4 m e i m i d ) 2 ] , [ C o ( b e n z i m i d ) 2 ] , a n d [Co3(innd)(imidH)2]. 2 x  x  6  x  x  c o m p o u n d s t h e m a g n e c t i m o m e n t d e c r e a s e s w i t h d e c r e a s n ig t e m p e r a t u r e f r o m a v a u le  a b o v e 4 p.R a t 3 0 0 K t o a v a u le b e o lw 1 u. a t 2 K ( F i g u r e 4 . 8 ) . T h i s s B  a n t f i e r r o m a g n e t c i c o u p n i lg b e t w e e nm a g n e c t i c e n t e r s , ac o n c u ls o in f u r t h e rs u p p o r t e db y t h e s u s c e p t i b i lt y d a t a f o r [Co(2-meimid)2] a n d [ C o ( 4 m e i m i d ) ] w h c ih s h o w b r o a d 2 x  x  m a x m i a a to lw t e m p e r a t u r e s . I n c o n t r a s tt o t h er e s u l t s f o r [Co(2-meimid)2] a n d [ C o ( 4 x  meimid)2], t h ed a t af o r [Co(imid)2], [Co(benzimid)2] a n d [Co3(imid)6(imidH)2] s h o w x  x  105  x  x  c l e a re v d ie n c e of m a g n e c t i a n o m a e i ls in the r e g i o nb e o lw 20 K. T h e s e are n o t c ie a b e l in b o t h the Lieff and % p l o t s , p a r t i c u l a r l y in the f o r m e r . The a b r u p tn ic r e a s e in % s u g g e s t s a t r a n s i t i o n to a f e r r o m a g n e t c i s t a t e for t h e s e c o m p o u n d s and c a u s e d by l a r g ea p p l i e df i e l d s can m a s ks u c hb e h a v o i r (See  s n ic e s a t u r a t i o n e f f e c t s C h a p t e r 3, s e c t o in 3 . 2 . 2 ) the  m a g n e c t i p r o p e r t i e s of all f i v e c o m p o u n d s w e r e e x a m n ie d at the o lw e r a p p l i e d field of 500 G. Lieff and % d a t a at 500 G o v e r the o lw t e m p e r a t u r er e g i o n (2-50 F g iu r e s 4.9 and 4.10,  K) are s h o w n in  r e s p e c t i v e l y . W h i l e the m a g n e c t i p r o p e r t e is of [Co(2-meimid)2] x  and [Co(4-meimid)2] are v i r t u a ly u n c h a n g e d at t h i s o lw e r a p p l i e d field, as e x p e c t e d x  w h e r e o n y l s h o r t r a n g e a n t f i e r r o m a g n e t c i i n t e r a c t i o n s are i n v o l v e d , % and Lieff d a t a of [Co(imid)2], [ C o ( b e n z i m i d ) ] and [Co3(imid)(imidH)2] are d r a m a t i c a l ya l t e r e db e o lw 2 x  x  6  x  the t e m p e r a t u r e of the a n o m a y l. B e o lw a critical t e m p e r a t u r e , T, (16 K, 13 K and 15 K c  for [Co(imid) ] , [ C o ( b e n z i m i d ) ] and [Co(imid)6(imidH)2] r e s p e c t i v e l y ) LL-ff n ic r e a s e s 2 x  2 x  3  a b r u p t y l to a m a x m iu m v a u l e (7.84 [ C o ( b e n z i m i d ) ] , and 60 .2 2 x  x  LIB at 9 K for [Co(imid)2], 55 .9 x  Li at 10 K for B  |i at 13 K for [Co3(imid)(imidH)]) b e f o r ed e c r e a s n ig a g a n i B  6  as the t e m p e r a t u r e d e c r e a s e s to 2 K ( F i g u r e 4.9).  2x  The m a g n e c t i t r a n s i t i o n at T is a s lo c  s e e n c l e a r l y in the % v e r s u s T p l o t s ( F i g u r e 4 . 1 0 ) . The  s u s c e p t i b i l t y n ic r e a s e s w i t h  d e c r e a s n ig t e m p e r a t u r eb e o lw 300 K and a b o v e T for [Co(imid)2], [Co(benzimid)2] and c  [Co3(imid)6(imidH)]. 2x  B e o lw T  c  the  x  s u s c e p t i b i l t y r i s e s a b r u p t y l as  t e m p e r a t u r ed e c r e a s e s b e f o r e l e v e l i n g off  106  x  the  and a p p r o a c h n ig a s a t u r a t i o n v a u l e for  10 [Co(imid) ] 2  x  [Co(2-meimid) ]  2 x  8  [Co(4-meimid) ]  2 x  [Co(benziinid) ]  2 x  [Co (iiiud) (iinidH) ] 3  6  2  J  6 ea  is 5  zL  I 1*1  8  20  10  30  8  8  40  8  50  T(K)  F g iu r e 4.9  Lieff  v e r s u s T p l o t s at 5 0 0 G for c o m p o u n d s [Co(imid)2], [Co(2x  meimid)2], [Co(4-meimid)2] , [ C o ( b e n z i m i d ) ] , and [Co3(iniid)6(imidH)2]. x  2 x  x  x  [ C o ( b e n z i m i d ) ] a n d [Co3(imid)6(imidH)]. T h es u s c e p t i b i l t y o f [ C o ( i m i d ) ] 2 x  2x  2 x  m a x m i z ie s at 11 K t h e n d e c r e a s e s on c o o l i n g f u r t h e r b e f o r e l e v e l i n g off at the o lw e s t t e m p e r a t u r e ss t u d e id ( F i g u r e4 . 1 0 ) .T h em a g n e c t i b e h a v o ir so f [Co(imid)2], x  [Co(benzimid)2] and [Co3(imid)6(imidH)] i n d i c a t e in al t h r e ec o m p o u n d s the p r e s e n c e x  2x  107  1.0 [Co(imid) ] 2  x  [Co(2-meimid) ] 2  0.8  x  [Co(4-meimid) ] 2  J-  0.6  &  0.4  o £  x  o  [Co(benzimid) ]  o  [Co (imid) (imidH) ]  2  3  6  x  2  x  OOOOOS6OQ o * o 0  0.2 i  0.0 0  10  20  30  40  50  T(K)  F i g u r e 4.10  %v e r s u s T p l o t s at 500 G for c o m p o u n d s [Co(imid)2], [ C o ( 2 x  meimid)2], [Co(4-meimid)2] , [Co(benzimid)2] , and [Co3(inn^)6(imidH)2]. x  x  x  x  of a n t f i e r r o m a g n e t c i c o u p n i lg b e t w e e n p a r a m a g n e c t i c e n t e r s as the p r m i a r y e x c h a n g e m e c h a n s im c o m b n ie d w i t h am a g n e c t i p h a s e t r a n s i t i o n to a f e r r o m a g n e t i c a l y o r d e r e d s t a t e at o lw t e m p e r a t u r e s . T h i s m a g n e c t i b e h a v o i r is v e r y s i m i l a r to t h a t r e p o r t e d for [Fe (imid) (imidH) ] [ 1 ] [ F e C 2 m e i m i d . )0 . 1 3 ( F e C p ) ][ 2 ] and [ F e ( 4 a b i m i d ) ] 3  6  2 x  2  2x  2 x  ( C h a p t e r 3), w h c ih s u g g e s t s af o r m of c a n t e d s p n i a n t f i e r r o m a g n e t c i c o u p n i lg l e a d i n g to w e a kf e r r o m a g n e t s im at o lw t e m p e r a t u r e s , as d s ic u s s e d in C h a p t e r 3, s e c t o in 3 . 2 . 2 .W e a k  108  F i g u r e4 . 1 1 M a g n e t z ia t o in v e r s u s a p p l i e d field p l o t s a t d i f f e r e n t t e m p e r a t u r e s f o r c o m p o u n d s [Co(imid)2], ( a ) ; [Co(2-meimid)2] , ( b ) ;[ C o ( 4 m e i m i d ) ] , (c); x  2 x  x  [ C o ( b e n z i m i d ) ] ,( d ) ;a n d [Co3(imid)6(imidH)], ( e ) . 2 x  2x  f e r r o m a g n e t s im is a s lo e v d ie n t in t h e m a g n e t z ia t o in v e r s u s field p l o t s a t s e v e r a l t e m p e r a t u r e sf o r [Co(imid)2], [ C o ( b e n z i m i d ) ]a n d [Co3(imid)6(imidH)] ( F i g u r e4 . 1 1 ) . 2 x  x  2x  P l o t s o fm a g n e t z ia t o in v e r s u s a p p l i e d field f o rt h e s ec o m p o u n d s a r el i n e a ra b o v eT a n c  e x t r a p o a lt e t o z e r o m a g n e t z ia t o in a t z e r o a p p l i e d field, w h i l e b e o lw T t h e y s h o w c  e x t r a p o a lt e d n e tm a g n e t z ia t o in a tz e r o field. I n c o n t r a s t , t h e d a t a o b t a n ie d a t c o r r e s p o n d n ig t e m p e r a t u r e s f o r [ C o ( 2 m e i m i d ) 2 ] a n d [ C o ( 4 m e i m i d ) 2 ]e x t r a p o a lt e t o x  109  x  z e r o m a g n e t z ia t o i n at all t e m p e r a t u r e s s t u d e id ( F i g u r e 4 . 1 1 ) . T h a t [Co(imid)2], x  [Co(benzimid)2] a n d [Co3(imid)6(imidH)2] e x h i b i to ln g r a n g e f e r r o m a g n e t c i o r d e r a n d x  x  s p o n t a n e o u s m a g n e t z ia t o in b e o lw T is f u r t h e ri lu s t r a t e db yh y s t e r e s s i s t u d i e s . In t h e s e c  s t u d i e s ,t h em a g n e t z ia t o in w a sm e a s u r e da st h ea p p l i e d field w a sc y c e ld b e t w e e n+ 5 00 0 G a n d -50 0 0 0G a t 4.8 K. P r e l i m i n a r yh y s t e r e s s i s t u d e is for t h e s e c o m p o u n d s s h o w e d e v d ie n c e t h a t the m i c r o c r y s t a l s w e r e a l i g n i n g w i t h the a p p l i e d field, r e s u l t i n g in a b n o r m a l s h a p e s of the h y s t e r e s s i p l o t s , a ss h o w n in F i g u r e 4.12 ( m d id e l p l o t ) for [Co(benzimid)2] . T h e s ep r e l i m i n a r yr e s u l t s p r o m p t e du s t o m u l the s a m p e l in n u j o l to x  p r e v e n t the a g i ln m e n t of the m i c r o c r y s t a l s w i t h the a p p l i e d field. T h e r e s u l t i n g h y s t e r e s s i o lo p s u s n ig n u j o l are s h o w n in F i g u r e 4.13. T h e s e o lo p s g i v e r e m n a n t m a g n e t z ia t o in s of 350, 2 8 0a n d2 0 0 cm G mol" a n d c o e r c v ie f i e l d s o f5 5 0 0 , 2 5 0 0 a n d 3  1  2 0 0 0 G for [Co(imid)2], [Co(benzimid)2] a n d [Co3(imid)6(imidH)2], r e s p e c t i v e l y . A x  x  x  s p n ic a n t e d s t r u c t u r e , for [Co(imid)2], [Co(benzimid)2] a n d [Co(imid)(iniidH)2] is x  3  x  6  x  a s lo s u p p o r t e d b y the f a c t t h a t t h e i r h g ih e s t m a g n e t z ia t o in s m e a s u r e d w e r e 2 9 2 4 , 2 2 5 3  a n d2 2 6 7 c m G m o l " ,r e s p e c t i v e l y , a t 4.8 K a n d5 5 0 0 0 G. T h e s ev a u le sa r ec o n s d ie r a b 3  1  o lw e rt h a nt h et h e o r e t i c a ls a t u r a t i o nm a g n e t z ia t o in v a u l e of 1 67 6 6c mGmol" for a nb= 3  1  3/2 s y s t e m [15].  M a g n e t c i p a r a m e t e r s for f i v ec o b a l t ( I )1 , 3 d i a z o l a t e c o m p o u n d s , i n c l u d i n g [Co(imid)2], [ C o ( b e n z i m i d ) ] a n d [Co3(imid)6(imidH)2], w h c ih e x h i b i t x  2 x  x  w e a k  f e r r o m a g n e t s im a r eg v ie n in T a b e l 4.1. T h eo n y l p a r a m e t e rw h c ih is r e l a t i v e l yc o n s t a n t in  t h i sg r o u po fc o m p o u n d s is t h e critical t e m p e r a t u r e w h c ih lies in t h en a r r o wr a n g eo f  110  -60000 -40000 -20000  0  20000 40000 60000  0  20000 40000 60000  2000 1000  J s  0-  -1000  -60000 -40000-20000  F i g u r e 4.12  H(G)  M a g n e t c i h y s t e r e s s i p l o t s at 4.8 K for c o m p o u n d s [Co(imid)2], x  ( t o p ) ; [Co(benzimid)2] ( m i d d l e ) ; [Co3(imid)6(imidH)], ( b o t t o m ) . 2x  X 5  Ill  a g n e t c i p a r a m e t e r sf o rs o m ec o b a l t ( H )w e a kf e r r o m a g n e t s T a b e l 4 . 1 M  C o m p o u n d  T(K) C  H ( G )  R e f .  coer  ( c n r G ' m o r ) 1  C o ( 4 a b i m i d )  1 1  4 0 0  2 2  C h a p t e r3  C o ( i m i d ) ( b i p y )  1 3  1 2 5  1 9 0 0  C h a p t e r5  C o ( i m i d )  1 6  66 2 0  3 3 4  T h i sC h a p t e r  1 3  52 8 0  2 5 7  T h i sC h a p t e r  1 5  41 4 0  1 7 5  T h i sC h a p t e r  2  2  4  2  C o ( b e n z i m i d ) 2  Co (imid) (imidH) 3  6  2  A b b r e v i a t i o n s : i m i d = i m i d a z o l a t e , b e n z m i d i - b e n z i m i d a z o l a t e , 4 a b i m i d = 4 a z a b e n z m i d ia z o a lt e ,b i p y=2 , 2 ' b i p y r i d i n e .  t o 1 6 K . S i n g l e c r y s t a l X r a y d i f f r a c t i o n s t u d e is o n [Co(imid) ] [3], a n d p o w d e r 2 x  d i f f r a c t i o n s t u d e is o n [ C o ( 4 a b i m i d ) ]( C h a p t e r 3 ) s h o w t h e s e c o m p o u n d s t o h a v e 2 x  e x t e n d e d3 Dl a t t i c e sw i t ht e t r a h e d r a lc o b a t l c e n t e r sl i n k e d via s i n g l y b r i d g i n ga z o a lt e st o  f o u r n e a r e s t n e g ih b o r s . I n s p i t e o f t h e s t r u c t u r a l similarities, t h e y h a v e s i g n i f i c a n t l y d i f f e r e n tm a g n e c t i p r o p e r t i e s , [Co(imid) ]b e n ig b o t has t r o n g e rm a g n e t( l a r g e rr e m n a n t 2 x  112  m a g n e t z ia t o in ) a n dah a r d e rm a g n e t( g r e a t e rc o e r c v ie field). T h em a g n e c t i p a r a m e t e r so f  C o ( 4 a b i m i d ) 2 h a v eb e e n d s ic u s s e d in s o m e d e t a i l in C h a p t e r3 . I t is s u f f i c i e n tt o p o  o u t h e r e t h a t in C h a p t e r 3 it w a s c o n c u ld e d t h a t t h e p r o p e r t e is o fc o b a l t ( I ) m o e lc  b a s e d m a g n e s t m a y b e i n f l u e n c e d s i g n i f i c a n t l yb y s i n g l e i o n e f f e c t s s u c h a s z e r o f i e l  splitting. D i f f e r e n c e s in t h e m a g n t u id e o ft h e z e r o f i e l d splitting, in t u r nb r o u g h t o nb  f a c t o r s s u c h a s d i f f e r e n c e s in t h e n a t u r e a n d d e g r e e o fd i s t o r t i o n o f t h e C0N4 c h r o m o p h o r e , will c a u s e s i g n i f i c a n t d i f f e r e n c e s in t h e p o p u a lt o in s o f z e r o f i e l d s p l i t  l e v e l s a t o lw t e m p e r a t u r e s w i t h c o n c o m t a in t e f f e c t s o n t h e e x c h a n g e a n d t h e m a g n e  p r o p e r t i e s .U n f o r t u n a t e y l t h en u m b e ro fc o m p o u n d so ft h i sc a ls sw i t hk n o w ns t r u c t u r e s is  t o o s m a l a t t h i s t m i e t o t r y t o c o r r e l a t e m a g n e c t i p a r a m e t e r s w i t h d e t a i l e d s t r u c t u f e a t u r e s .  I nc o n t r a s t t o t h e b e h a v o ir d s ic u s s e d a b o v e , [Co(2-meimid)2] x  a n d  [Co(4-meimid)2] e x h i b i to n y l s h o r t r a n g ea n t f i e r r o m a g n e t c i c o u p l i n g . P l o t so fm a g n e c t i x  s u s c e p t i b i l i t y , %, a n dm a g n e c t i m o m e n t , p^ff, v e r s u sTd a t a in a na p p l i e d field o f1 00 0 a r e s h o w n in F i g u r e4 . 7 a n d4 . 8 . Am a x m iu ma ta p p r o x m i a t e y l 2 1 K is o b s e r v e d in t h em a g n e c t i s u s c e p t i b i l t yp l o tf o r [Co(2-meimid)2] . Ap a r a m a g n e c t i i m p u r i t y in t h i s x  c o m p o u n d m g ih t b e t h e c a u s e o f t h e s m a l n ic r e a s e in m a g n e c t i s u s c e p t i b i l t y a t t h o lw e s t t e m p e r a t u r e s s t u d e id ( F i g u r e 4 . 7 ) . T h e m a x m iu m in t h e m a g n e c t i s u s c e p t i b i l t y  p l o to f [Co(4-meimid)2] is l e s sn o t i c e a b l es n ic e it a p p e a r sa tav e r yo lw t e m p e r a t u r eo f x  K ( F i g u r e 4 . 7 ) . A n t f i e r r o m a g n e t c i b e h a v o ir f o rt h e s e c o m p o u n d s is a s lo a p p a r e n t in t h e Lieff  v e r s u sTp l o t sd e t e r m n ie da t5 0 0G( F i g u r e4 . 1 0 ) .T h em a g n e c t i m o m e n td e c r e a s e s  113  t e m p e r a t u r e is l o w e r e d . T h a t t h e s e t w o p o y lm e r s d o n o tp r e s e n t a n e tm a g n e t z ia t o in  z e r o a p p l i e d field is s h o w n in t h e i r m a g n e t z ia t o in p l o t s a t t w o d i f f e r e n t t e m p e r a t u r e s  w h c ih e x t r a p o a lt et o z e r o a tz e r o a p p l i e d field ( F i g u r e4 . 1 1 ) . I n a d d i t i o n , m a g n e t z ia t o in  s t u d e is a t4 . 8 K o n t h e s e c o m p o u n d s , in w h c ih t h e a p p l i e d field is c y c e ld b e t w e e n  + 5 5 0 0 0 a n d- 5 5 0 0 0 G, r e v e a l n o e v d ie n c e o fs i g n i f i c a n th y s t e r e s s i b e h a v o ir ( F i g u  4 . 1 3 ) . I t is n o t p o s s b ie l t o q u a n t i f yt h em a g n t u id e o ft h e a n t f i e r r o m a g n e t c i c o u p n i l g in  [Co(2-meimid)2] a n d [Co(4-meimid)2] d u et o t h el a c ko fa s u i t a b l em o d e l f o r S= 3 / 2 x  x  e x t e n d e d3 Dl a t t i c es y s t e m s .  114  2000 H  1  0  0  0  1  O  E  P  i  0  S u -looo H  -60000  -40000  -20000  0  20000  40000  60000  40000  60000  Applied Field (G)  1  1 1  1  I  1  /  1  o £  rj  o  E -2000 -3000 -60000  . . . . -40000 -20000  0  20000  Applied Field (G)  F i g u r e 4.13 meimid)2], x  M a g n e t c i h y s t e r e s s i p l o t s at 4.8  ( t o p ) ; and  [ C o ( 4 m e i m i d ) 2 ] x  ( b o t t o m ) .  115  K for  c o m p o u n d s [ C o ( 2 -  4 . 3  AN I C K E L ( I )B E N Z L M L D A Z O L A T EP O L Y M E R  IT R O D U C T O IN 4 . 3 . 1N  T h em a g n e c t i p r o p e r t i e s o fs e v e r a l 1 D n i c k e l ( I I )p y r a z o a lt ep o y lm e r sh a v eb e e n  s t u d e id p r e v i o u s l y [ 1 6 ] . I n t h o s e s t u d e is it w a s f o u n d t h a t n i c k e l ( I I ) p y r a z o a lt e s w i t h s q u a r e p a ln a r c h r o m o p h o r e g e o m e t r y a r e d a im a g n e t c i, w h i l e t h o s e w i t h t e t r a h e d r a l g e o m e t r y a r e p a r a m a g n e c t i a n d e x h i b i t a n t f i e r r o m a g n e t c i e x c h a n g e c o u p n i lg [ 1 7 ] . I n c o n t r a s t , f e w n i c k e l ( I I ) i m i d a z o l a t e p o y lm e r s h a v e b e e n s y n t h e s z ie d p r e v i o u s l y [ 6 ] .  T h o s et h a th a v eb e e nm a d ea r es q u a r ep a ln a ra n dd a im a g n e t c i [ 6 ] .N o n eo ft h en i c k  p y r a z o a lt e o r i m i d a z o l a t e p o y lm e r s r e p o r t e d h a s b e e n o b t a n ie d a s m a c r o s c o p c i c r y s t a l s s u i t a b l ef o rs i n g l ec r y s t a lX r a yd i f f r a c t i o ns t u d i e s .  I n t h i s s e c t i o n , a b e n z m i d ia z o a lt e c o m p e lx o f n i c k e l ( H ) is e x a m n ie d . T h i s m i c r o c r y s t a l i n e m a t e r i a l , [ N i ( b e n z i m i d ) ] , w a s r e p o r t e d e a r l i e r [ 1 8 ] in a s t u d y w h c ih 2 x  n ic u ld e d s o m e s p e c t r o s c o p c i c h a r a c t e r i z a t i o n . T h em a g n e c t i p r o p e r t e is o ft h ec o m p o u n d  w e r e n o t s t u d e id in t h e e a r l i e rw o r k . T h e m a g n e c t i s t u d e is p r e s e n t e d h e r e f o r  [Ni(benzimid)2] , s h o w t h a t t h i s m a t e r i a l b e h a v e s a s a v e r y w e a k f e r r o m a g n e t a t o lw x  t e m p e r a t u r e s . T h e r e f o r e , [Ni(benzimid)2] is t h e first r e p o r t e d N i ( L I ) m i d ia z o a lt e b a s e d x  c o m p o u n dt h a tb e h a v e sa s am o e lc u e lb a s e dm a g n e t .  116  A t e m p t s t o p r e p a r e o t h e r m a g n e t c ia y l i n t e r e s t i n g N i ( I I ) i m i d a z o l a t e p o y lm e r s ,  s u c h a s [Ni(imid)2] a n d [Ni(4-meimid)2] , w e r em a d e , h o w e v e r , t h em a t e r i a l s o b t a n ie d x  x  w e r ef o u n dt ob ed a im a g n e t c i a n df o rt h i sr e a s o nw e r en o ti n v e s t i g a t e df u r t h e r .  4 . 3 . 2 R E S U L T SA N DD S IC U S S O IN 4 . 3 . 2 . 1S Y N T H E S S I,  S T R U C T U R A L ,  T H E R M A L  A N D P H Y S C IA L  C H A R A C T E R Z IA T O IN  [ N i ( b e n z i m i d ) ] w a s p r e p a r e d , w i t h s o m e m o d i f i c a t i o n s , f o l o w i n g t h e m e h to d 2 x  o u t l i n e db yG o o d g a m ea n dC o t o n[ 7 ] . I nt h i sm e t h o d ,as o l u t i o no fb e n z m i d ia z o e l in w a t e rw a s a d d e dt o a n a q u e o u s s o l u t i o no f Ni(N03)2* 6H2O. T h em x it u r ew a sh e a t e d  boiling, a n do nc o o l i n g , aa lv e n d e rp r e c i p i t a t ef o r m e d .D e t a i l so nt h i ss y n t h e s s i a r eg v i in C h a p t e r 9, s e c t i o n9 . 2 . 3 . 1 .  T h i s c o m p e lx is s t a b l eb o t h in a i ra n d in c o n t a c tw i t hm o s it u r e . I t is i n s o l u b l e w a t e r a n d m o s t o r g a n c i s o l v e n t s , n o n v o l a t i l e a n d t h e r m a l y r o b u s t . T h e U V V s iN L R  s p e c t r u mo f [Ni(benzimid)2] is s h o w n in F i g u r e4 . 1 4 . T h es p e c t r u m ,w h c ih h a sn o tb e x  p r e v i o u s l y a n a l y z e d , c o n s s it s o ft h r e e m a n i a b s o r p t o in s in t h e r a n g e s o f1 6 8 0 1 7 0 0 n m  ( b a r e l yo b s e r v a b l e ) , 7 5 5 7 8 0 n m a n d 5 0 0 5 5 0 n m , w h c ih c a nb et e n t a t i v e l ya s s g in e d t h ef o l o w i n gt r a n s i t i o n s ,Ti(F) > T,Ti(F) > A, a n dTi(F) >Ti(P), r e s p e c t i v e l y . 3  3  3  3  3  2  3  2  T h e r e is a n o t h e r a b s o r p t o i n in t h e r a n g e 8 3 5 8 6 0 n m , w h c ih h a s b e e n a s s g in e d p r e v i o u s l yt ot h es p i n f o r b i d d e nt r a n s i t i o nTi(F) -»T(D) [ 1 9 ] .T h e s eo b s e r v a b e l d d 3  !  2  117  I—'  200  1  '  1  1  1  '—I  1  1 — '  1 —  1  — I —  1  — I — ' — I  400 600 800 1000 1200 1400 1600 1800 2000 W a v e e ln g t h (nm)  F i g u r e 4.14  U V v i s i b l e n e a r L Rs p e c t r u m for [Ni(benzimid)2] -I n s e r t p l o t x  s h o w s the two h g ih e s te n e r g y d-d t r a n s i t i o nb a n d s .  t r a n s i t i o n s , t h r e e s p i n a o lw e d and one s p i n f o r b i d d e n , are e x p e c t e d for t e t r a h e d r a l or d i s t o r t e d t e t r a h e d r a l N ( i L T ) [20]. U s n i g the two h g ih e s t e n e r g yb a n d s (770 n m and 525 nm), and the c o r r e s p o n d n ig T a n a b e S u g a n o c o r r e l a t i o nd a ig r a m [10] for a d t e t r a h e d r a l 8  s y s t e m , Dq and B w e r ec a l c u l a t e d to be 711 cm" and 960 cm" r e s p e c t i v e l y . In a d d i t i o n , 1  1  s t r o n gc h a r g et r a n s f e rb a n d s are s e e n in the r e g i o n2 0 0 4 0 0 nm.  118  T h eT G Ap l o tf o r [Ni(benzirnid)2] is s h o w n in F i g u r e4 . 1 5 .A sc a nb es e e nt h x  is n o e v d ie n c e o f o ls s in m a s s d u e t o t h e r m a l d e c o m p o s t o in o r s u b m i l a t o in a t  t e m p e r a t u r eb e o lw ~ 4 5 0 °C. T h eT G A d a t a s u g g e s tt h a tt w o s t e p s o c c u r in t h et h e r  d e c o m p o s t o in o f fNi(benzimid)2]. T h e first o n ei n v o l v e s ar a p i dl o s to fn e a r y l 5 0%o x  t h e initial m a s s o ft h e s a m p e l b e t w e e n 4 5 0 ° C a n d 6 1 2 °C. T h e s e c o n d e v e n t is  g r a d u a lw i t ha na d d i t i o n a la p p r o x m i a t e y l 2 5 %o ft h e initial m a s sb e n ig l o s tb e t w e e n6 ° Ca n d8 0 0 °C.  110 100  100  200  300  400  500  600  T(°C)  F i g u r e4 . 1 5 T G Ap l o tf o r [Ni(benzimid)2] . x  119  700  800  H e n c e , a c c o r d n ig t o t h e e l e c t r o n i c s p e c t r o s c o p c i a n d t h e r m a l c h a r a c t e r i z a t i o n o f [Ni(benzimid)2], t h i sc o m p o u n ds h o w st h ep h y s i c a lp r o p e r t e is o fa c o o r d n ia t o in p o y lm e r x  a n d it, m o s t likely, p o s s e s s e s m e t a l o in s w i t h a t e t r a h e d r a l c o o r d n ia t o in g e o m e t r y s i m i l a r l yt ot h o s ef o u n d in [ C o ( 4 a b i m i d ) ]( C h a p t e r3 )o r [Co(imid)2] (vide supra). 2 x  x  4 . 3 . 2 . 2 M A G N E T C I P R O P E R T E IS  M a g n e t c i s u s c e p t i b i lt ya n d m a g n e c t i m o m e n t v e r s u s t e m p e r a t u r e d a t a o n  p o w d e r e d s a m p e ls o f [Ni(benzimid)2] in a na p p l i e dfieldo f5 0 0Ga r es h o w n in F g iu x  4 . 1 6 . T h e m a g n e c t i m o m e n t o f [ N i ( b e n z i m i d ) ] d e c r e a s e s f r o m 2 . 5 3 ii. a t 3 0 0 K 2 x  d e c r e a s e st o1 3 .5 [LB  B  a s t h et e m p e r a t u r e is o lw e r e d t o 2K .T h i s s u g g e s t s  a n t f i e r r o m a g n e t c i c o u p n i lg a t l h o u g h c o n f r im a t o in o f this, in t h e f o r m o fam a x m iu m in  t h e% v e r s u s T plot, is n o t s e e n ( F i g u r e4 . 1 6 ) . F u r t h e r m o r e , n o e v d ie n c e f o ro ln g r a n f e r r o m a g n e t c i i n t e r a c t i o n a s s e e n f o rt h e c o b a t l a n a o lg u e , [Co(benzimid)2] , is o b s e r v e d x  in t h i s 5 0 0Gd a t a .N o n e t h e e ls s ,t h ep o s s i b i l i t yt h a tt h i sn i c k e lc o m p o u n dh a sas t r u c  s i m i l a r t o t h a t o ft h e C o a n a o lg u e ( w h c ih e x h i b i t s m a g n e c t i p r o p e r t e is o fa m o e lc u e l  b a s e dm a g n e t )p r o m p t e du st oi n v e s t i g a t et h em a g n e c t i p r o p e r t e is o ft h en i c k e lc o m p o u n ftrrther.  F i g u r e 4 . 1 7s h o w s t h e m a g n e t z ia t o in p l o t s f o r [Ni(benzimid)2] a t d i f f e r e n t x  120  as  F g iu r e4 . 1 6 P l o t so f% a n dp ^ rv e r s u sTf o r ^i(benzimid)2]. x  t e m p e r a t u r e s . All t h em a g n e t z ia t o in p l o t se x t r a p o a lt et oz e r om a g n e t z ia t o in a tz e r o field,  e x c e p t f o r t h e o n e d e t e r m n ie d a t 4 . 8K . I na d d i t i o n , e x c e p t f o rt h eo n ed e t e r m n ie  4 . 8 K , all o t h e r m a g n e t z ia t o in p l o t s in F g iu r e 4 . 1 7 a r e l i n e a r . T h i s r e s u l t s u p p o r t s p o s s b ie l o ln g r a n g e f e r r o m a g n e t c i o r d e r n ig a t t e m p e r a t u r e s ~ 4 . 8 K a n d b e o lw f o r [Ni(benzimid)2] x  121  3500 3000  •  4.8 K 15 K 25 K 55 K  •  •  2500 H |  o .5  o  2000 -| 1500 H IOOO H •  o  500  A  o  A  0Ji-A 0 10000  o  20000  30000  40000  50000  60000  Applied Field (G)  F i g u r e 4.17  M a g n e t z ia t o in v e r s u s a p p l i e d field p l o t s at d i f f e r e n t t e m p e r a t u r e s  for [ N i ( b e n z i m i d ) 2 ] x -  T h a t [Ni(benzimid)2] e x h i b i t s o ln g r a n g e f e r r o m a g n e t c i o r d e r and s p o n t a n e o u s x  m a g n e t z ia t o i n at ~ 4.8 K is f u r t h e ri lu s t r a t e d by a h y s t e r e s s i s t u d y . M a g n e t z ia t o i n was m e a s u r e d as the a p p l i e d field was c y c e ld b e t w e e n +55 000 G and -55 000 G at 2 and 4.8 K. The r e s u l t i n gh y s t e r e s s i o lo p at 2 K is s h o w n in F g iu r e 4.18. T h i so lo pg v ie sar e m n a n t m a g n e t z ia t o i n of ~ 7 cm G mol" and a c o e r c v ie field of ~ 60 G for [Ni(benzimid)2] 3  1  x  w h c ih c h a r a c t e r i z et h i sc o m p o u n d as a v e r yw e a k and s o f tm o e lc u e lb a s e dm a g n e t .  122  F g iu r e4 . 1 8 M a g n e t c i h y s t e r e s s i p l o t a t 2 K f o r |>Ji(penziniid)2]x. T h e i n s e r t p l o ts h o w s am a g n i f i c a t i o no ft h ec e n t r a lp a r to ft h eh y s t e r e s s i c u r v e .  A sw a s f o u n d f o rt h ec o b a t l a n a o lg u e , [Co(benzimid)2] , as p n ic a n t e ds t r u c t u r e , x  f o r [Ni(benzimid)2] , is a s lo s u p p o r t e d b y t h e f a c t t h a t t h e h g ih e s t m a g n e t z ia t o in x  m e a s u r e dw a s3 0 8 9 c m G m o r ' a t4 . 8 Ka n d5 5 0 0 0 G. T h i sv a u l e is c o n s d ie r a b y l 3  123  t h a nt h et h e o r e t i c a l s a t u r a t i o nm a g n e t z ia t o in v a u le of 1 1 1 7 7 cmGmor e x p e c t e df o ra n 3  1  S= 1 s y s t e m[ 1 5 ] .  T o i n v e s t i g a t e f u r t h e rt h e p o s s i b i l i t yo fa f e r r o m a g n e t c i g r o u n d s t a t e f o r  [ N i ( b e n z i m i d ) 2 ] x , D C m a g n e c t i s u s c e p t i b i l t ym e a s u r e m e n s t a t a n a p p l i e d field o f5 0 G  w e r e c a r r i e d o u t o na s a m p e l o ft h i sp o y lm e ra s f o lo w s : t h e s a m p e l w a s c o o e ld in field t o2K , am a g n e c t i field o f5 0Gw a sa p p l i e da n dd a t aw e r ec o l e c t e dw h i l e  t h es a m p e l ( z e r o f i e l d c o o l e dm a g n e t z ia t o in - Z F C M ) ;t h e n ,t h es a m p e l w a sc o o e ld in t h e  s a m e field ( 5 0 G ) t o 2 K , a n d d a t a w e r e c o l e c t e d in t h e w a r m n ig m o d e ( f i e l d c m a g n e t z ia t o in - F C M ) ; finally, t h e s a m p e l w a s c o o e ld a g a n i t o 2 K , in a field o f  t h e n t h e field is r e m o v e d a n d d a t a a r e c o l e c t e d w h i l e w a r m n ig t h e s a m p e l ( r e m n  m a g n e t z ia t o in - R E M ) . T h e r e s u l t s o ft h i s d a t a c o le c t i o n s c h e m e a r e s h o w n in F g iu r e  4 . 1 9 . T h e Z F C M d a t a n ic r e a s e s g r a d u a l y t o a m a x m iu m a t ~ 6 . 5 K , t h e n d e c r e a  s l i g h t l yt on ic r e a s e a g a n i t o a s e c o n dm a x m iu m a t~ 2 . 5 K . T h eT v a l u e , d e t e r m n ie d c  t h e first m a x m iu m o nt h eZ F C M plot, is ~ 6 . 5 K,. W h e nt h ea p p l i e d field w a s s w  o f f a t 2 K a s m a l r e m n a n t m a g n e t z ia t o in o f~ 0 9 .5 c m G m o l " w a s f o u n d ( i n g 3  1  a g r e e m e n tw i t ht h ev a u le o f Mrem ~ 1 c m G m o l "o b t a n ie d in t h eh y s t e r e s s i s t u d ys h o 3  1  a b o v e ) . T h i s Mrem d e c r e a s e d s i g n i f i c a n t l y o n w a r m n ig t o 2 . 5 K t h e n d e c r e a s e d f u r t h e  u p o nw a r m n ig a n dv a n s ih e da t~ 5 . 5 K . [Ni(benzimid)2] e x h i b i t sa n o t h e rt r a n s i t i o na t~ x  2 . 5 K . T h e o r i g i n o f t h i s o lw e r t e m p e r a t u r e t r a n s i t i o n is n o t c l e a r . A s i m i l a r d o u b e l  t r a n s i t i o n h a s b e e n r e c e n t l y o b s e r v e d in t h e Z F C M F C M R E M s t u d e is in a 1 D  124  m o e lc u e lb a s e df e r r m i a g n e th a v n ig C u ( I )a n dM n ( L ) I o in s[ 2 0 ] .Ap o s s b ie l s o u r c eo ft h i s p h e n o m e n o nw a sn o td s ic u s s e d in t h i se a r l i e rr e p o r t .  F r o m t h e s e r e s u l t s it is e v d ie n t t h a t [Ni(penzimid)2] e x h i b i t s o ln g r a n g e x  f e r r o m a g n e t c i o r d e r a t o lw t e m p e r a t u r e s , a n d t h a t t h i s m a t e r i a l c a n b e c o n s d ie r e d m o e lc u e lb a s e dm a g n e t .  4.5 4.0  •  3.5-  o  £  3.0 H O  s  P  ZFCM FCM REM  2.5 • 2.0 -\  B  & 1.5 1.0-  *  0.5I  0.0  2  1  1  4  *JL. 6  1  1  1  1  8  1  10  1  12  1  1  14  1  1  16  1  1  18  1-  20  T(K)  F g iu r e4 . 1 9 Z e r o f i e l d c o o l i n g ( Z F C ) a n dfield-cooling( F C ) m a g n e t z ia t o in p l o t sf o r [Ni(penzimid)2]x a t5 0 G.  125  4 . 4C O P P E R ( ) IM I D IA Z O L A T EP O L Y M E R S 4 . 4 . 1  N IT R O D U C T O IN  m I d ia z o a lt e b r d ig e d c o p p e r ( I ) d m i e r c i a n d o l i g o m e r i c c o m p e lx e s h a v e b e e n  a c t i v e l y s t u d e id [ 2 2 2 3 ] m a n iy l t o u n d e r s t a n d t h e f a c t o r s d e t e r m n in ig t h e e x t e n t o f  c o u p n i lg b e t w e e n t w o m e t a l o in s a n d t o u s e t h e s e s m i p e l c o m p o u n d s a s m o d e s l  m e t a o le n z y m e s t h a t c o n t a n i t h e s a m e s t r u c t u r a l u n i t s [ 2 4 , 2 5 ] . S e v e r a l s t u d e is h a v e  a r le a d yb e e nr e p o r t e d in w h c ih s t r u c t u r a ld a t ah a v eb e e nu s e dt of i n du s e f u lc o r r e l a t i o  b e t w e e n s t r u c t u r e a n d m a g n e c t i c o u p n i lg [ 2 6 3 0 ] . O n t h e c o n t r a r y , s t r u c t u r a l a n d m a g n e c t i p r o p e r t e i so fi m i d a z o l a t e b r i d g e dc o p p e r ( I )p o y lm e r sh a v e n o t b e e n  e x t e n s i v e l ys t u d i e d .Ab u le f o r mo f [Cu(imid)2] is t h eo n y l c o m p o u n do ft h i sf a m i l yw i x  ak n o w nm o e lc u a lr s t r u c t u r e , a n d its m a g n e c t i p r o p e r t e i sh a v ea s lo b e e nd e t e r m n ie db o n y l a tt e m p e r a t u r e sb e t w e e n8 0- 3 0 0K[ 3 1 ,3 2 ] .  I n t h e p r e s e n t s e c t i o n , t h e s y n t h e s i s , c h a r a c t e r i z a t i o n , a n d o lw t e m p e r a t u r e m a g n e c t i s t u d e is o f [Cu(imid)2] a n df o u ro t h e rC u ( I ) s y s t e m si n c o r p o r a t i n gs u b s t iu t e d x  i m i d a z o l a t el i g a n d s : [ C u ( 2 m e i m i d ) ] ,[ C u ( 4 m e i m i d ) ] ,[ C u ( b e n z i m i d ) ] ,a n d[ C u ( 4 , 5 2 x  2 x  2 x  dichloroimid) ] ,a r ed s ic u s s e d .N o n eo ft h em a t e r i a l ss t u d e id h e r ew a si s o l a t e d in a f o r 2 x  s u i t a b l ef o rs i n g l ec r y s t a lX r a yd i f f r a c t i o ns t u d i e s .M o r e o v e r ,n od e f i n i t i v ed e t a i l so nt h e  s t r u c t u r e so ft h e s ec o m p o u n d sw e r eo b t a n ie da sn e i t h e rt h ee l e c t r o n i cs p e c t r an o rt h eX r a yp o w d e rd f if r a c t o g r a m sw e r ep a r t i c u l a r l yi n f o r m a t i v ef o rt h e s es y s t e m s . N o n e t h e e ls s ,  126  a sw i t hm o s to ft h eo t h e rc o m p o u n d ss t u d e id in t h i sw o r k ,t h ec o m p o u n d sa r ec o n s d i t ob ep o y lm e r c i b a s e do ns o l u b i l i t ya n dt h e r m a lg r a v i m e t r i cs t u d i e s .  W i t h t h e e x c u ls o in o f [Cu(imid)2] a n d [Cu(4-meimid)2] , w h c ih s h o w e d o n y l x  x  w e a k a n t f i e r r o m a g n e t c i c o u p l i n g , t h e o t h e r C u ( L ) I i m i d a z o l a t e p o y lm e r s e x h i b i t e d m a g n e c t i p r o p e r t e is t h a tc l a s s i f yt h e ma sw e a ko lw t e m p e r a t u r em o e lc u e lb a s e dm a g n e t s .  4 . 4 . 2 R E S U L T SA N DD S IC U S S O IN 4 . 4 . 2 . 1S Y N T H E S E S ,  S T R U C T U R A L ,  T H E R M A L  A N D P H Y S C IA L  C H A R A C T E R Z IA T O IN  D e t a i l e d d e s c r p it o in s o ft h e s y n t h e s e s o ft h e copper(n) i m i d a z o l a t e c o m p e lx e s  s t u d e id h e r e , c a n b e f o u n d in C h a p t e r 9, s e c t o in s 9 . 2 . 4 . 1 t h r o u g h 9 . 2 . 4 . 5 . T h e m o  g i la n d c o p p e rs h o tm e t h o d , w h c ih h a sb e e ns u c c e s s f u y l u s e dt oo b t a i ns i n g l ec r y s t a l so  b n ia r yc o p p e r ( I )p y r a z o a lt e s [ 3 3 ] ,w a s first t r i e d in a na t e m p tt oo b t a i ns i n g l ec r y s t a l s t h ec o m p o u n d s ;  h o w e v e r , all a t e m p t st op r o d u c em a c r o s c o p c i c r y s t a l s w e r e  u n s u c c e s s f u . lU l t i m a t e l y ,t h eo n y l c o m p o u n d p r e p a r e d u s n ig t h i sm e h to d w a s  [Cu(imid)2], w h c ih w a s o b t a n ie d a s a d a r k b u le p o w d e r . T h e o t h e r C u ( L ) I i m i d a z o l a x  c o m p o u n d sw e r ep r e p a r e db yw e tm e h to d sw h c ih i n v o l v e dt h eu s eo fc o p p e rs h o tw i t h  e t h a n o l i c s o l u t i o n o ft h e a p p r o p r a it e l i g a n d or, t h e r e a c t i o n o fa n a p p r o p r a it e s a l t o C u ( I ) w i t h t h e a p p r o p r a it e i m i d a z o l a t e in w a t e r . T h e s e s y n t h e t c i p r o c e d u r e s a r e m o d i f i c a t i o n so fp r e v i o u s l yr e p o r t e dm e h to d s[ 7 ,3 4 ] .  127  T h ef i v e c o p p e r ( I ) c o m p o u n d s , [Cu(imid)2], [Cu(2-meimid)2] , x  x  [ C u ( 4 -  meimid) ] , [ C u ( b e n z i m i d ) ]a n d [ C u ( 4 , 5 d i c h l o r o i m i d ) ] , a r e s t a b l eb o t h in a i ra n d in 2 x  2 x  2 x  c o n t a c t w i t h m o i s t u r e . T h e y a r e i n s o l u b l e in w a t e r a n d c o m m o n o r g a n c i s o l v e n t s n o n v o l a t i l e a n d t h e r m a l y r o b u s t . T h e y d e c o m p o s e w h e n t r e a t e d w i t h c o n c e n t r a t e d m n ie r a la c i d s .  T h e r m a l g r a v i m e t r i c a n a y ls e s o ft h e f i v e c o p p e r c o m p o u n d s s h o w n o m a s s o ls s  d u et o t h e r m a l d e c o m p o s t o in o rs u b m i l a t o in b e o lw 1 8 0 °C. A th g ih e rt e m p e r a t u r e s t h e c o m p o u n d s p r e s e n t s i m i l a r t h e r m a l d e c o m p o s t o in b e h a v i o r , s h o w n ig a w e g ih t l o s s in  t h r e e s t a g e s o v e r t h e t e m p e r a t u r e r a n g e s t u d e id ( F i g u r e 4 . 2 0 ) . [Cu(benzimid)2] is t h e x  m o s tt h e r m a l yr o b u s to ft h ef i v e in t h a tt h e r e is n oi n d i c a t i o no ft h e r m a l d e c o m p o s t o  b e o lw 3 2 0 °C. I ng e n e r a l ,t h eC u ( I ) c o m p o u n d sa r el e s st h e r m a l ys t a b e l t h a nt h eC m i d ia z o a lt e sr e p o r t e do na b o v e .  T h ea b s e n c eo fa VN-H s t r e t c h i n gv i b r a t i o n in t h ee l e c t r o n i cs p e c t r a (vide  infra) a n d  in t h e i n f r a r e d s p e c t r a o f t h e s e c o m p e lx e s ( S e e t h e d s ic u s s o in a b o v e c o n c e r n n ig t h e  o b s e r v a t o in o ft h i sb a n d in [Co (imid)6(imidH) ] ) is i n d i c a t i v eo ft h ea b s e n c eo fn e u t r a l 3  2 x  i m i d a z o l e in t h e s em a t e r i a l s .  128  it £  5  <H  [ C u C m i d i) ^ [ C u ( 2 m e i m i d ] ) [ C u ( 4 m e i m i d ) ] [ C u ( b e n z i m i d ) ] [ C u ( 4 , 5 d i c h l o r o i m i d ) ]  40H  i z  30-  2 i  20-  2 i  2 i  10i  100  200  300  — I —  I  500  600  400  Temperature  F i g u r e 4.20  TGA  1  1—  800  700  (°C)  p l o t s for c o m p o u n d s [Cu(imid) ] , [Cu(2-meimid)2] , [ C u ( 4 2 x  x  meimid)2], [Cu(benzimid)2] and [ C u ( 4 , 5 d i c M o r o i m i d ) 2 ] . x  x  x  The e l e c t r o n i c s p e c t r a of the c o p p e r d e r i v a t i v e s are s h o w n in F g iu r e 4.21 s u m m a r y is p r e s e n t e d in T a b e l 4.2. the r a n g e 800  to 950  In the NR I  and a  r e g i o n , ab a n dm a x m iu m is o b s e r v e d in  nm for [Cu(imid)2], [ C u ( 4 , 5 d i c h l o r o i m i d ) ] , [Cu(benzimid)2] x  2 x  x  and, l e s sc l e a r , for [Cu(4-meimid)2] . All f i v ec o m p o u n d ss h o wb a n d s a r o u n d 550 x  129  600  200  400  600  800 1000 1200 1400  W a v e l e n g t h (nm) F i g u r e4 . 2 1 U V V s iN L R s p e c t r a f o r [Cu(imid) ] , ( a ) ; [ C u ( 2 m e i m i d ) ] , ( b ) ; 2 x  2 x  [ C u ( 4 m e i m i d ) ] , (c); [ C u ( b e n z i m i d ) ] , (d); a n d[ C u ( 4 , 5 d i c h l o r o i m i d ) ] ,( e ) . 2 x  2 x  130  2 x  nm and 400 - 500 nm in the v i s i b l e r e g i o n a t l h o u g h for [Cu(4,5-dichloroimid)2] and x  [Cu(benzimid)2] the l a t t e r b a n d s are s o m e w h a t o b s c u r e d by n it e n s e b a n d s in the  UV  r e g i o n . All f i v ec o m p o u n d ss h o wb a n d sa s s g in a b e l to c h a r g e t r a n s f e r in the 200 - 400  nm  x  r e g i o n .  T a b e l 4.2  U V V s iN L R s p e c t r a of c o p p e r ( I ) i m i d a z o l a t e s . A p p r o x m i a t ew a v e e ln g t h  v a u le s or r e g o in s (nm)  Compound  2 0 0 - 4 0 0 nm  4 0 0 - 5 0 0 nm  (a) i m i d  - 200 - 300  -400  (b) 2 m e i m i d  ~ 200 - 380  ~ 400 and 490  (c) 4 m e i m i d  ~ 200 - 250  -400  (d) b e n z m i d i  - 200 - 400  ?  -570  -890  (e) 4,5-diclimid  ~ 200 - 290  ?  -560  -800  A c c o r d n i g to H a t h a w a y [35],  1 5 5 0 - 6 0 0 nm  1  - 600 ( s p l i t )  800-950 nm -910 N o n e  -600 600 ( s p l i t )  - 850 - 950  c o m p e lx e sw i t hC u Nc h r o m o p h o r e st h a te x h i b i t d4  db a n d s in the 500 to 550 nm r e g i o n are likely to h a v e s q u a r e p a ln a r s t e r e o c h e m s it r e is ,  131  w h i l e b a n d s in t h e 625 t o 850 n m r e g i o n a r e c h a r a c t e r i s t i c o fc o m p r e s s e d t e t r a h e d r a Q1N4 c h r o m o p h o r e s . T h e s e c r i t e r i a f o r C11N4 g e o m e t r y h a v e b e e n u s e d f o r r e l a t e d  c o p p e r ( I )p y r a z o a lt e s [36] a n dp y r a z o l y l g a l a t e s y s t e m s [37]. A s c a nb es e e n in F g iu r e  4.21 a n d T a b e l 4.2, t h e c o m p o u n d s s t u d e id h e r e e x h i b i t b a n d s in w a v e e ln g t h r e g o in s  c o r r e s p o n d n ig t ob o t hc h r o m o p h o r e s .Am x it u r eo ft w oo rm o r ec h r o m o p h o r eg e o m e t r e is  is p o s s b ie l f o r t h e s e s y s t e m s . A s d e s c r b ie d a b o v e , o n e f o r m o f [Cu(imid)2] h a s b e e x  s h o w nb ys i n g l ec r y s t a lX r a yd i f f r a c t i o ns t u d e is t oh a v eb o t hs q u a r e p a ln a ra n dd i s t o r t e d t e t r a h e d r a l  CUN4  c h r o m o p h o r e s .  A s p r e v i o u s l ym e n t o in e d , t h e c r y s t a l s t r u c t u r e o fab u le f o r m o f [Cu(imid)2] is x  k n o w n . T h r e e m a g n e t c ia y l d i f f e r e n tc r y s t a l m o d i f i c a t i o n s h a v e b e e n f o u n d f o r [Cu(imid)2] [31, 32], a b u le m o d i f i c a t i o n( p ^ f f = 1.57 u, a t 293 K ) , a g r e e nm o d i f i c a t i o n x  (Meff =  1-62  B  p. a t B  303 K )  a n d a b r o w n m o d i f i c a t i o n ([igs  =  1.46  jx a t B  303 K ) .  [Cu(imid)2] s y n t h e s z ie d in t h ep r e s e n tw o r kh a sad a r kb u l e color, w i t ha x  T h e  |ieff = 1.54  p  a t 300 K . T h e c o l o r o f o u r c o m p o u n d a n d its h i g h t e m p e r a t u r e m a g n e c t i p r o p e r t e is  s u g g e s t e dt o u s initially t h a tw eh a dp r e p a r e dt h eb u le f o r m o ft h ec o m p o u n d . T h e  m o d i f i c a t i o n is t h eo n l yo n et h a th a sb e e ns t u d e id b ys i n g l ec r y s t a lX r a yd i f f r a c t i o n[  I nt h i ss t r u c t u r e ,i m i d a z o l a t og r o u p sb r d ig eC u ( I )o in st of o r mc h a i n s , in w h c ih t h e r e  s y s t e m a t c i a l t e r n a t i o n o f a Cu(ll) i o n w i t h s q u a r e p a ln a r c o o r d i n a t i o n , f o l o w e d b y  a n o t h e r C u ( I ) i o n in a f l a t t e n e d t e t r a h e d r a l c o o r d i n a t i o n . T h e c h a n is a r e l i n k e d a t t  f l a t t e n e d t e t r a h e d r a l C u ( I ) i o n s o t h a t t h e w h o e l a s s e m b y l f o r m s a t h r e e d m i e n s o in a  n e t w o r k [32]. A r e p r e s e n t a t o in o ft h er e p e a tu n i to f blue-[Cu(imid) ] , a n das t e r e o v e iw 2 x  132  s h o w n ig t h e 3 D s t r u c t u r e o f t h i s p o y lm e r a r e s h o w n in F g iu r e s 4 . 2 2 a n d 4 . 2  r e s p e c t i v e l y . T h e s e v e iw s w e r e a c h e iv e d e m p o ly n ig t h e s o f t w a r e P o w d e r c e l [ 8 ] a n d u s n ig t h ec r y s t a l o g r a p h i cd a t ap r e v i o u s l yr e p o r t e d[ 3 2 ] .  F g iu r e4 . 2 2 R e p e a tu n i to f blue-[Cu(imid)2]. H y d r o g e na o tm sa r eo m i t t e d . x  133  Figure 4.23  Stereoview of a section of blue-[Cu(imid) ] including the unit cell. 2  x  Projection (001). No hydrogen atoms shown.  As shown in Figure 4.24, the experimental X-ray powder diffraction pattern of the sample of [Cu(imid)2] prepared in this thesis work does not coincide well with that x  calculated [8], employing single crystal X-ray diffraction data reported for the blue[Cu(imid)2] [32]. This implies that the [Cu(imid)2]x synthesized in this work is not x  isomorphous with blue-[Cu(imid)2]  x  [32]. The detailed structure of our compound  remains unknown.  134  i  5  5  10 15 20 25 30 35 40 45 50  u  ^  ^  ^  ^  10 15 20 25 30 35 40 45 50  29 (deg)  F g iu r e4 . 2 4 X r a yp o w d e rd f if r a c t o g r a m so fb l u e [ C u ( i m i d ) ]( t o p ,c a l c u l a t e d ) 2 x  a n d [Cu(imid) ]p r e p a r e dh e r e( b o t t o m ,e x p e r i m e n t a l ) . 2 x  T h e X r a y p o w d e r d i f f r a c t i o n p a t e r n s f o r [Cu(2-meimid) ]x, [ C u ( 4 m e i m i d ) ] , 2  2 x  [ C u ( 4 , 5 d i c h l o r o i m i d ) ]a n d[ C u ( b e n z i m i d ) ] ,a r es h o w n in F g iu r e4 . 2 5 .E a c hp a t t e r n is 2 x  2 x  u n q iu e s h o w n ig t h e r e is n o s io m o r p h s im a s s o c a it e d w i t h t h e d i f f e r e n t c o p p e r s y s t e m s  I n t e r e s t i n g l y , t h e p a t e r n s f o r t h e imid, 2 m e m i d i a n d b e n z m i d i c o p p e r c o m p o u n d s a r e  a s lo d i f f e r e n tfromt h o s e o ft h e c o r r e s p o n d n ig c o b a t l c o m p o u n d s ( s e e F g iu r e s 4 , 4 a n d  4 . 5 ) . I n t h e s es t u d e is w eh a v ef o u n dn oe x a m p e ls o fs io m o r p h o u sp a i r so fc o p p e r ( n )  135  ( b )  (a)  u 10  20  30 26  40  50  10  20  ( c )  -J 10  i  20  •  i  30 26  40  50  30 26  40  50  40  50  |  10  20  30 26  F i g u r e4 . 2 5 X r a yp o w d e rd i f f r a c t i o np a t e r n so f [Cu(2-meimid)2] ,( a ) ; [ C u ( 4 x  meimid) ] ,( b ) ;[ C u ( b e n z i m i d ) ] , (c); a n d[ C u ( 4 , 5 d i c W o r o i m i d ) ] , (d). 2 x  2 x  2 x  c o b a l t ( I) i m i d a z o l a t e s .T h i sc o n t r a s t ss h a r p y l w i t ht h es i t u a t i o nf o ri r o n ( I I )a n dc o b a l t ( I ) w h e r ew eh a v ed s ic o v e r e dt h r e ee x a m p e ls o fs io m o r p h o u s pairs.  136  T h e s t r u c t u r e s o ft h e c o p p e r ( I ) m i d ia z o a lt e s s t u d e id h e r ew h i l e likely i n v o l v i n g  3 D c o n n e c t i v i t i e s o ft h e t y p e s e e n in blue-[Cu(imid)2] [ 3 2 ] , a p p e a r t o b e s o m e w h a x  u n q iu e .T h i sm a yb ec a u s e db yt h ep r e s e n c eo ft w oo rm o r ed i f f e r e n tc h r o m o p h o r e s in  l a t t i c ea si n d i c a t e db yt h ee l e c t r o n i cs p e c t r o s c o p ys t u d i e s . A tt h i sp o i n t it is n o tp o s s b i t om a k eam o r ec o n c u ls v ie s t a t e m e n tr e g a r d n ig s t r u c t u r e s .  4 . 4 . 3 M A G N E T C I P R O P E R T E IS  M a g n e t c i s u s c e p t i b i lt i e sw e r em e a s u r e da t 1 00 0 0Gf r o m2t o3 0 0Kf o ra C u ( I ) i m i d a z o l a t e c o m p o u n d s . M a g n e t c i s u s c e p t i b i l i t y , %, a n d m a g n e c t i m o m e n t , \i^s,  v e r s u s T ( 2 t o 1 0 0 K ) d a t a o n p o w d e r e d s a m p e ls a r e s h o w n in F i g u r e 4 . 2 6 a n r e s p e c t i v e l y .  All five c o m p o u n d s s h o wb r o a dm a x m i a in t h e i r% v e r s u sTp l o t s o v e rt h e2 5 1 5 0 d e g r e e r a n g e i n d i c a t i n g t h e p r e s e n c e o fa n t f i e r r o m a g n e t c i e x c h a n g e . T h i s is  c o n f r im e d b y t h e f a c t all five c o m p o u n d s s h o w d e c r e a s n ig m a g n e c t i m o m e n s t w i t h  d e c r e a s n ig t e m p e r a t u r eo v e rt h i sr a n g e . All five o ft h ec o m p o u n d se x h i b i ta nn ic r e a s ei  Xa to lw e rt e m p e r a t u r e s . T h ep ^ fv e r s u s T plot, in p a r t i c u l a ra to lw t e m p e r a t u r e s ,c l e  s h o w sd i s t i n c t i v eb e h a v o ir f o rt h e five c o m p o u n d s . [Cu(4-meimid)2] s h o w sad e c r e a s e in x  137  0 0 .2 0 •  V V V  0 0 .1 5  V  [Cu(imid) ]  •  [ C u ( 2 m e i m j d ) ]  •  [ C u ( 4 m e i m i d ) ]  2 x  2 x  2 x  v[ C u ( b e n z i m i d ) ]  V  o •5 o.oio  o  2 x  O  V  [ C u ( 4 , 5 d i c h l o r o i m i d ) ] 2 x  s 61  0 0 .0 5  V  v  V »  V  ^  V  V  V  v  6  6  v o  o  I I  0 0 .0 0 2 5  5 0  7 5  1 0 0  T(K)  F i g u r e 4.26  x  v e r s u s T  P  lots a t  1 0 0 0 0 G f o r [Cu(imid)]x, [Cu(2-meimid) ] 2  2 x  [Cu(4-meimid) ]x, [ C u ( b e r i z i m i d ) ]a n d[ C u ( 4 , 5 d i c M o r o i m i d ) ] . 2  2 x  2 x  LL-ff w i t hd e c r e a s n ig t e m p e r a t u r ed o w nt o2K ,c o n s s it e dw i t ha n t f i e r r o m a g n e t c i e x c h a n g e  o v e rt h ee n t i r er a n g es t u d i e d .T h i s is c o n f r im e db yt h e%d a t ao b t a n ie df o rt h i sc o m p o  e m p o ly n ig a na p p l i e d field o f5 0 0 G. % s h o w s ab r o a dm a x m iu ma t~7 5K( F i g u r e T h e n ic r e a s e in  a tt h eo lw e s tt e m p e r a t u r e ss t u d e id s e e n in b o t ht h e 1 00 0 0a n d5  138  17 .5 s  15 .0  V  o  o  •  *  o  •  12 .5 o  3  10 .0  is  *  6  07 .5  [Cu(imid)]  2x  05 .0  [Cu(2-meimid)]  2x  [Cu(4-meimid)]  2x  02 .5  v  [Cu(benzimid)]  o  [Cu(4,5-dicWorimid)]  2x  2x  00 .0 2 5  7 5  50  1 0 0  1 2 5  1 5 0  T(K)  F g iu r e 4.27  LUff v e r s u s  Tp l o t s at 1 0 000 G for [Cu(imid)2], [ C u ( 2 m e i r n i d ) ] , 2 x  x  [Cu(4-meirnid)2] ,[ C u ( b e n z i m i d ) ] and [ C u ( 4 , 5 d i c h l o r o i m i d ) ] . x  2 x  2 x  d a t a is not l a r g e and likely a r i s e sfromthe p r e s e n c e of p a r a m a g n e c t i i m p u r i t i e s .  The m a g n e c t i b e h a v o i r of [Cu(imid)2] is s i m i l a rt ot h a t of [Cu(4-meimid)2] w i t h x  x  the e x c e p t o in t h a t the " p a r a m a g n e c t i tail" in the % p l o t is m u c hm o r ep r o n o u n c e d for t h i s  c o m p o u n d( F i g u r e4 . 2 6 ) .A sar e s u l t the p<.v e r s u sTp l o ts h o w sac l e a rt e n d e n c yt ol e ff  139  0.0045  0.0020 100  150  200  250  300  T (K)  F g iu r e 4.28  P l o t of % v e r s u s T for [ C u ( 4 m e i m i d ) ] at 500 G. 2 x  off ( s m a l e rs l o p e )b e o lw ~ 25 K. T h i ss u g g e s t s : (i) e i t h e rah g ih e rl e v e l of p a r a m a g n e c t i i m p u r i t y in t h i sm a t e r i a l or, (ii) m o r ec o m p e lx b e h a v o ir w i t h ad e c r e a s e in the s t r e n g t h of the a n t f i e r r o m a g n e t c i c o u p n i l g as the t e m p e r a t u r e is o lw e r e d or, (iii) a c h a n g e in the m a g n e c t i e x c h a n g em e c h a n s im f r o mp r i m a r i l y a n t f i e r r o m a g n e t c i t o f e r r o m a g n e t c i c o u p l i n g .  140  p r i m a r i l y  T h eo t h e rt h r e ec o m p o u n d s  g i v ec l e a r e v d ie n c eo f at r a n s i t i o n from  a n t f i e r r o m a g n e t c i t o f e r r o m a g n e t c i e x c h a n g ea to lw t e m p e r a t u r e s .T h i s is c l e a r l yt h ec a s e  f o r [Cu(benzimid)2] , w h c ih s h o w s a m a g n e c t i a n o m a y l a t ~ 1 5 K b e o lw w h c ih Lie x  n ic r e a s e s o n d e c r e a s n ig t h e t e m p e r a t u r e b e f o r e d e c r e a s n ig a g a n i b e o lw 8 K . S i m i l a a n o m a e i ls a r el e s sp r o n o u n c e df o r[ C u ( 4 , 5 d i c h l o r o i m i d ) 2 ] xa n d [Cu(2-meimid)2] w h e r e x  t h e LL-ff v a u le s a r e s e e nj u s tt o l e v e l o f fo nd e c r e a s n ig t h et e m p e r a t u r eb e f o r ed e c r e a s n i a g a n i a st h et e m p e r a t u r e is o lw e r e d( F i g u r e4 . 2 7 ) .  T o t e s t f o rt h e p r e s e n c e ( o r a b s e n c e ) o fo ln g r a n g e f e r r o m a g n e t c i o r d e r in t h e s e  f i v e c o p p e r s y s t e m s w e d e c d ie d t o u n d e r t a k e f i e l d c o o l e d ( F C ) a n d z e r o f i e l d c o o l e d  ( Z F C ) D C s u s c e p t i b i lt y m e a s u r e m e n s t a t a r e l a t i v e l y o lw a p p l i e d field o f 5 0 G. T h  p r o t o c o l f o r t h i s c o n s s it s o fc o o l i n g t h e s a m p e l a t z e r o field t o 2 . 0 K , t h e n , a p p y ln i  m a g n e c t i field ( 5 0 G ) t h e d a t a a r e c o l e c t e d w h i l e t h e s a m p e l w a r m s ( Z F C d a t a ) ;  s a m p e l is t h e nc o o e ld in t h e field o f5 0Gt o2 . 0K ,a n dd a t aa r ec o l e c t e dw h i l e  t h e s a m p e l ( F C d a t a ) . T h e r e s u l t s o ft h i s d a t a c o le c t i o n s c h e m e a r e s h o w n in F g iu 4 . 2 9 , 4 . 3 0 , 4 . 3 1 , 4 . 3 2 , a n d 4 . 3 3 , f o r[ C u ( b e n z i m i d ) ] , [ C u ( 2 m e i m i d ) ] , [ C u ( 4 , 5 2 x  2 x  dichloroimid) ] , [Cu(imid) ] ,a n d[ C u ( 4 m e i m i d ) ] ,r e s p e c t i v e l y . 2 x  2 x  2 x  I n a c o m p o u n d e x h i b i t i n g o ln g r a n g e f e r r o m a g n e t c i o r d e r i n g , t h e t e m p e r a t u r e -  d e p e n d e n c e o fm a g n e t z ia t o in c u r v e s will s h o w , g e n e r a l y , a b r e a k in t h e f i e l d c o o l e d m a g n e t z ia t o in ( F C M ) c u r v e a n d ap e a k f o rt h ez e r o f i e l d c o o l e dm a g n e t z ia t o in ( Z F C M )  c u r v e a t t h e o n s e t o ft h e m a g n e c t i t r a n s i t i o n (T). Also, t h e v a u le s o ft h e Z F C M c  141  a w la y so lw e rt h a nt h eF C Mv a u le sa tt e m p e r a t u r e sb e o lw t h em a g n e c t i t r a n s i t i o n .H e n c  t h e s e p l o t s c a n p r o v d ie o n e o f t h e m o s t a c c u r a t e w a y s t o d e t e r m n ie t h e criti t e m p e r a t u r e (T) [ 3 8 ] . c  1614-  ZFCM a FCM  •  12o  108-  8 0  O  6-  o  a  o°  4-  o a  2-  ^tato^r,  01  1  0  F i g u r e 4.29  5  1  1  1  10  1  15 T(K)  1  1  20  1  1  25  Z e r o f i e l d c o o l i n g ( Z F C ) a n d f i e l d c o o l i n g ( F C ) m a g n e t z ia t o in  p l o t sf o r [Cu(benzimid)2] a t5 0 G. x  142  0.44  H  0 . 0 8 4 — | — i — | — i — | — i — | — i — j — i — | — i — i — i — i — i — |  0  5  10  15  20  25  30  35 40  T(K)  F g iu r e 4.30  Z e r o f i e l d c o o l i n g (ZFC)  and f i e l d c o o l i n g (FC) m a g n e t z ia t o in  p l o t s for [Cu(2-meimid)2] at 50 G. x  As can be s e e n in F i g u r e 4.29, [Cu(benzimid)2] e x h i b i t s the FCM and Z F C M x  c h a r a c t e r i s t i c s of a m a t e r i a l s h o w n ig o ln g r a n g e f e r r o m a g n e t c i o r d e r . The critical t e m p e r a t u r e (T) for t h i sc o m p o u n d is d e t e r m n ie d to b e ~ 8 K. C o m p a r n ig the b e h a v o i r of c  [ C u ( 2 m e i m i d ) ]( F i g u r e 4.30) and [ C u ( 4 , 5 d i c M o r o i m i d ) ] ( F i g u r e 4.31) to t h a t of 2 x  [Cu(benzimid)2] , x  2 x  it a p p e a r st h a tt h e s et w op o y lm e r sa s lo e x h i b i t o ln g r a n g e  f e r r o m a g n e t c i o r d e r at o lw t e m p e r a t u r e s . E m p o ly n ig the m a x m iu m in the Z F C Mp l o t as the m e a s u r e of the critical t e m p e r a t u r e g e n e r a t e s T v a u le s of~ 1 5 K a n d - 1 4 K f o r c  143  0.23 -I  0.220.21-  •  ZFCM FCM  o •  • ° •  0.20-  o •  "o  £ O r| S  O  0.19-  °P  i S 0 •  0.180.17-  •  g  0.160.150  1  1  5  ' —  1  '  1  10  '  15  I 20  1-1  "i 25  T(K)  F g iu r e4 . 3 1 Z e r o f i e l d c o o l i n g ( Z F C ) a n d f i e l d c o o l i n g ( F C ) m a g n e t z ia t o in p l o t sf o r [Cu(4,5-dichloroimid)2]x a t5 0 G.  [ C u ( 2 m e i m i d ) ]a n d [Cu(4,5-dichloroimid)2] , r e s p e c t i v e l y . [ C u ( 2 m e i m i d ) ]s h o w s a 2 x  2 x  x  s e c o n dm a x m iu m in its Z F C Mp l o ta t~9K .I t is n o ta t all c l e a rw h a tt h eo r i g i n o lw e r t e m p e r a t u r e t r a n s i t i o n . A s i m i l a r d o u b e l t r a n s i t i o n a p p e a r s in t h e Z F C M F C M R E M s t u d e is c a r r i e d o u t o n [Ni(benzimid)2] a n d d e s c r b ie d e a r l i e r in t h i s C h a p t e r x  ( s e c t i o n4 . 3 . 2 . 2 ) . Also, a sm e n o t in e de a r l i e r ,as i m i l a rd o u b e l t r a n s i t i o nh a sb e e nr e c e n t r e p o r t e d in a 1 Dm o e lc u e lb a s e df e r r m i a g n e ti n v o l v i n gC u ( H )a n dM n ( I )o in s[ 2 0 ] .  144  In c o n t r a s t to the b e h a v o ir j u s td e s c r i b e d , the s t u d e is on [Cu(irnid)2] a n d [ C u ( 4 x  meimid)2] d o not r e v e a l p e a k s or l a r g e d i s c o n t i n u i t i e s in t h e i r Z F C M or FCM p l o t s x  ( F i g u r e s 4.32 and 4.33). For [ C u ( i m i d ) ] the Z F C M and FCM p l o t s s h o w o n y l s m a l 2 x  d i s c o n t i n u i t i e s at a r o u n d 1 5 K, the t e m p e r a t u r e at w h c ih the v a u le s of the FCM a n d Z F C M are the s a m e f o l o w i n g aw a r m n ig m o d e ( F i g u r e 4.32). I n t e r e s t i n g l y , t h i s c o m p o u n d s h o w s as e c o n dm n io ra n o m a y l a ta r o u n d 1 0 K. S i m i l a r l y , the m a g n e t z ia t o in  T (K)  F i g u r e 4.32  Z e r o f i e l d c o o l i n g (ZFC)  p l o t s for [ C u ( i m i d ) ] at 50 G. 2 x  145  and f i e l d c o o l i n g (FC) m a g n e t z ia t o in  c u r v e s of [Cu(4-meimid)2] h a v e s m a l b r e a k s at a r o u n d 15 K ( F i g u r e 4 . 3 3 ) . In x  c o n c l u s i o n , [Cu(imid) ] and [Cu(4-meimid)2] do not g i v e e v d ie n c e for o ln g r a n g e 2 x  x  f e r r o m a g n e t c i o r d e r e v e n in a p p l i e d f i e l d s as o lw as 50 G. T h i s is c o n s s it e n t w i t h the c o n v e n t o in a l DC m a g n e t z ia t o in s t u d e is d o n e at 500 and 10 000 G.  0.34-  •  0.32-J 0.30-J  o  o  0.28-  o  in S  F C M  •  0.26;  o S  •  ZFCM  •  0.240.220.20;  °  0.18-  •  o o  0.160.14-  c  0o  0.120.100.081  1  0  1  i  5  10  i  15  20  25  -r— 30  35  40  T(K)  F i g u r e 43 .3  Z e r o f i e l d c o o l i n g (ZFC)  p l o t s for [Cu(4-meimid)2] at 50 G. x  146  and f i e l d c o o l i n g (FC) m a g n e t z ia t o in  A sd e s c r b ie d in e a r l i e rs e c t o in so ft h i sC h a p t e r ,h y s t e r e s s i s t u d e is m a yb eu s e dt c o n f r im t h ep r e s e n c e o fo ln g r a n g e f e r r o m a g n e t c i o r d e r . A c c o r d n ig y l w e e x a m n ie dt h e  m a g n e t z ia t o in o f all five c o p p e r c o m p o u n d s a s t h e a p p l i e d field w a sc y c e ld b e t w e e n  + 5 5 0 0 0 G a n d5 5 0 0 0 G a t4 . 8 K . T h er e s u l t i n gh y s t e r e s s i o lo p s a r e s h o w ni 4 . 3 4 . T h e s e o lo p s g i v e r e m n a n t m a g n e t z ia t o in s o f0 . 2 5 , 6 . 0 a n d 0 0 .2 c mG m o l " 3  1  c o e r c v ie fields o f6 5 , 4 5 a n d 4 G f o r [Cu(2-meimid)2] , [Cu(benzimid)2] a n d [ C u ( 4 , 5 x  x  dichloroimid)2], r e s p e c t i v e l y ,w h c ih c h a r a c t e r i z et h e s ec o m p o u n d s a s v e r y s o f t x  m o e lc u e lb a s e dm a g n e t s .  I n c o n t r a s t , n o w e l d e f n ie d m a g n e c t i h y s t e r e s s i w a s f o u n d , a t 4 . 8 K , f o  [Cu(imid)2] a n d [ C u ( 4 m e i m i d ) ] , a s s h o w n in F i g u r e 4 . 3 5 . T h u s , t h e s e t w o c o p p e r 2 x  x  c o m p o u n d sc a n n o tb er e g a r d e da sm o e lc u e lb a s e dm a g n e t s .  A s p n ic a n t e d s t r u c t u r e ,l e a d i n g t o r e s i d u a ls p i n a t o lw t e m p e r a t u r e s , f o r [Cu(2-meimid)2] , [ C u ( b e n z i m i d ) ] a n d [Cu(4,5-dichloroimid)2] , is a s lo s u p p o r t e d b y x  2 x  x  t h e f a c t t h a t t h e i r h g ih e s t m a g n e t z ia t o in s m e a s u r e d w e r e 8 0 , 3 4 7 a n d 2 5 1 c m G m 3  r e s p e c t i v e l y , a t 4 . 8 K a n d 5 5 0 0 0 G. T h e s e v a u le s a r e c o n s d ie r a b y l o lw e r t h a n  t h e o r e t i c a ls a t u r a t i o nm a g n e t z ia t o in v a u le o f5 5 8 8c m G m o rf o ra n S= 1 2 / s y s t e m[ 1 5 3  147  1  300 v  o f  -200 -300  1  J  0 -100  i  1  •40000 -20000  0  20000 40000  400 o -e-°  C "3 £ P  2 0 0  o  E  CD  *s  -200  o O ° ' ° °  -40000 -20000  0  20000 40000  -40000 -20000  0  20000 40000  Applied Field (G)  F i g u r e 4.34  M a g n e t c i h y s t e r e s s i p l o t s at 4.8  K for  [ C u ( 4 , 5 dicloroirnid)2], x  ( t o p ) ; [Cu(benzimid)2] , ( m i d d l e ) ; and [Cu(2-meimid)2], ( b o t t o m ) . The i n s e r tp l o t ss h o w x  x  m a g n f i c ia t o in s of the c e n t r a lp a r t of the h y s t e r e s s i c u r v e s .  148  o  s  o  m  E  -60000 -40000 -20000  0  20000  40000  60000  Applied Field (G) 200  -I  150 @  100  J". "3  E  0  0  ©  8  @  50  iir-  0-  wE  ©  -50 -  •  -100 -150 -  ©  1  0  ©  -200 -60000 -40000 -20000  0  20000  40000  60000  Applied Field (G)  F i g u r e 4.35  M a g n e t c i h y s t e r e s s i p l o t s at 4.8 K for [Cu(imid)2], ( t o p ) , and x  [Cu(4-meimid)2] , ( b o t t o m ) . The i n s e r tp l o t s s h o w m a g n f ic a t o in s of the c e n t r a lp a r t of x  the h y s t e r e s s i c u r v e s .  149  T h em a g n e c t i b e h a v o ir s o f [ C u ( 2 m e i m i d ) ] , [ C u ( b e n z i m i d ) ]a n d 2 x  2 x  [ C u ( 4 , 5 d i c h l o r o i m i d ) ] , i n d i c a t e in all t h r e e c o m p o u n d st h e p r e s e n c e 2 x  o f  a n t f i e r r o m a g n e t c i c o u p n i lg b e t w e e n p a r a m a g n e c t i c e n t e r s a s t h e p r m i a r y e x c h a n g e  m e c h a n s im c o m b n ie d w i t h a m a g n e c t i p h a s e t r a n s i t i o n t o a f e r r o m a g n e t i c a l y o r d e r e d  s t a t ea to lw t e m p e r a t u r e s . T h e r e f o r e ,t h e s et h r e ec o p p e rc o m p o u n d sc a nb ec o n s d ie r e da m o e lc u e lb a s e d m a g n e t s . A g a i n , t h i s m a g n e c t i b e h a v o i r is v e r y c o m p a r a b e l t o t h a t r e p o r t e d f o r [Fe (imid) (imidH) ] [1], [ F e ( 2 m e i m i d ) . 0 . 1 3 ( F e C p ) ][ 2 ] 3  6  2 x  2  2x  a n d  [ F e ( 4 a b i m i d ) ] ( C h a p t e r 3), a n d t h e o n e o b s e r v e d p r e v i o u s l y in t h i s C h a p t e r f o r t w o 2 x  C o ( I )m i d ia z o a lt e sa n df o rt h eC o ( I) a n dN i ( I I )b e n z m i d ia z o a lt e s .  4 . 5  S U M M A R YA N DC O N C L U S O IN S  E a r l i e rs t u d i e s ,m a n iy l o nc o m p o u n d so fi r o n ( I I ) ,l e dt ot h es u g g e s t o in [ 1 , 2 ] t h a  a z o l a t e g i la n d s w h c ih b r d ig e t h r o u g h n t ir o g e n a o tm s s e p a r a t e d b y o n e c a r b o n in t h  h e t e r o c y c l i cr i n g will g e n e r a t es t r u c t u r e sw i t hs i n g l ea z o l a t eb r d ig e sa n de x t e n d e da r r a y s .  T h ew o r kd e s c r b ie d in t h i sC h a p t e ri n d i c a t e st h a t , e v e nt h o u g hn on e ws t r u c t u r e  w e r ed e t e r m n ie db ys i n g l ec r y s t a lX r a y diffraction, t h i s s t r u c t u r a lm o t i fe x t e n d sb e y o n d  c o m p o u n d so fi r o n ( I I )t oi n c l u d et h o s eo fc o b a l t ( I I ) ,n i c k e l ( L I ) a n dc o p p e r f f l ) . M o r e o v e r ,  all o ft h e s y s t e m s s t u d e id in t h i s C h a p t e r s h o w a n t f i e r r o m a g n e t c i e x c h a n g e c o u p l i n g ,  m e d a it e d b y t h e b r i d g i n g i m i d a z o l a t e l i g a n d s , a s t h e p r m i a r y e x c h a n g e p r o c e s s , a n d  m a n y , a t l h o u g h n o t all, o ft h e s y s t e m s g i v e e v d ie n c e f o r am a g n e c t i t r a n s i t i o nt o l o  150  r a n g e f e r r o m a g n e t c i o r d e ra to lw t e m p e r a t u r e s . I t a p p e a r st h a tt h ep h e n o m e n o no fs p i n c a n t i n g ,ac o n s e q u e n c eo ft h en o n c e n x lo s y m m e t r c i M-L-M e x c h a n g ep a t h w a yp r o v d ie d  b yt h es i n g l e b r i d g i n gi m i d a z o l a t eg i la n d sd o e sn id e e de x t e n dt om e t a ls y s t e m so t h e rt h a i r o n ( L T ) .  I t is n o t c l e a r a t t h i s p o i n t w h y s o m e , b u t n o t all, o ft h eb n ia r ym i d ia z o a lt e s  c o p p e r t j l ) a n d c o b a l t ( I) s h o w w e a k f e r r o m a g n e t s im . T h e r e a p p e a r s t o b e n o o b v o iu s l i g a n d c h a r a c t e r i s t i cd e t e r m n in i g this. F o re x a m p e l, w h i l e t h e r e is e v d ie n c e f o r  f e r r o m a g n e t c i o r d e r in t h eb i n a r yb e n z m i d ia z o a lt e so fb o t hc o b a t l a n dc o p p e r( n i c k e lt o o ,  a l b e i tv e r yw e a k ) ,t h eb i n a r yi m i d a z o l a t eo fc o b a l t ( I) s h o w so lw t e m p e r a t u r eo r d e rw h i l e  t h a t o fc o p p e r ( I ) d o e s n o t . I n c o n t r a s t , t h e 2 m e t h y m i l d ia z o a lt e o fc o p p e r s h o w s o r d e  a n dt h a to fc o b a t l d o e sn o t , w h i l en e i t h e rt h ec o b a t l n o rt h ec o p p e r4 m e t h y m i l d ia z o a lt s h o w so r d e r .  I t s e e m s t h a t t h e p r e s e n c e o r a b s e n c e o fm e a s u r a b e l o ln g r a n g e f e r r o m a g n e t c i  o r d e r in i m i d a z o l a t e s y s t e m s d e p e n d s o n s t r u c t u r a l d e t a i l s w h c ih in t u r n a f f e c t f a c t o r s  s u c h a s t h e d e g r e e o fs p i n c a n t i n g . L e s s m i p o r t a n t is t h e d c o n f i g u r a t i o n o ft h em n  c e n t e r( o t h e rt h a nt h a t it b eap a r a m a g n e c t i c o n f i g u r a t i o n ) .  151  R e f e r e n c e s  1.  S. J. R e t t i g , A. S t o r r , D. A. S u m m e r s , R. C. T h o m p s o n , and J. T r o t t e r . /. Am. Chem. Soc. 119, 8 6 7 5( 1 9 9 7 ) .  2.  S. J. R e t t i g , A. S t o r r , D. A. S u m m e r s , R. C. T h o m p s o n , and J. T r o t t e r . Can. J. Chem. 77, 425 ( 1 9 9 9 ) .  3.  V. M. S t u r m , F. B r a n d l , D. E n g e l , W. H o p p e . Acta Cryst., B31, 2 3 6 9( 1 9 7 5 ) .  4.  G. P. B r o w n , and S. A f t e r g u t . J. Polymer Sci., A2, 1839 ( 1 9 6 4 ) .  5.  F. Seel, and J. R o d r i a n . J. Organomet. Chem., 16, 479 ( 1 9 6 9 ) .  6.  A. M. V e c c h o iS a d u s . Trans. Met. Chem., 20,46 ( 1 9 9 5 ) .  7.  M. G o o d g a m e , and F. A. C o t t o n . J. Am. Chem. Soc. 84, 1543 ( 1 9 6 2 ) .  8.  PowderCell, v e r s i o n 2.3, W. K r a u s s and G. N o l z e ,F e d e r a lI n s t i t u t e for M a t e r i a l s R e s e a r c h and T e s t i n g( B A M ) , Berlin, 1997.  9.  F. A. C o t t o n , and G. W i l k i n s o n . Advanced Inorganic Chemistry. F o u r t h Edition. J o h nW i l e y&S o n s . New Y o r k . 1980. p. 770  10.  Y. T a n a b e and S. S u g a n o . J. Phys. Soc. Jpn. 9, 753 ( 1 9 5 4 ) .  11.  M. K. Ehlert, A. S t o r r , and R. C. T h o m p s o n . Can. J. Chem. 71,1412 ( 1 9 9 3 ) .  12.  W. J. Eilbeck, F. H o m l e s , C. E. T a y l o r , and A. E. Underhil. J. Chem. Soc. (A), 128 ( 1 9 6 8 ) .  13.  MGP-Suite  of Programs for Interpretation ofX-Ray Experiments, by J e a n  L a u g i e r t and B e r n a r dB o c h u ,E N S P L /a b o r a t o r ie des M a t e r a iu x et du G e n e i P h y s q iu e . BP 46. 3 8 0 4 2S a i n tM a r t i nd H 'e r e s ,F r a n c e .h t t p : / w w w . i n p g . f r / L M G P and h t p p : /w w w . c c p l 4 . a c . u k / t u t o r i a l /m g p / . 14.  F. A. C o t t o n , and G. W i l k i n s o n . Advanced Inorganic Chemistry. F o u r t h Edition. J o h nW i l e y&S o n s . New Y o r k . 1980. p. 771.  15.  R. L. Carlin. Magnetochemistry.  16.  A. S t o r r , D. A. S u m m e r s , and R. C. T h o m p s o n . Can. J. Chem. 76, 1130 ( 1 9 9 8 ) .  S p r i n g e r V e r l a g . Berlin. 1986.  152  pp.  7-9.  17.  D. A. S u m m e r s . Ph. D. T h e s i s . The U n i v e r s i t y of British C o u lm b a i. 1997.  18.  M. M. C o r d e s and J. L. W a l t e r . Spectrochim. Acta. 24, 1421 ( 1 9 6 8 ) .  19.  F. A. C o t t o n , and G. W i l k i n s o n . Advanced Inorganic Chemistry. F o u r t h Edition. J o h nW i l e y&S o n s . New Y o r k . 1980. p. 789.  20.  N. Fukita, M. O h b a , T. S h i g a , H. O k a w a , and Y. Ajiro. J. Chem. Soc, Dalton. Trans. 64 ( 2 0 0 1 ) .  21.  J. C. D e w a n and S. J. L i p p a r d . Inorg. Chem. 19, 2 0 7 9( 1 9 8 0 ) .  22.  H. M. J. H e n d r i c k s , P. J. M. W. L. Birker, G. C. V e r s h o o r , and J. R e e d i j k . J. Chem. Soc, Dalton Trans. 623 ( 1 9 8 2 ) .  23.  C. Benelli, R. K. B u n t i n g , D. G a t t e s c h i , and C. Z a n c h i n i . Inorg. Chem. 23, 3 0 7 4 ( 1 9 8 4 ) .  24.  J. A. b Ie r s and R. H. H o m l e s . Science. 209, 223 ( 1 9 8 0 ) .  25.  E. Colacio, J. M. D o m n ig u e z V e r a , M. G h a z i , R. K i v e k a s , M. Klinga, and J. M. M o r e n o . Inorg. Chem. 37, 3 0 4 0( 1 9 9 8 ) .  26.  J. T. L a n d r u m , C. A. R e e d , K. H a t a n o , and W. R. S c h e i d t . J. Am. Chem. Soc. 100, 3 2 3 2( 1 9 7 8 ) .  27.  M. S. H a d d a d and D. N. H e n d r c ik s o n . Inorg. Chem. 17, 2 6 3 6( 1 9 7 8 ) .  28.  C. L. O Y 'o u n g , J. C. D e w a n , H. R. Lilenthal, and S. J. L i p p a r d . J. Am. Chem. Soc. 100, 7291 ( 1 9 7 8 ) .  29.  G. Kolks, C. R. Frihart, P. K. C o u g h l i n , and S. J. L i p p a r d . Inorg. Chem. 20,2933 ( 1 9 8 1 ) .  30.  G. Kolks, S. J. L i p p a r d , J. V. W a s z c z a k , and H. R. Lilienthal. J. Am. Chem. Soc. 104, 717 ( 1 9 8 2 ) .  31.  M. I n o u e , M. Kishita, and M. K u b o . Inorg. Chem. 4, 626 ( 1 9 6 5 ) .  3 2 .  H. C. F r e e m a n . Advan. Protein Chem. 27, 257 ( 1 9 6 7 ) .  33.  M. K. Ehlert, S. J. R e t t i g , A. S t o r r , R. C. T h o m p s o n , and J. T r o t t e r . Can. J. Chem. 67, 1 9 7 0 ( 1 9 8 9 ) .  153  34.  G. P. B r o w n , S. A f t e r g u t . J. Polymer Sci. A2, 1839 ( 1 9 6 4 ) .  35.  B. J. H a t h a w a y . J. Chem. Soc. Dalton Trans. 1196 ( 1 9 7 2 ) .  36.  M. K. E h l e r t , A. S t o r r , and R. C. T h o m p s o n . Can. J. Chem. 70,1121 ( 1 9 9 2 ) .  37.  F. G. H e r r i n g , D. J. P a t m o r e , and A. S t o r r . J. Chem. Soc. Dalton Trans. 711 ( 1 9 7 5 ) .  38.  M. G. F. Vaz, L. M. M. P i n h e i r o , H. O. S t u m p f , A. F. C. A l c a n t a r a , S. G o h le n , L. O u a h a b , O. C a d o r , C. M a t h o n e ir e , and O. K a h n . Chem. Eur. J. 5, 1486 ( 1 9 9 9 ) .  154  TWO-DIMENSIONAL  Chapter 5  IRON(II) AND COBALT(II)  POL YMERS EXHIBITING  LONG-RANGE  IMIDAZOLATE  FERROMAGNETIC  ORDERING  5 . 1 N IT R O D U C T O IN  It has  a r le a d y b e e n s u g g e s t e d t h a t s t e r i c c o n s t r a n it s m i p o s e d by the 1 3 ,  p o s i t i o n i n g of the n t i r o g e n sp r e v e n td o u b e l i m i d a z o l a t eb r i d g i n gb e t w e e nm e t a l c e n t e r s [1]. One m i p o r t a n tc o n s e q u e n c e of the s i n g l ea z o l a t eb r i d g i n g in m e t a lm i d ia z o a lt e s has b e e n the  g e n e r a t o i n of e x t e n d e d s t r u c t u r e s w i t h 3-D  C h a p t e r 3).  c o v a e ln t c o n n e c t i v i t i e s (see  A n o t h e r m i p o r t a n t c h a r a c t e r i s t i c p r o p e r t y , not  s e e n in c o r r e s p o n d n ig  p y r a z o a lt e s ( s e eC h a p t e r 2), is t h a t m e t a l i m i d a z o l a t e p o y lm e r s  e x h i b i t  a n t f i e r r o m a g n e t c i c o u p n i lg a b o v e a critical t e m p e r a t u r e and o ln g r a n g e f e r r o m a g n e t c i o r d e r n ig b e o lw t h a t t e m p e r a t u r e , b e h a v o ir t h a t c h a r a c t e r z ie s h te m as o lw t e m p e r a t u r e m o e lc u e lb a s e dm a g n e s t [13 ].  The w o r kd e s c r b ie d in t h i sC h a p t e ra c h e iv e s an m i p o r t a n to b j e c t i v e in the s t u d y of t r a n s i t i o n m e t a l a z o l a t e p o y lm e r s . It e x p o lr e s w h a t e f f e c t s i g n i f i c a n t l y a l t e r i n g the e x t e n d e d s t r u c t u r e s of m e t a l i m i d a z o l a t e s y s t e m s w o u d l h a v e on t h e i r m a g n e c t i p r o p e r t i e s . In the w o r kd e s c r b ie d in t h i ss e c t i o n ,m a o jr s t r u c t u r a lm o d i f i c a t i o n has b e e n a c h e iv e d by i n c o r p o r a t i n g 2 , 2 'b i p y r i d i n e as a c a p p n ig l i g a n d in the c o m p o u n d  1 5 5  p o l y 2 , 2 'b i p y r i d i n e t e t r a k i s ( i m i d a z o l a t o ) d ir o n ( I) , [Fe(imid)4(bipy)]. T h i s m a t e r i a l 2  x  h a s au n q iu e d o u b e l l a y e r2 D e x t e n d e d lattice. L i k e t h e i r o n ( I I ) 4 a z a b e n z m i d ia z o a lt e s y s t e m , [Fe(4-abimid)2)] , ( C h a p t e r 3 ) it n ic o r p o r a t e s s i n g l e i m i d a z o l a t e b r d ig e s a n d , x  m o r e o v e r , it a s lo e x h i b i t sl o n gr a n g ef e r r o m a g n e t c i o r d e ra n d  s p o n t a n e o u s  m a g n e t z ia t o in a to lw t e m p e r a t u r e s . T o s e e w h e t h e r a s i m i l a r s t r u c t u r a l m o d i f i c a t i o n is p o s s b ie l w i t h o t h e r m e t a l s , t h e 2 , 2 'd i p y r i d i n e c o m p e lx o f c o b a t l (II) i m i d a z o l a t e a n a o lg u e w a s a s lo i n v e s t i g a t e d . P o l y 2 , 2 'b i p y r i d i n e t e t r a k i s ( i m i d a z o l a t o ) d i c o b a l t ( I) , [Co2(imid)4(bipy)], w a s s y n t h e s z ie da n d w a s f o u n d t ob e s io m o r p h o u s w i t h x  [Fe2(imid)(bipy)]. A ni n v e s t i g a t i o no ft h em a g n e c t i p r o p e r t e is o ft h ec o b a t l c o m p o u n d 4  x  r e v e a e ld t h a t it t o oe x h i b i t so ln gr a n g ef e r r o m a g n e t c i o r d e ra to lw t e m p e r a t u r e s .  T h e p o y lm e r [Fe2(imid)4(bipy)] is u n q iu e in t h a t it e x h i b i t s t w o r e v e r s i b l e x  s t r u c t u r a l p h a s e t r a n s i t i o n s o v e r t h e t e m p e r a t u r e r a n g e 2 t o 3 0 0 K . T h e s e p h a s  t r a n s i t i o n s , o n eo fw h c ih e x h i b i t st h e r m a lh y s t e r e s i s ,h a v eb e e ns t u d e id b yb o t hD Ca A C s u s c e p t i b i l t y m e a s u r e m e n t s , in a d d i t i o n t o M o s s b a u e r s p e c t r o s c o p y a n d X r a y c r y s t a l o g r a p h y .  P a r to ft h em a t e r i a ld s ic u s s e d in t h i sc h a p t e r is c u r r e n t l y in p r e s s .  5 . 2 P O L Y 2 , 2 B I P Y R I D I N E T E T R A K I S ( I M I D A Z O L A T O ) D I R O N ( I ) ,  5 . 2 . 1 R E S U L T SA N DD S IC U S S O IN  1 5 6  5 . 2 . 1 . 1S Y N T H E S S I, P H Y S C IA LA N DT H E R M A LC H A R A C T E R Z IA T O IN  T h e r e a c t i o n o f f e r r o c e n e w i t h i m i d a z o l e a n d e x c e s s m o t l e n 2 , 2 'b i p y r i d i n e p r o d u c e d t h e p o y lm e r c i m a t e r i a l , [Fe2(imid)4(bipy)], in m a c r o s c o p c i c r y s t a li n e f o r m , x  s u i t a b l e f o r s i n g l e c r y s t a l X r a y d i f f r a c t i o n s t u d i e s . D e t a i l s o f t h e s y n t h e s s i o f t h i s c o m p o u n da r eg v ie n in C h a p t e r 9, s e c t o in 9 . 2 . 1 . 2 . [Fe2(imid)4(bipy)] is m o d e r a t e y l airx  s e n s i t i v e , it d o e s n o t d i s s o l v e in c o m m o n o r g a n c i s o v le n t s a n d it is n o n v o l a t i l e . T h l a t t e rc h a r a c t e r i s t i c is f u r t h e rs u p p o r t e d b y t h e t h e r m a l g r a v i m e t r i c a n a y ls s i o f [Fe2(imid)4(bipy)]. A s s h o w n in F g iu r e 5 . 1 , [Fe2(imid)4(bipy)] d o e s n o t s t a r t t o x  x  d e c o m p o s e u n t i l ~ 2 5 0 °C. T h e T G A p l o t f o l o w s a t w o s t a g e w e g ih t loss. T h e  m a o jr w e g ih t o ls s ( ~ 4 0 % ) o c c u r s b e t w e e n 2 5 0 ° C a n d 3 3 5 °C, a n d t h e s e c o  w i t haw e g ih to ls so f~ 2 5 %o ft h e initial w e i g h t ,h a p p e n sb e t w e e n3 3 5 ° C a n d5  N o f u r t h e rw e g ih tl o s s o fa n ys i g n i f i c a n c eo c c u r su pt ot h eh g ih e s tt e m p e r a t u r es t u d e i  o f8 0 0 °C. T h e c a l c u l a t e d w e g ih t o ls s f o r t h e d i s s o c i a t i o n o f2 , 2 'b i p y r i d i n e is 2 9 %  H o w e v e r , t h eT G Ap l o t d o e s n o t s h o wt h e e x p e c t e dp l a t e a u , c o r r e s p o n d n ig t o s u c h e v e n tw h c ih w o u d l l e a dt ot h ef o r m a t o in o fp o l y b i s ( i m i d a z o l a t e ) i r o n ( I ) , [Fe(imid)2]. I t x  s e e m s t h a t t h i s i r o n c o m p o u n d is v e r y t h e r m a y l u n s t a b l e . T h i s c o n t r a d c it s w i t h t h e  t h e r m a lp r o p e r t e is o ft h ea n a o lg u e , [Co(imid)2], w h c ih c a nb eo b t a n ie du n d e rt h eT G A x  a n a y ls e r c o n d t io in s f r o m t h e r m o y ls s i o f [Co3(imid)6(imidH)] ( s e e C h a p t e r4 , s e c t o in 2x  4 . 2 ) .  1 5 7  100  200  300  400  500  600  700  800  T(°C)  F g iu r e5 . 1  T G Ap l o tf o r [Fe2(imid)4(bipy)]. x  5 . 2 . 1 . 2 X R A YD F IF R A C T O INS T U D E IS  R o o m t e m p e r a t u r e ( 2 9 4K ) X r a y d i f f r a c t i o n s t u d e is r e v e a e ld a n e x t e n d e d  s t r u c t u r ei n v o l v i n gd o u b e l l a y e rs h e e t so fi r o no in sl i n k e db ys i n g l ei m i d a z o l a t eb r i d g e s .  A sm e n o t in e d in t h ei n t r o d u c t i o n ,w eh a v ei d e n t i f i e dt h r e ed i f f e r e n ts t r u c t u r a lp h a s e s in t h i s m a t e r i a l a n dh a v el a b e l e dt h i s h g ih t e m p e r a t u r ep h a s et h e  a p h a s e .  C r y s t a l o g r a p h i c d a t a f o r [Fe2(imid)4(bipy)] a r e s h o w n in A p p e n d x i I, T a b e l 1 5 . T h e x  r e p e a tu n i to ft h ea p h a s eo f [Fe2(imid)4(bipy)] is s h o w n in F g iu r e5 . 2 . x  1 5 8  (71  F g iu r e5 . 2  V e iw o ft h e r e p e a t u n i t o f [Fe2(imid)4(bipy)] ( a p h a s e , 2 9 4 K ) x  a n da o tm n u m b e r n ig s c h e m e( 3 3 %p r o b a b i l t yt h e r m a le li p s o i d s ) .  T h e c a p p n ig o fi r o n c e n t r e sb y2 , 2 'b i p y r i d i n ea f f e c t st h ed m i e n s o in a t i ly o ft h i s  s y s t e m , r e s u l t i n g in a 2 D p o y lm e r , a s s e e n in F g iu r e s 5 . 3 a n d 5 . 4 . F o u r - a n d  c o o r d n ia t e d F e ( I I ) o in s a l t e r n a t e in t h e lattice, t h e l a t t e ro in sb e n ig c o o r d n ia t e db yb p i 1 5 9  g i la n d s in a d d i t i o n to b r i d g i n g i m i d a z o l a t e s . E a c h t e t r a h e d r a l y c o o r d n ia t e d i r o n is b o n d e d via the l i g a n d to f o u r o c t a h e d r a l i r o n s w i t h e a c h of t h e s e b o n d e d to f o u r t e t r a h e d r a lo n e s . The c a p p n ig b i p yg i la n d sp r e v e n tb r i d g i n g of m e t a lc e n t r e s in the t h i r d d m i e n s o in and o c c u p y s p a c eb e t w e e n the s h e e t s , i s o l a t i n g the s h e e t s f r o m e a c h o t h e r . By l o o k i n g at the i r o n ion c o n n e c t i v i t y d a ig r a m ( F i g u r e 5.4),  it can be s e e n t h a t the  c o n n e c t i v i t i e sb e t w e e n the two l a y e r s of a s h e e tf o r mf o u r m e m b e r e df u s e drings,w h i l e , the c o n n e c t i v i t i e sw i t h i n the l a y e r s , top and b o t o m ,f o r ms x im e m b e r e df u s e d rings.  W h e n DC  m a g n e c t i s u s c e p t i b i l t y m e a s u r e m e n s t w e r ep e r f o r m e d  [Fe2(imid)4(bipy)], a m a o jr d i s c o n t i n u i t y was x  m o m e n t of t h i s c o m p o u n d at a r o u n d 135 a p p a r e n t at ~ 150  K.  The  l a t t e r was  o n  d e t e c t e d (vide infra) in the m a g n e c t i K. A n o t h e r d i s c o n t i n u i t y was  a s lo b a r e l y  f u r t h e r c o n f r im e d by h g ih e r d e n s t i y DC  s u s c e p t i b i l t ym e a s u r e m e n s t (vide infra). T h e s ef i n d i n g sp r o m p t e d the d e t e r m n ia t o i n of the  s i n g l e c r y s t a lX r a ys t r u c t u r e o f [Fe2(imid)(bipy)] a to lw 4  x  t e m p e r a t u r e s t o  d e t e r m n ie w h e t h e r c r y s t a l o g r a p h i c p h a s e t r a n s i t i o n s w e r e i n v o l v e d . S u b s e q u e n t y l, s i n g l e c r y s t a l X r a y d i f f r a c t i o n s t u d e is of [Fe2(imid)4(bipy)] at ~ 143 K and ~ 113 K x  r e v e a e ld two new s t r u c t u r a lp h a s e s .  T h e s e s t r u c t u r a l s t u d e is w e r ec a r r i e d o u t o nd i f f e r e n t c r y s t a l s  o f  [Fe2(imid)(bipy)]; t h e r e f o r e , in o r d e r to e l i m i n a t e the p o s s i b i l i t y t h a t t h e s e t h r e e 4  x  d i f f e r e n tp o y lm o r p h sw e r ei s o l a t e df r o m the r o o mt e m p e r a t u r es y n t h e s i s , the u n i t cell of  1 6 0  F g iu r e5 3 .  O R T E P d a ig r a m s o f [Fe2(imid)4(bipy)] ( a p h a s e ) x  l o o k i n gd o w nt h eca x i s . I n t h eb o t o m v i e w ,b i p y r i d i n eg i la n d sh a v eb e e nr e m o v e d r e v e a lt h ed o u b l e l a y e rs h e e te x t e n d e d f r a m e w o r k . ( 5 0% p r o b a b i l t y t h e r m a l e li p s o i d s ) . 161  F g iu r e5 . 4  I r o n i o n c o n n e c t i v i t y d a ig r a m o fa s e c t o in o ft w o d o u b e la ly e r  s h e e t s f o r t h e a p h a s e o f [Fe2(imid)4(bipy)]. O c t a h e d r a l i r o n ( r e d ) , t e t r a h e d r a l i r o n x  ( g r e e n ) .V e iw a p p r o x m i a t e y l l o o k i n gd o w nt h eca x i s .  t h e c r y s t a l u s e d f o r t h e o lw e s t t e m p e r a t u r e ( 1 1 3 K ) s t u d y w a s d e t e r m n ie d initially  1 7 3 K . T h eu n i t cell a t 1 7 3 Kw a s f o u n dt ob et h e s a m e a s t h a to b t a n ie d a t  1 0 . 5 0 7 ( 4 ) , b= 1 3 . 7 3 0 ( 4 ) , c=9 . 1 8 8 ( 3 ) A, a = 1 0 6 . 5 1 ( 3 ) , f j = 1 0 8 . 3 2 ( 3 ) , y = 8 0 . 8 4 ( 3 )  d e g , V= 1 2 0 2 . 9 ( 2 ) , A]. W h e nt h es a m ec r y s t a lw a sc o o e ld d o w nf r o m 1 7 3t o 1 1 3 J  u n i t cell p a r a m e t e r s c h a n g e d [a = 1 0 . 4 1 4 ( 5 ) , b = 1 3 . 5 0 8 ( 5 ) , c =2 6 . 0 6 0 ( 1 ) A, a = 1 0 4 . 5 3 ( 2 ) , P= 9 3 . 8 9 2 ( 2 ) , y= 1 0 0 5 .1 2 ( 2 )d e g , V= 3 6 4 6 . 0 ( 2 ) , A ]. T h ep h a s ew i t ht h e s e 3  1 6 2  cell p a r a m e t e r s is l a b e l e dt h ey p h a s e . A s i m i l a rp r o c e d u r ew a su t i l i z e d in d e t e r m n in ig t h e s t r u c t u r e o f [Fe2(imid)4(bipy)] a t ~ 1 4 3 K . A c r y s t a l o f [Fe2(imid)4(bipy)] w a s x  x  e x a m n ie da b o v e 1 7 0Ka n df o u n dt oh a v et h es a m e cell p a r a m e t e r sa st h o s ed e t e r m  e a r l i e r a t 2 9 4 K . T h e s a m e c r y s t a l w a st h e nc o o e ld t o ~ 1 4 3 Ka n dt h e cell p a r o  w e r ed e t e r m n ie da n df o u n dt oh a v ec h a n g e d [a = 1 7 . 1 3 3 8 , b=1 8 . 5 4 2 6 , c= 2 3 6 .1 9 9 a= 8 0 . 4 2 4 , P= 7 5 . 3 6 4 , y= 8 0 8 .2 6 d e g , V=7 1 0 5 . 1 ( 2 ) A]. T h ep h a s ew i t ht h e s e 3  p a r a m e t e r s is l a b e l e dt h ep p h a s e .  T h e Pi s p a c e g r o u p is r e t a i n e d in t h e t h r e e s t r u c t u r e s d e t e r m n ie d a t 2 9 4 K  p h a s e ) , 1 4 3 K ( p p h a s e ) a n d 1 1 3 K (y-phase); t h e r e f o r e , t h e r e a r e n o c r y s t a l o g r a p h t r a n s i t i o n si n v o l v e d ,b u ts t r u c t u r a lp h a s et r a n s i t i o n sa r ee v d ie n t in [Fe2(imid)4(bipy)]. x  T h a tt h ev o u lm eo ft h eu n i t cell in t h ey p h a s e is t h r e et m i e sl a r g e rt h a nt h e  in t h ea p h a s e is d u et ot h ee x s it e n c eo fs i xu n q iu eF e ( I I )c h r o m o p h o r e s in t h es t r u c  o ft h ey p h a s e , a s s h o w nb y its a s y m m e t r c i u n i td e p c it e d in F g iu r e 5 . 5 . T h e FeN6 c o  i n v o l v i n g t h e Fe(l), F e ( 3 ) a n d F e ( 5 ) s i t e s in t h e y p h a s e h a v e b e e n s l i g h t l y m o d f i e i  c o m p a r e dt o t h eo c t a h e d r a l Fe(l) s i t e in t h e a p h a s e ( F i g u r e 5 . 2 ) . T h eF e ( l ) N ( 9 ) a n  F e ( l ) N ( 1 0 ) b o n d e ln g t h s a r e 2 . 2 1 7 ( 2 ) a n d 2 . 3 1 4 ( 2 ) A, r e s p e c t i v e l y , c o m p a r e d t o  2 . 2 6 2 ( 2 ) a n d2 . 2 9 9 ( 2 ) A, r e s p e c t i v e l y , a t2 9 4K . S e e lc t e db o n de ln g t h sf o rt h e a- a n d  p h a s e s , a r e s h o w n in A p p e n d x i I , T a b e l 1 6 . T h eb o n d a n g e ls a r e a s lo d i f f e r e n t a  t w o t e m p e r a t u r e s ; f o r i n s t a n c e , t h e N ( 1 0 ) F e ( l ) N ( l ) a n g e l o f 81.33(9)° a t 1 1 3 K  1 6 3  c o r r e s p o n d st ot h e N ( 2 ) F e ( l ) N ( 3 )a n g e l o f8 8 . 9 9 °a t2 9 4K .A sac o n s e q u e n c eo f  r e d u c t o i n in t h i s a n g e l t h e a d a jc e n t N ( 1 0 ) F e ( l ) N ( 7 ) a n g e l o f 91.00(9)° a t 1 1 3 K d i f f e r s s i g n i f i c a n t l y f r o m t h e c o r r e s p o n d n ig N ( 2 ) F e ( l ) N ( 8 ) a n g e l o f 83.61(9)° a t 2 9 4K .  F g iu r e5 . 5  V e iw o ft h e a s y m m e t r c i u n i to f [Fe2(imid)4(bipy)] ( y p h a s e , 1 1 3 x  K )a n da t o mn u m b e r n ig s c h e m e( 3 3 %p r o b a b i l t yt h e r m a l elipsoids).  1 6 4  S i g n i f i c a n td i f f e r e n c e sb e t w e e nt h e a- a n d y- p h a s e s in b o n de ln g t h sa n da n g e ls  i n v o l v i n g t h e FeN4 c o r e a r e a s lo s e e n . F e ( 2 ) N ( 6 ) is 2 . 0 1 9 ( 2 ) A a t 1 1 3 K a g a n i  2 . 0 3 6 ( 2 )Aa t2 9 4K . F u r t h e r m o r e ,t h eN ( 2 ) F e ( 2 ) N ( 4 )b o n da n g e l is 107.4° a t 1 1 3  c o m p a r e d t o t h e c o r r e s p o n d n ig N ( 7 ) F e ( 2 ) N ( 9 ) a n g e l o f 117.6° a t 2 9 4 K . S e e lc t e d  b o n d a n g e ls f o r t h e a- a n d y p h a s e s o f [Fe2(imid)4(bipy)], a r e s h o w n in A p p e n d x i I , x  T a b e l 1 7 .  T h e s i m i lt u d e o ft h e i r o ni o n c o n n e c t i v i t yd a ig r a m s o ft h e a- a n d y p h a s e s o f  [Fe2(imid)4(bipy)] ( F i g u r e s 5 . 4 a n d 5 . 6 ) s h o wt h a tt h es t r u c t u r a l c h a n g e sa r er e l a t i v e l y x  s u b t l e . N o n e t h e e ls s , t h e s e s t r u c t u r a l p h a s e t r a n s i t i o n s w e r e p r o p e r y l i d e n t i f i e d b yD C a n d A C m a g n e c t i s u s c e p t i b i lt y m e a s u r e m e n s t a s w e l a s M o s s b a u e r s p e c t r o s c o p y a s  will b e s h o w n in s u b s e q u e n t s e c t i o n s . A s p r e v i o u s l ym e n t o in e d , t h e ca x i s o ft h eu  cell o ft h ey p h a s e is a m l o s tt h r e et m i e so ln g e rt h a nt h a to ft h e a-phase. T h i s s i t u a  c a nb e u n d e r s t o o db e t t e rb y e x a m n in ig t h e o c t a h e d r a l i r o n c e n t e r s in t h e c o n n e c t i v  d a ig r a m s o ft h e s e p h a s e s ( F i g u r e s 5 . 4 a n d 5 . 6 , r e s p e c t i v e l y ) . H e n c e , f o r t h e a-phase  l o o k i n ga p p r o x m i a t e y l a o ln gt h e c axis, o c t a h e d r a li r o nc h r o m o p h o r e se q u v ia e ln tt ot h a t o n t h e first r o w , c a n b e f o u n d o n t h e s e c o n d a n d t h i r d r o w s s h o w n ( F i g u r e c o n t r a s t , in t h e y p h a s et h e r e a r e t h r e e d i f f e r e n t ,a n d u n q iu e , o c t a h e d r a l i r o n  c h r o m o p h o r e s in t h e first, s e c o n d a n d t h i r d r o w s . T h e f o u r t h r o w ( n o t s h o w n )  e q u v ia e ln t t o t h e first. ( F i g u r e 5 . 6 ) . A s a c o n s e q u e n c e , t h e u n i t cell n ic r e a s e s b a p p r o x m i a t e y l t h r e et m i e s in v o u lm ec o m p a r e dt ot h a to ft h ea p h a s e (vide supra).  1 6 5  F g iu r e5 . 6  I r o n i o n c o n n e c t i v i t y d a ig r a m o fa s e c t o in o ft w o d o u b e la ly e r  s h e e t s f o r t h e y p h a s e o f [Fe2(imid)4(bipy)]. O c t a h e d r a l i r o n ( r e d o r semi-filed), x  t e t r a h e d r a li r o n( g r e e no r non-filled). V e iw l o o k i n ga p p r o x m i a t e y l d o w nt h e c axis.  I n t e r e s t i n g l y , t h e P p h a s e h a s a u n i t cell v o u lm e s i x t m i e s l a r g e r t h a n t h e  p h a s e , a n dt w o t m i e s l a r g e rt h a nt h a to ft h ey p h a s ed s ic u s s e da b o v e . T h i s is a t t r i b u  t o t h e e x s it e n c e o f s i x u n q iu e o c t a h e d r a l i r o n ( I I ) c h r o m o p h o r e s a n d s i x u n q iu e t e t r a h e d r a l i r o n ( I I ) c h r o m o p h o r e s in t h e P-phase, a s s h o w n in F g iu r e 5 . 7 . C h a n g e s  b o n dd s it a n c e sa n da n g e ls o c c u r r n i g in t h e Pp h a s e , in c o m p a r s io nt ot h eo t h e rs t r u c t u  p h a s e s , a r e s i m i l a r t o t h o s e d s ic u s s e d f o r t h e a a n d y p h a s e s a b o v e . C r y s t a l o g r a p h i c  d a t a a n d s e e lc t e d b o n d e ln g t h s a n d a n g e ls f o r t h e P-phase, a r el i s t e d in A p p e n d x i  1 6 6  F i g u r e5 . 7  V e iw o ft h ea s y m m e t r c i u n i to f [Fe2(imid)4(bipy)] ( P p h a s e , 1 4 3 x  K )a n da t o mn u m b e r n ig s c h e m e .  T a b e ls 1 8 a n d1 9 ,r e s p e c t i v e l y . I nt h ec o n n e c t i v i t yd a ig r a mf o rt h ey p h a s e( F i g u r e5  g o n i gfroml e f t t o r i g h t a o ln g a " r o w " ( a l o n g t h e a a x i s ) t h e o c t a h e d r a l c e n t e r s a  i d e n t i c a la sa r et h et e t r a h e d r a l c e n t e r s . I nc o n t r a s t , in t h e( 3 p h a s et h e r ea r et w od i f f e  a n du n q iu eo c t a h e d r a lc h r o m o p h o r e sw h c ih a l t e r n a t ea o ln gt h eaa x i s .T h es a m ea p p e i ls  t ot h et e t r a h e d r a lc h r o m o p h o r e s . T h es i t u a t i o nr e g a r d n ig t h eca x i s is t h es a m ea sf o r  y p h a s e . A s a r e s u l t , t h e u n i t cell v o u lm e o ft h e ( 3 p h a s en ic r e a s e s a p p r o x m i a t e y l t w t m i e sc o m p a r e dt ot h a to ft h ey p h a s e {vide supra).  1 6 7  T h ec h a n g e in t h e a s y m m e t r c i u n i t s d e t e r m n ie d f o rt h e aa n d yp h a s e s ( F g iu r e  5 .2a n d5 . 5 ,r e s p e c t i v e l y ) is r e v e a e ld o na t e m p t n ig t oo v e r a lp t h et w os t r u c t u r e sa r o  a no c t a h e d r a li r o nc e n t r e .T h u s ,b ym a t c h n ig t h eb i p yg i la n d sa n do n eo ft h em i d ia z o  b r i d g i n gg i la n d s f r o m t h e a- a n dy p h a s e s , a s s h o w n in F g iu r e5 . 8 , a n o t h e rm i d ia z o a l  l i g a n d ( v e r t i c a l p o s i t i o n in F i g u r e 5 . 8 ) in t h e y p h a s e is o r i e n t e d d i f f e r e n t l y f r o m t h c o r r e s p o n d n ig o n e in t h ea p h a s e .  F g iu r e5 . 8  C o m p a r s io n o f c o o r d n ia t o in s p h e r e g e o m e t r e is b y o v e r a lp p n ig  o c t a h e d r a l i r o n s ( r e d c i r c l e ) in t h e a- ( b l a c k b o n d s ) a n d y - ( g r e e n b o n d s ) p h a s e s [Fe (imid) bipy] . 2  4  x  I ng e n e r a l ,a c c o r d n ig y l t oX r a yd i f f r a c t i o n ,r o t a t i o no fi m i d a z o l a t em o e it e is a b o u tt h eb r d ig ea x i ss e e m st ob et h em a o jr s t r u c t u r a ld i f f e r e n c eb e t w e e nt h et h r e e p h a s e s in [Fe2(imid)4(bipy)]. x  1 6 8  5.2.2.3  M A G N E T C I P R O P E R T E IS  V a r i a b l e t e m p e r a t u r e DC m a g n e c t i s u s c e p t i b i l i t i e s of a p o w d e r e d s a m p e l of [ F e ( i m i d ) ( b i p y ) ]w e r em e a s u r e d at f i e l d s of 500 and 10 000 G f r o m 2 to 300 K. The 2  Peff  4  x  v e r s u s T p l o t  (10 0 0 0  G,  2  to  300  K, F i g u r e  5.9)  s h o w sac l e a rd i s c o n t i n u i t yn e a r  135 K. A n o t h e ri r r e g u l a r i t y in the s a m ep l o t is b a r e l ya p p a r e n t at s l i g h t l ya b o v e 150 K. T h e s e two a n o m a e i ls are a t t r i b u t e d to s t r u c t u r a lp h a s et r a n s i t i o n s , as c o n f r im e d by o lw t e m p e r a t u r eX r a yd i f f r a c t i o ns t u d e is (vide supra). The s t r u c t u r a lp h a s et r a n s i t i o n sh a v e b e e n s t u d e id in d e t a i l by AC and DC s u s c e p t i b i l t ym e a s u r e m e n t s . T h e s e are p r e s e n t e d f o l o w i n g the d s ic u s s o i n of the m a g n e c t i p h a s e t r a n s i t i o n f o u n d in the y p h a s e of t h i s c o m p o u n d .  F i g u r e 5.10 p r e s e n t s the % v e r s u s T and y-[Fe2(imid)4(bipy)] b e o lw x  100  K at  500  u^r v e r s u s T d a t a o b t a n ie d for  G. The v a u l e of  peff  d e c r e a s e s s m o o t h y l w i t h  t e m p e r a t u r e f r o m 5.3 U\B at 300 K to a o lw of 3.96 (IB j u s t a b o v e 11 K. B e o lw t h i s t e m p e r a t u r e , j i ^ f f n ic r e a s e s a b r u p t y l to a m a x m iu m v a u l e of 12.6 (XB at 3 K b e f o r e d e c r e a s n ig a g a n i w i t h t e m p e r a t u r e to 11.2 \i& at 2 K. The o n s e t of the m a g n e c t i t r a n s i t i o n at a r o u n d  11  K is a s lo o b s e r v e d in the % v e r s u s Tp l o t ( F i g u r e  5.10).  The  m a g n e c t i s u s c e p t i b i l i t y , w h c ih n ic r e a s e s s m o o t h y l w i t hd e c r e a s n ig t e m p e r a t u r eb e o lw  169  50  100  150  200  250  300  T(K)  F g iu r e5 . 9  %a n d |i«ff v e r s u sTp l o t sa t 1 00 0 0Gf o r [Fe2(imid)2(bipy)]. x  3 0 0 K , r i s e s a b r u p t y l a s t h e t e m p e r a t u r e d e c r e a s e s b e o lw 1 1 K . T h e m a g n e t z ia t o i  v e r s u s field p l o t s a t t h r e e t e m p e r a t u r e s s h o w n in F g iu r e 5 . 1 1 , r e f l e c t t h i s u n u s u a m a g n e c t i b e h a v o iu r . T h e p l o t s a r e l i n e a r a t 3 0 a n d 2 0 K a n d e x t r a p o a lt e t o  m a g n e t z ia t o in a tz e r o a p p l i e d field w h i l ed i s t i n c tc u r v a t u r e is s e e na t 1 0a n d4 . 8 K  4 . 8Kt h ep l o te x t r a p o a lt e st og i v ean e tm a g n e t z ia t o in a tz e r oa p p l i e d field. C y c l i n g  a p p l i e d field b e t w e e n + 5 50 0 0a n d 5 50 0 0G a t4 . 8Kg e n e r a t e sah y s t e r e s s i l o o  1 7 0  0  1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0  1 0 0  T(K)  F g iu r e5 1 .0 x  M « fv e r s u sTp l o t sa t5 0 0Gf o ry - [Fe2(imid)2(bipy)]. x  c e n t r a l p o r t i o n o fw h c ih is s h o w n in F g iu r e 5 . 1 2 . F r o m t h i s is o b t a n ie d a r e m m a g n e t z ia t o in o f2 0 0c m G m o r ' a n dac o e r c v ie field o f1 5 G. 3  F u r t h e r e v d ie n c e f o r s t r u c t u r a l p h a s e t r a n s i t i o n s in [Fe2(imid)4(bipy)] c a n b e x  s e e n in t h e t r a d i t i o n a l C u r e iW e s is a n a y ls s i o f t h e m a g n e c t i d a t a . T h i s a n a y ls s i c a n  p r o v d ie e v d ie n c ef o rt h ep r m i a r ye x c h a n g ep r o c e s sp r e s e n t in t h es y s t e m . A p l o t o f%  1 7 1  1 2 0 0 0  c £  1 0 5 0 0 9 0 0 0  £  7 5 0 0  s o  6 0 0 0  a  4 5 0 0  c  3 0 0 0  A A  N  OX)  1 5 0 0t  |  0  o  o o  A  D  6 ° 1 0 0 0 0 2 0 0 0 0 3 0 0 0 04 0 0 0 0  5 0 0 0 06 0 0 0 0  Applied Field ( G )  F g iu r e5 . 1 1 M a g n e t z ia t o in v e r s u sa p p l i e d field p l o t sa td i f f e r e n tt e m p e r a t u r e s f o r Y-[Fe (imid) (bipy)] . 2  2  x  v e r s u sT( 1 00 0 0 G; 2 - 3 0 0K )f o r [Fe (imid) (bipy)] ( F i g u r e5 . 1 3 )r e v e a s l t w ol i n e 2  4  x  r e g i o n s , c o r r e s p o n d n ig t ot w oo ft h et h r e es t r u c t u r a lp h a s e sp r e s e n t . D e t e c t o i n of t h e| 3  p h a s e in t h i sp l o t is n o tp o s s i b l e ,c o n s s it e n tw i t ht h ef a c tt h a t its m a g n e c t i p r o p e r t e is b a r e l yd i s t i n g u i s h a b l e f r o m t h o s e o ft h ea p h a s e . F i t t i n gt h ed a t a in F g iu r e 5 1 .3 t o  C u r e iW e s is e q u a t o i n yields: (i) e m p o ly n ig d a t a in t h et e m p e r a t u r e r a n g e 3 0 0- 1 7 0K  C( C u r i ec o n s t a n t )=3 . 6 0 cmGmor', 6 ( W e s is c o n s t a n t )=6 . 7Ka n d (ii) f o rt h er a n 3  1 7 2  -200  -150  -100  -50  0  100  50  150  200  Applied Field (G)  F g iu r e 51.2  M a g n e t c i h y s t e r e s s i p l o t at 4.8  c n ^ G m o l " , 0 = -9.9  120  - 30 K, C = 30.4  are  c o n s s it e n t w i t h a n t f i e r r o m a g n e t c i c o u p n i l g as  o p e r a t n ig h e r e . H o w e v e r , the f a c t t h a t the  1  K. The  K for y- [Fe2(imid)4(bipy)]. x  o b s e r v e dn e g a t v ie W e s is c o n s t a n t s the  p r m i a r y e x c h a n g e p r o c e s s  i n t e r p r e t a t i o n of t h e s e p a r a m e t e r s is c o m p c i la t e d by  the  t h r e e p h a s e s of [Fe2(imid)4(bipy)] c o n t a n i o c t a h e d r a l c e n t r e s , w h c ih for x  h g ih s p n i d m e a n s first o r d e r o r b i t a l c o n t r i b u t i o n and 6  s p i n o r b i t c o u p l i n g . As a r e s u l t  t h e s e c e n t r e s w o u d l s h o w d e c r e a s n ig m o m e n s t w i t ht e m p e r a t u r e and  173  n e g a t v ie W e s is  0  50  100  200  150  250  300  T(K)  F g iu r e5 1 .3 P l o to f% v e r s u st e m p e r a t u r ea t 1 00 0 0Gf o r [Fe2(imid)4(bipy)]. x  c o n s t a n t s e v e n in t h e a b s e n c e o fa n t f i e r r o m a g n e t c i e x c h a n g e . I t s e e m s r e a s o n a b e l t o  a s s u m e t h a t t h e 9 v a u le s h e r e a r e a c o m p o s t e i o f s i n g l e i o n e f f e c t s a n d e x c h a n  i n t e r a c t i o n s b u t t o d e t e r m n ie t h e r e l a t i v e c o n t r b iu t o in s w o u d l b e difficult. O v e r a l t h e r e s u l t s a r e c o n s s it e n t w i t h [Fe2(imid)4(bipy)] e x h i b i t i n g a n t f i e r r o m a g n e t c i e x c h a n g e x  1 7 4  i n t e r a c t i o n s at h g ih t e m p e r a t u r e s and, c o u p e ld w i t h the o b s e r v e d net m o m e n t g r o u n d s t a t e ,t h i sc l a s s i f i e s it a s aw e a kf e r r o m a g n e t . The m a g n e c t i b e h a v o ir e x h i b i t e db y y-[Fe2(imid)4(bipy)] is s i m i l a r to t h a t r e p o r t e d for [Fe3(imid)6(imidH)2] [1], [ F e ( 2 x  x  meimid)2-0.13Cp2Fe] [2], a n d[ F e ( 4 a b i m i d ) ] ( C h a p t e r 3) a n d it is p o s s b ie l t h a t y2 x  x  [Fe2(imid)4(bipy)] like t h e o t h e r s y s t e m s listed, a s lo e x h i b i t s  c a n t e d s p n i  x  a n t f i e r r o m a g n e t s im . T h i sc o n c u ls o i n is s u p p o r t e d by the f a c tt h a t the h g ih e s t m a g n e t z ia t o in r e a c h e d , 1 0 940 c m G m o r ' (at 4.8 K a n d5 5 000 G), is s i g n i f i c a n t l y 3  s m a e lr t h a n the t h e o r e t i c a ls a t u r a t i o nv a u le o f2 2 300 c m ^mol" [5]. 1  As d e s c r b ie d in C h a p t e r 3, the s p i n c a n t n ig a n g l e , y, can b ee s t m i a t e d by e x t r a p o l a t i n g the p l o t of M v e r s u sH t o H = 0 at a t e m p e r a t u r eb e o lw T. D o n ig t h i s for c  y-[Fe(imid)4(bipy)] g v ie s a s a t u r a t i o n m o m e n t (M (0)) of 6 9 8 0 c m G m o f , a n d f r o m 3  2  x  1  s  this, a ne s t m i a t o i n of the s p i nc a n t n ig a n g l e , y, o f ~ 17°.  It s h o u d l be n o t e d t h a t u n l i k e [ F e ( 2 m e i m i d ) 2 0 . 1 3 C p 2 F e ][ 2 ]a n d [ F e ( 4 x  abimid)2] ( C h a p t e r 3), y-[Fe2(imid)4(bipy)] h a s as t r u c t u r e in w h c ih the n e a r e s t x  x  n e g ih b o r i n t e r a c t i o n s are b e t w e e n i r o n o in s t h a t d i f f e r s i g n i f i c a n t l y in t h e i r l i g a n d c h r o m o p h o r e s . B e c a u s e of the d i f f e r e n c e in g v a l u e s , the s i z e of the i n t e r a c t i n g m a g n e c t i d i p o l e s will d i f f e r and, h e n c e , e v e n p e r f e c t a n t i p a r a le l a g i ln m e n t of s p n is b e t w e e n n e g ih b o u r s w o u d l l e a d to a r e s i d u a l m o m e n t on the s h e e t s . T h i s f o r m of f e r r m i a g n e t s im , w h c ih w a ss u g g e s t e dt o p o s s b iy l o c c u r in the 1-D p o y lm e r , polybis(lm e t h y l 2 t h i o i m i d a z o l a t e ) i r o n ( I ) [ 7 ] (See C h a p t e r 7), c o u d l be the c a u s e of the  1 7 5  a n o m a o lu sm a g n e c t i b e h a v o iu ro b s e r v e df o r y-[Fe2(imid)4(bipy)] or, a tl e a s t ,c o n t r b iu t e x  s i g n i f i c a n t l yt o it.  I n a n e f f o r tt od e t e r m n ie t h e o n s e to ft h e m a g n e c t i t r a n s i t i o n in y [Fe2(imid)4(bipy)] t h e t e m p e r a t u r e d e p e n d e n c e o f t h e f i e l d c o o l e d m a g n e t z ia t o in x  ( F C M ) , z e r o f i e l d c o o l e d m a g n e t z ia t o in ( Z F C M ) a n d r e m n a n t m a g n e t z ia t o in ( R E M )  w e r ee x a m n ie d( F i g u r e5 . 1 4 ) . T h eF C Mc u r v e ,m e a s u r e db yc o o l i n gt h es a m p e l u n d e  D C field o f5 0 G, s h o w sac l e a rn ic r e a s e in M in t h e6- 8 Kr e g i o n . O nf u r t h e r  t h i sc u r v ee x h i b i t sam a x m iu m in t h e2- 3 Kr e g i o n .T h ed e r i v a t i v ec u r v e ,d ( F C M  h a s a n e x r t e m u m a t 3 . 5 K , w h c ih c a nb ec o n s d ie r e d a s t h e critical t e m p e r a t u r e , T  T h eZ F C M c u r v e ,m e a s u r e db yc o o l i n gt h es a m p e l in z e r o field, t h e nw a r m n ig in a  field o f5 0 G, e x h i b i t s a m a x m iu m a t ~ 3 K a n d is s i g n i f i c a n t l yo lw e r t h a n t h e  c u r v ea tt h i st e m p e r a t u r ea n da to lw e rt e m p e r a t u r e s .T h ed e r i v a t i v ec u r v e ,d ( Z F C M ) / d T ,  s h o w sa ne x r t e m u ma t4 . 0K .T h u s ,T cf o rt h i ss y s t e m ,a sm e a s u r e db yt h eF C M Z  e x p e r m i e n t ,c a nb ec o n s d ie r e da sT =3 7 .5 K ,w h c ih is t h ea v e r a g et e m p e r a t u r eo f c  o b t a n ie df r o mt h eF C Ma n dZ F C Mp l o t s . Finally, R E M ,o b t a n ie db yc o o l i n gt h es a m  in a 5 0 GD C field, t h e nc o le c t i n gt h ed a t aw h i l ew a r m n ig it in z e r o field v a n s ih s l i g h t l yh g ih e rt e m p e r a t u r e ( a t 5 K , a s c o n f r im e db yl o o k i n g a tt h ed a t ao b t a n ie d )  T, w h c ih a g r e e sb e t t e rw i t ht h eT d e t e r m n ie db yA C s u s c e p t i b i l t ym e a s u r e m e n s t o fy c  c  [Fe2(imid)4(bipy)], s h o w nb e o lw . x  1 7 6  8 0 0 7 0 0 •  6 0 0 -  •  *  ~_ 5 0 0 H o g rj 4 0 0 1 £ S 3 0 0 2 0 0 -  F C M Z F C M R E M  dZ F C M/d T  1 0 0 0 2  1 0  1 2  T(K)  F g iu r e 5.14  P l o t so fZ F C M , F C Ma n dR E Mf o rY [ F e ( i m i d ) ( b i p y ) ]a taD C 2  4  x  field o f 50 G.  F u r t h e r i n f o r m a t i o n o n t h e m a g n e c t i p h a s e t r a n s i t i o n o f Y-[Fe2(imid)(bipy)] 4  x  c a n b e d e d u c e d f r o m A C m a g n e c t i s u s c e p t i b i l t ym e a s u r e m e n t s . T h e i n p h a s e , x\ a n d o u t o f p h a s e ,  A C m o a lr m a g n e c t i s u s c e p t i b i l i t i e s , w i t haz e r o s t a t i cfielda n d a 125  H z o s c i la t i n gfieldo f 1 G, f o r y-[Fe2(imid)4(bipy)] a r ed s ip a ly e d in F g iu r e 5.15. x" is x  n o n z e r ob e o lw 6.1 K , w h c ih is in a g r e e m e n tw i t ht h eo n s e to fam a g n e c t i t r a n s i t i o n t h a tt e m p e r a t u r e . %'X" P^ e a  a t  5-8 a n d 5.7 K , r e s p e c t i v e l y , p r o v n ig t h em a t e r i a ly -  [Fe2(imid)4(bipy)] is a g e n u n ie m a g n e ta tt h e s et e m p e r a t u r e s . x  177  20  *  X'  15  s 5H  : : : : :  OH —I  5.5  6.0  '  1  1  6.5  1  7.0  : t t 1  t i n 1  7.5  1  8.0  T(K)  F g iu r e5 1 .5 T e m p e r a t u r e d e p e n d e n c e s o ft h e i n p h a s e , %\ a n d o u t o f p h a s e , A Cm a g n e c t i s u s c e p t i b i lt i e sf o r y-[Fe2(imid)4(bipy)] a tf = 1 2 5H za n d H= 1 G. x  I n a n e f f o r t t o b e t t e r c h a r a c t e r i z e t h e s t r u c t u r a l p h a s e t r a n s i t i o n s t h a t o c c u r in [Fe2(imid)4(bipy)] d e t a i l e d A C a n d D C m a g n e c t i s u s c e p t i b i lt i e s m e a s u r e m e n s t w e r e x  m a d eo v e rt h ea p p r o p r a it et e m p e r a t u r er a n g e s . I t is t h e first t m i es u c hs t u d e is h a v eb  m a d e o n am o e lc u e lb a s e d m a g n e t . T h e yj ( D C ) v e r s u s T plot, s h o w n in F g iu r e 5  r e v e a s l t w oi n f l e c t i o n s in t h e 1 3 0- 1 6 0K r e g o in f o l o w i n gac o o l i n gm o d e ,t h eh g i  1 7 8  3.53.4-  3.3•  "o 3.2-  £  •  3.1•  H  3.02.92.82.7-  100  120  T(K)  F g iu r e5 1 .6 yj v e r s u s T f o r [Fe (imid) (bipy)] . //DC = 1 0 0 0 0 G. C o o n i lg 2  4  x  m o d e .  t e m p e r a t u r e a n o m a y l b e n ig l e s s e v d ie n t t h a n t h eo lw e r o n e . I n o r d e r t o d e t e r m n ie t h t r a n s i t i o n t e m p e r a t u r e s a c c u r a t e l y , t h e t e m p e r a t u r e d e p e n d e n c e o ft h e d e r i v a t i v e d(xT)/dT, in t h ec o o l i n gm o d e ,w a sc a l c u l a t e da n dp l o t t e da ss h o w n in F g iu r e5 . 1 7 . g a v et r a n s i t i o nt e m p e r a t u r e so f1 5 0Kf o rt h e a —> p t r a n s i t i o na n d 1 3 5 Kf o rt h ep t r a n s i t i o n .  1 7 9  F g iu r e5 1 .7 T e m p e r a t u r ed e p e n d e n c eo ft h ed e r i v a t i v e sd ( ^ T ) / d T ( D C ) in t h e c o o l i n g m o d e a n d d e t e r m n ia t o in o ft h e t r a n s i t i o n t e m p e r a t u r e s f o r [Fe2(imid)4(bipy)]. x  HDC=  1 0 0 0 0 G .  F u r t h e r d e t a i l s o n t h e t w o p h a s e t r a n s i t i o n s o c c u r r n i g in [Fe2(imid)4(bipy)], x  w e r e o b t a n ie dfromD C m a g n e c t i s u s c e p t i b i l t y m e a s u r e m e n s t in b o t h , c o o l i n g a n d w a r m n ig m o d e s . Also, f o r h g ih e r a c c u r a c y , a h i g h e r d e n s i t y d a t a a c q u i s i t i o n w a s c a r r i e do u tc o ls et ot h ep h a s et r a n s i t i o n t e m p e r a t u r e r a n g e s .AD C field o f1 0 0 0  u t i l i z e d in t h e s e s t u d e is w i t h t h e h o p e o f o b t a n in ig a b e t t e r r e s o l u t i o n o f t h e h g i t e m p e r a t u r e p h a s e t r a n s i t i o n . I n F g iu r e 5 1 .8 t h e t e m p e r a t u r e d e p e n d e n c e o f yl ( 1 0 0 -  1 9 0K ) is s h o w n . A s t h et e m p e r a t u r e is o lw e r e d ( c o o l i n gm o d e ) , yl is d e c r e a s e s  1 8 0  F g iu r e5 1 .8 C o o l i n g a n d w a r m n ig m o d e s yT v e r s u s t e m p e r a t u r e p l o t s f o r  [Fe2(imid)4(bipy)]. //DC= 1 0 0 0 G. I n s e r t p l o t s h o w s a n a u g m e n t a o t in o ft h e OK-»|3 x  t r a n s i t i o nr e g i o n .  s l i g h t l yu n t i l it r e a c h e sat e m p e r a t u r eo f~ 1 5 2 K , it t h e nd e c r e a s e sa b r u p t y l u n t i l~ 1 K (a — > ( 3 ) a t t a i n i n g a " p l a t e a u " b e t w e e n ~ 1 5 0  1 3 8 K . Finally, yT d m i n is ih e  a b r u p t y l b e t w e e n t h e t e m p e r a t u r e s o f~ 1 3 8 K a n d ~ 1 3 2 K ( ( 3 -» y) b e f o r e" l e v e l  o f f "a g a i n . A st h et e m p e r a t u r e is n ic r e a s e d( w a r m n ig m o d e ) , t h et e m p e r a t u r ew h e r et h e  yT r i s e s s h a r p y l is s h i f t e db y~ 5 Kt o ~ 1 3 7 K , g i v i n gr i s et o t h eh y s t e r e t i cb e h a  1 8 1  s h o w n in F g iu r e 5 . 1 8 . H e n c e , t h e r m a l h y s t e r e s s i is e v d ie n t f o r t h e o lw t e m p e r a t u r e t r a n s i t i o n ( y  P). T h i s o lw t e m p e r a t u r e p h a s e t r a n s i t i o n , o c c u r r n ig w i t h t h e r m a l  h y s t e r e s i s , m a yb e c o n s d ie r e d a s b e n i g a first o r d e rt r a n s i t i o n [ 9 ] . A b o v e 1 3 7 K ,  f o l o w i n gaw a r m n ig m o d e ,% Tn ic r e a s e sg r a d u a l y ,f o l o w i n g t h ec o o l i n gc u r v e in t h i  r e g i o nr e a s o n a b y l c l o s e l y .T h e %T t h e nn ic r e a s e sa b r u p t y l o v e rt h e 1 5 0t o 1 5 2Kr e g  a g a n i f o l o w i n gt h ec o o l i n gm o d ec l o s e l y ,t h ea b r u p tc h a n g ec o r r e s p o n d n ig t ot h e P —  a t r a n s i t i o n . I n c o n t r a s t t o t h e P< > - y, t h e r e a p p e a r s t o b e n o s i g n i f i c a n t h y s t e r e a s s o c a it e dw i t ht h e P <-> a t r a n s i t i o n .  W en o t et h a ta b o v ea n db e o lw e a c ho ft h e s et r a n s i t i o n st h ed a t ao b t a n ie d in w a r m n ig m o d e a r e s l i g h t l yb e o lw t h o s e o b t a n ie d in t h e c o o l i n g m o d e . T h i s c o u d l  b e c a u s e t h e a — > P a n d p— > y t r a n s i t i o n s i n v o l v e c o o p e r a t v ie i n t e r a c t i o n b e t w e e n  c h r o m o p h o r e s w h c ih c a u s e t h e final s t a g e s o ft h e c o n v e r s o in t o o c c u r v e r y s l o w l y  H e n c ea te a c ht e m p e r a t u r es t u d e id o nc o o l i n gas m a la m o u n to ft h eh g ih e rt e m p e r a t u  p h a s er e m a n is . O nw a r m n ig , a t e a c ht e m p e r a t u r e t h e r e is l e s s o ft h eh i g ht e m p e r a t u  p h a s e" i m p u r i t y "p r e s e n ta n dh e n c et h e% Tv a u l e is s l i g h t l yl o w e r . T h i sc o u d l o fc o u b et e s t e db ya l o w i n gl o n gp e r o id s( o l n g e rt h a n 1 5m n iu t e sa o lw e d in t h es t a n d a r d  b e t w e e nc o le c t i n gd a t ap o n it so nc o o l i n g .I nv e iw o ft h er e l a t i v em n io re f f e c to b s e r v e  a n dt h ec o s to fd o n ig t h ee x t e n d e dt m i er u n s ,t h e s ee x p e r m i e n t sw e r en o tp e r f o r m e d .  I n o r d e rt od e t e r m n ie t h e t r a n s i t i o nt e m p e r a t u r e s m o r e a c c u r a t e l y , t h e  t e m p e r a t u r ed e p e n d e n c eo ft h ed e r i v a t i v ed ( % T ) d /T , in t h ec o o l i n ga n dw a r m n ig m o d e s 1 8 2  [ 1 0 ] , was  c a l c u l a t e d and p l o t t e d as s h o w n in F g iu r e 5.19.  T h i s g a v e t r a n s i t i o n  t e m p e r a t u r e s of 151 K for the a <-»• P t r a n s i t i o n , and 135 K for the p <-» y t r a n s i t i o n , the l a t t e rw i t hat h e r m a lh y s t e r e s s i w d it h of 4 K (133 - 137  K).  0.30 137 K 0.25133 K _~  w a r m i n g  0.20-  cooling  i  "o £  "a  0.15 H  o H  3| 0.10-1 H  ><  "° 0.05-1 0.00 -  100  i  —  |  —  110  i  —  |  —  120  i  —  |  —  130  i  —  |  —  140  i  —  |  —  150  i  —  |  —  160  i  —  |  —  170  i  —  |  —  180  i  -  190  T(K) F g iu r e 51 .9  T e m p e r a t u r ed e p e n d e n c e of the d e r i v a t i v e sd ( % T ) d /T (DC)  in the  c o o l i n g and w a r m n ig m o d e s and d e t e r m n ia t o i n of the t r a n s i t i o n t e m p e r a t u r e s for [Fe (imid) (bipy)] . 2  4  x  = 1 000 G.  1 8 3  A h i g h d e n s i t y AC m a g n e c t i s u s c e p t i b i l t ym e a s u r e m e n t s t u d y was a s lo p e r f o r m e d for the (3 <-» y s t r u c t u r a l p h a s e t r a n s i t i o n . % v e r s u s t e m p e r a t u r e d a t a , in the c o o l i n g m o d e , are s h o w n in F g iu r e 5.20.  As in the  DC m a g n e c t i s u s c e p t i b i l t y  0.0250  0.0150  F g iu r e 52 .0 500 Hz, H  AC  AC % v e r s u s Tp l o t for [Fe2(imid)4(bipy)]. C o o n i lg m o d e , f= x  = 2.5 G.  184  m e a s u r e m e n t s , ab r e a k in the p l o ta p p e a r sb e t w e e n 135 K and 132 K. M e a n w h e l i, in the w a r m n ig m o d e p l o t ( F i g u r e 5.21)  the a n o m a y l is s h i f t e d to h g ih e r t e m p e r a t u r e s ,  a p p e a r n ig b e t w e e n 135 K and 139 K. The t h e r m a l h y s t e r e s s i of the o lw t e m p e r a t u r e p h a s et r a n s i t i o n of [Fe2(imid)4(bipy)] is a s lo c o n f r im e d by the p l o t of yT (AC) v e r s u sT x  as s h o w n in F g iu r e 5.22. As b e f o r e ,t r a n s i t i o nt e m p e r a t u r e s may be d e t e r m n ie dm o r e  0.0250  0.0225 4  o £ 0.0200 H  fi-phase J.  Y-phase  * V * ^ ^  ^  £ 0.0175 H  0.0150 110  120  130  140  150  160  T(K)  F g iu r e 5.21 500 Hz, H  AC  = 2.5  AC x v e r s u s Tp l o t for [Fe2(imid)(bipy)]. W a r m n ig m o d e , f  :  4  G.  185  x  3.1  ©  E E 2.7  H  2.6  4  H  2.5 120  125  130  135  140  145  150  T(K) F g iu r e 52 .2  T e m p e r a t u r e d e p e n d e n c e of AC yj in the c o o l i n g and w a r m n ig  m o d e s for [Fe2(imid)4(bipy)]. f = 500 Hz, H c = 2.5 G. A r r o wd o w nr e f e r s to c o o l i n g x  A  m o d e ,a r r o w up r e f e r s to w a r m n ig m o d e .  a c c u r a t e y l f r o m the  e x t r e m e s of the  t e m p e r a t u r e d e p e n d e n c e s of the d e r i v a t i v e s  d(xT)/dT in b o t h the c o o l i n g and the w a r m n ig m o d e [10].  T h i s is s h o w n in F g iu r e 5.23.  T h e s et r a n s i t i o nt e m p e r a t u r e s are f o u n d to be 133 K in the c o o l i n gm o d e and 137 K in the w a r m n ig m o d e in t o t a l a g r e e m e n t w i t h the t e m p e r a t u r e s d e t e r m n ie d by the s u s c e p t i b i l t ym e a s u r e m e n s t (vide supra). H e n c e , the w d it h of the t h e r m a lh y s t e r e s s i in the (3 <> - yt r a n s i t i o n is 4 K.  186  DC  0.350.30-  o  £ E  H  0.25•  0.200.150.10-  H  0.050.001  F g iu r e5 2 .3 T e m p e r a t u r ed e p e n d e n c eo ft h ed e r i v a t i v e sd ( ^ T ) / d T( A C ) in t h e  c o o l i n ga n dw a r m n ig m o d e sa n dd e t e r m n ia t o in o ft h et r a n s i t i o nt e m p e r a t u r e sf o rt h e yp h a s eo f [Fe2(imid)(bipy)]. f = 5 0 0 Hz, H c = 2 . 5 G. 4  x  A  I n a n a t e m p t t o s t u d y t h e a < » pt r a n s i t i o n in m o r e detail, A C m a g n  s u s c e p t i b i lt ym e a s u r e m e n s t w e r e c a r r i e d o u t in t h e t e m p e r a t u r e r a n g efrom1 3 1 K t o  1 7 1 K in b o t hc o o l i n ga n dw a r m n ig m o d e s . U n f o r t u n a t e l y , a ss e e n in F g iu r e5 . 2 4 t h ep  yt r a n s i t i o n( s h o w n ig h y s t e r e s i s )w a sd e t e c t e db u tn oo t h e ra n o m a y l w a sf o u n  in t h ec o o l i n go rw a r m n ig m o d ec o r r e s p o n d n ig t ot h e a <-> P t r a n s i t i o n . A p p a r e n t y l t h e d i f f e r e n c e in t h e m a g n e c t i p r o p e r t e is b e t w e e n t h e a a n d pf o r m s is t o o s m a l t o o b s e r v e d in t h eA Cm e a s u r e m e n t s . 1 8 7  0.034 4  •  *•.  0.032 4  o g  0.030 -|  0.028 4 0.026 4  ^  -<  130  140  150  160  1 —  170  T(K)  F g iu r e 52 .4  C o o l i n g and w a r m n ig m o d e AC % v e r s u s t e m p e r a t u r e p l o t s for  [Fe (imid) (bipy)] . f = 500 Hz, H 2  4  x  AC  = 2.5 G.  5 . 2 . 1 . 4 M O S S B A U E RS P E C T R O S C O P Y  The r o o mt e m p e r a t u r eM o s s b a u e rs p e c t r u m of [Fe2(imid)4(bipy)] ( F i g u r e 5.25) x  c o r r e s p o n d s to two  o v e r a lp p n ig q u a d r u p o e l d o u b e lt sc o n s s it e n tw i t h the X r a y  188  Velocity Relative to Fe (mm s*) F g iu r e5 2 .5 M o s s b a u e rs p e c t r u mo f [Fe2(imid)4(bipy)] a t2 9 3 K . x  c r y s t a o lg r a p h y r e s u l t s a t t h a t t e m p e r a t u r e , t h a t i n d i c a t e e q u a l p o p u a lt o in o fd i s t o r t e d s i x a n d f o u r c o o r d i n a t e s i t e s . T h e M o s s b a u e r p a r a m e t e r s o b t a n ie d h e r e n i f o r t h e  n o m n ia l T da n d O h s i t e s a t 2 9 3 Ka r e :s io m e rs h i f t s ( 5 ) o f0 7 .4 m m s" a n d 1 0 .1 1  a n d q u a d r u p o e l s p l i t t i n g s ( A E ) o f2 . 0 1 m m s" a n d 1 0 .6 m m s", r e s p e c t i v e l y , v a 1  1  fairly c h a r a c t e r i s t i co fh i g h s p i ni r o n ( I I ) w i t h "all" n t i r o g e nl i g a t i o n [ 1 1 ] . A Ev a u le sa r e n o t r e l i a b l y d a ig n o s t c i o fc o o r d n ia t o in n u m b e r f o r h i g h s p i n f e r r o u s c o m p e lx e s . T h e  1 8 9  s p l i t t i n gv a u le r a n g e sc a no f t e no v e r a lp f o rf o u r , f i v ea n ds i xc o o r d n ia t o in e n v r i o n m e n t s  ( e v e n w i t h s i m i l a rl i g a n d s ) d e p e n d n ig o n t h e d e g r e e o f d i s t o r t i o n o f t h e l o c a l  c o o r d n ia t o in e n v r io n m e n t . O nt h eo t h e rh a n d ,s io m e rs h i f t sh a v eb e e nf o u n dt ob eq s e n s i t i v e t o c o o r d n ia t o in n u m b e r f o rfixeds p i n s t a t e a n d s i m i l a rl i g a t i o n . S p e c i f i c a ly ,  f o rs p i nq u i n t e ti r o n ( I I ) w i t hn t ir o g e no rm x ie dn t ir o g e n-h a o lg e n ligation, 8 v a u le sf  s i x c o o r d n ia t o in g e n e r a l yr a n g e f r o m ~ + 1 0 . t o 1 2 . m m s" [ 1 1 1 3 ] ; f i v e c o o r d i n a t i o n 1  f r o m+ 0 . 8 5 t o 0 9 .5 m m s" [ 1 3 1 5 ] a n df o u r c o o r d i n a t i o nf r o m~+ 0 7 .0 t o0 8 .5 m m 1  [ 1 6 ] a tr o o mt e m p e r a t u r e . H e n c e ,t h ep r e s e n t8v a u le s in c o m b n ia t o in w i t ht h ea v a i l a  l i t e r a t u r er e s u l t s a p p e a rt ou n e q u v io c a y l c o n f r im t h e six- a n df o u r c o o r d i n a t en a t u r eo f t h ei r o no f [Fe2(imid)4(bipy)]. x  T h e s t r u c t u r a l p h a s e t r a n s i t i o n s o c c u r r n i g in [Fe2(imid)4(bipy)] w e r e a s lo x  e x a m n ie d m e t c iu o lu s y l w i t h M o s s b a u e r s p e c t r o s c o p y . I n f a c t , t h e h g ih t e m p e r a t u r e t r a n s i t i o n (a < > - ( 3 ) o f [Fe2(imid)4(bipy)] w a s first f o u n d u s n ig t h i s s p e c t r o s c o p c i x  t e c h n q iu e , a n d l a t e rc o n f r im e dw i t ht h eX r a yd i f f r a c t i o n a n d D C s u s c e p t i b i l t ys t u d e is a s a r le a d yd e s c r i b e d . A s e to fM o s s b a u e rs p e c t r af o r [Fe2(imid)4(bipy)], d e t e r m n ie d in x  t h ew a r m n ig m o d efrom1 4 5 5 . Kt o 1 7 5 1 . K , is s h o w n in F g iu r e5 . 2 6 .A c c o r d n ig t o s t u d y t h e o lw t e m p e r a t u r e (P «-» y) p h a s e t r a n s i t i o n o c c u r s b e t w e e na b o u t 1 4 6 9 . a n d  1 4 8 3 . K , w h i l e t h e h g ih t e m p e r a t u r e p h a s e t r a n s i t i o n o c c u r s b e t w e e n a b o u t 1 6 0 2 . a n d 1 6 7 7 . K( F i g u r e5 . 2 6 ) .  1 9 0  —1  1  1  1  1  1  •  1  — i  ~w T = 145.5K  ^  T = 146.9K 1  ,  ,  y  1  1  i  1  v V  T = 160.2K  "•: il •i  V  ~^ A f T =150.0K  V  1  i  A. j  T = 148.3K  1  1  T = 157.3K 1  —«  1  T = 167.7K  ~ ~ ^  -  •: *' l'  i  A  1 ! *  i : I •  w  r\ 1r  ; f j• *I  : i  y  • •*  i •  T = 175.1K  ••  M  }  •  JJY  Velocity Relative to Fe (mm s ) F g iu r e 52 .6  M o s s b a u e rs p e c t r a in the w a r m n ig m o d e for [Fe2(imid)4(bipy)].  191  A f t e r h e a t n ig a s a m p e l of [Fe2(imid)4(bipy)] to 1697 . x  w e r e m e a s u r e d f r o m 1651 .  to 1299 .  K, M o s s b a u e r s p e c t r a  K ( c o o l i n g m o d e ) . As s h o w n in F g iu r e 5.27,  d a t ai n d i c a t et h a t the h g ih t e m p e r a t u r ep h a s et r a n s i t i o no c c u r sb e t w e e n 1651 . K, w h i l e , the o lw t e m p e r a t u r e p h a s e t r a n s i t i o n o c c u r s b e t w e e n 1449 .  and 1399 .  and  the 1627 .  K. In  the M o s s b a u e rs t u d y , the o lw t e m p e r a t u r et r a n s i t i o ne x h i b i t sh y s t e r e s s i of a r o u n d 3 to 5 K and the h g ih t e m p e r a t u r e t r a n s i t i o n e x h i b i t s no s i g n i f i c a n t h y s t e r e s i s , in q u a l i t a t i v e a g r e e m e n t w i t h the  AC  and  DC  m a g n e c t i s u s c e p t i b i l t y s t u d i e s . H o w e v e r , b o t h  s t r u c t u r a l p h a s e t r a n s i t i o n s a p p e a r to o c c u r at ~ 10 K h g ih e rt h a n i n d i c a t e d by the and  AC  s u s c e p t i b i l t y s t u d i e s . T h e r e is not  a t lh o u g h , ap o s s b ie l e x p a ln a t o i n may s p e c t r o s c o p y . It s e e m s the  DC  a s t r a g ih t f o r w a r d e x p a ln a t o i n for this,  i n v o l v e the d i f f e r e n t t i m e s c a l e of M o s s b a u e r  m c ir o s c o p c i M o s s b a u e r e f f e c td e t e c t s the  two p h a s e  t r a n s i t i o n s " e a r l i e r " t h a n the b u k l AC and DC m a g n e c t i s u s c e p t i b i l t ym e a s u r e m e n s t in the  c o o l i n g m o d e . H o w e v e r , in the  w a r m n ig m o d e , AC  and  DC s u s c e p t i b i l t y  m e a s u r e m e n s t d e t e c t the t r a n s i t i o n s" e a r l i e r " (vide supra). T h i ss i t u a t i o n may a s lo be an e x p e r m i e n t a le f f e c tr e g a r d n ig t h e s et e c h n q iu e s .M o s s b a u e rm e a s u r e m e n s t w e r ed o n e on m u s l w h i l e the AC and DC s u s c e p t i b i l t ym e a s u r e m e n s t w e r ep e r f o r m e d on c r y s t a l i n e solids, w h c ih c o u d l be  the  s o u r c e of  t e m p e r a t u r e s .  192  the  d i f f e r e n tp h a s e t r a n s i t i o n d e t e c t o in  i *  t •  * i  WM  I' i 5 1 V V \\ T = 165.1K i  •  i  Ti = 139.9K 1  i  \h\ i S o  -*-»•  a io X!  T = 163.6K  I  j  \  i  j  1  —*\  /  V  if  V  V  |  i  ~~'  1  '  1  1  '  i T = 132.7K  W\ V  T = 144.9K  '  |  • -  1  V  T = 135.0K J  y  V I  H  i  v |  r  V  I*  \\ y  T = 129.9K  i  A 1 •l  13 T = 162.7K  V  I  |  i  i  y  \A * V / i*  V  t <  i»  »•  |  V  Velocity Relative to Fe (mm s ) F g iu r e 52 .7  M o s s b a u e rs p e c t r a in the c o o l i n gm o d e for [Fe2(imid)4(bipy)]. x  193  5.3  POLY-2,2'-BJPYRIDINETETRAKIS(IMIDAZOLATO)DICOBALT(II)  5.3.1  R E S U L T S AND D S IC U S S O IN  5 . 3 . 1 . 1S Y N T H E S S I, T H E R M A L AND  The  S T R U C T U R A LC H A R A C T E R Z IA T O IN  r e a c t i o n of c o b a t l o c e n e w i t h i m i d a z o l e and e x c e s s m o t l e n 2 , 2 'b i p y r i d i n e  g e n e r a t e d , [Co2(imid)4(bipy)], as a m i c r o c r y s t a l i n ep o w d e r . D e t a i l s of t h i sr e a c t i o n are x  g v ie n in C h a p t e r 9, s e c t o in 9 . 2 . 2 . 7 .  A t l h o u g ht h i sm a t e r i a lc o u d l not be o b t a n ie d in a f o r ms u i t a b l e for s i n g l ec r y s t a l X r a yd i f f r a c t i o ns t u d i e s , it was p o s s b ie l to s h o w by p o w d e rd i f f r a c t i o ns t u d e is t h a t it is s io m o r p h o u s and  p r o b a b y l i s o s t r u c t u r a lw i t h the  [Fe2(imid)4(bipy)]. The x  r o o m t e m p e r a t u r ef o r m of  X r a y p o w d e r d i f f r a c t o g r a m of [Co (imid)4(bipy)] c o n ic d ie s 2  x  w e l w i t ht h a t c a l c u l a t e d f r o m the s i n g l e c r y s t a l d a t a of [Fe2(imid)4(bipy)] o b t a n ie d at x  r o o mt e m p e r a t u r e , e m p o ly n ig the p r o g r a mP o w d e r C e l [17]  ( F i g u r e5 . 2 8 ) . n Id e x n i g the  X r a y p o w d e r d i f f r a c t o g r a m of [ C o ( i m i d ) ( b i p y ) ] u s n i g the 2  4  p r o g r a m C e l r e f  x  g e n e r a t e d the l a t t i c e p a r a m e t e r s : a = 1 0 . 5 2 1 , b = 1 3 7 .2 9 and c = 91 .81 v e r y s i m i l a r to  the  r o o mt e m p e r a t u r el a t t i c e p a r a m e t e r so b t a n ie d for  [ F e ( i m i d ) ( b i p y ) ] (a = 1 0 . 5 0 7 , b = 1 3 7 .3 0 and c = 91 .88 2  4  x  i n f r a r e d s p e c t r a of a-[Fe2(imid)4(bipy)] and x  A). The  A. T h e s e are a-  r o o m t e m p e r a t u r e  [Co2(imid)4(bipy)] w e r e a s lo f o u n d to x  e x h i b i t the s a m ev i b r a t i o n a lb a n d s at a m l o s t the s a m ef r e q u e n c i e s .  194  [18],  •—w  1 0  2 0  3 0 2 0 "  4 0  5 0  F i g u r e5 2 .8 X R a yp o w d e rd f i f r a c t o g r a m so f [Co2(imid)4(bipy)] x  ( t o p ,  e x p e r m i e n t a ) l a n d [Fe2(imid)4(bipy)] ( b o t t o m ,c a l c u l a t e d ) . x  I n c o n t r a s t t o t h e i r o n ( I I ) a n a o lg u e , [Co2(imid)4(bipy)] is a i r s t a b l e , b u t b o t h x  c o m p o u n d s h a v e p r o p e r t e is c o n s s it e n tw i t h p o y lm e r c i s t r u c t u r e s ,f o r e x a m p e l  [Co (imid)4(bipy)] d o e sn o td i s s o l v e in c o m m o no r g a n c i s o v le n t sa n d it is n o n v o l a t i l e . 2  x  A t h e r m a l g r a v i m e t r i c s t u d y p e r f o r m e d o n t h e C o ( I ) m a t e r i a l g a v e n o e v d ie n c e f o  d e c o m p o s t o in u n t i l~2 5 0° C( F i g u r e5 . 2 9 ) . T h e T G A p l o t f o l o w s at w os t e pw e g i  1 9 5  0  1  1  200  1  1  1  400  1  1  600  1 800  T(°C)  F g iu r e5 2 .9 T G Ap l o tf o r [Co (imid) (bipy)] . 2  4  x  o ls sp r o f i l ea n dr e s e m b e ls t h a to f [Fe2(imid)4(bipy)]. T h efirstm a o jr w e g ih to ls s (~ 3 0 x  % )o c c u r sb e t w e e n2 2 5° Ca n d3 0 0 °C, a n dt h es e c o n do n e ,w i t haw e g ih to ls so  o ft h e initial w e i g h t ,h a p p e n sb e t w e e n3 9 0° C a n d6 6 0 °C. A w e g ih tp e r c e n t a g eo f  % r e m a n is a t t h e h g ih e s t t e m p e r a t u r e s t u d i e d , 8 0 0 °C. I n c o n t r a s t t o t h e T G A p l o t [Fe2(imid)4(bipy)], t h e r e is a p a lt e a u b e t w e e n 3 0 0 ° C a n d 3 9 0 ° C in t h e p l o t x  [Co2(imid)4(bipy)]. T h i s p a lt e a u s e e m s t o c o r r e s p o n dt o t h e f o r m a t o in o f[ C o ( i m i d ) ] x  2 x  b yo ls s o ft h eb i p y r i d i n el i g a n d (~ 2 9 %) in t h e first s t e po ft h et h e r m a ld e c o m p o s t i o A s i m i l a r s i t u a t i o n o c c u r r e d w h e n t h e t h e r m a l g r a v i m e t r i c s t u d y  1 9 6  o f  [Co3(imid)6(imidH)2] was c a r r i e d out and [Co(imid)2] was o b t a n ie d by the o ls s of the x  x  n e u t r a li m i d a z o l em o e lc u e ls ( C h a p t e r 4, s e c t o i n 4.2).  5.3.1.2  M A G N E T C I P R O P E R T E IS  A  n o t i c e a b l e d i f f e r e n c e in t h e m a g n e t o s t r u c t u r a l b e h a v o iu ro f  [Co2(imid)4(bipy)] v e r s u s [Fe2(imid)4(bipy)] is t h a t w h e r e a s the l a t t e rs h o w s a x  x  d i s c o n t i n u i t y in the (leff v e r s u s t e m p e r a t u r e p l o t at 135 K ( F i g u r e 5.9), no e q u v ia e ln t d i s c o n t i n u i t y is o b s e r v e d for [Co2(imid)(bipy)] ( F i g u r e 5.30). The c o b a t l d e r i v a t i v e 4  x  d o e sn o t a p p e a rt o u n d e r g ot h e s t r u c t u r a lp h a s et r a n s i t i o n s e x h i b i t e d  b y  [Fe2(imid)4(bipy)]. O t h e r w s ie the m a g n e c t i p r o p e r t e is of [Co2(imid)4(bipy)] p a r a le l x  x  t h o s e of [Fe2(imid)4(bipy)]. x  For [Co(imid)4(bipy)], the v a u l e of jieff, m e a s u r e d at an a p p l i e d field of 500 G, 2  x  d e c r e a s e sw i t hd e c r e a s n ig t e m p e r a t u r efrom4.35 U,B at 300 K to 2.89 p. at 13 K. B e o lw B  13 K it n ic r e a s e s a b r u p t l y , s i g n a l i n g the o n s e t of o ln g r a n g e f e r r o m a g n e t c i o r d e r n ig ( F i g u r e 5.31). T h i s m a g n e c t i b e h a v o iu r is a s lo s e e n in the % v e r s u s Tp l o t for the  c o m p o u n dw h c ih s h o w s an i n c i p i e n tm a x m iu m in % j u s ta b o v e 13 K and an a b r u p t rise in % b e o lw t h i s t e m p e r a t u r e . As the t e m p e r a t u r e is o lw e r e d f u r t h e r to 2 K, % t e n d s to s a t u r a t o in ( F i g u r e 5.31). S t u d e is at an a p p l i e dfieldof 10 000 G ( F i g u r e 5.30) s h o w a l e s s p r o m n ie n t n ic r e a s e in % and u « fb e o lw T t h a n o b s e r v e d in the 500 G d a t a .T h i s c  197  0.30  5.0 AA A AAAAAAAAAAAA  0.25  4.5 4.0  !_ o  0.20  I  0.15  3.5  £  3.0  m =L  2.5  0.10  2.0 0.05  1.5 1.0  0.00 50  100  150  200  250  300  T(K)  F g iu r e 5.30  r e s e m b e ls the  % and jieff v e r s u s Tp l o t s at 10 000 G for [Co2(imid)4(bipy)] x  b e h a v o iu r o b s e r v e d for  [Fe2(imid)(bipy)]. N o n e t h e e ls s , for b o t h 4  x  [Fe2(imid)4(bipy)] and [Co2(imid)(bipy)] the m a g n e c t i t r a n s i t i o n is c l e a r l y o b s e r v e d x  4  x  at t h i sh g ih e r field ( F i g u r e s 5.9 and 5.30, r e s p e c t i v e l y ) .  198  4 0 .  1 6  3 5 . i  1 4  -T 3 0 . }  1 2  h1 0  = L  | 2 0 . 1 5 . {  8  1 0 .  6  0 5 . H 0 0 . 0  f  as  | 2 5 .  A A  AAAAAA  A A A A  A  t  4  A2  1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0  1 0 0  T(K)  F g iu r e5 . 3 1 x ^ m  M-eff  v e r s u sTp l o t sa t5 0 0Gf o r [Co2(imid)4(bipy)]. x  T h e e f f e c t o ft h eo lw t e m p e r a t u r e m a g n e c t i t r a n s i t i o n in [Co2(imid)4(bipy)] is x  s e e n in t h e m a g n e t z ia t o in v e r s u s a p p l i e dfieldp l o t s a t d i f f e r e n t t e m p e r a t u r e s ( F i g u r e  5 . 3 2 ) . A t 4 . 8 Kt h ep l o t is n o n l i n e a ra n d , in c o n t r a s tt ot h eh g ih e rt e m p e r a t u r ep l o  d o e sn o te x t r a p o a lt et oz e r oa tz e r o a p p l i e dfield.C y c l i n gt h ea p p l i e d field b e t w e e n+  0 0 0a n d5 50 0 0G a t 4 . 8K g e n e r a t e s a h y s t e r e s s i o lo p ( F i g u r e5 . 3 3 )fromw h c  1 9 9  5 0 0 0 o I  4 0 0 0 j  *©  •  s o 0 0 0 i £ 3  • • A  a  •  ©  '5 2 0 0 0 US  •  N  *-C  A  S  § f 1 0 0 0  2  O  1 0 0 0 0 2 0 0 0 0 3 0 0 0 04 0 0 0 0  5 0 0 0 06 0 0 0 0  Applied Field ( G )  F g iu r e5 3 .2 M a g n e t z ia t o in v e r s u s a p p l i e d field p l o t s a td i f f e r e n tt e m p e r a t u r e s f o r [Co (imid) (bipy)] . 2  4  x  c o e r c v ie field o f 125 G a n d ar e m n a n tm a g n e t z ia t o in o f 1900 c m G m o l "a r eo b t a n ie d . 3  1  Ap l o to fx v e r s u s T (10 000 G d a t a ) is l i n e a ro v e rt h et e m p e r a t u r e r a n g e 300 - 25 K 1  a n d a C u r e iW e s is a n a y ls s i o ft h i s d a t a y i e l d s C = 2.64 c mGmor a n d 0 = -25 K 3  1  ( F i g u r e 5.34). A s d s ic u s s e d a b o v e f o r [Fe2(imid)4(bipy)], o v e r a lt h e s e m a g n e c t i x  2 0 0  Applied Field (G)  F g iu r e 53 .3  M a g n e t c i h y s t e r e s s i p l o t s at 4.8 K for [Co2(imid)4(bipy)]. x  p r o p e r t e is c l a s s i f y [Co2(imid)4(bipy)] as a w e a k f e r r o m a g n e t . H o w e v e r , it s h o u d l be x  n o t e dt h a t , s n ic e [Co2(imid)4(bipy)] c o n t a n is h g ih s p i no c t a h e d r a l d m e t a l c e n t e r s and 7  x  s n ic e s u c h c e n t r e s h a v efirsto r d e r o r b i t a l e f f e c t s c o n t r i b u t i n g to t h e i rm a g n e s t im , the c o m m e n s t m a d ea b o v ec o n c e r n n i g the i n t e r p r e t a t i o n of 6 v a u le s for [Fe2(imid)4(bipy)] x  a p p y l h e r ea l s o .  201  T(K)  Figure 5.34  Plot  of  %  versus  temperature  at  10  000  G  for  [Co (imid) (bipy)]x. 2  4  The highest magnetization measured for [Co2(imid)4(bipy)]  x  (4 515 cn^GmoF  1  at 4.8 K and 55 000 G) is significantly lower than the theoretical saturation value (16 766 c m G m o r ' for a S = 3/2 system [5]). A s discussed above for [Fe2(imid)4(bipy)] , 3  x  this result is not inconsistent with spin canting or ferrimagnetic exchange providing the source o f the residual spin at low temperatures.  202  E x t r a p o l a t i o n o f t h e M v e r s u s H p l o t t o H = 0 o n t h e m a g n e t z ia t o in c u r v e  o b t a n ie d a t 4 . 8 K ( F i g u r e 5 . 3 2 ) , y i e l d s t h e s p o n t a n e o u s m a g n e t z ia t o in , M (0) = 2 6 4 0 s  c m G m o l " . F r o m this, t h e c a n t n ig a n g e l is c a l c u l a t e d a s d e s c r b ie d p r e v i o u s l y f o r 3  1  [Fe (imid) (bipy)] ,t ob ey ~ 9°. 2  4  x  T h a t t h i s p o y lm e rb e h a v e s a s am a g n e tb e o lw T is c o n f r im e db yt h e s h a p e c  t h e Z F C M , F C M a n d R E M p l o t s in F i g u r e 5 . 3 5 . T h e z e r o f i e l d c o o l e d m a g n e t z ia t o in  ( Z F C M ) u n d e ra n a p p l i e d field o f5 0 G s h o w e d am a x m iu m a t 9 . 0K . T h ef i e l d c  m a g n e t z ia t o in ( F C M )u n d e ra na p p l i e d field o f5 0 Gn ic r e a s e dr a p i d l yb e o lw 1 0K  m a x m iu mv a u le o f- 1 3 7 0 c n ^ G m o " l a t2 K( F i g u r e5 . 3 5 ) . W h e nt h ea p p l i e d field 1  s w t i c h e d o f f a t 2 K a r e m n a n t m a g n e t z ia t o in o f - 1 1 9 0 c m G m o r ' r e m a n ie d t h a 3  d e c r e a s e d u p o n w a r m n ig a n d v a n s ih e d a t - 1 0 K . N o a m b g iu t i e s a r e f o u n d in t h  p l o t s , in c o n t r a s tt ot h eo n e sf o r [Fe2(imid)4(bipy)] w h e r et h ed e r i v a t i v eo ft h ep l o t sh x  t o b ec a l c u l a t e d in o r d e rt o e s t m i a t e T. T h u s , t h et e m p e r a t u r e s f o rt h eh g ih e s ts o lp e c  t h eF C M plot, t h ep e a ko nt h eZ F C M plot, a n dt h et e m p e r a t u r ea tw h c ih R E Mv a  a r e all w i t h i n t h e r a n g e b e t w e e n 9 . 0 a n d 1 0 K . H e n c e , t h e critical t e m p e r a t u r e  [Co2(imid)4(bipy)] is d e t e r m n ie d a s T = 9 . 5 K [ 8 ] . T h i st e m p e r a t u r e is in r e a s o n a b y l x  c  a g r e e m e n t w i t h t h e o n s e t t e m p e r a t u r e ( ~ 1 3 K ) o ft h e o ln g r a n g e m a g n e c t i o r d e r n i d e t e r m n ie db yD Cs u s c e p t i b i l i t y .  2 0 3  1400  H  •  _ ^ 1200  ZFCM FCM REM  •  "o  E  1000  u |  • *  800 600-|  | N  « C  I  400 -\ 2000-  -T  5  0  4i  15  10  20  25  T(K) F g iu r e5 3 .5 P l o t s o fZ F C M , F C M a n d R E M f o r [ C o ( i m i d ) ( b i p y ) ] u s n ig a 2  4  x  D C field o f5 0 G.  5 . 4  S U M M A R YA N DC O N C L U S O IN S  [Fe2(imid)4(bipy)], a n dt h es io m o r p h o u s c o b a t l c o m p o u n d , [Co2(imid)4(bipy)], x  x  h a v e2 D e x t e n d e ds t r u c t u r e s in w h c ih d o u b e l a ly e r e ds h e e t so fa l t e r n a t i n gt e t r a h e d r a l y  a n do c t a h e d r a l yc o o r d n ia t e dm e t a lo in sa r el i n k e db ys i n g l eb r i d g i n gi m i d a z o l a t e s .T h e o c t a h e d r a l m e t a l c e n t e r s a r e a d d i t i o n a l y c o o r d n ia t e d b y 2 , 2 'b i p y r i d i n e g i la n d s w h c ih  o c c u p yp o s i t i o n sb e t w e e nt h es h e e t s , i s o l a t i n gt h es h e e t s f r o me a c ho t h e r . T h ep r e s e n c  2 0 4  of the  two  d i f f e r e n t i r o n c e n t e r s in [Fe2(imid)4(bipy)] is c o n f r im e d by a m b e in t x  t e m p e r a t u r eM o s s b a u e rs t u d i e s .  The m a g n e c t i p r o p e r t e is of t h e s e m a t e r i a l s r e v e a l at r a n s i t i o n to o ln g r a n g e f e r r o m a g n e t c i o r d e rb e o lw 6 K for  [Fe2(imid)4(bipy)] and  b e o lw 9.5  x  K  for  [Co2(imid)4(bipy)]. B o t hm a t e r i a l sr e v e a lm a g n e c t i h y s t e r e s s i at 4.8 K. A n a l y s i s of the x  d a t a yield, for [Fe2(imid)4(bipy)] and [Co2(imid)4(bipy)] r e s p e c t i v e l y , c o e r c v ie fields x  x  of 15 and 125 G and r e m n a n t m a g n e t z ia t o in s of 200 and 1900  c m G m o l " . M a g n e t c i 3  1  p a r a m e t e r s for t h r e e p a i r s of a n a o lg o u s i r o n ( I I ) and c o b a l t ( I ) i m i d a z o l a t e c o m p o u n d s , i n c l u d i n g y-[Fe2(imid)4(bipy)] and x  [Co2(imid)4(bipy)], w h c ih e x h i b i t x  f e r r o m a g n e t s im are s h o w n in T a b e l 5.1. For e a c h pair, H  coet  w e a k  is a w la y s g r e a t e r for  the  c o b a t l s y s t e m s u g g e s t n ig c o b a t l m a g n e s t are g e n e r a l yh a r d e rt h a na n a o lg o u si r o no n e s . In c o n t r a s t to w h a t m g ih t h a v e b e e n e x p e c t e d it s e e m s t h a t the m a g n e t s t r e n g t h , as m e a s u r e d by M , Km  is not a s m i p e l f u n c t i o n of the n u m b e r of u n p a r ie d e e lc t r o n s or  c a n t n ig a n g l e . W h i l e the c o b a t l m a t e r i a l has the h g ih e s tM  iem  Mrem in the o t h e r two.  M o r e o v e r , w h i l e the o lw  c o n s s it e n t w i t ha o lw  for  M  c a n t n ig a n g e l ( C h a p t e r 3),  Km  the  in one p a i r it has the o lw e r [Co(4-abimid)2] s e e m s x  c a n t n ig a n g e l for  [Co2(imid)(bipy)] is o lw e rt h a nt h a t of its i r o na n a o lg u e yet the M 4  x  Km  is g r e a t e r for  the  c o b a t l s y s t e m .  [Fe2(imid)4(bipy)] is u n q iu e in p r e s e n t n i g two s t r u c t u r a l p h a s et r a n s i t i o n s , at ~ x  151 K and  ~ 135 K,  as d e t e r m n ie d by DC  205  and  AC  m a g n e c t i s u s c e p t i b i l t y  T a b e l 5 . 1  M a g n e t c i p a r a m e t e r sf o rt h r e ep a i r so fa n a o lg o u si r o n ( I I )a n dc o b a l t ( I )  w e a kf e r r o m a g n e t s .  C o m p o u n d  R e f .  H ( G ) coet  ( c n ^ G m o f ) 1  Y F e ( i m i d ) ( b i p y )  1 5  2 0 0  C o ( i m i d ) ( b i p y )  1 2 5  1 9 0 0  F e ( 4 a b i m i d )  8 0  2 1 0 0  C h a p t e r3  C o ( 4 a b i m i d )  4 0 0  2 2  C h a p t e r3  2 0 0  2 0 0 0  2  4  2  4  2  2  Fe (imid) (imidH) 3  6  2  Co (imid) (imidH) 3  6  2  4 1 4 0  1 7 5  T h i sC h a p t e r  T h s iC h a p t e r  [ 1 ]  C h a p t e r4  A b b r e v i a t i o n s :i m i d=i m i d a z o l a t e ,4 a b i m i d=4 a z a b e n z m i d ia z o a lt e , b i p y=2 , 2 ' b i p y r i d i n e .  m e a s u r e m e n t s . T h e s e s t r u c t u r a l p h a s e t r a n s i t i o n s h a v e a s lo b e e n s t u d e id in d e t a i l b y M o s s b a u e rs p e c t r o s c o p y .T h e s es t u d e is y i e l d e dt r a n s i t i o nt e m p e r a t u r e so f~ 1 0Kh g ih e r  t h a nt h o s e d e t e r m n ie db ym a g n e c t i s t u d i e s . T h e r m a l h y s t e r e s s i b e h a v o i r is e v d ie n t f o r  2 0 6  t h e o lw t e m p e r a t u r e p h a s e t r a n s i t i o n (p < > - y )  a s  d e t e r m n ie d b y DC a n d AC  s u s c e p t i b i l t y a s w e l a s M o s s b a u e r s p e c t r o s c o p y . S i n g l e c r y s t a l X r a y d i f f r a c t i o n  s t u d e is a t 1 1 3 Ka n d 1 4 3 Kr e v e a e ld t h a tw h i l et h ec r y s t a li n t e g r i t yw a sr e t a i n e d ,a  a st h eb a s c i d o u b e l l a y e rs t r u c t u r a lm o t i ff o u n d in t h er o o mt e m p e r a t u r ea p h a s e , t h e  w e r e s i g n i f i c a n t c h a n g e s in cell a n d b o n d p a r a m e t e r s f o r t h e P- a n d y p h a s e s o [Fe (imid) (bipy)] . 2  4  x  T o t h e a u t h o r s ' k n o w e ld g et h i s is t h e first t m i e t h a tt w o p h a s et r a n s i t i o n s h a b e e n d e t e c t e d in a m o e lc u e lb a s e d m a g n e c t i m a t e r i a l ([Fe2(imid)4(bipy)]) a n d s t u d e id x  in d e t a i lb yac o m b n ia t o in o fX r a yc r y s t a l o g r a p h y , AC a n d DC m a g n e c t i s u s c e p t i b i l t y m e a s u r e m e n s t a n dM o s s b a u e rs p e c t r o s c o p y .  2 0 7  R e f e r e n c e s  1.  S.J. R e t t i g , A. S t o r r , D. A. S u m m e r s , R. C. T h o m p s o n , and J. T r o t t e r , J Amer. Chem. Soc. 119, 8 6 7 5( 1 9 9 7 ) .  2.  S. J. R e t t i g , A. S t o r r , D. A. S u m m e r s , R. C. T h o m p s o n , and J. T r o t t e r , Can J. Chem. 77, 425 ( 1 9 9 9 ) .  3.  S. J. R e t t i g , V. S a n c h e z , A. S t o r r , R. C. T h o m p s o n , and J. T r o t t e r , J. Chem. Soc, Dalton Trans. 3931 ( 2 0 0 0 ) .  4.  O. K a h n . Molecular Magnetism. VCH.  New Y o r k . 1993.  p.  321.  5.  R. L. Carlin. Magnetochemistry. S p r i n g e r V e r l a g . Berlin. 1986.  6.  F. P a l a c i o , M. A n d r e s , R. H o m e , and A. J. van D u y e n e v e d lt . J. M a g n .M a g n . M a t e r . 54-57, 1 4 8 7 ( 1 9 8 6 ) .  7.  S.J. R e t t i g , V. S a n c h e z , A. S t o r r , R. C. T h o m p s o n , and J. T r o t t e r .I n o r g .C h e m . 38, 5 9 2 0( 1 9 9 9 ) .  8.  O. K a h n . Acc Chem. Res. 33 (10)  9.  C. N. R. Rao, and K. J. Rao. Phase Transitions in Solids. An Approach to the Study of the Chemistry and Physics of Solids. M c G r a w H i l . L o n d o n . 1978.  pp.  7-9.  647 ( 2 0 0 0 ) .  pp.  17-24. 10.  Y. G a r c i a , O. K a h n , L. R a b a r d e l , B. C h a n s o u , L. S a m l o n , and J. P. T u c h a g u e s . Inorg. Chem. 38, 4 6 6 3( 1 9 9 9 ) .  11.  N. N. G r e e n w o o d , and T. C. G i b b . Mossbauer Spectroscopy. C h a p m a n and Hall Ltd. L o n d o n . 1971.  12.  B. W. D o c k u m , and W. M. Reiff. Inorg. Chim. Acta. 35, 285 ( 1 9 7 9 ) .  13.  F. F. C h a r r o n , and W. M. Reiff. Inorg. Chem. 25, 2 7 8 6( 1 9 8 6 ) .  14.  W. M. Reiff, N. E. E r i c k s o n , and W. A. B a k e r . Inorg. Chem. 8, 2119 ( 1 9 6 9 ) .  15.  D. S e d n e y , M. K a h j e h n a s s i r i , and W. M. Reiff. Inorg. Chem.20, ( 1 9 8 1 )3 4 7 6 .  16.  B. W. D o c k u m , and W. M. Reiff. Inorg. Chim. Acta. 120, 61 ( 1 9 8 6 ) . 208  1 7 .  P o w d e r C e l ,v e r s i o n2 . 3 ,W .K r a u s sa n d G. N o l z e ,F e d e r a lI n s t i t u t ef o r M a t e r i a l sR e s e a r c ha n dT e s t i n g( B A M ) , Berlin, 1 9 9 7 .  1 8 .  L M G P S u t ie o fP r o g r a m sf o rI n t e r p r e t a t i o no fX R a yE x p e r m i e n t s ,b yJ e a n L a u g i e r ta n dB e r n a r dB o c h u ,E N S P L /a b o r a t o r ie d e sM a t e r a iu xe td uG e n e i P h y s q iu e .B P4 6 .3 8 0 4 2S a n it M a r t i nd H 'e r e s ,F r a n c e . h t t p : / w w w . i n p g . f r / L M G Pa n dh t p p : w / w w c .c p1 4 . a c . u k / t u t o r i a l / l m g p / .  2 0 9  POLY-2,2  Chapter 6  TETRAIRON(II).  ':6',2"-TERPYRIDINEOCTAKIS(IMIDAZOLATO)-  A  VERY  SOFT  2-D  MOLECULE-BASED  MAGNET  6.1  N IT R O D U C T O IN  The r e m a r k a b e l i n f l u e n c e of 2 , 2 'b i p y r i d i n e on the s t r u c t u r e s of the i r o n ( I I ) and c o b a l t ( I ) i m i d a z o l a t e p o y lm e r s was  d e s c r b ie d in the p r e v o iu s c h a p t e r . The  e f f e c t of  t h e i r s t r u c t u r a l d m i e n s o in a t i ly on the p h y s i c a l and m a g n e c t i p r o p e r t e is of t h e s e 2-D p o y lm e r s , e n c o u r a g e d the i n v e s t i g a t i o n of s i m i l a r s y s t e m s utilizing a d i f f e r e n t n e u t r a l m u l t i d e n t a t e l i g a n d , n a m e y l 2 , 2 : '6 , '2 " t e r p y r i d i n e ( t e r p y ) . It was v i r t u e of the  e x p e c t e d t h a t , by  t r i d e n t a t e m e r i d i o n a l c o o r d n ia t o in m o d e of t e r p y , the c o n s d ie r a b e l  g e o m e t r c i d e m a n d s of t h i s l i g a n d m g ih t i n f l u e n c e the i m i d a z o l a t ep o y lm e r s , in a s i m i l a r way  s t r u c t u r e of t r a n s i t i o n m e t a l  to the b i p yl i g a n d ,y i e l d i n gf u r t h e re x a m p e ls of  i n t e r e s t i n gt w o d m i e n s o in a le x t e n d e ds y s t e m s .  The  title c o m p o u n d , [Fe4(imid)g(terpy)], was x  s y n t h e s z ie d by the r e a c t i o n of  f e r r o c e n e w i t h i m i d a z o l e in the p r e s e n c e of t e r p y r i d i n e in a s e a e ld t u b e at e e lv a t e d t e m p e r a t u r e s . T h i sp o y lm e r has a n o v e l 2-D ray  e x t e n d e ds t r u c t u r e , as d e t e r m n ie d by an X-  c r y s t a o lg r a p h y s t u d y , in w h c ih w r i n k l e d s h e e t s of f o u r c o o r d i n a t e (two u n q iu e  c e n t e r s of t h i s t y p e ) , f i v e c o o r d i n a t e and  210  s i x c o o r d i n a t e i r o n ( I I ) o in s are l i n k e d by  s i n g l eb r i d g i n gi m i d a z o l a t e s . T h ep r e s e n c eo ft h ef o u ru n q iu ei r o ns i t e s is c o n f r im e db y M o s s b a u e rs p e c t r o s c o p y .  D C m a g n e c t i s u s c e p t i b i l t ym e a s u r e m e n s t r e v e a l a n t f i e r r o m a g n e t c i i n t e r a c t i o n s  b e t w e e nm e t a lc e n t e r sa b o v ea b o u t 1 2K ,a n dt h eo n s e to fa t r a n s i t i o nt oaf e r r o m a  s t a t e b e o lw t h i s t e m p e r a t u r e . L o n g r a n g e f e r r o m a g n e t c i o r d e r n ig b e o lw T = 6 . 5 K is c  c o n f r im e db yA Cm a g n e c t i s u s c e p t i b i l i t y ,z e r o f i e l d c o o l e dm a g n e t z ia t o in a n d  M o s s b a u e r s t u d i e s . A v e r y u n q iu e h y s t e r e s s i l o o p , d e t e r m n ie d b y field-depe m a g n e t z ia t o in s t u d i e s ,s h o wt h em a t e r i a lt ob eav e r ys o f tm o e lc u e lb a s e dm a g n e t .  6 . 2  R E S U L T SA N DD S IC U S S O IN  6 . 2 . 1S Y N T H E S S I A N DP H Y S C IA LP R O P E R T E IS  D e t a i l s o f t h e s y n t h e s s i o f [Fe4(imid)g(terpy)] a r e d e s c r b ie d in C h a p t e r 9 , x  s e c t o in 9 . 2 . 1 . 4 . F e r r o c e n e , i m i d a z o l e a n d t e r p y r i d i n e w e r e s e a e ld u n d e r v a c u u m in a  C a r u is t u b e a n d t h e m x it u r e w a s h e a t e d . T h e d e s r ie d c o m p o u n d w a s i s o l a t e d a s g c r y s t a l ss u i t a b l ef o rX r a yc r y s t a l o g r a p h y .  [Fe4(imid)8(terpy)] a p p e a r e d t o b e m o s it u r e s e n s i t i v e b u t c o u d l b e h a n d e ld x  b r i e f l y u n d e r n o r m a l a t m o s p h e r c i c o n d i t i o n s . P o w d e r e d s a m p e ls o f t h i s c o m p o u n d  w o u d l t u r nr e du p o n e x p o s u r et o a i rf o ra r o u n d aw e e k . T h e c o m p o u n d is i n s o l u b  2 1 1  c o m m o n o r g a n c i s o l v e n t s . T h eT G Ap l o t o b t a n ie d f o r [Fe (imid)8(terpy)] ( F i g u r e6 . 1 ) 4  x  s h o w st h et h e r m a lr o b u s t n e s so ft h i sc o m p o u n d . T h e r e is n oa p p a r e n td e c o m p o s t o in o f  100  200  300  400  500  600  700  800  T(°C)  F g iu r e6 . 1  T G Ap l o to f [Fe4(imid)g(terpy)] . x  t h i sp o y lm e ru n t i l at e m p e r a t u r eo f2 7 0 ° C is r e a c h e d .Ad e c r e a s e in w e g ih t is o b s e r v  b e t w e e n 2 7 0 ° C a n d 6 3 0 °C, w i t h ~ 6 9 % o ft h e initial w e g ih t l o s t a t t h e h g i t e m p e r a t u r e . T h et h e r m a ld e c o m p o s t o in b e h a v o ir s h o w nb y [Fe (imid)8(terpy)] is v e r y 4  s i m i l a rt ot h a te x h i b i t e db y [Fe2(imid)6(bipy)] ( C h a p t e r5 ,s e c t o in 5 . 2 . 1 . 1 . ) x  2 1 2  x  6 . 2 . 2 X R A YD F IF R A C T O INS T U D E IS  S i n g l ec r y s t a lX r a yd i f f r a c t i o ns t u d e is r e v e a l [Fe4(imid)8(terpy)] t ob ec o m p r s ie d x  o f d i s t o r t e d t e t r a h e d r a l ( t w o u n q iu e c h r o m o p h o r e s o f t h i s t y p e ) , d i s t o r t e d t r i g o n a l b p iy r a m d ia la n dd i s t o r t e do c t a h e d r a li r o n ( I I )o in sl i n k e db ys i n g l eb r i d g i n gm i d ia z o a lt e s ( F i g u r e 6 . 2 ) , f o r m n ig a n o v e l 2 D e x t e n d e d s t r u c t u r e r e s e m b n i lg w r i n k l e d s h e e t s ( F i g u r e s 6 . 3 , 6 . 4 a n d 6 . 5 ) . C r y s t a l o g r a p h i c d a t a , a t o m c o o r d n ia t e s , s e e lc t e d b o n d e ln g t h sa n da n g e ls a p p e a r in A p p e n d x i I ,T a b e ls I 1 0a n d1 1 1 .  T h es i x c o o r d i n a t e dm e t a l c e n t e r sa r ec o o r d n ia t e db yb r i d g i n gi m i d a z o l a t eg i la n d s  a n d t e r p y g i la n d s ( F i g u r e 6 . 2 ) t h a t o c c u p y p o s i t i o n s b e t w e e n t h e s h e e t s , i s o l a t i n g t h e  s h e e t s f r o m e a c h o t h e r , a s c a n b e s e e n in F g iu r e 6 . 3 . T h i s c a p p n ig o fi r o n c e n t r  t e r p yc o n t r o s l t h ed i m e n s i o n a l i t y , r e s u l t i n g in a 2 D p o y lm e r( F i g u r e 6 . 3 ) , in a m a n n  s i m i l a r t o t h a t o b s e r v e d in [Fe2(imid)6(bipy)]. A n i r o n i o n c o n n e c t i v i t y p i c t u r e o fa x  s e c t o in o ft h es t r u c t u r eo f [Fe4(imid)g(terpy)] is g v ie n in F g iu r e6 . 5 . x  T h e u s e o f t e r p y t o i n f l u e n c e t h e s t r u c t u r a l d m i e n s o in a t i ly h a s b e e n r e p o r t e d  r e c e n t l y f o r h y b r i d m e t a l o x d ie s e x t e n d e d s y s t e m s [ 1 ] . H o w e v e r , n o r e p o r t s o n t h p r e s e n c e o ft h r e e d i f f e r e n t i r o n ( I I ) c h r o m o p h o r e g e o m e t r e is in t h e s a m e c o o r d n ia t o in c o m p o u n d ,w e r ef o u n d in t h el i t e r a t u r e .  2 1 3  F g iu r e6 . 2 R e p e a t u n i to f [Fe4(imid)g(terpy)] s h o w n ig t h e a o tm n u m b e r n ig x  s c h e m e ;3 3 %p r o b a b i l t yt h e r m a le li p s o i d sa r es h o w n .  2 1 4  F g iu r e6 . 3  V e iw o fa s e c t o in o f [Fe4(imid)8(terpy)] l o o k i n gd o w nt h eaa x i s . x  T e r p yg i la n d s a n d C 4 a n d C 5 o fi m i d a z o l a t eg i la n d sh a v eb e e no m t ie d in t h eb o t o v e iw f o r clarity. H y d r o g e na o tm sa r en o ts h o w n .  2 1 5  F g iu r e6 . 4  V e iw o fa s e c t o i no f [Fe4(imid)g(terpy)] l o o k i n gd o w nt h eba x i s . x  F o r clarity, t e r p yg i la n d sa n dC 4a n dC 5o fi m i d a z o l a t eg i la n d sh a v eb e e no m t ie d in t h eb o t o mv i e w .H y d r o g e na o tm sa r en o ts h o w n . 2 1 6  F g iu r e 6.5  I r o n i o n c o n n e c t i v i t y d a ig r a m f o r  a s e c t o in o f  [Fe4(imid)g(terpy)] .F o u r c o o r d n ia t e o in s( g r e e n a n d p i n k / b l a c k elipsoids), s i x x  c o o r d n ia t eo in s( b l u ee li p s o i d s )a n df i v e c o o r d i n a t eo in s( r e d elipsoids). 217  6 . 2 . 3 M O S S B A U E RS P E C T R O S C O P Y  T h e r o o m t e m p e r a t u r e ( 2 9 3 K ) M o s s b a u e r s p e c t r u m o f [Fe4(imid)8(terpy)] x  s h o w s t h e e x p e c t e d n u m b e r o f l i n e s ( e i g h t ) c o r r e s p o n d n ig t o t h e o v e r a lp o f f o u r  q u a d r u p o e l d o u b e lt s [ 2 ] ( F i g u r e 6 . 6 ) . T h i s is c o n s s it e n t w i t h t h e X r a y s i n g l e c r y s t a l  d i f f r a c t i o n s t u d e is t h a t s h o w t h e r e a r e t w o u n q iu e t e t r a h e d r a l , o n e u n q iu e t r i g o n a l  p y r a m d ia la n do n eu n q iu eo c t a h e d r a li r o n site, all o fh te md i s t o r t e d , in t h ef r a m e w o r k t h i sc o m p o u n d( F i g u r e6 . 2 ) .  2 1 8  6.2.4  M A G N E T C I P R O P E R T E IS  DC  m a g n e c t i s u s c e p t i b i lt y and  p^f v e r s u s t e m p e r a t u r e (2 - 300  K) d a t a on  p o w d e r e d s a m p e ls of [Fe4(imid)g(terpy)] in an a p p l i e dm a g n e c t i field of 10 000 x  s h o w n in F i g u r e 6.7. U\B  at 300  K to 4.27  |IB  G are  As the t e m p e r a t u r e is l o w e r e d , the u«ff v a u le d e c r e a s e s f r o m 49 .6 at ~ 17 K. At a b o u t 16 K,  u«ff  n ic r e a s e s a b r u p t l y , r e a c h n ig a  m a x m iu m at a b o u t 7 K b e f o r e d e c r e a s n ig w i t h d e c r e a s n ig t e m p e r a t u r e in the o lw e s t t e m p e r a t u r e r e g i o n . The  b e h a v o ir e x h i b i t e d by % and  u«ff ( F i g u r e 6.7) s u g g e s t s  a n t f i e r r o m a g n e t c i e x c h a n g e b e t w e e n the m e t a l c e n t e r s in [Fe4(imid)8(terpy)] a b o v e a x  t e m p e r a t u r e of ~ 16 K, and a f e r r o m a g n e t c i t r a n s i t i o nb e o lw t h i st e m p e r a t u r e .  DC s u s c e p t i b i lt ys t u d e is w e r ea s lo p e r f o r m e d at 500  G for [Fe4(imid)g(terpy)]. x  The t r e n d of the % and u^f d a t av e r s u st e m p e r a t u r e (2 - 50 K) are s h o w n in F g iu r e 6.8. The r e s u l t s s h o w field d e p e n d e n c e at o lw  t e m p e r a t u r e s ,p a r t i c u l a r l yb e o lw ~ 12 K.  m a g n e c t i t r a n s i t i o n w h c ih is c l e a r l y s e e n in the o b t a n ie df r o m the 10 000  G d a t a( F i g u r e 6.7).  500  The  G d a t a is c o m p a r a b e l to t h a t  A n o t c ie a b e l d i f f e r e n c e is t h a t the o n s e t  t e m p e r a t u r e for the m a g n e c t i t r a n s i t i o n ( t e m p e r a t u r e at w h c ih % and j i ^ f fv a u le s s t a r t to n ic r e a s e ) a p p e a r s to be l o w e r , ~ 12 K, at the o lw e r field s t u d i e d . T h i s s i t u a t i o na r i s e s , p e r h a p s ,fromthe f a c t t h a t the m a g n e c t i t r a n s i t i o n o b s e r v e d in [Fe4(imid)g(terpy)] is x  not an a b r u p t one,  but r a t h e rag r a d u a l one.  s u s c e p t i b i lt ys t u d i e s .  219  T h e r e f o r e , it is not e a s i l yd e t e r m n ie d by  DC  60 .  0.8  ^  t  55 .  0.6 i  I  O  E E  V  A A A AA A A A A A A A A A A A A ,  5.0 1  4.5  =L  4.0  ®  0.2  © ©  3.5  V  0.0  -|  0  50  100  1  3.0 300  -  150  200  250  T(K)  F g iu r e 6.7  The AC  DC % and  peff  v e r s u s T at 10 000 G for [Fe4(imid)8(terpy)]„  a c t u a l critical t e m p e r a t u r e of [Fe4(imid)g(terpy)] was l a t e r c o n f r im e d by x  s u s c e p t i b i l t ym e a s u r e m e n t s , M o s s b a u e rs p e c t r o s c o p y and z e r o f i e l d c o o l e d  m a g n e t z ia t o in s t u d e is (vide infra).  220  j 22  - 20  18 16 pp.  14  u  12 10  <  - 8 6  %  i 0  10  15  20  25  30  35  40  45  2  50  T(K)  F g iu r e6 . 8  D Cxa n d u«ff v e r s u sTa t5 0 0Gf o r [Fe4(imid)8(terpy)]. x  A C m a g n e c t i s u s c e p t i b i l t y m e a s u r e m e n s t o n [Fe4(imid)8(terpy)] r e v e a e ld a x  f e r r o m a g n e t c i o r d e r n ig a tT =6 3 .5 K , w h c ih is d e t e r m n ie da st h e x' m a x m iu m( F i g u c  6 . 9 ) . T h e f a c t t h a t x" ( o u t o fp h a s e c o m p o n e n t ) is d i f f e r e n t f r o m z e r o a t T c o n f r im c  d e f i n i t i v e l y t h a t t h e r e is a n o n z e r o n e t m o m e n t g r o u n d s t a t e , a s w a s a s lo d e t e r m n ie f r o mt h em e d u im a n dh g i h field ( s t a t i c )D Cs u s c e p t i b i l t ys t u d e is m e n o t in e da b o v e .  221  4  6  10  8  12  14  16  T(K) F g iu r e6 . 9  A Cm a g n e c t i s u s c e p t i b i lt yf o r [Fe4(imid)g(terpy)] , HAC x  =  1 G,  f= 1 2 5 Hz.  T h e t e m p e r a t u r e o ft h e o n s e t o ft h e m a g n e c t i t r a n s i t i o n in [Fe4(imid)g(terpy)] x  w a s c o n f r im e d b y t h e t e m p e r a t u r e d e p e n d e n c e o f t h e f i e l d c o o l e d m a g n e t z ia t o in ( F C M ) , z e r o f i e l d c o o l e d m a g n e t z ia t o in ( Z F C M ) a n d r e m n a n t m a g n e t z ia t o in ( R E M )  s t u d e is ( F i g u r e6 . 1 0 ) .T h e FCM, m e a s u r e db yc o o l i n gt h es a m p e l u n d e raD C field o  G, s h o w sa ni n f l e c t i o na r o u n d7 . 5 K . A c c o r d n ig t ot h ed ( F C M ) d /T p l o tt h et e m p e r a t u  o f~ 7 K c a nb ec o n s d ie r e d asT ( F i g u r e6 . 1 0 ) . A s is t y p i c a ly o b s e r v e d ,t h e Z F C M c  222  F g iu r e6 . 1 0 P l o t s o fZ F C M , F C M a n d R E M f o r [ F e ( i m i d ) ( t e r p y ) ] . #DC = 4  8  x  5 0 G.  m e a s u r e db yc o o l i n gt h e s a m p e l in z e r o field, t h e nw a r m n ig u pu n d e raD C field  5 0 G , is o lw e rt h a nt h eF C M a t all t e m p e r a t u r e sb e o lw T [ 3 ] . T h eR E M , o b t a n ie d c  c o o l i n gt h es a m p e l in a 5 0 G field, t h e nw a r m n ig u p in z e r o field, v a n s ih e sa t~T a s is e x p e c t e d T h e s e r e s u l t s c o n f r im t h a t [Fe4(imid)8(terpy)] b e h a v e s a s a w e a k x  f e r r o m a g n e tb e o lw T = 7 K . T h i s T v a u l e is in c o ls ea g r e e m e n tw i t ht h a td e t e r m n i c  c  (T = 6 3 .5 K )e m p o ly n ig A Cs u s c e p t i b i l t ym e a s u r e m e n s t ( v i d es u p r a ) . c  223  A d d i t i o n a l e v d ie n c e for a f e r r o m a g n e t c i t r a n s i t i o n in [Fe (imid)8(terpy)] c o m e s 4  x  from m a g n e t z ia t o in v e r s u s DC a p p l i e d field p l o t s p e r f o r m e d at d i f f e r e n t t e m p e r a t u r e s ( F i g u r e 6 . 1 1 ) . At 20 K ( a b o v e T), the p l o t is l i n e a rfrom20 000 G to z e r o field and c  e x t r a p o a lt e s to z e r o m a g n e t z ia t o i n at z e r o a p p l i e d field. The p l o t s h o w s m u c h m o r e c u r v a t u r e at a t e m p e r a t u r en e a r T (10 K) and at t e m p e r a t u r e sb e o lw T (2 K and 4.8 K), c  c  the p l o t s are not l i n e a r and e x t r a p o a lt e to a n e g a t v ie m a g n e t z ia t o i n (not s h o w n in F g iu r e 6.11)  at z e r oa p p l i e d field (see f o l o w i n gd i s c u s s i o n ) .  14000  12000 i  o S  u  10000  s s  .2 «N •a*  CJ  S ex  10000  20000  30000  40000  50000  60000  Applied Field (G)  F i g u r e 6.11  P l o t of  m a g n e t z ia t o in v e r s u s a p p l i e d field at d i f f e r e n t  t e m p e r a t u r e s for [Fe4(imid)g(terpy)] . x  224  Ah y s t e r e s s i o lo p is p r o d u c e db yc y c l i n gt h ea p p l i e d field b e t w e e n+ 5 5 0 0 0a  5 5 0 0 0 G a t 4 . 8 K ( F i g u r e 6 . 1 2 ) , a s e x p e c t e d f o r a m a t e r i a l e x h i b i t i n g o ln g r a n f e r r o m a g n e t c i o r d e r i n g . F r o m t h i s h y s t e r e s s i l o o p , a c o e r c v ie field o f ~5 Ga n d  -300  -200  -100  0  100  200  300  Applied Field ( G )  F g iu r e6 1 .2 F i e l d d e p e n d e n c e o f m a g n e t z ia t o in a t 4 . 8 Kf o r [Fe4(imid)8(terpy)]. C e n t r a l p o r t i o n o fh y s t e r e s s i o lo p s h o w n . T h e d a t a o b t a n ie d o n x  d e c r e a s n ig t h e a p p l i e d field a r e s h o w n a s T w h i l et h ed a t ao b t a n ie d o nn ic r e a s n ig a p p l i e d filed a r es h o w na s A. 225  r e m n a n t m a g n e t z ia t o in o f4 0 c m G m o l " , a r e o b t a i n e d . A m a g n e t is s a i d t o b e s o f t 3  1  h a r da c c o r d n ig t ow h e t h e rt h ec o e r c v ie field is s m a lo rl a r g e[ 3 ] . T h ev e r yo lw v a u l t h e c o e r c v ie field c l a s s i f i e s [Fe (imid)8(terpy)] a s a v e r y s o f tm o e lc u e lb a s e d m a g n e t . 4  x  I n a n o r m a l h y s t e r e s s i o lo p (i.e., s e e C h a p t e r 5 , s e c t o in 5 . 2 . 2 . 3 ) t h e d o w n f i e l d m a g n e t z ia t o in d a t a a p p r o a c h n ig z e r o a p p l i e d field a r e p o s i t i v e , w h i l e t h e u p f i e l d m a g n e t z ia t o in v a u le s a r e n e g a t v ie c o ls e t o z e r o a p p l i e d field. F o r [ F e ( i m i d ) g ( t e r p y ) ] , 4  x  h o w e v e r , q u i t e d i f f e r e n t b e h a v o i r is o b s e r v e d . T h e d o w n f i e l d m a g n e t z ia t o in d a t a  a c t u a l yc r o s st h ez e r o field l i n ea tn e g a t v ie m a g n e t z ia t o in v a u le sw h i l et h eu p f i e l dd a c r o s st h ez e r o field l i n ea tp o s i t i v em a g n e t z ia t o in v a l u e s . T h i sr e s u l t s in a " c r o s s i n g "  t h ed o w n f i e l da n du p f i e l dm a g n e t z ia t o i n lines, g e n e r a t n ig a r a r em a g n e t z ia t o in o lo p in  t h e c e n t r a l p a r t o ft h ep l o t ( F i g u r e 6 . 1 2 ) . C o n f r im a t o in o ft h i s d i s t i n c t i v eb e h a v o ir w a s  o b t a n ie d in a s e p a r a t e e x p e r m i e n t in w h c ih t h e a p p l i e d field w a sc y c e ld ( 5 50 0 0 + 5 5 0 0 0 ) t h r e e t m i e s a t 4 . 8 K . T h e r e s u l t s o f t h i s s t u d y , s h o w n in F g iu r e  c o n f r im e dt h a tt h i su n q iu em a g n e t z ia t o in o lo p is r e a l a n dr e p r o d u c i b l e , s n ic e it a p p e a r s  in t h e s a m e r e g i o n in e v e r yo n e o ft h e c y c e ls c a r r i e d o u t , a n d c a n n o tb e " r e m o v e r e p e a t e d y l o s c i la t i n gt h ea p p l i e d field.  A p o s s b ie l e x p a ln a t o in f o r t h e d i s t i n c t i v e m a g n e t z ia t o in o lo p  o f  [Fe4(imid)8(terpy)] is t h e f o lo w i n g . T h e r e a r e f o u ru n q iu e i r o n c h r o m o p h o r e s in t h i s x  c o m p o u n d ,w h c ih c a nb ei d e n t i f i e da c c o r d n ig y l t ot h e i rc o o r d n ia t o in n u m b e ra s4 , 4', 5  226  Applied Field (G)  F g iu r e 61 .3  Field d e p e n d e n c e of  m a g n e t z ia t o i n at  4.8  K  for  [Fe (imid) (terpy)] .C e n t r a lp o r t i o n of h y s t e r e s s i o lo ps h o w n . 4  and 6. The  8  x  s i z e of the m a g n e c t i d i p o l e on e a c h s i t e will be d i f f e r e n t . For the s a k e of  d s ic u s s o i n we a s s u m e the d i p o l e on s i t e 5 is s i g n i f i c a n t l ys m a e lr t h a nt h o s e on the o t h e r t h r e e s i t e s w h i c h , in t u r n are a p p r o x m i a t e y l the  s a m e . A s s u m n ig a n t f i e r r o m a g n e t c i  c o u p l i n g , the c o n n e c t i v i t i e s r e q u i r e the s p n i s in 4 and 4' to be p a r a le l to e a c h o t h e r , w i t h the 5 and 6 s i t es p n is a n t i p a r a le l to t h e s e as f o lo w s : 227  T h i sa r r a n g e m e n tw o u d l g i v ean e ts p i n T. W en o ws p e c u a lt et h a ta st h ep o s i t i v e  is r e d u c e dt o z e r o all o ft h e s p n is r a n d o m z ie ( a s e x p e c t e d in a m a t e r i a lw h c ih is  " m a g n e t " ) e x c e p t f o r t h e s p i n o n 5 , w h c ih r e t a i n s a Xp r e f e r e n c e ( c a u s e d b y s o l  r e l a x a t i o n ) . T h i s w o u d l g i v e an e g a t v ie M a t H =0 . A s H is n ic r e a s e d in t h en e g a t v i  d i r e c t i o n H (-1) t h e s p n is o n all s i t e s o r i e n t w i t h t h e r e v e r s e d i r e c t i o n t o t h a t s h o  a b o v e , g i v i n g a n e t s p i n i. T h e n , r e d u c n ig t h e n e g a t v ie H ( 1 ) t o z e r o all s p n i  r a n d o m z ie e x c e p tf o rt h es p i no n5 ,w h c ih r e t a i n st h eTp r e f e r e n c e( s o lw r e l a x i n g ) .T s i t u a t i o ng v ie sap o s i t i v eM a tH=0 .  S u p p o r t f o rt h e s p e c u a lt o in a b o v e c o m e s f r o m M o s s b a u e r s t u d i e s . P r e l i m i n a r y  r e s u l t s s u g g e s t t h a t o n e o ft h e s i t e s u n d e r g o e s m a g n e c t i h y p e r f n ie s p l i t t i n g o w n ig t o s o lw p a r a m a g n e c t i r e l a x a t i o n( n o to r d e r i n g ) in t h ed e c r e a s n ig t e m p e r a t u r er a n g e 77 t o7 K .B e o lw t h el a t t e rt e m p e r a t u r e all f o u rs i t e sa r eh y p e r f n i e split.  T h em a g n e c t i p r o p e r t e is o f [Fe4(imid)g(terpy)] a r eq u i t ed i f f e r e n tf r o mt h o s eo f x  t h e o t h e rm o e lc u e lb a s e d m a g n e s t d e s c r b ie d in t h i s t h e s i s .W h e l i t h e p r m i a r y  228  m e c h a n s im o fe x c h a n g e is a n t i f e r r o m a g n e t i c , a s in t h e o t h e r s y s t e m s , in t h i s c a s e t h e  a n o m a o lu s m a g n e c t i b e h a v o ir l e a d i n g t o ap h a s e t r a n s i t i o nb e o lw 7 K a p p e a r s t o a r i s  from t h ec o u p n i lg o fd i p o l e so fd i f f e r e n ts t r e n g t h s ,af o r mo ff e r r m i a g n e t s im .M o r e o  r a t h e r t h a n o ln g r a n g e o r d e r n ig o f all s p n is s i t e s b e o lw T, t h r e e o ft h e s i t e s u n d e r g c  r a p i dr e l a x a t i o nw i t ht h ef o u r t hr e t a i n i n go r i e n t a t i o n in t h e field t h u sg e n e r a t n ig t h en  m a g n e t z ia t o in a tz e r o a p p l i e d field. I t is h o p e dt h a tm o r ed e t a i l e d s t u d ya n da n a y ls s i  t h eM o s s b a u e rs p e c t r ao ft h i sm a t e r i a l ( c u r r e n t l yo n g o n ig ) will p e r m t i u st oi d e n t i f yt h e  s o lw r e l a x i n g s i t e a n d t h e r e b yr e m o v e s o m e o ft h es p e c u a lt o in s u r r o u n d n ig t h eu n q iu e m a g n e c t i b e h a v o ir o ft h i sm a t e r i a l .  6 . 3  S U M M A R YA N DC O N C L U S O IN S  T h e r e a c t i o n o ff e r r o c e n e w i t h m o t l e n i m i d a z o l e a n d t e r p y r i d i n e y i e l d s g r e e n c r y s t a l s o f c o m p o s t i o n [Fe4(imid)8(terpy)]. T h e s t r u c t u r e o f t h i s m a t e r i a l h a s b e e n x  d e t e r m n ie db y s i n g l e c r y s t a l X r a yd i f f r a c t i o n s t u d e is a n d is s h o w nt o c o n s s it o fn o v  2 D w r i n k l e d s h e e t s f o r m e d b y f o u r c o o r d i n a t e ( t w o u n q iu e o in s o ft h i s t y p e ) , fivec o o r d n ia t e a n d s i x c o o r d i n a t e i r o n ( I I ) o in s l i n k e db y s i n g l eb r i d g i n g i m i d a z o l a t e s . T h e s i x c o o r d i n a t e m e t a l o in s a r e a d d i t i o n a l y c o o r d n ia t e d b y t e r p y r i d i n e g i la n d s t h a t  o c c u p yp o s i t i o n sb e t w e e nt h es h e e t s , i s o l a t i n gt h es h e e t sfrome a c ho t h e r . T h ep r e s e n c e o ff o u ru n q iu e i r o n s i t e s in [Fe4(imid)g(terpy)] w a s c o n f r im e d b y M o s s b a u e r x  s p e c t r o s c o p y .  229  I nt h ef o r m a t o in o ft h i su n q iu e2 Di r o n ( I I )i m i d a z o l a t ep o y lm e r ,s o m ed e g r e eo  s t r u c t u r a l c o n t r o l h a s b e e n n it r o d u c e d b y t h e t r i d e n t a t e l i g a n d , t e r p y , w h c ih o c c u p e is  c o o r d n ia t o in s i t e s o n t h e m e t a l o in s a n d p r o v d ie s s t e r i c c o n s t r a i n s , t h u s p r e v e n t n ig s p a t i a le x t e n s o in o ft h ep o y lm e r c i s t r u c t u r et ot h r e e d m i e n s o in s .  D C m a g n e c t i s u s c e p t i b i lt ym e a s u r e m e n s t r e v e a l a n t f i e r r o m a g n e t c i i n t e r a c t i o n s  b e t w e e n m e t a l c e n t e r s a b o v e a t e m p e r a t u r e o f~ 1 2 K a n d t h e o n s e t o fo ln g r a f e r r o m a g n e t c i o r d e r n ig b e o lw t h i s t e m p e r a t u r e . A t r a n s i t i o n t o a f e r r o m a g n e t c i s t a t e  b e o lw t h e s et e m p e r a t u r e s w a s s e e n in b o t h D C a n dA C s u s c e p t i b i lt i e s a n d zero-field c o o e ld m a g n e t z ia t o in s t u d i e s . T h e critical t e m p e r a t u r e , T ~ 6 . 5 K , f o r t h e m a g n e c t i c  t r a n s i t i o nw a sd e t e r m n ie df r o mt h e s el a t t e rs t u d i e s .  [Fe4(imid)g(terpy)] r e p r e s e n t s a n o t h e r r a r e e x a m p e l o f a 2 D c o o r d n ia t o in x  p o y lm e re x h i b i t i n gw e a kf e r r o m a g n e t s im a to lw t e m p e r a t u r e s . T h ec o m p o u n d s h o w sa  u n q iu e n e g a t v ie h y s t e r e s s i o lo p a n d s p e c u a lt o in t o a c c o u n t f o r t h i s p o n it s t o t h e p o s s i b i l i t y o f a f o r m o f f e r r o m a g n e t c i c o u p n i lg c o m b n ie d w i t h s o lw p a r a m a g n e c t i  r e l a x a t i o n a t o lw t e m p e r a t u r e s o f o n e o f t h e f o u r u n q iu e m e t a l c e n t e r s . A d d i t i o n a l  i n s i g h t s i n t o t h i s m a t e r a r e e x p e c t e d f r o m o n g o n ig M o s s b a u e r s t u d i e s . R e g a r d e ls s o f  t h em e c h a n s im ,t h i sm a t e r i a l d o e se x h i b i tn e tm a g n e t z ia t o in a tz e r o a p p l i e d field (MOT  =4 0c m G m o ) rc l a s s i f y i n g it a saw e a km o e lc u e lb a s e dm a g n e t . I t sc o e r c v ie field o 3  I  5Gc l a s s i f i e s it a sav e r ys o f tm a g n e t .  230  R e f e r e n c e s  1 .  P.J. H a g r m a na n d J. Z u b i e t a . Inorg. Chem. 39, 5 2 1 8( 2 0 0 0 ) .  2 .  N. G r e e n w o o d , T. C. G i b b . M o s s b a u e r S p e c t r o s c o p y , C h a p m a n a n d Hall Ltd. L o n d o n , 1 9 7 1 .  3  O .K a h n . Acc. Chem. Res. 33 ( 1 0 )6 4 7( 2 0 0 0 ) .  231  POLYBIS(l-METHYL-2-THIOIMIDAZOLATO)IRON(II).  Chapter 7  DIMENSIONAL  MATERIAL  MAGNETIC  7.1  A  EXHIBITING  ONE-  LONG-RANGE  ORDERING  N IT R O D U C T O IN  As d e s c r b ie d b e f o r e , m e t a l p o y lm e r s f o r m e d w i t h b r i d g i n g i m i d a z o l a t e g i la n d s are u s u a l y of h i g h d m i e n s o in a t i ly (2-D  or 3-D)  as a r e s u l t of the 1 , 3 p o s i t i o n i n g of the  N d o n o ra o tm s of the i m i d a z o l a t em o i e t y , w h c ih a o lw s the f o r m a t o i n of s i n g l eb r d ig e s b e t w e e n m e t a l c e n t e r s . H o w e v e r , w i t h the  N-l  p o s i t i o n b o lc k e d w i t h a m e t h y l  s u b s t i t u e n t , as it is in the c a s e for the l i g a n dp r e c u r s o r l m e m y l 2 t h i o l i m i d a z o l e( 1 M e 2 S H i m i d ) , d e p r o t o n a t o i n of the thiol f u n c t i o n a l i t yw o u d l g e n e r a t e ab r i d g i n gl i g a n d , 1M e 2 S i m i d , c a p a b e l of f o r m n ig d o u b e l b r d ig e s b e t w e e n Fe(U) p o y lm e r [1]. the  c e n t e r s in a rod like  P r e v o iu s s t u d e is had r e v e a e ld t h i st y p e of b o n d n ig m o d e for t h i sl i g a n d in  d m i e r c i m o e lc u e ls [ M e G a ( l M e 2 S i m i d ) ] and [Mo(Ti-CH)(CO)(l-Me-2-S3  2  2  3  5  2  imid)] [2]. 2  The  r o d l i k e 1-D  s t r u c t u r a l m o t i f was  o b s e r v e d in the m a t e r i a l c h a r a c t e r z ie d  h e r e , [Fe(l-Me-2-S-imid) 0.5Cp Fe] .I n t e r e s t i n g l y , the 2  2  x  232  p h e n o m e n o n of o ln g r a n g e  f e r r o m a g n e t c i o r d e r n ig b e o lw a critical t e m p e r a t u r e ,p r e v i o u s l ys e e no n y l in 1 , 3 d i a z o l a t e  c o m p e lx e sw i t h2 Da n d 3-D e x t e n d e dl a t t i c e s( C h a p t e r s 3, 4, 5 a n d 6), is o b s e r v e d in u n q iu eF e ( I I )c o o r d n ia t o in p o y lm e r .  A n a r t i c l e c o n t a n in ig m o s t o f t h e r e s u l t s d s ic u s s e d in t h i s c h a p t e r h a s b e e n p u b s i lh e d [1].  7 . 2  R E S U L T SA N DD S IC U S S O IN  7 . 2 . 1S Y N T H E S S I, P H Y S C IA LA N DT H E R M A LP R O P E R T E IS  D e t a i l s o f t h e s y n t h e s s i o f [Fe(l-Me-2-S-imid)2-0.5Cp2Fe] a r e d e s c r b ie d in x  C h a p t e r 9, s e c t o i n 9.2.1.5. F o l o w i n gt h es u c c e s so ft h ep r e v i o u s l yr e p o r t e dr e a c t o in so f e r r o c e n e w i t h i m i d a z o l e a n d 2 m e t h y l i m i d a z o l e , w h c ih g e n e r a t e c r y s t a li n e p o y lm e r s  [3, 4], t h e s y n t h e t c i m e h to d i n v o l v i n g f e r r o c e n e a n d t h e m o t l e n l i g a n d p r e c u r s o r w a s utilized h e r e .T h ed e s r ie dc o m p o u n dw a si s o l a t e da sg o d le nn e e d l e l i k ec r y s t a l s .  [Fe(l-Me-2-S-imid)-0.5Cp2Fe] a p p e a r e d t o b e fairly a i r s t a b l e a n d c o u d l b e 2  x  h a n d e ld b r i e f l y u n d e r n o r m a l a t m o s p h e r c i c o n d i t i o n s . T h e c o m p o u n d is i n s o l u b l e in  c o m m o n o r g a n c i s o v le n t s a n dw a t e r . T h e c o m p e lx is n o n v o l a t i l e . T h e r m a l g r a v i m e t r i c  a n a y ls s i (35 ° C t o 8 0 0 °C) m e a s u r e m e n s t w e r e m a d e a n d t h e T G A p l o t is s h o w n  F g iu r e 7 . 1 . T h e s e r e s u l t s s h o w t h e c o m p e lx t o b e t h e r m a y l s t a b l e t o1 9 7 °C  D e c o m p o s t o in w i t h c o n t n iu o u s w e g ih t l o s s o c c u r sfrom1 9 7 t o 8 0 0° C w i t h at o  233  200  400  800  600  T e m p e r a t u r e(° C ),  F i g u r e7 . 1  T G Ap l o tf o r [Fe(l -Me-2-S-imid) 0.5Cp Fe] 2  2  x  w e g ih tl o s so f6 9 %o ft h e initial m a s s .T h i sc o m p a r e sf a v o r a b l yt oa6 5 %l o s st h a t o c c u r if o n y l F e Sr e m a n is a t8 0 0 °C.  234  7.2.2  X R A YC R Y S T A L L O G R A P H Y  The s t r u c t u r e of a s e c t o i n of the p o y lm e rc h a n i is s h o w n in F i g u r e 7.2, and a v e iw of the  lattice, a m l o s tp a r a le l to the  p o y lm e rc h a i n , is d e p c it e d in F g iu r e 7.3.  C r y s t a l o g r a p h i c d a t a , a t o m c o o r d n i a t e s , s e e lc t e d b o n d e ln g t h s and a n g e ls a p p e a r in A p p e n d x i I, T a b e ls 1-12 and 1-13.  The s t r u c t u r ec o n s s it s of c h a n i s of d i s t o r t e dt e t r a h e d r a l  i r o n ( I I ) o in s d o u b e lb r d ig e d by the l m e m y l 2 t h i o i m i d a z o l a t e l i g a n d s , g i v i n g r i s e to e g ih t m e m b e r e dr i n g sl i n k e d by the Fe o in s in a p s e u d o s p r io c o n f o r m a t o in ( F i g u r e 7.2). The g i la n d s b i n d t h r o u g h the u n s u b s t i u t e d n i t r o g e n (N2 in F i g u r e 7.2)  and the s u l f u r  a o tm s and o r i e n t a o ln g the c h a n i in a m a n n e r t h a t e la d s to d i s t i n c t i v e FeN4 and FeS4 c h r o m o p h o r e sw h c ih a l t e r n a t et h r o u g h o u t the p o y lm e rc h a i n s .  T h e s e s t r u c t u r a l c h a r a c t e r i s t i c s p r o d u c e a r o d l i k e s h a p e to the p o y lm e r c i c h a n i ( F i g u r e 7.3 ). The F e ( 2 ) Nb o n d d s it a n c e s are s i g n i f i c a n t l ys h o r t e r at 2 0 .5 4At h a n the Fe(l)-S b o n d s at 2 3 .6 8 A. The S-Fe(l)-S b o n d a n g e ls are c o ls e to t e t r a h e d r a l ,r a n g n ig f r o m 1 0 8 . 3 2 ° to 110.05°, w h i l e the N F e ( 2 ) N a n g e ls arefartherf r o m t e t r a h e d r a l r a n g n ig f r o m 1 0 4 . 9 1 ° to 119.05°. M o e lc u e ls of f e r r o c e n e , one for e v e r y two r e p e a t n ig u n i t s in the c h a i n , are t r a p p e db e t w e e n the p o y lm e rc h a n is ( F i g u r e 7.3).  T h e s em o e lc u e ls  c a n n o t be r e m o v e d by t h e r m o y ls s i w t i h o u t d e c o m p o s t o in of the p o y lm e r (See F i g u r e 7.1).  235  F i g u r e 7.2  M o e lc u a lr s t r u c t u r e of the p o y lm e rc h a n i of [Fe( 1 M e 2 S -  imid)2-0.5Cp2Fe] s h o w n ig the a t o mn u m b e r n ig s c h e m e ; 33 % p r o b a b i l t yt h e r m a l x  e li p s o i d s are s h o w n .( H y d r o g e na o tm s are o m i t t e d ) .  236  F g iu r e7 . 3 .  V e iw o ft h e c r y s t a l s t r u c t u r e o f [Fe(l-Me-2-S-imid)-0.5Cp2Fe] 2  d o w nt h e c axis. 5 0%t h e r m a le li p s o i d sa r es h o w n .  237  x  7 . 2 . 3 M A G N E T C I P R O P E R T E IS  T h e D C m a g n e c t i s u s c e p t i b i l i t i e s , %, a n d % T v e r s u s t e m p e r a t u r e , o n p o w d e r e d s a m p e ls o f [Fe(l-Me-2-S-imid)0.5Cp2Fe] in a n a p p l i e d m a g n e c t i field o f5 0 0 G, a r e 2  x  s h o w n in F i g u r e 7.4. A st h et e m p e r a t u r e is o lw e r e df r o m3 0 0K ,t h e% Tv a u le d e c  A ta b o u t8K ,% Tn ic r e a s e sa b r u p t l y ,r e a c h n ig a m a x m iu ma ta b o u t 5Kb e f o r ed e c r e w i t h d e c r e a s n ig t e m p e r a t u r e in t h e o lw e s t t e m p e r a t u r e r e g i o n . T h e b e h a v o ir s u g g e s t s  a n t f i e r r o m a g n e t c i e x c h a n g eb e t w e e nt h em e t a lc e n t e r sa b o v et h e critical t e m p e r a t u r e , T, c  o f5K ( t h i s t e m p e r a t u r e c o n f r im e db yA C s u s c e p t i b i lt ya n d M o s s b a u e rm e a s u r e m e n s t (vide infra)), a n daf e r r o m a g n e t c i t r a n s i t i o nb e o lw t h i st e m p e r a t u r e .  A C s u s c e p t i b i lt y m e a s u r e m e n s t i n d i c a t e t h e f e r r o m a g n e t c i o r d e r n ig a tT = c  5K , w h c ih is d e t e r m n ie d a s t h e a v e r a g e t e m p e r a t u r eb e t w e e n t h e %' p l o t m a x m iu m  5.20 K a n dt h e %" p l o tm a x m iu ma t4 . 8 5K[ 3 ] ( F i g u r e 7.5). T h ef a c tt h a t /" ( o u to f  o rm i a g n ia r yc o m p o n e n t ) is d i f f e r e n tfromz e r oa tT c o n f r im su n e q u v io c a y l t h a tt h e r e is c  a n o n z e r o n e t m o m e n t g r o u n d s t a t e . T h e r e f o r e , t h e n e a r z e r o field r e s u l t s r e v e a l  p r e s e n c e o f a o ln g r a n g e f e r r o m a g n e t c i o r d e r b e o lw T in c o n c o r d a n c e w i t h t h e D C c  s u s c e p t i b i lt ys t u d e is d s ic u s s e da b o v e .  238  ^  1.25  0.00  100  50  150  200  250  300  T e m p e r a t u r e( K )  F g iu r e7 . 4  D C% a n d yj  v e r s u st e m p e r a t u r ep l o t s a t5 0 0 G f o r  [Fe(l-Me-2-S-imid)2-0.5Cp2Fe] T h el i n e is f r o mt h e o r ya sd e s c r b ie d in t h et e x t . x  S u p p o r t f o ra f e r r o m a g n e t c i t r a n s i t i o n c o m e s f r o mm a g n e t z ia t o in v e r s u s a p p l i e d  field p l o t sa td i f f e r e n tt e m p e r a t u r e s( F i g u r e7 . 6 ) .A t 1 5 K( a b o v e T), t h ep l o t is l i n e a c  o v e r 2 0 0 0 0 G a n d e x t r a p o a lt e s t o z e r o m a g n e t z ia t o in a t z e r o a p p l i e dfield.A  t e m p e r a t u r e sb e o lw T, t h ep l o t sa r en o tl i n e a ra n de x t r a p o a lt et o yield n e tm a g n e t z ia t o i c  a tz e r oa p p l i e d field.  239  F g iu r e 7.5 H  AC  =  A C m a g n e c t i s u s c e p t i b i lt y f o r [Fe(l-Me-2-S-imid)0.5Cp2Fe], 2  x  1 G, f = 1 2 5H z .  C y c l i n gt h e a p p l i e d field b e t w e e n +55 0 0 0 a n d -55 0 0 0 G a t4 . 8 Kg e n e r a t e s h y s t e r e s s i o lo p( F i g u r e 7.7), a s e x p e c t e d f o ra m a t e r i a le x h i b i t i n g o ln g r a n g e  f e r r o m a g n e t c i o r d e r i n g .F r o mt h i sh y s t e r e s s i l o o p ,ac o e r c v ie field o f4 0Ga n dar e m m a g n e t z ia t o in o f1 9 0c m G mol" ,a r eo b t a i n e d . 3  1  240  4 0 0 0 A 3 5 0 0 A -r  3000 o  S  o -I  2 5 0 0  £ c  1 o  -I—I  o  a  "i  1 0 0 0 0  1  2 0 0 0 0  r  3 0 0 0 0 4 0 0 0 0  5 0 0 0 0 6 0 0 0 0  A p p e i ld M a g n e c t i F i e l d( G )  F g iu r e7 . 6  P l o to fm a g n e t z ia t o in v e r s u sa p p l i e d field a tt h r e et e m p e r a t u r e sf o r  [ F e ( 1 -Me-2-S-imid) 0.5Cp Fe] . 2  2  x  241  4 0 0 3 0 0 2 0 0 1 0 0  0  1 0 0  2 0 0  3 0 04 0 0  A p p e i ld M a g n e c t i F i e l d( G )  F g iu r e7 . 7  Field d e p e n d e n c e o f m a g n e t z ia t o in a t 4 . 8 K f o r [ F e ( l M e 2 S -  imid)2-0.5Cp2Fe]. C e n t r a lp o r t i o no fh y s t e r e s s i o lo ps h o w n . x  M a g n e t c i s u s c e p t i b i lt i e s w e r e m e a s u r e d a s a f u n c t i o n o ft e m p e r a t u r e a t 1 0 0 0 0  a n d5 00 0 0Ga sw e l a sa t5 0 0G( F i g u r e7 . 8 ) .T h er e s u l t ss h o w field d e p e n d e n c  t e m p e r a t u r e s ,p a r t i c u l a r l yb e o lw T. T h em a g n e c t i t r a n s i t i o nw h c ih is c l e a r l ys e e n in t h e c  242  5 0 0Gd a t a is m u c hl e s sp r o n o u n c e d in t h e 1 00 0 0Gd a t aa n d is a b s e n ta t5 0 f e r r o m a g n e t c i o r d e r n i g is c l e a r l yr e p r e s s e db yl a r g ea p p l i e d fields.  T e m p e r a t u r e( K )  F i g u r e7 . 8  P l o t o f% T v e r s u s t e m p e r a t u r e a t t h r e ev a u le s o fa p p l i e d field f o r  [ F e ( 1 -Me-2-S-imid) 0.5Cp Fe] . 2  2  x  243  T h em a g n e c t i p r o p e r t e is o f[ F e ( l M e 2 S i m i d ) 0 . 5 C p F e ]p a r a le lc l o s e l yt h o s e 2  o f [Fe(imid)(imidH)]x 3  6  2  [4],  2  x  [ F e ( 4 i m i d a z o l a c e t a t e ) ] [5], a n d 2 x  [ F e ( 2 M e -  imid) 0.13Cp Fe] [ 6 ] ,c o m p o u n d sf o rw h c ih t h ep r m i a r ye x c h a n g ep r o c e s s is c o n s d ie r e d 2  2  x  t o i n v o l v e a n t f i e r r o m a g n e t c i c o u p n i lg b e t w e e n i r o n c e n t e r s w i t h a c a n t n ig o fs p i n s . A  s p n ic a n t e ds t r u c t u r ef o rt h ec o m p o u n ds t u d e id h e r e is a s lo s u p p o r t e db yt h ef a c tt h a t  h g ih e s tm a g n e t z ia t o in r e a c h e d ( 3 9 6 0 c mGm o l "a t2 K a n d 5 5 0 0 0 G ) is s i g n i f 3  1  s m a e lr t h a nt h et h e o r e t i c a ls a t u r a t i o nv a u le ( 2 2 3 0 0c mgm o l " ) [ 7 ] .A d d i t i o n a l s u p 3  1  f o rt h e c a n t e d s p i n s t r u c t u r e c o m e s f r o m s t r u c t u r a l d a t a . T h e s e s h o w a f e a t u r e  c h a r a c t e r i s t i c o fs u c h s y s t e m s , t h a t o fa s y s t e m a t c i a l t e r n a t i o n o ft h er e l a t i v eo r i e n t a t i o n  o fn e g ih b o r n ig m e t a lc h r o m o p h o r e s [ 4 ] .A s am e a s u r eo f this, t h ed i h e d r a la n g e l b e t w e t h e S(l)-Fe(l)-S(l)  c  a n d N(l)-Fe(2)-N(l) d  e  p a ln e s i s 27.6°. T h e r e f o r e ,  a n t f i e r r o m a g n e t c i c o u p n i lg b e t w e e nn e g ih b o r n ig m e t a l c e n t e r s a o ln gt h ec h a n i c a no c c u r  w i t h m i p e r f e c t a n t i p a r a le l a g i ln m e n t o fs p i n s , l e a d i n g t o r e s i d u a l s p n is o n t h e c h a i n F e r r o m a g n e t c i o r d e r n ig o f t h e r e s i d u a l s p n is g e n e r a t e s o ln g r a n g e t h r e e d m i e n s o in a l  m a g n e c t i o r d e r n ig a n ds p o n t a n e o u sm a g n e t z ia t o in a to lw t e m p e r a t u r e s .I ts h o u d l b en o t e d t h a t t h e c h a n i s in [ F e ( l M e 2 S i m i d ) 0 . 5 C p F e ]a r e i s o l a t e d ( F i g u r e 7 . 3 ) , a n d 2  2  x  t h e r e f o r e , a n y i n t e r c h a i n i n t e r a c t i o n c a n n o t b e m e d a it e d b y b o n d n ig i n t e r a c t i o n s . T h i s c o n t r a s t s w i t h t h e s i t u a t i o n f o r [Fe3(imid)6(imidH)] [ 4 ] a n d 2x  [ F e ( 2 M e -  i m i d ) 0 . 1 3 C p F e ] [ 6 ] w h e r e c o v a e ln t b o n d n ig i n t e r a c t i o n s c o n n e c t t h e p a r a m a g n e c t i 2  2  x  c e n t e r s in t h r e e d m i e n s o in s a n d f o r [ F e ( 4 i m i d a z o l a c e t a t e ) ] [5], w h e r e h y d r o g e n 2 x  b o n d n ig i n t e r a c t i o n sc o n n e c ts h e e t so fc o v a l e n t l yl i n k e dm e t a lc e n t e r s .  S u c h  c o n s d ie r a t o in s m a yp l a ya nm i p o r t a n tr o l e in d e t e r m n in ig t h em a g n t u id eo ft h ec o e r c v i  244  field in t h e s e s y s t e m s , a s [Fe(l-Me-2-S-imid)2-0.5Cp2Fe] e x h i b i t st h es m a e ls tc o e r c v ie x  field o ft h ef o u rc o m p o u n d sc o n s d ie r e dh e r e .  F u r t h e re v d ie n c e in s u p p o r to ft h ep r m i a r ya n t f i e r r o m a g n e t c i i n t r a c h a i nc o u p n i lg in [Fe(l-Me-2-S-imid)2-0.5Cp2Fe] c a n b e g a t h e r e d b y e x a m n in ig fits o ft h e m a g n e c t i x  s u s c e p t i b i lt y in t h e h i g h t e m p e r a t u r e r e g i o n t o t h e e x p r e s s o in d e r v ie d e m p o ly n ig a n i s o t r o p i cH a m t l i o n a in o ft h ef o r m H= -US1S2 f o ral i n e a rc h a n i o fa n t i f e r r o m a g n e t i c a l y c o u p e ld S - 2 c e n t e r s [8], a s w a s p r e v i o u s l y d o n e f o r [Fe(pz)2] ( C h a p t e r 2). T h a t x  e q u a t o i n is  w h e r e JC = \J\ I kT, J is t h e e x c h a n g e c o u p n i lg c o n s t a n t a n d g is t h e L a n d e f a c t o r . B  e m p o ly n ig s u s c e p t i b i lt y d a t a o b t a n ie d a t t h e t h r e e d i f f e r e n t f i e l d s ( 5 0 0 , 1 00 0 0 a n d  5 00 0 0 G), n os a t i s f a c t o r y fits w e r eo b t a n ie dw h e nd a t ab e o lw 5 0Kw e r ei n c l u d e d .  fits w e r e ,h o w e v e r ,o b t a n ie df o rd a t a in t h er a n g e5 0 3 0 0Ka s is i lu s t r a t e df o rt h e  % T d a t a in F i g u r e 7 . 4 . T h e l a c k o fa g r e e m e n t b e t w e e n t h e o r y a n d e x p e r m i e n t a t  t e m p e r a t u r e s is n o t s u r p r i s i n g s n ic e t h e m o d e l d o e s n o t a c c o m m o d a e t t h e e f f e c t s o  r e s i d u a l s p i n d u e t o s p i n c a n t n ig o r i n t e r c h a i n i n t e r a c t i o n s , b o t h o fw h c ih a r e m  p r o n o u n c e da to lw t e m p e r a t u r e s .T h et h e o r y line s h o w n in F i g u r e7 . 5w a sc a l c u l a t e dw  245  -J=  3 . 9 2 ( 6 )c m "a n d g =2 . 2 1 ( 1 )( F =0 . 0 0 0 3 3 ) .T h em o d e lu s e d is l i m i t e db yt h ef a c 1  e m p o ly sas i n g l eg v a l u e ,w h i l et h es t r u c t u r eo ft h ec o m p o u n dr e q u r ie sd i f f e r e n tgv a u le s f o rt h e FeN a n d FeS c h r o m o p h o r e s . T h e b e s t f i t g v a u le o f 2 . 2 1 p r e s u m a b y l 4  4  a p p r o x m i a t e s t h e a v e r a g e g f o r t h e s y s t e m . T h e s t r e n g t h o f t h e a n t f i e r r o m a g n e t c i  c o u p n i l g in t h i s c o m p o u n d , a s u jd g e d b y t h e m a g n t u id e o f - J, s e e m s t o b e s l i g h g r e a t e r t h a n t h a t s e e n in [Fe3(imid)6(inudH)] [ 4 ] a n d [ F e ( 2 m e i m i d ) 0 . 1 3 C p F e ][ 6 ] 2x  2  2  x  f o rw h c ih - / v a u le so f2 . 3a n d2 7 .5 cm" ,r e s p e c t i v e l y ,h a v eb e e nr e p o r t e d . 1  T h e a l t e r n a t i o n in c h r o m o p h o r e t y p e a n d , t h e r e f o r e , g v a u le a o ln g t h e c h a n i s h o u d l g e n e r a t em i p o r t a n tm a g n e c t i c o n s e q u e n c e s f o rt h i s a n t i f e r r o m a g n e t i c a l yc o u p e ld  s y s t e m . T h e s i z e o ft h e i n d i v i d u a l m a g n e c t i d i p o l e s will a l t e r n a t e a o ln g t h e c h a i n , a n  e v e np e r f e c t a n t i p a r a le l a g i ln m e n tb e t w e e nn e g ih b o r s will l e a dt o ar e s i d u a lm o m e n to  t h e c h a i n , w h c ih c a n b e c o n s d ie r e d a s a n e x a m p e l o f f e r r m i a g n e t s im . T h i s s a m  p h e n o m e n o nw a sd e s c r b ie d in e a r l i e rc h a p t e r sa sap o s s b ie l c a u s eo ft h er e s i d u a ls p i n t h el a t t i c e so f [Fe (imid) (bipy)] ( C h a p t e r5 )a n d [ F e ( i m i d ) ( t e r p y ) ]( C h a p t e r 6). W h e l i 2  4  x  4  8  x  t h i s p r o b a b y l c o n t r b iu t e s t o t h e o b s e r v e d m a g n e c t i p r o p e r t e is o ft h e s y s t e m , a s m i p  c a l c u l a t i o ni n d i c a t e s it c a n n o tb et h es o l es o u r c eo ft h er e s i d u a lc h a n i m a g n e t z ia t o in .T h s a t u r a t i o nm a g n e t i z a t i o n ,M s ,f o r a S =2 c e n t e r is [ 7 ]  M = Ng$S s  246  The net s a t u r a t i o nm a g n e t z ia t o in , A/ , for a c h a n i of p e r f e c t a n t i p a r a le l c o u p e ld 5 = 2 n e t  m e t a lc e n t e r sw i t hr e g u l a r l ya l t e r n a t i o n of g v a u le s is, per m o e l of m e t a lc e n t e r ,  M  n e t  = /2AM =iVpAg 1  s  I n s e r t i n g3 9 6 0 cm G mol" (the m a g n e t z ia t o in m e a s u r e d at 2 K and 55 000 G) for M 3  1  net  the a b o v ee q u a t o in y i e l d s a Ag v a u l e of 0.71. g v a u le s for  the  f e r r m i a g n e t s im to  FeN4 and a c c o u n t for  in  H e n c e , an u n r e a l i s t i c a ly l a r g ed i f f e r e n c e in  FeS4 c h r o m o p h o r e s w o u d l be r e q u i r e d to n iv o k e the  l a r g e s tm a g n e t z ia t o i n (not  e v e n s a t u r a t i o n  m a g n e t z ia t o in ) o b s e r v e d . T h e r e f o r e , s p i n c a n t n i g is likely the p r m i a r y s o u r c e of the r e s i d u a l m a g n e t z ia t o i n on the c h a i n s , a t l h o u g h f e r r m i a g n e t s im c a n n o t be r u l e d out as a c o n t r i b u t i n gf a c t o r .T h i sl a t t e rp h e n o m e n o n is f u r t h e rd s ic u s s e d in the f o l o w i n gs e c t i o n .  7.2.4  M O S S B A U E RS P E C T R O S C O P Y  The r o o m t e m p e r a t u r e M o s s b a u e r s p e c t r u m of [Fe(l-Me-2-S-imid)2-0.5Cp2Fe] x  c o r r e s p o n d s to t h r e eo v e r a lp p n ig q u a d r u p o e l d o u b e lt s ( F i g u r e 7.9),  w h c ih are c o n s s it e n t  w i t h the X r a ys i n g l ec r y s t a ld i f f r a c t i o ns t u d e is t h a ti n d i c a t ee q u a lp o p u a lt o i n of d i s t o r t e d f o u rc o o r d n ia t e d( t e t r a h e d r a l ) FeN and FeS4 s i t e s and h a l f as m a n y f e r r o c e n e m o e lc u e ls 4  247  { F e S J  2.0 H 1 -  1  1  2  1  1  -  1  1  1  0  1  1  1  1  2  Velocity Relative to Fe (mm s ) F i g u r e 7.9  M o s s b a u e rs p e c t r u m of [Fe( 1 M e 2 S i m i d ) 0 . 5 C p F e ] at 293 K. 2  2  x  b e t w e e n the p o y lm e r c i c h a n is ( F i g u r e s 7.2 and 7.3).  The c o r r e s p o n d n ig M o s s b a u e r  p a r a m e t e r s ( s io m e rs h i f t (8), q u a d r u p o e l s p l i t t i n g (AE)  for FeN4, FeS4 and F e ( C p )s i t e s  at 293 K are (0.8 m m s " , 14 .2 m m s " ) , (0.64 1  1  2  m m s " , 30 .3 m m s " ) and (0.45 1  1  m m s " , 22 .6 1  m m s " )r e s p e c t i v e l y .T h e s e are fairly t y p i c a lv a u le s for i r o n ( J J ) FeN and FeS4 and for the 1  4  S = 0f e r r o c e n e [9]. The r e s u l t s at 77 K are (0.94 m m s " ) and (0.52 1  m m s " , 2.52 m m s " ) , (0.76 1  m m s " , 2 . 4 1 m m s " )r e s p e c t i v e l y( F i g u r e7 . 1 0 ) . 1  1  248  1  m m s " , 33 .0 1  Velocity relative to Fe (mm s") 1  F g iu r e 71 .0  M o s s b a u e rs p e c t r u m of [Fe( 1 -Me-2-S-imid)2-0.5Cp Fe] at 77 K. 2  x  As m e n o t in e d in C h a p t e r 3, s e c t i o n 3 . 2 . 3 , the s p l i t t i n g v a u le r a n g e s can o f t e n o v e r a lp for f o u r ,fiveand six c o o r d n ia t o in e n v r io n m e n t s ( e v e n w i t h s i m i l a r l i g a n d s ) d e p e n d n ig on the d e g r e e of d i s t o r t i o n of the l o c a l c o o r d n ia t o in e n v r i o n m e n t [ 9 1 1 ] . On the o t h e r h a n d , s io m e r s h i f t s h a v e b e e n f o u n d to be q u i t e s e n s i t i v e to c o o r d n ia t o in n u m b e r forfixeds p i n s t a t e s and  s i m i l a rl i g a t i o n[ 9 1 4 ] . For  t e t r a h e d r a l FeS4  c h r o m o p h o r e s , t h e r e is e v e n f u r t h e r r e d u c t o i n of the s io m e r s h i f t r e l a t i v e to FeN4 to  249  v a u le sr a n g n ig f r o m~+ 0 6 .0 mms"  to 0.75 mms"  o w n ig to the n ic r e a s e d c o v a e ln c e of  the s u l f u rl i g a t i o ne n v r io n m e n t [15, 16]. T h u s , the p r e s e n t 8v a u le s in c o n u jc t o in w i t h the a v a i l a b l e l i t e r a t u r e r e s u l t s a p p e a r to u n e q u v io c a y l fartherc o n f r im the f o u r c o o r d i n a t e , t e t r a h e d r a l FeN4 and  FeS4, n a t u r e of the  h i g h s p i n i r o n ( I I ) of [ F e ( l M e 2 S -  imid)2-0.5Cp2Fe] and the p r e s e n c e of f e r r o c e n e . x  As e x p e c t e d , the M o s s b a u e rs p e c t r u m of the m a g n e t c ia y l o r d e r e dp h a s e of [Fe(lMe-2-S-imid)2-0.5Cp2Fe] ( F i g u r e 7.11) x  c o r r e s p o n d s to the o v e r a lp of two Z e e m a n  p a t e r n s and the w e l k n o w n (8 = 0.55 m m s", AE = 2.47 m m s") q u a d r u p o e l d o u b e lt of 1  1  f e r r o c e n e . The e x t r e m et r a n s i t i o np a i r s of the FeN and FeS4 h y p e r f n ie p a t t e r n s , and the 4  d o u b e lt of f e r r o c e n e , are d e s g in a t e dw i t ha r r o w s in F i g u r e 7.11.  The  FeS4  s i t ee x h i b i t sa s m a e lr t e m p e r a t u r e d e p e n d e n c et h a n FeN4  (< +03 . m m s" vs +11 . m m s") o v e r the d e c r e a s n ig t e m p e r a t u r er a n g e 293 K to 77 K, and 1  1  has an a b s o u lt ev a u l e of q u a d r u p o e l s p l i t t i n gl a r g e rt h a nt h a t for FeN c h r o m o p h o r e by ~ 4  0.8 m m s" at 77 K. T h e s e o b s e r v a t o in s i n d i c a t e as i g n i f i c a n t l y l a r g e r o lw s y m m e r t y 1  l i g a n d ; field c o m p o n e n t s p l i t t i n g (A) of the g r o u n dE t e r m of the r e g u l a rt e t r a h e d r o n to 5  the n o n d e g e n e r a t e B and A s t a t e s of d i s t o r t e d FeS4 and, in a d d i t i o n , a c o n c o m t a in t 5  5  g r e a t e rq u e n c h n ig of the o r b i t a lc o n t r i b u t i o n s to the m o m e n t for FeS t h a n FeN4 via the 4  250  { 1 -5  [Fe(Cp) ] 2  1  1  •  1 5  0  Velocity Relative to Fe (mm s") 1  F g iu r e 7.11  M o s s b a u e rs p e c t r u m of [Fe( 1 -Me-2-S-imid)2-0.5Cp Fe] at 4.2  u s u a l first o r d e r and  2  s p i n o r b i t c o u p n i lg e f f e c t s [9,  17].  x  K.  T h e s e e f f e c t s can l e a d to  s i g n i f i c a n td i f f e r e n c e s in the e f f e c t i v eg v a u le s for the FeN and FeS c h r o m o p h o r e sw i t h 4  4  g likely c l o s e r to 2 for the l a t t e r .T h e s ea r g u m e n t ss u p p o r t the p o s s i b i l i t y of the e x s it e n c e of a s u b t l e ri n t r i n s i c" i n t r a c h a i nf e r r i m a g n e t i s m " ,w h c ih a r i s e sf r o mg f a c t o rm o d u a lt o in ( a l t e r n a t i o n ) a o ln g the p o y lm e r c i c h a n i c o n t r i b u t i n g , t h u s , to the w e a k f e r r o m a g n e s t im e x h i b i t e d by [Fe(l-Me-2-S-imid) 0.5Cp Fe] . 2  2  251  x  7 . 3  S U M M A R YA N DC O N C L U S O IN S  [Fe(l-Me-2-S-irmd)2-0.5Cp2Fe] h a s ar o d l i k e p o y lm e r s t r u c t u r e in w h c ih i r o n x  o in s a r ed o u b e l b r d ig e db y l m e t h y l 2 t h i o i m i d a z o l a t el i g a n d s . T h em e t a lc h r o m o p h o r e s  a l t e r n a t ea o ln gt h ec h a n i b e t w e e n FeS4 a n d FeN4. D Cm a g n e t z ia t o in s t u d e is o np o w d e r e d s a m p e ls r e v e a l a n e t m a g n e t z ia t o in a t z e r o field a n d t e m p e r a t u r e s b e o lw 8 K .  m a g n e t z ia t o in s t u d e is c o n f r im t h e o ln g r a n g e f e r r o m a g n e t c i o r d e r in t h i s s y s t e m a n d  p e r m t i a na c c u r a t ee v a l u a t i o no ft h e critical t e m p e r a t u r e , T = 5K .M a g n e t z ia t o in v e r s u s c  a p p l i e d field s t u d e is a t4 . 8 Kg e n e r a t eah y s t e r e s s i o lo pw i t har e m n a n tm a g n e t z ia t o in  1 9 0c m G m o Ta n dac o e r c v ie field o f4 0 G. A n t f ie r r o m a g n e t c i i n t r a c h a i nc o u p n i lg w i t h 3  1  s p i nc a n t n ig g e n e r a t n ig r e s i d u a ls p i no nt h ec h a n is t h a tu n d e r g oo ln g r a n g ef e r r o m a g n e t c i o r d e r n i g is b e l i e v e dt ob e ap r o b a b e l c a u s eo ft h em a g n e c t i b e h a v o iu ro b s e r v e d f o r m a t e r i a l .A na l t e r n a t i v ee x p a ln a t o in f o rt h ew e a kf e r r o m a g n e t s im e x h i b i t e db y[ F e ( l M e -  2-S-imid)2-0.5Cp2Fe], w h c ih is t h e a l t e r n a t i o no ft h egv a u le s a o ln gt h ep o y lm e rc h a i n , x  h a s b e e n c o n s d ie r e d f o l o w i n g t h e M o s s b a u e r s p e c t r o s c o p y r e s u l t s , in p a r t i c u l a r t h e t e m p e r a t u r e d e p e n d e n c e a n d l i m i t i n g v a u le s o ft h e q u a d r u p o e l s p l i t t i n g so f t h e  p a r a m a g n e c t i f e r r o u s s i t e s o f t h i s s y s t e m . I t is c o n c u ld e d t h a t b o t h m e c h a n s im s a r e p r o b a b y l o p e r a t v ie h e r e .  [Fe(l-Me-2-S-imid)2-0.5Cp2Fe] p o s s e s s e s v e r y u n q iu e a n d c o m p e lx m a g n e c t i x  p r o p e r t e is w h c ih m a y r e q u i r e f u r t h e r s t u d y t o m a k e a d e f i n i t i v e a s s e s s m e n t o f t h  d o m n ia n t p h e n o m e n o n , s p i n c a n t n ig v e r s u s g f a c t o r d i f f e r e n c e s , t h a t g e n e r a t e s t h e  252  m a g n e c t i g r o u n ds t a t eo ft h i ss y s t e m .D e t e r m n ia t o in o ft h em a g n e c t i s t r u c t u r eb yn e u t r o n  d i f f r a c t i o ns t u d e is c o u d l p r o v d ie n e wi n s i g h t st ot h i sm a t t e r ;h o w e v e r , s u f f i c i e n t l yl a r g e , d e u t e r a t e d , s i n g l ec r y s t a l s a m p e ls o f [Fe(l-Me-2-S-imid)2-0.5Cp2Fe] w o u d l b er e q u r ie d x  f o rt h i sw o r k .  253  R e f e r e n c e s  1 .  S. J. R e t t i g , V. S a n c h e z , A. S t o r r ,R . C. T h o m p s o n ,a n d J. T r o t t e r , Inorg. Chem 38, 5 9 2 0 ( 1 9 9 9 ) .  2.  D . A. C o o p e r , S. J. R e t t i g ; A. S t o r r ,a n d J. T r o t t e r . Can. J. Chem. 64, 1 6 4 3( 1 9  3.  O. K a h n . Acc. Chem. Res. 33 ( 1 0 )6 4 7( 2 0 0 0 ) .  4 .  S. J. R e t t i g , A. S t o r r , D . A. S u m m e r s , R . C. T h o m p s o n , a n d J. T r o t t e r . J. A Chem. Soc. 119, 8 6 7 5( 1 9 9 7 ) .  5 .  S. J. R e t t i g , A. S t o r r ,D . A. S u m m e r s ,R . C. T h o m p s o n ,a n d J. T r o t t e r . Can. J. Chem. 77,425 ( 1 9 9 9 ) .  6 .  M . A. M a r t i n e z L o r e n t e , V. P e t r o u l e a s , R . P o i n s o t , J. P . T u c h a g u e s , J. M . S a v a r i a u l t ,a n dM . Drillon, Inorg. Chem. 30, 3 5 8 7( 1 9 9 1 ) .  7 .  R . L. Carlin. Magnetochemistry. S p r i n g e r V e r l a g . Berlin. 1 9 8 6 .  8 .  W . Hiller, J. S t r a h l e , A. D a t z ,M . H a n a c k ,W . F. Hatfield, a n dP . Gutlich, Am Chem. Soc. 106, 3 2 9( 1 9 8 4 ) .  9.  N . N .G r e e n w o o da n d T. C. G i b b . Mossbauer Spectroscopy. C h a p m a na n d Hall Ltd. L o n d o n . 1 9 7 1 .  1 0 .  B. W .D o c k u m ,a n dW .M . Reiff. Inorganica Chimica Acta. 35, 2 8 5( 1 9 7 9 ) .  1 1 .  F. F. C h a r r o n ,a n dW .M . Reiff. Inorg. Chem. 25,2786(1986).  1 2 .  W .M . Reiff, N. E. E r i c k s o n ,a n dW . A. B a k e r . Inorg. Chem. 8 , 2 1 1 9( 1 9 6 9 ) .  1 3 .  D .S e d n e y ,M .K a h j e h n a s s i r i ,a n dW .M . Reiff. Inorg. Chem. 20, 3 4 7 6( 1 9 8 1 ) .  1 4 .  B. W .D o c k u m ,a n dW .M . Reiff. Inorganica Chimica Acta. 120, 6 1 ( 1 9 8 6 ) .  1 5 .  W .M . Reiff, I.E. G r e y , A. F a n , Z. Eliezer, a n d H. S t e i n f i n k . J. Solid State Che 13, 3 2( 1 9 7 5 ) .  1 6 .  K .K .R a o ,M . C. W .E v a n s ,R .C a m m a c k ,D . O. Hall, C. L. T h o m p s o n ,P .J J a c k s o n ,a n d C. E. J o h n s o n . Biochem, J. 129, 1 0 6 3( 1 9 7 2 ) .  254  R .M .G o l d i n g ,K . F. M o k ,a n d J. F. D u n c a n . Inorg. Chem. 5, 7 7 4( 1 9 6 6 ) .  255  Chapter 8  8.1  GENERAL SUMMARY AND SUGGESTIONS FOR FUTURE WORK  G E N E R A LS U M M A R Y  T h i s d i s s e r t a t i o n d e s c r b ie s an i n v e s t i g a t i o n of the  s y n t h e s i s , s t r u c t u r a l and  p h y s i c a l c h a r a c t e r i z a t i o n , and in p a r t i c u l a r the m a g n e c t i p r o p e r t i e s , of one-,  two-  and  t h r e e d m i e n s o in a lt r a n s i t i o nm e t a lp o y lm e r si n v o l v i n gp y r a z o a lt e and, m a i n l y , i m i d a z o l a t e and i m i d a z o l a t ed e r v ie dg i la n d s as b r i d g i n gs p e c i e s .  1 , 2 D i a z o l a t e s( p y r a z o l a t e s ) in c o m b n ia t o in w i t hd i v a l e n tp a r a m a g n e c t i t r a n s i t i o n m e t a s l t y p i c a ly f o r m 1-D  c h a n i s t r u c t u r e s w i t h d o u b e lb r d ig n ig a z o l a t e l i g a n d s ,  m a t e r i a l s w h c ih s h o w s h o r t r a n g e a n t f i e r r o m a g n e t c i i n t e r a c t i o n s b e t w e e nm e t a l c e n t e r s . A new  c o m p o u n d in t h i s s e r i e s , [Fe(pz)2], has b e e n s y n t h e s z ie d and s t r u c t u r a l y and x  m a g n e t c ia y l c h a r a c t e r i z e d . As e x p e c t e d , the s t r u c t u r e of t h i s 1-D p o y lm e rr e s e m b e ls a c h a i n , due  to the  d o u b l e b r i d g i n g c h a r a c t e r i s t i c of the  p y r a z o a lt e l i g a n d s . A l s o as  e x p e c t e d , t h i s c o m p o u n d e x h i b i t e d s h o r t r a n g e a n t f i e r r o m a g n e t c i e x c h a n g e , w i t h -J 0 . 5 9 1 ( 5 ) cm", 1  av a u le t h a tr e p r e s e n t s the w e a ka n t f i e r r o m a g n e t s im o c c u r r n ig b e t w e e n the  t e t r a h e d r a lm e t a lc e n t e r s in t h i sc o m p o u n d .  In c o n t r a s t , w h e n 1 , 3 d i a z o l a t e sg i la n d s( i m i d a z o l a t e s )w e r e utilized, e x t e n d e d 2D and 3-D l a t t i c e sw i t hs i n g l yb r i d g i n ga z o a lt e sb e t w e e n the m e t a lc e n t e r sw e r eo b t a i n e d .  256  M a n yo ft h e s em a t e r i a l sw e r es h o w nt oe x h i b i t ,a to lw t e m p e r a t u r e s ,n e tm a g n e t z ia t o in z e r oa p p l i e d field, a p r o p e r t yw h c ih c l a s s i f i e st h e ma sm o e lc u e lb a s e dm a g n e t s .  T h e r e a c t i o n o ff e r r o c e n e w i t h m o t l e n 4 a z a b e n z m i d ia z o e l r e s u l t e d in t h e  i s o l a t i o n o f a 3 D iron(n) c o o r d n ia t o in p o y lm e r . T h i s c o m p o u n d w a s o b t a n ie d a s a  c r y s t a li n em a t e r i a l a n d its s t r u c t u r e d e t e r m n ie db ys i n g l e c r y s t a l X r a yd i f f r a c t i o n . T h e s t r u c t u r e i n v o l v e s a u n q iu e s i n g l e ( n o n i n t e r p e n e t r a t i n g ) , t o t a ly c o v a l e n t , d a im o n d o d i  a r r a yo fF e ( I I ) c e n t e r s , w h c ih a r e s i n g l eb r d ig e db yt h e 1 , 3 d i a z o l a t eg i la n d s i n t o a 3 a r r a y o ff u s e dringse a c h c o n t a n in ig s i x d i s t o r t e d t e t r a h e d r a l F e ( I I ) c e n t e r s . R e p a lc n ig f e r r o c e n eb yc o b a t l o c e n ep r o d u c e dt h ec o b a t l a n a o lg u ea s am i c r o c r y s t a l i n ec o m p o u n d . X r a yp o w d e rd i f f r a c t i o ns t u d e is r e v e a e ld t h et w oc o m p o u n d sa r es io m o r p h o u s .V a r i a b l e t e m p e r a t u r eD Cm a g n e c t i s u s c e p t i b i lt y s t u d e is o nt h e s ec o m p o u n d s  r e v e a l  a n t f i e r r o m a g n e t c i c o u p n i lg b e t w e e nn e g ih b o r n ig m e t a lo in sa b o v ea b o u t2 0Kf o rt h ei r o  c o m p o u n d a n d 1 1 K f o r t h e c o b a t l a n a o lg u e . B e o lw t h e s e t e m p e r a t u r e s b o t h m a t e r s h o wo ln g r a n g e f e r r o m a g n e t c i o r d e r i n g . T h i sb e h a v o iu rs u g g e s t s c a n t e d s p n i s t r u c t u r e s  a r e p r e s e n t in t h e s e c o m p o u n d s . B y c y c l i n g t h e D C a p p l i e d field a t 4 . 8 K , h y s t e r o lo p sw i t h Mrem o f2 1 0 0a n d2 2 c m G m o " l a n dH  coer  o f8 0a n d 1 0 0Gw e r eo b t a  [Fe(4-abimid)2] a n d t h e c o b a t l a n a o lg u e , r e s p e c t i v e l y . A C m a g n e c t i s u s c e p t i b i lt y x  s t u d e is c o n f r im e d t h e m a g n e c t i t r a n s i t i o n o c c u r r n i g in [Fe(4-abimid)2]. M o s s b a u e r x  s p e c t r o s c o p ys t u d e is in t h i s c o m p o u n dr e v e a e ld a f e r r o m a g n e t c i t r a n s i t i o n a t 1 8 Ka n t h ep o s s i b i l i t yo fa s t r u c t u r a lp h a s et r a n s i t i o na to lw t e m p e r a t u r e .  2 5 7  T h e  c o b a l t ( I l )  c o m p o u n d s ,  [Co(imid)2],  [Co(benzimid)2] a n d  x  x  [Co3(imid)6(imidH)2], all e x h i b i t e d as u d d e nn ic r e a s e in t h e i rm a g n e c t i m o m e n s t b e o lw x  t e m p e r a t u r e s of ~ 16, 1 3a n d1 5 K, r e s p e c t i v e l y , a n d m a g n e c t i h y s t e r e s s i b e h a v o i r at t e m p e r a t u r e s o lw e r t h a n t h e s e . X r a y p o w d e r d i f f r a c t i o n s t u d e is  s h o w e d  [Co3(imid)6(imidH)2] to b es io m o r p h o u s w i t h the i r o n a n a o lg u e w h c ih w a s r e p o r t e d x  p r e v i o u s l y [1], a n d w h c ih h a s a 3-D s t r u c t u r e w i t h s i n g l e b r i d g i n g i m i d a z o l a t e l i g a n d s . T h es t r u c t u r e s o ft h e o t h e rt w oc o b a t l c o m p o u n d s are n o tk n o w nw i t h c e r t a i n t yb u t are  t h o u g h tt ob e 3-D a s well. T h u s ,a c c o r d n ig t ot h e i rm a g n e c t i p r o p e r t i e s ,t h e s et h r e ec o b  c o m p o u n d s are c o n s d ie r e d t o b e o ln gt o the c a ls s o fm a t e r i a l s k n o w n a sm o e lc u e lb a s e d m a g n e t s . In a d d i t i o n , t w oo t h e r c o b a t l i m i d a z o l a t e c o m p o u n d s , [ C o ( 2 m e i m i d ) ] a n d 2 x  [Co(4-meimid)2] ,w h e r es t u d i e d .H o w e v e r ,t h e s et w oc o m p o u n d s ,w h c ih likely h a v e 3-D x  s t r u c t u r e sa l s o , s h o wo n y l w e a ka n t f i e r r o m a g n e t c i c o u p n i lg w i t hn o s t r o n ge v d ie n c eo f t r a n s i t i o n t o a f e r r o m a g n e t c i s t a t e at o lw t e m p e r a t u r e s . T h el a c k o fd e f i n i t i v e s t r u c t u r a l i n f o r m a t i o n for t h e s e c o b a t l p o y lm e r s p r e c u ld e d f u r t h e r e x p a ln a t o i n of t h e i r m a g n e c t i b e h a v o iu r s .  O t h e r t r a n s i t i o n m e t a l i m i d a z o l a t e c o m p o u n d s s y n t h e s z ie d n ic u ld e d n i c k e l ( H ) b e n z i m i d a z o l a t e , the c h a r a c t e r i z a t i o n of w h c ih s h o w e d it to b e thefirstr e p o r t e d m o e lc u e lb a s e d m a g n e tc o n t a n in ig n i c k e l ( I I )i o n s .T h i sc o m p o u n d e x h i b i t s n e t  m a g n e t z ia t o in a tz e r o a p p l i e d field, a n dZ F C M a n dF C M c u r v e s h a p e s t h a tr e v e a l l o r a n g e f e r r o m a g n e t c i o r d e r n ig b e o lw a T  c  o f ~ 6.5 K. I n a d d i t i o n , t h r e e  c o p p e r ( I ) i m i d a z o l a t e c o m p o u n d s , [Cu(2-meimid)2] , x  2 5 8  [Cu(benzimid)2] x  a n d  [Cu(4,5-dichloroimid)2] , w e r e f o u n d t o b e m o e lc u e lb a s e d m a g n e t s . T h i s w a s r e v e a e ld x  b y D C m a g n e c t i s u s c e p t i b i l t y s t u d i e s , t h a t s h o w a n n ic r e a s e in b o t h %a n d M«f  a  t e m p e r a t u r e so f -25, 1 5a n d 1 4K ,r e s p e c t i v e l y . Also, t h ep r e s e n c eo fa h y s t e r e s s i o lo p f e id ld e p e n d e n t m a g n e t z ia t o in s t u d e is a t o lw t e m p e r a t u r e a s w e l a s Z F C M F C M e x p e r m i e n t s c o n f r im e d t h ee x s it e n c eo fa m a g n e c t i t r a n s i t i o n t oa o ln g r a n g e f e r r o m a g n e t c i s t a t e f o rt h e s e t h r e e c o p p e r c o m p o u n d s . T w o a d d i t i o n a l c o p p e r t T ) I i m i d a z o l a t e s , [Cu(imid)2] a n d [Cu(4-meimid)2] , w e r e p r e p a r e d . T h e s e s h o w e d o n y l x  x  w e a ka n t f i e r r o m a g n e t c i b e h a v o iu ra n dg a v en oe v d ie n c ef o ro ln g r a n g em a g n e c t i o r d e r .  E f f o r t st o m o d f i y t h e m o e lc u a lr d i m e n s i o n a l i t y , a n d h e n c e t h e m a g n e c t i p r o p e r t i e s ,o ft r a n s i t i o nm e t a lm i d ia z o a lt e sb yi n c o r p o r a t i n gn e u t r a lc h e l a t i n gg i la n d si n t o  t h el a t t i c er e s u l t e d in t h ef o r m a t o in o f [Fe2(imid)4(bipy)] a n d its c o b a t l a n a o lg u e . S i n g l e x  c r y s t a lX r a yd i f f r a c t i o ns t u d e is o n [Fe2(imid)4(bipy)] s h o was t r u c t u r ei n v o l v i n gd o u b e l x  l a y e rs h e e t so fi r o no in ss i n g l e b r i d g e db yi m i d a z o l a t el i g a n d s . F o u r -a n ds i x c o o r d i n a t e d  o in s a l t e r n a t e in t h e lattice, t h e l a t t e r o in s b e n ig c o o r d n ia t e d b y t h e b i p y g i la n d s  a d d i t i o n t o t h eb r i d g i n g i m i d a z o l a t e s . T h i s c a p p n ig o fi r o n c e n t r e s b yb i p y c o n t r o s l t h d i m e n s i o n a l i t y , r e s u l t i n g in t h e 2 D p o y lm e r . [Fe2(imid)(bipy)] is u n q iu e in s h o w n ig 4  x  t w o s t r u c t u r a lp h a s et r a n s i t i o n s a t~ 1 5 1 Ka n d~ 1 3 5 K , w h c ih h a v eb e e n c h a r a c t e  b yac o m b n ia t o in o fs i n g l ec r y s t a l X r a y d i f f r a c t i o n , D C a n dA Cm a g n e c t i s u s c e p t i b i l t y a n d M o s s b a u e r s p e c t r o s c o p y s t u d i e s . I n a d d i t i o n , [Fe2(imid)4(bipy)] s h o w s a s h a r p x  n ic r e a s e in t h eD Cm a g n e c t i s u s c e p t i b i l t yb e o lw 1 1 K , a n dan o n z e r oA C o u t o f p h m a g n e c t i s u s c e p t i b i l t yb e o lw t h a tt e m p e r a t u r e , i n d i c a t i v eo fa t r a n s i t i o n t o a  2 5 9  f e r r o m a g n e t i c a l yo r d e r e d s t a t e a to lw t e m p e r a t u r e s . V a r i a b l et e m p e r a t u r e D C m a g n e c t i s u s c e p t i b i l t y s t u d e is o n [Fe2(imid)4(bipy)] a n dt h ec o b a t l a n a o lg u e r e v e a e ld x  a n t f i e r r o m a g n e t c i c o u p n i lg b e t w e e n n e g ih b o u r n ig m e t a l o in s a b o v e T( 1 1 a n d 1 3 K c  r e s p e c t i v e l y ) . B e o lw T b o t h m a t e r i a l s e x h i b i t o ln g r a n g e f e r r o m a g n e t c i o r d e r i n g . T h e c  p r e s e n c e o f c a n t e d s p n i s t r u c t u r e s in b o t h c o m p o u n d s is s u g g e s t e d b y t h i s b e h a v o iu r ;  h o w e v e r , a n o v e l t y p e o ff e r r m i a g n e t s im , d u e t o t h e s y s t e m a t c i a l t e r n a t i o n o ff o u r - a n  s i x c o o r d i n a t e c h r o m o p h o r e s h a s a s lo b e e n n iv o k e d a s a p o s s b ie l m e c h a n s im f o r t h e o b s e r v e dm a g n e c t i b e h a v o iu r .  [Fe4(imid)8(terpy)] h a s a n o v e l 2 D e x t e n d e d s t r u c t u r e in w h c ih " w r i n k l e d " x  s h e e t s o f f o u r c o o r d i n a t e ( t w o u n q iu e c e n t e r s o f t h i s t y p e ) , f i v e c o o r d i n a t e a n d sixc o o r d n ia t e i r o n o in s a r e l i n k e d b y s i n g l e b r i d g i n g i m i d a z o l a t e l i g a n d s . T h e s i xc o o r d n ia t e m e t a l c e n t e r s a r e a d d i t i o n a l y c o o r d n ia t e d b y t e r p y g i la n d s t h a t o c c u p y  p o s i t i o n s b e t w e e nt h e s h e e t s , i s o l a t i n g t h e s h e e t sfrome a c ho t h e r . T h ep r e s e n c e o ff o u u n q iu ei r o n s i t e sw a s c o n f r im e db yM o s s b a u e rs p e c t r o s c o p y . D Cm a g n e c t i s u s c e p t i b i l t y m e a s u r e m e n s t r e v e a e ld a n t f i e r r o m a g n e t c i i n t e r a c t i o n s b e t w e e n m e t a l c e n t e r s a b o v e T  c  a n d a t r a n s i t i o n t o a f e r r o m a g n e t c i s t a t e b e o lw t h i s t e m p e r a t u r e . A T o f6 . 5 K , c  c o n f r im e d b y A C m a g n e c t i s u s c e p t i b i l t y a n d Z F C M F C M R E M s t u d i e s . M a g n e t c i  h y s t e r e s s i s t u d e is r e v e a e ld t h em a g n e c t i p r o p e r t e is o ft h i ss y s t e mt ob eu n q iu ea m o n gt i m i d a z o l a t e s y s t e m s s t u d e id h e r e . N e g a t v ie m a g n e t z ia t o in s a t z e r o field w e r e e x p a ln ie d  b y i n v o k i n g a m e c h a n s im in w h c ih t h r e e o ft h e f o u r u n q iu e s i t e s a c t a s f a s t r e l a  2 6 0  p a r a m a g n e t s w i t h the f o u r t h a c t i n g as a s o lw r e l a x i n g p a r a m a g n e t and g e n e r a t n i g the o b s e r v e dm a g n e t z ia t o i n in z e r o field.  [ F e ( l M e 2 S i m i d ) 2 0 . 5 Cp2Fe] has  a u n q iu e r o d l i k e p o y lm e r s t r u c t u r e in  x  w h c ih i r o no in s are d o u b e l b r d ig e d by l m e t h y l 2 t h i o i m i d a z o l a t el i g a n d s . FeS4 and FeN4 m e t a l c h r o m o p h o r e s a l t e r n a t e a o ln g the  c h a i n s . M a g n e t c i s t u d e is s h o w e d a  net  m a g n e t z ia t o i n at z e r o field and t e m p e r a t u r e s b e o lw 8 K. M a g n e t z ia t o in v e r s u s a p p l i e d field s t u d e is at 4.8 K g e n e r a t e ah y s t e r e s s i o lo p w i t h ar e m n a n t m a g n e t z ia t o i n of  190  c m G m o l " and a c o e r c v ie field of 40 G. A n t f ie r r o m a g n e t c i i n t r a c h a i nc o u p n i lg w i t hs p i n 3  1  c a n t n i g was p r o p o s e d to g e n e r a t e r e s i d u a l s p i n on the c h a n is t h a t u n d e r g o o ln g r a n g e f e r r o m a g n e t c i o r d e r b e o lw ~ 8 K. Due  to the  a l t e r n a t i o n on the  FeS4 and  FeN4  c h r o m o p h o r e s t h r o u g h o u t the c h a i n s , ap o s s b ie l n o v e l t y p e of f e r r m i a g n e t s im has a s lo b e e n p r o p o s e d to c o n t r i b u t e to the m a g n e c t i o r d e r n ig e x h i b i t e d by t h i s c o m p o u n d . M o s s b a u e rs p e c t r o s c o p yp r o v d ie du n a m b g iu o u se v d ie n c e for the p r e s e n c e of the two i r o n c h r o m o p h o r e s and f e r r o c e n e as w e l as the m a g n e c t i t r a n s i t i o n in t h i s c o m p o u n d . T h i s m a t e r i a l p r o v d ie s ar e l a t i v e l y r a r e e x a m p e l of a m o e lc u e lb a s e d m a g n e t in w h c ih the c o v a e ln tc o n n e c t i v i t i e s in the l a t t i c e are  In s u m m a r y , ar e l a t i v e l y new  1-D.  f a m i l y of m o e lc u e lb a s e d m a g n e s t i n c o r p o r a t i n g  m i d ia z o a lt e b a s e dg i la n d s as m e d a it o r s of m a g n e c t i e x c h a n g eb e t w e e n the m e t a lo in s has b e e ne s t a b s i lh e d in t h i sw o r k . It has b e e nd e m o n s t r a t e dt h a th e t e r o c y c l i ca z o l a t eg i la n d s w i t h two d o n o rn t i r o g e n s s e p a r a t e d by a s i n g l ec a r b o n in the r i n g (as in the i m i d a z o l a t e  261  i o n ) will f o r ms i n g l el i g a n db r d ig e sa n de x t e n d e ds t r u c t u r e s .M o r e o v e rt h e s eg i la n d sw  c r e a t e ab r d ig eg e o m e t r yt h a te la d s t o as y s t e m a t c i a l t e r n a t i o n in t h er e l a t i v eo r i e n t a t i o  o fn e g ih b o r n ig c h r o m o p h o r e s in t h e lattice, a s i t u a t i o nt h a tc a np r o d u c e s i g n i f i c a n t s p i n c a n t n ig a n d ,a sac o n s e q u e n c e ,o ln g r a n g ef e r r o m a g n e t c i o r d e r n ig a to lw t e m p e r a t u r e s .  E x a m p e ls n o w e x i s to fi r o n ( I I ) c o m p e lx e s i n c o r p o r a t i n g m i d ia z o a lt e b a s e d  g i la n d sw h i c h ,a sc o n f r im e db ys i n g l ec r y s t a lX r a y diffraction, h a v e 1 D { [ F e ( l M e 2 S imid) -0 . 5 C p F e ] } , 2 D { [ F e ( i m i d ) b i p y ) ]a n d [ F e ( i m i d ) ( t e r p y ) ] } , a n d3 D { [ F e ( 4 2  2  x  2  6  x  4  8  x  a b i m i d ) ] }e x t e n d e d c o v a e ln t lattices. All o f t h e s e c o m p o u n d s e x h i b i t m a g n e c t i 2 x  p r o p e r t e is t h a tc l a s s i f yt h e ma sm o e lc u e lb a s e dm a g n e t s .  8 . 2  S U G G E S T O IN SF O RF U T U R EW O R K  I n o r d e r t o l e a r n m o r e a b o u t t h e p o s s b ie l o lw t e m p e r a t u r e s t r u c t u r a l p h a s e  t r a n s i t i o n o c c u r r n i g in [ F e ( 4 a b i m i d ) ] a s i n g l e c r y s t a l X r a y d i f f r a c t i o n s t u d y a t H e 2 x  t e m p e r a t u r e s is r e q u i r e d . T h i s m a y a o l w a b e t t e r u n d e r s t a n d n ig o f t h e m a g n e c t i p r o p e r t e is o ft h i s d a im o n d o d i c o m p o u n d . I n a d d i t i o n , n e u t r o nd i f f r a c t i o n s t u d e is w o u d l c o n t r b iu t et ot h ec o m p e lt eu n d e r s t a n d n ig o ft h em a g n e c t i p r o p e r t i e s .  I n r e g a r d t o t h e c o b a l t ( I I ) , n i c k e l ( I I ) a n c o p p e r ( I ) i m i d a z o l a t ep o y lm e r s , f u r t h e r  s y n t h e t c i a t e m p t st op r o d u c es i n g l ec r y s t a l s s u i t a b l ef o rX r a yd i f f r a c t i o ns t u d e is w o u d l b ew o r t h w h i l e .  2 6 2  n Ic o r p o r a t o in o f o t h e r c h e l a t i n g g i la n d s ( s u c h a s 5 , 5 'd i m e t h y l 2 , 2 'b i p y ) i n t o m e t a l i m i d a z o l a t e s t r u c t u r e s t o o b t a i n c o m p o u n d s s i m i l a r t o [Fe2(imid)4(bipy)] a n d x  [Fe4(imid)g(terpy)] is e n c o u r a g e d t o t r y t o g e n e r a t e e x t e n d e d 2 D s y s t e m s w i t h s u b t e l x  s t r u c t u r a l m o d i f i c a t i o n s . T h i s w o u d l a o lw t h e i n v e s t i g a t i o n o f t h e e f f e c t o f s u c h s t r u c t u r a l c h a n g e s o n m a g n e c t i p r o p e r t i e s . M o r e o v e r , e s p e c i a l y f o rm a t e r i a l s s i m i l a rt o [Fe2(imid)4(bipy)], t h e s t u d y o fp o t e n t i a l s t r u c t u r a l p h a s e t r a n s i t i o n s in t h e s e s y s t e m s x  w o u d l b eo fs i g n i f i c a n ti n t e r e s t .  D u e t o t h e c o m p e lx m a g n e c t i p r o p e r t e is f o u n d in [ F e ( l M e 2 S i m i d ) 2 0 . 5  Cp2Fe] , a n d in o r d e r t o g e t m o r e i n s i g h t a b o u t t h e p r e d o m n ia n t p h e n o m e n o n ( s p i n x  c a n t n ig v e r s u sgf a c t o rd i f f e r e n c e s )r e s p o n s b ie l f o rt h eo ln g r a n g ef e r r o m a g n e t c i o r d e r n ig  e x h i b i t e d b y t h i s m a t e r i a l , n e u t r o n d i f f r a c t i o n s t u d e is c o u d l b e a t e m p t e d . T h i s w o u d l r e q u i r et h es y n t h e s s i o fl a r g e ,d e u t e r a t e d ,s i n g l ec r y s t a l so ft h ec o m p o u n d .  Finally, t h e p y r a z o e l c o m p e lx e s [Cu(pzH)4(N03)2], [Co(pzH)4(NC»3)2], a n d [Ni(pzH) (N0 ) ] a s w e l a s [ C o ( 2 ( 2 p y ) b e n z i m i d H ) ( C 1 0 ) 2 ] ( p y = p y r i d i n e ) w e r e 4  3 2  3  4  s y n t h e s z ie d in t h e c o u r s e o ft h i s w o r k . T h e s em a t e r i a l sh a v et h ep o t e n t i a l t ob eu s e  b u i l d i n g b o lc k s f o r t h e f o r m a t o in o fh e t e r o b i m e t a l i c f e r r i m a g n e t i c 1 D , 2 D o r 3 D n e t w o r k s[ 2 ] .  2 6 3  R e f e r e n c e s  1 .  S. J. R e t t i g , A. S t o r r , D . A. S u m m e r s , R . C. T h o m p s o n a n d J. T r o t t e r , J Ame Chem. Soc. 119, 8 6 7 5( 1 9 9 7 ) .  2.  F. L a m b e r t , J-P. R e n a u l t , C. Policar, I . M o r g e n s t e r n B a d a r a u , a n d M . C e s a r i o . Chem. Commun. 3 5 ( 2 0 0 0 ) .  2 6 4  Chapter 9  9.1  EXPERIMENTAL  N IT R O D U C T O IN  The  e x p e r m i e n t a l d e t a i l s of t h i sw o r ki n c l u d i n gs y n t h e t c i a s p e c t s and m a t e r i a l s  e m p o ly e d are d e s c r b ie d h e r e . The n is t r u m e n t s and m e h to d s e m p o ly e d in the p h y s i c a l c h a r a c t e r i z a t i o n of the c o m p o u n d ss t u d e id are a s lo d e s c r i b e d .  9.2  S Y N T H E S E S  The c h e m c ia s l u s e d in t h i s t h e s i sw e r e of r e a g e n tg r a d e and w e r eu s e dw t i h o u t f u r t h e rp u r i f i c a t i o n . The c o m m e r c a il s o u r c e s for m o s t of c h e m c ia lr e a g e n t s utilized in the s y n t h e s e s c a r r i e d out in the p r e s e n t w o r k are g v ie n in T a b e l 9.1.  The m a j o r i t y of  c o m p o u n d s p r e p a r e d h e r e are air s t a b l e , h e n c e t h e yw e r e s y n t h e s z ie d w t i h o u t s p e c i a l p r e c a u t o in s . T h o s e c o m p o u n d s t h a t e x h i b i t e d s e n s i t i v i t y to o x y g e n or m o s it u r e w e r e p r e p a r e du s n ig S c h e ln kt e c h n q iu e s and h a n d e ld in a V a c u u mA t m o s p h e r e sC o r p o r a t o in M o d e l HE 43-2  D r i L a b g o lv e b o x u n d e r a d i n i t r o g e n a t m o s p h e r e . All  s o v le n t s u s e d  w i t ht h e s ea i r s e n s i t i v ec o m p o u n d sw e r ef r e e of w a t e r and d e o x y g e n a t e d . The s o v le n t s w e r e d r i e d u s n i g the f o l o w i n g m e t h o d s : a c e t o n i t r i l e was  r e f l u x e d w i t h p h o s p h o r o u s  p e n t o x d i e and distilled u n d e r d i n i t r o g e n ; b e n z e n e was r e f l u x e d w i t h p o t a s s u im m e t a l  265  and distilled u n d e r d i n i t r o g e n ; x y e ln e s w e r e r e f l u x e d w i t h s o d u im and b e n z o p h e n o n e and distilled u n d e rd i n i t r o g e n .  T a b e l 9.1  C o m m e r c a il s o u r c e of m o s t c h e m c ia l r e a g e n t s e m p o ly e d in t h i s t h e s s i  ( c o n t n iu e do v e r l e a f ) .  Commercial source  Compound A c e t o n i t r i l e  A l d r i c h  4 A z a b e n z i m i d a z o l e  A l d r i c h  B e n z e n e  A l d r i c h  B e n z m i d ia z o e l  E a s t m a n  4,5-dichloroimidazole  A l d r i c h  C o b a t l o c e n e  S t r e m  C o b a t lc h l o r i d eh e x a h y d r a t e  F s ih e r  C o b a t ln i t r a t eh e x a h y d r a t e  M a l i n c k r o d t  C o p p e rs u p lh a t ep e n t a h y d r a t e  J. T. B a k e r  F e r r o c e n e  S t r e m  i m i d a z o l e  A l d r i c h L a n c a s t e r  2 m e r c a p t o 1m e t h y m i l d ia z o e l  L a n c a s t e r  2 m e t h y l i m i d a z o l e  266  4 m e t h y m i l d ia z o e l  A l d r i c h  !  3,5-dimethylpyra2ole  A l d r i c h  |  M a l i n c k r o d t  •  N i c k e ln i t r a t eh e x a h y d r a t e  BDH  P h o s p h o r o u sp e n t o x d ie  A n a a lR  P o t a s s u im h y d r o x d ie ;  P y r a z o e l  A l d r i c h  |  2 ( 2 p y r i d y l ) b e n z i m i d a z o l e  A l d r i c h  2,2'-l>ipyridine  M a t h e s o n ,C o e lm a n & Bell  22':6',2"-terpyridine  M a t h e s o n ,C o e lm a n & Bell  r  A n a a lR  S o d u im h y d r o x d ie  A l d r i c h  X y e ln e s  9.2.1  L R O N ( ) I A Z O L A T EP O L Y M E R S  9 . 2 . 1 . 1 P o l y b i s ( p y r a z o l a t o ) i r o n ( n ) , [Fe(pz) ] 2 x  F e r r o c e n e (0.3  g, 16 . m m o ) l , and p y r a z o e l (0.2  g, 2.9 m m o ) l w e r e m x ie d in a  C a r u is t u b e , and t h e n s e a e ld u n d e r v a c u u m . The m x it u r e was h e a t e d to 145 °C for 5 d a y s . D u r n ig t h a t t i m e , p r o d u c t in the f o r m of n e e d e ls c r y s t a li z e d f r o m the o r a n g e s o l u t i o n . A f t e r c o o l i n g to r o o m t e m p e r a t u r e , the C a r u is t u b e was o p e n e d u n d e r a d i n i t r o g e n a t m o s p h e r e . The  p r o d u c t was  267  e x t r a c t e d by w a s h n ig the s o l i d o b t a n ie d  t h o r o u g h y l w i t ha c e t o n i t r i l e . It was i s o l a t e d as r e d b r o w na i r s e n s i t i v ec r y s t a l ss u i t a b l e for  X r a y c r y s t a l o g r a p h i c a n a l y s i s . Yield 0.11  g (37  %).  A n a l y s i s c a l c u l a t e d for  CHFeN: C 3 7 . 9 ; H 3 . 2 ; N 2 9 . 5 ;f o u n d :C 3 7 . 7 ; H 3 . 4 ; N 2 9 . 4 . 6  6  4  9 . 2 . 1 . 2 P o l y 2 , 2 'b i p y r i d i n e t e t r a k i s ( i m i d a z o l a t o ) d i k o n ( n ) , [Fe2(imid)(bipy)]. 4  F e r r o c e n e (0.3 b i p y r i d i n e (0.5  g, 16 . m m o ) l , i m i d a z o l e (0.2  g, 2.9  m m o ) l and  x  e x c e s s 2,2-  g, 3.2 m m o ) l w e r e p a lc e d in a C a r u is t u b e w h c ih was  s e a e ld u n d e r  v a c u u m . The t u b e was h e a t e d to 130 °C for 2 d a y s .U n d e rt h o s ec o n d i t i o n s , the o r i g i n a l o r a n g e s o l u t i o n of f e r r o c e n e in m o t l e n l i g a n d b e c a m e am x it u r e of d a r k c r y s t a l s and b r o w n s o l u t i o n . U p o n c o o l i n g to r o o m t e m p e r a t u r e , the p r o d u c t a p p e a r e d to be a c r y s t a li n e d a r kb r o w n g r e e n s o l i d e m b e d d e d in n o n r e a c t e d l i g a n d , l i g a n d p r e c u r s o r s and f e r r o c e n e . The C a r u is t u b e was o p e n e du n d e r ad i n i t r o g e na t m o s p h e r e . The e x c e s s of l i g a n d and l i g a n d p r e c u r s o r s was e x t r a c t e d w i t h a c e t o n i t r i l e and b e n z e n e s o l v e n t s . The p r o d u c t was i s o l a t e d as d a r k g r e e n m o s it u r e s e n s i t i v e c r y s t a l s s u i t a b l e for X r a y c r y s t a l o g r a p h i ca n a l y s i s . Yield 05 .2 49.3;  H 3.8; N 26.1;  f o u n d : C 49.6;  g (60 %). A n a l y s i sc a l c u l a t e d for C22H20 Fe2Ni : C 0  H 3.7; N  26.4.  9 . 2 . 1 . 3P o l y b i s ( 4 a z a b e n z i m i d a z o l a t o ) i r o n ( n ) , [Fe(4-abimid)2] . x  F e r r o c e n e (0.2  g, 10 .7  m m o ) l and 4 a z a b e n z m i d ia z o e l ( 0 . 5 1 2 g , 4.3 m m o ) lw e r e  p a lc e d in a C a r u is t u b ew h c ih was s e a e ld u n d e rv a c u u m . The t u b e was h e a t e d at 145  268  °C  f o r6 d a y s . U n d e rt h e s e c o n d i t i o n s , t h eo r i g i n a l o r a n g es o l u t i o no ff e r r o c e n e in m o t l e n  4 a z a b e n z m i d ia z o e l b e c a m eam x it u r eo fb r o w n r e d solid a n da no r a n g es o l u t i o n .U p o n  c o o l i n g t o r o o m t e m p e r a t u r e , t h e p r o d u c t a p p e a r e d a s a c r y s t a li n e b r o w n s o l i d e m b e d d e d in t h e e x c e s s , n o n r e a c t e d i m i d a z o l e . T h e C a r u is t u b e w a s o p e n e du n d e r d i n i t r o g e n a t m o s p h e r e . T h e e x c e s s o f4 a z a b e n z m i d ia z o e l w a s e x t r a c t e d w i t h d r ya n d  o x y g e n f r e ea c e t o n i t r i l ea n dx y l e n e s . T h ep r o d u c t , w h c ih d i dn o td e c o m p o s e in a i rf o r  p e r o id su pt ot w om o n h ts ( l o n g e rp e r o id so ft m i ew e r en o te x a m n ie d ) ,w a si s o l a t e d  a m b e r g r e e n c r y s t a l s s u i t a b l e f o r s i n g l e c r y s t a l X r a y a n a l y s i s . Yield 0 0 .5 2 g ( 1 6 % ) .  A n a l y s i s c a l c u l a t e d f o r CiHFeN: C 4 9 . 3 ; H, 2 . 8 ; N 2 8 . 7 ; f o u n d : C 4 9 . 4 ; H 2 . 7 2  8  6  2 8 . 4 .  9 . 2 . 1 . 4 Poly-2,2':6', 2 " t e r p y r i d i n eo c t a k i s ( i m i d a z o l a t o ) t e t r a i r o n ( I ) , [Fe (imid) (terpy)] . 4  8  x  F e r r o c e n e ( 0 . 3 0 g, 1 6 .3 m m o ) l , i m i d a z o l e ( 0 . 2 2 g, 3 2 .6 m m o ) l a n d 2,2':6',2"-  t e r p y r i d i n e ( 0 . 3 8 g, 1 6 .3 m m o ) l w e r ep a lc e d in a C a r u is t u b ew h c ih w a s s e a e ld u  v a c u u m .T h et u b ew a sh e a t e dt o 1 3 5° Cf o r3 d a y s .U n d e rt h o s ec o n d i t i o n s ,t h eo  o r a n g e s o l u t i o n o ff e r r o c e n e in m o t l e n l i g a n d b e c a m e a m x it u r e o fd a r k c r y s t a l s a n b r o w n s o l u t i o n . U p o n c o o l i n g t o r o o m t e m p e r a t u r e , t h e p r o d u c t a p p e a r e d t o b e c r y s t a li n e d a r k g r e e n s o l i d e m b e d d e d in n o n r e a c t e d l i g a n d , l i g a n d p r e c u r s o r s , a n d  f e r r o c e n e . T h e C a r u is t u b e w a s o p e n e du n d e r a d i n i t r o g e n a t m o s p h e r e . T h e e x c e s s o  l i g a n d a n d l i g a n d p r e c u r s o r s w a se x t r a c t e dw i t ha c e t o n i t r i l ea n dt o u le n es o l v e n t s .T h e  269  p r o d u c t was  i s o l a t e d as d a r k g r e e n m o s it u r e s e n s i t i v e c r y s t a l s s u i t a b l e for X r a y  c r y s t a l o g r a p h i ca n a l y s i s . Yield 04 .3 47.2;  H 3.5; N 26.8;  f o u n d : C 47.5;  g (26 %). A n a l y s i sc a l c u l a t e d for C39H Fe4Ni9: C 35  H 3.6; N  26.9.  9 . 2 . 1 . 5P o l y b i s (1m e m y l 2 t h i o i m i d a z o l a t o ) i r o n ( I ) h e m i d i c y c l o p e n t a d i e n y l i r o n (H), [ F e ( l M e 2 S i m i d ) 0 . 5 CpFe]. 2  F e r r o c e n e (0.5 (1.5  g, 131 .4  2  g, 26 .8  x  m m o ) l and an e x c e s s of 2 m e r c a p t o l m e t h y l i m i d a z o l e  m m o ) l w e r ec o m b n ie d in a C a r u is t u b ew h c ih was s e a e ld u n d e rv a c u u m .  T h i sm x it u r e was h e a t e d at 145 °C for 6 d a y s .D u r n ig t h i sp e r i o d , ad a r k red s o l u t i o n of f e r r o c e n e in m o t l e n l i g a n d is o b t a n ie d and l i g h t y e o lw c r y s t a l s d e p o s t i e dfromthe s o l u t i o n . The r e a c t i o nm x it u r e was t h e na o lw e d to c o o ld o w n to r o o mt e m p e r a t u r e , and the  C a r u is t u b e was  p r e c u r s o r was  o p e n e d u n d e r a d i n i t r o g e n a t m o s p h e r e . The  e x c e s s of l i g a n d  e x t r a c t e d w i t h dry and o x y g e n f r e e a c e t o n i t r i l e , and r e s i d u a l f e r r o c e n e  was r e m o v e dw i t h dry t o l u e n e . The c o m p o u n d was i s o l a t e d as g o d le nn e e d e l c r y s t a l s , w h c ih w e r e s t a b l e for at l e a s t am o n h t of e x p o s u r e to air ( o l n g e rp e r o id s of t m i ew e r e not i n v e s t i g a t e d ) . Yield 0 0 .9 4 g (9 %). A n a l y s i sc a l c u l a t e d for CiHiFei.NS: C 3  H 4.0; N 14.9;  f o u n d : C 41.5;  H 4.0; N  14.7.  270  5  5  4  2  41.6;  9.2.2  C O B A L T ( H )M I D IA Z O L A T EP O L Y M E R S  9 . 2 . 2 . 1 P o l y b i s ( i m i d a z o l a t o ) c o b a l t ( I ) , [Co(imid) ] . 2 x  C o b a l t ( I ) n i t r a t eh e x a h y d r a t e (7.5 g, 3 3m m o ) l w a sd s is o v le d in 1 0 m l o fh o t  w a t e ra n d a d d e dd r o p w s ie t o as o l u t i o no fi m i d a z o l e (3.4 g, 5 0m m o ) l in 4 0m lo w a t e r . The m x it u r e w a sb r o u g h t to boil a n dt h e n m i m e d a it e y l filtered.The s o l i d  o b t a n ie dw a sw a s h e dw i t h hot w a t e rfirst,t h e nw i t ha c e t o n e . The p r o d u c tw a si s o l a t e d a s a m i c r o c r y s t a l i n e p u r p e l p o w d e r a n dw a sd r i e d in vacuo at 1 0 0 °C. Yield 02 .5 g (5%). A n a l y s i sc a l c u l a t e d forCHNCo: C 37.3, H 3.1, N 29.0; f o u n d : C 37.6, H 3.0, N 6  6  4  28.7. T h i s c o m p o u n dw a s a s lo o b t a n ie db yr e m o v a l ( t h e r m o l y s i s ) o ft w om o e lc u e ls of n e u t r a l i m i d a z o l e f r o m c o m p o u n d [Co3(imid)6(imidH)2] (see s e c t o in 9 . 2 . 2 . 5 b e l o w ) . x  T h i s t h e r m a l t r e a t m e n t of [Co3(imid)6(imidH)2] w a s c a r r i e d out u n d e r afluxof x  d i n i t r o g e n utilizing a T An Is t r u m e n t sT G A5 1 u n i t . At h i r t ym n iu t es io t h e r ma t3 2 5 °C  w a sp r o g r a m m e d in t h en is t r u m e n t in o r d e rt or e m o v et h en e u t r a li m i d a z o l ec o m p e lt e y l A n a l y s i sf o u n d : C 37.1, H 3.0, N 28.8.  9 . 2 . 2 . 2P o l y b i s ( 2 m e t h y l i m i d a z o l a t o ) c o b a l t ( I ) ,[ C o ( 2 m e i m i d ) ] . 2 x  C o b a l t ( I ) n i t r a t e h e x a h y d r a t e (1.0 g, 3.7 m m o ) l w a sd s is o v le d in 1 0 ml of  e t h a n o l a n da d d e dd r o p w s ie t o as o l u t i o no f2 m e t h y m i l d ia z o e l (3.0 g, 3 7m m o ) l in 4 ml of e t h a n o l . The p u r p e l p r e c i p i t a t e w h c ih f o r m e d m i m e d a it e y l w a sfilteredoff,  271  w a s h e d w i t h e t h a n o l , and d r i e d for c a l c u l a t e d for CHCoN: C 43.4, 8  1 0  1h o u r at 115  H 4.6, N 25.3;  4  °C. Yield 01 .5  f o u n d : C 43.0,  H 4.3, N  g (18  %). A n a l y s i s  24.9.  9 . 2 . 2 . 3P o y lb s i( 4 m e m y m i l d ia z o a lt o ) c o b a t l( L T ) ,[ C o ( 4 m e i m i d ) ] . 2 x  C o b a l t ( I ) c h l o r i d e h e x a h y d r a t e (1.0  g, 4.2 m m o ) l was  d s is o v le d in 15 ml  w a t e r and a d d e dd r o p w s ie to a s o l u t i o n of 4 m e t h y m i l d ia z o e l (3.0 of w a t e r . S o d u im h y d r o x d i e (1.48  g, 37 m m o ) l was  of  g, 37 m m o ) l in 30 ml  d s is o v le d in 5 ml of w a t e r and  a d d e d d r o p w s ie to the m x it u r e to c o m p e lt e the p r e c i p i t a t i o n of a f i n ep u r p e l p o w d e r . The p r e c i p i t a t e was  f i l t e r e d off,  r o o mt e m p e r a t u r e . Yield 03 .6 4.6, N 25.3;  f o u n d : C 43.6,  w a s h e d w i t hw a t e r and t h e n e t h a n o l , and a i r d r i e d at g (39 %). A n a l y s i sc a l c u l a t e d for C g H o iC o N ^ C 43.5,  H 4.5, N  H  25.0.  9 . 2 . 2 . 4P o l y b i s ( b e n z i m i d a z o l a t o ) c o b a l t ( I ) , [Co(benzimid)2] . x  B e n z m i d ia z o e l (11.8  g, 100  m m o ) l was  d s is o v le d in 20 ml of hot w a t e r and  a d d e d to a s o l u t i o n of c o b a t l ( L T )n i t r a t eh e x a h y d r a t e (15.0  g, 515 .  m m o ) ld s is o v le d in 80  ml of hot w a t e r . A p u r p e l p r e c i p i t a t ef o r m e dm i m e d a it e y l. The m x it u r e was b r o u g h t to boil. A f t e r the s o l u t i o n was c o o l e d , the p r e c i p i t a t e was f i l t e r e d off, w a s h e dw i t he t h a n o l , w a t e r and a c e t o n e , and d r i e du n d e rv a c u u m . Yield 5.1 g (34 %). A n a l y s i sc a l c u l a t e d , for C14H10C0N4:  C 57.3,  H 3.4, N 19.1;  f o u n d : C 57.5,  272  H 3.3, N  19.2.  9 . 2 . 2 . 5P o y lb s i( m i d ia z o e l) h e x ^  [Co3(imid)6(imidH)]x. 2  T h i s c o m p o u n d w a s o b t a n ie d a s ap u r p e l p o w d e rb yh e a t i n g , t o 1 5 0 ° C f o r  d a y s , a m x it u r e o fa n e x c e s s o fi m i d a z o l e ( 2 . 0 g, 2 6 m m o ) l w i t h c o b a t l o c e n e ( 0 . 2  1 0 .6 m m o ) l in a s e a e ld a n d e v a c u a t e d C a r u is t u b e . D r yx y e ln e s a n d a c e t o n i t r i l e w  u s e dt oi s o l a t et h ep r o d u c tf r o mr e s i d u a ll i g a n dp r e c u r s o r . Yield 0 3 .4 g ( 4 5% ) .A n a c a l c u l a t e df o r C 4H26Co3N : C 4 0 . 3 ,H3 . 6 ,N3 1 . 3 ;f o u n d :C4 0 . 8 ,H3 . 6 ,N3 1 . 2 . 2  16  9 . 2 . 2 . 6P o l y b i s ( 4 a z a b e n z i m i d a z o l a t e ) c o b a l t ( I ) , [Co(4-abimid)2]. x  C o b a t l o c e n e ( 0 2 . g, 1 0 .6 m m o ) l a n d 4 a z a b e n z m i d ia z o e l ( 0 . 5 1 2 g , 4 . 3 m m o ) l  w e r ep a lc e d in a C a r u is t u b ew h c ih w a s s e a e ld u n d e rv a c u u m . T h et u b ew a sh e a t e  1 4 5 ° C f o r 4 d a y s . U p o n c o o l i n g t o r o o m t e m p e r a t u r e , t h e C a r u is t u b e w a s o p u n d e r a d i n i t r o g e n a t m o s p h e r e . T h e e x c e s s o f4 a z a b e n z m i d ia z o e l w a s e x t r a c t e dw i t h  d r ya n do x y g e n f r e ea c e t o n i t r i l ea n dx y l e n e s .T h ep o y lm e rw a si s o l a t e da sad a r kp u r p  m i c r o c r y s t a l i n e solid. Yield 0 0 .9 g ( 2 9% ) .A n a l y s i sc a l c u l a t e df o r CiHCoN: C 4 8 . 8 ; 2  8  6  H2 . 7 ;N2 8 . 5 ;f o u n d :C5 0 . 1 ;H2 . 8 ;N2 8 . 4 .R e p e a t e da n a y ls s i o nt w od i f f e r e n t o f [Co(4-abimid)2] c o n s i s t e n t l y g a v e g o o d H a n d N r e s u l t s a n d h i g h C. T h e r e is x  e x p a ln a t o in f o r t h e h i g h C e x c e p t t o s u g g e s t t h e r e m a yb e s m a l a m o u n s t o fs o v l t r a p p e d in t h es a m p e l.  273  9 . 2 . 2 . 7 P o l y 2 , 2 'b i p y r i d i n e t e t r a l d s ( i m i d a z o l a t o ) d i c o b a l t ( l T ^ [Co (imid) (bipy)] . 2  C o b a t l o c e n e (0.3 b i p y r i d i n e (0.5  g, 16 . m m o ) l , i m i d a z o l e (0.2  4  x  g, 2.9 m m o ) l and e x c e s s 2,2'-  g, 3.2 m m o ) l w e r e p a lc e d in a C a r u is t u b e w h c ih was s e a e ld u n d e r  v a c u u m . The t u b e was h e a t e d to 130 °C for 2 d a y s . The C a r u is t u b e was o p e n e du n d e ra d i n i t r o g e n a t m o s p h e r e . The e x c e s s of l i g a n d and l i g a n dp r e c u r s o r s was e x t r a c t e dw i t h a c e t o n i t r i l e and  b e n z e n es o l v e n t s . The  m i c r o c r y s t a l i n e solid. Yield 04 .7 48.7;  9.2.3  H 3.7; N 25.8.  F o u n d : C 49.0;  p r o d u c t was  o b t a n ie d as  ap u r p e l  g (54 %). A n a l y s i s c a l c u l a t e d for C22H20C02N10'. C H 3.7; N  25.6.  N C IK E L ( H )M I D IA Z O L A T EP O L Y M E R  9 . 2 . 3 . 1 P o l y b i s ( b e n z i m i d a z o l a t o ) n i c k e l ( I ) ,[ N i ( b e n z i m i d ) ] . 2 x  B e n z m i d ia z o e l (11.8  g, 100 m m o ) l was d s is o v le d in 20 ml of hot w a t e r and  a d d e d to a s o l u t i o n of n i c k e l ( I I )n i t r a t eh e x a h y d r a t e (15.0  g, 51.5 m m o ) ld s is o v le d in 80  ml of hot w a t e r . Al i g h tv i o l e t p r e c i p i t a t e was f o r m e d m i m e d a it e y l. The m x it u r e was b r o u g h t to the boil. A f t e r the s o l u t i o n was c o o l e d , the p r e c i p i t a t e was f i l t e r e d off, w a s h e dw i t he t h a n o l , w a t e r and a c e t o n e , and d r i e du n d e rv a c u u m . Yield 08 .2 A n a l y s i s c a l c u l a t e d for CiHiNiN: C 57.5, 4  0  4  19.2.  274  H 3.4, N 19.2;  f o u n d : C 57.2,  H 3.4, N  g (5  %).  9 . 2 . 4 C O P P E RM I D IA Z O L A T EP O L Y M E R S  I n t h e f o l o w i n g s y n t h e s e s , w h e r e v e r c o p p e r is u s e d a s a r e a c t a n t it r e f e r s t o c o p p e rm e t a lb e a d s ( 3 5 m md a im e t e r )w h c ih h a db e e nc e la n e db yw a s h n ig t h e m 1 2MH C 1 ,w a t e r ,a n da c e t o n ep r i o rt ou s e .  9 . 2 . 4 . 1 P o l y b i s ( i m i d a z o l a t o ) c o p p e r ( I ) , [Cu(imid)2]. x  C o p p e r( 8 . 1 3 g , 1 2 8m m o ) la n di m i d a z o l e( 1 0 g, 1 4 7m m o ) lw e r ep a lc e d in a  m l r o u n d b o t o m e d f l a s k f i t t e d w i t h a c o n d e n s e r . T h er e a c t i o nm x it u r ew a s h e a t e dt o  1 1 0° Ca n da i rw a sb u b b e ld i n t ot h em x it u r e via a P y r e xt u b ef o r4 8 h. A d a r kb  b e g a nt of o r m .S u b m i l e di m i d a z o l ew a sp e r i o d i c a ly s c r a p e db a c ki n t ot h er e a c t i o nf l a s k  d u r n ig t h e r e a c t i o n . U p o n c o o l i n g , t h e solidified m x it u r e w a s e x t r a c t e d w i t h e t h a n o l ,  s u c t o i n filtered, a n d f u r t h e r w a s h e d w i t h a c e t o n e , a n d a i r d r i e d a t r o o m t e m p e r a t u r e .  T h ed a r kb u le p o w d e r yc o m p o u n dw a si s o l a t e db yp h y s i c a l s e p a r a t o in f r o mt h ec o p p e  s h o t . A 8 4 % yield w a s o b t a n ie d b a s e d o n a m o u n t o f c o p p e r r e a c t e d . A n a l y s i s c a l c u l a t e d forCHCuN: C 3 6 . 4 ,H3 . 1 ,N2 8 . 3 ;f o u n d :C3 6 . 5 ,H3 . 0 ,N2 7 . 9 . 6  6  4  9 . 2 . 4 . 2 P o l y b i s ( 2 m e t h y l i m i d a z o l a t o ) c o p p e r ( I ) , [Cu(2-meimid)2] . x  C o p p e r( 1 . 9 g, 3 0 m m o ) l a n d a n e t h a n o l i cs o l u t i o n ( ~ 7 5 m l ) o f 2 -  m e t h y m i l d ia z o e l ( 3 . 0 g, 3 7m m o ) lw e r ep a lc e d in a r o u n d b o t o m e d flask. T h er e a c t i o n  275  m x it u r e w a s s t i r r e d a t r o o m t e m p e r a t u r e f o r 3 d a y s . A d a r kb r o w np r e c i p i t a t e , w h  f o r m e d , w a s s u c t o i n filtered a n d w a s h e d t h o r o u g h y l w i t h e t h a n o l a n d a c e t o n e . Air  d r y i n ga tr o o mt e m p e r a t u r ey i e l d e d al i g h tb r o w np o w d e r . A 7 7 % yield w a s o b t a n i  ( b a s e do na m o u n to fc o p p e rr e a c t e d ) .A n a l y s i sc a l c u l a t e df o rC g H o iC u N ^C4 2 . 6 , H 4.5 N2 4 . 8 ;f o u n d :C4 2 . 4 , H 4.3, N 2 4 . 5 .  9 . 2 . 4 . 3P o l y b i s ( 4 m e t h y l i m i d a z o l a t o ) c o p p e r ( U ) ,[ C u ( 4 m e i m i d ) ] . 2 x  C o p p e r ( I ) s u p lh a t e h e x a h y d r a t e ( 1 . 0 g, 3 . 7 m m o ) l w a s d s is o v le d in 1 5 m l o  w a t e ra n da d d e dd r o p w s ie t oas o l u t i o no f4 m e t h y m i l d ia z o e l ( 3 . 0 g, 3 7m m o ) l in 5 0  o fw a t e r .3 5m lo fa 1 M a q u e o u ss o l u t i o no f NH3 w a sa d d e dd r o p w s ie t ot h em  c o m p e lt e t h e p r e c i p i t a t i o n o fa f i n e b r o w n p o w d e r . T h e p r e c i p i t a t e w a s f i l t e r e d off  w a s h e d w i t h w a t e r a n d t h e n e t h a n o l , a n d a i r d r i e d a t r o o m t e m p e r a t u r e . A b r o w  p o w d e r y solid w a s o b t a i n e d . Yield 0 5 .7 g ( 6 8 % ) . A n a l y s i sc a l c u l a t e df o rC HioCuN 8  C4 2 . 6 , H 4.5, N 2 4 . 8 ;f o u n d :C4 2 . 6 , H 4.5, N 2 4 . 5 .  9 . 2 . 4 . 4P o l y b i s ( b e n z i m i d a z o l a t o ) c o p p e r ( n ) ,[ C u ( b e n z i m i d ) ] . 2 x  C e la nc o p p e rb e a d s( 1 . 0 g, 1 6m m o ) la n da ne t h a n o l i cs o l u t i o no fb e n z m i d ia z o e l  ( 3 . 6 g, 3 0m m o ) lw e r ep a lc e d in a r o u n db o t o m flask. A f t e r5d a y so fv g io r o u ss  o ft h es o l u t i o na tr o o mt e m p e r a t u r e , ar e dp r e c i p i t a t ew a sf o r m e d .T h e solid w a ss u c  filtered a n d w a s h e d w i t h e t h a n o l . A f t e r a i rd r y i n g a tr o o mt e m p e r a t u r et h e c o m p o u n d  276  was  o b t a n ie d as a red p o w d e r . 79 % y i e l d was  o b t a n ie d b a s e d on a m o u n t of c o p p e r  r e a c t e d . A n a l y s i s c a l c u l a t e d for CiHiCuN: C 56.5, 4  3.4, N  0  4  H 3.4,  N 18.8;  f o u n d : C 56.2,  H  18.6.  9 . 2 . 4 . 5P o l y b i s ( 4 , 5 d i c h l o r o i m i d a z o l a t o ) c o p p e r ( I ) , [Cu(4,5-dichloroimid)2] x  C o p p e r ( I ) s u p lh a t ep e n t a h y d r a t e (1.0  g, 4.0 m m o ) l was  d s is o v le d in 15 ml  w a t e r and a d d e dd r o p w s ie to a s o l u t i o n of 4 , 5 d i c h l o r o i m i d a z o l e (3.0 ml of hot w a t e r . 20 ml of a 1 M a q u e o u s s o l u t i o n of NH3 was  of  g, 22 m m o ) l in 60  a d d e d d r o p w s ie to  the  m x it u r e to c o m p e lt e the p r e c i p i t a t i o n of a f i n eg r a y p n ik p r e c i p i t a t e . The p r e c i p i t a t e was f i l t e r e d off,  w a s h e dw i t hw a t e r and t h e ne t h a n o l , and air d r i e d at r o o mt e m p e r a t u r e . A  v i o l e t p o w d e r y p r o d u c t was C6H Cl4CuN : C 21.5, 2  4  o b t a i n e d . Yield 03 .7  H 0.6, N 16.7;  f o u n d : C 21.6,  g ( 28 %).  H 0.8, N  9.3  P H Y S C IA LM E T H O D S  9.3.1  M A G N E T C I S U S C E P T B IL IT IY M E A S U R E M E N T S  DC  A n a l y s i s c a l c u l a t e d for  17.0.  m a g n e c t i s u s c e p t i b i lt y m e a s u r e m e n s t w e r e p e r f o r m e d u s n ig a Q u a n u tm  D e s g in ( M P M S )S Q U D I m a g n e t o m e t e r .T h e s em e a s u r e m e n s t w e r e m a d e at t e m p e r a t u r e s o v e r the r a n g e 2 3 0 0 K and, 500  and  10 000  u n e ls s o t h e r w s ie s t a t e d , at a p p l i e dfieldsof  G. M a g n e t z ia t o in s t u d e is as a f u n c t i o n of field s t r e n g t h (0-55  277  000  G)  w e r em a d ea t s e v e r a lt e m p e r a t u r e s a n dh y s t e r e s s i m a g n e t z ia t o in d a t aw e r eo b t a n ie db y  o s c i la t i n gt h ea p p l i e dm a g n e c t i field b e t w e e n+ 5 5 0 0 0Ga n d5 5 0 0 0Gu s u a l ya  K . T h e s a m p e l h o d le r is m a d eo f PV Cp l a s t i ca n d is d e s g in e dt o g ou n d e t e c t e db  m a g n e t o m e t e r . T h eP V C s a m p e l h o d le ra n dd e t a i l sr e g a r d n ig t h eu s eo ft h ee q u p im e n h a v eb e e nd e s c r b ie db e f o r e [1]. M a g n e t c i s u s c e p t i b i lt i e sw e r ec o r r e c t e df o rb a c k g r o u n d  a n d f o r t h e d a im a g n e s t im o f all a o tm s u s n ig P a s c a s l ' c o n s t a n t s [2]. All m a g n e c t i  m e a s u r e m e n s t w e r ed o n eo nf i n ep o w d e r e ds a m p e ls a n dt h ed a t ar e p o r t e dh e r ea r eo  p e rm o e l o fm e t a li o nb a s i s .T e m p e r a t u r ec a l i b r a t i o n so nt h eS Q U D I m a g n e t o m e t e ra r e p e r f o r m e d u s n ig a n e x t e r n a l p a lt n iu m r e s s it a n c e t h e r m o m e t e r a n d a t e m p e r a t u r e a c c u r a c yw i t h i n 0 1 .% is a t t a i n e d . M a g n e t c i s u s c e p t i b i lt ys i g n a l sw e r ec a l i b r a t e du s n ig u l t r a p u r en i c k e ls t a n d a r da n da c c u r a c yw i t h i n1 % is o b t a i n e d .  W h e nam a t e r i a l is s u s p e c t e dt ob e h a v ea sam o e lc u e lb a s e dm a g n e tb e o lw a T  s u c h a s t h e m a j o r i t y o ft h e t r a n s i t i o n m e t a l i m i d a z o l a t e c o m p o u n d s d e s c r b ie d in t h i s  t h e s i s ,c e r t a i np r e c a u t o in sm u s tb et a k e n in t h ed e t e r m n ia t o in o f its m a g n e c t i p r o p e r t i e s t o a v o d i m s ie la d n ig r e s u l t s . P r o b e lm s a r e e n c o u n t e r e d if t h e r e m n a n t m a g n e t z ia t o in  p r e s e n ta f t e rt h ec o le c t i o no fo n es e to fm a g n e c t i d a t a is n o tr e m o v e db e f o r ea n o t h e r  o fm a g n e c t i d a t a is c o le c t e d . If n o tr e m o v e d ,t h er e m n a n tm a g n e t z ia t o in m a yi n f l u e n c e  o rd o m n ia t ea n yn e wm a g n e c t i s i g n a ld e t e c t e db yt h em a g n e t o m e t e r .Ac o n v e n e in tw a y  t o r e m o v e t h i s m a g n e t z ia t o i n is t o h e a t t h e s a m p e l a b o v e its T, t h e n , s e tt h e a p c  field t o z e r o b yo s c i la t i n gt h e field b e t w e e np o s i t i v e a n d n e g a t v ie v a u le s ( d e c r e a s n ig  t h e m a g n t u id e o ft h e field in e a c h oscilation), a n d finally c o o l i n g t h e s a m p e l t o t  278  d e s r ie d t e m p e r a t u r e in z e r o a p p l i e d field. T h i s p r o c e d u r e w a s a p p l i e d t o e v e r y m o e lc u e lb a s e dm a g n e ti n v e s t i g a t e d in t h i sd i s s e r t a t i o n .  A C m a g n e c t i s u s c e p t i b i l t y m e a s u r e m e n s t w e r e m a d e b y W . M . R e i f f a t N o r t h e a s t e r n U n i v e r s i t y u s n ig a L a k e S h o r e C r y o t r o n c is Co. M o d e l 7 0 0 0 A C  s u s c e p t o m e t e r ,g e n e r a l yo v e rt h et e m p e r a t u r er a n g e4 . 2 Kt o3 0 K in a nA C field o Go r2 . 5Ga tf r e q u e n c e is o f1 2 5H zo r5 0 0H z .  9 . 3 . 2 S N IG L EC R Y S T A LX R A YD F IF R A C T O IN  M e a s u r e m e n t s w e r em a d eb y S. J. R e t t i ga n d B. O . P a t r i c k o ft h i s D e p a r t m e n u s n ig e i t h e r a R g ia k u A /D S C C C D d i f f f a c t o m e t e r o r a R g ia k u AFC6S d i f f r a c t o m e t e r , b o t h w i t h g r a p h t i e m o n o c h r o m a e td M o K a r a d i a t i o n . T h e o lw t e m p e r a t u r e s i n g l e c r y s t a lX r a yd i f f r a c t i o ns t u d yo f [Fe2(imid)4(bipy)] w a sp e r f o r m e db y B. O .P a t r i c k . x  9 . 3 . 3 P O W D E RX R A YD F IF R A C T O IN  P o w d e rd f i f r a c t o g r a m sw e r er e c o r d e da tr o o mt e m p e r a t u r eo naR g ia k uR o t a f l e x R U 2 0 0 B H r o t a t i n g a n o d e p o w d e r X r a y d i f f r a c t o m e t e r ( g r a p h i t e m o n o c h r o m a e td C u  Ka r a d i a t i o n ) . S a m p e ls w e r e p r e p a r e d b y a p p y ln ig a h e x a n e s s l u r r yo ft h e c o m p o u n d o n t oag a ls sp l a t ea n da l o w i n gt h es o v le n tt oe v a p o r a t e .  279  9 . 3 . 4 E L E M E N T A LA N A L Y S S I  M i c r o a n a l y s i sw e r ep e r f o r m e db yP .B o r d ao ft h i sD e p a r t m e n t .AC a r l oE r b a  M o d e l 1 1 0 6o raF s io n s( E r b a )n Is t r u m e n t sE A1 1 0 8C H N OE e lm e n t a lA n a y lz e rw e r e utilized f o rd e t e r m n ia t o in o fc a r b o n ,h y d r o g e na n dn i t r o g e np e r c e n t a g e s .E e lm e n t a l a n a y ls e sa r ec o n s d ie r e dt oh a v ea na b s o u lt ea c c u r a c yw i t h i n ±0.3%.  9 . 3 . 5 M O S S B A U E RS P E C T R O S C O P Y  T h e M o s s b a u e r s p e c t r a w e r e o b t a n ie d b y W . M .R e i f fa t N o r t h e a s t e r n U n i v e r s i t yu s n ig a c o n v e n t o in a l c o n s t a n ta c c e l e r a t i o n s p e c t r o m e t e ro p e r a t e d in  m u t l c ih a n n e l s c a l i n gm o d e . T h eg a m m ar a ys o u r c e( D uP o n t -M e r c kC o . ) c o n s s it e do  5 1 5 . m C i o f Co in a r h o d u im m e t a l m a t r x i t h a t w a s m a n it a n ie d a t a m b e in 5 7  t e m p e r a t u r e .T h es p e c t r o m e t e rw a sc a l i b r a t e du s n ig a 6 m c ir o nt h i c kn a t u r a la b u n d a n c e  i r o n foil. s Io m e r s h i f t s a r e r e p o r t e d r e l a t i v e t o t h e c e n t e r o ft h e m a g n e c t i h y p e r f n ie  p a t t e r no ft h el a t t e r foil t a k e na sz e r ov e l o c i t y . A p e iz o n Ng r e a s em u l s a m p e ls ( w h e t h ec o m p o u n d s s t u d e id w e r e in a m a c r o c r y s t a l i n ef o r m ) ,w e r e u s e d in all  m e a s u r e m e n s t c a r r i e do u t . S a m p e l t e m p e r a t u r ev a r i a t i o nw a sa c h e iv e du s n ig a s t a n d a r d  e x c h a n g eg a s liquid h e u i lm c r y o s t a t( C r y oI n d u s t r i e so fA m e r i c a ,I n c . )w i t ht e m p e r a t u r e  m e a s u r e m e n ta n dc o n t r o lb a s e do n silicon d o id et h e r m o m e t r y in c o n u jn c t o in w i t ha 1 m c ir o a m p e r e e x c i t a t i o n s o u r c e ( L a k e s h o r e C r y o t r o n i c s , I n c ) . S p e c t r a w e r e fit t o u n c o n s t r a n ie dL o r e n t z a in su s n ig t h ep r o g r a mO R G IN I ( M i c r o c a lS o f t w a r e ,I n c . ) .  280  9 . 3 . 6 E L E C T R O N C I S P E C T R O S C O P Y  E l e c t r o n i c s p e c t r a ( 2 0 0 3 0 0 0 n m ) w e r e o b t a n ie d a t r o o m t e m p e r a t u r e u s n ig a V a r i a nC a r y5 U V V i s N I R s p e c t r o p h o t o m e t e r . S a m p e ls w e r ep r e p a r e da sN u j o lm u s l p r e s s e db e t w e e nq u a r t zp l a t e s .  9 . 3 . 7  T G A  T h e r m a l g r a v i m e t r i c a n a l y s i s ( 3 5 ° C t o 8 0 0 °C) w a s d o n e u s n ig a T A  n Is t r u m e n t sT A2 0 0 0 s y s t e mw i t haT G A 5 1 unit. P o w d e r e ds a m p e ls ( 71 2m g )  h e a t e d in a d i n i t r o g e n a t m o s p h e r e a t a r a t e o f 1 0 ° C p e r m n iu t e t o a m a x m i t e m p e r a t u r eo f8 0 0 °C.  9 . 3 . 8N IF R A R E DS P E C T R O S C O P Y  I n f r a r e d s p e c t r a ( 4 0 0 0 4 0 0 c m " ) w e r e r e c o r d e d a t r o o m t e m p e r a t u r e o n a 1  B o m e m F T R I s p e c t r o p h o t o m e t e r u s n ig K B r d s ik s a m p e ls o r N u j o l m u s l p r e s s e d b e t w e e nK B rd i s k s .B a n dfrequenciesa r ea c c u r a t et ow i t h i n± 4 cm" . 1  281  9 . 3 . 9 N M RS P E C T R O S C O P Y  N u c e la r m a g n e c t i r e s o n a n c e s p e c t r a w e r e r e c o r d e d in a B r u k e r A C 2 0 0 FT-  N M RS p e c t r o m e t e r .N M Rs o v le n t sw e r eu s e da si n t e r n a ls t a n d a r d sf o rc a l i b r a t i o no ft h e o b s e r v e dc h e m c ia l shifts.  282  R e f e r e n c e s  1.  M. K. E h l e r t . Ph. D. T h e s i s .U n i v e r s i t y of British C o u lm b a i, 1992.  2.  E. K o n i g . Landolt-Bdrstein Numerical Data and Functional Relationships Science and Technology. New S e r i e s , Vol. I/2. K. H. H e w l e g e and A. M H e w l e g e Eds. S p r i n g e r V e r l a g , Berlin, 1966.  283  A P P E N D X I I  T a b e l 1-1  S N IG L EC R Y S T A LX R A YD F IF R A C T O I ND A T A  C r y s t a l o g r a p h i cd a t a for [Fe(pz)2] x  M o e lc u a lr f o r m u a l  CHFeN  f w  9 4 9 .9  C r y s t a ls y s t e m  o r t h o r h o m b c i  S p a c eg r o u p  b Ia m (No.  a/A  7 . 5 1 5 ( 2 )  blk  1 4 . 6 0 4 ( 4 )  elk  7 . 3 5 9 ( 1 )  6  6  4  V/k  8 0 7 . 7 ( 2 )  Z  8  3  DJg  72)  1 5 .6 2  cm" 3  /I ( M o K o O c /m "  1 8 0 .2  C r y s t a ls z ie m / m  0 . 5 0 x 0 . 1 0 x 0 . 1 0  R(Ff  0 0 .2 4  Rw iff  0 0 .3 2  1  R{F) =  l  S||Fo|-|Fc||/2|F |, Rw 0  (F ) 2  -  (2Zw\\F \-\F \\rLw\F \ ) 2  0  284  2  c  2 2  0  T a b e l 1 2  S e e lc t e d b o n d e ln g t h s ( A ) a n d a n g e ls (°) f o r [Fe(pz) ] w i t h e s t m i a t e d 2 x  s t a n d a r dd e v i a t i o n s in p a r e n t h e s e s .  F e ( l ) — N ( l )  N ( l ) — C ( 3 )  2 . 0 2 7 ( 1 )  1 . 3 3 7 ( 2 )  N ( l > — F e ( l ) — N ( l a )1 1 0 . 2 7 ( 6 )  N ( l ) — F e ( l ) — N ( l b )1 0 8 . 9 3 ( 6 )  N ( l ) — F e ( l ) — N ( l c )  1 0 9 . 2 2 ( 6 )  N ( l a ) — F e ( l } — N ( l b )  1 0 9 . 2 2 ( 9 )  N ( l a > — F e ( l ) — N ( l c ) 1 0 8 . 9 3 ( 9 )  N ( l b ) — F e ( l ) — N ( l c )  1 1 0 . 2 7 ( 9 )  T a b e l 1 3  C r y s t a l o g r a p h i cd a t af o r[ F e ( 4 a b i m i d ) ] . 8  2 x  M o e lc u a lr f o r m u a l  CHFeN  f w  2 9 2 0 .8  C r y s t a ls y s t e m  o r t h o r h o m b c i  S p a c eg r o u p  P 2 i 2 ! 2 i( N o . 1 9 )  a/A  9 . 6 5 5 ( 2 )  b/A  1 0 3 .4 0 3 ( 6 )  elk  1 2 4 .6 7 1 ( 7 )  1 2  6  6  U/A  1 2 4 4 . 6 ( 2 )  Z  4  3  285  ZVg  1 5 .5 9  cm" 3  5 9 2 0 .0  F ( 0 0 0 ) H( M o K a V c m "  120 .4  C r y s t a ls z ie m / m  0 . 1 5 x 0 . 2 0 x 0 . 2 0  26max/°  6 0 . 1  T o t a lr e f l e c t i o n s  11118  U n q iu er e f l e c t i o n s  3 2 3 3  No. w i t h / > 3 o ( i )  1685  No. of v a r i a b l e s  172  R ; R w ( i % / > 3 a ( 7 ) )  0 . 0 3 4 ;0 0 .2 4  R; Rw (F\  0 . 0 8 4 ;0 0 .5 5  1  al d a t a )  1 2 .2  gof  a  T e m p e r a t u r e 180 K, R g ia k u A /D S C CCD d i f f r a c t o m e t e r , Mo Ka (k = 0 . 7 1 0 6 9 ) ,g r a p h t i e  m o n o c h r o m a t o r ,t a k e o f fa n g e l 6.0°, m m f r o m the c r y s t a l , o^)  a p e r t u r e 94.0 x 94.0 m m at a d s it a n c e of 3 9 . 2 2 ( 7 )  = (C + Z ? ) L /p 2 (C = s c a nc o u n t ,B=b a c k g r o u n dc o u n t ) ,  2  f u n c t i o nm n im i z ie d l.w(\Fo \-\Fc \) w h e r e w = l/o^fF), R(F) = S||Fo|-[Fcl|/S|F|, Rw (F ) 2  2  2  2  2  0  = (S||Fo|-|Fc||/Iw|Fo|), and gof = [Sw(|F|-|Fc|)/(m-n)] . 2  2  222 1 /  2  W  0  286  22  2 1 /  T a b e l 1 4  S e e lc t e d b o n d e ln g t h s ( A ) a n d a n g e ls (°) f o r [Fe(4-abimid)2] w i t h x  e s t m i a t e ds t a n d a r dd e v i a t i o n s in p a r e n t h e s e s * .  F e ( l ) — N ( l )  2 . 0 3 0 ( 3 )  F e ( l ) — N ( 2 )  2 . 0 4 6 ( 3 )  F e ( l ) — N ( 4 )  2 . 0 4 4 ( 3 )  F e ( l > — N ( 5 )  2 . 0 3 4 ( 3 )  a  b  N ( l ) — F e ( l ) — N ( 2 )  1 1 0 3 .9 ( 1 1 )  N ( l ) — F e ( l ) — N ( 4 )  1 0 2 1 .0 ( 1 1 )  N ( l > — F e ( l ) — N ( 5 )  1 1 1 7 .6 ( 1 1 )  N ( 2 — ) F e ( l ) — N ( 4 )  1 0 4 3 .1 ( 1 1 )  N ( 2 ) — F e ( l ) — N ( 5 )  1 0 9 5 .5 ( 1 1 )  N ( 4 ) — F e ( > l— N ( 5 )  1 1 8 2 .4 ( 1 1 )  (l)_N(l)—C(l)  1 2 8 . 8 ( 3 )  F e ( l ) — N ( l ) C ( 6 )  1 2 7 . 8 ( 2 )  F e — ( ) l N ( 2 > — C ( 2 )  1 3 2 . 6 ( 2 )  F e ( l ) — N ( 2 ) — C ( l )  1 2 3 . 5 ( 2 )  F e ( ) l — N ( 4 > — C ( 1 2 )  1 3 1 . 1 ( 2 )  F e ( ) l — N ( 4 ) — C ( 7 )  1 2 4 . 1 ( 3 )  F e ( l — ) N ( 5 ) — C ( 7 )  1 2 7 . 6 ( 2 )  F e ( l ) — N ( 5 ) — C ( 8 )  1 2 9 . 1 ( 2 )  a  b  a  b  F e  c  a  a  b  c  d  * S u p e r s c r p it sr e f e rt os y m m e r t yo p e r a t i o n s :( a )1 / 2 + x ,3 / 2 y , 1 z ( b ) 1 x ,1 / 2 + y ,3 / 2 z ( c ) 1 / 2 + x ,3 / 2 y , 1 z ( d ) 1 x , 1 / 2 + y ,3 / 2 z  287  T a b e l 1-5  C r y s t a l o g r a p h i cd a t a for a- and y-[Fe2(imid)(bipy)]x. 4  a p h a s e  y p h a s e  M o e lc u a lr f o r m u a l  C22H2oFe2Nio  C22H2oFe2Nio  f w  5 3 6 1 .6  5 3 6 1 .6  C r y s t a ls y s t e m  triclinic  triclinic  S p a c eg r o u p  PI (No.  PI (No.  o  2)  2)  a, A  1 0 . 5 0 7 ( 4 )  1 0 4 .1 3 8 ( 5 )  b, A  1 3 . 7 3 0 ( 4 )  1 3 5 .0 7 5 ( 5 )  c, A  9 . 1 8 8 ( 3 )  2 6 . 0 6 0 ( 1 )  oc, deg  1 0 6 . 5 1 ( 3 )  1 0 4 5 .3 0 ( 2 )  Meg  1 0 8 . 3 2 ( 3 )  9 3 . 8 9 2 ( 2 )  y , d e g  8 0 . 8 4 ( 3 )  1 0 0 5 .1 2 ( 2 )  V, A  1 2 0 2 . 9 ( 2 )  3 6 4 6 . 0 ( 2 )  Z  2  2  1 4 .8 0  1 5 .4 2  p. ( M o K a ) , cm"  1 2 3 .6  1 2 8 .8  C r y s t a l size, m m  0 . 3 5 x 0 . 1 5 x 0 . 1 5  04 .5 x 03 .5 x 02 .0  2 9 3  1 1 3  3  peak, g / c m 3  1  288  R(F)  a  a  0 0 .3 4  0 0 .3 5  0 0 .3 0  0 0 .4 9  R(F) = Z H F o l I F c l/ Z F o l , RwiF ) = (Ew||Fo|-|F||/2:>v|Fo|) 2  2  2  2 2 2 / 1  c  T a b e l 1 6  S e e lc t e db o n de ln g t h s( A )f o r a- a n d y-[Fe2(imid)(bipy)], w i t he s t m i a t e d 4  s t a n d a r dd e v i a t i o n s in p a r e n t h e s e s .  a p h a s e  y p h a s e  F e ( l ) — N ( l )  2 . 2 6 2 ( 2 )  F e ( l ) — N ( 1 0 )  2 . 3 1 4 ( 2 )  F e ( l ) — N ( 2 )  2 . 2 9 9 ( 2 )  F e ( l ) — N ( 9 )  2 . 2 1 7 ( 2 )  F e ( l ) — N ( 3 )  2 . 1 9 6 ( 2 )  F e ( > l— N ( 7 )  2 . 2 0 7 ( 2 )  F e ( l ) — N ( 5 )  2 . 1 5 3 ( 2 )  F e ( l ) — N ( 3 )  2 . 1 6 2 ( 3 )  F e ( l ) — N ( 8 )  2 . 1 9 2 ( 2 )  F e ( l ) — N ( l )  2 . 1 9 5 ( 2 )  F e ( > l— N ( 1 0 )  2 . 1 5 3 ( 2 )  F e ( > l— N ( 5 )  2 . 1 3 6 ( 2 )  F e ( 2 ) — N ( 4 )  2 . 0 2 4 ( 2 )  F e ( 2 ) — N ( 6 )  2 . 0 1 9 ( 2 )  F e ( 2 ) — N ( 6 )  2 . 0 3 6 ( 2 )  F e ( 2 ) — N ( 4 )  2 . 0 3 2 ( 2 )  F e ( 2 ) — N ( 7 )  2 . 0 2 7 ( 2 )  F e ( 2 ) — N ( 2 )  2 . 0 3 0 ( 2 )  F e ( 2 ) — N ( 9 )  2 . 0 2 8 ( 2 )  F e ( 2 ) — N ( l)  2 . 0 2 4 ( 2 )  x  F e ( 3 > — N ( 1 2 )  2 . 1 8 6 ( 2 )  F e ( 3 ) — N ( 1 3 )  2 . 1 5 2 ( 3 )  F e ( 3 ) — N ( 1 5 )  2 . 1 5 5 ( 2 )  F e ( 3 ) — N ( 1 7 )  2 . 2 6 3 ( 2 )  F e ( 3 > — N ( 1 8 )  2 . 3 0 2 ( 2 )  F e ( 3 ) — N ( 2 2 )  2 . 1 8 7 ( 2 )  F e ( 4 ) — N ( 1 6 )  2 . 0 3 5 ( 2 )  F e ( 4 ) — N ( 1 9 )  2 . 0 2 4 ( 2 )  F e ( 4 ) — N ( 2 1 )  2 . 0 3 9 ( 2 )  F e ( 4 > — N ( 2 3 )  2 . 0 3 7 ( 2 )  F e ( 5 ) — N ( 2 0 )  2 . 0 1 1 ( 2 )  F e ( 5 > — N ( 2 4 )  2 . 0 1 9 ( 2 )  F e ( 5 ) — N ( 2 5 )  2 . 0 1 6 ( 2 )  F e ( 5 ) — N ( 2 7 )  2 . 0 0 3 ( 2 )  F e ( 5 ) — N ( 2 9 )  1 . 9 5 7 ( 2 )  F e ( 5 ) — N ( 3 0 )  1 . 9 7 0 ( 2 )  F e ( 6 ) — N ( 8 )  2 . 0 5 9 ( 2 )  F e ( 6 ) — N ( 1 4 )  2 . 0 5 6 ( 3 )  F e ( 6 ) — N ( 2 6 )  2 . 0 3 4 ( 2 )  F e ( 6 ) — N ( 2 8 )  2 . 0 3 8 ( 2 )  T a b e l 1 7  S e e lc t e db o n d a n g e ls (°) f o r a- a n d y-[Fe (imid)4(bipy)] , w i t h e s t m i a t e d 2  x  s t a n d a r dd e v i a t i o n s in p a r e n t h e s e s .  y p h a s e  a p h a s e  N ( l ) — F e ( l ) — N ( 2 )  7 1 . 7 8 ( 9 )  N ( 1 0 ) ^ F e ( > l— N ( 9 ) 7 2 . 5 4 ( 9 )  N ( l ) — F e ( l ) — N ( 3 )  8 9 . 6 8 ( 9 )  N ( 1 0 ) — F e ( > l— N ( 7 ) 9 0 . 0 2 ( 9 )  N ( > l— F e ( ) l — N ( 5 )  1 6 8 . 2 2 ( 9 )  6 9 . 5 9 ( 9 ) N ( 1 0 > — F e ( ) l — N ( 3 ) 1  N ( l ) — F e ( l ) — N ( 8 )  8 8 . 9 1 ( 8 )  N ( 1 0 ) — F e ( l ) — N ( l ) 8 1 . 3 3 ( 9 )  7 . 1 2 ( 9 ) N ( > l— F e ( ) l — N ( 1 0 ) 9  N ( 1 0 > — F e ( ) l — N ( 5 ) 9 6 . 6 7 ( 9 )  N ( 2 > — F e ( ) l — N ( 3 )  8 8 . 9 9 ( 9 )  N ( 9 ) — F e ( ) l — N ( 7 )  9 0 . 0 2 ( 9 )  N ( 2 ) — F e ( ) l — N ( 5 )  9 6 . 5 1 ( 9 )  N ( 9 ) — F e ( > l— N ( 3 )  9 8 . 3 3 ( 9 )  N ( 2 ) — F e ( ) l — N ( 8 )  8 3 . 6 1 ( 9 )  N ( 9 ) — F e ( l ) — N ( l )  8 9 . 4 2 ( 9 )  6 8 . 3 3 ( 9 ) N ( 2 ) — F e ( ) l — N ( 1 0 ) 1  N ( 9 > — F e ( ) l — N ( 5 )  1 6 9 . 2 1 ( 9 )  N ( 3 ) — F e ( ) l — N ( 5 )  8 8 . 7 5 ( 9 )  N ( 7 ) — F e ( ) l — N ( 3 )  8 7 . 9 8 ( 9 )  N ( 3 > — F e ( ) l — N ( 8 )  1 7 2 . 5 3 ( 9 )  N ( 7 > — F e ( ) l — N ( ) l  1 7 2 . 1 9 ( 9 )  N ( 3 ) — F e ( ) l — N ( 1 0 ) 9 4 . 6 5 ( 9 )  N ( 7 ) — F e ( > l— N ( 5 )  9 3 . 8 2 ( 9 )  9 1 . 1 4 ( 9 )  N ( 3 ) — F e ( l ) — N ( l )  9 1 . 1 3 ( 9 )  4 . 6 5 ( 9 ) N ( 5 ) — F e ( ) l — N ( 1 0 ) 9  N ( 3 ) — F e ( ) l — N ( 5 )  9 2 . 3 ( 1 )  2 . 8 0 ( 9 ) N ( 8 ) — F e ( ) l — N ( 1 0 ) 9  N ( l ) — F e ( l ) — N ( 5 )  9 3 . 9 7 ( 9 )  N ( 4 ) — F e ( 2 > — N ( 6 )  N ( 6 ) — F e ( 2 ) — N ( 4 )  1 0 8 . 7 ( 1 )  N ( 5 ) — F e ( ) l — N ( 8 )  1 1 1 . 3 ( 1 )  291  N ( 4 ) — F e ( 2 > — N ( 7 ) 1 1 0 . 1 5 ( 9 )  N ( 6 ) — F e ( 2 ) — N ( 2 )  1 0 9 . 1 ( 1 )  N ( 4 ) — F e ( 2 ) — N ( 9 ) 1 0 6 . 9 6 ( 9 )  N ( 6 ) — F e ( 2 ) — N ( l ) 1 1 7 . 8 ( 1 )  N ( 6 ) — F e ( 2 ) — N ( 7 ) 1 0 5 . 3 3 ( 9 )  N ( 4 ) — F e ( 2 ) — N ( l ) 1 0 2 . 9 ( 1 )  N ( 6 ) — F e ( 2 ) — N ( 9 ) 1 0 5 . 4 7 ( 9 )  0 7 . 4 ( 1 ) N ( 2 ) — F e ( 2 ) — N ( l ) 1  N ( 7 > — F e ( 2 ) — N ( 9 ) 1 1 7 . 6 ( 1 )  0 7 . 4 ( 1 ) N ( 2 ) — F e ( 2 ) — N ( l1 )1 6 . 8 5 ( 9 ) N ( 1 2 ) — F e ( 3 ) — N ( 1 3 )8 3 . 5 1 ( 9 ) N ( 1 2 ) — F e ( 3 ) — N ( 1 5 )9 N ( 1 2 ) — F e ( 3 ) — N ( 1 7 )8 7 . 4 1 ( 9 ) 9 . 7 8 ( 9 ) N ( 1 2 ) — F e ( 3 ) — N ( 1 8 )8 N ( 1 2 > — F e ( 3 ) — N ( 2 2 )1 7 4 . 2 6 ( 9 ) N ( 1 3 ) — F e ( 3 ) — N ( 1 5 )9 7 . 3 ( 1 ) N ( 1 3 ) — F e ( 3 ) — N ( 1 7 )1 6 3 . 3 9 ( 9 ) 2 . 6 7 ( 9 ) N ( 1 3 ) — F e ( 3 ) — N ( 1 8 )9 2 . 2 1 ( 9 ) N ( 1 3 ) — F e ( 3 > — N ( 2 2 )9 N ( 1 5 > — F e ( 3 ) — N ( 1 7 )9 8 . 5 6 ( 9 ) 6 9 . 6 ( 1 ) N ( 1 5 ) — F e ( 3 ) — N ( 1 8 )1 N ( 1 5 ) — F e ( 3 ) — N ( 2 2 )9 2 . 2 2 ( 9 ) 1 . 7 3 ( 9 ) N ( 1 7 ) — F e ( 3 > — N ( 1 8 )7 N ( 1 7 ) — F e ( 3 > — N ( 2 2 )9 1 . 9 5 ( 9 ) 4 . 6 1 ( 8 ) N ( 1 8 ) — F e ( 3 ) — N ( 2 2 )8 N ( 1 6 ) — F e ( 4 ) — N ( 1 9 )1 0 9 . 1 ( 1 )  292  1 4 . 8 ( 1 ) N ( 1 6 > — F e ( 4 ) — N ( 2 1 )1 0 4 . 2 ( 1 ) N ( 1 6 ) — F e ( 4 ) — N ( 2 3 )1 1 2 . 7 ( 1 ) N ( 1 9 ) — F e ( 4 ) — N ( 2 1 )1 0 9 . 9 ( 1 ) N ( 1 9 > — F e ( 4 ) — N ( 2 3 )1 0 5 . 7 ( 1 ) N ( 2 1 > — F e ( 4 ) — N ( 2 3 )1 8 . 4 1 ( 1 ) N ( 2 0 > — F e ( 5 ) — N ( 2 4 )8 2 . 3 1 ( 9 ) N ( 2 0 ) — F e ( 5 ) — N ( 2 5 )9 7 7 . 7 1 ( 9 ) N ( 2 0 > — F e ( 5 ) — N ( 2 7 )1 0 . 9 ( 1 ) N ( 2 0 ) — F e ( 5 ) — N ( 2 9 )9 0 . 9 8 ( 9 ) N ( 2 0 ) — F e ( 5 > — N ( 3 0 )9 9 . 2 ( 1 ) N ( 2 4 ) — F e ( 5 > — N ( 2 5 )8 1 . 7 ( 1 ) N ( 2 4 > — F e ( 5 ) — N ( 2 7 )9 7 6 . 8 ( 1 ) N ( 2 4 ) — F e ( 5 ) — N ( 2 9 )1 5 . 1 ( 1 ) N 2 (4 > — F e 5 (> — N 3 (0 )9 9 . 9 8 ( 9 ) N ( 2 5 ) — F e ( 5 > — N ( 2 7 )8 N ( 2 5 ) — F e ( 5 > — N ( 2 9 )9 4 . 0 ( 1 ) N ( 2 5 ) — F e ( 5 ) — N ( 3 0 )1 7 4 . 7 ( 1 ) N 2 (7 > — F e 5 (> — N 2 (9 )8 8 . 9 ( 1 ) N ( 2 7 > — F e ( 5 ) — N ( 3 0 )8 6 . 7 3 ( 1 ) N ( 2 9 ) — F e ( 5 > — N ( 3 0 )8 1 . 8 ( 1 ) N ( 8 > — F e ( 6 ) — N ( 1 4 ) 1 1 4 . 8 ( 1 )  N ( 8 ) — F e ( 6 > — N ( 2 6 )1 0 5 . 9 5 ( 9 ) N ( 8 ) — F e < 6 ) — N ( 2 8 )1 0 4 . 7 4 ( 9 )  T a b e l 1-8  N ( 1 4 ) — F e ( 6 ) — N ( 2 6 )  1 0 2 . 7 ( 1 )  N ( 1 4 ) — F e ( 6 ) — N ( 2 8 )  1 0 0 . 8 ( 9 )  N ( 2 6 ) — F e ( 6 > — N ( 2 8 )  1 2 8 . 3 ( 1 )  C r y s t a l o g r a p h i cd a t a for P-[Fe2(imid)4(bipy)]. x  M o e lc u a lr f o r m u a l  C22H2oFe2Nio  fw  5 3 6 1 .6  C r y s t a ls y s t e m  triclinic  S p a c eg r o u p  PI (No.  o  2)  a, A  1 7 1 .3 3 8 ( 4 )  b, A  1 8 5 .4 2 6 ( 4 )  c, A  2 3 . 6 1 9 9 ( 3 )  a, deg  8 0 . 4 2 4 ( 3 )  P,deg  7 5 . 3 6 4 ( 3 )  y , d e g  8 0 . 8 2 6 ( 3 )  V, A  7 1 0 5 . 1 ( 2 )  3  p ic g / c m  1 4 .4 0  3  ca  \i ( M o K a ) , cm"  1 2 3 .6  1  C r y s t a l size, mm  02 .5  T, K  1 4 3  i?(i^,/>2c(/))  0 1 .4 5  R (F f  0 3 .3 9  2  w  3  x 0.20  x  0.20  R(F) = SIlFol-IFcll/SIFol, RM.F ) = (2Z \\Fo \-\Fc \\/2Zw\F \ ) 2  2  2 2 m  2  W  T a b e l 1-9  0  S e e lc t e db o n da n g e ls (°) for (3-[Fe (imid)4(bipy)] ,w i t he s t m i a t e ds t a n d a r d 2  x  d e v a it o in s in p a r e n t h e s e s .  F e ( l a ) — N ( 5 a )  2 . 1 3 9 ( 2 )  F e ( l a ) — N ( 3 )  2 . 1 4 4 ( 2 )  F e ( l a ) — N ( 8 a )  2 . 1 9 3 ( 2 )  F e ( l a ) — N ( 2 0 )  2 . 1 9 7 ( 2 )  F e ( l a ) — N ( 2 a )  2 . 2 6 3 ( 2 )  F e ( l a ) — N ( l a )  2 . 2 9 9 ( 2 )  F e ( l b ) — N ( 1 3 )  2 . 1 5 5 ( 2 )  F e ( l b ) — N ( 3 8 )  2 . 1 7 0 ( 2 )  F e ( b l) — N ( 1 0 a )  2 . 1 8 1 ( 2 )  F e ( l b ) — N ( 1 5 )  2 . 1 8 8 ( 2 )  F e ( l b ) — N ( 2 b )  2 . 2 1 5 ( 2 )  F e ( l b ) — N ( l b )  2 . 2 8 0 ( 2 )  F e ( l c ) — N ( 1 8 )  2 . 1 4 5 ( 2 )  F e ( l c ) — N ( 2 3 )  2 . 1 7 4 ( 2 )  F e ( l c ) — N ( 2 5 )  2 . 2 0 1 ( 2 )  F e ( l c ) — N ( 4 8 )  2 . 2 1 8 ( 2 )  F e ( l c ) — N ( 2 c )  2 . 2 4 6 ( 2 )  F e ( l c ) — N ( l c )  2 . 2 7 3 ( 2 )  F e ( l d ) — N ( 2 8 )  2 . 1 3 0 ( 3 )  F e ( l d ) — N ( 3 0 )  2 . 1 5 9 ( 2 )  F e ( l d ) — N ( 3 3 )  2 . 1 6 7 ( 2 )  F e ( l d ) — N ( 3 5 )  2 . 1 8 5 ( 2 )  F e ( l d ) — N ( l d )  2 . 2 3 2 ( 2 )  F e ( d l> — N ( 2 d )  2 . 2 7 6 ( 2 )  F e ( l e ) — N ( 4 5 )  2 . 1 5 5 ( 2 )  F e ( l e ) — N ( 5 0 )  2 . 1 6 8 ( 2 )  F e ( l e ) — N ( 4 0 )  2 . 1 7 0 ( 2 )  F e ( l e ) — N ( 4 3 )  2 . 1 8 9 ( 2 )  F e ( l e ) — N ( 2 e )  2 . 2 2 0 ( 2 )  F e ( l e > — N ( l e )  2 . 3 1 0 ( 2 )  F e ( f l > — N ( 5 9 )  2 . 1 3 2 ( 2 )  F e ( l f ) — N ( 5 8 )  2 . 1 4 0 ( 2 )  F e ( l f ) — N ( 5 5 )  2 . 1 8 7 ( 2 )  F e ( l f > — N ( l f )  2 . 1 9 6 ( 2 )  F e ( l f ) — N ( 5 2 )  2 . 1 9 9 ( 2 )  F e ( l f ) — N ( 2 f )  2 . 2 5 4 ( 2 )  F e ( 2 a ) — N ( 9 a )  2 . 0 3 1 ( 2 )  F e ( 2 a ) — N ( 7 a )  2 . 0 3 9 ( 2 )  F e ( 2 a ) — N ( 5 7 )  2 . 0 4 6 ( 2 )  F e ( 2 a ) — N ( 6 a )  2 . 0 4 6 ( 2 )  F e ( 2 b ) — N ( 1 9 )  2 . 0 1 8 ( 2 )  F e ( 2 b > — N ( 1 7 )  2 . 0 2 3 ( 2 )  F e ( 2 b ) — N ( 1 6 )  2 . 0 3 9 ( 2 )  F e ( 2 b ) — N ( 1 4 )  2 . 0 4 7 ( 2 )  F e ( 2 c > — N ( 2 7 )  2 . 0 1 7 ( 2 )  F e ( 2 c ) — N ( 5 6 )  2 . 0 3 8 ( 3 )  F e ( 2 c ) — N ( 2 6 )  2 . 0 4 0 ( 2 )  F e ( 2 c > — N ( 2 9 )  2 . 0 4 1 ( 2 )  F e ( 2 d > — N ( 3 6 )  2 . 0 1 5 ( 2 )  F e ( 2 d ) — N ( 3 9 )  2 . 0 2 4 ( 2 )  F e ( 2 d > — N ( 3 7 )  2 . 0 3 6 ( 2 )  F e ( 2 d > — N ( 2 4 )  2 . 0 4 4 ( 2 )  F e ( 2 e ) — N ( 4 9 )  2 . 0 0 4 ( 2 )  F e ( 2 e > — N ( 4 6 )  2 . 0 1 3 ( 2 )  F e ( 2 e ) — N ( 4 7 )  2 . 0 1 7 ( 3 )  F e ( 2 e ) — N ( 5 1 )  2 . 0 2 7 ( 2 )  F e ( 2 f > — N ( 4 4 )  2 . 0 2 7 ( 2 )  F e ( 2 f > — N ( 3 4 )  2 . 0 2 8 ( 2 )  F e ( 2 f ) — N ( 4 )  2 . 0 3 4 ( 2 )  F e ( 2 f ) — N ( 6 0 )  2 . 0 4 4 ( 2 )  N ( 5 a ) — F e ( a l) — N ( 3 )  9 4 . 0 2 ( 9 )  N ( 5 a ) — F e ( a l) — N ( 8 a )  9 0 . 3 2 ( 9 )  N ( 5 a ) — F e ( a l) — N ( 2 0 )  9 1 . 2 8 ( 9 )  N ( 5 a ) — F e ( a l) — N ( 2 a )  1 6 8 . 1 3 ( 9 )  N ( 5 a > — F e ( a l) — N ( a l)  9 6 . 4 3 ( 9 )  N ( 3 ) — F e ( a l> — N ( 8 a )  9 5 . 0 7 ( 9 )  N ( 3 > — F e ( a l) — N ( 2 0 )  9 2 . 9 3 ( 9 )  N ( 3 ) — F e ( a l) — N ( 2 a )  9 7 . 8 3 ( 9 )  N ( 3 ) — F e ( l a ) — N ( l a )  1 6 8 . 3 4 ( 9 )  N ( 8 a > — F e ( a l) — N ( 2 0 )  1 7 1 . 7 1 ( 9 )  N ( 8 a > — F e ( a l) — N ( 2 a )  8 9 . 3 7 ( 9 )  N ( 8 a ) — F e ( l a ) — N ( l a )  9 0 . 0 3 ( 9 )  N ( 2 0 ) — F e ( a l) — N ( 2 a )  8 7 . 4 0 ( 9 )  N ( 2 0 > — F e ( a l) — N ( a l)  8 1 . 7 1 ( 9 )  N ( 2 a ) — F e ( l a ) — N ( l a )  7 1 . 7 0 ( 9 )  N ( 1 3 ) — F e ( b l) — N ( 3 8 )  9 6 . 8 3 ( 9 )  N ( 1 3 ) — F e ( b l) — N ( 1 0 a )  8 9 . 0 3 ( 9 )  N ( 1 3 ) — F e ( b l) — N ( 1 5 )  8 6 . 6 5 ( 9 )  N ( 1 3 ) — F e ( b l) — N ( 2 b )  1 6 7 . 0 4 ( 9 )  N ( 1 3 ) — F e ( l b ) — N ( l b )  9 4 . 4 6 ( 9 )  N ( 3 8 ) — F e ( b l) — N ( 1 0 a )  9 2 . 0 6 ( 9 )  N ( 3 8 ) — F e ( b l) — N ( 1 5 )  9 3 . 5 2 ( 9 )  N ( 3 8 ) — F e ( b l) — N ( 2 b )  9 5 . 9 5 ( 9 )  N ( 3 8 > — F e ( b l) — N ( b l)  1 6 8 . 2 3 ( 1 )  N ( 1 0 a ) — F e ( b l) — N ( 1 5 )  1 7 3 . 3 1 ( 1 )  N ( 1 0 a ) — F e ( b l) — N ( 2 b )  9 2 . 6 8 ( 9 )  N ( 1 0 a ) — F e ( l b ) — N ( l b )  8 4 . 8 0 ( 9 )  N ( 1 5 ) — F e ( b l) — N ( 2 b )  9 0 . 4 1 ( 9 )  N ( 1 5 ) — F e ( l b ) — N ( l b )  9 0 . 4 4 ( 9 )  N ( 2 b ) — F e ( l b ) — N ( l b )  7 2 . 9 2 ( 9 )  N ( 1 8 ) — F e ( c l) — N ( 2 3 )  9 5 . 4 4 ( 9 )  N ( 1 8 ) — F e ( c l) — N ( 2 5 )  9 3 . 3 9 ( 9 )  N ( 1 8 ) — F e ( c l) — N ( 4 8 )  9 4 . 6 5 ( 9 )  N ( 1 8 > — F e ( c l) — N ( 2 c )  1 6 7 . 7 2 ( 9 )  N ( 1 8 ) — F e ( l c ) — N ( l c )  9 5 . 5 9 ( 9 )  N ( 2 3 > — F e ( c l) — N ( 2 5 )  9 2 . 0 8 ( 9 )  297  N ( 2 3 ) — F e ( c l) — N ( 4 8 )  8 7 . 9 4 ( 9 )  N ( 2 3 > — F e ( c l) — N ( 2 c )  9 6 . 5 2 ( 9 )  N ( 2 3 ) — F e ( c l> — N ( c l)  1 6 8 . 9 2 ( 9 )  N ( 2 5 ) — F e ( c l) — N ( 4 8 )  1 7 1 . 9 2 ( 9 )  N ( 2 5 > — F e ( c l) — N ( 2 c )  8 3 . 4 5 ( 9 )  N ( 2 5 > — F e ( c l) — N ( c l)  8 8 . 2 7 ( 9 )  N ( 4 8 > — F e ( c l) — N ( 2 c )  8 8 . 5 2 ( 9 )  N ( 4 8 > — F e ( c l) — N ( c l)  9 0 . 1 7 ( 9 )  N ( 2 c ) — F e ( l c ) — N ( l c )  7 2 . 5 1 ( 9 )  N ( 2 8 ) — F e ( d l) — N ( 3 0 )  9 6 . 8 3 ( 9 )  N ( 2 8 > — F e ( d l) — N ( 3 3 )  8 7 . 6 4 ( 9 )  N ( 2 8 > — F e ( d l) — N ( 3 5 )  9 1 . 8 6 ( 9 )  N ( 2 8 > — F e ( d l) — N ( d l)  1 6 7 . 0 5 ( 9 )  N ( 2 8 ) — F e ( d l) — N ( 2 d )  9 4 . 7 1 ( 9 )  N ( 3 0 ) — F e ( d l) — N ( 3 3 )  9 4 . 5 7 ( 9 )  N ( 3 0 > — F e d ( l> — N ( 3 5 )  9 1 . 3 8 ( 9 )  N ( 3 0 ) — F e ( l d ) — N ( l d )  9 6 . 0 6 ( 9 )  N ( 3 0 ) — F e ( d l) — N ( 2 d )  1 6 7 . 7 4 ( 9 )  N ( 3 3 > — F e ( d l) — N ( 3 5 )  1 7 4 . 0 5 ( 9 )  N ( 3 3 > — F e ( d l) — N ( d l)  9 0 . 0 4 ( 9 )  N ( 3 3 ) — F e ( d l) — N ( 2 d )  9 0 . 0 4 ( 8 )  N ( 3 5 ) — F e ( l d ) — N ( l d )  8 9 . 1 3 ( 9 )  N ( 3 5 > — F e d ( l) — N ( 2 d )  8 4 . 0 9 ( 9 )  N ( l d ) — F e ( l d ) — N ( 2 d )  7 2 . 5 4 ( 9 )  N ( 4 5 > — F e ( e l) — N ( 5 0 )  9 4 . 2 0 ( 9 )  N ( 4 5 > — F e ( e l) — N ( 4 0 )  8 8 . 2 8 ( 9 )  N ( 4 5 > — F e ( e l) — N ( 4 3 )  8 9 . 9 4 ( 9 )  N ( 4 5 ) — F e ( e l> — N ( 2 e )  1 6 7 . 4 9 ( 9 )  N ( 4 5 > — F e ( e l) — N ( e l)  9 5 . 3 7 ( 9 )  N ( 5 0 ) — F e ( e l) — N ( 4 0 )  9 5 . 8 1 ( 9 )  N ( 5 0 ) — F e ( e l) — N ( 4 3 )  9 1 . 2 5 ( 9 )  N ( 5 0 ) — F e ( e l> — N ( 2 e )  9 8 . 2 7 ( 8 )  N ( 5 0 ) — F e ( l e ) — N ( l e )  1 6 9 . 1 0 ( 1 )  N ( 4 0 > — F e ( e l) — N ( 4 3 )  1 7 2 . 8 3 ( 1 )  N ( 4 0 ) — F e ( e l) — N ( 2 e )  8 9 . 4 7 ( 9 )  N ( 4 0 > — F e ( e l> — N ( e l)  8 9 . 7 0 ( 9 )  N ( 4 3 ) — F e ( e l) — N ( 2 e )  9 0 . 7 9 ( 9 )  N ( 4 3 > — F e ( e l) — N ( e l)  8 3 . 5 6 ( 9 )  N ( 2 e ) — F e ( l e ) — N ( l e )  7 2 . 3 1 ( 9 )  N ( 5 9 > — F e ( f l ) — N ( 5 8 )  9 5 . 5 4 ( 9 )  N ( 5 9 > — F e ( f l ) — N ( 5 5 )  8 8 . 7 6 ( 9 )  N ( 5 9 > — F e ( l f ) — N ( l f )  1 6 8 . 9 1 ( 9 )  298  N ( 5 9 ) — F e ( f l ) — N ( 5 2 )  9 0 . 5 1 ( 9 )  N ( 5 9 ) — F e ( l f ) — N ( 2 f )  9 5 . 5 1 ( 9 )  N ( 5 8 ) — F e ( f l ) — N ( 5 5 )  9 3 . 1 1 ( 9 )  N ( 5 8 ) — F e ( l f ) — N ( l f )  9 5 . 5 4 ( 9 )  N ( 5 8 ) — F e ( f l > — N ( 5 2 )  9 1 . 4 1 ( 9 )  N ( 5 8 ) — F e ( f l > — N ( 2 f )  1 6 7 . 8 3 ( 9 )  N ( 5 5 ) — F e ( l f ) — N ( l f )  9 0 . 8 3 ( 9 )  N ( 5 5 > — F e ( f l ) — N ( 5 2 )  1 7 5 . 4 7 ( 9 )  N ( 5 5 ) — F e ( l f ) — N ( 2 f )  9 2 . 1 9 ( 9 )  N ( l f ) — F e ( l f ) — N ( 5 2 )  8 9 . 0 3 ( 9 )  N ( l f ) — F e ( l f ) — N ( 2 f )  7 3 . 4 3 ( 9 )  N ( 5 2 ) — F e ( l f ) — N ( 2 f )  8 3 . 4 3 ( 9 )  N ( 9 a ) — F e ( 2 a ) — N ( 7 a )  1 0 7 . 7 9 ( 9 )  N ( 9 a ) — F e ( 2 a ) — N ( 5 7 )  1 2 1 . 7 4 ( 9 )  N ( 9 a > — F e ( 2 a ) — N ( 6 a )  1 0 4 . 8 9 ( 9 )  N 7 (a > — F e 2 (a > — N 5 (7 )  1 0 7 . 5 5 ( 9 )  N ( 7 a ) — F e ( 2 a ) — N ( 6 a )  1 1 0 . 7 5 ( 1 )  N 5 (7 > — F e 2 (a > — N 6 (a )  1 0 3 . 8 7 ( 1 )  N ( 1 9 ) — F e ( 2 b ) — N ( 1 7 )  1 2 1 . 1 1 ( 1 )  N ( 1 9 ) — F e ( 2 b ) — N ( 1 6 )  1 1 0 . 7 9 ( 1 )  N ( 1 9 ) — F e ( 2 b ) — N ( 1 4 )  1 0 3 . 9 9 ( 9 )  N ( 1 7 ) — F e ( 2 b ) — N ( 1 6 )  1 0 3 . 8 6 ( 9 )  N ( 1 7 ) — F e ( 2 b ) — N ( 1 4 )  1 0 5 . 3 9 ( 9 )  N ( 1 6 ) — F e ( 2 b > — N ( 1 4 )  1 1 1 . 6 3 ( 9 )  N ( 2 7 ) — F e ( 2 c > — N ( 5 6 )  1 1 4 . 6 0 ( 9 )  N ( 2 7 ) — F e ( 2 c ) — N ( 2 6 )  1 0 1 . 6 5 ( 9 )  N ( 2 7 ) — F e ( 2 c ) — N ( 2 9 )  1 0 5 . 0 6 ( 9 )  N ( 5 6 ) — F e ( 2 c > — N ( 2 6 )  1 1 0 . 1 2 ( 9 )  N ( 5 6 ) — F e ( 2 c ) — N ( 2 9 )  1 0 5 . 7 1 ( 9 )  N ( 2 6 ) — F e ( 2 c ) — N ( 2 9 )  1 1 9 . 9 6 ( 9 )  N ( 3 6 > — F e ( 2 d ) — N ( 3 9 )  1 1 0 . 8 2 ( 9 )  N ( 3 6 ) — F e ( 2 d ) — N ( 3 7 )  1 1 7 . 4 8 ( 9 )  N ( 3 6 ) — F e ( 2 d ) — N ( 2 4 )  1 0 4 . 1 5 ( 9 )  N 3 (9 > — F e 2 (d > — N 3 (7 )  1 0 8 . 6 9 ( 9 )  N ( 3 9 ) — F e ( 2 d ) — N ( 2 4 )  1 0 9 . 5 6 ( 9 )  N ( 3 7 > — F e ( 2 d ) — N ( 2 4 )  1 0 5 . 7 6 ( 9 )  N ( 4 9 ) — F e ( 2 e ) — N ( 4 6 )  1 0 2 . 6 3 ( 9 )  N ( 4 9 ) — F e ( 2 e > — N ( 4 7 )  1 0 9 . 2 3 ( 9 )  N ( 4 9 ) — F e ( 2 e ) — N ( 5 1 )  1 1 6 . 7 0 ( 9 )  N ( 4 6 ) — F e ( 2 e ) — N ( 4 7 )  1 1 2 . 0 1 ( 9 )  N ( 4 6 > — F e ( 2 e ) — N ( 5 1 )  1 0 6 . 9 4 ( 9 )  N ( 4 7 ) — F e ( 2 e ) — N ( 5 1 )  1 0 9 . 2 1 ( 9 )  299  N ( 4 4 ) — F e ( 2 f ) — N ( 3 4 )  1 0 9 . 8 8 ( 9 )  N ( 4 4 > — F e ( 2 f ) — N ( 4 )  1 1 8 . 2 4 ( 9 )  N ( 4 4 ) — F e ( 2 f > — N ( 6 0 )  1 0 5 . 6 0 ( 1 )  N ( 3 4 > — F e ( 2 f ) — N ( 4 )  1 0 7 . 0 7 ( 1 )  N ( 3 4 ) — F e ( 2 f ) — N ( 6 0 )  1 1 2 . 5 7 ( 1 )  N ( 4 > — F e ( 2 f > — N ( 6 0 )  1 0 3 . 4 4 ( 9 )  T a b e l I-10  C r y s t a l o g r a p h i cd a t a for [Fe (imid)8(terpy)] . 4  M o e lc u a lr f o r m u a l  x  C39H3sFe4Ni9  fw  9 9 3 2 .2  C r y s t a ls y s t e m  triclinic  S p a c eg r o u p  Pi (No.  2)  a/A  1 1 . 3 5 1 ( 2 )  blk  1 3 . 6 2 8 ( 1 )  elk  1 5 . 7 4 8 ( 4 )  a, deg  1 1 3 5 .5 0 ( 3 )  P, deg  1 0 3 6 .9 6 ( 3 )  y , d e g  9 1 . 8 2 6 ( 3 )  V,k  2 1 4 7 . 6 ( 6 )  Z  2  3  A/gem"  1 5 .3 6  F ( 0 0 0 )  1 0 1 2 0 .  3  300  jj. ( M o K o O c /m "  1 3 7 .7  C r y s t a ls z ie m / m  0 . 6 x 0 . 1 0 x 0 . 0 3  1  5 6 . 0 T o t a lr e f l e c t i o n s  1 8 2 0 8  U n q iu er e f l e c t i o n s  8 1 0 0  N o .w i t h / > 3 o ( 7 )  4 7 9 3  N o .o fv a r i a b l e s  5 5 9  R ; R w ( F , / > 3 o ( 7 ) )  0 . 0 3 9 ;0 0 .4 9  R ;R w (F , all d a t a )  0 . 0 7 9 ;0 1 .1 4  g o f  1 0 .7  2  a  T e m p e r a t u r e1 7 3K ,R g ia k u A /D S CC C Dd i f f r a c t o m e t e r ,M o Ka (k = 0 . 7 1 0 6 9 ) ,g r a p h t i e  m o n o c h r o m a t o r ,t a k e o f fa n g e l 6.0°, a p e r t u r e9 4 . 0x9 4 . 0m ma tad s it a n c eo f4 0 4 .8 m  from t h e crystal, c ^ ) = ( C+i ? ) / L p 2( C= s c a nc o u n t , B =b a c k g r o u n dc o u n t ) ,f u 2  m n im i z ie d Zw(|F|-|F|) w h e r e w = l/o^F*), R(F) = 2||Fo|-|F||/I|Fo|, Rw (F ) = 2  2 2  0  c  2  c  (Zw||F|-|Fc||/Iw|Fo|), a n dg o f = [Iw(|F|-|F|)/(/n-n)]. 2  2  222 1 /  0  T a b e l 1 1 1  F e ( l ) — N ( l )  2  2 2  0  c  2 1 /  S e e lc t e db o n de ln g t h s( A )a n da n g e ls (°) f o r [Fe (imid) (terpy)] . 4  2 . 0 2 3 ( 4 )  F e ( l ) — N ( 2 )  301  2 . 0 3 7 ( 4 )  8  x  F e ( > l— N ( 3 )  2 . 0 2 5 ( 4 )  F e ( l ) — N ( 4 )  2 . 0 4 0 ( 4 )  F e ( 2 ) — N ( 1 2 )  2 . 0 1 7 ( 4 )  F e ( 2 > — N ( 1 0 )  2 . 0 2 4 ( 4 )  F e ( 2 ) — N ( l)  2 . 0 3 0 ( 4 )  F e ( 2 ) — N ( 9 )  2 . 0 4 1 ( 4 )  F e ( 3 > — N ( 1 5 )  2 . 0 7 2 ( 4 )  F e ( 3 ) — N ( 8 )  2 . 1 4 1 ( 3 )  F e ( 3 ) — N ( 5 )  2 . 1 4 8 ( 4 )  F e ( 3 > — N ( 1 3 )  2 . 1 5 1 ( 4 )  F e ( 3 > — N ( 6 )  2 . 1 5 6 ( 3 )  F e ( 4 > — N ( 1 8 )  1 . 8 5 8 ( 4 )  F e ( 4 > — N ( 1 9 )  1 . 9 6 1 ( 4 )  F e ( 4 ) — N ( 1 7 )  1 . 9 7 6 ( 4 )  F e ( 4 ) — N ( 1 4 )  1 . 9 9 2 ( 3 )  F e ( 4 ) — N ( 1 6 )  1 . 9 9 4 ( 3 )  F e ( 4 > — N ( 7 )  2 . 0 0 2 ( 4 )  N ( l ) — F e ( l ) — N ( 3 ) 1 0 8 . 6 4 ( 2 )  N ( l ) — F e ( l ) — N ( 2 ) 1 0 6 . 8 5 ( 1 )  N ( l ) — F e ( l ) — N ( 4 ) 1 1 5 . 6 1 ( 2 )  N 3 (> — F e (1> — N 2 () 1 1 3 . 5 0 ( 2 )  N ( 3 > — F e > ( l— N ( 4 ) 1 0 6 . 0 8 ( 2 )  N ( 2 > — F e ( ) l — N ( 4 ) 1 0 6 . 3 5 ( 2 )  N 1 (2 > — F e 2 (> — N 1 (0 )  N ( 1 2 > — F e ( 2 ) — N ( ) l  1 1 3 . 5 8 ( 2 )  1 0 1 . 5 6 ( 2 )  N 1 (2 > — F e 2 (> — N 9 () 1 1 4 . 3 2 ( 2 )  N (1 0 ) — F e ( 2 ) — N (1 1 )  1 1 7 . 2 4 ( 2 )  N ( 1 0 > — F e ( 2 ) — N ( 9 )1 0 8 . 1 5 ( 1 )  N ( l ) — F e ( 2 ) — N ( 9 )1 0 1 . 5 2 ( 2 )  N 1 (5 > — F e 3 (> — N 8 () 1 0 4 . 1 0 ( 1 )  N 1 (5 > — F e 3 (> — N 5 () 9 9 . 0 3 ( 2 )  N ( 1 5 ) — F e ( 3 ) — N ( 1 3 ) 9 8 . 2 8 ( 2 )  N ( 1 5 ) — F e ( 3 ) — N ( 6 )1 0 1 . 5 5 ( 1 )  N ( 8 > — F e ( 3 ) — N ( 5 ) 8 6 . 7 3 ( 1 )  N ( 8 ) — F e ( 3 > — N ( 1 3 )8 7 . 5 0 ( 1 )  N ( 8 > — F e ( 3 ) — N ( 6 ) 1 5 4 . 3 0 ( 2 )  N ( 5 ) — F e ( 3 ) — N ( 1 3 )1 6 2 . 6 1 ( 2 )  N ( 5 ) — F e ( 3 ) — N ( 6 ) 9 0 . 7 5 ( 1 )  N ( 1 3 ) — F e ( 3 ) — N ( 6 )8 7 . 3 6 ( 1 )  N (1 8 ) — F e ( 4 ) — N (1 9 )  N ( 1 8 ) — F e ( 4 ) — N ( 1 7 )  8 1 . 9 5 ( 2 )  8 1 . 4 8 ( 2 )  N ( 1 8 ) — F e ( 4 ) — N ( 1 4 ) 9 3 . 2 5 ( 1 )  N ( 1 8 ) — F e ( 4 ) — N ( 1 6 ) 9 0 . 7 3 ( 1 )  N ( 1 8 ) — F e ( 4 ) — N ( 7 )1 7 8 . 6 0 ( 1 )  N ( 1 9 ) — F e ( 4 ) — N ( 1 7 )  1 6 3 . 4 3 ( 2 )  N ( 1 9 ) — F e ( 4 ) — N ( 1 4 ) 9 0 . 9 7 ( 1 )  N ( 1 9 ) — F e ( 4 > — N ( 1 6 )  8 7 . 7 7 ( 1 )  N ( 1 9 ) — F e ( 4 ) — N ( 7 )9 8 . 3 7 ( 2 )  N ( 1 7 > — F e ( 4 ) — N ( 1 4 ) 9 0 . 0 7 ( 1 )  N ( 1 7 ) — F e ( 4 > — N ( 1 6 )  9 2 . 3 5 ( 1 )  N ( 1 7 ) — F e ( 4 ) — N ( 7 )9 8 . 1 9 ( 2 )  N ( 1 4 ) — F e ( 4 > — N ( 1 6 )  1 7 5 . 6 2 ( 1 )  N ( 1 4 > — F e ( 4 ) — N ( 7 )8 8 . 1 1 ( 1 )  N ( 1 6 > — F e ( 4 ) — N ( 7 )8 7 . 9 3 ( 1 )  T a b e l I 1 2  C r y s t a l o g r a p h i cd a t af o r[ F e ( 1 -Me-2-S-imid) -0.5Cp Fe] . a  2  M o e lc u a lr f o r m u a l  CisHjsFej^Sj  f w  3 7 5 1 .8  S p a c eg r o u p  P 4 / n( N o .8 5 )  a, A  1 3 2 .8 6 2 ( 7 )  c, A  8 . 7 6 6 5 ( 4 ) 1 5 4 7 4 .9 ( 1 1 )  z  4  p e a k ,g / c m  1 6 .1 0  F ( 0 0 0 )  7 6 8  3  303  2  x  r a d i a t i o n  M o  u, cm"  1 6 8 .8  X,A  0 7 .1 0 6 9  R  0 0 .7 7  1  R  0 0 .6 3  T, °C  9 3  w  a R = I||Fo|-Fc||/L| Fo|,tf = (Lw(\Fo \-\ Fc \frLw Fo ) ' 2  2  2  2  2  4  1 2  w  T a b e l I-13  S e e lc t e db o n de ln g t h s (A) and a n g e ls (°) for [Fe( 1 M e 2 S -  imid)2-0.5Cp2Fe]* x  F e ( l ) — S ( l )  2 . 3 6 7 7 ( 8 )  F e ( 2 ) — N ( l )  2 . 0 5 4 ( 2 )  S(l)-C(l)  1 . 7 3 2 ( 3 )  N(l)-C(l)  1 . 3 4 2 ( 3 )  N(l)-C(2)  1 . 3 8 3 ( 4 )  N(2)-C(l)  1 . 3 6 4 ( 3 )  N(2)-C(3)  1 . 3 7 5 ( 4 )  N(2)-C(4)  1 . 4 5 5 ( 4 )  C ( 2 ) C ( 3 )  1 . 3 5 8 ( 4 )  S(l)—Fe(l)—S(l) 1 1 0 . 0 5 ( 2 )  S ( l ) — F e ( l ) — S ( l ) *  1 1 0 . 0 5 ( 2 )  S ( l > — F e ( l ) — S ( l )  N ( l > — F e ( 2 ) — N ( l /  1 0 4 . 9 1 ( 6 )  lf  c  1 0 8 . 3 2 ( 4 )  304  N ( l > — F e ( 2 ) — N ( l )  N ( l ) — F e ( 2 ) — N ( l ) 1 0 4 . 9 1 ( 6 )  c  e  1 1 9 0 .5 ( 1 3 )  F e ( l > — S ( l ) — C ( l )  9 5 . 6 7 ( 1 0 )  F e ( 2 > — N ( ) l — C ( ) l  1 2 5 . 9 ( 2 )  F e ( 2 > — N ( ) l — C ( 2 )  1 2 8 . 0 ( 2 )  C ( > l— N ( > l— C ( 2 )  1 0 6 . 0 ( 2 )  C ( ) l — N ( 2 ) — C ( 3 )  1 0 8 . 0 ( 3 )  C ( ) l — N ( 2 ) — C ( 4 )  1 2 6 . 5 ( 3 )  C ( 3 ) — N ( 2 ) — C ( 4 )  1 2 5 . 5 ( 3 )  S ( l ) — C ( l ) — N ( l )  1 2 5 . 4 ( 2 )  S(l>—C(ly—N(2)  1 2 4 . 7 ( 2 )  N ( l ) — C ( l ) — N ( 2 )  1 0 9 . 9 ( 3 )  N ( l ) — C ( 2 ) — € ( 3 )  1 0 9 . 9 ( 3 )  N ( 2 ) — C ( 3 ) — C ( 2 )  1 0 6 . 2 ( 3 )  *S u p e r s c r p it n u m b e r sr e f e rt os y m m e r t yo p e r a t o in (a) 'A+y, 1 x , -z (b) 1 y ,1 / 2 + x , -z (c) 3/2-x,l/2-y, z (d) '/a+yj-xj-z ( e ) 1 y , 1 / 2 + x , 1 z  305  

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