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Spectroscopic and magnetic properties of pyridine and pyrazine complexes of divalent iron and copper Haynes, John Stephen 1985

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SPECTROSCOPIC AND MAGNETIC PROPERTIES OF PYRIDINE AND PYRAZINE COMPLEXES OF DIVALENT IRON AND COPPER by JOHN STEPHEN HAYNES M.Sc, U n i v e r s i t y Of B r i t i s h Columbia, 1980 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES Department Of Chemistry We accept t h i s t h e s i s as conforming to the r e a u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA J u l y 1985 \ John Ste'phen Haynes, 1985 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make Department of The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 i . . DE-6 f'T/R-n i i Abstract Magneto-structural correlations have been made for a number of pyridine and pyrazine complexes of iron(II) and copper(Il), involving anions of a range of coordinating a b i l i t i e s , for example, sulfonate, R S 0 3 " (where R is CF 3, CH 3 f or p-CHaCgHu); halide, C l " , Br" or I"; pseudohalide, NCO" or NCS"; perchlorate and hexafluoroarsenate. Structure was determined by infrared, electronic and Mossbauer spectroscopy and d i f f e r e n t i a l scanning calorimetry, and, in some instances, by si n g l e - c r y s t a l X-ray d i f f r a c t i o n . Spectroscopic results were used to investigate the nature of both anion and neutral ligand coordination. In complexes of stoichiometry ML a ( R S 0 3 ) 2 (where M i s Fe or Cu, L i s pyridine, pyrazine or 2-methylpyrazine and R i s CF 3, CH3 or p-CH 3C 6H„), the neutral ligands were found to adopt a unidentate mode of coordination. For several of these complexes, X-ray crystallography revealed a square-planar array of pyridine ligands around the central metal, with anions coordinated in a unidentate mode above and below this plane. A monomeric molecular structure results in which the paramagnetic centres are well isolated from each other giving r i s e to magnetically-dilute species. In complexes of stoichiometry M(pyz) 2X 2 (where M is Fe or Cu and X" i s CF 3 S 0 3", CH 3 S0 3", C l " , Br", I", C10«" or NCS"), pyrazine was found to coordinate through both nitrogen donor atoms and inorganic coordination polymers were produced. X-ray crystallography revealed a two-dimensional l a t t i c e in Cu(pyz) 2(CH 3 S 0 3 )2 with two d i s t i n c t kinds of bridging pyrazine groups and monodentate sulfonate anions. For the remaining bis(pyrazine) complexes, spectroscopic evidence supports similar structures with unidentate anion coordination and bidentate bridging pyrazine ligands leading to sheet-like polymers. C u ( p y z ) 2 ( C H 3 S O 3 ) 2 and Fe(pyz) 2(NCS) 2 exhibit magnetic s u s c e p t i b i l i t i e s which reveal the antiferromagnetic nature of these materials (x at temperatures of 7.0 and 8.0 K max respectively); the data were analysed in terms of a two-dimensional Heisenberg model. For the copper complex, in which the structure shows stronger pyrazine coordination along one dimension, the data were also analysed in terms of a linear chain model. Mossbauer spectroscopy showed Fe(pyz) 2(NCS) 2 to undergo a t r a n s i t i o n to a magnetically-ordered state at 9.2 K. The magnitude of the exchange coupling through bridging pyrazine in Fe(pyz) 2X 2 complexes (where X - i s CF 3S0 3~, CH 3S0 3", C l " , Br -, I" or C10«") i s considerably less than that present in either C u ( p y z ) 2 ( C H 3 S O 3 ) 2 or Fe(pyz) 2(NCS) 2. Spectroscopic evidence indicates that for F e ( p y ) 2 ( C F 3 S 0 3 ) 2 and complexes of stoichiometry M(pyz)X 2 (where M is Fe or Cu and X- i s CF 3S0 3", p-CH 3C 6H f lS0 3", C l " or NCO") bridging anionic ligands are present and for the mono(pyrazine) complexes the neutral ligand also coordinates in a bridging mode. Fe(pyz)(CF 3S0 3) 2, Fe(pyz)(NCO) 2 and Cu(pyz)(CF 3SO 3) 2 a l l exhibit magnetic s u s c e p t i b i l i t y data c h a r a c t e r i s t i c of antiferromagnetic materials (x v at temperatures of 4.4, 38 and 7.0 K max respectively). The magnetic s u s c e p t i b i l i t i e s for these materials were analysed in terms of the two-dimensional iv Heisenberg model and a linear chain model. Mossbauer spectroscopy shows both Fe(pyz)(CF 3S0 3) 2 and Fe(pyz)(NCO) 2 to undergo a t r a n s i t i o n to long-range magnetic ordering at temperatures of 3.9 and 27.0 K respectively. Low-temperature (4.2-130 K) magnetic s u s c e p t i b i l i t y measurements for the iron(II) sulfonate compounds, Fe(RS0 3) 2 (where R i s F, CF 3, CH 3 or p-CH 3C 6H„) are reported. For the compounds where R i s F, CF 3 or p-CH 3C 6H« the magnetic moment data were assessed in terms of c r y s t a l - f i e l d s p l i t t i n g e f f e c t s . The magnetic moment data for a and j3 forms of Fe(CH 3S0 3) 2 are indica t i v e of antiferromagnetic exchange interactions and the ch a r a c t e r i s t i c s of the s u s c e p t i b i l i t y curve for the /3 isomer are explained on the basis of a t r a n s i t i o n from short-range to long range three-dimensional magnetic ordering at 22 K. V Table of Contents Page Abstract i i Table of Contents v L i s t of Tables xi L i s t of Figures x i i Li s t of Abbreviations and Symbols xv Acknowledgements xvi CHAPTER 1 INTRODUCTION 1 1.1 GENERAL INTRODUCTION 1 1.2 OBJECTIVES, PREVIOUS WORK AND SCOPE OF THE THESIS 6 1.3 METHODS OF COMPOUND CHARACTERISATION 16 1.4 ORGANISATION OF THE THESIS 21 CHAPTER 2 EXPERIMENTAL PROCEDURES 23 2.1 GENERAL SYNTHETIC METHODS 23 2.2 PHYSICAL EXPERIMENTAL TECHNIQUES 24 2.2.1 Infrared Spectroscopy 24 2.2.2 Electronic Spectroscopy 24 2.2.3 Magnetic S u s c e p t i b i l i t y Measurements 24 2.2.4 Mossbauer Spectroscopy 26 2.2.5 X-Ray Crystallography 27 2.2.6 D i f f e r e n t i a l Scanning Calorimetry 27 2.2.7 Elemental Analysis 29 CHAPTER 3 COMPLEXES CONTAINING AN MNaX2 CHROMOPHORE 30 3.1 INTRODUCTION 30 3.2 SYNTHETIC METHODS 33 3.2.1 Tetrakis(pyridine) Complexes 33 v i 3.2.1.1 T r a n s - b i s ( t r i f l u o r o m e t h a n e s u l f o h a t o - O ) t e t r a k i s -( p y r i d i n e ) i r o n d l ) , F e ( p y ) „ ( C F 3 S 0 3 ) 2 34 3.2.1.2 T r a n s - b i s ( m e t h a n e s u l f o n a t o - O ) t e t r a k i s ( p y r i d i n e ) -i r o n d l ) , F e ( p y ) 4 ( C H 3 S 0 3 ) 2 34 3.2.1.3 T r a n s - b i s ( p - t o l u e n e s u l f o n a t o - O ) t e t r a k i s ( p y r i d i n e ) -i r o n d l ) , F e ( p y ) « ( p - C H 3 C 6 H a S 0 3 ) 2 35 3.2.1.4 T e t r a k i s ( p y r i d i n e ) i r o n d l ) f l u o r o s u l f o n a t e , F e ( p y ) , ( F S 0 3 ) 2 35 3.2.1.5 T r a n s - b i s ( t r i f l u o r o m e t h a n e s u l f o n a t o - O ) t e t r a k i s -TpyrTdine)copper(II), C u ( p y ) „ ( C F 3 S 0 3 ) 2 37 3.2.1.6 T e t r a k i s ( p y r i d i n e ) c o p p e r ( I I ) methanesulf onate, Cu(py)«, (CH 3 S 0 3) 2 38 3.2.2 T e t r a k i s ( p y r a z i n e ) and T e t r a k i s ( 2 - m e t h y l p y r a z i n e ) Complexes 38 3.2.2.1 Tetrak i s (2-methylpyrazine) i r o n d l ) methanesulfonate, Fe(2-mepyz) f t(CH 3 S 0 3) 2 39 3.2.2.2 T e t r a k i s ( p y r a z i n e ) i r o n ( 1 1 ) h e x a f l u o r o a r s e n a t e d i h y d r a t e , F e(pyz)„(AsF 6) 2.2H 20 39 3.2.2.3 T e t r a k i s ( p y r a z i n e ) c o p p e r ( I I ) t r i f l u o r o -methanesulfonate monohydrate, Cu(pyz)„(CF 3 S 0 3 ) 2.H 20 41 3.2.3 B i s ( p y r a z i n e ) Complexes 41 3.2.3.1 B i s ( p y r a z i n e ) i r o n ( 1 1 ) t r i f l u o r o m e t h a n e -s u l f o n a t e methanol s o l v a t e , F e ( p y z ) 2 ( C F 3 S 0 3 ) 2 . C H 3 O H 41 3.2.3.2 B i s ( p y r a z i n e ) i r o n d l ) methanesulfonate, F e ( p y z ) 2 ( C H 3 S 0 3 ) 2 42 3.2.3.3 T r a n s - b i s ( m e t h a n e s u l f o n a t o - O ) b i s ( y - p y r a z i n e ) -c o p p e r ( I I ) , C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 43 3.2.3.4 B i s ( p y r a z i n e ) i r o n d l ) c h l o r i d e , F e ( p y z ) 2 C l 2 ... 43 3.2.3.5 B i s ( p y r a z i n e ) i r o n d l ) bromide, F e ( p y z ) 2 B r 2 44 3.2.3.6 B i s ( p y r a z i n e ) i r o n d l ) i o d i d e , F e ( p y z ) 2 l 2 45 3.2.3.7 B i s ( p y r a z i n e ) i r o n d l ) t h i o c y a n a t e , F e ( p y z ) 2 ( N C S ) 2 45 3.2.3.8 B i s ( p y r a z i n e ) i r o n d l ) p e r c h l o r a t e , F e ( p y z ) 2 ( C 1 0 „ ) 2 46 v i i 3.2.4 Attempted Preparations 47 3.3 RESULTS AND DISCUSSIONS 48 3.3.1 X-Ray Structure Determinations 48 3.3.1.1 X-Ray structure determination of Fe(py)«(RS0 3) 2) complexes 48 3.3.1.2 X-ray structure determination of Cu(py)«(CF 3S0 3) 2 58 3.3.1.3 X-ray structure determination of Cu(pyz) 2(CH 3S0 3) 2 62 3.3.2 Infrared Spectroscopy 73 3.3.2.1 Infrared spectral results for t e t r a k i s -(pyridine) complexes 74 3.3.2.2 Infrared spectral results for b i s -(pyrazine)iron(II) halide and thiocyanate complexes 81 3.3.2.3 Infrared spectral results for bis-(pyrazine) complexes containing sulfonate or perchlorate anions 87 3.3.2.4 Infrared spectral results for t e t r a k i s -(pyrazine) complexes 93 3.3.3 Electronic Spectroscopy 99 3.3.3.1 Electronic spectral results for complexes containing an FeN a0 2 chromophore 99 3.3.3.2 Electronic spectral results for complexes containing a CuNtt02 chromophore 103 3.3.3.3 Electronic spectral results for complexes containing an FeN aX2 chromophore 107 3.3.4 Magnetic Properties 111 3.3.4.1 Magnetic s u s c e p t i b i l i t y results for complexes containing a CuN„0 2 chromophore 111 3.3.4.2 Magnetic s u s c e p t i b i l i t y results for complexes containing an FeN a0 2 chromophore 121 3.3.4.3 Magnetic s u s c e p t i b i l i t y results for complexes containing an FeNflX2 chromophore 137 3.3.5 Mossbauer Spectroscopy 147 v i i i 3.3.5.1 Mossbauer spectral parameters for complexes containing an FeN a0 2 chromophore 151 3.3.5.2 Mossbauer spectral parameters for b i s -(pyrazine)iron(11) halide and thiocyanate complexes and Fe(pyz)«(AsF 6) 2.2H 20 155 3.3.5.3 Low-Temperature Mossbauer Spectra of Fe(pyz) 2(NCS) 2 156 3.3.6 Thermal Studies 166 CHAPTER 4 COMPLEXES CONTAINING AN MN2X, CHROMOPHORE 184 4.1 INTRODUCTION 184 4.2 SYNTHETIC METHODS 188 4.2.1 Bis(pyridine) Complexes 189 4.2.1.1 Bis(pyridine)iron(II) trifluoromethane-sulfonate, F e ( p y ) 2 ( C F 3 S 0 3 ) 2 190 4.2.2 Mono(pyrazine) Complexes 190 4.2.2.1 Mono(pyrazine)iron(II) trifluoromethane-sulfonate, Fe(pyz)(CF 3S0 3) 2 190 4.2.2.2 Mono(pyrazine)iron(II) p-toluenesulfonate bis(methanol) solvate, Fe(pyz)(p-CH 3C 6H 4S0 3) 2.2CH 3OH 191 4.2.2.3 Mono(pyrazine)iron(II) p-toluenesulfonate, Fe(pyz)(p - C H a C e H a S O a) 2 192 4.2.2.4 Mono(pyrazine)copper(II) trifluoromethane-sulfonate, Cu(pyz)(CF 3S0 3) 2 192 4.2.2.5 Mono(pyrazine)iron(II) chloride, Fe(pyz)Cl 2 ... 192 4.2.2.6 Mono(pyrazine)iron(II) cyanate, Fe(pyz)(NCO) 2 . 193 4.3 RESULTS AND DISCUSSION 194 4.3.1 Infrared Spectroscopy 194 4.3.1.1 F e ( p y ) 2 ( C F 3 S 0 3 ) 2 194 4.3.1.2 Fe(pyz)Cl 2 and Fe(pyz)(NCO) 2 196 4.3.1.3 Mono(pyrazine) sulfonate complexes 199 4.3.2 Electronic Spectroscopy 204 ix 4.3.2.1 Fe(pyz)(CF3SO3) 2, Fe(pyz)(p-CHaCcH^SOa) 2 and i t s bis(methanol) solvate, Fe(pyz)(CF3SO3) and Cu(pyz)(CF3SO3) 2 204 4.3.2.2 Fe(pyz)Cl 2 and Fe(pyz)(NCO) 2 205 4.3.3 Magnetic Properties 207 4.3.3.1 Cu(pyz)(CF3SO3) 2 2 0 7 4.3.3.2 Mono(pyrazine) and bis(pyridine)iron(11) complexes 211 4.3.4 Mossbauer Spectroscopy 224 4.3.4.1 Low-temperature Mossbauer studies on Fe(pyz)(NCO) 2 and Fe(pyz)(CF 3S0 3) 2 225 4.3.5 Thermal Studies 240 CHAPTER 5 MAGNETIC PROPERTIES OF IRON(II) SULFONATE COMPLEXES 24 3 5.1 INTRODUCTION . 243 5.2 SYNTHETIC METHODS 245 5.3 RESULTS AND DISCUSSION 245 5.3.1 Fe(FS0 3) 2, Fe(CF 3S0 3) 2 and Fe(p-CH 3C 6H„S0 3) 2 245 5.3.2 a- and 0-Fe (CH 3S0 3 ) 2 249 CHAPTER 6 SUMMARY AND CONCLUSIONS 254 REFERENCES 262 APPENDICES I. Complete X-Ray Structural Parameters 273 II . Vibrational Assignments for Pyridine and some of i t s Complexes 288 II I . Vibrational Assignments for Sulfonate Anions and Unassigned Bands 289 IV. Vibrational Assignments for Pyrazine and Bis(pyrazine) Complexes 291 X V. V i b r a t i o n a l Assignments f o r the N e u t r a l Ligands i n Fe(2-mepyz) j, ( C H 3 S O 3 ) 2 , Cu(pyz) „ (CF 3S0 3) 2 .H 20 and Fe(pyz)»(AsF 6) 2.2H 20 292 VI. V i b r a t i o n a l Assignments f o r Pyrazine and Mono(pyrazine) Complexes 293 V I I . E l e c t r o n i c S p e c t r a l R e s u l t s 294 V I I I . Magnetic S u s c e p t i b i l i t y R e s u l t s f o r Copper(II) Complexes 296 IX. Magnetic S u s c e p t i b i l i t y R e s u l t s f o r I r o n d l ) Complexes 298 X. Mossbauer S p e c t r a l R e s u l t s 306 xi L i s t of Tables Page 3.1 Selected Mean Bond Distances (A) and Angles (°) for some Fe(py)«(RS0 3) 2 Complexes 50 3.2 Selected Bond Distances (A) and Angles (°) for C u ( p y ) 4 ( C F 3 S O 3 ) 2 59 3.3 Selected Bond Distances (A) and Angles (°) for C u ( p y z ) 2 ( C H 3 S O 3 ) 2 64 3.4 Vibrations of the Perchlorate Anion as a Function of Symmetry 90 3.5 Cryst a l F i e l d Parameters for Fe(py)«(RS0 3) 2 Complexes 126 3.6 Zero-Field S p l i t t i n g Parameters 129 3.7 Low-temperature Mossbauer Spectral Parameters for Fe(pyz) 2(NCS) 2 157 3.8 Thermal Parameters for Tetrakis(pyridine) and Bis(pyrazine) Complexes 167 3.9 Thermal Parameters for Bis(pyrazine)iron(II) Halide and Thiocyanate Complexes 177 3.10 Thermal Parameters for Fe(2-mepyz),(CH 3S0 3) 2, C u ( p y z ) a ( C F 3 S O 3 ) 2 . H 2 0 and Fe(pyz),(AsF 6) 2•2H 20 .... 179 4.1 Selected Magnetic Moment Data for Iron(II) T r i f l a t e Complexes 222 4.2 Linewidths and Intensities (27.0-31.4 K) for Fe(pyz) (NCO) 2 229 4.3 Internal Hyperfine F i e l d and Line Intensity Ratios for Fe(pyz) (NCO) 2 231 4.4 Thermal Parameters for Bis(pyridine) and Mono(pyrazine) Complexes 241 5.1 C r y s t a l - F i e l d S p l i t t i n g Parameters for Fe(RS0 3) 2 Compounds - r - r - i - . 247 6.1 C l a s s i f i c a t i o n of Complexes 255 x i i L i s t of Figures Page 1.1 Pyrazine and Pyridine 6 1.2 Two Possible Structures for M(pyz) 2X 2 Complexes 8 3.1 ORTEP Plot of the Structure of Fe(py),(CF 3S0 3) 2 ... 51 3.2 ORTEP Plots of the Structure of Fe(py)„(CH 3S0 3) 2 .. 52 3.3 ORTEP Plot of the Structure of Fe(py)„(p-CH 3C 6H,,S0 3) 2 53 3.4 ORTEP Plot of the Structure of Cu(py),(CF 3S0 3) 2 ... 60 3.5 View of a Single Layer in Cu(pyz) 2(CH 3S0 3) 2 65 3.6 ORTEP Plot of the Inner Coordination Sphere About Copper in Cu(pyz) 2(CH 3S0 3) 2 66 3.7 Two Adjacent Layers in Cu(pyz) 2(CH 3S0 3) 2 Viewed Along the c-Axis 69 3.8 Two Adjacent Layers in Cu(pyz) 2(CH 3S0 3) 2 Viewed Along the b-Axis . 70 3.9 Infrared Spectra of Fe(py) f l(CH 3S0 3) 2, Fe(pyz) 2(CH 3S0 3)2 and Fe(2-mepyz) u(CH 3S0 3)2 75 3.10 Infrared Spectra of Cu(py)„(CH 3S0 3) 2 and Cu(pyz) 2(CH 3S0 3) 2 77 3.11 Infrared Spectra of F e ( p y z ) 2 l 2 and Fe (pyz) 2 (NCS) 2 83 3.12 Infrared Spectrum of Fe(pyz)„(AsF 6) 2.2H 20 96 3.13 Electronic Energy Levels for High-Spin I r o n d l ) ... 101 3.14 Electronic Spectra of Fe(py)„(RS0 3) 2 Complexes 101 3.15 2-methylpyrazine 101 3.16 Electronic Energy Levels for Copper(II) 104 3.17 Magnetic Moments vs Temperature for Cu(py) f l(CH 3S0 3) 2 and Cu(pyz) 2(CH 3S0 3) 2 113 x i i i 3.18 Magnetic S u s c e p t i b i l i t y vs Temperature for Cu(pyz) 2(CH 3S0 3) 2 114 3.19 Magnetic Moments vs Temperature for Fe(py) 4(RS0 3) 2 Complexes 122 3.20 Zero-Field S p l i t t i n g for High-Spin Iron(II) 127 3.21 Magnetic S u s c e p t i b i l i t y vs Temperature for Fe(py),(CH 3S0 3) 2 129 3.22 Magnetic Moments vs Temperature for Fe(py),(CH 3S0 3) 2 and Fe(pyz) 2(CH 3S0 3) 2 132 3.23 Magnetic S u s c e p t i b i l i t y vs Temperature for Fe(pyz) 2(CF 3S0 3) 2.CH 3OH 133 3.24 Magnetic S u s c e p t i b i l i t y vs Temperature for Fe(pyz) 2(CH 3S0 3) 2 135 3.25 Magnetic Moments vs Temperature for Fe(pyz) 2X 2 Complexes 137 3.26 Magnetic Moment vs Temperature for Fe(pyz)2(NCS) 2 141 3.27 Magnetic S u s c e p t i b i l i t y vs Temperature for Fe(pyz) 2 (NCS) 2 141 3.28 1 ,2,4-Triazole 144 3.29 Isomer S h i f t and Quadrupole S p l i t t i n g 148 3.30 Mossbauer Spectrum of Fe(py)„(CH 3S0 3) 2 at 78 K .... 152 3.31 Low-temperature Mossbauer Spectra of Fe(pyz) 2(NCS) 2 158 3.32 Combined Effects of Magnetic and Quadrupole Interactions 161 3.33 Relation Between H^ n t and the E.F.G. Axis System 163 3.34 D.S.C. Curves for Fe(py)»(CF 3S0 3) 2 and Fe(py),(CH 3S0 3) 2 168 3.35 D.S.C. Curves for Cu(py),(CF 3S0 3) 2 and Cu(py)„(CH 3S0 3) 2 173 3.36 D.S.C. Curve for Fe(2-mepyz),(CH 3S0 3) 2 180 3.37 D.S.C. Curve for Cu(pyz),(CF 3S0 3) 2.H 20 181 x i v 3.38 D.S.C. Curve f o r F e ( p y z ) , ( A s F 6 ) 2 . 2 H 2 0 183 4.1 Some P o s s i b l e S t r u c t u r e s of Mono(pyrazine) and B i s ( p y r i d i n e ) Complexes 186 4.2 I n f r a r e d Spectra of F e ( p y z ) C l 2 and Fe(pyz)(NCO) 2 197 4.3 I n f r a r e d Spectrum of F e ( p y z ) ( C F 3 S 0 3 ) 2 200 4.4 Magnetic Moments vs Temperature f o r C u ( p y z ) ( C F 3 S 0 3 ) 2 and C u ( p y z ) » ( C F 3 S 0 3 ) 2 . H 2 0 208 4.5 Magnetic S u s c e p t i b i l i t y vs Temperature f o r C u ( p y z ) ( C F 3 S 0 3 ) 2 209 4.6 Magnetic Moments vs Temperature f o r F e ( p y z ) ( N C O ) 2 and F e ( p y z ) ( C F 3 S 0 3 ) 2 213 4.7 Magnetic S u s c e p t i b i l i t y vs Temperature f o r Fe(pyz)(NCO) 2 214 4.8 Magnetic S u s c e p t i b i l i t y vs Temperature f o r F e ( p y z ) ( C F 3 S 0 3 ) 2 215 4.9 Low-temperature Mossbauer S p e c t r a of Fe(pyz)(NCO) 2 226 4.10 P o s s i b l e E.F.G. A x i s System f o r Fe(pyz)(NCO) 2 232 4.11 H y p e r f i n e F i e l d vs Temperature f o r Fe(pyz)(NCO) 2 233 4.12 Low-temperature Mossbauer Sp e c t r a of F e ( p y z ) ( C F 3 S 0 3 ) 2 237 4.13 Mossbauer Spectrum of F e ( p y z ) ( C F 3 S 0 3 ) 2 at 1 .60 K 239 4.14 D.S.C. Curve f o r Fe(pyz)(NCO) 2 242 4.15 D.S.C. Curves f o r Fe(pyz)(p - C H a C g H f l S O a) 2.2CH 3OH and F e ( p y z ) ( p - C H a C g H a S O a ) 2 242 5.1 Proposed S t r u c t u r e of F e ( R S 0 3 ) 2 Compounds 244 5.2 Magnetic Moments vs Temperature f o r F e ( R S 0 3 ) 2 Compounds 246 5.3 Magnetic Moment vs Temperature f o r F e ( C F 3 S 0 3 ) 2 .... 248 5.4 Magnetic S u s c e p t i b i l i t y vs Temperature for 0-Fe(CH 3SO 3) 2 250 X V L i s t t r i f l a t e p-tosylate py pyz s m w br sh B.M. 9 N k xm " e f f . J E.F.G. D.S.C. TN 5 q r Anal. Calcd of Abbreviations and Symbols Trifluoromethanesulfonate, CF 3 S 0 3 " p-Toluenesulfonate, p-CH 3C 6H„S0 3 " Pyridine Pyrazine Strong Medium Weak Broad Shoulder Bohr Magneton Lande s p l i t t i n g factor Avagadro's number Boltzmann's constant Molar magnetic s u s c e p t i b i l i t y E f f e c t i v e magnetic moment Exchange coupling constant E l e c t r i c f i e l d gradient D i f f e r e n t i a l scanning calorimetry Neel temperature Isomer s h i f t Cjuadrupole s p l i t t i n g Mossbauer linewidth Analysis calculated xvi Acknowledgements I would l i k e to express sincerest thanks to my research directors Dr. R.C. Thompson and Dr. J.R.. Sams for the enlightening discussions throughout the l a s t four years. Thanks go to Dr. F. Aubke for his constructive remarks during the f i n a l preparation of t h i s thesis. The research described in this thesis would have been rendered painstakingly slow i f i t were not for the technical expertise of the mechanical, electronic and glassblowing shops. In p a r t i c u l a r , many thanks go to M. Vagg whose ingenuity was tested many times by the vibrating sample magnetometer. Many thanks go to Dr. S.J. Rettig for the c r y s t a l structure determinations, A. Sallos for processing Mossbauer data, P. Borda for his microanalytical services and to Dr. I. Thorburn and L. Gradnitzer for their proof-reading a b i l i t i e s . F inancial a i d from the U.B.C. Graduate Scholarship Committee i s g r a t e f u l l y acknowledged. I would l i k e to express a special thank you to Louisa Gradnitzer whose many words of encouragement during the last four years extended well beyond the c a l l of duty. 1 CHAPTER 1  INTRODUCTION 1.1 GENERAL INTRODUCTION In recent years, there has been an increasing interest shown by both p h y s i c i s t s and chemists in the solid-state properties of low-dimensional materials. 1 Low dimensionality i s ascribed to substances that exhibit large, anisotropic ratios in some of their physical properties. Chemists have been involved in the synthesis of a diverse range of such compounds whose e l e c t r i c a l , magnetic, o p t i c a l , as well as s t r u c t u r a l and chemical properties have been evaluated. The use of a wide array of techniques to c l a s s i f y these compounds has permitted structure-property relationships to be examined in an attempt to provide a rational approach to the design of new materials having s p e c i f i c properties. To a large degree, however, the a b i l i t y to perform such custom design of materials with predictable magnetic and e l e c t r i c a l properties s t i l l l i e s in the future. The types of compounds which have been studied are varied, and range from compounds of an organic nature to inorganic coordination polymers. Examples of polymeric organic compounds include donor-acceptor complexes, the so-called organic metals, 2 such as tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ), where both the donors and acceptors are arranged in stacks to form pseudo-one-dimensional conductors; polyacetylenes 3 comprise 2 another class of organic polymers and the linear chain p o l y s u l f u r n i t r i d e complexes* provide an inorganic example. Intercalation compounds of linear chain compounds, for example, polymeric (SN) X 5 as well as two-dimensional layer materials such as graphite, 6 FeOCl, 7 and the group 4 and 5 metal chalcogenides, for example, T i S 2 8 and TaS 2, 9 are currently being investigated in an attempt to modify the host l a t t i c e by the presence of a suitable intercalant. The intercalation of lithium into layered dichalcogenides has led to the recent development of a new, high-energy density, rechargeable b a t t e r y . 1 0 Inorganic polymers have been studied for over a century. In 1842, K 2Pt (CN) flC.l0.3 .xH20 was f i r s t synthes i sed, 1 1 and was later found to possess a high conductivity, and in 1968 an X-ray structure determination revealed i t to be a linear chain polymer. 1 2 More recently, inorganic polymers have been prepared from a wide range of t r a n s i t i o n metals and ligands; for example, transition-metal complexes of porphyrins, phthalocyanines and glyoximes have been found to exhibit interesting conduction, e l e c t r i c a l and opti c a l p r o p e r t i e s . 1 3 Inorganic coordination polymers may also be formed by u t i l i s i n g anions with the a b i l i t y to bridge metal centres. Examples of this type include phosphinates, R 2P0 2", 1" where the anions bridge metal atoms to form linear chains, and phosphate 1 5 and sulfonate complexes, 1 6 in which RP0 3 2" and RS0 3" anions have the potential to bridge three metal centres to form two-dimensional layered structures. A common feature of these inorganic coordination polymers is that metal ions are much more closely spaced in some 3 directions than others. In the case of transition-metal coordination polymers, the metal ions are separated from each other by either a- or a- and 7r-bonded fragments. These intervening groups are found to influence the magnetic properties of the complex, and give r i s e to the. so-called superexchange e f f e c t s . At the present time, there is a wide interest in compounds which exhibit these magnetic exchange phenomena. I n i t i a l l y , coordination chemists investigated simple magnetic exchange interactions and the dimeric copper(II) carboxylates 1 1. 1 8 were among the f i r s t to be extensively studied. In recent years, researchers have studied empirically the variation of the exchange constant, J, with bond lengths and angles in a variety of dimers, trimers, and small c l u s t e r s , as well as in polymeric materials. For example, in a - s e r i e s of planar bis-M~hydroxo copper(II) dimers Crawford et a l . 1 9 demonstrated that the exchange coupling varies l i n e a r l y with the Cu-O-Cu angle and that the exchange changes from ferromagnetic to antiferromagnetic as the bridging angle i s increased. Other factors, such as the stereochemistry around the metal and the nature of non-bridging ligands, are also important in determining magnetic exchange interactions. The coordination chemist can interpret magnetic s u s c e p t i b i l i t y data by using models for magnetic exchange developed primarily by p h y s i c i s t s . In t h i s way, progress in understanding the chemistry and physics associated with low-dimensional materials has involved the collaboration of chemists, physicists and material s c i e n t i s t a l i k e . 4 Extensive research has been carried out in t h i s laboratory on transition-metal phosphinate and sulfonate compounds in an attempt to correlate their structural and magnetic properties. It was found in the case of the linear chain copper(II) dialkylphosphinates 1*< 2 ° - 2 1 that two types of d i s t o r t i o n of the CuOs chromophore are possible and i t i s th i s d i s t o r t i o n which plays an important role in determining the nature of the magnetic exchange interaction. For the complexes Cu(R 2P0 2) 2, where R i s n-octyl, n-decyl or n-dodecyl, 2 1 two structural modifications have been isolated and magnetic s u s c e p t i b i l i t y measurements at low temperatures have distinguished these two forms. The a modifications are antiferromagnetic, whereas, the /3 isomers are ferromagnetic; the superexchange interaction i s propagated through the O-P-0 bridges. Studies on the anhydrous and hydrated dimethylphosphinates of manganese(II) 2 2 indicate that strong antiferromagnetic exchange interactions are also present in the anhydrous species. Conversely, in the dihydrate, Mn ((CH 3) 2P0 2) 2•2H 20, a temperature-independent magnetic moment has been observed. An X-ray structure determination of the dihydrate revealed the existence of a strong hydrogen-bonding network linki n g the chains together, and i t is thought that this e f f e c t i v e l y dampens magnetic exchange in this material. The transition-metal sulfonate compounds, M(RS0 3) 2 are thought to adopt a polymeric two-dimensional layered structure, as has been found for Ca(CH 3S0 3) 2. 1 6 No X-ray s t r u c t u r a l data exist for the anhydrous i r o n d l ) sulfonates, Fe(RS0 3) 2, where R is F, CF 3, CH3 or p-CH 3C 6H 4; however, application of a 5 combination of techniques, the so-called "sporting methods", has enabled the structures of the complexes to be proposed. 2 3" 2 5 The techniques of infrared, Mossbauer and electronic spectroscopy indicate a distorted Fe0 6 chromophore with each sulfonate anion bridging to three d i f f e r e n t metal centres resulting in a two-dimensional l a t t i c e . Fe(CH 3S0 3) 2 exists in two forms and the P isomer has been shown by Mossbauer spectroscopy to undergo a t r a n s i t i o n to an antiferromagnetically-ordered s t a t e ; 2 6 presumably the superexchange in this material i s via the O-S-0 bridging units. The other iron(II) sulfonate compounds are magnetically d i l u t e . Several conclusions may be drawn from these e a r l i e r studies on phosphinates and sulfonates which are applicable to this study. The combination of X-ray structure determinations and magnetic s u s c e p t i b i l i t y measurements i s important i f meaningful conclusions are to be drawn concerning the nature of the bridging ligand, the metal chromophore and the effects of these on superexchange. In the absence of X-ray d i f f r a c t i o n studies, i t i s important to examine a large number of closely related complexes by a variety of physical techniques in order to correlate magnetic and structural properties. F i n a l l y , magnetic s u s c e p t i b i l i t y measurements have to be made at low temperatures in order to probe weak exchange interactions often observed in multi-atom bridges. 6 1.2 OBJECTIVES, PREVIOUS WORK AND SCOPE OF THE THESIS This section provides the main objectives of the present study and outlines previous research in the f i e l d of transition-metal pyrazine chemistry. An overview of the research c a r r i e d out in the current study is also given. One objective was to synthesise inorganic coordination polymers of divalent iron and copper. The strategy adopted to induce polymer formation was to use both nitrogen donor atoms of pyrazine (1,4-diazine, F i g . 1.1) to bridge metal centres. Fi g . 1.1 Pyrazine and Pyridine 1,4-Diazine A^-^V N( )N Pyrazine, pyz Azine Pyridine, py Several of the anionic ligands used in the present study also have the a b i l i t y to act as multidentate groups and to bridge metal centres. For example, the sulfonate ligands, RS03", can coordinate through more than one of the oxygen donor atoms. The complexes were characterised by a variety of spectroscopic techniques and in some instances structure was determined by X-ray crystallography. The objective of these spectroscopic and X-ray studies was to ident i f y the metal chromophore and the nature of the bridging ligand system. Once these factors were 7 elucidated, a primary aim of the research was to investigate the magnetic properties of the materials and to probe magneto-structural c o r r e l a t i o n s . When the b a s i c i t i e s of the two nitrogen atoms of pyrazine (pKa values of 0.6 and -6.0 re s p e c t i v e l y 2 7 - 2 8 ) were taken into account, i t was i n i t i a l l y thought that the a b i l i t y of pyrazine to use both nitrogen atoms in a bridging fashion would be rather poor. For comparison, the basi c i t y of the single nitrogen atom of pyridine (azine, F i g . 1.1) i s considerably higher as measured by i t s p K & value of 5 . 2 . 2 9 These observations, combined with the fact that experimentally i t i s found that pyrazine only quaternises at one nitrogen atom, 3 0 suggested that the second nitrogen of pyrazine is deactivated after the f i r s t i s protonated. Experimental evidence, however, indicates that pyrazine often uses both nitrogen atoms when i t reacts with Lewis acids. For example, the bis(pyrazine) adduct i s formed upon reaction of pyrazine with two moles of boron t r i c h l o r i d e (Eqn. 1.1). 3 1 2 B C 1 3 + > C 1 3 B - » / Q \ « - B C 1 3 ...Eqn. 1.1 In the early 1960's, Lever, Lewis and Nyholm were the f i r s t to investigate a series of pyrazine and methyl-substituted pyrazine complexes of cobalt-, ni c k e l - and copper h a l i d e s . 3 1 " 3 * They were p a r t i c u l a r l y interested in a comparison with the well characterised pyridine analogues, 3 5- 3 6 and used room-temperature magnetic s u s c e p t i b i l i t y measurements and u l t r a v i o l e t - v i s i b l e and infrared spectroscopy as a means of probing the nature of the 8 metal chromophore. Their i n i t i a l studies on metal-pyrazine halide complexes concluded that polymeric systems were indeed formed, however, there was debate as to whether the polymers contained bridging pyrazine and terminal halide anions or terminal pyrazine ligands and bridging halide anions (Fig. 1.2). F i g . 1.2 Two Possible Structures for M(pyz) 2X 2 Complexes a). Two-Dimensional Layer b). Linear Chain 9 Infrared spectral results for these complexes caused confusion regarding the mode of pyrazine coordination and both bidentate bridging and terminal modes were proposed. 3 1" 3"' 3 7 " 3 9 An X-ray structure determination of Co(pyz) 2C1 2" 0 proved d e f i n i t i v e and shows pyrazine to be bridging to form a polymeric two-dimensional l a t t i c e with trans-oriented terminal chloride anions. Other studies have demonstrated the a b i l i t y of pyrazine to link metals to form chains (as in Ag(pyz)N0 3" 1 and Cu(pyz)(N0 3) 2" 2) and to form layer compounds (as in Cu(p y z ) 2 ( C l O f l ) 2 " 3 ) . After the i n i t i a l debate, i t was concluded that a combination of infrared and Raman spectroscopy provides d e f i n i t e c r i t e r i a for the mode of pyrazine coordination in such complexes."" A bridging pyrazine molecule is also present in the extensively studied Creutz-Taube complex," 5'" 6 [(NH 3) 5Ru(pyz)Ru(NH3)5] 5 +; there i s s t i l l , however, c o n f l i c t i n g evidence concerning the electronic structure of this mixed-valence i o n . " 7 Pyrazine-bridged complexes are of interest to magnetochemists as they represent examples of materials which may exist as one-dimensional linear chains or two-dimensional l a t t i c e s with the p o s s i b i l i t y of magnetic exchange interactions propagating through the bridging pyrazine system. The most extensive series of pyrazine complexes investigated have been derivatives of copper(II). Copper(II) chloride and bromide complexes have been synthesised with a series of mono- and dimethyl-substituted pyrazine ligands;" 8 a l l exhibit a maximum 10 in the magnetic s u s c e p t i b i l i t y versus temperature curve, in d i c a t i v e of antiferromagnetic interactions. In these i n i t i a l studies, however, the infrared data were interpreted as indicating the presence of terminal pyrazine ligands and i t was suggested that the exchange occurred through bridging halide anions rather than through bridging pyrazine ligands. In 1971, V i l l a and H a t f i e l d " 9 established pyrazine as a ligand capable of transmitting magnetic information in the n i t r a t e complex, Cu(pyz) ( N 0 3) 2• Previous researchers" 2 found that bridging pyrazine leads to a linear chain structure in t h i s complex and although the copper ions are separated by nearly 7 A, a maximum is observed in the magnetic s u s c e p t i b i l i t y data as a result of superexchange via the bridging pyrazine groups. The s i n g l e - c r y s t a l magnetic s u s c e p t i b i l i t y data have been f i t to the Heisenberg linear chain model. 5 0 The superexchange mechanism in polymeric, pyrazine-bridged copper(II) complexes of the type CuL ( N 0 3 ) 2 , was investigated by using a variety of substituted pyrazine ligands, L . 5 1 Richardson and H a t f i e l d elegantly demonstrated that the variation in antiferromagnetic coupling correlates neither with the 0 —basicity nor with s t e r i c factors associated with the ligand * but with the energy of the ir-ir t r a n s i t i o n of the pyrazine ligand, L in the complex. These results indicate the presence of an exchange mechanism involving the pyrazine 7r-system. The importance of the pyrazine w-system in propagating magnetic exchange interactions has been further demonstrated through the use of magnetic measurements on two copper(II) 11 dimers of the type [Cu 2 (tren) 2 L j (ClOi,),, 5 2 (where tren i s 2,2',2''-triaminotriethylamine). One complex, containing pyrazine as the bridging ligand, L, shows magnetic exchange interactions; whereas, in the second dimer, where L i s DABCO (DABCO i s 1,4-diazobicyclo[2.2.2]octane), no magnetic exchange interactions are observed. The lack of a 7r-system in DABCO has been proposed to account for the magnetic properties of this compound. Another important factor in determining the nature of the magnetic exchange interactions in copper(II) pyrazine complexes has been found to be the overlap between the copper d-orbitals and the pyrazine n—system. This interaction i s influenced by the degree of t i l t i n g of the pyrazine ring with respect to the xy coordination plane. For example, in Cu ( p y z ) ( N 0 3 ) 2 4 2 this angle i s 48° and o r b i t a l overlap between the pyrazine 7r-system and the d 2_ 2 ground state of copper i s possible, resulting in x y an e f f e c t i v e route for magnetic exchange interactions. However, in C u ( p y z ) ( h f a c ) 2 , 5 3 (where hfac is hexafluoropentane-1,4-dionate) a linear chain structure results from pyrazine bridging between the square-planar Cu(hfac) 2 units, with pyrazine coordinating along the d i r e c t i o n of the z-axis. There i s no ef f e c t i v e 7r-orbital overlap between pyrazine and the copper d x 2 _ y 2 ground state, and no magnetic exchange interactions are observed. 5* Cu 2(OAc)„(pyz), (where OAc is acetate) i s another copper-pyrazine system which has been investigated. The structure consists of copper acetate dimers linked in a linear chain through bridging pyrazine groups. 5 5 An 12 alternating-dimer model has been proposed with strong intradimer exchange through bridging acetate ligands, J=-325 cm"1, and weak interdimer exchange through bridging pyrazine, J=-0.1 cm" 1. 5 6 Cu(pyz) 2(C10„) 2 has been shown to exist as a two-dimensional sheet-like polymer* 3 in which the bridging pyrazine groups are canted at a angle of 66.1° to the CuN„ plane; in t h i s orientation pyrazine provides an e f f e c t i v e route for antiferromagnetic exchange interactions. Pyrazine complexes of other t r a n s i t i o n metals have also been investigated; for example, the lanthanide ytterbium forms the dimer, (7j 5-Cp 3Yb) 2 (pyz ) . 5 7 In this complex there i s no evidence of magnetic interactions even at temperatures as low as 3 K and formulation of the bonding as largely ionic is proposed to account for t h i s s i t u a t i o n . Investigations on cobalt(II) pyrazine halides, C o ( p y z ) 2 X 2 , 5 8 (where X" is C l " or Br"), over the temperature range 1.8-300 K, show no evidence for magnetic interactions. S i m i l a r l y , for the nickel(II) derivatives, N i ( p y z ) 2 X 2 3 7 (where X" i s C l " , Br" or I"), a temperature-independent magnetic moment i s observed between 90 and 300 K. Evidence for magnetic exchange, however, has been found in the s i l v e r ( I I ) complex, Ag(pyz) 2S 20 8; in t h i s case the magnetic moment i s observed to decrease from 1.61 B.M. at room temperature to 1.27 B.M. at 80 K.5 9 The studies described above c l e a r l y demonstrate the a b i l i t y of pyrazine - to form inorganic coordination polymers with a variety of anions and t r a n s i t i o n metals. For these complexes low-temperature magnetic s u s c e p t i b i l i t y measurements y i e l d 13 valuable information regarding the nature of the spin system and the magnitude of the magnetic exchange. Relatively l i t t l e research has been undertaken on i r o n d l ) complexes of pyrazine, a fact which may be due to the problems associated with the r e l a t i v e ease of oxidation of i r o n d l ) to i r o n d l l ) , and to the d i f f i c u l t i e s in analysing magnetic s u s c e p t i b i l i t y data in i r o n d l ) systems. The present study includes the synthesis and characterisation of some i r o n d l ) pyrazine complexes. Previous work on the i r o n d l ) pyrazine halides involved the preparation of Fe(pyz)C1 2, 6 0 F e ( p y z ) 2 C 1 2 6 1 and F e ( p y z ) 2 B r 2 6 2 and a hydrate, Fe(pyz) 2C1 2.H 20. 6 2 Characterisation of these complexes has included thermal s t u d i e s , 6 1 infrared spectroscopy, 6 0* 6 2, 6 3 and room-temperature magnetic s u s c e p t i b i l i t y measurements. 6 2 The pseudohalide complex, Fe(pyz) 2(NCS) 2 6 * has been reported, but no synthetic procedure was given and the sole method of characterisation involved magnetic s u s c e p t i b i l i t y measurements in the 80-300 K temperature region. In the case of pyrazine complexes, the magnitude of J, the exchange coupling parameter, i s l i k e l y to be small, and hence, i t i s important that low-temperature magnetic studies are carried out. The synthesis of the complex Fe(pyz) 2 (ClOi,) 2.2H 20 6 0 has also been reported, however, characterisation involved only v i b r a t i o n a l assignments in the mid-infrared region (140-500 cm" 1). An X-ray structure determination has shown pyrazine to bond in a unidentate fashion in Fe(CO)„(pyz); 6 5 whereas, a linear chain polymer i s formed through bridging pyrazine in Fe(pyz)(dmg) 2 (where dmg i s 14 dimethylglyoximate). 6 6 In the present study, two groups of pyrazine complexes have been prepared and characterised in an attempt to correlate their magnetic and structural properties. The f i r s t group are the iron(II) pyrazine halide and pseudohalide complexes and comprises the following: Fe(pyz) nX 2, where n i s 1 and X" is C l " and NCO"; and where n i s 2 and X" is C l " , Br", I" and NCS". The feature common to compounds of the second group i s a sulfonate anion, RS0 3", where R is either CF 3, CH3 or p-CH 3C 6H„. Complexes of this group which have been investigated are represented by various stoichiometries, M(pyz) (RS0 3) 2, where M is Fe or Cu and n i s either 1,2 or 4. Magnetic s u s c e p t i b i l i t y results for iron(II) complexes are usually more d i f f i c u l t to interpret than those of analogous copper(II) systems. For example, the observation of a s i g n i f i c a n t l y temperature-dependent magnetic moment for a copper(II) species is indicative of magnetic exchange interactions, and in these S=l/2 systems the magnetic exchange effects can often be modelled in terms of an isotropic Heisenberg exchange Hamiltonian. Conversely, a temperature-dependent magnetic moment i s usually observed in the case of high-spin iron(II) compounds even in the absence of magnetic concentration. A temperature dependence arises from either the ground-state o r b i t a l degeneracy and/or z e r o - f i e l d s p l i t t i n g e f f e c t s of an S=L=2 ion. In high-spin iron(II) complexes, the problem is to dis t i n g u i s h single-ion e f f e c t s from magnetic exchange interactions. 15 An attempt was made to surmount t h i s problem i n the present study, by comparing the magnetic p r o p e r t i e s of the p y r a z i n e complexes with those of the analogous p y r i d i n e d e r i v a t i v e s . P y r i d i n e ( F i g . 1.1) cannot a c t as a b r i d g i n g l i g a n d and i n these complexes s i n g l e - i o n e f f e c t s are expected to determine the magnetic p r o p e r t i e s . The p y r i d i n e h a l i d e and pseudohalide complexes, F e ( p y ) n X 2 , (where n i s 2 and 4 and X" i s C l " , Br", I", NCO" and NCS") have been prepared p r e v i o u s l y and i n v e s t i g a t e d by a v a r i e t y of techniques, i n c l u d i n g Mossbauer, i n f r a r e d and e l e c t r o n i c spectroscopy and magnetic s u s c e p t i b i l i t y measurements. 6 7 The molecular s t r u c t u r e s of F e ( p y ) « C 1 2 6 8 and F e ( p y ) a ( N C S ) 2 6 9 have been determined by s i n g l e - c r y s t a l X-ray d i f f r a c t i o n . Both of these compounds have o c t a h e d r a l c o o r d i n a t i o n about the metal i n v o l v i n g a square-planar arrangement of n i t r o g e n atoms and the anions occupy a x i a l c o o r d i n a t i o n s i t e s . No magnetic exchange e f f e c t s are observed in these t e t r a k i s ( p y r i d i n e ) complexes, as expected f o r systems in which the paramagnetic c e n t r e s are i s o l a t e d from each o t h e r . 6 7 In c o n t r a s t , the corresponding b i s ( p y r i d i n e ) i r o n d l ) h a l i d e and pseudohalide d e r i v a t i v e s are proposed to be polymeric and c o n t a i n b r i d g i n g anions; the c h l o r i d e and th i o c y a n a t e d e r i v a t i v e s e x h i b i t magnetic moments which i n c r e a s e with decreasing temperature; a r e s u l t of ferromagnetic exchange i n t e r a c t i o n s propagating through the b r i d g i n g a n i o n s . 7 0 " 7 3 The present study p r o v i d e s a comparison between the magnetic and s t r u c t u r a l p r o p e r t i e s of the b i s - and t e t r a k i s ( p y r i d i n e ) i r o n ( I I ) h a l i d e and pseudohalide complexes and 16 the corresponding mono- and b i s ( p y r a z i n e ) i r o n d l ) derivatives. A similar comparison involving the M(pyz) n(RS0 3) 2 complexes required the synthesis and characterisation of the analogous tetrakis(pyridine) complexes, M(py) (RS0 3) 2, where M i s Fe or Cu. The f i n a l part of thi s study involved measuring the magnetic properties of the anhydrous sulfonate comopounds, Fe(RS0 3) 2, (where R i s F, CF 3, CH 3 and p-CH3C6H,,) in order to further investigate magnetic interactions through the O-S-0 bridging unit. These complexes have been previously studied in this l a b o r a t o r y ; 2 3 " 2 6 the proposed structure involves a two-dimensional layered array, with each anion bonded to three d i f f e r e n t metal centres. Magnetic interactions are possible through the O-S-0 bridging units and for 0-Fe(CH 3S0 3) 2 these interactions have been observed by Mossbauer spectroscopy. 2 6 Our e a r l i e r research on these compounds involved the measurement of magnetic properties to 80 K;2 5 in the present study, additional magnetic s u s c e p t i b i l i t y measurements were made at lower temperatures to further investigate the p o s s i b i l i t y of magnetic exchange and to corroborate the low-temperature Mossbauer spectral data. 1.3 METHODS OF COMPOUND CHARACTERISATION The measurement of the magnetic s u s c e p t i b i l i t i e s of the complexes was one of the main fo c a l points of this study. For magneto-structural correlations to be made a range of spectroscopic tools was required. These techniques are now 1 7 b r i e f l y introduced. The magnetic properties of transition-metal compounds, when recorded as a function of temperature, provide information on the nature of the ground state of the metal. The magnitude and temperature dependence of the magnetic moment - data of magnetically-dilute complexes are determined by several factors, for example, d-orbital occupancy and degeneracy, l i g a n d - f i e l d symmetry, spin-orbit coupling and electron-delocalisation e f f e c t s . The theory of magnetic s u s c e p t i b i l i t y of transition-metal complexes i s well covered in several t e x t s . 7 " In magnetically-concentrated systems, the factors mentioned above are also present, and any magnetic interaction i s superimposed upon these single-ion phenomena. Q u a l i t a t i v e l y , magnetic exchange interactions may be thought of as a r i s i n g from unpaired spin densities on neighbouring paramagnetic centres being aligned either p a r a l l e l or opposed to each other, resulting in ferromagnetism or antiferromagnetism respectively. Magneto-structural correlations emphasise the importance of the stereochemistry around the metal, the e f f i c i e n c y of metal-ligand o r b i t a l overlap, the geometry of the bridging ligands, the type of substituent on the bridging group and the nature of any non-bridging ligands. The theoretical aspects of magnetic exchange interactions in transition-metal compounds and the models used to interpret the empirical data have been the subject of extensive i n v e s t i g a t i o n s . 7 5 Some of the mathematical relations developed in previous studies are used in t h i s study to model the magnetic s u s c e p t i b i l i t y data. 18 In order for magneto-structural correlations to be made, structure determinations by X-ray crystallography are p a r t i c u l a r l y relevant. This technique provides precise d e t a i l s of bond lengths and angles, and establishes the exact nature of the bridging system and the arrangement of non-bridging ligands. In the present study, several materials were obtained in a c r y s t a l l i n e form and the c r y s t a l and molecular structures were solved. From these data the interactions between the metal, neutral ligands and anions have been investigated. One d i s t i n c t advantage of iron-containing compounds i s that 5 7 F e exhibits a Mossbauer resonance. Mossbauer spectroscopy i s capable of elucidating the electronic properties about the iron centre. From a Mossbauer spectrum two chemically important parameters are obtained, namely, the isomer s h i f t and quadrupole s p l i t t i n g . The isomer s h i f t i s determined by the t o t a l s-electron density at the nucleus and has been found to be useful in determining the oxidation state of the metal. The a b i l i t y to measure quadrupole s p l i t t i n g s i s one of the more useful features of Mossbauer spectroscopy; The quadrupole s p l i t t i n g i s related to the e l e c t r i c f i e l d gradient (E.F.G.) at the iron nucleus, established when the d i s t r i b u t i o n of the surrounding electrons and/or ligands has lower than cubic symmetry. In the case of 5 7 F e , a t r a n s i t i o n occurs between the ground state (1=1/2) and the excited state (1=3/2) of the iron nucleus. The presence of a quadrupole interaction results in the s p l i t t i n g of the excited state and Mossbauer tra n s i t i o n s occur between the singly-degenerate ground state and the 19 doubly-degenerate excited state. Mossbauer spectroscopy is a powerful technique for probing the nature of magnetic exchange interactions, p a r t i c u l a r l y when the interactions result in a t r a n s i t i o n to a magnetically-ordered state. In such a system the nuclear energy levels are s p l i t further to produce a complex magnetic hyperfine spectrum. It has been in thi s manner that magnetic exchange interactions have been observed for /3 i r o n d l ) methanesulf onate in t h i s l a b o r a t o r y . 2 6 The combined uses of Mossbauer spectroscopy and magnetic s u s c e p t i b i l i t y measurements are complementary for probing magnetic interactions. The thermal properties of materials can be measured by d i f f e r e n t i a l scanning calorimetry (D.S.C). This technique, when applied to transition-metal complexes, provides a means of determining thermal s t a b i l i t i e s . Enthalpies and temperatures at which chemical and physical changes occur can also be established quantitatively by such measurements. In addition, thermolysis has been shown to be a valuable preparative technique; for example, some bis ( p y r i d i n e ) i r o n ( 1 1 ) halide and pseudohalide complexes have been prepared from the corresponding tetrakis(pyridine) complexes by thermolysis. 6 7 In the present study, d i f f e r e n t i a l scanning calorimetry has proven a useful aid to synthesis by assessing the f e a s i b i l i t y of a par t i c u l a r thermolysis reaction. The use of D.S.C. combined with thermogravimetric analysis (T.G.A.) allows reactions to be monitored not only by changes in enthalpy but also by the weight changes associated with a 20 thermolysis reaction. In t h i s study, a T.G.A. accessory was not available; however, improvised T.G.A. experiments were performed and t h i s method has provided information concerning the intermediates produced during thermolysis. The coordination geometry of transition-metal complexes can be determined from the number of absorptions and their frequencies in the u l t r a - v i o l e t and v i s i b l e regions of the electromagnetic spectrum. Electronic absorption spectroscopy has been used throughout the study as a means of probing the l i g a n d - f i e l d environment of the central metal ion. The correlations between the spectra and the chromophore were especially important when the nature of the chromophore had been determined by X-ray crystallography; the results obtained for complexes of known structures were then extended to probe the nature of the chromophore in compounds of undetermined structures. V i b r a t i o n a l spectroscopy plays a role in structure determination as well. Infrared spectroscopy provides information on the coordination of neutral and anionic ligands through the analysis of the number of dignostic bands and their energies. Infrared c r i t e r i a have been developed to determine the mode of sulfonate anion c o o r d i n a t i o n . 2 3 ' 7 6 In the case of the neutral ligands employed here, coordinated pyridine exhibits s i g n i f i c a n t s h i f t s in the positions of several bands when compared to free p y r i d i n e 7 7 and the infrared spectra of pyrazine and i t s complexes are p a r t i c u l a r l y applicable for assigning either a unidentate or bidentate bridging mode of coordination. 21 Free pyrazine and coordinated bidentate pyrazine possess a centre of symmetry, hence, the infrared and Raman bands are mutually exclusive. By coordination through only one nitrogen atom, however, the symmetry in terminally coordinated pyrazine ligands i s reduced to at least and some of the Raman active modes become infrared a c t i v e . 4 " The infrared spectral results obtained in the present study were then used in conjunction with X-ray structural data to support the use of infrared c r i t e r i a in assessing the nature of anion and ligand coordination modes. Elemental analyses of C, H, N, and in some cases 0 , were obtained routinely as a means of determining the stoichiometry and purity of the complexes is o l a t e d . 1.4 ORGANISATION OF THE THESIS The i r o n d l ) and copper (II) complexes prepared in the present study contain chromophores with a combination of N and X donor sets (where N i s from pyrazine or pyridine, and X arises from a halide, pseudohalide, sulfonate or perchlorate anion). For these complexes, the chromophore i s either MN„X 2 or MN2Xa and the complexes containing these chromophores are discussed separately in Chapters 3 and 4 respectively. In some cases the chromophore was c l e a r l y i d e n t i f i e d by an X-ray structure determination. In the absence of such conclusive evidence, the c l a s s i f i c a t i o n was based upon spectroscopic methods, for example, infrared, Mossbauer and electronic spectroscopy. Chapters 3 and 4 are s i m i l a r l y organised. Each chapter begins with a discussion of the experimental procedures used for 22 the preparation of the complexes. Following t h i s , the results a r i s i n g from the characterisation are presented and interpreted, and a brief summary is given at the end of each section. General experimental procedures and techniques are described in Chapter 2. Results of magnetic s u s c e p t i b i l i t y measurements performed on the anhydrous i r o n d l ) sulfonate compounds are presented in Chapter 5. In Chapter 6, a c l a s s i f i c a t i o n of complexes based upon their magnetic and s t r u c t u r a l properties i s given and some general conclusions are presented. 23 CHAPTER 2 EXPERIMENTAL PROCEDURES 2.1 GENERAL SYNTHETIC METHODS A l l chemicals used in th i s study were at least of reagent grade quality and obtained from commercial sources. Solvents were dried prior to use by the following procedures. Methanol and ethanol were refluxed in the presence of the corresponding magnesium alkoxide, diethyl ether was refluxed over sodium benzophenone ketyl, a c e t o n i t r i l e and dichloromethane were refluxed in the presence of calcium hydride, acetone was refluxed in the presence of potassium carbonate, and pyridine was refluxed over barium oxide. After drying, solvents were d i s t i l l e d under a dry nitrogen atmosphere. Most i r o n ( l l ) compounds prepared were a i r - and moisture-sensitive and hence care was taken to avoid their exposure to the atmosphere. Standard vacuum-line techniques for the manipulation of a i r - s e n s i t i v e compounds were used; 7 8 in addition, compounds were handled in an inert nitrogen atmosphere dry box, (D.L. Herring Corporation Dri-Lab (model HE-43)) equipped with a dry tr a i n (model HE-93). These precautions were found to be unnecessary for the preparation of the copper(II) compounds. 24 2.2 PHYSICAL EXPERIMENTAL TECHNIQUES 2.2.1 Infrared Spectroscopy Infrared spectra were recorded on samples mulled in Nujol sandwiched between KRS-5 plates (58% T i l , 42% TlBr, Harshaw Chemical Co.). A Perkin Elmer model 598 spectrophotometer was used in the region of 250-4000 cm"1. A l l spectra were calibrated by using a polystyrene f i l m (907 and 1601 cm" 1). Tabulated frequencies are considered accurate to ±5 cm"1 for broad bands and ±2 cm"1 for sharp bands. 2.2.2 Electronic Spectroscopy Solid-state electronic spectra were obtained at room temperature by using Nujol mulls pressed between s i l i c a glass windows. A Cary model 14 spectrophotometer was used over the frequency range of 4,000-30,000 cm"1. Due to the broad nature of these absorptions, electronic spectral frequencies quoted are considered accurate to ±200 cm"1. 2.2.3 Magnetic S u s c e p t i b i l i t y Measurements Three techniques were used to measure magnetic s u s c e p t i b i l i t i e s . Routine temperature-dependent studies from 4.2-130 K were made using a Princeton Applied Research model 155 vibrating sample magnetometer. 2 0 A magnetic f i e l d of 7.50 or 9.63 T was employed for the ir o n ( I l ) and copper(II) complexes respectively. Magnetic f i e l d s were set to an accuracy of 0.5% and measured by using an F.W. B e l l model 620 gaussmeter. 25 Accurately weighed samples of approximately 100 mg, contained in gelatin capsules, were attached to a Kel-F holder with an epoxy resin. Corrections were made for the diamagnetic background of the holder. Ultrapure nickel metal was used to c a l i b r a t e the instrument. Temperature measurement was achieved with a chromel versus Au-0.02% Fe thermocouple 7 9 located in the sample holder immediately above the sample. The thermocouple was calibrated by using the known s u s c e p t i b i l i t y versus temperature behaviour of tetramethylenediammonium tetrachlorocuprate(II) and checked with mercury(II) te t r a t h i o c y a n a t o c o b a l t a t e ( I I ) . 8 0 From the scatter in the data points from four separate c a l i b r a t i o n s , the temperatures are estimated to be accurate to ±1% over the range studied, 2-130 K. The accuracy of the magnetic s u s c e p t i b i l i t y values as measured by this technique i s estimated to be ±1%. A Gouy balance 8 1 was used in the temperature region 80-300 K to measure the magnetic s u s c e p t i b i l i t y of the i r o n d l ) complexes. Samples were packed in a Pyrex tube which had been previously cal i b r a t e d to correct for i t s diamagnetism. Measurements were made in a nitrogen atmosphere at a magnetic f i e l d strength of 0.45 T. HgCo(NCS)„ was again used as a c a l i b r a n t . 8 0 The accuracy of the magnetic s u s c e p t i b i l i t y values obtained using the Gouy method i s estimated as approximately ±5%. A Faraday balance 8 2 was used to measure magnetic s u s c e p t i b i l i t i e s at room temperature, free from any packing error. The Gouy method i s prone to such errors. Measurements were made at magnetic f i e l d gradients of 0.0253, 0.0526 and 26 0.0869 T 2 cm"1 in the case of the i r o n ( I l ) complexes, and for the copper(II) species measurements were made only at the two higher f i e l d gradients. The accuracy of the magnetic s u s c e p t i b i l i t y values obtained by thi s technique i s better than ± 1 %. Molar magnetic s u s c e p t i b i l i t i e s were corrected for the diamagnetism of the metal ions and l i g a n d s . 8 3 The diamagnetic corrections (units of 10"6 cm3 mol" 1) are: F e 2 + , 13; Cu 2 +, 11; C F 3 S O 3 - , 46; CH 3S0 3", 35; p-CHaCgH^SOa", 89; AsF 6", 97; NCO", 21; NCS", 35; CIO,", 34; C l " , 26; Br", 36; I", 52; H20, 13? C H 3 O H , 34; pyridine, 49; pyrazine, 45; 2-methylpyrazine, 57. In addition, the copper(Il) complexes were corrected for the temperature-independent-paramagnetism of Cu 2 +, 60. 2.2.4 Mossbauer Spectroscopy 5 7 F e Mossbauer spectra were obtained as reported previously. 8* To a l l e v i a t e problems of sample decomposition nylon c e l l s , containing the f i n e l y powdered sample, were sealed with an epoxy glue. Spectra were recorded in transmission geometry, the radiation source was 5 7Co in a Cu or Rh matrix. The Doppler velocity scale was calibrated by using a metallic iron f o i l absorber, and isomer s h i f t s are quoted r e l a t i v e to the centre of an iron f o i l spectrum. Temperature-dependent (8-300 K) Mossbauer studies were carried out in a Janis model DT-6 cryostat. The temperature was set and maintained to within ±0.02 K with a Cryogenic Research model TC-101 temperature c o n t r o l l e r . Temperatures were measured 27 with c a l i b r a t e d Ge and Pt resistance thermometers. Spectra were f i t t e d to Lorentzian curves with a least-squares treatment of the data points. The programme treats the positions, l i n e widths and areas as unconstrained f i t t i n g parameters. The estimated precision of the quadrupole s p l i t t i n g and isomer s h i f t parameters i s considered to be ±0.01 mm s" 1. Low-temperature Mossbauer spectra of Fe(pyz) 2(NCS) 2, F e ( p y z ) ( C F 3 S O 3 ) 2 and Fe(pyz)(NCO) 2 were measured by Dr. J.R. Sams at the Nuclear Research Centre, Demokritos, Greece. 2.2.5 X-Ray Crystallography A l l X-ray structure determinations were performed by Dr. S.J. Rettig of this department. Crystals suitable for X-ray analysis were obtained as described in the relevant experimental sections. The complexes whose c r y s t a l structures were determined in the present study are named in the appropriate experimental sections according to I.U.P.A.C. nomenclature. In subsequent discussions, however, a less rigourous naming system is used; for example, trans-bi s(methanesulfonato-O)tetrakis(pyridine)irondl) becomes tet r a k i s ( p y r i d i n e ) i r o n ( I I ) methanesulfonate. 2.2.6 D i f f e r e n t i a l Scanning Calorimetry (D.S.C.) Typical D.S.C. runs were performed in an inert atmosphere of nitrogen at a nitrogen flow rate of 50 mL min" 1. Finely powdered samples of approximately 5-10 mg were accurately 28 weighed into aluminum crucibles and the temperature range (308-723 K) was programmed by using a Mettler TC-10A processor in conjunction with a Mettler DSC-20 c e l l ; a rate of temperature increase of 4 K per minute was used. The temperature c a l i b r a t i o n of the Pt sensor was achieved by using the known fusion temperatures of indium, lead and zinc. The heat flow was calibrated by using an exactly known quantity of indium. For each determination an empty crucible was placed on the reference sensor. The temperature and enthalpy of a p a r t i c u l a r thermal event were obtained from the maximum (or minimum) in the D.S.C. curve and the integrated area underneath the curve respectively. The accuracy of these values is determined somewhat by the nature of the peak. For example, two poorly resolved peaks are d i f f i c u l t to analyse, as are asymmetrical peaks. These d i f f i c u l t i e s may be caused by the physical c h a r a c t e r i s t i c s of the sample or the d i s t i b u t i o n of the sample in the pan. For a series of c a l i b r a t i o n s using indium metal, i t was found that the fusion temperature was accurate to ±0.1 K and the integrated peak area was accurate to ±2 J g" 1, which generally represents an error of approximately ±1% in both measurements. These values are considered to be the upper l i m i t s of accuracy for the instrument and where broad or overlapping curves occur the temperatures and enthalpy values are considered accurate to ±5 K and ±5% respectively. Thermogravimetric analysis was possible by removal of the aluminum crucible prior to and following a thermal event and 29 weighing by a n a l y t i c a l balance. The weight changes were small and the accuracy of the weight loss figure is approximately ±5%. 2.2.7 Elemental Analysis Carbon, hydrogen, nitrogen and, in some cases oxygen analyses were performed by P. Borda of t h i s department. A n a l y t i c a l data are considered accurate to ±0.3%. Oxygen analysis was not possible for samples containing the combination of fluorine and hydrogen. 30 CHAPTER 3 COMPLEXES CONTAINING AN MN<,X2 CHROMOPHORE 3.1 INTRODUCTION The s y n t h e s i s and c h a r a c t e r i s a t i o n of s e v e r a l groups of complexes having an MN,X2 chromophore are d e s c r i b e d i n t h i s chapter. The f i r s t group c o n s i s t s of the t e t r a k i s ( p y r i d i n e ) complexes, M ( p y ) „ ( R S 0 3 ) 2 , (where M i s Cu and R i s CF 3 or CH 3; and where M i s Fe and R i s C F 3 , CH 3 or p-CH 3C 6H,)i These compounds were s y n t h e s i s e d f o r two major reasons. Complexes of t h i s type have been proposed to have s t r u c t u r e s i n v o l v i n g an MNft02 chromophore i n which the four n i t r o g e n atoms of the p y r i d i n e l i g a n d s are c o o r d i n a t e d i n a square plane around the metal and the s u l f o n a t e anions occupy a x i a l c o o r d i n a t i o n s i t e s . 7 6 Magnetic exchange i n t e r a c t i o n s a re expected to be non-existent or weak i n such complexes, and indeed, no i n t e r a c t i o n s have been observed i n the p r e v i o u s l y s t u d i e d t e t r a k i s ( p y r i d i n e ) i r o n d l ) compounds, Fe(py)«,X 2, (where X" i s a h a l i d e or p s e u d o h a l i d e ) . 6 7 A second reason f o r i n v e s t i g a t i n g these compounds i s that t h e i r magnetic moment data served as a ba s e l i n e from which magnetic exchange i n t e r a c t i o n s i n the analogous b i s ( p y r a z i n e ) complexes c o u l d be measured. In a d d i t i o n , the s t r u c t u r a l p r o p e r t i e s of the t e t r a k i s ( p y r i d i n e ) complexes are i n t e r e s t i n g i n t h e i r own r i g h t . S e v e r a l of the t e t r a k i s ( p y r i d i n e ) complexes were s u i t a b l e f o r X-ray s t r u c t u r e d etermination and the c r y s t a l and molecular s t r u c t u r e s of 31 F e ( p y ) , ( R S 0 3 ) 2 , (where R i s C F 3 , CH 3 or p-CH 3C 6H f l) and C u ( p y ) a ( C F 3 S 0 3 ) 2 , were s o l v e d . These s t r u c t u r e s p r o v i d e an o p p o r t u n i t y t o examine not o n l y the bonding parameters of the p y r i d i n e l i g a n d s , but a l s o the c o o r d i n a t i o n mode of the s u l f o n a t e a n i o n s as a f u n c t i o n of the group R and the m e t a l . With a c c u r a t e s t r u c t u r a l d a t a a v a i l a b l e f o r t h e s e compounds i t was p o s s i b l e t o t e s t p r e v i o u s l y d e v e l o p e d i n f r a r e d and o t h e r s p e c t r o s c o p i c c r i t e r i a f o r s t r u c t u r e i n M(py)„ (RS0 3 ) 2 c o m p l e x e s . 7 6 The second group of compounds c o m p r i s e s the b i s ( p y r a z i n e ) d e r i v a t i v e s c o n t a i n i n g s u l f o n a t e a n i o n s . The f o l l o w i n g complexes were i s o l a t e d : F e ( p y z ) 2 ( C F 3 S 0 3 ) 2 . C H 3 O H , F e ( p y z ) 2 ( C H 3 S 0 3 ) 2 and the copper s p e c i e s C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 . The s t e r e o c h e m i s t r y around the m e t a l i s a g a i n dependent upon the mode of c o o r d i n a t i o n of the p y r a z i n e l i g a n d and the s u l f o n a t e a n i o n . I n the case of the copper d e r i v a t i v e , the chromophore and t h e b r i d g i n g system were d e t e r m i n e d by X-ray c r y s t a l l o g r a p h y ; however, b o t h b i s ( p y r a z i n e ) i r o n ( I I ) compounds were i s o l a t e d i n forms u n 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-ray d i f f r a c t i o n s t u d i e s and thus c h a r a c t e r i s a t i o n of the i r o n s p e c i e s was s o l e l y by s p e c t r o s c o p i c methods. The magnetic p r o p e r t i e s of the b i s ( p y r a z i n e ) complexes were compared t o those of the a n a l o g o u s t e t r a k i s ( p y r i d i n e ) d e r i v a t i v e s i n o r d e r t o e x p l o r e t h e e f f e c t s of b r i d g i n g p y r a z i n e groups on magnetic exchange i n t e r a c t i o n s . A t h i r d group of complexes t o be d i s c u s s e d i n t h i s c h a p t e r are the b i s ( p y r a z i n e ) i r o n ( I I ) s p e c i e s , F e ( p y z ) 2 X 2 , (where X" i s 32 a halide, C l " , Br" or I"; pseudohalide, NCS"; or perchlorate, CIO,"). In the case of the halide and pseudohalide anions l i s t e d above, the corresponding t e t r a k i s ( p y r i d i n e ) i r o n d l ) derivatives have been synthesised and characterised by other researchers. 6 7 This previous work provided a data set for comparing s t r u c t u r a l , spectroscopic and magnetic properties of the pyrazine-bridged complexes, prepared in the present work, with the properties of analogous tetrakis(pyridine) compounds which contain no bridging ligands. The bis(pyrazine) derivatives prepared in the present study represent a range of compounds in which the anion varies from being rather weakly coordinating (for example, sulfonate or perchlorate) to more strongly coordinating (for example, halide or pseudohalide). Such a series permitted an examination of possible correlations between spectroscopic and magnetic properties and anion b a s i c i t y . As described in Chapter 1 (Section 1.2), one of the main objectives of the present study was to prepare pyrazine complexes in which the pyrazine group would occupy a bridging position, and subsequently to investigate the e f f i c i e n c y of t h i s ligand for the propagation of magnetic exchange interactions. During the course of the present research, however, several compounds were isolated in which the neutral pyrazine ligand to metal r a t i o was 4:1; these complexes are Fe(2-mepyz),(CH 3S0 3) 2, Cu(pyz) n(CF 3S0 3) 2.H 20 and Fe(pyz)„(AsF 6) 2.2H 20. Spectroscopic evidence, to be presented in t h i s chapter, suggested that the complexes contain unidentate pyrazine ligands resulting in an 33 MN„X 2 chromophore and a d i s c u s s i o n of these complexes i s r e l e v a n t here. The magnetic and s p e c t r o s c o p i c p r o p e r t i e s of C u ( p y z ) « ( C F 3 S 0 3 ) 2 . H 2 0 and F e ( 2 - m e p y z ) „ ( C H 3 S 0 3 ) 2 are a l s o of i n t e r e s t i n r e l a t i o n to the p r o p e r t i e s of the t e t r a k i s ( p y r i d i n e ) and b i s ( p y r a z i n e ) compounds. For example, these t e t r a k i s ( p y r a z i n e ) complexes p r o v i d e a means of t e s t i n g the i n f r a r e d c r i t e r i a which have been developed f o r determining e i t h e r the b r i d g i n g or t e r m i n a l nature of p y r a z i n e i n i t s complexes. 3 7- * 4 C u ( p y z ) „ ( C F 3 S 0 3 ) 2 . H 2 0 proved a u s e f u l s t a r t i n g m a t e r i a l f o r the p r e p a r a t i o n of the mono(pyrazine) complex C u ( p y z ) ( C F 3 S 0 3 ) 2 ( S e c t i o n 4.2.2.4). The i s o l a t i o n of Fe(pyz)n ( A s F 6 ) 2 . 2 H 2 0 r e s u l t e d from attempts to prepare the b i s ( p y r a z i n e ) d e r i v a t i v e , F e ( p y z ) 2 ( A s F 6 ) 2 . The b i s ( p y r a z i n e ) complex c o u l d not be i s o l a t e d i n the present study and attempts to produce the d e s i r e d b i s ( p y r a z i n e ) compound by t h e r m o l y s i s of Fe(pyz)«(AsF 6) 2.2H 20 were u n s u c c e s s f u l . 3.2 SYNTHETIC METHODS 3.2.1 T e t r a k i s ( p y r i d i n e ) Complexes Compounds of formula M ( p y ) f t ( R S 0 3 ) 2 , where M i s Fe and R i s CF 3, CH 3 and p - C H 3 C 6 H „ , and M i s Cu and R i s CF 3 and CH 3 were prepared by the r e a c t i o n of the a p p r o p r i a t e anhydrous m e t a l ( I I ) s u l f o n a t e d i s s o l v e d i n methanol, w i t h an excess of p y r i d i n e . M(RS0 3) 2 + 4py > M ( p y ) « ( R S 0 3 ) 2 ...Eqn. 3.1 The i r o n ( I I ) complexes were prepared i n an i n e r t atmosphere dry 3.4 box to avoid oxidation. No such precautions were taken for the preparation of the copper(II) d e r i v a t i v e s . 3.2.1.1 T r a n s - b i s ( t r i fluoromethanesulfonato-Q)tetrakis-{pyridine)iron(11), Fe(py),(CF 3S0 3) 2 Iron(II) trifluoromethanesulfonate 2 5 (0.486 g, 1.37 mmol) was dissolved in methanol (5 mL). This resulted in a pale-green solution. An excess of pyridine (4 mL, 50 mmol) was added dropwise and the colour of the solution i n t e n s i f i e d . Overnight, pale-green, needle-shaped c r y s t a l s formed; th i s s o l i d product was isolated in 64% y i e l d a f t e r f i l t r a t i o n and washing with small quantities of methanol and d i e t h y l ether. Anal. calcd for FeC 2 2H2oNi,F 6S20 6 : C, 39.41; H, 3.01; N, 8.36; found: C, 39.41 ; H, 3.10; N, 8.28. 3.2.1.2 Trans-bis(methanesulfonato-Q)tetrakis(pyridine)iron(11), Fe(py)„(CH 3S0 3) 2 An excess of pyridine (5 mL, 62 mmol) was added to the pale-green solution resulting from the dissolution of either a-or |3-Fe(CH3S03 ) 2 2 5 (0.98 g, 4.0 mmol) in hot methanol (5 mL). Overnight, green, p l a t e - l i k e c r y s t a l s formed; t h i s s o l i d product was isolated by f i l t r a t i o n and washed with small quantities of methanol and diethyl ether ( y i e l d 70%). Anal. calcd for FeC22H26N(,S20 6 : C, 46.98; H, 4.67; N, 9.96; 0, 17.07; found: C, 46.70; H, 4.67; N, 9.72; 0, 17.01. 35 3.2.1.3 Trans-bis(p-toluenesulfonato - O )tetrakis-(pyridine) i r o n d l ) , Fe(py) „ (p-CHaCgHttSOa) 2 I r o n d l ) p-toluenesulfonate 2 5 (0.83 g, 2.1 mmol) was dissolved in methanol (18 mL). Pyridine (4 mL, 50 mmol) was added dropwise to t h i s solution and a yellow p r e c i p i t a t e formed immediately. Upon standing for 30 minutes th i s s o l i d became an o i l . In an attempt to c r y s t a l l i s e t h i s o i l , d i e t h y l ether (10 mL) was added and overnight, green, triangular c r y s t a l s formed. The material was isolated by f i l t r a t i o n , and washed with small amounts of methanol and diethyl ether ( y i e l d 25%). The t o t a l y i e l d was increased to 60% by allowing the f i l t r a t e to evaporate slowly to approximately one half of i t s o r i g i n a l volume; subsequently a microcrystalline s o l i d was isolated from this solution by f i l t r a t i o n . Anal. calcd for F e C 3 f t H 3nH*S 20 6: C, 57.13; H , 4.80; N, 7.84; 0, 13.43; found (for f i r s t crop): C, 56.87; H , 4.82; N, 7.64; 0, 13.20. 3.2.1.4 Tetrakis(pyridine)iron(11) fluorosulfonate, Fe(py)„(FS0 3) 2 The general method used to prepare the t e t r a k i s ( p y r i d i n e ) i r o n d l ) sulfonate complexes f a i l e d to produce the desired product when the anion was FS0 3". This was thought to be due to the hydrolysis of the S-F bond which i s extremely susceptible to trace amounts of moisture. When the general route was followed (Eqn. 3.1) a yellow product was obtained whose infrared spectrum lacked absorptions in the region of 1260-1340 cm"1, where the asymmetric S0 3 stretching vibrations 36 are expected to occur; the presence of a medium intensity band at 1540 cm"1 indicated the presence of the pyridinium c a t i o n . 7 7 These observations indicate decomposition of the anion and protonation of the neutral ligand. Paul et a _ l . 8 5 . prepared bi s (pyr idine) iron (11) fluorosulfonate by suspending Fe(FS0 3) 2 in carbon tetrachloride and subsequently adding pyridine. This reaction could not be successfully repeated here, and, after t h e i r procedure was followed the infrared spectrum of the product indicated the presence of the pyridinium c a t i o n . 7 7 D i f f i c u l t i e s in synthesising Fe(py)„(FS0 3) 2 have been encountered previously. The complexes, M(py)„(FS0 3) 2, (where M is Ni, Cu and Zn) have been prepared in this l a b o r a t o r y 7 6 and i t was noted that the i r o n d l ) complex was not i s o l a b l e . 8 6 In the present study several other methods were investigated in an attempt to synthesise the iron derivative from F e ( F S 0 3 ) 2 ; 2 3 they are as follows: (i) Direct addition of pyridine to F e ( F S 0 3 ) 2 . ( i i ) Addition of pyridine to a suspension of Fe(FS0 3) 2 in dichloromethane. ( i i i ) Addition of pyridine to a suspension of Fe(FS0 3) 2 in nitromethane. (iv) Addition of excess pyridine (5 mL, 62 mmol) to i r o n d l ) f l u o r o s u l f onate (0.16 g, 0.63 mmol) dissolved in warm a c e t o n i t r i l e (20 mL). This resulted in the formation of a yellow s o l i d which was isolated by f i l t r a t i o n and washed with diethyl 37 ether. Attempts (i) to ( i i i ) resulted in sol i d s which have an infrared absorption around 1540 cm"1, indicative of the pyridinium c a t i o n , 7 7 and microanalytical data which do not relate to any value of n in the complex F e ( p y ) n ( F S 0 3 ) 2 . The yellow s o l i d obtained by method (iv) has the following microanalytical r e s u l t s : C, 50.26; H, 4.29; N, 11.54. These data eliminate the p o s s i b i l i t y of the complex being Fe(py)«(FS0 3) 2, for which the anal. calcd i s C, 42.12; H, 3.53; N, 9.82. These experimental a n a l y t i c a l data suggest that either the hexakis(pyridine) complex, F e ( p y ) 6 ( F S 0 3 ) 2 i s formed; anal, calcd for FeC 3 0H 3oN 6F 2 S 20 6: C, 49.46; H, 4.15; N, 11.53; or Fe(py ) a S O „ i s formed; anal, calcd for F e C 2 o H 2 0N « S O , ,: C, 51.30; H, 4.30; N, 11.96. Infrared data (1185s, 11l9sh, 1111s, I040sh, 1029s cm"1) indicate the complex isolated from method (iv) i s Fe(py ) „ S O i , which results from the decomposition of the fluorosulfonate anion. The complex also showed infrared absorptions which were attributable to coordinated pyridine (1598m, 630m, 625m, 620m, 434m cm" 1); whereas, no absorption was present at 1540 cm"1 indicating the absence of the pyridinium i o n . 7 7 3.2.1.5 Trans-bis(trifluoromethanesulfonato-O)tetrakis-(pyridine)copper(II), Cu(py)„(CF 3S0 3) 2 C u ( C F 3 S 0 3 ) 2 8 7 (0.994 g, 2.75 mmol) was dissolved in hot methanol (11 mL). An excess of pyridine (5 mL, 62 mmol) was added dropwise, whereupon, an intense blue-coloured solution 38 formed. On cooling, a blue, c r y s t a l l i n e s o l i d resulted which was isolated by f i l t r a t i o n . The product was r e c r y s t a l l i s e d from a solution of pyridine in methanol (1:4 v/v) and isolated in 82% y i e l d . Anal, calcd for C u C 2 2 H 2 0 N « F 2 S 2 0 6 : C, 38.97; H, 2.97; N, 8.26; found: C, 38.99; H, 2.97; N, 8.29. 3.2.1.6 Tetrakis(pyridine)copper(lI) methanesulfonate, Cu(py)„(CH 3S0 3) 2 C u ( C H 3 S 0 3 ) 2 8 7 (1.051 g, 4.139 mmol) was dissolved in hot methanol (8 mL) yie l d i n g a pale-blue solution. On addition of an excess of pyridine (5 mL, 62 mmol) the blue colour of the solution i n t e n s i f i e d . Overnight, dark-blue rectangular c r y s t a l s formed; the product was isolated by f i l t r a t i o n in 73% y i e l d . Anal, calcd for CuC 2 2H 2 6N f tS20 6: C, 46.35; H, 4.60; N, 9.83; found: C, 46.60; H, 4.70; N, 9.80. 3.2.2 Tetrakis(pyrazine) and Tetrakis(2-methylpyrazine) Complexes The synthesis of two tetrakis(pyrazine) species and Fe(2-mepyz)«(CH 3S0 3)j are now described. Fe(2-mepyz)«(CH 3S0 3) 2 was prepared and handled in an inert atmosphere dry box, whilst for the synthesis of Fe(pyz)„(AsF 6) 2.2H 20 a l l manipulations were performed under a nitrogen atmosphere by using standard Schlenk techniques. No such precautions were taken for the preparation of Cu(pyz)„(CF 3S0 3)2.H 20. 39 3.2.2.1 Tetrakis(2-methylpyrazine)iron(11) methanesulfonate, Fe(2-mepyz)„(CH 3S0 3) 2 Iron(II) methanesulfonate 2 5 (0.319 g, 1.30 mmol of either the a or /3 form) was dissolved in hot methanol (10 mL) and an excess of 2-methylpyrazine (5 mL, 55 mmol) was added to the pale-green solution. Green, p l a t e - l i k e c r y s t a l s contaminated by brown flecks formed overnight. The s o l i d was isolated by f i l t r a t i o n and washed with a small quantity of methanol (the product appeared highly soluble in thi s solvent). The crystals were then washed with diethyl ether and isolated in 61% y i e l d . Anal. calcd for FeC 2 2H 3 0N 8S 20 6: C, 42.45; H, 4.86; N, 18.00; found: C, 42.09; H, 4.63; N, 18.20. The s l i g h t discoloration of the product and the a n a l y t i c a l data suggested a small amount of impurity, hence the product was r e c r y s t a l l i s e d from 2-methylpyrazine. Anal. found: C, 42.47; H, 4.84; N, 17.77. 3.2.2.2 Tetrakis(pyrazine)iron(II) hexafluoroarsenate dihydrate, Fe(pyz),(AsF 6) 2.2H 20 Potassium hexafluoroarsenate (0.975 g, 4.27 mmol) was dissolved in methanol (10 mL) and added to a methanolic solution (10 mL) of i r o n ( l l ) perchlorate hexahydrate (0.720 g, 1.98 mmol). The potassium perchlorate which formed (Eqn. 3.2) was removed by f i l t r a t i o n . To remove any remaining C10fl", a second addition of KAsF 6 was made (0.500 g, 2.19 mmol; in methanol, 5 mL) and the solution s t i r r e d for 3 h. 40 Fe(C10«) 2.6H 20 + 2KAsF6 > [ F e ( A s F 6 ) 2 3 + 2KC10« ...Eqn. 3.2 KC10« was again removed by f i l t r a t i o n and the f i l t r a t e was added to a solution of pyrazine (2.10 g, 26.3 mmol) in methanol (5 mL). Overnight, a yellow, microcrystalline s o l i d formed; this was isolated by f i l t r a t i o n and washed with a small amount of methanol ( y i e l d 63%). Anal, calcd for FeC, 6H 2o N8As2 F12 O 2 5 C, 24.32; H, 2.55; N, 14.18; found: C, 24.30; H, 2.58; N, 14.24. Attempts were made to prepare the bis(pyrazine) complex by using a r a t i o of Fe(C10„) 2•6H 20 to pyrazine of 1:2; under these conditions, however, no complex was isolated and employing a ratio of 1:4 resulted in the formation of the tetrakis(pyrazine) compound. Several attempts were made to convert the tetrakis(pyrazine) complex to the analogous bis(pyrazine) derivative, F e ( p y z ) 2 ( A s F 6 ) 2 . Fe(pyz),(AsF 6) 2.2H 20 was placed in a desiccator over phosphorus(V) oxide at reduced pressure; however, even after a week the infrared spectrum of the sample remained unchanged. Heating the tetrakis(pyrazine) complex in vacuo at a temperature of 323 K had no e f f e c t ; heating at higher temperatures, approximately 343 K, resulted in a brown s o l i d which exhibited strong infrared absorbtions in the 600 and 450 cm"1 regions. Absorptions in these regions are attributed to Fe-F vibrations, suggesting decomposition of the AsF 6" anion. 41 3.2.2.3 Tetrakis(pyrazine)cbpper(II) trifluoromethanesulfonate monohydrate, Cu(pyz)»(CF 3S0 3) 2.H 20 Copper(II) trifluoromethanesulfonate 8 7 (0.565 g, 1.55 mmol) was dissolved in hot methanol (3 mL). The copper(Il) solution was then added to a hot solution of pyrazine (1.781 g, 22.3 mmol) dissolved in methanol (5 mL). A dark-blue solution resulted, and after a period of 30 min, a blue, c r y s t a l l i n e s o l i d formed; the product was isolated by f i l t r a t i o n in 92% y i e l d . Anal. calcd for CuC, 8 H , 8 N „ F 6 S 2 0 7 : C, 30.88; H, 2.59; N, 16.01; found: C, 30.65; H, 2.57; N, 15.75. 3.2.3 Bis(pyrazine) Complexes Several iron(II) complexes of stoichiometry Fe(pyz) 2X 2 (where X" is CF 3S0 3", CH 3S0 3 _, C l " , Br" I', NCS" or ClO„-), were prepared by the following general route: MX2 + 2pyz > M(pyz) 2X 2 ...Eqn. 3.3 The copper(II) species, Cu(pyz) 2(CH 3S0 3) 2 was also isolated. Fe(pyz)j(NCS) 2 was synthesised in the absence of oxygen by using standard Schlenk techniques; the other iron(II) complexes were prepared in an inert atmosphere dry box. No such precautions were necessary for the preparation of Cu(pyz) 2(CH 3S0 3) 2• 3.2.3.1 Bis(pyrazine)iron(II) trifluoromethanesulfonate methanol solvate, Fe(pyz) 2(CF 3S0 3) 2.CH 3OH A solution of pyrazine (0.55 g, 6.9 mmol) in methanol (5 42 mL) was added to i r o n d l ) trifluoromethanesulfonate 2 5 (0.741 g, 2.09 mmol) dissolved in methanol (5 mL). A yellow solution resulted and after 24 h, p r e c i p i t a t i o n of a yellow s o l i d was f a c i l i t a t e d by the addition of dieth y l ether (30 mL). The product was removed by f i l t r a t i o n and washed with d i e t h y l ether and isolated in 72% y i e l d . Anal, calcd for FeC,,H, 2N„F 6S20 7: C, 24.19; H, 2.21; N, 10.26; found: C, 24.12; H, 2.34; N, 10.27. Attempts were made to remove the solvent of c r y s t a l l i s a t i o n by thermolysis; however, d i f f e r e n t i a l scanning calorimetry results (Section 3.3.6) indicate that the methanol i s strongly held and that one mole of pyrazine, as well as the methanol solvent molecule are removed simultaneously. Attempts to prepare the anhydrous bis(pyrazine) complex in other solvents, for example, acetone, a c e t o n i t r i l e , dichloromethane and ethanol were a l l unsuccessful. The infrared spectrum of each of the products indicates either inclusion of solvent which could not be removed by heating at low temperatures, or, in the case of dichloromethane, i t shows the product as the mono(pyrazine) complex, F e ( p y z ) ( C F 3 S O 3 ) 2 • 3.2.3.2 B i s ( p y r a z i n e ) i r o n d l ) methanesulfonate, F e ( p y z ) 2 ( C H 3 S 0 3 ) 2 Pyrazine (1.28 g, 16.0 mmol) was dissolved in methanol (5 mL) and thi s solution was added to a solution of i r o n d l ) methanesulfonate 2 5 (1.09 g, 4.43 mmol) in methanol (20 mL). A yellow p r e c i p i t a t e formed immediately. The product was isolated in 83% y i e l d after f i l t r a t i o n and washing with methanol and 43 diethyl ether. Anal. calcd for FeC, 0H,«,N„S 20 6: C, 29.56; H, 3.48; N, 13.79; 0, 23.63; found: C, 29.47; H, 3.66; N, 13.50; 0, 23.95. 3.2.3.3 Trans-bis (methanesulf onato-O) bis (ii-pyrazi ne) copper (11) , C u ( p y z ) 2 ( C H 3 S O 3 ) 2 Copper(II) methanesulfonate 8 7 (0.535 g, 2.11 mmol) was dissolved in hot methanol (3mL). This copper(II) solution was added to a hot solution of pyrazine (2.298 g, 28.7 mmol) dissolved in methanol (5 mL). The pale-blue pre c i p i t a t e which formed immediately was removed by f i l t r a t i o n . The f i l t r a t e was l e f t to stand and over a period of several hours a grey-blue c r y s t a l l i n e s o l i d started to form. The small c r y s t a l s which grew overnight were subsequently isolated by f i l t r a t i o n . Both products gave i d e n t i c a l infrared spectra and similar microanalytical data. The t o t a l y i e l d of product was 81%. Anal. calcd for CuC, 0H,,N aS 20 6: C, 29.02; H, 3.41; N, 13.54; found, for the c r y s t a l l i n e material: C, 28.56; H, 3.52; N, 13.04. These poor a n a l y t i c a l data and the infrared spectrum of the product (Section 3.3.2.3) suggest the presence of water, although t h i s was undetected in the X-ray structure determination (Section 3.3.1.3). 3.2.3.4 B i s ( p y r a z i n e ) i r o n d l ) chloride, F e ( p y z ) 2 C l 2 The synthesis of the bis(pyrazine) complex was described previously although few d e t a i l s were given. Beech and Mortimer 6 1 obtained the anhydrous compound by mixing ethanolic 44 or aqueous s o l u t i o n s of hydrated i r o n d l ) c h l o r i d e and p y r a z i n e . F e r r a r o et a l . 6 2 d e s c r i b e d the s y n t h e s i s of a hydrated s p e c i e s , F e ( p y z ) 2 C 1 2 , H 2 0 ; by mixing F e C l 2 and the l i g a n d i n a 1:2 r a t i o , the s o l v e n t being e t h a n o l . In t h i s study a hydrate was i s o l a t e d from ethanol when the r a t i o of F e C l 2 to p y r a z i n e was 1:2. The presence of water was i n d i c a t e d by i n f r a r e d a b s o r p t i o n s i n the 3500 and 1600 cm"1 regions, and by m i c r o a n a l y t i c a l data. When the l i g a n d to i r o n d l ) c h l o r i d e r a t i o was in c r e a s e d to 11:1 the product obtained showed no i n f r a r e d a b s o r p t i o n s i n e i t h e r the 0-H s t r e t c h i n g or bending r e g i o n s i n d i c a t i n g the absence of any OH c o n t a i n i n g s p e c i e s . The s y n t h e t i c procedure i n v o l v e d the a d d i t i o n of an e t h a n o l i c s o l u t i o n (20 mL) of F e C l 2 (0.503 g, 3.97 mmol) to pyrazine (3.54 g, 44.3 mmol) d i s s o l v e d i n eth a n o l (10 mL). The deep-red s o l i d which formed was i s o l a t e d by f i l t r a t i o n and washed w i t h ethanol and d i e t h y l ether ( y i e l d 62%). A n a l . c a l c d f o r F e C 8 H 8 N „ C l 2 : C, 33.49; H, 2.81; N, 19.53; found: C, 33.28; H, 2.89; N, 19.65. 3.2.3.5 B i s ( p y r a z i n e ) i r o n ( 1 1 ) bromide, F e ( p y z ) 2 B r 2 The p r e p a r a t i o n of t h i s complex was b r i e f l y d e s c r i b e d i n an e a r l i e r r e p o r t . 6 2 The f o l l o w i n g method was used i n the present study. Anhyd rous i r o n d l ) bromide (0.490 g, 2.27 mmol) was d i s s o l v e d i n methanol (15 mL). The r e s u l t i n g s o l u t i o n was f i l t e r e d i n t o a s o l u t i o n of p y r a z i n e (0.80 g, 10 mmol) d i s s o l v e d in methanol (5 mL). A red p r e c i p i t a t e s t a r t e d to form a f t e r s e v e r a l minutes; the s o l u t i o n was l e f t to stand f o r three hours 45 and subsequently the product was isolated by f i l t r a t i o n and washed with portions of methanol and diethy l ether ( y i e l d 74%). Anal. calcd for FeC 8H 8N f tBr 2: C, 25.57; H, 2.15; N, 14.91; found: C, 26.06; H, 2.41; N, 14.51. 3.2.3.6 B i s ( p y r a z i n e ) i r o n d l ) iodide, F e ( p y z ) 2 I 2 I r o n d l ) iodide (0.524 g, 1.69 mmol) was dissolved in methanol (10 mL) and f i l t e r e d into a methanolic solution (10 mL) of pyrazine (0.62 g, 7.75 mmol). The solution f i r s t turned yellow, then orange and after five minutes an orange cloudiness formed. Overnight, a lustrous, maroon s o l i d formed; the product was isolated by f i l t r a t i o n , and washed with methanol and diethyl ether ( y i e l d 44%). Anal, calcd for FeC 8H 8N„I 2: C, 20.45; H, 1.72; N, 11.92; found: C, 20.41; H, 1.75; N, 12.09. 3.2.3.7 Bis(pyrazine)iron(II) thiocyanate, Fe(pyz) 2(NCS) 2 The procedure may be represented by the following scheme: FeSO«.7H 20 + 2KCNS s> [Fe(NCS) 2] +K2SOa ...Eqn. 3.4 pyz i > Fe(pyz) 2(NCS) 2 I r o n d l ) sulfate heptahydrate (0.672 g, 4.84 mmol) and potassium thiocyanate (0.470 g, 4.84 mmol) were dissolved in water (10 and 5 mL respectively; immediately prior to use the solvent was 46 degassed by several freeze-pump-thaw c y c l e s ) . The potassium thiocyanate solution was added to the iron(II) solution and the resulting mixture was f i l t e r e d d i r e c t l y into a solution of pyrazine (0.535 g, 6.69 mmol) dissolved in water (10 mL). An orange-brown pre c i p i t a t e resulted; the solution was s t i r r e d for 3/4 h and the product was isolated by f i l t r a t i o n and washed with water and methanol ( y i e l d 67%). Anal, calcd for FeC 1 0H 8N 6S 2: C, 36.18; H, 2.43; N, 25.31; found: C, 35.82; H, 2.30; N, 25.10. 3.2.3.8 Bis(pyrazine) iron (11) perchlorate, Fe (pyz) 2 (C10«) 2 The preparation of the dihydrate, Fe(pyz) 2(C10 4) 2.2H 20, has been reported r e c e n t l y . 6 0 The method involved the addition of a solution of hydrated i r o n ( l l ) perchlorate to a solution of the ligand, both reagents being dissolved in the minimum amount of water. In the previous report, i t was noted that drying the product over s i l i c a gel at reduced pressure f a i l e d to produce the anhydrous species. The same procedure was followed in the present study and the hydrate was isolated; t h i s was subsequently dehydrated by applying more stringent conditions. The dihydrate was heated in an Aberhalden drying p i s t o l at a temperature of approximately 390 K for a period of 46 h at reduced pressure, in the presence of phosphorus(V) oxide. Due to the unpredictably explosive nature of perchlorates, caution should be taken when handling t h i s material. The anhydrous compound was isolated in 72% y i e l d . Anal. calcd for FeC 8H 8N f lCl 20 8 : C, 23.16; H, 1.94; N, 13.50; O, 30.85; found: C, 23.13; H, 1.92; N, 13.46; 0, 31.00. 47 3.2.4 Attempted P r e p a r a t i o n s During the course of the present study attempts were made to prepare the b i s ( p y r a z i n e ) complexes, F e ( p y z ) 2 ( p - C H 3 C 6 H a S 0 3 ) 2 and F e ( p y z ) 2 ( N C O ) 2 . Attempts i n v o l v e d the a d d i t i o n of "FeX 2" (where X" i s p - C H 3 C 6 H „ S 0 3 " or NCO"), to an excess of pyrazine (FeX 2 to p y r a z i n e r a t i o of 1:20); i n both cases, however, only the mono(pyrazine) complex was i s o l a t e d ( S e c t i o n 4.2.2). For the cyanate d e r i v a t i v e t h i s may be r e l a t e d to the extreme i n s o l u b i l i t y of Fe(pyz)(NCO) 2 i n most s o l v e n t s , f o r example, water, methanol, acetone and dichloromethane. In the case of the p - t o s y l a t e , however, the reason f o r the n o n - i s o l a t i o n of a b i s ( p y r a z i n e ) s p e c i e s i s not apparent. 48 3.3 RESULTS AND DISCUSSION 3.3.1 X-ray Structure Determinations Several of the complexes containing an MN„0 2 chromophore were isolated in a form suitable for s i n g l e - c r y s t a l X-ray analysis. The c r y s t a l and molecular structures of Fe(py)»(RS0 3) 2 (R=CF3, CH3 and p-CH 3C 6Hft), Cu(py)„(CF 3S0 3) 2 and Cu(pyz) 2(CH 3S0 3) 2 were determined and the crystallographic data are presented below. 3.3.1.1 X-ray structure determination of Fe(py)„(RS0 3) 2 complexes It was of interest to solve the structures of the tetrakis(pyridine) iron(II) compounds and to obtain the relevant bonding parameters for two reasons: (i) Previous research in th i s laboratory resulted in spectroscopic evidence indicating unidentate anion coordination in M(py)„(FS0 3) 2 complexes. 7 6 In the present study, s i n g l e - c r y s t a l X-ray structure analysis has provided d e f i n i t i v e evidence on the nature of the anion-cation interaction, and provided a q u a l i t a t i v e basis for assessing the r e l a t i v e b a s i c i t i e s of the di f f e r e n t sulfonate anions. ( i i ) Sulfonate anions, in pa r t i c u l a r the t r i f l a t e anion, have been used extensively in both organic and inorganic chemistry as counter ions, as they are weakly coordinating and act as good leaving 49 groups. 8 8" 9' This has resulted in a large number of X-ray structure reports on compounds containing ionic sulfonate groups (see for example, references 92-95), but r e l a t i v e l y l i t t l e s tructural data where the anion is coordinated in a u n i - , 9 6 " 1 0 0 b i - , 1 0 1 " 1 0 " or tridentate mode 1 6- 1 0 5' 1 0 6 or chelating f a s h i o n . 1 0 7 Views of the molecular structures of the Fe(py)«(RS0 3) 2 complexes and the atom numbering schemes are shown in Figs. 3.1-3.3. Selected intramolecular bond distances and angles are given in Table 3.1 and a complete compilation of structural parameters i s given in Appendix I. These structural analyses show a l l three complexes as having an octahedral geometry with trans-coordinated monodentate sulfonate groups. With the possible exception of weak hydrogen bonds, each of the three structures consists of discrete molecules separated by normal van der Waals distances. Two d i s t i n c t molecular units are observed in the R=CH3 compound, the difference between them involves s l i g h t l y d i f f e r e n t orientations of the CH 3S0 3" groups with respect to the O-Fe-0 vector. The two independent R=CH3 molecules and the ' R=CF3 molecule have approximate C 2 symmetry and for R=p-CH 3C 6H„ the molecule possesses exact C 2 symmetry. In each case the two-fold axis l i e s in the FeN, plane and bisects c i s N-Fe-N angles. 50 Table 3.1 Selected Mean Bond Distances (A) and Angles (°) for some Fe(py) a(RS0 3) 2 Complexes R GROUP CF 3 CH3 p-CHaCeH,, Bond Distances Fe-0 2.11 2.06 2.08 Fe-N 2.21 2.23 2.24 S-0 (linking) 1 .47 1 .48 1 .49 S-0 (terminal) 1 .44 1 .45 1 .44 s-c 1 .82 1 .78 1 .78 Bond Angles O-Fe-0 175 1 73 175 N-Fe-N 179 1 79 173 o-s-o 1 15 1 1 2 1 1 3 o-s-c 104 1 06 106 51 F i g . 3.1 ORTEP Plot of the Structure of Fe(py)«(CF 3S0 3) 2 52 F i g . 3.2 ORTEP Plots of the Structure of Fe(py)„(CH 3S0 3) 2 0(9) C(43) 53 F i g . 3.3 ORTEP Plot of the Structure of Fe(py)«(p-CH 3C 6H f lS0 3) 2 54 The FeN„ groups are non-planar in a l l three compounds. For the R=CH3 and CF 3 compounds, the maximum deviation from the mean plane is 0.284(4) A. In the R=CF3 compound, the four pyridine nitrogen atoms are coplanar, the Fe atom being displaced 0.015(1) A from the N« plane. The pyridine rings are generally planar to within experimental error; while the pyridine rings containing N(1), N(4) and N(6) in the R=CH3 compound and N(2) in the R=p-CH3C6H, structure are non-planar, no atom deviates by more than 0.0154(4) A from the mean plane. The bond distances and angles around the pyridine rings are si m i l a r to those found for pyridine by electron d i f f r a c t i o n s t u d i e s 1 0 8 and microwave spectroscopy. 1 0 9 An interesting structural feature present in a l l three compounds is the arrangement of the pyridine ligands in a propeller configuration; the trans-pyridine rings are nearly orthogonal to one another. This configuration appears to minimise interactions between adjacent pyridine rings as well as interactions between pyridine rings and sulfonate anions. This p r o p e l l e r - l i k e arrangement has been previously observed in Fe(py),C1 2 6 8 and Fe(py)„(NCS) 2. 6 9 In a l l three t e t r a k i s ( p y r i d i n e ) i r o n d l ) sulfonate complexes, the O-Fe-0 angles deviate from l i n e a r i t y by no more than 7°. In the t r i f l a t e and methanesulfonate derivatives, the trans-pyridine N-Fe-N bond angles are very close to 180°; whereas, in the p-tosylate derivative, t h i s angle i s 173° (Table 3.1). In a l l three examples, the overall d i s t o r t i o n of the FeN 40 2 chromophore is not great and the environment around the iron atom may be 55 approximated as D 4 n . The mean Fe-N d i s t a n c e s f o r the CF 3, CH 3 and p - C H 3 C 6 H « d e r i v a t i v e s are 2.21, 2.23 and 2.24 A r e s p e c t i v e l y . These values are comparable to the mean Fe-N d i s t a n c e of 2.23 A r e p o r t e d f o r F e ( p y ) , C 1 2 , 6 8 2.26 A f o r F e ( p y ) 0 ( N C S ) 2 6 9 and 2.26 A f o r [ F e ( p y ) 6 ] [ F e „ ( C O ) 1 3 ] . 1 1 0 The mean Fe-0 d i s t a n c e s range from 2.11 A i n the t r i f l u o r o m e t h a n e s u l f o n a t e complex, to 2.06 A i n the methanesulfonate analogue. Of the three complexes s t u d i e d , F e ( p y ) f t ( C F 3 S 0 3 ) 2 has the longest Fe-0 bonds and the s h o r t e s t Fe-N bonds. T h i s may be a consequence of the r e l a t i v e l y weaker c o o r d i n a t i n g s t r e n g t h of the t r i f l a t e anion compared to the other s u l f o n a t e anions i n these complexes. Assuming that the Fe-0 bond d i s t a n c e i n s u l f o n a t e complexes p r o v i d e s a good measure of the s t r e n g t h of the metal-anion i n t e r a c t i o n , then i t i s i n t e r e s t i n g t o note that i n [ TJ 5-C 5 (CH 3) 5 ] (CO) 2FeOS0 2CF 3 the Fe-0 d i s t a n c e i s o n l y 2.007(3) A . 1 0 0 The presence of the strong 7 r - a c i d l i g a n d s i n t h i s complex makes the i r o n c e n t r e s t r o n g l y e l e c t r o p h i l i c and a "strong e l e c t r o s t a t i c i r o n - t r i f l a t e i n t e r a c t i o n " ensues which r e s u l t s i n a s h o r t e r Fe-0 bond than observed i n the t r i f l a t e d e r i v a t i v e s t u d i e d here. The i n t e r n a l bonding parameters f o r the t r i f l a t e anion i n F e ( p y ) « ( C F 3 S 0 3 ) 2 show that the bond d i s t a n c e s and angles observed f o r the C F 3 S 0 3 " part of the molecule appear comparable to those of other unidentate t r i f l a t e g r o u p s . 9 7 " 1 0 0 The anion assumes a staggered-ethane c o n f i g u r a t i o n about the S-C bond and w h i l s t the mean C-F bond length i s g r e a t e r than u s u a l f o r i o n i c C F 3 S 0 3 " c o n t a i n i n g compounds 9 2" 9 5 i t i s t y p i c a l f o r a unidentate 56 t r i f l a t e a n i o n . 9 7 " 1 0 0 Repulsions between oxygen atoms are greater than those between oxygen atoms and the trifluoromethyl group; as a re s u l t , the O-S-0 angles are consistently greater than the C-S-0 angles. The effect of unidentate anion coordination i s most evident in range of S-0 bond distances. The S-0 bond involving the oxygen coordinated to iron is the longest such distance in the compound and the mean bond length for the terminal S-0 bonds (1.44 A) is close to the value found in ionic t r i f l a t e complexes. The methanesulfonate anion in Fe(py)„(CH 3S0 3) 2 exhibits similar structural features to those found for the anion in Fe(py) f l(CF 3S0 3) 2• For example, the methanesulfonate anion has a staggered-ethane configuration and the O-S-0 angles are greater than, whilst the C-S-0 angles are smaller than, the tetrahedral angle. The mean S-C bond distance (1.78 A) i s intermediate between those observed in Fe(py)„(CF 3S0 3) 2 and in C a ( C H 3 S 0 3 ) 2 1 6 (where the S-C bond lengths are 1.82 and 1.75 A respectively). In Fe(py),(CH 3S0 3)2r where the anions act as unidentate ligands, the range of S-0 bond lengths (1.439-1.490 A) i s , as expected, somewhat greater than where the sulfonate anion acts as a tridentate bridging ligand with each oxygen atom involved in equivalent coordination to a metal centre. For example, C a ( C H 3 S 0 3 ) 2 1 6 and Cu(CO)(C 2H 5S0 3) 1 0 5 contain tridentate anions and the S-0 bond lengths range from 1.429-1.456 A and 1.444-1.462 A respectively. Two other methanesulfonate complexes with known structures are relevant to the present study, C u ( H 2 0 ) „ ( C H 3 S 0 3 ) 2 9 6 and 57 C d ( H 2 0 ) 2 ( C H 3 S O 3 ) 2 • 1 0 2 In the copper complex, the water molecules form the equatorial plane of a tetragonally elongated octahedron with the unidentate CH 3S0 3" anions occupying the two a x i a l positions. Somewhat sur p r i s i n g l y , and in contrast to what i s found for the pyridine complexes studied here, the S-0 bonds involving the terminal oxygen atoms in Cu(H 20) f t(CH 3S0 3) 2, are longer than those involving the oxygen atoms coordinated to the metal. This has been attributed to intermolecular hydrogen bonding interactions between terminal oxygen atoms and hydrogen atoms from water molecules on adjacent Cu(H 20)«(CH 3S0 3) 2 molecules. Cd(H 20) 2(CH 3S0 3) 2 consists of cadmium atoms bridged by bidentate methanesulfonate groups to form an i n f i n i t e chain s t r u c t u r e . 1 0 2 In this case, the mean terminal S-0 bond (1.44 A) i s s l i g h t l y shorter than these bonds in Fe(py)«(CH 3S0 3) 2 (1.45 A). This result is expected, since, in the cadmium complex, the sulfur to oxygen 71—bonding primarily involves only one terminal S-0 bond; whereas, in Fe(py)„(CH 3S0 3) 2, the two terminally bonded oxygen atoms are involved in n—bonding to s u l f u r . For the p-tosylate anion in Fe(py) ft (p-CH3C6Hj,S03 ) 2, the geometry around the sulfur i s approximately tetrahedral and the benzene ring is planar within experimental error; the bond lengths and angles around t h i s ring show no unusual f e a t u r e s . 1 1 1 The effect of unidentate anion coordination i s readily seen in the S-0 bond distances; for example, the S-0 distances for the bonds involving terminal oxygen atoms are shorter (1.44 A) than the distances involving the coordinated oxygen atoms (1.49 A). In organic p - t o l u e n e s u l f o n a t e s , 1 1 2 " 1 1 * the S-0 distances of the 58 S-0-R group are even longer, being approximately 1.5-1.6 A. This c l e a r l y i l l u s t r a t e s the difference in the mode of bonding between p-tosylate and a metal ion on the one hand, and carbon on the other; the former i s a more ionic interaction which does not perturb the anion as s i g n i f i c a n t l y as does the formation of a covalent bond to carbon. In fact, the S-0 bond distances in the pyridine complex more closely resemble those found in H 30 + ( p - C H 3 C 6 H „ S 0 3 " ) . 1 1 5 This compound exists as an oxonium sa l t with a l l the S-0 bonds approximately equivalent, with a mean S-0 bond distance of 1.45 A. 3.3.1.2 X-ray structure determination of Cu(py)«(CF 3S0 3) 2 The structure of Cu(py),(CF 3S0 3) 2 shows many s i m i l a r i t e s with the structure of the analogous iron complex discussed above; however, some s i g n i f i c a n t differences are also noted. A view of the molecular structure of Cu(py)„(CF 3S0 3) 2 i s shown in Fi g . 3.4 and selected intramolecular bond distances and angles are given in Table 3.2. A complete compilation of X-ray s t r u c t u r a l data i s given in Appendix I. 59 Table 3.2 Selected Bond Distances (A) and Angles (°) for Cu(py),(CF 3S0 3) 2 1 Bond Distances Cu-0(1) 2.425(4) Cu-N(1) 2.045(6) Cu-N(2) 2.053(6) Cu-N(3) 2.020(5) S-0(1) l i n k i n g 1.439(5) S-0(2) terminal 1 .422(4) Bond Angles 0(1)-Cu-0(1) 179.8(2) N( 1 )-Cu-N(2) 180.0 O-S-0 1 1 5 o-s-c 103 1). Estimated standard deviations in parenthesis 60 F i g . 3.4 ORTEP Plot of the Structure of Cu(py)«(CF 3S0 3) 2 61 As found for the analogous iron derivative, the coordination sphere around copper consists of a square-planar array of nitrogen atoms from four pyridine moieties and a x i a l coordination s i t e s occupied by oxygen atoms from trans-coordinated unidentate t r i f l a t e anions. Unlike the coordination sphere about the metal in the analogous iron derivative, the coordination sphere in the copper complex i s strongly distorted from regular octahedral geometry. The difference between the Cu-0 (2.425(4)A) and Cu-N (2.05 A) bond distances r e f l e c t s the large tetragonal d i s t o r t i o n of the coordination sphere. This situation is often found in six-coordinate copper(II) compounds and is attributed to the Jahn-Teller e f f e c t . 1 1 6 C u ( p y ) a ( C F 3 S O 3 ) 2 possesses a two-fold axis of symmetry, but unlike the analogous iron(II) derivative in which the two-fold axis bisects the c i s N-Fe-N angle, the two-fold axis in Cu(py)„ ( C F 3 S O 3) 2 l i e s along the Cu-N(3) vector. The four nitrogen atoms and the copper atom l i e in one plane and the pyridine rings are planar within experimental error. The pyridine rings are canted out of the CuN, plane (56.7-64.7°) in a p r o p e l l e r - l i k e arrangement as found for the analogous iron(II) derivative. In C u ( p y ) o ( C F 3 S O 3 ) 2 , the mean Cu-N distance (2.04 A) is t y p i c a l for a Cu-N bond in which the nitrogen-containing ligand is bound in the equatorial plane. For example the Cu-N bond distances in Cu(pyz) 2(CIO,,) 2* 3 and Cu(NH 3)„SO„.H 20 1 1 7 are 2.06 and 2.05 A respectively. The Cu-0 bond distance in 62 C u ( p y ) « ( C F 3 S 0 3 ) 2 (2.425(4) A) and i n two r e l a t e d s t r u c t u r e s p r o v i d e f o r an i n t e r e s t i n g comparison. The inner c o o r d i n a t i o n sphere i n C u ( p y z ) 2 ( C 1 0 „ ) 2 * 3 and C u ( H 2 0 ) « ( C H 3 S 0 3 ) 2 9 6 are both d i s t o r t e d by a t e t r a g o n a l e l o n g a t i o n and anions are weakly bonded i n the a x i a l p o s i t i o n s ; the Cu-0 bond lengths are 2.373(12) and 2.381(8) A f o r the p e r c h l o r a t e and methanesulfonate complexes r e s p e c t i v e l y . The longer Cu-0 bond length in the t r i f l a t e compound s t u d i e d here, s i g n i f i e s a weaker c a t i o n - a n i o n i n t e r a c t i o n i n t h i s complex which may r e f l e c t the more weakly basic nature of the t r i f l a t e anion i n comparison to p e r c h l o r a t e and methanesulfonate a n i o n s . The bonding parameters f o r the t r i f l a t e anion are s i m i l a r to those found f o r the analogous i r o n d l ) d e r i v a t i v e ( S e c t i o n 3.3.1.1). For example, the t r i f l a t e anion adopts a staggered-ethane c o n f i g u r a t i o n about the S-C bond and the O-S-0 angles are greater than the C-S-0 a n g l e s . The S-0 bond l e n g t h s are s i m i l a r to those found i n F e ( p y ) „ ( C F 3 S 0 3 ) 2 , the S-0(1) bond i n v o l v i n g the oxygen bound to copper being longer than S-0(2), i n v o l v i n g the t e r m i n a l l y bound oxygen atom. 3.3.1.3 X-ray s t r u c t u r e d e t e r m i n a t i o n of C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 The X-ray s t r u c t u r e d e t e r m i n a t i o n of C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 was re l e v a n t to the present study f o r s e v e r a l reasons. I t e s t a b l i s h e d the mode of c o o r d i n a t i o n of p y r a z i n e and the o r i e n t a t i o n of the p y r a z i n e 7 r-system with r e s p e c t t o the d - o r b i t a l s of the copper i o n . T h i s p a r t i c u l a r d 7 r - p 7 r i n t e r a c t i o n has been proposed as p l a y i n g an important r o l e i n determining 63 the nature of the magnetic exchange interaction in copper(II)-pyrazine complexes. 5" The present study also established the mode of coordination of the methanesulfonate anion and permitted the bonding parameters for this part of the molecule to be compared to those in other CH 3S0 3~ containing spec ies. Complete str u c t u r a l parameters for Cu(pyz) 2(CH 3S0 3) 2 are given in Appendix I. The X-ray structure analysis revealed the complex to be made up of p a r a l l e l sheets each consisting of an i n f i n i t e square array of copper(II) ions bridged by bidentate pyrazine ligands; one such sheet i s i l l u s t r a t e d in F i g . 3.5. The inner coordination sphere around each copper ion i s made up of two nitrogen atoms (Cu-N(1) distance of 2.058(2) A), and two oxygen atoms (Cu-0(1) distance of 1.9559(13) A); the ax i a l coordination s i t e s are occupied by pyrazine groups with s i g n f i c a n t l y longer Cu-N bond lengths (Cu-N(2) bond distances of 2.692(2) A). This i s i l l u s t r a t e d in F i g . 3.6 together with the atom numbering scheme and selected bond distances and angles are presented in Table 3.3. In spite of being coordinated to copper at d i f f e r e n t distances, the pyrazine rings in Cu(pyz) 2(CH 3S0 3) 2 have similar internal bonding parameters. Both types of pyrazine ring are planar within experimental error and the bond lengths and angles within the pyrazine rings are similar to those found in free p y r a z i n e . 1 1 8 The dimensions of the pyrazine rings compare well with those reported for other metal complexes containing bidentate bridging pyrazine ligands. For example, in the 64 Table 3.3 Selected Bond Distances (A) and Angles (°) for Cu(pyz) 2(CH 3S0 3) 2 1 Bond Distances Cu-0(1) 1 .9559(13) Cu-N(1) 2 .058(2) Cu-N(2) 2 .692(2) S-0(1) (linking) 1 .4832(13) S-0(2) (terminal) 1 .4423(13) S-C(1) 1 .765(2) Bond Angles 0(1)-S-0(1) 180 N(1)-Cu-N(1) 180 N(2)-Cu-N(2) 180 o-s-o 1 12 o-s-c 106 1). Estimated standard deviations in parenthesis 65 F i g . 3.5 View of a Single Layer in Cu(pyz) 2(CH 3S0 3) 2 a > C 66 67 Creutz-Taube complex the mean C-N bond l e n g t h i s 1.348(9) A and the C-C d i s t a n c e i s 1.382(10) A ; 4 6 i n C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 these d i s t a n c e s are 1.341 and 1.390 A r e s p e c t i v e l y . The p y r a z i n e r i n g s i n v o l v e d i n the s t r o n g e r bonding to copper ( h e r e a f t e r c a l l e d the e q u a t o r i a l l y bound p y r a z i n e l i g a n d s ) are canted at an angle of 28.50(8)° to the CuN 20 2 (xy) plane; whereas, the p y r a z i n e r i n g s bonded weakly to copper ( h e r e a f t e r c a l l e d the a x i a l l y bound p y r a z i n e l i g a n d s ) l i e i n the CuN 20 2 (xz) plane. The methanesulfonate anion i n C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 adopts a staggered-ethane c o n f i g u r a t i o n as found f o r F e ( p y ) n ( C H 3 S 0 3 ) 2 ( S e c t i o n 3.3.1.1). The S-0(1) bond le n g t h (1.4832(13) A) i s s i g n i f i c a n t l y longer than the d i s t a n c e of 1.4423(13) A found f o r the t e r m i n a l l y bound S-0(2) bond as a r e s u l t of c o o r d i n a t i o n of oxygen atom 0(1) to copper. The remaining bonding parameters f o r the anion, f o r example, the S-C bond l e n g t h and the O-S-0 and O-S-C bond angles, are of a comparable magnitude to those found i n F e ( p y ) , ( C H 3 S 0 3 ) 2 ( S e c t i o n 3.3.1.1). The Cu-0 bond d i s t a n c e i n C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 (1.9959(13) A) i s t y p i c a l f o r an oxygen atom bound to copper i n the e q u a t o r i a l p lane; f o r example in C u ( p y z ) ( N 0 3 ) 2 the e q u a t o r i a l Cu-0 bond d i s t a n c e i s 2.010(4) A. 4 2 The Cu-N(D d i s t a n c e (2.062(3) A) i s almost i d e n t i c a l to the value of 2.058(2) A found i n C u ( p y z ) 2 ( C 1 0 f t ) 2 ; 4 3 whereas, the Cu-N(2) d i s t a n c e (2.692(2) A) i n C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 i s much longe r . T h i s a x i a l p y r a z i n e group i s f u r t h e r removed from the copper atom than the a x i a l p y r azine groups i n C u ( p y z ) ( h f a c ) 2 5 3 (Cu-N of 2.529(9) A) and 68 Cu 2(OAc) f t(pyz) 5 5 (Cu-N of 2.171(6) A), indicating a much weaker copper axial-pyrazine interaction in the methanesulfonate complex. There are several hydrogen-bonding interactions which may play a role in determining the overall structure of C u ( p y z ) 2 ( C H 3 S O 3 ) 2 (Figs. 3.7-3.8). Intralayer hydrogen-bonding interactions between the sulfonate oxygen atom 0(1) and the hydrogen atoms attached to the pyrazine rings appear to influence the canting of the pyrazine rings. The hydrogen-bond distances, H(4)-0(1) and H(2)-0(1) are 2.50 and 2.46 A respectively. The f i r s t of these interactions holds the a x i a l pyrazine group in the CuN 20 2 plane; whereas, the second interaction may p a r t i a l l y result in the observation that the eguatorially bound pyrazine ligand i s canted at an angle of 28° to the CuN 20 2 plane. In C u ( p y z ) 2 ( C H 3 S O 3 ) 2 , the layers are separated by a distance of 6.565 A. In comparison, the interlayer separation in C u ( p y z ) 2 ( C 1 0 u ) 2 " 3 i s 7.012 A. The proximity of adjacent layers in the methanesulfonate complex may result from intralayer hydrogen-bonding interactions. There are two such interactions, H(1b)-0(2) (2.38 A) and H(2)-0(2) (2.50 A), which may be s i g n i f i c a n t . Both involve the terminally bound sulfonate oxygen atom, 0(2), which interacts with a hydrogen atom of a methanesulfonate anion on an adjacent layer, and a hydrogen atom on the equatorially bound pyrazine ligand. 69 3.7 Two A d j a c e n t L a y e r s i n C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 Viewed A l o n g the c - A x i s Hydrogen bonding i n t e r a c t i o n s shown by broken l i n e s 70 3.8 Two Adjacent Layers in Cu(pyz) 2(CH 3S0 3) 2 Viewed Along the b-Axis Hydrogen bonding interactions shown by broken lines 71 It is informative to compare the s i m i l a r i t i e s and differences between the structures of Cu(pyz) 2(CH 3S0 3) 2 and Cu(pyz ) 2 (C10„) 2 • * 3 Both complexes contain bidentate bridging pyrazine groups resulting in a two-dimensional l a t t i c e . For Cu(pyz) 2(ClOu)2 i the copper ions are surrounded by a square-planar array of nitrogen atoms. In contrast, the square plane in Cu(pyz) 2(CH 3S0 3) 2 consists of two trans-pyrazine groups and two trans-oxygen donor atoms from unidentate methanesulfonate anions. For Cu(pyz) 2(C10„) 2, i t is the perchlorate anions which are weakly coordinated in a x i a l s i t e s ; whereas, in the methanesulfonate derivative two pyrazine groups weakly interact with the copper centre and are coordinated along the z-axis; the methanesulfonate anions being coordinated strongly in the equatorial plane. In Cu(pyz) 2(CH 3S0 3) 2, this type of anion coordination does not appear to be related to the weakly basic nature of the anion. From a consideration of anion b a s i c i t y , i t might be expected that the anion would coordinate weakly in the a x i a l s i t e s , as i s the case in Cu(H 20)u(CH 3S0 3)2• 9 6 One possible explanation for strong methanesulfonate anion coordination in t h i s case, may be that in th i s coordination mode a s i g n i f i c a n t hydrogen-bonding interaction takes place between the coordinated sulfonate oxygen atom, 0(1) and the hydrogen atom, H(4) on the a x i a l l y bound pyrazine ring, 0(1)-H(4) distance i s 2.50 A. In Cu(H 20) « (CH 3S0 3 ) 2 , 9 6 t h i s type of hydrogen-bonding interaction cannot take place. In Cu(pyz) 2(C10 f t) 2* 3 the canting of the pyrazine rings e f f e c t i v e l y eliminates t h i s interaction. 72 In summary, the X-ray d i f f r a c t i o n studies described in Sections 3.3.1.1-3.3.1.3 permitted the determination of the structure of some iron and copper complexes containing pyridine, pyrazine and sulfonate anions as ligands. The tetrakis(pyridine) i r o n d l ) and copper(II) sulfonate complexes exist as isolated molecular units, containing square-planar arrangements of pyridine ligands and a x i a l l y coordinated unidentate sulfonate anions. Cu(pyz) 2(CH 3S0 3) 2 i s a two-dimensional sheet-like polymer containing two d i s t i n c t types of bridging pyrazine moieties and unidentate methanesulfonate anions. In the t e t r a k i s ( p y r i d i n e ) i r o n d l ) complexes, the coordination sphere about the metal shows a small tetragonal compression; whereas, in both copper complexes studied, the coordination sphere i s distorted by a s i g n i f i c a n t tetragonal elongation, as a result of the Jahn-Teller e f f e c t . The following sections of th i s chapter discuss the spectroscopic and magnetic properties of these compounds in view of their known structures. These spectrocopic and magnetic properties are also compared with those of other complexes for which detailed structural analyses have not yet been possible. 73 3.3.2 I n f r a r e d Spectroscopy I n f r a r e d s p e c t r a l r e s u l t s f o r complexes with an M N AX 2 chromophore are presented i n t h i s s e c t i o n . The s p e c t r a have been a s s i g n e d i n terms of v i b r a t i o n s which a r i s e s e p a r a t e l y from the n e u t r a l l i g a n d and the a n i o n . In the l i g h t of t h e i r known s t r u c t u r e s , the t e t r a k i s ( p y r i d i n e ) i r o n d l ) complexes and C u ( p y ) f l ( C F 3 S O 3 ) 2 are d i s c u s s e d f i r s t ; the i n f r a r e d spectrum of C u ( p y ) « ( C H 3 S O 3 ) 2 i s a l s o c o n s i d e r e d i n S e c t i o n 3.3.2.1. Fol l o w i n g t h i s , the i n f r a r e d data f o r the F e ( p y z ) 2 X 2 compounds (where X " i s C l " , Br", I" or NCS") are c o n s i d e r e d (Section 3.3.2.2), and because of the s i m p l i c i t y of the anion spectra-, these examples are presented p r i o r to d i s c u s s i o n of the i n f r a r e d data f o r the b i s ( p y r a z i n e ) complexes c o n t a i n i n g s u l f o n a t e or p e r c h l o r a t e anions ( S e c t i o n 3.3.2.3). F i n a l l y , the i n f r a r e d s p e c t r a l data f o r F e ( 2 - m e p y z ) „ ( C H 3 S 0 3 ) 2 , C u ( p y z ) , ( C F 3 S 0 3 ) 2 . H 2 0 and F e ( p y z ) A ( A s F 6 ) 2 , 2 H 2 0 are a n a l y s e d (Section 3.3.2.4). The s p e c t r a l bands a s s i g n e d t o p y r i d i n e v i b r a t i o n s i n the t e t r a k i s ( p y r i d i n e ) compounds are compiled i n Appendix II and s u l f o n a t e anion v i b r a t i o n s and unassigned bands are l i s t e d i n Appendix I I I . To f a c i l i t a t e comparisons between complexes c o n t a i n i n g the same s u l f o n a t e anion, Appendix I I I i s d i v i d e d i n t o P a r t s A, B and C. Each p a r t t a b u l a t e s the i n f r a r e d assignments of the anions f o r the compounds c o n t a i n i n g t r i f l a t e , methanesulfonate and p - t o s y l a t e anions r e s p e c t i v e l y . V i b r a t i o n a l assignments f o r p y r a z i n e i n the b i s ( p y r a z i n e ) complexes are given i n Appendix IV. 74 3.3.2.1 Infrared spectral results for tetrakis(pyridine) complexes The M(py)«(RS0 3) 2 complexes have v i b r a t i o n a l bands in the infrared region which are assigned separately to the pyridine ligand and the sulfonate anion (Appendices II and III respectively). A representative spectrum of this class of compound, that of Fe(py)„(CH 3S0 3) 2, i s shown in F i g . 3.9a. Previous r e s e a r c h 7 7 has suggested that each band in the infrared spectrum of pyridine i s reproduced in pyridine complexes with only minor s h i f t s or s p l i t t i n g s . Such a 1:1 correspondence i s also observed in t h i s study and allowed the coordinated pyridine vibrations to be ascertained by a direct comparison with the spectrum of the uncomplexed base. The assignments of the normal v i b r a t i o n a l modes of l i q u i d pyridine, made by Kline and T u r k e v i c h 1 1 9 and the more recent assignment of o v e r t o n e s 1 2 0 are given in Appendix I I . Upon coordination of pyridine, most bands s h i f t in frequency by up to 10 cm"1. As observed p r e v i o u s l y , 7 7 the 8a, 6a and 16b vibrations show a more pronounced coordination dependence and s h i f t by 20-30 cm"1 to higher frequency upon coordination. Some of the pyridine bands exhibit small s p l i t t i n g s which, in t h i s and e a r l i e r studies, are attributed to interactions between adjacent pyridine r i n g s . 1 2 1 In the free sulfonate anion, RS03", the symmetry i s Cg v and six infrared-active bands (3E and 3A,) are expected to a r i s e from the CS0 3" fragment of the anion; these fundamental vibrations have been designated c, to v6. 75 F i g . 3.9 Infrared Spectra of Fe(py)„(CH 3S0 3) 2, Fe(pyz) 2(CH 3S0 3) 2 and Fe(2-mepyz)„(CH 3S0 3) 2 T • 1 • i • 1 • 1 1 i • r WAVENUMBER / c m ' 1 76 These bands have been assi g n e d i n a number of anhydrous metal s u l f o n a t e complexes, M(RS0 3 ) 2 , 2 3' 2 5- 8 7 where the anion r e t a i n s ^3v symmetry by adopting a t r i d e n t a t e mode of c o o r d i n a t i o n . If the anion c o o r d i n a t e s i n any other way than by using three oxygen atoms i n an e q u i v a l e n t f a s h i o n , then the anion symmetry i s reduced to e i t h e r C or C-; the degenerate E modes (P«, vs and p 6 ) are expected to s p l i t and a t o t a l of nine i n f r a r e d - a c t i v e v i b r a t i o n s should be observed. For the F e ( p y ) „ ( R S 0 3 ) 2 complexes, a s p l i t t i n g of some of the doubly degenerate anion bands i s e v i d e n t . In p a r t i c u l a r , the s p l i t t i n g of vn, the asymmetric S0 3 s t r e t c h i n g v i b r a t i o n , i s the l a r g e s t (approximately 80 cm" 1) and most c l e a r l y observed i n a l l cases; whereas, s p l i t t i n g of vs, the asymmetric S0 3 deformation, when observed, i s much smaller (approximately 10 cm" 1). In the present study, *»6, the S-C deformation mode, i s d i f f i c u l t to a s s i g n due to i t s weak nature and the p o s s i b i l i t y that i t i s obscured by the 16b v i b r a t i o n of p y r i d i n e . The s p l i t t i n g s of the doubly degenerate modes, i n p a r t i c u l a r the s p l i t t i n g of vk, i n d i c a t e that the anion symmetry i s reduced below C^ v which i s c o n s i s t e n t w i t h unidentate anion c o o r d i n a t i o n as r e v e a l e d by X-ray c r y s t a l l o g r a p h y ( S e c t i o n 3.3.1.1). The i n f r a r e d s p e c t r a of C u ( p y ) „ ( C F 3 S 0 3 ) 2 and C u ( p y ) „ ( C H 3 S 0 3 ) 2 (Appendices II and , I I I ) e x h i b i t both s i m i l a r i t i e s and d i f f e r e n c e s with those of the analogous i r o n d l ) d e r i v a t i v e s . The i n f r a r e d spectrum of C u ( p y ) a ( C H 3 S 0 3 ) 2 i s shown in F i g . 3.10a and may be compared with that of F e ( p y ) „ ( C H 3 S 0 3 ) 2 ( F i g . 3.9a). 77 F i g . 3.10 Infrared Spectra of Cu(py),(CH 3S0 3) 2 C u ( p y 2 ) 2 ( C H 3 S 0 3 ) 2 - l • 1 . 1 i • i • i . i 1&00 H 0 0 1200 1000 800 600 400 WAVENUMBER / c m " 1 78 The s i m i l a r i t i e s between the infrared spectra of the copper and iron derivatives are c l e a r l y seen . In the copper complexes, three absorptions are observed in the S0 3 stretching region (1000-1280 cm"1) as expected upon reduction of anion symmetry below The other anion bands occur at frequencies similar to those observed for the iron analogues. V i b r a t i o n a l assignments for the neutral ligand also show s i m i l a r i t i e s in the two groups of compounds. Pyridine ligand absorptions are reproduced in the copper complexes with some s h i f t s and s p l i t t i n g s when compared to the spectrum of pyridine. These infrared spectral data indicate that the basic structure of the copper and iron derivatives i s similar and t h i s has been confirmed by X-ray crystallography (Sections 3.3.1.1 and 3.3.1.2). Several important differences are noted, however, between the infrared spectra of the copper and iron derivatives. F i r s t l y , for the copper(II) derivatives the magnitude of the s p l i t t i n g of the S0 3 asymmetric stretching mode, v^, i s approximately half the value found for the iron(II) compounds, i.e . , approximately 90 and 50 cm"1 for the iron and copper complexes respectively. Secondly, the infrared spectra of both tetrakis(pyridine)copper(II) derivatives have the asymmetric S0 3 deformation mode, pSl remaining as one single unsplit band; whereas, in the analogous i r o n d l ) complexes th i s band i s s p l i t by approximately 10 cm"1. F i n a l l y , an additional difference between the copper and iron complexes, i s the extent to which the 8a, 6a and 16b vibrations of pyridine are shifted from those 79 observed i n the spectrum of f r e e p y r i d i n e . For example, f o r the M ( p y ) „ ( C F 3 S 0 3 ) 2 complexes, the 16b v i b r a t i o n occurs at 428 and 443 cm" 1, where M i s Fe and Cu r e s p e c t i v e l y . These s p e c t r a l d i f f e r e n c e s i n d i c a t e s t r u c t u r a l d i f f e r e n c e s between the two groups of compounds. For the copper complexes, the smaller degree of s p l i t t i n g of when compared to the i r o n compounds, and the l a c k of s p l i t t i n g of vs, i n d i c a t e t h a t there i s a weaker c a t i o n - a n i o n i n t e r a c t i o n i n the copper complexes. T h i s decrease i n s t r e n g t h of the c a t i o n - a n i o n i n t e r a c t i o n appears to c o r r e l a t e with an i n c r e a s e of the c o p p e r - p y r i d i n e i n t e r a c t i o n , as measured by the g r e a t e r frequency i n c r e a s e of the 16b band i n the co p p e r ( I I ) d e r i v a t i v e s . These i n f r a r e d r e s u l t s are c o n s i s t e n t with the f i n d i n g s of the X-ray s t r u c t u r e d e t e r m i n a t i o n s f o r the M ( p y ) , ( C F 3 S 0 3 ) 2 complexes (where M i s Fe and Cu, S e c t i o n s 3.3.1.1 and 3.3.1.2 r e s p e c t i v e l y ) . For example, the Cu-0 bond d i s t a n c e (2.425 A) i n C u ( p y ) f l ( C F 3 S 0 3 ) 2 i s c o n s i d e r a b l y longer than the mean Fe-0 bond d i s t a n c e (2.11 A) i n the i r o n complex and the mean M-N d i s t a n c e s are 2.04 and 2.21 A f o r the copper and i r o n d e r i v a t i v e s r e s p e c t i v e l y . The J a h n - T e l l e r d i s t o r t i o n in the c o p p e r ( I I ) complexes accounts f o r the weak c a t i o n - a n i o n and strong c a t i o n - p y r i d i n e i n t e r a c t i o n when compared to the i r o n d l ) complexes. For M(py) <, (RS0 3) 2 compounds, the bands which are not assigne d to e i t h e r the p y r i d i n e l i g a n d or the s u l f o n a t e anion v i b r a t i o n s are l i s t e d i n Appendix I I I , P a r t s A-C. These "unassigned" bands may i n c l u d e the v6 v i b r a t i o n of the anion and a l s o the i n t e r n a l v i b r a t i o n s of the anion a s s o c i a t e d with the 80 CF 3, CH3 or p-CH 3C 6Hi, groups. These bands are not generally useful in determining the mode of coordination of the anion. For compounds containing trifluoromethyl groups, absorption bands in the 1150-1250 cm"1 region have been previously assigned to C-F stretching v i b r a t i o n s . 1 2 2 In the present study, these bands occur in the same region as the intense S-0 stretching vibrations. In the t r i f l a t e complexes, Fe(py)«(CF 3S0 3) 2 and Cu(py) A(CF 3S0 3) 2, several bands, in addition to the S0 3 symmetric and asymmetric stretching vibrations, are present in this region and are proposed to arise from C-F stretching v i b r a t i o n s . Likewise, the C-F deformation modes have been previously observed around 580 cm - 1 in AgCF 3S0 3, 1 2 2 and the t r i f l a t e derivatives prepared in this study exhibit weak absorptions in t h i s region which may be attributed to these vibrations (Appendix III , Part A). Methanesulfonate derivatives are expected to show bands c h a r a c t e r i s t i c of the methyl group, for example, bands a r i s i n g from C-H deformation modes in the 1300-1350 cm"1 r e g i o n . 1 2 2 In t h i s study the methanesulfonate-containing compounds exhibit weak absorptions in this part of the spectrum which may be assigned to these v i b r a t i o n a l modes (Appendix I I I , Part B). Of the tetrakis(pyridine) derivatives studied here, Fe(py),(p-CH 3C 6HflS0 3) 2 exhibits the most complex i n f r a r e d spectrum. No attempt has been made to assign the i n t e r n a l vibrations of the p-CH 3C 6H„ group. Anion spectra very similar to those reported here have been used previously to infer unidentate sulfonate anion 81 c o o r d i n a t i o n . 7 6 The combination of X-ray d i f f r a c t i o n and infrared spectroscopy which were used in t h i s study, has validated these e a r l i e r conclusions and supports the use of infrared c r i t e r i a for the determination of anion coordination and pyridine bonding in such complexes. Furthermore, the current study has shown that the magnitude of the s p l i t t i n g of S0 3 asymmetric stretching mode, (>«), i s a p a r t i c u l a r l y good measure of the degree of interaction between the sulfonate anion and the metal, and the s h i f t s in the pyridine 6a and 16b vibrations correlate well with the strength of the metal-pyridine interaction. 3.3.2.2 Infrared spectral r e s u l t s for bis(pyrazine)iron(II) halide and thiocyanate complexes Previous studies on the infrared spectra of pyrazine complexes of cobalt(II) and n i c k e l ( I l ) halides have used the presence or absence of a single band in the 980 cm"1 region as a basis for determining whether pyrazine coordinates in a uni- or bidentate mode.32- 3 3- 3 8 Later studies have demonstrated this mid-infrared c r i t e r i o n to be sometimes misleading; however, by using a combination of infrared and Raman spectroscopy, Goldstein et a l . were able to unambiguously determine the mode of pyrazine bonding in a series of M(pyz) 2X 2 3 7 and Sn(pyz) nX„* * compounds. Their approach considered the d i f f e r e n t symmetries of unidentate and bidentate pyrazine groups and the effect of ligand symmetry on the infrared and Raman spectra of pyrazine complexes. Electron d i f f r a c t i o n r e s u l t s 1 2 3 indicate that 82 p y r a z i n e i s p l a n a r ; the symmetry may be represented by the p o i n t group and i n f r a r e d assignments have been made and subsequently d i s c u s s e d on t h i s b a s i s . 1 2 " When both n i t r o g e n atoms of p y r a z i n e c o o r d i n a t e e q u i v a l e n t l y to metal c e n t r e s i n a b r i d g i n g mode, then the symmetry remains the same as i n the uncomplexed l i g a n d and a mutual e x c l u s i o n of i n f r a r e d and Raman bands o c c u r s . When p y r a z i n e c o o r d i n a t e s through only one ni t r o g e n atom, i n a unidentate mode, the symmetry i s reduced to at l e a s t and v i b r a t i o n a l bands f o r m a l l y f o r b i d d e n i n symmetry become a c t i v e i n the i n f r a r e d spectrum of the complex. I n f r a r e d s p e c t r a were r o u t i n e l y recorded i n the present study, but the inten s e red-brown c o l o u r of the h a l i d e and th i o c y a n a t e complexes has precluded any c h a r a c t e r i s a t i o n by Raman spectroscopy. The i n f r a r e d s p e c t r a of the b i s ( p y r a z i n e ) complexes, F e ( p y z ) 2 X 2 are t a b u l a t e d i n Appendix IV. The assignments of fr e e p y r a z i n e are those of Lord et a _ l . 1 2 * A r e p r e s e n t a t i v e spectrum of t h i s c l a s s of complex, that of F e ( p y z ) 2 I 2 , i s shown in F i g 3 . 1 1 . P r e v i o u s l y r e p o r t e d i n f r a r e d s p e c t r a l d a t a 6 2 6 3 f o r the c h l o r o - and bromo d e r i v a t i v e s are comparable t o the data presented i n t h i s study. The i n f r a r e d a c t i v i t y of the p y r a z i n e v i b r a t i o n a l modes i n these complexes i s s i m i l a r to that observed i n known p y r a z i n e - b r i d g e d complexes, f o r example, Sn(pyz)X„,"" and M ( p y z ) 2 X 2 3 7 (where X* i s C l " , Br" or I " ) ; but i s markedly d i f f e r e n t from that of Sn(pyz) 2X„"" (where X" i s C l " or B r " ) , i n which p y r a z i n e c o o r d i n a t e s i n a unidentate mode. 83 F i g . 3.11 Infrared Spectra of F e ( p y z ) 2 I 2 and Fe(pyz) 2(NCS) 2 F e ( p y z ) 2 I 2 J — i — i — i — i — l — i l/L-. 1 . I , i . i . i . i 2500 2000 i MOO 1200 1000 eoo 600 400 WAVENUMBER / c m " 1 84 The infrared spectra of complexes containing unidentate pyrazine groups and the Raman spectrum of free p y r a z i n e 1 2 " exhibit bands at approximately 1230, 920 and 750 cm"1. For the bis(pyrazine)iron(11) compounds there are no absorption bands in these regions, indicating that the pyrazine ligand retains symmetry upon complex formation by acting as a bidentate bridge between metal centres. Most of the pyrazine absorptions exhibit s h i f t s upon coordination of pyrazine. The most coordination sensitive of these absorption bands, at 417 cm"1 in the uncoordinated l i g a n d , 1 2 * i s shifted to considerably higher frequency (30-40 cm"1) upon complex formation. Small s p l i t t i n g s of some of the pyrazine vibrations are observed upon coordination and t h i s may arise from interactions between adjacent pyrazine rings, as has been proposed for pyridine complexes. 1 2 1 Different orientations of the pyrazine rings about their N-N axes may result in dif f e r e n t environments for the pyrazine groups, another possible cause of the s p l i t t i n g s . The infrared spectrum of Fe(pyz) 2(NCS) 2 provides insight not only on pyrazine coordination but also on anion coordination. Infrared c r i t e r i a have been d e v e l o p e d 1 2 5 " 1 2 8 to determine the mode of coordination of the thiocyanate anion. Several alternatives e x i s t : coordination to the metal through nitrogen only (thiocyanato-N), coordination to the metal through sulfur only (thiocyanato-S), or bridging two metal ions to form M-NCS-M' units. These three types of coordination are well known. 1 2 7 Other modes of bridging such as >NCS" or >SCN" are 85 also possible. The v i b r a t i o n a l modes of the anion are appreciably mixed but can be designated: c, as VQ^, V2 as &£jjs and v3 as f ^ g . The infrared spectrum of the free anion in KCNS 1 2 9 exhibits three bands, as expected for a linear triatomic ion, which have been assigned (values are in cm"1) as follows: " i v2 t>3 2053s 486m 746m 471m The s p l i t t i n g of v2 i s attributed to a solid- s t a t e e f f e c t . The infrared spectrum of Fe(pyz) 2(NCS) 2 i s i l l u s t r a t e d in Fi g . 3.11. The anion bands are assigned as follows: "2 Vj 2060s 493m 824m 2000sh The intense C-N stretching vibration, v,, occurs at 2060 cm"1 which i s similar to the value of 2065 cm"1 observed in the thiocyanato-N complex, Fe(py)«(NCS) 2. 6 7 Empirical d a t a 1 2 7 indicate that thiocyanato-N coordination results in l i t t l e change in the position of thi s band from the free-ion value of 2053 cm"1, while S-bonding res u l t s in an increase to approximately 2100 cm"1. In bridging thiocyanate (-NCS-) complexes, t h i s band occurs well above 2100 cm" 1. 1 2 7 The value of 2060 cm'1 observed for Fe(pyz) 2(NCS) 2 is consistent with the presence of an N-terminally bonded NCS" anion. The frequency of the carbon-sulfur stretching vibration, ( j v 3 ) , also has been used to diagnose thiocyanate 86 c o o r d i n a t i o n . 1 2 7 The intensity of t h i s absorption i s often low and in some cases i s d i f f i c u l t to i d e n t i f y . Frequencies in the 700 cm"1 region are taken as indi c a t i v e of S-bonding, while those at approximately 800 cm"1 indicate N-bonding. The infrared spectrum of Fe(pyz) 2(NCS) 2 lacks absorption bands in the 650-750 cm"1 region and hence S-bonding i s not suspected. There are three bands near 800 cm"1, two of which are assigned to pyrazine, and a t h i r d weak band at 824 cm"1 which is assigned to the carbon-sulfur stretching v i b r a t i o n . This value compares favourably with the value of 810 cm"1 found in Fe(py)t(NCS) 2 6 7 and hence, the value of 824 cm"1 supports an N-coordination mode for the anion. Another c r i t e r i o n of thiocyanate coordination i s based upon the frequency and m u l t i p l i c i t y of the anion deformation mode (v2). A single sharp band in the region of 480 cm"1 i s indic a t i v e of N-bonding, while several bands of low intensity near 400 cm"1 indicates S-bonding. 1 2 7 Fe(pyz) 2(NCS) 2 exhibits two sharp bands of medium intensity in the 450-500 cm"1 region. Pyrazine i s expected to show one absorption in this region (which may be s p l i t ) and assignment of either of these bands to either pyrazine or the anion i s d i f f i c u l t . Both bands, however, are c e r t a i n l y well above the range observed for S-bonded thiocyanate and thus thiocyanato-N i s indicated. The band at 493 cm"1 i s tentatively assigned to thi s anion vib r a t i o n . These v i b r a t i o n a l assignments provide a substantial indication for the coordination of the anion through the nitrogen donor atom. To summarise these infrared data: the pyrazine groups 87 retain the symmetry of the free ligand by functioning as bidentate bridging ligands; a polymeric structure is formed, with halide anions or nitrogen atoms from NCS" anions completing the coordination sphere around the iron centre. 3.3.2.3 Infrared spectral results for bis(pyrazine) complexes containing sulfonate or perchlorate anions V i b r a t i o n a l assignments for the pyrazine ligand are l i s t e d in Appendix IV, whilst the infrared spectral data pertaining to the sulfonate anion and any unassigned vibrations are tabulated in Appendix I I I , Parts A and B. For F e ( p y z ) 2 ( C F 3 S O 3 ) 2 . C H 3 O H , Fe(pyz) 2(CH 3S0 3) 2 and C u ( p y z ) 2 ( C H 3 S O 3 ) 2 the intense, broad anion vibrations, p a r t i c u l a r l y in the S-0 stretching region between 1000 and 1200 cm"1, make i t advantageous to discuss these vibrations prior to the neutral ligand vibrations. The various modes of sulfonate anion coordination, the concomitant anion symmetry and the resulting e f f e c t s on the infrared spectra were discussed in Sect ion 3.3.2.1. V i b r a t i o n a l assignments for Cu(pyz) 2(CH 3S0 3) 2 are readily made in terms of monodentate CH 3S0 3" anion coordination (Appendix I I I , Part B). Coordination results in the s p l i t t i n g of the doubly degenerate S0 3 asymmetric stretching and bending modes (vn and vh) by 95 and 13 cm"1 respectively (Fig. 3.10b). It has been noted (Section 3.3.2.1) that in Cu(py)„(CH 3S0 3) 2 the s p l i t t i n g of these bands i s s i g n i f i c a n t l y l e s s , for example, is s p l i t by 49 cm"1 and vh i s not observed to s p l i t (Section 88 3.3.2.1). These r e s u l t s i n d i c a t e that the c a t i o n - a n i o n i n t e r a c t i o n i n C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 i s stronger than that i n C u ( p y ) „ ( C H 3 S 0 3 ) 2 • These i n f r a r e d data f o r C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 are c o n s i s t e n t with the X-ray s t r u c t u r e r e s u l t which shows the anion to be c o o r d i n a t e d s t r o n g l y i n the e q u a t o r i a l plane. In both of these copper-methanesulfonate compounds, the metal achieves one of i t s p r e f e r r e d c o o r d i n a t i o n geometries by having four s h o r t ( e q u a t o r i a l ) and two long ( a x i a l ) i n t e r a c t i o n s . In the p y r a z i n e compound, the r e l a t i v e l y weak b a s i c i t y of the p y r a z i n e l i g a n d precludes an e q u a t o r i a l geometry i n which the p y r a z i n e l i g a n d s f u l f i l l a l l four strong i n t e r a c t i o n s . In t h i s case, the four s t r o n g i n t e r a c t i o n s are p r o v i d e d by the two s u l f o n a t e oxygen atoms p l u s two bonds to p y r a z i n e , while the two weaker i n t e r a c t i o n s are p r o v i d e d by two bonds to p y r a z i n e ( S e c t i o n 3.3.1.3). In the p y r i d i n e complex, the four n e u t r a l l i g a n d s c o o r d i n a t e s t r o n g l y i n the e q u a t o r i a l plane and the anions adopt a x i a l c o o r d i n a t i o n s i t e s . The i n f r a r e d spectrum of C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 e x h i b i t s a broad a b s o r p t i o n i n the 2800-3500 cm"1 r e g i o n , i n d i c a t i n g the presence of an O-H c o n t a i n i n g s p e c i e s . T h i s i s somewhat s u r p r i s i n g s i n c e the X-ray a n a l y s i s showed no evidence f o r such a s p e c i e s . I t seems p o s s i b l e that small amounts of water or methanol may be present.on the c r y s t a l s u r f a c e and l e a d to t h i s i n f r a r e d a b s o r p t i o n . •The i n f r a r e d s p e c t r a of F e ( p y z ) 2 ( C F 3 S 0 3 ) 2 . C H 3 O H and F e ( p y z ) 2 ( C H 2 S 0 3 ) 2 are s i m i l a r to that of the copper complex. A s p l i t t i n g of the S0 3 asymmetric s t r e t c h i n g and bending modes (VA 89 and vs) i s c l e a r l y observed i n d i c a t i n g a r e d u c t i o n of anion symmetry to below C j v which presumably a r i s e s from a unidentate mode of s u l f o n a t e anion c o o r d i n a t i o n . A comparison of the number and p o s i t i o n of the anion v i b r a t i o n s f o r the b i s ( p y r a z i n e ) i r o n d l ) s u l f o n a t e s p e c i e s and the analogous t e t r a k i s ( p y r i d i n e ) complexes gave the f o l l o w i n g r e s u l t s . The methanesulfonate anion s p e c t r a are v i r t u a l l y i d e n t i c a l f o r F e ( p y ) „ ( C H 3 S O 3 ) 2 and F e ( p y z ) 2 ( C H 3 S 0 3 ) 2 ( F i g . 3.9a,b and Appendix I I I , Part B). In view of the X-ray s t r u c t u r a l data f o r F e ( p y ) f t ( C H 3 S 0 3 ) 2 , i n which the anion i s c l e a r l y demonstrated as c o o r d i n a t i n g i n a unidentate mode, i t i s concluded that the anion i s c o o r d i n a t e d to the metal i n a s i m i l a r f a s h i o n i n F e ( p y z ) 2 ( C H 3 S O 3 ) 2 . The s p l i t t i n g s of the S0 3 asymmetric s t r e t c h i n g and bending modes are v i r t u a l l y of the same magnitude which may i n d i c a t e a s i m i l a r degree of c a t i o n - a n i o n i n t e r a c t i o n f o r both complexes. S i m i l a r l y , f o r F e ( p y z ) 2 ( C F 3 S 0 3 ) 2 . C H 3 O H the mode of anion c o o r d i n a t i o n was a s c e r t a i n e d by a comparison with the anion bands of F e ( p y ) f t ( C F 3 S 0 3 ) 2 (Appendix I I I , Part A). Both complexes show a c l o s e c o r r e l a t i o n f o r the bands assigned to the anion, and unidentate anion c o o r d i n a t i o n i n the b i s ( p y r a z i n e ) complex i s i n f e r r e d . The s p l i t t i n g s of the S0 3 asymmetric s t r e t c h i n g and bending modes a l s o i n d i c a t e a s i m i l a r degree of c a t i o n - a n i o n i n t e r a c t i o n i n the two compounds. In F e ( p y z ) 2 ( C F 3 S 0 3 ) 2 . C H 3 O H the broad a b s o r p t i o n between 3400-2500 cm"1 c l e a r l y demonstrates the presence of an O-H c o n t a i n i n g s p e c i e s , i n agreement with the m i c r o a n a l y t i c a l data which suggest the presence of one mole of methanol per mole of 90 complex. B e f o r e a d i s c u s s i o n of the v i b r a t i o n a l a s s i g n m e n t s f o r the an i o n i n Fe(pyz) 2(C10„) 2, i t i s r e l e v a n t t o comment on the r e l a t i o n s h i p between the number and f r e q u e n c y of the a n i o n v i b r a t i o n a l bands and p e r c h l o r a t e a n i o n symmetry. The f r e e p e r c h l o r a t e a n i o n belongs t o the symmetry p o i n t group T^. There are f o u r normal v i b r a t i o n a l modes ( T a b l e 3.4) and of the s e o n l y the asymmetric s t r e t c h i n g and bending modes iv3 and J > 4 , r e s p e c t i v e l y ) a re i n f r a r e d a c t i v e . T a b l e 3.4 V i b r a t i o n s of the P e r c h l o r a t e Anion as a F u n c t i o n of Symmetry SYMMETRY (R=RAMAN, I=INFRARED ACTIVE) "3 V u F 2 ( I , R ) F 2 ( I , R ) A A V\ • V* »3 "5 A ( I , R ) E(I,R) A(I,R) E ( I , R ) In the i n f r a r e d s p e c t r a of i o n i c p e r c h l o r a t e - c o n t a i n i n g compounds, t h e s e bands g e n e r a l l y o c c u r a t a p p r o x i m a t e l y 1110 and 630 cm" 1 r e s p e c t i v e l y ; 1 3 0 the former a p p e a r i n g as a v e r y broad s t r o n g band which i s o c c a s i o n a l l y s p l i t . Upon c o o r d i n a t i o n t h r ough a s i n g l e oxygen atom, the symmetry i s reduced a t l e a s t t o a s p l i t t i n g of the two t r i p l y d egenerate normal v i b r a t i o n a l modes r e s u l t s and the two symmetric modes become i n f r a r e d a c t i v e (Table 3.4). There a r e two f e a t u r e s i n the i n f r a r e d spectrum of Fe(pyz) 2 (ClOi,) 2 which i n d i c a t e t h a t the symmetry of the a n i o n i s '3v A(R) A,(I,R) " 2 E(R) " 6 E ( I , R ) 91 not T^. The s p l i t t i n g s of the t r i p l y degenerate modes {v3 and vn i n T^ symmetry) i n d i c a t e a lowering of anion symmetry and the presence of a strong a b s o r p t i o n at 918 cm" 1 would not be expected i f the anion r e t a i n e d T^ symmetry. Assuming C^ v anion symmetry f o r the p e r c h l o r a t e anion i n Fe(pyz) 2(C10«) 2, the f o l l o w i n g assignments are made: v2(k) *>,(A) p , (E ) v3(h) and vs(E) 918s 1026s 1145s 637m, 626s, 617s *>6 i s not observed. These v i b r a t i o n a l assignments are very s i m i l a r t o those made f o r some M(py) i, (C104 ) 2 complexes where unidentate anion c o o r d i n a t i o n has been p r o p o s e d . 8 6 The i n f r a r e d s p e c t r a l data presented here i n d i c a t e a s i m i l a r mode of anion c o o r d i n a t i o n i n Fe(pyz) 2(C10«) 2. V i b r a t i o n a l assignments f o r p y r a z i n e i n these b i s (pyrazine) i r o n d l ) . s u l f o n a t e and p e r c h l o r a t e complexes are made more d i f f i c u l t by the strong a b s o r p t i o n s of the s u l f o n a t e and p e r c h l o r a t e anions; as a r e s u l t , some of the p y r a z i n e bands are obscured. Some assignments have been made by a comparison of the i n f r a r e d s p e c t r a of the M ( p y z ) 2 ( R S 0 3 ) 2 complexes with those of the n e u t r a l l i g a n d 1 2 " and of the F e ( p y z ) 2 X 2 complexes ( S e c t i o n 3.3.2.2); these are given i n Appendix IV. The i n f r a r e d spectrum of C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 i s i l l u s t r a t e d i n F i g . 3.10b and i t may be seen that the 1000-1300 cm"1 region of the spectrum i s not p a r t i c u l a r l y u s e f u l f o r a s s e s s i n g the c o o r d i n a t i o n mode of p y r a z i n e . The occurence of two bands at 813 and 846 cm"1 and two a b s o r p t i o n s at 440 and 494 cm" 1, 92 however, i s informative. For comparison, in free pyrazine these infrared absorptions are observed at 804 and 417 cm"1 r e s p e c t i v e l y , 1 2 " and upon coordination, minor s h i f t s are expected which are sometimes accompanied by small s p l i t t i n g s of usually less than 10 cm"1. The magnitudes of the s p l i t t i n g s of these bands in Cu(pyz) 2(CH 3S0 3) 2, by 33 and 54 cm"1 , appear too large to be associated with interactions between adjacent pyrazine rings but are consistent with the X-ray structural result which shows two d i s t i n c t pyrazine groups. Presumably, the absorptions at the two higher frequencies (494 and 846 cm"1) are associated with the ligand more strongly bonded to copper, whilst for the more weakly bound pyrazine group, the s h i f t s to higher frequency are of a lesser extent (to 440 and 804 cm' 1). The infrared spectra of Fe(pyz) 2(CF 3S0 3) 2.CH 3OH and Fe(pyz) 2(CH 3S0 3) 2 show differences and s i m i l a r i t i e s in the absorptions assigned to pyrazine, when compared to Cu(pyz)2(CH 3S0 3) 2. Both bis(pyrazine) i r o n ( l l ) derivatives exhibit only small s p l i t t i n g s (of less than 10 cm"1) of the absorption in the 470 cm"1 region which may indicate the presence of only one type of pyrazine ligand in the iron compounds. The bands assigned to pyrazine in Fe(pyz) 2(CF 3S0 3) 2.CH 3OH are more numerous than in F e ( p y z ) 2 ( C H 3 S O 3 ) 2 , and t h i s may be a result of additional interactions between the pyrazine and methanol in the t r i f l a t e compound. Such interactions are absent in Fe(pyz) 2(CH 3S0 3) 2. It i s d i f f i c u l t to use the previously established infrared c r i t e r i a to determine the mode of neutral ligand coordination in 93 these complexes. If unidentate pyrazine groups are present, then absorption bands may be activated in the infrared spectrum at approximately 1230, 1020 and 750 cm"1. For the complexes under investigation here, i t is l i k e l y that i f these bands are present, then they are obscured by the presence of the strong anion vibrations in these regions. The s i m i l a r i t i e s between the spectra of the three bis(pyrazine) sulfonate complexes, together with the X-ray structural evidence for the copper derivative, strongly suggest that Fe(pyz) 2 ( C F 3 S O 3) 2.CH 3OH and Fe(pyz) 2(CH 3S0 3) 2 contain unidentate sulfonate anions; however, evidence for bidentate bridging pyrazine groups i s rather weak. The assignment of infrared absorptions a r i s i n g from pyrazine in Fe(pyz) 2(C10„) 2 is beset by problems similar to those encountered for the sulfonate derivatives, i . e . , strong absorptions of C10„" in the 900-1200 cm"1 region. The pyrazine bands which are assigned (Appendix IV) provide inconclusive evidence for pyrazine coordination. 3.3.2.4 Infrared spectral results for tetrakis(pyrazine) complexes The infrared spectrum of Fe(2-mepyz)„(CH 3S0 3) 2 is i l l u s t r a t e d in Fig 3.9c, the spectra of Fe(py )„(CH 3S0 3) 2 and F e ( p y z ) 2 ( C H 3 S O 3 ) 2 are shown for comparison (Figs. 3.9a and 3.9b respectively). The vibrations assigned to the sulfonate anion are l i s t e d in Appendix II I , Part B. The s i m i l a r i t i e s between the anion spectra of the 2-methylpyrazine complex and the other 94 two methanesulfonate derivatives (Section 3.3.2.1 and 3.3.2.3 respectively), are readily apparent. For example, the s p l i t t i n g s of the asymmetric S0 3 stretching and bending modes (by 95 and 17 cm"1 respectively) are of a similar magnitude to those found in the other i r o n d l ) methanesulfonate complexes, and a unidentate mode of anion coordination i s proposed for Fe(2-mepyz) j, ( C H 3 S O 3 ) 2 ; a similar degree of cation-anion interaction i s also indicated. The absorptions a r i s i n g from the 2-methylpyrazine ligand in the complex are given in Appendix V, and these bands are similar to those previously observed in other 2-methylpyrazine d e r i v a t i v e s . 3 3 The free ligand lacks a centre of symmetry, and c r i t e r i a which are sometimes useful in determining the mode of pyrazine coordination cannot be applied to 2-methylpyrazine complexes. The infrared spectrum of Cu(pyz)«(CF 3S0 3) 2.H 20 is characterised by absorptions from pyrazine groups, t r i f l a t e anions and water moieties. The absorptions of the t r i f l a t e anion and unassigned vibrations are given in Appendix I I I , Part A. Several bands occur in the S0 3 stretching region and three of these were tentatively assigned to the asymmetric and symmetric S0 3 stretching modes by comparison with the spectral data for the other t r i f l a t e - c o n t a i n i n g compounds prepared in this study ( i t i s l i k e l y that the other absorptions in this region arise from the CF 3 stretching v i b r a t i o n s ) . A reduction in anion symmetry to below Cg v i s indicated and suggests a unidentate mode of anion coordination. Vibrations assigned to 95 pyrazine are l i s t e d in Appendix V and due to the complex nature of the infrared spectrum in the 900-1300 cm"1 region i t i s d i f f i c u l t to conclusively i d e n t i f y pyrazine bands; hence, no d e f i n i t e conclusions are drawn concerning the nature of pyrazine coordination. The . broad absorptions centred at 3400 and 1630 cm"1 indicate the presence of an OH-containing species, presumably water. C l a s s i f i c a t i o n of Fe(pyz) 4(AsF 6) 2.2H 20 as having an FeN 4X 2 chromophore i s dependent upon two c r i t e r i a . F i r s t l y , the pyrazine ligands must be coordinated in a unidentate fashion; and secondly, either the water molecules or the hexafluoroarsenate anions must occupy the remaining coordination s i t e s . Infrared spectroscopy i s capable of determining whether these conditions pertain. The infrared spectrum of the complex i s shown in F i g . 3.12 and the vibrations assigned to the pyrazine ligand are given in Appendix V. The presence of bands near 3000 and 1600 cm"1 c l e a r l y indicate the presence of water. Their broad nature suggests that the water molecules may be coordinated to the metal centre. The free AsF 6" anion has symmetry and i s expected to exhibit two infrared active vibrations. In the ionic s a l t , C s A s F 6 , 1 3 1 these vibrations are observed at 699 and 392 cm"1. When anion coordination occurs the symmetry of the anion is reduced below 0^ and t h i s r e s u l t s in band s p l i t t i n g s and the appearence of infrared absorptions which are forbidden in octahedral symmetry. For Fe(pyz)„(AsF 6) 2.2H 20, anion bands are 96 assigned at 700 and 400 cm - 1. The occurrence of only two anion bands and the fact that these bands show no s p l i t t i n g indicate that the anion retains octahedral symmetry and is not coordinated to the metal, as expected for this very weakly basic ligand. F i g . 3.12 Infrared Spectrum of Fe(pyz)„(AsF 6) 2.2H 20 97 Because of the presence of only two anion bands, vi b r a t i o n a l assignments for pyrazine are made more eas i l y than those for the sulfonate complexes (Section 3.3.2.3). The assignments are given in Appendix IV and from these i t appears that a number of pyrazine bands are s p l i t ; this could arise either from there being two dif f e r e n t environments for the ligand or interactions between neighbouring pyrazine rings. Weak absorptions are observed at 1232 and 920 cm"1; bands are observed at comparable frequencies in the Raman spectrum of free p y r a z i n e 1 2 " and in the infrared spectra of unidentate-pyrazine containing compounds."" The activation of these bands in the infrared spectrum of Fe(pyz)„(AsF 6) 2•2H 20 i s proposed to arise from a reduction in ligand symmetry below which may indicate a unidentate mode of of pyrazine coordination. Further evidence for this mode of pyrazine coordination comes from the observation that Cu(pyz)„(AsF 6) 2 1 3 2 exhibits similar infrared spectral features as those described here and unidentate pyrazine coordination has been proposed in thi s copper complex. These infrared spectral results suggest ionic hexafluoroarsenate anions, terminal unidentate pyrazine groups and coordinated water molecules which supports the proposal of an FeN„0 2 chromophore and the absence of a bridging network in this complex. In summary, infrared spectroscopy indicates unidentate anion coordination in Fe(2-mepyz) t t(CH 3S0 3) 2 and Cu(pyz) f t(CF 3S0 3) 2 «H 20; whereas, ionic non-coordinated anions are proposed for Fe(pyz)„(AsF 6) 2.2H 20. The infrared spectral data 98 are i n c o n c l u s i v e as to the mode of 2-methylpyrazine and p y r a z i n e c o o r d i n a t i o n i n the methanesulfonate and t r i f l a t e d e r i v a t i v e s r e s p e c t i v e l y ; on the other hand, i n f r a r e d spectroscopy i n d i c a t e s unidentate p y r a z i n e c o o r d i n a t i o n i n the h e x a f l u o r o a r s e n a t e compound. 99 3.3.3 E l e c t r o n i c Spectroscopy E l e c t r o n i c s p e c t r a over the frequency range 4,000-30,000 cm"1 were recorded f o r a l l of the complexes i n v e s t i g a t e d i n t h i s study. I t was a n t i c i p a t e d that such s t u d i e s would not only provide c o n f i r m a t o r y evidence r e g a r d i n g the nature of the metal chromophore but a l s o c o u l d be used to f u r t h e r i n v e s t i g a t e the d i f f e r e n c e s i n the c o o r d i n a t i n g tendencies of the v a r i o u s l i g a n d s i n v o l v e d . 3.3.3.1 E l e c t r o n i c s p e c t r a l r e s u l t s f o r complexes c o n t a i n i n g an FeN„0 2 chromophore The e l e c t r o n i c ground s t a t e f o r h i g h - s p i n F e 2 + i s represented by the 5D term symbol. In l i g a n d f i e l d s of c u b i c 5 5 symmetry the ground s t a t e s p l i t s t o g i v e T 2 and E s t a t e s y y 5 separated by lOD^. In o c t a h e d r a l symmetry the T 2 g s t a t e l i e s lowest in energy and one s p i n - a l l o w e d d-d t r a n s i t i o n i s expected and i s u s u a l l y observed as a broad band i n the n e a r - i n f r a r e d region of the e l e c t r o m a g n e t i c spectrum. The band i s o f t e n asymmetric i n c h a r a c t e r , w h i l s t sometimes i t i s c l e a r l y r e s o l v e d i n t o two components. These o b s e r v a t i o n s are a t t r i b u t e d to the s p l i t t i n g of the e x c i t e d s t a t e i n l i g a n d f i e l d s of l e s s than symmetry. The e l e c t r o n i c energy l e v e l diagram f o r h i g h - s p i n i r o n d l ) complexes in l i g a n d f i e l d s of o c t a h e d r a l , t e t r a g o n a l and t r i g o n a l symmetry i s shown in F i g . 3.13. The o r d e r i n g of the energy l e v e l s on the right-hand s i d e of t h i s f i g u r e i s f o r a t e t r a g o n a l compression, and takes i n t o account the a-bonding e f f e c t s of the l i g a n d s . T h i s o r d e r i n g i s expected f o r the 100 Fe(py)„(RS0 3) 2 complexes because of the presence of a tetragonally compressed coordination sphere about the metal (Section 3.3.1.1). The electronic spectral parameters for the Fe(py)„(RS0 3) 2 complexes are presented in Appendix VII, Part A, and the spectra are i l l u s t r a t e d in F i g . 3.14. In a l l three cases, a p r i n c i p a l absorption band i s observed around 11,000 cm"1 and for the R=CH3 and p-CH3C6H, compounds, the band shows a small degree of asymmetry at low energy. For the t r i f l a t e derivative, a more d i s t i n c t shoulder (9,000 cm"1) is observed at low-energy. Of the Fe(py)„(RS0 3) 2 complexes studied by X-ray d i f f r a c t i o n (Section 3.3.3.1), the coordination sphere about the metal i s least distorted in the t r i f l a t e complex. The greater tetragonal compression in the methanesulfonate and p-tosylate complexes would be expected to produce larger s p l i t t i n g s of the excited state than that produced by the t r i f l a t e complex, which would result in the observation of band s p l i t t i n g in the former two complexes; t h i s , however, i s not observed. The r e l a t i v e l y small tetragonal compression in the t r i f l a t e complex would not be expected to lead to band s p l i t t i n g . Thus, i t appears l i k e l y that the shoulder at 9,000 cm"1 in Fe(py) f l(CF 3S0 3) 2, is not caused by the s p l i t t i n g of the excited state but may be due to a v i b r a t i o n a l band, possibly an overtone. This band i s not observed in the other two complexes and th i s may be because the absorption bands are considerably broadened. 101 F i g . 3.13 Electronic Energy Levels for High-Spin I r o n d l ) F i g . 3.14 Electronic Spectra for Fe(py) f l(RS0 3) 2 Complexes ENERGY x10'3 /cm-' 102 The t e t r a k i s ( p y r i d i n e ) i r o n ( I I ) complexes show only small differences in the frequencies of the maximum absorption, " m a x . For these complexes, the values of 1OD^ (of approximately 11,000 cm"1, as measured by **max) a r e s i g n i f i c a n t l y higher than the value of 8,000 cm"1, observed for the anhydrous sulfonate species, F e ( R S 0 3 ) 2 • 2 2 5 This i s consistent with the stronger ligand f i e l d associated with the FeN«0 2 chromophore in the pyridine complexes, compared to the ligand f i e l d associated with the Fe0 6 chromophore present in the sulfonate complexes. Electronic spectral data for the b i s ( p y r a z i n e ) i r o n d l ) complexes, Fe(pyz) 2(CF 3S0 3) 2.CH 3OH and Fe(pyz) 2(CH 3S0 3) 2 are given in Appendix VII, Part A. Both complexes exhibit electronic spectra which are very similar to those of the te t r a k i s ( p y r i d i n e ) i r o n ( I I ) sulfonate complexes. This observation supports the assignment of an FeN«0 2 chromophore in the bis(pyrazine) derivatives and also the conclusion that pyridine and pyrazine occupy positions close to each other in the spectrochemical ser i e s . The electronic spectrum of Fe(2-mepyz) f l(CH 3S0 3) 2 exhibits one broad band at 9,800 cm"1, which i s in the range expected for high-spin octahedral i r o n d l ) compounds. This value indicates the presence a weaker ligand f i e l d than that which exists in the analogous tetrakis(pyridine) or b i s ( p y r a z i n e ) i r o n d l ) complexes. From these observations an FeN f l0 2 chromophore seems l i k e l y and this would require the neutral ligand to be coordinated in a terminal unidentate manner. Two alternatives e x i s t : coordination through either N(1) or N(4) (Fig. 3.15). 103 F i g . 3.15 2-Methylpyrazine The former nitrogen atom i s more basic than that of pyrazine (pK values of 1.45 and -0.6 r e s p e c t i v e l y 2 8 ) and coordination a through t h i s nitrogen atom might be expected to produce a stronger ligand f i e l d . By judging from the " m a x ' a stronger ligand f i e l d i s not present which suggests that t h i s mode of coordination i s either hindered by the presence of the methyl group or that coordination takes place through the less basic nitrogen atom N(4). 3.3.3.2 Electronic spectral results for complexes containing an CuN„0 2 chromophore The copper(II) ion has a d 9 electron configuration which gives r i s e to a 2D free-ion ground term. The energy l e v e l diagram for a copper(II) ion in c r y s t a l f i e l d s of 0^ and symmetry i s shown in F i g . 3.16. Since the ground state in a 2 octahedral ligand f i e l d i s the E^ state, i t i s subject to a considerable Jahn-Teller i n s t a b i l i t y , and as a result the majority of octahedral copper(Il) complexes are tetragonally distorted with four short copper-ligand bonds in one plane (xy) and two longer copper-ligand bonds ly i n g along the z-axis above and below t h i s plane. 104 F i g . 3.16 E l e c t r o n i c Energy L e v e l s f o r Copper(II) In symmetry, three a b s o r p t i o n s are expected, but o f t e n i n the case of t e t r a g o n a l l y d i s t o r t e d c o p p e r ( I I ) compounds only one broad asymmetric band i s observed i n the v i s i b l e r e g i o n ; the p o s i t i o n of t h i s band may be taken to represent the average l i g a n d f i e l d , lOD g. The e l e c t r o n i c s p e c t r a l parameters f o r the t e t r a k i s ( p y r i d i n e ) c o p p e r ( I I ) complexes and C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 are given i n Appendix V I I , P a r t B. For comparison, the r e s u l t s from a p r e v i o u s study on C u ( p y ) „ ( F S 0 3 ) 2 and C u ( p y ) „ ( p - C H 3 C 6 H 4 S 0 3 ) 2 are a l s o i n c l u d e d . 7 6 The t e t r a k i s ( p y r i d i n e ) c o p p e r ( I I ) s u l f o n a t e 105 complexes a l l exhibit a single broad asymmetric band which presumably i s of a composite nature. For a large number of bis(ethylenediamine)copper(II) complexes, 1 3 3 the position of the v i s i b l e band has been correlated with the degree of tetragonality of the copper chromophore; these previous studies demonstrated that the position of the band s h i f t s to higher energies with increasing tetragonal d i s t o r t i o n . Hathaway et a)-. 1 3* have shown from polarised radiation s i n g l e - c r y s t a l electronic spectral studies, that the highest energy component in the v i s i b l e band of these complexes arises from the 2 2 . . . B^g *• Eg t r a n s i t i o n and i t i s largely the s h i f t of t h i s t r a n s i t i o n to higher energies on increasing tetragonal d i s t o r t i o n that accounts for the o v e r a l l s h i f t of the v i s i b l e band. For the tetrakis(pyridine)copper(II) complexes, as the R group of the anion changes from CH 3 to p-CHsCgHi, to F to C F 3 , ''max * s ° b s e r v e 3 t o increase. This indicates a greater degree of tetragonality in the same order and t h i s would be predicted on the basis of r e l a t i v e l y weaker anion b a s i c i t i e s for FS0 3~ and CF 3S0 3" when compared to those of the methanesulfonate and p-tosylate. The absorption bands for the copper-pyridine complexes are at s i g n i f i c a n t l y higher frequencies (approximately 17,000 cm"1) than those for the corresponding anhydrous sulfonate compounds, Cu(RS0 3) 2, 8 7 where absorbtion bands are present in the range of 8,000-14,000 cm"1. As described for the iron complexes, t h i s i s attributable to a stronger ligand f i e l d afforded by four pyridine ligands and two sulfonate oxygen atoms in the pyridine 106 complexes, in comparison to six sulfonate oxygen atoms in the anhydrous sulfonates. The electronic spectral data for Cu(py)„(CF 3S0 3) 2 are e n t i r e l y consistent with the X-ray structure result which revealed a pseudooctahedral coordination geometry distorted by a tetragonal elongation (Section 3.3.1.2). The electronic spectrum of Cu(pyz) 2(CH 3S0 3) 2 shows a broad absorption at 14,000 cm"1; t h i s i s at a considerably lower energy than that observed for Cu(py)„(CH 3S0 3) 2, 16,800 cm"1. An X-ray structure determination shows Cu(pyz) 2(CH 3S0 3) 2 to possess a CuN 20 2N 2 chromophore (Section 3.3.1.3); whereas, infrared and e l e c t r o n i c spectroscopy suggest that Cu(py)„(CH 3S0 3) 2 has a CuN f t0 2 chromophore (Section 3.3.2.1). The difference in the e l e c t r o n i c spectra of the two complexes possibly r e f l e c t s the greater degree of tetragonality associated with the CuN„0 2 chromophore in Cu(py)„(CH 3S0 3) 2 as well as the s l i g h t l y higher p o s i t i o n of pyridine over pyrazine in the spectrochemical series and also the fact that in the pyrazine complex, one of the bridging ligands i s only very weakly bonded to copper. The electronic spectrum of Cu(pyz)«(CF 3S0 3) 2.H 20 exhibits a broad absorption band at 16,100 cm"1, This i s at a s l i g h t l y lower energy than that observed for Cu(py)„(CF 3S0 3) 2 (17,400 cm" 1). Again, the lower frequency of the absorption band in the pyrazine complex i s consistent with a weaker ligand f i e l d and/or a lesser degree of tetragonality in the tetrakis(pyrazine) complex. 107 3.3.3.3 Electronic spectral results for complexes containing an FeN„X 2 chromophore The electronic spectral parameters for the b i s ( p y r a z i n e ) i r o n d l ) halide, thiocyanate and perchlorate derivatives, and Fe(pyz),(AsF 6) 2.2H 20 are l i s t e d in Appendix VII, Part C. The perchlorate and hexafluoroarsenate compounds are yellow; whereas, the colours of the halide and thiocyanate complexes are p a r t i c u l a r l y intense and range from maroon for F e ( p y z ) 2 I 2 to red for the chloro- and bromo derivatives; Fe(pyz) 2(NCS) 2 i s brown. In comparison, the i r o n d l ) complexes with sulfonate anions (Section 3.3.3.1) are pale green or yellow. Absorption bands are seen in the near-infrared region (11,000-13000 cm" 1); these band positions are diagnostic of high-spin octahedral i r o n d l ) complexes. The absorptions are of a broad nature and evidence for band s p l i t t i n g i s observed in the spectra of F e ( p y z ) 2 I 2 and Fe(pyz) 2(NCS) 2. As was done for the tetrakis(pyridine) complexes, 6 7 the average ligand f i e l d in the pyrazine complexes i s represented by taking either the centre of the unsplit absorption band or, in the case where band s p l i t t i n g i s observed, by taking the average position of the two bands. 108 These values (cm"1) together with those for the tetrakis(pyridine) complexes 6 7 are as follows: X Fe(pyz) 2X 2 Fe(py)„X 2 Cl 11,800 9620 Br 11,200 9280 I 9,200 8620 NCS 11,500 10,670 These data indicate that pyrazine provides a s l i g h t l y stronger ligand f i e l d than does pyridine. This apparently stronger ligand f i e l d afforded by pyrazine may be a consequence of the 5 s t a b i l i s a t i o n of the T~ le v e l s as a resu l t of the better 2g 7r-acceptor properties of pyrazine over pyridine. The intense colours of the bis(pyrazine)iron(II) halide and thiocyanate complexes are presumably a consequence of charge-transfer bands in the v i s i b l e region of the spectrum (Appendix VII, Part C). Charge-transfer spectra have been observed in other i r o n d l ) complexes 1 3 5 and in view of the re l a t i v e ease of oxidation of iron(II) to iron(III) these spectra are proposed to be predominantly metal to ligand in character. Previously in metal-pyrazine complexes, charge transfer has been proposed to be from the metal to a low-lying empty 7 r-antibonding o r b i t a l of the pyrazine moiety 3" and th i s i s probably the case here. The colour of the t e t r a k i s ( p y r i d i n e ) i r o n d l ) halides and thiocyanate complexes are 1 0 9 pale-yellow; 6 7 and the metal to ligand charge-transfer band presumably occurs at higher energy in the u l t r a v i o l e t region. These results are consistent with the better ff-acceptor properties of pyrazine over pyridine. In t h i s study, i t was noted that for the complexes to be intensely coloured the combined presence of pyrazine and either halide or pseudohalide was necessary. Complexes which lacked t h i s combination of ligands were found to be pale in colour. For example, F e ( p y z ) 2 ( C H 3 S 0 3 ) 2 and F e ( p y ) „ C 1 2 6 7 are pale yellow; whereas, F e ( p y z ) 2 C l 2 i s deep-red. This suggests that the halide or pseudohalide anions also play a role in the charge-transfer process; presumably a role which the sulfonate anions cannot engage i n . Because of the ease of oxidation of halide and pseudohalide anions i t i s l i k e l y that the role of the anion in the charge-transfer process i s ligand to metal in nature which then f a c i l i t a t e s metal to pyrazine charge transfer. Before considering the magnetic properties, i t i s worthwhile summarising the structural evidence for these compounds. Electronic spectral data indicate that the complexes contain pseudooctahedrally coordinated metal centres r e s u l t i n g in an MN„X 2 chromophore. For the bis(pyrazine) complexes, infrared spectroscopy strongly suggests unidentate anion coordination and in some cases bidentate bridging pyrazine moieties. The tetrakis(pyridine) complexes also contain anions coordinated in a unidentate fashion as well as coordinated pyridine ligands. The major difference between the bis(pyrazine) and tetrakis(pyridine) compounds i s that a 1 1 0 two-dimensional l a t t i c e i s present in the former group; whereas, monomeric species are present in the tetrakis(pyridine) complexes. X-ray crystallography has confirmed both of these structural types. Discussions in subsequent sections ( 3 . 3 . 5 - 3 . 3 . 6 ) of this chapter attempt to probe the e f f e c t s that these s t r u c t u r a l differences have on the magnetic, Mossbauer and thermal properties of these materials. 111 3.3.4 Magnetic Properties One of the i n i t i a l objectives of t h i s work was the study of the magnetic properties of pyrazine-bridged metal complexes in an e f f o r t to determine the magnitude of magnetic exchange propagation via this ligand and to investigate correlations between magnetic exchange and st r u c t u r a l features of such complexes. As described e a r l i e r in t h i s chapter, for both divalent iron and copper, i t was possible to obtain and characterise not only complexes with bridging pyrazine groups but also analogous complexes with i d e n t i c a l chromophores but without bridging ligands. It was anticipated that a better evaluation of exchange effects via bridging pyrazine would be possible by comparing the magnetic properties of these two groups'of compounds. The magnetic s u s c e p t i b i l i t y data from the vibrating-sample magnetometer, Gouy and Faraday techniques for the copper and iron complexes are given in Appendices VIII and IX respectively. 3.3.4.1 Magnetic s u s c e p t i b i l i t y results for complexes containing a CuN„0 2 chromophore At a l l temperatures studied, Cu(py)«(CF 3S0 3) 2, Cu(py),(CH 3S0 3) 2 and Cu(pyz)„(CF 3S0 3) 2.H 20 have magnetic moments within the range of 1.7-2.1 B.M., there being only a s l i g h t variation with temperature for a l l three examples (Appendix VIII). For copper(II) complexes, a temperature-independent magnetic moment is expected for magnetically-dilute systems and such comlexes often exhibit room-temperature magnetic moment 1 1 2 values close to the spin-only value of 1.73 B.M. The magnetic moment data for Cu(py) <, (CF 3S0 3) 2 indicate the lack of magnetic exchange interactions and thi s i s in accord with the X-ray structure result (Section 3.3.1.2) which shows the paramagnetic centres well isolated from each other. The magnetic moment data for Cu(py),(CH 3S0 3) 2 are consistent with a structure similar to that of the t r i f l a t e derivative. The temperature-independent magnetic moment observed for the Cu(pyz)«(CF 3S0 3) 2.H 20 compound i s consistent with the conclusion that the pyrazine groups are coordinated to the copper ion in a unidentate fashion. Bridging pyrazine groups may be expected to lead to magnetic concentration effects at low temperatures (see l a t e r ) . The magnitude and temperature dependence of the magnetic moment data presented here are similar to those previously observed for some related Cu(py)„X 2 compounds (where X" i s FS0 3", p - C H a C g H f l S O a " , CIO," and B F „ ~ ) . 7 6 In this previous study, however, magnetic measurements were limited to the temperature range of 80-300 K. The magnetic properties of the bis(pyrazine) complex, Cu(pyz)2(CH 3S0 3)2, were found to be quite d i f f e r e n t from those of the complexes discussed above. Although the room-temperature moment is of a similar magnitude to those of the other complexes, the data exhibit a strong temperature dependence, »*eff. ranging from 1.87 B.M. at room temperature, to 0.85 B.M. at 4.2 K. For a comparison, the temperature dependencies of the magnetic moments of the bis(pyrazine) and tetrakis(pyridine)copper(II) methanesulfonate complexes are depicted in F i g . 3.17. The strong temperature dependence of 1 1 3 M e f f ^ o r t n e bis(pyrazine) derivative is almost c e r t a i n l y due to the presence of antiferromagnetic exchange. The effect of magnetic concentration i s more c l e a r l y seen in the magnetic s u s c e p t i b i l i t y data, where the s u s c e p t i b i l i t y exhibits a maximum at approximately 6.2 K (Fi g . 3.18). Such behaviour can only be accounted for by invoking antiferromagnetic exchange e f f e c t s . Rather long Cu-Cu distances (6.1934(2) and 8.1991(4) A) tend to rule out d i r e c t exchange interactions between metal centres and the presence of pyrazine bridges suggests superexchange through the bridging ligands. F i g . 3.17 Magnetic Moments vs Temperature for Cu(py)„(CH 3S0 3) 2 and Cu(pyz) 2(CH 3S0 3) 2 ^ CSI o < * »4 44" fl fl fl fl O O O O if A Cu(py),(CH 3S0 3) a o' ta fl° • Cu(pyz) 2(CH 3S0 3) 2 0 20 40 60 TEMPERATURE /K 80 1 14 F i g . 3.18 Magnetic S u s c e p t i b i l i t y vs Temperature for C u ( p y z ) 2 ( C H 3 S O 3 ) 2 a) . Two-dimensional model; s o l i d l i n e generated from J=-2.48 cm"1, g=2.15 b) . Linear chain model; s o l i d l i n e generated from J=-3.82 cm"1, g=2.13 a). Two-dimensional model 1 1 1 1 1 I T 1 r 0 20 40 60 80 T E M P E R A T U R E / K 1 15 Magneto-structural correlations have been made for several related copper(II)-pyrazine complexes. P a r t i c u l a r l y relevant are the studies on Cu(pyz) 2(C10„) 2.* 3- 5 2 X-ray crystallography has revealed important structural s i m i l a r i t i e s and differences between Cu(pyz) 2 ( C 1 0 „) 2 and Cu(pyz) 2(CH 3 S 0 3) 2 (Section 3.3.1.3). It was of interest to determine whether these structural c h a r a c t e r i s t i c s were manifested in the magnetic properties of the two compounds. The magnetic s u s c e p t i b i l i t y of Cu(pyz) 2(C10 f t) 2 exhibits a maximum value at 12.1 K5 2 and Darriet et a l . " 3 successfully modelled these data by using Lines' high-temperature series-expansion expression for a two-dimensional square-planar antiferromagnet in the Heisenberg l i m i t . 1 3 6 In general terms, the expression for the magnetic s u s c e p t i b i l i t y i s given by the following: Ng 2? 2 = 3e +f ...Eqn. 3.5 n=l 6 where 0=kT/JS(S+1), g is the Lande g factor, N is the number of spins in the l a t t i c e and the c o e f f i c i e n t s , C n, have been determined for spin S=1/2 for values of n up to 6. For S=l/2 these c o e f f i c i e n t s are as follows: C 1 r 4; C 2, 2.667; C 3, 1.185; C„, 0.149; C 5, -0.191; C 6, 0.001. 1 3 6 The parameters obtained from the f i t of the magnetic s u s c e p t i b i l i t y data to thi s expression for Cu(pyz) 2 ( C 1 0 «) 2 are the exchange coupling constant, J=-5.3 cm"1 and g=2.l07.* 3 Before the si n g l e - c r y s t a l X-ray analysis revealed the two-dimensional nature of Cu(pyz) 2 ( C 1 0 4) 2, the magnetic 116 s u s c e p t i b i l i t y data had been f i t reasonably well to a model based on a tetrameric s t r u c t u r e . 5 2 The small differences between calculated and experimental values for the two models indicate that i t i s not always possible to determine the nature of the polymeric structure merely by the fact that the magnetic s u s c e p t i b i l i t y data are well represented by a p a r t i c u l a r model and emphasises the importance of X-ray structure determination in the study of magneto-structural correlations. Based on the structure of Cu(pyz) 2(CH 3S0 3) 2 the magnetic s u s c e p t i b i l i t y data for t h i s compound were analysed by using the two-dimensional model as represented by Eqn. 3.5. A good f i t between the experimental and calculated s u s c e p t i b i l i t i e s was obtained (the s o l i d l i n e in F i g . 3.18a represents the best f i t ) . The parameters obtained from t h i s f i t are J=-2.48 cm'1 and g=2.l5. These values were obtained from a least-squares f i t t i n g procedure by allowing both J and g to vary u n t i l a minimum value was obtained for the function F (Eqn. 3.6). In this case F i s 0.0118. ...Eqn. 3.6 In Eqn. 3.4, NT is the number of data points, and x° C 31C are the experimental and calculated molar magnetic s u s c e p t i b i l i t i e s , respectively. As measured by the exchange coupling parameter J, the magnitude of the magnetic exchange in the methanesulfonate complex i s approximately one half of that calculated for 1 1 7 Cu(pyz) 2(C10„) 2. Several p o s s i b i l i t i e s exist to explain t h i s r e l a t i v e diminution of J in Cu(pyz) 2(CH 3S0 3) 2. The f i r s t i s that the methanesulfonate anion, by acting as a stronger Lewis base than the perchlorate anion towards copper, e f f e c t i v e l y decreases the a c i d i t y of the copper(Il) ions towards the bridging pyrazine groups and hence, lowers the intralayer exchange interaction. A second al t e r n a t i v e mechanism i s related to the fact that in the, perchlorate derivative the pyrazine groups are equivalent and oriented in a way so as to interact e f f e c t i v e l y with the unpaired electron density on the copper(II) ions, r e s u l t i n g in an equal contribution from each pyrazine ligand to the o v e r a l l exchange interaction. In Cu(pyz)2(CH 3S0 3) 2, however, there are two d i s t i n c t pyrazine ligands and the exchange integral for each bridging pyrazine' i s l i k e l y to be dependent upon two factors: the degree of separation of the two copper ions and the orientation of the pyrazine n—system with respect to the copper d- o r b i t a l s . In Cu(pyz) 2(CH 3S0 3)2, adjacent copper(II) ions are separated by either 6.1934(2) A, when the intervening pyrazine group i s strongly bound in the equatorial plane, or 8.1991(4) A, when the intervening pyrazine group i s weakly bound in an a x i a l p o s i t ion. Considering bond lengths alone, i t would be expected that the shorter the Cu-Cu separation i s , then the greater would be the magnetic exchange e f f e c t . Thus, the equatorially bound pyrazine groups may transmit exchange coupling effects more e f f i c i e n t l y than the a x i a l l y bound pyrazine groups. In Cu(pyz)2(CH 3S0 3) 2, the two d i f f e r e n t orientations of the 118 pyrazine groups with respect to the copper d-orbitals may also play an important role in determining the nature of the exchange interaction. Electronic spectral results (Section 3.3.3.2) combined with the presence of a tetragonally elongated pseudooctahedral environment about copper (Section 3.3.1.3) indicate that the unpaired electron i s in the d 2_ 2 o r b i t a l . x -y Previous research 5* has demonstrated that for copper-pyrazine complexes with t h i s electronic configuration and structure, the magnitude of the antiferromagnetic exchange is determined from the overlap of the d 2_ 2 o r b i t a l and the pyrazine 7r-system. x — y This in t e r a c t i o n , however, i s only possible when the pyrazine ring i s canted out of the xy plane. For example, the pyrazine rings in Cu(pyz) 2(C10„) 2* 3 and Cu(pyz)(N0 3) 2* 2 are canted out of the xy plane by an angle of 66.1. and 50° respectively and s i g n i f i c a n t magnetic exchange interactions are observed. 4 3'* 9 On the other hand, in Cu(pyzA) 2(C10 4) 2 (where pyzA i s pyrazine-2-carboxamide), the pyrazine rings l i e in the xy p l a n e 1 3 7 resulting in orthogonal overlap and a magnetically-dilute system. 1 3 8 These previous studies* 2 -* 3- 1 3 7- 1 3 8 and the X-ray structure result for C u ( p y z ) 2 ( C H 3 S O 3 ) 2 (Section 3.3.1.3) suggest that the equatorially bound pyrazine group in the methanesulfonate compound, which i s canted out of the xy plane by 28.5°, i s suitably oriented to present a w-pathway for magnetic interactions between copper centres. The pyrazine coordinated further away from copper i s oriented in a substantially d i f f e r e n t fashion with respect to 119 the copper d-orbitals than the equatorial pyrazine ligand. The plane of the a x i a l pyrazine ring l i e s in the xz plane of the CuN 20 2 unit; this type of pyrazine ligand orientation has been observed previously in C u ( p y z ) ( h f a c ) 2 5 3 (where hfac i s 1,1,1,5,5,5-hexafluoropentane-2,4-dionate). In spite of the presence of bridging pyrazine ligands no magnetic exchange interactions were observed in t h i s compound.5" It was argued that the only symmetry-allowed overlap between the copper d-orbitals and the pyrazine 7r-system arises from ^ ^ - i K b ^ ) overlap and a combination of the small amount of unpaired spin density in the d o r b i t a l and poor e f f e c t i v e overlap results in xy a poor 7r-pathway for magnetic exchange. The st r u c t u r a l s i m i l a r i t i e s between the pyrazine ligand in Cu(pyz)(hfac) 2 and the a x i a l l y bound pyrazine group in Cu(pyz) 2(CH 3S0 3) 2 suggest that t h i s group may also be i n e f f e c t i v e in propagating magnetic exchange interactions. The comparison of the pyrazine group orientations in Cu(pyz) 2 (CH 3S0 3) 2 with those in other copper(II)-pyrazine complexes suggests that the magnetic exchange interaction in the methanesulfonate derivative proceeds via two d i f f e r e n t routes, with the exchange interaction through the equatorially bound pyrazine, J f iq, proposed to be s i g n i f i c a n t l y stronger than the exchange, J _ v , through the pyrazine bound in the a x i a l position. In the extreme case where J >>J_„ r the magnetic properties may eq ax be more closely represented by a one-dimensional linear chain model. A model has been proposed for the analysis of the magnetic s u s c e p t i b i l i t y of a Heisenberg linear chain for S=1/2 1 20 ions. H a l l 1 3 9 and H a t f i e l d 1 * 0 developed the model proposed by Bonner and F i s h e r ; 1 * 1 t h i s resulted in an expression for the molar s u s c e p t i b i l i t y of a l i n e a r chain of interacting S=l/2 spins as a polynomial expansion: = Nq 2ff 2 r xm kT 0.250+0.14 995x-1+0.30094x-2 .Eqn. 3.7 1 + 1 .9862X" 1+0.68854x- 2 + 6.0626x" 3_ where x=kT/|J|. The best f i t of the data for Cu(pyz) 2(CH 3S0 3) 2 to this expression i s equally as good as the best f i t to the two-dimensional model; for the one-dimensional model the parameters obtained from the best f i t are J=-3.82 cm"1 and g=2.13, with F=0.0118. The best f i t i s represented by the s o l i d l i n e in F i g . 3.18b. The data for Cu(pyz) 2(C10 4) 2, however, gave a f i t to the one-dimensional model which was poorer (F=0.0460) than that for the two-dimensional model, as expected on the basis of the equivalent pyrazine ligands present in this compound. From these observations the methanesulfonate compound may be considered as consisting of linear chains of -Cu-pyz-Cu-units, in which there are r e l a t i v e l y strong intrachain magnetic exchange interactions and although these l i n e a r chains are crosslinked through the weakly bound a x i a l pyrazine groups the interchain interactions appear to be of a much smaller magnitude. The results provided in t h i s section demonstrate that there are s i g n i f i c a n t differences between the magnetic properties of the complexes studied. The tetrakis(pyridine) and 121 tetrakis(pyrazine)copper(II) complexes are magnetically d i l u t e as i s consistent with their monomeric (non-bridged) structures involving i s o l a t e d CuNfl02 chromophores. Cu(pyz) 2 (CH 3S0 3) 2 has two d i s t i n c t types of bridging pyrazine groups one of which may be oriented in such a way so as to provide a more ef f e c t i v e overlap with the d 2 2 o r b i t a l of copper and hence be more x y e f f i c i e n t in propagating magnetic exchange interactions. The magnetic s u s c e p t i b i l i t y data are well represented by a two-dimensional model in spite of the inequivalence of the bridging pyrazine ligands. The data are also well represented by a li n e a r chain model which may present a more r e a l i s t i c picture of the exchange interaction being along one unique d i r e c t i o n of the two-dimensional material. 3.3.4.2 Magnetic s u s c e p t i b i l i t y results for complexes containing an FeN„0 2 chromophore Magnetic s u s c e p t i b i l i t y data for the tetrakis(pyridine) and b i s ( p y r a z i n e ) i r o n d l ) sulfonate complexes are presented in Appendix IX, Part A. The magnetic s u s c e p t i b i l i t i e s for Fe(2-mepyz)„(CH 3S0 3) 2 (Appendix IX, Part A) are also discussed in t h i s section. The magnetic moment data for the Fe(py),(RS0 3) 2 complexes and Fe(2-mepyz) f t(CH 3S0 3) 2 a l l show a si m i l a r temperature dependence. At room temperature the magnetic moment values for these complexes are in the range of 5.2-5.4 B.M. which is consistent with their formulation as high-spin i r o n d l ) compounds. The magnetic moment values remain f a i r l y constant as 122 the temperature i s decreased and i t i s not u n t i l below 15 K that a more s i g n i f i c a n t decrease in n e f f i s observed. The magnetic moment temperature dependencies for the Fe(py)„(RS0 3) 2 complexes are shown in F i g . 3.19. Fi g . 3.19 Magnetic Moments vs Temperature for Fe(py)„(RS0 3) 2 Complexes 5.6-4.8- o 8 DD LLI ?4.8-| LU5.6-< 4.8-^5 o 6 o <§> o oco do ns O O ° ° ° O-R=CR 4 ^oouu a fliPu un ° ° Q 2 9 Q  R = p-CH 3 C 6 H 4 v 9 o <p o ooo cn o o © o o o o _ R=CH-T 1 1 r ~i 1 1 r T r 0 100 200 TEMPERATURE / K 300 123 For these complexes, the observed temperature dependence of u-e£f may arise from a combination of several factors. A temperature-dependent magnetic moment i s expected for F e 2 + c compounds (d 6) with a t r i p l y degenerate T^g ground state. Small z e r o - f i e l d s p l i t t i n g effects may also be invoked to explain such a temperature dependence. The X-ray st r u c t u r a l data for the Fe(py)„(RS0 3) 2 complexes show the paramagnetic centres well isolated from each other. Hence, the small decrease in ^ett. a t i o w temperatures i s unlikely to be associated with any magnetic exchange e f f e c t s . Further indirect evidence in support of the magnetically d i l u t e nature of these iron complexes comes from the results presented in the preceeding section which indicate the absence of magnetic interactions in the analogous copper complexes. For the monomeric Fe(py)«(RS0 3) 2 complexes, no magnetic concentration was expected and the temperature dependence of f-ei\£ f° r Fe(2-mepyz) f t(CH 3S0 3) 2 (similar to that observed for Fe(py) i, (CH 3S0 3) 2) indicates that the 2-methylpyrazine ligand coordinates in a terminal unidentate mode resulting in a monomeric species. Bridging 2-methylpyrazine groups may be expected to give r i s e to magnetic exchange e f f e c t s . The magnetic properties of the Fe(py)„(RS0 3) 2 complexes studied are proposed to arise from single-ion e f f e c t s and hence, the magnetic moment data were analysed by two d i f f e r e n t methods which take into account such phenomena. The f i r s t method was i n i t i a l l y proposed by Figgis and Lewis 6* and simultaneously developed by Konig and Chakravarty. 1" 2 The Figgis model has been 124 applied to a number of transition-metal complexes 6"' 1 , 3 " H j and the approach used may be i l l u s t r a t e d by high-spin i r o n d l ) 5 compounds having a T2g 9 r o u n ^ term. The model involves 5 simultaneous perturbation of the 15-fold degenerate Tjg basis set by the effects of spin-orbit coupling and an a x i a l l y symmetric l i g a n d - f i e l d d i s t o r t i o n (either tetragonal or t r i g o n a l ) . The temperature dependence of the magnetic moment i s analysed in terms of three parameters. F i r s t l y , the a x i a l - d i s t o r t i o n parameter A (sometimes c a l l e d 3Ds). This i s 5 5 the separation between the °2q a n c^ E g s t a t e s a r i s i n g from the cubic f i e l d ground state, in the presence of an a x i a l l y symmetric ligand f i e l d (Fig. 3.13). A positive value of A 5 corresponds to the o r b i t a l l y non-degenerate B 2g state lying lowest. . The spin-orbit coupling constant, X, i s the second parameter and, in complexes, i t s value i s expected to be reduced somewhat below the free-ion value of -100 cm - 1. 1* 7 The t h i r d parameter i s the o r b i t a l reduction factor, K . This variable allows for electron d e l o c a l i s a t i o n from the t 2 g o r b i t a l set. The F i g g i s model has several drawbacks which have been previously pointed out. F i r s t l y , i t i s d i f f i c u l t to unambiguously determine the sign of A from magnetic s u s c e p t i b i l i t y data obtained on powdered p o l y c r y s t a l l i n e samples. In fact, Gregson and M i t r a 1 " 8 contend that the measurement of the average magnetic s u s c e p t i b i l i t y i s incapable of giving r e l i a b l e results for either A or K and that measurements on single c r y s t a l s are required to deduce meaningful values for these l i g a n d - f i e l d parameters. Another 125 shortcoming of the model has been pointed out by F i g g i s : 1 * 9 the relationship between observed n values and the electronegativity and 7r-bonding c h a r a c t e r i s t i c s of various ligands i s unclear. The following method was used to f i t the magnetic moment data for the Fe(py)„(RS0 3) 2 complexes to this model. Figgis et a_l. 6* have tabulated magnetic moment data as a function of A/X and K; in the present study, these data were used to produce plots of » * e f f a s a function of kT/X which were then compared vi s u a l l y with the experimental data. The best f i t s between calculated and experimental data are obtained by using the parameter values given in Table 3.5 and the best f i t s are represented by the s o l i d l i n e s in F i g . 3.19. While reasonable f i t s are obtained in the temperature region of 25-300 K, care must be taken not to place too much emphasis on interpreting these parameter values, due to the inherent l i m i t a t i o n s of the model. At temperatures below 25 K the agreement betweeen experimental and calculated magnetic moment values is not as good and thi s i s not unexpected because the model ignores z e r o - f i e l d s p l i t t i n g e f f e c t s which may be s i g n i f i c a n t for F e 2 + under these conditions. 126 Table 3.5 Crystal F i e l d Parameters for Fe(py)„(RS0 3) 2 Complexes R A/cm'1 X /cm"1 K CF 3 600 -80 1.0 CH3 700 -70 0.7 p-CH 3C 6H„ 600 -60 0.8 As mentioned above, the information contained in magnetic s u s c e p t i b i l i t y data from powdered p o l y c r y s t a l l i n e samples i s i n s u f f i c i e n t to determine the sign of A unambiguously. Interpretation of the Mossbauer spectral data (Section 3.3.5.1), however, suggests strongly that-the ground state in each of the tetrakis(pyridine)iron(11) sulfonate species must be nondegenerate. Hence, only positive values of A were considered when f i t t i n g the magnetic moment data. From the values of A in Table 3.5, i t appears that the a x i a l d i s t o r t i o n s are of approximately the same magnitude in a l l three cases. The values of X are, as expected upon complex formation, reduced from the free-ion value of -100 cm"1. For the methanesulfonate derivative, X and K are reduced by corresponding amounts which is c l e a r l y fortuitous as such a correlation does not exist in the other two cases. 1 27 The second model considers z e r o - f i e l d s p l i t t i n g . This phenomenon, results when spin-orbit coupling induces mixing in of higher energy leve l s and leads to p a r t i a l removal of the ground-state degeneracy and thus to a temperature-dependent magnetic moment. Spin-orbit coupling has the ef f e c t of p a r t i a l l y l i f t i n g the degeneracy of the M levels (Fig. 3.20). F i g . 3.20 Zero-Field S p l i t t i n g for High-spin I r o n d l ) i ±2 i i i i i i i i i i i 1 28 The r e l a t i v e energies of the three z e r o - f i e l d levels of 0, D and 4D are shown for a posit i v e value of D. The l e v e l sequence i s reversed where D i s less than zero. When the z e r o - f i e l d s p l i t t i n g parameter i s non-zero and posit i v e and the magnitude of D i s of the order of kT, then as the sample temperature is decreased the Ms=±2 and Ms=±1 levels are depopulated and th i s is manifested in a decrease in the magnetic moment. In the present study, the a x i a l z e r o - f i e l d s p l i t t i n g parameter D, and the g values were found by least-squares f i t s of the temperature dependence of the molar magnetic s u s c e p t i b i l i t y to the following expression: 1 5 0 * = C ^'"-Be-4* f ( 1-e-») * 3-*x(e-*-e-4") l*2e-*+2e-ix = ° 1 * 2 e - x + 2 e - 4 x ...Eqn. 3.8 where x=D/kT, C=Ng202/kT and x p=i ( X,/ + 2xJ/3 ] . When isotropic g values are used i t was found that the minima in the f i t t i n g function, F, are shallow, making i t d i f f i c u l t to obtain unique values of g , g and D. When isotropic g values are employed, an approach used previously by Klein e_t a l . , 15 0 the minima in F are steeper and g and D values were obtained and are shown in Table 3.6. The s o l i d l i n e in Fi g . 3.21 represents the best f i t of this model to the magnetic s u s c e p t i b i l i t y data for F e ( p y ) « ( C H 3 S O 3 ) 2 . 129 Table 3.6 Zero-Field S p l i t t i n g Parameters COMPOUND D/cnr 1 g;«o F F e ( p y ) a ( C F 3 S 0 3 ) 2 6.1 2.15 0.0076 Fe(py)«(CH 3S0 3) 2 3.4 2.08 0.0122 Fe(py)„(p-CH 3C 6HflS0 3) 2 3.9 2.09 0.0108 Fe(pyz) 2(CF 3S0 3) 2-CH 3OH 14.5 2.11 0.0353 Fe(pyz) 2(CH 3S0 3) 2 13.5 2.03 0.0354 Fig. 3.21 Magnetic S u s c e p t i b i l i t y vs Temperature for Fe(py),(CH 3S0 3) 2 O „ G 600H E L J \ o X £400H i r — ( CD y— CL CO CO LU ID < 200-0-Z e r o - f i e l d s p l i t t i n g model; s o l i d l i n e generated from D=3 . 4 cm"1, g=2.08 0 40 80 T E M P E R A T U R E / K 120 130 Information contained in the powder magnetic s u s c e p t i b i l i t y data is i n s u f f i c i e n t to determine the sign of D and equally good f i t s are obtained using either positive or negative D values. The value of D i s largest for the t r i f l a t e derivative and somewhat smaller, for the p-tosylate and methanesulfonate compounds. Previously the z e r o - f i e l d s p l i t t i n g parameter has been approximated from the following e x p r e s s i o n : 1 5 1 D = i - i - ...Eqn 3.9 16 E( 5E)-E( 5B) Thus, the magnitude of the z e r o - f i e l d s p l i t t i n g i s expected to 5 5 be inversely proportional to the separation of the E^ and B 2g 5 states (arising from the T2g ground state) and proportional to the square of the single-electron spin-orbit coupling constant, £. The magnitude of the D values in Table 3.6 indicates that 5 5 the separation of the Eg and B 2g states i s smallest for the t r i f l a t e d erivative and of a comparable magnitude in the other two cases. This i s in contrast to the Figgis model where the ax i a l d i s t o r t i o n parameter, A, was found to be approximately the same in a l l three cases. To summarise, the magnetic properties of the Fe(py)«(RS0 3) 2 complexes and of Fe(2-mepyz)«(CH 3S0 3) 2 are consistent with their formulation as high-spin i r o n d l ) compounds. The temperature dependence of M e£f arises from single-ion e f f e c t s . There is no evidence for magnetic concentration, t h i s being e n t i r e l y consistent with their monomeric molecular nature. These complexes then serve as a baseline from which magnetic exchange 131 ef f e c t s in the related bis(pyrazine) derivatives were measured. The magnetic properties of the bis(pyrazine) complexes ( F e ( p y z ) 2 ( C F 3 S 0 3 ) 2 . C H 3 O H and Fe(pyz) 2(CH 3S0 3) 2) are s i g n i f i c a n t l y d i f f e r e n t from those of the Fe(py)„(RS0 3) 2 compounds. The differences are not s i g n i f i c a n t at room temperature, where the magnetic moment values for the tetrakis(pyridine) and b i s ( p y r a z i n e ) i r o n d l ) compounds are very similar (within the range of 5.1-5.4 B.M.), indicative of the high-spin nature of the complexes. The bis(pyrazine) complexes, however, exhibit much stronger temperature dependencies in their M e f f . v a l u e s than do the tetrakis(pyridine) complexes and at l i q u i d helium temperatures the magnetic moments for the two groups of compounds diverge by about 1.3 B.M. A comparison of the temperature dependence of magnetic moment data for Fe(pyz)2(CH 3S0 3) 2 and Fe(py)„(CH 3S0 3) 2 i s shown in F i g . 3.22. A similar comparison can be made for the bis(pyrazine) and tetrakis(pyridine) t r i f l a t e derivatives (Appendix IX, Part A). Unlike Cu(pyz) 2(CH 3S0 3) 2, the bis(pyrazine)iron(II) species exhibit no maxima in t h e i r magnetic s u s c e p t i b i l i t y versus temperature plots down to 4.2 K, and hence, no conclusive evidence for antiferromagnetic exchange interactions in the iron complexes can be obtained from the X m versus temperature p l o t s . Comparing bis(pyrazine) to tetrakis(pyridine) complexes, the greater temperature dependence of the magnetic moment data for the former group may aris e from either weak antiferromagnetism or a larger z e r o - f i e l d s p l i t t i n g e f f e c t . Further support for t h i s conclusion i s provided by the fact that 132 the Figgis model, which provides a satis f a c t o r y f i t for the magnetic properties of the tetrakis(pyridine) compounds, proves to be e n t i r e l y unsatisfactory for the bis(pyrazine) derivatives. The parameters t r i e d are quite incapable of reproducing the observed magnetic moment behaviour. The experimental "gff values are always substantially below any values which the model generates. The unsatisfactory r e s u l t s for the bis(pyrazine) compounds gives further support for the proposal that z e r o - f i e l d and/or magnetic exchange effects play a s i g n i f i c a n t role in determining th e i r magnetic properties. F i g . 3.22 Magnetic Moments vs Temperature for Fe(py)«(CH 3S0 3) 2 and Fe(pyz) 2(CH 3S0 3) 2 ^5.0-i— L U O 4.0-< 3.0-& o o o o o o O A . A A A A A A A A o o ° o o ° o A A A A * 0 • Fe(py) l l(CH 3S0 3) 2 A Fe(pyz) 2(CH 3S0 3) 2 I I I 50 100 TEMPERATURE /K 150 133 To take into account z e r o - f i e l d e f f e c t s , the model which was used previously to analyse the magnetic properties of the tetrakis(pyridine) complexes was applied to the bis(pyrazine) compounds. The parameters obtained from the least-squares f i t s are given in Table 3.6. For Fe(pyz) 2(CF 3S0 3) 2.CH 3OH the. best f i t of the data is shown in F i g . 3.23. F i g . 3.23 Magnetic S u s c e p t i b i l i t y vs Temperature for Fe(pyz) 2(CF 3S0 3) 2.CH 3OH Zero-f i e l d s p l i t t i n g model; s o l i d l i n e generated from D=14.5 cm'1, g=2.11 0 100 200 300 TEMPERATURE / K 1 34 To reproduce the magnetic s u s c e p t i b i l i t y data of the bis(pyrazine) complexes i t i s necessary to employ a s i g n i f i c a n t l y larger D value than that used for the analogous tetrakis(pyridine) complexes. It should be noted that using t h i s model results in a rather poorer f i t , as measured by the value of F, for the bis(pyrazine) complexes, compared to the F values for their tetrakis(pyridine) analogues. The t h i r d model chosen to represent the magnetic properties of the bis(pyrazine) complexes i s the Lines' two-dimensional model. This model was discussed previously (Section 3.3.4.1) when applied to the magnetic properties of the two-dimensional complex, C u ( p y z ) 2 ( C H 3 S O 3 ) 2 • The choice of this model was thought to be appropriate based upon the proposed two-dimensional layer structure of these bis(pyrazine) compounds and the p o s s i b i l i t y that weak magnetic interactions may be propagated via the bridging pyrazine ligand. By substituting the following c o e f f i c i e n t s 1 3 6 into Eqn. 3.5 the model can be applied to S=2 systems; C,, 4; C 2, 1.500; C 3, 0.252; C , 0.258; C 5, 0.124; C 6, 0.015. Excellent agreement between calculated and experimental data was obtained by using t h i s model using the following parameter values: -J/cm-1 9 F F e ( p y z ) 2 ( C F 3 S O 3 ) 2 . C H 3 O H 0.20 2. 16 0.0122 Fe(pyz) 2(CH 3S03 ) 2 0.18 2.07 0.0143 135 The best f i t of the data for the methanesulfonate complex i s shown as the s o l i d l i n e in F i g . 3.24. Fig . 3.24 Magnetic S u s c e p t i b i l i t y vs Temperature for F e ( p y z ) 2 ( C H 3 S O 3 ) 2 Two-dimensional model; s o l i d l i n e generated from J=-0.18 cm"1, g=2.07 1 36 The small negative values of J indicate that i f exchange interactions are present they are of a weak antiferromagnetic nature. The treatment of the magnetic properties of the bis(pyrazine) compounds by using the two-dimensional and the z e r o - f i e l d s p l i t t i n g models, together with the parameters from the z e r o - f i e l d s p l i t t i n g model for the tetrakis(pyridine) complexes, provide a rationale for the di f f e r e n t magnetic properties of the two groups of compounds. Both groups have an FeN.j,02 chromophore and would be expected to possess similar single-ion e f f e c t s , r e s u l t i n g in similar D values. However, treating the bis(pyrazine) complexes using the z e r o - f i e l d s p l i t t i n g model only, and ignoring magnetic exchange e f f e c t s , generates D values which we believe are u n r e a l i s i c a l l y large compared to those for the tetra k i s ( p y r i d i n e ) complexes. Ignoring z e r o - f i e l d s p l i t t i n g e f f e c t s , and treating the bis(pyrazine) complexes using the two-dimensional magnetic exchange model, generates better f i t s to experiment than for the z e r o - f i e l d s p l i t t i n g model, giving strong support to the conclusion that weak exchange e f f e c t s are present in these complexes. Therefore, i t i s proposed that the differences in the magnetic properties of the two groups are most l i k e l y a consequence of the major str u c t u r a l difference between the two groups; i . e . , the presence of bridging pyrazine ligands in the pyrazine compounds. Such groups could provide a suitable pathway for antiferromagnetic exchange coupling, as in the copper complex discussed above. 137 3.3.4.3 Magnetic s u s c e p t i b i l i t y results for complexes containing an FeN,X2 chromophore The results of the magnetic measurements are tabulated in Appendix IX, Part A. The magnetic moment data for the three b i s ( p y r a z i n e ) i r o n d l ) halide derivatives are i l l u s t r a t e d in Fi g . 3.25. F i g . 3.25 Magnetic Moments vs Temperature For Fe(pyz) 2X 2 Complexes 5.5-4.5-2I5.5H CO L U o 4.5-o 5.5H < 4.5-0 O 0 0 o o o o ° o o ° x~=cr 0 o o 0 oo o ° ° ° ° o o o X"=Br_ oo=°° o o 0 o 0 0 0 o o x"=r 100 200 TEMPERATURE / K 300 138 The chloro- and bromo species have magnetic moments which remain f a i r l y constant down to approximately 50 K and then decrease more s i g n i f i c a n t l y , especially at temperatures less than 20 K. At room temperature the magnitudes of the magnetic moments follow the order I>Br>Cl and of the three compounds F e ( p y z ) 2 I 2 exhibits the largest temperature dependence, the magnetic moment plot passing through a broad maximum at approximately 160 K before f a l l i n g to 4.2 B.M. at 4.2 K. The magnetic s u s c e p t i b i l i t y versus temperature plot for each of the three compounds implies Curie-Weiss behaviour and the absence of a maximum in this plot indicates a lack of strong magnetic exchange interactions. Magnetic moments for Fe(pyz) 2Br 2 and the monohydrate, Fe(pyz) 2C1 2 .H20 have been measured at room temperature (Gouy technique) by other researchers. 6 2 For Fe(pyz) 2C1 2.H 20, 6 2 a room temperature magnetic moment of 4.7 B.M. was reported. Whilst in the present study for F e ( p y z ) 2 C l 2 , a considerably higher value of 5.20 B.M. is found at room temperature. The bromide 6 2 was found to have a room temperature moment of 4.4 B.M. which does not compare well with the value of 5.3 B.M. obtained in this study. Ferraro et a _ l . 6 2 surmised that the low magnetic moment value was a result of magnetic exchange interactions, but from the more extensive data set obtained here t h i s appears u n l i k e l y . The reason for the large discrepancy for the room temperature magnetic moment of Fe(pyz) 2Br 2 i s not f u l l y understood, but i t appears that the Gouy measurements of Ferarro et a _ l . 6 2 were not corrected for any packing errors. On the 139 other hand, in the present study, packing errors were found to be no more than 5%, a possible source of error too small to account for the disagreement. The temperature dependence of the magnetic moments for the b i s ( p y r a z i n e ) i r o n d l ) halides may be compared with data obtained by other researchers for the tetra k i s ( p y r i d i n e ) complexes, investigated over the temperature range 20-300 K.6 7 The results show a similar temperature dependence for both groups of compounds; i . e . , for the Fe(py)«X 2 compounds, the magnetic moment remains f a i r l y constant from room temperature down to 60 K. Below t h i s temperature, a sl i g h t decrease in magnetic moment is observed. Compared to the magnetic properties of the bis(pyrazine) and t e t r a k i s ( p y r i d i n e ) i r o n d l ) sulfonate derivatives, much smaller differences are found for the analogous halide complexes. The implication i s that magnetic exchange interactions, i f present at a l l , are of an extremely weak nature in the bis(pyrazine)iron(11 ) halide complexes. A similar conclusion was reached for the c o b a l t ( I I ) 5 8 and n i c k e l ( I I ) 3 7 pyrazine halide derivatives. The r e s u l t s of the magnetic s u s c e p t i b i l i t y measurements for Fe(pyz) 2(C10«) 2 and Fe(pyz)„(AsF 6) 2.2H 20 (Appendix IX, Part A) also indicate a lack of strong magnetic exchange e f f e c t s . Both complexes exhibit a magnetic moment which decreases with decreasing temperature. No maximum i s observed in the s u s c e p t i b i l i t y data; thus, magnetic exchange interactions in both compounds are, at most, weak. This may be expected for Fe(pyz)4(AsF 6) 2.2H 20 as spectroscopic evidence indicates 140 monodentate p y r a z i n e l i g a n d s . Magnetic exchange i n t e r a c t i o n s might be expected i n the p e r c h l o r a t e complex; s p e c t r o s c o p i c evidence suggests a s t r u c t u r e which i s s i m i l a r t o that of the copper a n a l o g u e 0 3 and, i f t h i s i s the case, then magnetic exchange may be expected through the b r i d g i n g p y r a z i n e groups. If exchange i n t e r a c t i o n s are present i n F e ( p y z ) 2 ( C 1 0 « ) 2 , i t i s c l e a r that they are s u b s t a n t i a l l y weaker than i n the copper d e r i v a t i v e . These r e s u l t s i n d i c a t e the l a c k of any s u b s t a n t i a l magnetic i n t e r a c t i o n s through p y r a z i n e i n a number of F e ( p y z ) 2 X 2 complexes. On the other hand, t h i s c l e a r l y does not apply g e n e r a l l y to p y r a z i n e - b r i d g e d i r o n d l ) complexes, as i l l u s t r a t e d by the magnetic moment data f o r F e ( p y z ) 2 ( N C S ) 2 . The r e s u l t s of the magnetic measurements f o r F e ( p y z ) 2 ( N C S ) 2 are given i n Appendix IX, Part A and a p l o t of magnetic moment versus temperature i s shown i n F i g . 3.26. The magnetic moment shows a l a r g e temperature dependence, f a l l i n g m o n o t o n i c a l l y from a value of 5.2 B.M. at room temperature, to 4.8 B.M. at 50 K, and then decreasing more r a p i d l y to 1.87 B.M. at 4.2 K. T h i s behaviour i s almost c e r t a i n l y due to the presence of a n t i f e r r o m a g n e t i c i n t e r a c t i o n s , a f a c t more c l e a r l y r e v e a l e d by a maximum i n the magnetic s u s c e p t i b i l i t y p l o t at approximately 8.0 K ( F i g . 3.27). 141 F i g . 3.26 Magnetic Moment vs Temperature for Fe(pyz) 2(NCS) 2 5.0H C D 4.0H < 2.0H I 0 —1 . | 1 1 r 40 80 TEMPERATURE /K 120 F i g . 3.27 Magnetic S u s c e p t i b i l i t y vs Temperature for Fe(pyz) 2(NCS) 2 •r^ Two-dimensional model; s o l i d l i n e generated from J=-0.44 cm"1, g=2.2l 5160-v120-CD Sh 80H ZD oo 40-i — * h -LU < 2: 0- -1 ' 1 1 i -40 80 TEMPERATURE / K 120 1 4 2 Magnetic s u s c e p t i b i l i t y data i n the temperature range 80-300 K have been r e p o r t e d p r e v i o u s l y 6 4 f o r t h i s complex. The agreement between the r e p o r t e d data and those obtained i n the present study i s poor. Magnetic s u s c e p t i b i l i t y data reported here were recorded over the temperature range 4.2-300 K on two separate occasions u s i n g two independently prepared samples of F e ( p y z ) 2 ( N C S ) 2 . The agreement between each of the data s e t s was e x c e l l e n t . The reason f o r poor agreement between the data obtained here and those obtained p r e v i o u s l y i s not understood; however, i n the e a r l i e r s t u d y , 6 " n e i t h e r the method of p r e p a r a t i o n nor any a d d i t i o n a l s p e c t r o s c o p i c data were r e p o r t e d . T h i s lack of i n f o r m a t i o n makes a comparison with the complex prepared i n t h i s study impossible, which i s u n f o r t u n a t e . I t appears l i k e l y t h a t the two complexes, as w e l l as p o s s e s s i n g d i f f e r e n t magnetic p r o p e r t i e s , probably have d i s t i n c t i v e s p e c t r o s c o p i c p r o p e r t i e s a l s o . The magnetic p r o p e r t i e s , r e p o r t e d here, are q u i t e d i f f e r e n t from those of the analogous t e t r a k i s ( p y r i d i n e ) c o m p l e x . 1 5 2 For Fe(py)«(NCS) 2, ^ e f f s n o w s only a s l i g h t temperature dependence; however, magnetic measurements on t h i s compound have been l i m i t e d to temperatures above 90 K. A comparison suggests that the presence of b r i d g i n g p y r a z i n e l i g a n d s r e s u l t s i n the d i s t i n c t i v e magnetic p r o p e r t i e s of F e ( p y z ) 2 ( N C S ) 2 . S e v e r a l other t h i o c y a n a t e complexes of i r o n d l ) , a l s o e x h i b i t unusual magnetic phenomena: F e ( p y ) 2 ( N C S ) 2 7 1 " 7 3 undergoes a metamagnetic t r a n s i t i o n at approximately 6 K to a one-dimensional f e r r o m a g n e t i c a l l y ordered s p e c i e s and the magnetic 143 s u s c e p t i b i l i t y plot of Fe(bpy)(NCS)2 1 5 3' 1 5 * (where bpy is 2,2'-bipyridine) shows a maximum at 18 K. It i s proposed that the magnetic exchange interactions in these two cases take place through the bridging thiocyanate network. For Fe(pyz) 2(NCS) 2, however, spectroscopic evidence, in pa r t i c u l a r infrared data (Section 3.3.2.2), suggests strongly terminal unidentate anions and a bridging pyrazine network resulting in a two-dimensional l a t t i c e . If Fe(pyz) 2(NCS) 2 exists in thi s s t r u c t u r a l form, i t is reasonable to assume that the bridging pyrazine groups are responsible for the observed magnetic ef f e c t s rather than superexchange through the anion. As suggested by the proposal of a two dimensional structure, the magnetic s u s c e p t i b i l i t y data were analysed in terms of the Lines' model (as described in Section 3.3.4.2). The best f i t was obtained by using the parameters: J=-0.44 cm - 1 and g=2.2l, (F=0.0221). This f i t is represented by the s o l i d l i n e in Fig 3.27. The calculated and experimental values do not correspond very closely in the region of the s u s c e p t i b i l i t y maximum and the parameters obtained from the f i t are, at best, semi-quantitative and should be viewed with caution. This may be att r i b u t e d to inadequacies in the model for high-spin i r o n d l ) complexes. The model describes the nearest-neighbour interactions between iron centres in the iso t r o p i c Heisenberg l i m i t and i t i s usually not possible to represent the magnetic properties of i r o n d l ) compounds accurately by either the pure iso t r o p i c or the anisotropic Ising model. There has been no solution developed for a two-dimensional Ising model applicable 144 to spin S=2. As well as neglecting z e r o - f i e l d s p l i t t i n g e f f e c t s , the model also ignores any extended three-dimensional interactions which are not ne g l i g i b l e in Fe(pyz) 2(NCS) 2, especially at temperatures below 8 K, as indicated by the low-temperature Mossbauer data (Section 3.3.5.3). Magneto-structural correlations previously reported for Fe(trz) 2(NCS) 2 (where trz is 1,2,4-triazole, see F i g . 3.28) are relevant to these studies on Fe(pyz) 2(NCS) 2. F i g . 3.28 1,2,4-Triazole Powder d i f f r a c t i o n s t u d i e s 1 5 5 have shown the t r i a z o l e complex to be isomorphous with C o ( t r z ) 2 ( N C S ) 2 1 5 6 which exists as a two-dimensional sheet-like polymer, formed by the t r i a z o l e ligand using nitrogen atoms N(2) and N(4) to bridge adjacent metal centres. The thiocyanate groups are N-bonded in a x i a l positions to complete the MN6 chromophore. A similar structure i s proposed for Fe(pyz) 2(NCS) 2. For the t r i a z o l e compound, powder s u s c e p t i b i l i t y d a t a 1 5 5 reveal a maximum at a temperature of 8.8 K while s i n g l e - c r y s t a l measurements 1 5 7 reveal a maximum in the s u s c e p t i b i l i t y at 12.2 K. In the present study, the N N H / 145 G magnetic s u s c e p t i b i l i t y data for the pyrazine-bridged species show a maximum at a temperature of approximately 8.0 K. The s i m i l a r i t y in these two sets of magnetic data indicates that pyrazine and 1,2,4-triazole propagate magnetic exchange effects to about the same degree in both complexes. It i s useful to summarise the results for the bis(pyrazine) halide and thiocyanate complexes. The magnetic properties of the b i s ( p y r a z i n e ) i r o n d l ) halide complexes are similar to those of the analogous tetrakis(pyridine) derivatives. It is concluded that in complexes of thi s type pyrazine i s a poor ligand for propagating magnetic exchange interactions, however, in Fe(pyz) 2(NCS) 2, the neutral ligand i s shown to be e f f e c t i v e in propagating magnetic interactions. As a result, the magnetic properties of Fe(pyz) 2(NCS) 2 are substantially d i f f e r e n t from those of the monomeric Fe(py),(NCS) 2 compound. From these results, i t appears that the nature of the anionic ligand (for example, a- and jr-donor properties) may play a role in influencing the strength of the superexchange interaction through the neutral ligand. Changes in pyrazine ligand orientation and interlayer separation also have an effect upon the magnetic exchange interactions and X-ray structural results are necessary before these e f f e c t s can be investigated. It would be worthwhile to investigate further magneto-structural correlations in M(pyz) 2(NCS) 2 compounds by choosing M to be either Cu or Mn. In the present study, the cyanate derivative Fe(pyz)2(NCO) 2 was not isola t e d . Further attempts should be made to isol a t e t h i s complex as i t s magnetic properties may also 146 provide for an interesting comparison with the results reported in the present study. 147 3.3.5 Mossbauer Spectroscopy Two parameters routinely measured in a Mossbauer experiment are the isomer s h i f t , 6, and the quadrupole s p l i t t i n g , AE . Before the Mossbauer spectra of the complexes prepared in the present study are discussed, a brief summary of the interactions responsible for isomer s h i f t and quadrupole s p l i t t i n g and their chemical interpretation i s worthwhile. 1 5 8 The isomer s h i f t arises from the e l e c t r o s t a t i c interaction between charge density at the nucleus and those electrons which have a f i n i t e p r o b a b i l i t y of being located in the region of the nucleus, i . e . , the s-electrons. During a nuclear 7 - t r a n s i t i o n the e f f e c t i v e nuclear size usually changes, thereby s l i g h t l y a l t e r i n g the nucleus-electron interaction energy. Assuming spherical electron d i s t r i b u t i o n , t h i s interaction does not lead to a s p l i t t i n g of nuclear energy leve l s but results in a s h i f t in energy which, in general, i s d i f f e r e n t for the source and absorber. It i s this difference in r e l a t i v e energies between source and absorber which i s the isomer s h i f t (Fig. 3.29). An expression which relates the isomer s h i f t to nuclear and electronic factors i s : 6=5jrZe 2r 2(6r/r[ |^/ s(0) A| 2 - | ^ / s ( 0 ) B | 2] ...Eqn. 3.10 where Z is the atomic number, e i s the positive elementary charge, r is the mean nuclear radius, 6r=r e~rg, (the difference in nuclear r a d i i of the excited and ground states respectively) and l'/' s(0) A| 2 and l ^ s ( 0 ) B | 2 are the s-electron densities at the 148 nucleus for source and absorber respectively. F i g . 3.29 Isomer Sh i f t and Quadrupole S p l i t t i n g m. ±3/2 1=3/2 1 = 1/2 Q.S. ±1/2 ±1/2 ISOMER SHIFT QUADRUPOLE SPLITTING 1 49 The isomer s h i f t i s dependent upon two factors: a nuclear factor which i s constant for any given nuleus and a factor which arises from the s-electron density at the nucleus. If |^ ( 0 ) . | 2 is 5 A kept constant by using the same source, then the isomer s h i f t w i l l be proportional to the s-electron density at the absorber nucleus. In the case of 5 7 F e , the nucleus expands as i t emits a 7~ray in going from the excited to ground state and hence, 6r/r is negative, and therefore, an increase in s-electron density leads to a decrease in isomer s h i f t . Since p- and d-electrons can exert a screening effect on the s-electrons, changes in p-and d - o r b i t a l occupancy influence the isomer s h i f t by e f f e c t i v e l y a l t e r i n g the s-electron density at the nucleus. This screening effect is c l e a r l y seen from the range of 6 values for high-spin iron compounds. Iron(III) compounds, d 5, have isomer s h i f t s in the range 0.2-0.6 mm s" 1, while iron(II) compounds, d 6, have isomer s h i f t s in the range 0.7-1.5 mm s" 1 (quoted r e l a t i v e to iron metal). The presence of an extra d-electron in i r o n d l ) complexes screens the s-electron density and thus the isomer s h i f t increases. The preceeding discussion on the isomer s h i f t applies to systems with spherical or cubic electron-density d i s t r i b u t i o n s . The degeneracy of the nuclear energy l e v e l s for nuclei with I>l/2 i s removed by a non-cubic electron or ligand d i s t r i b u t i o n . 1 5 0 The appropriate nuclear quadrupole coupling Hamiltonian i s given by: $f = ^ 2 [ 3 I ! - I ( I + 1 ) + (TJ/2)(I 2 + I 2 ) ] ...Eqn. 3 . 1 1 41(21-1) 2 where eQ i s V , the z-component of the e l e c t r i c f i e l d gradient (E.F.G.), 7? is the asymmetry parameter, I i s the nuclear spin operator, and I + and I . are s h i f t operators. 5 7 F e has a ground state with 1=1/2 and hence zero quadrupole moment and a f i r s t excited state with 1=3/2. In the presence of an e l e c t r i c f i e l d gradient the 1=3/2 l e v e l i s s p l i t into two substates nu=±3/2 and ± 1 / 2 . The separation of the two substates i s termed the quadrupole s p l i t t i n g , AE and has units of mm s _ 1 , (Fig. 3.29) and in most cases the Mossbauer spectrum consists of two l i n e s of equal i n t e n s i t i e s whose separation i s |AE |. From a symmetric two-line Mossbauer spectrum of a randomly oriented p o l y c r y s t a l l i n e absorber only the magnitude of AE can be determined. No information concerning either the sign of V__ or the value of TJ is gained. The magnitude of the quadrupole s p l i t t i n g i s found to be dependent upon the oxidation state and spin m u l t i p l i c i t y of the iron centre. For example, the high-spin iron(III) cation has a spherically symmetric d 5 electronic configuration and the e l e c t r i c f i e l d gradient (E.F.G.) can only a r i s e from an asymmetrical arrangement of the ligands and the value of AE^ i s expected to be small and temperature independent. For high-spin i r o n d l ) the si t u a t i o n i s somewhat more complicated. In an octahedral ligand f i e l d the 151 s i x t h d - e l e c t r o n i s e q u a l l y d i s t r i b u t e d w i t h i n the t 2 g set and i n t h i s case there i s no net E.F.G. In cases of lower symmetry about the metal c e n t r e , such as a t r i g o n a l or t e t r a g o n a l , the degeneracy of the t 2 g set i s removed and a non-zero E.F.G. i s produced. Thermal p o p u l a t i o n of the l o w - l y i n g e x c i t e d s t a t e s then causes a v a r i a t i o n i n the e l e c t r o n c o n f i g u r a t i o n with temperature and s i n c e the 3 d - o r b i t a l s have d i f f e r i n g c o n t r i b u t i o n s to the E.F.G. a temperature-dependent AEg i s expected. The Mossbauer s p e c t r a l r e s u l t s f o r the complexes c o n t a i n i n g an FeN(X 2 chromophore are d i s c u s s e d under two headings. F i r s t l y , the r e s u l t s f o r complexes c o n t a i n i n g an FeN,,02 chromophore are c o n s i d e r e d i n S e c t i o n 3.3.5.1, i . e . , the t e t r a k i s ( p y r i d i n e ) - , t e t r a k i s ( p y r a z i n e ) - and b i s ( p y r a z i n e ) i r o n d l ) s u l f o n a t e d e r i v a t i v e s . Secondly, the r e s u l t s f o r the b i s ( p y r a z i n e ) i r o n ( I I ) compounds, i . e . , F e ( p y z ) 2 X 2 , where X" i s C l " , Br", I", NCS" and CIO,~, are r e p o r t e d i n S e c t i o n 3.3.5.2. Low-temperature (1.8-10 K) Mossbauer s p e c t r a f o r F e ( p y z ) 2 ( N C S ) 2 are d i s c u s s e d i n S e c t i o n 3*3»5»3« 3.3.5.1 Mossbauer s p e c t r a l parameters for complexes c o n t a i n i n g an FeN f l0 2 chromophore The Mossbauer s p e c t r a l parameters are given i n Appendix X, Part A. The s p e c t r a c o n s i s t of a symmetrical q u a d r u p o l e - s p l i t doublet as expected f o r t e t r a g o n a l l y d i s t o r t e d pseudooctahedral h i g h - s p i n i r o n d l ) compounds. A t y p i c a l spectrum, that of 1 5 2 F e ( p y ) , ( C H 3 S O 3 ) 2 , i s shown i n F i g . 3.30. F i g . 3.30 Mossbauer Spectrum of F e ( p y ) 4 ( C H 3 S 0 3 ) 2 a t 78 K 1 1 1 1 1 1 r --2.0 0.0 +2.0 *A.O VELOCITY (mm.s-1) For the t e t r a k i s ( p y r i d i n e ) i r o n ( I I ) s u l f o n a t e s p e c i e s , the room-temperature isomer s h i f t s a r e v i r t u a l l y i d e n t i c a l and a p p r o x i m a t e l y 0.3 mm s" 1 lower than t h o s e of the c o r r e s p o n d i n g anhydrous i r o n ( I l ) s u l f o n a t e s d e r i v a t i v e s . 2 " ' 2 5 The lower isomer s h i f t s f o r the p y r i d i n e complexes a r e a t t r i b u t a b l e t o the more c o v a l e n t n a t u r e of the Fe-N bond, which l e a d s t o a g r e a t e r e l e c t r o n d e n s i t y a t the i r o n n u c l e u s than i n the more " i o n i c " F e ( R S 0 3 ) 2 compounds w i t h an F e 0 6 chromophore. E v i d e n t l y , i n the s u l f o n a t e complexes w i t h an FeN,0 2 chromophore, d i f f e r e n c e s i n 1 53 anion b a s i c i t y are not large enough to have an appreciable ef f e c t on the isomer s h i f t . This r e s u l t contrasts with that found for the corresponding halide complexes, Fe(py) f lX 2, where the room temperature isomer s h i f t decreases s l i g h t l y from 1.06 mm s" 1 for the chloride, to 0.99 mm s~ 1 for the i o d i d e . 6 7 The room-temperature isomer s h i f t values for the two bis (pyrazine) i r o n d l ) sulfonate complexes and for Fe(2-mepyz)« ( C H 3 S O 3) 2 (Appendix X, Part A) are s l i g h t l y higher than those of the corresponding tetrakis(pyridine) complexes. This suggests a greater degree of covalency in the pyridine complexes which i s consistent with the r e l a t i v e base strengths of pyridine, pyrazine and 2-methylpyrazine. With the exception of the isomer s h i f t for Fe(py)«(CH 3S0 3) 2, a s l i g h t temperature dependence of 6 i s observed. This temperature dependence i s attributable to a second-order Doppler ef f e c t and has no chemical s i g n i f i c a n c e . On the other hand, the temperature-independent isomer s h i f t for Fe(py ) t t(CH 3S0 3) 2 arises because the spectra were recorded with the source and absorber at the same temperature. At a l l temperatures the quadrupole s p l i t t i n g values exceed 3 mm s _ 1 . The magnitude of AE provides some indication of the nature of the ground state in the complexes. For these octahedral i r o n d l ) complexes the degeneracy of the T 2g ground state i s removed by the presence of a tetragonally d i s t o r t e d ligand f i e l d (Fig. 3.13) and a non-zero e l e c t r i c f i e l d gradient is produced by the s i x t h d-electron occupying either the singly 5 5 or doubly degenerate ground state ( B0_ or E ). A 1 54 non-degenerate ground state is expected to produce an E.F.G. in proportion to +4/7<r_3>, twice the value and of opposite sign to that produced by a doubly degenerate ground state. For these complexes, the observation of a quadrupole s p l i t t i n g value substantially greater than 2 mm s' 1 i s diagnostic evidence for the presence of a non-degenerate ground state which corresponds to the d Xy o r b i t a l lying lowest in energy. This is precisely as required by the molecular geometries discussed in Section 3.3.3.1, which show, in the case of the tet r a k i s ( p y r i d i n e ) i r o n ( I I ) sulfonate compounds, an a x i a l l y compressed octahedron of approximately symmetry. With this combination of a non-degenerate ground state and a tetragonal compression of the FeN„0 2 chromophore, a posit i v e value of V is indicated and V i s presumably directed along the z z pseudo-tetragonal O-Fe-0 axis. Previous research has involved the evaluation of l i g a n d - f i e l d parameters (A and X) from the temperature dependence of the quadrupole s p l i t t i n g data. 8" Except for Fe(py)«(CH 3S0 3) 2, the data set obtained in the present study is too limited for such an analysis. For Fe(py)„(CH 3S0 3) 2, the temperature dependence of AE was analysed using t h i s model and the parameter values obtained are A=650 cm*1 and X=-80 cm"1. These values are quite similar to those obtained from the analysis of the magnetic moment data using the Figgis model, in spite of the theoretical l i m i t a t i o n s of the l a t t e r treatment (Section 3.3.4.2) 155 3.3.5.2 Mossbauer spectral parameters for b i s ( p y r a z i n e ) i r o n d l ) halide and thiocyanate complexes and Fe(pyz) a(AsF 6) 2.2H 20 The Mossbauer spectral parameters are presented in Appendix X, Part B. At room and l i q u i d nitrogen temperatures the complexes show symmetric, quadrupole s p l i t Mossbauer spectra with isomer s h i f t and quadrupole s p l i t t i n g values consistent with their formulation as high-spin i r o n d l ) compounds. The b i s ( p y r a z i n e ) i r o n d l ) halide complexes exhibit no appreciable differences in isomer s h i f t s . This i s unexpected considering the d i f f e r e n t a-donating a b i l i t i e s of the halide anions. For the t e t r a k i s ( p y r i d i n e ) i r o n d l ) halide species, small changes in isomer s h i f t values do correlate with the differences in a-donating a b i l i t i e s of the anionic l i g a n d s . 6 7 The presence of a halide anion dependence for the isomer s h i f t s of the pyridine complexes where there i s none for the pyrazine complexes indicates that in the former group of complexes the s-electron density at the iron nucleus increases with the a-donating a b i l i t y of the halide anion in the order C l " > Br - > I - ; whereas, in the l a t t e r group, s-electron density at the iron nucleus remains f a i r l y constant in spite of the increased a-donation from the halide anions. This observation may be related to the fact that pyrazine i s a better 7r-acceptor ligand than pyridine. Thus, a-electron density from the anion i s transferred to the metal in the pyridine complexes and in the pyrazine complexes, i t i s transferred one stage further onto the neutral ligand. This seems to suggest a rather f a c i l e charge-transfer process in the pyrazine complexes, and i s 156 consistent with the observation of charge-transfer bands in the v i s i b l e region of the spectrum (Section 3.3.2.3). At room temperature, the isomer s h i f t value for Fe(pyz) 2(NCS) 2 is very similar to that reported for F e ( p y ) a ( N C S ) 2 6 7 which indicates that both compounds have similar s-electron densities as a result of their i d e n t i c a l FeN^Nj' chromophores. The quadrupole s p l i t t i n g s for the bis(pyrazine) halide and thiocyanate complexes are greater than 2 mm s _ 1 which indicates a non-degenerate ground state. 3.3.5.3 Low-temperature Mossbauer spectra of Fe(pyz) 2(NCS) 2 It may be recalled that the magnetic s u s c e p t i b i l i t i e s for Fe(pyz)2(NCS)2 (Section 3.3.4.3) show a maximum at approximately 8.0 K, indicating the presence of short-range magnetic interactions. Mossbauer spectra were recorded in the temperature range 1.8-10K in order to ascertain the extent of any three-dimensional magnetic ordering. The spectra are i l l u s t r a t e d in F i g . 3.31 and the results are presented in Table 3.7. (Note, the spectra were recorded and f i t t e d by Dr. J.R. Sams) 157 Table 3.7 Low-Temperature Mossbauer Spectral Parameters for Fe(pyz) 2(NCS) 2 TEMP 6 r1 H i n t 6 V K mm s" 1 mm s~ 1 mm s~1 T deg 1 .8 1.14 2.68 0.18 27.7 41 0.07 4.2 1.14 2.70 0.18 27. 1 40 0.07 5.7 1.13 2.72 0.18 26.9 41 0.06 6.7 1.14 2.70 0.21 25.2 40 0 8.0 1.13 2.76 0.20* 22.9 40* 0* 9.8 1.13 2.65 0.29 0 - -1 ) . r values are quoted for halfwidth at halfheight * Constrained At 9.8 K, the Mossbauer spectrum remains a single, symmetric quadrupole doublet, and the the isomer s h i f t and quadrupole s p l i t t i n g values at th i s temperature are similar to those found at l i q u i d nitrogen temperature. It is concluded that no phase change takes place over this temperature range, and that the ground state i s e f f e c t i v e l y i s o l a t e d . Between 9.8 and 8.0 K the l i n e s of the quadrupole doublet broaden and s p l i t . The Neel temperature i s estimated to be 9.2 ±0.5 K which i s unexpected as t h i s i s at a higher temperature than the maximum in the s u s c e p t i b i l i t y curve (8.0 K). An interpretation of t h i s phenomenom would be somewhat tenuous at th i s stage, because in t h i s temperature region d i f i c u l t i e s were encountered with temperature control of the Mossbauer cryostat. Below 8.0 K, a f u l l y - r e s o l v e d magnetic hyperfine spectrum res u l t i n g from the presence of a magnetic-dipole interaction in addition to the e l e c t r i c quadrupole interaction i s observed. 158 F i g . 3.31 Low-Temperature Mossbauer Spectrum of Fe(pyz) 2(NCS) 2 VELOCITY / mm s"1 159 F i g . 3.31 Continued I 1 I 1 I 1 I 1 I 1 I 1 I 1 I 1 I 1 I -9 -7 -5 -3 -1 1 3 5 7 9 VELOCITY / mm s-1 160 The ori g i n s of the quadrupole interaction have been previously described (Section 3.3.5) and the o r i g i n of the magnetic-dipole interaction may be thought to a r i s e in the following manner. The 5 7 F e nucleus has a magnetic moment in the ground and excited state. These moments interact with a magnetic f i e l d at the nucleus to l i f t the degeneracy of the states (Fig. 3.32) according to the Hamiltonian: where 9 n i s the nuclear gyromagnetic r a t i o and 0n i s the nuclear magneton. The magnetic s p l i t t i n g produces 21+1 l e v e l s for each state. Thus, the ground state (1=1/2) is s p l i t into two levels (m. =+1/2 and -1/2) and the excited state (1=3/2) into four r e s t r i c t the allowed t r a n s i t i o n s to those for which Am^=0,±1 so that a s i x - l i n e spectrum r e s u l t s . For most paramagnetic complexes the electron spins which generate the internal magnetic f i e l d are subject to rapid electronic spin relaxation. The f i e l d i s time-averaged to zero and consequently, no magnetic hyperfine spectra are observed. 3.12 levels (m^ =+1/2, -1/2, +3/2 and -3/2). The selection rules 161 F i g . 3.32 Combined Effects of Magnetic and Quadrupole Interactions 1 = 3/2 V + 3/2 + 1/2 -1/2 "3/2 -1/2 1 = 1/2 MAGNETIC MAGNETIC + QUADRUPOLE + 1/2 162 For materials which show magnetic ordering, the electronic spin-relaxation rate decreases and the iron nucleus experiences an internal magnetic f i e l d which, at temperatures below the ordering temperature, is not time-averaged to zero, resulting in a complex Mossbauer spectrum. In general, the magnetic-dipole interaction i s represented by the Hamiltonian: / , B - q ( i H. t [ I cos0+(I cos^+I sin0)sin0)] ...Eqn. 3.13 3 n int z x y For any given combination of magnetic-dipole (Eqn. 3.13) and electric-quadrupole (Eqn. 3.11) interactions a Mossbauer spectrum may be computed by constructing the energy l e v e l diagram (for example, F i g . 3.32) and c a l c u l a t i n g the t r a n s i t i o n energies and p r o b a b i l i t i e s . From an analysis of a Mossbauer hyperfine spectrum the following parameters are obtained: H ^ n t i s the magnitude of the hyperfine f i e l d at the iron nucleus, B and <t> are the polar angles which specify the d i r e c t i o n of H^ n t with respect to the E.F.G. axis system (Fig. 3.33), TJ i s the asymmetry parameter, where „=(V -V )/V„„ ...Eqn. 3.14 ' xx yy zz M 163 The magnitude and sign of the quadrupole s p l i t t i n g , e2qQ, and hence the sign of V' are also obtained from such an analysis. z z By using t h i s type of approach and a program based upon the results of Kundig, 1 5 9 Mossbauer spectra were computed and compared with the spectra of Fe(pyz) 2(NCS) 2• The s o l i d l i n es in Fig. 3.31 were generated by a least-squares f i t t i n g procedure using the parameters l i s t e d in Table 3.7. From T^ down to approximately 7 K, the spectral l i n e s are broadened due to spin-relaxation e f f e c t s , with an electronic-spin relaxation time comparable to the Mossbauer time scale (10* 7 s ) . Below 7 K, the spectra are well f i t t e d using the parameters given in Table 3.7. These values provide substantial information in support of the proposed structure of Fe(pyz) 2(NCS) 2. The asymmetry parameter, TJ, i s found to be very small which implies the e l e c t r i c f i e l d gradient to have e f f e c t i v e l y a x i a l symmetry. Because of this, 1 64 a l l orientations of the hyperfine f i e l d , H^ n t r e l a t i v e to the xy plane (of the E.F.G. axis system) are equally probable and hence, the angle > (Fig. 3.33) is indeterminate. The positive value of e 2qQ indicates a tetragonal compression of the FeN„N 2' polyhedron, with the Fe-N(anion) distance somewhat shorter than the Fe-N(pyz) length and a non-degenerate ground state (d xy o r b i t a l at lower energy than d x z and d x y ) . Axial symmetry i s also suggested by the infrared spectral data (Section 3.3.2.2) which indicate a square planar array of bridged F e ( p y z ) 2 2 + units and monodentate NCS" anions coordinated trans to each other in axial s i t e s . The polar angle, 6 was found to be 40°, and assuming that the p r i n c i p a l axis of the E.F.G. tensor (V ) i s coincident with the N(anion)-Fe-N(anion) axis., then the easy axis of magnetisation i s tipped towards the xy-plane. This indicates that the magnetic exchange pathway through pyrazine i s not s u f f i c i e n t l y strong to alig n the spins in the xy-plane, as a value of 0=90° would then be expected. The internal hyperfine f i e l d at the iron nucleus, H ^ n t f as a function of temperature i s given in Table 3.7. It can be seen that the f i e l d saturates rapidly below 9.8 K and then slowly approaches a maximum value of approximately 28 T at 1.8 K. The contributions to H^nfc are given by: H i n t = H F + H l + H d i p 3 * 1 5 For high-spin i r o n d l ) complexes, the contribution to H^ n t from the Fermi contact interaction, H„, i s approximately 44 T . 1 5 8 The 165 opposing o r b i t a l contribution to H i n t * s expected to be r e l a t i v e l y small in view of the near spin-only moment at high temperatures and the non-degenerate ground state. On the other hand, the dipolar contribution, H ^ j p i s probably not ne g l i g i b l e as l H { j i p l = 0 V 2 Z 1 5 8 a n ^ ^ s usually of oposite sign to Hp. Hence, for Fe(pyz) 2(NCS) 2 the value of 25 T is not unreasonable for the expected Fermi contribution, reduced somewhat by both opposing dipolar and to a lesser extent o r b i t a l contributions. In summary, the analysis of the low-temperature Mossbauer spectra of Fe(pyz) 2(NCS) 2 i s consistent with the proposed two-dimensional layer structure and weak magnetic exchange interactions propagating through the bridging pyrazine ligands. 166 3.3.6 Thermal Studies The range of thermal s t a b i l i t i e s of these tetrakis(pyridine) and bis(pyrazine) complexes was established by using d i f f e r e n t i a l scanning calorimetry (D.S.C). A comparison of the re l a t i v e thermal s t a b i l i t i e s for the two groups of complexes was interesting in view of their d i f f e r e n t structures (monomeric or polymeric). D.S.C. results were also informative in regard to the p o s s i b i l i t y of obtaining complexes with lower ligand to iron ratios by u t i l i s i n g thermolysis as a preparative technique. Gravimetric measurements made during the course of a D.S.C. experiment were p a r t i c u l a r l y useful in this respect. The thermolysis results for the tetrakis(pyridine)iron(11) and copper(II) sulfonate derivatives are given in Table 3.8. The D.S.C. curves for Fe(py)«(CF 3S0 3) 2 (Fig. 3.34a) and Fe (py) 4 (p-CH 3C 6Hi,S0 3) 2 exhibit two endothermic events in the temperature range of 400-520 K. Exothermic decomposition is noted above 800 K. The D.S.C. curve for the methanesulfonate derivative (Fig. 3.34b) shows an endothermic event at 414 K; however, above t h i s temperature several endothermic peaks are recorded, indicating a more complex thermolysis for Fe(py)«(CH 3S0 3)2 than for either the t r i f l a t e or p-tosylate derivative. The weight loss data obtained after the occurence of several of these thermal events are given in Table 3.8. 167 Table 3.8 Thermal parameters 1 for some Tetrakis(pyridine) and Bis(pyrazine) Complexes Compound Peak Temp. AH Weight loss (%) K kJ mol" 1 C a l c . 2 Obs. Fe(py) f l(CF 3S0 3) 2 465 95 24 26 513 60 47 44 Fe(py)«(CH 3S0 3) 2 414 91 28 28 3 56 55 Fe(py)„(p-CHaCgH^SOa) 2 419 94 22 24 458 109 44 42 Cu(py),(CF 3S0 3) 2 509 - - -520 — — — Cu(py) a(CH 3S0 3) 2 453 91 - -469 51 — — Fe(pyz)2(CF 3S0 3) 2.CH 3OH 415 1 04 21 21 603 60 35 37 Fe(pyz) 2(CH 3S0 3) 2 503 84 20 22 583 40 39 42 Cu(pyz) 2(CH 3S0 3)2 461 62 19 19 570 61 39 39 * 1) . Estimated error l i m i t s : Peak Temp. ±5 K, AH ±5%, weight loss ±5%. 2) . For explanation of calculated values see text 3) . For discussion of thermolysis above 450 K see text 168 F i g . 3.34 D.S.C Curves for Fe(py)«(CH 3 S 0 3 ) 2 Fe(py)«(CF 3 S 0 3) 2 and E \ ce UJ o a). Fe(py)«(CF 3 S 0 3 ) 2 300 E \ CH o Qu 400 500 TEMPERATURE /K 600 b). Fe(py)»(CH 3 S 0 3 ) 2 i r 300 400 500 600 TEMPERATURE / K 700 169 For the F e ( p y ) „ ( R S 0 3 ) 2 compounds, a f t e r completion of the f i r s t thermal event, the weight l o s s data (Table 3.8) i n d i c a t e the l o s s of two moles of p y r i d i n e per mole of complex, suggesting the formation of b i s ( p y r i d i n e ) complexes a c c o r d i n g t o : F e ( p y ) , ( R S 0 3 ) 2 ^ F e ( p y ) 2 ( R S O 3 ) 2 + 2py ...Eqn. 3.16 where R i s C F 3 , CH 3 or p-CHaCgH,,. For t r i f l a t e and p - t o s y l a t e d e r i v a t i v e s , the weight l o s s data a f t e r the second thermal event i n d i c a t e the removal of the two remaining p y r i d i n e groups in one step, to form the anhydrous s u l f o n a t e s p e c i e s : F e ( p y ) 2 ( R S O 3 ) 2 > F e ( R S O 3 ) 2 + 2py ...Eqn. 3.17 where R i s CF 3 or p-CHaCeH,,. As noted above, t h e r m o l y s i s of the methanesulfonate complex ( F i g . 3.34b) all o w s the o b s e r v a t i o n of s e v e r a l a d d i t i o n a l endothermic events. A more complex t h e r m o l y s i s p a t t e r n than that represented by Eqn. 3.17 i s i n d i c a t e d . A f t e r the f i n a l endothermic event, a weight l o s s of 55% suggests t o t a l removal of p y r i d i n e . These o b s e r v a t i o n s i n d i c a t e that the f i n a l two moles of p y r i d i n e are removed i n s e v e r a l s t e p s . T h i s i s not without precedent; f o r example, F e ( p y ) a C l 2 undergoes thermal decomposition through s e v e r a l i n t e r m e d i a t e s : F e ( p y ) 2 C l 2 , F e ( p y ) C l 2 , Fe(py) 2/3CI2, before F e C l 2 i s p r o d u c e d . 1 6 0 For these F e ( p y ) « ( R S 0 3 ) 2 complexes, F e ( R S 0 3 ) 2 was i n d i c a t e d 170 to be the f i n a l product of thermolysis (before exothermic decomposition) not only by gravimetric data but also by infrared spectroscopy. The infrared spectra of the thermolysis products were i d e n t i c a l to the infrared spectra of the F e ( R S 0 3 ) 2 compounds synthesised by published methods. 2 5 The temperature at which each thermal event occurs is measured during a D.S.C. experiment. The values indicate the thermal s t a b i l i t y of the complexes with respect to loss of ligand. For the tetrakis(pyridine)iron(11) complexes, the temperature at which the f i r s t thermal event occurs shows only a small anion dependence (Table 3.8), with very similar thermal s t a b i l i t y found for a l l three complexes. Another parameter measured during the course of a D.S.C. experiment i s the enthalpy change, AH, associated with each event. The magnitude of AH i s l i k e l y to be dependent on a number of contributing factors. (i) the Fe-N bond strength as pyridine is removed ( i i ) the Fe-0 bond strength as the anion changes i t s mode of coordination during thermolysis. ( i i i ) the energy change involved when the monomeric tetrakis(pyridine) complexes convert to polymeric anhydrous sulfonates. It i s noted for the f i r s t endothermic event that AH i s independent of anion (Table 3.8). This observation, consistent with the gravimetric data, suggests the same process i s taking place in a l l three compounds; i . e . , the removal of the f i r s t two pyridine groups, with a similar concomitant change in the 171 coordinating behaviour of the anionic groups. A considerable dependence upon the sulfonate anion i s noted for the enthalpy values associated with the second thermal event in the t r i f l a t e and p-tosylate derivatives. This i s somewhat surprising, as gravimetric results show that t h i s event i s a result of the removal of the second two pyridine moieties in both cases. Previous researchers 6 7 have employed thermolysis as a preparative technique for the conversion of some tet r a k i s ( p y r i d i n e ) i r o n ( I I ) complexes to their bis(pyridine) derivatives. The results obtained in t h i s study indicate that the i s o l a t i o n of the b i s ( p y r i d i n e ) i r o n ( I I ) sulfonate complexes should be possible by a thermolysis route. Indeed, the F e ( p y ) 2 ( C F 3 S O 3 ) 2 was obtained by thermolysis in vacuo (Section 4.2.1.1). Thermolysis data for Cu(py)„(CF 3S0 3) 2 and Cu(py),(CH 3S0 3) 2 are l i s t e d in Table 3.8 and th e i r D.S.C. curves are shown in F i g . 3.35. The D.S.C experiments for both copper compounds exhibit two endothermic events which are separated by temperatures of 11 and 16 K for the t r i f l a t e and methanesulfonate complexes respectively. For the t r i f l a t e derivative, the close proximity of the two thermal steps and the r e l a t i v e l y broad nature of the second event make i t d i f f i c u l t to characterise individual weight or enthalpy changes associated with each event. The peak temperature i s the only parameter to be evaluated (Table 3.8). The two events are accompanied by a t o t a l weight loss of 20% which i s close to that expected (23%) for the removal of two 172 pyridine groups from Cu(py)„(CF 3S0 3) 2• For the c o p p e r - t r i f l a t e complex, the presence of two peaks suggests that the f i r s t two pyridine groups are lost in a stepwise manner rather than simultaneously as found in the thermolysis of Fe(py) f t(CF 3S0 3) 2. Presumably, for Cu(py),(CF 3S0 3) 2, the two remaining pyridine groups are lost at higher temperatures and i t appears l i k e l y that these events are obscured by the exothermic decomposition of the compound above approximately 580 K (Fig. 3.35a). Cu(py)„(CH 3S0 3) 2 exhibits endothermic events at 453 and 469 K and whilst the enthalpy changes associated with these events were approximated, i t was d i f f i c u l t to est a b l i s h weight changes associated with each event. The gravimetric results were found to be irreproducible from one D.S.C. experiment to another and meaningful conclusions could not be made. Information was obtained, however, by heating Cu(py) 4(CH 3S0 3) 2 to a temperature s l i g h t l y above the temperature of the second thermal event. An overall weight loss of 36% was measured, a value which i s intermediate between the weight decrease expected for the loss of two and three moles of pyridine (28 and 42% r e s p e c t i v e l y ) . As was also noted above for Fe(py)„(CH 3S0 3) 2, a more complex decomposition route involving loss of a non-integral number of pyridine ligands is suggested. Exothermic decomposition takes place at temperatures above approximately 530 K. 174 It i s interesting to compare the r e l a t i v e thermal s t a b i l i t i e s of M(py),(CF 3S0 3) 2 and M(py) f t(CH 3S0 3) 2, where M i s either Fe or Cu. The infrared spectra of these complexes (Section 3.3.2.1) show the coordination-sensitive pyridine vibrations, in p a r t i c u l a r , the 16b vi b r a t i o n , to s h i f t to higher frequencies. This s h i f t i s more pronounced for the copper(II) complexes, indicating a stronger M-N(pyridine) interaction in these derivatives. For the M(py)„(CF 3S0 3) 2 complexes (where M i s either Fe or Cu), X-ray crystallography (Sections 3.3.1.1 and 3.3.1.2 respectively) shows a considerably shorter M-N bond length in the copper complexes. It was interesting to investigate whether these observations correlate with greater thermal s t a b i l i t y in the copper compounds. Using the temperature of the f i r s t thermal event as a measure of thermal s t a b i l i t y , i t i s noted that the copper derivatives are indeed, thermally more stable than the analogous iron derivatives by approximately 40 K. No attempt was made to prepare the bis(pyridine)copper(II) sulfonate derivatives. The preceeding data suggest that thermolysis may prove successful in i s o l a t i n g C u ( p y ) 2 ( C F 3 S 0 3 ) 2 , but would be i n e f f e c t i v e for the synthesis of Cu(py) 2(CH 3S0 3) 2. Both the effect of a weaker Lewis base, pyrazine compared to pyridine, and i t s presence in a bridging configuration are expected to result in quite d i f f e r e n t thermal properties for the pyrazine compounds from those discussed above for the tetrakis(pyridine) complexes. The data obtained from the D.S.C. measurements for the 175 bis(pyrazine) sulfonate compounds, Fe(pyz) 2(CF 3S0 3) 2.CH 3OH, Fe(pyz) 2(CH 3S0 3) 2 and Cu(pyz) 2(CH 3S0 3) 2, are given in Table 3.8. A l l three complexes show two endothermic events in the temperature range studied and the results of gravimetric analysis again provide an insight into the thermolysis pathways. For Fe(pyz) 2(CF 3S0 3) 2.CH 3OH, after the f i r s t thermal event a weight loss of 21% was measured. Removal of methanol would be accompanied by a weight change of only 6%. For the loss of pyrazine alone, a weight reduction of 15% would be expected. Hence, the observed weight loss indicates simultaneous removal of methanol and the f i r s t mole of pyrazine. The f i r s t step in thermolysis may be represented as follows: Fe(pyz) 2(CF 3S0 3) 2.CH 3OH >Fe(pyz)(CF 3S0 3) 2+pyz+CH 3OH ...Eqn. 3.18 An overall reduction in weight of 37% accompanies the second thermal event, consistent with the loss of the second pyrazine group and the formation of F e ( C F 3 S 0 3 ) 2 . Similar D.S.C. curves are observed for Fe(pyz) 2(CH 3S0 3) 2 and the analogous copper derivative. 176 Two endothermic events with weight losses consistent with the successive removal of pyrazine in two d i s t i n c t steps are observed according to the following scheme: M(pyz) 2 ( C H 3 S O 3 ) 2 s-M(pyz) ( C H 3 S O 3 ) 2 » M ( C H 3 S 0 3 ) 2 ...Eqn. 3.19 where M is Fe or Cu. Presumably for Cu(pyz) 2(CH 3S0 3) 2, the more weakly bound a x i a l pyrazine group i s removed f i r s t . A comparison of the r e l a t i v e thermal s t a b i l i t y of these tetrakis(pyridine) and bis(pyrazine) complexes was made by using the - temperature of an event in the D.S.C. curve. As stated, the f i r s t thermal event for the two groups of compounds corresponds to the removal of either two moles of pyridine or one mole of pyrazine per mole of complex. From the temperatures at which these events occur no s t a b i l i t y trend i s apparent. In some instances the bis(pyrazine) compounds are thermally more stable than the analogous tetrakis(pyridine) species and the opposite i s also found, making a consistent interpretation hazardous. Where the second thermal event arises from loss of either the remaining pyrazine or pyridine groups, the temperature of t h i s event i s always higher by at least 100 K for the pyrazine complexes. This added thermal s t a b i l i t y of the intermediate pyrazine complexes over the bis(pyridine) complexes may result from the type of polymer present in these thermolysis intermediates. 1 77 D.S.C. measurements were also c a r r i e d out on the bis(pyrazine) complexes containing the halide anions, C l " , Br -or I - and the pseudohalide, NCS-. The results are presented in Table 3.9. Table 3.9 Thermal Parameters for Bis(pyrazine)iron(11) Halide and Thiocyanate Complexes Compound Peak Temp. AH Weight Loss (%) K kj mol - 1 Calc. 1 Obs. Fe(pyz) 2C1 2 477 70 28 34 723 86 56 59 Fe(pyz) 2Br 2 508 75 21 23 742 41 43 48 F e ( p y z ) 2 I 2 516 59 2 69 Fe(pyz) 2(NCS) 2 563 47 24 25 638 40 48 60 1) . For explanation of calculated values see text 2) . For discussion of this complex see text Due to the well-known highly unstable nature of perchlorate compounds and the desire to maintain the f r a g i l e D.S.C. sensor intact, Fe(pyz) 2(C10 f l) 2 was not included in t h i s thermal study. The D.S.C. curves for the chloro- and bromo derivatives show two endothermic events, indicating thermolysis to take place in two stages. 1 78 From the gravimetric analyses (Table 3.9) i t i s tentatively suggested that the two endothermic events result from the loss of pyrazine in a stepwise fashion as observed for the bis(pyrazine) sulfonate complexes according to: Fe(pyz) 2X 2 >Fe (pyz )X2+pyz =>FeX2+pyz ...Eqn. 3.20 where X i s C l " or Br~ Heating the iodo derivative produces one single endothermic event and a weight loss of 69%. The removal of one or two moles of pyrazine would correspond to weight losses of 17 and 34% respectively. The gravimetric measurements, together with the observation of a brown ring around the pin hole in the aluminum crucible after heating the compound to 540 K, indicate the loss of iodine and suggest more extensive sample decomposition in th i s compound. Heating the complex to 473 K, well before the onset of any detectable thermal event, r e s u l t s already in an observed weight loss of 7%. Thus decomposition of the complex occurs over a wide temperature range. The D.S.C. curve for Fe(pyz) 2(NCS) 2 shows two endothermic events and the weight loss (Table 3.9) which accompanies the f i r s t event suggests that one of the two pyrazines i s removed. The second event i s accompanied by a weight loss of 60%. Not only removal of the remaining pyrazine but also decomposition of the anion are implied. The thermolysis results for the tetrakis(pyrazine) complexes are given in Table 3.10. 179 Fe(2-mepyz)«(CH 3S0 3) 2 exhibits a complex D.S.C. thermogram as i l l u s t r a t e d in F i g . 3.36. Table 3.10 Thermal Parameters for Fe(2-mepyz),(CH 3S0 3) 2, Cu(pyz)n (CF 3SO 3)2•H 20 and Fe(pyz)„(AsF 6) 2.2H 20 Compound Peak Temp. AH K k J m o l " 1 Fe(2-mepyz),(CH 3S0 3) 2 382 400 467 81 540 12 570 -11 750 180 Cu(pyz),(CF 3S0 3) 2.H 20 398 53 460 175 650 Fe(pyz)„(AsF 6) 2.2H 20 430 71 500 40 590 180 180 I I I I I I I I I I I 300 400 500 600 700 800 TEMPERATURE /K The broad nature of the peak around 400 K and i t s close proximity to the f i r s t thermal event at 381 K preclude any estimation of the enthalpy changes associated with these two events. For both events a combined weight loss of 35% was recorded which is close to the expected value (30%) for the removal of two 2-methylpyrazine ligands from the tetrakis(2-methylpyrazine) complex. On further heating, a sharp endothermic peak i s observed (467 K, AH=81 kJ mol" 1) and an accumulated weight loss of 54% was determined; this figure i s close to that expected for the loss of three neutral ligands. When the complex i s heated to approximately 560 K , about 20 K 181 above the temperature of the minor endothermic event at 540 K, an accumulated weight loss of 59% i s observed. This loss agrees even more closely with that expected for the removal of three ligands. A major endothermic event i s evident at a higher temperature ,750 K, (180 kJ mol - 1) and thi s is associated with a tot a l weight loss of 85%. It i s obvious from t h i s value that other decomposition reactions are taking place as well. Between 370 and 470 K, the D.S.C. curve for Cu ( p y z ) « ( C F 3 S O 3 ) 2 . H 2 0 (Fig. 3.37) reveals two broad endothermic peaks; the event at 460 K exhibits a low temperature shoulder. F i g . 3.37 D.S.C. Curve for Cu(pyz),(CF 3S0 3) 2-H 20 X 400 500 600 700 TEMPERATURE / K Heating the complex to 410 K, s l i g h t l y above the temperature of 182 the f i r s t event, results in a small weight loss of approximately 5%. This appears to indicate the removal of water from the complex, expected weight loss of 3%. Further heating to 483 K , beyond the temperature of the second event, results in a weight loss of 36%. This compares favourably with 37% expected when not only water but also three pyrazine molecules are lost from the compound. The r e s u l t s also indicate a high thermal s t a b i l i t y for Cu(pyz)(CF 3S0 3) 2, and have s p e c i f i c relevance for the synthesis of the mono(pyrazine) derivative by thermolysis (Section 4.2.2.4). On additional heating to a temperature of 600 K, the D.S.C. curve shows a broad exothermic event accompanied by a weight loss of approximately 77%. Both observations are consistent with extensive sample decomposition at these temperatures. Fe(pyz)„(AsF 6) 2.2H 20 undergoes thermolysis as i l l u s t r a t e d in F i g . 3.38. Three events are observed. The f i r s t , at 433 K, is accompanied by a 13% weight loss, consistent with the loss of both water molecules and one pyrazine group, (expected weight loss of 15%). At 490 K, a second thermal event occurs accompanied by a tota l weight loss of 30%. This loss i s intermediate between the values expected for the removal of one or two addit i o n a l pyrazine groups (25 or 35% weight losses r e s p e c t i v e l y ) . A th i r d broad endotherm i s centred around 590 K. At t h i s temperature the weight loss figure of 76% indicates that extensive decomposition has set in (the loss of four pyrazine groups and both water molecules would represent a 45% weight l o s s ) . It appears that thermolysis above temperatures of 500 K 183 follows a more complex route than would be predicted by mere loss of neutral ligands. These results indicate that i t is unlikely that F e ( p y z ) 2 ( A s F 6 ) 2 i s formed during thermolysis. Other investigations (Section 3.2.2.2) showed that heating a sample of Fe(pyz),(AsF 6) 2.2H 20, in vacuo, at 320 K had no ef f e c t ; whereas, heating at 340 K resulted in formation of a brown s o l i d and sample decomposition. F i g . 3.38 D.S.C. Curve for Fe(pyz)„(AsF 6) 2.2H 20 300 400 500 600 TEMPERATURE / K 184 CHAPTER 4 COMPLEXES CONTAINING AN MN,Xa CHROMOPHORE 4.1 INTRODUCTION The synthesis and characterisation of complexes containing an MNnX2 chromophore were discussed in the preceeding chapter; complexes in which two of the nitrogen donor atoms are removed from the MN„X 2 chromophore are considered in t h i s chapter. Preparation and characterisation of mono(pyrazine) and bis(pyridine) compounds were performed because a variety of polymeric or monomeric structures may be v i s u a l i s e d . It was found that for the complexes which contain an MN„X 2 chromophore, the anions coordinate in a unidentate fashion; upon removal of two nitrogen donors the coordination mode of the anion may be either unaltered, resulting in a four-coordinate complex (MN2X2 chromophore), or the anion may assume bidentate coordination so as to . maintain a six-coordinate metal centre (MN2X„ chromophore). In both of these situations the structure of the complex i s dependent upon the coordination mode of the neutral ligand. For the four-coordinate complex, where the ligand is pyridine, a monomeric species would result (Fig. 4.1a); whereas, incorporation of pyrazine results in the formation of a polymer (Fig. 4.1b). For the anions used in th i s study, however,the preferred mode of coordination i s not necessarily unidentate. For example, sulfonate anions have the potential to use more than one oxygen atom to bridge metal centres, and a 185 bridging mode for h a l i d e 1 6 1 and pseudohalide 1 2 7 ligands i s well known. In these bis(pyridine) and mono(pyrazine) compounds, a bridging bidentate coordination mode for the anion would result in an MN2Xa chromophore. Again, several structural modifications may ex i s t , dependent upon the neutral ligand. In the case where the two nitrogen donor atoms are from pyridine, then the only bridging groups are the anionic ligands and polymers may be formed as shown in F i g . 4.1c (i) and ( i i ) . For complexes where the two nitrogen atoms arise from pyrazine, a combination of bridging pyrazine and bridging anionic ligands may lead to more complex polymeric materials and possible structures are shown in F i g . 4.1d (i) and ( i i ) . If such polymeric structures are formed for the bis(pyridine) or mono(pyrazine) complexes isolated in this study, then magnetic interactions are possible through the bridging network. Various spectroscopic methods were employed in this study in an attempt to distinguish between the possible structures. The results of these studies enabled conclusions to be drawn concerning the coordination sphere around the metal, the nature of the bridging group or groups and the extent of any magnetic exchange interactions. Comparisons are made between the structures and properties of these complexes and those of the complexes containing an MN4X2 chromophore. 186 F i g . 4.1 Some Possible Structures of Mono(pyrazine) and Bis(pyridine) Complexes 187 F i g . 4.1 Continued 4.1d). (i) 188 4.2 SYNTHETIC METHODS Either a solution or a thermolysis route was used for the preparation of the mono(pyrazine) and bis(pyridine) complexes. With regard to the thermolysis method, D.S.C. results (Section 3.3.6) are useful in that they indicate thermolysis often occurs by stepwise loss of neutral ligand. These results also show that thermal events often take place at temperatures higher than those attainable in t h i s laboratory using conventional heating methods, for example, an o i l bath or a drying p i s t o l . By heating in vacuo, temperatures required for thermolysis on a preparative scale were lower than those indicated by the D.S.C. studies. The choice of temperature for bulk thermolysis was found to be quite c r i t i c a l and was determined by heating at gradually increasing temperature and monitoring the changes in the infrared spectrum of the material as well as monitoring the microanalytical data. It was found that heating at too high a temperature resulted in the loss of more than the required amount of ligand (either pyrazine or pyridine), whilst heating at too low a temperature had the opposite e f f e c t . Experiment showed that in every case the compounds obtained by t h i s route were unique materials, rather than being stoichiometric mixtures; for example, the infrared spectrum of the product obtained from thermolysis of Fe(py) f l(CF 3S0 3) 2 i s quite di f f e r e n t from the spectrum which would resu l t from a 1:1 mixture of Fe(py),(CF 3S0 3) 2 and Fe(CF 3S0 3) 2 (Section 4.3.1.1). 189 4.2.1 Bis(pyridine) Complexes Two synthetic routes for the preparation of b i s ( p y r i d i n e ) i r o n d l ) sulfonate complexes were attempted. The f i r s t involved thermolysis of the analogous te t r a k i s ( p y r i d i n e ) complexes. This route has been used successfully for the synthesis of several b i s ( p y r i d i n e ) i r o n d l ) halide and pseudohalide complexes. 6 7 D.S.C. results indicate the loss of two molecules of pyridine from the t e t r a k i s ( p y r i d i n e ) i r o n d l ) derivatives occurs as the f i r s t step. Thermolysis of F e ( p y ) « ( C F 3 S O 3 ) 2 , in vacuo, indeed leads to the i s o l a t i o n of the bis(pyridine) analogue. For the methanesulfonate and p-tosylate derivatives, however, thermolysis in vacuo proved unsuccessful in i s o l a t i n g the desired bis(pyridine) complexes. Heating to temperatures of 360 and 350 K for the methanesulfonate and p-tosylate complexes respectively, results in no loss of pyridine, as monitored by infrared spectroscopy and microanalytical data; whereas, at the higher temperatures of 370 and 360 K respectively, the same techniques indicate loss of more than the two moles of pyridine. These observations suggest that the choice of temperature for the vacuum thermolysis of these two materials is more c r i t i c a l than for the corresponding t r i f l a t e d e r i v a t i v e . The second preparative route involved the addition of pyridine to a methanolic solution of the appropriate i r o n d l ) sulfonate in a 2 to 1 mole r a t i o . Slow evaporation of the resulting solution consistently gave the t e t r a k i s ( p y r i d i n e ) i r o n d l ) complexes. Attempts at obtaining 190 bis(pyridine) complexes by using pyridine to metal ratios of less than 2 to 1 were also unsuccessful. 4.2.1.1 B i s ( p y r i d i n e ) i r o n d l ) trifluoromethanesulfonate, F e ( p y ) 2 ( C F 3 S 0 3 ) 2 On a preparative scale i t was found that heating F e ( p y ) 4 ( C F 3 S O 3 ) 2 > in vacuo, at a temperature of approximately 360 K for 22 h resulted in loss of two moles of pyridine and production of F e ( p y ) 2 ( C F 3 S 0 3 ) 2 . Anal. calcd for FeC, 2H, 0N 2F 6S 20 6: C, 28.14; H, 1.97; N, 5.47; found: C, 28.15; H, 2.04; N, 5.63. Upon further heating at t h i s temperature no further loss of pyridine was recorded. 4.2.2 Mono(pyrazine) Complexes Several mono(pyrazine) complexes were isola t e d during the course of t h i s study. A thermolysis route proved successful in the i s o l a t i o n of Fe(pyz)(CF 3S0 3) 2, Fe(pyz)(p-CH 3C 6H f lS0 3) 2, Cu(pyz)(CF 3S0 3) 2 and F e ( p y z ) C l 2 . The mono(pyrazine) complexes: Fe(pyz)(p-CH 3C 6H 4S0 3) 2.2CH 3OH, and Fe(pyz)(NCO) 2 were isolated via a solution method. 4.2.2.1 Mono(pyrazine)iron(II) trifluoromethanesulfonate, Fe(pyz)(CF 3S0 3) 2 Thermal analysis (Section 3.3.6) indicates the formation of the mono(pyrazine) derivative by the loss of pyrazine and methanol from Fe(pyz) 2(CF 3S0 3) 2.CH 3OH. The same chemical change took place when the bis(pyrazine) complex was heated for 15 h 191 (in vacuo) at 380 K in the presence of P 20 5 in an Aberhalden drying p i s t o l . The infrared spectrum of the product shows si g n i f i c a n t changes from that of the st a r t i n g material and the microanalytical data are consistent with the formation of the mono(pyrazine) complex. Anal. calcd for FeC 6H aN 2F 6S 20 6: C, 16.60; H, 0.93; N, 6.45; found: C, 16.85; H, 0.98; N, 6.38. Heating for longer periods of time at the same temperature resulted in no further loss of pyrazine, as judged by infrared spectroscopy and microanalytical data. 4.2.2.2 Mono(pyrazine)irondl) p-toluenesulfonate bis(methanol) solvate, Fe(pyz)(p-CH 3C 6H«S0 3) 2.2CH 3OH I r o n d l ) p-toluenesulf onate 2 5 (0 .87 g, 2.2 mmol) was dissolved in methanol (10 mL). Pyrazine (0.77 g, 9.6 mmol), dissolved in methanol/diethyl ether (12 mL, 1:5v/v), was then added to t h i s solution. Small, orange-yellow c r y s t a l s formed after 1/2 h and after three days the s o l i d was removed by f i l t r a t i o n and the product was washed with a small amount of diethyl ether ( y i e l d 66%). Anal. calcd for F eC 2 0H 2 6N 2S 20 8: C, 44.29; H, 4.83; N, 5.16; found: C, 44.05; H, 4.71; N, 4.93. 192 4.2.2.3 Mono(pyrazine)irondl) p-toluenesulfonate, Fe(pyz)(p-CH 3C 6H aS0 3) 2 The unsolvated compound was prepared by heating the solvate, prepared as described above, at approximately 340 K in vacuo for 16 h. Anal. calcd for FeC, 8H, 8N 2S 20 6: C, 45.20; H, 3.79; N, 5.85; 0, 20.07; found: C, 44.98; H, 3.77; N, 5.77; 0, 19.86. 4.2.2.4 Mono(pyrazine)copper(II) trifuoromethanesulfonate, C u ( p y z ) ( C F 3 S O 3 ) 2 D.S.C. results (Section 3.3.6) indicate the loss of not only water but also three moles of pyrazine from C u ( p y z ) 4 ( C F 3 S O 3 ) 2 , H 2 0 . Upon heating the tetrakis(pyrazine) complex in an Aberhalden drying p i s t o l at a temperature of 360 K in the presence of phosphorus(V) oxide for 14 h in vacuo the mono(pyrazine) complex was produced. Anal. calcd for CuC 6H aN 2F 6S 20 6: C, 16.31; H, 0.91; N, 6.34; found: C, 16.33; H, 1.00; N, 6.24. 4.2.2.5 Mono(pyrazine)irondl) chloride, Fe(pyz)Cl 2 The synthesis involved the thermolysis of F e ( p y z ) 2 C l 2 for 3 days at a temperature of 380 K in an Aberhalden drying p i s t o l . Anal. calcd for FeC«H„N 2Cl 2: C, 23.23; H, 1.95; N, 13.54; found: C, 23.15; H, 1.99; N, 13.36. 193 4.2.2.6 Mono(pyrazine)irondl) cyanate, Fe(pyz)(NCO) 2 The mono(pyrazine) complex was prepared by a similar route to that used for Fe(pyz) 2(NCS) 2, (Section 3.2.3.7); for the cyanate d e r i v a t i v e , KCNO was used in place of KCNS. I r o n d l ) sulfate heptahydrate (1.079 g; 3.88 mmol) was dissolved in water (5 mL). To t h i s solution was added an aqueous solution (5 mL) of potassium cyanate (0.644 g; 8.06 mmol). This solution was f i l t e r e d d i r e c t l y into an aqueous solution (10 mL) of pyrazine (0.645 g; 7.93 mmol). A dark-purple s o l i d formed instantly and the mixture was s t i r r e d for 2 h. The product was isolated in 77% y i e l d a f t e r f i l t r a t i o n and washing with a small amount of water and methanol. Anal, calcd for FeC6Hi,N,,02: C, 32.76; H, 1.83; N, 25.47; O, 14.55; found: C, 32.69; H , 1.89; N, 25.31; 0, 14.62. 194 4.3 RESULTS AND DISCUSSION 4.3.1 Infrared Spectroscopy 4.3.1.1 F e ( p y ) 2 ( C F 3 S 0 3 ) 2 V i b r a t i o n a l assignments for the bis(pyridine) derivative were made on the basis that the absorption bands originate from two constituent parts, namely, the pyridine groups and the t r i f l a t e anions. Vibrational assignments for the pyridine ligands are given in Appendix II for comparison with those of the t e t r a k i s ( p y r i d i n e ) complexes. The 8a and 16b pyridine ligand vibrations are shifted considerably, by approximately 20 cm"1, from those of the free ligand; the 6a pyridine v i b r a t i o n i s probably obscured by the anion band at 635 cm"1. The s h i f t s and s p l i t t i n g s of the pyridine vibrations are similar to those present in the infrared spectrum of Fe(py)«(CF 3S0 3) 2 and indicate the coordination of pyridine. The v i b r a t i o n a l assignments for the anion are given in Appendix I I I , Part A. The bands assigned to the t r i f l a t e anion show many s i m i l a r i t i e s with the corresponding absorption bands in Fe(py)„(CF 3S0 3) 2 and the anion spectra for the bis(pyridine) complex are assigned on the basis of a reduction of anion symmetry below that of the free ion ( i . e . , below C.j v). For example, the s p l i t t i n g of the asymmetric S0 3 stretching mode, v„, i s a clear indication of this reduction of anion symmetry. The magnitude of the s p l i t t i n g of this band i s , however, di f f e r e n t in the two t r i f l a t e derivatives and t h i s provides 195 information on the mode of anion coordination. For F e ( p y ) 2 ( C F 3 S O 3 ) 2 , the s p l i t t i n g of thi s band i s 111 cm*1; whereas, in the tetrakis(pyridine) complex the s p l i t t i n g i s s i g n i f i c a n t l y lower, 85 cm"1. The degree of s p l i t t i n g of the band has been used to indicate bidentate anion coordination in ( C H 3 ) 2 S n ( F S O 3 ) 2 . 1 6 2 In t h i s t i n complex, bidentate anion coordination was proposed on the basis of spectroscopic measurements including infrared data. It was noted that the s p l i t t i n g of the anion band, v^, was substantially larger than in complexes where the anion is coordinated in a unidentate mode. A bidentate mode of coordination was subsequently established by X-ray c r y s t a l l o g r a p h y . 1 6 3 The larger s p l i t t i n g of vu in the bis(pyridine) complex, when compared to F e ( p y ) u ( C F 3 S O 3 ) 2 , suggests a bidentate mode of anion coordination in the former compound. The remaining absorption bands assigned to the anion show only small differences with the assignments made for F e ( p y ) 0 ( C F 3 S O 3 ) 2 (Appendix I I I , Part A) and indicate that these bands are insensitive to the mode of anion coordination. These infrared spectral data c l e a r l y eliminate the p o s s i b i l i t y that the product of the thermolysis of Fe(py) f l(CF 3S0 3) 2 i s an equimolar mixture of the tetrakis(pyridine) compound and Fe ( C F 3 S 0 3 ) 2 . In p a r t i c u l a r , infrared spectroscopy would detect the anhydrous sulfonate compound through the presence of an intense band at 1239 cm'1 (the asymmetric S0 3 stretching v i b r a t i o n 2 5 ) and thi s i s not observed in the spectrum of F e ( p y ) 2 ( C F 3 S 0 3 ) 2 . 196 4.3.1.2 Fe(pyz)Cl 2 and Fe(pyz)(NCO) 2 The infrared spectra of these complexes are i l l u s t r a t e d in F i g . 4.2 and the absorptions assigned to pyrazine are tabulated in Appendix VI. The infrared spectrum of Fe(pyz)Cl 2 i s r e l a t i v e l y simple, e s p e c i a l l y in comparison to that of F e ( p y z ) 2 C l 2 (Section 3.3.2.2). The pyrazine vibrations in Fe(pyz)Cl 2 show no evidence for band s p l i t t i n g in contrast to the s p l i t t i n g observed in the infrared spectrum of F e ( p y z ) 2 C l 2 (Appendix IV). For the bis(pyrazine) complex, the s p l i t t i n g was attributed to interactions between adjacent pyrazine rings and in the mono(pyrazine) compounds these interactions are l i k e l y to be absent i f the pyrazine rings are trans-disposed to one another (Fig. 4.1c). The infrared a c t i v i t y of the pyrazine vibrations in Fe(pyz)Cl 2 i s similar to that in known pyrazine-bridged s p e c i e s 3 7' and i s consistent with the ligand retaining symmetry by coordinating in an equivalent manner to two metal centres. The infrared spectrum of Fe(pyz)(NCO) 2 is i l l u s t r a t e d in F i g . 4.2 and the spectral data assigned to pyrazine are tabulated in Appendix VI. From F i g . 4.2 the s i m i l a r i t i e s and differences between the infrared spectrum of Fe(pyz)(NCO) 2 and Fe(pyz)Cl 2 are immediately apparent. In p a r t i c u l a r , the absorptions assigned to pyrazine are v i r t u a l l y i d e n t i c a l for the two complexes and a bidentate bridging mode of coordination for pyrazine i s proposed for both complexes. The differences between the two spectra are attributed to the strong absorptions of the cyanate anion in the infrared spectrum of Fe(pyz)(NCO) 2. 1 9 7 . 4.2 Infrared Spectra of Fe(pyz)Cl 2 and Fe(pyz)(NCO) 2 WAVENUMBER / c m - 1 1 98 P r e v i o u s r e s e a r c h 1 2 e > 1 2 7/ 1 6 *> 1 6 5 on the n a t u r e of NCO" c o o r d i n a t i o n s u g g e s t s s e v e r a l modes a r e p o s s i b l e and these i n c l u d e : t e r m i n a l b o n d i n g , t h r o u g h e i t h e r oxygen or n i t r o g e n ; and b r i d g i n g , e i t h e r M-NCO-M' or M-N-M'. I n f r a r e d c r i t e r i a have been e s t a b l i s h e d f o r d e t e r m i n i n g some of thes e c o o r d i n a t i o n modes. 1 2 6< 1 2 7< 1 6 0 The t h r e e normal v i b r a t i o n s of the t r i a t o m i c NCO" a n i o n a re the asymmetric s t r e t c h i n g v i b r a t i o n , "CN' ^ v^'' t n e bending v i b r a t i o n , 6..^, ( v 2 ) , and the pseudo-symmetric s t r e t c h i n g v i b r a t i o n , (J > 3 ) . In cyan a t e compounds, t h e s e v i b r a t i o n a l modes a r e a p p r e c i a b l y mixed. From the i n f r a r e d spectrum of KNCO 1 6 6 the f o l l o w i n g v i b r a t i o n a l a s s i g n m e n t s (cm" 1) have been made f o r the a n i o n : f l " 2 " 3 2170 629 1254 The v a l u e of v3 was c a l c u l a t e d from the Fermi resonance i n t e r a c t i o n . 1 6 7 From the i n f r a r e d spectrum of F e ( p y z ) ( N C O ) 2 the f o l l o w i n g a s signments (cm" 1) a r e made: 2200s 658s 2 l 0 0 s h 620s The vx and v2 v i b r a t i o n s appear t o be s p l i t and vz was not ob s e r v e d . I t has been noted p r e v i o u s l y , t h a t upon c o o r d i n a t i o n of the cyanate a n i o n the f r e q u e n c y of v, i n c r e a s e s when compared t o t h e f r e e - i o n v a l u e 1 2 6 * 1 2 1> 1 6 4 and t h i s a l s o o c c u r s f o r F e ( p y z ) ( N C O ) 2 . For t h i s complex, the v a l u e of 2200 cm" 1 f a l l s w i t h i n the range f o r e i t h e r a t e r m i n a l l y N-bonded or b r i d g i n g 199 cyanate anion, and t h i s absorption i s not useful in distinguishing these two coordination modes. The magnitude of the s p l i t t i n g of the v2 vibration has been found to be a good indicator for the presence of bridging NCO' a n i o n s . 1 2 6 ' 1 2 7 ' 1 6 4 In terminally N-bonded cyanate complexes, thi s band i s often s p l i t but the magnitude of the s p l i t t i n g i s usually of the order of a few wavenumbers. The s p l i t t i n g of the v2 vibration in Fe(pyz)(NCO) 2, by 38 cm - 1, indicates a bridging mode for the anionic ligand. The >NCO mode of cyanate bridging has been observed by X-ray crystallography in AgNCO16 8 and is the most common bridging mode. In thi s s i l v e r s a l t , which contains zig-zag chains of -Ag-N-Ag-N- units, the v2 vibration is s p l i t by 59 cm' 1. 1 6* The magnitude of the s p l i t t i n g of the v2 vibration in Fe(pyz)(NCO) 2 suggests an anion bridging mode in this complex, possibly s i m i l a r to that observed in AgNCO. The v3 vibration i s not observed in the infrared spectrum of Fe(pyz)(NCO) 2. This i s not unexpected and in other complexes containing bridging cyanate groups th i s band i s often of a much-reduced i n t e n s i t y . 1 2 7 4.3.1.3 Mono(pyrazine) sulfonate complexes. Infrared spectral assignments for the neutral ligand (Appendix VI) and the sulfonate anions (Appendix I I I , Parts A and C) are discussed for the following complexes: F e ( p y z ) ( C F 3 S O 3 ) 2 , Fe(pyz)(p-CH 3C 6H f lS0 3) 2 (and i t s bis(methanol) solvate), and Cu(pyz)(CF 3S0 3) 2. The spectrum of a representative member of t h i s class of compound, that of 200 F e ( p y z ) ( C F 3 S O 3 ) 2 , i s i l l u s t r a t e d in F i g . 4.3. F i g . 4.3 Infrared Spectrum of Fe(p y z ) ( C F 3 S 0 3 ) 2 1 1 1 ' r 1 1 1 r H00 1200 1000 800 600 400 WAVENUMBER / c n r 1 In general, i t i s noted that the v i b r a t i o n a l assignments made for the anions in these compounds (Appendix I I I , Parts A and C) bear a strong resemblance to those made for the sulfonate anions in the analogous t e t r a k i s ( p y r i d i n e ) and bis(pyrazine) complexes (Section 3.3.2.1 and 3.3.2.3). For example, three absorption bands are observed in the S0 3 stretching region and the s p l i t t i n g of the asymmetric S0 3 stretching vibration, vit i s conclusive evidence for the reduction of anion symmetry to below C j v . Such a reduction, either to C g or C^, can result from either uni- or bidentate anion coordination. It was hoped that these infrared data would provide evidence for the mode of anion 201 coordination. From the results for F e ( p y ) 2 ( C F 3 S 0 3 ) 2 (Section 4.3.1.1) i t was suggested that an increase in the s p l i t t i n g of the anion band, v^, may arise from a bidentate mode of coordination. For the mono(pyrazine) complexes, the magnitude of t h i s band s p l i t t i n g i s , in general, larger ( i . e . , greater than 100 cm"1) than for either the bis(pyrazine) or tetrakis(pyridine) compounds ( i . e . , less than 100 cm - 1). This may indicate a bidentate mode of anion coordination in these mono(pyrazine) complexes. It i s intere s t i n g to note that the s p l i t t i n g of of 115 cm - 1 for Fe(pyz)(CF 3S0 3) 2 is of a similar magnitude to the value of 111 cm - 1 observed for F e ( p y ) 2 ( C F 3 S 0 3 ) 2 ; this would be expected i f both complexes have a similar mode of anion coordination possibly of a bidentate nature. A large s p l i t t i n g of v« indicates bidentate sulfonate anion coordination but i t should also be pointed out that the lack of a large s p l i t t i n g of thi s band does not necessarily eliminate the p o s s i b i l i t y of bidentate anion coordination, as the following example has demonstrated. X-ray crystallography demonstrated the presence of bidentate bridging methanesulfonate anions in an indium porphyrin complex; 1 0* anions link the porphyrin units to form an i n f i n i t e linear chain compound. The infrared spectrum was assigned and the symmetric S0 3 stretching v i b r a t i o n (v}) occurs at 1040 cm - 1 and the asymmetric stretching vibrations U«) are at 1130, 1150, 1250 and 1260 cm"1. The vu v i b r a t i o n shows additional small s p l i t t i n g s but the positions of the bands are similar to those observed for unidentate methanesulfonate anions (for example, see the data for 202 F e ( p y ) « ( C H 3 S O 3 ) 2 in Appendix II I , Part B). It should be noted that the other v i b r a t i o n a l assignments for the anions in the mono(pyrazine) sulfonate complexes studied here are similar to those made for the sulfonate anions which were shown to be coordinated in a unidentate manner, (Section 3.3.2.1) and i t appears that these absorption bands are insensitive to the mode of anion coordination. The absorption bands assigned to the neutral ligand are l i s t e d in Appendix VI. Many of the pyrazine absorptions are obscured by the strong absorptions of the anions (1000-1200 cm - 1 region) but some information concerning the coordination of the neutral ligand was obtained from the bands which were assigned. As observed for Fe(pyz)(NCO) 2 and Fe(pyz)Cl 2, the pyrazine vibrations in the mono(pyrazine) sulfonate compounds show no s p l i t t i n g s ; in contrast to the bis(pyrazine) complexes for which pyrazine band s p l i t t i n g was found to be the rule rather than the exception. The r e l a t i v e l y simple nature of these pyrazine-ligand spectra (with the exception of Fe(pyz)(p-CH 3C 6H 4S0 3) 2•2CH 3OH), may be a result of there only being one d i s t i n c t type of pyrazine ligand; moreover, an interaction between pyrazine groups which can lead to band s p l i t t i n g would be expected to be non-existent when the pyrazine moieties are trans-disposed to one another. The vibrational assignments for pyrazine in Fe(pyz) (p-CH3C6H,,S03) 2.2CH3OH, however, do show additional s p l i t t i n g s which may be due to interactions of the pyrazine groups with the methanol solvent molecules present in the l a t t i c e . A similar explanation was 2 0 3 proposed for the complex infrared spectrum of F e ( p y z ) 2 ( C F 3 S 0 3 ) 2 . C H 3 O H (Section 3.3.2.3). For these mono(pyrazine) complexes, the remaining unassigned absorptions are l i s t e d in Appendix II I , Parts A and C. No useful information concerning the coordination modes of the either the anionic or neutral ligands was obtained from these absorptions which primarily arise from either the CF 3, CH3 or p-CH 3C 6H„ groups and, in one case, solvent molecules. It i s useful to summarise the infrared spectral results for these mono(pyrazine) and bis(pyridine) complexes. There i s evidence to suggest bidentate bridging pyrazine and terminally coordinated pyridine ligands respectively. There i s strong evidence for bridging cyanate anions in Fe(pyz)(NCO) 2; whereas, the evidence for the mode of anion coordination i s not as conclusive in the sulfonate complexes. The s p l i t t i n g of v« indicates either C or C. anion symmetry and a bidentate mode of anion coordination i s suggested by the magnitude of t h i s s p l i t t i n g . 204 4.3.2 Elect r o n i c Spectroscopy In t h i s section the electronic spectral data are reported and from the analysis of t h i s data the chromophore determined. The complexes are considered in two categories. The results for mono(pyrazine) and bis(pyridine) sulfonate compounds are presented in Section 4.3.2.1, and in Section 4.3.2.2 the ele c t r o n i c spectral results for Fe(pyz)Cl 2 and Fe(pyz)(NCO) 2 are discussed. 4.3.2.1 F e ( p y z ) ( C F 3 S O 3 ) 2 , Fe(pyz)(p-CH 3C 6H 4S03) 2 (and i t s bis(methanol) solvate), F e ( p y ) 2 ( C F 3 S 0 3 ) 2 and Cu(pyz)(CF 3S0 3) 2 E l e c t r o n i c spectral data are given in Appendix VII, Parts A and B, for the iron and copper complexes respectively. The colour of the iron complexes ranges from pale-yellow to orange, and a l l exhibit a broad absorption band in the near-infrared region of the electromagnetic spectrum. The position of the absorption maximum occurs at approximately the same frequency (10,800-10,900 cm - 1) which i s strong evidence to suggest the same chromophore in a l l instances. In general, the mono(pyrazine) and b i s ( p y r i d i n e ) i r o n d l ) complexes exhibit an absorption maximum at s l i g h t l y lower frequency than do the corresponding bis(pyrazine) or tetrakis(pyridine) derivatives. Since pyrazine and pyridine are both higher in the spectrochemical series than the weakly basic sulfonate anions, the observation of a s h i f t in the absorption maxima to lower frequency i s consistent with the removal of either two terminal pyridine ligands or one bidentate bridging pyrazine group and 205 conversion of the sulfonate anion from a uni- to a bidentate mode of coordination resulting in an FeN2Ofl chromophore. The results are also consistent with a distorted pseudooctahedral arrangement since geometries such as square-planar or tetrahedral are expected to exhibit a d i f f e r e n t number of absorptions occurring at d i f f e r e n t frequencies from those observed here. C u ( p y z ) ( C F 3 S O 3 ) 2 i s a pale-blue colour and shows a broad absorption band in the v i s i b l e region of the spectrum, the frequency of t h i s band (13,900 cm - 1) i s similar to that of C u ( p y z ) 2 ( C H 3 S O 3 ) 2 (14,000 cm - 1). This observation i s consistent with C u ( p y z ) ( C F 3 S O 3 ) 2 possessing a d i s t o r t e d pseudooctahedral chromophore. It i s concluded on the basis of t h i s e lectronic spectral analysis that the mono(pyrazine) and bis(pyridine) sulfonate complexes contain an MN 20„ chromophore. For F e ( p y ) 2 ( C F 3 S 0 3 ) 2 , t h i s would involve bidentate bridging t r i f l a t e anions and coordinated pyridine groups. In addition to containing bridging anions, the mono(pyrazine) compounds are considered to possess bridging pyrazine ligands. Possible structures which f u l f i l l these coordination requirements for both the neutral ligand and the anions are shown in Figs. 4.1c and 4.1d. 4.3.2.2 Fe(pyz)Cl 2 and Fe(pyz)(NCO) 2 Both compounds exhibit absorptions in the near-infrared region at approximately 11,000 cm - 1 which i s a t y p i c a l value for distorted pseudooctahedral i r o n d l ) complexes. The close 206 s i m i l a r i t y between the band positions for the mono(pyrazine) and bis(pyrazine) chloride complexes indicates the equivalent ligand f i e l d strengths associated with the two complexes. During the course of the present study, i t was observed that several of the complexes are intensely coloured (brown, red or purple). For complexes containing an FeNnX2 chromophore, the combined presence of pyrazine and either halide or thiocyanate appear to be a prerequisite for an intense colouration (Section 3.3.3.3). For the iron complexes discussed here a similar observation was made. For example, F e ( p y z ) C l 2 a n d Fe(pyz)(NCO) 2 are red-brown and dark-purple respectively. On the other hand, the mono(pyrazine) sulfonate complexes (Section 4.3.2.1) are either pale-yellow or orange and the pyridine complexes F e ( p y ) 2 C l 2 and Fe(py) 2(NCO) 2 are pale yellow. 6 7 An explanation for the orig i n s of these colours was made in Section 3.3.3.3 and may also apply here; i . e . , the intense colour i s due to charge-transfer absorption bands which involve not only metal to neutral ligand but also anionic ligand to metal. For the complexes which contain sulfonate anions or pyridine ligands, the charge-transfer t r a n s i t i o n i s of high energy and i s not observed in the v i s i b l e region of the spectrum. 207 4.3.3 Magnetic Properties For these mono(pyrazine) and bis(pyridine) complexes there are no X-ray st r u c t u r a l data; however, st r u c t u r a l information was obtained from the techniques of infrared and electronic spectroscopy (Sections 4.3.1 and 4.3.2 respectively). These data indicate that the metal centre maintains six coordination and an MN2Xfl chromophore results from the coordination of four donor atoms from bidentate anionic ligands, together with two nitrogen donor atoms from either a single bidentate bridging pyrazine or two terminal pyridine ligands. It appears l i k e l y that these materials are polymeric and possible structures for these complexes are shown in Fi g . 4.1c and d. The magnetic s u s c e p t i b i l i t i e s of these complexes were measured in an attempt to determine the presence of magnetic exchange interactions and to correlate the magnetic properties with structure. For the purpose of this discussion, the complexes are divided into two categories according to the metal. The magnetic properties of C u ( p y z ) ( C F 3 S O 3 ) 2 are discussed p r i o r to the results for the i r o n d l ) compounds, F e ( p y ) 2 ( C F 3 S 0 3 ) 2 , Fe(pyz)(CF 3S0 3) 2, Fe(pyz)(p-CHaCgH^SOs) 2 (and i t s bis(methanol) solvate), Fe(pyz)Cl 2 and Fe(pyz)(NCO) 2. 4.3.3.1 Cu(pyz)(CF 3S0 3) 2 Results of the magnetic measurements are presented in Appendix VIII. The magnetic moment of Cu(pyz)(CF 3S0 3) 2 shows a si g n i f i c a n t temperature dependence; at room temperature the magnetic moment is 1.9 B.M. and t h i s decreases to 1.7 B.M. at 208 100 K, at 4.2 K the moment i s reduced further to 0.85 B.M. The temperature dependence i s shown in F i g . 4.4, along with the plot for the magnetically-dilute complex, Cu(pyz)„(CF 3S0 3) 2.H 20 for comparison. The magnetic s u s c e p t i b i l i t y (Fig. 4.5) increases with decreasing temperature u n t i l a maximum i s observed at approximately 7 K. Below th i s temperature, down to 4.2 K, the magnetic s u s c e p t i b i l i t y decreases. These temperature dependencies of ve£f a n c< a r e c l e a r l y a consequence of antiferromagnetic exchange interactions propagated through the bridging ligands. F i g . 4.4 Magnetic Moments vs Temperature for Cu(pyz)(CF 3S0 3) 2 and Cu(pyz),(CF 3S0 3) 2.H 20 CD • Cu(pyz)„(CF 3S0 3) 2.H 20 2.0-ttKaDo€ o o 0 o o o o o o a n o o o o o 1.0-A Cu(pyz)(CF 3S0 3) 2 I D < o- n 1 1 i i i r 20 40 60 80 TEMPERATURE /K 0 100 209 F i g . 4.5 Magnetic S u s c e p t i b i l i t y vs Temperature for C u ( p y z ) ( C F 3 S O 3 ) 2 a) . Two-dimensional model, s o l i d l i n e generated from J=-2.43 cm"1, g=2.l0 b) . Linear chain model, s o l i d l i n e generated from J=-3.78 cm"1, g=2.08 1- 20H o E CO E L J \ o T — X >-GO CO ZD CO < 10" 20-10H 0-a). Two-dimensional model b). Linear chain model 0 20 i i i i i i r 40 60 80 100 TEMPERATURE / K 210 Infrared and electronic spectroscopic results (Sections 4.3.2 and 4.3.3 respectively) suggest that Cu(pyz)(CF 3S0 3) 2 contains bridging pyrazine and bridging t r i f l a t e anions and hence, a polymeric structure i s l i k e l y (Fig 4.1d). From the spectroscopic data presented above, i t i s d i f f i c u l t to distinguish between the possible structures shown in F i g . 4.1d. The magnetic s u s c e p t i b i l i t y data for the t r i f l a t e derivative and Cu(pyz) 2(CH 3S0 3) 2 exhibit similar temperature dependencies which suggests that the dominant magnetic exchange pathway may be similar in both compounds. Considering t h i s proposal, the Lines' two-dimensional model (Eqn. 3.5) was employed to represent the magnetic s u s c e p t i b i l i t y data of Cu(pyz)(CF 3S0 3) 2 and the best f i t i s represented by the s o l i d l i n e in F i g . 4.5a which was generated from the following parameters: J=-2.43 cm"1, g=2.l0, (F=0.0216). The s u s c e p t i b i l i t y data for Cu(pyz) 2(CH 3S0 3) 2 were analysed equally as well using a one-dimensional linear chain model (Section 3.3.4.1); th i s was explained by the presence of two inequivalent exchange pathways through pyrazine. Spectroscopic evidence indicates that Cu(pyz)(CF 3S0 3) 2 has a structure which may be represented by one of those shown in F i g . 4.1d. From these structures i t i s clear that there are at least two d i s t i n c t pathways for magnetic exchange, one route through bridging pyrazine rings and the second route through bridging t r i f l a t e anions. These pathways are unlikely to be equivalent and indeed, the magnetic properties of the mono(pyrazine) derivative are also successfully represented by the l i n e a r chain 21 1 model (Eqn. 3.7). The parameters obtained with th i s model are as follows: J=-3.78 cm"1, g=2.08, (F=0.0126); the best f i t is shown as the s o l i d l i n e in F i g . 4.5b. In fact, for C u ( p y z ) ( C F 3 S O 3 ) 2 , the f i t of the magnetic s u s c e p t i b i l i t y data to the one-dimensional model i s s l i g h t l y improved over that for the two-dimensional model as measured by the re l a t i v e values of F and judged v i s u a l l y . The s i m i l a r i t y between the magnetic properties of Cu(pyz)(CF 3S0 3) 2 and Cu(pyz) 2(CH 3S0 3) 2 suggests that the feature common to both complexes i s strongly bridging pyrazine groups along one dimension. This ligand may provide a more f a c i l e route for magnetic exchange interactions than other bridging e n t i t i e s (the a x i a l pyrazine group in one case and the t r i f l a t e anion in the other). 4.3.3.2 Mono(pyrazine) and bis ( p y r i d i n e ) i r o n ( I I ) complexes The magnetic s u s c e p t i b i l i t y measurements for compounds of these two types are l i s t e d in Appendix IX, Part B. The mono(pyrazine) compounds, Fe(pyz)(CF 3S0 3) 2 and Fe(pyz)(NCO) 2 exhibit p a r t i c u l a r l y interesting magnetic properties, with both compounds showing strongly temperature-dependent magnetic moments (Fig. 4.6). At room temperature both complexes exhibit a magnetic moment value of approximately 5 B.M., as expected for high-spin iron(II) compounds; whereas, at 4.2 K the magnetic moment value decreases to 0.88 and 2.94 B.M. for the cyanate and t r i f l a t e derivatives respectively. Both species exhibit a maximum in th e i r magnetic s u s c e p t i b i l i t y data (Figs. 4.7 and 4.8), a cl e a r indication of antiferromagnetic exchange 212 interactions. The maximum for the cyanate derivative occurs at approximately 38 K indicating a much stronger interaction than in the t r i f l a t e where the maximum i s at the lower temperature of approximately 4.4 K. A further difference between the two magnetic s u s c e p t i b i l i t y curves i s that down to the lowest temperature studied the t r i f l a t e derivative has a s u s c e p t i b i l i t y which decreases and tends to zero; whereas, the s u s c e p t i b i l i t y for the cyanate derivative remains f a i r l y constant below a temperature of approximately 11 K. This low-temperature magnetic behaviour for the cyanate complex-may be attributed to the presence of a small amount of material which remains paramagnetic and is not converted to the antiferromagnetic phase. This i s suggested by the Mossbauer spectral data (Section 4.3.4.1). Structural evidence from spectroscopic data (Sections 4.3.1 and 4.3.2) indicates that both complexes possess bridging pyrazine moieties and either bridging t r i f l a t e or bridging cyanate anions. It is l i k e l y that both of these bridging units contribute to some extent to the superexchange between metal centres. 213 F i g . 4 .6 Magnetic Moments vs Temperature f o r Fe(pyz)(NCO) 2 and F e ( p y z ) ( C F 3 S 0 3 ) 2 5.0-A F e ( p y z ) ( C F 3 S 0 3 ) 2 cri 4.0- • Fe(pyz)(NCO) 2 S 3.0-51 I—« I— U J I D < 2.0H 1.0-0 20 40 60 80 TEMPERATURE /K 100 120 214 Fi g . 4.7 o E "E40-X >-30-00 &I20H L U 00 Magnetic S u s c e p t i b i l i t y vs Temperature for Fe(pyz)(NCO) 2 a) . Weng linear chain model, s o l i d l i n e generated from J=-5.18 cm"1, g=2.28 b) . Two-dimensional model, s o l i d l i n e generated from J=-3.94 cm'1, g=2.31 a). Weng linear chain model oo o -i 1 1 1 1 1 r 20 40 60 80 TEMPERATURE /K 100 120 215 Fi g . 4.8 O e CO e ^30(H ro o X >-r — • — i I t——i C D 20H a ioo-CO 00 0-Magnetic S u s c e p t i b i l i t y vs Temperature for Fe(pyz)(CF 3S0 3) 2 a) . Weng linear chain model, s o l i d l i n e generated from J=-0.76 cm*1, g=2.25 b) . Two-dimensional model, s o l i d l i n e generated from J=-0.26 cm - 1, g=2.20 0 a). Weng linear chain model 20 40 60 80 TEMPERATURE / K 10 120 „ 300H E L J \ o20H X >-00 ZD CO 0 0 20 b). Two-dimensional model T T 40 60 80 TEMPERATURE / K 100 120 216 The presence of a complex bridging network i s l i k e l y and th i s makes the analysis of the s u s c e p t i b i l i t y data rather d i f f i c u l t . The exchange mechanisms are almost certainly d i f f e r e n t through the pyrazine 71—system and through either a sulfonate bridge (O-S-0) or a cyanate bridge (possibly the single nitrogen atom, >NCO). In the extreme case, where one magnetic exchange mechanism is dominant, the magnetic s u s c e p t i b i l i t y may be represented by a one-dimensional linear chain model. . In another extreme case, where magnetic exchange proceeds to an equal extent through both bridging ligands then a model which allows for interactions in two dimensions may be more appropriate. From an experimental consideration, Mossbauer spectroscopy (Section 4.3.4.1) demonstrates that both Fe(pyz)(NCO) 2 and Fe(pyz)(CF 3S0 3) 2 magnetically order and in.the presence of long-range three-dimensional interactions any model which allows for interactions between neighbouring centres along a linear chain or throughout a two-dimensional l a t t i c e w i l l have limited a p p l i c a t i o n . With these lim i t a t i o n s in mind, the magnetic properties of the two compounds were analysed via a linear chain model and a two-dimensional model for S=2 in the isotropic Heisenberg l i m i t . For the anisotropic case, the Ising l i m i t , closed form solutions exist for both p a r a l l e l and perpendicular s u s c e p t i b i l i t i e s for only the S=l/2 linear chains, but these models are of limited application to S=2 systems. Within the Heisenberg l i m i t , two theoreti c a l approximations have been derived for antiferromagnetic linear chain systems which may be applied to 217 S=2. Wagner and F r i e d b e r g 1 6 9 have scaled the exact results of F i s h e r 1 7 0 to the series expansion results of Rushbrooke and Wood 1 7 1 and obtained the following expression for magnetic s u s c e p t i b i l i t y : x Nq 2g 2S(S+1) . i+U ...Eqn. 4.1 m kT 1-u where U=cothK-1/K and K=2JS(S+1)/kT. The other approximation method i s an interpolation scheme developed by Weng. 1 7 2 H i l l e r et a _ l . 1 7 3 have generated a series of c o e f f i c i e n t s to reproduce Weng's numerical re s u l t s . Accordingly: Xm « mill _ih±Ml±_ ... Eqn. 4.2 kT [1+Cx+Dx3] where x=|J|/kT, and for S=2, A=2.000, B=71.938, C=10.482, D=955.56. The experimental results for both compounds were analysed using these two models. The models produce s i m i l a r l y shaped curves with a rounded maximum. With the J and g values which were t r i e d , the computed curves never gave a sati s f a c t o r y match to the experimental data over the entire temperature range. Agreement between computed and experimental curves i s reasonable above the s u s c e p t i b i l i t y maximum but in the region of the maximum, and at lower temperatures, discrepancies between the two curves become larger. The Weng model was used to generate the s o l i d l i n e s in Figs. 4.7a and 4.8a; the l i n e s were 218 generated by using the following parameters: WENG -J/cnr 1 g F F e ( p y z ) ( C F 3 S O 3 ) 2 0.76 2.25 0.086 Fe(pyz)(NCO) 2 5.18 2.28 0.158 By using values of J and g which c l o s e l y resemble those given above, the model based upon the Wagner and Friedberg approach resulted in f i t s very similar to those shown in Figs. 4.7 and 4.8. WAGNER AND FRIEDBERG -J/cnr 1 g F F e ( p y z ) ( C F 3 S O 3 ) 2 0.84 2.26 0.104 Fe(pyz)(NCO) 2 5.18 2.31 0.158 From the f i t s i t appears that the magnetic properties of these two complexes are not well represented by the linear chain models. Attempts were made to f i t the magnetic s u s c e p t i b i l i t y data for both complexes to the Lines' two-dimensional model which was used to represent the magnetic properties of Cu(pyz) 2(CH 3S0 3) 2 (Sect ion 3.3.4.1) and Fe(pyz) 2(NCS) 2 (Section 3.3.4.3). The best f i t to the cyanate data i s shown in Fig . 4.7 where the s o l i d l i n e was generated using the following parameters: J=-3.94 219 cm - 1, g=2.31. This f i t i s not e n t i r e l y adequate; the calculated magnetic s u s c e p t i b i l i t y values diverge considerably from the experimental data esp e c i a l l y at temperature below 35 K. This may be attributed to either an inadequacy of the model or i t s i n a p p l i c a b i l i t y to i r o n d l ) complexes. The model ignores long-range three-dimensional magnetic ordering which i s not negl i g i b l e in Fe(pyz)(NCO) 2 as Mossbauer spectroscopy indicates a t r a n s i t i o n to a magnetically-ordered state at 27 K (Section 4.3.4.1). For F e ( p y z ) ( C F 3 S O 3 ) 2 , the agreement between the experimental and calculated magnetic s u s c e p t i b i l i t y data from the Lines' two-dimensional model i s excellent. The s o l i d l i n e through the data points (Fig. 4.8) represents the best f i t using the following parameter values: J=-0.26 cm"1 and g=2.20 (F=0.0381). This may r e f l e c t the two-dimensional nature of the exchange interaction in Fe(pyz)(CF 3S0 3) 2. The success of the two-dimensional model in representing the magnetic s u s c e p t i b i l i t y data for these two complexes may be a result of their proposed structures. For both complexes bridging anions may give r i s e to a one-dimensional li n e a r chain; these chains are then cross-linked through pyrazine (Fig. 4.1d(i)). Exchange interactions have been observed previously in Fe(py) 2(NCO) 2. 6 7 The bis(pyridine) complex and Fe(pyz)(NCO) 2 are proposed to contain cyanate ligands which l i n k metal centres by using a one atom bridge, i . e . , the single nitrogen. For Fe(py)2(NCO)2 this results in a linear chain structure (Fig. 4.1c(i)) and the coordination sphere around the metal is 220 completed by nitrogen donors from pyridine groups. In spite of the structural s i m i l a r i t i e s between these two complexes caused by the presence of bridging anionic ligands, their magnetic properties are s t r i k i n g l y d i f f e r e n t . The present study indicates that Fe(pyz)(NCO) 2 i s antiferromagnetic; whereas, the e a r l i e r magnetic s u s c e p t i b i l i t y study 6 7 showed that Fe(py) 2(NCO) 2 is ferromagnetic. The lack of X-ray structural data for both complexes makes i t d i f f i c u l t to explain the pronounced difference between their magnetic properties, however, the following rationale i s put forward. Since Fe(py) 2(NCO)2 is ferromagnetic, the o r b i t a l overlap through the nitrogen atom of the bridging cyanate group must be of an orthogonal nature. A similar ferromagnetic interaction along the chains in Fe(pyz)(NCO) 2 might be expected. The chains in the pyridine complex are e f f e c t i v e l y isolated; for the pyrazine complex, however, adjacent chains are linked through bridging pyrazine. The 7r-system of pyrazine i s l i k e l y to present an antiferromagnetic exchange pathway, and hence, the neighbouring chains are coupled in an antiferromagnetic sense, resulting in a net antiferromagnetic interaction. The results of the magnetic measurements for F e ( p y ) 2 ( C F 3 S O 3 ) 2 , Fe(pyz)(p-CH 3C 6H f tS0 3) 2, and i t s bis(methanol) solvate, and Fe(pyz)Cl 2 are tabulated in Appendix IX, Part B. The magnetic moment data for these complexes a l l decrease with decreasing temperature. None of these complexes, however, exhibits a maximum in the magnetic s u s c e p t i b i l i t y data and hence conclusive evidence for magnetic interactions i s lacking. The 221 absence of, or much weaker degree of, magnetic exchange in these compounds, makes for an interesting comparison with complexes such as Fe(pyz)(NCO) 2 and Fe(pyz)(CF 3S0 3) 2 which exhibit s i g n i f i c a n t exchange e f f e c t s . For example, i t may be expected that the structures of the mono(pyrazine)iron(II) cyanate and chloride derivatives would be s i m i l a r . Spectroscopic evidence suggests both complexes possess an FeN 2X 4 chromophore and that bridging anionic ligands as well as bridging pyrazine groups are present. Indeed, there are numerous examples of complexes in which bridging halide anions act as e f f i c i e n t agen-ts for the propagation of magnetic exchange i n t e r a c t i o n s 1 6 1 and i t i s surprising that such interactions are undetected in Fe(pyz)Cl 2 even at temperatures as low as 2 K. Spectroscopic evidence also indicates a close structural relationship between Fe(pyz)(p-CH 3C 6H aS0 3) 2 and Fe(pyz)(CF 3S0 3)2, i . e . , bridging pyrazine and bidentate bridging anionic ligands. The magnetic properties of the two materials, however, are quite d i s t i n c t . The p-tosylate derivative exhibits a weakly temperature-dependent magnetic moment in comparison to the r e l a t i v e l y greater temperature-dependent moment exhibited by the t r i f l a t e derivative. Due to lack of X-ray structural evidence for these complexes i t i s d i f f i c u l t to r a t i o n a l i s e these differences but a possible explanation may l i e in the more weakly basic nature of the t r i f l a t e r e l a t i v e to the p-tosylate anion. This could result in a stronger iron-pyrazine interaction in the t r i f l a t e derivative and therefore a more s i g n i f i c a n t exchange e f f e c t via pyrazine. 222 The four i r o n d l ) t r i f l a t e derivatives prepared in t h i s study provide for an int e r e s t i n g comparison (Table 4.1). Table 4.1 Selected Magnetic Moment Data for I r o n d l ) T r i f l a t e Complexes COMPOUND TEMP/K MAGNETIC MOMENT/B.M. Fe(py)„(CF 3S0 3) 2 300 5.38 4.2 4.54 F e ( p y ) 2 ( C F 3 S 0 3 ) 2 300 5.54 4.2 3.61 Fe(pyz) 2(CF 3S0 3) 2.CH 3OH 300 5.31 4.2 3.34 Fe(pyz)(CF 3S0 3) 2 300 5.42 4.2 3.04 For each compound the magnitude of the magnetic moment at 300 K l i e s in the narrow range 5.3-5.5 B.M.; whereas, at 4.2 K a si g n i f i c a n t spread in magnetic moment values occurs. At 4.2 K the magnetic moment values are in the order: Fe(py)„(CF 3S0 3) 2 > F e ( p y ) 2 ( C F 3 S 0 3 ) 2 > Fe(pyz)2(CF 3S0 3) 2.CH 3OH > Fe(pyz)(CF 3S0 3) 2. This order indicates an increase in antiferromagnetic interactions from the tetrakis(pyridine) complex to the mono(pyrazine) complex which appears to be in agreement with the proposed nature of the bridging system in each complex, i . e . , the lack of a bridging network in Fe(py)„(CF 3S0 3) 2, bridging t r i f l a t e only in F e ( p y ) 2 ( C F 3 S 0 3 ) 2 , bridging pyrazine in Fe(pyz) 2(CF 3S0 3) 2,CH 3OH and both bridging pyrazine and bridging t r i f l a t e anions in Fe ( p y z ) ( C F 3 S 0 3 ) 2 . No magnetic interactions 223 are observed in the complex which lacks bridging ligands and the magnetic interaction increases with the increasing number of bridging ligands; the combination of bridging t r i f l a t e and bridging pyrazine groups providing the most f a c i l e magnetic exchange pathway in t h i s series of complexes. 224 4.3.4 Mossbauer Spectroscopy In a l l cases Mossbauer spectra were recorded at l i q u i d nitrogen and room temperatures and the results are given in Appendix X, Parts A and B. Because of the presence of antiferromagnetic interactions in Fe(pyz)(NCO) 2 and F e ( p y z ) ( C F 3 S O 3 ) 2 additional spectra were measured from temperatures s l i g h t l y above the temperature of the s u s c e p t i b i l i t y maximum down to 4.2 and 1.6 K respectively. For the cyanate derivative, the analysis of the spectra provided substantial evidence for structure; however, such a treatment for the t r i f l a t e derivative has s t i l l to be performed. At l i q u i d nitrogen temperature, the bis(pyridine) and mono(pyrazine) complexes exhibit isomer s h i f t values in the range of 1.0-1.3 mm s" 1 as expected for octahedral high-spin i r o n d l ) complexes. Small differences in isomer s h i f t values are observed for these complexes which may be correlated with the nature of the metal chromophore. For example, the t r i f l a t e derivatives, F e ( p y ) 2 ( C F 3 S 0 3 ) 2 and Fe(pyz)(CF 3S0 3) 2 have isomer s h i f t s which are s l i g h t l y higher than that of Fe(py)„(CF 3S0 3) 2. This increase probably arises from the more ionic bonding in the f i r s t two complexes which contain an FeN2Oi, chromophore compared to an FeN„0 2 chromophore in Fe(py) f l(CF 3S0 3) 2. A similar increase in isomer s h i f t i s observed for the p-tosylate derivatives. 225 4.3.4.1 Low-temperature Mossbauer studies on Fe(pyz)(NCO) 2 and F e ( p y z ) ( C F 3 S O 3 ) 2 The magnetic s u s c e p t i b i l i t y results for both compounds (Section 4.3.3) are c h a r a c t e r i s t i c of antiferromagnetic materials. Low-temperature Mossbauer spectra were recorded to determine the extent of any three-dimensional interactions. For Fe(pyz)(NCO)2 the low-temperature (4.2-31.4 K) Mossbauer spectra are shown in F i g . 4.9. The spectrum at 31.4 K i s e s s e n t i a l l y the same as that measured at 78 K. There i s some s l i g h t temperature-independent asymmetry in the intensity of the two li n e s of the quadrupole doublet at 78 K which p e r s i s t s down to 31.4 K; t h i s is attributed to a texture effect a r i s i n g from a preferred orientation of the c r y s t a l l i t e s in the absorber. Between 31.4 and 27.0 K the l i n e s of the quadrupole doublet broaden asymmetrically; t h i s can be seen from the linewidths and the intensity ratios given in Table 4.2. This l i n e broadening i s evidence for slow paramagnetic relaxation, probably as a result of residual short-range correlations between metal centres. Between 27.0 and 26.8 K resolved magnetic hyperfine s p l i t t i n g becomes apparent as a result of long-range three-dimensional ordering. From th i s observation i t is concluded that the Neel temperature i s within t h i s temperature range. At temperatures lower than T^ the quadrupole doublet p e r s i s t s and the spectra consist of two components, a paramagnetic phase and a magnetically-ordered phase. 2 2 6 F i g . 4.9 Low-Temperature Mossbauer Spectra of Fe(pyz)(NCO) 2 VELOCITY /mm s-1 227 F i g . 4.9 C o n t i n u e d VELOCITY /mm s-1 228 F i g . 4.9 Continued I 1 I 1 I 1 I 1 I 1 I 1 I 1 I - 7 - 5 - 3 - 1 1 3 5 7 V E L O C I T Y / m m s " 1 229 Table 4.2 Linewidths and Int e n s i t i e s (27.0-31.4 K) for Fe(pyz)(NCO) 2 TEMP/K r , 1 T 2 I , / I 2 27.0 0.28 0.25 0.750 27.2 0.24 0.21 0.802 27.4 0.26 0.23 0.845 31 .4 0.20 0.20 0.917 1). Linewidths are in units of mm s~ 1 a n d subscripts 1 and 2 refer to the low and high ve l o c i t y l i n e s respectively As the temperature is decreased, the disappearence of the paramagnetic component can be seen by the decrease in the intensity of the l i n e at approximately 2.5 mm s - 1 . At a temperature of 22.4 K (T/TN=0.83) the intensity of t h i s l i n e has decreased to such an extent that only a shoulder i s seen to the high-velocity side of the peak centred at approximately 1.7 mm s - 1 . Below 22.4 K, the paramagnetic phase appears to have been converted e n t i r e l y to the antiferromagnetically-ordered state and the spectra are as a result of just t h i s one component. This superparamagnetic behaviour could arise from the presence of small domain clusters which may aris e during the rapid p r e c i p i t a t i o n of the complex. The model used to describe the Mossbauer spectra of Fe(pyz) 2(NCS)2 (Section 3.3.5.3) was also employed to analyse the Mossbauer spectra of the cyanate compound. For Fe(pyz)(NCO)2 the Mossbauer spectra in the temperature range of 230 22-27 K were computed assuming one antiferromagnetic component and one paramagnetic component, the r e l a t i v e amounts of the two components used to f i t the spectra are related by the r a t i o indicating the presence of only the ordered phase; on the other hand, the s u s c e p t i b i l i t y data (Section 4.3.2.2) suggest that a small amount of paramagnetic phase pe r s i s t s to below 11 K. It appears that magnetic s u s c e p t i b i l i t y measurements are a more sensitive means of detecting such "impurities". At 22.4 K, the effect of ignoring any paramagnetic component may be seen. At this temperature the spectrum was f i t t e d in two d i f f e r e n t ways. The f i r s t method assumes the presence of only the antiferromagnetic phase; whereas, the second f i t takes into account both components. It can be seen that the second f i t is the better of the two. A l l spectra at T<27.0 K gave good f i t s with the following parameters: I a f m / I t o t (Table 4.3). Below 22.4 K, th i s r a t i o is unity, 6=1.17±0.01 mm s - 1 AE g=+2.78±0.02 mm s T?=0.44±0.03 - 1 r=0.23±0.02 mm s - i 0=9O±2° «=90±5° 231 Table 4.3 Internal Hyperfine F i e l d and Intensity Ratios 1 for Fe(pyz)(NCO) 2 Temp/K H i n t / T I a£m / I t o t 4.2 17.9 1 .000 18.2 17.5 1 .000 22.4 16.7 0.952 23.5 16.2 0.893 24.4 15.7 0.813 25.0 15.1 0.722 25.4 14.7 0.657 25.8 14.3 0.595 26.3 13.8 0.522 26.6 12.7 0.399 26.8 11.6 0.306 27. 1 6.8 0. 163 1) * a f m represents the f r a c t i o n of the sample which is in the antiferromagnetic phase The internal hyperfine f i e l d , H^nfc as a function of temperature is given in Table 4.3. From a consideration of these values several important conclusions were drawn concerning the structure of Fe(pyz)(NCO) 2• Spectroscopic evidence suggests that t h i s cyanate complex contains both bridging anions and bridging pyrazine and possible structures are represented by those shown in F i g . 4.1d. If the structure were as in F i g . 4.1(d) ( i i ) , then by analogy with Fe(pyz) 2(NCS) 2, an a x i a l l y symmetric E.F.G. would be expected which i s c e r t a i n l y not the case for the cyanate species (17=0.44), and also the angle <t> would be expected to be indeterminate; whereas, the simulated spectra require that t h i s angle be close to 90°. On the other hand, for the structure represented by that shown in F i g . 4.1d ( i ) , one can put forward an interpretation of the parameters that i s p l a u s i b l e . A not unreasonable choice of E.F.G. axis 232 system is shown for this structure in F i g . 4.10. Fig. 4.10 Possible E.F.G. Axis System for Fe(pyz)(NCO) 2 X=NC0 The xy-plane of the E.F.G. axis system i s in the plane of the paper and the z-axis i s normal to t h i s plane. The experimental result gives e2qQ>0, T?=0.44 and 6 and <t> approximately 90°, so that H^ n t i s p a r a l l e l to v v v ' From the sign and magnitude of e 2qQ and the magnitude of TJ, i t is clear that an a x i a l l y compressed structure is required and that the x- and y-directions must be inequivalent. The structure (Fig. 4.10) would f u l f i l l these two requirements i f the Fe-N(anion) bonds were shorter than the Fe-N(pyz) bonds. The observation that H i n t * s P a r a l l e l t o V y V indicates that the spins l i e close to th i s axis which indicates that the exchange coupling i s stronger through the cyanate ligands than through the pyrazine rings 233 which i s not unreasonable in view of the fact that magnetic exchange interactions through the pyrazine TJ—system are usually weak; whereas, through the single nitrogen atom of the cyanate anion they are l i k e l y to be s i g n i f i c a n t l y stronger. The hyperfine f i e l d at the iron nucleus (Table 4.3) is plotted as a function of temperature (Fig 4.11). F i g . 4.11 Hyperfine F i e l d vs Temperature for Fe(pyz)(NCO) 2 234 The hyperfine f i e l d saturates rapidly below 27.0 K and H^nfc at 0 K is found, by extrapolation, to be approximately 18.3 T. The temperature dependence of the internal hyperfine f i e l d provides support for the two-dimensional nature of the exchange interaction. In the c r i t i c a l region, the sublattice magnetisation, M(T), varies in the following way: 1 7" M(T)=M ( 0)D( 1 - T / T N ) 0 ...Eqn. 4.3 where |3 i s the c r i t i c a l exponent, D i s a reduction factor and M(0) i s the magnetisation at 0 K. If one assumes that M(T) is proportional to the internal f i e l d one can replace M by H^nfc. A plot of ln(.H i n t/H(0) ) versus l n ( l - T / T N ) should result in a straight l i n e whose slope i s /3. In the present study, such a log-log plot in the temperature range of 22-27 K gives a straight l i n e with a slope of 0.13. Theoretical e s t i m a t e s 1 7 5 have been made for the value of /3; for example, for a three dimensional Heisenberg model a 0 value of 0.333 has been calculated and for a two-dimensional Ising model 0=0.125. There have been no theore t i c a l estimates of /3 for either the two-dimensional Heisenberg or the three-dimensional Ising model. The value of /? of 0.13 found in the present study, i s close to that predicted by the two-dimensional model and indicates that Fe(pyz)(NCO) 2 may be regarded as a two-dimensional antiferromagnet even in the ordered phase. The magnitude of the internal magnetic hyperfine f i e l d is not unreasonable when one considers the factors which constitute 235 H i n t ( E c3 n* 3.15). For high-spin i r o n d l ) <S> = 2 and thus the expected contribution from the Fermi contact term, H p is approximately 44.0 T. The o r b i t a l contribution, H^, i s expected to oppose Hp and to be r e l a t i v e l y small in view of the near spin-only magnetic moment and the o r b i t a l singlet ground term of the complex. The dipolar contribution, H^p, has been assumed to be appreciable for complexes with a large e l e c t r i c f i e l d gradient and as for usually has the opposite sign to Hp,. Thus the value of H^ n t is expected to be somewhat reduced from the Fermi contact value primarily by the dipolar contribution and to a lesser extent by the o r b i t a l contribution. This is as observed and the H i n t value at 4.2 K is 18.3 T. Low-temperature (4.2-1.6 K) Mossbauer spectra for F e ( p y z ) ( C F 3 S O 3 ) 2 are shown in F i g . 4.12. The spectrum at 4.2 K shows considerable l i n e broadening and asymmetry which may be attributed to either texture effects and/or the effects of spin relaxation. Between 3.80 and 3.70 K the l i n e s show further broadening and there is evidence for the development of a magnetic hyperfine pattern as magnetic ordering sets i n . The Neel temperature i s taken to be in t h i s temperature range. Below 3.70 K, the spectra c l e a r l y show the combined effects of magnetic and quadrupole interactions. At the present time only a li m i t e d attempt has been made to f i t the spectra. A preliminary f i t of the spectrum at 1.60 K is shown in F i g . 4.13. The f i t , represented by the s o l i d l i n e , i s not t o t a l l y s a t i s f a c t o r y , especially with regard to l i n e i n t e n s i t i e s , but this may also be due to intermediate s p i n - l a t t i c e relaxation 236 rates. The values which were used to generate the f i t are as follows: 6=1.31 mm s~ 1 AE =+3.33 mm s _ 1 T=0.25 mm s" 1 6=77° <t> indeterminate H i n t = 25 T r,=0 The values of 6, <t> and T? are s i g n i f i c a n t l y d i f f e r e n t from those for Fe (pyz) (NCO) 2 • The values of T? and <p indicate an e f f e c t i v e a x i a l E.F.G. and the equivalence of the x- and y-axes; presumably V „ l i e s along the N-Fe-N axis. The spins are then *Zt til canted away from this axis by 77° towards the xy-plane. This indicates that the strength of the magnetic in t e r a c t i o n , whether i t i s through pyrazine. or O-S-0 bridges, is not s u f f i c i e n t l y strong to al i g n the spins in the xy-plane or along the N-Fe-N axis. 237 Fi g . 4.12 Low-Temperature Fe(pyz)(CF 3S0 3) 2 Mossbauer Spectra of 100-9 8 -100-98-100H ^ 100-1 0 0 H 98H 9 6 H i I i I . I V**^ T=A.20 K -\ T=3.8A K h T=3.75 K h 100H T=3.70 K T=3.63 K T -7 M l M M - 5 M M I - 3 - 1 1 3 5 V E L O C I T Y / m m s - i 238 Fi g . 4.12 Continued I • I i I • I • I • I 100-9 9 ; 100-9 9 : 100-9 8 : 100-is) 99-to " co -z. < cr 100-9 9 -100-98H I • , r T=3.55 K T = 3.A5 K • • • \ • % • T = 3.35 K v % v » A / A T=3.13 K V I. ^ v v ^ 1=2.77 K • • # V • . • . ^ V ^ T = 1 . 6 0 K \ l • • y . r, .' I I ! • ' * • • . 1 I I * • • . I I I I • I • I • I I I 1 I 1 I 1 I 1 I 1 I 1 I 1 I 1 -7 - 5 - 3 - 1 1 3 5 7 V E L O C I T Y / m m s-1 239 F i g . 4.13 Mossbauer Spectrum of Fe(pyz)(CF 3S0 3) 2 at 1.60 VELOCITY / m m s-i 240 4.3.5 Thermal Studies The thermal parameters for the mono(pyrazine) and bis(pyridine) complexes prepared in t h i s study are given in Table 4.4. From these data i t can be seen that in general the D.S.C. curves for these complexes are very similar to those of the corresponding tetrakis(pyridine) or bis(pyrazine) complexes, once the f i r s t two pyridine groups or a single pyrazine ligand has been removed. For example, the l a s t two pyridine groups in Fe(py)„(CF 3S0 3) 2 are removed at 513 K (AH=60 kJ mol" 1) which corresponds reasonably closely to the values for the loss of the pyridine groups from F e ( p y ) 2 ( C F 3 S 0 3 ) 2 (Table 4.4). Similar comparisons exist for the pairs of compounds: Fe(pyz) 2(CF 3S0 3) 2.CH 3OH and Fe(pyz)(CF 3S0 3) 2, Cu(pyz)„(CF 3S0 3) 2.H 20 and Cu(pyz)(CF 3S0 3) 2, and F e ( p y z ) 2 C l 2 and Fe(pyz)Cl 2. For Fe(pyz)(NCO) 2 in the temperature range 310-520 K one endothermic event i s noted ( F i g . 4.14) and i s probably associated with the loss of pyrazine. The D.S.C. curve for Fe(pyz)(p-CH 3C6H„S0 3) 2.2CH 3OH i s more complex than the corresponding anhydrous species (Fig. 4.15). Two thermal events are observed at r e l a t i v e l y low temperatures for the bis(methanol) solvate. These events are probably associated with the consecutive loss of each methanol molecule. The AH values for the two events, 13 and 33 kJ mol" 1 indicate that one methanol molecule being more strongly bound than the other. After the solvent molecules are removed from Fe(pyz)(p-CH 3C 6H„S0 3) 2•2CH 3OH the thermogram i s similar to that of the anhydrous species. One broad endothermic peak occurs at 241 approximately 545 K in both instances which i s probably associated with the removal of the pyrazine ligand. There i s poor agreement between the AH values for t h i s event in the two compounds but thi s discrepancy may be due to the broad nature of th i s event together with the proximity of the exothermic decomposition of the complexes s l i g h t l y above t h i s temperature. Table 4.4 Thermal Parameters for Bis(pyridine) and Mono(pyrazine) Complexes Compound Peak Temp. K AH kJ mol" 1 F e ( p y ) 2 ( C F 3 S 0 3 ) 2 557 54 Fe(pyz)(CF 3S0 3) 2 606 64 Fe(pyz) (p-CH3C6H,,S03 ) 2 .2CH3OH 329 13 367 33 548 100 Fe(pyz)(p-CH 3C 6H«S0 3) 2 543 47 Fe(pyz)Cl 2 730 60 Fe(pyz)(NCO) 2 605 40 Cu(pyz)(CF 3S0 3) 2 650 90 242 F i g . 4.14 D.S.C. Curve for Fe(pyz)(NCO) 2 300 400 500 600 700 TEMPERATURE / K F i g . 4.15 D.S.C Curves for Fe (pyz) (p-CH3C6H,,S03) 2 . 2CH3OH and Fe(pyz)(p-CH 3C 6H f tS0 3) 2 300 400 500 600 TEMPERATURE /K 243 CHAPTER 5 MAGNETIC PROPERTIES OF IRON(II) SULFONATE COMPLEXES 5.1 INTRODUCTION The iron(II) sulfonate complexes, Fe(RS0 3) 2 (where R is F, CF 3, CH 3 or p-CH3C6Hfl) have been prepared and characterised previously in t h i s l a b o r a t o r y . 2 3 " 2 6 From these e a r l i e r studies and by analogy to the known structure of C a ( C H 3 S0 3 ) 2 , 1 6 i t was proposed that these compounds adopt a polymeric two-dimensional layer structure, in which each sulfonate anion acts as a tridentate bridging ligand to three d i f f e r e n t metal centres (Fig. 5.1). Each metal s i t e i s surrounded by an octahedral arrangement of oxygen atoms, with each oxygen atom being from a di f f e r e n t sulfonate anion. Previous s t u d i e s 2 5 2 6 have shown Fe(CH 3S0 3) 2 to exist in two forms; both isomers exhibit magnetic moments which show a more s i g n i f i c a n t temperature dependence (80-300 K) than those observed for the other i r o n d l ) sulfonate compounds. Mossbauer spectroscopy has shown 0-Fe(CH 3S0 3) 2 to undergo a magnetic phase t r a n s i t i o n to an antiferromagnetically-ordered state at approximately 23 K. 2 6 To conclude these previous studies, low-temperature magnetic s u s c e p t i b i l i t y measurements (4.2-130 K) were undertaken in the current work in order to further investigate the magnetic properties of /3-Fe(CH3S03) 2 in the region of the phase t r a n s i t i o n and to compare these magnetic properties with those of the other anhydrous i r o n d l ) sulfonate complexes. 244 F i g . 5.1 Proposed S t r u c t u r e of F e ( R S 0 3 ) 2 Compounds 245 5.2 SYNTHETIC METHODS The detailed synthetic procedures for the preparation of the i r o n d l ) sulfonate complexes have been described p r e v i o u s l y . 2 3 , 2 5 These methods were followed in the present study and the purity of the products was determined by elemental analysis and infrared spectroscopy. 5.3 RESULTS AND DISCUSSION The magnetic s u s c e p t i b i l i t y data are l i s t e d in Appendix IX, Part C. The data obtained from the magnetometer technique and the Gouy method 2 5 are in excellent agreement in the temperature region (80-130 K) where the two techniques provide overlapping data sets. The temperature dependence (4.2-130 K) of the magnetic moment data for these compounds i s i l l u s t r a t e d in Fig . 5.2; for a-Fe(CH 3S0 3) 2 additional data were obtained down to a temperature of 1.97 K. 5.3.1 F e ( F S 0 3 ) 2 , Fe(CF 3S0 3) 2 and Fe(p-CH 3C 6H„S0 3) 2 The magnetic moment data for these compounds show a similar temperature dependence (Fig. 5.2) and the magnetic s u s c e p t i b i l i t y data follow Curie-Weiss behaviour, no maximum being observed. For Fe(FS0 3 ) 2 2 < t and Fe (p-CH 3C 6H„S0 3 ) 2 , 1 7 6 these res u l t s are consistent with the Mossbauer spectral studies in which, at 4.2 K, a symmetric quadrupole doublet i s observed, indicative of these compounds behaving as paramagnets with no evidence for magnetic hyperfine i n t e r a c t i o n s . 1 7 7 In the case of Fe ( C F 3 S 0 3 ) 2 the Mossbauer spectrum at 4.2 K exhibits a 246 F i g . 5.2 Magnetic Moments vs Temperature for Fe(RS0 3) 2 Compounds 6.CH CO 4.0-i — i ^ 2.0 I D < •© 8 O O o A o o s o A o in A S § A o A o A 0 A o A OP A O A O A + 0.0-0 40 80 TEMPERATURE / K 120 * Fe(FS0 3) 2 • Fe(CF 3S0 3) 2 O Fe(p-CH 3C 6H,S0 3) 2 • a- Fe(CH 3S0 3) 2 A /3-Fe(CH 3S0 3) 2 247 quadrupole doublet which shows a small degree of asymmetric l i n e broadening and some evidence for magnetic hyperfine inter a c t i o n s . These observations were attributed to a decrease in the s p i n - l a t t i c e relaxation rate at low temperatures and not to magnetic exchange i n t e r a c t i o n s . 1 7 7 In this study, the low-temperature magnetic s u s c e p t i b i l i t y results are consistent with these e a r l i e r conclusions. For these Fe(RS0 3) 2 compounds, the magnetic moment data (80-300 K) were previously analysed in terms of the Figgis model. 6 4 The method involved obtaining A and X values by f i t t i n g the temperature dependence of the quadrupole s p l i t t i n g and varying the o r b i t a l reduction factor, K , u n t i l agreement was attained between the computed and experimental magnetic moment values. These values obtained from the previous studies are given in Table 5.1. Table 5.1 C r y s t a l - F i e l d S p l i t t i n g Parameters for Fe(RS0 3) 2 Compounds 1R A/cm - 1 X/crn"1 K F 1 -290 -90 0.95 C F 32 -180 -90 0.80 p - C H a C g H V -270 -90 0.75 1) . V a l u e s from reference 24 2) . Values from reference 25 With the additional magnetic moment data i t was of interest to 248 observe whether these parameters applied to the low-temperature region. In general, i t was found that at lower temperatures the agreement between calculated . and experimental magnetic moment values i s poor. In p a r t i c u l a r , at temperatures below approximately 50 K the observed magnetic moment data are s i g n i f i c a n t l y less than the values predicted by the model (Fig. 5.3). As noted in Section 3.3.4.2, several c r i t i c i s m s have been l a i d against t h i s model and i t appears that for these compounds either the model i s not v a l i d over the entire temperature range of 4.2-300 K or weak antiferromagnetic exchange interactions may be present which reduce the magnetic moment values. F i g . 5.3 Magnetic Moment vs Temperature for Fe( C F 3 S 0 3 ) 2 Figgis Model, l i n e generated from A=180 cm - 1, X=-90 cm - 1, K=0.80 6-cri x 5-I— L U 0 O o o 40 80 TEMPERATURE / K 120 249 5.3.2 a- and 0-Fe(CH 3S0 3) 2 For the a and j3 isomers of Fe(CH 3S0 3) 2 the temperature dependencies of the magnetic moment data (Fig. 5.2) are much more pronounced than those of the i r o n d l ) sulfonate compounds discussed in the preceeding section. The magnetic moment for 0-Fe(CH 3S0 3) 2 f a l l s monotonically with decreasing temperature to approximately 25 K. A discontinuity in the magnetic moment plot is observed at approximately 23 K and the magnetic moment then decreases to 1.04 B.M. at 4.2 K. This type of magnetic behaviour i s ascribed to antiferromagnetic exchange interactions which are c l e a r l y observed in the magnetic s u s c e p t i b i l i t y data (Fig. 5.4). The magnetic s u s c e p t i b i l i t y increases as the temperature decreases and exhibits a maximum at approximately 22.5 K-. Below th i s temperature the magnetic s u s c e p t i b i l i t y decreases u n t i l a s l i g h t increase i s noted at temperatures below approximately 5.5 K. This small increase in the s u s c e p t i b i l i t y at low temperatures i s sometimes observed in antiferromagnetic species and i s often attributed to the presence of a small amount of paramagnetic "impurity". In t h i s case, the impurity is possibly a-Fe(CH 3S0 3) 2, as the 0 isomer i s prepared by conversion of the paramagnetic a m o d i f i c a t i o n , 2 5 and i t i s d i f f i c u l t to detect the presence of a small amount of unconverted a form in the /3 product. 250 F i g . 5.4 Magnetic S u s c e p t i b i l i t y vs Temperature 0-Fe(CH 3SO 3) 2 for 6(H o o 40H CD O O O 20-0 40 80 TEMPERATURE / K 120 251 In the case of 0-Fe(CH 3S0 3) 2, at a temperature s l i g h t l y below that of the maximum in the magnetic s u s c e p t i b i l i t y curve, a sharp decrease in the magnetic s u s c e p t i b i l i t y i s observed. This i s indicative of a t r a n s i t i o n from short-range magnetic interactions, possibly of a two-dimensional type, to long-range three-dimensional magnetic ordering. The onset of three-dimensional ordering occurs at approximately 22.5 K which is in good agreement the temperature of 23 K at which the Mossbauer quadrupole doublet s p l i t s into a complex magnetic hyperfine pattern. a-Fe(CH 3S0 3) 2 also shows a s i g n i f i c a n t l y temperature-dependent magnetic moment; however, in contrast to the /3 isomer, no maximum i s observed in the magnetic s u s c e p t i b i l i t y curve, even down to a temperature of 1.97 K. This indicates that short-range exchange interactions in the a isomer are much weaker than those present in /3-Fe(CH2S03) 2. At 4.2 K, Mossbauer spectrocopy 2 6 shows a single quadrupole doublet and these observations are consistent with the a isomer being antiferromagnetic, i . e . , exhibits short-range order, but with no indication of long-range magnetic ordering. Magnetic exchange interactions have been observed in other i r o n d l ) sulfate complexes. Indeed, FeSO„ was one of the f i r s t compounds to reveal a maximum in the magnetic s u s c e p t i b i l i t y versus temperature p l o t ; 1 7 8 bridging sulfate anions result in an extended three-dimensional l a t t i c e and superexchange i s through O-S-0 b r i d g e s . 1 7 9 Other i r o n d l ) compounds with O-S-0 bridging units have been found to exhibit magnetic properties 252 c h a r a c t e r i s t i c of low-dimensional materials and in some cases Mossbauer spectroscopy has demonstrated a t r a n s i t i o n to a magnetically-ordered s t a t e . 1 8 0 - 1 8 3 In some instances, the compounds were found to be linear chain compounds and the magnetic properties have been analysed in terms of an exchange Hamiltonian in either the Ising or Heisenberg l i m i t . 1 8 2 1 8 3 In the case of /3-Fe (CH 3S0 3) 2, however, analysing the magnetic data is made d i f f i c u l t by several factors. The choice of either the Heisenberg or Ising case i s usually not appropiate for i r o n d l ) complexes. These models do not apply to a system where three-dimensional interactions are also present, as is true in the case of /3-Fe(CH3S03) 2 below 22.5 K. The two-dimensional model which was used in th i s study for analysing the magnetic s u s c e p t i b i l i t y data of both Cu(pyz) 2(CH 3S0 3) 2 and Fe(pyz) 2(NCS) 2 is not applicable in t h i s instance as this model takes into account interactions between one paramagnetic centre and the four nearest neighbours in a square array. For /3-Fe(CH3S03) 2 the proposed two-dimensional l a t t i c e consists of each metal centre being surrounded by six nearest neighbours (Fig. 5.1). From the results presented here, i t is demonstrated that the only i r o n d l ) sulfonate compound to show d e f i n i t e evidence for three-dimensional long-range magnetic ordering i s /3-Fe(CH3S03) 2• From the temperature at which the maximum i s observed in the magnetic s u s c e p t i b i l i t y data, a r e l a t i v e l y strong degree of magnetic interaction i s inferred, especially as the magnetic pathway i s presumably via the three-atom bridge, O-S-0; whereas, in the other i r o n d l ) sulfonate compounds 2 5 3 exchange interactions, i f present at a l l , are much less s i g n i f i c a n t . Mossbauer s t u d i e s 2 5 on these complexes indicate that the Fe0 6 chromophore present in the a modification of Fe(CH 3S0 3) 2 i s distorted by a trigonal compression, while that in the |3.form i s t r i g o n a l l y elongated. The presence of a t r i g o n a l l y elongated Fe0 6 octahedron, however, i s not a s u f f i c i e n t condition for determining the extent of magnetic exchange interactions in these complexes. Mossbauer spectroscopy also suggests the presence of th i s type of chromophore in the fluorosulfonate, t r i f l a t e and p-tosylate compounds, but there i s no evidence for s i g n i f i c a n t magnetic exchange interactions in these complexes. The degree of magnetic exchange in these compounds i s presumably a function of the O-S-0 bridging angle, the Fe-0 and S-0 bond distances and the s t e r i c and electronic properties of the R group. Unfortunately, in the absence of any X-ray crystallographic evidence i t i s d i f i c u l t to make detailed magneto-structural correlations for these compounds in order to explain the strong magnetic interaction observed for 0-Fe(CH 3S0 3) 2. 254 CHAPTER 6 SUMMARY AND CONCLUSIONS The present study involved the synthesis and characterisation of divalent iron and copper complexes with the neutral donor ligands pyrazine or pyridine and a range of anions of varying coordinating a b i l i t y . In the pyrazine complexes, the neutral ligand was found to coordinate in either a uni- or bidentate mode and these two di f f e r e n t modes held s i g n i f i c a n t consequences for the magnetic properties of the materials. Pyridine, as expected, was found to coordinate only as a unidentate ligand using i t s unique nitrogen donor atom. Spectroscopic methods were used not only to i d e n t i f y the coordination modes of "the neutral ligands but also the anionic ligands and several of the anions were found to coordinate in either a uni- or a bidentate mode. Based upon magneto-structural correlations i t i s possible to divide the complexes into three groups and each group can be further subdivided dependent upon the type of bridging ligands present (Table 6.1). GROUP 1 The complexes of Group 1 show only a moderate temperature dependence to the i r magnetic moments over a wide temperature range (50-300 K), with a s l i g h t increase in temperature dependence at temperatures below 20 K. These complexes are considered to be magnetically d i l u t e . 255 Table 6.1 C l a s s i f i c a t i o n of Complexes GROUP 1 MAGNETICALLY DILUTE B Fe(py)«(CF 3S0 3) 2 Fe(py) q(CH 3S0 3) 2 Fe(py),(p-CH 3C 6H,S0 3) 2 Fe(2-mepyz)„(CH 3S0 3) 2 Cu(py)„(CF 3S0 3) 2 Cu(py)«(CH 3S0 3) 2 Cu(pyz)„(CF 3S0 3) 2 ,H20 Fe(pyz),(AsF 6) 2.2H 20 GROUP 2 MAGNETICALLY CONCENTRATED A Fe(pyz) 2(NCS) 2 Cu(pyz)2(CH 3S0 3)2 Fe(pyz) 2C1 2 Fe(pyz) 2Br 2 F e ( p y z ) 2 I 2 Fe(pyz) 2(C10„) 2 Fe(pyz)(p-CH 3C 6H«S0 3) 2.2CH 3OH Fe(pyz)(p-CH 3C 6H aS0 3) 2 B Fe(pyz)(NCO) 2 Fe(pyz)(CF 3S0 3) 2 Cu(pyz)(CF 3S0 3)2 GROUP 3 MAGNETIC PROPERTIES INTERMEDIATE BETWEEN GROUPS 1 AND 2 A B Fe(pyz) 2(CF 3S0 3) 2.CH 3OH Fe(pyz)Cl 2 Fe(pyz) 2(CH 3S0 3) 2 C F e ( p y ) 2 ( C F 3 S 0 3 ) 2 256 (IA) The complexes in thi s sub-group are of stoichiometry ML„(RS0 3) 2 and for several compounds of t h i s type X-ray crystallography has shown conclusively that the metal centres are well isolated from each other and the magnetic properties are consistent with their formulation as monomeric molecular species. Fe(pyz)„(AsF 6) 2.2H 20 f a l l s into this category as the spectroscopic properties are also consistent with a monomeric structure. (IB) Although pyrazine adopts a bridging configuration in the Fe(pyz) 2X 2 complexes (where X" is C l " , Br", I" or C10„"), the magnetic properties are similar to those of the complexes of sub-group 1A, showing no evidence for magnetic exchange. (IC) The structure of the mono(pyrazine) p-tosylate complexes consists of bridging anionic- ligands and bridging pyrazine. In spite of t h i s bridging network the magnetic results do not indicate any s i g n i f i c a n t magnetic interactions. GROUP 2 The complexes of group 2 exhibit magnetic properties which show d e f i n i t e evidence for magnetic concentration of an antiferromagnetic nature. This evidence comes from the observation of a substantial temperature dependence of the magnetic moment, together with a maximum in the magnetic s u s c e p t i b i l i t y data, and, in the case of the i r o n d l ) compounds, a complex magnetic hyperfine Mossbauer spectrum resulting from magnetic ordering. The complexes in this group may be divided into two sub-categories dependent upon the proposed bridging 2 5 7 network. (2A) The structures of complexes in thi s sub-category consist of two-dimensional l a t t i c e s resulting from bridging pyrazine ligands. X-ray crystallography has demonstrated t h i s type of structure to be present in Cu(pyz) 2(CH 3S0 3) 2 and i t i s concluded that the two d i s t i n c t copper-pyrazine interactions result in inequivalent pathways for magnetic exchange. Two-dimensional short-range and long-range interactions are present in the second member of this sub-category, Fe(pyz) 2 (NCS) 2 and, in t h i s instance, spectroscopic data indicate the presence of equivalent magnetic exchange pathways through bridging pyrazine ligands. (2B) Magnetic exchange interactions are also observed for the members of this sub-category, i . e . , the mono(pyrazine) complexes: Fe(pyz)(NCO) 2, Fe(pyz)(CF 3S0 3) 2 and Cu(pyz)(CF 3S0 3) 2. The compounds in this group, however, d i f f e r s t r u c t u r a l l y from those in group 2A in that there is strong spectroscopic evidence to indicate the presence of bridging anions as well as bridging pyrazine ligands. Further research to obtain s i n g l e - c r y s t a l X-ray structural data i s required to confirm this s t r u c t u r a l feature. GROUP 3 The magnetic properties of the t h i r d class of compound are intermediate between those of the f i r s t two groups. For these compounds the magnetic moment shows a s i g n i f i c a n t temperature dependence; the temperature dependence being greater 258 than that observed for the analogous complexes in group 1. Unlike the compounds of group 2, however, the compounds of group 3 exhibit no maximum in the magnetic s u s c e p t i b i l i t y data and hence, while magnetic exchange interactions are postulated for this group of complexes, they are of a weaker nature than those present in the compounds of group 2. Spectroscopic evidence enabled compounds in t h i s group to be further c l a s s i f i e d in accord with the nature of the bridging ligand network. (3A) The Fe(pyz) 2(RS0 3) 2 compounds (where R is CF 3 or CH3) contain bridging pyrazine ligands and non-bridging anions resulting in two-dimensional l a t t i c e s . (3B) Fe(pyz)Cl 2 contains bridging anions and bridging pyrazine ligands (3C) Bridging anions are present in F e ( p y ) 2 ( C F 3 S 0 3 ) 2 From t h i s c l a s s i f i c a t i o n of magnetic properties and structures i t i s possible to draw some important conclusions regarding, in p a r t i c u l a r , the a b i l i t y of pyrazine to transmit magnetic exchange e f f e c t s . The complexes which contain only terminal pyrazine ligands a l l appear in Group 1 and are e f f e c t i v e l y magnetically d i l u t e . In terms of thi s i n a b i l i t y to transmit magnetic exchange effects terminal pyrazine ligands behave no d i f f e r e n t l y from pyridine. Two copper complexes which contain bridging pyrazine ligands were prepared, and both appear in Group 2. In Cu(pyz) 2(CH 3S0 3) 2, there are two bridging pyrazine ligands per copper resu l t i n g in a two-dimensional array, and while both 259 neutral ligands may contribute to the exchange e f f e c t , an X-ray structure determination shows that one is p a r t i c u l a r l y strongly bound, generating what is e f f e c t i v e l y a one-dimensional type of exchange. In the other copper complex, Cu(pyz)(CF 3S0 3) 2, the bridging pyrazine i s thought to provide the main pathway for exchange. These results, considered in conjunction with previous studies on copper-pyrazine complexes, show that pyrazine is an e f f i c i e n t ligand for propagating magnetic exchange between copper centres. The s i t u a t i o n in regard to bridging pyrazine and magnetic exchange in i r o n d l ) complexes i s by no means straightforward. The iron complexes of Groups 1A, 2A and 3A a l l have stoichiometrics Fe(pyz) 2X 2 with bridging pyrazine ligands forming a tvo-dimensional array and terminal anionic ligands. The presence of a similar bridging pathway in these complexes i s obviously not a s u f f i c i e n t condition for predicting the extent of magnetic exchange in these complexes. The nature of the terminal ligand is playing a v i t a l role here. Where X i s either a halide or perchlorate, the complex is magnetically d i l u t e ; where the anionic ligand i s sulfonate, there i s evidence for weak exchange and where X i s thiocyanate, r e l a t i v e l y strong exchange ef f e c t s are observed. At the present time, i t does not seem possible to correlate these d i f f e r e n t e f f e c t s with either electronic or s t e r i c properties of the various anionic ligands. It should be noted, however, as has been observed previously for pyrazine-bridged copper complexes, that small differences in pyrazine ring orientation in these complexes, caused by the 260 d i f f e r e n t terminal anions, may s i g n i f i c a n t l y affect the e f f i c i e n c y of the exchange through pyrazine. For this reason, i t would be useful to obtain s i n g l e - c r y s t a l X-ray structure data on complexes of this type. In the present study, several attempts to obtain single c r y s t a l s of these species were made, but were unsuccessful. F i n a l l y , i t i s noted that the iron complexes in groups 1C, 2B and 3B have stoichiometrics Fe(pyz)X 2, and a l l have bridging anions in addition to a one-dimensional bridging pyrazine network. Again, in spite of possible s i m i l a r i t i e s in structure, a range of magnetic properties are observed. While the difference in the two sulfonate derivatives may be accounted for on the basis of the d i f f e r e n t b a s i c i t i e s of the anions, as mentioned e a r l i e r , i t is d i f f i c u l t to r a t i o n a l i s e the magnetic properties of the other complexes in terms of anionic properties. Differences in orientation of bridging pyrazine ligands possibly accounts for the d i f f e r e n t magnetic properties and s i n g l e - c r y s t a l X-ray d i f f r a c t i o n studies would be invaluable in this regard. The magnetic properties of the complexes were treated from several t h e o r e t i c a l standpoints. For the copper complexes, C u ( p y z ) 2 ( C H 3 S O 3 ) 2 and Cu(pyz)(CF 3S0 3) 2, the magnetic properties were analysed in two d i f f e r e n t ways by considering magnetic interactions throughout . a two-dimensional l a t t i c e or along a one-dimensional chain. 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J ^ Solid State Chem. 1974,  10, 151. 273 APPENDIX I, Complete X-ray Structural Parameters PART A, Fe(py)„(RS0 3) 2 Complexes F i n a l p o s i t i o n a l ( f r a c t i o n a l x 10", Fe and S x 10 6, H x 10 3) o and i s o t r o p i c thermal parameters (U x 10 3 A 2) with estimated standard devia t i o n s in parentheses* Atom X 1 z Fe(NC 5H 5), (CH 3S0 3) 2 F e d ) 40090 68958( 6) 63300 37 Fe(2) 90418( 6) 66988( 6) 62924( 5) 34 S(1) 49188(10) 91714(12) 78340( 8) 43 S(2) 35615(10) 44572(15) 48373( 9) 53 S(3) 86211(10) 94617(13) 49533( 8) 49 S U ) 96112( 9) 3561 3 (13) 73588( 8) 46 0(1) 4294( 2) 8465( 4) 7167( 2) 56 0(2) 3596( 3) 5326( 4) 5495( 2) 59 0(3) 8660( 2) 8477( 4) 5578( 2) 48 0(4) 9304( 2) 5035( 4) 7085( 2) 54 0(5) 521 1 ( 4) 8 1 76 ( 5) 8462( 2) 85 0(6) 5602( 3) 9844( 4) 7654( 3) 69 0(7) 3246( 4) 5303( 7) 4 1 63 ( 3) 1 1 4 0(8) 4361 ( 3) 3759( 6) 4933( 4) 108 0(9) 8199( 3) 88 1 4 ( 5) 4229( 2) 75 0(10) 9486( 3) 10013{ 5) 5041 ( 3) 82 0(11) 10516( 3) 3528( 5) 7723( 4) 98 0( 12) 9261 ( 4) 2481 ( 4) 6798( 3) 95 N( 1 ) 331 0( 3) 5609( 5) 6971 ( 2) 45 N(2) 2842( 3) 8207( 4) 5735( 2) 43 N(3) 4719( 3) 81 46( 4) 5707( 2) 44 N(4) 51 79 ( 3) 5584 ( 4) 6892( 2) 42 N(5) 7829( 3) 5567( 4) 561 7 ( 2) 41 N(6) 8394( 3) 7831 ( 4) 70 1 4 ( 2) 41 N(7) 10235( 2) 7832( 4) 6966( 2) 39 K(8) 97 1 4 ( 3) 5687( 4) 5575( 2) 40 C(1 ) 4327( 5) 10595( 8) 8065( 4) 64 C(2) 281 4 ( 6) 3064( 9) 4803( 6) 115 C(3) 8053( 5) 10997( 7) 5078( 4) 76 C(4) 91 62 ( 8) 32 1 2 ( 10) 8066( 6) 121 C(5) 3678( 3) 5335( 6) 7704( 3) 50 C(6) 3329( 4) 4370( 6) 8094( 3) 55 C(7) 2574( 4) 3680( 7) 771 5( 4) 64 C(8) 2174( 4) 3992( 7) 6959( 4) 62 C(9) 2561 ( 3) 4945( 6) 6608( 3) 51 C( 10) 24 1 3 ( 3) 8901 ( 6) 6123( 3) 52 C( 1 1 ) 1 71 1 ( 4) 9793( 7) 5779( 4) 63 C( 12) 1 440 ( 3) 9947( 7) 501 2( 4) 60 C(13) 1861 ( 3) 9243( 6) 4596( 3) 54 C( 1 4) 2564( 3) 8396( 6) 4978( 3) 47 continued-•• 274 PART A ,Continued C(15) 4699( 4) 9600( 6) 5691 ( 3) 55 C(16) 5092( 4) 10451( 6) 5288( 4) 68 C(17) 5538( 4) 9730( 8) 4887( 4) 76 C(18) 5577( 4) 8237( 8) 491 0 ( 4) 71 C(19) 51 65 ( 4) 7479( 6) 5328( 3) 56 C(20) 51 38 ( 4) 4 1 23 ( 5) 6946( 3) 55 C(21 ) 5839( 4) 3282( 6) 7356( 4) 67 C(22) 6595( 4) 3957( 7) 77 1 3 { 4) 68 C(23) 6655( 3) 5453( 7) 7651 ( 3) 61 C(24) 5937( 3) 6221 ( 5) 7235( 3) 48 C(25) 7508( 3) 5660( 6) 4868( 3) 48 C(26) 6751 ( 4) 4996( 7) 4429( 3) 61 C(27) 6295( 4) 4203( 7) 4795( 4) 63 C(28) 661 4 ( 4) 4084( 7) 5560( 4) 65 C(29) 7382( 3) 4771 ( 6) 5960( 3) 54 COO) 7667( 4) 8587( 6) 6689( 3) 53 C(31 ) 7299( 4) 9422( 7) 7109( 4) 76 C(32) 7695( 6) 9505( 8) 7873( 5) 88 C(33) 8430( 5) 8732( 9) 8216( 3) 77 C(34) 8747( 4) 7873( 6) 7756( 3) 53 C(35) 10269( 3) 9285( 5) 7072( 3) 44 C(36) 10989( 4) 10003( 6) 7534( 4) 57 C(37) 11716( 4) 9201 ( 6) 79 1 3 ( 3) 58 C(38) 11702( 3) 77 1 7 ( 6) 7804( 3) 56 C(39) 10960( 3) 7057( 5) 7331 ( 3) 48 C(40) 9624( 4) 4273( 5) 5386( 3) 51 C(41 ) 9979( 4) 3634( 6) 4892( 3) 57 C(42) 10457( 4) 4469( 7) 45B1 ( 3) 59 C(43) 10567( 4) 5934( 6) 4775( 3) 58 C(44) 10187( 3) 6502( 5) 5270( 3) 48 Fe(NC 5H 5) 1 1 (CF 3S0 3 2 Fe 46180 49617(16) 49420 37 S(1 ) 68694(23) 25378(29) 43403(18) 50 S(2) 28680(25) 74813(30) 60146(18) 50 F( 1 ) 7322( 7) 239( 8) 3430( 6) 106 F(2) 5526( 7) 224( 6) 4010( 4) 87 F(3) 571 8( 7) 1490( 8) 2821 ( 4) 85 F(4) 1 61 4 ( 8) 9892( 8) 5878( 6) 107 F(5) 3071 ( 7) 9703( 7) 4959( 5) 96 F(6) 1321 ( 7) 8558( 9) 4687( 5) 104 0(1 ) 5659( 6) 3246( 7) 4450( 5) 57 0(2) 7693( 6) 3349( 9) 381 7 ( 5) 78 0(3) 7431 ( 8) 1896( 8) 51 64 ( 5) 84 0(4) 3466( 6) 6670( 7) 5333( 4) 49 0(5) 1 798 ( 7) 6761 ( 9) 6331 ( 5) 79 0(6) 3778( 7) 8136( 8) 6684( 5) 72 N(1 ) 4607( 7) 3841 ( 9) 6284( 5) 41 N(2) 4608( 7) 6101 ( 10) 361 1 ( 5) 46 N(3) 2873( 7) 3798( 9) 4405( 5) 40 N(4) 6357( 6) 6139( 9) 5508( 5) 43 C(1 ) 631 B( 9) 1058(11) 361 4( 7) 56 C(2) 2 1 80 ( 1 1 ) 8993(13) 5362( 8) 72 cont inued• 275 PART A, Continued C(3) 4487( 9) 2407(11) 6314( 7) 57 C U ) 4400(1 1 ) 1644(1 1 ) 71 16( 8) 69 C(5) 4387(1 1 ) 2401(18) 7927( 7) 77 C(6) 4534(1 0) 3857(12) 7914( 7) 65 C(7) 4624(1 0) 4525( 9) 7084( 7) 57 C(B) 3551 ( 9) 6801(10) 3244( 6) 57 C O ) 3495( 9) 7604(12) 2457( 7) 65 C( 10) 4605(1 1 ) 7724(13) 2027( 7) 62 C( 11 ) 5675(1 0) 7023(12) 2376( 7) 68 C(12) 5655( 8) 6206(10) 3167( 6) 51 C( 13) 2805( 8) 3078(10) 3607( 6) 52 C(14) 1 7 1 4 ( 9) 2362 (11 ) 3240( 6) 60 C( 1 5) 682(1 0) 2319(14) 3710( 7) 63 C( 16) 71 0 ( 8) 3058( 1 1 ) 4 5 3 K 7) 56 C(17) 1 832 ( 8) 3778( 9) 4 8 6 K 6) 46 C( 18) 6437( 9) 7551(10) 539B( 6) 58 C( 19) 7541(1 1 ) 8315(11 ) 5662( 7) 63 C(20) 8638( 9) 7590(16) 6058( 7) 61 C(21 ) 8552( 8) 6156(12) 6167( 7) 60 C(22) 7408( 9) 5466( 9) 5899( 6) 54 Fe (NC $H 5 ) 4 ( C H 3 C tH( s o 3 ) 2 Fe 25000 25000 25000 31 S 18614( 2) 3502( 8) 21696 ( 5) 43 • 0(1) 2140(<1 ) 1019( 2) 2555( 1) 44 0(2) 1 628 ( 1 ) 1335{ 3) 1905( 2) 78 0(3) 1968( 1 ) -607( 3) 1611( 2) 71 N(1 ) 2253( 1 ) 3772( 3) 1619( 2) 39 N(2) 2224( 1 ) 3554( 3) 3445( 2) 39 C( 1 ) 1669( 1 ) -573( 3) 2916( 2) 40 C(2) 1764 ( 1 ) - 1870( 4) 3082( 2) 57 C(3) 1 608 ( 1 ) -2583( 4) 365K 3) 67 C(4) 1 360 ( 1 ) -2029( 4) 4083( 2) 58 C(5) 1269( 1 ) -705( 5) 3913( 3) 65 C(6) 141 9( 1 ) 14( 4) 3 3 4 K 3) 55 C(7) 1 1 88 ( 2) -2812( 7) 4703( 4) 88 C(8) 2241 ( 1 ) 5125( 3) 1714( 2) 49 C(9) 2094( 1 ) 5967( 5) 1186( 3) 63 C( 10) 1 952 ( 1 ) 5438( 5) 540( 3) 72 C(1 1 ) 1969( 1 ) 4054( 6) 436( 3) 69 C(12) 21 18( 1 ) 3266( 4) 983( 2) 50 C( 13) 2373( 1 ) 41 13( 4) 4 0 5 K 2) 56 C(14) 221 1 ( 1 ) 4450( 5) 4720( 2) 68 C( 15) 1 884 ( 1 ) 4246( 5) 4773( 2) 58 C( 16) 1723( 1 ) 3710( 4) 4158( 2) 50 C(17) 1899 ( 1 ) 3 3 7 K 3) 3504( 2) 42 H(2) 1 89 ( 1 ) -22K 5) 282( 3) 64(14) H(3) 1 66 { 2 ) -357( 8) 386( 5) 137(23) H(5) 1 1 0 { 2 ) -35( 8) 429( 6) 164(31) H(6) 1 36 { 1 ) 97( 5) 325( 3) 62(11) H(7a) 1 15( 1 ) -380( 7) 449( 4) 111(20) H(7b) 1 35 ( 1 ) -312( 6) 491( 4) 85(19) H(7c) 98 ( 3 ) -254( 9) 464( 8) 187(39) H(8) 233( 1 ) 550( 3) 211( 3) 37( 8) H(9) 206( 1 ) 685( 6) 123( 3) 75(14) H( 10) 1 88 ( 2 ) 616( 7) 11( 5) 125(22) H( 1 1 ) 1 87 ( 1 ) 3 7 K 5) 4( 3) 74(14) H( 12) 2 1 4 ( 1 ) 235( 4) 95( 2) 42( 9) H(13) 259( 1 ) 4 2 K 3) 399( 2) 44( 9) H(14) 233( 1 ) 477( 4) 51 1( 3,) 71(13) H( 15) 1 76 ( 1 ) 446( 6) 522( 4) 99(18) H( 16) 1 48 ( 1 ) 357( 5) 417( 3) 78(14) H(17) 1 78 ( 1 > 296( 3) 306( 2) 35( 8) * U = 1/3 trace(diagonalized U) 276 PART A, Continued Bond l e n g t h s (A) w i t h e s t i m a t e d s t a n d a r d d e v i a t i o n s i n p a r e n t h e s e s Bond u n c o r r . c o r r . Bond u n c o r r . c o r r . F e ( N C 5 H 5 ) , ( C H 3 S O 3 ) 2 F e ( 1 ) - 0 ( 1 ) 2.052 3) 2 .057 N 6) -COO) 1 .338 6) 1.339 F e d )-0(2) 2.054 (3) 2 .059 N 6) -C(34) 1 .309 6) 1.310 F e d )-N( 1 ) 2.254 (4) 2 .258 N 7) -C(35) 1 .337 6) 1.339 F e ( 1 ) - N ( 2 ) 2.219 (4) 2 .223 N 7) -C(39) 1 .358 6) 1.360 F e ( 1 ) - N ( 3 ) 2.227 (4) 2 .231 N 8) -C(40) 1 .331 6) 1 .332 F e d )-N(4) 2.211 4) 2 .214 N 8) -C(44) 1 .338 6) 1 .339 F e ( 2 ) - 0 ( 3 ) 2.057 (3) 2 .062 C 5) -C(6) 1 .389 7) 1 .390 F e ( 2 ) - 0 ( 4 ) 2.059 (3) 2 .064 C 6) -C(7) 1 .360 8) 1 .362 F e ( 2 ) - N ( 5 ) 2.224 (4) 2 .22B C 7) - C O ) 1 .370 9) 1 .372 F e ( 2 ) - N ( 6 ) 2.239 4) 2 .243 C 8) -C(9) 1 .371 8) 1 .373 F e ( 2 ) - N ( 7 ) 2.201 (4) 2 .205 C 10 )-C(11) 1 .382 8) 1 .383 F e ( 2 ) - N ( 8 ) 2.213 4) 2 .217 c 1 1 )-C(12) 1 .356 8) 1 .358 S ( 1 ) - 0 ( 1 ) 1 .469 4) 1 .491 c 12 )-C(13) 1 .367 8) 1 .368 S ( 1 ) - 0 ( 5 ) 1 .431 4) 1 .455 c 13 )-C(14) 1 .374 7) 1 .374 S( 1 )-0(6) 1 .422 4) 1 .445 c 15 )-C(16) 1 .386 8) 1 .387 S ( 1 ) - C ( 1 ) 1 .764 6) 1 .788 c 16 ) - C ( l 7 ) 1 .384 10) 1 .386 S ( 2 ) - 0 ( 2 ) 1 .446 4) 1 .478 c 17 )-C(18) 1 .363 9) 1 .364 S ( 2 ) - 0 ( 7 ) 1.416 5) 1 .448 c 18 )-C(19) 1 .383 8) 1 .384 S ( 2 ) - 0 ( 8 ) 1 .421 5) 1 .453 c 20 )-C(21 ) 1 .383 6) 1 .383 S ( 2 ) - C ( 2 ) 1 .758 7) 1 .788 c 21 )-C(22) 1 .349 9) 1.350 S ( 3 ) - 0 ( 3 ) 1 .456 3) 1 .475 c 22 )-C(23) 1 .374 9) 1 .376 S ( 3 ) - 0 ( 9 ) 1 .422 4) 1 .440 c 23 )-C(24) 1 .369 7) 1 .370 S ( 3 ) - 0 ( 1 0 ) 1 .470 4) 1 .490 c 25 )-C(26) 1 .380 8) 1 .382 S ( 3 ) - C ( 3 ) 1 .745 6) 1 .763 c 26 )-C(27) 1 .381 9) 1 .383 S ( 4 ) - 0 ( 4 ) 1 .466 3) 1 .484 c 27 )-C(28) 1 .349 9) 1 .352 S(4)-0(11 ) 1.417 5) 1 .445 c 28 )-C(29) 1 .384 8)- 1 .386 S ( 4 ) - 0 ( 1 2 ) 1.411 4) 1 .439 c 30 )-C(31 ) 1 .375 8) 1 .375 S ( 4 ) - C ( 4 ) 1 .750 9) 1 .787 c 31 )-C(32) 1 .355 10) 1 .357 N ( 1 ) - C ( 5 ) 1.319 6) 1 .321 c 32 )-C(33) 1 .361 1 1 ) 1 .362 N ( 1 ) - C ( 9 ) 1 .336 6) 1 .339 c 33 )-C(34) 1 .390 8) 1 .390 K ( 2 ) - C ( 1 0 ) ' 1 .332 7) 1 .333 c 35 )-C(36) 1 .376 7) 1 .376 N ( 2 ) - C ( 1 4 ) 1 .341 6) 1 .343 C( 36 )-C(37) 1 .378 8) 1 .379 N ( 3 ) - C ( 1 5 ) 1 .326 6) 1 .327 C( 37 )-C(38) 1.3671 8) 1 .369 N ( 3 ) - C ( 1 9 ) 1 .330 7) 1 .332 c< 38 )-C(39) 1.381 ( 7) 1 .381 N ( 4 ) - C ( 2 0 ) 1 .339 6) 1 .341 c< 40 )-C(41 ) 1 .379 < 7) 1 .380 N ( 4 ) - C ( 2 4 ) 1 .330 6) 1 .331 C( 41 )-C(42) 1.361( 8) 1 .362 K ( 5 ) - C ( 2 5 ) 1.319 6) 1 .322 c( 42 )-C(43) 1.379( 8) 1 .380 N ( 5 ) - C ( 2 9 ) 1 .344 6) 1 .347 C( 43 )-C(44) 1.383( 8) 1 .384 c o n t i n u e d - • • 277 PART A, C o n t i n u e d F e f N C s H s M C F ^ O j J j Fe -OO ) 2 .102(6) 2 .107 N ( 2 ) - C ( 8 ) 1.343(11) 1 .345 Fe -0(4) 2 .110(6) 2 .115 N ( 2 ) - C ( 1 2 ) 1.337(11) 1 .338 Fe -NO ) 2 .223(8) 2 .227 N ( 3 ) - C ( 1 3 ) 1.340(11) 1 .342 Fe -N(2) 2 .215(8) 2 .219 N ( 3 ) - C ( 1 7 ) 1.338(10) 1 .339 Fe -N(3) 2 .190(7) 2 .193 N ( 4 ) - C ( 1 8 ) 1 . 3 2 6 0 2 ) 1 .328 Fe -N(4) 2 .203(7) 2 .206 N ( 4 ) - C ( 2 2 ) 1 .337( 1 1 ) 1 .338 S O ) - O O ) 1 .452(7) 1 .471 C ( 3 ) - C ( 4 ) 1.383(13) 1 .384 S(1 ) -0(2) 1 .429(7) 1 .449 C ( 4 ) - C ( 5 ) 1.38(2) 1 .38 S(1 ) -0(3) 1 .412(7) 1 .427 C ( 5 ) - C ( 6 ) 1.36(2) 1 .37 S O > -CO ) 1 .793(10) 1 .813 C ( 6 ) - C ( 7 ) 1.375(13) 1 .377 S(2) -0(4) . 1 .446(7) 1 .461 C ( 8 ) - C ( 9 ) 1 .368(13) 1 .368 S(2) -0(5) 1 .425(7) 1 .441 C ( 9 ) - C ( 1 0 ) 1.383(13) 1 .385 S(2) -0(6) 1 .423(7) 1 .439 C ( 1 0 ) - C ( 1 1 ) 1.346(14) 1 .348 S(2) -C(2) 1 .803(11) 1 .822 C O 1 )-C(1 2) 1.385(13) 1 .386 F ( l ) - C O ) 1 . 3 4 8 0 0 ) 1 .372 C ( 1 3 ) - C ( 1 4 ) 1.377(12) 1 .378 F ( 2 ) - C O ) 1 .315(11) 1 .339 C ( 1 4 ) - C ( 1 5 ) 1.343(14) 1 .345 F ( 3 ) - C O ) 1 . 3 1 9 0 0 ) 1 .343 C( 15)-C(16) 1 .381(14) 1 .382 F ( 4 ) -C(2) 1 . 3 1 0 0 2 ) 1 .330 C ( 1 6 ) - C ( 1 7 ) 1 .391(11) 1 .391 F ( 5 ) -C(2) 1 .331(12) 1 .354 C(18)-C<19) 1 .374(13) 1 .375 F ( 6 ) -C(2) 1 .323(12) 1 .348 C ( 1 9 ) - C ( 2 0 ) 1.400(14) 1 .401 N(1 ) -C(3) 1 .340(12) 1 .342 C ( 2 0 ) - C ( 2 1 ) 1.35(2) 1 .35 N(1) -C(7) 1 .331(12) 1 .332 C ( 2 1 ) - C ( 2 2 ) 1 .376(12) 1 .376 Fe (NC sH 5 ) , ( C H 3 C 6 H , S 0 3 ) 2 Fe -OO ) 2 .076(2) 2 .080 C ( 2 ) - C ( 3 ) 1.371(6) 1 .378 Fe -NO ) 2 .221 (3) 2 .226 C ( 3 ) - C ( 4 ) 1.373(6) 1 .387 Fe -N(2) 2 .245(3) 2 .248 C ( 4 ) - C ( 5 ) 1.391(6) 1 .407 S - 0 ( 1 ) 1 .474(2) 1 .489 C ( 4 ) - C ( 7 ) 1.499(6) 1 .504 S -0(2) 1 .437(3) 1 .452 C ( 5 ) - C ( 6 ) 1.364(6) 1 .370 s -0(3) 1 .421(3) 1 .436 C ( 8 ) - C ( 9 ) 1 .375(6) 1 .377 s - C O ) 1 .768(3) 1 .777 C ( 9 ) - C ( 1 0 ) 1.365(7) 1 .368 N(1 ) -C(8) 1 .347(4) 1 .349 C <10)-C( 1 1 ) 1.380(8) 1 .382 N( 1 ) -C(12) 1 .330(4) 1 .333 C O 1 ) - C ( l 2 ) 1.372(6) 1 .375 N(2) -C(13) 1 .335(4) 1 .335 C ( 1 3 ) - C ( 1 4 ) 1.376(6) 1 .376 N(2) -C(17) 1 .341(4) 1 .343 C O 4 ) - C O 5) 1.355(6) 1 .356 C(1 ) -C(2) 1 .369(5) 1 .384 C ( 1 5 ) - C ( 1 6 ) 1.360(6) 1 .362 C O ) -C(6) 1 .386(5) 1 .401 C ( 1 6 ) - C ( 1 7 ) 1.384(5) 1 .385 278 PART A, Continued B o n d a n g l e s ( d e g ) w i t h estimated standard devia t i o n s in parentheses Bonds Angle(deg) Bonds Angle(deg) F e ( N C 5 H 5 ) 0 ( C H 3 S 0 3 ) 2 0(1 )-Fe(1) - 0 ( 2 ) 174. 1(2) F e ( 1 ) - N ( 2 ) - C ( 1 0) 121 .0 3 0(1 )-Fe(1 ) -N(1 ) 89. 1 (2) F e d )-N(2)-C(14) 121 .6 3 0(1 )-Fe( 1 ) -N(2) 86. 63(1 5) C( 1 0 ) - N ( 2 ) - C ( 1 4 ) 1 17 .3 4 0(1 )-Fe(1 ) -N(3) 90. 95(1 5) Fe(1 )-N(3)-C(15) 120 .7 4 0(1 )-Fe( 1 ) -N(4) 94. 49(1 5) F e ( 1 ) - N ( 3 ) - C ( 1 9 ) 122 .0 3 0(2 )-Fe(1 ) -N(1 ) 86. 8(2 C ( 1 5 ) - N ( 3 ) - C ( 1 9 ) 1 1 7 .3 5 0(2 )-Fe(1) -N(2) 89. 28( 5) F e d )-N(4)-C(20) 121 .0 3 0(2 )-Fe(1 ) -N(3) 93. 28(1 5) F e d )-N(4)-C(24) 121 .4 3 0(2 )-Fe(1 ) -N(4) 89. 69(1 5) C ( 2 0 ) - N ( 4 ) - C ( 2 4 ) 1 17 .5 4 N( 1 )-Fe(1 ) -N(2) 91 . 78( 5) F e ( 2 ) - N ( 5 ) - C ( 2 5 ) 122 . 1 3 N O )-Fe( 1 ) -N(3) 179. 06( 5) F e ( 2 ) - N ( 5 ) - C ( 2 9 ) 121 .0 3 N( 1 - F e d ) -N(4) 89. 44( 5) C ( 2 5 ) - N ( 5 ) - C ( 2 9 ) 1 16 .9 4 N(2 )-Fe(1) -N(3) 89. 16( 5) F e ( 2 ) - N ( 6 ) - C ( 3 0 ) 120 .2 3 N(2 - F e d ) -N(4) 178. 4(2 F e ( 2 ) - N ( 6 ) - C ( 3 4 ) 121 .3 3 N(3 )-Fe(1 ) -N(4) 89. 62( 5) C ( 3 0 ) - N ( 6 ) - C ( 3 4 ) 118 .2 4 0 ( 3 )-Fe(2) - 0 ( 4 ) 171 . 62( 5) F e ( 2 ) - N ( 7 ) - C ( 3 5 ) 122 .3 3 0(3 )-Fe(2) -N(5) 88. 81 ( 4) F e ( 2 ) - N ( 7 ) - C ( 3 9 ) 120 .6 3 0(3 )-Fe(2) -N(6) 85. 66( 4) C ( 3 5 ) - N ( 7 ) - C ( 3 9 ) 1 17 . 1 (4 0(3 )-Fe(2) -N(7) 91 . 07( 4) F e ( 2 ) - N ( 8 ) - C ( 4 0 ) 122 .0 3 0(3 )-Fe(2) -N(8) 92. 36( 4) F e ( 2 ) - N ( 8 ) - C ( 4 4 ) 120 .8 3 0(4 )-Fe(2) -N(5) 89. 71 ( 5) C ( 4 0 ) - N ( 8 ) - C ( 4 4 ) 1 17 .0 4 0(4 )-Fe(2) -N(6) 86. 15( 5) N ( 1 ) - C ( 5 ) - C ( 6 ) 122 .6 5 0(4 )-Fe(2) -N(7) 90. 33( 4) C ( 5 ) - C ( 6 ) - C ( 7 ) 1 19 .3 5 0(4 )-Fe(2) -N(8) 95. 89( 5) C ( 6 ) - C ( 7 ) - C ( 8 ) 1 18 .5 5 N(5 i - F e ( 2 ) -N(6) 91 . 86( 5) C ( 7 ) - C ( 8 ) - C ( 9 ) 118 .9 5 N(5 i - F e ( 2 ) -N(7) 179. 44( 5) N ( 1 ) - C ( 9 ) - C ( 8 ) 123 .2 5 N(5 )-Fe(2) -N(8) 90. 23( 5) N ( 2 ) - C ( 1 0 ) - C ( 1 1 ) 122 .9 5 N(6 )-Fe(2) -N(7) 87. 59( 5) C ( 1 0 ) - C ( 1 1 ) - C ( 1 2 ) 1 18 .4 5 N(6 )-Fe(2) -N(8) 177. 09( 5) C(1 1 ) - C d 2 ) - C ( l 3 ) 1 20 .2 5 N(7 )-Fe(2) -N(8) 90. 32( 5) C ( 1 2 ) - C ( 1 3 ) - C ( 1 4 ) 118 .2 (5 0(1 )-sd )-0 ( 5 ) 111. 2(2 N ( 2 ) - C ( 1 4 ) - C ( 1 3 ) 123 .0 5 0(1 )-S(1 )-0 ( 6 ) 111. 9(3 N ( 3 ) - C ( 1 5 ) - C ( 1 6 ) 124 .0 6 0(1 >-sd )-C(1 ) 104. 0(3 C( 1 5 ) - C ( 1 6 ) - C ( 1 7 ) 1 17 .6 5 0 ( 5 )-sd )-0 ( 6 ) 113. 2(3 C ( 1 6 ) - C ( 1 7 ) - C ( 1 8 ) 1 19 .0 6 0 ( 5 )-S(D- C(1 ) 109. 0(4 C ( 1 7 ) - C ( 1 8 ) - C ( 1 9 ) 119 .3 6 0 ( 6 )-S(D- C(1 ) 107. 0(3 N ( 3 ) - C ( 1 9 ) - C ( 1 8 ) 1 22 .8 5 0(2 ) - S ( 2 ) - 0 ( 7 ) 110. 7(3 N ( 4 ) - C ( 2 0 ) - C ( 2 1 ) 122 .6 5 0(2 ) - S ( 2 ) - 0 ( 8 ) 111. 8(3 C ( 2 0 ) - C ( 2 1 ) - C ( 2 2 ) 1 18 .8 5 0(2 ) - S ( 2 ) - C(2) 104. 5(3 C ( 2 1 ) - C ( 2 2 ) - C ( 2 3 ) 119 .5 5 0( 7 ) - S ( 2 ) - 0 ( 8 ) 113. 6(4 C ( 2 2 ) - C ( 2 3 ) - C ( 2 4 ) 1 18 .8 5 0(7 ) - S ( 2 ) - C(2) 108. 6(4 N ( 4 ) - C ( 2 4 ) - C ( 2 3 ) 122 .8 5 0(8 ) - S ( 2 ) - C ( 2 ) 107. 0(4 N ( 5 ) - C ( 2 5 ) - C ( 2 6 ) 123 .9 5 0 ( 3 ) - S ( 3 ) - 0 ( 9 ) 112. 4(2 C ( 2 5 ) - C ( 2 6 ) - C ( 2 7 ) 118 .21 5 0 ( 3 ) - S ( 3 ) - 0( 10) 110. 2(3 C ( 2 6 ) - C ( 2 7 ) - C ( 2 8 ) 119 .01 5 0 ( 3 ) - S ( 3 ) - C(3) 105. 4(3 C ( 2 7 ) - C ( 2 8 ) - C ( 2 9 ) 119 .5 5 0 ( 9 ) - S ( 3 ) - 0( 10) 113. 0(3 N ( 5 ) - C ( 2 9 ) - C ( 2 8 ) 122 .6 5 0 ( 9 ) - S ( 3 ) - C(3) 110. 4(3 N ( 6 ) - C ( 3 0 ) - C ( 3 1 ) 121 .9 5 0( 1 D ) - S ( 3 ) -C(3) 105. 0(3 C ( 3 0 ) - C ( 3 1 ) - C ( 3 2 ) 119 .0 6 0(4 ) - S ( 4 ) - 0 ( 1 1) 111. 8(3 C ( 3 1 ) - C ( 3 2 ) - C ( 3 3 ) 120 .0 6 0(4 ) - S ( 4 ) - 0 ( 1 2) 112. 0(2 C ( 3 2 ) - C ( 3 3 ) - C ( 3 4 ) 1 1 7 .6 6 0(4 ) - S ( 4 ) - C(4) 104. 2(3 N ( 6 ) - C ( 3 4 ) - C ( 3 3 ) 123 . 1 6 0(1 1 )-S(4) -0(12) 116. 2(4 N ( 7 ) - C ( 3 5 ) - C ( 3 6 ) 123 .31 5 0(1 1 ) - S ( 4 ) -C(4) 106. 4(5 C ( 3 5 ) - C ( 3 6 ) - C ( 3 7 ) 119 . 1 ( 50( 1 2 ) - S ( 4 ) -C(4) 105. 2(4 C ( 3 6 ) - C ( 3 7 ) - C ( 3 8 ) 1 18 .7 5 Fe( 1 ) - 0 ( 1 ) -sd) 149. 8(2 C ( 3 7 ) - C ( 3 8 ) - C ( 3 9 ) 1 19 .5 5 Fe( 1 ) - 0 ( 2 ) -S(2) 158. 9(3 N ( 7 ) - C ( 3 9 ) - C ( 3 8 ) 122 .3 4 Fe( 2 ) - 0 ( 3 ) -S(3) 157. 8(2 N ( 8 ) - C ( 4 0 ) - C ( 4 1 ) 123 .5 5 Fe( 2 ) - 0 ( 4 ) -S(4) 152. 8(3 C ( 4 0 ) - C ( 4 1 ) - C ( 4 2 ) 1 19 .3 5 Fe( 1)-N(1) -C(5) 120. 7(3 C ( 4 1 ) - C ( 4 2 ) - C ( 4 3 ) 118 .3 5 Fe( 1)-N(1) -C(9) 121 . 3(3 C ( 4 2 ) - C ( 4 3 ) - C ( 4 4 ) 1 19 .2( 5 C(5 )-N(1 )-C(9) 117. 5(4 N ( 8 ) - C ( 4 4 ) - C ( 4 3 ) 122 .7( 4 continued*•• 279 PART A, Continued F e t N C j H s M C F j S O j ) ! 0 ( 1 ) -Fe -0(4) 175 .2(3) C ( 1 3 ) - N ( 3 ) - C ( 1 7 ) 117. 3(7) 0(1 ) -Fe -N( 1 ) 90 .0(3) Fe - N ( 4 ) - C ( 1 8 ) 120. 4(6) 0(1 ) -Fe -N(2) 90 .8(3) Fe - N ( 4 ) - C ( 2 2 ) 122. 2(6) 0(1 ) -Fe -N(3) 86 .8(3) C ( 1 8 ) - N ( 4 ) - C ( 2 2 ) 117. 1(7) 0 ( 1 ) -Fe -N(4) 93 .9(3) S( 1 )-CO )-F( 1 ) 1 10. 2(7) 0 ( 4 ) -Fe -N( 1 ) 93 .1(3) S O )-C( 1 )-F(2) 111. 6(7) 0 ( 4 ) -Fe -N(2) 86 .1(3) S O ) - C O ) - F ( 3 ) 112. 2(7) 0 ( 4 ) -Fe -N(3) 89 .5(3) F(1 ) - C ( 1 ) - F ( 2 ) 107. 3(9) 0 ( 4 ) -Fe -N(4) 89 .8(3) F O ) - C O ) - F ( 3 ) 107. 5(8) N( 1 ) -Fe -N(2) 179 .2(4) F ( 2 ) - C ( 1 ) - F ( 3 ) 107. 8(8) N( 1 ) -Fe -N(3) 90 .0(3) S ( 2 ) - C ( 2 ) - F ( 4 ) 111. 9(8) N( 1 ) -Fe -N(4) 89 .2(3) S ( 2 ) - C ( 2 ) - F ( 5 ) 111. 3(7) N(2) -Fe -N(3) 89 .9(3) S ( 2 ) - C ( 2 ) - F ( 6 ) 110. 8(8) N(2) -Fe -N(4) 90 .9(3) F ( 4 ) - C ( 2 ) - F ( 5 ) 108. BOO) N(3) -Fe -N(4) 178 .9(3) F ( 4 ) - C ( 2 ) - F ( 6 ) 108. 2(9) 0 ( 1 ) - S O ) -0(2) 113 .8(5) F ( 5 ) - C ( 2 ) - F ( 6 ) 105. 7(10) 0 ( 1 ) - S O ) -0(3) 1 1 2 .5(5) N O ) - C ( 3 ) - C ( 4 ) 123. 6(9) 0(1 ) - S O ) - C O ) 100 .8(4) C ( 3 ) - C ( 4 ) - C ( 5 ) 118. 3(10) 0 ( 2 ) - S O ) -0(3) 117 .5(5) C ( 4 ) - C ( 5 ) - C ( 6 ) 118. 9(10) 0 ( 2 ) - S O ) - C O ) 105 .1(5) C ( 5 ) - C ( 6 ) - C ( 7 ) 118. 7(9) 0 ( 3 ) - S O ) - C O ) 104 .9(5) N ( 1 ) - C ( 7 ) - C ( 6 ) 124. 4(8) 0 ( 4 ) -S(2) -0(5) 113 .2(5) N ( 2 ) - C ( 8 ) - C ( 9 ) 123. 9(9) 0 ( 4 ) -S(2) -0(6) 1 12 .9(4) C ( 8 ) - C ( 9 ) - C ( 1 0 ) 117. 8(9) 0 ( 4 ) - S ( 2 ) -C(2) 102 .7(5) C ( 9 ) - C O 0 ) - C ( 1 1 ) 119. 5(10) 0 ( 5 ) -S(2) -0(6) 1 17 .8(5) C ( 1 0 ) - C ( 1 1 ) - C ( 1 2 ) 119. 5(9) 0 ( 5 ) - S ( 2 ) -C(2) 104 .9(5) N ( 2 ) - C ( 1 2 ) - C ( 1 1 ) 122. 3(8) 0 ( 6 ) -S(2) -C(2) 103 .1(5) N ( 3 ) - C ( 1 3 ) - C ( 1 4 ) 122. 9(8) Fe -OO ) - S O ) 150 .8(4) C ( 1 3 ) - C ( 1 4 ) - C ( 1 5 ) 119. 5(9) Fe - 0 ( 4 ) -S(2) 152 .0(4) C ( 1 4 ) - C ( 1 5 ) - C ( 1 6 ) 1 19. 3(9) Fe -NO ) -C(3) 120 .3(6) C ( 1 5 ) - C ( 1 6 ) - C ( 1 7 ) 118. 5(8) Fe -N( 1 ) -C(7) 123 .5(6) N ( 3 ) - C ( 1 7 ) - C ( 1 6 ) 122. 4(8) C(3) -N( 1 ) -C(7) 1 16 .0(8) N ( 4 ) - C ( 1 8 ) - C ( 1 9 ) 122. 7(9) Fe -N(2) -C(8) 120 .4(6) C(18)-C(19)-C(20) 119. 4(10) Fe -N(2) -C(12) 122 .5(6) C ( 1 9 ) - C ( 2 0 ) - C ( 2 1 ) 117. 6(9) C(8) -N(2) - C O 2) 1 16 .9(8) C ( 2 0 ) - C ( 2 1 ) - C ( 2 2 ) 1 19. 7(8) Fe -N(3) -C(13) 121 .4(6) N ( 4 ) - C ( 2 2 ) - C ( 2 1 ) 123. 4(8) Fe -N(3) -C(17) 121 .3(6) F e ( N C 5 H 5 ) , ( C H 3 C s H , S O , ) 2 0 ( 1 ) -Fe -NO) 96 .22(9) C( 1 3 ) - N ( 2 ) - C ( 1 7 ) 1 16. 4(3) 0(1 ) -Fe -N(2) 86 .38(9) S - C ( 1 ) - C ( 2 ) 120. 6(3) 0(1 ) -Fe - 0 ( 1 ) ' 174 .69(14) S - C ( 1 ) - C ( 6 ) 120. 1 (3) 0(1 ) -Fe -NO ) ' 87 .44(9) C ( 2 ) - C ( 1 ) - C ( 6 ) 119. 3(3) 0( 1 ) -Fe - N ( 2 ) ' 89 .75(9) C( 1 ) - C ( 2 ) - C ( 3 ) 119. 9(4) N( 1 ) -Fe -N(2) 90 .73(9) C ( 2 ) - C ( 3 ) - C ( 4 ) 122. 2(4) N( 1 ) -Fe - N O ) ' 92 .99(14) C ( 3 ) - C ( 4 ) - C ( 5 ) 117. 0(4) N( 1 ) -Fe - N ( 2 ) ' 173 .10(10) C ( 3 ) - C ( 4 ) - C ( 7 ) 122. 2(5) N(2) -Fe - N ( 2 ) ' 86 .18(14) C ( 5 ) - C ( 4 ) - C ( 7 ) 120. 8(5) 0(1 ) -S - 0 ( 2 ) 1 10 .6(2) C ( 4 ) - C ( 5 ) - C ( 6 ) 121 . 6(4) 0(1 ) -S -0(3) 1 1 1 .8(2) C( 1 ) - C ( 6 ) - C ( 5 ) 120. 0(4) 0 ( 1 ) -S - C O ) 103 .92(14) N O ) - C ( 8 ) - C ( 9 ) 122. 3(4) 0 ( 2 ) -s -0(3) 1 15 .8(2) C ( 8 ) - C ( 9 ) - C ( 1 0 ) 120. 1 (4) 0 ( 2 ) -s -C( 1 ) 1 06 .7(2) C ( 9 ) - C ( 1 0 ) - C ( 1 1 ) 117. 8(4) 0 ( 3 ) -s -C( 1 ) 1 07 .0(2) C( 1 0 ) - C ( i 1 ) - C ( 12) 1 19. 5(4) Fe -0(1 ) -s 147 .1(2) N(1 )-C(12)-C( 1 1 ) 123. 0(4) Fe -NO ) -C(8) 119 .6(2) N ( 2 ) - C ( 1 3 ) - C ( 1 4 ) 123. 2(3) Fe -NO ) -C(12) 123 .1(2) C ( 1 3 ) - C ( 1 4 ) - C ( 1 5 ) 119. 6(4) C(8) -NO ) - C O 2) 1 17 .3(3) C ( 1 4 ) - C ( 1 5 ) - C O 6) 118. 7(3) Fe -N(2) -C ( 13 ) 122 .6(2) C ( 1 5 ) - C ( 1 6 ) - C ( 1 7 ) 119. 2(3) Fe -N(2) - C O 7) 119 .3(2) N ( 2 ) - C ( 1 7 ) - C ( 1 6 ) 1 22. 9(3) Here and e l s e w h e r e primed atoms have c o o r d i n a t e s r e l a t e d by t h e symmetry o p e r a t i o n : 1/2-x, l/2-y_, z_. 280 PART B, C u ( p y ) « ( C F 3 S O 3 ) 2 F i n a l p o s i t i o n a l ( f r a c t i o n a l x 10*, Cu and S x 10 5) and i s o t r o p i c thermal parameters (U x 10 3 A2) with estimated standard d e v i a t i o n s in parentheses Atom x £ z * U /U. Cu 50000 38590( 6) 25000 58 s 22562(16) 38966(11) 10286(11 ) 61 F(1 ) 1735( 7) 4037( 5) -477( 3) 150 F ( 2 ) 3449( 6) 3370( 3) -200( 3) 145 F ( 3 ) 3422( 5) 4670( 3) -1 00 ( 3) 136 0(1 ) 3452( 4) 3856( 3) 1436( 3) 74 0 ( 2 ) 1572( 5) 4636( 3) 11 83 ( 4) 104 0 ( 3 ) 1537( 4) 3159( 3) 1041 ( 3) 81 N(1 ) 5000 51 14( 4) 2500 50 N(2) 5000 2598( 4) 2500 68 N(3) 3633( 5) 3824( 3) 3338( 4) 57 C(1 ) 2679( 1 ) 4027( 5) -20( 6) 106 C(2) 4801 ( 7) 5536( 4) 1838( 4) 67 C(3) 4781 ( 9) 6387( 4) 1 824 ( 5) 81 C(4) 5000 6807( 5) 2500 90 C(5) 3977( 6) 21 86 ( 4) 2268( 4) 77 C(6) 3954( 7) 1 342 ( 4) 2248( 5) 92 C(7) 5000 918( 5) 2500 99 C(8) 3774( 6) 34 1 6 ( 4) 401 8 ( 5) 70 C(9) 2873( 9) 3322( 5) 4559( 5) 92 C(10) 1699( 9) 3684( 6) 4423( 6) 105 c o n 1 528 ( 7) 41 02( 5) 3743( 5) 91 C(12) 2506( 7) 4177( 4) 3220( 4) 66 C a l c u l a t e d hydrogen coordinates ( f r a c t i o n a l x 10*) and i s o t r o p i c thermal parameters (U x 10 3 k2) Atom x v_ z U H(2) 4664 5239 1346 80 H(3) 4613 6677 1332 93 H(4) 5000 7403 2500 103 H(5) 3227 2488 2110 90 H(6) 321 1 1052 2059 105 H(7) 5000 322 2500 1 1 2 H(8) 4593 3170 41 24 83 H(9) 3030 3008 5039 104 HOO) 1021 3635 4809 1 1 7 H O D 714 4350 3626 104 H(12) 2379 4500 2742 79 2 8 1 PART B, C o n t i n u e d F i n a l a n i s o t r o p i c thermal parameters (U • -, x 10 3, Cu and S x 10« A 2 ) * ~ ^ and t h e i r estimated standard d e v i a t i o n s Atom Hi i H* 2 U 3 t y 1 2 y 1 3 y 2 3 Cu 466( 6) 369( 5) 899( 8) 0 67( 7) 0 S 541 ( 9) 552( 9) 749(12) 28(12) -33(10) -27(11 F( 1 ) 175( 7) 200( 8) 74( 4) -59( 6) -73( 4) 45( 4) F(2) 1 84 ( 6) 1 40 ( 5) 1 13( 4) -29( 4) 61 ( 4) -34( 4) F(3) 165( 5) 118 ( 4) 1 24 ( 4) -52( 4) 13( 4) 37( 4) 0(1) 52( 3) 77 ( 3) 94( 3) 9( 3) -10( 2) 1 ( 3) 0(2) 74( 3) 76( 3) 163( 5) 25( 3) -7( 4) -27 ( 4) 0(3) 6B( 3) 66( 3) 107( 4) . -23( 3) 1 1 ( 3) -2( 3) N(1) 55( 4) 36( 4) 58 ( 5) 0 14( 6) 0 N(2) 52( 4) 37( 4) 1 14( 7) 0 -7( 6) 0 N(3) 48( 3) 40( 3) 83( 4) -1 ( 3) 5( 3) 6( 4) C(1) 130( 8) 73( 6) 116( 9) -10( 6) 32( 8) 12( 6) C(2) 79( 5) 52( 4) 70( 5) 0( 4) 8( 5) 6( 4) C(3) 100( 7) 50( 4) 93( 6) 9( 5) 18( 6) 17( 4) C(4) 1 04 ( 8) 38( 6) 1 28 ( 12) 0 44( 11) 0 C(5) 62{ 4) 46( 4) 1 23 ( 8) -5( 3) -20( 5) 6( 4) C(6) 77( 5) 49( 4) 150( 9) -21 ( 3) -14( 6) -1 ( 4) C(7) 101 ( 9) 37( 5) 160( 11) 0 -6( 10) 0 C(8) 50( 4) 62( 4) 98( 6) -15( 4) 2( 5) 31 ( 5) C(9) 75( 6) 99( 6) 100 ( 7) -20( 5) -7( 6) 45( 5) C(10) 81 ( 6) 135( 8) 98 ( 7) -2K 6) 33( 6) 37( 7) C( 1 1 ) 58 ( 5) 1 24 ( 8) 92( 7) 14( 5) 12( 5) 26( 6) C(12) 61( 5) 61 ( 4) 76( 5) 5( 4) 1 1 ( 4) 10( 4) •The a n i s o t r o p i c thermal parameters employed in the refinement are U.. in the expression: J f = f 0exp(-2»r 2IZU. h h a *a *) - i j - y - i — j - u — i 282 PART B, Continued Bond lengths (A) with estimated standard d e v i a t i o n s in parentheses Bond Length(A) Bond Length(A) Cu -0(1) 2.425(4) N(2)-C(5) 1.331(6) Cu -NO) 2.045(6) N(3)-C(8) 1.331(8) Cu -N(2) 2.053(6) N(3)-C(12) 1.336(7) Cu -N(3) 2.020(5) C(2)-C(3) 1.386(8) S -0(1) 1.439(4) C(3)-C(4) 1.347(8) S -0(2) 1.428(5) C(5)-C(6) 1.375(9) S -0(3) 1.422(4) C(6)-C(7) 1.370(8) S -CO) 1.832(10) C(8)-C(9) 1.326(10) F ( D - C O ) 1 .259( 1 1 ) C(9)-C(10) 1 .392(11 ) F(2)-C(1) 1.378(9) C(10)-C(11) 1.343(10) F(3)-C(1) 1.317(9) C( 1 1)-C(12) 1.363(9) NO )-C(2) 1.325(7) Bond angles (deg) with estimated standard d e v i a t i o n s in parentheses Bonds Angle(deg) Bonds Angle(deg) 0(1 ) -Cu -NO) 90.12(11) Cu -N(3)-C(8) 122.3(5) OO) -Cu -N(2) 89.88(11) Cu -N(3)-C(12) 121.4(5) 0(1 ) -Cu -N(3) 91.9(2) C(8)-N(3)-C(12) 116.2(6) 0(1) -Cu -0(1)' 179.8(2) S - C O ) - F ( I ) 113.4(7) 0(1) -Cu -N(3)' 88. 1(2) S -CO )-F(2) 105.4(6) NO) -Cu -N(2) 180 S -C(1)-F(3) 109.7(7) NO) -Cu -N(3) 91 .59(15) F( 1 )-C(1)-F(2) 110.1(10) N(2) -Cu -N(3) 68.41(15) F(1 )-C(1)-F(3) 113.5(9) N(3) -Cu -N(3)' 176.8(3) F(2)-C(1)-F(3) 104.1(8) 0(1 ) -S -0(2) 113.3(3) NO )-C(2)-C(3) 122.3(7) 0(1 ) -S -0(3) 115.0(3) C(2)-C(3)-C(4) 119.4(7) 0(1) -S -CO) 104.5(4) C(3)-C(4)-C(3) ' 118.9(8) 0(2) -s -0(3) 116.1(3) N(2)-C(5)-C(6) 121.7(6) 0(2) -s -CO ) 101.6(4) C(5)-C(6)-C(7) 118.9(6) 0(3) -s -CO) 104.0(4) C(6)-C(7)-C(6)' 119.4(8) Cu -oo) -s 160.7(3) N(3)-C(8)-C(9) 124.6(6) Cu -NO) -C(2) 121.2(4) C(8)-C(9)-C(10) 118.5(7) C(2) -NO) -C(2)' 117.6(7) C(9)-C(10)-C(11) 118.3(8) Cu -N(2) -C(5) 120.3(3) C(10)-C(11)-C(12) 119.6(7) C(5) -N(2) -C(5)' 119.3(7) N(3)-C(12)-C(11) 122.7(6) 283 PART B, Continued Torsion angles (deg) with estimated standard devia t i o n s in parentheses Atoms Value(deg) N 1 -Cu -0(1)-s -81.6(9) 0(3)-S - C ( U - F O ) 55 .9(8) N 2 -Cu -0(1)-s 98.4(9) 0(3)-S -C(1)-F(2) -64 .6(7) N 3 -Cu -0(1)-s 10.0(9) 0(3)-S -C(1)-F(3) -176 .1(7) 0( 1 '-Cu -0(1)-S 98.4(9) Cu -N(1)-C(2)-C(3) 179 .2(6) K( 3 '-Cu -0(1)-s -173.2(10) C(2)'-N(1)-C(2)-C(3) -0 .8(6) 0< 1 -Cu -N(1)-C(2) -31.7(4) Cu -N(2)-C(5)-C(6) 178 .8(6) 0< 1 -Cu -N(1)-C(2)' 148.3(4) C(5)'-N(2)-C(5)-C(6) -1 .2(6) NI 2 -Cu -N(1)-C(2) 148 Cu -N(3)-C(8)-C(9) -174 .6(6) N 2 -Cu -N(1)-C(2)' 148 C(12)-N(3)-C(8)-C(9) 2 .0(10) N 3 -Cu -N(1)-C(2) -123.6(4) Cu -N(3)-C(12)-C(11) 174 .0(6) N 3 )-Cu -N(1)-C(2)' 56.4(4) C(8)-N(3)-C(12)-C(11) -2 .6(10) 0 1 '-Cu -N(1)-C(2) 148.3(4) N( 1 )-C(2)-C(3)-C(4) 1 .6(13) 0 1 '-Cu -N(1)-C(2)' -31.7(4) C(2)-C(3)-C(4)-C(3)' -0 .8(6) N 3 '-Cu -N(1)-C(2) 56.4(4) N(2)-C(5)-C(6)-C(7) 2 .3(11) N 3 '-Cu -N(1)-C(2)' -123.6(4) C(5)-C(6)-C(7)-C(6)' -1 .1(5) 0( 1 -Cu -N(2)-C(5) -27.8(4) N(3)-C(8)-C(9)-C(10) -1 .2(13) 0( 1 -Cu -N(2)-C(5)' 152.2(4) C(8)-C(9)-C(10)-C(11) 1 .0(14) N( 1 -Cu -N(2)-C(5) •152 C(9)-C(10)-C(11)-C(12) -1 .6(13) N 1 -Cu -N(2)-C(5)' 152 C(10)-C(11)-C(12)-N(3) 2 .5(12) N< 3 -Cu -N(2)-C(5) 64.2(4) N( 3 -Cu -N(2)-C(5)' -115.8(4) 0< 1 '-Cu -N(2)-C(5) 152.2(4) 0< 1 '-Cu -N(2)-C(5)' -27.8(4) N 3 '-Cu -N(2)-C(5) -115.8(4) N 3 '-Cu -N(2)-C(5)' 64.2(4) 0 1 -Cu -N(3)-C(B) 144.8(5) 0 1 -Cu -N(3)-C(12) -31.6(5) N 1 -Cu -N(3)-C(8) -125.0(5) N( 1 -Cu -N(3)-C(12) 58.6(5) N( 2 -Cu -N(3)-C(8) 55.0(5) N( 2 -Cu -N(3)-C(12) -121.4(5) 0( 1 *-Cu -N(3)-C(8) -34.9(5) OI 1 '-Cu -N(3)-C(12) 148.7(5) N 3 '-Cu -N(3)-C(B) 55.0(5) NI 3 '-Cu -N(3)-C(12) -121.4(5) OI 2 -s -0(1)-Cu 56.2(10) 0( 3 -s -0(1)-Cu -80.7(10) Cl 1 -S -0(1)-Cu 165.9(9) OI 1 -S -C(1)-F(1) 176.9(7) OI 1 -s -C(1)-F(2) 56.4(7) 0 1 -s -C(1)-F(3) -55.1(8) 0 2 -s -C(1)-F(1) -65.0(8) 0 2 -s -C(1)-F(2) 174.5(6) 0 2 -s -C(1)-F(3) 63.0(8) continued /. .. 2 8 4 PART C, C u ( p y z ) 2 ( C H 3 S O 3 ) 2 F i n a l p o s i t i o n a l ( f r a c t i o n a l x 10 5, H x 10*) and i s o t r o p i c thermal parameters (U x 10 3 A 2) with estimated standard d e v i a t i o n s in parentheses Atom X Y. z U /U. Cu 50000 50000 50000 23 S 54201( 6) 25913( 3) 50000 22 0(1) 44607(17) 35490(10) 50000 23 0(2) 63567(18) 24874( 9) 32452(22) 45 N(1) 50000 50000 20228(23) 21 N(2) 17181(21) 50709(12) 50000 27 C(1) 39006(28) 16391(15) 50000 32 C(2) 40744(16) 43483( 9) 1.0041(18) 23 C(3) 7585(26) 58949(16) 50000 30 C U ) 9358(25) 41751(15) 50000 28 H( 1a) 4467(51 ) 851(33) 5000 67(11) H(1b) 3239(25) 1709(15) 3882(26) 42( 5) H(2) 3471(21 ) 3887(13) 1702(26) 29( 4) H(3) 1236(31 ) 6524(22) 5000 24( 6) H U ) 1412(32) 3600(24) 5000 34( 7) 285 PART C, Continued F i n a l a n i s o t r o p i c thermal parameters (U. x 10* A 2 ) * and t h e i r estimated standard d e v i a t i o n s Atom Hi i U 2 2 P.33 U i 2 Ui 3 P.2 3 Cu 41 2 ( 2) 155( 2) 1 20 ( 2) -26( 1 ) 0 0 S 202( 2) 175( 2) 277( 2) 16( 1) 0 0 0(1 ) 263( 6) 1 64 ( 5) 258( 6) 18( 4) 0 0 0(2) 4 1 4 ( 6) 424( 6) 528( 8) -21 ( 4) 246( 6) -135( 6) N(1 ) 267( 7) 21 3 ( 7) 1 38 ( 6) -41( 4) 0 0 N(2) 225( 7) 298( 8) 302( 8) -10( 5) 0 0 CO ) 333(10) 245( B) 396(11) -59( 7) 0 0 C(2) 300( 6) 248( 5) 156( 5) -95( 4) 9( 4) 7( 4) C(3) . . 270(10) 258( 8) 372 ( 1 1 ) -38( 7) 0 0 C U ) 245( 9) 251 ( 8) 347(10) 18( 6) 0 0 *The a n i s o t r o p i c thermal parameters employed in the refinement are U „ in the expression: f = f°exp(-2ir2ZZU . h.h. a. *a-*) - " i j - K i - ' - i l - " - J 286 PART C, Continued Bond lengths (£) with estimated standard d e v i a t i o n s in parentheses Bond Length(A) Bond Length(A) Cu -0(1) 1 .9559( 13) N( 1)-C(2) 1 .3431 ( 1 4) Cu -N(1 ) 2.058(2) N(2)-C(3) 1 .338(3) Cu -N(2) 2.692(2) N(2)-C(4) 1.340(2) S -0(1) 1.4832(13) C(2)-C(2) 1 1.388(2) S -0(2) 1.4423(13) C(3)-C(4) 2 1.392(3) S -C(1) 1.765(2) Table Bond angles (deg) with estimated standard d e v i a t i o n s in parentheses Bonds Angle(deg) Bonds Angle(deg) 0(1 )-Cu -NO ) 90 0(2) -s -CO) 107.99(7) 0(1 >-Cu -N(2) 78. 92(5) 0(2) -s -0(2)" 1 14.53(14) 0(1 -Cu - 0 ( 1 ) 3 180 Cu -0(1) -s 134.90(9) 0(1 )-Cu -N(2) 3 101 . 08(5) Cu -NO) -C(2) 121.62(7) 0(1 >-Cu -NO )" 90 Cu -NO ) - C ( 2 ) 3 121.62(7) N(1 -Cu -N(2) 90 C(2) -NO) - C ( 2 ) 3 116.75(15) N(1 -Cu -N(2) 3 90 Cu -N(2) -C(3) 128.01(13) NO )-Cu -NO)" 180 Cu -N(2) -C(4) 116.62(12) N(2 -Cu -N(2) 3 180 C(3) -N(2) -C(4) 115.4(2) 0(1 -s -0(2) 111. 26(6) NO ) -C(2) - C ( 2 ) 1 121.62(7) 0(1 -CO ) 103. 07(9) N(2) -C(3) - C ( 4 ) J 122.2(2) 0(1 )-s - 0 ( 2 ) ' 111. 26(6) N(2) -C(4) - C ( 3 ) 2 122.4(2) 2 8 7 PART C, Continued Bond lengths i n v o l v i n g hydrogen atoms (X) with estimated standard d e v i a t i o n s in parentheses Bond Length(A) Bond Length(A) C(1)-H(1a) 1.13(4) C(3)-H(3) 0.91(3) C(1)-H(1b) 0.95(2) C(4)-H(4) 0.85(3) C(2)-H(2) 0.92(2) Table Bond angles i n v o l v i n g hydrogen atoms (deg) with estimated standard d e v i a t i o n s in parentheses Bonds Angle(deg) Bonds Angle(deg) S - C d ) - H ( l a ) 111(2) N(1 )-C(2)-H(2) 116.7(11) S - C ( l ) - H d b ) 109.6(12) C(2) 1-C(2)-H(2) 121.7(4) S - C ( l ) - H d b ) ' 109.6(12) N(2)-C(3)-H(3) 119(2) H d a ) - C ( l ) - H d b ) 109(2) C(4) J-C(3)-H(3) 119(2) H(1a)-C(1)-H(1b)' 109(2) N(2)-C(4)-H(4) 124(2) H(1b)-C(1)-H(1b)* 109(2) C(3) 2-C(4)-H(4) 114(2) APPENDIX I I . V i b r a t i o n a l Assignments f o r P y r i d i n e ' and some of i t s Complexes' P y r i d i n e Assignment 3080s 20b 3054s 3030s 2 2 0 a 3004s 8b+l9b 1580s 8a 1482s 19a 1437s 19b 1217s 9a 1 146s 15 1067s 18a 1029s 12 990s 1 93Bw 5 883w 10a 746s 10b 702s 1 1 601s 6a 405s 16b F e ( p y ) . ( C F , S O , ) 2 3IO0sh 3065w 3040w 3010w 1632w 1603s 1577w 1490m 1448s 1225sh 1160sh 1070m 1040sh 1010m 995w 960w 880w 765s 712s 704s 632sh 428m Fe ( p y ) , ( C H j S O , ) , 3100sh 3040-3000w.br 1601m 1574w 1486w 1445s 1232sh 1219W 1145sh 1060sh a 1 006m 960w 880w 770s 760sh 705s 626s 427m Fe( p y ) , ( p - C H 3 C , H , S O j ) 2 3080w 3060w 3050w 3040w 3005w 1600s 1571m 1 489m 1446s 1229w 1221m 1150sh 1072m a 1010s a 896m 886m 766m 758m 714s 705s 625m 425m C u ( p y ) . ( C F , S O j ) 2 3200-3000w.br 1607m 1490w 1450s 1228m 1170sh 1081m 1072m 1022w 991 vw 960vw 892vw 770sh 760sh 704s a 443w Cu(py),(CH,SO,) 2 31 1 5 w 3095w 3070w 3043w 30l5w 1 606m 157 3w 1494m 1484m 1448s 1220m 1211m 1 154s 1 143s 1081w 1 070m 1018m I001w 960w 895w 767s 705s 641S 440m 429w F e ( p y ) 2 ( C F 3 S 0 3 ) 2 3080w 3060w 1610m 1574vw 1493m 1448s a 1 158sh 1 1 54m 1073m a 1015w 951vw 890vw 755m 702s a 430m 424sh 1 ). From r e f e r e n c e 1 1 9 2). A l l v a l u e s a r e i n cm -' a), obscured by a n i o n a b s o r p t i o n APPENDIX I I I . V i b r a t i o n a l Assignments for Sulfonate Anions and Unassigned Bands1- 2 PART A. Compounds Containing the CF 3S0 3~ Anion ANION VIBRATIONS ( C 3 v SYMMETRY) „, AND UNASSIGNED VIBRATIONS COMPOUND v» v, »2 t>5 v2 (E) (A,) (A,) (E) (A,) F e ( p y ) , ( C F 3 S 0 3 ) 2 1329s 1 320s 1 240s 1035s 756sh 527m 518m 636s 1305sh 1285w 1219s 1I80sh 1 170s 1 1 1 Ow 675w 656m 594w 576w 394w 372w 325w Cu ( p y ) , ( C F 3 S 0 3 ) 2 1293s 1250s 1035s 765m 525m 642s 1280sh 1245sh 1228m 1161s 658m 582w Cu(pyz),(CF 3S0 3) 2.H 20 1280s 1225s 1027s 761w 521m 635s 3400m.br  1630w.br 1245s 1 172m 1 150s 751w 702w 672w 580w 360w Fe(pyz) 2(CF 3S0 3) 2.CH 3OH 1331s 1 325s 1236s 1033s 756w 529w 520m 639s 3400-2500m.br 1304sh 1251sh 1206s 1 187m 1 173s 1160sh 595w 580w 436w 380w 360sh F e ( p y ) 2 ( C F 3 S 0 3 ) 2 1 316s 1205s 1039s 769w 522m 635s 1304sh 1271w 1232s 1 184s 984vw 590w 380vw F e ( p y z ) ( C F 3 S 0 3 ) 2 1 320s 1205s 1037s 773w 524m 639s 1226sh 1 186s 1 154m 587m 391w 356vw 336w Cu ( p y z ) ( C F 3 S 0 3 ) 2 1 310s 1209s 1030s 771w 528sh 521m 640s 1231m 1195sh 1185sh 1 160m 1 140sh 598w 584w 1) A l l values are in cm"' 2) Assignments made according to reference 122 APPENDIX I I I . Continued PART B. Compounds Containing the CH 3S0 3" Anion COMPOUND ANION VIBRATIONS V„ V, V2 (E) (A,) (A,) ( C 3 v SYMMETRY) (E) " 3 (A,) Fe(py),(CH 3S0 3) 2 1252s 1 162s 1038s 779sh 543m 523m 556s 1325w 1315sh 364w Cu(py),(CH 3S0 3) 2 1232s 1 183s 1043s 773s 532s 559s 1419w 1330w 1105w 1 31 2w Fe(2-mepyz),(CH 3S0 3) 2 1247s 1 152s 1035s 779s 541s 524s 557s 1340w 1316w 495w 370m F e ( p y z ) 2 ( C H 3 S 0 3 ) 2 1264s 1 160s 1038s 783s 548m 519s 565s 558sh 1341m 1321m 1240m 447w 392sh 372m 347sh C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 1257s 1 162s 1035s 778s 542m 529m 572s 1345w 1330vw 360w APPENDIX I I I . Continued PART C. Compounds Containing the p-CH 3C tH,S0 3" Anion to o COMPOUND ANION VIBRATIONS ( C 3 v SYMMETRY) Vt V , V 2 V5 V3 (E) (A,) (A,) (E) (A,) vt AND UNASSIGNED VIBRATIONS Fe(py),(p-CH 3C sH 0SO 3) 2 1260s 1030s 682s 547w 577m 1660w 1290m 1181sh 844w 653w 497w 385m 1170s 1630vw 1249m 1116s 819m 307m 1237w 802w Fe(pyz)(p-CH 3C 6H,S0 3) 2.2CH 3OH 1248s 1037s 686s 557m 573s 3270s.br 1640vw 1282sh 1119s 890w 710w 627m 492vw 392m 1158s 3130w 1600w 1207vw 448vw 380sh 309m Fe(pyz)(p-CH 3C sH,S0 3) 2 1257s 1045s 682s 555s 584m 3120w 1598w 1287w H80sh 894vw 714w 498w 374m 1141s 1211w 1125s 854w 709sh 415sh 302m 405m 291 APPENDIX IV. V i b r a t i o n a l Assignments for Pyrazine 1 and Bis(pyrazine) Complexes 2 Pyrazine 3066w 1490s 1178m 1067vs 926vw 823vw 789w 597w 2973w 1418VS 1148vs 1048VW 804vs 752vw 417m 1125w 1032vw 700vw 1110m 1022m I006w Fe(pyz ) 2 C 1 2 F e ( p y z ) 2 B r 2 F e ( p y z ) 2 I 2 Fe(pyz) 2(NCS) 2 31 04w 3093vw 3095vw 3085w 3096vw 3075w 311 0m 3090m 3040m 1483m 1163m 14!5sh 1154s Fe(pyz) 2(CF 3S0 3) 2.CH 3OH 3127m 31 08m 3060w F e ( p y z ) 2 ( C H 3 S 0 3 ) 2 C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 F e ( p y z ) 2 ( C 1 0 , ) 2 31 05m 3095m 3030w 31 39w 3120w 31 OOw 3050w 3020w 3120sh 31 10W 3020vw 1411s 1480w 1412s 1 120s 1114s 1 1 55m 1 1 1 9m 1485w 1152m 1414sh 1118m 1410s 1489m 1161s 1415s 1125s 1 1 1 2m 1492w 1426m 1 490w 1422s 1 1 47w 1 1 26w 1 1 2 1 w 1 1 01W 1 121w 1 1 05w I086vw 993w 1052s 990w 1087VW 989w 1 054s 822s 81 9m 812s 875vw 816s I089w 1056s 988m 817s 1083w 982w 1051s 972w 970sh I090vw 836m 1083w 827m 1060m 815W 1057sh 1 007m 1056sh 997w 848m 1007W 987w 826m 975vw 967w 1422m 1150sh 1099m 976w 846m 14l8sh 1140s 1082w 8l3m 1131m 1071m 1 1 1 6m 1 10lsh 799s 790s 1426m 1175sh I095w 1120m 1063m 997w 825sh 770w 820m 473s 470sh 474s 470s 472s 461s 480m 472m 478m 468m 494s 440m 475m 466m 1 ). From reference T24 2). A l l values are in cm"1 APPENDIX V. Vibrational Assignments 1 for the Neutral Ligands in Fe(2-mepyz)„(CH 3S0 3) 2, CuCpyz),(CF 3S0 3) 2.H 20 and Fe(pyz),(AsF 6)2.2H 20 COMPOUND ASSIGNMENTS Fe(2-mepyz)„(CH 3S0 3) 2 3120sh 3100W 3080sh 3020w 1 595w 1 520w 141Osh 1 400w 1 304w 1 076m 1 067m 990sh 975w 965sh 865m 841m 754w 746w 655vw 427s Cu(pyz)„ ( C F 3 S O 3) 2.H 20 31 OOw 1421sh 1 41 5m 1 1 22m 1115sh 1 083m 1 055m 974w 805s 460s 453s Fe(pyz)„(AsF 6) 2.2H 20 1 495m 1421s 1 41 2m 1 235w 1169sh 1 1 58m 1 1 46w 1 1 27m 1 1 1 8w 1 088w 1 055s 91 Ow 801m 470m 451s 439s 1 ) . A l l values are in cm-APPENDIX VI. Vibrational Assignments for Pyrazine 1 and Mono(pyrazine) Complexes2 Pyrazine 3066w 2973w 1 490s 1483vs 1 1 78m 1148vs 1 1 25w 1 1 1 0m 1067vs 1048vw 1032vw 1 022m 1 006w 926vw 823vw 804vs 789w 752vw 700vw 597w 41 7m Fe(pyz)Cl 2 31 00m 3040w 1 485m 1418s 1 1 68s 1 1 1 9s 1 089w 1054s 794s 475s Fe(pyz)(NCO) 2 31 00m 1 487m 1 41 6s 1171m 1 1 20s 1 062s 798s 467s Fe(pyz)(CF 3S0 3) 2 31 40w 3130vw 1491vw 1 428m 1 1 30m 1 097w 1064s 806s 477m Fe(pyz) (p-CH 3C 6H a S0 3)2.2CH 3OH 31 1 Ow 3060w 1 495w 1431s 1 098m 1 058m 1024s 1 01 3s 996m 947w 827m 808s 476m Fe(pyz)(p-CH 3C 6H« s o 3 ) 2 3050w 3020w 1 491W 1 424m 1156sh 1 089m I054sh 1 01 3m 821m 812s 473m C u ( p y z ) ( C F 3 S O 3 ) 2 31 40w 3070w 1 432m 1 1 27m 1 108m 1 081m 81 3s 504s C u ( p y z ) ( C H 3 S O 3 ) 2 • H20 31 35w 3120w 1 422m 1 1 1 5m 1 094m 1 078m 965w 838m 506m 1 001m 1 ). From reference i~24 2). A l l values are in cm"1 294 APPENDIX VII. Electronic Spectral Results PART A. I r o n d l ) Compounds Containing Sulfonate Anions COMPOUND ABSORPTION MAXIMA (cm"1) Fe(py) f l ( C F 3 S 0 3 ) 2 11,500 9,000sh Fe(py)„(CH 3S0 3) 2 11,400 Fe(py),(p-CH 3C 6H,S0 3) 2 11,000 F e ( p y ) 2 ( C F 3 S 0 3 ) 2 10,800 Fe(2-mepyz)„(CH 3S0 3) 2 9,800 Fe ( p y z ) 2 ( C F 3 S 0 3 ) 2 .CH3OH 10,800 Fe(pyz) 2(CH 3S0 3) 2 11,600 9,500sh Fe(pyz)(CF 3S0 3) 2 10,900 Fe(pyz)(p-CH 3C6H„S0 3) 2.2CH 3OH 10,800 8,900sh Fe(pyz)(p-CH 3C 6H 4S0 3) 2 10,800 8,900sh sh : shoulder 295 APPENDIX VII. Continued PART B. Copper(II) Compounds Containing Sulfonate Anions COMPOUND ABSORPTION MAXIMA (cm"1) Cu(py)«(FS0 3) 2 1 17,200 Cu(py)„ ( C F 3 S O 3 ) 2 17,400 Cu ( p y),(CH 3S0 3) 2 16,800 Cu(py) a(p-CH 3C 6H,S0 3) 2 1 16,900 Cu(pyz)„ ( C F 3 S O 3) 2.H 20 16,100 C u ( p y z ) 2 ( C H 3 S O 3 ) 2 14,000 C u ( p y z ) ( C F 3 S O 3 ) 2 13,900 1) From reference 76 APPENDIX VII. Continued PART C. I r o n d l ) Pyrazine Complexes Containing Various Anions COMPOUND ABSORPTION MAXIMA (cm"1) Fe(pyz),(AsF 6) 2.2H 20 12,500 Fe(pyz) 2C1 2 19,000 11,800 Fe(pyz) 2Br 2 19,000 11,200 F e ( p y z ) 2 I 2 16,100 11,000 7,350 Fe(pyz) 2(NCS) 2 19,400 12,900 10,200 Fe(pyz) 2(C10«) 2 11,400 Fe(pyz)Cl 2 16,700 11,400 Fe(pyz)(NCO) 2 16,000 11,200 296 APPENDIX V I I I . Magnetic S u s c e p t i b i l i t y R e s u l t s 1 for Copper(II) Complexes 1. C u ( p y ) , ( C F 3 S 0 3 ) 2 2. Cu(py),(CH 3S0 3) 2 3. Cu(pyz)„(CF 3S0 3) 2,H 20 T xm " e f f . T xm " e f f . T xm " e f f . 9.06 45.9 1 .82 4.24 98.3 1 .83 4.30 98.6 1 .84 10.1 43.3 1 .87 6.30 65.9 1 .82 4.85 88.5 1 .85 11.5 39.4 1 .90 7.28 56.2 1 .81 5.62 75.6 1 .84 12.9 35.0 1 .90 8.50 47.9 1 .80 6.43 66.2 1 .84 14.8 30.5 1 .90 9.38 43.5 1 .81 6.64 61 .8 1 .84 17.4 26.0 1 .90 10.4 39.3 1.81 7.60 56.4 1 .85 21.3 21.3 1 .90 11.3 36.2 1.61 8.37 49.7 1 .82 25.3 17.8 1 .90 13.1 30.8 1 .79 9.38 44.0 1 .82 29.1 15.5 1 .90 15.3 26.4 1 .80 9.45 44. 1 1 .82 32.6 13.7 1 .89 21 .7 18.7 1 .80 11.3 36.7 1 .82 37.9 11.8 1 .89 27.5 14.7 1 .80 13.0 31.6 1.81 42.8 10.2 1 .86 34.7 11.4 1 .77 14.9 27.4 1.81 47.2 9.09 1 .85 44.4 8.56 1 .74 17.3 23.7 1 .81 51 .3 8.32 1 .85 52.7 7.16 1 .74 21.2 19.4 1 .81 55.6 7.71 1 .85 55.2 6.94 1 .75 22.9 18.0 1 .82 61.1 6.95 1 .84 60.9 6.19 1 .74 25.2 16.3 1.81 65.9 5.71 1 .73 28.8 14.2 1 .81 Faraday Results 74.7 5.05 1 .74 32.4 12.6 1 .80 81 .7 4.61 1 .74 37.7 10.7 1 .79 Temperature 295 K 40.4 9.90 1 .79 Faraday. Results 42.6 8.50 1 .79 H.dH/dx xm " e f f . 51.1 7.85 1 .79 Temperature 294 K 55. 1 7.30 1 .79 0.0526 1 .64 1 .97 61.2 6.60 1 .80 0.0869 1 .57 1 .92 H.dH/dx xm " e f f . 70.9 5.65 1 .79 82.4 4.80 1 .78 0.0526 1 .86 2.09 92.5 4.20 1 .76 0.0869 1 .87 2.10 Faraday Results Temperature 294 K H.dH/dx 0.0526 1 0.0869 1 53 50 1 .90 1 .88 1). Temperatures are in K: molar s u s c e p t i b i l i t i e s (xm) are in 10 3 cm3 mol"'; magnetic moments ( v ) are in B.M.; and magnetic f i e l d gradients (H.dH/dx) are in T 2 cm"1. 297 APPENDIX V I I I . Continued 4. C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 T *m "e£f 4.22 21 .5 0.851 4.47 21 .7 0.880 4.93 22.0 0.930 5.19 22.2 0.959 5.62 22.5 1 .00 5.91 22.7 1 .03 6.23 22.8 1 .06 6.84 22.7 1.11 7.28 22.7 1.15 7.54 22.7 1.17 8.01 22.7 1 .20 8.44 22.4 1 .23 8.63 22.4 1 .24 9.56 21 .8 1 .29 10.2 21.4 1 .32 1 1.9 20.5 1 .40 13.3 19.5 1 .44 15.3 18.1 1 .49 15.4 18.1 1 .49 17.2 16.9 1 .52 21.8 14.6 1 .59 25.7 13.0 1 .63 29.1 11.7 1 .65 30.8 11.2 1 .66 32.8 10.5 1 .66 38.0 9.28 1 .68 42.8 8.38 1 .69 47.3 7.64 1 .70 51.4 7.18 1 .72 55.8 6.78 1 .74 61.4 6.27 1 .75 65.8 5.93 1 .77 70.5 5.60 1 .78 81.8 4.86 1 .78 Faraday Results Temperature 294 K H.dH/dx x m M 0.0526 1.48 1.87 0.0869 1.47 1.86 5. C u ( p y z ) ( C F 3 S 0 3 ) 2 m 1 *m " e f f 4.32 20.9 0.849 4.70 21.1 0.890 5.00 21.4 0.924 5.48 21 .6 0.972 5.84 21.8 1.01 6.30 22.0 1 .05 6.84 22. 1 1.10 7.16 22. 1 1.12 7.60 22.0 1.16 8.00 21.9 1.18 8.24 21 .8 1 .20 8.76 21.6 1 .23 8.95 21.5 1 .24 9.70 21 .1 1 .28 10.4 20.8 1.31 1 1.7 19.9 1 .36 13.1 19.0 1.41 15.1 17.7 1 .46 15.5 17.5 1 .47 16.8 16.6 1 .49 21.3 14.4 1 .56 25.3 12.8 1.61 29. 1 11.5 1 .63 32.7 10.5 1 .65 34.3 10.0 1 .65 38.0 9.12 1 .66 42.5 8.20 1 .67 46.8 7.56 1 .68 51.0 7.02 1 .69 54.9 6.56 1 .70 56.7 6.46 1.71 61.6 5.99 1.71 66.3 5.64 1 .73 75.1 4.96 1 .73 82.6 4.47 1 .72 92.5 3.97 1.71 100.2 3.58 1 .69 Faraday Results Temperature 296 K H.dH/dx x m M e f £ . 0.0526 1.56 1.92 0.0869 1.52 1.90 298 APPENDIX IX. Magnetic S u s c e p t i b i l i t y R e s u l t s 1 f o r I r o n d l ) Complexes PART A. Complexes Containing an FeN,X2 Chromophore 1. F e ( p y ) , ( C F 3 S O 3 ) 2 2. Fe ( p y ) , ( C H 3 S 0 3 ) 2 3. Fe(py),(p-CH 3C 6H,S0 3) 2 T xm " e f f . T xtn • " e f f . T xm "e f f 4.22 610 4.54 4.22 684 4.80 4.22 646 4.67 4.4B 579 4.55 4.46 616 4.70 4.54 605 4.69 5.03 536 4.64 5. 1 1 564 4.80 5.11 567 4.81 5.70 486 4.71 5.76 505 4.82 5.55 524 4.82 6.72 432 4.82 6.38 462 4.86 6.83 434 4.87 7.76 388 4.91 7.81 392 4.95 7.76 388 4.91 9.38 333 4.99 9.32 336 5.00 9.20 336 4.97 10.6 300 5.04 10.7 297 5.04 10.6 . 296 5.00 11.7 272 5.05 11.8 267 5.01 11.9 261 4.98 13.9 231 5.06 14.1 226 5.04 13.8 227 5.01 15.8 206 5.11 16.3 196 5.05 16.2 195 5.02 19.3 172 5.15 19.4 164 5.04 19.5 162 5.03 22.6 146 5.17 22.6 141 5.04 22.9 139 5.04 26.8 126 5.20 26.8 119 5.05 26.8 119 5.05 30.7 1 1 1 5.21 30.7 104 5.06 30.6 105 5.06 34.4 99.2 5.23 34.4 92.7 5.05 34.2 93. 3 5.05 39.8 85.9 5.23 39.7 80.8 5.07 39.6 81 . 1 5.07 44.5 77.2 5.24 44.4 72.3 5.07 44.5 72. 8 5.09 52.9 65.2 5.25 52.6 61 .6 5.09 52.7 61 . 7 5.10 60.8 57.3 5.28 60.5 53.8 5.10 61 .0 53. 9 5.13 61.3 56.7 5.27 61.3 53.3 5.11 61 .2 53. 7 5. 13 70.3 49.6 5.28 70.4 46.5 5.12 70.5 46. 6 5. 13 81.6 42.8 5.29 80.0 41.0 5.12 80.0 41 . 4 5.15 83.0 41.8 5.26 81.9 40. 1 5.13 82. 1 40. 2 5.14 91.7 38. 1 5.28 92.0 35.8 5.13 91.8 35. 9 5.14 100.5 34.8 5.29 100.5 32.7 5.13 100.5 32. 9 5.14 106.0 32.8 5.28 105.0 31.6 5.15 105.0 31 . 9 5.17 110.2 31.6 5.28 110.5 29.7 5.13 111.4 29. 7 5.14 125.0 27.9 5.28 125.8 26.2 5.14 124.4 26. 6 5.14 131.0 26.7 5.29 130.0 25.6 5.16 131.0 25. 6 5.18 156.0 23.0 5.35 1 53.0 21.8 5.16 154.0 21 . 8 5.19 181.0 19.6 5.36 178.0 16.8 5.17 180.0 IB. 8 5.20 206.0 17.4 5.36 201 .0 16.5 5.16 204.0 16. 7 5.21 232.0 15.8 5.41 226.0 14.8 5.18 229.0 14. 9 5.23 256.0 14.3 5.41 250.0 13.4 5.18 253.0 13. 4 5.20 282.0 13.1 5.43 276.0 12.2 5.19 278.0 12. 4 5.24 307.0 11.8 5.38 297.0 11.4 5.20 304.0 1 1 . 4 5.27 Faraday Results Faraday Results Faraday Results Temperature 294 ! K Temperature 292 I K Temperature 294 K H.dH/dx X m M e £ f. H.dH/dx x m M c £ £. H.dH/dx x m W . 0.0253 12.30 5.38 0.0253 11.49 5.19 0.0253 11.68 5.24 0.0526 12.33 5.38 0.0526 11.50 5.20 0.0526 11.73 5.25 0.0869 12.27 5.37 0.0869 11.47 5.18 0.0869 11.68 5.24 1) Temperatures (T) are in K; molar s u s c e p t i b i l i t i e s (xm) are in 10 3 cm3 mol" 1; magnetic moments ( v ) are in B.M.; and magnetic f i e l d gradients (H.dH/dx) are in T 2 cm"1. 299 APPENDIX IX PART A. Continued 4. Fe(pyz) 2(CF 3S0 3) 2.CH 3OH 5. F e ( p y z ) 2 ( C H 3 S 0 3 ) 2 6. Fe(2-mepyz),(CH 3S0 3) 2 T xm " e f f . T xm •'eff. T xm " e f i 4.22 333 3.34 4.22 338 3.38 . 4.62 567 4.58 4.65 326 3.48 4.61 320 3.43 5.14 566 4.83 5.20 314 3.61 5.11 313 3.58 5.99 550 5.13 5.80 304 3.75 5.88 291 3.70 6.43 525 5.20 6.60 290 3.91 7.02 271 3.90 7.04 490 5.25 8.40 256 4.14 8.06 251 4.03 7.70 449 5.26 10.1 228 4.29 9.32 232 4.15 8.12 426 5.27 12.1 204 4.43 10.7 213 4.26 9.32 380 5.32 14.2 183 4.56 12.2 194 4.36 10.3 347 5.34 16.4 165 4.64 14.3 173 4.45 11.1 324 5.35 18.4 150 4.70 16.4 155 4.52 13.2 277 5.41 20.3 138 4.74 19.7 134 4.60 15.4 241 5.44 22.2 128 4.77 22.9 117 4.64 17.5 212 5.45 24.6 119 4.83 26.8 103 4.69 19.3 193 5.46 27.5 108 4.87 30.7 90.8 4.72 23.3 161 5.48 30.4 99.2 4.91 34.2 82.0 4.74 27. 1 139 5.50 33.1 92.1 4.94 39.7 72.1 4.78 30.8 124 5.52 35.6 86. 1 4.97 44.6 65. 1 4.82 34.5 110 5.50 41.9 74.3 4.99 52.8 55.7 4.85 39.5 95.9 5.50 47.6 66.2 5.02 61.1 49.0 4.89 44.4 86.0 5.53 59.3 54.0 5.06 61.3 48.8 4.89 48.7 78.3 5.52 66.8 47. 1 5.09 70.5 42.8 4.91 53.9 70.7 5.52 80.0 41 .9 5.18 81 .9 37.2 4.93 59.4 61 .6 5.41 80.2 40.6 5.11 82.0 36.8 4.92 64.7 55. 1 5.34 90.2 36.4 5.12 91 .8 33.3 4.95 70.7 49.5 5.29 98.8 33.2 5.13 100.5 30.6 4.96 75.8 46.0 5.28 110.8 30.1 5.16 105.0 29.8 5.00 80.4 43.5 5.29 120.2 27.3 5.13 110.6 27.8 4.96 84.3 41.4 5.28 130.5 26.0 5.21 124.4 24.9 4.97 93. 1 37.3 5.27 155.0 22. 1 5.23 130.0 24.4 5.04 103.0 33.8 5.27 180.0 19.2 5.26 1 54.0 20.8 5.06 113.6 30.6 5.27 205.5 16.9 5.28 179.0 18.1 5.09 125.6 27.8 5.28 230.0 15.2 5.28 204.0 15.9 5.09 137.8 25.2 5.26 255.0 13.8 5.30 231 .0 14.0 5.09 280.0 12.6 5.30 253.0 12.9 5.11 Faraday Results 305.0 11.6 5.31 277.0 11.7 5.10 300.0 10.8 5.08 Temperature 295 K Faraday Results Temperature 293 K H.dH/dx x m M e £ £ i 0.0253 12.09 5.32 0.0526 11.96 5.29 0.0869 11.92 5.29 Faraday Results Temperature 295 K H.dH/dx xm * e £ f i 0.0252 11.02 5.10 0.0526 11.06 5.11 0.0869 11.04 5.11 H.dH/dx x m „ e £ £ | 0.0253 11.70 5.25 0.0526 11.62 5.24 0.0869 11.58 5.23 300 APPENDIX IX. PART A. 7. F e ( p y z ) 2 C l 2 T xm "e f f 4.22 661 4.72 4.70 607 4.76 4.93 569 4.74 5.42 528 4.79 5.84 489 4.78 6.58 449 4.86 7.04 421 4.87 7.60 392 4.88 8.04 369 4.86 8.88 340 4.87 9.94 306 4.93 10.5 290 4.94 11.1 274 4.94 12.6 244 4.96 14.6 21 4 5.00 15.5 199 4.98 16.0 193 4.98 17.7 177 5.01 19.2 163 5.01 20.4 154 5.01 21 .2 150 5.03 23. 1 137 5.03 25.0 127 5.04 27.0 118 5.05 28.9 1 10 5.06 30.8 104 5.06 32.4 98. 3 5.05 34.2 93. 2 5.05 36.9 86.9 5.06 39.5 80. 9 5.06 42.6 75. 2 5.06 45.6 70. 5 5.07 48.4 66. 5 5.08 52.5 61 . 6 5.09 56.5 57. 6 5.11 59.9 54. 6 5.1 1 63.9 51 . 2 5.12 67.9 48. 4 5.13 72.0 45. 7 5.13 76.2 42. 9 5.12 82.1 40. 0 5.13 91.2 35. 0 5.05 109.5 30. 2 5.14 130.0 25. 4 5.14 155.7 21 . 4 5.17 180.5 18. 6 5.18 205.6 16. 3 5.18 232.0 14. 6 5.20 256.6 13. 2 5.19 282.6 1 1 . 8 5.17 307.3 1 1 . 1 5.21 Faraday Results Temperature 295 K H.dH/dx xm M e £ £. 0.0253 11.49 5.21 0.0526 11.45 5.20 0.0869 11.41 5.19 Continued 8. F e ( p y z ) 2 B r 2 T xm " e f l 4.22 716 4.92 4.78 656 5.01 5.62 572 5.07 6.91 480 5.15 7.48 442 5.14 8.17 404 5.14 9.19 363 5.17 9.95 339 5.20 10.9 309 5.19 12.7 266 5.20 15.1 226 5.21 17.0 201 5.22 18.4 185 5.22 21.2 162 5.24 25.1 137 5.24 26.8 119 5.24 32.5 106 5.24 37.6 90. 6 5.23 40.2 85. 5 5.24 42.7 80. 5 5.24 46.9 72. 5 5.22 51.3 66. 4 5.22 55.6 61 . 9 5.25 61.3 56. 5 5.26 70.3 49. 7 5.29 82. 1 42. 4 5.28 92. 1 37. 7 5.27 100.3 34. 8 5.28 107.3 32. 4 5.28 130.5 26. 7 5.28 155.7 22. 6 5.31 180.6 19. 6 5.32 206.0 17. 2 5.33 230.5 15. 3 5.31 255.9 13. 7 5.30 281 .2 12. 5 5.31 305.5 1 1 . 6 5.33 Faraday Results Temperature 295 K H.dH/dx Xm M e f £ > 0.0253 12.03 5.33 0.0526 12.00 5.32 0.0869 11.94 5.31 9. F e ( p y z ) 2 I 2 T xm " e f i 4.22 528 4.22 4.62 507 4.33 5.16 496 4.52 5.70 473 4.64 6.12 453 4.71 6.78 428 4.62 7.35 408 4.90 8.00 382 4.95 8.83 358 5.03 9.88 324 5.06 10.3 312 5.07 11.1 294 5. 1 1 12.8 262 5.18 14.3 235 5.19 15.1 223 5. 19 16.3 210 5.23 17.8 192 5.23 19.3 178 5.25 20.1 171 5.24 23.5 150 5.31 25.3 139 5.31 26.6 131 5.31 27.3 130 5.33 29.0 123 5.34 31 .1 1 16 5.37 32.8 1 10 5.37 34.1 105 5.36 36.7 98. 2 5.37 39.5 91 . 9 5.39 42.6 85. 8 5.41 45.7 86. 6 5.43 48.5 76. 3 5.44 52.5 71 . 1 5.46 56.5 66. 7 5.49 59.9 63. 3 5.51 63.9 59. 8 5.53 67.7 56. 7 5.54 71.9 53. 6 5.55 76.1 50. 5 5.55 81.6 47. 4 5.56 90.2 42. 8 5.55 99.4 39. 3 5.59 105.0 37. 9 5.64 109.9 35. 5 5.59 123.2 31 . 8 5.60 128.6 31 . 3 5.67 155.7 26. 2 5.72 180.4 22. 6 5.71 205.3 19. 9 5.71 231 .4 17. 6 5.70 256.3 15. 8 5.68 281 .5 14. 2 5.65 305.4 12. 9 5.62 Faraday Results Temperature 295 K H.dH/dx x m n e £ £ . 0.0253 13.65 5.67 0.0526 13.55 5.65 0.0869 13.46 5.64 3 0 1 APPENDIX IX, PART A. Continued 10. Fe(pyz)j(NCS)j 11. F e ( p y z ) 2 ( C I O , ) 2 12. Fe(pyz),(AsF s) 2.2H 20 T xm " e f f . T xm " e f f - T xm "e f f 4.22 104 1 .87 4.22 552 4.31 9.06 247 4.23 4.61 1 10 2.02 4.65 493 4.28 11.1 219 4.40 5.76 132 2.46 5.18 460 4.37 12.8 197 4.49 6.09 142 2.63 6.02 407 4.43 14.7 177 4.55 6.16 145 2.67 6.83 367 4.47 16.7 160 4.63 6.83 162 2.97 8.14 319 4.56 21.8 130 4.76 6.90 162 2.99 9.58 280 4.63 25.6 1 13 4.81 7.10 165 3.06 10.6 253 4.67 29.2 101 4.85 7.50 168 3.17 12.3 224 4.69 32.7 90.8 4.87 7.69 168 3.22 14.3 196 4.73 37.9 79.9 4.92 7.93 169 3.27 16.6 174 4.80 42.8 71.5 4.95 8.00 169 3.29 19.3 151 4.82 47.2 65.6 4.98 6.39 169 3.36 22.8 128 4.84 51.3 60.9 5.00 8.88 166 3.46 27.1 1 1 1 4.90 55.5 57.1 5.04 6.94 168 3.46 27.8 108 4.90 61.0 52.0 5.04 9.25 167 3.51 30.8 97.9 4.91 106.0 31.0 5.12 9.32 167 3.53 34.3 88.4 4.92 130.0 25.2 5.12 10.0 164 3.62 36.3 83.8 4.93 153.2 21.5 5.13 10.3 162 3.66 44.5 69.5 4.97 179.3 18.7 5.17 10.8 161 3.73 52.9 59.2 5.00 204.0 16.6 5.20 11.3 158 3.78 61 .2 51.8 5.04 228.5 14.7 5.18 12.2 153 3.87 71 .0 45.0 5.06 253.4 13.3 5.20 13.4 1 48 3.98 82.5 38.9 5.07 278.5 12.3 5.23 15.6 1 36 4.13 93.3 34.6 5.08 303.5 11.1 5.19 17.9 126 4.25 102.1 31.5 5.08 21 .3 1 1 1 4.35 114.0 28.5 5.10 Faraday Results 24.9 100 4.46 129.0 25.2 5.10 28.9 89. 3 4. 54 155.0 20.7 5.07 Temperature 293 K 32.6 81 . 2 4.60 181.5 16.0 5.12 37.2 73. 3 4.67 206.5 15.9 5.12 H.dH/dx xm " e f f 42.2 66. 1 4.72 232.0 14.2 5.14 48.9 58. 6 4.79 255.5 12.9 5.13 0.0253 11 .39 5.17 55.8 52. 4 4.83 281 .0 11.8 5.15 0.0526 1 1 .32 5.15 60.8 48. 7 4.87 304.0 10.8 5.12 0.0869 11 .42 5.17 61 .2 46. 4 4.87 70.0 42. 7 4.89 Faraday Results 104.0 29. 5 4.96 128.0 24. 5 5.00 Temperature 294 K 153.5 20. 9 5.06 179.3 18. 3 5.12 H.dH/dx xm " e f f . 204.7 16. 1 5.14 229.1 14. 5 5.15 0.0253 1 1 .27 5.15 254.9 13. 1 5.17 0.0526 1 1 .23 5.14 281 .0 12. 0 5.19 0.0869 1 1 .22 5.14 306.8 1 1 . 2 5.25 Faraday Results Temperature 295 K H.dH/dx x m M e f £. 0.0253 '1.55 5.22 0.0526 H.54 5.22 0.0869 11.51 5.21 302 APPENDIX IX, PART B. Complexes Containing an FeN 2X, Chromophore 1. F e ( p y ) 2 ( C F 3 S 0 3 ) 2 2. F e ( p y z ) ( C F 3 S 0 3 ) 2 3. Fe(pyz)(p-CH 3C eH,S0 3) 2 T xm " e f f . T *m " e f f . T xm "e f f 4.22 385 3.61 1 .97 161 1 .59 4.22 558 4.34 5.26 355 3.87 2.08 167 1 .67 5.47 465 4.51 5.64 346 3.95 2.11 168 1 .69 6.31 416 4.56 6.15 338 4.06 2.50 180 1 .90 7.09 377 4.62 6.95 321 4.22 2.79 196 2.09 8.00 345 4.70 7.68 300 4.48 3.08 217 2.31 9.32 308 4.79 8.72 287 4.61 3.46 241 2.58 11.0 265 4.83 9.57 277 4.72 3.98 257 2.86 15.5 200 4.96 10.6 263 4.75 4.22 258 2.94 20.8 154 5.05 11.4 247 4.75 4.42 262 3.04 25.9 126 5.10 12.6 232 4.84 4.47 261 3.06 30.7 107 5.12 14.6 209 4.94 4.86 261 3.19 39.3 83.6 5.13 16.6 188 5.00 4.98 262 3.23 51 .0 65.2 5.16 18.4 174 5.06 5.54 260 3.39 61.0 56.2 5.24 20.5 160 5.12 5.56 259 3.40 61.2 55.3 5.20 21.8 152 5.15 6.16 255 3.55 70.5 48.5 5.23 25. 1 138 5.26 6.30 253 3.57 78.0 45.0 5.30 28.2 126 5.33 6.58 251 3.64 81.9 41.9 5.24 31.2 1 15 5.37 6.98 247 3.71 91.5 37.5 5.24 33.7 108 5.39 7.35 242 3.78 100.7 33.8 5.22 36.2 102 5.43 • 7.93 236 3.87 108.0 32.7 5.31 39.6 94.0 5.46 8.83 229 4.02 110.3 30.9 5.22 42.6 86.4 5.49 9.75 216 4.10 124.0 28.5 5.31 48.2 79.1 5.52 10.8 205 4.21 124.2 27.5 5.22 55.3 70.9 5.60 12.8 190 4.41 146.5 24.1 5.31 60.8 64.7 5.61 14.3 176 4.48 172.0 20.5 5.30 70.3 56.7 5.65 16.0 164 4.57 180.0 19.5 5.30 81 .8 48.8 5.65 17.5 1 53 4.63 205.9 17.2 5.32 92.3 41.7 5.55 19.0 1 45 4.69 231 .2 15.2 5.29 109.0 35.9 5.59 20.9 135 4.75 254.0 14.0 5.33 130.0 29.7 5.56 23.0 126 4.82 279.1 12.6 5.30 156.0 25.2 5.61 24.9 119 4.86 302.8 11.7 5.32 180.5 21 .9 5.62 26.6 1 12 4.89 205.5 19.2 5.61 28.5 106 4.91 Faraday Results 230.5 17.1 5.61 30.3 100 4.93 255.0 15.3 5.59 32.3 95. 9 4.98 Temperature 292 I K 281 .0 14.0 5.61 33.2 92. 4 4.95 305.0 12.6 5.54 38.7 80. 9 5.00 H.dH/dx xm "e f f 44.1 72. 0 5.04 Faraday Results 49.9 64. 6 5.0B 0.0253 12.08 5.32 52.7 61 . 7 5.10 0.0526 12.06 5.32 Temperature 59.9 54. 9 5.13 0.0869 12.01 5.30 64.2 48. 9 5.16 H.dH/dx " e f f . 72.1 46. 5 5.18 81.6 41 . 5 5.20 0.0253 1 3.44 5.59 91.1 37. 4 5.22 0.0526 13.31 5.59 99.9 34. 3 5.24 0.0869 13.34 5.59 109.0 33. 0 5.37 109.5 31 . 3 5.24 122.4 28. 1 5.24 130.0 27. 6 5.36 153.7 23. 5 5.38 180.6 20. 3 5.41 205.2 IB. 0 5.44 230.2 16. 0 5.44 256.0 14. 5 5.44 281 .0 13. 1 5.43 305.0 12. 0 5.42 Faraday Results Temperature 294 K H.dH/dx X m M e f f . 0.0253 12.66 5.46 0.0526 12.51 5.42 0.0869 12.51 5.42 303 APPENDIX IX, PART B. Continued 4. Fe(pyz)(p-CH 3C sH,S0 3)j.2CH 3OH 5. Fe(pyz)(NCO) 2 6. F e ( p y z ) C l 2 T xm " e f f . T xm w e f f . T xm "e f f 4.22 710 4.86 4.22 22.8 0.876 1 .86 264 1 .98 4.96 563 4.81 4.77 22.9 0.934 2.00 262 2.05 6.02 489 4.85 5.18 22.9 0.975 2.10 262 2.10 6.83 437 4.89 5.88 22.9 1 .04 2.20 261 2.14 7.55 397 4.90 6.30 23.0 1 .08 2.40 258 2.23 8.39 359 4.91 7.10 23.0 1.14 2.69 256 2.35 9.64 315 4.93 8.06 23.1 1 .22 3.04 253 2.48 11.1 280 4.97 9.76 23.2 1 .35 3.51 249 2.64 12.3 254 4.99 . 10.9 23.3 1 .43 4.07 244 2.82 14.9 217 5.09 13.3 23.8 1 .59 4.20 244 2.86 17.2 191 5.12 15.4 24.5 1 .74 4.75 238 3.01 19.9 165 5.13 18.7 26.3 1 .98 5.11 233 3.09 22.9 143 5.13 21.2 28.8 2.21 5.47 229 3.17 27.2 122 5.15 22.6 30.9 2.36 5.63 230 3.22 31.1 107 5.17 24.9 32.7 2.55 6.12 223 3.30 34.8 96.7 5.19 26.8 33.8 2.69 7.16 213 3.49 39.9 84.7 5.20 29. 1 34.4 2.83 8.06 205 3.64 44.7 76.1 5.22 30.9 35.0 2.94 9.76 190 3.85 53.0 64.3 5.22 32.5 35.1 3.02 10.9 180 3.97 61.4 56.0 5.24 34.7 35.4 3.11 12.5 169 4.11 71.0 48.4 . 5.24 36.3 35.3 3.20 14.6 154 4.24 82.6 41.5 5.24 38.0 35.6 3.29 16.6 142 4.35 93.7 36.7 5.25 39.7 35.3 3.35 19.6 128 4.48 102.4 33.6 5.24 42.3 35.3 3.46 23.1 113 4.50 109.0 32.4 5.32 44.6 34.9 3.53 27.1 102 4.69 113.5 30.2 5.24 48.8 34.6 3.68 30.8 92. 4 4.77 129. 1 26.7 5.24 52.9 33.8 3.78 34.4 84. 8 4.83 130.0 27.0 5.30 57.3 33.2 3.90 39.7 76. 0 4.91 154.7 22.7 5.30 61 .3 32.4 3.99 44.6 69. 4 4.97 180.1 19.6 5.31 66.2 31.6 4.09 52.9 60. 5 5.06 206.0 17.2 5.33 74.5 30.0 4.23 61.5 53. 8 5.14 231 .3 15.4 5.33 81.9 28.5 4.32 70.9 47. 5 5.19 256.2 13.8 5.32 91.9 26.8 4.44 82.8 41 . 6 5.25 280.7 12.6 5.31 100.7 25.4 4.52 91 .3 38. 2 5.28 305. 1 11.6 5.32 109.0 24.5 4.62 93.4 37. 4 5.28 110.4 24.0 4.60 102.6 34. 3 5.31 Faraday Results 123.7 22.3 4.69 109.5 33. 1 5.39 129.8 21 .8 4.76 114.3 31 . 2 5.34 Temperature 295 K 155.3 19.3 4.89 129.8 27. 7 5.36 180.0 17.2 4.97 131.0 26. 0 5.42 H.dH/dx "off 206.2 15.5 5.06 155.3 23. 8 5.44 111 231 .4 14.1 5.10 180. 1 21 . 0 5.50 0.0253 12.00 5.32 255.8 12.8 5.11 189.6 19. 9 5.49 0.0526 12.00 5.32 281 . 1 11.9 5.17 205.6 18. 3 5.48 0.0869 12.01 5.32 305.8 10.9 5.17 207.7 16. 3 5.52 233.0 16. 3 5.51 .Faraday Results 257.2 14. 5 5.47 257.4 14. 6 5.48 Temperature 295 K 281 .7 13. 2 5.45 306.5 12. 2 5.47 H.dH/dx x„ m " e f f . 319.5 1 1 . 9 5.51 0.0253 11.45 5.20 Faraday Results 0.0526 11.35 5.18 0.0869 11.33 5.17 Temperature 294 K H.dH/dx x m n e f f . 0.0253 12.96 5.52 0.0526 12.80 5.49 0.0869 12.77 5.48 304 APPENDIX IX, PART C. Anhydrous I r o n d l ) Sulfonate Complexes 1. Fe(FSC >»>2 2. Fe(CF 3SO,) 2 3. Fe(p-CH 3C tH, S 0 3 ) 2 T xm " e f f . T xm " e f f . T xm " e f f 4.22 540 4.27 4.22 377 3.57 4.22 330 3.33 5.40 438 4.35 8.62 243 4.14 5.08 305 3.52 6.38 388 4.45 13.5 181 4.42 5.78 285 3.63 7.12 352 4.48 16.0 147 4.60 6.17 273 3.67 8.04 318 4.52 19.9 136 4.66 7.83 237 3.86 9.81 278 4.67 23.2 120 4.73 9.13 216 3.97 1 1 .4 247 4.75 27.4 106 4.82 11.3 189 4.14 13.3 217 4.80 32.7 92.0 4.90 13.1 172 4.25 15.3 191 4.84 42.8 74.6 5.05 15.4 155 4.36 18.7 164 4.95 49.1 66.5 5.11 18.2 138 4.49 21 .0 149 5.00 55.9 60. 1 5.19 21 . 1 125 4.60 24.8 128 5.04 67.0 51.5 5.25 26.2 108 4.75 28.8 113 5.10 78.7 44.5 5.29 30.8 95.7 4.85 34.4 96. 7 5.16 89.7 39. 1 5.30 35.4 66.4 4.95 41.5 82. 5 5.23 94. 1 38.0 5.35 39.5 79.3 5.01 51.9 68. 0 5.31 99.4 35.7 5.33 45.8 70.6 5.08 60.6 59. 3 5.37 111.1 32.1 5.34 48.4 67.3 5.10 61 .6 58. 4 5.37 124.5 28.7 5.34 51 .2 64.6 5.14 70.2 52. 0 5.40 56.8 59.7 5.21 81 .7 44. 9 5.42 61 .3 56.4 5.26 91 .2 40. 4 5.43 66. 1 52.7 5.28 100.0 37. 2 5.45 74.8 47.6 5.34 110.4 33. 8 5.46 82.0 43.3 5.33 123.8 30. 2 5.47 92. 1 39.2 5.37 100.1 36.2 5.38 110.1 33. 1 5.40 124.5 29.5 5.42 305 APPENDIX IX, PART C. Continued 4. a-Fe(CHjS0 3)2 5. 0-Fe(CH 3S0 3) 2 T " e f f . T *m " e f f 1 .97 194 1 .75 4.22 32.1 1 .04 2.00 193 1 .76 5.32 31.8 1.16 2.10 192 1 .80 5.94 31.7 1 .23 2.20 192 1 .84 6.58 31.7 1 .29 2.30 191 1 .87 7.23 31.8 1 .36 2.59 189 1 .98 7.94 32. 1 1 .43 2.89 186 2.07 8.88 32.6 1.52 3.29 183 2.19 10.0 33.6 1 .64 3.73 180 2.32 11.3 35.3 1 .79 4.20 178 2.44 12.3 37. 1 1 .91 4.35 177 2.48 13.4 39.4 2.05 4.88 173 2.60 14.3 41.4 2.18 4.99 175 2.64 15.5 44.5 2.35 5.55 171 2.75 16.6 47.7 2.52 6.16 168 2. 88 18.0 52.2 2.74 7.23 164 3.08 18.2 52.7 2.77 8.00 161 3.21 19.0 55.7 2.91 12.5 145 3.80 19.2 56.0 2.93 16.5 129 4.13 19.9 59. 1 3.07 19.7 114 4.24 20.3 61.2 3.15 22.5 109 4.42 20.5 61.3 3.17 22.6 105 4.35 21.2 65.2 3.32 27. 1 94. 0 4.51 21 .5 65.5 3.36 30.5 86. 3 4.59 22.0 65.6 3.40 34.3 79. 4 4.67 23.1 65.5 3.48 39.8 71 . 2 4.76 23.2 65.5 3.49 44.5 65. 4 4.82 24.5 65.0 3.57 52.8 57. 0 4.91 25.1 64.8 3.61 60.9 50. 8 4.97 26.4 64.2 3.68 61.6 50. 3 4.98 26.9 63.8 3. 70 70.5 44. 7 5.02 28.2 63. 1 3.77 82.2 39. 0 5.06 28.8 62.7 3.80 92.0 35. 2 5.09 30. 1 62.0 3.86 100.3 32. 4 5.10 30.7 61.5 3.88 110.5 29. 7 5.12 32.7 60. 1 3.96 125.2 26. 4 5.14 34 .4 59.0 4.03 39.7 55.6 4.20 44.6 52.6 4.33 52.9 48.0 4.51 61 .2 44. 1 4.65 71 .0 39.9 4.76 82.9 35.8 4.87 92.7 32.9 4.94 102.5 30.4 4.99 113.5 28. 1 5.05 128.7 25.2 5.10 306 APPENDIX X. Mossbauer Spectral Results PART A. Mossbauer Spectral Parameters 1 for Pyridine and Pyrazine I r o n d l ) Sulfonate Complexes COMPOUND TEMP 6 r,2 r2 F e ( p y ) f l ( C F 3 S O 3 ) 2 293 3.09 1 .07 0.26 0.25 78 3.68 1.14 0.26 0.25 Fe(py) f l.(CH 3S0 3) 2 293 3.53 1 .07 0.28 0.26 120 3.81 1 .07 0.27 0.27 78 3.83 1 .07 0.27 0.26 30 3.83 1 .07 0.25 0.29 8.4 3.83 1 .08 0.30 0.31 Fe(py)«(p-CH 3C 6H 1 1S03) 2 293 3.47 1 .08 0.26 0.28 78 3.63 1.16 0.26 0.28 F e ( p y z ) 2 ( C F 3 S O 3 ) 2 . C H 3 O H 293 3.45 1.16 0.32 0.32 78 3.71 1 .25 0.40 0.38 F e ( p y z ) 2 ( C H 3 S O 3 ) 2 293 3.08 1.14 0.46 0.46 78 3.20 1 .23 . 0.43 0.43 Fe(2-mepyz),(CH 3S0 3) 2 293 3.01 1.19 0.42 0.36 78 3.40 1 .28 0.35 0.32 F e ( p y ) 2 ( C F 3 S 0 3 ) 2 293 1 .65 1.19 0.31 0.28 78 2.45 1 .22 0.35 0.34 F e ( p y z ) ( C F 3 S O 3 ) 2 293 2.79 1.19 0.52 0.44 78 3.59 1 .27 0.36 0.35 Fe(pyz)(p-CH 3C 6H„S0 3) 2.2CH 3OH 293 3.21 1.18 0.47 0.39 78 3.49 1 .29 0.44 0.39 Fe(pyz)(p-CH 3C 6H f lS0 3) 2 293 2.54 1 .22 0.43 0.40 78 2.80 1 .24 0.56 0.50 1) . Temperatures are in K; quadrupole s p l i t t i n g s , AE isomer s h i f t s , 5 and linewidths, T, are in units of mm s" 1 " 2) . T values are linewidths at half height. 307 APPENDIX X, PART B. Mossbauer Spectral Parameters for I r o n d l ) Pyrazine Complexes COMPOUND TEMP ^ q 6 r, r 2 Fe(pyz) 2C1 2 293 3.19 0.98 0.31 0.30 78 3.33 1 .08 0.33 0.34 Fe(pyz) 2Br 2 293 3.17 0.98 0.39 0.40 78 3.47 1 .09 0.39 0.33 F e ( p y z ) 2 I 2 293 2.01 0.97 0.41 0.35 78 2.50 1 .08 0.39 0.33 Fe(pyz) 2(NCS) 2 293 2.45 1 .01 0.33 0.30 78 2.63 1.11 0.35 0.33 F e ( p y z ) 2 ( C l O a ) 2 293 3.24 1 .07 0.36 0.32 78 3.74 1.16 0.35 0.33 Fe(pyz)Cl 2 293 1 .72 1 .04 0.46 0.39 78 2.52 1.15 0.48 0.45 Fe(pyz)(NCO) 2 293 2.04 1 .05 0.38 0.32 78 2.75 1.17 0.44 0.42 Fe(pyz)„(AsF 6) 2.2H 20 293 2.99 1.11 0.36 0.32 78 3.09 1.19 0.35 0.35 PUBLICATIONS Thompson, R.C; Haynes, J.S.; Sams, J.R., Chem. Phys*  Lett. 1980, 21» 596. Thompson, R.C; Haynes, J.S.; Sams, J.R., Can. J. Chem.  1981, 59, 669. Sams, J.R.; Haynes, J.S.; Hume, A.R.; Thompson, R.C, Chem. Phys. 1983, 78, 127. Thompson, R.C; Haynes, J.S.; Oliver, K.W.; Rettig, S.J.; Trotter, J., Can. J. Chem. 1984, 62, 891. Thompson, R.C; Haynes, J.S.; Clcha, W.V.; Oliver, K.W.; Rettig, S.J.; Trotter, J., Can. J. Chem. 1985, 63, 1055. Thompson, R.C; Haynes, J.S.; Oliver, K.W.; Rettig, S.J.; Trotter, J., Can. J. Chem. 1985, 63, 1111. Haynes, J.S.; Sams, J.R.; Thompson, R.C, Can. J. Chem.  1985, submitted for publication. Haynes, J.S.; Rettig, S.J.; Sams, J.R.; Thompson, R.C; Trotter, J., Can. J. Chem. 1985, submitted for publication. 

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