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The synthesis and characterization of pyrazine and 2-methylpyrazine complexes of divalent copper and… Otieno, Tom 1988

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THE SYNTHESIS AND CHARACTERIZATION OF PYRAZINE AND 2-METHYLPYRAZINE COMPLEXES OF DIVALENT COPPER AND NICKEL by TOM OTIENO B . S c . (Hons . ) , U n i v e r s i t y of N a i r o b i , 1986 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE 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 q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA October 1988 © Tom O t i e n o , 1988 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, 1 agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of C_W-<L-WA Vvft-y The University of British Columbia Vancouver, Canada Date Q C \ Q-^Vw DE-6 (2/88) i i ABSTRACT A number of d i v a l e n t copper and n i c k e l complexes have been prepared and c h a r a c t e r i z e d using p h y s i c a l methods such as thermal a n a l y s i s , v i b r a t i o n a l 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. One mono-v a l e n t copper complex has been i s o l a t e d as s i n g l e - c r y s t a l s and i t s s t ruc ture determined by X-ray c r y s t a l l o g r a p h y . The l i g a n d s , L , employed i n t h i s study inc lude p y r a z i n e , 2-methyl-pyrazine and p y r i d i n e while the anions , X, used are C F 3 S 0 3 ~ , C H 3 S 0 3 ~ , p - C H 3 C 6 H i i S 0 3 - and N 0 3 " . Complexes of the M L 4 X 2 type are a l l c h a r a c t e r i z e d as being molecular with both n e u t r a l l igands and anions bonded i n a unidentate f a s h i o n . Spectroscopic evidence i n d i c a t e s that complexes of s to ichiometry M L 3 X 2 contain both b r i d g i n g and terminal pyrazine groups whereas i n those of the M L 2 X 2 type only b r i d g i n g pyrazine l igands are present . Both types of complexes contain monodentate anions . Compounds of the type MLX2 are charac ter ized as conta ining b r i d g i n g n e u t r a l l igands and b r i d g i n g (sulfonates) or c h e l a t i n g (ni t ra te ) anions . The copper(I) complex (ML2X) has been found by X-ray a n a l y s i s to possess both b r i d g i n g and terminal pyrazine l igands and monodentate sul fonate groups. Magneto-s t ructural c o r r e l a t i o n s have been made f o r a l l the d i v a l e n t metal complexes i n v e s t i g a t e d . A l l complexes of s toichiometry M L 4 X 2 are found to be, as expected, magnet ica l ly d i l u t e . A l l copper(II) complexes conta ining b r i d g i n g u n i t s , on the other hand, are found to be magnet ica l ly concentrated and t h e i r magnetic s u s c e p t i b i l i t i e s have been analyzed i n terms of a l i n e a r I l l chain model and a two-dimensional Heisenberg model. In the case of n i c k e l ( complexes, however, i t has been observed that the presence of a b r i d g i n g network does not n e c e s s a r i l y lead to measurable magnetic concentra t ion . i v TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS i v LIST OF TABLES i x LIST OF FIGURES x LIST OF ABBREVIATIONS AND SYMBOLS x i i ACKNOWLEDGEMENTS x i v CHAPTER 1 INTRODUCTION 1 1.1 PREVIOUS WORK ON COORDINATION POLYMERS CONTAINING PYRAZINE AND 2-METHYLPYRAZINE 2 1.2 PURPOSE OF THE PRESENT WORK 5 1.3 ORGANIZATION OF THE THESIS 7 1.4 SOME POSSIBLE STRUCTURES OF THE COMPLEXES INVESTIGATED IN THIS WORK 7 CHAPTER 2 EXPERIMENTAL PROCEDURES 10 2.1 GENERAL SYNTHETIC METHODS 10 2.2 PHYSICAL EXPERIMENTAL TECHNIQUES . . . . 11 2.2.1 Elemental A n a l y s i s 11 2.2.2 Thermal A n a l y s i s 11 2.2.3 I n f r a r e d Spectroscopy 12 2.2.4 Raman Spectroscopy 13 2.2.5 E l e c t r o n i c Spectroscopy 13 2.2.6 Magnetic S u s c e p t i b i l i t y Measurements 13 2.2.7 X - r a y C r y s t a l l o g r a p h y 14 V Page CHAPTER 3 DIVALENT COPPER COMPLEXES 16 3.1 INTRODUCTION 16 3.2 SYNTHETIC METHODS 17 3.2.1 Tet rakis (pyraz ine)copper ( I I ) 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 , C u ( p y z ) A ( C F 3 S 0 3 ) 2 17 3.2.2 Tetrakis (2 -methylpyrazine)copper(I I ) 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 , C u ( 2 - m e p y z ) 4 ( C F 3 S 0 3 ) 2 17 3.2.3 Tetrakis (2 -methylpyrazine)copper(I I ) n i t r a t e , Cu(2-mepyz) , (N0 3 ) 2 18 3.2.4 T r i s ( p y r a z i n e ) c o p p e r ( I I ) n i t r a t e , C u ( p y z ) 3 ( N 0 3 ) 2 . . . 18 3.2.5 Mono(pyrazine)copper(II) methanesulfonate, C u ( p y z ) ( C H 3 S 0 3 ) 2 19 3.2.6 Mono(pyrazine)copper(II) p - t o l u e n e s u l f o n a t e , C u ( p y z ) ( p - C H , C , H 4 S 0 , ) a 19 3.2.7 Mono(2-methylpyrazine)copper(II) t r i f luoromethane-s u l f o n a t e , Cu(2-mepyz) (CF 3 S0 3 ) 2 19 3.2.8 P o l y - u - p y r a z i n e d i n i t r a t o - 0 copper ( I I ) , C u ( p y z ) ( N 0 3 ) 2 . 20 3.2.9 Mono(2-methylpyrazine)copper(II) n i t r a t e , Cu(2-mepyz) (NO,) 2 20 3.2.10 Attempted Syntheses 20 3.3 RESULTS AND DISCUSSION 3.3.1 Thermal Studies 21 3.3.2 Infrared Spectroscopy 24 3 .3 .2 .1 Theory of V i b r a t i o n a l Spectra and Bonding . . 26 3 .3 .2 .2 Infrared S p e c t r a l Resul ts f o r Copper(II) Complexes Containing Sulfonate Anions . . . . 28 3 .3 .2 .3 Infrared S p e c t r a l Results for Copper(II) Complexes Containing N i t r a t e Anions 32 v i Page 3.3.3 E l e c t r o n i c Spectroscopy 36 3 .3 .3 .1 Theory of Copper(II) Spectra 36 3 .3 .3 .2 E l e c t r o n i c S p e c t r a l Results for Copper(II) Complexes 38 3 .3 .A Magnetic Proper t ies 40 CHAPTER A DIVALENT NICKEL COMPLEXES 55 A . l INTRODUCTION 55 A.2 SYNTHETIC METHODS . . . 55 A.2 .1 T e t r a k i s ( p y r i d i n e ) n i c k e l ( I I ) methanesulfonate, N i ( p y ) 4 ( C H , S O , ) a 56 A.2 .2 T e t r a k i s ( p y r i d i n e ) n i c k e l ( I I ) p - t o l u e n e s u l f o n a t e , N i ( p y ) , ( p - C H 3 C 6 H A S 0 3 ) 2 56 A.2 .3 T e t r a k i s ( 2 - m e t h y l p y r a z i n e ) n i c k e l ( I I ) n i t r a t e monohydrate, N i ( 2 - m e p y z ) u ( N 0 3 ) 2 » H 2 0 56 A . 2 . A T r i s ( p y r a z i n e ) n i c k e l ( I I ) methanesulfonate methanol s o l v a t e , N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 » C H 3 O H 57 A.2 .5 B i s ( p y r a z i n e ) n i c k e K I I ) n i t r a t e , Ni(pyz) 2 (N0 3) 2 . . . . 57 A . 2 . 6 Mono(pyrazine)nickel (II ) p - t o l u e n e s u l f o n a t e , N i ( p y z ) ( p - C H 3 C 6 H , S 0 3 ) 2 58 A.2 .7 Mono(2-methylpyrazine)nickel(II ) n i t r a t e , Ni (2 -mepyz) (N0 3 ) 2 58 A . 2 . 8 Attempted Syntheses 58 A.3 RESULTS AND DISCUSSION 59 A.3 .1 Thermal Studies 59 A . 3 . 2 Inf rared Spectroscopy 62 A . 3 . 2 . 1 Infrared S p e c t r a l Results f o r N i c k e l ( I I ) Complexes Containing Sulfonate Anions . . . . 6A A . 3 . 2 . 2 Infrared S p e c t r a l Results f o r N i c k e l ( I I ) Complexes Containing N i t r a t e Anions 66 v i i Page A . 3 . 3 E l e c t r o n i c Spectroscopy 69 4 .3 .3 .1 Theory of N i c k e l ( I I ) Spectra 69 4 .3 .3 .2 E l e c t r o n i c S p e c t r a l Results f o r N i c k e l ( I I ) Complexes 72 4 .3 .4 Magnetic Proper t ies 78 CHAPTER 5 POLY-u-PYRAZINEPYRAZINE(TRIFLUOROMETHANE SULFONATO-0)COPPER(I), C u ( p y z ) 2 ( C F 3 S 0 3 ) 96 5.1 INTRODUCTION 96 5.2 SYNTHETIC METHOD 97 5.3 RESULTS AND DISCUSSION 98 5.3.1 X-Ray Structure Determination 98 5.3.2 V i b r a t i o n a l Spectroscopy 102 5 .3 .2 .1 Infrared S p e c t r a l Results for C u ( p y z ) 2 ( C F 3 S 0 3 ) 102 5 .3 .2 .2 Raman S p e c t r a l r e s u l t s 105 CHAPTER 6 CONCLUSIONS AND SUGGESTIONS FOR FURTHER STUDY 107 6.1 CONCLUSIONS 107 6.2 SUGGESTIONS FOR FURTHER WORK I l l REFERENCES 113 APPENDICES . 118 I . V i b r a t i o n a l Assignments for P y r i d i n e and i t s Complexes . . . 118 I I . V i b r a t i o n a l Assignments f o r Pyrazine and i t s Complexes . . . 119 I I I . V i b r a t i o n a l Assignments for 2-Methylpyrazine and i t s Complexes 120 IV. V i b r a t i o n a l Assignments f o r Sulfonate Anions and Unassigned Bands 121 v i i i Page V. V i b r a t i o n a l Assignments f o r the N i t r a t e Anion and Unassigned Bands 123 V I . E l e c t r o n i c Spec t ra l Results 124 V I I . Magnetic S u s c e p t i b i l i t y Results f o r Copper(II) Complexes . . 126 V I I I . Magnetic S u s c e p t i b i l i t y Results f o r N i c k e l ( I I ) Complexes . . 129 IX. X- ray S t r u c t u r a l Parameters f o r C u ( p y z ) 2 ( C F 3 S 0 3 ) 131 X. Raman S p e c t r a l Results 133 i x LIST OF TABLES Page Table 3.1 Thermal Parameters f o r Copper(II) Complexes 22 3.2 S h i f t s of the 410, 472 and 1021 cm" 1 Bands of 2-Methylpyrazine upon Coordinat ion 35 3.3 Magnetic Parameters f o r Copper(II) Complexes obtained from the One-Dimensional Model (Eqn. 3.1) . . 45 3.4 Magnetic Parameters for Copper(II) Complexes obtained from the Two-Dimensional Model (Eqn. 3.3) . . 49 4.1 Thermal Parameters for N i c k e l ( I I ) Complexes 61 4.2 Spectrochemical Parameters f o r N i c k e l ( I I ) Complexes; C . I . Not Included 75 4.3 Spectrochemical Parameters for N i c k e l ( I I ) Complexes; C . I . Included 77 4.4 Z e r o - F i e l d S p l i t t i n g Parameters for N i c k e l ( I I ) Complexes . . . 83 4.5 Magnetic Parameters for N i c k e l ( I I ) Complexes obtained from Chain Models 91 5.1 C r y s t a l l o g r a p h i c Data for Cu(pyz) 2 (CF 3 S0 3 ) 99 5.2 Internal Bonding Parameters f o r the T r i f l a t e Anion 103 5.3 A c t i v a t e d Infrared Absorptions Around 919 and 1232 cm" 1 . . . 106 6.1 C l a s s i f i c a t i o n of Complexes 108 X LIST OF FIGURES Page Figure 1.1 Symmetry Allowed d ^ . y j - i T Overlap i n Cu(pyz) (N0 3) 2 5 1.2 Pyrazine and 2-Methylpyrazine 6 1.3 Two P o s s i b l e Structures for M L 4 X 2 Complexes 8 1.4 Two P o s s i b l e Structures f o r M L 3 X 2 Complexes 8 1.5 Two P o s s i b l e Structures f o r M L 2 X 2 Complexes 9 1.6 Three P o s s i b l e Structures f o r MLX2 Complexes 9 3.1 D . S . C . Curves f o r Cu(2-mepyz) 4 (N0 3 ) 2 and Cu(2-mepyz)(N0 3 ) 2 . . 25 3.2 Infrared Spectra of Cu(2-mepyz) A ( C F 3 S O 3 ) 2 and Cu(2-mepyz) (CF 3 S0 3 ) 2 30 3.3 E l e c t r o n i c Energy Levels for Copper(II) 38 3.4 Magnetic Moments vs Temperature for C u ( 2 - m e p y z ) u ( C F 3 S 0 3 ) 2 and Cu(2-mepyz) (CF 3 S0 3 ) 2 43 3.5 Magnetic S u s c e p t i b i l i t i e s vs Temperature f o r C u ( p y z ) ( N 0 3 ) 2 and Cu (2-mepyz) (N03) 2 44 3.6 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 ) 3 ( N 0 3 ) 2 . . 51 3.7 Magnetic S u s c e p t i b i l i t y vs Temperature f o r Cu(2-mepyz) (CF 3 S0 3 ) 2 52 3.8 Magnetic S u s c e p t i b i l i t y vs Temperature f o r Cu(pyz) ( p - C H 3 C 6 H i ( S 0 3 ) 2 53 3.9 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 H 3 S 0 3 ) 2 . . 54 4.1 D . S . C . Curves f o r N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 * C H 3 0 H and N i ( p y z ) 2 ( N 0 3 ) 2 63 4.2 Inf rared Spectra of N i ( p y z ) A ( N 0 3 ) 2 * H 2 0 and Ni(2 -mepyz) (N0 3 ) 2 . 67 4.3 E f f e c t s of Cubic and A x i a l Ligand F i e l d s and Second Order S p i n - O r b i t Coupling on the T r i p l e t Terms of N i c k e l ( I I ) i o n . . 70 4.4 Room Temperature S o l i d State E l e c t r o n i c Spectrum of N i ( p y ) , ( p - C H 3 C 6 H 4 S 0 3 ) 2 73 4.5 Magnetic Moments vs Temperature f o r N i L 4 X 2 Complexes 82 4.6 Magnetic S u s c e p t i b i l i t y vs Temperature f o r N i ( p y ) k ( C H 3 S 0 3 ) 2 . 85 x i Page Figure 4.7 Magnetic Moment vs Temperature f o r N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 • C H 3 O H . . 85 4.8 Magnetic S u s c e p t i b i l i t y vs Temperature f o r N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 ' C H 3 O H 92 4.9 Magnetic S u s c e p t i b i l i t y vs Temperature f o r Ni(2 -mepyz) (N0 3 ) 2 . 93 4.10 Magnetic Moment vs Temperature f o r N i ( p y z ) 2 ( N 0 3 ) 2 94 4.11 Magnetic S u s c e p t i b i l i t y vs Temperature f o r N i ( p y z ) 2 ( N 0 3 ) 2 . . 94 4.12 Magnetic Moment vs Temperature for Ni(pyz) ( p - C H 3 C 6 H ( ( S 0 3 ) 2 . . 95 4.13 Magnetic S u s c e p t i b i l i t y vs Temperature f o r N i ( p y z ) ( p - C H 3 C 6 H , S 0 3 ) 2 95 5.1 Proposed Structure for C u 2 L X 2 Complexes 96 5.2 Atom Numbering and Coordinat ion Around Copper for C u ( p y z ) 2 ( C F 3 S 0 3 ) 100 5.3 A Stereoview of the Uni t C e l l i n Cu(pyz) 2 (CF 3 S0 3 ) 100 5.4 A Schematic Representation of the Polymer Chain i n C u ( p y z ) 2 ( C F 3 S 0 3 ) 101 5.5 Infrared Spectrum of C u ( p y z ) 2 ( C F 3 S 0 3 ) 104 x i i LIST OF ABBREVIATIONS AND SYMBOLS N B . M . k br D . S . C . 2,2-DMP 2.5- dimepyz 2 .6- dimepyz ^ e f f . J max. g m 2-mepyz X m or S u s c e p t i b i l i t y obs. % Mono pyz py Avagadro 1 s number Bohr magneton Boltzmann's constant Broad D i f f e r e n t i a l scanning c a l o r i m e t r y 2,2-Dimethoxypropane 2 .5- Dimethylpyrazine 2 .6- Dimethylpyrazine E f f e c t i v e magnetic moment Exchange coupling constant Frequency of maximum absorption Lande s p l i t t i n g f a c t o r Medium 2-Methylpyrazine Molar magnetic s u s c e p t i b i l i t y Observed Per cent monomer Pyrazine (1 ,4 -Diazine) P y r i d i n e (Azine) X l l l sh sp s T(X ) *max. p - t o s y l a t e t r i f l a t e vs vw w Shoulder S p l i t Strong Temperature of maximum magnetic s u s c e p t i b i l i t y p-Toluenesul fonate , p-CH 3 C 6 H S O 3 " Tr i f luoromethanesulfonate , C F 3 S 0 3 " Very strong Very weak Weak x i v ACKNOWLEDGEMENTS I would l i k e to express ray deep gra t i tude to my s u p e r v i s o r , Dr . R . C . Thompson, f o r h i s guidance and encouragement during the course of t h i s work. I am extremely g r a t e f u l to J . Peers, J - L . Du, M. E h l e r t and Linda Lo f o r t h e i r i n v a l u a b l e help i n var ious aspects of t h i s work. Thanks are a l s o due to D r . S . J . R e t t i g for the c r y s t a l s t ruc ture determination and P. Borda f o r h i s M i c r o a n a l y t i c a l S e r v i c e s . 1 CHAPTER 1  INTRODUCTION 1.1 PREVIOUS WORK ON COORDINATION POLYMERS CONTAINING PYRAZINE AND 2-METHYLPYRAZINE The f i r s t polymeric t r a n s i t i o n metal -pyrazine complexes were reported by Lever , Lewis and Nyholm i n 1961.^ These were complexes of the type MLX2 and M L 2 X 2 where M i s Co or N i and L i s pyrazine or i t s mono- or d i -methyl s u b s t i t u t e d d e r i v a t i v e s and X i s C I , Br or I . They used room-temperature magnetic s u s c e p t i b i l i t y measurements and e l e c t r o n i c and i n f r a r e d spectroscopy as means of probing the nature of the metal chromophore. They observed that the M L 2 X 2 complexes e x h i b i t e d an extra i n f r a r e d absorpt ion band which was not observed i n the spectra of the corresponding MLX2 complexes. This extra band appeared at about 980 and 1250 c m - 1 when L was pyrazine and 2-methylpyrazine r e s p e c t i v e l y . The presence of t h i s band was taken as c h a r a c t e r i s t i c of monodentate l i g a t i o n . On t h i s b a s i s , these workers concluded that f o r a l l polymeric octahedral complexes of the M L 2 X 2 c l a s s br idge formation i s through the halogen, while for those of the MLX2 c l a s s i t i s through the n e u t r a l 2 3 l i g a n d s . ' The m i d - i n f r a r e d c r i t e r i o n f o r determining the mode of pyrazine 4 5 c o o r d i n a t i o n was disputed by G o l d s t e i n and coworkers. ' They concluded, from i n f r a r e d and Raman spectroscopic s t u d i e s , that the M L 2 X 2 complexes have sheet s t r u c t u r e s , containing b r i d g i n g pyrazine groups and t r a n s - t e r m i n a l halogen 2 atoms, rather than the halogen-bridged chain s t ruc tures p r e v i o u s l y proposed. The disagreement over the s t r u c t u r e of the M L 2 X 2 complexes was resolved with an X - r a y s t ruc ture determination^ which showed that C o ( p y z ) 2 C l 2 does indeed form a two-dimensional sheet s t r u c t u r e . The sheet s t ruc ture has s ince been observed i n other b i s ( p y r a z i n e ) complexes such as C u ( p y z ) 2 ( C 1 0 A ) 2 and C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 . 8 Examples of polymeric pyrazine complexes of the MLX2 type whose s t ruc tures have been determined by X - r a y c r y s t a l l o g r a p h y i n c l u d e A g ( p y z ) ( N 0 3 ) ? C u ( p y z ) ( N 0 3 ) 2 * ^ and C u ( p y z ) ( h f a c ) 2 , where hfac i s 1 , 1 , 1 , 5 , 5 , 5 - h e x a f l u o r o p e n t a n e - 2 , A - d i o n a t e . Pyraz ine-br idged complexes are of i n t e r e s t to magnetochemists because of the p o t e n t i a l f o r magnetic exchange i n t e r a c t i o n s between metal ions being propagated v i a the b r i d g i n g pyrazine system. V a r i a b l e temperature magnetic s u s c e p t i b i l i t y measurements have been made on a number of pyrazine and 2-methylpyrazine bridged complexes. Among the f i r s t to be i n v e s t i g a t e d were 12 Cu(2-mepyz)Cl 2 and Cu(2-mepyz)Br 2 . T h e i r s u s c e p t i b i l i t y versus temperature curves e x h i b i t maxima at 19K and 28K, r e s p e c t i v e l y , i n d i c a t i v e of ant i ferromagnetic i n t e r a c t i o n s . The s t ruc tures of these compounds are unknown. However, Inman and H a t f i e l d proposed an extended polymeric s t r u c t u r e i n which both h a l i d e and 2-methylpyrazine l igands p a r t i c i p a t e i n b r i d g i n g , but with the former t r a n s m i t t i n g much of the s p i n - s p i n i n t e r a c t i o n . Magnetic s u s c e p t i b i l i t y measurements made on C o ( p y z ) a X 2 [X = C l , Br] 13 down to 1.8K showed no s i g n of exchange i n t e r a c t i o n . N i ( p y z ) 2 X 2 [X = C l , Br , I] a l so showed no evidence of s p i n - s p i n i n t e r a c t i o n from magnetic s u s c e p t i b i l i t y data taken i n the 90 to 330K temperature range. 3 From low temperature magnetic s tudies on C u ( p y z ) ( N 0 3 ) 2 , V i l l a and 14 H a t f i e l d demonstrated that pyrazine i s capable of t r a n s m i t t i n g magnetic exchange between copper ions separated by a dis tance of 6.7A. In order to i n v e s t i g a t e the mechanism of exchange i n p y r a z i n e - b r i d g e d copper(II) complexes, Richardson and Hatf ie ld*"* i n v e s t i g a t e d the i s o s t r u c t u r a l complexes C u L ( N 0 3 ) 2 where L = p y z , C l p y z , 2-mepyz, 2 ,5-dimepyz, 2,6-dimepyz and phenazine. they showed that the v a r i a t i o n of the antiferromagnetic coupling c o r r e l a t e s ne i t he r wi th the o - b a s i c i t y nor wi th s t e r i c f a c t o r s but wi th the energy of the IT •* TT t r a n s i t i o n of the l i g a n d s . These r e s u l t s i n d i c a t e the presence of an exchange mechanism i n v o l v i n g the pyrazine Tr -system. Further evidence f o r the importance of a IT pathway i n the propagation of magnetic exchange has been provided by the magnetic p r o p e r t i e s of vanadyl complexes of the type [ V O ( h f a c ) 2 ] 2 L . ^ When L i s pyrazine or 2-methylpyrazine a maximum i s observed i n the s u s c e p t i b i l i t y versus temperature curves but when L i s Dabco [Dabco = 1 ,4 -Diazabicyc lo [2 .2 .2 ]oc tane and a f f o r d s only a o-type pathway] there i s no evidence of magnetic exchange i n t e r a c t i o n s . S i m i l a r r e s u l t s are obtained from dimeric copper(II) complexes of the type [ C u 2 ( t r e n ) 2 L ] ( C l O ^ ) ^ where t r e n i s 2 , 2 ' , 2 " - t r i a m i n o t r i e t h y l a m i n e . The lack of a TT-system i n Dabco has been proposed to account f o r the absence of magnetic exchange between metal centres br idged by t h i s l i g a n d . The unpaired e l e c t r o n i n a copper(II) i o n i n a t e t r a g o n a l l y elongated l i g a n d environment i s predominantly i n the d 2 _ 2 o r b i t a l . * ^ Overlap between x y t h i s o r b i t a l and the pyrazine n-system i s e s s e n t i a l f o r propagation of magnetic exchange through pyrazine b r i d g e s . The most e f f e c t i v e overlap occurs when there i s a non-zero d i h e d r a l angle between the plane of the pyrazine and A the xy copper p lane . In C u ( p y z ) ( N 0 3 ) 2 the pyrazine r ings are canted at an angle of A8° out of the copper xy p l a n e 1 0 ( F i g . 1 .1) . In the two-dimensional s h e e t - l i k e polymer C u ( p y z ) 2 ( C 1 0 A ) 2 , the pyrazine r i n g s are canted at an angle of 6 6 . 1 ° to the CuNA p l a n e . 7 One set of pyrazine r ings i n C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 g i s canted out of the xy plane by 2 8 . 5 ° . A l l the three complexes e x h i b i t maxima i n t h e i r s u s c e p t i b i l i t y versus temperature curves . No evidence of magnetic exchange, however, has been observed i n the 18 s u s c e p t i b i l i t y data f o r C u ( p y z ) ( h f a c ) 2 . T h i s compound has a l i n e a r s t ruc ture r e s u l t i n g from pyrazine b r i d g i n g i n the a x i a l ( i . e . z axis) d i r e c t i o n between square planar C u ( h f a c ) 2 u n i t s . 1 1 The absence of exchange i n t e r a c t i o n has been a t t r i b u t e d to the fac t that the plane of the pyrazine bridge l i e s i n the xz plane of the C u ( h f a c ) 2 . In such an o r i e n t a t i o n , there i s no e f f e c t i v e t T - o r b i t a l overlap between the pyrazine n-system and the copper d , , o r b i t a l . X 2 _ y 2 While magnetic exchange i n p y r a z i n e - b r i d g e d copper complexes i s r e l a t i v e l y common and reasonably w e l l understood, such i s not the case f o r 19 20 r e l a t e d i r o n complexes. Recent ly , Haynes et a l . ' have reported v a r i a b l e temperature magnetic s tudies on a large number of polymeric i r o n ( I I ) - p y r a z i n e complexes. Magnetic s u s c e p t i b i l i t y measurements taken to l i q u i d helium temperature revealed no s u b s t a n t i a l magnetic i n t e r a c t i o n through pyrazine i n a number of F e ( p y z ) 2 X 2 [X = C l " , B r " , I " , C 1 0 A - , C H 3 S 0 3 " ] complexes and F e ( p y z ) 2 ( C F 3 S 0 3 ) 2 » C H 3 0 H . Conclusive evidence of exchange coupling was a lso not found f o r the mono(pyrazine)iron(II) complexes, F e ( p y z ) ( p - C H 3 C 6 H A S 0 3 ) 2 and i t s bis(methanol) s o l v a t e , and F e ( p y z ) C l 2 . S i g n i f i c a n t antiferroraagnetic coupling was, however, detected i n F e ( p y z ) 2 ( N C S ) 2 , Fe(pyz)(NCO) 2 and 5 F e ( p y z ) ( C F 3 S 0 3 ) 2 , each of which e x h i b i t s a maximum i n a p l o t of magnetic s u s c e p t i b i l i t y versus temperature. F i g . 1.1 Symmetry Allowed d 2_ 2-TT Overlap i n Cu(pyz) (N0 3) 2 1.2 PURPOSE OF THE PRESENT WORK This work i s an extension of previous s tudies i n t h i s labora tory on p y r a z i n e - b r i d g e d c o o r d i n a t i o n polymers. We set out to add to the number of p y r a z i n e - b r i d g e d copper(II) sul fonates i n v e s t i g a t e d and to extend the s t u d i e s to i n c l u d e analogous n i c k e l ( I I ) complexes f o r the f i r s t t ime. The complexes were synthesized and s tudied with the f o l l o w i n g o b j e c t i v e s i n mind: ( i ) To extend the range of known p y r a z i n e - b r i d g e d metal sul fonate complexes. ( i i ) To obta in s t r u c t u r a l informat ion on the complexes by i d e n t i f y i n g the. metal chromophore and a lso l i g a n d and anion c o o r d i n a t i o n modes. 6 ( i i i ) To i n v e s t i g a t e the magnetic p r o p e r t i e s of the m a t e r i a l s and to probe magneto-structural c o r r e l a t i o n s . ( iv) To compare pyrazine and 2-methylpyrazine ( F i g . 1.2) as b r i d g i n g groups. For comparison purposes, and because of t h e i r own i n t e r e s t i n g p r o p e r t i e s too , some n i t r a t o complexes were a lso prepared and c h a r a c t e r i z e d . X-ray c r y s t a l l o g r a p h y i s the most important t o o l for s t r u c t u r a l determinat ion. However, s ince X- ray q u a l i t y s i n g l e c r y s t a l s of inorganic polymers are not very common, chemists have r e l i e d on other p h y s i c a l methods to e l u c i d a t e the s t ruc tures of these complexes. The p h y s i c a l techniques used to charac ter ize compounds i n t h i s work i n c l u d e d d i f f e r e n t i a l scanning ca lor imetry ( D . S . C . ) , v i b r a t i o n a l 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. The s to ichiometry and p u r i t y of the complexes were determined by elemental a n a l y s i s of C, H and N. F i g . 1.2 Pyrazine and 2-Methylpyrazine a) P y r a z i n e b) 2 - M e t h y l p y r a z i n e 7 1.3 ORGANIZATION OF THE THESIS Some p o s s i b l e s t ruc tures f o r the complexes i n v e s t i g a t e d i n t h i s work, and which are f r e q u e n t l y r e f e r r e d to i n the t e x t , are a l l grouped together i n the next s e c t i o n . General experimental procedures are discussed i n Chapter 2. The synthesis and c h a r a c t e r i z a t i o n of d i v a l e n t copper and n i c k e l complexes are presented i n Chapters 3 and 4 r e s p e c t i v e l y . Only one monovalent copper complex was i s o l a t e d i n t h i s s tudy. I ts synthesis and s t r u c t u r a l determination are discussed i n Chapter 5. Raman s p e c t r a l s tudies on 4 5 metal -pyrazine complexes seem to have been l i m i t e d to a few t i n and cobal t compounds. We attempted to obta in Raman spectra of the pyrazine complexes i n v e s t i g a t e d i n t h i s work. These spectra were of poor q u a l i t y and p o s s i b l e reasons for t h i s are discussed i n Chapter 5. Some general conclusions about t h i s work are presented i n Chapter 6. 1.4 SOME POSSIBLE STRUCTURES FOR THE COMPLEXES INVESTIGATED IN THIS WORK No d i v a l e n t copper or n i c k e l complex was i s o l a t e d i n a form s u i t a b l e for s i n g l e - c r y s t a l X- ray s t r u c t u r a l determinat ion. I n f r a r e d s p e c t r a , i n p a r t i c u l a r , and to some extent e l e c t r o n i c s p e c t r a , were very u s e f u l i n working out the b a s i c s t ruc tures of these m a t e r i a l s . Some of these s t ruc tures are i l l u s t r a t e d i n Figures 1 .3-1 .6 . The most probable s t r u c t u r e f o r each compound s t u d i e d i s assigned i n the t e x t . 8 F i g . 1.3 Two P o s s i b l e S t r u c t u r e s f o r ML 4X 2 Complexes F i g . 1.4 Two P o s s i b l e S t r u c t u r e s f o r ML-X- Complexes 3 A 9 10 CHAPTER 2  EXPERIMENTAL PROCEDURES 2.1 GENERAL SYNTHETIC METHODS A l l chemicals and solvents were at l e a s t of reagent grade q u a l i t y and were used without fur ther p u r i f i c a t i o n . Nearly a l l the compounds i n t h i s study were a i r - s e n s i t i v e as determined by exposing small samples to the atmosphere and monitoring t h e i r i n f r a r e d spectra and/or m i c r o a n a l y t i c a l data . The compounds were, t h e r e f o r e , handled i n a n i t r o g e n atmosphere dry box ( D . L . Herr ing Corporat ion D r i - L a b (Model HE-43)) equipped with a dry t r a i n (Model HE-93) . Outside the dry box, standard vacuum-line techniques for the 21 manipulat ion of a i r s e n s i t i v e compounds were used. Two general s y n t h e t i c techniques were employed. The f i r s t method i n v o l v e d d i s s o l v i n g the reagents i n a s u i t a b l e solvent and then mixing the s o l u t i o n s . Since most of the s t a r t i n g metal s a l t s were hydrated, the 22 dehydrating agent 2,2-dimethoxypropane was r o u t i n e l y added to the solvents i n approximately 1:10 v / v r a t i o . In most reac t ions the n e u t r a l l i g a n d was used i n excess. I t was noted i n some pyrazine complexes, however, that even i f the n e u t r a l l i g a n d was i n excess, the m e t a l - l i g a n d r a t i o was s t i l l c r i t i c a l . For i n s t a n c e , i n the r e a c t i o n i n v o l v i n g e t h a n o l i c s o l u t i o n s of C u ( C F 3 S 0 3 ) 2 and p y r a z i n e , C u ( p y z ) A ( C F 3 S 0 3 ) 2 was obtained by us ing a 1:8 m e t a l - l i g a n d r a t i o whereas a 1:12 r a t i o gave C u ( p y z ) v s ( C F 3 S 0 3 ) 2 . The a d d i t i o n a l h a l f mole of pyrazine per mole of copper, presumably present as l a t t i c e p y r a z i n e , was detected by elemental a n a l y s i s , thermal a n a l y s i s and the 11 increase i n r e l a t i v e i n t e n s i t y , to medium, of the very weak i n f r a r e d band at A21 c m " 1 . The second prepara t ive method employed i n t h i s study was t h e r m o l y s i s . Complexes wi th greater than 1:1 l i g a n d to metal r a t i o s were degraded to t h e i r mono(ligand) d e r i v a t i v e s by c a r e f u l l y c o n t r o l l e d h e a t i n g . Results from thermal s tudies (sect ions 3.3.1 and A.3.1) were used to assess the f e a s i b i l i t y of a p a r t i c u l a r thermolysis r e a c t i o n . I t was noted that by heating i n vacuo, temperatures r e q u i r e d for thermolysis on a preparat ive sca le were lower than those i n d i c a t e d by the D . S . C . s t u d i e s . The choice of temperature for bulk thermolysis was found to be qui te c r i t i c a l and was determined by heating at g r a d u a l l y i n c r e a s i n g temperatures and monitoring the changes i n the i n f r a r e d spectrum of the m a t e r i a l as w e l l as monitoring the m i c r o a n a l y t i c a l data . The time required to obta in the d e s i r e d product v a r i e d i n each case and these are g i v e n , together with other s y n t h e t i c d e t a i l s for each compound, i n sec t ions 3.2 and A . 2 . 2.2 PHYSICAL EXPERIMENTAL TECHNIQUES 2.2 .1 Elemental A n a l y s i s Carbon, hydrogen and n i t r o g e n analyses were performed by Mr. P. Borda of t h i s Department. 2 .2 .2 Thermal A n a l y s i s D i f f e r e n t i a l scanning c a l o r i m e t r y s tudies were performed using a M e t t l e r DSC-20 c e l l i n t e r f a c e d with a M e t t l e r TC 10 TA processor and a P r i n t 12 Swiss Matr ix p r i n t e r / p l o t t e r . F i n e l y powdered samples of approximately 4 to 14 mg were a c c u r a t e l y weighed and sealed i n t o aluminum pans. A small hole punched i n the l i d allowed f o r f ree access to the measuring c e l l atmosphere, i n t h i s case an i n e r t atmosphere of n i t r o g e n gas at a flow rate of 50 ml m i n " 1 . The samples were heated from 35 to 450°C at a rate of 4°C per minute. The temperature of the Pt sensor was c a l i b r a t e d using the known f u s i o n temperatures of indium, lead and z i n c . The heat flow was c a l i b r a t e d by using an exac t ly known quant i ty of indium. The maximum i n the D . S . C . curve and the i n t e g r a t e d area underneath the curve y i e l d e d r e s p e c t i v e l y , the temperature and enthalpy of a p a r t i c u l a r event. From a s e r i e s of c a l i b r a t i o n s using indium metal the f u s i o n tempera-ture was found to be accurate to ± 0.1K and the i n t e g r a t e d area was accurate to ± 2 J g " 1 , represent ing an e r r o r of approximately ± 1% i n both measurements. However, where broad or overlapping curves occur the temperature and enthalpy values are considered accurate to ± 5K and + 5% r e s p e c t i v e l y . Thermogravimetric a n a l y s i s was performed by weighing the aluminum pan p r i o r to and f o l l o w i n g a thermal event. The accuracy of the weight loss f i g u r e i s approximately 5%. 2.2.3 Inf rared Spectroscopy A Perkin-Elmer Model 598 Spectrophotometer was used to record i n f r a r e d spectra over the range 200 to 4000 c m " 1 . F i n e l y ground samples were mulled i n Nujol and sandwiched between KRS-5 p l a t e s (58% t h a l l i u m i o d i d e , 42% t h a l l i u m bromide, Harshaw Chemical C o . ) . Complexes containing the n i t r a t o group were mulled i n 1,3-hexachlorobutadiene as w e l l . The p l a t e s were sealed with 13 p l a s t i c tape to prevent h y d r a t i o n of samples. A l l spectra were c a l i b r a t e d at 907 and 1601 cm" 1 with a polystyrene f i l m . Tabulated frequencies are considered accurate to ± 5 cm" 1 for broad bands and ± 2 cm" 1 f o r sharp bands. 2 .2 .4 Raman Spectroscopy Raman spectra were recorded on a Spex Ramalog 5 spectrometer equipped with a Spectra Physics 164 argon i o n l a s e r . The green l i n e at 514.5 nm was used f o r e x c i t a t i o n . The samples were packed i n t o mel t ing p o i n t c a p i l l a r i e s and sealed with grease (Apiezon) i n the drybox; permanent f lame-seals were then made as soon as p o s s i b l e . 2.2.5 E l e c t r o n i c Spectroscopy S o l i d - s t a t e e l e c t r o n i c spectra i n the n e a r - i n f r a r e d and v i s i b l e regions (4 000 to 30 000 cm" 1) were recorded on a Cary model 14 spectrophotometer. S i l i c a glass windows containing t h i c k N u j o l mulls and N u j o l were placed i n the sample and reference beams r e s p e c t i v e l y . The absorbance l e v e l was adjusted with n e u t r a l d e n s i t y f i l t e r s . Due to the broad nature of these absorpt ions , e l e c t r o n i c s p e c t r a l frequencies quoted are considered accurate to ± 200 c m " 1 . 2 .2.6 Magnetic S u s c e p t i b i l i t y Measurements Temperature-dependent magnetic s u s c e p t i b i l i t y s tudies i n the range 4.2-82K were made using a Pr inceton A p p l i e d Research Model 155 v i b r a t i n g 23 sample magnetometer. A magnetic f i e l d of 9225 gauss was employed f o r a l l the compounds except f o r C u ( p y z ) ( C H 3 S 0 3 ) 2 , i n which a f i e l d of 9625 gauss was used (there was no p a r t i c u l a r reason for t h i s ) . Checks for f i e l d dependence 14 of the magnetic s u s c e p t i b i l i t i e s were made using a f i e l d of 7501 gauss. No evidence of f i e l d dependence was found i n any of the compounds s t u d i e d . Magnetic f i e l d s were set to an accuracy of ± 0.5% and measured by an F.W. B e l l Model 620 gaussmeter. A c c u r a t e l y weighed samples of approximately 80 mg, contained i n K e l - F capsules , were attached to a K e l - F holder wi th an epoxy r e s i n . Correc t ions were made f o r the diamagnetic background of the h o l d e r . Ul trapure n i c k e l metal was used to c a l i b r a t e the instrument. Temperature 24 measurement was achieved with a chromel versus Au-0.02% Fe thermocouple located i n the sample holder immediately above the sample. The thermocouple was c a l i b r a t e d by using the known s u s c e p t i b i l i t y versus temperature behaviour of tetramethylenediammonium te t rachlorocuprate ( I I ) and checked with 25 mercury(II) t e 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 ) . The temperatures are estimated to be accurate to ± 1% from the sca t te r i n the data p o i n t s from four separate c a l i b r a t i o n s . The accuracy of the magnetic s u s c e p t i b i l i t y values as measured by t h i s technique i s estimated to be ± 1%. Molar magnetic s u s c e p t i b i l i t i e s were correc ted f o r the diamagnetism of 26 the metal ions and l i g a n d s . The diamagnetic cor rec t ions i n u n i t s of 10" 6 cm3 m o l " 1 a re : Cu* + , 11; N i J + , 11; C F 3 S 0 3 - , 46; C H 3 S 0 3 " , 35; p - C H 3 C 6 H i ( S 0 3 " , 89; N 0 3 " , 20; H 2 0 , 13; CH 3 0H, 34; p y r i d i n e , 49; p y r a z i n e , 45; 2 -methyl-p y r a z i n e , 57. The complexes were a lso correc ted f o r the temperature-independent paramagnetism of C u 2 + , 60, and N i 2 * , 200, i n u n i t s of 10" 6 cm3 m o l " 1 . 2 .2.7 X- ray Crys ta l lography The X- ray s t ruc ture determination of C u ( p y z ) 2 ( C F 3 S 0 3 ) was performed by D r . S . J . R e t t i g of t h i s Department. The name of t h i s complex, according to 15 I . U . P . A . C . nomenclature, i s p o l y - u - p y r a z i n e p y r a z i n e ( 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 - 0 ) c o p p e r ( I ) . In d i s c u s s i o n s i n the t e x t , however, a l e s s r igorous naming system i s used. It i s thus r e f e r r e d to as b is (pyraz ine)copper ( I ) 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 . The l a t t e r naming system i s used f o r a l l the other complexes s ince t h e i r s t ruc tures could not be confirmed by X-ray c r y s t a l l o -graphy. 16 CHAPTER 3  DIVALENT COPPER COMPLEXES 3.1 .INTRODUCTION . . The synthesis and c h a r a c t e r i z a t i o n of copper(II) complexes are descr ibed i n t h i s chapter . Although the primary aim of t h i s work was to study polymeric m a t e r i a l s , some mononuclear species of the general formula M L 4 X 2 were a lso i n v e s t i g a t e d , p r i m a r i l y for two reasons. Previous s tudies on 8 27 28 r e l a t e d complexes have revealed no magnetic exchange i n t e r a c t i o n s . ' ' The absence of b r i d g i n g l igands a lso renders such exchange u n l i k e l y . Thus t h e i r magnetic moment data g e n e r a l l y serve as a b a s e l i n e from which magnetic i n t e r -ac t ions i n analogous polymeric complexes can be measured. Secondly, the i n f r a r e d s p e c t r a l data of these compounds can be used to probe the mode of bonding of mult identate moiet ies present i n r e l a t e d complexes (see s e c t i o n 3 . 3 . 2 ) . Two of the polymeric complexes discussed i n t h i s chapter , C u ( p y z ) ( N 0 3 ) 2 and Cu(2-mepyz)(N0 3 ) 2 , have been reported before . Despite the f a c t that the former has been e x t e n s i v e l y s t u d i e d , ^ ' ^ ' ^ i t s i n f r a r e d s p e c t r a l data have not been repor ted . In the l i g h t of i t s known s t r u c t u r e , such data could be u s e f u l i n e l u c i d a t i o n of s t r u c t u r a l informat ion from spectra of r e l a t e d complexes. Our primary i n t e r e s t i n t h i s compound stemmed from t h i s c o n s i d e r a t i o n . A l t e r n a t i v e routes to those i n the l i t e r a t u r e f o r the syntheses of both C u ( p y z ) ( N 0 3 ) 2 and Cu(2-mepyz)(N0 3 ) 2 are a lso presented. 17 3.2 SYNTHETIC METHODS A general d i s c u s s i o n of the s y n t h e t i c techniques used was given i n s e c t i o n 2 .1 . In t h i s s e c t i o n , the a c t u a l d e t a i l s f o r the syntheses of a l l copper(II) complexes i n v e s t i g a t e d are g i v e n . 3.2.1 Tet rakis (pyraz ine)copper ( I I ) 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 , C u ( p y z ) k ( C F 3 S 0 3 ) 2 31 Copper(II) t r i f luoromethanesulfonate (0.509 g, 1.41 mmol) was d i s s o l v e d i n 4 ml ethanol containing about 10% v / v 2,2-DMP. The copper(II) s o l u t i o n was added to pyrazine (0.889 g, 11.1 mmol) d i s s o l v e d i n 3 ml of the same s o l v e n t . The blue p r e c i p i t a t e , which formed immediately, was i s o l a t e d by f i l t r a t i o n , washed with a small amount of solvent and d r i e d under vacuum for 3 h . A n a l , c a l c d . for C u ^ , H 1 6 N 8 F 6 S 2 0 6 : C, 31.70; H, 2.36; N, 16.43; found: C, 32.00; H, 2.48; N, 16.20. 3.2.2 Tetrakis (2 -methylpyrazine)copper(I I ) 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 , Cu(2 -mepyz) i ( (CF 3 S0 3 ) 2 31 Copper(II) t r i f luoromethanesulfonate (0.516 g , 1.43 mmol) was d i s s o l v e d i n 4 ml ethanol containing about 10% v / v 2,2-DMP. The copper(II) s o l u t i o n was added to 2-methylpyrazine (3.0 m l , 33 mmol). A deep blue m i c r o -c r y s t a l l i n e s o l i d formed a f t e r a few minutes and was i s o l a t e d by f i l t r a t i o n , washed with small amounts of solvent and d r i e d under vacuum f o r 2 1/2 h . A n a l , c a l c d . f o r C u C 2 2 H 2 , N 8 F 6 S 2 0 6 : C, 35.80; H, 3.28; N, 15.18; found: C, 36.06; H, 3.37; N, 15.37. 18 3.2.3 Tetrakis (2 -methylpyrazine)copper(II ) n i t r a t e , Cu(2-mepyz) u (N0 3 ) 2 Copper(II) n i t r a t e t r i h y d r a t e (0.645 g, 2.67 mmol) was d i s s o l v e d i n 9 ml ethanol containing about 10% v / v 2,2-DMP. The copper(II) s o l u t i o n was added to 2-methylpyrazine (6.0 m l , 66 mmol). A purple p r e c i p i t a t e formed immediately and was i s o l a t e d by f i l t r a t i o n . The p r e c i p i t a t e was not washed because of the l a b i l i t y of t h i s complex. Excess solvent and l i g a n d were removed by pumping on the p r e c i p i t a t e f o r 5 minutes. A n a l , c a l c d . f o r C u C 2 0 H 2 i N 1 0 0 6 : C, 42.59; H, 4.29; N, 24.83; found: C, 42.46; H, 4.26; N, 25.00. It was noted that d r y i n g t h i s complex f o r longer per iods of time than noted above l e d to l o s s of some n e u t r a l l i g a n d s . In f a c t , when the compound was l e f t exposed to the atmosphere for severa l days, i t l o s t three moles of 2-methylpyrazine to y i e l d the mono(2-methylpyrazine) d e r i v a t i v e ( sec t ion 3 .2 .9 ) . 3 .2 .4 T r i s ( p y r a z i n e ) c o p p e r ( I I ) n i t r a t e , C u ( p y z ) 3 ( N 0 3 ) 2 Copper(II) n i t r a t e t r i h y d r a t e (0.957 g , 3.96 mmol) was d i s s o l v e d i n 10 ml of ethanol containing about 10% v / v 2,2-DMP. The copper(II) s o l u t i o n was added to pyrazine (4.08 g , 51.0 mmol) d i s s o l v e d i n 10 ml of the same s o l v e n t . A blue p r e c i p i t a t e formed immediately and was i s o l a t e d by f i l t r a t i o n . The p r e c i p i t a t e was not washed because of the l a b i l i t y of t h i s complex. Excess solvent and pyrazine were removed by pumping on the p r e c i p i t a t e f o r 10 minutes. Drying f o r longer per iods of time lead to l o s s of some pyrazine as monitored by m i c r o a n a l y t i c a l data and i n f r a r e d s p e c t r a . A n a l . C a l c d . f o r C u C 1 2 H 1 2 N s 0 6 : C, 33.69; H , 2.83; N, 26.19; found: C, 33.77; H, 2.85; N, 26.40. 19 3.2.5 Mono(pyrazine) copper(II) methanesulfonate, C u ( p y z ) ( C H 3 S 0 3 ) 2 g Poly-bis (pyrazine)bis (methanesulfonato-O)copper(II ) was heated at 100°C i n vacuo for 2 h and then at 140°C f o r 8 h to y i e l d the pale green raono-(pyrazine) complex. A n a l , c a l c d . f o r C u C 6 H 1 0 N a S 2 0 6 : C, 21.59; H, 3.02; N, 8.39; found: C, 21.75; H, 3.05; N, 8.39. 3 .2.6 Mono (pyrazine) copper (II) p - t o l u e n e s u l f o n a t e , Cu(pyz) ( p - C H 3 C 6 H i ( S 0 3 ) 2 31 Copper(II) p - to luenesulfonate (0.604 g , 1.49 mmol) was d i s s o l v e d i n 10 ml ethanol cofftaining about 10% v / v 2,2-DMP to give a blue s o l u t i o n . The copper(II) s o l u t i o n was added to pyrazine (1.42 g , 17.7 mmol) d i s s o l v e d i n 4 ml of the same s o l v e n t . The blue p r e c i p i t a t e which formed was i s o l a t e d by f i l t r a t i o n , washed with a small amount of solvent containing some p y r a z i n e , d r i e d under vacuum f o r 6 h . and then heated i n vacuo at 70°C f o r 4 3/4 h . A n a l , c a l c d . for C u C 1 8 H 1 8 N 2 S 2 0 6 : C, 44.48; H, 3.73; N, 5.76; found: C , 44.57; H, 3.77; N, 5.87. 3 .2 .7 Mono(2-methylpyrazine)copper(II) 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 , Cu(2-mepyz) (CF 3 S0 3 ) 2 Tetrakis (2 -methylpyrazine)copper(I I ) t r i f l a t e ( sec t ion 3.2.2) was heated at 90°C i n vacuo for 5 h . and then at 100°C f o r 11 h to obtain the green mono(2-methylpyrazine) complex. A n a l . C a l c d . f o r C u C 7 H 6 N 2 F 6 S 2 0 6 : C, 18.45; H, 1.33; N, 6.15; found: C , 18.74; H, 1.47; N , 6.24. Heating the te t rakis (2 -methylpyraz ine) d e r i v a t i v e d i r e c t l y at 100°C before f i r s t heat ing i t at 90°C d i d not y i e l d Cu(2-mepyz) (CF 3 S0 3 ) 2 but ins tead decomposed to give a brownish black powder. See s e c t i o n 3.3 f o r fur ther d i s c u s s i o n . 20 3.2.8 P o l y - u - p y r a z i n e d i n i t r a t o - 0 copper ( I I ) , C u ( p y z ) ( N 0 3 ) 2 T h i s compound has been prepared p r e v i o u s l y as s i n g l e c r y s t a l s by slow evaporat ion of an aqueous 1:1 s o l u t i o n of copper(II) n i t r a t e and p y r a z i n e . This synthesis was s u c c e s s f u l l y repeated i n t h i s study. A n a l , c a l c d . f o r CuC.H^N^Og: C, 17.95; H, 1.51; N, 20.93; found: C, 17.90; H, 1.53; N, 21.00. The same compound, i n powder form, was obtained by leaving t r i s -(pyrazine)copper(II) n i t r a t e ( sec t ion 3 .2 .A) i n a d e s s i c a t o r , over D r i e r i t e , for about one week. The colour changed from blue to pale p u r p l e . Found: C, 17.76; H, 1.47; N, 20.83. 3.2.9 Mono(2-methylpyrazine)copper(II) n i t r a t e , Cu(2-mepyz)(N0 3 ) 2 This blue complex was obtained by heating Cu(2-mepyz) u (N0 3 ) 2 ( sec t ion 3.2.3) at 8 0 ° C , i n vacuo, f o r 12 h . A n a l , c a l c d . f o r C u C s H 6 N A 0 6 : C, 21.32; H , 2.15; N, 19.89; found: C, 21.65; H, 2.19; N, 20.09. H a t f i e l d et a l . * ' ' p r e v i o u s l y reported preparing t h i s compound by simply a l lowing the p r e c i p i t a t e obtained from a mixture of an e t h a n o l i c s o l u t i o n of copper(II) n i t r a t e and 2-methylpyrazine to a i r d r y . 3.2.10 Attempted Syntheses During the course of t h i s study attempts were made to prepare Cu(2-mepyz) n X 2 (X = C H 3 S 0 3 " , p - C H 3 C 6 H A S 0 3 - ) complexes. A d d i t i o n of excess 2-methylpyrazine to a methanolic s o l u t i o n of C u ( C H 3 S 0 3 ) 2 y i e l d e d a blue micro-c r y s t a l l i n e p r e c i p i t a t e a f t e r about two weeks. However, the p r e c i p i t a t e could not be i s o l a t e d i n a pure form, some par ts of i t always being green (the supernatant s o l u t i o n was green) . A second approach i n v o l v e d a d d i t i o n of 21 excess 2-methylpyrazine to s o l i d C u ( C H 3 S 0 3 ) 2 . Although m i c r o a n a l y t i c a l data of the r e s u l t a n t blue s o l i d d i d not correspond to any i n t e g r a l value of n , the r e s u l t s were c lose to those expected f o r n = 4. S i m i l a r approaches were employed i n attempts to synthesize C u ( 2 - m e p y z ) k ( p - C H 3 C 6 H 4 S 0 3 ) 2 , again without success• Attempts to synthesize C u ( p y z ) 2 ( C F 3 S 0 3 ) 2 , however, r e s u l t e d i n the i s o l a t i o n of C u ( p y z ) 2 ( C F 3 S 0 3 ) ins tead (see Chapter 5) . 3.3 RESULTS AND DISCUSSION 3.3.1 Thermal Studies The range of thermal s t a b i l i t i e s of the complexes was e s t a b l i s h e d by using d i f f e r e n t i a l scanning c a l o r i m e t r y ( D . S . C . ) . D . S . C . and thermo-gravimetr ic r e s u l t s were a lso informat ive i n regard to e x p l o r i n g the p o s s i b i l i t y of obta ining complexes with lower l i g a n d to metal r a t i o s by u t i l i z i n g thermolysis as a prepara t ive technique. The thermal parameters f o r copper(II) complexes are given i n Table 3 .1 . The D . S . C . curve f o r C u ( p y z ) 4 ( C F 3 S 0 3 ) 2 shows an endothermic event at 181°C which i s accompanied by a weight loss corresponding to the loss of three molecules of p y r a z i n e . Decomposition of the compound begins at about 3 6 5 ° C . These r e s u l t s suggest that i t i s p o s s i b l e to obtain the mono(pyrazine) complex by thermolysis of the t e t r a k i s ( p y r a z i n e ) compound. D . S . C . s tudies on 22 Table 3.1 Thermal parameters f o r copper(II) complexes Compound Peak Temp. °C AH kJ m o l - i Weight l o s s % 2 C a l c d . Obs. C u ( p y z ) 4 ( C F 3 S O s ) 3 181 3 365 172 35 35 Cu(2 -mepyz) i i (CF 3 S0 3 ) 2 153 300 3 52 13 15 Cu(2-mepyz) 4 (N0, ) a 102 3 220 195 50 50 C u ( p y z ) 3 ( N 0 3 ) 2 1191 130 J 3 290 121 37 38 C u ( p y z ) ( C H 3 S 0 3 ) 2 300 3 C u ( p y z ) ( p - C H 3 C 6 H 4 S 0 3 ) 2 290 3" Cu(2-mepyz) (CF 3 S0 3 ) 2 3 220 C u ( p y z ) ( N 0 3 ) 2 280 3 Cu(2-mepyz)(N0 3 ) 2 3 220 J 1) Estimated e r r o r l i m i t s : peak temp. ± 5 ° C , AH ± 5%, weight l o s s ± 5%. 2) For explanat ion of c a l c u l a t e d values see t e x t . 3) Onset of decomposition. 23 C u ( p y z ) u ( C F 3 S 0 3 ) 2 *H 2 0 lead to s i m i l a r c o n c l u s i o n s . On the b a s i s of the D . S . C . r e s u l t s , C u ( p y z ) ( C F 3 S 0 3 ) 2 was s u c c e s s f u l l y prepared i n the previous work c i t e d . In the case of C u ( 2 - m e p y z ) A ( C F 3 S 0 3 ) 2 , a sharp endothermic event i s observed at 1 5 3 ° C . The weight loss of 15% obtained by heat ing a sample of the compound to the end of t h i s event compares favourably wi th the value of 13% expected for the loss of one molecule of 2-methylpyrazine. On a prepara t ive s c a l e , however, i t was found that thermolysis of the sample at 100°C leads to the loss of three l igands ( sec t ion 3.2.7) ins tead of one, as i n d i c a t e d by the thermogravimetric measurements. I t was a lso noted that the sample had to be heated at 90°C for severa l hours before r a i s i n g the temperature to 100°C otherwise decomposition would occur . This suggests that C u ( 2 - m e p y z ) 4 ( C F 3 S 0 3 ) 2 i s unstable at 100°C and heating to 90°C produces a s table intermediate which then y i e l d s Cu(2-mepyz) (CF 3 S0 3 ) 2 on heating at 1 0 0 ° C . Based on the thermo-gravimetr ic r e s u l t s above, the intermediate may be t r i s ( 2 - m e t h y l p y r a z i n e ) -copper(II) t r i f l a t e . C u ( 2 - m e p y z ) A ( C F 3 S 0 3 ) 2 begins to undergo exothermic decomposition at about 3 0 0 ° C . The D . S . C . curve f o r Cu(2-mepyz) A (N0 3 ) 2 ( F i g . 3.1a) reveals two over-lapping endothermic events at 1 0 2 ° and about 1 3 0 ° C . The weight l o s s of 50% obtained on heating the sample to 136°C i s the same as that c a l c u l a t e d for the l o s s of three 2-methylpyrazine groups. Exothermic decomposition begins at about 2 2 0 ° C . These r e s u l t s i n d i c a t e that i t i s p o s s i b l e to prepare Cu(2-mepyz)(N0 3 ) 2 by thermolysis of Cu(2-raepyz) A (N0 3 ) 2 . The synthesis of the mono(2-methylpyrazine) complex was subsequently c a r r i e d out ( sec t ion 3 . 2 . 9 ) . The D . S . C . curve f o r C u ( p y z ) 3 ( N 0 3 ) 2 e x h i b i t s an endothermic event at 24 119°C wi th a shoulder at 1 3 0 ° C . The weight loss of 38% observed on heating the sample to 149°C compares favourably wi th the c a l c u l a t e d weight loss of 37% f o r the loss of two pyrazine m o i e t i e s . Exothermic decomposition does not beg-i n u n t i l about 2 9 0 ° C . These r e s u l t s suggest that C u ( p y z ) ( N 0 3 ) 2 can be obtained by thermolysis of the t r i s ( p y r a z i n e ) complex. In f a c t , the mono-(pyrazine) complex was obtained by simply leaving C u ( p y z ) 3 ( N 0 3 ) 2 i n a d e s s i c a t o r , over D r i e r i t e , f o r severa l days ( sec t ion 3 .2 .8 ) . A l l the mono(pyrazine)- and mono(2-methylpyrazine)copper(II) complexes s tudied here decompose without f i r s t l o s i n g the n e u t r a l l i g a n d . The temperatures which mark the onset of decomposition of these complexes are given i n Table 3 .1 . The thermal events of these complexes are complex at these temperatures, e x h i b i t i n g both exothermic and endothermic events . Consequently, enthalpy changes assoc ia ted with the decompositions were not determined. A representa t ive thermogram for t h i s group of complexes, that of Cu(2-mepyz) (N0 3 ) 2 , i s shown i n Figure 3 .1b. 3.3.2 Inf rared Spectroscopy Infrared s p e c t r a l r e s u l t s f o r copper(II) complexes are presented i n t h i s s e c t i o n . The assignments were made on the b a s i s that the absorption bands o r i g i n a t e from two const i tuent p a r t s , namely the n e u t r a l l i g a n d and the a n i o n . A l l these complexes e x h i b i t complex s p e c t r a , e s p e c i a l l y i n the 1000-1500 cm" 1 region and i t i s therefore d i f f i c u l t to c o n c l u s i v e l y i d e n t i f y a l l the bands. In p a r t i c u l a r , complexes containing t r i f l u o r o m e t h y l groups are 31a expected to e x h i b i t C-F s t r e t c h i n g v i b r a t i o n s i n the same region as the intense S-0 s t r e t c h i n g v i b r a t i o n s and i t was not p o s s i b l e to p o s i t i v e l y 26 i d e n t i f y the former i n the present work. However, the f i n e s t ruc ture observed i n bands assigned to S0 3 antisymmetric s t r e t c h i n g mode may be a t t r i b u t e d to C-F s t r e t c h i n g v i b r a t i o n s . The bands at about 580 c m - 1 i n the spectra of these complexes may be assigned to C-F deformation modes f o l l o w i n g the work of 3 l a Burger et a l on A g C F 3 S 0 3 . Comparison of the spectra of a l l the complexes i n v e s t i g a t e d here wi th those of s i m i l a r complexes, but conta ining h a l i d e 3 5 anions , ' helped i n i d e n t i f y i n g the n e u t r a l l i g a n d bands s ince m e t a l - h a l i d e v i b r a t i o n s g e n e r a l l y occur below 400 cm" 1 (see, f o r example, references 32 and 33) . A l l the n e u t r a l l igands (except p y r i d i n e ) and anions employed i n t h i s study can coordinate to the metal i o n i n more than one way. A general d i s c u s s i o n of these a l t e r n a t i v e modes of c o o r d i n a t i o n and the concomitant changes expected i n the i n f r a r e d absorptions assoc ia ted wi th these species i s presented before the i n f r a r e d s p e c t r a l r e s u l t s are d i s c u s s e d . 3.3.2.1 Theory of V i b r a t i o n a l Spectra and Bonding E l e c t r o n d i f f r a c t i o n i n v e s t i g a t i o n s of pyrazine have shown that i t 34 has a planar symmetrical s t r u c t u r e and i t s i n f r a r e d and Raman data have been 35 4 5 i n t e r p r e t e d i n terms of D^^ symmetry . G o l d s t e i n et a l . ' have demonstrated how the mode of pyrazine c o o r d i n a t i o n may be unambiguously assigned by using a combination of i n f r a r e d and Raman spectroscopy. When pyrazine coordinates i n a bidentate fashion i t r e t a i n s symmetry and a mutual e x c l u s i o n of i n f r a r e d and Raman bands occurs . However, i f i t coordinates i n a monodentate mode, the symmetry i s reduced to C£y and some p r e v i o u s l y forbidden v i b r a t i o n a l bands become a c t i v e i n the i n f r a r e d spectrum of the complex. 2-Methylpyrazine a lso has the p o t e n t i a l to coordinate i n a mono- or 27 bidentate mode. However, u n l i k e p y r a z i n e , i t lacks a centre of symmetry and the mutual e x c l u s i o n p r i n c i p l e does not a p p l y . A c r i t e r i o n f o r d i s t i n g u i s h i n g between mono- and bidentate 2-methylpyrazine has, however, been proposed i n the present study (sec t ion 3 . 3 . 2 . 3 ) . The l o c a l symmetry around the s u l f u r atom i n a f ree uncoordinated sulfonate anion , R S 0 3 " , i s C 3 y . S ix normal modes of v i b r a t i o n (3E and 3AX) are p r e d i c t e d by group theory. A l l s i x v i b r a t i o n s are i n f r a r e d a c t i v e . The sulfonate anion can u t i l i z e some or a l l of i t s oxygen atoms for c o o r d i n a t i o n . The mode of coordinat ion determines the symmetry of the anion and hence the number of i n f r a r e d a c t i v e fundamentals. The lowering of symmetry of the anion below C^y through mono- or bidentate c o o r d i n a t i o n i s expected to r e s u l t i n a s p l i t t i n g of the doubly degenerate E modes, r e s u l t i n g i n a t o t a l of nine i n f r a r e d a c t i v e bands. It i s not p o s s i b l e to d i s t i n g u i s h between these two modes of coordinat ion on the b a s i s of the number and p o s i t i o n s of the i n f r a r e d bands a lone . However, the degree of s p l i t t i n g of the asymmetric S0 3 s t r e t c h i n g mode, has been used to d i s t i n g u i s h between the two c o o r d i n a t i o n 27 modes. For ins tance , i n C u ( p y ) 4 ( C F 3 S 0 3 ) 2 , which has been shown by X - r a y c r y s t a l l o g r a p h y to contain monodentate sulfonate groups, i t was noted that the s p l i t t i n g of the \)A band i s s i g n i f i c a n t l y smaller than i n the r e l a t e d complex, C u ( p y z ) ( C F 3 S 0 3 ) 2 , where a bidentate sul fonate br idge has been proposed. I f , 31 36 on the other hand, the anion adopts 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 , then i t r e t a i n s C^^ symmetry and i s expected to show no s p l i t t i n g of the E modes, l i k e the free i o n . The free uncoordinated n i t r a t e i o n belongs to p o i n t group and group theory p r e d i c t s four normal modes of v i b r a t i o n [ A ' 1 ( \ ) 1 ) ; A " 2 ( \ ) 2 ) ; E ' ( v 3 ) ; E ' ( \ J a ) ] . The M 1 mode i s i n f r a r e d i n a c t i v e and only three bands are expected. 28 However, Mizushima and Quagliano observed that t h i s forbidden frequency appears i n the i n f r a r e d spectrum of compounds when the n i t r a t e i o n i s outside the c o o r d i n a t i o n sphere. They a t t r i b u t e d t h i s to the deformation of ions i n the molecular f i e l d of the c r y s t a l s . In 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 , symmetry i s r e t a i n e d and the anion i s expected, l i k e the f ree i o n , to show no s p l i t t i n g of the E modes. When the n i t r a t e group coordinates through one or two oxygen atoms, the symmetry i s lowered to C^v' a 1 1 ^ands become a c t i v e , s h i f t s i n band p o s i t i o n s occur and the degeneracy of the \)3 and vk bands i s 38 l i f t e d . C u r t i s and C u r t i s pointed out that the changes assoc ia ted wi th the lowering of symmetry from D^^ to due to mono- or bidentate modes of c o o r d i n a t i o n are more pronounced for the l a t t e r mode than f o r the former and that t h i s could be used to d i s t i n g u i s h between the two modes of n i t r a t o group c o o r d i n a t i o n , provided that the same c a t i o n was i n v o l v e d . Exceptions to t h i s 39 38 40 c r i t e r i o n have been observed. C u r t i s and C u r t i s and Lever et a l . have a lso c o r r e l a t e d the number and r e l a t i v e energies of n i t r a t e combination frequencies with the var ious c o o r d i n a t i o n modes of the n i t r a t e group. T h i s c r i t e r i o n , however, could not be used i n the present study because combination bands were not observed i n a l l the n i t r a t o complexes i n v e s t i g a t e d . 3 .3 .2 .2 Infrared S p e c t r a l Resul ts f o r Copper(II) Complexes Containing Sulfonate Anions The v i b r a t i o n a l assignments due to the var ious groups i n copper(II) sulfonate complexes are given i n appendices as f o l l o w s . The v i b r a t i o n s due to pyrazine and 2-methylpyrazine are i n Appendices II and III r e s p e c t i v e l y , whereas those due to the methanesulfonate, t r i f l a t e and p - t o s y l a t e anions are i n Appendix IV, par ts A, B and C r e s p e c t i v e l y . The s p l i t t i n g of \)h i n the 29 spectra of these complexes i n d i c a t e s a lowering of symmetry of the sul fonate group below C^y, as i s expected, on c o o r d i n a t i o n . The band i s s p l i t by 67 cm" 1 i n C u ( p y z ) A ( C F 3 S 0 3 ) 2 and 69 c m - 1 i n Cu(2-mepyz) A (CF 3 SO 3 ) 2 . In C u ( 2 - m e p y z ) ( C F 3 S 0 3 ) 2 , on the other hand, i t i s s p l i t by 101 c m " 1 . The i n f r a -red spectra of C u ( 2 - m e p y z ) 4 ( C F 3 S 0 3 ) 2 and Cu(2-mepyz) (CF 3 S0 3 ) 2 are i l l u s t r a t e d i n Figure 3.2. The r e l a t i v e l y l a r g e r s p l i t t i n g of \ J a i n the spectrum of the l a t t e r complex suggests that whereas the t e t r a k i s (neutral l igand) compounds contain monodentate anions , the mono(2-methylpyrazine) complex contains bidentate t r i f l a t e groups. Support f o r t h i s conclus ion comes from e a r l i e r 27 work on C u ( p y ) 4 ( C F 3 S 0 3 ) 2 and C u ( p y z ) ( C F 3 S 0 3 ) 2 . vu i s s p l i t by A3 cm" 1 i n the former compound and 101 cm" 1 i n the l a t t e r one. The s t ruc ture of C u ( p y ) A ( C F 3 S 0 3 ) 2 , as determined by X - r a y c r y s t a l l o g r a p h y , c o n s i s t s of t r a n s - a x i a l l y coordinated anions and e q u a t o r i a l l y bound p y r i d i n e l igands (s t ructure 1, F i g . 1 .3) . On the bas is of i n f r a r e d data , a s i m i l a r s t r u c t u r e i s proposed for C u ( p y z ) 4 ( C F 3 S 0 3 ) 2 and C u ( 2 - m e p y z ) 4 ( C F 3 S 0 3 ) 2 with both pyrazine and 2-methylpyrazine coordinat ing through one n i t r o g e n atom o n l y . For C u ( 2 - m e p y z ) ( C F 3 S 0 3 ) 2 , a sheet s t ruc ture (s t ructure 7, F i g . 1 .6) , i n which chains of copper atoms, doubly br idged by bidentate sulfonate groups, are c r o s s - l i n k e d by bidentate b r i d g i n g 2-methylpyrazine l i g a n d s , i s proposed. The symmetry of the anion i n Cu(pyz) ( p - C H 3 C 6 H l i S 0 3 ) 2 i s a l s o lowered below C^y upon c o o r d i n a t i o n , as i n d i c a t e d by the s p l i t t i n g of M U . The magnitude of t h i s s p l i t t i n g (111 cm" 1) compares w e l l w i t h that observed i n other compounds where bidentate p - t o s y l a t e coordinat ion has been proposed. In 20 Fe(pyz) ( p - C H 3 C 6 H < ( S 0 3 ) 2 \)k i s s p l i t by 116 cm" 1 whi le i n Ni(pyz) (p-CH 3 C 6 H i l i S0 3 ) 2 ( sec t ion A.3 .2 .1 ) i t i s s p l i t by 112 c m " 1 . G e n e r a l l y , 30 Fi g . 3.2 Infrared Spectra of Cu ( 2-mepyz ) 4 (CF3SC>3 ) 2 and Cu(2-mepyz)(CF 3S0 3) 2 a) Cu(2-mepyz) 4(CF 3S0 3) 2  1 1 1 1 1 1 i > r- ' i « r i J 1 — 1400 1000 WAVENUMBER / cm 600 -1 i 1 1 « - * • 200 31 there i s a c lose correspondence of most band assignments i n the spectra of these three complexes, which suggests that they have s i m i l a r s t r u c t u r e s . 8 X- ray s tudies have shown that C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 contains two types of pyrazine b r i d g e s . The presence of two s t r u c t u r a l l y d i s t i n c t b r i d g i n g pyrazine l igands i s r e f l e c t e d i n the doubling of some fundamentals, a t t r i b u t e d to p y r a z i n e , i n the i n f r a r e d spectrum of the complex. In c o n t r a s t , the i n f r a r e d spectrum of C u ( p y z ) ( C H 3 S 0 3 ) 2 shows e s s e n t i a l l y s i n g l e strong bands at 497 and 830 c m " 1 , which i s consis tent wi th the presence of only one type of pyrazine l i g a n d . Although conclusive evidence for the manner of bonding of the pyrazine l i g a n d i s l a c k i n g , comparison with the spectrum of C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 suggests a bidentate b r i d g i n g mode. The s p l i t t i n g of the doubly degenerate ( in C ^ v symmetry) S0 3 asymmetric s t r e t c h i n g and deformation modes, \ J a and \ J S , i n d i c a t e that there i s a lowering of anion symmetry below C ^ v upon c o o r d i n a -t i o n . Since i t has been proposed that pyrazine i s b r i d g i n g i n t h i s complex, the sulfonate anions must be bidentate i n order f o r the copper atoms to be s i x - c o o r d i n a t e . The \)A band i s s p l i t to e s s e n t i a l l y the same extent i n g C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 [95 cm" 1] and C u ( p y z ) ( C H 3 S 0 3 ) 2 [100 c m " 1 ] . The unexpected large s p l i t t i n g of v 4 ( r e l a t i v e to C u ( p y ) A ( C H 3 S 0 3 ) 2 ) i n C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 was a t t r i b u t e d to the f a c t that the sulfonate anion i s s t r o n g l y coordinated i n an e q u a t o r i a l p o s i t i o n . Nonetheless , the comparison with C u ( p y z ) ( C H 3 S 0 3 ) 2 s t i l l demonstrates that the use of the magnitude of t h i s s p l i t t i n g as a c r i t e r i o n for d i s t i n g u i s h i n g between mono- and bidentate sulfonate anions should be approached with c a u t i o n . The apparent s p l i t t i n g of the non-degenerate anion bands, \>1 and \ J 2 , i n the spectrum of Cu(pyz) (CH 3 S0 3 ) 2 may be a t t r i b u t e d to the presence of non-equivalent methanesulfonate s i t e s . Small s p l i t t i n g s r e s u l t i n g 32 from non-equivalence of anion s i t e s have been observed i n some metal f l u o r o -s u l f o n a t e s . ^ In summary, C u ( p y z ) 4 ( C F 3 S 0 3 ) 2 and C u ( 2 - m e p y z ) 4 ( C F 3 S 0 3 ) 2 are both concluded to have s i x - c o o r d i n a t e s t ruc tures of types 1 or 2 ( F i g . 1 .3) . The A l tendency f o r copper(II) to adopt t e t r a g o n a l l y d i s t o r t e d s t ruc tures favours 1 for these complexes. The mono(pyrazine) and mono(2-methylpyrazine)-copper(II) sulfonate complexes are a l l concluded to have s t ruc ture 7 ( F i g . 1.6) with bidentate b r i d g i n g n e u t r a l l igands (L 1 ) and sulfonate anions ( X 1 ) . A s t ruc ture s i m i l a r to the C u ( p y z ) ( N 0 3 ) 2 s t r u c t u r e , 2, i s a l s o p o s s i b l e , but less l i k e l y , given the s t r a i n i n four-membered chelate r i n g s g e n e r a l l y and the l o w - n u c l e o p h i l i c i t y of the sulfonate anions . Support f o r t h i s conclus ion comes from the f a c t that s i n g l e - c r y s t a l X - r a y s tudies have revealed the presence of b r i d g i n g , but not c h e l a t i n g , X r i f l a t e groups i n a number of A2 complexes. It i s noteworthy that i n the case of C u ( p y z ) ( N 0 3 ) 2 , where the n i t r a t e groups chela te , Cu-0 bonds are h i g h l y d i s t o r t e d , presumably to reduce the s t r a i n i n the four-membered" chelate r i n g s . 3 .3 .2 .3 Infrared Spect ra l Results f o r Copper(II) Complexes Containing N i t r a t e Anions A 35 Free pyrazine ' has s i n g l e i n f r a r e d absorptions at 80A and A17 c m - 1 and upon c o o r d i n a t i o n minor s h i f t s , which are sometimes accompanied by small s p l i t t i n g s of l e s s than 10 c m - 1 , are expected. The spectrum of C u ( p y z ) 3 ( N 0 3 ) 2 e x h i b i t s two pyrazine absorptions at 822 and 828 cm" 1 and two more at A66 and A98 c m - 1 (Appendix I I ) . The d i f f e r e n c e between the l a s t p a i r of bands i s 32 33 c m " 1 ; t h i s appears too large to be a t t r i b u t e d to i n t e r a c t i o n s between adjacent p y r a z i n e r i n g s and suggests that there are two d i s t i n c t pyrazine groups i n C u ( p y z ) 3 ( N 0 3 ) a . Support f o r t h i s conclus ion comes from the i n f r a r e d spectrum of C u ( p y z ) ( N O , ) 2 , i n which s i n g l e pyrazine absorptions are observed (Appendix I I ) , even i n cases where the corresponding bands i n the spectrum of C u ( p y z ) 3 ( N 0 3 ) 2 e x h i b i t some s p l i t t i n g . The proposed s t r u c t u r e f o r C u ( p y z ) 3 ( N 0 3 ) 2 ( s t ructure 3, F i g . 1.4) consis ts of l i n e a r chains of copper i o n s , M, br idged by bidentate pyrazine groups, L ' , wi th terminal monodentate p y r a z i n e , L , and n i t r a t e , X, groups completing the CuN A 0 2 chromophore. A s i m i l a r s t ruc ture has been proposed for N i ( p y z ) , ( C H , S O , ) 2 » C H , O H (sec t ion 4 . 3 . 2 . 1 ) . That i t i s p o s s i b l e to have both b r i d g i n g and terminal pyrazine groups i n the same compound has been confirmed by X - r a y s t r u c t u r a l determination of bis (pyrazine)copper ( I ) t r i f luoromethanesulfonate (see Chapter 5) . Absorptions a r i s i n g from the n i t r a t e anion are given i n Appendix V . The s p l i t t i n g of the \ J , band i n the spectra of Cu (2-mepyz) A (NO,) 2 [109 c m " 1 ] , C u ( p y z ) 3 ( N 0 3 ) 2 [104 c m " 1 ] , Cu(2-mepyz)(NO,) 2 [215 cm" 1] and Cu(pyz) (NO,) 2 [213 c m " 1 ] , i n d i c a t e s a reduct ion i n the N O , " symmetry to below D ^ ^ . The r e l a t i v e l y l a r g e r s p l i t t i n g of \), i n the spectra of the l a s t two complexes suggests that whereas the te t rakis (2 -methylpyrazine) and the t r i s ( p y r a z i n e ) compounds contain monodentate anions , t h e i r mono(ligand) analogues contain bidentate n i t r a t e anions . This conclus ion i s consis tent wi th the known s t r u c t u r e of C u ( p y z ) ( N 0 3 ) 2 . 1 0 The spectra of Cu(pyz) (NO,) 2 and Cu(2-mepyz)(N0 3 ) 2 a l so show a strong absorpt ion at about 345 cm" 1 which i s assigned to Cu-0 s t r e t c h i n g v i b r a t i o n of the coordinated n i t r a t e group. The presence of t h i s a b s o r p t i o n , which i s not observed i n the spectra of complexes 34 having a CuN^Oj chromophore, i n d i c a t e s the presence of strong Cu-0 bonding i n v o l v i n g the n i t r a t e group i n these mono(ligand) complexes. V i b r a t i o n s assigned to 2-methylpyrazine are tabulated i n Appendix I I I . The bands e x h i b i t e d by free 2-methylpyrazine at 410, 472 and 1021 cm" 1 seem to be more c o o r d i n a t i o n s e n s i t i v e than the r e s t , e x h i b i t i n g s h i f t s of vary ing magnitudes to higher f requencies . It i s proposed here that the degree of s h i f t s i n these frequencies can be used to d i s t i n g u i s h between 2-methyl-pyrazine bound through only one n i t r o g e n atom and that bound through both n i t r o g e n atoms, greater s h i f t s i n d i c a t i n g bidentate c o o r d i n a t i o n . However, s ince only a l i m i t e d number of compounds were i n v e s t i g a t e d , more data are necessary before t h i s c o r r e l a t i o n can be accepted as g e n e r a l . Inf rared 3 s p e c t r a l data on 2-methylpyrazine a v a i l a b l e i n the l i t e r a t u r e were recorded only above 650 c m " 1 . Table 3.2 shows the degree of s h i f t s of some 2-methyl-pyrazine bands upon c o o r d i n a t i o n . From these r e s u l t s i t i s concluded that the te t rakis (2 -methylpyrazine) complexes, as expected, contain unidentate l igands while the mono(2-methylpyrazine) ones have bidentate n e u t r a l l i g a n d s . 35 Table 3.2 S h i f t s of the A10, A72 and 1021 cm" 1 Bands of 2-Methylpyrazine upon Coordinat ion 2-methylpyrazine A10 A72 1021 Compound S h i f t i n band p o s i t i o n (cm - 1 ) Cu(2-mepyz) I i(N0 3) 2 16 36 20 N i ( 2 - m e p y z ) 4 ( N 0 3 ) a « H a 0 22 30 25 C u ( 2 - m e p y z ) A ( C F 3 S 0 3 ) a 21 33 a Cu(2-mepyz)(N0 3 ) 2 3A 58 A3 Ni(2 -mepyz) (N0 3 ) a 3A 52 37 Cu(2-mepyz) (CF 3 S0 3 ) a 56 a a a) obscured by anion absorpt ion It i s u s e f u l to summarize conclusions from the i n f r a r e d s p e c t r a l r e s u l t s of copper(II) complexes containing the n i t r a t e anion . As for C u L A ( C F 3 S 0 3 ) 2 [L = pyz , 2-mepyz] complexes, i t i s concluded that Cu(2-mepyz) u (N0 3 ) 2 has s t r u c t u r e 1 ( F i g . 1 .3) . The i n f r a r e d data for C u ( p y z ) 3 ( N 0 3 ) 2 support s t r u c t u r e type 3 ( F i g . l . A ) . Structure A i s a lso p o s s i b l e but s t e r i c fac to rs and the f a c t that the complex i s t e t r a g o n a l l y d i s t o r t e d ( sec t ion 3.3.3.2) renders t h i s u n l i k e l y . Cu(2-mepyz)(N0 3 ) 2 i s assigned the C u ( p y z ) ( N 0 3 ) 2 s t r u c t u r e , 9. 36 3.3.3 E l e c t r o n i c Spectroscopy 3 .3 .3 .1 Theory of Copper(II) Spectra A 2 D f r e e - i o n ground term r e s u l t s from the d 9 e l e c t r o n c o n f i g u r a t i o n of copper(II) i o n . In the presence of a regular cubic l i g a n d f i e l d the ground term i s s p l i t i n t o 2 T ~ and 2 E s t a t e s . The J a h n - T e l l e r theorem states that 2g g any n o n - l i n e a r i o n or molecule which i s i n an o r b i t a l l y degenerate s ta te w i l l d i s t o r t to r e l i e v e t h i s degeneracy. Copper(II) i o n has a " h o l e " i n the e o r b i t a l set which can be i n e i t h e r d , , or d , o r b i t a l s and i s therefore i n x 2 - y 2 z 2 an o r b i t a l l y degenerate s t a t e . I t i s t h e r e f o r e , e n e r g e t i c a l l y favourable f o r copper(II) to undergo a d i s t o r t i o n to l i f t t h i s degeneracy. Consequently most octahedral copper(II) complexes are t e t r a g o n a l l y d i s t o r t e d with four short i n - p l a n e bond lengths and two longer a x i a l bond lengths . From p o l a r i s e d s i n g l e - c r y s t a l e l e c t r o n i c s p e c t r a l s tudies the order of d o r b i t a l energies i n a x i a l y elongat d octahedral geometry has been 43 e s t a b l i s h e d a s d , , > d , > (d ) > d , d , wi th the p o s i t i o n of the d x 2 - y 2 z 2 xy xz yz r xy o r b i t a l l e s s c e r t a i n . These o r b i t a l orderings correspond to the energy l e v e l orderings 2 B 1 < 2 A . < 2 B _ < 2 E . By the hole formalism 2 B . i s the ground 6 l g l g 2g g J . l g 6 s t a t e . The energy l e v e l diagram f o r a copper(II) i o n i n c r y s t a l f i e l d s of 0^ and symmetry i s shown i n F i g . 3 .3 . Although three absorptions are expected i n the symmetry only one broad asymmetric band i s u s u a l l y observed i n the v i s i b l e region 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 copper(II) compounds. From s tudies of p o l a r i s e d s i n g l e - c r y s t a l e l e c t r o n i c spectra of tetraammine- and bis(ethylenediamine)copper(II ) complexes, Hathaway 43 44 and coworkers ' have found that the v i s i b l e band i n these complexes i s 37 indeed of a composite nature . From s tudies of a large number of b i s ( e t h y l e n e -45 diamine) complexes of copper ( I I ) , Lever and Mantovani showed that the p o s i t i o n of the band s h i f t s to higher energies as the te t ragonal d i s t o r t i o n i n c r e a s e s . 28 Thompson and A l l e y n e have demonstrated that the energy of the v i s i b l e band maximum provides a measure of the degree of te t ragonal d i s t o r t i o n i n 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 too . They a lso determined the r e l a t i v e coordinat ing strengths of var ious weakly b a s i c ions by assuming that as ^ m a x of the v i s i b l e band increases the coordinat ing a b i l i t y of the a n i o n i c species decreases. The f o l l o w i n g i s the s c a l e , based on the mull 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 for 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 (Appendix V I , Part B ) , of the coordinat ing a b i l i t y of some u n i v a l e n t anions . C F 3 C 0 2 - 2 8 > C H 3 S O 3 - 8 > p - C H 3 C 6 H A S 0 3 - 2 8 > F S 0 3 " 2 8 > C F 3 S 0 3 - 2 7 > C I O , , - 2 8 > N 0 3 - 2 8 > P F 6 - 4 6 38 F i g . 3.3 E l e c t r o n i c Energy Levels f o r Copper(II) 2 2 T 2 D / \ E (d , d ) g xz yz 2 B (d ) g xy 2 A _ (d ,) \ 2 E g X 2 B (d , .) ^ - • g x 2 - y 2 ' 0^ corresponding o r b i t a l s (hole formalism) 3.3.3.2 E l e c t r o n i c Spec t ra l Results f o r Copper(II) Complexes E l e c t r o n i c s p e c t r a l parameters f o r the copper(II) compounds obtained i n t h i s study are tabulated i n Appendix V I , Part A . For comparison, r e s u l t s from previous s tudies on a number of compounds re levant to the present study are presented i n Appendix V I , Part B. Each of the new complexes e x h i b i t s a s i n g l e broad asymmetric band i n the v i s i b l e or n e a r - i n f r a r e d r e g i o n s . The absorpt ion maxima for C u ( p y z ) 4 ( C F 3 S 0 3 ) 2 , C u ( 2 - m e p y z ) 4 ( C F 3 S 0 3 ) 2 and Cu(2-mepyz) 4 (N0 3 ) 2 are at 16 400, 16 500 and 17 400 cm" 1 r e s p e c t i v e l y . These values are lower than those of analogous p y r i d i n e complexes (Appendix V I , Part B) and consis tent with a l e s s e r degree of t e t r a g o n a l i t y , as expected, cons ider ing the r e l a t i v e base strengths of p y r i d i n e , 2-methylpyrazine and p y r a z i n e . The band maximum e x h i b i t e d by C u ( p y z ) 4 ( C F 3 S 0 3 ) 2 i s , w i t h i n 39 experimental e r r o r , i n good agreement with that shown by i t s monohydrate, 27 C u ( p y z ) k ( C F 3 S 0 3 ) 2 » H 2 0 . Cu(2-mepyz) h (N0 3 ) 2 absorbs at a higher frequency than i t s t r i f l a t e analogue. This i s consis tent wi th the c o n c l u s i o n that the t r i f l a t e anion i s more s t r o n g l y coordinated (though s t i l l weakly) than the n i t r a t e anion . C u ( p y z ) ( C H 3 S 0 3 ) 3 , C u ( p y z ) ( p - C H 3 C 6 H 4 S 0 3 ) 2 and Cu(2-mepyz) (CF 3 S0 3 ) 3 absorb i n the same region (13 000 to 14 000 c m - 1 ) which suggest that they contain the same chromophore. These complexes e x h i b i t absorpt ion maxima at considerably lower frequencies than do the corresponding 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 and Cu(2-mepyz) M (CF 3 S0 3 ) 2 and C u ( p y z ) k ( C F 3 S 0 3 ) 2 . This batho-chromic s h i f t i s consis tent wi th a change from a CuN 4 0 2 to a CuNjO^ chromo-phore, and the concomitant reduct ion i n the l i g a n d f i e l d , s ince the sulfonate anions are lower i n the spectrochemical s e r i e s than p y r i d i n e , 2-methylpyrazine and pyrazine l i g a n d s . The r e s u l t s are a lso consis tent with reduced te t rago-n a l i t y s ince the l e s s b a s i c sulfonate anions must now occupy at l e a s t two of the e q u a t o r i a l p o s i t i o n s . The r e l a t i v e i n f l u e n c e of these two fac tors on the s h i f t i n the band maxima i s d i f f i c u l t to t e l l . E l e c t r o n i c s p e c t r a l parameters for C u ( p y z ) ( N 0 3 ) 2 and Cu(2-mepyz)(N0 3 ) 2 have been reported before.*"* Values f o r absorpt ion maxima obtained i n the present study are somewhat lower than those reported p r e v i o u s l y . The reason f o r t h i s discrepancy i s u n c l e a r , but may be a r e s u l t of c o r r e c t i o n s to l i g h t s c a t t e r i n g being made to d i f f e r e n t extents . The absorpt ion maxima values of 17 400 and 17 100 cm" 1 f o r the mono(pyrazine)- and mono(2-raethylpyrazine)-copper(II) n i t r a t e complexes, r e s p e c t i v e l y , are s i g n i f i c a n t l y higher than those shown by t h e i r sulfonate analogues but comparable to those e x h i b i t e d by 40 Cu(pyz) 3 (N03) 2 and Cu(2-mepyz) 4 (N0 3) a . The change from a CuN 4 0 2 to a CuN 2 0 4 chromophore i s expected to lead to a s i g n i f i c a n t s h i f t , to lower wavenumbers, i n the p o s i t i o n of the band maximum since both pyrazine and 2-methylpyrazine are higher i n the spectrochemical s e r i e s than the n i t r a t e i o n . The occurrence of the absorpt ion maxima of C u ( p y z ) ( N 0 3 ) a and Cu(2-mepyz)(N0 3 ) 2 at higher frequencies than expected may be due to the very unsymmetrical manner i n which the n i t r a t e anion chelates i n the f o r m e r 1 0 (Structure 9, F i g . 1.6) and, as i s proposed, f o r the l a t t e r . This r e s u l t s i n two long and two short Cu-0 bonds, g i v i n g a h i g h l y d i s t o r t e d CuN 2 0 4 chromophore. In summary, e l e c t r o n i c s p e c t r a l data i n d i c a t e that the complexes contain pseudo-octahedral ly coordinated copper centres , r e s u l t i n g i n a CuN 4 0 2 chromophore for C u ( p y z ) 4 ( C F 3 S 0 3 ) 2 , Cu(2-mepyz) 4 ( C F 3 S O 3 ) 2 , Cu(2-mepyz) 4 (N0 3 ) a and C u ( p y z ) 3 ( N 0 3 ) 2 . A CuN 2 0 4 chromophore i s i n d i c a t e d f o r C u ( p y z ) ( C H 3 S 0 3 ) 2 , C u ( p y z ) ( p - C H 3 C 6 H 4 S 0 3 ) 2 and C u ( 2 - m e p y z ) ( C F 3 S 0 3 ) 2 . The r e s u l t s are consis tent with the known n i t r a t e c h e l a t i o n i n C u ( p y z ) ( N 0 3 ) 2 and proposed f o r Cu(2-mepyz) (N0 3 ) 2 . 3 .3.4 Magnetic Proper t ies The magnetic s u s c e p t i b i l i t y data f o r a l l the copper(II) complexes i n v e s t i g a t e d i n t h i s work are presented i n Appendix V I I . The magnetic moments of magnet ica l ly d i l u t e copper(II) complexes are g e n e r a l l y i n the range 1.75 -41 2.20 B .M. and are temperature-independent. The proposed s t ruc tures f o r C u ( p y z ) 4 ( C F 3 S 0 3 ) 2 , C u ( 2 - m e p y z ) 4 ( C F 3 S 0 3 ) 2 and Cu(2-mepyz) 4 (N0 3 ) 2 do not contain 41 any b r i d g i n g e n t i t i e s (Structure 1, F i g . 1 .3) . As a r e s u l t , these complexes are expected to be magnet i ca l ly d i l u t e . They a l l have magnetic moments i n the range 1.78 - 1.88 B .M. i n the 81 to 4.2K temperature range, which i s i n accord with t h e i r formulat ion as magnet ica l ly d i l u t e compounds. The magnitude and s l i g h t temperature dependence of the magnetic moment data of these complexes are s i m i l a r to those p r e v i o u s l y observed for some r e l a t e d compounds: C u t p y z ^ ^ S C ^ V H . O and Cu(py) „ (CF 3 S0 3 ) 2 , 2 7 Cu(py) k (CH 3 S0 3 ) 2 8 and Cu(py) ,X 2 28 (X = F S 0 3 " , C 1 0 A - , B F A - and p - C H j C g H ^ S O j - ) . For the C u ( p y ) 4 X 2 complexes, however, only high temperature (90 - 315K) magnetic moments were repor ted . C u ( p y z ) ( N 0 3 ) 2 , Cu(2-mepyz)(N0 3 ) 2 , C u ( p y z ) , ( N 0 3 ) 2 , Cu(2-mepyz) (CF 3 S0 3 ) 2 , C u ( p y z ) ( p - C H 3 C 6 H \ S 0 3 ) 2 and C u ( p y z ) ( C H 3 S 0 3 ) 2 a l l have very s i m i l a r magnetic behaviour . In contrast to complexes discussed i n the preceding paragraph, they a l l e x h i b i t strong temperature-dependent magnetic moments, with values decreasing from approximately 1.8 B .M. at 82K to about 0.7 B .M. at 2.4K, a behaviour c h a r a c t e r i s t i c of a n t i f e r r o m a g n e t i c a l l y coupled copper(II) systems. The temperature dependence of the moment of a representat ive member of the group, that of C u ( 2 - m e p y z ) ( C F 3 S 0 3 ) 2 , i s depic ted i n Figure 3.4, along with the corresponding data for the magnet ica l ly d i l u t e complex, C u ( 2 - m e p y z ) 4 ( C F 3 S 0 3 ) 2 , f o r comparison. The e f f e c t of magnetic concentrat ion i n these complexes i s more c l e a r l y seen i n v a r i a t i o n s of t h e i r magnetic s u s c e p t i b i l i t i e s wi th temperature, each of which e x h i b i t s a maximum below 10K ( F i g s . 3.5 - 3 .9 ) . At temperatures below the temperature of maximum s u s c e p t i b i l i t y , T(x m a x ) , the s u s c e p t i b i l i t y of Cu(pyz) ( p - C H 3 C 6 H i i S 0 3 ) 2 decreases and then remains constant with decreasing temperature, whereas that of Cu(2-mepyz) (CF 3 S0 3 ) 2 decreases A2 and then begins to r i s e . This type of behaviour i s a t t r i b u t e d to the presence of small amounts of paramagnetic s t r u c t u r a l i m p u r i t i e s . The c r y s t a l s t ruc ture of C u ( p y z ) ( N 0 3 ) 2 1 0 c o n s i s t s of l i n e a r - C u - p y z - C u -chains with n i t r a t e anions bonded i n an unsymmetrical chelate fashion (Structure 9, F i g . 1 .6) . A s i m i l a r s t ruc ture has been proposed for C u ( 2 - m e p y z ) ( N 0 3 ) 2 . ^ Inf rared s p e c t r a l r e s u l t s presented i n t h i s study provide fur ther evidence that the two compounds are i s o s t r u c t u r a l . 1A Low-temperature magnetic s tudies have been made on powdered and 30 s i n g l e - c r y s t a l samples of C u ( p y z ) ( N 0 3 ) 2 by H a t f i e l d and coworkers. They showed that the magnetic behaviour of t h i s complex can be accounted for s a t i s f a c t o r i l y by the i s o t r o p i c Heisenberg model, but not by the a n i s o t r o p i c Is ing Model, for l i n e a r ant iferromagnetic i n t e r a c t i o n s i n chains . We synthesized both C u ( p y z ) ( N 0 3 ) 2 and i t s 2-methylpyrazine analogue by routes d i f f e r e n t from those i n the l i t e r a t u r e . The magnetic s u s c e p t i b i l i t y data obtained from samples of these compounds were analyzed according to an 4 7 i s o t r o p i c Heisenberg model for chains of i n t e r a c t i n g S = 1/2 s p i n s . H a l l A8 A9 and H a t f i e l d et a l . developed the model proposed by Bonner and F i s h e r . This r e s u l t e d i n the f o l l o w i n g polynomial expression f o r the molar s u s c e p t i b i -l i t y : r = N g 2 B 2 kT 0.250 + 0.1A995 x~ 1 + 0.3009A x~ 2 3.1 1 + 1.9862 x " 1 + 0.6885A x~ 2 + 6.0626 x " 3 where x = Ul A3 Good f i t s between experimental and c a l c u l a t e d s u s c e p t i b i l i t i e s were obtained f o r both C u ( p y z ) ( N 0 3 ) 3 and Cu(2-mepyz)(N0 3 ) , ( F i g . 3 .5 ) . The p a r a -meters which give the best f i t , together with T(y^ ) of these complexes, are l i s t e d i n Table 3 .3 . There i s good agreement between our r e s u l t s and those from e a r l i e r s t u d i e s . The best f i t was considered to be that set of f i t t i n g parameters which gave the minimum value of the f u n c t i o n F (Eqn. 3 .2 ) . 1 NT NT 1 i * c a l c d *obs obs -1 1/2 3.2 In equation 3.2 NT i s the number of data p o i n t s , and a n c * * c a l c d a r e observed and c a l c u l a t e d s u s c e p t i b i l i t i e s , r e s p e c t i v e l y . F i g . 3 . 4 M a g n e t i c Moments v s T e m p e r a t u r e f o r C u ( 2 - m e p y z ) 4 ( C F ^ S O ^ a n d C u ( 2 - m e p y z ) ( C F 3 S 0 3 ) 2 CQ o CM in E-i W s o 2 o ° M i H EH M W z u o • • • • o • e e • • • C u ( 2 - m e p y z ) 4 ( C F 3 S 0 3 ) 2 . C u ( 2 - m e p y z ) ( C F 3 S 0 3 ) 2 20 40 60 80 100 TEMPERATURE / K 44 F i g . 3.5 Magnetic S u s c e p t i b i l i t i e s vs Temperature f o r C u ( p y z ) ( N 0 3 ) 2 and Cu(2-mepyz)(N0 3) 2 a) L i n e a r c h a i n model, s o l i d l i n e generated from J = -3.7 cm g = 2.08 b) L i n e a r c h a i n model, s o l i d l i n e generated from J = -3.5 cm g=2.15 45 Table 3.3 Magnetic Parameters f o r Copper(II) Complexes obtained from the One-Dimensional Model (Eqn. 3. 1) Compound - J / cm" I g % mono F C u ( p y z ) ( N 0 3 ) 2 2 6.2 3.7 2.08 0.7 0.0088 ( 3 . 7 ± 0 . 1) (2.08+0. 01) (0) — C u ( 2 - m e p y z ) ( N 0 3 ) 2 2 5.5 3.5 2.15 2.0 0.0190 ( 3 . 1 ± 0 . 1) ( 2 . 0 6 ± 0 . 04) (0) — C u ( p y z ) 3 ( N 0 3 ) 2 8.1 4.8 2.13 0.6 0.0073 C u ( p y z ) ( C H 3 S 0 3 ) 2 5.5 3.2 2.18 a 0.0810 (b) 2.6 2.12 — 0.0120 C u ( p y z ( p - C H , C 6 H 4 S O , ) a 5.3 3.2 2.16 1.3 0.0245 Cu(2-mepyz) (CF 3 S0 3 ) 2 7.0 4.4 2.09 2.7 0.0097 C u ( p y z ) ( C F 3 S 0 3 ) 2 3 ~7 3.78 2.08 - 0.0097 C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 A 6.2 3.82 2.13 - 0.0118 1) Estimated er ror l i m i t s : J ± 1 0 % , g±2%. 2) Values i n brackets are from reference 15. 3) Data from reference 27. 4) Data from reference 8. a) Attempts to vary % monomer y i e l d e d negative v a l u e s , hence t h i s parameter was set at z e r o . b) Only data above T (Y ) used. 46 From spectroscopic data (sections 3.3.2 and 3.3.3) i t was proposed that C u ( p y z ) 3 ( N 0 3 ) 2 c o n s i s t s of l i n e a r chains of copper(II) ions br idged by bidentate pyrazine groups with terminal pyrazine and n i t r a t e groups completing the CuN A 0 2 chromophore. Consequently i t s magnetic data were a lso analyzed by the one-dimensional model as represented by equation 3 .1 . E x c e l l e n t agreement between experimental and c a l c u l a t e d s u s c e p t i b i l i t i e s was obtained ( F i g . 3 .6 ) . The best f i t parameters are given i n Table 3 .3 . V i b r a t i o n a l and 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 presented i n the preceding sec t ions suggest that C u ( p y z ) ( C H 3 S 0 3 ) 2 , C u ( p y z ) ( p - C H 3 C 6 H A S 0 3 ) 3 and Cu(2-mepyz) (CF 3 S0 3 ) 2 contain both bidentate n e u t r a l l igands and anions . The proposed s t ruc ture for these complexes i s shown i n Figure 1.6 (Structure 7) . It cons is t s of a square array of copper ions br idged i n one dimension by double sulfonate bridges and i n the other by p y r a z i n e . This s t ruc ture i s 27 s i m i l a r to that proposed for C u ( p y z ) ( C F 3 S 0 3 ) 2 and Fe(pyz)X 2 (X = C I " , 19 20 C F 3 S 0 3 ~ , p - C H 3 C 6 H I ( S 0 3 " ) ' complexes. From the proposed s t ruc ture two d i s t i n c t pathways are a v a i l a b l e f o r magnetic exchange. I t was therefore deemed necessary to use both a one-dimensional model and a two-dimensional model to analyze the s u s c e p t i b i l i t y data f o r these compounds. I t was conjectured that i n the event that one magnetic exchange pathway i s dominant, the former model would give the best f i t between experimental and c a l c u l a t e d s u s c e p t i b i l i t i e s , whereas i f magnetic exchange proceeds to an equal extent through both pathways, then the l a t t e r model would be more a p p r o p r i a t e . 47 L i n e s ' high-temperature s e r i e s expansion expression f o r a two-dimensional square planar antiferromagnet i n the Heisenberg l i m i t " * 0 has been 7 8 used to model s u s c e p t i b i l i t y data f o r C u ( p y z ) 2 ( C 1 0 4 ) 2 and C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 , s u c c e s s f u l l y . In general terms, the expression f o r the magnetic s u s c e p t i b i -l i t y i s : ^ = 39 + I 3.3 * J n - i e 1 1 " 1 where 8 = k T / J S ( S + l ) , g i s the Lande g f a c t o r , B the Bohr magneton, N the number of spins i n the l a t t i c e , and the c o e f f i c i e n t s , C ^ , have been determined for s p i n S = 1/2 for values of n up to 6. For S = 1/2 these c o e f f i c i e n t s a r e : 5 0 C , , 4; C , , 2.667; C 3 , 1.185; C 4 , 0.149; C g > -0 .191 ; C 6 , 0.001. Both the one- and two-dimensional models, as represented by equations 3.1 and 3.3 r e s p e c t i v e l y , were used to analyze the s u s c e p t i b i l i t y data f o r the mono(ligand)copper(II) sulfonate complexes. Results of these analyses are presented i n Table 3.3 for the one-dimensional model and Table 3.4 f o r the two-dimensional model. Unfor tunate ly , exact comparison between the two sets of data i s not p o s s i b l e because the one-dimensional model, as used here , inc ludes a c o r r e c t i o n f o r paramagnetic i m p u r i t i e s whereas the two-dimensional model does not . Never theless , the one-dimensional model descr ibes the magnetic behaviour of Cu(2-mepyz) (CF 3 S0 3 ) 2 and C u ( p y z ) ( p - C H 3 C 6 H A S 0 3 ) 2 f a i r l y w e l l ( F i g s . 3.7a and 3.8a r e s p e c t i v e l y ) , and i n both cases bet te r than the two-dimensional model, and i t i s therefore concluded that i n these two complexes, one of the two p o s s i b l e pathways f o r magnetic exchange dominates 48 over the other . Comparison of the magnetic p r o p e r t i e s of these compounds wi th those of C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 may give a c lue as to which of the two p o s s i b l e g routes i s more f a c i l e for s p i n i n t e r a c t i o n s . Haynes et a l . have reported that the l a t t e r compound contains two d i s t i n c t types of p y r a z i n e : s t r o n g l y bound e q u a t o r i a l pyrazine groups which are canted at an angle of about 2 9 ° to the CuN 2 0 2 (xy) plane and l e s s s t r o n g l y bound a x i a l pyrazine r i n g s which l i e i n the CuN 2 0 2 (xz) p lane . On the b a s i s of s t r u c t u r a l c o n s i d e r a t i o n s , they concluded that most of the magnetic exchange i n t e r a c t i o n s occurred through the more s t r o n g l y b r i d g i n g pyrazine groups. From Table 3.3 , i t can be seen that the magnetic p r o p e r t i e s of C u ( p y z ) ( p - C H 3 C 6 H \ S 0 3 ) 2 and Cu(2-mepyz) (CF 3 S0 3 ) 2 are s i m i l a r to those of C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 and C u ( p y z ) ( N 0 3 ) 2 . The feature common to the four compounds (proposed f o r the f i r s t two and known f o r the l a s t two) i s the presence of a s t r o n g l y bound b r i d g i n g n e u t r a l l i g a n d . I t i s thus concluded that the pyrazine and 2-methylpyrazine groups i n C u ( p y z ) ( p - C H 3 C 6 H 4 S 0 3 ) 2 and Cu(2-mepyz) (CF 3 S0 3 ) 2 r e s p e c t i v e l y are more e f f i c i e n t agents f o r the propagation of the magnetic exchange, than the sulfonate b r i d g e s , i n these compounds and dominate the exchange. 49 Table 3.4 Magnetic Parameters* f o r Copper(II) Complexes obtained from the Two-Dimensional Model (Eqn. 3.3) Compound - J / c n r 1 g F C u ( p y z ) ( C H 3 S 0 3 ) 2 2.1 2.21 0.0765 (-a) 1.6 2.14 0.0157 C u ( p y z ) ( p - C H 3 C 6 H , S 0 3 ) 2 2.0 2.17 0.0299 Cu(2-mepyz) (CF 3 S0 3 ) 2 2.4 2.07 0.0679 C u ( p y z ) ( C F 3 S 0 3 ) 2 2 2.43 2.10 0.0216 C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 3 2.48 2.15 0.0118 1) Estimated e r r o r l i m i t s : J ± 10%, g + 2%. 2) Data from reference 27. 3) Data from reference 8. a) Only data above T (Y ) used. J Amax Both the one- and two-dimensional models gave poor f i t s to the magnetic s u s c e p t i b i l i t y data f o r C u ( p y z ) ( C H 3 S 0 3 ) 2 as judged from the values of F (Tables 3.3 and 3.4) and a l s o v i s u a l l y . The best f i t to the one-dimensional model i s i l l u s t r a t e d i n Figure 3 .9a. However, both models y i e l d e d good f i t s when only data above T(x ) were used, wi th the one-dimensional model being 50 s l i g h t l y b e t t e r . The best f i t to t h i s model i s represented by the s o l i d l i n e i n Figure 3.9b. These r e s u l t s , together with the r a p i d drop i n the s u s c e p t i b i -l i t y below T ( x ) , suggest that the m a t e r i a l may be undergoing t h r e e -JTlclX dimensional long-range magnetic o r d e r i n g . I t i s a l so p o s s i b l e that i n C u ( p y z ) ( C H 3 S O 3 ) 2 both b r i d g i n g pyrazine and sulfonate groups contr ibute to some extent to the s p i n i n t e r a c t i o n s between copper centres . The two pathways, however, are u n l i k e l y to be e q u i v a l e n t . Under these c o n d i t i o n s , ne i ther a one- nor a two-dimensional model can exac t ly descr ibe the magnetic behaviour of the complex. In summary, the magnetic p r o p e r t i e s of C u ( p y z ) h ( C F 3 S 0 3 ) 2 , C u ( 2 - m e p y z ) 4 ( C F 3 S O 3 ) 2 and Cu(2-mepyz) u (N0 3 ) 2 are consis tent wi th t h e i r formulat ion as magnet ical ly d i l u t e compounds. C u ( p y z ) 3 ( N 0 3 ) 2 , C u ( p y z ) ( N 0 3 ) 2 and C u ( 2 - m e p y z ) ( N O 3 ) 2 a l l e x h i b i t ant iferromagnetic coupling and t h e i r s u s c e p t i b i l i t y data were s u c c e s s f u l l y analyzed according to an i s o t r o p i c Heisenberg model f o r chains of i n t e r a c t i n g S = 1/2 s p i n s . S t r u c t u r a l evidence from spectroscopic data i n d i c a t e s that C u ( p y z ) ( p - C H 3 C 6 H 4 S 0 3 ) 2 , Cu(2-mepyz) (CF 3 S0 3 ) 2 and C u ( p y z ) ( C H 3 S 0 3 ) 2 possess both b r i d g i n g n e u t r a l l igands and sulfonate anions . For the l a t t e r compound, good f i t s could not be obtained using e i t h e r a one- or two-dimensional model. This may be a t t r i b u t e d to e i t h e r long-range magnetic order ing e f f e c t s or to both pyrazine and sul fonate groups t r a n s m i t t i n g some magnetic exchange, but to d i f f e r e n t extents . The s u s c e p t i b i l i t y data f o r C u ( p y z ) ( p - C H 3 C 6 H 4 S 0 3 ) 2 and Cu(2-mepyz) (CF 3 S0 3 ) 2 were s u c c e s s f u l l y analyzed by a one-dimensional model. T h i s , together wi th the f a c t that the J values are s i m i l a r , allows one to conclude that the exchange v i a pyrazine bridge predominates i n these compounds, and a l s o that pyrazine and 2-methylpyrazine are equal i n t h e i r 51 a b i l i t i e s to f a c i l i t a t e exchange. The equivalence of these two l igands i s seen more c l e a r l y when one compares the J values for C u ( p y z ) ( N O , ) 2 and Cu(2-mepyz)(NO,) 2 or C u ( p y z ) ( C F , S O , ) , and C u ( 2 - m e p y z ) ( C F , S O , ) 2 . The observat ion that the v a r i a t i o n of the ant i ferromagnet ic coupl ing does not c o r r e l a t e wi th e i t h e r the o - b a s i c i t y of the l igands or with s t e r i c fac tors i s consis tent with the r e s u l t s of Richardson and H a t f i e l d . 1 5 F i g . 3.6 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 ) 3 ( N 0 3 ) 2 L i n e a r c h a i n model, s o l i d l i n e generated from J = -4.8 cm" 1, g = 2.13 i r H O e cn o 0 n 1 ' ' " 0.0 40.0 80.0 TEMPERATURE / K 52 F i g . 3 . 7 M a g n e t i c S u s c e p t i b i l i t y v s T e m p e r a t u r e f o r C u ( 2 - m e p y z ) ( C F 3 S C > 3 ) 2 a) L i n e a r c h a i n m o d e l , s o l i d l i n e g e n e r a t e d f r o m J = -4.4 c m " 1 , g = 2 . 0 9 b) T w o - d i m e n s i o n a l m o d e l , s o l i d l i n e g e n e r a t e d f r o m J = -2.4 cm 1 , g - 2 . 0 7 TEMPERATURE / K TEMPERATURE / K 53 F i g . 3.8 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 ) ( p - C H 3 C g H 4 S 0 3 ) 2 a) L i n e a r c h a i n model, s o l i d l i n e generated from J = -3.2 cm ^, g = 2.16 b) Two-dimensional model, s o l i d l i n e generated from J =-2.0 cm - 1, g = 2.17 54 F i g . 3.9 Magnetic S u s c e p t i b i l i t y vs Temperature for Cu(pyz)(CH 3S0 3) 2 a) Linear chain model, s o l i d l i n e generated from J = -3.2 cm - 1, g = 2.18 b) Linear chain model, data above T(x ) , s o l i d l i n e generated from J = -2.6 cm - 1, g = 2.12 55 CHAPTER 4  DIVALENT NICKEL COMPLEXES 4.1 INTRODUCTION Part of the aim of the present work was to extend the i n v e s t i g a t i o n of p y r a z i n e - b r i d g e d c o o r d i n a t i o n polymers ( p a r t i c u l a r l y of metal sulfonates) to inc lude n i c k e l ( I I ) complexes. The synthesis and c h a r a c t e r i z a t i o n of n i c k e l ( I I ) compounds i s o l a t e d are descr ibed i n t h i s chapter . As wi th copper (Chapter 3) , i t was necessary to synthesize monomeric species of the ML A X 2 type whose s p e c t r a l and magnetic p r o p e r t i e s could serve as a reference for the corresponding p r o p e r t i e s i n analogous polymeric compounds. 4.2 SYNTHETIC METHODS A general d i s c u s s i o n of the prepara t ive methods employed was presented i n Sect ion 2 .1 . The a c t u a l d e t a i l s f o r the syntheses of the n i c k e l ( I I ) complexes are given i n t h i s s e c t i o n . The n i c k e l ( I I ) methanesulfonate used i n t h i s study was prepared by the r e a c t i o n of aqueous s o l u t i o n s of s i l v e r ( I ) methanesulfonate and n i c k e l ( I I ) c h l o r i d e hexahydrate i n s t o i c h i o m e t r i c p r o p o r t i o n s . The p r e c i p i t a t e d s i l v e r ( I ) c h l o r i d e was removed by f i l t r a t i o n and the f i l t r a t e evaporated to dryness . Complete dehydration was not achieved even on heat ing the sample to 140°C or r e f l u x i n g wi th 2,2-dimethoxypropane. Attempts to f u l l y charac ter ize t h i s compound have been p r e v i o u s l y made, i n t h i s l a b o r a t o r y , without success .^* N i c k e l ( I I ) p - to luenesulfonate was s i m i l a r l y prepared us ing 56 s i l v e r ( I ) p - to luenesulfonate and n i c k e l ( I I ) c h l o r i d e hexahydrate. A g a i n , complete dehydration was not achieved. A.2 .1 T e t r a k i s ( p y r i d i n e ) n i c k e l ( I I ) methanesulfonate, N i ( p y ) 4 ( C H 3 S 0 3 ) 2 Hydrated n i c k e l ( I I ) methanesulfonate (0.639 g) was d i s s o l v e d i n 12 ml of methanol containing about 10% v / v 2,2-DMP. The n i c k e l ( I I ) s o l u t i o n was added to p y r i d i n e (4.0 m l , 50 mmol). The blue m i c r o c r y s t a l l i n e p r e c i p i t a t e which formed w i t h i n a few minutes was i s o l a t e d by f i l t r a t i o n , washed with small amounts of d i e t h y l ether and d r i e d under vacuum f o r 1 3/4 h . A n a l , c a l c d . for N i C 2 2 H 2 6 N 4 S 2 0 6 : C, 46.74; H, 4.64; N, 9 .91; found: C, 46.63; H, 4.77; N, 10.01. 4 .2 .2 T e t r a k i s ( p y r i d i n e ) n i c k e l ( I I ) p - t o l u e n e s u l f o n a t e , N i ( p y ) , ( p - C H 3 C 6 H , S 0 3 ) 2 Hydrated n i c k e l ( I I ) p - to luenesulfonate (0.868 g) was d i s s o l v e d i n 4 ml of methanol containing about 10% v / v 2,2-DMP. The n i c k e l ( I I ) s o l u t i o n was added to p y r i d i n e (10.0 m l , 124 mmol). The blue p r e c i p i t a t e which formed w i t h i n a few minutes was i s o l a t e d by f i l t r a t i o n , washed with small q u a n t i t i e s of the solvent and d i e t h y l ether and then d r i e d under vacuum f o r 3 1/2 h . A n a l , c a l c d . for N i C 3 4 H 3 „ N 4 S 2 0 6 : C , 56.92; H, 4.78; N , 7.81; found: C, 57.12; H, 4.94; N, 7.85. 4.2.3 T e t r a k i s ( 2 - m e t h y l p y r a z i n e ) n i c k e l ( I I ) n i t r a t e monohydrate, N i ( 2 - m e p y z ) 4 ( N 0 3 ) 2 « H 2 0 N i c k e l ( I I ) n i t r a t e hexahydrate (1.23 g , 4.22 mmol) was d i s s o l v e d i n 5 ml ethanol containing about 10% v / v 2,2-DMP. The n i c k e l ( I I ) s o l u t i o n was 57 added to 2-methylpyrazine (3.6 m l , 39 mmol). The r e s u l t i n g blue s o l u t i o n was allowed to s i t and a f t e r severa l days a blue m i c r o c r y s t a l l i n e s o l i d p r e c i p i t a t e d out . The supernatant l i q u i d was decanted o f f and the s o l i d washed with small amounts of the solvent then d r i e d by pumping under vacuum f o r 3 h . A n a l , c a l c d . for N i C 2 0 H 2 6 N 1 0 O 7 : C, 41.62; H, 4.54; N, 24.27; found: C, 41.75; H, 4.74; N, 24.14. 4 .2 .4 T r i s ( p y r a z i n e ) n i c k e l ( I I ) methanesulfonate methanol s o l v a t e , N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 « C H 3 O H Hydrated n i c k e l ( I I ) methanesulfonate (0.544 g) was d i s s o l v e d i n 10 ml of methanol containing about 10% v / v 2,2-DMP. The n i c k e l ( I I ) s o l u t i o n was added to pyrazine (1.87 g. 23.4 mmol) d i s s o l v e d i n 4 ml of the same s o l v e n t . A blue p r e c i p i t a t e formed a f t e r a few minutes and was i s o l a t e d by f i l t r a t i o n , washed with small amounts of the solvent containing some pyrazine and d r i e d under vacuum for 5 h . A n a l , c a l c d . f o r N i C 1 5 H 2 2 N 6 S 2 0 7 : C, 34.57; H, 4.25; N, 16.12; found: C, 34.50; H, 4.50; N, 15.88. 4.2.5 B i s ( p y r a z i n e ) n i c k e l ( I I ) n i t r a t e , N i ( p y z ) 2 ( N 0 3 ) 2 N i c k e l ( I I ) n i t r a t e hexahydrate (2.04 g , 7.05 mmol) was d i s s o l v e d i n 5 ml methanol conta ining about 10% v / v 2,2-DMP. The n i c k e l ( I I ) s o l u t i o n was then added to pyrazine (3.10 g , 38.6 mmol) d i s s o l v e d i n 5 ml of the same s o l v e n t . The blue p r e c i p i t a t e , which formed immediately, was i s o l a t e d by f i l t r a t i o n and d r i e d under vacuum f o r 6 h . A n a l , c a l c d . for N i C a H 8 N 6 0 6 : C, 28.02; H, 2.35; N, 24.51; found: C, 27.78; H, 2.57; N , 24.70. 58 A.2 .6 Mono(pyrazine)nickeKII ) p - t o l u e n e s u l f o n a t e , Ni(pyz) ( p - C H 3 C 6 H A S 0 3 ) 2 Hydrated n i c k e l ( I I ) p - to luenesulfonate (0.963 g) was d i s s o l v e d i n 4 ml of methanol containing about 10% v / v 2,2-DMP. The green n i c k e l ( I I ) s o l u t i o n was added to pyrazine (1.96 g , 24.5 mmol) d i s s o l v e d i n 3 ml of the same s o l v e n t . A blue p r e c i p i t a t e formed a f t e r a few minutes and was i s o l a t e d by f i l t r a t i o n and d r i e d under vacuum f o r 2 1/2 h . The pale green mono-pyrazine complex was obtained by heating the p r e c i p i t a t e , i n vacuo, at 85°C f o r 13 h . and then at 100°C for 6 h . A n a l , c a l c d . f o r N i C 1 8 H l a N 2 S 2 0 6 : C, 44.93; H, 3.77; N, 5.82; found C, 45.00; H, 3.75; N, 6.01. 4 .2 .7 Mono(2-methylpyrazine)nickel(II ) n i t r a t e , Ni (2 -mepyz) (N0 3 ) 2 When N i ( 2 - m e p y z ) k ( N 0 3 ) 2 • H 2 0 (Section 4.2.3) was heated at a temperature of 90°C for 13 h , i n vacuo, the l i g h t blue mono(2-methylpyrazine) complex was produced. A n a l , c a l c d . for N i C 5 H 6 N 4 0 6 : C, 21.69; H, 2.18; N, 20.24; found: C, 21.81; H, 2.26; N, 20.45. 4 .2 .8 Attempted Syntheses Unsuccessful attempts were made to prepare Ni(2-raepyz) A X 2 (X = C H 3 S 0 3 " , p - C H 3 C 6 H i ( S 0 3 * ) complexes by t r e a t i n g methanolic s o l u t i o n s of N i ( C H 3 S 0 3 ) 2 * x H 2 0 and N i ( p - C H 3 C 6 H A S 0 3 ) 2 » x H 2 0 wi th excess 2-methylpyrazine. In both cases no p r e c i p i t a t e formed and blue s o l i d s were only obtained by evaporating the s o l u t i o n s to dryness . A d d i t i o n of excess 2-methylpyrazine d i r e c t l y to the s o l i d n i c k e l ( I I ) sulfonates a lso d i d not y i e l d the d e s i r e d product . In t h i s second approach, i t was noted that the n i c k e l ( I I ) sulfonates were s o l u b l e i n 2-methylpyrazine and p r e c i p i t a t e s ( i n low y i e l d s ) were obtained only a f t e r 59 leaving the r e a c t i o n mixtures s t i r r i n g overnight . These r e s u l t s suggest that N i ( 2 - m e p y z ) A ( C H 3 S 0 3 ) 2 and N i ( 2 - m e p y z ) 4 ( p - C H 3 C 6 H 4 S 0 3 ) 2 may have apprec iable s o l u b i l i t i e s i n 2-methylpyrazine. Attempts were a lso made to prepare N i ( p y z ) 4 ( C F 3 S 0 3 ) 3 . N i ( C F 3 S 0 3 ) 2 was prepared by t r e a t i n g N i C 0 3 with C F 3 S 0 3 H and i s o l a t i n g the product by f i l t r a t i o n . Complete dehydration was not achieved even on heat ing the sample to 1 5 0 ° C . A s u i t a b l e solvent to d i s s o l v e the N i ( C F 3 S 0 3 ) 2 was not found. However, a 1:8 or 1:12 N i ( C F 3 S 0 3 ) 2 - p y r a z i n e mixture s t i r r e d i n 2,2-DMP f o r 24-28 h . y i e l d e d a l i g h t blue compound. M i c r o a n a l y t i c a l data f o r t h i s complex correspond to those expected for Ni(pyz) 3 . s (CF 3 S0 3 ) 2 . 4.3 RESULTS AND DISCUSSION 4.3.1 Thermal Studies The thermal parameters for the n i c k e l ( I I ) compounds are given i n Table 4 .1 . The D . S . C . curve for N i ( p y ) 4 ( C H 3 S 0 3 ) 2 e x h i b i t s three endothermic events between 160 and 3 1 0 ° C . Thermogravimetric s tudies i n d i c a t e that the f i r s t two thermal events correspond to the loss of three p y r i d i n e moiet ies while the l a s t one corresponds to the loss of the remaining p y r i d i n e molecule . For N i ( p y ) 4 ( p - C H 3 C 6 H 4 S 0 3 ) 2 , two endothermic events are observed, the one at 180°C e x h i b i t i n g a low temperature shoulder . The c lose proximity of the two thermal steps make i t d i f f i c u l t to charac ter ize i n d i v i d u a l weight or enthalpy changes. The two events are accompanied by a t o t a l weight l o s s of 46% which i s c lose to the 44% expected f o r the removal of a l l the four p y r i d i n e groups. In both these n i c k e l ( I I ) s u l f o n a t e p y r i d i n e complexes, the c lose proximity of the events precludes thermal synthesis of complexes containing lower p y r i d i n e to n i c k e l r a t i o s . 60 The D . S . C . curve f o r Ni (2 -mepyz) u (N0 3 ) 2 *R 2 0 shows endothermic events at 93 and 1 3 9 ° C . The l a t t e r e x h i b i t s a high temperature shoulder . Heating a sample of the compound to 114°C leads to a weight loss of 18%, which agrees favourably with the value of 19% c a l c u l a t e d f o r the l o s s of one 2-methyl-pyrazine l i g a n d and one water molecule . In s p i t e of these r e s u l t s no attempt was made to synthesize the t r i s ( 2 - m e t h y l p y r a z i n e ) complex due to the closeness of the f i r s t two events . Further heat ing of the sample to 152°C leads to an a d d i t i o n a l weight loss of 32%. The t h e o r e t i c a l f i g u r e assoc ia ted wi th the loss of two moles of 2-methylpyrazine l igands i s 33%. Exothermic decomposi-t i o n of the sample commences at about 2 8 0 ° C . Based on these r e s u l t s , Ni(2-mepyz) (N0 3 ) 2 was synthesized by thermolysis of N i ( 2 - m e p y z ) A ( N 0 3 ) 2 » H 2 0 ( sec t ion 4 . 2 . 7 ) . The D . S . C . curve for the t r i s ( p y r a z i n e ) complex, N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 » C H 3 0 H , i s shown i n Figure 4 .1a . The f i r s t thermal event i n t h i s curve begins at about 4 0 ° C , i n d i c a t i n g that the compound contains l o o s e l y h e l d m o i e t i e s , presumably methanol. However, t h i s event overlaps wi th the second one and i t was not p o s s i b l e to determine the enthalpy and weight loss changes assoc ia ted with each of them s e p a r a t e l y . Heating a sample of the compound to 190°C leads to a weight loss of 25%, which corresponds wi th the c a l c u l a t e d weight l o s s of 22% f o r the loss of one pyrazine and one methanol molecule . The events at 250 and 375°C each correspond to a loss of one pyrazine l i g a n d as judged from weight loss r e s u l t s . Further heat ing of the sample between 3 9 0 ° (end of f o u r t h event) and 450°C r e s u l t i n an a d d i t i o n a l weight l o s s of 7%. T h i s , together with the nature of the curve i n t h i s temperature range, i n d i c a t e s that the loss of the l a s t pyrazine molecule i s fol lowed immediately by Table 4.1 Thermal parameters for n i c k e l ( I I ) complexes Compound Peak Temp. °C AH k J m o l ' 1 weight loss % 2 c a l c d . Obs. N K p y J j C I ^ S O j ^ 198) 184 42 42 215J 273 72 14 14 N K p y M p - C H ^ H . S C V , 1801 44 46 216J Ni(2-mepyz) li ( N 0 3 ) 2 « H 2 0 93 116 19 18 139 127 33 32 280 3 - - -N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 » C H 3 O H 113] 147 22 25 147J 250 27 15 12 375 75 15 16 N i ( p y z ) 2 ( N 0 3 ) 2 240 61 23 26 300 3 240 - 71 N i ( p y z ) ( p - C H 3 C 6 H A S 0 3 ) 2 311 75 17 18 Ni(2 -mepyz) (N0 3 ) 2 270 3 - - -1) Estimated e r r o r l i m i t s : Peak Temp. 2) For explanat ion of c a l c u l a t e d values ± 5 ° C , AH ±5%, , see t e x t . weight l o s s ±5%. 3) Onset of decomposition. 62 decomposition. Despite the reasonable c h a r a c t e r i z a t i o n of the events i n terms of weight l o s s e s , i t i s evident from the nature of the D . S . C . curve that the unsolvated complex or d e r i v a t i v e s wi th lower p y r a z i n e - n i c k e l r a t i o s are i n a c c e s s i b l e by t h e r m o l y s i s . This conclus ion was confirmed experimental ly when attempts at such syntheses were a l l u n s u c c e s s f u l . The D . S . C . curve f o r N i ( p y z ) 2 ( N 0 3 ) 2 ( F i g . 4.1b) e x h i b i t s an endothermic event at 240°C accompanied by a weight loss of 26%, which compares w e l l wi th the c a l c u l a t e d value of 23% for loss of one pyrazine l i g a n d . There i s a sharp exothermic event at 3 1 2 ° C . The high enthalpy change and high weight loss assoc ia ted with t h i s event suggest that there i s extensive sample decomposi-t i o n at these temperatures. The D . S . C . curve for Ni(pyz) ( p - C H 3 C 6 H l i S 0 3 ) 2 e x h i b i t s an endothermic event at 311°C which i s accompanied by a weight loss of 18%. This corresponds with the value of 17% c a l c u l a t e d f o r the loss of one pyrazine l i g a n d . Unl ike the pyrazine l i g a n d i n Ni(pyz) ( p - C H 3 C 6 H i ( S 0 3 ) 2 , the s i n g l e 2-methylpyrazine l i g a n d i n Ni(2 -mepyz) (N0 3 ) 2 i s not l o s t prior , to decomposi-t i o n of the complex. Decomposition of the l a t t e r compound begins at about 270°C and i s complex, e x h i b i t i n g both endothermic and exothermic events . Consequently, the enthalpy change associa ted wi th i t was not determined. 4 .3 .2 Infrared Spectroscopy Pyrazine , 2-methylpyrazine, and sulfonate and n i t r a t e anions a l l have the p o t e n t i a l of coordinat ing to the c e n t r a l metal i n more than one way. The var ious bonding modes and t h e i r e f f e c t on the i n f r a r e d spectra of complexes conta ining these species have been considered i n Sec t ion 3 . 3 . 2 . 1 . F i g . 4.1 D.S.C. Curves f o r Ni (pyz ) 3 (CH 3 S 0 3 ) 2 . CH3OH and N i (pyz ) 2 (NC>3 ) 2 64 4 .3 .2 .1 Infrared Spect ra l Results f o r N i c k e l ( I I ) Complexes Containing Sulfonate Anions The i n f r a r e d spectra of Ni(py) k (CH 3 S0 3 ) 2 and N i (py) k ( p - C H 3 C g H / ( S 0 3 ) 2 are discussed f i r s t . Band assignments due to p y r i d i n e and the sul fonate anions are given i n Appendices I and IV r e s p e c t i v e l y . I t has been p r e v i o u s l y reported that there are considerable frequency s h i f t s i n the i n f r a r e d 27 33 52 absorptions of coordinated p y r i d i n e r e l a t i v e to uncomplexed p y r i d i n e , ' ' with the 8a, 6a and 16b v i b r a t i o n s showing a more pronounced c o o r d i n a t i o n dependence. The r e s u l t s of the two complexes s tudied here are consis tent with these observat ions , with the 6a and 16b bands appearing at about 635 and 430 c m - 1 r e s p e c t i v e l y , as has been reported f o r other n i c k e l ( I I ) 33 52 53 complexes. ' ' A number of the p y r i d i n e bands e x h i b i t small s p l i t t i n g s which, as i n the e a r l i e r s tudies a l ready c i t e d , may be a t t r i b u t e d to devia t ions from p e r f e c t octahedral geometry to remove degeneracy, i n t e r a c t i o n s between adjacent p y r i d i n e r i n g s , or Fermi resonance e f f e c t s . Reduction i n symmetry of the RS0 3 " anion below C ^ , expected upon c o o r d i n a t i o n , i s i n d i c a t e d by the s p l i t t i n g of the vu and v 5 bands. The magnitude of the s p l i t t i n g of the former i s about 80 c m - 1 i n both cases . The same band i s s p l i t by 112 cm" 1 i n Ni(pyz) (p-CHjCgH^SOj) 3 [see below]. The r e l a t i v e l y smaller s p l i t t i n g of \)A i n the t e t r a k i s ( p y r i d i n e ) complexes i s consis tent wi th these complexes having monodentate sulfonate groups. A x i a l monodentate anions have been proposed f o r r e l a t e d copper(II) complexes, 28 8 C u ( p y ) 4 ( F S 0 3 ) 2 , C u ( p y ) A ( C H 3 S 0 3 ) 2 and confirmed by X-ray s t r u c t u r a l determination of C u ( p y ) A ( C F 3 S 0 3 ) 2 , 2 7 F e ( p y ) M ( R S 0 3 ) 2 5 A [R = C F 3 , C H 3 , p - C H 3 C 6 H j 65 complexes have a l l been shown by X - r a y s tudies to be s i x - c o o r d i n a t e wi th t r a n s - c o o r d i n a t e d monodentate sulfonate groups. A s i m i l a r s t r u c t u r e i s proposed f o r the t e t r a k i s ( p y r i d i n e ) n i c k e l ( I I ) sulfonates s tudied here . There i s s t r i k i n g s i m i l a r i t y between absorptions assigned to pyrazine (Appendix II) i n the spectra of N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 » C H 3 0 H and C u ( p y z ) 3 ( N 0 3 ) 2 [Section 3 . 3 . 2 . 3 ] . T h i s suggests that the pyrazine l igands are coordinated i n a s i m i l a r fashion i n both complexes. The bands assigned to the anion (Appendix IV, part A) are very s i m i l a r i n N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 » C H 3 0 H and g C u ( p y z ) 2 ( C H 3 S 0 3 ) 2 . The l a t t e r compound i s known to contain monodentate methanesulfonate groups. This s t r o n g l y suggests that N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 » C H 3 O H also has monodentate sulfonate anions . V i b r a t i o n a l assignments due to the p - t o s y l a t e group i n the i n f r a r e d spectrum of Ni(pyz) ( p - C H 3 C 6 H i i S 0 3 ) 2 are given i n Appendix IV, par t C. Bands assigned to the anion are broader i n the spectrum of the n i c k e l complex than i n that of i t s copper analogue (Section 3 . 3 . 2 . 2 ) . T h i s made p o s i t i v e i d e n t i -f i c a t i o n of bands d i f f i c u l t . The complexity of the spectrum i s compounded by the fac t that severa l anion and n e u t r a l l i g a n d bands occur i n the same r e g i o n (1000-1300 c m " 1 ) . However, by comparison of the spectrum with those of other 20 . complexes conta ining sulfonate groups s tudied here and elsewhere, i t was p o s s i b l e to make t e n t a t i v e assignments. The lowering of symmetry of p - t o s y l a t e anion below C^y i s i n d i c a t e d by the s p l i t t i n g of the S0 3 asymmetric s t r e t c h band, The band i s s p l i t by 112 and 85 c m - 1 i n Ni(pyz) ( p - C H 3 C 6 H i i S 0 3 ) 2 and Ni(py) 4 ( p - C H 3 C 6 H A S 0 3 ) 2 r e s p e c t i v e l y , suggesting the presence of bidentate sul fonate anions i n the mono(pyrazine) complex. On the b a s i s of s i m i l a r i t y of i n f r a r e d s p e c t r a , a s t ruc ture s i m i l a r to that proposed 66 f o r i t s i r o n and copper analogues i s proposed f o r N i ( p y z ) ( p - C H 3 C 6 H A S 0 3 ) 2 . In summary, the i n f r a r e d s tudies support s t r u c t u r e 1 or 2 ( F i g . 1.3) for the t e t r a k i s ( p y r i d i n e ) n i c k e l ( I I ) sulfonates (where X = Monodentate terminal anions and L = p y r i d i n e ) . The assignment of a trans rather than a 28 c i s s t ruc ture i s supported by previous s tudies on N i ( p y ) k ( F S 0 3 ) 2 and 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 (see l a t e r ) . As f o r C u ( p y z ) 3 ( N 0 3 ) 2 , i t i s concluded that N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 » C H 3 O H has s t ruc ture 3 ( F i g . 1 .4) . N i ( p y z ) ( p - C H 3 C 6 H A S 0 3 ) 2 i s assigned s t ruc ture 7 ( F i g . 1.5) for s i m i l a r reasons as those given i n Sect ion 3 .3 .2 .2 for mono(pyrazine)copper(II) s u l f o n a t e s . 4 .3 .2 .2 Infrared S p e c t r a l Results f o r N i c k e l ( I I ) Complexes Containing N i t r a t e Anions The i n f r a r e d spectra of N i ( 2 - m e p y z ) A ( N 0 3 ) 2 * H 2 0 , N i ( p y z ) 2 ( N 0 3 ) 2 and Ni(2 -mepyz) (N0 3 ) 2 are discussed i n t h i s s e c t i o n . The spectrum of N i ( 2 - m e p y z ) 4 ( N 0 3 ) 2 » H 2 0 ( F i g . 4.2a) i s c h a r a c t e r i z e d by absorptions from 2-methylpyrazine groups, n i t r a t e anions and water m o i e t i e s . The bands due to the water molecule are not very broad, suggesting the presence of l a t t i c e rather than coordinated water. The v i b r a t i o n s assigned to 2-methylpyrazine are given i n Appendix I I I . The r e l a t i v e l y small s h i f t s , upon complexation, of the 410, 472 and 1021 cm" 1 absorptions of the uncoordinated 2-methylpyrazine suggest that the n e u t r a l l i g a n d i s coordinated through one n i t r o g e n atom only i n t h i s complex (see Sect ion 3 . 3 . 2 . 3 ) . The r e l a t i v e l y l a r g e r s h i f t s of the corresponding bands i n the i n f r a r e d spectrum of Ni(2 -mepyz) (N0 3 ) 2 ( F i g . 4.2b) i n d i c a t e bidentate l i g a n d c o o r d i n a t i o n i n t h i s compound. 67 . 4 . 2 I n f r a r e d S p e c t r a o f N i ( 2 - m e p y z ) ^ ( N O ^ ) 2 - H 2 ° a n c ^ N i ( 2 - m e p y z ) ( N O , ) • i i 1 1 " 1 1 ' ' 1 - i 0 1400 1000 600 200 WAVENUMBER / c m " 1 b) N i ( 2 - m e p y z ) ( N O - ) i i i i 1 i 1 i 1 1 1 1 r 68 V i b r a t i o n a l assignments due to the pyrazine l igands i n Ni(pyz) 2 (N0 3 ) 2 are given i n Appendix I I . I t i s d i f f i c u l t to determine the mode of c o o r d i n a -t i o n for both the n e u t r a l l i g a n d and the anion because, i n a d d i t i o n to the complexity of the spectrum i n the 1000 - 1300 c m - 1 r e g i o n , a N03 v i b r a t i o n , \J2, occurs i n the same region (800 - 830 c m - 1 ) where a d i a g n o s t i c a l l y u s e f u l pyrazine absorpt ion occurs . However, the presence of only one band below 500 cm" 1 i n d i c a t e s that the two pyrazine groups are i d e n t i c a l . This conclus ion i s g supported by an e a r l i e r study on the r e l a t e d complex, Cu(pyz) 2 (CH 3 S0 3 ) 2 . X - r a y s t r u c t u r a l s tudies revealed the presence of two d i s t i n c t types of b r i d g i n g pyrazine groups i n t h i s complex, and t h i s i s manifested i n i t s i n f r a r e d spectrum i n the form of two w e l l separated (54 cm" 1) pyrazine absorptions below 500 c m " 1 . V i b r a t i o n a l assignments a r i s i n g from the n i t r a t e groups i n the three complexes under d i s c u s s i o n are tabulated i n Appendix V . A s p l i t t i n g of \), i s c l e a r l y observed i n d i c a t i n g a reduct ion of anion symmetry to below D ^ ^ . The band i s s p l i t by 107 and 133 cm" 1 i n the spectra of Ni(2-mepyz) k(N03)2•H20 and Ni (pyz) 2 (N0 3 ) 2 , r e s p e c t i v e l y , and by a s i g n i f i c a n t l y l a r g e r amount, 249 c m " 1 , i n the spectrum of Ni(2-mepyz)(N03)2. These r e s u l t s are consis tent wi th monodentate anion c o o r d i n a t i o n i n Ni(2-mepyz)A(N03)2»H20 and Ni(pyz) 2 (N0 3 ) 2 and bidentate n i t r a t e anion c o o r d i n a t i o n i n Ni(2-mepyz)(N03)2 (see Sect ion 3.3.2.1). The spectrum of Ni(2-mepyz)(N03)2 a l s o e x h i b i t s a strong band, assigned to Ni-0 s t r e t c h i n g v i b r a t i o n s , at 341 c m " 1 . In g e n e r a l , the spectra of Nit2-mepyz) k(N0 3) 2 *H20 and Ni(2-mepyz)(N03)2 are very s i m i l a r to those of t h e i r copper analogues. 69 In summary, the i n f r a r e d s tudies support s t ruc tures 1 and 2 ( F i g . 1.3) for N i ( 2 - m e p y z ) 4 ( N 0 3 )J» HJO . However, the t e t r a g o n a l l y elongated nature of t h i s complex (Section 4.3.3) favours 1. I t i s concluded that N i ( p y z ) 3 ( N 0 3 ) 2 i s a two-dimensional sheet polymer of s t ruc ture type 5 ( F i g . 1 .5) . Ni (2 -mepyz) (N0 3 ) 2 i s assigned the C u ( p y z ) ( N 0 3 ) 2 s t r u c t u r e , 9 ( F i g . 1.6) on the bas is of t h e i r s i m i l a r i n f r a r e d s p e c t r a l data . 4.3.3 E l e c t r o n i c Spectroscopy 4 .3 .3 .1 Theory of N i c k e l ( I I ) Spectra The n i c k e l ( I I ) i o n has a d 8 e l e c t r o n c o n f i g u r a t i o n which gives r i s e to the Russel-Saunders terms ( in order of i n c r e a s i n g energy) 3 F , 1 D , 3 P , 1 G , 1S. In an octahedral l i g a n d f i e l d the 3 F term i s s p l i t i n t o 3^2g' 3 ^2g a n c l 3 T , while the 3 P term transforms as 3 T . . Three s p i n - a l l o w e d t r a n s i t i o n s are l g lg therefore expected i n an octahedral n i c k e l ( I I ) complex, namely \ ) 1 ( 3 A 9 -• 3 T _ ) , ^g ^g v , ( 3 A _ - 3 T . (F ) ) , and \ ) , ( 3 A . - 3 T . (P)) . The i n t e n s i t i e s of these t r a n s i -2 2g lg 3 2g l g t i o n s w i l l be r e l a t i v e l y low s i n c e , being d-d t r a n s i t i o n s , they are Laporte f o r b i d d e n . In descending to symmetry, as a r e s u l t of te t ragonal d i s t o r t i o n , each of the three o r b i t a l l y degenerate T s tates i s s p l i t i n t o two components g i v i n g r i s e t o , i n theory , a t o t a l of s i x s p i n - a l l o w e d t r a n s i t i o n s ( F i g . 4 .3 ) . In p r a c t i c e a l l s i x bands are r a r e l y seen. Room temperature s o l i d s ta te e l e c t r o n i c spectra are g e n e r a l l y broad because they contain a number of component v i b r a t i o n a l t r a n s i t i o n s . Greater r e s o l u t i o n may be achieved i n low 70 Fig. 4.3 Effects of Cubic and Axial Ligand Fields and Second Order Spin-Orbit Coupling on the Triplet Terms of Nickel (11) Ion JT c , £ g ' A 2 g Free ion Cubic ligand field Axial ligand field Second order spin-orbit coupling 71 temperature s t u d i e s , as has been the case i n the mull spectra of N i ( p y ) 4 X 2 (X = C I , Br) complexes at l i q u i d n i t r o g e n temperature."^ Equating the energy of the 3 B^g ground state to zero and assuming the absence of c o n f i g u r a t i o n a l i n t e r a c t i o n between l e v e l s of the same symmetry, the energies of the e x c i t e d s tates a r e : " ^ = lODa T c y = lODa • T c y e < > A 2 g > = lODa • ocy = lODq • T r y D q x ^ i s the e q u a t o r i a l plane l i g a n d f i e l d parameter and Ds and Dt are t e t r a -gonal parameters. The s p l i t t i n g of the 3^2g^r? a n c * 3 ^ l g ^ h ? s tates are 35/4 Dt and 6Ds-5/4 Dt , r e s p e c t i v e l y . Ds and Dt are taken to be p o s i t i v e f o r compounds with a x i a l e longat ion . "* 7 The value of Dt may be d i r e c t l y obtained from the s p l i t t i n g of the lowest energy t r i p l e t and then Ds determined from the s p l i t t i n g of the second e x c i t e d s t a t e . Once Do^y and Dt are obta ined , the 58 a x i a l f i e l d parameter Dq may be c a l c u l a t e d from the express ion : z Dt = 4/7 ( D q ^ - Dq z ) 4.1 where D ^ molecules of the type t rans-ML^Z, are concerned. 72 4 .3 .3 .2 E l e c t r o n i c S p e c t r a l Results f o r N i c k e l ( I I ) Complexes E l e c t r o n i c s p e c t r a l data f o r the n i c k e l complexes s tudied here , together with assignments, are presented i n Appendix V I , par t C. For 28 55 comparison, r e s u l t s from previous s tudies on N i ( p y ) 4 ( F S 0 3 ) 2 and N i ( p y ) 4 X 2 (X = C l , Br) are i n c l u d e d . A l l the complexes e x h i b i t two absorpt ion bands i n the v i s i b l e region and one very broad band i n the n e a r - i n f r a r e d r e g i o n . The l a t t e r band i s s p l i t i n t o two, though i n some cases not w e l l r e s o l v e d , components. Most of the spectra a lso show a weak absorpt ion band at about 13 500 c m " 1 . A representa t ive spectrum of t h i s c l a s s of compounds, that of N i (py) 4 ( p - C H 3 C 6 H I ( S 0 3 ) 2 , i s shown i n Figure 4 .4 . The e l e c t r o n i c spectra of these complexes c l o s e l y resemble those of N i ( p y ) 4 X 2 (X = F S 0 3 " , C l " , B r " ) . A t e t r a g o n a l l y d i s t o r t e d s t r u c t u r e of the type trans-ML^Xj (Structure 1, F i g . 1.3) has been proposed f o r 28 N i ( p y ) u ( F S 0 3 ) 2 . The t e t r a k i s ( p y r i d i n e ) n i c k e l ( I I ) h a l i d e s are known by X - r a y a n a l y s i s to have an a x i a l l y d i s t o r t e d t rans-ML i i X 2 s t r u c t u r e . T h e same s t ruc ture i s proposed for the t e t r a k i s ( n e u t r a l l i g a n d ) n i c k e l ( I I ) complexes presented i n t h i s work, where L i s p y r i d i n e and X i s a terminal unidentate sul fonate anion or L i s 2-methylpyrazine and X i s a unidentate n i t r a t e i o n . On the b a s i s of i n f r a r e d s p e c t r a l r e s u l t s (Section 4.3.2) var ious s t ruc tures ( F i g s . 1.3 - 1.6) were assigned to the n i c k e l complexes s tudied here . The t e t r a k i s ( n e u t r a l l igand) complexes have been considered i n the preceding paragraph. N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 » C H 3 0 H was assigned s t r u c t u r e 3, where 74 L i s a terminal monodentate p y r a z i n e , L ' i s a bidentate b r i d g i n g pyrazine and X i s a terminal sulfonate anion . Inf rared s p e c t r a l data f o r N i ( p y z ) 2 ( N 0 3 ) 2 were found to be most consis tent with s t ruc ture type 5 i n which L ' i s a bidentate b r i d g i n g pyrazine and X a monodentate n i t r a t e a n i o n . N i ( p y z ) ( p - C H j C g H ^ S O j ) 3 , on the other hand, was assigned s t r u c t u r e 7, where L ' and X' are bidentate b r i d g i n g pyrazine and p - t o s y l a t e groups, r e s p e c t i v e l y . Ni (2 -mepyz) (N0 3 ) 2 was concluded to have the Cu(pyz)(N0 3 ) s t r u c t u r e , 9. The presence of more than three bands i n the e l e c t r o n i c spectra of a l l these complexes, and the s i m i l a r i t y of the spectra with those of N i ( p y ) 4 X 2 (X = F S 0 3 " , C I " , B r " ) , s t r o n g l y suggest that they a l l have t e t r a g o n a l l y d i s t o r t e d octahedral s t r u c t u r e s . The lowest energy absorpt ion band i n the e l e c t r o n i c spectrum of Ni(2 -mepyz) (N0 3 ) 2 extends from 7 800 to 11 800 cm" 1 without a w e l l - d e f i n e d maximum. The broadness of t h i s band suggests the existence of a lower symmetry than octahedral around the n i c k e l ( I I ) i o n . Unfor tunate ly , a d e t a i l e d assignment of the spectrum cannot be made. For the remaining n i c k e l ( I I ) complexes s t u d i e d , r e s u l t s of c r y s t a l f i e l d c a l c u l a t i o n s performed by the procedure descr ibed i n Sec t ion 4 .3 .3 .1 are given i n Table 4 .2 . For complexes where the s p l i t t i n g of the second band i s not observed, Ds values cannot be evaluated. 75 Table 4.2 Spectrochemical Parameters f o r N i c k e l ( I I ) Complexes; C . I . Not I n c l u d e d 2 Compound Dq xy Dq 2 Dt Ds N i ( p y ) 4 ( p - C H 3 C 6 H 4 S 0 3 ) a 1180 480 400 650 N i ( p y ) i i ( F S 0 3 ) 2 3 1176 519 375 547 N i ( p y ) 4 ( C H 3 S 0 3 ) 2 1180 580 340 605 N i ( 2 - m e p y z ) , ( N 0 3 ) 2 » H 2 0 1180 640 309 * N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 ' C H 3 O H 1060 700 206 * N i ( p y z ) 2 ( N 0 3 ) 2 1100 850 149 698 N i ( p y z ) ( p - C H 3 C 6 H , S 0 3 ) 2 890 810 46 210 1) A l l values are i n c m " 1 . 2) C . I . = c o n f i g u r a t i o n a l i n t e r a c t i o n . 3) From reference 61. *) See t e x t . The above c a l c u l a t i o n s assume the absence of c o n f i g u r a t i o n a l i n t e r -a c t i o n between states of the same s p i n and symmetry. With t h i s p e r t u r b a t i o n taken i n t o account, the energies of the s i x t r a n s i t i o n s are given by a l i n e a r equat ion , a two by two secular determinant and a three by three secular d e t e r -minant. The second order energies of the s tates ( E ( 3 B 1 ) = 0) are given 76 B 2 g - lODq' 10Dq'-ADs-5Dt+12B-E 6B 6B 20Dq'+2Ds-15Dt+3B-E = 0 35 V3 l O D q ' — D t - E + ^ (ADs+5Dt) 0 6B (4Ds+5Dt) 0 10Dq'+2Ds~Dt+12B-E 6B 20 D.q«-Ds-10Dt+3B-E = 0 a b where the two by two secular determinant i s on a ( A 2 g , ^ 2 g) b a s i s a n c ^ t n e 3. b c three by three determinant on a (E , E , E ) b a s i s . g g g A computer program which solves the three by three secular determinant, given Dq' (= Dq ) , e(»B, - 3 E a ) , e(»B. - 3E b>., an4 e(»B, - *E C) , has been w r i t t e n by F . G . Herr ing and J . Mayo of t h i s Department and has been used to c a l c u l a t e the te t ragonal parameters presented i n T a b l e A . 3 . 77 Table 4.3 Spectrochemical Paramaters f o r N i c k e l ( I I ) Complexes; 2 C . I . Included Compound Dt Ds B N i ( p y ) 4 ( p - C H 3 C 6 H , S 0 3 ) 2 351 849 888 N i ( p y ) 4 ( C H , S O , ) , 320 435 857 N i ( 2 - m e p y z ) , ( N 0 3 ) 2 « H 2 0 275 665 821 N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 ' C H 3 O H 196 299 987 N i ( p y z ) 2 ( N 0 3 ) 2 132 528 858 N i ( p y z ) ( p - C H 3 C 6 H , S 0 3 ) 2 35 48 901 1) A l l values are i n c m " 1 . 2) C . I . = c o n f i g u r a t i o n a l i n t e r a c t i o n . " M e t a l " e l e c t r o n clouds are more d i f f u s e i n complexes than i n f ree ions leading to reduced r e p u l s i o n s between d - e l e c t r o n s . Consequently the i n t e r -e l e c t r o n i c r e p u l s i o n parameter, B, i n complexes i s expected to be lower than i n free i o n s . The r e s u l t s of the present study are i n accord wi th t h i s obser-63 v a t i o n . Free n i c k e l ( I I ) i o n has a B value of 1080 c m " 1 . Comparison of the values of Dt from Tables 4.2 and 4.3 show that i n c l u s i o n of c o n f i g u r a t i o n a l i n t e r a c t i o n does not g r e a t l y a f f e c t the e v a l u a -64 t i o n of t h i s parameter. This i s consis tent wi th previous observat ions . On the other hand the e v a l u a t i o n of Ds i s a f f e c t e d apprec iably by the i n c l u s i o n of c o n f i g u r a t i o n a l i n t e r a c t i o n . Another f a c t o r that may lead to an appreciable er ror i n the Ds parameter i s the assumption that the p o s i t i o n of the 3 B . -* 3 A„ coinc ides wi th that of the s p i n - f o r b i d d e n t r a n s i t i o n s . 78 Dt i s determined d i r e c t l y from the s p l i t t i n g of the f i r s t e x c i t e d s t a t e . Since the s tate concerned s p l i t s i n t o two components as a d i r e c t consequence of the te t ragonal f i e l d , Dt i s a d i r e c t measure of the degree of t e t r a g o n a l i t y ( i . e . the d i f f e r e n c e between Dq z and Do^y a s def ined by Eqn. A . l ) . The Dt data i n Table A.3 show the expected t r e n d . The f i r s t three complexes i n the table have a N i N 4 0 2 chromophore and t h e i r Dt values are i n the range of 351 to 275 c m " 1 . The next compound has a N i N 2 N ' 2 0 2 chromophore and e x h i b i t s a lower Dt v a l u e . A b r i d g i n g pyrazine group a f f o r d s a lower ( in-plane) f i e l d s t rength because i t s e l e c t r o n densi ty i s shared between two metal centres . N i ( p y z ) 2 ( N 0 3 ) 2 , which has a N i N ' A 0 2 chromophore, e x h i b i t s a Dt value of 132 c m " 1 . In N i ( p y z ) ( p - C H j C g H ^ S O j ) 2 , two oxygen atoms from the weakly b a s i c sul fonate anion must now occupy at l e a s t two of the e q u a t o r i a l p o s i t i o n s . T h i s , coupled with the presence of b r i d g i n g pyrazine u n i t s , r e s u l t s i n the l e a s t te t ragonal d i s t o r t i o n . In summary, 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 of a l l the n i c k e l ( I I ) complexes i n v e s t i g a t e d here are consis tent wi th t h e i r having t e t r a g o n a l l y d i s t o r t e d octahedral s t r u c t u r e s . A . 3 . A Magnetic Proper t ies An octahedral n i c k e l ( I I ) i o n posseses a 3^2g g r o u n d term, which has s p i n (S = 1), but no o r b i t a l angular momentum associa ted with i t . For an e l e c t r o n i n a p a r t i c u l a r o r b i t a l to have o r b i t a l angular momentum about a given a x i s , i t must be p o s s i b l e , by r o t a t i o n about that a x i s , to transform the o r b i t a l i n t o an equivalent and degenerate o r b i t a l which does not a l ready contain an e l e c t r o n with the same s p i n . Since the d 2 and d 2 _ 2 o r b i t a l s 79 cannot be transformed i n t o each other by r o t a t i o n about any a x i s , there can be no o r b i t a l angular momentum, to f i r s t order , assoc ia ted with the e set of o r b i t a l s . The 3&2g g r o u n < ^ term of an octahedral n i c k e l ( I I ) i o n i s charac-t e r i z e d by the presence of unpaired e lec t rons i n the e set o r b i t a l s . Hence the o r b i t a l c o n t r i b u t i o n to the magnetic moment i s quenched and magnet ica l ly d i l u t e n i c k e l ( I I ) complexes are expected to e x h i b i t magnetic moments c lose to the s p i n only value of 2.83 B .M. To f i r s t order , the magnetic moment of such complexes i s given by Equation A . 2 : 1/2 V-eff' = g[S(S+l)] A.2 In p r a c t i c e , however, the magnetic moment u s u a l l y found l i e s between 2.9 and 3.3 B .M. and i s independent of temperature .^ 5 Deviat ions of the magnetic moment from the s p i n - o n l y value mainly depend on the magnitude of the o r b i t a l c o n t r i b u t i o n to second order . In the presence of s p i n - o r b i t coupl ing i t i s not p o s s i b l e to f a c t o r i z e the t o t a l wave-function a c c u r a t e l y i n t o s p i n and o r b i t a l p a r t s . Thus the ground s t a t e , although not s p l i t by s p i n - o r b i t c o u p l i n g , may be coupled to an e x c i t e d state by i t , so that separat ion of terms on the bas is of t h e i r d i f f e r i n g o r b i t a l angular momentum i s not e n t i r e l y v a l i d . The o r b i t a l c o n t r i b u t i o n i s brought back i n t o the s p i n - o n l y moment by m o d i f i c a t i o n of the s p l i t t i n g f a c t o r , g , which ins tead of being 2.00, as f o r a 63 term devoid of o r b i t a l angular momentum, i s 80 g = 2.00 (1-aX/lODq) 4.3 and hence s . o . (l-oX/10Dq) 4.4 e f f where X and Dq are s p i n - o r b i t coupl ing and c r y s t a l f i e l d parameters r e s p e c t i -v e l y , a i s 4 for A terms. The parameter X i s p o s i t i v e f o r l e s s than h a l f -f i l l e d s h e l l s and negative f o r more than h a l f - f i l l e d s h e l l s . There i s a l so a c o n t r i b u t i o n to the magnetic s u s c e p t i b i l i t y of A terms from the second-order Zeeman e f f e c t . This e f f e c t , which i s f i e l d induced, mixes the ground state with thermally non-populated, yet l o w - l y i n g , e x c i t e d paramagnetic s t a t e s . The s u s c e p t i b i l i t y due to t h i s e f f e c t , c a l l e d tempera-63 ture independent paramagnetism, T . I . P . , i s given by the expresssion where a i s 8 for A terms, N i s Avogadro's number, B i s the Bohr Magneton and Dq i s the c r y s t a l f i e l d parameter. The e f f e c t of T . I . P . i s to increase the magnetic s u s c e p t i b i l i t y of a complex. However, i t s c o n t r i b u t i o n i s very small and may be a s i g n i f i c a n t p r o p o r t i o n ( r e l a t i v e to the o v e r a l l paramagnetic s u s c e p t i b i l i t y of a complex) only at h i g h temperatures. The magnetic p r o p e r t i e s assoc ia ted with the 3 B^g ground term of a t e t r a g o n a l l y d i s t o r t e d n i c k e l ( I I ) complex are s i m i l a r to those assoc ia ted with the ground term of octahedral n i c k e l ( I I ) . T . I . P . aNB* 4.5 lODq 81 The magnetic s u s c e p t i b i l i t y data f o r n i c k e l ( I I ) complexes s tudied i n t h i s work are presented i n Appendix V I I I . On the b a s i s of s p e c t r a l r e s u l t s (Sections A.3 .2 and A.3.3) N i ( p y ) 4 ( C H 3 S 0 3 ) , , N i ( p y ) A ( p - C H 3 C 6 H A S 0 3 ) 2 and N i ( 2 - m e p y z ) A ( N 0 3 ) j » H j 0 were a l l assigned s t r u c t u r e type 1 ( F i g . 1 .3) . Since the proposed s t ruc ture does not contain any b r i d g i n g e n t i t i e s , these complexes are expected to be magnet ica l ly d i l u t e . At approximately 82K the three complexes have magnetic moments of about 3.1 B .M. The magnetic moment values remain f a i r l y constant , as the temperature i s decreased, to about 20K. Below t h i s temperature there i s a s i g n i f i c a n t decrease i n the magnetic moment, which a t t a i n s a value of about 2.A B.M. at approximately A.2K. The magnetic moment temperature dependencies for these three complexes are shown i n F i g . A . 5 . This temperature dependence may be explained i n terms of 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 ground term i s connected by s p i n - o r b i t coupling with the s p l i t o r b i t a l components of the higher 3 T « term. To second order , t h i s connection changes the energies of the s p i n s tates (M g = 0, ± 1 ) by d i f f e r e n t amounts. This p a r t i a l removal of the s p i n degeneracy, i n the absence of any magnetic f i e l d , i l l u s t r a t e d i n Figure A . 3 , leads to a temperature-dependent 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 obtained by leas t - 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 f o l l o w i n g e x p r e s s i o n . ^ 82 F i g . 4 . 5 M a g n e t i c Moments v s T e m p e r a t u r e f o r N i L 4 X 2 C o m p l e x e s CN 2 z w 2 o 2 u M EH u c o o r o oo CM CM CM* 0 . • * • a) N i ( p y ) 4 ( C H 3 S 0 3 ) 2 20 40 60 80 TEMPERATURE / K 100 2 Z w 2 o 2 U t H ir> W Z o 2 CQ Z W 2 O 2 EH W z CN r o O r o 00 CN L D CN CN CN CM 0 • • • • • • • • b) N i ( p y ) 4 ( p - C H 3 C 6 H 4 S 0 3 ) 2 20 40 60 TEMPERATURE / K 80 100 CN • r o r H r o o • 1 r o c n CN 00 « CN t a CN VD CN • • * • • • c ) N i ( 2 - m e p y z ) 4 ( N 0 3 ) 2 . H 2 0 20 40 "io" "io~ 100 TEMPERATURE / K 83 2e -x (2/x)(l+e X ) = C. l+2e -x . XI = C» l+2e -x 4.6 where x = D / k T , C = N g 2 B 2 / k T and the powder magnetic s u s c e p t i b i l i t y i s X p - (x,,+2 X l)/3. Good f i t s to the powder magnetic s u s c e p t i b i l i t y equation were obtained f o r a l l the three complexes, Ni(py) A (CH 3 S0 3 ) 2 , Ni(py) 4 ( p - C H 3 C 6 H A S 0 3 ) 2 and N i ( 2 - m e p y z ) A ( N 0 3 ) 2 » H 2 0 . The best f i t of the data f o r N i ( p y ) 4 ( C H 3 S 0 3 ) 2 i s shown i n Figure 4.6 and i s representa t ive of t h i s group of complexes. The best f i t parameters are l i s t e d i n Table 4 .4 . I t i s seen that the energy d i f f e r e n c e of the spin m u l t i p l e t (Mg = 0, ± 1 ) i s about the same i n the t e t r a k i s ( p y r i d i n e ) n i c k e l ( I I ) sul fonate complexes and only s l i g h t l y l e s s i n N i ( 2 - m e p y z ) , ( N 0 3 ) 2 » H 2 0 . Table 4.4 Z e r o - F i e l d S p l i t t i n g Parameters f o r N i c k e l ( I I ) Complexes Compound D/cm" 1 g z F N i ( p y ) 1 , ( C H 3 S 0 3 ) 2 9.1 2.22 0.0168 N i ( p y ) A ( p - C H 3 C 6 H A S 0 3 ) 2 9.0 2.11 0.0068 N i ( 2 - m e p y z ) A ( N 0 3 ) 2 » H 2 0 7.2 2.18 0.0101 N i ( p y z ) ( p - C H 3 C 6 H A S 0 3 ) 2 8.8 2.16 0.0118 N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 « C H 3 O H 11.7 2.12 0.0159 Ni(2 -mepyz) (N0 3 ) 2 11.9 2.15 0.0277 N i ( p y z ) 2 ( N 0 3 ) 2 19.0 1.92 0.0873 1) Estimated e r r o r l i m i t s : D ±10%, g ±2%. 84 The magnetic moments of N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 » C H 3 O H and Ni (2 -mepyz) (N0 3 ) 2 are 2.99 and 3.10 B .M. at approximately 82K r e s p e c t i v e l y . At 2.5K the moment of the former compound i s 1.63 B . M . , while that of the l a t t e r i s 1.66 B . M . Figure 4.7 shows the magnetic moment temperature dependency f o r N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 « C H 3 0 H , which i s representa t ive of the two. The decrease i n the magnetic moment i n both cases i s large compared to that observed i n the magnet ica l ly d i l u t e complexes discussed i n the preceding paragraph, and may a r i s e from e i t h e r weak antiferromagnetism or a l a r g e r z e r o - f i e l d s p l i t t i n g e f f e c t . A n a l y s i s of the s u s c e p t i b i l i t y data of these complexes by the z e r o -f i e l d s p l i t t i n g model (Eqn. 4.6) y i e l d e d D values which are higher than those of the magnet ica l ly d i l u t e complexes (Table 4 . 4 ) . T h i s suggests that the magnetic p r o p e r t i e s of N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 » C H 3 0 H and Ni(2 -mepyz) (N0 3 ) 2 cannot be accounted for by 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 o n l y . P l o t s of magnetic s u s c e p t i b i l i t y against temperature f o r both complexes l e v e l o f f below approximately 4K ( F i g s . 4.8 and 4 . 9 ) . Even though no maximum i s observed i n e i t h e r of these p l o t s , the behaviour of both magnetic moments and s u s c e p t i b i l i t i e s with decreasing temperature suggest the presence of weak ant i ferromagnet ic coupl ing i n these compounds. S u z u k i , Tsujiyaraa and Katsura have given an e x p r e s s i o n ^ 7 f o r the s u s c e p t i b i l i t y , x» ° f t n e o n e dimensional I s i n g model w i t h S = 1 as : 4.7 85 F i g . 4.6 Magnetic S u s c e p t i b i l i t y vs Temperature f o r N i ( p y ) 4 ( C H 3 S 0 3 ) 2 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 = 9.1 cm" 1, g =2.22 TEMPERATURE / K F i g . 4.7 Magnetic Moment vs Temperature f o r N i ( p y z ) 3 ( C H 3 S 0 3 ) .CH3OH £ 03 EH z W s o £ u r - i EH W z o < £ in » ro O r o in * CN O CN in • • • • • • • To 40 60 80 TEMPERATURE / K 100 86 where a = e x p ( - 2 J / k T ) , g i s the Lande s p l i t t i n g f a c t o r , 0 the Bohr Magneton, N the number of spins i n the l a t t i c e , k the Boltzmann constant , T the temperature and J , the exchange coupl ing constant , measures the magnitude of the exchange i n t e r a c t i o n . Within the Heisenberg l i m i t , two t h e o r e t i c a l approximations have been d e r i v e d for ant i ferromagnet ic l i n e a r chain systems which may be a p p l i e d to S = 1. Wagner and F r i e d b e r g ^ 8 have sca led the exact r e s u l t s of F i s h e r ^ to the s e r i e s expansion r e s u l t s of Rushbrooke and Wood 7 0 and obtained the f o l l o w i n g expression f o r magnetic s u s c e p t i b i l i t y : Ng J B 2 S(S+l ) 1+u X • A.S kT 1-u where u = c o t h K - l / K and K = 2JS(S+l) /kT. The other approximation method i s an i n t e r p o l a t i o n scheme developed by 71 72 Weng. H i l l e r et a l . have generated a s e r i e s of c o e f f i c i e n t s to reproduce Weng's numerical r e s u l t s . A c c o r d i n g l y : N g J B 2 / [A+Bx2] 4.9 kT \ [1+Cx+Dx»] where x = | J | / k T , and f o r S - l , A = 0.6667, B = 2.5823, C = 3.6035 and D = 39.558. Based on the proposed s t ruc tures f o r N i ( p y z ) 3 ( C H , S 0 3 ) 3 » C H 3 0 H (Structure 3, F i g . 1.4) and Ni(2 -mepyz) (N0 3 ) 3 (Structure 9, F i g . 1 .6) , t h e i r 87 magnetic s u s c e p t i b i l i t y data were analyzed by the I s i n g , F i s h e r and Weng chain models as represented by equations 4 .7 , 4.8 and 4 .9 , r e s p e c t i v e l y . A l l three models gave good f i t s between experimental and c a l c u l a t e d s u s c e p t i b i l i t i e s , except at very low temperatures, wi th the Weng model being s l i g h t l y b e t t e r than the other two. I t i s noteworthy, though, that s t r u c t u r a l paramagnetic i m p u r i t i e s were accounted f o r i n the I s i n g model o n l y . The best f i t parameters are presented i n Table 4 .5 . The best f i t s are represented by the s o l i d l i n e s i n Figure 4.8 f o r N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 » C H 3 O H and Figure 4.9 f o r N i ( 2 - m e p y z ) ( N 0 3 ) 2 . The small devia t ions observed at low temperatures may be a t t r i b u t e d to the f a c t that the three models, as used here , do not take i n t o account the e f f e c t s of z e r o - f i e l d s p l i t t i n g . These e f f e c t s are greatest at low temperatures. The magnetic moment of N i ( p y z ) 2 ( N 0 3 ) 2 shows a strong temperature dependence, decreasing from 2.91 B . M . at 81.8K to 1.15 B .M. at 2.3K ( F i g . 4 .10) . I ts s u s c e p t i b i l i t y data e x h i b i t a maximum at 3.2K ( F i g . 4 .11) . T h i s i s conclusive evidence that e l e c t r o n spins i n N i ( p y z ) 2 ( N 0 3 ) 2 are coupled a n t i -f e r r o m a g n e t i c a l l y . To take i n t o account 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 z e r o - f i e l d s p l i t t i n g model (Eqn. 4.6) was used to analyze the magnetic s u s c e p t i b i l i t y data f o r N i ( p y z ) 2 ( N 0 3 ) 2 . A rather poor f i t r e s u l t e d , as measured by the value of F (Table 4 .4 ) . The value of D obtained was a lso s i g n i f i c a n t l y l a r g e r than those obtained for the magnet ica l ly d i l u t e n i c k e l ( I I ) complexes. These r e s u l t s i n d i c a t e that 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 , a lone , cannot account for the magnetic p r o p e r t i e s of N i ( p y z ) 2 ( N 0 3 ) 2 . These p r o p e r t i e s can a l s o not be represented s a t i s f a c t o r i l y by the I s i n g , F i s h e r and Weng chain models 88 p r e v i o u s l y a p p l i e d to N i ( p y z ) 3 ( C H 3 S 0 3 ) 3 » C H 3 O H and N i ( 2 - m e p y z ) ( N 0 3 ) 2 . The best f i t parameters f o r these models are given i n Table 4 .5 . The best f i t to the I s i n g model i s represented by the s o l i d l i n e i n Figure 4.11a. From the proposed s t ruc ture f o r N i ( p y z ) 2 ( N 0 3 ) 2 (Structure 5, F i g . 1 .5) , two equivalent pathways are p o s s i b l e f o r magnetic exchange. A two-dimensional model may, t h e r e f o r e , be more appropriate f o r analyzing the s u s c e p t i b i l i t y data for t h i s compound. L i n e s ' two-dimensional model was chosen. This model was discussed i n Sect ion 3.3.4 when a p p l i e d to the magnetic p r o p e r t i e s of two-dimensional copper(II) complexes. By s u b s t i t u t i n g the f o l l o w i n g c o e f f i c i e n t s 5 0 i n t o Eqn. 3.3 the model can be a p p l i e d to S = 1 systems, C l f 4; C 2 , 1.834; C 3 , 0.445; C A , 0.224; C 5 , 0.132; C 6 , 0.019. The parameters obtained from the best f i t of the magnetic s u s c e p t i b i l i -ty data for N i ( p y z ) 2 ( N 0 3 ) 2 to t h i s expression are J = -0 .7 c m - 1 and g = 1.96. The best f i t i s represented by the s o l i d l i n e i n Figure 4.11b. The agreement between observed and c a l c u l a t e d s u s c e p t i b i l i t i e s i s s t i l l poor but s l i g h t l y bet ter (F = 0.0941) than that obtained from the Is ing one-dimensional model. Since L i n e s ' model, as used here , does not inc lude a c o r r e c t i o n f o r p a r a -magnetic i m p u r i t i e s , i t was necessary, f o r exact comparison, to use the best f i t parameters to the I s i n g model i n which % monomer i s set at zero (Table 4 .5 ) . The g value obtained for N i ( p y z ) 2 ( N 0 3 ) 2 i s u n r e a l i s t i c , being lower than the free i o n v a l u e . S e t t i n g t h i s parameter at 2.2 d i d not improve the f i t to e i t h e r the L i n e s ' two-dimensional model (J = 0.8 c m " 1 , F = 0.1768) or the I s ing chain model. S l i g h t improvement to the f i t s were obtained when only 89 data above T ( X m a x ) were used. The best f i t parameters f o r the Is ing chain model are i n Table A.5 while those f o r L i n e s ' two-dimensional model are J = -0 .8 c n r 1 , g = 2.031 (F = 0.0651). N o n - i n c l u s i o n of 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 i n these models, as used here , may p a r t i a l l y e x p l a i n the poor agree-ments between theory and experiment. I t i s a lso f e a s i b l e that the two p o s s i b l e pathways f o r magnetic exchange i n N i ( p y z ) 2 ( N 0 3 ) 2 are i n e q u i v a l e n t , r e s u l t i n g i n s p i n i n t e r a c t i o n s which are nei t her one- nor two-dimensional i n nature . The magnetic p r o p e r t i e s of Ni(pyz) ( p - C H 3 C 6 H i ( S 0 3 ) 2 are very s i m i l a r to those of the magnet ica l ly d i l u t e complexes discussed e a r l i e r on i n t h i s s e c t i o n . A p l o t of magnetic moment versus temperature f o r t h i s compound i s shown i n Figure A.12. The observed temperature dependence of the magnetic moment at low temperatures may be a t t r i b u t e d to 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 a lone . No maximum i s observed i n the s u s c e p t i b i l i t y curve f o r t h i s complex ( F i g . A .13) . From the proposed s t ruc ture f o r t h i s compound (Structure 7, F i g . 1 .6) , two pathways are a v a i l a b l e f o r magnetic exchange: one path through the pyrazine bridges and the second one through the sulfonate b r i d g e s . Consequently, i t s s u s c e p t i b i l i t y data were analyzed by both the chain models and L i n e s ' two-dimensional model p r e v i o u s l y a p p l i e d to N i ( p y z ) 2 ( N 0 3 ) 2 . A l l the models reproduced the s u s c e p t i b i l i t y data f o r t h i s compound reasonably w e l l . The best f i t parameters f o r the I s i n g , F i s h e r and Weng chain models are given i n Table A.5 while those f o r the two-dimensional model are J = -0 .3 c m " 1 , g = 2.22 (F = 0.0193). The best f i t to the two-dimensional model i s represented by the s o l i d l i n e i n Figure A.13 . 90 The magnetic s u s c e p t i b i l i t y data for N i ( p y z ) ( p - C H j C j H ^ S O , ) 2 were a lso analyzed by the z e r o - f i e l d s p l i t t i n g model as represented by Equation 4 .6 . The best f i t parameters f o r t h i s model are shown i n Table 4 .4 . The f i t i s s l i g h t l y be t te r than the f i t s to the chain models and to L i n e s ' two-dimensional model, as i n d i c a t e d by the value of F . The value of D i s a l so s i m i l a r to those obtained for the magnet ica l ly d i l u t e complexes. Thus the magnetic proper t ies of N i ( p y z ) ( p - C H 3 C 6 H 4 S 0 3 ) 2 can be descr ibed s a t i s f a c t o r i l y i n terms of 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 a lone . In summary, the magnetic p r o p e r t i e s of N i ( p y ) 4 ( C H 3 S 0 3 ) 2 , N i ( p y ) A ( p - C H 3 C 6 H A S 0 3 ) a and Ni(2-mepyz) u ( N 0 3 ) 2 ' H 2 0 are consis tent wi th t h e i r monomeric nature . N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 » C H 3 0 H and Ni(2 -mepyz) (N0 3 ) 2 are chain compounds containing b r i d g i n g pyrazine and 2-methylpyrazine l i g a n d s , r e s p e c t i v e l y . They both e x h i b i t some magnetic exchange which i s reasonably modelled using I s i n g , F i s h e r and Weng chain models. The f a c t that the magnetic p r o p e r t i e s of these complexes are descr ibed e q u a l l y w e l l by a n i s o t r o p i c and i s o t r o p i c models may be a consequence of the very weak nature of the magnetic exchange i n the complexes. N i ( p y z ) ( p - C H 3 C 6 H 4 S 0 3 ) 2 and N i ( p y z ) 2 ( N 0 3 ) 2 have (two-dimensional) sheet s t ruc tures i n which the exchange ( i f i t occurs at a l l ) i s too weak to measure i n the former compound and i s measurable i n the l a t t e r but cannot be modelled w e l l . Table 4.5 Magnetic Parameters for N i c k e l ( I I ) Complexes obtained from Chain Models • Is ing model F i s h e r model Weng model Compound - J (cm" 1) g % mono F - J (cm"1) 1 % mono F - J (cm" 1) g % mono F N i ( p y z ) ( p - C H 3 C 6 H 4 S 0 3 ) J 0.6 2.22 a 0.0188 0.6 2 .22 e 0. 0184 0.5 2.24 a 0.0228 N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 » C H 3 0 H 1.0 2.14 0.8 0.0238 0.9 2 .20 e 0. 0271 0.8 2.20 e 0.0223 Ni(2-mepyz)(N0 3 ) 2 1.0 2.20 0.5 0.0154 0.9 2 .26 e 0. 0216 0.8 2.26 e 0.0124 N i ( p y z ) 2 ( N 0 3 ) 2 2.2 1.91 2.3 0.0504 1.5 2 .04 e 0. 0537 1.7 2.09 6.9 0.0470 b 2.8 1.91 3.3 0.0327 c 1.5 2.20 0 0.2283 d 1.2 1.92 0 0.1188 1) Estimated error l i m i t s : J±10%, g±2%. a) Data d i d not converge when % monomer was v a r i e d , hence t h i s parameter set at z e r o . b) Only data above T (xm a x) used. c) g set at 2.2. d) % monomer set at zero for comparison with L i n e s ' model (see l a t e r ) . e) Attempts to vary % monomer y i e l d e d , negative numbers, hence t h i s parameter set at z e r o . 92 F i g . 4.8 Magnetic S u s c e p t i b i l i t y vs Temperature f o r N i ( p y z ) 3 ( C H 3 S 0 3 ) .CH3OH a) I s i n g c h a i n model, s o l i d l i n e generated from J = -1.0 cm *", g = 2.14 _ ± b) F i s h e r c h a i n model, s o l i d l i n e generated from J = -0.9 cm g = 2.20 _ x c) Weng cha i n model, s o l i d l i n e generated from J = -0.8 cm , g = 2.20 I O 0 ^ E .0 —i TEMPERATURE / K I TEMPERATURE / K TEMPERATURE / K 93 F i g . 4.9 Magnetic S u s c e p t i b i l i t y vs Temperature f o r Ni (2-mepyz ) (NC>3 ) 2 a) I s i n g c h a i n model, s o l i d l i n e generated from J = -1.0 cm - 1, g = 2.20 b) F i s h e r c h a i n model, s o l i d l i n e generated from J = -0.9 cm , g = 2.26 c) Weng cha i n model, s o l i d l i n e generated from J = -0.8 cm , g =2.26 r-i O I TEMPERATURE / K TEMPERATURE / K TEMPERATURE / K 94 F i g . 4 . 1 0 M a g n e t i c Moment v s T e m p e r a t u r e f o r N i ( p y z ) 2 ( N O ^ ) 2 CQ EH u S o s u M H u 2 o in CN O • • CN 20 40 60 80 100 TEMPERATURE / K F i g . 4 . 1 1 M a g n e t i c S u s c e p t i b i l i t y v s T e m p e r a t u r e f o r N i ( p y z ) 2 ( N 0 3 ) 2 a) I s i n g c h a i n m o d e l , s o l i d l i n e g e n e r a t e d f r o m J = - 2 . 2 c m - 1 , g = 1 . 9 1 b) T w o - d i m e n s i o n a l m o d e l , s o l i d l i n e g e n e r a t e d f r o m J = - 0 . 7 c m - 1 g = 1 . 9 6 TEMPERATURE / K TEMPERATURE / K 95 F i g . 4.12 Magnetic Moment vs Temperature f o r N i ( p y z ) ( p - C H 3 C 6 H 4 S 0 3 ) 2 s EH Z u s o s u M E-« u z O CN ro o ro oo CN • H : CN • • * • • • • ™ 0 20 40 60 80 100 TEMPERATURE / K F i g . 4.13 Magnetic S u s c e p t i b i l i t y vs Temperature f o r N i ( p y z ) ( p - C H 3 C 6 H 4 S 0 3 ) 2 Two-dimensional model, s o l i d l i n e generated from J = -0.3 cm ^, g= 2.22 S 1 "I 1 I I 1 0.0 40.0 80.0 TEMPERATURE / K 96 CHAPTER 5 POLY-u-PYRAZINEPYRAZINE(TRIFLUOROMETHANESULFONATO-O)COPPER(I). C u ( p y z ) a ( C F , S O , ) 5.1 INTRODUCTION 13 73 Many copper ( I I ) -pyrazine complexes are known. ' In c o n t r a s t , very l i t t l e work has been reported on Copper(I ) -pyrazine compounds. Except for complexes of the type C u 2 L X 2 , where L i s pyrazine or"a methylpyrazine and X i s 1 74 C I , Br , I or CN, reported by Lever , Lewis and Nyholm ' i n the e a r l y 1960's, no other copper ( I ) -pyrazine complexes seem to have been r e p o r t e d . But even i n the work already c i t e d , with pyrazine as the l i g a n d , the c h l o r i d e and bromide complexes were repor tedly unstable and not i s o l a t e d i n a pure form. Based on the i n f r a r e d spectrum of the cyano d e r i v a t i v e , a b i n u c l e a r s t r u c t u r e ( F i g . 5.1) was proposed for these complexes. F igure 5.1 Proposed Structure for Cu 2 LXj Complexes 97 Attempts to prepare the copper(II) complex, C u ( p y z ) 2 ( C F 3 S 0 3 ) 2 , i n the course of the present work r e s u l t e d ins tead i n the i s o l a t i o n of C u ( p y z ) 2 ( C F 3 S 0 3 ) . The compound was obtained i n a form s u i t a b l e f o r s i n g l e -c r y s t a l X - r a y a n a l y s i s . T h i s , then, represents the f i r s t copper(I) pyrazine complex that has been charac ter ized by X-ray s t r u c t u r a l s t u d i e s . Not only so , i t a l so represents the f i r s t X- ray s t ruc ture determination on a complex containing both terminal and b r i d g i n g pyrazine groups. The presence of both mono- and bidentate coordinated pyrazine l igands i n the same compound has been proposed for two other compounds elsewhere i n t h i s t h e s i s . The s y n t h e s i s , X - ray s t r u c t u r a l determination and v i b r a t i o n a l s p e c t r a l r e s u l t s f o r C u ( p y z ) 2 ( C F 3 S 0 3 ) are presented i n the f o l l o w i n g s e c t i o n s . Since the copper(I) i o n has a d 1 0 e l e c t r o n i c c o n f i g u r a t i o n , t h i s complex i s expected to be diamagnetic and no magnetic s u s c e p t i b i l i t y measurements were made. A l s o , no d-d t r a n s i t i o n s are p o s s i b l e and the observed colour i s a t t r i b u t e d to charge t r a n s f e r bands. 5.2 SYNTHETIC METHOD Pyrazine (0.237 g , 2.96 mmol), d i s s o l v e d i n 3 ml of methanol conta ining about 10% v / v 2 ,2-DMP. , was added to 0.524 g (1.35 mmol) of C u ( C F 3 S 0 3 ) 2 , 3 1 d i s s o l v e d i n 4 ml of the same s o l v e n t . A green s o l u t i o n r e s u l t e d . The r e a c t i o n f l a s k was covered with p a r a f i l m . A f t e r about three weeks, orange-brown c r y s t a l s had formed. The supernatant s o l u t i o n was decanted and the c r y s t a l s washed severa l times wi th f r e s h s o l v e n t , then allowed to dry i n the glove box. Subsequent exposure to the atmosphere revealed that the complex i s e s s e n t i a l l y a i r s t a b l e . I t was noted that the c r y s t a l s contained some b l a c k 98 p a r t i c l e s which could not be removed by washing. A n a l , c a l c d . f o r C u C 9 H 8 N 4 F 3 S 0 3 : C, 29.00; H, 2.15; N, 15.03; found: C, 28.24; H, 2.25; N, 14.84. The m i c r o a n a l y t i c a l data i n d i c a t e that samples exposed to the atmosphere undergo some h y d r a t i o n ( t y p i c a l l y less than h a l f a mole of water g per mole of complex). This i s not without precedence. Haynes et a l . made s i m i l a r observations on Cu(pyz) 2 ( C H 3 S 0 3 ) 2 . 5.3 RESULTS AND DISCUSSION 5.3.1 X-Ray Structure Determination The c r y s t a l l o g r a p h i c data f o r C u ( p y z ) 2 ( C F 3 S 0 3 ) are given i n Table 5.1 and a more d e t a i l e d compilat ion of i t s s t r u c t u r a l parameters i s given i n Appendix IX. Table 5.1 C r y s t a l l o g r a p h i c Data f o r C u ( p y z ) 2 ( C F 3 S 0 3 ) C r y s t a l System T r i c l i n i c space group P T (#2) a,A 8.312(2) b.A 10.903(3) c ,A 8.201(2) a , deg 92.53 (2) 8, deg 113.77 (2) T.deg 91.40 (2) z 2 v,A 3 678.8 (3) D c , g c m - 3 1.82 1) Standard devia t ions i n parentheses. 99 The geometry around each copper(I) i o n i n C u ( p y z ) 2 ( C F 3 S 0 3 ) i s a d i s t o r t e d tetrahedron and t h i s , together wi th the atom numbering scheme, i s i l l u s t r a t e d i n Figure 5 .2 . A stereoview of the u n i t c e l l i s shown i n Figure 5 .3 . The s t ruc ture c o n s i s t s of a s p i r a l of copper ions l i n k e d by pyrazine b r i d g e s . The tetrahedron around the copper i s completed by coor-d i n a t i o n to a n i t r o g e n atom from a terminal pyrazine and an oxygen atom from a monodentate t r i f luoromethanesulfonate group. The d i s t o r t i o n of the c o o r d i n a -t i o n sphere around the copper i o n i s r e f l e c t e d i n the Cu-N (1.971, 1.985 and 2.027A) and Cu-0 (2.331A) bond d i s t a n c e s . S u r p r i s i n g l y ) the b r i d g i n g pyrazine has both the longest and the shortest Cu-N bond lengths . Both terminal pyrazine groups and t r i f l a t e anions are arranged s y n d i o t a c t i c a l l y along the polymer s k e l e t o n . Figure 5.4 shows t h i s s t ruc ture s c h e m a t i c a l l y . A l l the pyrazine r ings are planar w i t h i n experimental e r r o r . The plane of the terminal pyrazine r i n g i s approximately orthogonal to the planes of the b r i d g i n g pyrazine l i g a n d s . This o r i e n t a t i o n minimizes r e p u l s i o n s between the terminal pyrazine and the t r i f l a t e anion . 100 F i g . 5.2 Atom Numbering and C o o r d i n a t i o n Around Copper f o r C u ( p y z ) 2 ( C F 3 S 0 3 ) F i g . 5.3 A Stereoview of the U n i t C e l l i n Cu (pyz ) 2 (CF3SC>3 ) 101 Despite the fac t that one set of pyrazine r i n g s i s b r i d g i n g whi le the other set i s t e r m i n a l , both types have very s i m i l a r bonding parameters which are comparable to those found i n f r e e p y r a z i n e . 7 ^ The mean C-N and C-C bond lengths i n the terminal pyrazine i n C u ( p y z ) 2 ( C F j S 0 3 ) are 1.329 and 1.365A r e s p e c t i v e l y . In the b r i d g i n g pyrazine these dis tances are 1.331 and 1.379A r e s p e c t i v e l y while i n free pyrazine the mean C-N dis tance i s 1.33AA and the mean C-C dis tance i s 1.378A. Figure 5 . A A Schematic Representation of the Polymer Chain i n C u ( p y z ) 2 ( C F 3 S 0 3 ) M = C u ( l ) , L = terminal p y r a z i n e , L ' = b r i d g i n g p y r a z i n e , X = C F 3 S 0 3 _ 102 The t r i f l a t e anion i n C u ( p y z ) 2 ( C F 3 S 0 3 ) adopts a staggered-ethane c o n f i g u r a t i o n about the S-C bond. Repulsions between oxygen atoms are apparently greater than those between oxygen atoms and the t r i f l u o r o m e t h y l group; consequently, the O-S-0 angles are greater than, while the C-S-0 angles are l e s s than, the t e t r a h e d r a l angle of 1 0 9 . 5 ° . As expected, the S-0 bond i n v o l v i n g the oxygen coordinated to the copper i s longer than the terminal S-0 bonds. The inequivalence of the terminal S-0 bonds may be a consequence of hydrogen bond i n t e r a c t i o n s between H(6) and 0(3) . In ternal bonding parameters for the t r i f l a t e anion i n the compound are s i m i l a r to those observed i n other t r i f l a t e complexes. The mean bond dis tances and bond angles i n C F 3 S 0 3 " from the present work and those from some previous s tudies are presented i n Table 5 .2 . I t can be seen that the mode of anion c o o r d i n a t i o n does not g r e a t l y a f f e c t these parameters. 5 .3.2 V i b r a t i o n a l Spectroscopy 5 .3 .2 .1 Infrared Spect ra l Results f o r C u ( p y z ) 2 ( C F 3 S 0 3 ) The i n f r a r e d spectrum of C u ( p y z ) 2 ( C F 3 S 0 3 ) i s shown i n Figure 5 .5 . Absorpt ion bands due to the pyrazine l i g a n d are presented i n Appendix I I , whereas those p e r t a i n i n g to the t r i f l a t e anion are l i s t e d i n Appendix IV, par t B. The assignments were made by comparison of the i n f r a r e d spectrum of 4 35 the t i t l e compound with those of the n e u t r a l l i g a n d ' and r e l a t e d complexes 27 74 s tudied here and elsewhere. ' Pure l i q u i d pyrazine has a strong band at 804 cm" 1 and a medium one at 417 c m " 1 . Four corresponding bands were observed i n the spectrum of b i s -(pyrazine)copper(I) t r i f l a t e . T h i s apparent doubling of fundamentals i s Table 5.2 Internal Bonding Parameters f o r the T r i f l a t e Anion Anion coordinat ion mode Monodentate Monodentate Bidentate Ionic Mean bond angles (deg) O-S-0 114.7 114.8 114.8 115.2 F-C-S 111.5 109.5 111.8 111.6 C-S-0 103.6 103.4 103.4 103.0 F - C - F 107.4 109.2 107.1 107.2 Bond distances (A) C-F 1.311 1.318 1.33 1.34 S-0 (bridging) 1.440 1.439 1.441 -S-0 (terminal) 1.427 1.425 1.422 1.430 S-C 1.806 1.832 1.80 1.816 Reference This work 27 76 77 104 consis tent wi th the presence of two d i f f e r e n t types of pyrazine l igands i n t h i s compound. Monodentate t r i f l a t e anion c o o r d i n a t i o n r e s u l t s i n a symmetry lower than C ^ v around the sulphur atom (see Sec t ion 3 . 3 . 2 . 1 ) . Consequently, the doubly degenerate S0 3 antisymmetric s t r e t c h i n g (\>4) and deformation (\>5) modes are expected to s p l i t . Although no s p l i t t i n g i s observed i n the l a t t e r , the former i s s p l i t by 32 c m " 1 . T h i s magnitude of s p l i t t i n g i s to be compared with the value of 43 c m - 1 observed i n C u ( p y ) k ( C F 3 S 0 3 ) 2 which i s a l s o known to 27 contain monodentate t r i f l a t e anions . Thus the i n f r a r e d spectrum of C u ( p y z ) 2 ( C F 3 S 0 3 ) i s consis tent with i t s s t r u c t u r e . F i g . 5.5 Infrared Spectrum of C u ( p y z ) 2 ( C F 3 S 0 3 ) I I I l 1 I I I I I I I I. l 105 5 .3 .2 .2 Raman Spect ra l Results Presumably because of the intense colour of most of the compounds i n v e s t i g a t e d i n t h i s work, the q u a l i t y of the Raman spectra were ra ther poor (low s i g n a l to noise r a t i o ) . Hence o n l y a few of the more intense Raman a c t i v e l i n e s were observed and these are l i s t e d i n Appendix X. A 5 G o l d s t e i n et a l . ' have demonstrated how, by invoking the mutual e x c l u s i o n p r i n c i p l e , the mode of pyrazine c o o r d i n a t i o n may be determined from i n f r a r e d and Raman s p e c t r a . However, i t should be p o s s i b l e to d i s t i n g u i s h between the two c o o r d i n a t i o n modes from i n f r a r e d spectra a lone . A bidentate b r i d g i n g pyrazine l i g a n d r e t a i n s the symmetry of the uncoordinated p y r a z i n e . A monodentate pyrazine l i g a n d , on the other hand, has a lower symmetry, C 2 V > and some p r e v i o u s l y forbidden v i b r a t i o n a l bands become a c t i v e i n the i n f r a r e d spectrum of the complex. Of p o t e n t i a l d i a g n o s t i c value are the bands e x h i b i t e d at 919 and 1232 c m - 1 i n the Raman spectrum of f ree 4 p y r a z i n e . We have observed that only i n f r a r e d spectra of complexes containing monodentate pyrazine groups e x h i b i t bands i n these r e g i o n s . Examples are given i n Table 5 .3 . We propose that the presence of these bands i s c h a r a c t e r i s t i c of monodentate p y r a z i n e . However, the absence of these bands does not n e c e s s a r i l y e l i m i n a t e the presence of monodentate pyrazine 4 groups. For instance S n ( p y z ) J B r l i and C u ( p y z ) a ( C F 3 S 0 3 ) show no i n f r a r e d absorpt ion around 920 c m - 1 though they both contain monodentate p y r a z i n e . In the present work, the u t i l i t y of the 1232 c m - 1 band was l i m i t e d because other groups i n the complexes absorb s t r o n g l y i n t h i s r e g i o n . However, i n the spectrum of C u ( p y z ) a ( C F 3 S 0 3 ) where the antisymmetric S0 3 s t r e t c h i n g mode of the t r i f l a t e anion occurs at a r e l a t i v e l y higher frequency 106 than i n other sulfonate complexes, a band of medium i n t e n s i t y i s observed at 1228 c m " 1 . There i s no reason to b e l i e v e that the band i s not a c t i v a t e d i n the spectra of the other sulfonate complexes containing monodentate pyrazine groups. Table 5.3 A c t i v a t e d Infrared Absorptions Around 919 and 1232 cm" 1 Compound Bands Reference S n ( p y z ) a C l 4 900w, 1230m 4 Sn(pyz) 2 Br l i - , 1220w 4 F e ( p y z ) 4 ( A s F 6 ) a 910w, 1235w 20 C u ( p y z ) A ( A s F 6 ) 2 920vw,1238w 78 C u ( p y z ) , ( P F 6 ) 2 920m, 1236m 78 C u ( p y z ) 4 ( C F 3 S 0 3 ) 2 911w, a This work C u ( p y z ) 3 ( N 0 3 ) 2 929vw,1233m This work C u ( p y z ) 2 ( C F 3 S 0 3 ) 1228m T h i s work N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 » C H 3 O H 918w, a T h i s work 1) A l l values are i n c m " 1 . a) Obscured by anion a b s o r p t i o n . 107 CHAPTER 6 CONCLUSIONS AND SUGGESTIONS FOR FURTHER STUDY Various experimental techniques were used to charac ter ize a number of copper and n i c k e l c o o r d i n a t i o n compounds i n t h i s s tudy. T h i s chapter discusses some conclusions to be made from t h i s work and the d i r e c t i o n s which fur ther research may take. 6.1 CONCLUSIONS The metal complexes i n v e s t i g a t e d here may be d i v i d e d i n t o four groups based upon t h e i r magnetic p r o p e r t i e s (Table 6 .1) . Group 1 A l l the copper complexes i n t h i s group e x h i b i t temperature-independent magnetic moments over the range 82-A.2K. Magnetic moments of the n i c k e l complexes show some temperature dependence below approximately 25K, but t h i s has been s a t i s f a c t o r i l y accounted f o r by invoking 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 . A l l the complexes i n t h i s group are considered magnet ica l ly d i l u t e . S t r u c t u r a l l y , a l l these complexes, except Ni(pyz) (p-CH 3C 6H l (S03) 2 , were c h a r a c t e r i z e d as being molecular (Structure 1, F i g . 1.3) and containing no b r i d g i n g groups hence t h e i r magnetic p r o p e r t i e s a r e , i n f a c t , as expected. The presence of Ni(pyz) (p-CHjCgH^SOj) 2 i n t h i s group i s somewhat s u r p r i s i n g s ince i t contains b r i d g i n g pyrazine u n i t s which may be expected to lead to 108 Table 6.1 C l a s s i f i c a t i o n of Complexes Group 1: MAGNETICALLY DILUTE C u ( p y z ) , ( C F 3 S O 3 ) a N i ( 2 - m e p y z ) , ( N 0 3 ) a » H a 0 C u ( 2 - m e p y z ) 4 ( C F 3 S 0 3 ) a N i ( p y ) 4 ( C H 3 S 0 3 ) a Cu(2-mepyz), (N0 3) a Ni(py) 4 ( p - C H , C 6 H , S 0 , ) a N i ( p y z ) ( p - C H , C 6 H , S 0 3 ) a Group 2: MAGNETICALLY CONCENTRATED C u ( p y z ) ( C H 3 S 0 3 ) a C u ( p y z ) 3 ( N 0 3 ) a C u ( p y z ) ( p - C H 3 C 6 H 4 S 0 3 ) a C u ( p y z ) ( N 0 3 ) a Cu(2-mepyz) (CF 3 S0 3 ) a Cu(2-mepyz)(N0 3 ) a N i ( p y z ) a ( N 0 3 ) a Group 3: MAGNETIC PROPERTIES INTERMEDIATE BETWEEN GROUPS 1 and 2 N i ( p y z ) 3 ( C H 3 S O 3 ) a ' C H 3 O H Ni(2-mepyz)(NO,) a Group A: DIAMAGNETIC C u ( p y z ) a ( C F , S O , ) 109 magnetic concentrat ion at low temperatures. Nine other d i v a l e n t copper and n i c k e l compounds were s tudied and a l l s t r u c t u r a l l y c h a r a c t e r i z e d as having b r i d g i n g pyrazine and a l l e x h i b i t at l e a s t some evidence f o r magnetic exchange. Group 2 A l l the complexes i n t h i s group e x h i b i t strong temperature-dependent magnetic moments. Each, a l s o , shows a maximum i n i t s s u s c e p t i b i l i t y data . These magnetic p r o p e r t i e s o f f e r conclus ive evidence f o r magnetic concentrat ion of an ant i ferromagnetic nature . A n a l y s i s of the magnetic s u s c e p t i b i l i t y data for N i ( p y z ) 2 ( N 0 3 ) 2 by three d i f f e r e n t chain models and L i n e s ' two-dimensional model d i d not y i e l d good f i t s between experiment and theory . The omission of 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 i n the models may p a r t i a l l y account f o r t h i s . I t i s a l so conceivable that the two p o s s i b l e pathways f o r magnetic exchange i n t h i s compound are i n e q u i v a l e n t , r e s u l t i n g i n s p i n i n t e r a c t i o n s which are ne i ther one- nor two-dimensional i n nature . The magnetic s u s c e p t i b i l i t y data f o r C u ( p y z ) ( N 0 3 ) 2 , Cu(2-mepyz)(N0 3 ) 2 and C u ( p y z ) 3 ( N 0 3 ) 2 were s u c c e s s f u l l y modelled according to a one-dimensional Heisenberg model. This i s consis tent wi th t h e i r chain s t ruc tures (known f o r C u ( p y z ) ( N 0 3 ) 2 and proposed f o r the other two). The s u s c e p t i b i l i t y data f o r the copper(II) sul fonate complexes i n t h i s group were analyzed by both one-and two-dimensional Heisenberg models. Only the former could account f o r the magnetic p r o p e r t i e s of Cu(2-mepyz) (CF 3 S0 3 ) 2 w e l l . The magnetic p r o p e r t i e s of C u ( p y z ) ( p - C H 3 C 6 H 4 S 0 3 ) 2 were descr ibed s a t i s f a c t o r i l y by both models, but wi th the one-dimensional model g i v i n g s l i g h t l y be t te r r e s u l t s . In c o n t r a s t , 110 ne i ther model could reproduce the s u s c e p t i b i l i t y data f o r C u ( p y z ) ( C H 3 S 0 3 ) 2 s a t i s f a c t o r i l y . These three complexes were c h a r a c t e r i z e d as having sheet s t ruc tures i n which both sulfonate anions and n e u t r a l l igands p a r t i c i p a t e i n b r i d g i n g . It i s concluded that the pyrazine and 2-methylpyrazine groups i n C u ( p y z ) ( p - C H j C g H ^ S O j ) 2 and Cu(2-mepyz) (CF 3 S0 3 ) 2 r e s p e c t i v e l y are more e f f i c i e n t agents f o r the propagation of the magnetic exchange, than the sulfonate b r i d g e s , i n these compounds and dominate the exchange. The i n a b i l i t y of e i t h e r model to account f o r the magnetic p r o p e r t i e s of C u ( p y z ) ( C H 3 S 0 3 ) 2 may be a t t r i b u t e d to e i t h e r long-range magnetic order ing e f f e c t s , or to both pyrazine and sulfonate groups t r a n s m i t t i n g some magnetic exchange, but to d i f f e r e n t extents . It i s noteworthy that the magnetic exchange coupling constants , J , f o r a l l the copper complexes i n t h i s group f a l l w i t h i n the narrow range of 3 .2-4.8 c m " 1 , regardless of the b r i d g i n g network present . T h i s suggest that even where sulfonate bridges are present , most of the magnetic exchange i s propagated v i a pyrazine or 2-methylpyrazine. These r e s u l t s a l so i n d i c a t e that pyrazine and 2-methylpyrazine are equal i n t h e i r a b i l i t i e s to f a c i l i t a t e exchange, whereas one might have thought that s t e r i c i n t e r a c t i o n s i n v o l v i n g the methyl group might a f f e c t r i n g canting i n the l a t t e r l i g a n d and hence the magnitude of the exchange. Group 3 The temperature dependence of the magnetic moments of these two complexes i s greater than that observed f o r the n i c k e l ( I I ) complexes i n group 1. Although they show no maxima i n t h e i r s u s c e p t i b i l i t y versus I l l temperature p l o t s , the s u s c e p t i b i l i t y a t t a i n s a constant value at very low temperatures, thereby suggesting the presence of very weak ant iferromagnetic c o u p l i n g . The s u s c e p t i b i l i t y of both compounds were modelled reasonably w e l l according to the I s i n g , FisheT and Weng chain models. The f a c t that the magnetic p r o p e r t i e s of these complexes are descr ibed e q u a l l y w e l l by models of d i f f e r e n t s p i n - d i m e n s i o n a l i t i e s may be a consequence of the very weak nature of the magnetic exchange i n these complexes. Group A No magnetic s u s c e p t i b i l i t y measurements were made f o r C u ( p y z ) 2 ( C F 3 S 0 3 ) but , being a copper(I) complex, i t i s expected to be diamagnetic . These r e s u l t s show that p y r a z i n e and 2-methylpyrazine are e f f i c i e n t l igands f o r propagating magnetic exchange between copper centres . The same, however, does not seem to always h o l d true wi th regard to n i c k e l centres . I t has been observed that e f f e c t i v e overlap between metal d o r b i t a l s and the pyrazine TT system i s c r i t i c a l i n the superexchange mechanism. Thus d i f f e r e n c e s i n o r i e n t a t i o n of b r i d g i n g pyrazine l igands may account f o r the d i f f e r e n t magnetic p r o p e r t i e s of the n i c k e l ( I I ) complexes. S i n g l e - c r y s t a l X - r a y s t r u c t u r a l s tudies would be i n v a l u a b l e i n t h i s regard . 6.2 SUGGESTIONS FOR FURTHER WORK The r e s u l t s of magnetic s t u d i e s on N i ( p y z ) 2 ( N 0 3 ) 2 have demonstrated that pyrazine i s capable of t r a n s m i t t i n g magnetic exchange between n i c k e l 112 centres . I t would, t h e r e f o r e , be i n t e r e s t i n g to r e - i n v e s t i g a t e the magnetic p r o p e r t i e s of N i ( p y z ) 2 X j (X = C I , Br , I) complexes. These compounds were concluded to be magnet ica l ly d i l u t e on the b a s i s of h i g h temperature (90-330K) magnetic s u s c e p t i b i l i t y measurements,"* C r i t e r i a f o r d i s t i n g u i s h i n g between mono- and bidentate pyrazine and 2-methylpyrazine groups from i n f r a r e d spectra have been proposed i n the present s tudy. More complexes should be i n v e s t i g a t e d to see i f the trends observed here are genera l . In t h i s respec t , i t would be more u s e f u l to s e l e c t anions , l i k e h a l i d e s , whose absorptions do not occur i n the same region as those of the n e u t r a l l i g a n d s . S i n g l e - c r y s t a l s t r u c t u r a l s tudies remain an important goal i n t h i s area . Such s tudies would lead to be t te r magneto-structural c o r r e l a t i o n s and would a lso confirm the v a l i d i t y , or otherwise , of the var ious c r i t e r i a , based on spectroscopic evidence, that have been developed f o r determining the d e n t i c i t y of var ious l igands and anions . 113 REFERENCES 1. Lever , A . B . P . ; Lewis, J ; Nyholra, R . S . , Nature, 1961, 189, 58. 2. Lever , A . B . P . ; Lewis, J . ; Nyholm, R . S . , J . Chem. S o c , 1962, 1235. 3. Lever , A . B . P . ; Lewis, J . ; Nyholra, R . S . , J . Chem. S o c , 1963, 5042. 4. G o l d s t e i n , M . ; Unsworth, W . D . , Spectrochim. A c t a , 1971, 27A, 1055. 5. G o l d s t e i n , M. ; T a y l o r , F . B . ; Unsworth, W.D. , J . Chem. S o c , Dal ton T r a n s . , 1972, 418. 6. Carreck, P .W. ; G o l d s t e i n , M . ; M c P a r t l i n , E . M . ; Unsworth, W . D . , Chem. Comm., 1971, 1634. 7. D a r r i e t , J . ; Haddad, M . S . ; Duesler , E . N . ; Hendrickson, D . N . , Inorg. Chem., 1979, 18, 2679. 8. Haynes, J . S . ; R e t t i g , S . J . ; Sams, J . R . ; Thompson, R . C ; T r o t t e r , J . , Can. J . Chem., 1987, 65, 420. 9. Vranka, R . G . ; Amma, E . L . , Inorg . Chem., 1966, 5, 1020. 10. Santoro, A . ; M i g h e l l , A . D . ; Reiraann, C . W . , Acta C r y s t a l l o g r . , 1970, B26, 979. 11. B e l f o r d , R . C . E . ; Fenton, D . E . ; T r u t e r , M . R . , J . Chem. S o c , Dalton T r a n s . , 1974, 17. 12. Inman, G.W. ; H a t f i e l d , W . E . , Inorg. Chem., 1972, 11, 3085. 13. Inoue, M . ; Kubo, M . , Coord. Chem. R e v . , 1976, 21, 1. 14. V i l l a , J . F . ; H a t f i e l d , W . E . , J . Am. Chem. S o c , 1971, 93, 4081. 15. Richardson, H .W. ; H a t f i e l d , W . E . , J . Am. Chem. S o c , 1976, 98, 835. 16. Haddad, M . S . ; Hendrickson, D . N . ; Cannady, J . P . ; Drago, R . S . ; B i e k s z a , D . S . , J . Am. Chem. S o c , 1979, 101, 898. 17. Kokoszka, G . F . ; Reimann, C . W . , J . Inorg. N u c l . Chem., 1970, 32, 3229. 18. Richardson, H . W . ; Wasson, J . R . ; H a t f i e l d , W . E . , Inorg. Chem., 1977, 16, 484. 114 19. Haynes, J . S . ; Sams, J . R . ; Thompson, R . C . , Inorg. Chem., 1986, 25, 3740. 20. Haynes, J . S . , Ph .D. T h e s i s , U n i v e r s i t y of B r i t i s h Columbia, 1985. 21. S h r i v e r , D . F . , "The Manipula t ion of A i r - S e n s i t i v e Compounds", M c G r a w - H i l l : New York, 1969. 22. K e t t l e , S . F . A . , " C o o r d i n a t i o n Compounds", (Studies i n Modern Chemistry, T . C . Waddington, e d . ) , T . Nelson ans Sons L t d . : London, 1969, 33. 23. Haynes, J . S . ; O l i v e r , K . W . ; R e t t i g , S . J . ; Thompson, R . C ; T r o t t e r , J . , Can. J . Chem., 1984, 62, 891. 24. Sparks, L . L . ; Powell , R . L . , J . Res. N a t l . Bur. Standards, 1972, 76A, 263. 25. Brown, D . B . ; Crawford, V . H . ; H a l l , J . W . ; H a t f i e l d , W . E . , J . Phys. Chem., 1977, 81, 1303. 26. a) Mabbs, F . E . ; Machin, D . J . , "Magnetism and T r a n s i t i o n - M e t a l Complexes", Chapman and H a l l : London, 1973. b) K o n i g , E . , " L a n d o l t - B o r n s t e i n Numerical Data and Fundamental R e l a t i o n s h i p s i n Science and Technology, New Series I I / 2 , Hellwege, K . H . ; Hellwege, A . M . , E d s . , S p r i n g e r - V e r l a g : B e r l i n , 1966. 27. Haynes, J . S . ; R e t t i g , S . J . ; Sams, J . R . ; T r o t t e r , J . ; Thompson, R . C , Inorg. Chem., 1988, 27, 1237. 28. A l l e y n e , C . S . ; Thompson, R . C , Can. J . Chem., 1974, 52, 3218. 29. Boyd, P . D . W . ; M i t r a , S . , Inorg. Chem., 1980, 19, 3547. 30. Losee, D . B . ; Richardson, H .W. ; H a t f i e l d , W . E . , J . Chem. P h y s . , 1973, 59, 3600. 31. A r d u i n i , A . L . ; Garnet t , M. ; Thompson, R . C ; Wong, T . C . T . , Can. J . Chem., 1975, 53, 3812. 31a. Burger, H . ; Burczyk, K . ; B l a s c h e t t e , A . , Monat. fur Chem. 1970, 101, 102. 32. D o r r i t y , I . A . ; O r r e l l , K . G . , J . Inorg . N u c l . Chem., 1974, 36, 230. 33. C l a r k , R . J . H . ; W i l l i a m s , C . S . , Inorg . Chem., 1965, 4, 350. 34. Schomaker, V . ; P a u l i n g , L . , J . Am. Chem. S o c , 1939, 61, 1769. 35. L o r d , R . C ; Marston, A . L . ; M i l l e r , F . A . , Spectrochim. A c t a , 1957, 9, 113. 115 36. A l l e y n e , C . S . ; M a i l e r , K . O . ; Thompson, R . C , Can. J . Chem., 1974, 52, 336. 37. Mizushima, S . ; Quagliano, J . V . , J . Am. Chem. S o c , 1953, 75, 4870. 38. C u r t i s , N . F . ; C u r t i s , Y , M . , Inorg. Chem., 1965, 4, 804. 39. James, D . W . ; Kimber, G . M . , Aust . J . Chem., 1969, 22, 2287. 40. Lever , A . B . P . ; Mantovani, E . ; Ramaswamy, B . S . , Can. J . Chem., 1971, 49, 1957. 41. Cot ton, F . A . ; W i l k i n s o n , G . , "Advanced Inorganic Chemistry" , 4th Edn. I n t e r s c i e n c e : New York, 1980 . 42. Lawrance, C A . , Chem. R e v . , 1986, 86, 17. 43. Hathaway, B . J . ; B i l l i n g , D . E . ; N i c h o l l s , P . ; P r o c t e r , I . M . , J . Chem. Soc. (A) , 1969, 319. 44. Tomlinson, A . A . G . ; Hathaway, B . J . ; B i l l i n g , D . E . ; N i c h o l s , P . , J . Chem. Soc. (A), 1969, 65. 45. Lever , A . B . P . ; Mantovani, E . , Inorg . Chem., 1971, 10, 817. 46. M a y f i e l d , H . G . ; B u l l , W . E . , J . Chem. Soc. (A) , 1971, 2279. 47. H a l l , J . W . , Ph.D. T h e s i s , U n i v e r s i t y of North C a r o l i n a , 1977. 48. E s t e s , W.E. ; H a t f i e l d , W . E . ; Van O o i j e n , J . A . C ; Reedi jk , J . , J . Chem. S o c , Dalton Trans . , 1980, 2121. 49. Bonner, J . C ; F i s h e r , M . E . , Phys. R e v . , 1964, 135, A640. 50. L i n e s , M . E . , J . Phys. Chem. S o l i d s , 1970, 31, 101. 51. Haynes, J . S . , M . S c T h e s i s , U n i v e r s i t y of B r i t i s h Columbia, 1980 . 52. G i l l , N . S . ; N u t t a l l , R . H . ; S c a i f e , D . E . ; Sharp, D . W . A . , J . Inorg, N u c l . Chem., 1961, 18, 79. 53. Frank, C . W . ; Rogers, L . B . , Inorg . Chem. 1966, 5, 615. 54. Haynes, J . S . ; R e t t i g , S . J . ; Sams, J . R . ; Thompson, R . C ; T r o t t e r , J . , Can. J . Chem. 1986, 64, 429. 55. Rowley, D . A . ; Drago, R . S . , Inorg. Chem. 1967, 6, 1092. 56. Baker, W . A . ; P h i l l i p s , M . G . , Inorg. Chem., 1966, 5, 1042. 116 57. P i p e r , T . S . ; C a r l i n , R . L . , J . Chem. Phys. 1960, 33, 1208. 58. Wentworth, R . A . D . ; P i p e r , T . S . , Inorg. Chem., 1965, 4, 709. 59. Antsyshkina , A . S . ; P o r a i - K o s h i t s , M . A . , Soviet P h y s i c s , C r y s t a l l o g r a p h y , 1958, 3, 684. 60. See reference 55 and references t h e r e i n . 61. A l l e y n e , C . S . , M.Sc . T h e s i s , U n i v e r s i t y of B r i t i s h Columbia, 1973. 62. Lever , A . B . P . , " Inorganic E l e c t r o n i c Spectroscopy" , E l s e v i e r : Amsterdam, 1968, 409. 63. F i g g i s , B . N . , " I n t r o d u c t i o n to Ligand F i e l d s " , I n t e r s c i e n c e : New York, 1966. 64. Lever , A . B . P . , Coord. Chem. R e v . , 1968, 3, 119. 65. Sacconi , L . , T r a n s i t i o n Met. Chem., 1968, 4, 199. 66. O'Connor, C . J . i n "Progress i n Inorganic Chemistry" , L i p p a r d , S . J . ( e d . ) , 1982, 29, 203. 67. S u z u k i , M . ; Tsujiyama, B . ; Katsura , S . , J . Math. P h y s . , 1967, 8, 124. 68. Wagner, G . R . ; F r i e d b e r g , S . A . , Phys. L e t t . , 1964, 9 , 11. 69. F i s h e r , M . E . , Am. J . P h y s . , 1964, 32, 343. 70. Rushbrooke, G . S . ; Wood, P . J . , M o l . P h y s . , 1958, 1, 257. 71. Weng, C . H . , Ph .D. T h e s i s , Carnegie-Mellon U n i v e r s i t y , 1968. 72. H i l l e r , W.; S t r a h l e , J . ; Datz , A . ; Hanack, M . ; H a t f i e l d , W . E . ; Haar, L . W . ; G i i t l i c h , P . , J . Am. Chem. S o c , 1984, 106, 329. 73. Kaim, W., Angew. Chem. I n t . E d . E n g l . , 1983, 22, 171. 74. Lever , A . B . P . ; Lewis, J . ; Nyholm, R . S . , J . Chem. S o c , 1963, 3156. 75. Wheatley, P . J . , Acta C r y s t a l l o g r . , 1957, 10, 182. 76. Dedert , P . L . ; S o r r e l l , T . ; Marks, T . J . ; Ibers , J . A . , Inorg. Chem., 1982, 2JL, 3506. 77. Peng, S . M . ; Ibers , J . A . ; M i l l a r , M . ; Holm, R . H . , J . Am. Chem. S o c , 1976, 98, 8037. 117 78. Thompson, R . C . , Unpublished data . 79. Wilmshurst , J . K . ; B e r n s t e i n , H . J . , Can. J . Chem., 1957, 35, 1183. 80. K l i n e , C . H . ; T u r k e v i c h , J . , J . Chem. P h y s . , 1944, 12, 300. 81. Herzberg, G . , " I n f r a r e d and Raman Spectra of Polyatomic M o l e c u l e s " , D. Van Nostrand Company I n c . , New York, 1945, 178. Appendix I. Vibrational Assigrments for Pyridine and i ts Complexes Pyridine 3083s 3054s 3036s 1583s 1572s 1482s 1439s 1218s 1148w 1068m 1030s 992s 749 700 652m 605s 405s Assigrroant 20b 2 20a 8a 8b 19a 19b 9a 15 18a 12 1 4 11 6b 6a 16b NKpy^CCHjSOj), 3100w 3070w 3040w 1603s 1572w 1489m 1449s 1225m a 1071m a 1014m a 707S 655w 635s 437m NiCpy^Cp-OIjC^SOj), 1605s 1574m 149Qn 1448s 1223s 1149s 1070s a 1009s 759s 699s 655m 636s 437m 1585w 766w 707s 1) AssigrnEnts are based on the work of Wilmshurst and Bernstein vising the notation of Kline and Turkevich . 2) A l l values are i n cm - 1 . a) Obscured by anion absorption. 119 Appendix I I . V i b r a t i o n a l Assignments for P y r a z i n e 1 and i t s Complexes 2 Pyrazine 2973w 3066w 1418vs 1490s 1110m 1125w 1148vs 1178m 1006w 1022m 1032vw 1048vw 1067vs 926vw 804vs 823vw 417m 597w C u ( p y z ) ( C H 3 S 0 3 ) 2 3045w 3091w 3115w 1423s 1437s 1120sh a a 1077s 1097m 963vw 982vw 825s 835m 497s C u ( p y z ) ( p - C H 3 C 6 H l i S 0 3 ) 2 3120w 1429m 1492w 1122s a 1010s 1077m 1097m 954vw 819s 43 2w 502m N i ( p y z ) ( p - C H 3 C 6 H , S 0 3 ) 2 3058w 3128vw 1430m,sp 1496w 1125s 1162s 1014s 1067m 1092w 812s 460w 494s C u ( p y z ) ( N 0 3 ) 2 3028w 3060w 3110V 3132w 1428s 1108m 1123s 1164s 1082s 816w 824s 504s C u ( p y z ) 2 ( C F 3 S 0 3 ) 3092w 1417s 1435s 1112m 1156s 1051m 1064vw 1085w 811w 823sh 831m 452m 472m N i ( p y z ) 2 ( N 0 3 ) 2 3050vw 3100w 1424s H O l w 1123s 1157s 1066s a 491s C u ( p y z ) 3 ( N 0 3 ) 2 3022w 3062m 3083w 3097w 3135w 1428s 1127s,sp 1155m 1169m 1076s 1084s 1098w 929vw 1098w 822s 828s 466s 498s N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 » C H 3 O H 3052w 3110w 3130w 1420s 1102n 1119n 1127m a 1006w a 1084m 918w 815s 837m 458s 496m C u ( p y z ) , ( C F 3 S 0 3 ) 2 3038w 3059w 3098w 1418s 1125s 1141s 1057s 1084m 911w 978vw 992vw 809vs 421vw 464s ,s] 1) From reference 35. 2) A l l values i n c m " 1 . a) Obscured by anion 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 2-Methylpyrazine and i t s Complexes 2-Methylpyrazine 2920w 1527w 1402s 1306s 1252m 1156s 1021s 9,79w 831s 641w 358w 2995w 1581m 1457m 1176m 1058s 752m 410s 3045w 1478s . 472w Cu(2-mepyz)(CF 3 S0 3 ) 2 3079vw 3147w 1533w 1411w a a a a 1107m 835s a 466m a Cu(2-mepyz)(N0 3 ) 2 3048vw 2098vw a 1407w 1317s a 1164s 1184sh 1058s 1097s 840s a 444m 530s Ni(2-mepyz)(N0 3 ) 3069vw 3090vw 3115vw 1609w 1623w 1405w 1317s a 1164s 1185sh 1058s 1092s 841s a 444s 524s C u ( 2 - m e p y z ) 4 ( C F 3 S 0 3 ) 2 3098vw 1525m 1600m 140 lw a a 1161s 1189sh a 1080s 922w 983w 841s a 431s 505m Cu(2-raepyz) t (N0 3 ) 2 3028v 3067w 1513w 1601m a a 1256w 1167m 1179m 1041m 1085m 99 lw 849m 863w a 426m 508m N i ( 2 - m e p y z ) 4 ( N 0 3 ) 2 » H 2 0 1527w 1601w a a 1252w 1163s 1046s 1077s 987w 847s 857m a 432m 502m 1) This work. 2) A l l values are i n c m " 1 . a) Obscured by anion absorpt ion . i o Appendix IV. V i b r a t i o n a l Assignments for Sulfonate Anions and Unassigned Bands Part A. Compounds containing the C H 3 S 0 3 " anion Compound Anion v i b r a t i o n s ( C 3 v symmetry) (E) (A,) (A,) v 3 ( A j ) and v 5 ( E ) \)6 and unassigned v i b r a t i o n s C u ( p y z ) ( C H 3 S 0 3 ) , 1140], 1163)' 1251s 1028s 1 0 5 1 b £ 775s 787s 530s 555s 566s 1322vw 1340w 310m 350w 360w 398w N i ( p y z ) j ( C H 3 S 0 j ) 2 • C H 3 0 H 1168s 1245s 1031m 1057bs 778s 527s 542m 559s 3465S,br 1322vw 755w 1340w 376w Ni(py),(CH 3S03), 1170s 1250s 1051s,sp 772s,sp 524m 539m 558s 1330w,br 363w 1) Assignments made according to reference 8. 2) A l l values are i n c m " 1 . b) May be n e u t r a l l igand band. Appendix IV. Continued Part B. Compounds containing the C F 3 S 0 3 - anion Compound Anion v i b r a t i o n s ( C ^ symmetry) \>6 and unassigned v i b r a t i o n s ( E ) (A,) U 2 (A,) \ ) 3 (A a ) and M E ) Cu(2-mepyz)(CF 3 S0 3 ) 2 Cu(2-mepyz) k (CF 3 S0 3 ) 2 Cu(pyz) i > (CF 3 S0 3 ) C u ( p y z ) 2 ( C F 3 S 0 3 ) 1186 1210 1237 1312s 1224Y 1302s iHlS 1247s 1279s 1038s 1029s 1031s 1027s 769w 760m 716m 760w 520bm 528m 642s 525m 638s 525s 637s 526s 641s 1598w 1222bm 1228bm 745w 744m 701w 751w 774w 584w 597w 580w 584m 584m 375w 357w Part C. Compounds containing the p - C H 3 C 6 H 4 S 0 3 " anion Compound Anion ( E ) v i b r a t i o n s ( A X ) <C3v 3 ^ 2 ( A , ) ymmetry) \ J 3 ( A X ) and \ J 5 ( E ) V 6 and unass igned v i b r a t ions Cu(pyz) ( p - C H , C 6 H 4 S 0 , ) a 1149s 1035s 687s 563m,sp 1598w 1182w 717w 309w 1260s 589m 1215vw 85 2w N i ( p y z ) ( p - C H 3 C 6 B \ S 0 3 ) 2 1146s 1046s 682s 574s 160.1w 705w 1258s 587sh 1214vw 1290vw 713w 845vw N i ( p y ) 4 ( p - C H 3 C 6 H 4 S 0 3 ) 2 1167s 1032s 682s 558m 1117s 607w 382w 1252s 577s 1290w 800w 817s 857w 40 lw Appendix V . V i b r a t i o n a l Assignments for the N 0 3 " Anion and Unassigned Bands Compound Anion v i b r a t i o n s (D-^ symmetry) Unassigned bands v 3(E') W > MV> M E ') Ionic N 0 3 " 1390 1050 831 720 C u ( p y z ) ( N 0 3 ) 2 1281s,br 1015s 808s 713w 2022w 1721w 345s c 1494s,br 754s 2287w 1885w 774w 2495w 1956w Cu(2-mepyz)(N0 3 ) 2 1287s,br 1012s 805s 712w 2298vw 321m 1502s,br 755m 2496vw 34ys c 413w 740w Ni(2-mepyz) (N0 3 ) 2 1 2 5 7 l s 1019s 804s 758s 2029w 1710w 295m 1276/ 2255w 1777w 341s c 1515s,br 2510w 1945w 407w 744w N i ( p y z ) 2 ( N 0 3 ) 2 1312s,br 1038m 817s 1377w 701vw 1445s,br 825 sh C u ( p y z ) 3 ( N 0 3 ) 2 1298s,br 1040s 816s 754w 2007vw 1749w 1490w 1019w 309w 1402s 2080vw 1957w 1516w 1052s 641vw 2320w 1597w 1233m 700w 2432vw 1360s Cu(2-mepyz)1 ((N03)2 1292s 1029s 826s 744m 1333m 701vw 1401s N i ( 2 - m e p y z ) 4 ( N 0 3 ) 2 » H 2 0 1 2 9 9 A s 1032s 819m 747m 1672v,br 1309RJ 826w 3032w,br 140l b l 1421 J 1) From reference 81. 2) A l l values are i n c m - 1 . b) May be neutra l l igand band. c) \)(M-0). 124 Appendix V I . E l e c t r o n i c S p e c t r a l Results Part A. Copper(II) Complexes from the Present Study Compound Absorpt ion Maxima (cm - 1 ) C u ( p y z ) , ( C F 3 S 0 3 ) 3 16 400 C u ( 2 - m e p y z ) A ( C F 3 S 0 3 ) 2 16 500 Cu(2-mepyz) i i (N0 3 ) 2 17 400 C u ( p y z ) 3 ( N 0 3 ) 2 16 700 C u ( p y z ) ( C H 3 S 0 3 ) 2 13 300 C u ( p y z ) ( p - C H , C « H 4 S 0 s ) a 13 600 Cu(2-mepyz)(CF 3 SO 3 ) 2 13 200 C u ( p y z ) ( N 0 3 ) 2 17 400 (17 900) Cu(2-mepyz)(N0 3 ) 2 17 100 (17 900) The values i n brackets are from reference 15. Part B. Copper(II) Complexes from Previous Studies Compound Absorpt ion Maxima (cm - 1 ) Cu(py) , Cu(py) , Cu(py) , Cu(py) , Cu(py) A Cu(py) , Cu(py) 4 C u t p y ) , C F 3 C 0 2 ) 2 A C H 3 S 0 3 ) 2 2 p - C H 3 C 6 H 4 S 0 3 ) 2 ' F S O , ) , 1 C F 3 S 0 3 ) 2 3 1 * C 1 0 4 ) / ' N O , ) , 1 LPF ) 6 2 C u ( p y z ) A ( C F 3 S 0 3 ) 2 « H 2 0 ' C u ( p y z ) ( C F 3 S 0 3 ) 2 3 15 700 16 800 16 900 17 200 17 400 17 800 18 300 19 100 16 100 13 100 1) 2) 3) From reference 28. From reference 8. From reference 27. 4) From reference 46. * D i f f u s e r e f l e c t a n c e spectrum. Appendix V I . Continued Part C. N i c k e l ( I I ) Compounds-1' Compound lg g 3 I V 3 B 2 g 3 I V B 2g 3 A a  A 2g 3 B 1 „ - 3 E b lg g 3 B lg 3 A b  A 2g c 3 Eg N i ( p y ) 4 ( C H 3 S O , ) , 8 800 11 800 13 500 16 700 27 000 N i ( p y ) i i ( p - C H 3 C 6 H 4 S 0 3 ) 2 8 300 11 800 13 500 16 900 27 400 N i ( p y ) , ( F S 0 3 ) 2 3 8 480 11 800 13 600 16 400 27 200 N i ( p y ) , C l 2 A > * 9 042 11 730 12 12 14 620 804 930 16 818 26 759 N i ( p y ) 4 B r 2 A ' * 8 430 11 490 12 12 14 260 450 080 16 390 26 030 N i ( 2 - m e p y z ) t ( N 0 3 ) 2 « H 2 0 9 100 11 800 - 17 200 27 000 N i ( p y z ) 3 ( C H 3 S 0 3 ) 2 » C H 3 O H 8 800 10 600 - 16 000 27 800 N i ( p y z ) 2 ( N 0 3 ) 2 9 800 11 100 13 200 17 200 27 500 N i ( p y z ) ( p - C H 3 C 6 H , S 0 3 ) 2 8 500 8 900 13 500 14 700 25 500 Ni(2-mepyz)(N0 3 ) 2 7 800 - 11 800, broad 14 300 18 200 24 400 1) Assignments made according to reference 28. 2) A l l absorption maxima are i n c m " 1 . 3) Data from reference 28. 4) Data from reference 55. *) L i q u i d ni t rogen temperature spectrum. 126 Appendix V 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 z ) i i ( C F 3 S 0 3 ) 2 2. Cu(2-- m e p y z ) A ( C F 3 S 0 3 ) 2 3. Cu(2-mepyz) i ( (N0 3 ) 2 T ^m »eff. T *m ^ e f f . T *m ^ e f f . 4.18 101 1.84 4.18 99.9 1.83 4.18 97.3 1.80 6.44 66.3 1.85 5.91 72.4 1.85 6.24 66.5 1.82 8.63 48.3 1.83 7.99 52.1 1.82 8.76 46.9 1.81 11.8 35.6 1.83 11.4 36.4 1.82 11.3 36.0 1.80 16.8 24.7 1.82 16.6 24.8 1.81 16.6 24.5 1.80 21.9 19.0 1.82 21.4 19.2 1.81 21.5 19.3 1.82 26.8 15.4 1.82 26.3 15.8 1.82 26.8 15.5 1.82 31.3 13.0 1.80 30.7 13.4 1.81 31.1 13.2 1.81 40.7 9.97 1.80 40.6 10.0 1.80 40.7 10.3 1.83 48.2 8.36 1.80 47.9 8.53 1.81 48.2 8.71 1.83 60.8 6.67 1.80 54.7 7.51 1.81 55.1 7.77 1.85 65.8 6.06 1.79 60.3 6.86 1.82 60.7 7.12 1.86 70.3 5.70 1.79 65.5 6.30 1.82 65.8 6.56 1.86 74.5 5.35 1.79 70.0 5.75 1.79 70.4 6.18 1.86 82.0 4.84 1.78 74.2 5.38 1.79 74.5 5.92 1.88 81.3 5.00 1.80 81.9 5.41 1.88 1) Temperatures (T) are i n K; molar s u s c e p t i b i l i t i e s ( x m ) are i n 10" 3 cm3 m o l " 1 ; and magnetic moments ( p e f f ) are i n B .M. c a l c u l a t e d according to the express ion : u e f f < = 2 .828f ( X ^-TIP)T where x ^ = m ° l a r s u s c e p t i b i l i t y corrected f o r diamagnetism of a l l atoms and TIP = temperature independent paramagnetism and was taken as 60x10" 6 cm3 m o l " 1 f o r C u 2 + . 127 Appendix V I I . Continued A. C u ( p y z ) 3 ( N 0 3 ) 3 T ^ e f f . 2.30 15.A 0.53 2.70 15.5 0.58 3.20 15.8 0.6A 3.89 16.A 0.71 4. AO 16.6 0.76 A.78 16.9 0.80 5.91 17.7 0.92 6.17 17.9 0.9A 7.67 18.A 1.06 8.A2 18.A 1.12 11.6 17.7 1.28 16.6 15.A 1.A3 21.9 13.A 1.53 27.0 11.6 1.59 31.5 10.5 1.63 AO. 8 8.A8 1.66 A8.2 7.A1 1.69 55.2 6.66 1,71 60.7 6.1A 1.73 65.9 5.75 1.7A 70.A 5.35 1.7A 7A.6 5.07 1.7A 82.1 A.68 1.75 C u ( p y z ) ( N 0 3 ) 2 T *m ^ e f f . 2.20 19. A 0.58 2.50 19.7 0.63 2.98 20.0 0.69 3. A3 20.7 0.75 A.2A 21.5 0.85 A.AO 21.6 0.87 5.3A 22.3 0.98 5.62 22.5 1.01 6.00 22.6 1.0A 6.37 22.6 1.07 7.28 22.A 1.14 7.99 22.3 1.19 11.2 20.3 1.35 16.3 16.8 1.A8 21.5 1A.1 1.56 26.5 12.1 1.60 30.8 10.7 1.62 AO.A 8.A5 1.65 A7.9 7.32 1.67 5A.9 6.59 1.70 60.6 6.06 1.71 65.8 5.68 1.73 70.2 5.30 1.72 7A.A 5.01 1.73 81.8 A.6A 1.7A Cu(2-mepyz)(N0 3 ) 2 T ^ e f f . 2.20 2A.2 0.65 2.AO 24.3 0.68 2.79 2A.7 0.7A 3.5A 25.5 0.85 A.2A 25.8 0.9A A.55 26.1 0.98 5.56 26.A 1.08 5.8A 26.3 1.11 8.15 25.0 1.28 11.2 22.2 1.A1 16.6 17.9 1.5A 21.8 1A.9 1.61 26.8 12.8 1.65 31.A 11.2 1.67 AO.6 9.06 1.72 A7.8 7.90 1.7A 5A.9 7.09 1.76 60. A 6.57 1.78 65.5 6.10 1.79 70.1 5.80 1.80 7A.5 5.50 1.81 81.7 5.03 1.81 128 Appendix V I I . Continued 7. C u ( p y z ) ( C H 3 S O 3 ) , l T ^ e f f . 2.70 20.0 0.66 3.20 24.2 0.79 3.88 27.9 0.93 4.44 31.0 1.05 4.62 30.4 1.06 6.13 31.9 1.25 7.16 31.3 1.34 8.17 30.2 1.41 10.1 27.5 1.49 11.1 25.9 1.52 12.6 23.9 1.55 18.1 18.4 1.63 22.9 15.3 1.67 27.9 12.9 1.70 32.3 11.3 1.71 33.0 11.2 1.72 40.0 9.47 1.74 52.8 7.54 1.78 67.0 5.94 1.78 79.0 5.03 1.78 8. C u ( p y z ) ( p - C H 3 C 6 H A S 0 3 ) a T ^ e f f . 2.40 25.9 0.71 2.60 25.9 0.73 3.20 27.0 0.83 3.98 27.9 0.94 4.07 27.9 0.95 4.40 28.1 0.99 4.85 28.5 1.05 4.93 28.3 1.06 5.56 28.7 1.13 5.70 28.6 1.14 6.30 28.3 1.19 7.80 28.5 1.33 8,70 26.2 1.35 11.6 23.1 1.46 16.8 18.4 1.57 21.7 15.3 1.63 26.6 12.9 1.66 30.7 11.5 1.68 31.1 11.8 1.71 40.4 9.41 1.74 48.0 8.10 1.76 55.0 7.30 1.79 60.6 6.67 1.80 65.7 6.34 1.83 70.2 5.99 1.83 74.3 5.67 1.84 81.8 5.23 1.85 9. Cu(2-mepyz) (CF3SO3) T *m ^ e f f . 2 2.20 19.4 0.58 2.40 19.3 0.61 2.70 19.2 0.64 3.11 19.1 0.69 3.89 19.3 0.78 4.07 19.1 0.79 4.93 19.6 0.88 5.99 19.7 0.97 6.17 20.0 0.99 8.37 19.5 1.14 11.2 18.5 1.29 16.6 15.7 1.44 21.7 13.3 1.52 26.7 11.6 1.57 31.3 19.3 1.61 40.6 8.39 1.65 48.1 7.35 1.68 55.0 6.56 1.70 60.7 6.04 1.71 65.8 5.59 1.71 70.3 5.26 1.72 74.5 4.95 1.72 82.0 4.53 1.72 129 Appendix V I I I . Magnetic S u s c e p t i b i l i t y Results for N i c k e l ( I I ) Complexes 1. N i ( p y ) 4 ( C H , S 0 , ) , 2. N i ( p y ) 4 ( p - C H , C 6 H 4 S 0 , ) 2 3. N i ( 2 - m e p y z ) 4 ( N O , ) 2 » H 2 0 T ^m R e f f . T ^m R e f f . T ^m R e f f . 4.12 180 2.44 4.24 161 2.34 4.24 200 2.60 6.24 152 2.76 6.13 141 2.63 5.77 170 2.80 8.37 124 2.88 8.57 114 2.79 7.67 136 2.88 11.3 97.3 2.97 11.5 88.9 2.86 10.8 103 2.99 16.6 69.1 3.03 17.0 63.1 2.93 16.2 71.4 3.04 21.9 54.0 3.08 21.7 50.1 2.95 21.2 55.4 3.06 26.8 44.6 3.09 26.9 40.6 2.96 31.2 38.1 3.08 31.2 38.3 3.09 31.5 34.5 2.95 40.4 29.3 3.07 40.6 29.7 3.11 40.6 27.2 2.97 47.9 24.9 3.09 47.9 25.3 3.11 48.1 23.1 2.98 54.8 21.9 3.10 54.9 22.4 3.14 55.1 20.4 3.00 60.5 19.9 3.10 60.6 20.5 3.15 60.7 18.4 2.99 65.5 18.4 3.11 65.7 18.9 3.16 65.8 17.0 2.99 70.1 17.2 3.10 70.2 17.7 3.15 70.3 15.8 2.98 74.4 16.1 3.10 74.4 16.7 3.16 74.5 15.0 2.99 81.6 14.7 3.10 81.7 15.3 3.16 81.8 13.7 3.00 1) Temperatures (T) are i n K ; molar s u s c e p t i b i l i t i e s ( x m ) are i n 10" 3 cm3 m o l " 1 ; and magnetic moments ( u e f f ) are i n B .M. c a l c u l a t e d according to the express ion : R e f f . " 2 . 8 2 8 f ( X m - T I P ) T where x^ = molar s u s c e p t i b i l i t y correc ted f o r diamagnetism of a l l atoms and TIP = temperature independent paramagnetism and was taken as 200x10" 6 cm3 mol" f o r N i J + . 130 Appendix V I I I . Continued A. N i ( p y z ) 3 ( C H , S O s ) a « C H , O H 5. N i ( p y z ) 2 ( N 0 3 ) 2 6. N i ( p y z ) ( p - C H 3 C 6 H 4 S 0 3 ) 2 T X T X u T X V* m e f f . m e f f . m e f f . 2.30 13A 1.57 2.30 72.0 1.15 A.2A 175 2.AA 2.50 13A 1.63 2.50 72.2 1.20 5.77 151 2.6A 3.08 13A 1.81 2.88 72.7 1.29 11.2 9A.1 2.90 3.70 13A 1.81 3.08 72.9 1.3A 16.6 67.2 2.99 A.2A 130 2.09 3.A6 72.8 1.A2 21.7 52.8 3.03 A.31 131 2.12 3.81 72.A 1.A9 26.5 A3.7 3. OA 5.19 126 2.28 A.AO 71.6 1.59 31.1 37.6 3.06 5.99 118 2.38 5.00 70.3 1.68 AO.A 29.0 3.06 11.2 83.1 2.73 6.17 66.7 1.81 A7.8 2A.6 3.07 16.6 61.A 2.86 7.35 62.8 1.92 5A.7 21.6 3.07 21.5 A9.3 2.91 7.5A 62.5 1.9A 60.3 19.7 3.08 26.5 AO.9 2.9A 8.83 57.6 2.02 65.5 18.0 3.07 30.9 35.A 2.96 10.0 5A.5 2.09 69.7 16.9 3.07 AO.5 27.5 2.98 11.8 50.2 2.18 7A.2 15.8 3.06 A7.8 23.3 2.99 16.9 AO.5 2.3A 81.8 1A.3 3.06 5A.9 20.6 3.01 21.7 3A.6 2.A5 60. A 18.7 3.00 31.3 26.9 2.60 7. Ni(2--mepyz)(N0 3 ) 2 65. A 17.A 3.02 AO. 8 22.3 2.70 70.1 15.9 2.98 A8.2 19.8 2.76 2.50 138 1.66 7A. 1 15.1 2.99 58.1 17.2 2.83 2.60 138 1.69 81.5 13.8 2.99 65.6 15.6 2.86 3.08 137 1.8A 7A.5 1A.0 2.89 3.88 136 2.05 81.8 12.9 2.91 A.2A 13A 2.13 A.50 132 2.18 5.70 125 2.39 6.13 121 2.AA 8.57 103 2.66 11.3 8A.1 2.76 16.A 62.7 2.87 21.6 A9.8 2.93 26.9 A1.2 2.97 31.1 35.8 2.99 AO. 7 28.0 3.02 A8.1 2A.1 3.05 55.1 21.3 3.07 60.8 19.5 3.08 65.7 18.1 3.08 70.2 17.0 3.09 7A.5 16.1 3.09 81.6 1A.7 3.10 131 Appendix IX. X- ray S t r u c t u r a l Parameters f o r C u ( p y z ) 3 ( C F 3 S 0 3 ) Bond lengths i n v o l v i n g nonhydrogen atoms, with estimated standard d e v i a t i o n s i n the l e a s t s i g n i f i c a n t f i g u r e i n parentheses Bond Length (A) Bond Length (A) Cu -N(3) 1.971(2) N( l ) -C(5 ) 1.335(4) Cu - N ( l ) 1.985(2) N(2)-C(4) 1.322(5) Cu -N(4) 2.027(2) N(2)-C(3) 1.330(4) Cu -0(1) 2.331(2) N(3)-C(7) 1.324(4) S -0(2) 1.422(3) N(3)-C(6) 1.331(4) S -0(3) 1.432(3) N(4)-C(9) 1.325(4) S -0(1) 1.440(2) N(4)-C(8) 1.331(4) S - C ( l ) 1.806(4) C(2)-C(3) 1.361(5) F ( l ) - C ( l ) •1.328(5) C(4)-C(5) 1.368(5) F ( 2 ) - C ( l ) 1.325(5) C(6)-C(7) 1.381(4) F ( 3 ) - C ( l ) 1.279(5) C(8)-C(9) 1.376(4) N( l ) -C(2 ) 1.330(4) Bond lengths i n v o l v i n g hydrogen atoms, with estimated standard d e v i a t i o n s i n the l e a s t s i g n i f i c a n t f i g u r e i n parentheses Bond Length (A) Bond Length (A) C(2)-H(2) C(3)-H(3) C(4)-H(4) C(5)-H(5) 1.05(3) 0.88(4) 0.93(3) 0.96(4) C(6)-H(6) C(7)-H(7) C(8)-H(8) C(9)-H(9) 0.90(3) 0.88(3) 0.85(4) 0.93(3) 132 Bond angles i n v o l v i n g nonhydrogen atoms, with estimated standard devia t ions i n the l e a s t s i g n i f i c a n t f i g u r e i n parentheses Bond Angle (deg) Bond Angle (deg) N(3) - C u - N ( l ) 126.4(1) C(6) -N (3) - C u 124.1(2) N(3) - C u -N (4) 110.6(1) C(9) -N (4) -C(8) 115.6(2) N(3) - C u -0(1) 106.9(1) C(9) -N (4) - C u 121.9(2) N ( l ) - C u -N (4) 114.0(1) C(8) -N (4) - C u 122.4(2) N ( l ) - C u -0(1) 97.9(1) F(3) - C ( l ) -F(2) 107.5(4) N(4) - C u -0(1) 94.4(1) F(3) - C ( l ) - F ( l ) 109.1(4) 0(2) -S -0(3) 114.5(2) F(3) -c ( i ) -S 112.2(3) 0(2) -S -0(1) 114.7(1) F(2] - c ( l ) - F ( l ) 105.5(3) 0(2) -S - C ( l ) 104.3(2) F(2) - C ( l ) -S 111.5(3) 0(3) -S -0(1) 114.8(2) F ( l ) - C ( l ) -S 110.8(3) 0(3) -S - C ( l ) 103.5(2) N ( l ) -C(2) -C(3) 121.6(3) 0(1) -S - C ( l ) 102.9(2) N(2) -C(3) -C(2) 123.3(3) S -0(1) - C u 142.8(1) N(2) -C(4) -C(5) 122.9(3) C(2) - N ( l ) -C(5) 115.8(3) N ( l ) -C(5) -C(4) 121.6(3) C(2) - N ( l ) - C u 123.5(2) N O ; -C(6) -C(7) 121.5(3) C(5) - N ( l ) - C u 120.6(2) N(3) -C(7) -C(6) 122.4(3) C(4) -N(2) -C(3) 114.8(3) N(4I -C(8) -C(9) 122.4(3) C(7) -N(3) -C(6) 116.1(2) N(4) -C(9) -C(8) 122.0(3) C(7) -N(3) - C u 119.5(2) Bond angles i n v o l v i n g hydrogen atoms, wi th estimated standard devia t ions i n the l e a s t s i g n i f i c a n t f i g u r e i n parentheses Bond Angle (deg) Bond Angle (deg) H(2) -C(2) -N(l ) 117(2) H(6)-C(6)-N(3) 117(2) H(2)-C(2)-C(3) 122(2) H(6)-C(6)-C(7) 122(2) H(3)-C(3)-N(2) 114(3) H(7)-C(7)-N(3) 119(2) H(3)-C(3)-C(2) 122(3) H(7)-C(7)-C(6) 119(2) H(4)-C(4)-N(2) 116(2) H(8)-C(8)-N(4) 117(2) H(4)-C(4)-C(5) 121(2) H(8)-C(8)-C(9) 121(2) H(5) -C(5) -N(l ) 121(2) H(9)-C(9)-N(4) 118(2) H(5)-C(5)-C(4) 117(2) H(9)-C(9)-C(8) 120(2) 133 Appendix X. Raman S p e c t r a l Results P y r a z i n e 1 ( l i q u i d ) 1523 1232 1015p 703dp 516 1584p 1118 753 609 919 641 Cu(pyz)(CH 3 S 0 3 ) j 1524w 1530w 1617w 1044s 1059m 774m 788m 549w 67 4w 699m 204w 337w 356w C u ( p y z ) ( p - C H 3 C 6 H , S 0 3 ) 2 1520w 1620w 1216w 1492w 1039s 1051m 1135s 1187w 709w 806s 640m 209w 25 2w 287w 301w N i ( p y z ) ( p - C H 3 C 6 H , S 0 3 ) 2 1531w 1602s 1214w 1037vs 1058s 1133s 1143s 704s 803s 817m 640s 685w 308m Cu(pyz)(NO,) 3 ' 2 1018m 1048s 698m 207w C u ( p y z ) 2 ( C F 3 S 0 3 ) 1608vs 1240m 1284w 103lvs 669m 214w N i ( p y z ) , ( C H , S O , ) •CH,0H 1526w C u ( p y z ) 4 ( C F , S 0 , ) ; 1529w 121 lw 123 lw 1243w 1250w 1256w 1233w 1014w 1023s 1038s 1059m 1159m 1023s 1033m 1057m 703m 780m 70 lw 772w 536w 558w 684w 213w 206w 1) Data from references 4 and 35. 

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