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UBC Theses and Dissertations

Synthesis, structure and properties of some transition metal hexafluorophosphate and hexafluoroarsenate… Morrison, Raymond Maxwell 1980

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SYNTHESIS, STRUCTURE AND PROPERTIES OF SOME TRANSITION METAL HEXAFLUOROPHOSPHATE AND HEXAFLUOROARSENATE COMPLEXES by RAYMOND MAXWELL MORRISON B.Sc, The University of B r i t i s h Columbia, 1975 A THESIS SUBMITTED IN THE REQUIREMENTS DOCTOR OF PARTIAL FULFILLMENT OF FOR THE DEGREE OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES (Chemistry) We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA March, 1980 © Raymond Maxwell Morrison, 1980 In presenting t h i s thes is in p a r t i a l f u l f i l m e n t of the requirements fo r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e fo r reference and study. I fu r ther agree that permission for extensive copying of th is thes is fo r s c h o l a r l y purposes may be granted by the Head of my Department or by h is representa t i ves . It i s understood that copying or p u b l i c a t i o n of th is thes is f o r f i n a n c i a l gain s h a l l not be allowed without my wr i t ten permission. Department of The U n i v e r s i t y of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 D E - 6 B P 75-51 1 E ABSTRACT A number o f p y r i d i n e , 3 - m e t h y l p y r i d i n e , and 4-methyl-p y r i d i n e complexes o f c o b a l t ( I I ) , n i c k e l ( I I ) , and c o p p e r ( I I ) h e x a f l u o r o p h o s p h a t e and h e x a f l u o r o a r s e n a t e have been s y n t h e s i z e d and c h a r a c t e r i z e d . The p h y s i c a l methods o f i n v e s t i g a t i o n w h i c h were used i n c l u d e v i b r a t i o n a l s p e c t r o s c o p y , e l e c t r o n i c s p e c t r o s c o p y , e l e m e n t a l a n a l y s i s , and magnetic s u s c e p t i b i l i t y measurements. I n a d d i t i o n c h a r a c t e r i z a t i o n o f some complexes i n c l u d e d s i n g l e c r y s t a l and powder X-ray d i f f r a c t i o n s t u d i e s , e l e c t r o n s p i n resonance s p e c t r o s c o p y , mass s p e c t r o m e t r y , and d i f f e r e n t i a l t h e r m a l a n a l y s i s . The compounds s t u d i e d were o f two t y p e s , t h o s e con-t a i n i n g n o n - c o o r d i n a t e d h e x a f l u o r o m e t a l l a t e a n i o n s and t h o s e w i t h c o o r d i n a t e d a n i o n s . The compounds i n t h e former c l a s s have t h e c o m p o s i t i o n M ( p y ) g ( E F g ) 2 , M ( 4 m e p y ) g ( H 2 0 ) 2 ( E F g ) 2 , M ' ( 3 m e p y ) 6 ( H 2 0 ) 2 ( E F g ) 2 , and M " L 4 ( E F g ) 2 ( where M i s Co and N i , M' i s Co, N i , and Cu, M" i s Co, and L i s p y r i d i n e , 3-methyl-p y r i d i n e , and 4-methylpyrid;ine, and E i s P and As) The com-pounds i n t h e l a t t e r c l a s s a r e N i L ^ ( E F g ) 2 and C u L 4 ( E F g ) 2 . S p e c t r a l and magnetic s t u d i e s on t h e M ( p y ) g ( E F g ) 2 2+ compounds show them t o c o n t a i n t h e c a t i o n i c s p e c i e s M ( p y ) g , where s i x p y r i d i n e l i g a n d s a r e o c t a h e d r a l l y c o o r d i n a t e d t o the m e t a l i o n . S i n g l e c r y s t a l X-ray d i f f r a c t i o n s t u d i e s on C o ( 4 m e p y ) g ( H 2 0 ) 2 ( P F 6 ) 2 , N i ( 4 m e p y ) Q ( H 2 0 ) 2 ( P F g ) 2 , and N i ( 3 m e p y ) g -( H 2 0 ) 2 ( P F g ) 2 show t h e m e t a l i o n t o be c o o r d i n a t e d by f o u r n i t r o g e n donors and two oxygen (f^O) donors i n t h e s e complexes. Based on comparisons o f e l e c t r o n i c s p e c t r a and magnetic p r o -p e r t i e s , t h e s t r u c t u r e s o f a l l M ( 4 m e p y ) g ( H 2 0 ) 2 ( E F g ) 2 and M'(3mepy)g(H 20) 2(EFg) 2 compound a r e c o n s i d e r e d t o be s i m i l a r . S p e c t r a l and m agnetic s t u d i e s on t h e C o L ^ ( E F g ) 2 complexes 2+ i n d i c a t e t h e y c o n t a i n t h e c a t i o n i c s p e c i e s , CoL^ , where f o u r n i t r o g e n l i g a n d s a r e t e t r a h e d r a l l y c o o r d i n a t e d around the c o b a l t ( I I ) i o n . T h i s s t r u c t u r e has been c o n f i r m e d by a s i n g l e c r y s t a l X-ray d i f f r a c t i o n s t u d y on C o(4mepy)^(PFg) 2• The a n i o n bands i n t h e i n f r a r e d s p e c t r a o f t h i s c l a s s o f compounds i n d i c a t e t h a t t h e EFg i o n s have o c t a h e d r a l (0^) symmetry, a l t h o u g h low s i t e symmetry e f f e c t s a r e e v i d e n t . S t u d i e s on t h e compounds c o n t a i n i n g c o o r d i n a t e d a n i o n s , i n c l u d e d a c o n s i d e r a t i o n o f c r i t e r i a f o r a n i o n i c c o o r d i n a t i o n based on t h e e l e c t r o n i c p r o p e r t i e s o f t h e m e t a l i o n , m o l e c u l a r s t r u c t u r e o f t h e complex and v i b r a t i o n a l s p e c t r a o f t h e a n i o n s . The e l e c t r o n i c p r o p e r t i e s o f t h e m e t a l i o n i n t h e N i L ^ ( E F g ) 2 complexes i n d i c a t e t h a t t h e f o u r n i t r o g e n donors a r e s t r o n g l y bound w i t h square p l a n a r s t e r e o c h e m i s t r y about n i c k e l . The i n f r a r e d s p e c t r a o f t h e a n i o n s and t h e r e s u l t s o f a s i n g l e c r y s t a l X-ray d i f f r a c t i o n s t u d y on N i ( 4 m e p y ) 4 ( P F g ) 2 i n d i c a t e t h a t t h e E F g - a n i o n s a r e v e r y w e a k l y c o o r d i n a t e d i n a x i a l p o s i t i o n s . The complex, N i ( p y ) ^ ( A s F g ) ^ < i - s unique i n t h a t , w h i l e i t s s t r u c t u r e i s l i k e t h a t o f o t h e r N i L ^ E F g ^ complexes a t room t e m p e r a t u r e , i t undergoes an i s o m e r i z a t i o n from 220 t o 160 K t o a d i f f e r e n t low t e m p e r a t u r e i s o m e r . The i v e l e c t r o n i c p r o p e r t i e s of the n i c k e l ( I I ) i o n and the v i b r a t i o n a l s p e c t r a i n d i c a t e t h a t the anions are more s t r o n g l y c o o r d i n a t e d i n the low temperature isomer. The e l e c t r o n i c p r o p e r t i e s and v i b r a t i o n a l s p e c t r a of the C u L ^ f E F g ^ complexes i n d i c a t e t h a t both the n i t r o g e n l i g a n d s and the anions are c o o r d i n a t e d to the copper, w i t h t e t r a g o n a l l y d i s t o r t e d o c t a h e d r a l stereochem-i s t r y around c o p p e r ( I I ) . The s t r e n g t h of anion c o o r d i n a t i o n i n these copper complexes i s c o n s i d e r e d to be comparable to t h a t p r e s e n t i n the low temperature isomer of N i ( p y ) 4 ( A s F g ) 2 and to be s i g n i f i c a n t l y g r e a t e r than t h a t p r e s e n t i n a l l o t h e r n i c k e l complexes s t u d i e d . V TABLE OF CONTENTS ABSTRACT i i LIST OF TABLES x i i LIST OF FIGURES x v i LIST OF ABBREVIATIONS x i x ACKNOWLEDGEMENTS x x CHAPTER 1: INTRODUCTION x 1.1 PREVIOUS WORK 2 1.1.1 Hexafluorophosphate and hexafluoroarsenate s a l t s 2 1.1.2 Coordination chemistry of hexafluorophosphate and hexafluoroarsenate anions 3 1.2 PURPOSE OF THE PRESENT WORK 8 1.3 ORGANIZATION OF THE THESIS 10 CHAPTER 2: THEORY AND BACKGROUND 12 2.1 INTRODUCTION TO THE THEORIES OF TRANSITION METAL COMPLEXES 13 2.2 PHYSICAL METHODS OF INVESTIGATION 16 2.2.1 Electronic spectroscopy 17 2.2.2 Magnetic s u s c e p t i b i l i t y 18 2.2.3 Electron spin resonance spectroscopy 21 2.2.4 Vib r a t i o n a l spectroscopy 24 2.2.4.1 Pyridine, 4-methyl-pyridine and 3-methyl-pyridine 24 v i 2.2.4.2 Hexafluorophosphate and h e x a f l u o r o a r s e n a t e 2.2.5 X-ray c r y s t a l l o g r a p h y ELECTRONIC STRUCTURE AND STEREO-CHEMISTRY 2.3.1 C o b a l t ( I I ) 2.3.1.1 Octahedral C o b a l t ( I I ) -E l e c t r o n i c s p e c t r a l p r o p e r t i e s 2.3.1.2 Oc t a h e d r a l C o b a l t ( I I ) -Magnetic p r o p e r t i e s 2.3.1.3 T e t r a h e d r a l C o b a l t ( I I ) -E l e c t r o n i c s p e c t r a l p r o p e r t i e s 2.3.1.4 T e t r a h e d r a l C o b a l t ( I I ) -Magnetic p r o p e r t i e s 2.3.2 N i c k e l ( I I ) 2.3.2.1 Octahedral and Te t r a g o n a l D i s t o r t e d O c t a h e d r a l N i c k e l ( I I ) - M a g n e t i c and s p e c t r a l p r o p e r t i e s 2.3.2.2 Square Pl a n a r N i c k e l ( I I ) -Magnetic and e l e c t r o n i c s p e c t r a l p r o p e r t i e s 2.3.3 Copper(II) v i i 2.3.3.1 Copper(II)-Electronic spectral properties 50 2.3.3.2 Copper(II)-Electron spin resonance spectroscopy 52 2.4 APPROACH TO COMPOUND CHARACTERIZATION 57 CHAPTER 3: COMPOUNDS CONTAINING NON-COORDINATED HEXAFLUOROPHOSPHATE AND HEXAFLUORO-ARSENATE 5 9 3.1 INTRODUCTION 6 0 3.2 OCTAHEDRAL PYRIDINE COMPLEXES OF COBALT(II); C o ( p y ) g ( E F g ) 2 62 3.2.1 INTRODUCTION 6 2 3.2.2 Results and Discussion 65 3.2.2.1 El e c t r o n i c spectra and magnetic properties 6 5 3.2.2.2 Vibrational spectroscopy 70 3.2.2.3 Thermal s t a b i l i t y 72 3.3 OCTAHEDRAL PYRIDINE COMPLEXES OF NICKEL(II); N i ( p y ) g ( E F g ) 2 78 3.3.1 Introduction 7 8 3.3.2 Results and discussion 78 3.4 OCTAHEDRAL METHYLPYRIDINE COMPLEXES OF COBALT(II), NICKEL(II), AND COPPER(II); M(4mepy) 8(H 20) 2(EF g) 2 and M(3mepy) g(H 20) 2~ ( E F g ) 2 83 3.4.1 Introduction 83 v i i i 3.4.2 Results and Discussion 84 3.4.2.1 Vibr a t i o n a l Spectra 84 3.4.2.2 Elect r o n i c spectral and magnetic properties and molecular structure 91 3.4.2.2.1 Co(4mepy)g-( H 2 0 ) 2 ( E F 6 ) 2 91 3.4.2.2.2 Ni(4mepy)g-( H 2 0 ) 2 ( E F 6 ) 2 96 3.4.2.2.3 Ni(3mepy) 6-( H 2 0 ) 2 ( E F 6 ) 2 103 3.4.2.2.4 Co(3mepy) 6-( H 2 0 ) 2 ( E F 6 ) 2 112 3.4.2.2.5 Cu(3mepy) 6-( H 2 0 ) 2 ( E F 6 ) 2 116 3.4.3 Relation to other work 121 3.5 TETRAHEDRAL-PYRIDINE AND METHYLPYRIDINE COMPLEXES OF COBALT(II); C o ( p y ) 4 ( E F g ) 2 , Co(3mepy) 4(EFg) 2 and Co(4mepy) 4(EFg) 2 3.5.1 Introduction 128 3.5.2 Results and Discussion 129 3.5.2.1 Electronic spectra and magnetic properties 129 3.5.2.2 Molecular structure of Co(4mepy) 4(PF 6) 2 3.5.2.3 Vibrational spectra 3.5.3 Relation to other work 134 140 144 i x CHAPTER 4: COMPOUNDS CONTAINING COORDINATED HEXAFLUORO-PHOSPHATE AND HEXAFLUOROARSENATE 4.1 CRITERIA FOR COORDINATION 150 4.2 COMPLEXES OF N I C K E L ( I I ) ; N i L 4 ( E F 6 ) 2 156 4.2.1 I n t r o d u c t i o n 156 4.2.2 R e s u l t s and D i s c u s s i o n 157 4.2.2.1 E l e c t r o n i c s p e c t r a l and magnetic p r o p e r t i e s 157 4.2.2.2 V i b r a t i o n a l s p e c t r a 161 4.2.2.3 M o l e c u l a r s t r u c t u r e o f N i ( 4 m e p y ) 4 ( P F 6 ) 2 166 4.2.2.4 Low t e m p e r a t u r e i s o m e r i z a t i o n o f N i ( p y ) 4 ( A s F g ) 2 174 4.2.2.4.1 M a g n e t i c and e l e c t r o n i c s p e c t r a l p r o p e r t i e s 174 4.2.2.4.2 E l e c t r o n i c s t r u c t u r e and s t e r e o c h e m i s t r y 189 4.2.2.4.3 V i b r a t i o n a l s p e c t r o s c o p y 191 4.2.2.5 Thermal s t u d i e s 199 4.2.2.5.1 Thermal p r e p a r a t i o n s o f N i ( 4 m e p y ) 4 ( P F g ) 2 and m agnetic p r o p e r t i e s o f p r o d u c t s 199 X 4.2.2.5.2 Thermal Decomposition S t u d i e s o f M L 4 ( E F g ) 2 Compounds 2 02 4.2.2.5.3 Thermal p r e p a r a t i o n o f N i ( p y ) 4 ( A s F 6 ) 2 and p r o p e r t i e s of t h i s m a t e r i a l 210 4.2.3 F a c t o r s Determining Anion C o o r d i n a t i o n i n N i L 4 A 2 Complexes 215 4.3 COMPLEXES OF COPPER(II): C u L 4 ( E F g ) 2 220 4.3.1 I n t r o d u c t i o n 220 4.3.2 R e s u l t s and D i s c u s s i o n 222 4.3.2.1 Magnetic p r o p e r t i e s 222 4.3.2.2 E l e c t r o n i c s p e c t r a l p r o p e r t i e s 223 4.3.2.3 E l e c t r o n s p i n resonance spectroscopy 230 4.3.2.4 V i b r a t i o n a l spectroscopy 236 4.3.3. R e l a t i o n t o other work 24 3 4.3.3.1 C u ( p y ) 4 ( P F 6 ) 2 243 4.3.3.2 Comparison of M L 4 ( E F g ) 2 Complexes 24 3 CHAPTER 5 SUGGESTIONS FOR FURTHER STUDY 2 53 5.1 SUGGESTIONS FOR FURTHER STUDY 254 CHAPTER 6 EXPERIMENTAL 2 57 6.1 MATERIALS 258 6.2 PREPARATIONS 259 x i 6.2.1 P y r i d i n e Complexes 261 6.2.2 4-methylpyridine Complexes 267 6.2.3 3-methylpyridine Complexes 271 6.2.4 Thermal S t u d i e s 27 5 6.2.5 U n s u c c e s s f u l P r e p a r a t i o n s 27 8 6.3 ANALYTICAL DATA 27 9 6.4 PHYSICAL EXPERIMENTAL TECHNIQUES 27 9 6.4.1 Magnetic S u s c e p t i b i l i t y Measurements 279 6.4.2 I n f r a r e d Spectroscopy 28 0 6.4.3 E l e c t r o n i c Spectroscopy 282 6.4.4 E l e c t r o n i c S pin Resonance Spectroscopy 283 6.4.5 S i n g l e C r y s t a l X-ray D i f f r a c t i o n 283 6.4.6 Raman Spectroscopy 284 6.4.7 Other Methods 284 6.5 SINGLE CRYSTAL X-RAY DIFFRACTION RESULTS 2 86 6.5.1 T e t r a k i s ( 4 - m e t h y l p y r i d i n e ) c o b a l t ( I I ) hexafluorophosphate Co(4mepy) 4 ( P F g ) 2 286 6.5.2 T e t r a k i s ( 4 - m e t h y l p y r i d i n e ) n i c k e l ( I I ) hexafluorophosphate N i ( 4 m e p y ) 4 ( P F g ) 2 291 6.5.3 H e x a k i s ( 3 - m e t h y l p y r i d i n e ) d i a q u o n i c k e l (II) hexafluorophosphate N i ( 3 m e p y ) g ( H 2 0 ) 2 ( P F g ) 2 295 6.5.4 H e x a k i s ( 3 - m e t h y l p y r i d i n e ) d i a q u o c o b a l t ( I I ) hexafluorophosphate C o ( 3 m e p y ) g ( H 2 0 ) 2 ( P F g ) 2 299 6.5.5 H e x a k i s ( 3 - m e t h y l p y r i d i n e ) d i a q u o c o p p e r ( I I ) hexafluorophosphate C u ( 3 m e p y ) g ( H 2 0 ) 2 ( P F g ) 2 299 REFERENCES 301 APPENDICES 311 x i i LIST OF TABLES 28 I - 1 M a g n e t i c moments o f some NiL^Ag. compounds I I - l V i b r a t i o n a l s p e c t r a o f some M ( E F g ) 2 (E=P,As) s a l t s I I - 2 C o r r e l a t i o n o f EFg (0^) v i b r a t i o n s i n some low e r symmetries .... 29 I I - 3 S p i n - a l l o w e d t r a n s i t i o n energy e x p r e s s i o n s f o r o c t a h e d r a l o r t e t r a h e d r a l T l (g) 9 r o u n ( ^ terms .... 35 I I - 4 S p i n a l l o w e d t r a n s i t i o n energy e x p r e s s i o n s f o r o c t a h e d r a l o r t e t r a h e d r a l n A 2 ^ ground terms I I I - l E l e c t r o n i c s p e c t r a l d a t a f o r C o ( p y ) g ( E F g ) 2 I I I - 2 S e l e c t e d i n f r a r e d s p e c t r a l d a t a f o r C o ( p y ) 6 ( E F 6 ) 2 2+ I I I - 3 E l e c t r o n i c s p e c t r a l d a t a f o r ' N i ( p y ) g 1 ....79 I I I - 4 S e l e c t e d i n f r a r e d s p e c t r a l d a t a f o r N i ( p y ) 6 ( E F 6 ) 2 I I I - 5 A n i o n bands i n t h e i n f r a r e d s p e c t r a o f M ( 4 m e p y ) 8 ( H 2 0 ) 2 ( E F 6 ) 2 and M 1(3mepy)g-( H 2 0 ) 2 ( E F 6 ) 2 I I I - 6 S e l e c t e d 4mepy bands i n t h e i n f r a r e d s p e c t r a o f t h e M ( 4 m e p y ) g ( H 2 0 ) 2 ( E F g ) 2 compounds I I I - 7 E l e c t r o n i c s p e c t r a l d a t a f o r Co(4mepy) g-( H 2 0 ) 2 ( E F g ) 2 40 66 71 81 85 90 92 X l l l I I I - 8 E l e c t r o n i c s p e c t r a l d a t a f o r Ni(4mepy)g-( H 2 0 ) 2 ( E F 6 ) 2 I I I - 9 E l e c t r o n i c s p e c t r a l d a t a f o r Ni(3mepy)g-( H 2 0 ) 2 ( E F 6 ) 2 111-10 Bond d i s t a n c e s and a n g l e s i n Ni(3mepy)g-( H 2 0 ) 2 ( P F 6 ) 2 I I I - l l E l e c t r o n i c s p e c t r a l d a t a f o r Co(3mepy)g-( H 2 0 ) 2 ( P F 6 ) 2 111-12 M a g n e t i c p r o p e r t i e s o f Co(3mepy)g-( H 2 0 ) 2 ( P F 6 ) 2 111-13 E l e c t r o n i c p r o p e r t i e s o f Cu(3mepy)g-( H 2 0 ) 2 ( E F 6 ) 2 111-14 E l e c t r o n i c s p e c t r a l d a t a f o r C o L 4 ( E F g ) 2 111-15 L i g a n d f i e l d p a rameters f o r C o L 4 ( E F g ) 2 111-16 Summary o f t h e magnetic p r o p e r t i e s o f C o L 4 ( E F g ) 2 111-17 Bond d i s t a n c e s and a n g l e s i n Co(4mepy) 4-( P F g ) , 111-18 S e l e c t e d n e u t r a l l i g a n d bands i n t h e i n f r a r e d s p e c t r a o f C o L 4 ( E F g ) 2 111-19 A n i o n bands i n t h e i n f r a r e d s p e c t r a o f C o L 4 ( E F g ) 2 111-20 L i g a n d f i e l d p arameters o f some t e t r a h e d r complexes o f c o b a l t ( I I ) x i v .164 .170 .189 .190 193 IV-1 E l e c t r o n i c s p e c t r a l d a t a f o r N i L 4 ( E F g ) 2 ....159 IV-2 S e l e c t e d n e u t r a l l i g a n d bands i n t h e i n f r a r e d s p e c t r a o f N i L 4 ( E F g ) 2 ....162 IV-3 A n i o n bands i n t h e i n f r a r e d s p e c t r a : o f N i L 4 ( E F 6 ) 2 IV-4 Bond d i s t a n c e s and a n g l e s i n N i ( 4 m e p y ) 4 ~ ( P F 6 ) 2 IV-5 E l e c t r o n i c spectrum o f N i ( p y ) 4 ( A s F g ) 2 IV-6 T e t r a g o n a l parameters f o r some N i ( p y ) 4 A 2 complexes IV-7 V i b r a t i o n a l s p e c t r a l d a t a f o r N i ( p y ) 4 ~ ( A S F 6 ) 2 IV-8 I n f r a r e d s p e c t r a l d a t a f o r N i ( p y ) 4 ( P F g ) 2 s u b l i m a t e and r e s i d u e . .. .204 IV-9 Mass s p e c t r a l d a t a f o r pyPF,. IV-10 Mass s p e c t r a l d a t a f o r pyAsF,-IV-11 Mass s p e c t r a l d a t a f o r 4mepyPF 5 IV-12 d s p a c i n g s o f N i ( p y ) 4 ( A s F g ) 2 ( a and 3) and N i ( 4 m e p y ) 4 ( P F g ) 2 IV-13 E l e c t r o n i c s p e c t r a l d a t a f o r C u L 4 ( E F g ) 2 IV-14 E . s . r . s p e c t r a l d a t a f o r C u L 4 ( E F g ) 2 IV-15 S e l e c t e d i n f r a r e d s p e c t r a l d a t a f o r C u L 4 ( E F g ) 2 IV-16 A n i o n bands i n t h e i n f r a r e d s p e c t r a o f C u L 4 ( E F g ) 2 VI-1 A n a l y t i c a l d a t a f o r p y r i d i n e compounds 205 206 207 ,213 ,224 .233 .237 .238 266 XV VI-2 A n a l y t i c a l d a t a f o r 4 - m e t h y l p y r i d i n e complexes VI-3 A n a l y t i c a l d a t a f o r 3 - m e t h y l p y r i d i n e complexes VI-4 Thermal p r e p a r a t i o n s o f N i ( 4 m e p y ) 4 ( P F g ) 2 XVI C o ( p y ) 6 ( P F 6 ) 2 3.3 I n f r a r e d s p e c t r u m (900-300 cm 1 ) o f C o ( p y ) g ( A s F g ) 2 3.4 V i s i b l e s p e c t r a o f c o b a l t ( I I ) - p y r i d i n e c o m p l e x e s 3.5 I n f r a r e d s p e c t r a (4000-2000 c m - 1 ) o f M ( 4 m e p y ) g ( H 2 0 ) 2 ( A s F g ) 2 L I S T OF FIGURES 2.1 Tanabe-Sugano d i a g r a m f o r c o b a l t ( I I ) ....3 3 4 2.2 T, t e r m u n d e r t h e s i m u l t a n e o u s p e r t u r -l g b a t i o n s o f s p i n o r b i t c o u p l i n g and low symmetry .... 37 2.3 Tanabe-Sugano d i a g r a m f o r n i c k e l ( I I ) ....42 2.4 E f f e c t on e l e c t r o n i c e n e r g y l e v e l s o f o c t a h e d r a l n i c k e l ( I I ) i n a x i a l l y e l o n g a t e d ( D 4 h ) symmetry 2.5 E f f e c t o f i n c r e a s i n g t e t r a g o n a l d i s t o r t i o n on t h e r e a l "d" o r b i t a l s 2.6 C o r r e l a t i o n o f band maxima and s t e r e o -c h e m i s t r y o f CuN 4_g c h r o m o p h o r e s 2.7 E n e r g y l e v e l d i a g r a m f o r S=l/2 a n d 1=3/2 ....53 2.8 A p p e a r a n c e o f a x i a l c o p p e r ( I I ) e . s . r . s p e c t r u m 3.1 M a g n e t i c p r o p e r t i e s o f C o ( p y ) g ( E F g ) 2 3.2 I n f r a r e d s p e c t r u m (1000-400 c m - 1 ) o f 45 48 51 .55 .69 .73 .74 .76 . .87 X V l l Infrared spectra (4000-2000 cm x) of M(3mepy) 6(H 20) 2(PF 6) 2 Magnetic properties of Co(4mepy)g-( H 2 0 ) 2 ( E F 6 ) 2 2+ View of Co(4mepy) 4(0H 2(4mepy) 2) 2 2+ View of Ni(4mepy) 4(0H 2(4mepy) 2) 2+ View of Ni(3mepy) 4(0H 2(3mepy)) 2 View of Ni(3mepy) 4(0H 2(3mepy)) 2(PF g) 2 E.s.r spectrum of Cu(3mepy) g(H 20) 2(PFg) 2 Infrared spectra (4000-2000 cm - 1) of Cu(3mepy) 6(H 20) 2(EFg) Stereoview showing the packing of anions about a cation (Co(4mepy) 4(PFg) 2) 2+ Stereoview of the Co(4mepy) 4 cation V i s i b l e spectra of N i L 4 ( A s F g ) 2 Infrared spectra (1000-300 cm - 1) of N i ( p y ) 4 ( E F 6 ) 2 View of Ni(4mepy) 4(PFg) 2 Stereoview of Ni(4mepy) 4(PFg) 2 Magnetic s u s c e p t i b i l i t i e s of Ni(py) 4(EFg) Magnetic s u s c e p t i b i l i t y of N i ( p y ) 4 ( A s F g ) 2 Electronic spectrum of N i ( p y ) 4 ( A s F g ) 2 (300 and 80 K) Ele c t r o n i c spectra of N i ( p y ) 4 ( A s F g ) 2 80 K and N i ( p y ) 4 ( C 1 0 4 ) 2 (300 K) 3 Plot of InK* against 10 /temperature Plot of AE against temperature XVIIX 4.11 I n f r a r e d s p e c t r a (800-350 cm ~~) o f N i ( p y ) 4 ( A s F g ) 2 (300 and 80K) 4.12 I n f r a r e d s p e c t r a (900-400 c m - 1 ) o f N i ( p y ) 4 ( P F g ) 2 (300 and 80K) 4.13 M a g n e t i c s u s c e p t i b i l i t y o f t h e t h e r m a l p r e p a r a t i o n s o f N i ( 4 m e p y ) 4 ( P F g ) 2 4.14 D i f f e r e n t i a l thermograms o f M ' ( p y ) 4 -( P F g ) 2 4.15 M a g n e t i c s u s c e p t i b i l i t y o f t h e a and 3 forms o f N i ( p y ) 4 ( A s F g ) 2 4.16 V i s i b l e e l e c t r o n i c s p e c t r a o f C u L 4 ( E F g ) 2 4.17 E . s . r . s p e c t r u m o f C u ( p y ) 4 ( P F g ) 2 as a powder a t 3 00 K 4.18 E . s . r . s p e c t r a o f C u ( p y ) 4 ( P F g ) 2 i n d i c h l o r o m e t h a n e s o l u t i o n a t 300 K and 80 K 4.19 I n f r a r e d s p e c t r a (1000-400 c m - 1 ) o f C u L 4 ( P F 6 ) 2 4.20 I n f r a r e d s p e c t r a (900-350 c m - 1 ) o f C u L 4 ( A s F g ) 2 4.21 I n f r a r e d s p e c t r a (900-350 c m - 1 ) o f N i L 4 ( A s F g ) 2 4.22 I n f r a r e d s p e c t r a (900-350 cm"1') of. NiCpyr) v4-| A'sFg) 2 a n d C u (PY) 4 ( A s F 6 ) 24.23 I n f r a r e d s p e c t r a (1000-400 c m - 1 ) o f N i L 4 ( P F g ) 2 LIST OF ABBREVIATIONS s s t r o n g m m e d i u m w weak vw v e r y weak b r b r o a d a s y a s y m m e t r i c s h s h o u l d e r n . o . n o t o b s e r v e d p y p y r i d i n e 4m.epy 4 - m e t h y l p y r i d i n e 3raepy 3 - m e t h y l p y r i d i n e p y z p y r a z i n e X X ACKNOWLEDGEMENTS I would l i k e t o e x p r e s s my g r a t i t u d e t o Dr. R.C. Thompson f o r h i s g u i d a n c e d u r i n g t h e c o u r s e o f t h i s work. I would l i k e t o thank P r o f . J . T r o t t e r f o r l e t t i n g me do some X-ray c r y s t a l l o g r a p h i c work w i t h o u t a f o r m a l r e l a t i o n s h i p . P r o f . T r o t t e r , Dr. S. R e t t i g , Dr. T. Greenhough, Dr. R. B a l l and R i c h a r d Paup.tit were -very h e l p f u l d u r i n g t h i s work and I would l i k e t o e x p r e s s s i n c e r e t h a n k s . I would a l s o l i k e t o acknowledge t h e use o f t h e r e s u l t s o f two c r y s t a l s t r u c t u r e d e t e r m i n a t i o n s performed by P r o f . T r o t t e r and Dr. S. R e t t i g . I am e x t r e m e l y g r a t e f u l t o Dr. F. Aubke, K e i t h Lee, and Dr. P a t r i c k Leung f o r a l l o w i n g me t o use t h e i r low temper-a t u r e c e l l s and t h e i r h e l p i n o p e r a t i n g t h e P e r k i n - E l m e r 225 and Ramalog 5 s p e c t r o m e t e r s . - 1 -CHAPTER 1 INTRODUCTION T h i s t h e s i s d e s c r i b e s t h e s y n t h e s i s and s t r u c t u r a l c h a r a c t e r i z a t i o n o f p y r i d i n e ( p y ) , 4 - m e t h y l p y r i d i n e (4mepy), and 3 - m e t h y l p y r i d i n e (3mepy) complexes o f c o b a l t ( I I ) , n i c k e l ( I I ) , and c o p p e r ( I I ) h e x a f l u o r o p h o s p h a t e and h e x a f l u o r o a r s e n a t e . Some g e n e r a l p r o p e r t i e s o f t h e s e h e x a f l u o r o - a n i o n s and a r e v i e w o f t h e p r e v i o u s work on t h e i r compounds w i t h f i r s t row t r a n s i t i o n m e t a l s w i l l be b r i e f l y p r e s e n t e d i n t h i s c h a p t e r . The purpose o f t h e p r e s e n t work and the o r g a n i z a t i o n o f t h e t h e s i s w i l l a l s o be o u t l i n e d . -2-1.1 PREVIOUS WORK 1.1.1 HEXAFLUOROPHOSPHATE AND HEXAFLUOROARSENATE SALTS Compounds containing the hexafluorophosphate and hexafluoroarsenate anions were i n i t i a l l y prepared i n the early decades of t h i s century. The f i r s t hexafluorophos-phate compound i s o l a t e d was nitronium hexafluorophosphate, C20 H16 N4 H" P F 6 ' b y L a n 9 e i n t h e l a t e 1920's(l). It was formed by the addition of nitron to a equilibrium mixture containing hexafluorophosphoric acid. The f i r s t hexafluoroarsenate compound prepared was SCl^AsFg i n 1906 (2). I t was formed by the reaction of SCl^ and AsF^ and was i n i t i a l l y formulated as S C l ^ A s F ^ ^ * A great many more compounds containing these anions were known by the 'early 1960's (2,3). The structure of these anions, EF g , i s that of an octahedron of fluorides about the central Group VA element in the formal oxidation state of +5. The E-F distances which were determined i n the c r y s t a l structures of NaPF g(4) and KAsFg(5) are 1.58A* and I . 8 0 8 respectively. The v i b r a t i o n -a l spectra of simple s a l t s , M'^ EFg, which are consistent with an octahedral EF g moiety (6-8), are discussed i n more d e t a i l in section 2.2.4.2. The EFg~ species are generally quite stable. Hexa-fluorophosphate i s stable i n basic, neutral and weakly a c i d i c solution; hydrolysis doesn't take place unless the pH i s less than 3 (1). Kinetic evidence(9) suggests the hexafluoro-arsenate anion i s more stable to hydrolysis than the hexafluoro-phosphate anion i n a c i d i c solutions. The thermal s t a b i l i t y - 3 -of the s a l t s i n the s o l i d state and whether they melt with or without decomposition depends upon the nature of the cation present. For example(10)} KPF g melts at 575°C with slow, decomposition to PF,. and KF, L i P F g has an appreciable d i s -sociation pressure (PF,.) at ordinary temperatures, and NMe.PFr i s stable up to 400°C. 4 b 1.1.2 COORDINATION CHEMISTRY OF HEXAFLUOROPHOSPHATE AND HEXAFLUOROARSENATE ANIONS. Several t r a n s i t i o n metal compounds containing hexa-fluorophosphate and hexafluoroarsenate have been reported i n the l i t e r a t u r e . There are two types of compounds which are of p a r t i c u l a r relevence to t h i s study. These are simple, anhy'drous compounds of the type M(EFg) 2 (E=P,As) and t h e i r i; ^ . pyridine or substituted pyridine complexes with f i r s t row t r a n s i t i o n metals i n the +2 oxid.ati.pn-. state. These compounds are of i n t e r e s t because they can be used to correlate the coordinating strength of anions with t h e i r basic properties. Anions such as perchlorate (ClO^ ), tetrafluoroborate (BF^ ), and substituted sulphates (XSO^ ) have been studied i n this wa^ The EF, anions can be considered to be weakly basic, although D the anhydrous acids HEF g cannot be i s o l a t e d . The compounds M(EFg) 2 are not well characterized. In fact, there have not been any reports i n the l i t e r a t u r e of the synthesis of M(PF g) 2 compounds while some reports of formation or attempted formation of M(AsF g) 2 compounds have -4-appeared (11,12). The o x i d a t i o n o f manganese, i r o n , c o b a l t and n i c k e l m e t a l w i t h a r s e n i c p e n t a f l u o r i d e y i e l d e d Mn(AsFg)^ and MF(AsF^) f o r t h e o t h e r s ( 1 1 ) . S i m i l a r s t u d i e s by Dean b (12) on t h e o x i d a t i o n o f n i c k e l and copper y i e l d e d two compounds, N i ( A s F g ) 2 ( S 0 2 ) 2 and Cu(AsFg) ( s u l p h u r d i o x i d e was used as t h e s o l v e n t ) . The u n s o l v a t e d compound N i ( A s F - ) n has been r e p o r t e d b Z t o be formed when the NF^-F^AsF,. system i s h e a t e d under p r e s s u r e i n monel v e s s e l s (13). The M ( A s F g ) 2 compounds (M=Co, Ni,Cu) c a n n o t , a t t h i s time,be c o n s i d e r e d t o be w e l l c h a r a c t e r i z e d . Some p y r i d i n e and s u b s t i t u t e d p y r i d i n e complexes o f n i c k e l ( I I ) and c o p p e r ( I I ) h e x a f l u o r o p h o s p h a t e have been r e p o r t e d , namely, N i ( p y ) g ( P F g ) 2 , N i ( p y ) 4 ( P F g ) 2 , N i ( 4 m e p y ) 4 ( P F g ) 2 , and C u ( p y ) 4 ( P F g ) 2 and t h e y have been c h a r a c t e r i z e d by a v a r i e t y o f t e c h n i q u e s . No h e x a f l u o r o a r s e n a t e compounds o f t h i s t y p e have been r e p o r t e d . The compounds o f h e x a f l u o r o p h o s p h a t e have some i n t e r e s t i n g p r o p e r t i e s , i n some c a s e s r a d i c a l l y d i f f e r e n t from t h o s e c o n t a i n i n g o t h e r weakly b a s i c a n i o n s . I n one c a s e , N i ( p y ) 4 ( P F g ) 2 / t h e o b s e r v e d magnetic p r o p e r t i e s a r e anomalous f o r a n i c k e l ( I I ) s p e c i e s . The r e a c t i o n o f n i c k e l ( I I ) n i t r a t e h e x a h y d r a t e , ammonium h e x a f l u o r o p h o s p h a t e , and an e x c e s s o f p y r i d i n e i n aqueous s o l u t i o n was found by M a y f i e l d and B u l l (14) t o . g i v e N i ( p y ) , ( P F - . ) _ . A s i m i l a r r e a c t i o n o f n i c k e l ( I I ) o 6 Z -5-p e r c h l o r a t e h e x a h y d r a t e i n aqueous s o l u t i o n w i t h an exc e s s o f p y r i d i n e gave the p r o d u c t N i ( p y ) 4 ( C 1 0 4 ) 2 ( 1 6 ) . The c h a r a c t e r -i z a t i o n o f N i (py) , (PF,.) „ suggested t h a t t h e s t r u c t u r e i n v o l v e d 6 6 2 2+ N i ( p y ) ^ c a t i o n s and n o n - c o o r d i n a t e d PF,. a n i o n s . I n c o n t r a s t , 6 6 N i ( p y ) 4 ( C 1 0 4 ) 2 has been a s s i g n e d a p s e u d o - o c t a h e d r a l f i r s t c o o r d i n a t i o n sphere w i t h the p e r c h l o r a t e a n i o n s c o o r d i n a t e d . These r e s u l t s i l l u s t r a t e t h e s i g n i f i c a n t d i f f e r e n c e i n t h e c o o r d i n a t i o n a b i l i t i e s o f C 10 4 and PFg and p r o v i d e d t h e 2+ f i r s t i n d i c a t i o n t h a t complex c a t i o n s s uch as M(py)g a r e more l i k e l y t o be o b t a i n e d w i t h PFg c o u n t e r i o n s than w i t h C 1 0 4 o r r e l a t e d i o n s such as B F 4 . 2+ The s y n t h e s i s o f M(py)g s p e c i e s i n t h e s o l i d s t a t e i s n o t a s i m p l e t a s k (17);.. i n d e e d N i ( p y ) g ( P F g ) 2 was o n l y t h e second w e l l documented example o f t h i s t y p e o f s p e c i e s i n t h e s o l i d s t a t e . ( F e ( p y ) g ) ( F e 4 C 0 1 3 ) (18) was t h e f i r s t . 2 -The i s o l a t i o n o f such s p e c i e s w i t h t h e PFg and Fe 4CO.^ a n i o n s s u g g e s t s t h e need f o r l a r g e and weakl y b a s i c a n i o n s t o s t a b i l i z e t h e c r y s t a l l a t t i c e . N l ( P Y ) 4 ( P F 6 ) 2 w a s p r e p a r e d by h e a t i n g N i ( p y ) g ( P F g ) 2 a t 100°C " i n vacuo" and N i ( 4 m e p y ) 4 ( P F g ) 2 was d e r i v e d v i a th e same r o u t e from a compound o f unknown c o m p o s i t i o n b u t s i m i l a r t o N i ( p y ) g ( P F g ) 2 ( 1 4 ) . The magnetic p r o p e r t i e s o f t h e s e compounds and t h e analogous p e r c h l o r a t e compounds show some i n t e r e s t i n g f e a t u r e s as i l l u s t r a t e d i n Table 1-1. N i (py) 4 ( C 1C>4) 2 n a s magnetic and s p e c t r a l p r o p e r t i e s t y p i c a l -6-TABLE 1-1 MAGNETIC MOMENTS FOR SOME N i L 4 A 2 COMPLEXES COMPLEX u e f f ( B . M . ) a REFERENCE N i ( p y ) 4 ( P F 6 ) 2 N i ( p y ) 4 ( c i o 4 ) 2 N i ( 4 m e p y ) 4 ( P F g ) 2 N i ( 4 m e p y ) 4 ( C 1 0 4 ) 2 1.98 (14) 3.24 (16) 0.0 (14) 0.0 (19-22) (a) a t room temperature, of ,. the n i c k e l (II) i o n i n a t e t r a g o n a l l y d i s t o r t e d pseudo-o c t a h e d r a l enviornment. The two 4-methylpyridine compounds have the magnetic and e l e c t r o n i c s p e c t r a l p r o p e r t i e s u s u a l l y a s s o c i a t e d w i t h square p l a n a r n i c k e l ( I I ) ; the s i n g l e c r y s t a l X-ray d i f f r a c t i o n study o f N i ( 4 m e p y ) 4 ( C 1 0 4 ) 2 comfirms t h i s s t r u c t u r e (23). N i ( p y ) 4 ( P F g ) 2 has an anomalous magnetic moment; i t i s not t y p i c a l o f e i t h e r the o c t a h e d r a l or the square p l a n a r form o f n i c k e l ( I I ) i n m a g n e t i c a l l y d i l u t e systems The authors, M a y f i e l d and B u l l (14), s t a t e two p o s s i b l e e x p l a n a t i o n s : the f i r s t , where t h e r e i s a s i n g l e t ground s t a t e and a t h e r m a l l y a c c e s s i b l e t r i p l e t e x c i t e d s t a t e as i n the Melson and Busch (24) model f o r the magnetic p r o p e r t i e s o f ~Ni(TAAB)Cl 2 H 20; and: the second, where -7-t h e r e i s a m i x t u r e o f s p i n f r e e ( y e f f (RT) ^ 3 . 2 B.M.) b i s -( h e x a f l u o r o p h o s p h a t o ) t e t r a k i s ( p y r i d i n e ) n i c k e l ( I I ) w i t h c o o r d i n a t e d a n i o n s and s p i n - p a i r e d ( d i a m a g n e t i c ) 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 e x a f l u o r o p h o s p h a t e w i t h " n o n - c o o r d i n a t e d " a n i o n s . T h i s l a t t e r s i t u a t i o n has b e e n e n c o u n t e r e d i n t h e y e l l o w f o r m o f b i s ( m e s o s t i l b e n e ) n i c k e l ( I I ) d i c h l o r o a c e t a t e ( 2 5 , 2 6 ) . F o r t h e h e x a f l u o r o p h o s p h a t e complex, t h e a u t h o r s f a v o r e d t h e f i r s t e x p l a n a t i o n b u t v a r i a b l e t e m p e r a t u r e mag-n e t i c s u s c e p t i b i l i t y measurements w h i c h c o u l d d i f f e r e n t i a t e b etween t h e two p o s s i b i l i t i e s were n o t p e r f o r m e d . The e l e c t r o n -i c s p e c t r u m w h i c h was r e p o r t e d f o r N i ( p y ) 4 ( P F g ) 2 was n o t d e f -i n i t i v e s i n c e i t c o u l d be i n t e r p r e t e d as a r i s i n g f r o m a s q u a r e p l a n a r n i c k e l ( I I ) s p e c i e s o r a m i x t u r e o f s q u a r e p l a n a r and t e t r a g o n a l p s e u d o - o c t a h e d r a l n i c k e l ( I I ) s p e c i e s . F i n a l l y , we r e f e r t o p r e v i o u s work on t h e p y r i d i n e c omplex o f c o p p e r ( I I ) h e x a f l u o r o p h o s p h a t e . U s i n g e x p e r i m e n t a l c o n d i t i o n s s i m i l a r t o t h o s e w h i c h l e d t o t h e i s o l a t i o n o f N i ( p y ) 6 ( P F g ) 2 ' M a y f i e l d and B u l l (14) o b t a i n e d C u ( p y ) 4 ( P F g ) 2 . The e . s . r . d a t a on t h i s compound have b e e n r e p o r t e d by McWhihftie e t a l ( 1 5 ) , a l t h o u g h t h e method o f p r e p a r a t i o n was n o t s p e c i f i e d . The c h a r a c t e r i z a t i o n o f t h i s compound i n d i c a t e d t h a t t h e h e x a f l u o r o p h o s p h a t e a n i o n s a r e c o o r d i n a t e d (27) t o c o p p e r ( I I ) , a l t h o u g h more w e a k l y t h a n t h e p e r c h l o r a t e a n i o n s i n C u ( p y ) 4 ( C l O ^ ) 2 . -8-1.2 PURPOSE OF THE PRESENT WORK Our i n i t i a l i n t e r e s t i n the coordination chemistry of hexafluorophosphate and hexafluoroarsenate ions was to examine the variable temperature magnetic s u s c e p t i b i l i t y properties of Ni (py) ^  ( p Fg) 2 a n < ^ s i m i l a r compounds. The variable temperature behavior of N i ( p y ) 4 ( P F g ) 2 should have"provided more information on the o r i g i n of the anomalous room temperature moment . mentioned i n 1.1.2. I f , indeed, these anomalous properties ari s e from a spin s i n g l e t - t r i p l e t thermal equilibrium (as favored by Mayfield and Bull) the phenomenon should manifest i t s e l f by giving a temperature dependent magnetic moment. On the other hand, i f the anomalous moment i s due to a mixture of paramagnetic and diamagnetic species, a l a r g e l y temperature independent magnetic moment should be observed. From some preliminary studies on NiL^(EFg)2 systems (28)/ we found that we could not reproduce the published magnetic properties of Ni ( p y ) 4 ( P F g ) 2 and t h i s led to a thorough investigation of t h i s compound and a wide range of related compounds. -"The purpose of the present work then was to synthesize a range of metal(II)-pyridine-EFg compounds with the expectation of obtaining complex cations }unattainable with other more coordinating anions and of observing highly tetragonal species i n complexes where the anions are coordinated. Included i n - 9 -t h i s work a r e t h e p r e v i o u s l y s t u d i e d compounds N i ( p y ) r (PF,)„, N i ( p y ) ( P F g ) 2 , N i ( 4 m e p y ) 4 ( P F g ) 2 , and C u ( p y ) 4 ( P F g ) 2 . The main c h a r a c t e r i z a t i o n t e c h n i q u e s were e l e m e n t a l (C, H, N) a n a l y s i s , v i b r a t i o n a l ( m a i n l y i n f r a r e d ) s p e c t r o s c o p y , e l e c t r o n i c s p e c t r o -scopy, v a r i a b l e t e m p e r a t u r e magnetic s u s c e p t i b i l i t y (Gouy) measurements, and s i n g l e c r y s t a l X-ray c r y s t a l l o g r a p h y . The t e c h n i q u e s o f • e l e c t r o n s p i n r e s o n a n c e , low t e m p e r a t u r e 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 o s c o p y , powder X-ray c r y s t a l -l o g r a p h y , and mass s p e c t r o m e t r y were used where a p p l i c a b l e . The r e s u l t s o f t h e c h a r a c t e r i z a t i o n s t u d i e s were used t o o b t a i n s t r u c t u r a l i n f o r m a t i o n on t h e complex s p e c i e s and t o c o r r e l a t e m o l e c u l a r s t r u c t u r e w i t h e l e c t r o n i c p r o p e r t i e s . -10-1.3 ORGANIZATION OF THE THESIS The b a s i c o u t l i n e o f t h e o r g a n i z a t i o n o f t h i s t h e s i s i s : background and t h e o r y ; r e s u l t s and d i s c u s s i o n ; s u g g e s t i o n s f o r f u r t h e r s t u d y ; and e x p e r i m e n t a l d e t a i l s . The a p p e n d i c e s c o n t a i n t h e i n f r a r e d and magnetic s u s c e p t i b i l i t y d a t a and X-ray d i f f r a c t i o n d a t a t a b l e s . C h a p t e r 2 w i l l d e s c r i b e some background m a t e r i a l f o r t h e p h y s i c a l t e c h n i q u e s used i n t h e c h a r a c t e r i z a t i o n o f t h e compounds. The l i g a n d f i e l d t h e o r y o f t r a n s i t i o n m e t a l complexes w i l l be v e r y b r i e f l y i n t r o d u c e d as w i l l some f a c e t s o f some o f t h e p h y s i c a l t e c h n i q u e s used. The d e r i v a t i o n o f v a r i o u s l i g a n d f i e l d p arameters f o r the m e t a l i o n s s t u d i e d here w i l l be .reviewed. F i n a l l y , t h e approaches ' we used t o c h a r a c t e r i z e the compounds w i l l be o u t l i n e d . Chapter 3 w i l l d i s c u s s t h e c h a r a c t e r i z a t i o n o f t h e c o o r d i n a t i o n compounds where the h e x a f l u o r o m e t a l l a t e a n i o n i s p r e s e n t i n t h e l a t t i c e as a c o u n t e r i o n n o t d i r e c t l y c o o r d i n a t e d t o t h e m e t a l . The compounds d i s c u s s e d here are M ( p y ) 6 ( E F 6 ) 2 , M ( 4 m e p y ) 8 ( H 2 0 ) 2 ( E F g ) 2 , M ' ( 3 m e p y ) g ( H 2 0 ) 2 ( E F g ) 2 and M " L 4 ( E F g ) 2 where M=Co, N i , M'=Co,Ni,Cu, E=P,As and L=py, 4mepy, 3mepy. The s t e r e o c h e m i s t r y and l i g a n d f i e l d parameters f o r each c a t i o n i c s p e c i e s w i l l be d e r i v e d and t h e r e s u l t s d i s c u s s e d i n r e l a t i o n t o o t h e r systems-. The e f f e c t s o f c a t i o n - a n i o n i n t e r a c t i o n s on t h e i n f r a r e d spectrum w i l l be d i s c u s s e d . -11-Chapter 4 w i l l d i s c u s s the c h a r a c t e r i z a t i o n o f the complexes where the E F g anions are co n s i d e r e d to be co o r d i n a t e d t o the metal i o n . The chapter begins w i t h a d i s c u s s i o n o f the concept o f c o o r d i n a t i o n . The c h a r a c t e r -i z a t i o n o f the compounds N i L 4 ( E F g ) 2 (L=py, 4mepy, 3mepy and E = P , As) i s o u t l i n e d and i s d i s c u s s e d i n r e l a t i o n t o t h i s concept. A l a r g e amount o f work was done on t h i s system, i n c l u d i n g thermal d e g r a d a t i o n s t u d i e s which r e l a t e our r e s u l t s to those o f p r e v i o u s r e p o r t s . Then, the r e s u l t s of the c h a r a c t e r i z a t i o n of the C u L 4 ( E F g ) 2 (L=py., 4mepy, 3mepy and E = F P , A S ) system w i l l be d i s c u s s e d . In t h i s s e c t i o n a l s o , i n f r a r e d c r i t e r i a f o r c o o r d i n a t i o n o f the E F g anions w i l l be summarized. Chapter 5 w i l l propose suggestions f o r f u r t h e r study. Chapter 6 w i l l d e s c r i b e the experimental d e t a i l s o f t h i s work. The m a t e r i a l s used, the p r e p a r a t i v e d e t a i l s , the d e t a i l s of the p h y s i c a l techniques employed, and the experimental d e t a i l s of the s i n g l e c r y s t a l X-ray d i f f r a c t i o n s t u d i e s w i l l be pre s e n t e d . -12-CHAPTER 2 THEORY AND BACKGROUND T h i s c h a p t e r w i l l p r e s e n t a b r i e f d e s c r i p t i o n o f the t h e o r y and o t h e r background m a t e r i a l a p p r o p r i a t e t o t h i s s t u d y . I t i s not meant t o be a th o r o u g h r e v i e w b u t i n s t e a d t o s i m p l y i n t r o d u c e t h e t e r m i n o l o g y and co n c e p t s used i n t h e rema i n d e r o f t h e t h e s i s . F i r s t , an i n t r o d u c t i o n t o t h e t h e o r i e s o f t r a n s i t i o n m e t a l complexes w i l l be p r e s e n t e d . Then, t h e p h y s i c a l methods o f i n v e s t i g a t i o n ; e l e c t r o n i c s p e c t r o s c o p y , magnetic s u s c e p t i b i l i t y , v i b r a t i o n a l s p e c t r o s c o p y , e l e c t r o n s p i n resonance s p e c t r o s c o p y , v i b r a t i o n a l s p e c t r o s c o p y , and s i n g l e c r y s t a l X-ray c r y s t a l l o g r a p h y w i l l be d i s c u s s e d . The c o r r e l a t i o n o f s t e r e o c h e m i s t r y w i t h e l e c t r o n i c s t r u c t u r e f o r c o b a l t ( I I ) , n i c k e l ( I I ) , and c o p p e r ( I I ) w i l l be summarized. F i n a l l y , o u r approach t o t h e c h a r a c t e r i z a t i o n o f t h e s e compounds w i l l be d i s c u s s e d . -13-2.1 INTRODUCTION TO THE THEORY OF TRANSITION METAL COMPLEXES The t r a n s i t i o n metals have been d e f i n e d (29) as those elements which have p a r t i a l l y f i l l e d "d" or " f " o r b i t a l s and those elements where p a r t i a l l y f i l l e d "d" o r " f " o r b i t a l s are p r e s e n t i n some o f t h e i r common o x i d a t i o n s t a t e s . The name " t r a n s i t i o n metals" has normally been a p p l i e d t o the d bl o c k elements of the f i r s t ( T i - C u ) , second (Zr-Ag), and t h i r d (Ta-Au) rows. As a g e n e r a l r u l e , the c o o r d i n a t i o n chemistry o f a t r a n s i t i o n element m a n i f e s t s i t s e l f i n the element's p o s i t i v e o x i d a t i o n ( e l e c t r o n d e f i c i e n t ) s t a t e s . The magnetic ( s u s c e p t i b i l i t y and s p i n resonance) and e l e c t r o n i c s p e c t r a l ( v i s i b l e , and near i n f r a r e d regions) p r o p e r t i e s can be e x p l a i n e d , as w e l l as some s t r u c t u r a l p r e f e r e n c e s and thermodynamic p r o p e r t i e s , i n terms df the d e l e c t r o n c o n f i g u -r a t i o n o f the metal i o n . Some approaches to t h i s are d e s c r i b e d below. The t h e o r i e s which have been used to e x p l a i n the p r o p e r t i e s o f t r a n s i t i o n metal complexes i n c l u d e valence bond theory ( 3 0 ) , l i g a n d f i e l d theory ( i n c l u d i n g c r y s t a l f i e l d theory) and a molecular o r b i t a l approach termed the angular o v e r l a p model (a.o.m.). Standard textbooks on t r a n s i t i o n metal chemistry ( r e f e r e n c e s 31-35, f o r example) u s u a l l y g i v e some i n s i g h t s i n t o the h i s t o r i c a l develop-ment, advantages and disadvantages o f each theory. Valence -14-b ond t h e o r y i s n o t u s e d i n modern t r a n s i t i o n m e t a l c h e m i s t r y b e c a u s e i t i s t o o q u a l i t a t i v e and makes no a t t e m p t t o e x p l a i n e l e c t r o n i c s p e c t r a . The a.o.m. ( 3 6 - 3 8 ) , a l t h o u g h more t h e o r e t i c a l l y s a t i s f y i n g , i s d i f f i c u l t t o u t i l i z e i n c o n j u n c t i o n w i t h t h e n o r m a l o b s e r v a b l e , b u l k p r o p e r t i e s o f f i r s t row t r a n s i t i o n m e t a l s . L i g a n d f i e l d t h e o r y i s t h e most commonly u s e d a p p r o a c h t o e x p l a i n t h e p r o p e r t i e s o f f i r s t row t r a n s i t i o n m e t a l s . I t i s t h e a p p r o a c h u s e d i n t h i s t h e s i s . L i g a n d f i e l d t h e o r y has i t s b a s i s i n c r y s t a l f i e l d t h e o r y ( C . F . T . ) , t h e l a t t e r b e i n g a p o i n t c h a r g e m o d e l . I n C.F.T., t h e m e t a l - l i g a n d i n t e r a c t i o n i s c o n s i d e r e d t o be e l e c t r o s t a t i c i n n a t u r e . F o r example i n an o c t a h e d r a l c omplex, t h e p o s i t i v e c e n t r a l m e t a l i o n i s c o n s i d e r e d t o be s u r r o u n d e d by p o i n t n e g a t i v e c h a r g e s a t t h e v e r t i c e s o f an o c t a h e d r o n . The e f f e c t on t h e d o r b i t a l s i s t h a t t h e f i v e f o l d d e g e n e r a t e d o r b i t a l s o f t h e s p h e r i c a l l y s y m m e t r i c g a s e o u s f r e e i o n a r e s p l i t i n t o two d e g e n e r a t e s e t s i n 0^ symmetry: t 2 g ( d x y , d y z , and d x z ) and e g ( d x 2 _ y 2 and d z 2 ) . The e n e r g y s e p a r a t i o n o f t h e two s e t s i n 0^ symmetry i s d e f i n e d as ^ o c ^ o r lODq. The e l e c t r o n i c e n e r g y l e v e l s o f t h e c omplex a r e d e t e r m i n e d by t h e v a r i o u s d e l e c t r o n c o n -c • • • ,, m n. f i g u r a t i o n s ( t 0 e ) . 2g g I n t h e c r y s t a l f i e l d m o d e l , Dq i s p a r a m e t e r i z e d 2-4 5 / a s (Ze r _ / a )/6 where Z i s t h e e f f e c t i v e n u c l e a r c h a r g e , e -4 i s t h e e l e c t r o n i c c h a r g e , r i s t h e f o u r t h power o f t h e mean r a d i u s o f t h e d o r b i t a l s , and a i s t h e m e t a l - l i g a n d bond -15-l e n g t h . The m a t h e m a t i c a l t r e a t m e n t s o f s y m m e t r i e s l o w e r t h a n 0^ o r T^ (as shown by G e r l o c h and S l a d e (33)) i n some c a s e s , i n t r o d u c e a s e c o n d o r d e r r a d i a l l i g a n d f i e l d -2 p a r a m e t e r , Cp, w h i c h i s p a r a m e t e r i z e d as 2 Ze r ~ . T h i s 7 a p a r a m e t e r i s i m p o r t a n t s i n c e i t i s n e e d e d t o e x p l a i n some o f t h e o b s e r v e d m a g n e t i c and s p e c t r a l p r o p e r t i e s o f d , d , p and d i o n s where t r i g o n a l l y o r t e t r a g o n a l l y d i s t o r t e d o c t a h e d r a l o r t e t r a h e d r a l . s t e r e o c h e m i s t r i e s a r e p r e s e n t . L i g a n d f i e l d t h e o r y i n c l u d e s t h e c r y s t a l f i e l d e f f e c t s ( w h i c h g i v e t h e s o - c a l l e d s t r o n g f i e l d c o n f i g u r a t i o n s ) and a l s o c o n s i d e r s t h e symmetry l o w e r e d s t a t e s o f t h e g a s e o u s f r e e i o n (39) ( g i v i n g t h e s o - c a l l e d weak f i e l d c o n f i g u r a t i o n s ) . The e n e r g y l e v e l o r d e r i n g o f t h e g a s e o u s f r e e i o n i s known as a f u n c t i o n o f t h e Racah i n t e r e l e c t r o n i c r e p u l s i o n p a r a m e t e r s B and C. T h e r e i s a o n e - t o - o n e c o r r e s p o n d e n c e between t h e s t r o n g and weak f i e l d s t a t e s and i n i n t e r m e d i a t e c a s e s t h e e n e r g y l e v e l s o f t h e m e t a l i o n c a n be e x p r e s s e d as f u n c t i o n s o f Dq, B, and C. The e f f e c t s o f m e t a l - l i g a n d i o n i c and c o v a l e n t b o n d i n g and i n t e r e l e c t r o n r e p u l s i o n c a n be e v a l u a t e d i n t e r m s o f t h e v a l u e s o f Dq, B, and C o b t a i n e d : Dq as compared t o i t s v a l u e i n o t h e r , c o m p l e x e s ; B and C as compared t o t h e f r e e i o n v a l u e s . The r e l a t i o n s h i p o f B t o m e t a l - l i g a n d c o v a l e n c y i s d e s c r i b e d n e x t . S i n c e B i s a measure o f t h e r e p u l s i v e i n t e r a c t i o n s o f e l e c t r o n s i n t h e d o r b i t a l s , i t i s p r i m a r i l y a f f e c t e d by t h e r a d i a l d i s p l a c e m e n t o f t h e s e o r b i t a l s . Any l i g a n d -16-w h i c h r e d u c e s t h e e f f e c t i v e n u c l e a r c h a r g e o f t h e m e t a l i o n and t h u s expands t h e d e l e c t r o n c l o u d o r i n c r e a s e s t h e mean r a d i a l d i s p l a c e m e n t by d e l o c a l i z a t i o n o f t h e d e l e c t r o n o v e r t h e m e t a l - l i g a n d bond d e c r e a s e s t h e v a l u e o f B. T h e s e two p r i n c i p a l mechanisms a r e c a l l e d c e n t r a l f i e l d c o v a l e n c y and symmetry r e s t r i c t e d c o v a l e n c y w i t h t h e f o r m e r p r o b a b l y t h e most i m p o r t a n t . The f a c t t h a t B i s u s u a l l y l o w e r t h a n t h e f r e e i o n v a l u e r e f l e c t s t h e f a c t t h a t t h e m e t a l - l i g a n d i n t e r a c t i o n i s p a r t i a l l y c o v a l e n t . The f a c t t h a t B i s a v a r i a b l e i n l i g a n d f i e l d t h e o r y a l l o w s f o r t h e i n t r o d u c t i o n o f c o v a l e n c y i n t o an e s s e n t i a l l y 2 3 7 8 e l e c t r o s t a t i c m o d e l . F o r d , d , d , and d m e t a l c o m p l e x e s w i t h a s p i n - f r e e g r o u n d s t a t e , a v a l u e o f B c a n be d e r i v e d f r o m t h e e l e c t r o n i c s p e c t r u m . F u r t h e r d i s c u s s i o n s on l i g a n d f i e l d t h e o r y a r e n o t a p p r o p r i a t e f o r t h i s t h e s i s . R e a d e r s a r e r e f e r r e d t o t h e t e x t b o o k s on l i g a n d f i e l d t h e o r y . 2.2 PHYSICAL METHODS OF INVESTIGATION The e x p e r i m e n t a l d e t a i l s a r e d e s c r i b e d i n s e c t i o n 6.4. and 6.5. H e r e we p r o v i d e some b a c k g r o u n d c o n c e r n i n g v a r i o u s p h y s i c a l methods o f i n v e s t i g a t i o n . -17-2.2.1 ELECTRONIC SPECTROSCOPY F i r s t row t r a n s i t i o n m e t a l s g e n e r a l l y have a b s o r p t i o n bands ( w h i c h c a n be a s s i g n e d t o d+d t r a n s i t i o n s ) i n t h e n e a r - i n f r a r e d and v i s i b l e r e g i o n s o f t h e e l e c t r o -m a g n e t i c s p e c t r u m . The t r a n s i t i o n e n e r g i e s , i n some c a s e s , c a n be a s s i g n e d t o t r a n s i t i o n s between e l e c t r o n i c s t a t e s as p r e d i c t e d b y t h e l i g a n d f i e l d m o d e l . I n t h e s e c a s e s , t h e y c a n be f i t t e d t o Dq and B w i t h i n t h e c o n t e x t o f t h i s m o d e l . S e c t i o n 2.3 d e s c r i b e s t h e p r o c e d u r e s u s e d f o r t h e m e t a l ( I I ) i o n s s t u d i e d h e r e . 2.2.2 MAGNETIC SUSCEPTIBILITY M a g n e t i c s u s c e p t i b i l i t y measurements p r o b e t h e n a t u r e o f t h e e l e c t r o n i c g r o u n d t e r m o f t h e t r a n s i t i o n m e t a l i o n . The n a t u r e o f t h i s g r o u n d t e r m i s d e p e n d e n t upon t h e m e t a l i o n d e l e c t r o n p o p u l a t i o n s and t h e s t e r e o -c h e m i s t r y p r o d u c e d by t h e l i g a n d a r r a n g e m e n t a r o u n d t h e m e t a l . The a t o m i c s u s c e p t i b i l i t y o f t h e m e t a l i o n i s d e p e n d e n t upon t h e s p i n ( s ) and o r b i t a l (£) a n g u l a r momentum a s s o c i a t e d w i t h t h e g r o u n d s t a t e and s t a t e s w i t h i n kT (208 c m - 1 a t 300K) o f t h e g r o u n d s t a t e . The e f f e c t i v e m a g n e t i c moment, U e f f / and i t s t e m p e r a t u r e dependence f o r v a r i o u s s t e r e o c h e m i s t r i e s , ' o f t h e m e t a l i o n s t u d i e d , h e r e a r e p r e s e n t e d i n S e c t i o n 2.3. -18-The p r i n c i p l e s i n v o l v e d i n t h e o p e r a t i o n o f t h e Gouy and Faraday b a l a n c e s (4 0) used i n t h i s s t u d y and t h e t h e o r y o f at o m i c s u s c e p t i b i l i t i e s (30,40,41) a r e d i s c u s s e d i n numerous t e x t b o o k s on t h e s u b j e c t . The magnetic moment of a m e t a l i o n h a v i n g s p i n ( s ) and o r b i t a l ( & ) a n g u l a r momenteum, i n t h e absence o f s p i n - o r b i t c o u p l i n g i s : ( i n Bohr magnetons) u = (4s ( s + D + AU+1) ) h When a pa r a m a g n e t i c body e x p e r i e n c e s a magnetic f i e l d , t h e r e i s a change i n t h e e n e r g e t i c s o f the system. M o d e l l i n g t h e para m a g n e t i c m e t a l i o n as a magnetic d i p o l e , t h e d i p o l e can a l i g n w i t h o r a g a i n s t t h e d i r e c t i o n o f t h e magnetic f i e l d . I n quantum m e c h a n i c a l t e r m s , t h i s i s e q u i v a l e n t t o removing t h e degeneracy o f t h e magnetic quantum number, mg; t h i s i s r e p r e s e n t e d below f o r a s i n g l e e l e c t r o n . The energy d i f f e r e n c e (hv) between t h e two m m =h ( + ) 7. s AE=hv ms=-3s( + ) APPLIED FIELD s t a t e s i s shown i n e q u a t i o n 2.2; where h i s Planck's c o n s t a n t hv=g8H (2.2) -19--2 7 6.6256x10 erg-s, v i s the t r a n s i t i o n frequency t y p i c a l l y 10 y a radiofrequency ( 10 Hertz), g i s the Lande s p l i t t i n g factor (2.002317 for a free electron), 3 i s the Bohr magneton -20 -1 (0.92731x10 erg gauss ) and H i s the magnitude of the applied magnetic f i e l d i n gauss. For an applied f i e l d of 3 00 G. on the free electron, the separation of two mg -1 ' le v e l s would be 0.23 cm which i s much less than kT. The d i s t r i b u t i o n of the metal ion dipoles having one of the two orientations w i l l be governed by a Boltzmann d i s t r i b u t i o n and there i s a small excess i n the lower l e v e l . As a r e s u l t of t h i s excess, there i s net magnetic dipole giving r i s e to a magnetic s u s c e p t i b i l i t y and because of the Boltzmann d i s t r i b u t i o n , the s u s c e p t i b i l i t i e s (molar, x m » a n d gram, x g ) are temperature dependent. The phenomenon described above i s the f i r s t order Zeeman e f f e c t . Since bulk magnetic s u s c e p t i b i l i t y measure-ments measure only the residual excess spins i n the ground state, the magnitude of the s u s c e p t i b i l i t y i s determined by the separation of these states. Moreover, i n cases where no other e l e c t r o n i c states are within kT of the ground state the s u s c e p t i b i l i t y i s inversely proportional to temperature (41) and as a r e s u l t U e£ f(=2.828 ( x mxT) 2) i s temperature inde-pendent. This i s the s i t u a t i o n for t r a n s i t i o n metal complexes with A or E ground states. However, t r a n s i t i o n metal complexes with T^ and ground e l e c t r o n i c states (and therefore o r b i t a l -20-a n g u l a r momenta a s s o c i a t e d w i t h them) u s u a l l y show t e m p e r a t u r e d e p e n d e n t moments; s p i n - o r b i t c o u p l i n g , i n t h e s e c a s e s , r e s u l t s i n t h e p r e s e n c e o f a t l e a s t one s p i n - o r b i t s t a t e w i t h i n kT o f t h e g r o u n d s t a t e ( S e c t i o n 2.3.1.2 d e s c r i b e s t h e model f o r 4 a term) . I t i s w o r t h m e n t i o n i n g , t h a t f o r A and E t e r m s , two o t h e r f a c t o r s have b e e n shown t o be p r e s e n t w h i c h may a f f e c t t h e t e m p e r a t u r e d e p e n d e n c e o f x m « They a r e a s e c o n d o r d e r Zeeman e f f e c t ( t e m p e r a t u r e i n d e p e n d e n t p a r a m a g n e t i s m ( t . i . p . ) ) and s p i n - o r b i t c o u p l i n g e f f e c t s t h a t a r e p r e s e n t i n l o w e r t h a n c u b i c ( 0 ^ and T^) symmetry. The t . i . p . c o n t r i b u t i o n i s i n d u c e d by t h e a p p l i e d m a g n e t i c f i e l d and as t h e name i m p l i e s i s t e m p e r a t u r e i n d e -p e n d e n t . The r e s u l t o f t h i s s e c o n d o r d e r Zeeman e f f e c t i s t h a t some e x c i t e d s t a t e c h a r a c t e r i s m i x e d i n t o t h e g r o u n d s t a t e . When t h e o v e r a l l e n e r g y l e v e l d i a g r a m f o r a m e t a l i o n i s known, a t . i . p . c o r r e c t i o n c a n be made i . e . X e £ f = X A - t . i . p . ; t h e s y m b o l s a r e d e f i n e d i n S e c t i o n 6.3.2. When a m e t a l i o n w i t h a A o r E g r o u n d s t a t e i s i n a c u b i c symmetry, x m s h o u l d be i n v e r s e l y p r o p o r t i o n a l t o t e m p e r a t u r e (x 1/T) . I n t h e p r e s e n c e o f l i g a n d f i e l d s o f l e s s t h a n c u b i c symmetry, x m m a Y be i n v e r s e l y , - -p r o p o r t i o n a l t o T - 9, , where 8 i s t h e W e i s s c o n s t a n t . The i n t e r c e p t o f t h e t e m p e r a t u r e a x i s when 1 / X m 1 S p l o t t e d a g a i n s t t e m p e r a t u r e ( i n K e l v i n ) g i v e s 6 -21-i n K e l v i n . F o r A 2 t e r m s , t h i s c o n s t a n t has b e en r e l a t e d t o s e c o n d o r d e r s p i n - o r b i t c o u p l i n g i n low symmetry l i g a n d e n v i r o n m e n t s ( 4 2 ) . 2.2.3 ELECTRON SPIN RESONANCE SPECTROSCOPY. The f u n d a m e n t a l s o f e l e c t r o n s p i n r e s o n a n c e s p e c t r o -s c o p y , w i t h r e s p e c t t o t h e t r a n s i t i o n m e t a l s s t u d i e d h e r e , h a v e b e e n r e v i e w e d ( 4 3 - 4 5 ) . Of t h e t h r e e m e t a l s s t u d i e d (Co,Ni,Cu) o n l y c o p p e r ( I I ) c o m p l e x e s g e n e r a l l y g i v e o b s e r v a b l e s p e c t r a u n d e r t h e e x p e r i -m e n t a l c o n d i t i o n s u s e d : powder; room t e m p e r a t u r e s o l u t i o n ; a n d g l a s s e s ( l i q u i d n i t r o g e n " f r o z e n " s o l u t i o n s ) . The s p e c t r a o f n i c k e l ( I I ) and c o b a l t ( I I ) c o m p l e x e s where r e p o r t e d a r e u s u a l l y o b s e r v e d i n h o s t l a t t i c e s o r a t l i q u i d h e l i u m t e m p e r a t u r e s . E . s . r . i s , l i k e t h e m a g n e t i c s u s c e p t i b i l i t y m e a s u r e -ments o f 2.2.2., a m a g n e t i c t e c h n i q u e b u t a l s o i s a r e s o n a n c e t e c h n i q u e . E . s . r . m e a s u r e s t h e e n e r g y n e e d e d t o r e v e r s e t h e s p i n o f a e l e c t r o n i n an a p p l i e d m a g n e t i c f i e l d (m -m ) . E q u a t i o n 2.2 d e s c r i b e s t h e r e s o n a n c e c o n d i t i o n , and knowing t h e v a l u e s o f v and H, t h e g v a l u e s c a n be d e r i v e d d i r e c t l y f r o m t h e s p e c t r u m . The g v a l u e s o b t a i n e d a r e d i f f e r e n t i n m a g n i t u d e f r o m t h e f r e e e l e c t r o n g v a l u e , g , and a l s o may be o r i e n t a t i o n d e p e n d e n t . F o r e l e c t r o n s • p.ossessi-ng s p i n and o r b i t a l - 2 2 -a n g u l a r momentum w h i c h c o u p l e t o g e t h e r t o form J , t h e form o f t h e g f a c t o r i s as i n e q u a t i o n 2 . 3 . S i n c e l i g a n d f i e l d s quench a n g u l a r momentum, A and E ground terms (eg. c o p p e r ( I I ) ) g = 3J(J+1) + S(S+1) + L(L+1) ( 2 . 3 ) 2J(J+1) s h o u l d n o t p o s s e s s o r b i t a l a n g u l a r momenta;• however, t h e g v a l u e s o b s e r v e d a r e n o t g e n e r a l l y g . S p i n - o r b i t c o u p l i n g w i t h e x c i t e d s t a t e s i n t r o d u c e s some e x c i t e d s t a t e c h a r a c t e r i n t o t h e ground s t a t e . E q u a t i o n 2.4 shows t h e r e l a t i o n s h i p between t h e g v a l u e s where n i s d e t e r m i n e d by t h e e x c i t e d s t a t e . g = g e (1 - (nX/A)) ( 2 . 4 ) A l s o , t h e g v a l u e may be o r i e n t a t i o n dependent, i . e . each c a r t e s i a n a x i s may have a c h a r a c t e r i s t i c g v a l u e . T h i s depends upon t h e symmetry around t h e m e t a l i o n . I n c u b i c symmetry, t h e g v a l u e i s independent o f t h e o r i e n t a t i o n o f t h e m o l e c u l e (g = g = g ) and i s termed i s o t r o p i c . I n x y z l o w e r symmetry, t h e g v a l u e i s o r i e n t a t i o n dependent and termed a n i s o t r o p i c . I n a x i a l symmetry (g = g ^ g ) , g (=g„) x y z x y i s d e f i n e d as g± and g z i s d e f i n e d as g J t when by c o n v e n t i o n , z i s t h e a x i s w i t h t h e h i g h e s t symmetry about i t . I n symmetries lo w e r t h a n a x i a l , (eg. rhombic) a l l t h r e e g v a l u e s a r e d i f f e r e n t . I n some s o l u t i o n s p e c t r a , t h e g v a l u e s o b s e r v e d w i l l appear i s o t r o p i c , even though t h e m o l e c u l a r s p e c i e s may have a n i s t r o p i c ( a x i a l ) g v a l u e s . T h i s o c c u r s when t h e t u m b l i n g o f t h e pa r a m a g n e t i c i o n s i s f a s t e r t h a n t h e t i m e s c a l e o f t h e e . s . r . measurement. E q u a t i o n 2.5 shows t h e r e l a t i o n s h i p o f t h e o b s e r v e d s o l u t i o n g v a l u e , g , and t h e a x i a l g v a l u e s , g A and g„ , g Q = 1/3 (2g x+g„) (2.5) The appearance o f t h e e . s . r . spectrum w i l l be a f f e c t e d by h y p e r f i n e i n t e r a c t i o n o f t h e e l e c t r o n s p i n w i t h t h e n u c l e a r s p i n o f copper. T h i s , a l o n g w i t h t h e form o f e q u a t i o n 2.4 as a f u n c t i o n o f s t e r e o c h e m i s t r y f o r c o p p e r ( I I ) , w i l l be p r e s e n t e d i n S e c t i o n 2.3.3.2. - 2 4 -2.2.4= VIBRATIONAL SPECTROSCOPY This section deals"with previous work (Raman and infrared spectr-a) on the neutral ligands studied here (py, 4mepy, 3mepy) i n metal complexes and 6n< the appropriate hexafluorometallate anions. 2.2.4.1 PYRIDINE, 4-METHYLPYRIDINE, AND 3-METHYLPYRIDINE. The v i b r a t i o n a l spectrum of pyridine has been studied and unequivocal assignments made (46-47). The differences i n the in f r a r e d spectra of pyridine as a free base and of pyridine present i n coordination compounds have been studied by G i l l and co-workers (48) . For most of the bands, there are minor s h i f t s upon coordination; however, for three bands 8a, 6a, and 16b (1572, 603, and 403 cm - 1 i n the free base) there are s i g n i f i c a n t s h i f t s to higher energy '(^ 2 0 cm ^) . These authors found few systematic changes i n the band po s i t i o n with changes i n mass, el e c t r o -negativity, or valency of the central atom or with changes i n the other ligands bonded to the metal. In the compounds M(py) 2 X2' w n e r e M=Mn,Fe,Co,Ni,Cu, and Zn and X=C1 and Br,,. however, the 6a and 16b vibrations have been shown to have energies which decrease with the increasing p o l a r i z i n g power of the metal ion. -25-W e l l d e f i n e d s p l i t t i n g s have been o b s e r v e d f o r some o f t h e fundamental v i b r a t i o n s o f p y r i d i n e . S i n c e t h e s e fundamental v i b r a t i o n s a r e n o t degenerate v i b r a t i o n s , t h e s p l i t t i n g s a r e l i k e l y due t o one o r more o f : ( i ) i n t e r -a c t i o n s between m o l e c u l e s i n t h e u n i t c e l l ; ( i i ) low l a t t i c e s i t e symmetry f o r t h e complex; ( i i i ) d i f f e r e n c e s i n t h e e x t e n t o f r o t a t i o n o f t h e c o o r d i n a t e d p y r i d i n e m o l e c u l e s about the m e t a l - n i t r o g e n bond. As p o i n t e d o u t by G i l l and co-workers ( 4 8 ) , i t i s d i f f i c u l t t o r e l a t e t h e s e s p l i t t i n g s t o t h e o v e r a l l c o n f i g u r a t i o n o f t h e complex. L i t t l e and Long (49) have s t u d i e d t h e complexes Fe(py) X„ where X=C1, B r , I , NCO, NCS, and NCSe and x=2 o r 4. They have n o t e d l a r g e s h i f t s f o r f i v e bands o f p y r i d i n e * '8a, 1, 11, 6a, and 16b, compared t o t h e f r e e b ase. They b e l i e v e t h a t t h e i n c r e a s e i s a r e s u l t o f p y r i d i n e r i n g / p y r i d i n e r i n g i n t e r a c t i o n s i n t h e t e t r a k i s -( p y r i d i n e ) complexes and p y r i d i n e r i n g / b r i d g i n g l i g a n d ( X ) i n t e r a c t i o n s i n t h e b i s ( p y r i d i n e ) complexes. They s t a t e t h a t each o f t h e normal v i b r a t i o n s (except 11) w i l l t e n d t o move t h e p y r i d i n e towards the c e n t e r o f t h e complex and t h e s e bands t h e n s h i f t t o h i g h e r energy because t h e v i b r a t i o n a l modes i n c r e a s e t h e s t e r i c i n t e r a c t i o n o f a d j a c e n t p y r i d i n e m o l e c u l e s . These a u t h o r s r e p o r t t h a t t hey a r e w o r k i n g on a normal c o o r d i n a t e a n a l y s i s t o v e r i f y t h e s e i d e a s but t h i s work had n o t appeared i n t h e l i t e r a t u r e when t h i s t h e s i s was w r i t t e n . The s p e c t r a of c o o r d i n a t i o n compounds, c o n t a i n i n g c o o r d i n a t e d . p y r i d i n e only, should not show bands a t 1572, 603, and 403 cm" 1 i n . the i n f r a r e d .region. These bands, 8a, 6a, and 16b, u n l i k e the 1 and 11 bands, are w e l l separated from other bands and thus provide a good t e s t f o r p y r i d i n e c o o r d i n a t i o n . Goodgame and Hayward have st u d i e d the e f f e c t of c o o r d i n a t i o n t o metal ions on the v i b r a t i o n s of 4-methyl-p y r i d i n e (50) . As i n the s t u d i e s on p y r i d i n e , most of the bands observed i n the f r e e base spectrum appear i n the spectrum of the coordinated base w i t h minor and g e n e r a l l y random s h i f t s i n energy. There are f i v e bands which undergo s i g n i f i c a n t s h i f t ; 8a, 9a, 1, 10b+12, and 6a at 1608, 1224, 997, 800, and 515 cm 1 r e s p e c t i v e l y i n the f r e e base. The absence of these free base bands provides good evidence t h a t a l l the 4-methylpyridine l i g a n d s i n a complex are coordinated. Again, some minor s p l i t t i n g may be observed due t o i n e g u i v a l e n t 4-methylpyridine l i g a n d s . Studies of the e f f e c t of c o o r d i n a t i o n on the v i b r a t i o n s of 3-methylpyridine have not been reported i n the l i t e r a t u r e . In our work, the 3-methylpyridine bands i n the i n f r a r e d s p e c t r a of the compounds w i l l be compared to the free base and some attempt w i l l be made to c o r r e l a t e the s h i f t s (see Appendix. 1, Table Al-3).. -27-2.2.4.2 HEXAFLUOROPHOSPHATE AND HEXAFLUOROARSENATE There a r e many h e x a f l u o r o - m e t a l l a t e s p e c i e s , MF, n, known (where n = -3, -2, - 1 , 0 depending on M and i t s o x i d a t i o n s t a t e ) ( 5 1 ) . The group t h e o r y and a n a l y s i s o f t h e v i b r a t i o n a l modes o f t h e h e x a f l u o r o m e t a l l a t e m o i e t y i n o c t a h e d r a l symmetry r e q u i r e s t h a t t h e y have s i x fundamental v i b r a t i o n s ; 2 T l u ' s ' ( i n f r a r e d a c t i v e ) and an A ^ g f a T 2 g ' and an E v i b r a t i o n ( a l l t h r e e Raman a c t i v e ) and a T„ g 2u v i b r a t i o n ( n e i t h e r i n f r a r e d n or Raman a c t i v e ) . T a b l e I I - l shows t h e band p o s i t i o n s and a s s i g n -ments i n t h e v i b r a t i o n a l s p e c t r a o f some h e x a f l u o r o p h o s p h a t e and h e x a f l u o r o a r s e n a t e s a l t s . As would be e x p e c t e d when t h e s e a n i o n s p o s s e s s 0^ symmetry, t h r e e bands a r e o b s e r v e d i n t h e Raman s p e c t r a and two bands i n t h e i n f r a r e d . The p o s i t i o n o f t h e ^^(^2^ v l k r a t i o n has been c a l c u l a t e d ; a t 402 c m - 1 f o r P F g - (7) and a t 228 c m - 1 f o r AsFg" ( 8 ) . I f t h e EF ~ a n i o n has a symmetry lo w e r than 0, t h e b n appearance o f t h e Raman and i n f r a r e d s p e c t r a may change. T a b l e } i'II-2 shows t h e c o r r e l a t i o n f o r t h e EFg (0^) v i b r a t i o n s i n some lo w e r symmetries. T h e i r Raman and/or i n f r a r e d a c t i v i t i e s a r e a l s o i n d i c a t e d ( 55). One o b j e c t i v e o f .the c u r r e n t work i s t o . c o r r e l a t e t h e o b s e r v e d a n i o n i n f r a r e d "spectra w i t h t h e a n i o n e n v i r o n -ments i n t h e compounds s t u d i e d . Q u e s t i o n s t h a t we have TABLE I I - 1 VIBRATIONAL SPECTRA OF SOME M(EFg) (E=P, As) SALTS INFRARED RAMAN ( a ) COMPOUND REFERENCE ' V T l u > V T l u > w w KPF, 6 NaPFg (7) 830s 558m 751(10) 580 (2) 477 (4) ( 5 3 ) ( b ) 837s 559s 767(10) 580 (3) 475 (5) NH.PF, 4 6 ( 5 4 )( C ) 830s 565s 562s 748 (10) 580 ( .4) 476 (.1) KAsFg (52) 698s 382s 692 580 375 CsAsFg (7) 699s 392m 685(10) 576 (2.3) 372 (2.6) A s C l 4 A s F g (51) 706 402 389 682 583 372 (a) numbers i n b r a c k e t s i n d i c a t e r e l a t i v e i n t e n s i t y (b) spectrum a t 25°C (c) spectrum a t 298 K TABLE 11-2 CORRELATION OF E F g " (O h) VIBRATIONS IN SOME LOWER SYMMETRIES °h + D 4 h 4v ^ °3 2v T l u ( I ) * A 2 u ( I ) + A 1 ( I , R ) - A 2 ( I ) A 1 (I ,R) + E u ( I ) -> E (I,R) E (I,R) •> B 1 ( I , R ) B 2 ( I , R ) A l g ( R ) - A l g ( R ) -> A 1 ( I , R ) + A 1 ( R ) -* A 1 (I ,R) E g ( R ) + A l g ( R ) + B l g ( R ) -> A 1 ( I , R ) •+ B 1 ( R ) -> E(I,R) A-^  (I,R) -> A 2 ( R ) T 2 g ( R ) + B 2 g ( R ) * E g ( R ) B 2 ( R ) + E (I,R) -> A ]_(R) -> E (I,R) -> A^ ( I , R) -> B 1 ( I , R ) -»• B 2 ( I , R ) T 2 u ( - } ^ B 2 u ( - ) -»-B1(R) ->A 1(R) ->A 2(R) ->E (I.,R) ""E (I,R) - * B 1 ( I f R ) ^ B 2 (I,R) (I) i n f r a r e d a c t i v e , (R) Raman a c t i v e , (-) i n f r a r e d and Raman -30-a s k e d i n c l u d e : "What i s t h e t y p i c a l s p e c t r u m when t h e a n i o n i s i n l o w s i t e symmetry?"; "What i s t h e t y p i c a l s p e c t r u m when t h e a n i o n i s p e r t u r b e d by t h e p r e s e n c e o f a m e t a l i o n ? " ; " I n any o f t h e s e c a s e s , i s t h e r e s p l i t t i n g o f t h e d e g e n e r a t e v i b r a t i o n s , a c t i v a t i o n o f f o r m a l l y f o r -b i d d e n (O h) v i b r a t i o n s , o r s i g n i f i c a n t s h i f t s i n band p o s i t i o n ? " ; " I f t h e r e a r e c a s e s o f c o o r d i n a t i o n o f t h e a n i o n t o a m e t a l , what i s t h e i n f r a r e d c r i t e r i o n f o r c o o r d i n a t i o n ? " . 2.2.5 X-RAY CRYSTALLOGRAPHY The h i s t o r i c a l d e v e l o p m e n t and e s t a b l i s h e d p r i n c i p l e s o f X - r a y c r y s t a l l o g r a p h y a r e d e a l t w i t h i n a number o f ; s t a n d a r d t e x t b o o k s (5.6-58. f o r example) .. The c r y s t a l -l o g r a p h i c s y m b o l s a n d n o m e n c l a t u r e u s e d i n t h i s t h e s i s have t h e i r c o n v e n t i o n a l m e a n i n g as g i v e n i n t h e " I n t e r -n a t i o n a l T a b l e s f o r X - r a y C r y s t a l l o g r a p h y " ( 5 9 ) . The methods em p l o y e d i n t h e i n i t i a l s p a c e group., d e t e r m i n a t i o n s a r e d e s c r i b e d i n S e c t i o n 6.3.5, a l o n g w i t h t h e s e m i - a u t o m a t e d methods o f r e f l e c t i o n i n t e n s i t y m easure-ment. The m o l e c u l a r s t r u c t u r e s were d e t e r m i n e d e i t h e r b y t h e u s e b y t h e P a t t e r s o n f u n c t i o n o r by d i r e c t methods as d e s c r i b e d i n t h e a p p r o p r i a t e p a r t o f S e c t i o n 6.5. -31-2.3 ELECTRONIC STRUCTURE AND STEREOCHEMISTRY T h i s s e c t i o n d e a l s w i t h t h e c o r r e l a t i o n o f the o b s e r v a b l e magnetic and s p e c t r a l p r o p e r t i e s o f c o b a l t ( I I ) , n i c k e l ( I I ) , and c o p p e r ( I I ) c o o r d i n a t i o n compounds w i t h t h e s t e r e o c h e m i s t r y • o f t h e f i r s t c o o r d i n a t i o n sphere about the m e t a l i o n . The t h r e e dominant s o l i d s t a t e s t e r e o c h e m i s t r i e s f o r t h e s e m e t a l ( I I ) i o n s a r e square p l a n a r ( D ^ ^ ) , t e t r a -h e d r a l ( T ^ ) , and o c t a h e d r a l ( 0 ^ ) . A l t h o u g h , t h e microsymmetry about t h e m e t a l i o n may not s t r i c t l y be D^, T^, o r 0^, o f t e n t h e o b s e r v a b l e p r o p e r t i e s may be u n d e r s t o o d by the a n a l y s i s u s i n g one o f t h e s e f o r m a l symmetries. F o r example, i n a complex w i t h a N i N ^ ^ chromophore t h e h i g h e s t microsymmetry p o s s i b l e i s D ^ b u t i f t h e e l e c t r o n i c spectrum and t h e magnetic moment d i f f e r o n l y m a r g i n a l l y from t h a t e x p e c t e d and seen f o r n i c k e l ( I I ) complexes w i t h 0 h symmetry (eg. NiNg) , the s t r u c t u r e can be a s s i g n e d t o an " o c t a h e d r a l " complex o f n i c k e l ( I I ) . The same a p p l i e s t o t e t r a h e d r a l and square p l a n a r complexes. The c o b a l t ( I I ) , n i c k e l ( I I ) , and c o p p e r ( I I ) i o n s w i l l be d i s c u s s e d i n o r d e r . The f r e e i o n s t a t e s and t h e c o r r e l a t i o n w i t h t h e l i g a n d f i e l d s t a t e s i n o c t a h e d r a l , t e t r a g o n a l l y d i s t o r t e d o c t a h e d r a l , and t e t r a h e d r a l c o o r d i n a -t i o n geometry w i l l be d i s c u s s e d f o r c o b a l t ( I I ) and n i c k e l ( I I ) . The square p l a n a r c o o r d i n a t i o n geometry o f n i c k e l ( I I ) -32-and t h e t e t r a g o n a l l y d i s t o r t e d c o o r d i n a t i o n g e o m e t r y o f c o p p e r ( I I ) w i l l be d i s c u s s e d i n t e r m s o f d o r b i t a l s p l i t t i n g s . F o r " o c t a h e d r a l " and " t e t r a h e d r a l " c o o r d i n a t i o n g e o m e t r i e s , o n l y t h e h i g h s p i n s y s t e m s w i l l be c o v e r e d . 2.3.1 C O B A L T ( I I ) (60) C o b a l t ( I I ) h as s e v e n d e l e c t r o n s i n - i t s - v a l e n c e . s h e l l . 4 I n t h e g a s e o u s f r e e i o n , t h e g r o u n d s t a t e i s F, i n t h e a b s e n c e o f s p i n - o r b i t c o u p l i n g , w i t h a h i g h e r P t e r m o f t h e same s p i n m u l t i p l i c i t y . The v a l u e s o f B Q and X Q (31) a r e 971 and 172 cm-"'", r e s p e c t i v e l y . I n t h e p r e s e n c e o f an o c t a h e d r a l o r t e t r a h e d r a l l i g a n d f i e l d , t h e f r e e i o n g r o u n d t e r m i s 4 4 4 s p l i t i n t o 4 A 2 ( g ) , 4 T 2 ( g ) , and 4 T 1 ( g ) t e r m s and t h e P becomes a 4 T 1 ( g ) t e r m . The c o r r e l a t i o n o f t h e f r e e i o n s t a t e s and weak l i g a n d f i e l d s t a t e s - i s shown i n F i g u r e 2.1 2.3.1.1 OCTAHEDRAL COBALT(II) - ELECTRONIC SPECTRAL PROPERTIES I n an o c t a h e d r a l l i g a n d f i e l d , t h e g r o u n d t e r m i s 4 T The t h r e e s p i n - a l l o w e d t r a n s i t i o n s one w o u l d l g * e x p e c t to. s e e i n t h e e l e c t r o n i c s p e c t r a a r e t o t h e -34-4 T 0 , 4A„ , and 4T, (P) excited states. Table II-3 shows 2g' 2g' l g the dependence of the t r a n s i t i o n energies as a function of Dq and B (from r e f . 32 p. 181). In practice, usually only two r e l a t i v e l y strong bands are observed due to 4 T l g ( F ) * 4 T 2 g ( v 1 ) and 4 T l g ( F ) + 4 T l g ( P ) (v 3>; the 4 T l g - 4 A 2 g ( v , ) t r a n s i t i o n i s much weaker because i t i s formally a two 5 2 electron t r a n s i t i o n (strong f i e l d configuration (t ) (e ) g g 3 4 • . -*(t„ ) (e ) ). Given the two observed t r a n s i t i o n energies 2g g p v^'and v^, values of Dq and B can be obtained by substitution into the expressions of Table II-3. Calculated values of v-^ , v 2, and can then be obtained and compared with the observed t r a n s i t i o n energies. 2.3.1.2 OCTAHEDRAL COBALT(II)-MAGNETIC PROPERTIES 4 The ground term, T]_g' possesses both spin (3 unpaired electrons, S=3/2) and o r b i t a l ( L r l ) angular momentum. The value of Veff expected for an octahedral cobalt(II) complex would be higher than the spin only moment (3.87 B.M.) and be expected to be temperature dependent. The magnetic properties observed for octahedral cobalt(II) complexes-are very complex and F i g g i s 1 four parameter model (61) has been used to explain these magnetic properties. The model considers the energy lev e l s of the 4 . T^ g ground state under the simultaneous perturbations TABLE II-3 SPIN ALLOWED TRANSITION ENERGY EXPRESSIONS FOR OCTAHEDRAL OR TETRAHEDRAL n T ± ( g ) GROUND TERMS * = 5Dq-7.5B+^(225B 2+100Dq 2+180DqB) ** 2 ( n T 1 ( g ) ( F ) - > n A 2 g ) = 15Dq-7.5B+35 (225B 2+100Dq 2+180DqB) 3 ( n T 1 ( g ) ( F ) * n T 1 ( g ) ( P » » = (225B 2+100Dq 2+180DqB) 2 * n = 2S+1, n=4 f o r o c t a h e d r a l c o b a l t ( I I ) and n= 3 f o r t e t r a h e d r a l n i c k e l ( I I ) -36-o f low symmetry l i g a n d f i e l d s and s p i n - o r b i t c o u p l i n g . The f o u r p a r a m e t e r s u s e d i n t h e model a r e A,k', X, and A; F i g u r e 2.2 r e p r e s e n t s t h e r e l a t i o n s h i p s between them. "A" i s d e r i v e d f r o m t h e Dg and B v a l u e s d e t e r -m i n e d f r o m t h e e l e c t r o n i c s p e c t r u m . I t i s a. measure o f t h e 4 i n t e r a c t i o n o f t h e g r o u n d s t a t e T i g ( F ) a n d t n e e x c i t e d 4 s t a t e T ^ g ( P ) ; t h e y i n t e r a c t b e c a u s e t h e y have s i m i l a r symmetry ( T ^ ^ ) . "A" v a r i e s f r o m 1.5 (weak f i e l d l i m i t ) t o 1.0 ( s t r o n g f i e l d l i m i t ) . E q u a t i o n s 2.6 and 2.7 show how "A" may be c a l c u l a t e d : c=1.5-(7.5Dq/B-{25+45B/Dq+225/4 ( B / D q ) 2 } 3 2 . . . (2.6) A = ( 1 . 5 - c 2 ) / ( l + c 2 ) ...(2.7) 4 A i s t h e s p l i t t i n g o f t h e T i g s t a t e i n sym-4 m e t r y and i s p o s i t i v e when t h e o r b i t a l s i n g l e t ( A 2 g ) i s 4 4 4 l o w e r i n e n e r g y ( T i g ( ° j 1 ^ A 2 g + E g ^ D 4 h ^ a n d """s d e r i v e d f r o m t h e f i t o f t h e e x p e r i m e n t a l d a t a t o t h e t h e o r e t i c a l c u r v e . X i s t h e s p i n - o r b i t p a r a m e t e r and i s t r e a t e d as a v a r i a b l e u s e d i n t h e f i t t i n g p r o c e d u r e , k' i s t h e o r b i t a l r e d u c t i o n f a c t o r . The e x p e r i m e n t a l d a t a a r e p l o t t e d , V e f f v s . kT/X (where k i s t h e B o l t z m a n n c o n s t a n t and T i s t h e t e m p e r a t u r e i n K e l v i n ) , and f i t t e d t o a t h e o r e t i c a l c u r v e ( A , v = ( A / X ) , and k ' ) . Computer g e n e r a t e d v a l u e s o f VQ^f f o r d i f f e r e n t v a l u e s o f kT/X, v, A, and k' a r e a v a i l a b l e i n t h e l i t e r a t u r e ( 6 1 ) . -37-CUBIC TETRAGONAL a+b SPIN-ORBIT CUBIC F I E L D DISTORTION COUPLING FIELD (a) (b) F I G 2 . 2 4 T n TERM UNDER THE SIMULTANEOUS PERTURBATIONS OF l g SPIN-ORBIT COUPLING AND LOW SYMMETRY. -38-The a p p r o x i m a t i o n s i n h e r e n t i n t h i s model a r e ( 6 1 ) : ( i ) t h e low symmetry l i g a n d f i e l d components a r e o f a x i a l r a t h e r t h a n o f l o w e r symmetry. ( i i ) t h e s u b s t a n c e s a r e m a g n e t i c a l l y d i l u t e , ( i i i ) t h e magnitude o f t h e low symmetry l i g a n d f i e l d i s independent o f t e m p e r a t u r e . ( i v ) e x c i t e d terms a r e n o t i m p o r t a n t ( i . e . no c o n f i g u r a t i o n i n t e r a c t i o n ) . F i g g i s e t a l . have a l s o used t h i s t y p e o f model t o e x p l a i n t h e magnetic b e h a v i o r o f o t h e r h i g h s p i n o r b i t a l l y degenerate ground s t a t e s . The r e s u l t s o f t h e s e i n v e s t i g a t i o n s a r e a v a i l a b l e i n t h e l i t e r a t u r e f o r 2 T 2 g ( 6 2 ) , 5 T 2 g ( 6 3 ) , 3 T ; L ( 6 4 ) ground s t a t e s . 2.3.1.3 TETRAHEDRAL COBALT(II) - ELECTRONIC SPECTRAL PROPERTIES I n a t e t r a h e d r a l l i g a n d f i e l d , t h e ground term 4 . 4 i s A 2 . The t h r e e s p i n a l l o w e d t r a n s i t i o n s from A 2 t o 4 4 4 T 2, T 1 ( F ) , and T-L(P) ( v ^ , v 2 , and v^, r e s p e c t i v e l y ) s h o u l d be o b s e r v e d . I n p r a c t i c e , however, v-^  i s o f t e n n o t r e p o r t e d because i t i s a t low energy i n t h e near-i n f r a r e d o r i n f r a r e d r e g i o n s , o u t o f t h e range cov e r e d by t h e e x p e r i m e n t . The e x p r e s s i o n s f o r t h e t r a n s i t i o n e n e r g i e s f o r t h e t h r e e s p i n - a l l o w e d t r a n s i t i o n s a r e g i v e n -39-i n T a b l e I I - 4 . The v a l u e s o f Dq and B c a n be c a l c u l a t e d f r o m t h e q u a d r a t i c e q u a t i o n s (65 ) : 340Dq 2-18 ( V^+v^-Dq+ V j V-^O ....(2.8) B =(v 2+v 3-30Dq)/15 (2.9) 2.3.1.4 TETRAHEDRAL COBALT(II)-MAGNETIC PROPERTIES 4 The A 2 g r o u n d t e r m has s p i n ( S = 3 / 2 ) b u t no a n g u l a r momentum a s s o c i a t e d w i t h i t . The m a g n e t i c moment w o u l d be e x p e c t e d t o be c l o s e t o t h e s p i n - o n l y v a l u e and be t e m p e r a t u r e i n d e p e n d e n t . I n T^ symmetry, t h e r e c i p r o c a l o f x m s h o u l d be. d i r e c t l y p r o p o r t i o n a l t o T b u t d e v i a t i o n s f r o m t h i s b e h a v i o r (9^0) a r e o f t e n o b s e r v e d i n d i c a t i n g low symmetry components t o t h e l i g a n d f i e l d . The d e v i a t i o n o f t h e moment f r o m t h e s p i n - o n l y v a l u e i n d i c a t e s t h e e f f e c t s o f s p i n - o r b i t c o u p l i n g w i t h e x c i t e d s t a t e s ; as a r e s u l t t h e m a g n e t i c moment i s m o d i f i e d a c c o r d i n g t o : u - f=y (l-4A/10Dq) (2.10) o r y e f f = U s . o . (1-4 ( k ^ A ^ l O D q ) (2.11) X i s t h e s p i n - o r b i t c o u p l i n g p a r a m e t e r f o r t h e complex ( v a r i e s d e p e n d i n g on t h e complex), k 1 i s t h e o r b i t a l r e d u c t i o n f a c t o r and X Q i s t h e f r e e - i o n s p i n - o r b i t c o u p l i n g c o n s t a n t . TABLE I I - 4 SPIN-ALLOWED TRANSITION ENERGY EXPRESSIONS FOR OCTAHEDRAL OR TETRAHEDRAL R A 0 , N GROUND TERMS * 2 (g) v l ( n A 2 ( g ) " n T 2 ( g ) ) = lODq V n A 2 ( g r n T l ( g ) ( F ) ) = 7.5B+15Dq-%(225B 2+100Dq 2-180DqB) 2 V n W n T l ( g ) ( P ) ) = 7.5B+15Dq+ i5(225B 2+100Dq 2-180DqB) 2 ^ o I *n=2S+l, n=4 f o r t e t r a h e d r a l c o b a l t ( I I ) and n=3 f o r o c t a h e d r a l n i c k e l ( I I ) -41-2.3.2 N I C K E L ( I I ) (66) N i c k e l ( I I ) has e i g h t d e l e c t r o n s i n i t s v a l e n c e s h e l l 3 I n t h e g a s e o u s f r e e - i o n , t h e g r o u n d s t a t e i s F w i t h a h i g h e r o -1 e n e r g y P. The v a l u e s o f B and X ^ a r e 1080 .and 172 cm (31) " o o r e s p e c t i v e l y . I n t h e p r e s e n c e o f an o c t a h e d r a l o r t e t r a h e d r a l l i g a n d f i e l d , t h e f r e e i o n g r o u n d t e r m i s s p l i t i n t o r> 3 o 3 A~, ., T~, ,, and J T , , N terms and t h e P t e r m becomes a 2(g) 2(g) 1(g) 3 T-, , > t e r m . The c o r r e l a t i o n o f t h e f r e e i o n s t a t e s and t h e 1 (g) w e a k - f i e l d l i g a n d f i e l d s t a t e s f o r two s t e r e o c h e m i s t r i e s a r e shown i n F i g u r e 2.3. The e l e c t r o n i c s p e c t r a l and m a g n e t i c p r o p e r t i e s o f n i c k e l ( I I ) i n o c t a h e d r a l , s q u a r e p l a n a r , and t e t r a g o n a l l y d i s t o r t e d l i g a n d f i e l d e n v i r o n m e n t s w i l l be r e c o u n t e d . None o f t h e compounds i n t h i s s t u d y r e v e a l e d n i c k e l ( I I ) i n a t e t r a h e d r a l e n v i r o n m e n t , so t h i s s i t u a t i o n w i l l h o t be c o n s i d e r e d h e r e . ' t o TETRAHEDRAL OCTAHEDRAL C/B FOR TETRAHEDRAL =4.42 C/B FOR OCTAHEDRAL =4.7 2 -43-2.3.2.1 OCTAHEDRAL AND TETRAGONALLY DISTORTED OCTAHEDRAL NICKEL(II)-MAGNETIC AND SPECTRAL PROPERTIES The ground term of n i c k e l ( I I ) i n an o c t a h e d r a l 3 f i e l d i s A2g* T ^ e t r a n s i t l o n e n e r g i e s as f u n c t i o n s o f Dq and B are shown i n Table I I - 4 . The v a l u e s o f Dq and B can be c a l c u l a t e d as i n the c o b a l t ( I I ) t e t r a h e d r a l case or by u s i n g the energy as lODq, c a l c u l a t i n g B from and then comparing the c a l c u l a t e d and experimental v a l u e s of v 2 . The r e l a t i v e m e r i t s o f both methods have been d i s -cussed (67). We p r e f e r to use the former method because the d i f f u s e r e f l e c t a n c e bands ( f r e e o f background) can be used and a l s o because i t i s c o n s i s t e n t w i t h our treatment of the t e t r a h e d r a l c o b a l t ( I I ) complexes. 3 The magnetic behavior of the A 2 q. term i s s i m i l a r to t h a t o f the 4 A 9 term of t e t r a h e d r a l c o b a l t ( I I ) except *2 f o r the magnitude o f the moment. The s p i n - o n l y value f o r two unpaired e l e c t r o n s i s 2.83 B.M. The t . i . p . c o r r e c t i o n , the s i g n i f i c a n c e of the Weiss co n s t a n t ( 8 ) , and the c o r r e l a t i o n o f the v a r i a n c e o f U e f £ from .the s p i n - o n l y v a l u e are the same as recounted i n s e c t i o n 2.3.1.4. T e t r a g o n a l d i s t o r t i o n a r i s i n g from the decrease of the l i g a n d f i e l d s t r e n g t h a l o n g the z a x i s can i n o c t a h e d r a l -44-n i c k e l ( I I ) complexes cause t h e o r b i t a l l y d e g e n e r a t e T terms t o be s p l i t i n t o two components g i v i n g a t o t a l o f s i x s p i n -a l l o w e d e l e c t r o n i c t r a n s i t i o n s . The c o r r e l a t i o n diagram f o r n i c k e l ( I I ) i n 0^ and symmetries i s g i v e n i n F i g u r e 2.4. To a f i r s t a p p r o x i m a t i o n , t h e e n e r g i e s o f t h e s e 3 l o w e r symmetry ( D ^ ) s t a t e s (E( B^ g)=0) a r e g i v e n below: E ( 3 B 2 g ) = 1 0 D q x y E ( 3 E g ) = 1 0 D q x y - ( 3 5 / 4 ) D t E ( 3 A a )=10Dq +12B-4Ds-5Dt 2g' ^xy E ( 3 E b ) - 1 0 D q +12B+2Ds-25/4Dt g ^xy E ( 3 E C)=20Dq -Ds-10Dt+3B g M x y Dq i s the e q u a t o r i a l p l a n e l i g a n d f i e l d p a rameter, B has xy i t s u s u a l meaning, and Ds and Dt a r e t e t r a g o n a l p a r a m e t e r s . 3 The s p l i t t i n g o f t h e T 2 g ^ ^°h^ term i n t n e l o w e r symmetry i s (35/4) Dt and o f the 3 r r l g ( 0 h ) term i s 6Ds-(5/4) Dt. Dt i s e q u a l t o 4/7(Dq -Dq ) where Dq i s t h e a x i a l l i g a n d f i e l d xy z z parameter. Ds i s e q u a l t o ( c P X y ~ c P z ) where Cp i s t h e second o r d e r r a d i a l parameter (33) and t h e s u b s c r i p t s i n d i c a t e e q u a t o r i a l p l a n e and a x i a l s i t u a t i o n s . The i n c l u s i o n o f c o n f i g u r a t i o n i n t e r a c t i o n between 3 t h e E terms i s a f u r t h e r p e r t u r b a t i o n w h i c h can be c o n s i d e r e d g The d i a g o n a l i z a t i o n o f t h e c o n f i g u r a t i o n i n t e r a c t i o n m a t r i x w i t h 3 E a , 3 E b , and 3 E C as t h e b a s i s (Dq' i s Dq determined g g g xy 3 3 from t h e t r a n s i t i o n energy o f B]_g"*" B 2 g ^ s h o u l d g i v e v a l u e s of Ds, Dt, and B more t h e o r e t i c a l l y c o r r e c t ( i . e . t o second o r d e r ) . T h i s d e t e r m i n a n t i s g i v e n as f o l l o w s : - 4 5 -F I G . 2 .4 EFFECT ON ELECTRONIC ENERGY LEVELS OF OCTAHEDRAL N I C K E L ( I I ) IN AXIALLY E L O N G A T E D * ( D ) SYMMETRY 4n o -46-10Dq'-35Dt-E (3^/4) (4Ds+5Dt) 0 (3 %/4)(4Ds+5Dt) lODq'+Ds-(25/4)Dt+12B-E 6B 0 6B 20Dq'-Ds-10Dt+3B-E A computer program w h i c h s o l v e s t h i s d e t e r m i n a n t , g i v e n Dq , E ( 3 B , ->3Ea) , E ( 3 B , + 3 E b ) , and E ( 3 B 1 + 3E°) , has been ^xy l g g l g g l g g w r i t t e n by F . G . H e r r i n g and J.Mayo o f t h i s Department and has been used t o c a l c u l a t e t h e t e t r a g o n a l parameters d e r i v e d as a p a r t o f t h i s work. 3 The magnetic p r o p e r t i e s a s s o c i a t e d w i t h t h e 3 ground term a r e s i m i l a r t o t h o s e a s s o c i a t e d w i t h t h e A^^ term o f o c t a h e d r a l n i c k e l ( I I ) . The moments o f t h e s e compounds a r e u s u a l l y g r e a t e r t h a n 3.0 B.M. and non-zero C u r i e - W e i s s c o n s t a n t s a r e e x p e c t e d . 2.3.2.2 SQUARE PLANAR NICKEL(II)-MAGNETIC AND ELECTRONIC SPECTRAL.PROPERTIES I f n i c k e l ( I I ) i s surrounded by f o u r s t r o n g l y bound l i g a n d s w i t h t h e m e t a l and t h e l i g a n d donor atoms c o - p l a n a r , t h e s t e r e o c h e m i s t r y i s termed square p l a n a r . The c h a r a c t e r i s t -i c e l e c t r o n i c s p e c t r a l and magnetic p r o p e r t i e s o f square p l a n a r n i c k e l ( I I ) complexes a r e : ( i ) an one band spectrum, sometimes w i t h a weak band a t l o w e r energy; and ( i i ) a n e f f e c t i v e m a gnetic moment o f z e r o ( o r sometimes s l i g h t l y >0 due t o r e s i d u a l paramagnetism). -47-The e l e c t r o n i c s t r u c t u r e o f square p l a n a r complexes has been a f i e l d o f i n t e r e s t s i n c e t h e e a r l y 1960's (68) because a l l d-d t r a n s i t i o n s p o s s i b l e a r e n o t o b s e r v e d . F i g u r e 2.5 shows t h e d o r b i t a l s p l i t t i n g w i t h i n c r e a s i n g t e t r a g o n a l d i s t o r t i o n ( a x i a l e l o n g a t i o n ) . The symmetry of t h e s p i n 1 4 2 2 0 p a i r e d ground s t a t e i s A 1 ( ( e g ) ( a l g ) ( b2g^ ^ b l g ^ ^ w i t h 1 4 2 t h r e e p o s s i b l e e x c i t e d e l e c t r o n i c s t a t e s : A 2 g ( ( e g ) ( a i g ) ~ (b„ ) 1 ( b n ) 1 ) ; 1B, ( (e ) 2 (a n ) 1 ( b 0 ) 2 ( b , ) 1 ) ; and "'"E (e ) 3 -2g l g l g g l g 2g' l g g g 2 2 1 (a^g) (b2g) ( ^ i g ) )• Three d-d t r a n s i t i o n s a r e p o s s i b l e but o n l y one, o r perhaps two t r a n s i t i o n s , a r e o b s e r v e d . The pos-s i b i l i t y e x i s t s t h a t t h e two o r t h r e e o r b i t a l s e t s (e , b„ , and a-^g) a r e c l o s e i n energy and t h e o b s e r v e d spectrum i s due t o two o r t h r e e o f t h e s e t r a n s i t i o n s i n t h e band envelope (6.8.) 2.3.3 COPPER(II) q Copper ( I I ) has a d v a l e n c e e l e c t r o n c o n f i g u r a t i o n . 2 I n the f r e e - i o n , t h i s g i v e s r i s e t o a D ground s t a t e w h i c h i n the p r e s e n c e o f a r e g u l a r c u b i c l i g a n d f i e l d s p l i t s i n t o 2 2 -1 T 0> . and E, > terms. X f o r t h e f r e e - i o n i s 830 cm 2(g) (g) R e g u l a r c u b i c f i e l d s a r e n o t o b t a i n e d f o r c o p p e r ( I I ) because o f J a h n - T e l l e r d i s t o r t i o n s . The J a h n - T e l l e r theorem(69) s t a t e s t h a t any n o n - l i n e a r m o l e c u l a r system i n a degenerate e l e c t r o n i c s t a t e w i l l be u n s t a b l e and w i l l undergo some k i n d o f d i s t o r t i o n t o s p l i t t h e d e g e n e r a t e s t a t e . T h i s i s , p e r h a p s , b e s t u n d e r s t o o d -48-CUBIC D SYMMETRY SYMMETRY 4n • (AXIAL ELONGATION) INCREASING TETRAGONAL DISTORTION F I G . 2. 5 EFFECT OF INCREASING TETRAGONAL DISTORTION ON THE REAL "d" ORBITALS. - 4 9 -i n terms of the d o r b i t a l s p l i t t i n g and the "hole" formalism. Figure 2.5 shows the d o r b i t a l s p l i t t i n g for the free ion, cubic (0^) f i e l d , and increasing (axial elongation) tetragonal d i s t o r t i o n . Considering the cubic f i e l d case copper(II) has a "hole" i n the e g set, the hole can be i n d 2 2 or d 2 and by d e f i n i t i o n i s a degenerate state. It x -y :z J 3 i s e nergetically favorable for copper (II) to undergo a d i s t o r t i o n such that the d x2_ y2 and d z2 are no longer degenerate i n energy (the lowering i n the energy of the system i s 1/2 the separation of the d 2 2 (b, ) and d 2(a, ) o r b i t a l s . ^ x -y l g z l g There i s no reason f o r one type of d i s t o r t i o n according to t h i s argument, i . e . a x i a l elongation (d z2 lower i n energy) vs. a x i a l compression (d 2_ 2, lower i n energy), to be favored x y over the other but most "octahedral" complexes of copper (II) have the former type of d i s t o r t i o n (7 0). The magnetic and e l e c t r o n i c spectral properties of copper(II) complexes have been correlated with stereo-chemistry for CuN^ g chromophores by Hathaway (71). Magnetic s u s c e p t i b i l i t y measurements are generally.not useful for character-i z a t i o n except to d i s t i n g u i s h between magnetically d i l u t e and concentrated copper (II) species. A magnetic moment of 1.8-2.0 B.M. which i s e s s e n t i a l l y temperature independent indicates magnetically d i l u t e copper,i.e. a mononuclear complex. Electronic and e.s.r. (section 2.2.3) spectroscopy are more useful for s t r u c t u r a l assignment and are discussed i n more d e t a i l here. - 5 0 -2.3.3.1 COPPER(II)-ELECTRONIC SPECTRAL PROPERTIES C o n s i d e r i n g t h e d o r b i t a l s p l i t t i n g s f o r t h e p o s s i b l e l i g a n d s t e r e o c h e m i s t r i e s , t h e r e a r e , i n p r i n c i p l e f o u r p o s -s i b l e d->d t r a n s i t i o n w h i c h s h o u l d be o b s e r v e d . I n p r a c t i c e v e r y few compounds o f c o p p e r ( I I ) g i v e any i n d i c a t i o n o f more t h a n two b a n d s . Some c o m p l e x e s y i e l d s p e c t r a i n v o l v i n g two c l e a r l y r e s o l v e d b a n d s , b u t many c o m p l e x e s show a main band w i t h a low f r e q u e n c y s h o u l d e r o n l y p a r t i a l l y r e s o l v e d . O t h e r c o m p l e x e s y i e l d o n l y one band w i t h no i n d i c a t i o n o f s p l i t t i n g o r o f a s e c o n d band ( 7 1 ) . F i g u r e 2.6 shows Hathaway's c o r r e l a t i o n d i a g r a m o f t h e e n e r g y o f t h e c e n t e r o f g r a v i t y o f t h e m a i n a b s o r p t i o n b a n d o f c o p p e r ( I I ) and t h e p r e d i c t e d s t e r e o c h e m i s t r y o f t h e c h r o m o p h o r e , C u N 4 _ g , p r e s e n t ( 7 1 ) . T h i s d i a g r a m s e r v e s as a u s e f u l g u i d e f o r a s s i g n m e n t o f t h e s t e r e o c h e m i s t r y f o r C u ^ O y c h r o m o p h o r e s (4-x+y-6) a l s o . B u t i n some s y s t e m s (CuN^. and CuN g ( 7 2 ) , f o r example) t h e s c a l e s f o r t h e chromo-p h o r e s t e r e o c h e m i s t r y o v e r l a p and i t i s h a r d t o d i s t i n g u i s h b e tween t h e s t e r e o c h e m i s t r i e s . S e c t i o n 4.3.2.1 o f t h i s t h e s i s d e s c r i b e s t h e d e t a i l s o f t h e e l e c t r o n i c s p e c t r a , d e r i v e d f r o m s i n g l e c r y s t a l X - r a y m o l e c u l a r s t r u c t u r e d e t e r m i n a t i o n s and p o l a r i z e d e l e c t r o n i c s p e c t r a , f o r v e r y t e t r a g o n a l l y d i s t o r t e d o c t a h e d r a l c o m p l e x e s . CIS-DISTORTED OCTAHEDRAL CuNg TRIGONAL PYRAMIDAL CuN SQUARE BASED PYRAMIDAL CuN 5 TRIGONAL OCTAHEDRAL CuN g RHOMBIC OCTAHEDRAL CuNg RESTRICTED TETRAGONAL OCTAHEDRAL CuNg TETRAGONAL OCTAHEDRAL CuNg COMPRESSED TETRAHEDRAL C u N 4 SQUARE COPLANAR C u N 4 10 11 13 14 ^ ENERGY (kK= 10 .cm ) F I G . 2.6 CORRELATION OF BAND MAXIMA AND STEREOCHEMISTRY FOR CuN 4_g CHROMOPHORES -52-2.3.3.2 COPPER(II)-ELECTRON SPIN RESONANCE SPECTROSCOPY As m e n t i o n e d i n s e c t i o n 2.2.3, an e . s . r . s p e c t r u m o f a c o p p e r ( I I ) complex y i e l d s g v a l u e s w h i c h a r e c h a r a c t e r i s t i c o f t h e c o p p e r ( I I ) i o n i n t h a t m o l e c u l a r u n i t . Hathaway has a t t e m p t e d t o c o r r e l a t e l i n e s hape w i t h t h e s t e r e o c h e m i s t r y a b o u t c o p p e r ( I I ) ( 7 3 ) . We w i l l o n l y c o n s i d e r t h e c a s e where c o p p e r ( I I ) i s i n a d i s t o r t e d o c t a h e d r a l l i g a n d f i e l d and y i e l d s a x i a l (gj. and gn ) s p e c t r a . The f o r m s o f e q u a t i o n 2.4 w h i c h a p p l y f o r t e t r a -g o n a l l y d i s t o r t e d o c t a h e d r a l c o p p e r ( I I ) c o m p l e x e s a r e : f o r a x i a l e l o n g a t i o n : g„= g e (1- (8 X/E ( d x 2 _ y 2 - d x y ) ) ) (2.12) g i = g e ( l - ( 2 X / E ( d x 2 _ y 2 - d x z , d y z ) ) ) ....(2.13) and f o r a x i a l c o m p r e s s i o n : g„ = g e . (2.14) 5x= g e d - ( 6 X / E ( d z 2 - d x y , d y z ) ) ) (2.15) The two t y p e s o f t e t r a g o n a l d i s t o r t i o n s c a n a p p a r e n t l y , be d i s t i n g u i s h e d by t h e v a l u e o f g(| ,where g(j = g g i n d i c a t e s an a x i a l l y c o m p r e s s e d o c t a h e d r o n . The s p i n ( s = l / 2) o f t h e c o p p e r ( I I ) d e l e c t r o n i n t e r -a c t s w i t h t h e n u c l e a r s p i n (1=3/2) o f t h e c o p p e r n u c l e u s , g i v i n g r i s e t o f o u r (21+1) s t a t e s f o r e a c h g v a l u e . T h i s i s i l l u s -t r a t e d i n F i g u r e 2.7 where t h e a l l o w e d t r a n s i t i o n s ( s e l e c t i o n r u l e s : Am+=0; Am =1) a r e shown. T h e r e a r e f o u r t r a n s i t i o n s f o r e a c h g v a l u e . -53-F I G . 2. 7 ENERGY LEVEL DIAGRAM FOR S=l/2 AND 1=3/2 -54-The i n t e r a c t i o n between t h e e l e c t r o n s p i n and t h e n u c l e a r s p i n c a n be r e p r e s e n t e d by t h e s p i n H a m i l t o n i a n H (7.4) i n a x i a l symmetry as b e l o w : H = 8 ( g l ( H z S z + g x ( H x S x + H y S y ) ) + A S z I z + B ( S x L x + S y L y ) . . (2.16) where 6 i s t h e Bohr magneton,. H x ' y ' z """S t * i e m a g n e t i c f i e l d a l o n g e a c h a x i s , S x , y , z i s t h e e l e c t r o n s p i n on e a c h a x i s , I , , i s t h e n u c l e a r s p i n a t e a c h a x i s , and A and B a r e t h e x ' y ' z ^ h y p e r f i n e c o u p l i n g c o n s t a n t s p a r a l l e l and p e r p e n d i c u l a r t o t h e Z a x i s o f t h e m o l e c u l e r e s p e c t i v e l y . The m a g n i t u d e and s i g n o f A and B a r e d e p e n d e n t on t h e i n t e r a c t i o n between t h e n u c l e a r m a g n e t i c moment and t h e m a g n e t i c moment o f t h e u n p a i r e d d e l e c t r o n . I t h as b e e n shown by Sand (75) t h a t t h e e . s . r . s p e c t r u m o f c o p p e r ( I I ) i n a x i a l symmetry w i l l c o n s i s t o f a s e t o f f o u r weak l i n e s a r o u n d gu and a s e t o f f o u r s t r o n g l i n e s a r o u n d g x . F i g u r e 2.8 shows t h e a p p e a r a n c e o f t h i s s i t u a t i o n and how t h e p a r a m e t e r s gu, g x and A c a n be d e r i v e d f r o m t h e s p e c t r u m . B i s u s u a l l y v e r y s m a l l and c a n n o t be d e r i v e d f r o m t h e s p e c t r u m . However, i f an i s o t r o p i c s o l u t i o n s p e c t r u m i s a v a i l a b l e , B c a n be c a l c u l a t e d f r o m t h e v a l u e o f A Q ( c f . g Q , e q u a t i o n 2.5) by u s e o f e q u a t i o n 2.17. A Q = 1/3 (A + 2B) (2.17) E . s . r . s p e c t r a a r e r e c o r d e d a s t h e f i r s t d e r i v a t i v e s o f a b s o r p t i o n s p e c t r a . The components (g f > and g x ) o f t h e a x i a l s p e c t r u m have d i f f e r e n t l i n e s h a p e s ( 7 6 ) . g x c a n be A H„ H-I Ul l J L 4 -H, F I G . 2.8 APPEARANCE OF AXIAL COPPER(II) E.S.R. SPECTRUM -56-determined from the l a r g e i n f l e c t i o n p o i n t of the spectrum whereas g)( has t o be determined from the H^^.^(maxima of the peaks i n the f i r s t d e r i v a t i v e spectrum) values and the A value ( H ^ ^ y H A m ( I + l ) ^ * A n o t n e r method to determine g„ i f the i s o t r o p i c s o l u t i o n spectrum i s a v a i l a b l e i s by use of equation 2:. 5 (page 23). This i s d e s i r a b l e when the components of the perpendicular spectrum overlap w i t h the p a r a l l e l spectrum. -57-2.4 APPROACHES TO COMPOUND CHARACTERIZATION When a compound was f i r s t i s o l a t e d as a powder, t h e i n f r a r e d s p e c t r u m o f t h e compound was o b t a i n e d and examined f o r t h e p r e s e n c e o f n o n - c o o r d i n a t e d l i g a n d ( s e c t i o n 2.2.4) and l a t t i c e w a t e r . I f t h e s e were n o t p r e s e n t , t h e e l e m e n t a l a n a l y s i s was o b t a i n e d . I f t h e s e r e s u l t s i n d i c a t e d t h a t t h e compound was p u r e , t h e s t a n d a r d t e c h n i q u e s o f e l e c t r o n i c s p e c t r o s c o p y ( m u l l , d i f f u s e r e f l e c t a n c e , and, i f p o s s i b l e , s o l u t i o n s p e c t r a ) and m a g n e t i c s u s c e p t i b i l i t y measurements were p e r f o r m e d . I f t h e r e s u l t s o f t h e s e s t u d i e s were s e l f -c o n s i s t e n t f o r a g i v e n s t o i c h i o m e t r y and s t e r e o c h e m i s t r y , t h e b a s i c s t r u c t u r e was c o n s i d e r e d t o be known. The i n f o r m a t i o n d e r i v e d f r o m t h e s e measurements ( a l o n g w i t h o t h e r m easure-ments, e . s . r . , X - r a y s t u d i e s , e t c . where a p p l i c a b l e ) c o u l d be u s e d t o e v a l u a t e t h e e f f e c t s o f t h e l i g a n d f i e l d on t h e m e t a l i o n a n d t o i n v e s t i g a t e t h e e n v i r o n m e n t o f t h e a n i o n . I n some c a s e s , t h e d i f f e r e n t t e c h n i q u e s a r e more s e n s i t i v e f o r d i f f e r e n t m e t a l s . F o r example, t h e c h a r a c t e r i z a -t i o n o f C o ( p y ) g ( E F g ) 2 ( s e c t i o n 3.2.2) showed t h a t t h e p r e s e n c e o f a t e t r a h e d r a l c o b a l t ( I I ) s p e c i e s i n t h e p r e d o m i n a n t l y o c t a h e d r a l c o b a l t ( I I ) sample w o u l d be s e e n o n l y by t h e use o f ( d i f f u s e r e f l e c t a n c e ) e l e c t r o n i c s p e c t r o s c o p y . The o t h e r t e c h n i q u e s were i n s e n s i t i v e . S e c t i o n 4.2.2.5 i l l u s t r a t e s how m a g n e t i c s u s c e p t i b i l i t y measurements p r o v i d e a s e n s i t i v e t e s t f o r p a r a m a g n e t i c i m p u r i t i e s i n a d i a m a g n e t i c n i c k e l ( I I ) c omplex. -58-The n e x t two c h a p t e r s w i l l p r e s e n t and d i s c u s s t h e r e s u l t s o f o u r i n v e s t i g a t i o n s . The e l e c t r o n i c s p e c t r a l d a t a and t h e i n f r a r e d s p e c t r a l bands o f t h e a n i o n s w i l l be p r e s e n t e d i n t h e a p p r o p r i a t e s e c t i o n a l o n g w i t h s e l e c t e d m a g n e t i c d a t a and i n f r a r e d s p e c t r a l d a t a . The c o m p l e t e i n f r a r e d s p e c t r a l ( o t h e r t h a n due t o t h e E F g s p e c i e s ) and m a g n e t i c d a t a a r e p r e s e n t e d i n A p p e n d i c e s 1 a n d 2 r e s p e c t i v e l y . CHAPTER 3 COMPOUNDS CONTAINING NON-COORDINATED HEXAFLUORO-PHOSPHATE AND HEXAFLUOROARSENATE T h i s c h a p t e r d e s c r i b e s and d i s c u s s e s t h e c h a r a c t e r -i z a t i o n o f tho s e compounds where t h e h e x a f l u o r o p h o s p h a t e o r h e x a f l u o r o a r s e n a t e a n i o n s a r e p r e s e n t i n t h e s o l i d s t a t e l a t t i c e as c o u n t e r i o n s and do not d i r e c t l y i n t e r a c t w i t h t h e m e t a l i o n s . Of i n t e r e s t a r e t h e p r o p e r t i e s and s t r u c t u r e s o f the complex c a t i o n s and t h e n a t u r e o f t h e a n i o n environment as e v i d e n c e d by v i b r a t i o n a l ( i n f r a r e d ) s p e c t r a l s t u d i e s . -60-3 .1 INTRODUCTION 2 + I n t e r e s t i n f o r m i n g a s p e c i e s o f t h e t y p e M ( p y ) g w i t h f i r s t row t r a n s i t i o n m e t a l elements i s i n p r o p e r l y c h a r a c t e r i z i n g t h e s e h i g h l y symmetric s p e c i e s f o r comparison 2 + w i t h o t h e r c l a s s i c a l complex c a t i o n s , such as M ( H 2 0 ) g A l t h o u g h many complexes c o n t a i n i n g c o o r d i n a t e d p y r i d i n e a r e known, p r e v i o u s w o r k e r s have e x p e r i e n c e d c o n s i d e r a b l e d i f -f i c u l t y i n o b t a i n i n g complex s p e c i e s , p a r t i c u l a r l y i n t h e s o l i d s t a t e , where o n l y p y r i d i n e i s c o o r d i n a t e d t o t h e m e t a l . A v a r i e t y o f reas o n s can be advanced f o r t h i s i n c l u d i n g s o l u t i o n and l a t t i c e e nergy e f f e c t s , e n t r o p y and k i n e t i c f a c t o r s and s t e r i c f a c t o r s ( 1 7 ) . 2 + By t h e e a r l y 1970's, t h e o n l y two M ( p y ) g s p e c i e s c h a r a c t e r i z e d i n t h e s o l i d s t a t e were i n ( F e ( p y ) g ) ( F e 4 C 0 1 3 ) (18) and N i ( p y ) g ( P F g ) 2 ( 1 4 ) . X-ray s t r u c t u r a l s t u d i e s on 2+ the former compound showed the pr e s e n c e o f t h e F e ( p y ) g c a t i o n i c u n i t . The e l e c t r o n i c spectrum o f t h e l a t t e r compound was s i m i l a r t o t h e s o l u t i o n s p ectrum o f N i (py) 4 (Cl'O.^) 2 i n 2 + p y r i d i n e w h i c h had been a s s i g n e d t o a N i ( p y ) g s p e c i e s . 2 + The f o r m a t i o n o f t h e M ( p y ) g s p e c i e s i n t h e s e s i t u a t i o n s s u g g e s t s t h a t a l a r g e w e a k l y b a s i c a n i o n i s needed t o s t a b i l i z e t h e l a r g e c a t i o n i n t h e s o l i d s t a t e . There has been a v e r y r e c e n t r e p o r t o f the X-ray c r y s t a l and m o l e c u l a r s t r u c t u r e o f Ru(py) g ( B F 4 ) 2 ( 7 7) • T h i s -61-s t r u c t u r e shows t h e p r e s e n c e , ( i n t h i s i n s t a n c e w i t h a s e c o n d 2 + row t r a n s i t i o n m e t a l ) o f M ( p y ) g a g a i n w i t h a l a r g e and w e a k l y b a s i c a n i o n . T h i s c h a p t e r d e s c r i b e s t h e s y n t h e s i s and s t u d y o f s e v e r a l compounds t h a t c o n t a i n complex c a t i o n i c s p e c i e s and n p n ^ c o o r d i n a t e d E F g 7 " a n i o n s , I n c l u d e d h e r e a r e t h e c h a r a c t e r i z a -t i o n s o f C o ( p y ) g ( E F g ) 2 and N i ( p y ) g ( E F g ) 2 ( E = P , ' A s ) . N i ( p y ) g ( P F g ) 2 2+ has b e e n shown p r e v i o u s l y t o have t h e M ( p y ) g s p e c i e s i n t h e s o l i d s t a t e and t h e o t h e r t h r e e members o f t h e s e r i e s a r e shown h e r e t o have s i m i l - a r s t r u c t u r e s . "Attempts," i n t h e p r e s e n t work, t o o b t a i n a n a l o g o u s ( M L g ) ( E F g ) 2 c o m p l e x e s where L i s 4 - m e t h y l p y r i d i n e and 3 - m e t h y l p y r i d i n e were u n s u c c e s s f u l . I n s t e a d we o b t a i n e d compounds w i t h t h e s t o i c h i o m e t r y M ( 4 m e p y ) g ( H 2 0 ) 2 ( E F g ) 2 and M ' ( 3 m e p y ) g ( H 2 0 ) 2 ( E F g ) 2 where M-Co,Ni, M'=Co,Ni,Cu, and E=P,As. I n t h e s e c o m p l e x e s t h e f i r s t c o o r d i n a t i o n s p h e r e a r o u n d t h e m e t a l ( I I ) i o n c o n t a i n s f o u r n i t r o g e n d o n o r m o l e c u l e s (L) and two w a t e r m o l e c u l e s . T h i s c h a p t e r a l s o i n c l u d e s a d e s c r i p t i o n o f t h e s y n t h e s i s o f a s e r i e s o f compounds o f t h e t y p e C o L 4 ( E F g ) 2 -where L=py, 4mepy, and 3mepy and E=P, A s . Our work has r e v e a l e d t h a t t h e s e compounds c o n t a i n t h e n o v e l t e t r a h e d r a l 2 + C o L 4 s p e c i e s -62-3.2 OCTAHEDRAL PYRIDINE - COMPLEXES OF C O B A L T ( I I ) ; - C o ( p y ) g ( E F g ) 2 3.2.1 INTRODUCTION H e r l o c k e r a n d R o s e n t h a l (7 8) r e v i e w e d t h e l i t e r a t u r e p r i o r t o 1970 and c o n c l u d e d t h a t a t t h a t t i m e "no c o m p l e t e l y 2+ documented c a s e f o r t h e e x i s t e n c e o f C o ( p y ) g has y e t b e e n p r e s e n t e d . " Many compounds w i t h t h e e m p i r i c a l f o r m u l a , C o ( p y ) g X 2 , had b e e n p r e p a r e d a s s o l i d s t a t e m a t e r i a l s b u t 2+ p r e v i o u s t o 1970 t h e r e was no e v i d e n c e f o r C o ( p y ) g i t s e l f . When X i s a h a l i d e o r a p s e u d o h a l i d e , t h e l a t t i c e c o n s i s t s o f C o ( p y ) ^ X 2 u n i t s a n d 2 m o l e s o f n o n - c o o r d i n a t e d p y r i d i n e . When X i s n i t r a t e (NO^ ) t h e l a t t i c e c o n s i s t s o f C o ( p y ) ^ ( N O ^ ) 2 u n i t s and 3 m o l e s o f n o n - c o o r d i n a t e d p y r i d i n e . U n f o r t u n a t e l y f o r t h e compound w i t h X as p e r c h l o r a t e t h e w o r k e r s p r o v i d e d (7 9) no e v i d e n c e r e g a r d i n g t h e n a t u r e o f t h e f i r s t c o o r d i n a t i o n s p h e r e a r o u n d c o b a l t . H e r l o c k e r and R o s e n t h a l p o i n t o u t t h a t t h e c h a r a c t e r i z a t i o n o f t h e compound (Co (py)g) ( C o 2 ( C O ) g ) (8 0) i s i n c o m p l e t e ; however, s i n c e i t i s s i m i l a r t o ( F e ( p y ) 6 ) ( F e 3 ( C O ) 1 3 ) i n p r e p a r a t i o n , i t may c o n t a i n C o ( p y ) g ' 2 + Some e v i d e n c e f o r C o ( p y ) g i n s o l u t i o n h a s been p r e s e n t e d . H e r l o c k e r and R o s e n t h a l r e p o r t e d t h e s o l u t i o n e l e c t r o n i c s p e c t r u m o f C o ( p y ) 4 ( B F 4 ) 2 i n d r i e d d i s t i l l e d p y r i d i n e 2+ and a s s i g n e d i t t o t h e C o ( p y ) g s p e c i e s . They a l s o c r i t i c i z e d t h e r e p o r t o f J o n e s a n d B u l l (81) who have c l a i m e d t o o b s e r v e t h e 2+ -63-2 + e l e c t r o n i c s p e c t r u m o f C o ( p y ) g when C o ( p y ) 4 ( C l O ^ ) 2 i s d i s -s o l v e d i n p y r i d i n e . When H e r l o c k e r and R o s e n t h a l t r i e d t o d i s s o l v e C o ( p y ) ^ ( C l O ^ ) 2 i n d r i e d d i s t i l l e d p y r i d i n e , t h e y f o u n d t h a t i t was i n s o l u b l e ; however, t h e y f o u n d t h e compound t o be s o l u b l e i n n o n - d i s t i l l e d p y r i d i n e . I n 19 72 B e e c h (82) r e p o r t e d some t h e r m a l s t u d i e s on t h e p y r i d i n e c o m p l e x e s o f c o b a l t ( I I ) p e r c h l o r a t e and c o n -2 + e l u d e d t h a t t h e Co(py)g, s p e c i e s i s p r e s e n t i n Co (py) g (ClO^) 2 . T h i s c o n c l u s i o n was b a s e d on a n a l y t i c a l d a t a , l i m i t e d i n f r a -r e d d a t a and t h e r e s u l t s o f d i f f e r e n t i a l s c a n n i n g c a l o r i m e t r y . T h i s e v i d e n c e s h o u l d n o t be c o n s i d e r e d s a t i s f a c t o r y w i t h o u t a d e t a i l e d s t u d y o f t h e e l e c t r o n i c s p e c t r a l and m a g n e t i c p r o p e r t i e s o f t h e compound. T h i s i s n e c e s s a r y b e c a u s e t h e s e p r o p e r t i e s show w e l l d e f i n e d b e h a v i o r f o r o c t a h e d r a l c o b a l t ( I I ) and s h o u l d p e r m i t one t o i d e n t i f y t h e CoNg c h r o m o p h o r e . I n 1975, R. R i v e s t , P.P. S i n g h and c o w o r k e r s (83) r e p o r t e d t h e c h a r a c t e r i z a t i o n o f C o ( p y ) g M ( N C S ) 4 , M=Zn o r Cd. The m a g n e t i c p r o p e r t i e s (room t e m p e r a t u r e m a g n e t i c moment) and, i n some c a s e s , t h e v i s i b l e e l e c t r o n i c s p e c t r a l 2 + d a t a a r e c o n s i s t e n t w i t h t h e p r e s e n c e o f t h e C o ( p y ) g s p e c i e s 2-and M ( N C S ) 4 c o u n t e r i o n s . One c r i t i c i s m o f t h i s work i s t h a t t h e a n a l y t i c a l d a t a (C,H,N,S) were n o t p a r t i c u l a r l y good and t h e a s s i g n m e n t s o f t h e e l e c t r o n i c s p e c t r a were n o t d e f i n i t i v e . As n o t e d i n S e c t i o n 2.3.2.1, t h e l i g a n d f i e l d p a r a m e t e r s f o r c o b a l t ( I I ) compounds a r e d e r i v e d by f i t t i n g -64-c a l c u l a t e d and t r a n s i t i o n s to the observed energies. I t i s unwise to use v 2 i n the c a l c u l a t i o n since i t i s u s u a l l y a weak band. These authors, however, were forced to use v 2 and i n t h e i r c a l c u l a t i o n of Dq and B since they d i d not observe v-^  (the n e a r - i n f r a r e d region of the spectrum was not s t u d i e d ) . I n " a d d i t i o n , the e l e c t r o n i c spectrum^ of the compound wi t h M=Zn (two bands) i s d i f f e r e n t than that f o r the compound w i t h M=Cd ( s i x bands) and t h i s i s d i f f i c u l t to e x p l a i n . The room temperature magnetic moments observed f o r these compounds may a l s o be meaningless, since 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 some i m p u r i t i e s may have been present. In s h o r t , the c h a r a c t e r i z a t i o n of these compounds has not provided a c l e a r p i c t u r e of the e l e c t r o n i c s p e c t r a l and magnetic p r o p e r t i e s 2+ of the Co(py)g spec i e s . A f t e r our work on the Co ( p y ) g ( E F g ) systems was completed (and reported i n Inorganic and Nuclear Chemistry L e t t e r s V o l . 12, p. 937 (1976)), R. R i v e s t , P.P. Singh, and coworkers (84) reported the synthesis and c h a r a c t e r i z a t i o n of the compound, Co(py) gZn(NCSe) 4 which i s thought to contain 2 + the Co(py)g spec i e s . In l a t e r r e p o r t s (1978 and 1979), P.P. Singh and coworkers have reported the compounds Co(py)g-(M1 (SCNp^,-where M' i s Ag 1 (85) and Cu 1 (86)/ and where again the 2+ Co(py)g species i s thought to be present i n the s o l i d s t a t e . 2+ The e l e c t r o n i c spectra of the C o ( p y ) 6 species i n these l a t e r r e p o r t s are d i f f e r e n t from those reported f o r the com-pounds, Co(py)gM(NCS) 4 discussed i n the previous paragraph. 2 + We would n o t e x p e c t C o ( p y ) g t o have a d i f f e r e n t e l e c t r o n i c spectrum w i t h d i f f e r e n t n o n - c o o r d i n a t i n g a n i o n s . Moreover, we note t h a t t h i o c y a n a t o and s e l e n o c y a n a t o complex a n i o n s a re poor c h o i c e s as n o n - c o o r d i n a t i n g a n i o n s because NCS and NCSe--have two p o t e n t i a l l i g a t i n g s i t e s and thus c o u l d be p r e s e n t as bridging l i g a n d s , t h u s c o m p l i c a t i n g t h e s t r u c t u r a l p o s s i b i l i t i e s . 3.2.2 RESULTS AND DISCUSSION D e t a i l s o f the s y n t h e s i s o f t h e complexes a r e g i v e n i n C h a p t e r 6. On t h e b a s i s o f t h e obser v e d e l e c t r o n i c s p e c t r a and magnetic p r o p e r t i e s , t h e compounds Co (py) g (EFg) 2 , E=P and 2+ A s , have been a s s i g n e d s t r u c t u r e s - c o n t a i n i n g t h e Co(py)g c a t i o n s and n o n - c o o r d i n a t e d E F, a n i o n s . These d a t a w i l l be p r e s e n t e d and compared t o t h e work o f H e r l o c k e r and R o s e n t h a l p r e v i o u s l y d e s c r i b e d . As w e l l , t h e n a t u r e o f t h e i n s t a b i l i t y o f t h e compounds w i t h r e g a r d t o l o s s o f t h e f i f t h and s i x t h p y r i d i n e l i g a n d s w i l l be d i s c u s s e d . 3.2.2.1 ELECTRONIC SPECTRA AND MAGNETIC PROPERTIES The e l e c t r o n i c s p e c t r a o f Co(py)g ( P F g ) 2 and C o ( p y ) g ( A s F g ) 2 a r e v i r t u a l l y i d e n t i c a l and may be a s s i g n e d t o a c o b a l t ( I I ) o c t a h e d r a l s p e c i e s . The t r a n s i t i o n e n e r g i e s and assignments' a r e shown i n T a b l e I I I - l . The h i g h energy s h o u l d e r on i s p r o b a b l y b e s t a s s i g n e d t o a s p i n f o r b i d d e n -66-TABLE I I I - l ELECTRONIC SPECTRAL DATA FOR C o ( p y ) g ( E F g ) 2 Band p o s i t i o n (kK) COMPOUND C o ( p y ) 6 ( P F 6 ) 2 C o ( p y ) 6 ( A S F 6 ) 2 ASSIGNMENT (a) (b) (a) (b) Sg(F) *Sg A 8.70m 8. 70m 2g 18.5sh 18.5sh 18.5sh 18.5sh -> 4T l g(P) 19. 6s 19.8s 19.6s 19. 8s 20.6sh 20.6sh 20.4sh 20.6sh (a) d i f f u s e r e f l e c t a n c e (b) m u l l spectrum -67-t r a n s i t i o n (8;7.) . The Dq and B v a l u e s o f 985 and 820 cm~.^, d e t e r m i n e d u s i n g t h e method o f S e c t i o n 2.3.1.1 g i v e c a l c u l a t e d v a l u e s o f 8.65, 18.45 and 19.80 kK f o r , v 2 , and r e s p e c -t i v e l y , i n e x c e l l e n t a g r e e m e n t w i t h t h e o b s e r v e d t r a n s i t i o n e n e r g i e s . The s p e c t r a o f t h e C o ( p y ) g ( E F g ) 2 compounds a r e v e r y s i m i l a r t o t h e s o l u t i o n s p e c t r u m o f C o ( p y ) 4 ( B F ^ ) 2 i n p y r i d i n e (78) . A l t h o u g h t h e agreement o f t h e l i g a n d f i e l d p a r a m e t e r s c a l c u l a t e d i s q u i t e c l o s e we do n o t e t h a t Dq (1017 v s 985) i s l a r g e r a n d B (797 v s 820) i s s m a l l e r i n t h e s o l u t i o n s p e c t r u m . T h i s may r e f l e c t a d i f f e r e n c e i n t h e 2 + n a t u r e o f t h e s o l v a t e d and s o l i d s t a t e C o ( p y ) g s p e c i e s . Dq i s d e p e n d e n t upon t h e r e c i p r o c a l o f bond l e n g t h t o t h e -5 f i f t h power (a ) so t h i s s u g g e s t s t h e a v e r a g e Co-N d i s t a n c e i s p r o b a b l y l o n g e r i n t h e s o l i d s t a t e t h a n i n s o l u t i o n . The l a r g e r v a l u e o f B i n t h e s o l i d s t a t e i s a l s o c o n s i s t a n t w i t h t h i s s i n c e t h e l o n g e r t h e Co-N bond t h e l e s s l i k e l y i s e l e c t r o n d e l o c a l i z a t i o n i n t h e m e t a l - l i g a n d b o n d . The v a r i a t i o n s of;- .u -f w i t h . t e m p e r a t u r e f o r t h e C o ( p y ) 6 ( E F g ) 2 compounds a r e v i r t u a l l y i d e n t i c a l . A t room t e m p e r a t u r e t h e e f f e c t i v e m a g n e t i c moment i s 5.11-5.12 B.M. and a t 80 K, i t has d r o p p e d t o a r o u n d 4.5 B.M. The A v a l u e -68-c a l c u l a t e d from Dq and B i s 1.40 and t h i s value was used f o r f i t t i n g the magnetic data i n F i g g i s ' four parameter model (Section 2.4.1.1). Figure 2.1 compares the t h e o r e t i c a l curve f o r k'=1.0, A=1.40, v=0, and A=-14 5 cm 1 w i t h the experimental data and shows e x c e l l e n t agreement between theory and experiment. The parameters, v=0, A=0, deriv e d from the magnetic data i n d i c a t e t h a t the T^^(F) ground term i s not apprec i a b l y s p l i t by a t e t r a g o n a l d i s t o r t i o n . This can be taken t o i n f e r t h a t the symmetry of the CoNg chromophore i s 0^ and t h i s v i r t u a l l y excludes a weakly c o o r d i n a t i n g s p e c i e s , i e . PFg or AsFg , from the f i r s t c o o r d i n a t i o n sphere. The magnitude of X, the s p i n - o r b i t c o u p l i n g constant, i s reduced to -145 cm 1 compared to the fre e i o n value of-172 cm \ The value of '(A/A ) =0.843 i s almost i d e n t i c a l to the value of 6(B/B Q) = 0.844 c a l c u l a t e d from the e l e c t r o n i c spectrum. The correspondence of the two r a t i o s gives a f u r t h e r degree of confidence i n the t h e o r e t i c a l treatment of both the e l e c t r o n i c spectra and the magnetic p r o p e r t i e s since the r a t i o s obtained by the d i f f e r e n t techniques give semi-independent measures of the e l e c t r o n d e l o c a l i z a t i o n present. The magnetic s u s c e p t i b i l i t y measure-ments and the e l e c t r o n i c s p e c t r a l assignment are c o n s i s t e n t . • A comparison of the A, A, Dq, and B values f o r the CoNg chromophore i n these compounds w i t h the values f o r a CoOg chromophore gives not unexpected r e s u l t s . CotSO^F^ was chosen f o r the comparison s i n c e A=0 and ther e f o r e the e f f e c t of anisotropy i s absent. The A, A, Dq, and B values (88) -69-G D 5 . 2 H 100 2 0 0 3 0 0 Temperature (K) FIG. 3.1 MAGNETIC PROPERTIES OF C o ( p y ) g ( E F g ) 2 -1 ( l i n e a i s t h e t h e o r e t i c a l c u r v e f o r A=l.40,A=-145 cm v=0, and k'=1.0; t h e unshaded and shaded c i r c l e s a r e t h e the d a t a p o i n t s f o r E=As and E=P , r e s p e c t i v e l y ) -70-r e p o r t e d f o r t h i s compound a r e 1.42, 17 0 cm \ 7 65 cm ^ and 860 cm 1 r e s p e c t i v e l y . The v a l u e s o f A, - X , and B a r e g r e a t e r a n d Dq s m a l l e r i n m a g n i t u d e t h a n o b s e r v e d i n o u r C o ( p y ) g ( E F g ) 2 compounds. T h i s i s c o n s i s t e n t w i t h a weaker l i g a n d f i e l d s t r e n g t h o f t h e o x y g e n d o n o r compared t o o u r n i t r o g e n d o n o r . 3.2.2.2. VIBRATIONAL SPECTROSCOPY The m a g n e t i c and e l e c t r o n i c s p e c t r a l p r o p e r t i e s o f t h e s e C o ( p y ) g ( E F g ) 2 compounds a r e c o n s i s t e n t w i t h t h e 2 + C o ( p y ) g c a t i o n and t h e r e f o r e w i t h n o n - c o o r d i n a t e d a n i o n s , p r e s e n t as c o u n t e r - i o n s i n t h e s o l i d s t a t e l a t t i c e . The i n f r a r e d s p e c t r a l d a t a c o n f i r m a n d complement t h i s i n f o r m a t i o n t h r o u g h t h e v i b r a t i o n s o f p y r i d i n e and t h e E F g a n i o n . T a b l e I I I - 2 shows t h e i n f r a r e d bands a s s i g n e d t o t h e s t e r e o c h e m i c a l l y s e n s i t i v e p y r i d i n e v i b r a t i o n s and t o t h e i n t e r n a l v i b r a t i o n s o f . t h e E F g m o i e t y f o r t h e Co:(py) g (EF.g)'2 c o m p l e x e s . T h e r e i s no e v i d e n c e f o r n o n - c o o r d i n a t e d p y r i d i n e as w o u l d be i n d i c a t e d by bands a t 603 cm 1 and 403 cm 1 ; t h e s e bands a r e a t 625 and 426-430 cm 1 r e s p e c t i v e l y . The i n t e r n a l v i b r a t i o n s o f t h e EFg a n i o n a r e n o t g r e a t l y d i f f e r e n t f r o m t h o s e o b s e r v e d i n t h e s a l t s , KPFg and C s A s F g ( T a b l e I I - l ) , c o n s i s t e n t w i t h " i o n i c " , n o n - c o o r d i n a t e d a n i o n s . The i n f r a r e d a c t i v e T ^ u modes, and v ^ , show no s p l i t t i n g and have a l s o -71-TABLE I I I - 2 INFRARED DATA(cm" 1) FOR C o ( p y ) g ( E F g ) 2 COMPOUND C o ( p y ) 6 ( P F 6 ) 2 C o ( p y ) 6 ( A s F 6 ) 2 ( i ) P y r i d i n e v i b r a t i o n s 8 a 1601m 1601m 6a 16b ( i i ) E F g v i b r a t i o n s 623m 6 2 5 m 430m 4 2 6 m 418w v ( T ) 839vs 698vs v 3 u l u ; V 4 ( T l u ) 556s 393s v ( A ) 738vw (a) 1 l g 569vw v 2 ( E g ) (b) v 5 ( T 2 g ) n.o. n - ° -(a) p o s s i b l y o b s c u r e d by v 3 (b) p o s s i b l y o b s c u r e d by v 4 -72-i d e n t i c a l e n e r g i e s t o t h o s e i n t h e s a l t s . The and v 2 modes w h i c h a r e f o r m a l l y f o r b i d d e n i n 0^ symmetry a n d . w h i c h a r e o b s e r v e d as weak bands i n t h e s p e c t r a o f C o ( p y ) g ( P F g ) 2 and C o ( p y ) g ( A s F g ) 2 f r e s p e c t i v e l y , a r e p r o b a b l y p r e s e n t due t o s i t e symmetry e f f e c t s . The v 2 and bands o f C o ( p y ) g ( P F g ) 2 and C o ( p y ) g ( A s F g ) 2 r e s p e c t i v e l y , i f p r e s e n t , w o u l d be o b s c u r e d by one o f t h e f o r m a l l y a l l o w e d T ^ u v i b r a t i o n s . F i g u r e s 3.2 and 3.3 show - t h e i n f r a r e d s p e c t r a (1000-400 cm "*") f o r C o ( p y ) 6 ( P F g ) 2 and (1000-350 c m - 1 ) f o r C o ( p y ) g ( A s F g ) 2 . 3.2.2.3 THERMAL S T A B I L I T Y As n o t e d i n t h e e x p e r i m e n t a l s e c t i o n 6.2.1.1 and 6.2.1.2, t h e s e C o ( p y ) g ( E F g ) 2 compounds a r e v e r y s u s c e p t i b l e t o l o s s o f p y r i d i n e i n a vacuum a t room t e m p e r a t u r e . When C o ( p y ) g ( E F g ) 2 l o s e s two p y r i d i n e l i g a n d s , t h e compounds Co ( p y ) ^ ( E F g ) 2 a r e f o r m e d . S e c t i o n 3.5 d e s c r i b e s t h e c h a r a c t e r i z a t i o n o f t h e s e compounds as h a v i n g s t r u c t u r e s 2+ c o n t a i n i n g t e t r a h e d r a l c o b a l t ( I I ) , C o ( p y ) ^ , and non-c o o r d i n a t e d EF,. a n i o n s . As t h e l o s s o f p y r i d i n e l i g a n d s t a k e s p l a c e , t h e o r i g i n a l l i g h t p i n k m a t e r i a l becomes r e d -d i s h i n c o l o r and e v e n t u a l l y a t t a i n s t h e deep r e d - p u r p l e c o l o r o f t h e 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 . The p r e s e n c e o f C o ( p y ) ^ ( E F g ) 2 i m p u r i t y i n C o ( p y ) g ( E F g ) 2 c a n be d e t e c t e d e a s i l y b y d i f f u s e r e f l e c t a n c e s p e c t r o s c o p y . FIG 3.2 INFRARED SPECTRUM (1000-400 cm" ) OF C o ( p y ) g ( P F g ) 2 - 7 4 -FIG. 3.3 INFRARED SPECTRUM (1000-350 cm" ) OF C o ( p y ) g ( A s F g ) 2 -75-The v i s i b l e b a n d o f " o c t a h e d r a l " c o b a l t ( I I ) u s u a l l y h a s an e x t i n c t i o n c o e f f i c i e n t o f a r o u n d 30 M ''"cm "'"(for example C o ( p y ) ^ ( B F 4 ) 2 i n p y r i d i n e ( 7 8 ) ) w h e r e a s t h e v i s i b l e b and o f " t e t r a h e d r a l " c o b a l t h a s an e x t i n c t i o n c o e f f i c i e n t o f 600 M '"cm ^ ( f o r e x a m p l e , C o ( 4 m e p y ) 4 ( P F g ) 2 i n d i c h l o r o m e t h a n e .£= 611 S e c t i o n 3 . 5 . 2 . 1 ) . Co (py) g (EFg) 2 and Co (py) 4 (EFg) 2 have t h e i r maximum a b s o r b a n c e s w e l l s e p a r a t e d a t 505 and 565 nm, r e s p e c t i v e l y . A s s u m i n g t h e r e l a t i v e e x t i n c t i o n c o e f f i c i e n t s o f o c t a h e d r a l and t e t r a h e d r a l c o b a l t ( I I ) t o be 30 t o 600, t h e n f o r a 95% Co (py) • (PFg) / 5% Co ( p y ) ^ ([PFg) 2 m i x t u r e t h e r e l a t i v e i n t e n s i t y o f t h e 505 and 565 nm bands w o u l d be 1:1. The p r e s e n c e . o f Co.(py) 4 (PFg) 2 ( % i n t h i s r a n g e ) w o u l d p r o b a b l y m a n i f e s t i t s e l f as a s h i f t t o l o w e r e n e r g y . o f t h e 505 nm b a n d . F i g u r e 3.4 shows t h e s p e c t r a o f C o ( P Y ) 4 ( p F g ) 2 ' C o ( p y ^ 6 ^ P F 6 ^ 2 a n d a m i x t u r e o f t n e t w o -I t w o u l d be more d i f f i c u l t t o d e t e c t t h e p r e s e n c e o f Co (py) 4 ( C 1 0 4 ) 2 as an i m p u r i t y i n B e e c h ' s (82') compound, C o ( p y ) g ( C 1 0 4 ) 2 ' T n e e x t i n c t i o n c o e f f i c i e n t s and band p o s i t i o n s a r e v e r y s i m i l a r f o r b o t h t h e p s e u d o - o c t a h e d r a l Co(py)„ ( C 1 0 . ) 0 ( i n d i c h l o r o m e t h a n e ; A i s 525 nm, e=17) 4 Q A max 2+ and t h e C o ( p y ) g c a t i o n , and t h e r e f o r e one w o u l d n o t have a s e n s i t i v e t e s t f o r t h i s i m p u r i t y . I t i s i n t e r e s t i n g t o n o t e t h a t m a g n e t i c s u s c e p t i b i l i t y measurements a n d e l e m e n t a l (C,H,N) a n a l y s e s w o u l d n o t d e t e c t t h e p r e s e n c e o f s m a l l amounts o f C o ( p y ) 4 ( E F g ) 2 i n t h e FIG. 3.4 VISIBLE SPECTRA OF COBALT(II)-PYRIDINE COMPLEXES -77-c o r r e s p o n d i n g Co ( p y ) g ( E F g ) 2 s a m p l e . F o r example, a t room t e m p e r a t u r e C o ( p y ) 4 ( P F g ) 2 and C o ( p y ) g ( P F g ) 2 have y v a l u e s o f 4.33 and 5.11 B.M. r e s p e c t i v e l y . I f t h e r e was a 5%/95% m i x t u r e , t h e o b s e r v e d moment w o u l d be 5.07 B.M., i n d i s t i n g -u i s h a b l e due t o e x p e r i m e n t a l e r r o r f r o m t h e 5.11 B.M. e x p e c t e d f o r C o ( p y ) g ( P F g ) 2 . A t 80 K, t h e m i x t u r e above w o u l d y i e l d a moment o f 4.49 B.M., a l m o s t e x a c t l y t h e 4.50 B.M. e x p e c t e d f o r C o ( p y ) g ( P F g ) 2 . The p e r c e n t a g e o f C, H and N f o r t h i s m i x t u r e w o u l d be 43.38, 3.63, and 10.11 a l l w i t h i n a c c e p t a b l e a g r e e m e n t w i t h t h e v a l u e s o f 43.76, 3.67, and 10.20 c a l c u l a t e d f o r C o ( p y ) g ( P F g ) 2 . 3 . 3 OCTAHEDRAL; PYRIDINE..COMPLEXES'^F NICKEL ( I I ) ; " N i (py) g ( E F g ) 2 3.3.1 INTRODUCTION The compound, N i ( p y ) g ( P F g ) 2 , h a s b een c h a r a c t e r i z e d p r e v i o u s l y b y M a y f i e l d and B u l l (14) . Our c o n t r i b u t i o n t o t h e s t u d y o f t h e N i ( p y ) g ( E F g ) 2 compounds, b e s i d e s t h e p r e p a r a t i o n f o r t h e f i r s t t i m e o f t h e h e x a f l u o r o a r s e n a t e d e r i v a t i v e , i s t o c o n f i r m t h e o b s e r v e d s p e c t r a l p r o p e r t i e s o f N i ( p y ) g ( P F g ) 2 a n d t o s t u d y i t s c r y o m a g n e t i c p r o p e r t i e s . M o r e o v e r , i t i s i m p o r t a n t t h a t t h e s e compounds be o b t a i n e d p u r e and be w e l l c h a r a c t e r i z e d s i n c e t h e method o f p r e p a r a t i o n o f N i ( p y ) 4 ( P F g ) 2 and N i ( p y ) 4 ( A s F g ) 2 d e s c r i b e d l a t e r i n s e c t i o n s 6.2.7 and 6.2.8a r e q u i r e s p u r e N i ( p y ) g ( E F g ) 2 t o be e f f e c t i v e . 3.3.2 RESULTS AND DISCUSSION The d e t a i l s o f t h e s y n t h e s e s o f t h e s e c o m p l e x e s a r e g i v e n i n Chap.6. T a b l e I I I - 3 l i s t s t h e . e l e c t r o n i c s p e c t r a l d a t a f o r t h e N i ( p y ) , ( E F , ) „ compounds p r e p a r e d h e r e , f o r M a y f i e l d and b b 2. B u l l ' s N i ( p y ) g ( P F g ) 2 compound and f o r R o s e n t h a l and D r a g o ' s (16) s o l u t i o n o f N i ( p y ) 4 ( B F 4 ) 2 i n p y r i d i n e . I n t h e l a t t e r two c a s e s , t h e l i g a n d f i e l d p a r a m e t e r s were c a l c u l a t e d by u s i n g t h e e x p e r i m e n t a l v a l u e o f v-^ as 10 Dq and u s i n g 10 Dq and t o c a l c u l a t e B. The v a l u e s o f Dq a n d B i n T a b l e I I I - 3 a r e c a l c u l a t e d by t h e q u a d r a t i c e q u a t i o n method TABLE I I I - 3 ELECTRONIC SPECTRAL DATA FOR ' N i ( p y ) 6 2+, COMPOUND REFERENCE TECHNIQUE ASSIGNMENT 3 3 A 2 g * T 2 g . 3 T l g ( F ) T l g ( P ) N i ( p y ) 6 ( P F 6 ) 2 (14) (a) 10.05m 16.7m 23. 5w 27.4s N i ( p y ) 6 ( P F 6 ) 2 N i ( p y ) 6 ( A s F 6 ) 2 N i ( p y ) 4 ( B F 4 ) 2 t h i s work t h i s work (b) (c) (b) (c) (d) BAND POSITION (kK) 10.2m 10.0m 9.88 16.4m 16.0m 16.5m 16.0m 16.50 21.74w 21.74 n.o. 26.3s 26.04s 26.0s 26.04s 26.67 (16) (e) 9.57(9) 16.47 (15) n.o. 26.73(31) Dq(cm ) B (cm - 1) 1037 870 1000 800 1000 800 1035 808 1030 820 (a) m u l l spectra,80K. (b) m u l l spectra,room temperature, (c) d i f f u s e r e f l e c t a n c e , (d) s o l u t i o n spectrum ( p y r i d i n e ) (e) s o l u t i o n spectrum ( n i t r o m e t h a n e - p y r i d i n e ) ; molar e x t i n c t i o n c o e f f i c i e n t i n b r a c k e t s . -80-d e s c r i b e d i n s e c t i o n 2.3.1.3. A l l o f t h e s p e c t r a a r e s i m i l a r i n n a t u r e a l t h o u g h t h e r e a r e some s m a l l d i f f e r e n c e s i n t h e t r a n s i t i o n e n e r g i e s ( t h e s e may due t o t h e f a c t t h a t t h e s p e c t r a were r u n i n d i f f e r e n t c o n d i t i o n s ) . The m a g n e t i c p r o p e r t i e s o f t h e s e compounds a r e 3 c o n s i s t e n t w i t h t h e p r e s e n c e o f an A 2 g g r o u n d s t a t e and a r e t y p i c a l o f o c t a h e d r a l n i c k e l ( I I ) c o m p l e x e s . The m a g n e t i c moments a t 300K a r e 3.06 and 3.11 B.M. f o r t h e h e x a f l u o r o -p h o s p h a t e and h e x a f l u o r o a r s e n a t e compounds r e s p e c t i v e l y and a r e e s s e n t i a l l y t e m p e r a t u r e i n d e p e n d e n t i n t h e t e m p e r a t u r e r a n g e s t u d i e d . The W e i s s c o n s t a n t s . a r e 4.0.K, f o r - b o t h , . i n d i c a t i v e p e r h a p s o f some s m a l l d i s t o r t i o n o f t h e N i N g c h r o m o p h o r e f r o m symmetry . The bands i n t h e i n f r a r e d s p e c t r a , o f t h e s e compounds t h a t a r e a s s i g n e d to. t h e s t e r e o c h e m i c a l l y s e n s i t i v e v i b r a t i o n s o f p y r i d i n e . a n d t o t h e v i b r a t i o n s o f t h e E F g a n i o n s a r e l i s t e d i n T a b l e I I I - 4 . No e v i d e n c e f o r n o n c o o r d i n a t e d p y r i d i n e e x i s t s i n t h e i n f r a r e d s p e c t r a . The s h i f t s i n t h e s t e r e o -c h e m i c a l l y s e n s i t i v e bands o f p y r i d i n e a r e e s s e n t i a l l y t h e same as t h o s e o b s e r v e d f o r t h e Co ( p y ) g ( E F g ) 2 compounds as a r e t h e a n i o n v i b r a t i o n s . I t i s i n t e r e s t i n g t o n o t e t h a t M a y f i e l d and B u l l have a s s i g n e d a v e r y weak band a t 4 69 cm 1 t o t h e f o r m a l l y f o r b i d d e n v '(T n ) v i b r a t i o n o f P F , .(14). No e v i d e n c e f o r 5 2g 6 t h i s b and a p p e a r s i n t h e i n f r a r e d s p e c t r u m o f t h e N i ( p y ) g ( P F g ) 2 -81-TABLE III-4 INFRARED DATA (cm ) FOR N i ( p y ) g ( E F g ) 2 COMPOUND Ni(py) 6(PFg) 2 N i ( p y ) g ( A s F 6 ) 2 (i) P y r i d i n e v i b r a t i o n s 8a 1605s 6a 628m 16b 439m 1605s 626m-s 439m ( i i ) EFg v i b r a t i o n s v 3 ( T l u ) 842vs V T 1 U ) 5 5 8 3 v x ( A l g ) 740vw v 2 ( E g ) (b) V 5 ( T 2 g ) 699vs,br 392s (a) 570vw n. o. (a) p o s s i b l y obscured by v 3 (b) p o s s i b l y obscured by v 4 -82-synthesized here nor was i t observed i n the i n f r a r e d spectrum of Co (py) (PF,.) „ . I t i s important to note t h a t the Ni (py) , (EF ) „ compounds are s u s p e c t i b l e to l o s s of the f i f t h and s i x t h p y r i d i n e l i g a n d s although they are not as l a b i l e as i n the Co(py)g(EFg)2 compounds. Twenty-four hours of pumping " i n vacuo" w i l l cause a yellow-orange c o l o r (due to N i ( p y ) 4 ( E F g ) 2 ) to appear i n the robin's egg blue c o l o r of N i (py) g (EFg) 2 • We have found (see s e c t i o n 4.2.2.2 ) a band at 47 0 cm 1 assigned t o the 8a v i b r a t i o n of p y r i d i n e i n the i n f r a r e d spectra" of N i ( p y ) 4 ( E F g ) 2 compounds and we conclude t h a t the 4 69 cm 1 band reported by M a y f i e l d and B u l l i s probably t h i s band a r i s i n g from the presence of N i ( p y ) 4 (PFg) 2 i m p u r i t y i n t h e i r sample. -83-3.4 OCTAHEDRAL METHYLPYRID.INE : COMPLEXES OF COBALT(II), NICKEL(II), AND COPPER(II); M(4mepy) Q(H 20) 2(EFg) AND M 1(3mepy)g(H 20) 2(EFg) 2 3.4.1 . INTRODUCTION The compounds to be discussed i n t h i s section are M(4mepy) 8(H 20) 2(EFg) 2 and M'(3mepy) g(H 20) 2(EF g) 2 (where M=Co, Ni and M'=Co, Ni, Cu and E=P, As). The stoichiometries of these compounds are d i f f e r e n t from that of the pyridine complexes, M(py)g(EFg) 2, discussed e a r l i e r ; however, i n general, there are s i m i l a r i t i e s . The l a t t i c e structures of a l l these compounds are si m i l a r as shown by infrared studies which are consistent with non-coordinated anions and therefore with large complex cat i o n i c species. Also, when the compounds are transformed to complexes containing four pyridine or methylpyridine ligands per metal ion, the M'L^tEFg),, species are very s i m i l a r for a given metal ion i n terms of molecular and e l e c t r o n i c structure. Our i n i t i a l studies on the ele c t r o n i c spectra and magnetic properties of the complexes M(4mepy)g(H 20) 2(EFg) 2 and M'(3mepy)g(H 20) 2(EFg) 2 indicated octahedral coordination of the metal ion. Since the r a t i o of poten t i a l neutral l i g a t i n g species to metal ion in these complexes was found to be greater than s i x , some uncertainty existed as to the -84-n a t u r e o f t h e f i r s t c o o r d i n a t i o n s p h e r e o f t h e m e t a l i o n . , T h a t i s , was t h e w a t e r c o o r d i n a t e d t o t h e m e t a l o r was t h e w a t e r p r e s e n t a s l a t t i c e w a t e r w i t h m e t a l - l i g a n d c h r o m o p h o r e s o f "MN 40 2" o r "MNg", r e s p e c t i v e l y ? The X - r a y d i f f r a c t i o n s t u d i e s on C o ( 4 m e p y ) 8 ( H 2 0 ) 2 ( P F 6 ) 2 , N i ( 4 m e p y ) g ( H 2 0 ) 2 ( P F g ) 2 and N i ( 3 m e p y ) 6 ( H 2 0 ) 2 ( P F g ) 2 have shown t h e s t r u c t u r e s t o c o n t a i n "MN 4G 2" c h r o m o p h o r e s in--a 1-1 c a s e s . T h i s s e c t i o n b e g i n s w i t h a d e s c r i p t i o n o f t h e v i b r a -t i o n a l s p e c t r a o f t h e s e c o m p l e x e s . T h i s i s f o l l o w e d by a d e s c r i p t i o n and a n a l y s i s o f t h e e l e c t r o n i c s p e c t r a l a nd m a g n e t i c p r o p e r t i e s and, when a p p r o p r i a t e , t h e c r y s t a l and m o l e c u l a r s t r u c t u r e d e t e r m i n a t i o n s . F i n a l l y , t h e s e r e s u l t s w i l l be summarized and d i s c u s s e d i n r e l a t i o n t o p r e v i o u s work. D e t a i l s o f t h e s y n t h e s i s o f t h e c o m p l e x e s d e s c r i b e d h e r e a r e g i v e n i n C h a p t e r 6. 3.4.2. RESULTS AND DISCUSSION 3.4.2.1 VIBRATIONAL SPECTRA T a b l e I I I - 5 l i s t s t h e i n f r a r e d b a n d s a s s i g n e d t o t h e a n i o n i c s p e c i e s , E F g ~ , i n t h e compounds M(4mepy) g (H^O) 2 (EFg) 2 a n d M 1 ( 3 m e p y ) g ( H 2 0 ) 2 ( E F g ) 2 . T h e s e bands a r e v e r y s i m i l a r t o t h o s e o b s e r v e d f o r t h e M ( p y ) g ( E F g ) 2 compounds. The f o r m a l l y a l l o w e d ( i n 0^ symmetry) T^ v i b r a t i o n s a r e s t r o n g bands and t h e f o r m a l l y f o r b i d d e n A-^C^) a n d E g ^ v 2 ^ v i b r a t i o n s a r e - 8 5 -TABLE I I I - 5 ANION BANDS IN THE INFRARED SPECTRA OF M(4mepy) g (H^O) ^ CEFg) 2 AND M ' ( 3 m e p y ) 6 ( H 2 0 ) 2 ( E F 6 ) 2 ( i ) M(4mepy) 8(H 20) 2:(-EF 6) 2 M=Co M=Ni V T l u > V 4 ( T l u ) W W E=P 8 35vs 553s 740vw ( b ) E=P 840vs 554s 739vw ( b ) M=Co E=As 6 9 4 v s 3 9 4 s ___< a) 5 7 5 v w M=Ni E=As 695vs 392s n.o. ( i i ) M ' ( 3 m e p y ) g ( H 2 0 ) 2 ( E F g ) 2 M'=Co M'=Ni v 3 ( T l u > V T l u } V V V 2 ( V M'=Cu E=P M'-=Co M'=Ni M'=Cu E=As E=As E=As E=P E=P 8 3 9 v s , b r 8 3 0 v s , b r 8 3 9 v s 7 0 0 v s 7 0 0 v s 6 9 9 v s 5 5 5 s 7 4 1 w !(b) 5 5 5 v s 7 4 0 w ( b ) 5 5 5 v s n.o. 3 9 5 s 3 9 5 s 3 9 5 s (a) (a) _ ( a ) ( b ) 5 7 0 v w 5 6 8 w 5 7 0 v w (a) p o s s i b l y o b s c u r e d by v 3 o f A s F g (b) p o s s i b l y o b s c u r e d by v 4 o f P F g -86-o b s e r v e d as weak bands f o r t h e PFg and A s F g compounds r e s p e c t i v e l y . T h i s s u g g e s t s , as b e f o r e , t h a t t h e a n i o n s a r e b a s i c a l l y c o u n t e r i o n s i n t h e s o l i d s t a t e l a t t i c e and a r e s u b j e c t t o l o w e r t h a n 0^ s i t e symmetry. A g a i n , no e v i d e n c e f o r t h e ( T 2 ) v i b r a t i o n was o b s e r v e d . The i n f r a r e d s p e c t r a o f t h e s e compounds show some bands due t o w a t e r above 2500 cm 1 . The p o s i t i o n and a p p e a r a n c e o f t h e s e a b s o r p t i o n s a r e v e r y d i f f e r e n t f o r t h e 4mepy and 3mepy c o m p l e x e s . F i g u r e 3.5 shows t h e r e g i o n 4000-2000 c m - 1 o f t h e i n f r a r e d s p e c t r u m o f N i ( 4 m e p y ) g ( H ^ O ) 2 ( A s F g ) 2 and C o ( 4 m e p y ) g ( H 2 0 ) 2 ( A s F g ) 2 , i n N u j o l and HCB ( h e x a c h l o r o -b u t a d i e n e ) a n d N u j o l m u l l s r e s p e c t i v e l y . N u j o l has a s t r o n g , b r o a d a b s o r p t i o n i n t h e r a n g e 2950-2800 cm 1 b u t as t h e HCB m u l l shows, a l l o f t h e compounds have a v e r y b r o a d a b s o r p t i o n c e n t e r e d c l o s e t o 3100 cm 1 . O t h e r s have shown t h a t t h e i n f r a r e d s p e c t r u m o f l a t t i c e ( n o n - c o o r d i n a t e d ) w a t e r has a s t r o n g band a s s i g n e d t o v(O-H) a t 3550-3200 cm 1 ( 8 9 ( a ) ) . The s p e c t r a o b s e r v e d ( F i g . 3.5) a r e d i f f e r e n t f r o m t h i s and are due t o t h e v(O-H) when b o t h h y d r o g e n s o f t h e w a t e r m o l e c u l e a r e " h y d r o g e n - b o n d e d " t o 4 - m e t h y l p y r i d i n e m o l e c u l e s (as shown by t h e " m o l e c u l a r s t r u c t u r e s o f t h e s e compounds; s e e s e c t i o n 3.4.2.2.1 and 3.4.. 2 . 2 . 2 ) . •- - • . • The i n f r a r e d ^ - s p e c t r a o f -the 3 - m e t h y l p y r i d i n e c o m p l e x e s i n t h i s r e g i o n a r e d i f f e r e n t and a r e i l l u s t r a t e d i n F i g u r e 3.6. - 8 7 -4000 3000 2000 ENERGY (cm _ 1) FIGURE 3.5 INFRARED SPECTRUM OF M(4mepy) g(H 20) 2(AsF 6) 2 (Spectrum I i s Ni(mepy) R(H 20) ( A s F g ) 2 mulled i n HCB; spectrum I I i s N i ( 4 m e p y ) g ( H 2 0 ) 2 ( A s F 6 ) 2 mulled i n N u j o l ; spectrum I I I i s C o ( 4 m e p y ) 8 ( H 2 0 ) 2 ( A s F 6 ) 2 mulled i n N u j o l . * N u j o l band) - 8 8 -FIGURE 3.6 INFRARED SPECTRA OF M(3mepy) ( H j O ) 2 ( A s F g ) 2 ( Spectrum I i s C o ( 3 m e p y ) g ( H 2 0 ) 2 ( A s F g ) 2 mulled i n N u j o l ; spectrum I I i s Ni(3mepy) ( H 2 0 ) 2 ( A s F g ) 2 mulled i n N u j o l . * N u j o l band) - 8 9 -The band s t r u c t u r e f o r t h e s e compounds : i s d i f f e r e n t f r o m t h a t o f t h e 4 - m e t h y l p y r i d i n e c o m p l e x e s s i n c e t h e r e a r e now two bands i n t h e r e g i o n ; one s h a r p a t 3500 cm 1 and one broad, c e n t e r e d ^2800 cm 1 . I n t h e 3 - m e t h y l p y r i d i n e c o m p l e x e s , t h e r e a r e e i t h e r two d i f f e r e n t t y p e s o f w a t e r m o l e c u l e s o r t h e h y d r o g e n s o f t h e w a t e r m o l e c u l e s a r e i n two r a d i c a l l y d i f f e r e n t e n v i r o n m e n t s . The m o l e c u l a r s t r u c t u r e ( s e e .. s e c t i o n 3.4.2.2.3) o f Ni@mepy) 6 (H 20) 2 ( P F g ) 2 - • c o n f i r m s t h e l a t t e r p o s s i b i l i t y ; where one h y d r o g e n i s h y d r o g e n - b o n d e d t o a 3mepy m o i e t y and t h e o t h e r h y d r o g e n i s w e a k l y i n t e r a c t i n g w i t h t h e EFg a n i o n . The c r y s t a l s t r u c t u r e o f C o ( 3 m e p y ) g ( H 2 0 ) 2 ( P F g ) 2 i s i s o m o r p h o u s t o t h a t o f N i ( 3 m e p y ) g ( H 2 0 ) 2 ( P F g ) 2 and t h e two i n f r a r e d a r e v e r y s i m i l a r . The u n i t c e l l p arameters' i n d i c a t e t h a t C u ( 3 m e p y ) g ( H 2 0 ) 2 ( P F g ) 2 i s n o t i s o m o r p h o u s w i t h N i ( 3 m e p y ) g ( H 2 0 ) 2 ( P F g ) 2 and t h e i n f r a r e d s p e c t r u m o f t h i s compound i s s l i g h t l y d i f f e r e n t (see s e c t i o n 3.4.2.2.5). T a b l e I I I - 6 shows t h e p o s i t i o n s o f t h e s t e r e o c h e m i c a l l y s e n s i t i v e bands o f 4mepy i n t h e M ( 4 m e p y ) R ( H ^ O ) 2 ( E F g ) 2 compounds. T h e r e i s no e v i d e n c e f o r " n o n - c o o r d i n a t e d " 4mepy a l t h o u g h t h e r e a r e two d i f f e r e n t t y p e s o f 4mepy p r e s e n t : f o u r b o n d ed t o t h e m e t a l and f o u r h y d r o g e n - b o n d e d t o w a t e r m o l e c u l e s . The a s s i g n m e n t o f two bands t o e a c h o f t h e 6a, 10b+12, and 1 v i b r a t i o n s r e f l e c t s t h e two d i f f e r e n t t y p e s o f 4mepy m o i e t i e s e x p e c t e d f r o m t h e s t o i c h i o m e t r y and t h e ( X - r a y ) m o l e c u l a r s t r u c t u r e d e t e r m i n a t i o n s . -90-The i n f r a r e d s p e c t r a l bands of 3mepy i n the M ' ( 3 m e p y ) g ( H 2 0 ) 2 ( E F 6 ) 2 complexes (see Appendix 1, Table Al-3) do not show the w e l l d e f i n e d s p l i t t i n g s as the bands of 4mepy i n the M ( 4 m e p y ) 8 ( H 2 0 ) 2 ( E F g ) 2 complexes show. TABLE I I I - 6 SELECTED 4MEPY BANDS IN THE INFRARED SPECTRA OF THE M ( 4 m e p y ) 8 ( H 2 0 ) 2 ( E F g ) 2 COMPOUNDS BAND POSITION (cm" 1) 4-METHYLPYRIDINE M=Co VIBRATION E=P M=Co M=Ni M=Ni E=As E=P E=As 6a 526m 526m 525m 526m 536sh 538m 540m 54 0m 10b+12 (a) 810vs 800m 805s 810m 816s 1 1010s 1007s 1007s 1007s 1017s 1020s 1024s 1026s 9a 1230s 1227s 1229m 1229m,1235sh 19a 1504w 1504w 1509w 1506w 8a 1608s 1610s 1611s 1610s 1622sh (a) t h i s band i s obscured by the v 3 CI\ ) of l u PF ~ 6 -91-3.4.2.2 ELECTRONIC SPECTRAL AND MAGNETIC PROPERTIES AND MOLECULAR STRUCTURE 3.4.2.2.1 C o ( 4 m e p y ) R ( H 2 0 ) 2 ( E F 6 ) 2 The e l e c t r o n i c s p e c t r a and m a g n e t i c p r o p e r t i e s o f t h e s e compounds a r e c o n s i s t e n t w i t h a c o b a l t ( I I ) i o n i n an o c t a h e d r a l e n v i r o n m e n t . T a b l e I I I - 7 shows t h e a s s i g n m e n t o f t h e e l e c t r o n i c s p e c t r u m on t h i s b a s i s . The l i g a n d f i e l d p a r a m e t e r s Dq and B d e r i v e d a r e : 995 and 840 c m - 1 , E=P, and 1010 and 845 cm \ E=As. The c a l c u l a t e d p o s i t i o n s o f v and v 3 a r e 8.78 and 20.20 kK f o r E=P and 8.91 and 20.40 kK f o r E=As •, an e x c e l l e n t f i t t o t h e o b s e r v e d s p e c t r a . The c a l c u l a t e d v a l u e s o f t h e V 2 t r a n s i t i o n e n e r g y a r e 18.7 (E=P) and 19.0 kK (E=As), w h i c h a r e w i t h i n ' 4 0 nm o f t h e band, maxima o f and,-- b e c a u s e o f i t s i n t r i n s i c w eakness, :x>2 i s o v e r - s h a d o w e d by v ^ . - The A v a l u e c a l c u l a t e d f o r b o t h compounds i s 1.40. The e f f e c t i v e m a g n e t i c moments o f t h e s e compounds a r e t e m p e r a t u r e d e p e n d e n t . The moments a t 300 K are' 4.85 (E=P) and 4.86 (E=As) B.M. and t h e y d r o p t o 4.51 and 4.58 B.M. a t 80K r e s p e c t i v e l y . F i g u r e 3 .'7 shows t h e e x c e l l e n t a g r e e m e n t between t h e e x p e r i m e n t a l m a g n e t i c moments and t h e o r y . The m a g n e t i c d a t a i n d i c a t e t h a t t h e c o b a l t ( I I ) i o n i s i n a t e t r a g o n a l l y d i s t o r t e d o c t a h e d r a l -92-TABLE I I I - 7 . ELECTRONIC SPECTRAL DATA FOR Co (4mepy) g (-I^O) 2 (EFg) 2 BAND POSITION (kK) COMPOUND C o ( 4 m e p y ) g ( H 2 0 ) 2 ( P F g ) 2 C o ( 4 m e p y ) Q ( H 2 0 ) 2 ( A s F g ) 2 (a) (b) (a) (b) ASSIGNMENT 4T-, (F) + 4 T 0 (F) 8.77m — 8.93m l g 2g -> 4 T n (P) 20.0s 20.0s 20.8s 20.4s ig 20.8sh 21.1sh 21.5sh D q ( c m _ 1 ) 995 1010 B (cm ) I x 8 4 0 8 4 5 (a) m u l l s p e c t r a (b) d i f f u s e r e f l e c t a n c e - 9 3 -CD5.2-100 2 0 0 3 0 0 Temperature (K) FIGURE 3.7 MAGNETIC PROPERTIES OF C o ( 4 m e p y ) g ( H 2 0 ) 2 ( E F ) 2 ( f o r d e s c r i p t i o n o f l i n e ( a ) , shaded and unshaded c i r c l e s see F i g . 3.1 p.69; l i n e (b) i s t h e t h e r e o t i c a l c u r v e f o r A=1.40, v=5 ,A=-150cm-1, and k ' = . 9 3 ; l i n e (c) i s t h e t h e r e o t i c a l c u r v e f o r A=1.40, v=5 , A=-150cm 1 , and k'=.88; t h e shaded and unshaded squares are t h e d a t a p o i n t s f o r E=P and E=As, r e s p e c t i v e l y ) -94-environment i n both compounds. The s p l i t t i n g (A) of the cubic ^ T ^ g term due t o low symmetry i s approximately (vX) 750 cm - 1 although the s i g n of A i s not d e f i n i t e . The c r y s t a l and molecular s t r u c t u r e of Co(4mepy)g-(1^0) 2 (PFg) 2 was determined by s i n g l e c r y s t a l X-ray d i f -f r a c t i o n methods by Dr. S. R e t t i g and P r o f . J . T r o t t e r on the c r y s t a l provided by us. This work, which e s t a b l i s h e s the d e t a i l s of the molecular s t r u c t u r e geometry about the metal i o n , w i l l be b r i e f l y described here. The molecular s t r u c t u r e c o n s i s t s of d i s c r e t e cations,Co(4mepy)^ ( O H 2(4mepy)2 ) 2 and anions, PFg . Figure 3.8. shows the s t r u c t u r e of the c a t i o n . The c o b a l t ( I I ) i o n i s coordinated by four n i t r o g e n (4-methylpyridine) atoms and two oxygen (water) atoms to form a trans-CoN^C^ chromophore. A l l of the adjacent bond angles around c o b a l t are c l o s e to 90°. The Co-N d i s t a n c e s are 2.22 and 2.20 2 and the Co-0 d i s t a n c e s are 2.11 S, i n d i c a t i v e of an a x i a l l y compressed t e t r a g o n a l environment around c o b a l t (approximate D^ symmetry). The molecular arrangement of the a x i a l l i g a n d moieties i s a l s o of i n t e r e s t . Each water molecule i s apparently a s s o c i a t e d w i t h two 4-methylpyridine groups w i t h 0 N di s t a n c e s of 2.75 and 2.80 S and an N-O-N' angle of 90.2°. The i n f r a r e d spectrum i n d i c a t e d t h a t the v(O-H) bands are not those of fr e e water thus confirming the presence of a hydrogen-bonded i n t e r a c t i o n between the oxygen atom and the 4-methylpyridine molecules. 2+ I - 9 5 -FIGURE 3.8 VIEW OF C o ( 4 m e p y ) 4 ( 0 H 2 ( 4 m e p y ) 2 - 9 6 -The m o l e c u l a r s t r u c t u r e d e t e r m i n a t i o n o f Co(4mepy)g-( H o 0 ) ( P F , ) „ and t h e s p e c t r a l and m a g n e t i c p r o p e r t i e s o f Z Z o Z t h e C o ( 4 m e p y ) 8 ( H 2 0 ) 2 ( E F g ) 2 compounds a r e c o n s i s t e n t . The p r e s e n c e o f t h e d i s c r e t e EFg a n i o n s , t h e two d i f f e r e n t t y p e s o f 4mepy m o l e c u l e s , and t h e w a t e r - 4 - m e t h y l p y r i d i n e i n t e r a c t i o n were i n d i c a t e d by t h e i n f r a r e d s p e c t r a . " O c t a h e d r a l " symmetry a b o u t t h e c o b a l t ( I I ) i o n was i n d i c a t e d by t h e e l e c t r o n i c s p e c t r a and m a g n e t i c p r o p e r t i e s . I n a d d i t i o n , t h e m a g n e t i c d a t a showed t h e p r e s e n c e o f a low symmetry component t o t h e l i g a n d f i e l d . A l l o f t h e s e f e a t u r e s a r e c o n f i r m e d by: t h e . . m o l e c u l a r s t r u c t u r e - d e t e r m i n a t i o n . 3.4.2.2.2 N i ( 4 m e p y ) 8 ( H 2 0 ) 2 ( E F g ) 2 The e l e c t r o n i c s p e c t r a l d a t a f o r t h e s e compounds a r e p r e s e n t e d i n T a b l e I I I - 8 . The v a l u e s o f Dq and B were c a l c u l a t e d , a s s u m i n g o c t a h e d r a l symmetry, u s i n g t h e ^2 a n<3 t r a n s i t i o n e n e r g i e s f r o m t h e d i f f u s e r e f l e c t a n c e and t h e method o f s e c t i o n 2.3.2.1. The t r a n s i t i o n e n e r g y c o r -r e s p o n d s t o lODq and a g r e e s f a i r l y w e l l w i t h t h e c a l c u l a t e d v a l u e s i n t h e two compounds. The s t r u c t u r e o f t h e v-^ band o b s e r v e d f o r >Ni (4mepy) 8 (H^O) 2 (PFg) 2 g i v e s an i n d i c a t i o n o f t h e p r e s e n c e o f a low symmetry component t o t h e l i g a n d f i e l d . The e f f e c t i v e m a g n e t i c moments o f t h e s e compounds -97-TABLE I I I - 8 ELECTRONIC SPECTRAL DATA FOR N i ( 4 m e p y ) g ( H 2 0 ) 2 ( E F g ) 2 COMPOUND 3 A + 3T A 2 g L2g + 3T i g 5 T l g ( P ) BAND POSITION (kK) N i ( 4 m e p y ) 8 ( H 2 0 ) 2 ( P F g ) 2 N i ( 4 m e p y ) g ( H 2 0 ) 2 ( A s F g ) 2 { (a) 9.53m 11.1m n.o. 16.7s 27.4s (b) 16.7s 26. 8s (a) 10.3m 13. 3w 16.8s 27.4s (b) 16.7s 26.9s Dq (cm- 1 ) B (cm ) 1055 790 1050 805 (a) m u l l s p e c t r u m (b) d i f f u s e r e f l e c t a n c e - 9 8 -a r e e s s e n t i a l l y t e m p e r a t u r e i n d e p e n d e n t . M a g n e t i c moments o f 3.15 and 3.14 B.M. a t 300K a r e o b s e r v e d f o r t h e h e x a -f l u o r o p h o s p h a t e and h e x a f l u o r o a r s e n a t e compound, r e s p e c t i v e l y , c o n s i s t e n t w i t h a s p i n - t r i p l e t o r b i t a l l y n o n d e g e n e r a t e 3 3 g r o u n d t e r m , A 2 g B l g ^ * N o n - z e r o W e i s s c o n s t a n t s , 8 (-6 f o r E=P, +1 f o r E=As) a r e o b s e r v e d , a c o n s e q u e n c e p o s -s i b l y o f l o w symmetry components t o t h e l i g a n d f i e l d (due t o s e c o n d o r d e r s p i n - o r b i t c o u p l i n g e f f e c t s ) . The c r y s t a l and m o l e c u l a r s t r u c t u r e o f N i ( 4 m e p y ) R -( H 2 0 ) 2 ( P F g ) 2 w a s s o l v e d by D r . S. R e t t i g and P r o f . J . T r o t t e r ( u n p u b l i s h e d r e s u l t s ) and i s p r e s e n t e d h e r e i n an a b b r e v i a t e d f o r m . The s t r u c t u r e , as i n t h e c o b a l t ( I I ) c a s e , c o n s i s t s o f d i s c r e t e c a t i o n s and a n i o n s . F i g u r e 3.9 shows t h e m o l e c -u l a r a r r a n g e m e n t o f and some bond d i s t a n c e s i n t h e c a t i o n . The n i c k e l ( I I ) i s c o o r d i n a t e d by f o u r n i t r o g e n s and two o x y g e n s as i n t h e a n a l o g o u s c o b a l t ( I I ) compound. The w a t e r m o l e c u l e s , a g a i n , a p p e a r t o be h y d r o g e n - b o n d e d t o 4 - m e t h y l -p y r i d i n e m o l e c u l e s . The N i - N bond d i s t a n c e s r a n g e f r o m 2.10 t o 2.12 2, t h e N i - 0 bond d i s t a n c e s a r e 2.12 %, and t h e a d j a c e n t bond a n g l e s a b o u t n i c k e l ( I I ) a r e a l l c l o s e t o 9 0 ° . T h e s e l i g a n d s t h u s f o r m a f a i r l y " r e g u l a r o c t a h e d r a l " t r a n s - N i N 4 0 2 c h r o m o p h o r e . T h i s s h o u l d be c o n t r a s t e d w i t h t h e s t r u c t u r e o f t h e a n a l o g o u s c o b a l t c a t i o n s where t h e C o N 4 0 2 chromophore h a d c o m p r e s s e d t e t r a g o n a l g e o m e t r y . I t i s i n t e r e s t i n g t o s p e c u l a t e on t h e d i f f e r e n c e s - 9 9 --100-i n t h e c o o r d i n a t i o n g e o m e t r y o b s e r v e d i n t h e s e 4mepy com-pounds b e c a u s e t h e o n l y d i f f e r e n c e p r e s e n t i s t h e m e t a l ( I I ) i o n . We w i l l compare t h e c r y s t a l f i e l d s t a b i l i z a t i o n e n e r g i e s a c h i e v e d by d i s t o r t i o n o f a " r e g u l a r o c t a h e d r a l " c o o r d i n a t i o n g e o m e t r y . I n a t e t r a g o n a l d i s t o r t i o n , t h e t 2 o r b i t a l s w o u l d be s p l i t i n t o two s e t s ; e (d ,d ) and b „(d ) g x z y z 2 g X Y ( F i g u r e 2.5 (p., 48) s h o w s - t h i s s i t u a t i o n f o r a x i a l e l o n g a t i o n . ) . W i t h t h e e n e r g y d i f f e r e n c e o f t h e two s e t s d e f i n e d a s 6, t h e r e l a t i v e e n e r g i e s a r e ; e,. s e t , + 1/36 and b o r b i t a l g z y + 2/3<5 . I f t h e t e t r a g o n a l d i s t o r t i o n i s an a x i a l e l o n g a t i o n , t h e e s e t l i e s l o w e r i n e n e r g y and i f i t i s an a x i a l com-g p r e s s i o n , t h e b^ o r b i t a l l i e s l o w e r . i n e n e r g y . The r e s u l t o f t h e c a l c u l a t i o n o f t h e s t a b i l i z a t i o n 7 e n e r g i e s shows t h a t f o r o c t a h e d r a l c o b a l t ( I I ) ( d ) , i t i s e n e r g e t i c a l l y f a v o r a b l e f o r a d i s t o r t i o n t o ' o c c u r whereas f o r 8 7 o c t a h e d r a l n i c k e l ( I I ) ( d ) , i t i s n o t . I n h i g h s p i n d , t h e o c c u p a n c y o f t h e t 2 s e t ( i n o c t a h e d r a l symmetry) i s (t-^g) 4 1 F o r a x i a l e l o n g a t i o n t h e o c c u p a n c y (e ) (b ) g i v e s an g 2 -g e n e r g y o f ( 4 ( - 1 / 3 6 ) + 1 ( 2 / 3 6 ) ) -2/36 and f o r a x i a l c o m p r e s s i o n , 2 3 t h e o c c u p a n c y ( b 2 g ) ^ eg) g i v e s an e n e r g y o f (2 (-2/36) + 3(1/36 ) ) = - l / 3 6 r e l a t i v e t o t h e o c t a h e d r a l s t e r e o c h e m i s t r y . 8 6 F o r h i g h s p i n d , t h e o c c u p a n c y o f t h e t 2 s e t i s ( t 2 g ) and t h e r e i s no s t a b i l i z a t i o n e n e r g y g a i n i n t e t r a g o n a l symmetry compared t o t h e o c t a h e d r a l symmetry. I t s h o u l d be n o t e d t h a t a x i a l e l o n g a t i o n i s f a v o r e d 7 o v e r a x i a l c o m p r e s s i o n f o r t h e d c o n f i g u r a t i o n a c c o r d i n g t o t h e above a r g u m e n t s b u t t h e c o b a l t ( I I ) complex has an a x i a l l y 5 -101-c o m p r e s s e d t e t r a g o n a l symmetry. T h i s p r o b a b l y r e f l e c t s t h e s t e r i c r e q u i r e m e n t s o f t h e l i g a n d s p e c i e s , 4 - m e t h y l p y r i d i n e and w a t e r . The a n g l e a r o u n d n i t r o g e n i n t h e p y r i d i n e l i g a n d i s a p p r o x i m a t e l y 1 2 0 ° ( a n g l e C-N-C) whereas t h e a n g l e (H-O-H) i n t h e w a t e r m o l e c u l e i s a p p r o x i m a t e l y 1 0 7 ° . I n t h e w a t e r l i g a n d s , t h e n i t r o g e n h e t e r o c y c l e h y d r o g e n - b o n d e d t o i t i s 2.75 & f r o m t h e o x y g e n w i t h t h e O-H-N s y s t e m l i n e a r . I n t h e n i t r o g e n h e t e r o c y c l e bonded t o t h e m e t a l t h e r e a r e h y d r o g e n s a t t a c h e d t o c a r b o n s w i t h t h e a n g l e (N-C-H) c l o s e t o 1 2 0 ° . T h e s e f a c t o r s w o u l d l e a d t o g r e a t e r i n t e r - l i g a n d s t e r i c r e -p u l s i o n s w i t h t h e m e t h y l p y r i d i n e s c l o s e r t o t h e m e t a l i o n t h a n t h e w a t e r m o l e c u l e s . Thus we have r a t i o n a l i z e d t h e o b s e r v e d s t r u c t u r e o f t h e M ( 4 m e p y ) g ( H 2 0 ) 2 ( E F g ) 2 (M=Co, N i ) i n t e r m s o f CFSE and s t e r i c c o n s i d e r a t i o n s . As we s h a l l s e e i n t h e n e x t two s e c t i o n s , t h e M ( 3 m e p y ) 6 ( H 2 0 ) 2 ( E F g ) 2 a l s o e x h i b i t t h e s e s t r u c t u r e s , a s e v i d e n c e d by t h e c r y s t a l s t r u c t u r e o f N i ( 3 m e p y ) g ( H 2 0 ) 2 ( P F g ) 2 ( s e c t i o n 3.4.2.2.3) and t h e m a g n e t i c p r o p e r t i e s o f Co(3mepy)g-( H 2 0 ) 2 ( P F g ) 2 ( s e c t i o n 3.4.2.2.4). However, we have c h a r a c t e r i z e d t h e C o ( p y ) g ( E F g ) 2 ( s e c t i o n 3.2) and N i ( p y ) g ( P F g ) 2 ( s e c t i o n 3.3) compounds a s b o t h h a v i n g r e g u l a r o c t a h e d r a l MN g chromo-p h o r e s . We w o u l d h a v e e x p e c t e d a c c o r d i n g t o CFSE ar g u m e n t s , a d i s t o r t e d c hromophore f o r t h e c o b a l t ( I I ) compounds. I t s h o u l d be n o t e d ' t h a t t h e CFSE arguments d i s c u s s e d f o r t h e C o N 4 0 2 c h r o m o p h o r e s when a p p l i e d t o t h e CoNg chro m o p h o r e s 1 s h o u l d be c o n s i d e r e d i n t e r m s o f a J a h n - T e l l e r d i s t o r t i o n -102-(section 2.3.3, p. 47) of the t 2 set where the s t a b i l i z a t i o n energy i s small. This i s because the o r b i t a l s are not directed towards the metal as the e (0, : d 2 2 and d 2) y n x ~~ y z are and therefore are le s s affected by the ligands. In molecular o r b i t a l theory, the t 2 electrons are non-bonding (and these e electrons, anti-bonding) electrons. When the ligands around the metal ion are equivalent . i t i s not favorable (with respect to in t e r - l i g a n d s t e r i c repulsions) for the d i s t o r t i o n to be present. Apparently, i n the methyl-pyridine (derivatives) of c o b a l t ( I I ) , the CFSE consideration and s t e r i c factors are complementary such that they give r i s e to a d i s t o r t i o n . - 1 0 3 -3.4.2.2.3 N i ( 3 m e p y ) g ( H 2 0 ) 2 ( E F 6 ) 2 T a b l e I I I - 9 g i v e s t h e e l e c t r o n i c s p e c t r a l d a t a f o r t h e s e c o m p l e x e s . The s p e c t r a a r e s a t i s f a c t o r i l y a s s i g n e d on t h e b a s i s o f o c t a h e d r a l n i c k e l ( I I ) , t h e l i g a n d f i e l d p a r a m e t e r s were c a l c u l a t e d a s d e s c r i b e d i n s e c t i o n 2.4.2.2.2. C o n s i s t e n t w i t h o c t a h e d r a l n i c k e l ( I I ) , t h e e f f e c t i v e mag-n e t i c moments a r e e s s e n t i a l l y i n d e p e n d e n t o f t e m p e r a t u r e : f o r N i ( 3 m e p y ) 6 ( H 2 0 ) 2 ( P F 6 ) 2 , y f f ( 3 0 0 K ) = 3 . 1 7 ' B . M . and 6=-6K; and f o r N i (3mepy) g (H"20) 2 ( A s F g ) 2 , y f f (300K) =3 .16 B.M. and 9=-15. T h e s e p r o p e r t i e s a r e v e r y s i m i l a r t o t h o s e o b s e r v e d f o r t h e N i ( 4 m e p y ) 8 ( H 2 0 ) 2 ( E F g ) 2 c o m p l e x e s s u g g e s t i n g t h a t t h e n a t u r e o f t h e c h r o m o p h o r e i s v e r y s i m i l a r . The m o l e c u l a r s t r u c t u r e o f N i (3mepy) g (H 20) 2 ( P F g ) 2 , d e t e r m i n e d by X - r a y d i f f r a c t i o n , c o n f i r m s t h i s . The c r y s t a l and m o l e c u l a r s t r u c t u r e o f N i ( 3 m e p y ) g -( H 2 0 ) 2 ( P F g ) 2 was d e t e r m i n e d as p a r t o f t h i s work and w i l l be d i s c u s s e d i n more d e t a i l t h a n t h e m o l e c u l a r s t r u c t u r e s o f t h e M ( 4 m e p y ) g ( H 2 0 ) 2 ( P F g ) 2 (M=Co,Ni) c o m p l e x e s . E x p e r i m e n t a l p r o c e d u r e s and d e t a i l s o f how t h e s t r u c t u r e was d e t e r m i n e d a r e d e s c r i b e d i n s e c t i o n 6.5.3. The a t o m i c p o s i t i o n a l -104-TABLE I I I - 9 ELECTRONIC SPECTRAL DATA FOR N i ( 3 m e p y ) g ( H 2 0 ) 2 ( E F g ) 2 ASSIGNMENT BAND POSITION (kK) E=p E=As (a) (b) (a) (b) 3 3 V l ( A2q T2g) 10.8m-w 10.80m-w V 2 ( 3 A 2 g ^ 3 T l g ( F ) ^ 16.95m 16.67m 16.95m 16.67m v„ ( 3 A +3T., (P) ) 27.07m 26.81m 17.07m 26.81m 3 2g l g / - I N 1 0 8 0 1 0 8 0 Dq(cm ) xuou _ . - 1 , 7 8 0 7 8 0 B (cm ) 1 O K J (a) mull spectrum (b) d i f f u s e r e f l e c t a n c e -105-and thermal parameters are also given there. The bond distances and angles present i n the molecular structure are shown i n Table I I I - 10 . The structure consists of e s s e n t i a l l y d i s t i n c t Ni (3mepy) 4£(OH 2) ( 3mepy)]22 + cations and PF g anions although there i s some evidence for anion - H 20 in t e r a c t i o n . The bond distances and angles found i n the 3-methylpyridine ring are sim i l a r to those derived for pyridine from a microwave study (90)• The 3-methylpyridine moieties are a l l planar within experimental error. The P-F bond distances of two c r y s t a l -lographic d i s t i n c t PFg~ groups vary from 1.509(11) to 1.577(9)5 i n one group and 1.513(11) to 1.579(9) A* i n the other and the bond angles for adjacent P-F bonds from 85.8 ° to 91.4° and from 87.1° and 94.7° respectively. The thermal parameters are moderately large and there are apparent d i s t o r t i o n s i n the anion as i s usually observed for t h i s nearly spherical anion (9,1). Figure 3.10 shows a view of the cation with the non-coordinated 3mepy ligands shown. The Ni-N distances are not equal (Table 111-10); Ni-N(l) and Ni-N(4) are adjacent and equal at 2.094 IR whereas the Ni-N distances opposite these are s i g n i f i c a n t l y longer. The Ni-0 distances are also unequal at 2.090 (7) and 2.128(7)2. The atoms Ni, N.(l), N(3), 0(1), 0(2), and Ni, N(2), N(4), 0(1), 0(2) are planar within experimental error. But neither Ni, N ( l ) , N(2), N(3), N(4) nor N ( l ) , N(2), N(3), N(4) define a plane within experimental error. The deviation from the l e a s t squares plane through -106-TABLE III-10 BOND .DISTANCES AND ANGLES IN Ni(3mepy) g(HjO) 2(PFg) 2 (estimated standard deviations i n brackets) (i) BOND DISTANCES (X) Ni-N(l) = Ni-N(2) = Ni-N(3) = Ni-N(4) = RING 1 1. 349 (12) 1.372(14) 1.399 (16) 1.389 (18) 1.425(15) 1.373 (13) 1.503 (16) 2.094 (8)! 2.153(8) 2.156(8) 2.094 (8) RING 2 Ni-O(l) = 2.090 (7) Ni-0(2) = 2.128(7) 0(1)-N(5) =2.716(11) 0(2)-N(6) =2.718(11) RING 3 RING 4 N-C(l) C(l)-C(2) C(2)-C(3) C(3)-C(4)' C(4)-C(5) C(5)-N C(2)-C(6) N-C (1) C(l)-C(2) C(2)-C(3) C(.3)-C(4) C(4)-C(5) . C(5)-N-C(2)-C(6) 1.336(12) 1.335(13) 1.354(13) 1.343(14) 1.387(14) 1.376(14) 1.412(16) 1.402(17) 1.395(18) 1.396 (18) 1.414 (18) 1.414 (19) 1.403(15) 1.368(15) 1.363(16) 1.530(16) 1.361(13) 1.355(13) 1.530(16) 1.521(18) 1.525(18) RING 5 RING 6 1.356(16) 1.358(16) 1.397(17) 1.401(17) 1.400(18) 1.358(18) 1.347(18) 1.393(18) 1.435(18) 1.403(17) 1.324(15) 1.306(15) 1.486(19) 1.500(19) -107-TABLE 111-10 (cont'd) (i) BOND DISTANCES (ft) ANION 1 ANION 2 P-F(l) 1.552(11) 1.556(11) P-F(2) 1.565( 9) 1.517(12) P-F(3) 1.577 ( 9) 1.513(11) P-F(4) 1.562 (11) 1.579( 9) P-F(5) 1.509 (12) 1.564 ( 9) P-F(6) 1.526(12) 1.568(10) ( i i ) BOND ANGLES (deg) N(l)-Ni-N(2) 89.1(3) N(l)-Ni-N(3) 177 .3(4) N(l)-Ni-N(4) 92.3 (3) N(l)-Ni-0(1) 92. 3(3) N(l)-Ni-0(2) 88.5 (3) N(2)-Ni-N(3) 89. 7 (3) N (2)-Ni-N (4) 178.4(4) N(2)-Ni-0(1) 87. 7 (3) N(2)-Ni-0(2) 90.2 (3) N(3)-Ni-N(4) 88. 9(3) N(3)-Ni-0(1) 90.0(3) N(3)-Ni-0(2) 89. 1(3) N(4)-Ni-0(1) 91.5 (3) N(4)-Ni-0(2) 90. 6(3) 0(l)-Ni-0(2) 177.7(3) RING 1 RING 2 RING 3 RING 4 RING 5 RING 6 C(5)-N-C(l) 120(1) 119(1) 119(1) 119(1) 121(1) 120(1) N-C(l)-C(2) 124(1) 124(1) 124(1) 123(1) 123(1) 122(1) C(l)-C(2)-C(3) 119(1) 119(1) 116(1) 118(1) 116(1) 117(1) -108-TABLE 111-10 ( c o n t ' d ) ( i i ) BOND ANGLES (deg) RING 1 RING 2 RING 3 RING 4 RING 5 RING 6 C ( 2 ) - C ( 3 ) - C ( 4 ) 118(1) 118(1) 121(1) 119(1) . 121(1) 122(1) C ( 3 ) - C ( 4 ) - C ( 5 ) 122(1) 119(1) 117(1) 120(1) 120 (1) 118(1) C ( 4 ) - C ( 5 ) - N 118(1) 121(1) 123(1) 122(1) 119(1) 122(1) C ( l ) - C ( 2 ) - C ( 6 ) 120(1) 121(1) 120(1) 120(1) 120(1) 119(1) C(3).-C(2)-C(6) 121(1) 120(1) 123(1) 122(1) 124(1) 124(1) ANION 1* ANION 2* F ( l ) - P - F ( 2 ) 89.7 (7) 174.1(10) F ( l ) - P - F ( 3 ) 90.9(7) 90.8(10) F ( l ) - P - F (4) 87.1 (8) 87.1(6) F ( l ) - P - F ( 5 ) 88.9(10) 91.8 (7) F ( l ) - P - F ( 6 ) 176.3(11) 85.8 (7) F ( 2 ) - P - F ( 3 ) 178.3(7) 94.8 (11) F ( 2 ) - P - F ( 4 ) 91.1(7) 91.2 (7) F.(2)-P-F(5) 89.7 (7) 89.8(7) F ( 2 ) - P - F ( 6 ) 90.6 (7) 88.6(10) F ( 3 ) - P - F ( 4 ) 87.3 (6) 89.4 (7) F ( 3 ) - P - F ( 5 ) 92.0 (7) 91.4(7) F (3)-P-F(6) 88.8 (7) 176.5(10) F ( 4 ) - P - F ( 5 ) 175.9 (10) 178.6 (6) F (4)-P-F(6) 89.3 (10) 89.7 (6) F ( 5 ) - P - F (6) 94.7 (11) 89.3 (7) * t h e n u m b e r i n g s y s t e m o f t h e a n i o n s i s a r b i t r a r y -110-t h e n i c k e l atom r e v e a l s t h a t a d j a c e n t n i t r o g e n s a r e above and below t h e p l a n e (0.032) and t h e r e f o r e o p p o s i t e n i t r o g e n s a r e b o t h above o r below t h e p l a n e . I f t h e Ni-N d i s t a n c e s were a l l t h e same, the approximate symmetry about n i c k e l would 4 w i t h r e s p e c t t o t h e n i t r o g e n c o o r d i n a t e d t o i t . B ut t h e d i s t o r t i o n o f t h e chromophore from t h e 4 - f o l d p r o p e r r o t a t i o n a x i s and t h e two 2 - f o l d axes p e r p e n d i c u l a r t o i t a re not v e r y g r e a t , and t h e symmetry o f t h e l i g a n d f i e l d about t h e n i c k e l i o n can r e a s o n a b l y . b e d e s c r i b e d as 422 o r * F i g u r e 3.11 shows a v i e w o f t h e N i ( 3 m e p y ) g ( H 2 0 ) 2 ~ ( P F 6 ) 2 u n i t . The 0 ( l - ) - N ( 5 ) and 0(2)-N(6) d i s t a n c e s a r e 2.716(11) and 2.718 (11)2. r e s p e c t i v e l y , comparable t o t h e 0-N d i s t a n c e s o f t h e 0 H 2 (4mepy) 2 a x i a l s p e c i e s i n t h e M ( 4 m e p y ) g ( H 2 0 ) 2 ( P F g ) 2 m o l e c u l a r s t r u c t u r e . A g a i n hydrogen bonding i s l i k e l y i n v o l v e d i n t h e i n t e r a c t i o n . I t i s i n t e r -e s t i n g t o note t h a t o n l y one o f t h e hydrogen atoms i s found t o be H-bonded t o a n i t r o g e n h e t e r o c y c l e i n t h e 3mepy case whereas two 0 —H—N bonds a r e seen i n t h e 4mepy cas e . T h i s i s o b v i o u s l y t h e rea s o n t h a t t h e r e were two t y p e s o f (0-H) bands, one sharp and one b r o a d , seen i n t h e i n f r a r e d s p e c t r a ( S e c t i o n 3.4.1) o f t h e 3mepy complexes. S i g n i f i c a n t l y , o n l y one v e r y b road v(O-H) band i s seen i n t h e M ( 4 m e p y ) g ( H 2 0 ) 2 ( E F g ) 2 compounds where, b o t h hydrogens on each w a t e r m o l e c u l e a r e i n v o l v e d i n hydrogen-bonding. The c l o s e s t f l u o r i n e - o x y g e n d i s t a n c e s , i n the! N i ( 3 m e p y ) 6 ( H 2 0 ) 2 ( P F g ) 2 compound a r e 2.962(11 )2 between 0(1) -111-FIGURE 3.11 VIEW OF N i ( 3 m e p y ) g ( H 2 0 ) 2 ( P F g ) 2 -112-and P(2) and 2.957(12)8 between 0(2) and F ( l ) . I t i s v e r y i n t e r e s t i n g t o n o t e t h a t a l t h o u g h t h e r e i s c l e a r e v i d e n c e f r o m t h i s m o l e c u l a r s t r u c t u r e d e t e r m i n a t i o n t h a t t h e P F , 6 g r o u p s a r e i n v o l v e d i n H b o n d i n g t o 1^0 m o l e c u l e s ( a l b e i t , v e r y w e ak), t h e r e i s no e v i d e n c e o f t h i s i n t e r a c t i o n f r o m t h e i n f r a r e d s p e c t r a . I t i s c l e a r l y t o o weak t o be s e e n i n t h e i n f r a r e d and t h i s i n t u r n p o i n t s o u t t h e l i m i t a t i o n s o f i n f r a r e d c r i t e r i a f o r s u c h p u r p o s e s . 3.4.2.2.4 C o ( 3 m e p y ) 6 ( H 2 0 ) 2 ( E F 6 ) 2 The m a g n e t i c p r o p e r t i e s and t h e e l e c t r o n i c s p e c t r a o f C o ( 3 m e p y ) g ( H 2 O ) 2 ( P F g ) 2 a r e c o n s i s t e n t w i t h a c o b a l t ( I I ) i o n i n an o c t a h e d r a l l i g a n d f i e l d . ( C o ( 3 m e p y ) g ( H 2 0 ) 2 ( A s F g ) 2 was f o u n d t o be u n s t a b l e as a powder and t h e r e f o r e e l e c t r o n i c s p e c t r o s c o p y and m a g n e t i c s u s c e p t i b i l i t y measurements c o u l d n o t be p e r f o r m e d on t h i s compound.) The e l e c t r o n i c s p e c t r a l d a t a f o r C o ( 3 m e p y ) g ( H 2 0 ) 2 ( P F g ) 2 a r e g i v e n i n T a b l e I I I - l l . The v a l u e s o f Dq and B c a l c u l a t e d f r o m t h e m u l l s p e c t r a were 1040 and 860 cm \ The c a l c u l a t e d v a l u e s o f v-^, v ^ , and v 2 a r e 9.19, 20.87 and 19.57 kK r e s p e c t i v e l y and r e p r e s e n t a r e a s o n a b l e f i t t o t h e e x p e r i m e n t a l d a t a . The v a l u e o f A c a l c u l a t e d i s 1.40. The e f f e c t i v e m a g n e t i c moment o f Co(3mepy)g(H^O)^ ( p F 5 4 i s t e m p e r a t u r e d e p e n d e n t c o n s i s t e n t w i t h t h e n o m i n a l T ^ g -113-TABLE I I I - l l ELECTRONIC SPECTRAL DATA FOR C o ( 3 m e p y ) g ( H 2 0 ) 2 ( P F g ) 2 BAND POSITION(kK)* ASSIGNMENT V 3 ( 4T l g-> 4T l g(P) ) 22.82s Dq (cm" 1) 1 0 4 0 • r l B (cm ) 860 * mul l spectrum -114-g r o u n d s t a t e o f o c t a h e d r a l c o b a l t ( I I ) . The f i t o f t h e t h e o -r e t i c a l c u r v e s t o t h e e x p e r i m e n t a l d a t a ( T a b l e 111-12) shows t h a t t h e e l e c t r o n i c s t r u c t u r e o f t h i s 3 - m e t h y l p y r i d i n e complex i s t h a t o f a . t e t r a g o n a l l y d i s t o r t e d o c t a h e d r a l ( A = 465 cm c o b a l t ( I I ) . The v a l u e o f A i s v e r y s i m i l a r t o t h o s e o b s e r v e d f o r t h e C o ( 4 m e p y ) 8 ( H 2 0 ) 2 ( E F g ) 2 c o m p l e x e s o f s e c t i o n 3.4.2.1 where A i s 750 cm 1 . The i n f r a r e d e v i d e n c e p r e s e n t e d i n s e c t i o n 3.4.1 i n d i c a t e d t h a t N i ( 3 m e p y ) g ( H 2 0 ) 2 ( P F g ) 2 and Co(3mepy)g-(H20)2(PFg)2 a r e v e r y s i m i l a r w i t h r e g a r d s t o t h e n a t u r e o f t h e aquo l i g a n d p r e s e n t (and s e c t i o n 3.4.2.3 showed t h e MN^C^ c h r o mophore t o be p r e s e n t ) . I t i s r e a s o n a b l e t o assume t h a t t h e Co(3mepy)g(H2O)2( E Fg)2 c o m p l e x e s have t h e same t y p e o f chromo-p h o r e as t h e Co(4mepy)g(H2O)2(EFg)2 i . e . t e t r a g o n a l l y d i s t o r t e d ( a x i a l l y c o mpressed) o c t a h e d r a l t r a n s - C o N ^ C ^ c h r o m o p h o r e s . T h i s c hromophore w o u l d be e x p e c t e d f r o m t h e c o n s i d e r a t i o n s . o f CFSE's and s t e r i c f a c t o r s as p r e s e n t e d i n s e c t i o n 3.4.2.2. The p r e s e n c e o f t h e a x i a l l y c o m p r e s s e d CoN^C^ chromo-p h o r e c o u l d be v e r i f i e d by t h e r e s u l t s o f a s i n g l e c r y s t a l X - r a y d i f f r a c t i o n m o l e c u l a r s t r u c t u r e d e t e r m i n a t i o n . A l t h o u g h good c r y s t a l s a r e a v a i l a b l e , t h i s s t u d y had n o t b e en done on t h i s compound a t t h e t i m e t h i s t h e s i s was w r i t t e n . The e x a m i n a t i o n o f t h e p r e l i m i n a r y W e i s s e n b e r g and p r e c e s s i o n p h o t o g r a p h s pn C o ( 3 m e p y ) g ( H 2 0 ) 2 ( P F g ) 2 (see s e c t i o n 6.5.4) do i n d i c a t e t h a t t h e u n i t c e l l p a r a m e t e r s and d i f f r a c t i o n p a t t e r n a r e v e r y s i m i l a r ( i n f a c t , t h e same) as t h a t o b s e r v e d f o r N i ( 3 m e p y ) g ( H 2 0 ) 2 ( P F g ) 2 • However, t h i s does n o t mean t h a t t h e s t r u c t u r e p a r a m e t e r s a r o u n d c o b a l t have t o be t h e same as t h o s e o b s e r v e d a r o u n d n i c k e l ( I I ) - 1 1 5 -TABLE 1 1 1 - 1 2 MAGNETIC PROPERTIES OF Co (3mepy) g (H^O) 2 (PFg) 2 TTYPVRTMFNTAL T H E O R E T I C A L T E M P E R A T U R E EXPERlMjilN 1B.J-1 1 -i n R M ^ U ( i n B.M.) ( i n K e l v i n ) V e f f < i n B ' M * ) U e f f A = 1 . 4 0 , k ' = 0 . 9 5 v = 3 , : X=-155 :cm 2 9 6 . 2 4 . 9 3 4 . 9 2 2 7 2 . 8 4 . 8 8 4 . 9 0 2 5 1 . 3 4 . 8 2 4 . 9 0 2 2 6 . 5 4 . 8 5 4 . 8 8 2 0 3 . 0 4 . 8 3 4 . 8 5 1 7 7 . 9 4 . 7 8 4 . 8 2 1 4 9 . 6 4 . 7 0 4 . 7 5 1 3 9 . 8 4 . 7 2 4 . 7 3 1 0 4 . 0 4 . 6 4 4 . 6 1 84 . 8 4 . 5 2 4 . 5 0 -116-(see s e c t i o n 3.4.2.3) b e c a u s e o f t h e l o w c r y s t a l l o g r a p h i c sym-m e t r y o f t h e c a t i o n i c s p e c i e s , C g (see s e c t i o n 6.5.3). N e v e r -t h e l e s s , i t w o u l d be i n t e r e s t i n g and i n f o r m a t i v e t o o b t a i n t h e m o l e c u l a r s t r u c t u r e o f t h e c o b a l t ( I I ) complex i n o r d e r t o p r o v i d e s u p p o r t i n g e v i d e n c e f o r t h e a x i a l l y c o m p r e s s e d CoN^G^ c h r o m o p h o r e . 3.4.2.2.5 C u ( 3 m e p y ) 6 ( H 2 0 ) 2 ( E F g ) 2 The m a g n e t i c p r o p e r t i e s , e l e c t r o n i c s p e c t r a l d a t a and e . s . r . d a t a f o r t h e s e compounds a r e shown i n T a b l e 111-13. The e l e c t r o n i c s p e c t r a o f t h e s e compounds c o n s i s t o f a s i n g l e b a n d c e n t e r e d a t a p p r o x i m a t e l y 600 nm w h i c h a c c o r d i n g t o H a t h a w a y 1 s s c a l e ( F i g u r e 2.6 p. 51) w o u l d be due t o t h e a b s o r p t i o n o f e i t h e r a r h o m b i c o r t e t r a g o n a l o c t a h e d r a l CuNg c h r o m o p h o r e . G i v e n , t h e a b s e n c e o f w e l l - d e f i n e d s p l i t t i n g s o b s e r v e d i n t h e e l e c t r o n i c s p e c t r a o f t h e o t h e r compounds d e s c r i b e d i n t h i s s e c t i o n , i t i s n o t u n r e a s o n a b l e t o e x p e c t t h a t t h e e l e c t r o n i c s p e c t r a w o u l d be o f a C u N 4 0 2 chromophore i n s t e a d . W h a t ever t h e n a t u r e o f t h e chromophore (CuN^G^ o r CuNg), a x i a l symmetry i s i n d i c a t e d by t h e e . s . r . s p e c t r a . F i g u r e 3J.2 shows t h e e . s . r . s p e c t r u m o f Cu (3mepy) g ( ^ 0 ) 2 ( p F g ) 2 a n < ^ shows t h e l i n e s h a p e s e x p e c t e d f o r c o p p e r ( I I ) i n an a x i a l ( D 4 h ) symmetry ( c f . F i g u r e 2.8, p. 5 5 ) . The m a g n e t i c p r o p e r t i e s o f t h e s e compounds do n o t p r o v i d e any o t h e r i n f o r m a t i o n e x c e p t t h a t t h e c o p p e r ( I I ) i o n s a r e m a g n e t i c a l l y d i l u t e . The c o n c l u s i o n -117-TABLE I I I - 1 3 ELECTRONIC PROPERTIES OF Cu ( 3mepy) g (HjO) 2 ( E F g ) 2 C u ( 3 m e p y ) g ( H 2 0 ) 2 ( P F g ) 2 C u ( 3 m e p y ) g ( H 2 0 ) 2 ( A s F g ) 2 V B . M . ) ( a ) 1-82 1.88 e r r 9 ( i n K e l v i n s ) _ 5 -11 E (kK)i (b) max 16.67 16.81 (c) 16.67 16.67 g t d > 2.222 2.231 gj_ 2.061 2.061 a (e) 2.115 2,118 y o A ( i n gauss) 198 174 (a) a t 294K (b) m u l l s p e c t r a (c) d i f f u s e r e f l e c t a n c e s p e c t r a (d) e . s . r . s p e c t r a on powders (e) c a l c u l a t e d by use o f e q u a t i o n 2.5, p.23 -118-FIGURE 3.12 E.S.R. SPECTRUM OF C u ( 3 m e p y ) g ( H 2 0 ) 2 ( P F g ) 2 ( powder a t room t e m p e r a t u r e ) -119-t h a t c a n be r e a c h e d f r o m t h e d a t a o f T a b l e 111-13 i s t h a t t h e c o p p e r ( I I ) i o n i s i n a x i a l l y e l o n g a t e d t e t r a g o n a l " o c t a h e d r a l " e n v i r o n m e n t a l t h o u g h we do n o t know w h e t h e r i t i s a CuN^C^ o r CuNg c h r o m o p h o r e . As m e n t i o n e d i n s e c t i o n 3.4.1, t h e i n f r a r e d s p e c t r a (4000-2000 cm ^) o f t h e s e c o p p e r ( I I ) compounds show some d i f -f e r e n c e s f r o m t h o s e o f t h e o t h e r 3 - m e t h y l p y r i d i n e compounds o f t h i s s e c t i o n . F i g u r e 3.13 shows t h e i n f r a r e d s p e c t r a o f t h e C u ( 3 m e p y ) 6 ( H 2 0 ) 2 ( E F g ) 2 f r o m 4000 t o 2000 c m - 1 . C o m p a r i n g t h e c o n t o u r o f t h e s e s p e c t r a l bands t o t h o s e o f t h e o t h e r 3 - m e t h y l -p y r i d i n e c o m p l e x e s ( F i g u r e 3.6 p . 8 8 ) , i t i s s e e n t h a t t h e g e n e r a l shape o f t h e s p e c t r a i s s i m i l a r i n n a t u r e . The s p e c t r a o f C u ( 3 m e p y ) g ( H 2 0 ) 2 ( E F g ) 2 a p p e a r t o be made up o f t h r e e b a n d s ; two s h a r p and.one b r o a d b a n d ( a l t h o u g h a t h i g h e r e n e r g y t h a n i n t h e o t h e r 3 - m e t h y l p y r i d i n e c o m p l e x e s ) . I n t h e c o p p e r ( I I ) c o m p l e x e s , t h e bands a r e n o t a s w e l l s e p a r a t e d a s i n t h e o t h e r c o m p l e x e s . T h i s i n f r a r e d e v i d e n c e does s u g g e s t t h a t t h e a x i a l l i g a n d s i n C u ( 3 m e p y ) g ( ^ 0 ) 2 ( E F g ) 2 a r e s i m i l a r t o t h o s e o f t h e o t h e r 3 - m e t h y l p y r i d i n e c o m p l e x e s . T h i s i s c o n s i s t e n t w i t h t h e p r e s e n c e o f a C u N 4 0 2 chromophore i n t h e s e compounds. A s i n g l e c r y s t a l X - r a y s t u d y on C u ( 3 m e p y ) g ( H 2 0 ) 2 ~ (PFg ) 2 w o u l d p r o v i d e c o n c l u s i v e p r o o f as t o t h e n a t u r e o f t h e m e t a l - l i g a n d c h r o m o p h o r e . A l t h o u g h good c r y s t a l s a r e a v a i l a b l e and t h e c e l l d a t a f r o m t h e p r e l i m i n a r y . X - r a y - p h o t o -g r a p h s - h a v e b e e n d e t e r m i n e d / t h e d a t a c o l l e c t i o n and m o l e c -u l a r s t r u c t u r e d e t e r m i n a t i o n have n o t b e e n : c o m p l e t e d a t t h i s t i m e . -120-I I A B S 0 R P T I 0 N + 4000 3000 2000 ENERGY ( cm ) FIGURE 3.13 INFRARED SPECTRA (4000-200001*" ) o f Cu(3mepy) 6-(H 0) ( E F 6 ) . 2 ( spectrum I , E=P and spectrum I I , E=As) * N u j o l band) -121-3.4.3. RELATION TO OTHER WORK The 4-methylpyridine and 3-methylpyridine complexes d e s c r i b e d i n e a r l i e r p a r t s of t h i s s e c t i o n have s t o i c h i o m e t r i e s and s t r u c t u r e s d i f f e r e n t from those of the p y r i d i n e complexes d e s c r i b e d i n s e c t i o n s 3.1 and 3.2 of t h i s chapter. I t i s i n t e r -e s t i n g to compare the c a l c u l a t e d l i g a n d f i e l d parameters o b t a i n e d from the e l e c t r o n i c s p e c t r a o f these complexes wi t h r e s p e c t t o d i f f e r e n t l i g a n d s e t s around the metal i o n (metal i o n h e l d constant) and w i t h r e s p e c t to e f f e c t o f the same l i g a n d s e t t o a range of metal i o n s . F a c t o r s which have to be taken i n t o account f o r t h i s d i s c u s s i o n are the p r o p e r t i e s of the l i g a n d s themselves, the s t e r e o c h e m i s t r y o f the l i g a n d s e t , and the nature of the m e t a l - l i g a n d chromophore. T h i s s e c t i o n w i l l attempt t h i s comparison and w i l l a l s o attempt to r a t i o n a l i z e the chemistry which g i v e s r i s e t o the d i f f e r e n t compounds w i t h the d i f f e r e n t l i g a n d s p e c i e s . When a n a l y z i n g the l i g a n d f i e l d parameters, i t i s important to r e a l i z e t h a t , i n the absence of c a r e f u l low temperature s t u d i e s (67 ) , the v a l u e s probably are o n l y s i g -n i f i c a n t t o + 20 cm 1 . T h e r e f o r e v a l u e s of Dq and B w i t h i n t h i s range i n these comparisons w i l l be c o n s i d e r e d to be e q u i v a l e n t . A summary of the s t r u c t u r e s o f the chromophores w i l l be c o n s i d e r e d i n p r e p a r a t i o n f o r the d i s c u s s i o n . For the n i c k e l complexes,- the same g e n e r a l s t e r e o c h e m i s t r y (octahedral) i s observed f o r the two chromophores (NiN g and -122-NiN^C^) ; whereas, f o r the c o b a l t ( I I ) complexes, the s t e r e o -c h e m i s t r i e s are d i f f e r e n t f o r the two chromophores (CoNg " o c t a h e d r a l " v s . CoN^C^ compressed (D^) o c t a h e d r a l . F i n a l l y , the s u b t l e concepts o f the a p p l i c a t i o n o f the " r u l e o f average environment" w i l l be recounted. The d i s c u s s i o n s w i l l i n i t i a l l y assume t h a t t h i s r u l e i s upheld; any d e v i a t i o n from expected behavior of the l i g a n d f i e l d parameters may be d e a l t w i t h as an e x c e p t i o n to t h i s r u l e (the average e n v i r o n -ment r u l e means t h a t although t h e r e may be two v e r y d i f f e r e n t types o f l i g a n d s surrounding a metal i o n , the e l e c t r o n i c s t r u c t u r e o f the metal may r e f l e c t the average environment r a t h e r than the a n i s o t r o p y of the l i g a n d d i s t r i b u t i o n ) . For the compound, N i (py) g (EFg) 2 , the values o f Dq and B are 1000 and 800 c m - 1 r e s p e c t i v e l y . In the analogous 4mepy complexes o f n i c k e l the va l u e o f Dq i s h i g h e r (1050 cm "*") and o f B approximately the same and i n the 3mepy complexes, the value o f Dq i s h i g h e r s t i l l (1080 cm ^) and of B lower (780 cm ^ ) . The Dq v a l u e s f o r the 3mepy and 4mepy complexes are s i g n i f i c a n t l y h i g h e r than t h a t o f the py complexes whereas the B valu e s are pro b a b l y approximately e q u i v a l e n t . How do these parameters r e l a t e t o the s t r u c t u r e and bonding i n the complexes and the p r o p e r t i e s of the l i g a n d s i n the two chromophores? Water i s a weaker f i e l d l i g a n d than p y r i d i n e ?+ -1 (Dq f o r N i ( H 2 0 ) g =910 cm (16)) whereas 4-methylpyridine and 3-methylpyridine are s t r o n g e r bases (and thus probably -123-s t r o n g e r f i e l d l i g a n d s ) t h a n p y r i d i n e ( 1 6 ) . Water as a l i g a n d w o u l d be e x p e c t e d t o r e d u c e t h e v a l u e o f B f r o m B Q l e s s t h a n 2+ p y r i d i n e a s l i g a n d ( B ( N i ( H 2 0 ^ )=890); t h i s w o u l d a l s o be t h e c a s e w i t h t h e m e t h y l p y r i d i n e s b e c a u s e o f l e s s e l e c t r o n d e l o c a l i z a t i o n . G i v e n t h i s i n f o r m a t i o n , one w o u l d e x p e c t t h a t ( a s s u m i n g a p p r o x i m a t e l y e q u a l bond l e n g t h s ) t h e 4mepy a n d 3mepy c o m p l e x e s w i t h NiN^C^ c h r o m o p h o r e s w o u l d have a p p r o x i m a t e l y t h e same v a l u e o f Dq and a l a r g e r v a l u e o f B t h a n t h e p y r i d i n e c o m p l e x e s w i t h t h e N i N g c h r o m o p h o r e . However, t h i s i s n o t t h e c a s e . The o b s e r v e d p a r a m e t e r s c a n be r a t i o n a l i z e d by i n v o l v i n g t h e argument o f l e s s i n t e r - l i g a n d r e p u l s i o n s a r o u n d t h e m e t a l i o n i n t h e NiN^G^ c h r o m o p h o r e s t h a n i n t h e N i N g c h r o m o p h o r e s . I n t h e . f o r m e r c a s e , t h e n i c k e l ( I I ) i o n i s s u r r o u n d e d by f o u r l a r g e r h e t e r o c y c l i c a r o m a t i c r i n g s and two s m a l l e r , w a t e r m o l e c u l e s w hereas i n - t h e l a t t e r c a s e , t h e n i c k e l ( I I ) i s s u r r o u n d e d by s i x l a r g e h e t e r o c y c l i c l i g a n d s . T h i s s i t u a t i o n may r e s u l t i n s h o r t e r a v e r a g e m e t a l - l i g a n d bond l e n g t h s i n t h e 4mepy and 3mepy c o m p l e x e s t h a n i n t h e p y r i d i n e c o m p l e x e s . Thus, s i n c e Dq i s r e l a t e d t o (1/a ) t h e o v e r a l l e f f e c t w o u l d be an i n c r e a s e i n Dq and a d e c r e a s e i n B (due t o g r e a t e r t h a n e x p e c t e d m e t a l -l i g a n d i n t e r a c t i o n ) , compared t o t h e p y r i d i n e c o m p l e x e s , a s t h e e x p e r i m e n t a l d a t a i n d i c a t e . The c o m p a r i s o n among t h e c o b a l t ( I I ) c o m p l e x e s as m e n t i o n e d p r e v i o u s l y , b r i n g s i n t h e c o m p l i c a t i o n o f a n i s o t r o p i c f a c t o r s . T he c o m p a r i s o n o f t h e l i g a n d f i e l d p a r a m e t e r s o f t h e c o b a l t ( I I ) c o m p l e x e s w i t h t h o s e o f n i c k e l ( I I ) c o n t a i n i n g t h e same l i g a n d s show t h e s e e f f e c t s . F o r t h e C o ( p y ) g ( E F g ) ^ c o m p l e x e s , t h e v a l u e o f Dq, 985 cm i s v e r y s i m i l a r t o t h a t -124-observed, 1000 cm 1 f o r the N i ( p y ) g ( E F g ) 2 complexes; the value o f g=(B/B Q) f o r the c o b a l t ( I I ) complexes i s 0.84 whereas f o r the nickel.(II) complexes, i t i s 0.74. The Dq f o r the Co(4mepy)g ( H 2 0 ) 2 ( E F g ) 2 complexes i s 2% high e r then f o r the C o ( p y ) g ( E F g ) 2 complexes. The d i f f e r e n c e between the analogous n i c k e l complexe i s 5%. The f a c t t h a t t h e r e i s a s m a l l e r i n c r e a s e i n Dq f o r the c o b a l t ( I I ) complexes than f o r the n i c k e l ( I I ) complexes r e f l e c t s the f a c t t h a t o c t a h e d r a l and t e t r a g o n a l o c t a h e d r a l s t r u c t u r e s are b e i n g compared i n the c o b a l t complexes whereas o n l y o c t a -h e d r a l s t r u c t u r e s a re b e i n g compared i n the n i c k e l complexes. In the cobalt(II)-4mepy complexes, the weaker f i e l d l i g a n d s , H 20, are c l o s e r to the metal i o n than the st r o n g e r f i e l d l i g a n d 4mepy, whereas i n the analogous n i c k e l ( I I ) complexes, both types o f l i g a n d s are a t the same d i s t a n c e . I t appears t h a t the Dq and B va l u e s of the 3-methyl-p y r i d i n e and 4-methylpyrdine aquated complexes can be ex p l a i n e d i n terms o f the p r o p e r t i e s o f these l i g a n d m o i e t i e s and the s t r u c t u r e s o f the complexes i n r e l a t i o n to the more r e g u l a r p y r i d i n e complexes. But i t would be d i f f i c u l t t o make any f u r t h e r r a t i o n a l i z a t i o n s on these systems without the X-ray c r y s t a l l o g r a p h i c r e s u l t s and without analogous p y r i d i n e aquated complexes t o compare them t o . I t i s i n t e r e s t i n g t o s p e c u l a t e on the chemistry which g i v e s r i s e t o the d i f f e r e n c e s i n the products when p y r i d i n e , 4-methylpyridine, and 3-methylpyridine complexes are prepared under the same c o n d i t i o n s . Others have found -125-t h a t m e t a l ( I I ) p e r c h l o r a t e s w i t h p y r i d i n e , 4-methylpyridine, and 3-methylpyridine form a s i m i l a r a r r a y of d i f f e r e n t compounds. When N i ( C 1 0 4 ) 2 hydrate i s r e a c t e d w i t h these n e u t r a l l i g a n d s i n aqueous s o l u t i o n , the products formed are N i ( p y ) 4 ( C 1 0 4 ) 2 , N i ( 4 m e p y ) 4 ( H 2 0 ) 2 ( C 1 0 4 ) 2 , and N i ( 3 m e p y ) 4 ( H 2 0 ) 2 ( C 1 0 4 ) 2 . (15, 16). I t seems t h a t whether or not water c o o r d i n a t e s does not depend upon the anion present,but o n l y upon the nature of the n e u t r a l h e t e r o c y c l i c l i g a n d . T h i s c h e m i s t r y o f these systems w i l l be examined w i t h r e s p e c t to the theory of s o f t and hard a c i d s and bases (SHAB) (92) and the e q u i l i b r i a which are p r e s e n t i n s o l u t i o n . A c c o r d i n g to SHAB theory, l i g a n d s are bases and the metal i o n s are a c i d s . These a c i d s and bases can be s o f t , hard or i n t e r m e d i a t e i n c h a r a c t e r . An important concept of t h i s theory i s t h a t the b e s t energy match between a c i d s and bases i s when they are s i m i l a r i n c h a r a c t e r . Of the metal and l i g a n d s under study here ( i g n o r i n g the anions) ; water i s a hard base and p y r i d i n e i s an i n t e r m e d i a t e base and the c o b a l t ( I I ) and n i c k e l (II) ions are i n t e r m e d i a t e a c i d s . The methylsub-s t i t u t e d p y r i d i n e s can be c o n s i d e r e d to be i n t e r m e d i a t e bases but harder than p y r i d i n e . T h i s i s b e c a u s e ; i f the e l e c t r o n i c s t r u c t u r e of the m e t h y l p y r i d i n e s i s c o n s i d e r e d as a p e r t u r b a t i o n o f the e l e c t r o n i c s t r u c t u r e o f p y r i d i n e , the p r i n c i p a l con-c l u s i o n i s t h a t the methyl s u b s t i t u t e n t makes the n i t r o g e n more n u c l e o p h i l i c ( i . e . the l i g a n d i s harder) and makes the -126-l i g a n d a poorer TT acce p t o r ( i . e . the l i g a n d i s l e s s s o f t because o f l e s s a b i l i t y as a IT a c c e p t o r l i g a n d ) . Before c o n s i d e r i n g the a p p l i c a t i o n o f the SHAB theo r y i n these systems, the r e a c t i o n c o n d i t i o n s have to be understood. Using the hydrated m e t a l ( I I ) i o n s ( n i t r a t e s under our r e a c t i o n c o n d i t i o n s ) i n aqueous s o l u t i o n means t h a t b e f o r e the p y r i d i n e o r s u b s t i t u t e d p y r i d i n e are added the predominant 2+ s p e c i e s i n s o l u t i o n are the hexaquo i o n s , M(H 20)g . When the p y r i d i n e l i g a n d s are pr e s e n t i n s o l u t i o n , the e q u i l i b r i u m below i s s e t up: v Kx+i M ( H 2 0 ) ( 6 - x ) L x + + L i M ( H 2 0 ) ( 5 - x ) L ( x + l ) + V S i n c e the p y r i d i n e l i g a n d s are a b e t t e r match f o r the metal io n s (they are a l l i n t e r m e d i a t e i n c h a r a c t e r ) , the n e u t r a l l i g a n d s , L, w i l l d i s p l a c e the water molecules and co o r d i n a t e 2+ t o the metal. When the r e a c t i o n produces ML^ (H 20) 2 , there appears t o be d i f f e r e n c e s . i n b e h a v i o r , depending upon whether L i s a s u b s t i t u t e d p y r i d i n e o r p y r i d i n e i t s e l f . I f L i s a 2 + s u b s t i t u t e d p y r i d i n e , the M L 4 ( H 2 0 ) 2 i s the end product and p r e c i p i t a t e s (or c r y s t a l l i z e s ) out of s o l u t i o n . I f L i s 2+ - 2+ p y r i d i n e , the products formed are N i ( p y ) 4 (C10 4) or N i ( p y ) g (PF,~) where the water l i g a n d s are no lon g e r c o o r d i n a t e d . 6 These o b s e r v a t i o n s can be r a t i o n a l i z e d by the concept of symbiosis (9'3a) • The hardness o f an a c i d i c o r b a s i c s i t e i s not an in h e r e n t p r o p e r t y o f a p a r t i c u l a r atom but can be i n f l u e n c e d by the oth e r s u b s t i t u e n t s present; t h i s e f f e c t i s c a l l e d -127-s y m b i o s i s . The r e l a t i o n df t h i s c oncept t o t h e p r e s e n t d i s c u s s i o n i s t h a t as more p y r i d i n e l i g a n d s a r e c o o r d i n a t e d t o t h e m e t a l i o n (K^ t o K^) t h e complex becomes s o f t e r i n n a t u r e and thus water as a h a r d e r bases become l e s s c o m p a t i -a b l e as a l i g a n d and t h e w a t e r s become more l a b i l e and can be d i s p l a c e d . However, t h e m e t h y l p y r i d i n e bases a r e h a r d e r t h a n p y r i d i n e and when more o f them a r e added (K^ t o K^) 2+ t h e complex N i L 4 ( H 2 0 ) 2 i s h a r d e r t h a n t h e c o r r e s p o n d i n g p y r i d i n e complex and a p p a r e n t l y water l i g a n d s , h a r d b a s e s , a r e r e t a i n e d i n t h e f i r s t c o o r d i n a t i o n sphere o f t h e m e t a l ( I I ) i o n . -128-3.5 TETRAHEDRAL PYRIDINE AND METHYLPYRIDINE COMPLEXES OF C O B A L T ( I I ) ; C o ( p y ) 4 ( E F g ) 2 , C o ( 3 m e p y ) 4 ( E F g ) 2 and C o ( 4 m e p y ) 4 ( E F g ) 2 3.5.1 INTRODUCTION T h i s s e c t i o n d e a l s w i t h compounds o f t h e t y p e , C o L 4 ( E F g ) 2 where L=py, 4mepy, and 3mepy and E=P and A s . T h e s e m a t e r i a l s were o b t a i n e d , by h e a t i n g o r vacuum d r y i n g t e c h n i q u e s , f r o m t h e o c t a h e d r a l c o b a l t ( I I ) c o m p l e x e s d i s -c u s s e d i n t h e p r e v i o u s s e c t i o n s o f t h i s c h a p t e r . The u s u a l c o o r d i n a t i o n g e o m e t r y a b o u t t h e c o b a l t ( I I ) i o n i n c o m p l e x e s o f t h e t y p e , C o ( p y ) 4 A 2 i s a t e t r a g o n a l l y d i s t o r t e d o c t a h e d r o n w i t h c o o r d i n a t e d a n i o n s . The s o l i d s t a t e s t r u c t u r e s o f t h e C o L 4 ( E F g ) 2 c o m p l e x e s , however, show them t o c o n t a i n n o n - c o o r d i n a t e d a n i o n s a n d t e t r a h e d r a l 2+ " C o L 4 " comp l e x c a t i o n s . U n l i k e t h e n i c k e l ( I I ) and c o p p e r ( I I ) c o m p l e x e s t o be d i s c u s s e d i n t h e n e x t c h a p t e r , t h e s e C o L 4 ( E F g ) 2 compounds show a r a d i c a l d e p a r t u r e i n s t r u c t u r e f r o m t h o s e o f s i m i l a r compounds w i t h o t h e r w e a k l y b a s i c a n i o n s . T h i s s e c t i o n d i s c u s s e s t h e r e s u l t s o f t h e c h a r a c t e r i z a t i o n o f t h e s e compounds. The e l e c t r o n i c s p e c t r a and m a g n e t i c p r o p e r t i e s o f t h e s e compounds w i l l be d i s c u s s e d f i r s t , f o l l o w e d by a d i s c u s s i o n o f t h e i n f r a r e d s p e c t r a . The m o l e c u l a r s t r u c t u r e d e t e r m i n a t i o n o f -129-C o ( 4 m e p y ) ^ ( P F g ) 2 , w h i c h c o n f i r m s t h e f i n d i n g s o f t h e s e t e c h n i q u e s ^ w i l l be p r e s e n t e d ; t h e n , t h i s compound w i l l be compared t o o t h e r c o b a l t ( I I ) compounds w i t h t e t r a h e d r a l h o m o l i g a n d o r h e t e r o l i g a n d c h r o m o p h o r e s . F i n a l l y , t h e r e l a t i o n o f t h i s work t o p r e v i o u s work on C o ( p y ) 4 A 2 c o m p l e x e s w i t h o t h e r w e a k l y b a s i c a n i o n s w i l l be d i s c u s s e d . The d e t a i l s o f t h e s y n t h e s i s o f t h e s e compounds a r e g i v e n i n C h a p t e r 6. 3.5.2 RESULTS AND DISCUSSION 3.5.2.1 ELECTRONIC SPECTRA AND MAGNETIC PROPERTIES. The e l e c t r o n i c s p e c t r a l d a t a f o r t h e C o L ^ t E F g ^ c o m p l e x e s a r e p r e s e n t e d i n T a b l e 111-14 '.• In" t h e - m u l l s p e c t r a , t h e a b s o r p t i o n bands f o r a l l t h r e e s p i n - a l l o w e d t r a n s i t i o n s o f a t e t r a h e d r a l c o b a l t ( I I ) s p e c i e s a r e o b s e r v e d . The e x t i n c t i o n c o e f f i c i e n t s o f t h e bands ( e s p e c i a l l y t h e v i s i b l e band) i n t h e s o l u t i o n s p e c t r a a r e t o o l a r g e f o r a c e n t r o s y m -m e t r i c chromophore and a r e c o n s i s t e n t w i t h t h e p r o p o s e d t e t r a h e d r a l c h r o m o p h o r e . The d e t e r m i n e d Dq and B v a l u e s a r e g i v e n i n T a b l e I I I - 1 5 . T h e s e were c a l c u l a t e d f r o m t h e v 2 d e t e r m i n e d f r o m t h e m u l l s p e c t r u m and t h e c e n t e r o f g r a v i t y o f t h e band o b s e r v e d i n t h e d i f f u s e r e f l e c t a n c e s p e c t r u m (18.10 kK f o r L=3mepy, 18.20 kK f o r L=py, and 18.30 kK f o r L=4mepy). As n o t e d by C o t t o n (94) , t h e r e a r e some weak bands due t o s p i n 2 f o r b i d d e n t r a n s i t i o n s ( e x c i t e d s t a t e s f r o m t h e D f r e e i o n -130-TABLE 111-14 ELECTRONIC SPECTRAL DATA FOR C o L 4 ( E F g ) 2 ASSIGNMENT 4 A. BAND POSITION (kK) COMPOUND C o ( p y ) 4 ( P F 6 ) 2 Co(py) 4 ( A s F g ) 2 (a) (bj (a) (b) C o ( 4 m e p y ) 4 ( P F g ) 2 (a) (b) (c) C o ( 4 m e p y ) 4 ( A s F g ) 2 ( a ) (b) (c) C o ( 3 m e p y ) 4 ( P F g ) 2 (a) (b) (c) C o ( 3 m e p y ) 4 ( A s F g ) 2 ( a ) (b) (c) "T. T X ( F ) 5.33w,br 9.26m 5.4 6w,br 9.26m 5.56w,br 9.43m n.o.' { 9.17(83) 10.5sh 5.48w,br 9.43m n.o. 9.09(64) 5.21w,br 9.30m ^n.o. 8.51(79) 5.26w,br 9.30m n.o. 8.70 (77) i T 1 ( P ) (d) { { { { { { { { { { { { 22.7w 23.Ow 23. Ow 17.7s 22.7w 19.1sh ; 26.Ow 17-.9s • 19.4sh 17 .7s 19.5sh 17.7s 19.5sh 18.2s 19.0sh 17 .7s 18.9sh 17.9(611) 18.9sh 18.25s 18.9sh 17.7s 22.7w 18.9sh 25.3w 17.7 (489) 18.9sh 17.5s 22.7w 19.6sh 25.6w 17.7s 22.7w 18.9sh 25.6w rl7.98 (490) ^18.86sh 17.4s 23.3 19.0sh 17.7s 22.7w 19.2sh 26. Ow ,17 .86 (233) H s . e s h ; ( a ) m u l l s p e c t r u m (b) d i f f u s e r e f l e c t a n c e (c) s o l u t i o n s p e c t r u m ( C H 2 C 1 2 ) ; m o l a r e x t i n c t i o n c o e f f i c e n t s i n b r a c k e t s , (d) s p i n f o r b i d d e n t r a n s i t i o n s -131-TABLE 111-15 LIGAND FIELD PARAMETERS FOR C o L 4 ( E F g ) 2 COMPOUND Dq(cm 1 ) B (cm 1 ) C o ( p y ) 4 ( P F g ) 2 Co(py) 4 (AsF g) 2 Co(4mepy) 4 ( P F g ) 2 C o ( 4 m e p y ) 4 ( A s F g ) 2 C o ( 3 m e p y ) 4 ( P F g ) 2 C o ( 3 m e p y ) 4 ( A s F g ) 2 546 740 555 735 550 730 -132-term) near v^. Because of t h i s , the c e n t e r o f g r a v i t y had to be v i s u a l l y e stimated. The band p o s i t i o n s observed i n the s o l u t i o n s p e c t r a are s l i g h t l y d i f f e r e n t from those observed i n the s o l i d s t a t e s p e c t r a . T h i s may be a consequence of a s l i g h t l y d i f f e r e n t c o b a l t ( I I ) environment (with r e s p e c t t o Co-N bond d i s t a n c e s or angles) i n s o l u t i o n than i n the s o l i d s t a t e . The v a l u e s of lODq and the p o s i t i o n o f V-^  (defined as lODq) i n each spectrum do not agree e x a c t l y . However, t h i s i s perhaps not too s u r p r i s i n g s i n c e the V-^  band i s very weak and broad. A l s o i t i s s u b j e c t t o i n t e r f e r e n c e s from 4 4 v i b r a t i o n a l overtones and o v e r l a p w i t h v ^ ( &2~* T i ( F ) ) • Th e r e f o r e , the c e n t e r of g r a v i t y was d i f f i c u l t to determine. I t i s i n t e r e s t i n g to note t h a t the Dq value f o r C o ( p y ) 4 2 + , 546 cm - 1, i s about h a l f t h a t o f C o ( p y ) g 2 + , 985 c m - 1 ( s e c t i o n 3.2). In f a c t , c a l c u l a t i o n s based on a p u r e l y i o n i c model p r e d i c t f o r the same l i g a n d s and metal i o n wit h the same m e t a l - l i g a n d d i s t a n c e s , the Dq of the o c t a h e d r a l complex should be (9/4) t h a t o f the t e t r a h e d r a l complex. M u l t i p l y i n g 2+ the Dq obtained f o r C o ( p y ) 4 by (9/4) leads t o the p r e d i c t i o n 2+ -1 t h a t Dq f o r C o ( p y ) 6 should be 1229 cm o r some 25% l a r g e r than observed. The d i s c r e p a n c y i s l i k e l y i n p a r t due to the l i m i t a t i o n s of u s i n g a p u r e l y i o n i c model. However, the dis c r e p a n c y i s a l s o probably due t o d i f f e r e n c e s i n s t e r i c r e p u l s i o n s between the l i g a n d s i n the two complex s p e c i e s . That i s , the Co-N bond d i s t a n c e s are probably longer i n the -133-2+ C o ( p y ) g s p e c i e s t h a n i n t h e s t e r i c a l l y l e s s crowded 2 + C o ( p y ) 4 s p e c i e s . F o r example, t h e Co-N (and 0) d i s t a n c e s i n Co (4mepy) R (H 20) 2 (PFg) 2 a r e g r e a t e r t h a n 2.102. ( s e c t i o n 3.4.1.1) whereas t h e Co-N d i s t a n c e s i n C o ( 4 m e p y ) 4 ( P F g ) 2 ( s e c t i o n 3.5.2.2) a r e 2.01A*. S i n c e Dq i s p r o p o r t i o n a l t o 5 1/a , t h e 5% i n c r e a s e i n bond l e n g t h on g o i n g f r o m t e t r a -h e d r a l t o o c t a h e d r a l s t e r e o c h e m i s t r y may be u s e d t o c a l c u l a t e -1 2+ a Dq v a l u e o f 960 cm f o r C o ( p y ) g . The o b s e r v e d Dq o f 985 cm 1 i s i n r e m a r k a b l y - good a g r e e m e n t w i t h t h i s c a l c u l a t e d Dq. A c o n c e p t o f c o o r d i n a t i o n c h e m i s t r y u t i l i z i n g t h e c r y s t a l f i e l d m o del i s t h e " r u l e o f a v e r a g e e n v i r o n m e n t " . S i m p l y , t h e Dq o f a h y p o t h e t i c a l complex, C o X 2 Y 2 s h o u l d be t h e a v e r a g e o f t h e Dq's o f t h e C o X 4 and C o Y 4 c o m p l e x e s , i e . 1/2 D q ( C o X 4 ) + l / 2 D q ( C o Y 4 ) = D q ( C o X 2 Y 2 ) . One a p p r o p r i a t e 2+ c h o i c e i n o r d e r t o c a l c u l a t e a Dq v a l u e f o r C o ( p y ) 4 w o u l d be D q ( C o B r 4 ~ ) , 280 (9.4.") and Dq (Co (py) 2 B r 2 ) , 390 (9"5/). The v a l u e o f Dq c a l c u l a t e d by t h i s method i s 500 cm i n good a g r e e m e n t w i t h t h e e x p e r i m e n t a l v a l u e o f 54 6 cm 1 o b t a i n e d h e r e . The v a l u e s o f Dq o b t a i n e d f o r C o L 4 ( E F g ) 2 a r e d e p e n d e n t upon L and t h e f a c t t h a t Dq i s n o t d e p e n d e n t upon w h i c h E F g - a n i o n i s p r e s e n t i s f u r t h e r e v i d e n c e f o r non-c o o r d i n a t e d a n i o n s . The v a l u e s o f Dq a s a f u n c t i o n o f L a r e 5 4 6 ( p y ) , 550 (3mepy), and 555(4mepy). The d i f f e r e n c e s -134-o b s e r v e d i n t h e Dq v a l u e f o l l o w t h e t r e n d e x p e c t e d f r o m t h e b a s i c i t i e s o f t h e t h r e e l i g a n d s (96) (base s t r e n g t h : 4mepy >3mepy >py)• B u t i t i s p r o b a b l y b e t t e r t o c o n s i d e r t h e Dq 2+ -1 o f t h e s e CoL^ s p e c i e s t o be 550+5 cm b e c a u s e o f t h e e r r o r i n t h e c a l c u l a t i o n due t o b r e a d t h o f t h e s p e c t r a l b a n d s . The m a g n e t i c p r o p e r t i e s o f t h e s e C o L 4 ( E F g ) 2 com-pounds a r e summarized i n T a b l e 111-16 and a r e c o n s i s t e n t 4 w i t h a A 2 g r o u n d s t a t e . The e f f e c t i v e m a g n e t i c moments o f t h e s e compounds a r e t e m p e r a t u r e i n d e p e n d e n t . The 6 v a l u e s d e t e r m i n e d f r o m t h e m a g n e t i c p r o p e r t i e s a r e z e r o f o r t h e p y r i d i n e and n o n - z e r o i n t h e o t h e r c o m p l e x e s . T h i s s u g g e s t s t h a t t h e p y r i d i n e l i g a n d s have a more r e g u l a r t e t r a h e d r a l a r r a n g e m e n t a r o u n d t h e c o b a l t t h a n t h e m e t h y l -s u b s t i t u t e d p y r i d i n e l i g a n d s i n t h e o t h e r c o m p l e x e s . The s i n g l e c r y s t a l X - r a y d i f f r a c t i o n s t u d y on C o ( 4 m e p y ) 4 ( P F ^ ) 2 shows t h e C o ( 4 m e p y ) 4 2 + c a t i o n t o have a s l i g h t l y d i s t o r t e d t e t r a h e d r a l ^ c h r o m o p h o r e . 3.5.2.2 MOLECULAR STRUCTURE OF C o ( 4 m e p y ) 4 ( P F g ) 2 The d e t a i l s o f t h e c r y s t a l and m o l e c u l a r s t r u c t u r e d e t e r m i n a t i o n a r e p r e s e n t e d i n s e c t i o n 6.5.1.1. The m o l e c u l a r 2+ s t r u c t u r e c o n s i s t s o f d i s t i n c t c a t i o n s , C o ( 4 m e p y ) 4 , and a n i o n s , PF ~, and t h e c l o s e s t c o n t a c t between them i s 3.28(3)2 6 -135-TABLE 111-16 SUMMMARY OF MAGNETIC PROPERTIES OF C o L ^ ( E F g ) 2 COMPOUND y o « ( 295K) y f f ( 80K)1 0(1 " ( l i n B.M.) ( i n B.M.) C o ( p y ) 4 ( P F 6 ) 2 4.30 4.29 0 C o ( p y ) 4 ( A s F 6 ) 2 4.33 4.31 0 C o ( 4 m e p y ) 4 ( P F 6 ) 2 4.33 4.26 -7 Co (4mepy) 4 (AsF g)_ 4. 35 4.24 -5 C o ( 3 m e p y ) 4 ( P F 6 ) 2 4.28 4.28 1 Co(3mepy) 4(AsSF g) 2 4.42 4.40 2 -136-between F(2) C ( 6 ) . The c l o s e s t Co P d i s t a n c e i s 5.499(4) 8 and P Co P angles (between the Co and c l o s e s t P) d e f i n e d by one and two s u c c e s s i v e o p e r a t i o n s are 100.54(2°) and 129.35(4)°. F i g u r e 3.14 shows a stereoview o f the packing of these c l o s e s t anions around a c a t i o n . A l l o t h e r Co P d i s t a n c e s are g r e a t e r than 88. F i g u r e 3.15 shows a stereoview of the c a t i o n . The bond lengths and angles are l i s t e d i n Table 111-17. The c r y s t a l l o g r a p h i c symmetry about c o b a l t i s S 4(4) and the d e v i a t i o n o f the c a t i o n from T^ symmetry i s shown by the compression along the a x i s and the o r i e n t a t i o n of the r i n g s . The N-Co-N angles generated by one and two s u c c e s s i v e o p e r a t i o n s are 101.2(9)° and 113.8°, r e s p e c t i v e l y and r e p r e s e n t a compression along the a x i s because T^ symmetry would r e q u i r e both angles to be 109.47°. The 4-methylpyridine moiety i s p l a n a r w i t h i n experimental e r r o r but the c o b a l t atom l i e s 0. 288 out o f t h i s plane; the angle between the a x i s and the plane of the r i n g i s 2 8°; t e t r a h e d r a l symmetry would r e q u i r e the angle to be 0° o r 4 5°. The bond lengths and angles of the 4-methylpyridine r i n g are s i m i l a r t o those d e r i v e d i n a microwave study of p y r i d i n e ( 90 ) and observed f o r c o o r d i n a t e d 4-methyl-p y r i d i n e ( r e f . 97 f o r example). The bond lengths and angles of the PF ~ anion are c o n s i s t e n t w i t h those normally found b f o r t h i s anion. The thermal parameters i n d i c a t e l a r g e thermal motion, as has been observed by other authors (91, 98-103). -137-FIGURE 3.14 STEREOVIEW SHOWING THE PACKING OF ANIONS ABOUT A CATION. (The atoms of the anion and c a t i o n are drawn f o r 20% and 50% p r o b a b i l i t i e s , r e s p e c t i v e l y ) FIGURE 3.15 STEREOVIEW OF THE Co(4mepy) 4 CATION. ( A l l atoms are drawn f o r 50% p r o b a b i l i t y ) -138-TABLE III-17 BOND DISTANCES AND ANGLES IN Co(4mepy) 4 ( P F g ) 2 (estimated standard d e v i a t i o n s i n brackets) (i) BOND DISTANCES (8) Co-N ' = 2. 01(1) C(4)-C(5) = 1. 39 (2) N-C(l) 1. 39 (2) C(3)-C(6) = 1. 52(2) N-C(5) = 1. 37 (2) P-F (1) = 1. 54 (2) C ( l ) - C ( 2 ) = 1. 40(2) P-F(2) = 1. 51(2) C(2)-C(3) = 1. 40(3) P-F (3) = 1. 45(2) C( ;3)-C(4) = 1. 38 (2) ( i i ) BOND ANGLES (deg)* N-Co--N' =113.8(5) F(3)--P-F(3) ' = 180 (2) N-Co--N" =101.2(9) F(3)--P- F(2) ' = 91(1) C(5)- -N-C(l) =119 (2) F(3) -P-•F(l) ' = 91(1) N-C(l)-C(2) -'• = 121(2.) F(3) -P-•F(2) = 89(1) C ( l ) -C(2)-C(3) =120(2) F(3) -P--F ( l ) = 89(1) C(3) -C(4)-C(5) =121(2) F(2) -P--F(3) ' = 91(1) C(4) -C(5)-N =121(2) F(2) -P--F(2) 1 = 91(2) C(2) -C(3)-C(6) = 117 (2) F(2) -P-- F ( l ) ' =177(1) C(4) -C(3)-C(6) =123(2) F(2) -P-- F ( l ) = 92(1) F ( l ) - P - F ( 1 ) ' = 86(2) F ( l ) _p. -F(3) ' = 91(1) * atoms marked (' or ") are not c r y s t a l l o g r a p h i c a l l y unique but generated by the symmetry o p e r a t i o n s of the space group. -139-T h i s anion would be expected to have l a r g e temperature f a c t o r s and show c o n s i d e r a b l e apparent d i s t o r t i o n due to i t having n e a r l y s p h e r i c a l symmetry. The CO-N d i s t a n c e of 2.01 7A found i n our c a t i o n i c 2 + s p e c i e s , Co(4mepy) 4 , i s i n the range .normally observed f o r CoN^ t e t r a h e d r a l chromophores as shown by the f o l l o w i n g examples. The t e t r a h e d r a l CoN^ chromophore has been examined c r y s t a l l o g r a p h i c a l l y w iththe a n i o n i c l i g a n d , NCS i n the complexes, t e t r a k i s ( t h i o u r e a ) m e r c u r y ( I I ) t e t r a k i s ( i s o t h i o c y a n a t o ) c o b a l t a t e ( I I ) (104), potassium t e t r a k i s ( i s o t h i o c y a n a t o ) c o b a l t a t e ( I I ) t r i h y d r a t e (105), t r i s (ethylenediamLne) c o b a l t ( I I I ) t e t r a k i s ( i s o t h i o c y a n a t o ) c o b a l t a t e ( I I ) n i t r a t e (106), and 1,4-diphenyl-3-phenylamino-l, 2 , 4- t r i a z o l i u m t e t r a k i s ( i s o t h i o c y a n a t o ) c o b a l t a t e ( I I ) (107)- The Co-N d i s t a n c e s found i n these compounds are 2.01 (2), 1.949 (7), 1.928 (12)-1.966 (15), and 2.052 (5), r e s p e c t i v e l y . Examples of complexes : c o n t a i n i n g anionic. <bidentate l i g a n d s which a l s o g i v e t h i s CoN^ chromophores are b i s ( N - t e r t - b u t y l -p y r r o l e - 2 - c a r b o x y a l d i m i n o ) c o b a l t ( I I ) (108) and b i s ( d i h y d r o b i s ( 1 - p y r a z o l y l ) borato) c o b a l t ( I I ) (109); the Co-N d i s t a n c e s i n these compounds are 1.981 (7)-2 . 066 (8) and 1.967 (average) A1, r e s p e c t i v e l y . The s t r u c t u r a l parameter u s u a l l y used to i n d i c a t e d i s t o r t i o n from t e t r a h e d r a l (T d) to D 2 symmetry,is the angle, 8 . 3 i s d e f i n e d as the angle t h a t the metal l i g a n d bond makes with the a x i s and i n t e t r a h e d r a l symmetry i t i s 54.7°. The 2 + value observed f o r the Co(4mepy) 4 c a t i o n i n t h i s study i s -140-56.8°. The e f f e c t s of t h i s d i s t o r t i o n on the magnetic p r o p e r t i e s and e l e c t r o n i c s p e c t r a f o r the Co(4mepy)^(EFg) 2 complexes were d i s c u s s e d e a r l i e r . 3.5.2.3 VIBRATIONAL SPECTRA The c h a r a c t e r i z a t i o n of these C o L 4 ( E F g ) 2 compounds as being t e t r a h e d r a l complexes o f c o b a l t ( I I ) excludes the anions, EF, , from the f i r s t c o o r d i n a t i o n sphere. The anions b are, t h e r e f o r e , non-coordinated. The d e t a i l s of the molecular s t r u c t u r e o f Co(4mepy)^(PFg) 2 d e s c r i b e d i n the l a s t s e c t i o n , c o n f i r m the assignments based on the other p h y s i c a l t e c hniques. The i n f r a r e d s p e c t r a (with emphasis on the s t e r e o c h e m i c a l l y s i g n i f i c a n t bands of L and the observed anion v i b r a t i o n s ) w i l l be examined now w i t h r e s p e c t to t h i s assigned s t r u c t u r e . Table 111-18 g i v e s the p o s i t i o n s of the s t e r e o c h e m i c a l l y s e n s i t i v e bands of py and 4mepy f o r these complexes. As expected, there i s no evidence f o r non-coordinated p y r i d i n e or 4mepy. The bands o f 3mepy i n the i n f r a r e d spectrum of Co(3mepy)^(EFg) 2 (see Appendix 1, Table Al-3) show p o s i t i o n s w e l l removed from the f r e e base v a l u e s . Table 111-19 shows the bands i n the i n f r a r e d s p e c t r a a s s i g n e d t o the v i b a t i o n s of the anions. There i s no evidence f o r the v 5 ( T 2 g ) v i b r a t i o n and g e n e r a l l y (as f o r the other compounds d e s c r i b e d i n t h i s chapter) the compounds have the c h a r a c t e r i s t i c "non-coordinated" anion s p e c t r a . S p e c i f i c a l l y , and v^, the f o r m a l l y allowed (0^) t r a n s i t i o n s , are seen as s t r o n g bands and the (A^ g) and v 2 ( E g ) bands, f o r m a l l y f o r b i d d e n i n 0^ symmetry, are seen i n the s p e c t r a o f the PFg and AsFg -141-TABLE II 1 - 1 8 NEUTRAL LIGAND BANDS IN THE INFRARED SPECTRA OF C o L 4 ( E F 6 ) 2 (L=py and 4mepyj ( i ) PYRIDINE 8a 6a 16b E=P 415m 643m 1613m E=As 419m 646m 1613m ( i i ) 4-METHYLPYRIDINE 6a 10b+12 1 9a 19a 8a 816s 1240m 1512m 1622s 560m 810s (b) 1240w 1512m 1622s (a) o b s c u r e d by v 3 o f P F g (b) o b s c u r e d by p C H a t 1040 cm 1 -142-TABLE I I I - 1 9 ANION BANDS IN THE INFRARED SPECTRA OF C o L 4 ( E F g ) 2 ( i ) E=P V T l u }  V 4 ( T l u J W (a) L=py 848 836 554s 740w }vs ( i i ) E=As V 3 ( T l u } v l ( A l g y  v 2 ( E g ) , .(b) 710 685 395s 572w }vs L=4mepy 8 4 0 v s 557s 7 4 2w L=3mepy 840vs,br 555s n.o. 6 9 7 v s 392s 6 9 0 v s,br 395s n.o. n.o, (a) p o s s i b l y o b s c u r e d by v 4 o f P F 6 (b) p o s s i b l y o b s c u r e d by v 3 o f A s F g -143-compounds, r e s p e c t i v e l y ; as weak bands. That they are seen a t a l l i s probably a consequence of s i t e symmetry e f f e c t s . The d e t a i l e d appearance of the anion bands, i s d i f f e r e n t depending on the n e u t r a l l i g a n d p r e s e n t . For L=py, the v 3 ( T j u ) band appears to be made up of two components. T h i s may be due to very low s i t e symmetry o r t o f a c t o r group s p l i t t i n g , i e . two types of EFg anions i n the l a t t i c e . For L=3mepy t h e r e i s no evidence f o r e i t h e r the v ^ ( A ^ g ) o r the v 2 ( E g ) v i b r a t i o n , perhaps i n d i c a t i v e of 0^ symmetry environment f o r the anions. For L=4mepy, the "normal" behavior of the anion bands are observed c o n s i s t e n t w i t h s l i g h t l y lower than 0^ s i t e symmetry. I t i s i n t e r e s t i n g t o note the r e c i p r o c a l r e l a t i o n -2+ s h i p between the symmetry of the CoL^ c a t i o n as i n d i c a t e d by e (Table 111-16) and the symmetry of the EFg environment as d i s c u s s e d i n the l a s t paragraph. The p y r i d i n e complexes which have the h i g h e s t symmetry c a t i o n s (6=0) have the two i n e q u i v a l e n t EFg anions o r lowest s i t e symmetry anions; whereas, the 3mepy and 4mepy which have the more d i s t o r t e d c a t i o n s (6^0)' have h i g h e r symmetry environments f o r the anions. -144-3.5.3 RELATION TO OTHER WORK As mentioned i n s e c t i o n 3.5.1, most ( t e t r a k i s ) -p y r i d i n e complexes o f c o b a l t ( I I ) c o n t a i n i n g weakly b a s i c anions have been assigned pseudo-octahedral chromophores. The compounds Co(py)^A2, where A i s p e r c h l o r a t e (110), t e t r a -f l u o r o b o r a t e (no)/ t r i f l u o r o a c e t a t e (111), methylsulphate CH 3S0 3~ (113), and t r i f l u o r o m e t h y l s u l p h a t e C F 3 S 0 3 ~ (112), have been c h a r a c t e r i z e d as t h i s type of complex. The . CoL 4(EFg)2 compounds c h a r a c t e r i z e d here have been assigned 2+ t e t r a h e d r a l CoN^ chromophores. T h i s must be due to the weak c o o r d i n a t i n g a b i l i t i e s of hexafluorophosphate and hexa-f l u o r o a r s e n a t e compared t o the former ani o n s . Many compounds c o n t a i n i n g t e t r a h e d r a l l y c o o r d i n a t e d c o b a l t ( I I ) are known (60); Table 111-20 l i s t s some of these compounds wit h the l i g a n d f i e l d parameters d e r i v e d from the a n a l y s i s o f t h e i r e l e c t r o n i c s p e c t r a . The value o f Dq observed i n our CoL 4(EFg)2 compounds (550-5 cm "*") i s l a r g e r than a l l of the values- l i s t e d i n Table 111-20 . T h i s i s presumably a consequence o f the l i g a t i n g s p e c i e s being lower i n the sp e c t r o c h e m i c a l s e r i e s than the p y r i d i n e l i g a n d s s t u d i e d here. We w i l l now d i s c u s s some r e c e n t l i t e r a t u r e r e p o r t s 2+ o f complexes c o n s i d e r e d t o have the t e t r a h e d r a l CoL^ s p e c i e s (where L i s a p y r i d i n e l i g a n d ) . A l l these r e p o r t s appeared a f t e r our i n i t i a l r e p o r t i n Inorg. and N u c l . Chem. L e t t e r s (Vo l . 12 p. 937 (1976)). The compound (Co(py) 4) (Zn(NCSe) 4) - 1 4 5 -TABLE I I I - 2 0 LIGAND FIELD PARAMETERS OF SOME TETRAHEDRAL COMPLEXES OF COBALT(II) ( a ) COMPLEX 10Dq(cm }.) B(cm 1 ) C o C l 4 2 " 3125 710 C o B r 4 2 " 2800 695 C o ( N C S ) 4 2 " 4550 691 C o ( N C S e ) 4 2 ~ 4710 653 C o ( N 0 3 ) 4 2 " 4660 755 2 _ n~\ A7<-C\ 600 C o ( t u ) 4 (b) 4250C o ( N 3 ) 4 2 " 3920 658 (a) from r e f e r e n c e 33 (b) tu= t h i o u r e a -146-2+ has been assigned a s t r u c t u r e c o n t a i n i n g t e t r a h e d r a l C o ( p y ) 4 ' 2-c a t i o n s and t e t r a h e d r a l Zn(NCSe) 4 anions (84). The v a l u e s o f Dq and B c a l c u l a t e d f o r the c a t i o n from the e l e c t r o n i c spectrum were 4 89 and 608 cm-"1" r e s p e c t i v e l y . These parameters are i n disagreement w i t h those determined i n t h i s work. The 2-former Dq v a l u e i s much c l o s e r to t h a t r e p o r t e d f o r Co(NCSe) 4 s p e c i e s and i s , i n f a c t , i n e x c e l l e n t agreement wi t h the v a l u e c a l c u l a t e d by u s i n g the r u l e of average environment f o r the s p e c i Co (NCSe) ^  (py) ( c a l c u l a t e d Dq=492 cm "*") . T h i s perhaps i n d i c a t e s some scrambling of the l i g a n d s , py and NCSe , between the 2 + 2 + . two metal i o n s , Co and Zn i n the compound o f s t o i c h i o m e t r y , C o Z n ( p y ) 4 ( N C S e ) 4 . Some compounds where L i s a s u b s t i t u t e d p y r i d i n e have been r e p o r t e d and have been assigned a s t r u c t u r e c o n t a i n i n g 2+ the t e t r a h e d r a l CoL 4 s p e c i e s . These compounds are ( C o L 4 ) ( C u ( S C N ) 2 ) 2 where L=2-methylpyridine, 4-aminopyridine, and 3-aminopyridine (86). The Dq and B v a l u e s c a l c u l a t e d from the e l e c t r o n i c s p e c t r a a r e : 464 and 673 cm 1 (L=2mepy); 379 and 630 cm 1 (L=4ampy) . The spectrum f o r L=3ampy i s not 2+ r e p o r t e d . Assuming t h a t the Dq value f o r the CoL 4 s p e c i e s 2+ should be s i m i l a r t o the Dq f o r C o ( p y ) 4 , the value of Dq f o r C o L 2 ( N C S ) 2 from the average r u l e would be 456 cm 1 . T h i s 2+ i s s i m i l a r t o the observed Dq v a l u e s a s s i g n e d to the CoL 4 s p e c i e s . Again some l i g a n d scrambling i s suggested by t h i s a n a l y s i s . -147-.These two r e p o r t s on the i s o l a t i o n o f t e t r a h e d r a l 2 + CoL^ s p e c i e s (84,86) appear to.be erroneous. The Dq's were c a l c u l a t e d from e l e c t r o n i c s p e c t r a d i f f e r e n t from those observed i n t h i s work. The bands were observed a t 15.55, 16.14, 14.29, and 15.39 kK f o r C o ( p y ) 4 Z n (NCSe) 4, Co(2mepy) 4~ ( C u ( S C N ) 2 ) 2 , Co(4ampy) 4(Cu(SCN) 2) 2, and Co(3ampy) 4(Cu(SCN) 2) 2 i compared to 18.20 kK observed f o r the C o ( p y ) 4 ( E F g ) 2 compounds. T h i s corresponds to a i o f 64 3 and 54 9 nm f o r the p y r i d i n e L max complexes s t u d i e d by other workers and s t u d i e d here, a s i z a b l e d i s c r e p a n c y . The l a s t d i s c u s s i o n of t h i s s e c t i o n w i l l focus on thfe s o l i d s t a t e t r a n s f o r m a t i o n s which take p l a c e when samples o f C o ( p y ) 4 ( E F g ) 2 are exposed to p y r i d i n e vapor. As a r e s u l t of t h i s exposure, homogeneous C o ( p y ) g ( E F g ) 2 compounds are formed. The c h a r a c t e r i z a t i o n of these l a t t e r compounds was d e s c r i b e d i n s e c t i o n 3.2.2 and the means of d i f f e r e n t i a t i n g between the two d i f f e r e n t types of compounds i n 3.2.3. These t r a n f o r m a t i o n s are r a t h e r i n t e r e s t i n g because of the instantaneous change i n the c o b a l t ( I I ) chromophore from t e t r a h e d r a l CoN 4 to o c t a h e d r a l CoNg under the m i l d e s t of c o n d i t i o n s (vaporized p y r i d i n e ) . The process i s a l s o r e v e r s i b l e ; C o ( p y ) g ( E F g ) 2 when heated to 80°C " i n vacuo" converts q u i c k l y t o C o ( p y ) 4 ( E F g ) 2 . These two t r a n s f o r m a t i o n s are represented below: ("in vacuo" c o n d i t i o n s ) RT C o ( p y ) 4 ( E F g ) 2 + 2py -> Co (py) g (EF g) 2 (3.1) Co (py) g (EFg) 2 £ 0 o c C o ( p y ) 4 ( E F g ) 2 + 2py (3.2) -148-I f the pink compound, Co (py) g (EF g) 2, i s l e f t s t a n d i n g f o r a l o n g p e r i o d o f time (1-2 y e a r s ) , the r e d - p u r p l e t i n g e due to the presence o f Co (py) 4 (EF g) 2 i n the pink compound can be observed. T h i s suggests t h a t the t r a n s f o r m a t i o n (3.2) can take p l a c e a t room temperature and t h e r e f o r e t r a n s f o r m a t i o n (3.1) may r e a l l y be an e q u i l i b r i u m as below. C o ( p y ) 4 ( E F g ) 2 + 2py t C o ( p y ) 6 ( E F g ) 2 (3.3) And thus (3.1) and (3.2) are r e a l l y j u s t the c o n d i t i o n s needed to r a p i d l y s h i f t the e q u i l i b r i u m i n the d i r e c t i o n a p p r o p r i a t e f o r the d e s i r e d product. I f these s p e c i e s are t r u l y i n e q u i l i b r i u m , i t seems reasonable t h a t we should t r y to examine some thermodynamic parameters. The parameters a s s o c i a t e d w i t h thermodynamics i n c o o r d i n a t i o n chemistry are the c r y s t a l f i e l d s t a b i l i z a t i o n energy (CFSE) and o v e r a l l bond energy c o n s i d e r a t i o n s . CFSE and o v e r a l l bond energy c o n s i d e r a t i o n s (6 vs 4 Co-N bonds) w i l l f a v o r the formation of the CoN g over the CoN^ chromophore (provided enough N l i g a n d s are p r o v i d e d ) . In s p i t e of t h i s , the o c t a h e d r a l complex i s unstable even a t room temperature l o s i n g p y r i d i n e to form the t e t r a h e d r a l complex. Other f a c t o r s such as l a t t i c e energy e f f e c t s (which 2+ perhaps f a v o r the s m a l l e r Co ( p y ) 4 c a t i o n i n combination w i t h the EF ~ anion) and s t e r i c e f f e c t s c l e a r l y p l a y an import D r o l e i n determining the r e l a t i v e thermodynamic s t a b i l i t i e s .of 2+ 2+ the C o ( p y ) 4 and C o ( p y ) g s p e c i e s . -149-CHAPTER 4 COMPOUNDS CONTAINING COORDINATED HEXAFLUOROPHOSPHATE AND HEXAFLUOROARSENATE T h i s chapter w i l l d i s c u s s the r e s u l t s of our s t u d i e s on the compounds NiL 4(EFg) 2(L=py,4mepy,E=P, As and L=3mepy, E=As) and CuL 4(EF g) 2(L=py,4mepy,3mepy, E=P,As). The e l e c t r o n i c s p e c t r a l and magnetic p r o p e r t i e s of these compounds along w i t h i n f r a r e d s p e c t r a l data may be i n t e r p r e t e d i n terms of d i f f e r i n g degrees of metal-anion i n t e r a c t i o n . For t h i s reason, the concept o f and c r i t e r i a f o r a n i o n i c c o o r d i n a t i o n i n ML^A 2 complexes w i l l be d i s c u s s e d f i r s t . D e t a i l s of the c h a r a c t e r i z a t i o n of the n i c k e l complexes w i l l then be d i s -cussed. Included i n t h i s s e c t i o n are r e p o r t s on the X-ray s t r u c t u r e d e t e r m i n a t i o n of N i ( 4 m e p y ) 4 ( P F g ) 2 , the unusual v a r i a b l e temperature p r o p e r t i e s o f N i ( p y ) 4 ( A s F g ) 2 , and the thermal decomposition s t u d i e s t h a t the N i L 4 ( E F g ) 2 compounds were s u b j e c t e d t o . F i n a l l y , t h i s chapter w i l l c o n s i d e r the CuL,(EF,)~ compounds. D e t a i l s o f the methods of p r e p a r i n g these complexes are g i v e n i n Chapter 6. -150-4.1 CRITERIA FOR COORDINATION Whether o r not an anion c o o r d i n a t e s t o a metal i o n depends on many f a c t o r s : the nature of the oth e r l i g a n d s p r e s e n t , l a t t i c e energy e f f e c t s , the b a s i c i t y and s i z e o f the anion, and o t h e r s (17). F o r example, the o t h e r l i g a n d s may have a Lewis b a s i c i t y s u f f i c i e n t l y g r e a t e r than the a n i o n i c s p e c i e s such t h a t these l i g a n d s may s a t i s f y the c o o r d i n a t i o n requirements o f the metal. T h i s e f f e c t i s seen i n the s e r i e s of compounds N i ( X - p y ) ^ ( C l O ^ ) 2 (where X-py i s a s u b s t i t u t e d p y r i d i n e ) where i f the b a s i c i t y of X-py i s over a c e r t a i n l e v e l (pK • o f the corresp o n d i n g p y r i d i n i u m s a l t s , >6.00) the p e r c h l o r a t e i s not c o o r d i n a t e d (6.6). On the o t h e r hand, i f ther e are no oth e r l i g a n d s p r e s e n t ( i e . a compound of the s t o i c h i o m e t r y MA2, f o r example) the anions must be c o o r d i n a t e d . I t i s w e l l e s t a b l i s h e d t h a t the anions PF, and AsF, 6 D have l e s s c o o r d i n a t i n g a b i l i t y than most other anions such as p e r c h l o r a t e and t e t r a f l u o r o b o r a t e (as evidenced by the comparison of the s t r u c t u r e s of the C o ( p y ) 4 A 2 compounds presented i n s e c t i o n 3.5.3). I f the PFg and AsFg anions are i n t i m a t e l y a s s o c i a t e d w i t h the metal i o n i n M ( p y ) ^ ( E F g ) 2 compounds then, because o f the l a r g e d i f f e r e n c e s i n the c o o r d i n a t i n g s t r e n g t h s of p y r i d i n e and EFg , t h i s may l e a d to very t e t r a g o n a l l y d i s t o r t e d complexes. Indeed i t may l e a d t o complexes where i t i s not c e r t a i n even t h a t the anions should be con s i d e r e d c o o r d i n a t e d . I t i s important, then, t o develop c r i t e r i a which may be used as evidence f o r or a g a i n s t anion c o o r d i n a t i o n . -151-The c r i t e r i a f o r c o o r d i n a t i o n may i n v o l v e (i) the e l e c t r o n i c s p e c t r a l and magnetic p r o p e r t i e s of the complex under study, ( i i ) X-ray c r y s t a l l o g r a p h i c evidence, and ( i i i ) i n f r a r e d s p e c t r a l evidence ( i f the anion i s p o l y a t o m i c ) . S p e c i f i c a l l y : (i) The anion may be c o n s i d e r e d c o o r d i n a t e d i f the e l e c t r o n i c s p e c t r a l and magnetic p r o p e r t i e s i n d i c a t e t h a t the s t e r e o c h e m i s t r y , g i v e n the s t o i c h i o m e t r y of the compound, must i n c l u d e the anions i n the f i r s t c o o r d i n a t i o n sphere of the metal i o n . ( i i ) The anion may be c o n s i d e r e d c o o r d i n a t e d i f X-ray c r y s t a l l o g r a p h i c evidence i s a v a i l a b l e and shows M-A bond d i s t a n c e s which l i e w i t h i n the range o f the sum of the i o n i c r a d i i and the sum of the van der Waals r a d i i of. the metal i o n and donor atom o f the anion. Other c r y s t a l l o g r a p h i c evidence which would be c o n c l u s i v e would i n c l u d e l a r g e d i s t o r t i o n s of the anion s t r u c t u r e from it's " f r e e i o n " shape and a s t r u c t u r e which shows the donor atoms of the anion to occupy d e f i n i t e c o o r d i n a t i o n p o s i t i o n s w i t h r e s p e c t to the metal i o n ( f o r example i n M(py)^A 2, the anion would occupy d e f i n i t e t e t r a g o n a l p o s i t i o n s i n t r a n s - N i ( p y ) ^ A 2 s t r u c t u r e w i t h no evidence f o r i s o t r o p i c r o t a t i o n a l d i s o r d e r i n g ) . ( i i i ) The anion may be c o n s i d e r e d c o o r d i n a t e d i f the i n f r a r e d s p e c t r a l data i n d i c a t e t h a t the symmetry of the anion i s g r e a t l y reduced below i t s " f r e e i o n " symmetry c o n s i s t e n t w i t h the lower symmetry expected f o r a c o o r d i n a t e d -152-anion. F o r example, i f the symmetry o f the anion i s i n " i o n i c " s a l t s and C.j v i n the monodentate c o o r d i n a t e d s i t u a -t i o n , t h i s should be r e f l e c t e d i n the number and i n t e n s i t y of bands i n the i n f r a r e d s p e c t r a . An example o f the use of the above c r i t e r i a w i t h c o o r d i n a t i o n compounds of weakly b a s i c anions i s found i n the (114) e a r l i e r work on the compounds, Ni (3, 4-lutidine) 4 (ClO^) 2 (I) / and N i ( 3 , 5 - l u t i d i n e ) (ClO^,) 2 (II) , (where l u t i d i n e = d i m e t h y l -p y r i d i n e ) . The e l e c t r o n i c s p e c t r a l and magnetic p r o p e r t i e s , i n f r a r e d s p e c t r a , and s i n g l e c r y s t a l d i f f r a c t i o n s t u d i e s have been p u b l i s h e d . The e l e c t r o n i c s p e c t r a l and magnetic p r o p e r t i e s o f compound (I) show the c h a r a c t e r i s t i c behavior f o r square p l a n a r n i c k e l ( I I ) (one s t r o n g band i n the e l e c t r o n i c spectrumand y e f f = 0 ) /' whereas, compound (II) shows the c h a r a c t e r i s t i c b e h a v i o r o f pseudo-octahedral n i c k e l ( I I ) (two bands i n the v i s i b l e r e g i o n and ^ e f f = 3 ' 2 7 B.M.). T h i s a c c o r d i n g to c r i t e r i o n ( i ) , i m p l i e s non-coordinated and c o o r d i n a t e d p e r c h l o r a t e anions f o r compound (I) and compound (II) r e s p e c t i v e l y . The i n f r a r e d d a t a c o n f i r m t h i s . The p e r c h l o r a t e anions i s a f i v e atom sp e c i e s and t h e r e f o r e t h e r e are nine (=3N-6) degrees of v i b r a t i o n a l freedom. There are fo u r fundamental modes of v i b r a t i o n ; 2 T 2 ' s which are both i n f r a r e d and Raman a c t i v e and A and E modes both o f which are Raman a c t i v e o n l y . So, there, are two bands expected i n the i n f r a r e d spectrum of simple p e r c h l o r a t e s a l t s . The i n f r a r e d spectrum of KCIO^ (89b)., shows th r e e -153-bands, two s t r o n g ( v 3 ( T 2 ) 1050-1170 cm - 1, ^ 4 ( T 2 ) 630 cm - 1) and one weak (the f o r m a l l y f o r b i d d e n (T^) v-^(A^) 935 cm . For compound I (the p r e v i o u s workers d i d not r e p o r t the s p e c t r a below 700 cm "*") the spectrum shows o n l y one very s t r o n g band a t 1108 cm 1 a s s i g n a b l e to ClO^ i n d i c a t i v e of an " i o n i c " (non-coordinated) p e r c h l o r a t e . On the o t h e r hand, the spectrum of compound II shows three bands i n t h i s r e g i o n a s s i g n a b l e to ClO^ when i t possesses C 3 v symmetry, i n d i c a t i v e of u n i d e n t a t e c o o r d i n a t e d p e r c h l o r a t e . The molecular s t r u c t u r e d e t e r m i n a t i o n of compound I(T15)' i s c o n s i s t e n t with the assignment o f square p l a n a r c o o r d i n a t i o n of the s u b s t i t u t e d p y r i d i n e l i g a n d around n i c k e l and non-coordinated p e r c h l o r a t e anions. The n e a r e s t neighbour n i c k e l - o x y g e n d i s t a n c e i s 3.343 2 , a value g r e a t e r than the sum o f the van der Waals r a d i i (3.1-3.2 7A(93b)) f o r n i c k e l and oxygen and thus too long f o r a chemical l i n k a g e . The p e r c h l o r a t e anions are, moreover, d i s o r d e r e d , perhaps i n d i c a t i v e of the absence o f s t r o n g d i r e c t i o n a l c a t i o n - a n i o n i n t e r a c t i o n . The s t r u c t u r a l parameters of the c a t i o n (Ni-N d i s t a n c e i s 1.897(3) 2 and the angle between the NiN^ plane and the p l a n a r 3 , 4 - d i m e t h y l p y r i d i n e r i n g i s 90°) are t y p i c a l f o r square p l a n a r n i c k e l ( I I ) . The molecular s t r u c t u r e of compound I I (116) i s c o n s i s t e n t w i t h the assignment of pseudo-octahedral c o o r d i n a t i o n o f n i c k e l ( I I ) by f o u r 3 , 5 - d i m e t h y l p y r i d i n e l i g a n d s and two (trans) p e r c h l o r a t e anions. The n i c k e l - o x y g e n d i s t a n c e i s -154-2.187(2) 2 , c o n s i d e r a b l y s h o r t e r than the van der Waals d i s t a n c e and c l o s e to the sum of i o n i c r a d i i (2.10 2 ) . The e f f e c t of p e r c h l o r a t e c o o r d i n a t i o n i s seen i n n i c k e l -n i t r o g e n bond d i s t a n c e of 2.093(2) R and the angle between the average NiN^ plane and 3,5-dimethylpyridine plane of 46.6°. These are t y p i c a l v a l u e s f o r o c t a h e d r a l n i c k e l ( I I ) complexes. The -N-Ni-0 angles range from 81.3(2) to 97.7(3)° i n d i c a t i n g the p e r c h l o r a t e .anions occupy d e f i n i t e . . a x i a l p o s i t i o n s . Compound I I f u l f i l l s a l l c r i t e r i a f o r a n i o n i c , c o o r d i n a t i o n whereas compound I doesn't f u l f i l l any of these. But s e v e r a l s i t u a t i o n s can be e n v i s i o n e d where there may not be such c l e a r evidence r e g a r d i n g a n i o n c o o r d i n a t i o n . For example, c r i t e r i o n ( i ) works bes t when the metal i o n has q u i t e d i f f e r e n t e l e c t r o n i c p r o p e r t i e s i n d i f f e r e n t s t e r e o -c h e m i s t r i e s . N i c k e l ( I I ) s a t i s f i e s t h i s requirement, i n t h a t when i t i s square p l a n a r , i t i s s p i n - p a i r e d and when o c t a h e d r a l or t e t r a h e d r a l , i t i s s p i n - f r e e . On the other hand copper(II) does not change s p i n s t a t e as a f u n c t i o n of s t e r e o c h e m i s t r y and t h i s makes the a p p l i c a t i o n of c r i t e r i o n (i) more d i f f i c u l t i n t h i s case. Even i n the n i c k e l ( I I ) case i t i s c o n c e i v a b l e t h a t a t e t r a g o n a l l y d i s t o r t e d o c t a h e d r a l complex c o u l d be s p i n - p a i r e d thus making the a p p l i c a t i o n o f c r i t e r i o n (i> o n l y , a q u e s t i o n a b l e procedure f o r determining whether or not anions are c o o r d i n a t e d . A l s o c o n s i d e r i n g the o t h e r c r i t e r i a ( i i and i i i ) , t h e re may not be X-ray c r y s t a l l o g r a p h i c evidence or the -155-i n f r a r e d s p e c t r a l e v i d e n c e may n o t be d e f i n i t i v e . I n r e g a r d t o t h e l a t t e r , t h e m e t a l - a n i o n i n t e r a c t i o n , though d e f i n i t e , may o n l y cause a s m a l l p e r t u r b a t i o n o f the a n i o n ' s s t r u c t u r e and hence t h e i n t r i n s i c a l l y l o w e r symmetry o f t h e a n i o n when c o o r d i n a t e d may n o t be m a n i f e s t e d i n t h e i n f r a r e d spectrum. I n c o n c l u s i o n we f e e l t h a t i n a d d r e s s i n g t h e q u e s t i o n o f whether o r not t h e a n i o n s a r e c o o r d i n a t e d i n complexes o f t h e t y p e s t u d i e d h e r e , i t i s n e c e s s a r y t o a p p l y as many c r i t e r i a f o r c o o r d i n a t i o n as p o s s i b l e . T h i s we have done i n our r a t h e r d e t a i l e d s t u d i e s on t h e N i L ^ f E F g ^ compounds t o be d e s c r i b e d i n t h e n e x t s e c t i o n . -156-4 . 2 COMPLEXES OF NICKEL (II) ; NiL ^ ('EFg) 2 4.2.1 INTRODUCTION As noted i n the i n t r o d u c t i o n ( s e c t i o n 1.1.2), the compound N i ( p y ) 4 ( P F g ) 2 was found by M a y f i e l d and B u l l (14) to have an anomalous magnetic moment of 1.98 B.M., anomalous because i t i s i n d i c a t i v e o f a s p i n - d o u b l e t ground s t a t e , whereas, i n m a g n e t i c a l l y d i l u t e d n i c k e l ( I I ) systems o n l y a s i n g l e t o r t r i p l e t ground s t a t e i s p o s s i b l e . The compound was prepared by thermal d e g r a d a t i o n of N i ( p y ) g ( P F g ) 2 at 100°C " i n vacuo". No f u r t h e r p h y s i c a l c h a r a c t e r i z a t i o n o f t h i s compound has been r e p o r t e d by these authors. Our work on t h i s compound has y i e l d e d v e r y d i f f e r e n t r e s u l t s . We have observed the formation o f a white sublimate on the c o o l e r p o r t i o n s o f the vacuum f l a s k when N i ( p y ) g ( P F g ) 2 or N i ( p y ) ^ ( P F g ) 2 have been heated a t temperatures of 100°C o r h i g h e r . S e c t i o n 4.2.2.4.3 d e s c r i b e s the c h a r a c t e r i z a t i o n of t h i s s u b l i m i n a t e as the compound, .-py'PFg. C l e a r l y , then, the r e s i d u e l e f t behind cannot s t i l l be formulated as N i ( p y ) 4 ( P F g ) 2 . T h i s behavior i s g e n e r a l l y observed f o r the s e r i e s o f compounds N i L ^ ( E F g ) 2 , when they are heated above 100°C. Magnetic s u s c e p t i b i l i t y measurements on the r e s i d u e l e f t over a f t e r v a r y i n g p e r i o d s of h e a t i n g are d e s c r i b e d f o r the compound N i ( 4 m e p y ) 4 ( P F g ) 2 i n s e c t i o n 4.2.2.4.1. -157-The r e s u l t s show t h a t the molar magnetic s u s c e p t i b i l i t y i s a f u n c t i o n of the h e a t i n g time and temperature and i n d i c a t e t h a t the decomposition product i s paramagnetic. To o b t a i n pure N i L 4 ( E F g ) 2 complexes we concluded t h a t i t was necessary to a v o i d h e a t i n g where p o s s i b l e , and where not p o s s i b l e , to c a r e f u l l y p u r i f y the product by r e c r y s t a l l i z a t i o n . The N i ( p y ) ^ ( E F g ) 2 complexes were prepared i n the pre s e n t work from the N i ( p y ) g ( E F g ) ^ complexes a t room temperature by s t i r r i n g i n dichloromethane. T h i s method takes advantage of the v o l a t i l i t y o f p y r i d i n e i n the N i (py)g (EFg)^ compounds and avoids the p o s s i b i l i t y of s i g n i f i c a n t thermal decomposition. The Ni(4mepy) 4(EFg) 2 were prepared by h e a t i n g o f the i ( 4 m e p y ) R ( H 2 0 ) 2 ( E F g ) 2 compounds f o l l o w e d by r e c r y s t a l l i z a t i o n from a dichloromethane-chloroform s o l v e n t . The N i ( 3 m e p y ) 4 ( A s F g ) 2 compound was formed by room temperature " i n vacuo" d r y i n g of Ni(3mepy)g(H 2 0 ) 2(AsFg)2 ( t i l l the water band i n the i n f r a r e d disappeared) f o l l o w e d by s t i r r i n g i n c h l o r o f o r m . 4.2.2. RESULTS AND DISCUSSION 4.2.2.1 MAGNETIC AND ELECTRONIC SPECTRAL PROPERTIES With the e x c e p t i o n of N i ( p y ) 4 ( A s F g ) 2 (discussed i n 4.2.2.4), the magnetic and s p e c t r a l p r o p e r t i e s o f these N i L ^ ( E F g ) 2 compounds are a l l s i m i l a r i n nature. The e l e c t r o n i c N -158-s p e c t r a of these compounds c o n s i s t of a s i n g l e a b s o r p t i o n band i n the v i s i b l e r e g i o n (Table I V - 1 ) . T h i s s i n g l e band spectrum i s t y p i c a l f o r square p l a n a r n i c k e l ( I I ) complexes and the e x t i n c t i o n c o e f f i c i e n t of 80-90 M 1 cm 1 observed i n the N i ( 4 m e p y ) 4 ( E F g ) 2 complexes i s a l s o t y p i c a l (eg. N i ( 3 , 5 - l u t i d i n e ) 4 ( C 1 0 4 ) 2 , e=110M~ 1cm~ 1 (19)). Although a weaker band i s sometimes noted a t lower e n e r g i e s (eg. 16.55 kK, (e=ll) f o r N i ( 3 , 5 - l u t i d i n e ) 4 ( C 1 0 4 ) 2 ) i n the spectrum of square p l a n a r n i c k e l ( I I ) , no such bands have been found i n t h i s study. F i g u r e 4.1 shows the d i f f u s e r e f l e c t a n c e e l e c t r o n i c s p e c t a (350-740 nm) of the N i L 4 ( A s F g ) 2 complexes s t u d i e d here. The p o s i t i o n o f the c e n t e r of g r a v i t y of the band, v , appears to s h i f t t o h i g h e r energy i n the s e r i e s : 3mepy> nicix 4mepy>py. However, w i t h i n the compounds N i L 4 ( E F g ) 2 , the p o s i t i o n of v m a x i s independent o f E . I t i s i n t e r e s t i n g t o note t h a t the p o s i t i o n o f v f o r the Ni(4mepy).(EF,)« ^ max r j 4 6 2 compounds and f o r N i ( 4 m e p y ) 4 ( C 1 0 4 ) 2 (19) are d i f f e r e n t (22.1 v s . 22.9 kK i n d i c a t i v e perhaps of a d i f f e r e n t degree of metal-anion i n t e r a c t i o n w i t h the two types of anions (EF g vs. c i o 4 " ). The magnetic p r o p e r t i e s o f the N i L 4 ( E F g ) , compounds show them to be e s s e n t i a l l y diamagnetic although t h e r e appears to be — 6 — 1 3 some r e s i d u a l paramagnetism pres e n t (^300 x 10 mole cm a t 295K, (see Appendix 2 ) ) . T h i s r e s i d u a l paramagnetism i s b a s i c a l l y -159-TABLE IV-1 ELECTRONIC SPECTRAL DATA FOR N i L 4 ( E F g ) 2 BAND POSITION (kK) COMPOUND N i ( p y ) 4 ( P F 6 ) 2 (a) 21.51 (b) 21.41s N i ( p y ) 4 ( A s F 6 ) 2 (a) 21.51 (b) 21.41s Ni(4mepy) 4(PFg) 2 (a) 22.5s (b) 22.1s (c) 22.0(90) Ni(4mepy) 4(AsF g) 2 (a) 22.2s (b) 22.1s (c) 22.1 (82) Ni(3m e p y ) 4 ( A s F g ) 2 (a) 23.26 (b) 22.47s (c) 22.32(85) (a) mull s p e c t r a (b) d i f f u s e r e f l e c t a n c e s p e c t r a (c) s o l u t i o n s p e c t r a ( C H 2 C 1 2 ) ; molar e x t i n c t i o n c o e f f i c e n t s (M _ 1cm _ 1) i n b r a c k e t s . - 1 6 0 --161-temperature independent but some u n c e r t a i n i t y e x i s t s as t o i t s o r i g i n . There may be some mixing of e x c i t e d paramagnetic s t a t e s i n t o the ground term, through a second order Zeeman e f f e c t ( s e c t i o n 2.2.2). Whatever the cause, t h i s magnetic behavior seems to be a c h a r a c t e r i s t i c p r o p e r t y of these compounds. The e l e c t r o n i c s p e c t r a and magnetic p r o p e r t i e s are c o n s i s t e n t w i t h the f o r m u l a t i o n of the chromophore as square p l a n a r NiN^. The molecular s t r u c t u r e d e t e r m i n a t i o n o f Ni(4mepy)^(PFg) 2 d i s c u s s e d i n s e c t i o n 4.2.2.3 confirms t h i s but a l s o i n d i c a t e s presence of very weak a x i a l anion i n t e r -a c t i o n , the e f f e c t s of which are seen i n the i n f r a r e d s p e c t r a to be d i s c u s s e d next. 4.2.2.2 VIBRATIONAL- SPECTRA There is- no evidence f o r non-coordinated p y r i d i n e , 4-methylpridine, or 3-methylpyridine i n • t h e i n f r a r e d s p e c t r a o f these compounds. For the p o s i t i o n s of the bands of Ni(3mepy)^(AsFg)2 see Appendix-1 :(Table A l - 3 ) . As shown i n Table IV-2, there i s no band which can be assigned to the 8a v i b r a t i o n o f p y r i d i n e and the 16b v i b r a t i o n has a s h i f t of 7 0 cm~^~ to h i g h e r energy compared to the f r e e l i g a n d T h i s s h i f t i s l a r g e r than observed i n most p y r i d i n e c o o r d i n a t i o n compounds and t h i s b ehavior may be c h a r a c t e r i s t i c of p y r i d i n e when ve r y s t r o n g l y bound. The c o r r e s p o n d i n g s t e r e o c h e m i c a l l y -162-TABLE IV-2 SELECTED NEUTRAL LIGAND BANDS IN THE INFRARED SPECTRA OF N i L 4 ( E F g ) 2 ( i ) L=PY 8a N i L 4 ( P F g ) 2 N i L 4 ( A s F g ) 2 1612s 1612s 6a n.o. n.o. 16b 470w 469w 1620m 1620m 1513m 1513m ( i i ) L=4mepy 8a 19a 9a 1250vw,1240vw 1250w, 1240vw 1 1054w 1053w 10b+12 817s 820s 6a - - - ( a ) 5 7 5 m (a) p o s s i b l y o b s c u r e d by v 4 ( T l u ) o f P F g -163-s e n s i t i v e bands o f 4-methylpyridine show some i n t e r e s t i n g f e a t u r e s ; the 6a band i s s h i f t e d by +50 cm 1 r e l a t i v e to the f r e e base, and the l a band appears as a weak band when i t i s u s u a l l y a moderately s t r o n g band. Table IV-3 shows the i n f r a r e d bands assigned to the E F g - anions. The g e n e r a l f e a t u r e of the anion s p e c t r a , along w i t h the appearance of the f o r m a l l y allowed and bands, i s the presence of both the v, (A,-,) and v? (E^) bands, which are f o r m a l l y f o r b i d d e n i n 0^ symmetry. The v ^ ( A i g ) band of P F g - and the v 2 ( E g ) bands of AsFg are w e l l separated from o t h e r anion v i b r a t i o n s i n the i n f r a r e d s p e c t r a and they appear as bands of medium i n t e n s i t y . The (A^g) band of AsF - and the v» (E„) band of PF,- are o f t e n maslced by other b z g b anion v i b r a t i o n s . The appearance of these f o r m a l l y f o r b i d d e n ( i n 0^ symmetry) bands, suggests t h a t the symmetry of the a n i o n i c environment i s lower than 0^ i n these complexes. The and v i b r a t i o n s which would be expected to show some s p l i t t i n g i n lower symmetry do not. However, these bands are q u i t e broad and i n some cases s u b j e c t to i n t e r f e r e n c e by n e u t r a l l i g a n d v i b r a t i o n s and t h i s may account f o r the l a c k of r e s o l v e d s p l i t t i n g o f these bands. F i g u r e 4.2 shows the i n f r a r e d s p e c t r a (1000-350 cm 1 ) of the compounds N i (py) 4 (PFg) 2 and N i ( p y ) 4 ( A s F g ) 2 . These s p e c t r a show the f e a t u r e s d i s c u s s e d above. M a y f i e l d and B u l l (14) had a s s i g n e d the band a t 470 cm 1 i n N i ( p y ) 4 ( P F g ) 2 t o the v 5 ( T 2 g ) v i b r a t i o n of PFg-. However, t h i s band appears -164-TABLE I V - I ANION BANDS IN THE INFRARED SPECTRA OF N i L 4 ( E F g ) 2 ASSIGNMENT BAND POSITION (cm" 1) N i ( p y ) 4 ( E F g ) N i ( 4 m e p y ) 4 ( E F g ) 2 N i ( 3 m e p y ) 4 ( E F g ) 2 (i) E=P VTlu> 843vs,br 847vs,834vs v 4 ( T l u l ) 558m 558m vi (V v2 ( Eg ) 740m _ _ _ ( a ) 7 4 4m ___•(*) ( i i ) E=As v3(Tlu> 700vs 700vs 7 00vs V T l u } 395s 397s 392s W 67 2m-w 672m 665s W 565m 565m 555m-s (a) may be hidden by the v 4 ( T l u ) band envelope - J . O O -1000 800 - 600 400 ENERGY (cm - 1) FIGURE 4.2 INFRARED SPECTRA (1000-350 cm"1) OF N i ( p y ) 4 ( E F g ) 2 . ( spectrum I i s E=P and spectrum I I i s E=As) -166-i n the spectrum of N i ( p y ) 4 ( A s F g ) 2 and s i n c e AsFg doesn't have any bands i n t h i s r e g i o n , i t must be as s i g n e d to the 16b v i b r a t i o n o f p y r i d i n e . T h i s band a l s o appeared i n M a y f i e l d and B u l l ' s i n f r a r e d spectrum of N i ( p y ) g ( P F g ) 2 but was not observed i n our i n f r a r e d s p e c t r a o f Ni (py) g (EFg) 2 (E=R and A s ) . We conclude the oth e r authors observed the band i n t h e i r spectrum due to the presence of N i ( p y ) 4 ( P F g ) 2 i m p u r i t y i n t h e i r sample of N i ( p y ) g ( P F g ) 2 ( s e c t i o n 3.2.2). 4.2.2.3 MOLECULAR STRUCTURE OF N i ( 4 m e p y ) 4 ( P F g ) 2 The d e t a i l s o f the c r y s t a l and molecular s t r u c t u r e d e t e r m i n a t i o n o f N i ( 4 m e p y ) 4 ( P F g ) 2 are d e s c r i b e d i n s e c t i o n 6.5.2. T h i s s e c t i o n d i s c u s s e s the mol e c u l a r s t r u c t u r e and how i t can be r e l a t e d t o the observed magnetic and s p e c t r a l p r o p e r t i e s o f the N i L 4 ( E F g ) 2 compounds i n g e n e r a l . The n i c k e l atom i s s i t u a t e d on a c r y s t a l l o g r a p h i c c e n t e r of i n v e r s i o n and the two c r y s t a l l o g r a p h i c a l l y d i s t i n c t 4 -methylpyridine m o i e t i e s d e f i n e a square p l a n a r environment of n i t r o g e n s around the n i c k e l . There i s one c r y s t a l l o g r a p h i c a l l y d i s t i n c t PFg group and, because o f i n v e r s i o n symmetry, the PFg groups occupy p o s i t i o n s above and below the n i c k e l -n i t r o g e n square p l a n a r u n i t . F i g u r e s 4.3- and 4..4.- show a view and stereoview r e s p e c t i v e l y o f the formula u n i t N i(4mepy) 4(PF g) 2 -Ni(C6H7N)4.(P(^)2 FIGURE 4.3 VIEW OF N i ( 4 m e p y ) 4 ( P F g ) 2 . ( A l l atoms are drawn f o r 50% p r o b a b i l i t y ) -168-FIGURE 4.4 STEREOVIEW OF N i ( 4 m e p y ) 4 ( P F g ) 2 ( A l l atoms a drawn f o r 50% p r o b a b i l t y ) -169-The bond d i s t a n c e s and angles are shown i n Table IV-4. The bond d i s t a n c e s and angles w i t h i n the 4-methyl-p y r i d i n e molecules are t y p i c a l f o r c o o r d i n a t e d 4-methylpyridine as i n Co(4mepy)^(PFg) 2 ( s e c t i o n 3.5.2). The bond d i s t a n c e s and angles i n the PFg group are s i m i l a r to those observed i n simple s a l t s c o n t a i n i n g PFg,- ,P-F; 1.466-1.593 2 (when the P-F d i s t a n c e s are not c o r r e c t e d f o r thermal motions) adjacent F-P-F, 86.2 t o 92.3°, o p p o s i t e F-P-F ;175.7° to 177.8°. The apparent d i s t o r t i o n s and l a r g e thermal parameters which may i n d i c a t e a s m a l l d i s o r d e r i n g of the PFg groups are commonly observed f o r t h i s n e a r l y s p h e r i c a l anion (91 ). The Ni-N bond d i s t a n c e s are 1.916(9) and 1.919(10) 2 and the N^-Ni-N1 angle i s 91.6(4)°. The n e a r e s t n i c k e l anion c o n t a c t i s 3.031(9) 2 between N i and F ( l ) . The F ( l ) - N i - N angles are 89.2 and 92.6° f o r N ( l ) and N(2) r e s p e c t i v e l y . The c r y s t a l l o g r a p h i c symmetry about n i c k e l i s I (center of i n v e r s i o n ) but the approximate symmetry i s s i n c e Ni-N d i s t a n c e s are the same w i t h i n experimental e r r o r and a l l the angles around n i c k e l are c l o s e to 90°. The angles between the NiN^ plane and the 4-methylpyridine plane are 102.1° and 97.3°, whereas symmetry would r e q u i r e an angle of 0°(90°) or 45°. The Ni-N d i s t a n c e s observed here are i n the range commonly observed i n square p l a n a r NiN^ chromophores; . t e t r a k i s ( 4 - m e t h y l p y r i d i n e ) n i c k e l ( I I ) p e r c h l o r a t e ( 2 3 )Ni-N i s 1.8 95 (5)-1.900 (5)., t e t r a k i s (3 , 4 - l u t i d i n e ) n i c k e l (II) -170-TABLE IV-4 BOND DISTANCES AND ANGLES IN N i ( 4 m e p y ) 4 ( P F g ) ( e s t i m a t e d s t a n d a r d d e v i a t i o n i n b r a c k e t s ) BOND DISTANCES ( 2 ) N i - N ( l ) =1.916(9) P - F ( l ) =1. 588 (8) P -F(3) =1.567(11) P -F(5) =1.593 (13) Ni-N(2) =1.919(10) P -F(2) =1.556 (9) P -F(4) =1.466(12) P -F(6) =1.543 (9) N i - F ( l ) =3.031(8) RING 1 RING 2 N- C ( l ) 1.337 (.14) 1.322 (17) C ( l ) - C ( 2 ) 1. 368 (16) 1.393 (19) C(2)-C(3) 1.362(18) 1.385(19) C(3)-C(4) 1.383 (18) 1.353(19) C(4)-C(5) 1.386(18) 1.380 (22) C(5)-N 1.340(16) 1.360 (16) C(3)-C(6) 1.554 (17) 1.548 (20) BOND ANGLES (deg) N ( l ) - N i - N ( 2 ) =91.6 (4) N ( l ) - N i - F ( l ) = 89. 2(4) N ( 2 ) - N i - F ( l ) = 92.6 (4) F ( l ) - P - F ( 2 ) = 90. 7(5) F ( l ) - P - F (3) =88.3(5) F ( l ) - P - F ( 4 ) = 92. 0(7) F ( l ) - P - F ( 5 ) =86.2(6) F ( l ) - P - F ( 6 ) = 175 .7(7) F ( 2 ) - P - F (3) =176.7(9) F ( 2 ) - P - F ( 4 ) = '92. 2(9) F ( 2 ) - P - F ( 5 ) = 89.1 (8) F ( 2 ) - P - F ( 6 ) = = 89. 1(6) F ( 3 ) - P - F ( 4 ) = 91.0 (10) F ( 3 ) - P - F ( 5 ) = = 87. 7 (9) -171-TABLE IV-4 (cont'd) ( i i ) BOND ANGLES (deg) F(3)-P- F(6) 91.7(6) F(4) -P-F (5) 177.8 F(4)-P- F(6) 92.3(9) F(5) -P-F(6) 89.6 RING 1 RING 2 C(5)-N-C(l) 117. 8 (11) 117. 6(13) N- C ( l ) - C ( 2 ) 121. 6 (12) 123. 4(14) C ( l ) - C ( 2 ) - C ( 3 ) 120. 7 (12) 119. 3(14) C(2)-C(3)-C(4) 118. 8(12) 116. 5(16) C(3)-C(4)-C(5) 117. 5(14) 122. 7 (16) C(4)-C(5)-N 123. 3(13) 120. 5 U 4 ) C(2)-C(3)-C(6) 122. 3(13) 119. 0(16) C(4)-C(3)-C(6) 118. 8(14) 124. .5(15) -172-p e r c h l o r a t e (115) Ni-N i s 1.897(3) 8 , b i s ( d i e t h y l b i s ( 1 - p y r a z o l y l ) -b o r a t o ) n i c k e l ( I I ) (117) Ni-N i s 1.88 8 and the square p l a n a r b i s (mesostilbenediammine)nickel(II) d i c h l o r a c e t a t e (25 ) Ni-N i s 1.89 8 The angle between the N i N 4 plane and the planes of the ( s u b s t i t u t e d ) p y r i d i n e r i n g s i s u s u a l l y 90° i n square p l a n a r c o o r d i n a t i o n ( i n N i ( 3 , 4 - l u t i d i n e ) 4 ( C 1 0 4 ) , the angle i s 90°) and 45° i n o c t a h e d r a l c o o r d i n a t i o n •( i n N i ( 3 , 5 - l u t i d i n e ) 4 ~ ( C 1 0 4 ) 2 (116), the angle i s 46.6° and i n Ni(4mepy) 4(NCS) 2, the a n g l e . i s 49.7-5.9.5° (118) ). The comparison of molecular s t r u c t u r e s of t e t r a k i s -( 4 - m e t h y l p y r i d i n e ) n i c k e l ( I I ) p e r c h l o r a t e w i t h the t e t r a k i s -( 4 - m e t h y l p y r i d i n e ) n i c k e l ( I I ) hexafluorophosphate i s u s e f u l s i n c e the o n l y d i f f e r e n c e between the two i s i n the anion p r e s e n t . The c l o s e s t n i c k e l - a n i o n c o n t a c t i n the former compound i s 3.290(8) 8 w i t h a d i s o r d e r e d anion, whereas i n our compound i t i s 3.031(9) 8 w i t h no evidence f o r i s o t r o p i c d i s o r d e r i n g o f the anion. The sum of van der Waals r a d i i f o r oxygen and f l u o r i n e w i t h n i c k e l are i n the same range (3.1-3.2 8 (93(b))) so i t appears t h a t the N i - F ( l ) d i s t a n c e i s l e s s than t h i s sum whereas the Ni-0 d i s t a n c e i s g r e a t e r . A l s o , the thermal para-meters of F ( l ) are l e s s than those of the o t h e r f l u o r i n e s s u g g e s t i n g t h a t i t i s c o n s t r a i n e d by i n t e r a c t i o n w i t h the metal i o n . The c l o s e s t c o n t a c t s t h a t the PF, anion makes w i t h 6 the 4-methylpyridine r i n g s are F ( l ) - C ( . l ) which, have lengths of 3.7 and 3.19 8 f o r two c r y s t a l l o g r a p h i c a l l y d i s t i n c t m o i e t i e s . -173-C l e a r l y , the observed magnetic and s p e c t r a l p r o p e r t i e s of the N i L ^ ( E F g ) ^ compounds can be r e l a t e d to a g e n e r a l s t r u c t u r e s i m i l a r t o the molecular s t r u c t u r e o f Ni(4mepy) 4(PFg) 2 • The magnetic and e l e c t r o n i c s p e c t r a l p r o p e r t i e s of these com-pounds are p r i m a r i l y the r e s u l t of str o n g square p l a n a r c o o r d i n -a t i o n o f n i c k e l by the n e u t r a l l i g a n d (py, 4mepy, 3mepy). The i n f r a r e d s p e c t r a observed f o r the anions i n d i c a t e an asym-m e t r i c environment f o r them; t h a t i s , the metal-anion c o n t a c t of l e s s than the sum of van der Waals r a d i i and the. weak, anion r i n g i n t e r a c t i o n cause a s i g n i f i c a n t lowering of anion symmetry. I t should be noted t h a t the e l e c t r o n i c s p e c t r a o f N i ( 4 m e p y ) 4 ( P F g ) 2 and N i ( 4 m e p y ) 4 ( C 1 0 4 ) 2 are d i f f e r e n t ( s e c t i o n 4.2.2.1) and the p o s i t i o n i n g of the anions are a l s o d i f f e r e n t . T h i s , along w i t h the PFg - Ni s t r u c t u r a l parameters, suggest t h a t some type o f metal-anion i n t e r a c t i o n i s prese n t i n the PFg compound. The low temperature i s o m e r i z a t i o n o f N i ( p y ) 4 ( A s F g ) 2 d i s c u s s e d i n the next s e c t i o n , i n which the n i c k e l - a n i o n i n t e r a c t i o n i s weak a t room temperature and s i g n i f i c a n t l y s t r o n g e r a t low temperatures (,<17 0K) a l s o g i v e s c r e d i b i l i t y to the argument t h a t the EFg~ anions are weakly c o o r d i n a t e d i n the N i L . ( E F , ) 0 compounds g e n e r a l l y . The f a c t t h a t the 4 b £ e l e c t r o n i c s t r u c t u r e of the n i c k e l ( I I ) i o n i n these complexes i s t y p i c a l f o r square c o o r d i n a t i o n can be r a t i o n a l i s e d . For as ••• Maki (119) p o i n t s out i n h i s weak f i e l d c a l c u l a t i o n , -174-there i s no d i s t i n c t i o n i n e l e c t r o n i c s t r u c t u r e between square p l a n a r and v e r y t e t r a g o n a l l y d i s t o r t e d o c t a h e d r a l c o o r d i n a t i o n . 4.2.2.4 LOW TEMPERATURE ISOMERIZATION OF N i ( p y ) 4 ( A s F g ) 2 T h i s s e c t i o n d e s c r i b e s c r y o g e n i c s t u d i e s on Ni ( P Y ) 4 ( A s F g ) 2 • The magnetic, e l e c t r o n i c s p e c t r a l and v i b r a t i o n a l s p e c t r a l p r o p e r t i e s of t h i s compound are d i f -f e r e n t a t l i q u i d n i t r o g e n temperature (77K) and room temperature. We a s c r i b e the changes i n these p r o p e r t i e s to a i n c r e a s e i n metal-anion i n t e r a c t i o n as t h i s compound undergoes a change i n s t r u c t u r e on c o o l i n g . 4.2.2.4.1 MAGNETIC AND ELECTRONIC SPECTRAL PROPERTIES The compound N i ( p y ) 4 ( A s F g ) 2 prepared a c c o r d i n g t o 6.2.1.8(a) ( " s t i r " p r e p a r a t i o n ) has some unusual magnetic p r o p e r t i e s a t temperatures lower than 200K but!has.-the normal p r o p e r t i e s o f the oth e r N i L 4 ( E F g ) 2 compounds i n the range 300-220K. F i g u r e 4.5 shows the molar magnetic s u s c e p t i b i l i t y p l o t t e d a g a i n s t temperature f o r N i ( p y ) 4 ( P F g ) 2 and N i ( p y ) 4 ( A s F g ) 2 and i l l u s t r a t e s the d i s c o n t i n u i t y around 200 K f o r N i ( p y ) 4 ( A s F g ) 2 F i g u r e 4.6 shows the molar s u s c e p t i b i l i t y and magnetic moment p l o t t e d as a f u n c t i o n o f temperature over the range 300-77 K. From 300 to 220K, t h i s s u s c e p t i b i l i t y -175-loXwmor1) FIGURE 4.5 MAGNETIC SUSCEPTIBILITIES OF N i ( p y ) 4 ( E F g ) . (The shaded and unshaded c i r c l e s are the data p o i n t s f o r E=P and E=As, r e s p e c t i v e l y ) -176-T(K) FIGURE 4.6 MAGNETIC SUSPECTIBILITY OF N i ( p y ) 4 ( A s F g ) 2 i s t e m p e r a t u r e i n d e p e n d e n t and smal], c o r r e s p o n d i n g t o a — 6 3 — 1 p a r a m a g n e t i s m o f 300 x 10 cm mol ( c . g . s . u n i t s ) . From 220 t o 170 K, t h e s u s c e p t i b i l i t y i n c r e a s e s v e r y r a p i d l y and b e l o w 170 K, t h e s u s c e p t i b i l i t y o b e y s C u r i e law (i.e. l / x m a T ) . The e f f e c t i v e m a g n e t i c moment, f r o m 300-220 K, i s c l o s e t o 0.65 B.M., f r o m 220 t o 170 K i t i n c r e a s e s r a p i d l y , and b e l o w 170 K i t r e m a i n s e s s e n t i a l l y c o n s t a n t a t 2.85 B.M. T h i s t e m p e r a t u r e d e p e n d e n t m a g n e t i c b e h a v i o r may be r e l a t e d t o t h e s t e r e o c h e m i s t r y o f t h e n i c k e l ( I I ) i o n . C l e a r l y , t h e g r o u n d s t a t e o f t h e n i c k e l ( I I ) i o n above 220 K i s a s p i n - s i n g l e t i n d i c a t i v e o f s q u a r e p l a n a r s t e r e o c h e m i s t r y , w h e r e a s , b e l o w 170 K i t i s a s p i n - t r i p l e t ( s i n c e a U e f f o f 2.85 B.M. i s c l o s e t o t h e s p i n o n l y moment f o r 2 u n p a i r e d e l e c t r o n s (2.83 B.M.)). The s p i n - t r i p l e t g r o u n d s t a t e may be i n d i c a t i v e o f d i s t o r t e d o c t a h e d r a l o r t e t r a h e d r a l s t e r e o c h e m i s t r y a b o u t n i c k e l . The e l e c t r o n i c s p e c t r u m o f N i ( p y ) 4 ( A s F g ) 2 a t 80 K i s t h a t o f a t e t r a g o n a l l y d i s t o r t e d o c t a h e d r a l n i c k e l ( I I ) i o n as d i s c u s s e d n e x t . The e l e c t r o n i c s p e c t r u m o f N i ( p y ) 4 ( A s F g ) 2 a t 300 and 80 K i s shown i n F i g u r e 4.7 . The s p e c t r u m a t 300 K i s a t y p i c a l s p e c t r u m o f n i c k e l ( I I ) i n a s q u a r e p l a n a r e n v i r o n -ment as s e e n f o r t h e N i L 4 ( E F g ) 2 compounds g e n e r a l l y ( s e c t i o n 4 .3.2.1). The s p e c t r u m a t 80 K a p p e a r s t o be t h e s u p e r i m p o s i t o f two s p e c t r a J t h e s i n g l e band s p e c t r u m w h i c h i s o b s e r v e d a t 300 K a n d a new s p e c t r u m c o n s i s t i n g o f f i v e b a n d s . T h i s -178-FIGURE 4.7 ELECTRONIC SPECTRUM OF N i ( p y ) 4 ( A s F g ) 2 (300 and 80 (sample as a powder) -179-new spectrum i s s i m i l a r to t h a t observed f o r N i ( p y ) 4 ( C 1 0 4 ) 2 (Figure 4.8) where an a x i a l l y elongated d i s t o r t e d o c t a h e d r a l chromophore i s pr e s e n t . These f i v e bands may be assigned and l i g a n d f i e l d parameters c a l c u l a t e d . T h i s i s done i n s e c t i o n 4.2.2.4.2. But, i s the observed e l e c t r o n i c spectrum which i n d i c a t e s the presence o f a mixture of the square p l a n a r and t e t r a g o n a l s p e c i e s , c o n s i s t e n t w i t h the magnetic suscep-t i b i l i t y measurements? The va l u e o f y e f f observed a t 80 K, 0 2.85 B.M., i s low compared t o t h a t observed": f o r analogous t e t r a g o n a l l y d i s t o r t e d o c t a h e d r a l complexes ( f o r example the t e t r a g o n a l p y r i d i n e complex, N i ( p y ) 4 ( B F 4 ) 2 where y g r r i s 3.2 B.M.). Assuming t h a t t h e r e i s a mixture o f " o c t a h e d r a l " and "square p l a n a r " N i ( p y ) 4 ( A s F g ) 2 a t 80 K and the magnetic moment o f " o c t a h e d r a l " N i ( p y ) 4 ( A s F g ) 2 i s 3.2.B.M. and the magnetic s u s c e p t i b i l i t y o f "square p l a n a r " N i ( p y ) 4 ( A s F g ) 2 i s 300 x 10 -^ mole 1 cm 3 :, the experimental magnetic moment of 2.85 B.M. corresponds t o an 75:25% mixture o f the two. Having concluded t h a t a mixture of s t r u c t u r a l forms i s p r e s e n t a t 7 7K, the next step i s t o attempt t o account f o r the r e l a t i v e i n t e n s i t i e s o f the "square p l a n a r " and " o c t a h e d r a l " bands i n the 80 K e l e c t r o n i c spectrum. Here, the e x t i n c t i o n c o e f f i c i e n t s o f the v i s i b l e bands w i l l be co n s i d e r e d . The e x t i n c t i o n c o e f f i c i e n t s bf the v i s i b l e bands o f the d i s t o r t e d " o c t a h e d r a l " and "square p l a n a r " -180-1500 1000 500 X (nm) FIGURE 4.8 ELECTRONIC SPECTRA OF Ni ( p y ) 4 ( A s F g ) 2 (80K) AND N i ( p y ) 4 ( C 1 0 4 ) 2 (300K). ( N i ( p y ) 4 ( A s F 6 ) 2 as a powder and Ni(py).(CIO.)„ as a mulled sample) -181-complexes are d i f f e r e n t , e for the square planar band i s probably close 100 M c m - 1 ( c f Ni(4mepy) 4(PF g) 2 where £=90) whereas for the distorted "octahedral" complex, i t i s probably, -1 3 3 close to 5M cm (cf Big+ E 9 o f Ni(4mepy) 4(C10 4) 2 where e=5). The r e l a t i v e i n t e n s i t i e s of these d i s t o r t e d octahedral and square planar bands i n a 75:25% mixture would be 1:7; the absorption due to the square planar complex would appear as the strongest band i n the spectrum. We have accounted for the observed magnetic properties and el e c t r o n i c spectra of N i ( p y ) 4 ( A s F g ) 2 i n terms of a stereo-chemical change around nickel(II) which i s incomplete. It i s unusual but not unknown for nickel(II) compounds to have two types of chromophore e x i s t i n g i n the same l a t t i c e . As mentioned i n the introductory chapter (section 1.1.2), the c r y s t a l and molecular structure of bis(meso-stilbene) nickel(II) dichloroacetate ( 26) revealed three c r y s t a l l o g r a p h i c a l l y d i s t i n c t n i c k e l centers; two were six-coordinate and one was four-coordinate with coordinated and non-coordinated dichloroacetate anions respectively. Some other systems also show t h i s s t r u c t u r a l feature which Sacconi (60) has referred to by the term, interallogony. An important question remains to be answered, "What transformation takes place i n the temperature range 220 to 170 K as indicated by the magnetic s u s c e p t i b i l i t y measure-ments?". The e l e c t r o n i c spectral data indicate that most -182-of the n i c k e l ( I I ) c e n t e r s undergo a s t e r e o c h e m i c a l change from square p l a n a r t o d i s t o r t e d o c t a h e d r a l c o o r d i n a t i o n . The magnetic s u s c e p t i b i l i t y measurements i n d i c a t e a correspond-in g change i n the-ground s p i n s t a t e . We have r e f e r r e d t o t h i s t r a n s f o r m a t i o n as an i s o m e r i z a t i o n s i n c e i t i s apparent t h a t the anions are predominantly non-coordinated and c o o r d i n a t e d above 220 K and below 17 0 K, r e s p e c t i v e l y . In o r d e r t o make an attempt a t understanding the process t a k i n g p l a c e , the parameter K i s used. The d e f i n i t i o n of K i s given i n equation 4.1; t h a t i s ,K i s the r a t i o of n i c k e l ( I I ) c e n t e r s having h i g h s p i n c h a r a c t e r to those having low.spin c h a r a c t e r . T. mole f r a c t i o n of h i g h s p i n .T ... ,„ , > K=— T 2 T~- 3 — T — T - — = N, /N-, ...(4.1) mole f r a c t i o n of low s p i n hs' Is Assuming the h i g h - s p i n f r a c t i o n i s a C u r i e paramagnet w i t h U e f £ = 3.20 B.M., the molar s u s p e c t i b i l i t y of the h i g h - s p i n isomer, x ^ ' c a n be determined from: X h=(3.20/2.828) 2(1/T) ...(4.2) The molar s u s c e p t i b i l i t y of the l o w - s p i n isomer, X]_# i s assumed — 6 —1 3 to be 300 x 10 mole cm . The mole f r a c t i o n of h i g h - s p i n and low-spin isomers, N, and N, r e s p e c t i v e l y , may be determined by s o l v i n g the simultaneous equations 4.3 and 4.4.. below (X i s the experimental molar s u s c e p t i b i l i t y ) : N l s * l + N h s * h = X e x ...(4.3) N l s + N h s = 1 ...(4.4) -183-Thus K can be c a l c u l a t e d by use o f e q u a t i o n (4.1). Since we have seen t h a t only 75% of the N i ( p y ) 4 ( A s F g ) 2 w i l l undergo t h i s p r o c e s s , i t i s b e s t to n ormalize the and N^ s v a l u e s such as to d i s r e g a r d the 25% t h a t w i l l not under-go i s o m e r i z a t i o n . T h i s was done by d e f i n i n g as (N^ s~0.25) and the e q u i l i b r i u m constant K* as ( N h s / N J . s ) • The c a l c u l a t e d v a l u e s o f N, , N, , N* , K, and K* are shown i n Table A4-1 hs I s ' I s ' (p. 371). T h i s parameter, K*, can be c o n s i d e r e d to be a q u a s i -e q u i l i b r i u m c o n s t a n t s i n c e i t r e p r e s e n t s N i ( p y ) 4 ( A s F 6 ) 2 ( l . s s . ) f * N i ( p y ) 4 ( A s F 6 ) 2 ( h . s . ) ...(4.5] the e q u i l i b r i u m c o n s t a n t i f these s p e c i e s are i n e q u i l i b r i u m . I f t h i s process i s an e q u i l i b r i u m , In K* can be r e l a t e d to the thermodynamic parameters, enthalpy (AH) and entropy (AS), by use of e q u a t i o n 4.6. In K = (-AH/R) (1/T) + (AS/R) ...(4.6) F i g u r e 4.9 shows the p l o t of In K* a g a i n s t 1/T. For 3 the In K p l o t , the p l o t i s l i n e a r i n the range of 10 /T from 4.6 (217K) t o 5.5 (182K) and f o r the In K* p l o t , i n the range 4.6(217K) to 6.5 (174K). The v a l u e s of A H ( i n cm - 1) and AS 3 ( i n cal/(mole-K)) d e r i v e d from the In K p l o t are -2.52 x 10 and -44.8, r e s p e c t i v e l y , and f o r the In K* p l o t , they are 3 -2.58 x 10 and -38.9, r e s p e c t i v e l y . The meaning of the e n thalpy parameters i s t h a t the s p i n e q u i l i b r i u m process i s f a v o r a b l e a t 200K s i n c e i t i s an exothermic process and can overcome -184-(From the magnetic d a t a of N i ( p y ) 4 ( A s F g ) 2 ) -185-t h e t h e r m a l r a n d o m i z a t i o n p r o c e s s e s w h i c h would oppose i t (kT=^14 0 cm ~~) . The e n t r o p y v a l u e s i n d i c a t e t h a t t h e e n t r o p y a s p e c t s o f t h e " e q u i l i b r i u m " a r e u n f a v o r a b l e . S i n c e we have seen t h a t t h e b i n d i n g o f t h e h e x a f l u o r o a r s e n a t e t o t h e m e t a l i o n i s g r e a t e r i n t h e l o w e r t e m p e r a t u r e i s o m e r , t h e d i s -o r d e r o f t h e h e x a f l u o r o a r s e n a t e a n i o n d e c r e a s e s . Thus as t h e t e m p e r a t u r e i s l o w e r e d , t h e d i s o r d e r p r e s e n t d e c r e a s e s and t h i s g i v e s r i s e t o t h e u n f a v o r a b l e e n t r o p y term. The p h y s i c a l i n t e r p r e t i o n o f t h i s model i s t h a t o f e q u a t i o n 4.7; where t h e AH parameter d e r i v e d N i ( p y ) 4 2 + ( 4 c o o r d i n a t e ) + 2 A s F 6 ~ j N i ( p y ) 4 ( A s F g ) 2 ( s i x c o o r d i n a t e ) . . . ( 4 . 7 ) 3 -1 (^2.7 x 10 cm /mole(30.9 kJ/mole)) i n c l u d e s t h e bond e n e r g i e s o f r i g h t hand s i d e molecules compared t o t h o s e of. t h e l e f t , hand s i d e molecules p l u s t h e c o n t r i b u t i o n from t h e c r y s t a l l a t t i c e t r a n s f o r m a t i o n energy. T h i s model ( r e f e r r e d t o as m o d e l ( I ) ) i s based on t h e premise t h a t t h e t r a n s f o r m a t i o n i s between two e n t i r e l y d i s t i n c t s p i n systems; "N^ " m o l e c u l e s have a ground s t a t e s i n g l e t w i t h o u t a t h e r m a l l y a c c e s s i b l e t r i p l e t s t a t e and "N, " m o l e c u l e s have t h i s s i t u a t i o n r e v e r s e d , hs A n o t h e r model ( m o d e l ( I I ) ) can be assembled where t h e s p i n - s i n g l e t and s p i n - t r i p l e t a r e i n same s p i n system, i . e . t h e e l e c t r o n i c s t r u c t u r e o f t h e n i c k e l ( I I ) i o n (75% o f them) i n v o l v e s a ground s t a t e s i n g l e t w i t h a t h e r m a l l y a c c e s s i b l e t r i p l e t t e r m (at ^215K). The e q u a t i o n w h i c h d e s c r i b e s the Boltzmann -186-d i s t r i b u t i o n o f molecules i n the s i n g l e t and t r i p l e t s t a t e s i s equation (4.8) (where A E i s the s e p a r a t i o n In K* = -AE/RT + In 3 ...(4.8) of the s i n g l e t and t r i p l e t and i s p o s i t i v e f o r the s p i n s i n g l e t lower-and the ln3 terms a r i s e s from the l a r g e r s p i n entropy of the t r i p l e t compared t o s i n g l e t s t a t e ) . Use of the rearranged form o f equation (4.8), equation (4.9), a l l o w s A E t o be c a l -c u l a t e d i n the temperature range 215 to 160 K. The c a l c u l a t e d A E = RT(In 3-lnK) ...(4.9) are given i n Table A4-2 (p.37 2) and i l l u s t r a t e d i n F i g u r e 4.10. The A E value s v a r y between +707 cm 1 (at 215K) and -250 cm-"1" (at 160K) , where the l a t t e r v a l u e i n d i c a t e s t h a t the s p i n - t r i p l e t i s 250 cm 1 lower i n energy then the s p i n - s i n g l e t a t 160 K. The o v e r a l l temperature dependence of A E i n t h i s model i s s p i n - c r o s s o v e r b e h a v i o r . To summarize, model (I).'has analyzed the parameter K* (and thus the temperature dependence of X Q V ~ 4 - ) x n terms o f two separate s p i n systems, where the s p i n - s i n g l e t has ve r y weakly c o o r d i n a t e d AsFg anions and the s p i n - t r i p l e t has " c l a s s i c a l " c o o r d i n a t e d AsFg anions. M o d e l ( I I ) , on the o t h e r hand, has analyzed the parameter K* i n terms of the s p i n - s i n g l e t and s p i n - t r i p l e t energy s t a t e s being p r e s e n t and a c c e s s i b l e i n each n i c k e l ( I I ) i o n . The c o o r d i n a t i o n o f the AsFg anions would then be v a r i a b l e through the temperature range, v a r y i n g -187-600 400 200 AE ( i n 0 cm 1) -200 -400 | , , • . 170 190 210 TEMPERATURE ( i n K e l v i n ) FIGURE 4.10 PLOT OF AE AGAINST TEMPERATURE ( from the magnetic data of N i ( p y ) ^ ( A s F g ) 2 ) -188-from weakly c o o r d i n a t i n g t o " c l a s s i c a l l y " c o o r d i n a t e d . Magnetic s u s c e p t i b i l i t y measurements are a bulk p r o p e r t y of the m a t e r i a l and thus we can only make assumptions as t o the l i k e l y systems which g i v e r i s e t o the observed beh a v i o r , i . e . models (I) and ( I I ) . E l e c t r o n i c s p e c t r a i n t h i s temperature range would d i f f e r e n t i a t e between the two models. The e l e c t r o n i c spectrum o f a system based on model (I) would c o n s i s t of the s u p e r i m p o s i t i o n of two s p e c t r a , one due to a s p i n - s i n g l e t ground s t a t e , the o t h e r to s p i n - t r i p l e t ground s t a t e . The two s p e c t r a would vary i n i n t e n s i t y as the temperature i s v a r i e d . A system based on model(II) would have a spectrum i n which band p o s i t i o n s as w e l l as i n t e n s i t y v a r i e d w i t h temperature. Superimposed on both types o f s p e c t r a (of model(I) and model(II)) would be the e l e c t r o n i c spectrum of the s p i n - s i n g l e t n i c k e l ( I I ) system which does not undergo the t r a n s f o r m a t i o n (25% of the n i c k e l ( I I ) i o n s ) . In c o n c l u s i o n , on the b a s i s of the magnetic suscep-t i b i l i t y measurements,model(I) and model(II) cannot be d i f -f e r e n t i a t e d . But we have c o n s i d e r e d both i n an attempt to understand the process t a k i n g p l a c e between 220 and 160K i n the N i ( p y ) 4 ( A s F g ) 2 complex. -189-4.2.2.4.2 ELECTRONIC STRUCTURE AND STEREOCHEMISTRY Table IV-5 l i s t s the t r a n s i t i o n e n e r g i e s and a s s i g n -ments f o r the 80K spectrum of N i ( p y ) 4 ( A s F g ) 2 . As o u t l i n e d i n s e c t i o n 2.3.2.1, the t e t r a g o n a l parameters of N i ( p y ) 4 ( A s F g ) 2 can be obtained from the 80K spectrum. Table IV-6 l i s t s these parameters f o r N i ( p y ) 4 ( A s F g ) 2 and some t e t r a g o n a l n i c k e l -p y r i d i n e complexes w i t h other a n i o n i c s p e c i e s ( the parameters f o r the oth e r complexes were r e c a l c u l a t e d from the p u b l i s h e d d a t a t o i n c l u d e c o n f i g u r a t i o n i n t e r a c t i o n ( s e c t i o n 2.3.2.1) TABLE IV-5 ELECTRONIC SPECTRUM OF N i ( p y ) 4 ( A s F g ) 2 BAND POSITION ( k K ) ( a ) ASSIGNMENT ( b ) 6.92 3 B l g -> 3 E g ( 3 F ) 13.0 -> 3 B 2 g ( 3 F ) 14.3 - 3 A 2 g ( 3 F ) \ ( 3 F ) (c) 17.5 22.2 28.2 3 A „ ( 3P) * * 3 3 3 E g ( 3P) (a) powder a t 80K (b) see s e c t i o n 2.3.2.1 (c) square p l a n a r band, ^^ig^^iq -190-TABLE IV-6 TETRAGONAL PARAMETERS OF SOME N i ( p y ) f a COMPOUNDS COMPOUND N i ( p y ) 4 ( A s F g ) 2 N i ( p y ) 4 ( B F 4 ) 2 N i ( p y ) 4 ( c i o 4 ) 2 N i ( p y ) 4 ( F S 0 3 ) 2 PARAMETER VALUE (cm 1 ) Dq ^xy Dt Ds B REFERENCE 1300 568 1588 887 T h i s work 1300 540 1240 890 (120) 1290 500 930 930 (120) 1180 359 342 900 (121) The t e t r a g o n a l . p a r a m e t e r s o f the low temp e r a t u r e isomer of N i (py) ( A sF c) „ a r e v e r y s i m i l a r t o thos e of t h e compounds of 4 b z t e t r a f l u o r o b o r a t e and p e r c h l o r a t e l i s t e d above. The v a l u e s o f Dq a r e v i r t u a l l y i d e n t i c a l whereas th e v a l u e s o f Ds and Dt a r e l a r g e r f o r o ur compound. T h i s s u g g e s t s t h a t t h e a x i a l l i g a n d f i e l d s t r e n g t h o f t h e h e x a f l u o r o a r s e n a t e a n i o n i s l e s s t h a n t h o s e of' t h e s e o t h e r a n i o n s . As expected,- t h e complex w i t h c o o r d i n a t e d hexaf l u o r o a r s e n a t e i s - a v e r y - . d i s t o r t e d s p e c i e s The c r y o g e n i c e l e c t r o n i c s p e c t r a l and magnetic p r o p e r t i e s o f N i ( p y ) 4 ( A s F g ) ^ i n d i c a t e t h a t t h i s compound has an e s s e n t i a l l y square p l a n a r s t e r e o c h e m i s t r y a t room t e m p e r a t u r e and a p r e d o m i n a n t l y a x i a l l y e l o n g a t e d t e t r a g o n a l l y d i s t o r t e d o c t a h e d r a l s t e r e o c h e m i s t r y a t te m p e r a t u r e s below 170 K. U s i n g t h e c r i t e r i a o f s e c t i o n 4.1, t h e A s F g a n i o n s , must become c o o r d i n a t e d below 17 0 K because t h e s e p r o p e r t i e s a r e t y p i c a l f o r s i x - c o o r d i n a t e n i c k e l ( I I ) . Thus, t h e room te m p e r a t u r e form, 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 e x a f l u o r o --191-arsenate becomes, a t temperatures below 170 K, b i s ( h e x a f l u o r o -a r s e n a t o ) t e t r a k i s ( p y r i d i n e ) n i c k e l ( I I ) . The i s o m e r i z a t i o n which must be t a k i n g p l a c e i n the temperature range 220-170 K i s t h a t the anions are moving c l o s e r t o the n i c k e l and, per-haps, the p y r i d i n e r i n g s are moving f a r t h e r away. The other c r y o g e n i c experiments performed on N i ( P Y ) 4 ( A s F g ) 2 were the v a r i a b l e temperature v i b r a t i o n a l spectroscopy s t u d i e s and these are d i s c u s s e d i n the next s e c t i o n . 4.2.2.4.3 VIBRATIONAL SPECTROSCOPY One o b j e c t o f t h i s t h e s i s i s t o c o r r e l a t e the e f f e c t s o f d i f f e r i n g chemical environments on the observed i n f r a r e d s p e c t r a of EFg anions. As was d i s c u s s e d i n s e c t i o n 4.2.2.2, the anion environment i n N i L ^ E F g ^ compounds i s ve r y asym-m e t r i c and as i s shown i n S e c t i o n 4.2.2.3, t h i s i s probably p a r t i a l l y due t o weak c a t i o n - a n i o n , n i c k e l ( I I ) - E F g , i n t e r -a c t i o n . In the N i ( p y ) ^ ( A s F g ) 2 case to be d i s c u s s e d i n t h i s s e c t i o n , the d i f f e r e n c e s i n the i n f r a r e d s p e c t r a between a weakly c o o r d i n a t e d and more s t r o n g l y c o o r d i n a t e d h e x a f l u o r o -a r s e n a t e s p e c i e s can be examined. Since we have shown i n s e c t i o n 4.2.2.4.1 t h a t the low temperature i s o m e r i z a t i o n of N i (py) ^  (AsFg) ^  'is no't 100% e f f i c i e n t we would expect to see i n both the i n f r a r e d and -192-Raman s p e c t r a the s p e c t r a o f both isomers i n the low temper-a t u r e spectrum. The d i f f e r e n c e between the room termperature and the low temperature spectrum of N i ( p y ) ^ ( A s F g ) 2 i s due to the low temperature isomer. The v i b r a t i o n a l s p e c t r a l data f o r N i ( p y ) 4 ( A s F g ) 2 are t a b u l a t e d i n T a b l e IV-7. The r a t h e r b o u n t i f u l i n f r a r e d data w i l l be c o n s i d e r e d f i r s t and then the Raman s p e c t r a w i l l be d i s c u s s e d . The i n f r a r e d s p e c t r a were o b t a i n e d on powdered samples and because o f C h r i s t i a n s e n s c a t t e r i n g the s p e c t r a show good r e s o l u t i o n o n l y below 1000 cm 1 . The i n f r a r e d s p e c t r a (900-300 cm - 1) of N i ( p y ) 4 ( A s F g ) 2 a t 300 and 80 K are shown i n F i g u r e 4.7. D i f f e r e n c e s i n the observed anion v i b r a t i o n s and i n the 16 b v i b r a t i o n o f p y r i d i n e are p a r t i c u l a r l y n o t i c e -a b l e i n the two s p e c t r a . The d i f f e r e n c e s i n the v 2 ( E g ) A s F g and 16b p y r i d i n e v i b r a t i o n s o f the two isomers show some i n t e r e s t i n g f e a t u r e s . The band a t 5-66 cm 1 i n the room temperature spectrum i s as s i g n e d t o v 2 ( E g ) a n < ^ x n t n e 80K spectrum t h i s band i s s t i l l p r e s e n t and a l s o a new band appears a t 533 cm 1 . I f s u c c e s s i v e scans are performed i n the 500-600 -cm 1 r e g i o n when the s o l i d sample i s c o o l i n g from room temperature t o 80K, the 566 cm 1 band i s found t o decrease i n i n t e n s i t y w h i le the 533 cm 1 band i n c r e a s e s i n i n t e n s i t y . Since the sample i s c o o l i n g , t here must be r e l a t i v e l y l e s s o f the h i g h temperature and more of the low temperature isomer as the temperature i s lowered; t h i s new band i s t t h e r e f o r e be v 2 or a component of v 2 o f the c o o r d i n a t e d mu; -193-TABLE IV-7 VIBRATIONAL SPECTRAL DATA FOR N i ( p y ) 4 ( A s F g ) 2 ASSIGNMENTS (b) INFRARED RAMAN 300K 80K 300K 80K (i)ANION \) (A. ) — ( a ) — ( a ) 680(3) 703 (1) 1 l g 678(1) v (E ) 566m 562w n.o. n.o. 2 g 533m v (T, ) 695 vs,L705sh 3 l u b r 685vs br 660sh 370(2) 367(1) v,(T, ) 398vs 390vs 4 l u V 5 ( T 2 g ) ( i i ) PYRIDINE 9a 1218m 1212m 15 1155m 1145m 18a 1068m 1060m 1030(10) 1023(10) 4 762s 755s 6a (a) 632m 654(3) 653(1) 16b 471m 465w 432w (a) p o s s i b l y obscured by v 3 ( T l u ) o f A s F g (k) numbers i n br a c k e t s i n d i c a t e r e l a t i v e i n t e n s i t y ; the low temperature Raman spectrum hasu'more. i n t e n s e bands than the higher temperature spectrum. -194-FIGURE 4.11 INFRARED SPECTRA (800-350 cm" ) OF N i ( p y ) 4 ( A s F g ) 2 (300 and 80K) -195-A s F g s p e c i e s . The V 2 ( E ^ ) band o f A s F g appears p a r t i c u l a r l y s e n s i t i v e t o d i f f e r e n t environments t h a t A s F g must experience i n the two isomers. The same type of b e h a v i o r i s observed f o r the 470 cm ^ and 432 cm ~~ bands which are a s s i g n e d t o the 16b v i b r a t i o n of p y r i d i n e i n the h i g h and low temperature isomers r e s p e c t i v e l y . The l o w e r i n g of energy o f t h i s band i n the low temperature isomer i s s i g n i f i c a n t because i t may i n d i c a t e l e s s p y r i d i n e - n i c k e l ( I I ) i n t e r a c t i o n or at l e a s t a change i n the p i t c h of the r i n g s (towards 4 5°) i n the low temperature isomer. E i t h e r or both of these f a c t o r s would be expected f o r a change from a square p l a n a r n i c k e l ( I I ) s p e c i e s w i t h weakly c o o r d i n a t e d anions t o a t e t r a g o n a l pseudo-octahedral n i c k e l ( I I ) s p e c i e s w i t h f u l l y c o o r d i n a t e d anions. The anion v i b r a t i o n s observed a t room temperature are (T^ u) / v 4 ( T l u ) / a n d v2 ^ E g ^ t * i e f o r m e r t w o a r e f o r m a l l y allowed i n the i n f r a r e d when A s F g possesses 0^ symmetry, whereas, the l a t t e r i s not allowed. In the low temperature i n f r a r e d spectrum, i s broader and a t s l i g h t l y lower energy, v 4 i s at s l i g h t l y lower energy, and a new v 2 band appears. Another new band which appears a t 8OK may be a s s i g n e d t o the 16b v i b r a -t i o n of p y r i d i n e . Normally, i f t h e r e i s no s t r u c t u r a l change when the temperature i s lowered, the i n f r a r e d bands sharpen; t h i s i s seen by comparing the 80K and 300K s p e c t r a o f N i ( p y ) 4 ( P F g ) 2 ( F i g u r e 4.12). In c o n t r a s t , the v i b r a t i o n o f Ni (py) 4 ('AsF^) 2 -196--197-i n the low temperature spectrum i s much broader than i n the room temperature spectrum. In a d d i t i o n ; t h i s band shows some s t r u c t u r e . T h i s band i s probably composed of the "^'s of non-coordinated AsFg ( r e c a l l 25% o f the complex remains i n t h i s form even a t 80K)and c o o r d i n a t e d AsFg p l u s the (A-^) v i b r a t i o n s o f AsFg and the 6a v i b r a t i o n o f p y r i d i n e . The v i b r a t i o n i s not complicated by o t h e r v i b r a t i o n s and shows a s l i g h t broadening and s h i f t to lower energy on c o o l i n g . N e i t h e r the nor the bands show r e a l l y s i g n i f i c a n t changes because o f the s i m i l a r i t y o f the v i b r a t i o n s f o r the two types of AsFg and a l s o because of the poor r e s o l u t i o n a f f o r d e d by the s o l i d s t a t e spectrum. The Raman s p e c t r a l data f o r N i ( p y ) ^ ( A s F g ) 2 recorded i n Table IV-7 do not show any l a r g e s h i f t s i n band p o s i t i o n but the i n t e n s i t y o f the bands i n the 80K spectrum i s g r e a t e r and the b a s e l i n e b e h a v i o r i s d i f f e r e n t from t h a t o f the 3 00K spectrum. T h i s b ehavior i s not observed i n the 3 00 and 8OK Raman s p e c t r a o f the n o n - i s o m e r i z i n g compound N i ( p y ) 4 ( P F g ) 2 . The phenomenon observed i s probably due to the d i f f e r e n c e s i n the e l e c t r o n i c s t r u c t u r e s of the low temperature isomer of N i ( p y ) 4 ( A s F g ) 2 compared t o t h a t o f the N i L ^ ( E F g ) 2 complexes g e n e r a l l y . The N i L ^ ( E F g ) 2 compounds do not g e n e r a l l y g i v e a c c e p t a b l e Raman s p e c t r a w i t h the 540 nm e x c i t i n g l i n e , probably due t o the f a c t t h a t these compounds absorb energy of t h i s wave-l e n g t h . The low temperature form o f N i ( p y ) 4 ( A s F g ) 2 does not -198-absorb v e r y s t r o n g l y a t t h i s wavelength (Figure 4 . 7 ) and t h e r e f o r e s c a t t e r s w e l l and g i v e s a reasonable Raman spectrui The observed Raman spectrum can be co n s i d e r e d to be due o n l y to the low temperature isomer of N i ( p y ) 4 ( A s F g ) 2 . -199-4.2.2.5 THERMAL STUDIES We d e s c r i b e here some s t u d i e s made on samples of N i L 4 ( E F g ) 2 compounds which were prepared by thermal decomposi-t i o n . P r e v i o u s work p u b l i s h e d by o t h e r workers on the N i ( p y ) 4 ( P F g ) 2 and N i ( 4 m e p y ) 4 ( P F g ) 2 compounds i n v o l v e d i s o l a t i o n from p r e c u r s o r s by h e a t i n g t o 100°C " i n vacuo" (14) . The r e s u l t s o f t h i s s e c t i o n p r o v i d e s u p p o r t i n g evidence f o r our c o n t e n t i o n t h a t these c o n d i t i o n s are not s a t i s f a c t o r y f o r pure compounds of t h i s type. The v a r i a b l e , t e m p e r a t u r e magnetic s u s c e p t i b i l i t i e s o f d i f f e r e n t samples o f N i ( 4 m e p y ) 4 ( P F g ) 2 (each i n v o l v i n g d i f -f e r e n t h e a t i n g temperatures and l e n g t h of h e a t i n g time i n t h e i r p r e p a r a t i o n ) w i l l be examined. The decomposition products formed by h e a t i n g samples o f N i L 4 ( E F g ) 2 (and r e l a t e d c o b a l t and copper complexes f o r comparison) a t e l e v a t e d temperatures w i l l a l s o be d i s c u s s e d here. F i n a l l y , as an i n t e r e s t i n g s i d e l i g h t , the p r e p a r a t i o n o f samples of N i ( p y ) 4 ( A s F g ) 2 by thermal means w i l l be d i s c u s s e d ; t h i s m a t e r i a l was found hot. t o • e x h i b i t the low temperature i s o m e r i z a t i o n which c h a r a c t e r i z e s the behavior o f pure N i ( p y ) 4 ( A s F g ) 2 as d e s c r i b e d i n s e c t i o n 4.2.2.4. 4.2.2.5.1 THERMAL PREPARATIONS OF N i ( 4 m e p y ) 4 ( P F g ) 2 AND MAGNETIC PROPERTIES OF PRODUCTS The v a r i a b l e temperature magnetic s u s c e p t i b i l i t y of the t i t l e compound has been s t u d i e d as a f u n c t i o n of h e a t i n g -200-time and temperature used i n i t s . p r e p a r a t i o n . - The-magnetic suscep-t i b i l i t i e s o f these "thermal" p r e p a r a t i o n s and o f " r e c r v s t a l -l i z e d " Ni(4mepy)^(PFg) 2 are i l l u s t r a t e d i n F i g u r e 4.13. The pure ( " r e c r y s t a l l i z e d " ) sample.has what i s b a s i c a l l y a.temperature — 6 3 — 1 independent paramagnetism ( t . i . p . ) o f 60 xlO cm - mole ; whereas, the "impure" (thermal p r e p a r a t i o n s ) Ni(4mepy)^(PFg)2 sample have t h i s t . i . p . p l u s a superimposed paramagnetic s u s c e p t i b i l i t y a t lower temperatures. An a n a l y s i s o f t h i s magnetic behavior assuming t . i . p . p l u s an i m p u r i t y c o n t r i b u t i o n (impurity assumed t o be a s p i n - f r e e n i c k e l ( I I ) s p e c i e s w i t h u e £ £ o f 3.0 B.M.) g i v e s the f r a c t i o n o f paramagnetic i m p u r i t y as 0.05, 0.13, and 0.15 f o r three samples l a b e l l e d a, b, and c, r e s p e c t i v e l y , i n Table VI-4,(p.275 ). I t i s d i f f i c u l t t o be c e r t a i n about the assignment of these magnetic p r o p e r t i e s . The l i m i t e d temperature range (300-77K) and the l i m i t e d accuracy of f o r c e methods f o r measuring diamagnetic s u s c e p t i b i l i t i e s are sources o f e r r o r which should be taken i n t o account. I f the i m p u r i t y i s a complex w i t h b r i d g i n g f l u o r i d e s (as i s i n d i c a t e d by the thermal degradation s t u d i e s , s e c t i o n 4.2.2.5.2) there i s the p o s s i b i l i t y o f a mag-n e t i c a l l y c o n c e n t r a t e d system p r o v i d i n g the i m p u r i t y c o n t r i b -u t i o n . Regardless, i t i s c l e a r t h a t some type of i m p u r i t y i s pres e n t i n the samples when heat i s used i n t h e i r p r e p a r a t i o n s . -201-I Q ,P , , , TEMPERATURE ( i n K e l v i n s ) FIGURE 4.13 MAGNETIC SUSCEPTIBILITY OF THE THERMAL PREPARATIONS OF Ni(4mepy)^(PFg)2 ( The p r e p a r a t i v e method of a,b,and c are giv e n i n Table IV-4 , the p r e p a r a t i v e method of d i s g i v e n i n s e c t i o n 6.2.3.8) -202-4.2.2.5.2 THERMAL DECOMPOSITION STUDIES OF M L 4 ( E F g ) 2 As mentioned i n s e c t i o n 4.2.1, w h e n ' N i ( p y ) 4 ( P F g ) 2 or N i ( 4 m e p y ) 4 ( P F g ) 2 i s heated a t temperatures around and g r e a t e r then 100°C, a white sublimate i s observed to form on the c o o l e r p o r t i o n s of the vacuum f l a s k . A h e a t i n g temper-a t u r e c o u l d be found f o r each N i L 4 ( E F g ) 2 compound where copious amounts o f white m a t e r i a l sublimes. T h i s temperature i s g r e a t e r than 100°C whereas the i s o l a t e d white m a t e r i a l i t s e l f sublimes a t temperatures l e s s than 100°C.; T h i s : i n d i c a t e s t h a t the white m a t e r i a l i s not a c o n s t i t u e n t p a r t of the complex but i s formed as a decomposition product. In s e c t i o n 6.2.5, the decomposition c o n d i t i o n s and the elemental analyses (C,H,N) from the r e s i d u e s and sublimates r e s u l t i n g from the thermal decomposition of the N i L 4 ( E F g ) 2 are shown. The a n a l y t i c a l , i n f r a r e d s p e c t r a l , and mass spec-t r o m e t r i c evidence suggest t h a t the decomposition i s of the form: - • N i L 4 ( E F 6 ) 2 ->• N i L x ( E F 6 ) F + L" EF^ +(3-x)L The r e s i d u e i s N i L x ( E F g ) F and the white sublimate i s LEF,.. T h i s would seem t o r e p r e s e n t a somewhat s i m p l i f i e d view of the o v e r a l l decomposition r e a c t i o n , however, as the elemental analyses do not agree e x a c t l y w i t h the i n d i c a t e d products (see s e c t i o n 6.2.5). Supporting evidence f o r these proposed -203-products of r e a c t i o n comes from the i n f r a r e d s p e c t r a l data on the sublimates and r e s i d u e s and from the mass s p e c t r a o f the sublimates. The i n f r a r e d s p e c t r a o f NiL (EF,)F i n d i c a t e : X D the presence of a L moiety which i s i n a d i f f e r e n t chemical environment from t h a t o f the p r e c u r s o r ( N i L 4 ( E F g ) 2 ) ; the presence o f an " i o n i c " EFg ( i . e . the bands are s i m i l a r t o those observed i n the compounds d e s c r i b e d i n Chapter 3 )'; and the presence of a new type of compound i s i n d i c a t e d because of the o b s e r v a t i o n of a weak, broad band centered a t approximately 400 cm ^. T h i s band can be assigned t o v(Ni-F) s i n c e a band i n t h i s r e g i o n has been assig n e d t o t h i s v i b r a t i o n i n K N i F 3 (122) . The i n f r a r e d s p e c t r a o f the sublimates show the presence o f bands which are s i m i l a r t o those expected f o r E F ~ but, because of the mass s p e c t r a l evidence, which must b be a s s i g n e d t o the s k e l e t a l v i b r a t i o n s o f the LEF,- s p e c i e s . The bands t h a t are assig n e d t o the L moiety are d i f f e r e n t from those o f the p r e c u r s o r and the r e s i d u e ; Table IV-8 g i v e s the assignments o f the i n f r a r e d s p e c t r a of the r e s i d u e and sublimate from N i ( p y ) 4 ( P F g ) 2 heated t o 154°C " i n vacuo". The mass s p e c t r a o f the sublimates pyPF^, pyAsF,., and 4mepyPF 5 are r e p r e s e n t e d i n Tables IV-9, IV-10, and IV-11, r e s p e c t i v e l y . The peak w i t h the h i g h e s t (m/e) r a t i o may be assign e d to the s p e c i e s LEF,- +. Other peaks may be assigned -204-TABLE IV-8 INFRARED SPECTRAL DATA FOR N i (py) .(PF ) SUBLIMATE AND RESIDUE ASSIGNMENT ** SUBLIMATE RESIDUE 8a 1625s 1610m 8b 1580w n.o. 9a 1231m 1230m 15 1168m 1160m 18a 1090s 1080m-s 12 1050m-s V,(NPF C) ? 870vs,br 3 5 810vs,br V T l u } P F 6 1020w 850vs 4_ 715s 760s 11 715s 700s 6a 685s 640s v.(T, ) PF ~ 560s 4 l u 6 v.fNPF..)? 540vs,br,asy 4 o 16b 420vw 431m + v (Ni-F) 420 w ,vbr ** p y r i d i n e assignment u n l e s s otherwise i n d i c a t e d -205-TABLE IV - 9 MASS SPECTRAL DATA FOR pyPF m/e RATIO 187 186 185 107 104 88 85 80 79 78 77 76 75 RELATIVE HEIGHT* 7 6 0 ( p y P F 4 + ) 3 1 0 0(PF 4 +) 10 6 ( P F 3 + ) 7 13 100(py +) 17 3 4 5 m/e RATIO 69 53 52 51 50 49 45 39 38 37 32 31 RELATIVE HEIGHT* 4 14 60 30 10 6 3 14 6 3 15 3 *Assignment when a p p l i c a b l e i s i n b r a c k e t s -206-TABLE IV- 10 MASS SPECTRAL DATA FOR pyAsF m/e RELATIVE m/e RELATIVE RATIO HEIGHT* RATIO HEIGHT* 231 6 76 2 230 8 9 ( p y A s F 5 + ) 75 2 153 2 71 2 151 7 ( A s F c + ) 69 2 149 2 57 1 147 2 56 1 135 3 55 1 132 2 ( A s F 4 + ) 53 5 131 2 52 33 113 4 ( A s F 3 + ) 51 19 106 2 50 9 103 2 49 2 101 3 44 2 87 2 43 2 85 4 42 2 80 6 39 14 79 100(py +) 38 . 2 78 9 32 16 77 2 * Assignment when a p p l i c a b l e i n b r a c k e t s -207-TABLE IV-11 MASS SPECTRAL DATA FOR 4mepyPFr. m/e RELATIVE m/e RELATIVE RATIO HEIGHT* RATIO HEIGHT* 201 1 200 13(4mepyPF 4 +) 64 3 107 5 0 ( P F 4 + ) 63 5 104 1 62 2 95 1 61 1 94 12 54 6 93 100(4mepy +) 53 5 92 1 52 4 91 2 51 6 88 5 ( P F 3 + ) 50 4 78 2 ' 41 1 69 1 40 1 67 20 39 1 66 14 38 1 65 12 37 1 * Assignment when a p p l i c a b l e i s i n b r a c k e t s -208-to EF^ + , EF^"1", and the fragmentation p a t t e r n o f the L moiety. In c o n c l u s i o n t h i s evidence suggest t h a t the main component of the white sublimate from these thermal decomposition r e a c t i o n s i s a m a t e r i a l of the composition LEFr . . The LEFp. compounds, adducts o f pentafluorophosphorus (V) and p e n t a f l u o r o a r s e n i c (V) , are not unknown (12 3 ) . The c r y s t a l and molecular s t r u c t u r e of py'PFj-, prepared by bub-b l i n g PF^ (g) through an a c e t o n i t r i l e s o l u t i o n c o n t a i n i n g p y r i d i n e , has been determined 0-24). We have known t h a t the use o f " i n vacuo" h e a t i n g from p r e c u r s o r s i s u n s a t i s f a c t o r y f o r the p r e p a r a t i o n of pure samples of N i L 4 ( E F g ) 2 complexes. The same q u a l i f i c a t i o n has not been made f o r the p r e p a r a t i o n of c o b a l t ( I I ) and c o p p e r ( I I ) complexes, M L 4 ( E F g ) 2 , s t u d i e d here. Even though the d i f f e r e n t i a l thermo-grams are s i m i l a r i n nature f o r a l l these complexes, M(py)^-( P F g ) 2 (where M=N, Co and Cu) , as shown i n F i g u r e 4.14, there are some d i f f e r e n c e s . These d i f f e r e n c e s are i n the products formed at the decomposition temperature and i n the f a c t t h a t there appears not to be any s i g n i f i c a n t amount o f decomposition below the c r i t i c a l decomposition temperatures f o r the c o p p e r ( I I ) and c o b a l t ( I I ) complexes. The work on these compounds i s not comprehensive but some o b s e r v a t i o n s w i l l be r e p o r t e d . When C o ( p y ) ^ ( P F g ) 2 i s heated a t 145°C " i n vacuo", a white sublimate forms and a l i g h t pink r e s i d u e i s l e f t i n the r e a c t i o n f l a s k . The mass spectrum i n d i c a t e s the white m a t e r i a l i s pyPFj.'., but the -209-FIGURE 4.14 DIFFERENTIAL THERMOGRAMS OF M 1 (py) . (PF ) -210-i n f r a r e d spectrum o f the r e s i d u e i n d i c a t e s t h a t t h e r e i s no py or PFg s p e c i e s p r e s e n t ; i n f a c t only a broad band ^ 400 cm 1 i s observed, s u g g e s t i n g the r e s i d u e to be C 0 F 2 . The o v e r a l l decomposition r e a c t i o n i s presented below C o ( p y ) 4 ( P F g ) 2 £ C oF 2 + 2py'PF 5 + 2py When C u ( p y ) 4 ( P F g ) 2 was heated to 156°C, the decomposition d i d not look " c l e a n " . The m a t e r i a l which sublimed was a mixture of white and b l u e - p u r p l e components and the r e s i d u e was a non-homogeneous mixture o f brown, b l a c k , and y e l l o w m a t e r i a l s . Important from the p o i n t o f view of the s y n t h e t i c work, t h e r e was no evidence to suggest t h a t the h e a t i n g of the C o L 4 ( E F g ) 2 and C u L . ( E F r ) n t o 80-90°C and 40°C, r e s p e c t i v e l y , (the c o n d i t i o n s 4 0 z used t o prepare these compounds) r e s u l t e d i n an s i g n i f i c a n t amount of decomposition. Thus, by comparison w i t h our thermal s t u d i e s on the n i c k e l ( I I ) c o m p l e x e s , the chemistry of the thermal decomposition r e a c t i o n s of the c o b a l t ( I I ) and copper(II) complexes are seen t o be q u i t e d i f f e r e n t . More work on the i d e n t i f i c a t i o n o f the products o f these thermal decomposition r e a c t i o n s should be done. 4.2.2.5.3 THERMAL PREPARATION OF N i ( p y ) 4 ( A s F g ) ^ AND PROPERTIES OF THIS MATERIAL The c h a r a c t e r i z a t i o n of N i ( p y ) 4 ( A s F g ) ^ ( s e c t i o n 4.2.2.4) r e v e a l e d some r a t h e r n o v e l low temperature p r o p e r t i e s . T h i s -211-compound ( h e r e a f t e r r e f e r r e d t o as the a form) was prepared from Ni(py)g(AsFg) 2 by c r y s t a l l i z a t i o n by s t i r r i n g i n CHCl^- We found, however, t h a t when N i ( p y ) f i ( A s F g ) 2 i s heated at 60°C f o r 24 hours, a new form (3) of Ni(py)^(AsFg) 2, i s obtained which does not have the p r o p e r t i e s d e s c r i b e d i n s e c t i o n 4.2.2.4, but r a t h e r behaves much l i k e the o t h e r N i L ^ f E F g ^ compounds d e s c r i b e d i n t h i s c h a p ter. F i g u r e 4.15 shows the v a r i a b l e temperature magnetic s u s c e p t i b i l i t i e s o f these two forms. The p r o p e r t i e s o f these a and 3 forms of N i ( p y ) ^ -(AsFg)2 show some i n t e r e s t i n g f e a t u r e s . When the a form i s heated t o 60°C " i n vacuo" f o r 24 hours ( c o n d i t i o n s used i n the p r e p a r a t i o n of the 3 form) i t r e t a i n s the p r o p e r t i e s of the a form. In an attempt to i n v e s t i g a t e f u r t h e r the s t r u c t u r a l d i f f e r e n c e s of the a and 3 forms we o b t a i n e d X-ray powder photographs f o r the two forms and, f o r comparison, f o r the r e l a t e d complex, N i ( 4 m e p y ) 4 ( P F g ) 2 • The d-spacings are shown i n Table IV-12 . The d i f f r a c t i o n p a t t e r n s of the a and 3 forms of N i ( p y ) 4 ( A s F g ) 2 are very s i m i l a r i n nature although there are some d i f f e r e n c e s i n the d-spacings. I t i s d i f f i c u l t t o use t h i s technique f o r a - q u a n t i t a t i v e d i s c u s s i o n o f l a t t i c e s t r u c t u r e because N i ( p y ) ^ ( A s F g ) 2 probably has too low a l a t t i c e symmetry. I t seems the s t r u c t u r e s are s i m i l a r but not i d e n t i c a l . Some i n t e r e s t i n g f e a t u r e s of the i s o m e r i z a t i o n of the a form emerge when the low temperature i n f r a r e d and e l e c t r o n i c s p e c t r a are o b t a i n e d on mulled samples. There i s no n o t i c e a b l e change i n the e l e c t r o n i c spectrum o f a mulled sample on c o o l i n g -212-10% (cm3 mol"') 2 ^ 1 6 0 T(K) 2 6 0 300 FIGURE 4.15 MAGNETIC SUSCEPTIBILITY OF THE a AND 3 FORMS OF N i ( p y ) 4 ( A s F g ) 2 ( The c i r c l e s are the data p o i n t s f o r the a form and the t r i a n g l e s those of the 6 form) -213-TABLE IV-12 D-SPACINGS OF N i ( p y ) 4 ( A s F g ) 2 (a and g forms) AND N i ( 4 m e p y ) 4 ( P F g ) 2 N i ( p y ) 4 ( A s F g ) 2 Ni ( p y ) 4 ( A s F g ) 2 Ni(4mepy) 4 1 a B 1 8.66 m-s 8.64 m-s 9.62 m-s 2 7.62 s 7.60 s 8.79 s 3 7.11 s 7.10 s 8.09 vs 4 6.39 vs 6.16 vs,b r 7.4 6 w 5 5.96 vs 5.95 vs,b r 6.91 s 6 5.45 vw 5.45 w 6.26 w 7 4.98 s 4 . 95m 5.67 vs 8 4.69 m-s 4.65m 5.40 vs 9 4.39 vs,b r 4.48 s 4.79 s 10 4.19 vs 4.15 s 4.57 w 11 4.00 m 3.98 m 4.38 s 12 3.53 w 3.53 w 4 .16 vs 13 3.31 m 3.28m 4.02 vw 14 2.97 w 3.13 w 3.65 w-m 15 2.98 w 3.54 s 16 3.26 w 17 3.12 w -214-to l i q u i d n i t r o g e n temperatures. Moreover, the change i n the i n f r a r e d spectrum on c o o l i n g i s not as n o t i c e a b l e w i t h the mulled sample as w i t h the powdered sample (although the v~(E ) z g o f AsF ~ a t 570 cm ~~ ( s e c t i o n 4.2.3.3) does appear i n the b spectrum). These two o b s e r v a t i o n s suggest t h a t the isomer-i z a t i o n o f the a form doesn't go as e f f i c i e n t l y i n the mulled s t a t e as i n the powder. How are the mulled forms of a and B r e l a t e d ? The i s o m e r i z a t i o n o f a must be a s o l i d s t a t e e f f e c t , the e f f i c i e n c y of which must be r e l a t e d to r e g u l a r i t y o f the c r y s t a l l i n e l a t -t i c e . The m u l l i n g o f the a form must r e s u l t i n N i ( P Y )A (AsF,)- c l u s t e r s i n an i n e r t m atrix which l e s s e n s any 4 b Z l a t t i c e c o o p e r a t i v i t y e f f e c t s . I t i s l i k e l y t h a t the 3 form, which i s formed by thermal means, has a more d i s o r d e r e d l a t t i c e than the a form (which was o b t a i n e d by what can be c o n s i d e r e d t o be a c r y s t a l l i z a t i o n p r o c e s s ) . Hence, because o f i t s d i s o r d e r e d l a t t i c e , the B form, whether as a powder o r mulled w i l l not undergo i s o m e r i z a t i o n . The l a t t e r process r e q u i r e s a r e g u l a r l a t t i c e which i s present only i n the m i c r o c r y s t a l l i n e a powder. -215-4.2.3 FACTORS DETERMINING ANION COORDINATION IN N i L 4 A 2 COMPOUNDS In the p r e c e d i n g d i s c u s s i o n s of s e c t i o n s 4.2.2.1 and 4.2.2.2 we pro v i d e d evidence t h a t the s t r u c t u r e s o f the complexes N i ( p y ) 4 ( P F 6 ) 2 , N i ( 4 m e p y ) 4 ( P F 6 ) 2 , N i ( 4 m e p y ) 4 ( A s F g ) 2 , and N i ( 3 m e p y ) 4 ( A s F g ) 2 i n v o l v e square p l a n a r n i c k e l ( I I ) s p e c i e s w i t h the anions very weakly c o o r d i n a t e d i n a x i a l p o s i t i o n s . We a l s o p o i n t e d out t h a t they c o u l d be c o n s i d e r e d as s t r o n g l y t e t r a g o n a l l y d i s t o r t e d o c t a h e d r a l complexes. These s t r u c t u r e s are maintained over the temperature range 80 to 300 K. The c l o s e l y r e l a t e d complex, N i ( p y ) 4 ( A s F g ) 2 , i s q u i t e unique, how-ever. At room temperature, the anions are onl y very weakly c o o r d i n a t e d as f o r the other N i L 4 ( E F g ) 2 compounds wh i l e a t lower temperatures, another isomer i s formed i n which the anions become more s t r o n g l y c o o r d i n a t e d . I t seems a p p r o p r i a t e a t t h i s p o i n t to b r i e f l y review the l i t e r a t u r e o f the r e l a t e d N i L 4 A 2 complexes g e n e r a l l y i n an e f f o r t t o i d e n t i f y f a c t o r s t h a t determine whether or not the anion i s c o o r d i n a t e d i n such com-p l e x e s . T h i s p o i n t was a l l u d e d to i n s e c t i o n 4.1. A review of the l i t e r a t u r e shows t h a t s e v e r a l compounds of the types, N i L A-, (where L i s a p y r i d i n e o r s u b s t i t u t e d p y r i d i n e and A i s an a n i o n i c s p e c i e s ) have been c h a r a c t e r i z e d and show a v a r i e t y o f s t e r e o c h e m i s t r i e s around n i c k e l depending upon L and A (and s t o i c h i o m e t r y , x ) . We w i l l c o n s i d e r o n l y -216-t h o s e cases when x i s 4 because t h e s e a r e a p p r o p r i a t e f o r t h i s d i s c u s s i o n . Here t h e p s e u d o - o c t a h e d r a l and square p l a n a r s t e r e o c h e m i s t r i e s a r e predominant. Some N i L ^ A 2 compounds i n w h i c h L i s p y r i d i n e have been a s s i g n e d a t r a n s - " o c t a h e d r a l " c o o r d i n a t i o n N iN^A 2; t h e a n i o n s (A) b e i n g B F ^ - (16 ) , C10 4~ (16 ) , Re0 4~ (125), NCS~ (126) , NCO~ (126) , F S 0 3 ~ (121) , CF^.COO" (128) ,,"l"(127) , C l " (127)-, Br (127). Other p y r i d i n e complexes have square p l a n a r co-o r d i n a t i o n g e o m e t r i e s about n i c k e l ( I I ) and n o n - c o o r d i n a t e d o r o n l y v e r y weakly c o o r d i n a t e d a n i o n s ; some examples o f t h e s e are when t h e a n i o n i c s p e c i e s p r e s e n t i s I ^ (129), Sn(NCS)g (13 0 ) , and E F g - ( s t u d i e d h e r e ) . The n a t u r e o f L a l s o has an e f f e c t on t h e s t r u c t u r e o f t h e complex, w i t h t h i s e f f e c t most w i d e l y s t u d i e d i n t h e n i c k e l ( I I ) p e r c h l o r a t e complexes, N i L 4 ( C l 0 4 ) 2 (19 - 2 2 ) . When L i s p y r i d i n e , 3 - b r o m o p y r i d i n e , 4 - i s o p r o p y l p y r i d i n e , and 3 , 5 - d i m e t h y l p y r i d i n e (see s e c t i o n 4.1), t h e p e r c h l o r a t e anions' a r e c o o r d i n a t e d . When L i s 4 - m e t h y l p y r i d i n e , 4 - a m i n o p y r i d i n e , o r 3 , 4 - d i m e t h y l p y r i d i n e ( s e c t i o n 4.1), t h e p e r c h l o r a t e a n i o n s a r e n o t c o o r d i n a t e d . When L i s 3 - m e t h y l p y r i d i n e (21 ), t h e p e r c h l o r a t e a n i o n s may o r may not be c o o r d i n a t e d depending upon t h e method o f p r e p a r a t i o n ; r e f l u x i n g N i ( 3 m e p y ) 4 ( H 2 0 ) 2 ( C 1 0 4 ) 2 i n a benzene-2,2-dimethoxypropane m i x t u r e g i v e s t h e compound w i t h c o o r d i n a t e d p e r c h l o r a t e and vacuum d r y i n g o f N i ( 3 m e p y ) 4 ~ -217-(H 20) 2(C10 4) 2 g i v e s the compound w i t h non-coordinated anions. The b a s i c i t i e s of these L m o i e t i e s (131, 96) are arranged i n order of i n c r e a s i n g b a s i c i t y (pKa's i n brackets)below: 3-Brpy(2.84)< py(5.12)<3mepy(5.68)<4-isopropylpy(6.02) Mmepy (6 . 02l<3 ,5-dimepy (6 .15) <3 ,4-dimepy (6 . 46) < 4aminopy(8.96) The b a s i c i t i e s of the L m o i e t i e s appear to determine i n most cases whether the anion c o o r d i n a t e s t o the metal i o n . G e n e r a l l y when the base s t r e n g t h of L i s l e s s than t h a t o f 3mepy, the anions are c o o r d i n a t e d and when more then t h a t of 3mepy, the anions are not c o o r d i n a t e d i n the NiL^A2 complexes. When L i s 3mepy, the s o l i d s t r u c t u r e i s v a r i a b l e . One o f the exce p t i o n s t o t h i s r u l e i s when -L i s 3,5 - d i m e t h y l p y r i d i n e . T h i s case along w i t h the one where L i s 3-methylpyridine have some i n t e r e s t i n g s o l u t i o n chemistry. When e i t h e r form of N i ( 3 m e p y ) 4 ( C 1 0 4 ) 2 i s d i s s o l v e d i n d i c h l o r o -methane, an i d e n t i c a l mixture of the square p l a n a r and o c t a h e d r a l forms i s obt a i n e d . When Ni (3 , i 5-dimepy) 4 (C10 4 ) 2 i which has o c t a h e d r a l c o o r d i n a t i o n i n the s o l i d s t a t e , i s d i s s o l v e d i n dichloromethane the e l e c t r o n i c spectrum i n d i c a t e s the presence of a square p l a n a r n i c k e l ( I I ) complex. These N i L 4 ( C l 0 4 ) 2 complexes, then, have d i f f e r e n t p r o p e r t i e s i n the s o l i d s t a t e than i n s o l u t i o n . The s o l u t i o n p r o p e r t i e s o f these two complexes, when taken i n t o account conform w e l l w i t h the c o r r e l a t i o n o f b a s i c i t y of L and the o v e r a l l s t e r e o c h e m i s t r y o f the complex. But the f a c t t h a t the s t r u c t u r e s i n s o l u t i o n and s o l i d s t a t e are d i f f e r e n t when L i s 3-methylpyridine and -218-3 , 5 - d i m e t h y l p y r i d i n e does suggest t h a t l a t t i c e e n e r g i e s may have some e f f e c t on the s t r u c t u r e p r e s e n t . In f a c t , the authors (115) who r e p o r t e d the mol e c u l a r s t r u c t u r e of Ni(3,5dimepy)^(ClO^) 2 were s e a r c h i n g f o r s t r u c t u r a l c l u e s f o r anomalous o c t a h e d r a l s t e r e o c h e m i s t r y (based on base s t r e n g t h of 3,5-dimethylpyridine) by comparison to the s t r u c t u r e o f Ni(3,4-dimepy)^(ClO^) 2 (which f o l l o w s the t r e n d i n b a s i c i t y o f the n e u t r a l l i g a n d ) . They were f o r c e d to conclude t h a t t h e r e was not any simple e x p l a n a t i o n but t h a t the anomalous s t r u c t u r e must be due to "secondary" valence f o r c e s o r " l a t t i c e energy e f f e c t s . " I t i s i n t e r e s t i n g t o s p e c u l a t e on the reasons t h a t Ni(PY)4(AsFg)2 undergoes the low temperature i s o m e r i z a t i o n whereas o t h e r N i L ^ f E F g ^ complexes do not. Of a l l the thr e e n e u t r a l l i g a n d s (py, 3mepy, 4mepy) p y r i d i n e i s the l e a s t b a s i c , t h e r e -f o r e , from the s t u d i e s on the p e r c h l o r a t e complexes, the p y r i d i n e complexes would be most l i k e l y to have c o o r d i n a t e d anions. But s i n c e one would expect the base s t r e n g t h o f both PFg and AsF ~ t o be approximately equal one would expect both b p y r i d i n e complexes ( N i ( p y ) 4 ( E F g ) 2 ) to have a paramagnetic form whereas o n l y one does. Comparing these p y r i d i n e complexes, the AsFg" (As-F=1.80 2 ( 5)) anions are l a r g e r than the PFg (P-F=^l.50°0 anions but any c o n s i d e r a t i o n of anion s i z e would i n v o l v e l a t t i c e energy e f f e c t s . These e f f e c t s appear t o be q u i t e s u b t l e (cf N i L 4 ( C 1 0 4 ) 2 , L=3,4dimepy and 3,5-dimepy). -219-Other f a c t o r s w h i c h may be i m p o r t a n t a r e t h e i n t r i n s i c s t r e n g t h o f E-F bonds and t h e p o l a r i z i b i l i t y o f t h e EFg a n i o n . There-f o r e , i t i s d i f f i c u l t t o a s c e r t a i n t h e o r i g i n o f t h e low tem-p e r a t u r e i s o m e r i z a t i o n of N i ( p y ) 4 ( A s F g ) 2 . However, the p o i n t i s t h a t i t does t a k e p l a c e and t h e r e s u l t s o f t h e c h a r a c t e r i z a t i o n a r e u s e f u l i n a s s i g n i n g t h e s t r u c t u r e o f t h e N i L 4 ( E F g ) 2 complexes g e n e r a l l y . F u r t h e r work w h i c h c o u l d be done on t h e N i L ^ ( E F g ) 2 would i n c l u d e t h e s y n t h e s i s , and c h a r a c t e r i z a t i o n o f complexes where L i s a s u b s t i t u t e d p y r i d i n e o f lower base s t r e n g t h t h a n p y r i d i n e . Work on t h e s e systems would show whether t h e l o w e r base s t r e n g t h o f L c o u l d f o r c e t h e EFg a n i o n s t o c o o r d i n a t e . o -220-4.3 COMPLEXES OF COPPER(II); C u L 4 ( E F g ) 2 4.3.1 INTRODUCTION The compound, C u ( p y ) 4 ( P F g ) 2 , has been s t u d i e d p r e v i o u s l y by M a y f i e l d and B u l l (14) and by McWhinnie e t a l (15). The i n t e r p r e t i o n of the e l e c t r o n i c p r o p e r t i e s o f the compound by these authors was t h a t the copper(II) i o n i s i n a d i s t o r t e d o c t a h e d r a l environment w i t h semi-coordinated (27 ) PFg anions. I t i s i n t e r e s t i n g to examine the p u b l i s h e d i n f r a r e d data on C u ( p y ) 4 ( P F g ) 2 . M a y f i e l d and B u l l s t a t e t h a t there are bands, i n the i n f r a r e d spectrum of C u ( p y ) 4 ( P F g ) 2 a t 600, 429, 407 and 391 cm 1 . They s t a t e t h a t the 429 cm 1 band can probably be a s s i g n e d t o the 16b v i b r a t i o n of p y r i d i n e (14 ). As we have noted i n s e c t i o n 2.2.4, the presence o f bands a t ^604 and ^ 403 cm 1 , i n d i c a t e the presence of non-coordinated p y r i d i n e i n the l a t t i c e and thus, i t appears t h a t there i s some doubt as to the p u r i t y o f t h i s compound. McWhinnie e t a l (15) do not r e p o r t the p r e p a r a t i v e method used nor the f u l l i n f r a r e d spectrum and, moreover, t h e r e i s some disagreement i n the a s s i g n -ment of the PFg v i b r a t i o n s i n the two r e p o r t s . We have s y n t h e s i z e d the s e r i e s o f compounds C u L 4 ( E F g ) 2 where L i s py, 4mepy, and 3mepy and E i s P and As. With-these -221-combinations of n e u t r a l l i g a n d s and anions, i t i s p o s s i b l e to o b t a i n an unambiguous assignment o f the anion bands. As the d e s c r i p t i o n of the p r e p a r a t i o n s of the C u ( p y ) ^ ( E F g ) 2 complexes ( s e c t i o n 6.2.1.8-.9) i n d i c a t e , h e a t i n g at 40°C " i n vacuo" was n e c e s s r y to remove l a t t i c e p y r i d i n e (bands a t ^600 and ^400 cm ^ i n the i n f r a r e d spectrum d i s a p p e a r ) . A l s o , more d i l u t e s o l u t i o n s had to be used i n the p r e p a r a t i o f the Cu(4mepy)^(EFg)2 compounds i n o r d e r to o b t a i n "pure" m a t e r i a l s ( s e c t i o n 6.2.2.8-.9). -222-4.3.2 RESULTS AND DISCUSSION T h i s s e c t i o n w i l l d i s c u s s the r e s u l t s of our s t u d i e s on the C u L 4 ( E F g ) 2 complexes. F i r s t the r e s u l t s of the magnetic s u s c e p t i b i l i t y measurements w i l l be d i s c u s s e d b r i e f l y . Then, the e l e c t r o n i c s p e c t r a l and e l e c t r o n s p i n resonance data w i l l be presented and d i s c u s s e d w i t h r e f e r e n c e to p r e v i o u s work on o t h e r copper(II) complexes. F i n a l l y , the i n f r a r e d s p e c t r a l data w i l l be presented and d i s c u s s e d i n r e l a t i o n to the d a t a o b t a i n e d f o r the N i L 4 ( E F g ) 2 compounds of s e c t i o n 4.2 ( p a r t i c u l a r l y w i t h r e f e r e n c e t o the low temperature isomer ( N i ( p y ) 4 ( A s F g ) 2 ) spectrum, s e c t i o n 4.2.2.4.3). 4.3.2.1 MAGNETIC PROPERTIES A l l of these C u L 4 ( E F g ) 2 compounds have magnetic moments i n the range o f 1.8-2.0 B.M. (see Appendix 2) i n d i c a t i v e of m a g n e t i c a l l y d i l u t e copper(II) systems. -223-4.3.2.2 ELECTRONIC SPECTRAL PROPERTIES Table I V - 1 3 1 i s t s the e l e c t r o n i c s p e c t r a l data f o r the t i t l e compounds. The s p e c t r a c o n s i s t of a broad, asym-m e t r i c band centered i n the v i s i b l e r e g i o n . A c c o r d i n g t o Hathaways c o r r e l a t i o n diagram (Figure 2.7 p. 53 ), the a b s o r p t i o n maxima are c o n s i s t e n t w i t h an a x i a l l y elongated t e t r a g o n a l o c t a h e d r a l chromophore. The e x t i n c t i o n c o e f f i c i e n t s -1 -1 of the bands obtained i n the s o l u t i o n s p e c t r a ('WO M cm ) are c o n s i s t e n t w i t h t h i s t e t r a g o n a l chromophore s i n c e they are s i m i l a r to the value (e=52) observed f o r C u ( p y ) 4 ( S O ^ F ) 2 where a (trans-octahedral) t e t r a g o n a l CuN 40 2 chromophore has been p o s t u l a t e d . The band maxima observed f o r our compounds r u l e out the presence of a t e t r a h e d r a l "CuN 4" chromophore (cf F i g u r e 2.7). The square p l a n a r s t e r e o c h e m i s t r y of l i g a n d s around copper(II) i s u s u a l l y not observed u n l e s s the l i g a t i n g s p e c i e s have a g r e a t p r o p e n s i t y f o r ir-bonding (70 ). A l l of t h i s evidence supports the c o n c l u s i o n t h a t the copper(II) i o n i s i n a pseudo-octahedral environment and, g i v e n the s t o i -chiometry o f these complexes, has E F g anions a t l e a s t weakly c o o r d i n a t e d t o i t . The p r e v i o u s work on the C u ( p y ) 4 ( P F g ) 2 (14, 15) has l e d to-much the same .conclusion.. : • -Hathaway has done a gr e a t d e a l o f work on t e t r a g o n a l l y d i s t o r t e d o c t a h e d r a l complexes o f c o p p e r ( I I ) . The r e s u l t s of X-ray d i f f r a c t i o n and of s i n g l e c r y s t a l p o l a r i z e d e l e c t r o n i c -224-TABLE IV- 13 ELECTRONIC SPECTRAL DATA FOR CuL„(EF,)„ 4 6 2 BAND POSITION (kK) COMPOUND C u ( p y ) 4 ( P F 6 ) 2 (a) 18 .70 (b) 18.35 C u ( p y ) 4 (AsF 6) 2 (a) 18.70 (b) 18.18 C u ( 4 m e p y ) 4 ( P F 6 ) 2 (a) 19. 61 (b) 19.15 (c) 19.01(69) C u ( 4 m e p y ) 4 ( A s F g ) 2 (a) 19.61 (b) 18.87 -(c) 18.87(71) Cu(3mepy) 4 ( P F 6 ) 2 (a) 19.42 (b) 18. 87 (c) 19.01 (77) Cu (3mepy) 4 (AsF g) 2 (a) 19.42 (b) 18.87 (c) 18.90 (73) (a) m u l l spectrum .(b) d i f f u s e r e f l e c t a n c e spectrum (c) s o l u t i o n spectrum; molar e x t i n c t i o n c o e f f i c e n t s ( i n M^cm" 1) i n b r a c k e t s . -225-spectroscopy have been c o r r e l a t e d f o r tetraammines Cu(NH^)^X 2,(132) and b i s ( e t h y l e n e d i a m i n e ) , Cu (en) 2 X 2 ,(133 ) complexes of copper(II) (where X i s an anion w i t h a s i n g l e n e gative charge or X 2 i s an anion w i t h a (-2) ch a r g e ) . The d o r b i t a l o r d e r i n g s and the p o l a r i z a t i o n p r o p e r t i e s of the p o s s i b l e - t r a n s i t i o n s have been used t o e x p l a i n the c o r r e l a t i o n of observed(powder s p e c t r a ) a b s o r p t i o n maxima wit h the chromophore t e t r a g o n a l i t y p r e s e n t . The d o r b i t a l s p l i t t i n g i n a x i a l l y elongated t e t r a g o n a l o c t a h e d r a l geometry has been shown ( p.48) . The o r d e r i n g o f these o r b i t a l s can vary w i t h the degree of- t e t r a g o n a l d i s t o r t i o n • from 0^ symmetry. The o r d e r i n g of these l e v e l s i n o r d e r o f i n c r e a s i n g t e t r a g o n a l i t y a r e : e g < ' 3 2 g < a l g < ' : , l g ' e g < a l g < k 2 g < k l g ' and e^a^g<b 2g<b^g. These o r b i t a l o r d e r i n g s correspond to the energy l e v e l o r d e r i n g s : 2B,> 2A, >2B_ > 2E ; 2B. > 2B„ >2A, > y j r ^ l g l g 2g g' l g 2g l g 2 2 2 2 2 E^; and B i g > B 2 g > A l g ^ E g ' r e s P e c t l v e l Y • Hathaway has s t a t e d four c r i t e r i a f o r measuring the i n c r e a s e i n t e t r a g o n a l d i s t o r t i o n from t e t r a g o n a l o c t a h e d r a l geometry towards -a square p l a n a r c o n f i g u r a t i o n and they are,, as the t e t r a g o n a l i t y " i n c r e a s e s : ( i ) the high e r i s the energy of the d z2+d x2 2 2 2 . . ( B, -> A, ) t r a n s i t i o n v l g l g ' ( i i ) the h i g h e r i s the energy of the d , d 2 2 -*-d 2 2 ( B, -> E ) t r a n s i t i o n ; although to a l e s s e r x -y l g g' extent than i n ( i) - 2 2 6 -( i i i ) the s h o r t e r i s the i n - p l a n e copper-l i g a n d bond l e n g t h , R g (iv) the s m a l l e r i s the t e t r a g o n a l i t y parameter, T (=R g/R L, where P^ i n v o l v e s a c o r r e c t i o n f o r the ( a x i a l ) t e t r a g o n a l l i g a n d atom p r e s e n t . From t h e i r p o l a r i z e d 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 , Hathaway and coworkers (133) have found t h a t the band envelope i s made up 2 2 2 2 2 of the B, -*-E and B, -»- B- t r a n s i t i o n s . The B, -> E„ band l g g l g 2g l g g i s the most i n t e n s e t r a n s i t i o n p r e s e n t i n the spectrum ( i t i s a l s o the band w i t h the h i g h e s t t r a n s i t i o n energy o f any of the d-*-d t r a n s i t i o n s ) . The ot h e r bands are much weaker. The c o n c l u s i o n t h a t can be reached w i t h regard to powder e l e c t r o n i c spectroscopy i s t h a t as the v m a x i n c r e a s e s f o r the band envelope / the t e t r a g o n a l i t y o f the chromophore i n c r e a s e s . T h i s l a s t r u l e has been used to c o r r e l a t e the e l e c t r o n i c s p e c t r a l data of the Cu(py)^A 2 complexes to molecular s t r u c t u r e . T h i s i s necessary s i n c e there i s a d e f i n i t e absence of s i n g l e c r y s t a l s t u d i e s on these complexes (only Cu(py)^(CF^CC^) 2 has been s t u d i e d but o n l y r e c e n t l y (134)). Thompson and A l l e y n e have compiled the (powder) e l e c t r o n i c s p e c t r a l d a t a f o r a number of 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 c o n t a i n i n g weakly b a s i c anions. They have assumed t h a t as v of the v i s i b l e J max band i n c r e a s e s , the c o o r d i n a t i n g a b i l i t y o f the a n i o n i c s p e c i e s decreases. T h i s g i v e s r i s e to the s c a l e of c o o r d i n a t i n g a b i l i t y o f the anions (s tronger-> weaker; v (kK) i n b r a c k e t s , d i f f u s e r e f l e c t a n c e ) : -227-CF 3C0 2~(15.5)>p-CH 3CgH 2S0 3"(16.5)>S0 3F~(17.0) >BF 4~(17.7)> C10 4"(17.8)>N0 3"(18.1)>PF g~(19.1) The value f o r C u ( p y ) 4 ( P F g ) 2 i s t h a t o f M a y f i e l d and B u l l (14), whereas f o r the o t h e r complexes, two bands were observed (a s t r o n g band a t 19.1 kK and a shoulder at. 16.2 kK) . T h i s i s u n l i k e our r e s u l t s f o r the hexafluorophosphate and hexa-f l u o r o a r s e n a t e complexes where on l y one band was observed; however, M a y f i e l d a n d ' B u l l 1 s spectrum was run a t 7 7K-which might r e s u l t i n the r e s o l u t i o n of the low energy shoulder. McWhinnie et a l (15) r e p o r t the spectrum of C u ( p y ) 4 ( P F g ) 2 as c o n s i s t i n g of a main band a t 18.3 kK and a low energy shoulder a t 16.2 kK. We have not observed a low i n t e n s i t y shoulder. I t should be noted t h a t the C u ( 3 m e p y ) g ( H 2 0 ) 2 ( E F g ) 2 compounds ( s e c t i o n 3.4.2.2.5, Table 111-13 p.117) absorb i n t h i s range and presumably an aquated p y r i d i n e complex of s i m i l a r s t r u c t u r e would a l s o . I t i s d i f f i c u l t to be c e r t a i n about the p u r i t y of the C u ( p y ) 4 ( P F g ) 2 compounds p r e v i o u s l y s t u d i e d because o f the absence of p r e p a r a t i v e d e t a i l s i n the r e p o r t of McWhinnie et a l (15) and the ambiguous v i b r a t i o n a l data of M a y f i e l d and B u l l (presented i n s e c t i o n 4.3.1). N e v e r t h e l e s s , given the r e s u l t s o f Thompson and A l l e y n e (120), the v of C u ( p y ) A ( P F , ) 0 "has ; the. l a r g e s t v a l u e • (18!.3..kK, here')' of' a l l ' . " o f the" T t e t r a k i s - '/." •(-pyridine) c;Qpp.er"-(II) . complexes. The" other CuL 4 (PFg-) 2 complexes .'(where^'L'.is-- 3mepyand :-'4mepy): 'have, even larger - v a l u e s ° f . - v m a x ' The comparisons o f the v v a l u e s w i t h i n the CuL. (EF,) max 4 b z compounds show some i n t e r e s t i n g f e a t u r e s . The v m a x °f - 2 2 8 -C u ( p y ) ^ ( A s F g ) 2 i s lower i n energy (.2kK) than t h a t of Cu(py)^(PFg)2• T h i s may i n d i c a t e t h a t the h e x a f l u o r o a r s e n a t e anion i s more s t r o n g l y c o o r d i n a t e d (though s t i l l weakly) than . 1 the hexaf luorophosphate anion i n these complexes. The difference--i n X i s smal l (^ 5nm) and i t i s d i f f i c u l t t o t e l l whether t h i s i s a s i g n i f i c a n t d i f f e r e n c e . However, the v v a l u e s do :. ^ max ' seem to i n c r e a s e w i t h the L moiety p r e s e n t i n the s e r i e s : py<3mepy<4mepy; t h i s s e r i e s f o l l o w s the b a s i c i t y of the n e u t r a l l i g a n d , L, w i t h the more b a s i c l i g a n d being more s t r o n g l y bound.- Figure4.16 shows the d i f f u s e r e f l e c t a n c e s p e c t r a of' C u L „ ( P F C ) 0 f o r the three n e u t r a l l i g a n d s . 350 450 550 650 750 WAVELENGTH ( i n nm) FIGURE 4.16 VISIBLE ELECTRONIC SPECTRA OF CuL 4 I.EF g) 2 ( Spectrum I L i s 4mepy, spectrum I I L i s 3mepy, and Spectrum I I I .L i s py) -230-4.3.2.3 ELECTRON SPIN RESONANCE SPECTROSCOPY F i g u r e s 4.17 and 4.18 show the e . s . r . spectra o f Cu (py) 4 (PFg) 2 as a powder (300K) and i n s o l u t i o n .(300 and 77K) r e s p e c t i v e l y . The powder and 77K s o l u t i o n s p e c t r a have the l i n e shape expected f o r copper(II) in - an a x i a l ( D 4 n ) " o c t a h e d r a l " environment (see s e c t i o n 2.3.3.2). The l i n e shape of the 300K s o l u t i o n spectrum i s t h a t of copper (II) i n an i s o t r o p i c e n v i r o n -ment; the copper(II) complexes can tumble i n s o l u t i o n f a s t e r than the time s c a l e of the e . s . r . measurement such t h a t the observed g value i s an average o f the a x i a l v a l u e s gjj and gj. (equation 2.5, p.23). A l l o f the e . s . r . s p e c t r a of the C u L ^ t E F g ^ have the g e n e r a l f e a t u r e s of the s p e c t r a shown i n these two i l l u s t r a t i o n s . Table IV- 14 l i s t s the g v a l u e s and h y p e r f i n e c o u p l i n g constants (A and B) d e r i v e d from the s p e c t r a of the t i t l e compounds. I t should be noted t h a t the s o l u t i o n , s p e c t r a of the C u ( p y ) 4 ( E F g ) 2 are r e p o r t e d here; these compounds ar e o n l y s p a r i n g l y s o l u b l e i n dichloromethane but the parameters obtained from these s o l u t i o n s p e c t r a were s i m i l a r to those obtained from the powder spectrum i n d i c a t i v e o f the C u ( p y ) 4 ( E F g ) ^ s p e c i e s i n s o l u t i o n . The g v a l u e s obtained f o r these complexes are g r e a t e r than the g g value i n d i c a t i v e of copper(II) i n an a x i a l l y elongated t e t r a g o n a l l y d i s t o r t e d o c t a h e d r a l environment (see equations 2.12-.15 p. 52). FIGURE 4.17 E.S.R. SPECTRUM OF C u ( p y ) 4 ( P F g ) 2 AS A POWDER AT 8OK "•( * A r e f e r s t o absorbance and H r e f e r s t o magnetic f i e l d ) -232-dA/dHl FIGURE 4.18 E.S.R. SPECTRA OF Cu (py) ( P F g ) 2 IN DICHLORO-METHANE SOLUTION AT 300 AND 8OK ( * see F i g . 4.17 p.231) -233-TABLE IV- 14 E.S.R. DATA FOR CuL.(EF,) COMPOUND C u ( p y ) 4 ( P F 6 ) 2 C u ( p y ) 4 ( A s F 6 ) 2 C u ( 4 m e p y ) 4 ( P F 6 ) 2 5(1 g_L. g o (a) 2. .249 2, .054 (b) 2 , .256 2 .068 2, .128 193 31 85 84 (a) 2 .239 2 .064 -- 185 -(b) 2 .224 2 .062 2. .116 160 45 83 82 (a) 2 .239 2 .064 T "7 n X / U (b) 2 .296 2 .026 2 .116 205 25 85 84 (a) 2 .231 2 .061 1 Q K i y j (b) 2 .294 2 .030 2 .118 175 40 85 84 (a) 2 .228 2 .041 185 • (b) 2 .235 2 .058 2 .117 195 32 86 85 (a) 2 .228 2 ,055 185 • (b) 2 .223 2 .058 2 .113 195 27 83 82 6'2 (a) powder spectrum a t room temperature (b) s o l u t i o n (CH 2C1 2) s p e c t r a : g Q and A Q from room-temperature spectrum and g^and A from l i q u i d N 2 temperature spectrum g(| and B c a l c u l a t e d by use of equations 2.5 (p23) and 2.17 (p 54), r e s p e c t i v e l y (c) i n gauss (d) i n 10 4cm - 1:A(cm - 1)=A(gauss).(g/g g) 9.3484xl0~ 5 -234-I n s p e c t i o n o f e q u a t i o n 2.13 r e v e a l s t h a t gj_ i s a f u n c t i o n ( v i a s p i n - o r b i t c o u p l i n g ) o f t h e d 2 2r-d , d ^ ^ ^ x -y xy' yz s e p a r a t i o n . T h i s s e p a r a t i o n c o r r e s p o n d s t o t h e e l e c t r o n i c 2 2 t r a n s i t i o n B, E w h i c h a c c o r d i n g t o c r i t e r i o n ( i i ) (p.225) j_g g i n c r e a s e s i n energy w i t h i n c r e a s i n g t e t r a g o n a l d i s t o r t i o n . Thus, t h e v a l u e o f g ^ s h o u l d d e c r e a s e w i t h i n c r e a s i n g t e t r a g o n a l d i s t o r t i o n (assuming X stays'xeasonably c o n s t a n t i n a s e r i e s ) . 2 2 The gjj v a l u e v a r i e s w i t h t h e ^g"*" B 2 g t r a n s i t i o n (eg. 2.12) and s h o u l d i n c r e a s e w i t h i n c r e a s i n g t e t r a g o n a l d i s t o r t i o n . The v a l u e o f g Q s h o u l d d e c r e a s e w i t h i n c r e a s i n g t e t r a g o n a l d i s t o r t i o n s i n c e i t i s more dependent on g_j_ t h a n gj|. The i n s p e c t i o n o f t h e gj_ v a l u e s o b t a i n e d f o r t h e C u L 4 ( E F g ) 2 shows t h a t t h e y a r e q u i t e c o n s t a n t t h r o u g h the s e r i e s but t h e 2 2 E ( B, E ) t r a n s i t i o n v a r i e s depending upon L ( s e c t i o n 4.3.2.2). xg g The g Q and gj| v a l u e s a l s o appear more o r l e s s . c o n s i s t e n t . There-f o r e , t h e v a l u e o f A must change a l s o so > t h a t i t c o u n t e r -b a l a n c e s t h e s e changes i n t h e d o r b i t a l s e p a r a t i o n . F o r t h e s e complexes; X must be g r e a t e r ( i n a b s o l u t e v a l u e ) i n t h e s e r i e s f o r L: =4mepy>=3mepy>=py. Thompson and A l l e y n e (121) have r e p o r t e d t h e e . s . r . parameters f o r a number o f Cu(py)^A2 complexes. They have found t h a t as t h e c o o r d i n a t i n g a b i l i t y o f t h e a n i o n i c s p e c i e s d e c r e a s e s (as judged by t h e energy o f t h e v i s i b l e b a nd), t h e g v a l u e d e c r e a s e s and t h e A v a l u e i n c r e a s e s . The g and 3 o o o -235--4 -1 A Q v a l u e s ( i n 10 cm ) f o r the complexes are l i s t e d below: A 9 0 A o C10 4" 2.114 77 BF 4 " 2.114 78 S0 3F~ 2.121 73 pCH 3C 6H 5S0 3~ 2.128 65 The comparison of the v a l u e s of gQ and A Q observed f o r the C u ( p y ) 4 ( E F g ) 2 s t u d i e d here to those above shows t h a t g v a l u e s 3 o (2.128 and 2.116) do not f o l l o w the t r e n d expected from the 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 whereas the A Q v a l u e s (84 and 82) do. T h i s c o r r e l a t i o n w i t h the c o o r d i n a t i n g a b i l i t y o f the a n i o n i c s p e c i e s c o u l d be expected s i n c e the decrease i n the v a l u e of g Q i s l e s s than 1% f o r the complex w i t h A=pCH 3C gH 4S0 3 compared to A=C10 4 whereas the decrease i n the v a l u e o f A Q i s ^ 20%. Thus the d i f f e r e n c e s i n g Q are not always l a r g e enough to be detected whereas the v a r i a t i o n i n A_ i s . The v a l u e s of A„ observed o o i n the oth e r CuL 4(EFg)2 complexes are comparable t o those observed i n the C u ( p y ) 4 ( E F g ) ^ complexes. -236 4.3.2.4 VIBRATIONAL SPECTROSCOPY Table IV-15 g i v e s the p o s i t i o n s of the s t e r e o -c h e m i c a l l y s e n s i t i v e v i b r a t i o n s of p y r i d i n e and 4-methylpyridine i n the i n f r a r e d s p e c t r a of t h e i r compounds. There i s no evidence f o r non-coordinated n e u t r a l l i g a n d . The p o s i t i o n s of the v i b r a t i o n of the 3-methylpyridine i n the i n f r a r e d s p e c t r a o f C u ( 3 m e p y ) 4 ( E F g ) 2 are w e l l separated from those of the f r e e base (Table A l - 3 , p.317 )• Table IV-16 g i v e s the p o s i t i o n s of the i n f r a r e d s p e c t r a l bands assigned to the E F g s p e c i e s i n the C u L 4 ( E F g ) 2 compounds. F i g u r e 4.19 shows the i n f r a r e d s p e c t r a (1000-400 cm - 1) of C u L 4 ( P F g ) 2 and F i g u r e 4.20 shows the i n f r a r e d s p e c t r a (900-300 cm - 1) f o r : . C u L 4 ( A s F g ) 2 (where L i s py, 4mepy, and 3mepy). For the hexafluorophosphate compounds, the i n f r a r e d s p e c t r a show the bands due to v.j (T ) and v 4 (T^ u) a s ^ st r o n g bands with i n d i c a t i o n s of s p l i t t i n g , broadening, o r asymmetry. The f o r m a l l y f o r b i d d e n ( i n O^ symmetry) v-^(A-^g) v i b r a t i o n appears as a s t r o n g , sharp band. The appearance of the and v 4 bands can be e x p l a i n e d i n terms o f lower symmetry. The ( T l u ) band o f Cu ( p y ) 4 ( P F g ) 2 appears to be s p l i t i n t o two components whereas these bands i n the o t h e r hexafluorophosphate complexes appear a s . o n l y r a t h e r broad bands. The f a c t t h a t the bands of the l a t t e r complexes do not show s p l i t t i n g i s because of the presence of 4mepy and -237-TABLECIV-15 SELECTED INFRARED SPECTRAL DATA FOR C u L 4 ( E F 6 ) 2 C u L 4 ( P F 6 ) 2 C u L 4 ( A s F 6 ) 2 ( i ) L=py 8a 1609s 1611s 6a 642m 650m,642m 16b 440s,430w 440s, 430w ( i i ) L=4mepy 8a 1620s 1620s 19a 1512m 1512m 9a 1241m 1241m 1 n.o. n.o. 10b+12 (a) 810s 6a (b) n.o. (a) p o s s i b l y o b s c u r e d by v 3 ( T l u ) o f P F g (b) p o s s i b l y o b s c u r e d by v 4 ( T l u ) o f P F g -238-TABLE IV-1-6 ANION BANDS IN THE INFRARED SPECTRA OF C u L 4 ( E F g ) 2 ASSIGNMENT •(C) ( i ) E=P V 4 ( T l u ) • V l ( A l g } 2 g ( i i ) E=As V T l u } v l ( A l g ) W (b) BAND POSITION (cm 1 ) C u ( p y ) 4 - ( E F 6 ) 2 Cu(4mepy) 4 ( E F 6 ) 2 Cu (3mepy) 4 (EF g) 2 852s,828s 551s,asy 7 4 2m-s 705s,br 395s,br 67 5m-s 579w,556s 850s,br 555s,asy 7 4 0m-s (a) 7 05s,br 399s,395s 670s 579w,552s 830s,br 553s,asy 740s (a) 705s,br 395s,br 669s 578w,549s (a) may c o n t a i n n e u t r a l l i g a n d bands i n t h e band e n v e l o p e (b) may be h i d d e n i n t h e v 4 ( T 1 u ) band envelope (c) a s signments a r e based on O symmetry f o r the a n i o n - 2 3 9 --240-A B S 0 R P T I 0 N + r- L=3mepy L=4mepy L=py 900 700 ENERGY (cm 1) FIGURE 4.20 INFRARED SPECTRA (900-350cm _ 1) OF C u L 4 ( A s F g ) 2 -241-3mepy bands i n t h i s r e g i o n (see F i g u r e 4.19 i n the r e g i o n 800-830 cm ~~) which cause the s p l i t t i n g s not to be r e s o l v e d . The v i b r a t i o n s i n the i n f r a r e d s p e c t r a appear as s t r o n g , asymmetric bands. -. \ T h i s asymmetric appearance may be due t o unresolved s p l i t t i n g of the ( T x u ) v i b r a t i o n and to the a c t i v a t i o n and s p l i t t i n g of the f o r m a l l y f o r b i d d e n (0^ symmetry) v „ ( E ) v i b r a t i o n . /. g The i n f r a r e d bands of P F g ~ i n the C u L 4 ( E F g ) 2 are not much d i f f e r e n t from those observed f o r N i L 4 ( E F g ) 2 except f o r the s p l i t t i n g of ( i n one case) and the c h a r a c t e r i s t i c s of the band contour. I t i s i n t e r e s t i n g t o note t h a t McWhinnie e t a l . have a s s i g n e d t h r e e bands as components of (a band a t 885 cm ~~ and the two bands observed here) . However, the band a t 885 cm - 1 i n .our spectrum o f C u ( p y ) 4 ( P F g ) 2 has been assigned t o a p y r i d i n e v i b r a t i o n ; the p y r i d i n e band a t 880 em u s u a l l y occurs as a weak band (see F i g u r e 4.2 p. 165) but i n the P F g complexes i t appears as medium to stro n g on the h i g h energy s i d e of the band of P F g even i n complexes where the P F g anion has n e a r l y 0^ symmetry (for example, see the i n f r a r e d spectrum of Co ( p y ) g ( P F g ) 2 F i g u r e 3.2, p. 7 3 ) ) . I t i s a l s o i n t e r e s t i n g t h a t McWhinnie et a1, have assigned the s p l i t v 2 ^ E g ^ a n d v 4 ^ T l u ^ v i b r a t i o n s to the asymmetric band (and shoulders) around 560 cm We, however, have concluded t h a t the asymmetric shape of v 4 j u s t g i v e s an i n d i c a t i o n of s p l i t t i n g o f degenerate v i b r a t i o n s . -242-For the h e x a f l u o r o a r s e n a t e complexes, 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 very i n t e r e s t i n g because , v 2 , v^, and (or t h e i r low symmetry e q u i v a l e n t s ) v i b r a t i o n s of AsFg are pr e s e n t as w e l l separated bands. The f o r m a l l y allowed ( 0 ^ ) v i b r a t i o n s appear as s t r o n g , broad (v^ i s much broader than V 4 , though) bands. The f o r m a l l y f o r b i d d e n ( i n 0 ^ sym-metry) v ^ ( A ^ g ) a n& ( a component of) v 2 ( E g ) appear as str o n g bands. Perhaps, most s i g n i f i c a n t l y , the v^Eg 1) which i s a doubly degenerate v i b r a t i o n when AsFg i s i n 0 ^ symmetry appears to s p l i t i n t o two components i n the i n f r a r e d s p e c t r a of the C u L 4 ( A s F g ) 2 complexes. . T h i s assignment i s based on the f a c t t h a t p y r i d i n e does not have any. bands between 500 and 600 cm - 1 (cf C u ( p y ) 4 ( P F g ) 2 , F i g u r e 4.19) and thus the two bands i n C u ( p y ) 4 ( A s F g ) 2 t 5 7 9 and 556 cm if must be assigned to components of the E G ( 0 H ) v i b r a t i o n ; the band s t r u c t u r e and e n e r g i e s i n the i n f r a r e d s p e c t r a o f o t h e r h e x a f l u o r o -a r s e n a t e — c o p p e r ( I I ) complexes are s i m i l a r and are as s i g n e d as i n the p y r i d i n e complex (although, there may be i n t e r -f e r e n c e s due t o 4-methylpyridine or 3-methylpyridine v i b r a t i o n s i n t h i s region) . The i n f r a r e d s p e c t r a l data (the EFg v i b r a t i o n s ) of the C u L 4 ( E F g ) 2 have p r o v i d e d s u p p o r t i n g evidence f o r the weak, though d e f i n i t e , c o o r d i n a t i o n o f the EFg anions i n these complexes. • •._' - . '• ; _ * '• -243-4.3.3, RELATION TO OTHER WORK 4.3.3.1 C u ( p y ) 4 ( P F g ) 2 T h i s compound has been prepared by two o t h e r groups of workers. Our i n f r a r e d data d i f f e r from those r e p o r t e d by M a y f i e l d and B u l l (14); however, we have shown ( s e c t i o n 4.3.1) t h a t t h i s i s d o u b t l e s s a r e s u l t o f the presence of " f r e e " p y r i d i n e i n the p r e v i o u s workers' sample o f " C u ( p y ) 4 ( p F g ) 2 " • There are some d i f f e r e n c e s between the e l e c t r o n i c "spectrum we obtained and t h a t r e p o r t e d by .McWhinnie e t a l . ( see s e c t i o n 4.2.2) We are not a b l e t o account f o r the d i f f e r e n c e except f o r the p o s s i b i l i t y o f i m p u r i t i e s i n the p r e v i o u s l y s t u d i e d m a t e r i a l . McWhinnie e t a l d i d not r e p o r t the p r e p a r a t i v e method nor a n a l y t i c a l data on t h e i r sample of " C u ( p y ) 4 ( P F g ) 2 " . 4.3.3.2 COMPARISON OF M L 4 ( E F g ) 2 COMPLEXES A c o n s i d e r a t i o n of the i n f r a r e d s t u d i e s on the C u L 4 ( E F g ) 2 system compared t o the N i L 4 ( E F g ) 2 system lends i t s e l f to a d i s c u s s i o n of a n i o n i c c o o r d i n a t i o n i n compounds of hexafluorophosphate and h e x a f l u o r o a r s e n a t e . The c r i t e r i a f o r a n i o n i c c o o r d i n a t i o n i n compounds of t h i s type were advanced i n s e c t i o n 4.1 (p. 151). C r i t e r i a ( i ) and ( i i i ) are based on the e l e c t r o n i c s t r u c t u r e of the metal i o n and on the i n f r a r e d -244-s p e c t r a o b s e r v e d f o r t h e a n i o n i c s p e c i e s , r e s p e c t i v e l y . C r i t e r i o n ( i i ) d e a l s w i t h X-ray c r y s t a l l o g r a p h i c e v i d e n c e w h i c h i s not a v a i l a b l e f o r t h i s d i s c u s s i o n . Thus, i n o r d e r t o d i s c u s s a n i o n i c c o o r d i n a t i o n i n t h e C u L 4 ( E F g ) 2 and N i L 4 ( E F g ) 2 complexes, we s h o u l d draw some c o n c l u s i o n s r e g a r d i n g t h e m e t a l i o n s t e r e o c h e m i s t r y from t h e magnetic and e l e c t r o n i c s p e c t r a l p r o p e r t i e s o f t h e complexes. We have seen t h a t .the N i L 4 ( E F g ) 2 compounds g e n e r a l l y have been a s s i g n e d s t r u c t u r e s w i t h f o u r n e u t r a l l i g a n d s (L) s t r o n g l y bonded i n t h e e q u a t o r i a l p l a n e and two a n i o n s weakly c o o r d i n a t e d i n t h e a x i a l p o s i t i o n s . T h i s s t r u c t u r e has been c o n f i r m e d by t h e m o l e c u l a r s t r u c t u r e d e t e r m i n a t i o n o f N i ( 4 m e p y ) 4 ( P F g ) 2 ( s e c t i o n 4.2.2.3). One o f the. N i L 4 ( E F g ) 2 compounds, namely N i ( p y ) 4 ( A s F g ) 2 , ( s e c t i o n 4.2.2.4) ha s , a c c o r d i n g t o c r i t e r i o n ( i ) , c o o r d i n a t e d a n i o n s i n t h e low t e m p e r a t u r e form. We have shown t h a t t h e a x i a l l i g a n d f i e l d s t r e n g t h o f t h e AsFg a n i o n ( s e c t i o n 4.2.2.4.2) can be compared t o t h o s e o f t h e a x i a l a n i o n s i n o t h e r N i L ^ A 2 compounds w i t h c o o r d i n a t e d a n i o n s because o f t h e s i m i l a r e l e c t r o n i c s t r u c t u r e s o f t h e n i c k e l ( I I ) i o n s i n v o l v e d . The a p p l i c a t i o n o f c r i t e r i o n ( i ) f o r c o p p e r ( I I ) i s not as c l e a r -c u t as n i c k e l ( I I ) '."(i.e. copper does n o t change s p i n s t a t e on a n i o n c o o r d i n a t i o n ) . I t does appear however t h a t t h e a n i o n s a r e c o o r d i n a t e d i n t h e C u ( p y ) 4 ( E F g ) 2 complexes and,moreover, from t h e e l e c t r o n i c s p e c t r a i t appears t h a t c t h e EFg a n i o n s a r e more weakly c o o r d i n a t e d t h a n t h e a n i o n i c s p e c i e s , A, i n o t h e r C u ( p y ) ^ A 2 complexes ( s e c t i o n 4.3.2.2). -245-When t h e a n i o n s i n a M L ^ f E F g ^ compound c a n be c o m p a r e d q u a n t i t a t i v e l y t o o t h e r a n i o n s i n a s e r i e s o f KL^A^ compounds a n d t h e o b s e r v e d p r o p e r t i e s c a n be a s s i g n e d t o t h e weak c o -o r d i n a t i n g a b i l i t y o f E F , a n i o n s , . i t d o e s seem r e a s o n a b l e t o c l a s s i f y t h e s e E F ' a n i o n s as b e i n g c o o r d i n a t e d a n i o n s . b T h u s , t h e A s F g a n i o n i n t h e l o w t e m p e r a t u r e i s o m e r o f N i ( p y ) 4 ~ ( E F g ) 2 a n d t h e E F ^ a n i o n s i n t h e C u L 4 ( E F g ) 2 c o m p l e x e s c a n be c o n s i d e r e d t o b e , i n t h e c l a s s i c a l s e n s e , f u l l y c o o r d i n a t e d a n i o n s . I n t h e N i L 4 ( E F g ) 2 compounds g e n e r a l l y o n t h e o t h e r h a n d , f u l l c o o r d i n a t i o n b y t h e a n i o n s i s n o t p r e s e n t . T h i s i s so b e c a u s e o f t h e f a c t t h a t ' t h e e l e c t r o n i c s t r u c t u r e o f t h e n i c k e l ( I I ) i o n i s d i f f e r e n t f r o m t h a t o b s e r v e d i n N i ( p y ) 4 A 2 compounds w i t h " c l a s s i c a l " c o o r d i n a t e d a n i o n s . T h e c r y s t a l s t r u c t u r e o f N i ( 4 m e p y ) 4 ( p F g ) 2 d o e s i n d i c a t e how-e v e r some f o r m o f m e t a l - a n i o n i n t e r a c t i o n . I n t h e C o L 4 ( E F g ) 2 c o m p l e x e s , t h e s t e r e o c h e m i s t r y a r o u n d t h e c o b a l t ( I I ) i o n i s c o m p l e t e l y d i f f e r e n t ( t e t r a h e d r a l CoN^) t h a n t h a t ( D ^ ) o b s e r v e d f o r C o ( p y ) 4 A 2 c o m p l e x e s w i t h c o o r d i n a t e d a n i o n s . T h e E F g a n i o n s i n t h e C o L 4 ( E F g ) 2 c o m p l e x e s a r e c l e a r l y .not c o o r d i n a t e d t o c o b a l t ( I I ) . To s u m m a r i z e , t h e l o w t e m p e r a t u r e i s o m e r o f N i ( p y ) 4 ~ ( A s F 6 ) 2 a n d t h e C u L 4 ( E F g ) 2 c o m p l e x e s h a v e c o o r d i n a t e d a n i o n s , On t h e o t h e r h a n d , t h e , N i L . ( E F , ) „ c o m p o u n d s , g e n e r a l l y , h a v e v e r y w e a k l y c o o r d i n a t e d a n i o n s , i n a s e n s e s t r e t c h i n g t h e l i m i t s o f t h e c o n c e p t o f a n i o n i c c o o r d i n a t i o n . T h e C o L 4 ~ ( E F g ) 2 c o m p l e x e s h a v e n o n - c o o r d i n a t e d a n i o n s . -246-We have concluded t h a t cases f o r " c l a s s i c a l l y " co-o r d i n a t e d anions e x i s t i n the some of the compounds of t h i s study based on the metal i o n e l e c t r o n i c s t r u c t u r e . These compounds f u l f i l l c r i t e r i o n ( i ) of s e c t i o n 4.1. Important questions remain. "What c r i t e r i a f o r E F g c o o r d i n a t i o n may be developed from the i n f r a r e d spectrum of these compounds?", "How can the i n f r a r e d data f o r c o o r d i n a t e d EF, anions be d i f f e r e n t i a t e d from the s p e c t r a observed f o r very weakly co-o r d i n a t e d anions and non-coordinated EF, anions." The i n f r a r e d s p e c t r a o f the h e x a f l u o r o a r s e n a t e anions i n the M'L^tAsFg),, * (M'=Co,Ni, and Cu) complexes p r o v i d e the most e a s i l y i n t e r p r e t e d s p e c t r a and w i l l be c o n s i d e r e d f i r s t . When the AsF, anion i s i n a non-coordinated, weakly b c o o r d i n a t e d , or f u l l y c o o r d i n a t e d s i t u a t i o n , the s t r u c t u r e s and p o s i t i o n s o f the (T^ ) and (T-^ ) i n f r a r e d s p e c t r a l bands do not vary a p p r e c i a b l y . However, the s t r u c t u r e s and the p o s i t i o n s o f the v x a n c ^ v 2 ^ E g ^ b a n d s (which are both f o r m a l l y i n f r a r e d f o r b i d d e n i n 0^ symmetry) do change depending on the form o f c o o r d i n a t i o n . When AsF,, i s a non-coordinated b anion ( i n approximate 0^ symmetry) the (A^ ) band i s not observed and the v~(E ) band i s observed as a weak band a t g 570 cm-"1- i n the i n f r a r e d spectrum. When A s F g i s ve r y weakly c o o r d i n a t e d t o a metal i o n ( i . e ; the N i L ^ ( A s F g ) 2 compounds), the v i ( A ^ g ) band i s observed as a sharp, medium i n t e n s i t y band on the low energy s i d e of v 3 : ( T i u ) ' a n d t n e v 2 ( E g ) band appe< s a r s -247-as a sharp, medium to stro n g i n t e n s i t y band a t ^57 0 cm ^ i n the i n f r a r e d spectrum (Figure 4.21 shows the i n f r a r e d spectrum of the NiL.tAsF/) ~ complexes, 900-300 cm 1 ) . When AsF, i s 4 - 6 2 b f u l l y c o o r d i n a t e d t o a metal i o n , the (A-^g) band appears as i t does i n the weakly c o o r d i n a t i n g case; whereas, the v 2 (Eg) band .(of O^) appears as two bands, one weak a t ^ 580 cm and one strong a t ^ 560 cm ^ i n the i n f r a r e d s p e c t r a . F i g u r e 4.22 compares the i n f r a r e d s p e c t r a o f C u ( p y ) 4 ( A s F g ) 2 and N i ( p y ) 4 ( A s F g ) 2 (room temperature form) and shows the d i f -f e rences mentioned above; the comparison o f F i g u r e 4.22 t o F i g u r e 4.11 (p. 194) shows t h a t the spectrum of the low temper-a t u r e isomer o f N i ( p y ) 4 ( A s F g ) 2 and t h a t of C u ( p y ) 4 ( A s F g ) 2 have s i m i l a r d i f f e r e n c e s from the spectrum o f the room temper-atu r e isomer o f N i ( p y ) 4 ( A s F g ) 2 . Thus, the appearance of the \>2 ( Eg) band of AsFg appears t o be d i a g n o s t i c i n d i f f e r e n t i a t i n g d i f f e r e n t anion environments; a weak p e r t u r b a t i o n ( s i t e sym-metry e f f e c t s ) , g i v e s a weak a c t i v a t i o n , a very weak c o o r d i n -a t i v e p e r t u r b a t i o n g i v e s a s t r o n g a c t i v a t i o n and a f u l l co-o r d i n a t i v e i n t e r a c t i o n g i v e s a s t r o n g a c t i v a t i o n and a s p l i t t i n g o f the degenerate v i b r a t i o n . The i n f r a r e d s p e c t r a of the PFg anions i n the M'L^-( P F g ) 2 compounds do not g i v e as d i a g n o s t i c a p a t t e r n of band c h a r a c t e r . The d i f f e r e n c e between the i n f r a r e d s p e c t r a o f PF ~ i n the non-coordinated s i t u a t i o n and the very weakly D c o o r d i n a t e d case i s i n t h a t the v ^ ( A ^ g ) band i s weaker i n the former s i t u a t i o n . When the PF,. i s i n a f u l l y c o o r d i n a t e d b -248--249-A B S O R P T I O N + Ni(py)4(AsF6)2 300K Cu(py)4(AsF|)2 300K 800 600 400 t/(crrr1) FIGURE 4.22 INFRARED SPECTRA (800- 350 cm" 1) o f N i ( p y ) , ( A s F , ) _ 4 6 2 AND Cu(py) ( A s F g ) (mull e d i n N u j o l ) -250-s i t u a t i o n as i n the C u L 4 ( P F g ) 2 complexes, t h e r e are not many d i f f e r e n c e s from the very weakly c o o r d i n a t e d s i t u a t i o n . F i g u r e 4.23 g i v e s the i n f r a r e d s p e c t r a o f the N i L 4 (PFg ) 2 compounds from 1000-400 cm 1 ; comparison of t h i s i l l u s t r a t i o n t o F i g u r e 4.19 ( C u L 4 ( P F g ) 2 spectra) shows there are not many d i f f e r e n c e s . The q u a l i t a t i v e d i f f e r e n c e s are the g r e a t e r asymmetry ° f v 4 ( T i u ) and a s p l i t t i n g of the V 3 ( T ^ U ) i n the C u L 4 ( P F g ) 2 s p e c t r a (whereas no s p l i t t i n g i s observed f o r the N i L 4 ( E F g ) 2 complexes). The (A-^g) band appears as a medium to s t r o n g i n t e n s i t y , sharp ;band i n the spectrum of both complexes. The s p l i t t i n g o f v 3 ( T i u ) ' t n e asymmetry o f the v 4 ( T l u ) band contour, and the s t r o n g a c t i v a t i o n of the (A^ g) v i b r a t i o n can be seen to p r o v i d e i n f r a r e d c r i t e r i a f o r c o o r d i n a t i o n of the PFg anion. These f e a t u r e s have t o be seen together s i n c e s p l i t t i n g of the v 0 ( T n ) band has been observed i n the spectrum of 3 l u c C o ( p y ) 4 ( P F g ) 2 (Table I I I - l 9 p. 142), a complex i n which the anions are non-coordinated. The v,(A, ) band i n the i n f r a r e d 1 l g spectrum of C o ( p y ) 4 ( P F g ) 2 was observed as a very weak band and thus the anion i n f r a r e d spectrum o f C o ( p y ) 4 ( P F g ) 2 can be r a t i o n a l i z e d i n terms of s i t e symmetry e f f e c t s or f a c t o r group s p l i t t i n g s . The most d i a g n o s t i c f e a t u r e r e g a r d i n g c o o r d i n a t i o n o f A s F g - anions i s the s p l i t t i n g o f the v 2 (E g) v i b r a t i o n . The s p l i t t i n g of the v 2 ( E g ) v i b r a t i o n of the PFg" i n the C u L 4 ( P F g ) 2 compounds i s not observed but t h i s c o u l d r e s u l t from.'.interference from the s t r o n g band assigned t o the v 4 ( T x u ) v i b r a t i o n . The -251-FIGURE 4.23 INFRARED SPECTRA (1000- 400 cm" 1) of N i L 4 ( P F g ) 2 -252-q u e s t i o n a r i s e s , "Why do the s p l i t t i n g and i n t e n s i t y p a t t e r n of the ^ ( E g ) v i b r a t i o n imply c o o r d i n a t e d E F g anions?" As shown by Table III-2 (p. 29), the (degenerate) E v i b r a t i o n of the o c t a h e d r a l s p e c i e s s p l i t s i n t o two bands when the sym-metry o f the s p e c i e s i s lowered to ('4v' a n c ^ *~2v s y m m e t r Y • When the EF ~ anions are monodentate, the h i g h e s t p o s s i b l e u b symmetry of the anion i s C. and the s p l i t t i n g o f the v~(E ) v i b r a t i o n i s expected. The i n t e n s i t y p a t t e r n o f the A^ and B-^  v i b r a t i o n s i n the i n f r a r e d s p e c t r a can be e x p l a i n e d i n terms of t h e i r i n f r a r e d a c t i v i t i e s ; the A^ v i b r a t i o n i s both i n f r a r e d and Raman a c t i v e whereas the B.^  v i b r a t i o n i s o n l y Raman a c t i v e . Thus we can a s s i g n the h i g h e r i n t e n s i t y band (560-550 cm - 1) t o the v(A-L) v i b r a t i o n and the weaker band ( 580 cm - 1) to the v(B-^ v i b r a t i o n s o f A s F g ~ i n the C 4 v sym-metry. The f a c t t h a t the v(B-L) v i b r a t i o n i s seen a t a l l probably means t h a t s i t e symmetry e f f e c t s are p r e s e n t a l s o (that i s , a lthough the gross symmetry i s C 4 v , the p r e c i s e symmetry i s p robably G ). -253-CHAPTER 5 SUGGESTIONS FOR FURTHER STUDY T h i s chapter w i l l summarize the suggestions f o r f u r t h e r study which were proposed i n the p r e c e d i n g two cha p t e r s . In a d d i t i o n , i t w i l l suggest other work on hexa-fluorophosphate and h e x a f l u o r o a r s e n a t e complexes which might be attempted i n the f u t u r e . -254-5.1 SUGGESTIONS FOR FURTHER STUDY Suggestions f o r f u r t h e r study presented i n Chapter 3 i n c l u d e d the d e t e r m i n a t i o n o f molecular s t r u c t u r e s o f Co(3mepy)g-( H 2 0 ) 2 ( P F 6 ) 2 ( s e c t i o n 3.4.2.2.4) and C u ( 3 m e p y ) g ( H 2 0 ) 2 ( P F g ) 2 ( s e c t i o n 3.4.2.2.5). Such s t u d i e s would c o n f i r m o r d i s p r o v e the s t e r e o c h e m i s t r y which was a s s i g n e d on the b a s i s of magnetic and s p e c t r a l s t u d i e s . F u r t h e r r e s e a r c h on N i L ^ ( E F g ) 2 compounds, where L i s a s u b s t i t u t e d p y r i d i n e o f weaker base s t r e n g t h then p y r i d i n e , -was proposed i n s e c t i o n 4.2.3. T h i s would determine whether the lowering the b a s i c i t y of the n e u t r a l l i g a n d can r e s u l t i n the i s o l a t i o n of a complex wi t h room temperature p r o p e r t i e s s i m i l a r t o . t h e low temperature isomer of N i ( p y ) 4 ( A s F g ) 2 . In Chapter 4, i t was a l s o suggested t h a t more d e t a i l e d thermal d e g r a d a t i o n s t u d i e s on the M ' L 4 ( E F g ) 2 complexes (where M' i s Co, N i , and Cu) should be done. F u r t h e r work c o u l d i d e n t i f y more f u l l y the r e s i d u e s and sublimates and i t might be p o s s i b l e , as a r e s u l t of t h i s work, to e x p l a i n the d i f f e r e n t products obtained i n the i n i t i a l s t u d i e s . One area of f u r t h e r work which c o u l d be pursued i n v o l v e s the X-ray d i f f r a c t i o n s t u d i e s of the C u L 4 ( E F g ) 2 compounds. T h i s work would g i v e more d e t a i l e d i n f o r m a t i o n r e g a r d i n g metal-anion i n t e r a c t i o n s and would permit a more f r u i t f u l comparison of r e l a t e d copper(II) and n i c k e l ( I I ) complexes. -255-The s y n t h e s i s and c h a r a c t e r i z a t i o n o f h e x a f l u o r o -phosphate and h e x a f l u o r o a r s e n a t e compounds o f m e t a l s not c o v e r e d i n t h e p r e s e n t work (such as i r o n and manganese) and w i t h d i f f e r e n t n e u t r a l l i g a n d s p e c i e s would l e a d t o new and p o s s i b l y n o v e l complexes. As mentioned i n s e c t i o n 1.1.2, t h e M ( E F g ) 2 compounds a r e p o o r l y c h a r a c t e r i z e d m a t e r i a l s a t p r e s e n t . F u r t h e r work o f t h e t y p e r e c o u n t e d i n t h i s t h e s i s on such compounds would p r o v i d e u s e f u l d a t a on t h e v i b r a t i o n a l modes o f c o o r d i n a t e d EF,. a n i o n s , s i n c e , as mentioned i n b s e c t i o n 4.1, t h e b i s ( h e x a f l u o r o p h o s p h a t o ) - and b i s ( h e x a f l u o r o -a r s e n a t o ) - m e t a l ( I I ) anhydrous s a l t s would most c e r t a i n l y c o n t a i n c o o r d i n a t e d EF, a n i o n s . 6 A n o t h e r system o f complexes w h i c h would be i n t e r e s t i n g t o e x p l o r e i n v o l v e s p y r a z i n e and s u b s t i t u t e d p y r a z i n e l i g a n d s . P y r a z i n e i s a a r o m a t i c h e t e r o c y c l i c m o l e c u l e s i m i l a r t o p y r i d i n e e x c e p t ' t h e r e a r e two n i t r o g e n atoms i n " t r a n s " p o s i t i o n s (1 and 4 p o s i t i o n s ) and hence t h e m o l e c u l e has t h e p o t e n t i a l o f b e i n g a b r i d g i n g l i g a n d . T r a n s i t i o n m e t a l p y r a z i n e complexes c o n t a i n i n g h e x a f l u o r o p h o s p h a t e o r h e x a f l u o r o a r s e n a t e a n i o n s may e x h i b i t s i g n i f i c a n t l y d i f f e r e n t p r o p e r t i e s from p y r a z i n e complexes c o n t a i n i n g o t h e r a n i o n s . Some i n i t i a l work has been done by us on t h e system where M i s Cu and EF.g i s P F g and t h i s w i l l be b r i e f l y d i s c u s s e d n e x t . The i n i t a l work on t h i s system i n d i c a t e s t h a t C u ( p y z ) ^ -( P F g ) 2 can be i s o l a t e d . P r e l i m i n a r y d a t a s uggest t h e h e x a f l u o r o -- 2 5 6 -phosphate anions a r e not c o o r d i n a t e d and hence the complex c o n t a i n s complex c a t i o n s which are probably l i n k e d i n poly-meric a r r a y s by b r i d g i n g p y r a z i n e l i g a n d s . These c a t i o n s may e x h i b i t magnetic (Cu-Cu) i n t e r a c t i o n .and would t h e r e f o r e be p a r t i c u l a r l y i n t e r e s t i n g to study from t h i s p o i n t of view. -257-CHAPTER 6 EXPERIMENTAL T h i s chapter d e s c r i b e s the experimental d e t a i l s o f t h i s work. The m a t e r i a l s used, the s y n t h e s i s of the compounds s t u d i e d , the d e t a i l s o f u n s u c c e s s f u l p r e p a r a t i o n s and thermal degradations, the d e t a i l s on the a p p l i c a t i o n of the p h y s i c a l techniques o f i n v e s t i g a t i o n , and the d e t a i l s o f the i n v e s t i -g a t i o n s by s i n g l e c r y s t a l X-ray d i f f r a c t i o n w i l l be o u t l i n e d . -258-6.1 MATERIALS The m a t e r i a l s used i n t h i s work were of r e a g e n t grade and were used w i t h o u t f u r t h e r p u r i f i c a t i o n u n l e s s o t h e r w i s e s t a t e d . The commercial s o u r c e s o f t h e r e a g e n t s were: N i ( H 2 0 ) g ( N 0 3 ) 2 , AnalaR (BDH); C o ( H 2 0 ) g ( N 0 3 ) 2 , M a l l i n c k r o d t ; C u ( H 2 0 ) 3 ( N 0 3 ) 2 , F i s c h e r S c i e n t i f i c ; NH^PF^, A l f a P r o d u c t s ; and K A s F g , A l f a P r o d u c t s . The BDH r e a g e n t s , p y r i d i n e , 3 - m e t h y l p y r i d i n e , and 4 - m e t h y l p y r i d i n e , were r e c e i v e d as amber l i q u i d s . When r e f l u x e d o ver b a r i u m o x i d e f o r 24 hours and d i s t i l l e d a t a t m o s p h e r i c p r e s s u r e , they became c l e a r l i q u i d s . P y r i d i n e and 3 - m e t h y l p y r i d i n e remained c l e a r f o r a r e a s o n a b l e p e r i o d of t i m e , whereas 4 - m e t h y l p y r i d i n e t u r n e d an amber c o l o r w i t h i n a month of the d i s t i l l a t i o n . -259-6.2 PREPARATIONS Unless otherwise mentioned, a l l m a n i p u l a t i o n s of the compounds a f t e r being " i n vacuo" (a dynamic vacuum) were performed i n an i n e r t atmosphere p r o v i d e d by a D.L. H e r r i n g C o r p o r a t i o n D r i - L a b Model HE-43 equipped w i t h a Dry T r a i n Model 93. L- or K- grade N 2 p r o v i d e d the i n e r t atmosphere and was c i r c u l a t e d through Linde 4A molecular s i e v e s i n the dry t r a i n s . These molecular s i e v e s were regenerated 1 ..by the use o f an oven i n c o r p o r a t e d i n t o the system and t h i s was done p e r i o d i c a l l y (monthly). The g e n e r a l method used t o prepare the p y r i d i n e complexes i s g i v e n by: M I 3 : ( N 0 3 ) 2 xH 20+4yL+2M I (EFg) —> M I : EL-(H 20) z (EFg) 2+2M IN0 3 (aq) + (x-z) H 20+ 3yL II I I I I II where M i s Co , N i or Cu , L i s p y r i d i n e , 4-methylpyridine and 3-methylpyridine and M I ( E F g ) 2 r e f e r s t o NH^PFg o r KAsFg. The d e s i r e d product M I IL^,A 2, p r e c i p i t a t e s from the aqueous s o l u t i o n and a l l t h e . o t h e r s p e c i e s remain i n s o l u t i o n . S ince the hexafluoro-phosphate and -arsenate are g e n e r a l l y s t a b l e t o h y d r o l y s i s i n b a s i c aqueous s o l u t i o n (1 ), t h i s method i s a p p r o p r i a t e . With these p o o r l y c o o r d i n a t i n g anions the r a t i o I I of p y r i d i n e to metal, M , i s g e n e r a l l y g r e a t e r than f o u r . -260--r In the r e a c t i o n s where L=pyrid i n e , the compounds p r e c i p i t a t e d from aqueous s o l u t i o n as M i : i"Ly(EFg) 2 have y=6 f o r C o 1 1 and N i 1 1 and y=4 f o r C u 1 1 . In the l a t t e r case, the . f r e s h l y p r e c i p i t a t e d product i s blue and turns mauve on d r y i n g . The i n i t i a l product probably had y>4 but was un s t a b l e t o the d r y i n g c o n d i t i o n s . In g e n e r a l , w i t h these p y r i d i n e complexes, the i n f r a r e d s p e c t r a o f the i n i t i a l products showed the presence of l a t t i c e (non-coordinated) water and p y r i d i n e and the d r y i n g " i n vacuo" was necessary t o e l i m i n a t e these. In the p r e p a r a t i v e r e a c t i o n s where L i s 4-methylpyridine or 3-methylpyridine, the s o l u t i o n c hemistry was q u i t e d i f f e r e n t . When the reagents were s t i r r e d t o g e t h e r , a two phase system developed c o n s i s t i n g o f an " o i l y " s t r o n g l y c o l o r e d lower phase and an aqueous weakly c o l o r e d upper phase. G e n e r a l l y , the s e p a r a t i o n and slow e v a p o r a t i o n o f the lower phase gave m a t e r i a l s of the s t o i c h i o m e t r y M L ^ ( H 2 0 ) 2 ( E F g ) 2 where: (i) M=Co, Ni and L=4-me thy l p y r i d i n e , y=8 and ( i i ) -M=Cb, Ni*->eu<afid L= 3-methylpyridine, y=6. The only e x c e p t i o n was where M i s Cu and L=4-methylpyridine, i n t h i s case, the r e a c t i o n y i e l d s C u ( 4 m e p y ) 4 ( E F 6 ) 2 . The compounds c o n t a i n i n g p y r i d i n e , 4-methyl- and 3-methyl-pyridine having y>4 were used as the s t a r t i n g m a t e r i a l s f o r the p r e p a r a t i o n o r attempted p r e p a r a t i o n o f d e r i v a t i v e s w i t h y<4. -261-D e t a i l s o f the p r e p a r a t i v e procedures are g i v e n next and are c l a s s i f i e d as t o the n e u t r a l l i g a n d , L, i n v o l v e d : p y r i d i n e , 4-methylpyridine and 3-methylpyridine. At the end of the three s e c t i o n s , the a n a l y t i c a l data are compiled i n a t a b l e . 6.2.1 PYRIDINE COMPLEXES The a n a l y t i c a l data f o r these complexes are presented i n Table V I - I . 6.2.1.1 HEXAKIS(PYRIDINE)COBALT(II) HEXAFLUOROPHOSPHATE C o ( p y ) 6 ( P F 6 ) 2 C o b a l t ( I I ) n i t r a t e hexahydrate ( C o ( N 0 3 ) 2 6H 20,2.9g) was d i s s o l v e d i n a s o l u t i o n c o n s i s t i n g o f 50 ml. o f d i s t i l l e d water and p y r i d i n e (17 m l . ) . While t h i s s o l u t i o n was s t i r r e d m a g n e t i c a l l y , a f i l t e r e d s o l u t i o n of ammonium h e x a f l u o r o -phosphate (NH^PFg, 3.2g) i n d i s t i l l e d water (125 ml.) was added. The mixture was s t i r r e d u n t i l p r e c i p i t a t i o n o c c u r r e d (10-15 minutes). The orange p r e c i p i t a t e which formed was f i l t e r e d and washed wi t h a s o l u t i o n c o n s i s t i n g o f 50 ml. H 20 and p y r i d i n e (5 ml.). T h i s m a t e r i a l was d r i e d " i n vacuo" f o r about 1 day. Depending upon the d r y i n g c o n d i t i o n s used, the product a t t h i s p o i n t v a r i e d i n c o l o r from mauve to v i o l e t -262-and had a composition i n t e r m e d i a t e between the h e x a k i s ( p y r i d i n e ) and t e t r a k i s ( p y r i d i n e ) complexes. Complete c o n v e r s i o n t o the pink Co(py)g(PFg)2 compound was o b t a i n e d by a l l o w i n g the mauve-violet m a t e r i a l to e q u i l i b r a t e w i t h p y r i d i n e vapor ( p y r i d i n e v a p o r i z e d i n t o a vacuum) at room temperature f o r s e v e r a l hours. Exposing the product to a vacuum f o r a few minutes was u s u a l l y s u f f i c i e n t t o remove s u r f a c e p y r i d i n e from the sample without s i g n i f i c a n t decomposition. 6.2.1.2 HEXAKIS(PYRIDINE)COBALT(II) HEXAFLUOROARSENATE C o ( p y ) 6 ( A s F g ) 2 C o b a l t ( I I ) n i t r a t e hexahydrate (2.9 g) i n 50 ml. water was r e a c t e d w i t h potassium h e x a f l u o r o a r s e n a t e (KAsFg, 4.6 g) i n 125 n i l . water i n the same manner as i n 6.2.7.2. The i n i t i a l product o b t a i n e d i n the r e a c t i o n was orange. A f t e r washing, e q u i l i b r a t i n g w i t h A p y r i d i n e .-vapor and. d r y i n g Co(py)g(AsFg)2 was o b t a i n e d as a pink powder. 6.2.1.3 TETRAKIS(PYRIDINE)COBALT(II) HEXAFLUOROPHOSPHATE C o ( p y ) 4 ( P F g ) 2 6.2.1.4 TETRAKIS(PYRIDINE)COBALT(II) HEXAFLUOROARSENATE C o ( p y ) 4 ( A s F g ) 2 The C o ( p y ) g ( E F g ) 2 compound was heated a t 80-90°C -263-" i n vacuo" f o r 3 to 4 hours t o y i e l d the corres p o n d i n g product, C o ( p y ) ^ ( E F g ) 2 as an i n t e n s e red purple powder. ''fy 2.1.5 HEXAKIS (PYRIDINE) NICKEL (II) HEXAFLUOROPHOSPHATE N i ( p y ) 6 . ( P F 6 ) 2 6.2.1.6 HEXAKIS(PYRIDINE)NICKEL(II) HEXAFLUOROARSENATE N i ( p y ) g ( A s F 6 ) 2 N i c k e l ( I I ) n i t r a t e hexahydrate (Ni(N0 3) 2*6H 20,2.9g) was d i s s o l v e d i n a s o l u t i o n o f 50 ml. water and 16 ml. of p y r i d i n e and was r e a c t e d with >a-' f i l t e r e d . , agueous ^ s o l u t i o n of ammonium hexafluorophosphate (NH^PF^, 3.2 g) or; potassium h e x a f l u o r o a r s e n a t e (KAsEg, 4.7g). A l i g h t blue p r e c i p i t a t e was formed immediately. A f t e r a h a l f hour of s t i r r i n g , the p r e c i p i t a t e was f i l t e r e d , washed, and d r i e d i n vacuo f o r 1 day y i e l d i n g -.."the d e s i r e d m a t e r i a l , a s a " r o b i n s egg" blue powder. These compounds when d r i e d " i n vacuo" f o r prolonged p e r i o d s (4 or 5 days) would produce t r a c e s o f an orange y e l l o w c o l o r i n d i c a t i v e of the corresponding t e t r a k i s ( p y r i d i n e ) n i c k e l ( I I ) compounds. The p y r i d i n e vapor treatment of 6.2.1.1 would cause t h i s c o l o r t o dis a p p e a r . -264-6.2.1.7 TETRAKIS(PYRIDINE)NICKEL(II) HEXAFLUOROPHOSPHATE N i ( p y ) 4 ( P F 6 ) 2 T h i s compound or a compound s i m i l a r to i t was p r e v i o u s l y prepared (14) by thermal means from N i ( p y ) g ( P F g ) 2 . We have found t h i s t o be an u n s a t i s f a c t o r y , method,; g i v i n g - a r a t h e r impure compound due to decomposition. Since these p y r i d i n e compounds are not very s o l u b l e i n any of the common o r g a n i c s o l v e n t s (nitromethane, chloroform, dichloromethane, acetone, benzene, carbon t e t r a c h l o r i d e ) t r i e d , r e c r y s t a l l i z a t i o n was not p o s s i b l e . The method of p r e p a r a t i o n used, i n order to prevent thermal decomposition, i s a s t i r p r e p a r a t i o n which takes advantage o f the s o l u b i l i t y o f p y r i d i n e i n dichloromethane and the i n s t a b i l i t y o f N i ( p y ) 6 ( P F g ) 2 (3.3.2) to dynamic p y r i d i n e removal. In the dry box, a sample o f N i ( p y ) g ( P F g ) 2 was t r a n s -f e r r e d to an Erlenmeyer f l a s k ,andf 50. ml, of dichloromethane was added. T h i s mixture was s t i r r e d m a g n e t i c a l l y f o r 1 hour, d u r i n g which time, the i n i t i a l l y " r o b i n s egg" b l u e compound, present l a r g e l y as an i n s o l u b l e s o l i d , transformed to an orange y e l l o w s p a r i n g l y s o l u b l e compound. The supernatant l i q u i d had a f a i n t blue-green c o l o r . The contents o f the f l a s k were f i l t e r e d through a f l u t e d f i l t e r paper and the orange-yellow product was washed w i t h dichloromethane u n t i l the f i l t r a t e was l i g h t orange y e l l o w i n c o l o r . A f t e r b e i n g d r i e d " i n vacuo" for•1.day, an orange y e l l o w powder-was obtained. -265-6.2.1.8 TETRAKIS(PYRIDINE)NICKEL(II) HEXAFLUOROPHOSPHATE N i ( p y ) 4 ( A s F 6 ) 2 (a) " S t i r " p r e p a r a t i o n T h i s orange-yellow compound was prepared as above ( s e c t i o n 6.1.2.7) u s i n g N i ( p y ) g ( A s F g ) 2 as the s t a r t i n g m a t e r i a l . (b) "Heat" p r e p a r a t i o n As mentioned i n s e c t i o n 6.1.2.7, the thermal method i s not s a t i s f a c t o r y f o r hexafluorophosphate d e r i v a t i v e s . The h e x a f l u o r o a r s e n a t e compound can be prepared i n reasonably pure form by thermal means, however. A sample o f " r o b i n s egg" b l u e N i ( p y ) r (AsF,)„ was heated a t 60°C " i n vacuo" f o r 24 hours 6 b 2. y i e l d i n g an orange-yellow powder. 6.2.1.9 TETRAKIS(PYRIDINE)COPPER(II) HEXAFLUOROPHOSPHATE C u ( p y ) 4 ( P F 6 ) 2 6.2.1.10 TETRAKIS(PYRIDINE)COPPER(II) HEXAFLUOROARSENATE C u ( p y ) 4 ( A s F g ) 2 These compounds were prepared i n a manner s i m i l a r t o t h a t d e s c r i b e d i n r e f e r e n d e 14. C u p r i c n i t r a t e t r i h y d r a t e (Cu (N0 3) 2 • 3H 20, 4.8g) was d i s s o l v e d i n 50 ml H 20 and 16; ml of pyridine.' A f i l t e r e d aqueous s o l u t i o n of NH 4PF g (6.5g, 150ml) or KAsFg;(9 . 2g, 250ml) was added. P r e c i p i t a t i o n of a blue-mauve m a t e r i a l o c c u r r e d immediately. A f t e r one h a l f - h o u r of s t i r r i n g , the p r e c i p i t a t e was f i l t e r e d , washed ( s o l u t i o n of 50 ml water and 5 ml p y r i d i n e ) and d r i e d " i n vacuo". The i n f r a r e d s p e c t r a i n d i c a t e d t h a t non-coordinated p y r i d i n e was p r e s e n t . T h i s was - 2 6 6 -TABLE V I - 1 ANALYTICAL DATA-FOR. PYRIDINE COMPLEXES COMPOUND * - % EXPECTED a "5 FOUND C i H N C H N C o ( p y ) 6 (PFg) 2 43. 76 3. 67 10 .21 43 . 36 3 . 50 10 .26 C o ( p y ) g ( A s F g 39. 54 3. 34 9. 22 39. 3 0 3. 21 9. 12 C o ( p y ) 4 ( P F g ) 2 36. 11 3 . 03 8. 42 35. 97 3. 10 8. 22 C o ( p y ) 4 ( A s F 6 >2 31. .90 2. 68 7. 44 31. 81 2 . 73 7. 42 N i ( p y ) 6 ( P F g ) 2 43. , 77 3 . 67 10 .21 43. 69 3. 5 10 . 0 N i ( p y ) 6 ( A s F g }2 39. .54 3. 34 9. 22 39. 20 3. 3 8. 95 N i ( p y ) 4 ( P F g ) 2 36. .16 3. 03 8. 43 36. 12 2. 99 8. 49 N i ( p y ) 4 ( A s F g } 2 a \ 31, .90 2. 68 7 . 44 31. 70 2. 74 7. 31 3 • • 31 .90 2. 68 7. 44 31, .98 2. 83 7 . 15 C u ( p y ) 4 ( P F g ) 2 , 35 . 86 3. .01 8. 36 35. ,68 3. , 02 8. 45 C u ( p y ) 4 ( A s F £ i>2 31 .70 2 . 66 7 . 39 31. ,51 2. ,57 7 . ,27 -267-con f i r m e d by m i c r o a n a l y s i s , y>4. H e a t i n g o f t h e compound a t 40°C " i n vacuo" gave the d e s i r e d mauve•• . powder Cu (py) 4 (EFg) 2 6.2.2 4-METHYLPYRIDINE COMPLEXES The a n a l y t i c a l d a t a f o r t h e s e complexes are g i v e n i n T a b l e V I - 2 . 6.2.2.1 OCTAKIS(4-METHYLPYRIDINE)DIAQUOCOBALT(II) HEXAFLUOROPHOSPHATE C o ( 4 m e p y ) Q ( H 2 Q ) 2 ( P F g ) 2 6.2.2.2 OCTAKIS(4-METHYLPYRIDINE)DIAQUOCOBALT(II) HEXAFLUOROARSENATE C o ( 4 m e p y ) Q ( H 2 0 ) 2 ) A s F g ) 6.2.2.3 OCTAKIS (4-METHYLPYRIDINE) •DIAQUONICKEL(II-) HEXAFLUOROPHOSPHATE N i ( 4 m e p y ) g ( H 2 0 ) 2 ( P F g ) 2 6.2.2.4 OCTAKIS(4-METHYLPYRIDINE)DIAQUONICKEL(II) HEXAFLUOROARSENATE N i ( 4 m e p y ) g ( H 2 0 ) 2 ( A s F g ) 2 A l l f o u r compounds were p r e p a r e d by t h e same p r o c e d u r e . The a p p r o p r i a t e m e t a l ( I I ) n i t r a t e h e x a h y d r a t e (0.002 mole) was d i s s o l v e d i n 100 m l . o f d i s t i l l e d w a t e r c o n t a i n i n g 39 m l . of 4 - m e t h y l p y r i d i n e . To t h i s s o l u t i o n was added w i t h s t i r r i n g , a f i l t e r e d s o l u t i o n o f 0.04 moles o f ammonium h e x a f l u o r o p h o s p h a t e -268-i n 50 ml. water (or 0.04 moles o f potassium h e x a f l u o r o a r s e n a t e i n 250 ml. water). S t i r r i n g was continued f o r 1 hour d u r i n g which time a two phase system developed which c o n s i s t e d of an upper weakly c o l o r e d or c o l o r l e s s aqueous l a y e r , and a lower " o i l y " l a y e r , which was red f o r c o b a l t and blue f o r n i c k e l . The lower l a y e r was t r a n s f e r r e d w i t h a s e p a r a t o r y funnel t o an e v a p o r a t i n g d i s h which was p l a c e d over phosphorous pentoxide i n a vacuum d e s i c c a t o r . A f t e r a p e r i o d o f 2 to 3 weeks, orange-red c r y s t a l s o f the c o b a l t complexes and blue c r y s t a l s o f the n i c k e l complexes formed. The c r y s t a l s were washed wi t h a s o l u t i o n o f 5 ml. 4-methylpyridine i n 50 ml. water. Since the c r y s t a l s tend t o l o s e 4-methylpyridine on exposure t o the atmosphere or to a vacuum, they were s t o r e d o u t s i d e the dry box i n s e a l e d v i a l s s t i l l "wet" w i t h the washing l i q u i d . J u s t p r i o r t o use, the c r y s t a l s were d r i e d " i n vacuo" f o r about 15 minutes. 6.2.2.5 TETRAKIS(4-METHYLPYRIDINE)COBALT(II) HEXAFLUOROPHOSPHATE-Co(4mepy) 4(PFg) 2 -6.2.2.6 TETRAKIS(4-METHYLPYRIDINE)COBALT(II) HEXAFLUOROARSENATE-Co (4 mepy) 4(AsFg) 2 The corresponding d r i e d C o ( 4 m e p y ) g ( H 2 0 ) 2 ( E F g ) 2 complex was ground t o a f i n e powder i n the dry box and then heated at 80-90° C f o r 3-4 hours " i n vacuo". T h i s treatment y i e l d e d -269-the d e s i r e d i n t e n s e l y c o l o r e d r e d - p u r p l e complexes. 6.2.2.7 TETRAKIS(4-METHYLPYRIDINE)NICKEL(II) •! HEXAFLUOROPHOSPHATE N i ( 4 m e p y ) 4 ( P F g ) 2 6.2.2.8 TETRAKIS(4-METHYLPYRIDINE)NICKEL(II) HEXAFLUOROARSENATE N i ( 4 m e p y ) 4 ( A s F g ) 2 The corresponding N i ( 4 m e p y ) g ( H 2 0 ) 2 A 2 complexes was ground t o a f i n e powder i n the dry box and then heated a t -8 0°C f o r 3-4 hours i n a vacuum y i e l d i n g a yellow-orange product. S i n c e these compounds were moderately s o l u b l e i n dichloromethane, u n l i k e the analogous p y r i d i n e complexes, they were r e c r y s t a l l i z e d from t h i s s o l v e n t . 6.2.2.9 TETRAKIS(4-METHYLPYRIDINE)COPPER(II) HEXAFLUOROPHOSPHATE Cu(4mepy) 4(PFg) 2 6.2.2.10 TETRAKIS(4-METHYLPYRIDINE)COPPER(II) HEXAFLUOROARSENATE Cu(4mepy) 4(AsFg) 2 In these p r e p a r a t i o n s , the c o n d i t i o n s used i n 6.2.2.1 gave products w i t h high percentages of N, perhaps i n d i c a t i n g the presence o f N0~ i m p u r i t i e s . Reasonable a n a l y s i s were obt a i n e d by u s i n g more d i l u t e c o n d i t i o n s i n the r e a c t i o n . - 2 7 0 -The c o n d i t i o n s were o b t a i n e d by u s i n g the same volumes o f water as i n 6.2.2.1 but u s i n g 1/4 of the amount of reagents p r e s c r i b e d i n 6.2.2.1. S t i r r i n g o f these combined reagents gave an immediate p r e c i p i t a t e , which was t r e a t e d i n the same manner as d e s c r i b e d i n 2.2.1.9. 6.2.3 3-METHYLPYRIDINE COMPLEXES The a n a l y t i c a l data f o r these complexes are complied i n Table VI-3. * 6.2.3.1 HEXAKIS (3-METHYLPYRIDINE)DIAQUOCOBALT(II) HEXAFLUOROPHOSPHATE C o ( 3 m e p y ) g ( H g O ) 2 ( P F g ) 2 6.2.3.2 HEXAKIS (3-METHYLPYRIDINE)DIAQUOCOBALT(II) HEXAFLUOROARSENATE C o ( 3 m e p y ) g ( H 2 0 ) 2 ( A s F g ) 2 6.2.3.3 HEXAKIS (3-METHYLPYRIDINE)DIAQUONICKEL(II) HEXAFLUOROPHOSPHATE Ni(3mepy) 6 (H 20) 2 (PFg) 2 6.2.3.4 HEXAKIS (3-METHYLPYRIDINE)DIAQUONICKEL(II) HEXAFLUOROARSENATE N i ( 3 m e p y ) g ( H 2 0 ) 2 ( A s F g ) 2 6.2.3.5 HEXAKIS (3-METHYLPYRIDINE)DIAQUOCOPPER(II) HEXAFLUOROPHOSPHATE C u ( 3 m e p y ) g ( H 2 0 ) 2 ( P F g ) 2 -271-TABLE VI-.2 ANALYTICAL DATA FOR THE 4-METHYLPYRIDINE COMPLEXES % EXPECTED % FOUND COMPOUND C H N C H N ( i ) M ( 4 r a e p y ) 8 ( H 2 0 ) 2 ( E F 6 ) 2 M=Co, E=P 51.02 5. 35 9. ,92 51. ,00 5. 20 9. ,89 M=Co, E=As 47.34 4. 97 9. , 20 47. .50 4. ,80 9 , .10 M=Ni, E=P 51.03 5. 35 9. .92 51, .30 5. ,42 10, .10 M=Ni, E=As 47.35 4 . 96 9, .20 47 , .00 4 . , 99 9. .00 ( i i ) : M(4mepy) 4 ( E F 6 ) 2 M=Co, E=P 39.96 3. 91 7 .77 39 .70 3, .91 7 .87 M=Co, E=As 35.62 3. 49 6 .92 35 .60 3. .66 7 .17 M=Ni, E=P 39.97 3. ,91 7 .77 39 . 80 3 .71 7 .88 M=Ni , E=As 35.63 3. ,49 6 .93 35 .50 3 .53 7 .10 M=Cu, E=P 39.71 3 . 89 7 .72 39 .68 3 .88 7 .91 M=Cu, E=As 35.42 3, .47 6 .88 35 .57 3 .47 7 .00 -272-6.2.3.6 HEXAKIS (3-METHYLPYRIDINE)DIAQUOCOPPER(II) HEXAFLUOROARSENATE C u ( 3 m e p y ) g ( H 2 0 ) 2 ( A s F g ) 2 These complexes were prepared i n a s i m i l a r manner to 6.2.2.1-4 except t h a t 2 grams more of the hexafluoro-phosphate o r -arsenate s a l t was added. The a d d i t i o n o f the excess s a l t improved the c r y s t a l l i z a t i o n which took p l a c e w i t h i n 1-2 weeks of p r e p a r a t i o n . A f t e r c r y s t a l l i z a t i o n , the c r y s t a l s were f i l t e r e d and washed (50 ml. water-5 ml. 3-methylpyridine) and again l e f t "wet" wi t h the washing l i q u i d i n s e a l e d v i a l s i n a d e s i c c a t o r (not i n the dry box). 6.2.3.7 TETRAKIS(3-METHYLPYRIDINE)COBALT(II) HEXAFLUOROPHOSPHATE Co(3mepy) 4(PF g ) 2 6.2.3.8 TETRAKIS(3-METHYLPYRIDINE)COBALT(II) HEXAFLUOROARSENATE C o ( 3 m e p y ) 4 ( A s F g ) 2 These compounds were prepared from the co r r e s p o n d i n g d r i e d C o ( 3 m e p y ) g ( H 2 0 ) 2 A 2 complexes, by g r i n d i n g t o a f i n e powder and pumping " i n vacuo" f o r 24 hours. No h e a t i n g was r e q u i r e d . -273-6.2.3. 9. TETRAKIS (3-METHYLPYRIDINE) NICKEL (II)' HEXAFLUOROARSENATE N i ( 3 m e p y ) 4 ( A s F g ) 2 The t r e a t m e n t o f N i ( 3 m e p y ) g ( H 2 0 ) 2 A 2 v i a t h e method o f 6.2.3.7-.8 gave a l i g h t b l u e - y e l l o w powder. The i n f r a r e d s p e c t r a i n d i c a t e d t h e absence o f w a t e r . The m i c r o a n a l y s e s o f t h e s e compounds gave mole r a t i o s o f m e t a l t o 3 - m e t h y l p y r i d i n e o f 1:»' where 4< x< 6 . The a p p l i c a t i o n o f a 3 - m e t h y l p y r i d i n e atmosphere as i n 6.2.1.1 gave x=5.5. The t e t r a k i s ( 3 - m e t h y l p y r i d i n e ) compounds were p r e p a r e d by t r e a t i n g t h e d r i e d p r o d u c t above as i n 6.2.1.8(a) u s i n g c h l o r o f o r m as t h e i n e r t s o l v e n t . 6.2.3 .10 TETRAKIS(3-METHYLPYRIDINE)COPPER(II) HEXAFLUOROPHOSPHATE C u ( 3 m e p y ) 4 ( P F g ) 2 6.2.3 J.1 TETRAKIS (3-METHYLPYRIDINE) COPPER(II) HEXAFLUOROARSENATE C u ( 3 m e p y ) 4 ( A s F g ) 2 These compounds were p r e p a r e d from t h e c o r r e s p o n d i n g C u ( 3 m e p y ) g ( H 2 0 ) 2 A 2 complexes by d r y i n g " i n vacuo" f o r 24 h o u r s . These compounds were mauve powders. -274-. TABLE VI-3 ANALYTICAL DATA FOR THE 3-METHYLPYRIDINE COMPLEXES % EXPECTED % FOUND C H N C H N (i) M(3mepy) 6 ( H 2 0 ) 2 ( E F 6 ) 2 M=Co, E=P 45.8 4.91 8.91 45.5 5.15 8. 90 M=Co, E = A s ( a ) 41.9 .4.49 8.15 M=Ni, E=P 45.8 4.91 8. 91 45.8 4.77 8. ,99 M=Ni, E=As 41.9 4.50 8.15 41.9 4.49 8. .12 M=Cu, E=P 45.6 4. 89 8.86 45.4 5.00 8. .67 M=Cu, E=As 41.7 4.47 8.11 42.0 4.44 8. .15 ( i i ) M(3mepy) 4 ( E F 6 ) 2 M=Co, E=P 39.96 3.91 7.77 40.00 4.00 7 .79 M=Co, E=As 35.62 3.49 6.92 35.69 3.51 6 .98 M=Ni f E=As 35.63 3.49 6.93 35. 38, 3.50 6 :74 M=Cu, E=P 39.71 3.89 7.72 39.38 3.91 7 .67 M=Cu, E=As 35.42 3.47 6.88 35.31 3.46 6 .86 (a) no a n a l y t i c a l d ata are r e p o r t e d f o r C o ( 3 m e p y ) g ( H 2 0 ) 2 ( A s F g ) 2 however the Co ( 3 m e p y ) 4 ( A s F g ) 2 compound,which was prepared from it,was o b t a i n e d i n a pure form. -275-6.2.4 THERMAL STUDIES 6.2.4.1 TETRAKIS(4-METHYLPYRIDINE)NICKEL(II) HEXAFLUOROPHOSPHATE N i ( 4 m e p y ) 4 ( P F 6 ) 2 > A white m a t e r i a l s u b l i m i n g on the c o o l e r - p o r t i o n s of the vacuum t a k e - o f f adapter d u r i n g a thermal p r e p a r a t i o n (^100°C) of t h i s complex was the i n i t i a l o b s e r v a t i o n t h a t prompted t h i s study. T a b l e VI-4 g i v e s the h e a t i n g temperature and the d u r a t i o n o f t h i s h e a t i n g f o r the p r e p a r a t i o n o f the N i ( 4 m e p y ) 4 ( P F g ) 2 m a t e r i a l which was analyzed f o r paramagnetic i m p u r i t y i n s e c t i o n 4.2.2.5.1. The magnetic s u s c e p t i b i l i t i e s o f these samples are compiled i n Appendix 4, Table A4-3. TABLE VI-4 THERMAL PREPARATIONS OF N i ( 4 m e p y ) 4 ( P F g ) 2 SAMPLE TEMPERATURE(°C) DURATION (hr) a 72 45 b 110 32 r. 112 23 -276-6.2.4.2 THERMAL DEGRADATION STUDIES As mentioned i n s e c t i o n 6.2.4.1, when the Ni(4mepy) 4~ (PF^)„ i s heated a t 100°C a white sublimate i s observed 6 2 formirig .... When the NiL„ (EF,.) _ compounds are heated a t h i g h e r 4 D 2 temperatures, n o t i c e a b l e decomposition takes p l a c e . The remain-der o f t h i s s e c t i o n w i l l p r e s e n t the a n a l y t i c a l data f o r the r e s i d u e s and sublimates of the decomposition of N i (py) ^  (PF g) 2 , N i (py) .(AsF,)~, and Ni(4mepy).(PF,)„ and t h e i r c r i t i c a l de-4 b 2. 4 b 2 composition temperatures. When Ni (py) . (PF,.) _ i s heated a t 170°C copious amounts 4 b 2 of white m a t e r i a l sublimes of f and the r e s i d u e i s a p a s t e l green c o l o r . The C, H, and N analyses f o r the sublimate are 29.2 9%,;. 2.4 6%, and 6.83%; the v a l u e s expected f o r pyPF 5 are 28.66%, 2.36%, and 6.66%. Even though the v a l u e s o f the carbon and n i t r o g e n are 2% o f f the v a l u e s expected, the mole r a t i o C:H:N i s 5:5:1 which i n d i c a t e s t h a t t h e r e was not any decomposition of the p y r i d i n e moiety. The C, H, and N a n a l y s e s f o r the r e s i d u e i s 28.7 0%, 3.20%, and 6.62%; the v a l u e s expected f o r N i ( p y ) F ( P F g ) (and N i ( p y ) 2 F ( P F g ) ) are 19.90%, 1.67%, and 4.64%( and 31.5%, 2.65%,and 7.35%). There i s not very good agreement of' these s t o i c h i o m e t r i e s w i t h the v a l u e s observed i n the r e s i d u e ; a l s o the mole r a t i o C:H:N i n the r e s i d u e i s 5.1:6:1 which may be i n d i c a t i v e of some decomposition of the p y r i d i n e m o i e t i e s . -277-When N i ( p y ) 4 ( A s F g ) 2 i s heated at 180°C " i n vacuo", a white m a t e r i a l i s sublimed o f f and the r e s i d u e i s a p a s t e l green. The C, H, and N analyses f o r the sublimate were 2 3.53%, 1.91% and 5.43%, r e s p e c t i v e l y ; the va l u e s expected f o r pyAsFj-are 24.12%, 2.02%,and 5.63%. Again, as i n the Ni(py) ( P F g ) 2 case, the observed v a l u e s are 2% d i f f e r e n t from the expected v a l u e s ; the C:H:N mole r a t i o i s 5:4.9:1, which i n d i c a t e s t h a t the p y r i d i n e u n i t i s s t i l l i n t a c t i n the sublimate. These analyses f o r the re s i d u e a r e 19.57%, 2.53%, and 4.05%, r e s p e c t i v e l y ; the va l u e s expected f o r a compound of the s t o i c h i o m e t r y Ni(py)F(AsFg) are 17 . 37 %, 1.46% , and 4.05%. The comparison of expected and the found shows a f a i r l y good agreement. The C:H:N r a t i o found (5.6:8.7:1),however, shows t h a t decomposition of p y r i d i n e molecules has o c c u r r e d . When N i ( 4 m e p y ) 4 ( P F g ) 2 i s heated a t 162-172°C " i n vacuo", a white m a t e r i a l sublimes o f f and a p a s t e l y e l l o w r e s i d u e remains. The 6, H, and N analyses f o r the sublimate are 33.17%, 3.22%, and 6.29%, r e s p e c t i v e l y ; these v a l u e s f o r 4mepyPF 5 are 32.17%, 3.22%, and 6.39%. The observed" G:H:N r a t i o i s 6.0:7.0:1.0 which i s c o n s i s t e n t with a 4mepy moiety being present; but the observed v a l u e s of the elements show a d e v i a t i o n of approximately 2% from the expected v a l u e s . The C, H, and N analyses f o r the r e s i d u e are 22.83%, 2.50, and 5.00%; the v a l u e s expected f o r Ni(4mepy)F(PFg) are 22.82%, 2.23%, and 4.44%. The agreement of found and expected analyses i s not exact and the C:H:N r a t i o (5.3:6.9:1.0)indicates 4mepy decomposition. • -278-6.2.5 UNSUCCESSFUL PREPARATIONS The o n l y compound which would be a member of the s e r i e s of compounds s t u d i e d here which was not prepared was Ni(3mepy)^(PFg) 2- I t s s y n t h e s i s was not completed because of time l i m i t a t i o n s . As mentioned i n s e c t i o n 6.2.3.9, the Ni(3mepy)^(AsFg) 2 compound i s prepared by vacuum d r y i n g o f the Ni(3mepy)g(H 20) 2(AsFg) 2 compound t i l l the water band i n the i n f r a r e d spectrum disappeared. When t h i s was done wi t h the Ni(3mepy)g(H 20)2(PFg)2 compound, the water band i n the i n f r a r e d spectrum d i d not di s a p p e a r . When the "non-dry" Ni(3mepy)g(H 20)2(PFg)2 compound was heated a t 66°C " i n vacuo", the elemental analyses (C : 38.10%, H : 4.15%, and N : 7.74%) i n d i c a t e d t h a t decomposition had taken p l a c e because of the d e v i a t i o n from the expected percentages (39.97%, 4.15%, 7.74% r e s p e c t i v e l y ) and of the mole r a t i o . C:H:N (5.7:7.5:1) from the expected v a l u e s (6:7:1). When t h i s m a t e r i a l i s washed wit h c h l o r o f o r m , the f i l t r a t e was green and the m a t e r i a l on the f i l t e r paper,-a yellow-green s o l i d . - As the sample was washed, the yellow-green m a t e r i a l turned more y e l l o w i n t i n g e but the green c o l o r c o u l d not be removed. The Ni(3mepy)^(PFg) 2 compound can probably be s y n t h e s i z e d by the j u d i c i o u s use of r e a c t i o n c o n d i t i o n s , i . e . lower h e a t i n g temperature or a d i f -f e r e n t s o l v e n t f o r the " s t i r " p r e p a r a t i o n . -279-6.3 ANALYTICAL DATA Elemental analyses f o r carbon, hydrogen, and n i t r o g e n were done by Mr. P e t e r Borda of t h i s department. The accuracy of the d e t e r m i n a t i o n are c o n s i d e r e d to be +.3% on the percentage o f an element, i . e . 35.2 + .3. 6.4 PHYSICAL EXPERIMENTAL TECHNIQUES 6.4.1 MAGNETIC SUSCEPTIBILITY MEASUREMENTS The magnetic s u s c e p t i b i l i t e s o f the compounds prepared were determined-at f i e l d s t r e n g t h s of, approximately' 4 0 0 0 or 8000 gauss, u s i n g a Gouy apparatus p r e v i o u s l y d e s c r i b e d (135). The temperature range s t u d i e d was from 305K to 80K. The sample tube and apparatus was c a l i b r a t e d u s i n g HgCo(CNS) 4, mercuric t e t r a t h i o c y n a t o c o b a l t a t e (136), as the standard; the temperature monitered by the thermocouple, was c o r r e c t e d by a c a l i b r a t i o n based on the known v a r i a b l e temperature behavior of the standard, For a l l paramagnetic compounds, the r e s u l t s are f o r one or two packings through the temperature range and are c o r r e c t e d f o r packing e r r o r s and t e s t e d f o r f i e l d dependence by measure-ments at room temperature w i t h a Faraday balance. The magnetic s u s c e p t i b i l i t i e s were found to be f i e l d independent f o r a l l o f the complexes s t u d i e d . -280-The e f f e c t i v e magnetic moments were c a l c u l a t e d from the e x p r e s s i o n (41) y e f f = 2.828 ( x A-T) J s where T i s t h e a b s o l u t e t e m p e r a t u r e i n K e l v i n s and x A i s t h e molar s u s c e p t i b i l i t y i n e g i s . u n i t s c o r r e c t e d f o r diamagnetism o f a t o m i c m o i e t i e s p r e s e n t and, when a p p r o p r i a t e , f o r t e m p e r a t u r e independent paramagnetism; X A = X - ( d i a m a g n e t i c c o r r e c t i o n s ) - t . i . p . The d i a m a g n e t i c c o r r e c t i o n s were o b t a i n e d from s t a n d a r d s o u r c e s (40, 41, 137). The c o r r e c t i o n s used f o r t h e atomic s u s p e c t i b i l i t i e s o f t h e m e t a l i o n s a r e : C u ( I I ) = - 1 3 ; N i ( I I ) = i l 2 ; and C o ( I I ) = - 1 2 ; f o r t h e l i g a n d m o i e t i e s : p y r i d i n e = - 4 9 ; m e t h y l p y r i d i n e and 3 - m e t h y l p y r i d i n e =-61, f o r t h e a n i o n s : P F g = — — 6 "67, AsFg = -97. A l l d i a m a g n e t i c c o r r e c t i o n s a r e 10 e.g.s, — 6 3 u n i t s (10 cm m o l e ) . The t e m p e r a t u r e i n d e p e n d e n t paramagnetism term was i n c l u d e d when t h e e l e c t r o n i c s p e c t r a l d a t a i n d i c a t e d t h e p r e s e n c e o f an "A 2" o r "E" ground s t a t e . The c o r r e c t i o n f o r an "A 2" term i s : and f o r "E" term t . i . p . = 8N8 2/10Dq t . i . p . = 4N8 2/10Dq 6.4.2 INFRARED SPECTROSCOPY The room t e m p e r a t u r e ( r o u t i n e ) i n f r a r e d s p e c t r a were r e c orded o n a P e r k i n Elmer Model 4 57 G r a t i n g S p e c t r o m e t e r -281-over the range 4 000 - 250 cm ~~. The c e l l windows" used were KRS-5 (Harshaw Chemical Co.) and were composed of 42% T l B r and 58% T i l . The N u j o l m u l l s were prepared i n the dry box, spread on the p l a t e s , s e a l e d w i t h tape to prevent h y d r o l y s i s and examined as soon as p o s s i b l e . A l l s p e c t r a were c a l i b r a t e d w i t h the p o l y s t y r e n e standard at 1601 and 907 cm 1 . The low temperature s p e c t r a were recorded on a P e r k i n -Elmer Model 225 G r a t i n g Spectrometer over the same r e g i o n (4000 - 250 c m - 1 ) . The low temperature c e l l (138) has been d e s c r i b e d elsewhere. The sampling technique i n v o l v e d u s i n g a m u l l or powder sample between the KRS-5 p l a t e s which were p l a c e d i n the c e l l h o l d e r i n the dry box, j o i n e d t o the r e s t of the apparatus, and q u i c k l y evacuated on a vacuum l i n e . A t y p i c a l run, w i t h a p p l i c a t i o n o f a dynamic vacuum c o n s i s t e d of