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UBC Theses and Dissertations

Studies on pyridine : thiourea and substituted thiourea complexes of cobalt (II) arylcarboxylates Wong, Chun Tong 1973

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STUDIES ON PYRIDINE, THIOUREA AND SUBSTITUTED THIOUREA COMPLEXES OF COBALT(II) ARYLCARBOXYLATES BY CHUN TONG WONG B . S c , Chinese U n i v e r s i t y o f Hong Kong, 1965 B.Sc.Sp., U n i v e r s i t y o f Hong Kong, 1966 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN THE DEPARTMENT OF CHEMISTRY We accept t h i s t h e s i s as conforming t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA August, 1973 In presenting this thesis in part ia l fulfilment of the requirements for an advanced degree at the University of Br i t i sh Columbia, I agree that the Library shall make i t freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. The University of Br i t i sh Columbia Vancouver 8, Canada Department of i ABSTRACT A number of new t h i o u r e a and s u b s t i t u t e d t h i o u r e a complexes of c o b a l t ( I I ) c a r b o x y l a t e s , C o ( R C 0 2 ) 2 ' L 2 (where RCC>2 i s a c e t a t e or a r y l c a r b o x y l a t e and L i s t h i o u r e a , e t h y l e n e t h i o u r e a or N,N'-dimethylthiourea), have been prepared and c h a r a c t e r i z e d , mainly by s p e c t r a l s t u d i e s i n the i n f r a r e d , 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 and by magnetic s u s c e p t i b i l i t y s t u d i e s over the temperature range 80 - 320 °K. These s t u d i e s have shown t h a t , the molecular s t r u c t u r e s i n v o l v e a p s e u d o - t e t r a h e d r a l l i g a n d environment about c o b a l t w i t h two oxygen and two sulphur atoms forming the immediate environment about the metal (Co0 2S 2 chromophore). D i f f e r e n c e s i n the s o l i d s t a t e e l e c t r o n i c s p e c t r a of d i f f e r e n t c a r b o x y l a t e complexes are not simply r e l a t e d t o the nature of the c a r b o x y l a t e group or s u l p h u r - l i g a n d i n v o l v e d and are a s c r i b e d t o s o l i d s t a t e c r y s t a l packing e f f e c t s which r e s u l t i n v a r i a t i o n s i n the d e t a i l e d geometry about the c o b a l t i o n s . The magnetic p r o p e r t i e s of these complexes obey Curie-Weiss law w i t h magnetic moments i n the range 4.33 - 4.46 B.M. and Weiss con s t a n t s i n the range -2 to -7 °K. The data have been analyzed, assuming a z e r o - m a g n e t i c - f i e l d s p l i t t i n g of the ground s t a t e s p i n l e v e l s caused by l i g a n d f i e l d asymmetry. P y r i d i n e complexes of the g e n e r a l formula C o ( R C 0 2 ) 2 * p y 2 (where RC0 2 i s a c e t a t e , t r i f l u o r o a c e t a t e or a r y l c a r b o x y l a t e ) have been prepared and s p e c t r a l and cryomagnetic s t u d i e s show the complexes t o be pseudo-o c t a h e d r a l w i t h f o u r oxygen atoms and two n i t r o g e n atoms forming the immediate environment about c o b a l t (CoO^^ chromophore). The complexes have been c l a s s i f i e d i n t o two groups. One group, which i n c l u d e s the a c e t a t e , t r i f l u o r o -ac'etate and two o r t h o - s u b s t i t u t e d benzoate complexes, e x h i b i t s r e l a t i v e l y high magnetic moments (4.95 - 5.02 B.M.) and cryomagnetic 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 c o n s i s t e n t w i t h t e t r a g o n a l s t r u c t u r e s . These complexes are c o n s i d e r e d to have s t r u c t u r e s i n v o l v i n g b r i d g i n g c a r b o x y l a t e groups and t r a n s - c o o r d i n a t e d p y r i d i n e molecules. The other group of complexes which i n c l u d e s the benzoate and two pa r a -s u b s t i t u t e d benzoate complexes have much lower room-temperature magnetic moments (4.6 - 4.7 B.M.) and i n ge n e r a l e x h i b i t s s p e c t r a l and cryomagnetic p r o p e r t i e s s u g g e s t i v e of lower symmetry about c o b a l t . These complexes are c o n s i d e r e d t o have s t r u c t u r e s i n v o l v i n g c i s - c o o r d i n a t i o n of p y r i d i n e molecules. No obvious c o r r e l a t i o n between s t r u c t u r a l type and the nature of the c a r b o x y l a t e group was found. The s t a b i l i t i e s of these complexes towards p y r i d i n e d i s s o c i a t i o n were, however, found t o be r e l a t e d t o the nature of the anion i n v o l v e d , d e c r e a s i n g with i n c r e a s i n g base s t r e n g t h of the c a r b o x y l a t e i o n . i i i TABLE OF CONTENTS ABSTRACT i LIST OF ABBREVIATIONS AND SYMBOLS v LIST OF TABLES v i LIST OF FIGURES i x ACKNOWLEDGEMENT x i i i CHAPTER I : GENERAL INTRODUCTION 1 1-1. Metal Complexes of C a r b o x y l i c A c i d s 1 1-2. Purpose of the Present Work 6 1-3. O r g a n i z a t i o n of the Th e s i s 7 CHAPTER I I : STEREOCHEMISTRY AND ELECTRONIC STRUCTURE OF COBALT(II) COMPLEXES 8 I I - l . I n t r o d u c t i o n 8 II - 2 . T e t r a h e d r a l F i e l d Environment 11 II-2-1. E l e c t r o n i c Spectra 11 II-2-2. Magnetic P r o p e r t i e s 18 I I - 3 . Octahedral F i e l d Environment 24 II-3-1. E l e c t r o n i c Spectra 24 II-3-2. Magnetic P r o p e r t i e s 30 CHAPTER I I I : EXPERIMENTAL 35 I I I - l . M a t e r i a l s Used 35 I I I - 2 . Elemental Analyses 36 I I I - 3 . M olecular Weights 37 I I I - 4 . I n f r a r e d Spectra 38 I I I - 5 . E l e c t r o n i c Spectra 38 I I I - 6 . Magnetic S u s c e p t i b i l i t i e s 39 i v CHAPTER IV: THIOUREA AND SUBSTITUTED THIOUREA COMPLEXES OF COBALT(II) CARBOXYLATES 40 IV-1. Introduction 40 IV-2. Synthesis and Stoichiometry 43 IV-2-1. Synthesis 43 IV-2-2. Stoichiometry 59 IV-3. Characterization of Complexes 60 IV-3-1. Infrared Spectral Study 60 IV-3-2. Ele c t r o n i c Spectral Study 77 IV- 3-3. Magnetic S u s c e p t i b i l i t y Study 95 IV-4. Solution Studies 109 CHAPTER V: PYRIDINE COMPLEXES OF COBALT(II) CARBOXYLATES 130 V - l . Introduction 130 V-2. Synthesis and Stoichiometry 132 V- 2-1. Synthesis 132 V-2-2. Stoichiometry 144 V-3. Characterization of Complexes 146 V-3-1. rlnfrared'rSpectral-'Study 146 V-3-2. Elect r o n i c Spectral Study 166 V-3-3. Magnetic S u s c e p t i b i l i t y Study 174 V-4. Solution Studies 188 V-5. Hydrated Pyridine Complexes of Cobalt(II) Arylcarboxylates 210 CHAPTER VI: SUMMARY AND 'CONCLUSIONS 215 REFERENCES 226 APPENDIXES 236 V LIST OF ABBREVIATIONS AND SYMBOLS TU ... t h i o u r e a ETU ... e t h y l e n e t h i o u r e a DMTU ... N,N'-dimethylthiourea py ... p y r i d i n e y e £ £ ... the magnetic moment X + + ... the magnetic s u s c e p t i b i l i t y per mole of c o b a l t ( I I ) Co i o n s C O JL? DT X , ... the magnetic s u s c e p t i b i l i t y per mole of c o b a l t ( I I ) Co ions c o r r e c t e d f o r TIP TIP ... temperature independent paramagnetism X. ... the 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 f o r a term k ... e l e c t r o n d e l o c a l i z a t i o n f a c t o r g ... Lande or s p e c t r o s c o p i c s p l i t t i n g f a c t o r 8 ... z e r o - f i e l d second order s p i n - o r b i t c o u p l i n g s p l i t t i n g parameter 0 ... Weiss constant A ... the a x i a l l i g a n d f i e l d s p l i t t i n g v ... a magnetic parameter d e f i n e d as A/A A ... a parameter f o r o r b i t a l angular momentum Dq ... c u b i c c r y s t a l f i e l d s p l i t t i n g parameter B ... a Racah parameter f o r i n t e r e l e c t r o n i c r e p u l s i o n £ (<«) ... the molar e x t i n c t i o n c o e f f i c i e n t of a s p e c t r a l band a n t i ... antisymmetric -CO2 s t r e t c h i n g frequency sym" ... symmetric -C0o s t r e t c h i n g frequency v i LIST OF TABLES Table Page IV-1 A n a l y t i c a l R e s u l t s : C o b a l t ( I I ) A r y l c a r b o x y l a t e Hydrates 4 5 IV-2 A n a l y t i c a l R e s u l t s of Thiourea, E t h y l e n e -t h i o u r e a and N,N'-Dimethylthiourea Complexes . 47 IV-3 I n f r a r e d S p e c t r a l Assignments ( f o r Three C r i t i c a l Bands) of TU Complexes of Co b a l t (II) 64 IV-4 I n f r a r e d S p e c t r a l Assignments (for Three C r i t i c a l Bands) of DMTU Complexes of C o b a l t ( I I ) 67 IV-5 I n f r a r e d S p e c t r a l Assignments ( f o r Four C r i t i c a l Bands) of E t h y l e n e t h i o u r e a 68 IV-6 I n f r a r e d S p e c t r a l Assignments (for Four C r i t i c a l Bands) of ETU Complexes of C o b a l t ( I I ) 69 IV-7 S t r e t c h i n g Frequencies f o r S-Bonded C o ( R C 0 2 ) 2 « L 2 Complexes 75 IV-8 E l e c t r o n i c S p e c t r a l Parameters f o r S-Ligand Complexes of C o b a l t ( I I ) P e r c h l o r a t e and C h l o r i d e ( S o l i d State) 85 IV-9 E l e c t r o n i c S p e c t r a l Parameters f o r S-Ligand Complexes of Co b a l t (II) Carboxylates ( S o l i d State) 92 IV-10 Experimental u f f and Q Values of ETU, TU and DMTU Complexes of Co b a l t (II) 96 v i i IV-11 Comparison of H and 8 Values with Previous Work 97 IV-12 Experimental g and 6 Values of ETU, TU and DMTU Complexes of C o b a l t (II) 100 IV-13 Comparison of V ^ and 6 Values (from Slope of Curie-Weiss F i t ) w i t h Those C a l c u l a t e d from g and 6 Values 101 IV-14 S p i n - o r b i t C o u p l i n g Constant (A) and E l e c t r o n D e l o c a l i z a t i o n F a c t o r (k) from Magnetic Data . 103 IV-15 Crude S o l u b i l i t y T e s t s on TU, ETU and DMTU Complexes of Co b a l t (II) I l l IV-16 E l e c t r o n i c S p e c t r a l Parameters f o r S-Ligand Complexes i n Acetone S o l u t i o n 117 IV-17 E q u i l i b r i u m Constant Data of TU, ETU and DMTU Complexes of C o b a l t (II) 127 IV- 18 Comparison of E q u i l i b r i u m Constant Values between the Present Work and the Previo u s Work 128 V- l A n a l y t i c a l R e s u l t s of P y r i d i n e Complexes . . . 134 V-2 Changes of C r i t i c a l P y r i d i n e Bands as C r i t e r i a f o r P y r i d i n e C o o r d i n a t i o n 149 V-3 C r i t i c a l P y r i d i n e Ring V i b r a t i o n s of P y r i d i n e Complexes of Co b a l t (II) Carboxylates 150 V-4 I n f r a r e d S p e c t r a l Data and Assignments (1800 -1300 cm "S of T r i f l u o r o a c e t a t e Compounds and P y r i d i n e 153 v i i i V-5 I n f r a r e d S p e c t r a l Data and Assignments (1700 -1300 cm "*") of Aceta t e Compounds and P y r i d i n e 157 V-6 I n f r a r e d S p e c t r a l Data and Assignments (1700 -1300 cm ^) of Benzoate Compounds and P y r i d i n e 159 V-7 I n f r a r e d S p e c t r a l R e s u l t s on -C0 2 S t r e t c h i n g Frequencies of P y r i d i n e Complexes of C o b a l t ( I I ) C a r b o x y l a t e s 165 V-8 E l e c t r o n i c S p e c t r a l Parameters f o r Group A P y r i d i n e Complexes ( S o l i d State) 17 0 V-9 Room-temperature E f f e c t i v e Magnetic Moments of P y r i d i n e Complexes of C o b a l t ( I I ) C a r b o x y l a t e s . 175 V-10 Magnetic Parameters of Group A P y r i d i n e Complexes 177 V - l l Magnetic Parameters of Three of the Group B P y r i d i n e Complexes 181 V-12 Crude S o l u b i l i t y T e s t s on P y r i d i n e Complexes of C o b a l t ( I I ) C a r b o x y l a tes 190 V-13 M o l e c u l a r Weight R e s u l t s of P y r i d i n e Complexes of C o b a l t ( I I ) C a r b o x y l a tes 195 V-14 S p e c t r a l Parameters of S o l u t i o n E l e c t r o n i c S p e c t r a o f P y r i d i n e Complexes of C o b a l t ( I I ) C a r b o x y l a t e s 203 V-15 E l e c t r o n i c S p e c t r a l Parameters of Hydrated P y r i d i n e Complexes of C o b a l t ( I I ) A r y l c a r b o x y l a t e s ( S o l i d State) 213 V-16 Magnetic Parameters of Hydrated P y r i d i n e Complexes of C o b a l t ( I I ) A r y l c a r b o x y l a t e s . . . 214 i x LIST OF FIGURES F i g u r e I I - l Tanabe-Sugano Energy Diagrams f o r C o b a l t ( I I ) . 9 IV-1 The M o l e c u l a r Geometry o f C o ( C H 3 C 0 2 ) 2 « E T U 2 . . 42 IV-2 I n f r a r e d S p e c t r a of TU, C o ( p - B r - C 6 H 4 C 0 2 ) 2 • T U 2 and Co ( p - B r - C g H 4 C 0 2 ) 2 « 3 H 2 0 63 IV-3 I n f r a r e d S p e c t r a (1300 - 1700 cm - 1) of Complexes o f C o b a l t (II) p-Bromobenzoate . . . . 73 IV-4 Acetone S o l u t i o n S p e c t r a of TU, ETU and DMTU Complexes of C o b a l t ( I I ) P e r c h l o r a t e 79 IV-5 KBr P e l l e t S p e c t r a of TU, ETU and DMTU Complexes o f C o b a l t ( I I ) P e r c h l o r a t e 80 IV-6 Acetone S o l u t i o n S p e c t r a o f TU, ETU and DMTU Complexes o f C o b a l t (II) C h l o r i d e 82 IV-7 KBr P e l l e t S p e c t r a of TU, ETU and DMTU Complexes o f C o b a l t ( I I ) C h l o r i d e 83 IV-8 KBr P e l l e t S p e c t r a of ETU Complexes o f C o b a l t ( I I ) C a r b o x y l a t e s 88 IV-9 KBr P e l l e t S p e c t r a of TU Complexes of C o b a l t ( I I ) C a r b o x y lates 89 IV-10 KBr P e l l e t S p e c t r a o f DMTU Complexes of C o b a l t ( I I ) C a r b o x y lates 90 IV-11 KBr P e l l e t S p e c t r a o f TU, ETU and DMTU Complexes of C o b a l t ( I I ) m-Nitrobenzoate . . . . 94 X IV-12 Experimental t o Theory F i t of 1/x vs T C o + + A T y p i c a l Example 99 IV-13 u « vs KT/-A P l o t and T h e o r e t i c a l F i t f o r e r r Co(m-N0 2-C 6H 4C0 2) 2-ETU 2 108 IV-14 Acetone S o l u t i o n S p e c t r a o f S e v e r a l TU, ETU and DMTU Complexes of C o b a l t ( I I ) A r y l c a r b o x y l a t e s . 113 IV-15 Acetone S o l u t i o n S p e c t r a ( V i s i b l e Region) o f Co(p-Br-C|H 4C0 2)2" T U2 ~ D e P e n d e n c e on S-Ligand C o n c e n t r a t i o n 115 IV-16 Beer's Law P l o t s of Some S e l e c t e d S-Ligand Complexes ( V i s i b l e Region) 116 IV-17 E f f e c t of Adding Water t o S o l u t i o n s of S-Ligand Complexes on E l e c t r o n i c S p e c t r a l I n t e n s i t i e s . 122 IV- 18 Acetone S o l u t i o n S p e c t r a ( V i s i b l e Region) o f Co(ClO^) 2•TU^ - V a r i o u s C o n c e n t r a t i o n , S o l v e n t and Added S-Ligand 12 3 V- l I d e n t i f i c a t i o n of P y r i d i n e Bands i n the I n f r a -red Spectrum (1700 - 400 cm - 1) of Co ( p - N 0 2 - C 6 H 4 C 0 2 ) 2 * p y 2 as an Example 148 V-2 I n f r a r e d S p e c t r a (1800 - 1300 cm - 1) of P y r i d i n e and i t s Complexes of C o b a l t ( I I ) T r i f l u o r o a c e t a t e 154 V-3 I n f r a r e d S p e c t r a (1700 - 1300 cm - 1) of B i s -p y r i d i n e C o b a l t (II) A c e t a t e and P y r i d i n e . . . 158 V-4 I n f r a r e d S p e c t r a (1700 - 1300 cm - 1) of Benzoate Compounds and P y r i d i n e 160 x i V-5 I n f r a r e d S p e c t r a (1700 - 1300 cm ) of B i s p y r i d i n e Complexes of C o b a l t ( I I ) A r y l c a r b o x y l a t e s 162 V-6 S o l i d State E l e c t r o n i c Spectra of Group A Complexes 169 V-7 S o l i d State E l e c t r o n i c S p e c t r a of Group B Complexes 17 3 V-8 T y p i c a l F i t s of Experimental y e f £ vs K T / | A | P l o t s w i t h Theory f o r Group A P y r i d i n e Complexes 178 V-9 T y p i c a l F i t s of Experimental Ugf^ vs K T / | A | P l o t s w i t h Theory f o r Three of the Group B P y r i d i n e Complexes 182 V-10 Curie-Weiss P l o t s of Three Group B P y r i d i n e Complexes 184 V - l l T y p i c a l F i t of Experimental y e £ £ vs K T / | A | P l o t s with Theory f o r C o ( p - C H 3 0 - C 6 H 4 C 0 2 ) 2 « p y 2 187 V-12 S o l u t i o n I n f r a r e d S p e c t r a of P y r i d i n e ., Complexes of C o b a l t ( I I ) T r i f l u o r o a c e t a t e . . . 192 V-13 Benzene S o l u t i o n E l e c t r o n i c Spectra of the Two P y r i d i n e Complexes of C o b a l t (II) T r i f l u o r o -a c e t a t e w i t h and without Added P y r i d i n e . . . 197 V-14 Acetone S o l u t i o n E l e c t r o n i c S p e c t r a of B i s -p y r i d i n e Complexes of C o b a l t ( I I ) C a r b o x y l a tes 200 x i i V-15 Chloroform S o l u t i o n E l e c t r o n i c Spectra of B i s -p y r i d i n e Complexes of C o b a l t (II) C a r b o x y l a t e s 201 V-16 Benzene S o l u t i o n E l e c t r o n i c S p e c t r a of B i s -p y r i d i n e Complexes of C o b a l t ( I I ) C a r b o x y l a t e s 202 V-17 Benzene S o l u t i o n E l e c t r o n i c S p e c t r a ( V i s i b l e Region) of Co (CgHr-CC^) 2 • p y 2 and Co (o-Br-C g H 4 C 0 2 ) 2 * p y 2 - E f f e c t o f C o n c e n t r a t i o n . . . 206 V-18 E f f e c t of Adding P y r i d i n e t o Benzene S o l u t i o n of B i s p y r i d i n e C o b a l t (II) Benzoate 207 V-19 E f f e c t of Adding P y r i d i n e t o Benzene S o l u t i o n of B i s p y r i d i n e C o b a l t ( I I ) o-Bromobenzoate . . 208 V- 20 E l e c t r o n i c S p e c t r a o f Hydrated P y r i d i n e Complexes of C o b a l t (II) A r y l c a r b o x y l a t e s ( S o l i d State) 212 VI- 1 T y p i c a l Example of S t r u c t u r e s I n v o l v i n g B r i d g i n g C arboxylate Groups and Trans-Coordinated P y r i d i n e Molecules 220 VI-2 T y p i c a l Example of C i s - O c t a h e d r a l S t r u c t u r e s 222 VI-3 Proposed S t r u c t u r e Model f o r C o b a l t ( I I ) C a rboxylate Complexes 223 x i i i ACKNOWLEDGEMENT I am extremely g r a t e f u l to Dr. R. C. Thompson f o r h i s i n v a l u a b l e a d v i c e and continuous guidance and encouragement throughout the course o f t h i s work. I would a l s o l i k e t o thank Miss J a c i n t a Tao f o r her e x c e l l e n t t y p i n g of the manuscript. To Terisa 1 CHAPTER I GENERAL INTRODUCTION 1-1. METAL COMPLEXES OF CARBOXYLIC ACIDS In a r e c e n t a r t i c l e concerning complexes of simple c a r b o x y l i c a c i d s , Oldham (1) p o i n t e d out t h a t most of the chemical elements form c a r b o x y l a t e d e r i v a t i v e s , many of which have been known f o r a number of ye a r s . 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 metal c a r b o x y l a t e complexes have shown the v e r s a t i l i t y of the c a r b o x y l a t e group (RCO2) i n regard t o i t s mode of c o o r d i n a t i o n to metal i o n s (M). As d e s c r i b e d by Oldham, these complexes may be c l a s s i f i e d a c c o r d i n g to the f o l l o w i n g s i x b a s i c s t r u c t u r a l t ypes: 2 .0 " M + 0 R - C. 0 — M 0 R - CY M ^ 0 ' i o n i c unidentate bidentate che la t ing I II III R M. M' M 0 R - C 0 M R - Cf*' 0 — M 0 M bidentate br idg ing (anti-anti ) IV bidentate br idg ing (anti-syn) V bidentate br idging (syn-syn) VI The compound Na(HC02) (2) provides an example of an i o n i c carboxylate (Type I) i n which the two C-0 bond lengths are equivalent . Unidentate carboxylate coordinat ion (Type II) i s seen i n complexes such as L i (CH 3C0 2) . 2H20 (3), C o ( C H 3 C 0 2 ) 2 . 4 H 2 0 (4) and Co{(NH^)^(CH^CC^))C1(ClO^) (5). In these cases the two C-0 bond lengths i n the acetate group are s i g n i f i c a n t l y d i f f e r e n t . Bidentate che la t ing coordinat ion (Type III) requires the formation of a four-membered r ing which, on s t e r i c grounds, might be expected to be an unstable form of coord inat ion . However, there are a few compounds, such as Z n ( C H 3 C 0 2 ) 2 . 2 H 2 0 (6) and Na{U0 2 (CH 3 C0 2 ) 3 } (7), which exh ib i t t h i s kind of coord inat ion . The unfavourable s t e r i c e f fec t i s overcome in some complexes such as Z n ( C H 3 C 0 2 ) 2 . T U 2 (8), C o ( C H 3 C 0 2 ) 2 - E T U 2 ( 9 ) a n d { ( C 6 H 5 ) 4 A s ^ 2 C o ( C F 3 C 0 2 ) 4 ( 1 0 ) ' b ^ a 3 form of c o o r d i n a t i o n i n which the two oxygen atoms are non-e q u i v a l e n t l y bonded to the same metal with one s h o r t e r and one longer M-0 d i s t a n c e . These s t r u c t u r e s may be d e s c r i b e d as i n t e r m e d i a t e between Types I I and I I I . Bid e n t a t e b r i d g i n g appears to be the most common form o f c o o r d i n a t i o n e x h i b i t e d by c a r b o x y l a t e groups. Examples of the a n t i - a n t i form (Type IV) and the a n t i - s y n form (Type V) are Cu(HC0 2) 2.4H 20 (11) and C u ( H C 0 2 ) 2 (12) r e s p e c t i v e l y . The syn-syn form o f b r i d g i n g (Type V I ) , the most common type, y i e l d s a b i n u c l e a r cage s t r u c t u r e t y p i f i e d by the complex: C u 2 ( C H 3 C 0 2 ) 4 . 2 H 2 0 (13). The s t r u c t u r e has four c a r b o x y l a t e groups b r i d g i n g two metal ions with the oth e r two l i g a n d s a t both ends of the 'cage 1. T h i s s t r u c t u r e i s found in other complexes such as C r 2 ( C H 3 C 0 2 ) 4 . 2 H 2 0 (14), Re 2 (C 6H 5C0 2) 2 I 4 (15), Rh 2 (HC0 2) 4 . 2H 20 (16), Rh 2 (CH3CC>2) 4 . 2H 20 (17), M o 2 ( C H 3 C 0 2 ) 4 (18), C u 2 ( C H 3 C 0 2 ) 4 . p y 2 (19), R e 2 ( C 6 H 5 C 0 2 ) 4 . C l 2 . 2 H C l 3 (20) and C u 2 (ClH 2CC>2) 4 . 2 (<a-pic) (21). T h i s syn-syn form of b r i d g i n g i s a l s o found i n the more polymeric s t r u c t u r e s found i n compounds such as Be.0(CH_C0„), (22), Zn.0(CH oC0 n), (23, 24), 4 3 Z o 4 3 Z b C r 0 (CH_,C0„) , (OH) (NH-) t (25), { ZnU (CH_,C0o) , } (26) and 3 j z b 3 3 3 z o n {Ni(HC0~)~.2H~0} (27). S t r u c t u r e s c o n t a i n i n g more than one z z z n type of c a r b o x y l a t e c o o r d i n a t i o n have a l s o been observed. The compound { U 0 2 ( C H 3 C 0 2 ) 2 . P h 3 P 0 } 2 (28) e x h i b i t s c a r b o x y l a t e c o o r d i n a t i o n of Types I I I and VI, { C u ( C 2 H 5 C 0 2 ) 2 . ( C ? H 9 N ) > n (29) of Types I I and VI, and {CaM(CH 3C0 2) 4.6H 20> n (M = Cu, Cd) (30) of Types I I I and VI. 4 In s p i t e of the f a c t t h a t a l a r g e number of metal c a r b o x y l a t e complexes are now known and c h a r a c t e r i z e d , the nature of the c a r b o x y l a t e group i n determining the s t r u c t u r e s , s t e r e o c h e m i s t r i e s and p r o p e r t i e s of i t s complexes i s not w e l l understood. The understanding of the c o o r d i n a t i n g a c t i o n of c a r b o x y l a t e groups may be s i g n i f i c a n t l y enhanced by a s y s t e m a t i c and thorough study of a wide range of complexes of a given metal as evidenced by the very e x t e n s i v e work which has been done on copper(II) c a r b o x y l a t e complexes (31). These s t u d i e s have shown t h a t , f o r copper (II) complexes at l e a s t , the presence of a bulky o r t h o - s u b s t i t u e n t i n the a r y l c a r b o x y l a t e s e r i e s favours the formation of the d i n u c l e a r syn-syn c a r b o x y l a t e b r i d g i n g s t r u c t u r e (Type VI) over more polymeric s t r u c t u r e s . A l s o , i n the absence of such s t e r i c e f f e c t s , the formation of d i n u c l e a r molecules i s favoured where the a v a i l a b l e a - e l e c t r o n d e n s i t y on the c a r b o x y l a t e oxygen atoms, as measured by the pK of the parent a c i d , i s h i g h . a R e l a t i v e l y l i t t l e i s known about c a r b o x y l a t e com-plexes of c o b a l t ( I I ) , compared to the i n f o r m a t i o n now a v a i l a b l e on copper (II) complexes. As e a r l y as i n 1938 , s e v e r a l anhydrous c o b a l t ( I I ) s a l t s of o r g a n i c a c i d s such as a c e t i c , o x a l i c and l a c t i c a c i d s were s t u d i e d m a g n e t i c a l l y (32). T h i s work was l a t e r extended to cover c o b a l t (II) s t e a r a t e and l a u r a t e (33). In 1940, a systematic study of d i s s o c i a t i o n p r e s s u r e s and d e n s i t i e s of s e v e r a l c o b a l t (II) s a l t s of f a t t y a c i d s and t h e i r b i s p y r i d i n e adducts was r e p o r t e d (34). A s i n g l e c r y s t a l x-ray s t r u c t u r e d e t e r m i n a t i o n of c o b a l t ( I I ) 5 a c e t a t e t e t r a h y d r a t e has shown the presence of unidentate a c e t a t e groups s t r o n g l y hydrogen-bonded t o c o o r d i n a t e d water molecules (4). The magnetic s u s c e p t i b i l i t y of the complex was l a t e r measured over a wide temperature range (35, 36). The molecular and c r y s t a l s t r u c t u r e s of c o b a l t ( I I ) formate d i h y d r a t e (37) and t e t r a p h e n y l a r s o n i u m t e t r a k i s - ( t r i f l u o r o -acetato) c o b a l t ( I I ) (10) were a l s o determined. The former compound was found to be i s o s t r u c t u r a l w i t h i t s N i ( I I ) and Cu(II) analogs and to have a s t r u c t u r e i n which the formate groups a c t as b i d e n t a t e b r i d g e s g i v i n g r i s e to a h i g h l y p o l y -meric s t r u c t u r e . The l a t t e r compound, as mentioned e a r l i e r , has a s t r u c t u r e i n which the form of c a r b o x y l a t e c o o r d i n a t i o n i s i n t e r m e d i a t e between Types II and I I I . Thorough s p e c t r a l and magnetic s t u d i e s have been c a r r i e d out on both anhydrous c o b a l t ( I I ) a c e t a t e (38) and anhydrous c o b a l t ( I I ) t r i f l u o r o -a c e t a t e (39). P y r i d i n e complexes of c o b a l t ( I I ) alkanoates and h a l o a c e t a t e s (40) have a l s o been i n v e s t i g a t e d p r e v i o u s l y . The most complete work done i n t h i s area i s d e s c r i b e d i n a paper by Lever and Ogden (41) on the c h a r a c t e r i z a t i o n of h a l o a c e t a t e complexes. 6 1-2. PURPOSE OF THE PRESENT WORK The work d e s c r i b e d i n t h i s t h e s i s has i n v o l v e d the p r e p a r a t i o n and c h a r a c t e r i z a t i o n of new p y r i d i n e (py), t h i o u r e a (TU), e t h y l e n e t h i o u r e a (ETU) and N , N 1 - d i m e t h y l t h i o u r e a (DMTU) complexes of c o b a l t (II) c a r b o x y l a t e s . S e v e r a l complexes p r e v i o u s l y r e p o r t e d but not f u l l y c h a r a c t e r i z e d have been re-examined here. The g e n e r a l aim of t h i s study has been to attempt t o o b t a i n , through a d e t a i l e d study of the magnetic and s p e c t r a l p r o p e r t i e s of a wide range of c o b a l t (II) c a r b o x y l a t e complexes, a b e t t e r understanding of the c o o r d i n a t i n g a c t i o n of c a r b o x y l a t e groups i n metal complexes. Since t h i s work i s concerned p r i m a r i l y w i t h c o o r d i n a t i n g a c t i o n of c a r b o x y l a t e groups, i t i s important t h a t any other l i g a n d s p r e s e n t i n the complexes s t u d i e d be ones which are w e l l c h a r a c t e r i z e d by p r e v i o u s work. The e x c e l l e n t c o o r d i n a t i n g a b i l i t y of p y r i d i n e has made i t one of the most widely s t u d i e d l i g a n d s i n c o o r d i n a t i o n chemistry. In a d d i t i o n , a few p y r i d i n e complexes of c o b a l t ( I I ) c a r b o x y l a t e s are known (41) and f o r these reasons s t u d i e s on p y r i d i n e complexes of the type C o f R C ^ ^ P y ^ form a major p a r t of t h i s t h e s i s . The work on the p y r i d i n e complexes i n d i c a t e d t h a t they a l l have s t r u c t u r e s i n v o l v i n g s i x - c o o r d i n a t e c o b a l t (Co^O^ chromophore) . To extend the s t u d i e s t o i n c l u d e a g r e a t e r v a r i e t y of s t r u c t u r a l types a number of complexes of the g e n e r a l formula C o ( R C 0 2 ) 2 * L 2 , where: L = TU, ETU AND DMTU, have been s t u d i e d here. P r e v i o u s work has shown t h a t c o b a l t ( I I ) 7 complexes c o n t a i n i n g these ' s o f t ' l i g a n d s commonly c o n t a i n f o u r - c o o r d i n a t e c o b a l t . Indeed there appear t o be some r a t h e r n o v e l s t r u c t u r a l types i n v o l v i n g these l i g a n d s as a re c e n t s t r u c t u r a l d e t e r m i n a t i o n on the complex b i s a c e t a t o b i s -(ethylenethiourea) c o b a l t (II) has shown (9). 1-3. ORGANIZATION OF THE THESIS Chapter I I p r o v i d e s a b r i e f d e s c r i p t i o n of the st e r e o c h e m i s t r y of c o b a l t (II) complexes and how i n f o r m a t i o n c o n c e r n i n g s t e r e o c h e m i s t r y and bonding i n c o b a l t ( I I ) complexes can be obtained from magnetic s u s c e p t i b i l i t y and e l e c t r o n i c s p e c t r a l s t u d i e s . T h i s Chapter then o u t l i n e s theory r e l e v a n t t o the p r e s e n t work. Chapter I I I c o n t a i n s a d e s c r i p t i o n of a l l m a t e r i a l s used and the experimental d e t a i l s of a l l p h y s i c a l methods employed i n the c h a r a c t e r i z a t i o n of the complexes. Chapters IV and V d e s c r i b e the p r e p a r a t i o n and c h a r a c t e r i z a t i o n of the complexes while a g e n e r a l d i s c u s s i o n of the r e s u l t s o b t a i n e d and c o n c l u s i o n s drawn r e g a r d i n g c a r b o x y l a t e group c o o r d i n a t i o n to metals i s given i n Chapter VI. E x t e n s i v e t a b u l a t i o n s of "raw" magnetic and s p e c t r a l data are given i n the form of appendixes a t the end of the t h e s i s . 8 CHAPTER I I STEREOCHEMISTRY AND ELECTRONIC STRUCTURE." OF COBALT(II) COMPLEXES I I - l . INTRODUCTION 7 The c o b a l t (II) i o n has a 3d valence s h e l l e l e c t r o n i c c o n f i g u r a t i o n . The f r e e - i o n s p e c t r o s c o p i c terms a r i s i n g from 4 4 2 2 2 i t a re, i n the order of i n c r e a s i n g energy, F, P, H, G, F, 2 2 2 D, D and P. In the presence of a l i g a n d f i e l d , the degeneracies of some of the terms may be removed and the r e l a t i v e e n e r g i e s of a l l r e s u l t i n g s t a t e s are f u n c t i o n s of both the s t r e n g t h and symmetry of the l i g a n d f i e l d . The Tanabe-Sugano diagrams f o r c o b a l t ( I I ) i n l i g a n d f i e l d s of 0^ and T^ symmetries are giv e n i n F i g u r e I I - l . These diagrams gi v e the e n e r g i e s of a l l s t a t e s as a f u n c t i o n of Dq/B f o r Dq/B 3 2 1 0 1 2 3 Dq/B (tetrahedral) (octahedral) VO F i g u r e I I - l . Tanabe-Sugano Energy Diagrams f o r C o b a l t ( I I ) f o r o c t a h e d r a l : C/B = 4.6 3 f o r t e t r a h e d r a l : C / B = 4.50 10 f i x e d v a l u e s of C/B. Dq i s the c u b i c l i g a n d f i e l d parameter and C and B the Racah parameters of i n t e r e l e c t r o n r e p u l s i o n (42) . There are very few, i f any, Co (II) complexes which have e i t h e r very r e g u l a r o c t a h e d r a l or very r e g u l a r t e t r a h e d r a l s t r u c t u r e s . N e v e r t h e l e s s , i t i s convenient to use these i d e a l i z e d geometries as the b a s i s f o r d e s c r i b i n g the s t r u c t u r e s of complexes. Throughout t h i s t h e s i s the terms ' o c t a h e d r a l ' and ' t e t r a h e d r a l ' w i l l be used i n a q u a l i t a t i v e sense to d e s c r i b e those complexes i n which the c o b a l t ions are s i x -and f o u r - c o o r d i n a t e , r e s p e c t i v e l y , and i n which the geometry approximates the i d e a l i z e d geometry i m p l i e d by the names. As seen from F i g u r e I I - l , i n a very s t r o n g o c t a h e d r a l 2 2 lxgand f i e l d , a E s t a t e a r i s i n g from the f r e e - i o n G term becomes the ground s t a t e . T h i s corresponds to a s p i n - p a i r e d c o n f i g u r a t i o n of Co(II) which should occur o n l y a t h i g h l i g a n d f i e l d s t r e n g t h s as i s encountered f o r example i n R^BaCofNC^g (43). Otherwise, f o r most o c t a h e d r a l complexes and a l l t e t r a h e d r a l complexes, a component from the f r e e - i o n 4 F term w i l l form the ground s t a t 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 of Co (II) complexes are dependent on the nature as w e l l as the s t r e n g t h of the l i g a n d f i e l d and d e t a i l e d s t u d i e s of these p r o p e r t i e s of c o b a l t ( I I ) complexes w i l l u s u a l l y p r o v i d e a c o n s i d e r a b l e amount of i n f o r m a t i o n concerning the ligand environment about c o b a l t . The f o l l o w i n g g i v e s a b r i e f survey of theory as w e l l as some r e l e v a n t l i t e r a t u r e f i n d i n g s under the two separate headings, "the t e t r a h e d r a l f i e l d environment" and "the o c t a h e d r a l f i e l d environment". 11 I I - 2 . TETRAHEDRAL FIELD ENVIRONMENT II-2-1. E l e c t r o n i c Spectra The Tanabe-Sugano diagram f o r Co (II) i n a t e t r a h e d r a l l i g a n d environment i s shown i n F i g u r e I I - l . The f r e e - i o n 4 F term i s s p l i t i n a c u b i c t e t r a h e d r a l f i e l d i n t o three components, which are, i n the order of i n c r e a s i n g energy, 4 4 4 A 2 ( F ) , T 2 ( F ) and T 1 ( F ) . The only other q u a r t e t f r e e - i o n 4 4 term, P, i s not s p l i t and belongs t o a T^(P) r e p r e s e n t a t i o n . The most i n t e n s e bands i n the e l e c t r o n i c s p e c t r a o f Co (II) complexes w i l l a r i s e from t r a n s i t i o n s i n v o l v i n g these s t a t e s s i n c e t r a n s i t i o n s to s p i n - d o u b l e t s t a t e s such as those 2 a r i s i n g from the f r e e - i o n G term are s p m - f o r b i d d e n . The three s p i n - a l l o w e d t r a n s i t i o n s are shown i n the f o l l o w i n g s i m p l i f i e d energy l e v e l diagram: V \ \ v 3 > T 1 (P) T X ( F ) T 2 (F) A 2 (F) f r e e - i o n t e t r a h e d r a l f i e l d 12 The Tanabe-Sugano matrices (44) for these quartet states are: -2 Dq 12 Dq 4 Dq 6 Dq 15 B 4 Dq where Dq, the cubic l igand f i e l d s p l i t t i n g parameter, i s a measure of the strength of the l igand f i e l d and the Racah parameter B i s a measure of i n t e r e l e c t r o n repu l s ion , 15 B corresponding to the energy di f ference between the two 4 4 f ree- ion P and F terms. 4 The f i r s t band, v i , corresponding to the A 2 (F) 4 » T 2 (F ) t r a n s i t i o n , should give 10 Dq d i r e c t l y . I t occurs i n the 3000 - 5000 cm region (infrared) . Unlike 4 4 the other two A 2 (F) > T^ t r a n s i t i o n s , t h i s t r a n s i t i o n i s not allowed by the symmetry of the pure e l e c t r o n i c wave functions and hence i s expected to have i n t e n s i t y 10 to 100 4 4 times smaller than the A 2 (F) > T^ t r a n s i t i o n s . Because of t h i s , together with the fact that the region 3000 - 5000 cm i s usual ly masked by v i b r a t i o n a l bands of the molecule, Vi i s usual ly not observed. For example, for the pyr idinium and quinol inium sa l t s of the tetrachlorocobal tate( I I ) 4 4 i o n , the A 2 (F) > T 2 (F) t r a n s i t i o n (vi) i s completely obscured by the N-H s t re tching modes (45). However, a band at about 3400 cm has been assigned to t h i s t r a n s i t i o n for each of the corresponding tetramethylammonium and t e t r a e t h y l -ammonium s a l t s . Other examples i n which the Vi band was 13 -1 2+ observed a r e : f o r C s 3 C o C l 5 , V i = 3000 cm (46); f o r Co doped i n ^2Fe5Q12' Y3 A"^5°12 a n c ^ Y 3 G a 5 ° 1 2 < ? a r n e t s ' v i = 4600 c m - 1 (47) and f o r C o { ( C g H 5 ) 3 P } 2 C 1 2 ' v i = 3 9 0 0 c m _ 1 ( 4 8) • The other two s p i n - a l l o w e d t r a n s i t i o n s V2 and V3 occur i n the 5000 - 12000 cm - 1 r e g i o n ( n e a r - i n f r a r e d ) and 12000 -25000 cm r e g i o n ( v i s i b l e ) r e s p e c t i v e l y . Band i n t e n s i t i e s as measured by the e x t i n c t i o n c o e f f i c i e n t s , £;, a t the band maxima are u s u a l l y found to be of the order of 10 - 100 1/mole-cm f o r v 2 and 100 - 2000 1/mole-cm f o r V3. Assignment of these two bands permits the e v a l u a t i o n of the e l e c t r o n i c parameters Dq and B through the use of the Tanabe-Sugano diagrams and equations (42). E x p e r i m e n t a l l y , the V2 and V3 bands are u s u a l l y found to be r a t h e r broad and s t r u c t u r a l ( i . e . s p l i t i n t o two or more components). As p o i n t e d out r e c e n t l y by F l a m i n i e t a l . (49), the r a t h e r complex nature of the e l e c t r o n i c s p e c t r a of t e t r a h e d r a l c o b a l t ( I I ) complexes may be due to one or more of a number of e f f e c t s i n c l u d i n g low symmetry, s p i n - o r b i t c o u p l i n g , v i b r o n i c c o u p l i n g , J a h n - T e l l e r d i s t o r t i o n s and m i x i n g - i n of doublet s t a t e s . Complexes i n which the four i d e n t i c a l l i g a n d s are c o o r d i n a t e d to c o b a l t may have r e g u l a r T^ symmetry; however, t h i s i s u s u a l l y not the case. For example, the s t r u c t u r e s 2-of s e v e r a l complexes c o n t a i n i n g the CoCl^ i o n , namely, C s 2 C o C l 4 (50), {N ( C H 3 ) 2 > 2 C o C l 4 (51) and C s 3 C o C l 5 (52) have 2-been determined and i n each case the geometry of C o C l 4 i s not r e g u l a r and the C l — C o — C l angles d e v i a t e s i g n i f i c a n t l y 14 from the t e t r a h e d r a l v a l u e s . The c r y s t a l s p e c t r a of these complexes (5 3, 54) show three to f o u r band maxima i n each of the v 2 and V 3 r e g i o n s w i t h t o t a l band widths of the order of 3000 cm and 1000 cm ^ r e s p e c t i v e l y . D e t a i l e d analyses showed t h a t s p i n - o r b i t c o u p l i n g e f f e c t s alone c o u l d e x p l a i n n e i t h e r the b r e a t h nor the number of components a s s o c i a t e d with the V2 band and the band s p l i t t i n g was c o n s i d e r e d to a r i s e l a r g e l y from low symmetry e f f e c t s . Other t e t r a h e d r a l CoA^-type complexes which have been ?„ _ 2- *>•- 2-s t u d i e d spectroseopicalibyeinc'lude^ CqBr^, Cc(<55)', C o l ^ (55), C o ( N 3 ) 4 2 ~ (56), Co(NCO) 4 2" (56), Co{ (CgHg) 3AsO} 4 2 + (57), C o ( N C S e ) 4 2 " (58), C o ( N C S ) 4 2 " (59), Co{PO ( N ( C H 3 ) 2 ) 3 > 4 2 + (60), C o ( O N 0 2 ) 4 2 ~ (61), C o ( T U ) 4 2 + (62) and Co (ETU) 4 2 + (63). In a l l cases, r a t h e r broad and s t r u c t u r e d v 2 and v 3 bands were observed. As d e s c r i b e d b e f o r e , the measurement of the e n e r g i e s of v 2 and V 3 permit the e v a l u a t i o n of the e l e c t r o n i c parameters Dq and B. However, due to the above-mentioned e f f e c t s , the p o s i t i o n s of the two bands cannot be a c c u r a t e l y determined. The s i m p l e s t approach to t h i s problem i s t h a t suggested by Cotton e t a l . (55) and used by many authors s i n c e of e s t i -mating v i s u a l l y the c e n t e r of g r a v i t y of each band. In t h i s way, d e f i n i t e f r e q u e n c i e s may be assigned to v 2 and v 3 ( u s u a l l y c o n s i d e r e d accurate o n l y to ^+200 cm ^) and the e l e c t r o n i c parameters Dq and B c a l c u l a t e d . Using Dq and B v a l u e s determined i n t h i s manner f o r a number of CoA 4 com-pl e x e s the l i g a n d s have been arranged i n both s p e c t r o c h e m i c a l and n e p h e l a u x e t i c s e r i e s f o r t e t r a h e d r a l c o b a l t ( I I ) (64). 1 5 Complexes i n which fo u r n o n - i d e n t i c a l l i g a n d s are co o r d i n a t e d to c o b a l t ( I I ) (e.g. CoAB 3 and CoA 2B 2) have been s t u d i e d p r e v i o u s l y and those of the ge n e r a l formula CoA 2B 2 have p a r t i c u l a r r e l e v a n c e to the presen t work. The maximum p o s s i b l e symmetry f o r the c o b a l t ( I I ) ions i n such complexes i s C 2 v » C o n s i d e r i n g such complexes as d i s t o r t e d v e r s i o n s of r e g u l a r t e t r a h e d r a l complexes the s i m p l i f i e d energy l e v e l diagram f o r s t a t e s of maximum s p i n m u l t i p l i c i t y i s shown below ( r e l a t i v e o r d e r i n g of s t a t e s d e r i v e d from T s t a t e s i n T-, symmetry i s a r b i t r a r y ) . f r e e - i o n 16 The e l e c t r o n i c a b s o r p t i o n s p e c t r a o f such complexes are expected then to be r a t h e r complex with nine p o s s i b l e s p i n - a l l o w e d bands a r i s i n g from the e f f e c t s of a C 2 v l i g a n d f i e l d alone. The presence of s p i n - f o r b i d d e n t r a n s i t i o n s and the e f f e c t s of s p i n - o r b i t c o u p l i n g might f u r t h e r com-p l i c a t e the matter. The s p e c t r a of these complexes normally e x h i b i t broad 3000 cm band width) and s t r u c t u r a l bands i n the v i s i b l e and n e a r - i n f r a r e d r e g i o n s c o r r e s p o n d i n g q u a l i t a t i v e l y a t l e a s t to the v 3 { 4 A „ ( F ) > 4 T , (P) } and 4 v 2{ A 2 (F) > T-^(F)} t r a n s i t i o n s of t e t r a h e d r a l complexes (66) . E a r l y attempts t o make d e t a i l e d assignments of the s p e c t r a of these complexes met with r a t h e r l i m i t e d success although the s t u d i e s of Ferguson and o t h e r s have been p a r t i c u l a r l y important i n t h i s regard (49, 54). In most cases i t was concluded t h a t the low symmetry component of the l i g a n d f i e l d , r a t h e r than s p i n - o r b i t c o u p l i n g e f f e c t s i s l a r g e l y r e s p o n s i b l e f o r the breadth and s t r u c t u r e of the a b s o r p t i o n bands. Very r e c e n t l y , Tomlinson and co-workers (67) r e p o r t e d c r y s t a l p o l a r i z e d s p e c t r a of c o b a l t ( I I ) complexes c o n t a i n i n g CoP 2X 2 and C oS 2X 2 (X = h a l i d e ) chromophores and were able to deduce the sequence of components of the s p l i t T-^(F) and T^(P) terms (de r i v e d from T^ symmetry). In a d d i t i o n , by t r e a t i n g the c r y s t a l f i e l d parameters of the low symmetry components, D and D., as e m p i r i c a l parameters they were able to c a l c u l a t e v a l u e s f o r these. Studi e s i n v o l v i n g the use of data obtained from c r y s t a l p o l a r i z e d s p e c t r a i n combination with X-ray c r y s t a l s t r u c t u r e data as d e s c r i b e d i n the paper by Tomlinson e t a l . (67), w i l l u s u a l l y y i e l d more u s e f u l information concerning 17 the e l e c t r o n i c s t r u c t u r e s o f complexes than data obtained on powdered samples and s o l u t i o n s . T h i s i s not to say t h a t work of the l a t t e r type i s without v a l u e . Indeed r a t h e r e x t e n s i v e data on m i c r o c r y s t a l l i n e samples and s o l u t i o n s are a v a i l a b l e (62,63,6 8) and p r o v i d e d care i s taken i n the i n t e r p r e t a t i o n o f t h i s data, p a r t i c u l a r l y i n regard to comparison of s o l u t i o n and s o l i d s t a t e s p e c t r a , u s e f u l i n f o r m a t i o n c o ncerning the e l e c t r o n i c and molecular s t r u c t u r e s of the complexes can be o b t a i n e d . A common p r a c t i c e has been t o determine the ce n t e r o f g r a v i t y of each o f the v 2 and v 3 bands (as d e s c r i b e d before) and to use these f r e -quencies t o c a l c u l a t e the parameters Dq and B. For complexes c o n t a i n i n g n o n - i d e n t i c a l l i g a n d s , v a l u e s of Dq and B obta i n e d i n t h i s manner p r o v i d e a measure of the "average" l i g a n d environment about the c e n t r a l metal i o n . T h i s has been demonstrated by the f a c t t h a t Dq and B value s f o r complexes of the type CoA^^, f o r example, are u s u a l l y i n t e r m e d i a t e between the Dq and B value s observed f o r the s p e c i e s CoA^ and CoB^ (55,62,63,68). In the presen t work, e l e c t r o n i c s p e c t r a l s t u d i e s were made on p o l y c r y s t a l l i n e samples and s o l u t i o n s o f t e t r a h e d r a l c o b a l t ( I I ) complexes and the data have been t r e a t e d i n a manner as o u t l i n e d above. While the amount of i n f o r m a t i o n one can o b t a i n from such s t u d i e s i s l i m i t e d , i t can be use-f u l l y supplemented by magnetic s u s c e p t i b i l i t y s t u d i e s . The magnetic p r o p e r t i e s of powdered samples of c o b a l t (II) " t e t r a h e d r a l environment" complexes are d i s c u s s e d next. 18 II-2-2. Magnetic P r o p e r t i e s As was d e s c r i b e d i n the p r e v i o u s s e c t i o n , the ground 4 s t a t e of c o b a l t (II) 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 i s a A 2 s t a t e , i r r e s p e c t i v e of the f i e l d s t r e n g t h . In theory, the magnetic moment f o r such an o r b i t a l l y nondegenerate ground s t a t e would be ' s p i n - o n l y ' . However, experimental r e s u l t s on a l l t e t r a h e d r a l c o b a l t (II) complexes show t h a t i t i s p o s s i b l e f o r s p i n - o r b i t c o u p l i n g t o 'mix' some of the highe r T s t a t e s i n t o the ground s t a t e , thus i n t r o d u c i n g o r b i t a l angular momentum i n t o the l a t t e r . C o n s i d e r i n g the 4 4 'mixing-m' of the T 2 s t a t e a t 10 Dq above the ground A 2 s t a t e , the Lande s p e c t r o s c o p i c s p l i t t i n g f a c t o r , g, i n s t e a d of being 2.00 f o r a term de v o i d of o r b i t a l angular momentum, i s (42) g = 2.00 (1 — ) (i) and 10 Dq 4X . .... y e f f = u s o ( 1 )  e r r S * ° ' 10 Dq Since the 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 , X, i s a negative parameter f o r c o b a l t ( I I ) a value of U e f f which i s l a r g e r than the y value of 3.873 B.M. i s expected. Note too t h a t a c c o r d i n g t o equation ( i i ) the magnetic moment should be independent of temperature. The 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 , X, warrants some d e s c r i p t i o n here. I t i s , i n e f f e c t , the c o e f f i c i e n t of the o p e r a t o r f o r s p i n - o r b i t c o u p l i n g i n the form XL'S where 19 L~ i s the o r b i t a l angular momentum ope r a t o r and S i s the s p i n angular momentum op e r a t o r . In the f r e e - i o n case, X = X q where X Q , the 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 , i s equal t o -178 cm ^ f o r c o b a l t ( I I ) . In a l i g a n d f i e l d environment, the e x p r e s s i o n X L * S i s s u b j e c t t o change as a r e s u l t of the f o l l o w i n g two e f f e c t s : (i) The o r b i t a l angular momentum ope r a t o r L i s reduced to k - L as a r e s u l t of what i s g e n e r a l l y known as the e l e c t r o n d e l o c a l i z a t i o n e f f e c t (k i s the e l e c t r o n d e l o c a l i z a t i o n f a c t o r o r o r b i t a l r e d u c t i o n f a c t o r ) . k has o f t e n been used to d e s c r i b e the r e d u c t i o n i n the t o t a l o r b i t a l angular momentum as a r e s u l t of the e l e c t r o n d e l o c a l i z a t i o n onto the l i g a n d s where l i t t l e or no o r b i t a l c o n t r i b u t i o n i s made (42, 69, 70). In a molecular o r b i t a l approach which c o n s i d e r s the mixing of l i g a n d p - o r b i t a l s i n t o the metal 1 d ' o r b i t a l s , G e r l o c h and M i l l e r (71) c a l c u l a t e d k i n terms of the m e t a l - l i g a n d o v e r l a p i n t e g r a l and a l s o the o v e r l a p i n t e g r a l s between the ligand o r b i t a l s themselves. These l a t t e r terms p a r t i a l l y o f f s e t the r e d u c t i o n of the t o t a l o r b i t a l angular momentum simply due to d e l o c a l i -z a t i o n o f the metal e l e c t r o n s onto the l i g a n d s . ( i i ) The magnitude of the 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 , X , was shown (72) to be d i r e c t l y p r o p o r t i o n a l to the f o u r t h power of the e f f e c t i v e n u c l e a r charge f e l t by the e l e c t r o n and i n v e r s e l y p r o p o r t i o n a l t o the t h i r d power of the n u c l e u s - e l e c t r o n s e p a r a t i o n . When the metal i o n i s c o v a l e n t l y bonded to the l i g a n d s , the 'd' e l e c t r o n c l o u d i s 20 probably expanded, thereby reducing the e f fec t ive nuclear charge and increas ing the distance between the e lec t ron and the nucleus. This leads to a reduction of the A value. Furthermore, i t i s argued that the metal ' d ' e lectrons are subject to a t t r a c t i o n by the nuclear charges of the l igands . I f the l igand i s a heavy atom, and i f the e lec t ron d e r e a l i -zat ion i s rather extensive, the fourth power of the nuclear charge of the l igand may be more important than that of the metal nucleus and hence A may be ra i sed above i t s f ree- ion value. Values of A greater than the f ree- ion value have been observed for several chromium(III) (73) and iron(II ) (74, 75) complexes. As a r e s u l t of the above e f fec t s , A i s better described as R*A (76, 77) where R can be less o than or greater than u n i t y . AL-S becomes, consider ing both of the above ef fects on L and A, an expression of the form: kRAL«S Unfortunately, i t i s usua l ly not poss ible to separate the two parameters k and R and therefore the assumption k = R has been made (42). Equation ( i i ) subsequently becomes: 4k2A U e f f = y s o ( 1 ~ }  e r r S ' ° - 10 Dq I t has been pointed out (7 8) that k ca lcula ted from expression ( i i i ) i s re la ted to the extent of e lec t ron d e l o c a l i z a t i o n only for small metal- l igand overlap where k decreases with increas ing d-e lectron d e l o c a l i z a t i o n . For large metal- l igand over lap , k i s not a reasonable measure of d e l o c a l i z a t i o n ef fects and for s u f f i c i e n t l y large metal- l igand overlap, k may i n fact take on values greater than uni ty (7 8). Turning now to some experimental cons iderat ions , the quantity which i s a c tua l ly measured i s the magnetic s u s c e p t i b i l i t y per mole of sample, x m « The s u s c e p t i b i l i t y per mole of coba l t , x , , / 1 S r e a d i l y obtained by correc t ing Co for the bulk diamagnetism of the whole molecule. For systems such as te trahedra l c o b a l t ( I I ) , containing A 2 ground terms, i t i s common prac t ice to correct the s u s c e p t i b i l i t y for paramagnetism a r i s i n g from the second order Zeeman e f fect of the magnetic f i e l d . This contr ibut ion to the magnetic s u s c e p t i b i l i t y , c a l l e d the temperature independent 2 paramagnetism (TIP) i s , for A 2 terms, 8N$ /lODq (42). As lODq for te t rahedra l cobalt ( II ) complexes i s general ly small (^  4000 cm ^) , t h i s term contributes s i g n i f i c a n t l y to the o v e r a l l magnetic s u s c e p t i b i l i t y , e s p e c i a l l y at high temperatures. The f u l l y corrected molar magnetic suscept i -b i l i t y i s x C ° + + = X + + - TIP. The e f fec t ive magnetic Co Co moment i s ca lcula ted by use of the equation, *eff = ( l £ 2 ) % ^CT+"Vh <iv> e t r N3 C o + + — 16 where K = Boltzmann's constant (1.38 x 10 erg/deg) 23 N = Avogadro's number (6.02 x 10 /mole) -20 8 = Bohr Magneton (0.92 7 x 10 erg/gauss) X C ° + + = Molar magnetic s u s c e p t i b i l i t y (c .g . s . or erg/gauss'' C o mole) and T = Temperature (deg) I n s e r t i n g the above numbers, equation (iv) becomes: y e f f = 2.828 (xCOH'T)h (v) Co According t o equations ( i i ) and ( i i i ) the magnetic moment should be temperature independent and f o r t h i s to be so, a c c o r d i n g t o equation (v), xC O rI must be i n v e r s e l y Co p r o p o r t i o n a l t o T. Such behaviour, termed C u r i e Law, i s i n f a c t r a r e l y seen f o r t e t r a h e d r a l c o b a l t ( I I ) ; more commonly, Curie-Weiss law i s obeyed: oc T - 0 (vi) corr Co I n c o r p o r a t i n g the Weiss con s t a n t , 0, as a p u r e l y e m p i r i c a l q u a n t i t y , a temperature independent e f f e c t i v e magnetic moment can then be ob t a i n e d by: y e f f = 2.828 { X C ° + + ( T - Q)}k ( v i i ) Co For t e t r a h e d r a l c o b a l t (II) complexes, 0 v a l u e s of ,-1 to -10 are commonly observed and the e f f e c t i v e magnetic moments u s u a l l y l i e i n the range of 4.02 - 4.70 B.M. The p h y s i c a l meaning of Curie-Weiss behaviour, e s p e c i a l l y the s i g n i f i c a n c e of the 0 v a l u e , i s not y e t f u l l y understood. While departure from C u r i e law i s o f t e n a t t r i b u t e d t o magnetic i n t e r a c t i o n s o f ferromagnetic or a n t i - f e r r o m a g n e t i c nature (70, 77, 79), other f a c t o r s may be r e s p o n s i b l e f o r such behaviour. For t e t r a h e d r a l c o b a l t ( I I ) , a l i k e l y e x p l a n a t i o n f o r the commonly observed Curie-Weiss behaviour comes from a c o n s i d e r a t i o n of the e f f e c t o f a z e r o - m a g n e t i c - f i e l d s p l i t t i n g of s p i n l e v e l s caused by l i g a n d f i e l d asymmetry (70). A low symmetry l i g a n d f i e l d cannot d i r e c t l y remove the s p i n degeneracy of the ground 4 s t a t e A 2, y e t i t can r a i s e the o r b i t a l degeneracy of the 4 f i r s t e x c i t e d s t a t e T 2 , which i n t u r n p a r t i a l l y removes the s p i n degeneracy of the ground s t a t e by second order s p i n - o r b i t c o u p l i n g . D e f i n i n g 6 as the s e p a r a t i o n between the r e s u l t i n g s p i n s t a t e s , symbolized as {±-|>} and {± -|-} the average molar magnetic s u s c e p t i b i l i t y i s (70): co r r _ Ng 2 g 2 (1 + 20/x + 9 e " X - 20 e" X/x) , ... Y — ———•- — ^ — — — — — —— — — — — — — — — \ v i i i C o + + 12K T 1 + e ~ X where x = 5/K T and g, N, g, K and T have t h e i r u s u a l meanings. It should be noted here t h a t when 6 i s 0 equation ( v i i i ) becomes the simple C u r i e law e x p r e s s i o n . The paramete 6 i s d i r e c t l y r e l a t e d t o the degree of d i s t o r t i o n from r e g u l a r T^ symmetry. The r e l a t i o n s h i p between the z e r o - f i e l d s p l i t t i n g parameter 6* and the e m p i r i c a l l y determined Weiss constant 0 i s e a s i l y d e r i v e d . Upon r e a r r a n g i n g and expanding, equation ( v i i i ) can be reduced to the f o l l o w i n g form: 1 4K ( t + 26_ + 2896 2 T ~ l + __ ( ± x ) X C ° + + 5N3 2g 2 15 K 3600 K 2 Co For s m a l l 6's and h i g h temperatures (x<<l), the t h i r d and higher terms i n e q u a t i o n (ix) drop out l e a v i n g the simple e x p r e s s i o n 24 4 " ( T + ( x ) corr P . , „ 2 2 .. ,_ X 5N3 g 15K Co The term 26/15K i s simply '-0' i n the Curie-Weiss r e l a t i o n . Therefore, - 0 = = 0.1926 (xi) 15K where K = 0.6 95 cm 1 / d e g , 6 has the uni t of cm 1 and 6 of ° K . The p o s s i b i l i t y of obta ining useful s t ruc tura l information on pseudo-tetrahedral cobalt (II ) complexes by comparing experimental magnetic s u s c e p t i b i l i t i e s with s u s c e p t i b i l i t i e s ca lcu la ted using equation ( v i i i ) i s explored i n Chapter IV of t h i s t h e s i s . II-3. OCTAHEDRAL FIELD ENVIRONMENT II-3-1. E l e c t r o n i c Spectra The Tanabe-Sugano energy l e v e l diagram for cobalt (II ) i s given i n Figure I I - l . The s i m p l i f i e d energy l e v e l diagram for spin-free complexes (spin-quartet ground state) i s shown below. 25 -4, "TT" T l g ( P ) v 3 v 2 V l A 2 g ( F > T 2 g ( F ) T l g ( F ) f r e e - i o n o c t a h e d r a l f i e l d Whether the T i g ( P ) 1 S h i g h e r or lower i n energy than the ^ A 2 g depends o n the magnitude of Dq/B (see Tanabe-Sugano diagram). In f a c t , i n a l l of the complexes s t u d i e d i n the p r e s e n t work the r e l a t i v e o r d e r i n g of these l e v e l s i s as i s shown i n the s i m p l i f i e d diagram. The Tanabe-Sugano m a t r i c e s (44) f o r these s t a t e s a r e : T l g ( F ) T l g ( P ) l T 2 g ( F ) A 2 g < F ) •6Dq 4Dq 4Dq 15B 2Dq 12Dq where Dq and B have the u s u a l meanings. In octahedral complexes of c o b a l t ( I I ) , two p r i n c i p a l bands are usua l ly observed, vi i n the near- infrared region, and V 3 i n the v i s i b l e region corresponding to the two t r a n s i t i o n s 4 T l g ( F ) $• 4 , T 2 g ^ a n d ^ l g ^ ^ ^ l g ^ 4 4 r e spec t ive ly . The t h i r d band, T i g ( F ) ^ A 2 g ^ ' i n v ° l v e s 5 2 3 4 what i s formally a two e lec t ron transfer ( t „ e > t~ e ) 2g g 2g g and i s often too weak to be observed. Weak bands to the low energy side of the V 3 absorption band have been assigned to 2 + t h i s v 2 t r a n s i t i o n i n , for example, Co(H 20)g (80), C o C l 2 (81), Co ( C 1 2 H C G 0 2 ) 2 « p y 2 (41) and KCoF 3 (81). Lever has shown (41) that for commonly observed values of Dq and B the r a t i o of v 2 / v i i s c lose to or s l i g h t l y less than 2.2. This may put the frequency of v 2 very close to that of V 3 and i n some instances the presence of v 2 i n the neighbourhood of V 3 may p a r t i a l l y account for the breadth and structure of the V 3 band. Once Vi and v 3 are experimentally determined, i t i s poss ible to use the Tanabe-Sugano diagrams and equations to ca lcu la te the e l ec t ron ic parameters Dq and B. Again due to the broad and s t r u c t u r a l bands usual ly observed for most octahedral cobalt (II) complexes (especia l ly i n the v i s i b l e region v 3 ) , these values may be obtained by a quant i ta-t ive est imation of the centers of grav i ty of the bands. As was the case for te trahedra l complexes, i t i s general ly recognized that one of the most important factors contr ibut ing to the breadth and structure of the absorption 27 band i n 'octahedra l ' complexes i s low symmetry l igand f i e l d e f fects i . e . devia t ion from 0^ symmetry. As shown i n the diagram below of the states of maximum spin m u l t i p l i c i t y for cobalt ( II ) i n various l igand environments, the three bands predicted for complexes of 0^ symmetry become s ix for complexes of symmetry and nine for complexes of lower symmetry ( re la t ive ordering of states derived from T states i s a r b i t r a r y ) . Some examples of spect ra l assignments i n complexes of low symmetry fo l low. ' ^ " 4 4 . _ 2 4, A» 2g 2q_ f ree- ion 0 h D 4 h lower S 4 4 A B, A2 ! g - - -Sa V T 2a — — — 4 B B, - " 4 A s \ 4 " 4R 1 v 4 g s s i a A ~~- B 0 symmetry (e.g. C 2 v ) 2 8 Four bands were observed i n the v i s i b l e r e g i o n c r y s t a l spectrum of the v i o l e t form of C o C l 2 * p y 2 ( 8 2 ) . By assuming t h a t one of these bands i s the v 2 band the remaining three were assigned t o the three components 4 a r i s i n g from the T^ (P) s t a t e i n a c r y s t a l f i e l d of D 2 ^ symmetry. T h i s symmetry was e s t a b l i s h e d by an X-ray c r y s t a l s t r u c t u r e a n a l y s i s ( 8 3 ) . P o l a r i z e d c r y s t a l s p e c t r a of cobalt-doped KnF^ ( 8 4 ) have a l s o been s t u d i e d and the r e s u l t s showed t h a t the low E>2h symmetry of the c r y s t a l s i t e i s the dominant f a c t o r a f f e c t i n g the s p l i t t i n g of the v 3 s p e c t r a l band. E f f e c t s of s p i n - o r b i t c o u p l i n g were not d e t e c t e d . P y r i d i n e adducts of s e v e r a l c o b a l t ( I I ) a l k y l a c e t a t e s and h a l o a c e t a t e s ( 4 1 ) were examined wi t h r e s p e c t t o t h e i r v i s i b l e s p e c t r a a t room temperature. I t was concluded t h a t the m u l t i p l e s t r u c t u r e of the v 3 band i n these complexes i s p a r t i a l l y due to q u a r t e t - d o u b l e t s p i n - f o r b i d d e n t r a n s i t i o n s , A f t e r a s s i g n i n g these, two remaining bands i n the s p e c t r a 4 4 were then assi g n e d t o the two components, A 2 g and E , 4 a r i s i n g from the T i g ( p ) s t a t e i n symmetry. The v x bands of these complexes (and of the p r e v i o u s examples t o o ) , although r a t h e r broad, do not show the s p l i t t i n g expected f o r a low-symmetry l i g a n d f i e l d . Complexes which have r e g u l a r o c t a h e d r a l , 0 ^ , symmetry or t r a n s - o c t a h e d r a l , D ^, symmetry may be c l a s s i f i e d as centrosymmetric complexes. These complexes, i n g e n e r a l , show r a t h e r broad and sometimes s t r u c t u r a l v 3 and Vi bands. In a d d i t i o n the molar e x t i n c t i o n c o e f f i c i e n t s (E.) of such 29 bands are commonly found i n the range 10 - 100 1/mole-cm and 1 - 10 1/mole-cm r e s p e c t i v e l y . For example, the b i s p y r i d i n e c o b a l t ( I I ) h a l o a c e t a t e s mentioned above (41), which are c o n s i d e r e d to have t r a n s - o c t a h e d r a l geometries (approximate symmetry), have v a l u e s of £ of 30 - 55 f o r V 3 and 5 - 1 0 f o r V i . Recent s t u d i e s on a number of c o b a l t (II) n i t r a t e complexes which have non-centrosymmetric pseudo-octahedral s t r u c t u r e s showed t h a t they have q u i t e d i f f e r e n t s p e c t r a l and magnetic p r o p e r t i e s from those of centrosymmetric complexes. From the complete c r y s t a l s t r u c t u r e a n a l y s i s of C o { ( C H 3 ) 3 P O > 2 ( N 0 3 ) 2 (91), i t was e s t a b l i s h e d t h a t the n i t r a t e groups are b i d e n t a t e and occupy c i s - p o s i t i o n s i n a pseudo-octahedral geometry about c o b a l t , g i v i n g r i s e to a d i s t o r t e d o c t a h e d r a l s t r u c t u r e of a t most symmetry. X-ray powder analyses showed (86) t h a t other s i m i l a r complexes such as Co{ (CgH 5) 3PO} 2 (NOg) 2 and Co{ (CgH,.) 3As0> 2 (N0 3) are isomorphous. Other n i t r a t e complexes were claimed to have analogous s t r u c t u r e s (61, 85, 87, 88, 89, 90). With t h i s s t r u c t u r a l i n f o r m a t i o n , the s p e c t r a l p r o p e r t i e s of t h i s type of noncentrosymmetric complex may now be d i s c u s s e d . In terms of band width and s t r u c t u r e the V 3 band i n these n i t r a t e complexes i s l i t t l e d i f f e r e n t compared to t h a t of the r e g u l a r centrosymmetric complexes; y e t , the a b s o r p t i o n i n t e n s i t y i n s o l u t i o n i s g r e a t l y enhanced (§ 'v- 100 - 200 1/mole-cm) . T h i s i n c r e a s e i n i n t e n s i t y a r i s e s from the lowering of symmetry and the l o s s of a 30 center of symmetry i n the molecule. I t was described (85, 86) as due to the resemblance to a structure approaching to a te trahedra l point symmetry. The near-in f rared band, V i , on the other hand, i n these non-centrosymmetric complexes i s s p l i t in to at leas t two components by as much as 2000 cm ^ . Besides, the i n t e n s i t y of absorption of these peaks i n the near-in f rared region i s increased 10 - 20 1/mole-cm). Magnetic moments lower than those usual ly observed for octahedral complexes were also observed. Not a l l n i t r a t e complexes of cobalt (II ) have t h i s s t ructure . I t was reported (92), for example, that the complex Co(C^H^NO) 2(NO^) 2 has a trans-octahedral s t ructure . Spectra l studies showed that only one band i s observed i n the near- infrared region and the v i s i b l e spectrum i s t y p i c a l of other trans-octahedral complexes, with £ 'v 2 8 1/mole-cm. II-3-2. Magnetic Propert ies The magnetic behaviour of cobalt ( II ) i n a regular octahedral l igand f i e l d , 0^, i s character ized by 4 the o r b i t a l l y t r i p l y degenerate ground state T i g * T ^ e degeneracy of the ground state i s l i f t e d by sp in-orb i t coupling to give states which are separated by energies of 3 1 the o rder of KT (A f o r c o b a l t ( I I ) i s - 1 7 8 c m - 1 and KT a t o 3 0 0 ° K i s ^  2 1 0 cm ^ ) . As a r e s u l t , the magnetic moment i s a f u n c t i o n of temperature. A t h e o r e t i c a l treatment of the magnetic p r o p e r t i e s 4 of complexes w i t h T^ g ground s t a t e s under simultaneous p e r t u r b a t i o n by s p i n - o r b i t c o u p l i n g and a t e t r a g o n a l or t r i g o n a l l i g a n d f i e l d component has been given i n some d e t a i l by F i g g i s e t a l . ( 9 3 ) . T h i s treatment w i l l be out-l i n e d here and w i l l be r e f e r r e d t o i n t h i s t h e s i s as ' F i g g i s ' 4 model'. The b a s i s wave f u n c t i o n s of the T, terms a r i s e from i g 4 4 an admixture of both the f r e e - i o n F and the f r e e - i o n P terms by means of the c u b i c l i g a n d f i e l d . Thus, ^4 2 -k ^4 o +c ^4 o 4 T l g ( F ) = ( 1 + CZ ) H ( 4 T l ° ( F ) + C T X°(P) ) where ijj. 4 T n (F) i s the wave f u n c t i o n f o r the T, (F) i g , l g ' ^4 o ^4 o term i n a c u b i c l i g a n d f i e l d , T i g ^ F ^ a n d T l g ^ a r e t n e 4 4 wave f u n c t i o n s f o r the f r e e - i o n F and P terms r e s p e c t i v e l y 4 o and c i s the c o e f f i c i e n t of admixture of the T, (P) term i g i n t o the 4 T l g ( F ) term. From a quantum mechanical a p p l i c a t i o n of the op e r a t o r L (z-component of the o r b i t a l angular momentum) on 4 (F): z T l g ^4 ,+ , ^4 1 5 - c 2 < Sg<F> W\ Tlg< F> > = \ \ 2 = A ' ^ 1 + c The parameter A i s thus i n t r o d u c e d which r e p r e s e n t s the e f f e c t i v e o r b i t a l angular momentum f o r the ground s t a t e . T h i s parameter may be e v a l u a t e d from a knowledge of the s p e c t r a l parameters lODq and B f o r the system concerned (42),. 32 The combined a c t i o n of s p i n - o r b i t c o u p l i n g and a t e t r a g o n a l or t r i g o n a l f i e l d component i s d e s c r i b e d i n the f o l l o w i n g diagram: T l g ( F ) ' 1 X - X * 2 A A 3 o r b i t a l * „ doublet A 2A 3 o r b i t a l s ing le t T l g ( F ) cubic f i e l d s p m -orbi t coupling tetragonal or combined t r igona l cubic act ion d i s t o r t i o n f i e l d The e f f e c t of the low symmetry l i g a n d f i e l d component i s d e s c r i b e d by the parameter A , d e f i n e d as the s e p a r a t i o n between the o r b i t a l s i n g l e t and the o r b i t a l d oublet l e v e l s . When the o r b i t a l s i n g l e t l i e s lowest, A i s d e f i n e d as p o s i t i v e (94) . 4 The energy l e v e l s of the T^ term (ground term of o c t a h e d r a l c o b a l t ( I I ) species) under the oombined p e r t u r b a -t i o n s o f t e t r a g o n a l or t r i g o n a l f i e l d component and s p i n -o r b i t c o u p l i n g are (93) i n the form of m a t r i c e s : 4 + # ^ - f t " A-A- ( J ) 0 3, Js 2_A 3 X-A« (2) 0 X-A- (2) 3 2 33 and A 3 A 2 2A 3 and A 3 3A 2 In t h i s treatment, a parameter v i s i n t r o d u c e d which i s d e f i n e d as A/A. As A i s negative f o r c o b a l t ( I I ) , v has the op p o s i t e s i g n to A. The parameter A i s a measure of the d i s t o r t i o n of the system, from a c u b i c f i e l d environment to a t e t r a g o n a l or t r i g o n a l one. A parameter k i s i n t r o d u c e d i n the t h e o r e t i c a l treatment t o all o w f o r a r e d u c t i o n i n o r b i t a l angular momentum caused by e l e c t r o n d e l o c a l i z a t i o n . G e r l o c h and M i l l e r (71) have shown t h a t k i n v o l v e s both the metal-l i g a n d o v e r l a p i n t e g r a l s as w e l l as the l i g a n d - l i g a n d o v e r l a p i n t e g r a l s . These c o n t r i b u t e t o the t o t a l o r b i t a l angular momentum and are b e l i e v e d t o be r e s p o n s i b l e f o r the u s u a l l y h i g h minimum value of k observed e x p e r i m e n t a l l y f o r o c t a h e d r a l complexes. F i g g i s e t a l . (93) e v a l u a t e d t h e o r e t i c a l magnetic moments f o r v a r i o u s combinations of the parameters A, k, v and A. Examination of t h i s data shows t h a t a decrease i n k, f o r any p a r t i c u l a r value of A or v, causes the magnetic moment to reduce towards the s p i n - o n l y value o f 3.873 B.M. . The magnitude of the magnetic moment i s l e s s s e n s i t i v e to the low symmetry parameter v; however, as |v| becomes very l a r g e , y « decreases s i g n i f i c a n t l y . The curva t u r e of the p l o t of Veff versus K T / - A , however, depends great ly on v with v = 0 having the greatest curvature. A l s o , there i s a general reduction of Ve£f as the parameter A i s reduced from 1.5 to 1.0. The parameter A can usua l ly be determined separately from e l e c t r o n i c spect ra l data. A p lo t of experimental values of U e £ f ( in t h i s case ca lcu la ted from _ . . . j-the formula y c c = 2.828 (y , ,T) 2 ) versus K T / - A can then e f f A „ ++ Co be f i t t e d to fami l ies of t h e o r e t i c a l curves obtained by varying the parameters v , k and A . The best f i t i d e n t i f i e s i n t h i s theory at leas t these parameters for the complex and gives the best de sc r ip t ion of i t s magnetic proper t ie s . It was pointed out (93) that t h i s approach to the treatment of magnetic propert ies has the fol lowing l i m i t a t i o n s (i) the low-symmetry l igand f i e l d components are l i m i t e d to those of a tetragonal or t r i g o n a l nature only ; ( i i ) the theory appl ies to magnetically d i l u t e systems only ; ( i i i ) no allowance for the p o s s i b i l i t y of temperature dependence of the parameters i s made; (iv) the theory ignores contr ibut ions to magnetic propert ies from higher exc i ted terms. In spi te of these l i m i t a t i o n s t h i s model provides one of the most useful approaches ava i l ab le for the treatment of powder s u s c e p t i b i l i t y data . I t has been appl ied to a number of pseudo-octahedral complexes studied i n the present work. 35 CHAPTER I I I EXPERIMENTAL I I I - l . MATERIALS USED The f o l l o w i n g chemicals used i n the p r e p a r a t i o n of complexes were a l l a v a i l a b l e commercially as reagent grade, and were g e n e r a l l y used without f u r t h e r p u r i f i c a t i o n : a r y l c a r b o x y l i c a c i d s (Eastman Kodak Co., Rochester, New York, U.S.A.); c o b a l t ( I I ) c h l o r i d e hexahydrate, c o b a l t ( I I ) p e r c h l o r a t e hexahydrate ( A l f a I n organics Inc., B e v e r l y , Massachusetts, U.S.A.); c o b a l t ( I I ) a c e t a t e t e t r a h y d r a t e , c o b a l t ( I I ) carbonate, t r i f l u o r o a c e t i c a c i d (Baker and Adamson q u a l i t y , General Chemical Co., New York, New York, U.S.A.); t h i o u r e a (K and K Laboratory Inc., P l a i n v i e w , New York - Hollywood, C a l i f o r n i a , U.S.A.). 36 Ethylenethiourea and N,N 1 -d imethyl thiourea , both of reagent grade (K and K) were r e c r y s t a l l i z e d from 100% ethanol and dr ied i n a vacuum des iccator over anhydrous calcium chlor ide before use. Pyr id ine (Fisher S c i e n t i f i c C o . , F a i r Lawn, New Jersey, U .S .A . ) was dr ied over potassium hydroxide p e l l e t s and then d i s t i l l e d . Organic solvents used for preparations and spectra l and osmometic measurements were of reagent grade; acetone, 100% ethanol and chloroform were dr ied over D r i e r i t e (anhydrous calcium sulphate) and then d i s t i l l e d ; benzene was dr ied over phosphorus pentoxide and d i s t i l l e d . Other solvents used for preparat ions , such as d i e thy le ther , petroleum ether ( p r i n c i p a l l y n-hexane) and hexanes (as a mixture of i t s isomers, Fisher) were a l l reagent grade and were used without further p u r i f i c a t i o n . I I I-2 . ELEMENTAL ANALYSES The cobalt content of each complex was determined by a 'EDTA T i t r a t i o n ' method (95). The procedure involved the addi t ion of an excess of a standard ethylenediammine-te t raace t i c ac id (EDTA) so lu t ion (prepared by d i s s o l v i n g disodium ethylenediamminetetraacetate dihydrate i n d i s t i l l e d water) to an a c i d i c so lut ion of the cobalt complex and the t i t r a t i o n of t h i s excess with a standard copper so lu t ion i n the presence of an i n d i c a t o r . After the standard EDTA so lut ion was added to the a c i d i c cobalt s o l u t i o n , the pH was adjusted 37 to about 5 by n e u t r a l i z i n g the s o l u t i o n with sodium hydroxide u s i n g methyl r e d as i n d i c a t o r and then by adding a pH 5 acet a t e b u f f e r . The r e s u l t i n g s o l u t i o n was heated to b o i l i n g and was ' b a c k - t i t r a t e d ' w i t h the standard copper sulphate s o l u t i o n u s i n g 'PAN' (1-( 2 - p y r i d y l a z o ) - 2 - n a p h t h o l ) as i n d i c a t o r . The end p o i n t i s i n d i c a t e d by a change i n c o l o u r from y e l l o w to v i o l e t . A 'pendulum' end p o i n t technique was a l s o employed when necessary to p i n - p o i n t the end p o i n t (by t i t r a t i n g back and f o r t h w i t h EDTA and copper sulphate standard s o l u t i o n s ) . Standard s o l u t i o n s of c o n c e n t r a t i o n 0.01 M and samples c o n t a i n i n g ^ 0.1 minimole c o b a l t were employed. At l e a s t two analyses were performed on each sample and the accuracy i s co n s i d e r e d t o be + 1% Carbon, Hydrogen and Ni t r o g e n analyses of the complexes were ob t a i n e d i n the m i c r o a n a l y t i c a l l a b o r a t o r y i n t h i s Department. I I I - 3 . MOLECULAR WEIGHTS Mo l e c u l a r Weight s t u d i e s on s o l u t i o n s o f complexes i n benzene ( c o n c e n t r a t i o n ranges from lO -"^ t o 10 2 M) a t 37°C were made u s i n g a Mechrolab Model 301 A Osmometer. Benzene (Fisher) was s p e c t r a l grade and reagent grade b e n z i l (Fisher) was used as c a l i b r a n t . At l e a s t three samples ( i n the concen--3 -2 t r a t i o n range o f 10 -10 M) were s t u d i e d f o r each complex. Attempts to o b t a i n molecular weights i n acetone and c h l o r o f o r m as s o l v e n t u s i n g t h i s osmometer were u n s u c c e s s f u l . 38 I I I - 4 . INFRARED SPECTRA I n f r a r e d s p e c t r a were recorded over the frequency range 400 - 4000 cm u s i n g a Perkin-Elmer Model 457 Spectrophotometer. In g e n e r a l , mulls of complexes c o n t a i n e d between KBr or KRS-5 p l a t e s w i t h NUJOL (Plough Canada L i m i t e d , Toronto, Ontario) and HCB (hexachloro-1,3-butadiene, K and K) were used to g i v e complementary s o l i d s t a t e s p e c t r a . In a l l cases, s o l i d s p e c t r a were a l s o o b t a i n e d on KBr p e l l e t s . S o l u t i o n s p e c t r a recorded i n benzene, c h l o r o f o r m and acetone were o b t a i n e d u s i n g c e l l s w i t h 0.1 mm or 0.5 mm path l e n g t h and KBr or NaCl windows. I I I - 5 . ELECTRONIC SPECTRA 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 over the v i s i b l e r e g i o n (14300 - 30000 cm "*") were recorded on a Bausch and Lomb 'Spec t r o n i c 600' Spectrophotometer. Magnesium carbonate was used as a r e f l e c t a n c e standard and d i l u e n t f o r samples. KBr p e l l e t and s o l u t i o n s p e c t r a over the v i s i b l e -n e a r - i n f r a r e d r e g i o n (4000 - 30000 cm-"'") were recorded on a Cary Model 14 Spectrophotometer. ' P y r o c e l l ' g l a s s c e l l s w i t h path lengths of 1 cm and 5 cm were used f o r the s o l u t i o n work. E l e c t r o n i c s p e c t r a l data recorded i n t h i s work (such as p o s i t i o n s and a b s o r p t i o n i n t e n s i t i e s of s p e c t r a l band components) were taken from the apparent band maxima of the s p e c t r a w i t h no attempt made at c o r r e c t i n g f o r background a b s o r p t i o n or r e s o l v i n g band components. Where the energy 39 of a p a r t i c u l a r t r a n s i t i o n was estimated by o b t a i n i n g the "center of g r a v i t y " o f a band or group of bands, c o r r e c t i o n f o r background a b s o r p t i o n was made. I I I - 6 . MAGNETIC SUSCEPTIBILITIES Room-temperature s u s c e p t i b i l i t i e s were measured u s i n g a Faraday Magnetic Balance. An Alpha Model 9500 Water-cooled 6" Electromagnet, equipped with t i p s of Heyding d e s i g n ( I V p o l e gap) was used. Samples (a few m i l l i g r a m s ) were suspended i n a quartz bucket a t t a c h e d to a Cahn ' R g ' E l e c t r o b a l a n c e . Measurements were performed i n a n i t r o g e n c atmosphere and a t r e g i o n s of H(dH/dX) of 2.5 3 x 10 , 5.26 x 6 6 2 10 and 8.69 x 10 gauss /cm t o check f i e l d dependence of the samples. In f a c t , the magnetic s u s c e p t i b i l i t i e s of a l l com-ple x e s s t u d i e d i n t h i s work were found to be f i e l d independent. Mercury t e t r a t h i o c y a n a t o c o b a l t a t e ( I I ) (HgCo(CNS) 4) (96) was employed as the standard f o r c a l i b r a t i o n . Measurements of magnetic s u s c e p t i b i l i t i e s over the temperature range 80 - 320°K were recorded u s i n g the Gouy Magnetic Balance d e s c r i b e d p r e v i o u s l y (97) . A f i e l d s t r e n g t h of approximately 4500 gauss was employed. Pyrex Gouy tubes of i n n e r diameter between 3 mm and 4 mm h e l d samples [y 0.8 g.) u n i f o r m l y packed to a h e i g h t of 9 cm. Measurements were made i n a n i t r o g e n atmosphere. C a l i b r a t i o n of the apparatus was achieved u s i n g g r a v i m e t r i c a l l y analyzed n i c k e l (II) c h l o r i d e s o l u t i o n (98) and a l s o by u s i n g mercury t e t r a t h i o c y a n -a t o c o b a l t a t e (II) . 40 CHAPTER IV THIOUREA AND SUBSTITUTED THIOUREA COMPLEXES OF COBALT(II) CARBOXYLATES IV-1. INTRODUCTION T h i s chapter d e s c r i b e s the p r e p a r a t i o n and c h a r a c t -e r i z a t i o n o f c o b a l t ( I I ) complexes of t h i o u r e a (TU), ethylene-t h i o u r e a (ETU) and N, N 1 - d i m e t h y l t h i o u r e a (DMTU). H H CH — CH„ CH_ CH, I I I 2 I 2 I 3 I 3 N N N N N N H \ / H H \ / V H H / \ / N H c c c II II II s s s TU ETU DMTU 41 S t u d i e s on t r a n s i t i o n metal complexes of t h i o u r e a and i t s d e r i v a t i v e s have drawn c o n s i d e r a b l e a t t e n t i o n i n the past (99, 100, 101, 102, 103, 104). Although a l l known complexes of t h i o u r e a i n v o l v e c o o r d i n a t i o n t o the metal v i a the sulphur atom, the p o t e n t i a l f o r c o o r d i n a t i o n v i a n i t r o g e n i s t h e r e . In f a c t , as w i l l be seen l a t e r , some complexes of s u b s t i t u t e d t h i o u r e a s are known t o i n v o l v e N - c o o r d i n a t i o n . C o b a l t ( I I ) complexes of such l i g a n d s are g e n e r a l l y found t o i n v o l v e metal-sulphur bonding and to e x h i b i t 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 about c o b a l t (62, 63, 68). Octah e d r a l c o o r d i n a t i o n i s l e s s common but was observed i n a polymeric t h i o c y a n a t e complex, {Co(NCS) 2 *TU2} (105). These complexes a l l i n v o l v e m e t a l - t o - l i g a n d r a t i o s of 1:2 or 1:4. A s i x - c o o r d i n a t e d c o b a l t ( I I ) complex c o n t a i n i n g s i x unidentate l i g a n d s was r e p o r t e d f o r the l i g a n d N,N 1-d i c y c l o h e x y l t h i o u r e a (106). Only one c o b a l t ( I I ) c a r b o x y l a t e complex has been s t u d i e d p r e v i o u s l y i n any d e t a i l - the complex, Co (CH^CO,,) 2 • ETU When t h i s complex was f i r s t prepared and c h a r a c t e r i z e d (63) i t was thought, on the b a s i s of the s p e c t r a l and magnetic r e s u l t s t o i n v o l v e o c t a h e d r a l c o o r d i n a t i o n about c o b a l t . An X-ray d i f f r a c t i o n c r y s t a l s t r u c t u r e i n v e s t i g a t i o n by H o l t e t a l . l a t e r (9) showed the complex to have a p a r t i -c u l a r l y i n t e r e s t i n g molecular s t r u c t u r e i n which the form of c a r b o x y l a t e c o o r d i n a t i o n i s r a t h e r unique. The s t r u c t u r e (see F i g u r e IV-1) can be regarded as f o u r - c o o r d i n a t e d 43 d i s t o r t e d t e t r a h e d r a l , as suggested by the geometry of the f o u r n e a r e s t neighbours of the c o b a l t ( I I ) atom. C o n s i d e r i n g next n e a r e s t neighbours each a c e t a t e group i s b i d e n t a t e with one oxygen atom f u r t h e r away from c o b a l t than the o t h e r . Whether t h i s s t r u c t u r e i s common to o t h e r c a r b o x y l a t e complexes i s not known. The work d e s c r i b e d i n t h i s chapter extends the p r e v i o u s s t u d i e s on the c o b a l t ( I I ) a c e t a t e complexes to i n c l u d e complexes of a r y l c a r b o x y l i c a c i d s . In a d d i t i o n , i n order to o b t a i n as complete and accurate a p i c t u r e as p o s s i b l e of the c o o r d i n a t i n g a c t i o n of the S - l i g a n d s i n v o l v e d , the s p e c t r a l and magnetic p r o p e r t i e s of c o b a l t ( I I ) p e r c h l o r a t e and c h l o r i d e complexes of t h i o u r e a , e t h y l e n e -t h i o u r e a and N,N'-dimethylthiourea have been examined i n d e t a i l . IV-2. SYNTHESIS AND STOICHIOMETRY IV-2-1. Sy n t h e s i s Hydrated c o b a l t (II) a r y l c a r b o x y l a t e s were used as s t a r t i n g m a t e r i a l s i n the p r e p a r a t i o n of many complexes with t h i o u r e a , e t h y l e n e t h i o u r e a , N , N 1 - d i m e t h y l t h i o u r e a and, i n some cases, p y r i d i n e (Chapter V ) . A g e n e r a l method f o r t h e i r p r e p a r a t i o n i s given here. 44 Concentrated sodium hydroxide s o l u t i o n was added dropwise to a s t i r r i n g suspension of a r y l c a r b o x y l i c a c i d i n water u n t i l a c l e a r s o l u t i o n was obt a i n e d . To minimize contamination of the product by b a s i c s a l t i m p u r i t y , the s o l u t i o n was s a t u r a t e d w i t h the a r y l c a r b o x y l i c a c i d con-cerned such t h a t the f i l t e r e d s o l u t i o n had a pH value o f 5 . 5 or l e s s . A s l i g h t l y l e s s than s t o i c h i o m e t r i c amount of c o b a l t ( I I ) c h l o r i d e ( i . e . the c o b a l t r a c i d mole r a t i o b e i n g s l i g h t l y l e s s than 1 : 2 ) was added with s t i r r i n g . P r e c i p i t a t i o n was u s u a l l y instantaneous and the products o b t a i n e d were e i t h e r pink or gray i n c o l o u r . The product thus o b t a i n e d was u s u a l l y f i l t e r e d , washed r e p e a t e d l y w i t h d i s t i l l e d water and d r i e d i n a vacuum d e s i c c a t o r over anhydrous c a l c i u m c h l o r i d e . The degree o f h y d r a t i o n was estimated i n each case by c o b a l t a n a l y s i s and i n some cases, e s t a b l i s h e d by elemental m i c r o a n a l y s e s . Some r e s u l t s are presented i n Table I V - 1 . The t h i o u r e a , e t h y l e n e t h i o u r e a and N,N 1-dimethyl-t h i o u r e a complexes s t u d i e d i n t h i s work were g e n e r a l l y prepared by r e a c t i n g hydrated c o b a l t ( I I ) s a l t s w i t h the r e s p e c t i v e l i g a n d s i n 100% e t h a n o l . R e c r y s t a l l i z a t i o n of products was not commonly employed as a s u i t a b l e s o l v e n t c o u l d not be found, the products being, i n g e n e r a l , i n s u f -f i c i e n t l y s o l u b l e i n i n e r t s o l v e n t s such as benzene, d i e t h y l e t h e r and carbon t e t r a c h l o r i d e . Although some complexes were found t o be f a i r l y s o l u b l e in e t h a n o l and acetone, they underwent e x t e n s i v e l i g a n d d i s s o c i a t i o n i n 45 TABLE IV-1 A n a l y t i c a l Results : Cobalt(II) Arylcarboxylate Hydrates Complex Experimental weight percentages (Calculated % i n brackets) N C o ( m - N 0 o - C . H . C 0 „ ) o . 4 H „ 0 12.41 36.37 3.36 5.86 6.05 Co(p-N0 9-C (-H.C0 9) 9 . 6 H 9 0 11.62 44.73 3.90 5.64 A b 4 ^ ^ Z (11.80 33.68 4.04 5.61 C o ( m - C l - C 6 H 4 C 0 2 ) 2 . 3 H 2 0 C o ( p - C l - C 6 H 4 C 0 2 ) 2 . 3 H 2 0 C o ( p - B r - C g H 4 C 0 2 ) 2 . 3 H 2 0 C o ( p - C H 3 - C 6 H 4 C 0 2 ) 2 • 3 H 2 0 C o ( m - B r - C r H . C 0 „ ) „ . 4 H „ 0 b 4 2. 2. 2 CO C H 12. 41 36. 37 3. 36 ( . 72 36. 30 . 48 11. 62 44. 73 3. 90 ( 1. 80 33. 68 4. 04 13. 77 39. 80 3. 21 (13. 90 39. 65 3. 33 13. 77 39. 44 3. 15 (13. 90 39. 65 3. 33 11. 49 32. 94 2. 68 (11. 49 32. 77 2. 75 14. 92 50. 26 4. 95 (15. 38 50. 15 5. 26 11. 08 31. 75 2. 79 (11. 10 31. 66 2. 66 these s o l v e n t s . The a d d i t i o n of excess l i g a n d to r e p r e s s d i s s o c i a t i o n caused c o - p r e c i p i t a t i o n of the l i g a n d along with the product. F o l l o w i n g are d e t a i l e d d e s c r i p t i o n s of the e x p e r i -mental procedures employed i n the p r e p a r a t i o n of a l l complexes. Elemental a n a l y s e s , i n each case, i n d i c a t e d t h a t adequately pure products had been obt a i n e d . A n a l y t i c a l data are c o l l e c t e d i n Table IV-2. P r e p a r a t i o n of T e t r a k i s ( e t h y l e n e t h i o u r e a ) C o b a l t ( I I )  P e r c h l o r a t e : Co (ClO^) 2'ETU^ A method s i m i l a r to t h a t r e p o r t e d by C a r l i n and H o l t (63) was adopted. A hot suspension of 18.3 g. of c o b a l t ( I I ) p e r c h l o r a t e hexahydrate i n 25 ml. of 100% e t h a n o l was added to a hot s o l u t i o n of 2.5 g. of e t h y l e n e -t h i o u r e a i n 25 ml. of 100% e t h a n o l (the mole r a t i o of c o b a l t : e t h y l e n e t h i o u r e a being % 2:1). T h i s excess of the c o b a l t ( I I ) s a l t was r e q u i r e d to prevent any c o - p r e c i p i t a t i o n of e t h y l e n e t h i o u r e a with the complex. A blue s o l u t i o n was o b t a i n e d when hot and, on c o o l i n g , the blue c r y s t a l s . w h i c h p r e c i p i t a t e d were washed thoroughly with e t h a n o l and d r i e d i n a vacuum d e s i c c a t o r over anhydrous c a l c i u m c h l o r i d e . P r e p a r a t i o n of T e t r a k i s ( t h i o u r e a ) C o b a l t ( I I ) P e r c h l o r a t e : C o ( C 1 0 4 ) 2 » T U 1 Attempts to prepare the t h i o u r e a complex by a procedure analogous to t h a t d e s c r i b e d above f o r the 47 TABLE IV-2 A n a l y t i c a l Results : Thiourea, Ethylenethiourea and N,N'-Dimethylthiourea complexes Complex Experimental weight percentages (Calculated % i n brackets) Co(C10 4) 2 -ETU 4 C o(Cl0 4 ) 2 . T U 4 Co (C10 4) 2 .DMTU 4 C o C l 2 . E T U 2 C o C l 2 . T U 2 CoCl 2 .DMTU 2 Co(CH 3C0 2) 2 -ETU 2 Co (CH 3C0 2) 2- T U2 Co (CH 3C0 2) 2 -DMTU 2 C O ( C 6 H 5C0 2 ) 2 . T U 2 Co (C 6H 5C0 2) 2•DMTU2 Co ( p - B r - C 6 H 4C0 2) 2• E T U 2 C o ( p - B r - C 6 H 4C0 2) 2- T U 2 Co(p-Br-C 6 H 4C0 2 ) 2 .DMTU 2 Co C H N 8. 85 21. 44 3. 53 17. 01 ( 8. 84 21. 62 3. 63 16. 81) 10. 50 8. 41 2. 83 20. 34 (10. 48 8. 54 2. 87 19. 93) 8. 70 21. 20 4. 67 16. 85 ( 8. 73 21. 36 4. 78 16. 61) 17. 63 21. 50 3. 48 17. 02 (17. 63 21. 55 3. 59 16. 75) 20. 84 8. 64 2. 77 20. 10 (20. 89 8. 51 2. 86 19. 87) 17. 38 21. 30 4. 76 16. 82 (17. 42 21. 30 4. 77 16. 57) 15. 42 31. 80 4. 79 14. 61 (15. 45 31. 48 4. 76 14. 69) 17. 92 21. 60 4. 08 17. 40 (17. 90 21. 88 4. 29 17. 02) 15. 19 30. 86 5. 63 14. 85 (15. 29 31. 15 5. 75 14. 54) 12. 82 42. 02 3. 80 12. 32 (13. 00 42. 39 4. 00 12. 35) 11. 58 47. 25 4. 99 10. 89 (11. 58 47. 18 5. 15 11. 01) 8. 92 35. 96 2. 89 8. 68 ( 8. 88 36. 21 3. 04 8. 45) 9. 59 31. 39 2. 51 9. 44 ( 9. 64 31. 44 2. 64 9. 17) 8. 81 35. 92 3. 70 8. 40 ( 8. 83 36. 00 3. 62 8. 40) 48 TABLE IV-2 (Cont.) Complex Experimental weight percentages ( C a l c u l a t e d % i n brackets) Co C i H N Co (o-Br-C.-H.CCi ) „ .ETU„ 8. 85 36. 25 3. 19 8 .56 ( 8. 88 36. 21 3. 04 8 .45) Co(o-Br -C,H.CC) ) „ .TU„ 9. 60 31. 56 2. 52 9 .11 O 4 Z Z Z ( 9. 64 31. 44 2. 64 9 .17) Co(o-Br - C , H . C O „ )„.DMTU 0 8. 90 36. 23 3. 82 8 .42 o 4 Z • Z Z ( 8. 83 36. 00 3. 62 8 .40) Co(o - N 0 o - C c H , , C 0 o ) 0.ETU 0 9. 85 40. 40 3. 24 14 .25 Z b fi Z Z Z ( 9. 89 40. 33 3. 38 14 .10) Co(o - N 0 ~ - C c H . C 0 o ) n.TU 0 10. 80 34. 61 3. 30 15 .44 Z b 4 z z z (10. 84 35. 36 2. 97 15 .47) Co(o - N 0 o - C c H . C 0 o ) 0.DMTU 0 9. 93 39. 76 4. 01 . 14 .29 Z 0 4 Z Z Z ( 9. 83 40. 06 4. 03 14 .02) Co (m - N 0 o - C c H . C 0 o ) 0.ETU 0 10. 00 40. 28 3. 52 13 . 85 Z b 4 Z Z Z ( 9. 89 40. 33 3. 38 14 .10) Co (m -N0„-C c H.C0 o ) 0 .TU 0 10. 84 35. 17 2. 83 15 .68 Z b 4 Z Z Z (10. 84 35. 36 2. 97 15 • 47) Co (m -N0 o -C c H / 1 C0 o ) 0.DMTU„ 9. 82 39. 74 3. 79 14 .06 Z O 4 Z Z Z ( 9. 83 40. 06 4. 03 14 .02) CO(p -NO^-CcH.CO^)„.DMTU 0 9. 67 40. 02 4. 04 14 .19 Z b 4 z z z ( 9. 83 40. 06 4. 03 14 .02) 49 p r e p a r a t i o n of the e t h y l e n e t h i o u r e a d e r i v a t i v e y i e l d e d an o i l y product which c o u l d not be c r y s t a l l i z e d . The method used by Cotton, Faut and Mague (62) t o prepare t h i s complex was thus repeated here. C o b a l t ( I I ) p e r c h l o r a t e hexahydrate (lOg.) was d i s s o l v e d i n 10 ml. of hot i s o p r o p y l a l c o h o l and 8.6 g. of t h i o u r e a was added ( i n a mole r a t i o of ^ 1:4). The s o l u t i o n was c o o l e d and c h l o r o f o r m was added sl o w l y u n t i l an o i l y substance was o b t a i n e d . T h i s was l e f t f o r a few days u n t i l c r y s t a l l i z a t i o n o c c u r r e d . The product was then f i l t e r e d and r e c r y s t a l l i z e d from an i s o p r o p y l a l c o h o l -c h l o r o f o r m mixture. P r e p a r a t i o n of T e t r a k i s ( N , N ' - d i m e t h y l t h i o u r e a ) C o b a l t ( I I )  P e r c h l o r a t e : C o ( C l O ^ ) 2 *DMTU ^  C o b a l t ( I I ) p e r c h l o r a t e hexahydrate (18.3 g.) was d i s s o l v e d i n 25 ml. of 100% e t h a n o l and the s o l u t i o n was f i l t e r e d i n t o a hot s o l u t i o n of 20.8 g. of N,N 1-dimethyl-t h i o u r e a i n 100% e t h a n o l (mole r a t i o of ^ 1:4). The volume of the r e s u l t i n g s o l u t i o n was reduced to 10 ml. and on c o o l i n g i n i c e , a green p r e c i p i t a t e was o b t a i n e d . The product was so s o l u b l e i n e t h a n o l t h a t on washing on l y a s m a l l p a r t of i t was recovered. I t was f i n a l l y d r i e d i n a vacuum d e s i c c a t o r over anhydrous c a l c i u m c h l o r i d e . P r e p a r a t i o n of B i s ( e t h y l e n e t h i o u r e a ) C o b a l t ( I I ) C h l o r i d e : C o C l 2 ' E T U 2 A method analogous to t h a t d e s c r i b e d by C a r l i n and H o l t (63) was employed. Instead of u s i n g anhydrous c o b a l t ( I I ) 50 c h l o r i d e , the hydrated s a l t was used as the s t a r t i n g m a t e r i a l . C o b a l t ( I I ) c h l o r i d e hexahydrate (11.9 g.) was d i s s o l v e d i n 25 ml. of hot 100% e t h a n o l and the s o l u t i o n was mixed wi t h one c o n t a i n i n g 10.2 g. of e t h y l e n e t h i o u r e a (mole r a t i o of ^ 1:2). Upon c o o l i n g , blue c r y s t a l s formed from the blue s o l u t i o n . The product was washed wit h 100% e t h a n o l and d r i e d i n a d e s i c c a t o r over anhydrous c a l c i u m c h l o r i d e . P r e p a r a t i o n of B i s ( t h i o u r e a ) C o b a l t ( I I ) C h l o r i d e : CoCl^'TU^ F o l l o w i n g the method used by Cotton, Faut and Mague (62), 4.75 g. of c o b a l t ( I I ) c h l o r i d e hexahydrate was d i s s o l v e d i n 30 ml. of hot n - b u t y l a l c o h o l and 3 g. of t h i o u r e a was added i n a % 1:2 mole r a t i o . T h i s was heated t o give a c l e a r s o l u t i o n which on c o o l i n g i n i c e y i e l d e d blue c r y s t a l s of the product. The a d d i t i o n of benzene to the s o l u t i o n to f o r c e p r e c i p i t a t i o n of the product as d e s c r i b e d by Cotton e t a l . was found not to be necessary. The product was washed wit h n - b u t y l a l c o h o l and d r i e d i n the u s u a l manner. Attempts to prepare t h i s compound u s i n g 100% e t h a n o l as s o l v e n t were u n s u c c e s s f u l . P r e p a r a t i o n of Bis(N,N'-dimethylthiourea) C o b a l t ( I I ) C h l o r i d e : CoCl 2 >DMTU 2 The p r e p a r a t i o n was c a r r i e d out i n 10 0% e t h a n o l . C o b a l t ( I I ) c h l o r i d e hexahydrate (11.9 g.) was d i s s o l v e d i n 25 ml. of c o l d 100% e t h a n o l and t h i s was added to a s o l u t i o n of 10.4 g. of N,N'-dimethylthiourea (mole r a t i o of ^ 1:2). The product p r e c i p i t a t e d immediately as blue c r y s t a l s . I t was washed with 100% e t h a n o l and was d r i e d i n the u s u a l manner. P r e p a r a t i o n of B i s ( e t h y l e n e t h i o u r e a ) C o b a l t (II) A c e t a t e :  C o ( C H 3 C Q 2 ) 2 , E T U 2 C a r l i n and H o l t (63) r e p o r t e d the p r e p a r a t i o n of t h i s complex and t h e i r procedure was f o l l o w e d here. C o b a l t ( I I ) a c e t a t e t e t r a h y d r a t e (2.5 g.) was d i s s o l v e d i n 200 ml. of 100% e t h a n o l . The s o l u t i o n was f i l t e r e d and the f i l t r a t e -added to a hot s o l u t i o n of 2.0 g. of e t h y l e n e t h i o u r e a i n 50 ml. of 100% e t h a n o l (mole r a t i o of ^ 1:2). P u r p l e - b l u e c r y s t a l s were ob t a i n e d on c o o l i n g . The product was washed and d r i e d i n the u s u a l manner. P r e p a r a t i o n of B i s ( t h i o u r e a ) C o b a l t ( I I ) A c e t a t e : Co (CH 3CO 2 )_2 »TU 2 No p r e v i o u s p r e p a r a t i o n has been r e p o r t e d f o r t h i s complex. C o b a l t (II) a c e t a t e t e t r a h y d r a t e (12.5 g.) was mixed wi t h 7.6 g. of t h i o u r e a (mole r a t i o of ^ 1:2) i n 100 ml. of 100% e t h a n o l . A deep blue s o l u t i o n was obtained on warming. The s o l u t i o n was then evaporated almost to dryness and a p u r p l e - b l u e product was o b t a i n e d . A f t e r f i l t e r i n g , the product was washed s e v e r a l times w i t h 100% e t h a n o l and d r i e d under vacuum a t 9 0°C f o r 2 hours to y i e l d the deep p u r p l e - b l u e complex. P r e p a r a t i o n of Bis(N,N'-dimethylthiourea) C o b a l t ( I I ) A c e t a t e : Co (CH., CO 2 )_2 • DMTU0 C o b a l t (II) a c e t a t e t e t r a h y d r a t e (7.5 g.) was mixed with 6.3 g. of N , N 1 - d i m e t h y l t h i o u r e a (mole r a t i o of ^ 1:2) i n 125 ml. of 100% e t h a n o l . The deep blue s o l u t i o n was f i l t e r e d , reduced i n volume to 50 ml. and c o o l e d i n i c e . Purple c r y s t a l s s l o w l y p r e c i p i t a t e d . The product was washed and d r i e d i n the u s u a l manner. P r e p a r a t i o n of B i s ( t h i o u r e a ) C o b a l t (II) Benzoate: Co ( C , H c C 0 o ) 0 « T U 0 6 —O 2 —2 2 To a suspension of 11.3 g. of c o b a l t ( I I ) benzoate hydrate i n 100 ml. of c o l d 100% e t h a n o l , 4.6 g. of t h i o u r e a was added (mole r a t i o of ^ 1:2) with s t i r r i n g . On s t a n d i n g , s m a l l amounts of a white s o l i d p r e c i p i t a t e d from the deep blue s o l u t i o n . The s o l i d , t h i o u r e a , was removed by f i l t r a t i o n and the s o l u t i o n was then evaporated s l o w l y to about 2 0 ml. and c o o l e d i n i c e f o r a few days when an a p p r e c i a b l e amount of a p u r p l e s o l i d p r e c i p i t a t e d . The product was i s o l a t e d by f i l t r a t i o n , washed wit h 100% e t h a n o l and d r i e d under vacuum at 90°C f o r one day. P r e p a r a t i o n of Bis(N,N'-dimethylthiourea) C o b a l t ( I I ) Benzoate: Co (CrH,-C0o) «*DMTU 0 6—b 2—2 2 To a suspension of 11.3 g. of c o b a l t ( I I ) benzoate hydrate i n 100 ml. of c o l d 100% e t h a n o l , 6.3 g. of N,N1 -d i m e t h y l t h i o u r e a was added (mole r a t i o of ^ 1:2) w i t h 53 s t i r r i n g . The blue solution obtained was evaporated to about 5 ml. and the purple c r y s t a l s obtained were f i l t e r e d , washed with 100% ethanol and dried i n a vacuum desiccator over anhydrous calcium chloride. Preparation of Bis(ethylenethiourea) Cobalt(II) o-Bromo- benzoate: Co ( o - B r - C £ C O 2 )_2j^ETU2 Cobalt(II) o-bromobenzoate hydrate (10.6 g.) was dissolved i n 25 ml. of hot 100% ethanol and the r e s u l t i n g solution was mixed with one containing 4.1 g. of ethylene-thiourea (mole r a t i o of 'v 1:2). Upon cooling, purple c r y s t a l s formed and were washed with 100% ethanol and dried i n a desiccator over anhydrous calcium chloride. Preparation of Bis(thiourea) Cobalt(II) o-Bromobenzoate: Co (o-Br-C GH 4CO 2 )_2j^TU2 Cobalt(II) o-bromobenzoate hydrate (10.6 g.) was mixed with 3.1 g. of thiourea (mole r a t i o of 'v 1:2) i n 100 ml. of 100% ethanol. On warming, a deep blue solution was obtained. The solution was then evaporated almost to dryness when a purple product was obtained. The pr e c i p i t a t e f i r s t formed was i d e n t i f i e d by elemental analyses to be of the formula Co(o-Br-CgH 4C0 2) 2•TU 2•2H 20. When i t was pumped i n vacuum at 100°C for one day, water was removed to y i e l d the required anhydrous product. 54 P r e p a r a t i o n of Bis(N,N'-dimethylthiourea) C o b a l t (II) o-Bromobenzoate: Co(o-Br-CH.CO,,)„•DMTU~ 6—4 2.—2. 2. C o b a l t ( I I ) o-bromobenzoate hydrate (10.6 g.) was d i s s o l v e d i n 25 ml. of c o l d 100% et h a n o l and the s o l u t i o n was added to one c o n t a i n i n g 4.2 g. of N,N'-dimethylthiourea (mole r a t i o of ^ 1:2). The product came down slo w l y as a p u r p l e p r e c i p i t a t e which was washed and d r i e d i n the u s u a l manner. P r e p a r a t i o n of B i s ( e t h y l e n e t h i o u r e a ) C o b a l t ( I I ) p-Bromo- benzoate: Co(p-Br-CgH^CO^) 2'ETU^ C o b a l t ( I I ) p-bromobenzoate t r i h y d r a t e (12.8 g.) was d i s s o l v e d i n 25 ml. of hot 100% et h a n o l and the s o l u t i o n was mixed wi t h one c o n t a i n i n g 5.1 g. of e t h y l e n e t h i o u r e a (mole r a t i o of ^ 1:2). Upon c o o l i n g , some white s o l i d p r e c i p i t a t e d which was f i l t e r e d o f f . The volume of the s o l u t i o n was reduced to 15 ml. when pu r p l e c r y s t a l s were i s o l a t e d . The product was washed and d r i e d i n the u s u a l manner. P r e p a r a t i o n of B i s ( t h i o u r e a ) C o b a l t ( I I ) p-Bromobenzoate: Co ( p - B r - C c C O 2 )_2 »TU 2 To a suspension of 12.8 g\ of the c o b a l t ( I I ) p-bromobenzoate t r i h y d r a t e i n 100 ml. of c o l d 100% e t h a n o l , 3.8 g. of t h i o u r e a was added (mole r a t i o of ^ 1:2) with s t i r r i n g . A deep blue s o l u t i o n was ob t a i n e d . I t was evaporated t o about 20 ml. and c o o l e d i n i c e f o r a few days when an a p p r e c i a b l e amount of a p u r p l e s o l i d 55 p r e c i p t i a t e d . The product was f i l t e r e d , washed wit h 100% eth a n o l and d r i e d under vacuum a t 90°C f o r one day. P r e p a r a t i o n o f Bis(N,N'-dimethylthiourea) C o b a l t ( I I ) p-Bromobenzoate : Co (p-Br-C^H 4CO 2 )_2 «DMTU 2 C o b a l t ( I I ) p-bromobenzoate t r i h y d r a t e (12.8 g.) was d i s s o l v e d i n 25 ml. of hot 100% et h a n o l and the s o l u t i o n was added t o one c o n t a i n i n g 5.2 g. of N , N 1 - d i m e t h y l t h i o u r e a (mole r a t i o o f a, 1:2). The product p r e c i p i t a t e d r e a d i l y as p u r p l e c r y s t a l s . I t was washed and d r i e d i n the u s u a l manner. P r e p a r a t i o n of B i s ( e t h y l e n e t h i o u r e a ) C o b a l t ( I I ) o - N i t r o -benzoate: Co(o-N0„-C,H.C0„)„ •ETU-2. 6—4 2—2 2 C o b a l t ( I I ) o-nitrobenzoate hydrate (13.4 g.) was d i s s o l v e d i n 25 ml. of hot 100% e t h a n o l and the s o l u t i o n was mixed with one c o n t a i n i n g 5.1 g. of e t h y l e n e t h i o u r e a (mole r a t i o of ^ 1:2). Upon c o o l i n g , p u r p l e c r y s t a l s formed from the blue s o l u t i o n . - The product was washed and d r i e d i n the us u a l manner. P r e p a r a t i o n of B i s ( t h i o u r e a ) C o b a l t ( I I ) o-Nitrobenzoate: Co (o-N0 2-C 6H 4CO 2 )_2 «TU 2 To a suspension o f 13.4 g. of the c o b a l t ( I I ) o - n i t r o b e n z o a t e hydrate i n 100 ml. of c o l d 100% e t h a n o l , 3.8 g. of t h i o u r e a was added (mole r a t i o of a. 1:2) with s t i r r i n g . On st a n d i n g , s m a l l amounts of a white s o l i d p r e c i p i t a t e d from the deep blue s o l u t i o n . The s o l i d was removed by f i l t r a t i o n and the s o l u t i o n on e v a p o r a t i o n to reduce the volume y i e l d e d more of the white s o l i d . The f i l t e r e d s o l u t i o n was then t r e a t e d w i t h anhydrous d i e t h y l e t h e r i n a 1:3 volume r a t i o and on st a n d i n g a pu r p l e s o l i d p r e c i p i t a t e d . T h i s product was d r i e d i n a vacuum a t 90°C f o r one day. P r e p a r a t i o n o f Bis(N,N'-dimethylthiourea) C o b a l t ( I I ) o-Nitrobenzoate : Co (o-N0 2-C 6H 4CC> 2) 2 • DMTU,, C o b a l t ( I I ) o -nitrobenzoate hydrate (13.4 g.) was d i s s o l v e d i n 25 ml. of c o l d 100% et h a n o l and the s o l u t i o n was added t o one c o n t a i n i n g 5.2 g. of N,N'-dimethylthiourea (mole r a t i o of ^  1:2). The product p r e c i p i t a t e d immediately as p u r p l e c r y s t a l s and was washed and d r i e d i n the u s u a l manner. P r e p a r a t i o n of Bis(N,N'-dimethylthiourea) C o b a l t ( I I ) p-Nitrobenzoate : Co (p-NO^-CgH_4CO,, )_2 • DMTU,, C o b a l t ( I I ) p - n i t r o b e n z o a t e hexahydrate (12.5 g.) was suspended i n 25 ml. of c o l d 100% et h a n o l and the suspension was mixed wi t h a s o l u t i o n of 5.2 g. of N,N'-d i m e t h y l t h i o u r e a (mole r a t i o o f ^  1:2) wit h s t i r r i n g . The r e s u l t i n g mixture was f i l t e r e d and the concentrated f i l t r a t e was allowed to stand. The product p r e c i p i t a t e d s l o w l y as p u r p l e c r y s t a l s . I t was washed and d r i e d i n the u s u a l manner. 57 P r e p a r a t i o n of B i s ( e t h y l e n e t h i o u r e a ) C o b a l t ( I I ) m-Nitro- benzoate: Co (m-NO^-CgH^CC>2 )_2 • ETU 2 C o b a l t ( I I ) m-nitrobenzoate t e t r a h y d r a t e (11.6 g.) was d i s s o l v e d i n 25 ml. of hot 100% et h a n o l and the s o l u t i o n was mixed w i t h one c o n t a i n i n g 5.1 g. of e t h y l e n e -t h i o u r e a (mole r a t i o of ^  1:2). Upon c o o l i n g , p u r p l e c r y s t a l s were formed. The product was washed and d r i e d i n the us u a l manner. P r e p a r a t i o n of B i s ( t h i o u r e a ) C o b a l t ( I I ) m-Nitrobenzoate:  Co ( m - N Q 2 - C C O 2 )_2 -TU 2 To a suspension of 11.6 g. of the c o b a l t ( I I ) m-nitrobenzoate t e t r a h y d r a t e i n 100 ml. of c o l d 100% et h a n o l , 3.8 g. o f t h i o u r e a was added (mole r a t i o of ^ 1:2) with s t i r r i n g . A deep blue s o l u t i o n was obt a i n e d which c r y s t a l l i z e d s l o w l y . The product was washed and d r i e d i n the u s u a l manner. P r e p a r a t i o n of Bis(N,N'-dimethylthiourea) C o b a l t ( I I ) m-Nitrobenzoate: C o ( m - N 0 o - C , H . C 0 o ) « D M T U „ Z 6—4 Z—Z Z C o b a l t ( I I ) m-nitrobenzoate t e t r a h y d r a t e (11.6 g.) was d i s s o l v e d i n 25 ml. of c o l d 100% eth a n o l and the s o l u t i o n was added t o a s o l u t i o n of 5.2 g. of N,N'-dimethyl-t h i o u r e a (mole r a t i o o f ^  1:2). Purple c r y s t a l s p r e c i p i t a t e d r e a d i l y . The product was washed and d r i e d i n the u s u a l manner. 58 U n s u c c e s s f u l P r e p a r a t i v e Attempts Although both the t h i o u r e a and N , N 1 - d i m e t h y l t h i o u r e a d e r i v a t i v e s of c o b a l t ( I I ) benzoate were prepared without much d i f f i c u l t y , s e v e r a l attempts t o o b t a i n the e t h y l e n e -t h i o u r e a d e r i v a t i v e were u n s u c c e s s f u l . The hydrated c o b a l t ( I I ) benzoate was i n ' t h e f i r s t p l a c e o n l y s p a r i n g l y s o l u b l e even i n b o i l i n g 100% e t h a n o l . The a d d i t i o n of e t h y l e n e t h i o u r e a i n the form of a hot s o l u t i o n y i e l d e d a very d i l u t e s o l u t i o n of a c o b a l t ( I I ) complex; most of the c o b a l t ( I I ) s a l t remained unreacted and u n d i s s o l v e d . A f t e r f i l t e r i n g and on r e d u c i n g the volume of the f i l t r a t e , e t h y l e n e t h i o u r e a p r e c i p i t a t e d out from s o l u t i o n . No s u i t a b l e product c o u l d be ob t a i n e d . Attempts u s i n g other s o l v e n t s such as i s o p r o p y l a l c o h o l and acetone and v a r i o u s p r e p a r a t i v e procedures d e s c r i b e d i n the pr e v i o u s paragraphs a l s o f a i l e d to produce the r e q u i r e d complex. S i m i l a r attempts t o prepare t h i o u r e a and e t h y l e n e -t h i o u r e a d e r i v a t i v e s of c o b a l t ( I I ) p - n i t r o b e n z o a t e met with s i m i l a r r e s u l t s and the complexes were not o b t a i n e d i n the pr e s e n t work. S e v e r a l u n s u c c e s s f u l attempts a t the p r e p a r a t i o n of t r i f l u o r o a c e t a t e d e r i v a t i v e s were made. The hydrated c o b a l t ( I I ) t r i f l u o r o a c e t a t e was found t o be very s o l u b l e i n 100% e t h a n o l and on a d d i t i o n o f t h i o u r e a , e t h y l e n e t h i o u r e a or N,N'-dimethylthiourea, a deep p u r p l e s o l u t i o n was obtained i n each case. In both the t h i o u r e a and e t h y l e n e -t h i o u r e a cases, r e d u c t i o n i n the volume of the s o l u t i o n by e v a p o r a t i o n l e d o n l y to p r e c i p i t a t i o n of the l i g a n d s accompanied by a change i n the c o l o u r of the s o l u t i o n from p u r p l e to p i n k . No complexes were i s o l a t e d . In the case of N,N'-dimethylthiourea, the s o l u t i o n decomposed to a brown suspension on s t a n d i n g . Other attempts i n v o l v i n g the use of i n e r t o r g a n i c l i q u i d such as benzene, d i e t h y l e t h e r , petroleum e t h e r and c h l o r o f o r m to e f f e c t p r e c i p i t -a t i o n a l s o f a i l e d t o produce products. S o l v e n t s such as acetone, 1-butanol and benzene were a l s o employed i n s t e a d of e t h a n o l and s i m i l a r n e g a t i v e r e s u l t s were observed. IV-2-2. S t o i c h i o m e t r y The above prepared c a r b o x y l a t e complexes have, i n g e n e r a l , a metal to l i g a n d mole r a t i o of 1:2. Attempts to prepare complexes of o t h e r s t o i c h i o m e t r i e s , such as complexes wi t h metal to l i g a n d mole r a t i o s of 1:4 and 1:6 were u n s u c c e s s f u l . For example, i t was found t h a t , by mixing a mole of hydrated c o b a l t ( I I ) benzoate with e i t h e r f o u r or s i x moles of t h i o u r e a , l a r g e amounts of f r e e t h i o u r e a c o - p r e c i p i t a t e d with the b i s ( t h i o u r e a ) complex from s o l u t i o n . In an analogous experiment w i t h the N,N'-dimethylthiourea complex, the extent of c o - p r e c i p i t a t i o n of the l i g a n d along w i t h a product was l e s s but product was found t o have a metal to l i g a n d mole r a t i o c l o s e to 1:2. S i m i l a r r e s u l t s were ob t a i n e d f o r o t h e r complexes. Apparently a value other than 1:2 f o r the m e t a l : l i g a n d mole r a t i o i s g e n e r a l l y not favoured f o r such c o b a l t ( I I ) c a r b o x y l a t e complexes. 60 IV-3. CHARACTERIZATION OF COMPLEXES IV-3-1. I n f r a r e d S p e c t r a l Study The purpose of s t u d y i n g the i n f r a r e d s p e c t r a of these complexes i s t w o - f o l d . These l i g a n d s are known to e x h i b i t ambident c o o r d i n a t i o n behaviour i n t h e i r t r a n -s i t i o n metal complexes, being able to bond to the c e n t r a l metal i o n e i t h e r through S or through N. From t h e i r i n f r a r e d s p e c t r a i t should be p o s s i b l e to i d e n t i f y the s i t e of c o o r d i n a t i o n . Secondly, we have attempted to l o c a t e the two major c a r b o x y l a t e (-CO2) s t r e t c h i n g f r e q u e n c i e s i n the i n f r a r e d s p e c t r a of these complexes and to c o r r e l a t e these w i t h the nature of the c a r b o x y l a t e l i g a n d . Ligand V i b r a t i o n s of T h i o u r e a and Complexes I n f r a r e d (107), Raman (108), c r y s t a l l o g r a p h i c (109) and d i p o l e moment (110) s t u d i e s have a l l shown t h a t t h i o u r e a e x i s t s as a resonance h y b r i d of the f o l l o w i n g c a n o n i c a l forms: NH„ NHl NH„ / 2 _ / l S = C < » S - C <—» s - c \ \ ^ + NH 2 NH 2 NH^ I I I I I I Because of the s i g n i f i c a n t c o n t r i b u t i o n s from the l a t t e r two c a n o n i c a l forms to the h y b r i d , metal-sulphur bonding i s favoured i n the t h i o u r e a complexes. F a r - i n f r a r e d s p e c t r a l s t u d i e s of some t r a n s i t i o n metal - t h i o u r e a complexes (114) a l l showed M-S v i b r a t i o n bands. In a d d i t i o n , X-ray c r y s t a l l o g r a p h i c study of ZnCl 2«TU" 2 (115), PbCl 2'TU" 2 (116), N i C l 2 « T U 4 (117), N i(NCS) 2«TU 2 (118) andCuCl-TUg (119) a l l showed M-S l i n k a g e . When t h i o u r e a i s bonded to a metal through i t s S-atom, the c o n t r i b u t i o n from the c a n o n i c a l forms I I and I I I are i n c r e a s e d . As a r e s u l t , the bond order of the carbon-sulphur double bond (C=S) i s reduced and a t the same time the car b o n - n i t r o g e n (C-N) bond s t r e n g t h i s i n c r e a s e d . In other words, the C=S s t r e t c h i n g frequency of t h i o u r e a should decrease while the C-N s t r e t c h i n g f r e -quency should i n c r e a s e upon the formation of a S-bonded complex. By comparing the i n f r a r e d s p e c t r a o f t h i o u r e a and i t s complexes, i n f o r m a t i o n about bonding s i t e should be a v a i l a b l e . Assuming a p l a n a r C 2 v s t r u c t u r e , the normal v i b r a -t i o n s of t h i o u r e a were c a l c u l a t e d by Stewart (107), K u t z e l l n i g g and Mecke (111) and Yamaguchi e t a l . (102). D e t a i l e d v i b r a t i o n a l assignments were made. The i n f r a r e d s p e c t r a o f a number of t r a n s i t i o n m e t a l - t h i o u r e a complexes were s t u d i e d by Yamaguchi et a l . (102) and Swammathan and I r v i n g (112) and t h e i r r e s u l t s showed t h a t the d i f f e r e n c e s between the i n f r a r e d spectrum of t h i o u r e a i t s e l f and those of i t s metal complexes were c o n f i n e d to two bands o n l y . The band a t 1413 c m - 1 was s p l i t and t h a t a t 730 cm was both s p l i t and s h i f t e d t o lower energy i n the s p e c t r a of the complexes. S i m i l a r s t u d i e s by Yagupsky e t a l . (105) and S e l v a r a j a n (113) showed, i n a d d i t i o n , a h i g h frequency s h i f t of the 1473 cm band of t h i o u r e a to ^ 15 00 cm ^ i n the s p e c t r a of the complexes. These r e s u l t s are i n accordance with the assignments of these " c r i t i c a l " bands by Yamaguchi e t a l . (102) t h a t the 1473 cm ^ band i s a s s i g n e d to the C-N s t r e t c h i n g frequency and the 1413 cm ^ and 730 cm ^ bands are both d e s c r i b e d as mostly C=S s t r e t c h i n g . The l o c a t i o n of the three c r i t i c a l bands of t h i o u r e a i s made d i f f i c u l t i n the p r e s e n t work as v i b r a t i o n s a r i s i n g from c a r b o x y l a t e groups occur i n the same s p e c t r a l r e g i o n as those due to t h i o u r e a . N e v e r t h e l e s s , the c r i t i c a l bands of t h i o u r e a have been l o c a t e d by simply comparing the s p e c t r a of f r e e t h i o u r e a , the c o b a l t ( I I ) complex, and the c o r r e s p o n d i n g hydrated c o b a l t ( I I ) a r y l c a r b o x y l a t e s a l t . An example i s g i v e n i n F i g u r e IV-2 f o r i l l u s t r a t i o n . The r e s u l t s o b t a i n e d f o r the three c r i t i c a l bands of t h i o u r e a f o r a l l the t h i o u r e a complexes s t u d i e d i n t h i s work are c o l l e c t e d i n Table IV-3. From Table IV-3, two changes are apparent i n the spectrum of t h i o u r e a on complex formation. The band a t 1473 cm 1 a s s i g n e d mainly to the C-N s t r e t c h i n g v i b r a t i o n of t h i o u r e a i s s h i f t e d to h i g h e r energy. The other band a t 730 cm 1 , a s s i g n e d i n p a r t to the C=S s t r e t c h i n g v i b r a t i o n of t h i o u r e a , i s s h i f t e d to lower energy. The 1413 c m - 1 band i s p o s s i b l y s p l i t w i t h the lower energy component masked by c a r b o x y l a t e group v i b r a t i o n s . These r e s u l t s are c o n s i s t e n t with the complexes being S-bonded. 63 — 1 4 1 i 1 _i (_ 1600 1200 800 400 * TU ligand vibrations Figure IV-2. Infrared Spectra of TU, Co(p-Br-CgH^CG^)2 * TU and Co(p-Br-C 6H 4C0 2) 2•3H 20 6 4 TABLE I V - 3 I n f r a r e d S p e c t r a l Assignments ( f o r Three C r i t i c a l Bands) of Thiourea Complexes of C o b a l t ( I I ) Band P o s i t i o n (cm h TU 1 4 7 3 1 4 1 3 C=S s t . -+N-H rock. 7 3 0 C=S s t . Assignment ( 1 0 2 ) C-N s t . +C-N s t . +C-N s t . C o ( C l 0 4 ) 2 - T U 4 1 5 0 0 r l 4 2 0 i 1 3 9 0 7 0 5 C o C l 2 - T U 2 1 5 0 0 r l 4 3 0 l 1 3 9 0 7 1 0 C o ( C H 3 C 0 2 ) 2 - T U 2 1 5 0 0 r l 4 4 5 *• * 7 1 5 C o ( C 6 H 5 C 0 2 ) 2 . T U 2 1 5 0 0 r l 4 1 5 *• * 7 1 0 Co ( o - N 0 2 - C g H 4 C 0 2 ) 2 • T U 2 1 5 2 3 r l 4 4 5 7 0 5 C o ( m - N 0 2 - C 6 H 4 C 0 2 ) 2 - T U 2 1 5 0 0 r 1 4 4 5 ^ 1 3 7 5 7 1 0 C o ( o - B r - C 6 H 4 C 0 2 ) 2 • T U 2 1 5 0 0 r l 4 3 5 ^ * 7 1 0 C o ( p - B r - C g H 4 C 0 2 ) 2 * T U 2 1 5 0 0 , 1 4 1 2 1 1 3 8 5 7 1 2 * p o s s i b l y masked by c a r b o x y l a t e v i b r a t i o n 65 Ligand V i b r a t i o n s of N,N'-Dimethylthiourea and Complexes For s u b s t i t u t e d t h i o u r e a s , which i n c l u d e N,N'-d i m e t h y l t h i o u r e a as w e l l as e t h y l e n e t h i o u r e a , h y b r i d resonance s t r u c t u r e s s i m i l a r t o those i n t h i o u r e a can a l s o be drawn. Whereas no N-bonded t h i o u r e a has ever been found i n i t s complexes w i t h t r a n s i t i o n metals, complexes c o n t a i n i n g N-bonded s u b s t i t u t e d t h i o u r e a s are evidenced by i n f r a r e d s p e c t r a l s t u d i e s . For example, i n a s e r i e s of Nemethylthiourea (MTU) complexes, ZnCl 2«MTU 2, CdCl 2-MTU 2 (103), HgCl 2«MTU (114b) and {Co(NCS)-*MTU„ } (105) were found to be S-bonded whereas 2 2. n P t C l 2 « M T U 4 , P d C l 2 « M T U 4 , CuCl'MTU 4 (103), N i (C1C>4) 2 -MTUg and N i C l 2 « M T U 2 , (99) were found to be N-bonded. Recently, N-bonded complexes of N - a l l y l t h i o u r e a with Co (II) and N i ( I I ) h a l i d e s and p e r c h l o r a t e s have a l s o been c h a r a c t e r i z e d (120) . As p o i n t e d out by some of the above s t u d i e s (103, 114b) the assignments of the nature of the metal t o l i g a n d bond based on changes i n the C-N and C=S f r e q u e n c i e s may be erronous f o r complexes of the s u b s t i t u t e d t h i o u r e a s . T h i s i s because the f o r c e constants of v(C-N) and v (C-S) become so comparable f o r these l i g a n d s t h a t mixing between these v i b r a t i o n s w i l l be a p p r e c i a b l e . The normal c o o r d i n a t e a n a l y s i s of N,N'-dimethyl-t h i o u r e a , i n p a r t i c u l a r , was c a r r i e d out by Gosavi, Agarwala and Rao (121) and d e t a i l e d assignments were made. The i n f r a r e d s p e c t r a of s e v e r a l t r a n s i t i o n metal -N,N'-d i m e t h y l t h i o u r e a complexes were a l s o s t u d i e d (99, 114b) and two of the complexes, v i z . CuCl«DMTU 4 and P dCl 2«DMTU 4 (114b) were found to be N-bonded. From the changes of three " c r i t i c a l bands from l i g a n d to complexes, the f o l l o w i n g c r i t e r i a f o r c o o r d i n a t i o n were proposed (114b). The 1506 cm ^ band of N,N'-dimethylthiourea (assigned to a mixture of N-H bending, C=S s t r e t c h i n g and NCS deformation) i s expected to i n c r e a s e by 25 - 37 cm ^ f o r complexes i n v o l v i n g c o o r d i n a t i o n through sulphur but by o n l y 10 - 15 cm ^ f o r N-bonded complexes. The 1287 cm ^ band (assigned to a mixture of C=S s t r e t c h i n g and NCS deformation) i s expected to have a marked i n c r e a s e i n frequency and i n t e n s i t y f o r S-bonded complexes but remain unchanged f o r N-bonded complexes. F i n a l l y , the 760 cm ^ band (assigned to a mixture of C=S s t r e t c h i n g , C-N s t r e t c h i n g and C(methyl)-N s t r e t c h i n g ) i s expected to s h i f t t o lower energy i n S-bonded complexes but to higher energy i n N-bonded complexes. The r e s u l t s on these c r i t i c a l bands f o r the complexes s t u d i e d i n t h i s work are c o l l e c t e d i n Table IV-4. R e s u l t s i n Table IV-4 i n d i c a t e t h a t , i n p a r t i c u l a r , the 760 cm ^ band i s s i g n i f i c a n t l y s h i f t e d to lower f r e q u e n c i e s Besides, the 1506 cm ^ i s s h i f t e d to h i g h e r energy by an ex t e n t of 14 - 24 cm ^ and the 12 87 cm ^ band i s s l i g h t l y s h i f t e d up i n frequency and i s i n t e n s i f i e d . These observa-t i o n s are a l l i n accordance w i t h the e x p e c t a t i o n of metal-l i g a n d c o o r d i n a t i o n through sulphur. 67 TABLE IV-4 I n f r a r e d S p e c t r a l Assignments ( f o r Three C r i t i c a l Bands) of N , N 1 - d i m e t h y l t h i o u r e a Complexes o f C o b a l t ( I I ) Band P o s i t i o n (cm - 1) DMTU 1506 1287 760 Assignment (121) N-H bend. +C=S s t . +NCS def. C=S s t . +NCS def C= +C +C S s t . -N s t . •-N s t . Co(C10 4) 2-DMTU 4 1525 1300 715 C o C l 2 « D M T U 2 1530 1300 715 Co(CH 3C0 2) 2'DMTU 2 1525* 1300 715 Co (C gH' 5C0 2) 2 « D M T U 2 1528 1290 720 C o ( o - N 0 2 - C 6 H 4 C 0 2 ) 2 « D M T U 2 1525* 1300 700 Co(o-Br-C 6H 4C0 2) 2•DMTU 2 1525* 1300 700 CO(m-N0 2-C 6H 4C0 2) 2•DMTU 2 1525* 1300 715 Co(p-Br-C 6H 4C0 2) 2•DMTU2 1520 1300 710 Co(p-N0 2-C 6H 4C0 2) 2*DMTU 2 1520 1305 705 * p o s s i b l y obscured by c a r b o x y l a t e r i n g v i b r a t i o n Ligand V i b r a t i o n s of E t h y l e n e t h i o u r e a and Complexes. The normal v i b r a t i o n s of e t h y l e n e t h i o u r e a were c a l c u l a t e d by Mecke e t a l . (122) and Agarwala and Rao(123) by assuming a p l a n a r C 2 V symmetry f o r the molecule. Klaeboe (114d) a l s o t e n t a t i v e l y a s s i g n e d the v i b r a t i o n s u s i n g a C^ or C 9 symmetry. The main assignments are giv e n i n Table IV-5. 68 TABLE IV-5 I n f r a r e d S p e c t r a l Assignments ( f o r Four C r i t i c a l Bands) of E t h y l e n e t h i o u r e a Assignments Band P o s i t i o n (cm - 1) Mecke e t a l . (122) Agarwala and Rao (123) Klaeboe (114d) 1305 CH2 wagging 80% 12% C-N s t . N-H bending CH 2 wagging 1276 C-N s t . CH 2 t w i s t i n g r i n g s t . 1208 C=S s t . 36% 30% 24% C=S s t . C-N s t . N-H bending C=S s t . 680 C-N s t . +N-H r o c k i n g 46% 30% 11% C-N s t . C=S s t . r i n g def. N-H bending R e l a t i v e l y few e t h y l e n e t h i o u r e a complexes of t r a n s i t i o n metals have been s t u d i e d , e s p e c i a l l y with r e s p e c t to t h e i r i n f r a r e d s p e c t r a . Lane e t a l . (124) r e p o r t e d an i n f r a r e d s p e c t r a l study of Cu(N0 3)*ETU 4 which showed a s u p e r p o s i t i o n of the i n d i v i d u a l s p e c t r a of KNO^ and ETU. Yagupsky e t a l . (105) r e p o r t e d both o c t a h e d r a l and t e t r a h e d r a l m o d i f i c a t i o n s of the complex Co(NCS) 2•ETU 2. The i n f r a r e d s p e c t r a of both were claimed t o be comparable to the complex Co (NO^) 2 • ETU^ . No d e t a i l e d d i s c u s s i o n s of e t h y l e n e t h i o u r e a v i b r a t i o n s were made i n e i t h e r study. 69 The r e s u l t s o b t a i n e d f o r the c r i t i c a l bands of e t h y l e n e t h i o u r e a f o r a l l of the complexes s t u d i e d i n t h i s work are c o l l e c t e d i n Table IV-6 : TABLE IV -6 I n f r a r e d S p e c t r a l Assignments (f o r Four C r i t i c a l Bands) of E t h y l e n e t h i o u r e a Complexes of C o b a l t ( I I ) Band P o s i t i o n (cm" ETU 1305 1276 1208 680 Co (CIO.) ,-ETU. 1318 1280 1208 670sh ft Z ft 1200sh 665 C o C l 0 ' E T U 0 1320 1280 1225 670 z z 1220 660 C o ( C H 3 C 0 2 ) 2 « E T U 2 1328 1280 1248 1198 680sh 672 Co(p-Br-CgH 4C0 2) 2•ETU 2 1318 1280 1225 1220 680 C o ( o - N 0 2 - C 6 H 4 C 0 2 ) 2 * E T U 2 1320 1278 1240 1200 645 C o ( o - B r - C 6 H 4 C 0 2 ) 2 • E T U 2 1328 1280 1232 1193 648 Co(m-N0 2-C 6H 4C0 2) 2•ETU 2 1320 1280 1205 1200sh 652 As seen from Table IV-6, a band a t ^ 1280 cm i s observed f o r every complex s t u d i e d . T h i s i s b e s t d e s c r i b e d as due to the 1276 cm ^ of e t h y l e n e t h i o u r e a a s s i g n e d t o a CH 2 v i b r a t i o n - based on the f a c t t h a t the band does not vary i n p o s i t i o n from f r e e l i g a n d t o complex or from complex 70 t o complex. The o t h e r band of e t h y l e n e t h i o u r e a , a t 13 05 cm - 1, i n c r e a s e s to about 1320 cm 1 f o r the complexes. As the most e f f e c t e d v i b r a t i o n s are those i n v o l v i n g C-N or C=S v i b r a t i o n s , the above o b s e r v a t i o n s b e s t f i t the assignments by Agarwala and Rao i n which the 1305 cm 1 band i s a s s i g n e d to mainly a C-N s t r e t c h i n g mode. The f a c t t h a t t h i s C-N s t r e t c h i n g v i b r a t i o n s h i f t s to h i g h e r frequency i n d i c a t e s t h e r e f o r e t h a t the complexes are probably s u l p h u r - c o o r d i n a t e d . T h i s i s a l s o seen from the o b s e r v a t i o n t h a t the 6 80 cm 1 band of e t h y l e n e t h i o u r e a , a s c r i b e d i n p a r t t o C=S s t r e t c h i n g , i s u s u a l l y s h i f t e d down i n energy, and i s o c c a s i o n a l l y s p l i t . The other c r i t i c a l band at 1208 cm 1 of e t h y l e n e t h i o u r e a i s found to be s p l i t which f i t s the d e s c r i p t i o n of the a s s i g n -ment by Agarwala and Rao t h a t both C=S and C-N c h a r a c t e r s are i n v o l v e d . The above three d i v i s i o n s gave the same c o n c l u s i o n t h a t a l l the t h i o u r e a , e t h y l e n e t h i o u r e a and N,N'-dimethyl-t h i o u r e a complexes are sulphur-bonded to c o b a l t . H e r e a f t e r , these l i g a n d s w i l l be commonly r e f e r r e d to as S-bonded l i g a n d s or more simply as S - l i g a n d s . T h i s work a l s o serves t o extend the g e n e r a l o b s e r v a t i o n t h a t no N-bonded t h i o u r e a complex of c o b a l t (II) has y e t been observed. C a r b o x y l a t e (-CO.,) s t r e t c h i n g v i b r a t i o n s . As was d e s c r i b e d e a r l i e r i n Chapter I, c a r b o x y l a t e group may take on many p a t t e r n s of c o o r d i n a t i o n when bonded to a metal and i n f r a r e d spectroscopy has o f t e n been used to examine the e f f e c t of c o o r d i n a t i o n on the -C0 o s t r e t c h i n g 71 f r e q u e n c i e s (38, 39, 125). The major d i f f i c u l t y i n v o l v e d here a r i s e s from the a l r e a d y low symmetry ( C 2 v ) of the f r e e c a r b o x y l a t e i o n . As a r e s u l t , marked changes on c o o r d i n a t i o n such as those found f o r other ions of o r i g i n a l l y high symmetry ( l i k e NC>3 , SO^ and e t c . ) , e.g., s p l i t t i n g of bands, are not g e n e r a l l y found here. However, the modes of bonding of c a r b o x y l a t e groups to metals have f r e q u e n t l y been c o r r e l a t e d with (i) the p o s i t i o n s of the antisymmetric ( v a n t i ) and the symmetric (^sym) -C0 2 s t r e t c h i n g f r e q u e n c i e s and ( i i ) the s e p a r a t i o n of the two s t r e t c h i n g f r e q u e n c i e s (Av) . For example, i t has been shown t h a t i o n i c c a r b o x y l a t e s show i n g e n e r a l an i n t e n s e antisymmetric - C 0 2 s t r e t c h i n g frequency w i t h i n the range 1560 - 1600 cm 1 (1). Small Av i s u s u a l l y observed, c o r r e s p o n d i n g to the e q u i v a l e n c e of the two CO bonds. In a unidentate bonding s i t u a t i o n , the antisymmetric - C 0 2 s t r e t c h i n g frequency i n c r e a s e s and the symmetric -C0 2 s t r e t c h i n g frequency decreases (126). In g e n e r a l , the s e p a r a t i o n Av i s l a r g e f o r the unidentate s t r u c t u r e , c o r r e s p o n d i n g to the non-equivalence of the two CO bonds. Nakamoto e t a l . (127, 128) have i n d i c a t e d t h a t the l i m i t f o r the antisymmetric frequency w i t h unidentate bonding should be about 165 0 cm ^. For the other s t r u c t u r a l types, i . e . , b r i d g i n g and c h e l a t i n g ,A v v a r i e s g r e a t l y from compound to compound. For example, both the -C0 2 s t r e t c h i n g bands are sometimes found to s h i f t t o gether i n the same d i r e c t i o n upon changing the 72 metal, such as i n the case of some b i n u c l e a r c h l o r o a c e t a t e (129) and a c e t a t e (38, 127) complexes. The d e p e n d a b i l i t y of u s i n g Av to determine the mode of c o o r d i n a t i o n of the c a r b o x y l a t e group.to the metal has been s e r i o u s l y q u e s t i o n e d (38) . The s p e c t r a of complexes s t u d i e d i n the presen t work are extremely complex. The r e g i o n 1300 - 1700 cm - 1, where one would expect to f i n d the -CC^ s t r e t c h i n g v i b r a t i o n , i s complicated by the presence of v i b r a t i o n s of the a r y l p o r t i o n of the c a r b o x y l a t e groups as w e l l as by v i b r a t i o n s of oth e r l i g a n d molecules pres e n t i n the complex. As a t y p i c a l example, the s p e c t r a i n t h i s r e g i o n of a number of complexes of c o b a l t ( I I ) p-bromobenzoate are shown i n F i g u r e IV-3. In view of the complicated nature of the s p e c t r a i n v o l v e d , the i d e n t i f i c a t i o n of -CC^ s t r e t c h i n g v i b r a t i o n s i n these complexes i s a d i f f i c u l t problem; n e v e r t h e l e s s , an attempt was made. By c a r e f u l comparison of the s p e c t r a o f d i f f e r e n t complexes of a given c o b a l t ( I I ) a r y l c a r b o x y l a t e (e.g. hydrate, t h i o u r e a , e t h y l e n e t h i o u r e a , N,N 1-dimethyl-t h i o u r e a and p y r i d i n e complexes), the f r e e l i g a n d s themselves and where p o s s i b l e the a p p r o p r i a t e sodium a r y l c a r b o x y l a t e , i t was p o s s i b l e to separate the v i b r a t i o n s due to the n e u t r a l c o o r d i n a t e d l i g a n d s from those due to the a r y l c a r b o x y l a t e group. Of those bands assig n e d t o the a r y l c a r b o x y l a t e group the h i g h e s t frequency band i n the 1800 - 1500 cm 1 r e g i o n was, more or l e s s a r b i t r a r i l y a s s i g n e d to the antisymmetric -C0 o v i b r a t i o n s . 73 Co(p-Br-C gH 4C0 2) 2-3H 20 C o ( p - B r - C 6 H 4 C 0 2 ) 2 . T U 2 Co (p-Br-C 6H 4C0 2) 2- ETU"2 Co (p-Br-C cH.C0„)„•DMTU„ * T /* 6 4 2 2 2 fY Co(p-Br-C 6H- 4C0 2) 2.py 2 / C o ( p - B r - C 6 H 4 C 0 2 ) 2 . p y 2 . H 2 0 * r e s p e c t i v e l i g a n d v i b r a t i o n s j — : L -1 L L 1 6 0 0 1 4 0 0 1 2 0 0 F i g u r e IV-3. I n f r a r e d S p e c t r a (1300 - 1700 cm ) of Complexes of C o b a l t ( I I ) p-Bromobenzoate 74 There i s some j u s t i f i c a t i o n f o r a s s i g n i n g the h i g h e s t frequency c a r b o x y l a t e band to the antisymmetric -CC>2 s t r e t c h i n g v i b r a t i o n (or a t l e a s t f o r c o n s i d e r i n g t h i s band as a r i s i n g l a r g e l y from such a v i b r a t i o n ) . We observed, on comparing the c a r b o x y l a t e bands i n the 1800 - 1500 cm ^ r e g i o n f o r d i f f e r e n t complexes, t h a t the hi g h frequency band s h i f t e d s i g n i f i c a n t l y from one type of complex to another while o t h e r bands remained v i r t u a l l y unchanged. For example, c o n s i d e r i n g the p-bromobenzoate complexes, t h i s h i g h frequency band occurs a t 1590 cm ^ i n the e t h y l e n e t h i o u r e a complex, 15 88 cm ^ i n the t h i o u r e a complex, 15 85 cm 1 i n the N,N'-dimethylthiourea complex and s h i f t s markedly to 1614 cm i n the p y r i d i n e complex. I t seems reasonable t o expect t h a t v i b r a t i o n s i n v o l v i n g the c o o r d i n a t e d -CC>2 groups w i l l be most s e n s i t i v e to changes i n complex type (130, 131). Pr e v i o u s s t u d i e s on the v i b r a t i o n a l s p e c t r a of c a r b o x y l a t e complexes have shown the symmetric -CC>2 s t r e t c h i n g frequency t o be l e s s s e n s i t i v e than the antisymmetric s t r e t c h i n g frequency t o changes i n complex type. In a l l of the complexes under i n v e s t i g a t i o n here r e l a t i v e l y s t r o n g bands are observed around 1400 cm 1 and these are a s s i g n e d to the symmetric -CO 2 s t r e t c h i n g v i b r a t i o n . The r e s u l t s on the assignments of the two -CC^ s t r e t c h i n g v i b r a t i o n s f o r a l l the t h i o u r e a and s u b s t i t u t e d t h i o u r e a s complexes are c o l l e c t e d i n Table IV-7: TABLE IV-7 -CC>2 Stretching Frequencies (cm )^ for S-bonded C O ( R C 0 2 ) 2 « L 2 Complexes L • = RC0 2 " ETU TU DMTU v ant i V sym Av an t i V sym Av v a n t i V sym Av CH 3 C0 2 ~ 1550 1410 140 1560 1410 150 1590 1392 198 C 6 H 5 C 0 2 - - - - 1600 1360 240 1595 1410 185 p - B r - C 6 H 4 C 0 2 ~ 35 9 0 1400 190 1588 1402 186 1585 1405 180 m-N0 2 -C 6 H 4 C0 2 - 1620 1400 220 1630 1395 235 1635 1370 265 p - N 0 2 - C 6 H 4 C 0 2 - - - - - - - 1623 1407 216 o - B r - C g H 4 C 0 2 ~ 1545 1415 130 1582 1395 . 187 1595 1405 190 o-N0o-C,-H,,C0 ~ 2 6 4 2 1600 1384 216 1620 1390 230 1595 1408 187 76 As seen from the data i n the t a b l e there i s more v a r i a t i o n i n v .. from complex to complex than i n v a n t i c c sym The v a r i a t i o n i n the former does not c o r r e l a t e w i t h any known p h y s i c a l or chemical p r o p e r t y of the c a r b o x y l a t e group such as i t s b a s i c i t y (as measured by the pK of the parent acid) a or s t r u c t u r e ( i . e . whether there i s an o-, m- or p- s u b s t i t u e n t ) The most s t r i k i n g f e a t u r e of the data i s the d i f f e r e n c e i n v a n t i a n c ^ ^ v ^ o r ^ n e t n i o u r e a a n d e t h y l e n e t h i o u r e a complexes of c o b a l t ( I I ) a c e t a t e and the e t h y l e n e t h i o u r e a complex of c o b a l t ( I I ) o-bromobenzoate on the one hand and the r e s t of the complexes on the o t h e r . The former complexes have i n common r e l a t i v e l y low v a l u e s of v a n t ^ (1545 - 1560 cm ^) and Av (130 - 155 cm ^) compared to the v a l u e s ( v a n t ^ = 1582 -1635 cm ^ and Av = 180 - 265 cm ^) ob t a i n e d f o r the other complexes. The s t r u c t u r e of the e t h y l e n e t h i o u r e a complex of c o b a l t ( I I ) a c e t a t e i s known t o i n v o l v e a form of carboxy-l a t e c o o r d i n a t i o n i n t e r m e d i a t e between monodentate and c h e l a t i n g w i t h one long and one s h o r t metal-oxygen bond (9). The two CO bonds are very much e q u i v a l e n t i n l e n g t h being 1.254 A" and 1.241 A1 and the low Av value observed f o r t h i s complex may be a c h a r a c t e r i s t i c of t h i s p a r t i c u l a r form of c a r b o x y l a t e c o o r d i n a t i o n . The other two complexes C o ( C H 3 C 0 2 ) 2 * T U 2 a n d C o ( o - B r - C g H 4 C 0 2 ) 2 « E T U 2 which have low v .. and Av v a l u e s s i m i l a r to those of Co(CH_CO„)„•ETU„ antx 3 2 2 2 may have s i m i l a r s t r u c t u r e s . Such a p r o p o s a l i s h i g h l y s p e c u l a t i v e and i m p l i e s t h a t the other complexes s t u d i e d i n t h i s work which have h i g h e r v & n t ^ and l a r g e r Av v a l u e s assume s t r u c t u r e s d i f f e r e n t from the above i n terms of CO bond l e n g t h s . 77 IV-3-2. E l e c t r o n i c S p e c t r a l Study The e l e c t r o n i c s p e c t r a , i n the range of 4000 to 24000 cm 1 , are r e p o r t e d here f o r the t h i o u r e a , e t h y l e n e -t h i o u r e a and N,N'-dimethylthiourea complexes of c o b a l t ( I I ) p e r c h l o r a t e , c h l o r i d e , a c e t a t e and s e v e r a l a r y l c a r b o x y l a t e s . Both s o l i d s t a t e s p e c t r a (by d i f f u s e r e f l e c t a n c e and KBr p e l l e t techniques) and s o l u t i o n s p e c t r a ( i n acetone, i f s o l u b l e ) were measured and the s p e c t r a are reproduced i n Appendix IV-1. The KBr p e l l e t spectrum of each complex agrees q u i t e w e l l with the cor r e s p o n d i n g d i f f u s e r e f l e c t a n c e spectrum and i t i s t h e r e f o r e b e l i e v e d t h a t i n the formation of a p e l l e t , there i s b a s i c a l l y no change i n the s o l i d s t a t e s t r u c t u r e of the complex. Band p o s i t i o n and a b s o r p t i o n i n t e n s i t y data are recorded i n Appendix IV-2. Thiourea, E t h y l e n e t h i o u r e a and N,N'-Dimethylthiourea Complexes  of C o b a l t ( I I ) P e r c h l o r a t e and C h l o r i d e Cotton, Faut and Mague (6 2) r e p o r t e d e l e c t r o n i c s p e c t r a l s t u d i e s on some t h i o u r e a complexes of c o b a l t ( I I ) . In p a r t i c u l a r , they c a l c u l a t e d Dq and B value s of 425 cm 1 and 6 00 cm 1 r e s p e c t i v e l y f o r the complex Co ( C l O ^ ) 2 • T U 4 from the acetone s o l u t i o n s p e c t r a . On the other hand, C a r l i n and H o l t (6 3) r e p o r t e d the s p e c t r a of some e t h y l e n e -t h i o u r e a complexes of c o b a l t ( I I ) and they took the p e l l e t s p e c t r a of the complexes f o r the c a l c u l a t i o n of the e l e c t r o n i c parameters Dq and.B. Values of 378 cm 1 and 651 cm 1 r e s p e c t i v e l y were obtained f o r the complex 78 C o ( C 1 0 4 ) 2 * E T U 4 . These r e s u l t s p l a c e d these two l i g a n d s i n d i f f e r e n t p o s i t i o n s i n both the sp e c t r o c h e m i c a l and nep h e l a u x e t i c s e r i e s (64). The e l e c t r o n i c s p e c t r a i n acetone s o l u t i o n of TU, ETU and DMTU complexes of c o b a l t ( I I ) p e r c h l o r a t e i n both the absence and the presence of added excess S - l i g a n d are shown i n F i g u r e IV-4. The s p e c t r a are v i r t u a l l y i d e n t i c a l to each ot h e r , i n both band p o s i t i o n and s t r u c t u r e . The on l y d i f f e r e n c e i s the a b s o r p t i o n i n t e n s i t y a s s o c i a t e d with the s p e c t r a l band components. As w i l l be d i s c u s s e d more f u l l y l a t e r i n t h i s Chapter a l l three of these complexes undergo S - l i g a n d d i s s o c i a t i o n . When excess S - l i g a n d i s added t o these s o l u t i o n s a l i m i t i n g spectrum i s obta i n e d . W i t h i n experimental e r r o r , the l i m i t i n g s p e c t r a of a l l three complexes are i d e n t i c a l . I n d i v i d u a l measurements of the c e n t e r s o f g r a v i t y of both V3 and Vz t r a n s i t i o n s y i e l d e x a c t l y the same r e s u l t s and t h e r e f o r e the same e l e c t r o n i c parameters Dq and B are c a l c u l a t e d f o r the three p e r c h l o r a t e complexes i n s o l u t i o n . For each o f the p e r c h l o r a t e complexes there i s con-s i d e r a b l e resemblance between the s o l i d s t a t e spectrum and the s o l u t i o n spectrum (Appendix IV-1) and i t i s t h e r e f o r e assumed t h a t i n both the s o l i d s t a t e and i n s o l u t i o n the geometry of the complex i s " t e t r a h e d r a l " with a common CoS^ chromophore. The d i f f e r e n c e s which are observed in the s o l i d s t a t e s p e c t r a o f the three complexes (Figure IV-5) almost c e r t a i n l y a r i s e from s o l i d s t a t e c r y s t a l packing F i g u r e IV-4. Acetone S o l u t i o n Spectra of TU, ETU and DMTU Complexes of C o b a l t ( I I ) P e r c h l o r a t e data recorded i n Appendix IV-2 s o l v e n t : d i s t i l l e d acetone Figure IV-5. KBr P e l l e t Spectra of TU, ETU and DMTU Complexes of Cobalt(II) Perchlorate 81 e f f e c t s r a t h e r than from any i n t r i n s i c e l e c t r o n i c e f f e c t such as b a s i c i t y , of the l i g a n d s themselves. That t h i s i s so i s concluded from the f a c t t h a t 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 p e c t r a are seen o n l y i n the s o l i d s t a t e s p e c t r a and not i n the s o l u t i o n s p e c t r a . An examination of the s o l i d s t a t e and s o l u t i o n s p e c t r a of c o b a l t ( I I ) c h l o r i d e complexes of TU, ETU and DMTU (Figures IV-6, IV-7 and Appendix IV-1) y i e l d s i m i l a r o b s e r v a t i o n s and c o n c l u s i o n s t o those d e s c r i b e d f o r the p e r c h l o r a t e complexes. S p e c i f i c a l l y , the s o l u t i o n s p e c t r a are found t o be v i r t u a l l y i d e n t i c a l f o r the three complexes and the d i f f e r e n c e s between the s o l u t i o n spectrum and the s o l i d s t a t e s p e c t r a o f the three complexes more than l i k e l y a r i s e from c r y s t a l p acking e f f e c t s as d e s c r i b e d above. A comparison of both the s o l i d s t a t e and the s o l u t i o n s p e c t r a of the c h l o r i d e complexes on one hand and the p e r c h l o r a t e complexes on the other (Figures IV-4 and IV-6, F i g u r e s IV-5 and IV-7) shows the c h l o r i d e complexes t o e x h i b i t more d i s t i n c t and g r e a t e r s p l i t t i n g a t both the v 3 and v 2 bands. In d e t a i l , the v 3 t r a n s i t i o n s of the c h l o r i d e complexes are s p l i t i n t o three d i s t i n c t , e q u a l l y i n t e n s e bands and the v 2 t r a n s i t i o n s are a l s o c l e a r l y s p l i t i n t o a t l e a s t two components. Recently, i t has been shown by the c r y s t a l p o l a r i z e d s p e c t r a l study (67) of a s i m i l a r complex, C o C l 2 « D E T U 2 (where DETU = N , N ' - d i e t h y l t h i o u r e a ) , t h a t low-symmetry ( C 2 v ) l i g a n d f i e l d e f f e c t s , r a t h e r than s p i n -o r b i t c o u p l i n g i s mainly r e s p o n s i b l e f o r the s p e c t r a l 500 250 0 18 14 • ETU complex DMTU complex TU complex upper curves o b t a i n e d by adding excess S - l i g a n d 10 120 -60 00 ro 0 V x 1 0 " 3 c m " ' Figure IV - 6 Acetone S o l u t i o n Spectra o f TU, ETU and DMTU Complexes of C o b a l t ( I I ) C h l o r i d e data recorded i n Appendix IV - 2 s o l v e n t : d i s t i l l e d acetone Figure IV-7. KBr P e l l e t Spectra of TU, ETU and DMTU Complexes of Cobalt (II) Chloride 84 s t r u c t u r e observed. The e f f e c t of l i g a n d f i e l d s of C^v symmetry on c u b i c f i e l d T^ and T 2 s t a t e s was g i v e n i n Chapter I I . The same study a l s o d e r i v e d the sequence of 4 components f o r the T ^ F ) s t a t e to be < A 2 < B 2 and 4 f o r the T 1(P) s t a t e to be B 2 < A 2 < B^. As t h i s c h l o r i d e complex o f DETU and the t h r e e c h l o r i d e complexes s t u d i e d i n t h i s work have the same chromophore of C o S 2 C l 2 and the l a t t e r complexes have been shown to e x h i b i t s i m i l a r e l e c t r o n i c s p e c t r a i r r e s p e c t i v e of the nature of the S - l i g a n d , the above assignments of the s p e c t r a l band components f o r the DETU complex can reasonably be a p p l i e d to a l l these c h l o r i d e complexes. Hence the three components 4 4 of v 3 can be a s s i g n e d to t r a n s i t i o n t o the B 2 ( P ) , A 2 ( p ) 4 and B^(P) l e v e l s i n order of i n c r e a s i n g energy. Two components are observed f o r v2• The h i g h e r energy one 4 can be assigned to an u n r e s o l v e d composite of the B 2 ( F ) 4 and A 2 ( F ) l e v e l s as these are a l s o found to be almost degenerate i n the case of CoCl 2'DETU 2. The lower energy band component can then be a s s i g n e d to the t r a n s i t i o n to 4 the B ^ F ) s t a t e . D e s p i t e the s t r u c t u r a l c o m p l i c a t i o n s o f the v 3 and v 2 bands s i n g l e f r e q u e n c i e s may be a s s i g n e d t o each by u s i n g the c e n t e r of g r a v i t y method d e s c r i b e d by Cotton et a l . (55) (these f r e q u e n c i e s are c o n s i d e r e d a c c u r a t e t o ±200 cm ^ ) . The e l e c t r o n i c parameters Dq and B are then c a l c u l a t e d from the a p p r o p r i a t e Tanabe-Sugano equations and diagrams (these v a l u e s are c o n s i d e r e d s i g n i f i c a n t to w i t h i n o n l y ±15 and ±25 cm r e s p e c t i v e l y ) . The r e s u l t s are recorded i n Table IV-8 which i n c l u d e s the p r e v i o u s l y r e p o r t e d r e s u l t s f o r comparison. 85 TABLE IV-8 Spectra l Parameters for S-Ligand Complexes of Cobalt(II) Perchlorate and Chloride (Sol id State) Complex v 3 (cm ) r "IN v 2 (cm ) Dq (cm ) »/ -!N B (cm ) C o ( C 1 0 4 ) 2 . T U 4 14700 (14500) 7240 (7200) 425 (425) 616 (600)" Co(C10 4 ) 2 -ETU 4 14600 (14600) 6480 (6480) 377 (378) 661 (651) Co(C10 4 ) 2 -DMTU 4 14390 6560 381 635 C o C l 2 - T U 2 15000(15000) 6250 (6000) 360 (348) 706 (709) C o C l 2 « E T U 2 14100(14700) 5600 (5870) 321 (339) 677 (693) CoCl 2 'DMTU 2 14930 6060 348 702 - previous re su l t s i n brackets The main point concerning the Dq and B data i n t h i s table i s that no attempt should be made to corre la te the s o l i d state values with the nature of the S-l igand (e.g. ba s i c i ty ) since as described before these var i a t ions almost c e r t a i n l y ar i se from s o l i d state c r y s t a l packing e f fec t s . Thiourea, Ethylenethiourea and N,N'-dimethylthiourea Complexes  of Cobalt(II) Carboxylates When the compound Co(CH 3 C0 2 ) 2 'ETU, , was f i r s t studied (63), i t was thought of as an octahedral complex. Its e l e c t r o n i c spectrum i n g l a c i a l acet ic ac id showed bands at 18020 cm \ 14350 cm and 7350 cm ^ assigned re spec t ive ly to the v 3 , y 2 and Vi t r a n s i t i o n s of an octahedral complex 86 leading to a Dq value of 850 - 900 cm \ reasonable for octahedral coordinat ion . Besides, £ for the v 3 t r a n s i t i o n max 3 was estimated to be 20 - 60 (in g l a c i a l ace t i c acid) again as expected for an octahedral species . The magnetic moment of 4.6 4 B.M. at room temperature was, however, considered too low for an octahedral species . The c r y s t a l s tructure was l a te r reported for t h i s complex (9) and i t showed a d i s to r t ed te t rahedra l s t ructure . In the same report , the c r y s t a l spectrum of the complex at 80 °K was s tudied. The spectrum showed four bands i n the v i s i b l e region three of which the authors assigned to the three t r a n s i t i o n s from 4 4 the A 2 ground term to the three components of the T-^(P) term i n C 2 v symmetry. The fourth band they assigned to a 4 4 component of the v 2 t r a n s i t i o n ( A 2 (F ) > T^(F) ) . Such an assignment seems,however, u n l i k e l y since i t would require a very large s p l i t t i n g of some 70 00 cm 1 i n the 4 _1 T^(F) state with a much smaller s p l i t t i n g of ^4000 cm 4 i n the T^(P) s tate . At leas t there i s no precedent for such a large s p l i t t i n g . Besides, i t i s poss ible that one of the bands observed i n the v i s i b l e region i s a formally disal lowed quartet-doublet t r a n s i t i o n , i . e . , from ground 4 2 state A 2 to a component of G which gains enough in tens i ty 4 through mixing with the P state v i a s p i n - o r b i t coupling (53). I t i s assumed here that the v 3 t r a n s i t i o n does not contain any v 2 component and the usual way of ass igning v 3 and v 2 frequencies and of c a l c u l a t i n g Dq andB i s considered v a l i d and i s employed here. 87 As mentioned e a r l i e r , the e l e c t r o n i c s p e c t r a of the complex C o ( C H 3 C 0 2 ) 2 •ETU 2 i n g l a c i a l a c e t i c a c i d suggested o c t a h e d r a l c o o r d i n a t i o n about c o b a l t . T h i s i s not c o n s i s t e n t w i t h the c r y s t a l s t r u c t u r e r e p o r t e d f o r t h i s complex. I t i s t h e r e f o r e d o u b t f u l t h a t the complex r e t a i n e d i t s o r i g i n a l s o l i d s t a t e s t r u c t u r e on d i s s o l u t i o n i n g l a c i a l a c e t i c a c i d . U n f o r t u n a t e l y , t h i s complex i s not s u f f i c i e n t l y s o l u b l e i n any other o r g a n i c s o l v e n t f o r s o l u t i o n s t u d i e s , nor are the c o b a l t ( I I ) a c e t a t e complexes of TU and DMTU a l s o prepared i n t h i s work. However, the acetone s o l u t i o n s p e c t r a of a few a r y l c a r b o x y l a t e complexes of the three l i g a n d s are, as a r e s u l t of the p r e s e n t work, now a v a i l a b l e . While a d e t a i l e d d i s c u s s i o n of these s p e c t r a w i l l be presented i n S e c t i o n IV-4, i t i s important to mention at t h i s p o i n t t h a t these s o l u t i o n s p e c t r a are v i r t u a l l y i d e n t i c a l , independent of the nature of the a r y l c a r b o x y l a t e i n v o l v e d and a l s o independent of the type of S - l i g a n d i n v o l v e d . T h i s behaviour p a r a l l e l s t h a t found i n the p e r c h l o r a t e and c h l o r i d e complexes. F i g u r e s IV-8, IV-9 and IV-10 give the s o l i d s t a t e s p e c t r a of the t h i o u r e a , e t h y l e n e t h i o u r e a and N,N'-dimethyl-t h i o u r e a complexes of c o b a l t ( I I ) c a r b o x y l a t e s . A t y p i c a l s o l u t i o n spectrum i s i n c l u d e d i n each f i g u r e f o r comparison. The KBr p e l l e t s p e c t r a of the c a r b o x y l a t e complexes vary markedly from one complex to the o t h e r , i n the number of bands, band s t r u c t u r e , band shape and band width. No s i g n i f i c a n t t r e n d or p a t t e r n can be seen. Perhaps a n o t a b l e o b s e r v a t i o n i s t h a t among the e t h y l e n e -Figure IV-8. KBr P e l l e t Spectra of ETU Complexes of Cobalt (II) Carboxylates 89 F i g u r e IV-9. KBr P e l l e t S p e c t r a of TU Complexes of C o b a l t (II) Carboxylates 90 a - Co (CH 3C0 2) 2'DMTU 2 b - Co ( p - B r - C 6 H 4 C 0 2 ) 2 * D M T U 2 c - Co ( o - B r - C 6 H 4 C 0 2 ) 2 , D M T U 2 d - Co(o-N0 2-C 6H 4C0 2) 2-DMTU 2 e - Co (C gH 5C0 2) 2-DMTU 2 f - Co(m-N0 2-C 6H 4C0 2) 2*DMTU 2 g - Co(p-N0 2-C 6H 4C0 2) 2*DMTU 2 h - common l i m i t i n g s o l u t i o n J i i i i i i i 1 1 20 16 12 8 y X10" 3 cm"' F i g u r e IV-10. KBr P e l l e t Spectra o f DMTU Complexes' of C o b a l t ( I I ) Carboxylates 91 thiourea complexes a greater variation in spectral char-acteristics i s seen than is the case for, in particular, the thiourea complexes. As is the case for the corresponding chloride and perchlorate complexes, the differences observed in the solid spectra among various arylcarboxylate complexes are best described as due to solid state crystal packing effects resulting in variations in the detailed geometry about the cobalt atoms. In solution, these species are without such solid state restraints and the common chromo-phore of CoG^S^ is responsible for the same solution spectrum observed for a l l complexes. It is noted that band splitting in the solution spectra i s , in general, smaller than the splitting observed in the corresponding solid state spectra. It seems quite possible that in solution the form of carboxylate coordination i s of a conventional unidentate variety, while in the solid state, crystal packing effects favour a type of coordination in which the second oxygen of the carboxylate group participates in weak bonding to cobalt, as i s seen in the structure of Co(CH 3C0 2) 2•ETU 2 (Figure IV-1). This latter form of coordination could result in a greater band splitting in the solid state and furthermore the variation in band spli t t i n g observed in the solid state spectra could well arise from a variation from complex to complex of the strength of the bond involving the second carboxylate oxygen. 9 2 The s p e c t r a l parameters Dq and B were c a l c u l a t e d from the s o l i d s t a t e s p e c t r a by determining the ce n t e r s o f g r a v i t y of the v 3 and v 2 bands i n the us u a l way. The r e s u l t s are summarized i n Table I V - 9 . TABLE I V - 9 S p e c t r a l Parameters f o r S-Ligand Complexes of C o b a l t ( I I ) C a r b o x y l a t e s ( S o l i d State) S-Ligand - ETU TU DMTU Carboxylate Dq (cm 1 B ) (cm" Dq I v , " I ) (cm B ) (cm~ Dq 1 ^ / -) (cm B 1\ / " I v ) (cm ) C H 3 C 0 2 ~ 3 7 6 8 2 7 3 9 6 7 6 1 4 0 3 8 5 8 C.-H.-CO ~ 6 5 2 - - 4 1 7 7 7 9 4 4 4 7 9 8 p - B r - C g H 4 C 0 2 ~ 3 8 1 8 2 8 4 0 3 7 7 5 4 4 4 8 3 0 m - N 0 2 - C 6 H 4 C 0 2 - - - 4 1 2 8 1 5 4 4 6 7 5 0 p - N 0 2 - C 6 H 4 C 0 2 - - - - - 4 0 6 7 3 7 o-Br-C,H„CO ~ 6 4 2. 3 5 9 7 9 1 4 2 0 7 4 4 4 3 3 8 4 1 o - N 0 2 - C 6 H 4 C 0 2 - 3 6 3 7 9 0 4 2 5 7 5 8 4 1 0 8 5 3 Again, these parameters vary from complex t o complex and no t r e n d or c o r r e l a t i o n i s found with any chemical or p h y s i c a l p r o p e r t y of the c a r b o x y l a t e or S - l i g a n d i n v o l v e d . As d e s c r i b e d b e f o r e , the e s t i m a t i o n of the c e n t e r s o f g r a v i t y o f the s p e c t r a l bands from s o l i d s t a t e s p e c t r a may i n v o l v e l a r g e experimental e r r o r s and comparison among these s p e c t r a l data i s not to be over-emphasized. 93 The complex Co(m-N0 2-CgH 4C0 2) 2*ETU 2 stands out as a t y p i c a l o c t a h e d r a l complex on the b a s i s o f , i n p a r t i c u l a r , i t s magnetic p r o p e r t i e s , which w i l l be d i s c u s s e d l a t e r . A comparison of the e l e c t r o n i c spectrum of t h i s complex wi t h the s p e c t r a o f the t h i o u r e a and N,N'-dimethylthiourea analogues i s gi v e n i n F i g u r e IV-11. In c o n t r a s t t o the othe r complexes, the ETU complex shows a s i n g l e broad band ( p o s s i b l y with weak shoulders a t lower energy) i n the v i s i b l e r e g i o n . The n e a r - i n f r a r e d p o r t i o n of the spectrum i s a l s o d i f f e r e n t showing a broad s i n g l e band with no i n d i c a t i o n o f the band s p l i t t i n g seen i n the s p e c t r a of the other complexes. These d i f f e r e n c e s alone do not prove of course t h a t the complex i s an o c t a h e d r a l one. I t i s i n t e r e s t i n g t h a t the spectrum can be s a t i s f a c t o r i l y analyzed assuming e i t h e r a t e t r a h e d r a l geometry ( i n which case the low energy a b s o r p t i o n i s as s i g n e d t o the v 2 a b s o r p t i o n of a t e t r a h e d r a l molecule) or an o c t a h e d r a l geometry ( i n which case the low energy band i s assig n e d t o the \>i a b s o r p t i o n of an o c t a h e d r a l m o l e c u l e ) . The e l e c t r o n i c parameters Dq and B were s e p a r a t e l y c a l c u l a t e d assuming both a t e t r a h e d r a l and an o c t a h e d r a l s t r u c t u r e and the r e s u l t s are l i s t e d below. v 2 o r v i B -1 (cm ) S t r u c t u r e , "IN (cm ) T e t r a h e d r a l 18180 7460 428 856 Oct a h e d r a l 18180 7460 856 771 F i g u r e IV-11. KBr P e l l e t Spectra of TU, ETU and DMTU Complexes of C o b a l t ( I I ) m-Nitrobenzoate 95 Both c a l c u l a t i o n s y i e l d Dq and B v a l u e s which are i n the ranges expected f o r the r e s p e c t i v e geometries. The parameters c a l c u l a t e d assuming a t e t r a h e d r a l framework are s i m i l a r t o those of the other complexes s t u d i e d c o n c u r r e n t l y . The parameters c a l c u l a t e d assuming an o c t a h e d r a l framework are a l s o reasonable and comparable 2+ -1 -1 to those known f o r C o ( H 2 0 ) g (Dq = 920 cm and B = 825 cm ) (80); C o ( d i m e t h y l s u l p h o x i d e ) g 2 + (Dq = 848 cm" 1 and B = 824 cm - 1) (153) and C o C l 2 (Dq = 764 c m - 1 and B = 775 cm - 1) (81). In the case of t h i s p a r t i c u l a r complex magnetic suscept-i b i l i t y r e s u l t s (to be d i s c u s s e d l a t e r ) were needed to c o n f i r m a*: pseudo-octahedral geometry. IV-3-3. Magnetic S u s c e p t i b i l i t y Study Magnetic s u s c e p t i b i l i t y s t u d i e s on s e v e r a l of the complexes i n v e s t i g a t e d i n t h i s work have been r e p o r t e d p r e v i o u s l y . Cotton, Faut and Mague (62) r e p o r t e d data on the two complexes CoCl 2*Tu" 2 and Co (ClC>4) 2 • TU 4 a t ten temperatures between 300°K and 80°K and C a r l i n and H o l t (6 3) r e p o r t e d data on the corresponding ETU complexes at three temperatures over the same temperature range. The r e s u l t s were co n s i d e r e d t y p i c a l f o r t e t r a h e d r a l complexes. Magnetic data were a l s o r e p o r t e d on the complex C o ( C H 3 C 0 2 ) 2 * E T U 2 (6 3) and the observed magnetic moment of 4.64 B.M., f e l t a t the time to be low f o r the assumed o c t a h e d r a l s t r u c t u r e , was c o n s i d e r e d to be c o n s i s t e n t w i t h the t e t r a h e d r a l s t r u c t u r e l a t e r determined (9). Magnetic s u s c e p t i b i l i t y measurements over the temperature range 80 - 3 2 0 ° K were made on a l l of the S-bonded complexes prepared i n t h i s work. A l l experimental data are c o l l e c t e d i n Appendix IV-3. A l l of the complexes under inves t iga t ion here (with the s ingle exception of C o ( m - N O _ - C , H . C O „ ) ~ * E T U 0 -to be discussed la ter ) obey the Curie-Weiss law. From p lo t s of l / x C°yy versus T, values of the magnetic moment Co (from the slope) and the Weiss constant, 6, (from the intercept) were determined. Experimental p lo t s are given i n Appendix IV-4 and the values of and 0 obtained from these p lo t s and given i n Table IV-10 are t y p i c a l for te t rahedra l cobal t ( I I ) complexes. TABLE IV-10 Experimental V<e££ an& 6 Values of ETU, TU And DMTU Complexes of Cobalt(II) Ligand = ETU TU DMTU Anion y c c 0 p 0 y „ 0 M e f f p e f f M ef f c i o 4 4 . 7 1 - 1 0 4.28 -4 4.42 -4 C l " 4.44 - 1 1 4.47 -6 4.42 -5 C H 3 C 0 2 " 4.33 - 5 4. 37 -7 4.36 -5 C 6 H 5 C 0 2 " - - 4.34 -5 4.42 -5 p - B r - C 6 H 4 C 0 2 " 4. 34 - 5 4.40 -5 4.44 -4 m - N 0 2 - C 6 H 4 C 0 2 " - - 4.40 -5 4.45 -5 p - N 0 2 - C 6 H 4 C 0 2 - - - - - 4.43 -5 o - B r - C 6 H 4 C 0 2 ~ 4.42 - 2 4.43 -5 4.40 -4 O - N 0 2 - C 6 H 4 C 0 2 " 4.44 - 6 4.46 -4 4.40 -6 97 Magnetic data for f ive of the complexes studied here have been reported previous ly and the re su l t s are compared d i r e c t l y i n Table IV-11. We have no explanation for the poor agreement between our re su l t s and those published previous ly for Co (C1C>4) 2 • TU 4 and Co (CH^CC^) 2 * ETU For the other three complexes, agreement i s very good and within experimental e r r o r . TABLE IV-11 Comparison of y and 0 Values with Previous Work Present Results Previous Results y e f f e y e f f 0 Ref. Co(C10 4 ) 2 -ETU 4 4.71 -10 4 .71* -8 (62) C o C l 2 ' E T U 2 4.44 - i i 4.49* -9 (62) C o ( C l 0 4 ) 2 - T U 4 4.28 - 4 4.50* -9 (63) C o C l 2 ' T U 2 4.47 - 6 4.45* -12 (63) CO ( C H 3 C 0 2 ) 2 * E T U 2 4.33 - 5 4.64** -9 (62) *y ca l cu la ted ef f by 2.828 , cor r Co (T- • Q ) ) H **y ca lcu la ted ef f by 2.84 ( X m + + " Co (T-As discussed i n Chapter II the Curie-Weiss type of behaviour for these complexes most probably ar i ses from 4 a zero magnetic f i e l d s p l i t t i n g of the A 2 ground term of cobal t ( I I ) i n a non-cubic l igand f i e l d . Assuming t h i s , 98 the experimental data may be compared with t h e o r e t i c a l p lot s of l / x 0 0 ^ / obtained using equation ( v i i i ) (Chapter II) , Co versus temperature. To obtain the t h e o r e t i c a l curves, values of g ranging from 2.20 to 2.42 i n 0.01 u n i t in te rva l s and values of 6 ranging from 0 to 40 cm 1 i n 5 cm 1 in te rva l s were used. Experimental values of l / x c o ^ at various Co temperatures for a l l complexes were then g raph ica l ly compared to the t h e o r e t i c a l curves to obtain the best f i t pos s ib le , g iv ing best f i t values of g and 6. Values of g and 6 determined i n t h i s manner are considered accurate to ± 0.01 uni t and ± 5 - cm 1 r e s p e c t i v e l y . A t y p i c a l experiment to theory f i t i s given i n Figure IV-12. The magnetic parameters thus obtained (g and 6) are c o l l e c t e d i n Table IV-12. Again the experimental data for the complex Co (m-N0«-C,H / 1 C0») ^• ETU„ 2 b 4 2 2 2 could not be f i t t e d to the theory and spec ia l a t tent ion to t h i s exception w i l l be given at the end of t h i s s ec t ion . A comparison of the two approaches to the analys i s of the magnetic data w i l l now be g iven. As discussed e a r l i e r i n Chapter I I , V e £ £ i s re la ted to g by equation (i) and equation ( i i ) , \i J:^ = 1.937 g. K e f f 3 ue f f values ca lcu la ted from g values given i n Table IV-12, are compared with those obtained from the Curie-Weiss p lo t i n Table IV-10. Providing higher terms i n equation (ix) are n e g l i g i b l e the parameters 6 and 6 are a lso simply r e l a t e d , - 6 = 0.192 6 1 2 5 corr 7 5 2 5 5 0 g = 2.29 _ , 6 = 25 cm 1 J f g = 2 - 2 9 2 0 cm -1 1 0 0 2 0 0 3 0 0 vo vo TEMP ( °K) F i g u r e IV-12. Experiment to Theory F i t of 1/x cor r C o + + vs T A T y p i c a l Example on C o ( p - B r - C g H 4 C 0 2 ) 2 « D M T U 2 1 0 0 TABLE IV-12 Experimental g and <S Values of ETU, TU and DMTU Complexes of Cobalt(II) Ligand = ETU TU DMTU Anion g 6 (cm )^ g 6* (cm )^ g 6 (cm )^ c i o 4 " 2 . 4 1 35 2.20 15 2.28 20 C l ~ 2 . 2 9 35 2.30 25 2.28 25 C H 3 C 0 2 " 2 . 2 3 15 2 .25 30 2.25 25 C 6 H 5 C 0 2 - - - 2 . 2 3 20 2.28 20 p - B r - C 6 H 4 C 0 2 " 2 . 2 3 20 2.27 20 2.29 20 m-N0 2 -C 6 H 4 C0 2 - - - 2.27 20 2 . 2 9 20 p - N 0 2 - C 6 H 4 C 0 2 - - - - - 2 . 2 9 20 o - B r - C c H „ C O ~ 6 4 2 2.28 15 2 . 2 9 25 2.27 20 o - N 0 2 - C 6 H 4 C 0 2 - 2.29 20 2 . 3 1 30 2.27 25 with t h i s approximation, 9 values were calculated from the corresponding 6 values for a l l complexes and are compared with those obtained from the Curie-Weiss p l o t s . The re su l t s are summarized i n Table IV-13. Examination of the data i n Table IV-13 shows very good agreement between the re su l t s obtained by the two approaches. As pointed out i n Chapter I I , equation ( v i i i ) may be reduced to a l i n e a r from for small x. In the present TABLE IV-13 Comparison of u e f £ and 6 Values (from Slope of Curie-Weiss F i t ) with Those Calculated from g and 6 Values Ligand = E T U T U DMTU A n i o n P K a y e f f 9 y e f f 6 y e f f 8 * ** * ** * ** from from from from from from from from from from from from slope g slope 5 slope g slope 6 slope g slope 6 c i o 4 — 4. 71 4. 67 -10 -7 C l " - 4. 44 4. 44 -11 -7 CH 3 C0 2 ~ 4.75 4. 33 4. 32 - 5 -3 C 6 H 5 C 0 2 - 4.18 - - - -p - B r - C 6 H 4 C 0 2 " 4.00 4. 34 4. 32 - 5 -4 m-N0 2-CgH 4C0 2~ 3.47 - - - -p - N 0 2 - C 6 H 4 C 0 2 - 3.43 - - - -o - B r - C 6 H 4 C 0 2 ~ 2.85 4. 42 4. 42 - 2 -3 o - N 0 2 - C 6 H 4 C 0 2 - 2.17 4. 44 4. 44 - 6 -4 4.28 4.26 -4 -3 4.42 4.42 -4 -4 4.47 4.46 -6 -5 4.42 4.42 -5 -5 4.37 4.36 -7 -6 4.36 4.36 -5 -5 4.34 4.32 -5 -4 4.42 4.41 -5 -4 4.40 4.39 -5 -4 4.44 4.44 -4 -4 4.40 4.39 -5 -4 4.45 4.44 -5 -4 - - - - 4.43 4.44 -5 -4 4.43 4.44 -5 -5 4.40 4.40 -4 -4 4.46 4.47 -4 -6 4.40 4.39 -6 -5 * y e f f = 1.937 g ** 8 = -0.1926 102 s i t u a t i o n , where 6 i s 15 - 35 c m - 1 and T i s 80 - 3 2 0 ° K , the condi t ion that x < 1 i s met and s t ra ight l ine s are e f f e c t i v e l y obtained for the ' t h e o r e t i c a l ' p l o t s . Thus, a f i t t i n g of experimental p lo t s to these near- s t ra ight-l i n e t h e o r e t i c a l p lo t s has the same ef fect as drawing the best s t ra ight l i n e through a l l the experimental points i n the Curie-Weiss approach. The s i m i l a r i t i e s are thus expected. The parameter 6 has some phys ica l s ign i f i cance i n contrast to the purely empir ica l nature of the parameter 0. Its magnitude i s , however, only accurate to ± 5 cm ^ . The experimental observation that 6 i s found i n the range of 15 - 35 cm ^ indicates that the s p l i t t i n g of ground state due to the second order s p i n - o r b i t coupling e f fec t i s small and i s s i m i l a r for a l l complexes. As was discussed i n Chapter H , for tetrahedral cobalt ( II ) complexes the increase of y e f f above the spin-only value of 3.873 B.M. has been a t t r ibuted to the o r b i t a l contr ibut ion brought about by mixing of the 4 exci ted state T 2 (which i s lODq i n energy above the ground 4 state) into the ground state A 2 by sp in-orb i t coupl ing . The equation for y e f f i s given by: y e f f = y s o ( 1 ~ — > e r r S - ° * lODq From the experimental determinations of y e f f and Dq (from e l e c t r o n i c spectra) , A can be ca l cu la ted . Results are summarized i n Table IV-14. TABLE IV-14 S p i n - o r b i t Coupling Constant (A) and E l e c t r o n i c D e l o c a l i z a t i o n F a c t o r (k) from Magnetic Data Ligand = ETU TU DMTU Anion P K a Dq (cm - 1) A (cm - 1) k Dq (cm 1) A (cm - 1) k Dq (cm - 1) A (cm - 1) k c i o 4 ~ - 377 -203 1Q07 425 -111 0.79 381 -134 0.87 C l " - 322 -117 0.81 36 0 -138 0. 88 348 -122 0.83 CH 3C0 2~ 4.75 376 -111 0.79 396 -126 0.84 403 -126 0.84 C cH cC0 o~ 6 5 2 4.18 - - - 417 -124 0.84 444 -156 0.94 p-Br-C gH 4C0 2" 4.00 381 -115 0.80 403 -137 0.88 444 -161 0.95 m-N0 2-C 6H 4C0 2- 3.47 - - - 412 -141 0.89 446 -165 0.96 p-N0 2-C 6H 4C0 2- 3.43 - - - - - - 406 -146 0.91 o-Br-CgH 4C0 2~ 2. 85 359 -127 0.84 420 -151 0.92 433 -148 0.91 o-N0 2-CgH 4C0 2- 2.17 363 -134 0.87 425 -162 0.95 410 -139 0.88 Dq C a l c u l a t e d from S o l i d State S p e c t r a 104 The parameter k, the ' e l e c t r o n i c d e l o c a l i z a t i o n f a c t o r ' , can be c a l c u l a t e d from A by the e x p r e s s i o n 2 A = k A and k v a l u e s f o r a l l complexes s t u d i e d i n t h i s o work are a l s o c o l l e c t e d i n Table IV-14. A g e n e r a l comparison of the magnetic parameters f o r a l l complexes s t u d i e d i n t h i s work i s now g i v e n . (i) The Ve££ v a l u e s of the three p e r c h l o r a t e complexes vary markedly from complex to complex. In view of the s i m i l a r i t i e s i n the s p e c t r a l p r o p e r t i e s of these complexes, t h i s i s r a t h e r s u r p r i s i n g . However, as p o i n t e d out by Salzmann and Schmidtke (78), i t i s d i f f i c u l t to a t t a c h p h y s i c a l s i g n i f i c a n c e to the magnitude of the magnetic moments f o r complexes with l a r g e metal-l i g a n d o r b i t a l o v e r l a p . I t was a l s o p o i n t e d out t h a t |A| and k v a l u e s g r e a t e r than f r e e - i o n v a l u e s are c o n c e i v a b l e f o r such complexes. As S - l i g a n d s are i n the lowest p o s i t i o n i n the n e p h e l a u x e t i c s e r i e s , complexes c o n t a i n i n g f o u r such m e t a l - l i g a n d bonds i n a t e t r a h e d r a l a r r a y are expected to be very c o v a l e n t , w i t h very l a r g e o r b i t a l o v e r l a p e f f e c t s . The |A | value (and the c o r r e s p o n d i n g k value) of one of the complexes, Co(ClO^) 2*ETU i s i n f a c t observed to be g r e a t e r than the f r e e - i o n v a l u e . ( i i ) The y e f £ valu e s f o r the three c h l o r i d e complexes are s i m i l a r t o each o t h e r . The replacement of two S-bonded l i g a n d s by two c h l o r i d e s from the chromophore CoS^ has the e f f e c t of r e d u c i n g the o r b i t a l o v e r l a p and the c o v a l e n t c h a r a c t e r of the complexes. Assuming the o r b i t a l o v e r l a p i s reduced to such an e x t e n t to a l l o w 105 c o r r e l a t i o n of V e f £ / X and k w i t h the c o v a l e n t c h a r a c t e r of the complexes then the r e s u l t s i n d i c a t e a l l three complexes have s i m i l a r c o v a l e n t c h a r a c t e r s . ( i i i ) E i g h t e e n c a r b o x y l a t e complexes were s t u d i e d . A l l complexes (with the e x c e p t i o n of Co(m-N0 2-C 6H 4C0 2) 2*ETU 2) have magnetic moments r a n g i n g from 4.33 B.M. to 4.46 B.M., i n the range expected f o r t e t r a h e d r a l complexes (4.2 B.M. to 4.8 B.M.). As c a r b o x y l a t e groups occupy a very h i g h p o s i t i o n i n the n e p h e l a u x e t i c s e r i e s ( i . e . low c o v a l e n t c h a r a c t e r i n t h e i r bonds t o c o b a l t ) , i t may be assumed t h a t the complexes are of s m a l l o r b i t a l o v e r l a p type. Assuming, as f o r the c h l o r i d e complexes, o r b i t a l o v e r l a p i s s i g n i f i c a n t l y reduced, then U e f f i A and k may c o r r e l a t e w i t h the c o v a l e n t c h a r a c t e r o f the complex. Despite the very s m a l l v a r i a t i o n s i n magnetic moment among the c a r b o x y l a t e complexes, trends can be d e t e c t e d when they are arranged a c c o r d i n g t o the pK value of the parent a c i d . a I t should be p o i n t e d out t h a t the t o t a l v a r i a t i o n i n magnetic moments observed amounts to some 2.5%. T h i s i s c o n s i d e r e d to be a s i g n i f i c a n t v a r i a t i o n s i n c e the a b s o l u t e e r r o r i n an i n d i v i d u a l magnetic moment i s ^  1% while the r e l a t i v e e r r o r between v a l u e s f o r d i f f e r e n t complexes i s s i g n i f i c a n t l y l e s s . Examination of Table IV-13 shows t h a t i n both the ETU and TU s e r i e s the value of the magnetic moment decreases r e g u l a r l y as pK .increases. |X| and k a l s o decrease a c c o r d i n g l y (Table IV-14). I t can be reasoned t h a t , as pK i n c r e a s e s , the c a r b o x y l a t e anions become more b a s i c 106 and the bonds they form with the centra l metal ion become more covalent (|x| i s decreased, away from i t s f ree- ion value of 178 cm 1 and k decreases i n the same way, from i t s f ree- ion value of u n i t y ) . In the DMTU ser ie s , however, the trend i s less obvious. Pos s ib ly , s t e r i c factors a r i s i n g from the bulky nature of th i s S-bonded l igand are of more importance i n determining the e l e c t r o n i c and therefore magnetic propert ies i n th i s s e r ie s . Comparing ETU, TU and DMTU complexes of a given cobalt ( I I ) carboxylate, i n most instances , |x| and k values decrease on going from the DMTU to the TU to the ETU complex. For the o-subst i tuted carboxylates the r e l a t i v e order of the TU and DMTU complexes i s reversed. The above suggests that there i s a higher degree of covalent bonding i n the ETU complexes than i n the TU or DMTU complexes. The complex Co(m-N0 2 -CgH 4 C0 2 ) 2 •ETU 2 exh ib i t s very d i f f e rent magnetic propert ies from those of the other S-bonded complexes. Its e f fec t ive magnetic moment at room temperature i s 5.11 B . M . , t y p i c a l for an octahedral complex, and magnetic s u s c e p t i b i l i t i e s for the complex do not obey the Curie-Weiss law. This can be seen by comparing the standard dev ia t ion on 9 obtained from least-square analys i s for t h i s complex with those for several other complexes which obey Curie-Weiss law: 107 Complex -6 ( <K) (Experi-mental) -6 (UK) (Least-Square Analysis ) °Q ( °K) (Standard deviation) C o ( m - N 0 2 - C 6 H 4 C 0 2 ) 2 • E T U 2 Co(p-Br-CgH 4 C0 2 ) 2 •DMTU 2 C o ( o - N 0 2 - C g H 4 C 0 2 ) 2 • D M T U 2 Co(m-N0 2 -C 6 H 4 C0 2 ) 2 •DMTU 2 C o ( o - B r - C 6 H 4 C 0 2 ) 2 * E T U 2 C o ( o - N 0 2 - C 6 H 4 C 0 2 ) 2 * T U 2 C o ( m - N 0 2 - C 6 H 4 C 0 2 ) 2 « T U 2 4 6 5 2 4 5 14.6 4.8 5.8 4.9 3.1 4.2 5.3 2.3 0.1 0.2 0.2 0.1 0.1 0.2 In f ac t , the r e s u l t obtained by least-square analys i s to obtain the best s t r i g h t l i n e through the experimental points on a l / x c ° ^ v . s . T p l o t showed also that the Co previous v i s u a l s t ra ight l i n e analys is of data were adequate and r e l i a b l e . Treat ing t h i s complex as an octahedral complex the experimental magnetic moment values , obtained over a range of temperatures, were compared to t h e o r e t i c a l curves obtained by F igg i s (as described i n Chapter I I ) . A good f i t of the experimental values i s observed (Figure IV-13) with the t h e o r e t i c a l curve ca lcu la ted using the following parameter values . y e f f A A k v(A) 5.11 B.M. 1.40 -130 c m - 1 1.0 0 108 109 The parameter A was c a l c u l a t e d from a knowledge of Dq and B from the s o l i d s t a t e spectrum of the complex (as d e s c r i b e d i n Chapter I I ) . The r a t h e r low |X| value suggests s t r o n g c o v a l e n t bonding i n t h i s complex, not too s u r p r i s i n g f o r a complex c o n t a i n i n g an S-bonded l i g a n d . In chapter V a number o f o c t a h e d r a l c a r b o x y l a t e complexes c o n t a i n i n g N-bonded p y r i d i n e are examined and f o r these |X| i s s i g n i f i c a n t l y g r e a t e r . The f a c t t h a t A = 0 shows t h a t the degree of d i s t o r t i o n i s too s m a l l to be d e t e c t e d from the magnetic data, i n d i c a t i n g t h a t the complex has a f a i r l y r e g u l a r o c t a h e d r a l s t r u c t u r e with the c a r b o x y l a t e anion c o o r d i n a t i n g to c o b a l t i n a b i d e n t a t e c h e l a t i n g or b r i d g i n g f a s h i o n . The e l e c t r o n i c spectrum of the complex, d i s c u s s e d p r e v i o u s l y , i s now understood i n terms of an o c t a h e d r a l complex. In s o l u t i o n , t o be d i s c u s s e d i n the f o l l o w i n g s e c t i o n , there i s a breakdown of the b i d e n t a t e a c t i o n of the c a r b o x y l a t e anion and a t e t r a h e d r a l s p e c i e s i n v o l v i n g u nidentate c o o r d i n a t i o n of the c a r b o x y l a t e group i s formed. IV-4. SOLUTION STUDIES E a r l i e r i n t h i s Chapter the e l e c t r o n i c s p e c t r a of s o l u t i o n s i n acetone of ETU, TU and DMTU complexes of c o b a l t ( I I ) p e r c h l o r a t e , c h l o r i d e and a number of a r y l c a r b o x y -l a t e s were b r i e f l y d i s c u s s e d . I t was p o i n t e d out t h a t on 110 a d d i t i o n of excess S - l i g a n d , t o suppress d i s s o c i a t i o n , the complexes give t e t r a h e d r a l s p e c i e s i n s o l u t i o n , the s p e c t r a of which are governed almost e n t i r e l y by the nature of the immediate c o b a l t environment. Thus while the d i f f e r e n t chromophores CoS^, C o S 2 C l 2 and C o S 2 0 2 gave d i f f e r e n t s p e c t r a , changes i n the S - l i g a n d or c a r b o x y l a t e l i g a n d do not s i g n i f i c a n t l y change the s p e c t r a . In t h i s s e c t i o n we examine i n more d e t a i l the nature of these s o l u t i o n s and, i n p a r t i c u l a r , attempts are made to estimate, from the e l e c t r o n i c s p e c t r a , the nature and e x t e n t of the d i s s o c i a t i o n r e a c t i o n s . Crude s o l u b i l i t y t e s t s i n v a r i o u s o r g a n i c s o l v e n t s were conducted on a l l complexes. These were done by attempting _3 t o prepare a s o l u t i o n of a t l e a s t 10 M c o n c e n t r a t i o n f o r each complex and s o l v e n t combination. I f a c l e a r c o l o u r e d s o l u t i o n was o b t a i n e d , w i t h no evidence of s o l i d s o l u t e remaining the complex was c o n s i d e r e d s o l u b l e ; i f there was no evidence of d i s s o c i a t i o n w i t h the s o l v e n t remaining c o l o u r l e s s by v i s u a l examination, the complex was c o n s i d e r e d i n s o l u b l e ; i f the s o l v e n t became c o l o u r e d i n d i c a t i n g some d i s s o c i a t i o n , but some complex remained u n d i s s o l v e d i t was c o n s i d e r e d i n s u f f i c i e n t l y s o l u b l e . The r e s u l t s of these t e s t s are shown below i n Table IV-15. A l l complexes were found to be i n s o l u b l e i n benzene, carbon t e t r a c h l o r i d e and c h l o r o f o r m . S o l u b i l i t i e s i n acetone and 100% e t h a n o l were higher and as seen i n the t a b l e acetone appears to be the b e s t s o l v e n t f o r these I l l TABLE IV-15 Crude S o l u b i l i t y Tests on TU, ETU and DMTU Complexes of C o b a l t ( I I ) ^ \ L i g a n d Anion ETU TU DMTU 100% 100% 100% Acetone E t h a n o l Acetone Eth a n o l Acetone Ethanol c i o 4 " s o l i n s s o l s o l s o l s o l C l " s o l i n s s o l s o l s o l i n s CH 3C0 2~ i n s i n s i n s i n s i n s i n s p - Br-C 6H 4C0 2" i n s i n s s o l s o l * i n s o-Br-C,H.CO ~ 6 4 2. i n s i n s ** s o l * i n s p-N0 2-C 6H 4C0 2" - - - - s o l i n s o - N0 o-C cH.C0„~ 2 6 4 2 i n s i n s s o l s o l s o l i n s m-N0 2-C 6H 4C0 2- s o l i n s s o l s o l s o l i n s C 6 H 5 C 0 2 - — — ** s o l i n s i n s * i n s u f f i c i e n t l y s o l u b l e ** g i v i n g suspension - not prepared i n t h i s work complexes. For complexes t h a t were s o l u b l e i n acetone i n the absence of added l i g a n d , the p e r c h l o r a t e complexes gave green-blue s o l u t i o n s , the c h l o r i d e complexes gave deep blue s o l u t i o n s and the a r y l c a r b o x y l a t e complexes gave p a l e blue 112 s o l u t i o n s . As excess l i g a n d was added i n each case, a deep blue c o l o u r was obtained i r r e s p e c t i v e of the o r i g i n a l complex. Turn i n g now t o d e t a i l s of the e l e c t r o n i c s p e c t r a of these complexes, i t was p o i n t e d out e a r l i e r i n t h i s Chapter t h a t the e l e c t r o n i c s p e c t r a of the three p e r c h l o r a t e complexes i n s o l u t i o n i n acetone were v i r t u a l l y i d e n t i c a l r e g a r d i n g band p o s i t i o n s and s t r u c t u r e (shape and w i d t h ) , d i f f e r i n g only i n band i n t e n s i t i e s . A d d i t i o n cf excess S - l i g a n d to these s o l u t i o n s r e s u l t e d i n an i n c r e a s e i n band i n t e n s i t y , i n each case, w i t h no n o t i c e a b l e change i n band p o s i t i o n or s t r u c t u r e . A l i m i t i n g spectrum was obtained vhen f u r t h e r a d d i t i o n of S - l i g a n d r e s u l t e d i n no f u r t h e r i n c r e a s e i n band i n t e n s i t y (see F i g u r e IV-4). The same s p e c t r a l p r o p e r t i e s were observed f o r the c h l o r i d e s e r i e s of complexes (Figure IV-6) and as seen here s i m i l a r p r o p e r t i e s are e x h i b i t e d by the c a r b o x y l a t e s e r i e s of complexes (Figure IV-14). The e x p l a n a t i o n of t h i s behaviour i s f a i r l y simple. The complexes d i s s o l v e with d i s s o c i a t i o n of S - l i g a n d . I f i t i s assumed t h a t the s p e c i e s produced on d i s s o c i a t i o n do not absorb s t r o n g l y i n the r e g i o n under study, as would be the case f o r example i f the s p e c i e s i n v o l v e o c t a h e d r a l c o o r d i n a t i o n about c o b a l t , then the spectrum i s due to the s p e c i e s CoS^ ( f o r the p e r c h l o r a t e s ) , C 0 S 2 C I 2 (for the c h l o r i d e s ) and C 0 S 2 O 2 (for the c a r b o x y l a t e s ) . A d d i t i o n of excess S - l i g a n d simply i n c r e a s e s the c o n c e n t r a t i o n s of these s p e c i e s i n c r e a s i n g the i n t e n s i t i e s of the s p e c t r a u n t i l d i s s o c i a t i o n 120 80 4 0 Co(o-N0 2-C 6H 4C0 2) 2*DMTU 2 C o ( m - N 0 2 - C 6 H 4 C 0 2 ) 2 « E T U 2 Co(m-N0 2-C 6H 4C0 2) 2•DMTU 2 C o ( p - B r - C 6 H 4 C 0 2 ) 2 * T U 2 Co(m-N0 2-C 6H 4C0 2) 2*TU 2 l i m i t i n g spectrum of Co ( p - B r - C 6 H 4 C 0 2 ) 2 • T U 2 20 0 22 18 14 10 y X 1 0 cm" i—1 F i g u r e IV-14. Acetone S o l u t i o n Spectra of S e v e r a l TU, ETU and DMTU Complexes of Cobalt (II) A r y l c a r b o x y l a t e s data recorded i n Appendix IV-2 s o l v e n t : d i s t i l l e d acetone 114 i s completely r e p r e s s e d . T h i s i s i l l u s t r a t e d by an example of the S - l i g a n d c o n c e n t r a t i o n dependence of the v i s i b l e band of C o ( p - B r - C 6 H 4 C 0 2 ) 2 ' T U 2 as shown i n F i g u r e IV-15. F u r t h e r evidence of the presence of d i s s o c i a t i o n i s obtained from the o b s e r v a t i o n t h a t the s p e c t r a l band i n t e n s i t i e s , f o r s o l u t i o n s of the complexes i n acetone, as measured by the molar e x t i n c t i o n c o e f f i c i e n t £, are c o n c e n t r a t i o n dependent. A simple way of demonstrating the presence of a c o n c e n t r a t i o n dependent e q u i l i b r i u m i s to p l o t the measured absorbance A, a t a p a r t i c u l a r wavelength, a g a i n s t the c o n c e n t r a t i o n C. For a s t a b l e absorbing s p e c i e s i n s o l u t i o n , not i n v o l v e d i n chemical e q u i l i b r i u m with other s p e c i e s , Beer's law (A = 5 b C) r e q u i r e s t h a t , f o r a given path l e n g t h b, A i s p r o p o r t i o n a l to C. That the complexes d e v i a t e from t h i s simple Beer's law behaviour i s demonstrated i n F i g u r e IV-16 and demonstrates f u r t h e r the presence of a c o n c e n t r a t i o n dependent e q u i l i b r i u m . In the course of these i n v e s t i g a t i o n s s e v e r a l s p e c t r a , i n v o l v i n g d i f f e r e n t c o n c e n t r a t i o n s of c o b a l t complex and d i f f e r e n t amounts of added excess S - l i g a n d , were obtained f o r each complex. In Appendix IV-2 we have l i s t e d " t y p i c a l " s o l u t i o n s p e c t r a l data f o r each complex. The s o l v e n t used to o b t a i n these data was reagent grade acetone p u r i f i e d by d i s t i l l a t i o n as d e s c r i b e d i n Chapter I I I (to be r e f e r r e d to as ' d i s t i l l e d acetone' h e r e a f t e r ) . The importance of s p e c i f y i n g the type of acetone used w i l l be e x p l a i n e d l a t e r . 115 F i g u r e IV-15. Acetone S o l u t i o n Spectra ( V i s i b l e Region) of C o ( p - B r - C 6 H 4 C 0 2 ) 2 ' T U 2 - Dependence on S - l i g a n d C o n c e n t r a t i o n , s o l v e n t : d i s t i l l e d acetone b 1.5-1.0-0.5 a - • C o C l 2 - T U 2 @ 15000 cm o CoCl 2'ETU 2@ 15000 cm b - C o ( o - N 0 2 - C 6 H 4 C 0 2 ) 2 - T U 2 c - C o ( m - N 0 2 - C 6 H 4 C 0 2 ) 2 « T U 2 @ 16 810 cm @ 16810 cm -1 -1 -1 -1 OA C x10"3 M F i g u r e IV-16. Beer's Law P l o t s of Some S e l e c t e d S-Bonded Complexes ( V i s i b l e Region) s o l v e n t : d i s t i l l e d acetone, b = 1 cm 117 In the column headed 'excess S - l i g a n d ' the c o n c e n t r a t i o n of added l i g a n d i s s p e c i f i e d . The data i n t h i s column are i n f a c t the ' l i m i t i n g d a t a ' r e f e r r e d to e a r l i e r ; added S - l i g a n d would not a f f e c t these s p e c t r a . We c o n s i d e r now the d e t a i l s of the s p e c t r a of the complexes i n s o l u t i o n i n acetone i n the presence of excess S - l i g a n d . As e x p l a i n e d e a r l i e r these s p e c t r a are c o n s i d e r e d to be the s p e c t r a of the u n d i s s o c i a t e d complexes. From an e s t i m a t i o n of the c e n t e r of g r a v i t y of the v i s i b l e and n e a r - i n f r a r e d bands, e n e r g i e s can be assigned t o the V 3 and V 2 t r a n s i t i o n s as d e s c r i b e d p r e v i o u s l y and v a l u e s of the 'average' l i g a n d f i e l d parameters Dq and B may be obtained. The s o l u t i o n s p e c t r a of a l l the c a r b o x y l a t e complexes are so s i m i l a r t h a t s i n g l e v a l u e s of V 3 and v 2 , Dq and B are obtained and are r e p r e s e n t a t i v e of a l l of the complexes. Even band i n t e n s i t i e s vary very l i t t l e from one c a r b o x y l a t e complex to another. The same s i m i l a r i t i e s i n the s o l u t i o n s p e c t r a were observed f o r the three p e r c h l o r a t e complexes and f o r the three c h l o r i d e complexes. Values of these s p e c t r a l parameters are given i n Table IV-16. TABLE IV-16 S p e c t r a l Parameters f o r S-Ligand Complexes i n Acetone S o l u t i o n Complex £ E ^ _^ ^max _^ ^max _^ _, Type* v 3 ( c m ) ( f o r v 3 ) v 2 (cm ) ( f o r v 2 ) Dq (cm ) B (cm ) C o S 4 2 + 14620 715-741 7030 158-163 412 624 C o S 2 C l 2 15110 489-538 5780 90-107 331 735 C o S 2 ( R C 0 2 ) 2 16900 364-385 6800 100-121 390 805 * S r e f e r s t o TU, ETU or DMTU 118 C l e a r l y the s p e c t r a of these complex s p e c i e s i n s o l u t i o n are determined almost e n t i r e l y by the gross e f f e c t of the immediate environment about c o b a l t - i . e . whether the chromophore i s CoS^, C 0 S 2 C I 2 or CoS 2C> 2. Changes i n the nature of the l i g a n d beyond the atom bonded d i r e c t l y to the c o b a l t i o n (e.g. going from TU to ETU to DMTU or going from RCC>2 to R'CC^) do not s i g n i f i c a n t l y a f f e c t the s p e c t r a . Comparing the data i n Table IV-16 f o r the three complex types we o b t a i n u s e f u l i n f o r m a t i o n . F i r s t , B i n c r e a s e s i n the ord e r : C o S 2 ( R C 0 2 ) 2 > C o S 2 C l 2 > C o S 4 2 + T h i s suggests t h a t the r e l a t i v e o r d e r i n g of the l i g a n d s i n the n e p h e l a u x e t i c s e r i e s i s c a r b o x y l a t e > c h l o r i d e > t h i o u r e a s - i . e . the t h i o u r e a s cause a l a r g e s t r e d u c t i o n i n B (most covalent) and the c a r b o x y l a t e s the s m a l l e s t r e d u c t i o n i n B. I t has been known f o r some time t h a t complexes with low B v a l u e s ( i . e . c o n s i d e r e d to be h i g h l y covalent) u s u a l l y have i n t e n s e s p e c t r a . That i s as B decreases i n a s e r i e s of complexes, E. u s u a l l y i n c r e a s e s (65) . T h i s i n v e r s e r e l a t i o n s h i p between B and £. i s seen to h o l d very w e l l f o r the complexes s t u d i e d here (see Table IV-16). The t r e n d i n Dq value s i s seen to be: C o S 2 C l 2 < C o S 2 ( R C 0 2 ) 2 < C o S 4 2 + p l a c i n g the t h i o u r e a l i g a n d s h i g h e r than the c a r b o x y l a t e l i g a n d s and these i n t u r n higher than the c h l o r i d e i o n i n the s p e c t r o c h e m i c a l s e r i e s . By a p p l y i n g the 'Average Ligand F i e l d Approximation' (55) the value s of Dq and B 119 2-for the hypothetical species CoCRCG^^ were estimated. This together with the experimental re s u l t s obtained i n 2+ t h i s work for CoS 4 and previous experimental results reported for tetrahedral cobalt(II) species (64) give new spectrochemical and nephelauxetic series for tetrahedral cobalt(II) according to the order of magnitude of Dq and B. Spectrochemical Series (in order of increasing Dq) I~ < Br~ < C l ~ < Ph3PO ^ PhgAsO ^ R C 0 2 < TU(ETU, DMTU) < < NCO~ < NCS~ < NCSe" Nephelauxetic Series (in order of decreasing B) RCO~ ^ Ph3PO > PhgAsO > NCO~ > C l " > Br" > NCS~ > I~ > N~ > NCSe" > TU(ETU, DMTU) This section i s concluded with a discussion of some experiments performed i n an attempt to determine the nature of the d i s s o c i a t i o n reaction taking place i n solutions of the S-ligand complexes and to estimate the equilibrium constants involved for d i f f e r e n t complexes. Using an NMR method Eaton and Zaw (132) studied the d i s s o c i a t i o n of CoC^'T^, Co (C104) 2 * TU 4 and Co(ClO^)2*DMTU4 i n deuterated acetone (acetone-d^). They suggested the di s s o c i a t i o n reaction involves one S-ligand being replaced by one solvent molecule. In the case of thiourea, the e q u i l i b r i a suggested are: Co(TU) 4- (C10 4) 2 + S Co(TU) 3- (C10 4) 2-S + TU (i) C O ( T U ) 2 C I 2 + S K "> Cn (Tin - f l »s + TU ( i i ) 120 where K and K' are the d i s s o c i a t i o n constants a s s o c i a t e d w i t h the e q u i l i b r i a (i) and ( i i ) and S denotes a s o l v e n t molecule ( i . e . acetone-dg). The d i s s o c i a t i o n c onstants were c a l c u l a t e d f o r the complexes from the l i m i t i n g N-H s h i f t s a t i n f i n i t e c o n c e n t r a t i o n s of the complexes and some r e l e v a n t r e s u l t s are given l a t e r i n Table IV-18. In the p r e s e n t work we attempted to c a l c u l a t e e q u i l i b r i u m c o n s t a n t s from e l e c t r o n i c s p e c t r a l data. Before proceeding w i t h a d i s c u s s i o n of t h i s a n a l y s i s , however, i t i s necessary to c o n s i d e r the e f f e c t of water i m p u r i t y i n the acetone s o l v e n t on the d i s s o c i a t i o n e q u i l i b r i a . In the p r e v i o u s NMR work (132) the e q u i l i b r i u m constants were claimed to be independent of s o l v e n t com-p o s i t i o n , i . e . i n s e n s i t i v e to the water content of the acetone-dg used, a t water c o n c e n t r a t i o n s up to the 1 - 2 % l e v e l . In c o n t r a s t to the r e s u l t s of these p r e v i o u s workers, we have found the spectra of our complexes i n s o l u t i o n , and t h e r e f o r e presumably the p o s i t i o n of the e q u i l i b r i a i n v o l v e d , are very s e n s i t i v e t o water i m p u r i t i e s . The " d r i e s t " acetone we have used i s S p e c t r a l Grade, p r o v i d e d commercially by F i s h e r S c i e n t i f i c Company and c e r t i f i e d to c o n t a i n a t most 0.3% water i m p u r i t y . A very low water content i n t h i s acetone, i n f a c t l e s s than 0.3%, was confirmed by comparing i n t e g r a t e d areas under the resonance peaks 13 ass i g n e d to water and acetone C s a t e l l i t e (the l a t t e r i s known to correspond to ^ 1% t o t a l carbon content i n acetone) 121 i n the NMR spectrum. The e f f e c t of adding q u a n t i t a t i v e amounts of water to s o l u t i o n s of S - l i g a n d complexes i n t h i s s p e c t r a l grade acetone on the i n t e n s i t i e s of the e l e c t r o n i c s p e c t r a l bands i s shown ( f o r three s e l e c t e d complexes) i n F i g u r e IV-17. The decrease i n band i n t e n s i t y , we b e l i e v e , a r i s e s from an i n c r e a s e i n the percentage d i s s o c i a t i o n of the complex as water i s added. One p o i n t of i n t e r e s t i n regard to F i g u r e IV-17 i s t h a t the d i s s o c i a t i o n 2+ of the c a t x o n i c s p e c i e s Co(TU)^ i s more s e n s i t i v e to water i m p u r i t y than the d i s s o c i a t i o n of e i t h e r of the n e u t r a l s p e c i e s C o C l 2 « T U 2 or C o ( R C 0 2 ) 2 * T U 2 . Wherever the same complex was s t u d i e d i n both s p e c t r a l grade acetone and d i s t i l l e d acetone we found t h a t band i n t e n s i t i e s were high e r i n the s p e c t r a l grade acetone s o l u t i o n s i n d i c a t i n g a h i g h e r water i m p u r i t y content i n the normal d i s t i l l e d acetone. These s p e c t r a l r e l a t i o n s h i p s are shown i n F i g u r e IV-f o r the complex Co(ClO^) 2•TU^. One important p o i n t t o make here i s t h a t the l i m i t i n g spectrum o b t a i n e d on adding excess S - l i g a n d i s independent of the type of acetone used - i . e . independent of the water i m p u r i t y content. Although our r e s u l t s appear c o n t r a d i c t o r y to those of Eaton and Zaw (132) i n t h a t they demonstrate a g r e a t e r s e n s i t i v i t y t o water i m p u r i t y than i m p l i e d by the p r e v i o u s work i t should be s t r e s s e d t h a t the c o n c e n t r a t i o n s of -3 -3 complexes used i n the p r e s e n t work (1 x 10 - 5 x 10 M) are s i g n i f i c a n t l y lower than the c o n c e n t r a t i o n s used i n the t s j 0 0.1 0.2 Q3 0.4 0.5 gm H 20 per 20 ml s p e c t r a l acetone Fi g u r e IV-17. E f f e c t of Adding Water to S o l u t i o n s of S-Ligand Complexes on E l e c t r o n i c S p e c t r a l I n t e n s i t i e s 123 7 0 0 5 0 0 300 100-Conc 1.00x10 (M) -3 - 2.57x10 - 1.89x10 - 1.89x10" -3 -3 Acetone d i s t i l l e d II s p e c t r a l +1.5x10 3(TU) " common l i m i t i n g spectrum (+0.1M TU) V x i o ' 3 c m " ' F i g u r e IV-18. Acetone S o l u t i o n Spectra ( V i s i b l e Region) of C o ( C 1 0 4 ) 2 » T U 4 - Va r i o u s C o n c e n t r a t i o n , Solvent and Added S-Ligand 124 -3 -3 p r e v i o u s work (7 x 10 - 250 x 10 M). C l e a r l y a t lower complex c o n c e n t r a t i o n s a g r e a t e r s e n s i t i v i t y t o water i m p u r i t i e s i s expected s i n c e , r e l a t i v e l y speaking, the water content i s g r e a t e r . In summary then, the s p e c t r a l band i n t e n s i t i e s and, t h e r e f o r e , e q u i l i b r i u m c o n s t a n t s measured i n the p r e s e n t work depend s t r o n g l y on s o l v e n t composition and f o r t h i s reason the type of acetone s o l v e n t used i s s p e c i f i e d i n the d i s c u s s i o n t h a t f o l l o w s . I f one assumes t h a t the water content i n the d i s t i l l e d acetone on the one hand and the s p e c t r a l grade on the o t h e r remained f a i r l y c o nstant from experiment to experiment then comparison of e q u i l i b r i u m c onstants f o r d i f f e r e n t complexes i n the same s o l v e n t should be meaningful. In the treatment of data t h a t f o l l o w s the f o l l o w i n g assumptions are made: (a) E q u i l i b r i a of types (i) and ( i i ) i n v o l v i n g the l o s s of one o n l y of the S - l i g a n d s are a p p l i c a b l e to a l l the complexes s t u d i e d i n t h i s work, i n c l u d i n g the a r y l c a r b o x y l a t e complexes. In view ' of the s i m i l a r i t i e s of the s o l u t i o n s p e c t r a of a l l these complexes, t h i s i s a reasonable assumption. Besides, i t can be shown t h a t while reasonably constant v a l u e s of K can be c a l c u l a t e d f o r d i f f e r e n t con-c e n t r a t i o n assuming d i s s o c i a t i o n of o n l y one S - l i g a n d , such i s not the case i f the assumption i s made t h a t two l i g a n d molecules d i s s o c i a t e . 125 (b) The d i s s o c i a t i o n product (or products) i s assumed to c o n t r i b u t e i n s i g n i f i c a n t l y to the s p e c t r a l bands observed. In view of the great s i m i l a r i t i e s i n the s p e c t r a (band p o s i t i o n s , shapes and widths) at d i f f e r e n t c o n c e n t r a t i o n s of complex and v a r i o u s amounts of excess S - l i g a n d and water p r e s e n t , the formation of another 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 (with i t s expected h i g h i n t e n s i t y a b s o r p t i o n bands) as a r e s u l t of the d i s s o c i a t i o n seems u n l i k e l y . I t i s a l s o improbable to suggest t h a t any product r e s u l t i n g from d i s s o c i a t i o n would give an i d e n t i c a l spectrum as the o r i g i n a l c o b a l t ( I I ) s p e c i e s . I t i s t h e r e f o r e v i s u a l i z e d t h a t the p r o d u c t ( s ) of d i s s o c i a t i o n i s a s i x - c o o r d i n a t e ' o c t a h e d r a l ' s p e c i e s with r e l a t i v e l y low i n t e n s i t y a b s o r p t i o n bands. One l i g a n d molecule i s b e l i e v e d t o be r e p l a c e d by acetone and/or water molecules y i e l d i n g the s o i v a t e d ' o c t a h e d r a l ' product. In the cases of the a r y l c a r b o x y l a t e complexes a f u r t h e r p o s s i b i l i t y of i n c r e a s e d c o o r d i n a t i o n a r i s e s from the b i d e n t a t e nature of the a r y l c a r b o x y l a t e groups. F u r t h e r support f o r a l l of t h i s comes from the o b s e r v a t i o n t h a t f o r some complexes a t low c o n c e n t r a t i o n s where d i s s o c i a t i o n i s e x t e n s i v e , the s o l u t i o n s are almost c o l o u r l e s s and the s p e c t r a are very weak indeed. (c) The components of the s p e c t r a l t r a n s i t i o n s are not r e a d i l y r e s o l v e d i n a l l cases. T h e r e f o r e , c a l c u l a t i o n s were made u s i n g the e x t i n c t i o n c o e f f i c i e n t of the most i n t e n s e band or band component i n the s p e c t r a of each complex. 126 The general equation for the equilibria involved here i s , CoL X, K > CoL^ ,X,Sra + L ( i i i ) n 2 * , „ n-l 2 m +mS where n = 4 or 2, X = C104~ or C l - or RC02~ and m = number of solvent molecules to form a six-coordinated cobalt(II) species. The dissociation constant K for equilibrium ( i i i ) can be expressed as 2 0 a C K = 2 — ( i v ) 1 - a where a is the degree of dissociation and C is the i n i t i a l concentration of the complex. In the case where a known concentration (C ) of ligand L is added, a (aC + C ) K = ° ( v ) 1 - a If the molar extinction coefficient measured for the complex in solution is E, and the extinction coefficient measured at the same energy from the limiting spectrum (i.e. where the complex dissociation is repressed by added ligand) is £ then i t can be shown that, 3 max 1 - a = (vi) m^ax Values of equilibrium constants calculated from equation (iv) using data obtained for solutions of the complexes at different concentrations and in some cases in both d i s t i l l e d and spectral grade acetone are recorded in Table IV-17. 127 TABLE IV-17 Eq u i l i b r i u m Constant Data of TU, ETU and DMTU Complexes of Cobalt(II) Complex Concentration Type of Acetone * 5 4 * lO^K Co(C10 4) 2-TU 4 1.00 X l O " 3 d i s t i l l e d 380 4.0 2.57 X 10" 3 479 4.3 1.51 X l O " 3 s p e c t r a l 590 0.57 1.89 X 10" 3 " 615 0.42 2.67 X 10" 3 •1 626 0.47 26.87 X 10' 3 it 680 0.74 Co(C10 4) 2-ETU 4 2.37 X l O " 3 d i s t i l l e d 174 59.0 1.09 X 1 0 - 3 s p e c t r a l 346 6.6 1.93 X 10" 3 " 446 5.0 Co(C10 4) 2.DMTU 4 2.51 X l O " 3 d i s t i l l e d 172 63.0 1.02 X 1 0 - 3 s p e c t r a l 274 11.0 2.06 X 10" 3 407 7.3 CoCl 2-TU 2 1.05 X l O " 3 d i s t i l l e d 437 0.32 1.99 X 1 0 - 3 452 0.39 3.16 X l O " 3 s p e c t r a l 478 0.22 Co (n-N0 2-C gH 4C0 2: »2 3.30 X l O "3 •5 d i s t i l l e d 142 35.0 •TU 2 5.72 X 10 3 " 177 36.0 7.70 X 10" 3 200 35.0 3.99 X l O " 3 s p e c t r a l 228 13.0 CoCl 2- ETU 2 0.95 X 10" 3 d i s t i l l e d 403 0.80 1.11 X 10" 3 it 440 0.44 2.22 X 10" 3 ti 465 0.47 CoCl 2-DMTU 2 2.03 X l O " 3 d i s t i l l e d 394 0.88 Co(o-N0 2-CgH 4C0 2) 2 6.38 X l O "3 n 42 450.0 •DMTU2 Co(p-Br-C,H.C0 2) - 6.88 X l O " 3 il 38 560.0 •TU 2 19.2 X 10" 3 n 82 460.0 Co(m-NO ?-C gH 4C0 2) 2 3.61 X 10"3 n 94 78.0 •TU 2 6.31 X 10" 3 " 129 76.0 8.25 X l o " 3 144 77.0 Co(m-N0 2-C,H 4C0 2) 2 6.52 X l O "3 tt 83 180.0 •DMTUj Co(m-N0 2-C gH 4C0 2) 2 6.10 X l O "3 76 180.0 •ETUj 4.71 X 10" 3 n 65 190.0 Co(p-NO,-CfiH.CO,) 2 8.60 X l O "3 it 73 300.0 •DMTU2 5.34 X 10' 3 33 340.0 * Measured at band maximum i n v i s i b l e region 128 In some cases E, v a l u e s were measured a f t e r a d d i t i o n of enough excess S - l i g a n d t o permit c a l c u l a t i o n of K a c c o r d i n g to equation (v). In these cases K valu e s in s a t i s f a c t o r y agreement with those given here were obt a i n e d . Values of K o b t a i n e d on s o l u t i o n s i n d i s t i l l e d acetone are c o n s i s t e n t l y g r e a t e r than those obtained on s o l u t i o n s i n s p e c t r a l grade acetone f o r the same complex.. T h i s i s p a r t i c u l a r l y n o t i c e a b l e 2+ i n the case of the CoS^ complexes where the e q u i l i b r i u m i s c l e a r l y very s e n s i t i v e t o t r a c e s o f water. R e s u l t s obtained on three complexes i n the pr e s e n t work are compared ( i n Table IV-18) with those o b t a i n e d p r e v i o u s l y by the NMR method. TABLE IV-18 Comparison of E q u i l i b r i u m Constant Values Between The Present Work and Pr e v i o u s Work Complex 10 K Previou s Present work work (132) d i s t i l l e d acetone s p e c t r a l acetone C o ( C l 0 4 ) 2 - T U 4 Co (C10 4) 2-DMTU 4 CoCl 0«TU~ 53.5 29 .4 1.5 ^ 0.4 ^63 ^ 4 ^10 ^ 0.5 ^ 0.2 129 Although the r e s u l t s o b t a i n e d i n the p r e s e n t work are r a t h e r approximate, there i s c l e a r l y poor agreement between the d i f f e r e n t s e t s of r e s u l t s . A major assumption i n the p r e s e n t method of determining K has been t h a t the s p e c i e s produced on d i s s o c i a t i o n do not absorb s i g n i f i c a n t l y i n the s p e c t r a l r e g i o n s t u d i e d . I f t h i s approximation i s not a v a l i d one then the K v a l u e s c a l c u l a t e d are too s m a l l and t h i s may account f o r the d i s c r e p a n c y seen i n the v a l u e s of K. I t seems more l i k e l y though t h a t the K v a l u e s are a l l a t l e a s t approximately c o r r e c t and the v a r i a t i o n among them a r i s e s from a v a r i a t i o n i n the water i m p u r i t y content of the acetone. Comparing v a l u e s of K f o r d i f f e r e n t complexes (where s o l v e n t used was d i s t i l l e d acetone) i t can be seen t h a t the v a l u e s f o r the c h l o r i d e s ( C o S 2 C l 2 complexes) f a l l -4 -4 i n the range of 0.3 x 10 to 0.9 x 10 , those f o r the 2+ -4 p e r c h l o r a t e s (CoS 4 complexes) f a l l i n the range 4 x 10 -4 t o 60 x 10 , and those f o r the c a r b o x y l a t e s (C0S2O2 complexes) f a l l i n the range 30 x 10~ 4 to 500 x 10~ 4. C l e a r l y the s t a b i l i t i e s of the complexes i n s o l u t i o n ( l i k e t h e i r e l e c t r o n i c spectra) are determined more by the nature o f the atoms bonded d i r e c t l y to the c e n t r a l cobalt i o n s than by any d i f f e r e n c e s i n the nature of the l i g a n d s beyond t h i s immediate c o b a l t environment. The c a r b o x y l a t e s are the l e a s t s t a b l e to S - l i g a n d d i s s o c i a t i o n and the c h l o r i d e s are the most s t a b l e . 130 CHAPTER V PYRIDINE COMPLEXES OF COBALT(II) CARBOXYLATES V-1. INTRODUCTION Stu d i e s on 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 have a t t r a c t e d c o n s i d e r a b l e a t t e n t i o n i n the pa s t . T r a n s i t i o n metal p e r c h l o r a t e s and t e t r a f l u o r o -borates form s t a b l e o c t a h e d r a l t e t r a k i s p y r i d i n e complexes (133, 134) while b i s p y r i d i n e d e r i v a t i v e s are common f o r metal h a l i d e s and pseudohalides (135, 136, 137, 138). In a paper devoted l a r g e l y t o a study of m e t a l - l i g a n d v i b r a t i o n s , C l a r k and W i l l i a m s (137) l i s t 29 metal b i s p y r i d i n e d e r i v a t i v e s , the s t r u c t u r e s of which range from monomeric t e t r a h e d r a l (e.g. ZnCl 9*py„) and square p l a n a r complexes 131 (e.g. t r ans-PtCl2'PY^' c i s - P t B r 2 • p y 2 ) to anion-bridged polymeric o c t a h e d r a l complexes (e.g. C u C l 2 « p y 2 ) . The complex C o C l 2 « p y 2 i s known as both a v i o l e t p olymeric o c t a h e d r a l isomer and a blue t e t r a h e d r a l isomer and the p r o p e r t i e s of these two isomers have been used to i l l u s t r a t e the r e l a t i o n between s t e r e o c h e m i s t r y and the magnetic and s p e c t r a l p r o p e r t i e s o f t r a n s i t i o n metal complexes (136). Complexes c o n t a i n i n g p y r i d i n e to metal mole r a t i o s o t h e r than two and fou r are l e s s common. A l l a n e t a l . (139) l i s t some examples o f he x a k i s - and monokis- p y r i d i n e complexes (e.g. FeCl 2«pyg, C d C l 2 « p y ) . T r i s p y r i d i n e complexes are found i n some n i t r a t e complexes (e.g. M ( N 0 3 ) 2 « p y 3 , M(N0 3) 2 ' p y 3 * 3py where M = Z n ( I I ) , C d ( I I ) , Hg(II) (140), Co ( I I ) , N i ( I I ) (141), Cu(II) (142).) A number of p y r i d i n e complexes of t r a n s i t i o n metal c a r b o x y l a t e s have been c h a r a c t e r i z e d (31, 40, 41, 143). The most e x t e n s i v e l y s t u d i e d are those of copper (II) where s t o i c h i o m e t r i e s C u ( R C 0 2 ) 2 • p y 2 and Cu(RC0 2) 2«py are common. The l a t t e r are e s t a b l i s h e d as d i m e r i c complexes having the b i n u c l e a r 'copper a c e t a t e ' s t r u c t u r e . S t u d i e s on the magnetic p r o p e r t i e s o f these complexes, i n p a r t i c u l a r , have i n c r e a s e d our understanding of e l e c t r o n i c and s t e r i c e f f e c t s of c a r b o x y l a t e groups i n t r a n s i t i o n metal complexes. Lever and Ogden (41) have r e p o r t e d the most d e t a i l e d study of p y r i d i n e c o b a l t (II) c a r b o x y l a t e complexes t o date. Magnetic and s p e c t r a l s t u d i e s on the complexes of formulae 132 C o ( C H n C l 3 _ n C 0 2 ) 2 . p y 2 , where n = 1, 2 or 3, and C o ( C F 3 C 0 2 ) 2 'PY show t h a t they c o n t a i n s i x - c o o r d i n a t e d c o b a l t w i t h , i t i s suggested, a t r a n s - C o O ^ ^ s t e r e o c h e m i s t r y about c o b a l t . T e t r a k i s p y r i d i n e d e r i v a t i v e s of the above complexes, w i t h the e x c e p t i o n of the monochloro- complex, were a l s o prepared and c h a r a c t e r i z e d . The p r e s e n t work, i n v o l v i n g mainly the p r e p a r a t i o n and study of p y r i d i n e c o b a l t ( I I ) a r y l c a r b o x y l a t e s , i s an e x t e n s i o n of Lever's work aimed at o b t a i n i n g a b e t t e r understanding of the e f f e c t of the nature of the c a r b o x y l a t e group on the s t r u c t u r a l and e l e c t r o n i c p r o p e r t i e s of t r a n s i t i o n metal complexes. To f a c i l i t a t e comparisons w i t h the work done p r e v i o u s l y , the a c e t a t e and the t r i f l u o r o -a c e t a t e complexes r e p o r t e d by Lever have been prepared again and s t u d i e d i n more d e t a i l i n t h i s work. V-2. SYNTHESIS AND STOICHIOMETRY V-2-1. S y n t h e s i s In the p r e s e n t work, attempts have been made to prepare a wide range of p y r i d i n e complexes of c o b a l t (II) a r y l c a r b o x y l a t e s of the g e n e r a l formula Co(R-CgH 4C0 2) 2*PY n; where n = 2 or 4 and R = H, N0 2, Br, CH 30, CH 3, C l , or NH 2 s u b s t i t u t e d i n e i t h e r ortho or para p o s i t i o n s . To f a c i l i t a t e comparison with known complexes, b i s p y r i d i n e c o b a l t ( I I ) a c e t a t e and b i s - and t e t r a k i s - p y r i d i n e c o b a l t ( I I ) t r i f l u o r o a c e t a t e were a l s o prepared i n the present work. Although f o u r d i f f e r e n t s y n t h e t i c routes to p y r i d i n e -133 c a r b o x y l a t e complexes were e x h a u s t i v e l y t e s t e d , no g e n e r a l method a p p l i c a b l e to the p r e p a r a t i o n of a l a r g e number of such complexes was found. Experimental d e t a i l s of a l l s y n t h e t i c methods are d i s c u s s e d below, c a t e g o r i z e d a c c o r d i n g to the methods used. Elemental analyses of a l l complexes prepared are c o l l e c t e d i n Table V - l . Method A Reaction of anhydrous c o b a l t ( I I )  c a r b o x y l a t e s with p y r i d i n e T h i s method has been used p r e v i o u s l y f o r the p r e p a r a t i o n of p y r i d i n e copper (II) a r y l c a r b o x y l a t e s (31) and f o r the p r e p a r a t i o n of p y r i d i n e complexes of c o b a l t ( I I ) and n i c k e l ( I I ) alkanoates (40, 143) and c h l o r o a c e t a t e s (40). T h i s method, of course, r e l i e s on the s u c c e s s f u l p r e p a r a t i o n of the anhydrous c o b a l t (II) c a r b o x y l a t e s as the s t a r t i n g m a t e r i a l s . Attempts to prepare the anhydrous compounds by simple d e h y d r a t i o n of the c o r r e s p o n d i n g hydrates a t e l e v a t e d temperatures i n g e n e r a l f a i l e d , l e a d i n g i n s t e a d to decomposition or b a s i c s a l t formation (as evidenced by elemental analyses and i n f r a r e d a n a l y s e s ) . However, i n the case of the p - n i t r o b e n z o a t e d e r i v a t i v e , d e h y d ration of the hydrated compound proceeded smoothly under vacuum at room temperature. The product of d e h y d r a t i o n r e a c t e d r e a d i l y with p y r i d i n e to y i e l d the r e q u i r e d p y r i d i n e complex. P r e p a r a t i o n of Bi:spyridine C o b a l t (II) p -Nitrobenzoate: C o ( p-NQ 2-C 6H 4C0 2) 2-py 2 C o b a l t ( I I ) p - n i t r o b e n z o a t e hexahydrate (12.5 g.) 134 TABLE V - l A n a l y t i c a l Results of Pyr id ine Complexes Complex Experimental weight percentages (Calculated % i n brackets) C F 3 C 0 2 ) 2 . p y 4 C F 3 C 0 2 ) 2 . p y 2 C H 3 C 0 2 ) 2 . p y 2 C 6 H 5 C 0 2 ) 2 . p y 2 P - C H 3 O - C 6 H 4 C O 2 ) 2 - p y 2 p - B r - C 6 H 4 C 0 2 ) 2 . p y 2 p - N 0 2 - C 6 H 4 C 0 2 ) 2 . p y 2 o - B r - C 6 H 4 C 0 2 ) 2 . p y 2 o - N 0 2 - C 6 H 4 C 0 2 ) 2 . p y 2 p - C H 3 - C 6 H 4 C 0 2 ) 2 . p y 2 . H 2 0 o - C H 3 - C g H 4 C 0 2 ) 2 . py 2 . J5H20 o - C H 3 0 - C 6 H 4 C 0 2 ) 2 . p y 2 . H 2 0 P - C I - C 6 H 4 C O 2 ) 2 - p y 2 - H 2 ° P - N H 2 - C 6 H 4 C 0 2 ) 2 . p y 2 . H 2 0 p - B r - C g H 4 C 0 2 ) 2 - p y 2 - H 2 ° P - N 0 2 - C 6 H 4 C 0 2 ) 2 - P y 2 - 2 H 2 ° Co C H N 9. 74 47. 65 3. 45 9. 36 ( 9. 80 47. 93 3. 35 9. 32) 13. 06 37. 28 2. 23 5. 98 (13. 30 37. 94 2. 27 6. 32) 17. 16 49. 86 5. 15 8. 40 (17. 57 50. 15 4. 81 8. 36) 12. 83 62. 54 4. 16 6. 24 (12. 83 62. 75 4. 39 6. 10) 11. 15 60. 40 4. 58 5. 31 (11. 34 60. 12 4. 66 5. 39) 9. 40 46. 58 3. 06 4. 45 ( 9. 55 46. 70 2. 94 4. 54) 10. 51 52. 77 3. 41 10. 35 (10. 73 52. 47 3. 30 10. 20) 9. 41 46. 40 3. 00 4. 53 ( 9. 55 46. 70 2. 94 4. 54) 10. 50 52. 24 3. 47 10. 00 (10. 73 52. 47 3. 37 10. 20) 11. 49 61. 68 5. 10 5. 36 (11. 66 61. 78 5. 19 5. 54) 11. 69 62. 70 4. 95 5. 55 (11. 87 62. 90 5. 07 5. 64) 11. 08 58. 58 4. 81 5. 60 (10. 97 58. 10 4. 88 5. 21) 10. 71 52. 60 3. 55 4. 91 (10. 79 52. 77 3. 69 5. 13) 11. 61 57. 04 4. 60 10. 86 (11. 61 56. 80 4. 37 11. 04) 8. 92 45. 53 3. 07 4. 30 ( 9. 28 45. 38 3. 17 4. 41) 10. 01 49. 46 4. 18 10. 07 (10. 07 49. 24 3. 79 9. 57) 135 was d r i e d under vacuum a t room temperature f o r one day. The c o l o u r of the m a t e r i a l changed from pink of the hydrated compound to b l u e . As the i n f r a r e d spectrum of the blue product i n d i c a t e d the absence of water, i t was assumed to be the anhydrous s a l t . P y r i d i n e (4.0 g.) was then added to a suspension of t h i s blue compound i n 5 0 ml. of benzene, y i e l d i n g a r e d s o l u t i o n . Hexanes (commercially a v a i l a b l e , as a mixture of i t s isomers) was then added dropwise t o the s o l u t i o n r e s u l t i n g i n the p r e c i p i t a t i o n of a pink-brown product. A f t e r f i l t e r i n g , the product was washed s e v e r a l times with hot benzene. Although t h i s process reduced the y i e l d , due to the s o l u b i l i t y of the product i n hot benzene, the remains from the washing y i e l d e d the d e s i r e d p y r i d i n e complex. R e c r y s t a l l i z a t i o n from hot benzene gave a product having a h i g h e r c o b a l t weight percentage presumably due to l o s s of p y r i d i n e or decomposition d u r i n g the r e c r y s t a l l i z a t i o n p r o c e s s . Method B Reaction of c o b a l t ( I I ) c a r b o x y l a t e  hydrates w i t h p y r i d i n e . In view of the d i f f i c u l t i e s encountered i n attempting to dehydrate the c o b a l t (II) a r y l c a r b o x y l a t e hydrates, as d i s c u s s e d above, i t was d e c i d e d to attempt r e a c t i o n s of the hydrates themselves w i t h p y r i d i n e . I t was hoped t h a t p y r i d i n e would simply r e p l a c e the c o o r d i n a t e d water i n these complexes and y i e l d the d e s i r e d p y r i d i n e complexes. T h i s 136 g e n e r a l approach has not been used before i n p r e p a r i n g s i m i l a r c o b a l t (II) p y r i d i n e - c a r b o x y l a t e complexes. With the e x c e p t i o n of the a c e t a t e and the p-methoxybenzoate d e r i v a t i v e s , t h i s approach y i e l d e d mixed p y r i d i n e - h y d r a t e complexes. S e v e r a l of these mixed complexes were a l s o c h a r a c t e r i z e d i n t h i s work and p r e p a r a t i v e d e t a i l s and elemental analyses f o r these complexes are g i v e n below. Attempts to dehydrate these mixed p y r i d i n e -hydrate complexes by v a r i o u s methods of washing, d r y i n g , aging and r e c r y s t a l l i z i n g were i n g e n e r a l u n s u c c e s s f u l , l e a d i n g u s u a l l y to l o s s of p y r i d i n e and/or decomposition. Again, t h e r e was one e x c e p t i o n t o t h i s g e n e r a l phenomenon. B i s p y r i d i n e c o b a l t ( I I ) p-bromobenzoate monohydrate d r i e d over potassium hydroxide i n a d e s i c c a t o r f o r about one month y i e l d e d b i s p y r i d i n e c o b a l t (II) p-bromobenzoate. P r e p a r a t i o n of B i s p y r i d i n e C o b a l t (II) A c e t a t e : CojCH 3C0 2)_ 2 -py 2 Commercially s u p p l i e d anhydrous c o b a l t ( I I ) a c e t a t e was found to be impure and not s u i t a b l e as the s t a r t i n g m a t e r i a l . Attempts u s i n g the method employed by Davis and Logan (143) to prepare the anhydrous s a l t by r e f l u x i n g c o b a l t ( I I ) carbonate with a c e t i c a c i d with subsequent e v a p o r a t i o n of the f i l t e r e d s o l u t i o n to dryness f a i l e d due to the formation of b a s i c s a l t . Another method used by Edwards and Hayward (38) i n v o l v i n g r e f l u x i n g the commercially 137 ava i l ab le cobalt (II) acetate tetrahydrate with an excess of an ace t i c ac id-ace t i c anhydride mixture was a lso t r i e d without success. A l t e r n a t i v e l y , the hydrated s a l t was used as the s t a r t ing mater ia l and the preparative method used by Maggio et a l . (40) was modified to prepare the des ired complex. Commercially ava i l ab le cobalt ( II ) acetate tetrahydrate (12.5 g.) was suspended i n 100 ml . of chloroform. Pyr id ine was added u n t i l d i s s o l u t i o n was complete. The so lu t ion was f i l t e r e d and petroleum ether (reagent grade) was added dropwise u n t i l p r e c i p i t a t i o n occurred. The red product was f i l t e r e d , washed with petroleum ether, then ground up and kept i n a des iccator saturated with pyr id ine vapour for several days. Preparation of B i spyr id ine Cobalt(II) p-Methoxybenzoate: CO (p-CH 3O-CgH 4CO 2 )_2-py2 Hydrated cobalt ( I I ) p-methoxybenzoate was prepared i n a manner analogous to that used i n the preparation of other hydrates. The degree of hydration i n t h i s case was not determined. Ten grams of the hydrate was d i s so lved i n 100 ml . of pyr id ine and approximately 20 ml . of reagent grade d i e t h y l ether was added to the s o l u t i o n . The f i l t e r e d so lu t ion was then l e f t standing at room temperature for one day when grayish c ry s t a l s of the b i spyr id ine complex were obtained. 138 P r e p a r a t i o n of B i s p y r i d i n e C o b a l t ( I I ) p-Bromobenzoate  monohydrate: Co (p-Br-CgH^CC^) 2 , p y 2 ' H 2 0 a n < ^ B i s p y r i d i n e  C o b a l t (II) p-Bromobenzoate: Co (p-Br-C^ H ^ CO^ )_2 IPy 2 C o b a l t (II) p-bromobenzoate t r i h y d r a t e (10 g.) was suspended i n 100 ml. of c h l o r o f o r m and p y r i d i n e was added slo w l y u n t i l complete d i s s o l u t i o n . Petroleum e t h e r was then added dropwise 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 and the pink product was f i l t e r e d and washed with petroleum e t h e r . The i n f r a r e d spectrum of the product i n d i c a t e d the presence of water and elemental analyses showed i t to be b i s p y r i d i n e c o b a l t (II) p-bromobenzoate monohydrate. Drying the product i n a d e s i c c a t o r over potassium hydroxide f o r about one month gave the pink 'anhydrous' b i s p y r i d i n e complex. P r e p a r a t i o n of B i s p y r i d i n e C o b a l t ( I I ) p-Methylbenzoate  Monohydrate : Co (p-CH 3-C 6H^CC» 2) 2 'PY2 •H2° T h i s was prepared i n the same way as the corresponding p-bromobenzoate d e r i v a t i v e . F u r t h e r attempts t o dry t h i s product, as d e s c r i b e d e a r l i e r , f a i l e d t o y i e l d the anhydrous b i s p y r i d i n e complex. P r e p a r a t i o n of B i s p y r i d i n e C o b a l t ( I I ) p-Chlorobenzoate  Monohydrate: Co(p-Cl-C^H^CO,,) 2•py 2•H 20 T h i s was prepared i n the same way as the corresponding p-bromobenzoate d e r i v a t i v e . F u r t h e r attempts to dry t h i s product f a i l e d . 139 Preparation of Bispyridine Cobalt(II) p-Nitrobenzoate  Dihydrate : Co (p-NC^-CgH^CO,)) 2 'PY2 ' H^^ O This was prepared i n the same way as the corresponding p-bromobenzoate derivative. Further attempts to dry t h i s product f a i l e d . However, the 'anhydrous' bispyridine derivative was successfully prepared by method A. Method B was also applied to a number of other arylcarboxylates and i n each case a mixed pyridine-hydrate complex was formed. No further i d e n t i f i c a t i o n was made of these complexes. As further 'drying' f a i l e d to give the 'anhydrous' bispyridine complexes another preparative route was adopted. Method C Reaction of carboxylic acids with cobalt(II) carbonate and pyridine Previous use of t h i s method to prepare pyridine complexes i s l i m i t e d to the work of Lever and Ogden (41) on the preparation of haloacetate derivatives. In the present work, several complexes were successfully prepared by t h i s method and experimental d e t a i l s are given below. Preparation of Bispyridine Cobalt (II) Benzoate: COJC 6H 5C0 21 2 1 £ Z 2 Benzoic acid (12 g.) was mixed with a s l i g h t excess of cobalt(II) carbonate (7 g.) i n 100 ml. of pyridine and the mixture was refluxed for two hours. It was then f i l t e r e d and an equal volume of reagent grade d i e t h y l ether was added 140 to the f i l t r a t e . On s t a n d i n g f o r two days, the complex p r e c i p i t a t e d as a pink s o l i d which was f i l t e r e d and washed wit h d i e t h y l e t h e r . P r e p a r a t i o n of B i s p y r i d i n e C o b a l t ( I I ) o-Bromobenzoate: Co (o-Br-CgH^COgl2'JEL2 A mixture of o-bromobenzoic a c i d (20 g.) and c o b a l t (II) carbonate (7 g.) i n 100 ml. of p y r i d i n e was r e f l u x e d f o r two hours. The mixture was then f i l t e r e d and reagent grade d i e t h y l e t h e r was added t o the f i l t r a t e u n t i l c l o u d i n e s s was observed. P r e c i p i t a t i o n was almost complete a f t e r two days' aging. The pink product was f i l t e r e d , f i n e l y ground and washed wi t h d i e t h y l e t h e r . P r e p a r a t i o n of B i s p y r i d i n e C o b a l t ( I I ) o-Nitrobenzoate: Co ( o - N 0 2 - C g C O 2 )_2 -py 2 A mixture of o - n i t r o b e n z o i c a c i d (16 g.) and c o b a l t ( I I ) carbonate (7 g.) i n 100 ml. of p y r i d i n e was r e f l u x e d f o r two hours. I t was then f i l t e r e d and reagent grade d i e t h y l e t h e r was added. A f t e r aging f o r about two days, p r e c i p i t a t i o n was almost complete. The pink product thus o b t a i n e d was found to c o n t a i n a lower weight percentage of c o b a l t than t h a t expected f o r the d e s i r e d b i s p y r i d i n e complex. The i n f r a r e d spectrum a l s o i n d i c a t e d the presence of water and a mixed p y r i d i n e - h y d r a t e complex was suspected. T h i s mixed complex was found to be s o l u b l e i n hot benzene and the f i n a l p ink product o b t a i n e d on r e c r y s t a l l i z a t i o n from benzene was i d e n t i f i e d as the d e s i r e d b i s p y r i d i n e complex. 141 P r e p a r a t i o n of B i s p y r i d i n e C o b a l t (II) T r i f l u o r o a c e t a t e :  C o ( C F 3 C 0 2 ) 2 » p y 2 The experimental procedure was adopted from t h a t of Lever and Ogden (41). T r i f l u o r o a c e t i c a c i d (14.8 g.) was r e f l u x e d with excess c o b a l t (II) carbonate (10 g.) i n 200 ml. of 100% e t h a n o l f o r three hours. The mixture was f i l t e r e d and p y r i d i n e (10.3 g.) was added to the f i l t r a t e ( i n a mole r a t i o of 1:1 f o r a c i d : p y r i d i n e ) . The volume of the s o l u t i o n was allowed to decrease to about 50 ml. by e v a p o r a t i o n when red c r y s t a l s p r e c i p i t a t e d s l o w l y . The c r y s t a l s were f i l t e r e d and washed with 100% e t h a n o l . Elemental and i n f r a r e d s p e c t r a l analyses i n d i c a t e d excess p y r i d i n e i n the complex. In an attempt to r e c r y s t a l l i z e t h i s product from hot benzene, i t was found t h a t , by washing the product with b o i l i n g benzene, the d e s i r e d b i s p y r i d i n e complex was o b t a i n e d . P r e p a r a t i o n of T e t r a k i s p y r i d i n e C o b a l t ( I I ) T r i f l u o r o a c e t a t e : Co(CF 3 CO 2 )_2-py^ The experimental procedure used f o r t h i s p r e p a r a t i o n was analogous t o t h a t d e s c r i b e d by Lever and Ogden (41). To a s o l u t i o n of t r i f l u o r o a c e t i c a c i d (14.8 g.) i n 200 ml. of 100% e t h a n o l was added an excess of reagent grade c o b a l t ( I I ) carbonate (10 g.) and the mixture was r e f l u x e d f o r three hours. Excess of p y r i d i n e (about 40 g.) was then added to the f i l t e r e d s o l u t i o n . Red c r y s t a l s were obtained immediately and were washed with 100% e t h a n o l . 142 P r e p a r a t i o n of B i s p y r i d i n e C o b a l t ( I I ) p-Aminobenzoate  Monohydrate : Co (p-NH^-Cgl^CO,)) 2 >PY2 • H 2 ° In an attempt t o prepare the b i s p y r i d i n e c o b a l t ( I I ) p-aminobenzoate a mixed p y r i d i n e - h y d r a t e complex was obtai n e d . The compound c o u l d not be 'dehydrated' t o y i e l d the b i s p y r i d i n e d e r i v a t i v e without the l o s s o f p y r i d i n e or decomposition. The mixed complex i n t h i s case was i d e n t i f i e d by elemental a n a l y s e s . P-aminobenzoic a c i d (13.7 g.) and c o b a l t ( I I ) carbonate (10 g.) were r e f l u x e d i n 100 ml. of p y r i d i n e f o r three hours. The mixture was f i l t e r e d and d i e t h y l e t h e r was added t o the f i l t r a t e . On sta n d i n g f o r two days, pink c r y s t a l s formed. These were f i l t e r e d and washed wit h d i e t h y l e t h e r . Elemental and i n f r a r e d r e s u l t s on t h i s complex i d e n t i f i e d i t as a mixed p y r i d i n e - h y d r a t e complex. Attempts were a l s o made t o prepare the b i s p y r i d i n e complexes of other a r y l c a r b o x y l a t e d e r i v a t i v e s (such as p-CH 3-, o-CH^-, p - C l - , o - C l - and o-CH^O- benzoates) by method C. In ge n e r a l as above the formation of mixed p y r i d i n e - h y d r a t e complex seemed favoured. Some of these complexes were f u r t h e r i d e n t i f i e d by elemental a n a l y s e s . In g e n e r a l , t h i s phenomenon was e x p e r i m e n t a l l y r e p r o d u c i b l e and the mixed complexes so formed c o u l d not be e a s i l y dehydrated. 143 Method D Reaction of a r y l c a r b o x y l i c a c i d s w i t h  b i s p y r i d i n e c o b a l t ( I I ) a c e t a t e In view of the many d i f f i c u l t i e s e xperienced i n o b t a i n i n g "anhydrous" b i s p y r i d i n e complexes, the f o l l o w i n g s y n t h e t i c method was attempted: By r e a c t i n g b i s p y r i d i n e c o b a l t ( I I ) a c e t a t e with an a r y l c a r b o x y l i c a c i d i n the presence of p y r i d i n e , i t was hoped t h a t the a c e t a t e groups c o u l d be r e p l a c e d by the a r y l c a r b o x y l a t e groups. In f a c t , t h i s was a c t u a l l y observed. B i s p y r i d i n e c o b a l t (II) benzoate, which was s u c c e s s f u l l y prepared by method C, was a l s o prepared by t h i s method. The d e s c r i p t i o n below serves to i l l u s t r a t e the g e n e r a l procedure. B i s p y r i d i n e c o b a l t (II) a c e t a t e (3.4 g.) and benzoic a c i d (2.7 g.) were d i s s o l v e d i n 50 ml. of p y r i d i n e . To the f i l t e r e d s o l u t i o n , 10 0 ml. of d i e t h y l e t h e r was added. On s t a n d i n g , pink c r y s t a l s p r e c i p i t a t e d s l o w l y . The product was then f i l t e r e d and washed with d i e t h y l e t h e r . The i n f r a r e d spectrum of the product resembled completely to t h a t of b i s p y r i d i n e c o b a l t ( I I ) benzoate with the absence of bands due to a c e t a t e group and water. Elemental analyses p r o v i d e d f u r t h e r p r o o f : ( c a l c u l a t e d f o r b i s p y r i d i n e c o b a l t ( I I ) benzoate: Co: 12.83%, C: 62.75%, N: 6.10%, H: 4.36%; found: Co: 12.81%, C: 62.93%, N: 6.42%, H: 4.45%.) While the above example i n d i c a t e d the p o s s i b i l i t y of a t o t a l l y d i f f e r e n t p r e p a r a t i v e route to new p y r i d i n e 144 complexes, t h i s method was found t o be s u c c e s s f u l o n l y f o r some of the b i s p y r i d i n e complexes which had a l r e a d y been prepared by other means (such as the benzoate, the t r i f l u o r o a c e t a t e and the p-bromobenzoate d e r i v a t i v e s ) . Attempts to prepare other a r y l c a r b o x y l a t e complexes f a i l e d as n o n - s t o i c h i o m e t r i c amount of p y r i d i n e was u s u a l l y found i n the p r o d u c t s . Removal of excess p y r i d i n e ( i . e . a p y r i d i n e : c o b a l t mole r a t i o of s l i g h t l y g r e a t e r than 2:1) was found to be extremely d i f f i c u l t . T h i s would be seen from an i l l u s t r a t e d example below. B i s p y r i d i n e c o b a l t (II) a c e t a t e and p-methylbenzoic a c i d were mixed i n a 1:2 mole r a t i o i n p y r i d i n e . D i e t h y l e t h e r was added to the f i l t e r e d s o l u t i o n and on s t a n d i n g a pink product p r e c i p i t a t e d out. The i n f r a r e d spectrum of the product showed the absence of water but i n d i c a t e d the presence of f r e e p y r i d i n e . Elemental analyses showed a low c o b a l t content as w e l l as a high carbon and n i t r o g e n content f o r a b i s p y r i d i n e complex. However, no formation of a 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 was observed. Washing with v a r i o u s o r g a n i c s o l v e n t s f a i l e d to produce a pure complex. V-2-2. S t o i c h i o m e t r y Two types of p y r i d i n e complexes have been observed f o r c o b a l t ( I I ) c a r b o x y l a t e s , namely, the b i s p y r i d i n e and the t e t r a k i s p y r i d i n e d e r i v a t i v e s . While both b i s - and t e t r a k i s -145 p y r i d i n e complexes have been prepared f o r most h a l o a c e t a t e s , o n l y the b i s p y r i d i n e forms of the a l k y l c a r b o x y l a t e s have been prepared (41). Lever and Ogden (41) found t h a t the c o b a l t (II) s a l t s of t r i f l u o r o a c e t i c a c i d (pK - 0) , 3. t r i c h l o r o a c e t i c a c i d (pK = 0.89) and d i c h l o r o a c e t i c a c i d cl (pK & = 1.30) formed both b i s - and t e t r a k i s - p y r i d i n e complexes while the c o b a l t ( I I ) s a l t s of monochloroacetic a c i d (pK^ = 2.85) and a c e t i c a c i d (pK = 4.75) formed a a b i s p y r i d i n e complexes o n l y . These r e s u l t s suggest a c o r r e l a t i o n between the base s t r e n g t h of the c a r b o x y l a t e group, as measured by the pK of the parent a c i d , and the cl s t a b i l i t y of t e t r a k i s p y r i d i n e complexes:- the weaker the base s t r e n g t h of the c a r b o x y l a t e anion (lower the pK ), a the g r e a t e r the s t a b i l i t y of the 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 s t u d i e s done on the a r y l c a r b o x y l a t e s e r i e s i n the present work confirms t h i s c o r r e l a t i o n i n t h a t o n l y b i s p y r i d i n e d e r i v a t i v e s of these c o b a l t ( I I ) compounds c o u l d be i s o l a t e d . Attempts to prepare and i s o l a t e t h e i r t e t r a k i s p y r i d i n e d e r i v a t i v e s by r e a c t i o n s i n v o l v i n g very l a r g e excesses of p y r i d i n e f a i l e d i n a l l cases. Since the pK v a l u e s of the a parent a r y l c a r b o x y l i c a c i d s s t u d i e d i n the p r e s e n t work range from 2.17 f o r o - n i t r o b e n z o i c a c i d to 4.47 f o r p-methoxybenzoic, i t seems u n l i k e l y t h a t s t a b l 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 s of c o b a l t ( I I ) c a r b o x y l a t e s w i l l be formed u n l e s s the pK value of the parent a c i d i s l e s s than 2.17. 146 V-3. CHARACTERIZATION OF COMPLEXES Although there appears t o be no ^ - r a y s t r u c t u r e d e t e r m i n a t i o n of a p y r i d i n e c o b a l t ( I I ) c a r b o x y l a t e complex r e p o r t e d i n the l i t e r a t u r e , a l l p r e v i o u s s t u d i e s on the magnetic and s p e c t r a l p r o p e r t i e s (31, 40, 41, 143) of these complexes i n d i c a t e t h a t they have s i x - c o o r d i n a t e d c o b a l t (II) ions w i t h e i t h e r a CoN 20 4 or a CoN^O.^ l o c a l environment about c o b a l t . T h i s served as a s t a r t i n g p o i n t i n the a n a l y s i s of the magnetic and s p e c t r a l p r o p e r t i e s of the a r y l c a r b o x y l a t e complexes s t u d i e d i n the presen t work and, as w i l l be shown, the r e s u l t s are c o n s i s t e n t with t h i s g e n e r a l p i c t u r e . V-3-1. I n f r a r e d S p e c t r a l Study Because of the very complex nature of the molecules, the i n f r a r e d s p e c t r a o f the p y r i d i n e complexes s t u d i e d i n the p r e s e n t work show, i n g e n e r a l , a very l a r g e number of a b s o r p t i o n bands. Although t h i s makes a complete and d e t a i l e d a n a l y s i s d i f f i c u l t , p a r t i a l assignments i n v o l v i n g the i d e n t i f i c a t i o n of bands a r i s i n g from v i b r a t i o n s of p y r i d i n e as w e l l as the c a r b o x y l a t e -C0 2 group are obt a i n e d . The s p e c t r a are of use i n c o n f i r m i n g the absence or presence of water i n the complexes to support the a n a l y t i c a l data. None of the anhydrous p y r i d i n e complexes show avbroad band i n the 3550 - 3200 cm 1 r e g i o n , a s c r i b e d to the presence of water (126), whereas the corresponding hydrated p y r i d i n e 147 complexes e x h i b i t t h i s band. I n f r a r e d s p e c t r a were a l s o used to d e t e c t excess and uncoordinated p y r i d i n e i n the course of the p r e p a r a t i o n and p u r i f i c a t i o n of the p y r i d i n e complexes. P a r t i a l assignments of p y r i d i n e and c a r b o x y l a t e s t r e t c h i n g v i b r a t i o n s are d i s c u s s e d below. P y r i d i n e V i b r a t i o n s In s p i t e of the very complex nature of the s p e c t r a , i t proved r e l a t i v e l y easy to a s s i g n the p y r i d i n e v i b r a t i o n s . T h i s was done by comparing the spectrum of a p y r i d i n e complex w i t h those of the c o r r e s p o n d i n g hydrated s a l t and p y r i d i n e . By simple v i s u a l comparison of the three s p e c t r a , the p y r i d i n e v i b r a t i o n s i n the complex are i n g e n e r a l i d e n t i f i e d as sharp bands, i n some i n s t a n c e s s h i f t e d t o h i g h e r frequency than i n f r e e p y r i d i n e . An example i s shown i n F i g u r e V - l f o r the b i s p y r i d i n e c o b a l t ( I I ) p - n i t r o b e n z o a t e complex. For the r e s t of the complexes s t u d i e d i n t h i s work, s i m i l a r comparisons were made y i e l d i n g reasonably c e r t a i n assignments. To a f i r s t approximation, the v i b r a t i o n s of p y r i d i n e when c o o r d i n a t e d to a heavy metal do not i n g e n e r a l i n v o l v e the v i b r a t i o n of the m e t a l - n i t r o g e n bond (135). Through a d i r e c t comparison of the s p e c t r a of p y r i d i n e and i t s complexes, i t should then be p o s s i b l e to d e s c r i b e the observed bands i n terms of the corresponding f r e e p y r i d i n e v i b r a t i o n s . Previous work on a number of m e t a l - p y r i d i n e complexes (135) has i d e n t i f i e d changes i n s e v e r a l ' c r i t i c a l ' bands on c o o r d i n a t i o n ; changes which may be used as c r i t e r i a 1600 "~' T200 ' cTuTT ' 5TJ0 Frequency cm F i g u r e V - l . I d e n t i f i c a t i o n of P y r i d i n e Bands i n the I n f r a r e d Spectrum (17.00 - 400 cm - 1) of Co (p-N0 2~C 6H 4C0 2) 2 - p y 2 as an Example 149 f o r p y r i d i n e c o o r d i n a t i o n . A b r i e f d e s c r i p t i o n of these ' c r i t i c a l ' changes i s given i n Table V-2. TABLE V-2 Changes of ' C r i t i c a l ' P y r i d i n e Bands as C r i t e r i a f o r P y r i d i n e C o o r d i n a t i o n (135) Band P o s i t i o n Band P o s i t i o n (Coordinated Band Band (Free P y r i d i n e ) P y r i d i n e ) D e s c r i p t i o n N o t a t i o n * (cm - 1) (cm - 1) (144) (145) 1578 ^ 1600 i n - p l a n e r i n g def. 8a 1478 ^ 1483 II 19a 1436 ^ 1442 19b 991 ^ 1008 i n - p l a n e r i n g bre. 1 601 ^ 625 i n - p l a n e r i n g def. 6a 403 ^ 420 out - o f - p l a n e r i n g def. 16b * numbers d e s i g n a t e the fundamental modes of v i b r a t i o n s of p y r i d i n e d e s c r i b e d by K l i n e and T u r k e v i c h (145). a and b desig n a t e symmetric and antisymmetric r e s p e c t i v e l y . The c r i t i c a l bands are a l l observed t o s h i f t to hi g h e r frequency on c o o r d i n a t i o n . T h i s phenomenon has been a t t r i b u t e d t o an i n c r e a s e i n the e l e c t r o n d e n s i t y i n the 150 p y r i d i n e r i n g due to d^ - p^ bonding i n v o l v i n g t r a n s f e r of e l e c t r o n d e n s i t y from metal 'd' o r b i t a l s i n t o the c o r r e s -ponding 'p' o r b i t a l s of the p y r i d i n e r i n g (135). The c r i t i c a l p y r i d i n e r i n g v i b r a t i o n s of the p y r i d i n e complexes s t u d i e d i n t h i s work are i d e n t i f i e d and the r e s u l t s are c o l l e c t e d i n Table V-3. TABLE V-3 C r i t i c a l P y r i d i n e Ring V i b r a t i o n s of P y r i d i n e Complexes of C o b a l t ( I I ) Carboxylates Band P o s i t i o n i n Free P y r i d i n e 1578 1478 1436 991 601 403 Band N o t a t i o n 8a 19a 19b 1 6a 16b Expected S h i f t on C o o r d i n a t i o n 1600 1483 1442 1008 625 420 C o ( C F 3 C 0 2 ) 2 - p y 4 1600 1486 1445 1010 628 422 C o ( C F 3 C 0 2 ) 2 « p y 2 1602 1486 1445 1010 628 426 co ( C H 3 C O 2 ) 2 * p y 2 1602 1486 1446 1011 627 425 Co (p-CH 30-C 6H 4CO 2 ) 2 * P y 2 1602 1485 1446 1010 629 422 C o ( C 6 H 5 C 0 2 ) 2 . p y 2 1602 1488 1447 1010 624 428 Co(p-Br-C 6H 4C0 2) 2*P^2 1600 1484 1444 1012 628 425 Co (p-N0 2-C 6H 4C0 2 V p y 2 1600 1482 1444 1012 628 422 Co (o-Br-C 6H 4C0 2) 2 - p y 2 1602 1486 1445 1012 624 420 Co (o-N0 2-C 6H 4C0 2 >2*Py2 1602 1488 1447 1012 629 424 A l l u n i t s i n cm 151 The g e n e r a l o b s e r v a t i o n i s t h a t these v i b r a t i o n s are indeed s h i f t e d t o h i g h e r frequency i n the s p e c t r a of the complexes, to an ext e n t as expected f o r p y r i d i n e c o o r d i n a t i o n . F u r t h e r -more, the f r e q u e n c i e s of these sharp and i n t e n s e p y r i d i n e bands do not vary s i g n i f i c a n t l y from one p y r i d i n e complex to another, as found f o r p y r i d i n e complexes i n g e n e r a l (135). I t i s p o s s i b l e t o d e t e c t uncoordinated or ' l a t t i c e ' p y r i d i n e i n complexes from i n f r a r e d s p e c t r a , as t h i s p y r i d i n e e x h i b i t s the above c r i t i c a l a b s o r p t i o n s v i r t u a l l y unchanged from those observed i n pure p y r i d i n e . L a t t i c e p y r i d i n e has p r e v i o u s l y been d e t e c t e d by t h i s technique i n the f o l l o w i n g complexes: N i X 2 « p y 4 « 2 p y (X = NCS - and NCSe") (146), F e X 2 « p y 4 « 2 p y (X = i " and NCO~) (147), Cu (NC>3) 2 « p y 4 « 2py (148) and M ( N 0 3 ) 2 « p y 3 « 3 p y (M = Co (II) and N i ( I I ) ) (141). In the pr e s e n t study, no evidence of l a t t i c e p y r i d i n e was found f o r any of the b i s p y r i d i n e complexes. T h i s can be seen from the example g i v e n e a r l i e r i n F i g u r e V - l , i n which the f r e e p y r i d i n e v i b r a t i o n s do not reappear i n the spectrum o f the complex. The spectrum o f the t e t r a k i s p y r i d i n e complex of c o b a l t ( I I ) t r i f l u o r o a c e t a t e , however, shows very weak bands a t 991 cm \ 600 cm 1 and 402 cm 1 which may a r i s e from l a t t i c e p y r i d i n e . The very low i n t e n s i t y of these bands, on the other hand, suggest t h a t they probably a r i s e from t r a c e s o f p y r i d i n e d i s s o c i a t e d i n the mulls or l i b e r a t e d on p e l l e t - m a k i n g . T h i s o b s e r v a t i o n i s i n accordance with the r e s u l t , to be obtained and d i s c u s s e d l a t e r , t h a t of a l l the p y r i d i n e 152 complexes s t u d i e d , the t e t r a k i s p y r i d i n e complex i s the l e a s t s t a b l e towards p y r i d i n e d i s s o c i a t i o n . Carboxylate (-CO^) V i b r a t i o n s In c o n t r a s t to the f o r e g o i n g p y r i d i n e bands assignment, i d e n t i f i c a t i o n of i n f r a r e d bands a r i s i n g p r i m a r i l y from the fundamental modes of the -CO^ group i s not an easy matter. Previous work (41) has shown t h a t p y r i d i n e complexes of c o b a l t ( I I ) a c e t a t e and h a l o a c e t a t e e x h i b i t a t l e a s t one major antisymmetric and one major symmetric -CC^ s t r e t c h i n g mode. The bands, which are i n the range of 1700 - 1350 cm - 1, are u s u a l l y i n t e n s e , broad and sometimes r a t h e r s t r u c t u r a l with one or more sh o u l d e r s . Using t h i s i n f o r m a t i o n and by comparing the s p e c t r a w i t h those of r e l a t e d molecules, the i n f r a r e d s p e c t r a of a l l the complexes s t u d i e d i n t h i s work were examined i n the range of 1700 - 1300 c m - 1 (as there i s no a b s o r p t i o n i n the r e g i o n 1700 - 2000 cm ^) and very t e n t a t i v e assignments to the -CG^ s t r e t c h i n g v i b r a t i o n s were made. D e t a i l s are given below. The s p e c t r a of b 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 c o b a l t ( I I ) t r i f l u o r o a c e t a t e s and b i s p y r i d i n e c o b a l t ( I I ) a c e t a t e are re-examined here i n an attempt to o b t a i n an independent assignment of the two -CC>2 s t r e t c h i n g f r e q u e n c i e s . The f i r s t two complexes are t r e a t e d u s i n g the r e s u l t s and assignments p r e v i o u s l y r e p o r t e d on the s p e c t r a of c o b a l t ( I I ) t r i f l u o r o a c e t a t e (39) , sodium t r i f l u o r o a c e t a t e (149) and p y r i d i n e (135). The s p e c t r a are reproduced i n F i g u r e V-2 and the data summarized i n Table V-4. TABLE V-4 I n f r a r e d S p e c t r a l Data and Assignments (1800 - 1300 cm - 1) of T r i f l u o r o a c e t a t e Compounds and P y r i d i n e Co (CF3< C 0 2 ) 2 I P Y _ 2 C o ( C F 3 C 0 o ) o - p y d P y r i d i n e C o ( C F o C 0 o ) o Na(CF oC0 o), Assignment T h i s Previous T h i s Previous Work Work (41) Work Work(41) (135) (39) (149) 1710sh 1695b 1695 1667sh 1685b 1690 1653 1627w 1660 1689s v a n t i - C 0 2 py'l+6b' +'6a+12' 1622s 1593m py'l+6a' 1602s 1600s 1578s 1570w py'8a' py•8b' 1486s 1495s 1478m py'19a' 1486s 1445s 1445s py'19b' 1450sh 1350 1422s 1420 1436s 1440 1446w Vsym-C0 2 1380vw 1370vw 1372w py'14' 1350vw 1320vw 1350w py'6a+10b' - a l l u n i t s i n cm 154 TTOO 1500 1300 Frequency cm 1 F i g u r e V-2. I n f r a r e d Spectra (1800 - 1300 cm - 1) of P y r i d i n e and I t s Complexes of C o b a l t (II) T r i f l u o r o a c e t a t e 155 A very broad and i n t e n s e band, wi t h one or more sho u l d e r s , appearing a t a. 1690 cm 1 f o r both t r i f l u o r o -a c e t a t e complexes i s assig n e d to the antisymmetric -CC>2 s t r e t c h i n g v i b r a t i o n . The assignment of the band a t 1622 cm 1 i n the spectrum of the b i s p y r i d i n e d e r i v a t i v e to a combination mode of p y r i d i n e i s somewhat u n c e r t a i n s i n c e t h i s band i s normally very weak i n p y r i d i n e complexes (135). In agreement with p r e v i o u s work (41), the band at 1422 cm 1 i n the spectrum of the t e t r a k i s p y r i d i n e com-p l e x i s assigned t o the symmetric -CC^ s t r e t c h i n g frequency. In the case of the b i s p y r i d i n e d e r i v a t i v e , i t was r e p o r t e d (41) t h a t the symmetric-CC^ s t r e t c h i n g v i b r a t i o n occurs a t 1350 cm The spectrum o b t a i n e d i n the p r e s e n t study shows onl y a weak band a t 1350 cm ^, q u i t e u n l i k e the i n t e n s e bands normally a s s i g n e d t o symmetric - C 0 2 s t r e t c h i n g f r e q u e n c i e s . A neighbouring band, at 1445 cm \ appears f o r both the b i s - and the t e t r a k i s - p y r i d i n e complexes as a r a t h e r i n t e n s e band. T h i s band i s a s s i g n a b l e to the p y r i d i n e r i n g v i b r a t i o n '19b'. In the spectrum an obvious shoulder a t 1450 cm 1 on the 1445 cm 1 band assigned as a p y r i d i n e r i n g v i b r a t i o n '19b 1, suggests t h a t the symmetric-CC>2 s t r e t c h i n g mode of the b i s p y r i d i n e d e r i v a t i v e c o u l d have become degenerate with the p y r i d i n e v i b r a t i o n . The value of 1450 cm 1 f o r the frequency of the symmetric s t r e t c h i n g v i b r a t i o n i s c o n s i s t e n t w i t h the valu e s observed p r e v i o u s l y f o r c o b a l t ( I I ) t r i f l u o r o a c e t a t e and sodium 156 t r i f l u o r o a c e t a t e (see Table V-4). The pr e s e n t assignment y i e l d s a Av value (energy d i f f e r e n c e between v & n t ^ and vsym^ ^ o r ** n e k i s P y r i ^ i n e complex of a. 250 cm 1 i n c o n t r a s t to 345 cm 1 r e p o r t e d e a r l i e r (41). The s i g n i f i c a n c e of the Av value w i l l be d i s c u s s e d l a t e r . A s i m i l a r i n v e s t i g a t i o n of the complex: b i s p y r i d i n e c o b a l t ( I I ) a c e t a t e (see F i g u r e V-3 and Table V-5) r e v e a l s a broad band i n the 1500 - 1700 cm 1 r e g i o n w i t h maxima at 1622 cm 1570 cm 1 and 1547 cm \ wh i l e a b s o r p t i o n s a t 1602 cm 1 and 1570 cm 1 have p o s s i b l e o r i g i n s i n the p y r i d i n e r i n g v i b r a t i o n s '8a' and '8b' r e s p e c t i v e l y , the antisymmetric -CC^ s t r e t c h i n g frequency i s a p p a r e n t l y mixed wi t h these. C o n s i d e r i n g the r e l a t i v e l y high i n t e n s i t y of the 1622 cm 1 band maximum, i t i s as s i g n e d t o the a n t i -symmetric -CC>2 s t r e t c h i n g v i b r a t i o n as was done i n the pre v i o u s work on t h i s complex (41) . The symmetric -CC>2 s t r e t c h i n g v i b r a t i o n of b i s p y r i d i n e c o b a l t (II) a c e t a t e appears a t 1417 cm 1 as a broad and i n t e n s e band. T h i s i s a l s o i n agreement wi t h the r e s u l t o b t a i n e d p r e v i o u s l y (41). For the a r y l c a r b o x y l a t e complexes of p y r i d i n e , the r e g i o n where the antisymmetric and symmetric -CC>2 s t r e t c h i n g v i b r a t i o n s are expected to occur are f u r t h e r complicated by the r i n g v i b r a t i o n s a r i s i n g from the a r y l groups of the a r y l c a r b o x y l a t e s . L i t t l e work has been r e p o r t e d g i v i n g i n f r a r e d data on complexes of a r y l c a r b o x y l a t e s f o r d i r e c t comparison. Complete assignments on the i n f r a r e d s p e c t r a TABLE V-5 Infrared Spectral Data and Assignments (1700 - 1300 cm )^ of Acetate Compounds and Pyr id ine Co (CH3CQ2) 2 « p y 2 Pyridine Na (CH3CC»2) , Co (CH3CQ2) 2 Co (CH 3C0 2) 2 • 4H20 Assignment This Previous Work Work (41) (135) (149) (38) (38) 1627w py'l+6b' '6a+12' 1593m py 1 l+6a ' 1622s 1570m 1547m 1623 1575sh 1550sh 1583s 1590 1550 v a n t i 1602m 1578s 1570w py '8a 1 py'8b ' 1486s 1478m py'19a' 1446s 1436s 1440m py'19b' CH 3 bending 1417b 1416 1372w 1421s 1405 1395 V sym py'14 ' 1362vw 1350w py'6a+10b' 1340m 1333w CH 3 bending - a l l uni t s i n cm 158 F i g u r e V-3. I n f r a r e d Spectra (1700 - 1300 cm ) of B i s p y r i d i n e C o b a l t (II) A c e t a t e and P y r i d i n e 159 of v a r i o u s a l k a l i metal benzoates, however, have been r e p o r t e d (125). With t h i s i n f o r m a t i o n , b i s p y r i d i n e c o b a l t ( I I ) benzoate was examined i n more d e t a i l . Relevant s p e c t r a and data are giv e n i n F i g u r e V-4 and Table V-6. TABLE V-6 I n f r a r e d S p e c t r a l Data and Assignments (1700-1300 cm ^) of Benzoate Compounds and P y r i d i n e C o ( C 6 H 5 C 0 2 ) 2 »py 2 K(CgH 5C0 2) P y r i d i n e Assignment T h i s Work (125) (135) 1627w py'l+6b' •6a+12' 1621s 1621w bz'12+6b' 1612s '17b+C02 def. 1593m 1594s 1593m bz'8a', * 8b' py'l+6a' 1602s 1578s py'8a' 1570w py'8b' 1568s 1552 v . . i c o / i a n t i 1534s 1524sh bz'6a+C0 2 def.' 1493m 1502w bz'19a' 1488s 1478m py'19a' 1447s 1436s py'19b' 1417s 1407s bz'19b' 1395s v 1401s 1384s sym 1372w py'14' 1350w py'6a+10b' 1315w 1309w 1303w bz'14' bz - benzoate r i n g v i b r a t i o n ^ - a l l u n i t s i n cm 160 p y r i d i n e T^TTT5 ''-"'«""''' l4oO Frequency cm F i g u r e V-4. I n f r a r e d Spectra (1700 - 1300 cm ) of Benzoate Compounds and P y r i d i n e 161 In the spectrum of bispyridine cobalt(II) benzoate, at least six bands of comparable intensity are observed in the region of 1700 - 1500 cm - 1. They are at 1621 cm - 1, 1612 cm-1, 1602 cm-1, 1593 cm-1, 1568 cm - 1 and 1534 cm - 1. The peak at 1602 cm 1 is assignable to the '8a' pyridine ring and the peaks at 1621 cm 1 and 1612 cm 1 are assignable to a mixture of the pyridine combination modes ('l+6b' and '6a+12') and the benzoate ring combination modes ('12+6b' and 17b+CC>2 def.'). The 1593 cm - 1 peak may be assigned to one of the pyridine ring vibrations 'l+6a' and the benzoate ring vibrations '8b' and '8a' or both. One or other of the two peaks at 1568 cm - 1 and 1534 cm - 1 are l e f t to be assigned to the antisymmetric -C02 stretching vibration. It seems lik e l y that the 15 34 cm - 1 band i s a benzoate ring vibration leaving the band at 1568 cm - 1 assigned as the antisymmetric -C02 stretching frequency. One or other of the bands at 1417 cm - 1 and 1401 cm - 1 is likely due to the symmetric -C02 stretching vibration.. On .compar with the spectrum of potassium benzoate, the higher frequency component i s assigned to the benzoate ring vibration '19b'. The band at 1401 cm - 1 is tentatively assigned here as the symmetric -C0 2 stretching frequency. For the other arylcarboxylate-pyridine complexes, no direct comparison such as in the benzoate case can be made; however, i t is possible to make comparisons between a l l of these complexes themselves in the region of 1700 -1300 cm - 1 (Figure V-5). Except for the benzoate and 162 A C o ( p - C H 3 0 - C 6 H 4 C 0 2 ) 2 . p y 2 C o ( C 6 H 5 C 0 2 ) 2 . p y 2 rr C o ( p - B r - C 6 H 4 C 0 2 ) 2 - p y 2 C o ( p - N 0 2 - C 6 H 4 C 0 2 ) 2 . p y 2 Co ( o - B r - C 6 H 4 C 0 2 ) 2 * p y 2 C o ( o - N 0 2 - C 6 H 4 C 0 2 ) 2 . p y 2 T70D 13015 1300 -1 Frequency cm F i g u r e V-5. I n f r a r e d S p e c t r a (1700 - 1300 cm" 1) of B i s p y r i d i n e Complexes of C o b a l t (II) A r y l c a r b o x y l a t e s 16 3 p-methoxybenzoate d e r i v a t i v e s , the complexes a l l have s t r o n g bands above 1600 cm 1 (yet below 1700 cm which cannot be assi g n e d to p y r i d i n e v i b r a t i o n s . These bands a r i s e t h e r e f o r e from r i n g v i b r a t i o n s of the a r y l c a r b o x y l a t e groups or from the antisymmetric s t r e t c h i n g v i b r a t i o n s of the -CC^ group. In the pres e n t work the bands are t e n t a t i v e l y a s s i g n e d to the l a t t e r v i b r a t i o n s . The arguments ued to support such an assignment are i l l u s t r a t e d f o r the case of the p-bromobenzoate case below. The s p e c t r a of the complexes d i s c u s s e d below have been given p r e v i o u s l y i n F i g u r e IV-3. An i n t e n s e band a t 1614 cm 1 i n the spectrum of the b i s p y r i d i n e d e r i v a t i v e of c o b a l t ( I I ) p-bromobenzoate i s found to s h i f t to 16 30 cm 1 i n the spectrum of the corre s p o n d i n g mixed p y r i d i n e - h y d r a t e d e r i v a t i v e . T h i s band i s however m i s s i n g i n the s p e c t r a of the hydrated s a l t of c o b a l t ( I I ) p-bromobenzoate and of the three sulphur-bonded complexes. A medium-intensity band a t 1630 cm 1 observed i n the spectrum of the t h i o u r e a d e r i v a t i v e has p r e v i o u s l y been i d e n t i f i e d as a t h i o u r e a v i b r a t i o n . Lindsay e t a l . (125) have r e p o r t e d a s t r o n g to medium band a t 1622 - 16 44 cm 1 i n the s p e c t r a of a l k a l i - m e t a l s a l i c y l a t e s (o-hydroxybenzoate) and have a s c r i b e d i t to a C-C s t r e t c h i n g v i b r a t i o n , '8a', of the a r y l group. Whereas t h i s may suggest t h a t the s t r o n g bands a t ^ 16 00 cm 1 f o r the a r y l c a r b o x y l a t e - p y r i d i n e complexes are perhaps due to v i b r a t i o n s of t h i s nature, the absence of band i n the s p e c t r a of a l l other d e r i v a t i v e s ( i . e . the hydrate and the sulphur-bonded complexes) suggests t h a t t h i s i s u n l i k e l y . I t seems more l i k e l y t h a t t h i s band 164 a r i s e s from the -CC>2 antisymmetric s t r e t c h i n g v i b r a t i o n s s i n c e the energy of such a v i b r a t i o n would be expected t o vary from complex t o complex. In the hydrate and sulphur-bonded complexes i t occurs a t e n e r g i e s lower than 16 00 cm 1 as shown i n Chapter IV. The r e g i o n of 1700 - 1500 cm 1 i n the spectrum of b i s p y r i d i n e c o b a l t ( I I ) p-methoxybenzoate i s r e l a t i v e l y simple, w i t h two main a b s o r p t i o n s . The hi g h e r energy a b s o r p t i o n i s s p l i t i n t o peak maxima a t 1602 cm 1 and 1590 cm 1 and appears sharp and s t r o n g . These peaks are r e a d i l y a s s i g n a b l e t o p y r i d i n e and p-methoxybenzoate r i n g v i b r a t i o n s . By e l i m i n a t i o n , the other a b s o r p t i o n a t 1515 cm 1 which appears as a s i n g l e i n t e n s e band i s assigned to the antisymmetric -CG^ s t r e t c h i n g v i b r a t i o n . Although the exact assignments o f the antisymmetric -CC>2 s t r e t c h i n g f r e q u e n c i e s o f these p y r i d i n e - a r y l c a r b o x y l a t e complexes are r a t h e r u n c e r t a i n , i t i s important t o note t h a t there i s no doubt t h a t these bands occur i n the r e g i o n below 16 35 cm 1 (no bands above t h i s frequency can be reasonably a s s i g n e d t o such v i b r a t i o n s ) . In c o n t r a s t to t h i s the a n t i symmetries^©?; "c s t r e t c h i r i g i v i f c r a t i o n s i ofh thewtwcr: t r i f l u o r o -a c e t a t e complexes are at ^  1690 cm ^. Lever and Ogden (41) have d i s c u s s e d the dependence of v a n ^ - ^ o n the a c i d s t r e n g t h of the parent a c i d s i n p y r i d i n e complexes of a l k y l and h a l o a l k y l - c a r b o x y l a t e complexes. They found t h a t v a n t ^ i n c r e a s e s as the a c i d s t r e n g t h of the parent a c i d i n c r e a s e s . The p r e s e n t study confirms t h i s o b s e r v a t i o n . 1 6 5 Values of the antisymmetric and symmetric _ C 0 2 stretching frequencies for a l l complexes together with t h e i r differences (Av) are co l l e c t e d i n Table V - 7 . TABLE V - 7 Infrared Spectral Results on -CC>2 Stretching Frequencies of Pyridine Complexes of Cobalt(II) Carboxylates Complex* pK a v , . anti (cm - 1) V sym (cm - 1) Av (cm - 1) Co ( C H 3 C O 2 ) 2 * p y 2 4 . 7 5 1 6 2 2 1 4 1 7 2 0 5 Co ( P - C H 3 O - C 6 H 4 C O 2 ) 2 * p y 2 4 . 4 7 1 5 1 5 1 4 1 4 1 0 1 C o ( C 6 H 5 C 0 2 ) 2 . p y 2 4 . 1 8 1 5 6 8 1 4 0 1 1 6 7 Co ( p - B r - C G H 4 C 0 2 ) 2 • p y 2 4 . 0 0 1 6 1 4 1 4 0 0 2 1 4 co ( p - N O 2 - C 6 H 4 C O 2 ) 2 • p y 2 3 . 4 3 1 6 3 0 1 4 1 7 2 1 3 C o ( o - B r - C 6 H 4 C 0 2 ) 2 - p y 2 2 . 8 5 1 6 3 0 1 3 8 5 2 4 5 C O ( O - N O 2 - C 6 H 4 C O 2 ) 2 - p y 2 2 . 1 7 1 6 3 5 1 3 9 4 2 4 1 C o ( C F 3 C O 2 ) 2 * p y 2 % 0 1 6 9 5 1 4 4 5 2 5 0 Co ( C F 3 C 0 2 ) 2 - p y 4 0/ 0 1 6 8 5 1 4 2 2 2 6 3 * Arranged according to increasing a c i d i t y of the parent acid (decreasing pK &) 166 A t r e n d i s noted w i t h i n the a r y l c a r b o x y l a t e s e r i e s f o r the parameter ^ a n t ^ . T h i s frequency i s seen to i n c r e a s e as the r i n g s u b s t i t u e n t of the a r y l c a r b o x y l a t e group i s v a r i e d so as t o i n c r e a s e the a c i d s t r e n g t h of the a r y l -c a r b o x y l i c a c i d (as measured by a decrease of the pK a parameter of the a c i d ) . There i s no s y s t e m a t i c change i n Vsym a m o n 9 t n e complexes, however Av i s seen to i n c r e a s e as pK decreases. These trends are s i m i l a r to those observed e a r l i e r f o r the a c e t a t e and h a l o a c e t a t e complexes (41). I t should be noted t h a t i f one combines the r e s u l t s f o r the a r y l c a r b o x y l a t e s e r i e s w i t h those f o r the a c e t a t e and t r i f l u o r o a c e t a t e s e r i e s (see Table V-7) smooth trends i n v .. and Av with pK are not obtained i n t h a t the a n c i a values of v .. and Av f o r the a c e t a t e complex appear a n t i * too h i g h . T h i s o b s e r v a t i o n may r e f l e c t a s t r u c t u r a l anomaly i n the a c e t a t e complex, however, such a s u g g e s t i o n i s p u r e l y s p e c u l a t i v e s i n c e the reasons f o r the trends d i s c u s s e d above are not understood. V-3-2. E l e c t r o n i c S p e c t r a l Study The s o l i d s t a t e e l e c t r o n i c s p e c t r a of the complexes were recorded by both potassium bromide p e l l e t and d i f f u s e r e f l e c t a n c e techniques. S p e c t r a l data are reproduced i n Appendixes V - l and V-2. For each complex, the good agreement between the two types of s p e c t r a i n the v i s i b l e r e g i o n suggests there was no decomposition or major s t r u c t u r a l change i n the process of p e l l e t making. 167 As d e s c r i b e d e a r l i e r i n Chapter I I , the number of observed e l e c t r o n i c t r a n s i t i o n s w i l l depend very much on symmetry f a c t o r s . For the b i s p y r i d i n e complexes under c o n s i d e r a t i o n here, the h i g h e s t p o s s i b l e symmetry f o r 2+ the xmmedxate environment about Co i s D., , which a r i s e s 4 h as the p y r i d i n e molecules occupy t r a n s - p o s i t i o n s i n an ' o c t a h e d r a l ' a r r a y of f o u r 'O' atoms and two 'N' atoms. 4 R e f e r r i n g to S e c t i o n II-3-1, the degeneracy of the T 4 4 s t a t e s ( and T2g^ J- n °h symmetry w i l l be removed and s p l i t t i n g of the s p e c t r a l bands may be observed. Lever and Ogden (41) have r e p o r t e d the e l e c t r o n i c s p e c t r a of s e v e r a l b i s - and t e t r a k i s - p y r i d i n e complexes of c o b a l t ( I I ) h a l o a c e t a t e s . In g e n e r a l , the s p e c t r a a l l e x h i b i t e d i n the v i s i b l e r e g i o n a s i n g l e broad band with a w e l l - d e f i n e d shoulder. T h i s shoulder was r e p o r t e d to l i e on the h i g h energy s i d e of the main v i s i b l e band f o r the b i s p y r i d i n e complexes, but on the low energy s i d e f o r the c o r r e s p o n d i n g t e t r a k i s p y r i d i n e d e r i v a t i v e s . The assignment of t h i s shoulder to the s p i n - f o r b i d d e n t r a n s i t i o n 4 2 T l g ( F ) > T 1g(H) was excluded as the energy of t h i s t r a n s i t i o n would be expected to i n c r e a s e as Dq i n c r e a s e d i n p r oceeding from the b i s p y r i d i n e to the 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 . By a p r o c e s s of e l i m i n a t i o n , the v 3 band and the shoulder were assig n e d (41) r e s p e c t i v e l y to t r a n s i t i o n s 4 4 4 to the E and A„ components of the T.. (P) term under 9 2g l g D ^ symmetry. In the n e a r - i n f r a r e d r e g i o n , the complexes e x h i b i t e d a broad band near 90 00 c m - 1 which showed no 4 obvious s t r u c t u r e . A pparently the s p l i t t i n g of the T„ (F) 168 term i n such complexes i s s u f f i c i e n t l y s m a l l t h a t o n l y one broad band i s observed. Based on the above s p e c t r a l p r o p e r t i e s , Lever and Ogden (41) proposed t r a n s - CoO^^ and t r a n s - CoC^N^ s t r u c t u r e s f o r the complexes. In the p r e s e n t work, three of the complexes were re-examined and t h e i r s p e c t r a are shown i n F i g u r e V-6. In c o n t r a s t to the p r e v i o u s r e p o r t , we observed a w e l l -d e f i n e d shoulder, l o c a t e d on the h i g h energy s i d e of the main v i s i b l e band ( V 3 ) i n a l l three complexes. On the lower energy s i d e , a weak shoulder i s a l s o apparent i n a l l three complexes. T h i s c a s t s some doubt on the p r e v i o u s assignments of Lever and Ogden. An e q u a l l y p l a u s i b l e e x p l a n a t i o n of the v i s i b l e spectrum i s t h a t , l i k e the n e a r - i n f r a r e d band ( V i ) , s p l i t t i n g due to low symmetry e f f e c t s i s not seen and the high energy shoulder i s due to a s p i n - f o r b i d d e n t r a n s i t i o n (see r e f e r e n c e 150 and r e f e r e n c e s t h e r e i n ) while the low energy shoulder i s a s s i g n e d to the low i n t e n s i t y v 2 t r a n s i t i o n (see l a t e r ) . Of the s i x a r y l c a r b o x y l a t e complexes s t u d i e d i n the p r e s e n t work, o n l y the two o r t h o - s u b s t i t u t e d benzoate complexes g i v e s p e c t r a resembling the above. The s p e c t r a are a l s o presented i n F i g u r e V-6. For the purpose of f u r t h e r comparison, a l l of these complexes ( v i z . the t r i f l u o r o a c e t a t e , a c e t a t e , o-bromobenzoate and o - n i t r o -benzoate complexes) w i l l be c l a s s i f i e d as "group A" complexes. In g e n e r a l , these group A complexes e x h i b i t a s i n g l e band i n the v i s i b l e r e g i o n w i t h one or two a s s o c i a t e d s h o u l d e r s . The n e a r - i n f r a r e d band, V i , i s a l s o 169 26 22 18 14 10 6 V X 10~3 cm' 22 18 14 10 6 V X io 3 cm' Figure V-6 Solid State Electronic Spectra of Group A Pyridine Complexes 170 found t o be a s i n g l e broad band with no obvious a d d i t i o n a l s t r u c t u r e . Based on these s p e c t r a l p r o p e r t i e s and other evidence, such as the nagnetic p r o p e r t i e s to be d i s c u s s e d l a t e r , these group A complexes can be c o n s i d e r e d as having a t r a n s - o c t a h e d r a l s t r u c t u r e with approximately l i g a n d symmetry about c o b a l t . In view of the l a c k of e x t e n s i v e s p l i t t i n g of the bands one may reasonably c a l c u l a t e the l i g a n d f i e l d parameters Dq and B. The KBr p e l l e t s p e c t r a were used f o r t h i s purpose and the r e s u l t s are gi v e n i n Table V-8. TABLE V-8 E l e c t r o n i c S p e c t r a l Parameters f o r Group A P y r i d i n e Complexes ( S o l i d State) Complex v 3 V l Dq B v 2 ( c a l c . C o ( C F 3 C 0 2 ) 2 - p y 4 20410 9300 1047 821 19840 Co ( C F 3 C O 2 ) 2 * p y 2 20000 8850 1000 820 18940 C o ( C H 3 C 0 2 ) 2 « p y 2 20200 8850 1005 834 19010 Co ( o - B r - c 6 H 4 c o 2 ) 2 * p y 2 20000 8850 1000 820 18940 C o ( o - N 0 2 - C 6 H 4 C 0 2 ) 2 • p y 2 20000 8850 1000 820 18940 - a l l u n i t s i n cm 171 The magnitudes of Dq and B c a l c u l a t e d f o r these complexes are comparable to those of t y p i c a l o c t a h e d r a l 2+ complexes of chromophore CoL^ (e.g., Co (H 20) g where Dq = 920 c m - 1 and B = 825 c m - 1 (80); C o ( C 2 H 5 N ) 6 2 + where Dq = 1010 c m - 1 and B = 802 c m - 1 (154). I t i s a l s o p o s s i b l e to estimate the magnitudes of Dq and B from e m p i r i c a l parameters f o r i n d i v i d u a l metal ions and l i g a n d groups. The q u a n t i t i e s f and g are gi v e n (42) f o r some l i g a n d groups and metal i o n s and the product f x g g i v e s i n 2 -1 u n i t s of 10 cm the approximate Dq value expected f o r 2+ the a p p r o p r i a t e complex. F o r Co , g = 9.3 and f o r 6 CH^CC^ , f = 0.96; Dq f o r a s i x - c o o r d i n a t e complex between c o b a l t and a c e t a t e i s estimated by t h i s method to be 9.3 x 0.96 x 10 2 = 893 cm - 1. S i m i l a r l y , f o r 6 py, f = 1.25 and Dq f o r a h e x a k i s p y r i d i n e c o b a l t (II) i o n 2 -1 i s e s t i mated t o be 9.3 x 1.25 x 10 = 1163 cm . The Dq value of 1005 cm 1 o b t a i n e d here f o r the complex Co (CH-jCC^) 2*PY 2 ' t h e r e f o r e i s i n the range expected. From the process o f c a l c u l a t i o n of parameters Dq and B the p o s i t i o n of the v 2 t r a n s i t i o n can be estimated. These v2 (c a l c . ) v a l u e s are i n c l u d e d i n Table V-8. I t can be seen t h a t f o r each complex v 2 i s expected t o be c l o s e to and a t s l i g h t l y lower energy than v 3 . The lower energy shoulders o f the v 3 bands i n the s o l i d s t a t e s p e c t r a may, t h e r e f o r e , a r i s e from t h i s o r i g i n . 172 The other f o u r a r y l c a r b o x y l a t e complexes s t u d i e d i n t h i s work show r a t h e r d i f f e r e n t s p e c t r a l c h a r a c t e r i s t i c s . The s o l i d s t a t e e l e c t r o n i c s p e c t r a are reproduced i n F i g u r e V-7 and f o r convenience of d i s c u s s i o n these complexes ( i . e . the benzoate, p-bromobenzoate, p - n i t r o b e n z o a t e and p-methoxybenzoate complexes) are c l a s s i f i e d as "group B" complexes. As seen from F i g u r e V-7, the s p e c t r a are more s t r u c t u r a l than those of the group A"' complexes wi t h the l a r g e number of band maxima i n d i c a t i n g c o n s i d e r a b l y lower symmetry about c o b a l t . S i g n i f i c a n t s p l i t t i n g of the v 3 band has been observed b e f o r e f o r complexes of c o b a l t ( I I ) of symmetry lower than D 4 h > For example, the c r y s t a l 2+ spectrum of Co i n MnF2 (°2h symmetry) shows th r e e components a t 18500 cm - 1, 18900 c m - 1 and 20400 c m - 1 (84). S i m i l a r l y , the v i o l e t form of C o C l 2 * p y 2 a l s o shows th r e e bands i n i t s c r y s t a l spectrum corresponding t o i t s known D 2 h symmetry (82). While i n a l l these l i t e r a t u r e cases, very l i t t l e s p l i t t i n g o f the V i band i s seen, d e f i n i t e s p l i t t i n g of V j f o r three of the group B complexes s t u d i e d here i s seen. The V i band of the f o u r t h complex, the p-methoxybenzoate d e r i v a t i v e i s very broad but does not show a r e s o l v e d s p l i t t i n g . The c o n c l u s i o n t h a t the complexes c l a s s i f i e d as group B have much lower symmetries than those c l a s s i f i e d as group A i s supported with the s p e c t r a of complexes with known low symmetry s t r u c t u r e s . The e l e c t r o n i c s p e c t r a l data of s e v e r a l s i x - c o o r d i n a t e d n i t r a t e complexes of c o b a l t ( I I ) F i g u r e V - 7 . S o l i d State E l e c t r o n i c Spectra of 'Group B' P y r i d i n e Complexes 174 were d i s c u s s e d e a r l i e r i n Chapter I I . These complexes show e x t e n s i v e band s p l i t t i n g i n both the v i s i b l e and the n e a r - i n f r a r e d r e g i o n s and, i n p a r t i c u l a r , the near-i n f r a r e d r e g i o n shows d e f i n i t e band s p l i t t i n g i n t o a t l e a s t two components as observed here f o r the group B complexes. These n i t r a t e complexes have i n common a very d i s t o r t e d o c t a h e d r a l s t r u c t u r e , with the two b i d e n t a t e n i t r a t e groups ' c i s ' to each o t h e r . The symmetry of the molecules has been d e s c r i b e d as a t most 0.^. I t i s b e l i e v e d , t h e r e f o r e , t h a t the group B complexes are a l s o low-symmetry complexes. Indeed the s t r u c t u r e s may be q u i t e analogus to those of the n i t r a t e complexes i n v o l v i n g ' c i s ' p y r i d i n e c o o r d i n a t i o n r a t h e r than the 'trans' c o o r d i n a t i o n e x h i b i t e d by the group A complexes. F u r t h e r support f o r the above i s o b t a i n e d from magnetic and s o l u t i o n s t u d i e s to be d e a l t w i t h l a t e r . V-3-3. Magnetic S u s c e p t i b i l i t y Study. The a n a l y s i s of the e l e c t r o n i c s p e c t r a of b i s -p y r i d i n e c o b a l t (II) c a r b o x y l a t e s d e s c r i b e d i n the p r e v i o u s s e c t i o n has i n d i c a t e d t h a t , w hile the t r a n s - p y r i d i n e , b r i d g i n g c a r b o x y l a t e s t r u c t u r e p r e v i o u s l y proposed f o r such complexes (41) i s probably c o r r e c t f o r a l k y l - , h a l o a l k y l - and some a r y l - c a r b o x y l a t e d e r i v a t i v e s (group A complexes), other a r y l c a r b o x y l a t e d e r i v a t i v e s (group B complexes) have s t r u c t u r e s i n which the c o o r d i n a t i o n 175 geometry about the c o b a l t ions i s of lower symmetry. C o n f i r m a t i o n of these s t r u c t u r a l d i f f e r e n c e s should be o b t a i n a b l e from magnetic s u s c e p t i b i l i t y s t u d i e s . (see Chapter I I ) . Magnetic s u s c e p t i b i l i t y data, over the temperature range 80 - 320°C, f o r a l l of the p y r i d i n e complexes s t u d i e d i n t h i s work are given i n Appendix V-3 and the room-temperature va l u e s of y e f f are l i s t e d i n Table V-9. TABLE V-9 Room-temperature E f f e c t i v e Magnetic Moments of P y r i d i n e Complexes of C o b a l t (II) C a r b o x y l a t es i y (B.M.) Complex M e f f C o ( C F 3 C 0 2 ) 2 * p y 4 4.96 C o ( C F 3 C 0 2 ) 2 * P y 2 4.99 C o ( C H 3 C 0 2 ) 2 * p y 2 4.95 Co ( o - B r - C 6 H 4 C 0 2 ) 2 * p y 2 5.02 C o ( o - N 0 2 - C 6 H 4 C 0 2 ) 2 * p y 2 4.97 C o ( C 6 H 5 C 0 2 ) 2 - p y 2 4.69 C o ( p - B r - C 6 H 4 C 0 2 ) 2 * p y 2 4.58 Co ( p - N 0 2 - C 6 H 4 C 0 2 ) 2 * p y 2 4.60 Co (p-CH 30-CgH 4C0 2) 2*Py 2 4.93 y c a l c u l a t e d by 2.828 (x • T ) ^ a t T - 295°K e r r r C o 176 The room-temperature magnetic moments of the complexes which were c l a s s i f i e d p r e v i o u s l y as group A ( i . e . the f i r s t f i v e complexes l i s t e d i n Table V-9), and which are c o n s i d e r e d t o have h i g h symmetry t r a n s - o c t a h e d r a l s t r u c t u r e s are a l l r e l a t i v e l y high and f a l l w i t h i n the narrow range 4.95 - 5.02 B.M.. The magnitude of the magnetic moment i s i t s e l f t y p i c a l f o r s i x - c o o r d i n a t e c o b a l t w i t h l i t t l e d i s t o r t i o n from r e g u l a r 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 (see Chapter I I ) . The experimental magnetic moments of the group A complexes measured over the temperature range 80 - 320°C were compared t o those c a l c u l a t e d u s i n g the four-parameter (y(A), k, X and A) theory of F i g g i s e t a l . (93) as d e s c r i b e d i n Chapter I I (Se c t i o n I I - 3 - 2 ) . The value of A, which r e p r e s e n t s the e f f e c t i v e o r b i t a l angular momentum f o r the 4 ground s t a t e T i g ( F ) r e s u l t i n g from the admixture of the 4 e x c i t e d s t a t e T i g ( p ) i n t o the ground s t a t e , was c a l c u l a t e d from known values of Dq and B f o r each of these group A complexes. The r e s u l t s o f the c a l c u l a t i o n s g i v e a common A v a l u e of 1.40 f o r a l l of the complexes. Values of A of t h i s magnitude, r e p r e s e n t i n g r a t h e r weak l i g a n d f i e l d environments, were observed f o r the s i x - c o o r d i n a t e c o b a l t ( I I ) complexes s t u d i e d by F i g g i s e t a l . (93) ( f o r those complexes, A ranges from 1.35 to 1.42). The s i m i l a r i t y of A among the complexes e f f e c t i v e l y reduces the number of v a r i a b l e s i n the theory t o t h r e e . 177 By f i x i n g the value of A a t 1.40, t h e o r e t i c a l magnetic moments f o r v a r i o u s v a l u e s of the parameters k, y and X were ob t a i n e d by i n t e r p o l a t i o n of the data g i v e n by F i g g i s e t a l . (93). Numerous p l o t s of t h e o r e t i c a l magnetic moments versus KT / - X f o r d i f f e r e n t v a l u e s of the parameters k and y were made and graphs of experimental magnetic moments versus KT / - X were then compared wi t h the t h e o r e t i c a l curves to f i n d the best f i t s . Graphs of the experimental p o i n t s and b e s t - f i t t h e o r e t i c a l curves f o r each of the group A complexes are shown i n F i g u r e V-8. In a l l cases, more than one good f i t i s p o s s i b l e ; the v a l u e s of the parameters g i v i n g the best agreement between experimental and theory are l i s t e d i n Table V-10. TABLE V-10 Magnetic Parameters of Group A P y r i d i n e Complexes Complexes C o ( C F 3 C 0 2 ) 2 - p y 4 c o ( C F 3 C O 2 ) 2 * p y 2 Co(CH 3C0 2)2*Py 2 C o ( o - B r - C 6 H 4 C 0 2 ) 2 • p y 2 C o ( o - N 0 2 - C 6 H 4 C 0 2 ) 2 . p y 2 y e f f X A (R.T.) -1 -1 \B.M.) A (cm ) k v (cm 4.96 1.40 -160 0.92 2 -320 -160 0.93 -2 + 320 4.99 1.40 -140 0.95 2 -280 -150 0.93 1 -150 -150 0.93 0 -150 -150 0.93 -1 +150 -140 0.96 -2 + 280 4.95 1.40 -150 0.88 2 -300 -160 0.91 -2 + 320 5.02 1.40 -165 0.96 1 -165 -160 0.95 0 0 -165 0.96 -1 +165 4. 97 1.40 -155 0.93 2 -310 -150 0.91 1 -150 -145 0.91 0 0 -150 0.91 -1 + 150 -155 0.94 -2 + 310 178 (e) 0.4 0.8 ' KT F i g u r e V-8. T y p i c a l F i t s of Experimental u e f f vs JJJ P l o t s with Theory f o r Group A P y r i d i n e Complexes 179 Examination of the data i n Table V-10 shows t h a t while f o r a l l complexes, more than one combination of values f o r the three parameters v/ k and X i s p o s s i b l e , the range of p o s s i b l e v a l u e s i s not l a r g e . In f a c t , t here i s no r e a l s i g n i f i c a n t v a r i a t i o n i n the parameters from complex to complex. The s p i n - o r b i t c o u p l i n g constant, X, i s i n the range -140 to -165 c m - 1 or about 10 to 20% reduced below the f r e e i o n value of -178 cm ^. The parameter k i s f a i r l y h igh, i n the range 0.88 to 0.96. There i s n o t h i n g s u r p r i s i n g or f o r t h a t matter too i n f o r m a t i v e about the v a l u e s o b t a i n e d f o r these parameters; they are of a magnitude commonly found f o r o c t a h e d r a l complexes of c o b a l t ( I I ) (93, 150, 151). For each complex, good f i t s t o t h e o r e t i c a l curves with both p o s i t i v e and negative v values are p o s s i b l e (with s l i g h t l y d i f f e r e n t k and X v a l u e s ) . As a r e s u l t , as has been observed before (93), the s i g n of v f o r these complexes i s ambiguous. There i s , i n a d d i t i o n , u n c e r t a i n t y i n the magnitude of v; f o r the o - n i t r o b e n z o a t e complex, f o r example, good agreement between theory and experiment can be o b t a i n e d w i t h v v a l u e s of ± 2, ± 1 or 0. I t i s important t o note, however, t h a t the r e s u l t s do p l a c e an upper l i m i t of ± 2 on the parameter v f o r a l l of the group A complexes. Since v i s d e f i n e d as A/X where A i s the s p l i t t i n g i n cm 1 of the ground term by f i e l d s of t r i g o n a l or t e t r a g o n a l symmetry, A can be no g r e a t e r than ± 320 c m - 1 as seen from Table V-10. In other words, the d i s t o r t i o n , which i s probably t e t r a g o n a l i n nature, does not g i v e r i s e to a 180 s p l i t t i n g of the ground term by more than 320 cm ^. Turning now to the remainder of the pyridine complexes, those c l a s s i f i e d previously as group B, t h e i r magnetic properties are s i g n i f i c a n t l y d i f f e r e n t from those of the group A complexes. One of these complexes, the p-methoxybenzoate derivative, has a rather high magnetic moment of 4.93 B.M. l i k e those of the group A complexes, however, as w i l l be discussed i n more d e t a i l l a t e r , the cryomagnetic datum suggests rather large d i s t o r t i o n s of the ligand f i e l d from regular octahedral symmetry for this complex. The room-temperature magnetic moments of the other three group B complexes (the benzoate, the p-bromobenzoate and the p-nitrobenzoate derivatives) are found to l i e i n the range 4.58 - 4.69 B.M. (see Table V -9 ) , considerably lower than that expected for an octahedral cobalt(II) com-plex. In fact, the magnetic moments are comparable to those of the n i t r a t e complexes described i n Chapter II as having bidentate n i t r a t e groups i n a c i s - configuration about cobalt. Attempts were made to f i t the cryomagnetic data obtained for these complexes to the four-parameter theory of F i g g i s . The parameter A i s assumed to be i d e n t i c a l to that of the group A complexes by virt u e of the si m i l a r ligand environment about cobalt i n the two types of complexes ( i . e . CoO.N„ chromophore). Taking A to be 1.40, 181 the experimental magnetic moments were g raphica l ly f i t to t h e o r e t i c a l curves and the re su l t s are represented and c o l l e c t e d i n Figure V-9 and Table V - l l . In general , there i s only one f i t poss ib le for each of these three group B complexes. In a l l cases, v = -4 and A i s in the range of + 600 to + 640 cm ^ . This magnitude of A suggests greater d i s t o r t i o n i n comparison to that found for the group A complexes. A l s o , the p o s i t i v e sign of A indicates that 4 an o r b i t a l l y s i n g l e t l e v e l ( A~ ) , a r i s i n g from the s p l i t t i n g z g of the ^ T i g (F ) term, becomes the ground s tate . The sp in-orb i t coupling constant, A, i s found to be in the range of -150 to - 160 cm s i m i l a r to that observed for the group A complexes. The parameter k i s however found i n the range of 0.73 - 0.84, s i g n i f i c a n t l y lower -than that found for the group A complexes. TABLE V - l l Magnetic Parameters of Three of the Group B Pyridine Complexes (R.T.) (B.M.) A A v (cm 1 ) Complex k 4.69 4.60 4.58 1.40 1.40 1.40 -150 -150 -160 0.84 -4 +600 0.73 -4 +640 0.76 -4 +600 F i g u r e V-9. T y p i c a l F i t s of Experimental V e f f vs pp j - P l o t s with Theory f o r Three of the Group B P y r i d i n e Complexes 183 The p o i n t must be made here t h a t t h i s f o u r -parameter theory r e l i e s on the assumption of a t e t r a g o n a l or t r i g o n a l symmetry about the c e n t r a l i o n and s t r i c t l y speaking i t should not be a p p l i e d to complexes where the symmetry i s lower. T h i s i s very probably the case w i t h these group B complexes and t h i s c a s t s s e r i o u s doubts on the s i g n i f i c a n c e of the parameters d e r i v e d . N e v e r t h e l e s s i n a q u a l i t a t i v e sense, a t l e a s t , t h i s e x e r c i s e has been f r u i t f u l . I t has shown t h a t , whatever the d e t a i l s of the l i g a n d environment about c o b a l t i n these complexes, the magnetic p r o p e r t i e s are the same as those expected f o r 4 a 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 complex with a A 2 ground term. In o t h e r words these three group B complexes are almost c e r t a i n l y s i g n i f i c a n t l y d i s t o r t e d from r e g u l a r o c t a h e d r a l symmetry wi t h o r b i t a l l y non-degenerate ground terms. I t has been observed, f o r -the n i t r a t e complexes r e f e r r e d t o above, t h a t the magnetic s u s c e p t i b i l i t y over the temperature range 8 0 - 32 0°K obeys the Curie-Weiss law -a form of behaviour commonly shown by complexes w i t h o r b i t a l l y s i n g l e t ground terms. P l o t s of l/x00^!. versus Co temperature f o r the three group B complexes (where x°0++ Co i s the molar magnetic s u s c e p t i b i l i t y c o r r e c t e d f o r the 'TIP 1 term, the l a t t e r e stimated by the e x p r e s s i o n 2.09/10Dq) are given i n F i g u r e V-10. V e f f v a l u e s c a l c u l a t e d from the slopes of these s t r a i g h t l i n e s are found to l i e i n the F i g u r e V-10. Curie-Weiss P l o t s of Three Group B P y r i d i n e Complexes 185 range of 4.74 - 4.82 B.M.. A l s o , the 6 v a l u e s range from -16 t o -22°K. These values are higher than those u s u a l l y observed f o r t e t r a h e d r a l c o b a l t ( I I ) complexes ( U e f f = 4.3 - 4.7 B.M. and 0 ^-1 to-10°K) and i n d i c a t e t h a t these complexes should not be c o n s i d e r e d as t e t r a h e d r a l molecules. I t i s noted here t h a t s i m i l a r "Curie-Weiss P l o t s " f o r the group A complexes do not give reasonably l i n e a r l i n e s . T h i s i s i n d i c a t e d by a l e a s t - s q u a r e a n a l y s i s on the magnetic data which g i v e s standard d e v i a t i o n s on 0 from the be s t s t r a i g h t l i n e f i t : - 0 ( v i s i b l e - 0 ( l e a s t a Q ( s t a n d a r d s t r a i g h t l i n e square d e v i a t i o n ) Complex Group a n a l y s i s ) ( K) ana l y s i s ) ( K) ( UK) C o ( o - B r - C 6 H 4 C 0 2 ) 2 « p y 2 A - 38 1.2 C o ( o - N 0 2 - C 6 H 4 C 0 2 ) 2 « p y 2 A - 30 C o ( C 6 H 5 C 0 2 ) 2 - p y 2 B 16 1.4 C o ( p - B r - C 6 H 4 C 0 2 ) 2 * p y 2 B 22 24 0.1 C o ( p - N 0 2 - C 6 H 4 C 0 2 ) 2 * p y 2 B 18 18 0.2 18 0.1 186 The f a c t t h a t group B complexes obey the Curie-Weiss law i n d i c a t e s the e l e c t r o n p o p u l a t i o n of a s i n g l e t ground e l e c t r o n i c s t a t e with no thermal p o p u l a t i o n of e x c i t e d s t a t e s . For the group A complexes, the ground s t a t e i s e i t h e r o r b i t a l l y degenerate or i f there i s s p l i t t i n g r e s u l t i n g i n a s i n g l e t ground l e v e l , t h e r m a l l y a c c e s s i b l e e x c i t e d l e v e l s are a v a i l a b l e . The complex b i s p y r i d i n e c o b a l t ( I I ) p-methoxybenzoate has a room-temperature magnetic moment of 4.93 B.M.. The magnitude of t h i s moment i s s i m i l a r t o t h a t o f the group A complexes and i s t y p i c a l of r e g u l a r o c t a h e d r a l complexes. By f i t t i n g the temperature v a r i a t i o n of the experimental magnetic moments to the theory of Figgis;, a very good f i t i s o b tained. The r e s u l t s are presented i n F i g u r e V - l l , and summarized as f o l l o w s : Complex A X (cm "*") k v A. (cm ^) C o ( p - C H 3 0 - C 6 H 4 C 0 2 ) 2 « p y 2 1.40 -150 0.97 +5 -750 The parameter A was again s e t a t 1.40, by v i r t u e of the s i m i l a r i t i e s of a l l p y r i d i n e complexes under study here. X and k are s i m i l a r i n magnitude to the corresponding v a l u e s f o r group A complexes. v has, however, a l a r g e p o s i t i v e v alue of +5 which g i v e s A a value of -750 cm 1 . Th i s magnitude of A i n d i c a t e s a l a r g e d i s t o r t i o n from r e g u l a r o c t a h e d r a l geometry. I t i s b e l i e v e d t h a t , as a r e s u l t of the very good f i t o f the experimental-theory p l o t s , 187 Figure V - l l . Typical F i t of Experimental y e f f vs with Theory for Co (p-CH30-.C6H4C02) 2 • 188 the theory a p p l i e s f a i t h f u l l y t o t h i s complex. To e x p l a i n 4 the experimental r e s u l t s , the ground term T i g ( F ) °f c u b i c symmetry i s n e c e s s a r i l y s p l i t by the d i s t o r t i o n i n t o two 4 4 s t a t e s , a doublet E and a s i n g l e t A„ (see S e c t i o n II-3-2 g 2g i n Chapter I I ) . The negative s i g n of A observed i n t h i s 4 case suggests a doublet ground s t a t e ( i . e . E ). Thus, l i k e the other group B complexes, the p-methoxybenzoate d e r i v a t i v e i s s t r o n g l y d i s t o r t e d . T h i s d i s t o r t i o n , however, i s not of the same nature as t h a t e x h i b i t e d by the other group B complexes where a symmetry lower than 1 S l i k e l y . A p l o t of l/x C°Ty versus T shows approximate Curie-Weiss Co behaviour w i t h h i g h u f f (5.08 B.M.) and h i g h 8 (-17 K). Least-Square a n a l y s i s g i v e s 8 = -18°K and OQ = 0.6°K i n d i c a t i n g r e l a t i v e l y poor agreement wi t h Curie-Weiss behaviour than shown by o t h e r group B complexes. V-4. SOLUTION STUDIES In t h e i r paper on p y r i d i n e complexes of c o b a l t ( I I ) alkanoates and h a l o a c e t a t e s , Lever and Ogden (41) r e p o r t e d some s p e c t r o s c o p i c s t u d i e s on the complexes i n s o l u t i o n i n some o r g a n i c s o l v e n t s . The work p r o v i d e d some new and i n t e r e s t i n g i n s i g h t s i n t o the c o o r d i n a t i n g a c t i o n of c a r b o x y l a t e groups. On the b a s i s of the low molar e x t i n c t i o n c o e f f i c i e n t s of the p r i n c i p a l v i s i b l e a b s o r p t i o n band, 189 i t was suggested t h a t the complexes have a t r a n s - o c t a h e d r a l c o n f i g u r a t i o n . S o l v e n t c o o r d i n a t i o n was r u l e d out by the s o l u b i l i t y of the complexes i n non-donor s o l v e n t s and the s i m i l a r i t y of the s p e c t r a i n d i f f e r e n t s o l v e n t s . The t e t r a k i s p y r i d i n e d e r i v a t i v e s of c o b a l t ( I I ) h a l o a c e t a t e s gave non-conducting s o l u t i o n s i n acetone, i n d i c a t i n g no d i s s o c i a t i o n o f the h a l o a c e t a t e group, and were found r e a d i l y converted t o the b i s p y r i d i n e complexes i n s o l u t i o n w i t h the d i s s o c i a t i o n of p y r i d i n e . Evidence was a l s o o b t a i n e d from i n f r a r e d s t u d i e s f o r a concentration-dependent a s s o c i a t i o n e q u i l i b r i u m f o r the b i s p y r i d i n e h a l o a c e t a t e complexes i n ch l o r o f o r m . T h i s s e c t i o n d e s c r i b e s 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 l s t u d i e s and molecular weight s t u d i e s on s o l u t i o n s of p y r i d i n e c o b a l t ( I I ) a r y l c a r b o x y l a t e s i n some o r g a n i c s o l v e n t s . The b i s - and t e t r a k i s - p y r i d i n e c o b a l t (II) t r i f l u o r o a c e t a t e s were a l s o re-examined. The o b j e c t was to attempt t o i d e n t i f y the s p e c i e s p r e s e n t i n s o l u t i o n and t o o b t a i n i n f o r m a t i o n on the r e l a t i v e s t a b i l i t i e s of the complexes i n s o l u t i o n and how these are r e l a t e d t o the nature of the v a r i o u s c a r b o x y l a t e groups i n v o l v e d . A crude i n d i c a t i o n of the s o l u b i l i t y of each complex i n acetone, c h l o r o f o r m and benzene i s giv e n i n Table V-12. In the case of each combination of complex and s o l v e n t an _3 attempt was made t o prepare a 10 M s o l u t i o n . Where v i s u a l i n s p e c t i o n i n d i c a t e d a c l e a r c o l o u r e d s o l u t i o n the complex i s c o n s i d e r e d s o l u b l e i n t h a t s o l v e n t (designated ' s o l ' i n the t a b l e ) . Where v i s u a l i n s p e c t i o n i n d i c a t e d a t l e a s t 190 some of the complex remained u n d i s s o l v e d then the complex i s c o n s i d e r e d i n s o l u b l e i n t h a t s o l v e n t (designated ' i n s ' i n the t a b l e ) . TABLE V-12 Crude S o l u b i l i t y T e s t s on P y r i d i n e Complexes of C o b a l t ( I I ) C a r b o x y l a tes Acetone Chloroform Benzene C o ( C F 3 C 0 2 ) 2 - p y 4 s o l s o l s o l Co ( C F 3 C O 2 ) 2 - p y 2 s o l s o l s o l C o ( C H 3 C 0 2 ) 2 « p y 2 i n s * i n s C o ( C 6 H 5 C 0 2 ) 2 . p y 2 s o l s o l . s o l C o ( p - C H 3 0 - C 6 H 4 C 0 2 ) 2 « p y 2 s o l * * C o ( p - B r - C 6 H 4 C 0 2 ) 2 - p y 2 s o l s o l s o l c o ( P - N O 2 - C 6 H 4 C O 2 ) 2 - p y 2 i n s s o l i n s Co ( o - B r - C 6 H 4 C 0 2 ) 2 * p y 2 s o l s o l s o l C o ( o - N 0 2 - C 6 H 4 C 0 2 ) 2 . p y 2 s o l s o l i n s * g i v i n g suspension B i s - and T e t r a k i s - P y r i d i n e C o b a l t ( I I ) T r i f l u o r o a c e t a t e s Lever and Ogden (41) r e p o r t e d t h a t the c h l o r o f o r m s o l u t i o n i n f r a r e d spectrum of b i s p y r i d i n e c o b a l t ( I I ) d i c h l o r o a c e t a t e e x h i b i t s two a b s o r p t i o n bands a s s i g n a b l e t o 191 antisymmetric -CG^ s t r e t c h i n g f r e q u e n c i e s . From a concen-t r a t i o n study of the compound i t was found t h a t the lower energy band i n c r e a s e s i n i n t e n s i t y , a t the expense of the high e r energy band, as c o n c e n t r a t i o n decreases. From t h i s i t was concluded t h a t the hig h e r energy band a r i s e s from the antisymmetric s t r e t c h i n g of a b r i d g i n g c a r b o x y l a t e group and the lower energy band a r i s e s from a c h e l a t i n g c a r b o x y l a t e group. In the same study, the t e t r a k i s p y r i d i n e -h a l o a c e t a t e d e r i v a t i v e s were r e p o r t e d to d i s s o c i a t e p y r i d i n e t o g i v e b i s p y r i d i n e s p e c i e s i n s o l u t i o n . In f a c t , i n t h i s p r e v i o u s work very few r e s u l t s r e g a r d i n g the t r i f l u o r o -a c e t a t e complexes were g i v e n . We g i v e our r e s u l t s f u r t h e r d e t a i l e d examination of these complexes below. The i n f r a r e d s p e c t r a (1800 - 1300 cm - 1) of b 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 c o b a l t ( I I ) t r i f l u o r o a c e t a t e s i n c h l o r o f o r m s o l u t i o n with and without excess p y r i d i n e , are presented i n F i g u r e V-12. For the b i s p y r i d i n e complex, two main a b s o r p t i o n bands are observed, a t 1710 cm and 1670 cm 1 . As excess p y r i d i n e (> 1 M ) i s added, they are r e p l a c e d by a s i n g l e band a t 1685 cm with weak shoulders on both s i d e s . T h i s band corresponds to the 1690 cm band i n the s o l i d s t a t e spectrum of t e t r a k i s p y r i d i n e c o b a l t (II) t r i f l u o r o a c e t a t e s u g g e s t i n g t h a t i t can reasonably be as s i g n e d to a monodentate type of -CC^ v i b r a t i o n s . In support of t h i s the complex, Cu(CF^CG^)2*PY4 (152) of known s t r u c t u r e shows a monodentate -CO„ s t r e t c h i n g frequency a t 192 Co(CF 3C0 2) 2.py 4 Co ( C F 3 C O 2 ) 2 * p y 4 + excess pyridine co ( C F 3 C O 2 ) 2 * p y 2 Co ( C F 3 C O 2 ) 2 « p y 2 + excess pyridine 1700 1500 JL 1300 Frequency cm -1 Figure V-12. Solution Infrared Spectra of Pyridine Complexes of Cobalt (II) Trifluoroacetate (in Chloroform) 193 1690 cm-"''. The e f fec t of adding excess pyr id ine to the chloroform so lu t ion of the complex i s , thus, to favour the formation of a t e t r ak i spyr id ine species with monodentate carboxylate coord inat ion . The chloroform so lut ion of the t e t r ak i spyr id ine der iva t ive also shows two major bands at 1710 cm 1 and 1685 cm (see Figure V-12) . There i s a d e f i n i t e shoulder to the l a t t e r band at ^ 1670 cm ^ . As pyr id ine i s added i n excess (> 1 M), only one band at 1685 cm i s formed, with weak shoulders on both s ides . I t i s be l ieved that the t e t r ak i spyr id ine complex d i s soc ia te s i n chloroform to y i e l d , i n par t , the corresponding b i spyr id ine species , such that the in f ra red spectrum shows a mixture of bands a r i s i n g from both species . In p a r t i c u l a r , then, bands at 1710 cm 1 and 1670 cm 1 are due to the b i spyr id ine species , the higher energy band due presumably to br idg ing carboxylate coordinat ion and the lower energy band due to che la t ing carboxylate groups, and the band at 16 85 cm i s due to the monodentate carboxylate group i n the t e t r ak i spyr id ine species . On addi t ion of excess p y r i d i n e , the t e t r ak i spyr id ine der iva t ive predominates as the 1685 cm band p r e v a i l s . Figure V-12 indicates that the chloroform so lut ion in f ra red spectra of both the b i s - and the t e t r a k i s - pyr id ine cobalt (II ) t r i f luoroace ta te s show no band at a l l i n the region of 1430 -r 1300 cm ^ . This i s i n disagreement with the previous c la im that the symmetric - C O 2 s t re tching frequency of the b i spyr id ine der iva t ive (41) i s at 1350 c m - 1 . 194 As has been d i s c u s s e d p r e v i o u s l y ( S e c t i o n V-3-1) i t seems more l i k e l y t h a t the symmetric -CC>2 s t r e t c h i n g v i b r a t i o n occurs i n the r e g i o n of 14 50 cm ^ where i t i s a c c i d e n t a l l y degenerate with a p y r i d i n e r i n g v i b r a t i o n . The above d i s c u s s i o n leads to a c o n c l u s i o n t h a t the t e t r a k i s p y r i d i n e complex of c o b a l t ( I I ) t r i f l u o r o a c e t a t e d i s s o c i a t e s r e a d i l y i n c h l o r o f o r m to form the b i s p y r i d i n e s p e c i e s . F u r t h e r support of t h i s i s gained by examining the lower frequency r e g i o n of the i n f r a r e d s p e c t r a which shows t h a t the s o l u t i o n spectrum of the t e t r a k i s p y r i d i n e complex i s e s s e n t i a l l y a combination of the s p e c t r a of the b i s p y r i d i n e d e r i v a t i v e and f r e e p y r i d i n e . Bands as s i g n e d to f r e e p y r i d i n e were confirmed by n o t i n g an i n c r e a s e i n i n t e n s i t y as p y r i d i n e i s added. The spectrum of the b i s p y r i d i n e complex, however, does not show f r e e p y r i d i n e peaks and i t can be assumed t h a t the d i s s o c i a t i o n of p y r i d i n e accompanying d i s s o l u t i o n of the b i s p y r i d i n e complex i s q u i t e n e g l i g i b l e . I t was r e p o r t e d p r e v i o u s l y (41) t h a t m olecular weight data showed b i s p y r i d i n e c o b a l t ( I I ) t r i f l u o r o a c e t a t e t o be monomeric i n b o i l i n g acetone and b o i l i n g c h l o r o f o r m . The complex was claimed to be i n s u f f i c i e n t l y s o l u b l e i n benzene f o r molecular weight s t u d i e s ; however, i t was found -2 -3 i n the p r e s e n t work t h a t s o l u t i o n s of ^ 10 to 10 M c o u l d be prepared to permit molecular weight d e t e r m i n a t i o n . The r e s u l t s ( l i s t e d i n Table V-13) gave an average molecular 195 TABLE V-13 M o l e c u l a r Weight R e s u l t s of P y r i d i n e Complexes of C o b a l t ( I I ) C a r b o x y l a t e s Complex C o ( C F 3 C 0 2 ) 2 » p y 4 C o ( C F 3 C 0 2 ) 2 » p y 2 C o ( C 6 H 5 C 0 2 ) 2 . p y 2 C o ( p - B r - C 6 H 4 C 0 2 ) 2 • p y 2 Co ( o - B r - C 6 H 4 C 0 2 ) 2 ' P y 2 Concen-t r a t i o n E x p e r i -mental M o l e c u l a r Weight Average C a l c u l a t e d f o r Dimer 1.6xl0~ 3 1231 1204 1203 3.2xl 0 ~ 3 1208 4 . 4 x l 0 " 3 1174 1.2xl0~ 3 915 927 886 2 . 8 x l 0 ~ 3 987 4 . 2 x l 0 ~ 3 880 1.0xl0~ 3 837 921 919 1.9xl0~ 3 927 3.6xl 0 ~ 3 998 1 . 3 x l 0 ~ 3 1202 1263 1234 2 . 4 x l 0 ~ 3 1302 3 . 5 x l 0 ~ 3 1284 1 . 2 x l 0 ~ 3 1442 1236 1234 3.7xl 0 ~ 3 1091 4. 4 x l 0 ~ 3 1176 weight c o r r e s p o n d i n g t o dimer formation i n s o l u t i o n . T h i s agrees w e l l w i t h the p r e v i o u s r e s u l t s on the corr e s p o n d i n g d i - and t r i - c h l o r o a c e t a t e complexes which showed d i m e r i c behaviour i n benzene under s i m i l a r c o n d i t i o n s (41). As i s i n d i c a t e d from the i n f r a r e d r e s u l t s , the t e t r a k i s p y r i d i n e 196 complex d i s s o c i a t e s p y r i d i n e i n c h l o r o f o r m s o l u t i o n . D i s s o c i a t i o n i s s i m i l a r l y observed f o r t h i s complex i n benzene and i n acetone. In s p i t e of t h i s added c o m p l i c a t i o n m olecular weight s t u d i e s showed the complex to be a s s o c i a t e d i n s o l u t i o n (see Table V-13). That the presence of excess p y r i d i n e caused by d i s s o c i a t i o n d i d not s e r i o u s l y a f f e c t the molecular weight d e t e r m i n a t i o n s was confirmed by a d d i t i o n of p y r i d i n e to a s o l u t i o n of the p y r i d i n e complex (mole r a t i o o f added p y r i d i n e t o complex was ^ 4:1) and a l s o t o a s o l u t i o n o f the osmometic standard, b e n z i l . The readings o b t a i n e d on the Mecrolab vapour phase osmometer were not measurably a f f e c t e d by the a d d i t i o n of t h i s excess p y r i d i n e . C l e a r l y t h i s showed t h a t a s m a l l amount of p y r i d i n e i n a benzene s o l u t i o n of complex does not s e r i o u s l y a l t e r the vapour pressure of benzene. The e l e c t r o n i c s p e c t r a of the two p y r i d i n e complexes of c o b a l t ( I I ) t r i f l u o r o a c e t a t e i n s o l u t i o n s of benzene, c h l o r o f o r m and acetone were examined. Data are recorded i n Appendix V-2. A comparison of a l l the s o l u t i o n e l e c t r o n i c s p e c t r a of both complexes r e v e a l s the s i m i l a r i t i e s o f the s p e c t r a i r r e s p e c t i v e of the s o l v e n t (Appendix V-2). The above seems to r u l e out the p o s s i b i l i t y of s o l v e n t c o o r d i n a t i o n of these complexes i n s o l u t i o n . The a d d i t i o n o f p y r i d i n e to s o l u t i o n s o f the two complexes was a l s o s t u d i e d . The r e s u l t s i n d i c a t e t h a t there i s b a s i c a l l y no change i n the s p e c t r a as p y r i d i n e i s added to excess (Figure V-13'shows the V-13. Benzene S o l u t i o n E l e c t r o n i c Spectra of the Two P y r i d i n e Complexes of C o b a l t ( I I ) T r i f l u o r o a c e t a t e with and without Added P y r i d i n e data recorded i n Appendix V-2 198 e l e c t r o n i c s p e c t r a of these two complexes i n benzene w i t h and without added p y r i d i n e ) . As shown e a r l i e r from an i n f r a r e d study, the a d d i t i o n of p y r i d i n e t o s o l u t i o n s of the two t r i f l u o r o a c e t a t e complexes changes the b i s p y r i d i n e s p e c i e s t o the t e t r a k i s p y r i d i n e s p e c i e s . The s i m i l a r i t y i n the e l e c t r o n i c s p e c t r a of the two s p e c i e s i n s o l u t i o n i s t h e r e f o r e found t o be very s t r i k i n g . F i n a l l y i t should be p o i n t e d out t h a t the p o s s i b i l i t y of the formation of 2+ the s p e c i e s Co(py)g i n these s o l u t i o n s c o n t a i n i n g excess p y r i d i n e i s r u l e d out as the s p e c t r a observed here do not 2+ conform wi t h the r e p o r t e d s p e c t r a of Co(py)g (134). In c o n c l u s i o n the s t u d i e s d e s c r i b e d i n t h i s s e c t i o n have shown the t e t r a k i s p y r i d i n e complex of c o b a l t ( I I ) t r i f l u o r o a c e t a t e to be u n s t a b l e t o p y r i d i n e d i s s o c i a t i o n i n s o l u t i o n . The b i s p y r i d i n e complex i s q u i t e s t a b l e and i n benzene s o l u t i o n a t l e a s t , i s d i m e r i c . S p e c u l a t i o n on the s t r u c t u r e of t h i s d i m e r i c s p e c i e s i s r e s e r v e d u n t i l l a t e r ; however, the i n f r a r e d r e s u l t s suggest t h a t the s p e c i e s c o n t a i n s both b r i d g i n g and c h e l a t i n g c a r b o x y l a t e groups. B i s p y r i d i n e C o b a l t ( I I ) A r y l c a r b o x y l a t e s The i n f r a r e d s p e c t r a of b i s p y r i d i n e c o b a l t ( I I ) a r y l c a r b o x y l a t e s i n s o l u t i o n are u s u a l l y complicated over the r e g i o n of 1700 - 1300 cm 1 . No attempt was t h e r e f o r e made to a s s i g n the -CC^ s t r e t c h i n g f r e q u e n c i e s from these s o l u t i o n s p e c t r a . Despite the above, the f a c t t h a t these 199 complexes d i s s o c i a t e p y r i d i n e i n s o l u t i o n i s observed as a r e s u l t of the appearance of f r e e p y r i d i n e bands (e.g. a t 991 cm and 601 cm i n the s o l u t i o n s p e c t r a . The r e s u l t s of molecular weight s t u d i e s on complexes of c o b a l t (II) a r y l c a r b o x y l a t e complexes ( c o l l e c t e d i n Table V-13) i n d i c a t e an average d i m e r i c molecular weight i n benzene. Again, the d i s s o c i a t i o n of p y r i d i n e does not a f f e c t the outcome of the r e s u l t s . The r e s u l t s i n d i c a t e , then, t h a t i n s o l u t i o n , b r i d g i n g a c t i o n of the c a r b o x y l a t e groups i s n e c e s s a r i l y i n v o l v e d with c h e l a t i n g a c t i o n a l s o p r obably i n v o l v e d . C o n c e n t r a t i o n range used f o r e l e c t r o n i c s p e c t r a l measurements i s the same as t h a t used f o r both molecular weight and i n f r a r e d s p e c t r a l s t u d i e s , i . e . i n the range of 10~ 3 - 10~ 2 M. F i g u r e s V-14, V-15 and V-16 g i v e the s o l u t i o n s p e c t r a of a l l the b i s p y r i d i n e complexes of c o b a l t ( I I ) a r y l c a r b o x y l a t e s s t u d i e d i n t h i s work, i n the three s o l v e n t s used. Instead of d i s t i n c t l y d i f f e r e n t s p e c t r a l c h a r a c t e r i s t i c s between groups of complexes as observed i n the s o l i d s t a t e e l e c t r o n i c s p e c t r a d i s c u s s e d p r e v i o u s l y , the complexes show a range of s p e c t r a l d i f f e r e n c e s i n s o l u t i o n , which i s r e l a t e d t o the base s t r e n g t h of the a r y l c a r b o x y l a t e group i n v o l v e d . The r e s u l t s on the e s t i m a t i o n of the c e n t e r s of g r a v i t y of the V 3 and V i e l e c t r o n i c t r a n s i t i o n s as w e l l as the c a l c u l a t i o n of the e l e c t r o n i c parameters Dq and B f o r a l l complexes i n s o l u t i o n are summarized i n Table V-14. 24 20 16 1 2 8 4 v ' x i O ^ c m " 1 F i g u r e V-14. Acetone S o l u t i o n E l e c t r o n i c Spectra of B i s p y r i d i n e Complexes of C o b a l t ( I I ) Carboxylates data r e c o r d e d i n Appendix V-2 (complexes arranged from a to g a c c o r d i n g to i n c r e a s i n g pK of parent acid) F i g u r e V-15. Chloroform S o l u t i o n E l e c t r o n i c Spectra of B i s p y r i d i n e Complexes of C o b a l t ( I I ) Carboxylates data recorded i n Appendix V-2 (complexes arranged from a to g a c c o r d i n g to i n c r e a s i n g pK of parent a c i d ) F i g u r e V-16. Benzene S o l u t i o n E l e c t r o n i c Spectra of B i s p y r i d i n e Complexes of C o b a l t ( I I ) Carboxylates data r e c o r d e d i n Appendix V-2 (complexes arranged from a to g a c c o r d i n g to i n c r e a s i n g pK of parent acid) TABLE V-14 Spectral Parameters of Solut ion E l e c t r o n i c Spectra of Pyridine Complexes of Cobalt(II) Carboxylates Acetone Chloroform Benzene Complex P K a v 3 ( U V i (?) Dq B v 3 (?) V l (?) Dq B v 3 (?) V i (?) Dq B Co ( P - C H 3 0 - C 6 H 4 C O 2 ) 2 * P Y 2 4.47 17700 (119) 7690 (14.8) 874 731 - - - - - - - -C o ( C 6 H 5 C 0 2 ) 2 . p y 2 4.18 17860 (105) 7690 (12.0) 876 742 18020 (110L 7580 (13.8) 867 757 18020 (96.7) 7580 (12.3) 867 757 Co(p-Br-C 6 H 4 C0 2 ) 2 ^ 2 4.00 18020 (89.4) 7840 (10.9) 890 745 18020 (101) 7580 (12.3) 867 757 18020 (88.2) 7580 (11.2) 867 757 Co (p-N0 2 -C g H 4 C0 2 } 2 ' p y 2 3.43 — — — — 18180 (93.6) 7580 (12.8) 868 765 — — — — Co(o-Br-C 6 H 4 C0 2 ) 2 ^ 2 2.85 18180 (76.7) 7840 ( 8.6) 892 756 18350 (64.0) 8000 ( 8.6) 908 757 19050 (43.4) 8200 ( 6.8) 933 791 Co (o-N0 2 -CgH 4 C0 2 2.17 18180 (66.1) 7840 ( 6.4) 892 756 19050 (43.5) 8330 ( 6.8) 947 786 — — — — Co (CF 3C0 2) 2-'py 2 % 0 19800 (36.4) 8510 ( 5.2) 967 823 19800 (31.9) 8510 ( 5.2) 967 823 19800 (43.2) 8510 ( 5.7) 967 823 C O ( C F 3 C O 2 ) 2 - p y 4 % 0 19800 (39.0) 8510 ( 4.9) 967 823 19800 (38.3) 8510 ( 5.1) 967 823 19800 (45.3) 8510 ( 5.3) 967 823 Spectra data i n Appendix V-2 , v 3 , v i f Dq and B i n uni t s of cm ; ? i n un i t of 1/mole-cm 204 The bands V3 and v i are found to i n c r e a s e s t e a d i l y as pK (a measure of the base s t r e n g t h of the c a r b o x y l a t e cl group) decreases. In a d d i t i o n , £ decreases as pK a decreases These trends are a l s o c l e a r l y seen from F i g u r e s V-14, V-15 and V-16. A s p l i t t i n g of V i , a l s o appears i n some s o l u t i o n s and the ext e n t i s dependent on the pK of the complex; 3. s p l i t t i n g of V i being l e s s pronounced as pK decreases. The cl magnitudes of the parameters Dq and B are a l s o found t o i n c r e a s e as pK decreases, a A p l a u s i b l e e x p l a n a t i o n to these o b s e r v a t i o n s i s t h a t the a r y l c a r b o x y l a t e complexes d i s s o c i a t e p y r i d i n e t o d i f f e r e n t e xtents under s i m i l a r experimental c o n d i t i o n s (such as a f i x e d s o l v e n t and a s i m i l a r c o n c e n t r a t i o n ) a c c o r d i n g t o the e q u i l i b r i u m : C o ( R C 0 2 ) 2 . p y 2 ^ Co(RCQ 2) 2 « P V + py I I I Although the s p e c i e s I and I I are f o r s i m p l i c i t y d e p i c t e d as monomers here i t should be noted t h a t the molecular weight s t u d i e s suggest they are i n f a c t dimers. The u n d i s s o c i a t e d s p e c i e s I probably has a f a i r l y r e g u l a r s t r u c t u r e s i m i l a r to the type a s c r i b e d t o group A complexes i n the s o l i d s t a t e . The d i s s o c i a t e d s p e c i e s , on the other hand, probably has a more d i s t o r t e d o c t a h e d r a l s t r u c t u r e , or more p r e c i s e l y , a s t r u c t u r e of lower symmetry, as a r e s u l t of the d i s s o c i a t i o n of p y r i d i n e l i g a n d . Species 205 then g i v e s r i s e to a broader and more i n t e n s e spectrum wi t h p o s s i b l e s p l i t t i n g of the V i band i n case of s u f f i c i e n t l y low symmetry. F i g u r e V-17 g i v e s the benzene s o l u t i o n e l e c t r o n i c s p e c t r a ( i n the v i s i b l e region) a t d i f f e r e n t c o n c e n t r a t i o n s f o r each of the complexes Co (C^H^CC^) 2 *P V2 a n < ^ Co(o-Br-CgH 4C0 2) 2*py2' * f i n d i c a t e s t h a t the former complex g i v e s v i r t u a l l y the same s p e c t r a i n terms of s p e c t r a l s t r u c t u r e s and p o s i t i o n s i r r e s p e c t i v e of c o n c e n t r a t i o n ; the molar e x t i n c t i o n c o e f f i c i e n t does not vary with con-c e n t r a t i o n w i t h i n experimental e r r o r . T h i s i n d i c a t e s t h a t t h i s complex ( v i z . Co(CgHgCC^) 2'P v2) 1 S l a r g e l y d i s s o c i a t e d to g i v e mainly s p e c i e s I I i n benzene. The l a t t e r complex ( v i z . Co(o-Br-CgH 4C0 2) 2*P V2^ l s s n o w n i n F i g u r e V-17 t o g i v e d i f f e r e n t s p e c t r a f o r d i f f e r e n t c o n c e n t r a t i o n s . T h i s suggests t h a t a t the c o n c e n t r a t i o n s t u d i e d here t h i s complex i s o n l y p a r t l y d i s s o c i a t e d and the degree of d i s s o c i a t i o n v a r i e s s i g n i f i c a n t l y over the c o n c e n t r a t i o n range s t u d i e d . Some c o n f i r m a t i o n of the above was obtained by examining the e f f e c t of adding excess p y r i d i n e to benzene s o l u t i o n s of the a r y l c a r b o x y l a t e complexes. A d e t a i l e d a n a l y s i s was made of the benzoate and the o-bromobenzoate complexes and the r e s u l t s are presented i n F i g u r e s V-18 and V-19 r e s p e c t i v e l y . The a d d i t i o n of p y r i d i n e has the e f f e c t of s h i f t i n g the s p e c t r a l bands as w e l l as d e c r e a s i n g the a b s o r p t i o n 206 Figure V-17. Benzene Solution Electronic Spectra (Visible Region) of Co(C 6H 5C0 2) 2«py 2 and Co(o-Br-C 6H 4C0 2) 2*PY 2 - Effect of Concentration -3 Complex C o n e : 8.36x10 M / 100 5 0 a - 0 M py b - 0.14M py c - 0.30M py d - 0.96M py e - 1.64M py - P y r i d i n e S o l u t i o n Cone. : 8.42xl0~ 3 - KBr P e l l e t to o V x 1 0 " 3 c m ' 1 F i g u r e V-18. E f f e c t of Adding P y r i d i n e to Benzene S o l u t i o n of B i s p y r i d i n e C o b a l t ( I I ) Benzoate Complex C o n e : 10.6x10 M 24 20 16 12 8 V x 1 0 ' 3 c m _ l F i g u r e V-19. E f f e c t of Adding P y r i d i n e t o Benzene S o l u t i o n of B i s p y r i d i n e C o b a l t ( I I ) o-Bromobenzoate 209 i n t e n s i t i e s . The p o s i t i o n of the s p e c t r a l bands and the magnitude of £ are s h i f t e d towards the v a l u e s e x h i b i t e d by the t r i f l u o r o a c e t a t e complexes. In d e t a i l , V 3 i s s h i f t e d to h i g h e r energy on a d d i t i o n of p y r i d i n e w i t h both the breadth and the i n t e n s i t y g r a d u a l l y reduced. V i i s a l s o g r a d u a l l y d i m i n i s h e d i n i n t e n s i t y and the s p l i t t i n g i s l e s s pronounced as p y r i d i n e i s added. With excess p y r i d i n e added, both complexes y i e l d the same l i m i t i n g spectrum. The r e s u l t s then i n d i c a t e t h a t the two complexes have s i m i l a r s t r u c t u r e s i n the presence of excess p y r i d i n e i n s o l u t i o n d e s p i t e d i f f e r e n c e s i n the s o l i d s t a t e . The spectrum obtained on adding excess p y r i d i n e , i s i n f a c t very s i m i l a r to the s p e c t r a observed i n the s o l i d s t a t e f o r the group A complexes suggesting t h a t the s p e c i e s i n s o l u t i o n i s a b i s p y r i d i n e s p e c i e s with a s t r u c t u r e s i m i l a r to t h a t proposed f o r the group A complexes. However, the p o s s i b i l i t y of the formation of a t e t r a k i s p y r i d i n e s p e c i e s i n s o l u t i o n s c o n t a i n i n g l a r g e excesses of p y r i d i n e cannot be r u l e d out as such s p e c i e s would probably have s i m i l a r s p e c t r a l p r o -p e r t i e s as b i s p y r i d i n e s p e c i e s as i l l u s t r a t e d by the t r i f l u o r o a c e t a t e p a i r of complexes. The trends observed i n the e l e c t r o n i c s p e c t r a of d i f f e r e n t complexes with r e s p e c t t o pK of the parent a c i d a ( r e f e r r e d to p r e v i o u s l y ) may now be e x p l a i n e d . As pK of cl the parent a c i d decreases, the base s t r e n g t h of the c a r b o x y l a t e anion decreases r e s u l t i n g in a l a r g e r r e s i d u a l p o s i t i v e charge 210 on the cobalt ion i n the complex. This larger residual charge renders d i s s o c i a t i o n of pyridine more d i f f i c u l t . Hence, complexes derived from strong acids (e.g. t r i f l u o r o -acetic acid and o-bromobenzoic acid) with low pK a's undergo l i t t l e , i f any, d i s s o c i a t i o n of pyridine and t h e i r spectra are not much d i f f e r e n t from the spectra obtained i n solutions containing excess pyridine. Complexes derived from weaker acids on the other hand, such as the benzoate complex, undergo rather extensive d i s s o c i a t i o n of pyridine y i e l d i n g species of rather low symmetry which give r i s e to r e l a t i v e l y intense, broad and low energy bands i n the el e c t r o n i c spectrum. V - 5 . HYDRATED PYRIDINE COMPLEXES OF COBALT(II) ARYLCARBOXYLATES As described e a r l i e r i n t h i s Chapter, several of the attempts to prepare pyridine cobalt(II) arylcarboxylates yielded hydrated derivatives. The preparation and charact-e r i z a t i o n of such hydrated complexes was not persued extensively. Indeed, a considerable amount of time was spent attempting to obtain anhydrous pyridine complexes since i t was anticipated that the presence of a t h i r d type of ligand, i . e . water, i n the complexes would complicate the system and seriously hinder interpretation of the data. The spectral and magnetic properties of four of the hydrated complexes were, nevertheless, 211 recorded and t h i s s e c t i o n d e s c r i b e s the r e s u l t s of these experiments. The f o u r complexes under d i s c u s s i o n here are the monohydrates of b i s p y r i d i n e c o b a l t (II) p-methyl-, p-bromo-and p-chlorobenzoate and the d i h y d r a t e of b i s p y r i d i n e c o b a l t ( I I ) p - n i t r o b e n z o a t e . The i n f r a r e d s p e c t r a of a l l fo u r complexes show a broad band a t 3300 - 3400 cm a r i s i n g from the O-H s t r e t c h i n g v i b r a t i o n of the water molecules. In a d d i t i o n 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 the p y r i d i n e molecules i n the complexes are c o o r d i n a t e d and not p r e s e n t as l a t t i c e 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 on samples of a l l f o u r complexes as KBr p e l l e t s are shown i n F i g u r e V-20. The s p e c t r a may be analyzed assuming an approximate o c t a h e d r a l geometry about c o b a l t and average Dq and B valu e s f o r these complexes c a l c u l a t e d a c c o r d i n g l y . These l i g a n d f i e l d parameters, t a b u l a t e d i n Table V-15, are approximately the same as those c a l c u l a t e d f o r the anhydrous p y r i d i n e d e r i v a t i v e s , a r e s u l t which i s not too s u r p r i s i n g s i n c e the water molecules even i f they are i n v o l v e d i n d i r e c t c o o r d i n a t i o n t o c o b a l t , are expected t o p r o v i d e a l i g a n d f i e l d e f f e c t approximately the same as the p y r i d i n e and c a r b o x y l a t e l i g a n d s . Support f o r the assignment of an approximate o c t a h e d r a l geometry to these complexes comes from the magnetic s u s c e p t i b i l i t y d a t a . The room temperature magnetic Figure V-20. E lec t ron ic Spectra of Hydrated Pyr id ine Complexes of Cobalt(II) Arylcarboxylates (Solid State) 213 TABLE V-15 E l e c t r o n i c S p e c t r a l Parameters of Hydrated P y r i d i n e Complexes of C o b a l t ( I I ) A r y l c a r b o x y l a t e s ( S o l i d State) V3 v i Dq B Complex (cm ^) (cm ^) (cm ^) (cm "*") Co(p-CH 3-C 6H 4C0 2) 2 ' P y 2 ' H 2 ° 19300 9000 1030 770 C o ( p - C l - C 6 H 4 C 0 2 ) 2 •py 2,H 20 19300 8500 980 817 C o ( p - B r - C g H 4 C 0 2 ) 2 , P y 2 . H 2 0 19300 8500 980 817 Co (p-N0 2-C gH 4C0 2) 2-PY 2-2H 20 20500 9000 1006 847 moments are a l l high as expected f o r o c t a h e d r a l c o b a l t (II) and the cryomagnetic data ( d e t a i l s of which are given i n Appendix V-4) may be analyzed a c c o r d i n g to F i g g i s 1 model. The magnetic parameters obtained are l i s t e d i n Table V-16 and are very comparable to those obtained f o r the group A 'anhydrous 1 p y r i d i n e complexes d e s c r i b e d e a r l i e r i n t h i s Chapter. As was mentioned a t the beginning of t h i s s e c t i o n , a more d e t a i l e d i n t e r p r e t a t i o n of the data f o r these hydrated complexes i s d i f f i c u l t . For example, i t i s d i f f i c u l t t o determine whether the water molecules are c o o r d i n a t e d d i r e c t l y to the c o b a l t i o n s , whether they are simply hydrogen-bonded to c o o r d i n a t e d c a r b o x y l a t e groups or whether they are i n v o l v e d 214 TABLE V-16 Magnetic Parameters of Hydrated P y r i d i n e Complexes of C o b a l t ( I I ) A r y l c a r b o x y l a t e s y e f f Magnetic Parameters (R-T.) X _ 1 A Complex (B.M.) A (cm ) ^ k v (cm ) Co(p-CH 3-C 6H 4C0 2) 2-py 2-H 20 4.97 1.40 -150 0.99 -3 +450 C o ( p - C l - C g H 4 C 0 2 ) 2 « p y 2 - H 2 0 4.93 1.40 -150 0.96 -3 +450 C o ( p - B r - C 6 H 4 C 0 2 ) 2 » p y 2 - H 2 0 4.95 1.40 -150 0.92 +2 -300 Co(p-N0 2-C 6H 4C0 2) 2-py 2-2H 20 4.89 1.40 -150 0.92 -3 +450 i n both c o o r d i n a t i o n to c o b a l t ions and hydrogen-bonding to c a r b o x y l a t e groups (as found f o r example i n C o ( C H 3 C 0 2 ) 2 •4H 20 (4) ). One important c o n c l u s i o n t h a t can be drawn from t h i s study i s , however, t h a t whatever the d e t a i l e d s t r u c t u r e s of these complexes are, the water molecules p l a y an important r o l e i n deter m i n i n g these s t r u c t u r e s . T h i s i s seen by comparing 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 of the 'anhydrous' complexes Co(p-Br-CgH 4C0 2) 2*Py 2 and Co(p-N0 2-CgH 4C0 2) 2*py 2, c l a s s i f i e d e a r l i e r as group B complexes i n which the c o o r d i n a t i o n geometry about c o b a l t i s of low symmetry, wi t h the p r o p e r t i e s of the corres p o n d i n g 'hydrates' which are a k i n to those o f the group A complexes i n which the c o o r d i n a t i o n geometry about c o b a l t i s of r e l a t i v e l y h i g h e r symmetry. 215 CHAPTER VI SUMMARY AND CONCLUSIONS In the work d e s c r i b e d i n t h i s t h e s i s we have r e p o r t e d the p r e p a r a t i o n and c h a r a c t e r i z a t i o n of twenty-two new p y r i d i n e , t h i o u r e a and s u b s t i t u t e d t h i o u r e a complexes of c o b a l t ( I I ) c a r b o x y l a t e s . An e x t e n s i v e i n v e s t i g a t i o n of the magnetic and s p e c t r a l p r o p e r t i e s of these and r e l a t e d complexes i n the s o l i d s t a t e and i n s o l u t i o n was c a r r i e d out i n an attempt t o o b t a i n i n f o r m a t i o n on s t r u c t u r e and bonding i n these c o b a l t ( I I ) c a r b o x y l a t e complexes and i n so doing, i n c r e a s e our understanding of the metal c a r b o x y l a t e chemistry i n g e n e r a l . 216 The complexes s t u d i e d here are of two types: those i n v o l v i n g complexed t h i o u r e a and s u b s t i t u t e d t h i o u r e a l i g a n d s which have a Co0 2S2 chromophore, and those i n v o l v i n g complexed p y r i d i n e with a CoO^^ or CoO^N^ chromophore. They w i l l be d i s c u s s e d s e p a r a t e l y below. Thiourea and S u b s t i t u t e d Thiourea C o b a l t ( I I ) Carboxylate  Complexes These complexes are f o r m a l l y c o n s i d e r e d as ' t e t r a h e d r a l ' molecules (except f o r one complex to be d i s c u s s e d s e p a r a t e l y l a t e r ) which c o n t a i n a chromophore ( f i r s t or i n n e r c o o r d i n -a t i o n sphere) of C0O2S2. To a f i r s t approximation, t h e r e f o r e , the c a r b o x y l a t e groups are u n i d e n t a t e . Unidentate c o o r d i n a t i o n of c a r b o x y l a t e s has been claimed (1) before from X-ray c r y s t a l s t u d i e s on c o b a l t (II) complexes such as C o ( C H 3 C 0 2 ) 2 •4H 20 (4) and { ( C g H 5 ) 4 A s > 2 C o ( C F 3 C 0 2 ) 4 (10). However, i n both cases, the other oxygen atom of each c a r b o x y l a t e group i s i n v o l v e d i n bonding i n the second or outer c o o r d i n a t i o n sphere. For the former complex, one oxygen atom of the ac e t a t e group i s bonded to c o b a l t ( I I ) whereas the other i s s t r o n g l y H-bonded to a c o o r d i n a t e d water molecule. In the l a t t e r complex, the c o o r d i n a t i o n of the c o b a l t (II) i o n i s b e t t e r d e s c r i b e d as i n t e r m e d i a t e between t e t r a h e d r a l and dodecahedral w i t h the second oxygen i n v o l v e d i n weak c o o r d i n a t i o n t o the metal i o n . The molecular s t r u c t u r e of the complex Co (CH^C^) 2 *ETU 2 (9) shows a C o 0 2 S 2 chromophore 217 but the a c e t a t e groups a r e c o o r d i n a t e d i n such a way t h a t the c o o r d i n a t i o n number can be c o n s i d e r e d as i n t e r m e d i a t e between fo u r and s i x w i t h each a c e t a t e group having one oxygen s t r o n g l y bonded to c o b a l t and the other more weakly bonded to c o b a l t (see F i g u r e IV-1). 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 a l l the t h i o u r e a and s u b s t i t u t e d t h i o u r e a complexes were d e s c r i b e d i n Chapter IV and the f o l l o w i n g c o n c l u s i o n s were drawn. The e l e c t r o n i c s p e c t r a ( s o l i d s t a t e ) of these com-plexes were found to be r a t h e r s i m i l a r to each other and t o t h a t of the complex b i s ( e t h y l e n e t h i o u r e a ) c o b a l t ( I I ) a c e t a t e . In p a r t i c u l a r , the v i s i b l e and n e a r - i n f r a r e d bands were found s p l i t i n t o two or three bands a l l l y i n g i n about the same frequency r e g i o n s : 13000 - 19000 cm 1 and 6000 -9000 cm 1 r e s p e c t i v e l y . D i f f e r e n c e s i n the d e t a i l s of band s t r u c t u r e (number of components) and width were, however, observed f o r d i f f e r e n t complexes. The magnetic p r o p e r t i e s of these complexes were found to be q u i t e s i m i l a r . In p a r t i c u l a r , Curie-Weiss law was obeyed by a l l of these complexes and the e f f e c t i v e magnetic moments were i n the narrow range of 4.33 - 4.46 B.M. and Weiss con s t a n t s i n the narrow range of -2 - -7°K. The above experimental obser-v a t i o n s were i n t e r p r e t e d as i n d i c a t i n g t h a t these t h i o u r e a and s u b s t i t u t e d t h i o u r e a complexes of c o b a l t ( I I ) c a r b o x y l a t e s have s t r u c t u r e s very s i m i l a r to each other and very l i k e l y t o the s t r u c t u r e r e p o r t e d f o r b i s ( e t h y l e n e t h i o u r e a ) c o b a l t ( I I ) a c e t a t e (9) shown i n F i g u r e IV-1. 218 In s o l u t i o n the s p e c t r a become v i r t u a l l y i d e n t i c a l and the changes accompanying d i s s o l u t i o n were taken to i n d i c a t e t h a t they a l l have the same s t r u c t u r e s i n s o l u t i o n -one i n which the form of c a r b o x y l a t e c o o r d i n a t i o n more c l o s e l y approximates u n i d e n t a t e . The o b s e r v a t i o n t h a t the e l e c t r o n i c s p e c t r a f o r d i f f e r e n t complexes i n s o l u t i o n were v i r t u a l l y i d e n t i c a l was taken t o i n d i c a t e t h a t the e l e c t r o n i c s t r u c t u r e s of these complexes are not s i g n i f i c a n t l y a f f e c t e d by changes i n the nature of the ligands beyond the f i r s t c o o r d i n a t i o n sphere ( i . e . chromophore C0O2S2)• The complex b i s ( e t h y l e n e t h i o u r e a ) c o b a l t ( I I ) m-nitrobenzoate was found t o be, a p p a r e n t l y , pseudo-o c t a h e d r a l i n the s o l i d s t a t e . I t i s b e l i e v e d t h a t t h i s complex has b a s i c a l l y the same chromophore as the other c a r b o x y l a t e analogs d e s c r i b e d above; however, i n t h i s complex the i n t e r a c t i o n between the second oxygen atoms of the m-nitrobenzoate groups and c o b a l t ( I I ) are probably much stro n g e r and the s p e c i e s approximates a pseudo-octahedral complex. T h i s e x p l a i n s the d i f f e r e n c e i n the magnetic p r o p e r t i e s of t h i s complex compared t o those of the other analogous complexes. In s o l u t i o n (acetone), t h i s complex becomes a t y p i c a l t e t r a h e d r a l or f o u r - c o o r d i n a t e d s p e c i e s and i t s s o l u t i o n 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 f i t i n t o the trends observed f o r the other t e t r a h e d r a l c a r b o x y l a t e complexes. The reason why t h i s p a r t i c u l a r complex p r e f e r s an o c t a h e d r a l c o o r d i n a t i o n (or a stronger second oxygen atom i n t e r a c t i o n ) i n the s o l i d s t a t e i s , however, not understood. 219 B i s p y r i d i n e Complexes of C o b a l t ( I I ) Carboxylates These complexes can f o r m a l l y be regarded as o c t a h e d r a l molecules c o n t a i n i n g a chromophore ( f i r s t or i n n e r c o o r d i n a t i o n sphere) of CoO^^. The c a r b o x y l a t e groups are t h e r e f o r e n e c e s s a r i l y b i d e n t a t e . No X-ray c r y s t a l s t r u c t u r e study on any c o b a l t (II) complexes of t h i s type have been r e p o r t e d . Based on s t r u c t u r a l i n f o r m a t i o n obtained from complexes of other t r a n s i t i o n metals, c h e l a t i n g or b r i d g i n g c a r b o x y l a t e c o o r d i n a t i o n are p o s s i b l e . In the p a s t , the s t r u c t u r e s of o c t a h e d r a l c o b a l t ( I I ) c a r b o x y l a t e complexes have been i n f e r r e d from e l e c t r o n i c s p e c t r a l and magnetic s u s c e p t i b i l i t y measurements. For example, Lever and Ogden (41) measured these p r o p e r t i e s of s e v e r a l b i s p y r i d i n e c o b a l t ( I I ) alkanoates and h a l o a c e t a t e s and concluded an o c t a h e d r a l c o n f i g u r a t i o n f o r t h e i r complexes wi t h the two p y r i d i n e molecules t r a n s -c o o r d i n a t e d to c o b a l t ( I I ) . T h i s s t r u c t u r e was based on the o b s e r v a t i o n t h a t these complexes e x h i b i t e d magnetic moment va l u e s and e l e c t r o n i c s p e c t r a both t y p i c a l of ' r e g u l a r ' o c t a h e d r a l c o b a l t ( I I ) complexes. The p r e c i s e s t r u c t u r e s of these s p e c i e s are not known but probably i n v o l v e b r i d g i n g c a r b o x y l a t e groups. T h i s was i n f e r r e d from the c l o s e s i m i l a r i t y of the i n f r a r e d s p e c t r a of the s o l i d complexes to those of a s s o c i a t e d (polymeric) s p e c i e s i n s o l u t i o n . The b i s p y r i d i n e complexes of c o b a l t ( I I ) c a r b o x y l a t e s s t u d i e d i n t h i s work ( d e t a i l s i n Chapter V) were c l a s s i f i e d 220 i n t o two groups a c c o r d i n g t o t h e i r 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 . Group A complexes, which i n c l u d e d the two o r t h o - s u b s t i t u t e d benzoate, the a c e t a t e and the t r i f l u o r o -a c e t a t e complexes, e x h i b i t e d p r o p e r t i e s v i r t u a l l y i d e n t i c a l t o those r e p o r t e d e a r l i e r by Lever and Ogden (41). In p a r t i c u l a r , the e l e c t r o n i c s p e c t r a i n the s o l i d s t a t e were t y p i c a l of t r a n s - o c t a h e d r a l s t r u c t u r e s i n t h a t the v i s i b l e band was not g r e a t l y s p l i t and the n e a r - i n f r a r e d band appeared as a s i n g l e a b s o r p t i o n . The magnetic p r o p e r t i e s of these group A complexes were t y p i c a l o f t r a n s - o c t a h e d r a l s t r u c t u r e s , g i v i n g h i g h room-temperature magnetic moments (4.95 - 5.02 B.M.). These group A complexes may be assigned s t r u c t u r e s i n v o l v i n g b r i d g i n g c a r b o x y l a t e groups and t r a n s - c o o r d i n a t e d p y r i d i n e molecules. A t y p i c a l example of such s t r u c t u r e i s drawn i n F i g u r e VI-1. F i g u r e VI-1 T y p i c a l Example of S t r u c t u r e s I n v o l v i n g B r i d g i n g Carboxylate Groups and Trans-Coordinated P y r i d i n e Molecules Group B complexes, of b i s p y r i d i n e c o b a l t ( I I ) c a r b o x y l a t e s , which i n c l u d e d the benzoate, the p-bromobenzoate and the p - n i t r o -benzoate d e r i v a t i v e s e x h i b i t e d very d i f f e r e n t e l e c t r o n i c s p e c t r a l 221 and magnetic propert ies from the above. The e l e c t r o n i c spectra (in the s o l i d state) were very complex, bands were broad and the near- infrared band i n p a r t i c u l a r was s p l i t into at leas t two components. The spectra , i n general , indicated a lower symmetry structure for these complexes and the magnetic propert ies of these complexes further supported t h i s . These complexes exhibi ted low room-temperature magnetic moments i n the range of 4.6 -4.7 B.M. and the temperature var i a t ions of magnetic s u s c e p t i b i l i t y followed Curie-Weiss law. These magnetic r e su l t s alone pointed to a very d i s t o r t e d octahedral s tructure which has no center of symmetry. A l l the above e l ec t ron ic spect ra l and magnetic propert ies of these group B complexes were found to be i n c i d e n t a l l y i d e n t i c a l to those reported previous ly for several cobalt (II) n i t r a t e complexes described e a r l i e r i n t h i s the s i s . These n i t r a t e complexes have i n common a ' c i s - s t ructure ' i n which the two n i t r a t e groups are che la t ing to the same cobalt (II ) i o n . While these molecules could be considered as having a c i s -octahedral s t ructure , they could a lso be considered as having an e s s e n t i a l l y te trahedra l environment about cobalt ( II ) consider ing each n i t r a t e molecule as occupying one coordin-at ion p o s i t i o n . The e l e c t r o n i c spect ra l and magnetic propert ies were a l l consis tent with th i s approximate ' t e t r a h e d r a l ' stereochemistry. Because of these many s i m i l a r i t i e s between the n i t r a t e complexes and the group B 222 complexes studied i n t h i s work, they are considered to have s i m i l a r s t ructures . A t y p i c a l example of such structure i s given i n Figure VI-2 . L L - C N 0 / V C -Figure VI-2 T y p i c a l Example of Cis-Octahedral Structures For the carboxylate complexes, the two oxygen atoms of each carboxylate group are poss ib ly bonded i n a chela t ing fashion to the same cobalt ( I I ) i o n . However, the p o s s i b i l i t y of the - C 0 2 group br idging between cobalt (II ) ions cannot be ru led out as w i l l be seen l a t e r . The complex Co (p-CH-^O-CgH^CG^) 2 *PV2 w a s described e a r l i e r i n Chapter V as having s l i g h t l y d i f f e r e n t propert ies from i t s analogs. Al together , the re su l t s indicated a centrosymmetric, though highly d i s t o r t e d , s tructure for t h i s complex, which could be considered as intermediate between those of group A and group B complexes. One of the aims of the present work was to look for poss ible r e l a t i o n -ships between observed propert ies of cobalt (II ) carboxylate complexes and the nature of the carboxylate group - for example, the b a s i c i t y of the anion or the p o s i t i o n of a 223 s u b s t i t u e n t group on the a r y l r i n g . The reasons f o r the v a r i a t i o n s i n s t r u c t u r e among the p y r i d i n e - c a r b o x y l a t e complexes are not understood as there i s no obvious c o r r e l a t i o n between the s t r u c t u r a l type and the nature of the c a r b o x y l a t e group. The s t a b i l i t i e s of these complexes towards p y r i d i n e d i s s o c i a t i o n , however, do seem to be r e l a t e d d i r e c t l y t o the nature of the anion i n v o l v e d . As the s t u d i e s on the s o l u t i o n e l e c t r o n i c s p e c t r a showed, the s t a b i l i t y of b i s p y r i d i n e c o b a l t ( I I ) c a r b o x y l a t e complexes decreases as the base s t r e n g t h of the c a r b o x y l a t e anion (as measured by the pK of the parent a c i d ) i n c r e a s e s . a Based on the r e s u l t s observed above f o r a l l p y r i d i n e complexes s t u d i e d i n t h i s work, a g e n e r a l s t r u c t u r e model i s now proposed. The model i s drawn i n F i g u r e VI-3. F i g u r e VI-3 Proposed S t r u c t u r e Model f o r C o b a l t ( I I ) Carboxylate Complexes #-C O'O L~ Ligand S u b s t i t u e n t on -CO., Group In t h i s s t r u c t u r a l model c a r b o x y l a t e groups are c o o r d i n a t e d i n such a way t h a t one oxygen atom i s bonded to one c o b a l t ( I I ) i o n whereas the other oxygen atom l i n k s two neighbouring c o b a l t (II) ions i n d i f f e r e n t e x t e n t s f o r d i f f e r e n t complexes. T r i - c o o r d i n a t e d oxygen atoms have been observed (26, 30) before i n support of t h i s s u g g e s t i o n . Even though there are a t l e a s t two d i s t i n c t groups of 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 among a l l b i s -p y r i d i n e complexes of c o b a l t ( I I ) c a r b o x y l a t e s , i t i s p o s s i b l e to use the above model to account f o r both group c h a r a c t e r -i s t i c s and a l s o t h a t of the 'intermediate' complex ( i . e . the p-methoxybenzoate d e r i v a t i v e ) . R e f e r i n g t o F i g u r e VI-3, the c a r b o x y l a t e groups can be c o n s i d e r e d as e i t h e r b r i d g i n g or c h e l a t i n g depending on the comparative i n t e r a c t i o n s between the 0 ( i ) atoms wit h the two neighbouring c o b a l t ( I I ) i o n s . In the former case where b r i d g i n g c a r b o x y l a t e c o o r d i n a t i o n p r e v a i l s ( i n t e r a c t i o n between 0 ( i ) and C o ( i i ) i s g r e a t e r than t h a t between 0 ( i ) and C o ( i ) , the two p y r i d i n e molecules remain t r a n s to each other and a very centrosymmetric molecul i s o b t ained which i s i d e n t i c a l t o the one shown i n F i g u r e V I -In the l a t t e r case where c h e l a t i n g c a r b o x y l a t e c o o r d i n a t i o n p r e v a i l s ( i n t e r a c t i o n between 0 ( i ) and C o ( i ) i s g r e a t e r than t h a t between 0 ( i ) and C o ( i i ) . The s t r u c t u r e can e i t h e r be c o n s i d e r e d as a d i s t o r t e d dodecahedron or the two p y r i d i n e molecules are no longer 18 0° a p a r t from each other and the s t r u c t u r e favours a t e t r a h e d r a l arrangement such as the one i n F i g u r e VI-2. The p-methoxybenzoate d e r i v a t i v e has probably an in t e r m e d i a t e s t r u c t u r e w i t h comparable i n t e r a c t i o n between 0 ( i ) and the two neighbouring c o b a l t ( I I ) ions such t h a t a h i g h l y d i s t o r t e d but e s s e n t i a l l y centrosymmetric s t e r e o c h e m i s t r y r e s u l t s . T h i s s t r u c t u r e model i s a l s o seen t o be a p p l i c a b l e to the t e t r a h e d r a l c o b a l t ( I I ) c a r b o x y l a t e complexes (with t h i o u r e a and s u b s t i t u t e d t h i o u r e a ) . In those cases, the ca r b o x y l a t e groups are e s s e n t i a l l y c h e l a t i n g with very weak b r i d g i n g i n t e r a c t i o n and the s t r u c t u r e becomes a t e t r a h e d r a l one as d e s c r i b e d e a r l i e r i n F i g u r e IV-1. The complex t e t r a k i s p y r i d i n e c o b a l t ( I I ) t r i f l u o r o -a c e t a t e a l s o s t u d i e d i n t h i s work i s c o n s i d e r e d t o have a CoO^N^ chromophore which n e c e s s a r i l y i n v o l v e s 'unidentate' c a r b o x y l a t e c o o r d i n a t i o n . However, the q u e s t i o n t o whether the second oxygen atom of the t r i f l u o r o a c e t a t e group has any e f f e c t on the c o b a l t ( I I ) i o n s i s not answerable without an X-ray c r y s t a l s t r u c t u r a l study. As a ge n e r a l c o n c l u s i o n the form of c o o r d i n a t i o n of the c a r b o x y l a t e groups of c o b a l t ( I I ) complexes w i t h t h i o u r e a and s u b s t i t u t e d t h i o u r e a l i g a n d s i s probably i n t e r m e d i a t e between uni d e n t a t e and c h e l a t i n g . 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APPENDIXES I l l u s t r a t i o n s f o r E l e c t r o n i c S p e c t r a : A - Absorbance f o r the s o l i d s t a t e s p e c t r a ( s c a l e a r b i t r a r y ) £, (€) - Molar e x t i n c t i o n c o e f f i c i e n t f o r the s o l u t i o n s t a t e s p e c t r a ( l e f t s c a l e f o r the l e f t p o r t i o n : v i s i b l e r e g i o n and r i g h t s c a l e f o r the r i g h t p o r t i o n : n e a r - i n f r a r e d region) KBr - Potassium bromide p e l l e t spectrum D i f f u s e - D i f f u s e r e f l e c t a n c e spectrum Acetone - Acetone s o l u t i o n spectrum Chloroform - Chloroform s o l u t i o n spectrum Benzene - Benzene s o l u t i o n spectrum 236 A Electronic Spectra ol CofCIO^ • tu^ |/ x 1(5?cm"' Electronic Spectra o l C o C I ^ T U A uoi 2« 20 y xto'em"' Electronic Sjectro 01 Co(m-N0 2 -C a H 4 C0 2 ) 2 -TU 2 V X lO* em"' Electronic Spectra of Co(6-3r-C H CO ) • TU, 6 4 2 2 2 V X 1 0 cn V X10"3c VxlO cm Electronic Spectra ol Co(C_H CO) • TU 6 5 2 2 2 A V X l O c n Electronic Spectra ol Col CILCO ) • TU 3 2 2 2 Appendix IV-1. E l e c t r o n i c Spectra of TU, ETU and DMTU Complexes of Cobalt(II) Perchlorate, Chloride and Carboxylate: 237 A. y X103cm*' E l e c t r o n i c S p e c t r o of C o t p - B r - C H C O ) • E T U 6 4 Z 2 2 20 16 12 B t > xlO - 3cm" E l e c t r o n i c S p e c t r a o l Co I C I O ) , • E T J A 2 A V* x 1 0 3 c m * ' Electronic Spectra of Co(o-NO -C H.CO.) •ETU. 2 o A 2 2 2 A 24 20 24 20 Electronic Spectra of C o l o - B r - C ^ C O ^ - E r u ^ 24 20 Electronic Spectra of C o t o - W y C ^ C O ^ ' 0 M T U 2 Appendix IV-1 (Cont.) 238 V « ' 0 cm A Electrons Spectre ol CotCO,J • DMTU, 4 2 4 Electronic Spect'o cl Co Cl • D M T U 2 A e l e c t r o n i c S p e c t r a o l C o (p-NO^ c 6 H 4 c o 2 ' 2 ' C M T U j Electronic Spectra ol C o I p - B r - C ^ C O ^ - D M 7 U 2 VxlO cm Electronic Spectra ol CoCo-Br - C ^ C O ^ • D v . T U 2 V xto cm Electronic Spectro ol Co ( C g H j ^ ' j ' 0 M T U j Electronic Spectro ol CotCH J CO J ) ; [ - D M I U J Appendix IV -1 (Cont.) KBr Diffuse Acetone 239 APPENDIX IV-3 ELECTRONIC SPECTRAL DATA OF TU, ETU AND DMTU COMPLEXES OF COBALT(II) rKKCIILOKATE, CHLORIDE AND CAKBOXYLATES "Normal D i s t i l l e d " Acetone Acetone • Excess S-Ligand Complex Con. Frequency ( t l Con Frequency (t) Frequency Frequency (M), (cm' 1) (1/molc-cm) (M) (cm" 1) (1/mole-cm) (cm" 1) (cm" 1) 5.57x10" 3 15870sh (288) 2 57x10" 3+0.1SM 15870sh (424) 15600sh 15700sh 14560 (479) 145S0 (715) 14500 14500 13790 (436) 13790 (658) 13900 «.43x10" 7030 (146) 6 43x10" 3+0.15H 7030 (163) 7240+sh 3.37x10" 3 15870sh ( 95) 1. 0 x l O " 3+0.1 M 15870sh (454) 16100 15700sh 14580 (174) • 14SS0 (741) 14700 14f00 13790 (155) 13790 (659) 14100 5.92x10" 7030 ( 98) 5. 9 x l O " 3+0.1 M 7030 (163) 8330 6900 • 5560 2.51x10" 3 15B70sh ( 74) 1. 9 x l O " 3+0.1 M 15870sh (434) 15630 15630 14500 (172) 14500 (733) 14350 14770 13790 (140) 13790 (622) 13550 6.28x10" 7030 ( 95) 6. 75x10" 3+0.1 M 7030 (158) 7150 5810 1.05x10" 3 16120 (398) 1. 0 x l O " 3+0.22M 16210 (456) 16600 16300 15000 (437) 15000 (520) 15400 15400 14030 (389) 14030 (458) 13500 8.8 xlO" 7350 ( 60) 8. 8 x l O " 3+0.1 M 7350 ( 67) 8700sh 6200 ( 78) 6200 ( 85) 7690 5500 ( 98) S500 (107) 5780 0.95x10" 3 16210 (389) 0. 95x10" 3+0.1 M 16210 (480) 15850 15900 15000 (403) 15000 (538) 14600 14600 14030 (360) 14O30 (423) 13600 9.9 x l O " 7350 ( 55) 9. 9 x l O " +0.1 M 7350 ( 58) 7300 6200 ( 70) 6200 ( 77) 6120 5500 ( 89) 5500 (100) 5400 2.03xl0~ 3 16210 (374) 2. 03x10" +0.1 M 16210 (456) 16260 16130 15000 (394) 15000 (489) 15220 15220 14030 (330) 14030 (409) 13820 3.6 x l O " 7350 ( 44) 3. 6 x l o " +0.1 M 7350 ( SO) 7150 6200 ( 62) 6200 ( 70) 5490 5500 ( 78) 5500 ( 90) 19.2x10" 3 18350 ( B2) 2. 91x10" 3+0.4 M 18350 (364) 19690sh 19760sh 16860 ( 76) 16860 (361) 18730 18620 14900 ( 54) 14900 (298) 16720 16890 19.2x10" 8000 ( 16) 7. 3 x l O " +0.4 H 8000 ( 72) 15380 15630sh 6S80 ( 22) 6580 (106) 9520sh 8330 6250 i . s . i . s 18520 18520sh 17400 17610 15020 15380 9500 8330 6250 1.9. i . s 18870 18180 17240sh 16860sh 8700 7400 d. 2. 96x10" 3+0.4 M 18350 (385) 18870 18900 16890 (372) 16500 16500 14840 (290) 14710 14680 9. 6 x l o " 3+0.4 M 8000 ( 76) 10530sh 6580 (107) 8330 6330 i . a . i . s 19230 17950 17400+sh 16950sh 15150sh 8850 6670 d. 3 . 53x10" 3+0.35H 18380 (367) 18190 18180 16860 (356) 16950 17010 14930 (2B0) 15380 154B0 10.0x10 3+0.35M 8000 ( 70) 105303(1 6580 (105) 8700 C o ( C 1 0 4 ) j - T U 4 C o ( C10 4)j.ETU 4 C o ( p - B r - C 6 H 4 C 0 2 ) 2 - T U 2 Co(p-Br-CgH^COj) 2" E T U2 Co(p-Br-C sH 4COj) 2•DMTU2 C o ( C 6 H 5 C 0 2 ) 2 ' T U j Co(o-Br-C 6H 4COj) 2•TU 2 i . s . 18870 17540 14370 6250 18870 17420 14370 8250 6500 240 APPENDIX IV-J (Cont.) •Normal D i s t i l l e d " Acetone Acetone + Excess S-Ligand D i f f u s e KBr Complex con. Frequency (C> Cone. Frequency ( C ) Frequency Frequency |M) (cm* 1) (1/mole-cm) (M) (era" 1) (1/mole-cm) (cm" 1) (cm" 1) C o ( o - B r - C 6 H 4 C 0 2 ) 2 - D M T U 2 i . s . " 2 v - 6 " 4 ' - " 2 ' 2 - i " 2 C o ( o - K 0 2 - C g K < C 0 2 ) J . E T U J i . s . 0" 3  n-3 2 6"4 2 ' 2 2 " 2 - 6 4 ^ " 2 ' 2 2 " 2 > " 6 " 4 " " 2 ' 2 " " ' " 2 0 " 3 0" 3 0" 3 0 " 3 0 " 3 „ - 3 Co(CH 3C0 2) 2-TUj C o ( C H 3 C 0 2 ) 2 - E T U 2 i . s . O" 3 „-3 s a t u r a t e d 1 8 2 5 0 ( - ) 1 9 4 6 0 s h 1 8 5 2 0 1 6 6 7 0 ( - ) 1 7 7 0 0 1 7 2 4 0 s h 1 4 8 1 0 ( - ) 1 5 1 5 0 1 4 9 3 0 s h 8 7 0 0 6 3 8 0 1 8 0 2 0 ( 1 8 1 ) 2 . 8 x l o" 3+0 .4 M 1 8 0 0 0 ( 3 8 3 ) 1 8 2 5 0 1 8 2 5 0 1 6 8 1 0 ( 1 8 0 ) 1 6 8 1 0 (399) 1 6 7 5 0 1 6 8 6 0 1 5 0 4 0 ( 1 3 2 ) 1 5 0 4 0 ( 3 1 2 ) 1 5 2 2 0 1 5 4 3 0 8000 • ( 3 7 ) 5 . 7 2 x l 0~ 3+0 .4 M 8 0 0 0 ( 7 8 ) 8 6 2 0 6 5 8 0 ( 4 7 ) 6 5 8 0 ( 1 2 1 ) 6 0 6 0 i . s . 1 7 3 3 0 1 7 3 3 0 1 6 3 4 0 1 6 3 4 0 1 4 9 7 0 1 4 9 7 0 8 3 3 0 s h 6 3 2 0 1 8 2 5 0 ( 4 2 ) 1. , 8 x l 0" 3+0 . 4 H 1 8 2 5 0 ( 3 7 3 ) 1 9 2 3 0 s h 1 8 3 5 0 1 6 7 2 0 ( 36) 1 6 7 2 0 ( 3 2 6 ) 1 7 8 6 0 1 7 2 4 0 1 4 9 3 0 ( 1 8 ) 1 4 9 3 0 ( 2 8 4 ) 1 5 1 5 0 s h 1 5 1 5 0 s h .8000 ( 1 2 ) 6. ,4 x l 0" 3+0 . 4 M 8 0 0 0 ( 7 0 ) 8 4 0 0 6 5 8 0 ( 1 7 ) 6 5 8 0 ( 1 0 0 ) 6 6 7 0 1 8 2 8 0 ( 1 3 6 ) 3. . 6 7 x 1 0 " 3+0 . 2 M 1 8 1 8 0 ( 3 7 4 ) 1 9 2 3 0 1 9 0 5 0 1 6 9 5 0 (131) 1 6 8 1 0 ( 3 6 3 ) 1 6 8 6 0 1 6 9 8 0 1 5 0 4 0 ( 88) 1 4 9 7 0 ( 3 0 0 ) 1 5 1 7 0 1 5 3 1 0 8000 ( 19) 6. ,3 x l 0" 3+0 . 2 M 8 0 0 0 ( 7 1 ) 8 8 1 0 6 5 8 0 ( 2 5 ) 6 5 8 0 ( 1 0 7 ) 6 4 3 0 1 8 3 8 0 ( 76) 4. . 7 1 x l 0 " 3 + s a t ' 'd 1 8 3 8 0 ( 3 8 3 ) 2 0 4 0 0 s h 1 9 6 0 0 s h 1 6 8 4 0 ( 7 0 ) 1 6 8 4 0 ( 3 4 8 ) 1 8 4 2 0 + s h 1 3 4 2 0 + s h 1 4 8 4 0 ( 3 1 ) 1 4 8 4 0 ( 2 9 4 ) 8 0 0 0 ( 1 2 ) 4. . 7 1 x 1 0 t s a t 1 'd 8 0 0 0 ( 77) 8 5 0 0+sh 6 5 8 0 ( 1 8 ) 6 5 8 0 ( 1 1 5 ) 1 8 2 5 0 ( 8 3 ) 4. . 2 0 x 1 0 " 3+0 . 4 M 1 8 2 5 0 ( 3 8 0 ) 1 8 3 2 0 1 8 3 2 0 1 6 7 2 0 ( 7 2 ) 1 6 7 2 0 ( 3 5 0 ) 1 6 7 2 0 1 6 8 6 0 1 4 8 8 0 ( 4 0 ) 1 4 8 8 0 ( 3 1 0 ) 1 4 9 7 0 1 5 1 7 0 8 0 0 0 ( 1 4 ) 6. . 5 2 x 1 0 " 3+0 . 4 H 8 0 0 0 ( 7 1 ) 9 0 9 0 6 5 8 0 ( 2 0 ) 6 5 8 0 ( 1 1 0 ) 6 4 5 0 i . s . 1 8 5 2 0 1 S 3 2 0 1 7 2 4 0 1 7 5 4 0 1 5 9 0 0 1 5 9 0 0 s h 8 7 0 0 6 5 4 0 5 8 1 0 i . s . 1 8 5 2 0 1 8 5 2 0 1 7 1 0 0 1 7 1 0 0 1 4 3 3 0 1 4 3 7 0 8 7 0 0 6 5 4 0 5 8 1 0 s h i . s . 1 8 7 3 0 1 8 8 7 0 1 6 9 5 0 1 7 2 4 0 1 5 1 1 0 1 5 2 2 0 9 0 9 0 6 6 7 0 1 8 1 8 0 ( 7 3 ) 5 . 3 4 x l 0 " 3 + 0 . 5 M 1 8 1 8 0 ( 3 8 2 ) 1 7 5 4 0 1 7 5 4 0 1 6 6 7 0 ( 67) 1 6 6 7 0 ( 3 5 2 ) 1 5 7 2 0 1 5 9 7 0 1 4 9 5 0 ( 39) 1 4 9 5 0 ( 3 2 2 ) 1 4 7 5 0 1 5 0 6 0 8 0 0 0 ( 1 0 ) 5 . 3 4 x l 0 " 3 + 0 . 5 M 8 0 0 0 < 7 0 ) 8 0 0 0 6 5 8 0 ( 1 5 ) 6 5 8 0 ( 1 0 5 ) 6 6 5 0 241 APPENDIX IV-3 MAGNETIC DATA OF COBALT(II) COMPLEXES WITH TU, ETU AND DMTU A. Room-Temperature Measurements 1 0 6 X . 10 6(Dia.Corr.) 10 6 (TIP) 1 0 6 X C ° " Complex T(°K) , 9 . M.W. ' . , . „ r , , Co , r (c.g.s.) (c.g.s.) (c.g.s.) (c.g.s.) Co(C10 4) 2-ETU 4 293 .4 14.02 666.7 -302 507 9142 Co(C10 4) 2-TU 4 293 .5 13.97 562.3 -250 507 7598 Co(C10 4) 2'DMTU 4 286 .9 12.70 674.7 -339 507 8401 CoCl 2-ETU 2 295 .0 25.49 334.3 -173 630 8064 CoCl 2*TU 2 293 .8 30.78 282.1 -147 630 8200 CoCl 2-DMTU 2 285 .6 26.04 338.3 -192 630 8371 Co(CH 3C0 2) 2-ETU 2 295 .8 21.36 381.5 -191 540 7418 Co(CH 3C0 2) 2-TU 2 292 .0 25.28 329.3 -165 540 7950 Co(CH 3C0 2) 2-DMTU 2 287 .1 21.92 385.5 -210 540 8120 Co(C gH 5C0 2) 2-TU 2 295 .4 17.87 453.3 -242 540 7802 Co{CgH 5C0 2) 2•DMTUj 287 .1 16.86 509.1 -287 540 8330 Co(p-Br-C 6H 4C0 2) 2•ETU 2 .296. 0 12.10 663.4 -326 540 7813 CO(p-Br-CgH 4C0 2) 2•TU 2 293. 8 13.65 611.2 -300 540 8102 Co (p-Br-CgII 4C0 2) 2 • DMTU2 287. 1 12.97 667.4 -345 540 " 8461 Co(m-N0 2-C 6!I 4C0 2) 2-TU 2 285. .8 15.75 543.4 -258 540 8277 Co(m-N0 2-C 6H 4C0 2) 2-DMTUj 286. 0 14.51 599.6 -303 540 8463 Co (o-Br-C 6II 4C0 2) 2 • ETU 2 295. ,5 12.68 663.4 -326 540 8198 Co (o-Br-CgII 4C0 2) 2 -TU 2 295. ,0 13.72 611.2 -300 540 8145 Co(o-Br-CgH 4C0 2) 2•DMTUj 286. 8 12.70 667.4 -345 540 8281 C o ( o - K 0 2 - C g H 4 C 0 2 ) J ' E T U J 295. ,3 14.02 595.6 -284 540 8094 Co(o-N0 2-C 6H 4C0 2) 2-TU 2 292. .8 15.95 543.4 -258 540 8385 Co(o-N0 2-C gH 4C0 2) 2•DMTU 2 286. ,0 14.16 599.6 -303 540 8253 CO(p-N0 2-C gH 4C0 2)j•DMTU 2 286. .4 14.44 599.6 -303 540 (c.g.s.) 8421 W e f f ( B . M . : CO(m-K0 2-C gH 4CO 2) 2-ETU 2 285. .8 18.68 595.6 -284 11420 5 . 1 1 : 242 APPENDIX 1V--3 (Cont.) B . Variable* Temperature Measurements T( K) (e.g. s.) 1 0 6 \ , • • Co (c .g .s . ) T("K) 10'v 10 x„ vg Co ( c .g .s . ) ( c . g . s . ) " 6 X „ c c o i r 1 0 6 X • • T(°K) " * y "Co (c.g.s.) (c.g.s.) i o \ g (c.g.s.) 1 0 ' (c. C o t c i o ^ ) , . P : : T U ±4 CoJCHjCOjl^j-309.0 20 .38 7526 298 .6 21 .14 7819 289 .6 21.74 8051 270 . 4 23 .25 8633 242.9 25 .32 . 9624 213 .5 29 .17 10915 184 . 4 33 .57 12611 155 .2 39.40 14859 135 .5 44 .64 16879 117 .0 51 .49 19519 l o c o 56.32 21381 88 .2 6 5 . 6 0 24959 C o ( C 6 H 5 C Q 2 ) ? - 0 H T U ? 308.7 15 .79 7786 298.4 16.26 8025 287.5 16.83 8315 271.9 17.81 8814 241.5 19 .98 9919 214.0 22 . 5 3 11217 184.2 25.92 12943 155.2 30.50 15275 129.3 36 .09 18120 109.2 42.41 21338 93.0 49.30 24846 co(p-nr-cG ii ^  co, i2 -TU. 308.6 11. .79 7737 312. 2 24 .26 7633 298.6 12. ,21 8070 295 . 0 25 .49 8044 287 .8 12. .66 8364 280 . 9 26 .61 8419 271.1 13. 43 8693 2 4 9 . 7 29 .58 9412 242.0 15. OS 10006 2 2 1 . 4 33 .07 10578 212 .0 17. ,09 11363 192 . 6 37 .60 12093 186.5 19. ,34 12SS1 162 . S 43 .76 14152 156 .0 22. 99 15343 1 3 5 . 8 51 .49 16736 132 .3 26. 64 17S06 113 . S 58 .32 19019 116 .8 30. 19 20201 108. 0 63 .37 20708 99 .0 34. 87 23359 9 5 . 4 71 .32 23365 85 .7 39. ,45 26449 8 3 . 4 7 9 . 3 5 26050 CoCl2jTU2 CoClj• DMTU, 312.0 29 .11 7829 306 . 7 24.48 7844 304 .9 29. 74 8007 293. 8 25 .39 8151 299 .9 30. 19 8134 2 8 3 . 7 26.12 8398 294 .3 30 .71 8280 2 6 9 . 3 27.70 8933 287 .9 31 .36 8460 242 . 4 30.54 9894 274.6 32. 80 8870 2 1 3 . 5 34 .53 11243 272.9 33. 03 8935 188 . 0 38 .97 12746 238 .2 37. 33 10148 155 . 5 46 .43 15286 214.4 41. .70 11380 127 . 5 55.61 13375 112 . 1 63.01 20878 9 2 . 9 73 .87 24552 Co(CH3CO,). 211122 CoJCH3CO_2)_2lTU2 312.0 20 .28 7361 311. .2 23.76 7453 299 .8 21 .12 7681 300. .0 24 .69 7759 287 .5 21 .96 8002 287. , 8 25 .67 8082 273.6 22 .90 8360 270. .4 27 .23 8596 242 .9 25 .79 9463 243. .1 30.28 9600 214.0 29 .16 10748 214. ,6 33 .97 10815 185.7 33 .35 12347 186. .5 38 .89 12435 157.6 39 . 17 14567 156, .0 45 .57 14635 137.0 44 .32 16531 128. . 0 54.54 17589 11B.5 50 .68 13957 111. . 3 62 .08 20072 109 .7 54 .80 20529 98, .8 68 .80 22285 95 .8 61 .52 23092 87, .2 76 .20 24722 83 .5 69 .75 26232 ££l£i^9°21-2—2 310.4 17 . 05 7435 2 9 8 . 7 17. 65 7707 286 . 3 18. 38 8038 271 .9 19. ,45 8523 2 4 2 . 4 21 .75 9565 2 1 1 . 3 24. ,83 10961 1 6 2 . 0 28 .51 12630 1 5 3 . 7 33. ,40 14846 128 .2 39 .37 17552 1 1 2 . 3 44. ,56 19905 9 9 . 8 49 .18 21999 Co(p-Br ^6lL , C 0 2 );•ETU2 3 0 9 . 3 11, .63 7475 2 9 7 . 5 12, .07 7767 2 8 7 . 2 12, .48 8039 272 .0 13, .14 8477 243 .2 14, .66 9485 2 1 5 . 0 16, .52 10719 186 .2 19 .03 12385 155 .1 22 . i 0 14687 133 .8 25 .87 16922 1 2 1 . 5 28 .57 18713 1 1 0 . 2 31 .10 20392 9 6 . 9 34 .82 22860 8 3 . 5 39 .81 26170 3 1 0 . 5 2 9 7 . 5 2 8 7 . 0 2 7 0 . 8 2 4 1 . 5 2 1 2 . 7 1 8 5 . 4 1 5 5 . 5 1 3 2 . 0 1 1 1 . 0 9 6 . 9 8 5 . 0 14 .61 1 5 . 1 7 15 .72 16.62 18.61 2 1 . 0 5 23.94 2 8 . 2 7 32. 87 3 8 . 8 3 43 .91 4 9 . 2 6 7657 7961 S260 8749 9S31 11157 12727 15080 17530 20S1S 23579 26486 Co(o-Br-C|-H]C0,) ;.-ETU, C o ( p - D r - C c I I , C O ; )_2• 312 .5 13 .13 8506 311, ,4 13 .27 7220 310 .4 1 3 . 0 2 7722 3 1 1 . 5 12 .00 7> U 299.8 13.60 8952 299, .1 13 .80 7518 2 9 1 . 2 1 3 . 7 3 8166 300 .5 12 .41 8 i ; 7 288.6 14 .32 9299 283. .8 14 .45 78S3 2 7 0 . 3 14 .74 8773 286 .2 12 .91 6; 21 270 .0 15 .23 9906 265. .7 15 .19 8-169 242 .6 16 . 37 9769 271 .4 1 3 . 6 " 8 ; 42 242.9 16. 97 11066 242. .4 1 7 . 0 3 9334 2 1 5 . 0 18 .41 11016 242 .8 15. 2S 10: j 3 213 .0 19 .21 12559 212. .7 19.3-1 10633 184 .6 21 .21 12728 213 .9 17 .25 11.• : s 185.0 22 .07 1 4466 186. .8 21 .92 120S4 1 5 5 . 0 25 .04 15063 1 8 4 . 9 19 .94 1 3 : I 3 154 .3 25 .92 17033 154. .5 26 .21 14496 1 3 7 . 0 2 8 . 33 17079 154. 9 23.55 15: : 2 126.2 31.16 20526 129. 30.91 17139 116 . 3 32 .C6 19371 131 .5 27 .41 is: o c 108.4 35 .43 23373 111. .2 35 .63 19793 1 0 6 . 5 35.45 21431 115 .5 31 .17 20c : 5 93.7 40 .27 26600 96. ,5 40 .28 22407 9 4 . 9 3 9 . 5 2 23919 100. 8 35 .19 23 : Jl 87 .2 4 0 . 1 0 26: i 3 Co (n-SO.,-CgHl . C O , ) 309.1 299.4 2 6 S . 2 272 .3 242 .1 214 .0 194 .6 154 .7 131 .7 1 1 7 . 0 101 .5 88 .6 2 - ^ 6 ^ 13 .46 13 . 88 14 .41 15 . 25 17 .11 1 9 . 2 7 2 2 . 2 3 26 .25 30 .46 3 4 . 3 5 38 .86 43 .74 7S34 8C;5 84.'3 ss :7 ioc:2 112:7 13C52 15^ :3 19C:7 2 0 j ; 9 23C-:3 259.-0 C o ( o - B r - C 6 H . C S - , ) , • ? [ • • . 310 .1 1 2 . 1 0 7787 311 .3 1 3 . 0 5 7740 300 . 2 1 2 . 5 0 8053 295 .7 13 .71 8 K 4 2 8 7 . 1 1 3 . 0 8 8437 2 8 0 . 3 1 4 . 4 2 8573 267.0 1 4 . 0 2 9061 261.0 1 5 . 5 5 92f S 2 4 3 . 0 15 .41 9983 233 .5 1 7 . 2 7 10319 2 1 3 . 8 1 7 . 4 3 11323 204 .5 1 9 . 6 5 117"4 1 8 3 . 8 20 .21 13167 176 .0 22 .6 8 136:5 1 5 6 . 8 2 3 . 7 1 15489 175.0 22. 80 136J9 1 2 8 . 7 2 3 . 6 8 18786 145 .0 2 7 . 2 0 163:-? 112 .1 33 .02 21665 126 .2 30 .92 186£2 1 0 0 . 5 3 6 . 4 1 23921 109 .4 35 .36 21376 8 7 . 7 4 1 . 4 4 27251 94.4 4 0 . 1 7 24316 Co(o-Br ^ 6 ^ = 0 2 ' ,2 - D " ™ 2 Co(o-::o 2^£6&4C02 2 - 2 ^ 2 309.1 11 .86 7720 296 .8 1 3 . 9 3 8017 2 9 7 . 9 1 2 . 2 7 7994 286 .0 1 4 . 4 7 8335 2 8 5 . 3 1 2 . 7 5 8314 265 .9 15 .71 9075 267.6 13 .66 8922 242 .1 17 .20 9962 241 .4 1 5 . 1 2 9396 213 .3 19 .44 11255 2 1 2 . 2 17 .14 11244 184 .4 2 2 . 2 7 12932 1 8 3 . 5 19 .82 13033 154 .5 26 .31 15333 1 5 4 . 5 2 3 . 3 7 15402 126 .7 31 .59 18533 129 .4 2 7 . 5 4 18135 108 . 5 36.54 21461 1 1 1 . 5 3 1 . S 3 21032 93.6 41 .76 24593 9 3 . 3 3 7 . 3 5 24732 Co(o-SO 2 - C6!i4 C 02 i . 2 ^ 2 Co (o-::o 2^«4™ 3 1 0 . 7 1 5 . 0 8 7916 310. 3 13 .12 7637 2 9 7 . 8 1 5 . 7 3 3270 298 .0 13 .64 7942 285 .1 16 .34 8601 289 .0 1 4 . 0 7 819S 2 6 2 . 7 1 7 . 6 1 9231 272 .0 1 4 . 8 3 8653 234.4 2 0 . 0 7 10628 243 .0 16 .62 9723 2 3 4 . 3 20 .19 10633 213.8 18 .79 11023 2 0 4 . 0 22 .79 12106 185.0 21 .65 12744 1 7 3 . a 26 .36 14046 155.0 25 .46 15025 149.0 30 .52 16307 128.9 30 .15 17841 1 4 5 . 5 31 .52 16850 112.6 34.42 20401 124.4 36 .20 19393 90.0 42 .04 24970 110.0 4 0 . 7 2 21849 * 93.0 4 6 . 8 2 25164 10 v ++ A C o Co <p->:o 2^»4«'-2. ) 2-D:<TU2 (c.g.s.) (8.! 3 1 0 . 5 13 .38 7786 Co (n--:o. 2^«4£2 L2IES2 2 9 9 . 3 13 .85 8067 2 8 8 . 7 14 .36 8373 310.4 17.20 10528 5 . 1 : 270.2 1 5 . 3 0 8937 298.1 17 .88 10933 5 . : -241.0 17 .17 10058 289.0 18 .41 11249 5..;: 2 1 3 . 8 1 9 . 32 11347 271 .1 19 .79 12071 5 . 1 : 1 8 3 . 5 22 .28 13122 242.1 22.10 13447 5 . r 1 5 4 . 0 26 .24 15497 214.0 24 .91 15120 5 . 0 ! 1 3 0 . 2 30. 79 18225 184.3 29 .64 17342 5 . 0 ' 111.6 35 .94 21313 154 . 5 33.34 20141 4.9! 93.0 4 2 . 1 0 25006 135 . 5 37.24 22464 4.1 122.0 40.76 24 561 4 . ?' 107.0 45 .00 27086 4 . 5 : 88.5 5 1 . 2 5 30809 4.6: 243 Appendix IV-4. Curie-Weiss P l o t s of TU, ETU and DMTU Complexes of C o b a l t (II) P e r c h l o r a t e , C h l o r i d e and Carboxylates 244 Appendix IV-4 (Cont.) 245 TEMP ( °K) Appendix IV-4 (Cont.) Appendix V - l . Electronic Spectra of Pyridine Complexes of Cobalt (II) Carboxylates KBr Diffuse Acetone Chloroform •«•«« Benzene 247 A F I ' E N D I X V-2 E L E C T R O N I C S P E C T R A D A T A O F P Y R I D I N E C O M P U T E S O F C O H A L T ( I I ) C A R P.OXYl . A T E S Chloroform Complex +0.1M py • 0.1M py +0.1M py Cone. F r e q . F r e q . 10 ( t l 20920 20920 (35.2) (34.0) 19800b 19800b (45.3) (43.4) 16530* 16530W ( 6.4) ( 5.4) 8510 •8510 ( 5.3) ( 5.2) 20920sh 20920sh (33.4) (37) 19300b 19800b (43.2) (45.5) 16530W 16530W ( 8.4) ( 9.9) 8510 8510 ( 5.7) ( 5.9) Cone. F r e q . F r e q . Freq. Freq. U) F r e q . F r e q . CotCH.CO,) C o ( C F 3 C 0 2 ) 2 . p y 2 C o ( C H 3 C 0 2 ) 2 . p y 2 XlO C o ( p - C H 3 0 - C 6 H 4 C 0 2 ) j .py 2 d. C o ( C 6 H 5 C 0 2 ) 2 <>y2 xlO Co <p-Br-c 6H 4co 2) 2•py 2 C o ( p - N O j - C g H 4 C 0 2 ) 2 - p y 2 19050sh 21050sh (82.8) (37) 17700b 19420b (96.5) (55.8) 8510 17700 (12.3) (56.8) 7550 8510 (12.3) (11.4) 6900 6900 (12.2) ( 8.3) 19050sh 21190sh (76.6) 17700 19050 (88.2) (53.6) 8510 17700 (11.2) (55.7) 7410 8510 (108) (10.1) 6900 6900 (10.9) ( 7.9) i . s . 8.52 20920sh 20920sh 5.99 20920sh 20920ah 20830sh 20920sh xlO (29.9) 19800b (38.3) 8510 ( 5.1) 8.23 . ,„-3 d. 8.44 xlO'3 (25.4) 19800b (31.9) 8580 ( 4.7) XlO (26) 19420 (39.0) 20920sh 20920sh (31) 19690b (38.9) 8510 ( 5.2) (27.8) 19800b (35.8) 8S80 ( 5.5) 13.0^ 10.2 ». l n~3 8510 ( 4.9) (29) 19720b (39.0) 8580 ( 4.0) 20000 20200 19050sh 9300 20920sh 20920sh 20830sh 20920sh (26.5) 19420b (36.4) (30) 19720b (38.3) 19610b 19920 19.2 X l O - 3 i . s . 7.37 xlO"3 10.0 x l 0 ~ 3 19230sh 210S0sh (97.7) 17860b 19340b (110) (91.1) +sh 18350 (93.8) 8770 17090sh (13.5) (78.1) 7690 8700 (13.5) (15.2) 6850 7550sh (13.8) (14.6) 8400 ( 5.2) 18690 (100) 17540 (119) 16950sh 8700 (14.2) 7850 (14.8) 7000 (13.5) 18690sh (92) 17610 (105) 8700 (12.8) 7840 (13.5) 6900sh 19050sh 19230b X l 0 -J 19050sh (91.8) (79.9) (80) 17860 18350sh 17860 (101) (67.5) (89.4) 8700b 3620b 9.19 8160b 8330b (12.2) (13.0) X l O - 3 (10.9) (11.3) 7690b 7410sh 6900 (12.1) (11-8) (10) 6900b (12.3) 8510 8850 ( 5.8) 21280sh 21370 19800b 20370 19610sh 8930 22470 22730sh 19800 19800 18690sh 18870 8160b 15750 16950sh (13.6) 7000sh 9520b (12) 20830sh 20530sh 19050 19230 9800 . 8330b 7410sh (15.0) +sh 20830sh 20830sh 19230 19330 15630sh 10310 7300 20920sh 19050 (88.9) 18020 (93.6) 17090sh 8510 (72.8) 7410 (11.8) 6900 (11.6) 20920sh 19310 (74.2) 18420 (72.3) 17090sh 8510 (12.7) 7410sh 20620sh 20830 19010 19230 18520sh +ah 10530 7250 Co(o-Br-C,.H.CO,),'py, 8.29 21280sh 20960sh 7.52 21050sh (37.4) (33.7) 18760b 19800b (43.2) (39.8) 17240sh 17420sh XlO 8510 ( 6.8) +sh 8510 ( 6.4) C o ( o - N 0 2 - C s H 4 C 0 2 ) 2 ' p y 2 i.». 9.42 xlO - 3 20830sh 7.27 20920sh 20830sh 20830sh (37.5) X l O ' 3 (41.0) 19230b 19310b 18590sh 19610 19840 (58.5) (70.7) (66.3) 18020 18520b 17610 16130sh (64.0) (70.7) (76.7) 17240sh 17240sh 7.66 8510 8510 88SO 8510 8510 x l O "3 ( 8.6) 7040 ( 9.S) • ah ( 8.6) (11.7) ( 8 . 0 ) 20920sh 20920sh 5.48 208303b. 20830sh 20830sh 21050sh (30.3) (32.9) x l O ' 3 (36.5) (39) 19050b 19420b 19000 19310 19690 19920 (43.5) (49.9) (62.1) (62.1) 17090sh 17090fih 17860 183f.Osh 18870ah •ah (27.6) (28.9) (66.1) (58.4) 8510 8510 16950oh 16950 8890 { 6.8) ( 8.5) (55) (43.8) +ah 10.9 X l O " 3 8400 7040Bn 8510 ( 6.2) +ah 248 APPENDIX V-J MAGNETIC PATA OF PYRIDINE COMPLEXES OF COBALT I I I ) CARBOXYLATES A. Room-temperature Measurements T "'V 1 0 6 D i a . 1 0 6 x „ Complex ( c > g « s - J M.W. ( c ^ r r , ( c - g c S - ) *«fI<B.M.> C o ( C F 3 C 0 2 ) j - p y 4 294.0 16. .92 601. .4 -286 10462 4. .959 C o ( C F 3 C 0 2 ) j - p S - 2 294.2 23. .40 443. .2 -188 10559 4, .989 Co<p-CH 30-C 6H 4C0 2) 2-py 2 293.8 19. .35 519. .4 -278 10329 4. .926 C o ( C 6 H 5 C 0 2 ) 2 . F y 2 294.5 19. ,78 459. .4 -246 9333 4. .688 C o ( p - B r - C 6 l l 4 C 0 2 ) 2 - p y 2 295.4 13. .89 617. .2 -304 8877 4, .580 C o ( p - N 0 2 - C 6 H < C 0 2 ) 2 - p y 2 295.4 15. .85 549. .4 -262 8970 4. .604 C o ( o - B r - C 6 H 4 C 0 2 ) 2 - p y 2 295.4 16. .79 617. .2 -304 10667 5, .020 C o ( o - N 0 2 - C 6 H 4 C 0 2 ) 2 -py 2 295.1 18. ,57 549. .4 -262 10464 4. .969 C o ( C H 3 C 0 2 ) 2 - p y 2 29S.0 30. .41 335. .3 -169 10365 4, .954 B„ V a r i a b l e - t e m p e r a t u r e Measurements Temp(°K) ioS <e.« g I.s. ) (c.g.s.) ue£f (B.M.) Temp(°K) 1 ° % (c.g.s 106x„ .) (c.g.s.) " e f t (B.M.) Temp(°K) 1 0 \ (c.g.s. ) (c.g.s.) u e f f (B.M.: Co(CFjCO, ^ 2^4 Co(p-CH 30 -c 6 i :L|S° 2>-2^2 CO(C 6H 5 c g 2 i 2 ^ i 2 314.7 15. 73 9746 4. 953 308 .3 18 .44 9856 4.930 312.0 18. 74 8854 4. 700 287.2 17. 27 10672 4. 951 291 .8 19 .71 10515 4.954 291.7 19.97 9419 4. 688 263.1 18. 75 11562 4. 932 271 . 1 21 .03 11201 4.928 261.8 22.10 10398 4. 666 238.8 20. 55 12645 4 . 914 243, . 1 23 .57 12520 4.934 234.0 24.67 11578 4. 655 217.0 22. 52 13830 4. 899 186 .1 30 .28 16005 4.880 202.0 28. 32 132S5 4. 627 186.0 25. 76 15778 4. 848 167 .8 33 .17 17553 4.853 176.0 32.42 15138 4. 616 159.0 29. 39 17961 4. 779 136 .2 40 .05 21132 4.798 146.6 37.91 17660 4. 550 137.1 33. 20 20252 4. 712 120 .4 44 .73 23573 4. 764 128.2 42.93 19966 4. 525 116.7 37. 67 22941 4 . 627 108 .5 48 .92 25755 4.727 111.0 . 48.77 22648 4. 484 106.0 40. 52 24655 4. 572 97 .5 52 .62 27682 4.646 98.8 53.78 24950 4. 440 93.3 44. 69 27163 4. 502 84 .0 59 .83 31437 4.595 90.0 5B.38 27063 4. 414 79.7 49. 66 30152 4. 384 82.0 62.73 29061 4. 366 ColCFjCO, ColCHjCO, 2-2^2 Co(p-Br - C 6 H , C 0 2 ) 2 : ^ r 2 315.0 21. 96 9921 4. 999 296 .0 30 .63 10439 4.950 313.5 13.11 8395 4. 588 297.3 23. 08 10417 4. 990 290 .2 31 .22 10637 4.950 304.8 13.49- 8630 4. 587 285.5 24. 24 10931 4. 996 272 .3 32 .78 11160 4.930 292.7 14.03 8963 4. 581 280.4 24. 50 11046 4. 990 259 .0 34 .06 11589 4.900 273.6 14.93 9519 4. 564 252.7 26. 99 12150 4. 975 224 .5 38 .90 13212 4.870 245.0 16.51 10494 4. 535 234.6 29. 15 13107 4 . 956 209 .7 41 .78 14178 4.876 214.0 18:81 11914 4. 515 205.6 32. 89 14765 4 . 927 194 .0 44 .30 15023 4.828 184.5 21.45 13543 4. 470 171.0 38. 25 17140 4. 842 166 .0 50 .68 17162 4.773 160.7 24.33 15320 4. 437 145.7 43. 57 19498 4. 767 145 .5 56 .55 19130 4.718 136.2 28.20 17709 4. 392 126.5 48. 65 21750 4. 691 126 .2 63 .32 21400 4.648 127.2 30.90 19375 4. 351 109.2 54. 50 24342 4. 611 115 .7 66 .23 22376 4.605 111.2 33.45 20949 4. 316 96.8 59. 27 26456 4. 526 106 .7 72 .27 24401 4.563 101.0 36.19 22640 4. 277 84.2 64.75 28885 4. 410 9S .4 78 .39 26453 4.493 90.0 39.93 24949 4. 238 88 .0 83 .10 28032 4.442 76 .5 90 .95 30665 4.331 Co(p-NO,-£6«4£°2^ '-2^X2 Co(o-Br-C 6«4! ^2! 2^.2 CO(o-NO 2 ^ 6 « 4 C 0 2 l •2^.2 314.0 15. 02 8513 4 .624 312 .5 15 .89 10111 5.027 314.0 17.40 9821 4. 966 294.5 15. 90 8997 4. 603 290 .2 17 .14 10883 5.026 291.5 18.78 10557 4. 966 272.S 17. 07 9639 4. 583 269 .7 18 .36 11636 5.010 269.5 20.34 11436 4. 965 244.0 19. 03 10716 4 . 573 241 . 8 20 .44 12920 4.998 241.5 22.69 12727 4. 958 214.0 21. 52 12084, 4. 548 213 .5 22.91 14444 4.966 211.0 25.59 14320 4. 916 18S.7 24. 63 13792 4. 526 184 .0 26 .03 16370 4.908 181.8 29.21 16309 . 4. 870 156.0 29. 09 16243 4. 502 155 .6 29.78 18684 4.822 154.7 33.54 18687 4. 808 135.0 32. 92 18347 4. 451 134 .5 33 .21 20801 4.730 135.0 37.31 20758 4. 734 117.5 37. 66 20951 4. 437 118 .0 36 .83 23035 4.663 116.5 41.91 23285 4. 658 108.5 39. 89 22176 4. 387 104 .0 39.83 24887 4.550 108.0 44.24 24565 4. 606 96.0 44. ,12 24499 4. .3 37 94 .0 43.09 26899 4.497 96.0 47.99 26625 4. 521 83.0 49. ,87 27658 4. ,285 82 .0 47 .05 29343 4.387 83.5 53.02 29389 4. 430 249 APPENDIX V-4 MAGNETIC DATA OF HYDRATED PYRIDINE COMPLEXES OF COBALT(II) ARYLCARBOXYLATES Room-Temperature Measurements Complex Co(p-Cl-C 6H 4C0 2) 2py 2- H 20 Co(p-Br-C gH 4C0 2) 2- py 2- H 20 T(°K) 106 Xg M.W. 106Dia. Corr i o 6 X C o + + V e f f 294.7 18. 32 546. 2 -293 10300 4 .927 293.8 15. 93 635 . 2 -317 10436 4 .952 294 .5 20. 15 505. 4 -282 10471 4 .966 294. 0 16. 86 585. 4 -288 10157 4 .887 B. Variable-Temperature Measurements T(°K) 10 6 X, A C o J e f f T(°K) I O V io6x C o++ y e f f Co(p-Cl-C 6H 1C0 2) 2.py 2-H 2Q Co (p-CH 3-C 6H 4CQ 2) 2. py 2. H2Q 311.5 17. 33 9759 4. 931 310. 0 19. 07 9920 4 .959 292. 0 18. 46 10376 4. 922 290. 0 20. 49 10638 4 .967 272. 8 19. 87 11147 4. 931 266. 5 22. 35 11578 4 .968 242.5 22. 19 12414 4. 907 234. 3 25. 27 13053 4 .946 213. 3 24. 81 13845 4. 860 204. 0 28. 74 14807 4 .915 185.5 28. 40 15806 4. 842 174. 3 33. 19 17056 4 .876 155.5 33. 16 18406 4. 784 145. 7 38. 84 19912 4 .817 135.5 37. 40 20722 4. 739 125. 7 44. 06 22550 4 .761 117.0 42. 13 23306 4. 670 111. 5 48. 63 24860 4 .708 108.5 44. 94 24841 4. 643 96. 5 54. 31 27730 4 .626 96.0 48. 95 27031 4. 556 82. 8 61. 17 31197 4 .545 84.5 55. 47 30592 4. 547 Co (p-Br-^ 6 « 4 C 0 2 1 2 ^ 2 - il 2° Co (p £P.2)_2iEy.2: 2H 2° 312.0 14. 98 9832 4. 953 312. 2 15. 84 9560 4 .886 293.7 16. 06 10518 4. 970 290. 8 17. 02 10251 4 .883 284.0 16. 47 10779 4. 948 270. 0 18. 30 11000 4 .874 259.7 17. 99 11744 4. 939 240. 5 20. 44 12253 4 .855 230.5 20. 14 13110 4. 916 210. 2 23. 00 13752 4 .808 199.0 22. 86 14838 4. 860 181. 5 26. 40 15742 4 .780 169.5 26. '80 17340 4. 848 152. 0 30. 68 18247 4 .710 149.0 29. 74 19208 4. 784 133. 9 34. 55 20513 4 .687 129.7 33. 29 21463 4. 719 116. 2 38. 83 23018 4 .625 118.0 35. 90 23121 4. 671 108. 0 41. 11 24353 4 .586 105. 3 39. 07 25134 4. 600 95. 0 45. 48 26911 4 .522 95.0 41. 93 26951 4. 525 83. 5 50. 59 29902 4 .469 84.0 45. 97 29517 4. 453 

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