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Electron spin resonance of some vanadyl, copper and cobalt porphyrins Lau, Pui-Wah 1974

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ELECTRON"*S-PIN RESONANCE OF SOME VANADYL, COPPER AND COBALT PORPHYRINS by PUI-WAH LAU B.Sc. (cum l a u d e ) , Chinese U n i v e r s i t y o f Hong Kong, 1968 M . S c , U n i v e r s i t y o f B r i t i s h C o lumbia, 1970 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n t h e Department o f C h e m i s t r y We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH O c t o b e r , 197^ COLUMBIA In presenting th i s thesis in pa r t i a l fu l f i lment of the requirements for an advanced degree at the Univers i ty of B r i t i s h Columbia, I agree that the L ibrary shal l make it f ree ly ava i lab le for reference and study. I fur ther agree that permission for extensive copying of th i s thes is for scho lar ly purposes may be granted by the Head of my Department or by his representat ives. It is understood that copying or pub l i ca t ion of th i s thes is for f inanc ia l gain sha l l not be allowed without my writ ten permission. PUI-WAH LAU Department of Chemistry  The Univers i ty of B r i t i s h Columbia Vancouver 8, Canada 3 March 197 5 Date i ABSTRACT Electron Spin Resonance study was carried out on a series of metalloporphyrins (where metal = VO , Cu , and Co , porphyrin = (4-pyridyl)porphin, (p-carboxylphenyl)porphin, tetrabenzporphyrin, and octamethyltetrabenzporphyrin), magnetically d i l u t e d i n the free base porphyrins, or organic solvents, aiming at the understanding of the elec t r o n i c structures of these b i o l o g i c a l important compounds and the factors affected them. In the case of vanadyl porphyrin, the unpaired electron was found to be i n the b£ o r b i t a l . The changes i n ligand f i e l d energies as the function of porphyrins were found to correlate with the sizes of the porphyrin holes. Some solvent effects were noted. In the case of copper porphyrins, the unpaired electron was in o r b i t a l . The changes i n ligand f i e l d energies as the function of porphyrins showed the same trend as the vanadyl counter-parts. The solvent e f f e c t was also noted. However, the most i n t e r e s t i n g r e s u l t s were those of cobalt porphyrins, which gave dramatically d i f f e r e n t ESR spectra i n di f f e r e n t environments. When a cobalt porphyrin was magnetically d i l u t e d i n the free base porphyrin, gy< 2 .0 , "2 .0 < gj< 3 . 5, | A C O | ~ 100-200 x 10~^ cm"1, |B C oI~ 200-400 x 10" 4 cm - 1. The spin Hamil-tonian parameters correlated very well with the c r y s t a l packings. Upon d i s s o l v i n g i n pyridine under vacuum, the ESR spectrum showed i i s u p e r h y p e r f i n e s t r u c t u r e s at b o t h g and g^ p a r t s due t o two s o l v e n t m o l e c u l e s c o - o r d i n a t e d a t t h e a x i a l p o s i t i o n s , and changes i n o t h e r s p i n H a m i l t o n i a n parameters as w e l l . These r e s u l t s gave an i n s i g h t t o t h e e l e c t r o n i c s t r u c t u r e s o f c o b a l t p o r p h y r i n s . When t h e c o b a l t p o r p h y r i n - p y r i d i n e complex was exposed t o a i r , an oxygen m o l e c u l e r e p l a c e d a s o l v e n t m o l e c u l e . S i n c e g and A^°-tensors were not c o i n c i d e n t , a method f o r t r e a t -as ~ i n g the e x p e r i m e n t a l r e s u l t s was g i v e n . TABLE OF CONTENTS Page I . INTRODUCTION 1 . A. C r y s t a l S t r u c t u r e s 3 . B. E l e c t r o n i c S p e c t r a 8. C. M o l e c u l a r O r b i t a l Theory 9 . I I . THEORY 15• A. The S p i n H a m i l t o n i a n 1 6 . B. C r y s t a l F i e l d and L i g a n d F i e l d T h e o r i e s 2 0 . C. I n t e r p r e t a t i o n o f t h e ESR S p e c t r a 2 2 . I I I . EXPERIMENTAL 3 0 . A. P r e p a r a t i o n o f M e t a l l o t e t r a b e n z p o r p h y r i n s (MTBP) 3 0 . B. P r e p a r a t i o n o f O c t a m e t h y l t e t r a b e n z p o r p h y r i n and i t s T r a n s i t i o n - m e t a l d e r i v a t i v e s 3 3 . C. S y n t h e s i s o f m s - T e t r a p y r i d y l p o r p h i n , H 2 P y r P , and i t s M e t a l d e r i v a t i v e s 3 5 . D. S y n t h e s i s o f m s - T e t r a ( p - c a r b o x y l p h e n y l ) p o r p h i n , H2COOHTPP and i t s M e t a l d e r i v a t i v e s 3 6 . E. The S p e c t r o m e t e r s 3 6 . IV. VANADYL PORPHYRINS 3 9 . A. I n t r o d u c t i o n 3 9 . B. L i g a n d F i e l d O r b i t a l s o f V a n a d y l P o r p h y r i n s 42. C. ESR R e s u l t s 4 5 . D. D i s c u s s i o n 48. V. COPPER PORPHYRINS 5 6 . A. I n t r o d u c t i o n 5 6 . B. Theory 5 9 . 6 3 C. P r e p a r a t i o n o f t h e Cu P o r p h y r i n s 6 3 . D. ESR R e s u l t s 64. E. D i s c u s s i o n 7 0 . F. S o l v e n t E f f e c t s 7 4 . V I . COBALT PORPHYRINS A. I n t r o d u c t i o n B. C o b a l t P o r p h y r i n s M a g n e t i c a l l y d i l u t e d i n M e t a l - f r e e P o r p h y r i n s (a) I n t r o d u c t i o n (b) Theory ( c ) ESR R e s u l t s (d) D i s c u s s i o n C. C o b a l t P o r p h y r i n s i n P y r i d i n e (a) I n t r o d u c t i o n (b) P r e p a r a t i o n ( c ) ESR R e s u l t s (d) • D i s c u s s i o n D. Oxygen-adduct F o r m a t i o n E. C o n c l u s i o n A. D e r i v a t i o n o f t h e S p i n H a m i l t o n i a n B. D e r i v a t i o n o f K„ and Kj_ from A, B and 6 C. Micro-analysis r e s u l t s of some Porphyrins V LIST OF TABLES Ta b l e Page 1 . T r i v i a l names, a b b r e v i a t i o n s , and s t r u c t u r e s o f some p o r p h y r i n s . 4 . 2 . Summary o f p r e v i o u s ESR r e s u l t s o f v a n a d y l p o r p h y r i n s and p h t h a l o c y a n i n e . 4 l . 3 . Summary o f s p i n H a m i l t o n i a n parameters o f v a n a d y l p o r p h y r i n s i n t h i s s t u d y . 4 7 . 4 . C a l c u l a t e d bonding p a r a m e t e r s , and l i g a n d f i e l d t r a n s i t i o n e n e r g i e s o f v a n a d y l p o r p h y r i n s and p h t h a l o c y a n i n e . 5 1 - 2 5 . Summary o f p r e v i o u s ESR r e s u l t s o f copper p o r p h y r i n s and p h t h a l o c y a n i n e . 5 8 . 6 . Summary o f s p i n H a m i l t o n i a n parameters o f copper complexes i n t h i s s t u d y . 7 2 . 7 . C a l c u l a t e d b o n d i n g p a r a m e t e r s , and l i g a n d f i e l d t r a n s i t i o n e n e r g i e s o f copper p o r p h y r i n s and p h t h a l o c y a n i n e . 7 5 . 8 . Summary o f p r e v i o u s ESR r e s u l t s o f c o b a l t p o r p h y r i n s and s i m i l a r complexes. 84 9 . ESR r e s u l t s o f c o b a l t p o r p h y r i n s m a g n e t i c a l l y d i l u t e d i n t h e f r e e base, powders, 77°K. 8 9 . 1 0 . C a l c u l a t e d bonding p a r a m e t e r s , and l i g a n d f i e l d e n e r g i e s o f c o b a l t p o r p h y r i n s . 9 3 . 1 1 . ESR r e s u l t s o f c o b a l t p o r p h y r i n s i n p y r i d i n e , 77°K. 9 9 -1 2 . L i g a n d f i e l d e n e r g i e s and b o n d i n g parameters o f c o b a l t p o r p h y r i n s i n p y r i d i n e . 1 0 1 . 1 3 . R e s u l t s o f oxygen-adducts o f c o b a l t p o r p h y r i n s i n p y r i d i n e . 1 0 9 -vi LIST OF FIGURES F i g u r e Page 1 . P o r p h i n s k e l e t o n , w i t h " b e s t " s e t o f parameters f o r p o r p h y r i n s k e l e t o n . 2. 2. S t r u c t u r e s o f p h t h a l o c y a n i n e , c h l o r o p h y l l , and V i t a m i n e B 1 2 . 5 . 3 . S t r u c t u r e s o f (a) m s - t e t r a ( 4 - p y r i d y l ) p o r p h i n , (b) m s - t e t r a ( p - c a r b o x y l p h e n y l ) p o r p h i n , (c) t e t r a b e n z p o r p h y r i n , and (d) o c t a m e t h y l -t e t r a b e n z p o r p h y r i n . 6 . 4. E l e c t r o n i c s p e c t r a o f H 2 T B P and Z nTBP i n p y r i d i n e . 1 0 . 5 . G e n e r a l i z e d e n e r g y - l e v e l d i a g r a m f o r m e t a l l o -p o r p h y r i n s and t h e e f f e c t o f s o l v e n t s . 13. 6. T y p i c a l p o l y c r y s t a l l i n e ESR s p e c t r a f o r the case of S = h» I = h» s e c o n d - o r d e r h y p e r f i n e i n t e r -a c t i o n b e i n g n e g l e c t e d . 26. 7 . ESR spectrum o f v a n a d y l p y r i d y l p o r p h i n m a g n e t i c a l l y d i l u t e d i n t h e f r e e b a s e , powder, 77°K. 46. 8 . L i g a n d f i e l d t r a n s i t i o n e n e r g i e s o f some v a n a d y l p o r p h y r i n s and p h t h a l o c y a n i n e . 53. 9a. ESR spectrum of ^ c u P y r P m a g n e t i c a l l y d i l u t e d i n H " 2 P y r P , powder, 77°K. A i s t h e f r e e - r a d i c a l r e s o n a n c e , B i s anomalous l i n e s . 6 5 . 9b. C o m p u t e r - s i m i l a t e d ESR s p e c t r u m . 6 5 . 10. ESR spectrum o f 6 3 c u t e t r a ( p - c a r b o x y l p h e n y l ) p o r p h i n m a g n e t i c a l l y d i l u t e d i n t h e f r e e b a s e , powder, 77°K. 6 6 . 11. ESR spectrum of 63rju t e t r a b e n z p o r p h y r i n m a g n e t i c a l l y d i l u t e d i n t h e f r e e b a se, powder, 77°K. 6 7 . 12. ESR spectrum of 63Cu o c t a m e t h y l t e t r a b e n z p o r p h y r i n m a g n e t i c a l l y d i l u t e d i n t h e f r e e b a s e , powder, 77°K. 6 8 . 13. Region o f t h e spectrum t o t h e l o w - f i e l d s i d e o f g. (a) u n e n r i c h e d CuPyrP, (b) 6 3 C u P y r P . ± °9 • VII 14 . ESR resonance p o s i t i o n p a t t e r n f o r g_,_ p a r t , copper p o r p h y r i n . 7 1 . 1 5 . L i g a n d f i e l d t r a n s i t i o n e n e r g i e s o f some copper p o r p h y r i n s and p h t h a l o c y a n i n e . 1 6 . S t r u c t u r e o f t h e 5 , 6 d i m e t h y l b e n z i m i d a z o l e cobamide coenzyme. 1 7 . ESR spectrum o f CoTBP m a g n e t i c a l l y d i l u t e d i n H^TBP, powder, 77°K. 7 6 . 8 1 . 8 7 . 1 8 . A p l o t o f g, and gj_ v e r s u s AEJ . The e x p e r i m e n t a l p o i n t s a r e : ( 1 ) CoPyrP i n H^PyrP, t h i s s t u d y ; ( 2 ) CoCOOHTPP i n H 2COOHTPP, t h i s s t u d y ; ( 3 ) CoTBP i n H2TBP, t h i s s t u d y ; (4) CoOMTBP i n H2OMTBP, t h i s s t u d y ; ( 5 ) P-CoPc i n N i P c , r e f e r e n c e 4; ( 6 ) Co(p-OCH )TPP i n H 2(p-OCH )TPP, r e f e r e n c e 7 ; ( 7 ) CoTPP i n H 2TPP, r e f e r e n c e 5 . 90. 1 9 . ESR spectrum o f CoCOOHTPP i n p y r i d i n e , 77°K. 9 6 . 2 0 . ESR spectrum o f CoTBP i n p y r i d i n e , 7 7 °K. 9 7 . 2 1 . Q u a l i t a t i v e energy l e v e l s o f c o b a l t p o r p h y r i n s . . 103. 2 2 . ESR spectrum o f oxygenated s p e c i e s o f CoPyrP i n p y r i d i n e . 1 0 6 . 2 2 2 3 . A p l o t o f A and B v e r s u s 0 , t h e a n g l e between t h e oxygen m o l e c u l e and p o r p h y r i n p l a n e . 1 0 8 . vi i j ACKNOWLEDGMENT I would l i k e t o e x p r e s s s p e c i a l t h a n k s t o Dr. W. C. L i n , my r e s e a r c h s u p e r v i s o r . H i s u n t i r i n g a s s i s t a n c e and gu| dGfnce have been a so u r c e o f s t i m u l a t i o n i n t h e v a r i o u s a s p e c t s o f t h i s work. I a l s o w i s h t o thank Dr. P. G. H e r r i n g f o r h i s c o n t i n u a l i n t e r e s t and a d v i s e thoughout t h i s work, Dr. R. Booth f o r h i s h e l p f u l d i s c u s s i o n s , and t h e members o f t h e ESR group f o r t h e v a l u a b l e a s s i s t a n c e . F i n a l l y , my thanks go t o Mr. T. Markos f o r t e c h n i c a l a s s i s t a n c e . 1. I . INTRODUCTION M e t a l Porphyrins ( m e t a l l o p o r p h y r i n s ) o c c u r w i d e l y i n n a t u r e ( 1 ) , and t h e a b i l i t y t o s y n t h e s i z e t h e s e seems t o be p o s s e s s e d by almost a l l l i v i n g s p e c i e s t h a t are i n e x i s t e n c e t o d a y . Y e t , the s t o r y does not end h e r e . G e o l o g i c a l f i n d i n g s have p r o v i d e d e v i d e n c e t h a t p o r p h y r i n complexes were f u n c t i o n i n g m i l l i o n s o f y e a r s ago. At the p r e s e n t s t a g e of e v o l u t i o n , p o r p h y r i n s a re found , among o t h e r s , i n c h l o r o p h y l l s , hemoglobin and cytochromes. These systems, are r e l a t e d , d i r e c t l y o r i n d i r e c t l y t o p r o c e s s e s o f energy t r a n s f e r . I n the case o f cytochrome c, c o u p l e d o x i d a t i o n -r e d u c t i o n r e a c t i o n s r e s u l t i n t h e t r a n s f e r o f energy t o the " O u ^ - i l o u " ouinpuuiiu ATV. xu Oiie case o i ' i i e m o g i o u i n , c on i p i e x i n g w i t h m o l e c u l a r oxygen r e s u l t s i n the t r a n s p o r t o f the l a t t e r t o s i t e s where i t s e r v e s as an u l t i m a t e e l e c t r o n a c c e p t o r . And, i n the case o f c h l o r o p h y l l , energy i s t r a n s f e r e d t h r o u g h a c o m p l i c a t e d system t o a s i n g l e s p e c i a l m o l e c u l e which i s p h o t o e x c i t e d and s t a r t s a s e r i e s o f events w i t h the u l t i m a t e c o n v e r s i o n o f carbon d i o x i d e and water t o - c a r b o h y d r a t e s . The f a c t t h a t a l l t h e s e p o r p h y r i n s are i n v o l v e d i n en e r g y t r a n s f e r s u g g e s t s t h a t a f r u i t f u l approach t o u n d e r s t a n d t h e i r b i o l o g i c a l a c t i v i t y would be t h r o u g h an e x a m i n a t i o n o f t h e i r e l e c t r o n i c s t r u c t u r e s . C h e m i c a l l y , p o r p h y r i n s a r e a c l a s s o f t e t r a p y r r o l e m a c r o c y c l e s d e r i v e d from the p a r e n t compound p o r p h i n by s u b s t i t u t i o n at p o s i t i o n s 1 t o 8, and/or a t o 6 (see F i g . 1 ) . P i g . 1: P o r p h i n s k e l e t o n , w i t h " b e s t " s e t o f p arameters f o r p o r p h y r i n s k e l e t o n . 3 . M e t a l l o p o r p h y r i n s are t h e m e t a l d e r i v a t i v e s o f the c o r r e s p o n d -i n g m e t a l - f r e e p o r p h y r i n s , ( a l s o known as f r e e - b a s e p o r p h y r i n s ) . Some most common n a t u r a l l y o c c u r i n g p o r p h y r i n s , and some a r t i f i c i a l ones are t a b u l a t e d i n T a b l e 1, a l o n g w i t h t h e i r a b b r e v i a t i o n s used i n t h i s t h e s i s . M e n t i o n s h o u l d a l s o be made o f a c l o s e l y r e l a t e d compound, p h t h a l o c y a n i n e ( 2 ) , w h i c h i s s t r u c t u r a l l y s i m i l a r t o t e t r a b e n z p o r p h y r i n except t h a t the methine groups a r e r e p l a c e d by n i t r o g e n s . Shown i n F i g . 2 a r e t h e s t r u c t u r e s o f p h t h a l o c y a n i n e , and two o t h e r i m p o r t a n t n a t u r a l l y - o c c u r r i n g compounds, c h l o r o p h y l l and v i t a m i n A. Crystal,''; S t r u c t u r e s The d e t e r m i n a t i o n o f t h e d e t a i l e d s t r u c t u r e s o f p o r p h y r i n s and m e t a l l o p o r p h y r i n s ( i n c l u d i n g p h t h a l o c y a n i n e s ) has c o n t r i b u t e d v e r y much i n the u n d e r s t a n d i n g o f the p h y s i c a l and c h e m i c a l p r o p e r t i e s o f t h e s e compounds. Two r e c e n t r e v i e w s may be c i t e d ( 3 , 4 ) , and the f o l l o w i n g g e n e r a l c o n c l u s i o n s may be drawn. (a) M e t a l l o p h t h a l o c y a n i n e o r m e t a l l o p o r p h y r i n forms s q u a r e -p l a n a r c o - o r d i n a t i o n w i t h t h e m e t a l i o n i n t h e c e n t e r o f t h e p l a n e . I f a f i f t h l i g a n d i s c o - o r d i n a t e d t o t h e m e t a l , t h e m e t a l i o n would be out o f p l a n e and bonded t o t h e l i g a n d i n t h e a p i c a l 3+ p o s i t i o n . F o r i n s t a n c e , t h e h i g h - s p i n f e r r i c p o r p h y r i n (Fe bonds t o an a n i o n ) assumes a t e t r a g o n a l p y r a m i d a l geometry w i t h f e r r i c i o n out o f p l a n e by 0.5A (5, 6, 7 ) ; the magnesium i o n i n magnesium p h t h a l o c y a n i n e h y d r a t e i s 0.496A out o f t h e p y r r o l e n i t r o g e n p l a n e and bonded t o t h e water m o l e c u l e i n t h e PORPHYRINS ABBREV. E t i o p o r p h y r i n I E t i o I E t i o p o r p h y r i n I I E t i o I I E t i o p o r p h y r i n I I I E t i o I I I M e s o p o r p h y r i n I Meso I M e s o p o r p h y r i n IX Meso IX P r o t o p o r p h y r i n I P r o t o I P r o t o p o r p h y r i n IX P r o t o I X D e u t e r o p o r p h y r i n I Deut I D e u t e r o p o r p h y r i n IX Deut IX a> 9> * r , * - T e t r a -p h e n y l p o r p h i n TPP <*,g,Y,S-Tetra(4-p y r i d y D p o r p h i n * PyrP a , 8 ,Y,5-Tetra(4 c a r b o x y l p h e n y l ) -p o r p h i n * COOHTPP T e t r a b e n z p o r p h y r i n * TBP O c t a m e t h y l t e t r a -b e n z p o r p h y r i n * OMTBP SUBSTITUTIONS ON POSITION 1 2 3 4 5 6 7 8 a e 7 5 M E M E M E M E H H . H H M E E M M E E M H H H H M E M E M E E M H H H H M E M E M P M P H H H H M E M E M P P M H H H H M V M V M P M P H H H H M V M V M P P M H H H H M H M H M P M P H H H H M H M H M P P M H H H H H H H H H H H H Ph Ph Ph PI H H H H H H H H Py Py Py P: H H H H H H H H Car Car Car C, B B B B H H H H MB MB MB MB H H H H TABLE 1 : Names, a b b r e v i a t i o n s , and s t r u c t u r e s o f some p o r p h y r i n s . S i d e - c h a i n a b b r e v i a t i o n s : M, m e t h y l ; E, e t h y l ; P, p r o p i o n i c a c i d ; V, v i n y l ; H, hy d r o g e n ; Ph, p h e n y l ; Py> 4 - p y r i d y l ; C a r , 4 - c a r b o x y l p h e n y l ; B, benzo; MB, d i m e t h y l b e n z o . *For s t r u c t u r e s , see F i g . 3 . 5. Q phthalocyanine X / CH, ' " C0 2CH, \ u COJ@ chlorophyll N H l _ C 0 - C H J - C H J ^ C H v C H _ C O _ N H l N H : - C O - C H ; y C ^ C ^ N ^ C ^ c H _ c H i _ c H CH/ Co + CH CH / t \ 6 ^ ' V - S / C H 3 : N H 2 — C O — C H — H C I CO—CH 2 —CH 2 . , 0 1 1 3 :l / NH I C H , C H J - C H CH; ,c^ >^rH C H L H > \ : H 2 — C H J — C O — N H , 0 OH C — c N CH >rCHi ^ c - ^ c ^ "CH " C H 3 \ N ^ C ^ C \ CH^H H :CH H O — C H , vitamin Bj» F i g . 2: S t r u c t u r e s o f p h t h a l o c y a n i n e , c h l o r o p h y l , and V i t a m i n e B, 0. 1 (a) ( b ) P i g . 3 : S t r u c t u r e s o f (a) t e t r a ( 4 - p y r i d y l ) p o r p h i n , (b) t e t r a ( p - c a r b o x y l p h e n y l ) p o r p h i n , ( c ) t e t r a b e n z p o r p h y r i n , and (d) o c t a m e t h y l -t e t r a b e n z p o r p h y r i n . 7. a p i c a l p o s i t i o n ( 8 ) ; the z i n c i o n i n a 2:3 complex o f z i n c -p h t h a l o c y a n i n e and normal h e x y l a m i n e i s d i s p l a c e d from t h e p l a n e by 0.48A toward the n i t r o g e n atom o f the amine ( 9 ) ; i n z i n c t e t r a ( 4 - p y r i d y l ) p o r p h i n m o n o p y r i d i n e the z i n c atom l i e s 0.33A o u t - o f - p l a n e toward the p y r i d i n e l i g a n d ( 1 0 ) ; t h e vanadium o f the v a n a d y l - s u b s t i t u t e d e t i o p o r p h y r i n was a l s o n o t e d t o be 0.48A out o f p l a n e ( 1 1 ) . (b) The p o r p h y r i n m o l e c u l e i s not c o m p l e t e l y r i g i d , and i t s geometry can be g r e a t l y i n f l u e n c e d by i n t e r m o l e c u l a r i n t e r a c t i o n s . The p o r p h y r i n s range from a l m o s t p l a n a r i n p o r p h i n t o v e r y r u f f l e d i n the t e t r a p h e n y l p o r p h i n s e r i e s . The p o r p h y r i n s i n a " f r e e " environment p r o b a b l y e x i s t i n a n e a r - p l a n a r c o n f o r m a t i o n w i t h low energy b a r r i e r w i t h r e s p e c t t o d e v i a t i o n s from p l a n a r i t y . As a r e s u l t , i t i s d i f f i c u l t t o p r e d i c t the d e t a i l e d s t r u c t u r e o f a p o r p h y r i n under v a r i o u s c i r c u m s t a n c e s . With r e s p e c t t o t h e n o n - p l a n a r i t y o f p o r p h y r i n s , one f u r t h e r p o i n t needs t o be mentioned. W h i l e the p h e n y l groups i n t e t r a -p h e n y l p o r p h i n make an a n g l e o f app r o x i m a t e 60° w i t h the p l a n e o f the p o r p h i n a t o c o r e , the a - and 7-methine carbon atoms were a l s o found t o l i e 0.38A above t h e mean p l a n e w h i l e t h e /3 - and 5 - atoms, an e q u a l d i s t a n c e below. (c) I f the h o l e s i z e o f a p o r p h y r i n i s t a k e n as the average d i s t a n c e from the c e n t e r t o the p y r r o l e n i t r o g e n s , p h t h a l o c y a n i n e s are on the average 0.065A s m a l l e r t h a n the c o r r e s p o n d i n g p o r p h y r i n s . The s m a l l e r h o l e s i z e f o r p h t h a l o c y a n i n e causes the energy l e v e l s and the b o n d i n g b e h a v i o r t o be d i f f e r e n t from t h o s e 8. o f t h e o t h e r p o r p h y r i n s . T h i s p o i n t w i l l be d i s c u s s e d s p e c i f i c a l l y l a t e r . B. E l e c t r o n i c S p e c t r a The' u n d e r s t a n d i n g o f t h e e l e c t r o n i c s t r u c t u r e s o f p o r p h y r i n s can be a c q u i r e d t h r o u g h : (a) e l e c t r o n i c ( v i s i b l e ) s p e c t r o s c o p y , (b) e l e c t r o n s p i n resonance s p e c t r o s c o p y , and (c) m o l e c u l a r o r b i t a l c a l c u l a t i o n s . W h i l e the f i r s t y i e l d s i n f o r m a t i o n s about b o t h t h e ground and t h e e x c i t e d s t a t e s , the second m a i n l y concerns w i t h t h e d e t a i l e d knowledge o f the ground s t a t e , a l t h o u g h some i n f o r m a t i o n about the e x c i t e d s t a t e s may a l s o be d e r i v e d . The t h i r d method p r o v i d e s a n I n — c i p-h t i n t . n ' t h p r>f>"i;»1.1 n n h p t w p p n t . h p p Jl e n t r n n i T . "R'trU'oT .Ure and t h e p h y s i c a l o b s e r v a b l e s . M o l e c u l a r o r b i t a l c a l c u l a t i o n s , however, are c a r r i e d out under the most i d e a l c o n d i t i o n s and s h o u l d be j u d g e d a c c o r d i n g t o how w e l l t h e y i n t e r p r e t t h e e x p e r i m e n t a l r e s u l t s . The v i s i b l e spectrum o f a p o r p h y r i n i s due t o t h e s o - c a l l e d n - n t r a n s i t i o n s , t h a t i s , due t o an e l e c t r o n i n an o c c u p i e d n - M. 0. b e i n g e x c i t e d t o an u n o c c u p i e d IT - M. 0. F o r a m e t a l l o p o r p h y r i n , t h e r e a re a l s o d - d t r a n s i t i o n s I n v o l v i n g the e x c i t a t i o n s from one d o r b i t a l o f t h e m e t a l t o a n o t h e r . However the i n t e n s i t i e s a r e so much weaker ( l o g £ max ~ 1 - 2 ) t h a t t h e y are c o m p l e t e l y masked by the II - 11 t r a n s i t i o n s ( l o g C max ~ 5 ) . The v i s i b l e s p e ctrum o f a p o r p h y r i n can u s u a l l y be d e s c r i b e d 9. as f o l l o w s : I t c o n s i s t s o f a s t r o n g band ( l o g £ max ~ 5 - 6 ) a t about 4000A c a l l e d the S o r e t band (B b a n d ) , and a group o f bands ( Q band) i n the range 5 0 0 0 - 6 0 0 0 A , w i t h i n t e n s i t i e s weaker t h a n the S o r e t band. F i g . 4 shows t h e e l e c t r o n i c s p e c t r a o f t e t r a b e n z p o r p h y r i n and i t s z i n c d e r i v a t i v e i n p y r i d i n e . The main d i f f e r e n c e i s t h a t w h i l e t h e r e a r e two groups o f bands i n t h e l o w e r energy range ( 6 0 0 0 - 7000A ) f o r t h e f r e e b a s e , t h e r e i s o n l y one f o r the m e t a l d e r i v a t i v e . T h i s i s due t o t h e change o f symmetry from ^2h ^° ^4h w h e n ^he ^ w o hydrogens a r e r e p l a c e d by a m e t a l . As a r e s u l t , any 2 - f o l d degeneracy i n the symmetry i s removed. The S o r e t band a l s o s p l i t s i n t o two on g o i n g from t h e m e t a l to the f r e e - b a s e complex. C. M o l e c u l a r O r b i t a l Theory There have been numerous LCAO c a l c u l a t i o n s on p h t h a l o c y a n i n e s and p o r p h y r i n s . The r e s u l t s a r e i m p o r t a n t t o the u n d e r s t a n d i n g o f the ESR d a t a . The f i r s t M. 0. c a l c u l a t i o n was c a r r i e d out by Longuet-Higgins et a l . i n 1950 on f r e e base p o r p h i n ( 1 2 ) . They used t h e most n a i v e H u c k e l method t o t r e a t t h e ^ - e l e c t r o n s . The f r e e base p o r p h i n was t r e a t e d as a 24 c e n t e r s - 26 e l e c t r o n s system (2 e x t r a e l e c t r o n s due t o two p y r r o l e n i t r o g e n s ) . F o r the symmetry *There has been some c o n t r o v e r c y r e g a r d i n g the d e t a i l e d i n t e r -p r e t a t i o n o f the s p l i t t i n g o f t h e S o r e t band but t h i s would not con c e r n us h e r e . F i g . 4: E l e c t r o n i c s p e c t r a , o f H ?TBP and ZnTBP i n p y r i d i n e . group, the 2H rr-MO's were found t o b e l o n g t o t h e f o l l o w i n g i r r e d u c i b l e r e p r e s e n t a t i o n s : • b l u , b , and e l u ' a2u> " l u 5 2y The h i g h e s t o c c u p i e d MO was found t o be ^ 2 u * a n d t h e n e x t h i g h e s t ^ i u * T n e x ° w e s t empty MO's were found t o be a degenerate p a i r b e l o n g e d t o G . More r e f i n e d c a l c u l a t i o n s a r r i v e d a t v e r y much the same c o n c l u s i o n s and i n some cases ( e . g . TBP and Pc) was found t o be h i g h e r t h a n c l 2 u ( 1 3 , 14, 1 5 ) . I n m e t a l l o p o r p h y r i n s , t h e p a r t i a l l y f i l l e d , p r edomin-a n t l y m e t a l d - o r b i t a l s come g e n e r a l l y i n - b e t w e e n t h e l i g a n d f i l l e d and empty o r b i t a l s , w i t h b-, , t h e a n t i - b o n d i n g o r b i t a l r g w i t h p r e d o m i n a n t l y d 2 - 2 c h a r a c t e r , b e i n g much h i g h e r t h a n t h e x y r e s t , sometimes even above the empty G ( n ) ( 1 6 , 1 7 , 1 8 ) . T h i s no doubt i s due t o t h e s t r o n g o~ — b o n d i n g between - ^ 2 and the < r - o r b i t a l s o f the p o r p h y r i n r i n g . The o r d e r o f the r e m a i n i n g o r b i t a l s , a n t i - b o n d i n g a 1 , b ? , and 6 , p r e -d o m i n a n t l y d 2 , d , and (d , d ) r e s p e c t i v e l y , i s l e s s c e r t a i n . J z 3 xy' xz 5 y z ^ J ' I n most cases however, i t has been found t o be 3^ > ®g > b 2 g . The b 2 g o r b i t a l i s e s s e n t i a l l y non-bonding due t o t h e f a c t t h a t t h e n i t r o g e n p - o r b i t a l s a r e not a v a i l a b l e f o r i n - p l a n e L T - b o n d i n g i n the case o f the t e t r a d e n t a t e p o r p h y r i n , i n c o n t r a s t t o o t h e r s q u a r e - p l a n a r complexes w i t h mono-dentate l i g a n d s The o u t - o f - p l a n e n - b o n d i n g between m e t a l d , d and p o r p h y r i n x z y z 8_ i s p r o b a b l y r e s p o n s i b l e f o r t h e a n t i - b o n d i n g G b e i n g above 12. b 2 g . The p o s i t i o n o f ^ l g i s m o s t v a r i a b l e , b e i n g a f f e c t e d by t h e p r e s ence o f s o l v e n t m o l e c u l e s , n e x t - n e i g h b o r m o l e c u l e s i n t h e c r y s t a l s , or oxygen i n t h e a x i a l p o s i t i o n as i n the case o f the v a n a d y l complexes. I t seems, however, even i n t h e absence o f a l l t h e s e i n t e r a c t i o n s , i s s t i l l s l i g h t l y above e g and b_ , presumably due t o t h e p o s s i b i l i t y o f b o n d i n g between d , ^g z and t h e n i t r o g e n ? a — o r b i t a l s . The above p i c t u r e can be shown s c h e m a t i c a l l y i n a g e n e r a l i z e d e n e r g y - l e v e l diagram f o r a m e t a l l o p o r p h y r i n ( P i g . 5 ) . A l s o i n c l u d e d i n t h e diagram a r e t h e o r b i t a l s o f t h e a x i a l s o l v e n t m o l e c u l e s , whose e f f e c t s i n g e n e r a l are t o r a i s e t h e e n e r g i e s o f t h e m e t a l cl-,„ and e„ o r b i t a l s . 1 3 . eg 19 ig eg ; a 2W a,g (<T) eg ( I T ) a F i g . 5: G e n e r a l i z e d e n e r g y - l e v e l diagram f o r m e t a l l o -p o r p h y r i n s and t h e e f f e c t o f s o l v e n t s . 14. R e f e r e n c e s 1 . J.E. F a l k , " P o r p h y r i n s and M e t a l l o p o r p h y r i n s " , E l s e v i e r P u b l i s h i n g Co., Amsterdam, 1 9 6 4 . 2 . A.B.P. L e v e r , Advan. Inorg.Chem. Radiochem., 7 , 2 7 ( 1 9 6 5 ) . 3 . E.B. F l e i s c h e r , Account Chem. R e s e a r . , 3., 1 0 5 ( 1 9 7 0 ) . 4 . J . L . Hoard, S c i e n c e 17_4, 1 2 9 5 ( 1 9 7 1 ) . 5 . J . L . Hoard, S.H. Cohen, and M.D. G l i c k , J . Am. Chem. S o c , 8 9 , 1 9 2 2 ( 1 9 6 7 ) . 6 . J . L . Hoard, M.J. Hamor, T.A. Hamor and W.S. Caughey, J . Am. Chem. S o c , 8 7 , 2 3 1 2 ( 1 9 6 5 ) . 7- J . L . Hoard i n " S t r u c t u r a l C h e m i s t r y and M o l e c u l a r B i o l o g y " , A. R i c h and N. D a v i d s o n , Ed.; W. H. Freeman and Co., San F r a n c i s c o , C a l i f . , 1 9 6 8 . 8 . M.S. F i s c h e r , D.H. T e m p l e t o n , A. Z a l k i n , and M. C o l v i n , J . Am. Chem. S o c , 93, 2 6 2 2 ( 1 9 7 1 ) . 9 . T. K o b a y a s h i , T. A s h i d a , N. Uyeda, E. S u i t o , and M. Kakudo, B u l l . Chem. S o c J a p . , 44_, 2 0 9 5 ( 1 9 7 1 ) . 1 0 . D.M. C o l l i n s and J . L. Hoard, J . Am. Chem. S o c , £2, 3 7 6 1 ( 1 9 7 0 ) . 1 1 . R. P e t e r s o n and L. A l e x a n d e r , J . Am. Chem. S o c , 9_p_, 3 8 7 3 ( 1 9 6 8 ) . 1 2 . H.C. L o n g u e t - H i g g i n s , C.W. R e c t o r and J.R. P i a t t , J . Chem. Phys., 1 8 , 1 1 7 4 ( 1 9 5 0 ) . 1 3 . C. W e i s s , H. Kob o y a s h i and M. Gouterman, J . M o l . Spec., 1 6 , 415 ( 1 9 6 5 ) . 14. M. Sundbom, A c t a . Chim. Scand., 2 2 , 1 3 1 7 ( 1 9 6 8 ) . 1 5 . A . J . McHugh, M. Gouterman and C. W e i s s , Theor. Chim. A c t a , 2_4, 3 4 6 ( 1 9 7 2 ) . 1 6 . M. Z e r n e r , and M. Gouterman, Theor. Chim. A c t a , 4_, 4 4 ( 1 9 6 6 ) . 17. M. Z e r n e r and M. Gouterman, Inorg.Chem., 5 , 1 6 9 9 ( 1 9 6 6 ) . 1 8 . A.M. S c h a f f e r , M. Gouterman, and E.R. D a v i d s o n , T h e o r . Chim. A c t a , 3 0 , 9 ( 1 9 7 3 ) . I I . THEORY S i n c e Z a v o i s k y ( 1 ) f i r s t r e p o r t e d t h e phenomenon o f e l e c t r o n s p i n resonance (ESR) i n 1 9 ^ 5 , much e f f o r t has been d e v o t e d t o the development o f t h i s t e c h n i q u e f o r t h e s o l u t i o n o f c h e m i c a l problems. ESR can o n l y be o b s e r v e d i n m o l e c u l a r systems c o n t a i n -i n g u n p a i r e d e l e c t r o n ( s ) , o f w h i c h t r a n s i t i o n m e t a l complexes are i m p o r t a n t examples. The s p e c t r a o f t h e p a r a m a g n e t i c s p e c i e s can be s t u d i e d t o g a i n i n f o r m a t i o n about (a) t h e i d e n t i t y o f t h e p a r a m a g n e t i c u n i t ; (b) the symmetry of the s p e c i e s ; ( c ) t h e d i s -t r i b u t i o n o f t h e u n p a i r e d s p i n d e n s i t y i n t h e m o l e c u l e o r m o l e c u l a r fragment ; (d) l a t t i c e dynamics; (e) e q u i l i b r i u m c o n s t a n t s ; and ( f ) r e a c t i o n r a t e s and numerous o t h e r p r o p e r t i e s which may be o f d i r e c t i n t e r e s t t o c h e m i s t s . A number o f books and r e v i e w a r t i c l e s a re a v a i l a b l e . Bersohn and B a i r d ( 2 ) , and C a r r i n g t o n and McLachlan ( 3 ) , and r e c e n t l y , Wertz and B o l t o n ( 4 ) have w r i t t e n i n t r o d u c t o r y t e x t s . The e a r l i e s t r e v i e w on the ESR o f t r a n s i t i o n m e t a l complexes was t h e 1 9 5 3 a r t i c l e o f B l e a n e y and Stevens ( 5 ) . T h i s was f o l l o w e d by a s e r i e s o f papers from t h e same group ( 6 - 9 ) . McGarvey's ( 1 0 ) r e v i e w o f 1966 r e p r e s e n t s c h e m i s t s ' i n t e r e s t i n t h e same f i e l d and c o n t a i n s a f a i r l y d e t a i l e d a ccount o f the t h e o r e t i c a l a s p e c t . The r e v i e w o f Kuska and Rogers ( 1 1 ) c o v e r e d ESR r e s u l t s o f t h e f i r s t row t r a n s i t i o n m e t a l s up t o 1 9 6 6 . The most r e c e n t and f a i r l y comprehensive r e v i e w ( 1 9 7 0 ) was due t o Goodman and Raynor ( 1 2 16. A. The S p i n H a m i l t o n ! a n ESR s p e c t r o s c o p y o f t r a n s i t i o n m e t a l complexes concerns w i t h the ground s t a t e o f a par a m a g n e t i c i o n i n t h e pr e s e n c e o f the e l e c t r i c i n t e r a c t i o n s due t o t h e . l i g a n d s , t h e magnetic i n t e r -a c t i o n s due t o t h e o r b i t a l and s p i n moments and the magnetic i n t e r a c t i o n between t h e system and an e x t e r n a l magnetic f i e l d . I n t he c r y s t a l f i e l d a p p r o x i m a t i o n , t h e - g e n e r a l H a m i l t o n i a n , which summarizes the t o t a l energy o f the system, has been d e s c r i b e d by Abragam and P r y c e (13) as: H = ^ + + H,S +>W ^ H + >U + ^ N H w i t h each term h a v i n g the s p e c i f i c meaning t o be b r i e f l y d i s c u s s e d as f o l l o w s : / > T.I . . . . . , . / - A 5 - L . . . , \,i±) J up xs one uoiftinan-i/ • uer-m v ~ ±0 -cm -J "WfU'Cn -des-c r i b e s the energy o f the f r e e i o n : , R F = ZL^-^I+Z -7- •••<2>-i= 1 1 i<j 'J where P^ i s the l i n e a r momentum, and Tj i s the e l e c t r o n - n u c l e u s , and Z i s the n u c l e a r c h a rge. The summations are over N e l e c t r o n s , and N ( N - l ) / 2 e l e c t r o n .pairs'. (b) d e s c r i b e s the p o t e n t i a l energy a r i s i n g from the n e i g h b o r i n g ions- o r d i p o l e s . 2 -1 (c ) T_I d e s c r i b e s the energy ( — 10 cm ) due t o the J ^ LS c o u p l i n g o f th e s p i n t o th e o r b i t a l m o t i o n s . • KLS - £. " i j W&J ••••<3> i >J where a ^ ^ are c o n s t a n t s . I n the weak f i e l d a p p r o x i m a t i o n , i f 17. one c o n f i n e s oneself':>'.• t o a s t a t e o f d e f i n i t e L and S o f the same **** c o n f i g u r a t i o n , 3-/ = X L - S ...(4) where L and S are t h e t o t a l o r b i t a l a n g u l a r momentum o p e r a t o r and t o t a l s p i n o p e r a t o r , and X , t h e 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 . (d) s g d e s c r i b e s t h e mag n e t i c i n t e r a c t i o n between t h e e l e c t r o n s p i n s . I t o n l y e x i s t s i n the m o l e c u l a r system w i t h two or more u n p a i r e d e l e c t r o n s (S ^ 1 ) . (e) JJ( — 1 cm - 1) denotes t h e i n t e r a c t i o n w i t h the e x t e r n a l magnetic f i e l d , and i s g i v e n by: J-^ = 0 H . ( L + 2S) . . .(5) i n t h e weak f i e l d a p p r o x i m a t i o n , 0 i s the Bohr magneton; — 2 — 1 ( f ) t h e term 0~L ^ ( 1 0 ~ cm" ) e x p r e s s e s t h e mag n e t i c i n t e r a c t i o n between the n u c l e a r s p i n and t h e e l e c t r o n s p i n s . Assuming t h e r e i s o n l y one magnetic n u c l e u s , I r 3 r-5 ) 3 + L5 * 1 } 3^-i)2( . . . ( 6 ) d 1 21(1-1) { r 3 r 5 The n u c l e a r f i r s t term i s t h e d i p o l e and the e l e c t r o n s p i n s . - d i p o l e i n t e r a c t i o n between the The second term d e s c r i b e s the 18. " c o n t a c t " i n t e r a c t i o n between t h e e l e c t r o n and the n u c l e a r s p i n s , which i s i s o t r o p i c i n n a t u r e and was i n t r o d u c e d by Fermi (14) t o account f o r t h e non-zero d e n s i t y o f e l e c t r o n i c s - f u n c t i o n s at the n u c l e u s . The l a s t t e r m i s t h e e l e c t r o s t a t i c i n t e r a c t i o n o f the e l e c t r i c g u a d r u p o l e moment Q o f the n u c l e u s w i t h the g r a d i e n t o f the e l e c t r i c f i e l d . The s o - c a l l e d n u c l e a r Zeeman term i s g i v e n by: J(NH = _ G N % where g ^ and 0 ^ are t h e n u c l e a r g - f a c t o r and n u c l e a r magneton r e s p e c t i v e l y . As w r i t t e n above, t h e g e n e r a l H a m i l t o n i a n i s most i n c o n v e n i e n t t o use and i t i s i n d e e d a b l e s s i n g t h a t i t can be changed i n t o a form i n which o n l y t h e e l e c t r o n i c and t h e n u c l e a r s p i n o p e r a t o r s appear t o g e t h e r w i t h some n e c e s s a r y p a r a m e t e r s . T h i s was f i r s t c a r r i e d out by Abragam and P r y c e ( 1 5 , 1 6 ) . They have shown t h a t i f t h e ground s t a t e o f t h e p a r a m a g n e t i c i o n i s not o r b i t a l l y d e g e n e r a t e , t h e p r o p e r t i e s o f the s p i n and t h e n u c l e a r d e g e n e r a c i e s o f t h e l o w e s t s i n g l e t s t a t e can be d e s c r i b e d by t h e s o - c a l l e d " s p i n H a m i l t o n i a n " , X = BH.g-S + S-D-S + S-A-I -g a H-I + I - P - I ...(7) where g i s t h e s p e c t r o s c o p i c s p l i t t i n g t e n s o r and i m p l i c i t l y 1 9 . i n c l u d e s the o r b i t a l c o n t r i b u t i o n s t o the Zeeman term. I n f a c t , the d e v i a t i o n o f 9 from t h e g v a l u e o f a f r e e e l e c t r o n s p i n 2.0023 r e p r e s e n t s t h e c o n t r i b u t i o n o f the admixed e x c i t e d s t a t e s t h r o u g h s p i n - o r b i t c o u p l i n g . The t e n s o r D a r i s e s from e l e c t r o n i c /-<^» d i p o l a r term ^ and a second o r d e r s p i n - o r b i t c o u p l i n g term. s s F o r o r g a n i c t r i p l e t s t h e d i p o l a r term i s o f p r i m a r y i m p o r t a n c e , whereas f o r t r a n s i t i o n m e t a l complexes t h i s i s u s u a l l y l e s s t h a n 5% o f t h e t o t a l ( 1 7 ) . I n Appendix A i t i s shown t h a t t h e t e n s o r components o f g and D a r e : g ± J = 2.0023 ( S ± J - X A ) ...(8) Du = - * 2 A u ; • • • ( 9 ) where A . . = X ' < 0| L j n>< n| L j |o> _ ( 1 Q ) „ . E - E n^o n o and i s t h e k r o n e c k e r d e l t a . A, t h e s o - c a l l e d h y p e r f i n e c o u p l i n g t e n s o r a r i s e s from t h e f i r s t two terms o f J*t M , and P, t h e f i n e s t r u c t u r e t e n s o r a r i s e s from the t h i r d t e r m o f T h e i r e x p l i c i t e x p r e s s i o n s are shown i n Appendix A. I n g e n e r a l , t h e t e n s o r s g , A, D, and P, b e i n g symmetric t e n s o r s , have s i x components (g , g g „) but f o r an a x i a l l y symmetric system w i t h g , D and A a l l c o - a x i a l we can w r i t e Eq. ( 7 ) i n the p r i n c i p a l axes c o - o r d i n a t e system a s : 20. Ji = fi [ 9 u S z H z + § l ( S x H x + V V ] + D [ Sz> - 3 S ^ S + 1 ) ] + A „ S z I z + A ± ( S x I x + S y I y ) + P [ l z , - ^1(1 + 1)] - g N W z . . . ( 1 1 ) The convenience o f a s p i n H a m i l t o n i a n i s t h a t i t p e r m i t s e x p e r i m e n t a l r e s u l t s t o be e x p r e s s e d s i m p l y i n terms o f a s m a l l number o f p a r a m e t e r s , t h e s p i n H a m i l t o n i a n p a r a m e t e r s . The n e x t s t e p i s t o i n t e r p r e t t h e s e parameters i n terms o f t h e l i g a n d f i e l d s t r e n g t h , and the e l e c t r o n i c s t r u c t u r e s , e t c . B. C r y s t a l F i e l d and L i g a n d F i e l d T h e o r i e s I n t h e l a s t s e c t i o n one has not c o n s i d e r e d i n d e t a i l t h e e f f e c t o f t h e l i g a n d s on t h e m e t a l i o n . The magnitude o f t h i s i n t e r a c t i o n depends c r i t i c a l l y on whether th e v a l e n c e e l e c t r o n s are i n 3 d , 4 d , or 4 f o r b i t a l s , and on t h e l i g a n d s . F o r our c a s e , t h e magnitude of t h e l i g a n d f i e l d - i n t e r a c t i o n , V , l i e s between • H F and H L S • S e v e r a l t h e o r i e s have been d e v e l o p e d t o d e s c r i b e t h e b e h a v i o r of m e t a l d - e l e c t r o n s i n the p r e s e n c e o f s u r r o u n d i n g l i g a n d s ( 1 8 , 1 9 ) . I n p a r t i c u l a r , c r y s t a l f i e l d t h e o r y has been w i d e l y a p p l i e d . B r i e f l y , t h e c r y s t a l f i e l d t h e o r y i s based on an i o n i c model i n which t h e s u r r o u n d i n g l i g a n d s a r e t r e a t e d as p o i n t charges o r d i p o l e s . The o n l y f u n c t i o n o f t h e l i g a n d s i s t o s u p p l y an e l e c t r o -s t a t i c f i e l d which l i f t s t h e degeneracy o f the 3d energy l e v e l s o f the m e t a l i o n . F o r the case o f 3d energy l e v e l s s u b j e c t e d t o a t e t r a g o n a l f i e l d , such as i n the case o f m e t a l l o p o r p h y r i n s , the 21. degenerate d - o r b i t a l s s p l i t a c c o r d i n g t o t h e f o l l o w i n g scheme: d^.y2 b 1 9 dz2 a l g dxz.yz eg dXy b2g The d - e l e c t r o n s are p l a c e d w i t h t h e i r s p i n s a n t i p a r a l l e l a c c o r d -i n g t o P a u l i ' s e x c l u s i o n p r i n c i p l e i n the l o w e s t p o s s i b l e o r b i t a l s . However, the c r y s t a l f i e l d t h e o r y was found t o be i n a d e q u a t e t o d e s c r i b e the c o v a l e n t complexes, i n w h i c h t h e r e was an a p p r e c i a b l e o v e r l a p between t h e m e t a l and t h e l i g a n d o r b i t a l s . One has t o t r e a t the l i g a n d s as p a r t o f t h e m o l e c u l e , w h i c h means t h a t , i n s t e a d o f u s i n g pure m e t a l d - o r b i t a l s , one has t o use m o l e c u l a r o r b i t a l s w hich are c o n s t r u c t e d from d - o r b i t a l s as w e l l as l i g a n d o r b i t a l s . The c o m b i n a t i o n o f t h e c r y s t a l f i e l d and t h e m o l e c u l a r o r b i t a l c o n c e p t s r e s u l t e d i n the s o - c a l l e d " l i g a n d - f i e l d " t h e o r y . The l i g a n d f i e l d t h e o r y p r e s e r v e s the q u a l i t a t i v e a s p e c t s o f the s p l i t t i n g o f t h e d - o r b i t a l s by a c r y s t a l f i e l d but a l s o i n t r o d u c e s m o l e c u l a r o r b i t a l s f o r t h e complex by an a p p r o p r i a t e l i n e a r c o m b i n a t i o n o f the c e n t r a l i o n atomic o r b i t a l s and t h e l i g a n d a tomic o r b i t a l s . The e x p l i c i t forms o f the m o l e c u l a r o r b i t a l s and t h e i r m o d i f i c a t i o n t o the s p i n H a m i l t o n i a n p a r a m e t e r s . w i l l be d i s c u s s e d s e p a r a t e l y when t h e i n d i v i d u a l t r a n s i t i o n m e t a l complexes are d i s c u s s e d . C. I n t e r p r e t a t i o n o f t h e ESR S p e c t r a I t has been mentioned p r e v i o u s l y t h a t an ESR e x p e r i m e n t y i e l d s a s e t o f s p i n H a m i l t o n i a n p a r a m e t e r s , and t h e s e i n t u r n are r e l a t e d t o s t r u c t u r a l d e t a i l s w h i c h c h a r a c t e r i z e th e p a r a -m agnetic system. The purpose o f t h i s s e c t i o n i s t o d e s c r i b e how the parameters may be d e t e r m i n e d from the ESR s p e c t r a . The method i s s i m p l e i n p r i n c i p l e . F o r a s u i t a b l y chosen r e p r e s e n t a t i o n , one e v a l u a t e s m a t r i x elements o f the form, By s o l v i n g t h e r e s u l t i n g s e c u l a r e q u a t i o n , one o b t a i n s c e r t a i n e i g e n v a l u e s and e i g e n s t a t e s . One t h e n c a l c u l a t e s t h e p r o b a b i l i t i e s o f t r a n s i t i o n s between t h e s e s t a t e s s t i m u l a t e d by microwaves w i t h the magnetic v e c t o r p o l a r i z e d p e r p e n d i c u l a r t o an e x t e r n a l m a gnetic f i e l d . Of c o u r s e , one has t o choose a s u i t a b l e s e t j ^ j- t o s t a r t w i t h . For example, i n s t r o n g magnetic f i e l d s , t h e n u c l e i a r e e s s e n t i a l l y (12) d e c o u p l e d and q u a n t i z e d w i t h r e s p e c t t o the magnetic f i e l d (a Paschen-Back e f f e c t ) , t h e Mm r e p r e s e n t a t i o n i s t h e r e f o r e s u i t a b l e (where M and m are the magnetic quantum numbers f o r t h e Z-com-ponent o p e r a t o r s S and I , r e s p e c t i v e l y ) . I f t h e magnetic f i e l d i s weak, so t h a t the h y p e r f i n e c o u p l i n g term d o m i n a t e s , t h e n i t i s more c o n v e n i e n t t o use t h e PM„ scheme (where P = S + I ) . I n th e i n t e r m e d i a t e r e g i o n one may use the B r e i t - R a b i ( 2 0 ) s o l u t i o n . Coming t o t h e s p e c i a l case o f t r a n s i t i o n - m e t a l i o n s w i t h S = \ and I = J§, and w i t h s p i n H a m i l t o n i a n parameters d e s c r i b e d by an a x i a l symmetry, i . e . , g x = g y = g i > A x = A y = B ' we have: H - <>[s„ V, + g i ( H x S x • H y S y ) j + A S I + B(S I + S I ) z z x x y y' a . . . ( 1 3 ) t h e q u a d r u p o l e and n u c l e a r zeeman t e r m s , which are u s u a l l y s m a l l i n c o m p a r i s o n , b e i n g n e g l e c t e d . The a n g u l a r dependence o f t h e resonance f i e l d has been d e r i v e d from t h i s e q u a t i o n by B l e a n e y ( 2 1 ) , assuming t h e e l e c t r o n i c Zeeman terms t o be much l a r g e r t h a n t h e h y p e r f i n e term and c a r r y i n g the p e r t u r b a t i o n t o second o r d e r . For t h e a l l o w e d A = 0 t r a n s i t i o n s , H = H°- Kmj -4H°g 2 2 2 2 2 v2 2 K g [ K i + l ) m. 24. Here H° - |J. . . . ( 1 5 ) g 2 = g ( | 2 c o s 2 9 + g ^ 2 s i n 2 9 , . . . ( 1 6 ) K 2 g 2 = A 2 g ( | 2 c o s 2 9 + B 2 g l 2 s i n 2 9 , . . . ( 1 7 ) and 9 i s t h e a n g l e between t h e d i r e c t i o n o f t h e a p p l i e d m a g n e t i c f i e l d and t h e m o l e c u l a r symmetry a x i s ; A, B, and K are i n u n i t s o f gauss. Rollmann and Chan have t r e a t e d t h e case i n c l u d i n g q u a d r u p o l e e f f e c t s ( 2 2 ) . I n powders o r f r o z e n g l a s s e s , t h e m o l e c u l a r axes are randomly o r i e n t e d , t h e f r a c t i o n between t h e a n g l e s 9 and 9 + d9 b e i n g \ s i n 9 d9 ( 2 3 ) , the i n t e n s i t y o f a b s o r p t i o n i s p r o p o r t i o n a l t o the number of a b s o r b i n g m o l e c u l e s N, and the r a t e o f change o f N w i t h H can be c a l c u l a t e d from t h e d i f f e r e n t i a l e q u a t i o n , M = dN d9 = 1 N o s l n Q d9 _ ( l 8 ) dH d9 dH 2 dH where N„ i s the t o t a l number o f m o l e c u l e s . I n the absence o f quadr u p o l e i n t e r a c t i o n and s e c o n d - o r d e r h y p e r f i n e i n t e r a c t i o n , Neiman and K i v e l s o n ( 2 4 ) , and a l s o Rollmann and Chan (22) have shown t h a t t h e a b s o r p t i o n i n t e n s i t y i s g i v e n by: T h i s f u n c t i o n i s o f t h e form i l l u s t r a t e d i n the t o p c u r v e ( 1 9 ) o f F i g . 6 . The second c u r v e shows what one a c t u a l l y e x p e c t s t o observe f o r t h e a b s o r p t i o n because o f v a r i o u s b r o a d e n i n g mechanisms, and t h e t h i r d c u r v e shows t h e f i r s t d e r i v a t i v e o f t h e a b s o r p t i o n , w h i c h i s o b s e r v e d e x p e r i m e n t a l l y . When 9 = 0° and 9 = 90° , B l e a n e y ' s e q u a t i o n becomes: o dH 2 ° cos . . . ( 2 0 ) 9 = 90°, H = H° - BM I ( I + 1 ) - M I 2 . • . ( 2 1 ) (a) (b) i P i g . 6: T y p i c a l p o l y c r y s t a l l i n e ESR s p e c t r a f o r t h e case o f S = \ 3 I = hy s e c o n d - o r d e r h y p e r f i n e i n t e r a c t i o n b e i n g n e g l e c t e d . 27. I f f u r t h e r m o r e j the second o r d e r c o r r e c t i o n terms are s m a l l t h e n , the e q u a t i o n s become: 9 = 0° H = H° - AM 9 = 90° H = H° - BM I n t h i s c a s e , the measurement o f g ( | , , A and B becomes v e r y s i m p l e . The markings on t h e l a s t c u r v e i n F i g . 6(C) show how t h i s can be done. I f , however, t h e second o r d e r terms can not be n e g l e c t e d , the method d e s c r i b e d by Goodman and Raynor (12) can be f o l l o w e d t o d e t e r m i n e t h e g-and t h e A - t e n s o r s . . . .(22) . . .(23) 28. R e f e r e n c e s 1 . Ye.K. Z a v o i s k y , D o c t o r ' s D i s s e r t a t i o n , Moscow, PIAN, 1 9 4 4 ; J . Phys. U.S.S.R. 9 , 2 4 5 ( 1 9 4 5 ) . 2. M. Bersohn and J.C. B a i r d , E l e c t r o n P a r a m a g n e t i c Resonance, B e n j a m i n , New Y o r k , 1 9 6 6 . 3 . A. C a r r i n g t o n and A.D. Mc L a c h l a n , I n t r o d u c t i o n t o M a g n e t i c Resonance, Harper and Row, New Y o r k , 1 9 6 7 , 4 . J.E. Wertz and J.R. B o l t o n , E l e c t r o n S p i n Resonance, McGraw-? H i l l Book Company, New Yor k , 1972. 5 . B. Bl e a n e y and K.W.H. S t e v e n s , R e p t s . P r o g r , P h y s . , 16, 1 0 8 ( 1 9 5 3 ) . 6 . K.D..Bowers and J . Owen, R e p t s . P r o g r . P h y s , , 1 8 , 3 0 4 ( 1 9 5 5 ) , 7 . D.M.S. Bagguley and J . Owen, Rep t s . P r o g r , Phys., 20, 3 0 4 ( 1 9 5 7 ) . 8 . J.W. O r t o n , R e p t s . P r o g r . Phys., 22, 2 0 4 ( 1 9 5 9 ) . 9 . J . Owen and J.H.M. T h o r n l e y , R e p t s . P r o g r . P h y s . , 2 9 ( 1 1 ) , 675(1966). 10. B.R. McGarvey, i n " T r a n s i t i o n M e t a l C h e m i s t r y " , V o l , 3 , R.L. C a r l i n , Ed., Dekker, New Y o r k , 1 9 6 6 . 11. H.A. Kuska and M.T. Rogers, i n " R a d i c a l I o n s " , L. Kevan and E.T. K a i s e r , E ds., I n t e r s c i e n c e , New Y o r k , 1 9 6 8 . 12. B.A. Goodman and J.B. Raynor, i n "Advances i n I n o r g a n i c C h e m i s t r y and R a d i o c h e m l s t r y " , V o l . 13, H.J. Emeleus and A.S. Sharpe, E d s . , Academic P r e s s , New Y o r k , 1 9 7 0 . 1 3 . A. Abragam and M.H.L. P r y c e , P r o c . Roy. Soc, ( L o n d o n ) , A205, 135(1951). 14. E. F e r m i , Z. Phys., 6p_, 3 2 0 ( 1 9 3 0 ) . 1 5 . A. Abragam and M.H.L. P r y c e , P r o c . Roy. S o c , A205, 135(1951). 1 6 . M.H.L. P r y c e , P r o c . Phys. S o c , A6J., 2 5 ( 1 9 5 0 ) . 2 9 . 17. R.M. P i t z e r , C.W. Kern and W.N. Lipscomb, J . Chem. Phys., 3 7 , 2 6 7 ( 1 9 6 3 ) . 1 8 . C.J. B a l l h a u s e n , I n t r o d u c t i o n t o L i g a n d F i e l d Theory, M c G r a w - H i l l I n c . , New Y o r k , 1 9 6 2 . 1 9 . W. Low, Para m a g n e t i c Resonance i n S o l i d s , Academic P r e s s I n c . , New Y o r k , I 9 6 0 . 20. G. B r e i t and I . I . R a b i , Phys. Rev., 3_8, 3 0 8 2 ( 1 9 3 1 ) . 2 1 . B. B l e a n e y , P h i l . Mag., 42_, 441 ( 1 9 5 1 ) . 2 2 . L.D. Rollmann and S . I . Chan, J . Chem. Phys., 5 0 , 3416(1969) 23. R.H. Sands, Phys. Rev., 99., 1 2 2 2 ( 1 9 5 5 ) . 24. R. Neiman and D. K i v e l s o n , J . Chem. Ph y s . , 3 5 , 1 5 6 ( 1 9 6 1 ) . 3 0 . I I I . EXPERIMENTAL A. P r e p a r a t i o n o f M e t a l l o t e t r a b e n z p o r p h y r i n s (MTBP) Prom t h e c o m m e r c i a l l y a v a i l a b l e c h e m i c a l compounds t o MTBP, where M i s t h e d e s i r e d d i v a l e n t m e t a l i o n , t h e s y n t h e s i s c o n s i s t e d o f t h e f o l l o w i n g s t e p s : Step 1 : P r e p a r a t i o n o f O - c y a n o a l l o c i n n a m i c A c i d ( 1 ) . U HE 1 - n i t r o s o - /3 - n a p h t h o l ( I ) ( 4 3 g ) and t o l u e n e s u l f o n y l c h l o r i d e ( I I ) ( 4 7 g ) were d i s s o l v e d i n a minimum q u a n t i t y o f a c e t o n e . The s o l u t i o n was kept a t 5 5 - 6 0 °C w h i l e c a u s t i c soda (80% s o l u t i o n ) was added s l o w l y w i t h c o n s t a n t s t i r r i n g t o keep i t o n l y f a i n t l y a l k a l i n e . When i t f i n a l l y became pe r m a n e n t l y a l k a l i n e , t h e s o l u t i o n was c o o l e d , f i l t e r e d , and a c i d i f i e d . 38 grams o f o - c y a n o a l l o c i n n a m i c a c i d ( I I I ) were p r e c i p i t a t e d . 3 1 . Step 2 : P r e p a r a t i o n o f i s o - I n d o l i n o n e - 3 - a c e t i c A c i d ( 2 ) . a C H = C H C O O H C N O H III IV lOg o f o - c y a n o a l l o c i n n a m i c a c i d was r e - f l u x e d w i t h 10$ NaOH s o l u t i o n ( 6 0 ml) f o r t h r e e h o u r s , d u r i n g w h i c h some ammonia was e v o l v e d owing t o p a r t i a l h y d r o l y s i s . The s o l u t i o n was c o o l e d , a c i d i f i e d w i t h HC1, and l e f t o v e r n i g h t t i l l t h e p r e c i p i t a t e had c o m p l e t e l y s e p a r a t e d . i s o - I n d o l i n o n e - 3 - a c e t i c a c i d ( IV) c r y s t a l l i z e d from water i n c o l o r l e s s p r i s m a t i c n e e d l e s , m.p. 1 8 2 , ( y i e l d , 9 - 5 g ; 86%). Step 3 : C o n d e n s a t i o n o f Z i n c T e t r a b e n z p o r p h y r i n ( 3 ) . a o 4 C H C O O H IV V Ten t e s t - t u b e s ( 3 x 20 cm), s u p p o r t e d u p r i g h t , were p r e h e a t e d t o 340 -345°C i n a bath o f Wood's m e t a l , o v e r l a i d w i t h c h a r c o a l . N i t r o g e n gas was passed t h r o u g h t h e tubes and i n t o each was added an i n t i m a t e m i x t u r e o f i s o - i n d o l i n o n e - 3 - a c e t i c a c i d ( I V ) ( 3 . 5 g ) and Zn(OAc) 2"2H 20 ( 2 . 6 g ) . H e a t i n g was c o n t i n u e d f o r 3 . 5 h o u r s . A f t e r which the tubes were c o o l e d . The combined p r o d u c t was S o x l e t - e x t r a c t e d w i t h p y r i d i n e ( 8 0 0 c.c.) f o r 24 h o u r s . The deep-green s o l u t i o n was poured i n t o e t h e r ( 3 l i t e r s ) , f i l t e r e d , -and e v a p o r a t e d t o 50 ml. A l i t e r o f methanol was t h e n added, wh i c h p r e c i p i t a t e d t h e crude z i n c t e t r a b e n z p o r p h y r i n (V) ( 7 . 5 g ) . I t c o n t a i n e d 4.8g o f (V) (18% y i e l d ) . For p u r i f i c a t i o n , t he crude z i n c pigment was p l a c e d on one s i d e o f a f i l t e r - p l a t e and a g l a s s w o o l p l u g , l o c a t e d h a l f way down a h o r i z o n t a l tube o f Pyrex g l a s s ( 3 x 40 cm), t h r o u g h w h i c h n i t r o g e n gas was passed. The tube was h e l d i n an a s b e s t o s s l e e v e i n an i r o n p i p e , and h e a t e d a t 450°C f o r 30 m i n u t e s . D u r i n g t h i s t i me p y r i d i n e and a brown o i l c o l l e c t e d a t the c o l d e x i t end o f t h e t u b e , and o t h e r i m p u r i t i e s i n t h e pigment were c a r b o n i z e d . l Og o f crude pigment were thus t r e a t e d . The s u b l i m e d c r y s t a l s were c o o l e d and e x t r a c t e d w i t h p y r i d i n e (1 l i t e r ) , w h i c h was t h e n p a s s e d t h r o u g h a column (18 x 3 cm) o f e q u a l p a r t s o f a l u m i n a and diatomaceous e a r t h . The p y r i d i n e e l u a t e on concen-t r a t i o n t o s m a l l b u l k and d i l u t i o n w i t h methanol gave 6.5g o f p l a t e l e t s w i t h a b e a u t i f u l l u s t e r . H e a t i n g a t 130°C i n vacuum e x p e l l e d the r e m a i n i n g p y r i d i n e . 3 3 . Step 4 : P r e p a r a t i o n o f H~2TBP (VI) ( 3 ) . 1.6g o f pure ZnTBP was. d i s s o l v e d w i t h s t i r r i n g i n 125 ml o f c o l d c o n c e n t r a t e d s u l f u r i c a c i d . Hydrogen c h l o r i d e gas was b u b b l e d t h r o u g h th e s o l u t i o n at 0°C f o r one h o u r , a f t e r which i t was f i l t e r e d onto 300g of c r u s h e d I c e . The p r o d u c t was n e u t r a l i z e d w i t h aqueous ammonia (w h i c h h e l p e d t o c o a g u l a t e t h e p r e c i p i t a t e ) , r e a c i d i f i e d w i t h s u l f u r i c a c i d , and f i l t e r e d h o t . The p u r p l e -b l u e p r e c i p i t a t e was washed w i t h hot w a t e r u n t i l f r e e from s u l f a t e i o n , and t h e n w i t h a l c o h o l , and d r i e d , the y i e l d b e i n g l . l g (75$). Step 5 : P r e p a r a t i o n o f MTBP from H-, TBP ( 4 ) . I n what f o l l o w s t h e p r e p a r a t i o n o f CoTBP was used as an example. To a r e f l u x 200 ml r e a g e n t g r a d e N, N'- dimethyIformamide (DMF), which d i s s o l v e d 5 0 0 mg H 2TBP, an e x c e s s amount of c o b a l t s u l f a t e was added.' . The r e a c t i o n v.Tas , a l l o w e d t o ,pr„c,cc,ed ..ov.emight, and the f o r m a t i o n o f t h e CoTBP was checked s p e c t r o p h c t o m e t r i c a l l y . A f t e r c o o l i n g , t h e r e a c t i o n m i x t u r e was poured i n t o 200 ml o f c h i l l e d d i s t i l l e d w a t e r . The r e s u l t i n g p a r t i a l l y c r y s t a l l i n e p r e c i p i t a t e was f i l t e r e d , washed w i t h d i s t i l l e d w a t e r t i l l f r e e from c o b a l t s u l f a t e , and t h e n d r i e d . The p r o d u c t was f u r t h e r p u r i f i e d by a l u m i n a chromatography w i t h p y r i d i n e a s e l u t e n t . The s m a l l c r y s t a l s so o b t a i n e d was v a c u a t e d t o e x p e l t h e t r a c e of p y r i d i n e . B. P r e p a r a t i o n o f O c t a m e t h y l t e t r a b e n z p o r p h y r l n and i t s T r a n s i t i o n - m e t a l D e r i v a t i v e s t h e scheme f o r s y n t h e s i z i n g The f o l l o w i n g diagrams show 3 4 . o c t a m e t h y l t e t r a b e n z p o r p h y r i n and i t s m e t a l d e r i v a t i v e s . C X'] [ X J Step 1 : P r e p a r a t i o n o f 1 , 3 , 4 , 7 - t e t r a m e t h y l i s o i n d o l e ( 5 ) . A s o l u t i o n o f a c e t o n y l a c e t o n e ( V I I ) ( l 8 . 4 g ) i n 11$ aqueous ammonium s u l f a t e s o l u t i o n ( 3 2 0 ml) was r e f l u x e d f o r 18 hours i n an atmosphere o f n i t r o g e n . The s o l u t i o n was c o o l e d and made a l k a l i n e w i t h 20% sodium h y d r o x i d e s o l u t i o n t o y i e l d a p a l e y e l l o w s o l i d . The p r o d u c t was f i l t e r e d under n i t r o g e n , washed u n t i l n e u t r a l w i t h n i t r o g e n purged d i s t i l l e d w a t e r and d r i e d (P^Oc-) i n vacuo t o g i v e a p a l e y e l l o w s o l i d ( V I I I ) ( l O g , 3 6 $ ) . .35. Step 2: P r e p a r a t i o n o f Magnesium O c t a m e t h y l t e t r a b e n z -p o r p h y r i n ( I X ) (6). A m i x t u r e of 1, 3, 4, 7 - t e t r a m e t h y l i s o i n d o l e ( V I I I ) (1.32g) and magnesium powder (2.48g) i n a s e a l e d tube was h e a t e d a t 400 f o r t h r e e h o u r s . The m i x t u r e was e x t r a c t e d ( S o x h l e t ) w i t h p e t r o l e u m e t h e r (3 h o u r s ) , bezene ('I h o u r s ) and t h e n p y r i d i n e (7 h o u r s ) . The deep-green p y r i d i n e s o l u t i o n was f i l t e r e d h o t , and the f i l t r a t e was d i l u t e d w i t h p e t r o l e u m e t h e r . Dark b l u e c r y s t a l s (1.27g, o f d i p y r i d i n e m a g n e s i u m o c t a m e t h y l t e t r a b e n z -p o r p h y r i n (IX) formed g r a d u a l l y (m.p. > 360 ). "The m a t e r i a l was homogeneous on t h i n l a y e r chromatography (on a l u m i n a ; i r r i g a t e d w i t h 10% p y r i d i n e i n p e t r o l e u m e t h e r ) . S tep 3: P r e p a r a t i o n o f O c t a m e t h y l t e t r a b e n z p o r p h y r i n (X) (6) . D i p y r i d i n e m a g n e s i u m octamethy l t e t r a b e n z p o i ^ p h y r i n (0 .30g) was s t i r r e d i n t r i f l u o r o a c e t i c a c i d (20 ml) at room t e m p e r a t u r e f o r 1.5 h o u r s . The m i x t u r e was f i l t e r e d t h r o u g h a s i n t e r e d pad i n t o c r u s h e d i c e (lOOg) whereupon a green p r e c i p i t a t e was formed. T h i s was f i l t e r e d o f f , and washed w i t h w a t e r and w i t h p y r i d i n e t o y i e l d o c t a m e t h y l t e t r a b e n z p o r p h y r i n (0 . 22g , 9^%) (m.p. > 360 ). Step 4: P r e p a r a t i o n o f the M e t a l l o d e r i v a t i v e s The same method used i n s y n t h e s i z i n g MTBP from H^BP was employed.. . C. S y n t h e s i s o f T e t r a p y r l d y l p o r p h i n , HpPyrP; and i t s M e t a l  D e r i v a t i v e s (a) S y n t h e s i s o f HgPyrP (7). 36. A p r o p i o n i c a c i d s o l u t i o n , 0.24 M w i t h r e s p e c t t o bo t h p y r i d i n e - 4 - c a r b o x a l d e h y d e and p y r r o l e , was r e f l u x e d f o r 45 mi n u t e s . The s o l v e n t was f l u s h e d o f f , the r e s i d u e was washed w i t h DMF t o d i s s o l v e t h e t a r r y b y - p r o d u c t s and l e a v e the p u r p l e c r y s t a l s . (b) P r e p a r a t i o n o f MPyrP. The- method i s same as t h a t f o r s y n t h e s i z i n g MTBP from hyPBP. D. S y n t h e s i s o f T e t r a ( p - c a r b o x y I p h e n y 1 ) p o r p h i n , H^COOHTPP, and i t s M e t a l d e r i v a t i v e s ( 7 ) . (a). S y n t h e s i s o f H 2C00HTPP. A p r o p i o n i c a c i d s o l u t i o n , 0.24 M w i t h r e s p e c t t o b o t h When the r e a c t i o n m i x t u r e was c o o l e d , H^COOHTPP p r e c i p i t a t e d as p u r p l e c r y s t a l s . The y i e l d was 34.5$. I t was f u r t h e r p u r i f i e d by r e a y s t a l l i z a t i o n from a m e t h a n o l - c h l o r o f o r m s o l u t i o n . (b) P r e p a r a t i o n o f MCOOHTPP. T h i s f o l l o w e d the same method used i n the p r e p a r a t i o n o f MTBP from HgTBP. A l l t he f r e e - b a s e p o r p h y r i n s and t h e i r m e t a l d e r i v a t i v e s were c o n f i r m e d by v i s i b l e s p e c t r o s c o p y . The micro-analysis r e s u l t s of some porphyrins are shown i n Appendix C. E. The S p e c t r o m e t e r s The ESR measurements were made on two x-band s p e c t r o m e t e r s . One was a m o d i f i e d V a r i a n 4502 i n s t r u m e n t h a v i n g a 12 i n c h V a r i a n V-3900 magnet, equipped w i t h a V a r i a n mark I I f i e l d i a l . V a r i a n c a v i t y V4533 ( c y l i n d r i c a l ) was employed. The o t h e r s p e c t r o m e t e r used was a V a r i a n model E3 ESR s p e c t r o m e t e r , which was v e r y u s e f u l f o r p o l y c r y s t a l l i n e samples. The s p e c t r a o b t a i n e d by two s p e c t r o -meters showed no d i f f e r e n c e . Microwave f r e q u e n c i e s were made w i t h a H e w l e t t P a c k a r d model 5246L c o u n t e r equipped w i t h a 5256A c o n v e r t e r . M a g n e t i c f i e l d s t r e n g t h was c a l i b r a t e d w i t h an NMR probe and magnetometer c o n s t r u c t e d by the E l e c t r o n i c s group o f t h i s Department. 38. R e f e r e n c e s 1 . G.A. Edwards, J . Chem. S o c , 1 9 2 6 , 8 1 2 . 2 . F.M. Rowe, A.S. Haigh and A.T. P e t e r s , J . Chem. S o c , 1 9 3 6 , 1 0 9 8 . 3 . R.R. L i n s t e a d and P.T. W e i s s , J . Chem. S o c , 1 9 5 0 , 2 9 7 5 . 4 . A.D. A d l e r , F.R.L. Longo, F. Kamps, J . Kim, J . I n o r g . N u c l . Chem., 3 2 , 2443(1970) . 5 . H. F l e t c h e r , T e t r a h e d r o n 22. , 2 4 8 1 ( 1 9 6 6 ) . 6 . C O . Bender, R. Bonne t t and R.G. S m i t h , J . Chem. S o c , ( C ) , 1 9 7 0 , 1 2 5 1 . 7 . F.R. Longo, M.G. F i n a r e l l i and J.B. Kim, J . H e t e r o c l i c Chem. 6 , 9 2 7 ( 1 9 6 9 ) . 3 9 . IV. VANADYL PORPHYRINS A. I n t r o d u c t i o n V a n a d y l complexes o f p o r p h y r i n s d e r i v e d from c h l o r o p h y l l s were found t o o c c u r i n o i l s h a l e s ( l ) . T h i s s u g g e s t s t h a t v a n a d y l p o r p h y r i n s might have e x i s t e d i n p r i m i t i v e b i o l o g i c a l systems and were l a t e r r e p l a c e d by o t h e r t r a n s i t i o n m e t a l s ( e . g . i r o n , magnesium, and c o b a l t ) i n t h e c o u r s e o f e v o l u t i o n . B i o l o g i c a l i m p o r t a n c e a s i d e , v a n a d y l complexes seem t o be among th o s e w e l l s u i t e d f o r ESR s t u d i e s . The r e a s o n s are as f o l l o w s : (a) The ground s t a t e i s o r b i t a l l y n o n d e g e n e r a t e , and t h e energy s e p a r a t i o n s between the ground s t a t e and t h e e x c i t e d s t a t e s a r e l a r g e . T h i s e n a b l e s ESR t o be d e t e c t a b l e a t room t e m p e r a t u r e s . 51 (b) V i s almost 100$ abundant, and has a l a r g e m agnetic moment ( f* = 5-1392 n u c l e a r magneton), w h i c h makes a n a l y s i s o f s p e c t r a s i m p l e . The f i r s t ESR work on v a n a d y l p o r p h y r i n s was done by O ' R e i l l y ( 2 ) , who s t u d i e d v a n a d y l e t i o - p o r p h y r i n - I (VO E t i o I ) i n benzene and i n a h i g h - v i s c o s i t y o i l . A l t h o u g h t h e symmetry group o f VO E t i o I i s C 2 v , the immediate s u r r o u n d i n g s o f the vanadium i o n was found t o have a f o u r - f o l d symmetry. ^ A l t h o u g h s t r i c t l y s p e a k i n g , t h e m o l e c u l a r o r b i t a l s s h o u l d be d e s c r i b e d by t h e i r r e d u c i b l e r e p r e s e n t a t i o n s o f C i , v w i t h no d i s t i n c t i o n between t h e "g"'and "u" s p e c i e s . N e v e r t h e l e s s , many a u t h o r s had used the n o t a t i o n s p e r t a i n i n g t o the group D j j h which has a c e n t e r o f i n v e r s i o n . 40. The ground s t a t e was found t o be b^ w i t h the f i r s t e x c i t e d s t a t e b e i n g e. R o b e r t s e t a l . ( 3 ) s t u d i e d ESR o f v a n a d y l complexes o f e t i o p o r p h y r i n I I , m e s o p o r p h y r i n IX d i m e t h y l e s t e r , and d e u t e r o p o r p h y r i n IX d i m e t h y l e s t e r , and found t h a t they were i d e n t i c a l t o w i t h i n the e x p e r i m e n t a l e r r o r . K i v e l s o n and Lee (4) d i d a st u d y on VOTPP i n v a r i o u s l i q u i d s o l v e n t s and f r o z e n g l a s s e s . The s u p e r h y p e r f i n e ( s h f ) s t r u c t u r e due to. t h e p y r r o l e n i t r o g e n s were o b s e r v e d f o r the f i r s t t i m e . Other a u t h o r s have not been a b l e t o r e p r o d u c e t h i s o b s e r v a t i o n u n t i l v e r y r e c e n t l y ( 7 ) . The ESR r e s u l t was found t o be c o n s i s t e n t w i t h t h e u n p a i r e d e l e c t r o n b e i n g i n . t h e b 2 a n t i - b o n d i n g o r b i t a l . The f a c t t h a t t h e n i t r o g e n s h f s p l i t t i n g i s v e r y i s o t r o p i c was a t t r i b u t e d t o t h e b 2 o r b i t a l b e i n g l o c a l i z e d on t h e vanadium i o n . I t was thought t o be almost pure m e t a l d w i t h v e r y l i t t l e i n - p l a n e n -bonding. xy The o r i g i n o f the s h f s t r u c t u r e was e x p l a i n e d i n terms o f con-f i g u r a t i o n i n t e r a c t i o n ( 4 ) . Assour e t a l . ( 5 ) , and A s s o u r ( 6 ) s t u d i e d the ESR o f v a n a d y l p h t h a l o c y a n i n e and t e t r a p h e n y l p o r p h i n , m a g n e t i c a l l y d i l u t e d i n the c o r r e s p o n d i n g f r e e b a s e s , i n s u l f u r i c a c i d , and i n o t h e r s o l v e n t s . They c o n f i r m e d the placement o f t h e 3d u n p a i r e d e l e c t r o n i n d x y • S a t o and Kwan ( 7 ) s t u d i e d t h e ESR s p e c t r a o f v a n a d y l p h t h a l o c y a n i n e i n d i l u t e d g l a s s y m a t r i x o f c o n c e n t r a t e d s u l f u r i c a c i d , a - C I - n a p h t h a l e n e , and q u i n o l i n e a t 77°K. U s i n g v e r y low f i e l d - m o d u l a t i o n , t h e y found t h e s p e c t r a gave r i s e t o n i t r o g e n s h f s t r u c t u r e s . The r e s u l t s o f the p r e v i o u s s t u d i e s are summarized i n T a b l e 2. TEMP. (°K) VOTPP i n CHC1. VOTPP i n CHC1. VOTPP i n CHC1. VOTPP i n CS, VOTPP i n CS, VOTPP i n H 2TPP VOTPP i n H 2TPP VOPc i n HgSOjj VOPc i n HgSOj, VOPc i n H 2Pc VOPc i n ZnPc 77 77 77 77 77 300 77 77 77 300 77 1 . 9 6 1 1 . 9 6 6 1 . 9 6 2 ' 1 . 9 6 1 1 . 9 6 5 1 . 9 6 6 1 . 9 6 1 1 . 9 6 5 1 . 9 6 8 1 . 9 6 6 1 . 9 6 6 VO E t i o I i n P e t r o l e u m o i l 300 1.948 VO E t i o I I i n C a s t o r a l o i l 300 1.947 VO Meso IX diMe E s t e r i n C a s t o r a l o i l 300 1.947 VO Deut IX diMe E s t e r i n C a s t o r a l o i l 300 1.947 TABLE 2: Summary o f p r e v i o u s ESR A ( 5 1 V ) B ( 5 1 V ) A ( 1 4 N ) B ( 1 4 N ) ( 1 0 - 4cnf 1 )( l0" 4cm" 1) (G) (G) REF 1 . 9 8 9 1 6 1 52 2 . 9 2 . 8 4 1 . 9 8 5 1 6 1 55 6 1 . 9 8 6 159 55 2 . 7 - 3 . 0 7b 1 . 9 8 8 159 56 2 . 9 2 . 8 4 1 . 9 9 0 159 57 6 1 . 9 8 5 1 6 1 55 4 1 . 9 8 6 160 57 2 . 6 - 2 . 8 7b 1 . 9 8 8 159 59 5 1 . 9 8 7 161 57 k(k+B)> = 2 . 5 - 3 . 0 7 a 1 . 9 8 9 158 56 5 1 . 9 9 3 1 5 8 55 5 1 . 9 8 1 52 1 . 9 8 7 159 52 2 1 . 9 8 8 1 5 8 54 3 1 . 9 8 8 1 5 8 54 3 I . 9 8 8 1 5 8 54 3 o f v a n a d y l p o r p h y r i n s and p h t h a l o c y a n i n e . 42. B. L i g a n d F i e l d O r b i t a l s of V a n a d y l P o r p h y r i n s C r y s t a l l o g r a p h i c d a t a o f v a n a d y l p o r p h y r i n s are r e l a t i v e l y . r a r e . I t seems t h a t the o n l y d a t a a v a i l a b l e a r e t h o s e o f V a n a d y l D e o x o p h y l l o e r y t h r o e t i o p o r p h y r i n (an a n a l o g o f c h l o r o p h y l l ) (8, 9). The r e s u l t shows t h a t t h e f o u r p y r r o l e n i t r o g e n s a r e c o p l a n a r , t h e vanadium atom i s out o f p l a n e by 0.48A w i t h t h e V-0 bond l e n g t h being,1.62A . I t i s i n t e r e s t i n g t o note t h a t t h e s e l e n g t h s are s t r i k i n g l y s i m i l a r t o t h o s e o f the h i g h - s p i n m e t h o x y i r o n ( I I I ) p o r p h y r i n ( 1 0 ) . . ( t h e c o r r e s p o n d i n g l e n g t h s b e i n g 0.48A , 1.842A and 2.074A ) Extended H u c k e l MO c a l c u l a t i o n s on v a n a d y l p o r p h y r i n and t e t r a z a p o r p h y r i n were c a r r i e d out by Z e r n e r and Gouterman (11) and by S c h a f f e r , Gouterman and D a v i dson ( 1 2 ) . The former- a u t h o r s , i n . a s e r i e s c f c a l c u l a t i o n ? v a r y i n g ; t-bp p o s i t i o n o f the vanadium i o n a l o n g t h e Z - a x i s had come t o t h e c o n c l u s i o n t h a t t h e m e t a l i o n s h o u l d be out o f p l a n e . The e f f e c t o f t h i s on t h e MO e n e r g i e s and the ' b o n d i n g parameters w i l l be c o n s i d e r e d l a t e r , but f i r s t t h e v a r i o u s l i g a n d o r b i t a l s w i l l be . l i s t e d f o l l o w i n g t h e d e s c r i p t i o n o f K i v e l s o n and Lee ( 4 ) . Minor d i f f e r e n c e are i n t h e n o t a t i o n s o f t h e o r b i t a l c o e f f i c i e n t s , w hich have been s t a n d a r d i z e d h e r e so t h a t t h e same Greek l e t t e r r e f e r s t o the same o r b i t a l c o e f f i c i e n t r e g a r d l e s s o f w h i c h m e t a l i o n . complex i s b e i n g c o n s i d e r e d . . The r e l e v a n t m o l e c u l a r o r b i t a l s a r e : b l = ° d x 2 y 2 ~ ^ a ' ^2 + CT3 " ° V • • • ( ! ) b 2 - 0 d k y - h V ( P y l + P x 2 - P y 3 - P x i |) ...(2) a T = 7 T ( d o + s ) -I 1 Z'- o I cr 4 3 . . . ( 3 ) 7 T T ( d ? - S ) - h 7 T T«( ° \ . + cr + c- + cr^) ...(4) I I = T I I V C V ~ V " 2 r I I v 1 "2 ^ 3 1 e = [ 5 d x z - * , p x 5 V ? : « ( P z l " P z 2 } 1 . . . ( 5 ) ( 5 V " 5 ' 1 J y 5 " V S " ^ ^ r z 3 The d's r e p r e s e n t vanadium 3 d o r b i t a l s ; S 0 , t h e vanadium 4s o r b i t a l ; °~i r e f e r s t o an sp l i g a n d o r b i t a l on the i - t h l i g a n d d i r e c t e d towards t h e vanadium n u c l e u s ; t h e P.'s are l i g a n d 2p • o r b i t a l s d i r e c t e d a l o n g t h e i - t h m o l e c u l a r axes and t h e s u b s c r i p t 5 i n d i c a t e s the v a n a d y l oxygen. The a , n , y , y M I II and 5 are c o e f f i c i e n t s o f t h e m e t a l o r b i t a l s j whereas t h e a , /3' , y* , 7^ ' , 6* 5 and 6 are c o e f f i c i e n t s o f t n e l i g a n d o r b i t a l s . Note t h a t t h e m o l e c u l a r o r b i t a l s g i v e n above are a n t i - b o n d i n g o r b i t a l s . P r e v i o u s s t u d i e s ( 1 - 7 ) have shown t h a t /3' and g" are n e a r l y z e r o , and t h a t the u n p a i r e d e l e c t r o n i s i n t h e b 2 a n t i - b o n d i n g o r b i t a l . The ESR s p e c t r a o f V a n a d y l P o r p h y r i n s can be d e s c r i b e d by t h e s p i n H a m i l t o n i a n with- a x i a l symmetry (Eq. (13) o f C h a p t e r 2 ) . A and B r e f e r t o the h y p e r f i n e s p l i t t i n g s o f vanadium. F o l l o w i n g the t r e a t m e n t o f Abragam and P r y c e ( 1 3 ) , K i v e l s o n and Lee (4) d e r i v e d t h e f o l l o w i n g e x p r e s s i o n s r e l a t i n g t h e g - t e n s o r and the vanadium h y p e r f i n e t e n s o r components t o t h e c o e f f i c i e n t s o f the m o l e c u l a r o r b i t a l s . g„ = 2.0023 8 X/ 32 a 2 X 2 - y 2 j 44 (6) g x = 2.0023 A P 2 5 2 AE xz 1-A = P B = P _ ^ 2 ( ^ K ) _ 8 X a ^ 2 . 7 ^ 1 7 ^ x 2 - y 2 ^ x z i i 2 2 /32 ( y - K) - J L - L O l AE xz .(7) ...(8) ...(9) Here X i s t h e 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 t h e f r e e i o n i n t h e a p p r o p r i a t e v a l e n c e s t a t e , K r e p r e s e n t s t h e F e r m i c o n t a c t term f o r t h e vanadium atom, AE o 2 a n d _ are t h e t r a n s i t i o n x *~y xz e n e r g i e s from b 2 t o b.^  and e r e s p e c t i v e l y ; and P i s g i v e n by: P - 2.0023 0 o V v < r " " 3 > 3 d ..(10) where 7 i s t h e g y r o m a g n e t i c r a t i o o f t h e vanadium n u c l e u s ; and P are e l e c t r o n and n u c l e a r magnetons r e s p e c t i v e l y ; r i s t h e dis-t a n c e from t h e vanadium n u c l e u s t o t h e u n p a i r e d e l e c t r o n ; S,n and n 0 are the o v e r l a p i n t e g r a l s g i v e n by: S = 2 < d x 2 _ y 2 |<ri> ...(11) ...(12) n = 2 / d I p > = 2 < ^ d |p > ^ xy I r y i ' * \ a x z I z l ' n = / 0 N X Z x 5 > (13) 4 5 . T(n) i s g i v e n by: d r [_ 20 dr ...(14) where R 2 1 ( r ) and R 2 0 ( r ) are n o r m a l i z e d r a d i a l 2p and 2s l i g a n d f u n c t i o n s r e s p e c t i v e l y . R i s t h e c e n t r a l i o n l i g a n d i n t e r n u c l e a r 2 / 2 d i s t a n c e , n / (1 - n ) i s t h e r a t i o o f 2p t o 2s c h a r a c t e r i n t h e l i g a n d o r b i t a l . C. ESR R e s u l t s ESR s p e c t r a o f t h e f o l l o w i n g systems were s t u d i e d : VOPyrP, V0C00HTPP, VOTBP, and VOOMTBP, b o t h m a g n e t i c a l l y d i l u t e d i n t h e c o r r e s p o n d i n g f r e e bases and d i s s o l v e d i n some s o l v e n t s as f r o z e n -g l a s s e s . A t y p i c a l s p ectrum i s shown i n F i g . 7. The p o l y c r y s t a l l i n e s p ectrum i s t y p i c a l o f t h a t due t o t h e v a n a d y l i o n ( w i t h I = -y) s i t u a t e d a t an a x i a l l y symmetric l i g a n d f i e l d . Each spectrum c o n s i s t e d o f two p a r t s , 9 = 0°(g|| ) and 9 = 90° ( g ^ ) , where 9 i s t h e a n g l e between H and the V-0 bond. Each p a r t s p l i t s i n t o e i g h t vanadium h y p e r f i n e l i n e s w i t h e q u a l i n t e n s i t y though not o f e q u a l w i d t h . No s u p e r h y p e r f i n e s p l i t t i n g s due t o the p y r r o l e n i t r o g e n s were o b s e r v e d . The l a r g e vanadium h y p e r f i n e s p l i t t i n g n e c e s s i t a t e s t h e i n c l u s i o n o f t h e s e c o n d - o r d e r terms i n Eq. (20 and 21) o f C h apter 2. The s p i n H a m i l t o n i a n p a r a m e t e r s s o - o b t a i n e d are summerized i n T a b l e 3 . One t h i n g s h o u l d be mentioned h e r e i s t h a t from th e s o l u t i o n ESR s p e c t r u m , one knows t h a t A and B have the same s i g n , but one cannot d e t e r m i n e th e a b s o l u t e s i g n s . The p o s i t i v e s i g n s are 2 OOG I *H P i g . 7: ESR spectrum o f v a n a d y l p y r l d y l p o r p h i n m a g n e t i c a l l y d i l u t e d i n t h e f r e e b a se, powder, 77°K. -Er 4 7 . COMPOUND TEMP. (°K) VOPyrP i n H 2 P y r P 77 VOPyrP i n H 2 P y r P 3 0 0 VOPyrP i n P y r i d i n e 77 VOPyrP i n Q u i n o l i n e 77 VOPyrP i n HOAc 77 VOPyrP i n CHC13 77 VOTPPCOOH i n HgTPPCOOH 77 VOTPPCOOH i n H"2TPPCOOH 3 0 0 VOTPPCOOH i n P y r i d i n e 77 VOTPPCOOH i n CHC13 77 VOTPPCOOH i n CHgOH 77 VOTBP i n H 2TBP 77 VOTBP i n H 2TBP 3 0 0 VOTBP i n P y r i d i n e 77 VOOMTBP i n H2OMTBP 77 VOOMTBP i n H 2OMTBP 3 0 0 VOOMTBP I n P y r i d i n e 77 S i A - 4 -1 ( 1 0 cm 0 (10"4cm 1 . 9 6 1 + 0 . 0 0 1 " 1 . 9 8 4 + 0 . 0 0 1 " 1 5 6 . 5 + 0 . 5 5 4 . 4 + 0 . 5 1 . 9 6 4 1 . 9 8 6 1 5 5 . 9 5 4 . 1 1 . 9 6 7 1 . 9 8 2 150 . 6 5 1 . 7 1 . 9 6 4 1 . 9 8 3 1 5 4 . 2 5 2 . 2 1 . 9 6 5 1 . 9 8 1 1 5 3 . 5 5 0 . 5 1 . 9 6 6 1 . 9 8 2 1 5 2 . 8 _ 5 0 . 1 1 . 9 6 1 1 . 9 8 2 1 5 5 . 4 51.9 1 . 9 6 3 1 . 9 8 6 1 5 0 . 7 5 1 . 8 1 . 9 6 7 1 . 9 8 4 1 5 4 . 9 5 2 . 7 1 . 9 6 4 1 . 9 8 7 1 5 7 . 5 5 4 . 0 1 . 9 6 4 I . 9 8 O 1 5 4 . 1 4 9 . 2 1 . 9 6 2 1 . 9 8 5 149 . 7 5 0 . 1 1 . 9 6 2 1 . 9 8 8 1 5 3 . 4 5 3 . 0 1 . 9 6 2 1 . 9 8 2 1 5 5 . 1 5 3 . 9 1 . 9 4 4 1 . 9 8 0 1 6 2 . 5 57.9 1.948 1 . 9 8 2 1 5 8 . 0 5 3 . 0 1 . 9 4 3 1 . 9 8 0 1 6 0 . 3 5 0 . 1 TABLE 3 : Summary o f s p i n H a m i l t o n i a n parameters o f v a n a d y l p o r p h y r i n s i n t h i s s t u d y . 48. chosen because o n l y they gave m e a n i n g f u l r e s u l t s t o the c a l c u l a t i o n o f b o n d i n g p a r a m e t e r s . D. D i s c u s s i o n The' complete d e t e r m i n a t i o n o f the o r b i t a l c o e f f i c i e n t s and t h e e n e r g i e s i s i m p o s s i b l e s i n c e t h e number o f unknowns (see Eq. ( 6 - 9 ) ) exceeds t h a t o f t h e knowns ( g,( , g^ , A.and B) . An a p p r o x i m a t e t r e a t m e n t , has t o be used by e i t h e r o f t h e two methods: (a) t h e energy s e p a r a t i o n s o f t h e a n t i - b o n d i n g o r b i t a l s a r e chosen from o p t i c a l d a t a o f s i m i l a r compounds, so t h a t t h e o r b i t a l c o e f f i c i e n t s may be d e t e r m i n e d . (b) r e s o n a b l e v a l u e s f o r t h e b o n d i n g c o e f f i c i e n t s o f s i m i l a r compounds a r e chosen f i r s t , so t h a t A E ' s can be e s t i m a t e d . To d e c i d e w h i c h method t o use depends on t h e p a r t i c u l a r p roblem e n c o u n t e r e d . S i n c e t h e d-d t r a n s i t i o n s a r e c o m p l e t e l y masked by much s t r o n g e r f l - II t r a n s i t i o n s , o p t i c a l d a t a a r e o f l i t t l e use. P r e v i o u s s t u d i e s on VOTPP (4) and VOPc (5) have shown t h a t the b 2 o r b i t a l , i n w h i c h t h e u n p a i r e d e l e c t r o n r e s i d e s ^ i s l o c a l i z e d on t h e vanadium atom, w h i c h means t h a t t h e " i n - p l a n e n - b o n d i n g " i s s l i g h t ( 8 ^ 1 , 8'm o ). I t i s i n t e r e s t i n g t o note t h a t B a l l h a u s e n and Gray (14) had s e t 8 = 8 = 0 i n t h e i r e x t e n d e d H u c k e l c a l c u l a t i o n on 2+ VO(H„0),- . The s i m i l a r but more r e f i n e d c a l c u l a t i o n on 2 b v a n a d y l p o r p h i n by Z e r n e r and Gouterman ( 1 1 ) , which i n c l u d e d a l l v a l e n c e o r b i t a l s o f a l l t h e atoms, a l s o i n d i c a t e d « 0 and 19 t o 4 9 . W i t h t h i s a p p r o x i m a t i o n , Eq. ( 6 - 9 ) a r e s i m p l i f i e d g M = 2 . 0 0 2 3 - 8 X AE_ 2 _ v 2 = i _ = 2 . 0 0 2 3 -2 X 8 ' AE A = P B = P xz 6 2 7 X 5 AE p 2 x^-y^ xz J ( 7 " K ) " 11 2 7~" X 6 AE . ( 1 5 ) . ( 1 6 ) . ( 1 7 ) . ( 1 8 ) yz J The o v e r l a p i n t e g r a l s depend on the e f f e c t i v e n u c l e a r charges and the s e p a r a t i o n o f t h e b o n d i n g atoms. Assuming t h e V - N i n t e r n u c l e a r d i s t a n c e t o be 2.OA , t h e V - 0 d i s t a n c e , 1.6A , and the S l a t e r ' s r u l e s f o r e f f e c t i v e n u c l e a r c h a r g e , A s s p u r ( 6 ) c a l c u l a t e d , S = 0 . 3 2 , n 0 = 0 . 1 2 I n o r d e r t o i n t e r p r e t t h e ma g n e t i c d a t a i n terms o f t h e o r b i t a l s g i v e n by Eq. ( 1 - 5 ) , i t i s n e c e s s a r y t o have a v a l u e f o r 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 A f o r t h e vanadium i o n i n the a p p r o p r i a t e v a l e n c e s t a t e . The c a l c u l a t i o n s o f Z e r n e r and Gouterman ( 1 1 ) i n d i c a t e s t h a t vanadium i s i n a V + 0 * 5 ( d 3 " 5 ° S ° ' 3 5 p 0 . 6 5 ) s t a t e , t h e 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 e s t i m a t e d t o be 115 cm-"'" from a l i n e a r e x t r a p o l a t i o n between the v a l u e s o f the n e u t r a l atom and t h a t o f the mono-cation ( 1 5 ) . Eq. ( 1 5 - 1 8 ) s t i l l can not be s o l v e d c o m p l e t e l y and f u r t h e r a p p r o x i m a t i o n s have t o be made. One n o t i c e s t h a t t h e terms 5 0 . i n v o l v i n g o v e r l a p i n t e g r a l s i n Eqs. ( 1 5 and 16) are much l e s s t h a n one. T h e r e f o r e , i t i s q u i t e s u f f i c i e n t t o use K i v e l s o n and Lee's v a l u e s f o r t h e o r b i t a l c o e f f i c i e n t s i n e v a l u a t i n g t h e terms i n v o l v i n g t h e o v e r l a p i n t e g r a l s i n Eqs. ( 1 5 and 1 6 ) . T h i s e n a b l e s A E v 2 - 2 / a 2 a n d A E I h 2 t o be c a l c u l a t e d . The x y / xz / r e s u l t s t o g e t h e r w i t h the e x p e r i m e n t a l v a l u e s o f A and B a r e t h e n s u b s t i t u t e d i n Eqs. ( 1 7 and 1 8 ) t o s o l v e f o r P and K. The b o n d i n g parameters are summarized i n T a b l e 4. A p l o t o f th e "energy l e v e l s " , w i t h r e s p e c t t o t h a t o f as z e r o , i s shown i n F i g . 8 . I t s h o u l d be n o t i c e d t h a t because i t was not p o s s i b l e 2 2 t o e l v a l u a t e a and $ , t h e "energy l e v e l s " a r e t h e q u o t i e n t s 2 2 o f the e n e r g i e s and a and 8 , r e s p e c t i v e l y . The r e a l 2 2 e n e r g i e s s h o u l d be a o r s , t i m e s t h e r e s p e c t i v e q u o t i e n t s . I t i s r e a s o n a b l e t o suggest t h a t s t r o n g e r a - b o n d i n g means e i t h e r 2 t h e a n t i - b o n d i n g o r b i t a l b^ i s h i g h e r i n energy o r a i s s m a l l e r / 2 i n magnitude, b o t h o f which make A E ^ v2 / a l a r g e r . F o r 2 th e same r e a s o n l a r g e r A E / S means s t r o n g e r o u t - o f - p l a n e II -X Z / b o n d i n g . The v a r i a t i o n o f " e n e r g y - c o e f f i c i e n t q u o t i e n t s " i n F i g . 8 can be s i m p l y e x p l a i n e d on t h e b a s i s o f the g e o m e t r i e s o f v a n a d y l p o r p h y r i n s . I t has been mentioned b e f o r e t h a t t h e M-N d i s t a n c e i n t h e p h t h a l o c y a n i n e i s about 0.05A s m a l l e r t h a n i n the m e t a l l o -p o r p h y r i n s . T h i s would account f o r b o t h t h e s t r o n g e r i n - p l a n e o- -bonding and t h e s t r o n g e r o u t - o f - p l a n e II -bonding i n VOPc. VOTPP, VOPyrP, and V0C00HTPP a r e e x p e c t e d t o be s i m i l a r i n b o n d i n g c h a r a c t e r i s t i c s , due t o t h e i r s i m i l a r g e o m e t r i e s which i s i n d e e d Temp . (°K) P(10" 4 cm - 1 ) K A E 2 2/2 x-y/a (K cm-1) A E xz ,yz) (K cm-1) VOPyrP' i n H 2 P y r P 77 113 0. 75 17 . 8 11 . 5 VOPyrP i n H 2 P y r P 300 113 0. 75 19 .2 12 . 9 VOPyrP i n P y r i d i n e 77 111 0 . 74 20 . 8 10 .3 VOPyrP i n Q u i n o l i n e 77 114 0. 73 19 .2 10 . 9 VOPyrP i n HOAc 77 115 0. 71 19 . 7 9 . 8 VOPyrP i n CHC1 3 77 115 0. 71 20 . 3 10 . 3 VOPyrP i n CF 3COOH 77 119 0. 67 19 .2 9 . 8 VOTPPCOOH i n H 2TPPCOOH 77 115 0. 72 17 . 8 10 . 3 VOTPPCOOH i n H 2TPPCOOH 3 0 0 110 0 . 74 18 . 7 12 . 9 VOTPPCOOH i n P y r i d i n e 77 114 0. 73 20 . 8 11 . 5 VOTPPCOOH i n CHC1 3 77 115 0. 74 19 .2- 13 . 8 VOTPPCOOH i n CH 3OH 77 117 0. 68 19 .1 9 . 4 VOTBP'in H 2TBP 77 111 0. 72 18 .2 12 .2 VOTBP i n : HgTBP 300 112 0. 75 18 .2 14 . 8 VOTBP i n P y r i d i n e 77 112 0. 75 18 .2 10 . 3 VOOMTBP i n H2OMTBP 77 114 0. 78 12 . 6 9 . 4 VOOMTBP i n H2OMTBP 300 114 0. 73 13 . 5 10 . 3 VOOMTBP i n P y r i d i n e 77 119 0 . 6 8 12 . 4 . 9 . 4 VOTPP i n CHC1 0 300 121 0. 71 17 . 8 15 . 9 3 1 1 8 0. 74 20 . 3 12 .2 VOTPP i n CS~ 300 114 0. 76 17 . 8 14 . 8 c. 113 0. 78 19 . 7 17 .2 VOTPP i n H 2TPP 300 1 1 8 0. 74 20 . 3 12 .2 5 2 . VOPc i n H 2 S 0 4 77 111 0 .80 19 .7 14 . 8 VOPc i n H"2Pc 300 114 0 .77 20 .3 15 . 9 VOPc i n ZnPc 77 117 0 .73 20 .3 13 .8 VO E t i o p o r p h r i n I P e t r o l e u m 300 116 0 . 7 2 13 . 5 13 .8 VO M e s o p o r p h r i n IX diMe E s t e r 300 113 0 .75 13 .3 14 .8 VO D e u t e r o p o r p h r i n diMe E s t e r 300 113 0 .75 13 .3 14 .8 TABLE 4: C a l c u l a t e d b o n d i n g p a r a m e t e r s , and l i g a n d f i e l d t r a n s i t i o n e n e r g i e s o f v a n a d y l p o r p h y r i n s and p h t h a l o c y a n i n e . 53. 25 2 0 H2S04< CHCL-V \Pyr p»«»pyr I I C H C L J J ; »Hoac | • ^uin ^ • • " C H c U VO Complexes - 1 5 o CO o >-o ec LU LU m o .SO/ ZnPc 10 \ f - ^ C H C L j i— fCS 0 CHCI3 quin CHcLPyr H o a c i — t p y r / \ i < ' \ \ \ - J E b , . / * 2 0 P c T P P p y r P COOHTPP TBP OMTBP E t i o i Etio2 F i g . 8: L i g a n d f i e l d t r a n s i t i o n e n e r g i e s o f some v a n a d y l p o r p h y r i n s and p h t h a l o c y a n i n e . t h e case. U n f o r t u n a t e l y , no x - r a y a n a l y s i s has been done on t h e t e t r a b e n z p o r p h y r i n s . B u t , we can e xpect t h a t t h e i r p o r p h i n a t o r a d i i a re c l o s e r t o t h a t o f VOTPP, t h a n t o t h a t o f VOPc. The b o n d i n g c h a r a c t e r s o f VOTBP i s s i m i l a r t q t h o s e o f VOPyrP, and VOCOOHTPP. When t h e v a n a d y l p o r p h y i n s a r e d i s s o l v e d i n o r g a n i c s o l v e n t s , t h e s o l v e n t m o l e c u l e s can bond t o t h e v a n a d y l oxygen, o r t h e s i x t h l i g a n d p o s i t i o n . One t h i n g i s c o n s i s t e n t from t h e energy l e v e l diagram ( P i g . 8 ) , a l l s o l v e n t s m o l e c u l e s a f f e c t a p a r t i c u l a r b o n d i n g o f a p a r t i c u l a r v a n a d y l p o r p h y r i n s i n t h e same d i r e c t i o n . The i n c r e a s e i n E-^ / a 2 f o r VOPyrP and VOCOOHTPP ( i . e . s t r o n g e r a -bond) might be t h e r e s u l t o f t h e o c c u p a t i o n o f t h e s i x t h l i g a n d p o s i t i o n by a s o l v e n t m o l e c u l e , and hence the YC s r e u p j .? p'.'Jle^ -<?i n«#»T» - t o -the c e n t e r o f t h e •.p&of-ipiii&t.c -acre. The f a c t t h a t p y r i d i n e s o l v e n t has s t r o n g e r e f f e c t t h a n c h l o r o f o r m s u p p o r t s t h i s s p e c u l a t i o n . / 2 The s o l v e n t e f f e c t t o E e / 5 i s more c o m p l i c a t e d . W h i l e t h e b i n d i n g of a s o l v e n t m o l e c u l e at the s i x t h p o s i t i o n can a f f e c t t h e o u t - o f - p l a n e n - b o n d i n g , hydrogen-bonded t o v a n a d y l oxygen by a s o l v e n t m o l e c u l e a l s o has i t s e f f e c t . The change i n E e / ^ 2 upon s o l v a t i o n shows t h e p r e s e n c e o f s e v e r a l c o m p e t i n g f a c t o r s . 5 5 . References 1 . J.E. Falk, "Porphyrins and Metalloporphyrins", E l s e v i e r Publishing Company, New York, 1 9 6 4 , Page 1 3 8 . 2 . D.E. O'Reilly, J . Chem. Phys., 29_, 1 1 8 8 ( 1 9 5 8 ) ; 30., 5 9 1 ( 1 9 5 9 ) . 3 . E.M. Roberts, W,S. Koski and W.S. Caughey, J . Chem. Phys., 3 4 , 5 9 1 ( 1 9 6 1 ) . 4 . D. Kivelson and S.K. Lee, J . Chem. Phys., 4 l _ , 1 8 9 6 ( 1 9 6 4 ) . 5 . J.M. Assour, J . Goldmacher and S.E. Harrison, J . Chem. Phys., 4 3 , 1 5 9 ( 1 9 6 5 ) . 6 . J.M. Assour, J. Chem. Phys., 4_3, 2477 ( 1 9 6 5 ) . 7 a . M. Sato and T. Kwan, J . Chem. Phys., 50_, 5 5 8 ( 1 9 6 9 ) . 7 b . M. Sato and T. Kwan, B u l l . Chem. Soc. Japan, 4j_, 1 3 5 3 ( 1 9 7 4 ) . 8 . R.C. Petterson and L.E. Alexander, J . Am. Chem. S o c , £ 0 , 3 8 7 3 ( 1 9 6 8 ) . 9 . R.C. Petterson, Acta Cryst., B 2 5 , 2 5 2 7 ( 1 9 6 9 ) . 1 0 . J.H. Hoard, Science, 17_4, 1 2 9 5 ( 1 9 7 1 ) . 1 1 . M. Zerner and M. Gouterman, Inorg. Chem., 5., 1 6 9 9 ( 1 9 6 6 ) . 1 2 . A.M. Schaffer, M. Gouterman and E.R. Davidson, Theoret. Chim. Acta 3 0 , 9 ( 1 9 7 3 ) . 1 3 . A. Abragam and M.H.L. Pryce, Proc. Roy. S o c (London) A206, 1 6 4 ( 1 9 5 1 ) ; A205, 1 3 5 ( 1 9 5 1 ) . 14. C.J. Ballhausen and H.B. Gray, Inorg. Chem., 1 , 1 1 1 ( 1 9 6 2 ) . 1 5 . T.M. Dunn, Trans. Faraday, S o c , 5 7 , 144 ( 1 9 6 1 ) . 56. V. COPPER PORPHYRINS A. I n t r o d u c t i o n By f a r , t h e most e x t e n s i v e l y s t u d i e d m e t a l p o r p h y r i n s a re the copper p o r p h y r i n s , p a r t i c u l a r l y , copper p h t h a l o c y a i n e s . The r e a s o n s a re many: (a) they a re o b s e r v a b l e a t room t e m p e r a t u r e s due t o the l o n g s p i n - l a t t i c e r e l a x a t i o n t i m e s ; (b) t h e u n p a i r e d e l e c t r o n i s i n b l g ( d x> _ v * ) > a n d hence one can d e t e c t t h e l i g a n d s u p e r h y p e r f i n e s p l i t t i n g s ; ( c ) . copper i s r e a d i l y a v a i l a b l e f o r b i n d i n g i n b i o l o g i c a l compounds; f o r i n s t a n c e , hemocyanine, the nonheme r e s p i r a t o r y • • -° J - •- '-> ~ - i ^ ~ v«o ^ f namir p i m rn o T 1 11 <3 Ir s a w l ''<"vrMT5VtJPnr>. H O T S which b i n d s oxygen r e v e r s i b l y (1). Ingram and h i s co-workers (2) were the f i r s t t o i n v e s t i g a t e t h e ESR o f copper ( I I ) t e t r a p h e n y l p o r p h y r i n (CuTPP). Subsequent t o t h i s i n i t i a l s t u d y , much work has been c a r r i e d out on t h e ESR o f copper p o r p h y r i n s (3-14)., p a r t i c u l a r l y CuTPP and CuPc. However, owing t o a c e r t a i n c o m b i n a t i o n o f f a c t o r s t h e i n t e r p r e t a t i o n o f r e s u l t s have not always b e e n . i n agreement. Guzy e t a l . (15) . commented on t h e c o n f u s i o n not o n l y i n t h e a n a l y s i s o f the ESR s p e c t r a , but a l s o i n t h e i n t e r p r e t a t i o n o f the d e r i v e d p a r a m e t e r s . The magnitude o f the copper h y p e r f i n e t e n s o r was' not d e t e r m i n e d w i t h any degree o f c e r t a i n t y because o f t h e p r e s e n c e o f two copper i s o t o p e s ( 6 3 C u , 69.1$; 6 5 C u , 30.9$) w i t h n e a r l y e q u a l magnetic 5 7 . moments ( 6 3 C u , 2.2206 n u c l e a r magneton; 6 5 C u , 2.3790). T h i s 14 causes d i f f i c u l t y I n t h e a n a l y s i s o f t h e N h y p e r f i n e c o u p l i n g . Only i n some s p e c i f i c o r i e n t a t i o n s i n s i n g l e c r y s t a l s t u d i e s does the r e s o l u t i o n o f the f e a t u r e s a s s o c i a t e d w i t h t h e two i s o t o p e s become f e a s i b l e . Guzy e t a l . a l s o p o i n t e d out t h a t i n many e a r l i e r w o rks, A ( l i fN) was r e p o r t e d as l e s s t h a n o r e q u a l t o B ( l i J N ) wh i c h arose from an i n c o r r e c t i n t e r p r e t a t i o n o f t h e s p e c t r a . The b o n d i n g parameters d e r i v e d i n t h e s e s t u d i e s are t h e r e f o r e l e s s m e a n i n g f u l . Manoharan and Rogers ( 1 6 ) s t u d i e d t h e ESR o f copper t e t r a p h e n y l p o r p h i n j u s i n g pure s o l i d m a t e r i a l , s o l u t i o n s , m a g n e t i c a l l y d i l u t e d s i n g l e c r y s t a l s , and p o l y c r y s t a l l i n e powders. I t was p o s s i b l e t o o b t a i n r a t h e r complete ESR d a t a , i n c l u d i n g the h y p e r f i n e i n t e r a c t i o n t e n s o r s f o r N, ' ^Cu. T h e i r r e s u l t s p r o b a b l y are more a c c u r a t e t h a n o t h e r s on t h e same compound. U n f o r t u n a t e l y , the assignment o f A N and B N were r e v e r s e d . Guzy et a l . ( 1 5 ) s t u d y i n g t h e ESR o f CuPc showed t h a t t h e b o n d i n g parameters w i t h a c c u r a c y comparable t o s i n g l e c r y s t a l s t u d i e s c o u l d be d e r i v e d from p o l y c r y s t a l l i n e s p e c t r a o f an i s o t - o p i c a l l y pure compound. I n a r e c e n t p a p e r ; Y. Hsu ( 1 7 ) s t u d i e d t h e ESR o f ^copper ( I I ) p r o t o p o r p h y r i n IX d i m e t h y l e s t e r ( a n a t u r a l l y o c c u r i n g p o r p h y r i n ) i n p o l y c r y s t a l l i n e s t a t e i n b o t h Q-and X-bands. T h i s l a s t a u t h o r employed a t e c h n i q u e f o r t h e i n t e r p r e t a t i o n o f t h e s p e c t r a not u n l i k e t h a t recommended by Guzy e t a l . The purpose o f t h e p r e s e n t work i s , l i k e i n t h e case of the v a n a d y l complexes, t o e x t e n d ESR st u d y t o i n c l u d e the t e t r a b e n z -58. Cu Cufi N A Nfi g. (lO^cm"1) (IO 4 cm-') (IO 4 cm"1) (lO^cnf') REF. 6 3CuPc i n H 2Pc 2 . 1 6 0 2 .045 217G 3 1 . 5G 19 • 5G 15 .4G 15 CuPc i n ZnPc 2 .162 2 .047 215 28 17 . 4 15 . 8 3 , 8 CuPc i n H 2 S 0 2 | 2 . 1 8 0 2 . 0 3 7 13 .6G 15 .4G 5 CuPc i n H2SOi| 2 . 1 7 4 6 2 .045 2 0 2 32 14. 4G 6 , 7 CuPc i n H 2Pc 2 . 1 7 9 2 . 0 5 0 2 0 2 19 14 . 5 17 . 8 9 , 1 0 CuTPP i n H 2Pc 2 .170 2 .042 1 8 0 5 3 . 6 17 . 0 12 . 4 12 CuTPP i n H2TPP 2 . 1 9 3 2 . 0 7 1 - 2 0 2 - 2 9 14 . 5 16 . 1 1 1 , 1 3 , 1 2 CuTPP i n CHC13 2 . 1 8 7 , 2 . 0 6 7 2 1 8 39 14 . 5 16 . 5 11 CuTPP i n CHC13 2 . 1 8 7 2 . 0 3 2 2 0 9 3 1 . 8 14 .48 15 . 9 16 CuTPP i n R"2TPP (Single-crystal) 2 . 1 9 0 2 .045 2 1 1 ( 6 5 c u ) 2 0 1 ( 6 3 c u ) 3 3 . 0 14 . 5 6 16 .14 16. CuTPP i n H2TPP (P o l y c r y s t a l l i n e ) 2 . 1 8 7 2 .045 214 ( 6 5 C u ) 2 0 2 ( 6 3 C u ) 3 2 . 9 14 . 5 16 . 1 16 CuTPP 2 .17 2 .05 2 5 0 30 2 Cu Etioporphrin II 2 .169 2 .061 4 6 3 C u PPIXDME* 2 . 1 9 1 9 2 . 0 5 4 - 2 0 0 . 1 - -42. 6 17 . 1 14 . 4 17 Cu NaChlorophyllin 2 .2033 2 .0518 205 .1 30. 1 16 . 5 12 . 8 14 TABLE 5: Summary of previous ESR re s u l t s of copper porphyrins and phthalocyanine. *Cu PPIXDME stands for cupric protoporphyrin IX dimethyl ester. 59. p o r p h y r i n s and some o t h e r TPP ty p e l i g a n d s . I n o r d e r t o e l i m i n a t e t h e b r o a d e n i n g e f f e c t due t o u n r e s o l v e d -Cu and 5 C u h y p e r f i n e 63 s t r u c t u r e s , i s o t o p i c a l l y pure Cu was used. Computer s i m u l a t e d s p e c t r a were c o n s t r u c t e d t o o b t a i n t h e f i n a l s e t o f ' s p i n H a m i l t o n i a n p a r a m e t e r s . F i n a l l y , t h e same t r e a t m e n t o f the parameters o f ours and o f t h e p r e v i o u s s t u d i e s was c a r r i e d out i n o r d e r t h a t . a l l d a t a can be compared on e q u a l and t h e r e f o r e m e a n i n g f u l b a s i s . . B. Theory X-ray a n a l y s i s shows t h a t t h e copper p o r p h y r i n s have s q u a r e -p l a n a r symmetry at t h e c u p r i c i o n s i t e t o an e x c e l l e n t degree o f a p p r o x i m a t i o n . The p o i n t group i s t h e r e f o r e Each n i t r o g e n atnm has a v a i l a b l e • 2s. ' 2 D . . . 2p._, and -2p„ o r b i t a l s f o r t h e f o r m a t i o n o f m o l e c u l a r o r b i t a l s w i t h the a t o m i c d - o r b i t a l s o f the c e n t r a l i o n . W i t h t h i s i n mind, t h e f o l l o w i n g a n t i - b o n d i n g m o l e c u l a r o r b i t a l s f o r a 3d 1 h o l e c o n f i g u r a t i o n can be formed: ~ B . , = a d 2 ? - ¥~ (" 0 - 1 • + CT2 + 0 - 3 -O- 1*) . . . (1 ) I g xd-yd 2 v x y x y B o = f i d - ( P 1 + P 2 - P 3 - P1*) . . . (2 ) 2g p xy 2 y x y x' - 4 ( e r 1 V a 2 -2 v x y 3 S ^ x .(3) 60. The d's r e p r e s e n t copper 3d o r b i t a l s . The s u p e r s c r i p t s 1 and 3 o f the n i t r o g e n o r b i t a l s l a b e l the n i t r o g e n atoms on t h e sp h y b r i d o r b i t a l on the i - t h n i t r o g e n p o i n t i n g towards t h e copper n u c l e u s . p i r e f e r s t o a 2p o r b i t a l a l o n g t h e j - a x i s on t h e i - t h n i t r o g e n . Note t h a t the a n t i - b o n d i n g MO's a r e a r r a n g e d i n the o r d e r o f i n c r e a s i n g e n e r g i e s a c c o r d i n g t o t h e c a l c u l a t i o n o f Z e r n e r and Gouterman ( 1 8 ) , and S c h a f f e r et a l . ( 1 9 ) . The b o n d i n g c o e f f i c i e n t s a and a ' a r e a measure o f the degree 2 o f c o - v a l e n c y o f the o -bond. F o r i n s t a n c e , a = 1 and •2 a- = 0 c o r r e s p o n d t o pure i o n i c bond w i t h t h e e l e c t r o n b e i n g 2 l o c a l i z e d at t h e c e n t r a l atom. On t h e o t h e r hand, i f a = a ' 2 = \ ( n e g l e c t i n g the o v e r l a p ) the bond i s p u r e l y c o v a l e n t . S i m i l a r l y ( , 8' ) and ( 5 , 8' ) a r e r e s p e c t i v e l y measures o f the degrees o f t h e i n - p l a n e and t h e o u t - o f - p l a n e b o n d i n g . The ESR d a t a of copper p o r p h y r i n s can be d e s c r i b e d by t h e f o l l o w i n g s p i n H a m i l t o n i a n s , assuming the. l i g a n d f i e l d t o be x - a x i s , 2 and H are n i t r o g e n s on the y - a x i s . °"i r e f e r s t o a 2 f-{ = g a H S + g, (H S + H S ) + A C"S I J 6 u p z z & J L x x y y z z 4 + B.(S , 1 . + S 1 X 1 X ' The v a r i o u s q u a n t i t i e s have the u s u a l meaning. N o t i c e t h a t t h e d i r e c t i o n o f z' o f i - t h n i t r o g e n i s t h a t from the n i t r o g e n t o t h e copper atom. 2+ The ESR d a t a measured f o r the Cu p o r p h y r i n s a re c o n s i s t e n t w i t h t h e assignment o f t h e 3 d u n p a i r e d e l e c t r o n i n the b, ground s t a t e . When t h e wave f u n c t i o n f o r the b, s t a t e i s a p p l i e d t o l g t h e s p i n H a m i l t o n i a n , t h e magnetic parameters o b t a i n e d a r e g i v e n i n t he f o l l o w i n g r e l a t i o n s w h i c h was f i r s t d e r i v e d by Maki and McGarvey ( 2 0 ) and was m o d i f i e d by K i v e l s o n and Neiman ( 2 1 ) w i t h o v e r l a p c o r r e c t i o n s . K = 2 0 0 2 3 - 8 ^ 2 ^ fi_«l S- ^ ) « 2 S 2 a' «' 3' T(n) \ = 2 . 0 0 2 3 -.(6) ...(7) = P B = P - a 2 ( y + K) 2 ( k l _ + 3 _ S 'xy \ y xz / 2,2 v s 22 \ a 2 S 2 X Z . . . ( 8 ) -...(9) I n t h e s e e q u a t i o n s X i s t h e 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 2+ —1 o f t h e f r e e Cu i o n , and i s s e t t o be - 8 2 8 cm ; P = 2 8 8 N 7 C u ^ d x 2 - y 2 - 3 d x 2 - y 2 ) ; y„ i s t h e magnetic moment C u 6 o f c opper; 8 , t h e Bohr magneton; and t h e n u c l e a r magneton. The c o n s t a n t K, i n t r o d u c e d by Abragam and P r y c e ( 2 2 ) , s t a n d s f o r the F e r m i c o n t a c t term and r e s u l t s from the m i x i n g - i n 8 8 o f e x c i t e d conf i g u f a t i o n s , n o t a b l y 3 s 3 d and 3 d 4 s . S i s t h e 62. o v e r l a p i n t e g r a l between t h e _ y 2 o r b i t a l and the n o r m a l i z e d n i t r o g e n c r - o r b i t a l s , s = 2 ( d x 2 _ y2|°i> • • - ( 1 0 ) and 8 R ( l - n 2 ) ^ (Z -Z ) (Z Z ) 5 / 2 . n. T(n) = n - s P 3 P . . . ( I D ( Z s + Z p ) 5 a o 2 ^ where n = ( j ) 2 f o r t r i g o n a l h y b r i d i z a t i o n , R i s t h e m e t a l - n i t r o g e n i n t e r n u c l e a r d i s t a n c e , Z and Z a r e t h e e f f e c t i v e n u c l e a r charges ' s p on t h e s and p o r b i t a l s o f n i t r o g e n atom; and a Q i s t h e Bohr r a d i u s . The n i t r o g e n s u p e r h y p e r f i n e s t r u c t u r e i s e x p r e s s e d a s : A N = 3 S N ^ ^ 2 ( 0 ) f S + | g P G N ^ < r " 3 > f p • ' • ( 1 2 ) b N = I F M N ^ 2 ( 0 ) f s T g f , G N % < R " 3 > F P • • • ( 1 3 ) 2 Assume t h a t t h e p y r r o l e n i t r o g e n uses sp h y b r i d s t o form a-1 2 1 2 bond, th e n f = T-TT a ? . and f = -r a' . s 12 p 6 Assour (11) has c a l c u l a t e d S = 0.092 and T(n) = 0.33 f o r t h e case o f t r i g o n a l n i t r o g e n h y b r i d o r b i t a l s , m e t a l - n i t r o g e n d i s t a n c e b e i n g 2.OA , e f f e c t i v e n u c l e a r charges b e i n g d e t e r m i n e d by S l a t e r ' s r u l e s . I f l i g a n d h y p e r f i n e s t r u c t u r e i s o b s e r v a b l e , such as i n the case o f Cu complexes, a can be more p r e c i s e l y c a l c u l a t e d from the i s o t r o p i c F e r m i i n t e r a c t i o n energy; a = I ( A N + 2 B N } = T W ( 0 ) •« . . .(14) and the n o r m a l i z a t i o n r e l a t i o n f o r t h e b l g o r b i t a l a 2 + a 2 - 2 cm' S = 1 . . .(15) 63 C. P r e p a r a t i o n o f t h e U J C u P o r p h y r i n s /To 20 mg o f ^CuO (Oak Ridge N a t i o n a l Lab.) was d i s s o l v e d i n 2 ml c o n c e n t r a t e d HC1 ( R e a g e n t ) . The e x c e s s HC1 was d r i v e n out by h e a t i n g t h e s o l u t i o n I n an e v a p o r a t i n g d i s h t i l l almost d r y -n e s s . The r e s i d u e was t r e a t e d s e v e r a l t i m e s w i t h water and h e a t e d t o almost d r y n e s s t o remove th e e x c e s s HC1 c o m p l e t e l y . i n 50.0 ml d i m e t h y l f o r m a m i d e . 100.0 mg I-^PyrP (162 x 10 m moles) were d i s s o l v e d i n 50.ml d i m e t h y l f o r m a m i d e . To t h i s r e f l u x s o l u t i o n , 0.66 ml o f t h e C u C l 2 c o n t a i n i n g d i m e t h y l f o r m a m i d e s o l u t i o n (3-2 x 10 m moles) was added. The m i x t u r e was a l l o w e d t o p r o c e e d f o r c o m p l e t i o n ( i t took l e s s t h a n 3 0 . m i n u t e s ) . A f t e r c o o l i n g , i t was poured i n t o 200 ml o f c h i l l e d d i s t i l l e d w a t e r and the r e s u l t i n g p a r t i a l l y c r y s t a l l i n e p r e c i p i t a t e was f i l t e r e d , washed w i t h d i s t i l l e d w ater u n t i l f r e e from C u C l ^ , and t h e n d r i e d . The p r o d u c t was '. f u r t h e r p u r i f i e d by an a l u m i a column chromatography, u s i n g p y r i d i n e as an e l u t e n t . D. ESR R e s u l t s F i g u r e s 9-12 show the ESR s p e c t r a o f p o l y c r y s t a l l i n e ^Cu p o r p h y r i n s d i l u t e d i n the c o r r e s p o n d i n g f r e e bases at l i q u i d n i t r o g e n t e m p e r a t u r e . The powder s p e c t r a a r e i n t e r p r e t e d as c u p r i c i o n s i t u a t e d at an a x i a l l y symmetric l i g a n d f i e l d s due t o t h e f o u r p y r r o l e n i t r o g e n s . Each spectrum i s composed o f two p a r t s , 9 = 0 ° ( g ( ) ) p a r t and 9 = 90° ( gj_ ) p a r t , where 9 i s t h e a n g l e between H and the a x i s p e r p e n d i c u l a r t o the c o o r d i n a t i o n p l a n e . The p a r a l l e l p a r t s p l i t s i n t o f o u r copper h y p e r f i n e l i n e s and each l i n e f u r t h e r s p l i t s i n t o n i n e e q u a l l y spaced l i n e s w i t h i n t e n s i t y r a t i o o f 1:4 :10 :16 :19 :16 :10 :4:1, w h i c h i s a s s o c i a t e d w i t h t h e i n t e r a c t i o n between t h e u n p a i r e d e l e c t r o n and f o u r Cu e q u i v a l e n t n i t r o g e n atoms. P a r t o f t h e m^ = -h l i n e s and a l l Cu 3 of t h e m.j. = ~2 l i n e s o v e r l a p p e d w i t h t h e g ^ p a r t . The copper p e r p e n d i c u l a r p a r t i s a l s o a s s o c i a t e d w i t h f o u r copper h y p e r f i n e l i n e , each o f w h i c h f u r t h e r s p l i t s i n t o n i n e n i t r o g e n s u p e r -h y p e r f i n e l i n e s but they o v e r l a p c o n s i d e r a b l y . The " f r e e - r a d i c a l " r esonance and anomolous l i n e s , w h i c h had been a n a l y s e d by K i v e l s o n and Neiman ( 2 3 ) , and by Gersmann and Swalen ( 2 4 ) , a r e a l s o o b s e r v e d ( F i g . 9 ( a ) ) Fig." 13 shows the more d e t a i l e d h y p e r f i n e s t r u c t u r e s one can observe by r e p l a c i n g n a t u r a l l y - a b u n d a n t copper w i t h i s o t o p i c a l l y pure copper-63. The i n t e r p r e t a t i o n f o r 9 = 0 ° p a r t i s s t r a i g h t f o r w a r d , g can be c a l c u l a t e d from the c e n t e r o f t h e f o u r copper h y p e r f i n e l i n e s ; the s e p a r a t i o n between the copper m T = h and m T = -\ l i n e s F i g . 9a: ESR spectrum o f J C u P y r P m a g n e t i c a l l y d i l u t e d i n H 2 P y r P , powder, 77°K. A i s t h e f r e e - r a d i c a l r e s o n a n c e , B i s anomalous l i n e s . P i g . 9b: C o m p u t e r - s i m i l a t e d ESR spectrum. ll 1 1 HP i 1 1 1 Y 1 , 100 G 1 H 1 ... F i g . 10: ESR spectrum o f Cu t e t r a ( p - c a r b o x y l p h e p y l ) p o r p h i n m a g n e t i c a l l y d i l u t e d i n t h e f r e e b a s e , powder, 77°K. 67. P i g . 11: ESR spectrum o f 6 3 C u t e t r a b e n z p o r p h y r i n m a g n e t i c a l l y d i l u t e d i n t h e f r e e b a s e , powder, 77°K. P i g . 12: ESR s p e c t r u m o f ^Cu o c t a m e t h y l t e t r a b e n z -p o r p h y r i n m a g n e t i c a l l y d i l u t e d i n t h e f r e e b a s e , powder, 77°K. [ b ] Region o f t h e spectrum t o t h e l o w - f i e l d s i d e o f gi (a) u n e n r i c h e d CuPyrP, (b) 63cuPyrP. 7 0 . Cu g i v e s A , and the s e p a r a t i o n between th e two a d j a c e n t n i t r o g e n N l i n e s g i v e s B . D i r e c t i n t e r p r e t a t i o n o f p e r p e n d i c u l a r l i n e s i s d i f f i c u l t due t o t h e i r e x t e n s i v e o v e r l a p p i n g . An i n i t i a l guess at the v a l u e s o f gj_ , B C u and A N was f i r s t a c h i e v e d by c o n s t r u c t -i n g r e s o n a n c e p a t t e r n l i k e t h a t shown i n F i g . l U . The f i n a l a c c e p t e d parameters were o b t a i n e d by c o m p u t e r - s i m u l a t i o n o f t h e s p e c t r a u s i n g a t r i a l and e r r o r p r o c e d u r e . T a b l e 6 l i s t s t h e f i n a l s e t o f the s p i n H a m i l t o n i a n p a r a m e t e r s . E. D i s c u s s i o n The c a l c u l a t i o n o f the e l e c t r o n i c p a r a m e t e r s from ESR d a t a were s i m i l a r t o t h a t d e s c r i b e d f o r the v a n a d y l p o r p h y r i n s . But h e r e one i s i n a more adventageous p o s i t i o n i n t h a t t h e n i t r o g e n s u p e r h y p e r f i n e s p l i t t i n g was o b s e r v e d , from w h i c h a and 0 ' c o u l d be d i r e c t l y d e t e r m i n e d from Eq. ( 1 2 ) and ( 1 3 ) . Former s t u d i e s showed t h a t B and 6 were c l o s e t o u n i t y , Eq. ( 6 ) and ( 7 ) t h e r e f o r e s i m p l i f y t o : 8\a.2fl2 g„ = 2 . 0 0 2 3 — ( 1 - 7 - S ) . . . ( 1 6 ) AE xy 2 2 g, = 2 . 0 0 2 3 - 2 X a S ( 1 - - f S) . . . ( 1 7 ) x AE a xz *The computer program " M a r l e f " was w r i t t e n by Dr. J e a n M a r u a n i , ( C e n t r e de Me'chanique, O n d u l a t o i r e A p p l i q u e e , 23 Rue du Maroc, 75 P a r i s - 1 9 E , F r a n c e ) , s e t up f o r use on an I.B.M. 3 7 0 / 1 6 8 computer. Second o r d e r terms had been i n c l u d e d i n c a l c u l a t i n g t h e magnetic f i e l d p o s i t i o n s . 71.. 1 r • — r 1 — ' i ,Cu F i g . 14: ESR resonance p o s i t i o n copper p o r p h y r i n . p a t t e r n f o r g ^ p a r t , 7 2 . TEMP. g | | g j_ A C u* &CU* A N B N ( o K ) (lO^cm - 1) (10 4cm _ l) (G) (G) CuPyrP i n H„PyrP 77 2 . 1 8 3 3 + 2 . 0 4 3 + 1 9 6 . 4 + 2 8 . 0 + 1 9 . 6 + 1 3 . 8 + 0 .0002" 0 .001 0 .1" 0 .5 0.5 0 .2 6 3CuCOOHTPP i n H2COOHTPP 77 2 .1934 2 .048 193 . 7 30 .9 19.3 13 .1 6 3CuTBP i n H 2TBP 77 2 . 2 0 9 5 2 .049 186 .4 28 .0 16.8 12 .4 6 3CuOMTBP i n H2OMTBP 77 2 .2158 2 .052 1 8 3 .9 27 .4 17.1 12 .1 6 3CuCOOHTPP i n P y r i d i n e 77 2 . 2 0 8 8 2 . 0 5 9 179 .1 31 .9 18.4 13 .9 CuPyrP i n P y r i d i n e 77 2 .2718 2 .062 1 6 1 .0 27 .9 17.6 12 .3 CuPyrP i n CF^COOH 77 2 .2007 2 .062 201 .5 31 .7 19.1 15 .0 CuPyrP i n DMF 77 2 .2679 2 . 0 6 2 1 8 5 .5 25 .9 A N+B N : = 27 .6 TABLE 6: Summary o f s p i n H a m i l t o n i a n p a r a m e t e r s o f copper complexes i n t h i s s t u d y . *The s o l u t i o n ESR s p e c t r a i n d i c a t e d t h a t A and B had t h e same s i g n . But o n l y t h e case i n which b o t h A and B h a v i n g n e g a t i v e s i g n s gave m e a n i n g f u l r e s u l t . 73. which g i v e /? 2 / A E x y a n d ^ 2 / A E x z a ^ t e r s u b s t i t u t i n g i n the e x p e r i m e n t a l v a l u e s o f g ( | and g^ , and the assumed v a l u e s o f X and S. 2 i 2 1 . N e x t , the c a l c u l a t e d v a l u e s o f /? ' / A E v and $ /AE and / xy . * x z the e x p e r i m e n t a l d a t a o f A and B were s u b s t i t u t e d i n Eq. (18) and (19) t o s o l v e f o r P and K. The parameters so o b t a i n e d a r e shown i n T a b l e 7• The attempt t o c a l c u l a t e t h e b o n d i n g c o e f f i c i e n t s i n b j ^ and e m o l e c u l a r o r b i t a l s i s hampered by t h e f a c t t h a t d-d t r a n s i t i o n s i n t h e s e complexes are much weaker i n i n t e n s i t i e s t h a n t h e l i g a n d n - TT t r a n s i t i o n s . F u r t h e r m o r e , as p o i n t e d out by Z e r n e r and Gouterman ( 1 8 ) , low-energy m e t a l - t o - l i g a n d c h a r g e -t r a n s f e r t r a n s i t i o n s and l i g a n d - t o - m e t a l c h a r g e - t r a n s f e r t r a n -s i t i o n s a r e p o s s i b l e , w h i c h can be o f c o n s i d e r a b l y l a r g e r i n t e n -s i t i e s t h a n the pure d-d t r a n s i t i o n s . F o r t h e s e r e a s o n s , i t would be d i f f i c u l t t o p i n p o i n t t h e t r a n s i t i o n s r e q u i r e d f o r the c a l c u l a t i o n s . A s s o u r (11), and Manoharan and Rogers (16) p o i n t e d out t h e weakness o f Thomas and M a r t e l l ' s assignment (25.) o f the a b s o r p t i o n bands near 580 and 560 " I M i n copper TPP as a r i s i n g from d-d t r a n s i t i o n s . The c o n v i n c i n g e v i d e n c e a g a i n s t t h i s assignment i s t h e pr e s e n c e o f the same weak bands even i n z i n c , p a l l a d i u m and p l a t i n u m d e r i v a t i v e s . The assignment o f 33,300 c m - 1 and 17,000 c m - 1 as B-, ~> B ? and B-, ' E t r a n s i t i o n s by Guzy l g iig -Lg g et a l . (15) i n t h e case o f CuPc can o n l y be r e g a r d e d as t e n t a t i v e . We p r e f e r t o be s a t i s f i e d w i t h the d e t e r m i n a t i o n o f AE //? 2 and * E x z / * 2 ' 74. L i s t e d i n T a b l e 7 are the v a r i o u s parameters f o r t h e copper p o r p h y r i n s c a l c u l a t e d b o t h from the p r e s e n t s t u d y and from some of the e a r l i e r work . A p l o t o f t h e l i g a n d - f i e l d e n e r g i e s w i t h r e s p e c t t o t h e energy o f d r as z e r o i s ' s h o w n i n . F i g . 1 5 . Comparing the energy diagram o f v a n a d y l p o r p h y r i n s ( F i g . 8) w i t h t h a t o f copper p o r p h y r i n s , s e v e r a l p o i n t s can be mentioned: (a) the v a r i a t i o n o f (E n / j 9 2 ) ' s w i t h r e s p e c t t o l i g a n d s has t h e same t r e n d f o r v a n a d y l and copper complexes, i . e . (E ^ j j9 2 ) ' s d e c r e a s e from P c , t o (TPP, P y r P , and COOHTPP), and t o (TBP, OMTBP). T h i s s h o u l d be the case because they are the measure o f the <r - b o n d i n g s t r e n g t h o f t h e l i g a n d s . (b) ( E e js )'s o f v a n a d y l p o r p h y r i n s are much l a r g e r t h a n t h o s e o f copper p o r p h y r i n s . ' T h i s no doubt i s due t o the s t r o n g CuPyrP, CuCOOHTPP, CuTBP, CuOMTBP and Cu C h l o r o p h y l l i n . T h i s means t h a t , i f the o u t - o f - p l a n e r - b o n d i n g i s z e r o , e i s the ground s t a t e . However, i f t h e r e i s o u t - o f - p l a n e TT—bonding, t h e e o r b i t a l s w i l l be r a i s e d above the b-, o r b i t a l s . U n f o r t u n a t e -g l g l y , t h e e x t e n t o f o u t - o f - p l a n e n-bonding i s not known. F. S o l v e n t E f f e c t s The e f f e c t o f s o l v e n t s on the ESR parameters of copper complexes has been demonstrated e x p e r i m e n t a l l y i n p r e v i o u s s t u d i e s (26, 27, 28). I t was found t h a t the i n c r e a s e i n g - t e n s o r , and the d e c r e a s e i n A - t e n s o r always r e s u l t e d when c u p r i c complexes F i g . 15 a l s o shows t h a t CuTPP, 7 5 . ,2 2 AE /«2 AE / S 2 P a' a xy' » xz ,yz (cm 1 ) ( c m - 1 ) (G) 6 3 C u P y r P i n H 2 P y r P 0, . 3 3 9 0, .748 2 5 6 9 0 2 8 3 0 0 350 0. , 4 4 6 3CuCOOHTPP i n H 2C00HTPP 0. . 3 2 7 0. . 7 6 0 24740 2 5 6 0 0 340 0. .46 6 3CuTBP i n H 2TBP 0 , . 2 9 9 0. . 7 8 6 2 3 6 9 0 2 6 5 0 0 3 2 0 0. . 4 5 6 3CuOMTBP i n H2OMTBP 0", . 2 9 7 0. . 7 8 8 2 3 0 5 0 2 5 0 0 0 3 2 0 0. . 4 5 6 3CuCOOHTPP i n P y r i d i n e 0. . 3 3 2 0, . 7 5 5 2 2 7 4 0 2 0 6 0 0 310 0. . 4 9 CuPyrP i n P y r i d i n e 0 , .303 0. . 7 8 2 1 8 1 1 0 2 0 3 0 0 300 0, . 4 7 CuPyrP i n CFgCOOH 0 , . 3 5 3 0. . 7 3 5 2 2 9 9 0 1 9 2 0 0 3 7 0 0, . 4 7 CuPc 0 , . 3 6 1 0, . 7 2 7 2 8 5 7 0 26400 3 9 0 0, . 4 5 CuTPP i n H 2TPP ( s i n g l e c r y s t a l ) 0, . 3 2 6 0, . 7 6 0 2 5 2 2 0 2 7 7 0 0 3 5 0 0, .46 6 3 C u PPIXDME 0, .330 0, . 7 5 6 2 4 8 1 0 2 2 8 0 0 330 0, .52 Cu C h l o r o p h y l l i n 0, . 3 0 4 0, . 7 8 1 24260 24600 350 0, . 4 5 TABLE 7 : C a l c u l a t e d b o n d i n g p a r a m e t e r s , and l i g a n d f i e l d t r a n s i t i o n e n e r g i e s o f copper p o r p h y r i n s and p h t h a l o c y a n i n e . 76. Cu Complexes 2 5 2 0 i u n ^ ' o 1 5 Cf.COOH « Pyr ; s Pyr >-o Of LU Z I U _ 10 Pyr B M / \ Oxy] — Eb29 " Eeg/ 42 [Exz,yz/j p c TPP PyrP COOHTpP J B P O M T E P ppixdme Chlorophyllin F i g . 15: L i g a n d f i e l d t r a n s i t i o n e n e r g i e s o f some copper p o r p h y r i n s and p h t h a l o c y a n i n e . 77. were d i s p e r s e d i n s o l v e n t s . A c o r r e l a t i o n ^ , ' had been o b t a i n e d between the s p e c t r a l d a t a and t h e n a t u r e o f the s o l v e n t l i g a n d . The same t r e n d was found i n the p r e s e n t s t u d y o f copper p o r p h y r i n s (see T a b l e 6 ) . The r e a s o n f o r t h e i n c r e a s e i n g^ f o r cppper p o r p h y r i n i s o b v i o u s . F i g . 5 ( C h a p t e r 2) shows t h a t when a l i g a n d w i t h f i l l e d ir - o r b i t a l s bonds t o t h e a x i a l l i g a n d p o s i t i o n s o f a copper p o r p h y r i n , t h e energy l e v e l o f d , w i l l be r a i s e d , and i n c r e a s e d g ^ w i l l be r e s u l t e d . However, t h e change o f g ( | i s not so o b v i o u s . A n t o s i k e t . a l . (27) t r e a t e d t h e e f f e c t o f s o l v e n t s on t h e ESR parameters o f t e t r a g o n a l copper complexes t h e o r e t i c a l l y . They c o n s i d e r e d t h e e f f e c t o f the s o l v e n t m o l e c u l e s on t h e a x i a l l i g a n d p o s i t i o n s o f a t e t r a g o n a l p l a n a r copper complex as a p e r t u r b a t i o n due t o two e l e c t r i c d i p o l e s . They were a b l e t o p r e d i c t the f o l l o w i n g changes. (a) g|| f o r the s o l v a t e d m o l e c u l e s h o u l d be g r e a t e r t h a n t h a t I n t h e i s o l a t e d c u p r i c complex. Cu (b) A f o r the s o l v a t e d complex s h o u l d be n u m e r i c a l l y s m a l l e r t h a n t h a t f o r an i s o l a t e d c u p r i c complex. A l t h o u g h t h i s t r e a t m e n t i s a n a i v e one, however, i t does p r e d i c t t h e r i g h t d i r e c t i o n o f the changes i n t h e s p i n H a m i l -t o n i a n . 7 8 . R e f e r e n c e s 1. A.J.M. Schoot U i t e r k a m p and U.S. Mason, P r o c . Nat. Acad. S c i . U.S.A., 7 0 , 9 9 3 ( 1 9 7 3 ) . 2 . D.J.E. Ingram e t a l . , J . Am. Chem. S o c , 7_8, 3 5 ^ 5 ( 1 9 5 6 ) . 3. J.E. B e n n e t t and D.J.E. Ingram, N a t u r e , 1 7 5 , 1 3 0(1955). 4. E.M. R o b e r t s , and W.S. K o s k i , J . Am. Chem. S o c , 8 2 , 3 0 0 6 ( 1 9 6 0 ) 5 . E.M. R o b e r t s , and W.S. K o s k i , J . Am. Chem. S o c , 8 3 , 1 8 6 5 ( 1 9 6 1 ) 6. D. K l v e l s o n and R. Neiman, J . Chem. Phys., 35, 149 ( 1 9 6 1 ) . 7 . R. Neiman and D. K l v e l s o n , J . Chem. Ph y s . , 3 5 , 1 5 6 ( 1 9 6 1 ) . 8. R.M. D e a l , D.J.E. Ingram and R. S r i n i v a s a n , P r o c . 1 2 t h C o l l o q . Ampere, 2 3 9 ( 1 9 6 3 ) . 9. J.M. A s s o u r , and S.E. H a r r i s o n , Phys. Rev,, 1 3 6 , A 1 3 6 8 ( 1 9 6 4 ) . 1 0 . S.E. H a r r i s o n and J.H. A s s o u r , i n "Paramagnetic .Re-s-Oi-vaii-u-e" (W. Low, e d . ) , V o l . 2 , 8 5 5 . Academic P r e s s , New Y o r k , 19fc>3; J . Chem. Phys., 4 0 , 3 6 5 ( 1 9 6 4 ) . 1 1 . J.M. A s s o u r , J . Chem. Phys., 4_3, 2477 ( 1 9 6 5 ) . 1 2 . Y. A o y a g i , K. Masuda, and J . Yamaguchi, J . Phys. Soc. J a p a n , 2 3 , 1 1 8 8 ( 1 9 6 7 ) . 13. Y.V. G l a z k o v and K.N. S o l o v e r , Zh. P r i k l . S p e k t r o s k . , 6 , 2 6 2 ( 1 9 6 7 ) • 14. G. S c h o f f a , Z. N a t u r f o r s c h , 2 3 a , 5 5 0 ( 1 9 6 8 ) . 1 5 . CM. Guzy, J.B. Raynor, and M.C.R. Symmons, J . Chem. Soc. A, 1 9 6 9 , 2 2 9 9 . 16.. P.T. Manoharan, and M.T. Rogers, i n " E l e c t r o n S p i n Resonance of M e t a l Complexes", Teh Fu Yen ed., Plenum P r e s s , New Y o r k , 1 9 6 9 , P. 143. 17. Y. Hsu, M o l e c u l a r Phys., 2 1 , 1 0 8 7 ( 1 9 7 1 ) . 18.. M. Z e r n e r , and M. Gouterman, T h e o r e t . Chim. A c t a , 4_, 4 4 ( 1 9 6 6 ) . 79. R e f e r e n c e s 1 9 . A.M. S c h a f f e r , M. Gouterman and E.R. D a v i d s o n , T h e o r e t . Chim. A c t a , 3 0 , 9 ( 1 9 7 3 ) . . 20. A.H. Maki and B.R. McGarvey, J . Chem. Phys., 29, 3 1 ( 1 9 5 8 ) and 3 5 ( 1 9 5 8 ) . 21. R. Neiman and D. K i v e l s o n , J . Chem. Phys., 35., 1^9, 156, 162(1961). 2 2 . A. Abragam and-M. H.L. P r y c e , P r o c . Roy. Soc. (London )A20_6, 1 6 4 ( 1 9 5 1 ) . 23. D. K i v e l s o n and R. Neiman, J . Chem. Ph y s . , 35., 149, 1 5 6 ( 1 9 6 1 ) . 24. H.R. Gersmann and J.D. Swalen, J . Chem. Phys., 3_6, 3 2 2 1 ( 1 9 6 2 ) . 2 5 . D.W. Thomas and A.E. M a r t e l l , A r c h . Biochem. B i o p h y s . , 7 6 , 2 6 6('1 9 4 6 ) . • • 2 6 . A. MacCragh, C.B. Storm and W.S. K o s k i , J . Am. Chem. S o c , 8 7 , 1 4 7 0 ( 1 9 6 5 ) • 2 7 . S. A n t o s i k , N.M.D. Brown, A.A. M c C o n n e l l and A.L. P o r t e , J . Chem. S o c , A I 9 6 9 , 5 4 5 . 28. I . Adato and I.E. L i e z e r , J . Chem. Phys., 5_4, 1 4 7 2 ( 1 9 7 1 ) . 8 0 . V I . COBALT PORPHYRINS A; I n t r o d u c t i o n The most i m p o r t a n t c o b a l t compound known t o e x i s t i n n a t u r e i s , o f c o u r s e , v i t a m i n B 1 2> which has r e c e i v e d a g r e a t d e a l o f a t t e n t i o n s i n c e i t s f i r s t s u c e s s f u l i s o l a t i o n i n 1948. The s t r u c t u r e o f t h e coenzyme form o f v i t a m i n B ] _ 2 ' c a l l e d cob amide coenzyme, i s shown i n F i g . 1 6 . The c e n t r a l s t r u c t u r e i s t h e p o r p h y r i n - l i k e c o r r i n r i n g system. The d i v a l e n t c o b a l t , i n a d d i t i o n t o b o n d i n g t o t h e f o u r p y r r o l e n i t r o g e n atoms, a l s o bonds t o t h e n i t r o g e n o f 5, 6 - d i m e t h y l b e n z i m i d a z o l e and a carbon atom i n 5'-deoxyadenosine i n a x i a l p o s i t i o n s . The m o l e c u l e o f 5, 6 - d i m e t h y l b e n z i m i d a z o l e can be r e p l a c e d by o t f t e r n u c l e o t i d e s . From t h e c h e m i c a l p o i n t o f v i e w , c o b a l t ( I I ) p o r p h y r i n s occupy a unique p o s i t i o n . The s q u a r e - p l a n a r s t r u c t u r e o f t h e complexes r e s u l t i n the e l e c t r o n i c c o n f i g u r a t i o n b e i n g a l o w - s p i n d and t h e u n p a i r e d e l e c t r o n b e i n g i n t h e d 2 o r b i t a l ( 1 - 7 ) . As a r e s u l t , t h e ESR s p e c t r u m i s v e r y s e n s i t i v e t o s o l v a t i o n or c r y s t a l l i n e e nvironment. So much so t h a t i t becomes c o n v e n i e n t t o c l a s s i f y t h e ESR s p e c t r a i n t o t h r e e t y p e s . (a) c o b a l t p o r p h y r i n s d i l u t e d i n the r e s p e c t i v e m e t a l - f r e e p o r p h y r i n s o r p o r p h y r i n s o f d i a m a g n e t i c - m e t a l s . I n t h i s c a s e , g„<2.0023, 2 . 0 0 2 3 < gj_< 3.5, 1AI ~ 1 0 0 — 200 x 10"^ c m - 1 , and j B (—200 - 400 x 10"1* cm" 1. (b) c o b a l t p o r p h y r i n s d i l u t e d i n p y r i d i n e o r o t h e r o r g a n i c O H O H FIG.1 6 Structure of the 5.6-dimethylbenzimidazole cobamide coenzyme. 8 2 . bases under vacuum. The ESR s pectrum shows c o b a l t h y p e r f i n e s t r u c t u r e as w e l l as s u p e r h y p e r i n e s t r u c t u r e due t o two s o l v e n t m o l e c u l e s c o o r d i n a t e d a t t h e two a x i a l p o s i t i o n s . The t y p i c a l s p i n H a m i l t o n i a n parameters a r e : g ( | = 2 . 0 , g^= 2 . 2 - 2 . 3 , | A ^ ° | ~ I B C o I ~ 60 x 10~^ cm" 1, I A N H B N | ~ 1 0 X 1 0 " 4 cm" 1 ( c ) when the s o l u t i o n o f (b) i s exposed t o a i r , s pectrum (b) d e c r e a s e s i n i n t e n s i t y and a new s i g n a l b u i l d s up g r a d u a l l y . The new s pectrum does not v a r y a p p r e c i a b l y w i t h t h e c h e m i c a l n a t u r e o f t h e p o r p h y r i n s . I t i s t h e r e s u l t o f one s o l v e n t m o l e c u l e b e i n g r e p l a c e d by an oxygen m o l e c u l e . I n a d d i t i o n t o t h e above t h r e e t y p e s , at c e r t a i n c o n c e n t r a t i o n s o f an o r g a n i c base ( e . g . p y r i d i n e ) i n an i n e r t s o l v e n t ( e . g . t o l u e n e ) , o n l y one o f t h e two a x i a l c o - o r d i n a t i o n p o s i t i o n s i s o c c u p i e d by the o r g a n i c base ( 7 ) . A l l t h e t h r e e t y p e s o f ESR s p e c t r a have been o b s e r v e d f o r a l l t h e f o u r c o b a l t p o r p h y r i n s s e l e c t e d f o r t h i s s t u d y . By a n a l y s i n g t h e ESR parameters o b t a i n e d i n t h i s work and t h o s e a v a i l a b l e from the l i t e r a t u r e , we s h a l l hope t o u n d e r s t a n d t h e f a c t o r s a f f e c t i n g t h e e l e c t r o n i c s t r u c t u r e s o f t h e c o b a l t p o r p h y r i n s . For c o n v e n i e n c e , t h e t h r e e t y p e s o f ESR s p e c t r a w i l l be d i s c u s s e d s e p a r a t e l y . B. C o b a l t P o r p h y r i n s M a g n e t i c a l l y D i l u t e d i n M e t a l - f r e e P o r p h y r i n s (a) I n t r o d u c t i o n The e a r l i e s t work on t h e ESR o f c o b a l t p o r p h y r i n s was t h a t o f t h e p h t h a l o c y a n i n e by Ingram et a l . ( 1 - 3 ) . L a t e r , A s s o u r 8 3 . et a l . ( 4 - 5 ) s t u d i e d t h e ESR o f c o b a l t p h t h a l o c y a n i n e d i l u t e d i n b o t h m e t a l - f r e e p h t h a l o c y a n i n e and d i a m a g n e t i c - m e t a l d e r i v a t i v e s o f p h t h a l o c y a n i n e . They found t h a t two p o l y m o r p h i c forms o f c o b a l t p h t h a l o c y a n i n e s ( a and (J forms) g i v e r i s e t o two d i s t i n c t l y d i f f e r e n t ESR s p e c t r a , o f w h i c h t h e more s t a b l e one ( i 3 - c o b a l t p h t h a l o c y a n i n e ) was s t u d i e d i n the s i n g l e c r y s t a l form. The ESR r e s u l t s can be d e s c r i b e d by t h e s p i n H a m i l t o n i a n o f Eq. ( 1 3 ) o f Chapter 2 . The i n t e r p r e t a t i o n o f t h e s p i n H a m i l t o n i a n parameters., t o g e t h e r w i t h t h o s e o f c o b a l t p h t h a l o c y a n i n e d i s s o l v e d i n p y r i d i n e ( 6 ) , p r o v e d d e f i n i t e l y t h a t the c o b a l t i o n was at t h e c e n t e r o f a s q u a r e - p l a n a r l i g a n d w i t h t h e u n p a i r e d e l e c t r o n b e i n g i n d 2 • The r e s u l t s o f t h e s e s t u d i e s t o g e t h e r w i t h o t h e r p r i o r works were c o l l e c t e d and shown i n T a b l e 8 . (b) Theory G r i f f i t h ( 8 ) ( i n 1 9 5 8 ) was t h e f i r s t t o d e r i v e t h e o r e t i c a l e x p r e s s i o n s f o r t h e i n t e r p r e t a t i o n of t h e ESR parameters o f c o b a l t p h t h l o c y a n i n e and p o r p h y r i n s . Assuming the c o b a l t complex i s low-s p i n , and t h e u n p a i r e d e l e c t r o n i s i n d 2 , z e r o o r d e r ground s t a t e i s r e p r e s e n t e d by t h e f o l l o w i n g Kramers d o u b l e t s , % + = I 1 ± ( - l ) ± M ± 0 + > I ) ± M ± 0 " > . . . ( 1 ) . . . ( 2 ) I n t h e s e and t h e f o l l o w i n g e q u a t i o n s , | 0 > , | « > , and|M>represent d 2 > d 2 2» a n d d r e s p e c t i v e l y ; and | 1 >and|-l>span the same 84. g l l s l A (lO^cnf 1 B )(lO"4cm-1) REF a-CoPc i n ZnPc 2 . 0 0 7 2.422 116 66 4 /3-CoPc i n ZnPc 1 . 9 2 2 . 9 0 1 7 0 2 7 0 3 ^-CoPc i n ZnPc 1 . 9 1 2 . 9 1 160 2 6 5 4 (3-CoPc i n H 2Pc 1 . 8 9 2 . 9 4 160 2 8 0 4 p-CoPc i n N i P c I . 8 9 2 . 9 4 150 2 8 0 4 CoTPP i n H 2TPP 1 . 7 9 8 3 . 3 2 2 197 3 9 5 5 Co(p-OCH 3)TPP i n Ni(p-OCH 3)TPP 1 . 7 5 3 . 3 1 7 1 9 5 4 0 3 7 Co(p-OCH 3)TPP i n H 2(p-OCH 3)TPP 1 . 8 1 3 . 2 6 4 1 7 1 3 7 4 7 Co(p-CH 3)TPP i n H 2(p-CH 3)TPP 1.84 3 . 1 9 3 1 7 3 3 5 2 7 TABLE 8 : Summary o f p r e v i o u s ESR r e s u l t s o f c o b a l t p o r p h y r i n s and s i m i l a r complexes. 8 5 . space as d . d : + and - r e p r e s e n t t h e e l e c t r o n s p i n s ; and t h e ke t n o t a t i o n i m p l i e s a n t i - s y m m e t r i z a t i o n . N e x t , one c o n s i d e r s the s t a t e s which are mixed i n t o t h e ground s t a t e ^1 by s p i n - o r b i t c o u p l i n g . These a r e : *1 = *2 = *3 = * 4 = *5 = \±( 1\~ ± ± + > 1 -( -1 ) /i - o e > 1±(-1,±M~ o + « + •> 1 ( .1 ) ± M ± o + € ~ > 1-(_1)~M o € > (3) (4) ( 5 ) ( 6 ) ( 7 ) A s i m i l a r s e t o f >&'s mix w i t h . The f i r s t - o r d e r wave * o f u n c t i o n s t h e n y i e l d t h e f o l l o w i n g e x p r e s s i o n s when t h e zeeman term and t h e h y p e r f i n e i n t e r a c t i o n t e rm o f t h e s p i n H a m i l t o n i a n are a p p l i e d . g„ = 2 . 0 0 2 3 g. = 2 . 0 0 2 3 + 6 y . A = P B = P [-[-„ , 1 2 6 6 f 7 ~ 7 y l ~ 7 ( y ; K - h 2 + t » ! ] . . . ( 8 ) . . . ( 9 ) . . . ( 1 0 ) . . . ( 1 1 ) *The o r i g i n a l G r i f f i t h ' s e q u a t i o n s do not c o n t a i n t h e o r b i t a l c o e f f i c i e n t 7 l . T h i s was i n c l u d e d i n Eq. ( 1 1 ) and ( 1 2 ) so t h a t t h e parameter P can be r e g a r d e d as a c o n s t a n t f o r the f r e e i o n . 8 6 . In t h e s e e x p r e s s i o n , y< = _ - T — — i — ' . - . ( 1 2 ) i 1 E ( * 4 ) - E( * 0 ) S i n c e g ( ) i s l e s s t h a n 2 f o r c o b a l t p h t h a l o c y a n i n e o r p o r p h y r i n s (see T a b l e 8 ) , the above e q u a t i o n s o b v i o u s l y cannot e x p l a i n t h e g - t e n s o r . One has t o go t o h i g h e r o r d e r - p e r t u r b a t i o n , The s e c o n d - o r d e r wave f u n c t i o n s g i v e : g | | = 2 . 0 0 2 3 - 3 y 2 + 3 y 2 - 3 y 2 + 4 y 2 y 3 - 4 y 4 y 5 . . . ( 1 3 ) g, = 2 . 0 0 2 3 + 6 Y l - 6 y 2 * ...(14) ( c ) ESR R e s u l t s ESR o f CoPyrP, CoCOOHTPP, CoTBP, and CoOMTBP m a g n e t i c a l l y d i l u t e d (about 1 : 1 0 0 0 ) i n the c o r r e s p o n d i n g f r e e base were s t u d i e d at 77°K. A t y p i c a l spectrum i s shown i n F i g . 1 7 . The p o l y c r y s t a l l i n e spectrum i s t y p i c a l o f t h a t due t o t h e c o b a l t i o n ( w i t h 1=^) s i t u a t e d at an a x i a l l y - s y m m e t r i c l i g a n d f i e l d . The l a r g e c o b a l t h y p e r f i n e s p l i t t i n g n e c e s s i t a t e s the use o f t h e s e c o n d - o r d e r terms i n Eqs. ( 2 0 ) and ( 2 1 ) o f C hapter 2 . The s p i n H a m i l t o n i a n p arameters s o - o b t a i n e d were f u r t h e r used t o c o m p u t e r - s i m u l a t e th e ESR s pectrum. S l i g h t m o d i f i c a t i o n s were 2 * I n G r i f f i t h ' s e x p r e s s i o n , t h e r e i s an a d d i t i o n a l term ( - ^ 2 ^ ^ gor gj^, w h i c h we have f a i l e d t o d e r i v e . oo —j 8 8 . needed f o r m a t c h i n g . The s p i n H a m i l t o n i a n parameters are summarized i n T a b l e 9. (d) D i s c u s s i o n The o b j e c t i n t h i s s e c t i o n i s t o c o r r e l a t e t h e e x p e r i -m e n t a l r e s u l t s w i t h t h e b o n d i n g schemes o f c o b a l t p o r p h y r i n s . F i r s t of a l l , one n o t i c e s t h a t t h e r e a r e t o o many unknowns i n v o l v e d i n Eq. ( 1 3 ) • T h e r e f o r e , some a p p r o x i m a t i o n s have t o be made i n o r d e r t o s i m p l i f y t h e a n a l y s i s . C o n s i d e r the o r b i t a l energy l e v e l diagram f o r a c o b a l t p o r p h y r i n i n t h e absence o f a s o l v e n t m o l e c u l e , t h e energy o f do must be v e r y low. S i n c e A E . ^ i s much s m a l l e r t h a n o t h e r energy s e p a r a t i o n s , t h a t i s , y-, i s l a r g e r t h a n o t h e r y ^ ' s , i t i s not u n r e a s o n a b l e t o o n e g l e c t a l l second o r d e r terms except t h e y'£ term. i n i/nia a p p r o x i m a t i o n , Eq.' ( 1 3 ) i s s i m p l i f i e d t o : g ( | = 2 . 0 0 2 3 - 3 y 2 . . . ( 1 5 ) S i n c e t h e e x p r e s s i o n s f o r gjj and g^ now c o n t a i n o n l y one unknown y^, the y^ c a l c u l a t e d from g|( and from g^, s h o u l d be t h e same i f t h e a p p r o x i m a t i o n s made a r e good. A c t u a l l y one can use the c o n s i s t e n c y o f y^ t o check t h e a p p r o x i m a t i o n s made f o r g ( | . A p l o t o f gj| and g^ v e r s u s y^^i = A E - ^ w a s s h - o w n i n F i g - 1 8 . From the f i g u r e i t i s c l e a r t h a t when the a x i a l l i g a n d f i e l d ' A E 1 i s i n f i n i t e l y l a r g e , a h y p o t h e t i c a l c a s e , b o t h g ( 1 and g^ have f r e e e l e c t r o n g - f a c t o r ( 2 . 0 0 2 3 ) . When t h e a x i a l l i g a n d CoPORPHYRIN, 77°K g . l S l * [ l o A m - 1 ] * r B 10~4 cm" CoPyrP i n H" 2PyrP 1.774 + 0.005 3.218 + 0.005 213 + 2 383 + 2 CoCOOHTPP i n H2COOHTPP 1.810 3.156 115 318 CoTBP i n H 2TBP 1.949 2.901 128 218 CoOMTBP i n H2OMTBP 1.884 3.080 123 290 TABLE 9: ESR parameters o f c o b a l t p r o p h y r i n s d i l u t e d i n f r e e base p o r p h y r i n s measured at 77 K. *We a s s i g n e d A and B t o be p o s i t i v e , f o r o n l y p o s i t i v e A and.B g i v e m e a n i n g f u l r e s u l t s . F i g . 1 8 : A p l o t o f g|( and gj_ v e r s u s AE-j_. The e x p e r i m e n t a l p o i n t s a r e : ( 1 ) CoPyrP i n HpPyrP, t h i s s t u d y ; ( 2 ) CoCGOHTPP i n HoCOOHTPP, t h i s s t u d y ; ( 3 ) CoTBP i n H 2TBP, t h i s s t u d y ; ( 4 ) CoOMTBP i n H 2OMTBP, t h i s s t u d y ; ( 5 ) 0-CoPc i n N i p c , r e f e r e n c e 4 ; ( 6 ) Co(p-OCryTPP i n H 2(p-OCH 3)TPP, r e f e r e n c e 7 ; ( 7 ) CoTPP i n H2TPP, r e f e r e n c e 5 . f i e l d g r a d u a l l y d e c r e a s e s i n s t r e n g t h , g | ( d e c r e a s e s , and g^ i n c r e a s e s (more s h a r p l y ) u n t i l i t r e a c h e s 3 . 5 and t h e n d e c r e a s e s . The ESR r e s u l t s o f t h e f o u r c o b a l t p o r p h y r i n s s t u d i e d and t o g e t h e r w i t h some t y p i c a l r e s u l t s from t h e l i t e r a t u r e a r e p l o t t e d i n t h e s e two c u r v e s . One n o t i c e d t h a t : ( i ) t h e e x p e r i m e n t a l p o i n t s o f g M a r e a r r a n g e d i n about t h e same o r d e r , as t h o s e o f gj_ on the two c u r v e s . The o r d e r o f t h e a x i a l - c r y s t a l - f i e l d - s t r e n g t h s i s : CoTBP > CoPc > CoOMTBP > CoCOOHTPP > CoPyrP > Co(p-OCH" 3)TPP > CoTPP One can e x p l a i n t h i s o r d e r i n g p u r e l y from m o l e c u l a r p a c k i n g s i n t h e c r y s t a l s . One knows t h a t CoTBP and CoPc a r e p l a n a r and are e x p e c t e d t o be t h e most c l o s e d l y - p a c k e d . X-ray r e s u l t s (8) showed t h a t t h e a z i d e n i t r o g e n s o f t h e n e i g h b o r i n g m o l e c u l e s a r e o n l y 3.38A from t h e Co i o n i n a m e t a l p h t h a l o c y a n i n e c r y s t a l . I n the case o f CoTPP, t h e r u f f l e d p h e n y l groups p r e v e n t the c l o s e approach o f o t h e r m o l e c u l e s (9) i n t h e c r y s t a l . A l t h o u g h t h e r e i s no x - r a y a n a l y s i s f o r TBP and CoOMTBP, i t i s r e a s o n a b l e t o suggest t h a t t h e e i g h t m e t h y l groups i n t h e l a t e r case would have a d e f i n i t e e f f e c t on t h e c l o s e n e s s o f approach by n e x t - n e i g h b o r -m o l e c u l e s , though t h e e f f e c t would not be as l a r g e as t h e b u l k i e r p h e n y l g r o u p s . The l a r g e r A E 1 ' s o f CoCOOHTPP, CoPyrP, and Cotp-OCH^TPP, compared .with t h o s e o f CoTPP, may be due t o t h e p o s s i b l e hydrogen-bondings formed by t h e s e m o l e c u l e s . 0-1) i f Eqs. (14) and ( 1 5 ) a r e good enough t o r e p r e s e n t g and gj_, the e x p e r i m e n t a l p o i n t s on gj ( and g ^ c u r v e s f o r t h e same c o b a l t complex s h o u l d c o r r e s p o n d t o t h e same v a l u e o f AE^. I t i s o b v i o u s from F i g . 18 t h a t t h i s i s not t h e c a s e . The d i f f e r e n c e i n A E ^ f o r a l l the e x p e r i m e n t a l v a l u e s s u g g e s t s t h a t the c u r v e f o r g j | s h o u l d be moved upward. T h i s means, t h a t the h i g h e r o r d e r -terms which have been n e g l e c t e d f o r g.jj a r e p o s i t i v e i n n a t u r e . I f one makes t h e r e a s o n a b l e a s s u m p t i o n t h a t and y^ are s m a l l , t h a t y 2 v 3 a n d ^4^5 p a r t i a l l y c a n c e l each o t h e r , and t h a t y^ i s n e g l i g i b l e i n comparison w i t h y 2 > t h e n one a r r i v e s a t the f o l l o w -i n g e x p r e s s i o n f o r g , g | | = 2.0023 - 3 y x 2 + 3y£ . . . (16) F i g . (18) can be used t o e s t i m a t e y 2 , and hence,' A E 2 ( = X / y 2 ) . Note t h a t t h e e s t i m a t e d y 2 r e p r e s e n t s the l o w e s t extreme r e a l i z e d o n l y when y^ i s z e r o . T h i s means t h a t t h e e s t i m a t e d A E 2 i s t h e h i g h e s t p o s s i b l e . The c o b a l t h y p e r f i n e s p l i t t i n g s , by means o f Eqs. (10) and 2 ( 1 1 ) , can be used t o s o l v e f o r 7 and K ( y ^ i n Eq. (10) i s n e g l e c t e d by t h e same argument used f o r d i s c u s s i n g ) , i f we assume a v a l u e f o r P. Z e r n e r and Gouterman's c a l c u l a t i o n (10) i n d i c a t e d t h a t t h e net charge on c o b a l t atom i s close.''*'to z e r o , t h e r e f o r e , we s h a l l use P = 202 x 10"^ c m - 1 and x = 455 • cm" 1. The c a l c u l a t e d b o n d i n g parameters f o r CoPyrP, CoCOOHTPP, CoTBP, and CoOMTBP, as w e l l as some o t h e r c o b a l t p o r p h y r i n s , are t a b u l a t e d i n T a b l e 10. One sees t h a t ( I ) f o r a l l c o b a l t K 7 E 1(cm 1) E 2(cm" CoPyrP i n H"2PyrP - 0 . 50 1 . 2 2 1 6 1 0 7410 CoCOOHTPP i n H2COOHTPP - 0 . 22 1 . 0 5 1 7 5 0 7 6 6 0 CoTBP i n H2TBP - 0 . 23 1 . 0 8 2 4 8 0 3 5 9 0 CoOMTBP i n H2OMTBP - 0 . 26 1 . 0 8 1 9 4 0 3 6 2 0 CoPc i n ZnPc (Gibson) - 0 . 46 1 . 0 3 2 4 8 0 5 7 6 0 CoPc i n ZnPc (Assour) - 0 . 41 1 . 0 2 2 4 5 0 7 3 0 0 CoPc i n H 2Pc - 0 . 42 0 . 9 9 2 3 5 0 2 7 0 0 0 CoPc i n NiPc - 0 . 40 0 . 9 5 2 3 5 0 2 7 0 0 0 CoTPP i n H2TPP - 0 . 38 1 . 3 5 1 3 9 0 2 3 1 0 Co(p-OCH3)TPP i n Ni(pOCH 3)TPP - 0 . 40 1 . 3 0 1400 3 1 2 0 Co(p-OCH3)TPP In H 2(p-OCH 3)TPP - 0 . 36 1 .24 1 5 1 0 2 7 9 0 Co(p-CH 3)TPP i n H 2(p-CH 3)TPP - 0 . 40 1 . 1 9 1 6 7 0 3 1 7 0 a-CoPc i n H 2Pc - 0 . 13 1 . 0 0 6 0 0 0 5 2 9 0 TABLE 1 0 : Calculated bonding parameters, and ligand f i e l d energies of cobalt porphyrins. p o r p h y r i n s , K i s n e g a t i v e . T h i s i s the case f o r c o b a l t t e t r a g o n a l p l a n a r complexes w i t h the u n p a i r e d e l e c t r o n b e i n g i n d 2 , s i n c e , i n t h i s symmetry d 2 can mix d i r e c t l y w i t h 4 s . ( i i ) 7's a r e s l i g h t l y l a r g e r t h a n 1 . The l a r g e r v a l u e s are due t o t h e i r s e n s i t i v i t y t o t h e assumed v a l u e o f P. I f one chooses P t o be l e s s t h a n 2 0 2 x 10~^ c m - 1 , 7 can be l e s s t h a n 1 . ( i i i ) F i n a l l y , t h e c a l c u l a t i o n s show t h a t t h e f i r s t e x c i t e d s t a t e i s v e r y c l o s e d t o the ground s t a t e ( ~ 2 0 0 0 c m - 1 ) . T h i s i s i n agreement w i t h t h e e x p e r i m e n t a l o b s e r v a t i o n t h a t the ESR o f c o b a l t p o r p h y r i n s can o n l y be o b s e r v e d at 7 7 °K. C. C o b a l t P o r p h y r i n s i n P y r i d i n e (a) I n t r o d u c t i o n Assour (6) s t u d i e d t h e s o l v e n t e f f e c t s on t h e e l e c t r o n i c 2+ s t r u c t u r e o f the square-bonded Co i o n i n p h t h a l o c y a n i n e , u s i n g s e v e r a l h e t e r o c y c l i c amines. One n o t a b l e f e a t u r e o f t h e ESR s p e c t r a i s t h e s u p e r - h y p e r f i n e s t r u c t u r e o f t h e g ^ t r a n s i t i o n s a r i s i n g from t h e m agnetic i n t e r a c t i o n between the u n p a i r e d e l e c t r o n and t h e two e q u i v a l e n t o u t - o f - p l a n e s o l v e n t m o l e c u l e s . The ESR r e s u l t c o n f i r m s the assignment o f t h e u n p a i r e d e l e c t r o n s t o the d 2 o r b i t a l . U n f o r t u n a t e l y , t h e h y p e r f i n e s p l i t t i n g s due t o the n i t r o g e n s a t g ^ p a r t i s u n d i s c e r n a b l e . T h e r e f o r e , one i s unable t o deduce a l l the s p i n H a m i l t o n i a n p a r a m e t e r s . Walker ( 7 ) d i d s i m i l a r ESR s t u d i e s o f c o b a l t ( I I ) t e t r a ( p -methoxyphenyl) p o r p h i n i n t o l u e n e g l a s s e s i n t h e p r e s e n c e o f v a r i o u s c o n c e n t r a t i o n s o f a number o f d i f f e r e n t amines. The s u p e r h y p e r f i n e s t r u c t u r e was g e n e r a l l y a b s e n t , however, 95. t h e p e r p e n d i c u l a r c o b a l t h y p e r f i n e s t r u c t u r e was c l e a r l y r e s o l v e d . I n one sample (1 M q u i n n o l i d i n e i n t o l u e n e ) s u p e r h y p e r f i n e s t r u c t u r e was ob s e r v e d a t the g ^ r e g i o n w i t h t h e g ^ l i n e s b e i n g compressed i n t o one b r o a d a b s o r p t i o n e n v e l o p e . In t h i s work s i m i l a r s t u d i e s were c a r r i e d out on t h e e f f e c t o f the p y r i d i n e s o l v e n t on CoPyrP, CoCOOHTPP, CoTBP, and CoOMTBP. (b) P r e p a r a t i o n The c o b a l t complex was d i s s o l v e d i n r e a g e n t - g r a d e p y r i d i n e . The c o n c e n t r a t i o n was v a r i e d u n t i l b e s t r e s o l u t i o n o f ESR spectrum was a c h i e v e d ( ~ 0.002 M\ I t was found t h a t r e s o l u t i o n c o u l d be improved by p a s s i n g t h e s o l u t i o n t h r o u g h a chromatography column ( e q u a l p o r t i o n s o f a l u m i n a and diatomaceous e a r t h ) and t h e n d e - g a s s i n g . ( c ) ESR R e s u l t s F i g . 19 shows t h e ESR s p e c t r u m o f CoCOOHTPP d i s s o l v e d i n p y r i d i n e and measured a t 77°K. The p e r p e n d i c u l a r c o b a l t h y p e r f i n e s t r u c t u r e i s c l e a r l y r e s o l v e d i n t h e l o w - f i e l d (gj^ ) r e g i o n , w i t h each h y p e r f i n e l i n e , i n t u r n b e i n g s p l i t i n t o f i v e s u p e r - h y p e r f i n e l i n e s due t o two e q u i v a l e n t p y r i d i n e n i t r o g e n s and w i t h an i n t e n s i t y r a t i o o f a p p r o x i m a t e l y 1:2:3:2:1. The h i g h -f i e l d (g|j ) r e g i o n i s l e s s w e l l r e s o l v e d due t o i n t e r f e r e n c e by the s t r o n g s i g n a l o f the f r e e r a d i c a l . However, some h y p e r f i n e l i n e s a r e r e c o g n i z a b l e and each o f t h e s e a l s o s p l i t s i n t o f i v e s u p e r h y p e r f i n e l i n e s . F i g . 20 shows t h e ESR spectrum o f CoTBP i s p y r i d i n e at 77°K. I t has the s i m i l a r p a t t e r n as t h a t o f CoCOOHTPP, ex c e p t t h a t o n l y 1 OOG F i g . 19: ESR spectrum of CoCOOHTPP i n p y r i d i n e , 77°K. F i g . 20: ESR spectrum o f CoTBP i n p y r i d i n e , 77°K. 98. c 7 two h y p e r f i n e l i n e s ( a s s o c i a t e d w i t h Mj = and = a r e d i s c e r n a b l e a t the g ( ! r e g i o n , o t h e r s b e i n g masked by the much s t r o n g e r s i g n a l s due t o the g ^ l i n e s . The. o t h e r two c o b a l t p o r p h y r i n s d i s s o l v e d i n p y r i d i n e gave s i m i l a r ESR s p e c t r a . The s p i n H a m i l t o n i a n parameters ( g | ( , gj_ , A 0 0, B C 0 , A N and B N ) , d e t e r m i n e d by B l e a n e y ' s e q u a t i o n s (see Chapter 2) are t a b u l a t e d i n Ta b l e 11. The most pronounced change when a c o b a l t p o r p h y r i n d i s s o l v e d i n p y r i d i n e i s t h a t becomes g r e a t e r t h a n C O C O 2.0023, and A and B are r e d u c e d many t i m e s , w h i c h u n d o u b t l y are due t o the d e l o c a l i z a t i o n o f t h e u n p a i r e d e l e c t r o n t o the s o l v e n t molecules... (d) D i s c u s s i o n The same e q u a t i o n s f o r g ( | , g j_ , A and B used i n the l a s t s e c t i on were u s e d her>p. Prnm o- s n r i a-. on<=> i ^ o h i o -f-o - II J i . -o b t a i n y^ and y 2 , and hence, t h e s e p a r a t i o n s between ground s t a t e and the two e x c i t e d s t a t e s , AE.^ and AE^. S i n c e n i t r o g e n s u p e r h y p e r f i n e s p l i t t i n g s were o b s e r v e d , one has t o m i x - i n the l i g a n d o r b i t a l s t o d 2 . The r e s u l t i n g m o l e c u l a r o r b i t a l i s g i v e n by : . • .(17) where cT5 and CT are s p 2 h y b r i d s o f t h e p y r i d i n e n i t r o g e n s . From the s u p e r h y p e r f i n e s p l i t t i n g s , one .can o b t a i n 7 ' b y : C o P o r p h y r i n i n ACo B C O A N B N P y r i d i n e , 77°K g g (lO^cm 1) ( l t i ^ c m 1 ) (lO'^cm 1) (lO^cm 1) CoPyrP 2. .089 + 2, .237 + 61 + 1 63, .8 + 11, .5 + 9. 3 + 0. .005 0, .001 0, .5 0, .5 0. 5 CoCOOHTPP 2, , 0 5 4 2, .236 53 5 1 . .7 12, .3 10. 3 CoTBP 2. .145 2, .254 50 63, .2 12, .5 10 . 9 CoOMTBP 2. .112 2, .240 52 63, .4 7. • 9 u n r e s o l v e d TABLE 11: ESR r e s u l t s o f c o b a l t p o r p h y r i n s i n p y r i d i n e , 77°K. 100. i s o 8TT 2 * (0) ( 1 8 ) where a i s o = "T" U N + 2 B N ) • • * ( 1 9 ) The n o r m a l i z a t i o n c o n d i t i o n o f t h e ground s t a t e m o l e c u l a r o r b i t a l i s e x p r e s s e d by: 7 2 + 7 ' 2 - 2 7 7'S = 1 ...(20) where S = < d 2 2 2 ( ( T ~ <T )> i s t h e o v e r l a p i n t e g r a l between Z o o 2+ t h e Co a t o m i c o r b i t a l d o a n d t h e Q- o r b i t a l s o f t h e o u t - o f -p l a n e n i t r o g e n s . Assuming t h e a x i a l c o b a l t - n i t r o g e n i n t e r n u c l e a r d i s t a n c e t o be 2.1A , and t h e e f f e c t i v e n u c l e a r charges t o be t h o s e c a l c u l a t e d by S l a t e r r u l e s , A s s o u r e s t i m a t e s S = 0.14 ( 6 ) . The Y's c a l c u l a t e d from Eq. ( 1 8 ) a r e t a b u l a t e d i n T a b l e 12 (under the h e a d i n g o f ">expt.) U s i n g t h e same e x p r e s s i o n s f o r g^ , g^ , A^° and o f s e c t i o n A (Eqs. ( 1 1 ) , ( 1 2 ) , ( 1 4 ) and ( 1 6 ) ) , and assuming X = 4 5 5 c m - 1 and P = 2 2 8 x 10~^ c m - 1 f o r the Co i o n , t h e energy l e v e l s e p a r a t i o n s , K and 7 were c a l c u l a t e d and l i s t e d i n T a b l e 11. The f a c t t h a t t h e c a l c u l a t e d 7 ( 7 cale.) i s s l i g h t l y g r e a t e r t h a n 1 comes from the a p p r o x i m a t i o n used i n t h e e x p r e s s i o n f o r A. I f we i n c l u d e the term i n v o l v i n g y^, 7 would be l e s s t h a n 1. The most s i g n i f i c a n t changes o c c u r e d when c o b a l t p o r p h y r i n s are d i s s o l v e d i n p y r i d i n e can be seen from comparing t h e 1 0 1 . C o P o r p h y r i n i n P y r i d i n e , 77°K 7 e x p t . 7 c a l c . K E 1 ( c m X ) E 2 ( c m " CoPyrP 0 . 9 9 1 . 0 8 0 . 2 1 11,140 2 , 6 0 0 CoCOOHTPP 0 . 9 9 1 . 0 1 0 . 2 0 1 1 , 1 9 0 3 , 3 0 0 CoTBP 0 . 9 9 1 . 0 9 0 . 2 3 1 0 , 3 6 0 2 , 0 0 0 CoOMTBP — 1 . 0 7 0 . 2 3 1 1 , 0 0 0 2 , 3 0 0 TABLE 1 2 : L i g a n d f i e l d e n e r g i e s and b o n d i n g parameters o f c o b a l t p o r p h y r i n s i n p y r i d i n e . 102. parameters i n T a b l e 12 and 10: ( I ) the energy s e p a r a t i o n s between 4^ and ^ (Eg) d e c r e a s e s s l i g h t l y which means t h a t the q u a r t e t s t a t e % i s at a somewhat h i g h e r energy i n a s o l v a t e d m o l e c u l e . • " . ( i i ) more s i g n i f i c a n t l y , E 1 i n c r e a s e s about s i x - f o l d , which means d o i s r a i s e d so much t h a t t h e energy E, becomes h i g h e r t h a n the q u a r t e t s t a t e energy Eg. F i g . 21, which i s a q u a l i t a t i v e energy l e v e l d i a g r a m , shows t h e change i n E^ and Eg upon changing the a x i a l - l i g a n d f i e l d s t r e n g t h . D. Oxygen-adduct F o r m a t i o n The f i x a t i o n and a c t i v a t i o n o f m o l e c u l a r oxygen on t r a n s i t i o n m e t a l complexes i s a t o p i c d i r e c t l y r e l a t e d t o b i o l o g i c a l systems. iuc JL c o J J _ L x a v wxjr jjxgmcn i/ b ai'c auxc J . I A OJvjgjen muic^uico i. x'Giii t h e atmosphere, t o t r a n s p o r t them t o t h e i r s i t e s o f r e a c t i o n , and t h e r e t o r e l e a s e them. A l t h o u g h t h e n a t u r a l "oxygen c a r r i e r s " are i r o n complexes, Hoffman and P e t e r i n g (11) d e m o n s t r a t e d t h a t a r t i f i c i a l m y oglobin and hemoglobin s u b s t i t u t e d w i t h c o b a l t o u s p r o t o p o r p h y r i n IX f o r protoheme were c a p a b l e o f r e v e r s i b l e oxygen-a t i o n . Y o n e t a n i e t a l . (12, 13> 1*0 succeeded i n p r e p a r i n g a s e r i e s o f a r t i f i c i a l m y o g l o b i n s and hemoglobins c o n t a i n i n g c o b a l t o u s p r o t o - , meso-, and d e u t e r o p o r p h y r i n s , i n v e s t i g a t e d the thermodynamic and k i n e t i c parameters o f t h e i r r e v e r s i b l e o x y g e n a t i o n p r o c e s s e s , and performed ESR s t u d i e s . C h i e n and D i c k i n s o n (15) s t u d i e d ESR o f s i n g l e , c r y s t a l s o f o x y c o b a l t m y o g l o b i n and found c o t h a t g and A t e n s o r s d i d not s h a r e the same p r i n c i p a l a x e s , and t h a t the C o - 0 - 0 bond a n g l e was 9 0 ° . 103. 119 / / / / / / / / / / W V w / \ \ \ \ / 7 / / w \ \ h t in pyridine D in free base '4h 2 B i g 2 A 2 g • 4 E 4 A • 2B 29 29 - 2 A i g *3,5 *1 Axial - Ligand-Field Strength 21: Q u a l i t a t i v e energy l e v e l s o f c o b a l t p o r p h y r i n s . 104. T h i s a c t i v a t i o n o f m o l e c u l a r oxygen by t r a n s i t i o n m e t a l complexes was s t u d i e d as e a r l y as 1852 ( 1 6 ) . I t i s now known t h a t a g r e a t number o f t r a n s i t i o n m e t a l complexes w i t h oxygen as a l i g a n d e x i s t . These i n c l u d e , i r o n , n i c k e l , p l a t i n u m , r h o d i u m , i r i d i u m and r u t h e n i u m complexes. However, by f a r , the l a r g e s t number o f s y n t h e t i c oxygen complexes c o n t a i n c o b a l t . C o b a l t ( I I ) p o r p h y r i n i s a good example. D i f f e r e n t a s p e c t s o f t h e a c t i v a t i o n o f m o l e c u l a r oxygen by t r a n s i t i o n m e t a l complexes have been e x p l o r e d and are s t i l l b e i n g e x p l o r e d . These i n c l u d e s s y n t h e s i s o f new oxygen c a r r i e r s ( 1 7 , 1 8 ) , x - r a y a n a l y s e s ( 1 9 , 2 0 ) , k i n e t i c and mechanism s t u d i e s (21) and s p e c t r o s c o p i c s t u d i e s . A r e c e n t r e v i e w g i v e s an i n t r o d u c t i o n t o t h e c h e m i s t r y o f t h i s s t i l l grow-i n g f i e l d ( 2 2 ) . ESR s p e c t r o s c o p y has p r o v e n t o be h e l p f u l i n t h e stu d y o f t h e e l e c t r o n i c s t r u c t u r e . Numerous s t u d i e s have been made on oxygen-a t e d c o b a l t ( I I ) S c h i f f base complexes ( 2 3 - 2 5 ) , and c o b a l t p o r -p h y r i n s ( 2 , 2 6 ) . I t has been shown t h a t t h e oxygenated complex i s b e s t c h a r a c t e r i z e d as super—oxo (O2"") a d d u c t s o f Co ( I I I ) . A l t h o u g h i t has been awared t h a t the a n g l e Co-0-0 was somewhere between 90° and l 8 0 ° , and hence t h e p r i n c i p a l axes o f t h e g (z || 0 - 0 a x i s ) and t h e A C o ( z j _ t o t h e p l a n e o f t h e S c h i f f base o r p o r -p h y r i n ) were not c o i n c i d e n t , t h e h y p e r f i n e s p l i t t i n g s a s s o c i a t e d w i t h g | J and g j L i n the p o l y c r y s t a l l i n e s p e c t r u m were g e n e r a l l y m i s t a k e n as t h e p r i n c i p a l v a l u e s o f c o b a l t h y p e r f i n e s p l i t t i n g , A C o and B C o ( 7 , 24, 2 5 , 2 6 ) . I n t h i s work, ESR s t u d i e s have been made on t h e oxygen-adducts 1 0 5 . o f CoPyrP, CoCOOHTPP, CoTBP, CoOMTBP i n p y r i d i n e . When an e v a c u a t e d sample of t h e c o b a l t complexes d i s s o l v e d i n p y r i d i n e (from s e c t i o n C) was exposed t o a i r f o r about 1 0 - 1 5 m i n u t e s , a o new s i g n a l appeared ( F i g . 2 2 ) . T h i s was measured at 77 K, and was found t o be s i m i l a r t o t h o s e r e p o r t e d b e f o r e ( 7 » 2 3 - 2 6 ) . S i m i l a r s p e c t r a were o b t a i n e d f o r a l l f o u r c o b a l t p o r p h y r i n s s t u d i e d . The p r o c e s s e s o f o x y g e n a t i o n and d e o x y g e n a t i o n were r e v e r s i b l e . The p r i n c i p a l axes system f o r g ( x y z ) components and ( x ' y ' z 1 ) components are r e l a t e d by the f o l l o w i n g d i a g r a m ( t h e y- and y'- axes a r e i n the' same d i r e c t i o n ) . Appendix B shows t h a t f o r t h e p o l y c r y s t a l l i n e ESR s p ectrum the c o b a l t h y p e r f i n e s p l i t t i n g a s s o c i a t e d w i t h g (j ( d e s i g n a t e d as K„) and t h a t a s s o c i a t e d w i t h g_L ( d e s i g n a t e d as KJL) a r e r e l a t e d t o A and B by t h e f o l l o w i n g e q u a t i o n s : 106. F i g . 22: ESR spectrum o f oxygenated s p e c i e s o f CoPyrP i n p y r i d i n e . 1 0 7 . 2_, 2^ v 2 _ 2 D . . . ( 2 1 ) A  ^ ^ 2 = K|| s i n 9 - Kj. cos 9 2 2 s i n 9 - cos 9 2 _ , 2 „ v 2 _ 2 „ . . . ( 2 2 ) B 2 _ K i s i n 9 - Kn cos 9 ? 2 s i n 9 - cos "9 I t i s o b v i o u s t h a t the h y p e r f i n e s p l i t t i n g s shown i n t h e ESR spectrum cannot be equated t o A and B. A c t u a l l y , o n l y i n t h e case when 9 i s known can one deduce A and B from K|( and Kj_. F i g . 2 2 2 3 , which i s a p l o t o f A and B v e r s u s 9 f o r CoPyrP • P y r i d i n e • 0„, demons i, r a t e s such r e l a t i o n s h i p . A l t h o u g h we cannot d e c i d e what i s t h e a n g l e 9 between t h e 0 - 0 bond and t h e p o r p h y r i n p l a n e . ESR r e s u l t s do r e s t r i c t t h e v a l u e f o r 9. F i g . 23 shows t h a t 9 cannot be between 3 3 - 5 ° and 5 6 . 5 , because i n t h i s r e g i o n , A o r B 2 becomes n e g a t i v e . Moreover, i f one knows |A| > J B J , 9 > 5 6 . 5 ° ; i f |A | < | B| , 9 < 33 . 5° • I f one assumes | B| > j A j as i n t h e case of unoxygenated s p e c i e s , t h e 0 - 0 a x i s w i l l be i n a p o s i t i o n c l o s e d b e i n g p a r a l l e d t o t h e p o r p h y r i n p l a n e . The r e g i o n s f o r 9 and the, ESR d a t a are t a b u l a t e d i n T a b l e 1 3 . The f a c t t h a t one i s not a b l e t o d e r i v e t h e p r i n c i p a l com-ponents o f c o b a l t h y p e r f i n e t e n s o r , due t o an unknown 9, i s s u r e l y a d i s a p p o i n t m e n t . Perhaps i t s h o u l d be p o i n t e d out t h a t ESR s t u d y on s i n g l e c r y s t a l s can y i e l d a l l t h e s e i n f o r m a t i o n s . 108. P i g . 2 3 : A p l o t o f A and B v e r s u s 6 , the a n g l e between the oxygen m o l e c u l e and p o r p h y r i n p l a n e . C o P o r p h y r i n i n K|( Kj_ P y r i d i n e & Oxy£ ;en g . l S l (G) (G) e > e < CoPyrP 2 , .0770+ 2, .0036+ 15. 7± 10 . 4+ 5 6 . 0 5 33 .5' 0. ,0002 0, .0002 0 . 1 0 . 1 CoCOOHTPP 2, .0795 2, ,0047 1 6 . 6 10 .5 ' 5 7 . 7° 32 .3 CoTBP 2, ,0698 . 2, .0040 12. 5 8 .7 55. 2 9 34 .8 CoOMTBP 2. .0760 2, .0040 15. 8 10 .5 5 6 . 4° 33 .6 CoOMTBP i n p - p i c o l i n e 2, . 0 6 8 8 2, .0021 13. 8 8 .3 59. 0° 31 .0 TABLE 13: R e s u l t s . o f oxygen-adducts o f c o b a l t p o r p h y r i n s i n p y r i d i n e . 110. I t i s not easy t o f i n d a c o b a l t p o r p h y r i n which can form a s t a b l e oxygen adduct and y e t grows i n s i n g l e c r y s t a l forms s u i t a b l e f o r ESR s t u d y . E. C o n c l u s i o n From t h e ESR r e s u l t s o f c o b a l t p o r p h y r i n s i t i s c l e a r t h a t the b o n d i n g scheme i s v e r y s e n s i t i v e t o t h e env i r o n m e n t . Not o n l y t h a t t h e s o l v e n t m o l e c u l e s change t h e s p i n H a m i l t o n i a n p a r a m e t e r s , t h e same c o b a l t p o r p h y r i n m a g n e t i c a l l y d i l u t e d i n d i f f e r e n t d i a m a g n e t i c m e t a l p o r p h y r i n s a l s o g i v e s d i f f e r e n t r e s u l t s (see T a b l e 8 ) . T h e r e f o r e , i f one wants t o s t u d y t h e e f f e c t due t o t h e change i n t h e c h e m i c a l n a t u r e o f t h e l i g a n d s , one has t o c a r r y out t h e ESR s t u d i e s i n t h e same envir o n m e n t . On t h e o t h e r hand, t h e s e n s i t i v i t y o f the ESR spectrum o f a c o b a l t p o r p h y r i n t o t h e environment can be u t i l i z e d as an advantage. F o r example we can use ESR t o s t u d y t h e environment o f m y o g l o b i n and hemoglobin m o l e c u l e s , such as t h e c h e m i c a l n a t u r e , the d i s t a n c e o f the a x i a l m o l e c u l e s , e t c , F i n a l l y , I would l i k e t o p o i n t out t h a t p h t h a l o c y a n i n e i s not a good model f o r p o r p h y r i n . Because o f i t s s m a l l e r p o r -p h i n a t o h o l e s i z e . The m e t a l complexes form much s t r o n g e r i n -p l a n e a -bond and o u t - o f - p l a n e n-bond, as shown by t h e energy l e v e l s o f VoPc and CuPc ( F i g . 8 and 1 5 ) . 1 1 1 . R e f e r e n c e s 1 . J.E. B e n n e t t , D.J.E. Ingram, N a t u r e , 1 7 5 , 1 3 0 ( 1 9 5 5 ) . 2 . J.E. B e n n e t t , D.J.E. Ingram, D i s c u s s i o n Faraday Soc., 1 9 , 1 4 0 ( 1 9 5 5 ) . 3. J.F. G i b s o n , D.J.E. Ingram and D. S c h o n l a n d , D i s c u s s i o n Faraday S o c , 2 6 , 7 2 ( 1 9 5 8 ) . 4. J.M. As s o u r and W.K. Kahn, J . Am. Chem. S o c , 87_, 2 0 7 ( 1 9 6 5 ) . 5. J.M. A s s o u r , J . Chem. Phys., 43. , 2477 ( 1 9 6 5 ) . 6. J.M. A s s o u r , J . Am. Chem. S o c , 8j_, 4 7 0 1 ( 1 9 6 5 ) . 7. F.A. W a l k e r , J . Am. Chem. S o c , 9 2 , 4 2 3 5 ( 1 9 7 0 ) . 8. J.M. R o b e r t s o n , J . Chem. S o c , 1 6 1 5 ( 1 9 3 5 ) . 9. E.B. F l e i s c h e r , C.K. M i l l a r and L.E. Webb, J . Am. Chem. S o c , 8 6 , 2 3 4 2 ( 1 9 6 4 ) . 1 0 . M. Z e r n e r and M. Gouterman, T h e r e t . Chim. A c t a , 4., 44 ( 1 9 6 6 ) . 1 1 . B.M. Hoffman and D.H. P e t e r i n g , P r o c . Nat. Acad. S c i . A6_7_, 6 3 7 ( 1 9 7 0 ) . 1 2 . H. Yamamoto, F . J . Kayne, and T. Y o n e t a n i , J . B i o l . Chem., 249, 6 9 1 ( 1 9 7 4 ) . 1 3 . T. Y o n e t a n i , H. Yamamoto and G.V. Woodrow I I I , J . B i o l . Chem., 249, 6 8 2 ( 1 9 7 4 ) . 14. T. Y o n e t a n i , H. Yamamoto and T. I i z u k a , J . B i o l . Chem., 249, 2 1 6 8 ( 1 9 7 4 ) . 1 5 . J.C.W. C h i e n , and C. D i c k i n s o n , P r o c . Nat. Acad. S c i . 6_£, 2 7 8 3 ( 1 9 7 2 ) . 1 6 . E. Fremy, L i e b i g s Ann. Chem. 8 3 , 2 2 7 , 2 8 9 ( 1 8 5 2 ) . 1 7 - J.E. B a l d w i n and J . H u f f , J . Am. Chem. S o c , 95. , 5 7 5 7 ( 1 9 7 3 ) . 1 8 . J.P. Collma n e t a l . , J . Am. Chem. S o c , 9 5 , 7 8 6 8 ( 1 9 7 3 ) . J.P. Collman et a l . , J . Am. Chem. S o c , 9 j | , 2 6 2 9 ( 1 9 7 4 ) . 112. 1 9 . J.P. Collman et a l . , P r o c . Nat. Acad. S c i . , 7 1 , 1 3 2 6 ( 1 9 7 4 ) . 2 0 . G.A. Rodley and W.T. R o b i n s o n , Nature 23_5, 4 3 8 ( 1 9 7 2 ) . 2 1 . D.V. S t y n e s , H.C. S t y n e s , B.R. James and J . A . ' I b e r s , J . Am. Chem. S o c , 9 5 , 1 7 9 6 , 1 1 4 2 ( 1 9 7 3 ) . 2 2 . G. H e n r i c i - O l i v e and S. O l i v e , Angew. Chem. I n t e r n a t . E d i t . , . 1 3 , 2 9 ( 1 9 7 4 ) . 2 3 . J.S. G r i f f i t h , P r o c Roy. S o c , A 2 3 5 , 2 3 ( 1 9 5 6 ) . 24. B.M. Hoffman, D.L. Diemente, and P. B a s o l o , J.Am. Chem. S o c , 9 2 , 6 1 ( 1 9 7 0 ) . 2 5 . E . I . O c h i a i , J . I n o r g . N u c l . {Chem., 3 5 , 1 7 2 7 ( 1 9 7 3 ) . 2 6 . E.W. A b e l , J.M. P r a t t and R. Whelan, Chem. Commun., 1 9 7 1 , 4 4 9 . 633 113. V I I . APPENDIX A. D e r i v a t i o n o f t h e S p i n H a m i l t o n i a n The g e n e r a l H a m i l t o n i a n i s g i v e n by: The meaning o f each term has been g i v e n i n Chapter 2. Our g o a l i s t o t r a n s f o r m Eq. (1) t o a form i n which o n l y t h e e l e c t r o n i c and t h e n u c l e a r s p i n o p e r a t o r s , t o g e t h e r w i t h some n e c e s s a r y parameters appear. We f i r s t assume t h a t t h e l o w e s t e i g e n s t a t e (ground s t a t e ) i o f / t F and Ji, v i s an o r b i t a l s i g l e t , | 0 > . T b i s snouict always be t h e case f o r n o n l i n e a r p o l y a t o m i c m o l e c u l e s i n view o f Jahn-T e l l e r ' s theorem, which s t a t e s t h a t a m o l e c u l e i n an o r b i t a l l y d e g enerate ground s t a t e w i l l d i s t o r t i n such a way as t o remove the degeneracy. We t r e a t L S a n d - H ^ as p e r t u r b a t i o n s . To f i r s t , o r d e r , we have: y y ' y .+ 2 8H-S ...(2) 114. However, < o| 0 > =<01 L y 10 > = < 0 | L z |0 > = 0 f o r a s i n g l e t s t a t e which i s a n o t h e r way o f s a y i n g t h a t the o r b i t a l a n g u l a r momentum i s quenched. To t h i s degree o f a p p r o x i m a t i o n , one th e r e -f o r e has a s p i n - o n l y term which can be w r i t t e n as : 2 " £ \ ) H i S J •••(3) 1 > J where h., i s the K r o n e c k e r d e l t a . To second o r d e r , one has < O j f l H - ( L + 2S) +X L-S,|n>| n ^ 0 E - E n o (4) = + ^ > < o l l J n > ] ^ ( g - H - + "lL-lo>1 . - . ( 5 ) n ^ 0 E - E n o One can w r i t e t h i s a s : -^2 ( ? 2 H i A i j H j + 2 ? 3 , H i A i j s j + x 2 s i A i j s j ) • • • ( 6 ) 115. where \i " E { < ° l ^ n > < n | L j | ° ^ E n - E o ) } ...(7) n^o S i n c e t h e f i r s t t e r m i n Eq. (6) does not c o n t r i b u t e t o t h e s p l i t t -i n g o f t h e s p i n s t a t e s , one h a s , c o r r e c t t o second o r d e r , l , j * H i ( 2 , i J " 2 * A I J > S j " X \ A i J S J ...(8) T h i s can be w r i t t e n i n the f o r m , ( f H i « i J S j + S i D U S J ) " - ( 9 ) where g ^ and a r e g i v e n by g i j - s 0 ( 8 i j -*V •••(10) w i t h g = 2 , and °o D U = " ^ A i j .-.(ID The f i r s t t e r m i n Eq. (10) r e p r e s e n t s t h e Zeeman i n t e r a c t i o n and the second term a c c o u n t s f o r t h e z e r o - f i e l d s p l i t t i n g . J"{, a l s o s s a c c o u n t s f o r z e r o - f i e l d s p l i t t i n g but i s u n i m p o r t a n t f o r t r a n -s i t i o n m e t a l i o n s . The terms f o r "3~L ^  and ^ are s i m p l e s i n c e t hey do not i n v o l v e L. 1 1 6 . -L , J J- > J ...(12) i n w hich A. . = <0 U. , 3r. r . 1 1 0 > + !!gffgN% * (0) • • • ( 1 3 ) _ e 2Q U,, 1(1+1) 3 ( r , r . ) P 4 . = ^ 2 < 0 I i <M 0> • ...(14) i j • I • -a R I 21(1 - 1) r J r J where LL a r e t h e components o f u n i t d y a d i c . The term f o r ^ N H remain unchanged s i n c e i t c a r r i e s no o p e r a t o r s f o r j 0 > . I n summary t h e g e n e r a l H a m i l t o n i a n can be r e p l a c e d by a s p i n H a m i l t o n i a n , H. -E ( » H A j S j + S i D l j S j + V i ^ j + V i j 1 ; - g N ^ i V ...(15) 117. or an e q u i v a l e n t t e n s o r i c a l e x p r e s s i o n , K. = ^S"S-S.+ S-D-S +-S-A-I + I - P - I - g N 0 NH-I ...(16) I f t h e r e i s more t h a n one magnetic n u c l e u s i n v o l v e d , t h e l a s t t h r e e terms s h o u l d be summed o v e r t h e n u c l e i . B. D e r i v a t i o n o f K M and K i from A, B and 9 A - t e n s o r i s d i a g o n a l i n t h e c o o r d i n a t e system ( a , b, c), w h i l e g - t e n s o r i s d i a g o n a l i n ( i , j , k ) , w i t h j b e i n g e q u a l t o b. The t r a n s f o r m a t i o n o f A i n t o t h e g_frame can be a c c o m p l i s h e d by a s i m p l e r o l a t i o n about b and t h e r e s u l t i n g A i s ( 1 ) : 1 1 8 . A = s i n 9 0 -cos 9 0 0 l_cos 9 9 s i n 9j |_ "B B AJ s i n 9 0 cos 9' 0 0 L-cos 9 0 s i n 9j "B s i n 2 9 + A c o s 2 9 0 (B-A) s i n 9 cos 9" 0 L(B-A) s i n 9 cos 9 B 0 0 B c o s 2 + A s i n 2 9 • . . ( 1 ) When t h e magnetic f i e l d i s a l o n g an o r b i t r a r y d i r e c t i o n , th e h y p e r f i n e s p l i t t i n g A E i s g i v e n by ( 1 ) : ( A E ) 2 = I • A2- I ...(2) When t h e magnetic f i e l d i s a l o n g t h e d i r e c t i o n o f g | (, t h e h y p e r f i n e s p l i t t i n g K|( i s g i v e n by: K, - [0 0 l ] B s i n 2 9 + A c o s 2 9 0 (B-A) s i n 9 cos 9 0 B 0 (B-A) s i n 9 cos 9 2 2 0 B cos 9 + A s i n 9 0 0 1 2 2 2 2 = A s i n 9 + B cos 9 ...(3) When t h e magnetic f i e l d i s a l o n g t h e d i r e c t i o n o f gj_, t h e h y p e r f i n e s p l i t t i n g i s g i v e n by: 119. K ± 2 = [ l 0 o] r* i - -. B s i n 2 9 + A c o s 2 9 0 (B-A) s i n 9 cos 9 1 0 B 0 0 (B-A) s i n 9 cos 9 0 A s i n 2 9 + B c o s 2 9 0 2 2 2 2 = A cos 9 + B s i n 9 2 2 From Eq. (3) and ( 4 ) , A and B are the n g i v e n by A 2 = K i t2 s i n 2 9 - Kj _ 2 c o s 2 9 2 2 s i n 9 - cos 9 .-..(5) B 2. _ K L2 s i n 2 9 - K||2 c o s 2 9 ...(6) C. Micro-analysis r e s u l t s of some porphyrins The micro-analysis r e s u l t s of some porphyrins are as follows: Found: C, 80.08; H, 5.66; N, 11.10%. Calc. f o r C c oH r nN„Mg (pyridine adduct of MgOMTBP): C, 80.33; H, 5.78; N, 11.11%. Found: C, .75.36; H, 3.78; N, 10.85%. Calc. f o r C^H^NgZn (pyridine adduct of ZnTBP): C, 75.50; II, 3.83; N, 11.50%. Found: C, 77.50; H , 4.81; N, 17.5%. Calc. f o r C 5 C J H 3 6 N 1 C j (pyridine adduct of H 2PyrP): C, 77.20; H, 4.80; N, 18.01%. . Found: C, 72.32; H, 4.10; N, 7.37%. Calc. f o r C,.„H,J 0 (H.COOHTPP): Ho oU 4 o I C, 72.91; H, 3.92; N, 7.09%. 120 . R e f e r e n c e s 1. A^. C a r r i n g t o n and A.D.' M c L a c h l a n , I n t r o d u c t i o n t o M a g n e t i c "Resonance, Harper and Row, New Y o r k , 1967-

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