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The metal i o n catalysed aquation of t h e trisoxdlatochromium(111) i o n has been s t u d i e d i n t h e presence and absence of added electrolytes with emphasis on t h e copper (11) i o x catalysed aquation. The i n t e r p r e t - a t i o n of t h e observed c a t a l y t i c cff c c t s of t h e c o p p e r ( l l ) i o n , h a s been attempted i n terms of io:i a s s o c i a t i o n . The p r o p o s e d scheme, f o r t h e aquation, i n v o l v e s m e t a l l a t i o n of' t h e CrOX 3- species t o account f o r
3
the promoting e f f e c t of t h e c o p p e r ( l l ) ions. The s p e c i f i c r a t e s of aquation and t h e formation constants of t h e v a r i o u s s p e c i e s formed between the copper (11) i o n and t h c C r O X
*
i o n have been obtained u s i n g3
curve f i t t i n g techniques, F u r t h e r , t h e dependence of t h e formation c o n s t a n t s and the s p e c i f i c r a t e s of aquation on temperature h a s been shown t o y i e l d r e a l i s t i c thermodynamic and a c t i v a t i o n parameters for t h e proposed model,
I n c r e a s i n g the pH was found t o have an a c c e l e r a t i n g a f f e c t on the aquation of t h e t r i s o x a l a t o c h r o n i m ( ~ ~ ~ ) i o n a t c o n s t a n t copper i o n concentraTion. This has been discussed, using ion a s s o c i a t i o n , rn terms of c a t a l y s i s of the aquation r e a c t i o n by h y d r o l y s i s products of t h e c o p p e r ( l l ) i o n , i n p a r t i c u l a r t h e CuOH
+
ion.The c a t a l y s e d and uncatalysed isomerisation of t h e bisoxalato- chromiwn(111) ion has been i n v e s t i g a t e d i n t h e presence and absence of v a r i o u s e l e c t r o l y t e s and t h e k i n e t i c d a t a has been r a t i o n a l i s e d i n terms of an i o n a s s o c i a t i o n model.
It has a l s o been proposed, from comparisons of s t u d i e s on t h e
c o p p e r ( l l ) ion c a t a l y s e d aquation and racemisation of t h e t r i s o x a l a t o - chromium(111) ion, t h a t a copper(11) i o n a s s o c i a t e s w i t h t h e C r O X 3-
3 i o n through t h r e e carboxyl oxygen atoms, one from each o x a l a t e group t o form a monometallated species, F u r t h e r comparison of t h e s e studies has led us t o p o s t u l a t e , i n the aquation, t h a t a second c o p p e r ( l l ) ion, proposed t o a s s o c i a t e with t h e monometallated species, associates with two carbonyl oxygen atoms of one of the o x a l a t e groups of the CrOX 3-
3 ion. This, and t h e comparison of the s p e c i f i c r a t e s of aquation of the monometallated and b i n e t a l l a t e d species, led us t o t h e conclusion t h a t aquation occurs by a r a p i d one ended d i s s o c i a t i o n of an oxalate ligand followed by a rate determining loss of t h e oxalate group.
A number of o t h e r r e s u l t s of relevance t o t h e s u b s t i t u t i o n and rearrangement r e a c t i o n s of chronim(111)-oxalate complexes, have a l s o been included.
