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ABSTRACT
A study of t h e influence of several " s o f t donor" ligands on t h e cupric ion has been completed. Nitrogen and sulphur donors were chosen since these a r e considered t o be present i n "biological copper" s i t u a t i o n s , some of t h e conditions of which i t was hoped t o duplicate.
Compl icated reactions were found w i t h several d i f f e r e n t types o f 1 igands.
hose
containing imine functions, when compl exed t o copper(11),
were invariably found t o cieave due t o the presence of external nucleophiles and i t wasconsidered t h a t f o r such donors t o be important i n "biological" s i t u a t i o n s
they would need t o be shielded by bulky ligand systems. The cleavage reactions were found t o have t h e i r origin in e l e c t r o n i c mechanisms and e a r l i e r suggestions
based on s t e r i c interactions were c r i t i c i s e d .
A study of sulphur donors showed t h a t , whereas thioethers had a poor a f f i n i t y f o r coppcr(1 I ) , t h i o l s bonded very strongly. Reduction t o copper(1)
invariably took place, b u t w i t h 1 igands containing TT-del ocal ised aromatic t h i o l s as well a s amine donors mixed-valent complexes of copper were formed.
The properties of most o f these complexes were unusual and one, e s p e c i a l l y , ( N-( 2 -thiophenol )pyridine-2-a1 dimindo)copper(II) chloride, showed reactions and properties t h a t suggested i t niay be a s u i t a b l e model Tor cupro-enzymes.
Corr;pl eyes with t h i o l Cio~~ors were f;ermed "anomal ous" i n v-iew of t h e i r compl icatcd physical properties
,
whereas c~mpounds with other donors showed"normal
"
bet.~aviout-. Absorption spectral s t u d i e s were undertaken in an' attempt t o understznd t h e e l e c t r o n i c s t a t e s of t h e " s o f t donor" complexes; a t t h e same tinie a? assessment of a recent scheme f o r assigning stereochemistries from v i s i b l e spectra as applied t o " s o f t donor" systems was possible.An X-ray s t r u c t u r a l detern~inatisn of t h e ~omplex
w s il~?dcrtaken, p a r t l y Sccaase O F i t s ~!nusual syntilztic and physical cliaractor-
i s t i c s . Two copper c e n t r e s , one f i v e - and the other s i x - co-ordinate,
were found t o be linked by a bridging chloride ion. The geometries about each copper ion were considerably d i s t o r t e d from ~ ~ u a r e - ~ ~ r a r n i dal and octahedral respectively; the ligand systems a l s o showed unusual e l e c t r o n i c e f f e c t s . Comparison with o t h e r recent s t r u c t u r a l investigations suggested t h a t five- co-ordination i s favoured by the copper ion i n " s o f t donor" environments, and t h i s was thought t o be s i g n i f i c a n t i n terms of oxygen-carrying a b i l i t y , where an increase in co-ordination number must occur. Several attempts t o oxygenate prepared complexes were ~ilade, b u t no concl r~sitle re s u l t s were obtained, although several somewhat unstable c r y s t a l l i n e prodticts were produced.
