SPECTRAL AND ELECTROCHEMICAL INVESTIGATIONS OF COPPER(II) N-SALICYLIDENE-AMINO ACIDATO COMPLEXES AND THEIR IMIDAZOLE, PYRAZOLE AND PYRIDINE ADDUCTS

Copper(II) Schiff base complexes derived from salicylaldehyde and amino acids such as glycine, L-alanine, L-serine, L-threonine, and beta-alanine, Cu(sal-aa)(H2O) and their imidazole, pyrazole and pyridine adducts, Cu(sal-aa)L have been prepared. Their electronic spectral and e.s.r. data in water concur with information obtained in dioxane-H2O mixtures; cyclic voltammetric (c.v.) and differential pulse voltammetric (d.p.v.) data were collected in aqueous media; based on the experimental data, a three-step electrode mechanism has been proposed. In pH 5-3.5 the presence of protonated species, [Cu(sal-aaH)(H2O)]+ is evident from c.v. profiles. The electronic spectra of Cu(sal-aa)L adducts show a shift of ca. 10-20 nm in the d-d band position to lower wavelengths. E.s.r. paramerters g(iso), g parallel-to and A parallel-to are lower and A(iso) higher for the adducts compared to the parent complexes. These changes are commensurate with increased planar covalency resulting from the replacement of H2O molecules by N-donor ligands. The electrochemical behavior of pyridine adducts is similar to that of Cu(sal-aa)(H2O) complexes. Imidazole and pyrazole adducts show irreversible one-electron reduction, this difference in electrochemical behaviour being related to the difference in electron acceptor ability of the N-donor ligands. At low pHs, the electrochemical behaviour of the adducts is similar to that of the parent complexes.