Copper(III) and nickel(III) complexes of tripeptides, dipeptide schiff bases and related ligands

Abstract

Trivalent copper and nickel complexes of tripeptides, dipeptide Schiff bases and related ligands were comparatively studied by cyclic voltammetry. Depending upon the nature of the coordinated groups and the structure of fused ring systems the electrode potentials of Cu(III)Cu(II) and Ni(III)Ni(II) couples vary in the range 0.7–1.4 V. The stronger donating groups such as amino and deprotonated amide nitrogens assist the stabilizing of metal ions in the higher oxidation state, although aromatic nitrogen and oxygen do not contribute effectively for this. The trivalent copper and nickel with smaller ionic radii are stabilized by the 5-5-5 but not by the 5-6-5 or 6-5-6 fused ring structure as in bivalent copper and nickel. These redox characters were related with ESR and the absorption spectral feature of parent and trivalent metal complexes.