Spectral characteristics of the copper(III) and nickel(III) coordination compounds with open-chain and macrocyclic dioxotetraamines

Electronic absorption spectra of copper(III) and nickel(III) complexes with open-chain and macrocyclic ligands containing two amide and two amine grou ps have been described. The absorption bands assigned to the sigma- (high-e nergy) and pi- (low energy) LMCT transitions show definite dependence on th e structure of the ligands. Thus, the spectra of the complexes with a five- membered chelate ring bearing an isolated carbonyl group are most closely r elated to the spectra of metal(III) peptides. In some cases the splitting o f the sigma -LMCT band is observed. Two absorption bands are also character istic for the spectra of oxamide derived complexes, though several nickel(I II) compounds display only a low-energy pi -LMCT transition. The most typic al spectral feature of the coordination compounds of malonamide derived lig ands is the lack of well-resolved low energy bands which could be assigned to pi -LMCT transitions and only one band is observed in the UV region whic h apparently includes both possible transitions. (C) 2000 Elsevier Science B.V. All rights reserved.