Ground state and electronic spectrum of Cu(II) and Cu(III) complexes of N,N '-1,2-phenylenebis-2-mercaptoacetamide

The electronic structure and the UV- vis spectrum of reduced and oxidized model systems of the N, N'- 1,2phenylenebis( 2- mercapto- 2- methylpropionamide) copper complex have been studied using a multiconfigurational quantum chemical method ( CASSCF/ CASPT2). The bonds between Cu and the two sulfur ligand atoms have a large covalent character in the oxidized Cu( (III)) form. As a result of the increased covalency, the effective charge on the Cu atom is actually smaller in the oxidized form. The electronic spectrum for both oxidation states of the complex is in agreement with the experiment for excitation energies and intensities showing that the theoretical description of the electronic structure is essentially correct. All bands that involve excitations from either Cu or S localized orbitals to the empty or half empty CuS antibonding orbital have been characterized