Epr spectra of copper complexes with quinoxalinic and naphthoquinonic ligands

The electron paramagnetic resonance EPR spectra of a number of copper complexes with six quinoxalinic and naphthoquinonic ligands were measured in DMF solution and as crystalline powders both of which exhibited spectra with very sharp lines. The following ligands were investigated: 2,3-dihydroxyquinoxaline, 6-nitro-2,3-dihydroxyquinoxaline, 6,7-dinitro-2,3-dihydroxyquinoxaline, 2-hydroxy-3-mercaptomethyl-1,4-naphthoquinone, 2-amino-3-mercaptomethyl-1,4-naphthoquinone and 2,3-diamino-1,4-naphthoquinone. A complete analysis of the spectra was made and the covalence parameter a and the isotropic and anisotropic g values were obtained. The covalence parameters of the copper complexes of quinoxalinic ligands are high indicating an appreciable ionic character of the metal-ligand bond, whilst the amino derivatives of the naphthoquinonic complexes show low values indicating a markedly covalent metal-ligand bond. Copyright (C) 1996 Elsevier Science Ltd