Electronic Structures of Tris(2,2′-bipyridyl) Complexes of Transition Metals in Lower Oxidation States

The electronic structures of various transition metal complexes with 2,2′-bipyridyl in low oxidation states are studied theoretically by the composite system method. The results show that the excess electrons are not localized on the metal ion but are transferred to some extent to the ligand antibonding π-molecular orbitals with the lower oxidation states of complex ions. The present theory can explain reasonably and systematically the observed magnetic moments and ESR spectra of the complexes, the simple one-electron treatment being inappropriate for a theoretical explanation of their magnetic properties. According to the present treatment, their electronic absorption spectra can be explained satisfactorily from a qualitative point of view as the overlapping of the π–π* transition bands in the ligands with the metal-ligand charge-transfer transition bands.