Electronic Absorption Spectra of Zero-Valent Tris-(2,2′-bipyridine) Metal Complexes

Abstract

Abstract Electronic absorption spectra of zero-valent tris(2,2′-bipyridine) metal complexes of the first transition metals from titanium to cobalt have been studied. These spectra give a criterion to determine whether the central metal atom or the ligand is trapping the electrons furnished by reducing reagents upon syntheses of the complexes, if the absorption spectra of the coordinating negative ions are fairly free from the influence of the configuration interactions by the “ligand-metal” charge transfer excited states and/or by the “metal-ligand” ones. The vanadium complex is concluded as a complex of the metal atom in zero oxidation state and neutral bipyridine molecules, where the ‘metal-ligand’ charge transfer bands are observed. The iron- and the manganese-complexes are ionic complexes of the metal ion in a non-zero oxidation state and the negative ions of bipyridine, where the (π-π*) absorption bands of coordinating bipyridine negative ion are observed. On the basis of their spectral character, the complexes of the other transition metals might be assigned to be a hybrid of the two typical electron traps given above.