Optical and electron spin resonance spectra of cobalt complexes related to vitamin B12

Abstract

The optical spectra of the dipyridinecobalt(III) corrole, the cobalt(II) corrole anion, and the cobalt(II) 1,19-diethoxycarbonyltetradehydrocorrin cation have been measured in tetrahydrofuran and pyridine. Except for the cobalt(II) corrole anion, distinct differences in the optical spectra were observed in the two solvents, and have been interpreted in terms of the changes in the state of further co-ordination of the complex. E.p.r. studies of the cobalt(II) corrole anion and tetradehydrocorrin cation show the two complexes to have different electronic ground states for the central cobalt(II) ion, in spite of the similarity of the ligand moieties. This conclusion is supported by the optical studies, and is explained in terms of the changes in in-plane π-bonding and the difference in charge of the two species.