Syntheses and properties of mononuclear cobalt-dioxolene complexes with the ancillary ligand containing bulky quinoline rings – Electronic state manipulation of the complexes by steric effect

Abstract

Two types of mononuclear cobalt complexes with two ancillary ligands containing isoquinoline groups and 3, 5-di-tert-butylcatechol (3, 5-DBCat) were synthesized. The crystal structures and spectroscopic, electrochemical, and magnetic properties of these complexes and complexes with ancillary ligands containing multiple quinoline groups were compared to clarify the steric effect of quinoline derivatives around the cobalt center. In particular, a comparison of the crystal structures of the mononuclear cobalt complexes containing tris(2-quinolylmethyl)amine (tqa) and tris(3-isoquinolylmethyl)amine (isotqa) as ancillary ligands, each of which has three isoquinoline and three quinoline rings, showed that the isotqa complex was less congested than the tqa complex around the cobalt center. As a result, the tqa complex contains Co (II), whereas the isotqa complex has the stable Co (III) electronic state due to the stronger ligand field. In this report, the steric influence of ancillary ligand substituents on the electronic states of complexes is clarified from several perspectives such as spectroscopic, electrochemical and magnetic properties.