Bivalent Cobalt Complexes with 1-(2-Pyridylazo)-2-naphthol and Analogous Ligands

Bivalent cobalt complexes with the title ligands were synthesized, isolated, and characterized by absorption spectra and magnetic moments. It has been suggested that the cobalt(II) complexes have more flexible structures than the corresponding cobalt(III) complexes. The cobalt(II) complexes were found to be oxidized to the cobalt(III) complexes in DMSO in the presence of copper(II) ions. Cyclic voltammetry elucidated the reversible CoII/CoIII couples of the cobalt complexes in acetonitrile. The values of E1⁄2 for the CoII/CoIII couples were found to depend on the coordinating ligands. The relation between E1⁄2 and pKa of the ortho-hydroxyl group in the ligands was discussed.