REDOX PROPERTIES OF COBALT(II) AND METHYLCOBALT(III) COMPLEXES WITH DIANIONIC MACROCYCLIC POLYCHELATE LIGANDS

Redox potentials of a series of complexes of cobalt(II) and organocoba lt(III) with tetraazamacrocyclic (N4) and N2O2-noncyclic polychelate l igands have been determined by cyclic voltammetry. Introduction of an o-phenylene fragment instead of an ethylene fragment into an equatoria l ligand and/or exchange of an N4-coordination chromophore for the N2O 2-analog has been shown to result in the anodic shift of redox potenti als of MeCo(IV)L/MeCo(III)L, MeCo(III)L/MeCo(II)L, and Co(II)L/Co(I)L pairs. It has been established that the solvent effect on redox potent ial is larger for Co(III)L/Co(II)L than for other pairs. Apparently, t his is the first case when quasi-reversible stages of oxidation of MeC o(III)L to MeCo(IV)L+ and MeCo(IV)L+ to [MeCo(IV)L]2+ can be simultane ously observed. A relatively stable complex of methylcobalt(IV) with a long lifetime at approximately 20-degrees-C has been registered by th e ESR method.