The Stabilization of High Oxidation States of Metals Through Coordination by Poly-aza Macrocycles

Abstract

The incorporation of a transition metal ion into a poly-aza macrocyle favors the access to unusually high oxidation states (e.g. Ni^III, Cu^III). The tendency to stabilize trivalent cations, which is expressed by the value of the potential of the M^III/M^III redox couple, is regulated by the structural features of the macrocycle (ring size, number and type of the donor nitrogen atoms). In general, formation of trivalent complexes is favored by strong equatorial interactions and the Cu^II/Cu^III oxidation process profits from the ligand-field contribution to a larger extent than does the corresponding Ni^II/Ni^III process. The solvent may profoundly influence the M^III/M^III redox change through axial coordination of one of the redox-active macrocyclic complexes.