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

Abstract

Abstract The incorporation of a transition metal ion into a poly-aza macrocyle favors the access to unusually high oxidation states (e.g. NiIII, CuIII). The tendency to stabilize trivalent cations, which is expressed by the value of the potential of the MIII/MIII 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 CuII/CuIII oxidation process profits from the ligand-field contribution to a larger extent than does the corresponding NiII/NiIII process. The solvent may profoundly influence the MIII/MIII redox change through axial coordination of one of the redox-active macrocyclic complexes.