MANGANESE COMPLEXES OF BIS-BENZIMIDAZOLYL LIGAND AS NOVEL QUENCHERS OF SUPEROXIDE RADICAL-ANION

A series of manganese(II)/manganese(III) complexes have been synthesis ed utilising an exogenous anionic ligand OAc, SCN with tridentate bis (2-benzimidazolyl methyl) ether and tetradentate 1,2-bis(2-benzimidazo lyloxamethyl) benzene ligands. The visible spectra of the Mn-III compo unds suggests pseudo C-4v symmetry, and the EPR data on the manganese( II) complexes indicates a similar geometry. Cyclic-voltammetric studie s reveal that the E-1/2 for the manganese(II)/manganese(III) couple sh ifts to a positive value with acetate as an anionic ligand, implying t hat this anion stabilises the manganese(II) oxidation state while the E-1/2 data for SCN reveals that the anion stabilises the manganese(III ) state. The reoxidation step of the superoxide formed in the cyclic-v oltammetric experiments becomes irreversible in the presence of mangan ese complexes; suggesting that these complexes act as good quenchers f or superoxide anion. (C) 1997 Elsevier Science Ltd.