Manganese complexes of bis-benzimidazolyl ligand as novel quenchers of superoxide radical anion

Abstract

A series of manganese II/manganese III complexes have been synthesised utilising an exogenous anionic ligand OAc, SCN with tridentate bis (2-benzimidazolyl methyl) ether and tetradentate 1,2- bis(2-benzi-midazolyloxamethyl) benzene ligands. The visible spectra of the Mn III compounds suggests pseudo C 4v symmetry, and the EPR data on the manganese II complexes indicates a similar geometry. Cyclic-voltammetric studies reveal that the E 1 2 for the manganese II/manganese IIIcouple shifts to a positive value with acetate as an anionic ligand, implying that 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-voltammetric experiments becomes irreversible in the presence of manganese complexes ; suggesting that these complexes act as good quenchers for superoxide anion