REDOX CHEMISTRY AND SPECTROSCOPY OF 2-MERCAPTOBENZOIC ACID AND ITS MANGANESE(II) AND MANGANESE(III) COMPLEXES IN DIMETHYLSULFOXIDE

The redox behaviour of the ligand 2-mercaptobenzoic acid has been studied in dimethylsulphoxide. The combination of the dianion of the ligand with manganese(II) in a 1:2 mole ratio forms a colourless complex whose stability constant has been determined polarographically as 2.8 x 109 M-2. Oxidation of this complex at -0.45 V vs SCE yields a red complex of manganese(III) whose stoichiometry is also 1:2. The complexes have been characterized by cyclic voltammetry, controlled-potential electrolysis, optical spectroscopy and magnetic susceptibility measurements. The formation constant of the [MnIII(2-MBA)2]- complex has been evaluated spectrophotometrically as 9.3 x 107 M-2. These results may be relevant to the development of an adequate model for the active centre of acid phosphatases. © 1990.