Abstract

The redox chemistry of the ligand 3,4-dihydroxybenzoic acid (3,4-DHBA) has been studied in dimethylsulphoxide and the conditions for the formation of the corresponding semiquinone and quinone have been determined. The manganese(II) and manganese(III) complexes with the different forms of this ligand have been characterized by cyclic voltammetry, UV-vis spectroscopy and magnetic susceptibility measurements. Neither the neutral nor the monoanionic form of the ligand show the formation of complexes with the metal ions. The dianion can be oxidized electrochemically to the corresponding semiquinone, at a more positive potential due to the presence of a deactivating group, forming a “peroxo-type” dimer. The subsequent oxidation of this species generates the corresponding quinone. The dianion and the semiquinone forms of the ligand produce manganese(II) and manganese(III) complexes with 1:2 stoichiometry, which is favoured by the ortho position of the hydroxide groups. These results may be relevant for the development of models for biological systems.