Abstract

Cyclic voltammetry and controlled-potential electrolyses were carried out on solutions of 1,2-naphthoquinone (1,2-NQ), 1,2-dihydroxynaphthalene [1,2-Di(OH)-Cat] and their reduction and oxidation products in dimethyl sulfoxide. A study of the interaction of these species with MnII and MnIII has been undertaken. The complexes MnIII(Cat2-)33-, MnII(Cat2-)22- and MnII-(Cat2-), where Cat2- represents the dianion of 1,2-dihydroxynaphthalene, were obtained in solution and the species MnIISQ has been detected only on the surface of the electrode. An attempt to obtain the latter complex quantitatively caused intramolecular charge-transfer yielding the more stable MnIII-catechol complex. The MnIII-semiquinone complex is unstable and the ligand is easily oxidized. The charge-transfer reaction between MnIII(Cat2-)33- and MnII(Cat2-)22- is observed at -0.54/-0.52 V versus s.c.e. whereas the MnII complexes are reduced beyond the electrochemical window (at a potential more negative than -2.00 V versus s.c.e). On the other hand, all these species are destroyed when the coordinated ligand is oxidized. U.V.-vis. spectroscopy and magnetic susceptibility measurements were performed on the compounds in solution in order to characterize and to confirm the oxidation states of the metal ion in the species.