Abstract

In DMSO the 2,​3-​dimethoxy-​1,​4-​naphthoquinone (Q) is reduced in 2 successive 1-​electron steps, which are electrochem. reversible at low scan rates. At -​0.72 V vs. SCE the semiquinone anion radical is formed and at -​1.42 V vs. SCE a 2nd redn. to the corresponding dianion is obsd. A mixt. of zinc(II) and the dianion of 2,​3-​dimethoxy-​1,​4-​naphthoquinone at a mole ratio of 1:1 in Me2SO yields a stable complex. The zinc(II)​-​semiquinone complex is formed only on the surface of the electrode because under these conditions this radical ligand disproportionates producing the corresponding quinone and the dianion. The different forms of the ligand and the zinc(II)​-​dianion complex were characterized by cyclic voltammetry, UV-​visible spectroscopy and magnetic susceptibility measurements. The stability consts. for the 1:1 zinc(II)​-​dianion and zinc(II)​-​semiquinone complexes are large, but it was not possible to det. their exact value as their voltammetric behavior was irreversible. However the high stability of the dianion complex causes the disproportionation of the ligand in the semiquinone complex.