Redox chemistry of 2-hydroxy-1,4-naphthoquinone (Lawsone) and of its manganese complexes in aprotic media
When mixts. of Mn(II) and 2-hydroxy-1,4-naphthoquinone (Lawsone) with 1:1 and 1:2 mol ratios are reduced in aprotic solvents, stable [MnIII(ONO2)] and [MnIV(ONO2)2]2- complexes are formed, resp. The ONO2 represents the trianion of the fully reduced ligand. These complexes and their redox products were characterized by cyclic voltammetry, controlled-potential electrolysis, optical spectroscopy, and magnetic susceptibility measurements in DMSO and MeCN solvents. On the basis of these results, a self-consistent redox mechanism is presented for the interconversion of the various species of Mn(II)-Lawsone systems with mole ratios 1:1 and 1:2. The formation const. for the [MnIII(ONO2)] complex was evaluated voltammetrically to be 4 × 1014 M-1. The direct interaction of Mn(III) with semiquinone leads to disproportionation, yielding Mn(II) and the free ligand. These results may be relevant to the mechanism of the O evolution reaction in photosystems II of green-plant photosynthesis.
|Título de la Revista:||Anales de Química|
|Editorial:||Real Sociedad Española de Química|
|Fecha de publicación:||1986|
|Página de inicio:||309|