Redox characteristics of Schiff base manganese and cobalt complexes related to water-oxidizing complex of photosynthesis

In an effort to obtain synthetic analogues of water-oxidizing complex (WOC) of photosystem II (PS II) of plant photosynthesis, a Schiff base manganese and a cobalt complex, employing Niten, a SALEN type ligand, have been prepared. Cyclic and square wave voltammetric measurements have been performed to assess their redox characteristics. Both complexes undergo several reduction processes in cathodic negative potential region at more or less similar potentials. In view of these reductions being independent of the nature of the metal, they are thought to be ligand-localized. Although similar in negative region, a marked difference in the behavior of the complexes is observed in anodic region. While the cobalt complex is electrochemically inactive in the positive potentials up to +1.0 V vs. Ag/AgCl, the manganese complex displays two oxidation waves at +0.25 and +0.5 V vs. Ag/AgCl. The presence of oxidation wave in manganese complex at +0.5 V vs. Ag/AgCl or +0.7 V vs. NHE suggests that this complex can catalyze the oxidation of water and can, thus, simulate the WOC of PS II. Copyright (C) 1999 Elsevier Science S.A.