Effects of chloride ions on electrochemical reactions of manganese(III) complexes

Electrochemical reactions of manganese(III) complexes, MnIII(L)X (L; salen, salpn, 5-NO2–salen or 5-NO2–salpn, X; Cl, Br or NO2) and MnIII(L’)2X (L’; N-Bu-sal, N-Oct–sal, N-Oct–5-Br–sal or N-Oct–5-NO2–sal, X; Cl or Br), were investigated by voltammetry at a glassy carbon electrode in the absence/presence of Cl− in acetonitrile solution. By the addition of Cl−, oxidation processes of MnIII(L)X and MnIII(L’)2X have been found to be improved from quasi-reversible to reversible, and their oxidation products, [MnIV(L)X]+ and [MnIV(L’)2X]+, were stabilized by the combination with Cl− resulting in [MnIV(L)Cl2] and [MnIV(L’)2Cl2], respectively. On the other hand, the reduction processes of MnIII(L)X and MnIII(L’)2Cl were not so significantly affected by Cl− as those observed for their oxidation. Other types of manganese(III) complexes and iron(III) complex were also investigated. The present study may clarify the role of Cl− being involved in OEC (oxygen-evolving center) in photosystem II.

Graphical abstractElectrochemical reactions of manganese(III) complexes such as MnIII(R1-salen)Cl were investigated by voltammetry in the absence/presence of Cl−. By the addition of Cl−, oxidation processes of MnIII(salen)Cl have been found to be improved from quasi-reversible to reversible, and their oxidation products, [MnIV(salen)Cl]+ was stabilized by the combination with Cl− resulting in [MnIV(salen)Cl2]. The present study may clarify the role of Cl− being involved in OEC in photosystem II.Figure optionsDownload full-size imageDownload as PowerPoint slide