Electrochemical study of the Mn(II/III) oxidation of tris(polypyridine)manganese(II) complexes

Abstract

The electrochemical behaviour of a series of tris(polypyridine)manganese(II) complexes containing substituents ranging from electron withdrawing (Cl) to electron donating (OMe) is presented. The Mn(II/III) redox couple shows irreversible behaviour with large peak potential separations and small peak current ratios. A density functional theory (DFT) study shows the unstable oxidized Mn(III) complex to be either a high spin Jahn-Teller distorted (S = 2) or an intermediate spin (S = 1) species. Geometry distortion or electron rearrangement upon oxidation provides possible reasons for the observed irreversible electrochemical behaviour of the Mn(II/III) redox couple. A linear relationship obtained between the DFT calculated solvent phase (acetonitrile) highest molecular orbital energies and experimental reduction potentials (½(Epa + Epc) – obtained experimentally in acetonitrile for complexes 1–7 in this study) were used to predict the experimental reduction potentials of related complexes (½(Epa + Epc) of complexes 8–10 (previously published) accurately within 0.04 V of the published data.