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

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 (1/2(Epa + Epc) - obtained experimentally in acetonitrile for complexes 1 -7 in this study) were used to predict the experimental reduction potentials of related complexes (1/2(Epa + Epc) of complexes 8 -10 (previously published) accurately within 0.04 V of the published data. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study presents the electrochemical behavior of a series of tris(polypyridine) manganese(II) complexes with substituents ranging from electron withdrawing to electron donating. The Mn(II/III) redox couple shows irreversible behavior, which may be attributed to geometry distortion or electron rearrangement upon oxidation. The study also establishes a linear relationship between DFT calculated solvent phase energies and experimental reduction potentials, accurately predicting the reduction potentials of related complexes.