A Novel Five-coordinate Mn Complex with a Redox-active SNNNS Ligand System

Abstract

Synthesis and characterization of a manganese complex of a new redox-active diaminocyclohexane derivative of a thiourea-based ligand with SNNNS donor atom set is reported. The molecular structure of the complex exhibits a pentadentate SNNNS ligand coordinated in the neutral form to the Mn(II) center. The coordination around the central metal is best described as distorted trigonal bipyramidal with the pyridine nitrogen and the two sulfur atoms being in the equatorial plane and the remaining two nitrogen donors occupying the apical positions of the bipyramid. Cyclic voltammetry in DMSO shows the MnII/MnIII redox couple with the oxidation peak at −0.199 V and the reduction peak at −0.587 V vs. Fc/Fc+ (scan rate 0.5 V s−1). The ligand itself possesses redox activity and exhibits prominent oxidation and reduction peaks at −1.194 and −1.481 V vs. Fc/Fc+, respectively. The results of electrochemical experiments under oxygen atmosphere suggest that upon reaction with electrochemically generated superoxide the redox-active ligand is modified causing decomposition of the complex.