Solvent and salt effects on the redox behaviour of trisacetylacetonato manganese(III)

Abstract

The polarographic and voltammetric behaviour of trisacetylacetonato manganese(III) [Mn(acac) 3] has been studied in methanol, ethanol, tetrahydrofurane, butyrolactone, propylenecarbonate, N,N-dimethylformamide, acetonitrile, nitromethane, N-methylpyrrolidone(2), 1,2-dichloroethane, dichloromethane, dimethylsulfoxide and acetic acid, Mn(acac) 3 was found to undergo a reversible one-electron reduction to Mn(acac) 3 − in most of the solvents mentioned. A further reduction at very negative potentials has been also observed in several solvents. The oxidation of Mn(acac) 3 to Mn(acac) 3 + has been studied by cyclovoltammetry in dichloromethane, nitromethane, acetonitrile, propylenecarbonate, N-methylpyrrolidinone(2), N,N-dimethylformamide and dimethylsulfoxide. The polarographic behaviour of NaMn(acac) 3 and Mn(acac) 2 has been investigated in the seven solvents listed above as well as in methanol. The half-wave potentials and the peak potentials referred to bisbiphenylchromium(I)/bisbiphenylchromium(0) as a reference redox system were found to vary with the nature of the solvent. Conductivity studies of Mn(acac) 3 and NaMn(acac) 3 have been carried out in these solvents. U.v.-visible and near i.r. spectra have been recorded of Mn(acac) 3, NaMn(acac) 3, Mn(acac) 2 and Na(acac) in the solvents mentioned. It has further been observed that the half-wave potentials for the polarographic reduction of Mn(acac) 3 shifted to more positive values by the addition of alkali metal ions and to more negative values by the addition of halide ions. The interactions of the solvent with Mn(acac) 3 and the variation of redox potentials with both the solvent and the added electrolytes will be discussed.