SOLVENT AND SALT EFFECTS ON THE REDOX BEHAVIOR OF TRIS-ACETYLACETONATO MANGANESE(III)

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. © 1979 Elsevier Sequoia S.A., Lausanne.