Solvent effects on the redox potentials of tetraethylammonium hexacyanomanganate(III) and hexacyanoferrate(III)

Tetraethylammonium hexacyanomanganate(III) was studied in formamide, N-methylformamide, methanol, propylenecarbonate, N,N-dimethylthioformamide, N-methylthiopyrrolidinone(2), butyrolactone, acetonitrile, dimethylsulfoxide, N,N-dimethylformamide, N-methylpyrrolidinone(2), nitromethane and tetramethylenesulfone employing polarographic and voltammetric techniques. Reversible or nearly reversible behaviour for the reaction Mn(CN)₆^3?/Mn(CN)₆^2? was observed in most solvents on the stationary platinum electrode. The reaction Mn(CN)₆^3?/Mn(CN)₆^4? was studied on both the dropping mercury electrode and the stationary platinum electrode. Besides the reaction Mn(CN)₆^3?/Mn(CN)₆^4? several anodic waves due to successive reactions of mercury with the cyano-ligand of the complex occurred at the dropping mercury electrode. No redox reaction for (et₄N)₃Mn(CN)₆ was found in nitromethane. The polarographic behaviour of tetraethylammonium hexacyanoferrate(III) was studied in formamide, N-methylformamide, N-methylpyrrolidinone(2) and butyrolactone. The variation of E_1/2 and 1/2 (E_pa+E_pc) values versus bisphenylchromium(I)/bisbiphenylchromium(0) as reference redox system of the processes Mn(CN)₆^3?/Mn(CN)₆^2?, Mn(CN)₆^3?/Mn(CN)₆^4? and Fe(CN)₆^3?/Fe(CN)₆^4? with the nature of the solvent is discussed within the donor-acceptor concept. Correlations between the E_1/2 and 1/2(E_pa+E_pc) values and the acceptor properties of the solvent have been observed. The preparation of tetraethyl- and tetrabutylammonium hexacyanomanganate(III) is described.