Solvent effects on the redox potential of hexacyanoferrate(III)-Hexacyanoferrate(II)

The redox behaviour of the system hexacyanoferrate(III)-hexacyanoferrate(II) has been studied by polarographic and voltammetric methods in the following solvents: N-methylpyrrolidinone, N,N-dimethylformamide, acetonitrile, dimethylsulfoxide, N,N-dime-thylthioformamide,1,2-propanediolcarbonate, nitromethane, ethanol, methanol and water. The halfwave potentials of this reversible one-electron reduction have been measured against bisbiphenylchromium(I) iodide as a reference system, and the variation in the half-wavepotentials in these solvents has been explained as a function of coordinative interactions (the hexacyanoferrate ion being the donor and the solvent the acceptor). A semiquantitative order for the acceptor properties of the solvents has been derived.