Standard Redox Potentials of R−/R+ Reference Redox Couples and Solvent Activity Coefficients

The standard redox potentials of five R−/R+ redox couples that can be considered as candidates for the reference redox couple, i.e., the anion/cation couples of tris(2,2′-bipyridine)iron(II), tris(2,2′-bipyridine)ruthenium(II), cobaltocene, perylene, and 9,10-diphenylanthracene, have been determined in acetonitrile, dimethyl sulfoxide, N,N-dimethylformamide and propylene carbonate by means of polarography and voltammetry. The results confirmed that the standard potentials of these redox couples are independent of the solvents studied so that they can be used as solvent-independent reference points for potential comparisons. The solvent activity coefficients of the silver ion have been estimated on the basis of these reference redox couples.