Electrochemical Behavior of Iron(III)/Iron(II) Couple in Dimethylformamide

The electrochemical behavior of the iron(III)/iron(II) couple was investigated in both complexing (Cl⁻) and noncomplexing (ClO⁻₄) media in dimethylformamide (DMF), and the results were compared with the results obtained in aqueous solutions. The diffusion coefficients for iron(III) and iron(II) in DMF are larger in complexing medium than in noncomplexing medium, contrary to the results obtained in aqueous solutions. The heterogeneous electron transfer rate constants for the iron(III)/iron(II) couple obtained in DMF were found to be smaller in DMF solution as a result of the specific adsorption of DMF. The formal potential of the Fe(III)/Fe(II) couple in DMF is about 0.2 V less positive in noncomplexing medium as a result of the greater stabilization of iron(III) by the strongly cation-solvating DMF. The formal potential of the same couple in complexing medium (Cl⁻) was found to be 0.5 V less positive due to a combination of solvation and complexation effects. Cyclic voltammetric investigations show a quasi-reversible electron transfer without any coupled chemical reaction.