Redox behavior and Ion-Pairing thermodynamics of ferrocene and its derivatives in the organic phase

The redox behavior and ion-pairing thermodynamics of ferrocene and its derivatives (dimethylferrocene and decamethylferrocene) in a nitrobenzene (NB) thin film imposed between a graphite electrode and an aqueous electrolyte solution have been studied. We have shown that the presence of supporting electrolytes in the organic phase complicates their redox behavior, i.e., both the oxidation potential and peak area change significantly with time. In the absence of supporting electrolytes in the NB phase, the redox potential of the ferrocene molecules also shifts when the concentration of the supporting electrolytes (NaClO₄ or HClO₄) in the aqueous phase varies. It has been confirmed upon considering the influence of liquid-liquid junction potential that such a potential shift is dictated by the formation of ion pairs between the electrochemically generated ferricenium cations and the counteranions in the organic phase. On the basis of the determination of anion (ClO₄^-) concentrations in the NB film, we were able to quantitatively evaluate the correlation between molecular structure and the formation constant of Fc⁺ • ClO₄^- ion pairs.