A Cyclic Voltammetry Experiment Illustrating Redox Potentials, Equilibrium Constants, and Substitution Reactions in Coordination Chemistry

We report a cyclic voltammetry experiment focusing on the [Ru^III(EDTA)(H₂O)]^- complex and its equilibrium reaction with dimethyl sulfoxide (DMSO) in aqueous solution, yielding the [Ru^III(EDTA)(κS-DMSO)]^- complex. From the electrochemistry data, the formation constants for the [Ru^III(EDTA)(κS-DMSO)]^- and [Ru^II(EDTA)(κS-DMSO)]^2- complexes were calculated as 2.0 mol^-1 dm³ and 2.7 x 10⁹ mol^-1 dm³, respectively. The results illustrate the kinetic lability of the ruthenium(III)-EDTA complexes and the role of backbonding stabilization in ruthenium(II)-DMSO complexes. The experiment has been successfully performed in a Coordination Chemistry course, exploiting fundamental aspects of metal complexes and the applications of that important electrochemical technique.