Clay modified electrodes: Part IV. The electrochemistry and electron spin resonance of methyl viologen incorporated into montmorillonite films

Abstract

The electrochemical behavior of methyl viologen (N,N′-dimethyl-4,4′-bipyridinium or MV 2+) incorporated into montmorillonite modified electrodes was studied. The first reduction to the cation radical (MV + ) leads to the formation of a dimer that is not oxidizable within the clay film at potentials near the MV 2+/MV + wave. The presence of the dimer was confirmed by spectroelectrochemistry and electron spin resonance (ESR) spectroscopy. The dimeric viologen could be reoxidized via a mediation or charge from the electrode surface by Fe(CN) 3− 6. The equilibrium constant for the dimerization reaction 2 MV + ⇆ (MV + ) 2 was estimated as 5 x 10 4 M −1 based on the ESR data compared to ca. 380 M −1 for this reaction in aqueous solution.