New multi-charged viologen derivatives. Part 2. Unusual electrochemical behaviour in solution

The electrochemical behaviour of a new viologen derivative, C₅V³⁺, has been studied at gold electrodes. C₅V³⁺ displays an unexpected voltammetric behaviour, manifested as a tremendous difference between the peak currents of the two (reversible) reduction waves. A variety of electrochemical and spectroscopie techniques have been applied in order to resolve this unusual behaviour. The results indicate that C₅V³⁺ undergoes an overall two-electron reduction, but, unlike other viologens (e.g. methyl viologen), the charge partition between the two reduction steps is 0.5:1.5. A mechanisin is suggested which includes charge transfer accompanied by radical/parent ion dimerization. The mechanism is discussed in detail and shown to be in good agreement with the experimental results.