DEPENDENCE OF ELECTRON-TRANSFER KINETICS OF THE FERROCENE FERROCENIUMCOUPLE ON THE VISCOSITY IN AMBIENT-TEMPERATURE CHLOROALUMINATE IONIC LIQUIDS/

The heterogeneous electron transfer kinetics of the ferrocenium/ferroc ene couple have been measured throughout the basic range of compositio n of the ambient temperature chloroaluminate ionic liquid composed of 1-ethyl-3-methylimidazolium chloride (ImCl) and aluminum chloride. Nor mal and reverse pulse voltammetries with pulse times as short as 5 mu s were employed. After subtraction of the background currents, the exp erimental voltammograms were directly compared with those calculated f rom the COOL algorithm using a model for reversible and quasi-reversib le electron transfer reactions. The standard rate constants, uncorrect ed for double layer effects, were found to decrease from 0.45+/-0.35 c m s(-1) at 0.95:1 to 0.027+/-0.004 cm s(-1) at 0.45:1 mole ratio of al uminum chloride to ImCl. Possible factors contributing to the observed dependence are discussed. The most likely reason for the retardation of the electron transfer rate is the slow relaxation of the increasing ly associated basic ionic liquid.