Voltammetric studies of the reduction of [alpha-SiW12O40](4-) have been reported previously in highly acidic media. In this study, the systematic use of rotating disk and cyclic voltammetry over the less acidic pH range 2.1-6.8 provided access to a significant number of parameters that could be determined experimentally and then incorporated into a realistic simulation of the complex reaction scheme needed to account for the pH dependence. The simulated voltammograms reproduce many of the key features detected experimentally and imply that the general scheme for an overall four-electron redox reaction is [GRAPHICS] with different pathways being dominant at different pH values. Simulations of the simpler voltammetry detected in aprotic acetonitrile media (0.1 M Bu4NPF6) for reduction of [alpha-SiW12O40](4-) and [alpha-PW12O40](3-) also are presented and enable the solvent dependence of reversible potential data to be compared. The reversible potential in water for the [alpha-SiW12O40](6-/7-) process is a volt less negative than that for the analogous process in aprotic media. Reasons for this very large difference are considered in terms of solvent and electrolyte properties. (c) 2006 Elsevier B.V. All rights reserved.