Multiple electron transfer steps observed in the reduction of [S2Mo18O62](4-), when LiClO4 is used as electrolyte, are accounted for by assuming that Li+ acts as a moderately strong Lewis acid. For example, in the 95:5 CH3CN + H2O solvent mixture (0.1 M NBu4ClO4), the voltammetric behavior obtained on addition of Li+ can be simulated according a reaction scheme involving an extensive series of reversible potentials and equilibrium constants. Precipitation of highly reduced polyoxometalate salts occurring at the electrode surface complicates the voltammetry at very negative potentials when 0.1 M LiClO4 is used as the electrolyte. (C) 2000 Published by Elsevier Science B.V. All rights reserved.