Redox chemistry of the Keggin heteropolyoxotungstate anion in ionic liquids

The solid salts of the 1-ethyl-3-methytimidazolium and the 1-n-pentyl-3-methylimidazolium cations, abbreviated [C(2)mim](+) and [C(5)mim](+), respectively, of the Keggin heteropolyanion, alpha-[PW12O40](3-), were prepared. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) measurements of both [C(n)mim](3)[alpha-PW12O40] salts (for n = 2 and 5) were performed in acetonitrile containing either tetra-n-butyl ammonium hexafluorophosphate, abbreviated TBAPF(6), or the corresponding [C(n)mim]BF4 ionic liquids (ILs) as electrolytes. The results are compared with the corresponding data obtained in the neat [C(n)mim]BF4 ILs without addition of other electrolytes. The effects of countercation and supporting electrolyte on the voltammetry of the Keggin ion alpha-[PW12O40](3-) are interpreted as resulting from an amalgamation of isomerization, ion-association, and redox processes. The combination of the unique solvent/electrolyte properties of ILs with the well-known electrochemistry of molecular polyoxometalates (POMs) like the Keggin anion leads to redox behavior that may have impact on the research and technology of catalytic and energy-storage phenomena. (C) 2004 Elsevier B.V. All rights reserved.