Redox chemistry of the Keggin heteropolyoxotungstate anion in ionic liquids

Abstract

The solid salts of the 1-ethyl-3-methylimidazolium and the 1- n-pentyl-3-methylimidazolium cations, abbreviated [C 2mim] + and [C 5mim] +, respectively, of the Keggin heteropolyanion, α-[PW 12O 40] 3−, were prepared. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) measurements of both [C n mim] 3[α-PW 12O 40] salts (for n=2 and 5) were performed in acetonitrile containing either tetra- n-butylammonium hexafluorophosphate, abbreviated TBAPF 6, or the corresponding [C n mim]BF 4 ionic liquids (ILs) as electrolytes. The results are compared with the corresponding data obtained in the neat [C n mim]BF 4 ILs without addition of other electrolytes. The effects of countercation and supporting electrolyte on the voltammetry of the Keggin ion α-[PW 12O 40] 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.