Synthesis and characterization of hybrid materials based on 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid and Dawson-type tungstophosphate K7[H4PW18O62] • 18H2O and K6[P2W18O62] • 13H2O

In this study, we synthesized hybrid materials using well-Dawson polyoxometalates (POMs), K-7[H4PW18O62] center dot 18H(2)O or K-6[P2W18O62] center dot 13H(2)O and a room temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]). K, W, P and CHN elemental analysis showed that one mole of [H4PW18O62](7-) reacts with 6 moles of BMIM+ and one mole of [P2W18O62](6-) reacts with 4 moles of BMIM+ to form, respectively, K[BMIM](6)H4PW18O62 and K-2[BMIM](4)P2W18O62. X-ray diffraction illustrated amorphous structure of the hybrid materials. FT-IR spectra showed the presence of both 1-butyl-3methylimidazolium cation and the Dawson anion. TG analysis displayed a relative thermal stability of the hybrid materials compared to the parents Dawson POMs. Cyclic voltammetry showed that the reduction peak potentials of the Dawson anion in the hybrid materials shift towards negative values and the shift is more pronounced for K[BMIM](6)H4PW18O62 compared to K-2[BMIM](4)P2W18O62. This was attributed to a decrease in the acidity of the Dawson POM anion in the hybrid material. (C) 2011 Elsevier Inc. All rights reserved.