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), K7[H4PW18O62]·18H2O or K6[P2W18O62]·13H2O 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]6H4PW18O62 and K2[BMIM]4P2W18O62. X-ray diffraction illustrated amorphous structure of the hybrid materials. FT-IR spectra showed the presence of both 1-butyl-3-methylimidazolium 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]6H4PW18O62 compared to K2[BMIM]4P2W18O62. This was attributed to a decrease in the acidity of the Dawson POM anion in the hybrid material.

Graphical abstractPowder XRD patterns of (a) PW18, (b) K[BMIM]6H4PW18O62, (c) P2W18, and (d) K2[BMIM]4P2W18O62. Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► 1-butyl-3-methylimidazolium tetrafluoroborate([BMIM][BF4]) reacts with K7[H4PW18O62]·18H2O to form K[BMIM]6H4PW18O62. ► [BMIM][BF4] reacts with K6[P2W18O62]·13H2O to form K2[BMIM]4P2W18O62. ► K[BMIM]6H4PW18O62 and K2[BMIM]4P2W18O62 displayed amorphous structures. ► K[BMIM]6H4PW18O62 and K2[BMIM]4P2W18O62 illustrated low water content. ► K[BMIM]6H4PW18O62 and K2[BMIM]4P2W18O62 showed improved thermal stability.