The role of charge-enhanced C-H•••O interactions in gel-like mixtures prepared from ionic liquids and tungsten(VI) oxide nanoparticles

Gel-like mixtures were prepared by mixing 1,3-dimethyliniidazolium methyl sulfate with tungsten(VI) oxide nanopowder. Close interactions of the charge-enhanced C-H center dot center dot center dot 0 type have been analyzed via high-pressure infrared and Raman spectroscopy. The presence of tungsten(VI) oxide nanopowder has a negligible effect on the peak frequency of the methyl C-H stretching band. However, the pressure dependence of imidazolium C-H stretching modes displays significant changes as tungsten(VI) oxide nanoparticles were added. The results demonstrate that the imidazolium. C-H center dot center dot center dot O3W interactions can offer an additional stability to perturb the local structure of 1,3-dimethylimidazolium methyl sulfate. Such a molecular ordering may trigger clustering of the surrounding anions and cations and interconnect neighboring WO3 nanoparticles to form physical gel. Raman spectra of a gel-like 1,3-dimethylimidazolium methyl sulfate/tungsten(VI) oxide mixture revealed a new low energy band at 788 cm(-1). We attribute the 788 cm(-1) band to the interactions between the ionic liquid and surface WO3. (c) 2006 Elsevier B.V. All rights reserved.