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-dimethylimidazolium methyl sulfate with tungsten(VI) oxide nanopowder. Close interactions of the charge-enhanced C–H⋯O 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⋯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.