Easily Vaporizable Ionic Liquids – No Contradiction!

Abstract

It was a big surprise to see crystals of an ionic liquid (IL) forming by sublimation at room temperature. ILs are gen- erally accepted to have negligible vapour pressures at ele- vated temperatures, making their sublimation or distillation very difficult. ILs that sublime easily contain silylimid- azolium-based cations. In order to establish the details of the unusual behaviour of this subclass of ILs, a combined spec- troscopic, X-ray crystallographic, physicochemical and theo- retical characterization was performed. The results are com- pared with those of other easily vaporizable compounds, like ammonium chloride and naphthalene. The single-crystal X- ray structure analysis of one of these compounds, N-methyl- N?-dimethyl(phenyl)silylimidazolium chloride (monoclinic, C2/c), clearly shows the existence of isolated ions, demon- strating that the compound is an ionic liquid.