A dime a dozen: common structural attributes of 1,2-dimethylimidazolium halide ionic liquids†

A homologous series of 1,2-dimethylimidazolium-based ionic liquids with halide anions are examined by Hirshfeld surface analysis to draw out key structural details of the cation, allowing for a deep understanding of the structure and interactions present within this class of ionic liquids. With respect to cation structures, three distinct alkyl torsion angles are noted when examining the compounds currently reported within the structural database. These alkyl chains account for the largest percentage of cation⋯cation close contacts through a combination of H⋯H and H⋯π interactions. Further, the halide-containing crystals are contrasted with a hydrated form of the compounds, allowing for detailed examination of the changes in non-covalent interactions within the asymmetric unit. It is noted that for the hydrated compound, hydrogen bonding interactions between the water molecule and cation replace the anion⋯cation interactions, accounting, in part, for the lower melting points of these hydrated species.