Competition between Cation-Solvent and Cation-Anion Interactions in Imidazolium Ionic Liquids with Polar Aprotic Solvents.

The subtle interplay between ion solvation and association was analyzed in mixtures of imidazolium-based ionic liquids (ILs) with polar aprotic solvents. A site-specific pattern of cation-solvent and cation-anion interactions was disclosed by a careful analysis of the H and C NMR chemical shift dependence of the mixture composition. It was established that the less polar but more donating γ-butyrolactone is more prone to establish H-bonds with the imidazolium-ring hydrogen atoms of the IL cations than propylene carbonate, particularly at the H site and at high dilutions x <0.1. The H site was found to be more sensitive to intermolecular interactions compared to H in the case of ILs with asymmetric anions like trifluoromethanesulfonate (TfO ) or bis(trifluoromethylsulfonyl)amide (TFSA ).