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-1 and C-13 NMR chemical shift dependence of the mixture composition. It was established that the less polar but more donating gamma-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-2 site and at high dilutions x(IL)< 0.1. The H-2 site was found to be more sensitive to intermolecular interactions compared to H-4,H-5 in the case of ILs with asymmetric anions like trifluoromethanesulfonate (TfO @) or bis(trifluoromethylsulfonyl) amide (TFSA @).