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

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 ¹ H and ¹³ 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 H² site and at high dilutions x_IL <0.1. The H² site was found to be more sensitive to intermolecular interactions compared to H^4, 5 in the case of ILs with asymmetric anions like trifluoromethanesulfonate (TfO^- ) or bis(trifluoromethylsulfonyl)amide (TFSA^- ).