Differences in Ion Interactions for Isoelectronic Ionic Liquid Homologs.

Specific cation-anion interactions for two pairs of isoelectronic ionic liquids (ILs) have been investigated using nuclear Overhauser effect (NOE) 2D NMR methods to explore proximities between ions. The four ILs comprise the bis(trifluoromethylsulfonyl)amide anion paired with the following cations: triethyloctylammonium, (2-ethoxyethoxy)ethyltriethylammonium, triethyloctylphosphonium, and (2-ethoxyethoxy)ethyltriethylphosphonium. Substantial interactions are observed between the anion (19)F nuclei and all of the protons on the triethyl chains for each of the four cationic head groups. Significantly different interactions are observed for each of the four cationic tail groups and the anions.