Liquid Structure of and Li+ Ion Solvation in Bis(trifluoromethanesulfonyl)amide Based Ionic Liquids Composed of 1-Ethyl-3-methylimidazolium and N-Methyl-N-propylpyrrolidinium Cations

Liquid structures of the bis(trifluoromethanesulfonyl)amide based ionic liquids composed of 1-ethyl-3-methylimidazolium and N-methyl-N-propylpyrrolidinium ([C2mIm+][TFSA–] and [C3mPyrro+][TFSA–], respectively) and Li+ ion solvation structure in their lithium salt solutions were studied by means of high-energy X-ray diffraction (HEXRD) technique with the aid of MD simulations. With regard to neat ionic liquids, a small but significant difference was found at around 3.5 A in the intermolecular radial distribution functions Ginter(r)s for these two ionic liquids; i.e., Ginter(r) for [C2mIm+][TFSA–] was positioned at a slightly shorter region relative to that for [C3mPyrro+][TFSA–], which suggests that the nearest neighboring cation–anion interaction in the imidazolium ionic liquid is slightly greater than that in the other. With regard to Li+ ion solvation structure, Ginter(r)s for [C2mIm+][TFSA–] dissolving Li+ ion exhibited additional small peak of about 1.9 A attributable to the Li+–O (TFSA–) atom–atom co...