title: 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.
abstract: Liquid structures of the bis(trifluoromethanesulfonyl)amide based ionic liquids composed of 1-ethyl-3-methylimidazolium and N-methyl-N-propylpyrrolidinium ([C(2)mIm(+)][TFSA(-)] and [C(3)mPyrro(+)][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 Å in the intermolecular radial distribution functions G(inter)(r)s for these two ionic liquids; i.e., G(inter)(r) for [C(2)mIm(+)][TFSA(-)] was positioned at a slightly shorter region relative to that for [C(3)mPyrro(+)][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, G(inter)(r)s for [C(2)mIm(+)][TFSA(-)] dissolving Li(+) ion exhibited additional small peak of about 1.9 Å attributable to the Li(+)-O (TFSA(-)) atom-atom correlation, though the corresponding peak was unclear in [C(3)mPyrro(+)][TFSA(-)] due to overlapping with the intramolecular atom-atom correlations in [C(3)mPyrro(+)]. In addition, the long-range density fluctuation observed in the neat ionic liquids diminished with the increase of Li(+) ion concentration for both ionic liquid solutions. These observations indicate that the large scale Li(+) ion solvated clusters are formed in the TFSA based ionic liquids, and well support the formation of [Li(TFSA)(2)](+) cluster clarified by previous Raman spectroscopic studies. MD simulations qualitatively agree with the experimental facts, by which the decrease in the long-range oscillation amplitude of r(2){G(r) - 1} for the Li(+) containing ionic liquids can be ascribed to the variation in the long-range anion-anion correlations caused by the formation of the Li(+) ion solvated clusters.
authors.affiliation: Department of Chemistry, Faculty of Science, Kyushu University, Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan. yumeb@chem.kyushu-univ.jp
authors.forename: Yasuhiro
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authors.lastname: Umebayashi
authors.forename: Hiroshi
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authors.lastname: Hamano
authors.forename: Shiro
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authors.lastname: Seki
authors.forename: Babak
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authors.lastname: Minofar
authors.forename: Kenta
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authors.lastname: Fujii
authors.forename: Kikuko
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authors.lastname: Hayamizu
authors.forename: Seiji
authors.initials: S
authors.lastname: Tsuzuki
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Kameda
authors.forename: Shinji
authors.initials: S
authors.lastname: Kohara
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Watanabe