Watanabe Hikari, Arai Nana, Han Jihae, Kawana Yui, Tsuzuki Seiji, Umebayashi Yasuhiro
Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba, 278-8510, Japan.
Graduate School of Science and Technology, Niigata University, 8050 Ikarashi, 2-no-cho, Nishi-ku, Niigata City, 950-2181, Japan.
Anal Sci. 2022 Aug;38(8):1025-1031. doi: 10.1007/s44211-022-00121-7. Epub 2022 Jun 8.
Isotopic H/D or Li substitution Raman spectroscopy was applied to new kinds of ionic liquids; N-methylimidazole (CIm) and acetic acid (CHCOOH) as the pseudo-protic ionic liquid (pPIL), and both of the neat and the 2,2,3,3-tetrafluoropropyl ether (HFE) diluted Li-glyme solvate ionic liquids (SIL) [Li(Gn)][TFSA] (Gn, glyme n = 3 or 4); TFSA, bis(trifluoromethanesulfonyl)amide) to clarify the proton transfer or the Li solvation/ion pair formation. The isotopic substitution Raman (ISR) spectra were obtained as the difference between the samples containing the same composition except the substituted isotope. The calculated and theoretical ISR spectra were also evaluated for comparison. With the CIm-CHCOOH(D) pPIL, the Raman bands attributable to the CIm/CHIm gave signals of differential shape, and they were well reproduced with the curve fitting by taking the small amount of CHIm and CHCOO generation into consideration. The ISR spectra for the SIL were well explained by the formation of the Li-TFSA contact ion pair (CIP) and the solvent shared ion pair (SSIP) in the [Li(G3)][TFSA] SIL. In addition, the ISR spectra for the HFE-diluted [Li(G4)][TFSA] SIL clearly proved that the HFE hardly coordinates to the Li in the HFE-diluted SIL. Here, the ISR spectroscopy is proposed as a new tool for studying the ion solvation and the ion pair formation in ionic liquids.
将同位素H/D或Li取代拉曼光谱应用于新型离子液体；N-甲基咪唑（CIm）和乙酸（CHCOOH）作为准质子离子液体（pPIL），以及纯的和2,2,3,3-四氟丙基醚（HFE）稀释的Li-甘醇二甲醚溶剂化离子液体（SIL）[Li(Gn)][TFSA]（Gn，甘醇二甲醚，n = 3或4）；TFSA，双（三氟甲磺酰）酰胺），以阐明质子转移或Li溶剂化/离子对形成。同位素取代拉曼（ISR）光谱是作为除取代同位素外具有相同组成的样品之间的差异获得的。还对计算的和理论的ISR光谱进行了评估以作比较。对于CIm-CHCOOH(D) pPIL，归因于CIm/CHIm的拉曼带给出了不同形状的信号，通过考虑少量CHIm和CHCOO的生成进行曲线拟合，它们得到了很好的再现。SIL的ISR光谱通过[Li(G3)][TFSA] SIL中Li-TFSA接触离子对（CIP）和溶剂共享离子对（SSIP）的形成得到了很好的解释。此外，HFE稀释的[Li(G4)][TFSA] SIL的ISR光谱清楚地证明了HFE在HFE稀释的SIL中几乎不与Li配位。在此，ISR光谱被提议作为研究离子液体中离子溶剂化和离子对形成的一种新工具。
