Conformational equilibrium of bis(trifluoromethanesulfonyl) imide anion of a room-temperature ionic liquid: Raman spectroscopic study and DFT calculations
Conformational equilibrium of bis(trifluoromethanesulfonyl) imide anion of a room-temperature ionic liquid: Raman spectroscopic study and DFT calculations
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DOI：
10.1021/jp0612477
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发表时间：
2006-04-27
影响因子：
3.3
通讯作者：
Ishiguro, SI
中科院分区：
文献类型：
--
作者：
Fujii, K;Fujimori, T;Ishiguro, SI
用拉曼光谱和密度泛函理论计算研究了双三氟甲磺酰亚胺（TFSI-）的液态结构。1-乙基-3-甲基咪唑鎓（EMI+）TFSI（-）的拉曼光谱在约398和407 cm（-1）处显示出由TFSI-产生的相对较强的谱带。有趣的是，407 cm（-1）谱带相对于398 cm（-1）谱带，随着温度的升高而明显增强，这表明在液态下TFSI-构象之间建立了平衡。根据密度泛函理论计算和频率分析，两种C-2和C-1对称构象分别构成了全局和局部极小值，能量差为2.2-3.3 U mol（-1）. C_1构象的ω-SO_2摆动振动出现在396和430 cm（-1）处，C_1构象的ω-SO_2摆动振动出现在387和402 cm（-1）处。将在380-440 cm（-1）范围内观察到的拉曼光谱解卷积以提取TFSI-构象体的本征谱带，并评估从C-2到C-1的构象变化的焓。焓值与理论计算值吻合较好。因此，我们得出结论，在液体EMI+TFSI-中，TFSI-的C-1和C-2构象之间建立了构象平衡，并且C-2构象比C-1构象更有利。
The structure of bis(trifluorornethanesulfonyl) imide (TFSI-) in the liquid state has been studied by means of Raman spectroscopy and DFT calculations. Raman spectra of 1-ethyl-3-methylimidazolium (EMI+) TFSI(-)show relatively strong bands arising from TFSI- at about 398 and 407 cm(-1). Interestingly, the 407 cm(-1) band, relative to the 398 cm(-1) one, is appreciably intensified with raising temperature, suggesting that an equilibrium is established between TFSI- conformers in the liquid state. According to DFT calculations followed by normal frequency analyses, two conformers of C-2 and C-1 symmetry, respectively, constitute global and local minima, with an energy difference 2.2-3.3 U mol(-1). The wagging omega-SO2 vibration appears at 396 and 430 cm(-1) for the C, conformer and at 387 and 402 cm(-1) for the C, one. Observed Raman spectra over the range 380-440 cm(-1) were deconvoluted to extract intrinsic bands of TFSI- conformers, and the enthalpy of conformational change from C-2 to C-1 was evaluated. The enthalpy value is in good agreement with that obtained by theoretical calculations. We thus conclude that a conformational equilibrium is established between the C-1 and C-2 conformers of TFSI- in the liquid EMI+TFSI-, and the C-2 conformer is more favorable than the C-1 one.