Anion conformation of low-viscosity room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl) imide
Anion conformation of low-viscosity room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl) imide
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DOI：
10.1021/jp074325e
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发表时间：
2007-11-08
影响因子：
3.3
通讯作者：
Ishiguro, Shin-ichi
中科院分区：
文献类型：
--
作者：
Fujii, Kenta;Seki, Shiro;Ishiguro, Shin-ichi
通过拉曼光谱和理论DFT计算研究了低粘度室温离子液体1-乙基-3-甲基咪唑鎓他(氟磺酰)亚胺(EMI+FSI-)的阴离子构象。在 293、328 和 360 cm(-1) 处发现了三个强拉曼带，这归因于 FSI- 离子。这些拉曼带显示出显着的温度依赖性，这意味着两个 FSI 构象异构体平衡共存。理论计算支持了这一点，即 FSI- 离子以 C-2（反式）或 C-1（顺式）构象异构体的形式存在；前者给出了全局最小值，后者具有更高的SCF能量，约为4 W mol(-1)。完整的几何优化和正常频率分析表明，在 293、328 和 360 cm(-1) 处观察到的谱带归因于 Q 构象异构体。根据280-400 cm(-1)范围内观察到的拉曼谱带的去卷积提取了305、320和353 cm(-1)处的相应振动，并将其归因于C-2构象异构体。从C-2到C-1的构象变化的焓Delta H度经实验评估为约。 4.5 W mol(-1),与理论计算预测值吻合较好。双(三氟甲磺酰基)酰亚胺阴离子(TFSI-)显示C-1和C-2类似物之间的构象平衡(Delta H度= 3.5 kJ mol(-1))。然而，FSI-（F-S-N-S二面角）构象变化的势能面轮廓与TFSI-（C-S-N-S二面角）显着不同。
Anion conformation of a low-viscosity room-temperature ionic liquid 1-ethyl-3-methylimidazolium his(fluorosulfonyl) imide (EMI+FSI-) has been studied by Raman spectra and theoretical DFT calculations. Three strong Raman bands were found at 293, 328, and 360 cm(-1), which are ascribed to the FSI- ion. These Raman bands show significant temperature dependence, implying that two FSI- conformers coexist in equilibrium. This is supported by theoretical calculations that the FSI- ion is present as either C-2 (trans) or C-1 (cis) conformer; the former gives the global minimum, and the latter has a higher SCF energy of about 4 W mol(-1). Full geometry optimizations followed by normal frequency analyses show that the observed bands at 293, 328, and 360 cm(-1) are ascribed to the Q, conformer. The corresponding vibrations at 305, 320, and 353 cm(-1) were extracted according to deconvolution of the observed Raman bands in the range 280-400 cm(-1) and are ascribed to the C-2 conformer. The enthalpy Delta H degrees of conformational change from C-2 to C-1 was experimentally evaluated to be ca. 4.5 W mol(-1), which is in good agreement with the predicted value by theoretical calculations. The bis(ti-ifluoromethanesulfonyl) imide anion (TFSI-) shows a conformational equilibrium between C-1 and C-2 analogues (Delta H degrees = 3.5 kJ mol(-1)). However, the profile of the potential energy surface of the conformational change for FSI- (the F-S-N-S dihedral angle) is significantly different from that for TFSI- (the C-S-N-S dihedral angle).