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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Impact of Size and Electronegativity of Halide Anions on Hydrogen Bonds and Properties of 1-Ethyl-3-methylimidazolium-Based Ionic Liquids
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Impact of Size and Electronegativity of Halide Anions on Hydrogen Bonds and Properties of 1-Ethyl-3-methylimidazolium-Based Ionic Liquids

机译：卤化物阴离子对卤化物阴离子对氢键的影响和基于1-乙基-3-甲基咪唑鎓离子液体的性能

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摘要

The effect of the anion size and electronegativity of halide-based anions (Cl-, Br-, I-, and BF4-) on the interionic interaction in 1-ethyl-3-methylimidazolium-based ionic liquids (ILs) C(2)mim X (X = Cl, Br, I, and BF4) is studied by a combined approach of experiments (Raman, IR, UV-vis spectroscopy) and quantum chemical calculations. The fingerprint region of the Raman spectra of these C(2)mim X ion-pairs provides evidence of the presence of the conformational isomerism in the alkyl chain of the C(2)mim(+) cation. The Raman and IR bands of the imidazolium C-2-H stretch vibration for C(2)mim X (X = Cl, Br, I, and BF4) were noticeably blue-shifted with the systematic change in size of anions and the electronegativity. The observed blue shift in the C-2-H stretch vibration follows the order C(2)mim BF4 > C(2)mim I > C(2)mim Br > C(2)mim CI, which essentially indicates the strong hydrogen bonding in the C(2)mim Cl ion-pair. DFT calculations predict at least four configurations for the cation-anion interaction. On the basis of relative optimized energies and basis-set superposition-error (BSSE) corrected binding energies for all ion-pair configurations, the most active site for the anion interaction was found at the C2H position of the cation. Besides information about the C2H position, our DFT results give insights into the anion interaction with the ethyl and methyl chain of the cation, which was also confirmed experimentally [Chem. Commun. 2015, 51, 3193]. The anion interaction at the C2H site of the cation favors a planar geometry in C(2)mim X for X = Cl, Br, and I; however, for BF4, the system prefers a nonplanar geometry where the anion is located over the imidazolium ring. TD-DFT results were used to analyze the observed UV-vis absorption spectra in a more adequate way giving insights into the electronic structure of the ILs. Overall, a reasonable correlation between the observed and the DFT-predicted results is established.
机译：卤化物的阴离子（CL-，BR-，I-和BF4-）对基于1-乙基-3-甲基咪唑鎓基离子液体（ILS）C（2）的相互作用相互作用的影响通过综合实验方法（拉曼，IR，UV-VIS光谱）和量子化学计算来研究MIM X（X = CL，BR，I和BF4）。这些C（2）MIM X离子对的拉曼光谱的指纹区域提供了C（2）MIM（+）阳离子的烷基链中的构象异构性存在的证据。用于C（2）MIM X（X = CL，BR，I和BF4）的咪唑鎓C-2-H拉伸振动的拉曼和IR条带显着蓝色移位，随着阴离子和电负性的系统变化。 C-2-H拉伸振动中观察到的蓝色换档遵循顺序C（2）MIM BF4> C（2）MIM I> C（2）MIM BR> C（2）MIM CI，其基本上表示强氢气在C（2）MIM CL离子对中键合。 DFT计算预测阳离子相互作用的至少四种配置。基于相对优化的能量和基础设定的叠加误差（BSSE）校正所有离子对配置的结合能量，在阳离子的C2H位置发现了阴离子相互作用的最活跃的部位。除了关于C2H位置的信息，我们的DFT结果还能对阳离子的乙基和甲基链的阴离子相互作用，还在实验[化学。安排。 2015,51,3193]。阳离子的C2H位点的阴离子相互作用有助于C（2）MIM X的平面几何形状，用于X = CL，BR和I;然而，对于BF4，系统更喜欢阴离子位于咪唑啉环上的非平面几何形状。 TD-DFT结果用于以更适当的方式分析观察到的UV-Vis吸收光谱，以欣赏ILS的电子结构。总的来说，建立了观察到和DFT预测结果之间的合理相关性。

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