Intermolecular Interactions and Vibrational Perturbations within Mixtures of 1-Ethyl-3-methylimidazolium Thiocyanate and Water,The Journal of Physical Chemistry C

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Intermolecular Interactions and Vibrational Perturbations within Mixtures of 1-Ethyl-3-methylimidazolium Thiocyanate and Water
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2018-09-10 , DOI: 10.1021/acs.jpcc.8b07114
Sarah N. Johnson ₁ , Charles R. Hutchison ₁ , Chad M. Williams ₁ , Charles L. Hussey ₁ , Gregory S. Tschumper ₁ , Nathan I. Hammer ₁

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A Raman spectroscopic analysis of the room temperature ionic liquid 1-ethyl-3-methlimidazolium thiocyanate, [EMIM][SCN], has revealed that certain stretching vibrations associated with both the anion and cation shift to higher energy (or blue-shift) as water is introduced to the system (by up to 15 cm^–1 for a CH stretching mode associated with EMIM⁺ and up to 12 cm^–1 for the CS stretch of SCN^–). Density functional theory was employed to gain molecular level insight into the origins of these spectral perturbations by computing changes in the structures, energetics, and harmonic vibrational frequencies of the [EMIM][SCN] ion pair as a single explicit water molecule was added to the system. The computed harmonic vibrational frequency shifts for the low-energy structures of the ion pair and the corresponding monohydrated complex reproduce the experimentally observed trends. These results indicate that the donation of a hydrogen bond from water to the N atom of SCN^– produces the blue-shifts associated with the CN and CS stretching modes. In contrast, the vibrational frequency shifts associated with CH stretches of EMIM⁺ do not appear to require a direct interaction with the water molecule.

中文翻译：

1-乙基-3-甲基咪唑鎓硫氰酸盐和水的混合物之间的分子间相互作用和振动扰动

室温离子液体1-乙基-3-甲基咪唑硫氰酸盐[EMIM] [SCN]的拉曼光谱分析显示，与阴离子和阳离子相关的某些拉伸振动随着将水引入系统（对于与EMIM ⁺相关的CH拉伸模式，最长15 cm ^–1，对于SCN的CS拉伸最大12 cm ^–1^–）。通过计算[EMIM] [SCN]离子对的结构，能级和谐波振动频率的变化，通过将密度泛函理论用于分析这些光谱扰动的起源，从而获得了分子水平的见解。系统。离子对的低能结构和相应的一水合物的计算出的谐波振动频移再现了实验观察到的趋势。这些结果表明，从水氢键SCN的N原子的捐赠^-产生与CN和CS伸缩模式相关联的蓝移。相反，与EMIM ^+的CH拉伸相关的振动频率偏移似乎不需要与水分子直接相互作用。

更新日期：2018-09-11

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