Katsyuba Sergey A, Zvereva Elena E
Arbuzov Institute of Organic and Physical Chemistry, FRC Kazan Scientific Centre of RAS, Arbuzov st. 8, 420088, Kazan, Russia.
IFP Energies Nouvelles, 1 et 4 avenue de Bois-Préau, 92852 Rueil-Malmaison Cedex, France.
Phys Chem Chem Phys. 2022 Mar 23;24(12):7349-7355. doi: 10.1039/d1cp05745f.
The recently developed efficient protocol to explicit quantum mechanical modeling of the structure and IR spectra of liquids and solutions [Katsyuba , , 2020, , 6664-6670] is applied to ionic liquid 1-ethyl-3-methyl-imidazolium tetrafluoroborate [Emim][BF], and its C2-deuterated analog [Emim-d][BF]. It is shown that the solvation strongly modifies the frequencies and IR intensities of both cationic and anionic components of the ionic liquids. The main features of the bulk spectra are reproduced by the simulations for cluster ([Emim][BF]), representing an ion pair solvated by the first solvation shell. The geometry of the cluster closely resembles the solid-state structure of the actual ionic liquid and is characterized by short contacts of all CH moieties of the imidazolium ring with [BF] anions. Both structural and spectroscopic analyses allow the contacts to be interpreted as hydrogen bonds of approximately equal strength. The enthalpies of these liquid-state H-bonds, estimated with the use of empirical correlations, amount to 1.2-1.5 kcal mol, while the analogous estimates obtained for the gas-phase charged species [Emim][BF] and [Emim][BF] increase to 3.6-3.9 kcal mol.
最近开发的用于对液体和溶液的结构及红外光谱进行显式量子力学建模的高效协议[Katsyuba，，2020，，6664 - 6670]被应用于离子液体1 - 乙基 - 3 - 甲基咪唑四氟硼酸盐[Emim][BF₄]及其C₂ - 氘代类似物[Emim - d][BF₄]。结果表明，溶剂化强烈改变了离子液体阳离子和阴离子组分的频率及红外强度。通过对簇（[Emim][BF₄]）的模拟再现了体相光谱的主要特征，该簇代表由第一溶剂化层溶剂化的离子对。簇的几何结构与实际离子液体的固态结构非常相似，其特征是咪唑环的所有CH基团与[BF₄]阴离子有短接触。结构和光谱分析都表明这些接触可解释为强度大致相等的氢键。利用经验相关性估算的这些液态氢键的焓为1.2 - 1.5千卡/摩尔，而对气相带电物种[Emim][BF₄]⁺和[Emim][BF₄]⁻获得的类似估算值增加到3.6 - 3.9千卡/摩尔。
