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Solvent influence on imidazolium based ionic liquid contact pairs
Journal of Molecular Liquids ( IF 6 ) Pub Date : 2020-06-24 , DOI: 10.1016/j.molliq.2020.113615
Chiara Valsecchi , Marcileia Zanatta , Jessé Neumann , Graciane Marin , Jairton Dupont , Francisco P. dos Santos , Hubert K. Stassen

The interaction and solvent influence on two different imidazolium based ion pairs have been investigated by molecular dynamics simulations and Nuclear Magnetic Resonance. The cations 1,2,3,4,5-pentamethyl imidazolium and 1,3,4,5-tetramethyl imidazolium were considered with the imidazolate anion to evaluate the influence of the acidic hydrogen at the position 2 of the imidazolium ring on the ion pair formation in different solvents. The selected solvents are chloroform, dichloromethane, acetone, dimethylsulfoxide, and water, covering a broad range of polarity and permittivity. The binding free energy of the ion pair was computed by umbrella sampling. We observed that, with the increase of the dielectric constant, the ion pairs become more transient being separated in water. The free energies of binding corroborate ion pair stabilization by the hydrogen bond at carbon 2 of the imidazolium cations. In dichloromethane, we obtained weaker bound ion pairs than in acetone due to intercalation of dichloromethane into the ion pair. Thus, the ion pair stability is not only a consequence of the solvent's dielectric constant, but also due to local structural details.



中文翻译:

溶剂对咪唑基离子液体接触对的影响

通过分子动力学模拟和核磁共振研究了相互作用和溶剂对两个不同咪唑基离子对的影响。考虑将咪唑鎓阳离子上的阳离子1,2,3,4,5-五甲基咪唑鎓和1,3,4,5-四甲基咪唑鎓离子评估咪唑鎓环2位上的酸性氢对离子的影响对在不同溶剂中形成。选择的溶剂是氯仿,二氯甲烷,丙酮,二甲基亚砜和水,其极性和介电常数范围很广。通过伞式采样计算离子对的结合自由能。我们观察到,随着介电常数的增加,离子对在水中的分离变得更加瞬态。结合的自由能通过咪唑鎓阳离子的碳2处的氢键证实了离子对的稳定。在二氯甲烷中,由于二氯甲烷插入离子对中,因此获得的结合离子对比丙酮弱。因此,离子对稳定性不仅是溶剂介电常数的结果,而且还取决于局部结构的细节。

更新日期:2020-07-08
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