Nature of Hydrogen Bonding in Charged Hydrogen-Bonded Complexes and Imidazolium-Based Ionic Liquids
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- 作者：Ekaterina I. Izgorodina ; Douglas R. MacFarlane
- 刊名：Journal of Physical Chemistry B
- 出版年：2011
- 出版时间：December 15, 2011
- 年：2011
- 卷：115
- 期：49
- 页码：14659-14667
- 全文大小：879K
- 年卷期：v.115,no.49(December 15, 2011)
- ISSN：1520-5207
文摘
The nature of hydrogen bonding was compared in neutral complexes and negatively charged complexes consisting of either the HF molecule or the halide anion (fluoride and chloride) and the C鈥揌 bond in the methane molecule with a varying degree of fluorination (such as CH4, CH2F2, and CHF3). Both linear (C3v symmetry) and nonlinear (C2v symmetry) hydrogen-bonded complexes were studied. Symmetry-adapted perturbation theory was used to decompose interaction energies into fundamental components such as Coulomb, repulsion, induction and dispersion to analyze the interplay among these forces in stabilizing hydrogen bonding. In the linear charged complexes, both Coulomb attraction and induction significantly contributed to the stabilization of hydrogen bonding. In the nonlinear charged complexes, mainly Coulomb attraction contributed to the HB complex stabilization, with the inductive forces playing a less important role. Contrary to the neutral complexes, dispersion forces played only a marginal role in the charged complexes. Interplay between the fundamental forces was also investigated in the ion pairs of the imidazolium-based ionic liquid, [C2mim]Cl, that were categorized as either (1) typical ion鈥搃on interaction, with the anion interacting from above or below the imidazolium plane; or (2) hydrogen-bonding interaction, with the anion interacting with the C2鈥揌 bond of the imidazolium cation. Both types of interactions were found to induce similar charge transfers, and the analysis of the energetic components revealed only a slight difference in the ion pairs studied: (1) both interactions were electrostatically driven, between 86% and 88% of the overall attractive energy, with the electrostatic component being slightly lower in the hydrogen-bonded ion pairs by 8 kJ mol鈥?; and (2) dispersion forces were found to be stronger in the typical ion鈥搃on interactions by 15 kJ mol鈥? and could be possible only due to the fact that the anion was able to move closer to the cation with no steric hindrance. From the experimental point of view, a vibrational red shift is expected in the hydrogen-bonded complexes of imidazolium-based ionic liquids, whereas the ion鈥搃on interactions are more likely to produce a slight blue shift.