高等学校化学学报 ›› 2018, Vol. 39 ›› Issue (9): 1954.doi: 10.7503/cjcu20180309

• 物理化学 • 上一篇    下一篇

烷基乙二胺-CF3CO2型质子化离子液体的分子间氢键作用

徐宇, 花儿()   

  1. 北方民族大学化学与化学工程学院, 银川 750021
  • 收稿日期:2018-04-23 出版日期:2018-09-07 发布日期:2018-06-26
  • 作者简介:

    联系人简介: 花 儿, 女, 博士, 副教授, 主要从事离子液体合成及理论计算研究. E-mail: huaer0101@hotmail.com

  • 基金资助:
    北方民族大学科技创新类重点科研项目(批准号: 2017 KJ182)和宁夏高等学校科学研究项目(批准号: NGY2017164)资助.

Hydrogen Bonding Study on Protic Ionic Liquids Composed of N-Alkyl Ethylenediaminum Cations with Trifluoroacetic Anion

XU Yu, HUA Er*()   

  1. Chemical Science and Engineering College, North Minzu University, Yinchuan 750021, China
  • Received:2018-04-23 Online:2018-09-07 Published:2018-06-26
  • Contact: HUA Er E-mail:huaer0101@hotmail.com
  • Supported by:
    † Supported by the Key Scientific Research Projects of North Minzu University, China(No.2017KJ18) and the Foundation of Ningxia Higher Education, China(No.NGY2017164).

摘要:

利用密度泛函理论M06-2X方法, 在6-311G(d,p)水平下, 对由N-烷基乙二胺阳离子[HAlkyl]+(Alkyl=Hex, Oct, EtHex)与三氟乙酸阴离子[TFA]-形成的[HHex][TFA], [HOct][TFA] 及[HEtHex][TFA]型质子化离子液体(PILs)的离子对进行了理论研究. 通过几何优化和分子振动频率分析3种PILs均得到5种较稳定构型[HAlkyl][TFA]S1~S5. 结果表明, [HAlkyl]+与[TFA]-间发生了质子转移形成了O—H…N型氢键. 3种PILs的基组重叠误差校正后的分子间相互作用能(ΔEintBSSE)在-449.91~-522.87 kJ/mol范围内. 由于分子间形成了较强的O—H…N氢键作用, 引起N—H振动频率消失, 在2200~2700 cm-1范围内出现了较强的O—H键振动. 通过自然键轨道(NBO)及分子中原子(AIM)理论计算, 研究了分子间氢键作用的相对强度及其对分子构型稳定性的影响. NBO分析结果表明, 其稳定化能主要源自于[HAlkyl]的氨基中孤对电子LP(N)与[TFA]中O—H反键轨道σ*(H—O)间的相互作用, 即LP(N)→σ*(H—O). 并探讨了阳离子部位[HAlkyl]+的质子化位置以及烷基链长、 支链的引入对[HAlkyl]与[TFA]间氢键作用强度的影响.

关键词: 质子化离子液体, 密度泛函理论, 分子间氢键作用, 自然轨道理论, 分子中原子理论

Abstract:

All possible molecular structures of chelating mono-protic ionic liquids(PILs) composed of N-alkyl(hexyl, octyl and 2-ethylhexyl) ethylenediaminum cations with trifluoroacetic acid(TFA) anion that form [HHex][TFA], [HOct][TFA] and [HEtHex][TFA] were studied by the density functional theory(DFT) at M06-2X/6-311G(d,p) level. Hydrogen bond and stabilites of five possible structures S1—S5 were investigated. The obtained data show that the hydrogen atom has been transferred from N—H of [HAlkyl]+ to O of [TFA]- in the ion pairs, and O—H…N hydrogen bond was formed. The obtained inter-molecular interaction energies(ΔEintBSSE) corrected by BSSE for all the structures are in the region of -449.91—-522.87 kJ/mol. The IR results show that N—H vibration spectra is disappeared. In the meantime, the stronger O—H vibration spectra was appeared in the region of 2200—2700 cm-1 since stronger O—H…N hydrogen bond was formed between [Alkyl] and [HTFA]. The natural bond orbital(NBO) and the atoms in molecules(AIM) analysis were applied to quantify the strength of hydrogen bond interactions and the effects of hydrogen bonding interactions on the stability of molecular configurations. NBO analysis shows that the stabilization energy mainly caused by the interaction between the lone pair electron LP(N) in the [HAlkyl] and the anti-bonding orbital σ*(H—O) in the [TFA]-LP(N)→σ*(H—O). The protonation site of [HAlkyl]+, and the effect of the alkyl chain length and side chain on the strength of the hydrogen bonding between [HAlkyl] and [TFA] were also discussed.

Key words: Protic ionic liquid, Density functional theory, Inter-molecular hydrogen bonding, Natural bond orbital(NBO), Atoms in molecules theory(AIM)

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