Magnitude and directionality of interaction in ion pairs of ionic liquids: Relationship with ionic conductivity
Magnitude and directionality of interaction in ion pairs of ionic liquids: Relationship with ionic conductivity
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DOI：
10.1021/jp0533628
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发表时间：
2005-09-01
影响因子：
3.3
通讯作者：
Watanabe, M
中科院分区：
文献类型：
--
作者：
Tsuzuki, S;Tokuda, H;Watanabe, M
通过MP2/6-311G**级从头计算研究了室温离子液体的九个离子对的分子间相互作用能。 1-乙基-3-甲基咪唑鎓 (emim) 配合物的相互作用能大小遵循 CF3CO2->BF4->CF3SO3->(CF3SO2)(2)N- 的趋势，与 PF6- 类似（分别为 -89.8、-85.2、-82.6、-78.8 和 -78.4 kcal/mol）。 BF4- 配合物与 emim、乙基吡啶鎓 (epy)、N-乙基-N,N,N-trimetliylamnioniuni ((C2H5)(CH3)(3)N) 和 N-乙基-N-甲基吡咯烷鎓 (empro) 的相互作用能差别不大 (-85.2. -82.8. -84.6. 和 -84.4 kcal/mol），而相互作用能的方向依赖性大小遵循emim > epy 的趋势，类似于(C2H5)(CH3)(3)N > empro。与实验离子电导率的比较表明，离子对相互作用能的大小和方向性对决定离子液体中离子解离/缔合动力学起着至关重要的作用，静电相互作用是离子间吸引力的主要来源。诱导作用虽小但不可忽略。与咪唑鎓 C-2-H 的氢键对于离子对中的吸引力并不重要。 BF4-配合物与I-乙基,2,3-二甲基咪唑鎓(em2im)(-81.8 kcal/mol)的相互作用能仅比emim配合物小4%。
The intermolecular interaction energies of nine ion pairs of room temperature ionic liquids were studied by MP2/6-311G** level ab initio calculations. The magnitude of the interaction energies of 1-ethyl-3-methylimidazolium (emim) complexes follows the trend CF3CO2- > BF4- > CF3SO3- > (CF3SO2)(2)N- similar to PF6- (-89.8, -85.2, -82.6, -78.8, and -78.4 kcal/mol, respectively). The interaction energies of BF4- complexes with emim, ethylpyridinium (epy), N-ethyl-N,N,N-trimetliylamnioniuni ((C2H5)(CH3)(3)N), and N-ethyl-N-methylpyrrolidinium (empro) are not very different (-85.2. -82.8. -84.6. and -84.4 kcal/mol, respectively), while the size of the orientation dependence of the interaction energies follows the trend emim > epy similar to (C2H5)(CH3)(3)N > empro. Comparison with the experimental ionic conductivities shows that the magnitude and directionality of the interaction energy of the ion pairs play a crucial role in determining the ionic dissociation/association dynamics in the ionic liquids, The electrostatic interaction is the major source of attraction between ions. The induction contribution is small but not negligible, The hydrogen bonding with the C-2-H of imidazolium is not essential for the attraction in the ion pair. The interaction energy of the BF4- complex with I-ethyl,2,3-dimethylimidazolium (em2im) (-81.8 kcal/mol) is only 4% smaller than that of the emim complex.