Matthews Richard P, Ashworth Claire, Welton Tom, Hunt Patricia A
Department of Chemistry, Faculty of Natural Sciences, Imperial College London, London, SW7 2AZ, UK.
J Phys Condens Matter. 2014 Jul 16;26(28):284112. doi: 10.1088/0953-8984/26/28/284112. Epub 2014 Jun 12.
In this paper the structural and energetic landscapes of ion-pair dimer conformers of 1,3-dimethylimidazolium based ionic liquids have been explored ([C1C1im][A])2, A = Cl(-), NO3, MeSO4, OTf and BF4). A common low-energy conformer has been selected for full electronic structure analysis. We have compared and contrasted each cluster based on the relative hydrogen bonding ability (β-value) of the anion, which varies experimentally as Cl(-) > NO3 ≈ MeSO4 > OTf ≈ BF4. Correlations between experimental β-values, computed binding energies, charge transfer and various hydrogen bonding data have been made and outliers have been explained in terms of environmental effects present in the liquid phase. This is most evident in the structurally similar MeSO4 and OTf anions that have very similar hydrogen bonding motifs, but significantly different β-values. Moreover, detailed analysis of the cluster molecular orbitals, for each anion, reveals a subtle interplay between two modes of interaction, an in-plane traditional H-bonding and inter-planar anion-π interaction. Inter-planar anion-π interactions are particularly prominent for the NO3 cluster. We have rationalized how the full range of interactions could impact on the structuring of ILs at surfaces and the effect these may have on viscosity.
在本文中，我们探索了基于1,3 - 二甲基咪唑鎓的离子液体（[C1C1im][A]）₂（A = Cl⁻、[NO₃]⁻、[MeSO₄]⁻、[OTf]⁻和[BF₄]⁻）的离子对二聚体构象的结构和能量景观。已选择一种常见的低能量构象进行完整的电子结构分析。我们根据阴离子的相对氢键能力（β值）对每个簇进行了比较和对比，实验中β值的变化为Cl⁻>[NO₃]⁻≈[MeSO₄]⁻>[OTf]⁻≈[BF₄]⁻。已建立了实验β值、计算的结合能、电荷转移和各种氢键数据之间的相关性，并根据液相中存在的环境效应解释了异常值。这在结构相似的[MeSO₄]⁻和[OTf]⁻阴离子中最为明显，它们具有非常相似的氢键基序，但β值却显著不同。此外，对每个阴离子的簇分子轨道的详细分析揭示了两种相互作用模式之间的微妙相互作用，即面内传统氢键和平面间阴离子 - π相互作用。平面间阴离子 - π相互作用在[NO₃]⁻簇中尤为突出。我们已经阐明了所有相互作用如何影响离子液体在表面的结构形成以及这些作用可能对粘度产生的影响。
