Panja Sumit K, Haddad Boumediene, Kiefer Johannes
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore, 560012, Karnataka, India.
Department of Chemistry, Dr Moulay Tahar University, Saïda, EN-NASR, BP:138, Algeria.
Chemphyschem. 2018 Nov 19;19(22):3061-3068. doi: 10.1002/cphc.201800684. Epub 2018 Oct 8.
Interonic interactions determine the macroscopic properties of ionic liquids (ILs). Hence, unravelling the relationships between the microscopic and macroscopic scales is key for rational design. Combining density functional theory (DFT) calculations of isolated ion pairs and vibrational spectroscopy of the condensed phase (fluid or solid) has become a very common approach. In the present work, we make a step towards understanding how the physicochemical effects in small gas phase clusters of a hydroxyl functionalized imidazolium-picrate IL relate with the molecular structure and interactions of the corresponding solid material taking 1-hydroxyethyl-3-methylimidazolium picrate, C OHmimPic, as an example. In the isolated ion pair, strong alkyl-OH⋅⋅⋅Pic hydrogen bonding interactions are found rather than the commonly observed hydrogen bonding interactions at the slightly acidic C(2)-H site of the imidazolium ring. However, this part of the cation plays an important role when clusters of ion pairs in the gas phase and inside a crystal lattice are considered. For example, in the dimeric ion-pair cluster, one centre (O*) with two interaction sites (C(2)-H-O* and alkyl OH-Pic) is observed. This configuration is suggested by single crystal X-ray diffraction (XRD), vibrational spectroscopy, and the dispersion-corrected DFT calculations. Hence, the study provides evidence for the appearance of theoretical gas phase clusters in an actual solidified ionic liquid. This ion pair dimer formation may be a general behavior of hydroxyl functionalized imidazolium ILs, but further research is needed to draw a final conclusion. Moreover, the Raman spectra confirm the exclusive gauche conformation of the hyroxyl functionalized alkyl chain.
离子间相互作用决定了离子液体（ILs）的宏观性质。因此，揭示微观和宏观尺度之间的关系是合理设计的关键。将孤立离子对的密度泛函理论（DFT）计算与凝聚相（流体或固体）的振动光谱相结合已成为一种非常常见的方法。在本工作中，我们以1-羟乙基-3-甲基咪唑鎓苦味酸盐（COHmimPic）为例，朝着理解羟基官能化咪唑鎓-苦味酸盐离子液体的小气相团簇中的物理化学效应如何与相应固体材料的分子结构和相互作用相关联迈出了一步。在孤立离子对中，发现了强的烷基-OH⋅⋅⋅Pic氢键相互作用，而不是在咪唑环的微酸性C(2)-H位点常见的氢键相互作用。然而，当考虑气相和晶格内的离子对团簇时，阳离子的这一部分起着重要作用。例如，在二聚离子对团簇中，观察到一个具有两个相互作用位点（C(2)-H-O和烷基OH-Pic）的中心（O）。单晶X射线衍射（XRD）、振动光谱和色散校正的DFT计算表明了这种构型。因此，该研究为实际固化离子液体中理论气相团簇的出现提供了证据。这种离子对二聚体的形成可能是羟基官能化咪唑鎓离子液体的普遍行为，但需要进一步研究才能得出最终结论。此外，拉曼光谱证实了羟基官能化烷基链的唯一gauche构象。
