Lu Xiaoxing, Xie Hujun, Lei Qunfang, Fang Wenjun
School of Pharmacy, Guangdong Pharmaceutical University, Guangzhou 510006, P. R. China.
Phys Chem Chem Phys. 2019 Aug 15;21(32):17720-17728. doi: 10.1039/c9cp02999k.
Mixtures of ionic liquids (ILs) have shown their potential in both physical and chemical processes, regarded as alternatives to common ILs. In this work, four guanidinium-based ILs, 2-ethyl-1,1,3,3-tetramethylguanidinium ethyl sulfate ([TMG(C2)][C2OSO3]) and bis(trifluoromethylsulfonyl)imide ([TMG(C2)][NTf2]), and 2,2-diethyl-1,1,3,3-tetramethylguanidinium ethyl sulfate ([TMG(C2)2][C2OSO3]) and bis(trifluoromethylsulfonyl)imide ([TMG(C2)2][NTf2]), are employed to investigate the structures, interactions and properties of four systems of IL-IL binary mixtures, including [TMG(C2)][C2OSO3]x[NTf2]1-x, [TMG(C2)]x[TMG(C2)2]1-x[C2OSO3], [TMG(C2)]x[TMG(C2)2]1-x[NTf2] and [TMG(C2)2][NTf2]x[C2OSO3]1-x. Combining experiments with theory, the relationships among H-bond interactions, structures and volumetric properties have been revealed. 1H NMR characterizations show the changes of H-bond interactions in the IL-IL mixtures in relation to composition, and DFT calculations reveal significant cation-anion interactions through the active hydrogen atom (N+-H) and the methyl groups in the cations with the anions in the manner of HO and HF. The ethyl group in the [C2OSO3]- anion hardly forms interactions with other components. The size effect of the calculated system has been evaluated for the IL-IL clusters with 2, 4 and 8 ions. Different structures due to variation of cationic and anionic species have remarkable influence on the volumetric properties of the IL-IL mixtures. Negative excess molar volume (VEm) is found in [TMG(C2)]x[TMG(C2)2]1-x[C2OSO3], and it is caused by the close packing of ions. Positive VEm values indicate that interaction loss occurs in the other three systems, where a linear arrangement or square packing of ions with low space utilization is found.
离子液体（ILs）混合物在物理和化学过程中都展现出了潜力，被视为普通离子液体的替代品。在这项工作中，四种基于胍的离子液体，即2-乙基-1,1,3,3-四甲基胍硫酸乙酯（[TMG(C2)][C2OSO3]）和双（三氟甲基磺酰）亚胺（[TMG(C2)][NTf2]），以及2,2-二乙基-1,1,3,3-四甲基胍硫酸乙酯（[TMG(C2)2][C2OSO3]）和双（三氟甲基磺酰）亚胺（[TMG(C2)2][NTf2]），被用于研究四种离子液体-离子液体二元混合物体系的结构、相互作用和性质，包括[TMG(C2)][C2OSO3]x[NTf2]1-x、[TMG(C2)]x[TMG(C2)2]1-x[C2OSO3]、[TMG(C2)]x[TMG(C2)2]1-x[NTf2]和[TMG(C2)2][NTf2]x[C2OSO3]1-x。通过将实验与理论相结合，揭示了氢键相互作用、结构和体积性质之间的关系。1H NMR表征显示了离子液体-离子液体混合物中氢键相互作用随组成的变化，密度泛函理论（DFT）计算揭示了通过活性氢原子（N+-H）以及阳离子中的甲基与阴离子以HO和HF的方式存在的显著阳离子-阴离子相互作用。[C2OSO3]-阴离子中的乙基几乎不与其他组分形成相互作用。对含有2、4和8个离子的离子液体-离子液体簇的计算体系的尺寸效应进行了评估。由于阳离子和阴离子种类的变化而导致的不同结构对离子液体-离子液体混合物的体积性质有显著影响。在[TMG(C2)]x[TMG(C2)2]1-x[C2OSO3]中发现了负的过量摩尔体积（VEm），这是由离子的紧密堆积引起的。正的VEm值表明在其他三个体系中发生了相互作用损失，在这些体系中发现了离子的线性排列或空间利用率低的方形堆积。
