Takamuku Toshiyuki
Department of Chemistry and Applied Chemistry, Faculty of Science and Engineering, Saga University, Honjo-Machi, Saga, 840-8502, Japan.
Anal Sci. 2025 May;41(5):609-622. doi: 10.1007/s44211-025-00741-9. Epub 2025 Mar 14.
Room-temperature ionic liquids (ILs) attract much attention as green solvents because of their negligible volatility and non-flammability. In analytical chemistry, the application of ILs to chemical separation and solvent extraction has been investigated. However, there have been a smaller number of reports on the mechanisms of chemical equilibria in the solvents of ILs at a molecular level. In this review, the series of our investigations on the complex formation of Ni ion with molecular liquids (MLs) in imidazolium-based ILs, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([Cmim][TFSA]) and 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)amide ([Cmim][TFSA]) was summarized. The MLs involved methanol (MeOH), ethanol (EtOH), acetonitrile (AN), and dimethyl sulfoxide (DMSO). In [Cmim][TFSA], the Ni-ML complexes are stabler in the sequence of DMSO >> AN > EtOH ≈ MeOH complexes, which almost depends on the electron donicities of MLs. In contrast, in [Cmim][TFSA], the sequence changes to AN > DMSO > EtOH > MeOH complexes, despite of the lowest electron donicity of AN. Thus, only the electron donicities of MLs do not decide the stability of the complexes. The reasons for the stabilities of the Ni-ML complexes were interpreted in terms of the microscopic interactions between ML and the ILs' cation observed by the infrared (IR) and H and C nuclear magnetic resonance (NMR) spectroscopic techniques. Furthermore, to clarify the effects of ML cluster formation on the complex formation mechanisms, the heterogeneous mixing between IL and ML were quantitatively evaluated by small-angle neutron scattering (SANS) at the mesoscopic scale.
室温离子液体（ILs）因其可忽略不计的挥发性和不可燃性而作为绿色溶剂备受关注。在分析化学中，已对离子液体在化学分离和溶剂萃取中的应用进行了研究。然而，关于离子液体溶剂中分子水平化学平衡机制的报道较少。在本综述中，总结了我们对镍离子与咪唑基离子液体1-乙基-3-甲基咪唑双（三氟甲基磺酰）酰胺（[Cmim][TFSA]）和1-甲基-3-辛基咪唑双（三氟甲基磺酰）酰胺（[Omim][TFSA]）中的分子液体（MLs）形成配合物的一系列研究。所涉及的分子液体包括甲醇（MeOH）、乙醇（EtOH）、乙腈（AN）和二甲亚砜（DMSO）。在[Cmim][TFSA]中，镍-分子液体配合物的稳定性顺序为DMSO >> AN > EtOH ≈ MeOH配合物，这几乎取决于分子液体的给电子能力。相比之下，在[Omim][TFSA]中，尽管乙腈的给电子能力最低，但顺序变为AN > DMSO > EtOH > MeOH配合物。因此，仅分子液体的给电子能力并不能决定配合物的稳定性。通过红外（IR）以及氢和碳核磁共振（NMR）光谱技术观察到的分子液体与离子液体阳离子之间的微观相互作用，解释了镍-分子液体配合物稳定性的原因。此外，为了阐明分子液体簇形成对配合物形成机制的影响，通过小角中子散射（SANS）在介观尺度上对离子液体和分子液体之间的非均相混合进行了定量评估。
