Analytical Sciences

Solvation Structures of Some Transition Metal(II) Ions in a Room-Temperature Ionic Liquid, 1-Ethyl-3-methylimidazolium Bis(trifluoromethanesulfonyl)amide

Kenta FUJII,* Takahiro NONAKA,** Yu AKIMOTO,** Yasuhiro UMEBAYASHI,** and Shin-ichi ISHIGURO**

*Department of Chemistry and Applied Chemistry, Faculty of Science and Engineering, Saga University, Honjo-machi, Saga 840-8502, Japan
**Department of Chemistry, Faculty of Science, Kyushu University, Hakozaki, Higashi, Fukuoka 812-8581, Japan

Solvation structures of manganese(II), cobalt(II), nickel(II) and zinc(II) ions in 1-ethyl-3-methylimidazolium bis(trifluoro-methanesulfonyl) amide (EMI⁺TFSA^-) have been studied by UV-Vis, FT-IR and FT-Raman spectra. The ionic liquid involves TFSA^- conformers with C₁ (cis) and C₂ (trans) symmetries, and both conformers coexist in equilibrium in the liquid state. The results showed that these metal(II) ions are all six-coordinated with three TFSA^- ions, i.e., TFSA^- ligates as a bidentate O-donor in the ionic liquid. Although the metal ion strongly prefers the C₁ conformer in crystals, the metal ion coordinates both the C₁ and C₂ conformers in the liquid state, and the conformational equilibrium in the bulk only slightly shifts to the C₁ conformer in the coordination sphere. We concluded that the conformational equilibrium in the coordination sphere is strongly temperature-sensitive.

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