Structural Studies on the Basic Ionic Liquid 1-Ethyl-1,4-diazabicyclo[2.2.2]octanium Bis(trifluoromethylsulfonyl)imide and Its Bromide Precursor

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• 作者：Yansen Lauw ; Thomas R眉ther ; Michael D. Horne ; Kia S. Wallwork ; Brian W. Skelton ; Ian C. Madsen ; Theo Rodopoulos
• 刊名：Crystal Growth & Design
• 出版年：2012
• 出版时间：June 6, 2012
• 年：2012
• 卷：12
• 期：6
• 页码：2803-2813
• 全文大小：571K
• 年卷期：v.12,no.6(June 6, 2012)
• ISSN：1528-7505

文摘

The structure of 1-ethyl-1,4-diazabicyclo[2.2.2]octanium bis(trifluoromethylsulfonyl)imide ([C₂DABCO][NTf₂]) was determined by single crystal X-ray diffraction, and its behavior with temperature was examined by synchrotron powder diffraction, differential scanning calorimetry (DSC), and Raman spectroscopy. [C₂DABCO][NTf₂] undergoes a solid鈥搒olid phase transition at 309 K and a solid鈥搇iquid (melting) transition at 350 K, as reported previously in the literature. The crystal structure of [C₂DABCO][NTf₂] was determined at temperatures below the solid鈥搒olid transition (solid-I phase), whereas in situ synchrotron powder diffraction enabled the unit cell of the solid phase observed above the solid鈥搒olid transition temperature (solid-II phase) to be indexed. High-resolution synchrotron powder diffraction data indicated the coexistence of a metastable phase with the solid-I and solid-II phases around the temperature of the solid鈥搒olid phase transition. A variable temperature Raman study suggested rotational movement of both [C₂DABCO]⁺ and [NTf₂]^{鈭?/sup> in the solid-II phase indicating the formation of a rotator phase. The structure of the [C₂DABCO][NTf₂] precursor 1-ethyl-1,4-diazabicyclo[2.2.2]octanium bromide ([C₂DABCO][Br]) was also determined by single crystal X-ray diffraction and its phase transitions were examined by differential scanning calorimetry. A comparison of the structures and phase transitions of the two analogous salts provides insights into the relative electrostatic attraction between the ions and the relative packing density and efficiency in the crystal lattices.}