High-Pressure Crystal Polymorphs In 1-Butyl-3-Methylimidazolium Perfluorobutanesulfonate

The high-pressure (HP) crystal polymorph of a fluorinated ionic liquid (fIL) was determined using X-ray diffraction and Raman spectroscopy. The irreversible crystal polymorph of 1-butyl-3-methylimidazolium perfluorobutanesulfonate ([C(4)mim][PFBS]) was observed upon compression and decompression using X-ray diffraction. Conformational variance/invariance of [C(4)mim](+) and [PFBS](-) in the Raman spectra corresponded to the HP crystal polymorph. By the degrees of freedom of the conformations and their conformational flexibilities, the conformational variance was switched at the specific pressure for a volume contraction under HP, at which point the crystal system changed. The HP crystal polymorph was entirely different from the low-temperature crystal polymorph. (C) 2021 Elsevier B.V. All rights reserved.