Pinning down the solid-state polymorphism of the ionic liquid [bmim][PF6]

Sofiane Saouane, Sarah E. Norman, Christopher Hardacre*, Francesca P. A. Fabbiani

*Corresponding author for this work

Research output: Contribution to journalArticle

56 Citations (Scopus)

Abstract

The solid-state polymorphism of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF6], has been investigated via low-temperature and high-pressure crystallisation experiments. The samples have been characterised by single-crystal X-ray diffraction, optical microscopy and Raman spectroscopy. The solid-state phase behaviour of the compound is confirmed and clarified with respect to previous phase diagrams. The structures of the previously reported gamma-form, which essentially exhibits a G'T cation conformation, as well as those of the elusive beta- and alpha-forms, are reported. Crystals of the beta-phase are twinned and the structure is heavily disordered; the cation conformation in this form is predominantly TT, though significant contributions from other less frequently encountered conformers are also observed at low temperature and high pressure. The cation conformation in the alpha-form is GT; the presence of the G'T conformer at 193 K in this phase can be eliminated on cooling to 100 K. Whilst X-ray structural data are overall in good agreement with previous interpretations based on Raman and NMR studies, they also reveal a more subtle interplay of intermolecular interactions, which give rise to a wider range of conformers than previously considered.

Original languageEnglish
Pages (from-to)1270-1280
Number of pages11
JournalChemical Science
Volume4
Issue number3
DOIs
Publication statusPublished - 01 Mar 2013

Keywords

  • RELAXATION
  • SOLVENTS
  • HIGH-PRESSURE
  • IN-SITU CRYSTALLIZATION
  • 1-BUTYL-3-METHYLIMIDAZOLIUM HEXAFLUOROPHOSPHATE
  • MOLECULAR-DYNAMICS SIMULATION
  • CRYSTAL POLYMORPHISM
  • ANIONS
  • 1,3-DIMETHYLIMIDAZOLIUM CHLORIDE
  • AB-INITIO

ASJC Scopus subject areas

  • Chemistry(all)

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