Superpressing of a Room Temperature Ionic Liquid, 1‑Ethyl-3-methylimidazolium Tetrafluoroborate

• Published in: The journal of physical chemistry. B Vol. 117; no. 40; pp. 12296 - 12302
• Main Authors: Yoshimura, Yukihiro, Abe, Hiroshi, Takekiyo, Takahiro, Shigemi, Machiko, Hamaya, Nozomu, Wada, Ryoichi, Kato, Minoru
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 10.10.2013
• Subjects: Cations; Condensed matter: structure, mechanical and thermal properties; Crystallization; Crystals; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Glass; Imidazoles - chemistry; Ionic liquids; Ionic Liquids - chemistry; Liquids; Phase Transition; Physical chemistry; Physics; Polymorphism; Pressure; Specific phase transitions; Spectrum Analysis, Raman; Temperature; X-Ray Diffraction; Imidazole derivatives; Pressure effects; Overpressure; Phase transformations; Glass; Fluoroborates; High pressure; Ionic liquid; Polymorphism
• DOI: 10.1021/jp4055507
• ISSN: 1520-6106

We have investigated the phase behavior of 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF4]) at 298 K under high pressure conditions. We found that [emim][BF4] can be superpressed without crystallization up to ∼7 GPa. We propose that [emim][BF4] behaves as a superpressurized glass above 2.8 GPa. In view of the results, the environment around the alkyl-chain (C6 and C7–C8) of [emim][BF4] is largely perturbed rather than that around the imidazolium-ring in the superpressed state. We also discussed the results in view of the conformational isomerism of [emim]+ cation. Remarkably, as an alternative to pressure-induced crystallization, we have found that such a metastable liquid shows crystal polymorphism around 2.0 and 1.0 GPa upon decompression. The behavior is in contrast with the earlier results of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]).