Structural organization and phase behaviour of 1-butyl-3-methylimidazolium hexafluorophosphate: an high pressure Raman spectroscopy study

Abstract

The complexity of the phase diagram of a representative room temperature ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF 6 ]) is explored by means of Raman spectroscopy at high pressure (up to 1000 MPa) and high temperature (from room temperature to 100 1C) conditions. The first experimental evidence of the existence of a second crystalline phase for this salt at high pressure conditions is provided. By comparing the low frequency vibrational bands for the liquid state and the two observed crystalline phases, we confirm the scenario that considers the crystal polymorphism in this class of materials as a consequence of the rotational isomerism of the butyl chain. Furthermore the pressure dependence of other vibrational bands indicates the existence of a structural rearrangement across p E 50 MPa at ambient temperature.

Intermolecular interactions, ion solvation, and association in mixtures of 1‐n‐butyl‐3‐methylimidazolium hexafluorophosphate and γ‐butyrolactone: insights from Raman spectroscopy

“…e . enhancing denser packing and interactions with larger number of neighboring cations . We note that there was no higher wavenumber minor contribution observed in contrast to the results of Chaurasia et al .…”

“…Literature data suggest that the P―F symmetrical stretching vibration of PF 6 − anion is rather sensitive to changes in the symmetry of the microenvironment upon changing the polarity of the solvent used to dilute IL and to the structural pattern of H‐bonding interactions whose changes may be induced by applying high pressure to neat IL . In the mixtures of BmimBF 4 with water a slight blueshift in the Raman spectra of a similar symmetric B―F stretching of anion was observed upon dilution of the IL.…”

“…The 741 cm −1 band was shown to be rather sensitive to the interionic interactions both in IR and in Raman and was thus selected for consideration in the present study. At the same time the 931 cm −1 band is known to be insensitive to the intermolecular interactions, and it was used in the normalization procedure for the 2DCoS analysis.…”

Local structures of ionic liquids in the presence of gold under high pressures

“…Studies have shown the potential significant effect that pressure has on probing the nature of microscopic structures of ionic liquids. 30 Su et al 31 and Russina et al 32 6 ] experienced a liquid-solid phase transition at about 0.5 GPa. Under high pressures, the relative weights of the intermolecular forces defining the aggregation state are altered, and the repulsive side of the intermolecular side of the intermolecular potential is explored.…”

Heterogeneity of propyl-ammonium nitrate solid phases obtained under high pressure

“…With this purpose, aprotic ILs have been studied under high pressure for several years [15][16][17][18][19][20]. On the contrary, studies about the effect of high pressure on PILs started to appear in the literature only a few years ago [12][13][14]21].…”