High-pressure conformational and crystal polymorphs in 1-hexyl-3-methy- limidazolium perfluorobutanesulfonate ionic liquid

An ionic liquid (IL) with conformational polymorphs indicated complicated phase transitions under high pres-sure (HP). The IL was 1-hexyl-3-methylimidazolium perfluorobutanesulfonate ([C6mim][PFBS]), which has cationic and anionic conformational degrees of freedom. Using HP Raman spectroscopy, a competition between cation and anion conformers corresponded to the HP crystal polymorph. The folding cation appeared at 3.7 GPa due to its flexibility. The rigid [PFBS]- anion also formed the gauche' conformer at 7.6 GPa for higher packing efficiency. The conformational flexibility was adjusted depending on pressure. The pressure-variant/invariant conformations were connected with the HP crystal polymorph of [C6mim][PFBS].

Automated summary

The ionic liquid [C6mim][PFBS] exhibited complicated phase transitions under high pressure, which were studied using high pressure Raman spectroscopy. The competition between cation and anion conformers determined the crystal polymorph of [C6mim][PFBS]. The flexible folding cation appeared at 3.7 GPa, while the rigid [PFBS]- anion formed the gauche' conformer at 7.6 GPa for higher packing efficiency.