Properties of new low melting point quaternary ammonium salts with bis(trifluoromethanesulfonyl)imide anion

Eight new monocationic quaternary ammonium (QA) salts with the bis(trifluoromethanesulfonyl)imide (TFSI) anion were prepared by metathesis using our previously reported QA halides as precursors. New salts were characterized both in liquid and solid state using 1H and 13C NMR techniques, mass spectroscopy and elemental analysis together with X-ray diffraction and thermoanalytical methods. In addition, residual water content, viscosity and conductivity measurements were made for three of the room-temperature ionic liquids (RTILs). The crystal structures of three compounds were determined by X-ray single crystal diffraction. Powder diffraction was used to study the crystallinity of the solid salts and to compare structural similarities between the single crystals and the microcrystalline bulk powders. Three of the salts are liquid below room temperature, having broad liquid ranges (∼300 °C), and in total five out of eight salts melt below 100 °C. Moreover, powder diffraction data of the two RTILs were able to be measured at sub-ambient temperatures using in situ low-temperature powder X-ray diffraction revealing high crystallinity on both RTILs below their freezing point. The RTILs presented relatively high conductivities (∼0.1–0.2 S m−1) and moderate to relatively low viscosities. The determined physicochemical properties of the reported ILs suggest their applicability on various applications such as heat transfer fluids, high temperature synthesis and lubricants.