Novel cyclic sulfonium-based ionic liquids: Synthesis, characterization, and physicochemical properties

A new series of ionic liquids composed of three cyclic sulfonium cations and four anions has been synthesized and characterized. Their physicochemical properties, including their spectroscopic characteristics, ion cluster behavior, surface properties, phase transitions, thermal stability, density, viscosity, refractive index, tribological properties, ion conductivity, and electrochemical window have been comprehensively studied. Eight of these salts are liquids at room temperature, at which some salts based on [NO₃]^- and [NTf₂]^- ions exhibit organic plastic crystal behaviors, and all the saccharin-based salts display relatively high refractive indices (1.442-1.594). In addition, some ionic liquids with the [NTf₂] ^- ion exhibit peculiar spectroscopic characteristics in FTIR and UV/Vis regions, whilst those salts based on the [DCA]^- ion show lower viscosities (34.2-62.6 mPa s at 20°C) and much higher conductivities (7.6-17.6 mS cm^-1 at 20°C) than most traditional 1,3-dialkylimidazolium salts.