The effect of structural modifications on the thermal stability, melting points and ion interactions for a series of tetraaryl-phosphonium-based mesothermal ionic liquidsWe use the term 'mesothermal' to denote ionic liquids that do not necessarily have melting points below 100 °C, but which do melt at temperatures less than those typical of purely inorganic salts, i.e., NaCl (Tm = 801 °C).Electronic supplementary information (ESI) available. See DOI: 10.1039/c7cp06278h

• Main Authors: Cassity, Cody A, Siu, Benjamin, Soltani, Mohammad, McGeehee, Jimmy L, Strickland, Katie J, Vo, Matt, Salter, E. Alan, Stenson, Alexandra C, Wierzbicki, Andrzej, West, Kevin N, Rabideau, Brooks D, Davis, James H
• Format: Article
• Language: English
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c7cp06278h

A family of mesothermal ionic liquids comprised of tetraarylphosphonium cations and the bis(trifluoromethanesulfonyl)amidate anion are shown to be materials of exceptional thermal stability, enduring (without decomposition) heating in air at 300 °C for three months. It is further established that three specific structural elements - phenoxy, phenacyl, and phenyl sulfonyl - can be present in the cation structures without compromising their thermal stability, and that their incorporation has specific impacts on the melting points of the salts. Most importantly, it is shown that the ability of such a structural component to lower a salt melting point is tied to its ability to lower cation-cation repulsions in the material. New mesothermal ionic liquids (left).