Carborane-derivatized low-melting salts with ether-functionalized cations - Preparation and properties

A new series of low-melting ammonium salts based on the [nido-7,8-C ₂B₉H₁₂]^- anion have been synthesized and characterized, and their physicochemical properties including spectroscopic properties, thermal properties, surface properties, solubility, density, viscosity, electrochemical properties, and tribological properties have been studied in detail. In comparison with previously reported carborane-derivatized imidazolium or pyridinium salts, these diether-functionalized ammonium salts display lower phase transition temperatures (T_g = -76 to -57 °C), and four exist as liquids at room temperature due to their flexible alkoxy chains. TGA analysis revealed that the weight loss rates of these carborane-derivatized low-melting salts were ca. 30-80 wt.-% after thermal decomposition, which is different from the traditional RTILs. SEM images showed that the resulting residue had hollow reticular shell morphology, and XPS and XRD analyses indicate that the main components of the skeleton are B ₂O₃ and amorphous carbon. This provides a new strategy for preparing new inorganic porous materials by thermal decomposition of these low-melting salts.