Alkali Metal Salts with Designable Aryltrifluoroborate Anions

Aryltrifluoroborate ([ArBF3]−) has a designable basic anion structure. Various [ArBF3]−-based anions were synthesized to create novel alkali metal salts using a simple and safe process. Nearly 40 novel alkali metal salts were successfully obtained, and their physicochemical characteristics, particularly their thermal properties, were elucidated. These salts have lower melting points than those of simple inorganic alkali halide salts, such as KCl and LiCl, because of the weaker interactions between the alkali metal cations and the [ArBF3]− anions and the anions’ larger entropy. Moreover, interestingly, potassium cations were electrochemically reduced in the potassium (meta-ethoxyphenyl)­trifluoroborate (K­[m-OEtC6H4BF3]) molten salt at 433 K. These findings contribute substantially to furthering molten salt chemistry, ionic liquid chemistry, and electrochemistry.