Thermal properties, crystal structures, and phase diagrams of ionic plastic crystals and ionic liquids containing a chiral cationic sandwich complex

Abstract

To investigate the effects of chirality on the phase behavior of ionic plastic crystals and ionic liquids, salts of a chiral sandwich complex with various anions were synthesized. The synthesized salts have the general chemical formula [Ru(C₅H₅)(C₆H₅CHCH₃OCH₃)]X (X = CB₁₁H₁₂, CF₃BF₃, PF₆, CPFSA (= CF₂(SO₂CF₂)₂N)), where the ruthenium complex possesses a chiral substituent. The racemates of the salts with the CB₁₁H₁₂, CF₃BF₃, and PF₆ anions crystallized as a solid solution, racemic compound, and conglomerate, respectively. The (S)-enantiomer and the racemate of the CB₁₁H₁₂ salt exhibited phase transitions to the ionic plastic phase and melted at high temperatures. Further, this salt exhibited polymorphism, as crystallographically investigated. Most of the other salts were ionic liquids exhibiting no plastic phase. The CPFSA salt was liquid and exhibited glass transition at low temperatures.