Phase Transitions, Crystal Structures, and Magnetic Properties of Ferrocenium Ionic Plastic Crystals with CF3BF3 and Other Anions

Abstract

AbstractSalts of cationic sandwich complexes often exhibit an ionic plastic phase; however, only a few exhibit a plastic phase at room temperature. To explore the use of the CF3BF3 anion to lower the transition temperature to the plastic phase, we prepared salts of CF3BF3 with various ferrocene derivatives, [D][CF3BF3] (D=FeCp*2, Fe(C5Me4H)2, Fe(C5H4Me)2, FeCp(C5H4Me), FeCp2; Cp*=C5Me5, Cp=C5H5). Although [FeCp*2][CF3BF3] exhibited a plastic phase above 417 K, the other salts formed room‐temperature ionic plastic crystals with a phase transition to the plastic phase in the range 266–291 K. The crystal structure and thermal properties of [FeCp2][OTf] were elucidated for comparison. In addition, decamethylferrocenium salts with other anions were synthesized and structurally characterized: [FeCp*2][X] (X=N(SO2F)2 and B(CN)4) exhibited a phase transition to the plastic phase above 400 K, whereas carborane‐containing salts [FeCp*2]2[B12F12] and [FeCp*2][Co(C2B9H11)2] did not exhibit a plastic phase.