Phase Transitions, Crystal Structures, and Magnetic Properties of Ferrocenium Ionic Plastic Crystals with CF 3 BF 3 and Other Anions

Salts 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 CF 3 BF 3 anion to lower the transition temperature to the plastic phase, we prepared salts of CF 3 BF 3 with various ferrocene derivatives, [D][CF 3 BF 3 ] (D=FeCp* 2 , Fe(C 5 Me 4 H) 2 , Fe(C 5 H 4 Me) 2 , FeCp(C 5 H 4 Me), FeCp 2 ; Cp*=C 5 Me 5 , Cp=C 5 H 5 ). Although [FeCp* 2 ][CF 3 BF 3 ] 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 [FeCp 2 ][OTf] were elucidated for comparison. In addition, decamethylferrocenium salts with other anions were synthesized and structurally characterized: [FeCp* 2 ][X] (X=N(SO 2 F) 2 and B(CN) 4 ) exhibited a phase transition to the plastic phase above 400 K, whereas carborane‐containing salts [FeCp* 2 ] 2 [B 12 F 12 ] and [FeCp* 2 ][Co(C 2 B 9 H 11 ) 2 ] did not exhibit a plastic phase.