Phase transitions and crystal structures of organometallic ionic plastic crystals comprised of ferrocenium cations and CH2BrBF3 anions

Salts of cationic sandwich complexes often exhibit a phase transition to an ionic plastic phase at high temperature. In this study, we synthesized the salts [Fe(C5Me5)2][CH2BrBF3] (1), [Fe(C5Me4H)2][CH2BrBF3] (2), and [Fe(C5H5)2][CH2BrBF3] (3) containing the CH2BrBF3 anion in order to investigate the effect of anion symmetry. These salts underwent phase transitions to a plastic phase at 360.8, 269.9, and 328.8 K; only 2 exhibited a plastic phase below 300 K. Moreover, the crystal structures of the plastic phases and low temperature phases were investigated. The results were discussed and compared with the corresponding CF3BF3 salts.