Tuning Order-Disorder Phase Transition through Regulating the Substituent Group of Anion

The structural phase transition compound {[(CH3)(2)CHCH2](2)NH2}center dot[CF3COO] (1) has been synthesized based on the diisobutylamine and trifluoroacetic acid. The DSC data reveal that 1 undergoes a phase transition at 277 K (T-c). When one chlorine atom replaces one fluorine atom on trifluoroacetate anion, three order-disorder phase transitions at 251 K (T-1), 282 K (T-2) and 290 K could be achieved owing to a stepwise release of rotation motions of the anion and cation in {[(CH3)(2)CHCH2](2)NH2}center dot[CF2ClCOO] (2). Based on the variable temperature crystal structures, the phase transition in compound 1 is triggered by the rotation of three fluorine atoms on the trifluoroacetate anion synchronized with the motions of the methyl groups on the diisobutylammonium cation. However, in compound 2, the phase transitions can be realized by a sequence of motions of both the anion and cation. Besides, the dielectric-temperature dependences were investigated in order to prove this regulation process. All of this investigation will be beneficial to design and synthesis of the novel phase transition materials and molecular dielectric materials on purpose.