Regulating Reversible Phase Transition Behaviors by Poly-H/F Substitution in Hybrid Perovskite-Like 2[CHFCHNH]·[CdCl].

The molecular design and regulation has shown bright future for constructing smart molecular materials such as ferroelectrics, dielectric switches, electro-optic effect, and so forth. Here, by poly-H/F substitution in a simple organic-inorganic hybrid 2[CHFCHNH]·[CdCl], (CHFCHNH = fluorine ethylamine cation), we obtained two novel hybrids, namely, 2[CHFCHNH]·[CdCl], (CHFCHNH = 2,2'-difluorine ethylamine cation) and 2[CFCHNH]·[CdCl], (CFCHNH = 2,2',2″-trifluorine ethylamine cation). Further investigations show that compounds , , and experience solid reversible phase transitions with temperatures at 294, 319, and 329 K respectively. These unique phase transitions were confirmed by their remarkable dielectric and heat anomalies around the phase transition temperatures. X-ray single-crystal diffraction analyses before and after the phase transitions show that the order-disorder motions of F atoms and the twist motions from the 2D [CdCl] framework lead to these solid reversible phase transitions. Also, the Hirshfeld surface calculation of compounds , , and suggests that the increasing ratio of the F···F interaction from the intermolecular interaction makes a major contribution for the substantial increase of their phase transition temperatures.