High-Temperature Reversible Phase-Transition Behavior, Switchable Dielectric and Second Harmonic Generation Response of Two Homochiral Crown Ether Clathrates

The solid reversible phase transitions of crystalline materials have been widely applied in ferroelectrics, nonlinear optical materials and dielectric switches, however high-temperature phase transition materials with multi-function are rare and have attracted much attention for their higher practical value. Here we report two new crown ether clathrates, [Han-(18-crown-6)](+)[ClO4](-) (1) and [Han-(18-crown-6)](+)[BF4](-) (2) (Han=protonated aniline), which undergo reversible phase transition at approximately 338 K. The single-crystal structures show that compounds 1 and 2 belong to the homochiral space group P2(1)2(1)2(1) at room temperature. The rotation of protonated aniline cations and the order-disordered motions of both 18-crown-6 crown host molecules and perchlorate (tetrafluoroborate) guest anions induce the reversible phase transition. Both compounds display switchable dielectric, heat anomalies and second harmonic generation (SHG) response around 338 K, further confirming the reversible phase transition behavior.