Switchable Dielectric Phase Transition Triggered by Pendulum-Like Motion in an Ionic Co-crystal

Molecular-based ionic co-crystals, which have the merits of low-cost/easy fabrication processes and flexible structure and functionality, have already exhibited tremendous potential in molecular memory switches and other electric devices. However, dipole (ON/OFF switching) triggering is a huge challenge. Here, we introduce a pendulum-like dynamic strategy to induce the order-disorder transition of a co-crystal [C5H7N3Cl](3)[Sb2Br9] (compound 1). Here, the anion and cation act as a stator and a pendulum-like rotor (the source of the dielectric switch), respectively. The temperature-dependent dielectric and differential scanning calorimetry (DSC) analyses reveal that 1 undergoes a reversible phase transition, which stems from the order-disorder transition of the cations. The thermal ON/OFF switchable motions make 1 a promising candidate to promote the development of bulk crystals as artificial intelligent dielectric materials. In addition, the pendulum-like molecular dynamics and distinct arrangements of two coexisting ions with a notable offset effect promotes/hinders dipolar reorientation after dielectric transition and provides a rarely observed but fairly useful and feasible strategy for understanding and modulating the dipole motion in crystalline electrically polarizable materials.