Thermal Responsive Cation Flipping and Dielectric Constant in an Organic-Inorganic Hybrid Crystal

Abstract

Controllable molecular motion in densely packed crystals is essential for dynamic functional materials but is often hindered by spatial constraints and restrictive strong intermolecular interactions. We report an organic-inorganic hybrid compound (PrMeNC4H8)2[ZnBr4] (1), which undergoes a reversible structural phase transition at 313 K, driven by the flipping motion of a crystallographically independent (PrMeNC4H8)+ cation, as revealed by the structural analysis, molecular dynamics simulation and dielectric measurement. The N2-containing cation, which flips within a smaller accessible space compared to the N1-containing cation, is predominantly surrounded by non-directional C–H···H–C van der Waals contacts that provide a flexible microenvironment for reorientation, while the N1-containing cation is constrained by a higher proportion of directional C–H···Br hydrogen bonds that imposing stronger spatial restrictions. Our findings provide impetus for developing dynamic crystalline materials with tunable dielectric switching near room temperature, which is attractive for switchable dielectric devices and related applications.