The structure and dielectric properties of ionic compounds with flexible ammonium moiety

Phase transition and switchable dielectric behaviours in an organic-inorganic hybrid compound: (3-nitroanilinium)2(18-crown-6)2(H2PO4)2(H3PO4)3(H2O)

An organic-inorganic hybrid compound with an extensive three-dimensional (3D) crystal structure, (3-nitroanilinium)₂(18-crown-6)₂(H₂PO₄)₂(H₃PO₄)₃(H₂O) (1), was synthesized under slow evaporation conditions. Differential scanning calorimetry measurements indicated that 1 underwent a reversible phase transition at ca 231 K with a hysteresis width of 10 K. Variable-temperature X-ray single-crystal diffraction revealed that the phase transition of 1 can be ascribed to coupling of pendulum-like motions of its nitro group with proton transfer in O-H···O hydrogen bonds of the 3D framework. The temperature dependence of its dielectric permittivity demonstrated a step-like change in the range of 150-280 K with remarkable dielectric anisotropy, making 1 a promising switchable dielectric material. Potential energy calculations further supported the possibility of dynamic motion of the cationic nitro group. Overall, our findings may inspire the development of other switchable dielectric phase transition materials by introducing inorganic anions into organic-inorganic hybrid systems.

[C6 H14 N]PbBr3 : An ABX3 -Type Semiconducting Perovskite Hybrid with Above-Room-Temperature Phase Transition

Organic-inorganic hybrid perovskites, with the formula ABX₃ (A=organic cation, B=metal cation, and X=halide; for example, CH₃ NH₃ PbI₃ ), have diverse and intriguing physical properties, such as semiconduction, phase transitions, and optical properties. Herein, a new ABX₃ -type semiconducting perovskite-like hybrid, (hexamethyleneimine)PbBr₃ (1), consisting of one-dimensional inorganic frameworks and cyclic organic cations, is reported. Notably, the inorganic moiety of 1 adopts a perovskite-like architecture and forms infinite columns composed of face-sharing PbBr₆ octahedra. Strikingly, the organic cation exhibits a highly flexible molecular configuration, which triggers an above-room-temperature phase transition, at T_c =338.8 K; this is confirmed by differential scanning calorimetry (DSC), specific heat capacity (C_p ), and dielectric measurements. Further structural analysis reveals that the phase transition originates from the molecular configurational distortion of the organic cations coupled with small-angle reorientation of the PbBr₆ octahedra inside the inorganic components. Moreover, temperature-dependent conductivity and UV/Vis absorption measurements reveal that 1 also displays semiconducting behavior below T_c . It is believed that this work will pave a potential way to design multifeatured perovskite hybrids by utilizing cyclic organic amines.

Exceptional bi-step switching of quadratic nonlinear optical properties in a one-dimensional channel compound

A new solid-state channel compound shows exceptional bi-step switching between three distinct nonlinear optical states.