Phase transition and switchable dielectric behaviours in an organic-inorganic hybrid compound: (3-nitroanilinium)(18-crown-6)(HPO)(HPO)(HO).

An organic-inorganic hybrid compound with an extensive three-dimensional (3D) crystal structure, (3-nitroanilinium)(18-crown-6)(HPO)(HPO)(HO) (), was synthesized under slow evaporation conditions. Differential scanning calorimetry measurements indicated that underwent a reversible phase transition at 231 K with a hysteresis width of 10 K. Variable-temperature X-ray single-crystal diffraction revealed that the phase transition of 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.