Symmetry Breaking Phase Transition, Second-Order Nonlinear Optical and Dielectric Properties of a One-Dimensional Organic–Inorganic Hybrid Zigzag Chain Compound [NH₃(CH₂)₅NH₃]SbBr₅

A new one-dimensional organic–inorganic material, 1,5-pentanediammonium pentabromoantimonate (III) ( 1 ), exhibits a centrosymmetric-to-non-centrosymmetric symmetry breaking phase transition at 366.5 K, showing a prominent second harmonic generation (SHG) response and dielectric anomalies. The differential scanning calorimetry results indicate the phase transition is a second-order one. The variable-temperature structural analyses reveal that the space group changes from Pnma at 393 K in the high-temperature phase to P 2 1 2 1 2 1 at 293 K in the low-temperature phase, accompanied by the loss of a symmetry plane and inversion center. The crystal structure is composed of one-dimensional zigzag chains of corner-sharing SbBr 6 octahedra and 1,5-pentanediammonium cations. The origin of the phase transition can be attributed to both the deformation of the zigzag chains and the order–disorder transition of the 1,5-pentanediammonium cations. The compound is SHG-active below the transition temperature, demonstrating its second-order nonlinear optical properties. It is also SHG-inactive above the transition temperature, which further confirms the symmetry breaking phenomenon. These findings will pave a new way to explore organic–inorganic multifunctional phase transition material.