N‐Butyl Pyridinium Chlorobismuthates (III): A Soft Organic‐Inorganic Hybrid Transparent Solid‐State Ion Conductor

Abstract Transparent solid‐state ionic conductors are emerging as next‐generation materials for various modern optoelectronics and energy applications. In this study, an organic‐inorganic hybrid metal halide is introduced, tris‐N‐butyl pyridinium nonachlorido‐dibismuthate(III), (C4py)3[Bi2Cl9]. The material is an optically transparent solid‐state ion conductor with high ionic conductivity at room temperature. Single crystal analysis reveals a structure composed of N‐butyl pyridinium cations and [Bi2Cl9]3− anions, formed by edge‐sharing BiCl6 octahedra. The material is thermally stable up to 300 °C and undergoes a melting transition at 101.6 °C. Notably, it demonstrates unidirectional growth in thin films, boasting over 90% optical transparency in the visible wavelength and overall ionic conductivity of 10−3 mS cm−1 at room temperature. (C4py)3[Bi2Cl9] stands out as one of the first reported low‐melting, optically transparent ionic solids, showcasing superior ion conduction and holding promise for applications such as electrochromic devices and energy storage.