3D Perovskite (1,5-3.2.2-H<sub>2</sub>dabcn)CsBr<sub>3</sub> with Reverse Symmetry Breaking
Pan Wang, Mengxia Zhang, Zhenhong Wei, Wenqing Du, Ziqin Peng, Hu Cai
Abstract
Even though hybrid organic–inorganic perovskites (HOIPs) have been studied by many scholars in recent years, there are not many reports on three-dimensional (3D) alkali metal cesium halide perovskites. Here, we report an unprecedented 3D HOIP molecule (1,5-3.2.2-H2dabcn)CsBr3 (1), in which the 3D anionic framework is constructed by corner-sharing CsBr6 octahedra and organic cations [1,5-3.2.2-H2dabcn]2+ are located in the cavities formed by the octahedra. Organic cations interact with an inorganic metal frame via two N–H···Br hydrogen bonds. Compound 1 undergoes a reversible order–disorder phase transition and exhibits switchable dielectric and second-harmonic generation (SHG) properties. Interestingly, product 1 crystallizes in a non-centrosymmetric space group Pmn21 at the low-temperature phase (LTP) and transforms into a centrosymmetric space group P2/m at the high-temperature phase (HTP). The space group Pmn21 in the LTP has a higher symmetry than P2/m in the HTP. This inverted symmetry breaking is very unusual.