Exceptional Optical Anisotropy Enhancement Achieved Through Dual‐Ions Cosubstitution Strategy in Novel Hybrid Bismuth Halides

Abstract

AbstractGuided by a superb dual‐ions cosubstitution strategy, two novel, highly optically anisotropic hybrid bismuth halides are designed and synthesized. The first compound, Gu3Bi2NO3Cl8 (Gu = C(NH2)3), is developed using the 2D perovskite halide Cs3Bi2Cl9 as the maternal structure. This involved substituting all Cs+ cations with organic Gu+ and replacing some Cl− anions with [NO3]−. Further substitution of Cl− with additional [NO3]− resulted in the formation of nitrate‐rich Gu2Bi(NO3)3Cl2 crystal, exhibiting a 3.4‐fold increase in [NO3]− per unit volume. Both compounds have a structurally 0D nature, comprising bismuth‐centered polyhedra formed by coordinated chlorides and monodentate/bidentate nitrate moieties, with Gu+ serving as a separator and linker. Notably, the presence of superb optically anisotropic dual‐ions, i.e., planar Gu+ and [NO3]−, enables these crystals to possess sharply enhanced optical anisotropy, with birefringence values more than 1 order of magnitude higher than that of the initial crystal Cs3Bi2Cl9 (0.162/0.186vs 0.011 at 546 nm). The discovery and characterization of Gu3Bi2NO3Cl8 and Gu2Bi(NO3)3Cl2 crystals provide new insights into achieving expected modifications in optical properties through the utilization of a dual‐ions cosubstitution strategy.