Large optical anisotropy differentiation induced by the anion-directed regulation of structures

Exploring excellent ultraviolet (UV) birefringent crystals is of great significance. Herein, two novel UV organic–inorganic hybrid birefringent materials [C(NH2)3]2Sb3F3(HPO3)4 ((Gu)2Sb3F3(HPO3)4) and [C(NH2)3]SbFPO4·H2O ((Gu)SbFPO4·H2O) have been successfully synthesized by a facile hydrothermal reaction. Interestingly, though both the two title compounds exhibit similar 2D layered structures, and possess the same functional moieties including SbO4F square pyramids and C(NH2)3 planar groups, they exhibit significantly different optical anisotropies. (Gu)2Sb3F3(HPO3)4 exhibits a small birefringence of 0.027@546 nm while (Gu)SbFPO4·H2O exhibits a large birefringence of 0.151@546 nm. Detailed structural analysis along with calculations revealed that the large optical anisotropy differentiation originating from the anion-directing regulation structures affects the [HPO3]2− and [PO4]3− anionic groups. This work opens a new door to explore novel high-performance structure-driven functional materials in the future.