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

Abstract

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.