Ba ₅ Zn ₄ (B ₃ O ₆ ) ₂ (B ₁₂ O ₂₄ ): A Borate with Edge-Sharing [BO ₄ ] Tetrahedral Connection by Introducing Zn into β-BaB ₂ O ₄

The edge-sharing connection mode of [BO₄] tetrahedra has greatly enriched the structural chemistry of borates, which provides more options and possibilities for designing more materials with unique structures and excellent performance. A zinc borate Ba₅Zn₄(B₃O₆)₂(B₁₂O₂₄) (BaZnBO) was synthesized via a high-temperature solid reaction. Its uniqueness lies in not only introducing Zn into the structure of β-BaB₂O₄ but also containing the unusual edge-sharing [BO₄] tetrahedra. The functional building units are isolated [B₃O₆] and [B₁₂O₂₄] groups. The adjacent [B₃O₆] groups are linked to a layer in the ab plane and further stack along the [001] direction, while the [B₁₂O₂₄] groups are located in the middle of these layers, thus forming the "sandwich" structure. This work also analyzed the impact of introducing Zn into β-BaB₂O₄ on the structure of anions. In addition, BaZnBO also exhibits good thermal stability and excellent optical properties including the short cut-off edge (204 nm) and suitable birefringence (0.058@1064 nm).