Two Hydroxyfluorooxoborates Achieving Deep‐Ultraviolet Cutoff Edges and Moderate Birefringence by Assembling Multi‐Anionic Groups

Assembling multi-anionic groups is conducive to utilizing respective advantage to achieve the enhancement of optical performance. Two new hydroxyfluorooxoborates, Ama2-Rb₂B₃O₃F₄(OH) and K₈Cs₂B₁₅O₁₄(OH)₇F₂₀ ⋅ H₂O with [B₃O₃F₄(OH)] six-membered rings were synthesized for the first time. The title compounds exhibit short ultraviolet cutoff edges (<200 nm) and K₈Cs₂B₁₅O₁₄(OH)₇F₂₀ ⋅ H₂O possesses a moderate experimental refractive index difference of 0.051@546 nm.