SrB₅O₇F₃ Functionalized with [B₅O₉F₃]⁶⁻ Chromophores: Accelerating the Rational Design of Deep‐Ultraviolet Nonlinear Optical Materials

Fluorooxoborates, benefiting from the large optical band gap, high anisotropy, and ever-greater possibility to form non-centrosymmetric structures activated by the large polarization of [BO_x F_4-x ]^(x+1)- building blocks, have been considered as the new fertile fields for searching the ultraviolet (UV) and deep-UV nonlinear optical (NLO) materials. Herein, we report the first asymmetric alkaline-earth metal fluorooxoborate SrB₅ O₇ F₃ , which is rationally designed by taking the classic Sr₂ Be₂ B₂ O₇ (SBBO) as a maternal structure. Its [B₅ O₉ F₃ ]^6- fundamental building block with near-planar configuration composed by two edge-sharing [B₃ O₆ F₂ ]^5- rings in SrB₅ O₇ F₃ has not been reported in any other borates. Solid state ¹⁹ F and ¹¹ B magic-angle spinning NMR spectroscopy verifies the presence of covalent B-F bonds in SrB₅ O₇ F₃ . Property characterizations reveal that SrB₅ O₇ F₃ possesses the optical properties required for deep-UV NLO applications, which make SrB₅ O₇ F₃ a promising crystal that could produce deep-UV coherent light by the direct SHG process.