More than 3900 crystalline borates, including borate minerals and synthetic inorganic borates, in addition to a wealth of industrially-important boron-containing glasses, have been discovered and characterized. Of these compounds, 99.9 % contain only the traditional triangular BO₃ and tetrahedral BO₄ units, which polymerize into superstructural motifs. Herein, a mixed metal K₅Ba₂(B₁₀O₁₇)₂(BO₂) with linear BO₂ structural units was obtained, pushing the boundaries of structural diversity and providing a direct strategy toward the maximum thresholds of birefringence for optical materials design. ¹¹B solid-state nuclear magnetic resonance (NMR) is a ubiquitous tool in the study of glasses and optical materials; here, density functional theory-based NMR crystallography guided the direct characterization of BO₂ structural units. The full anisotropic shift and quadrupolar tensors of linear BO₂ were extracted from K₅Ba₂(B₁₀O₁₇)₂(BO₂) containing BO₂, BO₃, and BO₄ and serve as guides to the identification of this powerful moiety in future and, potentially, previously-characterized borate minerals, ceramics, and glasses.

除大量工业上重要的含硼玻璃外，还发现并鉴定了3900多种结晶硼酸盐，包括硼酸盐矿物和合成无机硼酸盐。在这些化合物中，99.9％仅包含传统的三角形BO ₃和四面体BO ₄单元，它们聚合成超结构基序。在此，获得了具有线性BO ₂结构单元的混合金属K ₅ Ba ₂（B ₁₀ O ₁₇）₂（BO ₂），推动了结构多样性的边界，并为光学材料设计的双折射最大阈值提供了直接策略。 。¹¹ B固态核磁共振（NMR）是研究玻璃和光学材料的普遍工具。在这里，基于密度泛函理论的NMR晶体学指导了BO ₂结构单元的直接表征。从含有BO ₂，BO ₃和BO _4的K ₅ Ba ₂（B ₁₀ O ₁₇）₂（BO ₂）中提取线性BO ₂的全各向异性张量和四极张量，并用作鉴定该有力部分的指南将来，以及以前表征过的硼酸盐矿物，陶瓷和玻璃。