Extending the Chemistry of Scheelite-type Oxides with Borates

Scheelite-type oxides have been extensively investigated in diverse inorganic systems due to their exceptional structural versatility and promising multifunctional properties, ranging from luminescence to ionic conduction. However, despite decades of research, borates have remained conspicuously absent from this important structural family. This exclusion stems from a fundamental synthetic and structure chemistry challenge: the difficulty in achieving the essential zero-dimensional anionic framework composed of isolated tetrahedral units, a defining characteristic of scheelite-type materials. In this work, we break this long-standing barrier by reporting the first successful isolation of [BO₂F₂] tetrahedra in a crystalline solid. This breakthrough was enabled by employing Sb's stereochemically active lone pair electrons to stabilize these discrete [BO₂F₂] units, ultimately leading to the discovery of SbBO₂F₂-the first borate compound adopting a scheelite-type structure. Through a combination of single-crystal X-ray diffraction, spectroscopic techniques, and first-principles calculations, we unequivocally confirm the scheelite-type framework of SbBO₂F₂ and demonstrate its remarkable multifunctional properties, including anisotropic thermal expansion, ionic conductivity, and large birefringence. This work not only expands the structural chemistry of scheelite-type oxides with borates but also opens new avenues for designing multifunctional materials through targeted anionic group isolation.