Fluorine‐Driven Chemical Scissor Effect in Scandium Borates: Structural Evolution with Retained Optically Active Motifs

Comprehensive Summary Structural design plays a pivotal role in the development of borate optical materials. In this work, fluorine acts as a "chemical scissor" to drive the continuous evolution of Sc‐centered coordination polyhedra, and under this scissor's precise steering, three novel rare‐earth scandium borate (fluoride) crystals, RbBaSc(BO 3 ) 2 , RbBaSc(B 2 O 5 )F 2 and Ba 3 Sc 2 (BO 3 ) 2 (B 2 O 5 )F 2 , were rationally designed and synthesized via high‐temperature solid‐phase synthesis. Structural analysis reveals a two‐step structural iteration process of the Sc‐centered polyhedra from [ScO 6 ] to [ScO 4 F 2 ] and finally to [ScO 5 F], while the favorable alignment of birefringence‐active B–O motifs is retained in the final ordered phase. Notably, Ba 3 Sc 2 (BO 3 ) 2 (B 2 O 5 )F 2 exhibits a UV cutoff edge below 200 nm and a calculated birefringence of 0.078 at 546 nm, demonstrating how the fluorine‐driven evolution of Sc‐centered polyhedra effectively enhances optical anisotropy while preserving deep‐UV transparency. This work provides strong structural evidence for understanding fluorination‐driven coordination reconstruction and framework evolution in borate optical materials.