Fluorination Strategy Towards Symmetry Breaking of Boron-centered Tetrahedron for Poly-fluorinated Optical Crystals

Borate crystals can be chemically and functionally modified by the fluorination strategy, which encourages the identification of emerging fluorooxoborates with a structure and set of characteristics not seen in any other oxide parents. However, the bulk of fluorooxoborates have been found accidentally, rational methods of synthesis are required, particularly for the infrequently occurring poly-fluorinated components. Herein, we reported the use of bifluoride salts as a potent source of fluorine to prepare fluorooxoborates that contain rarely tri-fluorinated [BF₃ X] (X=O and CH₃ ) tetrahedra and eleven compounds were found. We identified the optical properties of the organofluorinated group [CH₃ BF₃ ] and their potential for nonlinear optics for the first time. Among these, two non-centrosymmetric components hold potential for the production of 266 nm harmonic coherent light for nonlinear optics, and more crucially, have the benefit of growing large size single crystals. Our study establishes experimental conditions for the coexistence of the diverse functional groups, enabling the production of poly-fluorinated optical crystals.