Borates are one of the rich sources of optical crystals due to their diverse chemical structures and excellent optical properties. The [BO₂]_∞ chain with better optical anisotropy has attracted great interest from scientists in designing ultraviolet optical crystal materials. Currently, one-dimensional infinite chains in borates can be categorized into the following six types: the first one is combined by only [BO₃] units, the second one is combined by only [BO₄] units, the third one is combined by only [BO₂F₂] units, the fourth one is combined by [BO₃], [BO₃F], and [BO₂F₂] motifs, the fifth one is combined by [BO₃] and [BO₄] motifs, and the sixth one is combination of [BO₄] and [BO₃F] motifs (Chem. Rev., 2021, 12, 1130-1202). The exploration of novel one-dimensional chains is of great significance for the discovery of superior optical materials. Besides, studies on the influence of birefringence have mainly focused on the anionic framework, while metal cations with lone pairs, especially trivalent antimony cations, are still less investigated for their influence on birefringence. Although the first example of antimony borate has been discovered for many years, antimony fluorooxoborate with stereochemically active lone pair has not been found so far.

Research Center for Crystal Materials of Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, has been deeply involved in the research of new UV and deep UV optoelectronic functional crystals in borates for a long time. Recently, the researchers have successfully obtained the first single crystal of antimony(III) fluorooxoborate, with the chemical formula SbB₂O₄F, by the high-temperature solution method. For the first time, the researchers have found the seventh one-dimensional chain in the borate system, which is the [B₂O₄F]_∞ chain formed by the combination of [BO₃] and [BO₃F] units. By first-principles calculations, both the distorted antimony-oxygen polyhedra with strong stereochemical activity and the π-conjugated [BO₃] units contribute to birefringence. By combining the [B₂O₄F]_∞ chain with the system based on antimony, the SbB₂O₄F compound is obtained. SbB₂O₄F exhibits a large birefringence (？n = 0.171 @ 1064 nm) and a short UV cutoff edge (220 nm), which makes it a potential UV birefringent material.

The research results were published in Chemical Communications (Chem. Commun. 2024, 60, 2653-2656) with the title of “New antimony fluorooxoborates with strong birefringence and unprecedented structural characterization”. This work was financially supported by the Key Research and Development Program of Xinjiang, West Light Foundation of CAS, National Natural Science Foundation of China, Tianshan Talents, Young Science and Technology Top Talents Project, High-level Professional and Technical Personnel of Xinjiang, Xinjiang Major Science and Technology Project, and International Partnership Program of CAS.

Author List: Chenhui Hu, Mengfan Wu, Jian Han,* Zhihua Yang, Shujuan Han and Shilie Pan*

Article Link: https://doi.org/10.1039/D3CC05784D

Structural figure of borates with 1D B–O/F anionic frameworks and this work