Hydroxyfluorooxoborate Na[B3O3F2(OH)2]⋅[B(OH)3]: Optimizing the Optical Anisotropy with Heteroanionic Units for Deep Ultraviolet Birefringent Crystals

• Published in: Angewandte Chemie 2021-09, Vol.133 (37), p.20632-20638
• Main Authors: Jin, Congcong, Shi, Xuping, Zeng, Hao, Han, Shujuan, Chen, Zhen, Yang, Zhihua, Mutailipu, Miriding, Pan, Shilie
• Format: Article
• Language: English
• Subjects: Anions; Anisotropy; Birefringence; birefringent material; borate; Boric acid; Chemistry; Crystals; deep-ultraviolet; Extreme values; heteroanionic unit; hydroxyfluorooxoborate; Optimization; Polarized light; Sodium; Ultraviolet radiation
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.202107291

Maximizing the optical anisotropy in birefringent materials has emerged as an efficient route for modulating the polarization‐dependent light propagation. Currently, the generation of deep‐ultraviolet (deep‐UV) polarized light below 200 nm is essential but challenging due to the interdisciplinary significance and insufficiency of high‐performing birefringent crystals. Herein, by introducing multiple heteroanionic units, the first sodium difluorodihydroxytriborate‐boric acid Na[B3O3F2(OH)2]⋅[B(OH)3] has been characterized as a novel deep‐UV birefringent crystal. Two rare heteroanionic units, [B3O3F2(OH)2] and [B(OH)3], optimally align to induce large optical anisotropy and also the dangling bonds are eliminated with hydrogens, which results in an extremely large birefringence and band gap. The well‐ordered OH/F anions in [B3O3F2(OH)2] and [B(OH)3] were identified and confirmed by various approaches, and also the origin of large birefringence was theoretically discussed. These results confirm the feasibility of utilizing hydrogen involved heteroanionic units to design crystals with large birefringence, and also expand the alternative system of deep‐UV birefringent crystals with new hydroxyfluorooxoborates. The first sodium hydroxyfluorooxoborate Na[B3O3F2(OH)2]⋅[B(OH)3] has been characterized as a new deep‐UV birefringent crystal. Two rare heteroanionic units, [B3O3F2(OH)2] and [B(OH)3], are optimally aligned to induce large optical anisotropy and also the dangling bonds are eliminated with O−H bonds, which makes Na[B3O3F2(OH)2]⋅[B(OH)3] have a large birefringence and band gap.