An Antimony(III) Fluoride Oxalate with Large Birefringence

• Published in: Chemistry : a European journal Vol. 27; no. 14; pp. 4557 - 4560
• Main Authors: Chen, Yangxin, Chen, Zhangxian, Zhou, Yang, Li, Yanqiang, Liu, Youchao, Ding, Qingran, Chen, Xin, Zhao, Sangen, Luo, Junhua
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 08-03-2021
• Subjects: Anions; Antimony; Antimony fluorides; Birefringence; birefringent materials; Cations; Chemistry; Crystal structure; Electronegativity; first-principles calculations; Fluorides; Fluorine; Optical communication; oxalates; Oxalic acid; Polyhedra; structure–property relationships; birefringent materials; oxalates; first-principles calculations; structure-property relationships
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202004934

Birefringent materials play a key role in modulating the polarization of light and thus in optical communication as well as in laser techniques and science. Designing new, excellent birefringent materials remains a challenge. In this work, we designed and synthesized the first antimony(III) fluoride oxalate birefringent material, KSb2C2O4F5, by a combination of delocalized π‐conjugated [C2O4]2− groups, stereochemical active Sb3+ cations, and the most electronegative element, fluorine. The [C2O4]2− groups are not in an optimal arrangement in the crystal structure of KSb2C2O4F5; nonetheless, KSb2C2O4F5 exhibits a large birefringence (Δn=0.170 at 546 nm) that is even better than that of the well‐known commercial birefringent material α‐BaB2O4, even though the latter features an optimal arrangement of π‐conjugated [B3O6]3− groups. Based on first‐principles calculations, this prominent birefringence should be attributed to the alliance of planar π‐conjugated [C2O4]2− anions, highly distorted SbO2F2 and SbOF3 polyhedra with a stereochemically active lone pair. The combination of lone‐pair electrons and π‐conjugated systems boosts the birefringence to a large extent and will help the development of high‐performance birefringent materials.
A synergistic combination of different functional groups has led to the first antimony(III) fluoride oxalate material, KSb2C2O4F5, to exhibit a birefringent response (Δn=0.170 at 546 nm); this value is larger than that of the commercial α‐BaB2O4, despite its suboptimal anisotropic structure.