Cation-anion synergetic interactions achieving tunable birefringence in quasi-one-dimensional antimony(III) fluoride oxalates

Birefringent materials with large optical anisotropy, which can be used to modulate the polarization of light, play a key role in laser techniques and science. However, exploration studies new, superior birefringent develop extremely slowly due lack effective guidelines for rational design. Herein, three antimony(III) fluoride oxalates, namely, Na2Sb2(C2O4)F6, K2Sb2(C2O4)F6, Cs2Sb2-(C2O4)2F4·H2O, were successfully synthesized through combination π-conjugated C2O42− anions Sb3+ cations stereochemically active lone pairs. These oxalates feature unique quasi-one-dimensional chain structures that induce anisotropy. Remarkably, Cs2Sb2(C2O4)2-F4·H2O exhibits largest birefringence (0.325@546 nm) among all reported antimony(III)-based oxysalts. Detailed structural analysis theoretical calculations confirmed anisotropy these could tuned synergetic interactions templated anionic functional groups. This work may open door efficiently designing excellent guide further discovery other novel structure-driven materials.