A2Sb2SO4F6 (A = NH4+, Na+): two sulfate fluoride crystals exhibiting enhanced birefringence driven by stereochemically active antimony(iii)

Abstract

Two antimony sulfate fluoride birefringent crystals, (NH₄)₂Sb₂SO₄F₆ and Na₂Sb₂SO₄F₆, were successfully synthesized via a mild aqueous solution method. Compared with the alkali metal sulfates, they exhibit enhanced optical anisotropy with calculated birefringence of 0.055 and 0.100 at 1064 nm, respectively, which mainly depend on the stereochemically active [SbO₂F₃] and [SbOF₃] polyhedra.