Low temperature molten salt synthesis of noncentrosymmetric (NH4)3SbF3(NO3)3 and centrosymmetric (NH4)3SbF4(NO3)2

Abstract

Two fluorine antimony nitrates named (NH₄)₃SbF₃(NO₃)₃ and (NH₄)₃SbF₄(NO₃)₂ have been successfully synthesized by a low temperature molten salt method. Although these two title compounds possess NO₃⁻ groups and similar Sb-polyhedra, they exhibit completely different macroscopic centricities, (NH₄)₃SbF₃(NO₃)₃ being noncentrosymmetric while (NH₄)₃SbF₄(NO₃)₂ being centrosymmetric, which is induced by the discrepant coordination environments of Sb³⁺. Interestingly, the noncentrosymmetric (NH₄)₃SbF₃(NO₃)₃ exhibits a strong second harmonic generation response (3.3 × KDP), a large birefringence (0.098@546 nm) and a large band gap (3.77 eV), indicating its potential as a UV nonlinear optical material. Detailed structure–property analysis confirms that the superior optical property is due to the synergistic effect of the planar π-conjugated NO₃⁻ groups and the stereochemically active lone pair containing Sb³⁺ cations.