Cation-tuned synthesis of the A₂SO₄·SbF₃ (A = Na⁺, NH₄⁺, K⁺, Rb⁺) family with nonlinear optical properties

Four antimony fluoride sulfates named A₂SO₄·SbF₃ (A = Na⁺, NH₄⁺, K⁺, Rb⁺) have been successfully synthesized using a hydrothermal method by introducing Sb³⁺ cations with a stereochemically active lone pair in sulfates and subsequently tuning the structure through the second monovalent cations. All of the title compounds are stoichiometrically equivalent materials which share a common structural motif composed of a distorted SO₄ tetrahedron and an asymmetric SbF₃ polyhedron. However, the macroscopic centricities of these four compounds are significantly influenced by the size and coordination environment of cations; Na₂SO₄·SbF₃ crystallizes in centrosymmetric space groups Cmca and (NH₄)₂SO₄·SbF₃ in Pbca, while K₂SO₄·SbF₃ and Rb₂SO₄·SbF₃ crystallizes in noncentrosymmetric space group P2₁2₁2₁. Complete characterization including thermal analyses, infrared and UV-vis spectroscopy, and theoretical calculations is also reported. Powder second harmonic generation measurement for noncentrosymmetric K₂SO₄·SbF₃ and Rb₂SO₄·SbF₃ indicated that both of them are type I phase-matchable.