Hg₃(SeO₃)₂(SO₄): A UV Nonlinear Optical Mercury Selenite Sulfate Constructed by Neat [Hg₆O₈(SeO₃)₄] Layers and SO₄ Tetrahedra

The first noncentrosymmetric mercuryselenite sulfate Hg-3(SeO3)(2)(SO4) was designedand synthesized successfully, which exhibits excellent comprehensiveproperties of large SHG response, moderate birefringence, and wideband gap. A novel mercury selenite sulfate named Hg-3(SeO3)(2)(SO4) has been successfullysynthesized undera mild hydrothermal method. Hg-3(SeO3)(2)(SO4) crystallizes in a monoclinic space group P2(1) and features a unique three-dimensional (3D)frame structure formed by [Hg6O8(SeO3)(4)](infinity) layers and SO4 tetrahedra,which enables it to exhibit a comprehensive performance of a moderatesecond-harmonic generation (SHG) response of approximately 1.3 timesthat of baseline KH2PO4 (KDP), a moderate birefringence(0.118@546 nm), and a wide band gap (4.70 eV), which indicates thatit has potential for application as an ultraviolet (UV) nonlinearoptical material. Detailed theoretical calculations show that theHg(2+)-based polyhedra with large polarizability and deformabilityand the SeO3 groups with stereochemically active lone pair(SCALP) electrons are the main contributors to moderate optical properties.