Hg 3 (SeO 3 ) 2 (SO 4 ): A UV Nonlinear Optical Mercury Selenite Sulfate Constructed by Neat [Hg 6 O 8 (SeO 3 ) 4 ] ∞ Layers and SO 4 Tetrahedra.

A novel mercury selenite sulfate named Hg 3 (SeO 3 ) 2 (SO 4 ) has been successfully synthesized under a mild hydrothermal method. Hg 3 (SeO 3 ) 2 (SO 4 ) crystallizes in a monoclinic space group P 2 1 and features a unique three-dimensional (3D) frame structure formed by [Hg 6 O 8 (SeO 3 ) 4 ] ∞ layers and SO 4 tetrahedra, which enables it to exhibit a comprehensive performance of a moderate second-harmonic generation (SHG) response of approximately 1.3 times that of baseline KH 2 PO 4 (KDP), a moderate birefringence (0.118@546 nm), and a wide band gap (4.70 eV), which indicates that it has potential for application as an ultraviolet (UV) nonlinear optical material. Detailed theoretical calculations show that the Hg 2+ -based polyhedra with large polarizability and deformability and the SeO 3 groups with stereochemically active lone pair (SCALP) electrons are the main contributors to moderate optical properties.