Rb2SeOCl4·H2O: a polar material among the alkali metal selenite halides with a strong SHG response
An alkali metal selenite chloride, Rb2SeOCl4·H2O, has been hydrothermally synthesized and structurally characterized. It is the first example of an alkali metal selenite halide in the literature. The compound crystallizes in the noncentrosymmetric (NCS) space group, Cmc21(36), of the orthorhombic system with a = 10.342(3) Å, b = 10.124(3) Å, c = 9.158(3) Å, and α = β = γ = 90°. The anionic [SeOCl4]2− groups are arranged in the crystal in nearly the same direction, giving rise to a relatively large macroscopic dipole moment, causing the compound to display second harmonic generation (SHG) eight times as strong as that of KDP, measured using the Kurtz–Perry method on powders. First-principle density functional theory (DFT) calculations were carried out to interpret the relationship between the crystal structure and properties.