Synthesis, Crystal Structure, and Optical Properties of a New Quaternary Tin Polychalcogenide K2BaSnSe5

One new quaternary tin polychalcogenide K2BaSnSe5 has been synthesized by high temperature solid‐state reaction. It crystallizes in the centrosymmetric space group P21/c of the monoclinic system with cell constants a = 11.948(2) Å, b = 10.367(2) Å, c = 9.2902(19) Å, β = 91.33(3)°, and V = 1150.4(4) Å3. The compound features an interesting zero‐dimensional structure consisting of SnSe5 units, made up of SnSe4 tetrahedra and [Se2] unit, with K+, Ba2+ cations locating in the interstitial sites for charge‐balance. Diffuse reflectance spectrum indicates semiconducting property with an optical band gap of 1.45 eV. Theoretical calculations demonstrate that the band gap of the title compound is determined by [SnSe5] units, and the title compound has a large birefringence of 0.28 at wavelength 1.06 . which implies that K2BaSnSe5 may be an intriguing photoelectronic material.