Four new chalcohalides, namely NaBa₂SnS₄Cl, KBa₂SnS₄Cl, KBa₂SnS₄Br, and CsBa₂SnS₄Cl, have been synthesized by the conventional high temperature solid-state reactions. They crystallize in three different space groups: space group I4/mcm for NaBa₂SnS₄Cl and KBa₂SnS₄Cl, Pnma for KBa₂SnS₄Br, and P2₁/c for CsBa₂SnS₄Cl. In all four compounds, the X^？ halide anions are only connected to six alkali metal or Ba cations, and the Sn atoms are only tetrahedrally enjoined to four S atoms. However, the M–X–Ba pseudo layers and the SnS₄ tetrahedra are arranged in different ways in the three structural types, which demonstrates the interesting effect of ionic radii on the crystal structures. UV–vis–NIR spectroscopy measurements indicate that NaBa₂SnS₄Cl, KBa₂SnS₄Cl, KBa₂SnS₄Br, and CsBa₂SnS₄Cl have band gaps of 2.28, 2.30, 1.95, and 2.06 eV, respectively. 

Journal of Solid State Chemistry, 2015