Four new chalcohalides, NaBa2SnS4Cl, KBa2SnS4Cl, KBa2SnS4Br and CsBa2SnS4Cl: Syntheses, crystal structures and optical properties

Abstract

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 2.06eV, respectively.