The new semiconducting polychalcogenide Ba2SnSe5 exhibiting image units and distorted SnSe6 octahedra

The new polyselenide Ba2SnSe5 was prepared from the elements under exclusion of air at temperatures between 650 and 750 °C. Ba2SnSe5 crystallizes in the orthorhombic space group P212121, with the lattice parameters of image, image, image, image (image). Its structure comprises nonlinear image trimers, isolated SnSe4 tetrahedra and trimeric Sn3Se10 units, the latter consisting of a central (distorted) SnSe6 octahedron sharing two opposite basal edges with two SnSe4 tetrahedra. The structural differences to its Sr and Te analogs, Sr2SnSe5 and both modifications of Ba2SnTe5, are intriguing, and illustrated in detail in this article. Ba2SnSe5 is a dark brown semiconductor with a computed band gap of 1.2 eV.