Substitution of indium for chromium in TlIn(5−x)Cr(x)Se(8): crystal structure of TlIn(4.811(5))Cr(0.189(5))Se(8)

The new thallium penta­(indium/chromium) octa­selenide, TlIn(4.811(5))Cr(0.189(5))Se(8), has been synthesized by solid-state reaction. It crystallizes isotypically with TlIn(5)Se(8) in the space group C2/m. Although the two Tl positions are disordered and only partially occupied, no Tl deficiency was observed. The insertion of chromium in the structure has been confirmed by EDS analysis. Chromium substitutes indium exclusively at one of three In sites, viz. at one of the positions with site symmetry 2/m (Wyckoff position 2a). In the crystal structure, edge-sharing InSe(6) octa­hedra, and (In,Cr)Se(6) octa­hedra and InSe(4) tetra­hedra make up two types of columns that are linked into a framework in which two different types of channels parallel to [010] are present. The Tl atoms are located in the larger of the channels, whereas the other, smaller channel remains unoccupied.