Substitution of indium for chromium in TlIn5-x Cr x Se8: crystal structure of TlIn4.811(5)Cr0.189(5)Se8.

The new thallium penta-(indium/chromium) octa-selenide, TlIn4.811(5)Cr0.189(5)Se8, has been synthesized by solid-state reaction. It crystallizes isotypically with TlIn5Se8 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 InSe6 octa-hedra, and (In,Cr)Se6 octa-hedra and InSe4 tetra-hedra 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.