Two new ternary lanthanide antimony chalcogenides: Yb4Sb2S11.25 and Tm4Sb2Se11.68 containing chalcogenide Q2− and dichalcogenide (Q2)2− anions

Dark red and dark brown crystals of Yb4Sb2S11.25 and Tm8Sb4Se11.68, respectively, were obtained from the reaction of the elements in Sb2Q3 (Q=S, Se) fluxes. Both non-stoichiometric compounds are orthorhombic and crystallize in the same space group Pnnm, with two formula units per unit cell (a=12.446(2), b=5.341(1), c=12.058(2) for sulfide and a=13.126(2), b=5.623(1), c=12.499(2) for the selenide). Their crystal structures are dominated by lanthanide-chalcogenide polyhedra (CN=7 and 8), which share corners, edges, triangular- and square-faces to form a three-dimensional framework embedding antinomy cations. The latter are coordinated by three sulfide anions with 5(1+2+2) secondary contacts forming basically infinite chains running along [0 1 0]. The chalcogens in both compounds form chalcogenide Q2− and dichalcogenide (Q2)2− anionic units. The optical analysis made on those compounds shows that both are semiconductors with band gap of 1.71 and 1.22 eV for Yb4Sb2S11.25 and Tm4Sb2Se11.75, respectively.

Graphical AbstractThe crystal structure of Yb4Sb2S11 viewed along the [0 1 0].Figure optionsDownload as PowerPoint slideHighlights
► Lanthanide chalcogenides.
► Semiconductors.
► Tunnel structures.
► Lone-pair effects.