Penta­lanthanum zinc diplumbide, La5Zn1−xPb2+x (x ≃ 0.6)

The title non-stoichiometric penta-lanthanum zinc diplumbide, La5Zn1-x Pb2+x (x ≃ 0.6), was prepared from the elements in an evacuated silica ampoule. It adopts the Nb5Sn2Si-type structure (space group I4/mcm, Pearson symbol tI32), a ternary ordered superstructure of the W5Si3 type. Among the four independent crystallographic positions, three are fully occupied by La (Wyckoff 16k), La (4b), and Pb (8h) and one is occupied by a statistical mixture [occupancy ratio 0.394 (12):0.606 (12)] of Zn and Pb (4a). The structure is constructed by face-sharing 10-vertex polyhedra around the unmixed Pb sites. These fragments enclose channels of trans-face-sharing tetra-gonal anti-prisms occupied by the disordered Zn and Pb sites.