New quaternary rare-earth chalcogenides BaLnSn2Q6 (Ln = Ce, Pr, Nd, Q = S; Ln = Ce, Q = Se): synthesis, structure, and magnetic properties.

The first series of rare-earth chalcogenides with mixed-valence Sn atoms, namely the BaLnSn2Q6 (Ln = Ce, Pr, Nd, Q = S; Ln = Ce, Q = Se) compounds, were synthesized via stoichiometric solid-state reactions at 1100 °C. BaLnSn2Q6 belong to the polar space group Pmc2(1) of the orthorhombic system and contain mixed valent Sn atom in the ratio of Sn(2+)/Sn(4+) = 1:3. In the structure, the Sn(2+)Q5 rectangular pyramids, Sn(4+)Q5 trigonal bipyramids, Sn(4+)Q6 octahedra, and LnQ8 bicapped trigonal prisms are connected with each other to form a three-dimensional framework with interspaces occupied by Ba(2+) cations. As deduced from magnetic susceptibility measurements, BaPrSn2S6 and BaNdSn2S6 are paramagnetic and obey the Curie-Weiss law.