New Quaternary Rare-Earth Chalcogenides Ba<i>Ln</i>Sn₂Q₆ (<i>Ln</i> = Ce, Pr, Nd, Q = S; <i>Ln</i> = 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 Pmc21 of the orthorhombic system and contain mixed valent Sn atom in the ratio of Sn2+/Sn4+ = 1:3. In the structure, the Sn2+Q5 rectangular pyramids, Sn4+Q5 trigonal bipyramids, Sn4+Q6 octahedra, and LnQ8 bicapped trigonal prisms are connected with each other to form a three-dimensional framework with interspaces occupied by Ba2+ cations. As deduced from magnetic susceptibility measurements, BaPrSn2S6 and BaNdSn2S6 are paramagnetic and obey the Curie–Weiss law.