Ternary Rare-Earth Selenides with the U₃ScS₆ Structure Type: Synthesis, Characterization, and Some Magnetic Properties of Ln₃TSe₆ (Ln = Sm, Gd; T = In, Cr) and Tb₃CrSe₆

The new compounds Ln3TSe6 (Ln = Sm, Gd; T = In, Cr) and Tb3CrSe6 have been synthesized by the solid-state reactions of the elements at 850 °C. A KBr flux was used to promote crystal growth. These isostructural compounds crystallize with the U3ScS6 structure type. The crystal structure is built from LnSe7 pseudo-octahedra or LnSe8 bicapped trigonal prisms and TSe6 octahedra. Magnetic measurements show that Sm3TSe6 (T = In, Cr) and Tb3CrSe6 are paramagnetic down to 5 K whereas Gd3CrSe6 undergoes an antiferromagnetic transition at 10 K. Crystal data: orthorhombic, Pnnm, Z = 4, T = −120 °C, (compound, a (Å), b (Å), c (Å))Sm3InSe6, 14.177(3), 17.352(4), 4.0625(8); Gd3InSe6, 14.071(3), 17.286(4), 4.0202(8); Sm3CrSe6, 14.032(3), 16.782(3), 3.9841(8); Gd3CrSe6, 13.938(3), 16.780(3), 3.9559(8); Tb3CrSe6, 13.885(3), 16.672(3), 3.9215(8).