Syntheses, Structures, Magnetism, and Optical Properties of Lutetium-Based Interlanthanide Selenides

Ln3LuSe6 (Ln = La, Ce), β-LnLuSe3 (Ln = Pr, Nd), and LnxLu4-xSe6 (Ln = Sm, Gd; x = 1.82, 1.87) have been
synthesized using a Sb2Se3 flux at 1000 °C. Ln3LuSe6 (Ln = La, Ce) adopts the U3ScS6-type three-dimensional
structure, which is constructed from two-dimensional

slabs with the gaps between these slabs being
filled by octahedrally coordinated Lu3+ ions. The series of β-LnLuSe3 (Ln = Pr, Nd) are isotypic with UFeS3. Their
structures include layers formed from LuSe6 octahedra that are separated by eight-coordinate Ln3+ (Ln = Pr, Nd)
ions in bicapped trigonal prismatic environments. Sm1.82Lu2.18Se6 and Gd1.87Lu2.13Se6 crystallize in the disordered
F-Ln2S3 type structure with the eight-coordinate bicapped trigonal prismatic Ln(1) ions residing in the one-dimensional
channels formed by three different double chains via edge- and corner-sharing. These double chains are constructed
from Ln(2)Se7 monocapped trigonal prisms, Ln(3)Se6 octahedra, and Ln(4)S6 octahedra, respectively. The magnetic
susceptibilities of β-PrLuSe3 and β-NdLuSe3 follow the Curie−Weiss law. Sm1.82Lu2.18Se6 shows van Vleck
paramagnetism. Magnetic susceptibility measurements show that Gd1.87Lu2.13Se6 undergoes an antiferromagnetic
transition around 4 K. Ce3LuSe6 exhibits soft ferromagnetism below 5 K. The optical band gaps for La3LuSe6,
Ce3LuSe6, β-PrLuSe3, β-NdLuSe3, Sm1.82Lu2.18Se6, and Gd1.87Lu2.13Se6 are 1.26, 1.10, 1.56, 1.61, 1.51, and 1.56
eV, respectively.