Syntheses, structures, magnetism, and optical properties of lutetium-based interlanthanide selenides

Ln(3)LuSe(6) (Ln = La, Ce), beta-LnLuSe(3) (Ln = Pr, Nd), and Ln(x)LU(4)-,Se-6 (Ln = Sm, Gd; x = 1.82, 1.87) have been synthesized using a Sb2Se3 flux at 1000 degrees C. Ln(3)LuSe(6) (Ln = La, Ce) adopts theU(3)SCS(6)-type three-dimensional structure, which is constructed from two-dimensional 2 infinity [Ln(3)Se(6)](3-) slabs with the gaps between these slabs being filled by octahedrally coordinated Lu3+ ions. The series of beta-LnLuSe(3) (Ln = Pr, Nd) are isotypic with UFeS3. Their structures include layers formed from LuSe6 Octahedra that are separated by eight-coordinate Ln(3+) (Ln = Pr, Nd) ions in bicapped trigonal prismatic environments. Sm1.82Lu2.18Se6 and Gd1.87Lu2.13Se6 crystallize in the disordered F-Ln(2)S(3) 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)Se-7 monocapped trigonal prisms, Ln(3)Se-6 octahedra, and Ln(4)S-6 octahedra, respectively. The magnetic susceptibilities of beta-PrLuSe3 and beta-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, beta-PrLuSe3, beta-NdLuSe3, Sm1.82Lu2.18Se6, and Gd1.87Lu2.13Se6 are 1.26, 1.10, 1.56, 1.61, 1.51, and 1.56 eV, respectively.