Syntheses, structure, magnetism, and optical properties of the interlanthanide sulfides δ-Ln2−xLuxS3 (Ln=Ce, Pr, Nd)

δ-Ln2−xLuxS3 (Ln=Ce, Pr, Nd; x=0.67–0.71) compounds have been synthesized through the reaction of elemental rare-earth metals and S using a Sb2S3 flux at 1000 °C. These compounds are isotypic with CeTmS3, which has a complex three-dimensional structure. It includes four larger Ln3+ sites in eight- and nine-coordinate environments, two disordered seven-coordinate Ln3+/Lu3+ positions, and two six-coordinate Lu3+ ions. The structure is constructed from one-dimensional chains of LnSn (n=6–9) polyhedra that extend along the b-axis. These polyhedra share faces or edges with two neighbors within the chains, while in the [ac] plane they share edges and corners with other chains. Least square refinements gave rise to the formulas of δ-Ce1.30Lu0.70S3, δ-Pr1.29Lu0.71S3 and δ-Nd1.33Lu0.67S3, which are consistent with the EDX analysis and magnetic susceptibility data. δ-Ln2−xLuxS3 (Ln=Ce, Pr, Nd; x=0.67–0.71) show no evidence of magnetic ordering down to 5 K. Optical properties measurements show that the band gaps for δ-Ce1.30Lu0.70S3, δ-Pr1.29Lu0.71S3, and δ-Nd1.33Lu0.67S3 are 1.25, 1.38, and 1.50 eV, respectively. Crystallographic data: δ-Ce1.30Lu0.70S3, monoclinic, space group P21/m, a=11.0186(7), b=3.9796(3), c=21.6562(15) Å, β=101.6860(10), V=929.93(11), Z=8; δ-Pr1.29Lu0.71S3, monoclinic, space group P21/m, a=10.9623(10), b=3.9497(4), c=21.5165(19) Å, β=101.579(2), V=912.66(15), Z=8; δ-Nd1.33Lu0.67S3, monoclinic, space group P21/m, a=10.9553(7), b=3.9419(3), c=21.4920(15) Å, β=101.5080(10), V=909.47(11), Z=8.