Syntheses, structure, magnetism, and optical properties of the ordered mixed-lanthanide sulfides γ-LnLn′S3 (Ln = La, Ce;: Ln′ = Er, Tm, Yb)

gamma-LnLn'S-3 (Ln = La, Ce; Ln' = Er, Tm, Yb) have been prepared as dark red to black single crystals by the reaction of the respective lanthanides with sulfur in a Sb2S3 flux at 1000 degrees C. This isotypic series of compounds adopts a layered structure that consists of the smaller lanthanides (Er, Tm, and Yb) bound by sulfide in six- and seven-coordinate environments that are connected together by the larger lanthanides (La and Ce) in eight- and nine-coordinate environments. The layers can be broken down into three distinct one-dimensional substructures containing three crystallographically unique Ln' centers. The first of these is constructed from one-dimensional chains of edge-sharing [Ln'S-7] monocapped trigonal prisms that are joined to equivalent chains via edge sharing to yield ribbons. There are parallel chains of [Ln'S-6] distorted octahedra that are linked to the first ribbons through corner sharing. These latter units also share corners with a one-dimensional ribbon composed of parallel chains of [Ln'S-6] polyhedra that edge-share both in the direction of chain propagation and with adjacent identical chains. Magnetic susceptibility measurements show Curie-Weiss behavior from 2 to 300 K with antiferromagnetic coupling and no evidence for magnetic ordering. The theta(p) values range from -0.4 to -37.5 K, and spin-frustration may be indicated for the Yb-containing compounds. All compounds show magnetic moments substantially reduced from those calculated for the free ions. The optical band gaps for gamma-LaLn'S-3 (Ln' = Er, Tm, Yb) are approximately 1.6 eV, whereas gamma-CeLn'S-3 (Ln' = Er, Tm, Yb) are approximately 1.3 eV.