Structural Variations and Bonding Analysis of the Rare-Earth Metal Tellurides RETe_1.875±δ (RE = Ce, Pr, Sm, Gd; 0.004 ≤ δ ≤ 0.025)

Crystals of RETe_1.875±δ (RE = Ce, Pr, Sm, Gd; 0.004 ≤ δ ≤ 0.025) were grown using alkali halide flux and chemical transport reactions. The crystal structures are described in space group Amm2 (no. 38), with lattice parameters of a = 13.3729(5) Å, b = 17.7918(5) Å, c = 18.1561(4) Å for CeTe_1.87(1) (T = 100 K), a = 13.271(2) Å, b = 17.747(3) Å, c = 18.160(3) Å for PrTe_1.85(1) (T = 100 K), a = 13.1251(6) Å, b = 17.4269(8) Å, c = 17.8808(8) Å for SmTe_1.87(1) (T = 100 K), and a = 13.1762(4) Å, b = 17.4995(5) Å, c = 17.9591(5) Å for GdTe_1.88(1) (T = 296 K). The structures contain alternating stacks of puckered [RETe] slabs and planar [Te] layers. The latter are composed of small anionic entities, such as Te^2– and Te₂^2–, along with a large anionic eight-membered Te ring, as supported by electron localizability indicator-based bond analysis for an ordered model of GdTe_1.875. Slightly different patterns for individual compounds indicate a considerable structural flexibility. Temperature-dependent resistance measurements confirm semiconducting behavior for PrTe_1.875±δ and GdTe_1.875±δ (magnetic data evidence RE³⁺ and an antiferromagnetic transition at T_N = 4 K for CeTe_1.875±δ and T_N = 11 K for GdTe_1.875±δ), whereas PrTe_1.875±δ and SmTe_1.875±δ show no long-range order down to 2 K.