High‐Pressure Syntheses of Lanthanide Polysulfides and Polyselenides LnX1.9 (Ln = Gd–Tm, X = S, Se)

Abstract

AbstractThe polysulfides LnS1.9 and polyselenides LnSe1.9 of the lanthanide metals from gadolinium to thulium were prepared by high‐pressure high‐temperature synthesis. The compounds adopt the tetragonal CeSe1.9 structure type in space group P42/n (No. 86) with lattice parameters of 8.531 Å ≤ a ≤ 8.654 Å and 15.563 Å ≤ c ≤ 15.763 Å for the sulfides and 8.869 Å ≤ a ≤ 9.076 Å and 16.367 Å ≤ c ≤ 16.611 Å for the selenides. The atomic pattern consists of puckered double slabs [LnX]+ and planar chalcogenide layers with ten possible chalcogen positions, of which eight are occupied by chalcogen atoms forming dinuclear X22– dianions, one by a single X2– ion and one remaining vacant. This resembles a √5×√5 × 2 superstructure of the ZrSSi aristotype. Structural relationships to the aristotype and the related lanthanide polychalcogenides LnX2–δ (Ln = La–Tm, X = S–Te, δ = 0 – 0.3) are discussed. The samples synthesized under high‐pressure conditions (p > 1 GPa) decompose slowly under release of sulfur or selenium at ambient conditions. The crystal structure of a partially degraded thulium‐polysulfide sample can be described as an incommensurate variant of the original TmS1.9 motif. Additionally, the isostructural ternary compound Gd(S1–xSex)1.9 was synthesized and characterized by powder X‐ray diffraction.