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Z. Naturforsch. 2013,
68b, 751 – 760
doi:10.5560/ZNB.2013-3110
Oxide Fluoride Sulfides of the Lanthanoids with the Formula M6O2F8S3 (M = La–Nd, Sm, Gd)
Oxidfluoridsulfide der Lanthanoide vom Formeltyp M6O2F8S3 (M = La–Nd, Sm, Gd)
Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
Reprint requests to Prof. Dr. Thomas Schleid. Fax: +49(0)711/685-64241. E-mail:
schleid@iac.uni-stuttgart.de
Received March 28, 2013 / published online July 19, 2013
The lanthanoid(III) oxide fluoride sulfides M6O2F8S3 (M = La–Nd, Sm, Gd) can be obtained by reacting the rare-earth metals, their trifluorides and sesquioxides with elemental sulfur in appropriate molar ratios at 850 °C flux-assisted by NaCl in gas-tightly sealed niobium or tantalum ampoules. All compounds are colorless, except for those containing M = Pr with green, M = Nd with lilac and M = Sm with yellow color. They form transparent single crystals as needles or rods. The M6O2F8S3 representatives crystallize in a hexagonal structure (space group: P63/m;
a ≈ 1382–1326, c ≈ 398–376 pm, c/a ≈ 0.288–0.284; Z = 2) with two different crystallographic M3+ positions. The (M2)3+ cations reside in ninefold coordination of anions arranged as tricapped trigonal prisms formed by three F−, four mixed-occupied O2−/F− and two S2− anions, resembling the unique M3+ coordination sphere of the M3OF5S-type oxide fluoride sulfides. The (M1)3+ cations are surrounded by square antiprisms built of four O2−/F− and
S2− anions each, which are capped by one F− anion each, again resulting in a ninefold coordination similar to that of the A-MFS-type fluoride sulfides. While the crystallographically unique S2− anions have six cationic neighbors arranged in trigonal prisms, there are four different light-anion positions. Two of them, representing only fluoride anions, are situated in a triangular environment of cations ((F1)−: planar, (F2)−: non-planar). The mixed-occupied light-anion positions (F3)−/(O3)2− and (F4)−/(O4)2− exhibit tetrahedral coordination spheres with a ratio F− : O2−= 2:1. The M6O2F8S3 arrangement is characterized by an empty hexagonal channel structure created by (F1)− anions with a potential of accommodating alkali-metal cations like Na+. All single-crystal X-ray structure investigations did not indicate any ordering of the O2− and F− anions, but MAPLE calculations revealed a slightly favored oxygen occupation for the (F4)−/(O4)2− rather than for the (F3)−/(O3)2− position. Electron-beam microanalyses gave no evidence for the incorporation of either Na+ or Cl− ions stemming from NaCl used as the flux.
Key words: Lanthanoids, Oxide Fluoride Sulfides, Crystal Structures