Oxide fluoride sulfides of the lanthanoids with the formula 1M _3OF_5S (M = Nd, Sm, Gd-Ho)

摘要

First attempts to synthesize a lanthanoid(III) oxide fluoride sulfide were successful by reacting DyF_3 and Dy_2O_3 with dysprosium and sulfur in a 2: 5: 1: 3 molar ratio at 850 °C in tightly sealed tantalum ampoules. In analogy to the dysprosium compound Dy _3OF_5S, the other representatives of the M _3OF_5S series with M = Nd, Sm, Gd-Ho could be prepared as well. Almost phase-pure samples were obtained under similar flux-assisted (NaCl) conditions according to 2M +5MF_3 +M_2O_3 + 3S → 3M_3OF_5S. In the hexagonal crystal structure (space group: P6_3/m; a ≈ 961 - 939 pm, c ≈ 378 - 367 pm; c/a≈0.39,V_m ≈91 - 84 cm~3 mol~(-1), Z = 2), theM~(3+) cations reside in ninefold anionic coordination realized as tricapped trigonal prisms formed by seven light (O2-/F-) and two heavier S ~(2-) anions. One light-anion position exhibits the exclusive character of F~- in trigonal non-planar coordination (CN = 3), while the other position with a tetrahedral cationic environment (CN = 4) is mixed occupied by F~- and O~(2-) in a 2: 1 ratio. The S~(2-) anions are coordinated in a trigonal prismatic way by six M~(3+) cations. From the data of single-crystal X-ray structure analyses, no indication of any ordering for the O~(2-) and F~- anions could be obtained, but bond-valence and MAPLE calculations confirmed the results of electron-beam microanalyses carried out earlier to reveal ordered models for Dy _3OF_5S.