Oxide fluoride sulfides of the lanthanoids with the formula M3OF5S (M = Nd, Sm, Gd-Ho)

First attempts to synthesize a lanthanoid(III) oxide fluoride sulfide were successful by reacting DyF3 and Dy2O3 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 Dy3OF5S, the other representatives of the M3OF5S 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 + 5MF3 + M2O3 + 3S → 3M3OF5S. In the hexagonal crystal structure (space group: P63/m; a ∼ 961-939 pm, c ∼ 378-367 pm; c/a ∼ 0.39, Vm ∼ 91-84 cm3mol-1, Z = 2), the M3+ cations reside in ninefold anionic coordination realized as tricapped trigonal prisms formed by seven light (O2-/F-) and two heavier S2- 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 O2- in a 2: 1 ratio. The S2- anions are coordinated in a trigonal prismatic way by six M3+ cations. From the data of single-crystal X-ray structure analyses, no indication of any ordering for the O2- 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 Dy3OF5S. (orig.)