Three types of rare-earth(III) fluoride sulfides: A-LaFS, B-YFS, and C-LuFS

By reacting the elemental rare-earth metals (M = La, Y and Lu, resp.) with sulfur and the corresponding trifluorides (MF3) in gastight sealed tantalum ampoules (850 degrees C, 7 d) with 2:3:1 molar ratios of the educts (M:S:M P3), pure and single-phase fluoride sulfides of the composition MFS are obt ained. Equimolar quantities of NaCl added as a flux, promote the growth of lamellar, transparent single crystals, which proved to be insensitive to hy drolysis. The crystal structures were determined from X-ray single-crystal data for L aFS (A type: tetragonal, P4/nmm (no. 129); a = 404.38(4), c = 700.41(7) pm, c/a = 1.732, V-m = 34.49(1) cm(3)/mol, Z = 2), YFS (B type: hexagonal, P6( 3)/mmc (no. 194); a = 405.13(4), c = 1667.0(2) pm, c/a = 4.115, V-m = 35.67 (1) cm(3)/ mol, Z = 4), and LuFS (C type: trigonal, R (3) over bar m (no.16 6); a = 397.46(4), c = 2462.9(3) pm, c/a = 6.197, V-m = 33.82(1) cm(3)/ mol , Z = 6). In the PbFCl-type crystal structure of A-LaFS, the M3+ cations ar e present in a capped square antiprismatic coordination of our F- and five S2- anions, which again are surrounded by four and five cations, respective ly, in tetrahedral (F-) or square pyramidal (S2-) manner. Contrary to this the closely related crystal structures of B-YFS and C-LuFS each exhibit two crystallographically different M3+ cations. In both cases, M1 is surrounde d trigonal antiprismatically by six S2-, whereas M2 is hexagonal-bipyramida lly coordinated by eight anions (six F- within the equatorial plane, two S2 - as apical ligands) altogether. The anions themselves reside in a trigonal planar (F-) or a distorted tetrahedral (S2-) coordination of three and fou r cations, respectively. Regarding both the structures as built up by tripl e-((2)(infinity){(S2-)-(M3+)-(S2-)}-) and single-layer slabs ((2)(infinity) {(M3+)(F-)(2)}(+)) alternately stacked parallel (001), the B-type YFS and t he C-type LuFS structures only differ in their stacking sequence: In the B type a (2 x 2)H structure is present, while the C type on the other hand sh ows a (3 x 2)R arrangement, according to the Ramsdell nomenclature for laye red structures.