Synthese und Kristallstruktur des Fluorid‐ino‐Oxosilicats Cs2YFSi4O10

Abstract

AbstractSynthesis and Crystal Structure of the Fluoride ino‐Oxosilicate Cs2YFSi4O10The novel fluoride oxosilicate Cs2YFSi4O10 could be synthesized by the reaction of Y2O3, YF3 and SiO2 in the stoichiometric ratio 2 : 5 : 3 with an excess of CsF as fluxing agent in gastight sealed platinum ampoules within seventeen days at 700 °C. Single crystals of Cs2YFSi4O10 appear as colourless, transparent and water‐resistant needles. The characteristic building unit of Cs2YFSi4O10 (orthorhombic, Pnma (no. 62), a = 2239.75(9), b = 884.52(4), c = 1198.61(5) pm; Z = 8) comprises infinite tubular chains $\rm ^{1}_{\infty} \{[Si_{4}O_{10}]^{4-}\}$ of vertex‐condensed [SiO4]4− tetrahedra along [010] consisting of eight‐membered half‐open cube shaped silicate cages. The four crystallographically different Si4+ cations all reside in general sites 8d with Si–O distances from 157 to 165 pm. Because of the rigid structure of this oxosilicate chain the bridging Si–O–Si angles vary extremely between 128 and 167°. The crystallographically unique Y3+ cation (in general site 8d as well) is surrounded by four O2− and two F− anions (d(Y–O) = 221–225 pm, d(Y–F) = 222 pm). These slightly distorted trans‐[YO4F2]7− octahedra are linked via both apical F− anions by vertex‐sharing to infinite chains $\rm ^{1}_{\infty} \{[YO^{t}_{4/1}F^{v}_{2/2}]^{6-}\}$ along [010] (∢(Y–F–Y) = 169°, ∢(F–Y–F) = 177°). Each of these chains connects via terminal O2− anions to three neighbouring oxosilicate chains to build up a corner‐shared, three‐dimensional framework. The resulting hexagonal and octagonal channels along [010] are occupied by the four crystallographically different Cs+ cations being ten‐, twelve‐, thirteen‐ and fourteenfold coordinated by O2− and F− anions (viz.[(Cs1)O10]19−, [(Cs2)O10F2]21−, [(Cs3)O12F]24−, and [(Cs4)O12F2]25− with d(Cs–O) = 309–390 pm and d(Cs–F) = 360–371 pm, respectively).