Synthesis and Crystal Structure of the Fluoride-Rich Rubidium Scandium Fluoride Oxosilicate Rb3Sc2F5Si4O10

The new quinary fluoride-rich rubidium scandium oxosilicate Rb3Sc2F5Si4O10 was obtained from mixtures of RbF, ScF3, Sc2O3 and SiO2 in sealed platinum ampoules after seventeen days at 700 degrees C. The colourless compound crystallises orthorhombically in space group Pnma with a = 962.13(5), b = 825.28(4), c = 1838.76(9) pm and Z = 4. For the oxosilicate partial structure, [SiO4](4) tetrahedra are connected in (001) by vertex-sharing to form corrugated unbranched vierer single layers (2)(infinity){[Si4O10](4)} (d(Si-O) - 158-165 pm, angle(O-Si-O) - 103-114 degrees, angle(Si-O-Si) = 125-145 degrees) containing six-membered rings. Similar oxosilicate layers with 6(3)-net topology are well-known for the mineral group of micas or in sanbornite Ba2Si4O10. Regarding other systems, identical tetrahedral layers can be found in the synthetic boro-phosphate Mg(H2O)(2)[B2P2O8(OH)(2)]center dot H2O. The Sc3+ cations are coordinated octahedrally by four F and two O-2 anions. These cis-[ScF4O2](5) octahedra (d(Sc-F) = 200- 208 pm, d(Sc-O) = 202- 205 pm) share one equatorial and two apical F anions with others to build up slightly corrugated (1)(infinity){[(Sc2F2/1F6/2O4/1t)-F-t-O-v](7)} double chains along [010]. These are linked with the oxosilicate layers via two oxygen vertices to construct a three-dimensional framework with cavities apt to host the three crystallographically independent Rb+ cations with coordination numbers of eleven, twelve and thirteen.