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Keywords:

  • Scandium;
  • Oxosilicates;
  • Fluorides;
  • Rubidium;
  • Crystal structures

Abstract

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 °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 equation image{[Si4O10]4–} (d(Si–O) = 158–165 pm, ∠(O–Si–O) = 103–114°, ∠(Si–O–Si) = 125–145°) containing six-membered rings. Similar oxosilicate layers with 63-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 borophosphate Mg(H2O)2[B2P2O8(OH)2]·H2O. The Sc3+ cations are coordinated octahedrally by four F and two O2– 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 equation image{[Sc2Fequation imageFequation imageOequation image]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.