Flux Syntheses and Crystal Structures of New Compounds With Decorated Kröhnkite-like Chains

Maria Wierzbicka-Wieczorek,a,* Uwe Kolitschb and Ekkehart Tillmannsa

a Institute of Mineralogy and Crystallography, University of Vienna, Geocentre, Althanstr. 14, A-1090 Vienna, Austria
b Department of Mineralogy and Petrography, Natural History Museum Vienna, Burging 7, A-1010 Vienna, Austria
* Corresponding author: E-mail: maria.wierzbicka@univie.ac.at

The crystal structures of two novel compounds, KSr6Sc(SiO4)4 and Rb5In(MoO4)4, were determined from single-crystal X-ray diffraction data collected at room temperature. Both compounds have been synthesised by the flux growth technique in the course of a research project on new micro- and nanoporous alkali-M3+ silicates. KSr6Sc(SiO4)4 represents a new structure type and the first silicate containing decorated kröhnkite-like octahedral-tetrahedral chains. It is orthorhombic and crystallises in Pnma, with a = 19.137(4), b = 11.197(2), c = 7.125(1) Å, V = 1526.7(5) Å3, Z = 8. Rb5In(MoO4)4 has space group P2/c with a = 11.391(2), b = 7.983(2), c = 11.100(2) Å, = 113.74(3)°, V = 924.0(3) Å3, Z = 2. It is isotypic with Rb5Er(MoO4)4. The topologies of both compounds are characterised by isolated infinite decorated kröhnkite-like chains that are built from either ScO6 or InO6 octahedra corner-linked and decorated by SiO4 or Mo-O4 tetrahedra. These chains are separated by alkali or alkaline earth metals. A detailed comparison to the few other compounds based on decorated kröhnkite-like chains, viz. Ba2Ca(HPO4)2(H2PO4)2, CsM3+(H1.5AsO4)2(H2AsO4) (M3+ = Ga, Cr), CsAl(H2AsO4)2(HAsO4), K(H2O)M3+(H1.5AsO4)2(H2AsO4) (M3+ = Fe, Ga, In) and K5In(MoO4)4 is given.

Keywords: Decorated kröhnkite-like chains, rubidium indium molybdate, strontium potassium scandium silicate, flux growth, single-crystal X-ray diffraction