Matthew Mann

Hydrothermal Descriptive Chemistry and Single Crystal Structure Determination of Cesium and Rubidium Thorium Fluorides

Two new cesium thorium fluorides and three new rubidium thorium fluorides have been synthesized hydrothermally and structurally characterized. The structures of two polymorphs of CsTh(3)F(13) are described in space group P6/mmm with a = 8.2608(14) and c = 8.6519(17) and space group Pmc2(1) with a = 8.1830(16), b = 7.5780(15), and c = 8.6244(17). The analogous orthorhombic compound RbTh(3)F(13), with a = 8.1805(16), b = 7.4378(15), and c = 8.6594(17) in space group Pmc2(1), is also reported. Two other rubidium thorium fluorides are also described: RbTh(2)F(9) crystallizes in the space group Pnma where a = 8.9101(18), b = 11.829(2), and c = 7.4048(15), and Rb(7)Th(6)F(31) crystallizes in the space group R3 where a = 15.609(2) and c = 10.823(2). Comparison of these materials was made on the basis of their structures and synthesis conditions. The formation of these species in hydrothermal fluids appears to be dependent upon the concentration of the alkali fluoride mineralizer solution and, thus, the ratio of alkali ions to thorium in the system.

Hydro­thermally synthesized α-Ba2P2O7

Single crystals of α-Ba2P2O7, dibarium diphosphate, were obtained under hydrothermal conditions. The structure belongs to the diphosphate A 2P2O7 series with A being an alkaline earth cation. α-Ba2P2O7 crystallizes isotypically with α-Sr2P2O7. All atomic sites have site symmetry m with the exception of two O atoms which reside on general positions. Both Ba2+ cations are coordinated by nine terminal O atoms from eclipsed diphosphate P2O7 anions to form a three-dimensional network throughout the structure.

K3(Sc0.875Nb0.125)Nb2O9H1.75: a new scandium niobate with a unique cage structure

Potassium scandium niobate hydroxide, K(3)(Sc(0.875)Nb(0.125))Nb(2)O(9)H(1.75), is a new scandium niobate with a unique cage structure. The structure contains two non-equivalent K(+) sites (3m and 6m2 site symmetry), one disordered Sc(3+)/Nb(5+) site (3m site symmetry), one Nb(5+) site (3m site symmetry), two O(2-) sites (m and mm2 site symmetry) and one H(+) site (m site symmetry). Both scandium and niobium have octahedral environments, which combine to form cages around potassium. One K atom lies in a cube-like cage built of seven octahedra, while the other K atom is encapsulated by an eight-membered trigonal face-bicapped prism. The cages form sheets that extend along the ab plane.

Ba2Ti2Si2O9F2, a new titanium silicate

Dibarium dititanium difluoride dioxide heptaoxidodisilicate, Ba(2)Ti(2)Si(2)O(9)F(2), is a new edge-sharing titanate with a unique titanium silicate framework. All atoms in the structure are in general positions. Titanium oxyfluoride octahedra combine with silicon tetrahedra to form a double stacked chain, which is the base unit of the layered framework. The Ba atoms lie in channels that extend along the a axis.