NaSr(AsO4)(H2O)9: the (Sr,As) analogue of nabaphite and nastrophite

The crystal structure of the title compound, sodium strontium orthoarsenate(V) nona­hydrate, is isotypic with NaSr(PO4)(H2O)9 and the minerals nabaphite [NaBa(PO4)(H2O)9] and nastrophite [Na(Sr,Ba)(PO4)(H2O)9]. The Na and Sr atoms are located on threefold rotation axes and are in the centres of slightly distorted Na(H2O)6 octa­hedra and Sr(H2O)9 tricapped trigonal prisms, respectively. A framework structure is established via edge-sharing of these polyhedra. Disordered AsO4 tetra­hedra (with threefold symmetry) are situated in the inter­stitial space of the framework. Although reasonable H-atom positions of the water mol­ecules were not established, close O⋯O contacts between the disordered AsO4 tetra­hedra and the water mol­ecules suggest strong O—H⋯O hydrogen bonding

The cyclo-tetra­phosphate Cd2P4O12, a member of the isotypic series M 2P4O12 (M = Mg, Mn, Fe, Co, Ni, Cu)

The title compound, Cd2P4O12, dicadmium cyclo-tetra­phosphate, crystallizes isotypically with the members of the series M II 2P4O12, where M = Mg, Mn, Fe, Co, Ni or Cu. Two CdO6 octa­hedra, one with 2 and one with symmetry, share corners with the centrosymmetric P4O12 4− ring anion that is built up from four corner-sharing PO4 tetra­hedra. The isolated ring anions are arranged in layers parallel to (10) with the CdO6 octa­hedra situated between these layers. The main difference between the individual M II 2P4O12 structures pertains to the different sizes of the MO6 octa­hedra whereas the geometric parameters of all cyclo-P4O12 4− anions are very similar

NaFe(TeO3)2

The hydro­thermally prepared title compound, sodium iron(III) bis­[trioxotellurate(IV)], is isotypic with its GaIII analogue and consists of corrugated layers with an overall composition of [FeTe2O6]− together with Na+ cations. The layers extend parallel to (001) and are made up of [Fe2O10] edge-shared octa­hedral dimers and TeO3 trigonal pyramids sharing vertices. The Na+ cations are located in the cavities of this arrangement and link adjacent [FeTe2O6]− layers via distorted [NaO8] polyhedra

Pb3Te2O6Br2

Single crystals of the title compound, trilead(II) bis­[tellurate(IV)] dibromide, have been grown under hydro­thermal conditions. The structure is isotypic with that of the chloride analogue, Pb3Te2O6Cl2, and consists of three Pb, two Te, two Br and four O atoms in the asymmetric unit. Except for two of the O atoms, all atoms are located on mirror planes. The Pb3Te2O6Br2 structure can be described as being built up from ∞ 2[Pb3Te2O6]2+ layers extending parallel to (20) and Br− anions between the layers. Cohesion of the structure is accomplished through Pb—Br contacts of two of the three lead atoms, leading to highly asymmetric coordination polyhedra. The lone-pair electrons of both TeIV and PbII atoms are stereochemically active and point towards the anionic halide layers

Crystal structure of the thortveitite-related M phase, (MnxZn1-x)2V2O7 (0.75 < x < 0.913): a combined synchrotron powder and single-crystal X-ray study.

The determination of the crystal structure of the M phase, (MnxZn1-x)2V2O7 (0.75 < x < 0.913), in the pseudobinary Mn2V2O7-Zn2V2O7 system for x ≃ 0.8 shows that the previously published triclinic unit-cell parameters for this thortveitite-related phase do not describe a true lattice for this phase. Instead, single-crystal X-ray data and Rietveld refinement of synchrotron X-ray powder data show that the M phase has a different triclinic structure in the space group P-1 with Z = 2. As prior work has suggested, the crystal structure can be described as a distorted version of the thortveitite crystal structure of β-Mn2V2O7. A twofold superstructure in diffraction patterns of crystals of the M phase used for single-crystal X-ray diffraction work arises from twinning by reticular pseudomerohedry. This superstructure can be described as a commensurate modulation of a pseudo-monoclinic basis structure closely related to the crystal structure of β-Mn2V2O7. In comparison with the distortions introduced when β-Mn2V2O7 transforms at low temperature to α-Mn2V2O7, the distortions which give rise to the M phase from the β-Mn2V2O7 prototype are noticeably less pronounced.Funding for this research was provided by: Royal Society (joint international exchange programme award to Anjan Sil); British Council, New Delhi (UKIERI project No. SA07-0052 to Kevin Knowles, Anjan Sil)

Redetermination of the hexa­gonal struvite analogue Cs[Mg(OH2)6](PO4)

The structure of the hexa­gonal modification of caesium hexa­aqua­magnesium phosphate has been redetermined from single-crystal X-ray data. The previous refinement from photographic data [Ferrari, Calvaca & Nardelli (1955 ▶). Gazz. Chim. Ital. 85, 1232–1238] was basically confirmed, but with all H atoms located and with all non H-atoms refined with anisotropic displacement parameters. The structure can be derived from the NiAs structure type: the PO4 tetra­hedra (3m. symmetry) are on the Ni positions and the complex [Mg(OH2)6] octa­hedra (3m. symmetry) are on the As positions. The building units are connected to each other by hydrogen bonds. The Cs+ cations (3m. symmetry) are located in the voids of this arrangement and exhibit a distorted cubocta­hedral 12-coordination by the O atoms of the water mol­ecules