The alluaudite-like arsenate NaCaMg(3)(AsO(4))(3).
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ABSTRACT:
SUBMITTER: Haj Abdallah A
PROVIDER: S-EPMC2961449 | biostudies-literature | 2008 May
REPOSITORIES: biostudies-literature
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Project description:The title compound, NaCa(AsO(4)), was synthesized using a hydro-thermal method at 633-643?K. It has a dense structure composed of alternating layers of distorted [CaO(6)] octa-hedra and layers of [AsO(4)] tetra-hedra and distorted [NaO(6)] octa-hedra, stacked along the a axis. The As, Ca and two O atoms lie on the mirror plane at y = 1/4 (i.e. 4c), while the Na atom lies on an inversion centre (1/2, 1/2, 0) (i.e. 4b). Each distorted [CaO(6)] octa-hedron shares four equatorial common O vertices with four neighboring octa-hedra, forming a layer parallel to (100), whereas each distorted [NaO(6)] octa-hedron shares two opposite edges with two neighboring ones, forming a chain running along [010]. Each isolated [AsO(4)] tetra-hedron shares two edges with two different [NaO(6)] octa-hedra in one [NaO(6)] chain and a vertex with another chain. Simultaneously the above [AsO(4)] tetra-hedron located in a four-membered [CaO(6)] ring shares one edge of its base facet with one [CaO(6)] octa-hedron and three corners with three other [CaO(6)] octa-hedra of one [CaO(6)] layer, and the remaining apex is shared with another [CaO(6)] layer. [NaO(6)] octa-hedra and [CaO(6)] octa-hedra are linked to each other by sharing edges and vertices.
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Project description:In the title compound, tris-odium dicobalt arsenate diarsenate, Na₃Co₂AsO₄As₂O₇, the two Co atoms, one of the two As and three of the seven O atoms lie on special positions, with site symmetries 2 and m for the Co, m for the As, and 2 and twice m for the O atoms. The two Na atoms are disordered over two general and special positions [occupancies 0.72 (3):0.28 (3) and 0.940 (6):0.060 (6), respectively]. The main structural feature is the association of the CoO₆ octa-hedra in the ab plane, forming Co₄O₂₀ units, which are corner- and edge-connected via AsO₄ and As₂O₇ arsenate groups, giving rise to a complex polyhedral connectivity with small tunnels, such as those running along the b- and c-axis directions, in which the Na⁺ ions reside. The structural model is validated by both bond-valence-sum and charge-distribution methods, and the distortion of the coordination polyhedra is analyzed by means of the effective coordination number.
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Project description:The vanadium oxide arsenate with formula K₂V₂O₂(AsO₄)₂, dipotassium divanadium(IV) dioxide diarsenate, has been synthesized by solid-state reaction in an evacuated silica ampoule. Its structure is isotypic with K₂V₂O₂(PO₄)₂. The framework is built up from corner-sharing VO₆ octa-hedra and AsO₄ tetra-hedra, creating an infinite [VAsO₈](∞) chain running along the a- and c-axis directions. The K⁺ cations are located in hexa-gonal tunnels, which are delimited by the connection of the [VAsO₈](∞) chains.
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Project description:The new phase potassium penta-sodium trimanganese hexa-kis(molybdate), KNa5Mn3Mo6O24, has been synthesized using solid-state methods. The structure is composed of M 2O10 (M = Mn, Na) dimers and MoO4 tetra-hedra (point group symmetry 2) sharing corners and forming layers parallel to (100), which are linked via common corners of another type of MO4 tetra-hedra, forming a three-dimensional structure with two types of large channels along [001] in which two types of Na(+) cations (one with site symmetry 2, one with -1) and K(+) cations (site symmetry 2, half-occupation) are located. Mn(2+) and the third type of Na(+) cations are located at the same site M with occupancies of 0.75 and 0.25, respectively. A comparative structural description is provided between the structure of the title compound and those of the related phases Cu1.35Fe3(PO4)3 and NaAgFeMn2(PO4)3.
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Project description:A new triple molybdate, potassium sodium cobalt tris-(molybdate), K0.4Na3.6Co(MoO4)3, was synthesized using solid-state reactions. The Co(2+) and one Na(+) cation are located at the same general site, each with occupancy 0.5. Another site (site symmetry 2) is occupied by Na(+) and K(+) cations, with occupancies of 0.597 (7) and 0.402 (6), respectively. The other two Na(+) cations and one of the two Mo atoms lie on special positions (site symmetries -1, 2 and 2, respectively). The structure is characterized by M 2O10 (M = Co/Na) dimers, which are linked by MoO4 tetra-hedra, forming infinite layers. The latter are connected firstly by insertion of one type of MoO4 tetra-hedra and secondly by sharing corners with the other type of MoO4 tetra-hedra. This results in an open three-dimensional framework with the cavities occupied by the Na(+) and K(+) cations. The structure is isotypic with Na3In2As3O12 and Na3In2P3O12. A comparison is made with structures such as K2Co2(MoO4)3 and β-NaFe2(MoO4)3 and their differences are discussed.
| S-EPMC4331865 | biostudies-literature
Project description:The title compound, tetra-sodium cobalt(II) tris-[molyb-date(IV)], was prepared by solid-state reactions. The structure is isotypic with Na3In2(AsO4)3 and Na3In2(PO4)3. The main structural feature is the presence of infinite chains of edge-sharing X 2O10 (X = Co/Na) dimers, which are linked by MoO4 tetra-hedra, forming a three-dimensional framework enclosing two types of hexa-gonal tunnels in which Na(+) cations reside. In this alluaudite structure, Co and Na atoms are located at the same general site with occupancies of 0.503 (5) and 0.497 (6), respectively. The other three Na and one of the two Mo atoms lie on special positions (site symmetries 2, -1, 2 and 2, respectively). The structure is compared with similar structures and other members of alluaudite family.
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Project description:Suitable single crystals of the title compound, barium dicobalt(II) bis-[orthoarsenate(V)], were prepared under hydro-thermal conditions. This phase belongs to a series of compounds with general formula AM(2)(XO(4))(2), where A = alkaline earth metal, M = Mg or a divalent first-row transition element, and X = P, As or V. BaCo(2)(AsO(4))(2) is isotypic with BaNi(2)(XO(4))(2) (X = P, V or As) and is characterized by brucite-like sheets of edge-sharing CoO(6) octa-hedra (3 symmetry) parallel to (001), with one-third of the octa-hedral positions being vacant. The sheets are capped above and below by AsO(4) tetra-hedra (3 symmetry) and are inter-connected by distorted BaO(12) cubocta-hedra ( symmetry).
| S-EPMC2960660 | biostudies-literature
Project description:A strain of Halomonas bacteria, GFAJ-1, has been claimed to be able to use arsenate as a nutrient when phosphate is limiting and to specifically incorporate arsenic into its DNA in place of phosphorus. However, we have found that arsenate does not contribute to growth of GFAJ-1 when phosphate is limiting and that DNA purified from cells grown with limiting phosphate and abundant arsenate does not exhibit the spontaneous hydrolysis expected of arsenate ester bonds. Furthermore, mass spectrometry showed that this DNA contains only trace amounts of free arsenate and no detectable covalently bound arsenate.
| S-EPMC3845625 | biostudies-literature
Project description:Arsenic is a toxic and carcinogenic contaminant of potential concern. Ettringite [Ca6Al2(SO4)3(OH)12·26H2O] has the ability to incorporate oxyanions as a solid solution with SO42-, which could lower the soluble oxyanion concentrations. Therefore, ettringite containing SO42- and AsO43- has been synthesized. Results indicated that AsO43- could substitute for SO42- inside the channels of ettringite in the form of HAsO42-, and a linear correlation existed between Xinitial solution and Xsolid. The thermodynamic characterization of the solid samples was investigated by means of Visual MINTEQ, a freeware chemical equilibrium model, and the solubility product logK of -48.4 ± 0.4 was calculated for HAsO4-ettringite at 25°C. The Lippmann phase diagram and XHAsO4-XHAsO4,aq plot showed that the solid solution series containing arsenate has HAsO4-poor aqueous solutions in equilibrium. These findings can be helpful to arsenate solidification and arsenate leaching modeling projects.
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Project description:The title compound, sodium trimagnesium bis-(hydrogen phosphate) phosphate, was obtained under hydro-thermal conditions. In the crystal, two types of [MgO6] octa-hedra, one with point group symmetry 2, share edges to build chains extending parallel to [10-1]. These chains are linked together by two kinds of phosphate tetra-hedra, HPO4 and PO4, the latter with point group symmetry 2. The three-dimensional framework delimits two different types of channels extending along [001]. One channel hosts the Na(+) cations (site symmetry 2) surrounded by eight O atoms, with Na-O bond lengths varying between 2.2974 (13) and 2.922 (2) Å. The OH group of the HPO4 tetra-hedron points into the other type of channel and exhibits a strong hydrogen bond to an O atom of the PO4 tetra-hedron on the opposite side.
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