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The title compound, lithium/sodium iron(III) bis­[ortho­molyb­date(VI)], was obtained by a solid-state reaction. The main structure units are an FeO6 octa­hedron, a distorted MoO6 octa­hedron and an MoO4 tetra­hedron sharing corners. The crystal structure is composed of infinite double MoFeO11 chains along the b-axis direction linked by corner-sharing to MoO4 tetra­hedra so as to form Fe2Mo3O19 ribbons. The cohesion between ribbons via mixed Mo—O—Fe bridges leads to layers arranged parallel to the bc plane. Adjacent layers are linked by corners shared between MoO4 tetra­hedra of one layer and FeO6 octa­hedra of the other layer. The Na+ and Li+ ions partially occupy the same general position, with a site-occupancy ratio of 0.631 (9):0.369 (1). A comparison is made with AFe(MoO4)2 (A = Li, Na, K and Cs) structures.

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The title compound, disodium dimanganese(II) tris­[ortho­molybdate(VI)], was prepared by solid-state reactions. The structure can be described as being composed of Mn2Mo2O14 double-chains that are inter­connected by corner-sharing with MoO4 tetra­hedra, leading to a three-dimensional framework with channels propagating in [100] and [001] in which the Na+ counter-cations are located. One of these Na sites is located on an inversion centre, one is partially occupied [occupancy 0.341 (9)], and one is statistically occupied by Na and Mn in a ratio of 0.829 (5):0.171 (5). Na1.67Mn2.17(MoO4)3 is isotypic with structures of the Ag2M2(MoO4)3 (M = Zn, Mg, Co, Mn) family. A comparative structural description is provided between the structure of the title compound and those of related phases containing (MXO8)n chains (M = Mo, Mn and X = As) or M2O10 (M = Mo, Mn, Nb, V) dimers.

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The title compound, nona­niobium vanadium penta­cosa­oxide, was prepared by a solid-state reaction at 1198 K. It is isotypic with Nb9AsO25, Nb9PO25 and Ta9VO25. The structure consists of NbO6 octa­hedra (one with 4/m.. and two with m.. symmetry) and VO4 tetra­hedra (-4.. symmetry) sharing corners and edges to form a three-dimensional framework. This framework can be considered as a junction between ribbons made up from NbO6 octa­hedra and chains of NbO6 octa­hedra and chains of VO4 tetra­hedra. The V site shows half-occupancy, hence one half of the VO4 tetra­hedra is unoccupied. The structural differences with α-Nb9VO25, VOSO4, SbOPO4 and NbOPO4 oxides are discussed.

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The title compound α-ammonium iron(III) bis­[hydro­gen arsenate(V)], α-NH4Fe(HAsO4)2 (or poly[ammonium bis­(μ-hydro­gen arsenato)ferrate(III)], {NH4[Fe(HAsO4)2]}n), syn­the­sized hydro­thermally, is isostructural with NH4Fe(HPO4)2. Condensation of the hydro­gen arsenate groups with FeO6 coordination octa­hedra via common corners results in an overall three-dimensional framework containing inter­connected channels parallel to the a-, b- and c-axis directions. The NH4+ cations are located in three inter­secting tunnels, which is promising as an ion exchange. Hydrogen bonding of the types O—H...O and N—H...O consolidates the packing of the structure. The distortion of the coordination polyhedra is analyzed by means of the effective coordination number and distortion indices. Structural relationships with other compounds of general formula MIMIII[HXO4)]2 (X = P, As) are discussed.

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The title compound, dirubidium dimanganese(II) tris­(tetra­oxo­molyb­date), Rb2Mn2(MoO4)3, was prepared by solid-state reactions. The structure can be described as being composed of MnO6 octa­hedra sharing corners with MoO4 tetra­hedra. The three-dimensional framework contains cavities in which the rubidium ions are located. The Rb+ cations are within distorted nine- and 12-vertex polyhedra. The pairs of different Mn2+ and Rb+ cations are each located on threefold rotation axes.. Rb2Mn2(MoO4)3 is isotypic with compounds of the Cs2M2Mo3O12 (M = Ni, Fe) family. A comparative structural description is provided between the structure of the title compound and those of related phases. Differences with structures such as alluaudite are discussed.

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The title compound, tripotassium iron(III) bis­(ortho­molyb­date) dimolybdate, was obtained by a solid-state reaction. The main structural building units are one FeO6 octa­hedron, two MoO4 tetra­hedra and one Mo2O7 dimolybdate group, all with point group symmetries m. These units are linked via corner-sharing to form ribbons parallel to [010]. The three K+ cations are located between the ribbons on mirror planes and have coordination numbers of 10 and 12. Two O atoms of one of the MoO4 tetra­hedra of the dimolybdate group are disordered over two positions in a 0.524 (11):0.476 (11) ratio. The structure of the title compound is compared briefly with that of Rb3FeMo4O15.
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