β-K(VO₂)₂(PO₄)

A new vanadium oxide, potassium bis­(dioxovanad­yl) phosphate, β-K(VO₂)₂(PO₄), has been synthesized by a solid-state reaction. In the title compound, the [V₂PO₈] framework is built up from infinite pyramidal [V₂O₈]_∞ and [VPO₇]_∞ chains linked together by V—O—P bridges, leading to a three-dimensional framework which delimits two types of inter­secting tunnels running along [100] and [010] in which the four unique K⁺ ions, showing coordination numbers of nine and ten, are located.

Na₃Al(AsO₄)₂

The structure of the title compound tris­odium aluminium bis­(arsenate), Na₃Al(AsO₄)₂, is built up from AlO₄ and AsO₄ corner-sharing tetra­hedra, forming an undulating two-dimensional framework parallel to (100). The layers are constituted of large Al₆As₆O₃₆ rings made up from six AlO₄ and AsO₄ tetra­hedra in which two sodium cations are situated, the third sodium cation being located in the inter­layer space. The structural relationships between the title compound and Na₃Fe(PO₄)₂, NaAlCo(PO₄)₂ and Al₅Co₃(PO₄)₈ are discussed.

Na₇Cr₄(P₂O₇)₄PO₄

The title compound, hepta­sodium tetra­chromium(III) tetra­kis­(diphosphate) orthophosphate, was synthesized by solid-state reaction. Its structure is isotypic with that of Na₇M₄(P₂O₇)₄PO₄ (M = In, Al) compounds and is made up from a three-dimensional [(CrP₂O₇)₄PO₄]^7- framework with channels running along [001]. The three Na⁺ cations are located in the voids of the framework. One of the cations is situated on a general position, one is equally disordered around a twofold rotation axis and one is on a fourfold rotoinversion axis. The isolated PO₄ tetra­hedron of the anionic framework is also situated on the -4 axis. Structural relationships between the title compound and different diphosphates containing MP₂O₁₁ units (M = Mo, V) are discussed.

K(MoO₂)₄O₃(AsO₄)

A new compound with a non-centrosymmetric structure, potassium tetra­kis­[dioxomolybdenum(IV)] arsenate trioxide, K(MoO₂)₄O₃(AsO₄), has been synthesized by a solid-state reaction. The [(MoO₂)₄O₃(AsO₄)]⁺ three-dimensional framework consists of single arsenate AsO₄ tetra­hedra, MoO₆ octa­hedra, MoO₅ bipyramids and bi­octa­hedral units of edge-sharing Mo₂O₁₀ octa­hedra. The [Mo₂O₈]_∞ octa­hedral chains running along the a-axis direction are connected through their corners to the AsO₄ tetra­hedra, MoO₆ octa­hedra and MoO₅ bipyramids, so as to form large tunnels propagating along the a axis in which the K⁺ cations are located. This structure is compared with compounds containing M₂O₁₀ (M = Mo, V, Fe) dimers and with those containing M₂O₈ (M = V) chains.

LiCo₂As₃O₁₀: une nouvelle structure à tunnels inter­connectés

The title compound, lithium dicobalt(II) triarsenate, LiCo₂As₃O₁₀, was synthesized by a solid-state reaction. The As atoms and four out of seven O atoms lie on special positions, all with site symmetry m. The Li atoms are disordered over two independent special (site symmetry -1) and general positions with occupancies of 0.54 (7) and 0.23 (4), respectively. The structure model is supported by bond-valence-sum (BVS) and charge-distribution (CHARDI) methods. The structure can be described as a three-dimensional framework constructed from bi-octahedral Co₂O₁₀ dimers edge-connected to As₃O₁₀ groups. It delimits two sets of tunnels, running parallel to the a and b axes, the latter being the larger. The Li⁺ ions are located within the inter­sections of the tunnels. The possible motion of the alkali cations has been investigated by means of the BVS model. This simulation shows that the Li⁺ motion appears to be easier mainly along the b-axis direction and that this material may possess inter­esting conduction properties.

K_0.78Na_0.22MoO₂AsO₄

The title compound, potassium sodium dioxidomolybden­um(VI) arsenate, K_0.78Na_0.22MoO₂AsO₄, was synthesized by a solid-state reaction route. The structure is built up from corner-sharing MoO₆ octa­hedra and AsO₄ tetra­hedra, creating infinite [MoAsO₈]_∞ chains running along the b-axis direction. As, Mo and all but one O atom are on special positions (4c) with m symmetry and K (occupancy 0.78) is on a position (4a) of -1 in the tunnels. The possible motion of the alkali cations has been investigated by means of the bond-valance sum (BVS) model. The simulation shows that the Na⁺ motion appears to be easier mainly along the b-axis direction. Structural relationships between the different compounds of the AMoO₂AsO₄ (A = Ag, Li, Na, K, Rb) series and MXO₈ (M = V; X = P, As) chains are discussed.

Na₇Al₃(As₂O₇)₄

The title compound, hepta­sodium trialuminium tetrakis(diarsenate), has been isolated as single crystals from a solid-state reaction. Its structure, which is isotypic with that of the Na₇Fe₃(X₂O₇)₄ (X = As, P) family of compounds, consists of AlO₆ octa­hedra sharing their vertices with As₂O₇ groups, forming a three-dimensional [Al₃(As₂O₇)₄]_∞ framework incorporating channels occupied by the sodium ions. One of the aluminium ions lies on a crystallographic twofold axis. The sodium ions are situated over ten positions (one with site symmetry 2), all but one of which are partially occupied.

Li_0.5Al_0.5Mg₂(MoO₄)₃

The title compound, lithium/aluminium dimagnesium tetra­kis­[orthomolybdate(VI)], was prepared by a solid-state reaction route. The crystal structure is built up from MgO₆ octa­hedra and MoO₄ tetra­hedra sharing corners and edges, forming two types of chains running along [100]. These chains are linked into layers parallel to (010) and finally linked by MoO₄ tetra­hedra into a three-dimensional framework structure with channels parallel to [001] in which lithium and aluminium cations equally occupy the same position within a distorted trigonal-bipyramidal coordination environment. The title structure is isotypic with LiMgIn(MoO₄)₃, with the In site becoming an Mg site and the fully occupied Li site a statistically occupied Li/Al site in the title structure.

Lithium vanado(V)molybdate(VI), Li[VMoO₆]

Brannerite-type Li[VMoO₆] has been synthesized by a solid state reaction route. The V and Mo atoms statistically occupy the same site with mirror symmetry and are octa­hedrally surrounded by O atoms. The framework is two-dimensional and is built up from edge-sharing (V,Mo)O₆ octa­hedra forming (VMoO₆)_∞ layers that run parallel to the (001) plane. Li⁺ ions are situated in position with symmetry 2/m in the inter­layer space. The bond-valence analysis reveals that the Li⁺ ionic conductivity is along the [010] and [110] directions, and shows that this material may have inter­esting conduction properties. This simulation proposes a model of the lithium conduction pathways.

β-Xenophyllite-type Na₄Li_0.62Co_5.67Al_0.71(AsO₄)₆

The title compound, tetrasodium lithium cobalt aluminium hexa­(orthoarsenate), was synthesized by a solid state reaction route. In the crystal structure, Co²⁺ ions are partially substituted by Al³⁺ in an octa­hedral environment [M1 with site symmetry 2/m; occupancy ratio Co:Al = 0.286 (10):0.714 (10)]. The charge compensation is ensured by Li⁺ cations sharing a tetra­hedral site with Co²⁺ ions [M2 with site symmetry 2; occupancy ratio Co:Li = 0.690 (5):0.310 (5)]. The anionic unit is formed by two octa­hedra and three tetra­hedra linked only by corners. The CoM1M2As₂O₁₉ units associate to an open three-dimensional framework containing tunnels propagating along the a-axis direction. One Na⁺ cation is located in the periphery of the tunnels while the other two are situated in the centres: all Na⁺ cations exhibit half-occupancy. The structure of the studied material is compared with those of various related minerals reported in the literature.

Na₃Co₂(As_0.52P_0.48)O₄(As_0.95P_0.05)₂O₇

The title compound, trisodium dicobalt(II) (arsenate/phosphate) (diarsenate/diphosphate), was prepared by a solid-state reaction. It is isostructural with Na₃Co₂AsO₄As₂O₇. The framework shows the presence of CoX2₂O₁₂ (X2 is statistically disordered with As_0.95P_0.05) units formed by sharing corners between Co1O₆ octa­hedra and X2₂O₇ groups. These units form layers perpendicular to [010]. Co2O₆ octa­hedra and X1O₄ (X1 = As_0.54P_0.46) tetra­hedra form Co2X1O₈ chains parallel to [001]. Cohesion between layers and chains is ensured by the X2₂O₇ groups, giving rise to a three-dimensional framework with broad tunnels, running along the a- and c-axis directions, in which the Na⁺ ions reside. The two Co²⁺ cations, the X1 site and three of the seven O atoms lie on special positions, with site symmetries 2 and m for the Co, m for the X1, and 2 and m (× 2) for the O sites. One of two Na atoms is disordered over three special positions [occupancy ratios 0.877 (10):0.110 (13):0.066 (9)] and the other is in a general position with full occupancy. A comparison between structures such as K₂CdP₂O₇, α-NaTiP₂O₇ and K₂MoO₂P₂O₇ is made. The proposed structural model is supported by charge-distribution (CHARDI) analysis and bond-valence-sum (BVS) calculations. The distortion of the coordination polyhedra is analyzed by means of the effective coordination number.

Bis(1,4-diazo­niabi­cyclo­[2.2.2]octa­ne) di-μ-chlorido-bis­[tetra­chlorido­anti­monate(III)] dihydrate

The title salt, (C₆H₁₄N₂)₂[Sb₂Cl₁₀]·2H₂O, was obtained by slow evaporation of an acidic solution of 1,4-di­aza­bicyclo­[2.2.2]octane and SbCl₃. The crystal structure consists of (C₆H₁₄N₂)²⁺ cations, [Sb₂Cl₁₀]⁴⁻ double octa­hedra and lattice water mol­ecules. All mol­ecular components are situated on special positions. The cation and the lattice water mol­ecule exhibit mirror symmetry, whereas the anion has site symmetry 2/m. The cations, anions and water mol­ecules are alternately arranged into columns along [010]. Individual columns are joined into layers extending along (001). Intra­layer N—H...O and inter­layer N—H...Cl hydrogen-bonding inter­actions lead to the formation of a three-dimensional network.

2-Amino-6-methyl­pyridinium trans-di­aqua­dioxalatochromate(III) monohydrate

In the title compound, (C₆H₉N₂)[Cr(C₂O₄)₂(H₂O)₂]·H₂O, the Cr^III atom adopts a slightly distorted octa­hedral coordination environment defined by two chelating oxalate ligands in the equatorial plane and two water mol­ecules in axial positions. A three-dimensional network is generated by inter­molecular N—H...O and O—H...O hydrogen-bonding interactions involving the cation, the complex anion and the lattice water molecule.

Imidazolium trans-di­aqua­dioxalato­chromate(III) dihydrate

In the title hydrated mol­ecular salt, (C₃H₅N₂)[Cr(C₂O₄)₂(H₂O)₂]·2H₂O, the complete cation is generated by a crystallographic twofold rotation axis, with one C atom lying on the rotation axis. The complete anion is generated by crystallographic inversion symmetry (Cr^III site symmetry -1), to generate a slightly distorted CrO₆ octa­hedron with trans water mol­ecules and chelating oxalate dianions. The oxalate ion is almost planar (r.m.s. deviation = 0.017 Å) and the five-membered chelate ring is a shallow envelope with the metal ion displaced by 0.126 (1) Å from the ligand atoms. The crystal structure features O—H...O, N—H...O and C—H...O hydrogen bonds, which link the components into a three-dimensional network.