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The asymmetric unit of the title compound, Na2(MoO2)3(As2O7)2, is composed of two cyclic MoAs2O11 units and an MoO6 corner-sharing octa­hedron. The anionic framework can be decomposed into two types of layers, viz. MoO2As2O7 and Mo2As2O14, which use mixed Mo-O-As and As-O-Mo bridges to achieve a new three-dimensional structure with two types of large channels in which the Na+ cations are located. Two O atoms are disordered and are located in two positions close to their initial positions with occupancy ratios of 0.612 (17):0.388 (17) and 0.703 (12):0.298 (12).

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A new non-centrosymmetric compound, tris­odium tetra­niobium triarsenic nona­deca­oxide, Na3Nb4As3O19, has been synthesized by a solid-state reaction at 1123 K. The structure consists of AsO4 tetra­hedra and NbO6 octa­hedra sharing corners to form a three-dimensional framework containing two types of tunnels running along the c axis, in which the sodium ions are located. Na+ cations occupying statistically several sites, respectively, are surrounded by seven, six and four O atoms at distances ranging from 2.08 (1) to 2.88 (4) Å. The title structure is compared with those containing the same groups, viz. M2XO13 and M2X2O17 (M = transition metal, and X = As or P).

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Single crystals of wyllieite-type silver(I) manganese(II) tris­orthoarsenate(V), Ag1.09Mn3.46(AsO4)3, were grown by a solid-state reaction. The three-dimensional framework is made up from four Mn2+/Mn3+ cations surrounded octa­hedrally by O atoms. The MnO6 octa­hedra are linked through edge- and corner-sharing. Three independent AsO4 tetra­hedra are linked to the framework through common corners, delimiting channels along [100] in which two partly occupied Ag+ sites reside, one on an inversion centre and with an occupancy of 0.631 (4), the other on a general site and with an occupancy of 0.774 (3), both within distorted tetra­hedral environments. One of the Mn sites is also located on an inversion centre and is partly occupied, with an occupancy of 0.916 (5). Related compounds with alluaudite-type or rosemaryite-type structures are compared and discussed.

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In the title compound, tris­odium 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 octa­hedra 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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The tite compound, lithium penta­sodium nona­molybdate, LiNa5Mo9O30, was synthesized by solid-state reaction. The three-dimensional [Mo9O30]6- framework is built up from MoO6 octa­hedra and MoO5 bipyramids, linked together by edges and corners. The framework delimits two types of inter­secting tunnels running along [100] and [010] in which the Na+ and Li+ ions are located. The asymmetric unit contains one Mo, one Na and one Li site located on a twofold rotation axis. The crystal studied was a racemic twin with site a twin ratio of 0.51 (10):0.49 (10). Relationships between the structures of K2Mo3O10, K2Mo4O13, Cs2Mo7O22, Na6Mo10O33 and Na6Mo11O36 compounds are discussed.

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The title mixed-alkali-metal molybdenium oxide, hexa­kis­(lithium/sodium) undeca­molybdate, was synthesized by solid-state reaction at 793 K. Its [Mo11O36]6- framework is built up from MoO6 octa­hedra and MoO5 pyramids linked together by edges and vertices. The framework delimits two types of inter­secting tunnels running along [100] and [001], where the sodium and lithium ions are located. Two of the sodium ions and the lithium ion have fractional site occupancies. One of the Mo atoms has site symmetry 2, one sodium ion has site symmetry 2 and one has site symmetry -1, and the Li+ ion has site symmetry 2. Structural relationships between the title compound and the anatase and Na6Mo11O36 structures are discussed.

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Disodium molybdenum dioxide diarsenate, Na2MoO2As2O7, has been synthesized by a solid-state reaction. The structure is built up from MoAs2O12 linear units sharing corners to form a three-dimensional framework containing tunnels running along the a-axis direction in which the Na+ cations are located. In this framework, the AsV atoms are tetra­hedrally coordinated and form an As2O7 group. The MoVI atom is displaced from the center of an octa­hedron of O atoms. Two Na+ cations are disordered about inversion centres. Structural relationships between different compounds: A2MoO2As2O7 (A = K, Rb), AMOP2O7 (A = Na, K, Rb; M = Mo, Nb) and MoP2O7 are discussed.

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The structure of the title organic–inorganic hybrid compound, {(C2H7N4O)2[BiCl5]}n, consists of corrugated chains parallel to [100] of corner-joined [BiCl6] octa­hedra, separated by layers of organic 1-carbamoylguanidinum cations. The crystal cohesion is achieved by N—H...O and N—H...Cl hydrogen bonds, which link the organic and inorganic parts of the structure.

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In the crystal structure of the title compound, (C5H6ClN2)[Cr(C2O4)2(H2O)2]·1.5H2O, the CrIII atom adopts a distorted octa­hedral geometry being coordinated by two O atoms of two cis water mol­ecules and four O atoms from two chelating oxalate dianions. The cis-diaqua­dioxalatochromate(III) anions, 2-amino-5-chloro­pyridinium cations and uncoordinated water mol­ecules are linked into a three-dimensional supra­molecular array by O—H...O and N—H...O hydrogen-bonding inter­actions. One of the two independent lattice water molecules is situated on a twofold rotation axis.
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