K0.12Na0.54Ag0.34Nb4O9AsO4

Potassium sodium silver tetra­niobium nona­oxide arsenate, K0.12Na0.54Ag0.34Nb4AsO13, synthesized by solid-state reaction at 1123 K, adopts a three-dimensional framework delimiting tunnels running along [001] in which occupationally disordered sodium, silver, and potassium ions are located. Of the 11 atoms in the asymmetric unit (two Nb, one As, one Ag, one K, one Na and fiveO), nine are located on special positions: one Nb and the K, Ag, Na and two O atoms are situated on mirror planes, the other Nb is on a twofold rotation axis, and the As atom and one O atom are on sites of m2m symmetry

Non-centrosymmetric Na3Nb4As3O19

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. M 2XO13 and M 2 X 2O17 (M = transition metal, and X = As or P)

Structure cristalline de la triple molybdate Ag0.90Al1.06Co2.94(MoO4)5

Silver(I) aluminiun tricobalt(II) pentakis[tetraoxidomolybdate(VI)], Ag0.90Al1.06Co2.94(MoO4)5, was synthesized using a solid-state reaction at 845 K. The structure can be described as a three-dimensional framework formed from dimeric M2O10 (M = Co/Al) and trimeric M3O14 units linked to MoO4 tetrahedra by sharing corners, with the cavities occupied by disordered Ag+ cations. It is shown that the Co and Al atoms occupy common positions with different occupancies. The Ag+ cations are located at two different sites with occupancies of 0.486 (1) and 0.408 (1). The title coumpond is isotypic with NaMg3Al(MoO4)5 and NaFe4(MoO4)5. Differences and similarities with other related structures are discussed

β-Nb9VO25

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