Non-centrosymmetric Na(3)Nb(4)As(3)O(19).

A new non-centrosymmetric compound, tris-odium tetra-niobium triarsenic nona-deca-oxide, Na(3)Nb(4)As(3)O(19), has been synthesized by a solid-state reaction at 1123 K. The structure consists of AsO(4) tetra-hedra and NbO(6) octa-hedra 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(2)XO(13) and M(2)X(2)O(17) (M = transition metal, and X = As or P).