Synthesis and crystal structure of Na3NbO(AsO4)(2)

The compound Na3NbO(AsO4)(2) was prepared by a solid-state reaction. It cry stallizes in the monoclinic system, space group P2(1)/n, with a=9.637(3)Ang strom, b = 8.509(2)Angstrom, c = 10.593(2)Angstrom, beta=108.67(2)degrees, M=455.72, V=822.9(4) Angstrom(3), Z=4, rho = 3.687 g cm(-3). The crystal st ructure was refined (137 variables) from 1440 independent reflections colle cted on a Nonius CAD4 automatic diffractometer with MoK alpha radiation. Th e final R index and weighted wR index are 0.022 and 0.045, respectively, Th e three-dimensional network is built up from NbO6 octahedra and AsO4 tetrah edra-sharing corners; each NbO6 octahedron is bonded to five AsO4 tetrahedr a. This arrangement delimits three different tunnels running along [100], [ 010], and [001], respectively, at the intersection of which the sodium ions are located in a six-coordination mode. This structure is compared with th ose of the A(3)MX(2)O(9) (A = Na, K; M = Nb, Sb; X = P, As). (C) 1999 Acade mic Press.