Synthèse et structure cristalline de Na3NbO(AsO4)2

The compound Na3NbO(AsO4)2was prepared by a solid-state reaction. It crystallizes in the monoclinic system, space groupP21/n, witha=9.637(3) ?,b=8.509(2) ?,c=10.593(2) ?,=108.67(2)°,M=455.72,V=822.9(4) ?3,Z=4,=3.687 g cm-3. The crystal structure was refined (137 variables) from 1440 independent reflections collected on a Nonius CAD4 automatic diffractometer with MoKradiation. The finalRindex and weightedwRindex are 0.022 and 0.045, respectively. The threedimensional network is built up from NbO6octahedra and AsO4tetrahedra-sharing corners; each NbO6octahedron is bonded to five AsO4tetrahedra. 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 those of theA3MX2O9(A=Na, K;M=Nb, Sb;X=P, As).