Synthèse et étude structurale de Na9Cr(MoO4)6.

The title compound, nona-sodium chromium(III) hexa-kis[molybdate(VI)], Na9Cr(MoO4)6 was prepared by solid-state reactions. The basic structure units are isolated polyhedral clusters composed of a central CrO6 octa-hedron sharing vertices with six MoO4 tetrahedra to form an open framework in which the Na(+) cations are bound to the free vertices of the MoO4 tetra-hedra. The Cr(3+) cation has site symmetry of 32 (6a), one Na atom sits on a twofold axis (18e), and all other atoms are at general positions. The bond-valance-sum model confirms the expected values of ion charges. The title compound is isotypic with Na9Sc(MoO4)6 and Na9Fe(MoO4)6. It is compared and discussed with similar structures.