Synthesis and crystal structure of a new magnesium phosphate Na(3)RbMg(7)(PO(4))(6)

A new magnesium phosphate, Na(3)RbMg(7)(PO(4))(6) [tris­odium rubidium hepta­magnesium hexakis(ortho­phosphate)], has been synthesized as single crystals by the flux method and exhibits a new structure type. Its original structure is built up from MgO(x) (x = 5 and 6) polyhedra linked directly to each other through common corners or edges and reinforced by corner-sharing with PO(4) tetra­hedra. The resulting anionic three-dimensional framework leads to the formation of channels along the [010] direction, in which the Na(+) cations are located, while the Rb(+) cations are located in large inter­stitial cavities.