Crystal structure of alluaudite-type NaMg(3)(HPO(4))(2)(PO(4))

The title compound, sodium trimagnesium bis­(hydrogen phosphate) phosphate, was obtained under hydro­thermal conditions. In the crystal, two types of [MgO(6)] octa­hedra, one with point group symmetry 2, share edges to build chains extending parallel to [10-1]. These chains are linked together by two kinds of phosphate tetra­hedra, HPO(4) and PO(4), the latter with point group symmetry 2. The three-dimensional framework delimits two different types of channels extending along [001]. One channel hosts the Na(+) cations (site symmetry 2) surrounded by eight O atoms, with Na—O bond lengths varying between 2.2974 (13) and 2.922 (2) Å. The OH group of the HPO(4) tetra­hedron points into the other type of channel and exhibits a strong hydrogen bond to an O atom of the PO(4) tetra­hedron on the opposite side.