Crystal structure of alluaudite-type NaMg3(HPO4)2(PO4)

Abstract : The title compound, sodium trimagnesium bis­(hydrogen phosphate) phosphate, was obtained under hydro­thermal conditions. In the crystal, two types of [MgO6] 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, HPO4 and PO4, 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 HPO4 tetra­hedron points into the other type of channel and exhibits a strong hydrogen bond to an O atom of the PO4 tetra­hedron on the opposite side.