Na₇Mg₁₃Nd(PO₄)₁₂

Investigations of the quasi-ternary system Na₃PO₄–Mg₃(PO₄)₂–NdPO₄ allowed us to obtain the new phosphate hepta­sodium trideca­magnesium neodymium dodeca­kis­phosphate, Na₇Mg₁₃Nd(PO₄)₁₂, by applying a flux method. The crystal structure is isotypic with that of the previously reported Na₇Mg₁₃Ln(PO₄)₁₂ (Ln = Eu, La) compounds. It consists of a complex three-dimensional framework built up from an NdO₈ polyhedron (m symmetry), an MO₆ octa­hedron statistically occupied by M = Mg and Na, and eight MgO_x (x = 5, 6) polyhedra (four with site symmetry m), linked either directely by sharing corners, edges and faces, or by one of the eight unique PO₄ tetra­hedra through common corners. Two of the PO₄ tetra­hedra are statisticaly disordered over a mirror plane. The whole structure can be described as resutling from an assembly of two types of structural units, viz [Mg₄MP₄O₂₂]_∞² layers extending parallel to (100) and stacked along [100], and [Mg₄NdP₄O₃₆]_∞¹ undulating chains running along the [010] direction. The six different Na⁺ cations (five with site symmetry m and one with 0.5 occupancy) are situated in six distinct cavities delimited by the framework. The structure was refined from data of a racemic twin.