Na 7 Mg 13 Nd(PO 4 ) 12

Investigations of the quasi-ternary system Na 3 PO 4 –Mg 3 (PO 4 ) 2 –NdPO 4 allowed us to obtain the new phosphate heptasodium tridecamagnesium neodymium dodecakisphosphate, Na 7 Mg 13 Nd(PO 4 ) 12 , by applying a flux method. The crystal structure is isotypic with that of the previously reported Na 7 Mg 13 Ln (PO 4 ) 12 ( Ln = Eu, La) compounds. It consists of a complex three-dimensional framework built up from an NdO 8 polyhedron ( m symmetry), an M O 6 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 PO 4 tetrahedra through common corners. Two of the PO 4 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 [Mg 4 M P 4 O 22 ] ∞ 2 layers extending parallel to (100) and stacked along [100], and [Mg 4 NdP 4 O 36 ] ∞ 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.