Na 4Ni 7(PO 4) 6 crystallizes in the space group Cm with a = 10.550(2), b = 13.985(5), and c = 6.398(2)Å; β = 104.87(2)°. For Z = 2 the calculated density is 3.906 g/cm 3 ( V = 912.4 Å 3). Structure determination and refinement ( R = 0.041, RW = 0.045) were carried out on flux (NaF) grown crystals. The structure consists of layers of nickel-containing octahedra and phosphorus-containing tetrahedra interconnected to form a pseudocentrosymmetric framework. A layer consisting of parallel tunnels which run along the a direction contains the sodium ions in a noncentrosymmetric arrangement.