Preparation and crystal structure of sodium iron hydrogen phosphate, NaFe(HPO4)(H2PO4)2 • H2O

Single crystals of sodium iron hydrogen phosphate, NaFe(HPO4)(H2PO4)(2). H2O, were prepared hydrothermally by heating a mixture of Fe2O3, H3PO4 and Na2CO3 with a small amount of water. It crystallizes orthorhombic (Pbcn (N degrees 60), Z = 8, a = 872.91(7), b = 1249.54(8), c = 1894.4(1) pm). The crystal structure was solved by using 1121 unique reflections I > 2 sigma(I) and refined for a final conventional residual R = 0.039 (188 variables, 25 atoms including hydrogen in the asymmetric unit). The main feature of the crystal structure is a ReO3-like network formed by hydrogenphosphate-, dihydrogenphosphate-groups and FeO6 octahedra with channels along the [201], [010] and [<(2)over bar 01>] directions. Na+ and H2O molecules are occupying these channels. Effective Coordination Numbers (ECoN), Mean Fictive Ionic Radii (MEFIR) and the Madelung Part of Lattice Energy (MAPLE) are calculated for the title compound.