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° 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 > 2σ(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 Fe O₆ octahedra with channels along the 201], 010] and 201] 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.