Synthesis,Crystal Structure and Characterization of the Copper Iron Phosphate Cu8Fe2O5(PO4)4

The system CuO‐Fe₂O₃‐P₂O₅ has been investigated by means of the solid state reaction between CuO, Fe₂O₃ and (NH₄)₂HPO₄ in quartz crucibles at 900 °C. The powder samples were characterized by X‐ray diffraction, IR spectroscopy and TG/DTA. Single crystals of a new quaternary phase Cu₈Fe₂P₄O₂₁ were achieved by cooling from the melt of the compound in a sealed, evacuated quartz ampoule. Cu₈Fe₂O₅(PO₄)₄ crystallizes in the monoclinic space group C2/m (No 12) with a = 15.9733(8) Å, b = 5.9438(3) Å, c = 9.5530(5) Å, β = 113.76(1)°, Z = 2. The three‐dimensional framework consists of [FeO₆] octahedra, three different [CuO₅] polyhedra and [PO₄] tetrahedra. Cu₈Fe₂P₄O₂₁ exhibits an incongruently melting point at 945 °C.