A new lead iron(III) hydrated phosphate, Pb3Fe2(PO4)4(H2O), has been synthesised hydrothermally in Teflon-lined stainless steel autoclaves at 220 °C for 7 days, with an initial pH of 1.5. It is the first example of a synthetic hydrous Pb–Fe3+ phosphate. Crystals are small, colourless to white prisms, uniaxial (+) and non-pleochroic. The calculated refractive index for white light is n = 1.95. Single-crystal structure determination (R(F) = 0.0457) shows Pb3Fe2(PO4)4(H2O) to be tetragonal, space group P41212 (no. 92), with a = 9.0440(10), c = 16.766(3) Å, V = 1371.4(3) Å3 and Z = 4. Pb3Fe2(PO4)4(H2O) has a structure type which is based on a tetrahedral–octahedral framework of FeO6 octahedra sharing corners with PO4 tetrahedra, with Pb atoms and H2O molecules occupying voids in the framework. Pb3Fe2(PO4)4(H2O) is homeotypic with synthetic Pb3Cr2(PO4)4; both compounds share the same heteropolyhedral topology and the same space group, but only Pb3Fe2(PO4)4(H2O) contains an additional position occupied by a water molecule. The octahedral–tetrahedral chain of Pb3Fe2(PO4)4(H2O) is topologically similar to double–strand chains found in the structures of hannayite, galliskiite, kapundaite, PbIn(AsO4)(AsO3OH) and Na2.88Fe(PO4)2. Infrared spectroscopy is used to describe the vibrational properties of Pb3Fe2(PO4)4(H2O).

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