A new iron(III) phosphate Na3Fe3(PO4)(4) has been synthesized and characterized. It decomposes before melting at 860degreesC into FePO4 and Na3Fe2(PO4)(3). The structure of the compound was determined by single-crystal X-ray diffraction. The unit cell is monoclinic with the following parameters: a = 19.601(8) Angstrom, b = 6.387(1) Angstrom, c = 10.575(6) Angstrom and beta = 91.81(4)degrees; Z = 4; space group: C2/c. Na3Fe3(PO4)(4) exhibits a layered structure involving corner-linkage between FeO6 octahedra, and corner- and edge-sharing between FeO6 octahedra and PO4 tetrahedra. The Na+ cations occupying the interlayer space are six and seven-fold coordinated by oxygen atoms. The relationship between the structure of Na3Fe3(PO4)(4) and the previous reported hydrate K3Fe3(PO4)(4)H2O will be discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.