A new iron phosphonate-oxalate [Fe(O3PCH3)(C2O4)(0.5)(H2O)] (1), has been synthesized under hydrothermal condition. The single-crystal X-ray diffraction studies reveal that 1 consists of layers of vertex-linked FeO6 octahedra and O3PC tetrahedra, which are further connected by bis-chelate oxalate bridges, giving to a 3D structure with 10-membered channels. Crystal data: monoclinic, P2(1)/n (no. 14), a = 4.851(2) angstrom, b = 16.803(7) angstrom, c = 7.941(4) angstrom, beta = 107.516(6)degrees, V = 617.2(5) angstrom(3), Z = 4, R-1 = 0.0337 and wR(2) = 0.0874 for 1251 reflections [I > 2 sigma(I)]. M6ssbauer spectroscopy measurement confirms the existence of high-spin Fe(III) in 1. Magnetic studies show that I exhibits weak ferromagnetism with T-N = 30 K due to a weak spin canting. (c) 2006 Elsevier Ltd. All rights reserved.