New polymeric materials of formula [M(tcnp)2(H2O)2] (M = MnII, 1; FeII, 2; CoII, 3 and CuII, 4; tcnp- = [(NC)2CC(OEt)C(CN)2]- = 1,1,3,3-tetracyano-2-ethoxypropenide anion) have been synthesized and characterized by infrared spectroscopy and X-ray crystallography. Crystal structures were determined for 1, 3 and 4. In these compounds, the organic ligand acts in a bridging mode with two of its four nitrogen atoms arising from the two different C(CN)2 units; each metal ion has a centrosymmetric pseudo-octahedral trans-MN4O2 environment with four nitrogen atoms from four organic ligands and two oxygen atoms from water molecules. The octahedron, almost regular in 1 and 3, is distorted in 4, with a strong elongation along the pseudo fourfold axis. In all compounds (1-4), the molecular arrangement, which involves 16-membered M(NCCCCCN)2M dimetallacycles arising from the bridging mode of the organic ligand, can be described as chains of such dimetallacycles running along the [1-10] direction. Intra-chain M⋯M distances (9.017 Å in 1, 8.887 Å in 3 and 9.133 Å in 4) are significantly longer than those observed in the corresponding μ2-bridging dicyanamide derivatives (≈7.4 Å); these large differences can be explained from the coordination mode of the μ2-bridging tcnp ligand. Consequently, the shortest M⋯M distances are of the inter-chain type (8.282 Å in 1, 8.245 Å in 3 and 8.120 Å in 4); they occur along the [100] direction between metal ions of eclipsed chains and correspond to the a parameter. In the ab plane, the adjacent chains are connected by hydrogen bonds between the coordinated water molecules and one of the uncoordinated nitrogen atoms of the organic ligand, giving rise to 2D structures. For each compound, magnetic susceptibility measurements show a Curie law in the whole temperature range in agreement with the large separation between the paramagnetic ions. © 2003 Elsevier Science Ltd. All rights reserved.