New coordination polymers with a 2,2-dicyano-1-ethoxyethenolate (dcne−) bridging ligand: syntheses, structural characterisation and magnetic properties of [M(dcne)2(H2O)2] (M = MnII, FeII, CoII, NiII and ZnII) and [Cu(dcne)2(H2O)]

Abstract

New polymeric materials [M(dcne)₂(H₂O)₂] with M = Mn^II (1), Fe^II (2), Co^II (3), Ni^II (4) and Zn^II (5) and [Cu(dcne)₂(H₂O)] (6) (dcne⁻ = [(CN)₂CC(O)OEt)]⁻ = 2,2-dicyano-1-ethoxyethenolate anion) have been synthesised and characterised by infrared spectroscopy, X-ray crystallography and magnetic measurements. In these compounds, each organic ligand acts in a bridging mode with its two nitrogen atoms bound to two different metal cations. In compounds 1–5, each metal cation has a pseudo-octahedral cis-MN₄O₂ environment with four nitrogen atoms from four different organic ligands and two oxygen atoms from two water molecules. In compound 6, only one water molecule is coordinated and each copper(II) cation presents a CuN₄O distorted trigonal bipyramid environment with a perfectly planar CuN₂O equatorial plane. In all compounds the molecular arrangement involves 12-membered M(dcne)₂M dimetallacycles that share a M atom forming chains running along the [101] direction with alternated, almost orthogonal, dimetallacycles. The intra-chain M⋯M distances (7.4270(2) Å in 3, 7.4628(2) Å in 5 and 7.2299(3) Å in 6) are longer than the inter-chain ones (6.0430(4) Å in 3, 6.0907(3) Å in 5 and 5.9648(5) Å in 6). The chains are connected by hydrogen bonds between the coordinated water molecules and the terminal oxygen atom of the organic ligand, giving rise to a 3D structure. Magnetic measurements show very weak antiferromagnetic coupling between metal centres that can be satisfactorily reproduced with a regular antiferromagnetic classical spin chain model.