Synthesis, crystal structure, spectroscopic characterisation and magnetic properties of [Cu2(BIBM)2(C2O4)2]·4H2O (BIBM=bis(2-imidazolyl)bis(methoxycarbonyl)methylmethane)

The structure and spectroscopic and magnetic properties of bis(μ-1,2,3-oxalato)bis[bis(2-imidazolyl)bis(methoxycarbonyl)methylmethane]dicopper(II) tetrahydrate are described. The compound is built of centrosymmetric neutral dimeric [Cu2(BIBM)2(C2O4)2] entities linked through hydrogen bonds involving water molecules and oxalate groups. In the dimeric unit the two centrosymmetrically related copper — which are involved in CuN2O2O2′ chromophores lying in an elongated octahedral environment — are bridged through the oxalate group which acts in a bidentate–monodentate (μ-1,2,3) fashion. Both electronic and EPR spectra are indicative of an essentially dx2−y2 ground state for the copper(II) ions. Magnetic susceptibility measurements in the range 1.8–200 K show very weak antiferromagnetic exchange between the copper(II) ions (2J=−0.35 cm−1). This feature is discussed on the basis of the relative orientation of the coordination polyhedron around the metal atom and the bridging network.