Synthesis, structure and magnetic properties of a quasi-one-dimensional copper(II) compound. An unusual oxalato-bridged copper dimer

A new compound [Cu(Him)2(ox)]2[Cu(Him)2(H2O)]2 (Him=imidazole, ox=dianion of oxalic acid) has been prepared and structurally determined. The structure consists of quasi-one-dimensional chains built from two different neutral [Cu(Him)2(ox)]2 and [Cu(Him)2(H2O)(ox)]2 units linked by hydrogen bonds. Two centrosymmetrically related copper ions in the former unit are five-coordinated by two nitrogen atoms from the imidazole ligands and two oxygen atoms from the oxalate anion occupying the basal plane and the oxygen atom of another chelating oxalate situated at the apical position with a weak contact of 2.837(2) A. The coordination environment of the other two copper ions connected by O–H · · · O hydrogen bonds in the other unit can be described as a distorted square pyramid, with two oxygen atoms of the oxalate ion and two nitrogen atoms from the imidazole ligands in the basal plane and one oxygen atom of the coordinated water molecule in the apical position. The (Him)N–H · · · O(ox) hydrogen bonds connect the adjacent units to give rise to a quasi-one-dimensional structure. The room-temperature ESR study gives a g↑ value of 2.07 and a g∥ value of 2.23. From magnetic susceptibility measurements the compound was found to exhibit a weak antiferromagnetic interaction (J=−2.64 cm−1) between the copper(II) ions through the Cu–O–Cu pathways.