Crystal structure and magnetic properties of the complex [Cu(en)2]2[{Fe(edta)}2O]·2H2O. A heterobimetallic CuII–FeIII system containing a µ-oxo-di-iron(III) moiety

Abstract

The synthesis, structure, and magnetic properties are reported for the co-ordination polymer [Cu(en)₂]₂[{Fe(edta)}₂O]·2H₂O (en = ethylenediamine, edta = ethylenediamine-NNN′N′-tetra-acetate). Crystals are monoclinic, space group C2/c, a= 16.662(2), b= 15.254(3), c= 18.751(3)Å, β= 102.58(1)°, Z= 8 (for empirical formula C₁₄H₃₁CuFeN₆O₁₀); R= 0.0296 (R′= 0.0310) for 316 parameters and 3 105 observed reflections. The complex is a three-dimensional polymer consisting of µ-oxo iron(III) dimers connected with two different Cu(en)₂ moieties [Cu(1) and Cu(2)] sitting on non-equivalent inversion centres. The Cu–Fe connections are in one case [Cu(2)] through an iminoacetate group of the edta, and in the other via a hydrogen bond that connects Cu(1) with a carboxylate group co-ordinated to Fe. The extended covalently bonded network results in ordered bimetallic chains [⋯ Cu(2)⋯ Fe–Fe ⋯ Cu(2)⋯], with Cu(1) hydrogen bonded to them. The monodentate co-ordination of the COO groups bonded to Cu(2) precludes any significant magnetic interaction between Cu and Fe. Thus, magnetic susceptibility data down to 4 K are adequately described by assuming a coupled µ-oxo iron(III) dimer (J=–85 cm^–1, H=–2JS₁S₂) and two Cu^II monomers. The possibility of increasing the magnetic dimensionality of this system following a procedure similar to that reported for other edta bimetallic compounds is suggested.