The synthesis, EPR, magnetic and Mossbauer properties of two iron(III) complexes are reported. The heterodinuclear iron(III)-copper(II) complex Cu(salen)Fe(acac)2NO3 is obtained as an adduct from the reaction of the two mononuclear moieties, the Cu(salen) molecule and the mononuclear iron(III) molecule Fe(acac)2NO3 acting as a precursor of the dinuclear unit. The latter molecule itself has been prepared by ligand substitution from the tris-acetylacetonate Fe(acac)3. The dinuclear complex is characterized by comparing the properties of the mono- and the dinuclear complex. Fe(acac)2NO3 is identified from its typical IR spectrum with the main nitrate vibrations at 1380, 1250 and 1010 cm-1 and an axial S = 512 EPR spectrum in the solid state. Ligand rearrangement occurs in solution as indicated by the presence of only ionic nitrate and a rhombic EPR spectrum. The dinuclear molecule presents a very modified IR spectrum, where the copper(salen) phenolic oxygen vibration and the bound-nitrate vibrations have disappeared; additionally no EPR spectrum can be recorded at X-band frequency. The magnetic data have been interpreted using spin-Hamiltonian formalism. From magnetic susceptibility measurements, in the solid state, the following set of parameters has been determined: g = 1.99, D = 4.15 cm-1 for the mononuclear complex, and J = -3 cm-1, g = 2.05, D = -0.1 cm-1 for the dinuclear complex, indicating an effective antiferromagnetic interaction between the. two metal ions. The Mossbauer studies yield: D = 0.45 cm-1 for the mononuclear complex, and J = - 1.5 cm-1, D = -0.20 cm-1 for the dinuclear complex.

Magnetic susceptibility, EPR, Mossbauer, and X-ray studies have been performed on heteropolynuclear clusters containing iron(III) and copper(II) ions: {Cu(Mesalen)}2Fe(acac)(NO3)2 and {Cu(Mesalen)}3Fe(acac)(PF6)2 (Mesalen = 1,2-bis((methylsalicylidene)amino)ethane; acac = acetylacetonato(1-)). The spectroscopic results obtained for the trinuclear system {2CuFe} suggest strong antiferromagnetic coupling of iron(III) to the two copper(II) ions to yield a S = 3/2 ground-state system. X-ray studies reveal that the tetranuclear system {3CuFe} crystallizes in the hexagonal space group P6(1)22 with Z = 6, a = b = 14.471 (3) angstrom, and c = 50.372 (2) angstrom, it consists of a trinuclear unit {2CuFe} plus a mononuclear Cu(Mesalen) molecule, arranged in helicoidal polymeric chains. Magnetic susceptibility, EPR, and Mossbauer studies under moderate fields consistently show that the {2CuFe} and Cu(Mesalen) moieties are weakly interacting. Under high-field and low-temperature conditions, this interaction is not observable in Mossbauer spectroscopy. Since the Mossbauer spectra under these conditions are identical for the tri- and tetranuclear clusters, we conclude that the {2CuFe} moieties are very similar in both cluster types. The presence of the additional Cu(Mesalen) molecule in the tetranuclear cluster expresses itself in the Mossbauer spectra only at elevated temperatures by an enhancement of the spin-spin relaxation rates of nearly 1 order of magnitude larger compared to the trinuclear cluster.