The heterodinuclear iron(III) and copper(II) molecule Cu(salen)Fe(acac)₂NO₃ and its iron precursor Fe(acac)₂NO₃. Synthesis, magnetic susceptibility, EPR and Mössbauer investigations

The synthesis, EPR, magnetic and Mössbauer 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=5/2 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 Mössbauer 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.