Synthesis and ferromagnetically coupled heterodinuclear oxamido-bridged copper(II)-oxovanadium(IV) complexes

Three novel copper(II)-oxovanadium(IV) heterodinuclear complexes bridged by dianions of N,N′-oxamidobis(propionato)cuprate, [Cu(obp)], and endcapped with 2,9-dimethyl-1,10-phenanthroline (Me2phen), 4,7-diphenyl-1,10-phenanthroline (Ph2phen) or 5-methyl-1,10-phenanthroline (Mephen), respectively, have been synthesized and identified as [Cu(obp)VO(Me2phen)] (1), [Cu(obp)VO(Ph2phen)] (2) and [Cu(obp)VO(Mephen)] (3). The three dinuclear complexes have not yet been isolated in crystalline form suitable for X-ray structure analysis, but based on elemental analyses, IR and electronic spectra studies, magnetic moments at room temperature and molar conductivity measurements, these complexes are proposed to have an extended oxamido-bridged structure consisting of planar copper(II) and square-pyramidal oxovanadium(IV) ions. The three heterodinuclear complexes were further characterized by variable-temperature magnetic susceptibility (4.2-300 K) measurements and the magnetic data have been used to deduce the indicated heterodinuclear structure. The results derived from least-squares fit of the experimental data have confirmed that the operation of a ferromagnetic interaction between the adjacent copper(II) and oxovanadium(IV) ions through the oxamido bridge within each molecule takes place. Based on spin Hamiltonian, H^=-2JS^1·S^2, the exchange integral (J) was evaluated as J=+21.9cm-1 for (1), J=+18.8cm-1 for (2) and +26.5 cm−1 for (3). The influence of the symmetry of the magnetic orbitals and different terminal ligands on the nature and magnitude of the magnetic interaction between the paramagnetic centers is also discussed.