Synthesis, characterization and magnetic properties of copper(II)-iron(III) heterotetranuclear complexes bridged by tris(oxalato)ferrate(III)

The strategy of "complex as ligand" allowed us to synthesize three new muw-oxalato-bridged heterotetranuclear complexes identified as [Cu3Fe(ox)(3)(Me(2)bpy)(3)] (ClO4)(3) (1), [Cu3Fe(ox)(3)(Me(2)phen)(3)](ClO4)(3) (2) and [Cu3Fe(ox)(3)(phen)(3)](ClO4)(3) (3), where ox represents the oxalato dianions; Me(2)bpy, Me(2)phen and phen stand for 4,4'-dimethyl-2,2'-bipyridine, 2,9-dimethyl-1,10-phenanthroline or 1,10-phenanthroline, respectively. These complexes are the first examples of [(Cu3FeIII)-Fe-II] species bridged by oxalato groups. Based on elemental analyses, molar conductivity and magnetic moment (at room-temperature) measurements, IF, ESR and electronic spectral studies, these complexes are proposed to have oxalato-bridged structure consisting of three copper(II) ions and an iron(III) ion, in which the iron(III) ion has an octahedral environment, and the three copper(II) ions have a square-planar environment. The complexes (1) and (2) were further characterized by variable-temperature magnetic susceptibility (4.2similar to300 K) measurements and the observed data were simulated by the equation based on the spin Hamiltonian operator, (H) over cap = -2J((S) over cap (Cul) . (S) over cap (Fe) + (S) over cap (Cu2) . (S) over cap (Fe) + (S) over cap (Cu3) . (S) over cap (Fe)), giving the exchange integrals J = -9.15 cm(-1) for (1) and J -8.79 cm(-1) for (2). The results indicate the presence of an antiferromagnetic spin-exchange interaction between the copper(II) and iron(III) ions through the oxalato-bridge in both complexes (1) and (2).