Study of antiferromagnetic phenomenon for oxo-bridged iron (III) dimers in model molecules of methemerythrin Original Research Article

By introducing the covalent effect into the Girerd–Journaux–Kahnʹs magnetic theory a more general magnetic exchange formula for describing transition-metal ion pairs in covalent complex molecules has been established. By this formula and by the use of our double-slater-type-function (DSF) calculation procedure the relationship between the magnetic exchange coupling parameter J and the covalent factor N has been studied. It is shown that for the oxo-bridged Fe(III) dimer there exists a nearly linear relation between J and N, and that the stronger is the covalent effect the stronger is the antiferromagnetic coupling interaction. It is also shown that in a series of model molecules of methemerythrin derivatives, such as in (FeSalen)2O·2py, FeSalenCl·(CH3NO2)x, enH2[(FeHEDTA)2O]·6H2O, Na4[(FeHEDTA)2O]·12H2O, [(Fe(terpy))2O](NO3)4·H2O and Fe(terpy)Cl3, there are about 40% antiferromagnetic contributions that arise from the covalent effect, and that the theoretical values J=−95.5 to −100.7 cm−1 are in good agreement with the experimental findings J=−90 to −105 cm−1 for those model molecules.