材料期刊网

By introducing the covalent effect into the Girerd-Journaux-Kahn's 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)(2)O.2py, FeSalenCl.(CH3NO2)(x), enH(2)[(FeHEDTA)(2)O].6H(2)O, Na-4[(FeHEDTA)(2)O].12H(2)O, [(Fe(terpy))(2)O](NO3)(4).H2O and Fe(terpy)Cl-3, 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. (C) 2002 Elsevier Science Ltd. All rights reserved.