Theory of covalent heterodinuclear magnetic exchange interaction and its application to MnIIIFeIII and FeIIFeII spin clusters in complex molecules

A covalent heterodinuclear magnetic exchange interaction formula has been established and the antiferromagnetic coupling phenomena of both heterodinuclear MnIIIFeIII and homodinuclear FeIIFeII spin-clusters in complex molecules have been studied. It is demonstrated that the antiferromagnetic phenomenon of transition-metal ion-pairs in molecules should be attributed to the combined effect of the direct-exchange interaction, the kinetic exchange interaction and the covalent effect; the strong antiferromagnetic characteristic of MnIIIFeIII cluster in [L′MnIII(μ-O)(μ-CH3CO2)2FeIIIL′] is mainly due to the dxz–dxz and dyz–dyz orbital exchange interactions, while the weak antiferromagnetic coupling in deoxyhemerythrin should be attributed to a μ-OH−–FeIIFeII cluster with a long Fe–O bond length in its active site. The theoretical results agree well with the experimental findings.