An orbital model for the exchange interactions between low spin iron(III) and copper(II) ions

The effect of the quasi degenerate ground state of low spin iron(III) ion on the exchange interaction with an orbitally non-degenerate ion, such as copper(II), has been taken into account, using two formally different models which produce the same results when compared with the bilinear exchange spin hamiltonian. It is found that the four levels which originate from the interactions between the two ground Kramers' doublets are not generally grouped in a singlet and a triplet, but in a less regular fashion, due to the quasi degeneration of low spin iron(III). The model has been applied to some systems recently reported as mimicking the cyanide form of oxidized cytochrome oxidase.