Mössbauer and magnetic studies on the spin states of diiron(III)-porphyrin dicopper(II) complexes

Abstract

Several biological model complexes of cytochrome c oxidase analogues, such as X2(TPP)2Fe2(Apen)Cu2Cl4, where TPP=5, 10, 15, 20-tetraphenylporphine, Apen=bis(acetylpyrazine)-ethylenediimine, X=Cl−, N 3 − , Im, 1-Me-Im, 2-Me-Im, 4-Me-Im and OCH 3 − , were prepared. The electronic spin states of these complexes in solid state were studied by means of Mossbauer and EPR spectroscopies and magnetic susceptibility measurements. The iron(III) atom of these complexes is present in different spin states, depending upon the nature of the axial ligand X of Fe(III)-porphyrin; the N 3 − , Cl−, OCH 3 − , 2-Me-Im axial groups lead to complexes in a pure high-spin state independent of temperature. In contrast, the imidazole axial groups (e.g. Im, 4-Me-Im) behave differently and all show a temperature dependence of the6A1 ↔2T2 spin transition. The magnetic exchange behavior between Fe and Cu atoms in the present complexes is also discussed.