Theoretical model study of the quantumhyphen;mechanically mixedhyphen;spin (S=5/2,3/2) ground state in iron (III) porphyrins

摘要

After a selective review of some recent studies on structural and spin properties of ironndash;porphyrin complexes, the role of axial ligands and the porphyrinhyphen;structure effect on spin state is presented. It is shown that in crystalhyphen;field approximation the structure effects on spinhyphen;state differences in fivehyphen; and sixhyphen;coordinate complexes can be rationalized within the available xhyphen;ray data. In the framework of a vibronichyphen;coupling analysis, added to the lsquo;lsquo;chargendash;repulsionrsquo;rsquo; model of Saito and Kashiwagi, the possibility of a drastic reduction in the energy needed for triggering the intermediate (S=3/2) to highhyphen;spin (S=5/2) transition is numerically demonstrated. In addition, two supplementary quantumhyphen;mechanical effects through axial ligands on bond distances and spinhyphen;state preferences are described and illustrated by model calculations. The results are found to agree with the experimental data.