The crystal structures of porphinato-iron (III) complexes with an anomalous inter-mediate-spin state (S=3/2) were compared with those of high-and low-spin iron (III) porphyrins. The intermediate-spin state is arisen in an asymmetric coordination field around the central iron (III) ion with respect to the axial and equatorial ligand strengths, while both the low-and high-spin states have approximately octahedral fields. The axial iron ligand distance in the intermediate-spin state is significantly different from the equatorial distances. The geometric parameters consistent with the electron configuration of the intermediate-spin state.
The crystal structures of porphinato-ruthenium (IV) and osmium (IV) complexes as a model of peroxidase compound II were discussed also. The complexes consist of the μ-oxo dimer with the weak ligand (OH
-, Cl
- or OCH
3-) . The quadrivalent metallopor-phyrin was stabilized by a strong ligand of O
2- with σ
- and π-bonding natures. The diamagnetism in these complexes was explained by the dπ-pπ-dπ interaction in the M
IV-O-M
IVbond.
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