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Evidence for variable metal-radical spin coupling in oxoferrylporphyrin cation radical complexes
E Bill1, X Q Ding, E L Bominaar
1Institut für Physik, Medizinische Universität, Lübeck, Federal Republic of Germany.
European Journal of Biochemistry
|March 30, 1990
Summary
Strong ferromagnetic coupling was observed in oxoferrylporphyrin cation radical complexes derived from tetramesitylporphyrinatoiron(III) (TMPFe), with weaker coupling in related tetra(2,6-dichlorophenyl)porphyrinatoiron(III) (TPP(2,6-Cl)Fe) systems.
Area of Science:
- Inorganic Chemistry
- Spectroscopy
- Magnetochemistry
Background:
- Oxidation of iron(III) porphyrin complexes can generate oxoferrylporphyrin cation radicals.
- Understanding spin coupling in these radical systems is crucial for their electronic properties.
Purpose of the Study:
- To investigate the spin coupling between ferryl iron and porphyrin radical systems.
- To characterize the magnetic and spectroscopic properties of generated oxoferrylporphyrin cation radicals.
Main Methods:
- Generation of oxoferrylporphyrin cation radicals via m-chloroperoxybenzoic acid oxidation.
- Investigation using Mössbauer and Electron Paramagnetic Resonance (EPR) spectroscopy.
- Analysis of magnetic Mössbauer spectra with a spin Hamiltonian.
Main Results:
- Strong ferromagnetic coupling (J > 80 cm-1) observed in tetramesitylporphyrinatoiron(III) (TMPFe) derived systems.
- Weak coupling (J ≈ 1 cm-1) observed in tetra(2,6-dichlorophenyl)porphyrinatoiron(III) (TPP(2,6-Cl)Fe) derived systems.
- Consistent zero-field splitting parameter (D ≈ +6 cm-1) obtained from both EPR and Mössbauer data.
Conclusions:
- The strength of iron-porphyrin radical coupling is highly dependent on the porphyrin ligand structure.
- Spectroscopic parameters show minor solvent dependence but are largely independent of axial ligands in TMPFe complexes.