Electronic states and magnetic properties of triplet porphyrinato copper(II) cation radical complexes

The porphyrinato copper cation radical complexes were examined by EPR spectroscopy. The cation radical complexes having bulky peripheral substituents are present as monomers in fluid solution and show EPR spectra due to intramolecular spin coupling between the spins on copper and on the porphyrin ring. The cation radical complexes, having no such substituents, form a dimer in solution. On the other hand when they are oxidized in frozen solution by γ-ray irradiation, the cation radical complexes are always formed as a monomer, showing a triplet state EPR due to the intramolecular spin coupling. The zero field splitting and spin exchange parameters, |D| and 2J, obtained from EPR measurements were classified into two groups by their magnitudes. The tetraphenylporphyrinato copper(II) cation radical complex, [Cu(II)(tpp)]⁺, has a small |D| and a small negative 2J value, while the octaethylporphyrinato copper(II) cation radical complex, [Cu(II)(oep)]⁺, has a large |D| and a large negative 2J value. The other porphyrinato copper(II) cation radical complexes are classified into one of these two type of complexes. These classifications can be related to the electronic configuration of the porphyrin cation radicals. These |D| and 2J values also suggest that the triplet state monomer complexes of porphyrinato copper(II) cation must be deformed from the planar structure.