The ground electronic states of cobalt tetraphenylporphyrin and octaethylporphyrin cation radicals (CoIIITPP·+, CoIIIOEP·+) were reexamined by EPR spectroscopy. They are not purely an A1u or A2u state (nomenclature in D4h symmetry), but they contain A1u and A2u components, respectively. The contribution of the A2u state increases with increasing axial-ligand field. Equilibria were found between species having different axial-ligand interactions in solution. At low temperatures, the species having weaker axial-ligand interactions and having less A2u character are dominant. The marked line width broadening observed for the EPR spectra of CoIIIOEP·+ complexes ligated by Br-, Cl-, and CN- was explained by the effect of mixing of a locally excited triplet state. Such mixing is less important for CoIIITPP·+ complexes having an A2u dominant ground state.
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