Evidence for Porphyrin (π)−Chlorine (p) Orbital Overlap in the π-Cation Radicals of Zinc(II) and Magnesium(II) Tetrakis(o-dichlorophenyl)porphyrin

The EPR spectra of the porphyrin π-cation radicals ZnII(DCPP•)+ and MgII(DCPP•)+ (DCPP = tetrakis(o-dichlorophenyl)porphyrin)) have been examined in detail. The low-temperature EPR signals from these complexes exhibit a significant g-anisotropy. The introduction of angular momentum into the electronic ground state is attributed to overlap between the porphyrin a2u and chlorine p-orbitals. Overlap occurs because the bulky o-chloro-substituents force the aryl rings to be nearly perpendicular to the porphyrin ring.