Effects of a nonplanar porphyrin rings on the spin-spin interactions in low-spin ferric porphyrin radical cations

Low-spin ferric porphyrin radical cations formed by the oxidation of chloro(meso-tetraalkylporphyrinato)iron(III) followed by the addition of bulky 2-methylimidazole show antiferromagnetic coupling, which is interpreted in terms of the interaction between porphyrin a2u and iron dxy orbitals caused by the S4 ruffling of the porphyrin core.