Advanced Paramagnetic Resonance Studies on Manganese and Iron Corroles with a Formal d4 Electron Count

Metallocorroles wherein the metal ion is MnIII and formally FeIV are studied here using field and frequency domain electron paramagnetic resonance techniques. The MnIII corrole, Mn tpfc tpfc 5,10,15 tris pentafluorophenyl corrole trianion , exhibits the following S 2 zero field splitting zfs parameters D amp; 8722;2.67 1 cm 1, E 0.023 5 cm 1. This result and those for other MnIII tetrapyrroles indicate that when D amp; 8776; 2.5 0.5 cm 1 for 4 or 5 coordinate and D amp; 8776; 3.5 0.5 cm 1 for 6 coordinate complexes, the ground state description is [MnIII Cor3 ]0 or [MnIII P2 ] Cor corrole, P porphyrin . The situation for formally FeIV corroles is more complicated, and it has been shown that for Fe Cor X, when X Ph phenyl , the ground state is a spin triplet best described by [FeIV Cor3 ] , but when X halide, the ground state corresponds to [FeIII Cor 2 ] , wherein an intermediate spin S 3 2 FeIII is antiferromagnetically coupled to a corrole radical dianion S 1 2 to also give an S 1 ground state. These two valence isomers can be distinguished by their zfs parameters, as determined here for Fe tpc X, X Ph, Cl tpc 5,10,15 triphenylcorrole trianion . The complex with axial phenyl gives D 21.1 2 cm 1, while that with axial chloride gives D 14.6 1 cm 1. The D value for Fe tpc Ph is in rough agreement with the range of values reported for other FeIV complexes. In contrast, the D value for Fe tpc Cl is inconsistent with an FeIV description and represents a different type of iron center. Computational studies corroborate the zfs for the two types of iron corrole complexes. Thus, the zfs of metallocorroles can be diagnostic as to the electronic structure of a formally high oxidation state metallocorrole, and by extension to metalloporphyrins, although such studies have yet to be performe