NMR studies on the electronic structure of one-electron oxidized complexes of iron(III) porphyrinates

This review describes the relationship between the NMR chemical shifts and electronic structures of one-electron oxidized products of iron(III) porphyrins such as iron(III) porphyrin radical cations or iron(IV) porphyrins. In the case of the former complexes, the iron(III) ions are classified into four types; (i) high-spin (S = 5/2), (ii) mixed high- and intermediate-spin (S = 5/2, 3/2), (iii) low-spin with the (dxy)2(dxz, dyz)3 ground state, and (iv) low-spin with the (dxz, dyz)4(dxy)1 ground state. In the case of the latter complexes, they mostly have FeIVO bonds. There is only one iron(IV) complex that has no FeIVO bond. The complexes classified as above exhibit unique NMR chemical shifts. Thus, the NMR spectroscopy serves a quite useful tool to determine the fine electronic structures of the one-electron oxidized iron(III) porphyrin complexes.