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 (d_xy)²(d_xz, d_yz)³ ground state, and (iv) low-spin with the (d_xz, d_yz)⁴(d_xy)¹ ground state. In the case of the latter complexes, they mostly have Fe^IV{double bond, long}O bonds. There is only one iron(IV) complex that has no Fe^IV{double bond, long}O 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.