Do the One-Electron Oxidized Derivatives of Some Six-Coordinate Low-Spin Iron(III) Porphyrins Feature Strong Metal−Ligand Ferromagnetic Coupling?

Abstract

It has been recognized for some time that the high-valent complex [Fe´υTPP)(Ğ-Meūm) 2 ] 2 + (TPP = mesotetraphenylporphyrin, 1-Melm = 1-methylimidazole) exhibits an S = I ground state and has been described as a low-spin Fe(III) porphyrin π-cation radical with strong metal-porphyrin ferromagnetic coupling. Because strong metal-ligand ferromagnetic coupling is quite unusual, a DFT investigation of two truncated and symmetrized models of this complex, namely, [Fe(P)(Py 2 ] 2 + and [Fe(P)(ImH) 2 ] 2 + , was carried out. The results indicate that the ground-state electronic configurations may be described as low-spin Fe(IV)-like, with varying degrees of metal-to-porphyrin spin delocalization, which provides a natural explanation for the experimentalists' somewhat unusual description of the electronic structure of [Fe(TPP)( 1-MeIm) 2 ] 2 + .