Formation of an Aqueous Oxoiron(IV) Complex at pH 2–6 from a Nonheme Iron(II) Complex and H₂O₂

A ferryl cation in water: Iron(II) coordinated by the pentadentate ligand L reacts with H2O2 to form a low-spin FeIVO complex with S=1 (2 in scheme) under conditions similar to those of the classical Fenton reaction. Complex 2 differs from a recently obtained high-spin aquated oxoiron(IV) species and demonstrates the role of the supporting polydentate ligand in controlling spin state and product formation.