Electron structure of oxygen complexes of ferrous ion center

The electron structure of ferryl ion [FeO]2+ active in oxidation of hydrocarbons is studied using CASSCF theory followed by ISA-MRMP correction. [FeO]2+ is modeled by the OFe(OH)2 species. The 5A1 and 5B2 states are predicted to be low-lying states for the [FeO]2+ unit. At the decreased (H)O-Fe-O(H) angles 5B2 becomes the ground state. The 5B2 state appears to be a mixture of configurations with quite large weight of the split-electron-pair configuration. This state can be considered as anion-radical state of oxygen which seems to be responsible for the activity of the [FeO]2+ moiety toward the activation of the C-H bond.