Low-lying electronic states and molecular structure of Fe2O2

The structure, bonding and relative stabilities of the ground and low-lying excited states of Fe2O2 have been studied by the hybrid B3LYP density-functional and coupled-cluster molecular orbital methods. Calculations indicate that the (µ-O)2 rhombic 7B2u state is the ground state for Fe2O2. Stable molecular diiron oxo Fe2-O2 complexes in distorted tetrahedral and planar side-on modes have been also located on the potential-energy hypersurfaces of Fe2O2. The calculated IR-active frequencies corresponding to two in-plane deformations of the rhombic ring agree well with the observed values. The bonding features of the (µ-O)2 rhombic Fe2O2 have been discussed based on natural bond orbital and Bader topological analyses. These analyses show that an effective Fe–Fe bonding across the ring exists in the 7B2u ground state.