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 (mu-O)(2) rhombic B-7(2u) State is the ground state for Fe2O2. Stable molecular diiron oxo Fe-2-O-2 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 (mu-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 B-7(2u) ground state.