The nature of the bonding in XCO for X = Fe, Ni, and Cu

The bonding in the 5,3Σ- and 3Δ states of FeCO, the 3,1Σ+, 3Δ, and 3Π states of NiCO, and the 2Σ+ state of CuCO are analyzed using the constrained space orbital variation (CSOV) technique for both (CASSCF) and SCF wave functions. The bonding is discussed in terms of σ repulsion between the metal 4s and the CO 5σ, CO to metal σ donation when there is an empty or partly occupied dσ orbital and metal to CO 2π* backdonation. The bonding is compared for the different metals and between the different states. © 1986 American Institute of Physics.