CASSCF Study of Bonding in NiCO and FeCO

摘要

A series of CASSCF calculations were performed on the ground states of NiCO and FeCO. The contributions of the #sigma#/#pi# interactions are checked by examining the validity of the CASSC calculation to describe the molecule with a particular choice of the active space. The calculation results substantiate that the stability of MCO is determined by a balance between #pi# donation from the metal 3d_(#pi#) to the CO 2#pi# and repulsion between the metal #sigma# electrons and the CO 5#sigma# lone pair and, at the same time, emphasizes the importance of the synergistic #sigma#/#pi# interactions between the metal and the CO group. The relative importance of #sigma#/#pi# interactions depends on the nature of the metal. In the case of NiCO, it is the #pi# donation from Ni 3d_(#pi#) to CO 2#pi# that makes the largest contribution to the formation of the Ni-CO bond, while in the case of FeCO, it is the correlation of #sigma# electrons that holds the metal and CO together.