(QCO) as the model for bonding in non-classical carbonyls: a force approach study

As a model for non-classical metal carbonyls, we investigate CO in presence of a unit positive charge placed at different distances along the bond axis. We use the force approach, to look into the nature of the individual molecular orbitals. We find that in free CO the HOMO (σ(3)) is antibinding. As the positive charge approaches form carbon side, σ(1) and degenerate π orbitals become more binding, while σ(2) and σ(3) become more antibinding. The overall effect is more binding resulting in a shorter C–O bond. If the charge approaches from oxygen side, then σ(1), σ(3) and degenerate π orbitals become less binding, while σ(2) becomes slightly more binding, resulting in a lengthening of C–O bond.