Question

Antibonding molecular orbitals can be used to make bonds to other atoms in a molecule. For example, metal atoms can use appropriate d orbitals to overlap with the
π^*_2p orbitals of the carbon monoxide molecule. This is called d-π backbonding. (a) Draw a coordinate axis system in which the y-axis is vertical in the plane of the paper and the x-axis horizontal. Write “M” at the origin to denote a metal atom. (b) Now, on the x axis to the right of M, draw the Lewis structure of a CO molecule, with the carbon nearest the M. The CO bond axis should be on the x-axis. (c) Draw the CO π^*_2p orbital, with phases (see the “Closer Look” box on phases) in the plane of the paper. Two lobes should be pointing toward M. (d) Now draw the d_xy orbital of M, with phases. Can you see how they will overlap with the π^*_2p orbital of CO? (e) What kind of bond is being made with the orbitals between M and C, σ or π? (f) Predict what will happen to the strength of the CO bond in a metal–CO complex compared to CO alone.