Antibonding molecular orbitals can be used to make bondsto other atoms in a molecule. For example, metal atomscan use appropriate d orbitals to overlap with the π*2p orbitalsof the carbon monoxide molecule. This is calledd-π backbonding. (a) Draw a coordinate axis system inwhich the y-axis is vertical in the plane of the paper andthe x-axis horizontal. Write “M” at the origin to denote ametal atom. (b) Now, on the x-axis to the right of M, drawthe 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 “CloserLook” box on phases) in the plane of the paper. Two lobesshould be pointing toward M. (d) Now draw the dxy orbitalof M, with phases. Can you see how they will overlap withthe π*2p orbital of CO? (e) What kind of bond is being madewith the orbitals between M and C, σ or π ? (f) Predict whatwill happen to the strength of the CO bond in a metal–COcomplex compared to CO alone.
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 dxy 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.
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