Metal-CO carbonyl bond

Metal-CO bond

The unusual feature of metal carbonyl complexes for example in Ni(CO)4 is that CO is not very basic and Ni is zerovalent. Since both are stable in their own right why does a bond occur?
The bonding between CO and the metal consists of two components. The first part being the lone pair of electrons donated by the carbon.
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As the metal is more electron rich, it compensates this by interacting the filled d-orbital with the empty p orbital on the carbonyl ligand. This is known as a back bonding dative p bond.
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This overall bonding effect can be represented in the Molecular orbital theory diagram insert mo diagram here The p backbonding of the metal causes a weakening between the carbon and the oxygen.
The lone pair of the electron on the carbon is slightly anti-bonding . If the electron pair were removed then the CO bond strength would increase. The backbonding therefore rely's on the electron density to strengthen the M-CO bond. Terefore as CO becomes lectron rich it must become weaker. The nature of such effects can be shown spectroscopically.
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Thsi shows that the electrons from the metal are donated to the antibonding molecular orbital of CO. As a general rule most metal carbolnyl complex's show a CO wavenumber of about 2100cm-1 and below. Compounds that have strong electron withdrawing ligands can cause the back bonding to be somewhat negligeble. A classic example of the is observed
"History of organometallics" "Carbonyl compounds" "Metal-CO bonds" "Alkene oganometallics complexes" "Alkyne oganometallics complexes" "Arene oganometallics complexes" "Industrial uses of oganometallics