The higher stability of metal carbonyls is very evident on the basis of spectrochemical series. Identify the incorrect statements about metal-carbonyls.
A. The Metal-Carbon bond has both σ and π character.
B. Metal-Carbon bond is formed by donation of lone pair of electrons on carbonyl carbon into vacant d- orbital of metal.
C. Metal-ligand bond has synergic effect.
D. Transition metals never have zero oxidation state in carbonyls.
E. Metal-Carbon π bond is formed by donation of electrons from anti bonding molecular orbital of CO to Metal.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → D and E only
In a metal carbonyl the M–C bond has a σ part (lone pair of CO into a vacant metal orbital) and a π part (filled metal d orbital into the empty π* orbital of CO). Each part strengthens the other: this is the synergic bonding that makes carbonyls stable.
A. The Metal-Carbon bond has both σ and π character. — A correct statement. The bond has a σ part and a π part.
B. Metal-Carbon bond is formed by donation of lone pair of electrons on carbonyl carbon into vacant d- orbital of metal. — A correct statement. This is how the M–C σ bond is formed.
C. Metal-ligand bond has synergic effect. — A correct statement. σ donation and π back donation reinforce each other.
D. Transition metals never have zero oxidation state in carbonyls. — An incorrect statement. CO is a neutral ligand, so in homoleptic carbonyls such as \( \ce{[Ni(CO)4]} \), \( \ce{[Fe(CO)5]} \) and \( \ce{[Cr(CO)6]} \) the metal is in the zero oxidation state.
E. Metal-Carbon π bond is formed by donation of electrons from anti bonding molecular orbital of CO to Metal. — An incorrect statement. The direction is reversed: the π bond is formed by donation of electrons from a filled d orbital of the metal into the vacant antibonding π* orbital of CO.
NCERT (2026-27 edition):
Bonding in Metal Carbonyls – “The metal-carbon bond in metal carbonyls possess both σ and π character. The M–C σ bond is formed by the donation of lone pair of electrons on the carbonyl carbon into a vacant orbital of the metal. The M–C π bond is formed by the donation of a pair of electrons from a filled d orbital of metal into the vacant antibonding π* orbital of carbon monoxide. The metal to ligand bonding creates a synergic effect which strengthens the bond between CO and the metal.”