The higher stability of metal carbonyls is very evident on the basis of spectrochemical series. Identify the incorrect statement's about metal-carbonyls.

A. The Metal-Carbon bond has both and a characters.
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 a 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:

D and E only

The correct answer is Option (4) → D and E only.

Let us delve into the details of the properties and characteristics of metal carbonyls to clarify the incorrect statements:

Understanding Metal Carbonyls

Metal carbonyls are coordination complexes formed between transition metals and carbon monoxide (CO) ligands. They are characterized by strong metal-ligand bonds, and understanding these bonds is crucial for interpreting their behavior and properties.

Analysis of Each Statement

A. The Metal-Carbon bond has both σ and π characters.

The metal-carbon bond in metal carbonyls exhibits both \(\sigma \) and \(\pi \) bonding characteristics. The \(\sigma \) bond is formed when the lone pair of electrons from the carbon atom of \(CO\) is donated to a vacant d-orbital of the metal, resulting in a strong interaction.

The \(\pi \) bond arises from the back-donation of electron density from filled d-orbitals of the metal to the empty \(\pi ^*\) (anti-bonding) orbitals of \(CO\). This dual bonding nature contributes to the overall stability of the metal carbonyl complex.

B. Metal-Carbon bond is formed by the donation of a lone pair of electrons on carbonyl carbon into the vacant d-orbital of metal.

This statement is correct because the formation of the metal-carbon bond involves the donation of a lone pair of electrons from the carbon atom in \(CO\) to the metal's vacant d-orbital. This interaction is crucial for the stability of the complex and is a fundamental aspect of coordinate covalent bonding.

C. Metal-ligand bond has a synergic effect.

The term synergic effect refers to the cooperative interaction between the metal and the ligand. In metal carbonyls, there is a simultaneous donation of electrons from the \(CO\) ligand to the metal (\(\sigma \) donation) and from the metal back to the \(CO\) (\(\pi \) back-donation).

This back-donation stabilizes the \(CO\) ligand and enhances the strength of the metal-carbon bond, making this statement true.

D. Transition metals never have zero oxidation state in carbonyls.

This statement is incorrect. Many transition metals can exhibit a zero oxidation state in carbonyl complexes. For instance, in nickel carbonyl \((Ni(CO)_4)\), nickel is in the zero oxidation state. Therefore, it is inaccurate to say that transition metals never have a zero oxidation state in carbonyls.

E. Metal-Carbon σ bond is formed by the donation of electrons from the anti-bonding molecular orbital of CO to Metal.

This statement is incorrect. The \(\sigma \) bond is formed by the donation of electrons from the bonding orbital (not anti-bonding) of \(CO\) to the metal. The anti-bonding orbitals \((\pi ^*)\) are involved in the back-donation process, but they do not contribute to the formation of the σ bond. This misunderstanding makes the statement false.

Conclusion

From the analysis above, the following statements are incorrect:

D: Transition metals can indeed have a zero oxidation state in carbonyl complexes.

E: The σ bond does not form from the anti-bonding orbital; it is formed from the bonding orbital of CO.