Question

In metal carbonyls, metal-ligand bonds possess both sigma and pi character. Comment on whether the given statement is correct. Give a reason for your answer.

(a) Correct; due to hybridization
(b) Incorrect; only sigma character
(c) Incorrect; only pi character
(d) Correct; due to resonance

Answer 1

The statement is (a) Correct; due to hybridization. in metal carbonyls, metal-ligand bonds do have both sigma and pi character.

Step-by-step explanation:

The statement that in metal carbonyls, metal-ligand bonds possess both sigma and pi character is correct. Metal-carbonyl bonding involves a carbon monoxide molecule (CO) acting as a ligand towards the metal. This bonding exhibits two key interactions: a sigma bond formed by the donation of the lone pair electrons from the carbon end of CO to a metal orbital, and back-donation from the metal to the * antibonding orbital of carbon monoxide, which is a pi-type interaction.

This two-way interaction is crucial for describing the bonding in metal carbonyls, making them unique when compared to typical organic molecules which have clear sigma and pi bonds from hybridization. Unlike pi bonding in alkenes or alkynes, the pi character in metal carbonyl bonds arises primarily from this back-donation process, not the side-by-side overlap of unhybridized p orbitals. As such, the bond has both a strong sigma character and a notable pi character due to this electron back-donation, aligning with molecular orbital theory rather than simply hybridization or resonance alone.

Answer 2

The bonds in metal carbonyls have both sigma and pi character due to the overlap of metal and carbon monoxide orbitals and the process of back-donation. Resonance and delocalization of electrons in anti-bonding orbitals also contribute to the bonding characteristics, much like in benzene.

Step-by-step explanation:

Yes, the statement that in metal carbonyls, metal-ligand bonds possess both sigma and pi character is correct. The bond between the metal and carbon monoxide in a metal carbonyl is indeed composed of both a sigma bond and a pi bond component. The sigma bond is formed as a result of the overlap between a metal orbital and the carbon monoxide's carbon atom's sigma orbital. Meanwhile, the pi bond character comes from a process called back-donation, where the metal donates some of its electron density back into the anti-bonding pi* orbitals of the CO ligand.

This back-donation stabilizes the CO ligand and strengthens the metal-ligand bond, which can be clearly understood in terms of molecular orbital theory. Resonance also plays a role in metal carbonyls, as the delocalization of electrons within these anti-bonding orbitals contributes significantly to the bonding characteristics of these complexes, similar to how electrons are delocalized in the resonance forms of benzene.