Question

-Draw the structure which shows synergic bonding interaction in a carbonyl complex?

Answer 1

Synergic bonding involves transference of electrons from ligands to metal and the transference of electrons from filled metal orbitals to anti-bonding orbitals of ligands.

Complete step by step answer:
Synergic bonding is a bond between a ligand and a metal where a carbonyl group acts as a ligand. The carbonyl group $CO$ is a pi acid ligand where pi-acid ligands are those which have a lone pair of electrons to donate a metal atom and an empty anti bonding molecular orbital to back bond with the d-orbital electrons of metal atom. Synergic bonding is represented as,

Carbonyl donates a lone pair of electrons to metal to form a $M - C\sigma$ bond. Filled d orbital of metal donates lone pair of electrons to vacant anti bonding $\pi$ orbital of $CO$ to form $M - C\pi$ bond.

Additional Information:- Synergic bonding is a self-strengthening bond. In synergic bonding, the electrons are partially transferred from a d-orbital of the metal to anti bonding molecular orbitals of $CO$. This electron transfer strengthens the metal-C bond and weakens the $C - O$ bond. The strengthening of the $M - CO$ bond is reflected in the increase of the vibrational frequencies for the $M - C$ bond. The $M - CO$ bond length is shortened. The weakening of the $C - O$ bond is indicated by a decrease in the wave number.

Note:
Synergic bonding is also known as pi-back bonding. It is usually used in organometallic chemistry when there is a transition metal centre and a good pi acceptor ligands like $CO$. Many ligands other than $CO$ are strong backbonders.