In $\mathrm{Fe}(\mathrm{CO})_{5}$, the $\mathrm{Fe}-\mathrm{C}$ bond possesses

(B) both $\sigma$ and $\pi$ characters

JEE Main · 2006 · 30 Apr 2006 · Offline · Coordination Compounds

Fe (CO)_{5}

, the

Fe - C

bond possesses

(A) $π$ -character only
(B)both $σ$ and $π$ characters✓ Correct
(C)ionic character
(D) $σ$ -character only

Answer: (B)

Solution

The metal-carbon bond in a carbonyl such as

Fe (CO)_{5}

is synergic. Carbon monoxide first donates the lone pair on its carbon into an empty orbital of iron, forming a

σ

bond, and iron then returns electron density from its filled

d

orbitals into the empty

π^{*}

orbitals of CO, forming a

π

back-bond. Because both donations operate together, the

Fe - C

bond possesses both

σ

and

π

character.

JEE Main · 2006 · 30 Apr 2006 · Offline · Single correct option

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