If the bond length of CO bond in carbon monoxide is $1.128 \AA$, then what is the value of CO bond length in Fe(CO)$_5$?

JEE Advanced · 2006 · 09 Apr 2006 · Coordination Compounds

If the bond length of CO bond in carbon monoxide is

1.128 \overset{˚}{A}

, then what is the value of CO bond length in Fe(CO)

_{5}

(A) $1.15 \overset{˚}{A}$ ✓ Correct
(B) $1.128 \overset{˚}{A}$
(C) $1.72 \overset{˚}{A}$
(D) $1.118 \overset{˚}{A}$

Answer: (A)

Solution

In Fe(CO)

_{5}

, synergic bonding occurs between the metal and CO. The metal donates electron density to the antibonding π* orbitals of CO through back-bonding, which decreases the bond order of CO. A lower bond order corresponds to a longer bond length. Therefore, the CO bond length in Fe(CO)

_{5}

(

1.15 \overset{˚}{A}

) is greater than in free CO (

1.128 \overset{˚}{A}

JEE Advanced · 2006 · 09 Apr 2006 · One or more correct options

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