If the length of CO bond in carbon monoxide is. 1.128 Å, then what is the value of CÓ bond length in `Fe(CO)_5` ?

Options

A. `1.15 Å`
B. `1.128 Å`
C. `1.72 Å`
D. `1.118 Å`

Answer

A

Explanation

The metal-carbon bond in carbonyl possesses both `sigma` and `pi` character - Weak `sigma` bond being formed by donation of electron pair, from carboņ to metal `(M to C -= O)` and a stronger `pi`-bond being formed by backdonation of electronis from filled `d_(xy)`, orbital of metal into empty antibonding `pi_(2p)`, orbital of carbon `(pi M to C "bond")`. The total bonding is thus `M = C = O`.
Thus, bond order of C-O bond is reduced from triple bond to double bond. As a result, `C–O` bond length of 1.128 Å in CO increases to about 1.15 Å in many carbonyls.