If the bond length of CO bond in carbon monoxide is `1.128 Å`, then what is the value of CO 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 carbonyls possesses both `sigma` and `pi` character-weak `sigma` bond being formed by donation of electron pair from carbon to metal `(M larr C -= O)` and a stronger `pi`-bond being formed by back donation of electrons from filled `d_(xy)` orbital of metal into empty antibonding `pi_(2p_(y))^(*)` orbital of carbon `(pi M rarr 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 `1.128Å` in CO increases to about `1.15Å` in many carbonyls.