Which of the following is not true for metal carbonyls

Options

A. The oxidation state of the metal in the carbonyls is zero
B. The secondary carbonyls are obtained from photo- decomposition
C. Metal carbonyls are single bonded species
D. `dpi -p pi` overlap is observed in metal carbonyls

Answer

C

Explanation

(a) The oxidation state of the metal in the carbonyls is zero because carbonyl donates electron pair to the metal to form metal – ligand sigma bond. And metal from its d – orbital, tend to donate pair of electrons back to the ligand. Ligand accept these electron pair donated by metal in pi antibonding molecular orbitals to form metal – ligand `pi ` bond
Net result is the number of electron pair donated by ligand is equal to the number of electron pair accepted by ligands in back – bonding. Hence the oxidation state of metal is zero.
From the above explanation it is evident that M − CO bond is not pure single bond. Also the bond between C and O are not single.
`d pi` orbital of metal and `p pi` orbital of C overlap to form `pi-` bond.