Question

Which of the following has longest C-O bond length? (Free C-O bond length is Co is $1.128\dot{A}$)

• A. $Ni(CO{)}_4$
• B. $\left[Ni\right(CO{)}_3{]}^{+}$
• C. ${\left[Fe\right(CO{)}_4]}^{2-}$
• D. ${\left[\mathrm{Mn}\right(CO{)}_6]}^{+}$

Answer 1

The correct option is C ${\left[Fe\right(CO{)}_4]}^{2-}$

The higher the oxidation state of the central metal atom, the shorter will be the bond length of $C-O$ bond as the bond will be strong.

In $Ni(CO{)}_4\Rightarrow$ Oxidation state of $Ni=0$

In $\left[Ni\right(CO{)}_3{]}^{+}\Rightarrow$ Oxidation state of $Ni=+1$

In $\left[Fe\right(CO{)}_4{]}^{2-}\Rightarrow$ Oxidation state of $Fe=-2$

In $\left[Mn\right(CO{)}_6{]}^{+}\Rightarrow$ Oxidation state of $Mn=+1$

Therefore, the $Ni(CO{)}_4$ molecule has lowest oxidation state of central metal atom.

Therefore, it has the longest $C-O$ bond length.

Hence the correct option is C.