Question

Which of the following has longest $C-O$ bond length?
(Free $C-O$ bond length in $CO$ is $1.128\stackrel{o}{A}$)

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

Answer 1

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

$C-O$ will have highest bond length in $\left[Fe\right(CO{)}_4{]}^{2-}$, since metal atom is carrying maximum negative charge therefore it would show maximum synergic bonding and as a resultant $C-O$ bond length would be maximum.