Question

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

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

Answer 1

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

$\left[Fe\right(CO{)}_4{]}^{2-}$ has longest $C-O$ bond length. Since in the complex metal atom is carrying maximum negative charge therefore it would show maximum synergistic bonding due to which $C–O$ bond length would be maximum.