Question

The pair of metal carbonyl complexes that are isoelectronic is:

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

Answer 1

The correct option is D $\left[Co\right(CO{)}_4{]}^{-}$ and $Ni(CO{)}_4$

As $Co\left(d^7\right)$ and $Ni\left(d^8\right)$ elements differ by one electron and both contain four $\left(CO\right)$ groups thus $\left[Co\right(C{O}_4{]}^{-}$ and $\left[Ni\right(CO{)}_4]$ have same number of electrons.
Hence, both are isoelectronic.