Question

The pair of metal carbonyl complexes that are isoelectronic is :

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

Answer 1

Answer: (A)

As $Co \left(d^{7}\right)$ and $Ni \left(d^{0}\right)$ elements differ by one electron and both contain four (CO) groups thus $\left[ Co ( CO )_{4}\right]^{-}$ and $\left[ Ni ( CO )_{4}\right]$ have same number of electrons.

Hence, both are isoelectronic.