Question

Which of the following is anionic complexes?

• A. $\left[Cu\right(N{H}_3{)}_4]S{O}_4$
  
• B. $K_3\left[Fe\right(CN{)}_6]$
• C. $\left[Ni\right(CO{)}_4]$
• D. None of the above

Answer 1

The correct option is B $K_3\left[Fe\right(CN{)}_6]$

Coordination complex is classified into positive, negative and neutral complex based on the charge on coordination sphere.

$\left[Cu\right(N{H}_3{)}_4]S{O}_4$ dissociate as $\left[Cu\right(N{H}_3{)}_4{]}^{2+}$ and $S{O}_4^{2-}$. The charge on coordination sphere is +2. Hence, it is a cationic complex.

$K_3\left[Fe\right(CN{)}_6]$ dissociate as $\left[Fe\right(CN{)}_6{]}^{3-}$ and $3K^{+}$. The charge on coordination sphere is -3. Hence, it is a anionic complex.

Charge on coordination sphere of $\left[Ni\right(CO{)}_4]$ is absent. Hence, it is neutral complex.

Hence, (b) is correct.