Question

Which kind of isomerism is exhibited by octahedral $\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_4{\mathrm{Br}}_2\right]\mathrm{Cl}$?

• A. Geometrical isomerism
• B. Optical and ionization isomerism
• C. Geometrical and optical isomerism
• D. Geometrical and ionization isomerism

Answer 1

The correct option is D

Geometrical and ionization isomerism

Explanation for correct option

(D) Geometrical and ionization isomerism

Isomerism

• Isomerism is the phenomenon when two or more chemical compounds have the same chemical formula but distinct chemical structures.
• Stereoisomerism and structural isomerism are the two types of isomerism.
• Stereoisomerism is classified as Ionization isomerism, hydration isomerism, coordination isomerism, ligand isomerism, and linkage isomerism.
• Geometrical isomerism and optical isomerism are two types of stereoisomerism.

$\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_4{\mathrm{Br}}_2\right]\mathbf{Cl}$ complex

• In $\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_4{\mathrm{Br}}_2\right]\mathrm{Cl}$, center metal cobalt is in a $+3$ oxidation state.
• $\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_4{\mathrm{Br}}_2\right]\mathrm{Cl}$ has ionization isomers.
• This isomerism occurs due to the interchange of ions between the inner and the outer coordination sphere.
• Ionization isomers can be written as:

$\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_4{\mathrm{Br}}_2\right]\mathrm{Cl}$ and $\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_4\mathrm{BrCl}\right]\mathrm{Br}$

• This isomerism comes as a result of ion exchange between the inner and outer coordination spheres.
• Although it can form geometric isomers, cis and trans, neither is optically active.
• Structure are as follows:
  

Explanation for incorrect options

• The $\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_4{\mathrm{Br}}_2\right]\mathrm{Cl}$ complex exhibited Geometrical and ionization isomerism.
• Hence, all the other options (A), (B) and (C) are in correct.

Therefore the correct option is (D) Geometrical and ionization isomerism.