Question

Which of the following is an example of coordination isomerism?
(A) $\left[ Co{{\left( N{{H}_{3}} \right)}_{5}}Br \right]S{{O}_{4}}$ and $\left[ Co{{\left( N{{H}_{3}} \right)}_{5}}S{{O}_{4}} \right]Br$
(B) $\left[ Co{{\left( N{{H}_{3}} \right)}_{5}}N{{O}_{2}} \right]C{{l}_{2}}$ and $\left[ Co{{\left( N{{H}_{3}} \right)}_{5}}ONO \right]C{{l}_{2}}$
(C) $\left[ Cr{{\left( {{H}_{2}}O \right)}_{6}} \right]C{{l}_{3}}$ and $\left[ Cr{{\left( {{H}_{2}}O \right)}_{5}}Cl \right]C{{l}_{2}}.{{H}_{2}}O$
(D) $\left[ Cr{{\left( N{{H}_{3}} \right)}_{6}} \right]\left[ Co{{\left( CN \right)}_{6}} \right]$ and $\left[ Co{{\left( N{{H}_{3}} \right)}_{6}} \right]\left[ Cr{{\left( CN \right)}_{6}} \right]$

Answer 1

Hint: Brush up the concepts of coordination chemistry. Isomerism is the phenomenon in which compounds having the same molecular formula have different physical and chemical properties. Isomers are compounds having the same molecular formula but different spatial arrangement. Use this concept and try to relate with the term coordination isomerism to get the answer.

Complete step by step answer:
- Isomerism is the phenomenon in which compounds have the same molecular formula but different chemical and physical properties. Isomers are compounds exhibiting isomerism.
- Isomerism is broadly divided into two types, Stereo isomerism and Structural isomerism.
- Coordination isomerism is a type of structural isomerism. Structural isomerism indicates the compounds are structurally dissimilar.
- Coordination isomerism is a type of structural isomerism that arises due to different complex ions having the same molecular formula.
- In coordination isomerism, there is interchange of ligands between cationic and anionic entities of different metal ions present in a complex.
- Basically, in coordination isomers, each complex has two ions and they differ with respect to each other only in terms of ligands which get interchanged between the two metal atoms.

$\left[ Cr{{\left( N{{H}_{3}} \right)}_{6}} \right]\left[ Co{{\left( CN \right)}_{6}} \right]$ and $\left[ Co{{\left( N{{H}_{3}} \right)}_{6}} \right]\left[ Cr{{\left( CN \right)}_{6}} \right]$ is an example of coordination isomerism.

- In $\left[ Cr{{\left( N{{H}_{3}} \right)}_{6}} \right]\left[ Co{{\left( CN \right)}_{6}} \right]$, chromium is present in cationic complex having +3 oxidation state and cobalt is present in anionic complex having -3 oxidation state.

- In $\left[ Co{{\left( N{{H}_{3}} \right)}_{6}} \right]\left[ Cr{{\left( CN \right)}_{6}} \right]$, cobalt is present in cationic complex having +3 oxidation state and chromium is present in anionic complex having -3 oxidation state.

- Let’s see the other options.
(A) $\left[ Co{{\left( N{{H}_{3}} \right)}_{5}}Br \right]S{{O}_{4}}$ and $\left[ Co{{\left( N{{H}_{3}} \right)}_{5}}S{{O}_{4}} \right]Br$ are ionization isomers which when dissolved in solution form different ions.

(B) $\left[ Co{{\left( N{{H}_{3}} \right)}_{5}}N{{O}_{2}} \right]C{{l}_{2}}$ and $\left[ Co{{\left( N{{H}_{3}} \right)}_{5}}ONO \right]C{{l}_{2}}$ are linkage isomers which is seen only in case of ambidentate ligands which can form bonds with central metal atom using different atoms.

(C) $\left[ Cr{{\left( {{H}_{2}}O \right)}_{6}} \right]C{{l}_{3}}$ and $\left[ Cr{{\left( {{H}_{2}}O \right)}_{5}}Cl \right]C{{l}_{2}}.{{H}_{2}}O$ are hydrate isomers because interchange of water molecules has taken place inside and outside the coordination sphere.

- Therefore, an example of coordination isomerism is $\left[ Cr{{\left( N{{H}_{3}} \right)}_{6}} \right]\left[ Co{{\left( CN \right)}_{6}} \right]$ and $\left[ Co{{\left( N{{H}_{3}} \right)}_{6}} \right]\left[ Cr{{\left( CN \right)}_{6}} \right]$.
So, the correct answer is “Option D”.

Note: Remember there are four different types of structural isomerism. In ionization isomerism, there is exchange of ions inside and outside the coordination sphere. In linkage isomerism, there are ambidentate ligands which form bonds with central metal atoms with different atoms. In coordination isomerism, two complex ions are present which differ only in the arrangement of ligands around the central metal atom. In hydrate isomerism, water molecules get exchanged inside and outside the coordination sphere.