Question

An octahedral complex having molecular composition Co.5NH$_3$.Cl.SO$_4$ has two isomers A and B. The solution of A gives a white precipitate with AgNO$_3$ solution and the solution of B gives a white precipitate with BaCl$_2$ solution. The type of isomerism exhibited by the complex is,

• A. Co-ordinate isomerism
• B. Linkage isomerism
• C. Ionisation isomerism
• D. Geometrical isomerism

Hint:

In ionisation isomerism, even though the molecular formula is the same, the arrangement of ligands around the metal ion and the counter-ions can differ, leading to different ions being released in solution.

Answer 1

The Correct Option is C

The given problem involves identifying the type of isomerism exhibited by the octahedral complex with the composition Co.5NH₃.Cl.SO₄. The complex has two isomers, A and B, with distinct precipitation reactions.

1. Understand the complex's behavior:
   • Isomer A gives a white precipitate with AgNO₃ solution. This indicates the presence of Cl^- ions free in the solution, suggesting that Cl^- is outside the coordination sphere.
   • Isomer B gives a white precipitate with BaCl₂ solution. This implies the presence of SO₄^2- ions free in the solution, indicating that SO₄^2- is outside the coordination sphere.
2. Determine the coordination and chemical composition:
   • For Isomer A: The complex is [Co(NH₃)₅Cl]SO₄. The Cl is inside the coordination sphere, and SO₄^2- is outside.
   • For Isomer B: The complex is [Co(NH₃)₅(SO₄)]Cl. The SO₄^2- is inside the coordination sphere, and Cl^- is outside.
3. Identify the type of isomerism:
   • In both isomers, the only difference is the exchange of ions between the coordination sphere and the outer sphere.
   • This exchange leads to the formation of different ions in solution when dissolved in water, indicative of ionisation isomerism.
4. Conclusion: Based on the analysis, the type of isomerism exhibited by this complex is Ionisation isomerism.

This correct identification is vital for understanding coordination chemistry and its applications in various fields, including catalysis and pharmaceuticals.

Answer 2

Step 1: Understanding the molecular composition:
The complex is given as Co.5NH\(_3\).Cl.SO\(_4\). It consists of a central Co\(^3+\) ion surrounded by 5 ammonia molecules (NH\(_3\)) and one chloride (Cl) ion as well as a sulfate (SO\(_4^{2-}\)) ion.
Step 2: Identifying the isomers:
Isomer A: The solution of A gives a white precipitate with AgNO\(_3\) solution. This indicates the presence of chloride ions (Cl\(^-\)) in the solution because AgNO\(_3\) reacts with chloride ions to form a white precipitate of AgCl. Isomer B: The solution of B gives a white precipitate with BaCl\(_2\) solution. This indicates the presence of sulfate ions (SO\(_4^{2-}\)) in the solution because BaCl\(_2\) reacts with sulfate ions to form a white precipitate of BaSO\(_4\).
Step 3: Analyzing the isomerism:
The two isomers A and B are ionisation isomers.
In ionisation isomerism, two or more compounds have the same molecular formula but release different ions in solution.
In this case, the only difference between the two isomers is that in A, chloride (Cl\(^-\)) is the counter-ion, while in B, sulfate (SO\(_4^{2-}\)) is the counter-ion. These two isomers give different ions in solution, which is the defining characteristic of ionisation isomerism.
Step 4: Conclusion:
Since the two isomers differ in the ions that are released into the solution (chloride in A and sulfate in B), this is a classic example of ionisation isomerism.