Question

(i) Give a chemical test to show that \( [Co(NH_3)_5SO_4]Cl \) and \( [Co(NH_3)_5Cl]SO_4 \) are ionisation isomers.
(ii) What is meant by the 'Chelate effect'? Give an example.

Hint:

Precipitation tests only work for ions located outside the coordination sphere (brackets). Ions inside the brackets are not released in water.

Answer 1

Step 1: Understanding the Concept:
Ionisation isomers produce different ions in solution. These ions can be identified using specific precipitating reagents.
Step 2: Detailed Explanation:
(i) Ionisation Isomers Test:
1. Dissolve both compounds in water.
2. To the first solution \( [Co(NH_3)_5SO_4]Cl \), add \( AgNO_3 \). It gives a white precipitate of \( AgCl \) because \( Cl^- \) is the ionisable species. It does not react with \( BaCl_2 \).
3. To the second solution \( [Co(NH_3)_5Cl]SO_4 \), add \( BaCl_2 \). It gives a white precipitate of \( BaSO_4 \) because \( SO_4^{2-} \) is the ionisable species. It does not react with \( AgNO_3 \).
(ii) Chelate Effect:
When a multidentate ligand (like a didentate or polydentate ligand) binds to a central metal ion to form a ring structure, the resulting complex is exceptionally stable. This stabilization is called the chelate effect.
Example: The complex \( [Cu(en)_2]^{2+} \) is much more stable than \( [Cu(NH_3)_4]^{2+} \) because ethylenediamine (en) forms 5-membered chelate rings.
Step 3: Final Answer:
(i) Use \( AgNO_3 \) to detect \( Cl^- \) and \( BaCl_2 \) to detect \( SO_4^{2-} \).
(ii) Chelation provides stability; e.g., ethylenediamine complexes.