Question

Assertion (A) : Out of \( \mathrm{[Co(en)_3]^{3+}} \) and \( \mathrm{[Co(CN)_6]^{3-}} \), coordination compound \( \mathrm{[Co(en)_3]^{3+}} \) is a more stable complex.

Reason (R) : Ethane-1,2-diamine is a chelating ligand.

• A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Assertion (A) is false, but Reason (R) is true.

Hint:

Ethane-1,2-diamine forms five-membered chelate rings, and chelation makes the complex more stable, so R explains A.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
A ligand that binds through two or more donor atoms and forms a ring with the metal is called a chelating ligand.
Complexes with such rings are more stable than similar complexes with unidentate ligands. This is the chelate effect.

Step 2: Check the Reason:
Ethane-1,2-diamine (en) is \( \mathrm{H_2N-CH_2-CH_2-NH_2} \).
It has two nitrogen donor atoms, so it is bidentate.
It binds to the metal through both nitrogens and forms a five-membered ring.
So Reason (R) is true.

Step 3: Check the Assertion:
In \( \mathrm{[Co(en)_3]^{3+}} \) there are three five-membered chelate rings.
\( \mathrm{CN^-} \) in \( \mathrm{[Co(CN)_6]^{3-}} \) is unidentate and forms no ring.
On the NCERT chelate-effect argument, the en complex is the more stable one. So Assertion (A) is true.

Step 4: Relate R to A:
The extra stability of the en complex comes from the ring formation by the chelating ligand.
So R explains A.

Final Answer:
Both are true and R explains A, option (A). \[ \boxed{\text{(A)}} \]