GATE 2024 CY – Question 49
The complex(es) that exhibit(s) optical isomerism is (are)
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Correct answer: (A) $[\mathrm{Fe(acac)_3}]$; (B) cis-$[\mathrm{Co(en)_2Cl_2}]^+$; (D) $[\mathrm{Co(en)_3}]^{3+}$
Explanation
**Optical isomerism** (chirality) requires that the complex cannot be superimposed on its mirror image.
- **$[\text{Fe(acac)}_3]$:** a tris-chelate octahedral complex with three bidentate ligands. It has a propeller shape that exists as two non-superimposable mirror images ($\Delta$ and $\Lambda$). Chiral. ✓
- **cis-$[\text{Co(en)}_2\text{Cl}_2]^+$:** the two Cl are adjacent, and the two en rings can wrap in two mirror-image ways. Chiral. ✓
- **trans-$[\text{Co(en)}_2\text{Cl}_2]^+$:** has mirror planes (the two Cl are opposite each other). Achiral. ✗
- **$[\text{Co(en)}_3]^{3+}$:** the classic tris-chelate, chiral ($\Delta$ and $\Lambda$). ✓
Answer **A, B and D**.