A reaction of cobalt(III) chloride and ethylenediamine in a 1:2 mole ratio generates two isomeric products A…
Coordination Compounds · Class 12 · JEE Main Previous Year Question
A reaction of cobalt(III) chloride and ethylenediamine in a 1:2 mole ratio generates two isomeric products A (violet-coloured) and B (green-coloured). A can show optical activity, but B is optically inactive. What type of isomers do A and B represent?
- a
Coordination isomers
- b
Linkage isomers
- c
Ionisation isomers
- d✓
Geometrical isomers
Geometrical isomers
🧠 Identify the Isomer Type
Co(III) + en (1:2 ratio) → . Two products with different colours (violet vs green) are the cis and trans geometric isomers.
🗺️ Identify A and B
- A (violet) = cis-: chiral (has Δ/Λ enantiomers) → optically active. Violet colour.
- B (green) = trans-: has mirror plane → optically inactive. Green colour.
The ONLY difference between cis and trans is spatial arrangement of ligands, which is the definition of geometrical isomerism.
🗺️ Other Options Don't Fit
- Coordination isomerism: requires 2 complexes with cation/anion swap of ligands. Not the case here (single complex).
- Linkage isomerism: requires ambidentate ligand bonding through different atoms. en is bidentate via N only.
- Ionisation isomerism: requires swap of inner-sphere counter-ion. No counter-ion swap here.
⚡ Cis vs Trans Colour Difference
Cis and trans isomers absorb light at slightly different wavelengths (different ligand field environments) → different observed colours. Classic example: — violet (cis) vs green (trans).
⚠️ Geometrical ≠ Optical
Both cis and trans are geometric isomers of each other. The cis form is additionally chiral (separable into Δ/Λ optical isomers), but A and B as a pair are geometrically related.
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