Question

Number of possible stereoisomers for the complex $[Co(en)_2Cl_2]Cl$ will be:

• A. 3
• B. 4
• C. 2
• D. 1

Hint:

For $[M(AA)_2X_2]$ type: Trans (1, optically inactive) + Cis (2, optically active pair) = 3 stereoisomers.

Answer 1

The Correct Option is A

Step 1: Identify the complex.
$[Co(en)_2Cl_2]^+$ is an octahedral complex with two bidentate $en$ ligands and two $Cl^-$ ligands. It can show both geometric and optical isomerism.
Step 2: Geometric isomers.
The two $Cl^-$ ligands can be placed on the same side (cis) or on opposite sides (trans) of the octahedral complex, giving two geometric isomers.
Step 3: Optical isomers of each geometric isomer.
The trans isomer has a centre of symmetry and a mirror plane, so it is optically inactive (no enantiomers). The cis isomer is non-superimposable on its mirror image and exists as two optical isomers (d and l).
Step 4: Total count.
Total stereoisomers $= 1\,(\text{trans}) + 2\,(\text{cis: d and l}) = 3$.
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