Question

Which of the following complex show optical isomerism?
$(i) \text{cis} - [\text{COCl}(\text{en})_2 (\text{NH}_3)]^{2+} $ 
$(ii) \text{cis} - [\text{CrCl}_2(\text{ox})_2]^{3-}$ 
$(iii) \text{cis} - [\text{CO}(\text{en})_2\text{Cl}_2]\text{Cl}$ 
$(iv) \text{cis} - [\text{CO}(\text{NH}_3)_4 \text{Cl}_2]^+$

• A. (i), (ii), (iii)
• B. (i), (ii)
• C. (i), (iv)
• D. (i), (ii), (iv)

Hint:

For a complex to show optical isomerism, it must lack any symmetry and must have a non-superimposable mirror image, typically arising from a cis configuration.

Answer 1

The Correct Option is A

To determine which complexes exhibit optical isomerism, we must understand the conditions under which a complex can display optical isomerism. Optical isomerism occurs in certain coordination compounds that lack a plane of symmetry, center of symmetry, or any improper axis of rotation. It is commonly exhibited in octahedral complexes, especially with bidentate ligands.

Let's analyze each option:

1. cis-[$\text{CoCl}(\text{en})_2(\text{NH}_3)]^{2+}$: This complex has a 6-coordinate octahedral geometry with two bidentate ethylenediamine (en) ligands and one monodentate ammonia ligand. The presence of the bidentate $\text{en}$ ligands allows for chirality, as the arrangement can result in non-superimposable mirror images. Thus, it can exhibit optical isomerism.
2. cis-[$\text{CrCl}_2(\text{ox})_2]^{3-}$: This complex involves oxalate (ox) bidentate ligands. With the $\text{cis}$ configuration, optical isomerism is possible due to the potential for non-superimposable mirror images derived from its arrangement.
3. cis-[$\text{Co}(\text{en})_2\text{Cl}_2]\text{Cl}$: Similar to the first complex, this also contains bidentate $\text{en}$ ligands in a $\text{cis}$ configuration which allows for chirality, thereby enabling optical isomerism.
4. cis-[$\text{Co}(\text{NH}_3)_4\text{Cl}_2]^+$: This complex is a 6-coordinate octahedral system with only monodentate $\text{NH}_3$ and Cl ligands. It doesn't have bidentate ligands or suitable asymmetry within its arrangement to exhibit optical isomerism.

Thus, the complexes that show optical isomerism are:

• cis-[$\text{CoCl}(\text{en})_2(\text{NH}_3)]^{2+}$
• cis-[$\text{CrCl}_2(\text{ox})_2]^{3-}$
• cis-[$\text{Co}(\text{en})_2\text{Cl}_2]\text{Cl}$

The correct answer is: (i), (ii), (iii)

Answer 2

Optical isomerism in coordination compounds occurs when a compound cannot be superimposed on its mirror image. This phenomenon is typically present in chiral complexes. In the given options, we need to identify which complexes show optical isomerism by examining their structures:

• (i) cis - $[\text{CoCl}(\text{en})_2(\text{NH}_3)]^{2+}$: In this complex, the presence of ethylenediamine (en) as a bidentate ligand creates an asymmetric environment leading to chirality. Therefore, it can exist as enantiomers, showing optical isomerism.
• (ii) cis - $[\text{CrCl}_2(\text{ox})_2]^{3-}$: The oxalate (ox) ion is a bidentate ligand and the configuration with cis arrangement results in a chiral center. Hence, this complex can show optical isomerism.
• (iii) cis - $[\text{Co}(\text{en})_2\text{Cl}_2]$Cl: With the presence of (en) ligands, this complex is chiral, and the cis configuration allows for optical isomerism.
• (iv) cis - $[\text{Co}(\text{NH}_3)_4\text{Cl}_2]^+$: This complex is achiral because it contains only monodentate ligands, resulting in a symmetric configuration that does not support optical isomerism.

Based on the above analysis, the complexes that exhibit optical isomerism are (i), (ii), and (iii).