Question

Which Of The Following Complexes Will Show Optical Isomerism?

• A. $\left[\mathrm{Cr}{\left(\mathrm{en}\right)}_3\right]{\mathrm{Cl}}_3$
• B. $[\mathrm{Cr}{\left({\mathrm{NH}}_3\right)}_6{]}^{2+}$
• C. $[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6{]}^{2+}$
• D. $\left[\mathrm{Pt}{\left({\mathrm{NH}}_3\right)}_3\mathrm{Br}\right]{\mathrm{NO}}_3$

Answer 1

The correct option is A

$\left[\mathrm{Cr}{\left(\mathrm{en}\right)}_3\right]{\mathrm{Cl}}_3$

Explanation for the correct option:

A. $\left[\mathrm{Cr}{\left(\mathrm{en}\right)}_3\right]{\mathrm{Cl}}_3$

Optical isomerism

• Optical isomerism is the isomerism shown by optical isomers.
• These compounds are mirror images of each other.
• The optical isomers cannot be superimposed on one another and are optically active.
• In the coordination compound $\left[\mathrm{Cr}{\left(\mathrm{en}\right)}_3\right]{\mathrm{Cl}}_3$ there is no element of symmetry.
• It can rotate plane-polarized light left and right.
• It has two optical isomers, d (dextrorotatory) and l (laevorotatory) which are shown below:

Explanation for the incorrect options:

(B) $[\mathrm{Cr}{\left({\mathrm{NH}}_3\right)}_6{]}^{2+}$

• It has a mirror plane of symmetry and hence does not show optical isomerism.

(C) $[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6{]}^{2+}$

• It also has a mirror plane of symmetry and hence does not show optical isomerism.

(D) $\left[\mathrm{Pt}{\left({\mathrm{NH}}_3\right)}_3\mathrm{Br}\right]{\mathrm{NO}}_3$

• This coordination complex is of the type ${\mathrm{MA}}_3\mathrm{B}$. Hence, it is square planar in geometry with a plane of symmetry. Thus, it will not show optical isomerism.

Hence, the correct option is A i.e. $\left[\mathrm{Cr}{\left(\mathrm{en}\right)}_3\right]{\mathrm{Cl}}_3$.