Question

Which one of the following coordination compounds will exhibit both geometrical and optical isomerism?

• A. \([Cr(ox)_3]^{3-}\)
• B. \([Co(en)_2Cl_2]^+\)
• C. \([Co(CN)_6]^{3-}\)
• D. \([Co(NO_3)_3(NH_3)_3]\)

Hint:

Complexes of the type \([M(en)_2X_2]\) commonly show cis-trans geometrical isomerism, and the cis form can show optical isomerism.

Answer 1

The Correct Option is B

Step 1: Understand the requirement.
The compound must show both geometrical isomerism and optical isomerism.
Geometrical isomerism occurs when ligands can occupy different spatial arrangements such as cis and trans forms.
Optical isomerism occurs when a complex has non-superimposable mirror images.

Step 2: Analyse option (A).
\[ [Cr(ox)_3]^{3-} \]
This complex contains three bidentate oxalate ligands.
It can show optical isomerism due to chiral arrangement, but it does not show geometrical isomerism because all three ligands are identical bidentate ligands.
So, option (A) is not correct.

Step 3: Analyse option (B).
\[ [Co(en)_2Cl_2]^+ \]
Here, \(en\) is ethylenediamine, a bidentate ligand.
The complex has two \(en\) ligands and two chloride ligands.

Step 4: Check geometrical isomerism for option (B).
The two chloride ligands may be adjacent or opposite to each other.
Therefore, the complex shows:
\[ \text{cis and trans isomerism}. \]
So, it exhibits geometrical isomerism.

Step 5: Check optical isomerism for option (B).
The cis form of \([Co(en)_2Cl_2]^+\) is optically active because it has non-superimposable mirror images.
Thus, it also shows optical isomerism.

Step 6: Analyse remaining options.
\[ [Co(CN)_6]^{3-} \]
has six identical ligands, so it does not show geometrical or optical isomerism.
\[ [Co(NO_3)_3(NH_3)_3] \]
may show geometrical arrangement, but it is not the standard case showing both geometrical and optical isomerism like \([Co(en)_2Cl_2]^+\).

Step 7: Final conclusion.
The coordination compound that exhibits both geometrical and optical isomerism is:
\[ \boxed{[Co(en)_2Cl_2]^+} \]