Question

The total number of geometrical and optical isomers possible with \([CoCl_2(en)_2]Cl\) are respectively

• A. \(0,\;2\)
• B. \(2,\;0\)
• C. \(2,\;2\)
• D. \(2,\;4\)

Hint:

For octahedral complexes of type \[ [M(en)_2X_2] \]

• cis form \(\rightarrow\) optically active

• trans form \(\rightarrow\) optically inactive
Therefore: \[ 2 \text{ geometrical isomers} \] and \[ 2 \text{ optical isomers} \]

Answer 1

The Correct Option is C

Concept: The complex ion is \[ [CoCl_2(en)_2]^+ \] which is an octahedral complex containing two bidentate ligands (\(en\)) and two identical monodentate ligands (\(Cl^-\)).

Step 1: Determine geometrical isomers. For octahedral complexes of the type \[ [M(en)_2X_2] \] two geometrical isomers are possible:

• cis

• trans
Hence, \[ \text{Geometrical isomers}=2 \]

Step 2: Determine optical isomers. \[ \begin{aligned} \text{cis-form} &:\quad \text{Optically active } (\Delta \text{ and } \Lambda) \\ \text{trans-form} &:\quad \text{Optically inactive} \end{aligned} \] Thus the cis form exists as two optical isomers. \[ \text{Optical isomers}=2 \]

Step 3: Write the result. \[ \boxed{ \text{Geometrical isomers}=2,\qquad \text{Optical isomers}=2 } \] Hence, option \(\mathbf{(C)}\) is correct.