Question

The number of geometrical isomers possible for the complex \([Co(en)_2Cl_2]^+\) is:

• A. \(1\)
• B. \(2\)
• C. \(3\)
• D. \(4\)

Hint:

For octahedral complexes containing two identical monodentate ligands and bidentate ligands such as en, always check for cis and trans arrangements first. Most such complexes show exactly two geometrical isomers.

Answer 1

The Correct Option is B

Concept: Geometrical isomerism arises due to different spatial arrangements of ligands around the central metal ion. In octahedral complexes containing bidentate ligands such as ethylenediamine (en), cis and trans arrangements are possible when identical monodentate ligands are present.

Step 1: Determine the coordination environment. The complex is: \[ [Co(en)_2Cl_2]^+ \] Each ethylenediamine ligand occupies two coordination sites. Thus: \[ 2(en)=4 \text{ coordination sites} \] and \[ 2Cl^- =2 \text{ coordination sites} \] Total coordination number: \[ 4+2=6 \] Therefore, the geometry is octahedral.

Step 2: Examine possible arrangements of chloride ligands. The two chloride ligands can occupy:
• Adjacent positions (cis)
• Opposite positions (trans) Hence two geometrical isomers are possible.

Step 3: Verify if any additional geometrical forms exist. The bidentate ligands cannot generate additional geometrical arrangements beyond cis and trans. Thus the total number of geometrical isomers is: \[ 2 \] Hence option (B) is correct.