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

Step 1: Understanding the Concept:
Geometrical isomerism in octahedral coordination complexes involves the spatial arrangement of ligands around the central metal ion. For a complex of the type \([M(AA)_2a_2]\), the bidentate ligands (\(en\)) and monodentate ligands (\(Cl\)) can be arranged in specific ways.
Step 2: Key Formula or Approach:
The complex \([Co(en)_2Cl_2]^+\) can exhibit two geometrical isomers based on the position of the \(Cl^-\) ligands:
- Cis-isomer: The two \(Cl\) ligands are adjacent to each other (\(90^\circ\) angle).
- Trans-isomer: The two \(Cl\) ligands are opposite to each other (\(180^\circ\) angle).
Step 3: Detailed Explanation:

The cis-isomer is optically active (chiral) and exists as two enantiomers, while the trans-isomer is optically inactive (achiral). However, the question specifically asks for the number of "geometrical isomers," which refers to the distinct structural arrangements (cis and trans), resulting in a count of 2.
Step 4: Final Answer:
The number of geometrical isomers possible for this complex is 2.