Question

Identify the optically active compound from the following.

Hint:

Coordination complexes with three bidentate ligands like ethylenediamine often exhibit optical isomerism due to their chiral nature, leading to (Delta) and (Lambda) forms.

Answer 1

Step 1: Understanding Optical Activity in Coordination Compounds 
- Optical activity arises in coordination compounds when they lack a plane of symmetry and can exist in non-superimposable mirror image forms (enantiomers).
- This typically happens when the ligands are arranged in a chiral manner around the metal center. 
Step 2: Structure of \([ \text{Co(en)}_3 ] \text{Cl}_3\) 
- Ethylenediamine (\(\text{en}\)) is a bidentate ligand, meaning it forms two coordinate bonds with the central metal ion.
- The complex \([ \text{Co(en)}_3 ]^{3+}\) has a chiral octahedral structure due to the three ethylenediamine ligands binding in a way that restricts symmetry. 
Step 3: Optical Isomerism 
- The presence of three bidentate ethylenediamine ligands in a cis-arrangement leads to two non-superimposable mirror image forms: Delta (Δ) and Lambda (Λ) isomers.
- This results in optical activity because the compound can rotate plane-polarized light. 
Step 4: Conclusion 
- \([ \text{Co(en)}_3 ] \text{Cl}_3\) is optically active as it exhibits chirality.
- Unlike simple metal complexes with monodentate ligands, this complex does not have a plane of symmetry.