Question

Which of the following exhibit optical isomerism? I. \([Fe(C_2O_4)_3]^{3-}\) II. \([Cr(H_2O)_4Cl_2]^+\) III. \([Co(NH_3)_2(en)_2]^{3+}\)

• A. I, II only
• B. I, III only
• C. II, III only
• D. I, II, III

Hint:

Optical isomerism is common in chelate complexes like oxalates and ethylenediamine complexes when no plane of symmetry is present.

Answer 1

The Correct Option is B

Concept: Optical isomerism occurs when a coordination compound is non-superimposable on its mirror image. This generally happens when the complex lacks plane of symmetry and is chiral. Typical cases include:
• Chelate complexes with bidentate ligands
• Octahedral complexes with specific ligand arrangements

Step 1: Analyze complex I. \[ [Fe(C_2O_4)_3]^{3-} \] Oxalate is a bidentate ligand forming three chelate rings. Such tris-chelate octahedral complexes are optically active due to Δ and Λ forms. Thus I shows optical isomerism.

Step 2: Analyze complex II. \[ [Cr(H_2O)_4Cl_2]^+ \] This is an octahedral complex of type \(MA_4B_2\). It generally has a plane of symmetry and does not show optical isomerism. Thus II is optically inactive.

Step 3: Analyze complex III. \[ [Co(NH_3)_2(en)_2]^{3+} \] This complex contains bidentate ethylenediamine ligands. Such cis-arrangements lead to chirality and optical isomerism. Thus III shows optical isomerism.

Step 4: Final conclusion. Optically active complexes are: \[ I \text{ and } III \] Hence answer is: \[ \boxed{B} \]