Question

Which of the following complexes will exhibit optical isomerism?

• A. \([\text{Co}(NH_3)_4Cl_2]^+\)
• B. \([\text{Cr}(\text{en})_3]^{3+}\)
• C. \([\text{Fe}(CN)_6]^{3-}\)
• D. \([\text{Pt}(NH_3)_2Cl_2]\)

Hint:

Optical isomerism occurs in complexes with bidentate ligands forming chiral structures, commonly seen in octahedral complexes with 3 bidentate ligands like \([\text{Cr}(\text{en})_3]^{3+}\).

Answer 1

The Correct Option is B

Optical isomerism occurs in coordination complexes that are chiral, i.e., they cannot be superimposed on their mirror images. - (A) \([\text{Co}(NH_3)_4Cl_2]^+\): This is an octahedral complex with two chloride ligands. It can show geometrical isomerism (cis/trans) but not optical isomerism. - (B) \([\text{Cr}(\text{en})_3]^{3+}\): Here, "en" stands for ethylenediamine, a bidentate ligand. This complex has three bidentate ligands, forming an octahedral complex that is chiral. It exhibits optical isomerism (enantiomers). - (C) \([\text{Fe}(CN)_6]^{3-}\): Hexacyanoferrate(III) complex is octahedral but with six identical monodentate ligands. It is symmetrical and does not show optical isomerism. - (D) \([\text{Pt}(NH_3)_2Cl_2]\): This square planar complex exhibits cis-trans isomerism but no optical isomerism because square planar complexes are usually planar and symmetrical.