Question

Which of the following coordination compounds would exhibit optical isomerism?

• A. Pentamminenitrocobalt (III) iodide
• B. Tris-(ethylenediamine) cobalt (III) bromide
• C. Trans- dicyanobis (ethylenediamine)
• D. Diamminedinitroplatinum (II)

Answer 1

Answer: (B)

Tris-(ethylenediamine) cobalt (III) bromide

Complexes of the type $M{\left(AA\right)}_3$ (where AA is symmetrical bidentate ligands) such as

${\left[Co{\left(en\right)}_3\right]}^{3+}$ and ${\left[Cr{\left(ox\right)}_3\right]}^{3-}$ exist as optical isomers.

The transform does not show optical isomerism, i.e., it cannot be resolved into optical

isomers. The reason is that the molecule has a plane of symmetry. On the other hand, the

cis-isomer is unsymmetrical and can be resolved into optical isomers.

The coordination entity, ${\left[PtC{l}_2{\left(en\right)}_2\right]}^{2+}$ forms cis and trans-isomers. Only the cis-isomers show optical activity

Tris-(ethylene diamine) cobalt (III) bromide, i.e., [Co(en)3]Br3[Co(en)_{3}]Br_{3}[Co(en)3​]Br3​ exhibits, optical isomerism.