Question

Which of the following complex species is not expected to exhibit optical isomerism?
A. \[{[Co{(en)_2}C{l_2}]^ + }\]
B. \[{[Co{(N{H_3})_3}C{l_3}]^{}}\]
C. \[{[Co(en){(N{H_3})_2}C{l_2}]^ + }\]
D. \[{[Co{(en)_3}]^{3 + }}\]

Answer 1

Hint: Optical isomers are two compounds with the same number and kinds of atoms, bonds (i.e., molecule connectivity), and distinct spatial configurations of the atoms, but non-superimposable mirror images. An enantiomer is a non-superimposable mirror image structure.

Complete step by step answer:
Optical isomers are molecules that behave differently when exposed to plane-polarized light. In a molecule, they have various three-dimensional configurations of the same atoms/groups.
They are two compounds with the same number and kinds of atoms, bonds (i.e., molecule connectivity), and distinct spatial configurations of the atoms, but non-superimposable mirror images. An enantiomer is a non-superimposable mirror image structure.

If a molecule is not superimposable with its mirror image, it is called optical isomerism.

The isomer is called facial, or fac, when three similar ligands share one face. The isomer is considered to be meridional, or mer, if all three ligands and the metal ion are in the same plane.

Hence, it is evident that only complexes with no symmetry components exhibit optical isomerism.
From the given options \[{[Co{(N{H_3})_3}C{l_3}]^{}}\]exhibits both facial and meridional isomerism where others do not.
Also, \[{[Co{(N{H_3})_3}C{l_3}]^{}}\] has symmetry elements in it.
Hence \[{[Co{(N{H_3})_3}C{l_3}]^{}}\] is the correct answer.

Note: The isomer is called facial, or fac, when three similar ligands share one face. The isomer is considered to be meridional, or mer, if all three ligands and the metal ion are in the same plane. If a molecule is not superimposable with its mirror image, it is called optical isomerism.