Q48 / 180 · COMEDK 2022 · Chemistry
The complex which does not show optical isomerism is
- Acis $-\left[\mathrm{Co}(\mathrm{en})_2 \mathrm{Cl}_2\right] \mathrm{Cl}$
- Bcis $-\left[\mathrm{CiCl}_2(\mathrm{ox})_2\right]^{3-}$
- Ccis $-\left[\mathrm{CoCl}(\mathrm{en})_2\left(\mathrm{NH}_3\right)\right]^{2+}$
- Correct answerDcis - $\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_4 \mathrm{Cl}_2\right]^{+}$
Solution
Optical isomerism in coordination complexes requires the absence of a plane of symmetry or a center of inversion.
Option (1): cis-$[Co(en)_2Cl_2]^{+}$ has no plane of symmetry and is optically active.
Option (2): cis-$[CrCl_2(ox)_2]^{3-}$ has no plane of symmetry and is optically active.
Option (3): cis-$[CoCl(en)_2(NH_3)]^{2+}$ has no plane of symmetry and is optically active.
Option (4): cis-$[Co(NH_3)_4Cl_2]^{+}$ possesses a plane of symmetry (the plane containing the four $NH_3$ ligands and the $Co$ center, or the plane bisecting the $Cl-Co-Cl$ angle). Due to the presence of a plane of symmetry, it is optically inactive.
Answer: cis - $\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_4 \mathrm{Cl}_2\right]^{+}$
Option (1): cis-$[Co(en)_2Cl_2]^{+}$ has no plane of symmetry and is optically active.
Option (2): cis-$[CrCl_2(ox)_2]^{3-}$ has no plane of symmetry and is optically active.
Option (3): cis-$[CoCl(en)_2(NH_3)]^{2+}$ has no plane of symmetry and is optically active.
Option (4): cis-$[Co(NH_3)_4Cl_2]^{+}$ possesses a plane of symmetry (the plane containing the four $NH_3$ ligands and the $Co$ center, or the plane bisecting the $Cl-Co-Cl$ angle). Due to the presence of a plane of symmetry, it is optically inactive.
Answer: cis - $\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_4 \mathrm{Cl}_2\right]^{+}$
Hence, the correct answer is option: 'D'.