Q87 / 200 · NEET 2009 (Screening) · Chemistry

Which of the following does not show optical isomerism? (en = ethylenediamine)

  • A
    $\left[\mathrm{Co}(\mathrm{en})_2 \mathrm{Cl}_2\right]^{+}$
  • Correct answer
    B
    $\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_3 \mathrm{Cl}_3\right]^0$
  • C
    $\left[\mathrm{Co}(\mathrm{en}) \mathrm{Cl}_2\left(\mathrm{NH}_3\right)_2\right]^{+}$
  • D
    $\left[\operatorname{Co}(\mathrm{en})_3\right]^{3+}$

Solution

Optical isomerism is exhibited by only those complexes in which elements of symmetry are absent. Octahedral complexes of the types $\left[\mathrm{M}(\mathrm{aa})_3\right],\left[\mathrm{M}(\mathrm{aa}) \mathrm{x}_2, \mathrm{y}_2\right]$ and $\left[\mathrm{M}(\mathrm{aa})_2 \mathrm{x}_2\right]$ have absence of elements of symmetry, thus exhibit optical isomerism. Here, $a a$ represents bidentate ligand, $x$ or $y$ represents monodentate ligand and $M$ represents central metal ion. Hence, $\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_3 \mathrm{Cl}_3\right]^0$ due to presence of symmetry elements does not exhibit optical isomerism.

Hence, the correct answer is option: 'B'.

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