Q63 / 180 · AIIMS 2004 · Chemistry

Assertion : The $\left[\mathrm{Ni}(\text { en })_3\right] \mathrm{Cl}_2$ (en = ethylene diamine) has lower stability than $\left[\mathrm{Ni}\left(\mathrm{NH}_3\right)_6\right] \mathrm{Cl}_2$. Reason : In $\left[\mathrm{Ni}(\mathrm{en})_3\right] \mathrm{Cl}_2$ the geometry of $\mathrm{Ni}$ is trigonal bipyramidal.

  • A
    If both assertion and reason are true and reason is the correct explanation of assertion
  • B
    If both assertion and reason are true but reason is not the correct explanation of assertion
  • C
    If assertion is true but reason is false
  • Correct answer
    D
    If both assertion and reason are false.

Solution

$\left[\mathrm{Ni}(\mathrm{en})_3\right] \mathrm{Cl}_2$ is a chelating compound and chelated complexes are more stable than similar complexes with unidentate ligands as dissociation of the complex involves breaking of two bonds rather than one. In $\left[\mathrm{Ni}(\mathrm{en})_3\right] \mathrm{Cl}_2, \mathrm{Ni}$ with $d^8$ configuration shows octahedral geometry. Six electrons will occupy the $t_{2 g}$ orbitals and two electrons will occupy the $e_g$ orbitals.

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

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