JEE Main · 2010 · 11 Apr 2010 · Offline · Coordination Compounds

Which one of the following has an optical isomer?
(en = ethylenediamine)

(A) $[Zn (en) (NH X_{3}) X_{2}]^{2 +}$
(B) $[Co (en) X_{3}]^{3 +}$ ✓ Correct
(C) $[Co (H X_{2} O) X_{4} (en)]^{3 +}$
(D) $[Zn (en) X_{2}]^{2 +}$

Answer: (B)

Solution

Optical isomerism appears when a complex has no plane of symmetry, so that it and its mirror image cannot be superimposed. The tris-chelate

[Co (en)_{3}]^{3 +}

is octahedral with three ethylenediamine rings set like a three-bladed propeller; it has no mirror plane and exists as a non-superimposable pair of

Δ

and

Λ

forms. The other complexes each possess a plane of symmetry, so only

[Co (en)_{3}]^{3 +}

shows optical isomerism.

JEE Main · 2010 · 11 Apr 2010 · Offline · Single correct option

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