Question

Which of the following complexes do not exhibit geometrical isomerism? \[ \begin{aligned} \text{I.} \quad & [\mathrm{CrF_2(H_2O)_4}]Cl_2 \\ \text{II.} \quad & [\mathrm{Co(en)_3}]^{3+} \\ \text{III.} \quad & [\mathrm{CoF(NH_3)_5}](\mathrm{NO_3})_2 \end{aligned} \] The correct answer is

• A. I, II only
• B. II, III only
• C. I, III only
• D. I, II, III \bigskip

Hint:

For octahedral complexes:

• \([\mathrm{MA_4B_2}]\) \(\rightarrow\) cis-trans isomerism.
• \([\mathrm{MA_5B}]\) \(\rightarrow\) No geometrical isomerism.
• \([\mathrm{M(AA)_3}]\) (three identical bidentate ligands) \(\rightarrow\) Optical isomerism only.

Answer 1

The Correct Option is B

Step 1: Analyse Complex I. \[ [\mathrm{CrF_2(H_2O)_4}]^{2+} \] This is an octahedral complex of the type \[ [\mathrm{MA_4B_2}] \] Such complexes exhibit cis-trans geometrical isomerism. Hence, Complex I exhibits geometrical isomerism.

Step 2: Analyse Complex II. \[ [\mathrm{Co(en)_3}]^{3+} \] This is an octahedral complex containing three identical bidentate ligands. It exhibits optical isomerism but does not exhibit geometrical isomerism. Hence, Complex II does not exhibit geometrical isomerism.

Step 3: Analyse Complex III. \[ [\mathrm{CoF(NH_3)_5}]^{2+} \] This is an octahedral complex of the type \[ [\mathrm{MA_5B}] \] Such complexes possess only one possible arrangement and therefore do not exhibit geometrical isomerism. Hence, Complex III does not exhibit geometrical isomerism.

Step 4: Final conclusion. The complexes that do not exhibit geometrical isomerism are \[ \boxed{\text{II and III only}.} \] Hence, the correct option is \(\boxed{(B)}\).