Geometrical Isomerism and Ionization Isomers in Coordination Compounds

To determine the correct option, we analyze the complexes in Set-I for geometrical isomerism and the pairs in Set-II for ionization isomerism.

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1. Evaluation of Set-I Complexes

A coordination complex exhibits geometrical isomerism if its ligands can be arranged in spatially distinct non-superimposable configurations (e.g., cis/trans or fac/mer).

• Complex 1: $[\text{Co(NH}_3)_3(\text{NO}_2)_3]$

  • Geometry: Octahedral (Coordination Number = 6)
  • Type: $MA_3B_3$ (where $A = \text{NH}_3$ and $B = \text{NO}_2^-$)
  • Geometrical Isomers: It shows two geometrical isomers:
    1. Facial ($fac$): The three identical ligands occupy the corners of one triangular face of the octahedron.
    2. Meridional ($mer$): The three identical ligands lie around the meridian of the octahedron.
  • Conclusion: Shows geometrical isomerism.

• Complex 2: $[\text{Co(en)}_2\text{Cl}_2]^+$

  • Geometry: Octahedral (Coordination Number = 6)
  • Type: $M(AA)_2B_2$ (where $AA = \text{en}$, a symmetrical bidentate ligand, and $B = \text{Cl}^-$)
  • Geometrical Isomers: It shows two geometrical isomers:
    1. cis-isomer: The two $\text{Cl}^-$ ligands are adjacent to each other ($90^\circ$ angle).
    2. trans-isomer: The two $\text{Cl}^-$ ligands are opposite to each other ($180^\circ$ angle).
  • Conclusion: Shows geometrical isomerism.

Thus, both complexes in Set-I of Option (C) show geometrical isomerism.

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2. Evaluation of Set-II Complexes

Ionization isomers are coordination compounds that have the same molecular formula but give different ions in aqueous solution due to the exchange of a ligand inside the coordination sphere with an anion outside the coordination sphere.

• Pair: $[\text{Co(NH}_3)_5\text{Cl}]\text{SO}_4$ and $[\text{Co(NH}_3)_5(\text{SO}_4)]\text{Cl}$
• Dissociation in water: $[\text{Co(NH}_3)_5\text{Cl}]\text{SO}_4 \xrightarrow{\text{H}_2\text{O}} [\text{Co(NH}_3)_5\text{Cl}]^{2+} + \text{SO}_4^{2-}$ $[\text{Co(NH}_3)_5(\text{SO}_4)]\text{Cl} \xrightarrow{\text{H}_2\text{O}} [\text{Co(NH}_3)_5(\text{SO}_4)]^+ + \text{Cl}^-$

Since they yield different ions in solution ($\text{SO}_4^{2-}$ vs. $\text{Cl}^-$), they are ionization isomers of each other.

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3. Analysis of Incorrect Options

• Option (A): $[\text{Ni(CO)}_4]$ is a tetrahedral complex ($MA_4$ type, $sp^3$ hybridized) and does not show geometrical isomerism.
• Option (B): The pair $[\text{Co(NH}_3)_6][\text{Cr(CN)}_6]$ and $[\text{Cr(NH}_3)_6][\text{Co(CN)}_6]$ are coordination isomers, not ionization isomers.
• Option (D): $[\text{Cr(NH}_3)_5\text{Cl}]\text{Cl}_2$ is of $MA_5B$ type and does not show geometrical isomerism. Furthermore, the pair in Set-II are hydrate (solvate) isomers.

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Conclusion

Option (C) correctly satisfies all the conditions.

Correct Answer: (C)