Coordination Isomerism in Metal Complexes

To determine which of the given complexes exhibit coordination isomerism, we evaluate the structural requirements for this form of isomerism.

1. Definition of Coordination Isomerism

Coordination isomerism occurs in salts containing both complex cations and complex anions. It arises from the interchange of ligands between the cationic coordination sphere and the anionic coordination sphere.

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2. Analysis of the Given Complexes

• A. $[\text{Ag}(\text{NH}_3)_2][\text{Ag}(\text{CN})_2]$

  • Both the cationic and anionic entities contain the same metal center ($\text{Ag}^+$) with a coordination number of 2.
  • Exchanging all ligands yields $[\text{Ag}(\text{CN})_2]^- [\text{Ag}(\text{NH}_3)_2]^+$, which represents the identical chemical compound as the original salt.
  • Partial ligand exchange leads to neutral species ($[\text{Ag}(\text{NH}_3)(\text{CN})]$), which are not complex salts.
  • Therefore, A does not show coordination isomerism.

• B. $[\text{Co}(\text{NH}_3)_6][\text{Cr}(\text{CN})_6]$

  • The complex contains two different transition metal ions: $\text{Co}^{3+}$ in the cation and $\text{Cr}^{3+}$ in the anion.
  • Interchanging the ligands produces a distinctly new coordination isomer: $[\text{Cr}(\text{NH}_3)_6][\text{Co}(\text{CN})_6]$
  • Therefore, B shows coordination isomerism.

• C. $[\text{Co}(\text{NH}_3)_6][\text{Co}(\text{CN})_6]$

  • Both the cation and anion contain the same metal ion in the same oxidation state ($\text{Co}^{3+}$).
  • Complete interchange of ligands gives $[\text{Co}(\text{CN})_6]^{3-} [\text{Co}(\text{NH}_3)_6]^{3+}$, which is structurally identical to the original complex salt.
  • Therefore, C does not show coordination isomerism.

• D. $[\text{Fe}(\text{NH}_3)_6][\text{Co}(\text{CN})_6]$

  • The complex contains two different metal ions: $\text{Fe}^{3+}$ and $\text{Co}^{3+}$.
  • Interchanging the ligands produces the distinct coordination isomer: $[\text{Co}(\text{NH}_3)_6][\text{Fe}(\text{CN})_6]$
  • Therefore, D shows coordination isomerism.

• E. $[\text{Co}(\text{NH}_3)_6][\text{Fe}(\text{CN})_6]$

  • The complex contains two different metal ions: $\text{Co}^{3+}$ and $\text{Fe}^{3+}$.
  • Interchanging the ligands produces the distinct coordination isomer: $[\text{Fe}(\text{NH}_3)_6][\text{Co}(\text{CN})_6]$
  • Therefore, E shows coordination isomerism.

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Conclusion

The complexes that show coordination isomerism are B, D, and E Only.

Correct Option: B (B, D and E Only)