Question

Among the following statements about cobalt complexes, which is/are CORRECT? Given: Atomic number of Co is 27

• A. ([Co(NH_3)_4]^{2+}\) exhibits square planar geometry
• B. ([Co(en)_3]^{3+}\) does not show optical isomerism (en = ethylenediamine)
• C. ([Co(H_2O)_6]^{3+}\) is paramagnetic in nature
• D. ([Co(NH_3)_5Cl]^{2+}\) shows ligand-to-metal charge transfer

Hint:

Ligand-to-metal charge transfer occurs when an electron is transferred from a ligand to the metal center, or vice versa, and is commonly observed in certain metal-ligand complexes.

Answer 1

The Correct Option is D

Step 1: Analyzing the options.
- (A) \([Co(NH_3)_4]^{2+}\) exhibits square planar geometry: Incorrect. This is a tetrahedral complex, not square planar, since Co(II) in this case is a \(d^7\) configuration and prefers tetrahedral geometry.
- (B) \([Co(en)_3]^{3+}\) does not show optical isomerism: Incorrect. \([Co(en)_3]^{3+}\) can exhibit optical isomerism because the complex is octahedral and en is a bidentate ligand, leading to chirality.
- (C) \([Co(H_2O)_6]^{3+}\) is paramagnetic in nature: Incorrect. This complex has a \(d^6\) configuration and is low-spin, meaning it is diamagnetic, not paramagnetic.
- (D) \([Co(NH_3)_5Cl]^{2+}\) shows ligand-to-metal charge transfer: Correct. This complex can undergo ligand-to-metal charge transfer due to the involvement of the ammine and chloride ligands.
Step 2: Conclusion.
The correct answer is (D), as this complex exhibits ligand-to-metal charge transfer.