Question

Arrange the following complexes in increasing order of CFSE (\( \Delta o \))
(a) \( [Co(H_2O)_6]^{2+} \)
(b) \( [Co(H_2O)_6]^{3+} \)
(c) \( [Co(en)_3]^{3+} \)

• A. \( c>a>b \)
• B. \( c>b>a \)
• C. \( a>b>c \)
• D. \( b>a>c \)

Hint:

For a given metal, the higher the charge and the stronger the ligand, the greater the crystal field splitting and CFSE.

Answer 1

The Correct Option is B

Step 1: Understanding CFSE (Crystal Field Stabilization Energy).
CFSE is a measure of the energy stability of a complex due to the splitting of its d-orbitals in the presence of a ligand field. The greater the splitting, the higher the CFSE. Step 2: Analyzing the complexes.
- (a) \( [Co(H_2O)_6]^{2+ \):} The complex with \( \text{Co}^{2+} \), which has a lower charge compared to \( \text{Co}^{3+} \), resulting in a lower splitting energy (\( \Delta o \)).
- (b) \( [Co(H_2O)_6]^{3+ \):} The complex with \( \text{Co}^{3+} \), which has a higher charge and thus higher splitting energy, resulting in a higher CFSE than \( [Co(H_2O)_6]^{2+} \).
- (c) \( [Co(en)_3]^{3+ \):} The complex with \( \text{Co}^{3+} \) and ethylenediamine (en) ligands, which causes greater ligand field splitting, leading to the highest CFSE among the three.
Step 3: Conclusion.
The order of increasing CFSE is \( c>b>a \), making option (2) the correct answer. Final Answer:} \( c>b>a \).