Question

Arrange the following complexes in increasing order of C.F.S.E. (\( \Delta_0 \))
(a) \( [\text{Co}(\text{H}_2\text{O})_6]^{2+} \)
(b) \( [\text{Co}(\text{H}_2\text{O})_6]^{3+} \)
(c) \( [\text{Co}(\text{en})_3]^{3+} \)

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

Hint:

For ligands, stronger field ligands (like \( \text{en} \)) cause greater splitting of the d-orbitals, resulting in higher C.F.S.E. than weaker field ligands (like \( \text{H}_2\text{O} \)).

Answer 1

The Correct Option is C

Step 1: Understanding C.F.S.E.
The Crystal Field Stabilization Energy (C.F.S.E.) depends on the nature of the ligands, the oxidation state of the metal ion, and the arrangement of electrons in the d-orbitals of the metal ion. The greater the splitting energy (\( \Delta_0 \)), the greater the C.F.S.E. for a given complex.
Step 2: Comparison of the complexes.
- \( [\text{Co}(\text{H}_2\text{O})_6]^{2+} \): This is a \( d^7 \) complex with a weak field ligand (water). Water ligands cause a small splitting, leading to a lower C.F.S.E.
- \( [\text{Co}(\text{H}_2\text{O})_6]^{3+} \): This is a \( d^6 \) complex with a weak field ligand (water). A \( d^6 \) configuration typically results in a larger splitting than a \( d^7 \) configuration, giving a slightly higher C.F.S.E.
- \( [\text{Co}(\text{en})_3]^{3+} \): This is a \( d^6 \) complex with ethylenediamine (en) as the ligand. Ethylenediamine is a stronger field ligand than water, leading to greater splitting (\( \Delta_0 \)) and, thus, a higher C.F.S.E.
Step 3: Conclusion.
Therefore, the order of increasing C.F.S.E. is: \[ c>b>a \]
Final Answer: \( c>b>a \)