Question

Which order is correct in spectrochemical series of ligands:

• A. Cl^-<F^-<H₂O<[C₂O₄]^2-<CN^-
• B. Cl^-<F^-<CN^-<H₂O<[C₂O₄]^2- 
• C. F^-<Cl^-<CN^-<H₂O<[C₂O₄]^2- 
• D. F^-<Cl^-<H₂O<CN^-<[C₂O₄]^2- 
• E. Cl^-<F^-< [C₂O₄]^2-<H₂O<CN^-

Answer 1

The Correct Option is A

Spectrochemical Series Analysis:

Correct weak-to-strong field order: \[ \text{Cl}^- < \text{F}^- < \text{H}_2\text{O} < \text{C}_2\text{O}_4^{2-} < \text{CN}^- \]

Key features:

Halides are weak field (Cl^- weaker than F^-)

H₂O is intermediate field

CN^- is strongest field ligand

Thus, the correct option is (A): \(Cl^- < F^- < H_2O < [C_2 O_4]^{2-} < CN^-\).

Answer 2

1. Understanding the spectrochemical series:

The spectrochemical series is an arrangement of ligands based on their ability to cause crystal field splitting (\( \Delta \)) in a metal complex. Ligands that cause a larger splitting are called strong-field ligands, while those causing smaller splitting are weak-field ligands.

2. General order of common ligands in the spectrochemical series:

• Weak-field ligands (small \( \Delta \)): \( \text{Cl}^- < \text{F}^- < \text{H}_2\text{O} < \left[\text{C}_2\text{O}_4\right]^{2-} \).
• Strong-field ligands (large \( \Delta \)): \( \left[\text{C}_2\text{O}_4\right]^{2-} < \text{CN}^- \).

The correct order is:

\[ \text{Cl}^- < \text{F}^- < \text{H}_2\text{O} < \left[\text{C}_2\text{O}_4\right]^{2-} < \text{CN}^- \]

3. Analyze each option:

• (E) \( \text{Cl}^- < \text{F}^- < \left[\text{C}_2\text{O}_4\right]^{2-} < \text{H}_2\text{O} < \text{CN}^- \):
  • This is incorrect because \( \text{H}_2\text{O} \) has a smaller splitting than \( \left[\text{C}_2\text{O}_4\right]^{2-} \).
• (B) \( \text{Cl}^- < \text{F}^- < \text{CN}^- < \text{H}_2\text{O} < \left[\text{C}_2\text{O}_4\right]^{2-} \):
  • This is incorrect because \( \text{CN}^- \) is a strong-field ligand and should come after \( \left[\text{C}_2\text{O}_4\right]^{2-} \).
• (C) \( \text{F}^- < \text{Cl}^- < \text{CN}^- < \text{H}_2\text{O} < \left[\text{C}_2\text{O}_4\right]^{2-} \):
  • This is incorrect because \( \text{Cl}^- \) is weaker than \( \text{F}^- \), and \( \text{H}_2\text{O} \) comes before \( \left[\text{C}_2\text{O}_4\right]^{2-} \).
• (D) \( \text{F}^- < \text{Cl}^- < \text{H}_2\text{O} < \text{CN}^- < \left[\text{C}_2\text{O}_4\right]^{2-} \):
  • This is incorrect because \( \text{CN}^- \) is stronger than \( \left[\text{C}_2\text{O}_4\right]^{2-} \).
• (A) \( \text{Cl}^- < \text{F}^- < \text{H}_2\text{O} < \left[\text{C}_2\text{O}_4\right]^{2-} < \text{CN}^- \):
  • This is correct and matches the spectrochemical series.

4. Final answer:

The correct option is (A).