Question

Which of the following is the correct order of ligand field strength?

• A. CO<NH₃<en<C₂O₄²⁻<S²⁻
• B. S²⁻<C₂O₄²⁻<NH₃<en<CO
• C. NH₃<en<CO<S²⁻<C₂O₄²⁻
• D. S²⁻<NH₃<en<CO<C₂O₄²⁻

Hint:

Stronger field ligands induce greater crystal field splitting and favor low-spin complexes.

Answer 1

The Correct Option is B

Step 1: Understanding Ligand Field Strength
Ligand field strength follows the spectrochemical series.
The stronger the ligand field, the greater the splitting of d-orbitals in transition metal complexes.
Step 2: Spectrochemical Series Order \[ {S}^{2-}<{C}_2{O}_4^{2-}<{NH}_3<{en}<{CO} \] Explanation:
Sulfide (S$^{2-}$) is a weak field ligand.
Oxalate (C$_2$O$_4^{2-}$) is stronger than S$^{2-}$ but still weak.
Ammonia (NH$_3$) is a moderate field ligand.
Ethylenediamine (en) is stronger than NH$_3$ due to chelation effect.
CO is the strongest field ligand, leading to the greatest crystal field splitting.

Answer 2

The correct order of ligand field strength is:
S²⁻ < C₂O₄²⁻ < NH₃ < en < CO

Explanation:
- Ligand field strength determines the extent to which a ligand can split the d-orbitals of a central metal ion.
- S²⁻ (sulfide ion) is a weak field ligand because it is a soft base with less ability to donate electron density effectively.
- C₂O₄²⁻ (oxalate ion) is a bidentate ligand and has a slightly stronger field due to chelation compared to monodentate ligands like S²⁻.
- NH₃ (ammonia) is a stronger field ligand than oxalate because of its ability to donate a lone pair of electrons effectively.
- en (ethylenediamine) is a bidentate ligand with stronger field strength than NH₃ due to the chelate effect.
- CO (carbonyl) is a very strong field ligand because it can engage in back bonding with the metal, significantly increasing crystal field splitting.

Therefore, the order from weakest to strongest field ligand is:
S²⁻ < C₂O₄²⁻ < NH₃ < en < CO.