Question

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

• A. \(\text{CO} < \text{en} < \text{NH}_3 < \text{C}_2\text{O}_4^{2-} < \text{S}^{2-}\)
• B. \(\text{S}^{2-} < \text{NH}_3 < \text{en} < \text{CO} < \text{C}_2\text{O}_4^{2-}\)
• C. \(\text{NH}_3 < \text{en} < \text{CO} < \text{S}^{2-} < \text{C}_2\text{O}_4^{2-}\)
• D. \(\text{S}^{2-} < \text{C}_2\text{O}_4^{2-} < \text{NH}_3 < \text{en} < \text{CO}\)

Hint:

When solving ligand field strength problems, always refer to the spectrochemical series. Stronger field ligands cause larger splitting of d-orbitals in transition metal complexes.

Answer 1

The Correct Option is D

Step 1: Understand the Spectrochemical Series
The spectrochemical series arranges ligands based on their field strength, which affects the splitting of d-orbitals in a coordination compound. The increasing order of ligand field strength is:
\[\text{S}^{2-} < \text{C}_2\text{O}_4^{2-} < \text{NH}_3 < \text{en} < \text{CO}.\]
Step 2: Explanation of the Order
\(\text{S}^{2-}\): Sulfide ions are weak field ligands due to their large size and low charge density.
\(\text{NH}_3\): Ammonia has higher field strength due to its ability to donate lone pair electrons.
\(\text{en}\) (Ethylenediamine): A bidentate ligand with stronger field strength than \(\text{NH}_3\).
\(\text{CO}\) (Carbon monoxide): A strong field ligand due to its \(\pi\)-back bonding capability.