Question

Among the ligands \( {NH}_3, \, {en}, \, {CN}^-, \, {CO} \), the correct order of their increasing field strength is:

• A. \( {NH}_3<{en}<{CN}^-<{CO} \)
• B. \( {CN}^-<{NH}_3<{en} \)
• C. \( {en}<{CN}^-<{NH}_3<{CO} \)
• D. \( {CO}<{NH}_3<{en}<{CN}^- \)

Hint:

The spectrochemical series helps in determining the field strength of ligands, influencing the splitting of d-orbitals and the color of metal complexes.

Answer 1

The Correct Option is A

Step 1: The field strength of a ligand depends on its ability to split the d-orbital energy levels in a metal complex. Ligands are classified as strong, medium, or weak field ligands. 
Step 2: Based on the spectrochemical series: 
- \( {CO} \) is a strong field ligand. 
- \( {CN}^- \) is also a strong field ligand, but it is weaker than \( {CO} \). 
- \( {en} \) (ethylenediamine) is a medium field ligand. 
- \( {NH}_3 \) is a weak field ligand. 
Step 3: The increasing order of field strength is: \[ {NH}_3<{en}<{CN}^-<{CO} \] Thus, the correct order is option (A).