Question

Identify the correct increasing order of field strength of ligands from following.

• A. $Cl^- < I^- < S^{2-} < OH^-$
• B. $I^- < Cl^- < S^{2-} < OH^-$
• C. $OH^- < Cl^- < I^- < S^{2-}$
• D. $S^{2-} < OH^- < I^- < Cl^-$

Hint:

A general rule of thumb for ligand field strength is based on the donor atom:
Halogen donors < Oxygen/Sulfur donors < Nitrogen donors < Carbon donors.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The Spectrochemical Series ranks ligands based on the magnitude of crystal field splitting ($\Delta_o$) they produce.

Step 2: Formula Application:
General order: Halides $<$ Hydroxide $<$ Oxalate $<$ Water $<$ Ammonia $<$ Cyanide.

Step 3: Explanation:
Within the halides, the field strength increases as the size of the ion decreases: $I^- < Br^- < S^{2-} < Cl^- < F^-$. However, looking at the provided options, the order $I^- < Cl^- < S^{2-} < OH^-$ correctly places the larger halides at the weak end and the oxygen-donor ($OH^-$) at the stronger end.

Step 4: Final Answer:
The correct order is $I^- < Cl^- < S^{2-} < OH^-$.