Question

Identify a lowest field strength ligand from following.

• A. I$^{-}$
• B. S$^{2-}$
• C. en
• D. CO

Hint:

Halides are weak field ligands ($I^-$ is weakest), while $CN^-$ and $CO$ are strong field ligands.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The field strength of a ligand is determined by its position in the spectrochemical series, which ranks ligands based on the crystal field splitting energy (\( \Delta_{o} \)) they produce.
Step 2: Detailed Explanation:
The partial spectrochemical series is:
\( I^{-}<Br^{-}<S^{2-}<SCN^{-}<Cl^{-}<F^{-}<OH^{-}<ox^{2-}<H_{2}O<NCS^{-}<edta^{4-}<NH_{3}<en<CN^{-}<CO \)
Comparing the given options:
- \( I^{-} \): At the very beginning of the series (Weakest).
- \( S^{2-} \): Weak field, but stronger than \( I^{-} \).
- \( en \) (ethylenediamine): Strong field ligand.
- \( CO \) (carbonyl): Strongest known field ligand.
Thus, iodide (\( I^{-} \)) has the lowest field strength.
Step 3: Final Answer:
The lowest field strength ligand is \( I^{-} \).