Question

Which among the following is a strong field ligand?

• A. I⁻
• B. Cl⁻
• C. NH₃
• D. SCN⁻

Answer 1

The Correct Option is C

A strong field ligand is one that causes a large splitting of the d-orbitals in a coordination complex. This is determined by the spectrochemical series, which arranges ligands according to their field strength. Ligands higher in this series cause greater splitting. Here is a brief analysis of the given options:

• I⁻: Being a halide ion, iodide is a weak field ligand, causing minimal d-orbital splitting.
• Cl⁻: Also a halide, chloride is another weak field ligand, slightly stronger than iodide but still weaker compared to neutral molecules.
• NH₃: Ammonia is a neutral ligand with a strong field nature. It causes significant splitting due to its lone pair donation ability, making it a strong field ligand.
• SCN⁻: Thiocyanate is an ambidentate ligand that can act as either a weak or intermediate field ligand.

In conclusion, NH₃ is the strong field ligand among the given options.

Answer 2

In coordination chemistry, ligands are classified as strong field ligands or weak field ligands based on their ability to split the d-orbitals of the central metal ion in a complex.

• NH₃ (Ammonia) is a strong field ligand. It is capable of causing a large splitting of the d-orbitals, leading to low-spin complexes, especially with transition metals.
• I⁻ (Iodide) and Cl⁻ (Chloride) are weak field ligands, meaning they cause only a small splitting of the d-orbitals, leading to high-spin complexes.
• SCN⁻ (Thiocyanate) is an intermediate field ligand, meaning it can behave as both a weak field and strong field ligand depending on the metal ion it is bound to.

Therefore, the correct answer is NH₃ (Option C), which is a strong field ligand.