Question

Which one of the following is an ambidentate ligand?

• A. Oxalate
• B. Ethylenediamine
• C. Thiocyanate ion
• D. Ethane-1,2-diamine

Hint:

Ambidentate ligands can attach through two different atoms. Examples include \(\ce{NO2^-}\), \(\ce{SCN^-}\), and \(\ce{CN^-}\).

Answer 1

The Correct Option is C

Step 1: Understanding the Topic:
This problem belongs to the chapter "Coordination Compounds." Ligands are molecules or ions that donate electron pairs to a central metal atom. An ambidentate ligand is a unique type of ligand that possesses two different atoms through which it can coordinate, but it only uses one of these atoms at a time to bond with the metal. This capability leads to the formation of linkage isomers.
Step 2: Key Formulas and Approach:
We evaluate the denticity and donor atoms of each option:
Bidentate: Uses two donor sites simultaneously.
Hexadentate: Uses six donor sites simultaneously.
Ambidentate: Has two choices of donor atoms but uses only one at a time.

Step 3: Detailed Explanation:

A. Ethane-1,2-diamine (en): This is a bidentate ligand. It uses two Nitrogen donor atoms simultaneously to form a five-membered chelate ring with the metal.
B. EDTA: This is a hexadentate ligand. It uses two Nitrogen and four Oxygen donor sites to wrap around the metal ion.
C. Thiocyanate ($SCN^-$): This is an ambidentate ligand. It can coordinate via the Sulfur atom ($M-SCN$, thiocyanato) or via the Nitrogen atom ($M-NCS$, isothiocyanato). It is monodentate but has two different ways to "plug in" to the metal.
D. Oxalate ($ox$): This is a bidentate ligand using two Oxygen donor atoms simultaneously.
Step 4: Final Answer:
The only ambidentate ligand listed is Thiocyanate, which corresponds to option (C).