Question

Which of the following ligands forms a chelate complex?

• A. Ammonia
• B. Water
• C. NO\(_2\)
• D. Oxalate ion

Hint:

Common chelating ligands: Oxalate (\(C_2O_4^{2-}\)), Ethylenediamine (en), EDTA. They form stable ring complexes (Chelate effect).

Answer 1

The Correct Option is D

To determine which of the given ligands forms a chelate complex, we first need to understand what a chelate complex is.

A chelate complex involves a central metal atom bound to a ligand that forms at least two bonds with the metal ion. Such ligands, which can form multiple bonds with a single metal ion, are known as chelating ligands. Typically, they are polydentate ligands, possessing two or more donor atoms.

Let's analyze each option:

1. Ammonia (NH₃): Ammonia is a monodentate ligand with only one donor atom (the nitrogen), capable of forming only one bond with the metal ion. Thus, it cannot form a chelate complex.
2. Water (H₂O): Water is also a monodentate ligand with only one donor atom (the oxygen), allowing it to form just one bond with the metal ion. Therefore, it cannot form a chelate complex.
3. NO₂: This can exist as nitrite, a monodentate ligand. In some cases, it can act as an ambidentate ligand with different binding modes, but it generally forms only one bond in common coordination complexes. It does not usually form chelate complexes.
4. Oxalate ion (C₂O₄^2-): The oxalate ion is a classic example of a bidentate ligand with two oxygen atoms available to coordinate with the metal ion, forming a ring-like chelate complex. This makes it well-suited for chelation.

Based on the analysis above, the correct answer is the Oxalate ion because it is a bidentate ligand capable of forming a chelate complex with metal ions.