Question

Ethylene diaminetetraacetate (EDTA) ion is

• A. Tridentate ligand with three “N” donor atoms
• B. Hexadentate ligand with four “O” and two “N” donor atoms
• C. Unidentate ligand
• D. Bidentate ligand with two “N” donor atoms

Answer 1

The Correct Option is B

Ethylene diaminetetraacetate (EDTA) ion is an important chelating agent widely used in coordination chemistry. To understand its characteristics as a ligand, let's examine its structure and binding capability:

EDTA is a polyamino carboxylic acid and the ion form is EDTA^4-. Its structure allows it to act as a chelating ligand, capable of binding to metal ions. Here is how EDTA acts as a ligand:

1. EDTA contains four carboxyl (-COO^-) groups and two amine (NH) groups. Each carboxyl group can donate an oxygen atom, and each amine group can donate a nitrogen atom to metal ions.

2. This characteristic enables EDTA to use six donor atoms in total: four oxygen atoms from the carboxyl groups and two nitrogen atoms from the amine groups.

Based on these characteristics, EDTA is classified as a hexadentate ligand because it can form up to six coordinate bonds with a single metal ion using its six donor atoms.

Option Analysis:

• Tridentate ligand with three “N” donor atoms: Incorrect, as EDTA has two nitrogen donor atoms, not three.

• Hexadentate ligand with four “O” and two “N” donor atoms: Correct, as explained, EDTA uses four oxygen and two nitrogen atoms, making it hexadentate.

• Unidentate ligand: Incorrect, as EDTA can form six bonds, not just one.

• Bidentate ligand with two “N” donor atoms: Incorrect, because although EDTA has two nitrogen atoms, it forms more than two bonds, totalizing six.

Therefore, the correct answer is: Hexadentate ligand with four “O” and two “N” donor atoms.