Question

Which of the following ligands has two donor atoms?

• A. \( Cl^- \)
• B. \( I^- \)
• C. Oxalate (\( C_2O_4^{2-} \))
• D. \( H_2O \)

Hint:

Bidentate ligands form more stable complexes than monodentate ligands due to the chelate effect.

Answer 1

The Correct Option is C

Oxalate (\( C_2O_4^{2-} \)) is a bidentate ligand, meaning it has two donor atoms that can simultaneously coordinate with a metal ion. These donor atoms are the oxygen atoms in the carboxylate groups (-COO). 

Structure: \[ \text{[O-C=O]} - \text{[O-C=O]}. \] 

Explanation: \( Cl^- \) and \( I^- \) are monodentate ligands with one donor atom. \( H_2O \) is also a monodentate ligand with a single oxygen atom as the donor. 

Applications: Oxalate is commonly found in complexes such as potassium ferrioxalate (\( K_3[Fe(C_2O_4)_3] \)).