Which of the following is a bidentate ligand?

Solution

Chemistry ma’am · 3 steps

Count how many atoms in the ligand can each hand a lone pair to the metal at the same time.

1. What denticity means. Denticity is the number of donor atoms through which one ligand binds the metal. A bidentate ligand bonds through two donor atoms at once.

   Ligand	Donor atoms that bind	Denticity
   NH₃	one N	monodentate
   Cl⁻	one Cl	monodentate
   H₂O	one O	monodentate
   en, H₂N-CH₂-CH₂-NH₂	two N, one at each end	bidentate

2. Why en works. The two -NH₂ groups in en are joined by a flexible -CH₂-CH₂⁻ chain. Both N atoms can reach the same metal ion and close a stable five-membered ring, so en is a chelating ligand.
3. So. Only ethylenediamine bonds through two donor atoms, so the answer is (d).

The idea to keep. Denticity counts donor atoms that actually bond to the metal together, not lone pairs. Two donor atoms joined by a short chain, like en or oxalate, give a bidentate chelate.

Answer from the NTA final answer key. Solution by PrepWiser.