Since diethylene triamine has three amine groups, having one lone pair on each amine group, it has total of 3 lone pairs. So, it will donate 3 lone pairs to metal. Therefore, it is tridentate ligand.
Tridentate ligand is the one which donates three lone pairs to metal atom.
Since diethylene triamine has three amine groups, having one lone pair on each amine group, it has total of 3 lone pairs. So, it will donate 3 lone pairs to metal. Therefore, it is tridentate ligand.
Tridentate ligand is the one which donates three lone pairs to metal atom.