How can you determine if a complex is a polydentate?

[Adriana Rangel 1A]

I understand that a polydentate ligands are able to occupy more than 1 binding site simultaneously. How can you determine if a complex is a polydentate and if so, the type (bidentate, tridentate) and if it will form a chelate? I already memorized the ones mentioned in our book such as EDTA and theylenediamine.

[Suchita 2I]

To determine whether a ligand is a polydentate ligand count the number of atoms that have lone pairs and can thus act as donor atoms. For example, if there are two donor atoms, it is a bidentate ligand like ethylenediamine and the oxalate ion.
Since a chelating agent is a substance that can form two or more bonds with a central metal ion, all polydentate ligands can form chelates.

[Peter Dis1G]

So does it mean we need to draw Lewis Structure to count the lone pairs first?

[404995677]

So polydentate ligands have more than one bonding site to the central atom?

[Adriana Rangel 1A]

yes ^

[AtreyiMitra2L]

You determine if its polydentate if there are multiple atoms that have lone pairs on them that can form a coordinate covalent bond. A rule of thumb is that whenever you have Nitrogens, you are sure that the molecule is polydentate. Because there are two nitrogens as there is in ethylenediamine (en) (NH2CH2CH2NH2), the molecule is bidentate. Because there are 3 Nitrogens in diethylenetriamine (diet) (NH2CH2CH2NH2CH2CH2NH2), the molecule is polydentate. With O, it is more tricky. In oxalate (C2O4 2-), there are 4 atoms with a Lone pair. But the metal ion can not bind to all of them at once, only 2 at one side. Therefore, it is bidentate.