Question

Define polydentate ligand. Give an example.

Hint:

A polydentate ligand has more than one donor atom bound to the same metal ion, for example EDTA.

Answer 1

Step 1: Recall what a ligand does:
A ligand is an ion or molecule that donates a lone pair of electrons to the central metal atom or ion. The atom that donates the pair is called the donor atom.
Ligands are grouped by the number of donor atoms they use to bind the metal.

Step 2: Define the polydentate ligand:
A polydentate ligand is a ligand that has more than one donor atom.
It binds to the central metal ion through two or more donor atoms at the same time.
Such ligands usually form ring structures with the metal, called chelate rings.

Step 3: Give an example:
EDTA, that is ethylenediaminetetraacetate ion \( \mathrm{(EDTA)^{4-}} \), is a polydentate ligand.
It has six donor atoms, two nitrogen atoms and four oxygen atoms. So it is hexadentate.
Ethane-1,2-diamine (en) with two donor nitrogen atoms is a bidentate ligand and is also a common example.

Final Answer:
A ligand that binds the central metal through more than one donor atom is a polydentate ligand. Example: EDTA.
\[ \boxed{\text{Polydentate ligand: more than one donor atom. Example: EDTA}} \]