Polydentate Ligand
A ligand that binds to a single metal centre through three or more donor atoms.
Unit
Dimensionless
In depth
Also called multidentate, these ligands wrap around the metal and form several chelate rings at once, producing exceptionally stable complexes. A polydentate ligand that encircles the metal entirely, such as a macrocycle or cryptand, binds even more tightly.
Examples in the real world
EDTA using four oxygens and two nitrogens; the porphyrin ring in haem; the crown ethers binding alkali metals.