Tetradentate ligand

In chemistry, tetradentate ligands are ligands that bind four donor atoms to a central atom to form a coordination complex. This number of donor atoms that bind is called denticity and is a method of classifying ligands.

Tetradentate ligands are common in nature in the form of chlorophyll, which has a core ligand called chlorin, and heme, which has a core ligand called porphyrin. They are responsible for the colour observed in plants and humans. Phthalocyanine is an artificial macrocyclic tetradentate ligand that is used to make blue and green pigments.