This number can be used to characterize the distortion from an idealized geometry or to gauge the degree of ring strain. In the example on the right, we can see that the tetrahedral metal center is distorted from the ideal 109.5 o angle. Also called a chelate . The examples shown above for bidentate ligands as well as the bite angle example above are additional examples of chelating ligands. The two metals centers do not need to have identical ligands or coordination number, but are usually found as symmetric dimers.
Homoleptic complexes contain only one kind of ligand.
Monodentate Monodentate ligands have only one point of attachment to the metal center and occupy only one coordination site. A bidentate ligand may act in a monodentate fashion if one end is not attached to the metal center, in which case it is called ambidentate . Polydentate Polydentate ligands have more than one point of attachment to the metal center and occupy more than one coordination site. By definition, bidentate ligands as well as ambidentate ligands are subsets of polydentate ligands. The salen ligand is versatile dianionic, tetradendate ligand that has been exploited by Eric Jacobsen and many others.