Chemistry: ligands: the “-dentate” concept

Tutoring chemistry, one encounters terms. The tutor mentions the idea of dentates with ligands.

As I mention in my post from Jan 23, 2022, a ligand is a molecule, or perhaps an ion, one or more of which surround a central species, perhaps a metal ion or atom, in a coordination compound. The ligand typically acts as a Lewis base, while the central species, a Lewis acid.

The “dentate” idea refers to how many connections a ligand makes with the central atom. Monodentate means one connection: ligands like water or ammonia, containing only one atom that can act as a Lewis base, would be monodentates. For instance, the hexaaquaaluminum ion is an aluminum ion surrounded by six water ligands. Each water molecule, however, only binds to the aluminum ion once.

There are also bidentate ligands. A bidentate ligand attaches to the central species from two locations. Oxalate ion is bidentate ligand: dioxalatenickel(II) ion is a central nickel ion surrounded by two oxalate ions, each attached to the nickel ion from two locations. Therefore, the nickel ion has four attachments in total.

Polydentate ligands also exist: ligands that can each attach to the central atom from more than two locations. However, these tend to be more complicated molecules (or ions) that are not always discussed in high school chemistry.

Source:

chem.libretexts.org: Ligands

chem.libretexts.org: Metal Complexes

chem.libretexts.org: Nomenclature of Coordination Complexes

chem.purdue.edu: Structures with Bidentate Ligands