Ligand

This article is about ligands in inorganic chemistry. For ligands in biochemistry, see Ligand (biochemistry). For other uses, see Ligand (disambiguation).

Cobalt complex HCo(CO)4 with five ligands

In coordination chemistry, a ligand[a] is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electron pairs, often through Lewis bases.[1] The nature of metal–ligand bonding can range from covalent to ionic. Furthermore, the metal–ligand bond order can range from one to three. Ligands are viewed as Lewis bases, although rare cases are known to involve Lewis acidic "ligands".[2][3]

Metals and metalloids are bound to ligands in almost all circumstances, although gaseous "naked" metal ions can be generated in a high vacuum. Ligands in a complex dictate the reactivity of the central atom, including ligand substitution rates, the reactivity of the ligands themselves, and redox. Ligand selection requires critical consideration in many practical areas, including bioinorganic and medicinal chemistry, homogeneous catalysis, and environmental chemistry.

Ligands are classified in many ways, including: charge, size (bulk), the identity of the coordinating atom(s), and the number of electrons donated to the metal (denticity or hapticity). The size of a ligand is indicated by its cone angle.


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  1. ^ Burdge, J., & Overby, J. (2020). Chemistry – Atoms first (4th ed.). New York: McGraw Hill. ISBN 978-1260571349
  2. ^ Cotton, Frank Albert; Geoffrey Wilkinson; Carlos A. Murillo (1999). Advanced Inorganic Chemistry. Wiley-Interscience. p. 1355. ISBN 978-0471199571.
  3. ^ Miessler, Gary L.; Paul J. Fischer; Donald Arthur Tarr (2013). Inorganic Chemistry. Prentice Hall. p. 696. ISBN 978-0321811059.