Editing Ligand (section)

==Ligand motifs==
{{More citations needed section|date=January 2021}}

===Trans-spanning ligands===
{{Main|Trans-spanning ligand}}

Trans-spanning ligands are bidentate ligands that can span coordination positions on opposite sides of a coordination complex.<ref>von Zelewsky, A. "Stereochemistry of Coordination Compounds" John Wiley: Chichester, 1995. {{ISBN|047195599X}}.</ref>

===Ambidentate ligand===
{{Main|Linkage isomerism}}

In contrast to polydentate ligands, ambidentate ligands can attach to the central atom in either one of two (or more) places, but not both. An example is [[thiocyanate]], SCN<sup>−</sup>, which can attach at either the sulfur atom or the nitrogen atom. Such compounds give rise to [[linkage isomerism]].

Polydentate and ambidentate are therefore two different types of polyfunctional ligands (ligands with more than one [[functional group]]) which can bond to a metal center through different ligand atoms to form various isomers. Polydentate ligands can bond through one atom AND another (or several others) at the same time, whereas ambidentate ligands bond through one atom OR another. Proteins are complex examples of polyfunctional ligands, usually polydentate.

===Bridging ligand===
{{Main|Bridging ligand}}

A bridging ligand links two or more metal centers. Virtually all inorganic solids with simple formulas are [[coordination polymer]]s, consisting of metal ion centres linked by bridging ligands. This group of materials includes all anhydrous binary metal ion halides and pseudohalides. Bridging ligands also persist in solution. Polyatomic ligands such as [[carbonate]] are ambidentate and thus are found to often bind to two or three metals simultaneously. Atoms that bridge metals are sometimes indicated with the prefix "[[mu (letter)|''μ'']]". Most inorganic solids are polymers by virtue of the presence of multiple bridging ligands. Bridging ligands, capable of coordinating multiple metal ions, have been attracting considerable interest because of their potential use as building blocks for the fabrication of functional multimetallic assemblies.<ref>Sauvage,
J.-P.; Collin, J.-P.; Chambron, J.-C.; Guillerez, S.; Coudret, C.; Balzani, V.; Barigelletti, F.; De Cola, L.; Flamigni, L. Chem. ReV. 1994, 94, 993-1019</ref>

===Binucleating ligand===
{{Main|Binucleating ligand}}

Binucleating ligands bind two metal ions.<ref>Gavrilova, A. L.; Bosnich, B., "Principles of Mononucleating and Binucleating Ligand Design", Chem. Rev. 2004, volume 104, 349–383. {{doi|10.1021/cr020604g}}</ref> Usually binucleating ligands feature bridging ligands, such as phenoxide, pyrazolate, or pyrazine, as well as other donor groups that bind to only one of the two metal ions.

===Metal–ligand multiple bond===
{{Main|Metal–ligand multiple bond}}

Some ligands can bond to a metal center through the same atom but with a different number of [[lone pair]]s. The [[bond order]] of the metal ligand bond can be in part distinguished through the metal ligand [[bond angle]] (M−X−R). This bond angle is often referred to as being linear or bent with further discussion concerning the degree to which the angle is bent. For example, an imido ligand in the ionic form has three lone pairs. One lone pair is used as a sigma X donor, the other two lone pairs are available as L-type pi donors. If both lone pairs are used in pi bonds then the M−N−R geometry is linear. However, if one or both these lone pairs is nonbonding then the M−N−R bond is bent and the extent of the bend speaks to how much pi bonding there may be. ''η''<sup>1</sup>-Nitric oxide can coordinate to a metal center in linear or bent manner.

===Spectator ligand===
{{Main|Spectator ligand}}

A spectator ligand is a tightly coordinating polydentate ligand that does not participate in chemical reactions but removes active sites on a metal. Spectator ligands influence the reactivity of the metal center to which they are bound.

===Bulky ligands===
{{Main|Ligand cone angle}}

Bulky ligands are used to control the steric properties of a metal center. They are used for many reasons, both practical and academic. On the practical side, they influence the selectivity of metal catalysts, e.g., in [[hydroformylation]]. Of academic interest, bulky ligands stabilize unusual coordination sites, e.g., reactive coligands or low coordination numbers. Often bulky ligands are employed to simulate the steric protection afforded by proteins to metal-containing active sites. Of course excessive steric bulk can prevent the coordination of certain ligands.
[[File:1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (aka IMes).png|thumb|left|220px|The [[N-heterocyclic carbene|''N''-heterocyclic carbene]] ligand called [[IMes]] is a bulky ligand by virtue of the pair of mesityl groups.]]

===Chiral ligands===
{{Main|Chiral ligand}}

Chiral ligands are useful for inducing asymmetry within the coordination sphere. Often the ligand is employed as an optically pure group. In some cases, such as secondary amines, the asymmetry arises upon coordination. Chiral ligands are used in [[homogeneous catalysis]], such as [[asymmetric hydrogenation]].

===Hemilabile ligands===
{{Main|Hemilability}}
Hemilabile ligands contain at least two electronically different coordinating groups and form complexes where one of these is easily displaced from the metal center while the other remains firmly bound, a behaviour which has been found to increase the reactivity of catalysts when compared to the use of more traditional ligands.

===Non-innocent ligand===
{{Main|Non-innocent ligand}}

Non-innocent ligands bond with metals in such a manner that the distribution of electron density between the metal center and ligand is unclear. Describing the bonding of non-innocent ligands often involves writing multiple [[resonance (chemistry)|resonance form]]s that have partial contributions to the overall state.