Editing Ligand (section)

==Classification of ligands as L and X==
{{Main|Covalent bond classification method}}
Ligands are classified according to the number of electrons that they "donate" to the metal. L ligands are [[Lewis base]]s. L ligands are represented by [[amine]]s, [[phosphine]]s, [[carbon monoxide|CO]], N<sub>2</sub>, and [[alkene]]s.  Examples of L ligands extend to include [[dihydrogen]] and hydrocarbons that interact by [[agostic interaction]]s. X ligands are halides and [[pseudohalide]]s. X ligands typically are derived from anionic precursors such as chloride but includes ligands where salts of anion do not really exist such as hydride and alkyl.<ref>{{Cite journal |last=Rasmussen |first=Seth C. |date=2015-03-05 |title=The 18-electron rule and electron counting in transition metal compounds: theory and application |journal=ChemTexts |language=en |volume=1 |issue=1 |pages=10 |doi=10.1007/s40828-015-0010-4 |issn=2199-3793|doi-access=free }}</ref><ref>{{cite book|title=Organometallics|author=C. Elschenbroich|publisher=VCH|year=2006|isbn=  978-3-527-29390-2}}</ref>

Especially in the area of [[organometallic chemistry]], ligands are classified according to the "CBC Method" for Covalent Bond Classification, as popularized by [[Malcolm Green (chemist)|M. L. H. Green]] and "is based on the notion that there are three basic types [of ligands]... represented by the symbols L, X, and Z, which correspond respectively to 2-electron, 1-electron and 0-electron neutral ligands."<ref>{{Cite journal
| doi= 10.1016/0022-328X(95)00508-N
| issn= 0022-328X
| volume= 500
| issue= 1–2
| pages= 127–148
| last= Green
| first= M. L. H.
| title= A new approach to the formal classification of covalent compounds of the elements
| journal= Journal of Organometallic Chemistry
| date= 20 September 1995
}}</ref><ref>[http://www.columbia.edu/cu/chemistry/groups/parkin/mlxz.htm "mlxz plots – Columbia University"], Columbia University, New York.</ref>