Classification of ligands

Organometallic compounds of the transition elements. Classification of ligands and theories of bonding 

Number of electrons Name of ligand class Examples of group 

3 -enyl f/ -allyl NO, various bidentate groups e.g. acac f/ -benzyl 

Two series of iso-electronic 18-electron complexes are the sandwich compounds 

Some ligands can bond in more than one way to transition elements, particularly those with more than one double bond or with extended 7r-systems. 

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An J, Totrov M, Abagyan R et al (2005) Pocketome via comprehensive identification and classification of ligand binding envelopes. Mol Cell Proteomics 4 752-761... 

Classification of Ligands According to Their Likelihood of Obeying the 18-Electron Role... 

The ability of Lewis acids to bind to transition metals as o-acceptor ligands was recognized early on and the common classification of ligands as L (two-electron donor) and X (one-electron donor) was extended to Z (two-electron acceptor). In the latter case, the metal behaves as a Lewis base and engages in dative M Z interactions. Figure 7 provides a simplified orbital diagram for the corresponding two-center, two-electron interaction. ... 

Basic Classification of Ligand-Gated Ion Channels, Their Inhibitors and Activators... 

StaUaert, W., Dom, J. F., van der Westhuizen, E., Audet, M., Bouvier, M. (2012). Impedance responses reveal beta(2)-adrenergic receptor signahng pluridimensionahty and allow classification of ligands with distinct signahng profiles. PLoS One, 7(1), e29420. http // dx. doi.org/10.1371 /joumal.pone.0029420. 

Their tendency to complex with type B metals is the opposite sequence. This led to a classification of ligands into type A ligands (e.g. F"), which tend to complex with type A metals, and type B ligands (e.g. I ), which tend to complex with type B metals. The classification was introduced by Ahrland in 1958. See also HSAB principle. 

Classification of Ligands as Dative or Covalent, Neutral or Anionic, Even- or Odd-Electron, L-Type or X-Type... 

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