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A '''bridging ligand''' is a [[ligand]] that connects two or more atoms, usually metal ions.<ref>{{GoldBookRef|title=bridging ligand|url=http://goldbook.iupac.org/B00741.html}}</ref> The ligand may be atomic or polyatomic. Virtually all complex organic compounds can serve as bridging ligands, so the term is usually restricted to small ligands such as pseudohalides or to ligands that are specifically designed to link two metals. |
A '''bridging ligand''' is a [[ligand]] that connects two or more atoms, usually metal ions.<ref>{{GoldBookRef|title=bridging ligand|url=http://goldbook.iupac.org/B00741.html}}</ref> The ligand may be atomic or polyatomic. Virtually all complex organic compounds can serve as bridging ligands, so the term is usually restricted to small ligands such as pseudohalides or to ligands that are specifically designed to link two metals. |
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In naming a complex wherein a single atom bridges two metals, the bridging ligand is preceded by the [[Greek language|Greek]] character 'mu', [[Mu|μ]],<ref>{{GoldBookRef|title=µ- (mu)|url=http://goldbook.iupac.org/M03659.html}}</ref> with a superscript number denoting the number of metals bound to the bridging ligand. μ<sup>2</sup> is often denoted simply as μ. When describing coordination complexes care should be taken not to confuse μ with η ('eta'), which relates to [[hapticity]]. |
In naming a complex wherein a single atom bridges two metals, the bridging ligand is preceded by the [[Greek language|Greek]] character 'mu', [[Mu|μ]],<ref>{{GoldBookRef|title=µ- (mu)|url=http://goldbook.iupac.org/M03659.html}}</ref> with a superscript number denoting the number of metals bound to the bridging ligand. μ<sup>2</sup> is often denoted simply as μ. When describing coordination complexes care should be taken not to confuse μ with η ('eta'), which relates to [[hapticity]]. Ligands that are not bridging, are called '''terminal ligands''' (see figure). |
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:[[File:Mu-Cl.png|thumb|left|180px|In this ruthenium complex, two [[chloride]] ligands are terminal and two are μ<sup>2</sup> bridging.]] |
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==Illustrative bridging ligands== |
==Illustrative bridging ligands== |
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<gallery> |
<gallery> |
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File: |
File:DiboraneSchema.png|[[Diborane]] has two bridging hydride ligands as well as four terminal hydride ligands. |
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File:Di-µ-hydroxo-bis(tetraaquairon(III).png|In [Fe(III)(OH<sub>2</sub>)<sub>4</sub>)<sub>2</sub>(µ-OH)<sub>2</sub>]<sup>4+</sup>, featuring two [[hydroxide]] ligands as μ<sup>2</sup> bridging ligands.<ref>Classifications of ligands. http://chimge.unil.ch/En/complexes/1cpx7.htm</ref> |
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File:Mu3 compound.png|In the cobalt cluster (Co(CO)<sub>3</sub>)<sub>3</sub>(μ<sup>3</sup>-(C-''t''Bu), the [[alkylidyne complex|(μ<sup>3</sup>-(C-''t''Bu)]] ligand is triply bridging. |
File:Mu3 compound.png|In the cobalt cluster (Co(CO)<sub>3</sub>)<sub>3</sub>(μ<sup>3</sup>-(C-''t''Bu), the [[alkylidyne complex|(μ<sup>3</sup>-(C-''t''Bu)]] ligand is triply bridging. |
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File:DiboraneSchema.png|[[Diborane]] has two bridging hydride ligands as well as four terminal hydrides. |
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File:Fe3(CO)12lessFe-Fe.png|In [[triiron dodecarbonyl]], two CO ligands are bridging and ten are terminal ligands. |
File:Fe3(CO)12lessFe-Fe.png|In [[triiron dodecarbonyl]], two CO ligands are bridging and ten are terminal ligands. |
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File:Au6C(PPh3)6.png||The complex [Au<sub>6</sub>C(PPh<sub>3</sub>)<sub>6</sub>]<sup>2+</sup> features μ<sup>6</sup>-[[carbido ligand]].]] |
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File:Aluminium-trifluoride-3D-polyhedra.png|In [[rhenium trioxide]], the oxide ligands are all μ<sup>2</sup>, these ligands "glue" together the metal centres. |
File:Aluminium-trifluoride-3D-polyhedra.png|In [[rhenium trioxide]], the oxide ligands are all μ<sup>2</sup>, these ligands "glue" together the metal centres. |
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File:Zirconium-tetrachloride-3D-balls-A.png|In the case of [[ZrCl4|ZrCl<sub>4</sub>]], there are both terminal and doubly bridging chloride ligands. |
File:Zirconium-tetrachloride-3D-balls-A.png|In the case of [[ZrCl4|ZrCl<sub>4</sub>]], there are both terminal and doubly bridging chloride ligands. |
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</gallery> |
</gallery> |
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Virtually all ligands are known to bridge, with the exception of amines and ammonia.<ref>{{cite journal | last = Werner | first = H. | year = 2004 | title = The Way into the Bridge: A New Bonding Mode of Tertiary Phosphanes, Arsanes, and Stibanes | journal = [[Angew. Chem. Int. Ed.]] | volume = 43 | pages = 938–954 | doi = 10.1002/anie.200300627 | pmid = 14966876 | issue = 8}}</ref> Common inorganic bridging ligands include |
Virtually all ligands are known to bridge, with the exception of amines and ammonia.<ref>{{cite journal | last = Werner | first = H. | year = 2004 | title = The Way into the Bridge: A New Bonding Mode of Tertiary Phosphanes, Arsanes, and Stibanes | journal = [[Angew. Chem. Int. Ed.]] | volume = 43 | pages = 938–954 | doi = 10.1002/anie.200300627 | pmid = 14966876 | issue = 8}}</ref> Common inorganic bridging ligands include |
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* [[hydroxide|OH<sup>−</sup>]], |
* [[hydroxide|OH<sup>−</sup>]], |
Revision as of 13:19, 9 June 2013
A bridging ligand is a ligand that connects two or more atoms, usually metal ions.[1] The ligand may be atomic or polyatomic. Virtually all complex organic compounds can serve as bridging ligands, so the term is usually restricted to small ligands such as pseudohalides or to ligands that are specifically designed to link two metals.
In naming a complex wherein a single atom bridges two metals, the bridging ligand is preceded by the Greek character 'mu', μ,[2] with a superscript number denoting the number of metals bound to the bridging ligand. μ2 is often denoted simply as μ. When describing coordination complexes care should be taken not to confuse μ with η ('eta'), which relates to hapticity. Ligands that are not bridging, are called terminal ligands (see figure).
Illustrative bridging ligands
-
Diborane has two bridging hydride ligands as well as four terminal hydride ligands.
-
In the cobalt cluster (Co(CO)3)3(μ3-(C-tBu), the (μ3-(C-tBu) ligand is triply bridging.
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In triiron dodecarbonyl, two CO ligands are bridging and ten are terminal ligands.
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The complex [Au6C(PPh3)6]2+ features μ6-carbido ligand.]]
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In rhenium trioxide, the oxide ligands are all μ2, these ligands "glue" together the metal centres.
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In the case of ZrCl4, there are both terminal and doubly bridging chloride ligands.
Virtually all ligands are known to bridge, with the exception of amines and ammonia.[3] Common inorganic bridging ligands include
Cyanide usually bridges via M-NC-M' linkages, unlike the other entries on this list.
Many organic ligands form strong bridges between metal centers. Many common examples include derivatives of the above inorganic ligands (R = alkyl, aryl):
- OR−,
- SR−,
- NR2−
- NR2− (imido)
- P3− (phosphido)
- PR2− (phosphido, note the ambiguity with the preceding entry)
- PR2− (phosphinidino)
Polyfunctional ligands
Polyfunctional ligands can attach to metals in many ways and thus can bridge metals in diverse ways, including sharing of one atom or using several atoms. Examples of such polyatomic ligands are the oxoanions CO32− and the related Carboxylate, PO43−, and the polyoxometallates. Several organophosphorus ligands have been developed that bridge pairs of metals, a well-known example being Ph2PCH2PPh2.
See also
References
- ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "bridging ligand". doi:10.1351/goldbook.B00741
- ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "µ- (mu)". doi:10.1351/goldbook.B00741
- ^ Werner, H. (2004). "The Way into the Bridge: A New Bonding Mode of Tertiary Phosphanes, Arsanes, and Stibanes". Angew. Chem. Int. Ed. 43 (8): 938–954. doi:10.1002/anie.200300627. PMID 14966876.