View source for Quintuple bond

[[Image:Ar2Cr2PP.png|thumb|right|200px|The structure of [CrC<sub>6</sub>H<sub>3</sub>-2,6-(C<sub>6</sub>H<sub>4</sub>-2,6-(CHMe<sub>2</sub>)<sub>2</sub>)<sub>2</sub>]<sub>2</sub>]]
A '''quintuple bond''' in [[chemistry]] is an unusual type of [[chemical bond]] first reported in [[2005]] for a di[[chromium]] compound. [[Single bond]]s, [[double bond]]s, and [[triple bond]]s are commonplace in chemistry. [[Quadruple bond]]s are rarer but occur especially for Cr, Mo, W, and Re, e.g. [Mo<sub>2</sub>Cl<sub>8</sub>]<sup>4-</sup> and [Re<sub>2</sub>Cl<sub>8</sub>]<sup>2-</sup> .<sup>2</sup>  In a quintuple bond, 10 electrons participate in bonding between the two metal centers, allocated as σ<sup>2</sup>π<sup>4</sup>δ<sup>4</sup>. In some cases metal-metal bonding is facilitated by ligands that link the two metal centers and reduce the intermolecular distance.  In contrast, the chromium dimer with quintuple bonding is stabilized by bulky 2,6-[(2,6-diisopropyl)phenyl]phenyl [[ligand]]s or simply terphenyl ligand. The species is stable up to 200 [[°C]].<ref>''Quintuple Bond Makes Its Debut First stable molecule with fivefold metal-metal bonding is synthesized'' Steve Ritter [[Chemical & Engineering News]] September 26, '''2005''' Volume 83, Number 39 [http://pubs.acs.org/cen/news/83/i39/8339notw1.html Article]</ref><ref>''Synthesis of a Stable Compound with Fivefold Bonding Between Two Chromium(I) Centers'' Tailuan Nguyen, Andrew D. Sutton, Marcin Brynda, James C. Fettinger, Gary J. Long, and [[Philip Power|Philip P. Power]] Published online September 22 '''2005'''; 10.1126/[[Science (journal)|science]].1116789  [http://www.sciencemag.org/cgi/data/1116789/DC1/1 Support info]</ref> The chromium-chromium quintuple bond has been analyzed with multireference ab-initio and DFT methods <ref>''Quantum Chemical Study of the Quintuple Bond between Two Chromium Centers in [PhCrCrPh]: trans-Bent versus Linear Geometry'' Marcin Brynda, Laura Gagliardi, Per-Olof Widmark, Philip P. Power, Björn O. Roos Angewandte Chemie International Edition Published online May 3 '''2006'''[http://www3.interscience.wiley.com/cgi-bin/fulltext/112604898/PDFSTART Article]</ref>, which were also used to elucidate the role of the terphenyl ligand, in which the flanking aryls were shown to interact very weakly with the chromium atoms, causing only a small weakening of the quintuple bond.<ref>''Large Differences in Secondary Metal−Arene Interactions in the Transition-Metal Dimers ArMMAr (Ar = Terphenyl; M = Cr, Fe, or Co): Implications for Cr−Cr Quintuple Bonding'' Giovanni La Macchia,  Laura Gagliardi,  Philip P. Power,  and   Marcin Brynda [[J. Am. Chem. Soc.]] '''2008''' ASAP Article {{DOI|10.1021/ja0771890}}</ref> A 2007 theoretical study identified two global minima for quintuple bonded RMMR compounds: a trans-bent [[molecular geometry]] and surprisingly another trans-bent geometry with the R substituent in a bridging position.<ref>''The Many Ways To Have a Quintuple Bond'' Gabriel Merino, Kelling J. Donald, Jason S. D’Acchioli, and [[Roald Hoffmann]] [[J. Am. Chem. Soc.]] '''2007''' ASAP Article  {{DOI|10.1021/ja075454b}}</ref> 
Also in 2005, a quintuple bond was postulated to exist in the hypothetical [[uranium]] [[molecule]] U<sub>2</sub> based on [[computational chemistry]].<ref>''Quantum chemical calculations show that the uranium molecule U<sub>2</sub> has a quintuple bond'' Laura Gagliardi, Björn O. Roos [[Nature (journal)|Nature]] 433, 848-851 24 February '''2005''' [http://www.nature.com/nature/journal/v433/n7028/abs/nature03249.html Abstract]</ref><ref>''New look for chemical bonds'' Belle Dumé 23 February '''2005''' PhysicsWeb [http://physicsweb.org/articles/news/9/2/13/1#050213 Article]</ref> Diuranium compounds are rare but do exist such as the U<sub>2</sub>Cl<sub>8</sub><sup>2-</sup> anion.

In 2007 the shortest ever metal to metal bond (1.8028 [[Ångström|Å]]) was reported to exist also in a compound containing a quintuple chromium-chromium bond.<ref> ''The Shortest Metal-Metal Bond Yet: Molecular and Electronic Structure of a Dinuclear Chromium Diazadiene Complex'' Kevin A. Kreisel, Glenn P. A. Yap, Olga Dmitrenko, Clark R. Landis, and Klaus H. Theopold Web Release Date: 30-Oct-'''2007'''; (Communication) {{DOI|10.1021/ja076356t}}</ref>

== References ==
{{Wikinews|Delaware scientists create shortest ever metal to metal bond}}
{{reflist|2}}

== See also ==
[[Sextuple bond]]

{{chemical bonds}}

[[Category:Chemical bonding]]
[[Category:Chromium compounds]]

[[de:Fünffachbindung]]
[[ja:五重結合]]
[[zh:五重键]]