Quintuple bond

A quintuple bond in chemistry is an unusual type of chemical bond first reported in 2005 for a dichromium compound. Single bonds, double bonds, and triple bonds are commonplace in chemistry. Quadruple bonds are rarer but occur especially for Cr, Mo, W, and Re, e.g. [Mo₂Cl₈] ⁴⁻ and [Re₂Cl₈] ²⁻ . In a quintuple bond, 10 electrons participate in bonding between the two metal centers, allocated as σ²π⁴δ⁴. 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 ligands or simply terphenyl ligand. The species is stable up to 200 °C. ["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] ] ["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 P. Power Published online September 22 2005; 10.1126/science.1116789 [http://www.sciencemag.org/cgi/data/1116789/DC1/1 Support info] ] The chromium-chromium quintuple bond has been analyzed with multireference ab-initio and DFT methods ["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] ] , 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. ["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] 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. ["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] Also in 2005, a quintuple bond was postulated to exist in the hypothetical uranium molecule U₂ based on computational chemistry. ["Quantum chemical calculations show that the uranium molecule U₂ has a quintuple bond" Laura Gagliardi, Björn O. Roos Nature 433, 848-851 24 February 2005 [http://www.nature.com/nature/journal/v433/n7028/abs/nature03249.html Abstract] ] ["New look for chemical bonds" Belle Dumé 23 February 2005 PhysicsWeb [http://physicsweb.org/articles/news/9/2/13/1#050213 Article] ] Diuranium compounds are rare but do exist such as the U₂Cl₈²⁻ anion.

In 2007 the shortest ever metal to metal bond (1.8028 Å) was reported to exist also in a compound containing a quintuple chromium-chromium bond. [ "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]

References

See also

*Sextuple bond