A quintuple bond in chemistry is an unusual type of chemical bond first observed in 2005 in a chromium dimer in an organometallic compound. Single bonds, double bonds and triple bonds are commonplace in chemistry. Quadruple bonds are rare but can be found in some organometallic compounds with bridging pi-donor ligands and in some inorganic salts such as Mo₂Cl₈ and [Re₂Cl₈]^2- which also have pi donor species as ligands.² The quintuple bond has a total of 10 electrons participating in bonding between the two metal centers, and can be described as σ²π⁴δ⁴. The bonding character of the metal-metal interactions are typically facilitated by polydentate pi-donor ligands which chelate both atoms and reduce the intermolecular distances. For example, the chromium dimer is stabilized by two bulky 2,6-[(2,6-diisopropyl)phenyl]phenyl groups and is stable up to 200 °C ^{[1] [2]}. Theoretical description of the Chromium-Chromium quintuple bond was also recently carried out, using multireference ab-initio and DFT methods ^[3]. Also in 2005 a quintuple bond was postulated to exist in the hypothetical uranium molecule U₂ based on computational chemistry ^{[4] [5]}. Diuranium compounds are rare but do exist such as the U₂Cl₈^2- anion. This article or section includes a list of works cited or a list of external links, but its sources remain unclear because it lacks in-text citations. ... A chemical bond is the physical process responsible for the attractive interactions between atoms and molecules, and that which confers stability to diatomic and polyatomic chemical compounds. ... 2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ... General Name, Symbol, Number chromium, Cr, 24 Chemical series transition metals Group, Period, Block 6, 4, d Appearance silvery metallic Atomic mass 51. ... Organometallic have classically been compounds having bonds between one or more metal atoms and one or more carbon atoms of an organyl group. ... Covalently bonded hydrogen and carbon in a molecule of methane. ... Covalent bonding is a form of chemical bonding characterized by the sharing of one or more pairs of electrons between atoms, in order to produce a mutual attraction, which holds the resultant molecule together. ... Covalent bonding is a form of chemical bonding characterized by the sharing of one or more pairs of electrons between atoms, in order to produce a mutual attraction, which holds the resultant molecule together. ... Covalently bonded hydrogen and carbon in a molecule of methane. ... The degree Celsius (°C) is a unit of temperature named after the Swedish astronomer Anders Celsius (1701–1744), who first proposed a similar system in 1742. ... General Name, Symbol, Number uranium, U, 92 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery gray metallic; corrodes to a spalling black oxide coat in air Atomic mass 238. ... In science, a molecule is a group of atoms in a definite arrangement held together by chemical bonds. ... Computational chemistry is a branch of chemistry that uses the results of theoretical chemistry incorporated into efficient computer programs to calculate the structures and properties of molecules and solids, applying these programs to real chemical problems. ...

References

1. ^  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 Article
2. ^  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 Support info
3. ^  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 Article
4. ^  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 Abstract
5. ^  New look for chemical bonds Belle Dumé 23 February 2005 PhysicsWeb Article