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 considerbly more rare but can be found in organometalic compounds with particularly bulky ligands. The quintuple bond has a total of 10 electrons participating in bonding between the two metal centers, and can be described as σ²π⁴δ²δ*². The chromium dimer is stabilized by two bulky 2,6-^*phenyl groups and is stable up to 200 °C . Theoretical description of the Chromium-Chromium quintuple bond was also recently carried out, using multireference ab-initio and DFT methods . Also in 2005 a quintuple bond was postulated to exist in the hypothetical uranium molecule U₂ based on computational chemistry . Diuranium compounds are rare but do exist such as the U₂Cl₈^2- anion.

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 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
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

Chemical bonding