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A sextuple bond is a type of covalent bond involving 12 bonding electrons and in which the bond order is 6. The only known molecules with true sextuple bonds are the diatomic dimolybdenum (Mo2) and ditungsten (W2), which exist in the gaseous phase. There is strong evidence to believe that no two elements in the periodic table can form a bond with greater order than 6.[1]

Dimolybdenum and ditungsten

Dimolybdenum (Mo2) can be observed in the gas phase at low temperatures (7K) by a laser evaporation technique using molybdenum sheet with, for instance, near infrared spectroscopy or UV spectroscopy.[2] Like dichromium, a singlet state is expected from dimolybdenum.[3] Higher bond order is reflected in shorter bond length of 194 pm.

Other molecules

Although diatomic Cr2 and U2 have formal structures with twelve-electron bonds, their effective bond orders derived from quantum chemistry calculations are less than 5 (which would be quintuple bonds).[1]


1. ^ a b Roos, Björn O.; Antonio C. Borin, and Laura Gagliardi (2007). "Reaching the Maximum Multiplicity of the Covalent Chemical Bond". Angewandte Chemie International Edition 46: 1469. doi:10.1002/anie.200603600.
2. ^ D. Kraus, M. Lorenz and V. E. Bondybey (2001). "On the dimers of the VIB group: a new NIR electronic state of Mo2". PhysChemComm 4: 44–48. doi:10.1039/b104063b.
3. ^ Gabriel Merino, Kelling J. Donald, Jason S. D’Acchioli, and Roald Hoffmann (2007). "The Many Ways To Have a Quintuple Bond". J. Am. Chem. Soc. 129 (49): 15295–15302. doi:10.1021/ja075454b.

* Bruce E. Bursten; F. Albert Cotton; Michael B. Hall (1980). "Dimolybdenum: nature of the sextuple bond". Journal of the American Chemical Society 102: 6348. doi:10.1021/ja00540a034.
* Borin, A (2008). "A theoretical study of the binding and electronic spectrum of the Mo2 molecule". Chemical Physics 343: 210. doi:10.1016/j.chemphys.2007.05.028.
* Marvin M. Goodgame; William A. Goddard I I I (1981). "The "sextuple" bond of chromium dimer". The Journal of Physical Chemistry 85: 215. doi:10.1021/j150603a001.
* Chisholm, Mh (Feb 2007). "Metal to metal multiple bonds in ordered assemblies." (Free full text). Proceedings of the National Academy of Sciences of the United States of America 104 (8): 2563–70. doi:10.1073/pnas.0610364104. PMID 17299047. PMC 1815223. http://www.pnas.org/cgi/pmidlookup?view=long&pmid=17299047.

See also

* Norman, Joe G., Jr.; Ryan, P. Barry (1980). "Metal-metal bond energies in diatomic molybdenum, octachloromolybdate (Mo2Cl84-), and molybdenum formate (Mo2(O2CH)4)". Journal of Computational Chemistry 1 (1): 59–63. doi:10.1002/jcc.540010107.
* Atha, P. M.; Hillier, I. H.; Guest, M. F. (1980). "Electron correlation and the nature of the sextuple bond in the dimolybdenum molecule". Chemical Physics Letters 75 (1): 84–86. doi:10.1016/0009-2614(80)80469-6.
* Wood, Carol; Doran, Mark; Hillier, Ian H.; Guest, Martyn F. (1980). "Theoretical study of the electronic structure of the transition metal dimers, discandium, dichromium, dimolybdenum, and dinickel". Faraday Symp. R. Soc.

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