六重键

六重键（英语：Sextuple Bond），是指化学中，由6对价电子组成的共价键。

六重键的键级为6，含有六重键的化合物仅有双原子分子的 $\ce{Mo2}$ 和 $\ce{W2}$ ，而它们仅在非常低的温度下存在于气相。

尽管双原子的 $\ce{Cr2}$ 和 $\ce{U2}$ 也有名义上的6对价电子组成的键，但根据量子化学的计算，它们的有效键级小于5，可能是五重键。^[1]

有很强的证据显示，元素周期表中任何两个元素之间不可能形成键级超过六的化学键^[2]。

气相中的 $\ce{Mo2}$ 的观测必须在很低的温度（7K），使用激光蒸发技术，用近红外光谱或紫外光谱进行观测。^[3]

科学界期望可以于 $\ce{Mo2}$ 发现到与 $\ce{Cr2}$ 观察结果类似的一对双自由基^[4]。

更高的键级将会反映在更短的键长上，仅有1.94 Å。^{[来源请求]}

参见

钼（ $\ce{Mo}$ ）
钨（ $\ce{W}$ ）
铬（ $\ce{Cr}$ ）
铀（ $\ce{U}$ ）
价电子

参考文献

↑ Roos, Björn O.; Borin, Antonio C.; Gagliardi, Laura. Reaching the Maximum Multiplicity of the Covalent Chemical Bond. Angewandte Chemie. 2007-02-19, 119 (9): 1491–1494 [2018-01-30]. ISSN 1521-3757. doi:10.1002/ange.200603600 （英语）.
↑ Roos, Björn O.; Antonio C. Borin, and Laura Gagliardi. Reaching the Maximum Multiplicity of the Covalent Chemical Bond. Angewandte Chemie International Edition. 2007. doi:10.1002/anie.200603600.
↑ D. Kraus, M. Lorenz and V. E. Bondybey. On the dimers of the VIB group: a new NIR electronic state of Mo₂. PhysChemComm. 2001, 4: 44 – 48. doi:10.1039/b104063b.
↑ Gabriel Merino, Kelling J. Donald, Jason S. D’Acchioli, and Roald Hoffmann. The Many Ways To Have a Quintuple Bond. J. Am. Chem. Soc. 2007, 129 (49): 15295 –15302. doi:10.1021/ja075454b.

扩展阅读

Bruce E. Bursten; F. Albert Cotton; Michael B. Hall. Dimolybdenum: nature of the sextuple bond. Journal of the American Chemical Society. 1980, 102 (20): 6348. doi:10.1021/ja00540a034.
Borin, A; Gobbo, João Paulo; Roos, Björn O. A theoretical study of the binding and electronic spectrum of the Mo2 molecule. Chemical Physics. 2008, 343 (2–3): 210. doi:10.1016/j.chemphys.2007.05.028.
Marvin M. Goodgame; William A. Goddard I I I. The "sextuple" bond of chromium dimer. The Journal of Physical Chemistry. 1981, 85 (3): 215. doi:10.1021/j150603a001.
Chisholm, Mh. Metal to metal multiple bonds in ordered assemblies (Free full text). Proceedings of the National Academy of Sciences of the United States of America. Feb 2007, 104 (8): 2563–70 [2012-08-12]. PMC 1815223 . PMID 17299047. doi:10.1073/pnas.0610364104.
Norman, Joe G., Jr.; Ryan, P. Barry. Metal-metal bond energies in diatomic molybdenum, octachloromolybdate (Mo2Cl84-), and molybdenum formate (Mo2(O2CH)4). Journal of Computational Chemistry. 1980, 1 (1): 59–63. doi:10.1002/jcc.540010107.
Atha, P. M.; Hillier, I. H.; Guest, M. F. Electron correlation and the nature of the sextuple bond in the dimolybdenum molecule. Chemical Physics Letters. 1980, 75 (1): 84–86. doi:10.1016/0009-2614(80)80469-6.
Wood, Carol; Doran, Mark; Hillier, Ian H.; Guest, Martyn F. Theoretical study of the electronic structure of the transition metal dimers, discandium, dichromium, dimolybdenum, and dinickel. Faraday Symp. R. Soc. Chem. 1980, 14 (Diatomic Met. Met. Clusters): 159–169. doi:10.1039/fs9801400159.

[1] Roos, Björn O.; Borin, Antonio C.; Gagliardi, Laura. Reaching the Maximum Multiplicity of the Covalent Chemical Bond. Angewandte Chemie. 2007-02-19, 119 (9): 1491–1494 [2018-01-30]. ISSN 1521-3757. doi:10.1002/ange.200603600 （英语）.

[2] Roos, Björn O.; Antonio C. Borin, and Laura Gagliardi. Reaching the Maximum Multiplicity of the Covalent Chemical Bond. Angewandte Chemie International Edition. 2007. doi:10.1002/anie.200603600.

[3] D. Kraus, M. Lorenz and V. E. Bondybey. On the dimers of the VIB group: a new NIR electronic state of Mo₂. PhysChemComm. 2001, 4: 44 – 48. doi:10.1039/b104063b.

[4] Gabriel Merino, Kelling J. Donald, Jason S. D’Acchioli, and Roald Hoffmann. The Many Ways To Have a Quintuple Bond. J. Am. Chem. Soc. 2007, 129 (49): 15295 –15302. doi:10.1021/ja075454b.

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