Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Quantum chemical calculations show that the uranium molecule U2 has a quintuple bond


Covalent bonding is commonly described by Lewis's theory1, with an electron pair shared between two atoms constituting one full bond. Beginning with the valence bond description2 for the hydrogen molecule, quantum chemists have further explored the fundamental nature of the chemical bond for atoms throughout the periodic table, confirming that most molecules are indeed held together by one electron pair for each bond. But more complex binding may occur when large numbers of atomic orbitals can participate in bond formation. Such behaviour is common with transition metals. When involving heavy actinide elements, metal–metal bonds might prove particularly complicated. To date, evidence for actinide–actinide bonds is restricted to the matrix-isolation3 of uranium hydrides, including H2U–UH2, and the gas-phase detection4 and preliminary theoretical study5 of the uranium molecule, U2. Here we report quantum chemical calculations on U2, showing that, although the strength of the U2 bond is comparable to that of other multiple bonds between transition metals, the bonding pattern is unique. We find that the molecule contains three electron-pair bonds and four one-electron bonds (that is, 10 bonding electrons, corresponding to a quintuple bond), and two ferromagnetically coupled electrons localized on one U atom each—so all known covalent bonding types are contributing.

Your institute does not have access to this article

Relevant articles

Open Access articles citing this article.

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: The active molecular orbitals forming the chemical bond between two uranium atoms.


  1. Lewis, G. N. The atom and the molecule. J. Am. Chem. Soc. 38, 762–786 (1916)

    CAS  Article  Google Scholar 

  2. Heitler, W. & London, F. Wechselwirkung neutraler Atome und homöopolare Bindung nach der Quantenmechanik. Z. Phys. 44, 455–472 (1927)

    ADS  CAS  Article  Google Scholar 

  3. Souter, P. F., Kushto, G. P., Andrews, L. & Neurock, M. Experimental and theoretical evidence for the formation of several uranium hydride molecules. J. Am. Chem. Soc. 119, 1682–1687 (1997)

    CAS  Article  Google Scholar 

  4. Gorokhov, L. N., Emelyanov, A. M. & Khodeev, Y. S. Mass-spectroscopic investigation of stability of gaseous molecules of U2O2 and U2 . High Temp. 12, 1156–1158 (1974)

    Google Scholar 

  5. Pepper, M. & Bursten, B. E. Ab initio studies of the electronic structure of the diuranium molecule. J. Am. Chem. Soc. 112, 7803–7804 (1990)

    CAS  Article  Google Scholar 

  6. Cotton, F. A. & Harris, C. B. The crystal and molecular structure of dipotassium octachlorodirhenate(III) dihydrate, K2 [Re2Cl8]2H2O. Inorg. Chem. 4, 330–333 (1965)

    CAS  Article  Google Scholar 

  7. Cotton, F. A. & Walton, R. A. Multiple Bonds between Metal Atoms (Wiley & Sons, New York, 1982)

    Google Scholar 

  8. Roos, B. O. The ground state potential for the chromium dimer revisited. Collect. Czech. Chem. Commun. 68, 265–274 (2003)

    CAS  Article  Google Scholar 

  9. Roos, B. O. in Advances in Chemical Physics; Ab Initio Methods in Quantum Chemistry – II Ch. 69 (ed. Lawley, K. P.) 399–445 (Wiley & Sons, Chichester, 1987)

    Google Scholar 

  10. Andersson, K., Malmqvist, P.-Å., Roos, B. O., Sadlej, A. J. & Wolinski, K. J. Second-order perturbation theory with a CASSCF reference function. Phys. Chem. 94, 5483–5488 (1990)

    CAS  Article  Google Scholar 

  11. Pyykkö, P. Relativistic effects in structural chemistry. Chem. Rev. 88, 563–594 (1988)

    Article  Google Scholar 

  12. Karlström, G. et al. MOLCAS: a program package for computational chemistry. Comput. Mater. Sci. 28, 222–239 (2003)

    Article  Google Scholar 

  13. Gagliardi, L., Heaven, M. C., Wisborg Krogh, J. & Roos, B. O. The electronic spectrum of the UO2 molecule. J. Am. Chem. Soc. (in the press)

  14. Roos, B. O. & Malmqvist, P.-Å. Relativistic quantum chemistry–the multiconfigurational approach. Phys. Chem. Chem. Phys. 6, 2919–2927 (2004)

    CAS  Article  Google Scholar 

Download references


We thank P. Pyykkö and C. J. Cramer for comments on the manuscript, P.-Å. Malmqvist and B. E. Bursten for discussions, and V. Veryazov for graphical assistance. This work was partially supported by Ministero dell'Istruzione, dell'Università e della Ricerca (MIUR), the Swedish Research council (VR) and the Swedish Foundation for Strategic Research (SSF).

Author information

Authors and Affiliations


Corresponding author

Correspondence to Laura Gagliardi.

Ethics declarations

Competing interests

The authors declare that they have no competing financial interests.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Gagliardi, L., Roos, B. Quantum chemical calculations show that the uranium molecule U2 has a quintuple bond. Nature 433, 848–851 (2005).

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI:

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing