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Unwilling U-U bonding in U2@C80: cage-driven metal-metal bonds in di-uranium fullerenes

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Year of publication 2015
Type Article in Periodical
Magazine / Source Physical Chemistry Chemical Physics
MU Faculty or unit

Faculty of Science

Web DOI: 10.1039/C5CP04280A
Field Physical chemistry and theoretical chemistry
Keywords fullerene; uranium; bonding; QTAIM
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Description Endohedral actinide fullerenes are rare and a little is known about their molecular properties. Here we characterize U2@C80 system, which was recently detected experimentally by means of mass spectrometry (Akiyama et al., JACS 2001, 123, 181). Theoretical calculations predict a stable endohedral system, 7U2@C80 derived from the C80:7 IPR fullerene cage, with six unpaired electrons. Bonding analysis reveals a double ferromagnetic (one-electron-two-center) U-U bond at r(U-U) distance of 3.9 A. This bonding is realized mainly via U(5f) orbitals. The U-U interaction inside the cage is estimated to be about minus 18 kcal/mol. The U-U bonding is further studied along the U2@Cn (n = 60, 70, 80, 84, 90) series and the U-U bonds are also identified in U2@C70 and U2@C84 systems at r(U-U) ~4 A. It is found that the character of U-U bonding depends on the U-U distance, which is dictated by the cage type. A concept of unwilling metal-metal bonding is suggested: Uranium atoms are strongly bound to the cage and carry a positive charge. Pushing the U(5f) electron density into U-U bonding region reduces electrostatic repulsion between enclosed atoms, thus forcing U-U bonds.
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