Enhancement in the Stability of 36-Atom Fullerene through Encapsulation of a Uranium Atom

Abstract

With an objective to rationalize the experimentally observed intense U@C 36 peak in the mass spectrum of U@C 2n metallofullerene, structural, stability, and spectroscopic aspects of the uranium doped C 36 fullerene have been studied in a unified and systematic way using density functional theory (DFT) and its time-dependent variant. Relativistic effects have been taken into account within the framework of zeroth-order regular approximation using scalar and spin− orbit-based approaches. Among all of the 15 possible classical isomers reported for the C 36 fullerene cage system, singlet D 2d and triplet D 6h structures are found to be isoenergetic and most stable. Encapsulation of uranium atom into various C 36 cages leads to 15 distinct isomers with considerable energy differences. It has also been shown that this encapsulation process results in significant gain in thermodynamic stability. The most stable U@C 36 isomer is found to be associated with C 6v symmetry and closed-shell electronic configuration, derived from the open-shell D 6h structure of C 36 . The next stable isomer is associated with C s symmetry and obtained from the corresponding singlet D 2d structure of the C 36 cage. Distinct changes have also been found in the calculated vibrational and UV−visible spectra of the U@C 36 cluster as compared to the corresponding bare C 36 cage. All of the calculated quantities reported here suggest that the stability of the U@C 36 cluster is high enough for possible formation of cluster-assembled material leading to synthesis of this metallofullerene experimentally.

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

“…[16][17][18][19] The experimental formation of U@C 28 was studied recently. [28][29][30][31] To the best of our knowledge, the experimentally observed U 2 @C 80 molecule 17 has not been studied yet, and is the main concern of the present work. Mainly the An@C 28 compounds were studied.…”

“…Most of the up-to-date experimentally reported actinide EMFs were only observed as signals in the time-of-flight mass spectra (TOF-MS), as for example U@C 2n (n = and some of the U 2 @C 2n (n = [25][26][27][28][29][30] systems. Despite the great developments in EMF science 1-13 little is known of actinide endohedral fullerenes and their properties.…”

Evaluation of bonding, electron affinity, and optical properties of M@C28 (M = Zr, Hf, Th, and U): Role of d‐ and f‐orbitals in endohedral fullerenes from relativistic DFT calculations

“…WWW.C-CHEM.ORG and uranium derivatives are calculated to exhibit singlet and triplet electronic ground states, respectively, in accord with previous studies. [25,29,31] The zirconium and hafnium derivatives have a singlet electronic ground state, with a sizable HOMO-LUMO gap of 2.20 and 2.21 eV (TZ2P/ZORA-PBE), respectively, similar to that of the thorium counterpart Th@C 28 (2.39 eV). The uranium derivative U@C 28 , with a 34-ve count, has a triplet ground state with the two unpaired electrons located in molecular orbitals having mainly C 28 character.…”

“…Most EMFs have external C 60 or larger fullerene cages to provide sufficient interior volume for the encapsulated species. However, smaller endohedral fullerenes have also been reported . Early experiments by Guo et al generated the monouranium and diuranium metallofullerenes U@C n ( n = 28, 36, 44, 58, 60, 66, 70, and 72) and U 2 @C n ( n = 50, 52, 58, and 60).…”

“…However, smaller endohedral fullerenes have also been reported. [3,[25][26][27] Early experiments by Guo et al [28] generated the monouranium and diuranium metallofullerenes U@C n (n 5 28, 36, 44, 58, 60, 66, 70, and 72) and U 2 @C n (n 5 50, 52, 58, and 60). The relatively small metallofullerene U@C 28 appears as a major product in FT-ICR mass spectrum.…”