Robust metal‐pentagon interactions in the Th‐based endohedral metallofullerenes revealed by DFT calculations

Abstract

Endohedral metallofullerenes (EMFs) all feature obvious charge transfer from the metallic core to the carbon shell with the donated electrons largely accepted by the cage pentagons. In this work, a series of Th@C2n (2n = 64‐88) were thoroughly investigated by means of density functional theory calculations. Interestingly, we found that the tetravalent thorium atom mainly coordinates to three pentagonal rings with the metal–pentagon interactions independent on the distribution and distance among these pentagons. This coordination pattern is not only in sharp contrast to that of common organometallic complexes, where four pentagons are indispensable for stabilizing Th(IV), but also different from that of Ti‐containing fullerenes, whose valence state highly depends on the pentagon distribution. The specificity of Th‐based EMFs was rationalized by the synergetic effect of small metal ion size, low electronegativity, strong metal‐cage electrostatic attractions and effective orbital overlap between the metal and cage orbitals. Our work highlights the role of cage pentagons in the Th‐cage interactions, and points out the fundamental difference between EMFs and common organometallic complexes.

Crystallographic Characterization of U@C2n (2n = 82–86): Insights about Metal–Cage Interactions for Mono-metallofullerenes

“…It is worth mentioning that for fullerenes with 86 carbon atoms, 18 out of the 19 IPR isomers have at least one sumanene pattern on their topologies, and 17 out of 18 do show the U atom interacting with the sumanene as their most favorable site. This agrees with previous studies for Th@C 2n systems, where sumanene and phenalene patterns show coordination with the encapsulated actinide metal, 47,54 with enhanced covalent and electrostatic interactions. Out of the 19 IPR isomers of U@C 86 , five possess a symmetry plane, and all of them have the most stable uranium site on the symmetry plane (see Figure S9).…”

“…In addition, the U ions in U@ C 2 (8)-C 84 , U@ C s (15)-C 84 , and U@ C 1 (12)-C 86 all reside in the center over a hexagon with the closest U–cage contacts within very narrow ranges of 2.28–2.40, 2.33–2.48, and 2.28–2.40 Å, respectively. Furthermore, all the closest hexagons are surrounded by three pentagons and three hexagons, forming unique sumanene-type structures, in excellent agreement with previous theoretical predictions for the Th@ C 2 n family, suggesting the unique metal–cage interactions between actinide elements and fullerene cages.…”

“…Other symmetric thorium and uranium EMFs have been studied computationally, and for all of them the metal was found to be located on the mirror plane. 4,34,36,47,54 ■ CONCLUSIONS In summary, four new U-based mono-metallofullerenes, U@ C s (6)-C 82 , U@C 2 (8)-C 84 , U@C s (15)-C 84 , and U@C 1 (12)-C 86 , have been successfully synthesized, isolated, and characterized by mass spectrometry, UV−vis−NIR absorption spectroscopy, cyclic voltammetry, and single-crystal X-ray diffractometry. Based on the crystallographic results, showing that the U ions are located on the symmetry planes of C s (6)-C 82 and C s (15)-C 84 , previously crystallographically characterized mono-metallofullerenes with 30 different kinds of pristine cages were reinvestigated.…”

“…Patterns such as phenalene, sumanene, or as -indacene (Scheme ) have been shown to be particularly stabilizing for uranium endohedral metallofullerenes and other metals, , both for cages with and without symmetry planes. These patterns have a local inherent symmetry, such as C 3 v for sumanene and phenalene or C 2 v for as -indacene, which usually share one of the symmetry planes of the whole cage.…”

Synthesis and characterization of carbene derivatives of Th@C3v(8)-C82 and U@C2v(9)-C82: exceptional chemical properties induced by strong actinide–carbon cage interaction

“…[26][27][28][29][30] In particular, a strong interaction involving both unique 4 electron metal-tocage transfer and the covalent interactions was found between the encapsulated actinide metal ions and the host fullerene cages. [30][31][32][33][34][35] Thus, we expect that the chemical reactivity of actinide EMFs could be different from those of lanthanide based EMFs and such studies will be of great importance for the future application of actinide EMFs. Herein, photochemical reactions of Th@C 3v (8)-C 82 and U@C 2v (9)-C 82 were performed in the presence of 2-adamantane-2,3 0 -[3H]-diazirine (AdN 2 , 1) to probe the chemical properties of actinide EMFs for the rst time.…”