Small Cage Uranofullerenes: 27 Years after Their First Observation

Abstract

The tetravalently stabilized fullerene cage of C28 is historically the most elusive small fullerene cage observed by employing the laser vaporization synthesis methodology. Its first observation reported by Smalley et al. in 1992 suggests that C28 is potentially the smallest and most stable fullerene ever observed. By using the Krätschmer−Huffman arc discharge synthesis method, we have recently succeeded in synthesizing a series of uranium‐endohedral fullerenes which differ from those reported by Smalley and co‐workers. Intrigued by this interesting mismatch, we tuned our experimental conditions to favor the formation and detection of these missing species. Experiments done using solvents of varying polarity allowed the observation of several empty and uranofullerenes. Extractions with pyridine and o‐DCB allowed for observation of small U@C2n (2n=28, 60, 66, 68, 70) by high resolution Fourier‐Transform Ion Cyclotron Resonance Mass Spectrometry (FT‐ICR MS). This is the first time that U@C28 is observed in soot produced by the Krätschmer‐Huffman arc‐discharge methodology. Carbon cage selection and spin density distribution on the endohedral metallofullerenes (EMFs) U@C60, U@C70, and U@C72 were studied by means of density functional theory (DFT) calculations. A plausible pathway for the formation of U@D3h‐C74 from U@D5h‐C70 through two C2 insertions and one Stone‐Wales rearrangement is proposed.

Highly oxidized U(vi) within the smallest fullerene: gas-phase synthesis and computational study of boron-doped U@C27B

“…the smaller the carbon cage the larger the formal transfer to get the M@C 2n stabilized. 12 Other gas-phase detections of uranofullerenes 13,14 and computational studies on the U-cage interaction in small cages 15,16 or U-U bond in U 2 @C 60 have been reported. 17 However, it was not until 2017 that the first actinidofullerene was synthesized by an arc-discharge method and fully characterized.…”

Are U–U Bonds Inside Fullerenes Really Unwilling Bonds?

“…In the early work of Smalley and co-workers, it was already shown that in addition to several small and medium-sized mono-uranium endofullerenes, 38,39 small diuranium endofullerenes, such as U 2 @C 58 and U 2 @C 52 , could also be detected by mass spectrometry. Without a strong metal−metal interaction, it is very difficult to understand that such dimetallic fullerenes can be formed and grow at the very high temperatures at which these compounds are synthesized.…”

“…In the early work of Smalley and co-workers, it was already shown that in addition to several small and medium-sized mono-uranium endofullerenes, , small diuranium endo-fullerenes, such as U 2 @C 58 and U 2 @C 52 , could also be detected by mass spectrometry. Without a strong metal–metal interaction, it is very difficult to understand that such dimetallic fullerenes can be formed and grow at the very high temperatures at which these compounds are synthesized. , In the present paper, we report Car–Parrinello MD simulations in combination with DFT and CASPT2 calculations to evaluate under which conditions, if any, the formation of covalent bonds between two U ions within fullerenes is possible.…”

Энергетический Спектр И Спектр Оптического Поглощения Фуллерена С-=sub=-28-=/Sub=- В Модели Хаббарда

“…Дальнейшие исследования показали, что фуллерен С 28 является нестабильной молекулой, которая стабилизируется при образовании эндофуллеренов M@С 28 с элементами Zr, W, Mo, Os, Ti, Th, U, Ce, которые способны принимать электронные конфигурации M 4+ [4]. Исследованию свойств фуллерена С 28 посвящено довольно много работ [5][6][7][8].…”

“…Из диаграммы Шлегеля, изображенной на рис. 1, видно, что фуллерен С 28 с группой симметрии T d содержит три неэквивалентных связи, которые обозначены через a, b и c; и три группы неэквивалентных атомов углерода: G 1 = {1, 3, 5, 9, 13, 17, 19, 20, 22, 23, 25, 26}, G 2 = {2, 4,6,8,10,12,14,16,18,21,24, 27}, G 3 = {7, 11, 15, 28}. Связь а связывает между собой два пентагона, связь b связывает пентагон и гексагон, а связь с связывает между собой два гек-сагона.…”