Preparation of He@C60 and He2@C60 by an explosive method

Reactivity and Regioselectivity of Noble Gas Endohedral Fullerenes Ng@C60 and Ng2@C60 (Ng=He–Xe)

“…The effect of substituting He by Xe in Ng@C 60 is small, with energy differences of less than 0.1 kcal mol À1 according to our theoretical data. Experiments [19] also show small differences in reactivity, although slightly in favor of the He@C 60 over Xe@C 60 . In general, the computed reactivity differences are so small and below the average errors expected for these calculations that a clear trend cannot be derived, and one can only conclude that the reactivity of free C 60 is almost unchanged by encapsulation of a single noble gas atom.…”

“…[12,13] NMR studies on 3 He@C 60 and 3 He@C 70 indicate significant diamagnetic rings in C 60 and very large ones in C 70 . [14] Although Ng@C 60 (Ng = He-Xe) compounds have been theoretically studied in several works, [15,16] none of them analyzed their reactivity. Interestingly, endohedral fullerenes with a single noble gas atom were detected in deposits associated with the impact of a large bolide (asteroid or comet) with the Earth (i.e., the Sudbury Impact Crater).…”

“…Six years later, endohedral compounds with encapsulated noble gases were synthesized by collision of helium, neon, or argon atoms with C 60 + or of noble gas cations with neutral C 60 . [2] In 1993, Saunders and co-workers showed that, in fullerene preparation by the standard method (graphite arc in low-pressure helium), the endohedral compound He@C 60 was obtained for about one in a million free fullerene molecules. [3] Moreover, heating fullerenes to high temperatures under several atmospheres of 3 He or Ne produced the respective endohedral compounds.…”

“…The presence of a noble gas dimer inside the cage is expected to modify the exohedral reactivity of the C 60 cage with respect to that of free C 60 . To investigate the impact of encapsulated diatomic noble gas molecules on the chemical reactivity of C 60 , we analyzed the thermodynamics and the kinetics of [4+2] Diels-Alder cycloaddition of 1,3-cis-butadiene at all non-A C H T U N G T R E N N U N G equivalent bonds in free C 60 , Ng@C 60 , and Ng 2 @C 60 (Ng = He, Ne, Ar, Kr, and Xe). Our BP86/TZP calculations reveal that introduction of single noble gas atoms in Ng@C 60 and noble gas dimers He 2 and Ne 2 in Ng 2 @C 60 has almost no effect on the exohedral reactivity compared to free C 60 , in agreement with experimental results.…”

On the Problem of He–He Bond in the Endohedral Fullerene He2@C60

“…Another practical method for detecting such complexes is the rotational-vibrational spectroscopy, which allows some nonstandard peculiarities in the spectra to be revealed [63]. In 1997, Saunders et al experimentally observed He 2 @C 60 [64] (see also works [65,66]); and, later, Ng @C 60 with = 2 [67][68][69][70]. The researchers emphasized that endohedral fullerenes with clusters of three or more inert-gas atoms had not been revealed, although their existence had been predicted by computational methods.…”