Endohedral chemical shifts in higher fullerenes with 72-86 carbon atoms

Abstract

For all isolated pentagon isomers of the fullerenes C 60 ±C 86 with nonzero HOMO±LUMO gap and for one nonclassical C 72 isomer (C 2v ), endohedral chemical shifts have been computed at the GIAO-SCF/ 3-21G level using B3LYP/6-31G* optimized structures. The experimental 3 He NMR signals are reproduced reasonably well in cases where assignments are unambiguous (e.g. C 60 , C 70 and C 76 ). On the basis of the calculated thermodynamic stability order and the comparison between the computed and experimental 3 He chemical shifts, the assignments of the observed 3 He NMR spectra are discussed for all higher fullerenes, and new assignments are proposed for one C 82 and one C 86 isomer (C 82 :3 and C 86 :17). The calculated helium chemical shifts also suggest the reassignment of the d( 3 He) resonances of two C 78 isomers.

13C NMR fingerprint characterizes long time-scale structure of Sc3N@C80 endohedral fullerene

“…The low-energy isomer C 80 : 2 has been synthesized and characterized by the 13 C NMR technique 5 and its structural assignment was confirmed by simulation of the 13 C NMR fingerprint 5 and endohedral 3 He chemical shift. 6 As Sc 3 N has at most D 3h symmetry, the two-signal highsymmetry 13 C NMR pattern must be the time average of a dynamically changing lower symmetry structure due to the long time-scale of NMR measurements 1 . Later, Sc 3 N@C 80 was reported by other groups.…”

From Rare Gas Atoms to Fullerenes: Spherical Aromaticity Studied From the Point of View of Atomic Structure Theory

“…The 2(N1) 2 rule has been investigated in detail for several fullerenes and heterofullerenes in terms of magnetic properties of these systems, [14,15,16] and the spherical aromaticity concept applied to fullerenes has recently been reviewed in reference [17]. It has also been suggested to extend the spherical electron-counting concept to s-bonded systems like clusters of hydrogen atoms.…”

Structure and Electronic Properties of Fullerenes C52q+: Is C522+ an Exception to the Pentagon Adjacency Penalty Rule?

“…Many of these studies have focused on the understanding of the main factors that govern the stability of fullerenes. [3,4] The stability of fullerenes has been extensively studied from the experimental point of view; [5] in particular, fragmentation experiments have proved the existence of the so-called magic-number fullerenes, [6] that is, fullerenes with a certain size that present a greater stability than their closer neighbours, for instance C 50 , C 60 and C 70 .…”

“…[7] This second rule is know as the pentagon adjacency penalty rule, PAPR. [8] Fullerenes with fused pentagonal rings, such as C 50 Cl 10 and the chlorine derivatives of C 56 and C 54 , have been isolated very recently. [9,10] As indicated above, all these fullerenes necessarily present adjacent pentagons in their structure.…”

“…These shells are completely filled when the number of p electrons is equal to 2(l + 1) 2 and, in these cases, the fullerenes present spherical aromaticity. [49,50] The concept of spherical aromaticity and its consequences for the reactivity of fullerenes was reviewed recently. [48,51] In the case of C 52 2 + , the number of p electrons (50) corresponds to a situation in which the g shell (l = 4) is filled.…”