Relative Stability of Empty Exohedral Fullerenes: π Delocalization versus Strain and Steric Hindrance

Abstract

Predicting and understanding the relative stability of exohedral fullerenes is an important aspect of fullerene chemistry, since the experimentally formed structures do not generally follow the rules that govern addition reactions or the making of pristine fullerenes. First-principles theoretical calculations are of limited applicability due to the large number of possible isomeric forms, for example, more than 50 billion for CX. Here we propose a simple model, exclusively based on topological arguments, that allows one to predict the relative stability of exohedral fullerenes without the need for electronic structure calculations or geometry optimizations. The model incorporates the effects of π delocalization, cage strain, and steric hindrance. We show that the subtle interplay between these three factors is responsible for (i) the formation of non-IPR (isolated pentagon rule) exohedral fullerenes in contrast with their pristine fullerene counterparts, (ii) the appearance of more pentagon-pentagon adjacencies than predicted by the PAPR (pentagon-adjacency penalty rule), (iii) the changes in regioisomer stability due to the chemical nature of the addends, and (iv) the variations in fullerene cage stability with the progressive addition of chemical species.

Synthesis of a magnetic π-extended carbon nanosolenoid with Riemann surfaces

“…Thus, the design and synthesis of curved large π-extended graphene-based nanomaterials have attracted great research interest in the quest to develop carbon nanostructures with distinctive geometric shapes and optoelectronic properties. For example, a series of curved carbon molecules have been successfully synthesized, in which saddle-shaped geometries formed due to the presence of five-, seven-, or eight-membered-ring defects 28 , 30 – 37 or steric hindrance 38 , 39 . Some of these curved nanographenes have demonstrated interesting physical properties in organic field-effect transistors (OFET) 31 , 32 , 36 , near-infrared absorption and fluorescence 40 , 41 , two-photon absorption 28 , 35 , 37 , electronic circular dichroism (ECD) 28 , 35 , and circularly polarized luminescence (CPL) 42 , 43 .…”

Probing the structure of giant fullerenes by high resolution trapped ion mobility spectrometry

“…In order to confirm or rule out the presence of specific fullerene isomers in the essentially fragmentation free ion beams resulting from the fullerene mix (and thus to check for their presence in the soot extracts themselves), experimental CCS values were compared with computationally determined cross sections. The corresponding starting geometries (for neutral fullerenes) were obtained as xyz-files with the FULLFUN [42][43][44] software. Beginning with these neutral starting structures, all (di)anion and cation geometries were fully optimized, i.e.…”

Desorption of Fullerene Dimers upon Heating Non-IPR Fullerene Films on HOPG

“…To help gauge the relevance of potential coalescence processes, we have also calculated possible closed-shell fullerene products in the C 68 dimerization process at the same level of DFT theory as used for dumbbells. Figure shows the structures and binding energies (relative to two isolated C 68 cages) of two stable isomers chosen by the Fullfun program package: − a “nanotubelet” and a “spheroidal” cage each with isolated pentagon rings. The corresponding energies indicate that more than 25 eV of binding energy can be released once the necessary activation energy for coalescence is surmounted.…”

“…The geometries of the non-IPR-monomers, the C 50 ( D 5 h ), ,, and the C 68 ( C 2 ) , have been adopted from theoretical investigations from which they resulted as the most stable. Structures of C 136 as a stability limit for completely fused C 68 dimers have been generated using the FullFun package, − one of which was expected to be the lowest isomer. The manually generated starting geometries of all C 50 and C 68 monomers and dimers were preoptimized with the BP86 functional , and the def2-SVP basis in RI approximation with the Grimme-D3 correction in order to account for dispersion interactions between the cages.…”