Topology-Based Approach to Predict Relative Stabilities of Charged and Functionalized Fullerenes

Abstract

Understanding the relationship between structure and stability is one of the fundamental aspects of fullerene chemistry, as the number of possible cage isomers is very large and complexity increases by orders of magnitude when chemical groups are attached to the fullerene cage. The well-established stability rules valid for neutral fullerenes do not apply to many charged or functionalized fullerenes. Here we present the theory, implementation, and applications of two simple topology-based models that allow one to predict the relative stability of charged and functionalized fullerenes without the need for quantum chemistry calculations: (i) the charge stabilization index (CSI) model, based on the concepts of cage connectivity and frontier π orbitals, which offers a general framework for the relative stability of both positively and negatively charged fullerenes, as well as endohedral metallofullerenes, and (ii) the exohedral fullerene stabilization index (XSI) model, which incorporates all key factors governing the stability of exohedral fullerenes, namely, π delocalization, σ strain, and steric hindrance between addends. Based exclusively on topological information, both models are powerful prescreening tools for predicting the most stable structures of a large number of charged and functionalized fullerenes. For easy use by fullerene chemists, both models have been implemented in the FullFun (for Fullerene Functionalization) software package, whose effectiveness and efficiency are demonstrated by some illustrative examples.

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.…”

Exploring Reactivity and Regioselectivity of Dimerization of Paramagnetic Endohedral Metallofullerenes

“…Calculations using the latter method were carried out by the ORCA program. 53,54 We used the FullFun software 27,28,55 to construct the initial geometries of fullerene cages, with atoms canonically labeled following the protocol described in ref 28 based on a breadth-first search algorithm. 56 We performed geometry optimizations without any symmetry constraint and computed harmonic vibrational frequencies for verification of local minima on the potential energy surface.…”