Capturing the Antiaromatic #6094C68 Carbon Cage in the Radio-Frequency Furnace

Strain Release of Fused Pentagons in Fullerene Cages by Chemical Functionalization

According to the isolated pentagon rule (IPR), for stable fullerenes, the 12 pentagons should be isolated from one another by hexagons, otherwise the fused pentagons will result in an increase in the local steric strain of the fullerene cage. However, the successful isolation of more than 100 endohedral and exohedral fullerenes containing fused pentagons over the past 20 years has shown that strain release of fused pentagons in fullerene cages is feasible. Herein, we present a general overview on fused-pentagon-containing (i.e. non-IPR) fullerenes through an exhaustive review of all the types of fused-pentagon-containing fullerenes reported to date. We clarify how the strain of fused pentagons can be released in different manners, and provide an in-depth understanding of the role of fused pentagons in the stability, electronic properties, and chemical reactivity of fullerene cages.

Salvaging Reactive Fullerenes from Soot by Exohedral Derivatization

The awesome allotropy of carbon yields innumerable topologically possible cage structures of molecular carbon. This field is also related to endohedral metallofullerenes constructed by metal-atom encapsulation. Stable and soluble empty fullerenes and endohedral metallofullerenes are available in pure form in macroscopic amounts from carbon arc production or other physical processes followed by extraction and subsequent chromatographic separation. However, many other unidentified fullerene species, which must be reactive and insoluble in their pristine forms, remain in soot. These "missing" species must have extremely small HOMO-LUMO gaps and may have unconventional cage structures. Recent progress in this field has demonstrated that reactive fullerenes can be salvaged by exohedral derivatization, which can stabilize the reactive carbon cages. This concept provides a means of preparing macroscopic amounts of unconventional fullerenes as their derivatives.

On the regioselectivity of the Diels-Alder cycloaddition to C60 in high spin states

Controlling the regioselectivity in the exohedral functionalization of fullerenes and endohedral metallofullerenes is essential to produce specific desired fullerene derivatives. In this work, using density functional theory (DFT) calculations, we show that the regioselectivity of the Diels-Alder (DA) cycloaddition of cyclopentadiene to 2S+1C60 changes from the usual [6,6] addition in the singlet ground state to the [5,6] attack in high spin states of C60. Changes in the aromaticity of the five- and six-membered rings when going from singlet to high spin C60 provide a rationale to understand this regioselectivity change. Experimentally, however, we find that the DA cycloaddition of isoindene to triplet C60 yields the usual [6,6] adduct. Further DFT calculations and computational analysis give an explanation to this unanticipated experimental result by showing the presence of an intersystem crossing close to the formed triplet biradical intermediate.

Revisit of the Saito-Dresselhaus-Dresselhaus C2 ingestion model: on the mechanism of atomic-carbon-participated fullerene growth

We introduce a mechanistic study based on a controversial fullerene bottom-up growth model proposed by R. Saito, G. Dresselhaus, and M. S. Dresselhaus. The so-called SDD C₂ addition model has been dismissed as chemically inadmissible but here we prove that it is feasible via successive atomic-carbon-participated addition and migration reactions. Kinetic calculations on the formation of isolated pentagon rule (IPR)-obeying C₇₀ and Y₃N@C₈₀ are carried out by employing the SDD model for the first time. A stepwise mechanism is proposed with a considerably low barrier of ca. 2 eV which is about 3 eV lower than a conventional isomerization-containing fullerene growth pathway.

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

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 C₆₀X₈. 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.

An atlas of endohedral Sc2S cluster fullerenes

Low-energy Sc₂S@C_n isomers are connected by an intricate web of Stone–Wales isomerization and Endo–Kroto C₂ insertions, giving clues to their formation.

A computational study on Sc2S@C68 and Sc2O2@C68

In order to predict the structures of the detected and assumed endohedral metallofullerene Sc₂S@C₆₈, and Sc₂O₂@C₆₈, and provide insights into their properties, the isomers of C₆₈ and tens of candidate isomers of Sc₂S@C₆₈ and Sc₂O₂@C₆₈ were studied.

Regioselective chlorine-addition reaction toward C54Cl8 and role of chlorine atoms in Stone-Wales rearrangement

By means of density functional theory, detailed studies of regioselective chlorine-addition reactions of two C(54)Cl(8) isomers disclose a highly competitive advantage of (#540)C(54)Cl(8) in the chlorofullerene formation process. The regioselectivity of the addition pattern in (#540)C(54)Cl(8) is found to be dependent on both local and general factors. Special structural relationships reveal that the pristine cage of (#540)C(54)Cl(8) can transform to that of (#864)C(56)Cl(10) and (#913)C(56)Cl(12) through both C(2) addition and Stone-Wales rearrangement. It is found that Stone-Wales rearrangement, which is believed to be a high energy barrier reaction, can be facilitated remarkably well if chlorine atoms participate in the rearrangement process. Furthermore, investigation into the electronic properties of C(54) exohedral fullerenes reveal the different impacts of halogen and hydrogen atoms.