Stone-Wales Rearrangement Research Articles

Non-classical (NC), heptagon-containing fullerenes obtained via chlorination-promoted cage transformations: C76(NC2a)Cl24 and C76(NC2b)Cl28.

High-temperature chlorination of C76 fullerene with SbCl5 proceeds via five Stone-Wales rearrangements, resulting in non-classical (NC) C76(NC1a)Cl24 with two heptagons and 14 pentagons partically fused in pairs and triples. C76(NC2b)Cl28 with isomeric carbon cage was obtained by chlorination-promoted cage shrinkage of C80via two C2 losses. The pathways of skeletal cage trasformations, the chlorination patterns, and formation energies are discussed in detail.

Chlorination-Promoted Skeletal Transformations in Isolated-Pentagon Rule (IPR) Isomers of Fullerene C86 to Non-IPR Chloro- and Trifluoromethyl Derivatives.

Fullerene C86 contains two isomers obeying the Isolated-Pentagon Rule (IPR), CS-C86(16) and C2-C86(17). Both isomers undergo unprecedented skeletal transformations at high-temperature (400 °C) chlorination with SbCl5. One-step Stone-Wales rearrangement (SWR) in C86(17) results in the pentagon-fused #63614C86 cage found in the structure of #63614C86Cl24. CF3 derivatives with the same cage, two isomers of #63614C86(CF3)18 and #63614C86(CF3)18O2, were obtained by high-temperature trifluoromethylation of the chlorination products with CF3I, followed by HPLC separation. The skeletal transformation of C86(16) proceeds via two SWRs under the formation of a #63624C86 cage with one fused-pentagon pair found in the structure of #63624C86(CF3)18. The addition patterns in skeletally transformed molecules are discussed in detail, disclosing the influence of the pentagon fusions, isolated C=C bonds, and benzenoid rings on the stability of the molecules with non-IPR C86 cages. The chlorination-promoted SWRs in C86 isomers have been observed for the first time, which contribute a lot to the understanding of skeletal transformations in fullerenes.

Exploring exohedral functionalization of fullerene with automation and Neural Network Potential

Exohedral functionalized fullerenes have shown superior physicochemical properties over pristine carbon cages. The functional groups could significantly improve solubility, electron affinity, and photoelectric properties. However, their numerous distribution patterns have long been puzzling for theoretical chemists, and there are unmet needs for tools to unveil their functionalization mechanism. This work automates the traditional stepwise model as well as various analysis workflows within an open-source package AutoSteper. Besides, a Neural Network Potential (NNP) is trained, validated, and proven to have great generalization ability and transferability. Several case studies are performed with AutoSteper to explore functionalization mechanisms, such as the selectivity and the functionalization pathway of a specific isomer, and the Stone-Wales Rearrangement (SWR) in co-crystallization systems. In addition, to reasonably narrow down the screen scope for giant nanoclusters, a new variant stepwise model is proposed. Fruitful scientific discoveries demonstrate that AutoSteper is capable of providing complete, comprehensive, and cost-effective analysis. With the combination of Automation and NNP, a data-driven research paradigm is realized for fullerene chemistry.

Divergent Synthesis of Alternant Bisanthenequinone and Nonalternant Heptalenodifluorenedione Ring Systems via a Concentration-Dependent Rearrangement.

The synthesis of a diol containing a nonalternant aromatic core was investigated to access a nonalternant isomer of bisanthene with functional groups suitable for two-dimensional polymerization. An alternant diol and its nonalternant isomer were prepared in a short synthetic route from the same bifluorenylidene starting material. The bifluorenylidene reactant undergoes a Stone-Wales rearrangement in neat triflic acid, which unexpectedly provided both an alternant and nonalternant dione. The rearrangement was characterized by spectroscopy and single crystal X-ray diffraction of Grignard addition products of both isomers. The relative yield of the rearranged, alternant product increased along with the initial concentration of its polycyclic aromatic hydrocarbon (PAH) precursor, implicating a bimolecular rearrangement mechanism and enabling the divergent synthesis of both the nonalternant and alternant products. These findings offer convenient access to functional derivatives of two PAH classes of interest for their optoelectronic properties and serve as yet another warning about the importance of characterizing these materials with care, especially when insoluble products must be carried forward in a multistep synthetic route.

Fused-Pentagon Carbon Cages in Chloro and Trifluoromethyl Derivatives of C60: Non-IPR 1809C60Cl8, 1806C60(CF3)14, and Nonclassical C60(NC)Cl14.

High-temperature chlorination of conventional IPR C60 can produce chloro derivatives of non-IPR C60 by skeletal transformations via Stone-Wales rearrangements (SWRs) of the carbon cage. We report the synthesis and structure elucidation of non-IPR 1809C60Cl8 and nonclassical C60(NC)Cl14. The present isolation of 1809C60Cl8 hints at the possibility that the same product in the previously reported chlorine-doped arc-discharge synthesis could have, likewise, resulted from the initially formed IPR C60. C60(NC)Cl14 is the first chloride containing a nonclassical carbon cage with one heptagon and 13 pentagons known previously only in a CF3 derivative. Additionally, trifluoromethylation of non-IPR chlorides revealed the formation of 1806C60(CF3)14 with a new non-IPR carbon cage and unusual trifluoromethylation pattern. Thereby, the number of different, structurally confirmed non-IPR carbon cages of C60 now reaches eight.

A nanometric window on fullerene formation in the interstellar medium: Insights from molecular dynamics studies.

Understanding the fundamental mechanisms that underlie the synthesis of fullerene molecules in the interstellar medium (ISM) and in the environments of astrophysical objects is an open question. In this regard, using classical molecular dynamics, we demonstrate the possibility of in situ formation of fullerene molecules, such as C60 from graphite, which is known to occur in the ISM, in particular, circumstellar environments. Specifically, when graphite is subjected to thermal and mechanical stimuli that are typical of circumstellar shells, we find that the graphite sheet edges undergo significant restructuring and curling, leading to edge-induced interlayer-interactions and formation of mechanically strained five-membered-ring structural units. These units serve as precursors for the formation of fullerene structures, such as pristine and metastable C60 molecules. The pathways leading to molecular C60 formation consist of a series of steps that involve bond-breakage and subsequent local rearrangement of atoms, with the activation energy barriers of the rate-limiting step(s) being comparable to the energetics of Stone-Wales rearrangement reactions. The identified chemical pathways provide fundamental insights into the mechanisms that underlie C60 formation. Moreover, they clearly demonstrate that top-down synthesis of C60 from graphitic sources is a viable synthesis route at conditions pertaining to circumstellar matter.

A Chemiluminescent Tetraaryl Diborane(4) Tetraanion.

Two subvalent, redox‐active diborane(4) anions, [3]4− and [3]2−, carrying exceptionally high negative charge densities are reported: Reduction of 9‐methoxy‐9‐borafluorene with Li granules without stirring leads to the crystallization of the B(sp3)−B(sp2) diborane(5) anion salt Li[5]. [5]− contains a 2,2′‐biphenyldiyl‐bridged B−B core, a chelating 2,2′‐biphenyldiyl moiety, and a MeO substituent. Reduction of Li[5] with Na metal gives the Na+ salt of the tetraanion [3]4− in which two doubly reduced 9‐borafluorenyl fragments are linked via a B−B single bond. Comproportionation of Li[5] and Na4[3] quantitatively furnishes the diborane(4) dianion salt Na2[3], the doubly boron‐doped congener of 9,9′‐bis(fluorenylidene). Under acid catalysis, Na2[3] undergoes a formal Stone–Wales rearrangement to yield a dibenzo[g,p]chrysene derivative with B=B core. Na2[3] shows boron‐centered nucleophilicity toward n‐butyl chloride. Na4[3] produces bright blue chemiluminescence when exposed to air.

A Chemiluminescent Tetraaryl Diborane(4) Tetraanion

AbstractTwo subvalent, redox‐active diborane(4) anions, [3]4− and [3]2−, carrying exceptionally high negative charge densities are reported: Reduction of 9‐methoxy‐9‐borafluorene with Li granules without stirring leads to the crystallization of the B(sp3)−B(sp2) diborane(5) anion salt Li[5]. [5]− contains a 2,2′‐biphenyldiyl‐bridged B−B core, a chelating 2,2′‐biphenyldiyl moiety, and a MeO substituent. Reduction of Li[5] with Na metal gives the Na+ salt of the tetraanion [3]4− in which two doubly reduced 9‐borafluorenyl fragments are linked via a B−B single bond. Comproportionation of Li[5] and Na4[3] quantitatively furnishes the diborane(4) dianion salt Na2[3], the doubly boron‐doped congener of 9,9′‐bis(fluorenylidene). Under acid catalysis, Na2[3] undergoes a formal Stone–Wales rearrangement to yield a dibenzo[g,p]chrysene derivative with B=B core. Na2[3] shows boron‐centered nucleophilicity toward n‐butyl chloride. Na4[3] produces bright blue chemiluminescence when exposed to air.

Chloro- and Trifluoromethyl Derivatives of a Pentagon-Fused C60: 1810C60Cl24, 1810C60Cl20, and 1810C60(CF3)14.

The carbon cage of Ih-C60, obeying the isolated-pentagon rule (IPR), can be transformed to the non-IPR D2h-1810C60 cage via two successive Stone-Wales rearrangements in the course of high-temperature chlorination of C60 with SbCl5. Two chloro derivatives, C2v-1810C60Cl24 and C2v-1810C60Cl20, have been isolated by high-performance liquid chromatography (HPLC). High-temperature trifluoromethylation of the chlorination products with CF3I, followed by HPLC separation, afforded a non-IPR CF3 derivative, Cs-1810C60(CF3)14. Structural elucidation of the isolated compounds revealed that all eight sites of pentagon-pentagon fusions on the carbon cage are preferentially occupied by Cl atoms or CF3 groups. According to density functional theory calculations, chloro and CF3 derivatives of 1810C60 are more stable than the isomeric derivatives of 1809C60 or IPR 1812C60, possessing respectively four or no sites of pentagon fusion in their carbon cages.

Fused-Pentagon C70Cl6 and C70Cl8 Obtained via Chlorination-Promoted Skeletal Transformation of IPR C70

The isolated-pentagon-rule (IPR) D5h-C70 fullerene is least susceptible to skeletal transformations in comparison with higher fullerenes and even C60. A cage transformation in IPR C70 via a one-step Stone-Wales rearrangement was accomplished by high-temperature (440 °C) ampule chlorination with SbCl5. Subsequent dechlorination at 450 °C, followed by high-performance liquid chromatography separation, allowed the isolation of non-IPR C70Cl6 and C70Cl8. X-ray diffraction study revealed the presence of an unprecedented C70 carbon cage, possessing two pairs of fused pentagons and the chlorination patterns located on one cage hemisphere. A high energetic and thermal stability of both non-IPR chlorides was also confirmed by theoretical calculations of formation energies. Pathways of skeletal transformations of IPR C70 in comparison with those in C60 are discussed.

Skeletal Rearrangements of the C240 Fullerene: Efficient Topological Descriptors for Monitoring Stone–Wales Transformations

Stone–Wales rearrangements of the fullerene surface are an uncharted field in theoretical chemistry. Here, we study them on the example of the giant icosahedral fullerene C240 to demonstrate the complex chemical mechanisms emerging on its carbon skeleton. The Stone–Wales transformations of C240 can produce the defected isomers containing heptagons, extra pentagons and other unordinary rings. Their formations have been described in terms of (i) quantum-chemically calculated energetic, molecular, and geometric parameters; and (ii) topological indices. We have found the correlations between the quantities from the two sets that point out the role of long-range topological defects in governing the formation and the chemical reactivity of fullerene molecules.

Chlorination-Promoted Skeletal Transformations of Fullerenes.

Classical fullerenes are built of pentagonal and hexagonal rings, and the conventional syntheses produce only those isomers that obey the isolated-pentagon rule (IPR), where all pentagonal rings are separated from each other by hexagonal rings. Upon exohedral derivatization, the IPR fullerene cages normally retain their connectivity pattern. However, it has been discovered that high-temperature chlorination of fullerenes with SbCl5 or VCl4 can induce skeletal transformations that alter the carbon cage topology, as directly evidenced by single crystal X-ray diffraction studies of the chlorinated products of a series of fullerenes in the broad range of C60 to C102. Two general types of transformations have been identified: (i) the Stone-Wales rearrangement (SWR) that consists of a rotation of a C-C bond by 90°, and (ii) the removal of a C-C bond, i.e., C2 loss (C2L). Single- or multistep SWR and/or C2L transformations afford either classical non-IPR fullerenes bearing fused pentagons (highlighted in red in the TOC picture) or nonclassical (NCx) fullerenes with x = 1-3 heptagonal rings (highlighted in blue in the TOC picture) often flanked by fused pentagons. Several subtypes of the SWR and C2L processes can be further discerned depending on the local topology of the transformed region of the cage. Under the chlorination conditions, the non-IPR and NC carbon cages that would be energetically unfavorable and mostly labile in their pristine state are instantaneously stabilized by chlorination of the pentagon-pentagon junctions and by delimitation of the original spherical π-system into smaller favorable aromatic fragments. The significance of the chlorination-promoted skeletal transformations within the realm of fullerene chemistry is demonstrated by the growing body of examples. To date, these include single- and multistep SWRs in the buckminsterfullerene C60 and in the higher fullerenes C76(1), C78(2), C82(3), and C102(19), single and multistep C2Ls (i.e., cage shrinkage) in C86(16), C88(33), C90(28), C92(50), C96(80), C96(114), and C102(19), and multistep combinations of SWRs and C2Ls in C88(3), C88(33), and C100(18), (IPR isomer numbering in parentheses is according to the spiral algorithm). Remarkably, an IPR precursor can give rise to versatile transformed chlorinated fullerene cages formed via branched pathways. The products can be recovered either in their initial chlorinated form or as more soluble CF3/F derivatives obtained by an additional trifluoromethylation workup. Reconstruction of the skeletal transformation pathways is often complicated due to the lack of the isolable intermediate products in the multistep cases. Therefore, it is usually based on the principle of selecting the shortest pathways between the starting and the final cage. The quantum-chemical calculations illustrate the detailed mechanisms of the SWR and C2L transformations and the thermodynamic driving forces behind them. A particularly important aspect is the interplay between the chlorination patterns and the regiochemistry of the skeletal transformations.

Stable C92(26) and C92(38) as Well as Unstable C92(50) and C92(23) Isolated-Pentagon-Rule Isomers As Revealed by Chlorination of C92 Fullerene.

High-temperature chlorination of C92 fractions, followed by single-crystal X-ray diffraction, resulted in the structure determination of C92(38)Cl18, C92(38)Cl22, C92(26)Cl24, nonclassical C90( NC)Cl22, and non-isolated-pentagon-rule C90Cl26. Two latter chloro derivatives were obtained by chlorination-promoted cage transformations via a single C2 loss from C92(50) and a combination of a C2 loss from C92(23) and three Stone-Wales rearrangements. The chlorination patterns are stabilized by the formation of isolated C═C bonds and aromatic substructures on carbon cages. The presence of C92 isomer numbers 23, 26, and 50 in the arc-discharge fullerene soot has been confirmed for the first time.

Fused-pentagon C70Cl26 obtained via chlorination-promoted Stone-Wales cage transformations of C70.

High-temperature (360 °C) chlorination of C70 with VCl4 or SbCl5 yields only IPR C70Cl26/28. Chlorination with SbCl5 at 440 °C resulted in a skeletal transformation via a two-step Stone-Wales rearrangement and the formation of non-IPR 8005C70Cl26 with two fused pentagon pairs in the carbon cage which was established by single crystal X-ray diffraction.

Rebuilding C60: Chlorination-Promoted Transformations of the Buckminsterfullerene into Pentagon-Fused C60 Derivatives.

In recent years, many higher fullerenes that obey the isolated pentagon rule (IPR) were found capable of rearranging into molecules with adjacent pentagons and even with heptagons via chlorination-promoted skeletal transformations. However, the key fullerene, buckminsterfullerene I h-C60, long seemed insusceptible to such rearrangements. Now we demonstrate that buckminsterfullerene yet can be transformed by chlorination with SbCl5 at 420-440 °C and report X-ray structures for the thus-obtained library of non-IPR derivatives. The most remarkable of them are non-IPR C60Cl24 and C60Cl20 with fundamentally rearranged carbon skeletons featuring, respectively, four and five fused pentagon pairs (FPPs). Further high-temperature trifluoromethylation of the chlorinated mixture afforded additional non-IPR derivatives C60(CF3)10 and C60(CF3)14, both with two FPPs, and a nonclassical C60(CF3)15F with a heptagon, two FPPs, and a fully fused pentagon triple. We discuss the general features of the addition patterns in the new non-IPR compounds and probable pathways of their formation via successive Stone-Wales rearrangements.

Anomalous thermal stability in supergiant onion-like carbon fullerenes

Onion-like carbon fullerenes (OLCFs) are a promising material for applications in nanoscale devices, medicine, lubrication and superhard materials. Knowledge of the pyrolysis chemistry of OLCFs helps understanding the thermal-induced erosion of carbon-based resources and spacecraft materials. Here, using first-principle-based ReaxFF atomistic simulations, thermal and dynamical characteristics of supergiant 20-shell OLCF having concentric arrangement of C60@C240@ … @C24000 are explored. Fullerenes@20-shell OLCF yield larger average radii than isolated single-walled fullerenes (SWFs) at the same scale. The intershell-spacing@OLCF exhibits a reduction tendency from inner to outer shells, but is higher than that of bulk graphite. Because of nonbonded intershell forces, fullerenes@20-shell OLCF are energetically favorable over the corresponding isolated SWFs. In contrast to nonmonotonic variation of melting point with size and shell-index in SWFs and other nanoparticles, an anomalous shell-dependent melting instability in the 20-shell OLCF is identified due to the combined effects of geometrical size, nanoconfinement and surface; Both inner and outer fullerenes are not so resistive against heating, nor are they as strong as the identical-size isolated SWFs, however, the intermediate shells, locally similar to curved graphite, demonstrate higher heat-resisting property than identical-size isolated SWFs. Topological analysis reveals morphological transformation of four stages involving Stone-Wales rearrangement, heterogeneous defects nucleation, amorphization and fragmentation.

(Invited) Cage Skeletal Transformation of Fullerene Via Chlorination

A classical fullerene is composed of hexagons and pentagons only, and its stability is generally determined by the Isolated-Pentagon-Rule (IPR). In 2005 Taylor et al. reported the first cage skeletal transformation of fullerene C60 via fluorination at 550 0C, affording two stable non-classical fullerene derivatives containing heptagons. It is then intriguing to investigate whether cage skeletal transformation of fullerene can be fulfilled under less harsh conditions. Herein, we present our recent studies on cage skeletal transformations of classical higher fullerenes in the course of high-temperature chlorination. Chlorination-promoted cage skeletal transformations occur by Stone-Wales rearrangements (SWRs, i.e., a rotation of a C−C bond by ca. 90°) and/or losses of C2 units (C2Ls). In particular, the C2L realized by the removal of a 5:6 C-C bond from the cage generates a cage heptagon, thus resulting in the formation of a non-classical cage. We show several examples of chlorination-promoted one-, two-, and multi-step cage transformations in different higher fullerenes.

Versatility of chlorination-promoted skeletal transformation pathways in C76 fullerene.

We present the synthesis and crystal structure of a new chlorinated non-IPR isomer of C76 fullerene, 18387C76Cl30. The new chloride is formed from IPR-D2-C76via a sequence of chlorination-promoted Stone-Wales rearrangements concurrently with the previously known non-IPR compound 18917C76Cl24. A considerable difference between the two simultaneously forming non-IPR compounds suggests that higher fullerenes can exhibit a much higher versatility of skeletal transformations than the presently known compounds. Our theoretical analysis identifies yet further favorable Stone-Wales pathways in C76 and predicts several stable non-IPR and non-classical (i.e. heptagon-containing) C76 chlorides that may await experimental isolation.

Chlorination-promoted Transformation of Isolated Pentagon Rule C78 into Fused-pentagons- and Heptagons-containing Fullerenes.

Cage transformations in fullerenes are rare phenomena which are still not fully understood. We report the first skeletal transformation of an Isolated-Pentagon-Rule (IPR) isomer of C78 fullerene upon high-temperature chlorination which proceeds by six-step Stone-Wales rearrangements affording non-IPR, non-classical (NC) C78 (NC2)Cl24 with two cage heptagons, six pairs of fused pentagons, and an unprecedented loop-like chlorination pattern. The following loss of a C2 unit results in C76 (NC3)Cl24 containing three cage heptagons.

A quantum chemical study of the Fe@C 60 endocomplex

At the DFT (U)PBE0/cc-pVDZ level the structural parameters of a hypothetical Fe@C 60 endocomplex are determined. The (A 1//C 3v )–Fe@C 60 state characterized by the electron spin square of 3.07 au, the free valence of 4.15, the dipole moment of 1.15 D, and the 172 pm Fe nuclear shift relative to the center of inertia of С60 corresponds to the energy minimum. The Stone–Wales rearrangement in the quasi-triplet state increases the endocomplex energy by 1.56 eV and by 0.79 eV in the quasi-quintet state.