Six IPR Isomers of C90Fullerene Captured as Chlorides: Carbon Cage Connectivities and Chlorination Patterns

Hierarchical Self-Assembly of Water-Soluble Fullerene Derivatives into Supramolecular Hydrogels

Controlling the self-assembly of nanoparticle building blocks into macroscale soft matter structures is an open question and of fundamental importance to fields as diverse as nanomedicine and next-generation energy storage. Within the vast library of nanoparticles, the fullerenes-a family of quasi-spherical carbon allotropes-are not explored beyond the most common, C60. Herein, a facile one-pot method is demonstrated for functionalizing fullerenes of different sizes (C60, C70, C84, and C90-92), yielding derivatives that self-assemble in aqueous solution into supramolecular hydrogels with distinct hierarchical structures. It is shown that the mechanical properties of these resultant structures vary drastically depending on the starting material. This work opens new avenues in the search for control of macroscale soft matter structures through tuning of nanoscale building blocks.

Three-Dimensional Cubic and Dice-Like Microstructures of Higher Fullerene C78 with Enhanced Photoelectrochemical and Photoluminescence Properties

The single-crystal micro/nanostructures of fullerene species, namely C₆₀ and C₇₀ , have been previously studied, but studies on the morphology and properties of higher fullerenes have rarely been reported due to the limited amount of samples and their ellipsoidal isomeric structures. Herein, we report the formation of three-dimensional (3D) micro-cubes and micro-dice of a higher fullerene (C₇₈ ) via a facile liquid-liquid interfacial precipitation (LLIP) method. The micro-cubes were prepared by regulating the concentration of C₇₈ in trimethylbenzene (TMB) and the volume ratio of TMB and isopropanol. Interestingly, the micro-cubes are transformed into micro-dice with an open-hole on each crystal face by simply shaking the solution. X-ray diffraction and Fourier-transform infrared spectroscopic studies revealed a simple cubic unit cell with a lattice constant of 10.6 Å and intercalated TMB molecules in both crystals. The C₇₈ cubic and dice-like microstructures exhibited enhanced photoelectrochemical and photoluminescence properties compared with pristine C₇₈ powder, indicating their potential applications as photodetectors and photoelectric devices.

Combinatorics of Supergiant Fullerenes: Enumeration of Polysubstituted Isomers, Chirality, Nuclear Magnetic Resonance, Electron Spin Resonance Patterns, and Vibrational Modes from C70 to C150000

We have developed combinatorial techniques for the enumeration of isomers of polysubstituted giant fullerenes through icosahedral C₁₅₀₀₀₀ and applied the techniques to chirality of the isomers, NMR spectroscopy, and group theoretical analysis of the vibrational modes of supergiant fullerenes. We have employed a combination of distance-degree vectorial sequences, self-returning walk sequences followed by our generalization of Sheehan's version of Pólya's theorem, and Möbius inversion technique extended to all irreducible representations of the point groups of giant fullerenes. The concept of shell equivalence classes was utilized to analyze supergiant fullerenes. We have applied these techniques to golden fullerenes in the series C_60m² for m of up to 50 or C₁₅₀₀₀₀ as well as giant fullerenes in the series C_180m² and C₇₀(D_5h). We have employed computational and combinatorial tools to enumerate both chiral and achiral isomers of substituted and hetero giant fullerenes as well as NMR-generating functions for the giant fullerenes. The techniques also provide efficient tools to enumerate all of the vibrational modes of giant fullerenes in terms of the shell partitions. General combinatorial formulae are obtained for larger polysubstituted golden fullerenes of the series C_60m² for any m, and thus the techniques are applied to larger fullerenes such as C₁₅₀₀₀₀. New insights into chirality measures, NMR, ESR hyperfine structures, and vibrational modes of supergiant fullerenes are provided using the novel combinatorial techniques.

Combinatorics of Edge Symmetry: Chiral and Achiral Edge Colorings of Icosahedral Giant Fullerenes: C80, C180, and C240

We develop the combinatorics of edge symmetry and edge colorings under the action of the edge group for icosahedral giant fullerenes from C80 to C240. We use computational symmetry techniques that employ Sheehan’s modification of Pόlya’s theorem and the Möbius inversion method together with generalized character cycle indices. These techniques are applied to generate edge group symmetry comprised of induced edge permutations and thus colorings of giant fullerenes under the edge symmetry action for all irreducible representations. We primarily consider high-symmetry icosahedral fullerenes such as C80 with a chamfered dodecahedron structure, icosahedral C180, and C240 with a chamfered truncated icosahedron geometry. These symmetry-based combinatorial techniques enumerate both achiral and chiral edge colorings of such giant fullerenes with or without constraints. Our computed results show that there are several equivalence classes of edge colorings for giant fullerenes, most of which are chiral. The techniques can be applied to superaromaticity, sextet polynomials, the rapid computation of conjugated circuits and resonance energies, chirality measures, etc., through the enumeration of equivalence classes of edge colorings.

Trifluoromethyl Derivatives of Elusive Fullerene C98

Data concerning the isomeric composition of C₉₈ and the chemistry of C₉₈ derivatives are scarce due to very low abundance of C₉₈ in the fullerene soot. Trifluoromethylation of C₉₈ -containing mixtures followed by HPLC separation of CF₃ derivatives and single crystal X-ray diffraction study resulted in structural characterization of four compounds C₉₈ (248)(CF₃ )_18/20 , C₉₈ (116)(CF₃ )₁₈ , and C₉₈ (120)(CF₃ )₂₀ . To date, these compounds represent the largest fullerenes isolated as CF₃ derivatives with experimentally determined molecular structures. The addition patterns of C₉₈ (CF₃ )_18/20 are discussed in detail revealing the stabilizing factors, such as isolated double C=C bonds and benzenoid rings on C₉₈ fullerene cages. A detailed comparison with the addition patterns of the known C₉₈ Cl_n allowed us to contribute to the better understanding the chemistry of elusive C₉₈ fullerene.

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.

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

We present high-resolution trapped ion mobility spectrometry (TIMS) measurements for fullerene ions in molecular nitrogen.

Chlorination-promoted skeletal transformation of IPR C76 discovered via trifluoromethylation under the formation of non-IPR C76(CF3)nFm

High-temperature chlorination of IPR D₂-C₇₆ followed by trifluoromethylation resulted in X-ray structures of non-classical, non-IPR C₇₆(CF₃)₁₄, C₇₆(CF₃)₁₄F₂, and C₇₆(CF₃)₁₆F₆.

New Isolated-Pentagon-Rule Isomers of Fullerene C98 Captured as Chloro Derivatives

Fullerene C₉₈ possesses 259 isomers obeying the isolated pentagon rule (IPR), from which two, nos. 116 and 248, have been confirmed earlier as chloro derivatives. High-temperature chlorination of C₉₈-containing mixtures afforded crystals of several chloro derivatives, and their structure elucidation by X-ray crystallography revealed the presence of new isomers, nos. 107, 109, and 120, in the fullerene soot. Evidence for an isomer of no. 111 is also presented. In addition, a new chloride of the known isomer 248 has been isolated and structurally studied. The chlorination patterns of the chlorides are discussed in terms of the formation of isolated C═C bonds and aromatic substructures on the fullerene cages.

The First Experimentally Confirmed Isolated Pentagon Rule (IPR) Isomers of Higher Fullerene C98 Captured as Chlorides, C98(248)Cl22 and C98(116)Cl20

High-temperature chlorination of pristine C98 fullerene isomers separated by HPLC from the fullerene soot afforded crystals of C98Cl22 and C98Cl20. An X-ray structure elucidation revealed, respectively, the presence of carbon cages of the most stable C2-C98(248) and rather unstable C1-C98(116), which represent the first isolated pentagon rule (IPR) isomers of fullerene C98 confirmed experimentally. The chlorination patterns of the chlorides are discussed in terms of the formation of isolated C=C bonds and aromatic substructures on the fullerene cages.

New Isolated-Pentagon-Rule and Skeletally Transformed Isomers of C100 Fullerene Identified by Structure Elucidation of their Chloro Derivatives

High-temperature chlorination of C100 fullerene followed by X-ray structure determination of the chloro derivatives enabled the identification of three isomers of C100 from the fullerene soot, specifically numbers 18, 425, and 417, which obey the isolated pentagon rule (IPR). Among them, isomers C1-C100 (425) and C2-C100 (18) afforded C1-C100 (425)Cl22 and C2-C100 (18)Cl28/30 compounds, respectively, which retain their IPR cage connectivities. In contrast, isomer C2v -C100 (417) gives Cs -C100 (417)Cl28 which undergoes a skeletal transformation by the loss of a C2  fragment, resulting in the formation of a nonclassical (NC) C1-C98 (NC)Cl26 with a heptagon in the carbon cage. Most probably, two nonclassical C1-C100 (NC)Cl18/22 chloro derivatives originate from the IPR isomer C1-C100 (382), although both C1-C100 (344) and even nonclassical C1-C100 (NC) can be also considered as the starting isomers.

Unusual Chlorination Patterns of Three IPR Isomers of C88 Fullerene in C88 (7)Cl12/24 , C88 (17)Cl22 , and C88 (33)Cl12/14

High-temperature chlorination of three IPR isomers of fullerene C88 , C2 -C88 (7), Cs -C88 (17), and C2 -C88 (33), resulted in the isolation and X-ray structural characterization of C88 (7)Cl12 , C88 (7)Cl24 , C88 (17)Cl22 , and C88 (33)Cl12/14 . Chlorination patterns of C88 (7) and C88 (33) isomers are unusual in that one or more pentagons remain free from chlorination while some other pentagons are occupied by two or three Cl atoms. The addition patterns of the isolated chlorides are discussed in terms of the distribution of twelve pentagons on the carbon cages and the formation of stabilizing isolated C=C bonds and benzenoid rings.

Capturing an unstable C100 fullerene as chloride, C100(1)Cl12, with a nanotubular carbon cage

The chlorination of a HPLC C100 fraction afforded C100(1)Cl12 with an unprecedented nanotubular carbon cage of a highly unstable D5d-C100 fullerene.

Structures of chlorinated fullerenes, IPR C₉₆Cl₂₀ and non-classical C₉₄Cl₂₈ and C₉₂Cl₃₂: evidence of the existence of three new isomers of C₉₆

Chlorination of various HPLC fractions of C96 with a mixture of VCl4 and SbCl5 at 340-360 °C and single-crystal X-ray diffraction study of the products led to the identification of three new IPR isomers of C96. The C96(175) isomer forms a stable chloride, C96(175)Cl20, while chlorides of two other new isomers, C96(114) and C96(80), undergo cage shrinkage yielding C94(NC1)Cl28 and C96(NC2)Cl32 with non-classical (NC) cages. These two NC chlorides contain, respectively, one and two heptagons flanked by pairs of fused pentagons and are stabilized by chlorine attachment to the emerging pentagon-pentagon junctions. Thus, the number of the experimentally confirmed C96 isomers has reached nine, which corroborates the empirical rule that the C(6n) fullerenes exhibit particularly rich isomerism.

The most stable isomers of giant fullerenes C102 and C104 captured as chlorides, C102(603)Cl18/20 and C104(234)Cl16/18/20/22

The chlorination of HPLC fractions with pristine giant fullerenes, C102 and C104, followed by X-ray crystallographic study of chlorides, C102(603)Cl18/20 and C104(234)Cl16-22, confirmed the presence of the most stable IPR (IPR = Isolated Pentagon Rule) isomers, C102(603) and C104(234), in the fullerene soot. The discussion concerns the chlorination patterns of polychlorides and relative stability of pristine isomers of C102 and C104 fullerenes.

First isomers of pristine C104 fullerene structurally confirmed as chlorides, C104(258)Cl16 and C104(812)Cl24

Isolation and characterization of very large fullerenes is hampered by a drastic decrease of their content in fullerene soot with increasing fullerene size and a simultaneous increase of the number of possible IPR (Isolated Pentagon Rule) isomers. In the present work, fractions containing mixtures of C102 and C104 were isolated in very small quantities (several dozens of micrograms) by multi-step recycling HPLC from an arc-discharge fullerene soot. Two such fractions were used for chlorination with a VCl4/SbCl5 mixture in glass ampoules at 350-360 °C. The resulting chlorides were investigated by single-crystal X-ray diffraction using synchrotron radiation. By this means, two IPR isomers of C104 , numbers 258 and 812 (of 823 topologically possible isomers), have been confirmed for the first time as chlorides, C1 -C104(258)Cl16 and D2-C104 (812)Cl24, respectively, while an admixture of C2 -C104(811)Cl24 was assumed to be present in the latter chloride. DFT calculations showed that pristine C104(812) belongs to rather stable C104 cages, whereas C104(258) is much less stable.

The first structural confirmation of a C102 fullerene as C102Cl20 containing a non-IPR carbon cage

The chlorination of a pristine C102 fullerene separated by HPLC from fullerene soot afforded crystals of C102Cl20 with a non-IPR (IPR = isolated pentagon rule) cage containing two pairs of fused pentagons; structural reconstruction of a two-step Stone-Wales rearrangement revealed the starting IPR isomer (no. 19) of C102.