New Isolated-Pentagon-Rule Isomer of C92 Isolated as Trifluoromethyl and Chlorido Derivatives: C92(38)(CF3)14/16 and C92(38)Cl20/22

Three Isolated-Pentagon-Rule Isomers of C96 Fullerene Isolated as Trifluoromethyl Derivatives

The family of experimentally confirmed isolated-pentagon-rule (IPR) isomers of C₉₆ fullerene is extended by trifluoromethylation of a C₉₆ fraction of the fullerene soot, high-performance liquid chromatography separation of CF₃ derivatives, and a single-crystal X-ray diffraction study of C₉₆(CF₃)_n compounds with the use of synchrotron radiation. New cage isomers were revealed in C₉₆(94)(CF₃)_18/20 and C₉₆(182)(CF₃)₁₈ compounds, whereas isomer C₉₆(181), previously known in the adduct with nickel porphyrinate, was confirmed in C₉₆(181)(CF₃)_18/20 derivatives. Common and special features of the addition patterns of CF₃ groups on C₉₆ carbon cages are discussed in more detail. The investigated isomers belong to the most stable C₂-C₉₆(181) and slightly less stable C₁-C₉₆(94) and C₂-C₉₆(182) among the altogether 15 experimentally confirmed IPR isomers of C₉₆ 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.

Chlorination-Promoted Cage Transformation of IPR C92 Discovered via Trifluoromethylation under Formation of Non-classical C92 (NC)(CF3 )22

High-temperature trifluoromethylation of isolated-pentagon-rule (IPR) fullerene C₉₂ chlorination products followed by HPLC separation of C₉₂ (CF₃ )_n derivatives resulted in the isolation and X-ray structural characterization of IPR C₉₂ (38)(CF₃ )₁₈ and non-classical C₉₂ (NC)(CF₃ )₂₂ . The formation of C₉₂ (38)(CF₃ )₁₈ as the highest CF₃ derivative of the known isomer C₉₂ (38) can be expected. The formation of C₉₂ (NC)(CF₃ )₂₂ was interpreted as chlorination-promoted cage transformation of C₉₂ (38) followed by trifluoromethylation of non-classical C₉₂ (NC) chloride. Noticeably, C₉₂ (NC)(CF₃ )₂₂ shows the highest degree of trifluoromethylation among all known CF₃ derivatives of fullerenes. The addition patterns of C₉₂ (38)(CF₃ )₁₈ and C₉₂ (NC)(CF₃ )₂₂ are discussed and compared to the chlorination patterns of C₉₂ (38)Cl_n compounds.

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.

Synthesis, Isolation and Structure of Trifluoromethylated Fullerene D3-C78, C78(1)(CF3)10-18

High-temperature trifluoromethylation of fullerene C78 followed by HPLC separation of C78 (CF3)n derivatives resulted in the isolation and X-ray structural characterization of 15 compounds, that is, two C78(1)(CF3)10, three C78 (1)(CF3)12, four C78 (1)(CF3)14, and five C78 (1)(CF3)16 isomers as well as one isomer of C78(1)(CF3)18. The addition patterns of the C78(1)(CF3)n molecules are discussed in terms of trifluoromethylation pathways and relative formation energies.

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.