C100 is Converted into C94Cl22 by Three Chlorination‐Promoted C2 Losses under Formation and Elimination of Cage Heptagons

Chlorination of the C₁₀₀(18) fullerene with a mixture of VCl₄ and SbCl₅ gives rise to branched skeletal transformations affording non‐classical (NC) C₉₄(NC1)Cl₂₂ with one heptagon in the carbon cage together with the previously reported C₉₆(NC3)Cl₂₀ with three heptagons. The three‐step pathway to C₉₄(NC1)Cl₂₂ starts with two successive C₂ losses of 5:6 C?C bonds to give two cage heptagons, whereas the third C₂ loss of the 5:5 C?C bond from a pentalene fragment eliminates one of the heptagons. Quantum‐chemical calculations demonstrate that the two unusual skeletal transformations—creation of a heptagon in C₉₆(NC3)Cl₂₀ through a Stone–Wales rearrangement and the presently reported elimination of a heptagon through C₂ loss—are both characterized by relatively low activation energy.     

Chlorination of Two Isomers of C86 Fullerene: Molecular Structures of C86(16)Cl16, C86(17)Cl18, C86(17)Cl20, and C86(17)Cl22

Chlorination of a mixture of C₈₆ isomers no. 16 (C_s) and no. 17 (C₂) with VCl₄ or a (TiCl₄+Br₂) mixture afforded crystalline chlorides with 16 to 22 Cl atoms per fullerene cage. Single crystal X‐ray diffraction with the use of synchrotron radiation enabled us to determine the chlorination patterns of C₈₆(16)Cl₁₆, C₈₆(17)Cl₁₈, C₈₆(17)Cl₂₀, and C₈₆(17)Cl₂₂. At these degrees of chlorination, addition patterns of C₈₆(16) and C₈₆(17) chlorides have some features in common, owing to the close similarity in the cage structures of both isomers. The average energy of C?Cl bonds decreases with increasing number of attached Cl atoms.     

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.     

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), C_s‐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)Cl_12/14. 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.     

Two Successive C2 Losses from C86 Fullerene upon Chlorination with the Formation of Non‐classical C84Cl30 and C82Cl30

High‐temperature chlorination of a fullerene C₈₆ with VCl₄ afforded non‐classical C₈₄Cl₃₀ and C₈₂Cl₃₀ containing one and two heptagons, respectively, in the carbon cages. Two types of C₂ losses, which differ in the final arrangements of separate or fused pentagons, can occur successively in either order, producing rather flat or concave regions on the shrinked carbon cage. In the chlorination‐promoted skeletal transformation of C₈₆ (isomer no. 16) with the loss(es) of C₂ units, the structures of the starting, intermediate, and final compounds were all revealed unambiguously by X‐ray single crystal diffraction.     

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 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.     

Chlorination‐Promoted Skeletal‐Cage Transformations of C88 Fullerene by C2 Losses and a CC Bond Rotation

High‐temperature chlorination of fullerene C₈₈ (isomer 33) with VCl₄ gives rise to skeletal transformations affording several nonclassical (NC) fullerene chlorides, C₈₆(NC1)Cl_24/26 and C₈₄(NC2)Cl₂₆, with one and two heptagons, respectively, in the carbon cages. The branched skeletal transformation including C₂ losses as well as a Stone–Wales rearrangement has been comprehensively characterized by the structure determination of two intermediates and three final chlorination products. Quantum‐chemical calculations demonstrate that the average energy of the C?Cl bond is significantly increased in chlorides of nonclassical fullerenes with a large number of chlorinated sites of pentagon–pentagon adjacency.     

Chlorofullerenes with isomeric C86 carbon cages: C86(16)Cl16 and C86(17)Cl18,20

Chlorofullerenes C₈₆(16)Cl₁₆ and C₈₆(17)Cl_18,20 were prepared by chlorination of C_s-C₈₆(16) and C₂-C₈₆(17), respectively, with VCl₄ at 320–340 °C. An X-ray crystallo- graphic study with the use of synchrotron radiation revealed the chlorination patterns which show certain similarity due to only small differences between isomeric C₈₆ cages.     

Unstable Isomer of C90 Fullerene Isolated as Chloro Derivatives,C90(1)Cl10/12

High‐temperature chlorination of C₉₀‐containing fullerene fraction resulted in the isolation and X‐ray structural characterization of C₉₀(1)Cl_10/12, the first derivatives of a relatively unstable isomer D_5h‐C₉₀(1) with a nanotubular shape. In the crystal structure, three isomers of both C₉₀(1)Cl₁₀ and C₉₀(1)Cl₁₂ with similar chlorination patterns co‐crystallize in the same crystallographic site. Thus, in contrast to the previous reports, D_5h‐C₉₀(1) is present, though with a low abundance, in the fullerene soot produced by arc‐discharge method with undoped graphite rods.     

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)Cl_18/20 and C₁₀₄(234)Cl_16–22, 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.     

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.     

Preparation and crystal structure of C84(11)Cl20,22, chloro derivatives of a C84 minor isomer

Chlorofullerenes C₈₄(11)Cl₂₀ and C₈₄(11)Cl₂₂ were prepared by chlorination of C₂–C₈₄(11) with VCl₄ at 340–360 °C. An X-ray crystallographic study with the use of synchrotron radiation revealed the chlorination patterns featuring only para additions in C₆Cl₂ hexagons.