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.     

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.     

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.     

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 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.     

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.     

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(NC 2)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(NC 3)Cl₂₄ containing three cage heptagons.     

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 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.     

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.     

Synthesis,Structure, and Theoretical Study of Trifluoromethyl Derivatives of C84(22) Fullerene

Trifluoromethylation of higher fullerene mixtures with CF₃I was performed in ampoules at 400 to 420 and 550 to 560 °C. HPLC separation followed by crystal growth and X‐ray diffraction studies allowed the structure elucidation of nine CF₃ derivatives of D₂‐C₈₄ (isomer 22). Molecular structures of two isomers of C₈₄(22)(CF₃)₁₂, two isomers of C₈₄(22)(CF₃)₁₄, four isomers of C₈₄(22)(CF₃)₁₆, and one isomer of C₈₄(22)(CF₃)₂₀ were discussed in terms of their addition patterns and relative formation energies. DFT calculations were also used to predict the most stable molecular structures of lower CF₃ derivatives, C₈₄(22)(CF₃)_2–10. It was found that the addition of CF₃ groups to C₈₄(22) is governed by two rules: additions can only occur at para positions of C₆(CF₃)₂ hexagons and no additions can occur at triple‐hexagon‐junction positions on the fullerene cage.     

Isolation and Structural X‐ray Investigation of Perfluoroalkyl Derivatives of Six Cage Isomers of C84

Perfluoroalkylation of a higher fullerene mixture with CF₃I or C₂F₅I, followed by HPLC separation of CF₃ and C₂F₅ derivatives, resulted in the isolation of several C₈₄(R^F)_n (n=12, 16) compounds. Single‐crystal X‐ray crystallography with the use of synchrotron radiation allowed structure elucidation of eight C₈₄(R^F)_n compounds containing six different C₈₄ cages (the number of the C₈₄ isomer is given in parentheses): C₈₄ (23)(C₂F₅)₁₂ ( I ), C₈₄ (22)(CF₃)₁₆ ( II ), C₈₄ (22)(C₂F₅)₁₂ ( III ), C₈₄ (11)(C₂F₅)₁₂ ( IV ), C₈₄ (16)(C₂F₅)₁₂ ( V ), C₈₄ (4)(CF₃)₁₂ ( VI with toluene and VII with hexane as solvate molecules), and C₈₄ (18)(C₂F₅)₁₂ ( VIII ). Whereas some connectivity patterns of C₈₄ isomers (22, 23, 11) had previously been unambiguously confirmed by different methods, derivatives of C₈₄ isomers numbers 4, 16, and 18 have been investigated crystallographically for the first time, thus providing direct proof of the connectivity patterns of rare C₈₄ isomers. General aspects of the addition of R^F groups to C₈₄ cages are discussed in terms of the preferred positions in the pentagons under the formation of chains, pairs, and isolated R^F groups.     

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)Cl_28/30 compounds, respectively, which retain their IPR cage connectivities. In contrast, isomer C_2v‐C₁₀₀(417) gives C_s‐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)Cl_18/22 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.     

Synthesis,Structure, and Theoretical Study of Trifluoromethyl Derivatives of C84(23) Fullerene

Trifluoromethylation of a higher fullerene mixture with CF₃I was performed in ampoules at 550 °C. HPLC separation followed by crystal growth and X‐ray diffraction study resulted in the structure elucidation of nine CF₃ derivatives of D_2d‐C₈₄ (isomer 23). The molecular structures of C₈₄(23)(CF₃)₄, C₈₄(23)(CF₃)₈, C₈₄(23)(CF₃)₁₀, C₈₄(23)(CF₃)₁₂, two isomers of C₈₄(23)(CF₃)₁₄, two isomers of C₈₄(23)(CF₃)₁₆, and C₈₄(23)(CF₃)₁₈ were discussed in terms of their addition patterns and the relative formation energies. Extensive theoretical DFT calculations were performed to identify the most stable molecular structures. It was found that the addition of CF₃ groups to the C₈₄(23) fullerene is governed by two main rules: no additions in positions of triple hexagon junctions and predominantly para additions in C₆(CF₃)₂ hexagons on the fullerene cage. The only exception with an isolated CF₃ group in C₈₄(23)(CF₃)₁₂ is discussed in more detail.     

Fused-Pentagon Isomers of C60 Fullerene Isolated as Chloro and Trifluoromethyl Derivatives

The carbon cage of buckminsterfullerene I_h-C₆₀, which obeys the Isolated-Pentagon Rule (IPR), can be transformed to non-IPR cages in the course of high-temperature chlorination of C₆₀ or C₆₀Cl₃₀ with SbCl₅. The non-IPR chloro derivatives were isolated chromatographically (HPLC) and characterized crystallographically as ¹⁸⁰⁹C₆₀Cl₁₆, ¹⁸¹⁰C₆₀Cl₂₄, and ¹⁸⁰⁵C₆₀Cl₂₄, which contain, respectively two, four, and four pairs of fused pentagons in the carbon cage. High-temperature trifluoromethylation of the chlorination products with CF₃I afforded a non-IPR CF₃ derivative, ¹⁸⁰⁷C₆₀(CF₃)₁₂, which contains four pairs of fused pentagons in the carbon cage. Addition patterns of non-IPR chloro and CF₃ derivatives were compared and discussed in terms of the formation of stabilizing local substructures on fullerene cages. A detailed scheme of the experimentally confirmed non-IPR C₆₀ isomers obtained by Stone–Wales cage transformations is presented.     

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.     

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.     

Electronic structure of C84 and KxC84: Comparison to C60 and graphite

X ray photoemission spectra show ～10 valence band features in C₆₀ and C₈₄ films, although they are less distinct in C₈₄ because of the increased number of valence electrons and the decreased molecular symmetry. The presence of inequivalent carbon atoms in C₈₄ is reflected by the fact that the C 1s main line is ～0.2 eV wider than in C₆₀. The C 1s satellite region of C₈₄ exhibits four features within 15 eV of the main line and shows that the HOMO-LUMO π-π* excitation energy of C₈₄ is ～0.5 eV smaller than in C₆₀. Potassium 2p spectra for K-doped C₈₄ films suggest the formation of a phase with composition K₃C₈₄ with two spectroscopically-distinguishable K sites. A new spectral feature emerges when the K content is increased beyond K₃C₈₄, suggesting a phase transition and a saturated composition of K₆C₈₄, as for K_xC₆₀. These similarities are intriguing since K_xC₈₄ is insulating for all x while K₃C₆₀ is metallic and superconducting.     

Kinetics of the reactions of C2H5, n‐C3H7, and n‐C4H9 radicals with Cl2 at the temperature range 190–360 K

The kinetics of the C₂H₅ + Cl₂, n‐C₃H₇ + Cl₂, and n‐C₄H₉ + Cl₂ reactions has been studied at temperatures between 190 and 360 K using laser photolysis/photoionization mass spectrometry. Decays of radical concentrations have been monitored in time‐resolved measurements to obtain reaction rate coefficients under pseudo‐first‐order conditions. The bimolecular rate coefficients of all three reactions are independent of the helium bath gas pressure within the experimental range (0.5–5 Torr) and are found to depend on the temperature as follows (ranges are given in parenthesis): k(C₂H₅ + Cl₂) = (1.45 ± 0.04) × 10^?11 (T/300 K)^{?1.73 ± 0.09} cm³ molecule^?1 s^?1 (190–359 K), k(n‐C₃H₇ + Cl₂) = (1.88 ± 0.06) × 10^?11 (T/300 K)^{?1.57 ± 0.14} cm³ molecule^?1 s^?1 (204–363 K), and k(n‐C₄H₉ + Cl₂) = (2.21 ± 0.07) × 10^?11 (T/300 K)^{?2.38 ± 0.14} cm³ molecule^?1 s^?1 (202–359 K), with the uncertainties given as one‐standard deviations. Estimated overall uncertainties in the measured bimolecular reaction rate coefficients are ±20%. Current results are generally in good agreement with previous experiments. However, one former measurement for the bimolecular rate coefficient of C₂H₅ + Cl₂ reaction, derived at 298 K using the very low pressure reactor method, is significantly lower than obtained in this work and in previous determinations. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 614–619, 2007     

Ternäre Chloride mit trigonal-bipyramidalen Clustern: [M5(C2)]Cl9 (M = La?Pr)

Ternary Chlorides with Trigonal-Bipyramidal Clusters: [M₅(C₂)]Cl₉ (M = La? Pr) The chlorides [M₅(C₂)]Cl₉ (M = La? Pr) are obtained by metallothermic reduction of the respective trichlorides MCl₃ with caesium in the presence of the lanthanide metal and carbon in sealed niobium ampoules at 800°C. They contain trigonal-bipyramidal clusters [M₅(C₂)] crystallizing with the triclinic crystal system. Only seven of the nine edges of the trigonal bipyramids are brigded by chloride (Clⁱ). Each cluster is surrounded by twelve terminal ligands (Cl^a) so that units of the composition [M₅(C₂)Cl₇ⁱ]Cl₁₂^a have to be considered. These are connected not only via Cl^i–a and Cl^a–a–a bridges. Rather, Cl^a–a (one linear and one bent) and Cl^i–i bridges are also observed.