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.

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.

Facile Separation, Spectroscopic Identification, and Electrochemical Properties of Higher Trifluoromethylated Derivatives of [70]Fullerene.

We survey the structure and electronic properties of the family of higher trifluoromethylated C70 (CF3 )n molecules with n=14, 16, 18, and 20. Twenty-two available compounds, of which thirteen are newly obtained and characterized, demonstrate the broad diversity of π-system topologies, which enabled us to study the interplay between the CF3 addition pattern and the electronic properties. UV/Vis spectroscopic and cyclic voltammetric studies demonstrate the importance of the exact addition pattern rather than the plain number of addends. Of particular interest is the skew pentagonal pyramid (SPP) addition pattern, which enables formation of closed-shell cyclopentadienyl anions C70 (CF3 )n-1- through CF3 detachment upon electron transfer. A detailed study of the process is presented for a SPP-C70 (CF3 )16 where potentiostatic electrolysis at the second reduction potential gives C70 (CF3 )15- oxidizable to a persistent C70 (CF3 )15. radical. Together with the literature data for the lower C70 (CF3 )n compounds with n=2-12, the present results show good correlation between the experimental boundary level positions and the DFT predictions. The compounds turn out to be electron acceptor molecular semiconductors with experimental LUMO energies and HOMO-LUMO gaps within the ranges of -4.3 to -3.7 eV and 1.6 to 3.3 eV, respectively, depending on the shape of the conjugated fragments. The HOMO levels fall within the range of -5.6 to -6.9 eV and show linear correlation with the number of addends.

Evaporation Study of an Ionic Liquid with a Double-Charged Cation.

The evaporation of a dicationic ionic liquid, 1,3-bis(3-methylimidazolium-1-yl)propane bis(trifluoromethanesulfonyl)amide ([C3(MIm)22+][Tf2N-]2), was studied by Knudsen effusion mass spectrometry. Its evaporation is accompanied by a partial thermal decomposition producing monocationic ionic liquids, 1,3-dimethylimidazolium and 1-(2-propenyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)amides, as volatile products. This decomposition does not affect the vaporization characteristics of [C3(MIm)22+][Tf2N-]2, which were established to be as follows. The vaporization enthalpy (550 K) is equal to (155.5 ± 3.2) kJ·mol-1; the saturated vapor pressure is described by the equation ln( p/Pa) = -(18699 ± 381)/( T/K) + (30.21 ± 0.82) in the range of 508-583 K. 1,3-Bis(3-methylimidazolium-1-yl)propane bis(trifluoromethanesulfonyl)amide is the first dicationic ionic liquid, the vaporization characteristics of which were determined with an acceptable accuracy.

Tightly Bound Double-Caged [60]Fullerene Derivatives with Enhanced Solubility: Structural Features and Application in Solar Cells.

A series of novel highly soluble double-caged [60]fullerene derivatives were prepared by means of lithium-salt-assisted [2+3] cycloaddition. The bispheric molecules feature rigid linking of the fullerene spheres through a four-membered cycle and a pyrrolizidine bridge with an ester function CO2 R (R=n-decyl, n-octadecyl, benzyl, and n-butyl; compounds 1 a-d, respectively), as demonstrated by NMR spectroscopy and X-ray diffraction. Cyclic voltammetry studies revealed three closely overlapping pairs of reversible peaks owing to consecutive one-electron reductions of fullerene cages, as well as an irreversible oxidation peak attributed to abstraction of an electron from the nitrogen lone-electron pair. Owing to charge delocalization over both carbon cages, compounds 1 a-d are characterized by upshifted energies of frontier molecular orbitals, a narrowed bandgap, and reduced electron-transfer reorganization energy relative to pristine C60 . Neat thin films of the n-decyl compound 1 a demonstrated electron mobility of (1.3±0.4)×10-3  cm2 V-1 s-1 , which was comparable to phenyl-C61 -butyric acid methyl ester (PCBM) and thus potentially advantageous for organic solar cells (OSC). Application of 1 in OSC allowed a twofold increase in the power conversion efficiencies of as-cast poly(3-hexylthiophene-2,5-diyl) (P3HT)/1 devices relative to the as-cast P3HT/PCBM ones. This is attributed to the good solubility of 1 and their enhanced charge-transport properties - both intramolecular, owing to tightly linked fullerene cages, and intermolecular, owing to the large number of close contacts between the neighboring double-caged molecules. Test P3HT/1 OSCs demonstrated power-conversion efficiencies up to 2.6 % (1 a). Surprisingly low optimal content of double-caged fullerene acceptor 1 in the photoactive layer (≈30 wt %) favored better light harvesting and carrier transport owing to the greater content of P3HT and its higher degree of crystallinity.

Fullerene as Photocatalyst: Visible-Light Induced Reaction of Perfluorinated α,ω-Diiodoalkanes with C60.

Solution phase photochemical reaction of fullerene with perfluorinated alkyldiiodides I-RF-I can be efficiently initiated by visible range irradiation that targets solely the fullerene component. Photoinduced electron transfer from fullerene onto the diiodide component effects dissociative formation of alkyl radicals RFI• subsequently consumed by C60 to give the principal detectable radical intermediate C60RFI•. Experimentally established second-order kinetics with respect to the fullerene concentration evidence that fullerene plays its two roles of photocatalyst and reactant in a decoupled fashion, which suggests its catalytic ability to be of potential use in more complex photochemical systems. The main final product of the photochemical transformation observed is the singly linked dimer of the intermediates, I-RF-C60-C60-RF-I. Side reactions of C60RFI• with the environment lead to quenching of the unpaired electron density by ortho- or para- attachment of hydrogen or iodine. The outlined kinetic findings are discussed in detail.

Mass spectrometric studies of 1-ethyl-3-methylimidazolium and 1-propyl-2,3-dimethylimidazolium bis(trifluoromethyl)-sulfonylimides.

RATIONALE: Ionic liquids ([Cat(+)][An(-)]) were believed to decompose before reaching vaporization temperatures, but recently some of them have been shown to vaporize congruently. Low-temperature vaporization of ionic substances is an intriguing phenomenon, so the vapor-phase composition and reactions of ionic liquids deserve more extensive study. METHODS: Evaporation of two ionic liquids, [C2MIM(+)][Tf2 N(-)] and [C3MMIM(+)][Tf2N(-)], was studied by means of Knudsen effusion mass spectrometry. These liquids were also characterized using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry, UV/Vis, IR, NMR spectroscopy, and elemental analysis. RESULTS: The vaporization enthalpies of (118 ± 3) and (124 ± 2) kJ·mol(-1) were determined for [C2MIM(+)][Tf2N(-)] and [C3MMIM(+)][Tf2N(-)], respectively. The corresponding equations for their saturated vapor pressures are: ln(p{[C2MIM(+)][Tf2N(-)]}/Pa) = -(14213 ± 325)/(T/K) + (26.57 ± 1.04), ln(p{[C2MMIM(+)][Tf2N(-)]}/Pa) = -(14868 ± 221)/(T/K) + (27.19 ± 0.60). The MALDI studies (positive and negative ion modes) enabled detection of monomeric [Cat(+)] and [An(-)] ions, the cluster ions {[Cat(+)]2 [An(-)]}(+) and {[Cat(+)][An(-)]2}(-), and some complex anions {2[An(-)] + Na(+)}(-), {2[An(-)] + K(+)}(-), {2[An(-)] + Cu(+)}(-) and {3[An(-)] + Ca(2+)}(-). CONCLUSIONS: Knudsen effusion mass spectrometry proved to be a valuable method to study the thermodynamics of ionic liquids. The saturated vapor pressure and vaporization enthalpy of [C3MMIM(+)][Tf2N(-)] were accurately determined for the first time. MALDI is also capable of providing indirect information on hydrogen bonding.

Orienting Effect of the Cage Addends: The Case of Nucleophilic Cyclopropanation of C2 -C70 (CF3 )8.

C2 -C70 (CF3 )8 was found to be a very promising substrate in the Bingel and the Bingel-Hirsch reactions combining perfect regioselectivity with much higher reactivity compared to its analogs. The reactions with diethyl malonate yield a single isomer of the monoadduct C70 (CF3 )8 [C(CO2 Et)2 ] and a single C2 -symmetrical bisadduct C70 (CF3 )8 [C(CO2 Et)2 ]2 . The Bingel-Hirsch variation is particularly interesting in that it additionally affords, in a similar regioselective manner, the unexpected alkylated derivatives C70 (CF3 )8 [CH(CO2 Et)2 ]H and C70 (CF3 )8 [C(CO2 Et)2 ][CH(CO2 Et)2 ]H. The novel compounds have been isolated and structurally characterized by means of (1) H and (19) F NMR spectroscopy as well as single-crystal X-ray diffraction. The mechanistic and regiochemical aspects of the reaction are explained with the aid of DFT calculations.

C100 is Converted into C94 Cl22 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.

Transalkylation of higher trifluoromethylated fullerenes with C70: a pathway to new addition patterns of C70(CF3)8.

We report three new isomers of C70(CF3)8, structurally related to p(7)mp-C70(CF3)10, that are inaccessible by direct trifluoromethylation, but can be easily identified among the products of the transalkylation of higher trifluoromethylfullerenes with C70. The reported compounds are characterized by UV/Vis, 1 D and 2 D COSY (19)F NMR spectroscopy, and DFT calculations. A rather unusual addition pattern is observed in p(6),i-C70(CF3)8 in which one addend is attached remotely from the others; polarization of the adjacent unsaturated bonds by the addend makes the molecule readily oxidizable.

Alkali-metal trichloroacetates for dichloromethylenation of fullerenes: nucleophilic addition-substitution route.

The first experimental evidence that fullerenes react with alkali-metal trichloroacetates through a nucleophilic addition-substitution route, yielding dichloromethylenefullerenes as the final products, is reported. The intermediates, C60 (CCl3 )(-) and C70 (CCl3 )(-) anions, have been isolated in their protonated forms as ortho-C60 (CCl3 )H, as well as three ortho and one para isomer of C70 (CCl3 )H. The structures were unambiguously determined by means of (1) H, (13) C, and (1) H-(13) C HMBC NMR spectroscopy along with UV/Vis spectroscopy. The observed regiochemistry was analyzed with the aid of quantum chemical calculations. Conversion of the protonated compounds into the [6,6]-closed C60/70 (CCl2 ) cycloadducts under basic conditions can be effected only for the ortho isomers, whereas para-C70 (CCl3 )H decomposes back into pristine C70 .

Cage shrinkage of fullerene via a C2 loss: from IPR C90(28)Cl24 to nonclassical, heptagon-containing C88Cl22/24.

A new case of chlorination-promoted fullerene cage shrinkage is reported. Chlorination of C90 (isolated pentagon rule isomer no. 28) with VCl4 afforded C88Cl22 with a nonclassic carbon cage (NCC) containing 1 heptagon and 13 pentagons including 2 fused pairs flanking the heptagon. The pathway of C2 abstraction from the C90 cage is suggested on the basis of density functional theory calculations.

Trifluoromethylation of fullerenes: kinetic and thermodynamic control.

We present a survey and theoretical interpretation of the experimental results on trifluoromethylation of fullerenes. A thermodynamic model has been developed to describe the C60/70(CF3)n condensed phase mixtures capable of free exchange of addends and, consequently, of isomerization and changing the degrees of addition. It was found that the purely thermodynamic model affords at least satisfactory prediction of composition of products even for apparently nonequilibrium syntheses. Special cases can be identified by means of detailed kinetic modeling based on the BEP approach, which includes stepwise energetic analysis of the possible trifluoromethylation sequences. This analysis reveals two types of reactions with remarkable difference in rates: direct trifluoromethylation and rearrangements of the CF3 groups. Whenever a particular group of compounds is interrelated through direct addition/abstraction of CF3 groups, it is more or less safe to assume that the said group is in equilibrium describable by the thermodynamic model. In the same time, the slower migration of addends is controlled kinetically, and interference of the sublimation processes frequently prevents its equilibration. Among the most illustrative examples of hindered formation via rearrangements in absence of sufficiently favorable direct trifluoromethylation pathways are certain isomers of the C3v-C60(CF3)18, C70(CF3)18, and C70(CF3)20 compounds.

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 D2d-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.

Synthesis, structure, and theoretical study of trifluoromethyl derivatives of C84(22) fullerene.

Trifluoromethylation of higher fullerene mixtures with CF(3)I 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 CF(3) derivatives of D(2)-C(84) (isomer 22). Molecular structures of two isomers of C(84)(22)(CF(3))(12), two isomers of C(84)(22)(CF(3))(14), four isomers of C(84)(22)(CF(3))(16), and one isomer of C(84)(22)(CF(3))(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 CF(3) derivatives, C(84)(22)(CF(3))(2-10). It was found that the addition of CF(3) groups to C(84)(22) is governed by two rules: additions can only occur at para positions of C(6)(CF(3))(2) hexagons and no additions can occur at triple-hexagon-junction positions on the fullerene cage.

Skeletal transformation of isolated pentagon rule (IPR) fullerene C82 into non-IPR C82Cl28 with notably low activation barriers.

A novel case of chlorination-promoted skeletal transformation in higher fullerenes is reported. Chlorination of C(82) [isolated pentagon rule (IPR) isomer no. 3] with SbCl(5) results in two consecutive Stone-Wales rearrangements into non-IPR C(82)Cl(28) with one pair of fused pentagons. An extensive theoretical study of the transformation pathways in C(82) revealed that the thermodynamically favorable rearrangement into non-IPR C(82)Cl(28) needs a comparatively low activation energy.

Capturing C84 isomers as chlorides and pentafluoroethyl derivatives: C84Cl22 and C84(C2F5)12.

A mixture of higher fullerenes C(76)-C(96) was pentafluoroethylated with C(2)F(5)I at 250 °C affording a mixture of C(2)F(5) derivatives. After separation with high-performance liquid chromatography, the second C(2)F(5) derivative of C(84)(16), C(84)(C(2)F(5))(12), was investigated by X-ray crystallography and compared with the known isomer in terms of addition patterns and formation energies. Chlorination of a C(84) isomeric mixture with VCl(4) at 350-400 °C resulted in the formation of C(84)Cl(22). X-ray diffraction study revealed the superposition of several C(84)Cl(22) molecules with different isomeric C(84) cages but the same chlorination pattern.

Unexpected fullerene dimerization via [5,6]-bond upon functionalization of C(s)-C70(CF3)8 by the Bingel reaction.

The Bingel reaction of the C(s) isomer of C(70)(CF(3))(8) has been found to yield two C(70)(CF(3))(8)[C(CO(2)Et)(2)] monoadducts and one C(70)(CF(3))(8)[C(CO(2)Et)(2)](2) bisadduct as its major products. Malonate addition occurs at those [6,6]-bonds that radiate from the polar pentagons of the C(70)(CF(3))(8) cage. Unexpectedly, X-ray single crystal analysis reveals dimerization of the above substances during crystallization, providing two isomers of {C(70)(CF(3))(8)[C(CO(2)Et)(2)]}(2), one isomer of {C(70)(CF(3))(8)[C(CO(2)Et)(2)](2)}(2) and {C(70)(CF(3))(8)}(2). This dimerization represents [2+2]-cycloaddition via [5,6]-bonds and results in functionalization patterns resembling several known C(70)X(10) derivatives.

Smooth and jump-like metal-dielectric transitions in single-walled carbon nanotubes under functionalization.

We examine at the DFT level of theory the topology of side wall functionalization of the (5,5)metallic single-wall carbon nanotube (CNT) with carbenes (>CX(2)) and its effect on electronic properties of the system. It is demonstrated that specific substructures/topology known to stabilize functionalized fullerene molecules can play the same role in CNTs, as well. Upon deepening of functionalization, "uniformity" of addition motives and related continuous changes in properties transform into regular addition patterns with isolated aromatic islands on the nanotube backbone that give rise to jump-like changes in electronic structure.