Non-classical (NC), heptagon-containing fullerenes obtained via chlorination-promoted cage transformations: C76(NC2a)Cl24 and C76(NC2b)Cl28.

High-temperature chlorination of C76 fullerene with SbCl5 proceeds via five Stone-Wales rearrangements, resulting in non-classical (NC) C76(NC1a)Cl24 with two heptagons and 14 pentagons partically fused in pairs and triples. C76(NC2b)Cl28 with isomeric carbon cage was obtained by chlorination-promoted cage shrinkage of C80via two C2 losses. The pathways of skeletal cage trasformations, the chlorination patterns, and formation energies are discussed in detail.

Chlorination-Promoted Skeletal Transformations in Isolated-Pentagon Rule (IPR) Isomers of Fullerene C86 to Non-IPR Chloro- and Trifluoromethyl Derivatives.

Fullerene C86 contains two isomers obeying the Isolated-Pentagon Rule (IPR), CS-C86(16) and C2-C86(17). Both isomers undergo unprecedented skeletal transformations at high-temperature (400 °C) chlorination with SbCl5. One-step Stone-Wales rearrangement (SWR) in C86(17) results in the pentagon-fused #63614C86 cage found in the structure of #63614C86Cl24. CF3 derivatives with the same cage, two isomers of #63614C86(CF3)18 and #63614C86(CF3)18O2, were obtained by high-temperature trifluoromethylation of the chlorination products with CF3I, followed by HPLC separation. The skeletal transformation of C86(16) proceeds via two SWRs under the formation of a #63624C86 cage with one fused-pentagon pair found in the structure of #63624C86(CF3)18. The addition patterns in skeletally transformed molecules are discussed in detail, disclosing the influence of the pentagon fusions, isolated C=C bonds, and benzenoid rings on the stability of the molecules with non-IPR C86 cages. The chlorination-promoted SWRs in C86 isomers have been observed for the first time, which contribute a lot to the understanding of skeletal transformations in fullerenes.

Dimeric and 1D polymeric low-chlorinated C60 fullerenes, (C60Cl5)2 and (C60Cl4)∞.

Low-chlorinated fullerenes, dimeric (C60Cl5)2 and one-dimensional, polymeric (C60Cl4)∞, were obtained by high-temperature (270 °C) chlorination of C60 with a SbCl5/SbCl3 mixture, as revealed by X-ray crystallography. The compounds were characterized by IR and Raman spectroscopy and theoretical calculations. This is the first observation of a fullerene polymer with single C-C bonding and neutral building blocks.

Structural Chemistry of Pentagon-Fused C82 Fullerene Derivatives #39173C82(CF3)14,16,18 and #39173C82Cl28.

High-temperature chlorination of the most stable Isolated-Pentagon-Rule (IPR) isomer of fullerene C82, C2-C82(3), invariably produces non-IPR #39173C82Cl28, containing one pentagon-pentagon fusion in the carbon cage. High-temperature trifluoromethylation of #39173C82Cl28 followed by HPLC separation resulted in the isolation and structure elucidation of eight #39173C82(CF3)n (n = 14, 16, 18) compounds. Structural chemistry of #39173C82(CF3)14,16,18 and #39173C82Cl28 is characterized by the variation of the addition patterns in the region of a pentagon-pentagon fusion. The regiochemistry of CF3 addition in the remaining cage region is similar to that of the known IPR C82(3)(CF3)n compounds. Theoretical calculations revealed that #39173C82(CF3)n possess lower thermodynamic stability than isomeric IPR derivatives.

Fused-Pentagon Carbon Cages in Chloro and Trifluoromethyl Derivatives of C60: Non-IPR 1809C60Cl8, 1806C60(CF3)14, and Nonclassical C60(NC)Cl14.

High-temperature chlorination of conventional IPR C60 can produce chloro derivatives of non-IPR C60 by skeletal transformations via Stone-Wales rearrangements (SWRs) of the carbon cage. We report the synthesis and structure elucidation of non-IPR 1809C60Cl8 and nonclassical C60(NC)Cl14. The present isolation of 1809C60Cl8 hints at the possibility that the same product in the previously reported chlorine-doped arc-discharge synthesis could have, likewise, resulted from the initially formed IPR C60. C60(NC)Cl14 is the first chloride containing a nonclassical carbon cage with one heptagon and 13 pentagons known previously only in a CF3 derivative. Additionally, trifluoromethylation of non-IPR chlorides revealed the formation of 1806C60(CF3)14 with a new non-IPR carbon cage and unusual trifluoromethylation pattern. Thereby, the number of different, structurally confirmed non-IPR carbon cages of C60 now reaches eight.

Reversibly switchable methanofullerene by photoexcitation and reduction.

A cyclopropanated derivative of the trifluoromethylated fullerene Cs-C70(CF3)8 demonstrates reversible switching behavior triggered by excited state electron transfer or by negative charging. The switching between the state with connected 62-electron π-system and the state with disjoint 28- and 32-electron conjugated caps is effected by opening/closure of the cyclopropanated bond. A pronounced alteration of the electronic properties upon seemingly minor changes in a large fullerene molecule is an attractive feature for the organic electronic devices where similar fullerene compounds are commonly utilized as electron acceptor materials.

Oxidized Carbon-Based Spacers for Pressure-Resistant Graphene Oxide Membranes.

In this study, we report the influence of carbon-based spacer-oxidized derivatives of fullerenes (fullerenols) C60(OH)26−32 and graphene oxide nanoribbons on the performance and pressure stability of graphene-oxide-based composite membranes. The impact of the intercalant shape and composition on the permeance of the selective layers for water vapors has been studied under pressure gradients. It is shown that the insertion of ball-shaped fullerenols between graphene oxide nanoflakes allows a suppression in irreversible permeance loss to 2−4.5% and reversible permeance loss to <25% (at 0.1 MPa), while retaining large H2O/N2 selectivities of up to ~30,000. The demonstrated approach opens avenues for the highly effective stabilization of GO membranes at elevated pressures for industrial-scale dehumidification.

Difluoromethylenation of fullerene C70 provides isomeric diversity and availability of equatorial [5,6]-homofullerene C70(CF2).

We report synthesis, isolation, and spectroscopic characterization of the novel [5,6]-open C70(CF2) isomer III along with the already known [6,6]-closed and [6,6]-open C70(CF2) isomers I and II. The compounds were obtained in a ratio of I : II : III = 4 : 6 : 1 by means of thermal treatment of C70 fullerene with sodium chlorodifluoroacetate. This product composition is explained with the use of quantum chemical calculations that identify the reaction pathway as a two-stage nucleophilic cyclopropanation rather than the previously postulated carbene addition. We further report the first cyclic voltametric studies for the whole set of isomers of C70(CF2). Together with the DFT data, they demonstrate that the LUMO is stabilized in both isomer II ([6,6]-open) and III ([5,6]-open) by 0.1 eV with respect to the pristine C70, and isomer III has the lowest reorganization energy of all.

Crippling the C70 fullerene: non-classical C68Cl26(OH)2 and C68Cl25(OH)3 with three heptagons and only fused pentagons via chlorination-promoted skeletal transformations.

High-temperature (440 °C) chlorination of C70 with SbCl5 promotes Stone-Wales transformations and loss of the C2 fragment, which results in a non-classical C68Cl28 partially hydrolyzed to C68Cl26(OH)2 and C68Cl25(OH)3. X-ray diffraction reveals an unprecedented C68 cage with three heptagons and 15 pentagons arranged in fused pairs and triples. The shortest possible transformation pathways include one C2 loss step and four Stone-Wales transformation steps.

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.

Fused-Pentagon C70Cl6 and C70Cl8 Obtained via Chlorination-Promoted Skeletal Transformation of IPR C70.

The isolated-pentagon-rule (IPR) D5h-C70 fullerene is least susceptible to skeletal transformations in comparison with higher fullerenes and even C60. A cage transformation in IPR C70 via a one-step Stone-Wales rearrangement was accomplished by high-temperature (440 °C) ampule chlorination with SbCl5. Subsequent dechlorination at 450 °C, followed by high-performance liquid chromatography separation, allowed the isolation of non-IPR C70Cl6 and C70Cl8. X-ray diffraction study revealed the presence of an unprecedented C70 carbon cage, possessing two pairs of fused pentagons and the chlorination patterns located on one cage hemisphere. A high energetic and thermal stability of both non-IPR chlorides was also confirmed by theoretical calculations of formation energies. Pathways of skeletal transformations of IPR C70 in comparison with those in C60 are discussed.

Regioselective Mono- and Dialkylation of [6,6]-open C60 (CF2 ): Synthetic and Kinetic Aspects.

Alkylation of homofullerene [6,6]-C60 (CF2 )2- dianion with the set of alkyl halides, RX, was established to demonstrate an effect of RX nature on the conversion, product composition, and regioselectivity. The respective C60 (CF2 )RH, C60 (CF2 )R2 and C60 (CF2 )R'R'' compounds were obtained in the reaction with sterically unhindered RX, isolated by HPLC and unequivocally characterized. The kinetic studies evidenced SN 2 mechanism for both alkylation steps, yielding mono- and dialkylated C60 (CF2 ), respectively, and indicated the negative charge localization at the bridgehead carbon atoms as well as a steric hindrance of the CF2 moiety likely to be a key factors for the SN 2 reaction mechanism and observed regioselectivity. The significant difference in the rate constants of the first and the second steps is attributed to the different activation barriers predicted by DFT calculations which makes possible to develop synthetic methods for the regioselective preparation of monoalkylated C60 (CF2 )RH and heterodialkylated C60 (CF2 )R'R'' derivatives.

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

The carbon cage of buckminsterfullerene Ih -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 C60 Cl30 with SbCl5 . The non-IPR chloro derivatives were isolated chromatographically (HPLC) and characterized crystallographically as 1809 C60 Cl16 , 1810 C60 Cl24 , and 1805 C60 Cl24 , which contain, respectively two, four, and four pairs of fused pentagons in the carbon cage. High-temperature trifluoromethylation of the chlorination products with CF3 I afforded a non-IPR CF3 derivative, 1807 C60 (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.

Fused-pentagon C70Cl26 obtained via chlorination-promoted Stone-Wales cage transformations of C70.

High-temperature (360 °C) chlorination of C70 with VCl4 or SbCl5 yields only IPR C70Cl26/28. Chlorination with SbCl5 at 440 °C resulted in a skeletal transformation via a two-step Stone-Wales rearrangement and the formation of non-IPR 8005C70Cl26 with two fused pentagon pairs in the carbon cage which was established by single crystal X-ray diffraction.

Electronic Communication between S=1/2 Spins in Negatively-charged Double-caged Fullerene C60 Derivative Bonded by Two Single Bonds and Pyrrolizidine Bridge.

Radical anion salt {cryptand[2.2.2] (K+ )}2 (bispheroid)2- ⋅3.5C6 H4 Cl2 (1) of the double-caged fullerene C60 derivative, in which fullerene cages are linked by a cyclobutane bridging cycle and additionally by a pyrrolizidine moiety, was obtained. Each fullerene cage in this derivative accepts one electron on reduction, thus forming the (bispheroid)2- dianions with two interacting S=1/2 spins on the neighboring cages. Low-temperature magnetic measurements reveal a singlet ground state of the bispheroid dianions whereas triplet contributions prevail at increased temperature. An estimated exchange interaction between two spins J/kB =-78 K in 1 indicates strong magnetic coupling between them, nearly two times higher than that (J/kB =-44.7 K) in previously studied (C60 - )2 dimers linked via a cyclobutane bridge only. The enhancement of magnetic coupling in 1 can be explained by a shorter distance between the fullerene cages and, possibly, an additional channel for the magnetic exchange provided by a pyrrolizidine bridge. Quantum-chemical calculations of the lowest electronic state of the dianions by means of multi-configuration quasi-degenerate perturbation theory support the experimental findings.

Rebuilding C60: Chlorination-Promoted Transformations of the Buckminsterfullerene into Pentagon-Fused C60 Derivatives.

In recent years, many higher fullerenes that obey the isolated pentagon rule (IPR) were found capable of rearranging into molecules with adjacent pentagons and even with heptagons via chlorination-promoted skeletal transformations. However, the key fullerene, buckminsterfullerene I h-C60, long seemed insusceptible to such rearrangements. Now we demonstrate that buckminsterfullerene yet can be transformed by chlorination with SbCl5 at 420-440 °C and report X-ray structures for the thus-obtained library of non-IPR derivatives. The most remarkable of them are non-IPR C60Cl24 and C60Cl20 with fundamentally rearranged carbon skeletons featuring, respectively, four and five fused pentagon pairs (FPPs). Further high-temperature trifluoromethylation of the chlorinated mixture afforded additional non-IPR derivatives C60(CF3)10 and C60(CF3)14, both with two FPPs, and a nonclassical C60(CF3)15F with a heptagon, two FPPs, and a fully fused pentagon triple. We discuss the general features of the addition patterns in the new non-IPR compounds and probable pathways of their formation via successive Stone-Wales rearrangements.

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

High-temperature chlorination of an Isolated-Pentagon Rule (IPR) D2-C76 fullerene followed by high-temperature trifluoromethylation of non-IPR C76 chlorides with CF3I unexpectedly resulted in a series of non-IPR C76(CF3)nFm compounds. X-ray diffraction study with the use of synchrotron radiation revealed the mixed CF3/F structures of non-classical, non-IPR C76(CF3)14, C76(CF3)14F2, and C76(CF3)16F6.

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 (NC2)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 (NC3)Cl24 containing three cage heptagons.

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.