An Unconventional Hydrofullerene C66H4 with Symmetric Heptagons

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An Unconventional Hydrofullerene C66H4 with Symmetric Heptagons Retrieved in Low-Pressure Combustion Han-Rui Tian, Miao-Miao Chen, Kai Wang, Zuo-Chang Chen, Chao-Yong Fu, Qianyan Zhang, Shu-Hui Li, Shun-Liu Deng, Yang-Rong Yao, Su-Yuan Xie, Rong-Bin Huang, and Lan-Sun Zheng J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.9b01638 • Publication Date (Web): 18 Mar 2019 Downloaded from http://pubs.acs.org on March 18, 2019

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Journal of the American Chemical Society

An Unconventional Hydrofullerene C66H4 with Symmetric Heptagons Retrieved in Low-Pressure Combustion Han-Rui Tian⊥, Miao-Miao Chen⊥, Kai Wang, Zuo-Chang Chen, Chao-Yong Fu, Qianyan Zhang*, Shu-Hui Li, Shun-Liu Deng*, Yang-Rong Yao, Su-Yuan Xie*, Rong-Bin Huang, Lan-Sun Zheng State Key Lab for Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 (China) ABSTRACT: The combustion has long been applied for industrial synthesis of carbon materials such as fullerenes as well as carbon particles (known as carbon black), but the components and structures of the carbon soot are far from clarification. Herein, we retrieve an unprecedented hydrofullerene C66H4 from a soot of a low-pressure combustion of benzene-acetylene-oxygen. Unambiguously characterized by single-crystal X-ray diffraction, the C66H4 renders a nonclassical geometry incorporating two heptagons and two pairs of fused pentagons in a C2v symmetry. The common vertexes of the fused pentagons are bonded with four hydrogen atoms to convert the hydrogen-linking carbon atoms from sp2 to sp3 hybridization, which together with the adjacent heptagons essentially release the sp2-bond strains on the abutting-pentagon sites of the di-heptagonal fused pentagon C66 (dihept-C66). DFT computations suggest the possibility for in situ hydrogenation process leading to stabilization of the dihept-C66. In addition, the experiments have been carried out to study heptagons dependent properties of dihept-C66H4, indicating the key responsibility of heptagon for changing hydrocarbon activity and electronic properties. The present work with the unprecedented double-heptagons-containing hydrofullerene successfully isolated and identified as one of the low-pressure combustion products marks that the heptagon is new building block for constructing fullerene products in addition to pentagons and hexagons in the lowpressure combustion system.

INTRODUCTION The history for human being to use fire can be traced back to ancient times. When people began to use fire, they noticed that combustion produced the carbon soot, which actually contains carbon-rich derivatives as well as carbon particles that have now been widely applied as raw materials (known as carbon black) in rubber industry.1-4 The composition of the carbon soot, however, is very complex and changeable on reaction conditions. The combustion in low-pressure with a proper C/O rate has been reported for the synthesis of fullerenes in 1991.5 Such a combustion method stands out because it is a continuous process particularly efficient for industrial amplification for synthesis of fullerenes in larger scale, superior to other synthetic methods such as arcdischarge,6 pyrolysis,7 microwave plasma,8 glow discharg9 as well as organic synthesis.10, 11 However, fundamental attentions paid to the combustion were apparently less than other synthetic methods such as arc-discharge for fullerene formation. The reaction mechanism responsible for fullerenes formation as well as carbon particle growth in the combustion is still unclear,12 and the fullerene

components in the carbon soot are still far from well known. Until 2010 the fullerenes (including C60, C70 and larger fullerenes) and their hydrogenated derivatives from combustion soot strictly complied with the Isolated Pentagon Rule (IPR)13, stating that the stable fullerene should have all its 12 pentagons separation to each other. The combustion-produced non-IPR fullerenes have recently been reported, including a C64 with tripledirectly-fused pentagons and a C60 isomer with doublefused pentagons.14, 15 The smaller fullerene C50 with ten pairs of double-fused pentagons has been retrieved in combustion soot as well.16 Here we report an unprecedented non-IPR hydrofullerene C66H4 bearing two heptagons from a lowpressure benzene-acetylene-oxygen diffusion flame for the first time. The structure of C66H4 has been unambiguously identified by single-crystal X-ray crystallography, revealing that C66H4 has two heptagons with adjacencies of fused pentagons. The strain in the fused pentagons can be released by the adjacent heptagons and exohedral addition of four hydrogen atoms that converting the hydrogen-linking carbon atoms from sp2 to sp3 hybridization. DFT computations suggest that

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in situ hydrogenation process is critical for stabilizing the di-heptagonal C66H4 (named as dihept-C66H4 in this work) that is starkly different from other four isomers of C66 stabilized so far in arc-discharge experimentally.17-19 Considering the key responsibility of heptagon for changing geometric structures and electronic properties of the experimentally available carbon allotropes with negatively curved moieties,20-29 the occurrence of heptagon among the products of combustion might have a milestone significance as all the previously reported carbon allotropes from flame are positively curved. Notably, the dihept-C66 is also the minimum fullerene cage containing two heptagons synthesized to date. A number of heptagon-containing fullerenes have been experimentally synthesized by endohedral or exohedral derivatization,30-46 and some of them even contain more than one heptagon.33-35, 37, 40-42 Most of the previously reported heptagonal fullerenes were modified and shrunken from conventional fullerenes by chemical reactions. Only three cases of fullerenes with one heptagon (hept-C68Cl644, LaSc2N@Cs(hept)-C8045, 46 Sc2C2@Cs(hept)-C88 ) were directly produced in situ and isolated from the pristine products of arc-discharge. By contrast, the dihept-C66 we report here is the first fullerene cage with two heptagons captured in situ carbon-clustering growth process of combustion.

C66H4 shown (Figure S2), the pure dihept-C66H4 is very stable with strong peak at m/z 796.0 and difficult to dissociate into any fragment ions. To research the thermostability of dihept-C66H4 in gaseous phase, we carried out a series of mass spectrometric experiments at different ionization temperatures. As shown in Figure 1, molecular ions of dihept-C66H4 are always overwhelming at the temperature ranging from 200 to 500 °C. The dihept-C66H4 began to dissociate into pristine C66 cage if the ionization temperature was arisen to 450 °C. It is markedly different from the previously reported evidence8 that hydrofullerene of IPR C60 was readily decomposed into C60 fragments in the range of 300~350 °C, and dehydrogenation of non-IPR #1809C60H8 was occurred at the ionization temperatures going up to 350 °C. Notably, an obvious signal at m/z 792.0 belonging to C66 pristine cage can be detected at 500°C, indicating that the pristine dihept-C66 has a lifetime in the gas phase and possibility to be captured by chemical manipulation.

RESULT AND DISCUSSION Preparation and Isolation of Dihept-C66H4. The hydrofullerene-containing soot was synthesized in situ low-pressure combustion with a benzene-acetyleneoxygen diffusion flame15. The collected carbon soot was extracted with toluene by means of ultrasound and followed by filtration. The crude toluene-extracts are very complex and typically contain lots of polycyclic aromatic hydrocarbons (PAHs), empty fullerene cages and hydrofullerene derivatives. Therefore, multiple-stages of HPLC were performed to separate and purify the sample of dihept-C66H4 out of the crude toluene-extracting solution using a Cosmosil buckyprep column (I.D. 10 × 250 mm) and a Cosmosil 5PPB column (I.D. 10 × 250 mm) alternately. The procedure for the isolation of diheptC66H4 included six stages of HPLC runs with toluene as the mobile phase; the last three runs were performed in a recycling mode. The dihept-C66H4-containing fractions were confirmed by mass spectrometry in each step. After six cycles of separation, dihept-C66H4 with high purity (up to 99%) was obtained (Figure S1). Mass Spectrometric Analysis of Dihept-C66H4. The molecular weight of dihept-C66H4 was characterized by the mass spectrometry with atmospheric pressure chemical ionization (APCI) source. As shown in Figure 1, high purity of the isolated sample was identified by the strong and single peak at m/z 796.0 corresponding to the theoretical simulated molecular formula of dihept-C66H4, and the isotopic distribution of the experimental mass spectra matches nicely with the calculated peaks for dihept-C66H4. As the multistage mass spectra of dihept-

Figure 1. APCI-MS and thermostability studies of diheptC66H4 at different ionization temperatures. Experimental and simulated isotopic distributions for the molecular ions are inset. Crystallographic Identification of Dihept-C66H4. A black single crystal of dihept-C66H4 was obtained by slow evaporation of solvent from a toluene solution. The structure was unambiguously identified by single-crystal X-ray diffraction (the crystallographic data are listed in Table S1). The crystallographic data reveal the diheptC66H4 cage with C2v symmetry having 19 hexagons, 14 pentagons and 2 heptagons. Heptagon is a necessary building block for carbon allotrope with negative curvature28. The occurrence of heptagonal structure in the products of combustion has meaningful implication because, to our knowledge, all the previously combustion-produced carbon materials such as carbon particles and classical fullerenes are positively curved. In addition, the structure of hept-C66H4 has double negatively curved moieties with a two-fold symmetric axis, that are an import step towards longsought negatively curved carbon structures such as the theoretically well-defined Schwarzite carbon allotrope 22. Starting from this point, any more heptagons are highly expected to be included in the combustion process and it


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Journal of the American Chemical Society would be helpful for understanding the formation mechanism of carbon materials with negative curvature. As shown in Figure 2, the dihept-C66H4 involves in each of the two heptagons fused to an adjacent pentagons pair. Such a geometric structure is well coincided with the structural consequences of Euler’s theorem applied to fullerenes with pentagons, hexagons, and heptagons47, stating that the most stable isomers of heptagoncontaining fullerenes usually involve the heptagon fused to a pair of adjacent pentagons. Interestingly, the bottom part of the dihept-C66H4 structure has the same geometry as C60 (Figure 2). On the top the four pentagons connect to form two pairs of fused pentagons, in which reactive carbon atoms at the fused pentagon common edges are saturated by exohedral addends, in the present case the hydrogen addition, transforming the hydrogenated carbon atoms from sp2 to sp3 hybridization. Consequently, the four hydrogen atoms bond to the common vertexes of fused pentagons to relieve the unfavorable local strain and make the elusive structure stable. The shortest C-C bond lengths in the heptagons are 1.359(11) Å and 1.369(11) Å for two different cage orientations respectively. Note that these bonds are shorter than the other Csp2=Csp2 bonds in the diheptC66H4. However, the length of C-C bond formed by the hydrogenated atoms is 1.590, 1.588, 1.592, 1.570 Å in the asymmetric unit respectively, longer than any other single carbon bonds in the dihept-C66H4 (Figure Table S2). All bond lengths of Csp3-H (0.98 Å) in the dihept-C66H4 cage are substantially shorter than the Csp3-H (1.09 Å) in alkane48, 49.

6.06, 6.06 ppm) and the high field signal is another sextet split (5.95, 5.94, 5.94, 5.93, 5.92, 5.92 ppm) due to 1H-1H coupling. Considering the symmetry of C66H4 and the shielding effect influenced by the heptagons, it is reasonable to assign the signals in low field to the two equivalent H1 and H4, whereas the signals in high field can be assigned as the two equivalent H2 and H3 (Figure 2a). Together with the multistage mass spectra of diheptC66H4 having the four hydrogen atoms hard to shuck off, the NMR data corroborate the hydrogen atoms being bonded in the common vertexes of fused pentagons, absolutely coinciding with the X-ray crystallographic structure. Spectroscopic Study of Dihept-C66H4. The purified dihept-C66H4 dissolves well and presents a deep brown color in commonly used solvents such as toluene and carbon disulfide. The UV-Vis absorption spectrum of the high purity dihept-C66H4 dissolved in toluene is shown in Figure 3a. The longest absorption of dihept-C66H4 begins with a weak peak at 684 nm, followed by a series of major absorption peaks at 312, 340, 400 and 465 nm with weak shoulder peaks at 584 and 626 nm. There is no more discernible absorption in the near-IR region.

Figure 2. Two views of the structure of dihept-C66H4 as drawing with thermal ellipsoids at 50% probability level. The second dihept-C66H4 and the toluene molecules in the asymmetric unit are omitted for clarity. The two pairs of fused pentagons are highlighted in red, and the two heptagons are highlighted in green. To confirm the location of the hydrogen atoms on the dihept-C66H4 cage, macroscopic quantities of the sample were isolated and purified for 1H NMR identification on a 500 MHz spectrometer. As shown in Figure S4, the 1H NMR spectrum of dihept-C66H4 exhibits two groups of hydrogen and the integral ratios are nearly 1:1. A high resolution 1H NMR spectroscopic study shows that the low field signal is a sextet split (6.09, 6.08, 6.08, 6.07,



Figure 3. (a) UV-Vis spectrum of the dihept-C66H4 in toluene. (b) Experimental IR spectrum of the diheptC66H4 in comparison to simulated results. (c) Raman spectrum of the dihept-C66H4 and pristine C60 as a comparison at ambient temperature. Optical gap can indicate the kinetically stable of a molecule and roughly corresponds to the HOMO-LUMO gap. The optical band gap of dihept-C66H4 is 1.73 eV that are estimated from the onset of the UV-Vis absorption edge at ~714 nm. Using 1.0 eV as the reference limit to distinguish small and large bandgap for fullerenes,50 dihept-C66H4 can be assign as a large bandgap molecule. To gain further insight into the structure and electronic properties of heptagon-containing fullerene dihept-C66H4, experimental infrared spectrum of dihept-C66H4 was measured at room temperature with the simulated spectrum as a comparison (Figure 3b). The spectrum of dihept-C66H4 is dominated by four main groups of absorption bands. (1) The two bands of 3000~2800 cm-1 can be assigned to C-H stretching vibration modes, which provides a definitive proof of C-H bonds existing in the dihept-C66H4. The C-H stretching vibration of diheptC66H4 show similar absorption intensity as the previously reported non-IPR hydrofullerenes C64H414, C60H815, C50H1016, all of which have intensive absorptions for C-H stretching modes. However, according to the literature,51 the infrared absorption spectrum of IPR hydrofullerene C60H2 show only a weak C-H stretch at ~2900 cm-l. The evidence suggests that non-IPR fullerenes have stronger C-H stretching vibration than conventional IPR hydrofullerene. (2) The intensive absorption bands at intervals of 1600 cm-1 and 1300 cm-1 correspond to the aromatic C=C stretching vibration mode in fullerene cage. (3) The relative broad absorption bands in the fingerprint zone locating between 1100 and 1000 cm-1 arise from multiple C-H bending and C-C stretching vibration modes of dihept-C66H4. (4) The bands around 500 cm-1 can be attributed to breathing vibration modes of the carbon cage. It is worthy of note that the experimental infrared spectrum is basically consistent with the theoretical simulation (having somewhat differences likely due to the molecules relatively close to each other leading to the correlative effects between molecular vibrations). The dihept-C66H4 molecule was further investigated by Raman spectroscopy with pristine C60 as a comparison. The detailed calculation data for the Raman-active modes of the dihept-C66H4 are listed in Table S3. As show in Figure 3c, the Raman active modes of the dihept-C66H4 molecule are richer than those of C60, and the observed spectrum of dihept-C66H4 contains sharp peaks located at 489, 1469, 1574 cm-1 resembling to those of pristine C60,52 attributable to the bottom structure of the dihept-C66 cage having the same geometric structure as C60 (Figure 2). The low energy radial modes in the range of 250-750 cm-1 exhibit a considerable intensity enhancement relative to C60, caused by the breathing vibration mode of the entire

cage. The high energy tangential modes in the range of 1400-1600 cm-1 are related to the C-C bending vibration mode in the carbon cage. The rest Raman signals of dihept-C66H4 different from pristine C60 can be assigned to the Raman-active C-H bending and stretching vibrations as well as C-C stretching vibrational modes of the di-heptagonal hydrofullerene cage. Electrochemical Study of Dihept-C66H4. To further explore the electrochemical behavior of dihept-C66H4 featuring with heptagons and fused pentagons in fullerene cage, the cyclic voltammetry of dihept-C66H4 was measured in different scanning regions. To enable a proper comparison, the cyclic voltammetry of pristine fullerenes C60 and C70 were measured under the same experimental conditions. The characteristic redox potentials of them are summarized in Table S3 as a comparison. As shown in Figure 4, the electrochemical behavior of dihept-C66H4 reveals a complex redox behavior with four reduction peaks and irreversible reduction nature in general. The first reduction step of dihept-C66H4 was distinctly irreversible with a peak potential (Ep) at -1.05 eV and a broad oxidation wave (Figure 4), illustrating that a chemical reaction likely occurs after the dihept-C66H4 accepts one electron. Further reduction of the compound shows half-wave potentials (E1/2, red) at -1.36 eV, -1.56 eV, and -1.94 eV respectively. The irreversible cyclic voltammetry curve of dihept-C66H4 implies that the anionic species of diheptC66H4 are unstable in solution. To some extent, the results also illustrate that hydrogen atom play an important role in the stabilization of heptagons-containing C66H4 cage. In the present case, the reduction onset potential (Eredon)53 of dihept-C66H4 is about -0.89 V more negative than the corresponding value of C60 and C70 (Table S4).

Figure 4. Cyclic voltammograms of the dihept-C66H4 in odichlorobenzene/acetonitrile (5:1) solution with Bu4NPF6 as a supporting electrolyte. Scan rate, 100 mV/s. The potentials were measured with Pt disk as working electrode, Pt-wire as counter electrode and an Ag/Ag+ electrode as reference electrode. Letters I-IV label from the first to the fourth reduction peaks.


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Journal of the American Chemical Society Theoretical Analysis of Dihept-C66H4. To fully estimate the stability of dihept-C66H4, the most stable classical C66 cages54 (having both pentagons and hexagons but no heptagon) are selected to make a comparison with dihept-C66 at the B3LYP/6-31G (d) level by Gaussion 09. The relative energies of the isomers less than 40 kcal/mol are list in Table 1. Among these isomers, the #4169C66 cage has the lowest energies, and therefore is used as a reference. The pristine dihept-C66 cage is the third stable with the relative energy of 6.15 and 1.18 kcal/mol higher than #4169C66 and #4348C66 respectively, both of them have been observed by chlorinate derivatization experimentally. Moreover, the HOMO-LUMO gap of dihept-C66 is the second largest one among them with 0.13 eV smaller than #4169C66 but 0.65 eV larger than #4348C66. Even for the most stable #4169C66, it is unstable to be obtained if without further derivatization18. Hence, the pristine dihept-C66 with two heptagons and two pairs of fused pentagons should be very reactive and consequently elusive. By hydrogenation on the carbon cage, the HOMOLUMO gap of dihept-C66 is enlarged to 2.43 eV in diheptC66H4, and the localization of HOMO and LUMO are moved from adjacent pentagons region to other carbons (Figures 5b and 5c), illustrating that hydrogenation process in combustion system is beneficial to the stability of dihept-C66 cage. With the four carbon atoms chemically modified at vertexes of the fused pentagon sites by hydrogen additions, hybridization states of hydrogenated carbon atoms are changed from sp2 to sp3 and the bond strains are remarkably released, affording the high stability of the dihept-C66H4 structure finally. Table 1. Symmetry, Relative Energies and HOMOLUMO (H-L) Gaps for the Most Stable C66 Isomers. Isomers

symmetr y

ΔE (kcal mol-1)

H-L gap (eV)

Cs

0.00

1.96

C2v

4.97

1.18

C2v

6.15

1.83

C2

9.25

1.38

66

C1

16.27

1.63

66

C1

16.97

1.62

C2

30.03

0.85

66

C2

31.25

1.21

66

Cs

35.85

1.08

C1

37.39

1.08

#4169C

66

#4348C

66

diheptC66 #4466C 66 #4007C #3764C

#4439C

66

#4454C #4410C

#4398C

66

Figure 5. (a) Relative concentrations for the C66 isomers based on the RRHO approximation. (b) The LUMO and HOMO of pristine dihept-C66. (c) The LUMO and HOMO of the dihept-C66H4. Relative abundances along the range of temperatures have also been computed using the rigid rotor and harmonic oscillator (RRHO) method55. As shown in Figure 5a, #4169C66 is the most abundant C66 isomer in the whole range of temperatures from 0 to 5000K. The isomer of #4348C66 is the second abundant isomer below 1700 K. With temperature rising above 2000K, however, the molar fraction of dihept-C66 increases to more than 20% (larger than #4348C66) and becomes the second stable cage inferior to #4169C66. The calculation results suggest that the dihept-C66 isomer might be available as the two classical cages (#4169C66 and #4348C66) at high temperature. Interestingly, the two C66 isomers (#4169C66Cl1018, #4169C Cl 18, #4348C Cl 19) have a relatively high 66 6 66 10 abundance, and no form of dihept-C66 isomer was reported in arc discharge system to date. Nevertheless, dihept-C66H4 has a relatively high abundance rather than #4169C and #4348C66 species in the low-pressure 66 combustion system. Therefore, to some extent, the contradictory evidences indicate that the generations of fullerenes in low-pressure combustion and the arc discharge might undergo different fullerene growth mechanisms. In general, the unambiguous identification of dihept-C66H4 structure is of significance for exploring more new heptagons-containing fullerenes and understanding the formation mechanism of fullerenes in the combustion. It should be noted that the proposed hydrogenation process for stabilizing the dihept-C66H4 is just a possible route simply inferring from the existing experimental and theoretical results. However, it is not necessary to exclude the possibility for other pathways. The fullerene might be produced from a continuous growth of hydrocarbon itself (e.g., polycyclic aromatic hydrocarbon, bowl-shaped polycyclic aromatic hydrocarbons, small carbon radical molecules) in



flames.56-62 Further investigations for the authentic formation mechanism of fullerenes in combustion are still underway. CONCLUSIONS In summary, we have successfully synthesized and isolated an unconventional dihept-C66H4, which is the first fullerene cage with two heptagons retrieved during in situ carbon-clustering growth process by hydrogen additions in the low-pressure combustion system. The crystal structure of the dihept-C66H4 has been unambiguously characterized by single-crystal X-ray diffraction. The crystallographic data show that the dihept-C66H4 contains C2v-symmetric negatively curvature moieties of heptagons accompanying with fused pentagons. The four carbon atoms locating at vertexes of the fused pentagon sites are chemically modified into sp3 hybridization by hydrogen additions. Together with the heptagon involved, the sp2-to-sp3 hybridization change of the vertex carbon atoms remarkably releases bond strains in the pristine dihept-C66, rendering the stability of the dihept-C66H4 hydrofullerene. Theoretical calculations also support that hydrogenation of the pristine dihept-C66 is critical for stabilization of the non-IPR heptagoncontaining fullerene. Furthermore, the dihept-C66H4 exhibits better thermostability and more stable covalent C-H bonds than IPR-satisfying hydrofullerenes. Both special hydrocarbon activity and electronic properties have been revealed by spectroscopic and electrochemical studies for the unconventional dihept-C66H4. Therefore, negatively curved carbon structures are clearly within the recipe of experimentally available products by combustion techniques. The present work with the first non-classical fullerene produced in low-pressure flame can be a starting point for fundamentally researching new carbon clusters with negatively curved moieties, especially the symmetric ones with multiple heptagons, in combustion.

chemicals and solvents were of analytical grade and used without further purification. Synthesis of dihept-C66H4. The dihept-C66H4-containing soot was synthesized by our homemade setup in benzeneacetylene-oxygen diffusion combustion. The flame was maintained under a pressure of 10-20 torr. The synthetic conditions optimized to give optimal yield of diheptC66H4 in the soot and to keep the diffusion flame stable as long as possible are given as follows: chamber pressure: 15~20 torr; gas flow rate: O2, 0.55 L/min; C2H2, 1.10 L/min; vapored benzene, 1.0~1.1 L/min. The dihept-C66H4containing carbon soot was extracted with toluene by ultrasound and filtration. X-ray diffraction analysis. The black block crystals of dihept-C66H4 were obtained by solvent evaporation slowly from toluene solution. A suitable crystal was mounted with mineral oil on a cryoloop and transferred to an Agilent SuperNova diffractometer with a Cu Kα (λ = 1.54184 Å) microfocus X-ray source in the 100 K nitrogen cold stream. The data was processed using CrysAlisPro. The structure was solved by intrinsic phasing method and refined using full-matrix least-squares based on F2 with the programs SHELXT and SHELXL-201563 within OLEX264, respectively. The intensities were corrected for Lorentz and polarization effects. All non-hydrogen atoms were refined anisotropically, whereas hydrogen atoms were generated by the riding mode. A summary of the crystallographic data, bond lengths and bond angles are shown in Table S1-S2. The crystallographic data for the structure reported in this paper have been deposited at the Cambridge Crystallographic Data Centre (CCDC) under the deposition numbers CCDC 1827360. Copies of the data can be obtained free of charge from www.ccdc.cam.ac.uk/data_request/cif.

ASSOCIATED CONTENT Supporting Information

EXPERIMENTAL SECTION General information. Mass spectra was measured using a Bruker HCT ion trap instrument interfaced by an atmospheric pressure chemical ionization (APCI) source. All preparative HPLC was performed on a Shimadzu LC6AD HPLC instrument using toluene as eluent. UV-Vis absorption spectra was detected on a Shimadzu UV- 3510 spectrometer with a resolution of 0.5 nm. Emission spectra was measured with an F-4500 Hitachi spectrometer with a resolution of 0.2 nm. IR spectra (KBr tableting) was measured with a Nicolet 5DX spectrophotometer. 1H NMR (500 MHz) spectra were detected using a Bruker AV 500 Spectrometer. Emission spectra was recorded using a Hitachi F-7000 Fluorescence Spectrometer. The electrochemical property of C66H4 was measured by cyclic voltammetry on a CHI-660C electrochemical workstation. Unless otherwise noted, all

The Supporting Information is available free of charge on the ACS Publications website. HPLC chromatograms for the isolation and purification of dihept-C66H4; Multistage mass spectra of dihept-C66H4; Crystallographic information of dihept-C66H4; 1H NMR characterization for dihept-C66H4; Electrochemical study (PDF) X-ray crystallographic file for dihept-C66H4 (CIF)

AUTHOR INFORMATION Corresponding Authors *[email protected] *[email protected] *[email protected]

Author Contributions


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Journal of the American Chemical Society ⊥These

authors contributed equally to this work.

Funding Sources National Natural Science Foundation of China (21771152, 21721001, 21827801, 51572231, 21571151, 2170010228), the 973 Program of China (2015CB932301), the China Postdoctoral Science Foundation (2016M602067).

Notes

The authors declare no competing financial interest.

ACKNOWLEDGMENT This research was supported by the National Natural Science Foundation of China (21771152, 21721001, 21827801, 51572231, 21571151, 2170010228), the 973 Program of China (2015CB932301), the China Postdoctoral Science Foundation (2016M602067).

REFERENCES (1) Hayes, B. S. Soot and hydrocarbons in combustion. In Fossil Fuel Combustion; Bartok, W.; Saroﬁm A. F.; editors, New York: John Wiley & Sons, 1991; pp 261-327. (2) Dannenberg, E. M.; Paquin, L.; Gwinnell, H. Carbon black. In Encyclopedia of Chemical Technology; Kroschwitz, J. L.; HoweGrant, M. editors, New York: John Wiley& Sons, 1992; pp 10371074. (3) Bakirov, F. G.; Bashirov, N. K.; Zakharov, V. M.; Poleshchuk, I. Z.; Kruzhkov, V. N.; Shaikhutdinov, Z. G., Formation of carbon black in the combustion of homogeneous hexane-air mixtures at pressure up to 1.5 MPa. Combust. Explos. 1982, 18, 304-308. (4) Medalia, A. I.; Rivin, D.; Sanders, D. R. A comparison of carbon black with soot. Sci. Total. Environ. 1983, 31, 1-22. (5) Howard, J. B.; McKinnon, J. T.; Makarovsky, Y.; Lafleur, A. L.; Johnson, M. E. Fullerenes C60 and C70 in flames. Nature 1991, 352, 139-141. (6) Kraetschmer, W.; Lamb, L. D.; Fostiropoulos, K.; Huffman, D. R. Solid C60: a new form of carbon Nature. 1990, 347, 354-358. (7) Taylor, R.; Langley, G. J.; Kroto, H. W.; Walton, D. R. M. Formation of C60 by pyrolysis of naphthalene. Nature. 1993, 366, 728-731. (8) Xie, S. Y.; Huang, R. B.; Yu, L. J.; Ding, J.; Zheng, L. S. Microwave synthesis of fullerenes from chloroform. Appl. Phys. Lett. 1999, 75, 2764-2766. (9) Xie, S. Y.; Huang, R. B.; Chen, L. H.; Huang, W. J.; Zheng, L. S. Glow discharge synthesis and molecular structures of perchlorofluoranthene and other perchlorinated fragments of buckminsterfullerene. Chem. Commun. 1998, 1998, 2045-2046. (10) Boorum, M. M.; VasilPev, Y. V.; Drewello, T.; Scott, L. T. Groundwork for a rational synthesis of C60: cyclodehydrogenation of a C60H30 polyarene. Science. 2001, 294, 828-831. (11) Scott, L. T. Methods for the Chemical synthesis of fullerenes. Angew. Chem. Int. Ed. 2004, 43, 4994-5007. (12) Johansson, K. O.; Head-Gordon, M. P.; Schrader, P. E.; Wilson, K. R.; Michelsen, H. A., Resonance-stabilized hydrocarbon-radical chain reactions may explain soot inception and growth. Science. 2018, 361, 997-1000. (13) Kroto, H. W. The stability of the fullerenes Cn, with n = 24, 28, 32, 36, 50, 60 and 70. Nature. 1987, 329, 529-531.

(14) Gao, Z. Y.; Jiang, W. S.; Sun, D.; Xie, S. Y.; Huang, R. B.; Zheng, L. S. Synthesis of C3v-#1911C64H4 using a low-pressure benzene/oxygen diffusion flame: Another pathway toward nonIPR fullerenes. Combust. Flame. 2010, 157, 966-969. (15) Weng, Q. H.; He, Q.; Liu, T.; Huang, H. Y.; Chen, J. H.; Gao, Z. Y.; Xie, S. Y.; Lu, X.; Huang, R. B.; Zheng, L. S. Simple combustion production and characterization of octahydro[60]fullerene with a non-IPR C60 Cage. J. Am. Chem. Soc. 2010, 132, 15093-15095. (16) Chen, J. H.; Gao, Z. Y.; Weng, Q. H.; Jiang, W. S.; He, Q.; Liang, H.; Deng, L. L.; Xie, S. L.; Huang, H. Y.; Lu X.; Xie, S. Y.; Shi, K.; Huang, R. B.; Zheng, L. S. Combustion synthesis and electrochemical properties of the small hydrofullerene C50H10. Chem. Eur. J. 2012, 18, 3408-3415. (17) Yamada, M.; Kurihara, H.; Suzuki, M.; Guo, J. D.; Waelchli, M.; Olmstead, M. M.; Balch, A. L.; Nagase, S.; Maeda, Y.; Hasegawa, T.; Lu, X.; Akasaka, T. Sc2@C66 revisited: an endohedral fullerene with scandium ions nestled within two unsaturated linear triquinanes. J. Am. Chem. Soc. 2014, 136, 76114. (18) Tan, Y. Z.; Li, J.; Zhu, F.; Han, X.; Jiang, W. S.; Huang, R. B.; Zheng, Z.; Qian, Z. Z.; Chen, R. T.; Liao, Z. J.; Xie, S. Y.; Lu, X.; Zheng, L. S. Chlorofullerenes featuring triple sequentially fused pentagons. Nat. Chem. 2010, 2, 269 (19) Gao, C. L.; Li, X.; Tan, Y. Z.; Wu, X. Z.; Zhang, Q.; Xie, S. Y.; Huang, R. B. Synthesis of long-sought C66 with exohedral stabilization. Angew. Chem. Int. Ed. 2014, 53, 7853. (20) Mackay, A. L.; Terrones, H. Diamond from graphite. Nature. 1991, 352, 762-762. (21) Lenosky, T.; Gonze, X.; Teter, M.; Elser, V. Energetics of negatively curved graphitic carbon. Nature. 1992, 355, 333-335. (22) Phillips, R.; Drabold, D. A.; Lenosky, T.; Adams, G. B.; Sankey, O. F., Electronic structure of schwarzite. Phys. Rev. B. 1992, 46 (3), 1941-1943. (23) Terrones, H.; Mackay, A. L. The geometry of hypothetical curved graphite structures. Carbon. 1992, 30, 1251-1260. (24) Huang, M. Z.; Ching, W. Y.; Lenosky, T. Electronic properties of negative-curvature periodic graphitic carbon surfaces. Phys. Rev. B. 1993, 47, 1593-1606. (25) Park, N.; Yoon, M.; Berber, S.; Ihm, J.; Osawa, E.; Tomanek, D. Magnetism in all-carbon nanostructures with negative Gaussian curvature. Phys. Rev. Lett. 2003, 91, 237204. (26) Odkhuu, D.; Jung, D. H.; Lee, H.; Han, S. S.; Choi, S. H.; Ruoff, R. S.; Park, N. Negatively curved carbon as the anode for lithium ion batteries. Carbon. 2014, 66, 39-47. (27) Tagami, M.; Liang, Y.; Naito, H.; Kawazoe, Y.; Kotani, M. Negatively curved cubic carbon crystals with octahedral symmetry. Carbon. 2014, 76, 266-274. (28) Pun, S. H.; Miao, Q. Toward negatively curved carbons. Acc. Chem. Res. 2018, 51, 1630-1642. (29) Braun, E.; Lee, Y.; Moosavi, S. M.; Barthel, S.; Mercado, R.; Baburin, I. A.; Proserpio, D. M.; Smit, B. Generating carbon schwarzites via zeolite-templating. Proc. Nat. Acad. Sci. USA. 2018, 115, E8116-E8124. (30) Troshin, P. A.; Avent, A. G.; Darwish, A. D.; Martsinovich, N.; Abdul-Sada, A. K.; Street, J. M.; Taylor, R. Isolation of two seven-membered ring C58 fullerene derivatives: C58F17CF3 and C58F18. Science. 2005, 309, 278-281. (31) Ioffe, I. N.; Chen, C.; Yang, S.; Sidorov, L. N.; Kemnitz, E.; Troyanov, S. I. Chlorination of C86 to C84Cl32 with nonclassical heptagon-containing fullerene cage formed by cage shrinkage. Angew. Chem. Int. Ed. 2010, 49, 4784-4787. (32) Ioffe, I. N.; Mazaleva, O. N.; Sidorov, L. N.; Yang, S.; Wei, T.; Kemnitz, E.; Troyanov, S. I. Cage shrinkage of fullerene via a C2 loss: from IPR C90(28)Cl24 to nonclassical, heptagoncontaining C88Cl22/24. Inorg. Chem. 2013, 52, 13821-13823.



(33) Yang, S.; Wang, S.; Kemnitz, E.; Troyanov, S. I., Chlorination of IPR C100 fullerene affords unconventional C96Cl20 with a nonclassical cage containing three heptagons. Angew. Chem. Int. Ed. 2014, 53, 2460-2463. (34) Yang, S.; Wei, T.; Wang, S.; Ioffe, I. N.; Kemnitz, E.; Troyanov, S. I. Structures of chlorinated fullerenes, IPR C96Cl20 and non-classical C94Cl28 and C92Cl32: evidence of the existence of three new isomers of C96. Chem. Asian. J. 2014, 9, 3102-3105. (35) Wei, T.; Yang, S.; Kemnitz, E.; Troyanov, S. I. Two successive C2 losses from C86 fullerene upon chlorination with the formation of non-classical C84Cl30 and C82Cl30. Chem. Asian. J. 2015, 10, 559-562. (36) Ioffe, I. N.; Yang, S.; Wang, S.; Kemnitz, E.; Sidorov, L. N.; Troyanov, S. I. C100 is Converted into C94Cl22 by Three chlorination-promoted C2 losses under formation and elimination of cage heptagons. Chem. Eur. J. 2015, 21, 4904-4907. (37) Yang, S.; Wei, T.; Scheurell, K.; Kemnitz, E.; Troyanov, S. I. Chlorination-promoted skeletal-cage transformations of C88 fullerene by C2 losses and a C-C bond rotation. Chem. Eur. J. 2015, 21, 15138-15141. (38) Wang, S.; Yang, S.; Kemnitz, E.; Troyanov, S. I. New isolated-pentagon-rule and skeletally transformed isomers of C100 fullerene identified by structure elucidation of their chloro derivatives. Angew. Chem. Int. Ed. 2016, 55, 3451-3454. (39) Wang, S.; Yang, S.; Kemnitz, E.; Troyanov, S. I. New giant fullerenes identified as chloro derivatives: isolated-pentagon-rule C108(1771)Cl12 and C106(1155)Cl24 as well as nonclassical C104Cl24. Inorg. Chem. 2016, 55, 5741-5743. (40) Jin, F.; Yang, S.; Kemnitz, E.; Troyanov, S. I. Skeletal transformation of a classical fullerene C88 into a nonclassical fullerene chloride C84Cl30 bearing quaternary sequentially fused pentagons. J. Am. Chem. Soc. 2017, 139, 4651-4654. (41) Brotsman, V. A.; Ignat'eva, D. V.; Troyanov, S. I. Chlorination-promoted transformation of isolated pentagon rule C78 into fused-pentagons- and heptagons-containing fullerenes. Chem. Asian. J. 2017, 12, 2379-2382. (42) Tamm, N. B.; Brotsman, V. A.; Markov, V. Y.; Kemnitz, E.; Troyanov, S. I. Chlorination-promoted skeletal transformation of IPR C76 discovered via trifluoromethylation under the formation of non-IPR C76(CF3)nFm. Dalton. Trans. 2018, 47, 6898-6902. (43) Brotsman, V. A.; Tamm, N. B.; Markov, V. Y.; Ioffe, I. N.; Goryunkov, A. A.; Kemnitz, E.; Troyanov, S. I. Rebuilding C60: chlorination-promoted transformations of the buckminsterfullerene into pentagon-fused C60 derivatives. Inorg. Chem. 2018, 57, 8325-8331. (44) Tan, Y. Z.; Chen, R. T.; Liao, Z. J.; Li, J.; Zhu, F.; Lu, X.; Xie, S. Y.; Li, J.; Huang, R. B.; Zheng, L. S. Carbon arc production of heptagon-containing fullerene[68]. Nat. Commun. 2011, 2, 420. (45) Zhang, Y.; Ghiassi, K. B.; Deng, Q.; Samoylova, N. A.; Olmstead, M. M.; Balch, A. L.; Popov, A. A. Synthesis and structure of LaSc2N@Cs(hept)-C80 with one heptagon and thirteen pentagons. Angew. Chem. Int. Ed. 2015, 54, 495-9. (46) Chen, C. H.; Abella, L.; Ceron, M. R.; Guerrero-Ayala, M. A.; Rodriguez-Fortea, A.; Olmstead, M. M.; Powers, X. B.; Balch, A. L.; Poblet, J. M.; Echegoyen, L. Zigzag Sc2C2 carbide cluster inside a [88]fullerene cage with one heptagon, Sc2C2@Cs(hept)C88: a kinetically trapped fullerene formed by C2 insertion? J. Am. Chem. Soc. 2016, 138, 13030-13037. (47) Fowler, P. W.; Heine, T.; Mitchell, D.; Orlandi, G.; Schmidt, R.; Seifert, G.; Zerbetto, F. Energetics of fullerenes with heptagonal rings. J. Chem. Soc. Faraday.Trans. 1996, 92, 22032210. (48) Hazen, R. M.; Mao, H. K.; Finger, L. W.; Bell, P. M. Structure and compression of crystalline methane at high

pressure and room temperature. Appl. Phys. Lett. 1980, 37, 288289. (49) Lin, H.; Li, Y. L.; Zeng, Z.; Chen, X. J.; Lin, H. Q. Structural, electronic, and dynamical properties of methane under high pressure. J. Chem. Phys. 2011, 134, 064515. (50) Tang, Q. Q.; Abella, L.; Hao, Y. J.; Li, X. H.; Wan, Y. B.; Rodriguez-Fortea, A.; Poblet, J. M.; Feng, L.; Chen, N. Sc2O@C2v(5)-C80: Dimetallic oxide cluster inside a C80 fullerene cage. Inorg. Chem. 2015, 54, 9845-9852. (51) Henderson, C. C.; Cahill. P. A. C60H2: Synthesis of the simplest C60 hydrocarbon derivative. Science. 1993, 259, 18851887. (52) Bethune, D. S.; Meijer, G.; Tang, W. C.; Rosen, H. J. The vibrational Raman spectra of purified solid films of C60 and C70. Chem. Phys. Lett. 1990, 174, 219-222. (53) Sun, Q.; Wang, H.; Yang, C.; Li, Y. Synthesis and electroluminescence of novel copolymers containing crown ether spacers. J. Mater. Chem. 2003, 13, 800-806. (54) Alegret, N.; Abella, L.; Azmani, K.; Rodriguez-Fortea, A.; Poblet, J. M. Different factors govern chlorination and encapsulation in fullerenes: the case of C66. Inorg. Chem. 2015, 54, 7562-7570. (55) Slanina, Z.; Lee, S. L.; Uhlík, F.; Adamowicz, L.; Nagase, S. Computing relative stabilities of metallofullerenes by Gibbs energy treatments. Theor. Chem. Acc. 2007, 117, 315-322. (56) Baum, T.; Loffler, S.; Loffler, P.; Weilmunster, P.; Homann, K. H. Fullerene ions and their relation to PAH and soot in low-pressure hydrocarbon flames. Ber. Bunsenges. Phys. Chem. Chem. Phys. 1992, 96, 841-857. (57) Lafleur, A. L.; Howard, J. B.; Marr, J. A.; Yadav, T. Proposed fullerene precursor corannulene identified in flames both in the presence and absence of fullerene production. J. Phys. Chem. 1993, 97, 13539-13543. (58) Ahrens, J.; Bachmann, M.; Baum, T.; Griesheimer, J.; Kovacs, R.; Weilmunster, P.; Homann, K. H. Fullerenes and their ions in hydrocarbon flames. Int. J. Mass Spectrom. Ion Process. 1994, 138, 133-148. (59) Lafleur, A. L.; Howard, J. B.; Taghizadeh, K.;

Page 8 of 9

Plummer, E. F.; Scott, L. T.; Necula, A.; Swallow, K. C. Identification of C20H10 dicyclopentapyrenes in flames: Correlation with corannulene and fullerene formation. J. Phys. Chem. 1996, 100, 17421-17428. (60) Homann, K. H. Fullerenes and soot formation - New pathways to large particles in flames. Angew. Chem. Int. Ed. 1998, 37, 2435-2451. (61) Poater, J.; Fradera, X.; Duran, M.; Sola, M. An insight into the local aromaticities of polycyclic aromatic hydrocarbons and fullerenes. Chem. Eur. J. 2003, 9, 1113-1122. (62) Wu, X. Z.; Yao, Y. R.; Chen, M. M.; Tian, H. R.; Xiao, J.; Xu, Y. Y.; Lin, M. S.; Abella, L.; Tian, C. B.; Gao, C. L.; Zhang, Q.; Xie, S. Y.; Huang, R. B.; Zheng, L. S. Formation of curvature subunit of carbon in combustion. J. Am. Chem. Soc. 2016, 138, 9629-33. (63) Sheldrick, G. M. Crystal structure refinement with SHELXL. Acta Cryst. Sect. C: Struct. Chem. 2015, C71, 3-8. (64) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.; Puschmann, H. J. OLEX2: a complete structure solution, refinement and analysis program. J. Appl. Cryst. 2009, 42, 339341.


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An Unconventional Hydrofullerene C66H4 with Symmetric Heptagons

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