Pressure-Induced Diels–Alder Reactions in C6H6-C6F6 Cocrystal towards Graphane Structure

Article abstract of DOI:10.1002/anie.201813120

Pressure-induced polymerization (PIP) of aromatics is a novel method for constructing sp³-carbon frameworks, and nanothreads with diamond-like structures were synthesized by compressing benzene and its derivatives. Here by compressing a benzene-hexafluorobenzene cocrystal (CHCF), H-F-substituted graphane with a layered structure in the PIP product was identified. Based on the crystal structure determined from the in situ neutron diffraction and the intermediate products identified by gas chromatography-mass spectrum, we found that at 20 GPa CHCF forms tilted columns with benzene and hexafluorobenzene stacked alternatively, and leads to a [4+2] polymer, which then transforms to short-range ordered H-F-substituted graphane. The reaction process involves [4+2] Diels–Alder, retro-Diels–Alder, and 1-1′ coupling reactions, and the former is the key reaction in the PIP. These studies confirm the elemental reactions of PIP of CHCF for the first time, and provide insight into the PIP of aromatics.

Full text of DOI:10.1002/anie.201813120

A Journal of the Gesellschaft Deutscher Chemiker
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Accepted Article
Title: Pressure-Induced Diels-Alder Reactions in C6H6-C6F6 Cocrystal
towards Graphane Structure
Authors: Yajie Wang, Xiao Dong, Xingyu Tang, Haiyan Zheng, Kuo
Li, Xiaohuan Lin, Leiming Fang, Guang’ai Sun, Xiping Chen,
Lei Xie, Craig L. Bull, Nicholas P. Funnell, Takanori Hattori,
Asami Sano-Furukawa, Jihua Chen, Dale K. Hensley, George
Cody, Yang Ren, Hyun Hwi Lee, and Ho-kwang Mao
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201813120
Angew. Chem. 10.1002/ange.201813120
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10.1002/anie.201813120
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Pressure-Induced Diels-Alder Reactions in C6H6-C6F6 Cocrystal
towards Graphane Structure
Yajie Wang,[b] Xiao Dong,[b] Xingyu Tang,[b] Haiyan Zheng,*[a] Kuo Li,*[a] Xiaohuan Lin,[b] Leiming Fang,[b]
Guang’ai Sun,[b] Xiping Chen,[b] Lei Xie,[b] Craig L. Bull,[b] Nicholas P. Funnell,[b]Takanori Hattori,[b] Asami
Sano-Furukawa,[b] Jihua Chen,[b] Dale K. Hensley,[b] George Cody,[b] Yang Ren,[b] Hyun Hwi Lee,[b] Ho-
kwang Mao[b]
Abstract: Pressure-induced polymerization (PIP) of aromatics is a
novel method to construct sp3-carbon frameworks, and nanothreads
with diamond-like structures were synthesized by compressing
benzene and its derivatives. Here by compressing benzene-
hexafluorobenzene cocrystal (CHCF), we identified H-F-substituted
graphane with a layered structure in the PIP product. Based on the
crystal structure determined from the in situ neutron diffraction and
the intermediate products identified by the gas chromatography-
mass spectrum, we found that at 20 GPa CHCF forms tilted columns
with benzene and hexafluorobenzene stacked alternatively, which
leads to a [4+2] polymer, and then transfers to short-range ordered
hydrogenated-fluorinated graphane. The reaction process contains
[4+2] Diels-Alder, retro-Diels-Alder, and 1-1’ coupling, and the
former is the key reaction in the PIP. Our studies confirmed the
elemental reactions of the CHCF for the first time, which provides a
novel insight into the PIP of aromatics.
effective to construct sp3-hybridized carbon materials.[2] It is well
known that benzene polymerizes into amorphous hydrogenated
carbon under high pressure,[3] and with anisotropic stress, a well-
ordered single-crystal carbon nanothread was reported, which is
recognized as an ultra-thin sp3 carbon nanowire.[2a,2b] Similarly,
single-crystal carbon nitride was synthesized by compressing
pyridine slowly.[2c] Recently, it was reported that aniline forms
diamond-like polyaniline under external pressure and the H-
bond between the NH2 groups is believed to be responsible for
better crystallinity.[2d] Besides the one dimensional structure, the
graphane structure can also be obtained by compressing the
aromatics under high pressure and high temperature
conditions.[4]
The reaction mechanism of these pressure-induced
polymerization (PIP) was explored from various perspectives.
Various possible connections between benzene molecules were
theoretically proposed, and the energies of the formed dimers
were examined to evaluate the corresponding reactions.[5,6]
Experimentally, a possible reaction route including a [4+2]
cycloaddition reaction followed by an intramolecular 'zipper'
cascade reaction was proposed according to the π-π stacking of
the benzene molecules and the structural model of the
product.[2a] All of these reports suggest the reaction starts from
the bonding between the π-π stacked aromatics. However, more
experimental work is needed to understand the elemental
reactions in the PIP process and its relation to the π-π stacking.
Sp3-hybridized carbon-based materials have gained constant
attention due to their outstanding mechanical and optical
properties.[1] However, their types are very limited compared to
the diversity of the carbon-based molecules. Applying extreme
pressure to unsaturated molecules like aromatics is proved to be
[a]
[b]
Drs. H. Zheng, K. Li
Center for High Pressure Science and Technology Advanced
Research, Beijing, 100094, P. R. China
E-mail: zhenghy@hpstar.ac.cn; likuo@hpstar.ac.cn
Drs. Y. Wang, X. Dong, X. Tang, X. Lin, H. Mao
Center for High Pressure Science and Technology Advanced
Research, Beijing, 100094, P. R. China
Drs. L. Fang, G. Sun, X. Chen, L. Xie
C6H6-C6F6 1:1 cocrystal (abbreviated as CHCF hereafter)
provides an appropriate π-π stacking model due to the strong
electrostatic attraction between C6H6 and C6F6. The alternate
stacking of C6H6 and C6F6 can be recognized as half of benzene
molecules being substituted by hexafluorobenzene, which
provides a tracer during the reaction. Here, we report the PIP of
CHCF and its reaction mechanism under applied pressure. The
product of PIP contains a hydrogenated-fluorinated graphane-
like structure. Diels-Alder, retro-Diels Alder and 1-1’ coupling
reactions were identified during this process and the former is
the key elemental reaction directing to the polymerized material.
We described the PIP route of the aromatic molecules
systematically, which also provides an alternative method for
constructing substituted graphane with atomic-level uniformity.
Key Laboratory of Neutron Physics and Institute of Nuclear Physics
and Chemistry, China Academy of Engineering Physics, Mianyang,
621999, P. R. China
Drs. C. L. Bull, N. P. Funnell
ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon
OX11 0QX, United Kingdom
Drs. T. Hattori, A. Sano-Furukawa
J-PARC Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-
1195, Japan
Drs. J. Chen, D. K. Hensley
Center for Nanophase Materials Sciences, Oak Ridge National
Laboratory, Oak Ridge, TN, 37831, United States
Drs. G. Cody, H. Mao
CHCF forms rhombohedral crystals (phase I, R-3m) around
room temperature and experiences three phase transitions to
form phase II (I2/m), III (P-1), and IV (P21/a) at low temperature
and ambient pressure.[7] In all the phases, C6H6 and C6F6 are
alternately stacked.[7] Under high pressure, phase V (P21/c), VI,
VII, and VIII were identified and PIP was observed at ~ 20 GPa
after phase VIII.[8] Combining in situ synchrotron X-ray diffraction
(XRD, Fig.S1), constant wavelength and time of flight (TOF)
neutron diffraction under high pressure (Fig.S2), we determined
the structures of phase VI, VII, and VIII ab initio (Fig.S3),
Geophysical Lab, Carnegie Institution of Washington, 5251 Broad
Branch Road, NW, Washington, DC, 20015, United States
Dr. Y. Ren
Advanced Photon Source, Argonne National Laboratory, Lemont, IL,
60439, United States
Dr. H. H. Lee
Pohang Accelerator Laboratory, POSTECH, Pohang 790-784,
Republic of Korea
Supporting information for this article is given via a link at the end of
the document.
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10.1002/anie.201813120
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including the atomic positions using Rietveld refinement (Table
S1). The C6H6 and C6F6 molecules are still alternately stacked to
form columns in these phases; however, the columns are tilted
significantly, which are quite different from those under low
temperature. In order to understand the crystal structure at
reaction pressure threshold more precisely, we further optimize
the structure of phase VIII by using the Density Functional
Theory (DFT) calculation based on the experimental result at 20
GPa, which was shown in Figure 1. The stacked aromatic rings
are progressively tilted away from the previous column axis (c-
axis), and actually form closed packed layers on the (102) plane.
Every aromatic ring is curved and stacked on the interstitial site
among three rings of the neighbored layer, with two of the three
rings of the same type. Along the [001] direction, the nearest
C∙∙∙C distance between the C6F6 and C6H6 molecules in the
column is ca. 2.8 Å, close to the critical reaction distance
between the benzene molecules (2.8-3.0 Å) at 298 K (Fig.1b).[9]
This indicates a high possibility of the addition reaction between
the C6F6 and C6H6 in the CHCF columns.
S2), and the corresponding image shows a curved layered
structure with the interlayer d-spacing of 3.7 Å (Fig. 2c and 2d),
consistent with that in graphite.[11] This suggests that PE20 has a
layered graphitic skeleton constructed by C(sp3), F and H atoms,
and lost F and H when irradiated by the 200 kV electron beam.
The graphitic skeletal of PE20 is confirmed by the pair
distribution function (PDF) and TEM with lower voltage. The S(Q)
of neutron and X-ray PDF show bands at d = 2.2 Å and 1.1 Å,
which are ascribed to the 100 and 200 scattering of the 2D
graphitic lattice, respectively (Fig.2e). X-ray PDF (G(r), Fig. 2f)
also shows clear feature of hexagonal rings at r = 1.4, 2.5 and
2.9 Å, corresponding to the distance between 1-2,1-3 and 1-4
positions of a hexagonal carbon ring. When using a 120 kV TEM,
a diffraction ring at d=4.1 Å was observed in the selected area
electron diffraction (SAED) pattern (Fig. 2g). This d-spacing is
much smaller than the interlayer spacing of graphane (4.7 Å), [12]
but close to twice of the d(100) of the graphitic lattice, and hence
implies a superlattice of graphene, like a 2×2 lattice (hexagonal
lattice with a = 4.7 Å and d(100) = 4.0 Å, grey dashed line in Fig.
2h) or its distorted relatives (the orthorhombic lattice in blue in
Fig. 2h). This probably results from the ordered bonding of H
and F to the graphitic skeletal, but the details are complex and
beyond the scope of this paper (Fig. S6).
Figure 1. The crystal structure of C6D6-C6F6 before reaction (20 GPa). a)
viewed perpendicular to (102) and b) approximately along [010]. The black,
pink, and green atoms are carbon, hydrogen (deuterium) and fluorine,
respectively. This crystal structure is optimized by the DFT calculation based
on the structure obtained from the Rietveld refinement result of the neutron
data collected at PLANET, J-PARC Center[10] at 20 GPa.
Upon further compression of phase VIII using a Paris
Edinburgh (PE) press, we obtained white solid samples, and
their morphology varied with the applied pressure. The product
recovered from 18 GPa (PE18) has an irregular morphology (Fig.
S4), while that obtained from 20 GPa (PE20) shows an
obviously layered structure under scanning electron microscope
(SEM, Fig.2a). When recovered from 17 GPa, the solid sample
(PE17) is too limited to be analyzed, which means most of the
aromatic molecules did not react and evaporated upon
decompression. The Energy Dispersive Spectroscopy (EDS)
obtained from SEM shows PE20 maintains most of the fluorine
atoms (Table S2). Using solid-state nuclear magnetic resonance
(ssNMR, Fig.2b), we found three types of carbon species, C(sp2)
(131 ppm), C(sp3) connecting to fluorine (F-CR3) (94 ppm) and
non-fluorine atoms (H-CR3) (38 ppm), respectively. The ratio of
the peak area of the C(sp2) and C(sp3) is 1:4, which indicates
the C(sp3) is the dominant species. This is consistent with the
1H-ssNMR result (Fig.S5), which is well fitted using three peaks
at 1.3, 2.5, and 6.3 ppm, and recognized as H on C(sp3)(H-C-R3),
C(sp3) connected to a fluorine atom (H-CFR2) and C(sp2) (H-
CR=CR2), respectively. Hence, the ssNMR data proves that the
sample is mainly a H-F bonded sp3-C material.
Figure 2. a) SEM images, b) 13C CPMAS ssNMR, c) TEM image (200kV), d)
the corresponding statistical results of d-spacing in c), and e) the total
structure factor S(Q) derived from synchrotron X-ray and neutron diffraction of
PE20. f) Experimental (X-ray) and calculated G(r). g) SAED pattern (120kV
TEM) of the sample PE20. The modelled PDF in Fig.2f is derived from the h)
proposed H-F graphane model viewed along [001].
All the above results indicate that PE20 has a short-range
ordered hydrogenated-fluorinated graphitic structure (or
hydrogenated-fluorinated graphane). The synchrotron X-ray and
neutron PDF of PE20 show clear band at d = ~6.5 Å (Fig. 2e),
which is the typical interlayer distance of fluorinated graphite.[13]
Based on these experimental results and the reaction route
When we measured EDS by using the transmission electron
microscope (TEM) of 200 kV, PE20 lost most of fluorine (Table
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mentioned later, we proposed a hydrogenated-fluorinated (H-F)
graphane model for PE20 (Fig.2h) and simulated the G(r)
pattern, which fits the experimental data very well (Fig.2f).
fluorinated C=C bonds.[16a,18] These features clearly evidenced
the 1,2-addition of benzene. On the other side, the intense band
at around 1750-1756 cm-1 is attributed to the C=C vibration of
the non-conjugated cis-1,2-difluorosubstituted olefin, thus,
suggesting the occurrence of 1,4-addition for C6F6.[19] All these
results indicate that the [4+2] reaction happens between the
C6F6 and C6H6. The decreasing intensities of these featured
peaks under higher pressure indicated that the [4+2] products
are related to the intermediate product, which continues to react
at higher pressure.
Figure 3. IR absorption spectra of PE17 (orange), PE18 (pink), PE20 (red),
and CHCF starting material (black), and the calculated IR spectrum of H-F
graphane model. The assignments of the peaks in PE20 are presented in
Fig.S7 based on the calculated results. The assignments of the peaks in
CHCF cocrystal are listed in Table S3 in supporting information. [8]
The H-F graphane model for PE20 is also confirmed by the
IR spectra. We optimized the proposed H-F graphane model by
DFT and calculated its IR spectrum. As shown in Figure 3,
among the recovered samples, PE20 featured several strong
new peaks at 934, 1260, 1329, and 2924 cm-1 as well as a peak
at 1179 cm-1 with medium intensity, agrees well to the calculated
IR spectrum of the H-F graphane. The peaks at 3060 cm-1
(C(sp2)-H stretching), 1526 cm-1 (C(sp2)-C(sp2) stretching), 1018
cm-1 and 987 cm-1 (C(sp2)-F stretching) are similar to the peaks
of benzene or hexafluorobenzene, and are attributed to their
fragments (Fig. 3, marked by stars). The peak at 2924 cm-1 is
from the C(sp3)-H stretching which is much stronger than the
peaks above 3000 cm-1. This means PE20 mainly contains sp3-
carbon. The contribution from F atoms are mainly located in the
intermediate frequency range (933-1150 cm-1), while the modes
between 1160 and 1400 cm-1 are dominated by the carbon and
hydrogen atoms. The peak at 934 cm-1 contains the C-F
stretching, which is lower than that in F-graphane (C:F=1:1). [13a,
14] This is because the C-F stretching red-shifts when fluorine
atoms of F-graphane were partly substituted by hydrogen
atoms.[15] The peaks at 1179 cm-1, 1260 cm-1 and 1329 cm-1 are
contributed by the C-H deformation and C-C stretching. The
details of assignment are summarized in Figure S7 in the
supporting information.
Figure 4. a) A histogram of the comparison between the relative abundance of
major components in different high-pressure samples; b) the high-resolution
mass spectra of the C6H6-C6F6 tetramer at the retention time of 35.96 min in
sample PE20.
To identify the intermediates, we extracted the soluble
molecules from the samples and made Gas Chromatography-
Mass Spectrometry (GC-MS) investigation. Over 170
compounds were detected in PE20 (Table S4), but not in the
starting material. Twelve primary compounds with an abundance
of >1% are C12H5F5 (24.54%), C24H12F12 (22.01%), C11H5F5
(10.72%), C12H10 (9.04%), C11H5F5 (2.40%), C18H10F6 (2.11%),
C18F18 (1.84%), C18H6F12 (1.66%), C10H8 (1.42%), C18H12F6
(1.28%), C12H3F5 (1.18%), and C17H6F12 (1.12%). By comparing
the retention time to commercial samples and examining the
National Institute of Standards and Technology /Wiley standard
library, C12H5F5, C12H10 and C10H8 are identified as 2,3,4,5,6-
pentafluorobiphenyl, biphenyl and naphthalene, respectively
(Fig.S8).
More importantly, in the IR spectra of PE17 and PE18, the
new bands at around 699, 740, 1406 and 1753 cm-1 are more
intense than those in PE20 (red dashed arrows), and therefore,
most likely result from intermediate products. Specifically, the
peak at 699 cm-1 is likely from the olefinic CH wag bands of cis-
1,2-substitution.[16] The peak at 740 cm-1 is assigned to the
olefinic CH out-of-plane vibration and is a feature of the 1,3-
cyclohexadiene with a conjugated double bond, other than 1,4-
cyclohexadiene.[17] Correspondingly, the peak at 1406 cm-1 is
assigned to the C-H in-plane deformation related to non-
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Similar results are also observed in PE17 and PE18 (Table
S5 and Table S6). Figure 4a displays the relative abundance of
those representative products. C12H5F5 is the predominant
product, indicating that the 1-1' coupling reaction between C6H6
and C6F6 is a typical reaction of CHCF under applied pressure
(Scheme 1a). Considering H migrates to N in acetonitrile at a
distance of 2.0 Å,[20] the elimination of H, F species is not
surprising, because the shortest intermolecular distance
between H and F is 2.2 Å in phase VIII (Fig.1b). However, this
does not mean that the 1-1’ coupling reaction constructs the
polymerized material. This is first because terphenyl (C18H14)
and their fluorinated derivatives C18(H,F)14 like C18H10F4, C18H9F5,
C18H5F9, and C18H4F10 were detected in a very small amount in
all samples; in total 1.38% for PE17, 1.17% for PE18, and
1.06% for PE20. This indicates no successive reaction is
promoted via this pathway. Secondly, the IR spectra of the
recovered samples significantly differ from that of the poly-aryl
molecules (Fig.S9).
first time, which will provide an insight into the other aromatics.
The formation of fluorinated graphane highlights that the PIP of
the substituted aromatics is an alternative method to construct
sp3-hybridized carbon materials with diverse structures.
In contrast, a series of dimers (C12H6F6), trimers (C18H6F12
and C18H12F6) and tetramers (C24H12F12) were identified, which
highlights the addition between benzene and hexafluorobenzene.
As shown in Figure 4a, it is notable that the C24H12F12 tetramer
has a much higher content when synthesized under higher
pressure (PE20), which has the second highest percentage in
total. Therefore, it is reasonable to infer that the addition reaction
is the pathway to synthesize the CHCF polymer. In the MS of
Scheme 1 a) The selected elemental reactions of CHCF cocrystal under high
pressure; b) The proposed reaction route from CHCF cocrystal to H,F-
graphane. A 2×2 superlattice is shown in blue line on the product.
Experimental Section
+
the tetramer C24H12F12, the fragment C6H6 (m/z = 78.0465) and
+
+
C6F6 (m/z = 185.9900) are detected, and C18H12F6 and
Benzene (99.9%) and hexafluorobenzene (99.9%) were purchased from
Sigma Aldrich and used without further purification. The C6H6-C6F6
cocrystal (CHCF) was prepared by mixing equimolar amounts of C6H6
and C6F6 at 298 K, and storing it in a sealed bottle at low temperature. In
situ high-resolution X-ray diffraction of CHCF was conducted at Beamline
5A XRS-MS of PLS-II at Pohang Accelerator Laboratory (PAL). The
neutron diffractions with a constant wavelength were collected on the
Fenghuang diffractometer of China Mianyang Research Reactor (CMRR),
Institute of Nuclear Physics and Chemistry, China Academy of Engineer
+
+
C12H6F6 are also remarkably detected. However, no C12H12
+
and C12F12 ions are identified (Fig.4b). This indicates the
tetramers have an alternate connection like C6H6-C6F6-C6H6-
C6F6. Considering the [4+2] Diels-Alder reaction concluded from
the IR result, the PIP of C6H6 and C6F6 is most likely a process
of serial [4+2] Diels-Alder reactions. We also identified a
significant amount of 1,2,3,4-tetrafluonaphthalene in the GC-MS
result, which probably comes from the following reaction process.
The product of the Diels-Alder reaction undergoes a retro-Diels
Alder reaction to eliminate a C2(H,F)2 molecule and then
followed by an elimination of two F/H species (Scheme 1a). This
serial [4+2] Diels-Alder reaction of aromatics is also proposed in
the literature,[2a,5] and is consistent with the crystal structure of
phase VIII in the view of topo-chemistry.
Physics. Neutron measurements with TOF were measured at PEARL,
[21]
ISIS
and BL11 PLANET of J-PARC Center.[10] The samples PE17,
PE18, and PE20 were synthesized by a VX3 PE press equipped with
double-toroid sintered diamond anvils. SEM images were recorded on a
Carl Zeiss Merlin Compact Field-emission scanning electron microscope
operated at 1.0 kV and the EDS result was obtained in a Carl Zeiss
Merlin SEM operating at 10 kV with a system from Bruker Nano GmbH
using a XFlash detector 5030. Solid 1H and 13C NMR experiments were
performed with a Varian-Chemagnetic Infinity 300 Nuclear Magnetic
Resonance spectrometer. The TEM and SAED patterns were recorded
under a bias voltage of 120 kV (ZEISS, Libra 120), and field-emission
high resolution TEM were operated under a higher bias voltage of 200 kV
(JEOL, JEM-2100F). High-energy PDF measurement was performed at
the beamline 11-ID-C of the Advanced Photon Source (APS) at Argonne
National Laboratory. The neutron PDF measurement was carried out in
NOMAD, Spallation Neutron Source (SNS), Oak Ridge National
Laboratory (ORNL). Mid infrared spectra were measured on a Bruker
VERTEX 70v FTIR spectrometer with an IR microscope. High-resolution
So far there is still a gap between the serial [4+2] product
and H-F graphane, which is still under investigation. By
comparing their structures, we arguably propose a reaction
model as shown in Scheme 1b. The [4+2] polymer ribbons
connect to their neighbours to form H-F graphane with a layered
structure by eliminating some C, H and F species. This model
well explains all of our experimental results.
To conclude, in this paper we determined the crystal
structures of all the C6H6-C6F6 cocrystal phases under high
pressure and found it finally polymerized into H-F graphane with
layered structure. Several elemental reactions including the
Diels-Alder, retro-Diels Alder, and 1-1’ coupling reactions are
discerned and the serial [4+2] Diels-Alder reaction is evidenced
to be the key step of the PIP. Our investigation described the
PIP process, especially the elemental reactions of CHCF for the
GC-MS measurements were performed on a Thermo ScientificTM
Q
ExactiveTM GC hybrid quadrupole-Orbitrap mass spectrometer. Details of
the in situ high-pressure XRD, neutron diffraction, the synthetic method
of the samples PE17, PE18, and PE20, ssNMR, X-ray and neutron PDF
measurement, GC-MS measurement, and computational simulation
methods are given in the Supporting Information.
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[5]
[6]
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B. Chen, R. Hoffmann, N. W. Ashcroft, J. Badding, E. Xu, V. Crespi, J.
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Acknowledgements
A. Y. Rogachev, X. D. Wen, R. Hoffmann, J. Am. Chem. Soc. 2012,
134, 8062-8065.
The authors acknowledge the support of the National Natural
Science Foundation of China (NSFC) (Grant Nos.: 21601007,
21771011 and 21875006). The authors also acknowledge the
support from the Top 1000-Talents Award. Experiments at the
ISIS Neutron and Muon Source were supported by a beamtime
allocation from the Science and Technology Facilities Council.[22]
Neutron diffraction experiments at J-PARC were performed
through the J-PARC user programs (No.2016A0191). The
research at Oak Ridge National Lab’s Spallation Neutron Source
was sponsored by the Scientific User Facilities Division, Office of
Basic Energy Sciences, U.S. Department of Energy (DOE).
Electron microscopy experiments were conducted at the Center
for Nanophase Materials Sciences, which is a DOE Office of
Science User Facility. The research used resources of the
Advanced Photon Source, a U.S. DOE Office of Science User
Facility operated for the DOE Office of Science by Argonne
National Laboratory under Contract No. DE-AC02-06CH11357.
The calculations were performed on the TianheII supercomputer
at the Chinese National Supercomputer Center in Guangzhou.
The authors thank Dr. Joerg C. Neuefeind for his helps in
neutron PDF measurements and thank Dr. Qiaoshi Zeng and Dr.
Yufei Meng for their helps on the reduction of X-ray PDF data
and IR measurements.
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Keywords: C6H6-C6F6 cocrystal • Hydrogenated-fluorinated
graphane • Pressure-induced polymerization • Cycloadditions •
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This article is protected by copyright. All rights reserved.

10.1002/anie.201813120
Angewandte Chemie International Edition
COMMUNICATION
COMMUNICATION
Yajie Wang, Xiao Dong, Xingyu Tang,
Haiyan Zheng,* Kuo Li,* Xiaohuan Lin,
Leiming Fang, Guang’ai Sun, Xiping
Chen, Lei Xie, Craig L. Bull, Nicholas P.
Funnell, Takanori Hattori, Asami Sano-
Furukawa, Jihua Chen, Dale K. Hensley,
George Cody, Yang Ren, Hyun Hwi Lee,
Ho-kwang Mao
Short range ordered H,F-substituted graphane was obtained by compressing
benzene and hexafluorobenzene cocrystal. By using neutron diffraction and gas
chromatography-mass spectrum, we figured out the reaction process and elementary
reaction. The reaction process contains [4+2]Diels-Alder, retro-Diels Alder, and 1-1’
coupling, and the Diels-Alder reaction is the key reaction in the polymerization
process.
Page No. – Page No.
Pressure-Induced Diels-Alder
Reactions in C6H6-C6F6 Cocrystal
towards Graphane Structure
This article is protected by copyright. All rights reserved.