Simple combustion production and characterization of octahydro[60]fullerene with a non-IPR C60 cage

Article abstract of DOI:10.1021/ja108316e

For the first time an easier, operable combustion method is employed for the synthesis of non-IPR fullerene, and an octahydro[60]fullerene with a non-IPR C₆₀ cage (C₆₀ isomer ^#1809C₆₀) produced by combustion is isolated and characterized by MS, UV-vis, IR, and NMR spectroscopies in combination with DFT calculations. This finding shows that, in addition to chlorine, hydrogen can be an ample cataloreactant for the production of non-IPR fullerene derivatives under such conditions as arc-burning and diffusion combustion.

Full text of DOI:10.1021/ja108316e

Published on Web 10/08/2010
Simple Combustion Production and Characterization of
Octahydro[60]fullerene with a Non-IPR C60 Cage
Qun-Hong Weng,† Qiao He,† Ting Liu,† Hui-Ying Huang,‡ Jian-Hua Chen,† Zhi-Yong Gao,†
Su-Yuan Xie,*,† Xin Lu,*,† Rong-Bin Huang,† and Lan-Sun Zheng†
State Key Laboratory of Physical Chemistry of Solid Surface, and Department of Chemistry, College of Chemistry
and Chemical Engineering and School of Life Science, Xiamen UniVersity, Xiamen, 361005, China
Received April 15, 2010; E-mail: xinlu@xmu.edu.cn (X.L.); syxie@xmu.edu.cn (S.Y.X.)
Abstract: For the first time an easier, operable combustion
method is employed for the synthesis of non-IPR fullerene, and
an octahydro[60]fullerene with a non-IPR C60 cage (C60 isomer
#1809
C ) produced by combustion is isolated and characterized
60
by MS, UV-vis, IR, and NMR spectroscopies in combination with
DFT calculations. This finding shows that, in addition to chlorine,
hydrogen can be an ample cataloreactant for the production of
non-IPR fullerene derivatives under such conditions as arc-
burning and diffusion combustion.
Fullerenes violating the isolated pentagon rule (IPR)1 have caught
much attention2 ever since discovery of the first buckyball molecule
C60,3 which itself is the smallest IPR-satisfying fullerene. It was
believed that non-IPR fullerenes with abutting pentagons play a
pivotal role (e.g., as precursors) in the formation of stable IPR-
satisfying fullerenes.4,5 However, the inherent instability of non-
IPR fullerenes pertaining to their abutting pentagons6 poses
Figure 1. (a) HPLC/APCI-MS chromatogram of toluene-extracted soot
products. (b) APCI-MS for C60H8 with isotope distribution (high-resolution
difficulties in the synthesis, isolation, and chemical manipulation
MS) inset.
of pristine non-IPR fullerenes. Nevertheless, recent experimental
and theoretical investigations have shown that non-IPR fullerenes
can be effectively stabilized by endohedral encapsulation or
exohedral functionalization.2 An increasing number of non-IPR
fullerenes have been synthesized and characterized as endohedral
fullerenes, e.g., Sc3N@C687 and Sc2C2@C68,8 and exohedral deriva-
tives including C50Cl10,9 C58F18,10 C64X4 (X ) H11 and Cl9b),
C56Cl10,12 C60Cln (n ) 8,12),13 C76Cl24,14 C54Cl8, C56Cl12, C66Cl6,
and C66Cl10.15 Most of these non-IPR fullerene derivatives were
produced by means of graphite arc-discharge. It should be noted
that in the macroscopic production of fullerenes, graphite arc-
discharge is far less efficient than the combustion method. The
latter’s merits are easier operable synthetic device, higher yield of
fullerene soot, and consecutive synthesis.16,17 It is stimulating that
we recently detected in combustion-produced soot the presence of
C64H4,17c which likely has a non-IPR fullerene cage.11 Herein we
report the production of a new hydro[60]fullerene C60H8 with a
non-IPR cage (C60 isomer #1809 termed by the spiral algorithm18)
by the simple combustion method. The structure of this novel
fullride has been characterized by MS, UV/vis, IR, and NMR
spectroscopies in combination with density functional theory (DFT)
Figure 2. (a) 13C NMR spectrum of C60H8 (150 MHz, C6D6 solvent, room
temperature). The asterisk-marked signals are due to residual toluene. (b)
DEPT spectrum. (c) 1H NMR spectrum (600 MHz, C6D6 solvent, room
temperature).
calculations.
Soot containing C60H8 was produced by a modified diffusion
combustion approach,19 in which the mixtures of acetylene and
benzene with oxygen were burnt at 15-20 Torr in a steel chamber.
The optimized gas flow rates are 0.55 L/min for O2, 1.10 L/min
for C2H2, and 1.0-1.1 L/min for vaporous benzene. During the
process of combustion, hot flow of the gaseous products from the
chamber carried soot through a water-cooled conduit onto a filter
paper, just outside the combustion furnace for gathering the soot.
The soot productivity can be up to 5 g per hour efficiently.
† State Key Laboratory of Physical Chemistry of Solid Surface.
‡ School of Life Science.
9
10.1021/ja108316e  2010 American Chemical Society
J. AM. CHEM. SOC. 2010, 132, 15093–15095 15093

C O M M U N I C A T I O N S
Separation of C60H8 from the trapped soot was conducted using a
high pressure liquid chromatography (HPLC) (see Supporting
Information for the synthetic device and HPLC isolation of C60H8).
Figure 1a shows the HPLC/mass spectra of a prepurified extract
solution from the combustion soot; the major products are C60 and
C
70 with C60H8 as a minor component. An amount of ∼5 mg C60H8
with purity up to 99% was finally isolated and characterized by
means of UV/vis, IR, and NMR spectroscopies. The high-resolution
mass spectrum (Figure 1b) of purified C60H8 sample shows the
molecular ion peak of 728 amu, agreeing well with the simulated
mass spectrum of C60H8.
Solution of C60H8 in cyclohexane or benzene is light yellow.
The 13C NMR spectrum of C60H8 in C6D6 solvent (Figure 2a) shows
four upfield signals (4 × 2, 47.8, 48.7, 51.3, and 55.7 ppm) arising
from sp3-hybridized carbon atoms, and about 27 downfield signals
ranging from 132.3 ppm to 152.0 ppm pertaining to sp2-hybridized
carbon atoms. DEPT spectrum (Figure 2b) further indicates that
C60H8 has in total four types of sp3-hybridized carbon atoms attached
by H atoms, suggesting this molecule belongs to Cs, C2, or Ci point
group of symmetry.
1
Figure 3. Selected range of H-1H COSY spectrum of C60H8.
1
The H NMR spectrum of C60H8 in C6D6 solvent (Figure 2c)
comprises four parts (Ha, Hb, Hc, and Hd) with the peak-area integral
ratio 2:2:2:2. The doublet peak at 4.95 ppm (Hd) is clearly discerned
from the multiplet peaks around 4.2 ppm for Ha, Hb, and Hc. With
1
the aid of 2D H-1H COSY spectrum (Figure 3), the multiplet
peaks could be disassembled clearly: Ha (doublet, 4.19 ppm, 2H),
Hb (triplet, 4.22 ppm, 2H) and Hc (quadruplet, 4.26 ppm, 2H). The
COSY spectrum also indicates the following spin-spin coupling
correlations. First, Hd is weakly correlated to Hc with a coupling
constant (Jcd) of 2.4 Hz. Second, Ha is strongly correlated to Hb
(Jab ) 10.3 Hz). Third, Hb is strongly correlated to Ha and Hc. Based
on Jab and Jcd, the coupling constant Jbc for the spin-spin coupling
between Hb and Hc is estimated to be ∼7.0 Hz. Thus, the C60H8
has four types of H atoms; among them, Ha, Hb, and Hc are linked
to three sequentially neighboring carbon atoms, whereas the Hd-
linked carbon atom is by one or two sp2-hybridized carbon atoms
away from the Hc-linked carbon atom.
Figure 4. Schlegel diagrams (black dots: H-linked C atoms) for three low-
energy isomers 1-3 of C60H8, together with the ball-and-stick model of
the lowest-energy isomer 1. PBE/DNP-predicted symmetry and relative
energy (in kcal mol-1) are given in parentheses.
Yet, the aforementioned NMR spectra are not enough to afford
a clear-cut determination of the C60H8 structure. On account of the
harsh synthetic conditions, final products surviving from the
combustion process are likely thermodynamically favored. Hence,
we performed semiempirical PM320 calculations and DFT calcula-
tions at the PBE/DNP level of theory21 to search for the lowest-
energy structure of C60H8, in which the C60 cage may be the IPR-
satisfying one, i.e., #1812C60,18,22 or a non-IPR one, e.g., #1809C60.13
Figure 4 shows three low-energy isomers of C60H8 from PBE/DNP
calculations. Both isomers 1 and 2 contain the same non-IPR #1809C60
shifts are 52.9 (Ca), 52.5(Cb), 55.7 (Cc), and 59.4 (Cd) ppm,
corresponding to the measured ones, 48.7, 47.8, 51.3, and 55.7
ppm.24 The computed 13C chemical shifts for 27 types of sp2-
hybridized carbon atoms (25 × 2, 2 × 1) range from 132.1 to 150.7
ppm, in accordance with the measured ones ranging from 132.3 to
152.0 ppm (see Supporting Information for details). These com-
putational data clearly show that the synthesized C60H8 is isomer 1
with a non-IPR C60 cage.
cage with two pentagon-pentagon fusions, while isomer 3 has the
The IR spectrum of C60H8 (Supporting Information) shows
intense absorptions around 2900 cm-1, a fingerprint of tertiary CH
moieties.25 The UV/vis spectrum (Supporting Information) of C60H8
#1812
C
60
cage. Among them, the Cs-symmetric isomer 1 is the lowest-
energy isomer of C60H8; isomer 2, isostructural to the previously
13
#1809
synthesized
C Cl8, is by 4.6 kcal mol-1 less stable than 1;
60
in cyclohexane solution shows absorptions at 215, 254, 280, 342,
isomer 3 is by 15.8 kcal mol-1 higher in energy than 1. Notewor-
thily, the lowest-energy isomer 1 has the structural features
(symmetry and H positions) deduced from the NMR spectra.
#1812
and 393 nm, differing slightly from those of
C (absorptions
60
at 210, 256, 328, 405 nm).13 The PBE/DNP-predicted HOMO-
C H8 1 is 1.67 eV, equal to that of
Both UV/vis spectrum and DFT calculations show
wide band gap fulleride.
#1809
#1812
LUMO gap of
C .
60
60
We then computed the NMR chemical shifts and 1H-1H
spin-spin coupling constants of C60H8 1 at the GIAO-B3LYP/6-
C H8 is a
60
#1809
31G** level of theory.23 The DFT-predicted H-1H spin-spin
It is interesting to note that the newly synthesized
C H8
60
1
#1809
coupling constants (Jab ≈ 10.5, Jbc ≈ 7.5, Jcd ≈ 4.2 Hz) agree well
with the experimental ones (Jab ≈ 10.3, Jbc ≈ 7.0, Jcd ≈ 2.4 Hz).
The predicted 1H chemical shifts for the four types of H atoms (Ha
≈ 4.7, Hb ≈ 4.5, Hc ≈ 4.7, and Hd ≈ 5.4 ppm) are comparable to
the experimental ones (4.2, 4.2, 4.3, 4.9 ppm). For the four types
of sp3-hybridized carbon atoms, the DFT-calculated 13C chemical
isomer 1 (Figure 4) differs in structure from the previously reported
#1809
C Cl8 isomer 2, despite both compounds sharing the same non-
60
#1809
IPR
C
cage and having the same number of exohedral
60
addends. In accordance with such experimental observations, PBE/
DNP computations revealed that for the octa-chlorinated case
#1809
#1809
C Cl8 2 is by 3.0 kcal mol-1 more stable than
C Cl8 1,
60
60
9
15094 J. AM. CHEM. SOC. VOL. 132, NO. 43, 2010

C O M M U N I C A T I O N S
#1809
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while for the octa-hydrogenated case,
C H8 1 is by 4.6 kcal
60
mol-1 more stable than isomer 2. Thus, the exohedral addition
pattern of #1809C60 depends on the nature of addends. A similar trend
could be found for the different hydrogenation/chlorination patterns
26
#1812
of
C . That is, chlorine atoms are more spatial and more
60
sterically repulsive than hydrogen atoms, and as a result, addends
tend to lie together in C60Hn and to be separated apart in C60Cln.26
Note that #1809C60H8 isomer 1 and #1809C60Cl8 isomer 2 share the
common features that the active pentagon-pentagon fusions of the
non-IPR carbon cage are completely saturated by H or Cl atoms
and their small sp2-hybridized carbon fragments, i.e. a benzene-
#1809
like C6 ring in
C H8 1 and a naphthalene-like C10 ring in
C Cl8 isomer 2, fulfill the Hu¨ckel rule of aromaticity. These
60
#1809
60
two special addition patterns of H/Cl addends improve the planarity
of the sp2-hybridized carbon fragments and, hence, enhance their
π-electronic conjugation and delocalization.27 These features ac-
#1809
count for the stability of both non-IPR
C
derivatives. In
60
addition, the very small energy gap between isomers 1 and 2 for
both the chlorinated and hydrogenated cases suggests that #1809C60H8
isomer 2 and #1809C60Cl8 isomer 1 also could be synthetically viable
and deserve further experiments.28
In conclusion, we have synthesized a non-IPR fullerene derivative
by simple combustion of gaseous acetylene/benzene mixture. The
synthesized crown-shaped octahydro[60]fullerene, though sharing
13
#1809
#1809
the same non-IPR
C
60
cage with
C Cl8, is the first
60
hydrogenated fulleride of non-IPR C60. Moreover, the successful
synthesis of this non-IPR hydro[60]fullerene shows that in addition
to chlorine, hydrogen can be an ample cataloreactant for the
production of non-IPR fullerene derivatives under such conditions
as arc-burning and combustion. Further experiments are in progress
in our laboratory to synthesize other non-IPR fullerenes by the
hydrogen-involving arc-burning and combustion processes.
Acknowledgment. This work was sponsored by NSFC (Nos.
20525103, 20673088, 20973137, 20721001, 20423002, 21031004)
and 973 projects (Nos. 2007CB815301 and 2007CB815307).
(23) For the hybrid density functional B3LYP method, see: (a) Becke, A. D.
J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.; Yang, W.; Parr, R. G. Phys.
ReV. B 1988, 37, 785. For the GIAO method, see: (c) Wolinski, K.; Hilton,
J. F.; Pulay, P. J. J. Am. Chem. Soc. 1990, 112, 8251, and references therein.
The PM3 and GIAO-B3LYP calculations were performed with the Gaussian
09 A.02 suite of programs. (d) Frisch, M. J.; et al. Gaussian09, Rev. A.02;
Gaussian, Inc.: Wallingford CT, 2009.
Supporting Information Available: Scheme of synthesis apparatus,
chromatograms of isolation of C60H8, IR and UV/vis spectra of C60H8,
thermostability of C60H8, PM3- and PBE/DNP-computed relative
energies of C60H8 isomers, details of GIAO-B3LYP NMR calculations
of C60H8, Cartesian coordinates of C60H8 isomers, and complete ref
23d. This material is available free of charge via the Internet at http://
pubs.acs.org.
(24) The B3LYP-predicted chemical shifts of the sp3-hybridized carbon are
overestimated by ∼4 ppm compared to the experimental data. This is also
true for other hydrofullerenes such as C3V-C60H18 and C3V-C64H4. See the
Supporting Information for details.
(25) Henderson, C. C.; Cahill, P. A. Science 1993, 259, 1885.
(26) Troyanov, S. I.; Kemnitz, E. Eur. J. Org. Chem. 2005, 4951.
(27) Taylor, R. Phys. Chem. Chem. Phys. 2004, 6, 328.
(28) Zhou, T., Weng, Q. H., Xie, S. Y., Huang, R. B., Zheng, L. S. Unpublished
results.
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