A catalytic synthesis and structural characterization of a new [84]fullerene isomer

Article abstract of DOI:10.1039/b103679n

The synthesis, separation and isolation of a new [84]fullerene isomer from arc-burned soot of dysprosium-doped graphite composite rods is reported; high-resolution ¹³C NMR and electronic absorption UV-VIS-NIR spectroscopy were used to characterize this material, which was found to possess C₂ molecular symmetry; the successful synthesis of the new [84-C₂]fullerene isomer can be ascribed to a catalytic role played by the doped Dy metal atoms in the composite rods.

Full text of DOI:10.1039/b103679n

A catalytic synthesis and structural characterization of a new
[84]fullerene isomer
Nikos Tagmatarchis,a Kozue Okada,a Tetsuo Tomiyama,a Takuya Yoshida,b Yuji Kobayashib and
Hisanori Shinohara*a
a Department of Chemistry, Nagoya University, Nagoya 464-8602, Japan.
E-mail: nori@nano.chem.nagoya-u.ac.jp
b Department of Pharmacology, Osaka University, Osaka 565-0871, Japan
Received (in Cambridge, UK) 24th April 2001, Accepted 8th June 2001
First published as an Advance Article on the web 5th July 2001
The synthesis, separation and isolation of a new [84]full-
erene isomer from arc-burned soot of dysprosium-doped
of-flight (LD-TOF) mass spectrometry. The UV-VIS-NIR
spectrum was recorded between 400 and 2000 nm in carbon
disulfide solutions by using a Shimadzu UV-3101PC spectro-
photometer. Finally, the high resolution 13C NMR measure-
ments were performed on a Varian Inova-600 spectrometer at
600 MHz (CS2 solution, Cr(acac)3 relaxant, acetone-d6 lock at
25 °C).
graphite composite rods is reported; high-resolution 13
C
NMR and electronic absorption UV-VIS-NIR spectroscopy
were used to characterize this material, which was found to
possess C2 molecular symmetry; the successful synthesis of
the new [84-C2]fullerene isomer can be ascribed to a catalytic
role played by the doped Dy metal atoms in the composite
rods.
In the first HPLC stage, the fraction that contains the
[84]fullerene isomeric mixture was separated from the empty
[76], [78] and [86]fullerenes as well as from the endohedral
metallofullerenes Dy@C82 and Dy2@C84 by using a Buckyprep
column (15 ml min21 flow rate, toluene eluent).7 In the second
stage, the fraction, which was identified by LD-TOF mass
spectrometry as empty [84]fullerenes, was re-injected into a
5PYE column (15ml min21 flow rate, toluene eluent) and a
recycling HPLC was performed. After recycling for 90 min, the
mixture of the two most abundant [84]fullerene isomers with
D2(IV) and D2d(II) symmetry was separated from a mixture of
various minor [84]fullerene isomers. In the last HPLC stage, the
fraction that contained the mixture of the minor isomers was re-
injected into a 5PYE column (15 ml min21 flow rate, toluene
eluent) for the final separation. Four different compounds were
identified after recycling for more than 3 h, all of which
corresponded to [84]fullerene isomers. The purity of the
isolated material was more than 99.9% as determined by both
negative and positive laser desorption time-of-flight mass
spectrometry.
[84]Fullerene, C84, has been solvent extracted in macroscopic
quantities since the early stages of fullerene research.1 It is the
third most abundant fullerene having 24 structural isomers that
obey the so-called isolated pentagon rule (IPR).2 Taylor et al.
reported 13C NMR measurements on a partially separated
[84]fullerene mixture.3 However, to date only nine of these
isomeric materials have been isolated and structurally charac-
terized by high resolution 13C NMR spectroscopy. Two of them,
abundantly produced, possess D2(IV) and D2d(II) molecular
symmetry,4 while the other five minor isomers having Cs(a),
Cs(b), C2, D2(II) and D2d(I) symmetries5 and a mixture of D3d/
6
D6h have already been isolated and structurally charac-
terized.
One important aspect on the production and isolation of the
above minor [84]fullerene isomers is that some of them have
been produced only from metal-doped/graphite composite rods
and not from pure graphite rods. This means that such isomers
can be produced by catalytic effects of the doped metal atoms.
For example, the D3d/D6h isomers have been identified in the arc
burned soot of gadolinium doped composite rods6 while they
were absent in the arc burned soot of calcium doped composite
rods.5 In the latter, only the Cs(a), Cs(b), C2, D2(II) and D2d(I)
symmetrical [84]fullerenes were found, in different yields
compared to Gd-doped soot, together with the most abundant
D2(IV) and D2d(II) isomers. These findings led us to consider
the possibility that the doped metal atoms play a significant role
not only in the relative production yield of these isomers but
also in the nature of the isomer that is formed.
Three of the four isomeric [84]fullerenes described above
(hereafter referred as I, III and IV in order of increasing
retention time) showed identical UV-Vis-NIR absorption
spectra with those of the known minor [84]fullerene isomers
with molecular symmetries C2, Cs(b) and Cs(a), respectively,5
albeit in different yields. However, the material corresponding
In this communication, we report the production of a new
isomer of [84]fullerene, C84, by using arc burning of dyspro-
sium-doped composite rods. Briefly, soot containing various
dysprosium metallofullerenes7 was produced by the direct
current arc discharge method of Dy2O3–graphite composite
rods (12.5 3 12.5 3 300 mm, 0.8 wt%, Toyo Tanso Co.). The
dysprosium composite rods were heat treated at a high
temperature of 1600 °C. The soot produced was collected under
totally anaerobic conditions to avoid any degradation from air
during the collection procedure. It was then soxhlet extracted
first by carbon disulfide and then by pyridine. The separation of
[84]fullerene isomers was achieved by multi-stage high-
performance liquid chromatography (LC-908-C60, Japan Ana-
lytical Industry) using a Buckyprep (20 3 250 mm, nakalai
tesque) and a 5PYE (20 3 250 mm, nakalai tesque) columns.4–7
The purity of the newly synthesized material ( > 99.9%) was
confirmed by both positive and negative laser-desorption time-
Fig. 1 Electronic absorption UV-VIS-NIR spectrum of the C84(II) minor
isomer, with C2 molecular symmetry in carbon disulfide solution.
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Chem. Commun., 2001, 1366–1367
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b103679n

120,000 scans. The spectrum consists of forty-two equal
intensity lines which are spread over a wide range of the
chemical shift from 125 to 150 ppm. The current isolated
[84]fullerene isomer is thus unambiguously assigned to possess
C2 molecular symmetry. Rotation of 180 degrees around the
symmetry axis generates 42 equivalent carbon atoms. There are
six structural isomers of [84]fullerene with C2 symmetry that
satisfy the isolated pentagon rule.2 Two-dimensional high
resolution 13C NMR spectroscopy could reveal which one, out
of the six possible isomers, is the present [84-C2]fullerene, in
the future.
Theoretical calculations on the relative stability of isomeric
[84]fullerenes have shown a relatively good agreement between
the theoretical stability order and the observed abundance of the
isomers.8 These calculations predict that the most stable
isomers after D2(IV) and D2d(II) are those with C2(IV), Cs(V),
D3d and D6h molecular symmetries. We have found, however,
that under similar experimental conditions employing different
metal-doped composite rods not only the produced amounts of
minor isomers of [84]fullerenes are different but more im-
portantly different isomers are formed. This implies a catalytic
effect for the doped-metal in the early stage of the growth of
these isomers. Although progress in this research area is rapid,
there are still lots of questions opened concerning the growth
mechanism of fullerenes and metallofullerenes.9 The current
finding that the doped metal atoms play a crucial role in
producing a new [84]fullerene isomer strongly suggests the
presence of interplay between an encapsulation and a catalytic
role of the doped metal atoms in the early stage of fullerene
growth.
Fig. 2 High-resolution 13C NMR spectrum [600 MHz, CS2 solution,
Cr(acac)3 as relaxant and acetone-d6 for the internal lock] of the purified
minor isomer of C84(II) with C2 molecular symmetry. The chemical shifts
for the forty-two lines are at d: 148.93, 148.00, 146.87, 145.01, 144.77,
144.72, 143.66 (double line), 143.55, 143.48, 143.03, 142.98, 142.86,
142.76, 142.63, 141.12, 140.99 (double line), 140.32, 140.25, 139.21,
139.14, 138.88, 138.30, 138.00, 137.84, 137.56, 137.50 (double line),
137.29, 137.00, 136.91, 136.47, 136.42, 136.19, 136.09, 136.04, 134.67,
133.80, 132.28, 131.31 and 124.47 ppm. The * corresponds to two signals
which are overlapped with each other. Inset is an expanded region between
139.5–135.5 ppm for clarity.
N. T. thanks the Japan Society for the Promotion of Science
(JSPS) for a Post Doctoral Fellowship for Foreigner Re-
searchers. H. S. thanks JSPS for the Future Program on New
Carbon Nano-Materials.
to the second fraction on the 5PYE column, C84(II), showed an
entirely different absorption profile from those of the previously
isolated [84]fullerene isomers.
Notes and references
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2 P. W. Fowler and D. E. Manolopoulos, An Atlas of Fullerenes,
Clarendon, Oxford, 1995, pp. 73–80.
3 A. G. Avent, D. Dubois, A. Penicaud and R. Taylor, J. Chem. Soc., Perkin
Trans. 2, 1997, 1907.
4 T. J. S. Dennis, T. Kai, T. Tomiyama and H. Shinohara, Chem. Commun.,
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5 T. J. S. Dennis, T. Kai, K. Asato, T. Tomiyama, H. Shinohara, T.
Yoshida, Y. Kobayashi, H. Ishiwatari, Y. Miyake, K. Kikuchi and Y.
Achiba, J. Phys. Chem. A, 1999, 103, 8747.
6 N. Tagmatarchis, A. G. Avent, K. Prassides, T. J. S. Dennis and H.
Shinohara, Chem. Commun., 1999, 1023.
7 N. Tagmatarchis and H. Shinohara, Chem. Mater., 2000, 12, 3222.
8 B. L. Zhang, C. Z. Wang and K. M. Ho, J. Chem. Phys., 1992, 96,
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Fig. 1 shows the UV-VIS-NIR electronic absorption spec-
trum of [84]fullerene (II) in carbon disulfide solution. There are
characteristic absorptions at 444, 506, 631, 715, 782, 1231 nm
and a broad profile from 830 to 1400 nm with the onset around
1500 nm. From all isomeric [84]fullerenes, this particular
isomer has the lowest energy onset. Since the onset of a UV-
VIS-NIR electronic absorption spectrum corresponds to the
lowest electronic transitions, this is a good measure for the
HOMO–LUMO energy gap of fullerenes. Because of the red
shift of the absorption onset relative to the other [84]fullerene
isomers, the HOMO–LUMO band gap of [84]fullerene (II)
should be smaller than that of the rest materials.
Fig. 2 shows the high resolution 13C NMR spectrum of the
newly synthesized and isolated [84]fullerene (II) in carbon
disulfide solution with chromium tris(acetylacetonate) as relax-
ant and acetone-d6 as internal lock after accumulating more than
9 H. Shinohara, Rep. Prog. Phys., 2000, 63, 843.
Chem. Commun., 2001, 1366–1367
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