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Material Properties and Purity of C60.

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CAS Registry numbers:
5a, 107-19-7; Sb, 2028-63-4; Sc, 818-72-4; Sd, 115-19-5; Se, 764-01-2; 6,
141461-89-4; 7a, 141461-90-7; 7b, 141483-78-5; 7c, 141462-03-5; 7d, 14146204-6; 7e, 141462-05-7; 8, 135013-47-7; 9a, 141461-91-8; 9b, 141462-06-8; 9c,
141462-07-9; 9d. 141462-08-0; 9e, 141462-09-1; 10, 141461-92-9; 11, 14146193-0; 12, 88892-85-7; 13, 141461-94-1; 14, 115-18-4; 15, 141461-95-2; 17,
12422-42-5, 18, 1611-61-6; 19, 18913-31-0; 20, 141461-96-3; 21, 141461-97-4;
22, 141461-98-5; 23, 141461-99-6; 24, 110-65-6; 25, 141462-00-2; 26, 14146201-3; 27, 141462-02-4.
[I]
[2]
[3]
[4]
[S]
[6]
[7]
[8]
C. Christophersen, A. Holm, Actu Chem. Scund. 1970, 24, 1512-1526.
A. Holm. Adv. Heterocycl. Chem. 1976, 20, 145-174.
E. Lieber, C. B. Lawyer. J. P. Trivedi, J. Org. Chern. 1961, 26, 1644--1646.
The formation of isocyanurates is also a characteristic reaction of isocyanates. For example, in the presence of CsF/perhydrodibenzo-l8.~rown6/toluene, 9b trimerizes to a colorless solid. m.p. 66°C (pentane), yield
73%.
K. Banert. H. Hiickstddt. K. Vrobel, Anpew. Chem. 1992. 104, 72-74;
Angew. Chem. I n f . Ed. Engl. 1992, 3f390-92.
A. Gagneux, S. Winstein, W. G. Young, J. A m . Chem. Sac. 1960.82,59565957.
F. W Hoover, H. S. Rothrock, J Org. Chem. 1964, 29, 143-145.
L. Brandsma, H. D. Verkruijsse, Synthesis ofAcerylenes, Allrnes and Cumulene.9, Elsevier. Amsterdam, 1981, p. 188.
below room temperature with low abundancies of oxygen to
give carbon dioxide." 'I Evidence of stable adducts of fullerenes and OH or (CH,), (x = 1-7) was provided by mass
spectrometry." '1
All these reports point to the relevance of the analogy of
fullerenes and active charcoal, and provide reasons for invesC,, . Possitigating of the material properties of
ble impurites are solvent and/or components of the air. The
following experiments prove their presence in crystalline
powders of C,, .
Figure 1 shows powder diffraction diagrams of samples of
C,, treated in different ways. Only the sublimed sample provides a diffractogram that matches the diffraction pattern
simulated from the single-crystal data.[,] Positions, intensi-
I
25
Material Properties and Purity of C,,""
By Harald Werner, Daniela Bublak, Ulrich Gobel,
Bettina Henschke, Wolfgang Bensch, and Robert SchlogP
Since the production of larger amounts of fullerenes has
become possible by means of an electric
interest in
this new allotropic form of carbon has grown by leaps and
bound^.^^] The availability of C,, with reproducible quality
and the knowledge of the material properties of C,, in the
solid state are important for reliable research results as well
as potential technical applications. C,, forms van der Waals
crystals with a face-centered cubic structure.[5,6l Foreign
atoms can be deposited in the interstices giving the crystal
superconducting properties, for example.[71Fullerenes can
be considered molecular analogues of the microporous carbon materials, which because of their large inner surfaces are
used as adsorbents.[*] For the application, storage, and production of fullerenes it is crucial to know if this allotropic
form of carbon is also able to absorb substances from the
environment and thus change the properties of the crystals.
An indication of such effects is, for example, the fact that
we and others have found the experimentally determined
densities of the crystals to be too great (1.721.78 g ~ m - ~ ) . L ~(The
, ~ , density obtained from the X-ray
crystal structure analysis of C,, is only 1.68 gcrn-j.) The
reports of paramagnetic
paramagnetic impurities," 'I and an "excess" paramagnetism['21 for pure C,, are
also remarkable. There are several reports of presumed
changes in the crystal structure of C,, upon recrystallizat i ~ n [ ' ~and
] the formation of adducts with donor solv e n t ~ . [l 4~I ~Fullerene
oxides with an epoxide structure can
be obtained from dissolved fullerenes in the presence of oxygen and light["] or by reaction with oxygen-transfer
reagents.",' In ultrahigh vacuum (UHV) films of C,, react
[*I
[**I
868
Prof. Dr. R. Schlogl, Dip].-Chem. H. Werner. D. Bublak, Dipl.-Chem. U.
Gobel, DipLChem. B. Henschke, Dr. W. Bensch
Institut fur Anorganische Chemie der Universitat
Niedelurseler Hang, D-W-6000 Frankfurt 50 (FRG)
This research was supported by the Fonds der Chemischen Industrie, the
Hermann-Willkom-Stiftung, and the Max-Planck-Gesellschaft. We thank
Prof. G. Quinkert and Prof. H. Bock for their help In measuring the IR and
EPR spectra. respectively.
(0 VCH
Verlagspesellschuff mbH, W-6940 Weinheim. 1992
10.0
15.0
20.0
28
-
25.0
30.0
35.0
Fig. 1. X-ray powder diffraction patterns of analytically pure (C 99 %) samples
of C,, . The measurements were conducted in sealed capillaries under argon in
focussing Bragg-Brentano geometry with monochromated copper radiation. a)
After sublimation, h) recrystallized from benzene, c) recrystallized from
toluene. The sublimation was carried out in a quartz tube at 1 x lo-' mbarand
900K. I = relative intensity.
ties, and widths of the additional reflections of the recrystallized samples correlate with the amount of solvent detected
by IR spectroscopy. The position of the main reflections
(face-centered cubic lattice with a=1415.2 pm) differs only
slightly for the various samples. The additional reflections
indicate the formation of partially long range-ordered solvent adducts.
By rigorous drying of the samples under vacuum
mbar at about 350K, the solvent can be removed until
no C-H stretching bands remain in the IR spectrum. However, absorptions in the fingerprint region at 1627, 1537,[201
and especially at 1384 cm-' arise.
The band at 1384 cm-' is intense for sublimed samples
and becomes the strongest band in the spectrum when the
sample is stored with exposure to light and air; no other
absorptions arise, and the C,, bands do not change appreciably. The position and the isolated appearance of this band
could indicate the formation of a C-0 single bond similar to
those found in aryl ethers. The X-ray structure analysis of a
single crystal obtained by sublimation clearly showed electron density maxima outside the perimeter of C6,; these were
assigned to statistically occupied oxygen positions distributed over eight hexagonal surfaces.16]
The presence of paramagnetic impurites in extremely
varying concentrations was established by EPR spec-
o570-0833192lO707-0868 $3.50+ .25/0
Angen. Chem. I n t . Ed. Engl. 1992, 31. N o . 7
Fig. 2. Summary of the temperature-programmed decomposition experiments followed by mass spectrometry with recrystallized (large picture) and sublimed (small
picture) C , , . p = pressure in arbitrary units.
troscopy. The parameters of the spectra[221show that the
signals can hardly be attributed to an intrisic spin density['21
of pure C6,; rather they indicate paramagnetic impurities
that apparently can be removed efficiently but not completely by sublimation.
More detailed information about the nature of the trace
impurites is obtained from thermal degradation experiments
in UHV.[231The analysis can be conducted to be either bulk
specific or surface sensitive by varying the rate of heating
between 1 K s - ' and 10 Ks-'. In Figure 2 the bulk desorption of a C,, sample recrystallized from toluene is compared
to that of a sublimed sample. Only water and traces of CO,
and CO were released from the sublimed material at 500 K ;
no water but oxygen and numerous organic fragments escaped from the recrystallized material in two temperature
regions at 523 K and 723 K. The analysis of the peak profile
in Figure 2 reveals two series of fragments assigned to diethyl
ether ( m / z 27, 28, 29, 31,45, 59, 74) and toluene ( m / z 39, 51,
65,91,92). Neither CO nor CO, were detected in any significant amounts. Ether had been used to wash the crystals and
was apparently incorporated in the crystals in the same way
as the actual solvent had been, though the latter escapes
primarily at higher temperatures. The high temperatures required for desorption point to considerable binding energies
in the van der Waals crystal. It is certainly plausible that
these impurites could affect the lattice dynamics of the crystals,'4. 5,101
The release of a substantial amount of molecular oxygen
from the crystals containing solvent takes place at a different
temperature (670 K) than the release of the organic impurities. The oxygen in the crystal is present in a form that does
not lead to the oxidation of C,, upon thermal activation.
This finding is in agreement with the observed stability of
molecular C,, to oxidation.[3b,1 6 1 Comparison of the oxygen
desorption data with the IR spectra reveals that the intensity
of the band at 1384 cm- ' does not correlate with the amount
of liberated oxygen. If the oxygen actually arises from the
compound that produces this IR band, then it either reacts
in the sublimed material with hydrogen also present[21] to
form water, or it binds with the substrate. In material containing solvent the single atoms of oxygen react to give O,,
but never form CO,. This is in accord with earlier oxidation
Angrw. Chem. I n [ . Ed. Etigl. 1992, 31, N o . 7
:K
experiments,[24] in which formation of CO, was first observed above 700K in diluted oxygen.
Desorption experiments with rapid heating rates provide
a complementary picture. The data for the sublimed material
( a s ) and the recrystallized material (d-f) are summarized in
Figure 3. The desorption of toluene (not shown) exhibits the
same pattern as seen in Figure 2. The differences in the desorption behavior originate in the various reaction kinetics of
oxygen and not from experimental artifacts.
Figure 3 a verifies that untreated C,, indeed releases
molecular oxygen in two temperature ranges, possibly implying that the oxygen is located at different depth (subsurface and bulk) in the crystal. The desorption is complete after
f
T IOCI
-
m/z=ll
100
200
- LOO
300
riw
Fig. 3. Temperature profiles of selected mass spectral signals from desorption
experiments with crystalline powders of C,, after various pretreatments. a)-c)
Sublimed material, d)-f) solvent recrystallized and dried C6,,, See text for
details.
the sample is heated once, but oxygen can be readsorbed by
treatment of the sample with 200 mbar of 0, for 2 h at 300 K
(Fig. 3 b). Thus even the most pure material takes up oxygen
from the air or from impure inert gas. Storage under 1 mbar
of 0, for 48 h leads to surface oxidation, as demonstrated by
the formation of CO, (Fig. 3c); this behavior agrees with the
known spectral data."']
VCH Verlugsgesellschuft mbH. W-6940 Weinheirn, 1992
0570-0833/92/0707-0S69$3.50+ .2Sj0
869
Recrystallized material, on the other hand, contains oxygen in another binding state initially and provides a spectrum (Fig. 3d) similar to that in Figure 2. After desorption
of the solvent, at least from the regions close to the surface,
the sample can be loaded like the sublimed material (Fig. 3 e)
and is then sensitive to oxidation. Spectrum 3 f was obtained
from a sample that was treated analogously to the sample
that provided spectrum 3 b and shows that brief treatment
with 0, does not cause oxidation; however, heating the
sample under a low partial pressure of CO, leads to dissolution in the bulk (decrease in the baseline to 650 K).
In summary, these experiments show that solid C,, is not
an inert van der Waals crystal, but a solid with complex
reaction behavior. The internal surface of the crystal is either
saturated with solvent molecules or contains chemisorbed
atoms of oxygen. This matches the sorption properties of
active charcoal, the surface of which takes up organic substances and/or oxygen in chemisorbed or covalently bound
forms.[s1The characteristics of solid C,, also correspond to
those of a single fullerene molecule, which is capable of binding a large variety of functional groups on its
The interaction of oxygen atoms with C,, can be of various strengths. We identified an epoxide-like binding as the
weakest; it can be converted by tempering (sublimation) into
a stronger binding mode (dry1 ether). These two types of
binding differ in their IR data and in their behavior in thermal desorption; their existence is suggested by the data from
mass spectrometry, the ESR signals, and the results of singlecrystal X-ray diffraction experiments. These oxygen adducts
differ markedly from those that produce CO, upon thermal
decomposition; this latter type forms only slowly on the
crystal surface with exclusion of light and moisture and apparently gives rise to the precursor for the total oxidationrl7, of C60.The existence of chemically activated oxygen should be taken into account in considering the behavior
of C,, under catalytically oxidizing conditions.
The differing desorption behavior of the solvents ether
and toluene suggests that an intrinsic characteristic of C,, is
its ability to enter into specific electronic interactions; however, only experiments with thin films can eliminate possible
topochemical effects superimposed on this intrinsic property. Until now we have consciously conducted our investigations to avoid a photochemically assisted adsorption+ven
in the dark the effects of small amounts of foreign atoms are
complex enough.
Received: March 31, 1992 [Z5271lE]
German version: Angen,. Chem. 1992. 104.909
CAS Registry numbers:
C60,99685-96-8; C,,.XO,.
141849-16-3; Et,O, 60-29-7; toluene, 108-88-3
[l] W. Kriltschmer, L. D. Lamb, K. Fostiropoulos, D. R. Huffman, Nulure
1990, 347, 354; R. Ettl, 1. Chao, F. Diederich, R. L. Whetten, ibid. 1991,
353, 149. We used a direct current arc with approximately 1.5 kW power
and cooled the entire apparatus with a water-jacket. A continuous flow of
helium at a total pressure of 140 mbar proved to be advantageous. An
air-tight apparatus (leakproof under static high vacuum) and pure helium
are extremely important for respectable yields. The crude extract, obtained
in a maximum of 1 5 % yield, was separated by chromatography (in the
dark, eluting with toluene) into C,,, C,,, and higher fullerenes. The purity
of the fractions was determined by UVjVIS spectroscopy. This highly
sensitive method showed that at this point there is only an insignificant
amount of fullerene oxide.[l5,16] Conventional elemental analysis showed
about 99% C and less than 1 % H.
[2] H. W Kroto, J. R. Heath, S. C. O'Brien, R. F. Curl. R. E. Smalley, Nature
1985, 318, 162; H. Kroto. Science 1988, 242, 1139.
[3] a) H. W Kroto, Angnc. Chem. 1992, f04,113; Angen,. Chem. Int. Ed. Engl.
1992, 31, 111 ; b) H. Schwarz, ibid. 1992, 104, 301 and 1992, 31, 293.
[4] D. R. Huffman, Phys. Toduy 1991, 44 ( I l l 22.
[ 5 ] P. A. Heiney, J. E. Fischer, A. R. McGhie. W. J. Romanow, A. M. Den-
870
0 VCH
nenstein, J. P. McCauley, Jr., A. B. Smith 111, Phys. Rev. Lett. 1991, 66,
2911.
H. Werner. W. Bensch, R. Schlogl, Solid Slate Commun. 1992, in press.
K. Holczer, 0 .Klein, S. M. Huang, P. B. Kauer, K. J. Fu, R. L. Whetten,
F. Diederich, Science 1991,252. 1154.
R. C. Bansal, J. B. Donnet, F. Stoeckli, Active Carbon, Marcel Dekker,
New York, 1988, p. 335.
H. D. Beckhaus, C. Riichardt, M. Kao, F. Diederich, C. S. Foote, Angew.
Chem. 1992, 104. 69; Angen,. Chem. I n f . Ed. Engl. 1992, 31, 63.
C. S. Yannoni, R. D. Johnson, G. Meijer, D. S. Bethune, J. R. Salem, J.
Phys. Chem. 1991, 95. 9.
R. C. Haddon, L. F. Schneemeyer. J. V. Waszczak, S. H. Glarum, R. Tycko, G. Dabbagh, A. R. Kortan, A. J. Muller, A. M. Mujsce, M. J. Rosseinsky, S . M. Zahurak, A. V. Makhija, F. A. Thiel, K. Raghavachari, E.
Cockayne, V. Elser, Nature 1991, 350, 46.
P. M. Allemand, G. Srdanov, A. Koch, K. Khemani, F. Wudl, Y Rubin,
F. Diederich, M. M. Alvarez, S. J. Anz, R. L. Whetten, J Am. Chem. Soc.
1991. 113, 2780; P. N. Keizer, J. R. Morton, K. F. Preston, A. K. Sudgen,
J. Phys. Chem. 1991, 95, 7117.
D. Heymdnn, J. C . Stormer, M. L. Pierson, Carbon 1991, 29, 1053.
0. Ermer, Helv. Chim. Ada. 1991, 74,1339; S. M. Gorun, K. M. Creegan,
R. D. Sheerwood, D. M. Cox, V. W. Day, C. S. Day, R. M. Upton, C. E.
Briant, J. Chem. SOL..Chem. Commun. 1991, 1556.
K. M. Creegan. J. L. Robbms, W. K. Robbins, J. M. Millar, R. D. Sherwood, P. J. Tindall, D. M. Cox, J. P. Mc Cauley, Jr., D. R. Jones, T. T.
Gallagher. A. M. Smith III, J. Am. Chem. SOC.1992, f14, 1103.
Y. Elemes, S. K. Silverman, C. Sheu, M. Kao, C. S. Foote, M. M. Alvarez,
R. L. Whetten, Angrw. Chem. 1992,104,364; Angew. Chem. Int. Ed. Engl.
1992, 31, 351
G. H. Kroll, P. J. Benning, Y. Chen, T. R. Ohno, J. H. Weaver, L. P. F.
Chibante, R. E. Smalley, Chem. Phys. Leu. 1991, 181, 112.
J. M. Wood, B. Kahr, S. A. Hooke 11, L. Dejarme, R. G. Cooks, D. BenAmotz, J. Am. Chem. Soc. 1991, 113, 5907.
Our freshly recrystallized C,,[l] showed four IR bands at 1429,1184,577,
528cm-' andone '3CNMRsignalinsolutionat6=143[3a]withasignalto-noise ratio of 270.
The band at 1627 cm- I was assigned to a skeletal vibration of the aromatic
system that is intensified by oxygen;[l6] the band at 1537cm-' is also
described in the literature[4,21] and may be due to a C-H vibration of the
(CH,), derivatives [18] present in trace amounts. This band is found only
in dry samples. The accompanying C-H stretching vibration can be suppressed.[21]
H. Gaber, R. Hiss, H.-G. Busmann, J. V. Hertel, Verh. Dtsch. Phys. Ces.
1992, 3, 763.
Several samples of nominally pure C,, were examined by EPR spectroscopy in the solid state at 200K. The intensities correspond to spin
per C atom, the linewidth B is given in Gauss.
densities of up to N x
The following values for N , g, and B were obtained: Sublimed sample
(N=25, g=2.00007, B=4.3), recrystallized sample (N=125, g=2.00211,
B=0.90), a mixture of C,, and 10% C,, (N=125, ,p2.00187, B=1.3),
sublimation residue (N=1600, g=2.00262, B=0.58).
U. Gobel, W. Bensch, R. Schlogl, J. Anal. Chem. 1992, in press. For the
measurements. 10 mg of the crystalline powder was heated on a preheated
mbar) with a linear temperature
stainless steel substrate in UHV (1 x
program. The mass spectra of the desorbed material (Bakers QMG 112
quadropoie mass spectrometer) were corrected for the background signals.
For technical reasons the background signal at m / i 2 is so intense that
hydrogen desorption cannot be observed with certainty.
H. Werner, U. Tegtmeier, J. Blocker, D. Herein, R. Schlogl, T. SchedelNiedrig, M. Keil, A. M. Bradshaw, Chem. Phys. Let!. 1992, in press.
Verlugs~esellschaftmbH, W-6940 Weinheim, 1992
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