Single-stage plasma-arc synthesis of metallo-endofullerences

Article abstract of DOI:10.1134/S1070427207110213

Single-stage plasma-arc synthesis of metallo-endofullerences of the types C₆₀Pd, C₆₀Ni, and C₆₀Cr, whose content in a mixture of extracted fullerenes was 0.05 to 0.15 wt %, was performed. The effect of introduction of these metals into the reaction plasma on the total yield of fullerenes and on the fraction composition of the fullerene mixture was studied. The fullerene mixtures were analyzed by mass spectrometry and liquid chromatography.

Full text of DOI:10.1134/S1070427207110213

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2007, Vol. 80, No. 11, pp. 1888 1893. Pleiades Publishing, Ltd., 2007.
Original Russian Text V.I. Gerasimov, G.V. Kalinin, Yu.A. Nikonov, Yu.F. Titovets, A.E. Kalabushkin, O.S. Alekhin, K.V. Nekrasov, S.N. Rusetskaya,
O.V. Arapov, N.I. Alekseev, E.V. Kustova, V.V. Lishchuk, M.A. Pleshkov, K.N. Semenov, V.A. Keskinov, N.A. Charykov, 2007, published in Zhurnal
Prikladnoi Khimii, 2007, Vol. 80, No. 11, pp. 1864 1869.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
Single-Stage Plasma-Arc Synthesis of Metallo-Endofullerenes
V. I. Gerasimov, G. V. Kalinin, Yu. A. Nikonov, Yu. F. Titovets, A. E. Kalabushkin,
O. S. Alekhin, K. V. Nekrasov, S. N. Rusetskaya, O. V. Arapov, N. I. Alekseev,
E. V. Kustova, V. V. Lishchuk, M. A. Pleshkov, K. N. Semenov,
V. A. Keskinov, and N. A. Charykov
Innovation at Leningrad Institutes and Enterprises, Private Company, St. Petersburg, Russia
Ioffe Physicotechnical Institute, Russian Academy of Sciences, St. Petersburg, Russia
St. Petersburg State University, St. Petersburg, Russia
St. Petersburg State Institute of Technology (Technical University), St. Petersburg, Russia
Received July 6, 2007; in final form, September 2007
Abstract Single-stage plasma-arc synthesis of metallo-endofullerenes of the types C60Pd, C60Ni, and C60Cr,
whose content in a mixture of extracted fullerenes was 0.05 to 0.15 wt %, was performed. The effect of
introduction of these metals into the reaction plasma on the total yield of fullerenes and on the fraction com-
position of the fullerene mixture was studied. The fullerene mixtures were analyzed by mass spectrometry and
liquid chromatography.
DOI: 10.1134/S1070427207110213
As is known [1], endofullerenes is the commonly
accepted name for derivatives of light (C , C ) or
electrodes in an electric arc in an inert gas (plasma-arc
method), evaporation of graphite microparticles in
a thermal plasma under atmospheric pressure, com-
bustion of hydrocarbons in a laminar of volume flame
[6 13]. The basic issue is the way in which metal
ions (or atoms) are introduced into the carbon-contain-
ing reaction plasma generated in synthesis of ordin-
ary fullerenes.
60
70
heavy (C , n 72) fullerenes with one or several non-
n
carbon atoms (X) incorporated within the hollow
skeleton of fullerenes. To our knowledge, stable endo-
fullerenes based on the so-called ultralight fullerenes
or subfullerenes (C , n
scribed, although part of these can have a hollow
58) have not been de-
n
structure (C C ). The role of a heteroatom X can
36 58
Several methods have been described in the litera-
ture: impregnation of graphite articles (rods, discs)
be played both by atoms of metals: alkali, alkaline-
earth, transition, heavy, lanthanide, and actinide (X =
Li, Na, K, Cs, Ca, Mg, Hf, Ti, Zr, Y, Sc, La, Ce, Sm,
Gd, Tb, U, Pu, and some others) [2, 3], and by atoms
of some nonmetals and, primarily, noble gases (X =
He, Ne, Ar, Kr, Xe, N), as well as by some diatomic
molecules (X = CO, CN) [1, 4]. Typically, a single
with solutions of well-soluble salts of the type LaCl
3
[1, 2] in laser or flame-arc synthesis of fullerenes;
introduction of high-purity metal compounds, com-
monly oxides, directly into the material of a graphite
rod (anode) being evaporated, by compaction followed
by preliminary annealing, e.g., of La O , in plasma-
heteroatom is incorporated in fullerenes (C X com-
2 3
n
arc synthesis of a lanthanum-endofullerene C La
pounds), although endofullerenes have been described
with two (C X compounds) and even three hetero-
60
+
[14]; implantation of metal ions (e.g., Li ) into the
n
2
carbon plasma or, vice versa, implantation of fullerene
atoms (C X ), which may be identical (C La [2]) or
n
3
60
60
2
ions (e.g., C ) into a metal-containing plasma [3];
different (C Cs Rb [5]).
60
2
also possible is synthesis of endofullerenes by direct
introduction of some heteroatoms [He, Ne, Ar, Kr,
The main methods for synthesis of metallo-endo-
fullerenes are the same as those for ordinary fullerenes
[1]: namely, laser evaporation of graphite in the
atmosphere of inert gases, resistive and high-fre-
quency heating of graphite in an inert gas, evaporation
of graphite in focused solar light, burning of graphite
Xe, N (N )] into already synthesized fullerene voids
2
from the gas phase at comparatively high temperatures
(600 1000 C) and pressures (100 1000 atm) [4].
Metallo-endofullerenes can be used as high-tem-
1888

SINGLE-STAGE PLASMA-ARC SYNTHESIS OF METALLO-ENDOFULLERENES
1889
perature superconductors [5, 15 17], ferromagnetic
materials [18], heterogeneous catalysts in organic
synthesis and, in particular, in (de)hydrogenation [19],
medicine, pharmacology, etc.
ides of light fullerenes: C O and, possibly, C O);
60
70
metallo-endofullerenes C X (in this case, too, forma-
n
m
tion of mono derivatives of light fullerenes, C X and,
60
possibly, C , is the most probable).
70
The aim of this study was to develop a simple
technologically convenient single-stage method for
synthesis of metallo-endofullerenes and an analytical
method for their identification.
Fullerene mixtures are commonly analyzed by the
following methods: spectrophotometry (for proximate
analysis), high-resolution liquid chromatography,
mass spectrometry, and liquid chromatogeaphy mass
spectrometry (the latter technique is a combination
of the second and third methods).
Metallo-endofullerenes were synthesized by the
plasma-arc method [12] on an installation described in
[13]. The electrode being evaporated, anode, had
the form of a rod (ultrapure graphite, 99.999 wt %
carbon) 12 mm in diameter. An orifice 1 mm in diam-
eter was drilled in the electrode and a metallic wire of
the same diameter was pressed into this orifice. The
wire was composed of individual metals: Ni, Cr, Pd
(99 wt %), or Nichrome alloy (with 40 wt % Cr). No
metals were introduced into the cathode (12-mm
graphite rod). The synthesis was performed in the
atmosphere of ultrapure He (99.9995 vol %) at a pres-
sure of about 300 mm Hg.
The spectrophotometric analysis [20] is suitable
only for rough determination of the composition of
a fullerene mixture in terms of light fullerenes and ap-
proximate estimation of the total content of fullerenes
in the mixture and, therefore, cannot be used for our
purposes.
Liquid chromatography was used in the mode de-
scribed in [21]: Lumachrom chromatograph (manufac-
tured by Lumex Co., St. Petersburg), with UV detec-
tion at a wavelength
= 254 nm. A characteristic
example of the chromatograms obtained is shown
in Fig. 1. As can be seen from the chromatogram,
all the fullerene groups mentioned above can be
qualitatively identified. However, two groups of sub-
fullerenes, C companions, and the group C C ,
This synthesis method proved suitable only for suf-
ficiently high-melting metals with melting points not
lower than 1400 C. With lower-melting metals (e.g.,
Cu), microdrops of metals spattered and metal ions
were not delivered in sufficient amounts to the plasma
reaction zone, with the result that metallo-endoful-
lerenes were not formed in noticeable amounts.
60
62 84
C
companions, are eluted as two broad unresolved
70
peaks. Even after a 10-fold increase in the device
sensitivity, two well-resolved peaks of heavy ful-
Samples were prepared for analysis as follows: the
carbon black accumulated in the carbon-black receiver
and in the reaction chamber after synthesis was col-
lected and sieved on a sieve with a 40- m mesh; the
ordinary fullerenes and metallo-endofullerenes formed
were extracted with o-xylene (analytically pure grade)
at room temperature under vigorous stirring (magnetic
stirrer) in the course of 60 min. The phase ratio in
the extraction was 1 mg of carbon black per 1 ml of
o-xylene (the solvent was taken in manyfold excess).
lerenes of the C
C
group were followed by dif-
76 84
ficultly identifiable and poorly resolved broad peaks
of mixed origin, associated with heavier fullerene
groups C
C
and, possibly, with some metallo-
86 116
endofullerenes of uncertain composition. Thus, this
method is equally unsuitable for precise quantitative
determination of the fullerene composition of the
mixtures obtained (including metallo-endofullerenes).
A mass-spectrometric method was developed for
analysis of fullerene mixtures. This method enables
quantitative determination of the concentrations of all
the fullerene components of interest. For this purpose,
we dissolved fullerene mixtures without a residue in
o-xylene (analytically pure grade), with a solution
containing 0.1 mg of a sum of fullerenes per 1 ml of
solution. Then, a 1-ml sample of this solution was
taken and transferred to a quartz cell. After that, the
solvent was evaporated at 100 C, with the fullerenes
(about 100 g) forming in the process a thin yellowish
film on the quartz surface. The mass-spectrometric
analysis was made on an MKh-1320 instrument at
The solution of fullerenes was allowed to settle for
30 min and then twice filtered through a blue-band
paper filter. The filtrate was evaporated to a humid
paste on a rotary evaporator at 80 5 C. The paste
was evaporated to constant weight in a vacuum oven
for 150 min at 220 230 C and a residual pressure of
0.01 0.1 mm Hg (dynamic vacuum).
The expected forms of fullerenes in the resulting
mixtures are the following: light (C , C ) and heavy
60
70
fullerenes (C , n
72); subfullerenes (C , n 58);
n
n
fullerene oxides, the so-called epoxites (C O ) formed
n
m
because of the presence of oxygen or water vapor ad-
mixtures (the most probable is formation of monox-
7
a pressure of 10 mm Hg, sublimation temperature of
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 11 2007

1890
GERASIMOV et al.
10
J, mA
1
III + IV
II
I
, min
Fig. 1. Chromatogram of a fullerene extract containing subfullerenes, light and heavy fullerenes, monoxides of light fullerenes,
and PdC . (J) Current strength and ( ) elution time. (I) Subfluuerenes, (II) light fullerenes, (III) heavy fullerenes, and
60
(IV) fullerene derivatives; the same for Fig. 3.
I, arb. units
20
1
AM, amu
Fig. 2. Mass spectrogram of a fullerene extract containing subfullerenes, light and heavy fullerenes, monoxides of light fuller-
enes, and PdC . (I) Ion current and (AM) atomic mass.
60
250 480 C, and ionization by electron impact (ioni-
zation energy 10 100 eV). In the course of the analy-
sis, all the fullerene components were nearly com-
pletely evaporated from the surface of the quartz cell
(analysis for the residual content of fullerenes on
the cell of the KU brand was made spectrophotomet-
As a result, we obtained mass spectra whose typical
shape is schematically shown in Fig. 2 (chromatogram
of a Pd-containing fullerene extract). Figures 3a 3c
show the same mass spectrograms on the more con-
venient semilog scale. Similar mass spectrograms
were obtained for fullerene extracts containing in-
dividual Ni and Cr. However, these spectra exhibited
no specific features, compared with those in Fig. 3c,
and, therefore, are not presented here.
rically by the light absorption at a wavelength
=
335.67 nm, common to the absorption by light ful-
lerenes [20]).
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SINGLE-STAGE PLASMA-ARC SYNTHESIS OF METALLO-ENDOFULLERENES
1891
lnc [wt %]
(a)
II
III
(b)
I
IV
lnc [wt %]
IV
II
III
I
(c)
lnc [wt %]
II
III
I
IV
Fig. 3. Mass spectrograms of fullerene extracts containing (a) subfullerenes, light and heavy fullerenes, and monoxides C
O
60
(C O), (b) PdC , and (c) NiC + CrC . (c) Content of a fullerene in the mixture and (n) number of carbon atoms in C ful-
70
60
60
60
n
lerene. (a) Standard nonmetallized extract from a mixture of fullerenes for comparison, (b) Pd-containing fullerene extract, and
(c) (Ni + Cr)-containing fullerene extract.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 11 2007

1892
GERASIMOV et al.
Figure 2 shows sets of peaks corresponding to dif-
ferent extents of nondestructive ionization of fuller-
hand, even rough quantum-mechanical calculations
demonstrate that, just for metallofullerenes, formation
of endo forms is strongly preferential, compared with
exo forms.
3+
2+
+
enes, which increase in the series C
C
C
n
n
n
(in Fig. 3, these intensities corresponding to a single
fullerene form are summed up).
(2) Despite that the content of the synthesized
metallo-endofullerenes in the samples obtained is
comparatively low, up to 0.15 wt % in the sum of ful-
lerene products, their preparative recovery even in
comparatively large amounts (grams) is not difficult
because (according to the results of a preliminary
study) the solubility of metallo-endofullerenes in
some heterocyclic compounds, e.g., pyridine, marked-
When recording the mass spectrogram shown in
Fig. 2, we raised the instrument sensitivity by a factor
of 20, beginning with fullerene atomic masses exceed-
ing 1050 amu.
It can be seen from Figs. 2 and 3 that this analytic-
al technique enabled quantitative determination of
the concentrations of all forms of fullerenes, including
fullerene derivatives: metallo-endofullerenes and
epoxides.
ly exceeds that of their nonmetallized analogues, C
60
and C , which, in turn, are considerably better
70
soluble in ordinary aromatic solvents, e.g., o-xylene.
Thus, rather pure materials (<90 wt %) can be pro-
duced in a rather simple way by the method of recrys-
tallization recovery of metallo-endofullerenes at a
comparatively low recovery loss. Micro- and milli-
gram amounts of metallo-endofullerenes can, natural-
ly, be extracted by liquid chromatography.
The results obtained in extraction and mass-spec-
trometric measurements demonstrate the following:
(i) the total content of all the fullerene components
contained in the fullerene black is virtually independ-
ent of whether or not metallic phases are present in
the anode and equal to 12 1 wt % (typical value for
the installation described in [13]); (ii) the ratio of the
main fullerene components, light fullerenes C and
60
(3) The output capacity of the method we develop
can be improved (or, in other words, the fraction of
metallo-endofullerenes in the sum of fullerene prod-
ucts can be made larger), with its operation principle
[12, 13] preserved, by raising, based on general con-
siderations, the mass fraction of metals in the metal
carbon helium plasma in the zone of preferential for-
mation of metallo-endofullerenes (1500 4000 K).
A probably good solution in this case would be re-
moval of heat from metals in the reactor plasma by
heavier molecules of inert gases (with He possibly
replaced with Ne or Ar). However, in addition to the
expected rise in the fraction of metallo-endofullerenes
in the sum of fullerenes, such a replacement might
lead to a simultaneous decrease in the total content
of fullerenes in the fullerene black, so that such
a technological modification would require a rather
prolonged optimization.
C , is also nearly insensitive to presence of metallic
70
phases and equal to about 2.5/1.0; (iii) the content of
metallo-endofullerenes of the types C Pd, C Ni, and
60
60
C Cr in a mixture of extracted fullerenes is in the
60
range from 0.05 wt % (for C Pd and C Ni, irrespec-
60
60
tive of whether Ni or Cr are introduced into the anode,
or both these metals simultaneously) to 0.15 wt % (for
C Pd); (iv) upon introduction of Ni and/or Cr, the
60
content of subfullerenes in the fullerene black substan-
tially increases; and (v) no metallo-endofullerenes are
found in the fullerene black upon introduction of
a lower-melting metal (Cu) into the anode.
In the context of discussion of the results obtained,
we note some additional fundamental issues.
(1) The paper describes syntheses of just endo
forms of light-fullerene derivatives, i.e., metal atoms
are situated in these compounds within the carbon
skeleton of fullerenes. It is clear that direct mass-
spectrometric measurements cannot answer the ques-
tion as to what form, endo or exo (with a metal atom
outside the fullerene carbon skeleton), of metalloful-
lerenes is formed in a synthesis. Although we did not
carry out additional labor-consuming spectral studies
capable of tackling with this issue in a direct experi-
mental way, the answer seems to be quite obvious
because, on the one hand, no metallo-exofullerene of
the type C Me or C Me has been synthesized so
CONCLUSIONS
A comparatively simple and low-cost direct single-
stage plasma-arc method for synthesis of metallo-
endofullerenes and a proximate technique for their
identification in the fullerene black were developed.
The synthesis was performed for the example of
60
n
70
n
metallo-endo derivatives of light fullerenes, C and
far (whereas the tens of metallo-endofullerenes have
been synthesized and identified) and, on the other
60
C , with Ni, Cr, and Pd used as metals.
70
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SINGLE-STAGE PLASMA-ARC SYNTHESIS OF METALLO-ENDOFULLERENES
1893
ACKNOWLEDGMENTS
6. JPN Patent 05238717.
7. JPN Patent 5004810.
8. FR Patent 2710049.
9. EP Patent 568918.
The study was supported by the Federal Target
Research Program Research and Development in
Priority Areas of Science and Technology for 2002
2006 (State contract no. 02.467.11.7005 of May 23,
2005).
10. EP Patent 646644.
11. US Patent 5273729.
12. WO Patent 2005/070826.
13. WO Patent 2005/087662.
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