Method for the purification and separation of fullerenes

This invention relates to a method of purifying afullerenes by recrystallization of a fullerene-complexing agent complex and to a fullerene-complexing agent complex.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a method of purifying fullerenes by 
recrystallization of a fullerene-complexing agent complex and to a 
fullerene-complexing agent complex. 
2. Discussion of the Background 
Since their discovery by R. E. Smalley (in Physical and Theoretical 
Chemistry, Vol. 68, Elsevier Science: New York, 1990 pp. 1-68), molecular 
fullerenes have received considerable interest with anticipated 
applications in such varied fields such as polymers, batteries, 
high-temperature superconductors, catalysts, drug delivery systems and 
pharmaceuticals. Other applications include optical devices based on 
fullerene photoconductivity or photovoltaic properties, carbides, chemical 
sensors, gas separation devices, thermal insulation, diamonds, diamond 
thin films and hydrogen storage. In fact, fullerenes are even reported to 
be useful as a pigment for toner compositions (U.S. Pat. No. 5,188,918). 
In particular C.sub.60, also referred to as buckminsterfullerene, which 
has the molecular geometry of a truncated icosahedron, and thus resembles 
a molecular sized soccer ball, has received tremendous inquiry throughout 
the scientific community and the population at large. 
However, the difficulties in the preparation, isolation and purification of 
fullerene materials has greatly hindered their commercial exploitation. 
Presently, fullerenes are sold commercially from Texas Fullerenes 
Corporation, 2415 Shakespeare Suite 5, Houston, Tex. 77030-1034, Materials 
and Electrochemical Research (MER) Corporation, 7960 South Kolb Road, 
Tucson, Ariz. 85706, and Research Materials, Inc., 1667 Coal Boulevard, 
Golden, Colo. 80401. A mixture of C.sub.60/ C.sub.70 (i.e., fullerite) is 
availible from the Aldrich Chemical Company for a price of $900 per gram. 
The high cost of these materials is reflective of the difficulties in 
preparing, isolating and purifying these materials. It is presently not 
possible to efficiently purify fullerenes, on a large scale, in part due 
to inherent losses attributable to chromatographic techniques, arising 
from irreversible absorption of the fullerene material onto the stationary 
phase. 
Ajie et al (J.Phys Chem (1990) 94, 8630-8633) report the separation of 
C.sub.60 and C.sub.a by hexane chromatography on neutral alumina. Purified 
fractions of 99.85% C.sub.60 and &gt;99% C.sub.70 were obtained. The yield of 
purified material was not reported. 
Hawkins et al (J. Org. Chem. (1990) 55, 6250-6252) report the separation of 
C.sub.60 and C.sub.70 by preperative HPLC on a Pirkle phenylglycine-based 
column with hexanes as solvent. Amounts of about 0.5 mg per injection 
could be purified. 
Scrivens et al (J, Am. Chem. Soc., (1992) 114, 7917-7919) report the 
purification of C.sub.60 on a column of alkaline decolorizing carbon 
Norit-A and silica gel. 68% of a possible 75% of C.sub.60 was obtained. 
Khemani et al (J.Org. Chem. (1992) 57, 3254-3256) report the isolation of 
C.sub.60 and C.sub.70 by soxhlet chromatography with hexanes. 
In addition to the numerous chromatographic procedures reported, simple 
crystallization procedures have also been reported. 
Coustel et al (J. Chem. Soc Chem. Commun. 1992, 1402) report that C.sub.60 
crystallizes during toluene soxhlet extraction of fullerenes from soot. 
About 40 wt % of the fullerenes in the soot could be obtained as mostly 
C.sub.60 with trace impurities of C.sub.70. The trace impurities of 
C.sub.70 can be removed by a second recrystallization from a toluene 
soxhlet. By this method 99.99% pure C.sub.60 can be obtained. However, 
while high purity C.sub.60 could be obtained, the process is very 
inefficient. 
Prakash et al have reported (Chemical and Engineering News Sep. 20, 1993, 
p. 32) that C.sub.60 can be purified from C.sub.70 by precipitation of an 
AlCl.sub.3 -C.sub.60 complex, from CS.sub.2. C.sub.60 of greater than 
99.9% purity can be obtained by this method. However the use of CS.sub.2 
is not desirable due to its flammability and toxicity. 
Calixarenes are complex compounds containing a metacyclophane framework. 
Although some applications for some types of calixarenes compounds have 
been developed, research into calixarene chemistry is still progressing 
(see for Example Gutsche, Calixarenes, Royal Soc. Chem. 1989). 
Depending upon the reaction conditions, the condensation of 
o-dimethoxybenzene with formaldehyde has been shown to yield both a cyclic 
trimer, cyclotriveratrylene (CTV), and the analogous tetrameric species, 
cyclotetraveratrylene (CTTV). Apart from the utility of compounds derived 
from CTV in the synthesis of cryptophanes and other effective small 
molecule complexing agents, CTV and CTTV also exhibit an extensive 
host-guest chemistry. These molecules are meant to be typical bowl-, cup-, 
or cavitand-shaped molecules as hosts. 
Within the area of host-guest chemistry, calixarenes have been investigated 
in terms of their interaction with fullerene compounds (Williams et al 
Recueil Des Travaux Chimiques des Pays-bas, 111 531-532 1992)). This 
reference reports the selective formation of a complex of C.sub.60 with a 
water-soluble calix8!aryloxy-49, 50, 51, 52, 53, 54, 55, 
56-octakis-(propane-3-sulphonate). The calixarene host is functionalized 
with a 3-propanesulphonate group to provide water-solubility to the 
calixarene. However, since the material is not soluble in organic 
solvents, the calixarene is able to selectively extract C.sub.60, from a 
toluene mixture of C.sub.60 /C.sub.70, into the aqueous phase. The 
purified C.sub.60 can be obtained by toluene extraction of the dried 
aqueous residue. Thus the reference reports a method of purifying 
C.sub.60, by solubilization and extraction. 
In spite of these limited report, a simple and economical method of 
purifying fullerenes remains the subject of vigorous research. A simple 
and economical method of purifying fullerenes by recrystallization would 
be welcome. 
SUMMARY OF THE INVENTION 
Accordingly, one object of this invention is to provide a novel method of 
purifying fullerenes, through the recrystallization of complexes formed 
with a complexing agent. 
Another embodiment of this invention is directed to a method of purifying 
fullerite through the recrystallization of a complex formed with a 
complexing agent. 
Another embodiment of the invention is directed to a process of separating 
and purifying C.sub.60, and higher fullerenes, by recrystallization from a 
complex formed with a complexing agent. 
Another embodiment of the invention is directed to a process of separating 
and purifying C.sub.60, and higher fullerenes, by recrystallization from a 
complex formed with an immobilized complexing agent. 
Another embodiment of the present invention is directed to a complex of 
fullerene and a complexing agent, which is soluble in an organic solvent. 
The objects of the present invention are provided for by Applicants' 
discovery that calixarenes, cycloveratrylenes and other organic complexing 
agents allow for the selective complexation of fullerenes, which can then 
be purified by recrystallization from an organic solvent.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Throughout the specification, the terms C.sub.60 and fullerene-60 will be 
used interchangably. Also the terms C.sub.70 and fullerene-70 will be used 
interchangably. 
According to the present process a mixture of crude fullerene is contacted 
with a complexing agent. The nature of the fullerene being purified, will 
determine which complexing agent should be used. 
For example suitable complexing agents are the calixarenes. Suitable 
calixarenes for practicing the present invention are of the formula I 
##STR1## 
wherein 
R.sub.1 -R.sub.3+n are each independently H, primary C.sub.1-20 alkyl, 
secondary C.sub.3-20 alkyl, tertiary C.sub.4-20 alkyl, C.sub.1-20 alkoxy, 
C.sub.1-20 thioalkyl, C.sub.6-20 aryl, C.sub.6-20 aryloxy, C.sub.6-20 
aryl, nitro, halogen and CH.sub.2 NR.sup.1.sub.2 where R.sup.1 is a 
C.sub.1-20 alkyl; 
X.sub.1 - X.sub.3+n are each independently H, OH, SH, C.sub.1-20 alkoxy, 
C.sub.1-20 thioalkyl, C.sub.6-20 aryloxy, OC(O)C.sub.1-20 alkyl and 
C.sub.2-20 alkenyloxy; and 
n is an integer of 1 to 11, preferably 1-7, more preferably 1-5. 
Preferably R.sub.1 - R.sub.3+n may be hydrogen, methyl, ethyl, propyl, 
isopropyl, butyl, iso-butyl, sec-butyl, tert-butyl, phenyl, xylyl, 
phenyoxy, naphthyl, benzyl, fluorine, chlorine, bromine and iodine, 
methoxy, ethoxy, propoxy butoxy, N,N- dimethyl methyleneamine, N,N-diethyl 
methyleneamine, N,N- dipropyl methyleneamine, N,N-diphenyl methyleneamine, 
C.sub.6-20 aryl, NO.sub.2 or CH.sub.2 NR.sup.1.sub.2 where R.sup.1 is a 
C.sub.1-20 alkyl. 
Preferably X.sub.1 -X.sub.3+n may be H, OH, methoxy, ethoxy and propoxy. 
More specifically, suitable calixarenes are calix4!arene, calix5!arene, 
calix6!arene, calix7!arene, calix8!arene, calix9!arene and 
calix10!arene as well as para substituted derivatives thereof. 
The specific substituents located at the para position of the aromatic ring 
will in part influence the selectivity of the specific calixarene to the 
fullerene. For example, p-Bu.sup.t -calix8!arene selectively binds 
C.sub.60, while, p-Bu.sup.t -calix6!arene binds mostly C.sub.70. 
Calix6!arene binds to both C.sub.60 and C.sub.70. In addition, 
p-phenylcalix4!arene binds C.sub.60 while p-Bu.sup.t -calix4!arene does 
not bind to C.sub.60. Accordingly the size of the para substituent will 
affect the size of the calixarene cavity and the selectivity of the 
calixarene for a specific fullerene. 
Toluene solutions of p-Bu.sup.t -calix8!arene form a sparingly soluble 
brown/yellow precipitate in the presence of a toluene solution of purified 
fullerene-60, analyzing as the 1:1 complex. In the presence of toluene 
solutions of crude fullerene mixtures, a similar precipitate results which 
was shown by UV-visible spectroscopy (see FIG. 2) and FAB mass 
spectrometry to be the same complex containing some fullerene-70. The 
fullerene mixture retrieved from this precipitate by addition of 
chloroform (see FIG. 1) was shown by HPLC to be based exclusively on 
fullerene-60 and fullerene-70, 89% and 11% respectively, which represents 
ca 90% of the fullerene-60 content of the soot. One recrystallization of 
the precipitate, from toluene, enriched the fullerene-60 content to 96% 
with ca 10% of the fullerenes in the mother liquor as 26% fullerene-60 and 
74% fullerene-70. A second recrystallization gave &gt;99.5% purity 
fullerene-60, again with ca 10% of the fullerenes in the mother liquor, as 
72% fullerene-60 and 28% fullerene-70. 
The recovery of high purity fullerene-60 is essentially quantitative if the 
mother liquor solutions are recycled back to the crude fullerene mixture, 
along with p-Bu.sup.t -calix8!arene recovered from chloroform degradation 
of the complex. In addition, p-Bu.sup.t -calix8!arene has a higher 
affinity towards fullerene-60 relative to fullerene-70, noting purified 
fullerene-70 does not readily form a complex with p-Bu.sup.t 
-calix8!arene. 
The IR spectrum of complex 3 is a superposition of that for the calixarene 
and fullerene-60, except for the .nu..sub.OH stretching region (see FIG. 
3). Nevertheless the H-bonding network is retained and the fullerene most 
likely resides in the cavity, as a `ball and socket` nano-structure. 
Calix6!arene forms a sparingly soluble 1:2 complex with fullerene-60 in 
toluene, complex 6, (see FIG. 1) but not with fullerene-70 in the same 
solvent under the same conditions. Treatment of a toluene solution of 
crude fullerenes with the same calixarene yields a highly crystalline 
material containing both fullerene-60 and fullerene-70, 67% and 33% 
respectively (HPLC analysis of NaOH treated toluene solutions of the 
complex). Thus there is no discrimination between the two fullerenes. It 
has also been found that p-Bu.sup.t -calix6!arene, forms a 1:2 complex 
with fullerene-70, complex 7 (see FIG. 1). Treatment of the fullerene 
residue, depleted of most of the fullerene-60 as complex 3, with 
p-Bu.sup.t -calix8!arene yields a precipitate which on treatment with 
chloroform affords a material rich in fullerene-70 (87% along with 13% 
fullerene-60). 
The synthesis of calixarenes and substituted calixarenes is well known to 
those of ordinary skill in the art and can be prepared by conventional 
methods. For example the synthesis of p-phenylcalix4!arene is described 
in Juneja et al (J.Am. Chem. Soc. 1993 115:3818-3819). The synthesis of 
p4-(2-hydroxyethyl)piperazinomethyl!calix4!arene is described by Atwood 
et al (Angew. Chem. Int. Ed. Engl. 1993 32:1093-94). 
Other suitable complexing agents are a cyclotriveratrylene complexing agent 
of formula II 
##STR2## 
where R.sub.1 '-R.sub.6 ' are each independently H, C.sub.1-20 alkyl, 
benzyl, C.sub.1-20 alkyl substituted benzyl or C.sub.6-20 aryl; or a 
cyclotetraveratrylene complexing agent of formula III 
##STR3## 
where R.sub.1 "-R.sub.8 " are each independently H, C.sub.1-20 alkyl, 
benzyl, C.sub.1-20 alkyl substituted benzyl or C.sub.6-20 aryl. 
Suitable cyclotriveratrylene complexing agents of formula II are the 
compunds where R.sub.1 '-R.sub.6 ' are each H, C.sub.1-6 alkyl and benzyl, 
preferably H, CH.sub.3 and benzyl. 
Suitable cyclotetraveratrylene complexing agents of formula II are the 
compunds where R.sub.1 '-R.sub.6 ' are each H, C.sub.1-6 alkyl and benzyl, 
preferably H, CH.sub.3 and benzyl. 
Suitable cyclotriveratrylenes and cyclotetraveratrylenes can be synthesized 
by conventional methods known to those of ordinary skill in the art. 
Suitable complexing agents are also resorcinol derived calixarenes of the 
formula IV 
##STR4## 
wherein 
R.sub.1 -R.sub.3+n are each independently H, primary C.sub.1-20 alkyl, 
secondary C.sub.3-20 alkyl, tertiary C.sub.4-20 alkyl, C.sub.1-20 alkoxy, 
C.sub.1-20 thioalkyl, C.sub.6-20 aryl, C.sub.6-20 aryloxy, C.sub.6-20 
aryl, nitro, halogen and CH.sub.2 NR.sup.1.sub.2 where R.sup.1 is a 
C.sub.1-20 alkyl; 
X.sub.1 -X.sub.3+n are each independently H, OH, SH, C.sub.1-20 alkoxy, 
C.sub.1-20 thioalkyl, C.sub.6-20 aryloxy, OC(O)C.sub.1-20 alkyl and 
C.sub.2-20 alkenyloxy; and 
n is an integer of 1 to 11, preferably 1-7, more preferably 1-5. 
Preferably R.sub.1 -R.sub.3+n may be hydrogen, methyl, ethyl, propyl, 
isopropyl, butyl, iso-butyl, sec-butyl, tert-butyl, phenyl, xylyl, 
phenyoxy, naphthyl, benzyl, fluorine, chlorine, bromine, iodine, methoxy, 
ethoxy, propoxy butoxy, N,N- dimethyl methyleneamine, N,N-diethyl 
methyleneamine, N,N- dipropyl methyleneamine, N,N-diphenyl methyleneamine, 
C.sub.6-20 aryl, NO.sub.2 and CH.sub.2 NR.sup.1.sub.2 where R.sup.1 is a 
C.sub.1-20 alkyl. 
Preferably X.sub.1 -X.sub.3+n may be H, OH, methoxy, ethoxy and propoxy. 
The resorcinol derived calixarenes can be prepared by conventional methods 
known to those of ordinary skill in the art. 
Suitable complexing agents are also oxacalixarenes, in which the two or 
more of the individual arene groups of formula I, are separated by an 
oxygen atom. Accordingly a suitable oxacalixarene is analogous to the 
compound of formula I, in which one or more of the methylene groups, which 
bridge the individual arene groups, is replaced by an oxygen atom. 
The oxacalixarenes can be prepared by conventional methods known to those 
of ordinary skill in the art, for examples as described in Gutsthe 
(Calixarenes, Royal Soc. Chem. 1989 p. 61). 
Suitable complexing agents are also homooxacalixarenes, in which the 
individual arene groups are separated by one or more 2-propyleneoxy 
groups, such as p-Bu.sup.t dihomooxacalix4!arene of the formula V 
##STR5## 
tetrahomodioxacalix4!arene (Gutsche J.Org. Chem. (1983), 48:1536) and the 
cyclic trimer formed from 2,6-hydroxymethylphenol (Gutsche J.Org. Chem. 
(1983), 48:1536). 
The homooxacalixarenes can be prepared by conventional methods known to 
those of ordinary skill in the art. The synthesis of p-Bu.sup.t 
dihomooxacalix4!arene and tetrahomodioxacalix4!arene are reported in 
Gutsche (Calixarenes, Royal Soc. Chem. 1989 pp.61-62). 
The complexing agent used to practice the claimed invention has a low 
degree of water solubility and is soluble in organic solvents. The 
complexing agent of the present invention preferably has a water 
solubility at 23.degree. C. of .ltoreq.0.01 mol/L, more preferably 
.ltoreq.0.001 mol/L, even more preferably .ltoreq.0.0001 mol/L, most 
preferably .ltoreq.0.00001 mol/L. 
The complex of the fullerene and the complexing agent is preferably formed 
in an aromatic solvent such as toluene, xylenes, benzene or a mixture 
thereof. Toluene is most preferred. 
Of the aromatic solvents, the choice of toluene for complex formation is 
preferred. Complex of C.sub.60 and p-Bu.sup.t -calix8!arene 3 is slightly 
soluble in toluene at ambient temperature, affording yellow solutions 
whereas above ca 80.degree. C. it decomposes, as judged by the formation 
of magenta solutions characteristic of free fullerene-60 in toluene, and 
UV-visible spectroscopy. Dilute solutions of 3 in toluene at ambient 
temperature also contain free fullerene-60 (see FIG. 2). Xylenes and 
mesitylene rapidly decompose the complex 3 at 20.degree. C. yielding free 
fullerene and calixarene on evaporation. Greater solvation of the 
fullerene-60 by the more electron rich arenes may be at the expense of 
complex formation. The fullerene-complexing agent complex is preferably 
formed at a temperature of anywhere from the melting temperature of the 
solvent to the reflux temperature of the solvent. Typically the 
fullerene-complexing agent complex is formed in refluxing toluene. 
Recrystallization of the fullerene-complexing agent complex is achieved by 
filtering the hot fullerene-complexing agent complex, followed by cooling. 
A seed crystal of the fullerene-complexing agent complex can be added, if 
necessary. 
After the fullerene-complexing agent has crystallized, the complex is 
isolated by filtration. 
The fullerene-complexing agent complex can be decomposed, by introduction 
of a chlorinated hydrocarbon solvent, a fluoro hydrocarbon solvent or a 
chlorofluoro hydrocarbon solvent. Preferably solvents such as chloroform, 
dichloromethane and 1,2-dichloroethane are used. 
In addition, the fullerene-complexing agent complex can be decomposed by 
the addition of a base to a solution of the fullerene-complexing agent 
complex in an aromatic solvent. Suitable bases include inorganic bases 
such as NaOH, KOH, Ca(OH).sub.2, CaCO.sub.3, K.sub.2 CO.sub.3 and organic 
bases such a amines. It is not necessary that the inorganic base be 
soluble in the aromatic solvent. Pellets of NaOH are preferred. 
Complex 3 rapidly decomposes in chloroform which allows for an easy removal 
of fullerene-60 as a black precipitate (&gt;95% recovery) from the calixarene 
which crystallizes as a suspended solid (relative densities: 
fullerene-60&gt;chloroform&gt;p-Bu.sup.t -calix8!arene. Fullerene-60 has only 
sparing solubility in chloroform (0.16 mg/mL), and the procedure allows 
for recovery of the calixarene, either as a solid directly, or as a 
mixture of fullerene and calixarene on removal of the solvent in vacuo. 
Dichloromethane and 1,2-dichloroethane also result in decomposition of the 
complex, whereas the complex is stable in carbon tetrachloride and t-butyl 
chloride. The absence of hydrogen atoms attached to the carbon bearing a 
chloro group in these solvents, unlike that for the foregoing chlorinated 
solvents, relates to the ability of such hydrogen atoms to form 
significant interactions with aromatic .pi.-rings. 
Removal of the calixarene from the fullerene can also be achieved by 
refluxing a toluene solution over sodium hydroxide pellets for ca 10 
minutes (see FIG. 1), the calixarene separating as a sodium salt which 
fails to form a complex on cooling presumably because of disruption of the 
cavity. 
In another embodiment of the present invention, a process of purifying and 
separation of fullerenes is provided by forming a complex of a fullerene 
and a complexing agent, wherein the complexing agent is immobilized. 
Immobilization of the complexing agent may be by any means, wherein 
immobilization does not prevent formation of a complex with a fullerene. 
For example, in the case of the calixarenes and derivatives thereof, 
immobilization may be by coupling through the R group, to the immobilized 
support. The R group may be bonded directly to the immobilized support, or 
may be bonded through a linking group capable of binding to both the 
complexing agent and the immobilized support. Alternatively, binding of 
the calixarene to the immobilized support may be through one of the -OH 
groups at the para position to the R group. 
In the case of the cycloveratrylenes, immobilization may be by coupling 
thorough the R' or R" group, to the immobilized support. The R' or R" 
group may be bonded directly to the immobilized support, or may be bonded 
through a linking group capable of binding to both the complexing agent 
and the immobilized support. 
Suitable immobilized supports include for example polystyrene, polyester, 
polyamide, poly(meth) acrylate, polyurethane and polyvinyl chloride. The 
immobilized support must be such that when the complexing agent is bound 
to the immobilized support, the material is insoluble in organic solvents, 
particularly aromatic solvents. 
Purification using the immobilized complexing agent may be performed using 
the immobilized complexing agent as a chromatographic support. The column 
of the immobilized complexing agent is treated with crude fullerene to be 
purified, under conditions sufficient to form a complex of the fullerene 
with the immobilized complexing agent. Once the complex is formed with the 
fullerene, and the impurities are washed away, the fullerene can be 
retrieved, by decomplexing with either a decomplexing solvent or a base as 
similarly describe above, for decomplexation of the fullerene-complexing 
agent complex. 
Purification, using the immobilized complexing agent may also be performed 
by preparing a slurry of the immobilized complexing agent and the 
fullerene in an organic solvent, under conditions sufficient to form a 
complex of the fullerene with the immobilized complexing agent. After the 
complex of the fullerene and the immobilized complexing agent is formed, 
the slurry can be filtered to obtain the purified fullerene-immobilized 
complexing agent complex. The fullerene can be retrieved, by decomplexing 
with either a decomplexing solvent or a base as similarly describe above, 
for decomplexation of the fullerene-complexing agent complex. 
Crude fullerene mixtures may be prepared by conventional mean, known to 
those of ordinary skill in the art. For example, according the the method 
described by Kratschmer et al (Chem. Phys. Lett. (1990), 170:167), a 
carbon rod is evaporated by resitive heating under a partial helium 
atmosphere (0.3 bar). A plasma discharge reactor for the synthesis of 
crude fullerenes is described by Scrivens et al (J. Org. Chem (1992), 
57:6932-6936). 
Overall the ability to selectively recover high purity fullerene-60 from 
carbon arc soot via simple complex/recrystallization procedures, and also 
the enrichment of the fullerene-70 content of the residues is noteworthy. 
Moreover, formation of complex 3 as a sparingly soluble material is an 
attractive method of purifying fullerene-60 from crude fullerene mixtures 
and reaction mixtures. 
Other features of the invention will become apparent in the course of the 
following descriptions of exemplary embodiments which are given for 
illustration of the invention and are not intended to be limiting thereof. 
EXAMPLE 1 
Synthesis of Complex p-Bu.sup.t -calix8!arene with C.sub.60 and&gt;99.5% 
Purity Fullerene-60. 
In a typical experiment ca 7.5 g of fresh carbon arc soot was stirred with 
250 mL of toluene for one hour then, the mixture was filtered, and 1.0 g 
of the p-Bu.sup.t- calix8!arene added. After refluxing for 10 minutes the 
mixture was filtered, seeded with crystals of 3 then allowed to stand at 
ca 20.degree. C. over night. The yellow/brown plates of the complex were 
then collected and recrystallized twice: from toluene (1.0 g from 80 mLs 
of toluene), 90% yield, analysis: found C 88.20, H 5.25%; calc. C 88.07 H 
5.59%. Addition of chloroform (5 mLs) to the complex (0.85 g) afforded a 
precipitate of fullerene-60 (0.28 g, 92% recovery from the recrystallized 
complex). 
EXAMPLE 2 
Synthesis of Calix6!arene(C.sub.60).sub.2. 6. 
To a refluxing solution of fullerene-60 (5 mg) in toluene (5 mL) was added 
calix6!arene (4.4 mg). The hot solution was rapidly filtered and slowly 
cooled overnight yielding black prisms (5.5 mg, 77% yield, analysis: found 
C 94.18 H 1.87% calc.; H 1.75 C 93.63%). 
EXAMPLE 3 
Synthesis of p-Bu.sup.t -calix6!arene(C.sub.70).sub.2. 7. 
To a refluxing solution of fullerene-70 (5 mg) in toluene (2 mL) was added 
p-Bu.sup.t -calix6!arene (5.8 mg). The hot solution was rapidly filtered 
and slowly cooled overnight yielding red/brown needles (2.5 mg, 31% yield, 
analysis: found C 92.48, H 3.19% calc. C 93.2, H 3.19%). 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein.