Note: Descriptions are shown in the official language in which they were submitted.
' W0 93/11067 ~ 1 3 1 Pcr/uss2~10
NOVEL SALTS OF FULLERENES
FIELn OF THE INVENTIQN
The present ~nvention relates to novel salts of fullerenes
also known as fulleride salts, their preparation and use.
BACKGRQUND OF_~ I~VENTION
Diamond and graphite are two well known allotropic forl~s of
carbon. Another form, the fullerenes, have been prepared by graphite
volatilizat~on (See W. Kratschmer et al, Nature, 347, p. 354 (1990)).
Pot~ssium and other metal complexes of fullerenes have been observed
ln the gas phase by mass spectrometry (See D. M. Cox et al, J. Chem.
~PhYs. 88(3~, 1588 ~19B8)).
Fullerenes are hollow molecules composed only of carbon
ato~s and constltute a new allotropic form of car~on. Typically,
f~ renes ~ach have carbon atoms arranged as 12 pentagons, but
d~f~er1ng numbers of hex~gons having the formula C2n where n is equal
to or greater than 16 (hereinafter UfullerenesN). The pentagons are
requlred in order to allow the ourYature and eventual closure of the
c~osed surface upon ~tself. The most abundant species of fullerenes
ident1f~ed to date ~s the C60 molecule or Buchminsterfullerene (here-
~nafter ~C60~). C~o oons~sts of 12 pentagons and 20 hexagons.
Ho~ever9 other species, includ1ng C70 have also been ~dentified.
~MMARY OF ~HE INVENTION
The portion of this invention that relates to C60 fulleride
salts was f~rst dlsclosed by appllcants at a seminar in Boston,
Massa~husetts on November 29, 1990, and subsequently published in Mat.
Re$. Soc. SvmP. Proc., Vol. 206, p. 659 tl991). This invention
provides new composit~ons of matter having the formula AnCX~ wherein
C~ is a fullerene anion wherein x is preferably selected from the
group consisting Of C60 and C70 and wherein A is a monovalent cation.
WOg3/11067 ~J~ 3 PCr/US~2/10120
Preferred monovalent cations, in accordance with the present inven-
tion, include ammonium cations, alkyl ammonium cations such as quater-
nary ammunium cations, alkali metal cations, phosphonium and arsonium
cations, especially organophosphonium and organoarsonium ions, partic-
ularly phenylphosphonium and phenylarsonium cations. The preferred
fullerene used ~n the practice of the present invent~on is Cho.
In one embodiment of the present invention, the ~ulleride
salt compounds of the present ~nvention are prepared by passing a~
electr1c current through (electrolyzing) a non-aqueous solution of
fullerenes ~n the presence of a soluble salt containing a cat~on, A,
of the AnCX compound to be formed. The electric potential is applied
for ~ t~me sufficient to generate fullerene anions in the solut~on.
In another embod~ment of the present invention, the fulleride salt
compounds are prepared ~n the solid state. The ccmpounds of the
present ~nvention exhibit reversible electrochem~cal reduction; and,
consequently, are partlcularly useful as electrode components in
electrochem~cal cells sueh as secondary batteries.
The fullerene anions, C60-Y and C70-Y, wherein y is a charge
of from 1 to 3, spec~fically 1, 2, and 3 ~n the compound of the
present invant~on contain unpaired electrons and thus have paramag-
netic properties. In the case of, for example, c60-l and C6o-2~ these
propert~es are con~irmed by electron spin resonance spectroscapy
ESR~) ~or the tetralkyl ammonium fulleride salt containing ~he c60-l
monoan~on. The magnitude of the magnet~c suscept~b~llty of the
compound of the present invention var~es with the temperature accord-
lng to the Curie-We~ss law, wh~ch ls known to one hav~ng ordinary
sklll ~n the art. Since a one-to-one magnet~c susceptibillty tempera-
ture correspondence ex~sts, these compounds may be used as magnetic
thermometers. ~:
Sim~larly, fuller~de salts containing c60-l monoan~ons may
be used as semiconductors (See P. M. Allemand et al., J. Am. Chem.
Soc~, 113,2780 (1991)) wh~le those containing C60-3 ~nd alkali-metals
may be used as superconductors ~See A. F. Hebard et al., Nature
350,600 (199i)).
WO 93/11067 PCr/US92/10120
, ';' ~' '',1
... ,.~ i -. .1
-- 3 --
Alkali salts Of C60 also can serve as starting materials for
the preparation of other materials. The reaction of the lithium salt
of C60, for example, with alkyl halides yield alkyl derivatives of
fullerenes (See J. W. Bausch et al., J. Am. Chem. Soc., 113,320
(1991)) that may-be useful as polymer blends, composites and building
bl ~cks .
Further, the AnCX fulleride salts are stable in the absence
of a~r and other react~ve molecules. Their free radical charac~er may
make them suitable as spin labels. Spin labels are usually organic
~olecules that contain an unpaired electron ~for example, a nitrox~yl
rad~cal) and are used to render diamagnetic molecules to which they
are attached susceptible to analys~s by magnetic spin re!sonance
techniques. ~he AnCX spln labels m~xed, for example with polymers,
0ay allow valuable information concerning polymer dynamics and struc-
tures t~ be obtained.
qESCRIPT~ON OF THE PREFERRED EMBDDIMENTS
The present invention encompasses novel compositions of
matter ha~ing the formula AnCX~ wherein Cx is a fbllerene anion,
whcre~n Cx ls preferably selected from the group consisting of C60 and
C70, where1n A is a monovalent cation and wherein n is an integer from
1 to 3 ~nclusive, specifically 1, 2~ and 3. The cation, A, may be
selected from a w~de range of cations. The fullerene anion is further
selected from the group consist~ng of monovalent, divalent and trt-
valent an~ons. Its valence, however, depends on the formula of the
monovalent cation, An. Thus, for example where the monovalent catlon,
An~ has the formuls (A~ , Cx wlll be a monovalent anion; where An
has the formula (A~1)2, Cx w~ll be a divalent anion; for (A+1)3, Cx
w~ll be a triYalent anion. Particularly preferred cations for A
~nclude ammonium and alkyl ammon~um cations, organophosphon~um or
organoarsonium cations, espec~ally tetraorganophosphonium and tetra-
organoarsan~um ions, such as tetraphenylphosphonium and tetraphenyl-
arson~um cat~ns, alkali metal cations, and the like. Among the
alkali metal cations, L~, Na and K are especially preferred. The
WO 93/110~i7 PCl~US9~/10120
-i~ L r:
preferred fullerene used in the practice of the present invention is
c6o~
)
The starting materials for $he practice of the present
invention can be obtained from con~Tercial sources. In addition, ~he
fullerenes may be prepared by graphite volatilizatlon ~see W.
Kr~tschmer, et al, Nature, 347, p. 354 ~1990)).
When the compounds of the present inYention are made by
electrolyziny a non-aqueous solution containing fullerenes and a
soluble salt of a cat~on, A, such as one of the aforementioned ca~-
ions, the etectrochem~cal reduotion of fullerenes ~s conducted prefer-
ably ~n a low or h~gh polar~ty solvent as required tQ diss~lve the
reactants, but wh~ch will be inert to the reaction~ 'INon-aqueous'' as
used here~n means solvent systems wherein waterl if present, ~s
electrochemically and chem~cally ~nert. Thus, by way of example,
tolu~ne, d~chloromethane in the case where the cation, A, îs ~rganic
and a h~gh polar~y solvent such as dimethyl sulfoxide when the cation
A ~s ~norgan~c. Slngle, b~nary or mult~component mixtures of tetrahy-
drofuran, ethylene chlorlde, toluene, xylenes, d~methyl sul:fox~de,
d~chloromethane, benzene are part~cularly suitable for dissolving the
fullerenes. Add~t~onally, the salt conta~nlng the cat~on, A, of
de~red compound, A~CX, must have some solubility in the organic
solvent system used. Typically, therefore, salts containing organo
groups sueh as7 but not restr~cted to7 R4~Cl, R4AsCl, R4PCl, P(4NPF6,
and R4NBF4 are part~cu~arly su~table. In the forego~ng s~lts, R is
sel~!cted from the group cons~sting of hydro~en and an organ~c moiety.
lhe organ1c moiety should be chosen in order to render the salt
soluble in the solvent system. It is within the skill of one of
ordinary sk~ll ln the art to make a selection of the appropriate
solvent system. R may, for example, be selected from alkyl groups
having from 1 to 16 carbon atoms and phenyl groups. Other useful
sa~ts include alkali metal salts haYing anions containing sufficient
organic moiet~es to render the salt soluble in the solvent system.
Representat~ve examples include Na8Ph4, K8Ph4 where (~Ph" as used
herein means phenyl or substituted phenyl group). When ~norganic
salts containing the cation A are used, the solvent system is more
wo s3/lto67 .~ s~ ~ 9 1 PCT/uS92/10120
polar. Inorganic salts such as NaBF4, KCl and KBr should be used with
m~xtures of tetrahydrofuran, dimethyl sulfoxide, dimethyl formam;de,
toluene and the l~ke. The relative ratio o~ components of the solv~nt
mixtures should be such as to insure some degree of solubility of both
start~ng materials; i.e., fullerenes (which are soluble in relatively
non-polar solvents) and inorganic salts (more soluble in polar sol-
vents like dimethyl sulfoxide). It is within the skill of a person
with average skill in the art to select the optimum mixture of sol-
vents suitable for a given inorganic salt containing a desired A
cation. The resultant AnCX fulleride salts need not be soluble in the
solvent mixtures used and 1t is preferred that they are not ~f ~sola-
tion o~ the sol~d salt is desirable.
A commercially available PAR (Princeton Appl~ed Research)
System equlpped with Pt wire auxiliary electrode, standard calomel
reference e~ectrode (SCE) and a Pt gauze working electrode may be ~sed
to reduce, for example, up to gram quantit~es of the particular
fullerene. Other commerclal units ~ay be used to prepare larger
qu~nt1t~es of fulleride salts. A potentiostat regulates the potential
necess~ry to produce the desired reduction state (salt of anion) of
the fullerene in the particular solvent system. The molar rat;o of
salt to fullerene used in the solvent system will be generàlly greater
than 3:1 and, preferably, wlll be in the range of about 10 to 20. The
potent~al ~ay be appl~ed using any known source o~ direct current
after ~mmersing the work~ng and reference electrodes into the solvent
system. The aux~liary ele~trode may be isolated from the working
electrode compartment dur~ng appl~cation of the electric potential,
th~ ~ixture may be stirred, but such is not necessary. Typically, the
react~on takes place at room temperature and pressure under a blanket
of inert gas. Alternatively, an inert gas (for example, N2, Ar) may
be bubbled through the solvent mixture. For example, for the produc-
tion of C60-l monoanion from C60 a potential of -0.45 V versus SCE in
the DMSO solvent system uslng KBr as supporting electrolyte resulted
~n product10n of only the fullerene salts containing C60 monoanion.
Since the potential necessary to produce the anions of desired valence
is solvent dependent its value can be determined via cyclic voltam-
metry (CV) or d~fferential pulse polarography (DPP). Care must be
w ~ 93/11067 ~ 3 I PcT/uss2/l
taken in choosîng solvent system, electrolyte, temperature, eleotrode
type, etc. to obta~n reversible well separated waves in CV at slow
scan speeds. These conditions are necessary for selective production r
of the particular fullerene salt and to ensure that once produced they
àre not decomposed during the bulk electrolysis. For typical examples
of well separated waves in CV and DPP data on C60 and C7~ fullerenes,
see S. M. Gorun et. al, Mat. Res. Soc~_~ymD~_Proc. 206, 659 ~1931).
The process of the present inven~ion may be used t~ selec-
tively generate the salt of the fullerene anions in solutions of the
fullerenes and other hydrocarbons by applying a current to the solu-
tion, wherein the current is of sufficiently low voltage to selective-
ly reduce the particular fullerene to the correspondent salt off ~he
fullerene anion without reducing the other hydrocar60ns. The fuller-
ene anions have the formula Cx-Y, wherein Cx iS a fullerene, prefera-
bly a fullerene selected from the group cons~sting af C60 and C70 and
where~?n y is an integer of from 1 to 3, spec~fically 1, 2 and 3. ~he
range of electric potent~als will vary wi?lth the solvent system, but
can readily be selected by one havin~ ordinary skttl in the art. ~he
electric potentiial is ~rom about zero to about -0.7 V, when the
fullerene anion is selected from the group consisting of c60-l (when
: the fullerene ~?s C60) and c70-1 when the fullerene is C70; ~t is from
about -0.80 Y to about -1.1 V when the fullerene anion is setec~ed
~ro~ the group consist~ng of C6o-2 (when the fullerene is C60) and
C70-2 (when the ~ullerene ~s C60) and C70-2 (when the fullerene is
G70~; and it is from about -1.3 V to about -1.7 ~ when the fullerene
an~on t?s selected from the group consisting of C~o~~ (when the fu~ler-
ene ~s C60) and C70-3 ~when the ~ullerene is C7~3. For example,
c60-l~ which is prepared from C60 at a potentiial of -0.70 V in 1:2
d~?chloromethane/toluene milxtures, may be selectively prepared as the
sa~t of the c60-l an~on ~rom mixtures of C60 w~th other hydrocarbons
havin~ hlgher potentials (that is, having a chemical inertness with~n
~he range of potenti?als at which the c60-l anion is produced) by
apply~ng the foregoi?ng chemiical potentlals to the solution. The salt
of the fullerene anion may be present iin the solution or precipitated
therefrom. The actual voltage may vary, depending on the solvent in
which the reduct~on is conducted. However, the potential should be
WO 93/11067 PCI/US92/10120
. ~i .~ 1 1 3 1
- 7 -
chosen within the range of the electrochemical potential necessary to
generate the particular salt of the fullerene anion and within the
ranQe of chem~cal inertness for the other hydrocarbons. (For techni-
cal deta~ls see, for example, P. T~ Kissinger and Wm. H. Heineman,
Editors, ~aborat~ry Techniques in Electrochem;strY, Marcel Decker,
Inc., N.Y. (1984~; and A. Bard and L. Faulkner, lectrochemical
MethQds, Wiley and Sons, N.Y. (1980)).
During the electrolysis, the progress of the reaction is
~onitored by measuring the amount o~ current that passes through the
solut10n. Alternatively, s~nce the fullerene anions are paramagnetic
wh~le the start~ng fullerenes are diamagnetic, quantitative ESR
spectroscopy can be used for the same purpose. Similar results are
expected for c70-1 monoanion. (See, for example M. A. Greaney et al.,
. PhYs, Chem. 9~,7142 (1991) for the ESR signatures of the c60-l and
c70-1 and D. Dubo1s et al., J. Am. Chem. Soc. 113,4364 (199lJ for
C6o~2). For ~60, applicants found that the most convenient method to
detect c60-l is the monitoring of the near infrared spectrum of the
solut~on. ~ strong absorption band centered at approximately 1065 nm
~s present ~n c60-l~ but mlssing in C60. This band, which is attr1b-
uted to the HOMO-LUMO (highest occupied molecular orbital-lowest
unoccup1ed molecular orbital) electronic transition of C~o-1 disap-
pears upon ox~dat~on of c60-l to C60 and can be regenerated upon
furth~r reductlon. Its position and intensity is practically indepen-
dènt of the A cation, being observed for both organic (e.g., Bu4N) and
1n~rganic (e.g., K) salts of c60~ n a variety of solvents. As used
hereln, ~Bu~ means ~butyl~.
~ The AnCX product ~ay be isolated by precipitat~on; for
example, using a non-solvent or precipitatlng agent, such as toluene
or ether or by reducing the volume of the solvent used v~a vacuum
distillatlon or low temperature freez~ng. Using th~s technique, only
the fullerene salt precipitates. For example, ~f KCl is used as a
source of potassium cat~on, only KC60, not KCl is precipitated. Only
traces of chloride ~ons are detectable in the KC60 solid precipitate
~a scanning electron microscopy energy dispersive spectra technique.
WO93/11067 ' ~ PCr/US9:2110120
The following examples are intended to demonstrate the
invention and not limit ~t in any way.
EXAMPLES
In all of the following examples, the solvents were dried
and ~egassed according to standard methods. A blanket of inert gas
prevented the contact of the reaot~on mixture with the atmosphere.
All reactions are carried out at ambient temperature and prl~ssure
unless stated otherwise. Mixtures of C60fC70 were obtained by solvent
ex~racting the soot produced via the carbon arc synthesis method, as
statet ~n D. M. Cox et al., J.l4m. Çhem Soc. 113, 294Q ~19~13. P~re
C60 was produced by chromatography from ~ixtures ~f C60 and C70
full erenes, as descri bed in the 1 iterature. See, for exampl e, ~. M.
Cox et al~, ?. Am. Chem. Soc. 113, 2g40 (1991).
Exam,~
A methylene chloride/toluene solution (2~1 v/v~ containin~
0 025 ~ C60 and 0.5 9 (BU4N3~l(pF6)-l was ele~trolyzed at.-0.70 Y YS.
SCE for a time suffioient to reduce C60. Electronic spectroscopy and
ESR spectra ~ndiczted the formation of the alkyl ammonium C~o ful~er-
~de salt, (BU4N~lc6o~ yclic Yoltommetry and DPP conFirmed ~he
presence Of ~60-~-
E~Z
The procedure speoified in Example 1 was employed using Cand produced the alkyla~monium c70-1 fulleride salt (BU4N)+lC70^l~ as
shown by electrochem~cal and ESR analys~s~
~ample 3
.
A tetrahydrofuran solution containing 0~002 9 60 and 0.30 9
NaBF4 was electrolyzed at -0.7 V vs. SCE for a time sufficient to
reduce the C60. ~he properties of the resulting inorganic ful~eride
salt Na~lC60-l are similar to those of its BU4N+c6o-l counterpart in
WO93/11067 i i r~ ~ 1 9 1 PCl/US92/10120
Example 1 (as determined by electronic and magnetic resonance spec-
troscopy).
Example 4
A polar solvent system consisting of a dimethyl sulfoxlde
DMS0/toluene solution (6/1 v/v) containing a suspension of 0.1 9 C60
and 0.25 KCl was electrolyzed at -0.45 V vs. SCE for a time sufficient
to produce c60-l- The solution ~urned red at the end of the reduc-
tion. Add~t~on of toluene (about 5:1 toluene/DMS0) and refrigeration
overnlght at -20~C allowed for the removal of most of DMS0 and some
toluene as a frozen soltd. Addltion of freshly distilled diethyl
ether to the remaining solution resulted in the precipitation of KC60
as a black powder, which was isolated via filtration or decanting the
liqu1d~ Electronic and ESR spectra of DMS0 solutions of the solid
confirmed the presence of C60-1 in the inorganic K~C60-1 f~lleride
salt. Onlytracesofchloride ~ons were detected via scann~ng elec-
tron ~lcroscopy energy dispers~Ye speetroscopy, which also confirmed
the presence of the K~60 salt.
Ex~mp~
the procedure of Fxample 4 was repeated using KBr instead of
KCl to produc~ K~lC60-1 fulleride salt.
. x~mPle 6
-
This example illustrates the use of C60 as a solid state
electrode component. A toluene solution of C60 was deposited on a
glassy carbon electrode. Upon solvent evaporat;on, the electrode was
coated with sol~d C60. The coated electrode was immersed in an
aceton~tr~le solution containing 0.4 9 BU4NPF6 as the supportina
electrolyte. C60 and ~ts anions are not soluble in acetonitrile.
Cycl~c voltametrlc scans revealed the reversible formation of c60-l~
C60-~ C60-3 anions in the solid film. The additions of electrons to
C6Q was reversible; the CV scans are similar to those obtained previ-
ously by using a solution of C60. A control CV analysis of a
-
WO 93/11067 P(~/US92tlO120
' ~ ~lJ~
- 10 -
suspens~on Of C60 in acetonitrile solution conta~ning the same sup-
port~ng electrolyte revealed practioally nQ fullerene-an~on ~ormation~
~,.
