Process for Producing a Metal Fulleride

Europäisches Patentamt *EP001199281A1* (19) European Patent Office

Office européen des brevets (11) EP 1 199 281 A1

(12) EUROPEAN PATENT APPLICATION

(43) Date of publication: (51) Int Cl.7: C01B 31/02 24.04.2002 Bulletin 2002/17

(21) Application number: 00122854.3

(22) Date of filing: 20.10.2000

(84) Designated Contracting States: • Dubitzky, Yuri A. AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU 20159 Milano (IT) MC NL PT SE • Ricco, Mauro Designated Extension States: 43100 Parma (IT) AL LT LV MK RO SI • Sartori, Andrea 43010 Fontana (Parma) (IT) (71) Applicant: PIRELLI CAVI E SISTEMI S.p.A. 20126 Milano (IT) (74) Representative: Giannesi, Pier Giovanni et al Pirelli S.p.A. (72) Inventors: Industrial Property Dept. • Zaopo, Antonio Viale Sarca, 222 20137 Milano (IT) 20126 Milano (IT)

(54) Process for producing a metal fulleride

(57) The present invention relates to a process for acting in a liquid medium: 1) a first metal fulleride having, producing a metal fulleride. In particular, the present in- as counterion, a cation of a first metal forming a salt sub- vention relates to a process for producing a metal ful- stantially insoluble in said liquid medium, and 2) a salty leride by an ion exchange reaction in a liquid medium, of a second metal substantially soluble in said liquid me- preferably in liquid ammonia. More particularly, the dium, so as to produce a second metal fulleride having, present invention relates to a process for producing a as counterion, a cation of said second metal. metal fulleride, said process comprising the step of re- EP 1 199 281 A1

Printed by Jouve, 75001 PARIS (FR) 1 EP 1 199 281 A1 2

Description used to accomodate any metal ion inside (i.e., endohe- dral) or outside (i.e., exohedral) the fullerene cage. [0001] The present invention relates to a process for [0018] The second most abundant species of identi- producing a metal fulleride. fied fullerenes is C70 molecule, said molecule containing [0002] In particular, the present invention relates to a 5 12 pentagons combined with 25 hexagons. process for producing a metal fulleride by an ion ex- [0019] The C70 fullerene molecule presents a shape change reaction in a liquid medium. which is reminiscent of a rugby ball. [0003] More particularly, the present invention relates [0020] Furthermore, fullerene molecules containing to a process for producing a metal fulleride by an ion from 30 to many hundreds carbon atoms have been de- exchange reaction in liquid ammonia. 10 tected by mass spectrometry. [0004] Recently there has been a remarkable interest [0021] Fullerene films can be applied to a suitable in organic materials which possess conductive proper- support by using different techniques, such as impreg- ties or which can be suitably doped so as to show con- nation or spin-coating (i.e., obtaining a coating from a ductive properties. solution by using a centrifuge) from fullerene solutions [0005] For example, organic materials are generally 15 as well as deposition from a gas (vapour) phase. easily formed in thin films in order to be used as con- [0022] However, the obtained film exhibits very low ductive components in devices such as switches, anti- conductivity properties since fullerenes are in their zero static devices or magnetic shielding. oxidation state. [0006] Among said organic materials, typically used [0023] Therefore, in order to enhance conductivity of carbon-based conductors are graphite and polyacety- 20 a fullerene, it was proposed to intercalate the latter by lene. one or more alkali metals. [0007] Graphitic materials, characterized in having an [0024] For instance, US-5,294,600 discloses a super- infinite sheet-like structure of carbon atoms, present conducting material which comprises a fullerene doped conductivity values in the range from 103 to 105 Sie- with Rubidium and Caesium. The production process of mens/cm; however they are rather intractable and can 25 said material comprises at least one of the following not be used in a plurality of applications. processes: a) ultrasonically solid-phase mixing of an al- [0008] Polyacetylene, instead, is known to possess kali metal or metals and a fullerene before heat treat- conductivity values higher than 104 Siemens/cm only if ment; b) finely pulverizing a solid-phase fullerene before it is suitably doped. mixing with an alkali metal or metals; c) annealing a sin- [0009] Other organic conductors, such as those 30 tered body of an alkali metal or metals and a fullerene based on tetrathiafulvalene, are known to have high while heating and then gradually cooling. conductivity properties (103 Siemens/cm); however [0025] It is known that metal fulleride compositions -1 they are difficult to be shaped into desired geometries. containing fullerene monoanions, e.g. C60 , may be [0010] Among the organic materials, those based on used as semiconductors (P.M. Allemand et al., J. Am. fullerenes are generally known as insulators and many 35 Chem. Soc., 113, 2780 (1991)), while those containing -3 attempts have been made to modify their structure in fullerene trianions, e.g. C60 , and alkali metal cations order to improve their conductivity. having a valence of +1 may be used as superconductors [0011] Fullerenes represent a particular allotropic (A. F. Hebard et al., Nature, 350, 600 (1991)). form of carbon, and are typically represented by 12 pen- [0026] Therefore, due to an increasing interest in su- tagons combined with a plurality of hexagons to form a 40 perconductivity, many different methods of metal ful- cage structure. lerides synthesis have been arranged, above all since [0012] The pentagons are required in order to allow the discovery in 1991 of superconductivity in K3C60. the curvature and the closure of the surface upon itself. [0027] For instance, US-5,324,495 discloses a meth- [0013] Nowadays, the most abundant species of iden- od for obtaining a metal fulleride composition by con- 45 tified fullerenes is the C60 molecule or "Buckminster- tacting a metal and a fullerene in a solvent or a mixture fullerene" or "buckyball". of solvents in which the fullerene is at least partly solu- [0014] C60 fullerene is a hollow molecule the carbon ble. Typically the fullerene is dissolved or slurried in an atoms of which are located at the vertices of said 12 pen- appropriate solvent and the metal is added thereto. Ap- tagons and possessing 20 hexagons arranged to form propriate solvents comprise toluene, benzene, nitriles, 50 an icosahedron. liquid SO2, sulfolanes and the like. [0015] More particularly, the C60 fullerene molecule [0028] Similarly to US-5,324,495, the document "Syn- consists of 60 carbon atoms joined together to form a thesis and characterization of alkali metal fullerides: cage structure with 20 hexagonal and 12 pentagonal AxC60" by D. W. Murphy, M. J. Rosseisnky et al, J. Phys. faces symmetrically arrayed in a soccer ball-like struc- Chem. Solids, vol. 53, pages 1321-1332, Ed. 1992, dis- ture. 55 closes a method for producing a metal fulleride by [0016] C60 fullerene molecules form a close-packed means of a redox reaction. In particular, the method dis- solid material having a face-centered cubic structure. closed therein consists in contacting an alkali metal and [0017] The inner hollow space of the fullerene can be aC60 fullerene in a liquid ammonia medium. Therefore,

2 3 EP 1 199 281 A1 4 stoichiometric amounts of an alkali metal and of a C60 [0033] For instance, in order to enhance the conduc- fullerene are prepared in a powdery state and intro- tivity of a fullerene coating, it is known in the art to pre- duced inside of a flask under high vacuum. Successive- liminarily deposit a fullerene thin film on a suitable sup- ly, the obtained metal/fullerene mixture is cooled by port and successively doping said film by carrying out means of a dry-ice/isopropanol slush and anhydrous 5 its electrochemical reduction in an organic electrolytic ammonia is condensed into the flask. Since starting C60 solution containing a suitable cation, such as an alkali fullerene, i.e. in its zero oxidation state, is insoluble in metal cation, to obtain the corresponding fulleride, i.e. liquid ammonia, the complete dissolution of the fullerene the fullerene salt (see, for instance, Trans. Mat. Res. anion in liquid ammonia demonstrates that a charge Soc. Jpn. / 1994 Elsevier Science B.V. / Vol. 14B / pages 10 transfer from metal to starting C60 fullerene, and the 1107-1112). consequent formation of the metal fulleride, have oc- [0034] WO 93/11067 discloses a method for produc- cured. Then the flask is heated up to 150°C under vac- ing solutions or precipitates of fullerene by electrochem- uum conditions for about half an hour so as to allow the ical reduction in an organic electrolyte, said organic complete removal of ammonia from the solution by electrolyte containing a solution of an alkali metal salt 15 evaporation. and C60 fullerene or C70. According to said document [0029] US-5,223,479 and US-5,348,936 relate to a suitable electric potential is applied to a non-aqueous metal-doped fullerenes and, in particular, to a stoichio- solution of fullerenes in the presence of a soluble salt metrically-controlled method for the preparation thereof. containing a cation for a time sufficient to generate fuller- Said method consists in preparing a more fully doped ene anions in the solution. According to a further em- fullerene, preferably a metal-saturated fullerene, and 20 bodiment, the fulleride compounds are prepared in the then diluting the more fully doped moiety by contacting solid state. it, inside of a dry box, with a previously weighed amount [0035] Moreover, it is known in the art that a fulleride of non-doped fullerene to give a desired stoichiometry. coating can be obtained on a gold or a platinum elec- This accurate and difficult stoichiometric control is ex- trode by cathodic deposition from an electrolyte consist- 25 2- 3- tremely important to be achieved since the supercon- ing of an acetonitrile solution of C60 and C60 , said ductivity of a metal doped fullerene is sensitive to the solution being respectively prepared by bulk controlled- exact degree of doping. potential electroreduction (at -1,2 V) of a C60 suspen- [0030] A further method to obtain metal fullerides con- sion in solutions of CsAsF6, KPF6 or Ca(PF6)2 and by sists in carrying out an intercalation reaction in vapour bulk controlled-potential electroreduction (at -1,6 V) of 30 phase of suitable metal ions into a fullerene, i.e. by aC60 suspension in solutions of (TBA)ClO4 (see "Syn- n- means of a vapour phase deposition. thesis and Electrodoping of C60 (n = 0, 1, 2, 3) Films: [0031] For instance, US-5,391,323 and US- Electrochemical Quartz Microbalance Study in Ace- 5,698,497 relate to highly conducting tractable materials tonitrile Solutions of Alkali Metal, Alkaline-Earth Metal, (conductivity greater than 500 Siemens/cm at room tem- and Tetra-n-butylammonium Cations" by W. Koh, D. perature) which are obtained by electronic structure 35 Dubois, W. Kutner, M. T. Jones, K. Kadish; J. Phys. modifications of fullerenes. According to one embodi- Chem. 1993, 97, 6871-6879). ment disclosed therein, electrons are added to the fuller- [0036] A further method to obtain a metal fulleride ene structure by charge transfer from a species more consists in an ion exchange reaction by means of a cat- electropositive than the fullerene. For example, it is pos- ion exchange resin. sible to electronically modulate a fullerene by subjecting 40 [0037] For instance, document "Synthesis and NMR 3- it to an alkali metal vapour. Alkali materials, such as So- characterization of new C60 salts by ion exchange" (by dium, Potassium, Rubidium and Caesium, are signifi- R. Ziebarth, S.M. Lee, V.A. Stenger and C. Pennington, cantly more electropositive than fullerene and therefore Electrochemical Society Proceedings, Volume 95-10, 3- donate electrons to the fullerene structure. As described pages 316-329) discloses new C60 salts containing in US-5,391,323, said intercalation in a vapour phase 45 polyatomic cations prepared by using cation exchange can occur by contacting stoichiometric amounts of fuller- resins in anhydrous liquid ammonia. In details, by inter- ene and metal inside of a glass tube in a glove box (see action of the appropriate form of a cation exchange resin Examples 9 or 11) or by previously producing a fullerene with Rb3C60 in liquid ammonia, three new C60 salts, spe- layer at suitable pressure and temperature conditions cifically [(CH3)4N]3C60, [(Et)4N]3C60 and [(CH3)4P]3C60, (see Examples 1 and 3). The intercalation in the vapour 50 have been prepared. According to the method disclosed phase is achieved by evacuating the glass tube and therein, ion exchange was performed in anhydrous liq- heating (annealing) it by immersion in an oil bath (as uid ammonia at -45°C using a 3-4 fold excess of the cat- described in Example 3) or by placing it in a furnace at ion exchange resin with Rb3C60.Rb3C60 and the ion ex- 403 K for 12 hr and then at 703 K for more that three change resin were placed in a quartz reaction tube, the weeks with intermittent shaking. 55 system was evacuated and the liquid ammonia was con- [0032] A further method to obtain a metal fulleride densed on the mixture at -78°C. The reaction was consists in electrochemically depositing the latter from warmed to -45°C resulting in formation of a dark brown- suitable starting solutions. ish-black precipitate covered by a clear solution. The re-

3 5 EP 1 199 281 A1 6 action was held at -45°C for 1 hr prior to removal of am- [0045] With reference to the process according to monia by evaporation which left a dark brownish-black which a preliminary deposition of a fullerene film is fol- powder mixed with the ion exchange resin. Isolation of lowed by a doping phase of said film by means of its the sample from the resin was accomplished by dissolv- electrochemical reduction so that a fulleride coating is ing the sample in acetonitrile and filtering out the resin 5 obtained, it can be pointed out that said electrochemical under inert gas. Evaporation of the acetonitrile left the reduction is accompanied by a transfer of fullerene an- desired brownish-black product. ions into the electrolyte solution, thus causing degrada- [0038] According to the Applicant, the processes of tion and dissolution of the obtained fulleride coating. The the above described prior art show a plurality of draw- fulleride coating dissolution occurs also in the process backs and disadvantages which are mainly related to 10 according to document WO 93/11067. complexity and duration of the different steps involved [0046] As to the fulleride coating deposition carried in said processes, as well as to poor control of the inter- out by Koh et al. cited above, it has to be noted that, calation degree of said alkali metals. since neutral C60 fullerene is insoluble in acetonitrile, the [0039] For instance, the process described in docu- suspension of neutral C60 fullerene was firstly reduced 15 n- ment "Synthesis and characterization of alkali metal ful- to obtain the desired C60 solution and then the ob- n- lerides: AxC60" cited above, consisting in carrying out a tained C60 was oxydized to obtain the deposition of the redox reaction between a C60 fullerene and a metal in fulleride coating on the electrode surface, the fulleride a liquid ammonia medium, requires that a metal soluble being insoluble in acetonitrile. However this method is in said medium is to be selected, generally an alkali or rather complex and requires at least two separate steps, 20 an alkaline-earth metal. Furthermore, the metal and the i.e. the reduction of neutral C60 fullerene followed by the n- fullerene to be used as starting materials have to be cho- oxydation of reduced C60 species thus obtained. sen based on the redox potentials of each material so Moreover, this method reveals very high sensitivity of that the reaction is thermodynamically possible at the fullerene anions to oxygen and water traces due to C60 particular reaction temperature in the particular solvent. epoxidation and other subsequent reactions. [0040] Despite the apparent semplicity of said meth- 25 [0047] With reference to document "Synthesis and 3- ods based on a redox reaction, they are stoichiometri- NMR characterization of new C60 salts by ion ex- cally difficult to be controlled. In fact, since it is generally change" cited above, the ion exchange reaction is car- desirable to use a minimum amount of the relatively ex- ried out by means of a cation exchange resin, the latter 3- pensive fullerene, the amount of metal required is typi- being used for the introduction of new cations into C60 cally quite small and, therefore, difficult to accurately 30 salts. The main disadvantages of the above described dispense. procedure is a limited number of metal cations which [0041] Furthermore, since the superconductivity of can be used and the extremely slow rate of said ex- metal doped fullerenes is very sensitive to the degree change reaction. of doping, said methods do not ensure metal fullerides [0048] Furthermore, the procedure of preparation of of controlled superconductivity. In order to overcome 35 the resin, e.g. the drying step thereof, has to be partic- said drawbacks, documents US-5,223,479 and US- ularly accurate since the described method is very sen- 5,348,936 have suggested an improvement to said sitive to even trace amounts of air and moisture. For in- methods, but accurate and difficult stoichiometric con- stance, following preparation of the tetraalkyl ammoni- trols are still needed, as disclosed above. um or phosphonium form of the resin (i.e., the ion ex- [0042] With reference to the methods based on the 40 change resin was prepared in the appropriate cationic intercalation of metal ions into a fullerene in a vapour form by passing a saturated aqueous solution of phase it has to be noted that, once again, it is very dif- [(CH3)4N]Cl or [(CH3)4P]Cl through a column of Amber- ficult to accurately control the stoichiometry and the lite IRP-69 in the Na+ form), all water was carefully re- morphology of the resulting metal fullerides, even with moved (taking care not to collapse the resin pore struc- a very accurate and time consuming annealing. 45 ture) by repeatedly washing the latter with anhydrous [0043] Moreover, a further limitation of said methods liquid ammonia and successively drying it under dynam- comes from the evaporation temperature of the metal to ic vacuum at room temperature. From the foregoing, it be used. In fact, if said temperature is too high or the is clearly apparent that the use of a cation exchange res- metal does not have a vapour phase, said particular in requires very accurate and time consuming process metal fullerides can not be produced by using intercala- 50 steps. tion on a vapour phase. [0049] The Applicant has now found a process for pro- [0044] Furthermore, the intercalation of large ions ducing a metal fulleride which involves very few and sim- (like alkaline-earth ions) in C60 fullerene lattice interstic- ple steps remarkably decreasing the complexity and the es by means of diffusion in the gas phase is quite difficult duration of the processes known in the art. to be carried out due to the low mobility of said large 55 [0050] Furthermore, the process according to the ions. Besides, very long annealing times (e.g., several present invention advantageously increases the months) at high temeperatures (e.g., 500-600°C) are number of metal cations which can be suitably used for usually required to obtain a uniformly doped sample. said ion exchange reaction.

4 7 EP 1 199 281 A1 8

[0051] Therefore, the present invention relates to a earth metals. process for producing a metal fulleride, comprising the [0062] Even more preferably, said first metal is select- step of reacting in a liquid medium: ed from the group comprising: Lithium (Li), Sodium (Na) and Calcium (Ca). • a first metal fulleride having, as counterion, a cation 5 [0063] According to the present invention, the first of a first metal forming a salt substantially insoluble metal fulleride reacts with a salt of a second metal, said in said liquid medium, and salt being substantially soluble in the liquid medium, • a salt of a second metal substantially soluble in said preferably in liquid ammonia. liquid medium, [0064] In the present description and in the claims, the 10 wording "a salt substantially soluble in the liquid medi- so as to form a second metal fulleride having, as coun- um" means a salt having a solubility in the liquid medium terion, a cation of said second metal. equal to or higher than 6 mol/l at the reaction temper- [0052] In the following, the term "fullerene" indicates taure. any hollow, all carbon-containing molecule having car- [0065] Therefore, said second metal, forming said salt bon atoms located at the vertices of 12 pentagons (five 15 substantially soluble in liquid ammonia, is preferably se- membered carbon rings) combined with a plurality of lected from the group comprising: transition elements, hexagons (six membered carbon rings), said fullerene Lanthanides (rare-earth elements) and Actinides. corresponding to the general formula C2n wherein n≥12. [0066] More preferably, said second metal is selected [0053] According to a preferred embodiment of the from the group comprising: Potassium (K), Rubidium 20 present invention the fullerene molecule is C60 fuller- (Rb), Gadolinium (Gd), Lanthanum (La). ene. [0067] According to the present invention, the starting [0054] In the present description and claims, the term first metal fulleride can be obtained in any suitable man- "fulleride" indicates a salt of a fullerene, namely a neutral ner. For instance, if a Li3C60 fulleride is used, it can be molecule that can be represented by the formula An obtained by reacting Lithium azide and C60 fullerene un- 25 (Cx)m wherein Cx is a fullerene anion (preferably an an- der dynamic pressure and then by heating up to 180°C. ion of C60), m is the number of fullerene anions in the [0068] Alternatively Li3C60 fulleride can be obtained metal fulleride composition and is equal to the absolute by the direct redox reaction of metallic Lithium with C60 value of the valence of the metal, wherein A is a metal fullerene in a liquid medium, such as liquid ammonia. cation and n is a number that renders the composition [0069] According to the invention, the present proc- 30 neutral in charge. In particular, in the case a C60 fuller- ess comprises the step of separating the liquid medium ene is used, n is from +1 to +3 depending on the nega- from the resulting mixture of the ion exchange reaction. tive charge of the C60 fullerene which ranges from -1 to [0070] Preferably said separation is carried out by -3. evaporation. Therefore, the resulting product of said [0055] As mentioned above, the ion exchange reac- process substantially consists in a mixture of the desired tion of the present process occurs in a liquid medium 35 metal fulleride with the obtained salt which is substan- between a first metal fulleride, having as counterion a tially insoluble in the liquid medium. cation of a first metal, and a salt of a second metal, said [0071] According to a further embodiment of the in- salt being soluble in said liquid medium. vention, the present process comprises the step of sep- [0056] Preferably said liquid medium is selected from: arating the obtained salt from the resulting mixture of liquid ammonia, trimethylamine, triethylamine. More 40 the ion exchange reaction. preferably said liquid medium is liquid ammonia. [0072] Preferably said separation of the obtained salt [0057] Preferably said salt is a iodide. is carried out by filtering. [0058] According to the invention, the counterion of [0073] According to said further embodiment, succes- said first metal fulleride is selected so as to form a salt sively to said separating step of the obtained salt, the which is substantially insoluble in said liquid medium. 45 present process comprises the step of separating the [0059] In the present description and in the claims, the liquid medium from the metal fulleride. wording "a salt substantially insoluble in a liquid medi- [0074] Preferably said separation is carried by evap- um" means a salt having a solubility in said liquid medi- oration. um equal to or lower than 0.1 mol/l at the reaction tem- [0075] Some illustrative and non-limitative examples pertaure. 50 will now be given to describe the invention in further de- [0060] With the term "reaction temperature" is intend- tail. ed the temperature at which the reaction medium is in the liquid state. For instance, in the case liquid ammonia is used, said reaction temperature is selected from -50°C and -30°C. 55 [0061] Therefore, said first metal, forming said salt substantially insoluble in said liquid medium, is preferably selected from the group comprising alkali and alkali-

5 9 EP 1 199 281 A1 10

EXAMPLE 1 GdC60 metal fulleride was produced according to the following ion exchange reaction: Synthesis of GdC60

5 Li3C60 + GdI3 → GdC60 + 3 LiI ↓ (2) a) Synthesis of Li3C60

[0076] 0.072 g of C60 fullerene (purity 99.9% - pro- [0079] At the end of the stirring operation the temper- duced by Southern Chemicals Ltd.) were mixed with ature of the methanol bath was increased up to -30°C 0.0147 g of Lithium azide (LiN3) (purity 95%) inside of and the liquid ammonia slowly evaporated. After ammo- 10 a glove-box under Argon atmosphere (Oxygen concen- nia evaporation, the GdC60 / LiI mixture was heated, un- tration lower than 1.0 ppm, water vapour concentration der dynamic vacuum of about 10-3 Torr, from -30°Cto lower than 1.0 ppm). Inside of the glove-box the C60 room temperature and kept at this temperature for about fullerene / Lithium azide mixture was mechanically 30 minutes, and successively heated, under high vacu- crushed into a fine powder and introduced into a quartz um of about 10-3 Torr, up to 110°C. In order to remove test tube. A dynamic pressure of 10-6 Torr was reached 15 any possible ammonia trace still present inside of the into said test tube and a temperature growth from 20°C obtained mixture, the latter was maintained at 110°C for up to 120°Cata30°C/hr heating rate and, successively, about 15 hr. from 120°Cupto180°Cata5°C/hr heating rate was [0080] The obtained GdC60 / LiI mixture was succes- set up. Under such pressure and temperature condi- sively introduced into the glove-box and crushed into a tions the starting Lithium azide was subjected to thermal 20 fine powder. Some of it was sealed into a pyrex test tube, decomposition and a first metal fulleride, i.e. Li3C60, was under a Helium atmosphere, and some into 0.5 mm di- obtained in accordance with the following reaction: ameter quartz capillaries to carry out, respectively, NMR and X-Ray/ESR characterizations. [0081] NMR spectrum of the GdC / LiI mixture was C + 3 LiN → Li C + 9/2 N ↑ (1) 60 60 3 3 60 2 25 performed by using a Stelar Spinmaster solid state NMR spectrometer working on 13C isotope at a frequency of [0077] All the procedures concerning Li3C60 prepara- about 50 MHz. The broad signal (about 10 kHz) of the tion and handling are carried out in the glove box under NMR spectrum having a fast relaxation time (t1 = Argon atmosphere as described above. 0.46±0.02 s), if compared to that of a C60 fullerene, was 30 -3 typical of C60 fullerides (i.e., of metal fullerides having b) Synthesis of GdC60 a negative charge of -3 on the cage). Broad signal and fast relaxation time confirmed the complete charge [0078] The Li3C60 amount resulting from reaction (1) transfer from Gd to C60 fullerene and, therefore, the pro- (i.e., 0.074 g) was mixed with an amount of 0.0538 g of duction of the desired metal fulleride GdC60. 35 anhydrous Gadolinium iodide (GdI3) (purity 99.9% - pro- [0082] X-Ray diffraction measurements have been duced by Sigma Aldrich) inside of a glove-box under Ar- carried out on a diffractometer Siemens (Model D 500). gon atmosphere as described in step a). Inside of the The diffraction spectrum clearly showed the presence glove-box the Li3C60 / GdI3 mixture was mechanically of the peaks corresponding to the obtained LiI crystals crushed into a fine powder and introduced into a quartz as resulting products of the above mentioned ion ex- test tube inside of which a reduced pressure value of 40 change reaction (2). -3 about 10 Torr was established. A suitable amount of [0083] ESR spectra of the GdC60 / LiI mixture were ammonia in the gaseous state (purity 99.99% - pro- obtained by using a Bruker spectrometer (Model ER 200 duced by Sigma Aldrich) was made to enter into the test D) at a temperature of about 90 K. The spectrum of the tube by connecting it with an ammonia reservoir. Suc- starting GdI3 was characterized by a very broad signal 45 cessively, the test tube was cooled to a temperature of with peak to peak linewidth of about ∆Hpp = 3101 Gauss about -55°C by introducing it into a methanol bath and a g-value of about 2.3199. The spectra of the ob- cooled by a Neslab Model CC-100 freezing finger and tained GdC60 / LiI mixture were characterized by a nar- the temperature was controlled by a Eurotherm 2408 row signal with peak to peak linewidth of about ∆Hpp = Model. Under said pressure and temperature conditions 5.4 Gauss and a g-value of about 2.0047, said values 50 -3 the anhydrous ammonia entering the test tube began to being characteristic of C60 fullerides. Furthermore, condense. When an amount of about 7 ml of liquid am- said spectra demonstrated the complete absence of the monia was present inside the test tube, its condensation starting GdI3 and, therefore, the complete occurred was stopped by heating the reaction mixture (i.e., charge transfer from Gd to C60 fullerene. Li3C60, GdI3 and liquid ammonia) from -55°Cupto -40°C. The reaction mixture was maintained at -40°C 55 for about 40 minutes under intensive stirring by means of a Teflon covered magnetic stirring bar. Therefore,

6 11 EP 1 199 281 A1 12

EXAMPLE 2 arating said liquid medium from the resulting mixture. Synthesis of K3C60 3. Process according to claim 2, characterized in 5 a) Synthesis of Li3C60 that said liquid medium is separated by evaporation. [0084] Said first step was carried out as previously described in Example 1. 4. Process according to claim 1, characterized in that said process further comprises the step of sep- 10 b) Synthesis of K3C60 arating from the resulting mixture said salt substantially insoluble in said liquid medium. [0085] The Li3C60 amount resulting from reaction (1) (i.e., 0.074 g), was mixed with 0.0498 g of anhydrous 5. Process according to claim 4, characterized in Potassium iodide (KI) (purity 99.998% - produced by that said salt substantially insoluble in said liquid Sigma Aldrich) inside a glove-box under the same con- 15 medium is separated by filtering. ditions and according to the same operating procedure of Example 1. Therefore, K3C60 metal fulleride was pro- 6. Process according to claim 4, characterized in duced according to the following ion exchange reaction: that said process comprises the step of separating said liquid medium from said second metal fulleride. 20 Li C + 3 KI → K C + 3 LiI ↓ (3) 3 60 3 60 7. Process according to claim 6, characterized in that said liquid medium is separated by evapora-

[0086] The obtained K3C60 / LiI mixture, resulting form tion. reaction (3), was subjected to magnetic susceptibility measurements in order to reveal the presence of a su- 25 8. Process according to anyone of the preceding perconducting transition temperature. The temperature claims, characterized in that said liquid medium is dependence of the magnetization of the obtained mix- selected from: ture revealed a jump at 18 K showing the presence of a superconducting phase having a transition temperature liquid ammonia, trimethylamine, triethylamine, 30 (Tc) equal to 18 K, a value typical of a superconductive or mixture thereof. K3C60 material. A magnetometer (Quantum Design SQUID magnetometer equipped with a superconduct- 9. Process according to anyone of the preceding ing 1 T magnet) was used to perform magnetic suscep- claims, characterized in that said first metal is se- tibility measurements in the range from liquid helium lected from the group comprising alkali and alkali- (the mixture was introduced into a test tube under Heli- 35 earth metals. um atmosphere) to room temperature. [0087] Said measurements demonstrated the pres- 10. Process according to claim 9, characterized in ence of a large (more than 90%) superconducting frac- that said first metal is selected from the group com- tion corresponding to the production of K3C60. prising: Lithium, Sodium and Calcium. 40 11. Process according to anyone of the preceding Claims claims, characterized in that said second metal is selected from the group comprising: transition ele- 1. Process for producing a metal fulleride, comprising ments, Lanthanides and Actinides. the step of reacting in a liquid medium: 45 12. Process according to claim 11, characterized in • a first metal fulleride having, as counterion, a that said second metal is selected from the group cation of a first metal forming a salt substantial- comprising: Potassium, Rubidium and Gadolinium. ly insoluble in said liquid medium, and • a salt of a second metal substantially soluble in 50 said liquid medium,

so as to form a second metal fulleride having, as counterion, a cation of said second metal. 55 2. Process according to claim 1, characterized in that said process further comprises the step of sep-

7 EP 1 199 281 A1

8 EP 1 199 281 A1