Process for Producing a Metal Fulleride
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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.