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 | |||
| Names | |||
|---|---|---|---|
| Pronunciation | /ˌbʌkmɪnstərˈfʊləriːn/ | ||
| Preferred IUPAC name (C60-Ih)[5,6]fullerene[1] | |||
| Other names Buckyballs; Fullerene-C60; [60]fullerene | |||
| Identifiers | |||
3D model (JSmol) | |||
| 5901022 | |||
| ChEBI | |||
| ChemSpider |
| ||
| ECHA InfoCard | 100.156.884 | ||
| UNII | |||
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| Properties | |||
| C60 | |||
| Molar mass | 720.660 g·mol−1 | ||
| Appearance | Dark needle-like crystals | ||
| Density | 1.65 g/cm3 | ||
| insoluble in water | |||
| Vapor pressure | 0.4–0.5 Pa (T ≈ 800 K); 14 Pa (T ≈ 900 K)[2] | ||
| Structure | |||
| Face-centered cubic,cF1924 | |||
| Fm3m, No. 225 | |||
a = 1.4154 nm | |||
| Hazards | |||
| GHS labelling: | |||
 | |||
| Warning | |||
| H315,H319,H335 | |||
| P261,P264,P271,P280,P302+P352,P304+P340,P305+P351+P338,P312,P321,P332+P313,P337+P313,P362,P403+P233,P405,P501 | |||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
| Part of a series of articles on |
| Nanomaterials |
|---|
 |
| Carbon nanotubes |
| Fullerenes |
| Othernanoparticles |
| Nanostructured materials |
Buckminsterfullerene is a type offullerene with the formulaC
60. It has a cage-like fused-ring structure (truncated icosahedron) made of twentyhexagons and twelvepentagons, and resembles afootball. Each of its 60carbon atoms isbonded to its three neighbors.
Buckminsterfullerene is a black solid that dissolves inhydrocarbonsolvents to produce a purple solution. The substance was discovered in 1985 and has received intense study, although few real world applications have been found.
Molecules of buckminsterfullerene (or of fullerenes in general) are commonly nicknamedbuckyballs.[3][4]
Buckminsterfullerene is the most common naturally occurring fullerene. Small quantities of it can be found insoot.[5][6]
It alsoexists in space. NeutralC
60 has been observed inplanetary nebulae[7] and several types ofstar.[8] The ionised form,C+
60, has been identified in theinterstellar medium,[9] where it is the cause of several absorption features known asdiffuse interstellar bands in the near-infrared.[10]
Theoretical predictions of buckminsterfullerene molecules appeared in the late 1960s and early 1970s.[11][12][13][14] It was first generated in 1984 by Eric Rohlfing, Donald Cox, and Andrew Kaldor,[14][15] using a laser to vaporize carbon in a supersonichelium beam, although the group did not realize that buckminsterfullerene had been produced. In 1985 their work was repeated byHarold Kroto,James R. Heath,Sean C. O'Brien,Robert Curl, andRichard Smalley atRice University, who recognized the structure ofC
60 as buckminsterfullerene.[16]
Concurrent but unconnected to the Kroto-Smalley work, astrophysicists were working with spectroscopists to study infrared emissions from giant red carbon stars.[17][18][19] Smalley and team were able to use a laser vaporization technique to create carbon clusters which could potentially emit infrared at the same wavelength as had been emitted by the red carbon star.[17][20] Hence, the inspiration came to Smalley and team to use the laser technique on graphite to generate fullerenes.
Usinglaserevaporation ofgraphite the Smalley team found Cn clusters (wheren > 20 and even) of which the most common wereC
60 andC
70. A solid rotating graphite disk was used as the surface from which carbon was vaporized using a laser beam creating hot plasma that was then passed through a stream of high-density helium gas.[16] The carbonspecies were subsequently cooled and ionized resulting in the formation of clusters. Clusters ranged in molecular masses, but Kroto and Smalley found predominance in aC
60 cluster that could be enhanced further by allowing the plasma to react longer. They also discovered thatC
60 is a cage-like molecule, a regulartruncated icosahedron.[17][16]
The experimental evidence, a strong peak at 720daltons, indicated that a carbon molecule with 60 carbon atoms was forming, but provided no structural information. The research group concluded after reactivity experiments, that the most likely structure was a spheroidal molecule. The idea was quickly rationalized as the basis of anicosahedralsymmetry closed cage structure.[11]
Kroto, Curl, and Smalley were awarded the 1996Nobel Prize in Chemistry for their roles in the discovery of buckminsterfullerene and the related class of molecules, thefullerenes.[11]
In 1989 physicistsWolfgang Krätschmer,Konstantinos Fostiropoulos, andDonald R. Huffman observed unusual optical absorptions in thin films of carbon dust (soot). The soot had been generated by an arc-process between two graphiteelectrodes in a helium atmosphere where the electrode material evaporates and condenses forming soot in the quenching atmosphere. Among other features, theIR spectra of the soot showed four discrete bands in close agreement to those proposed forC
60.[21][22]
Another paper on the characterization and verification of the molecular structure followed on in the same year (1990) from their thin film experiments, and detailed also the extraction of an evaporable as well asbenzene-soluble material from the arc-generated soot. This extract hadTEM andX-ray crystal analysis consistent with arrays of sphericalC
60 molecules, approximately 1.0 nm invan der Waals diameter[23] as well as the expected molecular mass of 720 Da forC
60 (and 840 Da forC
70) in theirmass spectra.[24] The method was simple and efficient to prepare the material in gram amounts per day (1990) which has boosted the fullerene research and is even today applied for the commercial production of fullerenes.
The discovery of practical routes toC
60 led to the exploration of a new field of chemistry involving the study of fullerenes.
The discoverers of theallotrope named the newfound molecule after American architectR. Buckminster Fuller, who designed manygeodesic dome structures that look similar toC
60 and who had died in 1983, the year before discovery.[11] Another common name for buckminsterfullerene is "buckyballs".[25][4]
Soot is produced by laser ablation of graphite orpyrolysis ofaromatic hydrocarbons. Fullerenes are extracted from the soot with organic solvents using aSoxhlet extractor.[26] This step yields a solution containing up to 75% ofC
60, as well as other fullerenes. These fractions are separated usingchromatography.[27] Generally, the fullerenes are dissolved in a hydrocarbon or halogenated hydrocarbon and separated using alumina columns.[28]
Synthesis using the techniques of "classicalorganic chemistry" is possible, but not economic.[29]
Buckminsterfullerene is atruncated icosahedron with 60vertices, 32 faces (20 hexagons and 12 pentagons where no pentagons share a vertex), and 90 edges (60 edges between 5-membered & 6-membered rings and 30 edges are shared between 6-membered & 6-membered rings), with a carbon atom at the vertices of each polygon and a bond along each polygon edge. Thevan der Waals diameter of aC
60 molecule is about 1.01 nanometers (nm). The nucleus to nucleus diameter of aC
60 molecule is about 0.71 nm. TheC
60 molecule has two bond lengths. The 6:6 ring bonds (between two hexagons) can be considered "double bonds" and are shorter than the 6:5 bonds (between a hexagon and a pentagon). Its average bond length is 0.14 nm. Each carbon atom in the structure is bonded covalently with 3 others.[30] A carbon atom in theC
60 can be substituted by anitrogen orboron atom yielding aC
59N orC
59B respectively.[31]
| Centered by | Vertex | Edge 5–6 | Edge 6–6 | Face Hexagon | Face Pentagon |
|---|---|---|---|---|---|
| Image |  |  |  |  |  |
| Projective symmetry | [2] | [2] | [2] | [6] | [10] |
For a time buckminsterfullerene was the largest[quantify] known molecule observed to exhibitwave–particle duality.[32] In 2020 the dye moleculephthalocyanine exhibited the duality that is more famously attributed to light, electrons and other small particles and molecules.[33]
| Solvent | Solubility (g/L) |
|---|---|
| 1-chloronaphthalene | 51 |
| 1-methylnaphthalene | 33 |
| 1,2-dichlorobenzene | 24 |
| 1,2,4-trimethylbenzene | 18 |
| tetrahydronaphthalene | 16 |
| carbon disulfide | 8 |
| 1,2,3-tribromopropane | 8 |
| xylene | 5 |
| bromoform | 5 |
| cumene | 4 |
| toluene | 3 |
| benzene | 1.5 |
| carbon tetrachloride | 0.447 |
| chloroform | 0.25 |
| hexane | 0.046 |
| cyclohexane | 0.035 |
| tetrahydrofuran | 0.006 |
| acetonitrile | 0.004 |
| methanol | 0.00004 |
| water | 1.3 × 10−11 |
| pentane | 0.004 |
| octane | 0.025 |
| isooctane | 0.026 |
| decane | 0.070 |
| dodecane | 0.091 |
| tetradecane | 0.126 |
| dioxane | 0.0041 |
| mesitylene | 0.997 |
| dichloromethane | 0.254 |
Fullerenes are sparingly soluble in aromaticsolvents andcarbon disulfide, but insoluble in water. Solutions of pureC
60 have a deep purple color which leaves a brown residue upon evaporation. The reason for this color change is the relatively narrow energy width of the band of molecular levels responsible for green light absorption by individualC
60 molecules. Thus individual molecules transmit some blue and red light resulting in a purple color. Upon drying, intermolecular interaction results in the overlap and broadening of the energy bands, thereby eliminating the blue light transmittance and causing the purple to brown color change.[17]
C
60 crystallises with some solvents in the lattice ("solvates"). For example, crystallization ofC
60 frombenzene solution yields triclinic crystals with the formulaC60·4C6H6. Like other solvates, this one readily releases benzene to give the usual face-centred cubicC
60. Millimeter-sized crystals ofC
60 andC
70 can be grown from solution both for solvates and for pure fullerenes.[37][38]
In solid buckminsterfullerene, theC
60 molecules adopt the fcc (face-centered cubic) motif. They start rotating at about −20 °C. This change is associated with a first-order phase transition to an fcc structure and a small, yet abrupt increase in the lattice constant from 1.411 to 1.4154 nm.[39]
C
60 solid is as soft asgraphite, but when compressed to less than 70% of its volume it transforms into asuperhard form ofdiamond (seeaggregated diamond nanorod).C
60 films and solution have strong non-linear optical properties; in particular, their optical absorption increases with light intensity (saturable absorption).
C
60 forms a brownish solid with an optical absorption threshold at ≈1.6 eV.[40] It is an n-typesemiconductor with a low activation energy of 0.1–0.3 eV; this conductivity is attributed to intrinsic or oxygen-related defects.[41] FccC
60 contains voids at its octahedral and tetrahedral sites which are sufficiently large (0.6 and 0.2 nm respectively) to accommodate impurity atoms. When alkali metals aredoped into these voids,C
60 converts from a semiconductor into a conductor or even superconductor.[39][42]
C
60 undergoes six reversible, one-electron reductions, ultimately generatingC6−
60. Itsoxidation is irreversible. The first reduction occurs at ≈−1.0 V (Fc/Fc+
), showing thatC
60 is a reluctant electron acceptor.C
60 tends to avoid having double bonds in the pentagonal rings, which makes electrondelocalization poor, and results inC
60 not being "superaromatic".C
60 behaves like an electron deficientalkene. For example, it reacts with some nucleophiles.[23][43]
C
60 exhibits a small degree of aromatic character, but it still reflects localized double and single C–C bond characters. Therefore,C
60 can undergo addition with hydrogen to give polyhydrofullerenes.C
60 also undergoesBirch reduction. For example,C
60 reacts with lithium in liquid ammonia, followed bytert-butanol to give a mixture of polyhydrofullerenes such asC60H18,C60H32,C60H36, withC60H32 being the dominating product. This mixture of polyhydrofullerenes can be re-oxidized by2,3-dichloro-5,6-dicyano-1,4-benzoquinone to giveC
60 again.
A selective hydrogenation method exists. Reaction ofC
60 with 9,9′,10,10′-dihydroanthracene under the same conditions, depending on the time of reaction, givesC60H32 andC60H18 respectively and selectively.[44]
Addition offluorine,chlorine, andbromine occurs forC
60. Fluorine atoms are small enough for a 1,2-addition, whileCl
2 andBr
2 add to remote C atoms due tosteric factors. For example, inC60Br8 andC60Br24, the Br atoms are in 1,3- or 1,4-positions with respect to each other. Under various conditions a vast number of halogenated derivatives ofC
60 can be produced, some with an extraordinary selectivity on one or two isomers over the other possible ones. Addition of fluorine and chlorine usually results in a flattening of theC
60 framework into a drum-shaped molecule.[44]
Solutions ofC
60 can be oxygenated to theepoxideC60O. Ozonation ofC
60 in 1,2-xylene at 257K gives an intermediate ozonideC60O3, which can be decomposed into 2 forms ofC60O. Decomposition ofC60O3 at 296 K gives the epoxide, but photolysis gives a product in which the O atom bridges a 5,6-edge.[44]
TheDiels–Alder reaction is commonly employed to functionalizeC
60. Reaction ofC
60 with appropriate substituted diene gives the corresponding adduct.
The Diels–Alder reaction betweenC
60 and 3,6-diaryl-1,2,4,5-tetrazines affordsC
62. TheC
62 has the structure in which a four-membered ring is surrounded by four six-membered rings.
TheC
60 molecules can also be coupled through a [2+2]cycloaddition, giving the dumbbell-shaped compoundC
120. The coupling is achieved by high-speed vibrating milling ofC
60 with a catalytic amount ofKCN. The reaction is reversible asC
120 dissociates back to twoC
60 molecules when heated at 450 K (177 °C; 350 °F). Under high pressure and temperature, repeated [2+2] cycloaddition betweenC
60 results in polymerized fullerene chains and networks. These polymers remain stable at ambient pressure and temperature once formed, and have remarkably interesting electronic and magnetic properties, such as beingferromagnetic above room temperature.[44]
Reactions ofC
60 withfree radicals readily occur. WhenC
60 is mixed with a disulfide RSSR, the radicalC60SR• forms spontaneously upon irradiation of the mixture.
Stability of the radical speciesC60Y• depends largely onsteric factors of Y. Whentert-butyl halide is photolyzed and allowed to react withC
60, a reversible inter-cage C–C bond is formed:[44]
Cyclopropanation (theBingel reaction) is another common method for functionalizingC
60. Cyclopropanation ofC
60 mostly occurs at the junction of 2 hexagons due to steric factors.
The first cyclopropanation was carried out by treating the β-bromomalonate withC
60 in the presence of a base. Cyclopropanation also occur readily withdiazomethanes. For example, diphenyldiazomethane reacts readily withC
60 to give the compoundC61Ph2.[44]Phenyl-C
61-butyric acid methyl ester derivative prepared through cyclopropanation has been studied for use inorganic solar cells.
TheLUMO inC
60 is triply degenerate, with theHOMO–LUMO separation relatively small. This small gap suggests that reduction ofC
60 should occur at mild potentials leading to fulleride anions,[C60]n− (n = 1–6). The midpoint potentials of 1-electron reduction of buckminsterfullerene and its anions is given in the table below:
| Reduction potential ofC 60 at 213 K | |
|---|---|
| Half-reaction | E° (V) |
| C60 + e− ⇌ C−60 | −0.169 |
| C−60 + e− ⇌ C2−60 | −0.599 |
| C2−60 + e− ⇌ C3−60 | −1.129 |
| C3−60 + e− ⇌ C4−60 | −1.579 |
| C4−60 + e− ⇌ C5−60 | −2.069 |
| C5−60 + e− ⇌ C6−60 | −2.479 |
C
60 forms a variety ofcharge-transfer complexes, for example withtetrakis(dimethylamino)ethylene:
This salt exhibitsferromagnetism at 16 K.
C
60 oxidizes with difficulty. Three reversible oxidation processes have been observed by usingcyclic voltammetry with ultra-drymethylene chloride and a supporting electrolyte with extremely high oxidation resistance and low nucleophilicity, such as[nBu4N] [AsF6].[43]
| Reduction potentials ofC 60 oxidation at low temperatures | |
|---|---|
| Half-reaction | E° (V) |
| C60 ⇌ C+60 | +1.27 |
| C+60 ⇌ C2+60 | +1.71 |
| C2+60 ⇌ C3+60 | +2.14 |
C
60 forms complexes akin to the more common alkenes. Complexes have been reportedmolybdenum,tungsten,platinum,palladium,iridium, andtitanium. The pentacarbonyl species are produced byphotochemical reactions.
In the case of platinum complex, the labile ethylene ligand is the leaving group in a thermal reaction:
Titanocene complexes have also been reported:
Coordinatively unsaturated precursors, such asVaska's complex, foradducts withC
60:
One such iridium complex,[Ir(η2-C60)(CO)Cl(Ph2CH2C6H4OCH2Ph)2] has been prepared where the metal center projects two electron-rich 'arms' that embrace theC
60 guest.[45]
Metal atoms or certain small molecules such asH
2 and noble gas can be encapsulated inside theC
60 cage. These endohedral fullerenes are usually synthesized by doping in the metal atoms in an arc reactor or by laser evaporation. These methods gives low yields of endohedral fullerenes, and a better method involves the opening of the cage, packing in the atoms or molecules, and closing the opening using certainorganic reactions. This method, however, is still immature and only a few species have been synthesized this way.[46]
Endohedral fullerenes show distinct and intriguing chemical properties that can be completely different from the encapsulated atom or molecule, as well as the fullerene itself. The encapsulated atoms have been shown to perform circular motions inside theC
60 cage, and their motion has been followed usingNMR spectroscopy.[45]
The optical absorption properties ofC
60 match the solar spectrum in a way that suggests thatC
60-based films could be useful for photovoltaic applications. Because of its highelectronic affinity[47] it is one of the most commonelectron acceptors used in donor/acceptor based solar cells. Conversion efficiencies up to 5.7% have been reported inC
60–polymer cells.[48]
C
60 is sensitive to light,[49] so leavingC
60 under light exposure causes it to degrade, becoming dangerous. The ingestion ofC
60 solutions that have been exposed to light could lead to developing cancer (tumors).[50][51] So the management ofC
60 products for human ingestion requires cautionary measures[51] such as: elaboration in very dark environments, encasing into bottles of great opacity, and storing in dark places, and others like consumption under low light conditions and using labels to warn about the problems with light.
Solutions ofC
60 dissolved in olive oil or water, as long as they are preserved from light, have been found nontoxic to rodents.[52]
Otherwise, a study found thatC
60 remains in the body for a longer time than usual, especially in the liver, where it tends to be accumulated, and therefore has the potential to induce detrimental health effects.[53]
An experiment in 2011–2012 administered a solution ofC
60 in olive oil to rats, achieving a 90% prolongation of their lifespan.[52]C
60 in olive oil administered to mice resulted in no extension in lifespan.[54]C
60 in olive oil administered tobeagle dogs resulted in a large reduction ofC-reactive protein, which is commonly elevated incardiovascular disease andcerebrovascular disease.[55]
Many oils withC
60 have been sold as antioxidant products, but it does not avoid the problem of their sensitivity to light, that can turn them toxic. A later research confirmed that exposure to light degrades solutions ofC
60 in oil, making it toxic and leading to a "massive" increase of the risk of developing cancer (tumors) after its consumption.[50][51]
To avoid the degradation by effect of light,C
60 oils must be made in very dark environments, encased into bottles of great opacity, and kept in darkness, consumed under low light conditions and accompanied by labels to warn about the dangers of light forC
60.[51][49]
Some producers have been able to dissolveC
60 in water to avoid possible problems with oils, but that would not protectC
60 from light, so the same cautions are needed.[49]
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