Fullerene melting point. Fullerene - what is it? Properties and applications of fullerenes

Discovery of fullerenes - new form the existence of one of the most common elements on Earth - carbon, is recognized as one of the amazing and major discoveries in science of the 20th century. Despite the long-known unique ability of carbon atoms to bind into complex, often branched and bulky molecular structures, which form the basis of all organic chemistry, the actual possibility of the formation of stable framework molecules from only one carbon still turned out to be unexpected. Experimental confirmation that molecules of this type, consisting of 60 or more atoms, can arise in the course of naturally occurring processes in nature occurred in 1985. And long before that, some authors assumed the stability of molecules with a closed carbon sphere. However, these assumptions were purely speculative, purely theoretical. It was rather difficult to imagine that such compounds could be obtained by chemical synthesis. Therefore, these works remained unnoticed, and attention was paid to them only in hindsight, after the experimental discovery of fullerenes. New stage came in 1990, when a method was found for obtaining new compounds in gram quantities, and a method for isolating fullerenes in pure form was described. Very soon after that, the most important structural and physical and chemical characteristics fullerene C 60 - the most easily formed compound among the known fullerenes. For their discovery - the discovery of carbon clusters of composition C 60 and C 70 - R. Kerl, R. Smalley and G. Kroto in 1996 were awarded the Nobel Prize in Chemistry. They also proposed the structure of fullerene C 60 , known to all football fans.

As you know, the shell of a soccer ball is made up of 12 pentagons and 20 hexagons. Theoretically, 12,500 arrangements of double and single bonds are possible. The most stable isomer (shown in the figure) has a truncated icosahedral structure that lacks double bonds in the pentagons. This isomer of C 60 was named "Buckminsterfullerene" in honor of the famous architect named R. Buckminster Fuller, who created structures, the domed frame of which is constructed from pentagons and hexagons. Soon a structure for the C 70 was proposed, resembling a rugby ball (with an elongated shape).

In the carbon framework, the C atoms are characterized by sp 2 hybridization, with each carbon atom bonded to three neighboring atoms. Valency 4 is realized through p-bonds between each carbon atom and one of its neighbors. Naturally, it is assumed that p-bonds can be delocalized, as in aromatic compounds. Such structures can be built for n≥20 for any even clusters. They must contain 12 pentagons and (n-20)/2 hexes. The lowest of the theoretically possible C 20 fullerenes is nothing more than a dodecahedron - one of five regular polyhedra, which has 12 pentagonal faces and no hexagonal faces at all. A molecule of such a shape would have an extremely strained structure, and therefore its existence is energetically unfavorable.

Thus, in terms of stability, fullerenes can be divided into two types. The border between them allows you to draw the so-called. the rule of isolated pentagons (Isolated Pentagon Rule, IPR). This rule states that the most stable fullerenes are those in which no pair of pentagons has adjacent edges. In other words, the pentagons do not touch each other, and each pentagon is surrounded by five hexes. If fullerenes are arranged in order of increasing number of carbon atoms n, then Buckminsterfullerene - C 60 is the first representative that satisfies the rule of isolated pentagons, and C 70 is the second. Among fullerene molecules with n>70 there is always an isomer subject to IPR, and the number of such isomers increases rapidly with the number of atoms. Found 5 isomers for C 78 , 24 - for C 84 and 40 - for C 90 . Isomers that have adjacent pentagons in their structure are significantly less stable.

Chemistry of fullerenes

At present, the majority scientific research associated with the chemistry of fullerenes. More than 3 thousand new compounds have already been synthesized based on fullerenes. Such a rapid development of the chemistry of fullerenes is associated with the structural features of this molecule and the presence of a large number of double conjugated bonds on a closed carbon sphere. The combination of fullerene with representatives of many known classes of substances has opened up the possibility for synthetic chemists to obtain numerous derivatives of this compound.

Unlike benzene, where the lengths C-C ties are the same, bonds of a more "double" and more "single" nature can be distinguished in fullerenes, and chemists often consider fullerenes as electron-deficient polyene systems, and not as aromatic molecules. If we turn to С60, then there are two types of bonds in it: shorter (1.39 Å) bonds running along the common edges of adjacent hexagonal faces, and longer (1.45 Å) bonds located along the common edges of pentagonal and hexagonal faces. At the same time, neither six-membered nor, even more so, five-membered rings exhibit aromatic properties in the sense in which they are exhibited by benzene or other planar conjugated molecules obeying Hückel's rule. Therefore, usually shorter bonds in C 60 are considered double, while longer ones are single. One of key features fullerenes is that they have an unusually large number of equivalent reaction centers, which often leads to a complex isomeric composition of the reaction products with their participation. As a result, most chemical reactions with fullerenes are not selective, and the synthesis of individual compounds is very difficult.

Among the reactions for obtaining inorganic fullerene derivatives, the most important are the processes of halogenation and the production of the simplest halogen derivatives, as well as hydrogenation reactions. Thus, these reactions were among the first ones carried out with fullerene C 60 in 1991. Let us consider the main types of reactions leading to the formation of these compounds.

Immediately after the discovery of fullerenes, the possibility of their hydrogenation with the formation of "fulleranes" aroused great interest. Initially, it seemed possible to add sixty hydrogen atoms to the fullerene. Subsequently, in theoretical studies, it was shown that in the C 60 H 60 molecule, part of the hydrogen atoms should be inside the fullerene sphere, since six-membered rings, like cyclohexane molecules, should take the “chair” or “bath” conformations. Therefore, currently known polyhydrofullerene molecules contain from 2 to 36 hydrogen atoms for fullerene C 60 and from 2 to 8 for fullerene C 70 .

During the fluorination of fullerenes, full set compounds C 60 F n , where n takes even values ​​up to 60. Fluorine derivatives with n from 50 to 60 are called perfluorides and are found among the products of fluorination mass spectrally in extremely low concentrations. There are also hyperfluorides, that is, products of the composition C 60 F n , n>60, where the fullerene carbon cage is partially destroyed. It is assumed that this also takes place in perfluorides. The issues of the synthesis of fullerene fluorides of various compositions are an independent most interesting problem, the study of which is most actively studied in Faculty of Chemistry Moscow State University M.V. Lomonosov.

Active study of the processes of chlorination of fullerenes under various conditions began already in 1991. In the first works, the authors tried to obtain C 60 chlorides by reacting chlorine and fullerene in various solvents. To date, several individual fullerene chlorides C 60 and C 70 obtained by using various chlorinating agents have been isolated and characterized.

The first attempts to brominate fullerene were made already in 1991. Fullerene C 60 , placed in pure bromine at a temperature of 20 and 50 o C, increased the mass by a value corresponding to the addition of 2-4 bromine atoms per fullerene molecule. Further studies of bromination showed that the interaction of C 60 fullerene with molecular bromine for several days produces a bright orange substance, the composition of which, as determined by elemental analysis, was C 60 Br 28 . Subsequently, several bromo derivatives of fullerenes were synthesized, which differ in a wide range of values ​​for the number of bromine atoms in a molecule. Many of them are characterized by the formation of clathrates with the inclusion of free bromine molecules.

The interest in perfluoroalkyl derivatives, in particular trifluoromethylated derivatives of fullerenes, is associated primarily with the expected kinetic stability of these compounds in comparison with halogen derivatives of fullerenes prone to nucleophilic S N 2'-substitution reactions. In addition, perfluoroalkylfullerenes may be of interest as compounds with a high electron affinity due to acceptor properties of perfluoroalkyl groups that are even stronger than those of fluorine atoms. To date, the number of isolated and characterized individual compounds of the composition C 60/70 (CF 3) n, n=2-20 exceeds 30, and intensive work is underway to modify the fullerene sphere by many other fluorine-containing groups - CF 2 , C 2 F 5 , C 3 F 7 .

The creation of biologically active fullerene derivatives, which could find application in biology and medicine, is associated with imparting hydrophilic properties to the fullerene molecule. One of the methods for the synthesis of hydrophilic fullerene derivatives is the introduction of hydroxyl groups and the formation of fullerenols or fullerols containing up to 26 OH groups, and also, probably, oxygen bridges similar to those observed in the case of oxides. Such compounds are highly soluble in water and can be used for the synthesis of new fullerene derivatives.

As for fullerene oxides, the compounds C 60 O and C 70 O are always present in the initial mixtures of fullerenes in the extract in small amounts. Probably, oxygen is present in the chamber during the electric arc discharge and some of the fullerenes are oxidized. Fullerene oxides are well separated on columns with various adsorbents, which makes it possible to control the purity of fullerene samples and the absence or presence of oxides in them. However, the low stability of fullerene oxides hinders their systematic study.

What can be noted about the organic chemistry of fullerenes is that, being an electron-deficient polyene, C 60 fullerene exhibits a tendency to radical, nucleophilic, and cycloaddition reactions. Particularly promising in terms of the functionalization of the fullerene sphere are various cycloaddition reactions. Due to its electronic nature, C 60 is able to take part in α-cycloaddition reactions, and the most characteristic are cases when n = 1, 2, 3 and 4.

The main problem solved by synthetic chemists working in the field of the synthesis of fullerene derivatives remains the selectivity of the reactions carried out to this day. Features of the stereochemistry of addition to fullerenes consist in a huge number of theoretically possible isomers. So, for example, the compound C 60 X 2 has 23 of them, C 60 X 4 already has 4368, among them 8 are addition products at two double bonds. The 29 C 60 X 4 isomers, however, will not have a chemical meaning, having a triplet ground state arising from the presence of an sp2-hybridized carbon atom surrounded by three sp3-hybridized atoms forming C-X bonds. The maximum number of theoretically possible isomers without taking into account the multiplicity of the ground state will be observed in the case of C 60 X 30 and will be 985538239868524 (1294362 of them are addition products at 15 double bonds), while the number of non-singlet isomers of the same nature as in the above example, does not lend itself to simple accounting, but from general considerations it should constantly increase with the growth of the number of affiliated groups. In any case, the number of theoretically admissible isomers in most cases is enormous, while going over to less symmetric C 70 and higher fullerenes, it additionally increases by several times or by orders of magnitude.

In fact, numerous data of quantum chemical calculations show that most of the reactions of halogenation and hydrogenation of fullerenes proceed with the formation, if not the most stable isomers, then at least slightly differing from them in energy. The greatest discrepancies are observed in the case of lower fullerene hydrides, whose isomeric composition, as shown above, can even slightly depend on the synthesis route. However, the stability of the resulting isomers still turns out to be extremely close. The study of these patterns of formation of fullerene derivatives is interesting task, the solution of which leads to new achievements in the field of chemistry of fullerenes and their derivatives.

Fullerenes exist everywhere in Nature, and especially where there is carbon and high energies. They exist near carbon stars, in interstellar space, in places where lightning strikes, near volcano craters, and are formed when gas is burned in a home gas stove or in the flame of an ordinary lighter.

Fullerenes are also found in places of accumulation of ancient carbon rocks. A special place belongs to the Karelian minerals - shungite. These rocks, containing up to 80% pure carbon, are about 2 billion years old. The nature of their origin is still not clear. One of the assumptions is the fall of a large carbon meteorite.

Fullerenes in Shungites Stone is a topic widely discussed in many printed publications and on web pages. There are many conflicting opinions on this matter, in connection with which both readers and users of shungite products have a lot of questions. Do shungites really contain the molecular form of carbon – fullerenes? Do the medicinal "Marcial waters" contain fullerenes? Is it possible to drink water infused with shungite, and what will be the benefit of it? Based on our experience of scientific research on the properties of various shungites, below we present our opinion on these and some other frequently asked questions.

Currently wide use received products manufactured using Karelian shungites. These are various filters for water treatment, pyramids, pendants, products that shield from electromagnetic radiation, pastes and simply shungite crushed stone and many other types of products offered as preventive, therapeutic and health-improving means. At the same time, as a rule, in recent years, the healing properties of various types of shungite are attributed to the fullerenes contained in them.

Shortly after the discovery of fullerenes in 1985, the active search them in nature. Fullerenes have been found in Karelian shungite, as reported in various scientific publications. In turn, we have developed alternative methodological approaches to isolate fullerenes from shungites and prove their presence. The studies analyzed samples taken in different regions of Zaonezhye, where shungite rocks occur. Before analysis, shungite samples were crushed to a microdisperse state.

Recall that shungites are an openwork silicate lattice, the voids of which are filled with shungite carbon, which in its structure is an intermediate product between amorphous carbon and graphite. Also in shungite carbon there are natural organic low and high molecular weight compounds (NONVS) of unknown chemical composition. Shungites differ in the composition of the mineral base (aluminosilicate, siliceous, carbonate) and the composition of schungite carbon. Shungites are subdivided into low-carbon (up to 5% C), medium-carbon (5-25% C) and high-carbon (25-80% C). After the complete combustion of shungite in the ashes, in addition to silicon, Fe, Ni, Ca, Mg, Zn, Cd, V, Mo, Cu, Ce, As, W and other elements are found.

Fullerene in shungite carbon is in the form of special, polar donor-acceptor complexes with PONVS. Therefore, the effective extraction of fullerenes from it with organic solvents, for example, toluene, in which fullerenes are highly soluble, does not occur, and the choice of such an extraction method often leads to conflicting results about the true presence of fullerenes in shungite.

In this regard, we have developed a method for the ultrasonic extraction of a water-detergent dispersion of shungite, followed by the transfer of fullerenes from a polar medium to an organic solvent phase. After several stages of extraction, concentration and purification, it is possible to obtain a solution in hexane, the UV and IR spectra of which are characteristic of the spectra of pure C 60 fullerene. Also, a clear signal in the mass spectrum with m/z = 720 (Fig. below) is an unambiguous confirmation of the presence of only С60 fullerene in shungites.

252 Cf-PD mass spectrum of shungite extract. The signal at 720 a.m.u. is С60 fullerene, and the signals at 696, 672 are characteristic fragmentation С60 fullerene ions formed under plasma-desorption ionization conditions.

However, we found that not every sample of shungite contains fullerenes. Of all the shungite samples provided to us by the Institute of Geology of the Karelian Scientific Center of the Russian Academy of Sciences (Petrozavodsk, Russia) and selected from different areas of occurrence of shungite rocks, C 60 fullerene was found only in one sample of high-carbon shungite containing more than 80% carbon. Moreover, it contained about 0.04 wt. %. From this we can conclude that not every sample of shungite contains fullerene, at least in the amount available for its detection by modern highly sensitive methods of physical and chemical analysis.

Along with this, it is well known that shungites can contain enough a large number of impurities, including ions of heavy polyvalent metals. And therefore, water infused with shungite may contain unwanted, toxic impurities.

But why then Marcial water (Karelian natural water passing through shungite-bearing rocks) has such unique biological properties. Recall that even during the time of Peter I, and on his personal initiative, the healing spring "Marcial Waters" was opened in Karelia (for more details, see). For a long time, no one could explain the reason for the special healing properties of this source. It was assumed that the increased content of iron in these waters is the cause of the healing effects. However, there are many iron-containing sources on Earth, but, as a rule, the healing effects from their intake are quite limited. Only after the discovery of fullerene in shungite rocks, through which the source flows, did the assumption arise that fullerene is main reason, a manifestation of the therapeutic effect of the Martial waters.

Indeed, water passing through the layers of "washed" shungite rock for a long time does not contain any appreciable amounts of harmful impurities. Water is “saturated” with the structure that the rock gives it. Fullerene contained in shungite promotes ordering water structures and the formation of fullerene-like hydrate clusters in it and the acquisition of unique biological properties of Martial waters. Shungite doped with fullerene is a kind of natural structurizer of water passing through it. At the same time, no one has yet been able to detect fullerenes in Martial waters or in the water infusion of shungite: either they are not washed out of shungite, or if they are washed out, then in such scanty quantities that are not detected by any of the known methods. In addition, it is well known that fullerenes do not spontaneously dissolve in water. And if fullerene molecules were contained in Martial water, then its useful properties would be preserved for a very long time. However, it is only active for a short time. As well as "melt water", saturated with cluster, ice-like structures, Marcial water, containing life-giving fullerene-like structures, retains its properties for only a few hours. When storing Martial water, as well as "thawed", ordered water clusters self-destruct and water acquires structural properties like ordinary water. Therefore, it makes no sense to pour such water into containers and store it for a long time. It lacks a structure-forming and structure-supporting element, C60 fullerene in a hydrated state, which is capable of maintaining ordered water clusters for an arbitrarily long time. In other words, in order for water to retain its natural cluster structures for a long time, the constant presence of a structure-forming factor in it is necessary. For this, the fullerene molecule is optimal, as we have seen for many years, studying the unique properties of hydrated C 60 fullerene.

It all started in 1995, when we developed a method for obtaining molecular-colloidal solutions of hydrated fullerenes in water. At the same time, we got acquainted with a book that tells about the unusual properties of the Martial Waters. We tried to reproduce the natural essence of the Martial waters in laboratory conditions. For this, water of a high degree of purification was used, to which, according to a special technology, hydrated C 60 fullerene was added in very small doses. After that, various biological tests began to be carried out at the level of individual biomolecules, living cells and the whole organism. The results were amazing. In almost any pathology, we found only positive biological effects of the action of water with hydrated C 60 fullerene, and the effects of its use not only completely coincided, but even exceeded in many parameters the effects that were described for Martial waters back in Peter's times. Many pathological changes in a living organism go away, and it returns to its normal, healthy state. But this is not a targeted drug and not an alien chemical compound, but just a ball of carbon dissolved in water. Moreover, one gets the impression that the hydrated fullerene C 60 helps to return to " normal condition» any negative changes in the body due to the restoration and maintenance of the structures that it generated, as a matrix, in the process of the birth of life.

Therefore, apparently, it is no coincidence that Orlov A.D. in his book "Shungite - a stone of pure water.", comparing the properties of shungites and fullerenes, he speaks of the latter as the quintessence of health.

1. Buseck et al. Fullerenes from the Geological Environment. Science 10 July 1992: 215-217. DOI: 10.1126/science.257.5067.215.
2. N.P. Yushkin. Globular supramolecular structure of shungite: scanning tunneling microscopy data. DAN, 1994, v. 337, no. 6 p. 800-803.
3. V.A. Reznikov. Yu.S. Polekhovsky. Amorphous shungite carbon is a natural environment for the formation of fullerenes. Letters to ZhTF. 2000. v. 26. c. 15. p.94-102.
4. Peter R. Buseck. Geological fullerenes: review and analysis. Earth and Planetary Science Letters. V 203, I 3-4, 15 November 2002, Pages 781-792
5.N.N. Rozhkova, G. V. Andrievsky. Aqueous colloidal systems based on shungite carbon and extraction of fullerenes from them. The 4th Biennial International Workshop in Russia "Fullerenes and Atomic Clusters" IWFAC"99 October 4 - 8, 1999, St. Petersburg, Russia. Book of Abstracts, p.330.
6. N.N. Rozhkova, G.V. Andrievsky. Fullerenes in shungite carbon. Sat. scientific Proceedings of the International Symposium “Fullerenes and fullerene-like structures”: June 5-8, 2000, BSU, Minsk, 2000, pp. 63-69.
7. N.N. Rozhkova, G.V. Andrievsky. Shungite carbon nanocolloids. extraction of fullerenes with aqueous solvents. Sat. Scientific Proceedings III international seminar"Mineralogy and life: biomineral homologues", June 6-8, 2000, Syktyvkar, Russia, Geoprint, 2000, pp.53-55.
8. S.A. Vishnevsky. Medical areas of Karelia. State Publishing House of the Karelian ASSR, Petrozavodsk, 1957, 57 p.
9. Fullerenes: The Quintessence of Health. Chapter on p. 79-98 in the book: A.D. Orlov. "Shungite - a stone of pure water." Moscow-St. Petersburg: "DILYa Publishing House", 2004. - 112 p.; and on the Internet at the site (www.golkom.ru/book/36.html).

Fullerene C 60

Fullerene C 540

Fullerenes, buckyballs or buckyballs- molecular compounds belonging to the class of allotropic forms of carbon (others are diamond, carbyne and graphite) and representing convex closed polyhedra, composed of an even number of three-coordinated carbon atoms. These connections owe their name to the engineer and designer Richard Buckminster Fuller, whose geodetic structures are built on this principle. Initially, this class of joints was limited to structures containing only pentagonal and hexagonal faces. Note that for the existence of such a closed polyhedron constructed from n vertices that form only pentagonal and hexagonal faces, according to Euler's theorem for polyhedra, which asserts the validity of the equality | n | − | e | + | f | = 2 (where | n | , | e| and | f| respectively, the number of vertices, edges and faces), a necessary condition is the presence of exactly 12 pentagonal faces and n/ 2 − 10 hexagonal faces. If the composition of a fullerene molecule, in addition to carbon atoms, includes atoms of other chemical elements, then if the atoms of other chemical elements are located inside the carbon cage, such fullerenes are called endohedral, if outside - exohedral.

The history of the discovery of fullerenes

Structural properties of fullerenes

In fullerene molecules, carbon atoms are located at the vertices of regular hexagons and pentagons, which form the surface of a sphere or ellipsoid. The most symmetrical and most fully studied representative of the fullerene family is fullerene (C 60), in which carbon atoms form a truncated icosahedron, consisting of 20 hexagons and 12 pentagons and resembling a soccer ball. Since each carbon atom of C 60 fullerene simultaneously belongs to two hexagons and one pentagon, all atoms in C 60 are equivalent, which is confirmed by the nuclear magnetic resonance (NMR) spectrum of the 13 C isotope - it contains only one line. However, not all C-C bonds have the same length. The C=C bond, which is common side for two hexagons, is 1.39 , and C-C connection, common for a hexagon and a pentagon, is longer and equals 1.44 Å. In addition, the bond of the first type is double, and the second is single, which is essential for the chemistry of C 60 fullerene.

The next most common is the C 70 fullerene, which differs from the C 60 fullerene by inserting a belt of 10 carbon atoms into the C 60 equatorial region, as a result of which the C 70 molecule is elongated and resembles a rugby ball in its shape.

The so-called higher fullerenes containing more carbon atoms (up to 400), are formed in much smaller quantities and often have a rather complex isomeric composition. Among the most studied higher fullerenes, one can single out C n , n=74, 76, 78, 80, 82 and 84.

Synthesis of fullerenes

The first fullerenes were isolated from condensed graphite vapors obtained by laser irradiation of solid graphite samples. In fact, they were traces of the substance. The next important step was taken in 1990 by W. Kretchmer, Lamb, D. Huffman and others, who developed a method for obtaining gram quantities of fullerenes by burning graphite electrodes in an electric arc in a helium atmosphere at low pressures. . In the process of anode erosion, soot containing a certain amount of fullerenes settled on the chamber walls. Subsequently, it was possible to find optimal parameters electrode evaporation (pressure, atmospheric composition, current, electrode diameter), at which the highest yield of fullerenes is achieved, averaging 3-12% of the anode material, which ultimately determines the high cost of fullerenes.

At first, all attempts by experimenters to find cheaper and more productive ways to obtain gram quantities of fullerenes (combustion of hydrocarbons in a flame, chemical synthesis, etc.) did not lead to success, and the “arc” method remained the most productive for a long time (productivity is about 1 g / h) . Subsequently, Mitsubishi managed to establish the industrial production of fullerenes by burning hydrocarbons, but such fullerenes contain oxygen and therefore the arc method is still the only suitable method for obtaining pure fullerenes.

The mechanism of fullerene formation in the arc still remains unclear, since the processes occurring in the arc burning region are thermodynamically unstable, which greatly complicates their theoretical consideration. It was irrefutably established only that the fullerene is assembled from individual carbon atoms (or C 2 fragments). For proof, highly purified 13 C graphite was used as the anode electrode, the other electrode was made of ordinary 12 C graphite. After the extraction of fullerenes, it was shown by NMR that the 12 C and 13 C atoms are randomly located on the fullerene surface. This indicates the decay of the graphite material to individual atoms or fragments of the atomic level and their subsequent assembly into a fullerene molecule. This circumstance forced to abandon the visual picture of the formation of fullerenes as a result of the folding of atomic graphite layers into closed spheres.

Relatively fast increase total installations for the production of fullerenes and constant work to improve methods for their purification have led to a significant reduction in the cost of C 60 over the past 17 years - from $ 10,000 to $ 10-15 per gram, which has led to the boundary of their real industrial use.

Unfortunately, despite the optimization of the Huffman-Kretschmer (HK) method, it is not possible to increase the yield of fullerenes by more than 10-20% of total weight burnt graphite fails. Considering the relatively high cost of the initial product, graphite, it becomes clear that this method has fundamental limitations. Many researchers believe that it will not be possible to reduce the cost of fullerenes obtained by the XC method below a few dollars per gram. Therefore, the efforts of a number of research groups are aimed at finding alternative methods for obtaining fullerenes. Greatest Success This area was reached by the Mitsubishi company, which, as mentioned above, managed to establish the industrial production of fullerenes by burning hydrocarbons in a flame. The cost of such fullerenes is about $5/gram (2005), which did not affect the cost of electric arc fullerenes.

It should be noted that the high cost of fullerenes is determined not only by their low yield during graphite combustion, but also by the complexity of isolating, purifying, and separating fullerenes of various masses from carbon black. The usual approach is as follows: the soot obtained by burning graphite is mixed with toluene or another organic solvent (capable of effectively dissolving fullerenes), then the mixture is filtered or centrifuged, and the remaining solution is evaporated. After removing the solvent, a dark fine-crystalline precipitate remains - a mixture of fullerenes, usually called fullerite. The composition of fullerite includes various crystalline formations: small crystals of C 60 and C 70 molecules and C 60 /C 70 crystals are solid solutions. In addition, fullerite always contains a small amount of higher fullerenes (up to 3%). Separation of a mixture of fullerenes into individual molecular fractions is carried out using liquid chromatography on columns and high pressure liquid chromatography (HPLC). The latter is mainly used to analyze the purity of isolated fullerenes, since the analytical sensitivity of the HPLC method is very high (up to 0.01%). Finally, the last stage is the removal of solvent residues from the solid fullerene sample. It is carried out by keeping the sample at a temperature of 150-250 o C in a dynamic vacuum (about 0.1 Torr).

Physical properties and applied value of fullerenes

Fullerites

Condensed systems consisting of fullerene molecules are called fullerites. The most studied system of this kind is the C 60 crystal, less - the crystalline C 70 system. Studies of crystals of higher fullerenes are hampered by the complexity of their preparation. Carbon atoms in a fullerene molecule are linked by σ- and π-bonds, while there is no chemical bond (in the usual sense of the word) between individual fullerene molecules in a crystal. Therefore, in a condensed system, individual molecules retain their individuality (which is important when considering the electronic structure of a crystal). Molecules are held in the crystal by van der Waals forces, which largely determine the macroscopic properties of solid C 60 .

At room temperatures, the C 60 crystal has a face-centered cubic (fcc) lattice with a constant of 1.415 nm, but as the temperature decreases, a first-order phase transition occurs (Tcr ≈260 K) and the C 60 crystal changes its structure to a simple cubic one (lattice constant 1.411 nm) . At a temperature T > Tcr, C 60 molecules rotate randomly around their center of equilibrium, and when it drops to a critical temperature, the two axes of rotation are frozen. Complete freezing of rotations occurs at 165 K. Crystal structureС 70 at temperatures of the order of room temperature was studied in detail in the work. As follows from the results of this work, crystals of this type have a body-centered (bcc) lattice with a small admixture of the hexagonal phase.

Nonlinear optical properties of fullerenes

An analysis of the electronic structure of fullerenes shows the presence of π-electron systems, for which there are large values ​​of the nonlinear susceptibility. Fullerenes indeed have nonlinear optical properties. However, due to the high symmetry of the C 60 molecule, second harmonic generation is possible only when asymmetry is introduced into the system (for example, by an external electric field). From a practical point of view, the high speed (~250 ps), which determines the suppression of the second harmonic generation, is attractive. In addition, C 60 fullerenes are also capable of generating the third harmonic.

Another possible area for the use of fullerenes and, first of all, C 60 is optical shutters. The possibility of using this material for a wavelength of 532 nm has been experimentally shown. The short response time makes it possible to use fullerenes as laser radiation limiters and Q-switches. However, for a number of reasons, it is difficult for fullerenes to compete here with traditional materials. High cost, difficulties in dispersing fullerenes in glasses, the ability to quickly oxidize in air, non-record coefficients of nonlinear susceptibility, and a high threshold for limiting optical radiation (not suitable for eye protection) create serious difficulties in the fight against competing materials.

Quantum mechanics and fullerene

Hydrated fullerene (HyFn); (C 60 @ (H 2 O) n)

Aqueous solution C 60 HyFn

Hydrated C 60 - C 60 HyFn fullerene is a strong, hydrophilic supramolecular complex consisting of a C 60 fullerene molecule enclosed in the first hydration shell, which contains 24 water molecules: C 60 @(H 2 O) 24 . The hydration shell is formed due to the donor-acceptor interaction of lone pairs of oxygen oxygen molecules in water with electron-acceptor centers on the fullerene surface. At the same time, water molecules oriented near the fullerene surface are interconnected by a volumetric network of hydrogen bonds. The size of C 60 HyFn corresponds to 1.6-1.8 nm. At present, the maximum concentration of C 60 , in the form of C 60 HyFn, that has been created in water is equivalent to 4 mg/ml. Photo of an aqueous solution of C 60 HyFn with a concentration of C 60 0.22 mg/ml on the right.

Fullerene as a material for semiconductor technology

A molecular fullerene crystal is a semiconductor with a band gap of ~1.5 eV and its properties are largely similar to those of other semiconductors. Therefore, a number of studies have been related to the use of fullerenes as a new material for traditional applications in electronics: a diode, a transistor, a photocell, etc. Here, their advantage over traditional silicon is a short photoresponse time (units of ns). However, the effect of oxygen on the conductivity of fullerene films turned out to be a significant drawback and, consequently, a need arose for protective coatings. In this sense, it is more promising to use the fullerene molecule as an independent nanoscale device and, in particular, as an amplifying element.

Fullerene as a photoresist

Under the action of visible (> 2 eV), ultraviolet and shorter wavelength radiation, fullerenes polymerize and in this form are not dissolved by organic solvents. As an illustration of the use of a fullerene photoresist, one can give an example of obtaining submicron resolution (≈20 nm) by etching silicon with an electron beam using a mask of a polymerized C 60 film.

Fullerene Additives for the Growth of Diamond Films by the CVD Method

Another interesting possibility practical application is the use of fullerene additives in the growth of diamond films by the CVD method (Chemical Vapor Deposition). The introduction of fullerenes into the gas phase is effective from two points of view: an increase in the rate of formation of diamond cores on the substrate and the supply of building blocks from the gas phase to the substrate. Fragments of C 2 act as building blocks, which turned out to be a suitable material for the growth of a diamond film. It has been experimentally shown that the growth rate of diamond films reaches 0.6 µm/h, which is 5 times higher than without the use of fullerenes. For real competition between diamonds and other semiconductors in microelectronics, it is necessary to develop a method for heteroepitaxy of diamond films, but the growth of single-crystal films on non-diamond substrates remains an unsolvable problem. One possible way to solve this problem is to use a fullerene buffer layer between the substrate and the diamond film. A prerequisite for research in this direction is the good adhesion of fullerenes to most materials. These provisions are especially relevant in connection with intensive research on diamonds for their use in next-generation microelectronics. High performance (high saturated drift speed); The highest thermal conductivity and chemical resistance of any known material make diamond a promising material for next-generation electronics.

Superconducting compounds with C 60

Molecular fullerene crystals are semiconductors, however, in early 1991 it was found that doping solid C 60 with a small amount of alkali metal leads to the formation of a material with metallic conductivity, which, when low temperatures goes into a superconductor. Doping with 60 is produced by treating crystals with metal vapor at temperatures of several hundred degrees Celsius. In this case, a structure of the type X 3 C 60 is formed (X is an alkali metal atom). The first intercalated metal was potassium. The transition of the K 3 C 60 compound to the superconducting state occurs at a temperature of 19 K. This is a record value for molecular superconductors. It was soon established that many fullerites doped with alkali metal atoms in the ratio of either X 3 C 60 or XY 2 C 60 (X, Y are alkali metal atoms) have superconductivity. The record holder among the high-temperature superconductors (HTSC) of these types was RbCs 2 C 60 - its T cr =33 K.

Influence of small additives of fullerene soot on the antifriction and antiwear properties of PTFE

It should be noted that the presence of C 60 fullerene in mineral lubricants initiates the formation of a protective fullerene-full-dimensional film 100 nm thick on the counterbody surfaces. The formed film protects against thermal and oxidative degradation, increases the lifetime of friction units in emergency situations by 3-8 times, the thermal stability of lubricants up to 400-500ºС and the bearing capacity of friction units by 2-3 times, expands the working pressure range of friction units by 1.5 -2 times, reduces the running-in time of counter bodies.

Other applications of fullerenes

Other interesting applications include accumulators and electric batteries, in which fullerene additives are used in one way or another. These batteries are based on lithium cathodes containing intercalated fullerenes. Fullerenes can also be used as additives for producing artificial diamonds using the high pressure method. In this case, the yield of diamonds increases by ≈30%. Fullerenes can also be used in pharmacy to create new drugs. In addition, fullerenes have found application as additives in intumescent (intumescent) fire-retardant paints. Due to the introduction of fullerenes, the paint swells under the influence of temperature during a fire, a rather dense foam-coke layer is formed, which several times increases the heating time to the critical temperature of the protected structures. Also, fullerenes and their various chemical derivatives are used in combination with polyconjugated semiconducting polymers for the manufacture of solar cells.

Chemical properties of fullerenes

Fullerenes, despite the absence of hydrogen atoms, which can be replaced as in the case of ordinary

Fullerenes - ϶ᴛᴏ isolated molecules of a new allotropic modification of carbon(named after the American engineer and architect of honeycomb domes R. Buckminster Fuller). Fullerenes in the solid state are called fullerites.

Fullerenes are stable polyatomic carbon clusters with the number of atoms from several tens and more. The number of carbon atoms in such a cluster is not arbitrary, but obeys a certain pattern (the number of atoms in a cluster N= 32.44, 50, 58, 60, 70, 72, 78, 80, 82, 84, etc.). A fullerene molecule can only contain an even number of carbon atoms. . The shape of fullerenes is a hollow spheroid, the faces of which form pentagons and hexagons. The fullerene molecule is built from C atoms in the state sp 2-hybridization, due to which each atom has three neighbors associated with it by s-bonds. The remaining valence electrons form the π-system of the molecule from delocalized ʼʼcarbon-carbonʼʼ double bonds. To form a spherical surface, 12 pentagonal carbon fragments and any number of hexagonal ones are needed.

Of greatest interest is fullerene C 60 due to its greatest stability and high symmetry. All atoms in this molecule are equivalent, each atom belongs to two hexagons and one pentagon and is connected to its nearest neighbors by one double and two single bonds. The C 60 molecule is a hollow polyhedron with 12 pentagonal and 20 hexagonal symmetrically arranged faces, forming a shape similar to the shape of a soccer ball, also consisting of twelve pentagonal and twenty hexagonal facets (in this regard, it is also called ʼʼfootballinoʼʼ). There are no free bonds in the C 60 molecule, and this explains its great chemical and physical stability. Due to this, among allotropes of carbon, fullerenes and fullerites are the purest. The diameter of the C 60 molecule is 0.7024 nm. Valence electrons are distributed more or less uniformly over a spherical shell about 0.4232 nm thick. A cavity with a radius of about 0.1058 nm remains in the center of the molecule, practically free from electrons. So such a molecule is, as it were, a small empty cell, in the cavity of which atoms of other elements and even other molecules can be placed without destroying the integrity of the fullerene molecule itself.

Spherical C 60 molecules can combine with each other in a solid to form a face-centered cubic (fcc) crystal lattice. In a fullerite crystal, C 60 molecules play the same role as atoms in an ordinary crystal. The distance between the centers of the nearest molecules in a face-centered lattice, held by weak van der Waals forces, is about 1 nm.

It should be noted that, in terms of their electronic properties, pure C60 crystals and many complexes based on them represent a new class of organic semiconductors, which are extremely interesting both from a purely fundamental point of view and from the point of view of possible applications.

From a fundamental point of view, interest in fullerites is due, in particular, to the fact that, in contrast to "classical" semiconductors (such as silicon), the width of allowed energy bands in fullerene crystals is rather small, it does not exceed 0.5 eV. For this reason, strong effects associated with Coulomb correlations, lattice relaxation, and other effects are possible in these crystals, which is extremely interesting and can lead to the discovery and observation of new phenomena.

The width of the first band gap is about 2.2 ... 2.3 eV.

Modification of the surface of a fullerene molecule or filling its internal space with metal atoms leads to a noticeable change in physical properties, for example, a transition to a superconducting state or the manifestation of magnetism.

Diverse fullerene derivatives include intercalated compounds and endohedral fullerenes (or endohedral complexes). During intercalation, impurities are introduced into the voids of the fullerite crystal lattice, and endohedral fullerenes are formed when atoms of various types are introduced into the C cluster. P.

If it were possible to find a chemical reaction that would open a window in the fullerene framework, allowing an atom or a small molecule to enter there, and restore the cluster structure again, then a beautiful method for obtaining endohedral fullerenes would be obtained. At the same time, most endohedral metallofullerenes are currently produced either in the process of fullerene formation in the presence of foreign substance or by implantation.

Methods for obtaining and separating fullerenes. The most efficient way to obtain fullerenes is based on thermal decomposition graphite. With moderate heating of graphite, the bond between the individual layers of graphite breaks, but the evaporating material does not decompose into individual atoms. In this case, the evaporated layer consists of individual fragments, from which the construction of the C 60 molecule and other fullerenes occurs. To decompose graphite in the production of fullerenes, resistive and high-frequency heating of a graphite electrode, combustion of hydrocarbons, and laser irradiation of the graphite surface are used. These processes are carried out in a buffer gas, which is usually helium.

Most often, to obtain fullerenes, an arc discharge with graphite electrodes in a helium atmosphere is used. The main role of helium is apparently associated with the cooling of fragments that have a high degree of vibrational excitation, which prevents them from combining into stable structures.

Application of fullerenes.

There are a lot of supposed applications of fullerenes:

· The possibilities of their application in chemistry, microbiology and medicine are associated with the chemical stability and hollowness of fullerenes. For example, they can be used to pack and deliver to the required place not only atoms, but also whole molecules, incl. organic (pharmaceuticals, microbiology);

· Fullerenes as new semiconductor and nanostructural materials. The fullerene molecule is a ready-made nanoscale object for creating nanoelectronic instruments and devices based on new physical principles. Developed physical principles creation of an analogue of a transistor based on one fullerene molecule, which can serve as a current amplifier in the nanoampere range. In the field of nanoelectronics the greatest interest in terms of possible applications they call quantum dots (quantum dots). Such dots have a number of unique optical properties that make it possible to use them, for example, to control fiber optic communications, or as elements of a processor in an optical supercomputer currently being designed. Fullerenes are ideal quantum dots in many respects. Of interest for promising memory devices are also endohedral complexes of rare earth elements, such as terbium (Tb), gadolinium (Gd), dysprosium (Dy), which have large magnetic moments. A fullerene containing such an atom must have the properties of a magnetic dipole, the orientation of which can be controlled by the external magnetic field. These complexes (in the form of a multilayer film) can serve as the basis for a magnetic storage medium with a recording density of up to 10 12 bit/cm 2 .

· Fullerenes as new materials for nonlinear optics. Fullerene-containing materials (solutions, polymers, liquid crystals, fullerene-containing glass matrices) have highly non-linear optical properties and are promising for use as: optical limiters (attenuators) of intense laser radiation; photorefractive media for recording dynamic holograms; frequency converters; phase conjugation devices. The most studied area is the creation of optical power limiters based on liquid and solid solutions of C 60.

· Fullerite C 60 doped with an alkali metal is a conductor, and at a low temperature it is also a superconductor. The introduction of impurity atoms into a fullerite matrix is ​​associated with the phenomenon of intercalation. Intercalation compounds are a material in which impurity atoms or molecules are trapped between the layers of the crystal lattice. Formally, there is no chemical bond between the intercalant and the matrix. Impurity atoms (mainly alkali, alkaline earth, and rare earth metals) can penetrate into the intermolecular voids of a C 60 crystal without deforming the lattice. C 60 has a high electron affinity, alkali metals donate electrons easily. Crystal C 60 is a wide-gap semiconductor and its conductivity is low, and when doped with alkali atoms, it becomes a conductor. For example, when doping with potassium to form K 3 C 60, potassium atoms are ionized to K +, and their electrons are associated with the C 60 molecule, which becomes a negative ion. K 3 C 60 at 18 K is a superconductor.

Fullerenes are a material for lithography. Due to the ability to polymerize under the action of a laser or electron beam (the degree of polymerization in some cases exceeds 10 6) and form a phase insoluble in organic solvents, the use of fullerenes as a resist for submicron lithography is promising. At the same time, fullerene films withstand significant heating, do not contaminate the substrate, and allow dry development. Since polymerized C 60 clusters are themselves semiconductors, this technology can be very promising for the creation of single-electron transistors operating at room temperature. To do this, in tunnel gaps formed, for example, on the silicon surface, one can try to create very small C 60 clusters due to electron beam polymerization.

Chirality

Chirality- lack of symmetry with respect to the right and left sides. For example, if the reflection of an object is ideally flat mirror differs from the object itself, then the object is inherently chirality. Molecular chirality is the property of a molecule to be incompatible with its own mirror image any combination of rotations and movements in three-dimensional space. Any geometric figure that should not be aligned with its reflection is called chiral.

Chiral molecules form the basis of living nature, as well as many functional materials. For example, all amino acids that make up proteins are chiral (with the exception of glycine). This also applies to sugars - the building blocks of carbohydrates and nucleic acids. Accordingly, the macromolecules formed from them are also chiral - typical nanoobjects: proteins, nucleic acids, carbohydrates, etc.

Chirality is essential in the synthesis of complex compounds with medicinal properties, regular polymers, liquid crystals; the absence of a center of symmetry is a key condition for obtaining materials for nonlinear optics, ferroelectric and piezoelectric materials. Most natural poisons - polypeptides and alkaloids - are also chiral, and their ʼʼantipodesʼʼ are practically harmless to the human body. On the other hand, the ʼʼantipodesʼʼ of natural amino acids and sugars are simply not absorbed by living organisms and are not even recognized. Sometimes the antipodes of medicinal substances are very dangerous, therefore, in the production of drugs, various chiral agents are used to purify the substances obtained.

Fullerenes - concept and types. Classification and features of the category "Fullerenes" 2017, 2018.

Properties ... But first things first.

In the beginning - about shungite.

Shungite is a black mineral containing 93-98% carbon and up to 3-4% hydrogen, oxygen, nitrogen, sulfur, and water compounds. The mineral ash contains vanadium, molybdenum, nickel, tungsten, selenium. The mineral was named after the village of Shunga in Karelia, where its main deposits are located.

Shungite was formed from organic bottom sediments - sapropel - about 600 million years ago, and according to some sources - 2 billion years ago. These organic sediments (corpses of crustaceans, algae and other snails), covered from above with new layers, gradually became compacted, dehydrated and sank into the depths of the earth. Under the influence of compression and high temperature the process of metamorphosis was underway. As a result of this process, amorphous carbon dispersed in the mineral matrix was formed in the form of globule-fullerenes characteristic of shungite.

Now about fullerenes

What is this fullerene contained in shungite? Fullerenes are one of the varieties of carbon. So, from school we remember that carbon has several forms:

• diamond,
• graphite,
• coal.

Fullerenes are just another form of carbon. It differs in that fullerene molecules are globules of regular polyhedra, composed of molecules of the same carbon:

But why are fullerenes so useful?

Fullerenes are used in semiconductor technology, for various studies (optics, quantum mechanics), photoresistance, in the field of superconductors, in mechanics for the manufacture of substances to reduce friction, in battery technology, in the synthesis of diamonds, in the manufacture of photobatteries and many other industries. Of which one is for the manufacture of medicines.

And again we are back to our question - why are fullerenes so useful? Here you can turn to Grigory Andrievsky, who is working with a group of scientists at the Institute of Therapy of the Academy of Medical Sciences of Ukraine on this very issue. In his research, the scientist revealed what's what.

So, fullerenes in shungite are in a special form - hydrated. That is, they are connected to water and can dissolve in water. Accordingly, fullerenes can be washed out of shungite and form fullerene solution- the only active form fullerenes for today.

Further, aqueous solutions of fullerenes are powerful antioxidants. That is, they, like vitamins E and C (and other substances), help the body deal with free radicals- substances that are formed in the body during inflammatory processes and very aggressively interact with the surrounding substances - destroying the structures necessary for the body. But, unlike vitamins, fullerenes are not consumed when neutralizing free radicals - and can make them safe until they are removed from the body naturally.

Accordingly, the amounts of fullerenes that effectively work as antioxidants can be found in the body in much smaller amounts than vitamins. Compared to them

fullerenes can work in ultra-low doses.

Accordingly, using aqueous solutions of fullerenes, you can reduce the amount of free radicals in the body - and help the body cope with negative processes. What, in fact, does shungite water - the same water solution fullerenes.

And a very important addition from Grigory Andrievsky about the healing properties of shungite fullerenes:

So far, there have been only experiments on volunteers, including myself. Therefore, one should not stir up a stir and inspire unrealistic hopes in patients. Yes, we have promising results from basic research, mostly in animals and cell cultures. But, while the preparations and methods have not been tested and tested in in due course, we have no moral or other right to call them medicines and medical methods.

And finally, to shungite water

Shungite water - we return to it. There are two opposite opinions about the preparation and use of shungite water.

The first one was announced by Cand. chem. Sciences O. V. Mosin (Moscow State Academy of Fine chemical technology them. M. V. Lomonosov):

Water, infused with shungite, becomes not just pure drinking water, but also a molecular-colloidal solution of hydrated fullerenes, which belong to a new generation of medicinal and prophylactic agents with a multifaceted effect on the body.

The second opinion about the use of shungite is voiced by the director of the Institute of Geology of the Karelian Scientific Center of the Russian Academy of Sciences, Doctor of Geol.-M. n. Vladimir Shchiptsov:

The fact that shungite purifies water has been proven, but only if it is included as an integral part of special filters. Water, infused simply on a piece of mineral, can even be harmful - as a result chemical reaction essentially a low-concentration acid solution is formed.

So, to prepare shungite water, do you need to insist the water on the mineral or pass it through special filters? Let's delve into the topic. And, since shungite water is an aqueous solution of fullerenes, we will not get away from them.

Thus, fullerenes dissolve in water with great difficulty. On the other hand, if they are dissolved, then around each fullerene ball a multilayer shell is formed from correctly arranged water molecules, approximately in ten molecular layers. This water, in other words, hydrate, shell around the fullerene molecule can be called structured water.

The properties of water surrounding a fullerene molecule differ significantly from ordinary water. And it is very similar to bound water in the cells of the body. So, in a living cell, in fact, there is very little ordinary, familiar to us free water. All water is bound to the molecules around it. And it's kind of like jelly. Mechanism of Education bound water in cells is similar to the mechanism of formation of an aqueous shell around a fullerene molecule.

Thus, in a solution of shungite water, two types of water can be distinguished:

1. structured water surrounding fullerene molecules (as well as organic matter in cells)
2. and free water.

When evaporating solutions, it is free water that evaporates first. The same water shell with a lower melting point is formed around DNA molecules in enzyme solutions. That gives them resistance to both freezing and heating.

So, back to two different ways of preparing shungite - steeping and passing through a layer of shungite. How are these methods different? They differ in contact time. That is, the time during which fullerenes can leave the shungite structure and form an aqueous solution.

As we mentioned earlier, fullerenes can work in ultra-low doses. That is, for the formation of a really effective solution of fullerenes, it is enough to simply pass water through shungite or not very long infusion of water on shungite.

Naturally, the intensity of dissolution of fullerenes from shungite depends on the degree of grinding of shungite granules. So, if you have a piece of stone weighing a kilogram, then you can infuse water for a long time 🙂

Since there are no completed scientific studies with unambiguous recommendations on the use of shungite, there is no exact pattern - how long to infuse (filter) through granules of what size shungite to prepare a solution of fullerenes of the desired concentration.

Accordingly, the only way out for today is to experiment with shungite water on yourself.

And listen to your feelings. And, of course, to change the impact when the state of health worsens or improves.

Write the results of your experiments!