Schwarz-body carbon nanorings and their synthesis methods and applications

Abstract

The present invention discloses a Schwarz-body carbon nanoring, a synthesis method thereof, and its application in the separation of fullerene allotropes. The Schwarz-body carbon nanoring has a structure represented by the following formula (I): #imgabs0# In formula (I), n represents the number of dibenzocyclooctatetraene structural units in the Schwarz-body carbon nanoring, and is an integer selected from 3 to 7. The synthesis method comprises: synthesizing the Schwarz-body carbon nanoring by a Yamamoto coupling reaction catalyzed by a nickel catalyst using a compound having a structure represented by the following formula (V) as a monomer; #imgabs1##imgabs2#

Description

Technical Field

[0001] The present invention relates to the field of organic chemistry, and in particular to a Schwarz-body carbon nanoring, a synthesis method thereof, and an application thereof in the separation of fullerene allotropes. Background Art

[0002] Carbon is the most common element on Earth and in living things, including a class of elements composed of sp 2 Allotropes composed of hybrid carbon elements have unique photophysical, photochemical, and electromagnetic properties and have had a revolutionary impact on the development of physics, chemistry, and materials science. For example, zero-dimensional fullerenes, one-dimensional carbon nanotubes, and two-dimensional graphene, although they are all composed of sp 2 It is composed of hybridized carbon atoms, but the different combinations of carbon atoms give it completely different topological structures. It is worth noting that the zero-dimensional fullerene is composed of pentagonal and hexagonal carbon rings, so the Gaussian curvature of the structure is greater than zero; one-dimensional carbon nanotubes and two-dimensional graphene are composed of hexagonal carbon rings, and the Gaussian curvature of their surfaces is equal to zero. In 1991, Mackay and Terrones proposed that introducing octagonal carbon rings into hexagonal carbon networks would help form three-dimensional carbon nanostructures with negative Gaussian curvature, known as Mackay crystals. Later, Elser et al. suggested inserting heptagonal carbon rings into hexagonal carbon networks to generate structures with lower symmetry but the same topological characteristics. These sp 2 The three-dimensional structure of carbon atoms is called a "carbon Schwarz body" to commemorate the outstanding contribution of Schwarz bodies to the popularization of the mathematical concept of three-periodic minimal surfaces in the early 1890s. Based on the unique mathematical expression of TPMS, carbon Schwarz bodies can be divided into three types: Gyroid, Diamond, and Primitive. Although many theoretical studies predict that carbon Schwarz bodies may become the next generation of carbon-based materials, their unique structure and properties will have important potential applications in gas storage and separation, battery electrode materials, and catalysis. However, how to accurately synthesize carbon Schwarz bodies is a difficult problem in the field of carbon nanoscience that needs to be solved urgently and has not yet been achieved.

[0003] On this basis, chemists have discovered that molecular fragments similar to carbon Schwartz bodies can be prepared through organic synthesis methods and realize their corresponding functions to a certain extent. The literature (Yao-Ting Wu.Angew.Chem.Int.Ed.2013,52,7791–7794) discloses a derivative of [8]cyclopentyl aromatic hydrocarbon containing an octagonal carbon unit that can be used as an aromatic saddle fragment in carbon Schwartz bodies. The literature (Qian Miao.Angew.Chem.Int.Ed.2018,57,1581–1586) discloses that a nanographene structure with two heptagonal carbon units twisted is considered to be a key fragment of carbon Schwartz bodies. The literature (Frank Würthner.Angew.Chem.Int.Ed.2019,58,16504–16507) discloses a highly curved polycyclic aromatic hydrocarbon containing diheptane, the non-covalent assembly between which and C60 can induce the formation of a precursor molecule similar to carbon Schwartz bodies. Although the above studies have achieved the synthesis of carbon Schwarz body nanofragments containing heptagons or octagons, ring-shaped carbon nanostructures have always been considered the best alternative molecules to carbon Schwarz bodies because they are closer to the topological structure of carbon Schwarz bodies, but have not been effectively synthesized so far.

[0004] In summary, the synthesis of carbon Schwarz ring fragments containing more than three eight-membered rings remains a significant challenge. This is mainly due to the low yields of cyclization reactions in organic synthesis, and when the number of octagonal units exceeds two, the curvature of the fragment becomes uncontrollable, making it difficult to obtain the desired structure.

[0005] Furthermore, fullerenes are the fourth allotrope of carbon discovered after graphite, diamond, and amorphous carbon. Their discovery has greatly advanced the development of nanoscience. Fullerenes possess perfect spherical symmetry, ultra-stable structures at the nanoscale, and exceptional physical and chemical properties, earning them the nickname "Prince of Nano." The most representative fullerenes are C60 and C70. The industrialization of fullerenes has been a hotly contested pursuit among major material processing nations for the past 30 years. Currently, only a handful of countries in the world are capable of producing fullerenes, with low yields and high prices. While my country has made significant progress in fullerene production in recent years, its purification remains somewhat limited. Currently, the separation of C60 and C70 from soot typically involves a series of dissolution, evaporation, and filtration procedures using large amounts of benzene-containing solvents, based on their solubility in different solvents. This separation is associated with significant pollution, high energy consumption, and low efficiency. Therefore, it is very important and of national strategic significance to develop a more efficient and simple method to separate C60 and C70. Summary of the Invention

[0006] The present invention provides a Schwarz-body carbon nanoring, a novel series of carbon nanorings characterized by simple synthesis, high yield, and mild reaction conditions, enabling mass production. The present method for synthesizing the Schwarz-body carbon nanorings provides a simple and efficient method for constructing Schwarz-body ring fragments. These Schwarz-body carbon nanorings can efficiently separate fullerene allotropes such as C60 and C70.

[0007] A Schwarz carbon nanoring having a structure shown in the following formula (I):

[0008]

[0009] (I), which can be expressed as SNRs;

[0010] In formula (I), n represents the number of dibenzocyclooctatetraene structural units in the Schwarz-type carbon nanoring, and is an integer selected from 3 to 7.

[0011] Furthermore, the Schwarz carbon nanoring has a structure shown in any one of the following formulas (II) to (IV):

[0012]

[0013] (II), which can be denoted as SNR1;

[0014]

[0015] (III), which can be denoted as SNR2;

[0016]

[0017] (IV), which can be denoted as SNR3.

[0018] SNR1, SNR2 and SNR3 belong to the three types of carbon Schwarz body ring fragment molecules: Gyroid, Diamond and Primitive, respectively. There are also larger Schwarz body carbon nanorings with n of 5, 6 or 7.

[0019] The crystal of Schwarz carbon nanoring SNR1 belongs to orthorhombic crystal, the space group is Pnma, and its unit cell parameters are: α=90°, β=90°, γ=90°,

[0020] The crystal of Schwarz carbon nanoring SNR2 belongs to orthorhombic crystal, the space group is Cmce, and its unit cell parameters are: α=90°, β=90°, γ=90°,

[0021] The crystal of Schwarz carbon nanoring SNR3 is a monoclinic crystal with a space group of C2 / m and unit cell parameters of: α=90°, β=95.191(8)°, γ=90°,

[0022] The present invention also provides a method for synthesizing the Schwarz-body carbon nanorings, wherein the Schwarz-body carbon nanorings are synthesized by a Yamamoto coupling reaction catalyzed by a nickel catalyst using a compound 2,9-dibromodibenzo[a,e]-cyclooctene (which can be represented by 2,9-2Br-DBCOT) having a structure represented by the following formula (V) as a monomer;

[0023]

[0024] The present invention uses 2,9-2Br-DBCOT as a synthetic monomer and performs cyclization of different numbers of units through a Yamamoto coupling reaction catalyzed by a nickel catalyst to form corresponding Schwarz-body carbon nanorings, and its compound crystals can be obtained through slow crystallization.

[0025] The cyclization yield of the synthesis method of the Schwarz-body carbon nanorings of the present invention can exceed 75%.

[0026] The crystal of 2,9-2Br-DBCOT is a triclinic crystal with a space group of P-1 and unit cell parameters of: α=90.294(4)°, β=94.026(4)°, γ=100.869(3)°,

[0027] In one embodiment, the method for synthesizing the Schwarz-body carbon nanorings comprises dissolving bis(1,5-cyclooctadiene)nickel (Ni(cod)2), 2,2'-bipyridine (2,2'-bipyridine) and the compound 2,9-dibromodibenzo[a,e]-cyclooctene in an organic solvent, heating and stirring the mixture under the protection of an inert gas to react, and after the reaction, separating and purifying the product by column chromatography to obtain the Schwarz-body carbon nanorings.

[0028] In one embodiment, the molar ratio of bis(1,5-cyclooctadiene)nickel, 2,2'-bipyridine, and the compound 2,9-dibromodibenzo[a,e]-cyclooctene is 2:2:1. When the amounts of bis(1,5-cyclooctadiene)nickel and 2,2'-bipyridine are too small, the cyclization yield is significantly reduced; conversely, when the amounts are too large, the reactants have poor solubility, which is not conducive to the reaction.

[0029] In one embodiment, the ratio of the compound 2,9-dibromodibenzo[a,e]-cyclooctene to the organic solvent is 0.25 mmol:100-150 mL. When the amount of solvent is too small, the reactant concentration is too high, and polymers are easily formed, which is not conducive to the cyclization reaction. Conversely, when the amount of solvent is too large, the reaction efficiency is reduced.

[0030] The organic solvent can be at least one of anhydrous tetrahydrofuran (THF), toluene, and acetonitrile, preferably anhydrous tetrahydrofuran. Anhydrous tetrahydrofuran as an organic solvent is conducive to the Yamamoto coupling reaction and has the highest cyclization yield.

[0031] In one embodiment, the temperature of the heating and stirring reaction is 60-80° C. If the temperature is too low, the cyclization process will be slow and a large amount of raw materials will not react; if the temperature is too high, the polymerization process will be too fast and the product will mostly be a linear polymer instead of the target cyclization product.

[0032] In one embodiment, the heating and stirring reaction time is 20 to 28 hours.

[0033] In one embodiment, the column chromatography method uses 300 mesh silica gel as the stationary phase.

[0034] In one embodiment, the column chromatography method uses an ethyl acetate / chloroform mixed solvent with a volume ratio of 1:2 as the mobile phase.

[0035] The present invention also provides the use of the Schwarz-body carbon nanoring in the separation of fullerene allotropes.

[0036] Furthermore, the Schwarz carbon nanorings can be used to separate C60 and C70.

[0037] The present invention also provides a method for separating C60 and C70, comprising dissolving the Schwarz body carbon nanorings in a toluene solution containing C60 and C70, heating the resulting solution to 105-115° C. and then cooling to room temperature, precipitating complex crystals of the Schwarz body carbon nanorings and C60, while C70 remains in the liquid phase. The solid and liquid are separated, and the complex crystals of the Schwarz body carbon nanorings and C60 are redissolved in hot toluene. The Schwarz body carbon nanorings and pure C60 are recovered by column chromatography, and the liquid phase is concentrated and separated by column chromatography to obtain pure C70.

[0038] In the separation method of C60 and C70, the column chromatography separation can use 300 mesh silica gel as the stationary phase and a dichloromethane / ethyl acetate mixed solvent with a volume ratio of 1:1 as the mobile phase.

[0039] As a general inventive concept, the present invention also provides a method for synthesizing a compound 2,9-dibromodibenzo[a,e]-cyclooctene having a structure as shown in formula (V). Under inert gas protection, a mixture of anhydrous N,N-dimethylformamide (DMF) and sodium iodide (NaI) is stirred and heated to 165-175°C. Compounds A, A, A', A', and 4-pentabromo-o-xylene having a structure as shown in formula (VI) are added, and the mixture is stirred and reacted at 165-175°C. After the reaction, water and sodium thiosulfate are added. The solid product is collected, washed, dried, purified by silica gel column chromatography, and repeatedly recrystallized using hot ethyl acetate or hot ether to obtain the compound 2,9-dibromodibenzo[a,e]-cyclooctene.

[0040]

[0041] In one embodiment, the usage ratio of anhydrous N,N-dimethylformamide, sodium iodide, compound A, A, A', A', and 4-pentabromo-o-xylene is 10 mL:50 mmol:5 mmol.

[0042] In one embodiment, the stirring reaction time at 165-175° C. is 3-5 hours.

[0043] In one embodiment, the silica gel column chromatography uses petroleum ether as the mobile phase.

[0044] The anhydrous solvent used in the present invention can be a solvent dried with 4A molecular sieve.

[0045] In the present invention, the inert gas may be a rare gas and / or nitrogen.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] 1. The present invention provides a new type of Schwarz-body carbon nanorings, which are cyclized using a Yamamoto coupling reaction. This synthesis method is simple and efficient, avoiding the traditional cumbersome synthesis route, and can be achieved using a "one-pot method" with a high cyclization efficiency (>75%).

[0048] 2. The present invention provides a method for synthesizing the Schwarz-body carbon nanorings. The method has good universality, a simple operation process, low equipment requirements, no need for a specific reaction vessel, mild reaction conditions, and can produce products in large quantities.

[0049] 3. The present invention provides a new method for the effective separation of fullerene allotropes, especially C60 and C70. The method is simple to operate, has high separation efficiency (>90%), low energy consumption, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 The synthetic route of 2,9-2Br-DBCOT in Example 1 is shown;

[0051] Figure 2 This is the synthesis route of the Schwarz-body carbon nanoring in Example 2;

[0052] Figure 3 The single crystal structure of 2,9-2Br-DBCOT prepared in Example 1;

[0053] Figure 4 : This is a single crystal structure diagram of the Schwarz-body carbon nanoring SNR1 prepared in Example 2;

[0054] Figure 5 This is a single crystal structure diagram of the Schwarz-body carbon nanoring SNR2 prepared in Example 2;

[0055] Figure 6 This is a single crystal structure diagram of the Schwarz-body carbon nanoring SNR3 prepared in Example 2;

[0056] Figure 7 This is the ultraviolet absorption spectrum of the complex of Schwarz-body carbon nanoring SNR3 and C60 / C70 prepared in Example 2;

[0057] Figure 8 Schematic diagram of the formation of a eutectic by combining the Schwarz-body carbon nanoring SNR3 and C60 prepared in Example 2;

[0058] Figure 9 This is a single crystal structure diagram of the complex of Schwarz carbon nanoring SNR3 and C60 prepared in Example 2. DETAILED DESCRIPTION

[0059] The present invention will be further described below with reference to the accompanying drawings and specific examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0060] Example 1

[0061] Preparation of 2,9-2Br-DBCOT:

[0062] Figure 1 The synthetic route of 2,9-2Br-DBCOT is as follows:

[0063] Anhydrous N,N-dimethylformamide (10 mL) and sodium iodide (7.50 g, 50 mmol) were added to a 100 mL two-necked flask, and the suspension was stirred and heated to 170°C under nitrogen. Subsequently, the suspension was removed from heating, and compound A,A,A',A',4-pentabromo-o-xylene (2.50 g, 5.0 mmol) was added to the suspension under nitrogen with vigorous stirring. The flask was stirred at 170°C for 4 hours, and the hot reaction mixture was transferred to an Erlenmeyer flask. The residue in the reaction vessel was collected with N,N-dimethylformamide and water. Water (130 mL) and saturated aqueous sodium thiosulfate (20 mL) were added to the resulting mixture. The resulting mixture was filtered to obtain a brown solid, which was washed with water and then dried. The dried brown solid was purified by silica gel column chromatography (petroleum ether as the mobile phase) and repeatedly recrystallized from hot ethyl acetate or hot diethyl ether to obtain pure 2,9-2Br-DBCOT (150 mg, 17%) as a white solid.

[0064] The characterization data of the prepared product 2,9-2Br-DBCOT are as follows: 1 H NMR (600MHz, CD3COCD3): δ (ppm) 7.37 (m, 2H), 7.28 (d, J = 2.1Hz, 2H), 7.04 (d, J = 8.3Hz, 2H), 6.81 (s, 2H), 6.77 (s, 2H). 13 C NMR(151MHz,CD3COCD3): δ(ppm)140.1,137.0,133.8,133.6,132.4,131.8,131.0and121.4.HRMS(APCI):[M+H] + calcd for C 16 H 11 Br2 362.9207, found 362.9193.

[0065] Example 2

[0066] Preparation of Schwarz-body carbon nanorings:

[0067] Figure 2 The synthetic route of Schwarz carbon nanorings is as follows:

[0068] In a nitrogen-filled glove box, bis(1,5-cyclooctadiene)nickel (138 mg, 0.50 mmol), anhydrous tetrahydrofuran (20 mL), and 2,2'-bipyridine (78 mg, 0.50 mmol) were sequentially added to a glass bottle equipped with a stir bar, and the mixture was reacted at 60°C for 30 minutes. In the glove box, compound 2,9-2Br-DBCOT (90 mg, 0.25 mmol) and tetrahydrofuran (100 mL) were added to a thick-walled glass pressure vessel equipped with a stir bar. The mixture in the glass bottle was then transferred to the pressure vessel via syringe and reacted at 65°C for 24 hours. The reaction mixture was cooled to room temperature and purified by column chromatography (using 300 mesh silica gel as the stationary phase and a mixed solvent of ethyl acetate / chloroform with a volume ratio of 1:2 as the mobile phase) to obtain pure white powder Schwarz-body carbon nanorings SNR1 (25 mg, 50%), SNR2 (4.0 mg, 8%) and SNR3 (8.5 mg, 17%).

[0069] The characterization data of the prepared products are as follows:

[0070] SNR1: 1 H NMR (600MHz, CD2Cl2): δ (ppm) 7.54–7.49 (m, 2H), 7.32 (d, J = 2.0Hz, 2H), 7.18 (dd, J = 8.0, 1.8Hz, 2H), 7.11(dd,J=8.1,1.9Hz,2H),6.99(d,J=8.0Hz,2H),6.93(dd,J=11.1,8.1Hz,4H),6.83–6.68(m,16H). 13 C NMR (151MHz, CD2Cl2): δ (ppm) 140.5, 140.3, 138.2, 138.1, 138.0, 137.3, 136.6, 136.3, 134.9, 133. 9,133.6,133.5,133.5,133.4,133.1,129.9,128.9,128.85,128.75,128.4,125.1,124.9,123.7and 122.6.HRMS(MALDI):[M] + calcd for C 48 H 30 606.2348,found 606.2429.

[0071] SNR2: 1 H NMR (600MHz, CD2Cl2): δ (ppm) 7.61 (d, J = 2.1Hz, 6H),

[0072] 7.55(dd,J=8.3,2.0Hz,6H),6.99(d,J=8.3Hz,6H),6.89(s,6H),6.82(s,6H). 13 CNMR(151MHz,CD2Cl2):δ(ppm)and 138.3,137.0,134.8,133.8,133.2,129.0,123.9and122.5.HRMS(MALDI):[M] + calcd for C 48 H 30 606.2348, found 606.2350.

[0073] SNR3: 1 H NMR (600MHz, CDCl3): δ (ppm) 7.30 (dd, J = 8.1, 1.9Hz,

[0074] 8H),7.25(s,8H),7.08(d,J=8.1Hz,8H),6.82(s,8H),6.77(d,J=1.9Hz,8H). 13 CNMR (151MHz, CDCl3): δ (ppm) 139.3, 137.5, 136.2, 133.6, 133.2, 129.9, 129.2, 128.4, 127.9, 125.7. HRMS (MALDI): [M] + calcd for C 64 H 40 808.3130, found 808.3132.

[0075] Example 3

[0076] Preparation of 2,9-2Br-DBCOT single crystal:

[0077] Figure 3 Schematic diagram of the single crystal structure of 2,9-2Br-DBCOT, the specific preparation method is as follows:

[0078] 2,9-2Br-DBCOT (9 mg, 0.025 mmol) prepared in Example 1 was dissolved in 3 mL of dichloromethane and ultrasonicated for 2 minutes to promote its dissolution. The solution was then filtered and placed in a 10 mL sample bottle. The sample bottle was placed in a larger sample bottle with 6 mL of n-hexane, sealed, allowed to stand, and stored in the dark for 3 days to allow the n-hexane to fully and slowly diffuse into the dichloromethane. Regular colorless transparent crystals, i.e., 2,9-2Br-DBCOT crystals, can be observed at the bottom of the sample bottle.

[0079] The structure of the crystal can be characterized by X-ray single crystal diffraction. Figure 3 The specific structural parameters are listed in Table 1.

[0080] Table 1

[0081]

[0082] Example 4

[0083] Preparation of Schwarz-body carbon nanoring SNR1 single crystal:

[0084] Figure 4 Schematic diagram of the single crystal structure of SNR1. The specific preparation method is as follows:

[0085] SNR1 (5 mg, 0.008 mmol) prepared in Example 2 was dissolved in 3 mL of dichloromethane and ultrasonically promoted its dissolution for 2 minutes. The solution was then filtered and placed in a 10 mL sample bottle. The sample bottle was placed in a larger sample bottle containing 6 mL of normal hexane, sealed, allowed to stand, and stored in dark for 3 days to allow normal hexane to fully and slowly diffuse into the dichloromethane. Regular colorless transparent crystals, i.e., SNR1 crystals, were observed at the bottom of the sample bottle.

[0086] The structure of the crystal can be characterized by X-ray single crystal diffraction. Figure 4 The specific structural parameters are listed in Table 2.

[0087] Table 2

[0088]

[0089] Example 5

[0090] Preparation of Schwarz-body carbon nanoring SNR2 single crystal:

[0091] Figure 5 Schematic diagram of the single crystal structure of SNR2. The specific preparation method is as follows:

[0092] SNR2 (5 mg, 0.008 mmol) prepared in Example 2 was dissolved in 3 mL of dichloromethane and sonicated for 2 minutes to promote its dissolution. The solution was then filtered and placed in a 10 mL sample bottle. The sample bottle was placed in a larger sample bottle containing 6 mL of n-hexane, sealed, allowed to stand, and stored in the dark for 3 days to allow the n-hexane to fully and slowly diffuse into the dichloromethane. Regular colorless, transparent crystals, i.e., SNR2 crystals, were observed at the bottom of the sample bottle.

[0093] The structure of the crystal can be characterized by X-ray single crystal diffraction. Figure 5 The specific structural parameters are listed in Table 3.

[0094] Table 3

[0095]

[0096] Example 6

[0097] Preparation of Schwarz-body carbon nanoring SNR3 single crystal:

[0098] Figure 6 Schematic diagram of the single crystal structure of SNR3, the specific preparation method is as follows:

[0099] SNR3 (5 mg, 0.006 mmol) prepared in Example 2 was dissolved in 3 mL of chloroform, and ultrasonically promoted its dissolution for 2 minutes. The solution was then filtered and placed in a 10 mL sample bottle. The sample bottle was placed in a larger sample bottle containing 6 mL of methanol, sealed, left to stand, and stored in dark for 3 days so that methanol could fully and slowly diffuse into the chloroform. Regular colorless transparent crystals, i.e., SNR3 crystals, were observed at the bottom of the sample bottle.

[0100] The structure of the crystal can be characterized by X-ray single crystal diffraction. Figure 6 The specific structural parameters are listed in Table 4.

[0101] Table 4

[0102]

[0103] Example 7

[0104] Fullerenes, including C60 and C70, generally have typical electron-deficient properties. The Schwarz-body carbon nanoring SNR3 prepared by the present invention has a distinct electron-rich cavity, and the cavity size is very compatible with C60, allowing for a significant host-guest inclusion complex. The ultraviolet absorption spectrum of the Schwarz-body carbon nanoring SNR3 and C60 / C70 complex is shown in the figure below. Figure 7 As shown in Figure 2 , UV absorption spectroscopy titration revealed that gradually increasing the equivalent of C60 in a fixed concentration of SNR3 solution significantly enhanced the solution's UV absorption. Under the same conditions, the UV absorption increase in a mixed solution of SNR3 and C70 was smaller. This indicates a significantly stronger interaction between SNR3 and C60. This significant difference in the complexation between SNR3 and C60 / C70 can be further exploited to achieve effective separation of C60 / C70.

[0105] Example 8

[0106] The Schwarz-body carbon nanoring SNR3 crystallization process achieves effective separation of C60 and C70. The specific operation process is as follows:

[0107] SNR3 (3.2 mg, 0.004 mmol), C60 (2.88 mg, 0.004 mmol), and C70 (3.36 mg, 0.004 mmol) prepared in Example 2 were dissolved in 5 mL of toluene and sonicated for 2 minutes to promote dissolution. The solution was then filtered and placed in a 10 mL pressure-resistant sample bottle. The solution was heated to 110°C and then slowly cooled to 25°C. Dark red regular crystals were visible at the bottom of the sample bottle, which were single crystals of the complex of SNR3 and C60. Figure 8 A schematic diagram shows the process of SNR3 and C60 combining to form a cocrystal. C70 remains in the mother liquor. Proton NMR spectroscopy revealed that the complex crystals contain only SNR3 and C60, with no apparent C70, while the mother liquor contains only C70. This indicates that C60 is virtually completely removed through the crystallization process, with a separation efficiency of greater than 99%.

[0108] The SNR3 and C60 complex crystals are then collected and redissolved in hot toluene. SNR3 and pure C60 are recovered by column chromatography. The mother liquor is concentrated and then separated by column chromatography to obtain pure C70. The above column chromatography separation of SNR3, C60, and C70 employs 300-mesh silica gel as the stationary phase and a 1:1 volume ratio of dichloromethane / ethyl acetate mixed solvent as the mobile phase. This effectively separates and enriches C60 and C70, and SNR3 can be reused repeatedly, avoiding the high energy consumption and low efficiency of traditional separation methods.

[0109] The structure of the single crystal of the SNR3 and C60 complex can be characterized by X-ray single crystal diffraction. Figure 9 The specific structural parameters are listed in Table 5.

[0110] Table 5

[0111]

[0112] The above experimental and comparative results show that:

[0113] The present invention develops a novel method for synthesizing Schwarz-body carbon nanorings, resulting in a series of Schwarz-body carbon nanorings with different configurations and cavity sizes. Compared to traditional Schwarz-body molecular synthesis, the present method offers advantages such as efficient and convenient synthesis, high ring formation yield, good universality, simple operation, low equipment requirements, and mild reaction conditions. The resulting Schwarz-body carbon nanorings can be used for the effective separation of fullerene allotropes such as C60 and C70, effectively avoiding the high pollution, high energy consumption, and low efficiency of traditional separation processes, and have great application value in the separation of fullerene allotropes.

[0114] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A Schwarz carbon nanoring, characterized in that: It has the structure shown in the following formula (I): In formula (I), n represents the number of dibenzocyclooctatetraene structural units in the Schwarz-type carbon nanoring, and is an integer selected from 3 to 7.

2. The Schwarz carbon nanoring according to claim 1, wherein: The Schwarz carbon nanoring has a structure shown in any one of the following formulas (II) to (IV):

3. The method for synthesizing Schwarz-body carbon nanorings according to claim 1 or 2, wherein: The Schwarz-body carbon nanoring is synthesized by a Yamamoto coupling reaction catalyzed by a nickel catalyst using a compound 2,9-dibromodibenzo[a,e]-cyclooctene having a structure shown in the following formula (V) as a monomer; 4. The synthesis method according to claim 3, characterized in that Dissolve bis(1,5-cyclooctadiene)nickel, 2,2'-bipyridine and the compound 2,9-dibromodibenzo[a,e]-cyclooctene in an organic solvent, heat and stir to react under the protection of an inert gas, and separate and purify the product by column chromatography after the reaction to obtain the Schwarz-body carbon nanoring.

5. The synthesis method according to claim 4, characterized in that The molar ratio of bis(1,5-cyclooctadiene)nickel, 2,2'-bipyridine and the compound 2,9-dibromodibenzo[a,e]-cyclooctene is 2:2:1; The ratio of the compound 2,9-dibromodibenzo[a,e]-cyclooctene to the organic solvent is 0.25 mmol:100-150 mL; The organic solvent is at least one of anhydrous tetrahydrofuran, toluene, and acetonitrile; The inert gas is a rare gas and / or nitrogen; The heating and stirring reaction temperature is 60-80°C and the time is 20-28 hours; The column chromatography method used 300 mesh silica gel as the stationary phase and a mixed solvent of ethyl acetate / chloroform with a volume ratio of 1:2 as the mobile phase.

6. The synthesis method according to any one of claims 3 to 5, characterized in that The synthesis method of the compound 2,9-dibromodibenzo[a,e]-cyclooctene comprises the following steps: under inert gas protection, stirring and heating a mixture of anhydrous N,N-dimethylformamide and sodium iodide to 165-175° C., adding compounds A,A,A',A', and 4-pentabromo-o-xylene having the structure represented by the following formula (VI), and reacting at 165-175° C. with stirring. After the reaction, adding water and sodium thiosulfate, collecting a solid product, washing and drying it, purifying it by silica gel column chromatography, and repeatedly recrystallizing it using hot ethyl acetate or hot ether to obtain the compound 2,9-dibromodibenzo[a,e]-cyclooctene.

7. The synthesis method according to claim 6, characterized in that The ratio of anhydrous N,N-dimethylformamide, sodium iodide and compound A,A,A',A',4-pentabromo-o-xylene is 10 mL:50 mmol:5 mmol; The stirring reaction time at 165-175° C. is 3-5 hours; The silica gel column chromatography method uses petroleum ether as the mobile phase.

8. Use of the Schwarz-body carbon nanoring according to claim 1 or 2 in separation of fullerene allotropes.

9. The use according to claim 8, characterized in that The Schwarz carbon nanorings are used to separate C60 and C70.

10. A method for separating C60 and C70, characterized in that: The Schwarz body carbon nanorings according to claim 1 or 2 are dissolved in a toluene solution containing C60 and C70, and the resulting solution is heated to 105-115°C and then cooled to room temperature to precipitate complex crystals of the Schwarz body carbon nanorings and C60, while C70 remains in the liquid phase. The solid and liquid are separated, and the complex crystals of the Schwarz body carbon nanorings and C60 are redissolved in hot toluene. The Schwarz body carbon nanorings and pure C60 are recovered by column chromatography, and the liquid phase is concentrated and separated by column chromatography to obtain pure C70.

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