Chiral copper nanoclusters and methods of making the same

Abstract

The application belongs to the field of nanomaterials, and provides a chiral copper nanocluster and a preparation method thereof. 20 X 12 Y6, wherein X represents a dehydrogenated alkyne ligand, Y represents a dehydrogenated acid ligand, and the acid ligand is R-2-phenylpropionic acid or S-2-phenylpropionic acid. The chiral copper nanocluster has high structural stability, and the provided preparation method has mild reaction and high yield.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterials, and in particular to a chiral copper nanocluster and a preparation method thereof. Background Art

[0002] Metal nanoclusters are relatively stable aggregates of several to thousands of metal atoms, formed through chemical bonds or weak interactions. They can exhibit optical and catalytic properties distinct from those of bulk metals. In ligand-protected coinage metal nanoclusters, gold, silver, and copper all belong to the first subgroup and share the same outer electron structure. When ligands coordinate with these metals to form clusters, they possess identical or similar core and surface structures.

[0003] Compared to gold and silver, copper has a larger storage capacity, lower cost, and better catalytic properties. However, research on copper-based metal nanoclusters currently lags far behind that of gold and silver nanoclusters, particularly in the area of ​​chiral copper nanoclusters. This is because the preparation of copper clusters containing zero-valent copper atoms is more difficult than that of gold and silver clusters. For one thing, monovalent copper is difficult to reduce to zero-valent copper atoms. Even when sufficient reducing agents are provided in experiments, copper-hydrogen clusters (Cu(+1)-H(-1)) are more likely to form, rather than reduced clusters with free electrons. Furthermore, zero-valent copper atoms are more sensitive to oxygen and are easily oxidized in air.

[0004] The currently developed reduced copper nanoclusters are very limited. Related technologies include [Cu 25 H 22 (PPh3) 12 ]Cl、[Cu 29 Cl4H 22 (Ph2phen) 12 ]Cl, etc., as well as sulfur and alkyne ligand protected [Cu 13 (S2CN n Bu2)6(C≡CR)4](PF6) + However, these reduced copper nanoclusters still have problems such as air sensitivity and poor stability. No chiral reduced copper nanoclusters have been synthesized. Moreover, the synthesis conditions of reduced copper clusters are harsh, the synthesis process is complex, and the yield is low. There are two main synthesis methods: one uses copper salts as raw materials, and its yield does not exceed 50% (based on copper). The other uses other copper clusters as raw materials. Although the direct yield can reach up to 80%, the yield is still less than 50% when calculated based on the copper salt raw materials.

[0005] Therefore, the research and development of reduced copper nanoclusters still needs to be further deepened. Summary of the Invention

[0006] The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

[0007] According to the first aspect of the invention, the present invention provides a chiral copper nanocluster, wherein the chiral copper nanocluster has the molecular formula Cu 20 X 12 Y6, wherein X represents a dehydrogenated alkyne ligand, Y represents a dehydrogenated acid ligand, and the acid ligand is R-2-phenylpropionic acid or S-2-phenylpropionic acid. The chiral copper nanoclusters of the present invention provide dual protection of the copper core by the alkyne ligand and the phenylpropionic acid ligand, effectively improving the structural stability of the copper nanoclusters.

[0008] According to some embodiments of the present invention, the alkyne ligand includes at least one alkyne compound of the general formula ZC≡CH, wherein Z is a substituted or unsubstituted phenyl group, and the substituent is trifluoromethyl, methyl, methoxy, fluorine, chlorine, bromine or iodine.

[0009] According to some embodiments of the present invention, the molecular formula of the chiral copper nanocluster is

[0010] Cu 20 (p-CF3C6H4C≡C) 12 [R-C6H5CH(CH3)COO]6 or Cu 20 (p-CF3C6H4C≡C) 12 [S-C6H5CH(CH3)COO]6.

[0011] According to some embodiments of the present invention, the core of the chiral copper nanocluster is composed of 20 Cu atoms, the center of which is a tetrahedron [Cu4] containing two free electrons. 2+ There is a Cu atom above each face of the tetrahedron, forming Cu8 composed of 5 coplanar tetrahedra. The remaining 12 atoms are divided into 4 groups, 3 in each group, around the C3 axis, and each group is connected to one of the 4 vertices of the central tetrahedron.

[0012] According to a second aspect of the invention, the present invention provides a method for preparing the chiral copper nanoclusters, comprising:

[0013] (1) mixing a first solvent with a copper precursor, an alkyne ligand, and an acid ligand to obtain a first solution;

[0014] (2) mixing the first solution with a second solvent and performing a pre-reaction to obtain a first suspension;

[0015] (3) mixing the first suspension with a base to obtain a second suspension;

[0016] (4) Mixing the second suspension with a reducing agent to perform a reduction reaction.

[0017] The method provided by the present invention can synthesize chiral copper nanoclusters with high stability, and the method has mild reaction conditions, simple operation and high yield of the target product.

[0018] According to some embodiments of the present invention, the copper precursor includes [Cu(CH3CN)4]A, wherein A represents an anion and is BF4 - 、F - 、Cl - Br - 、ClO4 - PF6 - 、NO3 - or IO4 - .

[0019] According to some embodiments of the present invention, in step (1), the molar ratio of the copper precursor, the acid ligand and the alkyne ligand is 10:(2-6):(4-12).

[0020] According to some embodiments of the invention, the first solvent comprises dichloromethane and / or chloroform.

[0021] According to some embodiments of the invention, the second solvent comprises methanol and / or ethanol.

[0022] According to some embodiments of the present invention, in the first solution, the concentration of the copper precursor is 0.01-0.3 mol / L.

[0023] According to some embodiments of the present invention, the volume ratio of the second solvent to the first solvent is 1:(3-10).

[0024] According to some embodiments of the present invention, in step (3), the base includes triethylamine and / or tetramethylethylenediamine.

[0025] According to some embodiments of the present invention, the amount of the base used is 0.5-2 mol relative to 1 mol of the copper precursor.

[0026] According to some embodiments of the present invention, the reducing agent includes at least one of diphenylsilane, dimethylphenylsilane, sodium borohydride and a borane-tert-butylamine complex.

[0027] According to some embodiments of the present invention, step (4) comprises: adding the reducing agent to the second suspension in batches, with the amount added each time accounting for 10%-60% of the total amount of the reducing agent.

[0028] According to some embodiments of the present invention, the amount of the reducing agent is 0.8-5 mol relative to 1 mol of the copper precursor.

[0029] According to some embodiments of the present invention, the temperature of the pre-reaction is 10-40° C., and the time is 5-20 minutes.

[0030] According to some embodiments of the present invention, the reduction reaction is carried out at a temperature of 10-40° C. and for a time of 6-72 hours.

[0031] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic diagram of a process for preparing chiral copper nanoclusters according to some embodiments of the present invention;

[0033] Figure 2 is a molecular structure diagram of the chiral copper nanocluster obtained by X-ray single crystal diffraction according to Example 1;

[0034] Figure 3 Figures 1 and 2 are diagrams of the center of the copper core, the copper core, and the enantiomeric structures of the copper core coordinated with phenylpropionic acid according to some embodiments of the present invention;

[0035] Figure 4 is the UV-visible absorption spectrum of the chiral copper nanoclusters prepared according to Example 1;

[0036] Figure 5 is the ESI-MS mass spectrum of the chiral copper nanoclusters prepared according to Example 1;

[0037] Figure 6 is the H NMR spectrum of the chiral copper nanoclusters prepared according to Example 1;

[0038] Figure 7 Circular dichroism spectra of chiral copper nanoclusters prepared according to Examples 1 and 2. DETAILED DESCRIPTION

[0039] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be understood as limiting the present invention.

[0040] In a first aspect, the present invention provides a chiral copper nanocluster, wherein the molecular formula of the chiral copper nanocluster is Cu 20 X 12 Y6, wherein X represents a dehydrogenated alkyne ligand and Y represents a dehydrogenated acid ligand.

[0041] In the present invention, the acid ligand is R-2-phenylpropionic acid or S-2-phenylpropionic acid.

[0042] In the present invention, the terms "dehydrogenated alkyne ligand" and "alkyne ligand" have different meanings. "Alkyne ligand" refers to the alkyne compound itself that can serve as a copper ligand, while "dehydrogenated alkyne ligand" refers to the alkyne compound that has lost a hydrogen. Similarly, the terms "dehydrogenated acid ligand" and "acid ligand" also have different meanings, with the former referring to the latter that has lost a hydrogen. For example, when the acid ligand is R-2-phenylpropionic acid (R-C6H5CH(CH3)COOH), X in the molecular formula represents R-C6H5CH(CH3)COO.

[0043] In some embodiments, the alkyne ligand includes at least one of the alkyne compounds of the general formula ZC≡CH, wherein Z is a substituted or unsubstituted phenyl group, and the substituent in Z is trifluoromethyl, methyl, methoxy, fluorine (F), chlorine (Cl), bromine (Br) or iodine (I). It should be understood that when Z has a substituent, the number of substituents can be one or more, and when the number of substituents is multiple, each substituent can be the same or different. Specific examples of the alkyne compounds include, but are not limited to, phenylacetylene, 4-trifluoromethylphenylacetylene (p-CF3C6H4C≡CH), 3-trifluoromethylphenylacetylene, 3,5-bis(trifluoromethylphenylacetylene), 4-fluorophenylacetylene, 3-fluorophenylacetylene, 2-fluorophenylacetylene, 3,5-difluorophenylacetylene, 3,4,5-trifluorophenylacetylene, etc.

[0044] In some embodiments, the core of the chiral copper nanocluster is composed of 20 Cu, such as Figure 3 As shown in (a) and (b), the center is a tetrahedron [Cu4] with two free electrons 2+ There is an atom (Cu) directly above each face of the tetrahedron, forming a Cu8 composed of 5 coplanar tetrahedra. The remaining 12 atoms are divided into 4 groups, 3 in each group, around the C3 axis, and each group is connected to one of the 4 vertices of the central tetrahedron.

[0045] In some specific embodiments, the molecular formula of the chiral copper nanocluster is Cu 20 (p-CF3C6H4C≡C) 12 [R-C6H5CH(CH3)COO]6 or Cu 20 (p-CF3C6H4C≡C) 12 [S-C6H5CH(CH3)COO]6. Figure 2 As shown, Cu 20The core is protected by 6 dehydrogenated acid ligands (R-C6H5CH(CH3)COO or S-C6H5CH(CH3)COO) and 12 dehydrogenated alkyne ligands (p-CF3C6H4C≡C), which are arranged around the C3 and C2 axes of the core. The 12 alkyne ligands are all μ4 coordinated and connected to the metal core through σ and π bonds. Since phenylpropionic acid (R-2-phenylpropionic acid, S-2-phenylpropionic acid) is chiral and has no symmetry plane, the overall symmetry becomes T (ignoring the asymmetry caused by the rotation of the benzene ring and trifluoromethyl of the alkyne ligand, and only considering its coordination position). Figure 3 As shown in (c), phenylpropionic acid coordinates with copper through the carboxyl group, specifically through two oxygen atoms connected to the two copper atoms in the core.

[0046] In the chiral copper nanoclusters provided by the present invention, the core copper cluster is protected by chiral phenylpropionic acid and alkyne ligands, reducing the sensitivity of the copper cluster to air and solvents, and the nanoclusters have high stability. For example, the chiral copper nanoclusters can be stored in air for more than one year and are stable in dichloromethane for more than 15 days. In addition, the chiral copper nanoclusters can be applied to chiral catalysis, chiral sensing, chiral recognition and other fields: they can be used as catalysts to obtain chiral molecules in reactions, and can also perform chiral recognition on biomolecules, and use chiral signals to build chiral sensors; the chiral copper nanoclusters are reduced clusters with free electrons, which are more conducive to providing electrons in catalysis to improve catalytic activity compared to traditional copper clusters.

[0047] In a second aspect, the present invention provides a method for preparing the chiral copper nanoclusters, the method comprising the following steps:

[0048] (1) mixing a first solvent with a copper precursor, an alkyne ligand, and an acid ligand to obtain a first solution;

[0049] (2) mixing the first solution with a second solvent and performing a pre-reaction to obtain a first suspension;

[0050] (3) mixing the first suspension with a base to obtain a second suspension;

[0051] (4) Mixing the second suspension with a reducing agent to perform a reduction reaction.

[0052] According to the present invention, the copper precursor can be selected from various copper organic complexes. In some embodiments, the copper precursor includes [Cu(CH3CN)4]A, wherein A represents an anion and is BF4 - 、F - 、Cl - Br - 、ClO4 - PF6 - 、NO3 - or IO4- As an example, the copper precursor is [Cu(CH3CN)4]BF4.

[0053] According to the present invention, the alkyne ligand and the acid ligand are as described in the first aspect of the present invention, and will not be described in detail here.

[0054] In some embodiments, the molar ratio of the copper precursor, acid ligand, and alkyne ligand is 10:(2-6):(4-12); for example, 10:4:8, 10:5:8, 10:3:8, 10:4:9, 10:4:7, 10:3:9, etc. By controlling the molar ratio of the copper precursor, acid ligand, and alkyne ligand within the above range, the stability of the copper nanoclusters can be improved, and the reaction can be promoted to be stable and efficient, the production of by-products can be reduced, and the yield of the target product can be increased.

[0055] In some embodiments, the first solvent comprises dichloromethane and / or chloroform.

[0056] In some embodiments, in the first solution, the amount of the first solvent is such that the concentration of the copper precursor is 0.01-0.3 mol / L, for example, 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.05 mol / L, 0.08 mol / L, 0.1 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, etc.

[0057] In some examples, step (1) includes:

[0058] (1-1) contacting the copper precursor, the acid ligand, and a first solvent, and stirring until dissolved to obtain a first mixed solution;

[0059] (1-2) Adding the alkyne ligand dispersed in the first solvent to the first mixed solution to obtain the first solution.

[0060] According to the present invention, in step (2), the second solvent is added to the first solution, and the reactants start to react to obtain a suspension.

[0061] In some embodiments, the second solvent comprises methanol and / or ethanol.

[0062] In some embodiments, the volume ratio of the second solvent in step (2) to the first solvent in step (1) is 1:(3-10), for example, 1:3, 1:4, 1:5, 1:6, 1:7, 1:9, etc.

[0063] In some embodiments, in step (2), the temperature of the pre-reaction is 10-40°C, for example, 10°C, 15°C, 18°C, 20°C, 22°C, 25°C, 28°C, 30°C, 33°C, 36°C, etc.; the time of the pre-reaction is 5-20 minutes, for example, 5 minutes, 10 minutes, 15 minutes, etc.

[0064] According to the present invention, in step (3), the acid ligand and the alkyne ligand can be dehydrogenated by introducing a base, thereby coordinating with the copper. In some embodiments, the base comprises at least one of triethylamine and tetramethylethylenediamine. Preferably, the base is triethylamine, which can further improve the yield.

[0065] In some embodiments, the amount of the base used is 0.5-2 mol, such as 0.5 mol, 0.7 mol, 0.8 mol, 0.9 mol, 1 mol, 1.1 mol, 1.5 mol, etc., relative to 1 mol of the copper precursor.

[0066] According to the present invention, in step (4), the addition of the reducing agent can reduce the copper ions in the copper precursor to monovalent copper and zero-valent copper. The reducing agent can be a strong reducing agent (e.g., sodium borohydride) or a weak reducing agent (e.g., an arylsilane compound). In some embodiments, the reducing agent includes at least one of diphenylsilane, dimethylphenylsilane, sodium borohydride, and a borane-tert-butylamine complex. Preferably, the reducing agent is diphenylsilane and / or diphenyldimethylphenylsilane, which can further improve the stability of the reduction reaction.

[0067] In some embodiments, step (4) includes: adding the reducing agent to the second suspension in batches, with each addition amount accounting for 10%-60% of the total amount of the reducing agent (for example, 15%, 20%, 25%, 30%, 33%, 40%, 43%, 45%, 50%, 57%, 60%, 66%, 75%, etc. of the total amount of the reducing agent is added independently each time). This can further avoid the catalytic effect of copper causing hydrogen to overflow and weaken the reducing effect of the reducing agent. The inventors found that the generation rate of hydrogen is difficult to accurately control. Adding the reducing agent multiple times to perform a multi-stage reduction reaction can reduce the uncertainty of the decay rate caused by adding the reducing agent at one time, improve the reduction effect, and avoid excessive reduction causing cluster agglomeration, thereby increasing the yield of the target product.

[0068] In some embodiments, in step (4), the temperature of the reduction reaction is 10-40°C, for example, 10°C, 15°C, 18°C, 20°C, 22°C, 25°C, 28°C, 30°C, 33°C, 36°C, 40°C, etc.; the time of the reduction reaction is 6-72 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours, 11 hours, 12 hours, 15 hours, 16 hours, 20 hours, etc. As an example, the time of the reduction reaction is 6-15 hours. It should be understood that when the reducing agent is added in batches, the time of the reduction reaction refers to the total reduction reaction time. As an example, step (4) includes adding the reducing agent in batches (for example, twice, three times or more) to the second suspension for reduction reaction, and the time of the reduction reaction after each addition of the reducing agent is 0.5-12 hours, for example, 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, etc.

[0069] According to the present invention, in order to obtain high-purity chiral copper nanoclusters, in some embodiments, the method further comprises:

[0070] (5) The crude product obtained in step (4) (a solid-liquid mixture containing a solvent and chiral copper nanoclusters) is subjected to post-treatment. The post-treatment method can be carried out according to existing processes, for example, by removing the solvent by rotary evaporation of the solution, and the obtained product is washed with methanol to obtain a powder product.

[0071] Optionally, the method comprises:

[0072] (6) crystallizing the powder product. The crystallization may include dissolving the powder product in dichloromethane, using n-hexane or methanol as a precipitant, and performing diffusion crystallization at -30°C to 30°C for 5-14 days to obtain chiral copper nanocluster crystals. It should be understood that "optionally" means including or excluding the scenario described thereafter. For example, "optionally, the method includes: step (6)" means that the method may include step (6) or may not include step (6).

[0073] In some specific embodiments, the chiral copper nanoclusters prepared by the method of the present invention are Cu 20 (p-CF3C6H4C≡C) 12 [R-C6H5CH(CH3)COO]6 or Cu 20 (p-CF3C6H4C≡C) 12 [S-C6H5CH(CH3)COO]6, combined Figure 1 , the method includes the following process:

[0074] S1: Add Cu(CH3CN)4]BF4 solid, phenylpropionic acid viscous solution, 4-trifluoromethylphenylacetylene and dichloromethane into a flask and stir magnetically to obtain a colorless solution;

[0075] S2: Methanol is added to the colorless solution, and the solution gradually turns into a bright yellow suspension;

[0076] S3: Triethylamine was added to the suspension, and the suspension first turned reddish brown and then gradually turned yellow-green;

[0077] S4: Then, a portion of diphenylsilane (Ph2SiH2) is added to the yellow-green suspension to react to obtain a light brown suspension. A small amount of gas is generated during the reaction.

[0078] S5: adding the remaining diphenylsilane in one or more portions and continuing the reaction to obtain a transparent wine-red solution;

[0079] S6: The solution was rotary evaporated to remove the solvent, and the obtained product was washed with methanol (post-treatment) to obtain a bright orange powder product.

[0080] The method provided by the present invention has mild operating conditions. The reaction does not need to be isolated from oxygen and moisture and can be carried out in the air. The yield of the obtained chiral copper nanoclusters is high, reaching more than 70%, which is much higher than the yield of other methods for synthesizing reduced copper clusters.

[0081] The following are specific examples. Unless otherwise specified, all reagents used in the following examples are commercially available or can be synthesized according to known methods. Reaction conditions not listed are also readily available to those skilled in the art.

[0082] In the following examples, unless otherwise stated, the preparation of chiral copper nanoclusters was carried out at room temperature.

[0083] Example 1

[0084] Preparation of chiral copper nanoclusters Cu 20 (p-CF3C6H4C≡C) 12 [R-C6H5CH(CH3)COO]6 (hereinafter referred to as "R-Cu 20 ”).

[0085] [Cu(CH3CN)4]BF4 (2 g, 6.4 mmol) and R-2-phenylpropionic acid (346 mg, 2.3 mmol) were added to a 500 mL round-bottom flask. 200 mL of dichloromethane was added to the flask and stirred with a magnetic stirrer for 10 minutes. Next, 4-trifluoromethylphenylacetylene (645 μL, 4.6 mmol) was dispersed in 5 mL of dichloromethane using a pipette and added to the round-bottom flask to obtain a colorless, transparent solution.

[0086] 30 mL of methanol was added to the solution, resulting in a bright yellow suspension. After stirring for 10 minutes, triethylamine (960 μL, 6 mmol) was added via pipette. The suspension immediately turned reddish-brown and then gradually yellow-green. After stirring for 15 minutes, diphenylsilane (740 μL, 4 mmol) dispersed in 5 mL of methanol was added to the flask. Stirring continued for another 4 hours, the suspension gradually turned light brown with a small amount of gas evolution. Diphenylsilane (370 μL, 2 mmol) dispersed in 5 mL of methanol was added again, and stirring continued for another 4 hours, resulting in a transparent wine-red solution. The solution was removed from the solvent using a rotary evaporator and washed with methanol (3 times, 15 mL each time) to obtain a bright orange powder product with a yield of 1 g and a yield of 75% (based on the amount of copper). The powder product was dissolved in dichloromethane and crystallized using n-hexane as a precipitant at 4°C for 14 days to obtain a single crystal.

[0087] Example 2

[0088] Preparation of chiral copper nanoclusters Cu 20 (p-CF3C6H4C≡C) 12 [S-C6H5CH(CH3)COO]6 (hereinafter referred to as "S-Cu 20 ”).

[0089] [Cu(CH3CN)4]BF4 (629 mg, 2 mmol) and S-2-phenylpropionic acid (135 mg, 0.9 mmol) were added to a 250 mL round-bottom flask. 85 mL of dichloromethane was added to the flask and stirred with a magnetic stirrer for 10 minutes. Next, 4-trifluoromethylphenylacetylene (224 μL, 1.6 mmol) was dispersed in 5 mL of dichloromethane using a pipette and added to the round-bottom flask to yield a clear, colorless solution.

[0090] 15 mL of methanol was added to the solution, resulting in a bright yellow suspension. After stirring for 10 minutes, triethylamine (300 μL, 1.9 mmol) was added via pipette, causing the suspension to immediately turn reddish-brown and then gradually turn yellow-green. After stirring for 15 minutes, diphenylsilane (370 μL, 2 mmol) dispersed in 5 mL of methanol was added to the flask. Stirring continued for another 4 hours, the suspension gradually turned light brown with a small amount of gas evolving. Diphenylsilane (293 μL, 1.5 mmol) dispersed in 5 mL of methanol was added again, and stirring continued for another 4 hours, resulting in a transparent wine-red solution. The solution was removed from the solvent using a rotary evaporator and washed with methanol (3 times, 15 mL each time) to yield 298 mg of a bright orange powder, a yield of 71% (based on the amount of copper). The powder was dissolved in dichloromethane and crystallized using n-hexane as a precipitant at 4°C for 14 days to obtain single crystals.

[0091] The products prepared in Examples 1 and 2 were characterized. The single crystal data of the single crystal products were collected by single crystal X-ray diffractometer testing. All data were collected on Agilent SuperNova. The X-ray used was CuK α , the results are as follows Figure 2 and Figure 3 The UV-visible absorption spectrum (UV) of the powder product was collected by Cary 5000 using a 10 mm cuvette. Figure 4 Electrospray ionization time-of-flight mass spectrometry data (ESI-MS) were collected by Bruker impact II, and the results were shown in FIG. Figure 5 As shown; 1 H NMR data were collected on a JEOL ECS-400 spectrometer at 400 MHz. Figure 6 As shown; Circular dichroism absorption spectrum data (CD) was collected by J-1500 circular dichroism spectrometer, using nitrogen as protective gas and 10mm cuvette. The results are shown in Figure 7 shown.

[0092] Figure 2 R-Cu 20 As shown in the figure, Cu 20 The core is protected by 6 dehydrogenated acid ligands and 12 dehydrogenated alkyne ligands, which are arranged around the C3 and C2 axes of the core.

[0093] Figure 3 (a) and (b) represent R-Cu 20 and S-Cu 20 Core (Cu 20 ) central part, Cu20 Structural diagram of the core, Cu 20 In the core, the center is a tetrahedron [Cu4] with two free electrons 2+ , there is an atom (Cu) directly above each face of the tetrahedron, forming a Cu8 composed of 5 coplanar tetrahedra. The remaining 12 atoms are divided into 4 groups, 3 in each group, around the C3 axis, and each group is connected to one of the 4 vertices of the central tetrahedron; (c) is R-Cu 20 and S-Cu 20 Diagram of the enantiomeric structure of the copper core coordinated with phenylpropionic acid, which is coordinated to copper through the carboxyl group.

[0094] Figure 4 This is the UV-visible absorption spectrum of R-Cu20. It can be seen from the figure that the cluster has an absorption peak at 486nm and 322nm respectively. Among them, the absorption peak at 486nm comes from the electron transition between the core and the ligand, indicating the possible existence of free electrons.

[0095] Figure 5 R-Cu 20 ESI-MS mass spectrum of Cu 20 (p-CF3C6H4C≡C) 12 In [C6H5CH(CH3)COO]6, 20 Cu atoms are +1 valence atoms, and there are two free electrons that are regarded as -1 valence atoms. The phenylpropionic acid ligand and the alkyne ligand are -1 valence atoms, and the molecule is neutral. No other anions or cations that can serve as counterions were found in the single crystal data. Neutral molecules without charge cannot show signals in electrospray mass spectrometry, but for clusters, the departure of ligands or the coordination of additional ligands will make the cluster charge non-zero, and signals will also appear in ESI-MS. In the ESI-MS test, Cu 20 The crystals were dissolved in dichloromethane and ESI-MS signals were observed in negative ion mode. The strongest isotope peak in the spectrum was m / z = 4344.2, which was the same as [Cu 20 (C9H4F3) 12 (C8H9COO)7] - The simulated structure is consistent with that of Cu 20 The other three weaker isotope peaks are m / z = 4281.4, corresponding to [Cu 20 –(Cu + )+PPA(-1)+(H + )] - ; m / z = 4233.4, corresponding to [Cu 20 –2(Cu + )+(H + )+2(CH3OH)] -; m / z = 4068.4, corresponding to [Cu 20 –2(Cu + )+(H + )] - All peaks have a negative charge, and the charge balance of the molecular formula matches the assumption that the number of free electrons is 2. 20 It is a neutral molecule.

[0096] Figure 6 R-Cu 20 The H NMR spectrum in deuterated dichloromethane, where peaks a, b, and c are the peaks of the phenylpropionic acid ligand. 1 H, the peak area ratio is 1:3:5; peaks d and e are the peaks of the alkyne ligand 1 H, the peak area ratio is 1:1, which is consistent with the structure of their respective ligands. 1 The ratio of H. Comparison of the peak areas of the two ligands showed that the ratio of phenylpropionic acid ligand to alkyne ligand was 1:2.

[0097] Figure 7 R-Cu 20 and S-Cu 20 Circular dichroism spectrum of Cu 20 It is a single chiral cluster that can be characterized using circular dichroism spectroscopy. 20 The circular dichroism spectra showed that the Cu 20 They are single chiral and are enantiomers of each other. Figure 7 As shown, R-Cu 20 With S-Cu 20 The circular dichroism absorption spectrum curve of is mirror-symmetrical with zero absorption as the symmetry axis, which is a sign that the two are enantiomers. The absorption peaks are located at 530nm, 440nm, 405nm, 359nm, 307nm and 270nm. The maximum anisotropy factor g is 1.4×10 -3 , at 443nm. 20 The chirality is due to the coordination of the phenylpropionic acid ligand, but the circular dichroism absorption spectrum of phenylpropionic acid itself has no signal above 250nm. The enhanced circular dichroism signal after coordination comes from the electron transition between the metal core and the ligand. Phenylpropionic acid itself has chirality but no chromophore; the metal core can provide a chromophore but does not have chirality itself. When the two are combined, electrons can transition from the core to the chiral ligand, causing MLCT and energy transfer, which then reveals a spectrum with a strong circular dichroism signal. Cu 20 With a peak above 450nm, Cu 20 The free electrons in the ion participate in MLCT, are less bound, transition more easily, and require less energy, so they can exhibit circular dichroism absorption peaks at longer wavelengths.

[0098] In the description of this specification, the reference terms "one embodiment", "some embodiments", "implementation methods", "examples", "specific examples", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0099] In the description of the present invention, "a plurality of" or "at least one" means two or more, unless otherwise clearly and specifically defined.

[0100] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A chiral copper nanocluster, characterized in that: The molecular formula of the chiral copper nanocluster is Cu 20 X 12 Y6, wherein X represents a dehydrogenated alkyne ligand, Y represents a dehydrogenated acid ligand, and the acid ligand is R-2-phenylpropionic acid or S-2-phenylpropionic acid; The alkyne ligand comprises at least one alkyne compound of the general formula ZC≡CH, wherein Z is a substituted or unsubstituted phenyl group, and the substituent is trifluoromethyl, methyl, methoxy, fluorine, chlorine, bromine or iodine; The molecular formula of the chiral copper nanocluster is Cu 20 ( p -CF3C6H4C≡C) 12 [R-C6H5CH(CH3)COO]6 or Cu 20 ( p -CF3C6H4C≡C) 12 [S-C6H5CH(CH3)COO]6; The core of the chiral copper nanocluster is composed of 20 Cu atoms, the center of which is a tetrahedron [Cu4] containing two free electrons. 2+ , there is a Cu atom on each face of the tetrahedron, forming a Cu8 composed of 5 coplanar tetrahedra, and the remaining 12 atoms are divided into 4 groups of 3, around C 3 axes, each group is connected to one of the four vertices of the central tetrahedron.

2. A method for preparing the chiral copper nanoclusters according to claim 1, characterized in that: The method comprises the following steps: (1) mixing a first solvent with a copper precursor, an alkyne ligand, and an acid ligand to obtain a first solution; (2) mixing the first solution with the second solvent and performing a pre-reaction to obtain a first suspension; (3) mixing the first suspension with a base to obtain a second suspension; (4) Mixing the second suspension with a reducing agent to carry out a reduction reaction.

3. The method according to claim 2, characterized in that The copper precursor includes [Cu(CH3CN)4]A, wherein A represents an anion and is BF4 - 、F - 、Cl - Br - 、ClO4 - PF6 - 、NO3 - or IO4 - .

4. The method according to claim 2, characterized in that In step (1), the molar ratio of the copper precursor, the acid ligand and the alkyne ligand is 10:(2-6):(4-12); The first solvent includes dichloromethane and / or chloroform; The second solvent includes methanol and / or ethanol; In the first solution, the concentration of the copper precursor is 0.01-0.3 mol / L; The volume ratio of the second solvent to the first solvent is 1:(3-10).

5. The method according to claim 2, characterized in that In step (3), the base includes triethylamine and / or tetramethylethylenediamine; The amount of the base used is 0.5-2 mol relative to 1 mol of the copper precursor.

6. The method according to claim 2, characterized in that The reducing agent includes at least one of diphenylsilane, dimethylphenylsilane, sodium borohydride and borane-tert-butylamine complex; Step (4) comprises: adding the reducing agent to the second suspension in batches, with the amount added each time accounting for 10%-60% of the total amount of the reducing agent; The amount of the reducing agent used is 0.8-5 mol relative to 1 mol of the copper precursor.

7. The method according to claim 2, characterized in that The pre-reaction temperature is 10-40° C. and the reaction time is 5-20 minutes; and / or The reduction reaction temperature is 10-40° C., and the time is 6-72 hours.

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