An ultra-stable strong luminescent n-heterocyclic carbene-protected chiral heterometallic cluster and a preparation method thereof

Abstract

This invention belongs to the interdisciplinary field of coordination chemistry and nanomaterials, and discloses an ultrastable, strongly luminescent N-heterocyclic carbene-protected chiral heterometallic cluster and its preparation method. It is prepared by a simple synthetic method using a chiral N-heterocyclic carbene as the protecting ligand. Its chemical formula is: C 72 H 61 AuCl6Cu4F6N8O 0.5 P (abbreviated as: R / S -NHC ql -AuCu4 ‑ Cl), belongs to the orthorhombic crystal system, and its space group is chiral space group. C 2221. Another of the nanoclusters has the chemical formula: C 77 H 73 AuBr4Cl2Cu4F6N8O 1.5 P (abbreviated as: R / S -NHC ql -AuCu4 ‑ Br), belongs to the orthorhombic crystal system, and its space group is chiral space group. P 212121. These clusters have their structure in the air and can be stable up to 150°C. R / S -NHC ql -AuCu4 ‑ Br exhibits strong orange luminescence in air at room temperature, with a fluorescence quantum yield of 62%. Its chiral structure and strong luminescence give it excellent chiral luminescence properties, making it promising for applications in holographic projection, information storage, and cell imaging.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of coordination chemistry and nanomaterials, and relates to an ultrastable, strongly luminescent N-heterocyclic carbene-protected chiral heterometallic cluster and its preparation method. Background Technology

[0002] Atomic-precise coin metal (gold, silver, copper) clusters are a class of clusters with precise atomic structures, formed by three or more coin metal atoms through metalophilic interactions, with an outer layer protected by organic ligands. Nanoclusters represent a state of matter between atoms, molecules, and bulk materials, serving as a bridge connecting atoms, molecules, and macroscopic matter. Their size is typically on the nanometer scale, and they often exhibit quantum confinement effects, leading to many novel phenomena and properties. Their excellent photophysical properties and potential applications in catalysis, bioimaging, and other fields have become a research hotspot in materials science and inorganic chemistry in recent years.

[0003] Current research on coin metal nanoclusters mainly focuses on the synthesis and structure of novel nanoclusters. The excellent optical properties, superior lightfastness, and good biocompatibility of nanoclusters make them promising for a wide range of applications. However, the reported stability of coin metal nanoclusters at room temperature is relatively poor, and their luminescence quantum efficiency is also low. These shortcomings significantly hinder the application and development of nanoclusters. Therefore, designing and synthesizing atomically precise nanoclusters with high luminescence efficiency is one of the key research areas in the field of nanoclusters.

[0004] Chirality is a ubiquitous phenomenon in nature, and the chirality of nanoclusters can be endowed by chiral ligands. By selecting appropriate chiral ligands, chiral nanocluster structures can be synthesized. Chiral luminescence of chiral nanoclusters has significant potential applications in fields such as holographic projection, information storage, biological cell imaging, and diagnosis and treatment. Summary of the Invention

[0005] The present invention aims to provide an ultra-stable, strongly luminescent N-heterocyclic carbene-protected chiral heterometallic cluster; another objective is to provide a method for its preparation.

[0006] To achieve the objectives of this invention, an ultra-stable, strongly luminescent N-heterocyclic carbene-protected chiral heterometallic cluster was developed, with the chemical formula: C 72 H 61 AuCl6Cu4F6N8O 0.5 P (abbreviated as: R / S-NHC) ql -AuCu4-Cl), belongs to the orthorhombic crystal system, space group C2221, R-NHC ql -AuCu4-Cl: α=90°, β=90°, γ=90°; S-NHC ql -AuCu4-Cl: α=90°, β=90°, γ=90°.

[0007] Another chiral heterometallic cluster has the following chemical formula: C 77 H 73 AuBr4Cl2Cu4F6N8O 1.5 P (abbreviated as: R / S-NHC) ql -AuCu4-Br), belongs to the orthorhombic crystal system, space group is chiral space group P212121, R-NHC ql -AuCu4-Br: α=90°, β=90°, γ=90°; S-NHC ql -AuCu4-Br: α=90°, β=90°, γ=90°.

[0008] Among them, R / S-NHC ql -PF6 is a chiral N-heterocyclic carbene ligand, and its molecular structure is as follows:

[0009]

[0010] The method for preparing the chiral carbene ligand of the present invention is achieved through the following steps:

[0011] A methanol solution of (1R,2R)-(+)-1,2-diphenyl-1,2-ethylenediamine or (1S,2S)-(-)-1,2-diphenyl-1,2-ethylenediamine and glyoxylic acid monohydrate was stirred at room temperature. N-bromosuccinimide (NBS) was added to the mixture and stirred overnight at room temperature. The reaction was quenched with saturated sodium metabisulfite, and the solvent was removed under vacuum to obtain a solid. NaOH solution was added, and the solid was extracted with ethyl acetate. The organic layer was dried with anhydrous magnesium sulfate, and the solvent was removed under vacuum to obtain a chiral imidazole. The synthesized chiral imidazole was dissolved in ethanol, and 2-(chloromethyl)quinoline hydrochloride and sodium bicarbonate were added and refluxed for two days. After filtration, the solvent was removed under vacuum, and the resulting solid was dissolved in dichloromethane. The solid was dried with anhydrous magnesium sulfate, and the solution was filtered. The solvent was removed under vacuum to obtain an oily substance, which was mixed with tetrahydrofuran to obtain a powder. Further washing with tetrahydrofuran and drying under vacuum yielded a white powder. In a flask, the above powder was dissolved in methanol, and an excess of ammonium hexafluorophosphate aqueous solution was added dropwise to form a precipitate. The precipitate was filtered, thoroughly washed with water / methanol, and dried under vacuum to obtain the above R / S-NHC. ql -PF6 chiral carbene ligand ( Figure 1(As shown).

[0012] The method for preparing chiral heterometallic nanoclusters of the present invention is achieved through the following steps:

[0013] The chiral ligand, silver oxide, and tetrabutylammonium hexafluorophosphate were dispersed in a dichloromethane solution and reacted under light-protected conditions with stirring at room temperature. NaOH solution was then added, and the reaction was continued with stirring. The mixture was filtered, and the clear filtrate was concentrated to a minimum volume under vacuum. Ether was added to obtain a large amount of white powder. The white powder was dissolved in dichloromethane, and a dichloromethane solution of thiophene gold was added. The mixture was stirred under light-protected conditions to form a precipitate. The solution was filtered to remove the precipitate, and the clear filtrate was concentrated to a minimum volume. A large amount of ether was added to obtain a white powder. The powder was dissolved in dichloromethane, and CuCl or CuBr was added, with stirring continued to form a yellow solution. The mixture was filtered, and the clear filtrate was concentrated to a minimum volume. A yellow powder was precipitated with ether. The yellow powder was dissolved in dichloromethane and diffused in the gas phase with ether to obtain yellow crystals. The crystals were filtered, washed with ether, and dried at room temperature.

[0014] The chiral heterometallic nanoclusters described above are in the form of R-NHC ql Taking -AuCu4-Br as an example, it is a metallic core composed of four copper atoms and one gold atom, protected by two organic ligands and four iodide ions. Figure 2 (As shown in Figure 3). Five metal atoms form two nearly orthogonal triangular frameworks sharing a single gold atom through metalophilic interactions. Each central gold atom forms strong coordination bonds with a carbene carbon atom. Each copper atom is coordinated by two halogen atoms and one pyridine nitrogen atom.

[0015] The properties of the ultra-stable, strongly luminescent N-heterocyclic carbene-protected chiral heterometallic clusters of this invention are described in detail below:

[0016] The material possesses an ultra-stable crystal structure, maintaining its crystalline structure even at a high temperature of 150°C. Figure 4 (As shown). It exhibits strong orange emission at room temperature in air, with its optimal emission wavelength at 600 nm (excitation wavelength 400 nm). Figure 5 (As shown); the fluorescence quantum yield at room temperature is 62%, which is rare among N-heterocyclic carbene ligand-protected clusters reported to date. High quantum yield is an essential condition for excellent luminescent materials, and high quantum yield cluster materials are a goal pursued by cluster researchers. Chiral ligands endow the entire cluster molecule with chiral properties (as shown). Figure 6 As shown), its chiral structure and strong luminescence give it strong chiral luminescence properties. Figure 7 As shown in the figure, it has great application prospects in fields such as holographic projection, information storage and cell imaging.

[0017] The beneficial effects of this invention are that the heterometallic cluster material of this invention not only has high stability and can maintain its crystalline structure at a high temperature of 150℃, but also has ultra-high luminescence quantum yield and chiral luminescence characteristics, and has great potential for widespread application. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the molecular structure of the chiral carbene ligand of the present invention.

[0019] Figure 2 The present invention is R / S-NHC ql A schematic diagram of a pair of enantiomeric structures of the -AuCu4-Cl cluster material.

[0020] Figure 3 The present invention is R / S-NHC ql A schematic diagram of a pair of enantiomeric structures of the -AuCu4-Br cluster material.

[0021] Figure 4 The present invention is R / S-NHC ql -Powder XRD pattern of AuCu4-Br cluster material.

[0022] Figure 5 The present invention is R-NHC ql Excitation and emission curves of the -AuCu4-Br cluster material.

[0023] Figure 6 The present invention is R / S-NHC ql Chiral circular dichroism chromatogram of the -AuCu4-Br cluster material.

[0024] Figure 7 The present invention is R / S-NHC ql Circular polarization emission curve of the AuCu4-Br cluster material. Detailed Implementation

[0025] The invention will be further illustrated by the following examples:

[0026] Example 1: Synthesis of the chiral carbene ligand of the present invention

[0027] A methanol (100 mL) solution of (1R,2R)-(+)-1,2-diphenyl-1,2-ethylenediamine or (1S,2S)-(-)-1,2-diphenyl-1,2-ethylenediamine (3.00 g, 14.11 mmol) and glyoxylic acid monohydrate (1.50 g, 16.50 mmol) was stirred at room temperature for 4 hours. N-bromosuccinimide (NBS) (3.30 g, 18.00 mmol) was added to the mixture and stirred overnight at room temperature. The reaction was quenched with saturated sodium metabisulfite, and the solvent was removed under vacuum to obtain a solid. The solid was extracted with ethyl acetate after adding 5% NaOH solution. The organic layer was dried over anhydrous magnesium sulfate, and the solvent was removed under vacuum to obtain a chiral imidazole. The synthesized chiral imidazole (2.22 g, 10 mmol) was dissolved in ethanol (100 mL), and 2-(chloromethyl)quinoline hydrochloride (4.38 g, 20.40 mmol) and sodium bicarbonate (2.52 g, 31.12 mmol) were added and refluxed for two days. After filtration, the solvent was removed under vacuum, and the resulting solid was dissolved in dichloromethane, dried with anhydrous magnesium sulfate, and then the solution was filtered. The solvent was removed under vacuum to obtain an oily substance, which was mixed with 15 mL of tetrahydrofuran to obtain a powder. Further washing with tetrahydrofuran and drying under vacuum yielded a white powder. In a flask, the powder was dissolved in methanol, and the addition of excess aqueous solution of ammonium hexafluorophosphate immediately formed a precipitate. The precipitate was filtered, thoroughly washed with water / methanol, and dried under vacuum to obtain the above R / S-NHC. ql -PF6 chiral carbene ligand.

[0028] Example 2: Synthesis of heterometallic clusters of the present invention

[0029] The chiral ligand (0.65 g, 1 mmol), silver oxide (66 mg, 0.28 mmol), and tetrabutylammonium hexafluorophosphate (40 mg) were dispersed in 40 mL of dichloromethane solution and stirred in the dark for 10 minutes at room temperature. Then, 1 M NaOH solution was added, and stirring continued for 4 hours. The mixture was filtered, and the clear filtrate was concentrated to 2 mL under vacuum. Ether was then added to obtain a large amount of white powder. Next, the white powder (0.38 mg, 0.3 mmol) was dissolved in 30 mL of dichloromethane, and 10 mL of a dichloromethane solution of thiophene gold (0.096 g, 0.3 mmol) was added. The mixture was stirred in the dark for 30 minutes to form a precipitate. The solution was filtered to remove the precipitate, and the clear filtrate was concentrated to 2 mL. A large amount of ether was added to obtain a white powder. The above powder (0.05 mmol, 68 mg) was dissolved in 6 mL of dichloromethane. CuCl (0.2 mmol, 24 mg) or CuBr (0.2 mmol, 32 mg) was added, and the mixture was stirred for 3 hours to form a yellow solution. The mixture was filtered, and the clear filtrate was concentrated to 2 mL. The yellow powder was precipitated with diethyl ether. The yellow powder was dissolved in 1 mL of dichloromethane and diffused with diethyl ether in the gas phase to obtain yellow crystals. The crystals were filtered, washed with diethyl ether, and dried at room temperature for use in property testing.

[0030] The heterometallic cluster material of the present invention prepared in Example 2 was further characterized as follows:

[0031] (1) Crystal structure determination

[0032] X-ray single-crystal diffraction data of the complexes were determined using appropriately sized single-crystal samples on a Rigaku XtaLAB Pro single-crystal diffractometer. All data were obtained using graphite-monochromated CuKα rays. The diffraction source was collected at 200 K using ω-scan mode, and corrected for Lp factor and semi-empirical absorption. Structural analysis was performed by first obtaining the initial structure using the direct method with the SHELXL-97 program, and then refining it using the full-matrix least squares method with the SHELXL-97 program. All non-hydrogen atoms were refined using anisotropic thermal parameter methods. All hydrogen atoms were refined using isotropic thermal parameter methods. Detailed crystallographic data are shown in Tables 1 and 2; important bond length data are shown in Tables 3 and 4.

[0033] Tables 1 and 2 contain the main crystallographic data of the chiral heterometallic cluster materials of this invention.

[0034] Table 1. Main crystallographic data

[0035]

[0036] R1=∑||F o |-|F c || / ∑|F o|.wR2=[∑w(F o 2 -F c 2 ) 2 / ∑w(F o 2 ) 2 ] 1 / 2

[0037] Table 2 Main crystallographic data

[0038]

[0039] R1=∑||F o |-|F c || / ∑|F o |.wR2=[∑w(F o 2 -F c 2 ) 2 / ∑w(F o 2 ) 2 ] 1 / 2

[0040] Table 3 R-NHC ql -AuCu4-Cl important bond length

[0041]

[0042] Symmetrical code: 1 1-X,+Y,3 / 2-Z; 2 2-X,+Y,3 / 2–Z.

[0043] Table 4 R-NHC ql -AuCu4-Br important bond length

[0044]

[0045] The above embodiments are only used to illustrate the content of the present invention. Other embodiments of the present invention may also be implemented. However, all technical solutions formed by equivalent substitution or equivalent modification fall within the protection scope of the present invention.

Claims

1. A chiral heterometallic cluster protected by N-heterocyclic carbene, characterized in that: Its chemical formula is: C 72 H 61 AuCl6Cu4F6N8O 0.5 P, abbreviated as: R / S -NHC ql -AuCu4 - Cl belongs to the orthorhombic crystal system and has the space group chiral space group. C 2221, R -NHC ql -AuCu4 - Cl: a = 15.2368(11) Å, b = 25.7783(11) Å, c = 18.9604(11)Å, V = 7447.2(8) Å 3 , α = 90°, β = 90° γ = 90°; S -NHC ql -AuCu4 - Cl: a = 15.2263(15)Å, b = 25.7708(15) Å, c = 18.9483(15)Å, V =7435.2(10)Å 3 , α = 90°, β = 90° γ = 90°; Another chiral heterometallic cluster has the chemical formula: C 77 H 73 AuBr4Cl2Cu4F6N8O 1.5 P, abbreviated as: R / S -NHC ql -AuCu4 - Br belongs to the orthorhombic crystal system and has a chiral space group. P 212121, R -NHC ql -AuCu4 - Br: a = 18.0354(11) Å, b = 19.6631(10) Å, c = 25.8766(15) Å, V = 9176.7(9) Å 3 , α = 90°, β =90° γ = 90°; S -NHC ql -AuCu4 - Br: a = 18.1049(10)Å, b = 19.6370(10) Å, c =25.8205(14) Å, V = 9179.9(9) Å 3 , α = 90°, β = 90° γ = 90°; in R / S -NHC ql - For chiral N-heterocyclic carbene ligands R / S -NHC ql -PF6 forms a group after losing PF6. R / S -NHC ql The simplified structure of PF6 is as follows: 。 2. The chiral heterometallic cluster protected by N-heterocyclic carbene as described in claim 1, characterized in that: It consists of a metallic core composed of four copper atoms and one gold atom, surrounded by two organic ligands and four halide ions; the five metal atoms form two triangular frameworks sharing one gold atom through metalophilic interactions, and the two triangles are orthogonal; each central gold atom forms a strong coordination bond with the carbon atom of the carbene ligand, and each copper atom is coordinated by two halogen atoms and one pyridine nitrogen atom.

3. A method for preparing N-heterocyclic carbene-protected chiral heterometallic clusters as described in claim 1 or 2, characterized in that: This can be achieved through the following steps: (1) Chiral N-heterocyclic carbene ligand, silver oxide and tetrabutylammonium hexafluorophosphate were dispersed in dichloromethane solution in the dark and stirred at room temperature; then NaOH solution was added and the reaction was continued by stirring; the mixture was filtered, the transparent filtrate was concentrated under vacuum, and ether was added to obtain powder; (2) Dissolve the above powder in dichloromethane, add a dichloromethane solution of tetrahydrothiophene gold chloride; place the mixture in a light-protected environment and stir to form a precipitate; filter the solution to remove the precipitate, concentrate the filtrate, and add diethyl ether to obtain the powder; (3) Dissolve the above powder in dichloromethane, add CuCl or CuBr, and continue stirring to form a solution; filter the mixture, concentrate the filtrate, and precipitate the powder with diethyl ether; dissolve the powder in dichloromethane and diffuse it in the gas phase with diethyl ether to obtain the target crystal; the chiral N heterocyclic carbene ligand has the following structural formula: 。

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