High-nuclear rare earth-transition metal cluster compound with cavity and preparation method and application thereof

Abstract

The present invention discloses a high-nuclear rare earth-transition metal cluster compound with a cavity, a preparation method thereof, and an application thereof. The high-nuclear rare earth-transition metal cluster compound has a hollow cubic structure, and its molecular formula is Gd 120 Co 78 C 525 N 138 O 945 Cl 60 H 1386 or Eu 120 Co 78 C 530 N 138 O 930 Cl 60 H 1366 . The high-nuclear rare earth-transition metal cluster compound synthesized by the present invention can be used as a heterogeneous molecular catalyst to efficiently catalyze the cycloaddition reaction of epoxy compounds and carbon dioxide to generate cyclic carbonates; the size of the cavity of the high-nuclear rare earth-transition metal cluster compound molecule itself can be used to achieve substrate size selectivity, and it can selectively catalyze small-sized epoxy compounds, but has low catalytic activity for large-sized epoxy compounds, that is, the high-nuclear rare earth-transition metal cluster compound of the present invention can be used as a heterogeneous catalyst with size selectivity for raw materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of crystalline compounds, and in particular relates to a high-nuclearity rare earth-transition metal cluster compound with a cavity, a preparation method and an application thereof. Background Art

[0002] High-nuclear rare earth-transition metal cage clusters are a newly emerging class of crystalline compounds. They possess precise three-dimensional atomic arrangements and adjustable cavity sizes, exhibiting unique functionalities compared to other porous materials. Compared to mononuclear complexes, high-nuclear rare earth-transition metal cage structures offer abundant metal centers and limited space. Most reported high-nuclear rare earth-transition metal clusters are closed solid structures, and research has primarily focused on magnetism and luminescence, with limited research on catalysis. Furthermore, the majority of reported high-nuclear rare earth-transition metal clusters currently contain nickel, with few reports on cobalt-containing high-nuclear rare earth-transition metal clusters.

[0003] The unique geometry and nanometer size of caged, hollow, high-nuclearity rare earth-transition metal clusters, leveraging the potential for synergistic interactions between multiple metals within them and the specific size of the cavity, allow these compounds to function as heterogeneous Lewis acid catalysts in organic reactions. Carbon dioxide is thermodynamically stable and inert, an abundant, non-toxic gas that is also a major greenhouse gas contributing to global warming. Converting carbon dioxide as a renewable carbon source into various organic compounds is of great practical significance. Summary of the Invention

[0004] The present invention provides a high-nuclearity rare earth-transition metal cluster with a cavity, a preparation method thereof, and an application thereof, in order to solve one or more technical problems existing in the prior art and at least provide a beneficial option or create conditions.

[0005] To overcome the above technical problems, the present invention synthesizes a novel hollow, cubic, high-nuclearity rare earth-transition metal cluster using N-methyliminodiacetic acid as a ligand, Gd or Eu as a rare earth metal, and Co as a transition metal. By precisely controlling the component ratios and heat treatment conditions, this novel cluster solves the technical problem of efficiently and controllably synthesizing stable high-nuclearity rare earth-transition metal clusters. Furthermore, this high-nuclearity rare earth-transition metal cluster exhibits high stability and is suitable for catalyzing various Lewis acid-catalyzed organic reactions. It can also catalyze the cycloaddition reaction of epoxides and carbon dioxide to produce cyclic carbonates.

[0006] The first aspect of the present invention provides a high-nuclear rare earth-transition metal cluster compound, wherein the high-nuclear rare earth-transition metal cluster compound has a hollow cubic structure and a molecular formula of Gd 120 Co 78 C 525N 138 O 945 Cl 60 H 1386 or Eu 120 Co 78 C 530 N 138 O 930 Cl 60 H 1366 .

[0007] Preferably, the high-nuclear rare earth-transition metal cluster belongs to the trigonal system, space group R-3.

[0008] Preferably, the unit cell parameters of the high-nuclear rare earth-transition metal cluster are: a=b=41.410(7), c=92.415(12), α=β=90°, γ=120°, V=137239(49), corresponding to the cluster Gd 120 Co 78 C 525 N 138 O 945 Cl 60 H 1386 ; or a=b=41.411(5), c=92.328(9), α=β=90°, γ=120°, V=137233(36), corresponding to the cluster Eu 120 Co 78 C 530 N 138 O 930 Cl 60 H 1366 .

[0009] Preferably, the framework of the high-nuclear rare earth-transition metal cluster is assembled from two parts of assembly units, wherein: one part of the assembly units is 8 pyramid-shaped {GdCo3} units or {EuCo3} units, and the other part of the assembly units is 12 rod-shaped {Co 3.5 Gd8} unit or {Co 3.5 Eu8} unit; the two parts of the assembly unit are bridged by hydroxide, nitrate and deprotonated iminodiacetate ions.

[0010] The second aspect of the present invention is to provide a method for preparing the above-mentioned high-nuclear rare earth-transition metal cluster, comprising the following steps:

[0011] (1) dissolving N-methyliminodiacetic acid, a cobalt source, a rare earth metal source, and an alkali metal chloride in a solvent, adding a base, and mixing to obtain a mixed solution; the rare earth metal source is a gadolinium source or a europium source;

[0012] (2) heat-treating the mixed solution to obtain the high-nuclearity rare earth-transition metal cluster.

[0013] Preferably, in step (1), the cobalt source is a soluble cobalt salt.

[0014] Preferably, the soluble cobalt salt is at least one of cobalt acetate tetrahydrate, cobalt chloride hexahydrate, and cobalt nitrate hexahydrate.

[0015] Preferably, in step (1), the gadolinium source is a soluble gadolinium salt.

[0016] Preferably, the soluble gadolinium salt is gadolinium nitrate hexahydrate or gadolinium chloride hexahydrate.

[0017] Preferably, in step (1), the europium source is a soluble europium salt.

[0018] Preferably, the soluble europium salt is europium nitrate hexahydrate or europium chloride hexahydrate.

[0019] Preferably, in step (1), the alkali metal chloride is potassium chloride.

[0020] Preferably, in step (1), the base is an organic base.

[0021] Preferably, the organic base is triethylamine.

[0022] Preferably, in step (1), the solvent includes water and methanol.

[0023] Preferably, the volume ratio of the water to the methanol is 1:1.

[0024] Preferably, in step (1), the molar ratio of the rare earth metal source to the cobalt source is (1.0-1.5):1.

[0025] Further preferably, the molar ratio of the rare earth metal source to the cobalt source is (1.2-1.3):1.

[0026] Preferably, in step (1), the molar ratio of the cobalt source to the N-methyliminodiacetic acid is (0.8-1.2):1.

[0027] Further preferably, the molar ratio of the cobalt source to the N-methyliminodiacetic acid is (0.9-1.1):1.

[0028] Preferably, in step (1), the molar ratio of the base to the N-methyliminodiacetic acid is (2.0-2.6):1.

[0029] Further preferably, the molar ratio of the base to the N-methyliminodiacetic acid is (2.1-2.4):1.

[0030] Preferably, in step (2), the maximum temperature of the heat treatment is 150-170°C.

[0031] More preferably, the maximum temperature of the heat treatment is 155-165°C.

[0032] Preferably, in step (2), the holding time at the highest temperature is 60-90 hours.

[0033] More preferably, the holding time at the highest temperature is 70-80 hours.

[0034] Preferably, in step (2), the heating rate of the heat treatment is 60-70°C / h.

[0035] Preferably, the heating rate is uniform.

[0036] Preferably, in step (2), the cooling rate of the heat treatment is 5-15°C / h.

[0037] Preferably, the cooling rate is uniform.

[0038] The third aspect of the present invention is to provide the application of the high-nuclear rare earth-transition metal cluster in the field of catalysis.

[0039] Preferably, the high-nuclearity rare earth-transition metal cluster is used to catalyze organic reactions.

[0040] The high-nuclear rare earth-transition metal cluster of the present invention contains a plurality of rare earth ions (such as Gd 3+ or Eu 3+ ) and transition metal ions (such as Co 2+ ), and has a hollow geometric structure that can be used to catalyze organic reactions. The structural characteristics of the multi-metal center are conducive to the activation and conversion of CO2 by the cluster molecular cage.

[0041] Preferably, the catalyzed organic reaction comprises a Lewis acid-catalyzed organic reaction.

[0042] Preferably, the catalytic organic reaction comprises catalyzing a cycloaddition reaction of an epoxy compound and carbon dioxide to form a cyclic carbonate.

[0043] Compared with the prior art, the above technical solution of the present invention has at least the following technical effects or advantages:

[0044] (1) The high-nuclearity rare earth-transition metal cluster compound synthesized in the present invention is the Co-4f-based cluster compound with the highest nucleus number reported so far. Its molecular structure has a cavity and a cubic shape and has high stability.

[0045] (2) The conditions for synthesizing high-nuclear rare earth-transition metal clusters of the present invention, especially the selection, amount and ratio of raw materials, as well as the heat treatment temperature, can ensure the target product and the repeatability of the synthesis, and is a universal synthesis strategy.

[0046] (3) The high-nuclearity rare earth-transition metal clusters synthesized in the present invention can be used as heterogeneous molecular catalysts to efficiently catalyze the cycloaddition reaction of epoxy compounds and carbon dioxide to produce cyclic carbonates. By utilizing the cavity size of the high-nuclearity rare earth-transition metal cluster molecules themselves, substrate size selectivity can be achieved, enabling selective catalysis of small-sized epoxy compounds while exhibiting lower catalytic activity for large-sized epoxy compounds. In other words, the high-nuclearity rare earth-transition metal clusters of the present invention can be used as heterogeneous catalysts with size selectivity for the raw materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 Cationic cluster molecular skeleton [Co 78 Gd 120 (MIDA) 102 (OH) 216 (NO3) 36 (H2O) 108 ] 60+ Schematic diagram of a baseball bat;

[0048] Figure 2 Cubic framework cluster Co 78 Gd 120 Schematic diagram of the formation process, ball-and-stick views of the building blocks of cubic units, pyramidal {GdCo3} units, and rod-like {Co 3.5 Gd8} unit;

[0049] Figure 3 Cluster Co 78 Gd 120 Diagram of the Gd-O polyhedral unit cell in the structure;

[0050] Figure 4 Cluster Co 78 Gd 120 There are two different coordination environments of the Co-O / N polyhedral unit of Co(II) ion in the structure;

[0051] Figure 5 Cluster Co 78 Gd 120 Diagram of different coordination environments of the Co-O / N polyhedral unit of the central Co(II) ion in the structure;

[0052] Figure 6 With propylene oxide as substrate and catalyst Co 78 Gd 120 Powder diffraction patterns before and after five catalytic cycles;

[0053] Figure 7 Propylene oxide in the presence of catalyst Co 78 Gd 120 Yield plot after five cycles of catalysis. DETAILED DESCRIPTION

[0054] The present invention is described in detail below with reference to the examples to facilitate understanding of the present invention by those skilled in the art. It is necessary to point out that the examples are only used to further illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above-mentioned invention should still fall within the scope of protection of the present invention. At the same time, the raw materials mentioned below that are not described in detail are all commercially available products; the process steps or preparation methods that are not mentioned in detail are all process steps or preparation methods known to those skilled in the art.

[0055] Example 1: [Co 78 Gd 120 (NC5O4H7) 102 (NO3) 36 (OH) 216 (H2O) 108 ](Cl) 60 (H2O) 90 (CH3OH) 15 Synthesis

[0056] A synthesis of a high-nuclear rare earth-transition metal cluster comprises the following steps:

[0057] 1.0 mmol N-methyliminodiacetic acid, 1.0 mmol cobalt acetate tetrahydrate, 1.25 mmol gadolinium nitrate hexahydrate, and 1.7 mmol potassium chloride were dissolved in a mixed solvent of 4.0 mL water and 4.0 mL methanol, 2.40 mmol triethylamine was added, and the mixture was stirred at room temperature for 10-20 min. The resulting solution was transferred to a 20 mL stainless steel reactor lined with polytetrafluoroethylene, and the temperature was increased to 160 ° C. at a heating rate of 65 ° C. / h and kept at this temperature for 72 h, and then cooled to room temperature at a rate of 10 ° C. / h. The filtrate was filtered and poured into an open 25 mL beaker. It was evaporated at room temperature for 4 days to obtain pink block crystals, which are the high-nuclear rare earth-transition metal clusters of this embodiment, denoted as Co 78 Gd 120 Yield: 50%; Elemental analysis results: Gd 120 Co 78 C 525 N 138 O 945 Cl 60 H 1386: C 12.52, N 3.84H 2.77; Found: C 12.58, N 3.79, H 2.55. Infrared IR (KBr, cm -1 ):3369(w),1602(w),1552(s),1407(s),1338(w),1097(w),1020(w),931(w),819(w),719(w),655(w).

[0058] Example 2: [Co 78 Eu 120 (NC5O4H7) 102 (NO3) 36 (OH) 216 (H2O) 108 ](Cl) 60 (H2O) 70 (CH3OH) 20 Synthesis

[0059] A synthesis of a high-nuclear rare earth-transition metal cluster comprises the following steps:

[0060] 1.0mmol N-methyliminodiacetic acid, 1.0mmol cobalt acetate tetrahydrate, 1.25mmol europium nitrate hexahydrate, and 1.7mmol potassium chloride were dissolved in a mixed solvent of 4.0mL water and 4.0mL methanol, 2.40mmol triethylamine was added, and the mixture was stirred at room temperature for 10-20min. The resulting solution was transferred to a 20mL stainless steel reactor lined with polytetrafluoroethylene, and the temperature was increased to 160°C at a heating rate of 65°C / h and kept constant for 72h, and then cooled to room temperature at a rate of 10°C / h. The filtrate was filtered and poured into an open 25mL beaker. It was evaporated at room temperature for 4 days to obtain pink block crystals, which are the high-nuclear rare earth-transition metal clusters of this embodiment, denoted as Co 78 Eu 120 Yield: 55%; Elemental analysis results: Eu 120 Co 78 C 530 N 138 O 930 Cl 60 H 1366 :C 12.85, N 3.90; H 2.78. Found: C 12.92, N 3.93, H 2.59. Infrared IR (KBr, cm -1 ):3371(w),1604(w),1556(s),1407(s),1336(w),1105(w),1022(w),939(w),825(w),715(w),655(w).

[0061] Obviously, the above examples are merely illustrative examples for clarity of explanation and are not intended to limit the embodiments. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. For example, the molar ratios of N-methyliminodiacetic acid, soluble cobalt salt, soluble gadolinium salt (soluble europium salt), and triethylamine described herein; the heat treatment temperature, holding time, and ramp rates; can also produce high-nuclearity rare earth-transition metal clusters with similar structural effects to those of Examples 1-2. While it is not necessary and impossible to exhaustively enumerate all embodiments, obvious variations or modifications derived therefrom remain within the scope of the present invention.

[0062] Structural characterization

[0063] The X-ray single crystal diffractometer was used at 100K using a Bruker D8 micro-focus spot. The data were collected and indexed, integrated, and scaled using APEX3. Multi-scan absorption correction was performed using SADABS. Space groups were determined using XPREP in APEX3. All structures were solved using SHELXS and nonlinear least squares methods were used based on F 2 Analytical refinement was performed using the Olex2 program with the SHELXL program. Anisotropic refinement was performed on all non-hydrogen atoms. All hydrogen atoms were generated using geometric methods and refined using the riding model. Severely misaligned guest molecules and anions were masked with solvent using Olex2, and the cluster was confirmed to be Co by elemental analysis, thermogravimetric analysis, and charge balance. 78 Gd 120 and Co 78 Eu 120 The exact chemical formula and unit cell parameters of the crystal are shown in Table 1.

[0064] Table 1: Cluster Co 78 Gd 120 and Co 78 Eu 120 Crystallographic parameters of

[0065]

[0066]

[0067] From Table 1 we can see that: 78 Gd 120 For example, the cluster compound belongs to the trigonal crystal system, the space group is R-3, and the molecular formula is: [Co 78 Gd 120 (NC5O4H7) 102 (NO3) 36 (OH) 216 (H2O)108 ](Cl) 60 (H2O) 90 (CH3OH) 15 The unit cell parameters are: a=b=41.410(7), c=92.415(12), α=β=90°, γ=120°, V=137239(49). Cluster compound Co 78 Gd 120 It contains 120 Gd(III) ions, 78 Co(II) ions, 216 coordinated hydroxide ions, 108 coordinated water molecules, 36 nitrate ions, 102 deprotonated nitrogen-methyliminodiacetic acid ions (MIDA), 60 free chloride ions inside and outside the molecule, and 90 free water molecules and 15 free methanol molecules on the periphery.

[0068] Cluster Co 78 Gd 120 The crystal structure of Figure 1-5 shown.

[0069] in: Figure 1 The molecular skeleton of the cationic cluster [Co 78 Gd 120 (MIDA) 102 (OH) 216 (NO3) 36 (H2O) 108 ] 60+ Ball-and-stick diagram of atom Gd, with atomic colors: Gd pink, Co green, O red, C gray, and N blue.

[0070] Figure 2 Cubic framework cluster Co 78 Gd 120 Schematic diagram of the formation process ( Figure 2 a) Constructing the ball-and-stick view of the cube unit ( Figure 2 b) triangular pyramid-shaped {GdCo3} unit ( Figure 2 c, d / s-[GdCo3(MIDA)3]) and rod-shaped {Co 3.5 Gd8} unit ( Figure 2 d, MIDA)6(OH)7(NO3)3) (Type II); color code: Gd pink, Co green (atomic occupancy 1.0), Co acid orange (atomic occupancy 0.5), O red, C gray, N blue; hydrogen atoms are omitted for clarity.

[0071] Figure 3 Cluster Co 78 Gd 120The Gd-O polyhedral unit diagram in the structure shows a Gd-O / N polyhedron with two coordination environments. One is an octahedron composed of 1 μ3-OH, 2 O atoms of MIDA, 1 O atom of nitrate and 1 hydrated ligand, as well as 1 N atom (from MIDA); the other is a polyhedron composed of 9 O atoms (from 4 μ3-OH, 3 O atoms of MIDA and 2 O atoms of nitrate).

[0072] Figure 4 Cluster Co 78 Gd 120 The Co-O / N polyhedral unit of the Co(II) ion in the structure has two different coordination environments: one is octahedral, composed of 6 O atoms (from 5 μ3-OH and 1 hydrated ligand); the other is tetrahedral, composed of 4 O atoms (from MIDA, 2 hydrated ligands) and 1 N atom (from MIDA); color code: Gd, pink; Co, green (atomic occupancy 1.0); Co, acid orange (atomic occupancy 0.5); N, blue; O, red; C, gray.

[0073] Figure 5 Cluster Co 78 Gd 120 Diagram of the different coordination environments of the Co-O / N polyhedral unit of the central Co(II) ion in the structure. The Co-O / N octahedron consists of 5 O atoms (from MIDA, acetate, and μ3-OH) and 1 N atom (from MIDA); color code: Co, acid orange (atomic occupancy 0.5); N, blue; O, red; C, gray.

[0074] like Figure 2 As shown, the cluster compound Co 78 Gd 120 The framework can be considered as being composed of two assembly units, the first of which is a pyramid-shaped GdCo3(d / s-[GdCo3(MIDA)3]) and the second is a rod-shaped Co 3.5 Gd8(Co 3.5 Gd8(MIDA)6(OH)7(NO3)3), the entire molecular framework can be seen as consisting of 8 pyramidal GdCo3 units and 12 rod-shaped Co 3.5 The Gd8 units are assembled through bridges of hydroxide, nitrate, and deprotonated iminodiacetate ions.

[0075] like Figure 3 As shown, in the cluster compound Co 78 Gd 120In the ion structure, all Gd(III) ions are 9-coordinated, showing a slightly distorted three-capped triangular prism configuration. The Co(II) ions show three different coordination numbers and coordination configurations, such as Figure 4-5 As shown. The first type: Co(II) ion is coordinated with 5 hydroxide ions, presenting a 5-coordinate environment, which is a square pyramid configuration. The second type: Co(II) ion is coordinated with 5 hydroxide ions and 1 water molecule, with a total of 6-coordinate environment, which is an octahedral configuration. The third type: Co(II) ion is coordinated with 5 oxygen (from MIDA, acetate, and hydroxide ion) and 1 N atom (from MIDA), presenting a 6-coordinate environment, which is an octahedral configuration.

[0076] Performance Testing

[0077] The high-nuclear rare earth-transition metal cluster compound synthesized by the present invention is based on Co 78 Gd 120 For example, it contains multiple Lewis acidic Gd 3+ ions and Co 2+ ions, and its hollow geometric structure can be used to catalyze organic reactions. The structural characteristics of the multi-metal center can be used to activate and convert CO2 using cluster molecular cages.

[0078] The cluster compound Co 78 Gd 120 It is used as a Lewis acid catalyst to catalyze the cycloaddition reaction of epoxy compounds and carbon dioxide. The reaction process is as follows:

[0079]

[0080] Wherein: The structural formula and yield of cyclic carbonate converted from epoxy compound are as follows:

[0081]

[0082] At 25°C and in the absence of solvent, the applicability of cluster molecular cages to the reaction under mild conditions was studied. A series of epoxy compounds of different sizes, including propylene oxide, butylene oxide, epifluoropropane, epichlorohydrin, and epibromopropane, were selected, and the yields all reached over 90%, while the yield of larger styrene oxide was only 50%, and the yield of tert-butyl oxide-substituted propylene oxide was 35%.

[0083] Figure 6 With propylene oxide as substrate and catalyst Co 78 Gd 120 The powder diffraction patterns before and after five catalytic cycles were obtained. Figure 6 It can be seen that the catalyst did not decompose before and after the reaction and had high stability, which shows that Co 78 Gd 120It can act as a heterogeneous catalyst to catalyze such reactions.

[0084] Figure 7 Propylene oxide in the presence of catalyst Co 78 Gd 120 The yield diagram after five cycles of catalysis is given by Figure 7 It can be seen that after 5 catalytic cycles, the yield of cyclic carbonate is still greater than 90%.

[0085] For those skilled in the art to which the present invention belongs, a number of simple deductions or substitutions can be made without departing from the concept of the present invention, without having to resort to creative work. Therefore, based on the disclosure of the present invention, simple improvements made by those skilled in the art to the present invention should be within the scope of protection of the present invention. The above embodiments are preferred embodiments of the present invention, and all processes similar to the present invention and equivalent changes made should fall within the scope of protection of the present invention.

Claims

1. A high-nuclear rare earth-transition metal cluster, characterized in that: The high-nuclear rare earth-transition metal cluster has a hollow cubic structure and its molecular formula is Gd 120 Co 78 C 525 N 138 O 945 Cl 60 H 1386 or Eu 120 Co 78 C 530 N 138 O 930 Cl 60 H 1366 .

2. The high-nuclearity rare earth-transition metal cluster according to claim 1, characterized in that The high-nuclear rare earth-transition metal cluster belongs to the trigonal system, space group R -3.

3. The high-nuclearity rare earth-transition metal cluster according to claim 1, wherein The unit cell parameters of the high-nuclear rare earth-transition metal cluster are: a = b = 41.410(7), c = 92.415(12), α = β =90°, γ = 120°, V = 137239(49); or a = b = 41.411(5), c = 92.328(9), α = β =90°, γ = 120°, V =137233(36).

4. The high-nuclearity rare earth-transition metal cluster according to any one of claims 1 to 3, characterized in that: The framework of the high-nuclear rare earth-transition metal cluster is assembled from two parts of assembly units, wherein one part of the assembly units is 8 pyramid-shaped {GdCo3} units or {EuCo3} units, and the other part of the assembly units is 12 rod-shaped {Co 3.5 Gd8} unit or {Co 3.5 Eu8} unit; the two parts of the assembly unit are bridged by hydroxide, nitrate and deprotonated iminodiacetate ions.

5. A method for preparing a high-nuclearity rare earth-transition metal cluster according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) dissolving N-methyliminodiacetic acid, a cobalt source, a rare earth metal source, and an alkali metal chloride in a solvent, adding a base, and mixing to obtain a mixed solution; the rare earth metal source is a gadolinium source or a europium source; (2) heat-treating the mixed solution to obtain the high-nuclearity rare earth-transition metal cluster.

6. The method for preparing a high-nuclear rare earth-transition metal cluster according to claim 5, characterized in that: In step (1), the cobalt source is a soluble cobalt salt; and / or, the gadolinium source is a soluble gadolinium salt, and the europium source is a soluble europium salt; and / or, the base is an organic base; And / or, the alkali metal chloride is potassium chloride; And / or, the solvent includes water and methanol.

7. The method for preparing a high-nuclear rare earth-transition metal cluster according to claim 5, characterized in that: In step (1), the molar ratio of the rare earth metal source to the cobalt source is (1.0-1.5):1; and / or, the molar ratio of the cobalt source to the N-methyliminodiacetic acid is (0.8-1.2):1; And / or, the molar ratio of the base to the N-methyliminodiacetic acid is (2.0-2.6):

1.

8. The method for preparing a high-nuclear rare earth-transition metal cluster according to any one of claims 5 to 7, characterized in that: In step (2), the maximum temperature of the heat treatment is 150-170° C.; and / or the holding time at the maximum temperature is 60-90 hours.

9. The method for preparing a high-nuclear rare earth-transition metal cluster according to claim 8, characterized in that: The heating rate of the heat treatment is 60-70°C / h; and / or the cooling rate of the heat treatment is 5-15°C / h.

10. Use of the high-nuclearity rare earth-transition metal cluster compound according to any one of claims 1 to 4 in catalyzing the cycloaddition reaction of an epoxy compound and carbon dioxide.

Images