Stable high-nuclear rare earth-transition metal clusters and their preparation method and application

Abstract

The present invention discloses a stable high-nuclear rare earth-transition metal cluster compound and its preparation method and application. The high-nuclear rare earth-transition metal cluster compound has a hollow tetrahedral structure and its chemical formula is Ni 78 Gd 132 C 384 N 72 O 936 Cl 44 H 1196 or Ni 78 Eu 132 C 424 N 72 O 961 Cl 44 H 1326 The present invention uses iminodiacetic acid as a ligand, Gd or Eu as a rare earth metal, and Ni as a transition metal. By rationally and precisely controlling the component ratios and heat treatment conditions, a new tetrahedral high-nuclearity rare earth-transition metal cluster with a cavity is synthesized, solving the technical problem of efficiently and controllably synthesizing stable high-nuclearity rare earth-transition metal clusters. This high-nuclearity rare earth-transition metal cluster has high stability and is not only suitable for catalyzing various Lewis acid-catalyzed organic reactions, but can also be used as a heterogeneous molecular catalyst with size selectivity for the raw materials.

Description

Technical Field

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

[0002] Zero-dimensional high-nuclearity rare earth-transition metal clusters, as an emerging class of crystalline compounds, have established an important connection between single-atom materials and nanomaterials due to their unique geometric morphology and nanoscale size. This type of compound has shown unique advantages in fields such as bioimaging, low-temperature magnetic refrigeration, and catalysis. Although some research on high-nuclearity rare earth-transition metal clusters has achieved some results, most of the known compounds of this type are solid structures, with only a few having cavities, and their applications are mainly concentrated in the fields of luminescence, single-molecule magnetism, and magnetic refrigeration. The large-scale synthesis and structural stability issues of rare earth-transition metal clusters have limited their in-depth research in catalytic organic reactions.

[0003] Therefore, it is particularly important to synthesize stable high-core rare earth-transition metal clusters with cavities and nanometer size and apply them to catalytic research. Summary of the Invention

[0004] The present invention provides a stable high-nuclear rare earth-transition metal cluster and its preparation method and application to solve one or more technical problems existing in the prior art and at least provide a beneficial choice or create conditions.

[0005] To overcome the above technical problems, the present invention synthesizes a novel tetrahedral high-nuclearity rare earth-transition metal cluster with a cavity, using iminodiacetic acid as a ligand, Gd or Eu as a rare earth metal, and Ni as a transition metal, by rationally and precisely controlling the component ratios and heat treatment conditions. This solves the technical problem of efficiently and controllably synthesizing stable high-nuclearity rare earth-transition metal clusters. Furthermore, the high-nuclearity rare earth-transition metal cluster of the present invention exhibits high stability and is suitable not only for catalyzing various Lewis acid-catalyzed organic reactions, but also as a size-selective heterogeneous molecular catalyst for the raw materials.

[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 tetrahedral structure and a molecular formula of Ni 78 Gd 132 C 384 N 72 O 936 Cl 44 H 1196 or Ni 78 Eu 132 C 424 N 72 O961 Cl 44 H 1326 .

[0007] Preferably, the high-nuclear rare earth-transition metal cluster belongs to the cubic system, space group I-43m.

[0008] Preferably, the unit cell parameters of the high-nuclear rare earth-transition metal cluster are: a=b=c=39.314(2), α=β=γ=90°, V=60762(9), corresponding to the cluster Ni 78 Gd 132 C 384 N 72 O 936 Cl 44 H 1196 ; or a=b=c=39.6726(19), α=β=γ=90°, V=62441(9), corresponding to the cluster Ni 78 Eu 132 C 424 N 72 O 961 Cl 44 H 1326 .

[0009] Preferably, the high-nuclear rare earth-transition metal cluster is assembled from two assembly units connected by hydroxide bridges, wherein one assembly unit is 4 triangles {Gd 27 Ni 12} unit or {Eu 27 Ni 12} units, and the other part of the assembled units are 6 strip-shaped {Gd4Ni5} units or {Eu4Ni5} units.

[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 iminodiacetic acid, a nickel 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 compound.

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

[0014] Preferably, the soluble nickel salt is at least one of nickel acetate tetrahydrate, nickel chloride hexahydrate, and nickel 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 nickel source is (0.8-1.2):1.

[0025] Further preferably, the molar ratio of the rare earth metal source to the nickel source is (0.95-1.05):1.

[0026] Preferably, in step (1), the molar ratio of the nickel source to the iminodiacetic acid is (1.5-2.0):1.

[0027] Further preferably, the molar ratio of the nickel source to the iminodiacetic acid is (1.8-1.9):1.

[0028] Preferably, in step (1), the molar ratio of the base to the iminodiacetic acid is (9.0-10.4):1.

[0029] More preferably, the molar ratio of the base to the iminodiacetic acid is (10.0-10.2):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 48-72 hours.

[0033] More preferably, the holding time at the highest temperature is 60-72 hours.

[0034] Preferably, in step (2), the heating rate of the heat treatment is 60-80°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 compound of the present invention contains a plurality of rare earth ions and transition metal ions with Lewis acidity and has a hollow geometric structure, and is suitable for catalyzing organic reactions.

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

[0042] Compared with the prior art, the above technical solution of the present invention has at least the following technical effects or advantages:

[0043] (1) The high-nuclear rare earth-transition metal cluster compound synthesized in the present invention is the 3d-Gd-based cluster compound with the highest nucleus number reported so far. Its molecular structure has a cavity and a tetrahedral shape and is highly stable.

[0044] (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.

[0045] (3) The high-nuclearity rare earth-transition metal clusters synthesized by the present invention can be used as heterogeneous molecular catalysts to efficiently catalyze the Knoevenagel condensation reaction. The cavity size of the high-nuclearity rare earth-transition metal cluster molecules can be utilized to selectively activate aromatic aldehydes of different molecular sizes, selectively catalyzing small aromatic aldehydes while having lower catalytic activity for large aromatic aldehydes. 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

[0046] Figure 1 The molecular skeleton of the cationic cluster [Gd 132 Ni 78 (OH)292 (IDA) 48 (CH3COO) 96 (NO3) 12 (H2O) 78 ] 56+ Schematic diagram of a baseball bat;

[0047] Figure 2 Triangular {Gd 27 Ni 12} units and ribbon-like {Gd4Ni5} units are assembled into tetrahedral {Gd 132 Ni 78}Schematic diagram;

[0048] Figure 3 Gd cluster 132 Ni 78 The structure is a four-layer nested structure diagram from the inside out;

[0049] Figure 4 Gd cluster 132 Ni 78 Diagram of the Gd-O polyhedral unit cell in the structure;

[0050] Figure 5 Gd cluster 132 Ni 78 Diagrams of three different coordination environments of the Ni(II) ion in the Ni-O / N polyhedral unit of the structure;

[0051] Figure 6 Gd cluster 132 Ni 78 Simulated powder diffraction and comparison of powder diffraction before catalysis and after 8 catalytic cycles. DETAILED DESCRIPTION

[0052] 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.

[0053] Example 1

[0054] A synthesis of a high-nuclear rare earth-transition metal cluster comprises the following steps:

[0055] 0.50 mmol of iminodiacetic acid, 1.875 mmol of nickel acetate tetrahydrate, 1.875 mmol of gadolinium chloride hexahydrate, and 0.85 mmol of potassium chloride were dissolved in a mixed solvent of 4.0 mL of water and 4.0 mL of methanol, 5.0 mmol of triethylamine was added, and the mixture was stirred at room temperature for 15 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 cooling rate of 10° C. / h to obtain blue block crystals, which are the high-nuclear rare earth-transition metal cluster compounds (abbreviated as cluster compounds Gd) of this embodiment. 132 Ni 78 ). Yield: 33%; Elemental analysis results: Ni 78 Gd 132 C 384 N 72 O 936 Cl 44 H 1196 :C 9.47, N 2.07, H 2.47; Found: C 9.51, N 2.07H 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).

[0056] Example 2

[0057] A synthesis of a high-nuclear rare earth-transition metal cluster comprises the following steps:

[0058] 0.50mmol of iminodiacetic acid, 1.875mmol of nickel acetate tetrahydrate, 1.875mmol of europium nitrate hexahydrate, and 0.85mmol of potassium chloride were dissolved in a mixed solvent of 4.0mL of water and 4.0mL of methanol, 5.0mmol of triethylamine was added, and the mixture was stirred at room temperature for 15min. 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 at this temperature for 72h, and then cooled to room temperature at a cooling rate of 10°C / h to obtain blue block crystals, which are the high-nuclear rare earth-transition metal clusters (abbreviated as clusters Eu2O3) of this embodiment. 132 Ni 78 ). Yield: 30%; Elemental analysis results: Ni 78 Eu 132 C 424 N 72 O 961 Cl 44 H 1326:C 10.39, N 2.06, H 2.72; Found: C 10.35, N 2.10, H 2.85. 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).

[0059] Obviously, the above examples are merely illustrative examples for clarity of explanation and are not intended to limit the implementation methods. 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 iminodiacetic acid, soluble nickel salt, soluble gadolinium salt (soluble europium salt), and triethylamine described in this invention; 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 implementation methods, obvious variations or modifications derived therefrom remain within the scope of protection of this invention.

[0060] Structural characterization

[0061] 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 elemental analysis, thermogravimetric analysis, and charge balance analysis confirmed the cluster Gd 132 Ni 78 The exact chemical formula and unit cell parameters of the crystal are shown in Table 1.

[0062] Table 1: Cluster Gd 132 Ni 78 Crystallographic parameters of

[0063]

[0064] From Table 1 we can see that the cluster compound Gd 132 Ni 78 , belongs to the cubic crystal system, the space group is I-43m, and the molecular formula is: (NO3) 12 @[Gd132 Ni 78 (OH) 292 (IDA) 48 (CH3COO) 96 (NO3) 12 (H2O) 78 ]Cl 44 ·110H2O, where: IDA represents iminodiacetate; unit cell parameters are: a=b=c=39.314(2), α=β=γ=90°, V=60762(9). Cluster compound Gd 132 Ni 78 It contains 132 Gd(III) ions, 78 Ni(II) ions, 292 coordinated hydroxide ions, 78 coordinated water molecules, 24 nitrate ions, 96 acetate ions, 48 ​​deprotonated iminodiacetate ions, 12 free nitrate ions in the cavity, and 110 free water molecules on the periphery.

[0065] Cluster Gd 132 Ni 78 The crystal structure of Figure 1-5 As shown. Among them, Figure 1 The molecular skeleton of the cationic cluster [Gd 132 Ni 78 (OH) 292 (IDA) 48 (CH3COO) 96 (NO3) 12 (H2O) 78 ] 56+ Ball-and-stick diagram (color code: Gd pink, Ni green, O red, C gray, N blue); Figure 2 Triangular {Gd 27 Ni 12} units and ribbon-like {Gd4Ni5} units are assembled into tetrahedral {Gd 132 Ni 78} (color code: Gd pink, Ni green, O red, C gray, N blue); Figure 3 Gd cluster 132 Ni 78 The structure is a four-layer nested structure diagram from the inside out; Figure 4 Gd cluster 132 Ni 78 Diagram of the Gd-O polyhedral unit cell in the structure; Figure 5 Gd cluster 132 Ni 78 Three different coordination environment diagrams of the Ni(II) ion in the Ni-O / N polyhedral unit in the structure.

[0066] like Figure 2 As shown, the cluster compound Gd 132 Ni 78 It can be seen as being assembled from two assembly units, where the first assembly unit is a triangular {Gd 27 Ni 12}, the second assembly unit is approximately ribbon-shaped {Gd4Ni5}, and the entire molecule can be regarded as composed of four triangular {Gd 27 Ni 12} units and 6 ribbon {Gd4Ni5} units are assembled through hydroxide bridges. In addition, the molecular structure of the entire cluster can be regarded as a nested structure composed of four layers of metal ions. The metal distribution from the inside to the outside is 12 Gd(III) ions, 30 Ni(II) ions, 120 Gd(III) ions, and 48 Ni(II) ions. The arrangement of metal ions from the inside to the outside can be described by Gd 12 @Ni 30 @Gd 120 @Ni 48 To express, such as Figure 3 shown.

[0067] like Figure 4 As shown, in the cluster compound Gd 132 Ni 78 In the ion structure, all Gd(III) ions are 9-coordinated, showing a slightly distorted three-capped triangular prism configuration. The Ni(II) ions show three different coordination numbers and coordination configurations, such as Figure 5 As shown. The first type: Ni(II) ion is coordinated with 5 hydroxide ions, presenting a 5-coordinate environment, which is a square pyramid configuration. The second type: Ni(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: Ni(II) ion is coordinated with 5 oxygens (from iminodiacetic acid, acetate, and hydroxide ion) and 1 N atom (from iminodiacetic acid), presenting a 6-coordinate environment, which is an octahedral configuration.

[0068] Performance Testing

[0069] The high-nuclearity rare earth-transition metal clusters synthesized by the present invention contain multiple Lewis-acidic rare earth ions and transition metal ions and have a hollow geometric structure that can be used to catalyze organic reactions. The Knoevenagel condensation reaction is an important C-C bond formation reaction. For example, the condensation reaction between malononitrile and aldehyde under Lewis acid or base catalysis produces the target product. This reaction has been used to prepare biologically active molecules and is one of the important approaches for preparing covalent organic frameworks (COFs) materials.

[0070] The cluster compound Gd 132 Ni78 It is used as a Lewis acid catalyst to catalyze the condensation reaction of aromatic aldehydes and malononitrile. The reaction process is as follows:

[0071]

[0072] Wherein: The structural formula and yield of reaction product 3 are as follows:

[0073]

[0074] Aromatic aldehyde 1a and malononitrile 2a were used as the reaction substrates. At 60°C, under the conditions of a toluene (Toluene) and ethanol (EtOH) volume ratio of 1:1, the catalyst Gd 132 Ni 78 The dosage is 0.02 mol%, and aromatic aldehydes of different sizes show different activities under the same reaction conditions. The yields of benzaldehyde (3aa), p-methylbenzaldehyde (3ab), p-chlorobenzaldehyde (3ac), 1-naphthaldehyde (3ad), and 2-naphthaldehyde (3ae) reacted with malononitrile were as high as 99%, while the yield of 1-pyrenecarboxaldehyde (3af) with a relatively large size dropped to 59%, and the yield of 9-anthracenealdehyde (3ag) dropped to 20%. It can be seen that the cluster compound Gd 132 Ni 78 It can be used as a molecular catalyst that is selective for molecular size and is used to catalyze organic reactions.

[0075] After the catalyst was catalyzed for 8 cycles, it still had a high catalytic activity. The powder diffraction test showed that the powder diffraction of the catalyst after 8 catalytic cycles was not much different from that before catalysis, indicating that the structure of the catalyst did not collapse and had a high stability. Figure 6 shown.

[0076] 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 tetrahedral structure and its molecular formula is (NO3) 12 @[Gd 132 Ni 78 (OH) 292 (IDA) 48 (CH3COO) 96 (NO3) 12 (H2O) 78 ]Cl 44 110H2O, where IDA represents iminodiacetic acid with two protons removed.

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 cubic system, space group I -43 m .

3. The high-nuclearity rare earth-transition metal cluster according to claim 1, characterized in that The unit cell parameters of the high-nuclear rare earth-transition metal cluster are: a = b = c = 39.314(2), α = β = γ = 90°, V = 60762(9).

4. The high-nuclearity rare earth-transition metal cluster according to any one of claims 1 to 3, characterized in that: The high-nuclear rare earth-transition metal cluster is assembled from two assembly units connected by hydroxide bridges, wherein one assembly unit is composed of four triangles {Gd 27 Ni 12 } unit, and the other part of the assembly unit is 6 strip-shaped {Gd4Ni5} units.

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 iminodiacetic acid, a nickel 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; the molar ratio of the rare earth metal source to the nickel source is (0.8-1.2):1, the molar ratio of the nickel source to the iminodiacetic acid is (1.5-2.0):1, and the molar ratio of the base to the iminodiacetic acid is (9.0-10.4):1; (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 nickel source is a soluble nickel salt; and / or, the gadolinium source is a soluble gadolinium salt; and / or, the base is an organic base; And / or, the alkali metal chloride is potassium chloride; And / or, the solvent is a mixed solvent of water and methanol.

7. The method for preparing a high-nuclear rare earth-transition metal cluster according to claim 5 or 6, characterized in that: In step (2), the heat treatment temperature is 150-170° C., and the heat preservation time is 48-72 hours.

8. The method for preparing a high-nuclear rare earth-transition metal cluster according to claim 7, characterized in that: The heating rate of the heat treatment is 60-80°C / h; and / or the cooling rate of the heat treatment is 5-15°C / h.

9. Use of the high-nuclearity rare earth-transition metal cluster compound according to any one of claims 1 to 4 in a knoevenagel condensation reaction.

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