A rare earth cluster material for ultra-low temperature magnetic refrigeration and its preparation method

Abstract

The present invention belongs to the field of magnetic refrigeration technology, specifically relating to a rare earth cluster material for ultra-low temperature magnetic refrigeration and a preparation method thereof. The method comprises the following steps: dissolving Gd(NO3)3·5H2O, N-methyldiethanolamine, and triethylamine in anhydrous CH3OH to obtain a mixture; sealing the mixture and reacting it at 100°C to 150°C to obtain the rare earth cluster material. The present invention prepares a novel ultra-low temperature magnetic refrigeration material based on a "controlled solvent thermal hydrolysis" method. Under a 7T magnetic field, the material exhibits a peak magnetic entropy change near 2K, reaching a magnetic entropy change of 47.2 J kg ‑1 K ‑1 , which is the largest among the pure Gd clusters reported.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnetic refrigeration, and in particular relates to a rare earth cluster material for ultra-low temperature magnetic refrigeration and a preparation method thereof. Background Art

[0002] Ultra-low temperatures, defined as temperatures below 4.2K, are widely used in large scientific facilities, deep space exploration, scientific research, and other technical fields. Currently, three methods exist for achieving ultra-low temperatures: dilution refrigeration, adsorption refrigeration, and magnetic refrigeration. The first two require liquid helium as a refrigerant, a phenomenon known for its low reserves and difficulty in extraction. Magnetic refrigeration utilizes the magnetocaloric effect of magnetic fluids, achieving refrigeration through repeated cycles of isothermal magnetization and adiabatic demagnetization. Magnetic refrigeration offers the advantages of no liquid helium consumption, high efficiency, compactness, and independence from gravity. It is a highly promising technology with significant potential applications in aerospace, medical, electronics, and other fields.

[0003] However, the current ultra-low temperature magnetic refrigeration materials have a low magnetic entropy change at low fields, which is generally less than 15 J kg at 1 Tesla. - 1 K -1 , which restricts the widespread application of magnetic refrigeration technology. The development of materials with high magnetic entropy change at low fields is a key scientific issue currently facing the field of ultra-low temperature magnetic refrigeration.

[0004] Since the magnetic entropy change -ΔSm=nRln(2s+1) is proportional to the spin value s, high-performance magnetic refrigerants must have a large spin value. Gadolinium ion Gd(III) is the best choice for preparing single metal ions of this type of material because of its large ground state spin (4f orbital has 7 unpaired electrons, s=7 / 2) and small magnetic anisotropy. When designing magnetic refrigeration molecules, it is possible to consider aggregating and assembling a large number of gadolinium ions to achieve linear superposition of magnetic entropy changes. However, due to the large radius and high charge of gadolinium ions, how to assemble a large number of metal gadolinium ions to obtain a high magnetic entropy change remains a difficult problem. Summary of the Invention

[0005] In response to the above technical problems, the present invention provides a rare earth cluster material for ultra-low temperature magnetic refrigeration and a preparation method thereof. The present invention is based on the "controlled solvent thermal hydrolysis" method, using anhydrous CH3OH as the reaction solvent, Gd(NO3)3·5H2O as the raw material, N-methyldiethanolamine as the ligand, and under the action of the organic base triethylamine, the assembly of metal gadolinium ions is achieved. The assembled material has a magnetic entropy change peak near 2K under a 7T magnetic field, and the magnetic entropy change reaches 47.2J kg -1 K -1 , which is the largest among the pure Gd clusters reported.

[0006] The present invention is specifically implemented through the following solutions.

[0007] The present invention provides a method for preparing a rare earth cluster material for ultra-low temperature magnetic refrigeration, comprising the following steps:

[0008] Gd(NO3)3·5H2O, N-methyldiethanolamine and triethylamine were dissolved in anhydrous CH3OH to obtain a mixture;

[0009] The mixture is sealed and reacted at 100° C. to 150° C. During the reaction, the crystal water in Gd(NO3)3·5H2O provides water molecules required for the hydrolysis of gadolinium ions, and triethylamine is used to provide an alkaline environment for hydrolysis and to remove H from the hydroxyl group of N-methyldiethanolamine. Under the control of the N-methyldiethanolamine ligand, the gadolinium ions are hydrolyzed and polymerized into cluster materials.

[0010] The present invention is based on the "controlled solvent thermal hydrolysis" method, using anhydrous CH3OH as the reaction solvent and Gd(NO3)3·5H2O as the raw material. Under the action of the organic base triethylamine, the water molecules required for the hydrolysis of gadolinium ions are provided by the crystal water brought by the organic base. The gadolinium ions are hydrolyzed and polymerized into cluster materials under the control of N-methyldiethanolamine, avoiding the problem of precipitation of rare earth metal ions due to simultaneous large-scale hydrolysis, realizing the assembly of a large number of metal gadolinium ions, and successfully preparing a new ultra-low temperature magnetic refrigeration material.

[0011] Rare earth cluster materials for ultra-low temperature magnetic refrigeration, the chemical formula is:

[0012] [Gd 32 (OH) 54 (mdea) 12 (NO3) 12 (H2O) 24 (H2O)6](OH)6·24CH3OH·30H2O, wherein mdea is deprotonated N-methyldiethanolamine.

[0013] In a preferred embodiment of the present invention, the molar ratio of Gd(NO3)3·5H2O to N-methyldiethanolamine is 1:1-3, and the molar ratio of N-methyldiethanolamine to triethylamine is 1:2.

[0014] In a preferred embodiment of the present invention, the molar ratio of Gd(NO3)3·5H2O to anhydrous CH3OH is 10:1.

[0015] In a preferred embodiment of the present invention, after the mixture is sealed, a cluster material is prepared by a one-step reaction, the reaction time of the one-step reaction is 3 days, and after the reaction is completed, the mixture is cooled to room temperature and filtered to obtain the cluster material.

[0016] In a preferred embodiment of the present invention, after the mixture is sealed, a cluster material is prepared by a two-step reaction, and the two-step reaction specifically includes the following steps:

[0017] The mixture is first pre-reacted at 100° C. to 130° C. and filtered to obtain an intermediate compound; the intermediate compound and triethylamine are dissolved in anhydrous CH3OH to obtain a reaction system; the reaction system is placed at 130° C. to 150° C. to continue the reaction, and after completion, it is cooled to room temperature and filtered to obtain the rare earth cluster material.

[0018] In a preferred embodiment of the present invention, during the pre-reaction, the reaction is first carried out at 100° C. to 130° C. for 12 hours. After the reaction is completed, the mixture is naturally cooled to room temperature, allowed to stand for 3 days, and then filtered.

[0019] In a preferred embodiment of the present invention, during the pre-reaction, in the mixture, the molar ratio of Gd(NO3)3·5H2O to N-methyldiethanolamine is 1:1-3, and the molar ratio of N-methyldiethanolamine to triethylamine is 1:2.

[0020] In a preferred embodiment of the present invention, the reaction is continued at 130° C. to 150° C. for 3 days.

[0021] In a preferred embodiment of the present invention, when the reaction is continued, the molar ratio of the intermediate compound to triethylamine is 0.1:2, and the molar ratio of the intermediate compound to anhydrous CH3OH is 1:2.

[0022] Compared with the prior art, the present invention has the following technical effects:

[0023] The present invention is based on a "controlled solvent thermal hydrolysis" method, with anhydrous CH3OH as a reaction solvent, Gd(NO3)3·5H2O as a raw material, N-methyldiethanolamine as a ligand, triethylamine for providing an alkaline environment for hydrolysis and for removing H on the hydroxyl group of N-methyldiethanolamine, Gd(NO3)3·5H2O carries its own crystal water to provide water molecules required for the hydrolysis of gadolinium ions, under the action of the organic base triethylamine, the gadolinium ions are hydrolyzed and polymerized into cluster materials under the control of N-methyldiethanolamine, by limiting the water content in the synthetic reaction system, avoiding the problem of precipitation of rare earth metal ions due to simultaneous large-scale hydrolysis, thereby achieving the assembly of a large number of metallic gadolinium ions.

[0024] The novel ultra-low temperature magnetic refrigeration material prepared by the present invention has a chemical formula of rare earth cluster material [Gd 32 (OH) 54 (mdea) 12 (NO3) 12 (H2O) 24 (H2O)6](OH)6·24CH3OH·30H2O, where mdea is deprotonated N-methyldiethanolamine. Under a 7T magnetic field, its magnetic entropy change peak appears near 2K, and the magnetic entropy change reaches 47.2J kg -1 K -1, which is the largest among the pure Gd clusters reported. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 In which (a) is compound Gd 32 Molecular structure diagram, where purple balls represent gadolinium ions; orange balls represent oxygen atoms; blue balls represent nitrogen atoms; (b) is the metal skeleton structure.

[0026] Figure 2 In which (a) is compound Gd 32 The χ under 1000 Oe magnetic field T vs.T diagram; (b) is χ -1 vs.T curve and its Curie-Weiss fitting (50K~300K); (c) is compound Gd 32 Variable field magnetization intensity curve at 2K~10K; (d) is compound Gd 32 Temperature-dependent magnetic entropy change curves at different magnetic field values. The solid line in (a) and the colored lines in (c) are Monte Carlo calculations.

[0027] Figure 3 In which (a) is compound Gd 32 Molar specific heat data under different magnetic fields; (b) is a comparison diagram of magnetic entropy change calculated by specific heat data (hollow figure) and magnetic data (solid figure).

[0028] Figure 4 Gd 3+ The relationship between the theoretical and experimental maximum magnetic entropy change and magnetic density of the compound. DETAILED DESCRIPTION

[0029] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention is further described below with reference to specific examples and accompanying drawings. However, the examples are not intended to limit the present invention. The experimental methods and detection methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0030] The present invention provides a method for preparing a rare earth cluster material for ultra-low temperature magnetic refrigeration, comprising the following steps:

[0031] Gd(NO3)3·5H2O, N-methyldiethanolamine and triethylamine were dissolved in anhydrous CH3OH to obtain a mixture;

[0032] The mixture is sealed and reacted at 100°C to 150°C. During the reaction, the crystal water in Gd(NO3)3·5H2O provides the water molecules needed for the hydrolysis of gadolinium ions. Triethylamine provides an alkaline environment for hydrolysis and removes hydrogen from the hydroxyl group of N-methyldiethanolamine. Under the control of the N-methyldiethanolamine ligand, the gadolinium ions undergo hydrolysis and polymerization to form cluster materials. The water in the system originates from the crystal water. Controlling the water content avoids the problem of large-scale hydrolysis and precipitation of rare earth metal ions caused by high water content, thereby achieving the assembly of large amounts of metallic gadolinium ions.

[0033] It should be noted that after rare earth metal salt Gd(NO3)3·5H2O, organic chelating agent N-methyldiethanolamine and organic base triethylamine are added to anhydrous CH3OH, the mixture is fully stirred to form a clear solution, and if a small amount of precipitate is present, it is filtered to obtain a mixture.

[0034] In a preferred embodiment of the present invention, after the mixture is sealed, a cluster material is prepared by a one-step reaction. The reaction time of the one-step reaction is 3 days. After the reaction is completed, the mixture is cooled to room temperature and filtered to obtain the cluster material. In a preferred embodiment of the present invention, the mixture can be added to a high-temperature and high-pressure glass bottle, the lid with a rubber gasket is tightened, and the bottle is then placed in an oven and heated to 100°C to 150°C for three days. The crystal water of the rare earth nitrate provides the water molecules required for the hydrolysis of the rare earth ions, which promotes the hydrolysis and polymerization of the rare earth ions under the control of the methyldiethanolamine ligand to form the cluster material. After the reaction, the mixture is naturally cooled to room temperature, and colorless cubic block crystals are formed at the bottom of the bottle. The crystals are filtered, washed with a small amount of methanol, and then vacuum dried.

[0035] Gd(NO3)3·5H2O and organic chelating agent N-methyldiethanolamine can be reacted in a molar ratio range of 1:1 to 1:3 (N-methyldiethanolamine: triethylamine molar ratio = 1:2) to obtain the product. The chemical formula of the product is [Gd 32 (OH) 54 (mdea) 12 (NO3) 12 (H2O) 24 (H2O)6](OH)6·24CH3OH·30H2O, where mdea is deprotonated N-methyldiethanolamine. The product is named Gd 32 .

[0036] The following examples will be used to illustrate this in detail.

[0037] Example 1

[0038] A method for preparing a rare earth cluster material for ultra-low temperature magnetic refrigeration comprises the following steps:

[0039] Gd(NO3)3·5H2O (866 mg, 2 mmol), N-methyldiethanolamine (238 mg, 2 mmol), and triethylamine (405 mg, 4 mmol) were added to 8 mL of anhydrous CH3OH and stirred thoroughly to form a clear solution. If a small amount of precipitate was present, the solution was filtered to obtain a mixture.

[0040] The mixture was added to a 10 mL high-temperature and high-pressure glass bottle, the rubber-matted lid was tightened, and the bottle was placed in an oven and heated to 130°C. After three days of reaction, the temperature was allowed to slowly cool to room temperature. Colorless cubic crystals were formed at the bottom of the bottle. These crystals were filtered, washed with a small amount of methanol, and then vacuum-dried.

[0041] Yield: 270 mg, yield: 43.0% (based on Gd). Elemental analysis: theoretical value (C 84 H 408 Gd 32 N 24 O2O4): C 10.04, H 4.09, N 3.34; elemental analysis test value: C 10.02, H 3.94, N 3.43. Infrared spectrum absorption peak position (KBr pellet, cm -1 ): 3700-300(br,s), 2945(w), 2853(w), 1763(w), 1640(w), 1398(s), 1305(s), 1095(s), 1039(m), 991(w), 900(m), 816(w).

[0042] Example 2

[0043] A method for preparing a rare earth cluster material for ultra-low temperature magnetic refrigeration comprises the following steps:

[0044] Gd(NO3)3·5H2O (2 mmol), N-methyldiethanolamine (6 mmol), and triethylamine (12 mmol) were added to 8 mL of anhydrous CH3OH and stirred thoroughly to form a clear solution. If a small amount of precipitate was present, the solution was filtered to obtain a mixture.

[0045] The mixture was added to a 10 mL high-temperature, high-pressure glass bottle, the rubber-lined lid was tightened, and the bottle was placed in an oven and heated to 130°C. After three days of reaction, the temperature was allowed to slowly cool to room temperature. Colorless cubic crystals formed at the bottom of the bottle. These crystals were filtered, washed with a small amount of methanol, and then vacuum-dried. The yield was 19.4%.

[0046] Example 3

[0047] A method for preparing a rare earth cluster material for ultra-low temperature magnetic refrigeration comprises the following steps:

[0048] Gd(NO3)3·5H2O (2 mmol), N-methyldiethanolamine (4 mmol), and triethylamine (8 mmol) were added to 8 mL of anhydrous CH3OH and stirred thoroughly to form a clear solution. If a small amount of precipitate was present, the solution was filtered to obtain a mixture.

[0049] The mixture was added to a 10 mL high-temperature, high-pressure glass bottle, the rubber-lined lid was tightened, and the bottle was placed in an oven and heated to 130°C. After three days of reaction, the temperature was allowed to slowly cool to room temperature. Colorless cubic crystals formed at the bottom of the bottle. These crystals were filtered, washed with a small amount of methanol, and then vacuum-dried. The yield was 25.7%.

[0050] Example 4

[0051] A method for preparing a rare earth cluster material for ultra-low temperature magnetic refrigeration comprises the following steps:

[0052] Gd(NO3)3·5H2O (2 mmol), N-methyldiethanolamine (2 mmol), and triethylamine (4 mmol) were added to 8 mL of anhydrous CH3OH and stirred thoroughly to form a clear solution. If a small amount of precipitate was present, the solution was filtered to obtain a mixture.

[0053] The mixture was added to a 10 mL high-temperature, high-pressure glass bottle, the rubber-lined lid was tightened, and the bottle was placed in an oven and heated to 100°C. After three days of reaction, the temperature was allowed to slowly cool to room temperature. Colorless cubic crystals formed at the bottom of the bottle. These crystals were filtered, washed with a small amount of methanol, and then dried under vacuum. The yield was 11.2%.

[0054] Example 5

[0055] A method for preparing a rare earth cluster material for ultra-low temperature magnetic refrigeration comprises the following steps:

[0056] Gd(NO3)3·5H2O (2 mmol), N-methyldiethanolamine (2 mmol), and triethylamine (4 mmol) were added to 8 mL of anhydrous CH3OH and stirred thoroughly to form a clear solution. If a small amount of precipitate was present, the solution was filtered to obtain a mixture.

[0057] The mixture was added to a 10 mL high-temperature, high-pressure glass bottle, the rubber-lined lid was tightened, and the bottle was placed in an oven and heated to 150°C. After three days of reaction, the temperature was allowed to slowly cool to room temperature. Colorless cubic crystals formed at the bottom of the bottle. These crystals were filtered, washed with a small amount of methanol, and then vacuum-dried. The yield was 26.8%.

[0058] In the preparation of Gd 32 It can also be carried out in two steps, including the following steps:

[0059] Gd(NO3)3·5H2O, N-methyldiethanolamine and triethylamine were dissolved in anhydrous CH3OH to obtain a mixture;

[0060] The mixture is sealed and reacted at 100-150° C. During the reaction, the crystal water in Gd(NO 3 ) 3 · 5H 2 O provides water molecules required for the hydrolysis of gadolinium ions, and triethylamine is used to provide an alkaline environment for hydrolysis and to remove H from the hydroxyl group of N-methyldiethanolamine. Under the control of the N-methyldiethanolamine ligand, the gadolinium ions are hydrolyzed and polymerized into cluster materials.

[0061] In a preferred embodiment of the present invention, based on the above reaction mechanism, it can be achieved in two steps. The sealed mixture is first pre-reacted at 100°C to 130°C and filtered to obtain an intermediate compound; the intermediate compound and triethylamine are dissolved in anhydrous CH3OH to obtain a reaction system; the reaction system is placed at 130°C to 150°C to continue the reaction, and after the reaction is completed, it is cooled to room temperature and filtered to obtain the rare earth cluster material.

[0062] In a preferred embodiment of the present invention, during the specific operation, the mixture is added to a high-temperature and high-pressure glass bottle, the lid with a rubber gasket is tightened, and then the bottle is placed in an oven and heated to 100-130°C. The reaction is carried out for 12 hours. The crystal water of the rare earth nitrate provides the water molecules required for the hydrolysis of the rare earth, which promotes the hydrolysis and polymerization of the rare earth ions under the control of the methyldiethanolamine ligand. The temperature is naturally and slowly cooled to room temperature. After standing for three days, colorless block crystals are formed at the bottom of the bottle. The crystals are filtered, washed with a small amount of methanol, and then vacuum dried to obtain an intermediate compound. The collected intermediate compound is then added to a high-temperature and high-pressure glass bottle, triethylamine and anhydrous CH3OH are added, the lid with a rubber gasket is tightened, and then the bottle is placed in an oven and heated to 130-150°C for further assembly. After three days of reaction, the temperature is naturally and slowly cooled to room temperature. Colorless cubic block crystals of Gd are formed at the bottom of the bottle. 32 , filtered, washed with a small amount of methanol, and then dried in vacuo.

[0063] When preparing the intermediate compound, Gd(NO3)3·5H2O and the organic chelating agent N-methyldiethanolamine are in a molar ratio range of 1:1 to 1:3 (N-methyldiethanolamine:triethylamine molar ratio=1:2).

[0064] Reassembly to prepare Gd 32 When the molar ratio of the intermediate compound to triethylamine is 0.1:2, the molar ratio of the intermediate compound to anhydrous CH3OH is 1:2.

[0065] The product Gd can also be obtained by the above two-step method 32 The chemical formula of the product is [Gd 32 (OH) 54(mdea) 12 (NO3) 12 (H2O) 24 (H2O)6](OH)6·24CH3OH·30H2O, wherein mdea is deprotonated N-methyldiethanolamine. This is specifically described in the following examples.

[0066] Example 6

[0067] Gd(NO3)3·5H2O (866 mg, 2 mmol), N-methyldiethanolamine (238 mg, 2 mmol), and triethylamine (405 mg, 4 mmol) were added to 8 mL of anhydrous CH3OH and stirred thoroughly to form a clear solution. If a small amount of precipitate was present, the solution was filtered to obtain a mixture.

[0068] The mixture was added to a 10 mL high-temperature and high-pressure resistant glass bottle, the lid with a rubber pad was tightened, and the bottle was placed in an oven and heated to 130°C. The reaction was allowed to proceed for 12 hours. The crystal water of the rare earth nitrate provided the water molecules required for the hydrolysis of the rare earth, thereby promoting the hydrolysis and polymerization of the rare earth ions under the control of the methyldiethanolamine ligand. The temperature was slowly lowered to room temperature naturally. After standing for three days, colorless block crystals appeared at the bottom of the bottle. The crystals were filtered, washed with a small amount of methanol, and then vacuum dried to obtain the intermediate compound.

[0069] Then, 310 mg of the collected intermediate compound (0.1 mmol) was added to a 10 mL high temperature and high pressure glass bottle, triethylamine (202 mg, 2 mmol) and 8 mL of anhydrous CH3OH were added, the rubber-sealed lid was tightened, and the bottle was placed in an oven and heated to 130°C for further assembly. After three days of reaction, the temperature was slowly cooled to room temperature. Colorless cubic crystals of Gd 32 The product was filtered, washed with a small amount of methanol, and then dried in vacuo. The yield was 90 mg, with a yield rate of 32.0%.

[0070] The product Gd prepared in Example 1 32 As an example, the following characterization is performed.

[0071] Figure 1 In which (a) is compound Gd 32 Molecular structure diagram, where purple balls represent gadolinium ions; orange balls represent oxygen atoms; blue balls represent nitrogen atoms; (b) is the metal skeleton structure. Figure 2 (a) shows the compound Gd 32 The DC magnetic susceptibility of polycrystalline powder in a 1000 Oe magnetic field (1.9-300K). At room temperature (300K), the value of the χT product is 250.6 cm 3 mol - 1K, and pure spin 32 Gd 3+ (S Gd =7 / 2, g Gd =2.0) The sum of theoretical values ​​is 252.0cm 3 mol -1 K is in good agreement. When the temperature gradually decreases from 300K to about 100K, the χT value remains basically unchanged. Then, as the temperature continues to decrease, the χT value begins to decrease significantly and rapidly, reaching 88.2cm at 2K. 3 mol -1 K, which indicates that the compound Gd 32 At this time, there are still a large number of spin electrons in the paramagnetic state. -1 Curie-Weiss fitting of the T curve yields C = 253.8 cm3 mol -1 K and θ = -3.37K, see Figure 2 (b). Negative θ values ​​indicate that compound Gd 32 Antiferromagnetic exchange also plays a dominant role in this process. Figure 2 Where (c) is compound Gd 32 The variable field magnetization intensity M vs. H curve at 2-10K. At 2K and 7T, the magnetization intensity M value is 222.0μB, which is very close to the expected saturation value of 224.0μB. The experimental value at 2K is below the corresponding Brillouin function, which also indicates that the compound Gd 32 The magnetic exchange in the Gd is an antiferromagnetic effect. 32 The magnetic entropy change value under different magnetic field intensity is shown in Figure 2 (d) The maximum magnetic entropy change is 41.0 J kg at 3 K and ΔH = 7 T. -1 K -1 .

[0072] In order to obtain compound Gd 32 The peak value of magnetic entropy change, we continue to test its specific heat data in the range of 0.3-32K, see Figure 3 (a) and calculate its magnetic entropy change curve, see Figure 3 (b) In a 7T magnetic field, the peak value of its magnetic entropy change appears near 2K, reaching 47.2J kg -1 K -1 , which is the largest among the pure Gd clusters reported.

[0073] Because the magnetic entropy change is directly related to the mass magnetic density, we have counted some reported high-nuclear Gd 3+ The magnetic density, symmetry and magnetic entropy change of the cluster are shown in Table 1 and Figure 4 We can see that the overall trend is that with the increase of Gd3+ As the number of cluster nuclei increases, the magnetic density of the cluster tends to increase, making the magnetic entropy change more likely to increase. It is worth noting that the magnetic density is also affected by the mass percentage of non-magnetic components in the molecule, such as guest molecules.

[0074] Table 1 Magnetic density of some high nuclear purity Gd clusters (ρ = M Gd / M molecule ) and the corresponding magnetic entropy change

[0075]

[0076]

[0077] The references in Table 1 are:

[0078] 1. Peng JB, Kong XJ, Zhang QC, et al. Beauty, symmetry, and magnetocaloric effect—four-shell Keplerates with 104lanthanide atoms[J]. J. Am. Chem. Soc., 2014, 136: 17938-17941.

[0079] 2. Guo FS, Chen YC, Mao LL, et al. Anion-templated assembly and magnetocaloric properties of a nanoscale{Gd 38}cage versus a{Gd 48}barrel[J].Chem.Eur.J.,2013,19:14876-14885.

[0080] 3. Chang LX, Xiong G, Wang L, et al. A 24-Gd nanocapsule with a large magnetocaloric effect [J]. Chem. Commun., 2013, 49: 1055-1057.

[0081] 4. Wu M, Jiang F, Kong X, et al.Two polymeric 36-metal pure lanthanidenanosize clusters[J]. Chem. Sci., 2013, 4: 3104-3109.

[0082] 5. Qin L, Zhou GJ, Yu Y, et al.Topological self-assembly of highlysymmetric lanthanide clusters: a magnetic study of exchange-coupling “fingerprints” in giant gadolinium(III)Cages[J].J.Am.Chem.Soc.2017,139:16405-16411.

[0083] 6. Evangelisti M, Roubeau O, Palacios E, et al. Cryogenic magnetocaloric effect in a ferromagnetic molecular dimer[J]. Angew. Chem. Int. Ed., 2011, 50: 6606-6609.

[0084] 7. Liu SJ, Zhao JP, Tao J, et al. An unprecedented decanuclear Gd III cluster for magnetic refrigeration[J].Inorg.chem.,2013,52:9163-9165.

[0085] 8. Zangana KH, Pineda EM, McInnes EJL, et al. Central nine-metal rings of lanthanides[J]. Chem. Commun., 2014, 50: 1438-1440.

[0086] 9. Sharples JW, Zheng YZ, Tuna F, et al. Lanthanide discs chill well and relax slowly[J]. Chem. Commun., 2011, 47: 7650-7652.

[0087] It should be noted that, in the above embodiments, when water was used as the solvent, compound Gd could not be obtained. 32 The Gd prepared in the other examples 32 The product is the same as that in Example 1, and the performance is similar, so no further description is given.

[0088] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing rare earth cluster materials for ultra-low temperature magnetic refrigeration, characterized in that: The following steps are involved: Gd(NO3)3·5H2O, N-methyldiethanolamine and triethylamine were dissolved in anhydrous CH3OH to obtain a mixture; The mixture is sealed and reacted at 100°C to 150°C. During the reaction, the crystal water in Gd(NO3)3·5H2O provides water molecules required for the hydrolysis of gadolinium ions. Triethylamine is used to provide an alkaline environment for hydrolysis and to remove hydrogen from the hydroxyl group of N-methyldiethanolamine. Under the control of the N-methyldiethanolamine ligand, the gadolinium ions are hydrolyzed and polymerized into a cluster material. The chemical formula is: [Gd 32 (OH) 54 (mdea) 12 (NO3) 12 (H2O) 24 (H2O)6](OH)6·24CH3OH·30H2O, where mdea is deprotonated N-methyldiethanolamine; After the mixture is sealed, the cluster material is prepared through a two-step reaction, which specifically includes the following steps: The sealed mixture is pre-reacted at 100°C to 130°C and filtered to obtain an intermediate compound; the intermediate compound and triethylamine are dissolved in anhydrous CH3OH to obtain a reaction system; the reaction system is placed at 130°C to 150°C to continue the reaction, and after completion, it is cooled to room temperature and filtered to obtain the rare earth cluster material; In the pre-reaction, the molar ratio of Gd(NO3)3·5H2O and N-methyldiethanolamine was 1:1∼3, and the molar ratio of N-methyldiethanolamine and triethylamine was 1:2; When the reaction was continued, the molar ratio of the intermediate compound to triethylamine was 0.1:2, and the molar ratio of the intermediate compound to anhydrous CH3OH was 1:

2.

2. The preparation method according to claim 1, characterized in that During the preliminary reaction, the reaction was carried out at 100℃∼130℃ for 12 hours. After the reaction was completed, the mixture was naturally cooled to room temperature, allowed to stand, and then filtered.

3. The preparation method according to claim 1, characterized in that The reaction was continued at 130-150°C for 3 days.

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