Rare earth cluster material for extremely low temperature magnetic refrigeration and preparation method thereof

Abstract

The invention belongs to the technical field of magnetic refrigeration, and particularly relates to a rare earth cluster material for extremely low temperature magnetic refrigeration and a preparation method thereof.The preparation method comprises the following steps that Gd (NO3) 3.5 H2O, N-methyldiethanolamine and triethylamine are dissolved in anhydrous CH3OH, and a mixture is obtained; and sealing the mixture, and reacting at 100-150 DEG C to obtain the rare earth cluster material. The novel extremely-low-temperature magnetic refrigeration material is prepared on the basis of a controllable solvent thermal hydrolysis method, under a 7T magnetic field, the magnetic entropy change peak value of the novel extremely-low-temperature magnetic refrigeration material appears near 2K, the magnetic entropy change reaches 47.2 J kg <-1 > K <-1 >, and the novel extremely-low-temperature magnetic refrigeration material is the largest in reported pure Gd cluster compounds.

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 extremely low temperature magnetic refrigeration and a preparation method thereof. Background Art

[0002] Ultra-low temperature refers to temperatures below 4.2K. Ultra-low temperature refrigeration is widely used in large scientific facilities, deep space exploration, scientific research and other technical fields. At present, there are three methods to obtain ultra-low temperatures: dilution refrigeration, adsorption refrigeration and magnetic refrigeration. The first two methods require liquid helium as a refrigerant. Liquid helium reserves are low and difficult to mine. Magnetic refrigeration uses the magnetocaloric effect of magnetic working fluids to achieve refrigeration through repeated cycles of isothermal magnetization and adiabatic demagnetization. It has the advantages of no liquid helium consumption, high efficiency, compactness, and independence from gravity. It is a technology with great development potential and has great application potential 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 for this type of material because of its large ground state spin (4f orbit 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 view of 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 to prepare anhydrous CH 3 OH is the reaction solvent, Gd(NO 3 ) 3 ·5H 2 O as raw material, N-methyldiethanolamine as ligand, and under the action of organic base triethylamine, the assembly of metal gadolinium ions was achieved. The peak value of magnetic entropy change of the assembled material appeared near 2K under 7T magnetic field, and the magnetic entropy change reached 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 scheme.

[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] Will Gd(NO 3 ) 3 ·5H 2 O, N-methyldiethanolamine and triethylamine were dissolved in anhydrous CH 3 OH, a mixture is obtained;

[0009] The mixture is sealed and reacted at 100°C to 150°C. During the reaction, Gd(NO 3 ) 3 ·5H 2 The crystal water in O provides water molecules required for the hydrolysis of gadolinium ions, triethylamine is used to provide an alkaline environment for hydrolysis and to remove H from the hydroxyl group of N-methyldiethanolamine, and gadolinium ions are hydrolyzed and polymerized into cluster materials under the control of N-methyldiethanolamine ligands.

[0010] The present invention is based on the "controlled solvent thermal hydrolysis" method, using anhydrous CH 3 OH is the reaction solvent, Gd(NO 3 ) 3 ·5H 2 O is used as raw material. Under the action of organic base triethylamine, the water molecules required for the hydrolysis of gadolinium ions are provided by its own crystal water. The gadolinium ions are hydrolyzed and polymerized into cluster materials under the control of N-methyldiethanolamine, avoiding the precipitation of rare earth metal ions due to simultaneous large-scale hydrolysis, and realizing the assembly of a large number of metal gadolinium ions, thereby successfully preparing a new type of 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 (NO 3 ) 12 (H 2 O) 24 (H 2 O) 6 ](OH) 6 ·24CH 3 OH·30H 2 O, wherein mdea is deprotonated N-methyldiethanolamine.

[0013] In a preferred embodiment of the present invention, Gd(NO 3 ) 3 ·5H2 The molar ratio of O and N-methyldiethanolamine is 1:1-3, and the molar ratio of N-methyldiethanolamine and triethylamine is 1:2.

[0014] In a preferred embodiment of the present invention, Gd(NO 3 ) 3 ·5H 2 O and anhydrous CH 3 The molar ratio of OH 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, it 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, filtered, and an intermediate compound is obtained; the intermediate compound and triethylamine are dissolved in anhydrous CH 3 OH to obtain a reaction system; placing the reaction system at 130° C. to 150° C. to continue the reaction, cooling to room temperature after the reaction is completed, filtering, and obtaining 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, Gd(NO 3 ) 3 ·5H 2 The molar ratio of O and N-methyldiethanolamine is 1:1-3, and the molar ratio of N-methyldiethanolamine and 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 intermediate compound to anhydrous CH 3 The molar ratio of OH is 1:2.

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

[0023] The present invention is based on the "controlled solvent thermal hydrolysis" method, using anhydrous CH 3 OH is the reaction solvent, Gd(NO 3 ) 3·5H 2 O as raw material, N-methyldiethanolamine as ligand, triethylamine is used to provide alkaline environment for hydrolysis and to remove H, Gd(NO 3 ) 3 ·5H 2 O's own crystal water provides the water molecules needed 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, the problem of precipitation of rare earth metal ions due to simultaneous large-scale hydrolysis is avoided, thereby achieving the assembly of a large number of metal gadolinium ions.

[0024] The novel ultra-low temperature magnetic refrigeration material prepared by the present invention has a chemical formula of [Gd 32 (OH) 54 (mdea) 12 (NO 3 ) 12 (H 2 O) 24 (H 2 O) 6 ](OH) 6 ·24CH 3 OH·30H 2 O, 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 47.2 J 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, in which 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 1000Oe 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 Curves of magnetic entropy change under different magnetic field values. The solid line in (a) and the colored line in (c) are Monte Carlo calculation values.

[0027] Figure 3 In which (a) is compound Gd32 Molar specific heat data under different magnetic fields; (b) is a comparison diagram of magnetic entropy change calculated by specific heat data (hollow graph) and magnetic data (solid graph).

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

[0029] In order to enable those skilled in the art to better understand the technical solution of the present invention and implement it, the present invention is further described below in conjunction with specific embodiments and drawings, but the embodiments are not intended to limit the present invention. The experimental methods and detection methods described in the following embodiments are conventional methods unless otherwise specified; the reagents and materials described are all 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] Will Gd(NO 3 ) 3 ·5H 2 O, N-methyldiethanolamine and triethylamine were dissolved in anhydrous CH 3 OH, a mixture is obtained;

[0032] The mixture is sealed and reacted at 100°C to 150°C. During the reaction, Gd(NO 3 ) 3 ·5H 2 The crystal water in O provides the water molecules needed for the hydrolysis of gadolinium ions. Triethylamine is used to provide an alkaline environment for hydrolysis and to remove H on the alcoholic hydroxyl group of N-methyldiethanolamine. Gadolinium ions are hydrolyzed and polymerized into cluster materials under the control of N-methyldiethanolamine ligands. The water in the system comes from crystal water. Controlling the water content can avoid the problem of precipitation caused by the simultaneous hydrolysis of rare earth metal ions due to high water content, thereby achieving the assembly of a large number of metal gadolinium ions.

[0033] It should be noted that the rare earth metal salt Gd(NO 3 ) 3 ·5H 2 O, organic chelating agent N-methyldiethanolamine and organic base triethylamine were added to anhydrous CH 3 After being added to OH, the mixture was stirred thoroughly to form a clear solution. If a small amount of precipitate was present, it was 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, and the reaction time of the one-step reaction is 3 days. After the reaction is completed, the mixture is cooled to room temperature, filtered, and the cluster material is obtained. 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 pad is tightened, and then the bottle is placed in an oven and heated to 100°C to 150°C for three days, and the water molecules required for the hydrolysis of the rare earth are provided by the crystal water of the rare earth nitrate, so that the rare earth ions are hydrolyzed and polymerized into cluster materials under the control of the methyldiethanolamine ligand. After the reaction, the temperature is naturally slowly cooled to room temperature, and there are colorless cubic block crystals at the bottom of the bottle, which are filtered, the crystals are washed with a small amount of methanol, and then vacuum dried.

[0035] Gd(NO 3 ) 3 ·5H 2 O and organic chelating agent N-methyldiethanolamine in a molar ratio range of 1:1 to 1:3 (N-methyldiethanolamine: triethylamine molar ratio = 1:2) can obtain the product. The chemical formula of the product is [Gd 32 (OH) 54 (mdea) 12 (NO 3 ) 12 (H 2 O) 24 (H 2 O) 6 ](OH) 6 ·24CH 3 OH·30H 2 O, where mdea is deprotonated N-methyldiethanolamine. The product is named Gd 32 .

[0036] The following examples are used to provide a specific description.

[0037] Example 1

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

[0039] Will Gd(NO 3 ) 3 ·5H 2 O (866 mg, 2 mmol), N-methyldiethanolamine (238 mg, 2 mmol), triethylamine (405 mg, 4 mmol) were added to 8 mL of anhydrous CH 3 OH, stir thoroughly to form a clear solution, and filter if a small amount of precipitate is present to obtain a mixture.

[0040] 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. After three days of reaction, the temperature was naturally slowly cooled to room temperature. There were colorless cubic crystals at the bottom of the bottle, which 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 G 32 N 24 O 2 0 4 ): C 10.04, H4.09, N 3.34; elemental analysis test values: C 10.02, H 3.94, N 3.43. Infrared spectrum absorption peak position (KBr tablet, 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] Will Gd(NO 3 ) 3 ·5H 2 O (2 mmol), N-methyldiethanolamine (6 mmol), triethylamine (12 mmol) were added to 8 mL of anhydrous CH 3 OH, stir thoroughly to form a clear solution, and filter if a small amount of precipitate is present to obtain a mixture.

[0045] The mixture was added to a 10 mL high temperature and high pressure glass bottle, the lid with a rubber pad was tightened, and the bottle was placed in an oven and heated to 130°C. After three days of reaction, the temperature was naturally slowly cooled to room temperature. Colorless cubic crystals were found at the bottom of the bottle. The 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] Will Gd(NO 3 ) 3 ·5H 2O (2 mmol), N-methyldiethanolamine (4 mmol), triethylamine (8 mmol) were added to 8 mL of anhydrous CH 3 OH, stir thoroughly to form a clear solution, and filter if a small amount of precipitate is present to obtain a mixture.

[0049] 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. After three days of reaction, the temperature was naturally slowly cooled to room temperature. Colorless cubic crystals were found at the bottom of the bottle. The 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] Will Gd(NO 3 ) 3 ·5H 2 O (2 mmol), N-methyldiethanolamine (2 mmol), triethylamine (4 mmol) were added to 8 mL of anhydrous CH 3 OH, stir thoroughly to form a clear solution, and filter if a small amount of precipitate is present to obtain a mixture.

[0053] 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 100°C. After three days of reaction, the temperature was naturally slowly cooled to room temperature. There were colorless cubic crystals at the bottom of the bottle, which were filtered, washed with a small amount of methanol, and then vacuum dried. 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] Will Gd(NO 3 ) 3 ·5H 2 O (2 mmol), N-methyldiethanolamine (2 mmol), triethylamine (4 mmol) were added to 8 mL of anhydrous CH 3 OH, stir thoroughly to form a clear solution, and filter if a small amount of precipitate is present to obtain a mixture.

[0057] 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 150°C. After three days of reaction, the temperature was naturally slowly cooled to room temperature. Colorless cubic crystals were found at the bottom of the bottle. The 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] Will Gd(NO 3 ) 3 ·5H 2 O, N-methyldiethanolamine and triethylamine were dissolved in anhydrous CH 3 OH, a mixture is obtained;

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

[0061] In a preferred embodiment of the present invention, based on the above reaction mechanism, the reaction 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 CH 3 OH to obtain a reaction system; placing the reaction system at 130° C. to 150° C. to continue the reaction, cooling to room temperature after the reaction is completed, filtering, and obtaining the rare earth cluster material.

[0062] In a preferred embodiment of the present invention, in the specific operation, the mixture is added to a high temperature and high pressure glass bottle, the cover with a rubber pad is tightened, and then the bottle is placed in an oven and heated to 100-130°C, reacted for 12 hours, and the rare earth nitrate provides the water molecules required for the hydrolysis of the rare earth with the crystal water, so that the rare earth ions are hydrolyzed and polymerized under the control of the methyldiethanolamine ligand, and the temperature is naturally slowly cooled to room temperature. After standing for three days, there are colorless block crystals at the bottom of the bottle, which 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 CH 3 OH, tighten the lid with a rubber pad, and then place the bottle in an oven and heat it to 130-150°C for further assembly. After three days of reaction, the temperature naturally slowly cooled to room temperature, and colorless cubic block crystals of Gd 32 , filtered, washed with a small amount of methanol, and then dried in vacuo.

[0063] When preparing the intermediate compound, Gd(NO 3 ) 3 ·5H 2O 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 intermediate compound to anhydrous CH 3 The molar ratio of OH 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 (NO 3 ) 12 (H 2 O) 24 (H 2 O) 6 ](OH) 6 ·24CH 3 OH·30H 2 O, wherein mdea is deprotonated N-methyldiethanolamine. Specific examples are given below.

[0066] Example 6

[0067] Will Gd(NO 3 ) 3 ·5H 2 O (866 mg, 2 mmol), N-methyldiethanolamine (238 mg, 2 mmol), triethylamine (405 mg, 4 mmol) were added to 8 mL of anhydrous CH 3 OH, stir thoroughly to form a clear solution, and filter if a small amount of precipitate is present to obtain a mixture.

[0068] Add the mixture into a 10mL high-temperature and high-pressure resistant glass bottle, tighten the lid with a rubber pad, and then place the bottle in an oven and heat it to 130°C. React for 12 hours to provide the water molecules required for rare earth hydrolysis with the help of the crystal water of rare earth nitrate, so as to promote the hydrolysis and polymerization of rare earth ions under the control of methyldiethanolamine ligands. Slowly cool down to room temperature naturally. After standing for three days, there are colorless block crystals at the bottom of the bottle. Filter, wash the crystals with a small amount of methanol, and then vacuum dry to obtain an 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, and triethylamine (202 mg, 2 mmol) and 8 mL of anhydrous CH 3OH, tighten the lid with a rubber pad, and then place the bottle in an oven and heat it to 130°C for further assembly. After three days of reaction, the bottle was naturally cooled to room temperature. There were colorless cubic block crystals of Gd at the bottom of the bottle. 32 , filtered, washed with a small amount of methanol, and then vacuum dried. Yield 90 mg, yield 32.0%.

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

[0071] Figure 1 In which (a) is compound Gd 32 Molecular structure diagram, in which 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 1000Oe magnetic field (1.9-300K). At room temperature (300K), the value of the χT product is 250.6cm 3 mol - 1 K, with 32 Gd of pure spin 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 drops from 300K to about 100K, the χT value remains basically unchanged. Then as the temperature continues to drop, the χT value begins to drop 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 is antiferromagnetic. The compound Gd calculated by Maxwell equations32 The magnetic entropy change value under different magnetic field change intensities is shown in Figure 2 (d), where 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 the compound Gd 32 The peak value of magnetic entropy change, we continued 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). Under 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 Gd 3+ As the number of cluster nuclei increases, the magnetic density of the cluster tends to increase, so the magnetic entropy change value is 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 (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 andmagnetocaloric 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 largemagnetocaloric 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 ofhighlysymmetric 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 magnetocaloriceffect 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 IIIcluster 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 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 it will not be described in detail.

[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 protection scope 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, and triethylamine is used to provide an alkaline environment for hydrolysis and to remove H from the alcoholic hydroxyl group of N-methyldiethanolamine. The gadolinium ions are hydrolyzed and polymerized into cluster materials under the control of the N-methyldiethanolamine ligand.

2. The preparation method according to claim 1, characterized in that: 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.

3. The preparation method according to claim 1, characterized in that: The molar ratio of Gd(NO3)3·5H2O and anhydrous CH3OH is 10:

1.

4. The preparation method according to claim 1, characterized in that: After the mixture is sealed, a cluster material is prepared through a one-step reaction. The one-step reaction means that the mixture is reacted at 100° C. to 150° C. for 3 days, cooled to room temperature after the reaction, and filtered to obtain the cluster material.

5. The preparation method according to claim 1, characterized in that: After the mixture is sealed, the cluster material is prepared by a two-step reaction, which specifically includes the following steps: The sealed mixture is first pre-reacted at 100°C to 130°C, 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, cooled to room temperature after completion, filtered, and the rare earth cluster material is obtained.

6. The preparation method according to claim 5, characterized in that: During the preliminary reaction, the reaction was first carried out at 100°C to 130°C for 12 hours. After the reaction was completed, the mixture was naturally cooled to room temperature, allowed to stand, and then filtered.

7. The preparation method according to claim 5, characterized in that: The reaction was continued at 130°C to 150°C for 3 days.

8. The preparation method according to claim 5, characterized in that: 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.

9. The rare earth cluster material for ultra-low temperature magnetic refrigeration prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The chemical formula is: [Gd 32 (OH) 54 (mdea) 12 (NO3) 12 (H2O) 24 (H2O)6](OH)6·24CH3OH·30H2O, wherein mdea is deprotonated N-methyldiethanolamine.

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