CN111647163A - Gadolinium-based framework coordination material with high magnetocaloric effect and preparation method thereof - Google Patents
Gadolinium-based framework coordination material with high magnetocaloric effect and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a gadolinium-based framework coordination material with high magnetocaloric effect and a preparation method thereof. A gadolinium-based frame coordination material with high magnetocaloric effect has a molecular formula of [ (CH)3)2NH2]Gd(C2O4)(HCOO)2H2O·2H2O, molecular weight 435.4, belonging to monoclinic system,P21a/n space group; cell parameters ofa=9.6414 Å，b=11.5715 Å，c=12.1439 Å，α=γ=90°，β99.468 DEG, unit cell volumeV=1336.38 Å3. The preparation method of the gadolinium-based framework coordination material with high magnetocaloric effect has the advantages of simple and easily obtained raw materials, low cost, simple preparation method, high yield, good reproducibility and the like, and the coordination material prepared by the invention is used as a magnetic refrigeration material and has no pollution to the environment.
Description
Technical Field
The invention relates to the technical field of magnetic refrigeration materials, in particular to a gadolinium-based framework coordination material with high magnetocaloric effect and a preparation method thereof.
Background
The basic principle of magnetic refrigeration technology is to utilize the magnetocaloric effect exhibited by magnetic substances through isothermal and
the refrigeration is realized by repeated circulation of the adiabatic demagnetization process. In recent years, with the development of crystal engineering and molecular-based magnets, molecular-based low-temperature magnetic refrigeration materials have become hot spots of current research. Compared with the traditional magnetic refrigeration material, the molecular-based low-temperature magnetic refrigeration material not only has the advantages of high efficiency, energy conservation, no pollution, low noise and the like, but also has unique advantages in the aspects of monodispersity, structure and performance regulation.
In general, the preparation of a molecular-based low-temperature magnetic refrigeration material with excellent performance needs to have the following key factors: large spin ground states, low occupied excited states, negligible magnetic anisotropy, significant ferromagnetic interactions and high magnetic densities. The low-temperature magnetic refrigeration material is expected to replace the expensive and rare He-3 low-temperature refrigerant currently used. The molecular-based low-temperature magnetic refrigeration materials reported at present mainly focus on gadolinium-based clusters and coordination polymers, which is mainly because rare earth metal gadolinium ions have a large spin ground state and negligible magnetic anisotropy, and the electron shielding effect of the 4f orbit of the rare earth metal gadolinium ions makes the magnetic coupling effect in the complexes relatively weak. In addition, the linking ligand with small molecular weight, such as oxalic acid, is favorable for improving the magnetic density of the complex. Although a small amount of researches on the preparation of molecular-based low-temperature magnetic refrigeration materials by blending oxalic acid, dysprosium sulfate and other organic and inorganic ligands exist at present, the defects of complex preparation, higher cost, lower yield and the like exist.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide a gadolinium-based framework coordination material with high magnetocaloric effect and a preparation method thereof.
In order to solve the problems, the invention adopts the following technical scheme:
a gadolinium-based frame coordination material with high magnetocaloric effect has a molecular formula of [ (CH)3)2NH2]Gd(C2O4)(HCOO)2H2O·2H2O, molecular weight 435.4, belonging to monoclinic system,P21a/n space group; cell parameters ofa= 9.6414 Å，b=11.5715 Å，c=12.1439 Å，α=γ= 90°，β99.468 DEG, unit cell volumeV= 1336.38 Å3。
Preferably, the maximum magnetic entropy of the coordination material at a temperature T of 2.0K and an external field Δ H of 7T becomes 39.97 Jkg-1K-1(ii) a The maximum magnetic entropy at a temperature T of 2.0K and an external field Δ H of 3T becomes 18.26 jkg-1K-1。
The invention also provides a preparation method of the gadolinium-based framework coordination material with high magnetocaloric effect, which comprises the following steps:
preparing a mixture containing gadolinium salt, oxalate, N-dimethylformamide and water;
crystallizing the mixture at 120-140 ℃ for 60-80 h to obtain a massive colorless crystal;
the crystals were washed with the reaction mother liquor, ether in this order, and then dried.
Preferably, the gadolinium salt is gadolinium nitrate hexahydrate or gadolinium perchlorate hexahydrate.
Preferably, the oxalate salt is sodium oxalate.
Preferably, the molar ratio of the gadolinium salt, the oxalate, the N, N-dimethylformamide and the water in the mixture is 10 (15-20) to 1 (12-25) 1: (15-20).
Preferably, the crystallization process is carried out in a stainless steel reaction vessel with a polytetrafluoroethylene lining.
The invention also provides an application of the gadolinium-based framework coordination material with high magnetocaloric effect in a low-temperature magnetic refrigerant, wherein the maximum magnetic entropy of the coordination material at the temperature T of 2.0K and the external field delta H of 7T is changed into 39.97J kg-1K-1(ii) a The maximum magnetic entropy at a temperature T of 2.0K and an external field Δ H of 3T becomes 18.26 jkg-1K-1。
Compared with the prior art, the invention has the technical effects that:
the framework structure of the gadolinium-based framework coordination material with high magnetocaloric effect consists of oxalate bridged gadolinium ions, weak antiferromagnetic interaction is shown among the gadolinium ions in the structure, and the maximum magnetic entropy change (-delta) is realized at the temperature T of 2.0K and the external field delta H of 7TS m max) 39.97J kg-1K-1Maximum magnetic entropy change (- Δ) at temperature T2.0K and external field Δ H3TS m max) 18.26J kg-1K-1And the higher magnetocaloric effect shows that the compound has potential application prospect in the aspect of ultralow-temperature magnetic refrigeration.
The preparation method of the gadolinium-based framework coordination material with high magnetocaloric effect has the advantages of simple and easily obtained raw materials, low cost, simple preparation method, high yield and good reproducibility.
Drawings
FIG. 1 is a single crystal diffraction analysis structure diagram of a gadolinium-based framework coordination material with high magnetocaloric effect provided in embodiment 1 of the present invention;
FIG. 2 is a graph showing the variation of magnetic susceptibility with temperature of a gadolinium-based framework coordination material with high magnetocaloric effect provided in example 1 of the present invention;
FIG. 3 shows the magnetization intensity of gadolinium-based framework coordination material with high magnetocaloric effect at different temperatures and different magnetic fields according to example 1 of the present invention;
fig. 4 shows the magnetic entropy changes of gadolinium-based framework coordination materials with high magnetocaloric effect at different temperatures and different magnetic fields according to embodiment 1 of the present invention.
In FIG. 1, (a) is a schematic diagram of the coordination material minimum asymmetric unit; (b) is a schematic diagram of the coordination configuration of gadolinium ions in the coordination material; (c) is a schematic diagram of a three-dimensional framework structure formed by stacking the coordination material molecules.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The embodiment of the invention provides a gadolinium-based framework coordination material with high magnetocaloric effect and a preparation method thereof, wherein the gadolinium-based framework coordination material comprises the following steps:
(1) preparing a mixture containing gadolinium salt, oxalate, N-dimethylformamide and water, wherein the molar ratio of gadolinium salt, oxalate, N-dimethylformamide and water in the mixture is 10 (15-20) to 1 (12-25);
(2) crystallizing the mixture at 120-140 ℃ for 60-80 h in a 25mL stainless steel reaction kettle with a polytetrafluoroethylene lining to obtain massive colorless crystals;
(3) washing the crystal with reaction mother liquor and ethyl ether in sequence, and then drying to obtain the gadolinium-based framework coordination material with high magnetocaloric effect.
The following is a further description with reference to specific examples.
Example 1
The embodiment 1 of the invention provides a gadolinium-based framework coordination material with high magnetocaloric effect and a preparation method thereof:
uniformly mixing 45 mg of gadolinium nitrate hexahydrate, 20 mg of sodium oxalate, 1 mL of N, N-dimethylformamide and 4 mL of water, transferring the mixed solution into a 25mL stainless steel reaction kettle with a polytetrafluoroethylene lining, crystallizing for 72 hours in a 130 ℃ oven, cooling after 6-12 hours to obtain colorless blocky crystals, filtering, and washing by reaction mother liquor and diethyl ether in sequence to obtain a final product. The yield was about 82% (based on metallic gadolinium). The prepared coordination material is subjected to elemental analysis, and the elemental analysis result is as follows: anal, Calcd for C6H16NO11Gd： H 3.87%，C 17.09%，N 3.15%；found H 3.70%，C16.55%，N 3.22%。
The molecular formula of the coordination material crystal prepared in the embodiment 1 of the invention is [ (CH)3)2NH2]Gd(C2O4)(HCOO)2H2O·2H2O, molecular weight 435.4, belonging to monoclinic system,P21a/n space group. Cell parameters ofa= 9.6414 Å，b=11.5715 Å，c=12.1439 Å，α=γ= 90°，β99.468 DEG, unit cell volumeV= 1336.38 Å3. The coordination material has a three-dimensional framework structure in which gadolinium ions are coordinated with nine oxygen atoms, has a distorted capped square antiprism configuration, each gadolinium atom is coordinated with four oxalates and one water molecule, each oxalate connects two gadolinium atoms, thereby forming a three-dimensional network bridged with oxalates.
The single crystal diffraction experiment and the data analysis of the prepared colorless bulk crystal are carried out in the embodiment 1 of the invention, and the result shows that the obtained coordination material has a three-dimensional framework structure (shown in figure 1), the coordination material is formed by self-assembly coordination of rare earth metal gadolinium salt and oxalate, the framework structure is formed by oxalate bridging gadolinium ions, wherein gadolinium atoms are coordinated with nine oxygen atoms and have a distorted capped square inverse prism configuration, each gadolinium atom is coordinated with four oxalate and one water molecule, and each oxalate is connected with two gadolinium atoms, so that an oxalate bridging three-dimensional network structure is formed.
Meanwhile, the magnetic susceptibility of the coordination material prepared in the embodiment 1 of the present invention is measured along with the temperature change, the magnetization intensity thereof at different temperatures and different magnetic fields, and the magnetic entropy change thereof at different temperatures and different magnetic fields, and the measurement results are shown in fig. 2, fig. 3, and fig. 4. Magnetic tests show that the coordination material can present higher thermal stability and porous structure, can present higher magnetocaloric effect, and can be used as a low-temperature molecular-based magnetic coolant. Gadolinium ions in the complex structure show weak antiferromagnetic interaction, and the maximum magnetic entropy change (-delta) at the temperature T of 2.0K and the external field delta H of 7TS m max) 39.97J kg-1K-1Maximum magnetic entropy change (- Δ) at temperature T2.0K and external field Δ H3TS m max) 18.26J kg-1K-1The coordination material has potential application prospect in the aspect of ultralow temperature magnetic refrigeration.
Example 2
The embodiment 2 of the invention provides a gadolinium-based framework coordination material with high magnetocaloric effect and a preparation method thereof:
uniformly mixing 45 mg of gadolinium nitrate hexahydrate, 27 mg of sodium oxalate, 1 mL of N, N-dimethylformamide and 4 mL of water, transferring the mixed solution into a 25mL stainless steel reaction kettle with a polytetrafluoroethylene lining, crystallizing for 72 hours in a 130 ℃ oven, cooling after 6-12 hours to obtain colorless blocky crystals, filtering, and washing by reaction mother liquor and diethyl ether in sequence to obtain a final product. The structural characterization and experimental results of the obtained target product are the same as those in example 1.
Example 3
The embodiment 3 of the invention provides a gadolinium-based framework coordination material with high magnetocaloric effect and a preparation method thereof:
uniformly mixing 45 mg of gadolinium nitrate hexahydrate, 23.5 mg of sodium oxalate, 1 mL of N, N-dimethylformamide and 4 mL of water, transferring the mixed solution into a 25mL stainless steel reaction kettle with a polytetrafluoroethylene lining, crystallizing for 72 hours in a 130 ℃ oven, cooling after 6-12 hours to obtain colorless blocky crystals, filtering, and washing by reaction mother liquor and diethyl ether in sequence to obtain a final product. The structural characterization and experimental results of the obtained target product are the same as those in example 1.
The preparation method of the gadolinium-based framework coordination material with high magnetocaloric effect has the advantages of simple and easily obtained raw materials, low cost, simple preparation method, high yield and good reproducibility. The coordination material prepared by the invention is used as a magnetic refrigeration material, has no pollution to the environment, and is a safe and environment-friendly material.
The present invention is not limited to the above-described specific embodiments, and various modifications and variations are possible. Any modifications, equivalents, improvements and the like made to the above embodiments in accordance with the technical spirit of the present invention should be included in the scope of the present invention.
Claims (8)
1. The gadolinium-based framework coordination material with high magnetocaloric effect is characterized in that the molecular formula is [ (CH)3)2NH2]Gd(C2O4)(HCOO)2H2O·2H2O, molecular weight 435.4, belonging to monoclinic system,P21a/n space group; unit cell parameterNumber isa=9.6414 Å，b= 11.5715 Å，c=12.1439 Å，α=γ= 90°，β99.468 DEG, unit cell volumeV= 1336.38 Å3。
2. The gadolinium-based framework coordination material with high magnetocaloric effect as claimed in claim 1, wherein the maximum magnetic entropy of said coordination material at temperature T2.0K and external field Δ H7T becomes 39.97 jkg-1K-1(ii) a The maximum magnetic entropy at a temperature T of 2.0K and an external field Δ H of 3T becomes 18.26 jkg-1K-1。
3. The method for preparing a gadolinium-based framework coordination material with high magnetocaloric effect as claimed in claim 2, comprising the steps of:
preparing a mixture containing gadolinium salt, oxalate, N-dimethylformamide and water;
crystallizing the mixture at 120-140 ℃ for 60-80 h to obtain a massive colorless crystal;
the crystals were washed with the reaction mother liquor, ether in this order, and then dried.
4. The method for preparing a gadolinium-based framework coordination material with high magnetocaloric effect as claimed in claim 3, wherein said gadolinium salt is gadolinium nitrate hexahydrate or gadolinium perchlorate hexahydrate.
5. The method of claim 3, wherein the oxalate salt is sodium oxalate.
6. The method for preparing the gadolinium-based framework coordination material with high magnetocaloric effect according to claim 3, wherein the molar ratio of the gadolinium salt, the oxalate, the N, N-dimethylformamide and the water in the mixture is 10 (15-20) to 1 (12-25).
7. The method of claim 3, wherein the crystallization is performed in a stainless steel reactor with a teflon liner.
8. The use of a gadolinium-based framework coordination material having high magnetocaloric effect on low temperature magnetic refrigerants as claimed in claim 1, wherein the maximum magnetic entropy of said coordination material at temperature T2.0K and external field Δ H7T becomes 39.97 jkg-1K-1(ii) a The maximum magnetic entropy at a temperature T of 2.0K and an external field Δ H of 3T becomes 18.26 jkg-1K-1。
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