Six-core gadolinium-based complex, preparation method and application of six-core gadolinium-based complex in magnetic refrigeration material

Abstract

The invention belongs to the technical field of rare earth complex preparation, and discloses a six-core gadolinium-based complex, a preparation method and application of the six-core gadolinium-based complex in a magnetic refrigeration material. The preparation method provided by the invention comprises the following steps: mixing and dissolving Gd (AC) 3.6 H2O and an organic ligand H2mpcd in a mixed solution of methanol and acetonitrile according to a certain ratio, stirring for 5 minutes by using a magnetic stirrer, adding Na2CO3, continuously stirring for 2 hours, and reacting to obtain the orange blocky crystal hexanuclear gadolinium-based complex. The metal framework of the six-core gadolinium-based complex is triangular, and the six-core gadolinium-based complex has a magnetic refrigeration effect and can be applied to magnetic refrigeration materials.

Description

Technical Field

[0001] The invention belongs to the technical field of rare earth complex preparation, and relates to a hexanuclear gadolinium-based complex, a preparation method and application thereof in magnetic refrigeration materials. Background Art

[0002] Magnetocaloric materials are substances with magnetocaloric effect used in refrigeration systems. Due to their high refrigeration efficiency, low energy consumption and zero pollution, they play a vital role in various fields such as new materials, energy, and information (Nature, 410, 789-793). In recent years, magnetocaloric effect (MCE)-based magnetocaloric technology has become the research focus of rare earth-based complexes due to its high energy efficiency and environmental friendliness (Science, 2009, 326 (5954), 778-779; Journal of Rare Earths, 2023, 41 (7), 1073-1082). Molecular magnetic refrigerants with large magnetocaloric effect usually have the following characteristics: low-lying excited spin states, negligible magnetic anisotropy, large spin ground state S value, dominant ferromagnetic interaction, and high magnetic density. Among the lanthanide elements, Gd III (S=7 / 2, L=0) has the largest spin value in the periodic table and is the most common element in molecular cryogen materials (Inorg.Chem.2015,54(11),5249-5256; Inorg.Chem.2018,57(15),9020-9027; Journal ofRareEarths2022,40(6),916-923). Since magnetic cryogen materials are the basis of magnetic cryogens, the search for high-performance magnetic cryogen materials has always been the research focus and hotspot in the field of magnetic refrigeration. Summary of the invention

[0003] The purpose of the present invention is to provide a hexanuclear gadolinium-based complex, a preparation method and its application in magnetic refrigeration materials, so as to provide a new idea for finding high-performance magnetic refrigeration materials.

[0004] The technical solution provided by the present invention is as follows:

[0005] The first aspect of the present invention provides a hexanuclear gadolinium-based complex having an equilateral triangle metal skeleton, the hexanuclear gadolinium-based complex having a magnetic cooling effect, the hexanuclear gadolinium-based complex belongs to the monoclinic system, and the molecular formula is {Na 2 [Gd 6 (mpcd) 6 (μ 3 :η 2 :η 1 -AC) 6 (μ 3 -O)]}(1,H2 mpcd = (E)-N-[(2-hydroxy-3-methoxyphenyl)methylene]pyrazine-2-carboxylic acid hydrazide, mpcd = deprotonated (E)-N-[(2-hydroxy-3-methoxyphenyl)methylene]pyrazine-2-carboxylic acid hydrazide), the space group is C2 / c. The unit cell parameters are: α=90°, β=97.549(2)°, γ=90°.

[0006] A method for preparing the above-mentioned hexanuclear gadolinium-based complex comprises: 3 6H 2 O, organic ligand H 2 MPCd is mixed and dissolved in CH 3 OH and CH 3 CN mixed solvent, stirred with a magnetic stirrer and then added Na 2 CO 3 , continue stirring, and when the reaction is completed, orange-yellow block crystals, i.e., the hexanuclear gadolinium-based complex, can be obtained.

[0007] The synthetic route of the hexanuclear gadolinium-based complex is shown below:

[0008]

[0009] In the above formula, the hexanuclear gadolinium complex (complex 1) is {Na 2 [Gd 6 (mpcd) 6 (μ 3 :η 2 :η 1 -AC) 6 (μ 3 -O)]}.

[0010] Furthermore, in the above method for preparing the hexanuclear gadolinium-based complex, H 2 mpcd, Gd(AC) 3 6H 2 O and Na 2 CO 3 According to the millimolar ratio of 1:1:1.

[0011] Furthermore, in the above method for preparing the hexanuclear gadolinium-based complex, every 0.1 mmol Gd(AC) 3 6H 2 O correspondingly added 18 mL of the mixed solvent, in which CH 3 OH and CH 3 The volume ratio of CN is 2:1.

[0012] The present invention also provides an application of the above hexanuclear gadolinium-based complex or the hexanuclear gadolinium-based complex prepared by the above preparation method in magnetic refrigeration materials.

[0013] Compared with the prior art, the present invention adopts a synthesis strategy of stirring at room temperature to obtain a hexanuclear gadolinium-based complex with a magnetic cooling effect. The preparation method is simple and the raw materials are easily available. By combining rare earth gadolinium acetate with an organic ligand to generate a gadolinium magnetic cooling material, a new direction is provided for the exploration of the field of rare earth complexes. The synthesized magnetic cooling material has potential application value in the fields of coordination chemistry and quantum computing. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The molecular structure diagram of complex 1 is shown;

[0015] Figure 2 Coordination environment diagrams of Gd1 (a), Gd2 (b), Gd3 (c), and Gd4 (d) are shown;

[0016] Figure 3 The temperature-dependent magnetic susceptibility of complex 1 under a 1000 Oe DC field is shown;

[0017] Figure 4 The magnetization intensity diagram of complex 1 is shown;

[0018] Figure 5 shows the magnetization intensity diagram of complex 1 after reduction;

[0019] Figure 6 The -ΔS of complex 1 under different magnetic fields is shown. m Temperature variation graph. DETAILED DESCRIPTION

[0020] The present invention is further described in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and equivalent changes or modifications also fall within the scope defined by the claims of the present application.

[0021] It should be noted that all reagents in the following examples were purchased directly from the market and were of analytical grade and were not further purified before use.

[0022] Example 1: {Na 2 [Gd 6 (mpcd) 6 (μ 3 :η 2 :η 1 -AC) 6 (μ 3Preparation of complex 1

[0023] {Na 2 [Gd 6 (mpcd) 6 (μ 3 :η 2 :η 1 -AC) 6 (μ 3 -O)]}(complex 1): weigh 54.4 mg of organic ligand H 2 mpcd (0.2 mmol), 66.8 mg Gd (AC) 3 6H 2 O (0.2 mmol) was dissolved in 12 mL of CH 3 OH and 6 mL CH 3 CN mixed solution, stirred for 5 min to allow the solution to fully dissolve, then added 21.7 mg Na 2 CO 3 (0.2 mmol), continue stirring for 2 h, filter and evaporate, and about two weeks later, orange-yellow block crystals are obtained, which is the target complex 1.

[0024] Example 2: Crystal structure determination

[0025] Data were collected using a Rigaku Oxford diffractometer at 120 K with Mo Kα radiation from a graphite monochromator. The coordinates of hydrogen atoms on some water molecules were obtained by difference Fourier synthesis, the number of remaining crystal water was determined by thermogravimetric test results, and the coordinates of all non-hydrogen atoms were obtained by direct method and optimized by anisotropic thermal parameter correction and matrix least squares method. Hydrogen atoms were directly added to the molecular formula.

[0026] Single crystal X-ray diffraction analysis showed that complex 1 crystallized in the monoclinic C2 / c space group. The crystal structure of complex 1, such as Figure 1 The asymmetric structural unit of complex 1 consists of four crystallographically independent Gd III ions (Gd1, Gd2, Gd3, Gd4), six deprotonated ligand anions (mpcd 2- ), six coordinated AC - ion, a μ 3 -O 2- Ion. H 2 All MPCD ligands are μ 2 :η 2 :η 1 :η 1 :η1 The coordination mode of AC - Using μ 3 :η 2 :η 1 The coordination mode of the six Gd III The ions are bridged to form a triangular metal skeleton.

[0027] Gd1 and Gd4 are octa-coordinated, and the coordination configuration of Gd1 is a trigonal dodecahedron obtained by CShM ( Figure 2 a), Gd4 is a Johnson-type double-capped triangular prism coordination configuration ( Figure 2 d). Gd2 and Gd3 are nine-coordinated, and the coordination configuration can be described as a single-capped tetragonal antiprism ( Figure 2 b) and three-hat triangular prism ( Figure 2 c) The average bond length of Gd-O is The average bond length of Gd-N is All are within the normal range. The bond angle range of O-Nd-O is 57.0(2)-157.4(3)°, and the bond angle range of N-Nd-N is 70.4(3)-133.0(3)°. The bond angles of Gd2-Gd1-Gd3, Gd2A-Gd1A-Gd3, and Gd2-Gd4A-Gd3 are 65.24, 65.242, and 65.113°, respectively, proving that the metal skeleton of complex 1 is close to an equilateral triangle.

[0028] Table 1 Some CShM values ​​of Gd1 and Gd4 in complex 1

[0029]

[0030] Table 2 Partial CShM values ​​of Gd2 and Gd3 in complex 1

[0031]

[0032] Example 3: Magnetic properties of complex 1

[0033] In the temperature range of 2-300K, the powder sample of complex 1 was subjected to a 1000Oe external DC electric field to test the temperature-dependent magnetic susceptibility. The results are as follows: Figure 3 The room temperature χ of complex 1 is shown in M T value is 47.16cm 3 K mol -1 , close to 6 isolated Gd III Ions (S = 7 / 2, L = 0, 8 S 7 / 2 , g=2) theoretical value (47.25cm 3 mol -1 K). As the temperature decreases,M The T value gradually decreases to 40.7cm 3 mol -1 K, which may be due to the gradual decrease of excited state Stark sublevels and the Gd III The exchange interaction between the two. The magnetization intensity of complex 1 is shown as Figure 4 As shown in Figure 2, M increases rapidly at low fields and does not reach saturation at 7T. The 41.46Nμ observed at 2K and 7T B is close to six independent Gd III Theoretical saturation value of ions: 42Nμ B (S = 7 / 2). Mvsμ at 2.0-7.0K 0 HT -1 Data shows ( Figure 5 ), the reduced magnetization intensity curves of complex 1 basically coincide with each other, indicating that it is isotropic.

[0034] Maxwell equations (Formula 1) were used to calculate the -ΔS of complex 1 under different magnetic fields. m Temperature variation diagram ( Figure 6 ), the maximum magnetic entropy change (-ΔS m ) is 29.60 J kg -1 K -1 , slightly smaller than six uncoupled Gd III Theoretical magnetic entropy change (34.80 J kg -1 K -1 ). Compared with the reported hexanuclear gadolinium-based complexes, the -ΔS m Relatively high, with better magnetic cooling effect.

[0035]

[0036] Although some embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the present general inventive concept, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing a hexanuclear gadolinium-based complex, characterized in that: The metal skeleton of the hexanuclear gadolinium-based complex is an equilateral triangle and has a magnetocaloric effect. The hexanuclear gadolinium-based complex belongs to the monoclinic system, the space group is C2 / c, and the molecular formula is {Na2[Gd6(mpcd)6(μ3:η 2 :η 1 -AC)6(μ3-O)]}, the unit cell parameters are: α=90°, β=97.549(2)°, γ=90°, mpcd is deprotonated (E)-N-[(2-hydroxy-3-methoxyphenyl)methylene]pyrazine-2-carboxylic acid hydrazide).

2. A method for preparing the hexanuclear rare earth complex according to claim 1, characterized in that: include: Gd(AC)3·6H2O and organic ligand H2mpcd are dissolved in a mixed solvent of methanol and acetonitrile in a certain proportion, stirred with a magnetic stirrer, and then Na2CO3 is added and stirred continuously. When the reaction is completed, a hexanuclear gadolinium-based complex can be obtained. The hexanuclear gadolinium-based complex is an orange-yellow block crystal.

3. The preparation method according to claim 2, characterized in that: The molar ratio of organic ligand H2mpcd, Gd(AC)3·6H2O and Na2CO3 is 1:1:

1.

4. The preparation method according to claim 2, characterized in that: 18 mL of the mixed solvent was added for every 0.1 mmol of Gd(AC)3·6H2O, wherein the volume ratio of methanol to acetonitrile in the mixed solvent was 2:

1.

5. Use of the hexanuclear gadolinium-based complex according to claim 1 or the hexanuclear gadolinium-based complex prepared by the preparation method according to any one of claims 2 to 4 in magnetic refrigeration materials.

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