Gadolinium magnetocaloric material based on aromatic hydrazide and preparation method of gadolinium magnetocaloric material

Abstract

The invention relates to the technical field of magnetic materials, in particular to a gadolinium magnetocaloric material based on aromatic hydrazide and a preparation method of the gadolinium magnetocaloric material. The invention relates to a gadolinium magnetocaloric material based on aromatic hydrazide, the chemical formula is [Gd4 (L-) 4 (mu2-N3-) 3 (mu2-OH) (Cl) 4], the molecular formula is C52H44Cl4Gd4N25O9, and L is (E)-N '-((6-methoxypyridine-2-yl) methylene) pyridine hydrazide without one proton. The gadolinium magnetocaloric material based on the aromatic hydrazide belongs to a P21 / c space group of a monoclinic system, and cell parameters are as follows: a is equal to 14.8597 (10), b is equal to 20.6434 (15), c is equal to 23.4501 (16), alpha is equal to 90 degrees, beta is equal to 103.631 (2) degrees, gamma is equal to 90 degrees, and V is equal to 6990.8 (8) 3. The gadolinium magnetocaloric material based on the aromatic hydrazide has an excellent magnetocaloric effect, the preparation method is simple and convenient to operate, the product purity is high, and the reproducibility is good.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic materials, and in particular to a gadolinium magnetocaloric material based on aromatic hydrazide and a preparation method thereof. Background Art

[0002] The magnetocaloric effect is an intrinsic property of magnetic materials, a phenomenon in which the temperature of a magnetic material changes with changes in magnetic field strength during an adiabatic process. During this adiabatic process, changes in the magnetic field cause temperature changes in the magnetic material, altering the internal magnetic order with temperature. The magnetic sublattice couples in the magnetic field, causing the material to absorb or release heat due to changes in entropy. In recent years, magnetic refrigeration materials, which provide temperature changes in an adiabatic environment guided by changes in an external magnetic field, have attracted significant interest from researchers due to their environmentally friendly, low-noise, low-energy consumption, and high energy efficiency.

[0003] Hydrazides and their derivatives are not only useful for synthesizing heterocyclic systems but are also used in the preparation of organometallic complexes due to their rich coordination patterns and multiple O / N atoms. Aromatic hydrazides and their derivatives are extensively studied in a variety of fields, including photosensitive materials, fluorescent probes, pharmaceuticals, and organic synthesis, and have become a research hotspot in the chemistry and materials science communities in recent years.

[0004] Prior to the present patent application, there were no reports in patent literature or scientific papers on the self-assembly of (E)-N'-((6-methoxypyridin-2-yl)methylene)picolinylhydrazide, gadolinium chloride, sodium azide and the formation of magnetocaloric materials in a mixed solvent of methanol / acetonitrile. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a gadolinium magnetocaloric material based on aromatic hydrazide.

[0006] Another object of the present invention is to provide a method for preparing the above-mentioned gadolinium magnetocaloric material based on aromatic hydrazide.

[0007] The technical problem to be solved by the present invention is achieved through the following technical solutions: A gadolinium magnetocaloric material based on aromatic hydrazide, with the chemical formula [Gd4(L - )4( μ 2-N3 - )3( μ 2-OH)(Cl)4], the molecular formula is C 52 H 44 Cl4Gd4N 25 O9, wherein L is (E)-N'-((6-methoxypyridin-2-yl)methylene)picolinohydrazide which has lost a proton. The structural formula of (E)-N'-((6-methoxypyridin-2-yl)methylene)picolinohydrazide is: The gadolinium magnetocaloric material based on aromatic hydrazide belongs to the monoclinic system, P21 / c space group, and the unit cell parameters are a=14.8597(10)Å, b=20.6434(15)Å, c=23.4501(16)Å, α=90°, β=103.631(2)°, γ=90°, V =6990.8(8)Å 3 .

[0008] Furthermore, within the asymmetric structural unit of the aromatic hydrazide-based gadolinium magnetocaloric material, four independent crystallographic Gd(III) metal centers (Gd1, Gd2, Gd3, and Gd4) are present, all octacoordinated. The metal centers Gd1 and Gd4 are each coordinated by five nitrogen atoms, two oxygen atoms, and one chloride atom, forming an N5O2Cl coordination environment, while the Gd2 and Gd3 ions are each connected by four nitrogen atoms, three oxygen atoms, and one chloride atom, forming an N4O3Cl coordination environment. The octacoordinated Gd1 exhibits a tetragonal inverse prismatic geometry, while Gd2, Gd3, and Gd4 exhibit a dodecahedral geometry. The four Gd(III) ions are bridged by five μ2-O atoms and three μ2-N3 atoms, forming a nearly square Gd4 core. In the Gd4 core, the distances between adjacent Gd…Gd are 4.0447(7), 4.0860(7), 3.9201(7) and 4.0346(7)Å, respectively; the distances between diagonal Gd…Gd are 5.7249(7) and 5.6459(6)Å, respectively. The bond lengths of Gd-O / N are in the range of 2.287(7)-2.654(7)Å, and the bond lengths of Gd-Cl are in the range of 2.6722-2.6999Å. Each asymmetric structural unit includes four metal centers Dy 3+ ion, four deprotonated (E)-N'-((6-methoxypyridin-2-yl)methylene)picolinylhydrazide anions L - , 3 bridges μ 2-N3 - , 1 μ 2-OH and 4 chloride ions.

[0009] Furthermore, in the solid state structure, adjacent molecules can be further constructed parallel to the ac Two-dimensional supramolecular structure.

[0010] A method for preparing a gadolinium magnetocaloric material based on an aromatic hydrazide comprises the following steps: adding (E)-N'-((6-methoxypyridin-2-yl)methylene)picolinohydrazide, gadolinium chloride, and sodium azide to a mixed solution of methanol and acetonitrile, dropwise adding a small amount of triethylamine, stirring thoroughly, and filtering; then, placing the filtrate in a high-pressure reactor, heating the reaction under solvent thermal conditions, and slowly cooling the mixture to obtain the gadolinium magnetocaloric material based on an aromatic hydrazide.

[0011] Furthermore, the heating temperature is 70-90°C.

[0012] Furthermore, the heating reaction time is 48 to 72 hours.

[0013] Furthermore, the temperature is lowered to room temperature at a rate of 2°C / hour to 10°C / hour.

[0014] Furthermore, the volume ratio of methanol and acetonitrile in the mixed solution is 6:4.

[0015] Furthermore, the volume ratio of the molar number of (E)-N'-((6-methoxypyridin-2-yl)methylene)picolinylhydrazide to triethylamine in the solution is 1 mmol: 1 mL.

[0016] Furthermore, the molar ratio of (E)-N'-((6-methoxypyridin-2-yl)methylene)picolinohydrazide, gadolinium chloride, and sodium azide is 0.9-1.1: 0.9-1.1: 1.8-2.2.

[0017] Furthermore, the molar ratio of (E)-N'-((6-methoxypyridin-2-yl)methylene)picolinohydrazide, gadolinium chloride, and sodium azide is preferably 1:1:2.

[0018] Beneficial effects of the present invention: The present invention synthesizes gadolinium magnetocaloric materials based on aromatic hydrazide under solvent thermal conditions for the first time. Figure 7 As shown, the gadolinium magnetocaloric material based on aromatic hydrazide has high purity; Figure 8 、 9 As shown, the gadolinium magnetocaloric material based on aromatic hydrazide of the present invention has antiferromagnetic coupling and can be used as an antiferromagnetic material; Figure 10 As shown, the gadolinium magnetocaloric material based on aromatic hydrazide of the present invention has a large magnetic entropy change, exhibits a relatively excellent magnetocaloric effect, and can be used as a magnetic refrigeration material; the preparation method of the gadolinium magnetocaloric material based on aromatic hydrazide of the present invention has high product purity, simple and convenient operation, and good reproducibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Asymmetric structural unit diagram of the gadolinium magnetocaloric material based on aromatic hydrazide according to the present invention; Figure 2 Coordination environment diagram of the metal center Gd in the gadolinium magnetocaloric material based on aromatic hydrazide of the present invention; Figure 3 Coordination environment diagram of the aromatic hydrazide ligand in the aromatic hydrazide-based gadolinium magnetocaloric material of the present invention; Figure 4 Square Gd4 nuclear diagram in the gadolinium magnetocaloric material based on aromatic hydrazide of the present invention; Figure 5 The two-dimensional supramolecular structure of the gadolinium magnetocaloric material based on aromatic hydrazide according to the present invention; Figure 6 Infrared spectrum of the gadolinium magnetocaloric material based on aromatic hydrazide according to the present invention; Figure 7 The X-ray powder diffraction pattern of the gadolinium magnetocaloric material based on aromatic hydrazide of the present invention; Figure 8 The DC temperature-dependent magnetic susceptibility curve of the aromatic hydrazide-based gadolinium magnetocaloric material of the present invention; Figure 9 A Curie-Weiss law fitting curve diagram of the gadolinium magnetocaloric material based on aromatic hydrazide according to the present invention; Figure 10 Magnetic entropy change temperature curve of the gadolinium magnetocaloric material based on aromatic hydrazide described in the present invention. DETAILED DESCRIPTION

[0020] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0021] Example 1: 0.1mmol (E)-N'-((6-methoxypyridin-2-yl)methylene)picolinohydrazide, 0.1mmol GdCl3·6H2O and 0.2mmol NaN3 were dissolved in 20mL methanol and acetonitrile ( V : V =6:4) mixed solution, 0.1 mL of triethylamine was added dropwise, the mixture was stirred thoroughly at room temperature for 60 minutes, and then filtered. The filtrate was transferred to a stainless steel reactor lined with polytetrafluoroethylene. The stainless steel reactor was sealed and placed in an oven for solvothermal reaction at 80°C for 72 hours. The temperature was then cooled to room temperature at 2°C / hour, filtered, and washed to obtain pale yellow block crystals of the aromatic hydrazide-based gadolinium magnetocaloric material with a yield of 37.4% (based on Gd).

[0022] The structural characterization of the aromatic hydrazide-based gadolinium magnetocaloric material crystal prepared in this example is as follows: The X-ray diffraction data were measured using a Bruker Smart Apex CCD single crystal diffractometer. The X-ray diffraction data were obtained at 150 K using graphite monochromatized Mo Kα radiation ( λ= 0.071073 nm) as the radiation source, and diffraction data were collected. The scanning mode was φ-ω scanning, and Lp factor correction and empirical absorption correction were performed. The position coordinates of metal atoms and non-hydrogen atoms were determined by direct method. All non-hydrogen atomic coordinates and their anisotropic thermal parameters were corrected by full matrix least squares method. The crystallographic parameters are shown in Table 1, and the structure is shown in Figure 1 , Figure 2 , Figure 3 , Figure 4 .

[0023] Table 1 Main crystallographic data of the prepared aromatic hydrazide-based gadolinium magnetocaloric material The gadolinium magnetocaloric material based on aromatic hydrazide of the present invention has the chemical formula [Gd4(L - )4( μ 2-N3 - )3( μ 2-OH)(Cl)4], the molecular formula is C 52 H 44 Cl4Gd4N 25 O9, wherein L is (E)-N'-((6-methoxypyridin-2-yl)methylene)pyridine hydrazide which has lost a proton. The gadolinium magnetocaloric material based on aromatic hydrazide belongs to the monoclinic system, P21 / c space group, and the unit cell parameters are a=14.8597(10)Å, b=20.6434(15)Å, c=23.4501(16)Å, α=90°, β=103.631(2)°, γ=90°, V =6990.8(8)Å 3. In the asymmetric structural unit of the gadolinium magnetocaloric material based on aromatic hydrazide, there are four independent crystallographic Gd(III) metal centers (Gd1, Gd2, Gd3 and Gd4), all of which adopt an octa-coordinated structure. The metal centers Gd1 and Gd4 are both coordinated by five N atoms, two O atoms and one Cl atom to form a N5O2Cl coordination environment, while the Gd2 and Gd3 ions are both connected by four N atoms, three O atoms and one Cl atom to form a N4O3Cl coordination environment. The octa-coordinated Gd1 has a tetragonal anti-prism geometry, while Gd2, Gd3 and Gd4 have a dodecahedral geometry. The four Gd(III) ions are bridged by five μ2-O and three μ2-N3 to form an approximately square core of Gd4. In the Gd4 core, the distances between adjacent Gd…Gd are 4.0447(7), 4.0860(7), 3.9201(7) and 4.0346(7)Å, respectively; the distances between diagonal Gd…Gd are 5.7249(7) and 5.6459(6)Å, respectively. The bond lengths of Gd-O / N are in the range of 2.287(7)-2.654(7)Å, and the bond lengths of Gd-Cl are in the range of 2.6722-2.6999Å. Each asymmetric structural unit includes four metal centers Dy 3+ ion, four deprotonated (E)-N'-((6-methoxypyridin-2-yl)methylene)picolinylhydrazide anions L - , 3 bridges μ 2-N3 - , 1 μ 2-OH and 4 chloride ions. The adjacent molecules can be further constructed parallel to the ac Two-dimensional supramolecular structure.

[0024] The magnetic properties of the gadolinium magnetocaloric material based on aromatic hydrazide prepared in this example are studied as follows: The magnetic measurement is carried out using a superconducting quantum interference device (Quantum Design MPMS SQUID VSM) magnetic measurement system. The test temperature of DC magnetic susceptibility is 2.0-300K and the magnetic field is 0.1T. The DC temperature-dependent magnetic susceptibility curve is shown in Figure 2. Figure 8 As shown, when T=300K, its χ M T The value is 31.54 cm 3 K mol −1 , with 4 free Gd(III) ions ( 8 S 7 / 2 , L = 0, g = 2) The corresponding theoretical value is 31.52 cm 3 K mol−1 As the temperature decreases, χ M T The value remains constant in the temperature range of 300–50K, and thereafter χ M T The value drops rapidly to 2K χ M T The value reaches the minimum value of 23.77cm 3 K mol −1 . χ M T The downward trend of the T graph indicates that there is an antiferromagnetic interaction between Gd (III) ions in the gadolinium magnetocaloric material based on aromatic hydrazide according to the present invention. Figure 9 As shown, χ M T Curie-Weiss law fitting curve for T: χ M -1 = ( T - θ ) / C , we get two important parameters θ =−0.93 K, C = 31.87 cm 3 K mol −1 ,burden θ The parameters also demonstrate the existence of antiferromagnetic coupling between Gd(III) ions in aromatic hydrazide-based gadolinium magnetocaloric materials.

[0025] The magnetic refrigeration performance of the gadolinium magnetocaloric material based on aromatic hydrazide prepared in this example was further studied. The magnetocaloric effect can be evaluated by the magnetic entropy change, and the magnetic entropy change (−Δ S m ) can be obtained from Maxwell's equations: Δ S m ( T ) = ∫[∂ M ( T , H ) / ∂ T ] H d H , the magnetic entropy change-temperature curve is as follows Figure 10 As shown in the figure, it can be seen that the −ΔSm value increases as the temperature decreases from 10.0K to 2.0K, and the maximum −Δ S m The value reaches 31.89 J kg −1 K −1 ( T= 2.5 K and Δ H = 7.0 T), with excellent magnetocaloric effect.

[0026] In summary, the gadolinium magnetocaloric material based on aromatic hydrazide prepared in the present invention exhibits antiferromagnetic coupling and can be used as an antiferromagnetic material. It also has a relatively excellent magnetocaloric effect and can be used as a magnetic refrigeration material for magnetic refrigeration technology equipment.

[0027] Example 2: 0.09mmol (E)-N'-((6-methoxypyridin-2-yl)methylene)picolinohydrazide, 0.09mmol GdCl3·6H2O and 0.2mmol NaN3 were dissolved in 20mL methanol and acetonitrile ( V : V =6:4) mixed solution, 0.1 mL of triethylamine was added dropwise, the mixture was stirred thoroughly at room temperature for 60 minutes, and then filtered. The filtrate was transferred to a stainless steel reactor lined with polytetrafluoroethylene. The stainless steel reactor was sealed and placed in an oven for solvothermal reaction at 80°C for 96 hours. The temperature was then cooled to room temperature at 2°C / hour, filtered, and washed to obtain pale yellow block crystals of the aromatic hydrazide-based gadolinium magnetocaloric material with a yield of 34.5% (based on Gd).

[0028] Example 3: 0.11mmol (E)-N'-((6-methoxypyridin-2-yl)methylene)picolinohydrazide, 0.11mmol GdCl3·6H2O and 0.18mmol NaN3 were dissolved in 20mL methanol and acetonitrile ( V : V =6:4) mixed solution, 0.1 mL of triethylamine was added dropwise, the mixture was stirred thoroughly at room temperature for 60 minutes, and then filtered. The filtrate was transferred to a stainless steel reactor lined with polytetrafluoroethylene. The stainless steel reactor was sealed and placed in an oven for solvothermal reaction at 90°C for 48 hours. The temperature was then cooled to room temperature at a rate of 10°C / hour, filtered, and washed to obtain pale yellow block crystals of the aromatic hydrazide-based gadolinium magnetocaloric material with a yield of 35.3% (based on Gd).

[0029] Example 4: 0.1mmol (E)-N'-((6-methoxypyridin-2-yl)methylene)picolinohydrazide, 0.1mmol GdCl3·6H2O and 0.2mmol NaN3 were dissolved in 20mL methanol and acetonitrile ( V : V=6:4) mixed solution, 0.1 mL of triethylamine was added dropwise, the mixture was stirred thoroughly at room temperature for 60 minutes, and then filtered. The filtrate was transferred to a stainless steel reactor lined with polytetrafluoroethylene. The stainless steel reactor was sealed and placed in an oven for solvothermal reaction at 80°C for 72 hours. The temperature was then cooled to room temperature at a rate of 10°C / hour, filtered, and washed to obtain pale yellow block crystals of the aromatic hydrazide-based gadolinium magnetocaloric material with a yield of 36.2% (based on Gd).

[0030] Example 5: 0.11mmol (E)-N'-((6-methoxypyridin-2-yl)methylene)picolinohydrazide, 0.11mmol GdCl3·6H2O and 0.18mmol NaN3 were dissolved in 20mL methanol and acetonitrile ( V : V =6:4) mixed solution, 0.1 mL of triethylamine was added dropwise, the mixture was stirred thoroughly at room temperature for 60 minutes, and then filtered. The filtrate was transferred to a stainless steel reactor lined with polytetrafluoroethylene. The stainless steel reactor was sealed and placed in an oven for solvothermal reaction at 70°C for 72 hours. The temperature was then cooled to room temperature at 5°C / hour, filtered, and washed to obtain pale yellow block crystals of the aromatic hydrazide-based gadolinium magnetocaloric material with a yield of 34.8% (based on Gd).

[0031] The above-mentioned embodiments merely express the implementation methods of the present invention. The description thereof is relatively specific and detailed, but it cannot be understood as limiting the patent scope of the present invention. Any technical solution obtained in the form of equivalent replacement or equivalent transformation should fall within the scope of protection of the present invention.

Claims

1. A gadolinium magnetocaloric material based on aromatic hydrazide, the chemical formula of which is [Gd4(L - )4( μ 2-N3 - )3( μ 2-OH)(Cl)4], the molecular formula is C 52 H 44 Cl4Gd4N 25 O9, wherein L is (E)-N'-((6-methoxypyridin-2-yl)methylene)picolinohydrazide which has lost one proton, characterized in that The gadolinium magnetocaloric material based on aromatic hydrazide belongs to the monoclinic system, P21 / c space group, and the unit cell parameters are a=14.8597(10)Å, b=20.6434(15)Å, c=23.4501(16)Å, α=90°, β=103.631(2)°, γ=90°, V =6990.8(8)Å 3 .

2. The gadolinium magnetocaloric material based on aromatic hydrazide according to claim 1, characterized in that The asymmetric structural unit of the gadolinium magnetocaloric material based on aromatic hydrazide contains four independent crystallographic Gd(III) metal centers (Gd1, Gd2, Gd3, and Gd4), all of which adopt an octa-coordinated structure. The metal centers Gd1 and Gd4 are both connected by five N atoms, two O atoms, and one Cl atom to form a N5O2Cl coordination environment, while the Gd2 and Gd3 ions are both connected by four N atoms, three O atoms, and one Cl atom to form a N4O3Cl coordination environment. The four Gd(III) ions are bridged by five μ2-O and three μ2-N3 to form an approximately square Gd4 core, with diagonal Gd…Gd distances of 5.7249(7)Å and 5.6459(6)Å, respectively.

3. The method for preparing the gadolinium magnetocaloric material based on aromatic hydrazide according to claim 1 or 2, comprising the following steps: (E)-N'-((6-methoxypyridin-2-yl)methylene)picolinohydrazide, gadolinium chloride, and sodium azide are added to a mixed solution of methanol and acetonitrile, a small amount of triethylamine is added dropwise, the mixture is fully stirred and filtered, and the filtrate is then placed in a high-pressure reactor, heated under solvent thermal conditions for reaction, and then slowly cooled to obtain the gadolinium magnetocaloric material based on aromatic hydrazide.

4. The method for preparing the gadolinium magnetocaloric material based on aromatic hydrazide according to claim 3, characterized in that The molar ratio of (E)-N'-((6-methoxypyridin-2-yl)methylene)picolinohydrazide, gadolinium chloride, and sodium azide is 0.9-1.1: 0.9-1.1: 1.8-2.2; Furthermore, the molar ratio of (E)-N'-((6-methoxypyridin-2-yl)methylene)picolinohydrazide, gadolinium chloride, and sodium azide is preferably 1:1:

2.

5. The method for preparing the gadolinium magnetocaloric material based on aromatic hydrazide according to claim 3, characterized in that: The volume ratio of methanol to acetonitrile in the mixed solution is 6:

4.

6. The method for preparing the gadolinium magnetocaloric material based on aromatic hydrazide according to claim 3, characterized in that: The volume ratio of the molar number of (E)-N'-((6-methoxypyridin-2-yl)methylene)picolinylhydrazide to triethylamine in the solution is 1 mmol:1 mL.

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