Free radical binuclear rare earth monomolecular magnet complex as well as preparation method and application thereof

Abstract

The invention relates to the technical field of metal complexes, and provides a free radical binuclear rare earth monomolecular magnet complex as well as a preparation method and application thereof in order to solve the problem that a conventional self-assembly strategy cannot meet the development requirement of a high-performance multi-core rare earth monomolecular magnet. The hydroquinone bridged free radical rare earth monomolecular magnet complex Ln2 (L1) 2 (L2) (OTF) 2 (Py) 2 is obtained through design and synthesis, L1 and L2 are organic ligands, and Ln is any one of rare earth metal Dy, Gd or Y. The single-molecular magnet property of the prepared series of free radical binuclear rare earth complexes is mainly regulated and controlled by rare earth metal ions and bridging free radical ligands, the rare earth metal Dy ions have remarkable magnetic anisotropy and high magnetization intensity, and the magnetic interaction among the rare earth ions can be effectively enhanced through introduction of the bridging free radical ligands; and thus, effective regulation and control on the magnetization quantum tunneling and magnetic relaxation process of the single-molecule magnet are realized.

Description

Technical Field

[0001] This invention relates to the field of metal complex technology, specifically to radical binuclear rare earth single-molecule magnet complexes, their preparation methods, and applications. Background Technology

[0002] Developing novel rare-earth high-density magnetic storage materials has become a crucial issue in the future information field. The key to increasing magnetic storage capacity lies in continuously reducing the size of the magnetic particles used for recording information. However, when the size decreases to a certain extent, the superparamagnetic effect affects the stability of magnetically recorded information, significantly limiting the development of high-density information storage. To meet the demands for smaller, lighter, thinner, and more stable magnetic storage materials, molecular-based magnetic materials, primarily based on rare-earth single-molecule magnets, have emerged in recent years, effectively overcoming the shortcomings of traditional synthesis methods. These materials not only achieve true nanoscale magnetic storage but also break the superparamagnetic limit of materials.

[0003] Magnetization quantum tunneling in rare-earth single-molecule magnets mainly originates from magnetic moment reversals between ground-state doublets without thermal relaxation. Therefore, the stability of the ground-state doublet is crucial for suppressing magnetic quantum tunneling. Studies have found that strong axial ligand fields can effectively stabilize the ground-state bistable state of rare-earth ions, resulting in a good separation between the ground and excited states, and the compounds exhibit strong magnetic anisotropy.

[0004] Professor Richard A. Layfield's research group prepared rare-earth monomolecule magnets using sterically hindered cyclopentadiene ligands. The cyclopentadiene ligands provide the axial ligand field, and due to the steric hindrance effect of the ligands, there are no coordinating atoms in the equatorial plane of the rare-earth ions. Therefore, these magnets exhibit strong magnetic anisotropy, with an effective energy barrier as high as 1541 cm⁻¹. -1 With a magnetic blocking temperature exceeding that of liquid nitrogen (80 K), it is currently the best-performing single-molecule magnet, laying a solid foundation for the practical application of rare-earth single-molecule magnets in the future.

[0005] However, although the magnetic blocking temperature of cyclopentadiene-core rare earth single-molecule magnets has reached above the liquid nitrogen temperature, the preparation process of these single-molecule magnets is mainly based on strict anhydrous and oxygen-free operations, resulting in relatively poor chemical and thermal stability, which seriously limits the widespread application of rare earth single-molecule magnets in the future.

[0006] Simultaneously modulating the axial ligand fields of multiple rare-earth ions in multinuclear systems is extremely challenging. In recent years, Professor Selvan Demir's group has constructed several high-performance binuclear rare-earth single-molecule magnets using free radicals as strong magnetic exchange linking units. In these magnets, the free radicals transmit strong antiferromagnetic interactions, completely suppressing the quantum tunneling effect of the compounds. In 2022, Professor Jeffrey R. Long's group constructed a novel mixed-valence binuclear rare-earth single-molecule magnet by bridging rare-earth units with bromide ions and reducing one rare-earth ion to divalent using KC8. Because divalent rare-earth ions possess 4f... n With a 5d¹ electronic structure, two rare-earth ions share d electrons to form stable rare-earth-rare-earth bonds, exhibiting a high spin ground state and strong magnetic anisotropy. Quantum tunneling is effectively suppressed, with a coercive field exceeding 14 T and a magnetic blocking temperature exceeding 60 K. This successful example fully demonstrates that increasing the magnetic coupling between rare-earth ions can effectively suppress magnetized quantum tunneling and raise the magnetic blocking temperature of rare-earth single-molecule magnets. It also provides important reference for further designing multinuclear rare-earth single-molecule magnets with different topologies.

[0007] Currently, the effective energy barrier of air-stabilized rare-earth single-molecule magnets is comparable to that of mononuclear rare-earth single-molecule magnets; however, their blocking temperatures differ significantly. Through structural comparison, we found that while maintaining the rare-earth ion... D 5h / D 6h Based on the coordination configuration, by introducing magnetic interactions, rare earth ions are aligned in the same direction with magnetic anisotropy. By utilizing strong magnetic coupling, it is expected to further suppress quantum tunneling, thereby increasing the stability of rare earth single-molecule magnets and improving their blocking temperature.

[0008] However, due to the high coordination number and varied coordination configuration of rare earth ions, it is extremely difficult to simultaneously control the magnetic anisotropy of multiple rare earth ions in the same system. Conventional self-assembly strategies can no longer meet the development requirements of high-performance multinucleated rare earth single-molecule magnets. Summary of the Invention

[0009] To comprehensively address the aforementioned problems, this invention aims to provide radical binuclear rare-earth single-molecule magnetic complexes, their preparation methods, and applications. The series of complexes provided by this invention all possess well-defined single-crystal structures, high thermal stability, and different single-molecule magnetic properties.

[0010] Technical concept: The present invention is based on the design and synthesis of hydroquinone-linked radical rare earth single-molecule magnet complexes. By controlling the types of rare earth ions and the redox degree of the bridging ligands, the magnetization quantum tunneling and relaxation time of this series of radical rare earth single-molecule magnets can be controlled.

[0011] This invention proposes the design and synthesis of hydroquinone ligands, which improve the chemical and thermal stability of rare-earth single-molecule magnets while enhancing the magnetic anisotropy of rare-earth ions by strengthening the axial ligand field, thus aligning their magnetic anisotropy axes in the same direction. Simultaneously, by utilizing the free radical generation property of hydroquinone after oxidation-reduction, intramolecular magnetic coupling is used to suppress magnetization quantum tunneling, effectively increasing the blocking temperature of rare-earth single-molecule magnets, and achieving controllable assembly and performance regulation of high-performance binuclear rare-earth single-molecule magnets.

[0012] To achieve the above objectives and technical concepts, the first aspect of this invention provides a free radical binuclear rare earth single-molecule magnetic complex, with the chemical formula as follows: Ln2(L1)2(L2)(OTF)2(Py)2; Among them, L1 and L2 are organic ligands, and Ln is any one of rare earth metals Dy, Gd or Y; ; The structural formula of ligand L2 is: .

[0013] Preferably, Ln is the rare earth metal Dy, then the radical binuclear rare earth monomolecular magnet complex is Dy2(L1)2(L2)(OTF)2(Py)2, with the following structural formula: .

[0014] Preferably, Ln is the rare earth metal Gd, then the radical binuclear rare earth single-molecule magnet complex is Gd2(L1)2(L2)(OTF)2(Py)2, with the following structural formula: .

[0015] Preferably, Ln is a rare earth metal Y, then the radical binuclear rare earth single-molecule magnet complex is Y2(L1)2(L2)(OTF)2(Py)2, with the following structural formula: .

[0016] A second aspect of this invention provides a method for preparing radical binuclear rare-earth single-molecule magnetic complexes, comprising the following steps: S1: Ligand L1 is synthesized by reacting 2-(1-pyrazole)-pyridine with potassium borohydride under heating. S2: 2,5-Dicarboxylated terephthalic ether was dissolved in dichloromethane, then boron tribromide was added and reacted at room temperature, followed by the addition of ammonium chloride to quench the reaction, thus synthesizing ligand L2; S3: Dissolve rare earth metal salts and ligand L1 in pyridine and react. Then add ligand L2 and continue the reaction to synthesize free radical binuclear rare earth monomolecular magnet complexes.

[0017] Preferably, in S1, the molar ratio of 2-(1-pyrazole)-pyridine to potassium borohydride is 5:1.

[0018] Preferably, in S2, the molar ratio of 2,5-dicarboxylated p-phenylenedimethyl ether to boron tribromide is 1:3.

[0019] Preferably, in S3, the molar ratio of ligand L1, ligand L2 to rare earth metal is 2:2:1.

[0020] Preferably, in S3, the rare earth metal salt is any one of Dy(OTF)3, Gd(OTF)3 or Y(OTF)3.

[0021] A third aspect of the present invention provides an application of the free radical binuclear rare earth single-molecule magnet complex prepared as described above, for use in the preparation of molecular magnetic storage devices.

[0022] Compared with the prior art, the beneficial effects of the present invention are: This invention synthesizes two examples of multidentate ligands and assembles them with rare earth ions. By changing the oxidation state of the rare earth ions and the bridging radical ligands, the magnetization quantum tunneling and magnetic relaxation of this series of radical binuclear rare earth single-molecule magnetic complexes are effectively controlled. Specifically: (1) The present invention utilizes ligands L1 and L2 with Y(OTF)3 to obtain a binuclear rare earth single-molecule magnetic complex [Y2(L1)2(L2)(OTF)2(Py)2]. Magnetic tests show that the complex exhibits paramagnetism. Since the rare earth element Y and ligand L2 do not contribute magnetic moments, it indicates that the bridging ligand is a free radical. (2) The present invention utilizes ligands L1 and L2 with Gd(OTF)3 to obtain a binuclear rare earth single-molecule magnetic complex [Gd2(L1)2(L2)(OTF)2(Py)2]. Magnetic tests show that the magnetic susceptibility in the low temperature region is significantly increased, indicating that there is a free radical-transmitted ferromagnetic interaction in the compound. (3) The present invention utilizes ligands L1 and L2 with Dy(OTF)3 to obtain a binuclear rare earth single-molecule magnetic complex [Dy2(L1)2(L2)(OTF)2(Py)2]. Magnetic tests show that the magnetic susceptibility decreases significantly in the low-temperature region, indicating that the compound has obvious magnetic blockage. Hysteresis loop tests show that the compound has obvious hysteresis loop opening in the non-zero field, confirming that the compound has slow relaxation of magnetization intensity, and magnetization quantum tunneling is well suppressed, with an effective energy barrier of 223.8 K.

[0023] The above results indicate that the single-molecule magnet properties of the series of free radical binuclear rare earth complexes prepared in this invention are mainly regulated by rare earth metal ions and bridging free radical ligands. Among them, rare earth metal Dy ions have significant magnetic anisotropy and large magnetization. The introduction of bridging free radical ligands can effectively enhance the magnetic interaction between rare earth ions, thereby achieving effective regulation of the magnetization quantum tunneling and magnetic relaxation process of single-molecule magnets. Attached Figure Description

[0024] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0025] In the attached diagram: Figure 1 Is ligand L1 in DMSO-d 6 In 1 H-NMR spectrum; Figure 2 Is it ligand L2 in DMSO-d 6 In 1 H-NMR spectrum; Figure 3 This is the single crystal structure diagram of the complex Ln2(L1)2(L2)(OTF)2(Py)2; Figure 4 The infrared spectra of the complex Ln2(L1)2(L2)(OTF)2(Py)2 are as follows: (a) is the infrared spectrum of Dy2(L1)2(L2)(OTF)2(Py)2, (b) is the infrared spectrum of Gd2(L1)2(L2)(OTF)2(Py)2, and (c) is the infrared spectrum of Y2(L1)2(L2)(OTF)2(Py)2. Figure 5 Thermogravimetric curves of the complex Ln2(L1)2(L2)(OTF)2(Py)2 are as follows: (a) Thermal stability results of Dy2(L1)2(L2)(OTF)2(Py)2, (b) Thermal stability results of Gd2(L1)2(L2)(OTF)2(Py)2, and (c) Thermal stability results of Y2(L1)2(L2)(OTF)2(Py)2. Figure 6 This is the magnetic susceptibility diagram of the complex Ln2(L1)2(L2)(OTF)2(Py)2; Figure 7 This is the hysteresis loop diagram of the complex Ln2(L1)2(L2)(OTF)2(Py)2; Figure 8 The relaxation time diagram of the complex Ln2(L1)2(L2)(OTF)2(Py)2; Figure 9This is a flowchart of the preparation method of the present invention. Detailed Implementation

[0026] The following combination Figures 1-9 The preferred embodiments of the present invention are described herein. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0027] The raw materials and reagents involved in this invention are as follows: All solvents used in this invention are commercially available analytical grade reagents. Dichloromethane, ammonium chloride, 2,5-dicarboxymethyl terephthalate, and pyridine were purchased from Anaiji (Shanghai) Pharmaceutical Chemical Co., Ltd. Boron tribromide, 2-(1-pyrazole)-pyridine, Dy(OTF)3, Gd(OTF)3, and Y(OTF)3 were purchased from Shanghai Bid Pharmaceutical Technology Co., Ltd., and potassium borohydride was purchased from Sinopharm Group Pharmaceutical Co., Ltd.

[0028] Example 1: The chemical formula for the free radical binuclear rare earth single-molecule magnetic complex is: Ln2(L1)2(L2)(OTF)2(Py)2; L1 and L2 are organic ligands, and Ln is any one of the rare earth metals Dy, Gd or Y (Y corresponds to the rare earth element yttrium, a non-lanthanide element). The structural formula of ligand L1 is: ; The structural formula of ligand L2 is: .

[0029] If Ln is a rare earth metal Dy, then the radical binuclear rare earth single-molecule magnetic complex is Dy2(L1)2(L2)(OTF)2(Py)2, which belongs to the triclinic crystal system, space group P-1, and has the following cell parameters: a = 12.319(3)Å, b = 14.053(4)Å, c = 14.775(3)Å, α = 75.993(6)°, β = 66.199(4)°, γ = 84.748(6)°, ν = 2270.7(10)Å. 3 The structural formula is: .

[0030] If Ln is the rare earth metal Gd, then the radical binuclear rare earth single-molecule magnetic complex is Gd2(L1)2(L2)(OTF)2(Py)2, which belongs to the triclinic crystal system, space group P-1, and has the following cell parameters: a = 12.462(2)Å, b = 14.014(3)Å, c = 14.839(3)Å, α = 76.262(6)°, β = 65.843(4)°, γ = 84.820(5)°, ν = 2296.7(7)Å. 3 The structural formula is: .

[0031] If Ln is a rare earth metal Y, then the radical binuclear rare earth single-molecule magnetic complex is Y2(L1)2(L2)(OTF)2(Py)2, which belongs to the triclinic crystal system, space group P-1, and has the following cell parameters: a = 12.4471(18)Å, b = 14.335(2)Å, c = 15.018(2)Å, α = 75.784(2)°, β = 65.611(2)°, γ = 84.809(3)°, ν = 2365.6(6)Å. 3 The structural formula is: .

[0032] Example 2: The principle of this invention is as follows: The magnetism of rare-earth single-molecule magnets originates from the molecule itself, possessing advantages such as uniform size, ease of processing, and strong chemical modifiability. In particular, rare-earth ions exhibit large ground-state magnetic moments and unquenched orbital angular momentum, demonstrating strong magnetic anisotropy, making them ideal for preparing high-performance single-molecule magnets. Research on rare-earth single-molecule magnets has expanded from early mononuclear systems to systems with high nuclei, heterometallic, and radical coupling. However, rare-earth single-molecule magnets are often accompanied by magnetization quantum tunneling, which severely affects further increases in magnetic blocking temperature. How to effectively prepare high-performance multinuclear rare-earth single-molecule magnets has become an important issue in the field of molecular magnets. This invention designs and synthesizes a series of radical dinuclear rare-earth single-molecule magnet complexes, utilizing radical bridging ligands to transfer magnetic interactions, thereby achieving effective control of single-molecule magnetization quantum tunneling and magnetic relaxation processes.

[0033] Based on the above technical principles, such as Figure 9 The flowchart below shows a method for preparing a free radical binuclear rare earth single-molecule magnetic complex provided by the present invention. Figure 9 As shown, the preparation method includes the following steps: S1: Ligand L1 is synthesized by heating 2-(1-pyrazole)-pyridine with potassium borohydride.

[0034] Specifically, 2-(1-pyrazole)-pyridine and potassium borohydride were mixed at a molar ratio of 5:1 and circulated 3 times under vacuum-nitrogen atmosphere. The mixture was reacted at 210°C for 12 hours. After cooling, toluene was added, and the mixture was sonicated at room temperature for 3 hours. The mixture was then filtered, and the solid powder was collected to obtain ligand L1. S2: 2,5-Dicarboxylated terephthalic ether was dissolved in dichloromethane, and then boron tribromide was added to react at room temperature. The reaction was then quenched by adding ammonium chloride to synthesize ligand L2.

[0035] Specifically, 2,5-dicarboxylated terephthalic ether was dissolved in dichloromethane, and then boron tribromide was added (the molar ratio of 2,5-dicarboxylated terephthalic ether to boron tribromide was 1:3). The reaction was carried out at room temperature for 24 hours, and then ammonium chloride was added to quench the reaction (the molar ratio of boron tribromide to ammonium chloride was 1:3). The reaction solution was extracted with water, the organic phase was concentrated, recrystallized in ethanol, filtered, and the yellow solid powder was collected to obtain ligand L2. S3: Dissolve rare earth metal salts and ligand L1 in pyridine and react. Then add ligand L2 and continue the reaction to synthesize free radical binuclear rare earth monomolecular magnet complexes.

[0036] Specifically, the rare earth metal salts dysprosium trifluoromethanesulfonate Dy(OTF)3, gadolinium trifluoromethanesulfonate Gd(OTF)3, or yttrium trifluoromethanesulfonate Y(OTF)3 and ligand L1 obtained in step S1 are dissolved in pyridine and stirred at room temperature for 2 hours. Then, ligand L2 obtained in step S2 is added and stirred at room temperature for another 2 hours. After the reaction is completed, the mixture is filtered and the filtrate is diffused in the gas phase for 8 days to obtain a free radical binuclear rare earth monomolecular magnet complex.

[0037] The molar ratio of ligands L1 and L2 to any one of dysprosium trifluoromethanesulfonate Dy(OTF)3, gadolinium trifluoromethanesulfonate Gd(OTF)3, or yttrium trifluoromethanesulfonate Y(OTF)3 is 2:2:1.

[0038] Example 3: The application of the free radical binuclear rare earth single-molecule magnet complex in Example 1 is used for the preparation of molecular magnetic storage devices.

[0039] Experimental Analysis: 1. NMR characterization and analysis of ligands L1 and L2: The NMR spectra of ligands L1 and L2 were measured using a Bruker Avance 500 MHz NMR spectrometer with DMSO-d6 as the deuterated reagent.

[0040] Test results are as follows Figures 1-2 As shown, through Figures 1-2The results show that the proton NMR spectra of the two ligands correspond on the spectrum, and there are no other impurity peaks besides the solvent peak, indicating that the synthesized ligand is the target ligand with high purity and accurate structure, and the corresponding hydrogen atom chemical shifts have been marked on the spectrum. Figures 1-2 The chemical shifts of the two ligands in the proton NMR spectra are as follows: Ligand L1 δ = 8.50 (dd, J = 5.1, 1.8 Hz, 1H), 7.94 (d, J = 7.9 Hz, 1H), 7.73 (tt, J = 7.9, 2.4 Hz, 1H), 7.54 (d, J = 2.3 Hz, 1H), 7.18 (ddd, J = 7.6, 4.8, 1.3 Hz, 1H), 6.68 (d, J = 2.2 Hz, 1H); Ligand L2 δ = 10.31 (s, 1H), 10.29 (s, 1H), 7.23 (s, 1H).

[0041] 2. Single-crystal structure testing and analysis of single-molecule magnetic complexes: Single-crystal X-ray diffraction data were collected using a Bruker Apex II CCD diffractometer with monochromatic Mo-Kα radiation of graphite (λ = 0.71073 Å). The structure was solved using the SHELXT (direct method) in the Olex2 package, and all non-hydrogen atoms were refined for anisotropic thermal parameters of F2 using SHELXL (full matrix least squares technique). All hydrogen atoms were incorporated into the calculation positions and refined with a fixed geometry relative to their carrier atoms. The single-crystal structure of the complex was obtained using the Olex2 structure analysis program with the direct Patterson method and refined using the SHELX crystal package with full matrix least squares. The coordinates of non-hydrogen atoms and the anisotropic temperature coefficients were corrected to least squares using the full matrix method.

[0042] Test results are as follows Figure 3 As shown, through Figure 3 Structural analysis revealed that all three complexes possess a binuclear linear structure. Two ligands, L1, are located at either end of the structure and coordinate with two rare-earth ions, respectively. The two pyridine molecules further coordinate with rare-earth ions to form rare-earth coordination units. A ligand, L2, is located in the center of the structure, connecting the two rare-earth coordination units to form a linear binuclear host structure. Since the host molecule carries two positive charges, two negatively charged trifluoromethanesulfonate anions are located in the crystal lattice to balance the positive charge of the host molecule.

[0043] Furthermore, due to the similar ionic radii and coordination characteristics of the three rare earth ions, the structures of the three rare earth complexes are also similar, with only minor differences in cell parameters and coordination bond lengths. Among them, the complex Dy2(L1)2(L2)(OTF)2(Py)2 belongs to the triclinic crystal system, space group P-1, and its cell parameters are a = 12.319(3)Å, b = 14.053(4)Å, c = 14.775(3)Å, α = 75.993(6)°, β = 66.199(4)°, γ = 84.748(6)°, ν = 2270.7(10)Å. 3 The complex Gd2(L1)2(L2)(OTF)2(Py)2 belongs to the triclinic crystal system, space group P-1, and its cell parameters are a = 12.462(2)Å, b = 14.014(3)Å, c = 14.839(3)Å, α = 76.262(6)°, β = 65.843(4)°, γ = 84.820(5)°, ν = 2296.7(7)Å. 3 The complex Y2(L1)2(L2)(OTF)2(Py)2 belongs to the triclinic crystal system, space group P-1, and its cell parameters are a = 12.4471(18)Å, b = 14.335(2)Å, c = 15.018(2)Å, α = 75.784(2)°, β = 65.611(2)°, γ = 84.809(3)°, ν = 2365.6(6)Å. 3 .

[0044] 3. Infrared spectroscopy testing and analysis: Infrared spectra were measured on a Nicolet 6700 Fourier transform infrared spectrometer equipped with an iTR™-ATR accessory, with a wavelength range of 4000–500 cm⁻¹. -1 The test results are as follows: Figure 4 As shown, Figure 4 Image (a) shows the infrared spectrum of Dy2(L1)2(L2)(OTF)2(Py)2. Figure 4 Image (b) shows the infrared spectrum of Gd2(L1)2(L2)(OTF)2(Py)2. Figure 4 In the middle (c), the infrared spectrum of Y2(L1)2(L2)(OTF)2(Py)2 is obtained by... Figure 4 This indicates that the infrared data of the three complexes are basically similar, especially in the 3000-3500 cm⁻¹ range. -1 This is the stretching vibration peak of the benzene ring CH; 1500-1700 cm⁻¹ -1 The strong absorption is due to the vibrational peak of C=O; 650-800 cm⁻¹ -1This is the bending vibration peak of CH.

[0045] 4. Thermogravimetric analysis: Thermal stability data were obtained by testing the carbon heat loss and thermal stability of the samples using an HCT-1 thermogravimetric analyzer. Before testing, the samples were dried in a vacuum drying oven at 70℃ for 12 h. 5-10 mg of each sample was weighed and placed in a crucible, and the test was conducted under a N2 atmosphere at a temperature range of 35℃-800℃ and a heating rate of 10℃ / min. The test results are as follows: Figure 5 As shown, Figure 5 In the middle (a), the results show the thermal stability of Dy2(L1)2(L2)(OTF)2(Py)2. Figure 5 (b) shows the thermal stability results of Gd2(L1)2(L2)(OTF)2(Py)2. Figure 5 In the middle (c), the thermal stability results of Y2(L1)2(L2)(OTF)2(Py)2 are obtained through... Figure 5 It can be seen that all three complexes exhibit slight weight loss below 100℃, mainly due to the loss of some solvent molecules during heating. The thermogravimetric analysis of the complexes shows a plateau between 100-360℃, indicating that the complexes are stable within this temperature range. After 360℃, the compounds slowly lose weight, indicating that the complexes begin to decompose until they are completely transformed into rare earth oxides at 450℃.

[0046] 5. DC magnetic susceptibility testing and analysis: The magnetism of the complexes was tested using a Quantum Design MPMS-XL-7 SQUID magnetometer. This instrument operates from 1.8 to 300 K with a DC field strength of -7 to 7 T. Magnetization of all polycrystalline samples was measured below 100 K prior to detailed measurements to check for ferromagnetic impurities. All data were diamagnetic corrected according to the Pascal constant table.

[0047] Magnetic test results as follows Figure 6 As shown, through Figure 6 show: The room temperature χ of the complex Dy2(L1)2(L2)(OTF)2(Py)2 M The T (molar magnetic susceptibility) value is 27.43 cm. 3 K mol -1 Slightly lower than the theoretical value of 28.69 cm 3 K mol -1 This indicates the possible presence of magnetically open impurities in the molecule. As the temperature decreases, χ... M The T value gradually decreased, and then suddenly decreased at 20 K, indicating that the compound exhibited magnetic blocking at low temperatures, suggesting that the complex has potential single-molecule magnet properties.

[0048] χ² at room temperature of complex Gd2(L1)2(L2)(OTF)2(Py)2 M The T value is 17.56 cm. 3 K mol -1 Slightly higher than the theoretical value of 16.76 cm 3 K mol -1 This indicates the possible existence of ferromagnetic interactions within the molecules. As the temperature decreases, χ... M The T value remains unchanged, indicating that the compound has obvious isotropic properties. χ M The T value shows a significant increase at 19 K, indicating that the compound does indeed exhibit ferromagnetic interactions.

[0049] The room temperature χ of the complex Y2(L1)2(L2)(OTF)2(Py)2 M The T value is 0.45 cm. 3 K mol -1 Slightly higher than the theoretical value by 0.375 cm 3 K mol -1 This indicates the possible existence of weak ferromagnetic interactions within the molecule. Since the rare earth element Y lacks a magnetic quantum number and exhibits diamagnetism, the magnetic moment contribution of the compound originates from the single-electron behavior of the radical of the L2 ligand.

[0050] The above tests show that for different rare earth elements, χ M The T-curves show different patterns. The complex Y2(L1)2(L2)(OTF)2(Py)2, containing diamagnetic Y, exhibits paramagnetism, indicating that the ligand L2 has single-electron radical properties. The isotropic complex Gd2(L1)2(L2)(OTF)2(Py)2 shows ferromagnetic interactions at low temperatures, indicating that the radical ligand L2 can effectively transmit ferromagnetic interactions. The anisotropic complex Dy2(L1)2(L2)(OTF)2(Py)2 exhibits magnetic blocking at low temperatures, indicating that this compound has single-molecule magnetic properties.

[0051] To investigate the single-molecule magnetic behavior of the complex Dy2(L1)2(L2)(OTF)2(Py)2, we performed low-temperature hysteresis loop tests on the complex. The test results are as follows: Figure 7 As shown, through Figure 7 The results show that the complex exhibits a distinct butterfly-shaped hysteresis loop at 1.9 K, indicating that the compound possesses unimolecular magnetic properties. The zero-field hysteresis loop has a closed opening, indicating that the complex exhibits significant zero-field magnetization quantum tunneling behavior. This is attributed to the fact that the magnetic interaction transmitted by the free radical ligand L2 is insufficient to suppress the intrinsic magnetization quantum tunneling relaxation process of rare earth ions.

[0052] pass Figure 7 It can also be seen that this radical binuclear rare earth single-molecule magnet complex can be used to prepare molecular magnetic storage devices.

[0053] 6. AC magnetic susceptibility testing and analysis: To further investigate the relaxation mechanism of the complex Dy2(L1)2(L2)(OTF)2(Py)2, we conducted AC magnetic susceptibility tests on the complex and obtained the temperature-dependent relaxation time by extracting the relaxation times at different temperatures. Figure 8 By fitting Figure 8 The curves show that the effective energy barrier of this complex is 223.8 K, and the pre-exponential factor is 1.0 × 10⁻⁶. -7 The relaxation time exhibits a temperature-independent relaxation term in the low-temperature region, primarily due to magnetization quantum tunneling behavior, with a quantum tunneling relaxation time of 2.6 × 10⁻⁶. -3 This further demonstrates that the magnetic interactions transmitted by the ligand L2 radical are insufficient to suppress the intrinsic magnetization quantum tunneling of rare earth elements.

[0054] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A free radical binuclear rare earth single-molecule magnet complex, characterized in that, The chemical formula is: ； Among them, L1 and L2 are organic ligands, and Ln is any one of rare earth metals Dy, Gd or Y; The structural formula of ligand L1 is: ； The structural formula of ligand L2 is: 。 2. The free radical binuclear rare earth single-molecule magnet complex according to claim 1, characterized in that, If Ln is a rare earth metal Dy, then the radical binuclear rare earth monomolecular magnet complex is Dy2(L1)2(L2)(OTF)2(Py)2, with the following structural formula: 。 3. The free radical binuclear rare earth single-molecule magnet complex according to claim 1, characterized in that, If Ln is the rare earth metal Gd, then the radical binuclear rare earth monomolecular magnet complex is Gd2(L1)2(L2)(OTF)2(Py)2, with the following structural formula: 。 4. The free radical binuclear rare earth single-molecule magnet complex according to claim 1, characterized in that, If Ln is a rare earth metal Y, then the radical binuclear rare earth monomolecular magnet complex is Y2(L1)2(L2)(OTF)2(Py)2, with the following structural formula: 。 5. The method for preparing the free radical binuclear rare earth single-molecule magnet complex according to any one of claims 1-4, characterized in that, Includes the following steps: S1: Ligand L1 is synthesized by reacting 2-(1-pyrazole)-pyridine with potassium borohydride under heating. S2: 2,5-Dicarboxylated terephthalic ether was dissolved in dichloromethane, then boron tribromide was added and reacted at room temperature, followed by the addition of ammonium chloride to quench the reaction, thus synthesizing ligand L2; S3: Dissolve rare earth metal salts and ligand L1 in pyridine and react. Then add ligand L2 and continue the reaction to synthesize free radical binuclear rare earth monomolecular magnet complexes.

6. The method for preparing the free radical binuclear rare earth single-molecule magnet complex according to claim 5, characterized in that, In S1, the molar ratio of 2-(1-pyrazole)-pyridine to potassium borohydride is 5:

1.

7. The method for preparing the free radical binuclear rare earth single-molecule magnet complex according to claim 6, characterized in that, In S2, the molar ratio of 2,5-dicarboxylated p-phenylenedimethyl ether to boron tribromide is 1:

3.

8. The method for preparing the free radical binuclear rare earth single-molecule magnet complex according to claim 7, characterized in that, In S3, the molar ratio of ligands L1 and L2 to the rare earth metal salt is 2:2:

1.

9. The method for preparing the free radical binuclear rare earth single-molecule magnet complex according to claim 8, characterized in that, In S3, the rare earth metal salt is any one of Dy(OTF)3, Gd(OTF)3 or Y(OTF)3.

10. The application of the free radical binuclear rare earth single-molecule magnet complex according to any one of claims 1-4, characterized in that, Its application in the fabrication of molecular magnetic storage devices.

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