Cobalt-based ferroelectric single-molecular magnet molecular crystal and preparation method and application thereof

Abstract

The invention relates to a cobalt-based ferroelectric single-molecule magnet molecular crystal and a preparation method and application thereof, and belongs to the technical field of molecule-based magnetic materials. The chemical formula of the cobalt-based ferroelectric single-molecular magnet molecular crystal is [(CH3) 3S] 4 [Co (NCBH3) 6]. According to the invention, through the rational design of the molecular structure of an A4 [M (NCX) 6] type compound, the ordered-disordered phase change of organic cations is regulated and controlled to induce the symmetry breaking of the crystal so as to generate ferroelectricity; meanwhile, the transition metal center is endowed with strong magnetic anisotropy through ligand field engineering, so that the single-molecule magnet characteristic is realized, and the cobalt-based molecular crystal with the single-phase coexisting ferroelectricity and the single-molecule magnet characteristic is finally obtained; the problem that an existing A4 [M (NCX) 6] type compound cannot synergistically integrate ferroelectricity and the characteristics of a single-molecule magnet is solved.

Description

Technical Field

[0001] This invention belongs to the field of molecular-based magnetic materials technology, specifically relating to a cobalt-based ferroelectric single-molecule magnet molecular crystal, its preparation method, and its application. Background Technology

[0002] Molecular functional materials that combine magnetic and electrical long-range order are the core molecular platforms for cross-coupling functions in next-generation information technology. By integrating ferroelectricity with single-molecule magnets (SMMs), molecular-level magnetic relaxation can be achieved through electric field modulation. Their device design concept is fundamentally different from that of traditional magnetoelectric heterostructures. These materials, which combine ferroelectricity and single-molecule magnet properties, are called ferroelectric single-molecule magnets (FE-SMMs) and are a research hotspot in the field of molecular functional materials.

[0003] Almost all reported ferroelectric single-molecule magnets are based on rare-earth systems, with rare-earth ions (such as Dy) as the basis. 3+ Rare earth complexes have strong 4f electron localization, large spin-orbit coupling, and significant crystal field anisotropy, which naturally facilitates slow magnetic relaxation. However, the 4f orbital shielding effect of rare earth complexes is strong, resulting in weak response to ligand field modulation. Their coordination geometry is flexible and easily incorporates solvents, making it difficult to achieve predictable structural control. It is also difficult to achieve the symmetry breaking required for ferroelectric polarization in a wider chemical space. The inherent defects in structural tunability limit their application in the systematic design of ferroelectric single-molecule magnets.

[0004] The magnetic anisotropy and coordination symmetry of transition metals can be precisely controlled through ligand field engineering, making them ideal alternatives to rare earth systems. Octahedral-coordinated Co, in particular, is a significant candidate for this purpose. 2+ Complexes can exhibit significant zero-field splitting and strong spin-orbit coupling under suitable ligand conditions, and have the potential advantage of constructing ferroelectric single-molecule magnets. However, to date, there have been no reports on transition metal-based ferroelectric single-molecule magnets, and the development of transition metal-based ferroelectric single-molecule magnets has become a key technical challenge in the field of molecular functional materials.

[0005] In the existing technology, researchers mostly use A4[M(NCX)6] type compounds as structural platforms to carry out molecular functional materials research. These materials can provide a clear octahedral coordination environment for transition metal centers, and can also accommodate organic cations with orientation dynamics, providing an inherent structural basis for combining magnetic anisotropy and symmetry-broken ferroelectric phase transitions.

[0006] However, existing research using this type of structural platform only focuses on ferroelectric or magnetic properties, without achieving synergistic integration of the two. Furthermore, in the selection of ligands and organic cations, the regulatory effect of ligands on the magnetic anisotropy of transition metals, the influence of the order-disorder phase transition of organic cations on crystal symmetry, and the effect of the weak interaction between the two on maintaining the stability of the magnetic center environment are not considered. Therefore, it is impossible to achieve the coexistence of ferroelectricity and single-molecule magnetic properties in single-phase molecular crystals through structural design. Summary of the Invention

[0007] To address the problems of existing technologies, this application provides a cobalt-based ferroelectric single-molecule magnet molecular crystal, its preparation method, and its applications. This application achieves ferroelectricity by rationally designing the molecular structure of A4[M(NCX)6] type compounds, regulating the ordered-disorder phase transition of organic cations to induce crystal symmetry breaking, and simultaneously endowing the transition metal center with strong magnetic anisotropy through ligand field engineering to achieve single-molecule magnet properties. Ultimately, a cobalt-based molecular crystal with both single-phase ferroelectric and single-molecule magnet properties is obtained; this solves the problem that existing A4[M(NCX)6] type compounds cannot synergistically integrate ferroelectricity and single-molecule magnet properties.

[0008] First, this application provides a cobalt-based ferroelectric single-molecule magnet molecular crystal with the chemical formula [(CH3)3S]4[Co(NCBH3)6].

[0009] Furthermore, the cobalt-based ferroelectric single-molecule magnet molecular crystal, at a low temperature of <265K, belongs to the trigonal crystal system and crystallizes in the trigonal polar space group R3c (No. 161). 2+ Located on the triple helix axis, with 6 NCBH3 - The N atoms form an octahedral coordination, with an average bond length of 2.119 Å for Co-N and an octahedral distortion parameter of 75.4°. The cell parameters are a = 16.6172(7) Å, b = 16.6172(7) Å, c = 23.0141(15) Å, α = 90°, β = 90°, γ = 120°, and V = 5503.5(6) Å. 3 .

[0010] Furthermore, the cobalt-based ferroelectric single-molecule magnet molecular crystal, with a high-temperature phase >265K, belongs to the trigonal crystal system and crystallizes in the centrosymmetry space group R-3c (No. 167), [Co(NCBH3)6]. 4- Maintaining octahedral coordination, the average Co-N bond length is 2.110 Å, and the octahedral distortion parameter is 14.3°; the cell parameters are a=17.384(3) Å, b=17.384(3) Å, c=22.187(4) Å, α=90°, β=90°, γ=120°, and V=5807(2) Å. 3 .

[0011] Furthermore, the cobalt-based ferroelectric single-molecule magnet molecular crystal conforms to the characteristics of a second-order ferroelectric phase transition, and under an applied magnetic field, it also exhibits the slow magnetic relaxation behavior typical of single-molecule magnets.

[0012] Secondly, this application provides a method for preparing cobalt-based ferroelectric single-molecule magnet molecular crystals, comprising the following steps: S1. Dissolve trimethylthionium salt and cobalt hexacyanoborhydride in a solvent and stir to obtain a clear solution;

[0013] S2. Transfer the above solution to a glass petri dish and place it in a dust-free, constant-temperature environment for more than 5 days to obtain red blocky cobalt-based ferroelectric single-molecule magnet molecular crystals.

[0014] Furthermore, the trimethylthionium salt, cobalt hexacyanoborohydride, and solvent are all of analytical grade.

[0015] Furthermore, the molar ratio of trimethylthionium salt to cobalt hexacyanoborohydride is 4-6:1, preferably 4-5:1, and more preferably 4-4.5:1.

[0016] Further, the solvent is a mixture of methanol and ethanol, with a volume ratio of 1-3:1-3; preferably, the volume ratio of methanol to ethanol in the mixture is 1-2:1, more preferably 1:1.

[0017] Furthermore, the total concentration of trimethylthionium salt and cobalt hexacyanoboronide in the solution is 0.2-2 mol / L, preferably 0.3-1.5 mol / L, and more preferably 0.5-1 mol / L.

[0018] Furthermore, the temperature of the constant temperature environment in S2 is 23-28℃, preferably 25±1℃.

[0019] Furthermore, the settling time is 5-15 days, preferably 7-10 days.

[0020] Finally, this application also provides the application of the cobalt-based ferroelectric single-molecule magnet molecular crystal in magnetoelectric coupling functional devices and next-generation information storage devices.

[0021] The beneficial effects of this invention are: 1. The cobalt-based ferroelectric single-molecule magnet molecular crystal with the chemical formula [(CH3)3S]4[Co(NCBH3)6] provided in this application realizes the preparation of transition metal-based ferroelectric single-molecule magnets, which greatly enriches this research field, breaks the limitation that most existing ferroelectric single-molecule magnets rely on rare earth systems, and lays the foundation for the development of transition metal-based magnetoelectric coupling molecular functional materials.

[0022] 2. This application successfully achieved the coexistence of ferroelectricity and single-molecule magnet properties in a single-phase cobalt-based molecular crystal. This molecular crystal exhibits stable spontaneous ferroelectric polarization below 265 K (Ps≈0.126μC•cm). -2 ), which can achieve reversible polarization reversal; at the same time, Co 2+ The center exhibits strong easy planar magnetic anisotropy (D = +65.1 cm). -1 It exhibits typical slow magnetic relaxation behavior of a single-molecule magnet under a DC magnetic field of 1500 Oe, and is the first cobalt-based ferroelectric single-molecule magnet.

[0023] 3. This application achieves the decoupled regulation of ferroelectric phase transition and magnetic properties; the ordered-disorder phase transition of organic cations only induces changes in crystal symmetry to generate ferroelectricity. During the phase transition, the octahedral coordination structure of the inorganic magnetic center remains stable, and the magnetic anisotropy and slow magnetic relaxation characteristics are not destroyed, thus ensuring the coordinated stability of magnetic and electrical functions.

[0024] 4. Based on the A4[M(NCX)6] type structure platform, this application achieves the integration of magnetoelectric functions through ligand field engineering and organic cation phase transition design. The design strategy is clear and can be extended to other transition metal systems. It solves the problems of poor tunability and difficulty in systematic design of rare earth-based ferroelectric single-molecule magnet structures. Moreover, the preparation method is simple and easy to implement, without the need for complex high temperature, high pressure or template-assisted processes, and is easy to prepare on a large scale and for industrial application. Attached Figure Description

[0025] Figure 1 TG curve of cobalt-based ferroelectric single-molecule magnet molecular crystal.

[0026] Figure 2 Differential scanning calorimetry curves of powder samples of cobalt-based ferroelectric single-molecule magnets during heating and cooling scanning processes.

[0027] Figure 3 : The relationship between the intensity of the second-order nonlinear optical signal and temperature of the powder sample of cobalt-based ferroelectric single-molecule magnet molecular crystal.

[0028] Figure 4 Comparison of second-order nonlinear optical signals between cobalt-based ferroelectric single-molecule magnet molecular crystals and potassium dihydrogen phosphate (KDP).

[0029] Figure 5 Dielectric constants of powder samples of cobalt-based ferroelectric single-molecule magnets at different frequencies. ε ′)The relationship between temperature and temperature.

[0030] Figure 6 :based on Figure 5 Curie-Weiss law fitting curve for the data.

[0031] Figure 7 Spontaneous polarization intensity of cobalt-based ferroelectric single-molecule magnet molecular crystals ( P s) The relationship between temperature and s.

[0032] Figure 8 Cobalt-based ferroelectric single-molecule magnet molecular crystals χ M T The relationship between the value and temperature.

[0033] Figure 9 Field-dependent magnetization of cobalt-based ferroelectric single-molecule magnet molecular crystal samples in a DC magnetic field of 0~7T ( M - H Isotherm curve.

[0034] Figure 10 The product of in-phase magnetic susceptibility of cobalt-based ferroelectric single-molecule magnet molecular crystal samples under a DC magnetic field of 1500 Oe ( χ' M ) and heterogeneous magnetic susceptibility ( χ" M ) with frequency ( υ The relationship between the changes is shown in the diagram.

[0035] Figure 11 Coulomb diagram of cobalt-based ferroelectric single-molecule magnet molecular crystal under a DC magnetic field of 1500 Oe.

[0036] Figure 12 Magnetic relaxation time of cobalt-based ferroelectric single-molecule magnet molecular crystal samples under a DC magnetic field of 1500 Oe τ The relationship between temperature and temperature. Detailed Implementation

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0038] A cobalt-based ferroelectric single-molecule magnet molecular crystal with the chemical formula [(CH3)3S]4[Co(NCBH3)6]. Through a rational design strategy combining organic cation ordering with anisotropic engineering of the metal center, the A4[M(NCX)6] type molecular crystal structure constructed in this application specifies the selection of C3v symmetric [(CH3)3S]4[(CH3)3S]4[Co(NCBH3)6]. +(TMS) is an organic cation. Utilizing the low-barrier rotational properties of TMS cations, an order-disorder phase transition occurs in the crystal at the phase transition temperature, inducing symmetry breaking and endowing the crystal with ferroelectricity in the low-temperature phase. NCBH3 was selected. - For ligands, Co 2+ To establish a stable octahedral coordination environment for the transition metal center, ligand field engineering was used to equip Co with a suitable environment. 2+ The strong planar magnetic anisotropy enables the crystal to exhibit slow magnetic relaxation behavior characteristic of a single-molecule magnet; at the same time, the weak van der Waals interaction between organic cations and inorganic anions is used to ensure the structural stability of the inorganic magnetic center during the phase transition of organic cations, ultimately achieving the coexistence of ferroelectricity and single-molecule magnet characteristics in a single-phase cobalt-based molecular crystal.

[0039] For the realization of ferroelectric properties: In the low-temperature phase (<265 K), TMS cations are highly ordered, with two crystallographically different TMS cations, both oriented along the c-axis of the crystal. The dipole moments are superimposed along the c-axis, forming an uncompensated net dipole moment, causing the crystal to crystallize in the trigonal polar space group R3c (No. 161), without a center of symmetry and possessing a unique polar axis, resulting in spontaneous ferroelectric polarization. In the high-temperature phase (>265 K), TMS cations undergo significant rotational disorder around the triple axis and rearrange themselves within the crystal channels. The dipole moments are randomly distributed and cancel each other out, transforming the crystal into the centrosymmetric space group R-3c (No. 167), exhibiting paraelectric properties. This cation-order-disorder phase transition achieves a reversible ferroelectric-paraelectric phase transition of the crystal, and the weak interaction between cations and anions ensures that the magnetic center structure is not destroyed during the phase transition process.

[0040] Furthermore, the cobalt-based ferroelectric single-molecule magnet molecular crystal, in its low-temperature phase <265 K, belongs to the trigonal crystal system and crystallizes in the trigonal polar space group R3c (No. 161). 2+ Located on the triple helix axis, with 6 NCBH3 - The N atoms form an octahedral coordination, with an average bond length of 2.119 Å for Co-N and an octahedral distortion parameter of 75.4°. The cell parameters are a = 16.6172(7) Å, b = 16.6172(7) Å, c = 23.0141(15) Å, α = 90°, β = 90°, γ = 120°, and V = 5503.5(6) Å. 3 .

[0041] Furthermore, the cobalt-based ferroelectric single-molecule magnet molecular crystal, with a high-temperature phase >265 K, belongs to the trigonal crystal system and crystallizes in the centrosymmetry space group R-3c (No. 167), [Co(NCBH3)6]. 4-Maintaining octahedral coordination, the average Co-N bond length is 2.110 Å, and the octahedral distortion parameter is 14.3°; the cell parameters are a=17.384(3) Å, b=17.384(3) Å, c=22.187(4) Å, α=90°, β=90°, γ=120°, and V=5807(2) Å. 3 .

[0042] Furthermore, the cobalt-based ferroelectric single-molecule magnet molecular crystal conforms to the characteristics of a second-order ferroelectric phase transition, and under an applied magnetic field, it also exhibits the slow magnetic relaxation behavior typical of single-molecule magnets.

[0043] For achieving single-molecule magnet properties: Choosing Co 2+ As the metal center, NCBH3 - As a ligand, NCBH3 - The cyano group of the ligand provides a strong σ-electron-donating effect, and the steric hindrance of the cyanoboron group inhibits the rearrangement of the anion structure, thus providing Co 2+ Constructing a stable octahedral coordination environment; under the influence of the ligand field, Co 2+ Significant axial zero-field splitting was observed (D=+65.1cm). -1 It exhibits strong easy planar magnetic anisotropy, and under an applied DC magnetic field of 1500 Oe, the quantum tunneling effect of magnetization can be suppressed, making the crystal exhibit typical slow magnetic relaxation behavior and realizing the characteristics of a single-molecule magnet.

[0044] For the synergistic realization of magnetoelectric function: utilizing the weak van der Waals interaction dominated by H···H as the organic cation and [Co(NCBH3)6]3 4- The main interactions between inorganic anions are the absence of strong directional bonds, ensuring that the TMS cations [Co(NCBH3)6] can function effectively during the order-disorder phase transition. 4- The octahedral coordination geometry of inorganic anions remains stable, with no significant changes in Co-N bond length and octahedral distortion parameters. The magnetic anisotropy of the magnetic center remains unaffected, achieving decoupled control of ferroelectric phase transition and magnetic properties, and ensuring the stable coexistence of ferroelectricity and single-molecule magnetic properties in a single-phase crystal.

[0045] Secondly, this application provides a method for preparing cobalt-based ferroelectric single-molecule magnet molecular crystals, comprising the following steps: S1. Dissolve trimethylthionium salt and cobalt hexacyanoborhydride in a solvent and stir to obtain a clear solution; S2. Transfer the above solution to a glass petri dish and place it in a dust-free, constant-temperature environment for more than 5 days to obtain red blocky cobalt-based ferroelectric single-molecule magnet molecular crystals.

[0046] Furthermore, the trimethylthionium salt, cobalt hexacyanoborohydride, and solvent are all of analytical grade. Crystal growth is extremely sensitive to the purity of the precursor; the presence of impurities may become heterogeneous nucleation centers, leading to the formation of a large number of fine crystals, or directly interfering with molecular assembly, resulting in an unsuitable crystal phase.

[0047] Furthermore, the molar ratio of trimethylthionium salt to cobalt hexacyanoborohydride is 4-6:1, preferably 4-5:1, and more preferably 4-4.5:1.

[0048] Further, the solvent is a mixture of methanol and ethanol, with a volume ratio of 1-3:1-3; preferably, the volume ratio of methanol to ethanol in the mixed solvent is 1-2:1, more preferably 1:1. The selection and proportion of methanol and ethanol have a significant impact on the evaporation rate of the solvent and its solubility in the reactants, and may also induce intermolecular forces for crystal nucleation. First, methanol has a low boiling point (approximately 65°C) and evaporates quickly; ethanol has a higher boiling point (approximately 78°C) and evaporates slowly. Mixing them in a 1:1 ratio yields a moderate and stable evaporation rate between the two. This is crucial for crystal growth. If evaporation is too rapid, the solution will quickly reach supersaturation, instantly generating a large number of crystal nuclei, ultimately resulting in a large number of microcrystals or polycrystals, or even crystals containing defects, resulting in poor crystal quality. If evaporation is too slow, the growth cycle is too long, and raw material precipitation may occur due to solubility issues. The mixed solvent of this application provides a smooth supersaturation enhancement process, which is conducive to the slow growth and maturation of crystal nuclei, thereby obtaining single crystals with high crystal quality. Secondly, using a mixed solvent of methanol and ethanol allows for fine-tuning of the solubility of the two raw materials in the reaction system, making their concentration ratio in solution closer to the stoichiometry. This prevents premature precipitation of one reactant due to supersaturation, ensuring sufficient contact and coordinated crystallization of both into the final crystal lattice. Furthermore, as polar protic solvents, methanol and ethanol's hydroxyl groups (-OH) may form weak, dynamic hydrogen bonds with cyano (-CN) or borohydride (-BH3) groups on organic cations or anions during the initial and subsequent crystallization stages. While these interactions are not strong directional bonds in the final crystal structure, they may act as templates or guides during crystal assembly. A 1:1 mixture of methanol and ethanol may provide a suitable hydrogen bond network, guiding the TMS cations and Co... 2+ Anions and NCBH3 - The ligands are arranged in the correct orientation and stacking manner, eventually forming the expected crystal structure with only weak van der Waals forces.

[0049] Furthermore, the total concentration of trimethylthionium salt and cobalt hexacyanoborohydride in the solution is 0.2-2 mol / L, preferably 0.3-1.5 mol / L, and more preferably 0.5-1 mol / L. Adjusting the reactant concentration is to precisely control the initial supersaturation of the solution; this concentration range provides sufficient supersaturation driving force to ensure crystal nucleation and growth, while avoiding explosive nucleation or excessive solution viscosity due to excessive concentration, thereby achieving a balance between the number of crystal nuclei and crystal size, ensuring the acquisition of higher quality single crystals.

[0050] Furthermore, the constant temperature environment in S2 is 23-28℃, preferably 25±1℃. The solvent evaporation rate is exponentially related to temperature; if the temperature is too high, the solvent evaporates too quickly, leading to a sharp increase in supersaturation, resulting in a large number of crystal nuclei exploding instantly, and the product being microcrystalline powder. If the temperature is too low, the molecular kinetic energy is insufficient, making it difficult to overcome the energy barrier and arrange themselves in an orderly manner, which may lead to crystallization failure or the formation of a glassy state.

[0051] Furthermore, the settling time is 5-15 days, preferably 7-10 days. This time provides a complete kinetic cycle, ensuring the complete process from nucleation to growth of the crystal, and allowing solvent molecules to be completely expelled from the crystal lattice.

[0052] In the following examples, the trimethylthionium salt, cobalt hexacyanoboronide, and methanol / ethanol mixed solvent were all of analytical grade.

[0053] Example 1 This embodiment provides a cobalt-based ferroelectric single-molecule magnet molecular crystal with the chemical formula [(CH3)3S]4[Co(NCBH3)6];

[0054] The preparation method of the cobalt-based ferroelectric single-molecule magnet molecular crystal is as follows: S1. Dissolve 0.01 mol of trimethylsulfonium bromide and 0.0025 mol of cobalt hexacyanoborohydride in 20 mL of methanol / ethanol mixed solvent (volume ratio 1:1), stir at room temperature for 30 min to obtain a clear and transparent red solution;

[0055] S2. Transfer the above solution to a glass petri dish and place it in a dust-free constant temperature environment at 25°C for slow evaporation. After standing for 8 days, a red blocky [(CH3)3S]4[Co(NCBH3)6] single crystal is obtained, which is the target cobalt-based ferroelectric single-molecule magnet molecular crystal.

[0056] Example 2 This embodiment provides a cobalt-based ferroelectric single-molecule magnet molecular crystal with the chemical formula [(CH3)3S]4[Co(NCBH3)6];

[0057] The preparation method of the cobalt-based ferroelectric single-molecule magnet molecular crystal is as follows: S1. Dissolve 0.0108 mol of trimethylsulfonium bromide and 0.0024 mol of cobalt hexacyanoborohydride in 14 mL of methanol / ethanol mixed solvent (volume ratio 2:1), stir at room temperature for 40 min to obtain a clear and transparent red solution;

[0058] S2. Transfer the above solution to a glass petri dish and place it in a dust-free constant temperature environment at 25°C for slow evaporation. After standing for 7 days, a red blocky [(CH3)3S]4[Co(NCBH3)6] single crystal is harvested, which is the target cobalt-based ferroelectric single-molecule magnet molecular crystal.

[0059] Example 3 This embodiment provides a cobalt-based ferroelectric single-molecule magnet molecular crystal with the chemical formula [(CH3)3S]4[Co(NCBH3)6]; The preparation method of the cobalt-based ferroelectric single-molecule magnet molecular crystal is as follows: S1. Dissolve 0.01 mol of trimethylsulfonium bromide and 0.0025 mol of cobalt hexacyanoborohydride in 25 mL of methanol / ethanol mixed solvent (volume ratio 1.5:1), stir at room temperature for 20 min to obtain a clear and transparent red solution;

[0060] S2. Transfer the above solution to a glass petri dish and place it in a dust-free constant temperature environment at 25°C for slow evaporation. After standing for 10 days, a red blocky [(CH3)3S]4[Co(NCBH3)6] single crystal is obtained, which is the target cobalt-based ferroelectric single-molecule magnet molecular crystal.

[0061] Performance testing methods and results: 1. Thermal analysis test

[0062] (1) Thermogravimetric analysis (TG): Under a nitrogen atmosphere, the mass change of the sample in the range of 300-500K is tested at a heating rate of 10K / min to characterize the thermal stability of the sample.

[0063] Appendix Figure 1 The TG curves are shown for the cobalt-based ferroelectric single-molecule magnet molecular crystals prepared in Example 1; (See attached image) Figure 1 It can be seen that the sample remains stable at 420K under nitrogen atmosphere without significant mass loss, demonstrating excellent thermal stability.

[0064] (2) Differential scanning calorimetry (DSC): Under nitrogen atmosphere, the thermal effect of the sample in the range of 200-300K is tested at a heating / cooling rate of 5K / min to determine the phase transition temperature (Tc), and the entropy change is calculated by Boltzmann entropy formula ΔS=RlnN to analyze the phase transition mechanism.

[0065] Appendix Figure 2Differential scanning calorimetry (DSC) curves of the powder sample of the cobalt-based ferroelectric single-molecule magnet molecular crystal prepared in Example 1 during the heating and cooling processes. (See attached image.) Figure 2 It can be seen that the sample exhibits a pair of reversible anomalous peaks at 265K (heating) / 264K (cooling), indicating a reversible structural phase transition. The entropy change ΔS in the heating mode is 10.5 J·mol⁻¹. -1 ·K -1 The calculation yielded N≈3.0, confirming that the order-disorder phase transition was caused by the rearrangement of cation molecules.

[0066] 2. Second-order nonlinear optics (SHG) testing

[0067] Variable-temperature SHG testing was used to measure the SHG signal intensity of the sample in the range of 200-310K, with potassium dihydrogen phosphate (KDP) as a reference to characterize the changes in the centrosymmetry of the crystal and verify the polar / nonpolar structure transition.

[0068] Appendix Figure 3 The graph shows the relationship between the intensity of the second-order nonlinear optical signal and temperature of the powder sample of the cobalt-based ferroelectric single-molecule magnet molecular crystal prepared in Example 1; (See attached graph) Figure 4 This image shows a comparison of the second-order nonlinear optical signals of the cobalt-based ferroelectric single-molecule magnet molecular crystal prepared in Example 1 and potassium dihydrogen phosphate. As can be seen from the image, the sample exhibits a significant SHG signal at low temperature (<265K), with an intensity approximately 0.3 times that of KDP, confirming that the low-temperature phase is a non-centrosymmetric structure. However, at high temperature (>265K), the SHG signal decreases to noise levels, confirming that the high-temperature phase is a centrosymmetric structure.

[0069] 3. Crystal structure testing

[0070] Variable-temperature single-crystal X-ray diffraction (SCXRD) was used to test the crystal structure of samples at 100K (low-temperature phase) and 300K (high-temperature phase), respectively. The space group, atomic coordinates, bond lengths, bond angles, and octahedral distortion parameters were resolved, and the relationship between cation arrangement and crystal symmetry breaking was analyzed.

[0071] (1) Low-temperature phase (100K): crystallized in trigonal polar space group R3c (No. 161), Co 2+ Located on the triple helix axis, with 6 NCBH3 - The N atom forms an octahedral coordination, with an average Co-N bond length of 2.119 Å and an octahedral distortion parameter of 75.4°.

[0072] (2) High-temperature phase (300K): Crystallized in centrosymmetry space group R-3c (No. 167), TMS cations undergo rotational disorder, and their dipole moments cancel each other out; [Co(NCBH3)6] 4-It still maintains regular octahedral coordination, with an average Co-N bond length of 2.110 Å, and the octahedral distortion parameter is reduced to 14.3°, indicating that the inorganic magnetic center structure is stable;

[0073] (3) Hirshfeld surface analysis: The intermolecular interactions in the low-temperature phase are mainly H…H contacts (76.6%), while the H…H contacts in the high-temperature phase account for 79.8%. No strong directional bonds are formed, which confirms that the interactions in the crystal are weak van der Waals forces.

[0074] 4. Dielectric property testing

[0075] Polycrystalline samples were pressed into tablets and an impedance analyzer was used to test the complex permittivity (ε=ε′-iε″) of the samples in the range of 100-300K within the frequency range of 1kHz-1MHz. The order of the ferroelectric phase transition was determined by fitting the dielectric data using the Curie-Weiss law.

[0076] Appendix Figure 5 This paper shows the relationship between the dielectric constant (ε′) of the cobalt-based ferroelectric single-molecule magnet powder sample prepared in Example 1 and temperature at different frequencies. The real part of the complex dielectric constant ε′ exhibits a significant λ-shaped anomaly near 265 K, a typical characteristic of the ferroelectric phase transition. The C0 value is obtained by fitting the data using the Curie-Weiss law. 顺电 / C 铁电 =1.13 (see appendix) Figure 6 It conforms to the characteristics of a second-order ferroelectric phase transition; the relaxation peak of ε″ appears at 132-215K, which is caused by the rearrangement of TMS cations at low temperature, and the dielectric response has excellent repeatability.

[0077] 5. Ferropolarization performance test

[0078] The pyroelectric current test method was used to test the pyroelectric current of the sample under a prepolarization electric field of ±1.7 kV·cm⁻¹, and the spontaneous polarization intensity (Ps) was calculated to characterize the reversibility and magnitude of ferroelectric polarization.

[0079] Appendix Figure 7 This figure shows the relationship between the spontaneous polarization intensity (Ps) of the cobalt-based ferroelectric single-molecule magnet molecular crystal prepared in Example 1 and temperature, calculated by pyroelectric testing after forward and reverse polarization treatments. The values ​​are within ±1.7 kV·cm. -1 Under a pre-polarized electric field, the sample achieves reversible polarization reversal, with a spontaneous polarization intensity of approximately 0.126 μC·cm at low temperatures. -2 The ferroelectric polarization characteristics are stable.

[0080] 6. Magnetic performance test

[0081] (1) DC susceptibility test: Under a DC magnetic field of 1 kOe, the χ of the sample in the range of 2-300 K was tested. MThe T value characterizes the ground-state magnetic properties of the sample; the field-dependent magnetization intensity in the 0-7T magnetic field range is measured at 2-5K to analyze magnetic anisotropy.

[0082] Appendix Figure 8 χ² of cobalt-based ferroelectric single-molecule magnet molecular crystal in Example 1 M The relationship between T-value and temperature. (See attached image) Figure 9 The figures show the field-dependent magnetization (MH) isotherms of the cobalt-based ferroelectric single-molecule magnet molecular crystal sample from Example 1 at 2–5 K in a DC magnetic field of 0–7 T. (See attached figure.) Figures 8-9 It can be seen that: at room temperature χ M The T value is 3.24 cm. 3 ·mol -1 ·K, conforming to high-spin Co 2+ Magnetic characteristics of (S=3 / 2); χ when cooled to 2K M The T value dropped to 1.67 cm. 3 ·mol -1 The ·K value is due to spin-orbit coupling and intermolecular antiferromagnetic interactions; the magnetization reaches 2.17 Nβ at 2K and 7T, exhibiting high-field unsaturation and confirming significant magnetic anisotropy; the spin Hamiltonian fitting yields g = 2.7 and D = +65.1 cm⁻¹. -1 E=0.6 cm -1 Positive D value confirms Co 2+ It is an easy plane magnetic anisotropy.

[0083] (2) AC magnetic susceptibility test: Under a DC magnetic field of 0-2000 Oe, the AC magnetic susceptibility (χ′, χ″) of the sample in the range of 2-50K and 1-1000Hz was tested. The slow magnetic relaxation behavior was characterized by Cole-Cole plot fitting and relaxation time analysis.

[0084] Appendix Figure 10 The product of in-phase magnetic susceptibility (χ′) of the cobalt-based ferroelectric single-molecule magnet molecular crystal sample from Example 1 under a DC magnetic field of 1500 Oe. M ) and heterogeneous magnetic susceptibility (χ″) M The graph shows the relationship between frequency and magnetic field. Under zero DC magnetic field, there is no out-of-phase signal (χ″) with AC magnetic susceptibility. Under a 1500 Oe DC magnetic field, quantum tunneling of magnetization can be effectively suppressed, resulting in obvious frequency- and temperature-dependent χ′ and χ″ signals. (See attached graph.) Figure 11 The image shows the Coulomb-Colomb plot of the cobalt-based ferroelectric single-molecule magnet molecular crystal of Example 1 under a DC magnetic field of 1500 Oe. The solid line represents the optimal fit of the experimental data using the generalized Debye model, and it can be seen that the Coulomb-Colomb plot conforms to the generalized Debye model.

[0085] (3) Magnetic parameter fitting: The PHI40 program was used to fit the magnetic parameters through the spin Hamiltonian. By fitting DC magnetic susceptibility and magnetization data, the zero-field splitting parameters (D, E) and Landé factor (g) are obtained; AC magnetic susceptibility data are fitted using the CC-Fit program to obtain the relaxation time (τ), and the relaxation time (τ) is obtained through... -1 =CT n +AT fitting analysis of relaxation mechanism.

[0086] Appendix Figure 12 This describes the relationship between the magnetic relaxation time τ and temperature of the cobalt-based ferroelectric single-molecule magnet molecular crystal sample from Example 1 under a DC magnetic field of 1500 Oe. Based on the relaxation time analysis, ln(τ) and T... -1 The relationship is curvilinear, consistent with the Raman + direct relaxation mechanism, and the fitting parameter is C = 0.019(7)s. -1 ·K -7.85 n=7.85(2), A=47.18(3)s -1 ·K -1 This confirms that the sample exhibits slow magnetic relaxation behavior characteristic of a single-molecule magnet.

[0087] This application clarifies that the ordering of organic cations is the structural source of ferroelectricity, and that the anisotropy of the metal center regulated by ligand field engineering is the core of the single-molecule magnet properties. A clear structure-activity relationship has been established, providing a solid structural and experimental foundation for subsequent realization of electric field-controlled magnetic relaxation dynamics through molecular design.

[0088] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0089] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A cobalt-based ferroelectric single-molecule magnet molecular crystal, characterized in that, The chemical formula of the cobalt-based ferroelectric single-molecule magnet molecular crystal is [(CH3)3S]4[Co(NCBH3)6].

2. The cobalt-based ferroelectric single-molecule magnet molecular crystal according to claim 1, characterized in that, The cobalt-based ferroelectric single-molecule magnet molecular crystal is a low-temperature phase <265K, belonging to the trigonal crystal system, and crystallizes in the trigonal polar space group R3c (No. 161). 2+ Located on the triple helix axis, with 6 NCBH3 - The N atoms form an octahedral coordination; the cell parameters are a=16.6172(7)Å, b=16.6172(7)Å, c=23.0141(15)Å, α=90°, β=90°, γ=120°, V=5503.5(6)Å. 3 .

3. The cobalt-based ferroelectric single-molecule magnet molecular crystal according to claim 1, characterized in that, The cobalt-based ferroelectric single-molecule magnet molecular crystal is a high-temperature phase (>265K), belonging to the trigonal crystal system, and crystallizes in the centrosymmetry space group R-3c (No. 167), [Co(NCBH3)6]. 4- Maintain octahedral coordination; cell parameters are a=17.384(3)Å, b=17.384(3)Å, c=22.187(4)Å, α=90°, β=90°, γ=120°, V=5807(2)Å. 3 .

4. The cobalt-based ferroelectric single-molecule magnet molecular crystal according to claim 1, characterized in that, The cobalt-based ferroelectric single-molecule magnet molecular crystal conforms to the characteristics of a second-order ferroelectric phase transition and, under an applied magnetic field, also exhibits the slow magnetic relaxation behavior typical of single-molecule magnets.

5. A method for preparing a cobalt-based ferroelectric single-molecule magnet molecular crystal according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Dissolve trimethylthionium salt and cobalt hexacyanoborhydride in a solvent and stir to obtain a clear solution; S2. Transfer the above solution to a glass petri dish and place it in a dust-free, constant-temperature environment for more than 5 days to obtain red blocky cobalt-based ferroelectric single-molecule magnet molecular crystals.

6. The preparation method according to claim 5, characterized in that, The molar ratio of trimethylthionium salt to cobalt hexacyanoborhydride is 4-6:1, and the total concentration of trimethylthionium salt and cobalt hexacyanoborhydride in the solution is 0.2-2 mol / L.

7. The preparation method according to claim 5, characterized in that, The molar ratio of trimethylthionium salt to cobalt hexacyanoborhydride is 4-5:1, and the total concentration of trimethylthionium salt and cobalt hexacyanoborhydride in the solution is 0.3-1.5 mol / L.

8. The preparation method according to claim 5, characterized in that, The solvent is a mixture of methanol and ethanol in a volume ratio of 1-3:1-3; the constant temperature environment in S2 is 23-28℃; the standing time is 5-15 days.

9. The preparation method according to claim 5, characterized in that, The solvent is a mixture of methanol and ethanol, with a volume ratio of 1-2:1; the temperature of the constant temperature environment in S2 is 25±1℃; the standing time is 7-10 days.

10. The application of a cobalt-based ferroelectric single-molecule magnet molecular crystal according to any one of claims 1-4 in magnetoelectric coupling functional devices and next-generation information storage devices.

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