Aromatic hydrocarbon organic low-dimensional magnet and preparation method thereof

Abstract

The invention discloses an aromatic hydrocarbon organic low-dimensional magnet and a preparation method thereof, and belongs to the technical field of low-dimensional magnets, and the preparation method comprises the following steps: mixing bipyridine molecules with metal rubidium under the condition that the water content and the oxygen content are both lower than 0.1 ppm; and under the condition that the vacuum degree is lower than 10 <-4 > Pa, performing ultrasonic oscillation treatment on the mixture under a water bath condition, thereby obtaining the product. By the adoption of the method, rubidium atoms with extremely high reducibility can be effectively doped into a crystal structure, valence electrons of the rubidium atoms are injected into a pi-orbit of organic molecules, then the two-dimensional pi-electron antiferromagnetism is achieved, and the preparation method has the advantages of being easy to operate and convenient to produce.

Description

Technical Field

[0001] The invention belongs to the technical field of low-dimensional magnets, and particularly relates to an aromatic hydrocarbon organic low-dimensional magnet and a preparation method thereof. Background Art

[0002] Low-dimensional magnets, capable of maintaining spontaneous magnetization down to the thickness of a single unit cell in low dimensions, hold promise for technological innovation in areas such as high-density information storage, integrated circuits, and quantum computing. Currently, most reported low-dimensional magnets are achieved through mechanical exfoliation or molecular epitaxy, and the vast majority are inorganic, significantly limiting their development. Compared to inorganic materials, organic materials offer advantages such as low density, diverse structures, and multifunctional composites. If organic materials could be engineered into low-dimensional magnets through specific methods and characterized by specific electrical, magnetic, and optical properties, they would have significant practical applications in information technology. Currently, there are four main approaches to synthesizing organic magnets: constructing magnetic molecular complexes using paramagnetic metal ions and organic ligands, synthesizing magnetic molecular solids and polymers using organic free radicals, introducing defects or edge states into carbon-based materials, and doping aromatic hydrocarbons with alkali metals. However, among these numerous types of organic magnets, low-dimensional organic magnets composed entirely of s or p electron spins are extremely rare. In 2017, Takabayashi et al. reported a cesium-doped phenanthrene crystal with a triangular frustrated structure, which exhibited π-electron Heisenberg antiferromagnetic behavior with S=1 / 2 [Y.Takabayashi, et al.π-electron S=1 / 2quantum spin-liquid statein an ionic polyaromatic hydrocarbon.Nature Chemistry,2017,9(7):635-643.]. In 2018, Yang et al. reported a nanosheet polymer of tris(2,3,5,6-tetrachloro-ethynylphenyl)methyl radicals, which exhibited two-dimensional antiferromagnetism with a Neel characteristic temperature of approximately 42.5K [Yang Y, et al.Antiferromagnetismintwo-dimensional polyradical nanosheets.Polymer Chemistry,2018,9(46):5499-5503.]. These studies expanded the research scope of organic low-dimensional magnets to aromatic hydrocarbon compounds with π-conjugated structures, attracting widespread attention. However, since the above preparation method has harsh conditions and can only achieve low-dimensional magnetism for a specific organic molecular material, it is difficult to promote it in practical applications. Summary of the Invention

[0003] In response to the above-mentioned deficiencies in the prior art, the present invention provides an aromatic hydrocarbon organic low-dimensional magnet and a method for preparing the same. This method can effectively dope rubidium atoms with extremely strong reducing properties into the crystal structure, and inject the valence electrons of the rubidium atoms into the π-orbital of the organic molecules, thereby realizing two-dimensional π-electron antiferromagnetism. This preparation method has the advantages of simple operation and easy production.

[0004] To achieve the above-mentioned purpose, the technical solution adopted by the present invention to solve the technical problem is:

[0005] A method for preparing an aromatic hydrocarbon organic low-dimensional magnet, characterized by comprising the following steps:

[0006] (1) Mixing bipyridine molecules with metallic rubidium under conditions where both water and oxygen contents are less than 0.1 ppm;

[0007] (2) When the vacuum degree is lower than 10 -4 Pa conditions, the above mixture was subjected to ultrasonic oscillation in a water bath to obtain the product.

[0008] Furthermore, in step (1), the atomic molar ratio of bipyridine molecules to metallic rubidium is 1-2:1-2.

[0009] Furthermore, in step (1), the atomic molar ratio of bipyridine molecules to metallic rubidium is 1:1.

[0010] Furthermore, the bipyridine molecules in step (1) include 4-phenylpyridine, 2,2'-bipyridine and 2,4'-bipyridine.

[0011] Furthermore, in step (2), the water bath temperature is 85-100° C., and the treatment time is 8-12 h.

[0012] Furthermore, in step (2), water bath treatment is carried out in a calcium chloride aqueous solution.

[0013] An organic low-dimensional magnet is prepared by adopting the above method.

[0014] The beneficial effects produced by the present invention are:

[0015] The present invention selects bipyridine molecules containing heteroatoms as the base material to prepare organic magnets. The prepared molecular crystals are layered, and rubidium atoms are distributed within and between the pyridine molecular layers. The strong electronegativity of the pyridine ring is used to reduce the chemical reaction barrier between the aromatic hydrocarbon molecules and the rubidium atoms, which is more conducive to preparing doped crystals at low temperatures and improving the charge transfer efficiency. At the same time, the pyridine ring with strong electronegativity produces a strong magnetic coupling effect within the molecular layer, filling the gap in the current magnetic control method in the field of π-electron magnetism and forming a two-dimensional antiferromagnetic lattice. In this application, a calcium chloride solution with a higher boiling point than water is selected for a one-step constant temperature water bath ultrasonic treatment to control the process parameters of the grown crystals. Under mild reaction conditions, both the crystallization quality of the doped crystals and the efficiency of the grown crystals are guaranteed. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the crystal structure and spin density distribution of rubidium-doped bipyridine molecules;

[0017] Figure 2 The X-ray diffraction patterns of the samples in Example 1, Comparative Example 1 and Comparative Example 2 are shown;

[0018] Figure 3 PPMS magnetic measurement results of the sample in Example 1;

[0019] Figure 4 XRD patterns of samples of Comparative Examples 3, 4 and 5;

[0020] Figure 5 Magnetic measurement results of the sample in Example 6;

[0021] Figure 6 is the X-ray diffraction pattern of the samples in Example 2 and Example 3;

[0022] Figure 7 PPMS magnetic measurement results of the sample in Example 2;

[0023] Figure 8 This is the PPMS magnetic measurement result of the sample in Example 3. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. That is, the embodiments described are only part of the embodiments of the present invention, rather than all embodiments.

[0025] Therefore, the detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the invention as claimed, but is merely intended to represent selected embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0026] It should be noted that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus comprising the element.

[0027] The features and performance of the present invention are further described in detail below with reference to the embodiments and drawings.

[0028] Example 1

[0029] A method for preparing an aromatic hydrocarbon organic low-dimensional magnet comprises the following steps:

[0030] (1) In a glove box with water and oxygen content below 0.1 ppm, 4-phenylpyridine and rubidium were weighed and mixed in a molar ratio of 1:1, placed in a quartz tube, and the quartz tube containing the sample was evacuated to a high vacuum of 1×10 -4 After Pa, the quartz tube is subjected to high temperature melting and sealing treatment;

[0031] (2) A portion of the sealed quartz tube was taken, marked as Rb-4-PPD-B, and placed in a temperature-controlled ultrasonic heating container filled with calcium chloride solution. The temperature was raised to 98°C within 30 minutes, and the tube was covered and ultrasonically shaken in a constant temperature water bath at 98°C for 10 hours. After the ultrasonic treatment, the tube was slowly cooled in the ultrasonic container and cooled to below 60°C after 70 minutes. The tube was taken out to obtain the product.

[0032] Example 2

[0033] A method for preparing an aromatic hydrocarbon organic low-dimensional magnet comprises the following steps:

[0034] (1) In a glove box with water and oxygen content below 0.1 ppm, 2,2'-bipyridine and rubidium were weighed and mixed in a molar ratio of 1:1, placed in a quartz tube, and the quartz tube containing the sample was evacuated to a high vacuum of 1×10 -4 After Pa, the quartz tube is subjected to high temperature melting and sealing treatment;

[0035] (2) A portion of the sealed quartz tube was taken, marked as Rb-2,2'-BPD, and placed in a temperature-controlled ultrasonic heating container filled with calcium chloride solution. The temperature was raised to 85°C within 30 minutes, and the tube was covered and ultrasonically shaken in a constant temperature water bath at 85°C for 10 hours. After the ultrasonic treatment, the tube was slowly cooled in the ultrasonic container and cooled to below 60°C after 45 minutes. The tube was taken out to obtain the product.

[0036] Example 3

[0037] A method for preparing an aromatic hydrocarbon organic low-dimensional magnet comprises the following steps:

[0038] (1) In a glove box with water and oxygen content below 0.1 ppm, 2,4'-bipyridine and rubidium were weighed and mixed in a molar ratio of 1:1, placed in a quartz tube, and the quartz tube containing the sample was evacuated to a high vacuum of 1×10 -4 After Pa, the quartz tube is subjected to high temperature melting and sealing treatment;

[0039] (2) Take a portion of the sealed quartz tube, mark it as Rb-2,4'-BPD, put it into a temperature-controlled ultrasonic heating container filled with calcium chloride solution, raise the temperature to 85°C within 30 minutes, and cover it and ultrasonically shake it in a constant temperature water bath at 85°C for 10 hours. After the ultrasonic treatment, slowly cool it in the ultrasonic container and cool it to below 60°C after 45 minutes. Take it out to obtain the product.

[0040] Example 4

[0041] A method for preparing an aromatic hydrocarbon organic low-dimensional magnet comprises the following steps:

[0042] (1) In a glove box with water and oxygen content below 0.1 ppm, 4-phenylpyridine and rubidium were weighed and mixed in a molar ratio of 2:1, placed in a quartz tube, and the quartz tube containing the sample was evacuated to a high vacuum of 1×10 -4 After Pa, the quartz tube is subjected to high temperature melting and sealing treatment;

[0043] (2) Take a portion of the sealed quartz tube, mark it as Rb-4-PPD-B, put it into a temperature-controlled ultrasonic heating container filled with calcium chloride solution, raise the temperature to 98°C within 30 minutes, and ultrasonically shake it for 12 hours in a constant temperature water bath at 98°C with a cover. After the ultrasonic treatment, slowly cool it in the ultrasonic container and cool it to below 60°C after 70 minutes. Take it out to obtain the product.

[0044] Example 5

[0045] A method for preparing an aromatic hydrocarbon organic low-dimensional magnet comprises the following steps:

[0046] (1) In a glove box with water and oxygen content below 0.1 ppm, 2,2'-bipyridine and rubidium were weighed and mixed in a molar ratio of 1:2, placed in a quartz tube, and the quartz tube containing the sample was evacuated to a high vacuum of 1×10 -4 After Pa, the quartz tube is subjected to high temperature melting and sealing treatment;

[0047] (2) Take a portion of the sealed quartz tube, mark it as Rb-2,2'-BPD, put it into a temperature-controlled ultrasonic heating container filled with calcium chloride solution, raise the temperature to 85°C within 30 minutes, and cover it and ultrasonically shake it in a constant temperature water bath at 85°C for 8 hours. After the ultrasonic treatment, slowly cool it in the ultrasonic container and cool it to below 60°C after 45 minutes. Take it out to obtain the product.

[0048] Example 6

[0049] A method for preparing an aromatic hydrocarbon organic low-dimensional magnet comprises the following steps:

[0050] (1) In a glove box with water and oxygen content below 0.1 ppm, 4-phenylpyridine and rubidium were weighed and mixed in a molar ratio of 1:1, placed in a quartz tube, and the quartz tube containing the sample was evacuated to a high vacuum of 1×10 -4 After Pa, the quartz tube is subjected to high temperature melting and sealing treatment;

[0051] (2) Take a portion of the sealed quartz tube, mark it as Rb-4-PPD-B, and place it in a temperature-controlled ultrasonic heating container filled with calcium chloride solution. The temperature is raised to 98°C within 30 minutes, and the tube is covered and ultrasonically shaken in a constant temperature water bath at 98°C for 10 hours. After the ultrasonic treatment, the temperature is cooled to below 60°C by setting a cooling rate of 2°C / h (about 0.03°C / min) through the temperature control system, and the tube is taken out to obtain the Rb-4-PPD-B-2°C / h sample.

[0052] Comparative Example 1

[0053] A method for preparing an aromatic hydrocarbon organic low-dimensional magnet comprises the following steps:

[0054] (1) In a glove box with water and oxygen content below 0.1 ppm, 4-phenylpyridine and rubidium were weighed and mixed in a molar ratio of 1:1, placed in a quartz tube, and the quartz tube containing the sample was evacuated to a high vacuum of 1×10 -4 After Pa, the quartz tube is subjected to high temperature melting and sealing treatment;

[0055] (2) A portion of the sealed quartz tube was taken, marked as Rb-4-PPD-A, and placed in a temperature-controlled ultrasonic heating container filled with calcium chloride solution. The temperature was raised to 93°C within 30 minutes, and the tube was covered and ultrasonically shaken in a constant temperature water bath at 93°C for 10 hours. After the ultrasonic treatment, the tube was slowly cooled in the ultrasonic container and cooled to below 60°C after 65 minutes. The tube was then taken out to obtain the product.

[0056] Comparative Example 2

[0057] A method for preparing an aromatic hydrocarbon organic low-dimensional magnet comprises the following steps:

[0058] (1) In a glove box with water and oxygen content below 0.1 ppm, 4-phenylpyridine and rubidium were weighed and mixed in a molar ratio of 1:1, placed in a quartz tube, and the quartz tube containing the sample was evacuated to a high vacuum of 1×10 -4 After Pa, the quartz tube is subjected to high temperature melting and sealing treatment;

[0059] (2) A portion of the sealed quartz tube was taken, marked as Rb-4-PPD-C, and placed in a temperature-controlled ultrasonic heating container filled with calcium chloride solution. The temperature was raised to 103°C within 30 minutes, and the tube was covered and ultrasonically shaken in a constant temperature water bath at 103°C for 10 hours. After the ultrasonic treatment, the tube was slowly cooled in the ultrasonic container and cooled to below 60°C after 70 minutes. The tube was taken out to obtain the product.

[0060] Comparative Example 3

[0061] Based on the preparation method in Example 1, the ultrasonic oscillation time was reduced to 4 h to obtain the sample Rb-4-PPD-B-4h.

[0062] Comparative Example 4

[0063] Based on the preparation method in Example 1, the ultrasonic oscillation time was extended to 15 h to obtain the sample Rb-4-PPD-B-15h.

[0064] Comparative Example 5

[0065] Based on the preparation method in Example 1, the obtained sample was taken out and quickly cooled to room temperature within 4 minutes to obtain the finished product Rb-4-PPD-B-cooling.

[0066] Test example

[0067] Figure 1 Schematic diagram of the crystal structure and spin density distribution of rubidium-doped bipyridine molecules;

[0068] Taking the samples prepared in Example 1 and Comparative Examples 1-2 as examples, three samples were subjected to XRD tests, and the results are shown in FIG. Figure 2 The results showed that in the Rb-4-PPD-B sample, the diffraction peaks of rubidium and 4-phenylpyridine almost completely disappeared, and multiple new peaks appeared at multiple positions such as 11.4°, 13.9°, 20.7°, 30.1° and 31.5°, which could not match the RbH (RbH#54-0411) and RbCN (RbCN#47-0946) standard cards, indicating that new crystals with good crystallinity were synthesized.

[0069] The main diffraction peaks in the Rb-4-PPD-A sample are those of commercially purchased 4-phenylpyridine (4-PPD#Purchased) and metallic rubidium (Rb#89-4079), indicating that the reaction temperature conditions are insufficient and rubidium and organic molecules fail to react effectively.

[0070] In the Rb-4-PPD-C sample, the diffraction peak of the new crystal was greatly weakened, and an abnormally obvious bulge appeared in the range of 15-25°, accompanied by the diffraction peak of RbH, indicating that the organic molecules were decomposed and a large amount of amorphous phase and by-product RbH were generated.

[0071] PPMS magnetic test was performed on the Rb-4-PPD-B sample with good crystallinity, such as Figure 3 As shown in the figure, the zero-field cooling (ZFC) and the field cooling (FC) magnetic susceptibility curves were measured in succession under an external magnetic field of 1000 Oe. It can be seen that in the temperature range of 1.8-300 K, the two completely coincide with each other, and a peak value related to the antiferromagnetic properties appears near 81.8 K, showing typical low-dimensional antiferromagnetic characteristics. Under the fitting of the Heisenberg two-dimensional square lattice model, the fitting results have a good match with the experimental results, J / k B =77.5K, confirming its two-dimensional antiferromagnetic nature, while the upward curve below 20K can be attributed to paramagnetic impurities. The inset further confirms that the MH curves at 1.8, 80, and 300K are linear, consistent with antiferromagnetic characteristics, ruling out the possibility of superparamagnetism and spin glass.

[0072] The samples in Comparative Examples 3, 4 and 5 were subjected to XRD tests, and the results are shown in Figure 4, it can be seen that when the temperature is appropriate, insufficient ultrasonication time will lead to an incomplete reaction, resulting in residual organic molecules and metallic rubidium. The Rb-4-PPD-B-15h sample exhibits an unusually pronounced bulge in the 15-25° range, accompanied by the formation of the byproduct RbH. This indicates that when the temperature is appropriate, excessively prolonged ultrasonication time increases the degree of organic molecule decomposition, gradually generating amorphous products and impurities such as RbH over time, reducing crystal quality. In the Rb-4-PPD-B-cooling sample, the temperature drop was too rapid, resulting in the sample not crystallizing and forming an amorphous phase.

[0073] The magnetic properties of the sample in Example 6 were measured, and the results were as follows: Figure 5 As shown, it can be seen that there is no significant difference in the crystal magnetic properties obtained after slow cooling at 2°C / h and natural cooling in the container.

[0074] The samples in Example 2 and Example 3 were tested by XRD. The specific results are shown in Figure 6 The results show that the methods in Examples 2 and 3 can effectively dope rubidium into the crystal structure of 2,2'-bipyridine and 2,4'-bipyridine, obtaining molecular crystals with good crystallinity and no by-product RbH is generated. The crystal structure and spin density distribution diagram obtained by matching the experimental results with the first-principles calculation results are similar to those of rubidium-doped 4-phenylpyridine (see Figure 1 ).

[0075] The magnetic properties of the samples in Example 2 were measured. Figure 7 The results show that in the temperature range of 1.8-300K, the magnetic susceptibility curves of zero field cooling (ZFC) and applied field cooling (FC) measured under an external magnetic field of 500Oe completely overlap, showing a similar paramagnetic feature. χ -1 The linear fitting result of the -T curve shows that a negative Weiss constant (θ = -41.4K) indicates that there is a strong antiferromagnetic interaction between molecules. The two-dimensional square lattice model was fitted to the low temperature section (1.8-10K) and high temperature section (50-200K) of the experimental results, and the experimental results of the whole temperature range were simulated. The theoretical curve has a good match with the experimental results, and J / k B =26.5K, confirming that the sample has two-dimensional antiferromagnetism.

[0076] The magnetic properties of the samples in Example 3 were measured. Figure 8 The results show that in the temperature range of 1.8-300K, the magnetic susceptibility curves of zero field cooling (ZFC) and added field cooling (FC) measured under an external magnetic field of 500Oe are completely coincident. According to the formula χ -1The linear fitting of the -T curve also yields a negative Weiss constant (θ = -63.4K), indicating the existence of a strong antiferromagnetic interaction between molecules. The two-dimensional square lattice model is fitted to the low temperature section (1.8-10K) and high temperature section (50-200K) of the experimental results, and the experimental results of the whole temperature range are simulated. The theoretical curve has a good match with the experimental results, J / k B =38.5K, confirming that the sample also has two-dimensional antiferromagnetism.

Claims

1. A method for preparing an aromatic hydrocarbon organic low-dimensional magnet, characterized in that: The following steps are involved: (1) Mixing bipyridine molecules with metallic rubidium under conditions where both water and oxygen contents are less than 0.1 ppm; (2) When the vacuum degree is lower than 10 -4 Pa conditions, the above mixture was subjected to ultrasonic oscillation in a water bath to obtain the product.

2. The method for preparing an organic low-dimensional magnet according to claim 1, wherein: In step (1), the atomic molar ratio of bipyridine molecules to metallic rubidium is 1-2:1-2.

3. The method for preparing an organic low-dimensional magnet according to claim 1, wherein: In step (1), the atomic molar ratio of bipyridine molecules to metallic rubidium is 1:

1.

4. The method for preparing an organic low-dimensional magnet according to claim 1, wherein: The bipyridine molecules in step (1) include 4-phenylpyridine, 2,2'-bipyridine and 2,4'-bipyridine.

5. The method for preparing an organic low-dimensional magnet according to claim 1, wherein: In step (2), the water bath temperature is 85-100° C. and the treatment time is 8-12 h.

6. The method for preparing an organic low-dimensional magnet according to claim 1, wherein: In step (2), water bath treatment is carried out in a calcium chloride aqueous solution.

7. An organic low-dimensional magnet, characterized in that The method according to claim 1 is adopted to prepare the present invention.

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