A hafnium / zirconium complex of 2-picolinic acid and a preparation method and application thereof

Abstract

The application discloses hafnium / zirconium 2-pyridine carboxylate complexes, a preparation method and application thereof, and belongs to the technical field of compound preparation. The hafnium / zirconium 2-pyridine carboxylate complexes provided by the application have both the chelating characteristics of a ligand and the stability of hafnium and zirconium. The dielectric constant of the complexes is 7-9 at a medium-temperature stage (123-223 DEG C) and a low-medium frequency (100Hz-100kHz), the dielectric loss is extremely small, and the complexes can stably exist at 230 DEG C. Therefore, the complexes can be widely applied to the preparation of new energy automobile parts, power equipment precision insulation parts and industrial equipment dielectric insulation / transmission parts. The preparation method of the complexes is simple in operation and is beneficial to actual production.

Description

Technical Field

[0001] This invention belongs to the field of compound preparation technology, and particularly relates to a hafnium / zirconium 2-pyridinecarboxylate complex, its preparation method and application. Background Technology

[0002] Currently, aromatic compounds with carboxylic acid functional groups are preferred organic ligands, mainly because carboxylic acid ligands have multiple coordination modes and strong coordination abilities, which is beneficial for constructing stable MOF materials. The O- or OH groups of the carboxylic acid group facilitate the formation of hydrogen bond networks with guest molecules within the MOF pores, enabling efficient proton transport. Furthermore, the uncoordinated free -COOH groups within the MOF cavity both provide protons and can form abundant hydrogen bond networks within the framework.

[0003] A common ligand design approach involves anchoring carboxyl, sulfonic acid, and phosphonic acid groups to the MOF framework through condensation or substitution reactions. These groups can both donate protons and participate in the establishment of proton transport channels, improving the framework's acidity and hydrophilicity, thereby enhancing conductivity. Compared to carboxylic acid ligands, pyridine carboxylic acid ligands can form stable chelate structures such as five-membered rings with metal ions through the nitrogen atom on the pyridine ring and the oxygen atom of the carboxyl group. This structure has high symmetry and a stable spatial configuration, reducing ligand exchange or desorption. In contrast, carboxylic acid metal complexes rely solely on the carboxyl oxygen atom for coordination, making them prone to structural instability due to ligand exchange and difficult to synthesize single crystals that meet testing requirements. Currently, no complexes synthesized using 2-pyridinecarboxylic acid and hafnium / zirconium ions have been reported. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a 2-pyridinecarboxylic acid hafnium / zirconium complex that can form a stable crystal structure with high yield and purity, as well as its preparation method and application.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a hafnium 2-pyridinecarboxylate / zirconium complex, wherein the chemical formula of the hafnium 2-pyridinecarboxylate complex is Hf(PA)4·H2O, and the chemical formula of the zirconium 2-pyridinecarboxylate complex is Zr(PA)4·H2O, wherein PA is a 2-pyridinecarboxylate anion, and the structural formula of PA is shown in Formula I: Formula I.

[0006] As a preferred embodiment of the 2-pyridinecarboxylic acid hafnium / zirconium complex of the present invention, the 2-pyridinecarboxylic acid hafnium / zirconium complex belongs to the cubic crystal system, space group P42 / n.

[0007] As a preferred embodiment of the hafnium 2-pyridinecarboxylate / zirconium complex of the present invention, the hafnium 2-pyridinecarboxylate unit cell parameters are: a=11.1012(3) Å, b=11.1012(3) Å, c=9.5970(3) Å, β=90°, V=1182.70(6) Å. 3 .

[0008] As a preferred embodiment of the hafnium / zirconium 2-pyridinecarboxylate complex of the present invention, the cell parameters of the zirconium 2-pyridinecarboxylate are: a=11.1004(2)Å, b=11.1004(2)Å, c=9.5987(2)Å, β=90°, V=1182.74(5)Å. 3 .

[0009] In a preferred embodiment of the hafnium 2-pyridinecarboxylate / zirconium complex of the present invention, the hafnium 2-pyridinecarboxylate has a molecular weight of 3087.5~3111.1 cm⁻¹. -1 1437.6~1470.7cm -1 1604.6~1686.4cm -1 1049.1~1240.4cm -1 449.3±0.2cm -1 It has an infrared absorption band within the wavenumber range.

[0010] In a preferred embodiment of the hafnium / zirconium 2-pyridinecarboxylate complex of the present invention, the zirconium 2-pyridinecarboxylate has a molecular weight of 3476.1~3521.2 cm⁻¹. -1 3086.6~3109.6cm -1 1437.0~1469.9cm -1 1603.2~1683.0cm -1 1047.0~1239.3cm -1 445.1±0.2cm -1 It has an infrared absorption band within the wavenumber range.

[0011] The hafnium / zirconium 2-pyridinecarboxylate complex provided by this invention has a stable single-crystal structure. Studies have shown that its dielectric constant is 7-9 at medium temperature (123-223℃) and low frequency (100Hz-100kHz), with extremely low dielectric loss, and it can exist stably at 230℃.

[0012] A second aspect of the present invention provides a method for preparing the hafnium / zirconium 2-pyridinecarboxylate complex, the method comprising: (1) Add 2-pyridinecarboxylic acid and hafnium / zirconium salt to an organic solvent and heat to dissolve, then stir and filter, and collect the filtrate; (2) Heat the filtrate to 120-140℃ and react for 60-80h. After the reaction is completed, cool, filter, wash and dry to obtain 2-pyridinecarboxylic acid hafnium / zirconium complex.

[0013] The preparation method provided by this invention can prepare stable 2-pyridinecarboxylic acid hafnium / zirconium complexes with high product purity and high yield.

[0014] Preferably, the filtrate is heated to 130-140°C and reacted for 72-80 hours.

[0015] In a preferred embodiment of the preparation method described in this invention, the molar ratio of hafnium / zirconium salt to 2-pyridinecarboxylic acid is 1:(2-6).

[0016] Preferably, the molar ratio of the hafnium / zirconium salt to 2-pyridinecarboxylic acid is 1:(4-6).

[0017] In a preferred embodiment of the preparation method described in this invention, the sum of the masses of hafnium / zirconium salt and 2-pyridinecarboxylic acid to the volume ratio of the organic solvent is 1 g: (6-10) mL.

[0018] Preferably, the sum of the masses of hafnium / zirconium salt and 2-pyridinecarboxylic acid is in a volume ratio of 1 g to (8-10) mL of organic solvent.

[0019] In a preferred embodiment of the preparation method of the present invention, the hafnium salt includes at least one of hafnium nitrate, hafnium chloride, hafnium acetate, and hafnium oxychloride, and the zirconium salt includes at least one of zirconium nitrate, zirconium chloride, zirconium acetate, and zirconium oxychloride.

[0020] In a preferred embodiment of the preparation method of the present invention, the organic solvent includes any one of the following: a mixed solution of N,N-dimethylformamide and acetic acid, a mixed solution of methanol and formic acid, a mixed solution of dimethyl sulfoxide and acetic acid, and a mixed solution of methanol and acetic acid.

[0021] As a preferred embodiment of the preparation method described in this invention, In a preferred embodiment of the preparation method described in this invention, the volume ratio of N,N-dimethylformamide to acetic acid in the mixed solution of N,N-dimethylformamide and acetic acid is (5-7):1.

[0022] In a preferred embodiment of the preparation method of the present invention, the volume ratio of methanol to formic acid in the mixed solution of methanol and formic acid is (5-7):1.

[0023] In a preferred embodiment of the preparation method described in this invention, the volume ratio of dimethyl sulfoxide to acetic acid in the mixed solution of dimethyl sulfoxide and acetic acid is (5-7):1.

[0024] In a preferred embodiment of the preparation method described in this invention, the volume ratio of methanol to acetic acid in the mixed solution of methanol and acetic acid is (5-7):1.

[0025] In a preferred embodiment of the preparation method of the present invention, the heating and dissolving temperature in step (1) is 60-70°C.

[0026] In a preferred embodiment of the preparation method of the present invention, in step (1), the stirring temperature is 20-30℃ and the stirring time is 25-35min.

[0027] A third aspect of the present invention provides the application of the hafnium / zirconium 2-pyridinecarboxylate complex in the preparation of new energy vehicle components, precision insulating components for power equipment, and dielectric insulating / transmission components for industrial equipment.

[0028] For example, the new energy vehicle components include medium-temperature dielectric components, such as on-board OBCs, on-board charger arc isolation components, power battery busbar insulation supports, busbar support frames, etc.; the power equipment precision insulation components include medium-temperature and low-voltage power equipment precision insulation components, such as transformer / current transformer interlayer insulation, coil supports, end sealing components, switchgear / ring network cabinet insulators, insulating partitions, contact covers, power distribution equipment insulating sleeves, terminal insulating seats, smart grid sensor packaging substrates, signal isolation components, etc.; the industrial equipment dielectric insulation / transmission components include medium-temperature industrial equipment dielectric insulation / transmission components, such as chemical measurement and control / automation equipment sensor insulation packaging, signal transmission substrates, industrial power supplies, medium frequency power supply internal insulation structures, filter component substrates, high-temperature motor slot insulation, phase-to-phase insulation, end fixing components, etc.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows: The 2-pyridinecarboxylic acid hafnium / zirconium complex provided by this invention combines the chelating properties of ligands with the stability of hafnium and zirconium. Its dielectric constant is 7-9 at medium temperatures (123-223℃) and low to medium frequencies (100Hz-100kHz), exhibiting extremely low dielectric loss. Furthermore, this complex remains stable at 230℃. Therefore, it can be widely used in the preparation of components for new energy vehicles, precision insulating components for power equipment, and dielectric insulation / transmission components for industrial equipment. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the synthetic route for the hafnium 2-pyridinecarboxylate complex in Example 1; Figure 2 This is a schematic diagram of the synthetic route for the zirconium 2-pyridinecarboxylate complex in Example 2; Figure 3 This is a diagram showing the coordination environment of hafnium ions in the hafnium 2-pyridinecarboxylate complex in Example 1; Figure 4 This is a three-dimensional structural diagram of the hydrogen-bonded zero-dimensional structure in the hafnium 2-pyridinecarboxylate complex in Example 1. Figure 5 This is a diagram showing the coordination environment of hafnium ions in the zirconium 2-pyridinecarboxylate complex in Example 2; Figure 6 This is a three-dimensional structural diagram of the hydrogen-bonded zero-dimensional structure formed in the 2-pyridinecarboxylate zirconium complex in Example 2; Figure 7 The infrared spectrum of the hafnium 2-pyridinecarboxylate complex in Example 1; Figure 8 The infrared spectrum of the zirconium 2-pyridinecarboxylate complex in Example 2; Figure 9 The XRD pattern and standard XRD pattern of the 2-pyridinecarboxylic acid hafnium complex in Example 1 are shown below. Figure 10 The XRD pattern and standard XRD pattern of the 2-pyridinecarboxylic acid zirconium complex in Example 2 are shown below. Figure 11 The temperature-dependent X-ray diffraction pattern of the 2-pyridinecarboxylic acid hafnium complex in Example 1; Figure 12 The temperature-dependent X-ray diffraction pattern of the zirconium 2-pyridinecarboxylate complex in Example 2; Figure 13 Thermogravimetric curve of the hafnium 2-pyridinecarboxylate complex in Example 1; Figure 14 Thermogravimetric curve of the zirconium 2-pyridinecarboxylate complex in Example 2; Figure 15 Thermogravimetric curve of the 2,6-pyridinedicarboxylic acid zirconium complex in Comparative Example 1; Figure 16 This is a graph showing the change in dielectric constant of the 2-pyridinecarboxylic acid hafnium complex with temperature in Example 1. Figure 17 This is a graph showing the change in dielectric loss of the 2-pyridinecarboxylic acid hafnium complex with temperature in Example 1. Figure 18 This is a graph showing the change in dielectric constant of the 2-pyridinecarboxylic acid zirconium complex with temperature in Example 2. Figure 19 The graph shows the change in dielectric loss of the 2-pyridinecarboxylic acid zirconium complex with temperature in Example 2. Detailed Implementation

[0031] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0032] Example 1 This invention provides a hafnium 2-pyridinecarboxylate, the preparation process of which is illustrated in the schematic diagram below. Figure 1 As shown, it includes the following steps: (1) Add 0.5 mmol of hafnium oxychloride octahydrate and 2 mmol of 2-pyridinecarboxylic acid to 3.5 mL of organic solvent (a mixed solution of methanol and acetic acid in a volume ratio of 6:1). The total mass of hafnium oxychloride octahydrate and 2-pyridinecarboxylic acid is 3 g: 25 mL in volume to the organic solvent. After heating to 60 °C in a water bath until dissolved, stir at room temperature (25 °C) for 30 min and then filter to collect the filtrate. (2) The filtrate was placed in a stainless steel reactor lined with polytetrafluoroethylene, and then placed in an oven and reacted at 130°C for 72 h. After the reaction was completed, it was cooled to room temperature at a cooling rate of 5°C / min, then filtered and washed with N,N-dimethylformamide (DMF). After washing, it was dried in a forced-air drying oven at 60°C to obtain hafnium 2-pyridinecarboxylate.

[0033] Example 2 This invention provides a zirconium 2-pyridinecarboxylate, the preparation process of which is shown in the schematic diagram below. Figure 2 As shown, it includes the following steps: (1) Add 0.5 mmol of zirconium oxychloride octahydrate and 2 mmol of 2-pyridinecarboxylic acid to 3.5 mL of organic solvent (a mixed solution of methanol and acetic acid in a volume ratio of 6:1). The total mass of zirconium oxychloride octahydrate and 2-pyridinecarboxylic acid is in a volume ratio of 1 g to 10 mL of organic solvent. After heating to 60 °C in a water bath until dissolved, stir at room temperature (25 °C) for 30 min and then filter to collect the filtrate. (2) The filtrate was placed in a stainless steel reactor lined with polytetrafluoroethylene, and then placed in an oven and reacted at 130°C for 72 h. After the reaction was completed, it was cooled to room temperature at a cooling rate of 5°C / min, then filtered and washed with DMF. After washing, it was dried in a forced-air drying oven at 60°C to obtain 2-pyridinecarboxylic acid zirconium.

[0034] Example 3 The present invention explores the preparation conditions of hafnium 2-pyridinecarboxylate. Except for the differences listed in Table 1, the conditions are the same as those in Example 1. Table 1 Example 4 This invention explores the preparation conditions of zirconium 2-pyridinecarboxylate. Except for the differences listed in Table 2, the conditions are the same as in Example 2. Table 2 Example 5 This invention provides zirconium 2-pyridinecarboxylate, the preparation method of which includes the following steps: (1) Dissolve ZrCl4 (0.500 mmol) in 2.5 mL DMF to obtain zirconium solution, and dissolve pyridinecarboxylic acid (PicA) (1.400 mmol) in 2.5 mL DMF and heat to 60°C to obtain PicA solution; (2) Add PicA solution dropwise to zirconium solution and stir at 60°C for 30 minutes. Remove the reaction solution, cover and let stand to crystallize for 30 days. Then take out the crystals to obtain zirconium 2-pyridinecarboxylate.

[0035] Comparative Example 1 The present invention provides a comparative example of zirconium 2,6-pyridinedicarboxylate, the preparation method of which includes the following steps: Weigh 0.18 mmol of 2,6-pyridinedicarboxylic acid and 0.28 mmol of zirconium nitrate pentahydrate into a 20 mL glass bottle, then add 6 mL of DMF and 2 mL of nitric acid, and sonicate for 10 min until dissolved; then place in an 80 °C constant temperature oven for 12 days, and finally cool to room temperature to obtain colorless transparent cuboid crystals, namely zirconium 2,6-pyridinedicarboxylic acid.

[0036] Example 1 The yields of the 2-pyridinecarboxylic acid hafnium / zirconium complexes prepared in Examples 1-4 of this invention are recorded in Table 3. Yield = Actual crystal weight / Theoretical crystal weight × 100%; Chemical purity = instrument-measured mass concentration × constant volume / sample mass / theoretical metal content × 100%, where chemical purity is tested by inductively coupled plasma atomic emission spectroscopy. Crystal purity = total area of ​​all crystallization diffraction peaks / (total area of ​​all crystallization diffraction peaks + amorphous scattering background area) × 100%, where crystal purity is tested by X-ray powder diffraction. Table 3 As can be seen from Table 3, the preparation method of the present invention, especially when the preparation parameters are within the preferred range of the present invention, yields products with high yield and high purity.

[0037] Example 2 The crystal structure, infrared spectroscopy, and XRD analysis of hafnium 2-pyridinecarboxylate prepared in Example 1, zirconium 2-pyridinecarboxylate prepared in Example 2, and zirconium 2-pyridinecarboxylate prepared in Example 5 were specifically tested as follows: 1. Crystal structure testing The crystal structure was determined using a Bruker Smart Apex CCD single crystal diffractometer. The main crystal data of hafnium 2-pyridinecarboxylate prepared in Example 1 and zirconium 2-pyridinecarboxylate prepared in Example 2 are shown in Table 4 and Table 5, respectively. The main crystal data of zirconium 2-pyridinecarboxylate prepared in Example 5 are shown in Table 6. Table 4 The coordination environment diagram of hafnium ions in the hafnium complex of 2-pyridinecarboxylic acid prepared in Example 1 is shown below. Figure 3 As shown, the three-dimensional structure formed by hydrogen-bonded zero-dimensional structures is illustrated in the diagram. Figure 4 As shown in Table 4 and Figure 3-4 As can be seen from the above, the chemical formula of the 2-pyridinecarboxylic acid hafnium complex of the present invention is Hf(PA)4·H2O, wherein PA is the 2-pyridinecarboxylic acid anion ligand, and the prepared 2-pyridinecarboxylic acid hafnium complex belongs to the tetragonal crystal system, space group P42 / n, and the cell parameters are: a=11.1012(3)Å, b=11.1012(3)Å, c=9.5970(3)Å, β=90°, V=1182.70(6)Å. 3 .from Figure 3 As can be seen from the data, the smallest asymmetric unit in this complex contains a semi-crystallographically independent Hf(Ⅳ) ion center, a PA ligand, and a coordinated water molecule. In this complex, Hf(Ⅳ) is octetally connected to four nitrogen atoms (N1, N2, N3, N4) and four oxygen atoms (O1, O2, O3, O4). Figure 4 It can be seen that there are two types of coordination interactions mediating the crosslinking of secondary structural units in this Hf-based complex, one of which is Hf 4+ The first is an Hf-O coordinate bond formed with an uncoordinated oxygen atom in the carboxylate group of the adjacent 2-pyridinecarboxylic acid ligand; the second is an Hf-O coordinate bond. 4+ The Hf-N coordinate bond is formed with the nitrogen atom on the pyridine ring of the adjacent 2-pyridinecarboxylic acid ligand. The synergistic effect of these two types of coordinate bonds allows Hf to... 4+ The primary and secondary structural units are interconnected with organic ligands to construct a three-dimensional crystalline framework with long-range order. The differences in coordination sites of oxygen and nitrogen heteroatoms in the ligands further regulate the topology and bonding strength of the framework.

[0038] Table 5 The zirconium 2-pyridinecarboxylate complex prepared in Example 2 has the chemical formula Zr(PA)4·H2O, where PA is the 2-pyridinecarboxylate anionic ligand, as shown in Table 5. Figure 5-6It can be seen that the 2-pyridinecarboxylic acid zirconium complex belongs to the tetragonal crystal system, space group P42 / n, and the cell parameters are: a=11.1004(2)Å, b=11.1004(2)Å, c=9.5987(2)Å, β=90°, V=1182.74(5)Å. 3 .from Figure 5 As can be seen from the single-crystal X-ray diffraction analysis, its asymmetric unit contains a Zr. 4 + An ion, a pyridinecarboxylic acid ligand, a water molecule, and each Zr 4+ The ion has a cubic coordination configuration, surrounded by four carboxylic acid oxygen atoms and four nitrogen atoms of 2-pyridinecarboxylic acid ligands. The multi-coordinated central ion is chelated with four atoms (N1, N2, N3, N4) and multiple atoms (O1, O2, O3, O4) in the ligands. Two types of coordination interactions mediating the cross-linking of secondary structural units exist in this Zr-based complex, one of which is Zr... 4+ The first is a Zr-O coordination bond formed with an uncoordinated oxygen atom in the carboxylate group of the adjacent 2-pyridinecarboxylic acid ligand; the second is a Zr... 4+ Zr-N coordinate bonds are formed with nitrogen atoms on the pyridine ring of the adjacent 2-pyridinecarboxylic acid ligand. The synergistic effect of these two types of coordinate bonds allows Zr to... 4+ The primary and secondary structural units are interconnected with organic ligands to construct a three-dimensional crystalline framework with long-range order. The differences in coordination sites of oxygen and nitrogen heteroatoms in the ligands further regulate the topology and bonding strength of the framework.

[0039] Table 6 The main crystal data for Example 5 are shown in Table 6. [Zr(C6H4NO2)4]·2H2O crystallizes as a colorless cubic crystal, belonging to the tetragonal crystal system, space group P42 / n. IV The atoms are located on the crystallographic fourfold rotation inversion axis and coordinated with four pyridinecarboxylic acid ligands. The asymmetric unit contains half a solvent molecule, which is located on the double axis. The Zr-O and Zr-N bond lengths are 2.120(2) Å and 2.393(2) Å, respectively, and the N-Zr-O bite angle is 69.79(7)°. The coordination polyhedron around the metal center is approximately a tetragonal antiprism of N,O-coordinating atoms, which is distorted to a dodecahedral geometry.

[0040] 2. Infrared testing The tests were conducted using a Thermo Fisher Scientific Nicolet iS20 instrument from the United States. Samples were subjected to standard tablet compression at 400–4000 cm⁻¹. -1 Wavenumber range test.

[0041] The infrared spectrum of the hafnium 2-pyridinecarboxylate complex is shown below. Figure 7 As shown, the range is 3476.1~3521.1 cm. -1 The absorption peaks within the wavelength range correspond to the absorption peaks of water of crystallization molecules. This is in the range of 3087.5–3111.1 cm⁻¹. -1 The absorption peaks in the region correspond to the CH stretching vibration of the pyridine ring, ranging from 1437.6 to 1470.7 cm⁻¹. -1 The absorption peaks within the region correspond to the C=C skeletal vibrations of the pyridine ring, ranging from 1604.6 to 1686.4 cm⁻¹. -1 The absorption peaks within the region are due to the stretching vibrations of C=N, while the peaks are located between 1049.1 and 1240.4 cm⁻¹. -1 The absorption peak in the region corresponds to the stretching vibration of CO. Additionally, at 449.3 cm⁻¹... -1 The absorption peaks near the wavelength correspond to the stretching vibrations of Hf-O. Infrared spectral analysis indicates the presence of a 2-pyridinecarboxylic acid ligand in the compound, along with water of crystallization, and the formation of coordinate bonds between the central hafnium and the ligand.

[0042] The infrared spectrum of the 2-pyridinecarboxylic acid zirconium complex is shown below. Figure 8 As shown, the range is 3476.1~3521.2 cm. -1 The absorption peaks within the wavelength range correspond to the absorption peaks of water of crystallization. These peaks are located in the range of 3086.6–3109.6 cm⁻¹. -1 The absorption peaks within the region correspond to the CH stretching vibration of the pyridine ring, ranging from 1437.0 to 1469.9 cm⁻¹. -1 The absorption peaks within the region correspond to the C=C skeletal vibrations of the pyridine ring, ranging from 1603.2 to 1683.0 cm⁻¹. -1 The absorption peaks within the region are due to the stretching vibrations of C=N, while the range is 1047.0~1239.3 cm⁻¹. -1 The absorption peak in the region corresponds to the stretching vibration of CO. Additionally, at 445.1 cm⁻¹... -1 The absorption peaks near the wavelength correspond to the stretching vibrations of Zr-O. Infrared spectral analysis indicates the presence of a 2-pyridinecarboxylic acid ligand in the compound, along with water of crystallization, and the formation of coordinate bonds between the central zirconium and the ligand.

[0043] 3.3 XRD Test The tests were conducted using a Rigaku SmartLab SE instrument from Japan, employing Cu-Kα radiation at a scan rate of 5° / min.

[0044] The phase purity of the hafnium 2-pyridinecarboxylate complex was characterized by X-ray powder diffraction, with a test range of 2θ = 10°–50°. The experimentally obtained spectra were compared and analyzed with the simulated powder diffraction patterns of the single-crystal structure. The results are as follows: Figure 9 As shown, the characteristic diffraction peak positions of the experimental spectrum (blue curve / bottom curve) and the peak positions of the single-crystal simulated spectrum (black curve / top curve) show a good correspondence: the peak shapes and positions of the main diffraction peaks in the 2θ = 10°, 20°, and other intervals are highly matched, with only slight differences in the relative intensity of some peaks. This is due to the deviation between the crystal packing orientation of the experimental sample and the simulated ideal single-crystal powder state. These results indicate that the prepared target compound has high crystal phase purity, and its crystal form is completely consistent with the structure obtained by single-crystal X-ray diffraction analysis, with no obvious impurity diffraction peaks, indicating good crystal phase uniformity of the synthesized product.

[0045] The crystal phase purity of the zirconium 2-pyridinecarboxylate complex was characterized by X-ray powder diffraction (XPD) within the range of 2θ = 5°–50°. The experimentally obtained spectra were compared with those simulated from a single-crystal structure. The results are as follows: Figure 10 As shown, the characteristic diffraction peaks in the experimental spectrum (blue curve / bottom curve) correspond well with the peaks in the single-crystal simulated spectrum (black curve / top curve): the strong characteristic diffraction peak at 2θ=10°, the second strongest peak near 20°, and the series of weak diffraction peaks in the 20°-50° range all correspond one-to-one, indicating lattice defects, microcrystallization effects, or crystal orientation deviations present in the actual sample. These results show that its crystal form is completely consistent with the structure obtained from single-crystal X-ray diffraction analysis, with no obvious impurity diffraction peaks and high phase purity, but its crystallinity is lower than that of an ideal crystal, indicating certain crystal defects or microcrystallization characteristics.

[0046] Example 3 The present invention provides an example of the effect of performing variable-temperature X-ray diffraction tests on the complexes prepared in Examples 1-2 to study the thermally induced structural evolution of the complexes. Specifically, the tests were conducted according to a preset thermal program: a German Bruker D8 Advance multifunctional in-situ X-ray diffractometer was used for the tests, Cu-Kα radiation was used, the heating rate was 5℃ / min, and each temperature point was held for 5min to ensure the thermal equilibrium of the sample. The temperature range covered 30℃ to 310℃, and the interval between each test temperature point was 40℃.

[0047] The XRD pattern of the complex prepared in Example 1 is shown below. Figure 11As shown, the hafnium 2-pyridinecarboxylate sample at 30℃ exhibits a series of sharp and high-intensity diffraction peaks, reflecting its crystalline structure. In contrast, the original sharp diffraction peaks in the hafnium 2-pyridinecarboxylate sample treated at 190℃ show significant attenuation, while the sample treated at 230℃ has no sharp diffraction peaks, only broadened diffuse signals, corresponding to an amorphous structure. Furthermore, as the heat treatment temperature increases (from 30℃ to 230℃), the intensity of the crystalline diffraction peaks gradually decreases, indicating a continuous decrease in the crystallinity of the sample. The hafnium 2-pyridinecarboxylate sample treated at 310℃ shows stable diffuse peak characteristics in its XRD pattern, indicating that the sample maintains an amorphous morphology at this temperature.

[0048] The XRD pattern of the complex prepared in Example 2 is shown below. Figure 12 As shown, the zirconium 2-pyridinecarboxylate sample at 30℃ exhibits a series of sharp and high-intensity diffraction peaks, reflecting its crystalline structure. In contrast, the sharp diffraction peaks in the zirconium 2-pyridinecarboxylate sample heat-treated at 190℃ show significant attenuation, while the sample heat-treated at 230℃ has no sharp diffraction peaks, only broadened diffuse signals, corresponding to an amorphous structure. Furthermore, as the heat treatment temperature increases (from 30℃ to 230℃), the intensity of the crystalline diffraction peaks gradually decreases, indicating a continuous decrease in the crystallinity of the sample. The diffuse peak characteristics in the XRD pattern of the zirconium 2-pyridinecarboxylate sample heat-treated at 310℃ are stable, indicating that the sample maintains an amorphous morphology at this temperature.

[0049] Example of effect 4 The thermogravimetric analysis (TGA) test was performed on the complexes prepared in Examples 1-2 to study their stability. Specifically, the test was conducted using a Netzsch STA 449 F3 instrument from Germany, with a heating rate of 10 K / min under N2 (100 mL / min) protection. The thermogravimetric curve of the complex prepared in Example 1 is shown below. Figure 13 As shown, the weight loss mainly occurred in two stages: In the temperature range of 300–627 K (approximately 27–354 °C), the sample mass remained relatively stable with no significant weight loss, indicating that the structure of hafnium 2-pyridinecarboxylate remained unchanged within this temperature range, demonstrating good thermal stability. In the temperature range of 627–1273 K (approximately 367–1000 °C), a continuous and rapid weight loss process occurred, with a cumulative weight loss of approximately 70%. This can be attributed to the decomposition of the organic groups of the 2-pyridinecarboxylic acid ligand in hafnium 2-pyridinecarboxylate, accompanied by the thermal transformation of inorganic components. As the temperature increased to approximately 1273 K, the weight loss gradually leveled off. Finally, approximately 30% residue remained, presumably as hafnium oxide-like inorganic products. The test results indicate that hafnium 2-pyridinecarboxylate exhibits good thermodynamic stability before 627 K (354 °C).

[0050] The thermogravimetric curve of the complex prepared in Example 2 is shown below. Figure 14 As shown, the weight loss mainly occurred in two stages: In the temperature range of 300–627 K (approximately 27–354 °C), the sample mass remained relatively stable with no significant weight loss, indicating that the structure of zirconium 2-pyridinecarboxylate remained unchanged within this temperature range, demonstrating good thermal stability. In the temperature range of 627–1273 K (approximately 367–1000 °C), a continuous and rapid weight loss process occurred, with a cumulative weight loss of approximately 80%. This can be attributed to the decomposition of the organic groups of the 2-pyridinecarboxylic acid ligand in zirconium 2-pyridinecarboxylate, accompanied by the thermal transformation of inorganic components. As the temperature increased to approximately 1273 K, the weight loss gradually leveled off. Finally, approximately 20% residue remained, presumably inorganic products such as zirconium oxides. The test results indicate that zirconium 2-pyridinecarboxylate possesses good thermodynamic stability before 627 K (354 °C).

[0051] Thermogravimetric analysis (TGA) was further performed on the complex prepared in Comparative Example 1. Specifically, the tests were conducted using a TGA4000 Frontier thermogravimeter under N2 protection with a heating rate of 10 K / min to test thermal stability. The obtained TGA curves are shown below. Figure 15 As shown; from Figure 15 Slight weight loss of 4.8% was observed in the complex between 25°C and 135°C, indicating the loss of free nitric acid and DMF molecules around the crystals. Between 240°C and 290°C, a weight loss of 10.5% was observed, indicating the loss of the methylamino group in the structure. The rapid weight loss occurring above 330°C can be attributed to the decomposition of the organic ligands, with the final residue being zirconium dioxide.

[0052] from Figure 13-15 As can be seen from the data, the 2,6-pyridinedicarboxylic acid zirconium prepared in Comparative Example 1 has good thermodynamic stability before 330℃, and the 2-pyridinecarboxylic acid zirconium / hafnium has good thermodynamic stability before 354℃, that is, the 2-pyridinecarboxylic acid zirconium / hafnium has better thermal stability.

[0053] Example 5 The dielectric properties of the complexes prepared in Examples 1-2 were tested using a Novocontrol Concept 80 instrument. The test temperature range was 300-600K, and the test temperature spectrum had 5 frequency points. The dielectric constant of the complex prepared in Example 1 varies with temperature at different frequencies as follows: Figure 16As shown, all frequency curves exhibit a significant dielectric anomaly near 350 K, with the highest peak dielectric constant (approximately 8.2) at 500 Hz. The peak value gradually decreases with increasing frequency and shifts slightly towards higher temperatures, indicating a significant frequency dependence of the dielectric anomaly, possibly originating from dipole relaxation or ferroelectric phase transition in the material. Furthermore, the curve shows a trough in the 420-430 K range, followed by a slow recovery of the dielectric constant with increasing temperature. This phenomenon can be attributed to thermally activated carrier contributions or electrode polarization effects at high temperatures.

[0054] The dielectric loss of the complex prepared in Example 1 varies with temperature (300-580 K) at five frequencies: 500 Hz, 5 kHz, 50 kHz, 500 kHz, and 5 MHz, as shown below. Figure 17 As shown, near 350 K, the low-frequency curves (500 Hz, 5 kHz, 50 kHz) exhibit significant loss peaks, with the peak value increasing as the frequency decreases (approximately 0.058 at 500 Hz). As the frequency increases to 500 kHz and 5 MHz, the loss peaks significantly weaken and flatten, even becoming negative, primarily due to phase shift of the test signal or instrument baseline drift at high frequencies. At 550 K, the 500 Hz curve shows a resurgence in loss, which may be related to thermally activated conductivity or electrode interface losses at high temperatures. Overall, the frequency dependence and temperature evolution characteristics of dielectric loss reflect the transformation of the polarization relaxation mechanism and energy loss sources of the sample in different temperature ranges.

[0055] Based on the dielectric performance test results of Example 1 above, the following are examples of application scenarios for the product prepared by this invention: For example, the complex exhibits a significant dielectric anomaly peak near 350K, and the position of this peak shifts regularly with frequency, indicating that its dielectric response is highly sensitive to temperature. Therefore, this complex can be used to prepare temperature sensors, thermal switches, or over-temperature protection devices. For example, the dielectric loss of the complex approaches zero at frequencies of 500 kHz and above, and the dielectric constant remains stable, indicating excellent energy retention at high frequencies. Therefore, this complex can be used to prepare high-frequency capacitors, microwave devices, or dielectric layers in RFID tags. For example, the complex maintains a measurable dielectric response from room temperature to 580 K, and the peak dielectric constant at 500 Hz reaches 8.2, significantly better than most metal-organic framework materials, i.e., low loss. Therefore, this complex can be used in energy storage capacitors in high-temperature environments. For example, the complex exhibits a tunable dielectric response over a wide temperature range of 300-580K, and the dielectric constant and loss change regularly with temperature and frequency. Based on this, the complex can be used to prepare tunable microwave devices or phase shifters in phased array radars.

[0056] The dielectric constant of the complex prepared in Example 2 varies with temperature (300–600 K) at five different frequencies: 500 Hz, 5 kHz, 50 kHz, 500 kHz, and 5 MHz, as shown below. Figure 18 As shown, all frequency curves exhibit a significant dielectric peak at 350 K, and the peak dielectric constant decreases with increasing test frequency (e.g., approximately 9.0 at 500 Hz and approximately 8.1 at 5 MHz), demonstrating a clear frequency dependence. In the 400-500 K range, the dielectric constant at all frequencies decreases to a stable trough (approximately 7.5-7.8), with the curves converging, indicating a relatively stable polarization mechanism in this stage. In the 580-600 K range, extremely strong dielectric peaks (approximately 10.8) appear in the low-frequency range (especially at 500 Hz), while the dielectric constant in the high-frequency range shows only a slight increase. This phenomenon can be attributed to the activation of space charge polarization at high temperatures or electrode interface effects. Overall, the "bimodal-stable" change in dielectric constant with temperature reflects the structural evolution and polarization mechanism transformation of the sample in different temperature ranges.

[0057] The dielectric loss of the complex prepared in Example 2 varies with temperature (300-600K) at five different frequencies: 500 Hz, 5 kHz, 50 kHz, 500 kHz, and 5 MHz, as shown below. Figure 19 As shown, all frequency curves exhibit a dielectric loss peak at 350 K, and the peak value decreases with increasing test frequency (e.g., the peak value is approximately 0.12 at 500 Hz and close to 0 at 5 MHz), showing a clear frequency dependence. In the 400-500 K range, the dielectric loss at all frequencies tends to stabilize, remaining close to 0, and the curves at each frequency are close to each other, indicating that the polarization relaxation process of the sample is weak and the energy loss is small in this stage. In the 550-600 K range, the low-frequency segment (especially 500 Hz) shows an extremely strong dielectric loss peak (peak value close to 1.0), while the dielectric loss in the high-frequency segment only shows a slow increase. This phenomenon can be attributed to the conductivity loss of thermally activated charge carriers at high temperatures or the electrode interface effect. The space charge that is more easily accumulated at low frequencies is activated in this temperature range, thus causing a sharp increase in energy loss.

[0058] Based on the dielectric performance test results of Example 2 above, the following are examples of application scenarios for the product prepared by this invention: For example, the complex exhibits significant dielectric anomalous peaks in both the 350 K and 580-600 K temperature ranges, and the physical mechanisms of the two peaks are different (the former originates from dipole relaxation, and the latter from space charge polarization). Based on this, the complex can be used to prepare dual-mode temperature sensors or wide-temperature-range monitoring devices. For example, the complex shows a sharp increase in dielectric constant in the 580-600 K range (from about 7.5 to 10.8), exhibiting a significant dielectric switching effect. Based on this, the complex can be used to prepare thermally activated dielectric switches or over-temperature protection elements.

[0059] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of the present invention and not to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A hafnium / zirconium 2-pyridinecarboxylate complex, characterized in that, The chemical formula of the hafnium 2-pyridinecarboxylate complex is Hf(PA)4·H2O, and the chemical formula of the zirconium 2-pyridinecarboxylate complex is Zr(PA)4·H2O, wherein PA is a 2-pyridinecarboxylate anion, and the structural formula of PA is shown in Formula I: Formula I.

2. The hafnium / zirconium 2-pyridinecarboxylate complex according to claim 1, characterized in that, The hafnium 2-pyridinecarboxylate / zirconium complex belongs to the cubic crystal system, space group P42 / n.

3. The hafnium / zirconium 2-pyridinecarboxylate complex according to claim 2, characterized in that, The unit cell parameters of the hafnium 2-pyridinecarboxylate are: a = 11.1012(3) Å, b = 11.1012(3) Å, c = 9.5970(3) Å, β = 90°, V = 1182.70(6) Å. 3 ; And / or, the cell parameters of the 2-pyridinecarboxylate zirconium are: a = 11.1004(2) Å, b = 11.1004(2) Å, c = 9.5987(2) Å, β = 90°, V = 1182.74(5) Å. 3 .

4. The hafnium / zirconium 2-pyridinecarboxylate complex according to claim 2, characterized in that, The hafnium 2-pyridinecarboxylate has a molecular weight of 3087.5~3111.1 cm⁻¹. -1 1437.6~1470.7cm -1 1604.6~1686.4cm -1 1049.1~1240.4cm -1 449.3±0.2cm -1 It has an infrared absorption band within the wavenumber range; And / or, the zirconium 2-pyridinecarboxylate has a thickness of 3476.1~3521.2 cm⁻¹. -1 3086.6~3109.6cm -1 1437.0~1469.9cm -1 1603.2~1683.0cm -1 1047.0~1239.3cm -1 445.1±0.2cm -1 It has an infrared absorption band within the wavenumber range.

5. The method for preparing the 2-pyridinecarboxylic acid hafnium / zirconium complex according to any one of claims 1-4, characterized in that, The preparation method is as follows: (1) Add 2-pyridinecarboxylic acid and hafnium / zirconium salt to an organic solvent and heat to dissolve, then stir and filter, and collect the filtrate; (2) Heat the filtrate to 120-140℃ and react for 60-80h. After the reaction is completed, cool, filter, wash and dry to obtain 2-pyridinecarboxylic acid hafnium / zirconium complex.

6. The preparation method according to claim 5, characterized in that, The molar ratio of hafnium / zirconium salt to 2-pyridinecarboxylic acid is 1:(2-6). And / or, the sum of the masses of hafnium / zirconium salt and 2-pyridinecarboxylic acid in volume ratio to the organic solvent is 1 g : (6-10) mL.

7. The preparation method according to claim 5, characterized in that, The hafnium salt includes at least one of hafnium nitrate, hafnium chloride, hafnium acetate, and hafnium oxychloride; the zirconium salt includes at least one of zirconium nitrate, zirconium chloride, zirconium acetate, and zirconium oxychloride. And / or, the organic solvent includes any one of the following: a mixed solution of N,N-dimethylformamide and acetic acid, a mixed solution of methanol and formic acid, a mixed solution of dimethyl sulfoxide and acetic acid, or a mixed solution of methanol and acetic acid.

8. The preparation method according to claim 7, characterized in that, Satisfy at least one of the following: A. In the mixed solution of N,N-dimethylformamide and acetic acid, the volume ratio of N,N-dimethylformamide to acetic acid is (5-7):1; B. In the mixed solution of methanol and formic acid, the volume ratio of methanol to formic acid is (5-7):1; C. In the mixed solution of dimethyl sulfoxide and acetic acid, the volume ratio of dimethyl sulfoxide to acetic acid is (5-7):1; D. In the mixed solution of methanol and acetic acid, the volume ratio of methanol to acetic acid is (5-7):

1.

9. The preparation method according to claim 5, characterized in that, In step (1), the temperature for heating and melting is 60-70℃; And / or, in step (1), the stirring temperature is 20-30℃ and the stirring time is 25-35min.

10. The application of the 2-pyridinecarboxylic acid hafnium / zirconium complex as described in any one of claims 1-4 in the preparation of new energy vehicle components, precision insulating components for power equipment, and dielectric insulating / transmission components for industrial equipment.

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