Cobalt-based magnetic compound and preparation method and application thereof

Abstract

The present invention relates to a cobalt-based magnetic compound and a preparation method and application thereof. An example of an α-type cobalt-based magnetic compound has a molecular formula of [CoL2]2(α-Mo8O 26 )·3H2O (α-type). An example of a β-type cobalt-based magnetic compound has the molecular formula [CoL2]2(β-Mo8O 26 )·5H2O(β-type). Application of α-type cobalt-based magnetic compounds as antiferromagnetic materials. Application of β-type cobalt-based magnetic compounds as spin-state switching materials. The cobalt-based magnetic compound of the present invention is synthesized by a self-assembly synthesis strategy, and the magnetic center cobalt ion is protected by a terpyridine ligand, and then polymolybdenum oxygen clusters are introduced to form a stable cobalt-based magnetic compound. The two magnetic properties are mainly caused by the polymolybdenum oxygen clusters inducing different molecular stacking structures. Therefore, the magnetic properties of divalent cobalt can be regulated by changing the polymolybdenum oxygen clusters.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of novel magnetic materials, and specifically relates to a cobalt-based magnetic compound and a preparation method and application thereof, which can realize switching between antiferromagnetic interaction and spin state transition, and is applied to fields such as information storage and molecular switches. Background Art

[0002] In an era of rapid technological development, the development of new intelligent materials is particularly important. More and more scientific researchers are committed to the research and development of functional materials with excellent physical and chemical properties. Among them, magnetic materials have been widely used in information storage, molecular switches, memory elements and other fields. Traditional magnetic materials are mainly alloys or metal oxides, which are atomic-based magnetic materials composed of metallic bonds or ionic bonds. New molecular-based magnetic materials refer to compounds with clear structures synthesized from transition metals such as iron, cobalt, and nickel. Molecular-based magnetic materials are not only simple to prepare and easy to analyze structure-activity relationships, but also easy to process into devices. In order to further realize its application in aerospace and biomedicine, researchers are required to precisely control the magnetic properties of materials.

[0003] In recent years, people have prepared a large number of molecular-based magnetic materials and used various physical and chemical methods to regulate their magnetic properties. Among them, introducing organic ligands to protect the magnetic center and synthesize organic-inorganic hybrid target materials is a very effective preparation strategy. On the one hand, the introduction of organic ligands provides a suitable coordination field for the magnetic center. On the other hand, after protecting the magnetic center, the magnetic properties can be precisely regulated by modifying the ligands, changing the solvent and the guest molecules. In 2015, the applicant combined organic phosphonic acid ligands and polymolybdenum oxygen clusters with transition metal nickel to synthesize a hexanuclear nickel-based magnetic compound CsNa9[H2{Ni3O2(H2O)6}(PMo6O 21 )2{Ni(OOCCH2NHCH2PO3)2}3]·21H2O, the nickel ions in this material show antiferromagnetic interaction (Dalton Trans., 2015, 44, 17544–17550). Subsequently, the applicant introduced risedronic acid ligands into polymolybdenum oxygen clusters and synthesized four organic-inorganic hybrid transition metal derivatives Cs4Na2[{NiO(H2O)2}(Mo2O5L)]2·16H2O, Cs4Na2[{CoO(H2O)2}(Mo2 O5L)]2·16H2O, Cs2Na2H[(CrO2){(Mo2O5)(HL)}2]·17H2O, Cs 11Na4H7[MnO2{HL(Mo2O5)MnO2(H2O)(Mo2O4)L}2]2·26H2O[L={O3PC(O)(CH2-3-C5NH4)PO3},HL={O3PC(O)(CH2-3-C5NH5)PO3}], obtained a molecular-based magnetic material with antiferromagnetism and ferromagnetism (Synthetic Metals, 2017, 223, 19–25). In 2019, by adjusting the axial anionic ligands, the applicant reported a series of one-dimensional chain coordination polymers [Fe(dpds)2{C(CN)3}2]·dpds, [Fe(dpds)2(NCBH3)2], [Fe(dpds)2(NC Se)2]·3.5H2O (dpds=4,4'-bipyridine disulfide), among which the compounds containing {C(CN)3} and {NCBH3} ligands not only have thermally induced spin transition behavior, but also exhibit good photoinduced spin state transition properties (Dalton Trans., 2019, 48, 9243–9249). Summary of the invention

[0004] The purpose of the present invention is to provide a cobalt-based magnetic compound and a preparation method and application thereof, so as to achieve precise control of the properties of molecular-based magnetic materials and provide a new idea for the controllable preparation of new magnetic materials.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] An example of an α-type cobalt-based magnetic compound, the molecular formula of which is [CoL2]2(α-Mo8O 26 )·3H2O.

[0007] The preparation method of the α-type cobalt-based magnetic compound comprises the following steps: dissolving ammonium heptamolybdate in distilled water, adjusting the pH to 4.0, adding a mixed solution of acetonitrile and water in which CoCl2·6H2O and 4'-(4-pyridyl)-2,2':6',2"-terpyridine ligand are dissolved, and stirring for 30-40 minutes; then reacting for three days at 160°C, cooling, filtering, and obtaining red block crystals, which are the α-type cobalt-based magnetic compound; (NH4)6Mo7O 24 The molar ratio of ·4H2O, CoCl2·6H2O and 4'-(4-pyridyl)-2,2':6',2"-terpyridine is 16:3:2.

[0008] An example of a β-type cobalt-based magnetic compound, the molecular formula of which is [CoL2]2(β-Mo8O 26 )·5H2O.

[0009] The preparation method of the β-type cobalt-based magnetic compound comprises the following steps: dissolving sodium molybdate in distilled water, adjusting the pH to 4.0, adding a mixed solution of acetonitrile and water in which CoCl2·6H2O and 4'-(4-pyridyl)-2,2':6',2"-terpyridine ligand are dissolved, and stirring for 30-40 minutes; reacting for three days at 160°C, cooling, filtering, and obtaining red block crystals, which are the β-type cobalt-based magnetic compounds; the molar ratio of Na2MoO4·2H2O, CoCl2·6H2O and 4'-(4-pyridyl)-2,2':6',2"-terpyridine is 30:5:6.

[0010] The α-type cobalt-based magnetic compound is used as an antiferromagnetic material.

[0011] Application of the β-type cobalt-based magnetic compound as a spin state switching material.

[0012] The present invention provides the application of the above-mentioned α-type and β-type cobalt-based magnetic compounds as magnetic materials. Experiments have found that: there is an antiferromagnetic interaction between cobalt ions in α-type materials, and the spin state of cobalt ions in β-type materials can be reversibly switched between high spin and low spin with temperature. The two magnetic properties are mainly caused by different molecular stacking structures induced by polymolybdenum oxygen clusters. Therefore, the magnetic properties of divalent cobalt can be regulated by changing polymolybdenum oxygen clusters.

[0013] The cobalt-based magnetic compound of the present invention is synthesized by a self-assembly synthesis strategy, using a terpyridine ligand to protect the magnetic center cobalt ion, and then introducing multiple molybdenum oxygen clusters to form a stable cobalt-based magnetic compound. Compared with traditional magnetic materials, the present invention has the following advantages:

[0014] 1) The present invention uses X-ray single crystal diffraction technology to accurately analyze the molecular structure of the target product;

[0015] 2) The present invention adopts a self-assembly assembly strategy under solvent thermal conditions, which has simple experimental steps, is green and environmentally friendly, and has a high yield;

[0016] 3) The present invention utilizes terpyridine ligand to protect Co 2+ ions, providing a suitable coordination field for studying their spin states;

[0017] 4) This paper investigates the effect of the configuration of polymolybdenum oxygen clusters on Co 2+ The influence of ionic magnetic properties provides experimental basis and theoretical reference for regulating the magnetic properties of divalent cobalt;

[0018] 5) Compared with traditional magnetic materials, the mechanistic relationship between the structure and magnetism of the target product of the present invention is clearer. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is the molecular structure of α-type cobalt-based magnetic compounds;

[0020] Figure 2 It is the molecular structure of β-type cobalt-based magnetic compounds;

[0021] Figure 3 It is the molecular stacking structure of α-type cobalt-based magnetic compounds;

[0022] Figure 4 It is the molecular stacking structure of β-type cobalt-based magnetic compounds;

[0023] Figure 5 This is the infrared spectrum of α-type cobalt-based magnetic compounds;

[0024] Figure 6 This is the infrared spectrum of β-type cobalt-based magnetic compounds;

[0025] Figure 7 The X-ray powder diffraction experimental spectrum and theoretical simulation spectrum of α-type cobalt-based magnetic compounds;

[0026] Figure 8 The X-ray powder diffraction experimental spectrum and theoretical simulation spectrum of β-type cobalt-based magnetic compounds;

[0027] Fig. 9 is the temperature-dependent molar magnetic susceptibility curve of α-type cobalt-based magnetic compounds;

[0028] Fig.10 is 1 / χ of α-type cobalt-based magnetic compounds M -T curve;

[0029] Fig.11 is the temperature-dependent molar magnetic susceptibility curve of β-type cobalt-based magnetic compounds;

[0030] Fig.12 is the d(χ M T) / dT-T curve; DETAILED DESCRIPTION

[0031] like Figure 1 , 2 , 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 as shown:

[0032] An example of an α-type cobalt-based magnetic compound, the molecular formula of which is [CoL2]2(α-Mo8O 26)·3H2O. The preparation method of the α-type cobalt-based magnetic compound comprises the following steps: dissolving ammonium heptamolybdate in distilled water, adjusting the pH to 4.0, adding a mixed solution of acetonitrile and water in which CoCl2·6H2O and 4'-(4-pyridyl)-2,2':6',2"-terpyridine ligand are dissolved, and stirring for 30-40 minutes; then reacting at 160°C for three days, cooling, filtering, and obtaining red block crystals, which are α-type cobalt-based magnetic compounds; (NH4)6Mo7O 24 The molar ratio of ·4H2O, CoCl2·6H2O and 4'-(4-pyridyl)-2,2':6',2"-terpyridine is 16:3:2.

[0033] An example of a β-type cobalt-based magnetic compound, the molecular formula of which is [CoL2]2(β-Mo8O 26 )·5H2O. The preparation method of the β-type cobalt-based magnetic compound comprises the following steps: dissolving sodium molybdate in distilled water, adjusting the pH to 4.0, adding a mixed solution of acetonitrile and water in which CoCl2·6H2O and 4'-(4-pyridyl)-2,2':6',2"-terpyridine ligand are dissolved, and stirring for 30-40 minutes; then reacting at 160°C for three days, cooling, filtering, and obtaining red block crystals, which are β-type cobalt-based magnetic compounds; the molar ratio of Na2MoO4·2H2O, CoCl2·6H2O and 4'-(4-pyridyl)-2,2':6',2"-terpyridine is 30:5:6.

[0034] Application of the α-type cobalt-based magnetic compound as an antiferromagnetic material. Application of the β-type cobalt-based magnetic compound as a spin-state switching material. Method for regulating different magnetic properties of the α-type cobalt-based magnetic compound. Method for regulating different magnetic properties of the β-type cobalt-based magnetic compound.

[0035] The present invention will be described in detail below in conjunction with specific embodiments:

[0036] Example 1: The molecular formula is [CoL2]2(α-Mo8O 26 )·3H2O α-type cobalt-based magnetic compound preparation method, which comprises the following steps:

[0037] 1) 4.50g (NH4)6Mo7O 24·4H2O (3.64 mmol) was dissolved in 80 mL of water, and its pH was adjusted to 4.0 with CH3COOH and NH4OH to obtain solution A. 0.167 g of CoCl2·6H2O (0.702 mmol) and 0.144 g of 4'-(4-pyridyl)-2,2':6',2"-terpyridine (0.46 mmol) were dissolved in a mixed solution of 20 mL of acetonitrile and 10 mL of water to obtain solution B;

[0038] 2) Add solution B obtained in step 1) dropwise to solution A and stir for 30-40 minutes;

[0039] 3) The solution obtained in step 2) was evenly divided into 10 25 mL autoclaves, kept at 160° C. for three days, cooled and filtered to obtain red block crystals, which were α-type cobalt-based magnetic compounds.

[0040] Example 2: The molecular formula is [CoL2]2(β-Mo8O 26 )·5H2O beta-type cobalt-based magnetic compound preparation method, which comprises the following steps:

[0041] 1) 0.24 gg Na2MoO4·2H2O (1.0 mmol) was dissolved in 8 mL of water, and the pH value was adjusted to 4.0 with CH3COOH to obtain solution A. 0.04 g CoCl2·6H2O (0.168 mmol) and 0.06 g 4'-(4-pyridyl)-2,2':6',2"-terpyridine (0.2 mmol) were dissolved in 3 mL of acetonitrile to obtain solution B;

[0042] 2) Add solution B obtained in step 1) dropwise to solution A and stir for 30-40 minutes;

[0043] 3) The solution obtained in step 2) is transferred to a high-pressure reactor, maintained at 160° C. for three days, cooled, and filtered to obtain red block crystals, which are β-type cobalt-based magnetic compounds.

[0044] Example 3: Crystal samples of α-type and β-type cobalt-based magnetic compounds were collected and tested for temperature-dependent magnetic susceptibility. There is an antiferromagnetic interaction between cobalt ions in α-type materials, and the spin state of cobalt ions in β-type materials can be reversibly switched between high spin and low spin depending on the temperature.

[0045] The present invention uses X-ray single crystal diffraction technology to determine the crystal structure of the α-type cobalt-based magnetic compound prepared in Example 1 and the β-type cobalt-based magnetic compound prepared in Example 2. The unit cell parameters of the α-type target product are as follows: monoclinic system, C2 / c space group, unit cell parameter β=106.824(7), Z = 4, R1 = 0.0410, wR2 = 0.0998. The unit cell parameters of the β-type target product are as follows: triclinic system, Space group, unit cell parameters α=69.953(9), β=85.337(12), γ=74.563(15), Z=4, R1=0.0432, wR2=0.1146.

[0046] Figure 1 , 2 It is the molecular structure of α-type and β-type cobalt-based magnetic compounds. Figure 1 , 2 It can be seen that the α-type cobalt-based magnetic compound consists of 2 [CoL2] 2+ cation, 1 [α-Mo8O 26 ] 4- The anion is composed of three lattice water molecules. Its cation is formed by two molecules of 4'-(4-pyridyl)-2,2':6',2"-terpyridine ligand chelated with a cobalt ion, and the counter anion is [α-Mo8O 26 ] 4- The cobalt ion in the cation coordinates with six nitrogen atoms to form a distorted octahedral geometry, and the anion [α-Mo8O 26 ] 4- The spatial structure of the β-cobalt-based magnetic compound can be simplified as a cylinder, which is formed by six edge-sharing {MoO6} octahedra connected to two {MoO4} tetrahedra through triple bridging oxygen atoms. 2+ cation, 1 [β-Mo8O 26 ] 4- The anion is composed of 5 lattice water molecules. Its cation is the same as that of α-type cobalt-based magnetic compounds, and the anion is [β-Mo8O 26 ] 4- Its spatial structure can be simplified as a parallelepiped, with four {MoO6} octahedra connected by common edges to form a subunit, and two groups of this subunit are connected by two quadruple bridging oxygen atoms, four triple bridging oxygen atoms and two double bridging oxygen atoms.

[0047] Figure 3 , 4 It is the molecular stacking structure of α-type and β-type cobalt-based magnetic compounds. Figure 3 , 4 It can be seen that when the compound crystallizes, the molecular stacking mode in its lattice is affected by the anions, [β-Mo8O 26 ] 4-The molecules of the β-type cobalt-based magnetic compounds formed by anions are more densely packed, making the synergistic effect between the molecules stronger.

[0048] Figure 5 , 6 The infrared spectra of α-type and β-type cobalt-based magnetic compounds are shown in Figure 1. Figure 5 , 6 It can be seen that α-type and β-type cobalt-based magnetic compounds have similar infrared spectra, with a wavelength of 1618-1473 cm -1 The range corresponds to the cationic part [CoL2] 2+ The stretching vibration of ν(CH) of the organic ligand in -1 The range corresponds to the ν(Mo-O t ) and ν(Mo-O-Mo) stretching vibration.

[0049] Figure 7 , 8 The X-ray powder diffraction experimental and theoretical simulation spectra of α-type and β-type cobalt-based magnetic compounds are shown in Figure 2. Figure 7 , 8 It can be seen that the X-ray powder diffraction experimental spectra of the two compounds at room temperature have similar peak positions to the theoretical spectra simulated by single crystal data, indicating that the samples used for testing are all pure phases, and the differences in some peak intensities may be caused by the different diffraction of the powder samples on each crystal plane.

[0050] Fig. 9 , 10 The temperature-dependent molar magnetic susceptibility curve and 1 / χ of α-type cobalt-based magnetic compounds are shown in Figure 2. M -T curve, there is an antiferromagnetic interaction between divalent cobalt ions. Fig. 9 , 10 It can be seen that as the temperature decreases, the χ M The T value remains basically unchanged between 400-60K. When the temperature is further reduced, its χ M The T value decreases rapidly and reaches a minimum at 2 K. This change indicates that there is a weak antiferromagnetic interaction between cobalt ions in α-type cobalt-based magnetic compounds. Furthermore, through the Curie-Weiss law fitting, the Weiss constant θ is calculated to be -3.97 K, proving its antiferromagnetic coupling effect.

[0051] Fig.11 , 12 The temperature-dependent molar magnetic susceptibility curves and d(χ M T) / dT-T curve, the thermally induced spin transition temperature of divalent cobalt ion is 370K. Fig.11 ,12 It can be seen that at 100K, the χ M T value is 1.0cm 3 Kmol -1 , corresponding to two low-spin divalent cobalt ions (S = 1 / 2, g = 2.0, χ M T=0.75cm 3 Kmol -1 ). When the temperature rises to 355K, its χ M The T value slowly increases to 1.94cm 3 Kmol -1 . Then, its M The T value increased rapidly to 4.29cm 3 Kmol -1 , indicating that the low-spin divalent cobalt ion is completely transformed into a high-spin state. M The transition temperature is 370 K from the peak position of the T) / dT-T curve.

[0052] The present invention adjusts the magnetic properties of divalent cobalt by utilizing poly-molybdenum-oxygen clusters of different configurations, thereby realizing the switching between antiferromagnetic interaction and spin state transition, providing a new idea for the controllable preparation of new magnetic materials, which can be applied to fields such as information storage and molecular switches.

[0053] The above-described embodiments of the present invention are intended to be illustrative and non-restrictive, and the scope of the present invention is defined by the appended claims rather than the above description.

Claims

1. An example α- A cobalt-based magnetic compound characterized by: The molecular formula of the magnetic compound is [CoL2]2( α -Mo8O 26 )·3H2O, L represents 4'-(4-pyridyl)-2,2':6',2''-terpyridine.

2. According to claim 1 α- The method for preparing a cobalt-based magnetic compound is characterized by: The following steps are involved: Dissolve ammonium heptamolybdate in distilled water, adjust the pH to 4.0, add a mixed solution of acetonitrile and water containing CoCl2∙6H2O and 4'-(4-pyridyl)-2,2':6',2''-terpyridine ligand, and stir for 30-40 min; then react at 160 °C for three days, cool and filter to obtain red block crystals, which is α- Cobalt-based magnetic compounds; (NH4)6Mo7O 24 The molar ratio of 4H2O, CoCl2∙6H2O and 4'-(4-pyridyl)-2,2':6',2''-terpyridine is 16:3:

2.

3. An example β- A cobalt-based magnetic compound characterized by: The molecular formula of the magnetic compound is [CoL2]2( β -Mo8O 26 )·5H2O, L represents 4'-(4-pyridyl)-2,2':6',2''-terpyridine.

4. According to claim 3 β- The method for preparing a cobalt-based magnetic compound is characterized by: The following steps are involved: Sodium molybdate was dissolved in distilled water, the pH was adjusted to 4.0, and then a mixed solution of acetonitrile and water containing CoCl2∙6H2O and 4'-(4-pyridyl)-2,2':6',2''-terpyridine ligand was added and stirred for 30-40 min; then the mixture was reacted at 160 °C for three days, cooled and filtered to obtain red block crystals, which is β- type cobalt-based magnetic compound; the molar ratio of Na2MoO4·2H2O, CoCl2∙6H2O and 4'-(4-pyridyl)-2,2':6',2''-terpyridine is 30:5:

6.

5. According to claim 1 α- Application of cobalt-based magnetic compounds as antiferromagnetic materials.

6. According to claim 3 β- Application of cobalt-based magnetic compounds as spin-state switching materials.

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