Lattice-type iron-based complex based on cis-trans isomeric triazole and preparation method thereof

Abstract

The present invention relates to the technical field of molecular-based magnetic materials. In order to solve the problem that the synthesis of existing asymmetric lattice-type spin-crossover materials is difficult and it is difficult to achieve an asymmetric arrangement of coordination sites by synthesizing symmetrical multidentate ligands, a lattice-type iron-based complex based on cis-trans isomerized triazoles and a preparation method thereof are proposed. The spin-crossover material prepared by the present invention is based on a bidentate triazole ligand, and a lattice-type spin-crossover material is prepared by self-assembly of the ligand and transition metal ions; by adjusting the terminal substituent, the orientation of the ligand can be well adjusted to achieve the assembly of an asymmetric lattice-type spin-crossover material. The experimental operation of the present invention to prepare a bidentate triazole ligand by condensing a cyano compound with a hydrazide and then dehydrating it is simple, the yield is as high as more than 85%, and it is easy to promote and apply on a large scale.

Description

Technical Field

[0001] The invention relates to the technical field of molecule-based magnetic materials, and in particular to a lattice-type iron-based complex based on cis-trans isomerized triazole and a preparation method thereof. Background Art

[0002] Molecular-based magnetic materials are a type of magnetic compound formed by chemical assembly of paramagnetic ions and ligands. They are a frontier interdisciplinary subject combining magnetic chemistry and coordination chemistry. They combine structural design, supramolecular assembly, magnetic characterization and quantitative calculation to construct molecular-based magnetic materials with excellent performance, which are applied to the design of high-density information storage and spintronic devices. The main research directions of molecular-based magnetic materials can be subdivided into systems such as single-molecule magnets, single-molecule magnetic rings, single-chain magnets and spin cross-coordinates.

[0003] Compared with single-molecule magnets that exhibit slow magnetic relaxation behavior in response to changes in external magnetic fields at low temperatures, spin cross-complexes can respond to stimuli of different physical conditions such as temperature, light and pressure, that is, they can achieve switching between high and low spin states of transition metal ions through external stimuli. Therefore, it has also become an important branch in the field of molecular-based magnetic materials, with potential application value in high-density information storage, spin electronic devices and molecular switching devices.

[0004] However, so far, reports on spin crossover complexes are still mainly mononuclear systems, and reports on multinuclear systems are relatively rare. However, the different arrangements and possible multi-step thermal hysteresis behaviors exhibited in multinuclear systems are not available in mononuclear systems. A typical example is the tetranuclear [2×2] lattice spin crossover complex. Since the four transition metal ions in the lattice are arranged in a matrix in the molecule, Fe Ⅱ Taking ions as an example, the switch in the molecular matrix can be realized by valence state change or high-low spin state conversion: for example, through electrochemical means, a continuous redox process is carried out to finally obtain a stable mixed valence state; or, by changing the temperature and other physical conditions, multiple spin state switching is realized. Therefore, if the four sites can achieve stable multi-state transition, it is expected to be applied in the field of quantum cellular automation (QCA).

[0005] The lattice-type spin-crossing complexes reported so far can be divided into systems composed of different bridging ligands such as pyrimidine, pyrazole, imidazole, benzdiimidazole or oxygen atoms through different bridging groups. For most lattice-type complexes, their ligands are in cis configuration in the square matrix, and finally a symmetrical lattice complex is obtained. It was not until 2016 that Professor Mario Ruben and others first reported a cross-type symmetrical lattice complex assembled from all-trans configuration ligands. However, due to the high symmetry of the structure, the compound only exhibits one-step spin-crossing behavior.

[0006] From the perspective of topological structure, compared with the two previously reported topological structures, the asymmetric lattice with coexistence of cis and trans will have lower symmetry. The metal ions in the lattice structure are in different coordination environments. Through external stimulation, the central spin state of each metal ion can be controlled, and thus multi-step spin crossover behavior can be achieved. However, this asymmetric lattice type spin crossover material is difficult to synthesize, and it is difficult to achieve an asymmetric arrangement of coordination sites by synthesizing symmetric multidentate ligands. Summary of the invention

[0007] In order to comprehensively solve the above problems, the purpose of the present invention is to provide a lattice-type iron-based complex based on cis-trans isomeric triazole and a preparation method thereof. By introducing different substituents at both ends of the triazole ligand, the rotation of the CC bond on both sides of the triazole and the steric effect of the terminal substituent are changed, the cis-trans configuration of the bidentate ligand is transformed, and then a lattice-type iron-based magnetic material is assembled. This series of complexes have clear single crystal structures and temperature-dependent magnetic susceptibility data. Due to the orientation of the ligand, effective regulation of the structure and magnetism of the complex is achieved.

[0008] Technical idea: This invention uses the cis-trans isomerism of bidentate triazole ligands to achieve the cis- and trans-orientation of ligands in lattice-type complexes, and synthesizes a series of iron-based magnetic complexes with lattice configurations. By adjusting the substituents at the end sites of triazole to achieve structural regulation, the magnetic properties are also regulated.

[0009] In order to achieve the above-mentioned object, the first aspect of the present invention provides a lattice-type iron-based complex based on cis-trans isomeric triazole, the chemical formula of which is: Fe4(L)4(BF4)4;

[0010] Wherein, the ligand L is any one of L1, L2, L3 and L4, and the ligands L1, L2, L3 and L4 all have cis and trans configurations:

[0011] When the ligand L is L1, the structural formula of Fe4(L)4(BF4)4 is:

[0012] ;

[0013] Among them, the cis configuration of ligand L1 is: , the trans configuration is: ;

[0014] When the ligand L is L2, the structural formula of Fe4(L)4(BF4)4 is:

[0015] ;

[0016] Among them, the cis configuration of ligand L2 is: , the trans configuration is: ;

[0017] When the ligand L is L3, the structural formula of Fe4(L)4(BF4)4 is:

[0018] ;

[0019] Among them, the cis configuration of ligand L3 is: , the trans configuration is: ;

[0020] When the ligand L is L4, the structural formula of Fe4(L)4(BF4)4 is:

[0021] ;

[0022] Among them, the cis configuration of ligand L4 is: , the trans configuration is: .

[0023] The second aspect of the present invention provides a method for preparing a lattice-type iron-based complex based on cis-trans isomeric triazole, comprising: step 1: stirring a bidentate ligand and ferrous tetrafluoroborate in acetonitrile at room temperature to obtain a clear reaction solution;

[0024] Wherein, the bidentate ligand is any one of ligand L1, ligand L2, ligand L3, and ligand L4:

[0025] Ligand L1: ;

[0026] Ligand L2: ;

[0027] Ligand L3: ;

[0028] Ligand L4: ;

[0029] Step 2: Place the reaction solution of step 1 in ether vapor, wait for crystals to precipitate, then filter and collect to obtain an iron-based magnetic complex with a structural formula of Fe4(L)4(BF4)4, specifically:

[0030] When L is ligand L1, the structural formula of Fe4(L)4(BF4)4 is:

[0031] ;

[0032] Among them, the cis configuration of ligand L1 is: , the trans configuration is: ;

[0033] When L is ligand L2, the structural formula of Fe4(L)4(BF4)4 is:

[0034] ;

[0035] Among them, the cis configuration of ligand L2 is: , the trans configuration is: ;

[0036] When L is ligand L3, the structural formula of Fe4(L)4(BF4)4 is:

[0037] ;

[0038] Among them, the cis configuration of ligand L3 is: , the trans configuration is: ;

[0039] When L is ligand L4, the structural formula of Fe4(L)4(BF4)4 is:

[0040] ;

[0041] Among them, the cis configuration of ligand L4 is: , the trans configuration is: .

[0042] Preferably, in step 1, the molar ratio of the bidentate ligand to ferrous tetrafluoroborate is 1:1.

[0043] Preferably, the preparation method of ligand L1 is as follows: the intermediate obtained by the reaction of 6-(1-pyrazole)-pyridine-2-carboxylic acid hydrazide and 2-cyano-6-(1-pyrazole)-pyridine under alkaline conditions is dehydrated in ethylene glycol to finally prepare L1.

[0044] Preferably, the preparation method of ligand L2 is as follows: the intermediate obtained by the reaction of 6-formylhydrazide-2,2'-bipyridine and 6-cyano-2,2'-bipyridine under alkaline conditions is dehydrated in ethylene glycol to finally prepare L2.

[0045] Preferably, the preparation method of ligand L3 is as follows: the intermediate obtained by the reaction of 6-(1-pyrazole)-pyridine-2-carboxylic acid hydrazide and 6-cyano-2,2'-bipyridine under alkaline conditions is dehydrated in ethylene glycol to finally prepare L3.

[0046] Preferably, the preparation method of ligand L4 is as follows: the intermediate obtained by the reaction of 6-(3,5-dimethyl-1-pyrazole)-pyridine-2-carboxylic acid hydrazide and 6-cyano-2,2'-bipyridine under alkaline conditions is dehydrated in ethylene glycol to finally prepare L4.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] 1. The present invention successfully prepared four bidentate triazole ligands by condensing pyridine carboxyhydrazide derivatives and pyridine cyanide derivatives and then dehydrating them. The reaction steps are simple to operate and the yield is high, which is suitable for large-scale promotion.

[0049] 2. The present invention obtains a symmetrical lattice compound Fe4(L1)4(BF4)4 by using the ligand L1. The ligand in the structure is in a cis configuration, the molecule has a high symmetry, and the magnetic test shows that the compound is in a high spin state and does not show spin crossover properties;

[0050] 3. The present invention obtains an asymmetric lattice compound Fe4(L2)4(BF4)4 by changing the terminal substituent and using the ligand L2. Two ligands in the structure are in cis configuration and the other two ligands are in trans configuration, the molecular symmetry is reduced, and the magnetic test shows that three metal ions in the compound are in high spin and one is in low spin, and a weak spin conversion phenomenon begins to appear at 380 K;

[0051] 4. The present invention introduces different substituents on both sides of triazole and uses asymmetric ligand L3 to obtain an asymmetric lattice compound Fe4(L3)4(BF4)4. Two ligands in the structure are in cis configuration and the other two ligands are in trans configuration. The molecular symmetry is further reduced. Magnetic tests show that three metal ions in the compound are in high spin and one is in low spin. At 350 K, an obvious spin conversion phenomenon begins to appear, accompanied by a magnetic hysteresis loop.

[0052] 5. The present invention introduces a steric hindering group on one side of the asymmetric bidentate triazole ligand, and uses the asymmetric ligand L4 to obtain an asymmetric lattice compound Fe4(L4)4(BF4)4, in which two ligands are in cis configuration and the other two ligands are in trans configuration, and the molecular symmetry is relatively low. Magnetic tests show that three metal ions in the compound are in high spin and one is in low spin, and it exhibits slow spin crossover properties in the range of 100-400 K;

[0053] The above results show that the spin crossover properties of the series of lattice-type complexes prepared by the present invention are mainly regulated by the molecular symmetry and the side-end substituents, wherein reducing the molecular symmetry is conducive to the spin center being in a different coordination environment, thereby generating an active low-spin state. Increasing the steric hindrance of the side-end substituents is conducive to stabilizing the low-spin sites, thereby delaying the occurrence of spin crossover, and allowing the compounds to exhibit spin crossover properties over a wide temperature range. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0055] In the attached picture:

[0056] Figure 1 is the ligand L1 in DMSO-d6 1 H-NMR spectrum;

[0057] Figure 2 is the ligand L2 in DMSO-d6 1 H-NMR spectrum;

[0058] Figure 3 is the ligand L3 in DMSO-d6 1 H-NMR spectrum;

[0059] Figure 4 is the ligand L4 in DMSO-d6 1 H-NMR spectrum;

[0060] Figure 5 It is the single crystal structure diagram of Fe4(L1)4(BF4)4 complex;

[0061] Figure 6 It is the single crystal structure diagram of Fe4(L2)4(BF4)4 complex;

[0062] Figure 7 It is the single crystal structure diagram of Fe4(L3)4(BF4)4 complex;

[0063] Figure 8 It is the single crystal structure diagram of Fe4(L4)4(BF4)4 complex;

[0064] Fig. 9 It is the temperature-dependent magnetic susceptibility diagram of Fe4(L1)4(BF4)4 complex;

[0065] Fig.10 It is the temperature-dependent magnetic susceptibility diagram of Fe4(L2)4(BF4)4 complex;

[0066] Fig.11 It is the temperature-dependent magnetic susceptibility diagram of Fe4(L3)4(BF4)4 complex;

[0067] Fig.12 It is the temperature-dependent magnetic susceptibility diagram of Fe4(L4)4(BF4)4 complex;

[0068] Fig.13 It is a schematic diagram of the assembly of the lattice compound of the present invention. DETAILED DESCRIPTION

[0069] The following combination Figure 1-Figure 13 It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0070] The present invention provides a lattice-type iron-based complex based on cis-trans isomeric triazole, the chemical formula of which is: Fe4(L)4(BF4)4;

[0071] Wherein, the ligand L is any one of L1, L2, L3 and L4, and the ligands L1, L2, L3 and L4 all have cis and trans configurations:

[0072] When the ligand L is L1, the structural formula of Fe4(L1)4(BF4)4 is:

[0073] ;

[0074] Among them, the cis configuration of ligand L1 is: , the trans configuration is: ;

[0075] When the ligand L is L2, the structural formula of Fe4(L2)4(BF4)4 is:

[0076] ;

[0077] Among them, the cis configuration of ligand L2 is: , the trans configuration is: ;

[0078] When the ligand L is L3, the structural formula of Fe4(L3)4(BF4)4 is:

[0079] ;

[0080] Among them, the cis configuration of ligand L3 is: , the trans configuration is: ;

[0081] When the ligand L is L4, the structural formula of Fe4(L4)4(BF4)4 is:

[0082] ;

[0083] Among them, the cis configuration of ligand L4 is: , the trans configuration is: .

[0084] Example 1: Preparation of ligand L1:

[0085] ;

[0086] 2-Cyano-6-(1-pyrazole)-pyridine (0.510 g, 3 mmol) and sodium methoxide (0.036 g, 0.22 mmol) were added to a 50 mL schlenk flask and circulated three times under vacuum-nitrogen. Then, 15 mL of anhydrous methanol was added and reacted at room temperature for 1 hour. Then, 6-(1-pyrazole)-pyridine-2-carboxylic acid hydrazide (0.609 g, 3 mmol) was added and refluxed at 72°C for 5 hours. After the reaction was completed, the reaction was cooled to room temperature, the reactant was filtered, the obtained solid powder was collected, and then added to a 50 mL schlenk flask, and 12 mL of ethylene glycol was added under nitrogen atmosphere, and heated at 220°C for 3 hours. After the reaction was completed and cooled to room temperature, 200 mL of deionized water was added to dilute it, filtered, and the obtained solid was collected. According to the above synthesis method, ligand L1 can be finally obtained as a white powder with a yield of about 88%.

[0087] Example 2: Preparation of ligand L2:

[0088] ;

[0089] 6-Cyano-2,2'-bipyridine (0.543 g, 3 mmol) and sodium methoxide (0.036 g, 0.22 mmol) were added to a 50 mL schlenk flask and circulated three times under vacuum-nitrogen. Then, 15 mL of anhydrous methanol was added and reacted at room temperature for 1 hour. Then, 6-formylhydrazide-2,2'-bipyridine (0.642 g, 3 mmol) was added and refluxed at 72°C for 5 hours. After the reaction was completed, the reaction was cooled to room temperature, the reactant was filtered, the obtained solid powder was collected, and then added to a 50 mL schlenk flask, and 12 mL of ethylene glycol was added under nitrogen atmosphere, and heated at 220°C for 3 hours. After the reaction was completed and cooled to room temperature, 200 mL of deionized water was added to dilute it, filtered, and the obtained solid was collected. According to the above synthesis method, ligand L2 can be finally obtained as a white powder with a yield of about 87%.

[0090] Example 3: Preparation of ligand L3:

[0091] ;

[0092] 6-Cyano-2,2'-bipyridine (0.543 g, 3 mmol) and sodium methoxide (0.036 g, 0.22 mmol) were added to a 50 mL schlenk flask and circulated three times under vacuum-nitrogen. Then, 15 mL of anhydrous methanol was added and reacted at room temperature for 1 hour. Then, 6-(1-pyrazole)-pyridine-2-carboxylic acid hydrazide (0.609 g, 3 mmol) was added and refluxed at 72°C for 5 hours. After the reaction was completed, the reaction was cooled to room temperature, the reactant was filtered, the obtained solid powder was collected, and then added to a 50 mL schlenk flask, and 12 mL of ethylene glycol was added under nitrogen atmosphere, and heated at 220°C for 3 hours. After the reaction was completed and cooled to room temperature, 200 mL of deionized water was added to dilute it, filtered, and the obtained solid was collected. According to the above synthesis method, ligand L3 can be finally obtained as a white powder with a yield of about 88%.

[0093] Example 4: Preparation of ligand L4:

[0094] ;

[0095] 6-Cyano-2,2'-bipyridine (0.543 g, 3 mmol) and sodium methoxide (0.036 g, 0.22 mmol) were added to a 50 mL schlenk flask and circulated three times under vacuum-nitrogen. Then, 15 mL of anhydrous methanol was added and reacted at room temperature for 1 hour. Then, 6-(3,5-dimethyl-1-pyrazole)-pyridine-2-carboxylic acid hydrazide (0.693 g, 3 mmol) was added and refluxed at 72°C for 5 hours. After the reaction was completed, the reaction was cooled to room temperature, the reactant was filtered, the obtained solid powder was collected, and then added to a 50 mL schlenk flask, and 12 mL of ethylene glycol was added under nitrogen atmosphere, and heated at 220°C for 3 hours. After the reaction was completed and cooled to room temperature, 200 mL of deionized water was added to dilute it, filtered, and the obtained solid was collected. According to the above synthesis method, ligand L4 can be finally obtained as a white powder with a yield of about 85%.

[0096] Example 5: Preparation of bidentate triazole iron-based magnetic complex Fe(L)4(BF4)4:

[0097] Step 1: Stir a bidentate ligand (0.1 mmol) and ferrous tetrafluoroborate (0.1 mmol) in acetonitrile at room temperature for 3-5 hours, and filter to obtain a clear reaction solution; wherein the bidentate ligand is any one of ligand L1, ligand L2, ligand L3, and ligand L4;

[0098] Step 2: Place the reaction solution of step 1 in ether vapor for gas phase diffusion, place for 1-2 weeks, wait for crystals to precipitate, filter, and collect to obtain an iron-based magnetic complex with a structural formula of Fe4(L)4(BF2)4, specifically:

[0099] When L is ligand L1, the structural formula of Fe4(L)4(BF4)4 is:

[0100] ;

[0101] Among them, the cis configuration of ligand L1 is: , the trans configuration is: ;

[0102] When L is ligand L2, the structural formula of Fe4(L)4(BF4)4 is:

[0103] ;

[0104] Among them, the cis configuration of ligand L2 is: , the trans configuration is: ;

[0105] When L is ligand L3, the structural formula of Fe4(L)4(BF4)4 is:

[0106] ;

[0107] Among them, the cis configuration of ligand L3 is: , the trans configuration is: ;

[0108] When L is ligand L4, the structural formula of Fe4(L)4(BF4)4 is:

[0109] ;

[0110] Among them, the cis configuration of ligand L4 is: , the trans configuration is: .

[0111] Experimental analysis:

[0112] The structures of the ligands and asymmetric iron-based magnetic complexes prepared in Examples 1-5 of the present invention are studied below:

[0113] 1. NMR testing and analysis of ligands L1, L2, L3 and L4:

[0114] The NMR spectra of ligands L1, L2, L3 and L4 were tested by Bruker Avance 500 MHz NMR spectrometer, and the deuterated reagent was DMSO-d6. The test results are shown in Figure 1-Figure 4As shown, through Figure 1-Figure 4 It shows that the nuclear magnetic resonance hydrogen spectra of the three ligands can correspond to the spectrum. In addition to the solvent peak, there are no other impurity peaks or the impurity peaks are relatively small, indicating that the synthesized ligand is the target ligand, with high purity and accurate structure. The corresponding hydrogen atom chemical shift has been marked on the spectrum. Figure 1-Figure 4It can be seen that the H NMR chemical shifts of the four ligands are as follows: Ligand L1 δ = 8.93 (s, 1H), 8.20– 8.09 (m, 2H), 8.01 (d, J = 8.0 Hz, 1H), 7.88 (s, 1H), 6.68 – 6.62 (m, 1H); Ligand L2 δ = 15.10 (s, 1H), 8.96 (d, J = 8.0 Hz, 1H), 8.78 – 8.72 (m, 2H),8.57 (t, J = 10.6 Hz, 2H), 8.48 (d, J = 7.8 Hz, 1H), 8.30 – 8.24 (m, 2H),8.20 (d, J = 10.1 Hz, 1H), 8.16 – 8.09 (m, 1H), 8.05 (d, J = 7.9 Hz, 2H),7.53 (s, 2H); Ligand L3 δ = 15.12 (s, 1H), 8.92 (s, 1H), 8.75 – 8.72 (m, 1H),8.67 – 8.40 (m, 2H), 8.25 (d, J = 7.6 Hz, 1H), 8.15 (h, J = 8.6, 7.7 Hz, 3H),8.03 (d, J = 7.7 Hz, 2H), 7.89 (s, 1H), 7.51 (dd, J = 7.4, 4.8 Hz, 1H), 6.67(s, 1H); Ligand L4 δ = 8.83 (d, J = 7.9 Hz, 1H), 8.73 (ddd, J = 4.8, 1.8, 0.9Hz, 1H), 8.52 (dd, J = 7.8, 1.1 Hz, 1H), 8.22 (dd, J = 7.8, 1.2 Hz, 1H), 8.15(t, J = 7.7 Hz, 1H), 8.12 – 8.06 (m, 2H), 8.02 (td, J = 7.7, 1.8 Hz, 1H), 7.89 (dd, J = 6.3, 2.7 Hz, 1H), 7.50 (ddd, J = 7.5, 4.7, 1.2 Hz, 1H), 6.14(s, 1H), 2.80 (s, 3H), 2.25 (s, 3H).

[0115] 2. Single crystal structure test and analysis of asymmetric iron-based magnetic complexes:

[0116] Single crystal X-ray diffraction data were collected on a Bruker Apex II CCD diffractometer using graphite monochromated Mo-Kα radiation (λ = 0.71073 Å). The structure was solved using SHELXT (direct method) and all non-hydrogen atoms were refined using SHELXL (full matrix least squares technique) for anisotropic thermal parameters of F2 in the Olex2 package. All hydrogen atoms were introduced into the calculated positions and refined with fixed geometry relative to their carrier atoms. The single crystal structure of the complex was solved by the Olex2 structure solution program using the direct method Patterson and refined using the full matrix least squares method using the SHELX crystallographic software package. The non-hydrogen atomic coordinates and anisotropic temperature coefficients were corrected for least squares using the full matrix method.

[0117] Test results such as Figure 5-Figure 8 As shown, Figure 5 It is the single crystal structure diagram of Fe4(L1)4(BF4)4 complex; Figure 6 It is the single crystal structure diagram of Fe4(L2)4(BF4)4 complex; Figure 7 It is the single crystal structure diagram of Fe4(L3)4(BF4)4 complex; Figure 8 It is the single crystal structure diagram of Fe4(L4)4(BF4)4 complex; Fig.13 Schematic diagram of the assembly of the lattice compound of the present invention. Figure 5-Figure 8 The structural analysis showed that the four complexes all had a lattice structure. Fig.13 , where the four ligands act as the four sides of the lattice, and the iron ions are located at the four corners of the lattice structure, with an N6 coordination environment, which is conducive to the compound exhibiting spin conversion properties. The main structure of the complex carries four positive charges, so four anions are located in the lattice to balance these positive charges. The corresponding anion is BF4 - Due to the differences in the structures of the four ligands, the corresponding complexes also have different symmetries and configurations.

[0118] In the complex Fe(L1)4(BF4)4, both side ends of the ligand are pyrazole groups, and the corresponding steric hindrance is small, so the four ligands are arranged in cis, forming a lattice structure with high symmetry. Due to the large internal tension of the lattice and the large adjacent crossing angles, the corresponding metal center octahedral coordination configuration is greatly distorted, so the iron ions are all high-spin.

[0119] In the complex Fe(L2)4(BF4)4, both side ends of the ligand are pyridine groups, and the corresponding steric hindrance is moderate, so two ligands are arranged in cis and the other two are arranged in trans, forming a lattice structure with lower symmetry and appropriately reducing the internal tension of the lattice. The corresponding metal centers have three high spins and one low spin.

[0120] In the complex Fe(L3)4(BF4)4, one side of the ligand is a pyrazole group and the other side is a pyridine group. The corresponding steric hindrance is moderate. Two ligands are arranged in cis and the other two are arranged in trans. The symmetry is further reduced. Three of the corresponding metal centers are high-spin and one is low-spin.

[0121] In the complex Fe(L4)4(BF4)4, one side of the ligand is a dimethylpyrazole group and the other side is a pyridine group. The corresponding steric hindrance is further increased. Two ligands are arranged in cis and the other two are arranged in trans. The symmetry is further reduced. Three of the corresponding metal centers are high-spin and one is low-spin.

[0122] 3. Temperature-dependent magnetic susceptibility test and analysis of double-helical Fe(Ⅱ) magnetic complexes:

[0123] The magnetism of the complex provided in Example 5 of the present invention was tested by a Quantum Design MPMS-XL-7 SQUIDmagnetometer instrument. The operating temperature of the instrument is 1.8-300 K, and the DC field strength is -7~7 T. Before detailed measurements, the magnetization intensity of all polycrystalline samples was measured below 100 K to check for ferromagnetic impurities. All data were diamagnetic corrected according to the Pascal constant table.

[0124] Magnetic test results are as follows Figure 9-12 As shown, Fig. 9 It is the temperature-dependent magnetic susceptibility diagram of Fe4(L1)4(BF4)4 complex; Fig.10 It is the temperature-dependent magnetic susceptibility diagram of Fe4(L2)4(BF4)4 complex; Fig.11 It is the temperature-dependent magnetic susceptibility diagram of Fe4(L3)4(BF4)4 complex; Fig.12 It is the temperature-dependent magnetic susceptibility diagram of Fe4(L4)4(BF4)4 complex; Figure 6-Figure 12 show:

[0125] In the complex Fe(L1)4(BF4)4, the Fe ions are in a high spin state within the test temperature range, indicating that the complex does not exhibit spin conversion properties;

[0126] Before 380 K, three Fe ions of the complex Fe(L2)4(BF4)4 are in a high-spin state and the other is in a low-spin state, which is consistent with the test results of the single crystal sample. The magnetic susceptibility of the complex increases slowly from 380 to 400 K, indicating that the complex undergoes spin conversion, and the low-spin iron ions are converted to high-spin states.

[0127] Before 350 K, three Fe ions of the complex Fe(L3)4(BF4)4 are in a high-spin state and the other is in a low-spin state, which is consistent with the test results of the single crystal sample. The magnetic susceptibility of the complex increases rapidly between 350 and 400 K, indicating that the complex undergoes spin conversion, and the low-spin iron ions are converted to high-spin states.

[0128] Before 100 K, three Fe ions in the complex Fe(L4)4(BF4)4 are in a high-spin state and the other is in a low-spin state, which is consistent with the test results of the single crystal sample. The magnetic susceptibility of the complex continues to increase from 100 to 400 K, indicating that the complex undergoes spin conversion and the low-spin iron ions slowly transform into high-spin states.

[0129] The magnetic test results show that the spin crossover properties of the series of lattice-type complexes prepared by the present invention are mainly regulated by the molecular symmetry and the side-end substituents, wherein reducing the molecular symmetry is conducive to the spin center being in a different coordination environment, thereby generating an active low-spin state. Increasing the steric hindrance of the side-end substituents is conducive to stabilizing the low-spin sites, thereby delaying the occurrence of spin crossover, and allowing the compounds to exhibit spin crossover properties over a wide temperature range.

[0130] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A lattice-type iron-based complex based on cis-trans isomeric triazoles, characterized in that: The chemical formula is: Fe4(L)4(BF4)4; Wherein, the ligand L is any one of L1, L2, L3 and L4, and the ligands L1, L2, L3 and L4 all have cis and trans configurations: When the ligand L is L1, the structural formula of Fe4(L1)4(BF4)4 is: ； Among them, the cis configuration of ligand L1 is: , the trans configuration is: ; When the ligand L is L2, the structural formula of Fe4(L2)4(BF4)4 is: ； Among them, the cis configuration of ligand L2 is: , the trans configuration is: ; When the ligand L is L3, the structural formula of Fe4(L3)4(BF4)4 is: ； Among them, the cis configuration of ligand L3 is: , the trans configuration is: ; When the ligand L is L4, the structural formula of Fe4(L4)4(BF4)4 is: ； Among them, the cis configuration of ligand L4 is: , the trans configuration is: ; The preparation method of a lattice-type iron-based complex based on cis-trans isomeric triazole comprises: Step 1: Stirring the bidentate ligand and ferrous tetrafluoroborate in acetonitrile at room temperature to obtain a clear reaction solution; Wherein, the bidentate ligand is any one of ligand L1, ligand L2, ligand L3, and ligand L4: Ligand L1: ; Ligand L2: ; Ligand L3: ; Ligand L4: ; Step 2: Place the reaction solution of step 1 in ether vapor, wait for crystals to precipitate, then filter and collect to obtain an iron-based magnetic complex with a structural formula of Fe4(L)4(BF4)4, specifically: When L is ligand L1, the structural formula of Fe4(L)4(BF4)4 is: ； Among them, the cis configuration of ligand L1 is: , the trans configuration is: ; When L is ligand L2, the structural formula of Fe4(L)4(BF4)4 is: ； Among them, the cis configuration of ligand L2 is: , the trans configuration is: ; When L is ligand L3, the structural formula of Fe4(L)4(BF4)4 is: ； Among them, the cis configuration of ligand L3 is: , the trans configuration is: ; When L is ligand L4, the structural formula of Fe4(L)4(BF4)4 is: ； Among them, the cis configuration of ligand L4 is: , the trans configuration is: .

2. The lattice-type iron-based complex based on cis-trans isomeric triazole according to claim 1, characterized in that: The molar ratio of the bidentate ligand to ferrous tetrafluoroborate in step 1 is 1:

1.

3. The lattice-type iron-based complex based on cis-trans isomeric triazole according to claim 1, characterized in that the ligand The preparation method of L1 is as follows: the intermediate obtained by the reaction of 6-(1-pyrazole)-pyridine-2-carboxylic acid hydrazide and 2-cyano-6-(1-pyrazole)-pyridine under alkaline conditions is dehydrated in ethylene glycol to finally prepare L1.

4. The lattice-type iron-based complex based on cis-trans isomeric triazole according to claim 1, characterized in that the ligand The preparation method of L2 is as follows: the intermediate obtained by the reaction of 6-formylhydrazide-2,2'-bipyridine and 6-cyano-2,2'-bipyridine under alkaline conditions is dehydrated in ethylene glycol to finally prepare L2.

5. The lattice-type iron-based complex based on cis-trans isomeric triazole according to claim 1, characterized in that the ligand The preparation method of L3 is as follows: the intermediate obtained by the reaction of 6-(1-pyrazole)-pyridine-2-carboxylic acid hydrazide and 6-cyano-2,2'-bipyridine under alkaline conditions is dehydrated in ethylene glycol to finally prepare L3.

6. The lattice-type iron-based complex based on cis-trans isomeric triazole according to claim 1, characterized in that the ligand The preparation method of L4 is as follows: the intermediate obtained by the reaction of 6-(3,5-dimethyl-1-pyrazole)-pyridine-2-carboxylic acid hydrazide and 6-cyano-2,2'-bipyridine under alkaline conditions is dehydrated in ethylene glycol to finally prepare L4.

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