Triazole iron-based spin cross-coordination compound and preparation method thereof

Abstract

The invention discloses a triazole iron-based spin cross complex, which has the following chemical expression: [FeL2]X2; the invention also discloses a method for preparing the triazole iron-based spin cross complex: step 1, synthesizing ligand L by 2-cyano-6-(1-pyrazole)pyridine or 6-cyano-2,2'-bipyridine and hydrazide; step 2, reacting ligand L with ferrous salt in acetonitrile to obtain a reaction solution; step 3, placing the reaction solution in a closed container with ether and standing to precipitate crystals. The complex of the invention has a clear crystal structure and variable temperature magnetic susceptibility data, and the ligand field of the spin center can be adjusted by adjusting the terminal coordination point of the ligand L, and then the spin state of Fe(II) can be adjusted; by changing the substituent and counter anion on the ligand L to adjust the spin cross property of the complex, it has potential application value in the technical fields of high-density information storage and molecular switch devices.

Description

Technical Field

[0001] The invention belongs to the technical field of molecular-based magnetic materials, and in particular relates to a triazole iron-based spin cross complex 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. Combining structural design, supramolecular assembly, magnetic characterization and quantitative calculation, molecular-based magnetic materials with excellent performance can be constructed for application in 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-complexes.

[0003] In addition to single-molecule magnets, spin cross-coordinates also play an important role in molecular-based magnetic materials. Due to their potential application value in information storage, molecular opening and spin electronic devices, they have attracted much attention from scientific researchers.

[0004] Spin switching is generally accompanied by changes in the electronic structure of the central metal ion, which in turn affects the physical and chemical properties of the entire complex, and may also be accompanied by changes in physical properties such as structure, color or dielectric constant. Therefore, as an important branch in the research field of molecular-based magnetic materials, spin crossover complexes are expected to be applied in the fields of quantum bits, molecular switch devices and spintronic devices.

[0005] Triazole-based ligands have unique advantages in constructing spin-crossover materials. Some researchers have prepared a mononuclear Fe(Ⅱ) complex constructed by asymmetric triazole-based ligands. Under the action of hydrogen bonding and π-π stacking, a one-dimensional supramolecular chain structure is formed, which enhances the synergistic effect of the system. Due to the existence of a special supramolecular mechanism, the complex has a thermal hysteresis loop in the room temperature region, and the opening reaches 105K (J. Am. Chem. Soc. 2022, 144, 14297-14309). In addition, some researchers have used different chemical mixtures of two organic ligands to obtain four isostructural triazole-based coordination polymers; by embedding polymer solid particles into the sponge matrix, a series of hygroscopic spin-crossover composite materials were constructed, and color changes were achieved by changing the humidity (Dalton Trans., 2024, 53, 2333–2340). However, the above work did not regulate the spin crossover properties of the system in more dimensions through methods such as chemical synthesis, which is of little significance for exploring the factors affecting spin crossover and is not conducive to the expansion of the spin crossover system.

[0006] In the spin crossover system, the spin crossover properties of the complex can be effectively regulated by changing the coordination site of the ligand, the substituents of the ligand, the anions and cations, and the solvent molecules. Among them, by changing the coordination site of the ligand, the ligand field strength can be effectively adjusted, and changing the substituents of the ligand can affect the ligand field strength of the spin center through electronic effects and steric hindrance, while changing the counter anion can regulate the intramolecular / intermolecular supramolecular interactions, thereby regulating the spin crossover properties of the complex.

[0007] Therefore, designing and synthesizing Fe(Ⅱ)-based spin crossover complexes and studying the effects of ligand coordination sites, ligand substituents or counteranions on the spin crossover properties are of great significance for the design and preparation of high-density information storage and molecular switching devices. Summary of the invention

[0008] The purpose of the present invention is to overcome the deficiencies in the above-mentioned prior art and provide a triazole iron-based spin crossover complex. The triazole iron-based spin crossover complex has a clear crystal structure and temperature-dependent magnetic susceptibility data, wherein the ligand L is an asymmetric tridentate ligand with an NNN coordination site, and the ligand field of the spin center can be adjusted by adjusting the terminal coordination site of the ligand L, thereby adjusting the spin state of Fe(II); by changing the substituent and counter anion on the ligand L, the spin crossover property of the triazole iron-based complex can be adjusted, and it has potential application value in the fields of high-density information storage and molecular switch devices; and the problem of the prior art that the spin crossover property of the complex system is not multi-dimensionally adjusted is solved.

[0009] To achieve the above object, the technical solution adopted by the present invention is: triazole iron-based spin cross complex, the triazole iron-based spin cross complex has the following chemical expression:

[0010] [FeL2]X2;

[0011] The ligand L is one of L1, L2 and L3, and X is ClO4 - 、BF4 - and CF3SO3 - One of the above, and the structural formulas of L1, L2 and L3 are as follows:

[0012] L1;

[0013] L2;

[0014] L3.

[0015] The present invention changes the substituent at one end of the ligand L from the pyrazole nitrogen coordination site of L1 to the pyridine nitrogen coordination site of L2 or L3, thereby regulating the coordination field of the spin center, so that the triazole iron-based spin crossover complex undergoes a one-step slow and incomplete spin crossover behavior within the test temperature range; in addition, by changing the substituent at the other end of the ligand L (changing it to a naphthyl group or a pentyl group) and changing the type of the counter anion, the steric effect and the supramolecular interactions within and between molecules can be adjusted, thereby adjusting the spin crossover properties of the triazole iron-based spin crossover complex.

[0016] In addition, the present invention also discloses a method for preparing the above triazole iron-based spin cross complex, which comprises the following steps:

[0017] Step 1: Synthesis of ligand L:

[0018] Under vacuum conditions, 2-cyano-6-(1-pyrazole)pyridine and sodium methoxide are added to anhydrous methanol and stirred, and then indole-5-carboxylic acid hydrazide is added to reflux at 70°C to 75°C to obtain a solid product, and then the solid product is placed in ethylene glycol and reacted at 190°C to 220°C to obtain ligand L1;

[0019] Under vacuum conditions, 6-cyano-2,2'-bipyridine and sodium methoxide are added to anhydrous methanol and stirred, and then 1-naphthylacetylhydrazide or hexanoylhydrazide is added to react under reflux at 70°C to 75°C to obtain a solid product, and then the solid product is placed in ethylene glycol and reacted at 190°C to 220°C to obtain ligand L2 or L3;

[0020] Step 2, preparation of reaction solution: mix the ligand L obtained in step 1 with ferrous salt in acetonitrile solution and stir, and obtain a clear reaction solution after filtering; the ferrous salt is one of Fe(ClO4)2·6H2O, Fe(BF4)2·6H2O and Fe(CF3SO3)2;

[0021] Step 3, cultivation of single crystals: Place the clarified reaction solution obtained in step 2 into a container, place the container in a sealed container filled with ether, and let it stand for 6 to 8 days to precipitate red rod-shaped crystals, filter, wash and collect the red rod-shaped crystals to obtain triazole iron-based spin cross complexes.

[0022] In the above-mentioned method for preparing the triazole iron-based spin cross complex, the molar ratio of 2-cyano-6-(1-pyrazole)pyridine to indole-5-carboxylic acid hydrazide in step 1 is 1:1 to 1:1.2.

[0023] In the above-mentioned method for preparing triazole iron-based spin cross-complex, the molar ratio of 6-cyano-2,2'-bipyridine to 1-naphthylacetylhydrazide or hexanoylhydrazide in step 1 is 1:1 to 1:1.2.

[0024] In the above-mentioned method for preparing triazole iron-based spin cross-complex, the molar ratio of the ligand L to the ferrous salt in step 2 is 2:1-2.2:1, and the stirring speed is 200r / min-250r / min.

[0025] In the above-mentioned method for preparing triazole iron-based spin cross-complex, the volume ratio of the reaction solution to diethyl ether in step 3 is 1:8-1:12, and the washing is performed by rinsing with distilled water and ethanol multiple times.

[0026] In the above-mentioned method for preparing the triazole iron-based spin cross complex, the crystal yield of the triazole iron-based spin cross complex in step 3 is 70% to 75%.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] 1. The triazole iron-based spin crossover complex of the present invention is a mononuclear Fe(II) complex with a novel structure, a clear crystal structure and temperature-dependent magnetic susceptibility data, and chemical stability under normal temperature and air conditions. By regulating the terminal coordination point of the ligand, an asymmetric tridentate triazole-based ligand is synthesized using 2-cyano-6-(1-pyrazole)pyridine or 6-cyano-2,2'-bipyridine and hydrazide, so that the ligand L has an NNN asymmetric tridentate coordination point, which can adjust the ligand field of the spin center, and further adjust the spin state and magnetic properties of the mononuclear Fe(II) complex, so that the mononuclear Fe(II) complex exhibits thermally induced spin crossover behavior.

[0029] 2. The present invention can adjust the spin-crossing properties of triazole iron-based spin-crossing complexes by changing the substituents and counter anions on the ligand L, and has potential application value in the fields of high-density information storage and molecular switch devices.

[0030] 3. The triazole iron-based spin cross-complex prepared by the present invention has high crystal purity, intact crystal form, high yield, and the preparation method is simple and easy to operate, which is suitable for industrial mass production and is a potential user of functional devices.

[0031] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the crystal structure diagram of [Fe(L1)2](ClO4)2 prepared in Example 1 of the present invention.

[0033] Figure 2This is the crystal structure diagram of [Fe(L1)2](BF4)2 prepared in Example 2 of the present invention.

[0034] Figure 3 This is the crystal structure diagram of [Fe(L1)2](CF3SO3)2 prepared in Example 3 of the present invention.

[0035] Figure 4 This is the crystal structure diagram of [Fe(L2)2](ClO4)2 prepared in Example 4 of the present invention.

[0036] Figure 5 This is the crystal structure diagram of [Fe(L2)2](BF4)2 prepared in Example 5 of the present invention.

[0037] Figure 6 This is the crystal structure diagram of [Fe(L2)2](CF3SO3)2 prepared in Example 6 of the present invention.

[0038] Figure 7 This is the crystal structure diagram of [Fe(L3)2](ClO4)2 prepared in Example 7 of the present invention.

[0039] Figure 8 This is the crystal structure diagram of [Fe(L3)2](BF4)2 prepared in Example 8 of the present invention.

[0040] Fig. 9 This is the temperature-dependent magnetic susceptibility diagram of [Fe(L1)2](ClO4)2 prepared in Example 1 of the present invention.

[0041] Fig.10 This is the temperature-dependent magnetic susceptibility diagram of [Fe(L1)2](BF4)2 prepared in Example 2 of the present invention.

[0042] Fig.11 This is the temperature-dependent magnetic susceptibility diagram of [Fe(L1)2](CF3SO3)2 prepared in Example 3 of the present invention.

[0043] Fig.12 This is the temperature-dependent magnetic susceptibility diagram of [Fe(L2)2](ClO4)2 prepared in Example 4 of the present invention.

[0044] Fig.13 This is the temperature-dependent magnetic susceptibility diagram of [Fe(L2)2](BF4)2 prepared in Example 5 of the present invention.

[0045] Fig.14 This is the temperature-dependent magnetic susceptibility diagram of [Fe(L2)2](CF3SO3)2 prepared in Example 6 of the present invention.

[0046] Fig.15 This is the temperature-dependent magnetic susceptibility diagram of [Fe(L3)2](ClO4)2 prepared in Example 7 of the present invention.

[0047] Fig.16 This is the temperature-dependent magnetic susceptibility diagram of [Fe(L3)2](BF4)2 prepared in Example 8 of the present invention. DETAILED DESCRIPTION

[0048] Example 1

[0049] The chemical formula of the triazole iron-based spin cross complex of this embodiment is [Fe(L1)2](ClO4)2, and the crystal structure is as follows: Figure 1 As shown; wherein the structural formula of ligand L1 is:

[0050] .

[0051] The preparation method of this embodiment comprises the following steps:

[0052] Step 1: Synthesis of ligand L1:

[0053] Under vacuum conditions, 0.51 g of 2-cyano-6-(1-pyrazole)pyridine and 0.036 g of sodium methoxide were added to 15 mL of anhydrous methanol and stirred for 1 h, then 0.53 g of indole-5-carboxylic acid hydrazide was added and refluxed at 72° C. for 6 h, and then cooled, filtered, and collected to obtain a solid product. The solid product was then placed in 12 mL of ethylene glycol, reacted at 200° C. for 4 h, cooled, and then deionized water was added, filtered, and dried to obtain ligand L1. The synthetic reaction formula of ligand L1 is as follows:

[0054] ;

[0055] Step 2, preparation of reaction solution: at room temperature, 65.4 mg of ligand L1 obtained in step 1 and 36.3 mg of Fe(ClO4)2·6H2O were mixed in 5 mL of acetonitrile solution, stirred at 250 r / min for 2 h, and filtered to obtain a clear reaction solution;

[0056] Step 3. Cultivation of single crystals: At room temperature, place 1 mL of the clarified reaction solution obtained in step 2 into a small test tube, place the small test tube in a glass bottle containing 10 mL of ether, and let stand for 7 days to precipitate red rod-shaped crystals. Filter the red rod-shaped crystals, rinse them with distilled water and ethanol several times, and collect them to obtain triazole iron-based spin cross-complex [Fe(L1)2](ClO4)2.

[0057] The synthesis reaction formula of the triazole iron-based spin cross complex [Fe(L1)2](ClO4)2 in this embodiment is as follows:

[0058] .

[0059] After weighing, the yield of the triazole iron-based spin cross complex [Fe(L1)2](ClO4)2 in this example is 75%.

[0060] Example 2

[0061] The chemical formula of the triazole iron-based spin cross complex of this embodiment is [Fe(L1)2](BF4)2, and the crystal structure is as follows: Figure 2 shown.

[0062] The preparation method of this embodiment comprises the following steps:

[0063] Step 1: Synthesis of ligand L1:

[0064] Under vacuum conditions, 0.51 g of 2-cyano-6-(1-pyrazole)pyridine and 0.036 g of sodium methoxide were added to 15 mL of anhydrous methanol and stirred for 1 h, and then 0.58 g of indole-5-carboxyhydrazide was added and refluxed at 70 ° C for 6 h, and then cooled, filtered, and collected to obtain a solid product. The solid product was then placed in 12 mL of ethylene glycol, reacted at 190 ° C for 4 h, cooled, and then deionized water was added, filtered, and dried to obtain ligand L1;

[0065] Step 2, preparation of reaction solution: at room temperature, 68.7 mg of ligand L1 obtained in step 1 and 16.1 mg of Fe(BF4)2·6H2O were mixed in 5 mL of acetonitrile solution, stirred at 200 r / min for 3 h, and filtered to obtain a clear reaction solution;

[0066] Step 3. Cultivation of single crystals: At room temperature, place 1 mL of the clarified reaction solution obtained in step 2 into a small test tube, place the small test tube in a glass bottle containing 12 mL of ether, and let stand for 6 days to precipitate red rod-shaped crystals. Filter the red rod-shaped crystals, rinse them with distilled water and ethanol several times, and collect them to obtain triazole iron-based spin cross-complex [Fe(L1)2](BF4)2.

[0067] After weighing, the yield of the triazole iron-based spin cross complex [Fe(L1)2](BF4)2 in this example is 73%.

[0068] Example 3

[0069] The chemical formula of the triazole iron-based spin cross complex of this embodiment is [Fe(L1)2](CF3SO3)2, and the crystal structure is as follows: Figure 3 shown.

[0070] The preparation method of this embodiment comprises the following steps:

[0071] Step 1: Synthesis of ligand L1:

[0072] Under vacuum conditions, 0.51 g of 2-cyano-6-(1-pyrazole)pyridine and 0.036 g of sodium methoxide were added to 15 mL of anhydrous methanol and stirred for 1 h, and then 0.63 g of indole-5-carboxylic acid hydrazide was added and refluxed at 75 ° C for 6 h, and then cooled, filtered, and collected to obtain a solid product. The solid product was then placed in 12 mL of ethylene glycol, reacted at 220 ° C for 4 h, cooled, and then deionized water was added, filtered, and dried to obtain ligand L1;

[0073] Step 2, preparation of reaction solution: at room temperature, mix 71.9 mg of ligand L1 obtained in step 1 with 35.4 mg of Fe(CF3SO3)2 in 5 mL of acetonitrile solution, stir at 200 r / min for 2.5 h, and filter to obtain a clear reaction solution;

[0074] Step 3. Cultivation of single crystals: At room temperature, place 1 mL of the clarified reaction solution obtained in step 2 into a small test tube, place the small test tube in a glass bottle containing 8 mL of ether, and let stand for 8 days to precipitate red rod-shaped crystals. Filter the red rod-shaped crystals, rinse them with distilled water and ethanol several times, and collect them to obtain triazole iron-based spin cross-complex [Fe(L1)2](CF3SO3)2.

[0075] After weighing, the yield of the triazole iron-based spin cross-complex [Fe(L1)2](CF3SO3)2 in this example is 70%.

[0076] Example 4

[0077] The chemical formula of the triazole iron-based spin cross complex of this embodiment is [Fe(L2)2](ClO4)2, and the crystal structure is as follows: Figure 4 As shown; wherein the structural formula of ligand L2 is:

[0078] .

[0079] The preparation method of this embodiment comprises the following steps:

[0080] Step 1: Synthesis of ligand L2:

[0081] Under vacuum conditions, 0.54 g of 6-cyano-2,2'-bipyridine and 0.036 g of sodium methoxide were added to 15 mL of anhydrous methanol and stirred for 1 h, and then 0.60 g of 1-naphthylacetylhydrazine was added and refluxed at 72° C. for 6 h, and then cooled, filtered, and collected to obtain a solid product. The solid product was then placed in 12 mL of ethylene glycol, reacted at 200° C. for 4 h, cooled, and then deionized water was added, filtered, and dried to obtain ligand L2; the synthetic reaction formula of ligand L2 is as follows:

[0082] ;

[0083] Step 2, preparation of reaction solution: at room temperature, mix 72.7 mg of ligand L2 obtained in step 1 with 36.3 mg of Fe(ClO4)2·6H2O in 5 mL of acetonitrile solution, stir at 250 r / min for 2 h, and filter to obtain a clear reaction solution;

[0084] Step 3. Cultivation of single crystals: At room temperature, place 1 mL of the clarified reaction solution obtained in step 2 into a small test tube, place the small test tube in a glass bottle containing 10 mL of ether, and let stand for 7 days to precipitate red rod-shaped crystals. Filter the red rod-shaped crystals, rinse them with distilled water and ethanol several times, and collect them to obtain triazole iron-based spin cross-complex [Fe(L2)2](ClO4)2.

[0085] The synthesis reaction formula of the triazole iron-based spin cross complex [Fe(L2)2](ClO4)2 in this embodiment is as follows:

[0086] .

[0087] After weighing, the yield of the triazole iron-based spin cross-complex [Fe(L2)2](ClO4)2 in this example is 75%.

[0088] Example 5

[0089] The chemical formula of the triazole iron-based spin cross complex of this embodiment is [Fe(L2)2](BF4)2, and the crystal structure is as follows: Figure 5 shown.

[0090] The preparation method of this embodiment comprises the following steps:

[0091] Step 1: Synthesis of ligand L2:

[0092] Under vacuum conditions, 0.54 g of 6-cyano-2,2'-bipyridine and 0.036 g of sodium methoxide were added to 15 mL of anhydrous methanol and stirred for 1 h, and then 0.66 g of 1-naphthylacetylhydrazine was added and refluxed at 70 ° C for 6 h, and then cooled, filtered, and collected to obtain a solid product. The solid product was then placed in 12 mL of ethylene glycol, reacted at 190 ° C for 4 h, cooled, and then deionized water was added, filtered, and dried to obtain ligand L2;

[0093] Step 2, preparation of reaction solution: at room temperature, 75.8 mg of ligand L2 obtained in step 1 and 16.1 mg of Fe(BF4)2·6H2O were mixed in 5 mL of acetonitrile solution, stirred at 200 r / min for 3 h, and filtered to obtain a clear reaction solution;

[0094] Step 3. Cultivation of single crystals: At room temperature, place 1 mL of the clarified reaction solution obtained in step 2 into a small test tube, place the small test tube in a glass bottle containing 12 mL of ether, and let stand for 6 days to precipitate red rod-shaped crystals. Filter the red rod-shaped crystals, rinse them with distilled water and ethanol several times, and collect them to obtain triazole iron-based spin cross-complex [Fe(L2)2](BF4)2.

[0095] After weighing, the yield of the triazole iron-based spin cross-complex [Fe(L2)2](BF4)2 in this example is 72%.

[0096] Example 6

[0097] The chemical formula of the triazole iron-based spin cross complex of this embodiment is [Fe(L2)2](CF3SO3)2, and the crystal structure is as follows: Figure 6 shown.

[0098] The preparation method of this embodiment comprises the following steps:

[0099] Step 1: Synthesis of ligand L2:

[0100] Under vacuum conditions, 0.54 g of 6-cyano-2,2'-bipyridine and 0.036 g of sodium methoxide were added to 15 mL of anhydrous methanol and stirred for 1 h, and then 0.72 g of 1-naphthylacetylhydrazine was added and refluxed at 75 ° C for 6 h, and then cooled, filtered, and collected to obtain a solid product. The solid product was then placed in 12 mL of ethylene glycol, reacted at 220 ° C for 4 h, cooled, and then deionized water was added, filtered, and dried to obtain ligand L2;

[0101] Step 2, preparation of reaction solution: at room temperature, mix 79.4 mg of ligand L2 obtained in step 1 with 35.4 mg of Fe(CF3SO3)2 in 5 mL of acetonitrile solution, stir at 200 r / min for 2.5 h, and filter to obtain a clear reaction solution;

[0102] Step 3. Cultivation of single crystals: At room temperature, place 1 mL of the clarified reaction solution obtained in step 2 into a small test tube, place the small test tube in a glass bottle containing 8 mL of ether, and let stand for 8 days to precipitate red rod-shaped crystals. Filter the red rod-shaped crystals, rinse them with distilled water and ethanol several times, and collect them to obtain triazole iron-based spin cross-complex [Fe(L2)2](CF3SO3)2.

[0103] After weighing, the yield of the triazole iron-based spin cross-complex [Fe(L2)2](CF3SO3)2 in this example is 70%.

[0104] Example 7

[0105] The chemical formula of the triazole iron-based spin cross complex of this embodiment is [Fe(L3)2](ClO4)2, and the crystal structure is as follows: Figure 7 As shown; wherein the structural formula of ligand L3 is:

[0106] .

[0107] The preparation method of this embodiment comprises the following steps:

[0108] Step 1: Synthesis of ligand L3:

[0109] Under vacuum conditions, 0.54 g of 6-cyano-2,2'-bipyridine and 0.036 g of sodium methoxide were added to 15 mL of anhydrous methanol and stirred for 1 h, then 0.38 g of hexanoyl hydrazide was added and refluxed at 70° C. for 6 h, and then cooled, filtered, and collected to obtain a solid product. The solid product was then placed in 12 mL of ethylene glycol, reacted at 200° C. for 4 h, cooled, and then deionized water was added, filtered, and dried to obtain ligand L3. The synthetic reaction formula of ligand L3 is as follows:

[0110] ;

[0111] Step 2, preparation of reaction solution: at room temperature, 58.6 mg of ligand L3 obtained in step 1 and 36.3 mg of Fe(ClO4)2·6H2O were mixed in 5 mL of acetonitrile solution, stirred at 250 r / min for 2 h, and filtered to obtain a clear reaction solution;

[0112] Step 3. Cultivation of single crystals: At room temperature, place 1 mL of the clarified reaction solution obtained in step 2 into a small test tube, place the small test tube in a glass bottle containing 10 mL of ether, and let stand for 7 days to precipitate red rod-shaped crystals. Filter the red rod-shaped crystals, rinse them with distilled water and ethanol several times, and collect them to obtain triazole iron-based spin cross-complex [Fe(L3)2](ClO4)2.

[0113] The synthesis reaction formula of the triazole iron-based spin cross complex [Fe(L3)2](ClO4)2 in this embodiment is as follows:

[0114] .

[0115] After weighing, the yield of the triazole iron-based spin cross complex [Fe(L3)2](ClO4)2 in this example is 75%.

[0116] Example 8

[0117] The chemical formula of the triazole iron-based spin cross complex of this embodiment is [Fe(L3)2](BF4)2, and the crystal structure is as follows: Figure 8 shown.

[0118] The preparation method of this embodiment comprises the following steps:

[0119] Step 1: Synthesis of ligand L3:

[0120] Under vacuum conditions, 0.54 g of 6-cyano-2,2'-bipyridine and 0.036 g of sodium methoxide were added to 15 mL of anhydrous methanol and stirred for 1 h, and then 0.46 g of hexanoyl hydrazide was added to reflux at 75 ° C for 6 h, and then cooled, filtered, and collected to obtain a solid product. The solid product was then placed in 12 mL of ethylene glycol, reacted at 220 ° C for 4 h, cooled, and then deionized water was added to obtain ligand L3 after filtration and drying;

[0121] Step 2, preparation of reaction solution: at room temperature, 64.5 mg of ligand L3 obtained in step 1 and 16.1 mg of Fe(BF4)2·6H2O were mixed in 5 mL of acetonitrile solution, stirred at 200 r / min for 3 h, and filtered to obtain a clear reaction solution;

[0122] Step 3. Cultivation of single crystals: At room temperature, place 1 mL of the clarified reaction solution obtained in step 2 into a small test tube, and place the small test tube in a glass bottle containing 12 mL of ether. After standing for 7 days, red rod-shaped crystals precipitate. The red rod-shaped crystals are filtered, rinsed with distilled water and ethanol several times, and collected to obtain triazole iron-based spin cross-complex [Fe(L3)2](BF4)2.

[0123] After weighing, the yield of the triazole iron-based spin cross-complex [Fe(L3)2](BF4)2 in this example is 70%.

[0124] 1. Crystal structure test and analysis of triazole iron-based spin crossover complexes

[0125] The crystal structures of the triazole iron-based spin crossover complexes in Examples 1 to 8 were determined by a Bruker Apex II CCD single crystal X-ray diffractometer using a graphite monochromator Mo-Kα ( λ=0.71073Å) rays were used as the incident light source. The crystal structure analysis and refinement process of the complex were carried out in the Olex2 program package. The crystal structure was initially solved using the SHELXT program (intrinsic phasing algorithm), and then the coordinates of non-hydrogen atoms and anisotropic temperature factors were corrected by the SHELXL program based on the full matrix least squares method. The coordinates of hydrogen atoms were determined by the difference Fourier synthesis and theoretical hydrogenation program, and their isotropic thermal vibration parameters were fixed during the refinement process.

[0126] The crystal structures of the triazole iron-based spin crossover complexes in Examples 1 to 8 are as follows: Figures 1 to 8 As shown, the structural analysis shows that when the test temperature is 180K, the triazole iron-based spin cross complexes prepared in Examples 1 to 8 of the present invention, except for [Fe(L1)2](CF3SO3)2, crystallize in the orthorhombic system P bca space group, [Fe(L3)2](BF4)2 crystallizes in the monoclinic system I Except for the 2 / a space group, the remaining triazole iron-based spin-crossed complexes all crystallize in the triclinic system. P Space group. The two tridentate ligands in the triazole iron-based spin crossover complex provide NNN coordination pockets to coordinate with the spin center Fe(Ⅱ) to form a hexadentate chelated FeN6 coordination center. The Fe(Ⅱ) ion is in a distorted octahedral coordination configuration, and the periphery contains two X - Ions are used to balance the overall charge.

[0127] When the test temperature is 180K, the bond lengths of the Fe-N bonds of the complexes [Fe(L1)2]X2 prepared in Examples 1 to 3 are in the range of 2.15Å to 2.24Å, indicating that N 吡唑 -N 吡啶 -N 三氮唑 The ligand field formed by the coordination site is conducive to the high spin state of Fe(Ⅱ); and the bond lengths of the Fe-N bonds of the complexes [Fe(L2)2]X2 and [Fe(L3)2]X2 prepared in Examples 4 to 8 are in the range of 1.90Å to 2.02Å, indicating that N 吡啶 -N 吡啶 -N 三氮唑 The ligand field strength formed by the coordination site is higher, which is beneficial for Fe(Ⅱ) to be in a low-spin state, and the complex is expected to exhibit spin-crossing properties.

[0128] (II) Temperature-dependent magnetic susceptibility test of triazole iron-based spin crossover complexes

[0129] The magnetic tests of the triazole iron-based spin crossover complexes in Examples 1 to 8 were all completed by Quantum Design SQUID Magnetometer MPMS-XL7. The instrument operating temperature range is 2.0K~400.0K, and the DC field size is −7T~7T; the DC magnetic susceptibility test uses a DC field of 5000Oe, and all data are antimagnetic corrected according to the Pascal constant table.

[0130] The temperature-dependent magnetic susceptibility results of the triazole iron-based spin crossover complexes prepared in Examples 1 to 8 are as follows: Figure 9~Figure 16 As shown in Figure 2, when the temperature is above 50K, the product of the molar magnetic susceptibility and temperature of the triazole iron-based spin crossover complex constructed using ligand L1 is χ M T The value is consistent with that of high-spin Fe(Ⅱ) ions, and remains in the high-spin state as the temperature changes. When the temperature drops below 20K, χ M T The value drops rapidly, which is due to the magnetic anisotropy of the spin center Fe(Ⅱ). When the pyrazole nitrogen at one end of the ligand L is replaced with a pyridine nitrogen coordination site (the ligand is changed from L1 to L2 or L3), the coordination field of the spin center can be regulated, so that the triazole iron-based spin crossover complex undergoes a slow and incomplete spin crossover behavior within the test temperature range. In addition, by changing the substituent at the other end of the triazole ligand (such as replacing the naphthalene group with a pentyl group) and / or changing the counter anion, the spatial effect and the supramolecular interactions within and between molecules can also be adjusted, thereby regulating the spin crossover properties of the triazole iron-based spin crossover complex; for example, when the ligand L3 is used and the counter anion is BF4 - When the complex with ligand L2 and the complex with ligand L3 and the counter anion is ClO4 - Compared with the complexes of [Fe(L3)2](BF4)2, the spin crossover phenomenon of the complex is faster, and a higher proportion of spin centers are transformed into the high-spin state.

[0131] In summary, the triazole iron-based spin-crossing complex prepared by the present invention has a definite crystal structure, and the spin-crossing properties of the triazole iron-based complex can be regulated by changing the substituent and counter anion of the ligand L.

[0132] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural transformation made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A triazole iron-based spin crossover complex, characterized in that: The triazole iron-based spin crossover complex has the following chemical formula: [FeL2]X2; The ligand L is one of L1, L2 and L3, and X is ClO4 - 、BF4 - and CF3SO3 - One of the above, and the structural formulas of L1, L2 and L3 are as follows: L1； L2； L3。 2. A method for preparing the triazole iron-based spin cross complex as claimed in claim 1, characterized in that: The preparation method comprises the following steps: Step 1: Synthesis of ligand L: Under vacuum conditions, 2-cyano-6-(1-pyrazole)pyridine and sodium methoxide are added to anhydrous methanol and stirred, and then indole-5-carboxylic acid hydrazide is added to reflux at 70°C to 75°C to obtain a solid product, and then the solid product is placed in ethylene glycol and reacted at 190°C to 220°C to obtain ligand L1; Under vacuum conditions, 6-cyano-2,2'-bipyridine and sodium methoxide are added to anhydrous methanol and stirred, and then 1-naphthylacetylhydrazide or hexanoylhydrazide is added to react under reflux at 70°C to 75°C to obtain a solid product, and then the solid product is placed in ethylene glycol and reacted at 190°C to 220°C to obtain ligand L2 or L3; Step 2, preparation of reaction solution: mix the ligand L obtained in step 1 with ferrous salt in acetonitrile solution and stir, and obtain a clear reaction solution after filtering; the ferrous salt is one of Fe(ClO4)2·6H2O, Fe(BF4)2·6H2O and Fe(CF3SO3)2; Step 3, cultivation of single crystals: Place the clarified reaction solution obtained in step 2 into a container, place the container in a sealed container filled with ether, and let it stand for 6 to 8 days to precipitate red rod-shaped crystals, filter, wash and collect the red rod-shaped crystals to obtain triazole iron-based spin cross complexes.

3. The method for preparing the triazole iron-based spin cross complex according to claim 2, characterized in that: The molar ratio of 2-cyano-6-(1-pyrazole)pyridine to indole-5-carboxylic acid hydrazide in step 1 is 1:1 to 1:1.

2.

4. The method for preparing the triazole iron-based spin cross complex according to claim 2, characterized in that: The molar ratio of 6-cyano-2,2'-bipyridine to 1-naphthylacetohydrazide or hexanoylhydrazide in step 1 is 1:1 to 1:1.

2.

5. The method for preparing the triazole iron-based spin cross complex according to claim 2, characterized in that: In step 2, the molar ratio of the ligand L to the ferrous salt is 2:1-2.2:1, and the stirring speed is 200 r / min-250 r / min.

6. The method for preparing the triazole iron-based spin cross complex according to claim 2, characterized in that: In step 3, the volume ratio of the reaction solution to ether is 1:8-1:12, and the washing is performed by rinsing with distilled water and ethanol multiple times.

7. The method for preparing the triazole iron-based spin cross complex according to claim 2, characterized in that: The crystal yield of the triazole iron-based spin cross complex described in step 3 is 70% to 75%.

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