A novel ferromagnetic coupled cyanide-bridged iron complex and its preparation method

Abstract

The invention belongs to the field of molecular magnetic materials, and in particular relates to a novel ferromagnetic coupled cyanide-bridged iron complex and a preparation method thereof. The technical key points are as follows: the molecular formula of the complex is: {[Fe(Tp*)(CN)3][Fe(TBIA)(MeOH)]}ClO4·MeOH; wherein TBIA is tri(2-benzimidazole methylene)amine; Tp* is tri(3,5-dimethylpyrazole) potassium borate; the complex is a magnetic crystal, crystallized in the triclinic system, #imgabs0# space group, and the unit cell parameters are #imgabs1##imgabs2#α=74.403(1)°, β=78.633(1)°, γ=77.349(1)°, Z=2, #imgabs3#; the complex of the invention effectively conducts the magnetic effect between metal sites through the cyano bridge, forms a ferromagnetic complex with a certain solubility through hydrogen bonds and π-π interactions, the electron-rich group present in the complex produces a significant π contribution to significantly activate the cyanide bridge, thereby producing a strong ferromagnetic coupling, and has potential application prospects.

Description

Technical Field

[0001] The invention belongs to the field of molecular magnetic materials, and in particular relates to a novel ferromagnetic coupled cyanide-bridged iron complex and a preparation method thereof. Background Art

[0002] Molecular magnetic materials refer to magnetic compounds that are assembled and combined with paramagnetic ions (transition metals and rare earth metals) or free radicals and antimagnetic ligands by chemical methods. Such compounds have magnetic exchange as their main property at the microscopic scale, and have ferromagnetism or ferrimagnetism at the macroscopic scale and can be used as magnetic materials.

[0003] Prussian blue is a class of three-dimensional structural compounds. Through ingenious design, people have synthesized a large number of structurally precise Prussian blue compounds (PBAs) with cyanide ligands. The cyanide ion is a rigid ligand and adopts a linear coordination mode. At the same time, the cyanide bridge can effectively conduct the interaction between electrons and magnetism, giving the compound a diverse structure and interesting magnetism. This makes cyanide-bridged iron complexes attract much attention in the field of magnetic materials.

[0004] Although cyanide-bridged complexes have many advantages, the cyanide bridge in this type of complex belongs to a typical weak magnetic superexchange interaction. However, in the synthesis of molecular-based magnetic materials, maximizing the coupling strength is crucial because the operating temperature of bulk magnets, single-chain magnets, and single-molecule magnets is directly related to the magnetic coupling strength between paramagnetic centers. This makes a large number of cyanide-bridged complexes mostly antiferromagnetic or extremely weak ferromagnetic coupling. For the field of molecular magnetic materials, it is difficult to synthesize cyanide-bridged complexes with ferromagnetic coupling.

[0005] In view of the above-mentioned defects in the prior art, the inventors, based on their rich experience and professional knowledge in such materials for many years, combined with theoretical analysis, conducted research and innovation, and developed a new type of ferromagnetic coupled cyanide-bridged iron complex and a preparation method thereof. Summary of the invention

[0006] The first object of the present invention is to provide a novel ferromagnetic coupled cyanide bridged iron complex. The complex effectively conducts the magnetic interaction between metal sites through the cyanide bridge, forms a ferromagnetic complex with a certain solubility through hydrogen bonding and π-π interaction, and the electron-rich group present in the complex produces a significant π contribution to significantly activate the cyanide bridge, thereby generating a strong ferromagnetic coupling, and has potential application prospects.

[0007] The above technical objectives of the present invention are achieved through the following technical solutions:

[0008] The present invention provides a novel ferromagnetic coupled cyanide-bridged iron complex, the molecular formula of which is:

[0009] {[Fe(Tp*)(CN)3][Fe(TBIA)(MeOH)]}ClO4·MeOH;

[0010] Wherein, TBIA is tris(2-benzimidazole methylene)amine; Tp* is potassium tris(3,5-dimethylpyrazole)borate;

[0011] The complex is a magnetic crystal, crystallized in the triclinic system. The space group and unit cell parameters are α=74.403(1)°, β=78.633(1)°, γ=77.349(1)°, Z=2,

[0012] Since the three 3,5-dimethylpyrazole groups in the ferrocyanide building block [Bu4N][Fe(Tp*)(CN)3] have large steric hindrance, it is usually difficult to use a large auxiliary ligand to react to obtain a complex. In the present invention, tri(2-benzimidazole methyl)amine (NTB) is used as a ligand, and the electron-rich group of the benzimidazole group and the lone pair of electrons of the unsaturated nitrogen atom are used to bridge it with cyanide. The magnetic coupling is further enhanced by adding a paramagnetic metal fragment with a strong π antibonding, so that the unpaired electrons are delocalized to the cyanide ligand, thereby enhancing the magnetic coupling. The complex in which the cyanide connects two electron-rich, low-coordinated transition metal fragments will have a significant π contribution, thereby generating a stronger magnetic coupling.

[0013] Furthermore, in the complex, the Fe1 site is chelated by the three pyrazole nitrogens in tris(3,5-dimethylpyrazolyl)boronic acid, while the remaining three coordination sites are coordinated with the three cyanide carbons to form a cyanide building block, [(Tp*)Fe(CN)3] – The building block unit coordinates with Fe2 through the cyanide nitrogen atom to form a bridging structure. The three unsaturated nitrogen atoms of the benzimidazole group in the ligand NTB and the central saturated nitrogen atom chelate the Fe2 ion. The remaining coordination site of Fe2 is then coordinated by the oxygen atom in methanol, so that the Fe2 center forms a distorted octahedral FeN5O coordination environment. This coordination saturation mode avoids the influence of solvent molecules on the magnetism of the compound.

[0014] Furthermore, the five Fe-N bonds at the Fe2 center are The remaining Fe-O bond length is The Fe2 is high spin Fe(II).

[0015] Furthermore, in the c-axis direction, the minimum distance between the pyrazolyl group in the ferrocyanide building block of the binuclear structural unit of the complex provided by the present invention and the aromatic ring on the auxiliary ligand NTB in another unit is This distance indicates that there is a π-π interaction between the structural units, which is beneficial to the structural stability of the complex.

[0016] At the same time, hydrogen atoms on the two nitrogen atoms of the ligand NTB form hydrogen bonds with the nitrogen atoms of the terminal cyanide of the adjacent structural unit, and the hydrogen of the remaining nitrogen atom in the ligand NTB forms hydrogen bonds with the methanol molecules in the crystal lattice. It can be seen that the binuclear unit structures of the complex are stacked through supramolecular interactions such as π-π interactions and intermolecular hydrogen bonding interactions to further form the crystal structure of the complex, thus clarifying the structure-activity relationship between structure and properties.

[0017] Furthermore, the Curie constant C of the complex is 3.344 cm 3 ·K·mol –1 , and its Curie temperature θ is 19.18K, which indicates that the magnetic crystal provided by the present invention exhibits ferromagnetic coupling.

[0018] The second object of the present invention is to provide a method for preparing a novel ferromagnetic coupled cyanide-bridged iron complex, which has a simple synthesis method and a large yield.

[0019] The above technical objectives of the present invention are achieved through the following technical methods:

[0020] The present invention provides a novel method for preparing a ferromagnetic coupled cyanide-bridged iron complex, comprising the following steps:

[0021] Preparation of ligand: mixing nitrilotriacetic acid, o-phenylenediamine and ethylene glycol, heating, and purifying after the reaction to obtain ligand NTB;

[0022] Preparation of intermediate product Tp*: KBH4 and 3,5-dimethylpyrazole are mixed and heated until no gas is generated in the reaction system, the reaction is stopped, and the intermediate product Tp* is obtained after purification;

[0023] Preparation of precursor [Bu4N][Fe(Tp*)(CN)3]: Prepare Tp* into a methanol solution, prepare NaCN into an aqueous solution, successively add the two solutions dropwise into FeCl3·6H2O methanol solution, heat for reaction, filter to obtain a filtrate, add [Bu4N]Br into the filtrate, filter, and obtain a filter cake as the precursor [Bu4N][Fe(Tp*)(CN)3];

[0024] Preparation of magnetic crystals: Dissolve [Bu4N][Fe(Tp*)(CN)3], Fe(ClO4)2·6H2O and NTB in methanol respectively. First, mix the methanol solutions of Fe(ClO4)2·6H2O and NTB evenly, and then add the methanol solution of [Bu4N][Fe(Tp*)(CN)3]. After the reaction is completed, filter and let the filtrate stand for volatilization to obtain magnetic crystals.

[0025] Furthermore, the molar ratio of NTB, [Bu4N][Fe(Tp*)(CN)3] and Fe(ClO4)2·6H2O is 2:2:1.

[0026] Furthermore, in the step of preparing the intermediate product Tp*, the heating method is to increase the temperature in stages, the heating temperature is 200°C, and the temperature is increased to 220°C after the reaction gas is reduced, and the reaction time is 12 hours.

[0027] Furthermore, the steps for preparing the ligand are as follows: mixing nitrilotriacetic acid, o-phenylenediamine and ethylene glycol in a round-bottom flask, stirring and reacting at 170° C. for 8 to 12 hours, stopping the reaction, cooling to room temperature, adding ice water to the reaction mixture, filtering and drying the resulting brown-red precipitate and adding it to a round-bottom flask, then adding an appropriate amount of activated carbon and methanol and refluxing for 2 hours, filtering the solution while hot, and then standing to cool to precipitate the ligand NTB.

[0028] Furthermore, the steps of preparing the precursor [Bu4N][Fe(Tp*)(CN)3] are as follows: Tp* is prepared into a solution with methanol, NaCN is dissolved in water to prepare a solution, and the two are added dropwise into a round-bottom flask containing FeCl3·6H2O methanol solution, and then the temperature is raised to 80°C, refluxed for 24 hours, the heating is stopped, the mixture is cooled to room temperature, filtered and the filtrate is collected, [Bu4N]Br is added to the filtrate and stirred at room temperature for 3 hours, and then rotary evaporated and filtered, and the filter cake is dried at 70°C to obtain the precursor [Bu4N][Fe(Tp*)(CN)3].

[0029] Furthermore, the molar ratio of nitrilotriacetic acid to o-phenylenediamine is 1:3.

[0030] In summary, the present invention has the following beneficial effects:

[0031] The synthesis method of the cyanide bridged iron complex magnetic material of the present invention is simple and has a large yield. The complex effectively conducts the magnetic effect between metal sites through the cyanide bridge, forms a ferromagnetic complex with a certain solubility through hydrogen bonding and π-π interaction, and the electron-rich group present in the complex produces a significant π contribution to significantly activate the cyanide bridge, thereby generating a strong ferromagnetic coupling, and has potential application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a powder X-ray diffraction pattern of the complex of the present invention;

[0033] Figure 2 The temperature-dependent magnetic susceptibility curve and χ M –1 A graph of temperature T;

[0034] Figure 3 is the π-π stacking diagram of the complex crystal of the present invention;

[0035] Figure 4 It is a hydrogen bond display diagram of the complex crystal of the present invention;

[0036] Figure 5 It is the infrared spectrum of the complex crystal of the present invention and the auxiliary ligand NTB;

[0037] Figure 6 is a crystal structure diagram of the complex crystal of the present invention;

[0038] Figure 7 It is a schematic diagram of the reaction equation of the complex of the present invention. DETAILED DESCRIPTION

[0039] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, a novel ferromagnetic coupled cyanide-bridged iron complex and its preparation method proposed in the present invention, its specific implementation method, characteristics and effects are described in detail as follows.

[0040] Example

[0041] A new type of ferromagnetic coupled cyanide-bridged iron complex, the molecular formula of the complex is:

[0042] {[Fe(Tp*)(CN)3][Fe(TBIA)(MeOH)]}ClO4·MeOH, its structural formula is shown in Figure 6 As shown;

[0043] Wherein, TBIA is tris(2-benzimidazole methylene)amine; Tp* is potassium tris(3,5-dimethylpyrazole)borate;

[0044] The complex is a magnetic crystal, crystallized in the triclinic system. The space group and unit cell parameters are α=74.403(1)°, β=78.633(1)°, γ=77.349(1)°, Z=2, Specific crystallographic data are shown in Table 1.

[0045] Table 1. Crystallographic data of the complexes of the present invention

[0046]

[0047] It can be seen from this that in the novel cyanide-bridged iron complex provided in this embodiment, the Fe1 site is chelated by three pyrazole nitrogens in tris(3,5-dimethylpyrazolyl)boronic acid, and the remaining three coordination sites are coordinated with three cyanide carbons to form a cyanide building block. [(Tp*)Fe(CN)3] – The building block unit coordinates with Fe2 through the cyanide nitrogen atom to form a bridge structure. The three unsaturated nitrogen atoms of the benzimidazole group in the ligand NTB chelate the Fe2 ion with the saturated nitrogen atom in the center, and the remaining coordination site of Fe2 is coordinated by the oxygen atom in methanol, so that the Fe2 center forms a distorted octahedral FeN5O coordination environment. The five Fe-N bonds in the Fe2 center are The remaining Fe-O bond length is

[0048] From the bond length of Fe2, we can preliminarily judge that Fe2 is high-spin Fe(II).

[0049] The preparation method is as follows:

[0050] S1. Mix KBH4 (0.11 mol, 5.9 g) and 3,5-dimethylpyrazole (0.42 mol, 40.4 g) in a 1000 mL three-necked flask under nitrogen protection, and heat to 200 ° C in stages. After the gas generated by the reaction is reduced, heat to 220 ° C, and continue the reaction for 12 hours. When no gas is generated in the reaction system, stop the reaction, cool to 100 ° C, add toluene and stir at a constant temperature for half an hour, then cool to room temperature, filter, rinse repeatedly with n-hexane, obtain the intermediate product Tp*, and dry in vacuo at 70 ° C;

[0051] S2, prepare a solution of Tp* (0.015 mol, 5.04 g) with methanol, dissolve NaCN (0.05 mol, 2.5 g) in water to prepare a solution, and add them dropwise into a round-bottom flask containing 1000 mL of FeCl3·6H2O (0.015 mol, 4.05 g) methanol solution, then heat to 80°C, reflux for 24 hours, stop heating, cool to room temperature, filter and collect the filtrate;

[0052] S3, [Bu4N]Br (0.01 mol, 3.2 g) was added to the filtrate and stirred at room temperature for 3 hours, then rotary evaporated and filtered, and the filter cake was dried at 70°C to obtain the precursor [Bu4N][Fe(Tp*)(CN)3];

[0053] S4, nitrilotriacetic acid (9.6 g, 50 mmol) and o-phenylenediamine (16.2 g, 150 mmol) and 50 mL of ethylene glycol were mixed in a 100 mL round-bottom flask, and stirred at 170 ° C for 8-12 hours, the reaction was stopped, cooled to room temperature, ice water was added to the reaction mixture, the brown-red precipitate was filtered and dried and added to a 100 mL round-bottom flask, and then an appropriate amount of activated carbon and 30 mL of methanol were added and refluxed for 2 hours, the solution was filtered while hot, and then allowed to stand and cool to precipitate the ligand NTB, and the product was filtered and dried;

[0054] S5. Dissolve Fe(ClO4)2·6H2O (12.7 mg, 0.050 mmol) in methanol, then add a methanol solution containing NTB (40.8 mg, 0.100 mmol) and stir to react for 15 minutes. After stirring, add a methanol solution containing the precursor [Bu4N][Fe(Tp*)(CN)3] (65.3 mg, 0.100 mmol) and stir to react for 20 minutes. Filter the resulting dark red reaction solution and let it stand at ambient temperature to evaporate for one week to obtain dark red target crystals.

[0055] The magnetic properties of product M-1 were measured using a SQUID (MPMS-5S) magnetometer in the temperature range of 300–2K and a magnetic field of 1 kOe. The data were corrected for the diamagnetic contribution using the Pascal constant calculation. The magnetic data show the χ M The T value is 3.406cm 3 ·K·mol –1 , which is very close to the unique spin value of 3.375 cm for the uncoupled LS-Fe(III) (S=1 / 2) and HS-Fe(II) (S=2) centers. 3 ·K·mol –1 .

[0056] As the temperature continues to decrease, M The T value increases continuously until 3.01K, χ M The maximum value of T is 7.8cm 3 ·K·mol –1 This magnetic behavior indicates that there is ferromagnetic coupling between the metal centers of the complex. After that, the temperature continued to drop. At 2K, χ M The T value drops to 7.550cm 3 ·K·mol –1 The magnetic behavior is likely caused by zero field splitting (ZFS) and antiferromagnetic interactions (e.g. Figure 1 ).

[0057] The Curie-Weiss law was used to study the χ M–1 The Curie constant C of the complex was obtained by fitting the temperature T curve to be 3.344 cm 3 ·K·mol –1 , and its Curie temperature θ is 19.18 K. This indicates that the cyano-bridged complex exhibits ferromagnetic coupling in a wide temperature range and has the potential to be a new type of ferromagnetic material to replace conventional metals and metal oxides.

[0058] Figure 3 is the π-π stacking diagram of the crystal. It can be seen that the minimum distance between the aromatic ring on the auxiliary ligand NTB in the other unit of the pyrazolyl group in the ferrocyanide building block is This distance proves that there is π-π interaction between the structural units.

[0059] Figure 4 This is a crystal hydrogen bond display diagram. It can be seen that the hydrogen atom on the nitrogen atom of the ligand NTB in the c direction forms a hydrogen bond with the terminal cyanide nitrogen atom of its adjacent structural unit, and the hydrogen of the remaining nitrogen atom in the ligand NTB forms a hydrogen bond with the methanol molecule between the crystal lattices.

[0060] Figure 5 This is the infrared spectrum of the crystal and the auxiliary ligand NTB. By comparing the infrared data of the ligand with the data of the complex, it can be confirmed that the auxiliary ligand exists in the crystal. –1 and 2129cm –1 The two peaks at III Tp*(CN)3] – The terminal cyanide and Fe III LS (μ-CN)Fe II HS The bridged cyanide band was observed, confirming that the ferrocyanide precursor and the auxiliary ligand successfully reacted to form crystals.

[0061] The above description is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been presented as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A ferromagnetic coupled cyanide-bridged iron complex, characterized in that: The molecular formula of the complex is: {[Fe(Tp*)(CN)3][Fe(TBIA)(MeOH)]}ClO4·MeOH; Wherein, TBIA is tris(2-benzimidazole methylene)amine; Tp* is potassium tris(3,5-dimethylpyrazole)borate; The complex is a magnetic crystal, crystallized in the triclinic system, The space group and unit cell parameters are a = 12.9625(5)Å, b = 13.4416(4) Å, c = 15.2834(5) Å, α =74.403(1)°, β = 78.633(1)°, γ = 77.349(1)°, Z = 2, V = 2472.10(7) Å 3 .

2. A ferromagnetic coupled cyanide-bridged iron complex according to claim 1, characterized in that: In the complex, the Fe1 site is chelated by the three pyrazole nitrogens in tris(3,5-dimethylpyrazolyl)boronic acid, while the remaining three coordination sites are coordinated with the three cyanide carbons to form a cyanide building block, [(Tp*)Fe(CN)3] – The building block unit coordinates with Fe2 through the cyanide nitrogen atom to form a bridging structure. The three unsaturated nitrogen atoms of the benzimidazole group in the ligand TBIA and the central saturated nitrogen atom chelate the Fe2 ion. The remaining coordination site of Fe2 is then coordinated by the oxygen atom in methanol, forming a distorted octahedral FeN5O coordination environment at the Fe2 center.

3. A ferromagnetic coupled cyanide-bridged iron complex according to claim 2, characterized in that: The five Fe-N bond lengths of the Fe2 center are in the range of 2.069(3) Å to 2.408(3) Å, and the remaining Fe-O bond length is 1.805(3) Å. The Fe2 is high-spin Fe(II).

4. The ferromagnetic coupled cyanide-bridged iron complex according to claim 1, characterized in that: The Curie constant C of the complex is 3.344 cm 3 ·K·mol –1 , its Curie temperature θ is 19.18 K.

5. The method for preparing a ferromagnetic coupled cyanide-bridged iron complex according to any one of claims 1 to 4, characterized in that: The steps are as follows: Preparation of ligand: mixing nitrilotriacetic acid, o-phenylenediamine and ethylene glycol, heating, and purifying after the reaction to obtain ligand TBIA; Preparation of intermediate product Tp*: Mix KBH4 and 3,5-dimethylpyrazole and heat until no gas is generated in the reaction system, stop the reaction, and obtain the intermediate product Tp* after purification; Preparing a precursor [Bu4N][Fe(Tp*)(CN)3]: preparing Tp* into a methanol solution, preparing NaCN into an aqueous solution, successively adding the two solutions dropwise into a FeCl3∙6H2O methanol solution, heating for reaction, filtering to obtain a filtrate, adding [Bu4N]Br into the filtrate, filtering, and obtaining a filter cake as the precursor [Bu4N][Fe(Tp*)(CN)3]; Preparation of the complex: [Bu4N][Fe(Tp*)(CN)3], Fe(ClO4)2·6H2O and TBIA are dissolved in methanol respectively, the methanol solutions of Fe(ClO4)2·6H2O and TBIA are first mixed evenly, and then the methanol solution of [Bu4N][Fe(Tp*)(CN)3] is added thereto. After the reaction is completed, the solution is filtered and the filtrate is allowed to stand and evaporate to obtain the magnetic crystals.

6. The method for preparing a ferromagnetic coupled cyanide-bridged iron complex according to claim 5, characterized in that: The molar ratio of TBIA, [Bu4N][Fe(Tp*)(CN)3] and Fe(ClO4)2·6H2O is 2:2:

1.

7. The method for preparing a ferromagnetic coupled cyanide-bridged iron complex according to claim 5, characterized in that: In the step of preparing the intermediate product Tp*, the heating method is to increase the temperature in stages, the heating temperature is 200° C., and the temperature is increased to 220° C. when the reaction gas is reduced.

8. The method for preparing a ferromagnetic coupled cyanide-bridged iron complex according to claim 5, characterized in that: The steps of preparing the ligand are specifically as follows: mixing nitrilotriacetic acid, o-phenylenediamine and ethylene glycol in a round-bottom flask, stirring and reacting at 170° C. for 8 to 12 hours, stopping the reaction, cooling to room temperature, adding ice water to the reaction mixture, filtering and drying the resulting brown-red precipitate and adding it to the round-bottom flask, then adding an appropriate amount of activated carbon and methanol to reflux for 2 to 4 hours, filtering the solution while hot, and then standing and cooling to precipitate the ligand TBIA.

9. The method for preparing a ferromagnetic coupled cyanide-bridged iron complex according to claim 5, characterized in that: The steps of preparing the precursor [Bu4N][Fe(Tp*)(CN)3] are specifically as follows: preparing a solution of Tp* with methanol, dissolving NaCN with water to prepare a solution, and successively adding the two solutions dropwise into a round-bottom flask containing a FeCl3∙6H2O methanol solution, then heating to 80°C, reflux reaction, stopping heating, cooling to room temperature, filtering and collecting the filtrate, adding [Bu4N]Br to the filtrate and stirring at room temperature, then rotary evaporating and filtering, and drying the filter cake to obtain the precursor [Bu4N][Fe(Tp*)(CN)3].

10. The method for preparing a ferromagnetic coupled cyanide-bridged iron complex according to claim 5, wherein the molar ratio of the nitrilotriacetic acid to o-phenylenediamine is 1:3.

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