Double helical Fe(Ⅱ) magnetic complex, preparation method and application

Abstract

The invention discloses a double helix Fe (II) magnetic complex, a preparation method and an application thereof, and belongs to the technical field of metal complexes. The double helix Fe (II) magnetic complex has the following chemical expression: Fe 2 L 2 (X) 4 The present invention also provides a method for preparing the above-mentioned double helical Fe(II) magnetic complex, which is prepared by dissolving the synthesized ligand L1, L2 or L3 and ferrous trifluoromethanesulfonate or ferrous perchlorate in acetonitrile, stirring at room temperature for 3 hours to obtain a clear reaction solution, placing the reaction solution in ether vapor, and gas phase diffusion for 7 days. The present invention activates and regulates the spin crossover behavior of the series of helical Fe(II) magnetic complexes by changing the anion, the side end group and the length of the bridging alkyl chain.

Description

Technical Field

[0001] The invention belongs to the technical field of metal complexes, and in particular relates to a double-helix Fe(II) magnetic complex, a preparation method and an application thereof. Background Art

[0002] Molecular-based magnetic materials are a type of magnetic compounds formed by chemical assembly of paramagnetic ions and ligands. They are currently a cutting-edge interdisciplinary research subject that has attracted much attention. By combining structural design, supramolecular assembly, magnetic characterization and quantitative calculation, molecular-based magnetic materials with excellent performance are constructed and applied to the design of high-density information storage and spintronic devices.

[0003] Among them, spin cross-coordination complexes can achieve the control of 3d 4 -3d 7 The switching between high and low spin states of transition metal ions in electronic configuration is usually called spin crossover. This phenomenon 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, spin crossover complexes, as an important branch in the field of molecular-based magnetic materials research, are expected to be applied in the fields of quantum bits, molecular switch devices and spintronic devices. The performance of this series of materials can be better regulated by rationally designing ligands and accurately selecting metal ions.

[0004] At present, the focus of the spin crossover field is mainly on mononuclear ferrous complexes. In 2022, José AntonioReal et al. reported a triazole-based mononuclear ferrous complex. Due to the asymmetric conical configuration in the lattice, the complex formed a one-dimensional supramolecular chain stacking mode. In addition, due to the existence of a special supramolecular mechanism, the widest thermal hysteresis relaxation temperature for spin crossover behavior in the current room temperature region was successfully achieved, reaching an astonishing 105 K, creating conditions for the application of spin transition materials ("105 K Wide Room Temperature Spin Transition Memory Due to a Supramolecular Latch Mechanism", Maksym Seredyuk, Kateryna Znovjyak, Francisco Javier Valverde-Muñoz, Ivan da Silva, M. Carmen Muñoz, Yurii S. Moroz, and José Antonio Real, Journal of the American Chemical Society, 144 (31), 14297-14309, 2022). In 2023, Malcolm A. Halcrow et al. designed and synthesized a multidentate ligand bridged by butyl groups, and assembled it with iron salts to obtain a [2+2] helical Fe2 complex. In addition, since the bridging alkyl chain of the complex will twist to varying degrees at different temperatures, conditions are created for its spin crossover behavior to occur, ultimately achieving the transformation of two low-spin ferrous states to two high-spin ferrous states ("Di-Iron(II) [2+2] Helicates of Bis-(Dipyrazolylpyridine) Ligands: The Influence of the Ligand Linker Group on Spin State Properties", Rafal Kulmaczewski, Isaac T. Armstrong, Pip Catchpole, Emily SJ Ratcliffe, Hari Babu Vasili, Stuart L. Warriner, Oscar Cespedes, and Malcolm A. Halcrow, Chemistry-A European Journal, 29, e202202578, 2023).However, the above work only obtained one example of a spin-crossing complex bridged by butyl, and failed to better explain the relationship between the spin-crossing behavior and the flexibility of the bridging alkyl chain, which limited the synthesis and development of Fe2 magnetic complexes and further limited their application in the preparation of spin electronic devices. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a double-helical Fe(II) magnetic complex, a preparation method and an application. The series of complexes provided by the present invention all have a clear single crystal structure, high thermal stability and different spin crossover behaviors.

[0006] The idea of ​​the present invention is to obtain four helical Fe2 complexes bridged by alkyl chains through design and synthesis, and to achieve regulation of the spin crossover behavior of this series of complexes by regulating the anions in the crystal lattice and changing the side groups of the ligands and the flexibility of the bridging alkyl chains.

[0007] Principle of the present invention:

[0008] The spin crossover phenomenon of transition metal complexes is mainly due to the fact that when there is a 3d 4 -3d 7 When the electronic configuration of a transition metal ion is in an octahedral ligand field, its 3d orbital splits into doubly degenerate e g and the triply degenerate t 2g orbit, where the electron arrangement mainly depends on the relative size of the crystal field splitting energy and the electron pairing energy. Using this phenomenon, researchers can switch between high and low spin states by regulating external physical conditions, so that the complex can show different physical and chemical properties in the molecular dimension, making it have potential application value in the field of spin electronic devices and multifunctional molecular materials in the future. The present invention designs and synthesizes four binuclear helical ferrous complexes, and uses the mutual influence between multi-site metals to better achieve the regulation of spin crossover behavior.

[0009] The first object of the present invention is to provide a double helical Fe (II) magnetic complex, wherein the double helical Fe (II) magnetic complex has the following chemical expression:

[0010] Fe2L2(X)4;

[0011] Wherein, L is ligand L1, L2 or L3, X is OTF - or ClO4 - , and the structural formulas of ligands L1, L2 and L3 are shown below:

[0012] Ligand L1;

[0013] Ligand L2;

[0014] Ligand L3.

[0015] Preferably, the double helical Fe(II) magnetic complex is Fe2(L1)2(OTF)4, which belongs to the orthorhombic crystal system, has a space group of Cmce, and has unit cell parameters of a = 25.563(4), b = 24.734(4), c = 22.137(4), α = 90, β = 90, γ = 90, ν = 13997(4).

[0016] Preferably, the double helical Fe(II) magnetic complex is Fe2(L2)2(ClO4)4, which belongs to the monoclinic crystal system, has a space group of C2 / c, and has unit cell parameters of a = 24.041(7), b = 15.365(4), c = 20.765(5), α = 90, β = 111.324(9), γ = 90, ν = 7145(3).

[0017] Preferably, the double helical Fe(II) magnetic complex is Fe2(L2)2(OTF)4, which belongs to the monoclinic crystal system, has a space group of C2 / c, and has unit cell parameters of a = 21.396(6), b = 19.159(5), c = 23.676(6), α = 90, β = 112.723(6), γ = 90, ν = 8952(4).

[0018] Preferably, the double helical Fe(II) magnetic complex is Fe2(L3)2(OTF)4, which belongs to the monoclinic crystal system, has a space group of C2 / c, and unit cell parameters of a = 39.625(5), b = 13.524(9), c = 27.189(6), α = 90, β = 110.918(6), γ = 90, ν = 13610(4).

[0019] The second object of the present invention is to provide a method for preparing the above-mentioned double-helical Fe (II) magnetic complex, comprising the following steps:

[0020] S1. Synthesis of ligand L1, L2 or L3:

[0021] 2-cyano-6-(1-pyrazole)-pyridine or 6-cyano-2,2'-bipyridine and sodium methoxide are cycled three times under vacuum-nitrogen, anhydrous methanol is added, the reaction is carried out at room temperature for 1-2 hours, malonic hydrazide is added, reflux reaction is carried out at 72°C for 5-6 hours, after the reaction is completed, the reaction is cooled to room temperature, filtered, and solid powder is collected, ethylene glycol is added under nitrogen atmosphere, the reaction is carried out at 200°C for 3-4 hours, after the reaction is completed, the reaction is cooled to room temperature, diluted and filtered, and the solid is collected to obtain ligand L1 or L2;

[0022] 2-cyano-6-(1-pyrazole)-pyridine and sodium methoxide were cycled for 3 times under vacuum-nitrogen, anhydrous methanol was added, the reaction was carried out at room temperature for 1-2 hours, pentane dihydrazine was added, refluxed at 72°C for 5-6 hours, after the reaction was completed, cooled to room temperature, filtered, and solid powder was collected, ethylene glycol was added under nitrogen atmosphere, reacted at 200°C for 3-4 hours, after the reaction was completed, cooled to room temperature, diluted and filtered, and solid was collected to obtain ligand L3;

[0023] The molar ratio of one of 2-cyano-6-(1-pyrazole)-pyridine or 6-cyano-2,2'-bipyridine to one of malonic dihydrazide or pentane dihydrazide is 2.5:1;

[0024] S2. Synthesis of double helical Fe(Ⅱ) magnetic complexes:

[0025] Dissolve Fe(OTF)2 or Fe(ClO4)2 and the ligand L1, L2 or L3 obtained in step S1 in acetonitrile, stir and react at room temperature for 3 hours, filter after the reaction, and diffuse the filtrate in gas phase for 7 days to obtain a double helical Fe(II) magnetic complex;

[0026] The molar ratio of one of the ligands L1, L2 or L3 to one of Fe(OTF)2 or Fe(ClO4)2 is 1:1.

[0027] Preferably, step S1 comprises the following steps:

[0028] S11, Synthesis of 2-cyano-6-(1-pyrazole)-pyridine;

[0029] S12, Synthesis of 6-cyano-2,2'-bipyridine;

[0030] S13, cyclically treating the 2-cyano-6-(1-pyrazole)-pyridine obtained in step S11 or the 6-cyano-2,2'-bipyridine obtained in step S12 with sodium methoxide under vacuum-nitrogen for 3 times, adding anhydrous methanol, and reacting at room temperature for 1 hour to obtain a reactant;

[0031] S14, adding malonic acid hydrazide to the reactant obtained in step S13, and refluxing the mixture at 72° C. for 5-6 hours. After the reaction is completed, the mixture is cooled to room temperature, filtered, and solid powder is collected;

[0032] S15, adding ethylene glycol to the solid powder obtained in step S14 under a nitrogen atmosphere, reacting at 200° C. for 3-4 hours. After the reaction is completed, cooling to room temperature, diluting and filtering, collecting the solid, and obtaining ligand L1 or L2;

[0033] S16, cyclically treating the 2-cyano-6-(1-pyrazole)-pyridine obtained in step S11 with sodium methoxide under vacuum-nitrogen for 3 times, adding anhydrous methanol, and reacting at room temperature for 1-2 hours to obtain a reactant;

[0034] S17, adding pentanedihydrazine to the reactant obtained in step S16, and refluxing at 72° C. for 5-6 hours. After the reaction is completed, cooling to room temperature, filtering, and collecting solid powder;

[0035] S18, adding ethylene glycol to the solid powder obtained in step S17 under a nitrogen atmosphere, reacting at 200° C. for 3-4 hours. After the reaction is completed, cooling to room temperature, diluting and filtering, collecting the solid, and obtaining ligand L3;

[0036] The molar ratio of one of 2-cyano-6-(1-pyrazole)-pyridine or 6-cyano-2,2'-bipyridine to one of malonic dihydrazide or pentane dihydrazide is 2.5:1.

[0037] Preferably, step S11 specifically includes the following steps:

[0038] S111, Synthesis of 2-bromo-6-(1-pyrazole)-pyridine;

[0039] S112, 2-bromo-6-(1-pyrazole)-pyridine, potassium ferrocyanide and copper iodide obtained in step S111 are circulated three times under vacuum-nitrogen, and then N-methylimidazole is added, and the reaction is carried out at 160° C. for 16 hours. After the reaction is completed, the mixture is cooled to room temperature, water is added, and the mixture is extracted with ethyl acetate. The organic phase obtained by the extraction is dried over anhydrous magnesium sulfate, filtered, and a solution is obtained. The solvent is removed, and the mixture is purified to obtain 2-cyano-6-(1-pyrazole)-pyridine;

[0040] The molar ratio of the 2-bromo-6-(1-pyrazole)-pyridine, potassium ferrocyanide and copper iodide is 25.6:16:2.4.

[0041] Preferably, step S111 specifically includes the following steps:

[0042] Pyrazole and sodium hydride were cycled three times under vacuum-nitrogen, then anhydrous dimethyl sulfoxide was added, stirred and reacted at room temperature for 3 hours, then 2,6-dibromopyridine was added, stirred and reacted at 160° C. for 48 hours, and after the reaction was completed, the mixture was cooled to room temperature, the unreacted sodium hydride was quenched, and the organic phase obtained by extraction with ethyl acetate was purified to obtain 2-bromo-6-(1-pyrazole)-pyridine;

[0043] The molar ratio of the pyrazole to 2,6-dibromopyridine is 1:1.

[0044] Preferably, step S12 specifically includes the following steps:

[0045] S121, Synthesis of 2,2'-bipyridine-N-oxide:

[0046] S122. Under a nitrogen atmosphere, add anhydrous dichloromethane to the 2,2'-bipyridine-N-oxide obtained in step S121, lower the temperature to 0°C, add trimethylsilyl cyanide (TMSCN), and then drop benzoyl chloride. After the dropwise addition is completed, react for 24 hours. After the reaction is completed, add an aqueous sodium carbonate solution, extract with dichloromethane, dry, filter, evaporate under reduced pressure, and purify to obtain 6-cyano-2,2'-bipyridine;

[0047] The molar ratio of the 2,2'-bipyridine-N-oxide to trimethylsilyl cyanide is 1:5.

[0048] Preferably, step S121 specifically includes the following steps:

[0049] 2,2'-bipyridine, hydrogen peroxide and trifluoroacetic acid were stirred and reacted at room temperature for 6 hours. After the reaction was completed, sodium hydroxide was added to neutralize to pH=5, and extraction was performed. The obtained organic phase was washed, dried and filtered to obtain 2,2'-bipyridine-N-oxide;

[0050] The molar ratio of the 2,2'-bipyridine to hydrogen peroxide is 2:3.

[0051] The third object of the present invention is to provide an application of the above-mentioned double-helix Fe(II) magnetic complex in the preparation of spin electronic devices.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] (1) The present invention synthesizes three examples of multidentate ligands bridged by alkyl chains, assembles them with ferrous ions respectively, and prepares a series of double helical Fe2 complexes by changing the anions, side groups and the length of the bridging alkyl chains. The series of helical Fe2 complexes have different spin crossover properties, and show different magnetic properties and single crystal structures in the molecular dimension. Therefore, they have potential application value in the field of spin electronic devices. The experimental results show that the spin crossover properties of the synthesized complexes are regulated by the side groups and the length of the bridging alkyl chains, and are not regulated by the anions. This provides a direction for the synthesis of helical Fe2 complexes in the future, and promotes the synthesis and development of helical Fe2 complexes and their application in the preparation of spin electronic devices.

[0054] (2) The series of complexes provided by the present invention are prepared by simply reacting the ligand with the iron salt and then growing by vapor diffusion in ether. The preparation method is simple to operate, has a high yield, and has high crystal purity. The obtained complexes have stable physical and chemical properties and are easy to promote and apply on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 Ligand L1 in DMSO-d 6 In 1 H-NMR spectrum;

[0056] Figure 2 Ligand L2 in DMSO-d 6 In 1 H-NMR spectrum;

[0057] Figure 3 Ligand L3 in DMSO-d 6 In 1 H-NMR spectrum;

[0058] Figure 4 is an infrared spectrum of the complex Fe2L2(X)4 provided in an embodiment of the present invention;

[0059] Figure 5 It is a single crystal structure diagram of the complex Fe2L2(X)4 provided in an embodiment of the present invention;

[0060] Figure 6 is a thermogravimetric curve of the complex Fe2L2(X)4 provided in an embodiment of the present invention;

[0061] Figure 7 This is a temperature-dependent magnetic susceptibility diagram of the complex Fe2L2(X)4 provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0062] The following is a description of the embodiments of the present invention. Figures 1 to 7 , the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0063] The present invention provides a double helix Fe (II) magnetic complex, which has the following chemical expression:

[0064] Fe2L2(X)4;

[0065] Wherein, L is ligand L1, L2 or L3, X is OTF - or ClO4 - , and the structural formulas of ligands L1, L2 and L3 are shown below:

[0066] Ligand L1;

[0067] Ligand L2;

[0068] Ligand L3.

[0069] The infrared spectrum data of L1 is: (solid, ATR): ῦ [cm -1 ] = 2599 (br), 1983 (w), 1581 (m), 1555 (s), 1500 (s), 1455 (s), 1426 (s), 1379 (m), 1321 (w), 1262 (m), 1175 (m), 1137 (m), 1091 (w), 1011 (s), 916 (w), 822 (w), 785 (s), 746 (s), 690 (m), 635 (m), 618 (m), 531 (w), 484 (w), 399 (s);

[0070] The infrared spectrum data of L2 is: (solid, ATR): ῦ[cm -1 ] = 3257 (br), 3122 (w), 2153 (w), 1680 (w), 1606 (m), 1582 (m), 1523 (w), 1464 (s), 1394 (s), 1341 (w), 1283 (w), 1206 (m), 1147 (m), 1066 (s), 940 (s), 887 (w), 808 (m), 744 (s), 651 (m), 626 (w), 593 (w), 543 (w), 447 (w), 408 (m);

[0071] The infrared spectrum data of L3 is: (solid, ATR): ῦ [cm -1 ] = 3092 (br), 2915 (w), 2163 (w), 1715 (w), 1604 (m), 1577 (m), 1522 (m), 1485 (m), 1461 (s), 1394 (s), 1338 (w), 1310 (m), 1272 (w), 1207 (m), 1140 (m), 1068 (s), 991 (w), 944 (s), 913 (m), 806 (m), 779 (m), 738 (m), 651 (m), 625 (m), 592 (w), 545 (w), 485 (w), 437 (w).

[0072] The present invention also provides a method for preparing the above-mentioned double-helix Fe (II) magnetic complex, comprising the following steps:

[0073] S1. Synthesis of ligand L1, L2 or L3:

[0074] 2-cyano-6-(1-pyrazole)-pyridine or 6-cyano-2,2'-bipyridine and sodium methoxide are cycled three times under vacuum-nitrogen, anhydrous methanol is added, the reaction is carried out at room temperature for 1-2 hours, malonic hydrazide is added, reflux reaction is carried out at 72°C for 5-6 hours, after the reaction is completed, the reaction is cooled to room temperature, filtered, and solid powder is collected, ethylene glycol is added under nitrogen atmosphere, the reaction is carried out at 200°C for 3-4 hours, after the reaction is completed, the reaction is cooled to room temperature, diluted and filtered, and the solid is collected to obtain ligand L1 or L2;

[0075] 2-cyano-6-(1-pyrazole)-pyridine and sodium methoxide were cycled for 3 times under vacuum-nitrogen, anhydrous methanol was added, the reaction was carried out at room temperature for 1-2 hours, pentane dihydrazine was added, refluxed at 72°C for 5-6 hours, after the reaction was completed, cooled to room temperature, filtered, and solid powder was collected, ethylene glycol was added under nitrogen atmosphere, reacted at 200°C for 3-4 hours, after the reaction was completed, cooled to room temperature, diluted and filtered, and solid was collected to obtain ligand L3;

[0076] The molar ratio of the 2-cyano-6-(1-pyrazole)-pyridine or 6-cyano-2,2'-bipyridine to malonic acid hydrazide or pentane dihydrazide is 2.5:1;

[0077] The synthetic reaction formula of the above ligand L1, L2 or L3 is as follows:

[0078] ;

[0079] Wherein, R1 is pyrazole or pyridine, and R2 is or ;

[0080] Step S1 specifically includes the following steps:

[0081] S11, the synthesis of 2-cyano-6-(1-pyrazole)-pyridine, specifically comprising the following steps:

[0082] S111, the synthesis of 2-bromo-6-(1-pyrazole)-pyridine, specifically comprising the following steps:

[0083] Pyrazole and sodium hydride were cycled three times under vacuum-nitrogen, then anhydrous dimethyl sulfoxide was added, stirred and reacted at room temperature for 3 hours, then 2,6-dibromopyridine was added, stirred and reacted at 160° C. for 48 hours, and after the reaction was completed, the mixture was cooled to room temperature, the unreacted sodium hydride was quenched, and the organic phase obtained by extraction with ethyl acetate was purified to obtain 2-bromo-6-(1-pyrazole)-pyridine;

[0084] The molar ratio of the pyrazole to 2,6-dibromopyridine is 1:1;

[0085] The synthetic reaction formula of the above 2-bromo-6-(1-pyrazole)-pyridine is as follows:

[0086] ;

[0087] S112, 2-bromo-6-(1-pyrazole)-pyridine, potassium ferrocyanide and copper iodide obtained in step S111 are circulated three times under vacuum-nitrogen, and then N-methylimidazole is added, and the reaction is carried out at 160° C. for 16 hours. After the reaction is completed, the mixture is cooled to room temperature, water is added, and the mixture is extracted with ethyl acetate. The organic phase obtained by the extraction is dried over anhydrous magnesium sulfate, filtered, and a solution is obtained. The solvent is removed, and the mixture is purified to obtain 2-cyano-6-(1-pyrazole)-pyridine;

[0088] The molar ratio of 2-bromo-6-(1-pyrazole)-pyridine, potassium ferrocyanide and copper iodide is 25.6:16:2.4;

[0089] The synthesis reaction formula of the above 2-cyano-6-(1-pyrazole)-pyridine is as follows:

[0090] ;

[0091] S12, the synthesis of 6-cyano-2,2'-bipyridine specifically comprises the following steps:

[0092] S121, the synthesis of 2,2'-bipyridine-N-oxide, specifically comprising the following steps:

[0093] 2,2'-bipyridine, hydrogen peroxide and trifluoroacetic acid were stirred and reacted at room temperature for 6 hours. After the reaction was completed, sodium hydroxide was added for neutralization and extraction was performed. The obtained organic phase was washed, dried and filtered to obtain 2,2'-bipyridine-N-oxide;

[0094] The molar ratio of the 2,2'-bipyridine to hydrogen peroxide is 2:3.

[0095] The synthesis reaction formula of the above 2,2'-bipyridine-N-oxide is as follows:

[0096] ;

[0097] S122. Under a nitrogen atmosphere, add anhydrous dichloromethane to the 2,2'-bipyridine-N-oxide obtained in step S121, lower the temperature to 0°C, add trimethylsilyl cyanide, and then drop benzoyl chloride. After the dropwise addition is completed, react for 24 hours. After the reaction is completed, add an aqueous sodium carbonate solution, extract with dichloromethane, dry, filter, evaporate under reduced pressure, and purify to obtain 6-cyano-2,2'-bipyridine;

[0098] The molar ratio of the 2,2'-bipyridine-N-oxide to trimethylsilyl cyanide is 1:5.

[0099] The synthesis reaction formula of the above 6-cyano-2,2'-bipyridine is as follows:

[0100] ;

[0101] S13, cyclically treating the 2-cyano-6-(1-pyrazole)-pyridine obtained in step S11 or the 6-cyano-2,2'-bipyridine obtained in step S12 with sodium methoxide under vacuum-nitrogen for 3 times, adding anhydrous methanol, and reacting at room temperature for 1 hour to obtain a reactant;

[0102] S14, adding malonic acid hydrazide to the reactant obtained in step S13, and refluxing the mixture at 72° C. for 5-6 hours. After the reaction is completed, the mixture is cooled to room temperature, filtered, and solid powder is collected;

[0103] S15, adding ethylene glycol to the solid powder obtained in step S14 under a nitrogen atmosphere, reacting at 200° C. for 3-4 hours. After the reaction is completed, cooling to room temperature, diluting and filtering, collecting the solid, and obtaining ligand L1 or L2;

[0104] S16, cyclically treating the 2-cyano-6-(1-pyrazole)-pyridine obtained in step S11 with sodium methoxide under vacuum-nitrogen for 3 times, adding anhydrous methanol, and reacting at room temperature for 1-2 hours to obtain a reactant;

[0105] S17, adding pentanedihydrazine to the reactant obtained in step S16, and refluxing at 72° C. for 5-6 hours. After the reaction is completed, cooling to room temperature, filtering, and collecting solid powder;

[0106] S18, adding ethylene glycol to the solid powder obtained in step S17 under a nitrogen atmosphere, reacting at 200° C. for 3-4 hours. After the reaction is completed, cooling to room temperature, diluting and filtering, collecting the solid, and obtaining ligand L3;

[0107] The molar ratio of one of 2-cyano-6-(1-pyrazole)-pyridine or 6-cyano-2,2'-bipyridine to one of malonic dihydrazide or pentane dihydrazide is 2.5:1.

[0108] S2. Synthesis of double helical Fe(Ⅱ) magnetic complexes:

[0109] Dissolve Fe(OTF)2 or Fe(ClO4)2 and the ligand L1, L2 or L3 obtained in step S1 in acetonitrile, stir and react at room temperature for 3 hours, filter after the reaction, and diffuse the filtrate in gas phase for 7 days to obtain a double helical Fe(II) magnetic complex;

[0110] The molar ratio of one of the ligands L1, L2 or L3 to one of Fe(OTF)2 or Fe(ClO4)2 is 1:1.

[0111] Embodiment 1:

[0112] The embodiment of the present invention provides a double helical Fe (II) magnetic complex, and the double helical Fe (II) magnetic complex has the following chemical expression:

[0113] Fe2(L1)2(X)4;

[0114] Where X is OTF - , and the chemical structure of ligand L1 is:

[0115] .

[0116] The double helical Fe(II) magnetic complex in this embodiment is Fe2(L1)2(OTF)4, which belongs to the orthorhombic crystal system, the space group is Cmce, the unit cell parameters are a = 25.563(4), b = 24.734(4), c = 22.137(4), α = 90, β = 90, γ = 90, ν = 13997(4).

[0117] The present invention also provides a method for preparing the above-mentioned double-helical Fe (II) magnetic complex, comprising the following steps:

[0118] S1. Synthesis of ligand L1:

[0119] 7.83 mmol of 6-cyano-2,2'-bipyridine and 1.76 mmol of sodium methoxide were added to a 50 mL schlenk flask and circulated for 3 times under vacuum-nitrogen, 15 mL of anhydrous methanol was added, the mixture was reacted at room temperature for 1 hour, 3.13 mmol of malonic acid hydrazide was added, the mixture was refluxed at 72°C for 5 hours, and after the reaction, the mixture was cooled to room temperature. The reactant was filtered and the solid powder was collected. The solid powder was added to a 50 mL schlenk flask, and 12 mL of ethylene glycol was added under nitrogen atmosphere. The mixture was reacted at 200°C for 3 hours. After the reaction, the mixture was cooled to room temperature, 200 mL of deionized water was added to dilute the mixture, the mixture was filtered, and the solid powder was collected to obtain ligand L1.

[0120] The synthesis reaction formula of the above ligand L1 is as follows:

[0121] ;

[0122] The synthesis of ligand L1 in this example specifically comprises the following steps:

[0123] Step 1, Synthesis of 6-cyano-2,2'-bipyridine:

[0124] Step (1), synthesis of 2,2'-bipyridine-N-oxide, specifically comprises the following steps:

[0125] 0.05 mol of 2,2'-bipyridine, 0.075 mol of hydrogen peroxide (mass concentration of 30%) and 40 mL of trifluoroacetic acid were added to a 100 mL round-bottom flask, and the mixture was stirred at room temperature for 6 hours. After the reaction was completed, 6 N sodium hydroxide was added to neutralize to pH = 5, and chloroform (4×50 mL) was used for extraction. The obtained organic phase was washed with saturated sodium chloride solution, dried with anhydrous sodium sulfate, and filtered to obtain a white solid product, namely 2,2'-bipyridine-N-oxide, with a yield of 7.5 g (88%).

[0126] Step (2), add 1.74 mmol of 2,2'-bipyridine-N-oxide obtained in step (1) to a 50 mL schlenk flask, add 5 mL of anhydrous dichloromethane under nitrogen atmosphere, lower the temperature to 0°C, add 8.71 mmol of trimethylsilyl cyanide (TMSCN), and then slowly drop 404 uL of benzoyl chloride into the flask. After the dropwise addition is completed, react for 24 hours. After the reaction is completed, add 10 mL of a 10% sodium carbonate aqueous solution, extract with dichloromethane (3×5 mL), dry with anhydrous magnesium sulfate, filter, and remove most of the solvent by vacuum rotary evaporation (100 mbar, 50°C). The crude product is further purified by silica gel column chromatography using dichloromethane / ethyl acetate (v / v = 10:1) as the eluent to obtain a pure product as a white powder, namely 6-cyano-2,2'-bipyridine, with a yield of 285 mg (90%);

[0127] The synthesis reaction formula of the above 6-cyano-2,2'-bipyridine is as follows:

[0128] ;

[0129] Step 2, add 7.83 mmol of 6-cyano-2,2'-bipyridine obtained in step 1 and 1.76 mmol of sodium methoxide into a 50 mL schlenk flask, cycle 3 times under vacuum-nitrogen, add 15 mL of anhydrous methanol, react at room temperature for 1 hour to obtain a reactant;

[0130] Step 3: add 3.13 mmol of malonic acid hydrazide to the reactant obtained in step 2, and reflux for reaction at 72° C. for 5 hours. After the reaction is completed, cool to room temperature, filter, and collect solid powder;

[0131] Step 4: Add the solid powder obtained in step S13 into a 50 mL schlenk flask, and under a nitrogen atmosphere, add 12 mL of ethylene glycol, and react at 200° C. for 3 hours. After the reaction is completed, cool to room temperature, add 200 mL of deionized water to dilute and filter, collect the solid, and obtain ligand L1.

[0132] S2. Synthesis of double helical Fe(Ⅱ) magnetic complexes:

[0133] 0.1 mmol of Fe(OTF)2 and 0.1 mmol of ligand L1 obtained in step S1 were dissolved in acetonitrile, stirred and reacted at room temperature for 3 hours. After the reaction was completed, the mixture was filtered and the filtrate was diffused in the gas phase with ether. After 7 days of diffusion, a double helical Fe(II) magnetic complex was obtained.

[0134] The synthesis reaction formula of the double helical Fe(II) magnetic complex in the embodiment of the present invention is as follows:

[0135] ;

[0136] Where X is OTF - .

[0137] Embodiment 2:

[0138] The embodiment of the present invention provides a double helical Fe (II) magnetic complex, and the double helical Fe (II) magnetic complex has the following chemical expression:

[0139] Fe2(L2)2(X)4;

[0140] Where X is OTF - , and the chemical structure of ligand L2 is:

[0141] .

[0142] The double helical Fe(II) magnetic complex in this embodiment is Fe2(L2)2(OTF)4, which belongs to the monoclinic system, has a space group of C2 / c, and unit cell parameters of a = 21.396(6), b = 19.159(5), c = 23.676(6), α = 90, β = 112.723(6), γ = 90, ν = 8952(4).

[0143] The present invention also provides a method for preparing the above-mentioned double-helical Fe (II) magnetic complex, comprising the following steps:

[0144] S1. Synthesis of ligand L2:

[0145] 7.83 mmol of 2-cyano-6-(1-pyrazole)-pyridine and 1.76 mmol of sodium methoxide were added to a 50 mL schlenk flask and circulated for 3 times under vacuum-nitrogen, 15 mL of anhydrous methanol was added, the mixture was reacted at room temperature for 1 hour, 3.13 mmol of malonic acid hydrazide was added, the mixture was refluxed at 72°C for 5 hours, and after the reaction, the mixture was cooled to room temperature. The reactant was filtered and the solid powder was collected. The solid powder was added to a 50 mL schlenk flask, and 12 mL of ethylene glycol was added under nitrogen atmosphere. The mixture was reacted at 200°C for 3 hours. After the reaction, the mixture was cooled to room temperature, 200 mL of deionized water was added to dilute the mixture, the mixture was filtered, and the solid powder was collected to obtain ligand L2.

[0146] The synthesis reaction formula of the above ligand L2 is as follows:

[0147] ;

[0148] The synthesis of ligand L2 in this embodiment specifically comprises the following steps:

[0149] Step 1, Synthesis of 2-cyano-6-(1-pyrazole)-pyridine:

[0150] Step (1), the synthesis of 2-bromo-6-(1-pyrazole)-pyridine, specifically comprises the following steps:

[0151] 103 mmol of pyrazole and 110 mmol of NaH were added to a 500 mL schlenk flask. After three cycles of vacuum-nitrogen, 200 mL of anhydrous DMSO was added. After stirring at room temperature for 3 hours, 103 mmol of 2,6-dibromopyridine was added and stirred at 160°C for 48 hours. After the reaction was completed and cooled to room temperature, a trace amount of water was added to quench the unreacted NaH. After removing part of the solvent, an appropriate amount of water was added and extracted with ethyl acetate (3×50 mL). The obtained organic phase was further purified by silica gel column chromatography using petroleum ether / ethyl acetate (v / v = 10:1) as the eluent to obtain a pure product as a white powder, namely 2-bromo-6-(1-pyrazole)-pyridine, with a yield of 18.15 g (79.2%).

[0152] Step (2), add 25.6 mmol of 2-bromo-6-(1-pyrazole)-pyridine obtained in step (1), 16 mmol of potassium ferrocyanide and 2.4 mmol of copper iodide into a 250 mL schlenk flask, cycle three times under vacuum-nitrogen, add 60 mL of N-methylimidazole, and react at 160 ° C for 16 hours. After the reaction is completed and cooled to room temperature, add 400 mL of deionized water, extract with ethyl acetate (4×100 mL), dry the obtained organic phase with anhydrous magnesium sulfate, and filter to obtain a solution. After removing the solvent, further purify by silica gel column chromatography with petroleum ether / ethyl acetate (v / v = 4:1) as the eluent to obtain a white solid, namely 2-cyano-6-(1-pyrazole)-pyridine, with a yield of 2.65 g (61%);

[0153] The synthesis reaction formula of the above 2-cyano-6-(1-pyrazole)-pyridine is as follows:

[0154] ;

[0155] Step 2, add 7.83 mmol of 2-cyano-6-(1-pyrazole)-pyridine obtained in step 1 and 1.76 mmol of sodium methoxide into a 50 mL schlenk flask, cycle 3 times under vacuum-nitrogen, add 15 mL of anhydrous methanol, react at room temperature for 1 hour to obtain a reactant;

[0156] Step 3, add 3.13 mmol of malonic acid hydrazide to the reactant obtained in step 2, reflux at 72°C for 5 hours, and after the reaction is completed, cool to room temperature, filter, and collect solid powder;

[0157] Step 4: Add the solid powder obtained in step S13 into a 50 mL schlenk flask, and under a nitrogen atmosphere, add 12 mL of ethylene glycol, and react at 200°C for 3 hours. After the reaction is completed, cool to room temperature, add 200 mL of deionized water to dilute and filter, collect the solid, and obtain ligand L2.

[0158] S2. Synthesis of double helical Fe(Ⅱ) magnetic complexes:

[0159] 0.1 mmol of Fe(OTF)2 or Fe(ClO4)2 and 0.1 mmol of ligand L2 obtained in step S1 were dissolved in acetonitrile, stirred and reacted at room temperature for 3 hours. After the reaction was completed, the mixture was filtered and the filtrate was subjected to gas phase diffusion with ether for 7 days to obtain a double helical Fe(II) magnetic complex.

[0160] The synthesis reaction formula of the double helical Fe(II) magnetic complex in the embodiment of the present invention is as follows:

[0161] ;

[0162] Where X is OTF - .

[0163] Embodiment 3:

[0164] The present invention provides a double helical Fe (II) magnetic complex, the structure and preparation method of which are the same as those of the complex provided in Example 2, except that X in this embodiment is ClO4 - , specifically through a synthesis reaction between Fe(ClO4)2 and ligand L2.

[0165] The double helical Fe(II) magnetic complex in this embodiment is Fe2(L2)2(ClO4)4, which belongs to the monoclinic system, has a space group of C2 / c, and has unit cell parameters of a = 24.041(7), b = 15.365(4), c = 20.765(5), α = 90, β = 111.324(9), γ = 90, ν = 7145(3).

[0166] Embodiment 4:

[0167] The embodiment of the present invention provides a double helical Fe (II) magnetic complex, and the double helical Fe (II) magnetic complex has the following chemical expression:

[0168] Fe2(L3)2(X)4;

[0169] Where X is OTF - , and the chemical structure of ligand L3 is:

[0170] .

[0171] The double helical Fe(II) magnetic complex in this embodiment is Fe2(L3)2(OTF)4, which belongs to the monoclinic system, has a space group of C2 / c, and unit cell parameters of a = 39.625(5), b = 13.524(9), c = 27.189(6), α = 90, β = 110.918(6), γ = 90, ν = 13610(4).

[0172] The present invention also provides a method for preparing the above-mentioned double-helical Fe (II) magnetic complex, comprising the following steps:

[0173] S1. Synthesis of ligand L3:

[0174] 7.83 mmol of 2-cyano-6-(1-pyrazole)-pyridine and 1.76 mmol of sodium methoxide were added to a 50 mL schlenk flask and circulated for 3 times under vacuum-nitrogen, 15 mL of anhydrous methanol was added, and the mixture was reacted at room temperature for 1 hour, 3.13 mmol of pentane dihydrazine was added, and the mixture was refluxed at 72°C for 5 hours. After the reaction was completed, the mixture was cooled to room temperature, the reactant was filtered, and the solid powder was collected. The mixture was added to a 50 mL schlenk flask, and 12 mL of ethylene glycol was added under nitrogen atmosphere, and the mixture was reacted at 200°C for 3 hours. After the reaction was completed, the mixture was cooled to room temperature, 200 mL of deionized water was added to dilute the mixture, and the solid powder was collected to obtain ligand L3.

[0175] The synthesis reaction formula of the above ligand L3 is as follows:

[0176] ;

[0177] The synthesis of ligand L3 in this example specifically comprises the following steps:

[0178] Step 1, Synthesis of 2-cyano-6-(1-pyrazole)-pyridine:

[0179] Step (1), the synthesis of 2-bromo-6-(1-pyrazole)-pyridine, specifically comprises the following steps:

[0180] 103 mmol of pyrazole and 110 mmol of NaH were added to a 500 mL schlenk flask. After three cycles of vacuum-nitrogen, 200 mL of anhydrous DMSO was added. After stirring at room temperature for 3 hours, 103 mmol of 2,6-dibromopyridine was added. The mixture was stirred at 160°C for 48 hours. After the reaction was completed and cooled to room temperature, a trace amount of water was added to quench the remaining NaH. After removing part of the solvent, an appropriate amount of water was added and extracted with ethyl acetate (3×50 mL). The obtained organic phase was further purified by silica gel column chromatography using petroleum ether / ethyl acetate (v / v = 10:1) as the eluent to obtain a pure product as a white powder, namely 2-bromo-6-(1-pyrazole)-pyridine, with a yield of 18.15 g (79.2%).

[0181] Step (2), add 25.6 mmol of 2-bromo-6-(1-pyrazole)-pyridine obtained in step (1), 16 mmol of potassium ferrocyanide and 2.4 mmol of copper iodide into a 250 mL schlenk flask, cycle 3 times under vacuum-nitrogen, add 60 mL of N-methylimidazole, and react at 160°C for 16 hours. After the reaction is completed and cooled to room temperature, add 400 mL of deionized water, extract with ethyl acetate (4×100 mL), dry the obtained organic phase with anhydrous magnesium sulfate, and filter to obtain a solution. After removing the solvent, further purify by silica gel column chromatography with petroleum ether / ethyl acetate (v / v = 4:1) as the eluent to obtain a white solid, namely 2-cyano-6-(1-pyrazole)-pyridine, with a yield of 2.65 g (61%);

[0182] The synthesis reaction formula of the above 2-cyano-6-(1-pyrazole)-pyridine is as follows:

[0183] ;

[0184] Step 2, add 7.83 mmol of 2-cyano-6-(1-pyrazole)-pyridine obtained in step 1 and 1.76 mmol of sodium methoxide into a 50 mL schlenk flask, cycle 3 times under vacuum-nitrogen, add 15 mL of anhydrous methanol, react at room temperature for 1 hour to obtain a reactant;

[0185] Step 3: add 3.13 mmol of pentanedihydrazine to the reactant obtained in step 2, and reflux the mixture at 72°C for 5 hours. After the reaction is completed, cool the mixture to room temperature, filter the mixture, and collect the solid powder.

[0186] Step 4: Add the solid powder obtained in step S14 into a 50 mL schlenk flask, and under a nitrogen atmosphere, add 12 mL of ethylene glycol, and react at 200°C for 3 hours. After the reaction is completed, cool to room temperature, add 200 mL of deionized water to dilute and filter, collect the solid, and obtain ligand L3.

[0187] S2. Synthesis of double helical Fe(Ⅱ) magnetic complexes:

[0188] 0.1 mmol of Fe(OTF)2 and 0.1 mmol of ligand L3 obtained in step S1 were dissolved in acetonitrile, stirred and reacted at room temperature for 3 hours. After the reaction was completed, the mixture was filtered and the filtrate was diffused in ether for 7 days to obtain a double helical Fe(II) magnetic complex.

[0189] The synthesis reaction formula of the double helical Fe(II) magnetic complex in the embodiment of the present invention is as follows:

[0190] ;

[0191] Where X is OTF - .

[0192] The structures of the double-helical Fe(II) magnetic complexes and ligands L1, L2 and L3 prepared in Examples 1-4 of the present invention are studied below:

[0193] 1. NMR testing and analysis of ligands L1, L2 and L3:

[0194] The NMR spectra of ligands L1, L2 and L3 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 3 As shown, through Figure 1-Figure 3 It shows that the nuclear magnetic resonance hydrogen spectra of the three ligands can correspond to each other on the spectrum. In addition to the solvent peak, there are no other impurity peaks, 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 3It can be seen that the H NMR chemical shifts of the three ligands are as follows: Ligand L1 δ = 14.61 (s, 2H), 8.90 (d, J = 8.0 Hz,2H), 8.72 (d, J = 4.2 Hz, 2H), 8.48 (d, J = 7.0 Hz, 2H), 8.08 (t, J = 8.3 Hz,2H), 8.02 (t, J = 7.7 Hz, 2H), 7.51 (t, J = 5.0 Hz, 2H), 4.25 (s, 2H); Ligand L2 δ = 14.61 (s, 2H), 9.17 (d, J = 2.3 Hz, 2H), 8.13 (t, J = 8.0 Hz, 2H),7.98 (d, J = 7.0 Hz, 2H), 7.91 (d, J = 7.5 Hz, 2H), 7.88 (t, J = 10.5 Hz, 2H), 6.67 (d, J = 4.0 Hz, 2H), 4.24 (s, 2H).

[0195] 2. Infrared spectrum test and analysis of double helical Fe(Ⅱ) magnetic complexes:

[0196] The infrared spectra of the double-helical Fe(II) magnetic complexes synthesized in Examples 1-4 of the present invention were measured on a Nicolet 6700 Fourier transform infrared spectrometer equipped with an iTR™-ATR accessory, with a test wavelength range of 4000-500 cm -1 The test results are as follows: Figure 4 As shown, through Figure 4 The infrared data of the four complexes are basically similar, among which, 3000-3500cm -1 is the stretching vibration peak of benzene ring CH; 1500-1700 cm -1 The strong absorption is the vibration peak of C=N; 650-800 cm -1 It is the bending vibration peak of CH.

[0197] 3. Single crystal structure test and analysis of double helical Fe(Ⅱ) magnetic complexes:

[0198] Single crystal X-ray diffraction data were collected by a Bruker Apex II CCD diffractometer using graphite monochromated Mo-Kα radiation (λ = 0.71073 Å). In the Olex2 package, the structure was solved using SHELXT (direct method) and all non-hydrogen atoms were refined with anisotropic thermal parameters of F2 using SHELXL (full matrix least squares technique). 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 to least squares using the full matrix method. The test results are shown in Figure 5 As shown, through Figure 5 Structural analysis shows that all four complexes have a double helix structure, in which the iron ions are located in the N6 coordination environment at both ends of the ligand, which is conducive to the compounds showing 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 anions are OTF - or ClO4 - The single crystal structure information of the complexes provided by Example 1, Example 3 and Example 4 of the present invention are shown in Tables 1 to 3 below.

[0199] ;

[0200] ;

[0201] ;

[0202] From the results in Tables 1 to 3, it can be seen that for the complex Fe2(L1)2(OTF)4, in the temperature range of 150 K-273 K, its average Fe-N bond length is between 2.193-2.199 Å, corresponding to high-spin iron ions, which corresponds to the fact that the complex does not undergo spin conversion in this range. The subsequent magnetic test also shows that the XmT value of the complex does not change significantly in this temperature range, confirming that the complex has no spin conversion property; for the complex Fe2(L2)2(ClO4)4, in the temperature range of 113K-200 K, its average Fe-N bond length gradually changes from 1.84 Å (corresponding to low-spin Fe ions) to 2.195 Å (corresponding to high-spin Fe), indicating that the complex undergoes spin conversion in this temperature range, which is also consistent with the increase in the XmT value of the complex in this temperature range; the Fe-N bond lengths of the complex Fe2(L3)2(OTF)4 at 150 K and 194 K are 2.126 Å and 2.186 Å, corresponding to high-spin iron ions, also indicate that the complex does not undergo spin conversion, which is also consistent with the variable temperature XmT test results.

[0203] 4. Thermal stability test and analysis of double helical Fe(Ⅱ) magnetic complexes:

[0204] The thermal stability data was obtained by placing the complexes provided in Examples 1-4 of the present invention in a thermogravimetric analyzer for temperature testing. The test results are shown in FIG. Figure 6 As shown, through Figure 6 It can be seen that the four complexes all show a slight weight loss below 100°C, which is mainly due to the loss of some solvent molecules during the heating process; the thermogravimetric performance of the complexes shows a platform at 100-400°C, indicating that the complexes are stable within this temperature range; after 400°C, the compounds slowly lose weight, indicating that the complexes begin to decompose, until they are completely transformed into metal oxides at 550°C.

[0205] 5. Temperature-dependent magnetic susceptibility test and analysis of double-helical Fe(Ⅱ) magnetic complexes:

[0206] The magnetism of the complexes provided in Examples 1-4 of the present invention was tested using a Quantum Design MPMS-XL-7 SQUIDmagnetometer. 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 of all polycrystalline samples was measured below 100 K to check for ferromagnetic impurities. The AC magnetic susceptibility test used an AC field of 3 Oe and an oscillation frequency of 0.01~1500 Hz. All data were diamagnetic corrected according to the Pascal constant table. The magnetic test results are shown in Figure 2. Figure 7 As shown, through Figure 7The results show that: within the test temperature range, the Fe ions of the complex Fe2(L1)2(OTF)4 are all in the high-spin state, indicating that the complex does not exhibit spin conversion properties; before 150 K, one of the two Fe ions of the complex Fe2(L2)2(OTF)4 is in the high-spin state and the other is in the low-spin state, and the magnetic susceptibility of the complex increases slowly from 150 to 170 K, indicating that the complex undergoes spin conversion, and the low-spin iron ions are converted to the high-spin state; also before 150 K, one of the two Fe ions of the complex Fe2(L2)2(ClO4)4 is in the high-spin state and the other is in the low-spin state, and the magnetic susceptibility of the complex increases slowly from 150 to 170 K, indicating that the complex undergoes spin conversion, and the low-spin iron ions are converted to the high-spin state. The magnetic susceptibility of the K complex increases slowly, indicating that the complex undergoes spin conversion, and the low-spin iron ions are converted into high-spin states; in the Fe2(L3)2(OTF)4 complex within the test temperature range, the Fe ions are all in a high-spin state, indicating that the complex does not exhibit spin conversion properties, indicating that increasing the length of the flexible chain can alleviate the structural tension inside the double helix to a certain extent, but also stabilizes the iron ions in a high-spin state, thereby quenching the spin conversion properties of the complex. The specific conclusions are as follows:

[0207] (1) A double helical Fe2(L1)2(OTF)4 complex obtained by the present invention using ligand L1. Magnetic tests show that the complex does not exhibit spin state transition behavior;

[0208] (2) The present invention changes the terminal substituents and uses the ligand L2 to obtain the complex Fe2(L2)2(OTF)4, which exhibits a one-step slow spin conversion phenomenon at 150K, indicating that the spin conversion property of the complex is activated;

[0209] (3) The present invention adopts OTF - Anion replaced by ClO4 - anion, the obtained complex Fe2(L2)2(ClO4)4 also exhibits one-step spin conversion properties near 150 K, indicating that the change of anion will not affect the spin conversion properties of the system;

[0210] (4) In the present invention, by increasing the length of the flexible chain, the complex Fe2(L3)2(OTF)4 obtained by using the ligand L3 did not show the spin conversion phenomenon within the test temperature range, indicating that the spin conversion property of the complex was quenched.

[0211] The above results indicate that the spin conversion properties of the double-helix Fe2 complex prepared by the present invention are mainly regulated by the length of the side end groups and the flexible chains. Increasing the length of the flexible chains can alleviate the structural tension inside the double helix to a certain extent, but also stabilize the iron ions in a high-spin state, thereby quenching the spin conversion properties of the complex.

[0212] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for preparing a double-helical Fe (II) magnetic complex, wherein the double-helical Fe (II) magnetic complex has the following chemical expression: ； in, L is ligand L1, L2 or L3, X is OTF - or ClO4 - , and the structural formulas of ligands L1, L2 and L3 are shown below: Ligand L1; Ligand L2; Ligand L3; It is characterized by comprising the following steps: S1. Synthesis of ligand L1, L2 or L3: 2-cyano-6-(1-pyrazole)-pyridine or 6-cyano-2,2'-bipyridine and sodium methoxide are cycled three times under vacuum-nitrogen, anhydrous methanol is added, the reaction is carried out at room temperature for 1-2 hours, malonic hydrazide is added, reflux reaction is carried out at 72°C for 5-6 hours, after the reaction is completed, the reaction is cooled to room temperature, filtered, and solid powder is collected, ethylene glycol is added under nitrogen atmosphere, the reaction is carried out at 200°C for 3-4 hours, after the reaction is completed, the reaction is cooled to room temperature, diluted and filtered, and the solid is collected to obtain ligand L1 or L2; 2-cyano-6-(1-pyrazole)-pyridine and sodium methoxide were cycled for 3 times under vacuum-nitrogen, anhydrous methanol was added, the reaction was carried out at room temperature for 1-2 hours, pentane dihydrazine was added, refluxed at 72°C for 5-6 hours, after the reaction was completed, cooled to room temperature, filtered, and solid powder was collected, ethylene glycol was added under nitrogen atmosphere, reacted at 200°C for 3-4 hours, after the reaction was completed, cooled to room temperature, diluted and filtered, and solid was collected to obtain ligand L3; The molar ratio of one of 2-cyano-6-(1-pyrazole)-pyridine or 6-cyano-2,2'-bipyridine to one of malonic dihydrazide or pentane dihydrazide is 2.5:1; S2. Synthesis of double helical Fe(Ⅱ) magnetic complexes Dissolve Fe(OTF)2 or Fe(ClO4)2 and the ligand L1, L2 or L3 obtained in step S1 in acetonitrile, stir and react at room temperature for 3 hours, filter after the reaction, and diffuse the filtrate in gas phase for 7 days to obtain a double helical Fe(II) magnetic complex; The molar ratio of one of the ligands L1, L2 or L3 to one of Fe(OTF)2 or Fe(ClO4)2 is 1:

1.

2. The method for preparing a double-helical Fe(II) magnetic complex according to claim 1, characterized in that: The double helical Fe(II) magnetic complex is Fe2(L1)2(OTF)4, belongs to the orthorhombic crystal system, has a space group of Cmce, and has unit cell parameters of a = 25.563(4), b = 24.734(4), c = 22.137(4), α = 90, β = 90, γ = 90, ν = 13997(4).

3. The method for preparing a double-helical Fe(II) magnetic complex according to claim 1, characterized in that: The double helical Fe(II) magnetic complex is Fe2(L2)2(ClO4)4, belongs to the monoclinic crystal system, has a space group of C2 / c, and has unit cell parameters of a = 24.041(7), b = 15.365(4), c = 20.765(5), α = 90, β = 111.324(9), γ = 90, ν = 7145(3).

4. The method for preparing a double-helical Fe(II) magnetic complex according to claim 1, characterized in that: The double helical Fe(II) magnetic complex is Fe2(L2)2(OTF)4, belongs to the monoclinic crystal system, has a space group of C2 / c, and has unit cell parameters of a = 21.396(6), b = 19.159(5), c = 23.676(6), α = 90, β = 112.723(6), γ = 90, ν = 8952(4).

5. The method for preparing a double-helical Fe(II) magnetic complex according to claim 1, characterized in that: The double helical Fe(II) magnetic complex is Fe2(L3)2(OTF)4, belongs to the monoclinic crystal system, has a space group of C2 / c, and has unit cell parameters of a = 39.625(5), b = 13.524(9), c = 27.189(6), α = 90, β = 110.918(6), γ = 90, ν = 13610(4).

6. The method for preparing a double-helical Fe(II) magnetic complex according to claim 1, characterized in that: Step S1 comprises the following steps: S11, Synthesis of 2-cyano-6-(1-pyrazole)-pyridine; S12, Synthesis of 6-cyano-2,2'-bipyridine; S13, cyclically treating the 2-cyano-6-(1-pyrazole)-pyridine obtained in step S11 or the 6-cyano-2,2'-bipyridine obtained in step S12 with sodium methoxide under vacuum-nitrogen for 3 times, adding anhydrous methanol, and reacting at room temperature for 1-2 hours to obtain a reactant; S14, adding malonic acid hydrazide to the reactant obtained in step S13, and refluxing the mixture at 72° C. for 5-6 hours. After the reaction is completed, the mixture is cooled to room temperature, filtered, and solid powder is collected; S15, adding ethylene glycol to the solid powder obtained in step S14 under a nitrogen atmosphere, reacting at 200° C. for 3-4 hours. After the reaction is completed, cooling to room temperature, diluting and filtering, collecting the solid, and obtaining ligand L1 or L2; S16, cyclically treating the 2-cyano-6-(1-pyrazole)-pyridine obtained in step S11 with sodium methoxide under vacuum-nitrogen for 3 times, adding anhydrous methanol, and reacting at room temperature for 1-2 hours to obtain a reactant; S17, adding pentanedihydrazine to the reactant obtained in step S16, and refluxing at 72° C. for 5-6 hours. After the reaction is completed, cooling to room temperature, filtering, and collecting solid powder; S18, adding ethylene glycol to the solid powder obtained in step S17 under a nitrogen atmosphere, reacting at 200° C. for 3-4 hours. After the reaction is completed, cooling to room temperature, diluting and filtering, collecting the solid, and obtaining ligand L3; The molar ratio of one of 2-cyano-6-(1-pyrazole)-pyridine or 6-cyano-2,2'-bipyridine to one of malonic dihydrazide or pentane dihydrazide is 2.5:

1.

7. The method for preparing a double-helical Fe(II) magnetic complex according to claim 6, characterized in that: Step S11 specifically includes the following steps: S111, Synthesis of 2-bromo-6-(1-pyrazole)-pyridine; Pyrazole and sodium hydride were cycled three times under vacuum-nitrogen, then anhydrous dimethyl sulfoxide was added, stirred and reacted at room temperature for 3 hours, then 2,6-dibromopyridine was added, stirred and reacted at 160° C. for 48 hours, and after the reaction was completed, the mixture was cooled to room temperature, the unreacted sodium hydride was quenched, and the organic phase obtained by extraction with ethyl acetate was purified to obtain 2-bromo-6-(1-pyrazole)-pyridine; The molar ratio of pyrazole to 2,6-dibromopyridine is 1:1; S112, circulate the 2-bromo-6-(1-pyrazole)-pyridine, potassium ferrocyanide and copper iodide obtained in step S111 under vacuum-nitrogen for 3 times, then add N-methylimidazole, react at 160° C. for 16-20 hours, and after the reaction is completed, cool to room temperature, add water, and extract with ethyl acetate, dry the organic phase obtained by extraction with anhydrous magnesium sulfate, filter to obtain a solution, remove the solvent, and purify to obtain 2-cyano-6-(1-pyrazole)-pyridine; The molar ratio of the 2-bromo-6-(1-pyrazole)-pyridine, potassium ferrocyanide and copper iodide is 25.6:16:2.

4.

8. The method for preparing a double-helical Fe(II) magnetic complex according to claim 6, characterized in that: Step S12 specifically includes the following steps: S121, Synthesis of 2,2'-Bipyridine-N-oxide 2,2'-bipyridine, hydrogen peroxide and trifluoroacetic acid were stirred and reacted at room temperature for 6 hours. After the reaction was completed, sodium hydroxide was added to neutralize to pH=5, and extraction was performed. The obtained organic phase was washed, dried and filtered to obtain 2,2'-bipyridine-N-oxide; The molar ratio of 2,2'-bipyridine to hydrogen peroxide is 2:3; S122. Under a nitrogen atmosphere, add anhydrous dichloromethane to the 2,2'-bipyridine-N-oxide obtained in step S121, lower the temperature to 0°C, add trimethylsilyl cyanide, and then drop benzoyl chloride. After the dropwise addition is completed, react for 15-24 hours. After the reaction is completed, add an aqueous sodium carbonate solution, extract with dichloromethane, dry, filter, evaporate under reduced pressure, and purify to obtain 6-cyano-2,2'-bipyridine; The molar ratio of the 2,2'-bipyridine-N-oxide to trimethylsilyl cyanide is 1:5.

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