Quinoline acylhydrazone ligand, Fe (II) spin crossover complex thereof and synthesis method of Fe (II) spin crossover complex

Abstract

The invention discloses a quinoline acylhydrazone ligand, a Fe (II) spin crossover complex of the quinoline acylhydrazone ligand and a synthesis method of the Fe (II) spin crossover complex. The quinoline acylhydrazone ligand is (E)-4-bromine-N '-(quinoline-8-methylene) benzoyl hydrazine, the structural formula of the quinoline acylhydrazone ligand is # imgabs 0 #, and the structural formula of the complex is # imgabs 1 #. The coordination capacity of the ligand and metal is strong enough, the complex is not easy to oxidize in air, not easy to dissociate in a solution and good in acid resistance, the complex is low in spinning, meanwhile, the complex is suitable for using photoacid to switch the spinning state in the solution, and the complex is suitable for the fields of spin crossover molecular switches, acid-base stimulation sensors and the like.

Description

Technical Field

[0001] The invention belongs to the field of inorganic coordination chemistry and relates to a quinoline acylhydrazone ligand and its Fe(II) spin cross complex and a synthesis method. Background Art

[0002] Spin Crossover (SCO) is a concept in coordination chemistry, which refers to the 3d 4 -3d 7 Spin-crossover phenomena of the mononuclear Mn III complex tuned by metal dithiolene counteranions,2014,43(9):3783-3791].

[0003] The complex is composed of an inorganic or organic ligand with multiple coordinating atoms (usually nitrogen atoms and oxygen atoms) and a central metal ion. In the coordination process, the coordinating atoms on the ligand provide lone pairs of electrons, while the metal ion provides an empty d orbital. The two are combined together by Lewis addition to form a coordination bond. When the field strength of the ligand is a non-spherically symmetrical field, such as an octahedral field, taking Fe(Ⅱ) as an example, its five d orbitals with the same energy and degenerate energy levels will undergo energy level splitting to form two new e g Track and t 2g orbitals, the energy difference between the two orbitals is called the crystal field splitting energy Δ o , its size depends on the size of the ligand field strength. The larger the field strength, the larger the Δ o The larger the value, the smaller the value. At this time, the d electrons of the central metal ion will be redistributed on the e g Track and t 2g In the orbital, there is an electron pairing energy P between d electrons. o When <P, all electrons are arranged in pairs at t 2g orbit, forming a low spin state LS (Low Spin, t 2g 6 e g 0 ); when Δ o >P, the electrons begin to be arranged in e g orbit, forming a high spin state HS (High Spin, t 2g 4 e g 2 ); when Δ o=P, electrons can easily jump between the two orbits and achieve spin state conversion.

[0004] Acylhydrazone is essentially a Schiff base. Schiff base is a type of organic compound with a carbon-nitrogen double bond structure in which a nitrogen atom is connected to a carbon atom by a double bond. The general structural formula can be expressed as R′R″C=NR, where R′ and R″ are hydrogen atoms or organic groups, and R is an organic group. Schiff bases are usually produced by the dehydration condensation reaction of primary amines (-NH2) and aldehydes (-CHO) or ketones, while acylhydrazones are produced by the reaction of hydrazide compounds (R1CONHNH2) with aldehydes. This reaction is also called Schiff base reaction.

[0005] However, there are very few reports on quinoline acylhydrazone at home and abroad, with no more than 15 reports, and most of them are quinoline acylhydrazone coordinated with other transition metal ions such as Zn(Ⅱ), U(Ⅵ), Al(Ⅲ), Cd(Ⅱ), Pd(Ⅱ), Ag(Ⅰ), Mg(Ⅱ), etc., used as fluorescence and colorimetric chemical sensors to detect some of the above metal ions or to study the antibacterial properties of quinoline acylhydrazone complexes against Escherichia coli and Staphylococcus aureus, but not used to study spin crossover properties. The only report on quinoline acylhydrazone coordinated with Fe(Ⅱ) is still to detect Fe(Ⅱ) using colorimetric chemical sensors, as shown below:

[0006] (A novel quinoline derivative as dual chemosensor for selectivesensing of Al 3+ by fluorescent and Fe 2+ by colorimetric methods, 2021,1231:129965).

[0007] In addition, photoacid is a type of spiropyran organic compound. When exposed to light of a specific wavelength in a protic solvent (water, methanol), its structure will undergo isomerization from an open-ring form to a closed-ring form, while releasing protons and increasing its acidity. When in the dark, its structure will reversibly recover from a closed-ring form to an open-ring form, while withdrawing protons and reducing its acidity. Summary of the invention

[0008] The purpose of the present invention is to provide a quinoline acylhydrazone ligand and its Fe(II) spin cross complex and a synthesis method. The present invention synthesizes a novel quinoline acylhydrazone ligand by using quinoline-8-carboxaldehyde and 4-bromobenzoylhydrazide, and reacts with Fe 2+The coordination forms a complex, and the formed quinoline acylhydrazone Fe(Ⅱ) complex has potential applications in spin crossover molecular switches in solution and acid-base response sensors.

[0009] The technical solution for achieving the purpose of the present invention is as follows:

[0010] The quinoline hydrazone ligand is (E)-4-bromo-N'-(quinoline-8-methylene)benzoylhydrazide, and its structural formula is:

[0011]

[0012] The synthesis method of the above-mentioned quinoline acylhydrazone ligand has the following reaction formula:

[0013]

[0014] The specific steps are as follows:

[0015] Quinoline-8-carboxaldehyde and 4-bromobenzoylhydrazide are used as raw materials, ethanol is used as a reaction solvent, and the reaction is stirred and refluxed. After the reaction is completed, the solvent is removed by rotary evaporation to obtain a quinoline acylhydrazone ligand KL-Br.

[0016] Preferably, the molar ratio of quinoline-8-carboxaldehyde to 4-bromobenzohydrazide is 1:1.

[0017] Preferably, the reflux reaction temperature is 90±5° C. and the reaction time is 12 to 24 h.

[0018] The present invention provides a quinoline acylhydrazone Fe (II) complex, which is a KL-Br-Fe (II) complex, and its structural formula is

[0019]

[0020] The synthesis method of the above-mentioned quinoline acylhydrazone Fe (II) complex comprises the following specific steps:

[0021] (1) Triethylamine is added dropwise to a methanol solution of quinoline acylhydrazone ligand KL-Br to remove protons;

[0022] (2) Dissolve Fe(ClO4)2·6H2O in methanol, then add L-ascorbic acid to 3+ Reduction to Fe 2+ ;

[0023] (3) The solution of step (2) and the solution of step (1) are stirred and mixed uniformly, and allowed to stand at room temperature to allow the solvent to evaporate slowly, thereby precipitating KL-Br-Fe(II) complex crystals.

[0024] Preferably, in step (3), the molar ratio of the quinoline acylhydrazone ligand to Fe(ClO4)2·6H2O is 2:1.

[0025] Furthermore, the present invention also provides the use of the above-mentioned quinoline acylhydrazone Fe (II) complex in the preparation of a spin-crossing molecular switch or an acid-base stimulation sensor.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] (1) The quinoline acylhydrazone ligand has extremely good solubility in common organic solvents (such as methanol) and can be completely dissolved at room temperature by ultrasound or slight stirring without heating. The saturation concentration is high, and the ligand is easy to synthesize with high yield and high purity. It brings great convenience to the preparation of the complex and is also suitable for rapid industrial mass production, further improving the synthesis efficiency.

[0028] (2) Whether in the crystalline state or in solution, the quinoline acylhydrazone Fe(II) complex is not easily oxidized when exposed to air. The solution can remain green for a long time, and the crystals are always dark green without yellow spots when observed under a microscope. In addition, the complex does not need to be in a deoxygenated environment when prepared. In contrast, Fe(II) complexes with other types of ligands are more easily oxidized. Therefore, this characteristic of the quinoline acylhydrazone Fe(II) complex is not only simple to prepare, but also very easy to store for a long time, reducing the operation and storage costs.

[0029] (3) Quinoline acylhydrazone Fe(II) complex has a relatively small tendency to spontaneously dissociate in solution and is more acid-resistant than other types of Fe(II) complexes, that is, it dissociates to a lesser extent when exposed to acid, making it suitable for studying its spin-crossing properties in solution.

[0030] (4) The coordination ability of the quinoline acylhydrazone ligand is extremely strong, and the growth rate of the complex crystal is extremely fast, not only for Fe(Ⅱ), but also for other metals such as Zn(Ⅱ). This greatly reduces the time cost of complex preparation and brings convenience to other subsequent testing and research. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The figure is a schematic diagram of the existing method of detecting Fe(II) by using a colorimetric chemical sensor coordinated with quinoline acylhydrazone and Fe(II).

[0032] Figure 2 This is the H NMR spectrum of the quinoline acylhydrazone ligand KL-Br.

[0033] Figure 3 This is the infrared spectrum of quinoline acylhydrazone ligand KL-Br.

[0034] Figure 4 This is the crystal structure diagram of the KL-Br-Fe complex, where Fe: green; N: blue; O: red; Br: orange; C: gray; H: white.

[0035] Figure 5 This is the temperature-dependent molar magnetic susceptibility diagram of the KL-Br complex.

[0036] Figure 6 PXRD stacking diagrams of measured, simulated and heteromorphic Zn(Ⅱ) complexes of KL-Br complex.

[0037] Figure 7 This is the infrared stacking diagram of KL-Br and KL-Br-Fe.

[0038] Figure 8 This is the thermogravimetric curve of KL-Br complex.

[0039] Fig. 9 The UV spectrum and on / off diagram of the spin state switching of the Fe(Ⅱ) complex driven by photoacid in solution. DETAILED DESCRIPTION

[0040] The present invention is further described in detail below in conjunction with specific embodiments and drawings.

[0041] Example 1

[0042] 1. Synthesis of quinoline acylhydrazone ligand and its Fe(Ⅱ) spin cross complex:

[0043] (1) Synthesis steps of ligand KL-Br: Quinoline-8-carboxaldehyde (1.572 g, 10 mmol) and 4-bromobenzoylhydrazide (2.15 g, 10 mmol) were mixed and added to a 250 mL flask, and ethanol (50 mL) was added as a solvent. The mixture was heated and stirred at 90° C. for 24 h under reflux, and then the solvent was removed by a rotary evaporator to obtain a yellow solid with a yield of 95%. Its H NMR spectrum is shown as follows: Figure 2 shown.

[0044]

[0045] (2) Synthesis steps of complex KL-Br-Fe(Ⅱ): Weigh 0.2 mmol (71 mg) of KL-Br ligand into a beaker, add 20 mL of methanol and stir to fully dissolve it, and then add 2 drops of triethylamine to mix well; weigh 0.1 mmol (36 mg) of Fe(ClO4)2·6H2O into a centrifuge tube, add 3 mL of methanol and shake to dissolve it. At this time, the solution is yellow. Then add 1 mg of L-ascorbic acid and continue to shake until the solution turns colorless; pour the metal solution in the centrifuge tube into a beaker, stir and mix it with the ligand, and seal the beaker with plastic wrap. Finally, use a needle to poke several small holes in the plastic wrap and leave it at room temperature for several hours. Dark green block crystals will precipitate at the bottom of the beaker, which is the complex KL-Br-Fe(Ⅱ).

[0046] 2. Infrared characterization

[0047] The infrared spectrum data was obtained by using a Vacuum FT-IR Spectrometer with a test range of 4000 to 400 cm -1 The infrared spectrum of the ligand is shown in Figure 3 As shown, 1650cm -1 The strong characteristic peak at 1600 cm-1 is the stretching vibration of amide C=O, which belongs to the amide I band. -1 Nearby is the in-plane bending vibration of the NH on the amide, which belongs to the amide II band; the skeleton stretching vibration of the aromatic ring and the stretching vibration of C=C on the quinoline ring belong to 1600cm -1 In the structure of KL-Br, since the Br atom is directly connected to the benzene ring, there are stretching vibrations of CX and the skeleton stretching vibrations of the aromatic ring at the same time, which will affect each other. Therefore, the spectrum does not show the stretching vibration peak of pure CX, but appears in the form of connecting to the benzene ring, that is, the yellow area in the figure (bromobenzene), 1060cm -1 The characteristic absorption peak of KL-Br halogen atom is at 3300-3020 cm -1 The basic structure of KL-Br has been roughly characterized. Other characteristic absorption bands in the infrared spectrum are mostly CH vibrations on aromatic rings and quinoline rings, as well as vibrations of C=N and NN.

[0048] 3. Variable temperature molar susceptibility

[0049] The variable temperature molar susceptibility data were obtained using a Quantum Design MPMS-3SQUID-VSM at 2 K min -1 The scanning rate was measured at a magnetic field strength of 1T. The temperature measurement range of the KL-Br complex was 100-400K. The results are as follows Figure 5 As shown in the figure, the magnetic test results of the complex show that the KL-Br complex has no spin crossover phenomenon within the test temperature range, and Fe(Ⅱ) always maintains a low spin, indicating that temperature is not a factor affecting the spin state of the KL-Br complex. The magnetic susceptibility value within this temperature range can be reproduced in the subsequent cooling-heating cycle, which is reversible.

[0050] 3. Powder diffraction test

[0051] Powder diffraction (PXRD) data were obtained by Rigaku Ultimate IV powder diffractometer. Figure 6The PXRD spectrum shows that the powder diffraction results of the KL-Br complex match the single crystal X-ray diffraction simulation results, and there are almost no impurity peaks, indicating that the structure of the obtained quinoline acylhydrazone complex is consistent with the measured single crystal structure, which guarantees the accuracy of other tests. The powder diffraction results of the Zn complex and Fe(Ⅱ) complex of the quinoline acylhydrazone ligand are also basically consistent, indicating that the coordination characteristics of Zn and Fe(Ⅱ) with the quinoline acylhydrazone ligand are roughly similar, which belongs to the heterogeneous isomorphism phenomenon. They have the same molecular structure and crystal stacking characteristics.

[0052] 4. Infrared stacking diagram

[0053] Figure 7 The infrared stacking diagram of KL-Br ligand and complex shows that the free KL-Br ligand before coordination exists in a keto structure, with a characteristic absorption band at 1650cm -1 The stretching vibration peak of C=O nearby is called the amide I band. After coordination, the band will move to the low wave number direction, and the peak intensity will decrease (blue area in the figure). Since the ligand needs to be deprotonated to coordinate with the metal, it exists in the enol structure after coordination, at 1350cm -1 New CO will appear in the spectral bands of nearby complexes. - The absorption peaks (yellow area in the figure) can be used as signs to judge and distinguish before and after the alignment by identifying these two characteristic absorption peaks.

[0054] 5. Thermogravimetric analysis

[0055] Thermogravimetric data were recorded by a Mettler-Toledo TGA / SDTA851e thermal analyzer. Figure 8 The thermogravimetric curve shows that the complex is very stable below 300℃, with only a small mass loss caused by trace impurities attached to the sample surface, which shows that the KL-Br complex contains almost no solvent molecules and the sample is very dry. The KL-Br complex decomposes 70% at around 320℃, and continues to decompose slowly by 10% as the temperature rises.

[0056] 6. UV spectra and on / off diagrams of spin-state switching of Fe(Ⅱ) complexes driven by photoacid in solution

[0057] The 10 -4 3 mL of each 10 mol / L complex solution was placed in a quartz cuvette, and a small amount of iron powder was added to the cuvette to prevent oxidation. The first measurement was performed respectively; then 300-600 μL (1-2 eq) 10 -3 10 μL of methanol solution of photoacid was irradiated under a xenon lamp with a wavelength of 435 nm until the solution turned colorless or light yellow, and then measured for the second time; 60 to 105 μL (2 to 3.5 eq) of 10 -2The ligand methanol solution was allowed to stand in the dark to recover until the solution turned green, and then measured for the third time; then it was illuminated and recovered, and the test was repeated in this way.

[0058] Depend on Fig. 9 It can be seen that the initial strong absorption peak of the complex near 672nm originates from Fe Ⅱ (dπ)→L - (pπ * ) charge transfer transition, this absorption peak is the characteristic absorption peak of Fe(Ⅱ) in the low spin state, which corresponds to the spin state of the quinoline acylhydrazone complex in the solid phase. The spin state switching of the quinoline acylhydrazone Fe(Ⅱ) complex in the solution driven by photoacid is very successful. After the initial complex solution is added with photoacid and illuminated, the released protons almost completely dissociate the complex, and at this time the initial low spin strong absorption peaks all decrease and turn into high spin; after adding ligands and restoring the solution in the dark, the photoacid takes back the protons, the free ligands and metals are re-coordinated, and the high spin peak turns into low spin again. This cycle of illumination and dark placement is repeated many times. It can be seen from the on / off diagram that the spin state switching effect of the KL-Br complex is very good, and it is stable and cyclic without attenuation almost within the range of the red dotted line. Therefore, the spin state switching effect of the quinoline acylhydrazone Fe(Ⅱ) complex in the solution is ideal.

Claims

1. A quinoline acylhydrazone ligand, characterized in that: for( E )-4-Bromo- N' -(Quinoline-8-methylene)benzoylhydrazide, structural formula: 。 2. The method for synthesizing a quinoline acylhydrazone ligand according to claim 1, wherein The reaction formula is: ， The specific steps are as follows: Quinoline-8-carboxaldehyde and 4-bromobenzoylhydrazide are used as raw materials, ethanol is used as a reaction solvent, and the reaction is stirred and refluxed. After the reaction is completed, the solvent is removed by rotary evaporation to obtain a quinoline acylhydrazone ligand KL-Br.

3. The synthesis method according to claim 2, characterized in that The molar ratio of quinoline-8-carboxaldehyde to 4-bromobenzoylhydrazide is 1:

1.

4. The synthesis method according to claim 2, characterized in that The reflux reaction temperature is 90±5 ℃ and the reaction time is 12~24 h.

5. Quinoline acylhydrazone Fe(II) complex, characterized in that: It is a KL-Br-Fe(Ⅱ) complex, and its structural formula is 。 6. The method for synthesizing the quinoline acylhydrazone Fe (II) complex according to claim 5, characterized in that: The specific steps are as follows: (1) Triethylamine was added dropwise to a methanol solution of quinoline acylhydrazone ligand KL-Br to remove protons; (2) Dissolve Fe(ClO4)2·6H2O in methanol, then add L-ascorbic acid to 3+ Reduction to Fe 2+ ; (3) The solution of step (2) and the solution of step (1) are stirred and mixed uniformly, and allowed to stand at room temperature to allow the solvent to evaporate slowly, thereby precipitating KL-Br-Fe(II) complex crystals.

7. The synthesis method according to claim 6, characterized in that In step (3), the molar ratio of the quinoline acylhydrazone ligand to Fe(ClO4)2·6H2O is 2:

1.

8. Use of the quinoline acylhydrazone Fe(II) complex according to claim 5 in the preparation of a spin-crossing molecular switch or an acid-base stimulation sensor.

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