Polyacid-based metal organic framework molecular material, preparation method thereof and application of polyacid-based metal organic framework molecular material in photocatalytic synthesis of alpha-beta-unsaturated carbonyl compound

Abstract

The invention relates to a polyacid-based metal organic framework molecular material, the chemical formula of which is [Co2 (TPB) 1.5 (CoPW11O39) 4H2O] [Co (TPB) 0.55 H2O] 14H2O, which is called {PW11CoTPB} (TPB = 1, 2, 4, 5tetra (4pyridyl) benzene) for short. The synthesis method specifically comprises the following steps: uniformly mixing Co (NO3) 2.6 H2O, Na9 [APW9O34]. 7H2O and TPB in a mixed solvent of distilled water and methanol, then adjusting the pH value to 4-5, then transferring into a reaction kettle, reacting for 90-110 hours at the temperature of 110-130 DEG C, cooling to room temperature, separating out pink rhombic blocky crystals, washing and drying. The PW11CoTPB has relatively high thermal stability and chemical stability, a relatively wide light absorption range and a relatively low LUMO energy level, and active oxygen groups. O2 and. OH formed under light energy irradiation can be used for a Knoevenagel condensation reaction for green and efficient synthesis of alpha-beta-unsaturated carbonyl compounds.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation and application of polyacid-based metal organic framework molecular materials, and specifically relates to a novel polyacid-based metal organic framework molecular material, a preparation method and its application as a photocatalyst in the reaction of synthesizing α-β-unsaturated carbonyl compounds. Background Art

[0002] α-β-Unsaturated carbonyl compounds are important intermediates in organic synthesis. Structurally, these compounds possess a conjugated relationship between double bonds and carbonyl groups, which not only defines their fundamental characteristics but also allows for the introduction of diverse functional groups at different positions through a variety of modification strategies. Consequently, the synthesis and applications of these compounds have attracted significant attention. The Knoevenagel condensation reaction is an important organic reaction in which active methylene compounds react with aldehydes / ketones to form α-β-unsaturated carbonyl compounds. The formation of a C=C bond requires the preferential cleavage of the C−H bond, resulting in the formation of a carbon-centered radical with an open electronic structure. In the context of achieving carbon neutrality, solar photocatalytic reactions represent a promising and sustainable approach to replace fossil fuels, particularly C-C or C=C bond couplings, which can be catalyzed using mild catalysts and clean solvents without the addition of any sacrificial agents.

[0003] Hydrogen atom transfer (HAT) refers to a chemical transformation process in which a proton and electron are simultaneously transferred between two elementary particles in a single kinetic step. This mechanism plays an important role in catalytic reactions such as hydrocarbon combustion or oxidative degradation. Direct functionalization of carbon-hydrogen bonds offers a new avenue for constructing complex organic molecules. In this context, the intermolecular HAT process provides a direct method for activating C‒H bonds, making it one of the most efficient and atom-economical methods for C‒H functionalization. Traditionally, intermolecular HAT reactions, in addition to being performed under harsh conditions, often rely on the use of hazardous reagents such as chlorine and peroxides. Photoinduced HAT catalysis utilizes light as an abundant and environmentally friendly energy source, aligning with the principles of green chemistry and sustainable synthesis. If C‒C bonds are constructed, this photocatalytic reaction can connect carbon chain-extending chemicals, opening up a potential avenue for refining natural carbon sources.

[0004] Polyoxometalates (POMs), a class of polynuclear metal oxoclusters with well-defined structures, tunable redox activities, and excellent photoexcitation properties, hold great potential for application in various fields. Notably, POMs, with their atomically precise and highly tunable structures, are considered promising O-donating inorganic clusters for the construction of mono-, di-, tri-, and polysubstituted metals. Monometallated POMs, due to their simple structure and distinct active sites, have been widely used in catalysis. Due to their unique composition and structural characteristics, POMs can also act as protons, dissociating in humid environments to form polyoxometalate anions and hydrated protons (such as H⁺ and H⁺⁺). Furthermore, the abundant surface oxygen atoms of polyoxometalate anions can serve as carriers for hydrogen bonding networks. 1,2,4,5-tetra(4-pyridyl)benzene (TPB) exhibits excellent thermal stability, a broad visible light absorption range, efficient electron transfer, and potential redox activity. It can be incorporated into the framework as a photosensitizer via non-covalent or covalent strategies to enhance the light absorption capacity of the catalyst. Connecting the two through open transition metal sites to construct polyoxometalate-based metal-organic framework (POMOF) materials is a method for synthesizing photoredox catalysts with potential application value.

[0005] Based on this, this application was developed. Summary of the Invention

[0006] The present invention aims to overcome the defects of the prior art and provide a new polyacid-based metal organic framework molecular material, a synthesis method and its application as a photocatalyst in the photocatalytic synthesis of α-β-unsaturated carbonyl compounds.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows: A new type of polyacid-based metal-organic framework molecular material, whose molecular formula is: C 104 H 64 7N 16 O 124 P2W 22 , the chemical formula is [Co2(TPB) 1.5 (CoPW 11 O 39 )∙4H2O][Co(TPB) 0.5 ∙5H2O]∙14H2O, TPB= 1,2,4,5-tetrakis(4-pyridyl)benzene, abbreviated as {PW 11 Co‒TPB}. This compound crystallizes in the triclinic system and has a P-1 space group. This organic framework molecular material is capable of efficiently synthesizing α-β-unsaturated carbonyl compounds.

[0008] A method for preparing the above-mentioned polyacid-based metal organic framework molecular material, comprising: Co(NO3)2·6H2O, Na9[A‒PW9O34 ]·7H2O and 1,2,4,5-tetra(4-pyridyl)benzene (TPB) are placed in a solvent and mixed evenly. The pH is then adjusted to 4-5. The mixture is then transferred to a reactor and reacted at 110-130 °C for 90-110 hours. The mixture is cooled to room temperature to precipitate pink rhombus-shaped crystals, which are then washed and dried to obtain the product.

[0009] Specifically, the Co(NO3)2·6H2O, Na9[A‒PW9O 34 The mass ratio of 7H2O to 1,2,4,5-tetra(4-pyridyl)benzene (TPB) can be 7-8:5-6:1.

[0010] Furthermore, during the synthesis process, the solvent used can be a mixture of methanol and distilled water. Preferably, the volume ratio of methanol to distilled water is 1:2-3.

[0011] The present invention also discloses the use of the novel polyacid-based metal-organic framework molecular material as a photocatalyst in the photocatalytic synthesis of α-β-unsaturated carbonyl compounds. This application further involves using ethyl cyanoacetate and a benzene derivative as substrates to carry out the photocatalytic synthesis of α-β-unsaturated carbonyl compounds in an air atmosphere at room temperature under white light LED irradiation and in the presence of a solvent. The benzene derivative includes at least one of benzaldehyde, p-bromobenzaldehyde, 3-methoxybenzaldehyde, p-fluorobenzaldehyde, 4-methoxybenzaldehyde, and 2-methylbenzaldehyde; the solvent may be methanol or a mixture of methanol and water.

[0012] In this application, a two-dimensional crystalline material PW with a continuous hydrogen bond network and a single metal substituted POM is synthesized by a hydrothermal method. 11 Co‒TPB. Interestingly, the extensive free water molecules in the structure successfully establish a tight hydrogen-bonding network, laying the foundation for excellent proton conductivity. Through the single electron transfer (SET) strategy in the photoredox process, the activated substrate can obtain an electron from the photocatalyst, thereby generating a free radical intermediate. Simultaneously, the substrate molecule can donate an electron to the photocatalyst, which favors the formation of superoxide radicals. Unlike the traditional Knoevenagel condensation reaction, under the influence of the photocatalyst hydrogen bonds, the two substances can approach each other, allowing the highly selective synthesis of α-β-unsaturated carbonyl compounds.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1) The polyoxometallic metal-organic framework molecular material of the present invention can accurately analyze its crystal structure characteristics through X-ray single crystal diffraction, providing theoretical support for further speculation on the interaction between the active center and the reaction substrate and studying its catalytic reaction mechanism; 2) The large amount of H2O widely distributed in the structure of the polyoxometallic organic framework molecular material of the present invention fills the gaps with oxygen atoms at the ends of POM, forming closed or open strong hydrogen bonds (O···O = 2.537‒2.890 Å). 11 The hydrogen bonding sites on Co‒TPB can achieve efficient proton transfer. 11 In the Co‒TPB structure, the single metal substituted POM can continuously accept electrons and slowly release electrons like an electron sponge, thereby achieving efficient electron transfer and realizing ·O 2‒ The generation of 3) The polyacid-based metal-organic framework molecular material of the present invention has n-type semiconductor characteristics, with a high reduction potential LUMO energy level (-0.78 V vs. NHE) and a high oxidation potential HOMO energy level (1.04 V vs NHE). The negative reduction potential is conducive to •O2 – The production of α-β-unsaturated carbonyl compounds can achieve efficient formation; 4) This invention synthesized a new photocatalyst PW based on extensive hydrogen bonding 11 Co‒TPB provides favorable conditions for electron and proton conduction. Using clean, abundant O₂ as an oxidant, the efficient formation of α-β-unsaturated carbonyl compounds under 10 W white light irradiation is achieved, which is in line with the development concept of green chemistry. 5) The present invention obtains a highly efficient and stable PW by designing and adjusting the composition of the catalytic active site photosensitizer ligand TPB, the single metal cobalt substituted Keggin type POM and the active center Co(II). 11 The Co‒TPB photocatalyst achieves a reasonable match between the stereo and electronic effects between the catalyst and the substrate, thereby achieving efficient catalytic activity and laying a solid foundation for its practical application in organic synthesis. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 (a) PW 11 Asymmetric unit structure of Co‒TPB; (b) PW 11 Co-TPB a Coordinate direction; (c) PW 11 Co-TPB b Three-dimensional cross-stacked structure in the coordinate direction; (d) PW 11 Co-TPB c Coordinate direction and local enlargement Figure 2 Compound PW 11 Infrared spectrum of Co‒TPB; Figure 3 Compound PW11 PXRD pattern of Co‒TPB; Figure 4 Compound PW 11 Thermogravimetric analysis of Co‒TPB; Figure 5 Compound PW 11 XPS spectra of Co‒TPB; (a) full spectrum; (b) C 1s; (c) N 1s; (d) Co2p; Figure 6 (a) PW 11 UV-visible spectra of Co‒TPB and TPB; (b) PW 11 UV-visible spectra of Co-TPB over time; (c) PW 11 Tauc band gap diagram of Co‒TPB and TPB based on UV‒Vis spectroscopy; (d) PW 11 Mott-Schottky curve of Co-TPB; (e) Mott-Schottky curve of TPB; (f) PW 11 Band gap comparison of Co‒TPB and TPB; Figure 7 (a) The reaction was monitored at 0, 4, 8, 12, 16, and 20 h after the start of the reaction. 1 H NMR spectrum; (b) oxidation kinetics study; (c) leaching experiment; (d) recycling experiment. DETAILED DESCRIPTION

[0015] The technical solution of the present invention is further described in detail below in conjunction with the embodiments, but the protection scope of the present invention is not limited thereto.

[0016] In the following examples, the raw materials used are all common commercial products that can be purchased directly or can be prepared using conventional methods in the art.

[0017] Room temperature refers to 25±5°C.

[0018] Example 1 A method for preparing a polyacid-based metal-organic framework molecular material specifically comprises the following steps: 1. 1,2,4,5-tetrakis(4-pyridyl)benzene (TPB): Commercially available products can be purchased directly or synthesized according to existing literature (BM Ji, WZ Wang, DS Deng, Y. Zhang, L. Cao, L. Zhou, CS Ruan, TS Li, ​​Structural competition between π···π interaction and halogen bond: a crystallographic study, CrystEngComm, 2013, 15, 769-774.).

[0019] Compound Na9[A‒PW9O 34 ]·7H2O synthesis method can be found in the literature (R. Massart, R.Contant, J.-M. Fruchart, J.-P. Ciabrini, M. Fournier, 31 P NMR Studies onMolybdic and Tungstic Heteropolyanions. Correlation between Structure and Chemical Shift, InorganicChemistry, 1977, 16: 11.) for synthesis.

[0020] 2. Compound PW 11 Synthesis of Co‒TPB Compound PW 11 Co‒TPB was prepared by self-assembly under hydrothermal conditions: Co(NO3)2·6H2O (70 mg), Na9[A‒PW9O 34 ]·7H2O (48 mg) and TPB (9 mg) were added to a mixed solvent of distilled water (4 mL) and methanol (2 mL), stirred at room temperature to mix uniformly, and 0.5 M hydrochloric acid was used to adjust the pH to 4.62. The mixture was then transferred to an autoclave and heated to 120 °C for 72 hours. The mixture was slowly cooled to room temperature to precipitate pink rhombus crystals, which were washed with water and dried at 50 °C for 24 hours to obtain compound PW 11 Co‒TPB, yield 70% (based on Na9[A-PW9O 34 ] ·7H2O).

[0021] The above compound PW 11 The molecular formula of Co‒TPB is: C 104 H64 7N 16 O 124 P2W 22 , Elemental analysis and ICP (%): Calculated values ​​for compound: P 0.77, W 50.30, Co 5.13, C 15.54, H 0.80, N 2.79. Expected values: P 0.84, W 49.76, Co 5.15, C 15.58, H 0.93, N 2.73. Compound PW 11 The chemical formula of Co‒TPB is [Co2(TPB) 1.5 (CoPW 11 O 39 )∙4H2O][Co(TPB) 0.5 ∙5H2O]∙14H2O, TPB = 1,2,4,5-tetrakis(4-pyridyl)benzene).

[0022] Crystal structure analysis: Compound PW 11 Co‒TPB was used for crystal testing and analysis, and the results are shown in Table 1 below.

[0023] Table 1 Compound PW 11 Crystallographic data of Co‒TPB PW 11 The crystal structure of Co‒TPB clearly reveals the irregular distribution of free water, with each asymmetric unit comprising 18 water molecules ( Figure 1 a). The PW was determined by single crystal X-ray diffraction (SCXRD). 11 Co‒TPB crystallizes in the P‒1 triclinic space group. PW 11 There are four coordination modes of metallic Co in Co‒TPB, all of which belong to hexacoordinate structures, among which Co1 is coordinated with a nitrogen in a TPB ligand, replacing the position of a W on POM, and coordinated with five oxygen atoms on POM; Co2 is coordinated with three nitrogen atoms from three TPB ligands and two oxygen atoms from two H2O and one oxygen atom from a POM; Co3 is coordinated with four TPB ligands and two H2O atoms; Co4 is coordinated with one TPB ligand and five H2O molecules, and the Co4 unit exists independently as a fragment in the overall structure and is evenly distributed in the main structure. In the main structure, Co3 and the four N atoms of the TPB ligand extend on a two-dimensional plane to form a parallelogram structure ending with Co1 on both sides, which can be used as a secondary building unit ( Figure 1 b). Secondary building units are connected by each Co2 and extend longitudinally to form staggered "stairs", which facilitates rapid electron transfer ( Figure 1c). The fragments where Co4 is located are evenly distributed near the POM connected to the same Co2. A large amount of H2O in the crystal structure fills the gaps with the oxygen atoms at the end of the POM to form closed or open strong hydrogen bonds (O···O = 2.537‒2.890Å) ( Figure 1 d). These results indirectly indicate that PW 11 The large number of hydrogen bonding sites on Co‒TPB may be closely related to its superior proton transfer.

[0024] Infrared spectroscopy: Figure 2 PW is displayed in 11 The infrared spectrum of Co‒TPB is shown in the figure, with the wavelengths at 910−700 cm −1 The infrared absorption peaks at 2 and 3 correspond to the Keggin-type polytungsten oxide cluster anions [PW 12 O 40 ] 4‒ Stretching vibration of O−W−O and W=O bonds in 1750 ~ 1150 cm ‒1 The vibration bands show the C=N, C=C and C−C stretching vibrations of TPB.

[0025] X-ray powder diffraction: PW 11 The powder X-ray diffraction pattern of Co‒TPB is consistent with the simulation curve (see Figure 3 ), confirming the high purity of the obtained sample and also PW 11 The successful synthesis of Co‒TPB provides evidence.

[0026] Thermogravimetric analysis: Differential thermal analysis shows that from 50 ℃ to 1000 ℃, PW 11 The weight loss process of Co‒TPB is a two-step process (see Figure 4 ), the first step corresponds to the weight loss of lattice water molecules and CH3CN solvent molecules before 100 °C, and the second step of weight loss is the loss of TPB ligands and the decomposition of the polyacid skeleton.

[0027] X-ray photoelectron spectroscopy (XPS) analysis: X-ray photoelectron spectroscopy (XPS) test is used to analyze PW 11 Chemical state of elements in Co‒TPB. First, the signals of five elements, C, O, N, W and Co, were detected in the wide scan spectrum of XPS ( Figure 5 a). The C1s spectrum is fitted into three peaks at 284.8 eV, 286.5 eV, and 287.6 eV, corresponding to the C=C bond, C‒N bond, and C‒C bond (5b). The high-resolution spectrum of the N 1s spectrum is fitted into two peaks at binding energies of 399.4 eV and 401.3 eV ( Figure 5c), these two peaks originate from the N‒Co and C‒N bonds of the bridging nitrogen atoms. The peaks at 782.1 eV and 797.1 eV correspond to Co 2+ , the two satellite peaks also prove that Co 2+ The peaks at 786.2 eV and 799.0 eV prove the presence of Co in the sample. 3+ ( Figure 5 d).

[0028] Photoelectric properties: The compound PW was evaluated by UV-visible diffuse reflectance spectroscopy. 11 Light absorption properties of Co‒TPB and its corresponding ligands. Figure 6 As shown in a, the light absorption range of TPB is between 250‒350 nm, which is attributed to the π‒π and n‒π transitions of TPB ligands. 11 Co-TPB has a wider light absorption range, extending to 650 nm, showing its potential application in the field of photocatalysis. When the catalyst was irradiated in air for 5 minutes, 15 minutes, and 30 minutes, the absorption intensity of the UV-vis diffuse reflectance absorption spectrum in the range of 250 to 350 nm gradually increased, while the absorption intensity in the range of 450 to 600 nm gradually weakened ( Figure 6 b), which demonstrates the charge transfer from metal to ligand (MLCT, d‒π*). In addition, this application systematically studies the PW 11 The photoelectric properties of Co‒TPB were studied, and its band gap was calculated to be 1.82 eV using the Tauc plot. 11 The positive slope of the LUMO energy level of Co-TPB indicates that it has n-type semiconductor characteristics ( Figure 6 c). Compared with the standard hydrogen electrode (NHE), PW 11 The flat band potentials of Co‒TPB and TPB are ‒0.78 V and ‒0.83 V, respectively, which can be used as the conduction band (CB). PW calculated based on the band gap and CB 11 The valence band (VB) values ​​of Co‒TPB and TPB are +1.04 V and +2.3 V, respectively. Figure 6 d, 6e). PW 11 The LUMO energy level of Co‒TPB is more negative than the reduction potential of TPB, indicating that it has the thermodynamic ability to complete the O2 activation process (O2 / ·O2 ‒ =0.33 V, vs. NHE) feasibility ( Figure 6 f).

[0029] Example 2 Photocatalytic application experiment The photocatalytic reaction was carried out in a 20W WATTCAS parallel photoreactor (model: WP-TEC-1020HSL) with a continuous circulating cooling water device. In a typical reaction system, ethyl cyanoacetate (0.5 mmol), catalyst PW 11 Co‒TPB (10 mg) and methanol:water (1:1, 2 mL, volume ratio) were added to a quartz tube (15 mL) containing a spindle magnet. A 20 W white LED was used as the light source to illuminate the bottom of the quartz photocatalytic reaction tube. The reaction temperature was 25 ± 5°C. After 24 h of reaction, the PW was centrifuged and filtered. 11 The Co‒TPB sample was then extracted with ethyl acetate and dried over anhydrous sodium sulfate. All products were obtained by rotary evaporation at 40 °C. 1 H NMR was used for qualitative and quantitative analysis.

[0030] Study on photocatalytic properties Based on PW 11 Co-TPB's excellent photochemical properties and rich hydrogen-bonding network make it a promising photocatalyst for organic transformations via the HAT process. The study first used 0.5 mmol of ethyl cyanoacetate and 0.3 mmol of benzaldehyde as model substrates to photocatalyze the synthesis of α-β-unsaturated carbonyl compounds in air at room temperature under 20 W white LED illumination.

[0031] To verify PW 11 The proton transfer ability of Co‒TPB was studied to explore the effects of different solvents on the photocatalytic reaction within 24 h (see Table 2). The experiment found that MeOH was the best solvent compared with EtOH, CH3CN and CH2Cl2. 1 H NMR analysis showed that the yield of α-β unsaturated carbonyl compounds can reach 80%, while the corresponding yields of EtOH, CH3CN, and CH2Cl2 were 43%, 59%, and 66%, respectively. When pure water was used as the solvent, the yield was extremely low, at 30%. This phenomenon can be attributed to the fact that MeOH can interact with the surface of the photocatalyst, reducing the probability of electron-hole recombination, thereby improving the photocatalytic efficiency. Although H2O can provide protons in the reaction medium and react with PW 11 The active hydrogen atoms in Co‒TPB form hydrogen bonds, but the study found that when MeOH and H2O were mixed in different proportions as solvents, the best reaction yield could be obtained as the proton concentration increased. Solvent screening experiments showed that MeOH:H2O = 1:1 was the best solvent condition, with a yield of up to 99%. This shows that PW 11 The synergistic effect between the components in the Co‒TPB framework plays a key role in the photocatalytic process. 11When Co‒TPB or no light irradiation is used, the yield is extremely low, 27% and 41%, respectively, which indicates that the reaction is a light-driven catalytic process. 11 The potential of Co‒TPB in photocatalytic organic transformations also provides important guidance for optimizing reaction conditions.

[0032] Table 2: Exploration of photocatalytic Knoevenagel condensation reaction conditions a Under optimized reaction conditions, the photocatalytic system's applicability to substrates that form α-β-unsaturated carbonyl compounds was systematically investigated (Table 3). To comprehensively evaluate the catalytic system's universality, extended experimental studies were conducted under the same conditions with various benzaldehyde derivatives (e.g., p-bromobenzaldehyde, 3-methoxybenzaldehyde, p-fluorobenzaldehyde, 4-methoxybenzaldehyde, and 2-methylbenzaldehyde) (entries 1c–6c). The results demonstrated that the catalytic system exhibited excellent catalytic performance for aromatic aldehyde substrates containing diverse substituents. When the substrates contained electron-withdrawing groups (e.g., para-fluorine, chlorine, and bromine), yields of the target product reached as high as 99%, with no dehalogenation observed throughout the reaction. This finding demonstrates that the catalytic system effectively maintains the chemical integrity of halogenated aromatic aldehydes, providing a reliable pathway for the synthesis of halogen-containing functional molecules. At the same time, the study also found that substrates containing electron-donating groups (such as para-methoxy, meta-methoxy, ortho-methyl, etc.) can also be efficiently converted into target products, and the yields remain at a high level, 78%, 80%, and 93%, respectively. This result further confirms that the catalytic system has good compatibility with aromatic aldehyde substrates with different electronic properties. These experimental results not only show that PW 11 The broad application prospects of the Co-TPB photocatalytic system in the synthesis of α-β-unsaturated carbonyl compounds also provide important insights into the development of novel organic synthesis methods. In particular, the system's excellent tolerance to halogen-containing substrates opens up new avenues for the synthesis of potentially bioactive halogen-containing organic molecules.

[0033] Table 3: Substrate exploration for photocatalytic Knoevenagel condensation reaction In order to further explore the reaction process, we used 1 The template reaction of the photocatalytic Knoevenagel C=C coupling was monitored in real time by H NMR, with data collected every 4 h (7a). By monitoring the changes in reactant concentrations during the reaction, ln(C t The results show that the photocatalytic Knoevenagel condensation reaction follows pseudo-first-order kinetics ( Figure 7 b), this discovery provides an important basis for a deeper understanding of the reaction mechanism. The filtration experiment results show that PW 11 Co‒TPB exhibits excellent heterogeneous catalytic properties. Specifically, after 12 h of reaction, the PW 11 In the case of Co‒TPB, the reaction almost completely stopped, which fully proves that the reaction is caused by PW 11 Heterogeneous catalytic process driven by active sites on the Co-TPB surface ( Figure 7 c) PW 11 Co‒TPB can be efficiently recovered by simple centrifugation and can be directly used in subsequent catalytic cycles. It is worth noting that the catalyst still maintains a high catalytic activity after three consecutive cycles, with only a slight decrease ( Figure 7 d), which fully demonstrates its good stability. In addition, by comparing the infrared spectra before and after multiple catalytic cycles, it can be clearly observed that the catalyst framework structure remains intact during the reaction process, further confirming its excellent structural stability. 11 Co‒TPB has shown great potential as an efficient, stable, and recyclable heterogeneous photocatalyst, laying a solid foundation for its practical application in organic synthesis.

[0034] In summary, the present invention PW 11 Co‒TPB has high thermal and chemical stability, a wide light absorption range and a low LUMO energy level. Under light irradiation, the active oxygen groups formed 2‒ and ·OH can be used for the Knoevenagel condensation reaction of green and efficient synthesis of α-β-unsaturated carbonyl compounds.

Claims

1. A polyacid-based metal-organic framework molecular material, characterized in that: The chemical formula is [Co2(TPB) 1.5 (CoPW 11 O 39 )∙4H2O][Co(TPB) 0.5 ∙5H2O]∙14H2O, TPB = 1,2,4,5-tetrakis(4-pyridyl)benzene, belongs to the triclinic system, P-1 space group.

2. The method for preparing the polyacid-based metal-organic framework molecular material according to claim 1, characterized in that: Combine Co(NO3)2·6H2O, Na9[A‒PW9O 34 ]·7H2O and 1,2,4,5-tetrakis(4-pyridyl)benzene are placed in a solvent and mixed uniformly, and then the pH is adjusted to 4-5. The mixture is transferred to a reactor and reacted at 110-130 °C for 90-110 hours. The mixture is cooled to room temperature, crystals are precipitated, and the crystals are washed and dried to obtain the product.

3. The method for preparing a polyacid-based metal-organic framework molecular material according to claim 2, wherein: The Co(NO3)2·6H2O,Na9[A‒PW9O 34 The mass ratio of 7H2O and 1,2,4,5-tetrakis(4-pyridyl)benzene is 7-8:5-6:

1.

4. The method for preparing a polyacid-based metal-organic framework molecular material according to claim 2, wherein: The solvent is composed of a mixture of methanol and distilled water.

5. The method for preparing a polyacid-based metal-organic framework molecular material according to claim 4, wherein: The volume ratio of the methanol to distilled water is 1:2-3.

6. Use of the polyacid-based metal-organic framework molecular material according to claim 1 as a photocatalyst in the photocatalytic synthesis of α-β-unsaturated carbonyl compounds.

7. Use of the polyacid-based metal organic framework molecular material as a photocatalyst in the photocatalytic synthesis of α-β-unsaturated carbonyl compounds as claimed in claim 6, characterized in that: Using ethyl cyanoacetate and benzene derivatives as substrates, the photocatalytic synthesis of α-β unsaturated carbonyl compounds was carried out in the presence of solvents under white light LED irradiation and in air atmosphere at room temperature.

8. Use of the polyacid-based metal organic framework molecular material as a photocatalyst in the photocatalytic synthesis of α-β-unsaturated carbonyl compounds as claimed in claim 7, characterized in that: The benzene derivative includes at least one of benzaldehyde, p-bromobenzaldehyde, 3-methoxybenzaldehyde, p-fluorobenzaldehyde, 4-methoxybenzaldehyde, and 2-methylbenzaldehyde.

9. Use of the polyacid-based metal organic framework molecular material as a photocatalyst in the photocatalytic synthesis of α-β-unsaturated carbonyl compounds as claimed in claim 7, characterized in that: The solvent is methanol or a mixture of methanol and water.

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