A crystal form of a macrocyclic binuclear cobalt complex and its preparation method and application

Abstract

The present invention discloses a crystalline form of a macrocyclic binuclear cobalt complex, its preparation method, and application. The crystalline form is prepared by dissolving 2-hydroxy-5-methoxyisophthalide, ethylenediamine, and a cobalt salt in a mixed solvent consisting of methanol and acetonitrile in a 1:1 volume ratio, and conducting a solvothermal reaction. The applicant's experimental results show that when the complex is used as a catalyst at a concentration of 0.2 μM, photocatalytic CO2 reduction produces 2.05 μmol CO, with a turnover number (TON) value of 2050 for selective CO production, and a CO selectivity of 96%.

Description

Technical Field

[0001] The present invention relates to a metal coordination compound, in particular to a crystal form of a macrocyclic binuclear cobalt complex and a preparation method and application thereof. Background Art

[0002] Currently, the content of carbon dioxide (CO2) in the atmosphere is increasing. Excessive CO2 is increasing the greenhouse effect, which in turn leads to a series of environmental problems. As my country prioritizes high-quality economic development, CO2 emissions from industrial production and daily activities have increased significantly, seriously affecting our ecological environment and living comfort, and exacerbating energy shortages. Therefore, we need to take measures to reduce the concentration of CO2 in the atmosphere and even convert it into energy we need.

[0003] Photocatalytic water splitting to produce hydrogen and CO2 reduction are typical artificial photosynthesis processes that can convert solar energy into highly efficient clean energy and are known as the "crown" reaction of mankind. At present, the efficiency of converting solar energy into chemical energy is still relatively low, and this technology is difficult to apply industrially. The main reason is that the activity, selectivity and stability of the catalyst are too low, and it is still a long way from production application. Therefore, the development of new, efficient and low-cost catalysts remains the direction of efforts in the field of photocatalysis at home and abroad. Among them, metal complexes are typical homogeneous molecular catalysts. Because they have a clear molecular structure and catalytic active sites, it is easy to regulate the catalytic performance of the complex from the organic ligand and metal center, which is conducive to studying the catalytic mechanism at the molecular level.

[0004] In recent years, many metal complexes have been developed and applied to photocatalytic CO2 reduction. For example, the invention patent with publication number CN114031647A previously applied by the inventor team of this application provides a binuclear cobalt complex with the chemical formula [(C 33 H 33 N6O2)Co2(CH3COO)2](CH3COO)·H2O, using 2,6-bis((bis(pyridin-2-ylmethyl)amino)methyl)-4-methoxyphenol and cobaltous acetate tetrahydrate in methanol and / or ethanol, adjusting the pH value of the system to alkaline and then heating the reaction to obtain the obtained product. The complex described in this invention can be used as a homogeneous molecular catalyst for CO2 reduction to convert carbon dioxide into carbon monoxide with high selectivity and exhibits excellent catalytic activity under low concentration conditions of 0.1μm. For example, the invention patent with publication number CN117843694A discloses a hydroxyphenanthroline binuclear cobalt complex with the molecular formula C 48 H 26Cl2Co2N8O6. This invention utilizes the bidentate coordination properties of 2,9-dichloro-1,10-phenanthroline to form a coordination compound with cobalt ions. The resulting binuclear cobalt complex exhibits a certain photocatalytic effect, converting carbon dioxide into ethylene, but the catalytic activity is less than ideal. Currently, there are no reports on binuclear cobalt complexes with two central cobalt ions of different valence states, obtained by condensing 2-hydroxy-5-methoxyisophthalide and ethylenediamine, and their use as photocatalysts for CO2 reduction. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a crystal form of a macrocyclic binuclear cobalt complex and a preparation method and application thereof.

[0006] The crystalline form of the macrocyclic binuclear cobalt complex provided by the present invention belongs to the orthorhombic crystal system, the P212121 space group, and its unit cell parameters are: α=90.00°, β=90.00°, γ=90.00°.

[0007] The macrocyclic binuclear cobalt complex of the present invention is composed of a dianionic ligand obtained by condensing 2-hydroxy-5-methoxyisophthalide and ethylenediamine, which chelates two cobalt ions. Its molecular formula is C 22 H 22 Cl3Co2N4O4, the metal center cobalt ion Co1 is +3 valence, Co2 is +2 valence, the two cobalt ions are chelated together by a macrocyclic ligand, and coordinated with one or two chloride ions at the same time, forming a five-coordinate or six-coordinate geometric structure. The planar structure of the complex is shown in the following formula (I):

[0008]

[0009] The preparation method of the above-mentioned crystalline form of the macrocyclic binuclear cobalt complex is: dissolving 2-hydroxy-5-methoxyisophthalide, ethylenediamine and cobalt salt in a mixed solvent and performing a solvothermal reaction to obtain the crystalline form; wherein the mixed solvent is a composition composed of methanol and acetonitrile in a volume ratio of 1:1.

[0010] In the above preparation method, the cobalt salt can be CoCl2·6H2O or CoCl2, preferably CoCl2·6H2O. The reaction is preferably carried out at ≥50°C, more preferably at 80-100°C. When the reaction is carried out at 80-100°C, the reaction time is generally controlled to be 24-48 hours.

[0011] The applicants discovered in experiments that, when other conditions remain constant, the composition and ratio of the mixed solvent significantly influences the yield of the target product. Using methanol or acetonitrile alone as the solvent resulted in no crystals or only precipitation. While crystals were obtained when the ratio of methanol to acetonitrile was varied, the color and shape of the resulting crystals differed from the target product described herein.

[0012] The 2-hydroxy-5-methoxyisophthalide involved in the above preparation method can be prepared by referring to existing literature (Org. Biomol. Chem., 2016, 14, 669-673; J. Org. Chem. 2023, 88 (14), 10002-10013), which will not be described in detail here.

[0013] The present invention also includes the use of the above-mentioned macrocyclic binuclear cobalt complex crystal form in a photocatalyst. Furthermore, it is used as a photocatalyst in the photocatalytic reduction of carbon dioxide. During the photocatalytic reduction of carbon dioxide, the photocatalytic system includes a photosensitizer, a catalyst, a sacrificial agent, and a solvent. The catalyst is the above-mentioned mononuclear cobalt complex or crystal form, and the selection of the photosensitizer, sacrificial agent, and solvent is the same as in the prior art. Specifically, the photosensitizer can be [Ru(phen)3](PF6)2, [Ru(phen)3]Cl2, or [Ru(bpy)3]Cl2, preferably [Ru(phen)3](PF6)2; the sacrificial agent is preferably triethanolamine (TEOA) and / or triethylamine (TEA); and the solvent is preferably a mixed solution comprising water and acetonitrile, wherein the volume ratio of water to acetonitrile is preferably 1:4. In the photocatalytic system, the concentration of the photosensitizer is preferably 400-500 μM, the concentration of the catalyst is preferably 0.05-1 μM, and the concentration of the sacrificial agent is preferably 0.30-0.35 M.

[0014] The present invention also provides a catalyst containing the crystal form of the macrocyclic binuclear cobalt complex.

[0015] Compared to the prior art, the present invention synthesized a crystalline form of a macrocyclic binuclear cobalt complex via an in situ method. This complex, as a homogeneous molecular catalyst, selectively generates carbon monoxide during photocatalytic CO2 reduction, exhibiting high catalytic activity, selectivity, and stability. The applicant's experimental results showed that at a 0.2 μM concentration of this complex as a catalyst, photocatalytic CO2 reduction produced 2.05 μmol of CO, with a turnover number (TON) of 2050 for selective CO production, and a CO selectivity of 96%. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the infrared spectrum of the final product obtained in Example 1 of the present invention.

[0017] Figure 2This is a crystal structure diagram of the final product obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0018] In order to better explain the technical solution of the present invention, the present invention is further described in detail below with reference to examples, but the embodiments of the present invention are not limited thereto.

[0019] The 2-hydroxy-5-methoxyisophthalide involved in the following examples was prepared as follows:

[0020]

[0021] Hexamethylenetetramine (11.2012 g, 80 mmol) and 4-methoxyphenol (2.1608 g, 20 mmol) were dissolved in 15 mL of trifluoroacetic acid and heated in a 100°C N2 atmosphere for 6 hours. After the reaction was completed, 10 mL of ultrapure water was added to the reaction product, and then refluxed for 10 minutes. After the temperature of the reaction product was lowered to room temperature, 400 mL of ice water was added, and after settling for 10 minutes, the product was filtered to obtain a light yellow solid. The light yellow solid was dissolved in ethyl acetate, extracted with water to remove moisture, and then concentrated under reduced pressure to remove ethyl acetate to obtain 2-hydroxy-5-methoxyisophthalide (0.32 g, yield: 19%). 1 H NMR (400MHz, Chloroform-d), δ (ppm) 11.06 (2H, s), 10.15 (1H, s), 7.44 (2H, s), 3.79 (3H, s).

[0022] Example 1

[0023] 2-Hydroxy-5-methoxyisophthalide (0.0180 g, 0.1 mmol), ethylenediamine (0.1 mmol, 3.33 μL), and CoCl₂·6H₂O (0.1 mmol, 0.0237 g) were placed in a 20 cm long, sealed heat-resistant glass tube. 2 mL of a methanol / acetonitrile mixture (1:1 volume ratio) was added. The tube was then evacuated and sealed with a heat seal. The sealed thick-walled glass tube was placed in an 80°C oven for 48 h. After terminating the reaction, the temperature was slowly lowered to room temperature. Square, dark-red crystals were observed to precipitate in the tube. The crystals were collected and dried. The yield was 37% (0.0088 g, based on the amount of Co).

[0024] The product obtained in this example was characterized:

[0025] (1) Infrared spectrum, its spectrum is as follows Figure 1 shown.

[0026] IR(KBr,cm -1):3211w,2935m,1637vs,1583s,1557vs,1478s,1437s,1341s,1295vs,1229vs,1156s,1090s,1031s,942m,876m,803m,757m,634m,522w.

[0027] (2) Crystal structure analysis:

[0028] A square black-red crystal of moderate size was selected and placed on a Bruker SMART CCD diffractometer. The initial crystal structures of the products obtained in this example were solved by the SHELXS-97 direct method, and the geometric hydrogenation, non-hydrogen atomic coordinates and anisotropic thermal parameters were refined by the full matrix least squares method using SHELXL-97. The obtained crystallographic and structural refinement data are shown in Table 1 below, and some bond length and bond angle data are shown in Table 2 and Table 3 below, respectively. The structure of the obtained square block black-red crystals is shown in Figure 2 As shown, the obtained square block black-red crystals were determined to be the target product of the present invention.

[0029] Table 1 Crystallographic data of the cobalt complexes of the present invention

[0030]

[0031] Table 2 Partial bond length data of the cobalt complexes of the present invention

[0032]

[0033] Table 3 Partial bond angle data of the cobalt complexes of the present invention (°)

[0034]

[0035] Comparative Example 1-1

[0036] Example 1 was repeated, except that the volume ratio of methanol to acetonitrile was changed to 1:3.

[0037] After stopping the reaction, the temperature was slowly lowered to room temperature, and spherical brown crystals were observed to precipitate in the glass tube. After testing, it was found that the crystals were not the target product of the present invention.

[0038] Comparative Example 1-2

[0039] Example 1 was repeated, except that only methanol was used as the solvent.

[0040] After stopping the reaction, the temperature was slowly lowered to room temperature. The glass tube contained a clear liquid with no crystals or precipitation. The liquid in the glass tube was further concentrated under reduced pressure, but no crystals or precipitation was observed.

[0041] Comparative Examples 1-3

[0042] Example 1 was repeated except that only acetonitrile was used as the solvent.

[0043] After stopping the reaction, the temperature was slowly lowered to room temperature, and a black precipitate was precipitated in the glass tube. After testing, it was found that the precipitate was not the target product of the present invention.

[0044] Comparative Examples 1-4

[0045] Example 1 was repeated, except that only ethanol was used as the solvent.

[0046] After stopping the reaction, the temperature was slowly lowered to room temperature, and a brown-yellow emulsion appeared in the glass tube.

[0047] Example 2

[0048] Example 1 was repeated, except that the reaction was carried out at 100° C. and the reaction time was controlled to 36 h.

[0049] As a result, square block-shaped black-red crystals were precipitated, with a yield of 23% (0.0055 g, calculated based on the amount of Co).

[0050] The product obtained in this example was subjected to single crystal diffraction analysis, and it was determined that the obtained square block-shaped black-red crystals were the target product of the present invention.

[0051] Example 3

[0052] Example 1 was repeated, except that the reaction was carried out at 50° C. and the reaction time was controlled to 72 h.

[0053] As a result, square block-shaped black-red crystals were precipitated, with a yield of 26% (0.0062 g, calculated based on the amount of Co).

[0054] The product obtained in this example was subjected to single crystal diffraction analysis, and it was determined that the obtained square block-shaped black-red crystals were the target product of the present invention.

[0055] Experimental Example 1: The macrocyclic binuclear cobalt complex crystal form of the present invention was used as a homogeneous molecular catalyst to test its photocatalytic CO2 reduction performance in an aqueous mixed solvent system.

[0056] (1) Materials used:

[0057] Photosensitizer: [Ru(phen)3](PF6)2, catalyst: macrocyclic binuclear cobalt complex prepared according to Example 1 of the present invention (hereinafter referred to as complex 1), sacrificial agent: TEOA, LED light source (wavelength 450nm, light intensity 100mW·cm -2 , the irradiation area is 0.8cm 2 ), a 15-20 mL quartz reactor, CO2 gas, rubber tubing, analytical balance, stirrer and gas chromatograph.

[0058] (2) Photocatalytic experimental steps:

[0059] 2 mg of photosensitizer [Ru(phen)3](PF6)2 was weighed, 200 μL of sacrificial agent TEOA and complex 1 (0.5 μM) were pipetted into a quartz glass tube, 4 mL of ultra-dry acetonitrile and 1 mL of water were added, and the tube was sealed tightly with a rubber tube. After passing CO2 gas for 10 to 20 minutes, the tube was illuminated at a fixed wavelength of 450 nm and a light intensity of 100 m W·cm -2 , irradiation area is 0.8cm 2 The mixture was irradiated under an LED light with stirring for 10 hours. After completing the above operations, a gas sample was injected into a gas chromatograph to detect the CO2 reduction product CO. The results showed that when the complex 1 was 0.5 μM, it catalyzed the reduction of CO2 to produce 8.49 μmol of CO, the catalytic conversion number TON value was 1698, and the selectivity for CO was as high as 96%.

[0060] Different parallel experiments were conducted on the above method (as shown in Table 4). As shown in Table 4, under different catalytic system conditions, the catalytic effect of the macrocyclic binuclear cobalt complex crystal form of the present invention in photocatalytic CO2 reduction is significantly higher than that of most reported photocatalytic systems.

[0061] Table 4 Experimental data of photocatalytic CO2 reduction using the cobalt complex of the present invention as a catalyst

[0062]

[0063] Reaction conditions: at a constant temperature of 25°C, LED light (450 nm, 100 mW·cm -2 , illumination time 10h, illumination area 0.8cm 2) irradiated a 5 mL H2O / CH3CN (v / v 1:4) mixture containing a catalyst, a photosensitizer [Ru(phen)3](PF6)2 (0.4 mM), and a sacrificial agent TEOA (0.3 M). No. 1: Complex 1 (0.5 μM); No. 2: Complex 1 (0.2 μM); No. 3: No catalyst; No. 4: No sacrificial agent; No. 5: No photosensitizer; No. 6: No light; No. 7: No CO2, N2 atmosphere; No. 8: Xe lamp instead of LED; No. 9: 0.1 mL Hg(0) added.

[0064] As shown in Table 4, the complex crystal form of the present invention has a good photocatalytic CO2 reduction effect as a homogeneous catalyst in an aqueous system. In the photocatalytic system constructed by the present invention, when the complex 1 is 0.2μM, the catalytic conversion number TON value reaches 2050, and the selectivity of catalyzing CO is greater than 96%. However, when there is no catalyst 1 (Table 4, sequence number 2) or no CO2 (Table 4, sequence number 6) in the system, no CO is generated in the reaction system, indicating that the CO produced in this reaction does come from the photocatalytic CO2 reduction of complex 1. Experimental tests show that when a Xe lamp is used instead of an LED, the photocatalytic activity of complex 1 decreases and the CO selectivity decreases slightly (Table 4, sequence number 8), indicating that the light source has a significant effect on the catalytic performance. In addition, the Hg(0) poisoning experiment shows that the addition of Hg(0) to the reaction has a negligible effect on the photocatalytic activity, indicating that the photocatalytic CO2 reduction to CO is achieved by the complex molecular catalyst, further indicating that complex 1 is a stable molecular catalyst.

Claims

1. A macrocyclic binuclear cobalt complex having a planar structure as shown in the following formula (I): (I)。 2. A crystalline form of the macrocyclic binuclear cobalt complex according to claim 1, which belongs to the orthorhombic system, P2 1 2 1 2 1 The space group, whose unit cell parameters are: a =11.2125(1)Å, b =13.6635(2)Å, c =15.6352(2) Å; α=90.00°, β =90.00°, γ =90.00°.

3. The method for preparing the crystalline form of the macrocyclic binuclear cobalt complex according to claim 2, characterized in that: The method comprises dissolving 2-hydroxy-5-methoxyisophthalide, ethylenediamine and cobalt salt in a mixed solvent and performing a solvothermal reaction to obtain the product; wherein the mixed solvent is a composition composed of methanol and acetonitrile in a volume ratio of 1:1; and the cobalt salt is CoCl2·6H2O or CoCl2.

4. The preparation method according to claim 3, wherein The reaction was carried out at ≥50°C.

5. The preparation method according to claim 3, wherein The reaction is carried out at 80~100℃.

6. Use of the crystalline form of the macrocyclic binuclear cobalt complex according to claim 2 in photocatalysis.

7. The use according to claim 6, characterized in that: Application as a photocatalyst in photocatalytic carbon dioxide reduction.

8. A catalyst comprising the crystal form of the macrocyclic binuclear cobalt complex according to claim 2.

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