Preparation method and application of a binuclear silver complex

Abstract

The application discloses a preparation method and application of a silver dinuclear complex, and belongs to the technical field of complexes. Two silver ions and 2-(5-fluoropyridine-2-yl) acetic acid are simultaneously coordinated, and 2,2-bipyridine is used as an auxiliary ligand to increase coordination sites of the complex, a multi-nuclear structure is formed, and the silver dinuclear complex with a novel structure is obtained. It is found through cyclic voltammetry testing that the silver dinuclear complex has electrochemical performance, and can be applied to catalytic reduction of CO2 decomposition to prepare CO as a catalyst for catalytic reduction of carbon dioxide.

Description

Technical Field

[0001] This invention relates to the field of coordination technology, and in particular to a method for preparing a binuclear silver coordination compound and its application. Background Technology

[0002] With the continuous rise in atmospheric carbon dioxide concentration, global environmental and climate deterioration has become a pressing issue for humanity. Electrocatalytic carbon dioxide reaction systems, which convert renewable energy into value-added fuels and chemicals, represent one of the most promising pathways to achieving a sustainable energy economy and carbon neutrality. In recent decades, homogeneous catalytic systems using metal complexes as light-absorbing substances and catalysts have received widespread attention. Firstly, the central metal and ligands in metal complexes typically possess multiple redox valence states, making the multi-electron reduction process of carbon dioxide reduction feasible, allowing for the synthesis of metal complexes with different properties as needed. Secondly, the structure of metal complexes is easily tunable; different groups and frameworks can be designed and synthesized to regulate their structure, continuously optimizing their catalytic performance and leading to the search for highly efficient carbon dioxide reduction catalysts. To ensure the stability of the catalyst molecule during the CO2 reduction process, ligands with good stabilizing ability for high-valence metal atoms are required for coordination. Metal complexes with MOF structures are commonly used, while complexes of heterocyclic organic acids (silver) are rarely reported. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing a binuclear silver complex and its application, so as to solve the above-mentioned problems existing in the prior art.

[0004] To achieve the above objectives, the present invention provides the following solution:

[0005] One of the technical solutions of the present invention is a silver binuclear complex, the chemical structure of which is shown in formula (I):

[0006]

[0007] Furthermore, the molecular formula of the silver binuclear complex is C0 48 H 36 The molecular structure diagram of Ag2F4N8O8 is shown below. Figure 1 As shown; the silver binuclear complex is a colorless, transparent rod-shaped crystal.

[0008] The second technical solution of the present invention: A method for preparing the above-mentioned binuclear complex of silver, comprising the following steps: mixing silver nitrate solution and 2-(5-fluoropyridin-2-yl)acetic acid solution, then adding 2,2-bipyridine, stirring evenly, and heating to carry out a solvothermal reaction to obtain the silver binuclear complex. The chemical structural formula of 2-(5-fluoropyridin-2-yl)acetic acid is as follows. The chemical structural formula of 2,2-bipyridine is:

[0009] 2,2-Bipyridine is a bidentate auxiliary ligand, which increases the number of coordination sites. 2-(5-fluoropyridin-2-yl)acetic acid is a compound containing a nitrogen heterocycle and a fluorine atom, which has good chemical stability and reactivity. The combination of 2,2-bipyridine and 2-(5-fluoropyridin-2-yl)acetic acid can yield a stable complex with electrochemical properties.

[0010] Furthermore, the specific operation of mixing the silver nitrate solution and the 2-(5-fluoropyridin-2-yl)acetic acid solution is as follows: the silver nitrate solution is added to the 2-(5-fluoropyridin-2-yl)acetic acid solution.

[0011] Furthermore, the solvent of the silver nitrate solution is composed of methanol and acetonitrile in a volume ratio of 1:2, or ethanol and acetonitrile in a volume ratio of (1-5):1.

[0012] More preferably, the solvent of the silver nitrate solution is composed of methanol and acetonitrile in a volume ratio of 1:2.

[0013] Furthermore, the solvent of the 2-(5-fluoropyridin-2-yl)acetic acid solution is composed of methanol and acetonitrile in a volume ratio of 1:2, or of ethanol and acetonitrile in a volume ratio of (1-5):1.

[0014] More preferably, the solvent of the 2-(5-fluoropyridin-2-yl)acetic acid solution is composed of methanol and acetonitrile in a volume ratio of 1:2.

[0015] Furthermore, the silver nitrate solution is prepared by dissolving silver nitrate in a solvent (mixed solvent) under constant stirring to obtain a silver nitrate solution; the concentration of the silver nitrate solution is 0.02 mmol / mL.

[0016] Further, the 2-(5-fluoropyridin-2-yl)acetic acid solution is prepared by dissolving 2-(5-fluoropyridin-2-yl)acetic acid in a solvent (mixed solvent) under constant stirring to obtain a 2-(5-fluoropyridin-2-yl)acetic acid solution; the concentration of the 2-(5-fluoropyridin-2-yl)acetic acid solution is 0.04 mmol / mL.

[0017] Furthermore, the volume ratio of the silver nitrate solution to the 2-(5-fluoropyridin-2-yl)acetic acid solution is 1:1.

[0018] Furthermore, the molar ratio of silver nitrate in the silver nitrate solution, 2-(5-fluoropyridin-2-yl)acetic acid in the 2-(5-fluoropyridin-2-yl)acetic acid solution, and added 2,2-bipyridine is 1:2:1.

[0019] Furthermore, the temperature control procedure for the solvothermal reaction is as follows: heat to 85°C and hold for 60 min, continue to heat to 180°C and hold for 2 h, continue to heat to 200°C and hold for 60 min, then cool down to 180°C and hold for 2 h, continue to cool down to 85°C and hold for 60 min, and finally cool down to room temperature.

[0020] Furthermore, the heating rate during the heating process is 5°C / min, and the cooling rate during the cooling process is 5°C / min.

[0021] Furthermore, after the solvothermal reaction is completed, the process also includes steps of filtration, washing, and vacuum drying.

[0022] The third technical solution of the present invention: the application of the above-mentioned silver binuclear complex in the catalytic reduction of CO2 to CO.

[0023] Furthermore, the silver binuclear complex serves as a catalyst in the catalytic reduction of CO2 to CO process.

[0024] The present invention discloses the following technical effects:

[0025] (1) In this invention, two silver ions are simultaneously coordinated with 2-(5-fluoropyridin-2-yl)acetic acid, and 2,2-bipyridine is used as an auxiliary ligand to increase the coordination sites of the complex, forming a polynuclear structure and obtaining a novel binuclear silver complex. Cyclic voltammetry tests revealed that this binuclear silver complex has electrochemical properties and can be used as a catalyst for the catalytic reduction of CO2 to CO.

[0026] (2) The present invention adopts a solvothermal preparation method, and successfully prepares a colorless and transparent rod-shaped silver binuclear complex by programmably controlling the temperature of the solvothermal reaction (i.e., programmable temperature control). The colorless and transparent rod-shaped crystal has good crystal stability and stable catalytic activity in the catalytic reduction of CO2.

[0027] (3) The preparation method and post-processing method of the present invention are simple. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the molecular structure obtained by the crystallization software SHELXTL for the silver binuclear complex prepared in Example 1.

[0030] Figure 2 Infrared spectrum of the silver binuclear complex obtained in Example 1;

[0031] Figure 3 Cyclic voltammetry curves of the silver binuclear complex and its ligand 2-(5-fluoropyridin-2-yl)acetic acid obtained in Example 1 are shown.

[0032] Figure 4 The results show the catalytic stability test results of the silver binuclear complex prepared in Example 1. Detailed Implementation

[0033] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0034] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0035] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0036] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0037] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0038] This invention provides a binuclear complex of silver, with the chemical structural formula shown in formula (I):

[0039]

[0040] The molecular formula is C 48 H 36 Ag2F4N8O8 is a colorless, transparent, rod-shaped crystal.

[0041] The present invention also provides a method for preparing the above-mentioned silver binuclear complex, comprising the following steps: mixing silver nitrate solution and 2-(5-fluoropyridin-2-yl)acetic acid solution, then adding 2,2-bipyridine, stirring evenly, and heating to carry out a solvothermal reaction to obtain the silver binuclear complex.

[0042] Furthermore, the more specific operational steps include:

[0043] Under constant stirring, silver nitrate was dissolved in a mixed solvent (methanol:acetonitrile volume ratio = 1:2 or ethanol:acetonitrile volume ratio = (1-5):1) to obtain a silver nitrate solution (concentration of 0.02 mmol / mL); under constant stirring, 2-(5-fluoropyridin-2-yl)acetic acid was dissolved in a mixed solvent (methanol:acetonitrile volume ratio = 1:2 or ethanol:acetonitrile volume ratio = (1-5):1) to obtain a 2-(5-fluoropyridin-2-yl)acetic acid solution (concentration of 0.04 mmol / mL); the silver nitrate solution was added to the 2-(5-fluoropyridin-2-yl)acetic acid solution, and then 2,2-bipyridine (in the silver nitrate solution) was added. The silver nitrate, the 2-(5-fluoropyridin-2-yl)acetic acid in the 2-(5-fluoropyridin-2-yl)acetic acid solution, and the added 2,2-bipyridine were mixed in a molar ratio of 1:2:1. After stirring evenly, a solvothermal reaction was carried out. The specific temperature control program was as follows: the temperature was raised to 85℃ and held for 60 min, then raised to 180℃ and held for 2 h, then raised to 200℃ and held for 60 min, then lowered to 180℃ and held for 2 h, then lowered to 85℃ and held for 60 min, and finally lowered to room temperature (the heating rate was 5℃ / min and the cooling rate was 5℃ / min). The mixture was then filtered, washed, and vacuum dried to obtain the silver binuclear complex.

[0044] The present invention also provides an application of the above-mentioned silver binuclear complex in the catalytic reduction of CO2 to CO.

[0045] Furthermore, the silver binuclear complex serves as a catalyst in the catalytic reduction of CO2 to CO process.

[0046] The present invention will be further described below with reference to specific embodiments.

[0047] All raw materials and reagents used in the following examples and comparative examples are commercially available products.

[0048] Example 1

[0049] A binuclear complex of silver, prepared by the following steps:

[0050] Under constant stirring (1200 rpm), 16.9 mg (0.1 mmol) of silver nitrate was dissolved in 5 mL of a mixed solvent (methanol:acetonitrile volume ratio = 1:2) to obtain a silver nitrate solution. Under constant stirring (1200 rpm), 31.0 mg (0.2 mmol) of 2-(5-fluoropyridin-2-yl)acetic acid was dissolved in 5 mL of a mixed solvent (methanol:acetonitrile volume ratio = 1:2) to obtain a 2-(5-fluoropyridin-2-yl)acetic acid solution. The obtained silver nitrate solution was added to the 2-(5-fluoropyridin-2-yl)acetic acid solution, and then 15.6 mg (0.1 mmol) of 2,2-bipyridine was added. After stirring until homogeneous, the solution was obtained. A mixed solution was prepared and placed in a high-pressure reactor for a solvothermal reaction under programmed temperature control. The specific temperature control program was as follows: heat to 85°C and hold for 60 min, then heat to 180°C and hold for 2 h, then heat to 200°C and hold for 60 min, then cool to 180°C and hold for 2 h, then cool to 85°C and hold for 60 min, and finally cool to room temperature (heating rate and cooling rate were both 5°C / min). The solution in the reactor was then filtered, and the filtered product was washed three times with a mixed solvent (methanol:acetonitrile volume ratio = 1:2), and then vacuum dried. The resulting colorless, transparent rod-shaped crystals were the binuclear complex of silver (the calculated yield was 48.6%).

[0051] Comparative Example 1

[0052] Similar to Example 1, the only difference is that after obtaining the mixed solution, no solvothermal reaction is performed. Instead, the solvent is slowly evaporated at room temperature. Specifically, the mixed solution is placed in a container, the container is sealed with plastic wrap and small holes are punched in the plastic wrap. The sealed and perforated container is placed in a room temperature environment to allow the solvent to evaporate slowly. In the end, no testable crystals were obtained.

[0053] Comparative Example 2

[0054] Similar to Example 1, except that after the solvothermal reaction, the solution in the reactor was filtered and the filtered product was washed three times with a mixed solvent (methanol:acetonitrile volume ratio = 1:2). The washed product was then placed in a container, sealed with plastic wrap and small holes were punched in the plastic wrap. The sealed and perforated container was placed in a room temperature environment to allow the remaining solvent to evaporate slowly, and finally a powdered solid was obtained.

[0055] Comparative Example 3

[0056] Same as Example 1, except that the temperature control procedure during the solvothermal reaction was as follows: heat to 100°C and hold for 60 min, continue to heat to 150°C and hold for 60 min, continue to heat to 260°C and hold for 120 min, then cool to 150°C and hold for 60 min, continue to cool to 100°C and hold for 30 min, and finally cool to room temperature (heating rate is 5°C / min and cooling rate is 5°C / min). This comparative example ultimately yielded colorless snowflake-like crystals.

[0057] Comparative Example 4

[0058] Same as Example 1, except that the temperature control procedure during the solvothermal reaction was as follows: heat to 90°C and hold for 60 min, continue to heat to 120°C and hold for 60 min, continue to heat to 240°C and hold for 60 min, then cool to 120°C and hold for 60 min, continue to cool to 90°C and hold for 30 min, and finally cool to room temperature (heating rate is 5°C / min and cooling rate is 5°C / min). This comparative example ultimately yielded colorless snowflake-like crystals.

[0059] Comparative Example 5

[0060] Same as Example 1, except that the mixed solvent used was a methanol:acetonitrile mixed solvent with a volume ratio of 1:1. This comparative example finally yielded colorless snowflake-shaped crystals.

[0061] Comparative Example 6

[0062] Same as Example 1, except that the mixed solvent used was a methanol:acetonitrile mixed solvent with a volume ratio of 2:1. This comparative example finally yielded colorless needle-like crystals.

[0063] Example 1

[0064] Elemental analysis of the colorless, transparent rod-shaped crystals obtained in Example 1 yielded the following results: C 48 H 36 Ag2F4N8O8, molecular weight 1144.58.

[0065] Calculated values: C, 50.35; H, 3.14; N, 9.97;

[0066] Test values: C, 50.29; H, 3.18; N, 9.91.

[0067] The colorless, transparent rod-shaped crystal obtained in Example 1 was then tested using a Bruker SMART 1000 CCD surface diffractometer, specifically at a wavelength of [wavelength value missing]. MoKα rays were used in an ω-scan manner. Data reconstruction of the collected diffraction points was performed using the SAINT program, and data correction was performed using the SADABS program. Based on the full-angle least squares method, the coordinates of all non-hydrogen atoms were found on the difference Fourier plot using the direct method with the SHELLXTL 5.1 crystal solving software package. Then, all non-hydrogen atoms were refined using anisotropy. The resulting molecular structure diagram is shown below. Figure 1 As shown, the obtained crystallographic parameters are shown in Table 1:

[0068] Table 1

[0069]

[0070] R1=∑||F o |-|F c || / ∑|F o |,wR2=[∑w(F o 2 -F c 2 ) 2 / ∑w(F o 2 ) 2 ] 1 / 2

[0071] As shown in Table 1, the R1 value is close to 0.05, indicating that there are no errors in the structural analysis and the true molecular structure has been obtained.

[0072] Example 2

[0073] Figure 2 The infrared spectrum of the silver binuclear complex obtained in Example 1 is shown below. Figure 2 It can be seen that the complex is at 3060cm -1 The broadband width at 1320 cm⁻¹ is likely due to the ν(CH) stretching vibration in the pyridine ring. -1 There is a sharp peak at 1620 and 1505 cm⁻¹, which may be due to the ν(CF) stretching vibration in the pyridine ring. -1 The characteristics at this point are related to both asymmetric (COO-) and symmetric (COO-) stretching vibrations. The value of Δν(νas(COO-)-νs(COO-)) is 120 cm. -1 (less than 200cm) -1 The results indicate that the carboxylate is coordinated with Ag(I) in a chelate manner, which is in good agreement with the X-ray diffraction structure analysis.

[0074] Example 3

[0075] The silver binuclear complex prepared in Example 1 and its ligand 2-(5-fluoropyridin-2-yl)acetic acid were tested by cyclic voltammetry.

[0076] Test conditions: The cyclic voltammetry test was conducted using a CHI-630E electrochemical workstation manufactured by Shanghai Chenhua Instrument Co., Ltd., employing a three-electrode system: a glassy carbon electrode as the working electrode, an Ag / AgNO3 electrode (0.1M AgNO3 acetonitrile solution) as the reference electrode, and a platinum wire electrode as the counter electrode. The electrolytes were a complex solution and a ligand solution (0.5mM concentration). Rubber stoppers containing the electrodes were inserted into the mouths of three-necked flasks to seal them. CO2 gas was passed through for approximately 15 minutes to maintain the CO2 concentration in the electrolyte at 0.5mM. The scan rate was 100mV / s, and a well-sealed electrolytic cell was used. Cyclic voltammetry was performed on the electrochemical workstation to measure the electrochemically active surface area.

[0077] The cyclic voltammetry curves obtained from the test are as follows: Figure 3 As shown, by Figure 3 It can be seen that the electrochemically active surface area of ​​the binuclear silver complex prepared in Example 1 is higher than that of its ligand, indicating that both the binuclear silver complex and the ligand used have electrochemical activity and can be used as catalysts for the catalytic reduction of carbon dioxide. Moreover, compared with the ligand, the ability of the silver binuclear complex obtained by coordinating with silver salt is effectively improved.

[0078] Example of effect 4

[0079] The silver binuclear complex prepared in Example 1 was used to test the stability of the catalyst.

[0080] Test conditions: The stability test of electrocatalytic reduction of CO2 was conducted in an H-type electrolytic cell, with the cathode chamber filled with CO2-saturated 0.5M KHCO3 electrolyte. CO2 gas was introduced into the electrolyte at a flow rate of 20 mL / min using a flow controller, and the dissolved CO2 gas provided the feedstock for the cathode.

[0081] Test results are as follows Figure 4 As shown, the silver binuclear complex was subjected to constant voltage testing (0.42V vs. RHE) in an H-type electrolytic cell filled with 0.5M KHCO3 electrolyte. The current density curve of the silver binuclear complex showed that the current density remained relatively stable over 45 hours. CO production was detected in real-time using online gas chromatography. It can be seen that the CO yield remained at 86% after 45 hours, indicating that the silver binuclear complex can serve as a catalyst for CO2 reduction and possesses good electrocatalytic stability.

[0082] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A binuclear complex of silver, characterized in that, The chemical structural formula of the binuclear complex of silver is shown in formula (I): Formula (I).

2. A method for preparing a binuclear silver complex as described in claim 1, characterized in that, The process includes the following steps: mixing silver nitrate solution and 2-(5-fluoropyridin-2-yl)acetic acid solution, adding 2,2-bipyridine, stirring until homogeneous, and then heating to carry out a solvothermal reaction to obtain the silver binuclear complex; The temperature control procedure for the solvothermal reaction is as follows: heat to 85°C and hold for 60 min, continue to heat to 180°C and hold for 2 h, continue to heat to 200°C and hold for 60 min, then cool down to 180°C and hold for 2 h, continue to cool down to 85°C and hold for 60 min, and finally cool down to room temperature.

3. The method for preparing the binuclear silver complex as described in claim 2, characterized in that, The solvent of the silver nitrate solution is composed of methanol and acetonitrile in a volume ratio of 1:2, or ethanol and acetonitrile in a volume ratio of (1~5):

1.

4. The method for preparing the binuclear silver complex as described in claim 2, characterized in that, The solvent of the 2-(5-fluoropyridin-2-yl)acetic acid solution is composed of methanol and acetonitrile in a volume ratio of 1:2, or ethanol and acetonitrile in a volume ratio of (1~5):

1.

5. The method for preparing the binuclear silver complex as described in claim 2, characterized in that, The molar ratio of silver nitrate in the silver nitrate solution, 2-(5-fluoropyridin-2-yl)acetic acid in the 2-(5-fluoropyridin-2-yl)acetic acid solution, and added 2,2-bipyridine is 1:2:

1.

6. The method for preparing the binuclear silver complex as described in claim 2, characterized in that, The heating rate during the heating process is 5℃ / min, and the cooling rate during the cooling process is 5℃ / min.

7. The application of a silver binuclear complex as described in claim 1 in the catalytic reduction of CO2 to CO.

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