Nickel-based complex as well as preparation method and application thereof

Abstract

The invention belongs to the field of new materials, and particularly relates to a nickel-based complex and a preparation method and application thereof.The nickel-based complex is a three-dimensional metal organic framework material with nanoscale pore channels prepared from 1, 4-bis (5-carboxyl-1H-benzimidazole-2-yl) benzene (H2L), 4, 4-dipyridyl (bpy) and nickel chloride hexahydrate as raw materials; the complex has the capacity of separating C3H6 / C3H8 mixed gas, the crystallographic structure data of the nickel-based complex is expanded, research on the assembly mechanism of the nickel-based complex is facilitated, industrial scale production is promoted, and the complex has guiding significance for application expansion in the aspects of gas adsorption and separation; the preparation method provided by the invention is simple in synthesis process, green and efficient.

Description

Technical Field

[0001] The present invention relates to the field of new materials, and in particular to a nickel-based complex and a preparation method and application thereof. Background Art

[0002] Metal-Organic Framework (MOF) is an organic-inorganic framework material formed by self-assembly of organic ligands and metal ions or metal ion clusters through coordination bonds. As a typical porous material, MOF has the characteristics of ultra-high specific surface area, permanent porosity and highly designable structure. Based on the self-assembly behavior of molecules, metal atoms with coordination ability are often used to construct new MOF structures. Due to the designability of MOF structure, precise design can be achieved by tuning its pore structure. Therefore, it has a wide range of applications in gas adsorption / separation, drug delivery, chemiluminescence and catalysis. In addition, MOF has precise operability at the molecular level and can use chemical methods to regulate the material structure and application. It is a basic material with great potential for application expansion.

[0003] The separation and purification of C3 gas is one of the most challenging and energy-intensive separation processes. Propylene is the world's most produced chemical raw material (over 120 million tons annually), used in the manufacture of polypropylene, synthetic fibers, medical devices, and other applications. In industrial production, propylene often coexists with propane and must be purified to a purity of ≥99.5% to meet downstream demand. The primary reason for this separation difficulty is that the molecular size difference between propylene (C3H6) and propane (C3H8) is only 0.04 nanometers (4.0Å vs. 4.3Å), and their boiling points differ by only 5.7K (225.4K vs. 231.1K). This requires traditional distillation to operate at -47°C, consuming as much as 12.9 GJ / ton of propylene. While molecular sieving can achieve selective adsorption through size differences, its narrow pores restrict molecular diffusion, resulting in inefficient mass transfer. In fact, propylene / propane separation is considered one of the seven chemical separations that have revolutionized the world.

[0004] In the existing technology, metal organic frameworks (MOFs) face the following challenges in the use of C3H6 / C3H8 binary separation: (1) Dynamic pore and structural stability issues: The flexible framework of MOF is prone to the "opening door effect", that is, the pore deformation when the pressure changes leads to a decrease in molecular sieving ability. For example, flexible MOFs such as ZIF-8 have reversible distortion of the pore window under high pressure, reducing the selectivity of propylene. In addition, most MOF materials have insufficient chemical stability, especially sensitive to humidity and high temperature. For example, silver-containing MOFs are easily oxidized and deactivated, which limits their applicability in industrial environments. (2) "Trade-off effect" of adsorption performance: Although ultra-microporous MOFs (such as ZJU-75a) achieve high selectivity (>99.99%) through the molecular sieving effect, the narrow pore volume leads to limited propylene adsorption capacity (usually <3.2 mmol / g); while macroporous MOFs (such as some Hofmann materials) have high adsorption capacity but insufficient selectivity. This contradiction stems from the inherent constraints of pore structure on the affinity of molecular size, which needs to be balanced through pore distortion design (such as HIAM-301) or high-density binding sites (such as ZJU-75), but it has not yet been completely overcome. (4) The complexity of pore environment design: It is necessary to precisely control the polarity (such as the oxygen site of BUT-321) and non-polar regions (such as the O / N / F sites of Zn-IPA-F-DMTrz) to balance the adsorption of different gases, which is difficult to design.

[0005] Therefore, there is an urgent need for a metal-organic framework material that can effectively separate C3H6 / C3H8. Summary of the Invention

[0006] The present invention addresses many deficiencies in the prior art and provides a nickel-based complex, a preparation method, and an application thereof. The nickel-based complex uses 1,4-bis(5-carboxylic acid-1H-benzimidazol-2-yl)benzene (H2L), 4,4-bipyridine (bpy), and nickel chloride hexahydrate as raw materials to prepare a three-dimensional metal-organic framework material with nanoscale pores. The complex has the ability to separate a binary mixture of C3H6 / C3H8, filling the gap in the field of constructing a new nickel-based metal-organic framework complex using 1,4-bis(5-carboxylic acid-1H-benzimidazol-2-yl)benzene as a main ligand and 4,4-bipyridine as an auxiliary ligand and its application in the separation of C3H6 / C3H8. The preparation method provided has a simple synthetic process and is green and efficient.

[0007] The specific technical solutions of the present invention are as follows: A nickel-based complex has a molecular formula of Ni(L)(bpy)·DMF·H2O, wherein Ni represents a divalent nickel ion, L represents a deprotonated 1,4-bis(5-carboxylic acid-1H-benzimidazol-2-yl)phenylcarboxylate ligand, bpy represents 4,4-bipyridine, DMF represents free N,N-dimethylformamide, and H2O represents a free water molecule.

[0008] The complex crystallizes in the monoclinic C2 / c space group. Its basic structure is derived from the smallest asymmetric unit through symmetry operations (symmetry operations are (i) 3 / 2-x, 1 / 2-y, 1-z; (ii) 1 / 2+x, 3 / 2-y, 1 / 2+z; (iii) 1 / 2+x, -1 / 2+y, +z; (iv) -1 / 2+x, 3 / 2-y, -1 / 2+z; (v) -1 / 2+x, 1 / 2+y, +z). The nickel-based complex exhibits a three-dimensional framework with a porous structure. The interior of the channel is modified with imidazole functional groups, forming a square nanoscale channel with dimensions of approximately 8×19 Å. The imidazole groups, as typical Lewis basic groups, preferentially bind to unsaturated hydrocarbons, preferentially adsorbing the highly unsaturated C3H6 and virtually ignoring the less saturated C3H8, resulting in a remarkable selective adsorption characteristic. In the nickel-based complex provided by the present invention, the imidazole groups are densely distributed on the inner wall of the pores, so that the guest molecules and the skeleton have more sufficient contact conditions, providing good conditions for host-guest combination.

[0009] The unit cell parameters are: axis length a=20.5346 Å, b=9.24250 Å, c=41.2344 Å, α=90°, β=99.32°, γ=90°; the unit cell volume is 7722.61 Å 3 The basic asymmetric unit consists of a nickel (II) ion, a deprotonated H2L ligand, and a coordinated 4,4-bipyridine molecule. The nickel ion is hexacoordinated, with two oxygen atoms originating from a carboxylic acid on the same H2L ligand, two additional oxygen atoms from carboxylic acids on two different H2L ligands, and two nitrogen atoms from two different bpy ligands.

[0010] Correspondingly, the inventors also provide a method for preparing the above nickel-based complex, which is as follows: The ligand 1,4-bis(5-carboxylic acid-1H-benzimidazol-2-yl)benzene (H2L), 4,4-bipyridine (bpy) and nickel chloride hexahydrate are dissolved in an N,N-dimethylformamide mixed solution, ultrasonically treated in a water bath at room temperature, and then heat-insulated for crystallization to precipitate green block crystals. The crystals are separated from the liquid phase by filtration to obtain the nickel-based complex.

[0011] The 1,4-bis(5-carboxylic acid-1H-benzimidazol-2-yl)benzene used has a CAS number of 35532-09-3 and a structure as follows: Formula I.

[0012] The CAS number of the 4,4-bipyridine used is 553-26-4, and its structure is as follows: Formula II.

[0013] Furthermore, the molar ratios of the 1,4-bis(5-carboxylic acid-1H-benzimidazol-2-yl)benzene, 4,4-bipyridine and nickel chloride hexahydrate are 1:1:1-1:1:5 and 1:2:1-1:2:5.

[0014] Furthermore, the N,N-dimethylformamide mixed solution is a mixture of N,N-dimethylformamide and water, with a volume ratio of 1:1.

[0015] Furthermore, each 0.05 mmol of nickel chloride hexahydrate corresponds to 3 mL of N,N-dimethylformamide mixed solution.

[0016] Furthermore, the ultrasonic condition is 30 minutes at 40 Hz, and the heat preservation crystallization operation is to place the reaction system in a constant temperature blower and keep it warm at 100-110° C. for 48-72 hours.

[0017] The nickel-based complex obtained according to the above preparation method was washed with DMF and deionized water in sequence, and then immersed in fresh chromatographic methanol for solvent exchange (three exchanges, each soaking for 24 hours). Under the same operating conditions, the same solvent exchange operation was performed with fresh chromatographic dichloromethane. The complex was transferred to an adsorption tube and degassed under vacuum conditions at 100°C for 12 hours to obtain an activated material. The activated material can be used for the separation of C3H6 / C3H8 mixed gases, and preferentially adsorbs C3H6 gas with a greater degree of unsaturation during the separation process.

[0018] The nickel-based complex prepared in this invention can be used to prepare adsorption materials. It exhibits a significant difference in adsorption between C3H6 and C3H8, preferentially adsorbing C3H6. The separation capacity of a C3H6 / C3H8 binary mixture was predicted based on the ideal adsorption solution theory (IAST). The IAST selectivity for C3H6 / C3H8 was 2.55, demonstrating potential for practical separation.

[0019] Compared with the prior art, the preparation method provided by the present invention has the following advantages: (1) The nickel-based complex prepared by the present invention has a three-dimensional framework structure with a three-dimensional pore structure. The interior of the channel is modified by imidazole functional groups, forming a square nano-scale channel with a size of about 8×19Å. The imidazole group contained therein, as a typical Lewis basic group, has the advantage of preferentially binding to unsaturated hydrocarbons, preferentially adsorbing C3H6 with a large degree of unsaturation, and almost no adsorption of C3H8 with a small degree of saturation, thereby showing a significant selective adsorption feature. The imidazole group is densely distributed on the inner wall of the channel, so that the guest molecules and the skeleton have more sufficient contact conditions, providing good conditions for host-guest binding. Therefore, the nickel-based complex prepared by the present invention shows strong separation selectivity in the application of C3H6 / C3H8 separation, expands the crystallographic structure data of the nickel-based complex, helps to study the assembly mechanism of the nickel-based complex, promotes industrial-scale production, and has guiding significance for the expansion of applications in gas adsorption and separation.

[0020] (2) The reaction system of the nickel-based complex preparation method provided by the present invention is environmentally friendly, and the proportion of organic solvents used is low; the main solvent is water, which is green, environmentally friendly and pollution-free; the reaction conditions are simple, and the synthesis efficiency is high; the amount of ligand used is low, which saves costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the coordination mode of nickel ions in the nickel-based complex prepared in Example 1; Figure 2 It is the basic asymmetric structural unit in the nickel-based complex prepared in Example 1; Figure 3 Schematic diagram of the imidazole functionalized channel of the nickel-based complex prepared in Example 1; Figure 4 This is the thermogravimetric curve of the nickel-based complex prepared in Example 1; Figure 5 This is the infrared spectrum of the nickel-based complex prepared in Example 1; Figure 6 The powder X-ray diffraction pattern and acid-base stability test pattern of the nickel-based complex in Example 1; Figure 7 The C3H6 / C3H8 single-component adsorption curve of the nickel-based complex in Example 1 at 273K is shown; Figure 8 The IAST selectivity curve of the nickel-based complex in Example 1 at 273K and C3H6 / C3H8 mixed gas (volume ratio of 50:50) is shown. DETAILED DESCRIPTION

[0022] The present invention is further illustrated below with reference to the examples, which will help those skilled in the art to further understand the present invention, but will not limit the present invention in any form. It should be noted that, for those skilled in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. The experimental methods described in the following examples, unless otherwise specified, are all conventional methods; the instruments and drugs used, unless otherwise specified, can be obtained through normal commercial channels.

[0023] Example 1 A method for preparing a nickel-based complex comprises the following steps: (1) 1,4-Bis(5-carboxylic acid-1H-benzimidazol-2-yl)benzene (H2L) (0.01 mmol, 3.7 mg), 4,4-bipyridine (bpy) (0.01 mmol, 1.5 mg) and nickel chloride hexahydrate (0.05 mmol, 11.8 mg) were dissolved in 3 mL of a mixture of N,N-dimethylformamide and water (volume ratio of 1:1). The mixture was ultrasonicated at 40 Hz for 30 min in a water bath at room temperature. The reaction system was placed in a constant temperature blower oven at 100°C for 72 h to obtain green block crystals. The crystals were separated from the liquid phase by filtration to obtain the nickel-based complex with a yield of 60% (calculated based on the mass of the ligand input).

[0024] Example 2 A method for preparing a nickel-based complex comprises the following steps: The principles and operating steps of Example 2 are basically the same as those of Example 1, except that in step (1), the molar ratio of 1,4-bis(5-carboxylic acid-1H-benzimidazol-2-yl)benzene (H2L), 4,4-bipyridine (bpy) and nickel chloride hexahydrate is 1:1:1, and the nickel-based complex is prepared with a yield of 40% (calculated based on the mass of the input ligand).

[0025] Example 3 A method for preparing a nickel-based complex comprises the following steps: The principles and operating steps of Example 3 are basically the same as those of Example 1, except that in step (1), the molar ratio of 1,4-bis(5-carboxylic acid-1H-benzimidazol-2-yl)benzene (H2L), 4,4-bipyridine (bpy) and nickel chloride hexahydrate is 1:1:2, and the nickel-based complex is prepared with a yield of 53% (calculated based on the mass of the input ligand).

[0026] Example 4 A method for preparing a nickel-based complex comprises the following steps: The principles and operating steps of Example 4 are basically the same as those of Example 1, except that in step (1), the molar ratio of 1,4-bis(5-carboxylic acid-1H-benzimidazol-2-yl)benzene (H2L), 4,4-bipyridine (bpy) and nickel chloride hexahydrate is 1:1:3, and the nickel-based complex is prepared with a yield of 60% (calculated based on the mass of the input ligand).

[0027] Example 5 A method for preparing a nickel-based complex comprises the following steps: The principles and operating steps of Example 5 are basically the same as those of Example 1, except that in step (1), the molar ratio of 1,4-bis(5-carboxylic acid-1H-benzimidazol-2-yl)benzene (H2L), 4,4-bipyridine (bpy) and nickel chloride hexahydrate is 1:1:4, and the nickel-based complex is prepared with a yield of 63% (calculated based on the mass of the input ligand).

[0028] Example 6 A method for preparing a nickel-based complex comprises the following steps: The principles and operating steps of Example 6 are basically the same as those of Example 1, except that in step (1), the molar ratio of 1,4-bis(5-carboxylic acid-1H-benzimidazol-2-yl)benzene (H2L), 4,4-bipyridine (bpy) and nickel chloride hexahydrate is 1:2:1, and the nickel-based complex is prepared with a yield of 50% (calculated based on the mass of the input ligand).

[0029] Example 7 A method for preparing a nickel-based complex comprises the following steps: The principles and operating steps of Example 7 are basically the same as those of Example 1, except that in step (1), the molar ratio of 1,4-bis(5-carboxylic acid-1H-benzimidazol-2-yl)benzene (H2L), 4,4-bipyridine (bpy) and nickel chloride hexahydrate is 1:2:2, and the nickel-based complex is prepared with a yield of 56% (calculated based on the mass of the input ligand).

[0030] Example 8 A method for preparing a nickel-based complex comprises the following steps: The principles and operating steps of Example 8 are basically the same as those of Example 1, except that in step (1), the molar ratio of 1,4-bis(5-carboxylic acid-1H-benzimidazol-2-yl)benzene (H2L), 4,4-bipyridine (bpy) and nickel chloride hexahydrate is 1:2:3, and the nickel-based complex is prepared with a yield of 60% (calculated based on the mass of the input ligand).

[0031] Example 9 A method for preparing a nickel-based complex comprises the following steps: The principles and operating steps of Example 9 are basically the same as those of Example 1, except that in step (1), the molar ratio of 1,4-bis(5-carboxylic acid-1H-benzimidazol-2-yl)benzene (H2L), 4,4-bipyridine (bpy) and nickel chloride hexahydrate is 1:2:4, and the nickel-based complex is prepared with a yield of 66% (calculated based on the mass of the input ligand).

[0032] Example 10 A method for preparing a nickel-based complex comprises the following steps: The principles and operating steps of Example 10 are basically the same as those of Example 1, except that in step (1), the molar ratio of 1,4-bis(5-carboxylic acid-1H-benzimidazol-2-yl)benzene (H2L), 4,4-bipyridine (bpy) and nickel chloride hexahydrate is 1:2:5, and the nickel-based complex is prepared with a yield of 70% (calculated based on the mass of the input ligand).

[0033] Example 11 A method for preparing a nickel-based complex comprises the following steps: The principles and operating steps of Example 11 are basically the same as those of Example 1, except that in step (2), the preset temperature of the isothermal reaction is 110°C, and the nickel-based complex is obtained with a yield of 51% (calculated based on the mass of the input ligand).

[0034] Example 12 A method for preparing a nickel-based complex comprises the following steps: The principles and operating steps of Example 12 are basically the same as those of Example 1, except that in step (2), the isothermal reaction time is shortened to 48 h, and the nickel-based complex is obtained with a yield of 43% (calculated based on the mass of the input ligand).

[0035] The nickel-based complex prepared in Example 2-12 has the same structure as that obtained in Example 1, and has the molecular formula Ni(L)(bpy)·DMF·H2O, wherein Ni represents a divalent nickel ion, L represents a deprotonated 1,4-bis(5-carboxylic acid-1H-benzimidazol-2-yl)phenylcarboxylate ligand, bpy represents 4,4-bipyridine, DMF represents free N,N-dimethylformamide, and H2O represents a free water molecule.

[0036] like Figure 1-3As shown in Tables 1-3, the nickel-based complex crystallizes in the monoclinic C2 / c space group. The basic structure is derived from the minimum asymmetric unit through symmetry operations (symmetry operations are (i) 3 / 2-x, 1 / 2-y, 1-z; (ii) 1 / 2+x, 3 / 2-y, 1 / 2+z; (iii) 1 / 2+x, -1 / 2+y, +z; (iv) -1 / 2+x, 3 / 2-y, -1 / 2+z; (v) -1 / 2+x, 1 / 2+y, +z). Each metal secondary unit is connected to 1,4-bis(5-carboxylic acid-1H-benzimidazol-2-yl)benzene to form a three-dimensional network. The basic asymmetric unit consists of a Ni(II) ion, a deprotonated H2L ligand, and a coordinated 4,4-bipyridine molecule. The nickel ion adopts a hexacoordinate mode, in which two oxygen atoms come from a carboxylic acid on the same H2L ligand, the other two oxygen atoms come from carboxylic acids on two different H2L ligands, and the two nitrogen atoms come from two different bpy ligands.

[0037] The unit cell parameters are: axis length a=20.5346 Å, b=9.2425 Å, c=41.2344 Å, α=90°, β=99.32°, γ=90°; the unit cell volume is 7722.61 Å 3 ; Z=8. Figure 3 As shown, the pores of the crystal can be seen from different directions, wherein from the 100 crystal plane of the crystal it can be clearly seen that the structure has a one-dimensional pore surrounded by imidazole.

[0038] The single crystal structure was collected at room temperature using a Bruker Apex2 Smart CXD area detector. The single crystal structure was collected using a graphite monochromator with a λ (Cu Kα) of 1.54184 Å and a ω-2 θ The crystal structure was solved by direct method using the Sir97 program, and the structure of F2 was refined using the full-matrix least-squares method with the SHELXL-97 program, with anisotropic refinement of all non-hydrogen atoms.

[0039] The nickel-based complex prepared in Example 1 was subjected to infrared spectroscopy and X-ray diffraction analysis. Figure 5 It can be seen that 1408 cm -1 The strong absorption peak near 1605 cm is derived from the stretching vibration of C=N on 4,4-bipyridine; -1 and 1314 cm -1 The absorption peaks near the ligand are derived from the antisymmetric and symmetric stretching vibration peaks of the carboxylate group. Figure 6 It can be seen that the peak positions of the synthesized crystalline powder XRD are basically consistent with those of the simulated powder XRD, confirming the successful synthesis of the complex.

[0040] Table 1 Crystal data

[0041] Table 2 Typical bond length data of crystals (unit: Å)

[0042] Table 3 Typical bond angle data of crystals (unit: °)

[0043] Application Example 1 Thermal Stability Test of Nickel-Based Complex A sample of 10.4 mg was taken and placed in an alumina crucible. The mass change curve of the material under nitrogen atmosphere was recorded using a thermogravimetric analyzer (TGA) with programmed temperature control (heating rate 10°C / min). Figure 4 It can be seen that the complex loses water molecules and DMF molecules in the system at 150°C, and then the complex can be stabilized to 350°C. After 430°C, the complex structure completely collapses and decomposes, which shows that the complex has good thermal stability.

[0044] Application Example 2 pH Stability Test of Nickel-Based Complex Take 7 samples of 20 mg each and put them into 10 mL glass bottles. Add 5 mL of deionized water in turn. Adjust the pH with hydrochloric acid and sodium hydroxide to pH = 1, 3, 5, 7, 9, and 11. After standing for 24 hours, collect the samples by dripping with filter paper. The powder XRD test shows that the Figure 6 It can be seen that the complex can maintain good crystallinity at different pH values, so it can be seen that the complex has good acid-base stability.

[0045] Application Example 3 Adsorption Performance Test of Nickel-Based Complexes on C3H6 and C3H8 Take 150 mg of the nickel-based complex prepared in Example 1, wash the crystals with DMF, ethanol and deionized water in sequence, and soak them in fresh chromatographic methanol for solvent exchange (three exchanges, each soaking for 24 h). Under the same operating conditions, the same solvent exchange operation is performed with fresh chromatographic dichloromethane. The complex is transferred to an adsorption tube and degassed under vacuum at 100°C for 12 h to obtain 140 mg of an activated sample.

[0046] At 0℃, 0.129g of activated sample was taken and pressure swing adsorption of C3H6 and C3H8 was performed on the JW-BK200 microporous analyzer in turn. The pressure range was 0-110kPa, and the single component pressure swing adsorption curve was obtained. The experimental results are shown in Figure 2. Figure 7As shown, the complex exhibits obvious adsorption differences on C3H8 and C3H8, and has the characteristic of preferentially adsorbing C3H6, followed by C3H8.

[0047] At 0℃, 0.129g of activated sample was taken to adsorb C3H6 / C3H8 mixed gas in turn, and the volume ratio of the mixed gas was 50:50. The experimental results are shown in Figure 2. Figure 8 As shown, it can be clearly seen that the nickel-based complex has a significant adsorption difference for the two gases. According to the ideal adsorption solution theory, the IAST selectivity of C3H6 / C3H8 is 2.55, which can be used to separate C3H6 / C3H8, and preferentially adsorbs C3H6 gas with a greater degree of unsaturation during the separation process.

[0048] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments. Those skilled in the art can make various variations or modifications within the scope of the claims, which will not affect the essential content of the present invention.

Claims

1. A nickel-based complex, characterized in that Its molecular formula is Ni(L)(bpy)·DMF·H2O, where Ni represents divalent nickel ion, L represents deprotonated 1,4-bis(5-carboxylic acid-1H-benzimidazol-2-yl)phenylcarboxylate ligand, bpy represents 4,4-bipyridine, DMF represents free N,N-dimethylformamide, and H2O represents free water molecules.

2. The nickel-based complex according to claim 1, characterized in that The complex crystallizes in the monoclinic C2 / c space group and possesses a three-dimensional framework with a nanoporous structure. The interior of the channel is modified with imidazole functional groups, surrounding a square nanoscale pore with dimensions of approximately 8 × 19 Å. The unit cell parameters are: axis length a = 20.5346 Å, b = 9.2425 Å, c = 41.2344 Å, α = 90°, β = 99.32°, γ = 90°; and the unit cell volume is 7722.61 Å. 3 ; Z = 8; the basic asymmetric unit includes a Ni (II) ion, a deprotonated H2L ligand molecule and a coordinated 4,4-bipyridine molecule; The nickel ion adopts a hexacoordinate mode, in which two oxygen atoms come from a carboxylic acid on the same H2L ligand, the other two oxygen atoms come from carboxylic acids on two different H2L ligands, and the two nitrogen atoms come from two different bpy ligands.

3. The method for preparing the nickel-based complex according to claim 1, characterized in that: The specific steps are as follows: The ligand 1,4-bis(5-carboxylic acid-1H-benzimidazol-2-yl)benzene, 4,4-bipyridine and nickel chloride hexahydrate are dissolved in an N,N-dimethylformamide mixed solution, ultrasonically treated in a water bath at room temperature, and then heat-insulated for crystallization to precipitate green block crystals. The crystals are separated from the liquid phase by filtration to obtain the nickel-based complex.

4. The method for preparing the nickel-based complex according to claim 3, wherein The molar ratios of the 1,4-bis(5-carboxylic acid-1H-benzimidazol-2-yl)benzene, 4,4-bipyridine and nickel chloride hexahydrate are 1:1:1-1:1:5 and 1:2:1-1:2:

5.

5. The method for preparing the nickel-based complex according to claim 3, wherein: The N,N-dimethylformamide mixed liquid is a mixture of N,N-dimethylformamide and water, with a volume ratio of 1:

1.

6. The method for preparing the nickel-based complex according to claim 3, wherein: Every 0.05 mmol of nickel chloride hexahydrate corresponds to 3 mL of N,N-dimethylformamide mixture.

7. The method for preparing the nickel-based complex according to claim 3, wherein: The ultrasonic condition is 30 min at 40 Hz.

8. The method for preparing the nickel-based complex according to claim 3, wherein: The heat preservation crystallization operation is to place the reaction system in a constant temperature blower and keep it warm at 100-110° C. for 48-72 hours.

9. Use of the nickel-based complex according to claim 1 in separating C3H6 / C3H8 mixed gases.

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