Metal-organic structures and methods for manufacturing the same

Abstract

To provide means for producing a MOF having an RHO-type topology with high gas adsorption performance in high yields.SOLUTION: One aspect of the present invention relates to a metal organic framework containing metal ions as zinc cations and ligands as 2-ethylimidazole (2-EtIm) or monocarboxylic acid anions. The metal organic framework has an RHO-type topology in which the 2-EtIm anions are partially substituted with the monocarboxylic acid anions. Another aspect of the present invention relates to a method for producing the metal organic framework having the above-described features.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a metal-organic framework and a method for producing the same.

Background Art

[0002] A metal-organic framework (hereinafter also referred to as "MOF") is a crystalline porous material composed of a metal and an organic ligand. By combining the metal and the organic ligand used, properties such as the pore diameter and surface shape of the MOF can be designed at the molecular level. The MOF is expected to be applied to, for example, gas storage materials, heterogeneous catalysts, and conductive materials.

[0003] For example, Non-Patent Document 1 describes a method for synthesizing a Zn(2-EtIm)2 MOF having a RHO-type topology from a metal ion which is a zinc cation and a ligand which is an anion of 2-ethylimidazole (2-EtIm) by a mechanochemical reaction.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As described above, a method for producing a Zn(2-EtIm)2 MOF having a RHO-type topology by a mechanochemical reaction is known. However, in the case of the conventional method, there was a problem that the yield was low due to the low solubility of the zinc compound as a raw material in an organic solvent. In addition, there was room for improvement in the gas adsorption property of the MOF produced by the conventional method.

[0006] Therefore, the present invention aims to provide a means for producing MOFs having an RHO-type topology with high gas adsorption properties in high yield. [Means for solving the problem]

[0007] The inventors investigated various means to solve the above-mentioned problems. The inventors found that in the production of MOFs by mechanochemical reaction, by adding a monocarboxylic acid to the raw materials, a zinc compound and 2-ethylimidazole, a MOF having an RHO-type topology in which a portion of the 2-ethylimidazole is substituted with a monocarboxylic acid can be obtained in high yield. Based on the above findings, the inventors completed the present invention.

[0008] In other words, the present invention encompasses the following aspects and embodiments. (Embodiment 1) A metal-organic structure having an RHO topology, comprising a metal ion which is a zinc cation and a ligand which is a 2-ethylimidazole (2-EtIm) or monocarboxylic acid anion, wherein a portion of the 2-EtIm anion is substituted with a monocarboxylic acid anion. (Embodiment 2) The metal-organic structure according to Embodiment 1, wherein the monocarboxylic acid is benzoic acid or acetic acid. (Embodiment 3) The metal-organic structure according to Embodiment 1 or 2, wherein the abundance of monocarboxylic acid anions in the ligand is in the range of 1 to 20 mol% relative to the total number of moles of ligand. (Embodiment 4) Mechanochemical reaction step in which a zinc compound, 2-ethylimidazole (2-EtIm), and a monocarboxylic acid are reacted mechanochemically in the presence of a solvent. A method for producing a metal-organic structure according to any one of embodiments 1 to 3, including the method described above. (Embodiment 5) The method according to Embodiment 4, wherein the mechanochemical reaction includes mixing the raw materials using a ball mill. [Effects of the Invention]

[0009] The present invention provides a means for producing MOFs having an RHO-type topology with high gas adsorption properties in high yield. [Brief explanation of the drawing]

[0010] [Figure 1] The X-ray diffraction patterns of the powder product from Example 1 are shown. The horizontal axis represents the 2θ value (°), and the vertical axis represents the intensity (au). 100 rpm, 200 rpm, 300 rpm, 400 rpm, or 500 rpm represent the rotation speed of the planetary ball mill during manufacturing. RHO type, ANA type, or ZnO are shown as simulation results of the calculated X-ray diffraction patterns for RHO type Zn(2-EtIm)2, ANA type Zn(2-EtIm)2, and ZnO. [Figure 2] The X-ray diffraction patterns of the powder product from Example 2 are shown. The horizontal axis represents the 2θ value (°), and the vertical axis represents the intensity (au). 100 rpm, 200 rpm, 300 rpm, 400 rpm, or 500 rpm indicate the rotation speed of the planetary ball mill during manufacturing. RHO type, ANA type, or ZnO are shown, representing the simulation results of the calculated X-ray diffraction patterns for RHO type Zn(2-EtIm)2, ANA type Zn(2-EtIm)2, and ZnO. [Figure 3] The X-ray diffraction patterns of the powder product from Example 3 are shown. The horizontal axis represents the 2θ value (°), and the vertical axis represents the intensity (au). 100 rpm, 200 rpm, 300 rpm, 400 rpm, or 500 rpm indicate the rotation speed of the planetary ball mill during manufacturing. RHO type, ANA type, or ZnO show the calculated simulation results of the X-ray diffraction patterns for RHO type Zn(2-EtIm)2, ANA type Zn(2-EtIm)2, and ZnO. [Figure 4]The X-ray diffraction patterns of the powder product from Example 4 are shown. The horizontal axis represents the 2θ value (°), and the vertical axis represents the intensity (au). 100 rpm, 200 rpm, 300 rpm, 400 rpm, or 500 rpm represent the rotation speed of the planetary ball mill during manufacturing. RHO type, ANA type, or ZnO are shown as simulation results of the calculated X-ray diffraction patterns for RHO type Zn(2-EtIm)2, ANA type Zn(2-EtIm)2, and ZnO. [Figure 5] The abundance of RHO-type MOFs relative to the total weight of the products of the examples and comparative examples is shown. The horizontal axis represents the rotational speed (rpm) of the planetary ball mill during production, and the vertical axis represents the abundance of RHO-type MOFs (weight %). [Figure 6] The N2 adsorption amounts of the products of Examples 1 to 4 and Comparative Examples 1 to 4, as determined by N2 adsorption / desorption isotherm measurements, are shown. The horizontal axis represents the rotational speed (rpm) of the planetary ball mill during production, and the vertical axis represents the N2 adsorption amount (mL (STP)·g-1) at a relative N2 pressure of 50%, as determined by N2 adsorption / desorption isotherm measurements. [Modes for carrying out the invention]

[0011] Preferred embodiments of the present invention will be described in detail below.

[0012] <1: Metal-organic structure> Another aspect of the present invention relates to a metal-organic frame (MOF). The MOF in this aspect consists of a metal ion which is a zinc (Zn) cation and a ligand which is a 2-ethylimidazole (2-EtIm) or monocarboxylic acid anion, and has an RHO type topology in which a portion of the 2-EtIm anion is substituted with a monocarboxylic acid anion.

[0013] The MOF of Zn(2-EtIm)₂ composed of Zn and 2-EtIm can adopt various topologies. Among these, the MOF of Zn(2-EtIm)₂ having the RHO-type topology is known to have a large pore volume. Also, it is known that there is a certain correlation between the pore volume of the MOF and its gas adsorption property. Therefore, the MOF of this embodiment having the RHO-type topology can have a high gas adsorption property compared to MOFs having other topologies.

[0014] In the MOF of this embodiment, a part of the 2-EtIm anion is substituted by a monocarboxylic acid anion. The monocarboxylic acid is preferably benzoic acid, acetic acid or formic acid, more preferably benzoic acid or acetic acid, and even more preferably benzoic acid. By substituting a part of the 2-EtIm anion with a monocarboxylic acid anion, a MOF having large pores can be obtained due to the template effect of the monocarboxylic acid. Particularly, in the case of a monocarboxylic acid having a bulky group such as benzoic acid, the template effect of the monocarboxylic acid becomes more prominent, and a MOF having larger pores can be obtained.

[0015] In the MOF of this embodiment, the abundance ratio of the anion of the monocarboxylic acid in the ligand is preferably in the range of 1 to 20 mol% with respect to the total number of moles of the ligand, more preferably in the range of 3 to 20 mol%, and even more preferably in the range of 3 to 12 mol%. By the abundance ratio of the anion of the monocarboxylic acid in the ligand being within the above range, the MOF of this embodiment can have a high gas adsorption property.

[0016] The MOF of this embodiment usually has the following formula (I): Zn(2-EtIm x MCA y )₂ It is represented by formula (I). In formula (I), 2-EtIm is a ligand that is the anion of 2-ethylimidazole, and MCA is a ligand that is the anion of a monocarboxylic acid. x is preferably in the range of 0.8 to 0.99, more preferably in the range of 0.8 to 0.97, and even more preferably in the range of 0.88 to 0.97. y is preferably in the range of 0.01 to 0.2, more preferably in the range of 0.03 to 0.2, and even more preferably in the range of 0.03 to 0.12. The MOF of this embodiment represented by formula (I) can have high gas adsorption properties.

[0017] The gas adsorption capacity of the MOF in this embodiment can be evaluated, for example, by measuring the N2 adsorption isotherm of the MOF and calculating the amount of N2 adsorbed at a relative N2 pressure of 50%. The amount of N2 adsorbed by the MOF in this embodiment at a relative N2 pressure of 50% is typically 180 mL (STP)·g -1 The above applies, in particular, 180 to 410 mL (STP)·g -1 It is within the range of [the specified range].

[0018] <2:Method for producing metal-organic framework> Another aspect of the present invention relates to a method for producing a metal-organic structure according to an aspect of the present invention.

[0019] The method of this embodiment includes a mechanochemical reaction step. This step includes a mechanochemical reaction of a zinc compound, 2-ethylimidazole (2-EtIm), and a monocarboxylic acid in the presence of a solvent. In this specification, a mechanochemical reaction means a process in which a chemical reaction is carried out by changing the crystalline structure of the raw materials by applying mechanical stress, such as grinding, to the raw materials.

[0020] The zinc compound used in this process is preferably zinc oxide or zinc hydroxide, and more preferably zinc oxide. The zinc compounds exemplified above can have their reactivity improved by using the solvents exemplified below. Therefore, by carrying out this process using the zinc compounds exemplified above, the mechanochemical reaction can be efficiently carried out to obtain an MOF according to one embodiment of the present invention.

[0021] The monocarboxylic acid used in this process is preferably one of the compounds exemplified above as a ligand. The presence of a monocarboxylic acid in the mechanochemical reaction system promotes the decomposition of the starting material, the zinc compound, while not promoting the decomposition of the product, the MOF. Therefore, by adding the monocarboxylic acid exemplified above and carrying out this process, it is possible to obtain a MOF according to one embodiment of the present invention in high yield while promoting the decomposition of the starting material, the zinc compound.

[0022] The solvent used in this process is preferably a water-miscible organic solvent, more preferably N,N-dimethylformamide, methanol, N,N-diethylformamide, or ethanol, and even more preferably N,N-dimethylformamide or methanol. The solvents exemplified above can dissolve the starting material 2-ethylimidazole (2-EtIm) and / or monocarboxylic acid. Therefore, by carrying out this process using the solvents exemplified above, the mechanochemical reaction can be efficiently carried out to obtain an MOF according to one embodiment of the present invention.

[0023] In this process, the mechanochemical reaction preferably includes mixing raw materials using a ball mill. In the case of this embodiment, the rotation speed of the ball mill is preferably 50 rpm or more, more preferably in the range of 50 to 800 rpm, and even more preferably in the range of 100 to 500 rpm. Also, the mixing time by the ball mill is preferably 1 hour or more, and more preferably in the range of 1 to 3 hours. By carrying out this process under the above conditions, the mechanochemical reaction can proceed efficiently to obtain the MOF of one aspect of the present invention.

[0024] As described in detail above, the MOF of one aspect of the present invention has a RHO-type topology in which a part of the 2-EtIm anion as a ligand is substituted by a monocarboxylic acid anion, and thus can have a large pore volume and high gas adsorption properties. Therefore, the MOF of one aspect of the present invention can be applied to a gas adsorption material in a gas adsorption system, a gas separation system, or a gas storage system. Also, the production method of one aspect of the present invention can obtain the MOF of one aspect of the invention having the features described above in a high yield. Therefore, the production method of one aspect of the present invention can efficiently provide a material applicable to the uses exemplified above.

Examples

[0025] Hereinafter, the present invention will be described more specifically using examples. However, the technical scope of the present invention is not limited to these examples.

[0026] <I: Production of Metal-Organic Framework> [I-1: Reagents] Zinc oxide (ZnO): Fujifilm Wako Pure Chemical Corporation 0.02 μm Practical Grade 95.0+% 2-Ethylimidazole (2-EtIm): Tokyo Chemical Industry Co., Ltd. >98.0% Benzoic acid (BA): Fujifilm Wako Pure Chemical Corporation 99.5+% Acetic acid (AA): Fujifilm Wako Pure Chemical Corporation 99.7+% Phosphate (PA): Fujifilm Wako Pure Chemical Corporation 85.0+% Methanol (MeOH): Nacalai Tesque Co., Ltd., Nacalai Standard Grade 1, ≥99.0% Ethanol (EtOH): Kanto Chemical Co., Ltd., Special Grade, 94.8% to 95.8% N,N-dimethylformamide (DMF): Fujifilm Wako Pure Chemical Corporation, ultra-dehydrated, for organic synthesis, 99.5%+

[0027] [I-2: Comparative example 1-1] In a 45 mL ball mill container, the raw materials containing 1.22 g (15 mmol) of ZnO, 2.88 g (30 mmol) of 2-EtIm, and 3 mL of DMF, along with 50 g of Φ5 mm zirconia balls, were added. The ball mill container was placed in a planetary ball mill apparatus. The rotation speed of the planetary ball mill apparatus was set to 100 rpm, and the mixture of raw materials was mixed by rotating for 3 hours. The reaction mixture was collected, and the zirconia balls were removed from the reaction mixture. 50 mL of ethanol was added to the reaction mixture and stirred. The reaction mixture was centrifuged at 16,000 rpm for 15 minutes, and the supernatant was removed. The centrifugation and supernatant removal were repeated a total of four times. The collected precipitate was dried overnight at 60°C under reduced pressure. A powder was obtained by the above treatment.

[0028] [I-3: Comparative examples 1-2, 1-3, 1-4, 1-5] Powders of Comparative Examples 1-2, 1-3, 1-4, or 1-5 were obtained in the same manner as in Comparative Example 1-1, except that the rotational speed of the planetary ball mill device was changed to 200, 300, 400, or 500 rpm.

[0029] [I-4: Comparative example 2-1] The powder of Comparative Example 2-1 was obtained in the same manner as in Comparative Example 1-1, except that the amount of 2-EtIm was changed to 3.60 g (37.5 mmol).

[0030] [I-5: Comparative Examples 2-2, 2-3, 2-4, 2-5] Powders of Comparative Examples 2-2, 2-3, 2-4, or 2-5 were obtained in the same manner as in Comparative Example 2-1, except that the rotational speed of the planetary ball mill device was changed to 200, 300, 400, or 500 rpm.

[0031] [I-6: Comparative example 3-1] The powder of Comparative Example 3-1 was obtained in the same manner as in Comparative Example 1-1, except that the amount of DMF was changed to 6 mL.

[0032] [I-7: Comparative Examples 3-2, 3-3, 3-4, 3-5] Powders of Comparative Examples 3-2, 3-3, 3-4, or 3-5 were obtained in the same manner as in Comparative Example 3-1, except that the rotational speed of the planetary ball mill device was changed to 200, 300, 400, or 500 rpm.

[0033] [I-8: Comparative example 4-1] The powder of Comparative Example 4-1 was obtained in the same manner as in Comparative Example 1-1, except that DMF was replaced with 3 mL of MeOH.

[0034] [I-9: Comparative Examples 4-2, 4-3, 4-4, 4-5] Powders of Comparative Examples 4-2, 4-3, 4-4, or 4-5 were obtained in the same manner as in Comparative Example 4-1, except that the rotational speed of the planetary ball mill device was changed to 200, 300, 400, or 500 rpm.

[0035] [I-10: Example 1-1] The powder of Example 1-1 was obtained in the same manner as in Comparative Example 1-1, except that 0.916 g (7.5 mmol) of BA was added to the raw materials.

[0036] [I-11: Examples 1-2, 1-3, 1-4, 1-5] Powders of Examples 1-2, 1-3, 1-4, or 1-5 were obtained in the same manner as in Example 1-1, except that the rotation speed of the planetary ball mill device was changed to 200, 300, 400, or 500 rpm.

[0037] [I-12: Example 2-1] The powder of Example 2-1 was obtained in the same manner as in Example 1-1, except that DMF was replaced with 3 mL of MeOH.

[0038] [I-13: Examples 2-2, 2-3, 2-4, 2-5] Powders of Examples 2-2, 2-3, 2-4, or 2-5 were obtained in the same manner as in Example 2-1, except that the rotational speed of the planetary ball mill device was changed to 200, 300, 400, or 500 rpm.

[0039] [I-14: Example 3-1] The powder of Example 3-1 was obtained in the same manner as in Comparative Example 1-1, except that 0.450 g (7.5 mmol) of AA was added to the raw materials.

[0040] [I-15: Examples 3-2, 3-3, 3-4, 3-5] Powders of Examples 3-2, 3-3, 3-4, or 3-5 were obtained in the same manner as in Example 3-1, except that the rotational speed of the planetary ball mill device was changed to 200, 300, 400, or 500 rpm.

[0041] [I-16: Example 4-1] The powder of Example 4-1 was obtained in the same manner as in Example 3-1, except that DMF was replaced with 3 mL of MeOH.

[0042] [I-17: Examples 4-2, 4-3, 4-4, 4-5] Powders of Examples 4-2, 4-3, 4-4, or 4-5 were obtained in the same manner as in Example 4-1, except that the rotational speed of the planetary ball mill device was changed to 200, 300, 400, or 500 rpm.

[0043] [I-18: Comparative example 5-1] The powder of Comparative Example 5-1 was obtained in the same manner as in Comparative Example 1-1, except that 0.865 g (7.5 mmol) of PA was added to the raw materials.

[0044] [I-19: Comparative Examples 5-2, 5-3, 5-4, 5-5] Powders of Comparative Example 5-2, 5-3, 5-4 or 5-5 were obtained in the same manner as Comparative Example 5-1, except that the rotational speed of the planetary ball mill apparatus was changed to 200, 300, 400 or 500 rpm.

[0045] [I-20: Comparative Example 6-1] Powder of Comparative Example 6-1 was obtained in the same manner as Comparative Example 5-1, except that DMF was changed to 3 mL of MeOH.

[0046] [I-21: Comparative Examples 6-2, 6-3, 6-4, 6-5] Powders of Comparative Examples 6-2, 6-3, 6-4 or 6-5 were obtained in the same manner as Example 6-1, except that the rotational speed of the planetary ball mill apparatus was changed to 200, 300, 400 or 500 rpm.

[0047] <II: Analysis of Crystal Structure of Metal-Organic Framework>[ X-ray diffraction measurements were performed on the powders of the products obtained in Comparative Examples 1-1 to 6-5 and Examples 1-1 to 4-5, respectively. The measuring apparatus and measuring conditions are shown below. Measuring apparatus: RINT RAPID II (Rigaku Corporation) Measuring conditions: Voltage 50 V, current 100 mA, collimator diameter φ0.3, sample angle ω 5°

[0048] X-ray diffraction patterns were simulated by calculation for known MOFs, specifically RHO-type Zn(2-EtIm)2 (reported under the name MAF-6) and ANA-type Zn(2-EtIm)2 (reported under the names MAF-5 or ZIF-14), as well as the raw material ZnO. These simulations were then compared with the X-ray diffraction patterns of the product powders from the comparative examples and examples. The X-ray diffraction patterns of the product powders from Examples 1, 2, 3, and 4 are shown in Figures 1, 2, 3, and 4, respectively. In each figure, the horizontal axis represents the 2θ value (°), and the vertical axis represents the intensity (au). Furthermore, in each figure, 100 rpm, 200 rpm, 300 rpm, 400 rpm, or 500 rpm represent the rotation speed of the planetary ball mill during manufacturing. RHO-type, ANA-type, or ZnO are specified by calculation. X The simulation results of the linear diffraction pattern are shown.

[0049] From the X-ray diffraction pattern of the product powder of Comparative Example 1, it was clear that the product produced at 100 rpm was a mixture of the raw material ZnO and RHO-type MOF (X-ray diffraction pattern not shown). As the rotation speed of the planetary ball mill during production increased, the peak intensity of ZnO in the X-ray diffraction pattern decreased. Therefore, it is inferred that the amount of MOF produced increases with increasing rotation speed of the planetary ball mill during production. On the other hand, when the rotation speed of the planetary ball mill during production increased to 200 rpm or more, the peak intensity of ANA-type MOF in the X-ray diffraction pattern increased. From these results, it is inferred that when the rotation speed of the planetary ball mill during production is low, RHO-type MOF is mainly produced, but as the rotation speed increases, the amount of ANA-type MOF produced increases more than the amount of RHO-type MOF produced. Similar trends were confirmed in the X-ray diffraction patterns of the product powders of Comparative Examples 2, 3, and 4 (X-ray diffraction patterns not shown).

[0050] From the X-ray diffraction patterns of the powders of the products of Example 1, it was revealed that the product was a single phase of RHO-type MOF regardless of the rotation speed of the planetary ball mill during production (Figure 1). In Example 2, a slight presence of ZnO was confirmed in the products with a rotation speed of 100 rpm or 300 rpm of the planetary ball mill during production, but the main phase was RHO-type MOF (Figure 2). In Example 3 and Example 4, as the rotation speed of the planetary ball mill during production increased, a slight amount of ANA-type MOF was produced (Figures 3 and 4).

[0051] In the X-ray diffraction pattern of the powder of the product of Comparative Example 5, peaks not attributable to RHO-type or ANA-type were observed (the X-ray diffraction pattern is not shown). In the X-ray diffraction pattern of the powder of the product of Comparative Example 6, in addition to the peaks observed in Comparative Example 5, as the rotation speed of the planetary ball mill during production increased, a slight peak of ANA-type MOF was observed (the X-ray diffraction pattern is not shown). From these results, it became clear that although the addition of PA causes the decomposition of ZnO and the promotion of the reaction, for the formation of RHO-type MOF, the addition of monocarboxylic acids such as BA and AA is preferable.

[0052] From the peak intensities in the X-ray diffraction patterns of the powders of the products of the examples and comparative examples, the abundance ratios of RHO-type MOF, ANA-type MOF, and ZnO as the raw material were calculated. The abundance ratio of RHO-type MOF with respect to the total weight of the products of the examples and comparative examples is shown in Figure 5. In the figure, the horizontal axis is the rotation speed (rpm) of the planetary ball mill during production, and the vertical axis is the abundance ratio (wt%) of RHO-type MOF.

[0053] As shown in Figure 5, in the products of Comparative Examples 1 to 4, although the abundance ratio of ZnO decreased as the rotation speed of the planetary ball mill during production increased, the abundance ratio of RHO-type MOF decreased because the formation of ANA-type MOF became advantageous. In contrast, in the products of Examples 1 to 4, RHO-type MOF was obtained as the main phase under all conditions.

[0054] <III: Characterization of Metal-Organic Frameworks> [III-1: Evaluation of pore capacity of MOFs] The N2 adsorption isotherms were measured for the products of Examples 1 to 4 and Comparative Examples 1 to 4 after pretreatment. The amount of N2 adsorbed at a relative N2 pressure of 50% was also determined. The pretreatment equipment, pretreatment conditions, measuring equipment, and measurement conditions used in this measurement are shown below. Pre-treatment device: BELPREP vacII (Microtrac-Bel Co., Ltd.) Pretreatment conditions: Vacuum degree < 10 -2 Heat at Pa, 160°C for 6 hours Measurement device: BELSORP max (Microtrac-Bel Corporation) Measurement conditions: Temperature 77 K, N2 adsorption amount measured at N2 relative pressure from 0 to 99%.

[0055] Figure 6 shows the N2 adsorption amounts of the products of Examples 1 to 4 and Comparative Examples 1 to 4, as determined by N2 adsorption / desorption isotherm measurements. In the figure, the horizontal axis represents the rotational speed (rpm) of the planetary ball mill during production, and the vertical axis represents the N2 adsorption amount (mL (STP)·g) at a relative N2 pressure of 50%, as determined by N2 adsorption / desorption isotherm measurements. -1 )

[0056] As shown in Figure 6, the products of Examples 1 to 4 tended to have higher N2 adsorption levels compared to the products of Comparative Examples 1 to 4. In the case of the products of Comparative Examples 1 to 4, the proportion of RHO-type MOFs was low in the products produced at a planetary ball mill rotation speed of 400 rpm or 500 rpm (Figure 5), but the N2 adsorption level was not significantly lower. ANA-type MOFs have approximately half the pore capacity of RHO-type MOFs. Therefore, it is presumed that if ANA-type MOFs are produced instead of RHO-type MOFs, they will exhibit a certain amount of N2 adsorption. From these results, it is presumed that the addition of monocarboxylic acids (especially benzoic acid) promotes the decomposition of ZnO and the formation of RHO-type MOFs.

[0057] [III-2: Compositional Analysis of MOFs] The products of Examples 1 to 4 were decomposed and dissolved in a deuterated solvent. 1The ratio of 2-ethylimidazole and monocarboxylic acid (benzoic acid or acetic acid) contained in the MOF was determined from the integral ratio of the spectrum after measuring the 1H-NMR spectrum. The decomposition conditions, measuring equipment, and measurement conditions used in this measurement are shown below. Decomposition conditions: Decompose the product with a 10 wt% heavy water (D2O) solution of heavy sulfuric acid (D2SO4). Measurement device: INOVA300 (Agilent Technologies)

[0058] Products from Examples 1 to 4 1 Table 1 shows the composition of the RHO-type MOF determined from the 1H-NMR spectrum.

[0059] [Table 1]

[0060] The monocarboxylic acid added during synthesis becomes a -1 valent organic anion. Therefore, it is presumed that the monocarboxylic acid was incorporated into the MOF structure by substituting a portion of 2-ethylimidazole.

[0061] It should be noted that the present invention is not limited to the embodiments described above, and various modifications are included. For example, the embodiments described above are described in detail to make the present invention easier to understand, and are not necessarily limited to those having all the configurations described. In addition, it is possible to add, delete, and / or replace some of the configurations in each embodiment with other configurations.

Claims

1. A metal-organic structure having an RHO-type topology, consisting of a zinc cation metal ion and a 2-ethylimidazole (2-EtIm) anion ligand, with a portion of the 2-EtIm anion being substituted by a monocarboxylate anion.

2. The metal-organic structure according to claim 1, wherein the monocarboxylic acid is benzoic acid or acetic acid.

3. The metal-organic structure according to claim 1, wherein the abundance of monocarboxylic acid anions in the ligand is in the range of 1 to 20 mol% with respect to the total number of moles of ligand.

4. A mechanochemical reaction step in which a zinc compound, 2-ethylimidazole (2-EtIm), and a monocarboxylic acid are reacted mechanically in the presence of a solvent. A method for producing a metal-organic structure according to claim 1, including the method described in claim 1.

5. The method according to claim 4, wherein the mechanochemical reaction includes mixing the raw materials using a ball mill.

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