Metal organic structure and shaped body

Abstract

This metal organic structure for gas adsorption has: a first organic ligand that mainly forms a skeleton of the metal organic structure; and a second organic ligand different from the first organic ligand. Among atoms forming the first organic ligand and the second organic ligand, atoms having the highest electronegativity are included at least in the second organic ligand.

Description

Metal-organic framework and shaped body

[0001] The present disclosure relates to metal-organic frameworks.

[0002] Metal-organic frameworks that form porous structures by utilizing coordinate bonds between metal ions and organic substances have been known. Metal-organic frameworks are also generally referred to as MOFs (Metal Organic Frameworks) or PCPs (Porous Coordination Polymers). Because metal-organic frameworks are in powder form, shaping them has been investigated for practical use (see, for example, Patent Documents 1 to 3).

[0003] Patent No. 4980918 Patent No. 6272696 Patent No. 7229654

[0004] MOFs are expected to be used in gas and vapor adsorption and separation systems using PSA (Pressure Swing Adsorption) and TSA (Thermal Swing Adsorption) as adsorbents for gases and vapors. If the gas adsorption / desorption hysteresis of MOFs is large (the gas adsorption / desorption rate is slow), the throughput per unit time decreases, which may result in an increase in the size of the gas adsorption / desorption system and an increase in system costs.

[0005] In the techniques described in Patent Documents 1 to 3, a binder is added to give shape to the metal organic framework, but the addition of the binder may increase the hysteresis of gas adsorption / desorption. Therefore, there is a need for a technique to reduce the hysteresis of gas adsorption / desorption of a powder metal organic framework.

[0006] The present disclosure can be realized in the following aspects. (1) According to one aspect of the present disclosure, there is provided a metal-organic framework for gas adsorption, the metal-organic framework having a first organic ligand that mainly constitutes a skeleton of the metal-organic framework and a second organic ligand different from the first organic ligand, and among the atoms constituting the first organic ligand and the second organic ligand, an atom having the highest electronegativity is contained in at least the second organic ligand.

[0007] According to the metal organic framework of this form, the metal organic framework has a second organic ligand that is different from the first organic ligand that mainly constitutes the skeleton of the metal organic framework, and the second organic ligand has more gas / vapor adsorption sites than the first ligand, so that the hysteresis of gas adsorption / desorption can be reduced.

[0008] (2) In the metal organic framework of the above embodiment, the second organic ligand may have more oxygen atoms and / or more nitrogen atoms than the first organic ligand. The oxygen atoms and nitrogen atoms exhibit basicity. When the metal organic framework is used, for example, as a carbon dioxide adsorbent, the carbon dioxide interacts with the oxygen atoms or nitrogen atoms exhibiting basicity and is adsorbed by the metal organic framework. Therefore, the metal organic framework of this embodiment can reduce hysteresis in gas adsorption / desorption.

[0009] (3) In the metal organic framework of the above embodiment, the second organic ligand may have more —COOH groups and / or —COO— groups than the first organic ligand. The —COOH groups and —COO— groups promote the adsorption of gases and vapors, and this can further reduce the hysteresis of gas adsorption and desorption.

[0010] (4) In the metal-organic framework of the above embodiment, the metal-organic framework may be a flexible metal-organic framework having structural flexibility, which can realize more efficient gas storage and separation than a rigid metal-organic framework.

[0011] (5) In the metal organic framework of the above aspect, the gas may be carbon dioxide. When the gas to be adsorbed is carbon dioxide, the effect can be obtained by reducing the hysteresis of gas adsorption and desorption.

[0012] (6) In the metal organic framework of the above embodiment, when the saturated adsorption capacity of carbon dioxide of the metal organic framework at 0.975 atm is A and the saturated adsorption capacity of carbon dioxide of the second metal organic framework having the first organic ligand instead of the second organic ligand in the metal organic framework is B, (A−B) / A<0.1 may be satisfied. In this way, the adsorption and desorption capacities of the metal organic framework can be appropriately maintained.

[0013] (7) The metal organic framework of the above embodiment may have a crystal structure pattern equivalent to that of a second metal organic framework having the first organic ligand instead of the second organic ligand in the metal organic framework, thereby making it possible to appropriately maintain the adsorption and desorption amounts of the metal organic framework.

[0014] (8) According to another aspect of the present disclosure, there is provided a shaped body. The shaped body includes the metal organic framework of the above aspect. According to the shaped body of this aspect, the hysteresis of gas adsorption / desorption of the metal organic framework is small, so that even if a binder is included, the hysteresis of gas adsorption / desorption of the shaped body can be reduced.

[0015] The present disclosure can be realized in various forms other than those described above, for example, in the form of a gas separation adsorbent, a gas separation system, a method for manufacturing a metal organic framework, a method for manufacturing a shaped body, a method for manufacturing a gas adsorbent, etc.

[0016] FIG. 1 is a diagram showing an example of a first organic ligand L and a second organic ligand L' of a MOF. FIG. 2 is a process diagram showing an example of a method for producing a MOF. FIG. 3 is a diagram showing an XRD of a MOF powder to which a COO-group has been added. FIG. 4 is a diagram showing an IR of a MOF powder to which a COO-group has been added. FIG. 5 is a process diagram showing an example of a method for producing a shaped body. FIG. 6 is a diagram showing the composition of each sample and whether or not an increase in hysteresis in gas adsorption / desorption can be suppressed. ２ 1 is a graph showing the adsorption and desorption capacity of a shaped body sample. ２ 1 is a diagram showing adsorption / desorption capacity. 2 is a diagram showing the structural formula of a part of the particle interface of samples S1 and S3. 3 is a diagram showing the adsorption / desorption capacity. 4 is a diagram showing the structural formula of a part of the particle interface of samples S1 and S3. 5 is a diagram showing the adsorption / desorption capacity. ２ 1 is an explanatory diagram conceptually showing the interaction between oxygen and nitrogen and polar molecules;

[0017] <Embodiments> A. Structure of Metal-Organic Framework (MOF): A metal-organic framework according to an embodiment of the present disclosure is a metal-organic framework for gas adsorption, which comprises a first organic ligand that mainly constitutes the framework of the metal-organic framework, and a second organic ligand that is different from the first organic ligand, and among the atoms constituting the first organic ligand and the second organic ligand, the atom with the highest electronegativity is contained in at least the second organic ligand. Here, "mainly" means that the amount of the first organic ligand is the majority, and refers to 51% or more.

[0018] FIG. 1 is a diagram showing an example of the first organic ligand L and the second organic ligand L' of the MOF of this embodiment. When the MOF is an ELM (Elastic Layer-structured MOF), the organic ligand (first organic ligand L) is 4,4'-bipyridine. In MOF No. 1 of this embodiment, pyridine carboxylic acid (isonicotinic acid) is added, and the second organic ligand L' is pyridine carboxylic acid. The atoms constituting the first organic ligand L are carbon (C), nitrogen (N), and hydrogen (H). On the other hand, the atoms constituting the second organic ligand L' are carbon (C), nitrogen (N), hydrogen (H), and oxygen (O). Of carbon (C), nitrogen (N), hydrogen (H), and oxygen (O), oxygen (O) has the highest electronegativity. That is, MOF No. 1 shown in FIG. In the example of MOF No. 1, the atom with the highest electronegativity (O) among the atoms constituting the first organic ligand L and the second organic ligand L' is contained in the second organic ligand L'. Similarly, in MOF No. 2, the atom with the highest electronegativity (O) among the atoms constituting the first organic ligand L and the second organic ligand L' is contained in the second organic ligand L'. In MOFs Nos. 3 and 4, the atom with the highest electronegativity (N) among the atoms constituting the first organic ligand L and the second organic ligand L' is contained in both the first organic ligand L and the second organic ligand L'.

[0019] When the MOF is, for example, UIO-66, the second organic ligand L' can be, for example, 2-aminoterephthalic acid, which has a functional group containing nitrogen (N) or oxygen (O) in terephthalic acid.

[0020] According to the metal-organic framework of the present embodiment, the metal-organic framework has a second organic ligand different from the first organic ligand that mainly constitutes the framework of the metal-organic framework, and the second organic ligand has more gas / vapor adsorption sites than the first ligand, so that the hysteresis of gas adsorption / desorption can be reduced. Note that, if all of the first organic ligands that mainly constitute the framework of the metal-organic framework are changed to second organic ligands, it may become difficult to maintain the structure of the metal-organic framework, so the metal-organic framework has a first organic ligand that mainly constitutes the framework of the metal-organic framework and a second organic ligand different from the first organic ligand.

[0021] The type of MOF is not particularly limited, and examples include ELMs such as ELM-11, ELM-12, and ELM-31, which use 4,4'-bipyridine as an organic ligand, and rigid MOFs such as UIO and MIL-101, to which a second ligand has been added. Flexible MOFs with structural flexibility are preferred. This allows for more efficient gas storage and separation than rigid MOFs.

[0022] The gas to be adsorbed by MOFs is not particularly limited, and various gases such as carbon dioxide and water vapor can be adsorbed. Carbon dioxide is preferably the gas to be adsorbed. Carbon dioxide has an electron-poor region in which bonding electrons are strongly attracted to the oxygen side, which easily interacts with basic sites (unshared electron pairs). Carbon dioxide is more suitable because it is adsorbed by MOFs due to the interaction between this electron-poor region and basic sites (atoms with the highest electronegativity).

[0023] When the saturated adsorption capacity of carbon dioxide of the MOF at 0.975 atm is A and the saturated adsorption capacity of carbon dioxide of the second MOF having the first organic ligand instead of the second organic ligand in the MOF is B, it is preferable that (A - B) / A < 0.1. In this way, the adsorption and desorption capacity of the metal-organic framework can be maintained appropriately.

[0024] The MOF may have a crystal structure pattern equivalent to that of a second MOF having a first organic ligand instead of the second organic ligand, which allows the adsorption and desorption amounts of the metal-organic framework to be appropriately maintained.

[0025] The highly electronegative atom of the second organic ligand is not particularly limited, and atoms having a donor electron, such as halogen atoms, can be used. The second organic ligand preferably has more oxygen atoms and / or nitrogen atoms than the first organic ligand. The oxygen atoms and nitrogen atoms exhibit basicity. When the metal organic framework is used, for example, as a carbon dioxide adsorbent, the carbon dioxide interacts with the oxygen atoms and nitrogen atoms exhibiting basicity and is adsorbed by the metal organic framework. Therefore, the metal organic framework of this form can reduce the hysteresis of gas adsorption and desorption.

[0026] The second organic ligand preferably has more —COOH groups and / or —COO— groups than the first organic ligand, since —COOH groups and —COO— groups promote the adsorption of gases and vapors. In this case, the hysteresis of gas adsorption / desorption can be further reduced.

[0027] The organic ligands of the MOF can be identified by IR (infrared absorption spectrometry) and GC / MS (Gas Chromatography-Mass spectrometry).

[0028] B. Method for producing MOF: Figure 2 is a process diagram showing an example of a method for producing MOF. Figure 2 shows ELM-11 as an example of MOF. ELM-11 has a structure in which the organic ligand 4,4'-bipyridine and the metal ion copper tetrafluoroborate are crystallized through coordinate bonds.

[0029] In process P202, precursor solutions (precursor solution 1 and precursor solution 2) are prepared. Precursor solution 1 is a solution in which 4,4'-bipyridine (bpy) and isonicotinic acid are dissolved in methanol, and precursor solution 2 is a solution in which Cu(BF ４ ) ２ It is a solution in which

[0030] In process P204, precursor solution 1 is added dropwise to precursor solution 2 prepared in process P202 while stirring (at room temperature). For example, the addition time is 2 hours and the stirring speed is 800 rpm. This process allows isonicotinic acid to be coordinated to the MOF particles.

[0031] In process P206, the liquid phase synthesized in process P204 is filtered, and the powder is removed and washed. In process P208, the powder removed in process P206 is dried in vacuum at room temperature to recover pre-ELM-11 (water adsorbed). Note that the method for producing MOF is not limited to the method shown in FIG. 2, and various known methods can be used for production.

[0032] FIG. 3 shows the XRD (X-ray diffraction) of the MOF powder to which COO- groups have been added, and FIG. 4 shows the IR of the MOF powder to which COO- groups have been added. The Pre-ELM-11 stable phase and Pre-ELM-11 metastable phase shown in FIG. 3 are CIF file data of the structure in which water molecules are adsorbed to ELM-11 before thermal dehydration. "No isonicotinic acid added" shows pre-ELM-11 prepared without adding isonicotinic acid to the precursor solution 1 prepared in the above-mentioned process P202. FIG. 4 shows pre-ELM-11 prepared by changing whether or not isonicotinic acid was added to the precursor solution 1 prepared in the above-mentioned process P202. The concentration of isonicotinic acid added is 32 mM. mM is 10 －３ 3 and 4, the MOF powder to which COO-groups have been added is shown at the top, and below that, for comparison, MOF powder to which no COO-groups have been added and the like are shown.

[0033] As shown in Figure 3, both pre-ELM-11 prepared by the above method and pre-ELM-11 to which COO- groups had been added retained the structure of pre-ELM-11. In other words, it was confirmed that the structure of pre-ELM-11 was maintained even after the addition of COO- groups.

[0034] In FIG. 4, the peak position indicating the C═O stretching derived from COOH is indicated by band P, and the peak position indicating the COO －The peak position indicating antisymmetric stretching due to ions is indicated by band Q, and the peak position indicating symmetric stretching is indicated by band R. Bands P, Q, and R are cited from the following document 1. Document 1: Bunseki Kagaku Vol. 56 No. 6 99. 2 (2007) 457-464

[0035] As shown in Figure 4, the MOFs prepared by the above method (with or without isonicotinic acid) did not detect a peak corresponding to the COOH-derived C=O stretching detected in isonicotinic acid. － A peak corresponding to the symmetric stretching of ions was detected, confirming that the MOF prepared by the above method had COO- groups.

[0036] From the results shown in FIGS. 3 and 4, it was confirmed that the above production method can provide COO-groups while maintaining the structure of pre-ELM-11.

[0037] C. Shaped object containing metal-organic framework: Another embodiment of the present disclosure provides a shaped object containing a MOF having the above-described second ligand. Because the hysteresis of gas adsorption / desorption of the MOF particles is small, the hysteresis of gas adsorption / desorption of the shaped object can be reduced even when a binder is included.

[0038] D. Method for Producing a Shaped Object: FIG. 5 is a process diagram showing an example of a method for producing a shaped object. In step P102, the following (1) to (4) are prepared: (1) an MOF precursor (e.g., a product of pre-ELM-11 to which a COO-group has been added); (2) a silane coupling agent (e.g., silane KMB-3066 ((CH ３ O) ３ Si(CH ２ ) ６ Si(OCH ３ ) ３)) (3) Binder (organic binder) (4) Solvent (e.g., ethanol water (ethanol:water=90:10 wt %)) (1) may be prepared in step P102 or may be prepared in advance. An example of the method for preparing the MOF precursor is as described above.

[0039] In process P104, the above components (1) to (4) are mixed and stirred in a capped glass bottle using a stirrer and a magnetic starter at a predetermined rotation speed for a predetermined time. This process finely pulverizes the raw material powder, silane coupling agent, and binder, and mixes them with the solvent (ethanol water) to produce a slurry. For example, the rotation speed can be 800 rpm and the stirring time can be 24 hours.

[0040] In step P106, the lid of the glass bottle containing the slurry obtained in step P104 is removed, and the mixture is stirred at a rotation speed of 800 rpm and dried in a draft chamber to sufficiently volatilize the ethanol and turn it into a powder.

[0041] In step P108, the powder obtained in step P106 is placed in a mold and pressed using a uniaxial press to obtain a green compact. Depending on the shape of the pressing mold used in step P110, the final MOF shaped product can be molded into a desired shape. For example, it can be molded into a rectangular column, a cylindrical shape, a pellet, or the like.

[0042] In process P110, the green compact is removed, completing the MOF-containing shaped object 1. The method for producing the MOF-containing shaped object 1 is not limited to the method shown in FIG. 1 , and various known methods can be used.

[0043] Samples of MOF and shaped bodies containing MOF were prepared, and whether the increase in hysteresis was suppressed was evaluated. In this example, a regular pre-ELM-11 product (also referred to as a product without COOH groups) and a product with COOH groups were used as the MOF. For the shaped body, KBM-3066 (manufactured by Shin-Etsu Chemical Co., Ltd.) was used as the silane coupling agent, and ethyl cellulose was used as the organic binder. Samples of the shaped body were prepared by the manufacturing method of the above embodiment (FIG. 5).

[0044] [Sample Preparation] Synthesis of pre-ELM-11 (standard product) Precursor solution 1 was prepared by dissolving 5.34 g of 4,4'-bipyridine in 16.88 g of methanol. Precursor solution 2 was prepared by dissolving 8.76 g of a 45 wt % copper tetrafluoroborate aqueous solution in 14.7 g of ultrapure water (process P202). Using a syringe pump, precursor solution 1 was added dropwise over two hours to precursor solution 2, which was being stirred with a magnetic stirrer at 800 rpm, and stirring was continued for 24 hours (process P204). The resulting powder was then recovered by suction filtration (process P206) and vacuum dried for one day to volatilize the remaining solvent, yielding pre-ELM-11 (process P208).

[0045] Pre-ELM-11 (COO-group-added product) Precursor solution 1A was prepared by dissolving 5.34 g of 4,4'-bipyridine and 0.0843 g of isonicotinic acid with a COOH group in methanol. Using precursor solution 1A instead of precursor solution 1, the same procedure as above was carried out to obtain pre-ELM-11, to which isonicotinic acid with a COO-group (deprotonated during the synthesis process) was added.

[0046] Preparation of powder for MOF shaped body Xg of pre-ELM-11 powder (regular product) or pre-ELM-11 powder (COO-group-added product) with isonicotinic acid, Yg of silane coupling agent KBM-3066, and Zg of binder powder were added to a water and ethanol mixed solvent (water:ethanol = 10:90 wt%) and mixed and stirred at 800 rpm for 24 hours to prepare powder for MOF shaped body (steps P102 to P106). By changing the ratio of X, Y, and Z, powders for MOF shaped body with different compositions were prepared. Samples S2 and S4 have an X:Y:Z = 90:5:5 ratio.

[0047] - Preparation of MOF shaped body Using a press jig with a diameter of 3 mm, the powder for the MOF shaped body prepared above was uniaxially pressed at a pressure of 114 MPa to prepare a cylindrical MOF shaped body with a diameter of 3 mm and a height of 2 to 3 mm (steps P108 and P110).

[0048] [CO ２ Evaluation of adsorption and desorption characteristics] For each sample,２ The adsorption and desorption characteristics were evaluated. ２ The adsorption and desorption properties were evaluated using a high-vacuum physical adsorption analyzer, "AutoSorb iQ," manufactured by Anton Paar. To remove the adsorbed water contained in the MOF shaped body pre-ELM-11, a pretreatment was carried out by vacuum heating at 130°C for 5 hours. The evaluation conditions were a temperature of 0°C, equilibration time of 10 minutes, tolerance of 0, and measurement point of CO. ２ The partial pressure was in the range of 0.025 to 0.975 atm in increments of 0.025 atm. From the measurement results, the vertical axis is ２ adsorption amount) / (total weight of sample), the horizontal axis is CO ２ As a partial pressure, CO ２ The adsorption isotherm is plotted and the CO ２ The adsorption and desorption characteristics were evaluated.

[0049] Figure 6 shows the composition of each sample and whether or not the increase in gas adsorption / desorption hysteresis is suppressed. Samples S1 and S3 are MOF powders, and samples S2 and S4 are shaped bodies. For shaped body samples S2 and S4, the silane coupling agent used was KBM-3066 (manufactured by Shin-Etsu Chemical Co., Ltd.), which has bistrimethoxy groups at both ends. The MOFs in samples S1 and S2 are standard ELM-11 (without COO-groups), while the MOFs in samples S3 and S4 are ELM-11 with COO-groups. The ratio of ELM-11 (X): silane coupling agent (Y): binder (Z) shown in Figure 6 indicates the mixing ratio when the shaped body samples were prepared. This ratio approximately corresponds to the mass ratio of ELM-11 (MOF) contained in the shaped body to the silicon-based binder (resulting from the reaction of the silane coupling agent) and the organic binder. As shown in Fig. 6, the increase in hysteresis of gas adsorption / desorption was suppressed in sample S3 compared to sample S1 (shown as ◯ in Fig. 6), and the increase in hysteresis of gas adsorption / desorption was suppressed in sample S4 compared to sample S2 (shown as ◯ in Fig. 6).

[0050] FIG. 7 shows the CO ２ 7 is a graph showing the adsorption and desorption capacity. In FIG. 7, the vertical axis is (CO ２ The horizontal axis is the CO adsorption amount / (total weight of sample). ２ As a partial pressure, CO２ The adsorption isotherm is plotted, with STP on the vertical axis indicating that it is converted to standard conditions.

[0051] As shown in the figure, compared to sample S1 to which isonicotinic acid was not added, sample S3 to which isonicotinic acid was added had a higher CO ２ It was confirmed that the adsorption / desorption hysteresis was reduced.

[0052] FIG. 8 shows the CO ２ 8 is a graph showing the adsorption and desorption capacity. In FIG. ２ The horizontal axis is the CO adsorption amount / (total weight of sample). ２ As a partial pressure, CO ２ Adsorption isotherms are plotted.

[0053] As shown in the figure, even among the samples of the shaped body, sample S4 to which isonicotinic acid was added had a higher CO ２ It was confirmed that the adsorption / desorption hysteresis was reduced.

[0054] 9 is a diagram showing the structural formulas of a part of the particle interface of samples S1 and S3. As shown in the figure, in sample S3, the addition of isonicotinic acid increased the CO ２ It is thought that the number of adsorption sites has increased. ２ It is believed that the increased concentration may have improved the adsorption rate.

[0055] Figure 10 shows the relationship between oxygen, nitrogen and CO ２ 1 is an explanatory diagram conceptually illustrating the interaction of ２ Although there is no vacant orbital in CO, there is an electron-poor region where the bonding electrons are strongly attracted to the oxygen (O) side, making them more likely to interact with the base sites (lone electron pairs). ２ It is thought that it adsorbs to nitrogen (N) and oxygen (O), which show basicity.

[0056] FIG. 11 is an explanatory diagram conceptually showing the interaction between oxygen, nitrogen and polar molecules. ２It is believed that O and the like also interact with nitrogen (N) and oxygen (O) and are adsorbed.

[0057] The present disclosure is not limited to the above-described embodiments, and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted.

[0058] The present disclosure can also be realized in the following aspects. [Application Example 1] A metal-organic framework for gas adsorption, comprising: a first organic ligand that mainly constitutes the skeleton of the metal-organic framework; and a second organic ligand different from the first organic ligand, wherein at least the atom with the highest electronegativity among atoms constituting the first organic ligand and the second organic ligand is contained in the second organic ligand. [Application Example 2] The metal-organic framework according to Application Example 1, wherein the second organic ligand has at least one of oxygen atoms and nitrogen atoms in a greater number than the first organic ligand. [Application Example 3] The metal-organic framework according to Application Example 1 or Application Example 2, wherein the second organic ligand has at least one of —COOH groups and —COO— groups in a greater number than the first organic ligand. [Application Example 4] The metal-organic framework according to any one of Application Examples 1 to 3, wherein the metal-organic framework is a flexible metal-organic framework having structural flexibility. [Application Example 5] The metal-organic framework according to any one of Application Examples 1 to 4, wherein the gas is carbon dioxide. [Application Example 6] The metal-organic framework according to any one of Application Examples 1 to 5, wherein, when A is the saturated adsorption capacity of carbon dioxide at 0.975 atm of the metal-organic framework, and B is the saturated adsorption capacity of carbon dioxide at 0.975 atm of a second metal-organic framework having the first organic ligand instead of the second organic ligand in the metal-organic framework, the metal-organic framework satisfies (A-B) / A<0.1. [Application Example 7] The metal organic framework according to any one of Application Examples 1 to 6, having a crystal structure pattern equivalent to that of a second metal organic framework having the first organic ligand instead of the second organic ligand in the metal organic framework. [Application Example 8] A shaped body, comprising the metal organic framework according to any one of Application Examples 4 to 7.

[0059] 1…Shaped body 10…MOF (metal organic structure) L…First organic ligand L'…Second organic ligand

Claims

1. A metal-organic framework for gas adsorption, comprising: a first organic ligand that mainly constitutes a skeleton of the metal-organic framework; and a second organic ligand that is different from the first organic ligand, wherein, of the atoms constituting the first organic ligand and the second organic ligand, an atom having the highest electronegativity is contained in at least the second organic ligand.

2. The metal-organic framework according to claim 1, wherein the second organic ligand has more oxygen atoms and / or more nitrogen atoms than the first organic ligand.

3. A metal-organic framework according to claim 1, wherein the second organic ligand has more —COOH groups and / or —COO— groups than the first organic ligand.

4. The metal-organic framework according to claim 1, wherein the metal-organic framework is a flexible metal-organic framework having structural flexibility.

5. The metal organic framework according to claim 4, wherein the gas is carbon dioxide.

6. The metal-organic framework according to claim 4, wherein, when A denotes a saturated adsorption amount of carbon dioxide of the metal-organic framework at 0.975 atm, and B denotes a saturated adsorption amount of carbon dioxide of a second metal-organic framework having the first organic ligand instead of the second organic ligand in the metal-organic framework, the metal-organic framework satisfies (A-B) / A<0.

1.

7. The metal-organic framework according to claim 4, having a crystal structure pattern equivalent to that of a second metal-organic framework having the first organic ligand in place of the second organic ligand in the metal-organic framework.

8. A shaped body comprising the metal organic framework according to any one of claims 4 to 7.

Images