Metal organic framework

Abstract

To provide a metal organic framework containing an N element and an S element, the metal organic framework having an average particle diameter equal to or greater than a predetermined value.SOLUTION: The present disclosure is a metal organic framework containing a metal ion and a polyvalent carboxylic acid ligand, wherein the polyvalent carboxylic acid ligand does not include elemental S and elemental N, the metal organic framework includes elemental S and elemental N, the elemental S content and the elemental N content per 1 g of the metal organic framework are both 0.4 mmol / g or less, and the ratio (S / N) of the elemental S content (mmol / g) to the elemental N content (mmol / g) is 0.2-1.4.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Metal organic frameworks, also known as porous coordination polymers, are a type of material that forms a porous structure through coordination bonds between metal ions and organic ligands, and are expected to be used for gas adsorption / desorption and as catalysts.

[0003] A typical method for producing a metal organic framework is a method (hereinafter referred to as a solution method) in which a metal salt and an organic compound that can serve as an organic ligand are mixed in a solvent, as disclosed in Patent Document 1, and the metal organic framework can be separated and obtained by filtering the liquid after the reaction. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] WO2023 / 176917 Summary of the Invention [Problem to be solved by the invention]

[0005] The inventors have conducted studies and found that when a metal-organic framework is produced by a solution method, N and S elements originating from raw materials, solvents, etc. may be contained in the metal-organic framework, and in such cases, the average particle size of the obtained metal-organic framework may become small. A metal-organic framework with a small average particle size takes time to separate from the reaction solution by filtration, resulting in poor productivity.

[0006] Therefore, an object of the present disclosure is to obtain a metal organic framework containing an N element and an S element, and having an average particle size of a predetermined value or more. [Means for solving the problem]

[0007] The present disclosure that achieves the above object is as follows. [1] A metal organic framework comprising a metal ion and a polycarboxylic acid ligand, the polycarboxylic acid ligand does not contain an S element or an N element, the metal organic framework contains an S element and an N element, the S element content and the N element content per 1 g of the metal organic framework are both 0.4 mmol / g or less, A metal organic structure in which the ratio (S / N) of the S element content (mmol / g) to the N element content (mmol / g) is 0.2 to 1.4. [2] The metal organic framework according to [1], having a scattered light intensity D50 of 300 nm or more. [3] The metal organic framework according to [1], having a BET specific surface area of ​​610 m 2 / g or more. [4] The metal ions include ions of at least one metal selected from the group consisting of Al, Ga, In, Ti, Zr, Hf, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn; The polycarboxylic acid ligand is R(COO - ) n (R is an aromatic hydrocarbon group, and n is an integer of 2 or more and 4 or less). [Effects of the Invention]

[0008] The metal-organic framework of the present disclosure can have a scattered light intensity standard D50 of at least a predetermined value, and therefore can improve the filterability from the reaction solution during production. DETAILED DESCRIPTION OF THE INVENTION

[0009] <Metal organic structure> The metal organic structure of the present disclosure is a metal organic structure including a metal ion and a polycarboxylic acid ligand, the metal organic structure including an S element and an N element, the polycarboxylic acid ligand not including an S element and an N element, the S element content and the N element content per 1 g of the metal organic structure are both 0.4 mmol / g or less, and the ratio (S / N) of the S element content (mmol / g) to the N element content (mmol / g) is 0.2 to 1.4.

[0010] The S element content (hereinafter referred to as S amount) per 1 g of metal organic framework (hereinafter referred to as MOF) is preferably 0.35 mmol / g or less, more preferably 0.3 mmol / g or less. The S amount may be 0.05 mmol / g or more, 0.1 mmol / g or more, or 0.2 mmol / g or more. The S amount is preferably 0.05 to 0.35 mmol / g, more preferably 0.1 to 0.3 mmol / g, even more preferably 0.2 to 0.3 mmol / g, and even more preferably 0.2 to 0.30 mmol / g.

[0011] The N element content per 1 g of MOF (hereinafter referred to as N amount) is preferably 0.38 mmol / g or less, more preferably 0.35 mmol / g or less. The N amount may be 0.05 mmol / g or more, 0.1 mmol / g or more, 0.2 mmol / g or more, or 0.25 mmol / g or more. The N amount is preferably 0.05 to 0.38 mmol / g, more preferably 0.1 to 0.35 mmol / g, and even more preferably 0.2 to 0.35 mmol / g.

[0012] The ratio of the amount of S to the amount of N (hereinafter referred to as S / N) is preferably 0.4 to 1.2, more preferably 0.5 to 1.0. S / N may be 0.5 to 0.95, or may be 0.6 to 0.95.

[0013] Preferably, the S amount is 0.05 to 0.35 mmol / g, the N amount is 0.05 to 0.38 mmol / g, and the S / N is 0.4 to 1.2; more preferably, the S amount is 0.1 to 0.3 mmol / g (particularly 0.1 to 0.30 mmol / g), the N amount is 0.1 to 0.35 mmol / g, and the S / N is 0.5 to 1.0; even more preferably, the S amount is 0.2 to 0.3 mmol / g (particularly 0.2 to 0.30 mmol / g), the N amount is 0.2 to 0.35 mmol / g, and the S / N is 0.5 to 0.95; and even more preferably, the S amount is 0.2 to 0.3 mmol / g (particularly 0.2 to 0.30 mmol / g), the N amount is 0.2 to 0.35 mmol / g, and the S / N is 0.6 to 0.95.

[0014] The metal-organic framework of the present disclosure, in which the S content, N content, and S / N ratio are within the above ranges, can achieve a scattered light intensity-based D50 of 300 nm or more, thereby improving the filterability from the reaction solution during MOF production. The D50 is preferably 320 nm or more, more preferably 400 nm or more, and may be 1000 nm or less, 700 nm or less, or 600 nm or less. The D50 is preferably 300 to 1000 nm, more preferably 320 to 700 nm, and even more preferably 400 to 600 nm.

[0015] The BET specific surface area of ​​the MOF is 600m 2 / g or more is preferable, and 610m 2 / g or more is more preferable, and 620m 2 / g or more is more preferable, and 800m 2 / g or less, or 750m 2 / g or less. As will be described later, the MOF of the present disclosure can be produced by a solution method using an aqueous solvent, and such MOFs can have a BET specific surface area of ​​at least a predetermined value, allowing them to adsorb gases and organic molecules well. The BET specific surface area of ​​the MOF is 600 to 800 m 2 / g is preferred, and 610 to 750m 2 / g is more preferable, and 620 to 750m 2The BET specific surface area of ​​the MOF can be controlled by adjusting the concentrations of the metal compound and organic compound, which are the raw materials for the MOF, in the solvent, the reaction temperature, the reaction time, and the like.

[0016] <Metal ions> The metal ions constituting the MOF preferably contain at least one metal ion selected from the group consisting of elements in periods 4 to 6 and groups 3 to 12 of the long-form periodic table, Al, Ga, and In, more preferably at least one metal ion selected from the group consisting of Al, Ga, In, Ti, Zr, Hf, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn, still more preferably an Al ion, and particularly preferably the metal ion is an Al ion.

[0017] <Polycarboxylic acid ligand> The polycarboxylic acid ligand does not contain S or N elements and is R(COO - ) n (R is an n-valent group, n is an integer of 2 or more), and R is preferably an aliphatic chain hydrocarbon group, an aliphatic cyclic hydrocarbon group, an aliphatic heterocyclic hydrocarbon group (a group in which one or more carbon atoms of an aliphatic cyclic hydrocarbon group are replaced with heteroatoms other than S and N atoms), an aromatic hydrocarbon group, or an aromatic heterocyclic hydrocarbon group (a group in which one or more carbon atoms of an aromatic hydrocarbon group are replaced with heteroatoms other than S and N atoms), with an aromatic hydrocarbon group being most preferred. R preferably has 2 to 30 carbon atoms, more preferably 4 to 24, and even more preferably 6 to 18. n is preferably 2 or more and 4 or less, more preferably 2 or more and 3 or less, and most preferably 2.

[0018] The above-mentioned chain aliphatic hydrocarbon groups, cyclic aliphatic hydrocarbon groups, heterocyclic aliphatic hydrocarbon groups, aromatic hydrocarbon groups and heterocyclic aromatic hydrocarbon groups may further contain one or more -OH groups.

[0019] The aliphatic chain hydrocarbon group may be linear or branched, and may be a saturated or unsaturated hydrocarbon group. Examples of the aliphatic chain hydrocarbon group include groups obtained by removing n hydrogen atoms from ethane, ethylene, acetylene, butane, butene, or hexane.

[0020] Examples of the aliphatic cyclic hydrocarbon group include groups in which n hydrogen atoms have been removed from cyclopropane, cyclobutane, cyclohexane, cyclooctane, norbornene, or adamantane.

[0021] The preferred ranges for the number of carbon atoms in the aromatic hydrocarbon group are, in order, 6 or more and 30 or less, 6 or more and 24 or less, 6 or more and 18 or less, 6 or more and 12 or less, and 6 or more and 10 or less. Specifically, the aromatic hydrocarbon group is a group in which n (preferably 2 or 3) hydrogen atoms have been removed from benzene or biphenyl, and particularly a group in which n (preferably 2 or 3) hydrogen atoms have been removed from benzene.

[0022] The aromatic hydrocarbon group is preferably any one of the following formulae (A-1) to (A-9), more preferably any one of the formulae (A-1) to (A-3), and even more preferably formula (A-2). In the following formulae (A-1) to (A-9), * represents a bond.

[0023] [ka]

[0024] In the formulae (A-1) to (A-9), at least one of the hydrogen atoms bonded to the carbon atoms may be substituted with —OH, or the hydrogen atoms bonded to the carbon atoms may not be substituted.

[0025] Examples of aromatic heterocyclic hydrocarbon groups include groups obtained by removing n hydrogen atoms from furan.

[0026] The metal ions and polyvalent carboxylic acid ligands constituting the MOF can be appropriately combined within the above-described preferred ranges. For example, the metal ions include at least one metal ion selected from the group consisting of Al, Ga, In, Ti, Zr, Hf, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn, and the polyvalent carboxylic acid ligand is R(COO - ) n where R is an aromatic hydrocarbon group and n is an integer of 2 or more and 4 or less (particularly 2 or 3). A MOF containing such a polyvalent carboxylic acid ligand is preferred. A MOF in which the metal ion is an Al ion and the polyvalent carboxylic acid ligand is R(COO - ) n where R is any of the above formulas (A-1) to (A-3) and n is 2 is more preferred.

[0027] The molar ratio (metal ion / organic ligand) of the metal ions (total amount in the case of multiple species) to the polyvalent carboxylic acid ligand (total amount in the case of multiple species) is preferably 0.1 or more, more preferably 0.3 or more, still more preferably 0.5 or more, particularly preferably 0.9 or more, and preferably 5 or less, more preferably 4 or less, still more preferably 3 or less, particularly preferably 2.5 or less. The said molar ratio is preferably 0.1 or more and 5 or less, more preferably 0.3 or more and 4 or less, still more preferably 0.5 or more and about 3 or less, and even more preferably 0.9 or more and 2.5 or less. The amount of metal ions contained in the MOF is preferably 0.5×n to 1.5×n moles, more preferably 0.5×n to 1.2×n moles, per 1 mole of the polyvalent carboxylic acid ligand represented by R(COO - ) n .

[0028] <Method for producing MOF> The MOF of the present disclosure can be obtained by reacting a metal compound containing a metal sulfate with a polycarboxylic acid in an aqueous solvent in the presence of an organic amine such as triethylamine. When reacting a metal compound with a polycarboxylic acid in an aqueous solvent, the reaction is carried out in the presence of an organic amine, which not only produces a metal-organic framework, but also simplifies or eliminates the organic solvent removal process, thereby reducing production costs. Furthermore, the MOF of the present disclosure has good filterability, resulting in high productivity. According to this production method, the S element from the metal sulfate and the N element from the organic amine are contained in the metal-organic framework. However, the MOF of the present disclosure can be produced by adjusting the amounts of the metal sulfate, polycarboxylic acid, and organic amine used so as to satisfy all of the following conditions (i) to (iv).

[0029] (i) The molar ratio of the metal sulfate to the polycarboxylic acid (metal sulfate / polycarboxylic acid) is, for example, 0.55 to 0.90. (ii) The molar ratio of the organic amine to the polycarboxylic acid (organic amine / polycarboxylic acid) is, for example, 2.80 to 2.90. (iii) The molar ratio of the metal sulfate to the organic amine (metal sulfate / organic amine) is, for example, 0.15 to 0.30. (iv) The ratio of the number of moles of the organic amine to the volume of the aqueous solvent (mol / L) is, for example, 1.1 to 1.4.

[0030] In the production of the MOF of the present disclosure, it is preferable to prepare a polycarboxylic acid-containing solution A in which the polycarboxylic acid and organic amine are completely dissolved in a solvent a, and a metal sulfate-containing solution B in which a metal compound containing a metal sulfate is completely dissolved in a solvent b, and then dropwise add either solution A or solution B to the other to cause the two to react with each other.

[0031] The metal compound may further contain at least one selected from the group consisting of metal nitrates, acetates, chlorides, bromides, and alkoxides in addition to metal sulfates. n(R and n are the same as above).

[0032] The aqueous solvent has a water content of more than 80% by mass based on 100% by mass of the solvent. The solvent other than water may contain organic solvents such as alcohol solvents, amide solvents, ketone solvents, ester solvents, or ether solvents in a total amount of less than 20% by mass. The amount of water in 100% by mass of the aqueous solvent is preferably 85% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, and the aqueous solvent is most preferably a 100% by mass solvent. When preparing the above-mentioned solutions A and B, it is preferable that both solvent a and solvent b satisfy the preferred aspects of the aqueous solvents described above.

[0033] Examples of organic amines include aliphatic chain tertiary amines such as trimethylamine, triethylamine, tri-n-propylamine, N,N-diisopropylethylamine, and triisobutylamine; heterocyclic aliphatic tertiary amines such as hexamethylenetetramine, 1,4-diazabicyclo[2.2.2]octane, morpholine, and 4-methylmorpholine; and nitrogen-containing aromatic ring-containing tertiary amines such as imidazole and 1-methylimidazole. These can be used alone or in combination of two or more. The organic amine is preferably triethylamine.

[0034] After the reaction is complete (preferably after the dropwise addition is complete), the mixture is refluxed, stirred, or left to stand at room temperature (e.g., 25°C) to 200°C for about 5 minutes to 100 hours, and the reaction product is separated from the solvent by filtration, washed, and dried to obtain the desired MOF.

[0035] <Application> The MOFs of the present disclosure are suitable for adsorption and removal of gases and organic molecules. Examples of gases include water (water vapor), carbon dioxide, hydrogen, carbon monoxide, oxygen, nitrogen, hydrocarbons having 1 to 4 carbon atoms, rare gases, hydrogen sulfide, ammonia, sulfur oxides, nitrogen oxides, and siloxanes. Examples of organic molecules include hydrocarbons having 5 to 8 carbon atoms, alcohols having 1 to 8 carbon atoms, aldehydes having 1 to 8 carbon atoms, carboxylic acids having 1 to 8 carbon atoms, ketones having 1 to 8 carbon atoms, amines having 1 to 8 carbon atoms, esters having 1 to 8 carbon atoms, and amides having 1 to 8 carbon atoms. The organic molecules may contain an aromatic ring. [Example]

[0036] The present disclosure will be described in more detail below with reference to examples. The present disclosure is not limited to the following examples, and can of course be implemented with appropriate modifications within the scope of the above and below-described aims, all of which are encompassed within the technical scope of the present disclosure.

[0037] [Measurement of S content] The MOFs obtained in the following Examples and Comparative Examples were combusted under the following conditions using the automatic sample combustion apparatus described below, and the generated gas was absorbed into a solution, which was then analyzed by ion chromatography described below. The mass-based S concentration was obtained through the analysis and converted into the amount of S per gram of MOF (mmol / g). <Automatic sample combustion device> Mitsubishi Chemical Analytech automatic sample combustion device, ion chromatograph pretreatment device AQF2100H Reaction tube temperature (outer tube / inner tube): 1050℃ / 1000℃ Carrier gas: Ar 200 mL / min, O2 400 mL / min Ar flow rate for humidification: 150mL / min <Ion chromatograph> Thermo Fisher Scientific ion chromatography system Thermo Scientific DionexICS1600 Column used: TSKgel SuperIC-Anion HS, 4.6 x 100 mm Temperature: 40℃ Eluent: 1.0mmol / L Na2CO3, 9.0mmol / L NaHCO3 Injection volume: 20μL Flow rate: 0.9mL / min

[0038] [Measurement of N content] The MOFs obtained in the examples and comparative examples were loaded into an MT-5 manufactured by Yanaco Analytical Industry Co., Ltd. and analyzed under the following conditions. After obtaining the N concentration on a mass basis through the analysis, it was converted into the amount of N per 1 g of MOF (mmol / g). Combustion furnace temperature: 950℃ Oxidation furnace temperature: 850℃ Reduction furnace temperature: 590℃ Combustion gas flow rate: He gas 200 mL / min, O2 gas 20 mL / min

[0039] [Measurement of D50, the scattered light intensity standard of MOF] 1 mg to 2 mg of MOF was weighed and diluted with 1.5 mL of a mixed solution of water and acetone (water / acetone = 1 / 1 volume ratio) to prepare a measurement sample with a MOF concentration in the range of 0.67 to 1.34 g / L. The measurement sample was irradiated with ultrasound for 1 minute, and then the D50 of the MOF, which is the scattered light intensity standard, was measured using the following device and conditions. Equipment: Malvern Panalytical Zetasizer Nano ZS Measurement wavelength: 633nm Measurement angle: 173°

[0040] [Measurement of BET specific surface area of ​​MOF] Since the adsorption area of ​​nitrogen molecules is known in advance, the amount of gas molecules adsorbed only on the sample surface was measured, and the surface area of ​​the MOF sample was measured using the BET adsorption isotherm. Sample preparation: To remove water from the sample, the sample was heated under reduced pressure at 10 Pa or less and 200°C overnight. Equipment: Microtrac BEL Co., Ltd. BELSORP-mini Pretreatment conditions: (ai) Place a volume-reducing glass rod (for standard sample tubes) in the standard sample tube and plug it with a quick seal. Prepare this sample tube set with the samples to be measured (up to three samples per measurement), connect it to the pretreatment device (BELPREP VACII), evacuate the air from inside the sample tube, and then introduce N2 gas (purity 99.999% or higher) up to atmospheric pressure. (a-ii) Then, remove the sample tube from the pretreatment machine and measure its weight three times using a precision balance (displaying four or more decimal places) to obtain the average (W1). When using a precision balance, use an ionizer to eliminate the effects of static electricity. (a-iii) Weigh out approximately 50 mg of the sample to be measured onto a piece of medicine paper, and use a long-footed funnel to place the sample directly into the spherical part at the bottom of the standard sample tube. (a-iv) Return the glass rod to the sample tube, plug it with a quick seal, and then measure the total weight once to provisionally confirm the amount of sample added. (av) The sample tube containing the sample is connected to the pretreatment device, and the sample tube is evacuated. (a-vi) After the pressure inside the sample tube has reached a sufficiently low level, heating begins (vacuuming continues). Measurement conditions: (bi) After the pretreatment (vacuum heating) is completed, the sample tube is cooled while being kept under reduced pressure, and after it has returned to room temperature, N2 gas is introduced up to atmospheric pressure and the tube is removed from the apparatus. (b-ii) After pretreatment, measure the weight of the sample tube containing the sample three times using a precision balance and obtain the average (W2). Calculate W2 - W1 to obtain the weight of the sample. (b-iii) Enter the sample weight and information on N2 gas at liquid nitrogen temperature (such as the second virial coefficient) into the measurement software, enter the relative pressure you want to measure, and press the measurement start button. Then, following the software's instructions, the user installs a Dewar vessel filled with liquid nitrogen and a sample tube, and then performs measurements.

[0041] [Evaluation of filterability] Using a metal filter capable of reducing the internal pressure and filter paper (Kiriyama filter paper, φ40 mm, 5C), the suspension after the reaction was filtered at a reduced pressure of 75 kPaG (gauge pressure). The filterability was evaluated according to the following criteria. 〇: Filtration was completed in less than 50 minutes using vacuum filtration. ×: It took more than 50 minutes to complete filtration using vacuum filtration, or filtration was not possible using vacuum filtration (solid particles were too fine and passed through the filter paper), but filtration was possible using centrifugation.

[0042] Example 1 Polycarboxylic acid-containing solution A was prepared by mixing 4.86 mmol of isophthalic acid, 14.06 mmol of triethylamine, and 4.9 mL of ion-exchanged water. Metal sulfate-containing solution B was prepared by mixing 2.86 mmol of Al2(SO4)3·nH2O (n = 14-18) and 7.6 mL of ion-exchanged water. Metal sulfate-containing solution B was added dropwise to polycarboxylic acid-containing solution A at 25°C over 45 minutes. The resulting mixture was then refluxed at 100°C for 12 hours to obtain a suspension. This was filtered under reduced pressure, and the resulting solid was washed with 50 mL of ion-exchanged water and then with 50 mL of ethanol. It was then vacuum-dried at 60°C for 12 hours to obtain a metal-organic framework.

[0043] Example 2 Polycarboxylic acid-containing solution A was prepared by mixing 3.50 mol of isophthalic acid, 9.94 mol of triethylamine, and 8,060 mL of ion-exchanged water. Metal sulfate-containing solution B was prepared by mixing 2.54 mol of Al2(SO4)3·nH2O (n = 14-18) and 540 mL of ion-exchanged water. Metal sulfate-containing solution B was added dropwise to polycarboxylic acid-containing solution A over 45 minutes at 25°C. The resulting mixture was then refluxed at 100°C for 12 hours to obtain a suspension. This was filtered under reduced pressure, and the resulting solid was washed twice with 2,000 mL of ion-exchanged water and twice with 2,000 mL of methanol. It was then vacuum-dried at 100°C for 6 hours to obtain a metal-organic framework.

[0044] Comparative Example 1 Polycarboxylic acid-containing solution A was prepared by mixing 93.25 mmol of isophthalic acid and 75 mL of N,N-dimethylformamide at 25°C. Metal sulfate-containing solution B was prepared by mixing 91.50 mmol of Al2(SO4)3·nH2O (n = 14-18) and 300 mL of ion-exchanged water. Metal sulfate-containing solution B was added dropwise to polycarboxylic acid-containing solution A at 25°C over 45 minutes. The resulting mixture was then refluxed at 125°C for 24 hours to obtain a suspension. This was centrifuged, and the resulting solid was washed with 50 mL of ion-exchanged water, then with 50 mL of ethanol, and vacuum-dried at 80°C for 24 hours to obtain a metal-organic framework.

[0045] Comparative Example 2 Polycarboxylic acid-containing solution A was prepared by mixing 4.88 mmol of isophthalic acid, 15.06 mmol of triethylamine, and 2.2 mL of ion-exchanged water. Metal sulfate-containing solution B was prepared by mixing 5.71 mmol of Al2(SO4)3·nH2O (n = 14-18) and 7.8 mL of ion-exchanged water. Metal sulfate-containing solution B was added dropwise to polycarboxylic acid-containing solution A over 45 minutes at 25°C. The resulting mixture was then refluxed at 100°C for 12 hours to obtain a suspension. This was filtered under reduced pressure, and the resulting solid was washed with 65 mL of ion-exchanged water and then with 25 mL of methanol. It was then vacuum-dried at 60°C for 12 hours to obtain a metal-organic framework.

[0046] The MOFs obtained in the examples and comparative examples were evaluated by the above-mentioned methods, and the results are shown in Table 1.

[0047] [Table 1]

Claims

1. A metal organic framework comprising a metal ion and a polycarboxylic acid ligand, the polycarboxylic acid ligand does not contain an S element or an N element, the metal organic framework contains an S element and an N element, the S element content and the N element content per 1 g of the metal organic framework are both 0.4 mmol / g or less, A metal organic framework in which a ratio (S / N) of the S element content (mmol / g) to the N element content (mmol / g) is 0.2 to 1.

4.

2. 2. The metal organic structure according to claim 1, wherein D50 based on scattered light intensity is 300 nm or more.

3. BET specific surface area is 610m ２ / g or more.

4. the metal ions include ions of at least one metal selected from the group consisting of Al, Ga, In, Ti, Zr, Hf, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn; The polycarboxylic acid ligand is R(COO － ) ｎ (R is an aromatic hydrocarbon group, and n is an integer of 2 or more and 4 or less).

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