JP2009183918A - Hydrogen adsorbing material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen absorbing material comprising a three-dimensional high-molecular complex excellent in hydrogen adsorption. <P>SOLUTION: The hydrogen absorbing material is composed of the three-dimensional high-molecular complex formed by stacking two-dimensional structures, each formed of a metal ion and an organic ligand capable of being coordinated to the metal ion, through a pillar ligand capable of being coordinated to the metal ions, and the pillar ligand in the three-dimensional high-molecular complex contains a nitrogen-containing group having a lone pair of electrons of the nitrogen atom. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a hydrogen adsorbing material, and more particularly to a hydrogen adsorbing material comprising a three-dimensional polymer complex.

  Hydrogen has attracted attention as a clean fuel because it does not generate carbon dioxide when burned, and many studies have been conducted on storage and transportation of hydrogen to use hydrogen as a fuel. As a method for storing and transporting hydrogen, a high-pressure gas cylinder is generally used. However, the high-pressure gas cylinder is heavy, and there is a practical limit on the storage capacity per unit volume, and a large improvement in hydrogen storage efficiency cannot be expected.

  As a hydrogen storage method replacing such a high-pressure gas cylinder, for example, a method using a hydrogen adsorbing material made of a coordination polymer complex has been proposed.

In Patent Document 1, a general formula R- (COOH) _n (wherein R represents one heterocyclic ring selected from tetrazine, triazine, etc., and n represents an integer of 1 to 4) is represented. One organic ligand, a metal atom, and a bidentate second organic ligand having an atom capable of coordinating to the metal atom are three-dimensionally bonded. A three-dimensional polymer complex is described, and according to such a three-dimensional polymer complex, the nitrogen-containing heterocyclic (heterocyclic) skeleton in the first organic ligand improves the affinity with hydrogen, and It is described that the amount of occlusion increases.

  Patent Document 2 is composed of a divalent metal ion, a bidentate organic ligand having atoms that can coordinate to the metal ion at both ends of a rigid skeleton, and 2,3-pyrazinedicarboxylic acid Gas storage storable organometallic complexes are described, by using 4,4′-bipyridyl or 1,4-bis (4-pyridyl) benzene as the bidentate organic ligand It is described that a crystal lattice space suitable for adsorption storage of methane can be formed because of its chemical structure.

  In Patent Document 3, from at least one compound selected from dicarboxylic acids represented by the general formula HOOC-R-COOH (wherein R represents an alkenylene group, an arylene group, etc.), copper and rhodium, and the like. A dicarboxylic acid metal complex comprising at least one selected divalent metal and an organic ligand capable of bidentate coordination with the metal is described, and such a dicarboxylic acid metal complex is mainly composed of methane. It is described as being suitable as a gas storage material.

  In Patent Document 4, a two-dimensional sheet composed of a transition metal cation and a first organic bridging ligand forms a layer, and a second organic bridging ligand capable of bidentate coordination is present in each transition metal cation. Coordination polymers having a structure in which adjacent sheets are connected to each other by coordination and pores are formed between them are described. According to such coordination polymers, It is described that gas molecules can be aligned and held instantaneously using space.

Japanese Patent Laying-Open No. 2005-093181 JP 09-227572 A JP 2000-109485 A JP 2004-196594 A

  In Patent Document 1, as a second organic ligand (pillar ligand) capable of bidentate coordination, triethylenediamine and pyrazine can obtain a three-dimensional polymer complex in which a three-dimensional lattice is formed in a high yield. It is described as preferable from the viewpoint. However, in the said patent document 1, it did not describe about the interaction of said 2nd organic ligand and hydrogen, and there was room for improvement regarding the improvement of the hydrogen adsorption ability in a three-dimensional polymer complex. On the other hand, Patent Documents 2 to 4 do not specifically describe the hydrogen adsorption ability of the obtained organometallic complex.

  Then, an object of this invention is to provide the material which consists of a three-dimensional polymer complex excellent in adsorption | suction of hydrogen.

The present invention for solving the above problems is as follows.
(1) A three-dimensional polymer in which a two-dimensional structure formed by a metal ion and an organic ligand that can coordinate to the metal ion is stacked via a pillar ligand that can coordinate to the metal ion A hydrogen-adsorbing material comprising a complex, wherein a pillar ligand in the three-dimensional polymer complex includes a nitrogen-containing group having a lone electron pair of a nitrogen atom.
(2) The hydrogen-adsorbing material according to (1) above, wherein the nitrogen-containing group contains an azo group or a nitrogen-containing heterocyclic group.
(3) The pillar ligand is 4,4′-azopyridine, 3,6-bis (4-pyridyl) -1,2,4,5-tetrazine, 2,5-di-4-pyridinyl-pyrimidine, Selected from the group consisting of 2,5-di-4-pyridinyl-pyrazine, 2,2′-p-phenylenebis-s-triazine, and 2 ′, 5-di-4-pyridinyl-2,5′-bipyrimidine The hydrogen-adsorbing material according to (1) or (2) above, wherein
(4) The metal ion is a metal ion selected from the group consisting of copper, zinc, nickel, cobalt, and iron, as described in any one of (1) to (3) above Hydrogen adsorption material.
(5) The organic ligand is 2,3-pyrazine dicarboxylic acid, or a carboxyl group proton of 2,3-pyrazine dicarboxylic acid substituted with a metal ion, such as sodium 2,3-pyrazine dicarboxylate, The hydrogen-adsorbing material according to any one of (1) to (4) above, which is at least one selected from the group consisting of potassium 2,3-pyrazinedicarboxylate and the like.

  According to the present invention, it is possible to obtain a hydrogen adsorbing material composed of a three-dimensional polymer complex with significantly improved hydrogen adsorbing ability.

  In the hydrogen adsorption material of the present invention, a two-dimensional structure formed by a metal ion and an organic ligand capable of coordinating with the metal ion is stacked via a pillar ligand capable of coordinating with the metal ion. The pillar ligand in the three-dimensional polymer complex contains a nitrogen-containing group having a lone pair of nitrogen atoms.

  Conventional three-dimensional polymer complexes generally include a two-dimensional sheet formed of a metal ion and an organic ligand capable of coordinating to the metal ion, and an organic ligand capable of bidentate coordination such as pyrazine. It has a cross-linked three-dimensional structure. That is, such a three-dimensional polymer complex uses a metal ion and an organic ligand capable of coordinating to the metal ion, using an organic ligand capable of bidentate coordination as a pillar ligand (pillar ligand). The two-dimensional sheet has a periodic crystal structure that is regularly stacked. By laminating a two-dimensional sheet through an organic ligand capable of bidentate coordination in this way, pores are formed between the two-dimensional sheet and the two-dimensional sheet, and hydrogen molecules and the like are contained in the pores. Gas molecules can be adsorbed or occluded.

  In such a three-dimensional polymer complex, the distance between the two-dimensional sheets defining the pore size is determined by the molecular length of the organic ligand used as the pillar ligand. Therefore, conventionally, the improvement in the amount of hydrogen adsorbed in such a three-dimensional polymer complex is formed in the three-dimensional polymer complex by changing the organic ligand used as the pillar ligand to one having a long molecular length. It has been attempted by enlarging the pores, that is, by increasing the specific surface area of the three-dimensional polymer complex. However, there is a limit to the specific surface area of the three-dimensional polymer complex obtained in this way, simply changing the molecular length of the pillar ligand to a longer one, and the amount of hydrogen molecules adsorbed on the three-dimensional polymer complex, Specifically, sufficient hydrogen adsorption capacity cannot be obtained simply by increasing the amount of physical adsorption of hydrogen molecules.

  The present inventors have a tertiary structure in which a two-dimensional structure formed by a metal ion such as a copper ion and an organic ligand such as 2,3-pyrazinedicarboxylic acid is bridged by a pillar ligand capable of bidentate coordination. In the original polymer complex, when the pillar ligand in the three-dimensional polymer complex contains a nitrogen-containing group having a lone pair of nitrogen atoms, the hydrogen adsorption ability of the three-dimensional polymer complex is significantly improved. I found out. In addition, in the pillar ligand having the same basic skeleton in the three-dimensional polymer complex, when the nitrogen-containing group having a lone pair of nitrogen atoms is included and not included, the nitrogen-containing group described above is compared. Since the three-dimensional polymer complex composed of the pillar ligands having a high hydrogen adsorption ability, the present inventors have found that the above nitrogen-containing group has such improved hydrogen adsorption ability. We found that it originates from the electrostatic interaction between the lone pair of nitrogen atom and the hydrogen molecule.

  Although not intended to be bound by any particular theory, the hydrogen molecule has an electrostatic interaction between the nitrogen atom's lone pair and the hydrogen molecule, as described above. This is thought to be due to the quadrupole moment. More specifically, it is generally known that nuclei having a nuclear spin of 1 or more (I ≧ 1) have a quadrupole moment. Here, the hydrogen molecule has a nuclear spin of 1, and thus has a quadrupole moment. In this case, when a hydrogen molecule approaches the lone electron pair of the nitrogen atom, the charge distribution on the lone electron pair of the nitrogen atom changes due to the quadrupole moment of the hydrogen molecule, resulting in the isolation of the hydrogen molecule and the nitrogen atom. It is considered that an electrostatic interaction is induced between the electron pair and an attractive force is generated between the two. On the other hand, in the case of gas molecules such as methane, the quadrupole moment is canceled due to the symmetry of the molecular structure. Therefore, such a gas molecule does not have a quadrupole moment as a whole molecule. Therefore, even if gas molecules such as methane exist in the vicinity of a lone pair of nitrogen atoms, it is considered that no attractive force is generated as in the case of hydrogen molecules. That is, such an electrostatic interaction is considered to be a peculiar interaction that occurs between a lone pair of a nitrogen atom of a nitrogen-containing group and a hydrogen molecule.

  According to the present invention, such a nitrogen-containing group is not particularly limited as long as it has a lone electron pair of a nitrogen atom, and examples thereof include those having an azo group (-N = N-), Or what has nitrogen-containing heterocyclic groups, such as a tetrazine ring, is mentioned. Further, for example, the pores formed in the three-dimensional polymer complex can be enlarged by appropriately selecting the above nitrogen-containing group and making the pillar ligand have a long molecular length. By doing so, the specific surface area of the obtained three-dimensional polymer complex can be increased, so in addition to the effect of electrostatic interaction between the lone electron pair of the nitrogen-containing group and the hydrogen molecule. In addition, the hydrogen adsorption ability of the three-dimensional polymer complex can be further improved.

  The pillar ligand in the present invention has an atom capable of coordinating to a metal ion at both ends of the above nitrogen-containing group, preferably a nitrogen atom, or a group containing a nitrogen atom such as a pyridyl group. It further has a nitrogen heterocyclic group, and such a nitrogen atom or a nitrogen atom in the nitrogen-containing heterocyclic group is coordinated to a metal ion in a two-dimensional structure composed of a metal ion and an organic ligand. Thus, the two-dimensional structure is cross-linked to form a three-dimensional polymer complex. That is, such a three-dimensional polymer complex has a periodic crystal structure in which two-dimensional structures composed of metal ions and organic ligands are regularly stacked via pillar ligands. Hydrogen molecules can be adsorbed or occluded in the pores formed during the dimensional structure.

  Specific examples of such pillar ligands include 4,4′-azopyridine, 3,6-bis (4-pyridyl) -1,2,4,5-tetrazine, and 2,5-di-4. From -pyridinyl-pyrimidine, 2,5-di-4-pyridinyl-pyrazine, 2,2'-p-phenylenebis-s-triazine, and 2 ', 5-di-4-pyridinyl-2,5'-bipyrimidine A compound selected from the group consisting of: These compounds have a lone electron pair of a nitrogen atom such as an azo group or a tetrazine ring as the nitrogen-containing group in the present invention, and can exhibit an electrostatic interaction with a hydrogen molecule.

  According to the present invention, the metal ions are coordinated with an organic ligand to form a two-dimensional structure, and further coordinated with a pillar ligand to crosslink the two-dimensional structure. Any metal ion capable of forming a molecular complex can be used, preferably a metal ion selected from the group consisting of copper, zinc, nickel, cobalt and iron. For example, by selecting a relatively light metal ion such as nickel, cobalt, or iron as the metal ion, the surface area of the obtained three-dimensional polymer complex in weight units can be increased.

  According to the present invention, as the organic ligand, any compound capable of forming a two-dimensional structure by coordinating with the above metal ion can be used, preferably 2,3-pyrazine Selected from the group consisting of dicarboxylic acid and 2,3-pyrazinedicarboxylic acid having a carboxyl group proton substituted with a metal ion, such as sodium 2,3-pyrazinedicarboxylate, potassium 2,3-pyrazinedicarboxylate, etc. At least one compound is used, more preferably sodium 2,3-pyrazinedicarboxylate. The oxygen atom of the carboxyl group in these organic ligands or the nitrogen atom in the heterocycle forms a coordinate bond with the above metal ion, thereby forming a two-dimensional structure consisting of the metal ion and the organic ligand. Can do.

  In addition, although the ratio of said metal ion which comprises the three-dimensional polymer complex in this invention, an organic ligand, and a pillar ligand is not specifically limited, Generally it is 2: 2: 1 or 1: 2: 1 is preferable.

  The three-dimensional polymer complex in the present invention can be produced by any method known to those skilled in the art.

  For example, first, a metal salt that is a source of metal ions and a pillar ligand are mixed in a solvent at a predetermined ratio to form a complex, and then a solution containing the complex and an organic ligand are mixed. A three-dimensional polymer complex composed of a metal ion, an organic ligand, and a pillar ligand can be prepared by mixing the solution containing it at a predetermined ratio. Alternatively, first, a metal salt that is a source of metal ions and an organic ligand are mixed in a solvent at a predetermined ratio to form a complex, and then the resulting solution containing the complex and the pillar ligand are mixed. It may be prepared by mixing a solution containing

  As the metal salt, formate salts, acetates, sulfates, nitrates, carbonates, perchlorates, tetrafluoroborates, and the like of the metal ions described above can be used. Moreover, as a solvent, alcohols, such as methanol and ethanol other than water and acetone, can be used individually or in mixture. The mixed solution containing a metal ion, an organic ligand, and a pillar ligand is allowed to stand or stir for 1 day to several days, for example, at room temperature or under heating as necessary, and the resulting complex is filtered and dried. By doing so, a three-dimensional polymer complex can be obtained. The structure of the obtained three-dimensional polymer complex can be confirmed by techniques such as powder X-ray pattern, temperature change of magnetic susceptibility, and pore size distribution analysis by nitrogen or argon adsorption.

  According to the present invention, the hydrogen adsorption material of the present invention is composed of the above three-dimensional polymer complex. By configuring the hydrogen adsorbing material with the above three-dimensional polymer complex, the pillar ligand in the three-dimensional polymer complex can interact with the hydrogen molecule strongly, so the hydrogen adsorbing capacity of the hydrogen adsorbing material can be reduced. A significant improvement is possible.

  The hydrogen adsorbing material of the present invention can be used in any shape, and for example, a powder shape, a pellet shape, a monolith shape, a plate shape, a fiber shape, and the like can be appropriately selected according to use conditions. Further, the method of using the hydrogen adsorbing material of the present invention is not particularly limited, and for example, hydrogen is adsorbed or occluded by pressurizing the hydrogen adsorbing material of the present invention in contact with hydrogen, or the pressure is reduced. By placing it underneath, adsorbed or occluded hydrogen can be released. The temperature at which hydrogen is adsorbed or occluded and released is not particularly limited, but according to the hydrogen adsorbing material of the present invention, hydrogen can be adsorbed or occluded and released satisfactorily near room temperature.

  EXAMPLES Next, although an Example demonstrates this invention in detail, this invention is not limited to a following example.

  In this example, in a three-dimensional polymer complex composed of a metal ion, an organic ligand, and a pillar ligand, a material in which the pillar ligand in the three-dimensional polymer complex has a lone pair of nitrogen atoms is prepared. The hydrogen adsorption ability was investigated.

[Comparative Example 1]
As a comparative example, a three-dimensional polymer complex using pyrazine as a pillar ligand was prepared. First, 6.4 g of copper (II) perchlorate hexahydrate as a source of metal ion Cu ²⁺ was dissolved in 51 ml of a mixed solvent of water and ethanol (water: ethanol = 1: 1). A solution prepared by dissolving 13.9 g of pyrazine (pyz), which is a pillar ligand, in 50 ml of a mixed solvent of water and ethanol (water: ethanol = 1: 1) was added. Next, a solution obtained by dissolving 2.9 g of organic ligand sodium 2,3-pyrazinedicarboxylate (Napzdc) in 86 ml of a mixed solvent of water and ethanol (water: ethanol = 1: 1) was further added to the obtained solution. Added. This mixed solution was allowed to stand at room temperature for 1 day, and the resulting precipitate was filtered and dried to obtain a three-dimensional polymer complex A composed of [Cu ₂ (pzdc) ₂ (pyz)] _n .

[Comparative Example 2]
A tertiary consisting of [Cu ₂ (pzdc) ₂ (dpe)] _{n in the same} manner as in Comparative Example 1 except that trans-1,2-bis (4-pyridyl) ethylene (dpe) was used as the pillar ligand. The original polymer complex B was obtained.

[Example 1]
A three-dimensional polymer complex C composed of [Cu ₂ (pzdc) ₂ (azpy)] _n is obtained in the same manner as in Comparative Example 1 except that 4,4′-azopyridine (azpy) is used as the pillar ligand. It was.

  FIGS. 1A and 1B are diagrams showing infrared absorption spectra obtained by Fourier transform infrared spectroscopy (FT-IR) of the three-dimensional polymer complexes B and C prepared above. The absorption peak indicated by a circle in the figure is an absorption peak related to the carboxyl group of sodium 2,3-pyrazinedicarboxylate (Napzdc), which is a common organic ligand in each three-dimensional polymer complex, and is indicated by a square. The absorption peak is an absorption peak related to the pyridyl group of the pillar ligand. Here, in the three-dimensional polymer complex C (Example 1), the vinylene group (—CH═CH—) in the pillar ligand in the three-dimensional polymer complex B (Comparative Example 2) is an azo group (—N = N-), and has a basic skeleton almost equivalent to that of the three-dimensional polymer complex B. When (a) and (b) in FIG. 1 are compared, the absorption peak (absorption peak indicated by the triangle in FIG. 1 (a)) corresponding to the C═C double bond of the vinylene group in FIG. Except that it was not detected, the three-dimensional polymer complexes B and C showed almost the same infrared absorption spectrum. From these results, the synthesis of each of the three-dimensional polymer complexes B and C was confirmed.

[Evaluation of hydrogen adsorption capacity]
Next, the hydrogen adsorption ability of each of the three-dimensional polymer complexes prepared above was evaluated. The test was performed by pressurizing each three-dimensional polymer complex with a hydrogen pressure of 10 to 30 MPa at room temperature (25 ° C.). The result is shown in FIG.

  FIG. 2 is a graph showing the hydrogen adsorption amount of each three-dimensional polymer complex prepared in Example 1 and Comparative Examples 1 and 2. FIG. 2 shows the hydrogen pressure (MPa) on the horizontal axis and the hydrogen adsorption amount (mass%) on the vertical axis. As is clear from FIG. 2, the highest hydrogen adsorption amount can be obtained in the three-dimensional polymer complex C of Example 1 in which the pillar ligand in the three-dimensional polymer complex has a lone pair of nitrogen atoms. It was.

FIG. 3 is a graph showing the relationship between the specific surface area and the hydrogen adsorption amount of each three-dimensional polymer complex prepared in Example 1 and Comparative Examples 1 and 2. Each value of the hydrogen adsorption amount in FIG. 3 corresponds to each value of the three-dimensional polymer complexes A to C at a hydrogen pressure of 30 MPa in FIG. FIG. 3 shows the specific surface area (m ² / g) on the horizontal axis and the hydrogen adsorption amount (mass%) on the vertical axis.

  As is clear from FIG. 3, the three-dimensional polymer complex C of Example 1 has a high activity with respect to hydrogen adsorption despite having a lower specific surface area than the three-dimensional polymer complex B of Comparative Example 2. Indicated. This result is considered that the three-dimensional polymer complexes B and C have the same structure except for the vinylene group (—CH═CH—) and the azo group (—N═N—) in the pillar ligand. For example, it is considered to support the existence of a unique electrostatic interaction between a lone pair of nitrogen atoms and a hydrogen molecule.

[Example 2]
[Evaluation of hydrogen adsorption capacity by molecular simulation]
Next, based on the structure of the three-dimensional polymer complex prepared above, a molecular model of the three-dimensional polymer complex in which the pillar ligand is replaced with another compound is designed. Calculated.

  In performing the above molecular simulation, in order to confirm the effectiveness, for the three-dimensional polymer complexes A to C prepared in Example 1 and Comparative Examples 1 and 2, the experimental values were compared with the calculated values by the molecular simulation. went.

In the molecular simulation, intermolecular interaction between a hydrogen molecule and a three-dimensional polymer complex composed of a divalent copper ion, 2,3-pyrazinedicarboxylic acid (pzdc), and a pillar ligand using the following program and function: Based on the obtained intermolecular interaction, the hydrogen adsorption amount of the three-dimensional polymer complex was calculated using the following program and function. The specific calculation conditions are as follows.
[Calculation of intermolecular interactions]
・ Use program: Gaussian 03 (manufactured by Gaussian)
Function used: non-empirical molecular orbital method (Ab-initio MO method) / aug-cc-pVTZ
[Calculation of hydrogen adsorption amount]
-Program used: Towheee 4.16.5
Use function: Grand Canonical Monte Carlo method (Grand Canonical Monte Carlo method)
[Calculation condition]
・ Force: OPLS
・ Calculation of point charges in three-dimensional polymer complexes: density functional theory (DFT), secondary perturbation method (MP2)
・ Number of unit cells of the calculated 3D polymer complex: 6 × 2 × 3 ・ Crystal lattice: Fixed (without considering the mobility of the molecules constituting the 3D polymer complex)
・ Temperature: 25 ℃
・ Pressure: 10-30MPa
[Periodic boundary conditions]
・ Cutoff: 12mm
・ Calculation of electrostatic interaction: Ewald method (Ewald method)

  Table 1 summarizes each value of FIG. 2 which is an experimental value regarding the hydrogen adsorption amount of the three-dimensional polymer complexes A to C, and Table 2 shows the three-dimensional height obtained by the molecular simulation. The calculated value regarding the amount of hydrogen adsorption of the molecular complexes A to C is shown.

  In the calculation by molecular simulation, the mobility of each molecule constituting the three-dimensional polymer complex is not taken into consideration, so the pore space in the three-dimensional polymer complex formed by them is wider than the actual pore space. Estimated. For this reason, when each value of Table 1 (experimental value) and Table 2 (calculated value) is compared, the hydrogen adsorption amount of the three-dimensional polymer complex is calculated higher in the calculated value. However, the difference between the experimental values and the calculated values is about 0.1 mass% and is almost constant. Except for such a difference, the hydrogen adsorption amount is good between the experimental values and the calculated values obtained by the molecular simulation. I was able to confirm a good match. Therefore, it was found that the calculation method based on the above molecular simulation is an effective means for predicting the hydrogen adsorption ability of the three-dimensional polymer complex.

及び

で表される化合物、それぞれ４，４’−ビスビピリジルフェニレン及び３，６−ビス（４−ピリジル）−１，２，４，５−テトラジンで置き換えた三次元高分子錯体Ｄ及びＥについて、上記の分子シミュレーションにより、上記と同様にして水素吸着量を計算した。その結果を図４に示す。なお、図４では、三次元高分子錯体Ａ〜Ｃの分子シミュレーションによる計算値も併せて示している。 Next, the pillar ligand in the three-dimensional polymer complexes A to C is represented by the following chemical formula:

as well as

And the three-dimensional polymer complexes D and E substituted with 4,4′-bisbipyridylphenylene and 3,6-bis (4-pyridyl) -1,2,4,5-tetrazine, respectively, In the same manner as described above, the hydrogen adsorption amount was calculated by the molecular simulation. The result is shown in FIG. In addition, in FIG. 4, the calculated value by the molecular simulation of three-dimensional polymer complex AC is also shown collectively.

  FIG. 4 is a graph showing hydrogen adsorption amounts of the three-dimensional polymer complexes A to E calculated by molecular simulation. FIG. 4 shows the hydrogen pressure (MPa) on the horizontal axis and the hydrogen adsorption amount (mass%) on the vertical axis. From the result of FIG. 4, it can be seen that the hydrogen adsorption amount of the three-dimensional polymer complex increases as the molecular length of the pillar ligand increases. Such an increase in the amount of adsorbed hydrogen increases the molecular length of the pillar ligand, thereby increasing the pores formed in the three-dimensional polymer complex. As a result, the specific surface area of the three-dimensional polymer complex increases. This is thought to be due to the increase.

  On the other hand, with respect to the three-dimensional polymer complexes B and C and D and E constituted by pillar ligands having the same basic skeleton, that is, those having the same molecular length, the pillar coordination in the three-dimensional polymer complex When the child contains a nitrogen-containing group having a lone pair of nitrogen atoms (that is, in the case of the three-dimensional polymer complexes C and E), hydrogen is higher than the corresponding three-dimensional polymer complexes B and D, respectively. The amount of adsorption was shown.

  This suggests an electrostatic interaction between the lone pair of nitrogen atoms and the hydrogen molecule, and as described above, this electrostatic interaction is caused by the lone electrons of the nitrogen atom. It is thought to be a unique interaction that occurs between a pair and a hydrogen molecule. Therefore, in the three-dimensional polymer complex composed of a metal ion, an organic ligand, and a pillar ligand, the pillar ligand in the three-dimensional polymer complex should be a lone pair of nitrogen atoms. By selecting, it is possible to remarkably improve the hydrogen adsorption ability of the obtained three-dimensional polymer complex.

It is a figure which shows the infrared absorption spectrum by Fourier-transform infrared spectroscopy (FT-IR) of each three-dimensional polymer complex prepared in Example 1 and Comparative Example 2. It is a graph which shows the hydrogen adsorption amount of each three-dimensional polymer complex prepared in Example 1 and Comparative Examples 1 and 2. It is a graph which shows the relationship between the specific surface area and hydrogen adsorption amount of each three-dimensional polymer complex prepared in Example 1 and Comparative Examples 1 and 2. It is a graph which shows the hydrogen adsorption amount of the three-dimensional polymer complex AE calculated by molecular simulation.

Claims (5)

  A two-dimensional structure formed by a metal ion and an organic ligand capable of coordinating to the metal ion is composed of a three-dimensional polymer complex stacked via a pillar ligand capable of coordinating to the metal ion. A hydrogen-adsorbing material, wherein the pillar ligand in the three-dimensional polymer complex contains a nitrogen-containing group having a lone pair of nitrogen atoms.   The hydrogen-adsorbing material according to claim 1, wherein the nitrogen-containing group includes an azo group or a nitrogen-containing heterocyclic group.   The pillar ligand is 4,4′-azopyridine, 3,6-bis (4-pyridyl) -1,2,4,5-tetrazine, 2,5-di-4-pyridinyl-pyrimidine, 2,5 -Selected from the group consisting of di-4-pyridinyl-pyrazine, 2,2'-p-phenylenebis-s-triazine, and 2 ', 5-di-4-pyridinyl-2,5'-bipyrimidine. The hydrogen-adsorbing material according to claim 1 or 2, characterized in that   The hydrogen adsorption material according to any one of claims 1 to 3, wherein the metal ion is a metal ion selected from the group consisting of copper, zinc, nickel, cobalt, and iron.   The organic ligand is at least one selected from the group consisting of 2,3-pyrazinedicarboxylic acid and a proton obtained by substituting the carboxyl group of 2,3-pyrazinedicarboxylic acid with a metal ion. The hydrogen adsorption material according to any one of claims 1 to 4.

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