Cobalt coordination polymer based on pyrazole carboxylic acid ligand as well as preparation method and application of cobalt coordination polymer

Abstract

The invention discloses a cobalt coordination polymer based on pyrazole carboxylic acid ligands as well as a preparation method and application of the cobalt coordination polymer. The chemical formula of the cobalt coordination polymer is [Co (Hppca) 2] (H2O) 2, and H2ppca is 5-(4-methylphenyl)-1H-pyrazole-3-carboxylic acid; the preparation method of the cobalt coordination polymer comprises the following steps: sequentially placing a cobalt acetate aqueous solution, ethyl acetate and a methanol solution of H2ppca in a container, sealing, storing and reacting at room temperature, separating out orange-yellow clustered crystals in the container, and filtering, washing and drying the obtained product to obtain the cobalt coordination polymer, and the synthesis method is simple to operate and relatively high in yield; the prepared complex has a special crystal structure, good thermal stability and excellent fluorescence performance, and is expected to become a potential candidate material of a photochemical sensor.

Description

Technical Field

[0001] The invention relates to a cobalt coordination polymer, in particular to a cobalt coordination polymer based on pyrazole carboxylic acid ligands, and also to a preparation method and application of the cobalt coordination polymer. Background Art

[0002] Coordination polymer materials (CPs), also known as metal-organic frameworks (MOFs), are a type of periodic framework structure assembled by metal clusters or ions through strong coordination bonds and organic linkers. The complexes have extremely rich and varied structures, highly customizable and precisely designed pore structures, and incomparable high surface areas, which make them have rich application value in heterogeneous catalysis, magnetism, optics, gas storage, etc. This type of material is a very promising multifunctional luminescent material because both its inorganic and organic parts can provide a platform for generating luminescence, and the charge transfer-related luminescence of metal ligands in MOFs can also add another dimension of luminescence function. The fluorescence properties of metal complexes are greatly affected by the selectivity of metals and ligands, and the fluorescence properties can be adjusted by structural regulation.

[0003] In recent years, the research on transition metal complex luminescent materials has mostly focused on the outer electron configuration of d 10 (Zn 2+ , Cu + 、Ag + etc.) and d 8 (Ru 2+ etc.) of metal ions, and has d 7 The electronic configuration of Co ions is often used in the assembly research of magnetic materials, but there are relatively few studies on their fluorescence. Existing coordination polymers are mostly synthesized by hydrothermal method, which requires the use of hydrothermal reactors. The equipment conditions are high and it is difficult to expand production. It is urgent to develop new coordination compounds with fluorescent luminescence properties and suitable synthesis methods. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a cobalt coordination polymer based on pyrazole carboxylic acid ligands with a zero-dimensional structure, and also to provide a method for preparing the above cobalt coordination polymer and its application in photochemical sensors.

[0005] Technical solution: The cobalt coordination polymer based on pyrazole carboxylic acid ligands of the present invention is a Co(II) coordination polymer, and the chemical formula is [Co(Hppca - )2](H2O)2, wherein H2ppca is 5-(4-methylphenyl)-1H-pyrazole-3-carboxylic acid.

[0006] The basic structural unit of the cobalt coordination polymer is: Co(II) ion is used as the central metal ion, which coordinates with the pyrazole ring nitrogen atom and the carboxylic acid oxygen atom in the ligand.

[0007] The coordination polymer has a zero-dimensional structure, belongs to the triclinic system, has a space group of P-1, and has unit cell parameters of: α=92.763(5)°, β=94.079(7)°, γ=103.858(6)°, Z=2.

[0008] The method for preparing the above cobalt coordination polymer comprises the following steps:

[0009] (1) dissolving cobalt acetate in water to obtain a cobalt acetate aqueous solution;

[0010] (2) dissolving H2ppca in methanol to prepare a H2ppca methanol solution;

[0011] (3) placing aqueous cobalt acetate solution, ethyl acetate, and methanol solution of H2ppca in a container in sequence, sealing and storing at room temperature for reaction, and orange-yellow clustered crystals precipitate in the container;

[0012] (4) Filter, wash and dry the obtained crystals to obtain the target product.

[0013] Wherein, in step (3), ethyl acetate is used as a buffer layer to separate the aqueous solution of cobalt acetate and the methanol solution of H2ppca.

[0014] Wherein, in step (3), in the mixed solution obtained by mixing the cobalt acetate aqueous solution, the H2ppca methanol solution and the ethyl acetate, the molar ratio of cobalt acetate to H2ppca is 1:1-4:1.

[0015] Wherein, in step (3), the reaction temperature is room temperature and the reaction time is 10-20 days.

[0016] The above-mentioned cobalt coordination polymer based on pyrazole carboxylic acid ligands can also be used in photochemical sensors.

[0017] Principle of the invention: The present invention proposes a cobalt coordination polymer with fluorescent luminescence characteristics and a preparation method thereof. The cobalt coordination polymer based on pyrazole carboxylic acid ligands of the present invention adopts Co(II) and H2ppca self-assembly, and the obtained complex has excellent fluorescent properties. The main reason may be the coupling of the electronic transition from the metal center orbital to the localized orbital of the organic linker and the metal center transition. 2+ It's 3D 7In addition to the electronic configuration, the ligand 5-(4-methylphenyl)-1H-pyrazole-3-carboxylic acid used has a large conjugated π-electron system, which is conducive to the transmission of electrons in the complex and thus obtains materials with good optical properties. The complex obtained after self-assembly of Co(II) and H2ppca has good thermal stability. On the one hand, it is because there are a large number of coordination bonds, hydrogen bonds, and π...π stacking effects in the complex, which enhance the rigidity of the entire complex and make the structure more stable. On the other hand, it is because a new five-membered ring is formed in the complex, which makes the overall structural stability stronger, thereby effectively improving the thermal stability of the complex. The synthesis method of the present invention has mild conditions and is a diffusion method under room temperature conditions. The cobalt coordination polymer can be obtained by normal temperature reaction. It has certain application prospects for the equipment conditions and environmental conditions required in the synthesis process.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The cobalt coordination polymer based on pyrazole carboxylic acid ligands of the present invention has excellent fluorescence effect and good thermal stability, and has great application prospects in the construction of photochemical sensors; (2) The polymer preparation method of the present invention is simple to operate, has a considerable yield and high repeatability, and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the asymmetric unit of Co(II) coordination polymer;

[0020] Figure 2 Co(II) coordination polymer 2+ Schematic diagram of the coordination environment;

[0021] Figure 3 Schematic diagram of the one-dimensional structure of Co(II) coordination polymer along the b-axis;

[0022] Figure 4 The two-dimensional supramolecular stacking diagram of Co(II) coordination polymer along the c-axis direction;

[0023] Figure 5 [Co(Hppca - )2](H2O)2 complex PXRD pattern;

[0024] Figure 6 [Co(Hppca - TG diagram of )2](H2O)2 complex;

[0025] Figure 7 [Co(Hppca - )2](H2O)2 complex solid-state fluorescence emission diagram. DETAILED DESCRIPTION

[0026] The technical scheme of the present invention is further described below in conjunction with the examples. The test materials used in the examples can all be purchased through conventional channels.

[0027] Example 1

[0028] The cobalt coordination polymer based on pyrazole carboxylic acid ligands of the present invention is a Co(II) coordination polymer, and its chemical formula is [Co(Hppca - )2](H2O)2, wherein H2ppca is 5-(4-methylphenyl)-1H-pyrazole-3-carboxylic acid.

[0029] The above-mentioned Co(II) coordination polymer is prepared by the following method:

[0030] (1) dissolving cobalt acetate in distilled water to obtain a cobalt acetate aqueous solution;

[0031] (2) dissolving H2ppca in methanol to prepare a methanol solution of H2ppca;

[0032] (3) placing cobalt acetate aqueous solution, ethyl acetate, and H2ppca methanol solution in a test tube in the order of cobalt acetate and H2ppca in a molar ratio of 2:1, sealing and storing at room temperature, reacting for two weeks, and orange-yellow cluster crystals precipitated in the test tube;

[0033] (4) The obtained product was filtered, washed and dried to obtain the target product with a yield of 68%.

[0034] The infrared absorption peaks of the obtained Co(II) coordination polymer include: 3211(s), 1638(s), 1494(s), 1467(m), 1420(s), 1347(s), 1243(m), 1032(s), 963(w), 832(s), 780(s), 705(m), 643(w), 511(m), 454(w). The elemental analysis data are: C 53.11, H 4.42, N 11.26 (theoretical value); C 53.09, H 4.72, N11.17 (experimental value). The crystallographic data of the complex are: triclinic system, space group is P-1, and unit cell parameters are: α=92.763(5)°, β=94.079(7)°, γ=103.858(6)°, Z=2.

[0035] like Figure 1 The asymmetric unit of the Co(II) coordination polymer is shown in FIG. The asymmetric unit of the complex of the present invention comprises a Co(II) ion, an incompletely deprotonated Hppca - ligand anion and a coordinating water molecule.

[0036] like Figure 2 Shown is the Co(II) coordination polymer Co 2+ Schematic diagram of the coordination environment of each Co(II) center, where each Co(II) center is located in the N2O2 coordination environment of the ligand (each Co 2+ The metal center is hexacoordinated, with four of the six atoms coming from the ligands, namely N2, O2, N2A, and O2A), coordinated with two carboxylic acid oxygen atoms (O2, O2A) of the two asymmetric ligands, two pyrazole nitrogen atoms (N2, N2A), and two oxygen atoms of coordinated water (O1W, O1WA); therefore, the resulting CoO4N2 polyhedral geometry can be viewed as a distorted octahedron, with the equatorial positions occupied by O2, O2A, N2, and N2A atoms and the axial positions occupied by O1W and O1WA atoms (symmetry operation codes: -x, 1-y, 1-z), and with the conventional Key length.

[0037] like Figure 3 The figure shows a schematic diagram of the one-dimensional structure of the Co(II) coordination polymer along the b-axis. The single-molecule complexes are connected to form a one-dimensional chain structure through hydrogen bonds formed between the oxygen atoms on the carboxylic acid connected to the pyrazole ring and the coordinated water molecules.

[0038] like Figure 4 The figure shows the two-dimensional supramolecular stacking of Co(II) coordination polymer along the c-axis. Figure 3 Based on the one-dimensional chain structure shown, a two-dimensional network structure is formed through the π-π stacking of the pyrazole ring.

[0039] like Figure 5 Shown is [Co(Hppca - )2](H2O)2 complex, the PXRD pattern of the solid powder diffraction pattern and [Co(Hppca - )2](H2O)2 single crystal structure analysis simulation spectra are basically consistent, indicating that the complex crystallizes in pure phase.

[0040] The X-ray diffraction data of the Co(II) coordination polymer of the present invention was collected by an XtaLAB Synergy-R single crystal diffractometer using graphite monochromatized Mo-Kα radiation. Diffraction point data were collected at low temperature using ω scanning technology. The crystal structure was solved by direct method using olex2 software and refined using full matrix least squares method, and anisotropic displacement parameters were refined for all non-hydrogen atoms. The crystallographic parameters of the complex are shown in Table 1:

[0041] Table 1. Crystallographic parameters of the complexes

[0042]

[0043] Example 2

[0044] The Co(II) coordination polymer prepared in Example 1 was subjected to a thermal stability test:

[0045] The Co(II) coordination polymer prepared in Example 1 was heated in an alumina crucible at a rate of 20°C / min in a N2 atmosphere, with the heating range being 30 to 800°C.

[0046] like Figure 6 Shown is [Co(Hppca - )2](H2O)2 complex, the complex keeps structural stability below 110℃, 110℃-166℃ corresponds to the removal of coordinated water of the complex (theoretical value 92.8%, experimental value 93.1%), and as the temperature continues to rise, the complex loses weight rapidly, corresponding to the decomposition of organic ligands, and the skeleton completely collapses at 485℃. The solid residue finally obtained is presumed to be CoO (theoretical value 15.07%, experimental value 23.37%).

[0047] Example 3

[0048] The Co(II) coordination polymer prepared in Example 1 was subjected to a fluorescence performance test:

[0049] The solid-state fluorescence emission spectra of free ligand H2ppca and the complex were tested at room temperature.

[0050] like Figure 7 Shown is [Co(Hppca - )2](H2O)2 complex solid-state fluorescence emission diagram. Under 350nm excitation, the H2ppca ligand shows weak luminescence with a maximum emission wavelength of 397nm, which may be due to the electron migration of the semi-rigid ligand π-π*. The maximum emission wavelength of the complex under 350nm excitation is 407nm, and the fluorescence intensity is much greater than that of the free ligand. Compared with the free ligand H2ppca, the maximum emission peak of the complex has a slight red shift, indicating that the energy difference between the excited state energy level and the ground state energy level of the molecule is reduced. The fluorescence enhancement of the complex is partly due to the d 7 The Co(II) ions of the configuration are good luminescent centers; on the other hand, due to the formation of the framework structure, the structure makes the aromatic main chain rigid, maximizes the intramolecular / intermolecular interactions between organic linkers for energy transfer, and reduces the HOMO-LUMO energy gap in the ligand. Therefore, the coordination polymer of the present invention has excellent fluorescence properties and has great application prospects in the construction of photochemical sensors.

Claims

1. A cobalt coordination polymer based on pyrazole carboxylic acid ligands, characterized in that: The chemical formula of the cobalt complex is [Co(Hppca - )2](H2O)2, wherein H2ppca is 5-(4-methylphenyl)-1H-pyrazole-3-carboxylic acid.

2. The cobalt coordination polymer based on pyrazole carboxylic acid ligands according to claim 1, characterized in that: The basic structural unit of the cobalt coordination polymer is: Co(II) ion is used as the central metal ion, which coordinates with the pyrazole ring nitrogen atom and the carboxylic acid oxygen atom in the ligand.

3. The cobalt coordination polymer based on pyrazole carboxylic acid ligands according to claim 2, characterized in that: The coordination polymer has a zero-dimensional structure, belongs to the triclinic system, has a space group of P-1, and has unit cell parameters of: β=94.079(7)°, γ=103.858(6)°, Z=2.

4. A method for preparing the cobalt coordination polymer according to claim 1, characterized in that: The steps include: (1) preparing a cobalt acetate aqueous solution; (2) preparing H2ppca methanol solution; (3) placing aqueous cobalt acetate solution, ethyl acetate, and methanol solution of H2ppca in a container in sequence, sealing and storing at room temperature for reaction, and orange-yellow clustered crystals precipitate in the container; (4) Filter, wash and dry the obtained crystals to obtain the target product.

5. The method according to claim 4, characterized in that: In step (3), ethyl acetate is used as a buffer layer to separate the aqueous solution of cobalt acetate and the methanol solution of H2ppca.

6. The method according to claim 4, characterized in that: In step (3), in the mixed solution obtained by mixing the aqueous solution of cobalt acetate, the methanol solution of H2ppca and ethyl acetate, the molar ratio of cobalt acetate to H2ppca is 1:1-4:

1.

7. The method according to claim 4, characterized in that: In step (3), the reaction temperature is room temperature and the reaction time is 10-20 days.

8. Use of the cobalt coordination polymer based on pyrazole carboxylic acid ligands according to claim 1 in a photochemical sensor.

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