A magnetic / fluorescent bifunctional dysprosium complex and its preparation method

Abstract

The invention discloses a magnetic / fluorescent bifunctional dysprosium complex and a preparation method thereof. The complex exhibits a three-dimensional porous structure, and the structural formula is [Dy2(SBA)3(H2O)4]·DMA, wherein SBA is a 4,4'-sulfonyldibenzoic acid divalent anion with two carboxyl protons removed, and DMA is free N,N-dimethylacetamide. The two dysprosium ions in the complex are both in a bicap triangular prism configuration, and are assembled into a one-dimensional metal chain through the carboxyl bridge of the SDA ligand; and then expanded into a three-dimensional network structure through the extensibility of the SDA ligand. The complex exhibits obvious slow magnetic relaxation behavior under zero field, is a multidimensional single-molecule magnet, and has an effective energy barrier of 47.6K; and the sensitization effect of the SDA ligand can provide energy for the dysprosium ion to excite it, so that the complex exhibits a characteristic linear fluorescence spectrum of the dysprosium ion.

Description

Technical Field

[0001] The invention belongs to the technical field of multifunctional dysprosium complexes, and in particular relates to a multidimensional dysprosium complex with magnetic and fluorescent properties and a preparation method thereof. Technical Background

[0002] Rare earth refers to the general term for 17 kinds of metal elements of scandium, yttrium and lanthanum series. It is called the "vitamin" of modern industry and the "treasure house of new materials in the 21st century". It is widely used in cutting-edge scientific and technological fields such as metallurgy, petrochemical industry, military technology, information engineering, etc. It is a non-renewable strategic resource. As a country with rare earth resources, China's reserves accounted for 71.1% of the world's reserves at most, but due to unreasonable development, rare earth resources are seriously consumed. In order to achieve efficient utilization of rare earth resources, it is necessary to conduct in-depth exploration of the unique physical and chemical properties of rare earths and realize the rapid development of high-tech industries with rare earth resources as the core. Dysprosium is a heavy rare earth element with outstanding application prospects in the fields of magnetic materials and laser technology. By combining dysprosium ions with strong / weak field ligands to prepare specific complexes, a type of single-molecule magnet with slow magnetic relaxation behavior can be obtained. Its magnetic properties originate from the magnetic anisotropy of isolated molecules rather than the synergy between atoms, thus avoiding the superparamagnetic limit of traditional ferromagnets. It is expected to be used as a new type of soft magnetic material in ultra-high density information storage, quantum chemical calculations and molecular spin electronics (Nat. Mate., r 2008, 7, 179-186; Coordin. Chem. Rev., 2017, 346, 150-175). By combining dysprosium ions with conjugated polyacid ligands to prepare specific complexes, a class of lanthanide metal organic framework materials with special optical properties can be obtained. It has excellent optical properties, with the characteristics of high color purity, wide Stokes shift and linear emission peak. It can be used as a high-sensitivity and low-detection-limit fluorescence sensor to specifically identify trace substances in environmental science and life science. It can also be used as a sharp-line light source material in the field of high-purity lasers (Chem. Soc. Rev., 2021, 50, 4484-4513; Chem. Soc. Rev., 2020, 49, 7949-7977).

[0003] The luminescence energy transition and magnetic anisotropy of dysprosium ions are closely related to the electronic structure, and targeted optimization of the ligand field environment is required to achieve the two specific properties. When the energy level splitting of the dysprosium ion matches the energy level of the ligand, the ligand receives external energy and transforms into an excited state. Through non-radiative intramolecular transfer, the excited energy is transferred to the dysprosium ion, causing it to exhibit characteristic fluorescence. Due to the special energy level structure of the dysprosium ion and the weak luminescence intensity, few dysprosium-based fluorescent complexes have been developed. 4 F 9 / 2 → 6 H 15 / 2, 4 F 9 / 2 → 6 H 13 / 2 and 4 F 9 / 2 → 6 H 11 / 2 The three energy level transitions can produce sharp line light sources of specific frequencies, which are an indispensable component for the development of laser technology towards multi-bands. The fluorescent complex combined with magnetic anisotropy is a special multifunctional material. It is not only the sum of two properties, but also shows a strong interaction between optics and magnetism. When the ambient temperature is lower than the blocking temperature, the coercive force of the dysprosium ions themselves can form a local magnetic field, the energy levels will undergo Zeeman splitting, and the fluorescence spectrum will change. Therefore, it is necessary to develop new magnetic / fluorescent bifunctional dysprosium complexes, explore their multifunctional properties and clarify the intrinsic relationship between special properties, realize performance integration and optimization, and obtain new multifunctional materials that are conducive to the development of high-tech industries. Summary of the invention

[0004] In view of the outstanding problems in the prior art, the first object of the present invention is to provide a magnetic / fluorescent bifunctional dysprosium complex.

[0005] The second object of the present invention is to provide a high-yield preparation method for the above-mentioned magnetic / fluorescent bifunctional dysprosium complex.

[0006] To achieve the above-mentioned purpose, the magnetic / fluorescent bifunctional dysprosium complex used in the present invention has the structural formula Dy2(SBA)3(H2O)4]·DMA, wherein SBA is a divalent anion of 4,4'-sulfonyldibenzoic acid with two carboxyl protons removed, and DMA is a free N,N-dimethylacetamide molecule in the pore; the complex crystallizes in the triclinic system, belongs to the P-1 space group, and has unit cell parameters of: a=1.24006(3)nm, b=1.48629(5)nm, c=1.63354(4)nm, α=91.504(2)°, β=106.097(2)°, γ=113.788(3)°, V=2.61413(14)nm 3 ,ρ=1.775gm -3 、μ=16.957mm -1 , F(000)=1376.

[0007] The asymmetric unit of the magnetic / fluorescent bifunctional dysprosium complex of the present invention comprises two dysprosium ions, three SBA divalent anion ligands, four water molecules and a DMA molecule free in the pore. The two dysprosium ions exhibit different coordination modes, but both are bicapped triangular prism configurations of DyO8. The coordination atoms of Dy1 are five bridging carboxylic acid oxygen atoms, two chelated carboxylic acid oxygen atoms and one water molecule; the coordination atoms of Dy2 are five bridging carboxylic acid oxygen atoms and three water molecules. Dy1 and Dy2 are bridged by the carboxylic acid oxygen atoms of three ligands to form a {Dy2} unit; adjacent {Dy2} units are bridged by two carboxylic acid oxygen atoms to form a one-dimensional metal chain; and the metal chain is extended into a three-dimensional porous network structure through the extension of the SDA ligand that can coordinate on both sides. The coordinated Dy-O bond length is between 0.2233(4)nm and 0.2666(4)nm, and the distance between the nearest dysprosium ions is 0.4528nm.

[0008] The preparation method of the magnetic / fluorescent bifunctional dysprosium complex of the present invention comprises the following steps: adding dysprosium chloride hexahydrate and 4,4'-sulfonyldibenzoic acid into a mixed solution of distilled water and N,N-dimethylacetamide, reacting in a closed environment at 135-145°C in a high-pressure reactor for 60-80 hours, then cooling to room temperature at a rate of 3-5°C / h, filtering, washing, drying and collecting light yellow block crystals to obtain the magnetic / fluorescent bifunctional dysprosium complex.

[0009] In the above preparation method, the molar ratio of the dysprosium chloride hexahydrate to 4,4'-sulfonyldibenzoic acid is preferably 1:1 to 1.5.

[0010] In the above preparation method, the volume ratio of N,N-dimethylacetamide to distilled water is preferably 1:1-2.

[0011] The present invention uses 4,4'-sulfonyldibenzoic acid as the main ligand and water molecules as the auxiliary ligand to construct a magnetic / fluorescent bifunctional dysprosium complex with a peculiar structure. 4,4'-sulfonyldibenzoic acid constructs a one-dimensional metal chain through chelation and bridging coordination, and water molecules fill the remaining coordination sites, so that each dysprosium ion is in a stable state. Combining the characteristics of both sides of 4,4'-sulfonyldibenzoic acid that can be coordinated and the V-shaped structure, a porous complex with a peculiar structure is assembled. The energy level splitting of the ligand is relatively matched with the transition energy level of the dysprosium ion. The reasonable arrangement of the ligand and the water molecules maintains the significant magnetic anisotropy of the dysprosium ion, so that the complex exhibits both magnetic and fluorescent properties. In addition, the design and preparation method of the complex also provides a new synthetic idea for obtaining such complexes.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0013] 1. The magnetic / fluorescent bifunctional dysprosium complex of the present invention exhibits a unique spatial structure, has good stability, and has a relatively outstanding slow magnetic relaxation behavior of a zero-field single-molecule magnet and a linear emission fluorescence spectrum characteristic of dysprosium ions. It can be used as a multifunctional magnetic / optical material in special environments.

[0014] 2. The preparation method of the magnetic / fluorescent bifunctional dysprosium complex of the present invention is simple and easy, with low raw material cost. The preparation of bifunctional materials with high yield and high crystallinity can be achieved through hydrothermal reaction, which is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The diagrams are the coordination structure diagram (a), the chain structure diagram (b) and the three-dimensional structure diagram (c) of the magnetic / fluorescent bifunctional dysprosium complex of the present invention.

[0016] Figure 2 It is a temperature-dependent DC magnetic susceptibility diagram of the magnetic / fluorescent dual-functional dysprosium complex of the present invention under an external field of 1000Oe.

[0017] Figure 3 It is a test curve of the magnetization intensity of the magnetic / fluorescent bifunctional dysprosium complex of the present invention at 2K.

[0018] Figure 4 The real signal (a) and imaginary signal (b) of the variable temperature AC magnetic susceptibility signal of the magnetic / fluorescent bifunctional dysprosium complex of the present invention under zero field are shown.

[0019] Figure 5 The real signal (a) and imaginary signal (b) of the variable frequency AC magnetic susceptibility signal of the magnetic / fluorescent dual-functional dysprosium complex of the present invention under zero field are shown.

[0020] Figure 6 3 is a graph of relaxation time (τ) and temperature (T) of the magnetic / fluorescent bifunctional dysprosium complex of the present invention (the dotted line represents a single Aubach relaxation fit, and the solid line represents a full fit taking into account Aubach relaxation, quantum tunneling and Raman relaxation).

[0021] Figure 7 It is a fluorescence spectrum line diagram of the magnetic / fluorescent bifunctional dysprosium complex of the present invention.

[0022] Figure 8 It is a fluorescence lifetime diagram of a solid sample of the magnetic / fluorescent bifunctional dysprosium complex of the present invention.

[0023] Fig. 9 It is the X-ray powder diffraction pattern of the magnetic / fluorescent bifunctional dysprosium complex of the present invention. DETAILED DESCRIPTION

[0024] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments and their descriptions are only for the purpose of illustration and are not intended to constitute any form of limitation on the actual protection scope of the present invention, nor are they intended to limit the protection scope of the present invention to these.

[0025] Example 1

[0026] 0.0306g (0.1mmol) of 4,4'-sulfonyldibenzoic acid and 0.0377g (0.1mmol) of dysprosium chloride hexahydrate were added to a high-pressure reactor, and 2mL of N,N-dimethylacetamide and 2mL of distilled water were added. The reaction was carried out at 140℃ for 72h under closed conditions; then the temperature was slowly cooled to room temperature at a cooling rate of 3℃ / h. The light yellow block crystals were filtered, washed with distilled water, and collected to obtain a magnetic / fluorescent bifunctional dysprosium complex with a yield of 68%. The structural formula of the obtained complex is Dy2(SBA)3(H2O)4]·DMA, where SBA is a 4,4'-sulfonyldibenzoic acid divalent anion with two carboxyl protons removed, and DMA is a free N,N-dimethylacetamide molecule in the pore. The structure was determined using a Bruker Smart Apex CCD X-ray single crystal diffractometer, and the results are shown in Table 1. The bifunctional dysprosium complex crystallizes in the triclinic system and belongs to the P-1 space group. The unit cell parameters are: a=1.24006(3)nm, b=1.48629(5)nm, c=1.63354(4)nm, α=91.504(2)°, β=106.097(2)°, γ=113.788(3)°, V=2.61413(14)nm 3 ,ρ=1.775gm -3 、μ=16.957mm -1 , F(000)=1376.

[0027] Table 1 Crystallographic data of the complexes

[0028]

[0029]

[0030] Depend on Figure 1It can be seen that the asymmetric unit of the magnetic / fluorescent bifunctional dysprosium complex prepared in this embodiment contains two dysprosium ions, three SBA divalent anion ligands, four water molecules and one DMA molecule free in the pore. The complex crystallizes in the triclinic system and belongs to the P-1 space group. The coordinating atoms of Dy1 are five bridged carboxylic acid oxygen atoms, two chelated carboxylic acid oxygen atoms and one water molecule, forming a double-capped triangular prism configuration of DyO8; the coordinating atoms of Dy2 are five bridged carboxylic acid oxygen atoms and three water molecules, also forming a double-capped triangular prism configuration of DyO8. Dy1 and Dy2 are bridged by the carboxylic acid oxygen atoms of three SBA ligands to form a {Dy2} unit; adjacent {Dy2} units are bridged by the carboxylic acid oxygen atoms of two SBA ligands to form a one-dimensional metal chain; and then the metal chain is extended into a three-dimensional network structure through the extensibility of the SDA ligand that can be coordinated on both sides. The coordinated Dy-O bond length is between 0.2233(4)nm and 0.2666(4)nm, and the distance between the nearest dysprosium ions is 0.4528nm.

[0031] Comparative Example 1

[0032] The reaction temperature of the preparation process of Example 1 was adjusted to 130° C. or below, and the other conditions remained unchanged; the product was a powdery solid, and no complex crystals were precipitated.

[0033] Comparative Example 2

[0034] During the preparation of Example 1, no distilled water was added, but 4 mL of N,N-dimethylacetamide was used, and other conditions remained unchanged; the result was a completely soluble colorless solution without solid precipitation.

[0035] Comparative Example 3

[0036] In the preparation process of Example 1, the reaction time was less than 60 h, and the other conditions were not changed; the result was a powdery solid precipitate or very small crystals, and the structure could not be determined.

[0037] It can be seen from the comparison of Example 1 with Comparative Examples 1 to 3 that the preparation of the magnetic / fluorescent bifunctional dysprosium complex of the present invention needs to be carried out at a reaction temperature of 140°C, and distilled water and N,N-dimethylacetamide need to be added at the same time to form an external environment that is conducive to the reaction between the metal salt and the organic ligand, and is also conducive to the generated complex having a suitable solubility and crystallization, thereby obtaining a complex with good crystallinity and high purity.

[0038] Under an external magnetic field of 1000 Oe, the prepared dysprosium complex was subjected to a variable temperature DC magnetic susceptibility test in the temperature range of 2 to 300 K. Figure 2 As shown, at 300K, the molar magnetic susceptibility of the complex (χ M The test value of T) is 28.16cm 3K mol -1 , which is comparable to the theoretical value of 28.34 cm for two uncoupled dysprosium ions. 3 K mol -1 Closer (S = 5 / 2, L = 5, g = 4 / 3, 6 H 15 / 2 ). At 300-11K, the curve shows a downward trend as the temperature decreases, and the lower the temperature, the faster the rate of decrease. At 10K, the molar magnetic susceptibility value begins to increase; at 2K, it reaches a maximum value of 26.15cm 3 K mol -1 This increase can be attributed to the ferromagnetic interaction between the two dysprosium ions at low temperatures. The magnetization intensity of the prepared dysprosium complex was tested at a temperature of 2K and a magnetic field range of 0 to 70k Oe. Figure 3 As shown in the figure, with the increase of the external magnetic field, the magnetization intensity of the complex increases significantly; when it increases to a certain extent, the growth rate slows down and gradually tends to saturation, with a maximum value of 9.34Nβ, which is much lower than the theoretical value of 20Nβ of two isolated dysprosium ions, indicating that the complex has significant magnetic anisotropy.

[0039] In order to analyze the slow magnetic relaxation behavior of the bifunctional dysprosium complex prepared in Example 1, a variable temperature and variable frequency AC magnetic susceptibility test was performed under zero external magnetic field. Figure 4 and 5 As shown, both the variable temperature and variable frequency AC magnetic susceptibility tests show frequency-dependent slow magnetic relaxation behavior, which is a typical magnetic phenomenon unique to single-molecule magnets. The peak temperature corresponding to the variable temperature AC magnetic susceptibility test at 1000Hz is 6.5K; the temperature of the last curve of the variable frequency AC magnetic susceptibility test at the highest frequency is 8.0K. The Debye model is used to fit the variable frequency AC magnetic susceptibility test curve and extract the relaxation time τ. The Arrhenius formula is used to fit the high temperature data points to obtain the effective energy barrier U of the complex under zero field. eff =47.6K, the pre-exponential factor is τ0 = 4.13 × 10 -7 s(see Figure 6 ). However, as the temperature decreases, the relaxation time data points gradually deviate from the fitting line, indicating the existence of multiple relaxation mixing situations. Taking into account the quantum tunneling process, Raman relaxation process and Aubach relaxation process, the relaxation time is fitted to obtain the magnetic parameters: U eff =47.6K,τ0=5.35×10 -7 s, C = 10.36, n = 2.60, τ QTM =0.005s.

[0040] The fluorescence spectrum of the solid sample of the prepared magnetic / fluorescent bifunctional dysprosium complex was measured using an Edinburgh FS5 fluorescence spectrometer at room temperature (see Figure 7). The emission wavelength was fixed at 575nm, and the excitation spectrum was scanned between 300 and 450nm. Multiple excitation spectrum peaks were observed, and 350nm was determined to be the best excitation wavelength. The excitation wavelength was fixed at 350nm, and the emission spectrum was scanned between 400 and 700nm. The fluorescence emission peaks of the complex were observed at 482nm, 574nm, and 665nm, which belonged to the dysprosium ion, 4 F 9 / 2 → 6 H 15 / 2 , 4 F 9 / 2 → 6 H 13 / 2 and 4 F 9 / 2 → 6 H 11 / 2 The three energy level transitions produce an emission spectrum with a specific frequency. This characteristic spectrum is caused by the ligand absorbing energy, transitioning from the ground state to the excited singlet state, then transferring to the triplet state, and then transferring energy to the dysprosium ion. The ground state electrons of the dysprosium ion are excited and then transformed into an excited state, and then emit fluorescence in the form of radiation, releasing energy back to the ground state. Subsequently, the fluorescence lifetime of the solid sample of the bifunctional dysprosium complex was measured, which was 16ns (see Figure 8 ).

[0041] In order to detect the stability of the magnetic / fluorescent bifunctional dysprosium complex prepared in Example 1, the powder diffraction test pattern of the bifunctional dysprosium complex after being placed in air for 3 months was compared with the standard simulation pattern (see Fig. 9 ), the curves are basically consistent, indicating that the chemical properties of the complex are relatively stable and can be stored in an air environment for a long time.

[0042] Based on the above test results, it can be known that the magnetic / fluorescent bifunctional dysprosium complex of the present invention exhibits a unique spatial structure, has the slow magnetic relaxation behavior of a zero-field single-molecule magnet and a linear emission fluorescence spectrum characteristic of dysprosium ions, and can be used as a multifunctional magnetic / optical material in special environments. As for the preparation method, the preparation of the magnetic / fluorescent bifunctional dysprosium complex of the present invention is simple and easy, with low raw material cost, and the preparation of magnetic / fluorescent bifunctional materials with high yield and high crystallinity can be achieved through hydrothermal reaction. The bifunctional dysprosium complex can be used as a potential molecular-based magnetic material and sharp-line light source fluorescent material in the required special working environment, and has a high application value.

Claims

1. A magnetic / fluorescent bifunctional dysprosium complex, characterized in that: The complex has a structural formula of [Dy2(SBA)3(H2O)4]∙DMA, wherein SBA is a 4,4'-sulfonyldibenzoic acid divalent anion with two carboxyl protons removed, and DMA is a free N,N-dimethylacetamide molecule in the pore. The complex crystallizes in the triclinic system and belongs to the P-1 space group. The unit cell parameters are: a=1.24006(3) nm, b=1.48629(5) nm, c=1.63354(4) nm, α=91.504(2)°, β=106.097(2)°, γ=113.788(3)°, V=2.61413(14) nm. 3 , ρ = 1.775 gm -3 , μ = 16.957 mm -1 , F(000) = 1376; The two central dysprosium ions of the complex exhibit two different coordination modes, but both are double-capped triangular prism configurations of DyO8; the coordination atoms of Dy1 are five bridging carboxylic acid oxygen atoms, two chelated carboxylic acid oxygen atoms and one water molecule; the coordination atoms of Dy2 are five bridging carboxylic acid oxygen atoms and three water molecules; Dy1 and Dy2 are bridged by three ligand carboxylic acid oxygen atoms to form a {Dy2} unit; adjacent {Dy2} units are bridged by two carboxylic acid oxygen atoms to form a one-dimensional metal chain; Then, through the extension of the coordination on both sides of the SDA ligand, the metal chain is extended into a three-dimensional porous network structure.

2. A method for preparing the magnetic / fluorescent bifunctional dysprosium complex according to claim 1, characterized in that: Dysprosium chloride hexahydrate and 4,4'-sulfonyldibenzoic acid are added to a mixture of distilled water and N,N-dimethylacetamide, and reacted in a closed environment at 135-145°C in a high-pressure reactor for 60-80 hours, then cooled to room temperature at a rate of 3-5°C / h, filtered, washed, dried, and collected pale yellow block crystals to obtain a magnetic / fluorescent bifunctional dysprosium complex.

3. The method for preparing the magnetic / fluorescent bifunctional dysprosium complex according to claim 2, characterized in that: The molar ratio of the dysprosium chloride hexahydrate to 4,4'-sulfonyldibenzoic acid is 1:1 to 1.

5.

4. The method for preparing the magnetic / fluorescent bifunctional dysprosium complex according to claim 2, characterized in that: The volume ratio of the N,N-dimethylacetamide to distilled water is 1:1-2.

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