Multi-core rare earth complex based on Schiff base ligand as well as preparation method and application of multi-core rare earth complex

Abstract

The invention belongs to the technical field of rare earth complex preparation, and discloses a multi-core rare earth complex based on a Schiff base ligand, and a preparation method and application thereof. The preparation method comprises the following steps: adding Eu (CH3CO2) 3.4 H2O and H2mpcd into a mixed solution of CH3OH and CH3CN, and reacting to obtain the multinuclear rare earth complex Na2 [Eu6 (mpcd) 6 (mu 3: eta 2: eta 1-OAc) 6 (mu 3-O)]. The multi-core rare earth complex has excellent molecular magnetism and can be applied to preparation of molecular magnetic materials and molecular memory materials.

Description

Technical Field

[0001] The invention belongs to the technical field of rare earth complex preparation, and relates to a multi-nuclear rare earth complex based on a Schiff base ligand, a preparation method and an application thereof. Background Art

[0002] Rare earth complexes are an important class of coordination compounds, in which rare earth metal ions form stable compounds with organic or inorganic ligands. They have unique electronic structures and properties and have aroused widespread interest and research in many fields (Chem. Soc. Rev., 2018, 47 (7), 2431-2453; J. Am. Chem. Soc., 2023, 145 (3), 1572-1579). In fact, rare earth ions have an unfilled 4f electronic structure, which gives them a large orbital angular momentum and strong magnetic anisotropy, which is the basis for their use as magnetic functional elements of molecular nanomagnets. Schiff bases are renowned for their excellent stability, variable colors, and excellent redox ability. More importantly, Schiff base ligands are regarded as an important type of organic molecule in the field of rare earth coordination due to their simple synthesis methods, excellent coordination ability, and electron donor performance. In recent years, people have shown great interest in the phenomenon of stable complexes formed between Schiff base ligands and rare earth metals (Angew. Chem. Int. Ed., 2023, 62(12), e202218540; Inorg. Chem., 2016, 55(17), 8898-8904). The reason for this stability is the presence of lone pairs of electrons in the azodicarbonate (-N=CH-) bond in the Schiff base structure. At present, rare earth multinuclear complexes are mainly obtained by assembling O-rich multidentate ligands and rare earth ions. Their varied structures and excellent magnetic properties provide a solid research foundation for the development of molecular-based magnetic materials. Summary of the invention

[0003] The present invention aims to provide a multi-nuclear rare earth complex based on Schiff base ligand and a preparation method thereof. The rare earth complex contains six rare earth ions, has a triangular configuration and has excellent molecular magnetism.

[0004] The technical solution provided by the present invention is as follows:

[0005] A multinuclear rare earth complex based on Schiff base ligands, belonging to the monoclinic system, with a molecular formula of Na2[Eu6(mpcd)6(μ3:η 2 :η 1 -OAc)6(μ3-O)](H2mpcd=(E)-N-[(2-hydroxy-3-methoxyphenyl)methylene]pyrazine-2-carboxylic acid hydrazide), the space group is C2 / c, and the unit cell parameters are: α=90°, β=97.570(2)°, γ=90°,

[0006] A preparation method of a multi-nuclear rare earth complex based on a Schiff base ligand comprises: adding Eu(CH3CO2)3·4H2O and a Schiff base ligand H2mpcd into a reaction solvent, stirring, then adding Na2CO3, continuing to stir, filtering, standing and volatilizing, and obtaining orange-yellow long strip crystals after two weeks.

[0007] The synthetic route of multi-nuclear rare earth complexes is shown below:

[0008]

[0009] Furthermore, the reaction solvent is a mixture of a CH3OH solution and a CH3CN solution.

[0010] In the above formula, complex 1 is Na2[Eu6(mpcd)6(μ3:η 2 :η 1 -OAc)6(μ3-O)].

[0011] Furthermore, Eu(CH3CO2)3·4H2O, Schiff base ligand H2mpcd and Na2CO3 were prepared in a millimolar ratio of 1:1:1, and for every 0.2 mmol of Eu(CH3CO2)3·4H2O, 6 mL of CH3OH and 12 mL of CH3CN were added.

[0012] The present invention also provides an application of the above-mentioned multi-nuclear rare earth complex or the multi-nuclear rare earth complex prepared by the above-mentioned preparation method in molecular magnetic materials.

[0013] The present invention adopts a synthesis strategy of a room temperature stirring method to obtain a hexanuclear rare earth complex. The preparation method is simple and the raw materials are readily available. The rare earth complex is formed by designing an organic ligand structure to react with different rare earth metals, thereby enriching the structural types of rare earth complexes and providing a new direction for the exploration of their structural field. The synthesized compound can be applied to molecular magnetic materials or molecular memory materials and has potential application value in the fields of high-density information storage, quantum computing, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is the molecular structure diagram of complex 1;

[0015] Figure 2 is the coordination geometry of the central Eu ion in complex 1;

[0016] Figure 3 is the temperature-dependent magnetic susceptibility of complex 1 under a 1000Oe DC field;

[0017] Figure 4 is the magnetization intensity of complex 1;

[0018] Figure 5 is the reduced magnetization intensity of complex 1;

[0019] Figure 6 is the AC magnetic susceptibility of complex 1 at 0 Oe;

[0020] Figure 7 is the AC magnetic susceptibility of complex 1 at 3000 Oe. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art may make various changes or modifications to the present invention, and equivalent changes or modifications also fall within the scope limited by the claims of the present application.

[0022] It should be noted that all reagents in the following examples were purchased directly from the market and were of analytical grade and were not further purified before use.

[0023] Example 1: Na2[Eu6(mpcd)6(μ3:η 2 :η 1 Preparation of -OAc)6(μ3-O)](complex 1)

[0024] Eu(CH3CO2)3·4H2O (0.20mmol, 65.8mg) and H2mpcd (0.20mmol, 54.4mg) were dissolved in 6mLCH3OH and 12mLCH3CN solution, stirred for 5 minutes, then Na2CO3 (0.20mmol, 21.7mg) was added, and stirring was continued for 2 hours. The mixture was filtered and allowed to stand for evaporation. After two weeks, orange-yellow long strip crystals were obtained, which was the target complex 1.

[0025] Example 2: Crystal structure determination

[0026] Data were collected using a Rigaku Oxford diffractometer at 120 K with Mo Kα radiation from a graphite monochromator. The coordinates of hydrogen atoms on some water molecules were obtained by difference Fourier synthesis, the number of remaining crystal water was determined by thermogravimetric test results, and the coordinates of all non-hydrogen atoms were obtained by direct method and optimized by anisotropic thermal parameter correction and matrix least squares method. Hydrogen atoms were directly added to the molecular formula.

[0027] One molecule of complex 1 contains six Eu atoms and six deprotonated mpcd2- Ligand (see Figure 1 ), where mpcd 2- The ligand used is μ2-η 2 :η 1 :η 1 and μ2-η 2 :η 1 :η 1 :η 1 The two coordination modes connect the six Eu atoms to form a planar triangle. The center of the triangle is an O16 atom connected to Eu2, Eu2A, and Eu3.

[0028] The coordination configuration of rare earth ions was analyzed using Shape software (Table 1, Table 2). The results show that the coordination configuration of Eu1 is an octahedral triangular dodecahedron. Figure 2 The eight coordinated atoms of Eu1 shown in a are composed of a ligand mpcd 2- Provided by a N atom (N8) and two O atoms (O4, O5), another ligand mpcd 2- Provides one atom (N4) and two O atoms (O1, O2); two acetate groups provide two coordinated O atoms (O10, O12). The average bond length of Eu1-O is The average bond length of Eu1-N is The coordination configuration of Eu2 is a nine-coordinated single-capped tetragonal antiprism, such as Figure 2 As shown in b, among the nine coordinated atoms, two ligands, mpcd 2－ Provides two N (N1, N9) atoms and two O (O1, O7) atoms, four coordinated ions acetate provides four O atoms (O10, O13, O15, O14), and another coordinated ion O 2- provides one O16 atom. The average bond length of Eu2-O is The average bond length of Eu2-N is The coordination configuration of the central metal Eu3 is also nine-coordinated, but the nine coordinating atoms of Eu3 form a three-hat triangular prism coordination configuration ( Figure 2 c) Among the nine coordinating atoms of Eu3, two ligand ions mpcd 2- Each of the four ligand ions, acetate, provides an O atom, and one O atom comes from the central coordination ion O. 2- The average bond length of Eu3-O is The average bond length of Eu3-N is The coordination configuration of Eu4 atoms is an eight-coordinated bicapped triangular prism configuration ( Figure 2 d) Among the eight coordinating atoms of Eu4, there are two ligand ions mpcd2- They provide one N atom and two O atoms respectively, and the two coordinated acetate groups provide two O atoms (O15 and O13). The average bond length of Eu4-O is The average bond length of Eu4-N is

[0029] Table 1 Partial CShM values ​​of Eu1 and Eu4 in complex 1

[0030]

[0031] Note: CU-8 = cube; SAPR-8 = square anti-prism; TDD-8 = triangular dodecahedron; JGBF-8 = Johnson gyro; JBTP-8 = Johnson bicap triangular prism (J50); BTPR-8 = bicap triangular prism; JSD-8 = twisted wedge (J84).

[0032] Table 2 Partial CShM values ​​of Eu2 and Eu3 in complex 1

[0033]

[0034] Note: CCU-9 = single-capped cube; JCSAPR-9 = tetrahedral anti-prism (J10); CSAPR-9 = single-capped tetragonal anti-prism; JTCTPR-9 = three-capped triangular prism (J51); TCTPR-9 = three-capped triangular prism; JTDIC-9 = three-fold icosahedron (J63).

[0035] Example 3: Determination of magnetic properties

[0036] In the temperature range of 2-300K, a DC field of 1000Oe was applied to the powder sample of complex 1 to conduct a DC temperature-dependent magnetic susceptibility test. The results are as follows: Figure 3 At room temperature, the temperature-dependent magnetic susceptibility of 1 is 14.96 cm 3 K mol -1 , is due to the six Eu III ions. Although Eu III The ground state of the ion ( 7 F0) is anti-magnetic, but 7 F J (J = 1-6) The excited state is magnetic and has low potential energy, especially 7 F1 state (~300cm -1 ), so the ground state has thermal population at room temperature. As the temperature decreases, its magnetic susceptibility also decreases slowly, which is due to Eu III The thermal population of the ion excited state gradually decreases, reaching a minimum of 0 cm at 2 K. 3 K mol -1, which is attributed to the diamagnetic 7 F0 ground state term.

[0037] The curve of the magnetization intensity of complex 1 changing with the magnetic field is as follows: Figure 4 The results show that the magnetization intensity of complex 1 increases in the entire magnetic field region, with the maximum value reaching 0.64Nμ B In addition, the reduced magnetic intensity (M-μ0HT -1 )The curves do not overlap ( Figure 5 ), indicating the existence of an excited state with low potential energy.

[0038] The AC magnetic susceptibility of complex 1 was tested under an AC field of 5Oe. The results showed that complex 1 did not show temperature- and frequency-dependent AC magnetic susceptibility signals under zero field and applied field (3000Oe) conditions. Figure 6 , Figure 7 ).

Claims

1. A multinuclear rare earth complex based on Schiff base ligands, characterized in that: The chemical formula of the multi-nuclear rare earth complex is Na2[Eu6(mpcd)6(μ3:η 2 :η 1 -OAc)6(μ3-O)], where mpcd is protonated H2mpcd; the space group is C2 / c, and the unit cell parameters are: α=90°, β=97.570(2)°, γ=90.000°, The multi-nuclear rare earth complex is a monoclinic crystal system.

2. The method for preparing the multi-nuclear rare earth complex according to claim 1, characterized in that: Eu(CH3CO2)3·4H2O and Schiff base ligand H2mpcd are added to the reaction solvent and stirred, followed by the addition of Na2CO3, continued stirring, filtered, and allowed to stand for evaporation. After two weeks, orange-yellow long strip crystals can be obtained.

3. The preparation method according to claim 2, characterized in that: The reaction solvent is a mixture of a CH3OH solution and a CH3CN solution.

4. The method for preparing the multi-nuclear rare earth complex according to claim 3, characterized in that: The molar ratio of Eu(CH3CO2)3·4H2O, Schiff base ligand H2mpcd and Na2CO3 was 1:1:

1. For every 0.2 mmol of Eu(CH3CO2)3·4H2O, 6 mL of CH3OH and 12 mL of CH3CN were added.

5. Use of the multinuclear rare earth complex described in claim 1 or the multinuclear rare earth complex prepared by the preparation method described in any one of claims 2 to 4 in molecular magnetic materials or molecular memory materials.

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