A mononuclear cobalt complex with slow magnetic relaxation behavior and its preparation method

Abstract

The present invention relates to the technical field of single-molecule magnet preparation, and specifically to a mononuclear cobalt complex with slow magnetic relaxation behavior and a preparation method thereof, and its molecular formula is [CoL(CH3OH)2]·0.5H2O (L = C 24 H 14 N6). During synthesis, the transition metal salt Co(NO3)2·6H2O and the organic ligand L are dissolved in a mixed solution of methanol and acetonitrile, transferred to a 25 mL polytetrafluoroethylene reaction kettle, reacted at 140 °C for 56 hours, and slowly cooled to room temperature to obtain yellow-brown block crystals, namely the single crystal sample of the mononuclear cobalt complex. Under the condition of a 2000 Oe magnetic field, this complex exhibits slow magnetic relaxation behavior.

Description

Technical Field

[0001] The present invention belongs to the technical field of single-molecule magnet preparation, and specifically relates to a mononuclear cobalt complex with slow magnetic relaxation behavior and a preparation method thereof. Under the condition of a 2000 Oe magnetic field, this complex exhibits slow magnetic relaxation behavior and is applied in fields such as information storage devices and quantum computers. Background Art

[0002] Single-molecule magnets exhibit a magnetic hysteresis loop below the blocking temperature and slow relaxation phenomena in a magnetic field. Their magnetism originates from individual isolated molecules, and they are truly molecular magnets with a microscopic nanoscale. They have broad application prospects in fields such as quantum computing technology and ultra-high density storage devices. Different from traditional macroscopic magnets, single-molecule magnets can not only meet the research of the relationship between their magnetism and structure at the molecular level, providing an important model for the theoretical research of the magneto-structural relationship, but also can be designed and modified by means of chemistry, crystal engineering, etc. to conduct function-oriented regulation of their magnetic properties.

[0003] Since the discovery of the first single-molecule magnet, researchers have conducted very in-depth research on single-molecule magnets. Research has shown that a high-spin ground state (S) and significant negative anisotropy (D) are two essential elements that single-molecule magnets must possess, and the combination of the two generates an energy barrier for spin flipping. To achieve practical applications, it is not only necessary to increase the flipping energy barrier (U eff ) and blocking temperature (T B ), but also to ensure the stability of the material structure.

[0004] Currently, researchers have developed two approaches in the design and synthesis of single-molecule magnets with high performance: 1) using transition metal ions as magnetic centers and utilizing their large spin-orbit coupling and anisotropic magnetic exchange interactions; 2) using rare earth ions as magnetic centers and utilizing their orbital magnetic moments and strong spin-orbit coupling interactions.

[0005] Based on this, the present invention provides a mononuclear cobalt complex with slow magnetic relaxation behavior and a preparation method thereof, which have a simple experimental process, are environmentally friendly, and have a high synthesis rate. Summary of the Invention

[0006] The purpose of the present invention is to provide a mononuclear cobalt complex with slow magnetic relaxation behavior and a preparation method thereof, providing a theoretical research basis for the development of new single-molecule magnet materials, breaking through the flipping energy barrier and blocking temperature, and realizing applications in ultra-high density storage materials and spintronic devices.

[0007] To achieve the above purpose, the present invention provides the following technical solutions:

[0008] A mononuclear cobalt complex with slow magnetic relaxation behavior, and the molecular formula of the complex is [CoL(CH3OH)2]·0.5H2O (L = C 24 H 14 N6).

[0009] The mononuclear cobalt complex exhibits slow magnetic relaxation behavior under a magnetic field of 2000 Oe.

[0010] A preparation method of the mononuclear cobalt complex with slow magnetic relaxation behavior as described above, characterized by comprising the following steps:

[0011] 1) Dissolve Co(NO3)2·6H2O and the organic ligand L in a methanol and acetonitrile solution;

[0012] 2) After ultrasonic treatment for 5 min, transfer the above solution to a 25 mL polytetrafluoroethylene reaction kettle;

[0013] 3) React at 140 °C for 56 hours, and slowly cool to room temperature to obtain yellow-brown block crystals, namely the single crystal sample of the mononuclear cobalt complex.

[0014] The molar ratio of the dissolved transition metal salt Co(NO3)2·6H2O to the organic ligand L is 1:1, and the volume ratio of methanol to acetonitrile is 2:1.

[0015] The present invention provides the above mononuclear cobalt complex and its slow magnetic relaxation behavior. It has been found through experiments that the cobalt ions of the complex exhibit obvious magnetic anisotropy, and the real and imaginary parts of its alternating current magnetic susceptibility curves show dependence on both frequency and temperature.

[0016] Compared with traditional magnetic materials, the present invention has the following advantages:

[0017] 1) The molecular structure of the complex is accurately determined by single crystal X-ray diffraction technology in the present invention;

[0018] 2) The target product is synthesized in one step by the solvothermal method in the present invention, and the experimental operation process is simple and environmentally friendly;

[0019] 3) The conversion rate of the synthesis method in the present invention is high, and the yield of the mononuclear cobalt complex is as high as 70%;

[0020] 4) The slow magnetic relaxation behavior of the mononuclear cobalt complex in the present invention provides an experimental basis and theoretical reference for breaking through the switching energy barrier and blocking temperature;

[0021] 5) Compared with traditional magnetic materials, the structure-activity relationship between the structure and slow magnetic relaxation behavior of the mononuclear cobalt complex in the present invention is clearer. Description of the Drawings

[0022] Figure 1Molecular structure of mononuclear cobalt complex;

[0023] Figure 2 X-ray powder diffraction pattern of mononuclear cobalt complex;

[0024] Figure 3 Frequency-dependent real part (a) and imaginary part (b) ac susceptibility curves of mononuclear cobalt complex;

[0025] Figure 4 Temperature-dependent real part (a) and imaginary part (b) ac susceptibility curves of mononuclear cobalt complex;

[0026] Figure 5 Cole-Cole plot of mononuclear cobalt complex;

[0027] Figure 6 Plot of logarithm of magnetic relaxation time (lnτ) versus reciprocal of temperature (T -1 ) for mononuclear cobalt complex. Detailed implementation manners

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0029] The present invention will be described in detail below in conjunction with specific embodiments:

[0030] Example 1: A mononuclear cobalt complex with slow magnetic relaxation behavior, and the molecular formula of the complex is [CoL(CH3OH)2]·0.5H2O (L = C 24 H 14 N6). The mononuclear cobalt complex exhibits slow magnetic relaxation behavior under a magnetic field of 2000 Oe.

[0031] The preparation method of the above mononuclear cobalt complex with slow magnetic relaxation behavior includes the following steps:

[0032] 1) Dissolve 0.102 mmol Co(NO3)2·6H2O (29.7 mg) and 0.105 mmol organic ligand L (29.7 mg) in 10 mL of methanol and 5 mL of acetonitrile solution.

[0033] 2) After ultrasonic treatment for 5 min, transfer the above solution to a 25 mL polytetrafluoroethylene reaction kettle.

[0034] 3) React at 140 °C for 56 hours, and slowly cool to room temperature to obtain yellow-brown block crystals, namely the single crystal sample of the mononuclear cobalt complex.

[0035] Example 2:

[0036] A mononuclear cobalt complex with slow magnetic relaxation behavior, and the molecular formula of the complex is [CoL(CH3OH)2]·0.5H2O (L = C 24 H 14 N6). The mononuclear cobalt complex exhibits slow magnetic relaxation behavior under a magnetic field condition of 2000 Oe.

[0037] The preparation method of the above mononuclear cobalt complex with slow magnetic relaxation behavior includes the following steps:

[0038] 1) Dissolve 0.102 mmol Co(NO3)2·6H2O (29.7 mg) and 0.105 mmol organic ligand L (29.7 mg) in 10 mL of methanol and 5 mL of acetonitrile solution.

[0039] 2) After ultrasonic treatment for 5 min, transfer the above solution to a 25 mL polytetrafluoroethylene reaction kettle.

[0040] 3) React at 140 °C for 56 hours, and slowly cool to room temperature to obtain yellow-brown block crystals, namely the single crystal sample of the mononuclear cobalt complex.

[0041] Select a single crystal sample of the mononuclear cobalt complex with slow magnetic relaxation behavior that is suitable in size, crack-free and of high quality, and use X-ray single crystal diffraction technology to determine its molecular structure.

[0042] 1) The unit cell parameters of the complex are as follows: monoclinic system, C2 / c space group, unit cell parameters b = 11.2330(4), α = 90, β = 94.544(3), γ = 90, Z = 8, R1 = 0.0354, wR2 = 0.1091.

[0043] 2) Analyze the molecular skeleton by the direct method, refine the non-hydrogen atoms anisotropically through the SHELXL program, and optimize it by the full matrix least squares method. Add hydrogen atoms by the geometric hydrogenation method and refine the molecular structure using the riding model.

[0044] 3) Molecular structure analysis reveals that the transition metal cobalt ion coordinates with 4 nitrogen atoms from the organic ligand and oxygen atoms in 2 methanol molecules to form a 6-coordinate octahedral configuration.

[0045] Example 3:

[0046] A mononuclear cobalt complex with slow magnetic relaxation behavior, and the molecular formula of the complex is [CoL(CH3OH)2]·0.5H2O (L = C 24H 14 N6). The mononuclear cobalt complex exhibits slow magnetic relaxation behavior under a magnetic field of 2000 Oe.

[0047] The preparation method of the above-mentioned mononuclear cobalt complex with slow magnetic relaxation behavior includes the following steps:

[0048] 1) Dissolve 0.102 mmol Co(NO3)2·6H2O (29.7 mg) and 0.105 mmol organic ligand L (29.7 mg) in 10 mL of methanol and 5 mL of acetonitrile solution.

[0049] 2) After ultrasonic treatment for 5 min, transfer the above solution to a 25 mL polytetrafluoroethylene reaction kettle.

[0050] 3) React at 140 °C for 56 hours, and slowly cool to room temperature to obtain yellow-brown block crystals, namely the single crystal sample of the mononuclear cobalt complex.

[0051] Collect the single crystal sample, and after testing its purity by X-ray powder diffraction, perform direct current and alternating current variable temperature magnetic susceptibility tests. Under an external magnetic field of 2000 Oe, the mononuclear cobalt complex exhibits slow magnetic relaxation behavior.

[0052] Figure 1 It is the molecular structure of the complex prepared in Example 1. From Figure 1 It can be seen that: the complex prepared in Example 1 is of mononuclear structure, and the transition metal cobalt ion coordinates with 4 nitrogen atoms from the organic ligand and the oxygen atoms in 2 methanol molecules to form a 6-coordinate octahedral configuration.

[0053] Figure 2 It is the X-ray powder diffraction pattern of the complex prepared in Example 1. From Figure 2 It can be seen that: at room temperature, the peak positions of the X-ray powder diffraction experimental pattern and the theoretical pattern of the complex are the same, and the different peak intensities are due to the different diffractions of the powder sample on different crystal planes, proving that the prepared sample is pure.

[0054] Figure 3 It is the frequency-dependent real part (a) and imaginary part (b) alternating current magnetic susceptibility curve of the complex prepared in Example 1. From Figure 3 It can be seen that: in the temperature range of 2 K to 15 K, the real part and imaginary part alternating current magnetic susceptibility signals of the complex show obvious dependence on frequency.

[0055] Figure 4 It is the temperature-dependent real part (a) and imaginary part (b) alternating current magnetic susceptibility curve of the complex prepared in Example 1. From Figure 4 It can be seen that: the real part and imaginary part alternating current magnetic susceptibility signals of the complex show obvious dependence on temperature.

[0056] Figure 5 Cole-Cole plot of the complex prepared in Example 1. It can be seen from Figure 5 that the Cole-Cole curve of the complex is semicircular. The data is fitted with the Debye model, and the value range of the relaxation time distribution factor α is between 7.46×10 -5 -0.26.

[0057] Figure 6 Plot of the logarithm (lnτ) of the magnetic relaxation time of the complex prepared in Example 1 against the reciprocal of the temperature (T -1 ). It can be seen from Figure 6 that lnτ has an excellent linear correlation in the higher temperature region. According to the Arrhenius (τ -1 = τ0 -1 exp(-U eff / kT)) equation, U eff is 25.0 cm -1 , and τ0 is 1.27×10 -6 s.

[0058] The present invention uses a solvothermal method to synthesize a mononuclear cobalt complex with slow magnetic relaxation behavior in one step. Under the chelation of a planar tetradentate ligand, the transition metal cobalt ion has strong magnetic anisotropy and exhibits slow magnetic relaxation behavior, providing an important model for the theoretical study of the magnetic structure relationship and laying a foundation for breaking through the flipping energy barrier and blocking temperature and realizing its practical application.

Claims

1. A mononuclear cobalt complex with slow magnetic relaxation behavior, characterized in that: The molecular formula of the complex is [CoL(CH3OH)2]·0.5H2O, where L = C 24 H 14 N6.

2. The mononuclear cobalt complex with slow magnetic relaxation behavior according to claim 1, characterized in that: The mononuclear cobalt complex exhibits slow magnetic relaxation behavior under a magnetic field of 2000 Oe.

3. A preparation method of the mononuclear cobalt complex with slow magnetic relaxation behavior as claimed in claim 1, characterized in that, It includes the following steps: 1) Dissolve Co(NO3)2·6H2O and organic ligand L in a methanol and acetonitrile solution; 2) After ultrasonic treatment for 5 min, transfer the above solution to a 25 mL polytetrafluoroethylene reaction kettle; 3) React at 140 °C for 56 hours, and slowly cool to room temperature to obtain yellow-brown block crystals, namely the single crystal sample of the mononuclear cobalt complex.

4. The preparation method of the mononuclear cobalt complex with slow magnetic relaxation behavior according to claim 3, characterized in that: The molar ratio of the dissolved Co(NO3)2·6H2O and organic ligand L is 1:1, and the volume ratio of methanol and acetonitrile is 2:1.

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