A mononuclear metal complex and its preparation method and application

Abstract

The present invention discloses a mononuclear metal complex and a preparation method and use thereof. The structure of the mononuclear metal complex is: [M(A)(X) 2 ]. Wherein M is a metal element; A is a dipyridine ligand; and X is a halogen ion. The mononuclear metal complex provided by the present invention exhibits excellent thermal stability in air or an inert atmosphere, and has good stability in a solution while also exhibiting excellent electrochromic properties. More importantly, the mononuclear metal complex provided by the present invention is applied to a two-electrode system electrochromic device, and a reversible, high-contrast electrochromic effect can be achieved under a relatively low input voltage condition of 1.1V, and thus has potential application value in the fields of electrochromic glass and the like.

Description

Technical Field

[0001] The invention belongs to the field of complex functional materials and relates to a mononuclear metal complex and a preparation method and application thereof. Background Art

[0002] Electrochromism refers to a reversible process in which, under the drive of a specific external electric field, a substance undergoes a significant change in its optical properties such as reflection, transmission, and absorption of light, thereby causing a significant change in the color and transparency of the substance itself. The electrochromic process is accompanied by an electrochemically induced redox reaction, and the substance will be in different redox states under different voltages. Electrochromic materials have been widely used in many fields such as low-energy displays, goggles, anti-glare rearview mirrors, smart energy-saving glass, and military camouflage.

[0003] Scientists have studied and developed inorganic electrochromic materials such as transition metal oxides and Prussian blue systems, and organic electrochromic materials including viologen and conductive polymers. Under different voltages, the above materials can undergo easily controllable reversible transformations between different colors by adjusting the redox state. However, the development of electrochromic materials still faces many limitations and challenges (including limited types of color changes, insufficient stability, insufficient sensitivity of color change, insufficient chromaticity contrast before and after color change, and the number of color change cycles and service life need to be improved). Therefore, it is necessary to develop an electrochromic material with high stability and excellent electrochromic properties. Summary of the invention

[0004] In order to improve the above technical problems, the present invention provides a mononuclear metal complex and a preparation method and application thereof. The complex of the present invention has excellent electrochromic properties.

[0005] The purpose of the present invention is achieved by the following methods:

[0006] The present invention provides a mononuclear metal complex, the general structural formula of which is:

[0007] [M(A)(X)2];

[0008] in,

[0009] M is at least one metal element selected from manganese, cobalt, nickel, zinc, copper, iron, and ruthenium;

[0010] X is selected from F, Cl, Br or I, preferably Cl;

[0011] A is a bipyridine ligand, and its molecular structure is:

[0012]

[0013] R is independently alkyl or aryl;

[0014] According to an embodiment of the present invention, the structure of the mononuclear metal complex is shown in the following formula (1):

[0015]

[0016] in:

[0017] M is at least one metal element selected from manganese, cobalt, nickel, zinc, copper, iron, and ruthenium;

[0018] R is independently an alkyl group or an aryl group.

[0019] In the present invention, the alkyl group refers to a straight chain or branched chain alkyl group having a carbon number of 1 to 20. For example, the alkyl group includes methyl, ethyl, n-butyl, tert-butyl, tert-octyl, n-tridecyl, etc. or isomers thereof.

[0020] The aryl group refers to a monocyclic or polycyclic aromatic group having 6 to 20 carbon atoms, for example, phenyl, naphthyl, etc.

[0021] According to an embodiment of the present invention, the R is independently methyl, n-butyl, n-tridecyl, or phenyl.

[0022] According to an exemplary embodiment of the present invention, the complex may be:

[0023]

[0024] Compound 1: R in the bipyridine ligand A is methyl; M is Mn; X is Cl;

[0025] Compound 2: R in the bipyridine ligand A is methyl; M is Co; X is Cl;

[0026] Compound 3: R in the bipyridine ligand A is methyl; M is Ni; X is Cl;

[0027] Compound 4: R in the bipyridine ligand A is methyl; M is Zn; X is Cl;

[0028] Compound 5: R in the bipyridine ligand A is methyl; M is Mn; X is Br;

[0029] Compound 6: R in the bipyridine ligand A is phenyl; M is Mn; X is Cl;

[0030] Compound 7: R in the bipyridine ligand A is n-butyl; M is Mn; X is Cl;

[0031] Compound 8: R in the dipyridine ligand A is n-tridecyl; M is Mn; and X is Cl.

[0032] The present invention provides a method for preparing the mononuclear metal complex, comprising the following steps: reacting MX2 and A in an organic solvent to obtain a mononuclear metal complex, wherein: X, A, and M have the definitions and selections as described above.

[0033] According to an embodiment of the present invention, the organic solvent is preferably at least one of nitrile, alcohol and halogenated hydrocarbon. For example, the nitrile may be acetonitrile; the alcohol may be methanol.

[0034] According to an embodiment of the present invention, the reaction molar ratio of MX2 to A is (0.9-1.1):(1.0-2.0), exemplified by 0.9:1, 1:1, 1.1:1, 0.9:2, 1.1:2.

[0035] According to an embodiment of the present invention, the reaction temperature is 25-100°C, preferably 80-85°C, exemplified by 25°C, 40°C, 60°C, 80°C, 82°C, 85°C, 100°C; the reaction time is 2-6h, exemplified by 2h, 4h, 6h.

[0036] According to an embodiment of the present invention, the preparation method further comprises purifying the obtained mononuclear metal complex, for example, by purifying the obtained mononuclear metal complex by recrystallization.

[0037] The present invention also provides a mononuclear metal complex crystal, the general structural formula of the crystal is:

[0038] [M(A)(X)2];

[0039] in,

[0040] M is at least one metal element selected from manganese, cobalt, nickel, zinc, copper, iron, and ruthenium;

[0041] X is selected from F, Cl, Br or I, preferably Cl;

[0042] A is a bipyridine ligand, and its molecular structure is:

[0043]

[0044] R is independently an alkyl group or an aryl group.

[0045] According to an embodiment of the present invention, the crystal belongs to the orthorhombic system, and its structural schematic diagram is as follows: Figure 1 As shown, the space group is P212121, and the unit cell parameters are α=β=γ=90°, z=4.

[0046] According to an embodiment of the present invention, the crystal has substantially Figure 2Thermogravimetric curve shown.

[0047] According to an embodiment of the present invention, the structure of the crystal is shown in the following formula (1):

[0048]

[0049] in:

[0050] M is at least one metal element selected from manganese, cobalt, nickel, zinc, copper, iron, and ruthenium;

[0051] R is independently an alkyl group or an aryl group.

[0052] In the present invention, the alkyl group refers to a straight chain or branched chain alkyl group having a carbon number of 1 to 20. For example, the alkyl group includes methyl, ethyl, n-butyl, tert-butyl, tert-octyl, n-tridecyl, etc. or isomers thereof.

[0053] The aryl group refers to a monocyclic or polycyclic aromatic group having 6 to 20 carbon atoms, for example, phenyl, naphthyl, etc.

[0054] According to an embodiment of the present invention, the R is preferably independently methyl, n-butyl, n-tridecyl, or phenyl.

[0055] According to an exemplary embodiment of the present invention, the crystal may be:

[0056]

[0057] The present invention provides a method for preparing the above crystal, comprising reacting MX2 and A in an organic solvent for crystallization, and cooling after the crystallization to obtain a crystal, wherein: X, A, and M have the definitions and selections as described above.

[0058] According to an embodiment of the present invention, the organic solvent is preferably at least one of nitrile, alcohol and halogenated hydrocarbon. For example, the nitrile may be acetonitrile; the alcohol may be methanol.

[0059] According to an embodiment of the present invention, the reaction molar ratio of MX2 to A is (0.9-1.1):(1.0-2.0), exemplified by 0.9:1, 1:1, 1.1:1, 0.9:2, 1.1:2.

[0060] According to an embodiment of the present invention, the temperature of the crystallization reaction is 25-100°C, preferably 80-85°C, and exemplary are 25°C, 40°C, 60°C, 80°C, 82°C, 85°C, and 100°C; the time of the crystallization reaction is 2-6h, and exemplary are 2h, 4h, and 6h.

[0061] The present invention also provides the use of the above mononuclear metal complex and / or the mononuclear metal complex crystal in an electrochromic device. Preferably, the mononuclear metal complex is used as an electrochromic material in an electrochromic device.

[0062] The invention also provides an electrochromic device, which contains the mononuclear metal complex.

[0063] According to the embodiment of the present invention, the structure of the electrochromic device can be various structures known in the prior art.

[0064] According to an embodiment of the present invention, the electrochromic device also includes a working electrode and a counter electrode, which are arranged opposite to each other, and a cavity is formed around the working electrode and the counter electrode by bonding with a colloid (such as butyl rubber), and the cavity is filled with the above-mentioned mononuclear metal complex and / or the mononuclear metal complex crystals.

[0065] According to an embodiment of the present invention, the working electrode and the counter electrode are preferably transparent conductive glass, for example, ITO conductive glass or FTO conductive glass, preferably ITO conductive glass.

[0066] According to an embodiment of the present invention, the cavity is also filled with an electrolyte. Preferably, the electrolyte is at least one of tetra-n-butylammonium perchlorate, tetra-n-butylammonium hexafluorophosphate, potassium hexafluorophosphate and lithium hexafluorophosphate, preferably tetra-n-butylammonium perchlorate.

[0067] The present invention also provides a method for preparing an electrochromic device, comprising using transparent conductive glass as a working electrode and a counter electrode, and using a colloid (such as butyl glue) to surround a 2×2 cm 2 The region is used to fill a mixed solution of electrolyte and electrochromic material while separating the working electrode and the counter electrode; wherein the electrochromic material includes the above-mentioned mononuclear metal complex and / or the mononuclear metal complex crystal.

[0068] According to an embodiment of the present invention, the organic solvent used to prepare the mixed solution of electrolyte and electrochromic material is preferably nitrile, amide solvent or carbonate, more preferably N,N'-dimethylformamide (DMF).

[0069] The present invention tests the performance of an electrochromic device assembled with the mononuclear metal complex and / or the mononuclear metal complex crystal as an electrochromic material: when a voltage of 0.8 to 1.3 V is applied between the two electrodes of the device, the mononuclear metal complex undergoes single-electron oxidation to transform into a positive monovalent cation complex, and at the same time the device transforms from a transparent colorless (or light-colored) state to a dark blue colored state; when the applied voltage is 0 V or the external circuit is open, the positive monovalent cation complex in the dark blue state undergoes single-electron reduction to restore to the original neutral complex, and the device color fades from dark blue to a colorless (or light-colored) state. The above two processes are cyclically reversible, thereby realizing the controllable conversion of the device between the "transparent light-colored state" and the "dark blue colored state".

[0070] Compared with the prior art, the present invention has the following advantages:

[0071] Metal complexes, as a type of inorganic-organic hybrid compounds formed by coordination bonds between metals and ligands, have the advantages of inorganic stability, electrochemical reversibility and memory effect, as well as the advantages of colorful color changes of organics, sensitive electrochromic response, good film-forming properties and low driving voltage. As a new type of electrochromic material, it is expected to overcome the inherent disadvantages of traditional inorganic and organic electrochromic materials, and provide a unique development path for the large-scale and low-cost application of electrochromic technology. In view of this, the present invention proposes a mononuclear metal complex electrochromic material, which has good photothermal stability and excellent electrochromic performance, and has broad application prospects in the fields of electrochromic glass. Specifically:

[0072] 1) The mononuclear metal complex of the present invention has excellent stability, and the decomposition temperature in air or nitrogen is as high as 290°C or above ( Figure 2 ).

[0073] 2) The mononuclear metal complex of the present invention has obvious electrochromic properties in solution state, and can realize reversible and controllable conversion between "transparent light-colored state" and "dark blue colored state", so it has great application prospects in the fields of color-changing glass and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 Schematic diagram of the crystal structure of the mononuclear metal complex prepared in Example 1.

[0075] Figure 2 This is the thermogravimetric curve of the mononuclear metal complex prepared in Example 1.

[0076] Figure 3 The absorption spectra of the electrochromic device prepared in Example 9 under different voltage conditions are shown. DETAILED DESCRIPTION

[0077] The preparation method of the present invention will be described in further detail below in conjunction with specific examples. It should be understood that the following examples are only exemplary descriptions and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies realized based on the above content of the present invention are included in the scope of protection of the present invention.

[0078] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the reagents, materials, etc. used in the following examples, unless otherwise specified, can be obtained from commercial channels.

[0079] Example 1: Preparation of mononuclear metal complex Mn[(CH3)2NPhN(CH2py)2]Cl2(1)

[0080] Under nitrogen atmosphere, MnCl2 (272.1 mg, 2.16 mmol) and ligand (CH3)2NPhN(CH2py)2 (643.9 mg, 2.02 mmol) were added to a mixed solution of 30 ml acetonitrile and 5 ml methanol. The reaction mixture was heated to 82°C and cooled after 4 hours of reaction. The reaction mixture was placed in a fume hood with an open lid. Through the natural evaporation of the solvent, pale yellow crystals were obtained with a yield of 73%.

[0081] Elemental analysis (C 20 H 22 Cl2MnN4) calculated value: N, 12.61; C, 54.07; H, 4.99; measured value: N, 12.69; C, 53.38; H, 5.00; high resolution mass spectrum m / z: 408.0897 [M-Cl] + .

[0082] The product was characterized by X-ray single crystal diffraction, and the specific results are as follows:

[0083] Table 1. Crystallographic parameters of the mononuclear metal complex Mn[(CH3)2NPhN(CH2py)2]Cl2(1)

[0084]

[0085] The above data show that the target product mononuclear metal complex Mn[(CH3)2NPhN(CH2py)2]Cl2(1) was obtained in this example. The crystal structure diagram is shown in Figure 1 shown.

[0086] Figure 2 The thermogravimetric curve of the mononuclear metal complex prepared in Example 1 is shown in FIG. Figure 2 It can be seen that the mononuclear metal complex has excellent thermal stability, and its decomposition temperature is about 290°C in an air or nitrogen atmosphere.

[0087] Example 2: Preparation of mononuclear metal complex Co[(CH3)2NPhN(CH2py)2]Cl2(2)

[0088] Under nitrogen atmosphere, CoCl2 (83.0 mg, 0.64 mmol) and ligand (CH3)2NPhN(CH2py)2 (216.5 mg, 0.68 mmol) were added to 10 ml of acetonitrile, and the reaction mixture was heated to 82°C and allowed to react for 4 hours before cooling down. The reaction mixture was left open in a fume hood, and blue-purple crystals were obtained through natural evaporation of the solvent with a yield of 68%.

[0089] Elemental analysis (C 20 H 22 Cl2CoN4) calculated value: N, 12.50; C, 53.59; H, 4.95; measured value: N, 12.56; C, 53.02; H, 5.01; high resolution mass spectrum m / z: 412.0854 [M-Cl] + .

[0090] The product was characterized by X-ray single crystal diffraction, and the specific results are as follows:

[0091] Table 1. Crystallographic parameters of the mononuclear metal complex Co[(CH3)2NPhN(CH2py)2]Cl2(2)

[0092]

[0093] The above data show that the target product, the mononuclear metal complex Co[(CH3)2NPhN(CH2py)2]Cl2(2), was obtained in this example.

[0094] Example 3: Preparation of mononuclear metal complex Ni[(CH3)2NPhN(CH2py)2]Cl2(3)

[0095] Under nitrogen atmosphere, NiCl2·6H2O (227.1 mg, 0.96 mmol) and ligand (CH3)2NPhN(CH2py)2 (302.6 mg, 0.95 mmol) were added to 10 ml of acetonitrile, and the reaction mixture was heated to 82°C, reacted for 4 hours, and then cooled. The reaction mixture was placed in a fume hood with an open mouth, and the green crystalline product was obtained through natural evaporation of the solvent with a yield of 75%.

[0096] Elemental analysis (C 20 H 22Cl2NiN4) calculated value: N, 12.51; C, 53.62; H, 4.95; measured value: N, 12.67; C, 54.04; H, 4.90; high resolution mass spectrum m / z: 411.0879 [M-Cl] + .

[0097] The product was characterized by X-ray single crystal diffraction, and the specific results are as follows:

[0098] Table 1. Crystallographic parameters of mononuclear metal complex Ni[(CH3)2NPhN(CH2py)2]Cl2(3)

[0099]

[0100] The above data show that the target product, mononuclear metal complex Ni[(CH3)2NPhN(CH2py)2]Cl2(3), was obtained in this example.

[0101] Example 4: Preparation of mononuclear metal complex Zn[(CH3)2NPhN(CH2py)2]Cl2(4)

[0102] Under nitrogen atmosphere, ZnCl2 (292.2 mg, 2.14 mmol) and ligand (CH3)2NPhN(CH2py)2 (682.6 mg, 2.14 mmol) were added to 10 ml of acetonitrile, and the reaction mixture was heated to 82°C, reacted for 4 hours, and then cooled. The reaction mixture was placed in a fume hood with an open lid, and the solvent evaporated naturally to obtain a light yellow crystalline product with a yield of 78%.

[0103] Elemental analysis (C 20 H 22 Cl2ZnN4) calculated value: N, 12.32; C, 52.83; H, 4.88; measured value: N, 12.49; C, 53.18; H, 4.92; high resolution mass spectrum m / z: 417.0798 [M-Cl] + .

[0104] The product was characterized by X-ray single crystal diffraction, and the specific results are as follows:

[0105] Table 1. Crystallographic parameters of mononuclear metal complex Zn[(CH3)2NPhN(CH2py)2]Cl2(4)

[0106]

[0107] The above data show that the target product, mononuclear metal complex Zn[(CH3)2NPhN(CH2py)2]Cl2(4), was obtained in this example.

[0108] Example 5: Preparation of mononuclear metal complex Mn[(CH3)2NPhN(CH2py)2]Br2(5)

[0109] Under nitrogen atmosphere, MnBr2 (266.3 mg, 1.24 mmol) and ligand (CH3)2NPhN(CH2py)2 (382.0 mg, 1.20 mmol) were added to 20 ml of acetonitrile, and the reaction mixture was heated to 82°C and allowed to react for 4 hours before cooling down. The reaction mixture was left open in a fume hood, and light yellow crystals were obtained through natural evaporation of the solvent, with a yield of 81%.

[0110] Elemental analysis (C 20 H 22 Br2MnN4) calculated value: N, 10.51; C, 45.05; H, 4.16; measured value: N, 10.60; C, 45.31; H, 4.19; high resolution mass spectrum m / z: 532.0352 [M+H] + .

[0111] The product was characterized by X-ray single crystal diffraction, and the specific results are as follows:

[0112] Table 1. Crystallographic parameters of the mononuclear metal complex Mn[(CH3)2NPhN(CH2py)2]Br2(5)

[0113]

[0114]

[0115] The above data show that the target product, mononuclear metal complex Mn[(CH3)2NPhN(CH2py)2]Br2(5), was obtained in this example.

[0116] Example 6: Preparation of mononuclear metal complex Mn[(Ph)2NPhN(CH2py)2]Cl2(6)

[0117] Under nitrogen atmosphere, MnCl2 (157.2 mg, 1.25 mmol) and ligand (Ph)2NPhN(CH2py)2 (558.7 mg, 1.26 mmol) were added to 20 ml of acetonitrile, and the reaction mixture was heated to 82°C and allowed to react for 4 hours before cooling down. The reaction mixture was left open in a fume hood, and light yellow crystals were obtained through natural evaporation of the solvent, with a yield of 73%.

[0118] Elemental analysis (C 30 H 26 Cl2MnN4) calculated values: N, 9.86; C, 55.07; H, 5.14; measured values: N, 9.95; C, 55.31; H, 5.10.

[0119] The product was characterized by X-ray single crystal diffraction, and the specific results are as follows:

[0120] Table 1. Crystallographic parameters of the mononuclear metal complex Mn[(Ph)2NPhN(CH2py)2]Cl2(6)

[0121]

[0122] The above data show that the target product, mononuclear metal complex Mn[(Ph)2NPhN(CH2py)2]Cl2(6), was obtained in this example.

[0123] Example 7: Preparation of mononuclear metal complex Mn[(C4H9)2NPhN(CH2py)2]Cl2 (7)

[0124] Under nitrogen atmosphere, MnCl2 (145.6 mg, 1.16 mmol) and ligand (C4H9)2NPhN(CH2py)2 (470.3 mg, 1.17 mmol) were added to 20 ml of acetonitrile, and the reaction mixture was heated to 82°C, reacted for 4 hours, and then cooled. The reaction mixture was placed in a fume hood with an open mouth, and light yellow crystals were obtained through natural evaporation of the solvent, with a yield of 73%.

[0125] Elemental analysis (C 26 H 34 Cl2MnN4) calculated values: N, 10.60; C, 59.10; H, 6.49; measured values: N, 11.02; C, 58.53; H, 6.44.

[0126] The product was characterized by X-ray single crystal diffraction, and the specific results are as follows:

[0127] Table 1. Crystallographic parameters of the mononuclear metal complex Mn[(C4H9)2NPhN(CH2py)2]Cl2(7)

[0128]

[0129] The above data show that the target product, mononuclear metal complex Mn[(C4H9)2NPhN(CH2py)2]Cl2(7), was obtained in this example.

[0130] Example 8: Mononuclear metal complex Mn[(C 13 H 27 Preparation of )2NPhN(CH2py)2]Cl2(8)

[0131] Under nitrogen atmosphere, MnCl2 (104.5 mg, 0.83 mmol) and ligand (C 13H 27 )2NPhN(CH2py)2 (560.6 mg, 0.86 mmol) was added to 20 ml of acetonitrile, and the reaction mixture was heated to 82°C and allowed to react for 4 hours before cooling down. The reaction mixture was left open in a fume hood, and light yellow crystals were obtained through natural evaporation of the solvent, with a yield of 73%.

[0132] Elemental analysis (C 44 H 70 Cl2MnN4) calculated values: N, 7.17; C, 67.67; H, 9.04; measured values: N, 7.06; C, 67.92; H, 9.08.

[0133] The above data show that the target product mononuclear metal complex Mn[(C 13 H 27 )2NPhN(CH2py)2]Cl2(8).

[0134] Example 9: Assembly of electrochromic device

[0135] The electrochromic properties of the mononuclear metal complexes Mn[(CH3)2NPhN(CH2py)2]Cl2(1) and Zn[(CH3)2NPhN(CH2py)2]Cl2(4) prepared in Examples 1 and 4 were investigated. A 2×2 cm 2 The area is then covered with another piece of ITO conductive glass, and 0.5 ml of N,N'-dimethylformamide solution dissolved with tetra-n-butylammonium perchlorate electrolyte (1M) and the mononuclear metal complex Mn[(CH3)2NPhN(CH2py)2]Cl2(1)(25 mg / mL) prepared in Example 1 or the mononuclear metal complex Zn[(CH3)2NPhN(CH2py)2]Cl2(4)(25 mg / mL) prepared in Example 4 is injected into the gap area in the middle to obtain a two-electrode electrochromic device.

[0136] The performance test of the electrochromic device prepared above was carried out on Shanghai Chenhua CHI660D electrochemical instrument in constant potential mode in room temperature air environment. The absorption spectra at different voltages are shown in Figure 2. Figure 3 As shown. The black dotted line is the spectrum in the faded state. As the voltage applied between the two electrodes of the electrochromic device increases, two new strong absorption peaks appear at 569nm and 617nm in the electrochromic solution. This absorption band is attributed to the LMCT band of the mononuclear metal complex undergoing single electron oxidation to a positive monovalent cation complex. The LMCT band reaches its maximum value when the applied voltage is 1.1V ( Figure 3), at which time the electrochromic device is in a dark blue coloring state. This coloring state can be restored to the initial transparent light coloring state when the applied voltage drops to 0V or the voltage is disconnected, thereby realizing a cyclic reversible process between the "transparent light coloring state" and the "dark blue coloring state".

[0137] The above data indicate that the mononuclear metal complex prepared by the present invention can achieve a reversible electrochromic effect at a relatively low voltage (<2.5 V), and therefore has potential application value in the fields of electrochromic glass and the like.

[0138] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A mononuclear metal complex, characterized in that The structure of the mononuclear complex is shown in the following formula (1): in: M is at least one metal element selected from manganese, cobalt, nickel, zinc, copper, iron, and ruthenium; R is independently methyl, n-butyl, n-tridecyl, or phenyl.

2. The mononuclear metal complex according to claim 1, characterized in that The complex is: Compound 1: R in the bipyridine ligand A is methyl; M is Mn; X is Cl; Compound 2: R in the bipyridine ligand A is methyl; M is Co; X is Cl; Compound 3: R in the bipyridine ligand A is methyl; M is Ni; X is Cl; Compound 4: R in the bipyridine ligand A is methyl; M is Zn; X is Cl; Compound 6: R in the bipyridine ligand A is phenyl; M is Mn; X is Cl; Compound 7: R in the bipyridine ligand A is n-butyl; M is Mn; X is Cl; Compound 8: R in the dipyridine ligand A is n-tridecyl; M is Mn; and X is Cl.

3. A method for preparing the mononuclear metal complex according to any one of claims 1 to 2, characterized in that: The preparation method comprises the following steps: reacting MX2 and A in an organic solvent to obtain a mononuclear metal complex, wherein: X is selected from Cl; A is a bipyridine ligand, and its molecular structure is: M is at least one metal element selected from manganese, cobalt, nickel, zinc, copper, iron, and ruthenium.

4. The method for preparing a mononuclear metal complex according to claim 3, characterized in that: The organic solvent is at least one of nitrile, alcohol and halogenated hydrocarbon; The molar ratio of MX2 to A is (0.9-1.1):(1.0-2.0).

5. The method for preparing a mononuclear metal complex according to claim 3, characterized in that: The reaction temperature is 80-85° C.; the reaction time is 2-6 hours.

6. A mononuclear metal complex crystal, characterized in that: The structure of the crystal is shown in the following formula (1): in: M is at least one metal element selected from manganese, cobalt, nickel, zinc, copper, iron, and ruthenium; R is independently methyl, n-butyl, n-tridecyl, or phenyl.

7. The crystal according to claim 6, characterized in that The crystal is:

8. The crystal according to claim 7, characterized in that The crystalline compound 1 belongs to the orthorhombic system, the space group is P212121, and the unit cell parameters are α=β=γ=90°, z=4.

9. The method for preparing the crystal according to any one of claims 6 to 8, characterized in that: The preparation method comprises the following steps: MX2 and A are reacted and crystallized in an organic solvent, and after the crystallization is completed, the temperature is lowered to obtain a crystal, wherein: X is selected from Cl; A is a bipyridine ligand, and its molecular structure is: M is at least one metal element selected from manganese, cobalt, nickel, zinc, copper, iron, and ruthenium.

10. The preparation method according to claim 9, characterized in that: The organic solvent is at least one of nitrile, alcohol and halogenated hydrocarbon; The molar ratio of MX2 to A is (0.9-1.1):(1.0-2.0); The temperature of the crystallization reaction is 80-85° C.; the time of the crystallization reaction is 2-6 hours.

11. Use of the mononuclear metal complex according to any one of claims 1 to 2 and / or the mononuclear metal complex crystal according to any one of claims 6 to 8 in an electrochromic device.

12. An electrochromic device, characterized in that: It contains the mononuclear metal complex according to any one of claims 1 to 2 and / or the mononuclear metal complex crystal according to any one of claims 6 to 8.

13. The electrochromic device according to claim 12, characterized in that: The electrochromic device also includes a working electrode and a counter electrode, which are arranged opposite to each other. A cavity is formed around the working electrode and the counter electrode by bonding with butyl rubber, and the cavity is filled with the mononuclear metal complex described in any one of claims 1-2 and / or the mononuclear metal complex crystal described in any one of claims 6-8.

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