Halogenated schiff base Cu(ii) complex and preparation method and application thereof

Abstract

The application discloses a kind of halogenated schiff base Cu (II) complex and its preparation method and its application.The halogenated schiff base Cu (II) complex is Cu-Cl-Salmphen or Cu-Br-Salmphen;The energy gap value of the halogenated schiff base Cu (II) complex is 3.06eV and 3.08eV respectively, and the conductance value is 0.045S and 0.079S respectively.It is applied as the application of molecular wire material with low resistance, good conductivity and high electron transmission rate.Two kinds of novel halogenated coplanar schiff base Cu (II) complex are synthesized in the application, the inherent energy level of schiff base molecule is fine-tuned by introducing different halogen atoms, and the coordination mode and packing structure of the complex remain unchanged.Systematic research shows that when halogen atoms are used as substituents, the conjugated area of the molecule is effectively expanded, the charge carrier mobility is affected, the intermolecular interaction and electron transport pathway are increased, and the linear change of energy level can be realized.At the same time, the electrochemical behavior related to energy level change, such as diffusion coefficient and resistance, presents a consistent trend with the change of energy gap.

Description

A Halogenated Schiff Base Cu(II) Complex, Its Preparation Method and Application Technical Field

[0001] This invention belongs to the field of materials synthesis technology, specifically relating to a halo-Schiff base Cu(II) complex, its preparation method, and its application. Background Technology

[0002] The band gap, or band difference, defines the energy difference between the top of the valence band and the bottom of the conduction band in a solid material, and it largely determines many of the material's physical and chemical properties. In materials science, band gap tuning is not only a key focus of theoretical research but also crucial for achieving transformative technological advancements through the manipulation of material properties. Mastering band gap tuning strategies lays the foundation for several key areas, including efficient catalysts, novel semiconductors / superconductors, high-performance photovoltaic materials, advanced electronic devices, and optical instruments. Therefore, exploring reasonable methods for adjusting energy levels has gradually become a core issue in materials science.

[0003] To date, researchers in coordination chemistry have proposed various strategies for regulating the band gap of coordination compounds, including changing the central metal, ligand alkylation modification, adjustment of coordination geometry, and size effects and interface modulation. However, most of these methods are based on significant changes in the structure and composition of the starting materials, thus all suffer from problems such as large differences in reaction conditions, increased costs, and decreased product purity. More importantly, strategies such as changing the central metal atom or ligand alkylation modification can lead to fundamental changes in the coordination mode and structure of the coordination compound, making energy level modulation a difficult-to-predict process. Therefore, exploring effective and rational methods to regulate the energy level structure of coordination compounds and achieve linear regulation of their energy levels remains a significant challenge. Summary of the Invention

[0004] The first objective of this invention is to provide a halo-Schiff base Cu(II) complex, and the second objective of this invention is to provide a method for preparing the halo-Schiff base Cu(II) complex and its application.

[0005] The first objective of this invention is achieved as follows: the halo-Schiff base Cu(II) complex is Cu-Cl-Salmphen (Cl-Salmphen = N,N'-bis(3-chlorosalicylaldehyde)-m-xylene) or Cu-Br-Salmphen (Br-Salmphen = N,N'-bis(3-bromosalicylaldehyde)-m-xylene); the band gap values ​​of the halo-Schiff base Cu(II) complex are 3.06 eV and 3.08 eV, respectively, and the electrical conductivities are 0.045 S and 0.079 S, respectively.

[0006] The second objective of this invention is achieved by the method for preparing the halo-Schiff base Cu(II) complex, specifically through the following steps:

[0007] 1) Add halosalicylaldehyde and m-phenylenediamine to a methanol solution and stir for 5-6 hours;

[0008] 2) Add CuCl2·2H2O, stir for 2-3 hours, and then filter to obtain the filtrate;

[0009] 3) The filtrate was slowly evaporated at room temperature to obtain regular black crystals, which were washed repeatedly with a polar solvent and filtered. Finally, the crystals were allowed to evaporate and dry naturally to obtain the target complex.

[0010] The halogenated salicylaldehyde is 3-chlorosalicylaldehyde or 3-bromosalicylaldehyde.

[0011] The aforementioned halogenated Schiff base Cu(II) complex can be used as a molecular wire material with low resistance, good conductivity, and high electron transport rate.

[0012] The beneficial effects of this invention are as follows:

[0013] 1. This invention provides a halogenated coplanar Schiff base Cu(II) complex. This invention fine-tunes the intrinsic energy level of the Schiff base molecule by introducing different halogen atoms. The coordination mode and packing structure of the complex remain unchanged, and the molecular configuration is completely identical. It can be used as a research model for finely controlling the molecular energy level.

[0014] 2. The conductivity of non-halogenated Schiff base Cu(II) complexes is 0.032 S, while the conductivity of the halogen-regulated Schiff base Cu(II) complexes of this invention gradually increases. The conductivity values ​​of Cu-Cl-Salmphen and Cu-Br-Salmphen are 0.045 S and 0.079 S, respectively. This indicates that the introduction of halogen atoms can effectively expand the conjugated area of ​​the molecule, increase intermolecular interactions, and affect the mobility of charge carriers and electron transport pathways, thus achieving linear changes in energy levels. Simultaneously, the electrochemical behaviors related to energy level changes, such as diffusion coefficient and resistance, show a consistent trend with the change in band gap.

[0015] 3. This invention explores in detail the possible mechanisms by which different atomic (H, Cl, Br) substitutions cause different electrochemical properties through single-crystal structure analysis and DFT theoretical calculations, providing an ideal research model for linearly adjusting the physicochemical properties of crystal materials and designing and synthesizing crystal materials with controllable band gaps.

[0016] 4. The halo-Schiff base Cu(II) complex provided by this invention can be used as a molecular wire material with low resistance, good conductivity and high electron transport rate, and also provides new ideas for the design and development of high-performance molecular wire materials. Attached Figure Description

[0017] Figure 1 shows the synthesis circuit diagrams of Cu-H-Salmphen, Cu-Cl-Salmphen and Cu-Br-Salmphen in Comparative Example 1, Example 1 and Example 2;

[0018] Figure 2 shows the FT-IR spectra of H-Salmphen and Cu-H-Salmphen;

[0019] Figure 3 shows the UV-vis spectra of H-Salmphen and Cu-H-Salmphen;

[0020] Figure 4 shows the FT-IR spectra of Cl-Salmphen and Cu-Cl-Salmphen;

[0021] Figure 5 shows the UV-vis spectra of Cl-Salmphen and Cu-Cl-Salmphen;

[0022] Figure 6 shows the FT-IR spectra of Br-Salmphen and Cu-Br-Salmphen;

[0023] Figure 7 shows the UV-vis spectra of Br-Salmphen and Cu-Br-Salmphen;

[0024] Figure 8a shows the basic structure of the coplanar Schiff base Cu(II) complex Cu-Cl-Salmphen, where the two salon-type ligands are represented by different colors; b shows the cyclic supramolecular unit formed through multiple CH...Cl, CH...π, and π...π interactions; cf shows the magnified supramolecular ring and the binding mode of the intracyclic molecular unit.

[0025] The left image in Figure 9 shows a two-dimensional supramolecular layer formed by covalently connecting ring supramolecular molecules; the right image shows a three-dimensional supramolecular structure constructed by stacking two-dimensional supramolecular layers, with each layer represented by a different color.

[0026] Figure 10 shows the frontier molecular orbitals (FMOs) of Cu-H-Salmphen, Cu-Cl-Salmphen, and Cu-Br-Salmphen on the isosurface ρ = 0.02au;

[0027] Figure 11 shows the MEP plots of Cu-H-Salmphen, Cu-Cl-Salmphen, and Cu-Br-Salmphen on the isosurface ρ = 6.3 kcal / mol, where the cyan and yellow dots represent the minimum and maximum values ​​of MEP, in kcal / mol.

[0028] Figure 12 shows the NCI and AIM combination diagrams of Cu-Cl-Salmphen and Cu-Br-Salmphen. The isosurfaces directly represent different types of bonding isosurfaces in real space through color coding. Blue, green, and red represent strong attractive forces (hydrogen bonds), very weak forces (van der Waals), and strong repulsive forces (stereo collisions) interactions.

[0029] Figure 13a shows a schematic diagram of the UV-Vis titration of the complex; b shows the UV-Vis titration curves of Cu-Cl-Salmphen and c shows the UV-Vis titration curves of Cu-Br-Salmphen (the inset shows the absorbance as a function of Cu). 2+ (Dot plot of the change in the amount added); d is the Tauc plot of Cu-H-Salmphen, and e and f are the Tauc plots of Cu-Cl-Salmphen and Cu-Br-Salmphen, respectively (the inset is the UV-Vis absorption spectrum in the wavelength range of 300-500 nm);

[0030] Figure 14 shows the cyclic voltammograms of Cu-H-Salmphen, Cu-Cl-Salmphen, and Cu-Br-Salmphen at different scan rates (50-300 mV / s) in the potential range of -1.0 to 1.0 V, and the linear relationship between the peak current value and the square root of the scan rate for Cu-Br-Salmphen, Cu-Cl-Salmphen, and Cu-H-Salmphen, respectively.

[0031] In Figure 15, ac represents the temperature-dependent spectra of the electrochemical impedance of Cu-H-Salmphen, Cu-Cl-Salmphen, and Cu-Br-Salmphen, respectively; df represents the relationship between the charge transfer resistance and temperature of Cu-H-Salmphen, Cu-Cl-Salmphen, and Cu-Br-Salmphen, respectively; and gi represents the Arrhenius plots used to deduce the activation energies of Cu-H-Salmphen, Cu-Cl-Salmphen, and Cu-Br-Salmphen, respectively.

[0032] Figure 16 shows the variation of (a) the real part and (b) the imaginary part of the Cu-H-Salmphen impedance with frequency and temperature.

[0033] Figure 17 shows the variation of (a) the real part and (b) the imaginary part of the Cu-Cl-Salmphen impedance with frequency and temperature.

[0034] Figure 18 shows the variation of (a) the real part and (b) the imaginary part of the Cu-Br-Salmphen impedance with frequency and temperature. Detailed Implementation

[0035] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments, but this does not limit the present invention in any way. Any modifications or improvements made based on the teachings of the present invention shall fall within the protection scope of the present invention.

[0036] The present invention discloses a halogenated Schiff base Cu(II) complex, wherein the halogenated Schiff base Cu(II) complex is Cu-Cl-Salmphen or Cu-Br-Salmphen; the band gap values ​​of the halogenated Schiff base Cu(II) complex are 3.06 eV and 3.08 eV, respectively, and the electrical conductivities are 0.045 S and 0.079 S, respectively.

[0037] The halo-Schiff base Cu(II) complexes Cu-Cl-Salmphen and Cu-Br-Salmphen were synthesized using different haloligands, but without altering the length or pattern of the coordination bonds, resulting in identical molecular configurations. These can serve as models for finely controlling molecular energy levels. Compared to the halo-Schiff base complex Cu-Cl-Salmphen, Cu-Br-Salmphen exhibits additional hydrogen bonds between the two benzene rings, significantly increasing the electron density ρ(r). Simultaneously, the π-π interactions between the two benzene rings are stronger, and the symmetry is significantly reduced.

[0038] The band gap of the halogenated Schiff base Cu(II) complex narrows with the increase of the halogen atom (Cl and Br) coefficients, the activation energy of the complex decreases, the charge transfer resistance gradually decreases, the charge transfer rate increases, and the electron transport capacity and conductivity of the complex continue to increase.

[0039] The conductivity of the halo-Schiff base Cu(II) complex increases with increasing frequency and temperature, exhibiting negative temperature resistivity behavior.

[0040] This invention also provides a method for preparing the halo-Schiff base Cu(II) complex, which is specifically implemented according to the following steps:

[0041] 1) Add halosalicylaldehyde and m-phenylenediamine to a methanol solution and stir for 5-6 hours;

[0042] 2) Add CuCl2·2H2O, stir for 2-3 hours, and then filter to obtain the filtrate;

[0043] 3) The filtrate was slowly evaporated at room temperature to obtain regular black crystals, which were washed repeatedly with a polar solvent and filtered. Finally, the crystals were allowed to evaporate and dry naturally to obtain the target complex.

[0044] The halogenated salicylaldehyde is 3-chlorosalicylaldehyde or 3-bromosalicylaldehyde.

[0045] The molar ratio of halosalicylaldehyde, m-phenylenediamine, and CuCl2·2H2O is 2:1:1.

[0046] The volume ratio of m-phenylenediamine to methanol is 1:25000-500000.

[0047] The present invention further provides the application of the halo-Schiff base Cu(II) complex as a molecular wire material with low resistivity, good conductivity and high electron transport rate.

[0048] The present invention will be further described below with reference to embodiments and comparative examples.

[0049] Example 1: Synthesis of Cu-Cl-Salmphen

[0050]

[0051] A mixture of 3-chlorosalicylaldehyde (0.157 g, 1 mmol) and m-phenylenediamine (62 μL, 0.5 mmol) was dissolved in methanol (50 mL) and stirred at room temperature for 5 hours to obtain a yellow solution. Then, 0.085 g (0.5 mmol) of CuCl₂·2H₂O was added to the above solution, and the color of the mixed solution immediately turned dark brown. After stirring for another 3 hours, the solution was filtered, and the mixture was slowly evaporated at room temperature to obtain regular black crystals. The crystals were washed with methanol and dried in air (yield: 79.3%). FT-IR (KBr, cm⁻¹) -1 ):1602(C=N); 1261(CO); 1106(CN); 741(C-Cl); 657(Cu-N); 617(Cu-O), (Figure 4).UV–Visλ max 235, 270, 365 nm (Figure 5). The reaction formula is shown in formula (I).

[0052] Example 2: Synthesis of Cu-Br-Salmphen

[0053]

[0054] Except for the substitution of 3-bromosalicylic acid aldehyde (0.201 g, 1 mmol), the other steps were the same as in Example 1, finally yielding regular black crystals of Cu-Br-Salmphen (yield: 81.6%). FT-IR (KBr, cm⁻¹) -1 ): 1620 (C=N); 1265 (CO); 1105 (CN); 744 (C-Br); 657 (Cu-N); 619 (Cu-O), (Figure 6); UV–Visλmax: 232, 272, 364 nm (Figure 7). The reaction formula is shown in formula (II).

[0055] Crystal structure analysis of the complex prepared in Example 1

[0056] I. X-ray Diffraction Analysis

[0057] Single-crystal X-ray structural analysis revealed that both complexes crystallize in a monoclinic system (space group P21 / c) and are isomorphic. Minor differences in the crystal data are due to the substitution of different halogen atoms; therefore, the following discussion focuses primarily on Cu-Cl-Salmphen. Table 1 provides crystallographic data for both complexes, and Table 2 provides partial bond lengths and bond angles. As shown in Figure 8a, the asymmetric unit is a crystallographically independent Cu-Cl-Salmphen unit. Figure 8a shows the ORTEP diagrams and atom numbering schemes for the Cu-Cl-Salmphen and Cu-Br-Salmphen complexes. Unlike previously reported non-halogenated analogs, the lattices of Cu-Cl-Salmphen and Cu-Br-Salmphen do not contain any solvent molecules. Cu-Cl-Salmphen contains two independent Cu centers with twisted square planar coordination environments. Both Cu centers exhibit the same bidentate coordination environment with the N2O2 donor atoms from deprotonated phenolic hydroxyl groups and methylene nitrogen from two different Schiff base ligands. In Cu-Cl-Salmphen, the Cu-N bond lengths are 1.962 and 1.973, and the Cu-O bond lengths are 1.899 and 1.895; in Cu-Br-Salmphen, the Cu-N bond lengths are 1.953 and 1.959, and the Cu-O bond lengths are 1.896 and 1.897.

[0058] In the N₂O₂ coordination environment of the tetravalent chelate ring, the cis angle ranges of Cu-Cl-Salmphen and Cu-Br-Salmphen are 89.69–93.1° and 89.89–93.23°, respectively; while the anti-cis angle ranges are 154.32–167.82° and 155.51–167.28°, respectively. These parameters indicate that different halogenated ligands do not alter the length or pattern of the coordination bonds. That is, while changing the molecular composition, the molecular configuration remains completely identical. Such a structure can provide an ideal research model for the fine-tuning of molecular energy levels. In the stacked structure, three adjacent molecules form a semi-circular structure dominated by π...π interactions between the phenolic benzene rings, and two semi-circular structures further form a special cyclic supramolecular structure through quadruple CH...π interactions.

[0059] Furthermore, the cyclic supramolecular contains two molecular units connected to it. These two molecules, located at the junction of the two semi-circular structures, are further stabilized by multiple CH...π interactions, forming a circular supramolecular secondary structure composed of eight molecular units, as shown in Figure 9. This secondary structure is interconnected by covalent bonds of the outer ring molecular units, forming a two-dimensional supramolecular plane parallel to the ab axis diagonal.

[0060] Table 1. Crystal data and structural refinement of the complexes Cu-Cl-Salmphen and Cu-Br-Salmphen prepared in Examples 1 and 2.

[0061]

[0062] Table 2. Selective bond lengths and bond angles of the complexes Cu-Cl-Salmphen and Cu-Br-Salmphen prepared in Examples 1 and 2.

[0063]

[0064]

[0065] Comparative Example 1: Synthesis of Cu-H-Salmphen

[0066]

[0067] A methanol solution (75 mL) of salicylaldehyde (0.125 g, 1.0 mmol) and m-phenylenediamine (62 μL, 0.5 mmol) was mixed, stirred continuously, and slowly heated for 3 hours. The mixture was then cooled to room temperature, and a methanol solution of 0.1 g (0.5 mmol) of [Cu(Ac)₂·H₂O] was added dropwise while stirring continuously. During the reaction, the color changed from yellow to dark brownish-red. After filtration, the solution was slowly evaporated for 2 days to obtain brown, transparent Cu-H-Salmphen crystals, which were washed with ethanol and dried in air (yield: 85.3%). FT-IR (KBr, cm⁻¹) was used to analyze the crystals. -1 ):1615(C=N);1231(CO);1177(CN);653(Cu-N);617(Cu-O),(Figure 2);UV–Visλmax:233,268,366nm(Figure 3). The reaction formula is shown in formula (Ⅲ).

[0068] Theoretical analysis of the complexes prepared in Examples 1, 2 and 1 (Comparative Example 1)

[0069] 1. DFT theoretical calculations of the complexes prepared in Comparative Example 1, Example 1, and Example 2

[0070] In order to study the effect of halogen atom substitution on the band gap, this experiment introduced DFT theoretical calculations and further compared the differences in molecular orbital energy levels and electronic structures of the three complex molecules.

[0071] First, single-point energy calculations were performed on the optimized structures of these complex molecules. The results show that the addition of halogen atoms leads to a narrowing of the band gap in the complexes. As shown in Figure 10, although the HOMO orbitals of all three molecules are distributed throughout the molecule, the introduction of halogen atoms causes the HOMO orbitals of Cu-H-Salmphen and Cu-Cl-Salmphen to extend further from the benzene ring to the vicinity of the halogen atom. Furthermore, the increased conjugation also contributes to the reduction in the band gap. Calculations show that the band gaps of Cu-Cl-Salmphen and Cu-Br-Salmphen decrease from 3.18 eV (for the non-halogenated compounds) to 3.08 eV and 3.06 eV, respectively. The calculation results are in excellent agreement with optical and electrochemical experimental results. Moreover, compared to Cu-Cl-Salmphen, the HOMO level of Cu-Br-Salmphen increases from -5.91 eV to -5.80 eV, indicating an enhanced polarity and electron-accepting ability of the molecule. Therefore, orbital calculations show that bromine-substituted complexes are more inclined to donate electrons and have higher reactivity. Notably, in the non-halogenated Cu-H-Salmphen complex, the HOMOs are symmetrically distributed on both sides of the molecule. In contrast, the symmetry of the halogenated complex is significantly reduced. Generally, symmetrical molecules tend to have more leading molecular orbitals, resulting in a blue-shifted absorption spectrum. This calculation result is also consistent with the phenomena we observed in our UV experiments.

[0072] 2. Molecular electrostatic potential analysis (MEP) of the complexes prepared in Examples 1 and 2

[0073] Molecular electrostatic potential (MEP) analysis, as shown in Figure 11, reveals σ-vacancy extensions from the CX bond in Cu-Cl-Salmphen and Cu-Br-Salmphen, similar to most reported halogenated compounds. The negative regions of the halogen atoms are approximately at a 90° angle to the CX bond and merge with the negative regions of the aromatic π system of the benzene ring. Bromine atoms exhibit larger and more pronounced σ-vacancy (+10.41 kcal / mol), while chlorine atoms show relatively lower σ-vacancy (+2.48 kcal / mol).

[0074] 3. Atomic quantum theory analysis (QTAIM) of the complexes prepared in Examples 1 and 2

[0075] Quantitative analysis using quantum theory of atoms in a molecule (QTAIM) determines the electron density ρ(r) and the electron density Laplace vector by generating a bond critical point (BCP) between two interacting atoms. Topological properties of kinetic energy density G(r) and potential energy density V(r). The topological parameters are defined at BCP(3,-1), and detailed calculation results are shown in Table 3.

[0076] As shown in Figure 12, compared to Cu-Cl-Salmphen, Cu-Br-Salmphen not only forms additional hydrogen bonds between the two benzene rings, but also exhibits a significantly increased ρ(r) value, indicating a stronger interaction between the two benzene rings in the bromine-substituted compound. Since the interaction between the two benzene rings is an edge-to-face π-π stacking interaction, this type of interaction significantly reduces the symmetry of the structure. This finding is consistent with the electron density distribution observed in FMOs.

[0077] Table 3. Topological parameters of the complexes Cu-Cl-Salmphen and Cu-Br-Salmphen prepared in Examples 1 and 2 on BCP(3,-1). All parameters are in units of au.

[0078]

[0079]

[0080] Optical property analysis of the complexes prepared in Example 1, Comparative Example 1, Example 1, and Example 2

[0081] This experiment analyzed the coordination ratio of ligands to metal ions and the band gap value of each complex in the complexes prepared in Examples 1 and 2 using ultraviolet titration and Tauc plots.

[0082] Experimental results show that, through ultraviolet titration, it can be observed that as Cu... 2+ With increasing ion addition, the UV-Vis spectra of ligands Cl-Salmphen and Br-Salmphen changed significantly, clearly confirming the formation of copper complexes. As shown in Figure 13, the addition of Cu... 2+ After ionization, the complexes Cu-Cl-Salmphen and Cu-Br-Salmphen exhibit two isotropic absorption peaks, located at 333 nm and 396 nm, and 334 nm and 398 nm, respectively. Of particular note is the effect of adding 1.0 equivalent of Cu... 2+After metal solution treatment, the maximum absorbance in the ultraviolet spectrum shifts to higher energies. Specifically, the maximum absorption peaks shift from 413 nm and 416 nm for the ligands to 365 nm and 364 nm for the complexes Cu-Cl-Salmphen and Cu-Br-Salmphen. Furthermore, the absorbance of the complexes reaches its maximum at each absorption peak. With the addition of Cu... 2+ With further addition of ions, the absorbance no longer changed significantly, indicating that the titration endpoint had been reached. The inset shows the absorbance of the complex at 365 nm and 364 nm as a function of Cu. 2+ The dot plot of the change in the amount added clearly shows that in Cu 2+ Once the amount of ions reaches 1.0 equivalent, the absorbance no longer changes, further verifying that Cu under this special coordination mode... 2+ The coordination ratio of ions to ligands is 1:1.

[0083] In this experiment, the Tauc plot method was used to accurately estimate the band gap of the material. This method is derived from formula (1):

[0084] (αhν) 2 =A(hν-Eg) (1)

[0085] Where α is the absorption coefficient, h is Planck's constant, ν is the frequency of light, A is a constant, and Eg is the band gap. We plotted the Tauc diagram using the UV-Vis absorption spectrum of the complex in the wavelength range of 300-500 nm, thus depicting (αhν). 2 The relationship with hν. Extrapolating the linear portion of the Tauc diagram to α = 0, the band gap of the non-halogenated compound is 3.04 eV (d in Figure 13). With the introduction of halogenated ligands and the increase of the halogen atom coefficient, the band gaps of the halogenated Schiff base Cu(II) complexes Cu-Cl-Salmphen and Cu-Br-Salmphen decrease to 3.01 eV and 2.99 eV, respectively, indicating that the introduction of halogen atoms can fine-tune the band gap of the complexes. From a spectroscopic perspective, the enhanced light absorption of the halogenated complexes is mainly attributed to the substitution of halogen atoms. This substitution effect increases photon energy absorption and reduces the energy difference for electron transitions from the ground state to the excited state. The decrease in the band gap value of the halogenated Schiff base Cu(II) complexes improves conductivity and electrochemical kinetics performance.

[0086] Electrochemical performance analysis of the complexes prepared in Comparative Example 1, Example 1, and Example 2.

[0087] 1. Cyclic Voltammetry Analysis

[0088] The electrochemical performance of this experiment was studied using cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The electrolyte solution used in the experiment was 5 mM [Fe(CN)6]. 3- / 4- A mixture of 0.1 M KCl and a platinum electrode was used as the auxiliary electrode, Ag / AgCl as the reference electrode, and the working electrode was prepared by drop casting. Initially, 10 mg of the complex powder was uniformly suspended in 50 μL of α-terpineol using ultrasound, and then spin-coated onto a 1 cm² area. 2 On indium tin oxide (ITO) conductive glass. Cyclic voltammetry tests were performed on the complex at different scan rates (50-300 mV / s) within a potential range of -1.0 to 1.0 V.

[0089] Experimental results show that the cyclic voltammograms of the complexes Cu-H-Salmphen, Cu-Cl-Salmphen, and Cu-Br-Salmphen all exhibit an oxidation peak and a reduction peak (ac in Figure 14), and the peak potential shifts to higher potentials with increasing scan rate. More detailed electrochemical data are shown in Tables 4-6. At a scan rate of 50 mV / s, the peak resolution (ΔE) of the complexes is... P The peak current ratios were 0.613V, 0.501V, and 0.476V, respectively, and increased with increasing scan rate. Analysis of the cyclic voltammograms at different scan rates from 50 to 300 mV / s revealed that the peak current ratios of the complexes were all less than 1 (i...). pa / i pc <1), indicating that the redox reactions of the complexes Cu-H-Salmphen, Cu-Cl-Salmphen, and Cu-Br-Salmphen are irreversible. Furthermore, the peak current of the complexes increases linearly with the square root of the scan rate, and there are small potential changes in both the positive and negative directions during oxidation and reduction. Two straight lines can be obtained by plotting the peak current versus the square root of the scan rate, indicating that the electrochemical reaction of the complexes is a diffusion-controlled process, and the diffusion coefficient is obtained from equation (2) of the Randles-Sevcik equation:

[0090]

[0091] Where A is the electrode area (1.0 cm²). -2 C is the concentration (mol / cm³). -3 ), where ν is the scan rate in mV / s, and D is the diffusion coefficient (cm). 2 s -1 R is the gas constant (8.3144 J / Kmol). -1T represents temperature (K). Calculations show that the diffusion coefficient (D0) of the non-halogenated Schiff base Cu(II) complex Cu-H-Salmphen is 4.56 × 10⁻⁶. -7 cm 2 s -1 However, after halogenated ligand substitution, the diffusion coefficients of the Cu-Cl-Salmphen and Cu-Br-Salmphen complexes increased significantly, reaching 1.49 × 10⁻⁶. - 6cm 2 s -1 and 2.59×10 - 6cm 2 s -1 Experimental results show that the substitution of halogen atoms enhances the electron transport capability of the complex at the electrode, thereby altering the electrochemical properties of the complex.

[0092] Table 4. Cu-H-Salmphen in the presence of 5 mM [Fe(CN)6] 3- / 4- Electrochemical data from cyclic voltammetry tests in an electrolyte aqueous solution of 0.1 M KCl

[0093]

[0094] Table 5. Cu-Cl-Salmphen in the presence of 5 mM [Fe(CN)6] 3- / 4- Electrochemical data from cyclic voltammetry tests in an electrolyte aqueous solution of 0.1 M KCl

[0095]

[0096] Table 6. Cu-Br-Salmphen in the presence of 5 mM [Fe(CN)6] 3- / 4- Electrochemical data from cyclic voltammetry tests in an electrolyte aqueous solution of 0.1 M KCl

[0097]

[0098] Because there is a correlation between theoretical orbital energies and oxidation and reduction potentials, a specific mathematical relationship exists between electrochemical behavior and DFT calculations. The energy levels of the reported compounds were calculated using equations (3) and (4):

[0099]

[0100] LUMO = HOMO + E g (4)

[0101] The band gaps (Eg) were derived from the starting wavelengths of the UV-Vis spectra and were 3.06 eV, 3.00 eV, and 2.98 eV, respectively. Therefore, the HOMO and LUMO levels of the non-halogenated Schiff base Cu(II) complex Cu-H-Salmphen were -5.26 eV and 2.20 eV, respectively. However, for the halogenated derivatives, the levels of Cu-Cl-Salmphen and Cu-Br-Salmphen were -5.23 eV and -2.23 eV, and -5.22 eV and -2.24 eV, respectively, indicating that the HOMO-LUMO band gaps of the complexes decreased after halogen substitution.

[0102] 2. Electrochemical impedance spectroscopy analysis

[0103] Electrochemical impedance spectroscopy (EIS) is an important tool for analyzing electrode surface properties, used to determine the charge transfer resistance (Rct) between the electrolyte and electrode interface. In this experiment, the frequency range of the EIS spectra was 0.01–100 kHz, with a perturbation amplitude of 10 mV. Spectra were acquired at 25 °C, 35 °C, 45 °C, 55 °C, 65 °C, and 75 °C.

[0104] Figure 15(ac) shows the electrochemical impedance spectroscopy (EIS) spectra of Cu-H-Salmphen, Cu-Cl-Salmphen, and Cu-Br-Salmphen. It is clearly observed that all three complexes exhibit temperature-dependent behavior. Within the temperature range of 300–350 K, increasing temperature leads to a decrease in the semicircle diameter. Specifically, the charge transfer resistance (Rct) of the non-halogenated Schiff base Cu(II) complex Cu-H-Salmphen decreases from 31.6 Ω to 9.4 Ω, while the Rct values ​​of the halogenated complexes Cu-Cl-Salmphen and Cu-Br-Salmphen decrease from 22.4 Ω to 5.6 Ω and from 12.6 Ω to 2.1 Ω, respectively. This experimental result indicates that the charge transfer resistance of the non-halogenated Schiff base Cu(II) complex is higher than that of the halogenated Schiff base Cu(II) complex, suggesting that with the substitution of halogen atoms, the charge transfer resistance gradually decreases, while the conductivity of the complexes continuously increases. At 25 °C, the electrical conductivities of Cu-H-Salmphen, Cu-Cl-Salmphen, and Cu-Br-Salmphen are 0.032 S, 0.045 S, and 0.079 S, respectively. Furthermore, the activation energy of the charge transfer process for each complex can be obtained using the Arrhenius equation (5):

[0105]

[0106] In the above formula, A represents a constant, T represents temperature (K), and R is the gas constant (8.3144 J K mol). -1 Ea is the activation energy (kJ / mol). According to the formula, the activation energy (Ea) of the non-halogenated Schiff base Cu(II) complex Cu-H-Salmphen is 8.61 kJ / mol, while the activation energies of the halo-Salmphen Cu-Cl-Salmphen and Cu-Br-Salmphen are reduced to 7.76 kJ / mol and 6.32 kJ / mol, respectively. Experimental results show that halogen substitution can lower the activation energy and increase the charge transfer rate.

[0107] Figure 16-18 shows the variation of the real part (Z') and imaginary part (-Z") of the impedance of the complex with frequency at different temperatures. It can be seen that the Z value decreases with increasing frequency and temperature, and in the high-frequency region, the real part (Z') and imaginary part (-Z") of the complex tend to merge. This indicates that the conductivity of the complex increases with increasing frequency and temperature, exhibiting negative temperature resistivity (NTCR) behavior.

[0108] In summary, the electrochemical properties of the halo-Schiff base Cu(II) complexes Cu-Cl-Salmphen and Cu-Br-Salmphen designed and synthesized in this invention, such as diffusion coefficient, resistance, and conductivity, show a consistent trend with the change of band gap, and have good conductivity. Therefore, the halo-Schiff base Cu(II) complexes provided by this invention can be used as molecular wire materials with low resistance, good conductivity, and high electron transport rate, and also provide new ideas for the design and development of high-performance molecular wire materials.

Claims

1. A halo-Schiff base Cu(II) complex, characterized in that, The halo-Schiff base Cu(II) complex is Cu-Cl-Salmphen or Cu-Br-Salmphen, with the following chemical structural formula: X is Cl or Br; the band gap values ​​of Cu-Cl-Salmphen and Cu-Br-Salmphen are 3.08 eV and 3.06 eV, respectively, and the conductivities are 0.045 S and 0.079 S, respectively.

2. A method for preparing the halo-Schiff base Cu(II) complex according to claim 1, characterized in that, The following steps are performed: 1) Add halosalicylaldehyde and m-phenylenediamine to a methanol solution and stir for 5-6 hours. The halosalicylaldehyde is 3-chlorosalicylaldehyde or 3-bromosalicylaldehyde; 2) Add CuCl2·2H2O, stir for 2-3 hours, and then filter to obtain a filtrate; 3) Allow the filtrate to evaporate slowly at room temperature to obtain regular black crystals. Wash the crystals multiple times with a polar solvent and filter. Finally, allow the crystals to evaporate naturally and dry to obtain the target complex.

3. The preparation method according to claim 2, characterized in that, The molar ratio of halosalicylaldehyde, m-phenylenediamine, and CuCl2·2H2O is 2:1:

1.

4. The preparation method according to claim 2, characterized in that, The volume ratio of m-phenylenediamine to methanol is 1:25000~500000.

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