Luminescence detection of CH₂Cl₂ by varying Cu⋯Cu interactions in a flexible porous coordination polymer

Abstract

Owing to the weakness of the interaction between chlorohydrocarbon and the host framework, the development of reversible and vapochromic coordination polymer (CP)-based luminescence sensors for the detection of CH₂Cl₂ with a fast response is still challenging. In this study, a flexible Cu(I)-CP, [Cu₂I₂(PPh₃)₂(PYZ)] (CIPP, PPh₃ = triphenylphosphine, PYZ = pyrazine) is reported. The intra-cluster Cu⋯Cu distance in CIPP is quite sensitive to the external stimuli, resulting in the corresponding luminescence color and intensity change. Based on this feature, the fast (11 s), distinguishing (wavelength shift of 45 nm), and reversible luminescence response of CIPP for CH₂Cl₂ is realized. Crystallographic analysis suggests that the presence/removal of CH₂Cl₂ can affect the Cu⋯Cu distance, which is the origin of the responsive luminescence. In addition, the multiple weak interactions between CH₂Cl₂ and the framework afford the strong adsorption of CH₂Cl₂ into CIPP, which can be maintained for at least 5 minutes when exposed to air, thereby ensuring accuracy in the sensing process.

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Introduction

Volatile organic compounds (VOCs) refer to organic compounds with high vapor pressure and low boiling point under ambient conditions, therefore, they have high volatility.^1,2 Long-term exposures to VOCs possibly cause damage to human health, such as damage to the liver, kidneys, and nervous system; thus the detection of VOCs is of critical significance.^3–5 Emitting units in porous coordination polymers (CPs) or metal–organic frameworks (MOFs) can interact with VOCs, leading to changes in the intensity or the wavelength of the luminescence. For example, by generating C–H⋯O or Cl⋯H interactions between the host and guest molecules, the luminescence detection of tetrahydrofuran (THF), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and CH₂Cl₂ can be realized.^6–8 In addition, the process of guest-adsorption/desorption in a porous CP is usually accompanied by the structural transformation, which further exhibits changes in the conformation or the charge transfer of the luminescent chromophore.^9,10

Among VOCs, CH₂Cl₂ is widely used as a solvent or reagent not only in laboratories but also in a wide range of industrial applications, such as the production of paint removers, herbicides, and pesticides.¹¹ However, CH₂Cl₂ may cause damage to the liver and nervous system, and even potential carcinogenic effects.^12,13 Several methods have been developed for the detection of CH₂Cl₂, such as gas chromatography (GC)-mass spectrometry (GC-MS, 5 ng L⁻¹), gas chromatography-photo-ionization detectors (GC-PID, 1 ppm), and screen-printed electrodes (SPE, 17.3 μmol L⁻¹).^14–17 However, they display some shortcomings, such as the use of expensive instruments, tedious sample pretreatment processes, and the inability for in situ analysis. Compared to the above traditional ways, luminescence detection for VOCs based on porous CPs has unique advantages, such as fast response, visualization, and simplicity.^18–23 However, in comparison with usual VOCs, CH₂Cl₂ has difficulty forming strong interactions with the luminescent probes because of its low polarity and rather low boiling points. Therefore, reports about the luminescence response for CH₂Cl₂ in porous CPs and MOFs are rare.^8,24 Moreover, because of the weak interaction between CH₂Cl₂ and CPs, it is difficult for CH₂Cl₂ to directly affect the luminescent center in CPs and cause the solvatochromism/vapochromism. Generally, the reported luminescent CP sensors for CH₂Cl₂ with fast response are based on the emission intensity change. It is rather difficult to design and prepare luminescent CPs with both chromatic and fast responses to CH₂Cl₂. Compared with the color-changeable luminescence detection, the intensity-depending method is more likely to cause errors due to test conditions and methods.^25–27

Cu(I)-CPs have attracted much attention because of their low toxicity, low cost, and broad photophysical behaviors.^28–34 In particular, the intra-cluster Cu⋯Cu distance in copper clusters could be varied with external stimulus, resulting in changes in Cu⋯Cu interaction and corresponding emissions.^35,36 Based on this principle, we recently reported a series of Cu(I)-CPs with attractive optical properties, i.e., long afterglow and multi-stimuli-responsive, properties, including thermochromism, mechanochromism, and solvatochromism/vapochromism.^37–40

Herein, we report a Cu(I)-CP, [Cu₂I₂(PPh₃)₂(PYZ)] (CIPP, PPh₃ = triphenylphosphine, PYZ = pyrazine), which has a flexible one-dimensional (1D) chain structure. CIPP displays different blue shifts in the luminescence after the adsorption of CH₂Cl₂, CHCl₃, and CH₃CN vapors. In order to investigate the vapochromic mechanism, CIPP with corresponding guests was also prepared. Detailed structural analyses show that compared to CIPP, the adsorption of guest molecules makes the Cu⋯Cu distances longer, resulting in luminescent blue shifts and higher emission energy. Meanwhile, CIPP exhibits fast response speed (11 s) and satisfactory reversibility. Furthermore, CIPP can retain CH₂Cl₂ for a long time, which is helpful for applications in the detection processes.

Results and discussion

Syntheses and characteristics

CIPP·CH₂Cl₂ (CIPP-D) was synthesized by the reaction of CuI, PPh₃, and PYZ in a CH₂Cl₂ solution. After drying under vacuum, the CH₂Cl₂ guest in CIPP-D was removed and the red CIPP crystals were obtained, referring to the reported method of a similar structure.⁴¹ Single-crystal X-ray diffraction (SCXRD) demonstrates that CIPP belongs to the monoclinic C2/c space group. The crystallographic asymmetric unit of CIPP contains one and a half [Cu₂(μ-I)₂] clusters as nodes, a bridging bidentate PYZ, and three monodentate PPh₃ ligands, which directly coordinate with the copper ions (Fig. 1a). In contrast to the similar structure that has been reported,⁴² there are two different clusters in CIPP with intra-cluster Cu⋯Cu distances of 2.7338(13) Å (Cu1⋯Cu1A) and 2.8557(16) Å (Cu2⋯Cu2), respectively (Fig. S1†). These two types of copper clusters are arranged at the ABAB intervals along the CP chain. The [Cu₂(μ-I)₂] clusters are interconnected by PYZ as a bridging ligand into the 1D chains (Fig. 1b). These 1D chains are stacked with each other to form the 3D structure via aromatic C–H⋯π interaction (Fig. 1c and S2†). Thermogravimetric (TG) analysis indicated that the CIPP was stable up to 115 °C, and no significant weight loss was observed before the collapse, proving that there was no guest molecule in the CIPP (Fig. S3†).

Fig. 1 (a) The asymmetric unit and (b) 1D chain of CIPP. Color codes: Cu, orange; I, purple; N, indigo; P, pink; C, gray; H, light purple. (c) The stacking mode between the chains of CIPP. Different colors are employed to distinguish separate chains. Hydrogen atoms are omitted for clarity.

Photophysical properties

UV–vis absorption and emission spectra of CIPP are shown in Fig. 2a. It shows the strong absorption from 200 to 600 nm, and the maximum absorption wavelength (λ_abs) was centered at approximately 427 nm, which can be assigned to the mixed metal-to-ligand charge transfer (MLCT) and halogen-to-ligand charge transfer (XLCT) transitions.⁴³ Because the Cu⋯Cu distance in CIPP is about 2.8 Å, the strong Cu(I)⋯Cu(I) interaction should be considered, which will affect the mixed MLCT/XLCT transition, and is usually accompanied by the longer wavelength emission. As observed under 365 nm excitation, CIPP shows orange-red luminescence with the maximum emission wavelength (λ_em) at 663 nm (Fig. S4†). This λ_em with rather low energy indicates the fairly large MLCT composition and strong Cu(I)⋯Cu(I) interaction. Meanwhile, the emissions of CIPP and CIPP-D do not change when varying the excited wavelength (260–460 nm), demonstrating the same emission center (Fig. S5†). Because the luminescence of Cu(I) clusters is reported to be sensitive to temperature, the emission spectra of CIPP at different temperatures were measured. As shown in Fig. 2b, from 80 K to 120 K, the emission of CIPP displayed both red-shifting and intensity-decreasing tendencies with increasing temperature, which agreed with the common thermal quenching (TQ) phenomenon.⁴⁴ However, when the the temperature was further increased, contrastingly, the emissions of CIPP showed blue shifts with the gradually enhanced intensity (Fig. 2c). Detailedly, the emission of CIPP shifted from 710 nm to 663 nm (120–300 K), which showed a significant wavelength shift of 47 nm (0.12 eV). Although some studies have promoted that such temperature-dependent luminescence in Cu(I) complexes may be caused by the “thermally activated delayed fluorescence” mechanism,^45,46 in this work, we tend to attribute this phenomenon to the slight lengthening of the Cu(I)⋯Cu(I) distance,^47,48 as the SCXRD measurements at variable temperatures further confirmed it (Fig. S6 and Table S1†). The increase in the Cu(I)⋯Cu(I) distance weakens the Cu⋯Cu interaction, resulting in the luminescent blue shift. Because the luminescence blue shifts from the near-infrared to the visible region, its non-radiative transition is reduced. Thus, besides the blue shift, it also exhibits luminescence intensity enhancement at the same time.

Fig. 2 (a) UV–vis absorption and emission spectra (excited at 365 nm) of CIPP in air at room temperature. (b) Temperature-dependent emission spectra of CIPP, from 80 K to 300 K, excited at 365 nm. (c) A scatter plot of the integral emission intensity of CIPP at the corresponding temperature, based on (b).

Interestingly, the obvious vapochromism of CIPP was observed (Fig. 3). Especially, when exposed to CH₂Cl₂ vapor, the luminescence of CIPP exhibited a distinct blueshift (45 nm), with the emission color change from orange-red (663 nm) to orange-yellow (618 nm). Moreover, other VOC vapors, such as CH₃CN and CHCl₃, can also result in similar blue shifts but with smaller changes (30 and 38 nm, respectively, Fig. 3a and c, respectively). When CIPP was exposed to other types of halohydrocarbon vapors, for example, CH₂Br₂, CH₂I₂, and CHBr₃, it exhibited similar luminescent vapochromism behavior, indicating that CIPP can detect the molecules with a similar size to CH₂Cl₂ (Fig. S7†). On the contrary, exposure to other common VOC vapors did not lead to the obvious luminescence variation for CIPP (Fig. 3b and c), which suggested the selective luminescence sensing and the potential application of halohydrocarbon and CH₃CN detection.

Fig. 3 Emission spectra of CIPP before and after exposure in (a) acetonitrile, CH₂Cl₂, CHCl₃ vapors, and (b) other VOCs. (c) The λ_em that was obtained from (a) and (b), excited at 365 nm. Insert: a photographs of CIPP before and after exposure in CH₂Cl₂, under 365 nm UV light. (d) PXRD patterns of CIPP before and after exposure in different VOCs.

Mechanism of sensing for VOCs

Powder X-ray diffraction (PXRD) patterns were measured to reveal the structural transformation during the vapochromism. As shown in Fig. 3d, The PXRD results show that the structure of CIPP does not change after exposure to the most common VOC vapors, including CCl₄, ethanol, methanol, and cyclohexane, consistent with the corresponding irresponsive emission spectra shown in Fig. 3b and c. It is worth mentioning that the structure of CIPP in the gate-closing state is close-packed, making it difficult to adsorb these VOC molecules. The PXRD patterns in other VOC vapors, including CH₂Cl₂, CHCl₃, and CH₃CN, show remarkable changes (Fig. 3d). This means that these organic molecules are able to interact with CIPP by vapor diffusion, which opens the channels, illustrating the structural flexibility of CIPP. Such flexibility enables it to adsorb different molecules to form the structures in the opening state. The luminescence lifetimes of CIPP before and after exposure to VOC vapors are listed in Fig. S8,† which are all μs-scale and assigned to the phosphorescence.

To further clarify the structural transformations of CIPP in the vapochromic processes, the crystallographic structures of CIPP with different guest molecules were analyzed in detail, including CIPP-D (with CH₂Cl₂ guest), CIPP-C (with CHCl₃ guest), and CIPP-A (with acetonitrile guest), which crystallize from the corresponding organic solvents (Fig. S9†). The λ_em of the as-synthesized CIPP-D is almost the same as that of the fumigated CIPP powder in CH₂Cl₂ vapor. The comparison of the PXRD patterns of CH₂Cl₂-fumigated CIPP and CIPP-D indicates that the transformation from CIPP to CIPP-D is mostly complete (Fig. S10†). Meanwhile, the luminescence sensing is still sufficient by using only the surface of the compound, as the excitation light is difficult to deeply penetrate the crystals (Fig. S11†). The completed structural transformation was observed by directly immersing CIPP in CH₂Cl₂ solvent (Fig. S12†). Similar transformations for CIPP after exposure to CHCl₃ and CH₃CN can be also observed (Fig. S13 and S14†).

As shown in Fig. 4a and b, the molecular chains in CIPP-D are similar to those in guest-free CIPP, suggesting that they are not reconstructed after absorbing CH₂Cl₂. For CIPP-D, the gaps between molecular chains are filled with CH₂Cl₂ molecules, resulting in the expansion of the structure, which exhibits the flexibility of the crystal (Fig. 4b). Each CH₂Cl₂ molecule in CIPP-D is enclosed by four phenyl rings of PPh₃ and two PYZ ligands from the two adjacent chains (Fig. S15†). The chlorine atoms of the CH₂Cl₂ molecule point toward the pyrazine ligands of two adjacent chains. The dihedral angle between the pyrazine ligands of the two adjacent chains is ca. 25° and creates a void to accommodate a CH₂Cl₂ molecule (Fig. 4d). The chains of CIPP-D are also stacked by weak intermolecular interactions, such as those of CIPP (Fig. S16†). The structures in CIPP-C with CHCl₃ and CIPP-A with CH₃CN are similar with those of CIPP-D (Fig. S17†). The CH₂Cl₂ molecules are ordered in the crystal structure and stabilized by multi-weak interactions with PYZ and PPh₃ ligands in the lattice (Fig. 4d and S18†). The closest distance between Cl atoms of CH₂Cl₂ and H atoms of triphenylphosphine is 3.08 Å, which shows the large tendency of Cl⋯H hydrophobic interaction. In addition, the closest C–H⋯π distance between CH₂Cl₂ and the aromatic ring is only 3.56 Å. In order to analyze the proportion of multi-weak interactions, Hirshfeld surfaces analysis was used (Fig. S19†).^49,50 The 2D fingerprint plots illustrated that the weak host–guest Cl⋯H interactions occupied a higher fraction (58.5%). The theoretical calculation demonstrated that the total binding energy between CH₂Cl₂ and CIPP framework is 85 kJ mol⁻¹ (Table S2†). Meanwhile, the adjacent inter-chain distance in CIPP-D (11.44 Å) is markedly longer compared with that in CIPP (10.60 Å), due to the insertion of CH₂Cl₂ (Fig. 4c and d). Furthermore, the average occupancy area per chain for CIPP-D (31.2 Ų) is also larger than that for CIPP (27.9 Ų). Similarly, there is also a difference in the average occupancy areas of the molecular chains for CIPP-C (35.8 Ų per chain) and CIPP-A (30.3 Ų per chain), which are mainly dependent on the sizes of the guest molecules (Fig. S20†).

Fig. 4 Molecular chains stacking in (a) CIPP and (b) CIPP-D viewed along the b-axis, the purple cylinders represent the PYZ ligands and the gray ones are for the phenyl rings of PPh₃. The distance between adjacent molecular chains in (c) CIPP and (d) CIPP-D. Interactions in CIPP-D: Cl1⋯H1, 3.33 Å; Cl1⋯H2, 3.26 Å; Cl1⋯H3, 3.15 Å; Cl2⋯H3, 3.35 Å; Cl2⋯H4, 3.33 Å; Cl2⋯H5, 3.40 Å. (e) Cu⋯Cu distances of the [Cu₂(μ-I)₂] clusters in CIPP and CIPP-D. Color codes: Cu, orange; I, purple; Cl, green; N, indigo; P, pink; C, gray; H, light purple.

The intra-cluster Cu⋯Cu distance in CIPP is 2.73 Å, indicating a strong Cu⋯Cu interaction that leads to greatly reduced emission energy (1.87 eV). While for CIPP-D, with the lengthening of the inter-chain distance, [Cu₂(μ-I)₂] cluster stretches and the Cu⋯Cu distances increased to 3.28 Å, and 3.2378(8) Å for CIPP-A and 3.1479(7) Å for CIPP-C (Fig. S21†). For this reason, the intra-cluster Cu⋯Cu interaction in CIPP-D almost disappeared, thus it showed an obvious blueshift emission compared to that of CIPP (Fig. 4e). In addition, the increase of the Cu⋯Cu distance may enhance luminescence efficiency, as the photoluminescence quantum yields (PLQYs) are 38% for CIPP, and 54% for CIPP-D (Fig. 4e). This conclusion also explains why CIPP exhibits thermal luminescence enhancing phenomenon mentioned above, as the Cu⋯Cu distance in CIPP can slightly increase the warming process (120–298 K, Fig. S6†).

CH₂Cl₂ sensing properties

As CIPP shows the best sensing performance to CH₂Cl₂ with the greatest change of the luminescence among the VOCs, its responding performance to CH₂Cl₂ was analyzed in detail. First, when CIPP was exposed to the atmosphere of CH₂Cl₂ at different concentrations, it displayed a regularly changing tendency. As shown in Fig. 5, with the increase in CH₂Cl₂ concentration, the emission of CIPP gradually shifted from 663 nm to 618 nm. Moreover, a significant blueshift occurred at the CH₂Cl₂ concentration of 1 g L⁻¹ (Fig. 5a), suggesting that the channel begins to open at this concentration.

Fig. 5 (a) Emission spectra of CIPP in the atmosphere with various CH₂Cl₂ concentrations (0, 0.133, 0.265, 0.53, 0.795, 0.928, 1.06, 1.33, 1.59, 1.86, 2.12, 2.39, 2.65 g L⁻¹, from right to left) at room temperature. (b) The cyclic luminescence responses of CIPP under the alternation between saturated CH₂Cl₂ vapor and hot air (318 K). The vertical coordinate is the λ_em of the spectra per second. (c) Response curves in the range of purple square in (b) with a time range from 896 s to 907 s. (d) Time-dependent emission spectra of CIPP in saturated CH₂Cl₂ vapor, from 0 s to 11 s. (e) Time-dependent emission spectra of CH₂Cl₂-absorbed CIPP sample at 318 K, recorded once per second.

The sensing speed and reversibility of CIPP were also tested by in situ experiments. The real-time continuous emission spectra were recorded using a charge-coupled device (CCD). CH₂Cl₂ molecules absorbed in CIPP could be removed by heating at 318 K, which was proved by both PXRD patterns and emission spectra (Fig. S22 and S23†). Therefore, to test the reversibility, CIPP powder was alternately placed in the atmosphere of saturated CH₂Cl₂ vapors at room temperature, and warm air without CH₂Cl₂ at 318 K. It should be noted that CIPP still showed a similar response to CH₂Cl₂ vapors after 16 cycles and the structure was maintained even after cyclic responses (Fig. 5b and S22†). As shown in Fig. 5d, in the saturated CH₂Cl₂ vapor, the luminescence of CIPP rapidly blue shifts within 11 s, suggesting a rather fast response. After the stabilization of the luminescence spectra, which suggested the saturation of CH₂Cl₂ absorption, CH₂Cl₂ from the sample was removed by blowing heated air (318 K), and the recovery time (back to the luminescence of CIPP phase) was about 66 s (Fig. 5e). The regenerated CIPP-D was able to maintain the emission without significant shift for about 5 min at room temperature (Fig. S24†), indicating that CIPP showed a relatively strong absorption of CH₂Cl₂, thus reducing the luminescence change in the measurement and improving the accuracy. In addition to CH₂Cl₂, the response time for CHCl₃ and CH₃CN vapors were also measured. For CHCl₃, the blue shift of λ_em was completed within 3 min (Fig. S25†). Such wavelength shift is smaller, and the response time is longer compared with that of the CH₂Cl₂ vapor. While for CH₃CN, the luminescence blueshift was completed within 60 s (Fig. S26†). The faster response speed for CH₂Cl₂ may be attributed to the rather high saturation vapor pressure of CH₂Cl₂ (46.5 kPa at 293 K), compared with those of CHCl₃ (21.28 kPa at 293 K) and CH₃CN (9.33 kPa at 293 K).^51,52

Conclusions

A Cu(I)-CP named CIPP was synthesized and characterized extensively. CIPP displayed luminescence vapochromic response to CH₂Cl₂, CHCl₃, and CH₃CN vapors. Benefitting from the flexibility of CIPP, the intra-cluster Cu⋯Cu distance varies when it absorbs guest molecules and transforms into the gate-opening state. Especially, the interaction with CH₂Cl₂ allows CIPP to display a remarkable luminescence wavelength for the blue shift (45 nm). Moreover, CIPP exhibits fast luminescence color variation (ca. 11 s) and excellent reversibility for sensing CH₂Cl₂. Due to the multi-weak interactions, CIPP can hold CH₂Cl₂ for 5 minutes at room temperature in air.

Experimental

All the chemicals were obtained from commercial sources and used as received without further purification unless otherwise noted. Powder X-ray diffraction (PXRD) patterns were recorded on a Rigaku Mini diffractometer with Cu-Kα (λ = 1.54184 Å) radiation. UV-vis absorption spectra were recorded on a Shimadzu UV-3600i Plus UV-VIS-NIR absorption spectrometer. Thermogravimetric (TG) analyses were performed on a METTLER TOLEDO TGA/DSC 3+ instrument with a ramping rate of 10.0 °C min⁻¹ under a nitrogen atmosphere. Elemental analysis (C, H, and N) was performed on an Elementar Vario EL Cube.

Preparation

For CIPP-D and CIPP: PYZ (16 mg, 0.2 mmol) and PPh₃ (105 mg, 0.40 mmol) were completely dissolved in dichloromethane (5 mL), followed by the addition of CuI (76 mg, 0.4 mmol) at room temperature. The orange CIPP-D crystals were formed from the transparent liquid after about 7 hours. The crystals were filtered and washed with CH₂Cl₂, then dried under vacuum to obtain orange-red CIPP crystals (yield = 60%). Elemental analysis calcd for C₂₀H₁₇CuINP (CIPP): C, 48.75; H, 3.48; N, 2.84. Found: C, 48.80; H, 3.83; N, 2.64.

For CIPP-A: CIPP-A was synthesized by a similar method to that of CIPP-D by replacing the CH₂Cl₂ solvent with the CH₃CN solvent (yield = 54%).

For CIPP-C: PYZ (32 mg, 0.4 mmol) and PPh₃ (105 mg, 0.40 mmol) were completely dissolved in CHCl₃ (5 mL) at 278 K, followed by the addition of CuI (76 mg, 0.4 mmol). Then, the solution was kept at 278 K for about one day, and orange CIPP-C crystals were observed. The crystals were filtered and washed with cold CHCl₃ (yield = 47%). Among these, CIPP-A was reported in the previous literature.³⁶

Single-crystal X-ray diffraction

Diffraction data were collected on a Rigaku XtaLAB single-crystal diffractometer by using Cu-Kα radiation (λ = 1.54184 Å). The structures were solved using the direct methods and refined with the full-matrix least-squares method on F² using the SHELXTL package.⁵³ Anisotropic thermal parameters were used to refine all non-hydrogen atoms. All hydrogen atoms were generated geometrically. Crystallographic data and details of data collection and refinements are summarized in Table S1.† CCDC 2258386 (CIPP), 2258387 (CIPP-D), 2258388 (CIPP-C), and 2258389 (CIPP-150K) contain supplementary crystallographic data for this work.†

Photoluminescence measurement

Photoluminescence measurements were performed on an Edinburgh FLS1000 fluorescence spectrometer. The emission spectra were recorded on the spectrometer equipped with a continuous Xe lamp. The luminescence decay experiments were performed on the same spectrometer equipped with a variable pulsed laser (VPL) at 375 ± 10 nm as the excitation source. The temperature was controlled using an Oxford temperature controller. The photoluminescence quantum yields (PLQYs) were measured on the same spectrometer in the integrating sphere.

The in situ experiment was recorded using an Ocean QE Pro charge-coupled device (CCD) equipped with a 365 nm LED. Real-time sensing of CH₂Cl₂ was realized using CH₂Cl₂ liquid to provide the saturated vapor under ambient conditions. After removing CH₂Cl₂ using hot air at 318 K, CIPP was cooled to room temperature by blowing normal air (detected by thermometer).

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

We gratefully acknowledge the financial support of the National Natural Science Foundation of China (22101211, 21901189), Municipal Science and Technology Bureau (Jiangke 2021-76), MOE Key Laboratory of Bioinorganic and Synthetic Chemistry (BISC2022A04), Scientific Research Ability Improvement Project of Key Discipline Construction from the Education Department of Guangdong Province (2022ZDJS027), and the NSF of Guangdong Province (2017A030310258).

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Footnotes

† Electronic supplementary information (ESI) available. CCDC 2258386, 2258387, 2258388 and 2258389. For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d3qi01723k

‡ These authors contributed equally to this study.

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