English

• 1. INTRODUCTION

  Coordination polymers (CPs), which stand for a new class of organic-inorganic crystalline hybrid materials, have attracted extensive attention of researchers not only because of their structural diversity and modification, but also of their wide application prospects in the field of gas adsorption^[1-4], magnetic properties^[5-7], catalysis^[8-10], sensors^[11-16], etc. At present, luminescent coordination polymers (LCPs) have become one of the research hotspots as fluorescent probes, which have the advantages of fast response, time saving and convenience compared with traditional instrument detection methods, such as X-ray imaging, Raman spectroscopy, ion mobility spectrometry, plasma desorption mass spectrometry, and so on^[17-21]. Nitroaromatic compounds are important chemical raw materials and highly toxic pollutants. At the same time, the iron is not only an essential trace element in bodies' metabolic process, but also an important raw material that can not be missed in industrial processes. But their arbitrary discharge and treatment bring about a huge danger to the environment and human health^[22]. Therefore, it is very necessary to develop a method for quickly and easily identifying the above substances, and LCPs are one of the promising candidates^[23-26]. However, constructing a CP with fluorescent properties is a great challenge because its synthesis depends on many aspects, such as the ligand, central metal ion, temperature, pH, solvent type and reaction time. Among them, the rational choice of ligands and central metal ions is crucial. Because of their π-conjugated rigid rings and distinct electrical properties, 1,4,5,8-naphthalenediimides (NDIs, also called as naphthalene carbodiimides) have been widely used as linkers for efficiently synthesizing LCPs^[27]. As for the metal ions, zinc(Ⅱ) and cadmium(Ⅱ) with a d¹⁰ electronic configuration were generally chosen because they have good fluorescence characteristics themselves. When the above metal ions are coordinated with an organic ligand with a large conjugated electron system, the antenna effect of the ligand modulates the fluorescent properties of the metal ions, thereby obtaining CPs with excellent fluorescence properties.

  Inspired by the above situation, the NDI-related polycarboxylic acid, 5,5΄-(1,3,6,8-tetraoxobenzo-[lmn][3,8] phenanthrolin-2-7-diyl)bis-1,3-benzenedicarboxylic acid (H₄L), has been chosen as linker based on the following reasons: (1) It has a NDI chromophore unit and a large conjugated electron system, which is beneficial to construct CPs with good fluorescence performance; (2) Its rigidity makes it possible to synthesize structurally CPs with stable structure; (3) The carboxylate groups present versatile bonding modes to construct CPs with different structures^[28-30]. In addition, its four carbonyl oxygen atoms increase the fluorescent properties of CPs, which in turn contributes to the recognition of metal ions and nitroaromatic compounds.

  In this work, based on the H₄L ligand and Zn(Ⅱ)/Cd(Ⅱ), two new CPs of 1 and 2 have been successfully constructed under solvothermal method with the aid of 4,4΄-bis(benzoimidazo-1-yl)biphenyl (4,4΄-bbib)/1,4-bis(imidazol-1-ylmethyl)benzene (1,4-bimb) (Scheme 1). Furthermore, the fluorescent properties of 1 and 2 have been also studied.

  Scheme 1

  

  Scheme 1.  Ligands used in synthesizing 1 and 2

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  2. EXPERIMENTAL

  2.1 Materials and physical measurements

  H₄BIPA-TC and 4,4΄-bbib were purchased from Jinan Henghua Chemical Co., Ltd. (> 99%, AR). Other reagents were purchased from Shanghai Chemical Company and used without further purification. The elemental analyses (C, N and H) were measured on a Vario MACRO analyzer. Powder X-ray diffraction patterns were collected by using a Rigaku D/Max-2500 PC diffractometer with MoKα radiation (λ = 0.71073 Å) in the 2θ range of 5~50° at room temperature. IR spectra were carried out on a FTIR-8400s spectrometer in the range of 4000~400 cm^-1 in KBr pellets. TG curves were recorded from 25 to 800 ℃ (heating rate of 10 ℃·min^-1) on a METTLER TGA analyzer under nitrogen atmosphere. Luminescence experiments were recorded at 25 ℃ on an F-2700 fluorescence spectrophotometer. UV-vis spectroscopy measurements were performed on a Pgeneral TU-1901 in the range of 200~750 nm.

  2.2 Synthesis of CPs

  2.2.1   Synthesis of {[ZnH₂L(4,4΄-bibp)]·H₂O}_n (1)

  A mixture of H₄L (1.8 mg, 0.003 mmol), 4,4΄-bibp (1.7 mg, 0.006 mmol), Zn(NO₃)₂·6H₂O (1.8 mg, 0.006 mmol) and HNO₃ solution (0.1 mL, 0.15 mol·L^-1) was dissolved in 1 mL of H₂O/CH₃CN (1:1), sealed in a glass tube and heated at 130 ℃ for 3000 min. The mixture was naturally cooled to room temperature, and the resulting crystals were obtained by washing with water and filtration (yield: 37%, based on H₄L). Calcd. (%) for C₄₈H₃₀ZnN₆O₁₄: C, 59.87; H, 3.12; N, 8.73. Found (%): C, 59.90; H, 3.11; N, 8.77. IR (KBr pellet, cm^-1): 3410(m), 3130(m), 2355(m), 1733(m), 1700(s), 1560(m), 1518(m), 1350(s), 1249(s), 1115(m), 1062(m), 920(w), 835(w), 760(m), 655(m), 570(w), 540(w).

  2.2.2   Synthesis of {[CdL_0.5(1,4-bimb)_0.5(H₂O)]·EtOH}_n (2)

  H₄L (3.0 mg, 0.005 mmol), 1,4-bimb (0.006 mmol, 1.4 mg), Cd(NO₃)₂·4H₂O (0.010 mmol, 3.1 mg), H₂O/DMF/EtOH (1 mL, 2:1:1) and HNO₃ aqueous solution (0.1 mL, 0.15 mol·L^-1) were mixed and placed in a glass tube and heated at 105 ℃ for 3000 min. After that, the mixture was cooled naturally to room temperature, and the resulting crystals were collected by washing with water and filtering (Yield: 28%, based on H₄L). Calcd. (%) for C₂₄H₂₀CdN₃O₈: C, 48.74; H, 3.39; N, 7.11. Found (%): C, 48.66; H, 3.30; N, 7.06. IR (KBr pellet, cm^-1): 3539(w), 1684(m), 1656(m), 1560(s), 1518(m), 1344(m), 1250(w), 1110(w), 769(w), 739(w), 655(w), 613(w), 570(w).

  2.3 X-ray crystallography

  The structural data of 1 and 2 were collected using a Bruker Apex Ⅱ diffractometer using Mo-Kα radiation (λ = 0.71073 Å) at 100 (K). Absorption corrections were carried out using the multiple techniques. The structure was solved by direct methods with SHELXL program and refined by full-matrix least-squares on F² using the SHELXL packages^[31]. The non-hydrogen atoms were refined with anisotropic thermal parameters, and the hydrogen atoms were included in geometric positions. Crystallographic data and structure refinement details are given in Table 1. The selected bond lengths and bond angles of 1 and 2 are summarized in Table S1. The topology of CPs was analyzed by TOPOS 4.0^[32].

  Table 1

  

  Table 1.  Crystallographic Data of Complexes 1 and 2

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  Complex	1	2
  Empirical formula	C48H30ZnN6O14	C24H20CdN3O8
  Formula weight	980.12	590.83
  Temperature/K	100	100
  Crystal system	Monoclinic	Triclinic
  Space group	P21/c	$P \overline 1 $
  a (Å)	8.4560(4)	8.2437(4)
  b (Å)	15.1883(7)	10.3267(6)
  c (Å)	32.9959(15)	13.4783(6)
  α (°)	90	92.10
  β (°)	90.8470(10)	91.11
  γ (°)	90	109.4580(10)
  V (Å3)	4237.3(3)	1080.54(10)
  Z	4	2
  ρ (g·cm–3)	1.480	1.816
  μ/mm–1	0.655	1.071
  F(000)	1928.0	594.0
  θ range for data collection (°)	3.004 to 26.343	3.598 to 26.34
  Independent reflections (Rint)	8664 (0.1006)	4412 (0.0599)
  Data/restraints/parameters	8664/0/606	4412/0/326
  GOOF	1.020	1.059
  R, wR (I > 2σ(I))	0.0520, 0.1137	0.0445, 0.0902
  R, wR (all data)	0.0919, 0.1304	0.0575, 0.0989
  Largest diff. peak/hole (e·Å-3)	0.45/–0.46	1.19/–1.15
  CCDC number	1574250	1574251
  aR = Σ||Fo| – |Fc|/Σ||Fo|, bwR = {[Σw(Fo2 – Fc2)2/Σw(Fo2)2]}1/2

  3. RESULTS AND DISCUSSION

  3.1 Crystal structures

  3.1.1   Crystal structure of {[ZnH₂L(4,4΄-bibp)]·H₂O}_n (1)

  Complex 1 belongs to the monoclinic system with P2₁/c space group. There are one crystallographically independent Zn(Ⅱ) ion, one H₂L^2- ligand, one 4,4΄-bibp and one lattice water in the repeating unit. As exhibited in Fig. 1a, the Zn(Ⅱ) ion is four-coordinated by two O-atoms (O(1), O(4^ⅰ). Symmetry code: ⅰ: –x, 0.5+y, 0.5–z) from two monodentate carboxylate groups of two H₂L^2- ligands (Zn–O(1) = 1.933(2) Å and Zn–O(4^ⅰ) = 1.950(2) Å) and two N atoms (N(3), N(6^ⅱ). Symmetry code: ⅱ: x, 0.5–y, –0.5+z) of two 4,4΄-bibp (Zn–N(3) = 1.995(3) Å and Zn–N(6^ⅱ) = 2.016(2) Å), adopting a distorted tetrahedral coordination geometry.

  Figure 1

  

  Figure 1.  (a) Coordination environment of Zn(Ⅱ) in 1; (b) 2D layer structure of 1; (c) Topology of 1 (All hydrogen atoms are omitted for clarity. Symmetry codes: ⅰ: –x, 0.5+y, 0.5–z; ⅱ: x, 0.5–y, –0.5+z; ⅲ: –x, –0.5+y, 0.5–z)

  DownLoad: Full-Size Img PowerPoint

  The H₄L ligand in 1 is not fully deprotonated and takes a (к¹-к⁰)-(к¹-к⁰)-μ₂ coordination mode, in which both carboxylate groups present the η¹ coordinated mode. The H₂L^2- linkers bridge Zn(Ⅱ) ions to obtain 1D [ZnH₂L]_n chains (Fig. S1), which interconnect with another 1D chain [Zn(4,4΄-bibp)]_n (Fig. S2) formed by 4,4΄-bibp linking with adjacent Zn(Ⅱ) ions to obtain 2D layer structures (Fig. 1b). The 2D layers are further constructed into 3D supramolecular networks by H-bonding interaction (Table S2) between the adjacent 2D layers. Besides, the structure of 1 was strengthened by π···π interactions (Table S3). Topologically, the framework of 1 can be seen as a 2D network with the topology of sql (Fig. 1c).

  3.1.2   Crystal structure of {[ZnH₂L(4,4΄-bibp)]·H₂O}_n (1)

  Complex 2 crystallizes in the triclinic system with space group P$ \overline 1 $. The repeating unit is composed of one Cd(Ⅱ) ion, half a L^4- linker, half a 1,4-bimb, a coordination H₂O and a lattice EtOH. As exhibited in Fig. 2a, Cd(Ⅱ) ions present the same coordination environment, and each Cd(Ⅱ) ion is hexa-coordinated by four carboxylate O-atoms (O(1), O(2), O(4^ⅰ), O(4^ⅱ). Symmetry code: ⅰ: x, –1+y, z; ⅱ: –x, 1–y, 1–z) of three distinct L^4- linkers, one coordination water O-atom (O(1W)), and one N-atom from 1,4-bimb (N(2)), which gives a pseudo-octahedral geometry. The bond lengths of Cd–O vary from 2.279(3) to 2.477(3) Å, and the Cd−N(2) bond length is 2.227(4) Å. The O(1), O(2), O(4^ⅰ) and N(2) atoms occupy the equatorial plane, whereas O1W and O4^ⅱ lie in the axial vertexes and the bond angle of O(1W)–Cd(1)–O(4^ⅱ) is 169.27(9)º.

  Figure 2

  

  Figure 2.  (a) Coordination environment of Cd(Ⅱ) in 2; (b) 2D structure of 2; (c) Topology of 2 (All hydrogen atoms are omitted for clarity. Symmetry codes: ⅰ: x, –1+y, z; ⅱ: –x, 1–y, 1–z; ⅲ: –1–x, 1–y, –z; ⅳ: 1–x, –y, 2–z; ⅴ: x, 1+y, z; ⅵ: –x, –y, 1–z; ⅶ: –1–x, –y, –z; ⅷ: 1+x, y, –1+z)

  DownLoad: Full-Size Img PowerPoint

  In complex 2, four carboxylate groups of the H₄L linker are fully deprotonated and show two coordinated modes: μ₂-η² and η², while the H₄L linker displays the coordinated mode of (κ¹-κ¹)-(κ⁰-κ²)-(κ¹-κ¹)-(κ⁰-κ²)-μ₄. As presented in Fig. 2b, two carboxylate groups connect with two symmetrydependent Cd(Ⅱ) ions to form [Cd₂(COO)₂] SBUs with the Cd···Cd separation of 3.674(5) Å. And L^4- anions connect four [Cd₂(COO)₂] SBUs to construct a complicated 2D [Cd₂L]_n motif (Fig. S3), which expands into a 3D supramolecular network by π···π interaction and H-bonding between the adjacent 2D layers (Table S4 and Table S5). Meanwhile, the auxiliary ligand of 1,4-bimb plays a role of stabilizing the framework.

  Topologically, the network of 2 can be regarded as a 2-nodal (4,6)-c-(3²·4²·5²)(3⁴·4⁴·5⁴·6³)-4,6T26 network by denoting organic linkers and [Cd₂-(COO)₂] SBUs to the 4-c and 6-c nodes, respecttively (Fig. 2c).

  3.2 PXRD, thermogravimetric analysis (TGA) and infrared spectra

  Powder XRD patterns were tested at ambient temperature. As can be seen from Fig. S4, the peak positions of experimental PXRD patterns are consistent with those of the simulated ones, manifesting the high phase purity of CPs 1 and 2. The thermal stability of CPs 1 and 2 was analyzed by TGA. As exhibited in Fig. S5, for 1, the weight loss of 1.75% below 180 ℃ is attributed to the release of one lattice water molecule (calcd. 1.87%), and the framework decomposes above 380 ℃. When the temperature reaches 400 ℃, the organic ligands begin to decompose. The residual weight of 48.02% is attributed to ZnO (calcd. 0.08%) and carbonizing matter containing C, H and N (calcd. 47.94%). For 2, the weight loss of 10.00% belongs to that of one coordinatedH₂O molecules and one lattice EtOH molecule (calcd. 10.83%) in the range of 77 to 250 ℃, and the network begins to collapse at about 380 ℃. The second weight loss of 70.9% in the range of 380~800 ℃ is assigned to the removal of half of H₄L and half of 1,4-bimbligand (calcd.: 70.4%). The residue of 19.5% results from CdO (calcd.: 20.7 %). IR spectra of CPs 1 and 2 are also employed to confirm the characteristic functional groups of ligands in the framework (Fig. S6).

  3.3 Fluorescent property

  3.3.1   Fluorescent sensing of organic solvent molecules and nitroaromatic compounds

  The solid-state fluorescence emission spectra of CPs 1 and 2 and free H₄L ligand were measured under room temperature. As shown in Fig. S7, the free H₄L ligand exhibits a strong emission peak at 475 nm (λ_ex = 350 nm), which can be explained by the π-π* transitions of the benzene rings. The emission spectra of 1 and 2 exhibit strong peaks at 425 nm (λ_ex = 350 nm) and 387 (λ_ex = 320 nm), respectively. Compared with the free H₄L ligand, the emission peaks of CPs show slight blue-shifts (Δ = 50 nm for CP 1 and Δ = 88 nm for CP 2), which can be ascribed to the metal-ligand coordinative interactions.

  Recently, the potential applications of LCPs for the sensing of small organic molecules have attracted a great interest of researchers because of their high sensitivity. Here, fluorescence sensing properties of CPs 1 and 2 for different solvents, including DMF, DMSO, EtOH, CH₃CN, H₂O, N-butylalcohol and nitrobenzene (NB) were carried out. 2 mg complex sample was dispersed in 2 mL diverse solvents by stirring for 30 minutes to form a uniform suspension. As can be seen form Fig. S8 that the order of fluorescence intensity is 1@DMF > 1@EtOH > 1@n-butanol > 1@H₂O > 1@CH₃CN > 1@DMSO > 1@NB, and 2@DMF > 2@CH₃CN > 2@DMSO > 2@EtOH > 2@H₂O > 2@n-butanol > 2@NB. The fluorescence intensity of 1 and 2 suspensions depends on different solvents. Furthermore, the different order of fluorescence intensity of CPs 1 and 2 suspensions may be owing to their structural differences. By structural comparison, complex 1 exhibits a 3D supramolecular network formed by H-bonding interaction between the adjacent 2D layers.

  Both 1 and 2 display the strongest and weakest fluorescent intensity in DMF and NB, respectively. The quenching of NB to CPs΄ fluorescence encouraged us to further explore the potential of 1 and 2 for sensing other nitroaromatic compounds (NACs). Four different NACs were chosen as the analytes, including 4-nitrotoluene (NT), 4-nitrophenol (NP), nitrobenzene (NB) and 4-nitroaniline (NA). Fluorescence titration experiments are carried out under same conditions.

  As shown in Fig. 3, all NACs analytes display different quenching effects for the suspensions of 1 and 2. The quenching percentage (QP) was calculated by the equation^[33-35]: (QP) = (I₀ – I)/I₀ $ \times $100%, in which I₀ and I are the fluorescence intensity of the suspensions without and with the addition of NACs, respectively. When the concentration of NACs in the suspensions is up to 0.05 mM, the QP values are listed in Table 2 and quenching efficiency of 1 and 2 for NACs both are NP > NT > NA > NB. Stern-Volmer (SV) equation can be used to calculate the quenching constants (K_sv)^[36], (I₀/I) = K_sv [A] + 1, and [A] is the molar concentration of analyte. As presented in Fig. 4 and Fig. S9-S15, the SV curves are almost linear at lower concentrations, and the curves show a bend upwards with the concentration increase, which could show the coexistence of static and dynamic quenching^[37]. K_sv values were obtained directly at low concentrations (insets of Fig. 4b, and S9b-S15b) and listed in Table 2. Compared to the previously reported CPs^{[38, 39]}, 1 and 2 have high sensitive detection for some NACs. PXRD patterns of CPs used and the original ones match well (Fig. S4), indicating that CPs΄ framework remains unchanged in the process of sensing NACs. The fluorescence quenching mechanisms of NACs for CPs are contributed to the following aspects: (1) The fluorescence resonance energy transfer (FRET)^[40-42]. The resonance energy transfer significantly depends on whether the emission band of CPs and the absorption band of analyte can overlap. To verify whether RET exists or not, the UV-Vis spectra of all NACs were collected (Fig. S16). The excitation spectra of all NACs overlap partially with the emission spectra of 1 and 2; (2) The interaction (H-bonding) between NACs and the uncoordinated carbonyl O-atoms of the framework is partly responsible for the fluorescence quenching^[43-45].

  Figure 3

  

  Figure 3.  Percentage of fluorescence quenching of different NACs for 1 and 2

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  Table 2

  

  Table 2.  QP Values and K_sv for 1 and 2

  DownLoad: CSV

  CPs	Analyte	QP values	Ksv (M−1)
  1	NT	97.89%	1.70 × 105
  	NP	94.52%	1.12 × 105
  	NA	91.14%	6.11 × 104
  	NB	81.69%	6.03 × 104
  2	NT	97.58%	2.60 × 105
  	NP	91.96%	9.66 × 104
  	NA	91.00%	1.82 × 105
  	NB	77.31%	4.71 × 104

  Figure 4

  

  Figure 4.  (a) Concentration-dependent fluorescence intensities of 1 by the addition of NP in H₂O (1 mM). Inset: Sterne-Volmer plot of I₀/I versus the NP concentration. (b) Quenching efficiency of NP for 1

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  3.3.2   Sensing of the cations

  The high stability of 1 and 2 in various solvents prompted us to record the fluorescent response of CPs 1 and 2 to various metal ions. 2 mg complex sample was dispersed in 2 mL M(NO₃)_n aqueous solutions (1 × 10⁻² mol·L⁻¹, M = Ba²⁺, Pb²⁺, Mg²⁺, K⁺, Na⁺, Ca²⁺, Mn²⁺, Zn²⁺, Cd²⁺, Ni²⁺, Al³⁺, Ag⁺, Co²⁺, Cr³⁺, Fe³⁺) by agitation for 30 mins to obtain a homogeneous suspension. As shown in Figs. 5 and 6, the quenching effect of Fe³⁺ towards CPs΄ fluorescence is very obvious, and other metal ions present the difference of fluorescence intensity compared with the blank aqueous solutions.

  Figure 5

  

  Figure 5.  Fluorescence intensity of 1 in different cationic in H₂O solutions

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  Figure 6

  

  Figure 6.  Fluorescence intensity of 2 in different cationic in H₂O solutions

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  Moreover, to determine the sensitivity, the Fe(NO₃)₃ aqueous solution with the concentrations of 0~0.075 mM was gradually added into the suspension of 1 and 2 (2 mg). As shown in Fig. 7, the fluorescence intensities of CPs are weakened step by step with the addition of Fe(NO₃)₃ solution. The quenching curves can be fitted by the SV equation, and show good linearity at lower concentrations from 0 to 0.02 mM (Fig. S17). K_sv values of Fe³⁺ ion are calculated to be 1.48 × 10² M⁻¹ (1) and 64.4 M⁻¹ (2), which are comparable to other reported luminescent sensors for detecting Fe³⁺ ion^[46]. In addition, as shown in Fig. S18, the luminescence intensity of the suspension decreased to some extent with the addition of Fe³⁺ ions into CPs@H₂O in the presence of other ions, which proves that CPs have excellent anti-interference capability for sensing Fe³⁺ ions. PXRD patterns of CPs after sensing experiments are in line with those of the simulated ones, showing that the frameworks of CPs are unchanged (Fig. S4). Meanwhile, it is obvious that the quenching effect of Fe³⁺ to 1 is superior to that of 2, which may be due to the competition absorption between Fe³⁺ and 1 higher than that between Fe³⁺ and 2. The quenching mechanism of Fe³⁺ ions towards 1 and 2 is owing to electronic transfer from the donors (oxygen atoms of ligand) to acceptors (Fe³⁺) and ligand-to-metal charge transfer (LMCT)^[47]. Furthermore, energy migration is also the partial reason of the fluorescence quenching^[48].

  Figure 7

  

  Figure 7.  Concentration-dependent fluorescence intensities of 1 and 2 by the addition of Fe³⁺ in H₂O solutions

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  4. CONCLUSION

  In summary, based on H₄L and 4,4΄-bibp/1,4-bimb, two new 2D CPs have successfully been obtained and characterized by EA, single-crystal X-ray diffraction, PXRD and IR. Complex 1 is a 3D supramolecular network with the topology of sql, and complex 2 exhibits a 2-nodal (4,6)-c framework with the topology of (3²·4²·5²)(3⁴·4⁴·5⁴·6³)-4,6T26. Fluorescence properties indicated 1 and 2 have high sensitivity and selectivity for the recognition of NACs and Fe³⁺ ion.

  
  ACKNOWLEDGEMENT: The authors gratefully acknowledge the support of innovative research team of inorganic-organic hybrid functional materials in North University of China.
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• 

  Scheme 1  Ligands used in synthesizing 1 and 2

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  Figure 1  (a) Coordination environment of Zn(Ⅱ) in 1; (b) 2D layer structure of 1; (c) Topology of 1 (All hydrogen atoms are omitted for clarity. Symmetry codes: ⅰ: –x, 0.5+y, 0.5–z; ⅱ: x, 0.5–y, –0.5+z; ⅲ: –x, –0.5+y, 0.5–z)

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  Figure 2  (a) Coordination environment of Cd(Ⅱ) in 2; (b) 2D structure of 2; (c) Topology of 2 (All hydrogen atoms are omitted for clarity. Symmetry codes: ⅰ: x, –1+y, z; ⅱ: –x, 1–y, 1–z; ⅲ: –1–x, 1–y, –z; ⅳ: 1–x, –y, 2–z; ⅴ: x, 1+y, z; ⅵ: –x, –y, 1–z; ⅶ: –1–x, –y, –z; ⅷ: 1+x, y, –1+z)

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  Figure 3  Percentage of fluorescence quenching of different NACs for 1 and 2

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  Figure 4  (a) Concentration-dependent fluorescence intensities of 1 by the addition of NP in H₂O (1 mM). Inset: Sterne-Volmer plot of I₀/I versus the NP concentration. (b) Quenching efficiency of NP for 1

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  Figure 5  Fluorescence intensity of 1 in different cationic in H₂O solutions

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  Figure 6  Fluorescence intensity of 2 in different cationic in H₂O solutions

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  Figure 7  Concentration-dependent fluorescence intensities of 1 and 2 by the addition of Fe³⁺ in H₂O solutions

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  Table 1.  Crystallographic Data of Complexes 1 and 2

  Complex	1	2
  Empirical formula	C48H30ZnN6O14	C24H20CdN3O8
  Formula weight	980.12	590.83
  Temperature/K	100	100
  Crystal system	Monoclinic	Triclinic
  Space group	P21/c	$P \overline 1 $
  a (Å)	8.4560(4)	8.2437(4)
  b (Å)	15.1883(7)	10.3267(6)
  c (Å)	32.9959(15)	13.4783(6)
  α (°)	90	92.10
  β (°)	90.8470(10)	91.11
  γ (°)	90	109.4580(10)
  V (Å3)	4237.3(3)	1080.54(10)
  Z	4	2
  ρ (g·cm–3)	1.480	1.816
  μ/mm–1	0.655	1.071
  F(000)	1928.0	594.0
  θ range for data collection (°)	3.004 to 26.343	3.598 to 26.34
  Independent reflections (Rint)	8664 (0.1006)	4412 (0.0599)
  Data/restraints/parameters	8664/0/606	4412/0/326
  GOOF	1.020	1.059
  R, wR (I > 2σ(I))	0.0520, 0.1137	0.0445, 0.0902
  R, wR (all data)	0.0919, 0.1304	0.0575, 0.0989
  Largest diff. peak/hole (e·Å-3)	0.45/–0.46	1.19/–1.15
  CCDC number	1574250	1574251
  aR = Σ||Fo| – |Fc|/Σ||Fo|, bwR = {[Σw(Fo2 – Fc2)2/Σw(Fo2)2]}1/2

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  Table 2.  QP Values and K_sv for 1 and 2

  CPs	Analyte	QP values	Ksv (M−1)
  1	NT	97.89%	1.70 × 105
  	NP	94.52%	1.12 × 105
  	NA	91.14%	6.11 × 104
  	NB	81.69%	6.03 × 104
  2	NT	97.58%	2.60 × 105
  	NP	91.96%	9.66 × 104
  	NA	91.00%	1.82 × 105
  	NB	77.31%	4.71 × 104

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