English

• 0.   Introduction

  In recent decades, with the growth of population, the large‐scale development of human activities such as industry, agriculture, and aquaculture has led to the release of more and more dangerous chemicals, and their potential toxicity and non‐degradability have directly resulted in serious environmental problems^[1-2]. In particular, increasingly prominent water pollution poses a huge threat to the ecological environment and human health^[3].

  Iron ion is one of the necessary trace elements for the human body. It plays an important role in many physiological and pathological processes such as oxygen transport, hemoglobin formation, cell metabolism, and DNA replication^[4]. However, the lack or excess of Fe³⁺ ions in organisms will lead to liver damage^[5], anemia^[6], heart disease^[7], cancer^[8], and other physiological abnormalities. Therefore, effective detection of Fe³⁺ ions is of great importance for human health.

  Ciprofloxacin hydrochloride (CIP) is a thirdgeneration synthetic fluoroquinolone antibiotic, which is one of the most widely used clinical antibiotics in the world because of its minimal side effects. CIP has potent activity against both Gram‐positive and Gram‐negative bacteria and can treat infections caused by single or multiple resistance of bacteria to other antibiotics^[9]. However, more and more studies have shown that CIP can induce DNA damage^[10] and may lead to severe liver damage^[11] and hematuria^[12]. Therefore, the detection of CIP in the water environment is also essential.

  The common detection methods for Fe³⁺ ion and CIP include the atomic absorption method^[13], chromatography^[14], mass spectrometry^[15], atomic fluorescence^[16], etc. But these methods are often cumbersome. Therefore, it is quite necessary to develop or establish analytical techniques and strategies for detecting, monitoring, and removing harmful pollutants in the water environment, which are simple, rapid, and sensitive in operation to reduce the risk of pollution.

  The metal‐organic framework (MOF) is a new type of porous coordination polymer, which is comprised of electron‐donating organic ligands and coupling units (metal ions or metal‐oxygen cluster units) connected by coordination bonds^[17]. Due to its characteristics of low toxicity, porosity, large specific surface area, aperture structure, and functional diversity and tunability, it has been widely used in the fields of gas adsorption^[18], storage^[19], separation^[20], heterogeneous catalysis^[21], luminescence sensing^[22], magnetism^[23], biosensing^[24], and biomedicine^[25]. In particular, the lanthanide metal‐organic frameworks (Ln‐MOFs) material has the luminescence characteristics of π conjugates of organic ligands and lanthanide ions. It has unique advantages in the selective recognition and detection of metal cations and inorganic anions, which have been widely used in environmental science, medicine, life science, and the nuclear industry.

  In this work, different lanthanide metal salts and 3, 5‐bis(3′, 5′‐dicarboxyphenyl)‐1H‐1, 2, 4‐triazole (H₄BDT) as a connector were selected to synthesize four isostructural Ln‐MOFs by the solvothermal method: {[La₃(BDT)₂(HCOO)(H₂O)₅]·0.5H₂O·3DMF}_n (1), {[Ce₃(BDT)₂(HCOO)(H₂O)₅]·3DMF}_n (2), {[Pr₃(BDT)₂(HCOO)(H₂O)₅]·3DMF}_n (3), and {[Nd₃(BDT)₂(HCOO)(H₂O)₅]·3DMF}_n (4). And single‐crystal X‐ray diffraction elemental analyses, FT‐IR, powder X‐ray diffraction (PXRD), N₂ adsorption, and thermogravimetric analysis (TGA) were employed for characterizing the synthesized products. The fluorescence sensing performance of 2 was further discussed, and it was found that 2 showed special sensing and recognition to Fe³⁺ and CIP in aqueous solution.

  1.   Experimental

  1.1   Materials and methods

  The reagents used throughout this work were all commercially available and could be directly used in experimental research without any processing. Among them, organic ligands came from Jinan Henghua Technology Co., Ltd. And four lanthanide metal salts were all from Aladdin Co., Ltd. (Shanghai), and the purity was 99%, AR, CP, and 99.9%, respectively.

  Elemental analyses (C, H, and N) were performed using a Vario EL elemental analyzer. The crystallinity of the Ln‐MOFs synthesized particles was determined by PXRD using a Shimadzu XRD‐7000 X‐ray diffractometer with Cu Kα radiation (λ=0.154 06 nm, U=45 kV, I=40 mA, 2θ=5°‐30°). TGA was performed by a TGA5500 model. N₂ adsorption isotherm was observed by automatic specific surface and porosity analyzer (MicroActive 4.03). Infrared spectra were recorded by a Shimadzu IRAFFINITY‐1S spectrometer in a range of 4 000-500 cm^-1. Fluorescence spectra were recorded by a Hitachi F‐7000 fluorescence spectrophotometer. The UV‐Vis absorption spectrum was recorded by a UV3600PLUS220/230VC type UV‐Vis spectrophotometer of Shimadzu.

  1.2   Synthesis of Ln‐MOFs 1-4

  A mixture of lanthanide metal salts (La(NO₃)₃·6H₂O for 1, Ce(NO₃)₃·6H₂O for 2, PrCl₃·6H₂O for 3, and Nd(NO₃)₃·6H₂O for 4) (0.05 mmol), H₄BDT (0.1 mmol), 4, 4′‐bipyridine (0.05 mmol for 2, 0.1 mmol for 1, 3, 4), DMF (1.5 mL for 2, 2 mL for 1, 3, 4), H₂O (4 mL for 2, 3 mL for 1, 3, 4), HNO₃ (five drops, 10%) was added to a 25 mL Teflon lined stainless steel autoclave. The temperature was gradually increased to 160 ℃ through the operation of the set program and holding 72 h, and then reduced to room temperature at a rate of 3 ℃·h^-1. After filtering the synthesized crystals were fully washed with water and ethanol and naturally dried to obtain crystals.

  The colorless rod‐like crystals of 1 were collected (70% yield based on La). Anal. Calcd. for C₉₂H₉₄N₁₈O₅₃La₆(%): C, 35.26; H, 3.00; N, 8.05. Found(%): C, 35.20; H, 2.85; N, 7.64. FT‐IR (KBr pellet, cm^-1): 3 393(m), 3 054(m), 2 373(w), 2 341(w), 1 640(s), 1 617(s), 1 540(s), 1 114(w), 1 032(w), 926(w), 858(m), 789(s), 757(m), 667(w) (Fig.S1a, Supporting information).

  The colorless rod‐shaped crystals of 2 were collected (65% yield based on Ce). Anal. Calcd. for C₄₆H₄₆N₉O₂₆Ce₃(%): C, 35.37; H, 2.95; N, 8.07. Found(%): C, 35.39; H, 2.83; N, 7.78. FT‐IR (KBr pellet, cm^-1): 3 383(m), 2 343(m), 2 378(m), 1 653(s), 1 636(s), 1 560(s), 1 382(s), 1 116(w), 786(m), 755(m), 684(m), 675(w) (Fig.S1b).

  The green rod‐shaped crystals of 3 were collected (75% yield based on Pr). Anal. Calcd. for C₄₆H₄₆N₉O₂₆Pr₃(%): C, 35.32; H, 2.94; N, 8.06. Found(%): C, 35.68; H, 2.86; N, 7.96. FT‐IR (KBr pellet, cm^-1): 3 432(m), 3 086(m), 2 974(w), 2 347(w), 1 653(s), 1 555(s), 1 433(s), 1 381(s), 1 120(w), 1 026(w), 928(w), 787(s), 755(s), 693(m), 666(w) (Fig.S1c).

  The pink‐purple rod‐like crystals of 4 were collected (75% yield based on Nd). Anal. Calcd. for C₄₆H₄₆N₉O₂₆Nd₃(%): C, 35.10; H, 2.92; N, 8.01. Found(%): C, 35.14; H, 2.87; N, 7.98. FT‐IR (KBr pellets, cm^-1): 3 423(m), 2 378(w), 2 343(w), 1 645(s), 1 636(s), 1 555(s), 1 311(w), 1 124(w), 1 026(w), 928(w), 853(w), 791(m), 755(m), 684(m), 667(w) (Fig.S1d).

  1.3   Structure determination

  Crystallographic data for Ln‐MOFs were harvested on a Bruker D8 Venture′s single crystal diffractometer at 298 K (Mo Kα radiation, λ=0.071 073 nm), corrected for multi‐scan absorption using SADABS, and the analytical data were adjusted by SHELXL′s full‐matrix minimum square method for F ². All non‐ hydrogen atoms were optimized with anisotropic displacement parameters. The hydrogen atoms were refined isotropically on calculated positions using a riding model with their U_iso values constrained to 1.2 times the U_eq of their parent atoms. The solvent molecules are highly disordered, which are supposed to form a hydrogen bond with water molecules have been removed by the SQUEEZE routine in the PLATON software package. Crystallographic data and structure refinement details for 1-4 are shown in Table 1. The bond lengths and bond angles of 1-4 are listed in Table S1.

  Table 1

  

  Table 1.  Crystal data and structure refinement details for 1-4

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  Parameter	1	2	3	4
  Formula	C92H94N18O53La6	C46H46N9O26Ce3	C46H46N9O26Pr3	C46H46N9O26Nd3
  Formula weight	3 131.4	1 560.35	1 562.72	1 572.72
  Crystal system	Monoclinic	Monoclinic	Monoclinic	Monoclinic
  Space group	C2/m	C2/m	C2/m	C2/m
  a / nm	1.588 0(4)	1.586 2(7)	1.592 5(4)	1.577 7(5)
  b / nm	2.042 6(5)	2.039 9(9)	2.039 2(5)	2.025 9(7)
  c / nm	1.702 7(4)	1.699 3(11)	1.705 5(4)	1.693 4(6)
  β / (°)	110.026(3)	110.142(6)	110.171(3)	110.259(5)
  V / nm3	5.189(2)	5.162(5)	5.199(2)	5.078(3)
  Z	2	4	4	4
  Dc / (g·cm-3)	2.005	2.008	1.997	2.058
  Absorption coefficient / mm-1	2.507	2.682	2.847	3.104
  F(000)	2 596	2 588	2 600	2 612
  θ range for data collection / (°)	2.366-25.019	1.693-28.489	2.579-28.445	2.402-25.018
  Reflection collected	13 193	16 282	16 865	11 724
  Independent reflections (Rint)	4 721 (0.019 4)	6 443 (0.027 1)	6 551 (0.020 1)	4 575 (0.055 3)
  Data, restraint, number of parameters	4 721, 66, 343	6 443, 78, 336	6 551, 78, 336	4 575, 78, 336
  GOF on F 2	0.999	1.031	1.077	1.226
  Final R indices [I > 2σ(I)]*	R1=0.036 8, wR2=0.109 0	R1=0.043 9, wR2=0.138 3	R1=0.041 0, wR2=0.120 7	R1=0.067 5, wR2=0.183 4
  R indices (all data)	R1=0.041 9, wR2=0.112 9	R1=0.056 1, wR2=0.153 7	R1=0.047 7, wR2=0.125 8	R1=0.088 4, wR2=0.197 0
  $* R_1=\sum\left(\left|F_{\mathrm{o}}\right|-\left|F_{\mathrm{c}}\right|\right) / \sum\left|F_{\mathrm{o}}\right| ; w R_2=\left[\sum w\left(F_{\mathrm{o}}^2-F_{\mathrm{c}}^2\right)^2 / \sum w\left(F_{\mathrm{o}}^2\right)^2\right]^{1 / 2} .$

  1.4   Luminescence sensing experiments

  The powders of complex 2 (3 mg) were uniformly dispersed in 3 mL of different solutions, treated ultrasonically for a certain period to form a suspension, and stored at room temperature for 3 d for fluorescence measurement. These different solutions included 0.01 mol·L^-1 M(NO₃)_x (M^x+=Zn²⁺, Ag⁺, Pb²⁺, Bi³⁺, Cd²⁺, Co²⁺, Al³⁺, Hg₂²⁺, Ni²⁺, Fe³⁺, Cu²⁺) or drug solutions: amoxicillin (AMX), azithromycin (AZM), trihexyl hydrochloride (TRH), piroxicam (PIX), nitrofurantoin enteric‐coated(NEC), medroxyprogesterone acetate (MA), ribavirin(RBV), chlorpheniramine maleate (CPM), ampicillin(AMP), acetaminophen (ACM), vitamin B1 (VB1), cimetidine (CIM), phenolphthalein (PHPH) metoclopramide (MCPM), CIP.

  2.   Results and discussion

  2.1   Crystal structure of 1-4

  The results of X‐ray single crystal diffraction analysis show that Ln‐MOFs 1-4 belong to the monoclinic crystal system with the space group of C2/m (Table 1). Because the four complexes have the same 3D coordination frameworks, the structure of 1 is described herein as a representative.

  The asymmetric unit of complex 1 contains two crystallographically independent La(Ⅲ) ions, one BDT^4- anion, one HCOO^- anion, and four coordination water molecules (Fig. 1a). La1 lies in a nine‐coordination environment around with seven oxygen atoms (O1, O5, O4a, O7, O8, O3b, and O4b) from five different BDT^4- anions, one oxygen atom (O10) from a water molecule, and one oxygen atom (O9) from an HCOO^- anion. Among them, O3b and O4b, O7 and O8 are chelated, while O1, O4a, O5, and O9 are in a mono‐dentate bridge coordination position. La2 is centered in an eight‐coordinated pattern of four oxygen atoms (O2, O2c, O6c, and O6) from four different BDT^4- anions, four oxygen atoms (O11, O12, O11c, and O13) from four water molecules. The BDT^4- anion adopts a highly coordinated fashion: κ₁κ₁‐κ₁κ₁‐κ₁κ₂‐κ₁κ₁‐μ₇ connecting seven La(Ⅲ) ions (Fig. 1b). Two La1 ions are bridged by the bridging carboxylate oxygen atoms (O4a and O4b), meanwhile, La1 ion is bridged by the bridging carboxylate oxygen atoms (O1 and O5, O2 and O6) with La2 ion, forming a wavy zigzag La2‐La1‐La1‐La2 four‐metal chain (Fig. 2). The adjacent zigzag chains are cross‐peak connected by BDT^4- anions to form 2D layers (Fig. 3). The 2D layers are connected by BDT^4- anions to form 3D porous structures (Fig. 4a).

  Figure 1

  

  Figure 1.  (a) Asymmetric unit of complex 1; (b) Coordination environment of the BDT^4- ligand

  Symmetry codes: b: -x+1, y, -z+1; c: x, -y+1, z; e: -x+1, y, -z; f: -x+1/2, -y+1/2, -z; g: x-1/2, -y+1/2, z

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  Figure 2

  

  Figure 2.  Coordination diagram of La1, La2, and four metal chain unit

  Symmetry codes: a: x+1/2, -y+1/2, z; b: -x+1, y, -z+1; c: x, -y+1, z; h: 3/2-x, 1/2-y, 1-z; i: 3/2-x, -1/2+y, 1-z

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  Figure 3

  

  Figure 3.  Zigzag chain and 2D layer parallel to ab plane of 1

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  Figure 4

  

  Figure 4.  Three‐dimensional structures of 1-4

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  The 3D structures of Ln‐MOFs 2-4 are the same as that of 1 (Fig. 4b‐4d) with the difference in the size of the aperture, which is attributed to the difference in the length of the Ln—O bond and the angle of the O—Ln—O bond. The bond lengths of Ln—O are in a range of 0.237 0(4)‐0.273 8(4) nm (1), 0.234 9(5)‐0.273 7(4) nm (2), 0.234 4(4)‐0.273 9(3) nm (3), and 0.230 6(7)‐0.272 1(7) nm (4), respectively. The scope of O—Ln—O bond angles are in the range of 48.44(11)°‐153.22(19)° (1), 48.80(13)°‐153.4(2)° (2), 49.03(11)°‐153.62(19)° (3), 49.3(2)°‐150.1(3)° (4), respectively. These bond lengths and bond angles conform to the reported ranges of Ln—O bond length and O—Ln—O bond angle^[28]. The bond lengths and bond angles of 1-4 are presented in Table S1‐S4, respectively. In 1-4, with the increase of atomic number from 57 (La) to 60 (Nd), the average Ln—O bond lengths decreased from 0.250 7 to 0.245 8 nm gradually due to the lanthanide contraction effect^[29].

  2.2   PXRD and TGA

  PXRD patterns of complexes 1-4 are shown in Fig.S2. The positions of the main peaks in simulated and experimental patterns were consistent with each other, indicating that 1-4 had good phase purity.

  The TGA curves of complexes 1-4 all showed the slow weight loss and fast weight loss processes (Fig.S3). The first slow weight loss occurred before 500 ℃, mainly due to the loss of solvent molecules and coordination water molecules with 21.36% (Calcd. 20.32%) for 1, 20.79% (Calcd. 19.81%) for 2, 20.7% (Calcd. 19.80%) for 3 and 20.58% (Calcd. 19.66%) for 4. The second rapid weight loss occurred in a range of 500-600 ℃, due to the collapse process of the frameworks.

  2.3   Adsorption properties of 1-4

  The N₂ adsorption‐desorption isotherms of Ln‐MOFs 1-4 at 77.35 K were measured (Fig.S4), which exhibited the type Ⅱ mode of IUPAC taxon species. The adsorption capacity increased rapidly with the increase of pressure in the low‐pressure stage, while the adsorption capacity increased slowly in the middle‐pressure stage. They also showed an obvious H4‐type hysteresis loop which might be due to capillary condensation^[30]. All these results indicate that these complexes are mainly mesoporous structures.

  The Brunauer‐Emmett‐Teller (BET) surface area (S_BET), Langmuir surface area (S_Langmuir), single point adsorption total pore volume of pores less than 99.406 9 nm width at p/p₀=0.98 (V_TOT), t‐plot micropore volume (V_mic), Barret‐Joyner‐Halenda (BJH) adsorption average pore width (D_BJH), and optimum aperture (D_opt) of the four complexes materials are shown in Table S5, respectively. In particular, t‐plot micropore volumes were almost zero for 1-4, which further indicates that all four complexes are mesoporous structures.

  2.4   Luminescent properties of 1-4 in aqueous solution

  The fluorescence spectrum results of Ln‐MOFs 1-4 are shown in Fig. 5 (the measured voltage and slit were 600 V and 5.0 nm, respectively). When the excitation wavelength was 256 nm, the characteristic emission peak of 2 was more prominent at 354 nm and the fluorescence intensity was also relatively high. Therefore, the characteristic peak of complex 2 at 354 nm was selected as the detection peak of fluorescence sensing.

  Figure 5

  

  Figure 5.  Fluorescence intensity of complexes 1-4 in aqueous solution

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  2.5   Fluorescence sensing properties

  2.5.1   Sensing experiments for metal ions

  The luminescence spectra of 2 in different metal cation solutions are shown in Fig. 6a. It was found that the luminescence intensity of 2 was related to the metal cation species. Especially in the Fe³⁺ ion solution, the luminescence intensity was almost completely quenched. Moreover, by changing the concentration of Fe³⁺ at a range of 0-300 μmol·L^-1 (Fig.S4a), it was found that the luminescence intensity of 2 decreased exponentially with the concentration of Fe³⁺ ion (Fig. 6b), and the equation was y=1 225.65e^-x/11.44+ 3 549.18e^-x/482.84-1 599.99 (R²=0.997). Among them, when the concentration was in a range of 0-14 μmol·L^-1, there was a good linear relationship between the Fe³⁺ concentration and the luminescence intensity of 2 (the inset of Fig. 6b): y=69.95x+3 110 (R²=0.996). According to the formula 3σ/k (σ: standard deviation, k: slope), the detection limit was 4.59 μmol·L^-1. It indicates that 2 was expected to be used as a new type of luminescent material for Fe³⁺ ion detection. And the PXRD pattern showed that the structure remained integrated after quenching and recovery (Fig.S2b). It follows that 2 could be served as a stable and recyclable chemical sensing for detecting Fe³⁺ ions.

  Figure 6

  

  Figure 6.  (a) Luminescence spectra of complex 2 in different metal cation solutions; (b) Nonlinear and linear (Inset) relationships for identification of Fe3+ by sensor 2

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  To understand the fluorescence quenching mechanism, we tested the UV‐Vis absorption spectra of 2 in different metal cation solutions (Fig.S5b). It could be seen that only the Fe³⁺ solution had an obvious absorption peak at 300 nm, while other metal ions had no obvious absorption peak here. So the quenching of the fluorescence was caused by the energy competition absorption between Fe³⁺ and organic ligands. At the same time, the detection of fluorescence lifetime was an important means to study the quenching mechanism, so we experimentally determined the fluorescence lifetime of the system before and after complex 2 was quenched by Fe³⁺ (Fig. 7a). It was found that the fluorescence lifetime before and after quenching was the same. The results indicated that static quenching was the main mechanism of fluorescence quenching of complex 2 after adding Fe^{3+ [31]}.

  Figure 7

  

  Figure 7.  (a) Fluorescence emission decay curves of complex 2 and complex 2+Fe³⁺ system; (b) Ion‐selective recognition of Fe³⁺ by 2 in the presence of other metal cations

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  The interference of other metal ions on the identification of Fe³⁺ by sensor 2 is shown in Fig. 7b. 2 shows high selectivity for the identification of Fe³⁺. So it is affirmed that 2 can be used as a luminescence sensor for detecting Fe³⁺ in an aqueous solution.

  2.5.2   Sensing experiments for drug molecules

  By recording the fluorescence spectra of 2 in different drug aqueous solutions, we were surprised to find that 2 exhibited amazing luminescence properties in CIP aqueous solution (Fig. 8a). However, the CIP had no other emission peaks except a weak emission peak at 420 nm (Fig. 8b), indicating that its fluorescence did not interfere complex 2.

  Figure 8

  

  Figure 8.  (a) Fluorescence intensity of 2 in different drug solutions; (b) Comparison of fluorescence spectra of 2 and CIP at room temperature

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  The luminescence intensity of 2 increased gradually with the increasing concentration of CIP (Fig. 9a). There was a good linear relationship between the luminescence intensity of 2 and the concentration of CIP when the concentration was in a range of 1-10 μmol·L^-1, the linear equation was y=3 374.464+417.285x (R²=0.995), and the detection limit was 0.77 μmol·L^-1. The PXRD pattern showed that the structure remained integrated after sensing and recovery (Fig.S2b). It follows that 2 can be used as a stable and recyclable chemical sensing for detecting CIP.

  Figure 9

  

  Figure 9.  (a) Fluorescence spectra of 2 upon the addition of CIP; (b) Linear relationship for sensing CIP by sensor 2

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  The possible mechanism of CIP enhancing the fluorescence of complex 2 was further investigated. Because CIP is a kind of fluoroquinolone antibiotic that possesses β‐diketone moiety composed of its carboxylate and carbonyl, and β‐diketone has the double ketone groups linked with methylene group to produce the chelation with Ce³⁺, CIP can transfer its absorbed energy to Ce³⁺ and sensitize the fluorescence of Ce³⁺, a typical Ce³⁺ emission can be observed after the coordination of CIP with Ce^{3+ [9, 32]}.

  3.   Conclusions

  In summary, four isostructural 3D mesoporous Ln‐MOFs based on H₄BDT have been successfully synthesized. It is confirmed that they have the same structure, high phase purity, and good thermal stability through various characterizations. The fluorescence performance exhibits that 2 can be used as a diversified fluorescent probe to detect Fe³⁺ and ciprofloxacin hydrochloride in an aqueous solution with high sensitivity and selectivity. In addition, the mechanism of fluorescence detection of 2 has been preliminarily discussed. The sensing performance of 2 makes it expected to be further developed as an efficient detection material for water pollutants with application value.

  Supporting information is available at http://www.wjhxxb.cn

  
  Acknowledgments: This work was supported by the National Natural Science Foundation of China (Grant No.22063010). Conflicts of interest: The authors declare no competing financial interest.
  
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  Figure 1  (a) Asymmetric unit of complex 1; (b) Coordination environment of the BDT^4- ligand

  Symmetry codes: b: -x+1, y, -z+1; c: x, -y+1, z; e: -x+1, y, -z; f: -x+1/2, -y+1/2, -z; g: x-1/2, -y+1/2, z

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  Figure 2  Coordination diagram of La1, La2, and four metal chain unit

  Symmetry codes: a: x+1/2, -y+1/2, z; b: -x+1, y, -z+1; c: x, -y+1, z; h: 3/2-x, 1/2-y, 1-z; i: 3/2-x, -1/2+y, 1-z

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  Figure 3  Zigzag chain and 2D layer parallel to ab plane of 1

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  Figure 4  Three‐dimensional structures of 1-4

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  Figure 5  Fluorescence intensity of complexes 1-4 in aqueous solution

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  Figure 6  (a) Luminescence spectra of complex 2 in different metal cation solutions; (b) Nonlinear and linear (Inset) relationships for identification of Fe3+ by sensor 2

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  Figure 7  (a) Fluorescence emission decay curves of complex 2 and complex 2+Fe³⁺ system; (b) Ion‐selective recognition of Fe³⁺ by 2 in the presence of other metal cations

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  Figure 8  (a) Fluorescence intensity of 2 in different drug solutions; (b) Comparison of fluorescence spectra of 2 and CIP at room temperature

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  Figure 9  (a) Fluorescence spectra of 2 upon the addition of CIP; (b) Linear relationship for sensing CIP by sensor 2

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  Table 1.  Crystal data and structure refinement details for 1-4

  Parameter	1	2	3	4
  Formula	C92H94N18O53La6	C46H46N9O26Ce3	C46H46N9O26Pr3	C46H46N9O26Nd3
  Formula weight	3 131.4	1 560.35	1 562.72	1 572.72
  Crystal system	Monoclinic	Monoclinic	Monoclinic	Monoclinic
  Space group	C2/m	C2/m	C2/m	C2/m
  a / nm	1.588 0(4)	1.586 2(7)	1.592 5(4)	1.577 7(5)
  b / nm	2.042 6(5)	2.039 9(9)	2.039 2(5)	2.025 9(7)
  c / nm	1.702 7(4)	1.699 3(11)	1.705 5(4)	1.693 4(6)
  β / (°)	110.026(3)	110.142(6)	110.171(3)	110.259(5)
  V / nm3	5.189(2)	5.162(5)	5.199(2)	5.078(3)
  Z	2	4	4	4
  Dc / (g·cm-3)	2.005	2.008	1.997	2.058
  Absorption coefficient / mm-1	2.507	2.682	2.847	3.104
  F(000)	2 596	2 588	2 600	2 612
  θ range for data collection / (°)	2.366-25.019	1.693-28.489	2.579-28.445	2.402-25.018
  Reflection collected	13 193	16 282	16 865	11 724
  Independent reflections (Rint)	4 721 (0.019 4)	6 443 (0.027 1)	6 551 (0.020 1)	4 575 (0.055 3)
  Data, restraint, number of parameters	4 721, 66, 343	6 443, 78, 336	6 551, 78, 336	4 575, 78, 336
  GOF on F 2	0.999	1.031	1.077	1.226
  Final R indices [I > 2σ(I)]*	R1=0.036 8, wR2=0.109 0	R1=0.043 9, wR2=0.138 3	R1=0.041 0, wR2=0.120 7	R1=0.067 5, wR2=0.183 4
  R indices (all data)	R1=0.041 9, wR2=0.112 9	R1=0.056 1, wR2=0.153 7	R1=0.047 7, wR2=0.125 8	R1=0.088 4, wR2=0.197 0
  $* R_1=\sum\left(\left|F_{\mathrm{o}}\right|-\left|F_{\mathrm{c}}\right|\right) / \sum\left|F_{\mathrm{o}}\right| ; w R_2=\left[\sum w\left(F_{\mathrm{o}}^2-F_{\mathrm{c}}^2\right)^2 / \sum w\left(F_{\mathrm{o}}^2\right)^2\right]^{1 / 2} .$

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