English

• 0.   Introduction

  Metal-organic frameworks (MOFs) have experienced explosive development over the past two decades, driven by the topologically diverse architectures and multifunctional applications in adsorption/separation, catalysis, biomedicine, fluorescence detection, carbon capture, and conversion^[1-8]. It is well known that the rational design of MOFs is fundamentally governed by the synergistic combination of (ⅰ) judiciously selected organic linkers and (ⅱ) precisely engineered inorganic secondary building units (SBUs). This molecular-level control enables predictable construction of frameworks with targeted topologies and customized functionalities through reticular chemistry principles. Flexible carboxylic acids are commonly used as ligands and have good potential in the synthesis of novel structures^[9-13]. For example, Cao reported a dia-topology Zn(Ⅱ)-MOF constructed from tetrakis[4-(carboxyphenyl)oxamethyl]methane acid, where the flexible tetracarboxylate ligand and Zn(Ⅱ) ions assemble into chiral building blocks^[14]. Based on the flexible carboxylate ligands strategy, Bai′s group reported a series of acylamide-functionalized frameworks with high uptake of CO₂^[15-17]. Compared with the flexible ligands, rigid ligands make it easier to predict the structure and construct stable porous structures, such as 1, 3, 5-benzenetricarboxylic acid (H₃BTC) and its derivatives^[18-22]. Due to the advantages of flexible and rigid ligands, the semirigid V-shaped multicarboxylate ligands are receiving increasing attention^[23-28]. Among them, 4, 4′-oxybis(benzoic acid) (H₂L) as a ligand has been reported frequently, considering the following characteristics^[29-34]. Firstly, the ligand architecture features a central O atom bridging two rigid benzene-polycarboxylic moieties, creating a semirigid V-shaped configuration. The unique design combines the geometric predictability of rigid ligands with the adaptive conformational flexibility of fully flexible linkers. Secondly, the multicarboxylate groups have versatile coordination modes to provide diverse structures. Thirdly, the MOFs based on H₂L often have good stability and potential applications in photoluminescence, catalysts, gas sorption, and separation.

  Although H₂L as a ligand has been reported, it still has significance in synthesizing novel crystal structures due to multiple coordination characteristics and mixed ligand strategies. Herein, a novel 3D praseodymium-organic framework [Pr₂(L)₃(H₂O)₅·H₂O]_n (Pr-1) with an unusual broken layer structure built of a rarely observed 4-column rod SBU^[35] has been synthesized and characterized. The photoluminescence sensing properties and antibacterial activities of Pr-1 were investigated. The sensing experiment results showed that Pr-1 exhibited excellent selectivity toward Cd²⁺ ions, while the antibacterial activity results showed that Pr-1 had stronger antibacterial activity against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and Bacillus subtilis (B. subtilis).

  1.   Experimental

  1.1   Materials and methods

  For Pr-1, all chemicals and solvents were obtained as reagent-grade commercial products. Elemental analyses (C, H, N) of Pr-1 were conducted on a Perkin-Elmer 240 C Elemental Analyzer. Fourier-transform infrared (FTIR) spectra of Pr-1 were acquired on a Bruker Vector 22 FT-IR spectrophotometer in a range of 400-4 000 cm^-1 with KBr pellets. At room temperature, the powder X-ray diffraction (PXRD) pattern of the as-synthesized sample of Pr-1 was collected on a Bruker D8 Advance diffractometer (Cu Kα, λ=0.154 18 nm), operating at 40 kV and 40 mA with a 2θ range from 5° to 50°. Thermogravimetric analysis (TGA) of Pr-1 was performed on a SDT 2960 thermal analyzer under flowing N₂ with samples (ca. 10 mg) heated in crucibles from 30 ℃ to 800 ℃. UV-Vis spectra of H₂L and Pr-1 were measured on a Shimadzu UV-2600 spectrophotometer, using BaSO₄ as a reference (Scan range: 200-800 nm). Fluorescence property and luminescence sensing properties were performed on an Edinburgh FLS980 fluorescence spectrometer.

  1.2   Preparation of Pr-1

  H₂L (12.9 mg, 0.05 mmol), orotic acid (7.8 mg, 0.05 mmol) and Pr(NO₃)₃·6H₂O (29.1 mg, 0.067 mmol) were added into a 20 mL pressure-thick glass sample vial, and then DMF/H₂O (8 mL, 1∶5, V/V) was added. The glass sample vial was sealed and heated at 90 ℃ for 72 h in a temperature-controlled oven. After gradually cooling to room temperature, yellow-green crystals of Pr-1 suitable for X-ray diffraction were obtained with a yield of 42% (Amount of ligand substance). Anal. Calcd. for C₄₂H₃₆O₂₁Pr₂(%): C, 43.54; H, 3.13. Found(%): C, 43.62; H, 3.21. IR (KBr): 3 421(s), 1 685(w), 1 596(s), 1 529(s), 1 400(s), 1 306(w), 1 258(s), 1 163(m), 1 101(w), 1 012(w), 883(m), 859(m), 784(m) (Fig.S1, Supporting information).

  1.3   X-ray crystallography

  Single-crystal X-ray diffraction data for Pr-1 were collected at 296(2) K on a Bruker Apex Ⅱ CCD area-detector diffractometer with the Mo Kα radiation source (λ=0.071 073 nm) using the ω-scan technique. The SAINT software package was utilized for data integration and intensity correction, incorporating adjustments for both Lorentz and polarization effects. The crystal structure of Pr-1 was solved by direct methods using SHELXS with the non-hydrogen atoms refined anisotropically on F² by full-matrix least-squares minimization using SHELXL. For hydrogen atoms, they were all positioned geometrically with standard bond distances and refined using a riding model with isotropic displacement parameters. The final formula was calculated as C₄₂H₃₆Pr₂O₂₁ based on the crystallographic data results, TGA, and elemental analysis. Crystallographic parameters, data collection, and refinement details for Pr-1 are presented in Table 1, while selected bond lengths and angles are compiled in Table S1.

  Table 1

  

  Table 1.  Crystallographic data for Pr-1

  下载: 导出CSV

  Parameter	Pr-1		Parameter	Pr-1
  Formula	C42H36Pr2O21		Dc / (g·cm-3)	1.907
  Formula weight	1 158.53		μ / mm-1	2.477
  Crystal system	Monoclinic		F(000)	2 296
  Space group	P2/n		Number of unique reflections	8 474
  a / nm	2.340 7(6)		Number of observed reflections [I > 2σ(I)]	9 182
  b / nm	0.599 5(2)		Number of parameters	595
  c / nm	2.937 7(9)		GOF	1.048
  β / (°)	101.741(8)		Final R indices [I > 2σ(I)]*	R1=0.028 7, wR2=0.071 7
  V / nm3	4.036(2)		R indices (all data)	R1=0.031 5, wR2=0.073 5
  Z	4		Largest difference peak and hole / (e·nm-3)	593 and -628
  * ${R_1} = \sum | |{F_{\rm{o}}}| - |{F_{\rm{c}}}||/\sum | {F_{\rm{o}}}|, w{R_2} = \left[ {\sum w {{\left({F_{\rm{o}}^2 - F_{\rm{c}}^2} \right)}^2}} \right]/\sum w {\left({F_{\rm{o}}^2} \right)^2}{]^{1/2}}.$

  1.4   Topological analysis of crystal net

  Systre^[36] program and CrystalMaker X software were used to identify the underlying net^[37] of Pr-1 and to generate the crystal net file (.cgd). The ToposPro^[38] program was used for computing point symbol and vertex symbol^[39] using the.cgd file. The RCSR (Reticular Chemistry Structure Resource)^[40] and Topcryst (The Samara Topological Data Center)^[41] online databases can be used for searching nets and checking their occurrences in crystal structures.

  2.   Results and discussion

  2.1   Crystal structure and underlying net of Pr-1

  According to the result of single-crystal X-ray diffraction analysis, Pr-1 crystallizes in monoclinic space group P2/n. The asymmetric unit comprises two Pr³⁺ ions, three L^2- ligands, five coordinated H₂O molecules, and one free H₂O molecule. There are two crystallographically independent Pr³⁺ ions, both exhibiting an eight-coordination geometry. As shown in Fig. 1a, Pr1 is coordinated with six O atoms from six L^2- ligands and two O atoms from H₂O molecules, while Pr2 is coordinated with five O atoms from five L^2- ligands and three O atoms from H₂O molecules. Thus, Pr1 links six L^2- ligands and Pr2 links five L^2- ligands. By two carboxyl groups, the adjacent Pr1 and Pr2 can be further linked to form one [Pr₂(CO₂)₉(H₂O)₅] cluster (Fig.S2), in which there is a non-bridging carboxyl group. Along the a-axis direction, two [Pr₂(CO₂)₉(H₂O)₅] clusters link together by two bridging carboxyl groups to form one [Pr₄(CO₂)₁₆(H₂O)₁₀] unit in the arrangement of Pr2-Pr1-Pr1-Pr2, which cannot extend into 1D chain, because of the terminal carboxyl group coordinated with one Pr³⁺ ion (Pr2). Along the b-axis direction, Pr1 and Pr1 link together infinitely by carboxyl groups to form a 1D chain, which is the same as Pr2. Thus, Pr1, Pr2, and carboxyl groups are connected to form a rarely observed 4-column rod SBU^[35] (Fig.S3). Then the adjacent rod SBUs are linked together by L^2- ligands to form a special 3D framework (Fig. 1b).

  Figure 1

  

  Figure 1.  (a) Coordination environment of Pr3+ in Pr-1 with 50% probability thermal ellipsoid; (b) 3D structure of Pr-1; (c) Underlying net of Pr-1, showing parallel 4-column rod SBUs linked through ditopic L^2- as lines, leading to a rare broken layer structure

  Hydrogen atoms have been omitted for clarity; Symmetry codes: ^ⅰ 1/2-x, 1+y, 1/2-z; ^ⅱ 1/2-x, y, 1/2-z; ^ⅲ x, -1+y, z; ^ⅳ 1-x, 1-y, 1-z; ^ⅴ 1/2+x, 1-y, 1/2+z; ^ⅵ 1-x, 2-y, 2-z.

  下载: 全尺寸图片 幻灯片

  According to a consistent approach^{[35, 37, 42]}, to simplify the structure of Pr-1, the 4-column rod SBU is treated by linking the carboxylate-C atoms as the points of extension, giving a 3-periodic net which can be visioned as connected broken layers (Fig. 1c). Most of the rod MOFs contain 1-column rod SBUs, and there are only a few reported multiple-column rod structures^[35]. This rod net is new to both RCSR^[40] and ToposPro^[38] databases, and is named as rn-12 as suggested^[35]. Note that the ToposPro standard representation treated the ditopic L^2- ligand as a 3-connector to give a (3, 3, 9)-c net, which is unreasonable. The crystal net file (.cgd) and the calculated point symbol and vertex symbol for rn-12 are given in the Supporting information for clarity.

  2.2   Coordination pattern and synthesis of Pr-1

  The coordination mode of Pr-1 is centered on the bridging mode of —COO^- to construct a stable 3D MOF. In the asymmetric structural unit of Pr-1, there are three crystallographically independent L^2- ligands with different coordination modes (Fig.S4). Among them, every carboxyl group of L^2- ligands based on O3 and O8 with bridging mode connects to two Pr³⁺ ions, which promotes the extension of the 1D belt structure. While the ligand where O16 is located has a carboxyl group connecting two Pr³⁺ ions, and the other carboxyl group matches only one Pr³⁺ ion, which leads to the inability of the 1D belt structure to form 2D layers. In addition, it should be pointed out that during the synthesis process of Pr-1, orotic acid was added. Although in the final crystal structure orotic acid doesn′t exist, it is important. Because if orotic acid is not added, no crystals will be produced. The reason may be that orotic acid serves as a pH regulator or template.

  2.3   Thermal stabilities and PXRD of Pr-1

  For Pr-1, TGA showed that there were two weight loss processes on the TG curve. Below 200 ℃, it is mainly caused by the loss of solvent molecules and coordinated solvent molecules. Thereafter, Pr-1 did not lose weight until 500 ℃, indicating that the framework structure of Pr-1 does not collapse below 500 ℃. After 500 ℃, the framework structure began to collapse (Fig.S5). Thus, Pr-1 has good thermal stability.

  The PXRD pattern of Pr-1 at room temperature is shown in Fig.S6. The experimental PXRD pattern exhibited excellent agreement with the simulated pattern derived from single-crystal data of Pr-1, confirming the phase purity of the as-synthesized sample.

  2.4   Fluorescence property of Pr-1

  Due to the possible application of MOFs based on Pr(Ⅲ) in luminescent sensors, the solid-state fluorescence properties of Pr-1 were investigated at room temperature under ambient conditions. Although the emission peaks of free H₂L have been reported^[43-44], to better compare free H₂L with Pr-1, the solid-state excitation and emission spectra of free H₂L have been tested again. Firstly, the excitation wavelengths of free H₂L and Pr-1 were found, and the peaks were about 252 nm (Fig.S6). Then, when the excitation wavelength was 252 nm, the strongest emission peaks for the ligand H₂L and Pr-1 were 396 and 394 nm (Fig. 2), respectively, indicating that the luminescence of Pr-1 mainly comes from the ligand-ligand electronic transition, such as π*→π and π*→n transitions.

  Figure 2

  

  Figure 2.  Fluorescent emission spectra of Pr-1 and H₂L

  下载: 全尺寸图片 幻灯片

  To further research optical properties, the solid-state UV-Vis spectra of H₂L and Pr-1 were tested at room temperature with a wavelength range of 200-800 nm (Fig. 3). As shown in Fig. 3, the absorption wavelength ranges of H₂L and Pr-1 were similar with the strongest peaks both located between 250 and 290 nm, indicating the good light absorption ability in the UV-Vis light region. In addition, compared with H₂L, Pr-1 had two other absorption peaks around 430-485 nm and 590 nm, which may be mainly due to electron transfer between L^2- and Pr³⁺ ions^[48-50].

  Figure 3

  

  Figure 3.  Solid-state UV-Vis absorption spectra of H₂L and Pr-1

  下载: 全尺寸图片 幻灯片

  2.5   Luminescence sensing properties of Pr-1

  Due to the strong photoluminescence, the sensing properties of Pr-1 towards various organic solvents were investigated in detail. Pr-1 samples (10.0 mg) were first introduced into 10.0 mL solvents, methanol (MeOH), ethanol (EtOH), N-methylpyrrolidone (NMP), N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMA), dimethyl sulfoxide (DMSO), and 1, 4-dioxane. The obtained suspensions were sonicated for 30 min, and then the emission spectra of the suspensions were investigated. The results showed that the maximum emission bands were at 403-405 nm and the intensities were different in different solvents (Fig. 4). The solvent-dependent luminescence studies revealed a pronounced solvent effect, with the emission intensity following the order: MeOH > EtOH > NMP > DEF > 1, 4-dioxane > DMA > DMSO > DMF. Thus, in MeOH, the fluorescence intensity was the strongest. Besides, compared with the spectra of solid state, the suspensions of Pr-1 in these solvents exhibited a somewhat red shift, which may be attributed to the luminescence and solvent-ligand physical interactions that modulate energy absorption and transfer efficiency^[51-53].

  Figure 4

  

  Figure 4.  Fluorescence spectra of Pr-1 in different solvents

  下载: 全尺寸图片 幻灯片

  Luminescence sensing toward various metal cations was also investigated. Due to the strong fluorescence intensities in MeOH, we chose MeOH as the solvent. A sample of Pr-1 (3.0 mg) was ground and dispersed into MeOH (3.0 mL) solutions containing 1 mmol·L^-1 M(NO₃)_x (M^x+=Na⁺, Mg²⁺, Al³⁺, Cr³⁺, Mn²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Ag⁺, Cd²⁺, Pb²⁺) to obtain stable suspensions. The results showed that the maximum emission bands of suspensions were at ca. 403 nm with different intensities (Fig. 5). What′s more, the suspension of Pr-1 containing Cd²⁺ ions exhibited a significant quenching effect on the luminescence intensities, while other metal ions only showed small or mild changes. Thus, the results indicate that Pr-1 might be a promising sensor for the detection of targeted Cd²⁺ ions. The luminescence quenching of the emission of Pr-1 may be attributed to energy transfer and competitive absorption of excitation energy^[53].

  Figure 5

  

  Figure 5.  Fluorescent emission spectra of Pr-1 in different metal nitrate solutions

  下载: 全尺寸图片 幻灯片

  2.6   Antibacterial activity of Pr-1

  The antibacterial activities of H₂L and Pr-1 have been tested. The experiments are mainly conducted against one Gram-negative bacterium E. coli, and two Gram-positive bacteria, B. subtilis and S. aureus. The results, as inhibition zone diameter (IZD), are presented in Table 2. Compared with H₂L and Pr(NO₃)₂·6H₂O, Pr-1 had stronger antibacterial activity against E. coli, S. aureus, and B. subtilis under the same conditions, belonging to the broad-spectrum antibacterial.

  Table 2

  

  Table 2.  Antibacterial activities of H₂L, Pr-1, and Pr(NO₃)₂·6H₂O

  下载: 导出CSV

  Compound	Dose / (mg·mL-1)	Inhibition zone diameter / mm
  		E. coli	S. aureus	B. subtilis
  H2L	1	9.0	8.0	8.0
  Pr-1	1	11.0	13.0	10.0
  Pr(NO3)2·6H2O	1	7.0	7.0	9.0

  3.   Conclusions

  In summary, a novel 3D metal-organic framework Pr-1 has been synthesized by H₂L and Pr³⁺ ions, showing a new broken layer net, named as rn-12, built of rarely observed 4-column rod SBUs. The sensing experiments showed that Pr-1 could act as a fluorescent sensor to detect Cd²⁺ with good sensitivity, which supported its potential application in pollution detection. The antibacterial activities showed that Pr-1 had stronger antibacterial activity against E. coli, S. aureus, and B. subtilis, compared with the synthetic materials, indicating the potential of broad-spectrum antibacterial agents.

  
  Acknowledgements: We thank Li Mian (Shantou University) and RCSR (Reticular Chemistry Structure Resource, http://rcsr.net/) for help on the topological analysis of the crystal net. Supporting information is available at http://www.wjhxxb.cn
  
• 1. [1]

     CHAKRABORTY G, PARK I H, MEDISHETTY R, VITTAL J J. Two-dimensional metal-organic framework materials: Synthesis, structures, properties and applications[J]. Chem. Rev., 2021, 121(7):  3751-3891.

  2. [2]

     XU H Q, LI J, LIU L, LIANG F S, HAN Z B. Pore space partitioning MIL-88(Co): Developing robust adsorbents for CO₂/CH₄ separation featured with high CO₂ adsorption and rapid desorption[J]. Inorg. Chem., 2023, 62(33):  13530-13536.

  3. [3]

     CAI G R, YAN P, ZHANG L L, ZHOU H C, JIANG H L. Metal-organic framework-based hierarchically porous materials: Synthesis and applications[J]. Chem. Rev., 2021, 121(20):  12278-12326.

  4. [4]

     TUNINETTI J S, SERRANO M P, THOMAS A H, AZZARONI O, RAFTI M. Shelter for biologically relevant molecules: Photoprotection and enhanced thermal stability of folic acid loaded in a ZIF-8 MOF porous host[J]. Ind. Eng. Chem. Res., 2020, 59(51):  22155-22162.

  5. [5]

     CAAMANO K, HERAS-MOZOS R, CALBO J, CDIAZ J, WAERENBORGH J C, VIEIRA B J C, HERNANDEZ-MUNOZ P, GAVARA R, GIMENEZ-MARQUES M. Exploiting the redox activity of MIL-100(Fe) carrier enables prolonged carvacrol antimicrobial activity[J]. ACS Appl. Mater. Interfaces, 2022, 14(8):  10758-10768.

  6. [6]

     WANG C Y, QIN J C, YANG Y W. Multifunctional metal-organic framework (MOF)-based nanoplatforms for crop protection and growth promotion[J]. J. Agric. Food Chem., 2023, 71(15):  5953-5972.

  7. [7]

     YANG L, WEI F, LIU J M, WANG S. Functional hybrid micro/nanoentities promote agro-food safety inspection[J]. J. Agric. Food Chem., 2021, 69(42):  12402-12417.

  8. [8]

     DING M L, FLAIG R W, JIANG H L, YAGHI O M. Carbon capture and conversion using metal-organic frameworks and MOF-based materials[J]. Chem. Soc. Rev., 2019, 48(10):  2783-2828.

  9. [9]

     DAI F N, DOU J M, HE H Y, ZHAO X L, SUN D F. Self-assembly of metal-organic supramolecules: From a metallamacrocycle and a metal-organic coordination cage to 1D or 2D coordination polymers based on flexible dicarboxylate ligands[J]. Inorg. Chem., 2010, 49(9):  4117-4124.

  10. [10]

      CUI P P, WU J L, ZHAO X L, SUN D, ZHANG L L, GUO J, SUN D F. Two solvent-dependent zinc(Ⅱ) supramolecular isomers: Rare kgd and lonsdaleite network topologies based on a tripodal flexible ligand[J]. Cryst. Growth Des., 2011, 11(12):  5182-5187.

  11. [11]

      CUI P P, DOU J M, SUN D, DAI F N, SUN D F, WU Q Y. Reaction vessel-and concentration-induced supramolecular isomerism in layered lanthanide-organic frameworks[J]. CrystEngComm, 2011, 13:  6968-6971.

  12. [12]

      YU X Y, GU J M, LIU X Y, CHANG Z Y, LIU Y L. Exploring the effect of different secondary building units as Lewis acid sites in MOF materials for the CO₂ cycloaddition reaction[J]. Inorg. Chem., 2023, 62(29):  11518-11527.

  13. [13]

      TSANGARAKIS C, AZMY A, TAMPAXIS C, ZIBOUCHE N, KLONTZAS E, TYLIANAKIS E, FROUDAKIS G E, STERIOTIS T, SPANOPOULOS I, TRIKALITIS P N. Water-stable etb-MOFs for methane and carbon dioxide storage[J]. Inorg. Chem., 2023, 62(14):  5496-5504.

  14. [14]

      GUO Z G, CAO R, WANG X, LI H F, YUAN W B, WANG G J, WU H H, LI J. A multifunctional 3D ferroelectric and NLO-active porous metal-organic framework[J]. J. Am. Chem. Soc., 2009, 131(20):  6894-6895.

  15. [15]

      ZHENG B S, BAI J F, DUAN J G, WOJTAS L, ZAWOROTKO M J. Enhanced CO₂ binding affinity of a high-uptake rht-type metal-organic framework decorated with acylamide groups[J]. J. Am. Chem. Soc., 2011, 133(4):  748-751.

  16. [16]

      ZHANG M X, ZHOU W, PGAM T, FORREST K A, LIU W L, HE Y B, WU H, YILDIRIM T, CHEN B L, SPACE B, PAN Y, ZAWOROTKO M J, BAI J F. Fine tuning of MOF-505 analogues to reduce low-pressure methane uptake and enhance methane working capacity[J]. Angew. Chem.‒Int. Edit., 2017, 56(38):  11426-11430.

  17. [17]

      ZHANG M X, FORREST K A, LIU P H, DANG R, CUI H H, QIN G P, PHAM T, TANG Y F, WANG S. Significantly enhanced carbon dioxide selective adsorption via gradual acylamide truncation in MOFs: Experimental and theoretical research[J]. Inorg. Chem., 2022, 61(49):  19944-19950.

  18. [18]

      FENG L, WANG K Y, DAY G S, RYDER M R, ZHOU H C. Destruction of metal-organic frameworks: Positive and negative aspects of stability and lability[J]. Chem. Rev., 2020, 120(23):  13087-13133.

  19. [19]

      BAI Y, DOU Y B, XIE L H, RUTLEDGE W, LI J R, ZHOU H C. Zr-based metal-organic frameworks: Design, synthesis, structure, and applications[J]. Chem. Soc. Rev., 2016, 45(8):  2327-2367.

  20. [20]

      WANG K C, LI Y P, XIE L H, LI X Y, LI J R. Construction and application of base-stable MOFs: A critical review[J]. Chem. Soc. Rev., 2022, 51(15):  6417-6441.

  21. [21]

      SU R H, SHI W J, ZHANG X Y, HOU L, WANG Y Y. Cu-MOFs with rich open metal and F sites for separation of C₂H₂ from CO₂ and CH₄[J]. Inorg. Chem., 2023, 62(30):  11869-11875.

  22. [22]

      XIE H H, HAN L, TANG S F. Functionalized zirconium organic frameworks as fluorescent probes for the detection of tetracyclines in water and pork[J]. Inorg. Chem., 2022, 61(43):  17322-17329.

  23. [23]

      CHU Q, LIU G X, HUANG Y Q, WANG X F, SUN W Y. Syntheses, structures, and optical properties of novel zinc(Ⅱ) complexes with multicarboxylate and N-donor ligands[J]. Dalton Trans., 2007, (38):  4302-4311.

  24. [24]

      WANG H L, ZHANG D P, SUN D F, CHEN Y T, ZHANG L F, TIAN L J, JIANG J Z, NI Z H. Co(Ⅱ) metal-organic frameworks (MOFs) assembled from asymmetric semirigid multicarboxylate ligands: Synthesis, crystal structures, and magnetic properties[J]. Cryst. Growth Des., 2009, 9(12):  5273-5282.

  25. [25]

      ZHANG X Y, SHI W J, WANG G D, HOU L, WANG Y Y. One Co-MOF with F active sites for separation of C₂H₂ from CO₂, C₂H₄, and CH₄[J]. Inorg. Chem., 2023, 62(40):  16574-16581.

  26. [26]

      ZHANG M M, ZHAO J S, LI S Q, LUO X L, ZHANG S T, SHAO Y Z, ZHU X F. Cu-based metal-organic frameworks characterized by V-shaped ligands and application to efficient separation of C₂H₂/CO₂ and C₂H₂/CH₄[J]. Cryst. Growth Des., 2025, 25(7):  2002-2012.

  27. [27]

      SI C D, ZHANG J B, PAN F F, YAN X, WANG P, XUE D Q, LI X J, LIU J C, YUAN K. Tuning dimensions of complexes through selective in situ reaction, mechanistic insights into Ni(Ⅱ)-catalyzed Br-OH exchange, magnetic properties, and density functional theory studies[J]. Inorg. Chem., 2022, 61(49):  20159-20168.

  28. [28]

      GAO X J, WU T T, GE F Y, LEI M Y, ZHENG H G. Regulation of chirality in metal-organic frameworks (MOFs) based on achiral precursors through substituent modification[J]. Inorg. Chem., 2022, 61(46):  18335-18339.

  29. [29]

      TAO J, SHI J X, TONG M L, ZHANG X X, CHEN X M. A new inorganic-organic photoluminescent material constructed with helical[Zn₃(μ₃-OH)(μ₂-OH)] chain[J]. Inorg. Chem., 2001, 40(24):  6328-6330.

  30. [30]

      CHENG X N, ZHANG W X, CHEN X M. Metal ion modulation of polycatenation networks constructed by mixed rigid and flexible bridging ligands[J]. CrystEngComm, 2011, 13:  6613-6615.

  31. [31]

      MAHATA P, DRAZNIEKS C M, ROY P, NATARAJAN S. Solid state and solution mediated multistep sequential transformations in metal-organic coordination networks[J]. Cryst. Growth Des., 2013, 13(1):  155-168.

  32. [32]

      MASOOMI M Y, BAGHERI M, MORSALI A. Application of two cobalt-based metal-organic frameworks as oxidative desulfurization catalysts[J]. Inorg. Chem., 2015, 54(23):  11269-11275.

  33. [33]

      HU F L, MI Y, ZHU C, ABRAHAMS B F, BRAUNSTEIN P, LANG J P. Stereoselective solid-state synthesis of substituted cyclobutanes assisted by pseudorotaxane-like MOFs[J]. Angew. Chem.‒Int. Edit., 2018, 57(39):  12696-12701.

  34. [34]

      GOSCH J, VENTURI D M, GRAPE E S, ATZORI C, DONA L, STEINKE F, OTTO T, TJARDTS T, CIVALLERI B, LOMACHENKO K A, INGE A K, COSTANTINO F, STOCK N. Synthesis, crystal structure, and photocatalytic properties of two isoreticular Ce􀃯-MOFs with an infinite rod-shaped inorganic building unit[J]. Inorg. Chem., 2023, 62(13):  5176-5185.

  35. [35]

      SCHOEDEL A, LI M, LI D, O'KEEFFE M, YAGHI O M. Structures of metal-organic frameworks with rod secondary building units[J]. Chem. Rev., 2016, 116(19):  12466-12535.

  36. [36]

      DELGADO-FRIEDRICHS O, O'KEEFFE M. Identification of and symmetry computation for crystal nets[J]. Acta Crystallogr. Sect. A, 2003, A59(4):  351-360.

  37. [37]

      LI M, LI D, O'KEEFFE M, YAGHI O M. Topological analysis of metal-organic frameworks with polytopic linkers and/or multiple building units and the minimal transitivity principle[J]. Chem. Rev., 2014, 114(2):  1343-1370.

  38. [38]

      BLATOV V A, SHEVCHENKO A P, PROSERPIO D M. Applied topological analysis of crystal structures with the program package ToposPro[J]. Cryst. Growth Des., 2014, 14(7):  3576-3586.

  39. [39]

      BLATOV V A, O'KEEFFE M, PROSERPIO D M. Vertex-, face-, point-, Schläfli-, and delaney-symbols in nets, polyhedra and tilings: Recommended terminology[J]. CrystEngComm, 2010, 12:  44-48.

  40. [40]

      O'KEEFFE M, PESKOV M A, RAMSDEN S J, YAGHI O M. The reticular chemistry structure resource (RCSR) database of, and symbols for, crystal nets[J]. Accounts Chem. Res., 2008, 41(12):  1782-1789.

  41. [41]

      SHEVCHENKO A P, SHABALIN A A, KARPUKHIN I Y, BLATOV V A. Topological representations of crystal structures: Generation, analysis and implementation in the TopCryst system[J]. Sci. Technol. Adv. Mater. Methods, 2022, 2(1):  250-265.

  42. [42]

      O'KEEFFE M, YAGHI O M. Deconstructing the crystal structures of metal-organic frameworks and related materials into their underlying nets[J]. Chem. Rev., 2012, 112(2):  675-702.

  43. [43]

      TRIPATHI S, SACHAN S K, ANANTHARAMAN G. Crystal engineering of zinc and cadmium coordination polymers via a mixed-ligand strategy regulated by aromatic rigid/flexible dicarboxylate ancillary ligands and metal ionic radii: Tuning structure, dimension and photoluminescence properties[J]. Polyhedron, 2016, 119(24):  55-70.

  44. [44]

      SHI Z Q, LI Y Z, GUO Z J, ZHENG H G. Six new 2D or 3D metal-organic frameworks based on bithiophene-containing ligand and dicarboxylates: Syntheses, structures, and properties[J]. Cryst. Growth Des., 2013, 13(7):  3078-3086.

  45. [45]

      MAWAI K, NATHANI S, ROY P, SINGH U P, GHOSH K. Combined experimental and theoretical studies on selective sensing of zinc and pyrophosphate ions by rational design of compartmental chemosensor probe: Dual sensing behaviour via secondary recognition approach and cell imaging studies[J]. Dalton Trans., 2018, 47(18):  6421-6434.

  46. [46]

      崔培培, 孙悦, 查奕, 刘圣楠, 张梦欣, 曹际云, 王琦, 王晓晴. 二羧酸配体配位聚合物的合成、结构表征和荧光性质[J]. 无机化学学报, 2023,39,(12): 2358-2366. CUI P P, SUN Y, ZHA Y, LIU S N, ZHANG M X, CAO J Y, WANG Q, WANG X Q. Synthesis, structural characterization, and fluorescence property of three coordination polymers with dicarboxylate ligands[J]. Chinese J. Inorg. Chem., 2023, 39(12):  2358-2366.

  47. [47]

      CHAKI N K, MANDAL S, REBER A C, QIAN M, SAAVEDRA H M, WEISS P S, KHANNA S N, SEN A. Controlling band gap energies in cluster-assembled ionic solids through internal electric fields[J]. ACS Nano, 2010, 4(10):  5813-5818.

  48. [48]

      LI F F, ZHU M L, LU L P, WANG A. A novel monocapped square-antiprismatic Ba(Ⅱ) coordination polymer: A design for dual-responsive fluorescent chemosensor for Cr₂O₇^2- and Fe(Ⅲ)[J]. J. Solid State Chem., 2020, 290:  121582.

  49. [49]

      SHI Y, QU X L, LU Q L, ZHAO J, MA Q C, SUN W, OUYANG G X, FU W, TAO X Y, HUANG D S. Stable lanthanide-organic frameworks: Crystal structure, photoluminescence, and chemical sensing of vanillylmandelic acid as a biomarker of pheochromocytoma[J]. Inorg. Chem., 2023, 62(18):  6934-6947.

  50. [50]

      JIANG Q J, LIN J Y, HU Z J, HSIAO V K S, CHUNG M Y, WU J Y. Luminescent zinc(Ⅱ) coordination polymers of bis(pyridin-4-yl)benzothiadiazole and aromatic polycarboxylates for highly selective detection of Fe(Ⅲ) and high-valent oxyanions[J]. Cryst. Growth Des., 2021, 21(4):  2056-2067.

  51. [51]

      LIU W, CUI H L, ZHOU J, SU Z T, ZHANG Y Z, CHEN X L, YUE E L. Synthesis of a Cd-MOF fluorescence sensor and its detection of Fe³⁺, fluazinam, TNP, and sulfasalazine enteric-coated tablets in aqueous solution[J]. ACS Omega, 2023, 8(27):  24635-24643.

  52. [52]

      YANG Y T, TU C Z, LIU Z N, WANG J L, YANG X L, CHENG F X. 5-Nitro-isophthalic acid based Co(Ⅱ)-coordination polymers: Structural diversity tuned by imidazolyl ligands, efficient dye degradation and luminescence sensing[J]. Polyhedron, 2021, 206(15):  115339.

  53. [53]

      LI Y W, LI J, WAN X Y, SHENG D F, YAN H, ZHANG S S, MA H Y, WANG S N, LI D C, GAO Z Y, DOU J M, SUN D. Nanocage-based N-rich metal-organic framework for luminescence sensing toward Fe³⁺ and Cu²⁺ ions[J]. Inorg. Chem., 2021, 60(2):  671-681.

• 

  Figure 1  (a) Coordination environment of Pr3+ in Pr-1 with 50% probability thermal ellipsoid; (b) 3D structure of Pr-1; (c) Underlying net of Pr-1, showing parallel 4-column rod SBUs linked through ditopic L^2- as lines, leading to a rare broken layer structure

  Hydrogen atoms have been omitted for clarity; Symmetry codes: ^ⅰ 1/2-x, 1+y, 1/2-z; ^ⅱ 1/2-x, y, 1/2-z; ^ⅲ x, -1+y, z; ^ⅳ 1-x, 1-y, 1-z; ^ⅴ 1/2+x, 1-y, 1/2+z; ^ⅵ 1-x, 2-y, 2-z.

  下载: 全尺寸图片 幻灯片
  

  Figure 2  Fluorescent emission spectra of Pr-1 and H₂L

  下载: 全尺寸图片 幻灯片
  

  Figure 3  Solid-state UV-Vis absorption spectra of H₂L and Pr-1

  下载: 全尺寸图片 幻灯片
  

  Figure 4  Fluorescence spectra of Pr-1 in different solvents

  下载: 全尺寸图片 幻灯片
  

  Figure 5  Fluorescent emission spectra of Pr-1 in different metal nitrate solutions

  下载: 全尺寸图片 幻灯片

  Table 1.  Crystallographic data for Pr-1

  Parameter	Pr-1		Parameter	Pr-1
  Formula	C42H36Pr2O21		Dc / (g·cm-3)	1.907
  Formula weight	1 158.53		μ / mm-1	2.477
  Crystal system	Monoclinic		F(000)	2 296
  Space group	P2/n		Number of unique reflections	8 474
  a / nm	2.340 7(6)		Number of observed reflections [I > 2σ(I)]	9 182
  b / nm	0.599 5(2)		Number of parameters	595
  c / nm	2.937 7(9)		GOF	1.048
  β / (°)	101.741(8)		Final R indices [I > 2σ(I)]*	R1=0.028 7, wR2=0.071 7
  V / nm3	4.036(2)		R indices (all data)	R1=0.031 5, wR2=0.073 5
  Z	4		Largest difference peak and hole / (e·nm-3)	593 and -628
  * ${R_1} = \sum | |{F_{\rm{o}}}| - |{F_{\rm{c}}}||/\sum | {F_{\rm{o}}}|, w{R_2} = \left[ {\sum w {{\left({F_{\rm{o}}^2 - F_{\rm{c}}^2} \right)}^2}} \right]/\sum w {\left({F_{\rm{o}}^2} \right)^2}{]^{1/2}}.$

  下载: 导出CSV

  Table 2.  Antibacterial activities of H₂L, Pr-1, and Pr(NO₃)₂·6H₂O

  Compound	Dose / (mg·mL-1)	Inhibition zone diameter / mm
  		E. coli	S. aureus	B. subtilis
  H2L	1	9.0	8.0	8.0
  Pr-1	1	11.0	13.0	10.0
  Pr(NO3)2·6H2O	1	7.0	7.0	9.0

  下载: 导出CSV
•