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A Tb-calixarene coordination chain for luminescent sensing of Fe3+, Cr2O72− and 2,4-DNT
Polyhedron 163 (2019) 84–90
Contents lists available at ScienceDirect
Polyhedron journal homepage: www.elsevier.com/locate/poly
A Tb-calixarene coordination chain for luminescent sensing of Fe3+, Cr2O27 and 2,4-DNT Haitao Han a,b, Guoshuai Zhang a, Kaiyue Li a, Wuping Liao a,b,⇑ a State Key Laboratory of Rare Earth Resource Utilization, ERC for the Separation and Purification of REs and Thorium, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China b University of Chinese Academy of Sciences, Beijing 100049, China
a r t i c l e
i n f o
Article history: Received 4 January 2019 Accepted 27 January 2019 Available online 13 February 2019 Keywords: Terbium Calixarenes Coordination compounds Luminescent sensor Solvothermal synthesis
a b s t r a c t A terbium coordination chain {Tb4(OH)3(TC4A)2(CH3OH)2(DMF)2(HCOO)} (CIAC-239; H4TC4A = p-tertbutylthiacalix[4]arene) was synthesized under solvothermal conditions for the luminescent study. It is featured with some sandwich-like Tb4-(TC4A)2 units which are bridged by some formate ions into the chains. As a luminescent sensor, CIAC-239 can selectively sense Fe3+ and Cr2O27 in aqueous solutions and nitroaromatic reagents in a DMF solution by the luminescence quenching effect of these ions and reagents. Ó 2019 Elsevier Ltd. All rights reserved.
1. Introduction The lanthanide-based coordination compounds are some promising functional materials due to their excellent luminescent [1,2], magnetic [3], catalytic [4,5] properties and so on. They can act as the fluorescent sensors by the interaction between their host frameworks and the detected cations [2,6,7], anions [8], and small molecules [9], or the response to the changing pH value [10] and temperature [11]. Iron is one of the most necessary elements for humans and living organisms [6,7]. The lack or overload of iron may lead to various physiological disorders. On the other hand, chromium is a nonbiodegradable pollutant and serious environmental pollution would be caused by the improper disposal of its compounds or products [6,12,13]. Therefore, the sensitive and selective detection of these elements especially their ionic forms such as Fe3+ and Cr2O27 is of great importance. Up to now, the detection of these ions by the lanthanide coordination compounds are commonly investigated in some nonaqueous-solutions and the studies in water systems are rarely reported [14]. It is still a challenge to obtain some stable luminescent lanthanide coordination compounds for the detection of these ions in aqueous solutions. Furthermore, the detection of nitroaromatic compounds (NACs) ⇑ Corresponding author at: State Key Laboratory of Rare Earth Resource Utilization, ERC for the Separation and Purification of REs and Thorium, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China. Fax: +86 431 85262762. E-mail address: [email protected] (W. Liao). https://doi.org/10.1016/j.poly.2019.01.067 0277-5387/Ó 2019 Elsevier Ltd. All rights reserved.
such as NB, 2,4-DNT, and TNP is also important because the leakage of NACs would lead to some respiratory diseases, anemia, methemoglobinemia and other severe health problems [15]. However, most reported lanthanide compounds have been employed for the explosive detection, and there are very few compounds that can be used for the selective detection of 2,4-DNT [16,17]. Thus, it is urgent to develop some fluorescence probes that can discriminate Fe3+, Cr2O27 and 2,4-DNT efficiently. To construct desired luminescent lanthanide materials, the rigid ligands are widely studied [18]. Among them, calixarenes are reported to be a kind of effective multidentate ligands [19–21]. Here we present a stable 1D TbIII chain of p-tert-butylthiacalix[4] arene (CIAC-239) obtained by a solvothermal synthesis. Luminescence studies showed that CIAC-239 has excellent fluorescence sensing on Fe3+, Cr2O27 , and 2,4-DNT. 2. Experimental 2.1. Materials and general methods Starting materials and solvents were obtained from commercial sources and used without further purification. p-tert-Butylthiacalix [4]arene (H4TC4A) was prepared by the literature methods [22]. Elemental analysis of C, H, and N was performed using a VarioEL instrument. Powder X-ray diffraction (XRD) patterns were recorded on a Bruker D8 Advance diffractometer. Thermogravimetric analyse (TGA) was performed on a Perkin-Elmer Thermal Ana-
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Table 1 Crystal data and structure refinement for compound CIAC-239. Formula Formula wt Crystal system space group Unit cell dimensions a (Å) b (Å) c (Å) a (°) b (°) c (°) V(Å3) Z Dcalc (g cm 3) l (mm 1) F(0 0 0) Total data Unique data GOF R1a [I > 2r(I)] wR2b (all data) a b
C89H114N2O17S8Tb4 2375.98 monoclinic C2/c 39.454(3) 13.0993(12) 22.873(2) 90 115.384(8) 90 10680.1(17) 4 1.478 14.687 4744 4532 2987 0.924 0.0808 0.2182
R1 = R||Fo| |Fc||/R|Fo|. wR2 = {R[w(Fo2-Fc2)2]/R[w(Fo2)2]}1/2.
Fig. 1. A sandwich-like Tb4-(TC4A)2 SBU (left) and a chain formed by linking these SBUs with formate ions in CIAC-239. Symmetry code: (a) 1 x, 1 y, 1 z.
lyzer under air atmosphere at a heating rate of 5 °Cmin 1. The photoluminescence (PL) excitation and emission spectra were recorded with a Hitachi F-7000 spectrophotometer with a 150 W xenon lamp as the excitation source. The luminescence decay lifetimes were measured using a Lecroy Wave Runner 6100 digital osilloscope (1 GHz) with a tunable laser (pulse width = 4 ns; gate = 50 ns) as the excitation source (Contimuum Sunlite OPO).
Fig. 3. (a) Solid-state emission spectra for CIAC-239 excited at 291 nm; (b) Emission decay curve of CIAC-239 monitored at 549 nm. The solid line represents the best fit to the data using a single-exponential function. Inset: CIE chromaticity diagram for CIAC-239 and the corresponding photographs under a UV light of k = 356 nm (x = 0.26, y = 0.59).
Fig. 2. Extended structure of CIAC-239 viewed along the c axis.
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Tb(CH3COO)36H2O (0.04 g, 0.09 mmol), CH3OH/DMF (3 ml/3 ml), triethylamine (0.1 ml) in a 20 ml Teflon-lined autoclave which was kept at 130 °C for 3 days and then slowly cooled to room temperature at about 4 °C h 1. The crystals were isolated by filtration and washed with methanol and dried in air. Yield: ca. 41% with respect to H4TC4A. Elemental Analysis (%): Calc. for C89H114N2O17S8Tb4 (excluding the disordered solvents): C, 44.95; N, 1.18; H, 4.80. Found: C, 45.32; N, 1.26; H, 4.71. FT-IR (KBr pellet, cm 1): 3529 (m), 2957(s), 2865(w), 1638(s), 1573(s), 1445(s), 1360(m), 1348 (m), 1297(s), 1253(s), 1093(m), 835(s), 747(s), 675(m), 621(m), 549(W). 2.3. X-ray crystallography
Fig. 4. Luminescence intensity at 549 nm of CAIC-239 in the solutions of different metal cations.
2.2. Preparation of {Tb4(OH)3(TC4A)2(CH3OH)2 (DMF)2(HCOO)} (CIAC239) Colorless block crystals of CIAC-239 were obtained by the reaction of a mixture of H4TC4A (0.05 g, 0.0697 mmol),
The X-ray intensity data for compound CIAC-239 (Table 1) was collected on a Bruker D8 QUEST system with Cu Ka radiation (k = 0.154178 nm) operated at 50 W (50 kv, 1 mA). The crystal structure was solved by means of direct methods and refined employing full-matrix least squares on F2 (SHELXTL-97) [23]. Solvent molecules in this structure cannot be properly modeled, whose contributions were subtracted by the ‘‘SQUEEZE” command as implemented in PLATON [24]. Based on the void_volume/count_electrons results and TG analysis, there might be four CH3OH molecules per formula unit removed by the SQUEEZE process for CIAC-239. That is, the tentative formulae are {Tb4(OH)3(TC4A)2(CH3OH)2(DMF)2 (HCOO)}(CH3OH)4 for CIAC-239. The large wR2 factor of CIAC-239 might be due to the weak high angle diffractions and
Fig. 5. (a) Emission spectra for CIAC-239 excited at 291 nm in aqueous solutions of different concentrations of Fe3+ ions; (b) dependence of the quenching efficiency on the concentration of Fe3+, estimated based on the luminescence of 5D4 ? 7F5 transition at 549 nm.; (c) Ksv curve between I0/I with the concentration of Fe3+; (d) the fitting plot of the quenching efficiency with the increasing concentration of Fe3+ in the low concentration range.
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3. Results and discussion 3.1. Crystal structure of {Tb4(OH)3(TC4A)2(CH3OH)2(DMF)2(HCOO)} (CIAC-239)
Fig. 6. Luminescence intensity at 549 nm of CAIC-239 in the solutions of various anions.
the disorder of p-tert-butyl atoms. Non-hydrogen atoms were refined anisotropically, and hydrogen atoms of the organic ligands were generated theoretically onto the specific atoms and refined isotropically with fixed thermal factors.
Single-crystal X-ray diffraction analysis reveals that compound CIAC-239 crystallizes in the monoclinic system with space group C2/c, which is characterized with some coordination chains as shown in Fig. 1. In an asymmetric unit, there are two independent crystallographic Tb sites, Tb1 and Tb2. Both Tb sites are ninecoordinated by four phenolic oxygen atoms, two sulfur bridges, one l4-OH ion, and one OH ion and one formate ion or one methanol molecule and one DMF molecule. Four adjacent Tb atoms are linked by a l4-OH ion into a planar Tb1–Tb2–Tb1A–Tb2A tetragon which is further capped by two tail-to-tail TC4A molecules into a sandwich-like Tb4-(TC4A)2 secondary building unit (SBU). And then these sandwich-like SBUs are bridged by some formate ions into the chains. It should be noted that the HCOO anions in the structure would come from the decomposition of DMF [25] and its existence was confirmed by FT-IR spectra (Fig. S1) [26]. The protonation levels of central OH were determined by bond valence sum (BVS) calculations (Table S1). The extended structure of CIAC-239 was stacked by these coordination chains in the ab plane through supramolecular interactions (Fig. 2). There would be some CAH p interactions between the phen ring of calixarene molecule and the coordinated DMF molecule of the adjacent Tb4-(TC4A)2 fragments in a same
Fig. 7. (a) Emission spectra for CIAC-239 excited at 291 nm in aqueous solutions of different concentrations of Cr2O27 ions; (b) dependence of the quenching efficiency on the concentration of Cr2O27 , estimated based on the luminescence of 5D4 ? 7F5 transition at 549 nm.; (c) Ksv curve between I0/I with the concentration of Cr2O27 ; (d) the fitting plot of the quenching efficiency with the increasing concentration of Cr2O27 in the low concentration range.
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chain. The product was stable and only the title compound was obtained with different proportions of the feeds. However, if Tb (CH3COO)36H2O was changed to TbCl36H2O, an isolated tetranuclear {Tb4-(TC4A)2} compound will be obtained as the reported [27].
3.2. Luminescent properties
Fig. 8. Luminescence intensity at 549 nm of CAIC-239 in various solvents or 0.1 mol/l concentrations of NB, TNP, 2,4-DNT in DMF solutions.
The luminescent spectra of the as-synthesized samples of CIAC239 are measured at room temperature. The H4TC4A ligand exhibits an emission band at 401 nm (kex = 279 nm), which is probably derived from the p*–p or p*–n transitions (Fig. S2) [28]. Upon excitation of CIAC-239 at 291 nm, as illustrated in Fig. 3, the emission peaks at 494, 549, 589, and 625 nm can be ascribed to the 5D4 ? 7FJ (J = 6, 5, 4, 3) transitions of the TbIII cations. The emission spectra is dominated by the 5D4 ? 7F6 and 5D4 ? 7F5 transitions, which are stronger than the others, leading to a strong green emission output. No sign of the ligand emission indicates that the TC4A ligand processes efficient energy transfer to the TbIII ion. The emission decay curve was monitored within the 5D4 ? 7F5 transition and well fitted with the single-exponential function [I = I0 exp( t/s)]. The luminescence lifetime value is 843 ms, which is comparable to other Tb or Tb/Zn complexes reported [29,30].
Fig. 9. (a) Emission spectra for CIAC-239 excited at 291 nm in DMF solutions of different concentrations of 2,4-DNT; (b) emission spectra for CIAC-239 in DMF solutions of different concentrations of NB; (c) emission spectra for CIAC-239 in DMF solutions of different concentrations of TNP; (d) comparison of the quenching efficiency for these three reagents at 10 mM DMF solution.
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(Fig. 5d), which indicates high sensing sensitivity of CIAC-239 towards Fe3+. 3.4. Sensing of Cr2O27 anion To investigate the effect of the anions on the luminescence of CIAC-239, 3 mg of CIAC-239 was dispersed in 3 ml neutral aqueous solutions of the potassium salt of different anions such as C2O24 , I , IO3 , BrO3 , Cl , CO23 , F , NO3 , SO24 , PO34 and Cr2O27 in a same concentration (0.01 mol L 1), and then the suspensions were ultrasonicated for 10 min before the luminescence analysis. As shown in Fig. 6, the luminescence is quenched obviously by the Cr2O27 anion while the luminescent intensities are slightly enhanced by the addition of other anions. To further explore CIAC-239 as a luminescent probe for Cr2O27 , the Cr2O27 concentration-dependent luminescence of CIAC-239 was studied systematically (Fig. 7a). It is found that the luminescence intensities decrease with the increasing Cr2O27 concentration and the luminescence of CIAC-239 is almost completely quenched when the Cr2O27 concentration reaches 7.5 mmol L 1 (the quenching efficiency is 97.50%). The quenching constant (Ksv) for Cr2O27 is 1.84 103 (Fig. 7c) and the detection limit of CIAC-239 for Cr2O27 is 0.21 mmol L 1 (Fig. 7d). So CIAC-239 also exhibits high sensitivity for the sensing of the Cr2O27 ions (Table S3). 3.5. Detection of small organic molecules
Fig. 10. (a) Ksv curve between I0/I with the concentration of 2,4-DNT; (b) dependence of the quenching efficiency on the concentration of 2,4-DNT in DMF solution, estimated based on the luminescence of 5D4 ? 7F5 transition at 549 nm.
3.3. Sensing of Fe3+ cation The finely ground samples of CIAC-239 (3 mg) were dispersed into the aqueous solutions (3 ml) of 0.01 mol L 1 MClx (M = Na+, K+, Ca2+, Cr3+, Co2+, Cu2+, Mn2+, Ni2+, Zn2+ or Fe3+), which were vigorously agitated by ultrasound for 10 min. As illustrated in Fig. 4, only Fe3+ cation gives a significant fluorescence quenching effect. The unusual selective quenching by Fe3+ prompted us to further study CIAC-239 as a luminescent probe for Fe3+. Therefore, a series of experiments were performed with different Fe3+ concentrations. As shown in Fig. 5a, the fluorescent intensities of CIAC-239 decline sharply with the increasing Fe3+ concentration from 0 to10 mmol L 1. When the Fe3+ concentration is 10 mmol L 1, the quenching efficiency could reach 96.84%, which is comparable to the reported fluorescence sensors for Fe3+ (Table S2). Quantitatively, the quenching efficiency was analyzed by using the Stern-Volmer equation at lower concentrations (0– 0.4 mmol L 1), I0/I = 1 + Ksv[M] (Ksv is the quenching coefficient, and [M] is the Fe3+ concentration). The Ksv value is 2.90 103 calculated from the Stern–Volmer Equation (Fig. 5c). Detailed analysis further reveals that a good linear relationship is achieved with a linear correlation (R = 0.9852) between the quenching efficiency and the amount of Fe3+ in the low concentration range of 0– 0.4 mmol L 1, and the Fe3+ detection limit is calculated to be 0.19 mmol L 1, according to 3r/k (r: standard error; k: slope) [6]
As shown in Fig. 8, the luminescence intensity of CIAC-239 is highly dependent on the solvents. Among all the solvents such as DMF, CH3OH, DMA, acetone, CH3CN, toluene, NMP, CH2Cl2, chlorobenzene, THF and H2O, the suspensions of CIAC-239 in DMF exhibited the highest luminescence intensity. So DMF was chosen as the solvent for the study on the quenching effect of the nitroaromatic compounds nitrobenzene (NB), 2,4-dinitrotoluene (2,4-DNT) and 2,4,6-trinitrophenol (TNP). All these three nitroaromatic compounds exhibit obvious quenching efficiency on the luminescence of CIAC-239. As shown in Fig. 9, the luminescence intensity of CIAC-239 decreases with the increasing concentrations of NB, 2,4-DNT and TNP. Furthermore, the change of luminescence intensity is more sensitive to the concentration of 2,4-DNT than those of NB and TNP. For instance, when the concentration of nitroaromatic compound is 10 mmol L 1, the quenching efficiency of 2,4-DNT reaches 93.05% while those of NB and TNP are only 81.05% and 47.71%, respectively. The quenching efficiency follows the order 2,4DNT > NB > TNP. The Ksv value was calculated to be 602 M 1 for 2,4-DNT (Fig. 10). To investigate the quenching mechanism of Fe3+, Cr2O27 and 2,4-DNT towards CIAC-239, the UV–Vis absorption spectra of the solutions containing different metal cations, anions or nitroaromatic compounds were recorded (Figs. S4–S6). It is found that the wide UV–Vis absorption bands for Fe3+, Cr2O27 , 2,4-DNT and NB overlap the excitation spectrum of CIAC-239, which leads to the luminescence quenching. This mechanism was consistent with those proposed by other groups [31].
4. Conclusions In summary, a Tb-p-tert-butylthiacalix[4]arene chain-like compound was obtained via a solvothermal reaction, which is featured with some sandwich-like Tb4-(TC4A)2 SBUs. The compound exhibits a characteristic emission of Tb3+. The luminescence can be quenched selectively by Fe3+, Cr2O27 , and nitroaromatic reagents such as NB, TNP and 2,4-DNT. Among these three nitroaromatic
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reagents, 2,4-DNT has the highest quenching efficiency. This compound might be a potential multi-responsive luminescent sensor. Acknowledgements This work was supported by the National Natural Science Foundation of China (no. 21571172 and 21521092) and SKLRERU Open Research Fund (RERU2018022). Appendix A. Supplementary data CCDC 1888574 contains the supplementary crystallographic data for CIAC-239. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected]. Supplementary data to this article can be found online at https://doi.org/10.1016/j.poly.2019.01.067. References [1] D.T. Tu, W. Zheng, P. Huang, X.Y. Chen, Coord. Chem. Rev. 378 (2019) 104. [2] Z. Sun, Y.G. Li, Y. Ma, L.C. Li, Dyes Pigm. 146 (2017) 263. [3] F. Pointillart, O. Cador, B. Le Guennic, L. Ouahab, Coord. Chem. Rev. 346 (2017) 150. [4] A. Karmakar, G.M. Rúbio, A. Paul, M.F.C.G. da Silva, K.T. Mahmudov, F.I. Guseinov, S.A.C. Carabineiro, A.J.L. Pombeiro, Dalton Trans. 46 (2017) 8649. [5] Y.P. Wu, G.W. Xu, W.W. Dong, J. Zhao, D.S. Li, J. Zhang, X.H. Bu, Inorg. Chem. 56 (2017) 1402. [6] M. Chen, W.M. Xu, J.Y. Tian, H. Cui, J.X. Zhang, C.S. Liu, M. Du, J. Mater. Chem. C 5 (2017) 2015. [7] S. Dang, E. Ma, Z.M. Sun, H.J. Zhang, J. Mater. Chem. 22 (2012) 16920.
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Contents lists available at ScienceDirect
Polyhedron journal homepage: www.elsevier.com/locate/poly
A Tb-calixarene coordination chain for luminescent sensing of Fe3+, Cr2O27 and 2,4-DNT Haitao Han a,b, Guoshuai Zhang a, Kaiyue Li a, Wuping Liao a,b,⇑ a State Key Laboratory of Rare Earth Resource Utilization, ERC for the Separation and Purification of REs and Thorium, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China b University of Chinese Academy of Sciences, Beijing 100049, China
a r t i c l e
i n f o
Article history: Received 4 January 2019 Accepted 27 January 2019 Available online 13 February 2019 Keywords: Terbium Calixarenes Coordination compounds Luminescent sensor Solvothermal synthesis
a b s t r a c t A terbium coordination chain {Tb4(OH)3(TC4A)2(CH3OH)2(DMF)2(HCOO)} (CIAC-239; H4TC4A = p-tertbutylthiacalix[4]arene) was synthesized under solvothermal conditions for the luminescent study. It is featured with some sandwich-like Tb4-(TC4A)2 units which are bridged by some formate ions into the chains. As a luminescent sensor, CIAC-239 can selectively sense Fe3+ and Cr2O27 in aqueous solutions and nitroaromatic reagents in a DMF solution by the luminescence quenching effect of these ions and reagents. Ó 2019 Elsevier Ltd. All rights reserved.
1. Introduction The lanthanide-based coordination compounds are some promising functional materials due to their excellent luminescent [1,2], magnetic [3], catalytic [4,5] properties and so on. They can act as the fluorescent sensors by the interaction between their host frameworks and the detected cations [2,6,7], anions [8], and small molecules [9], or the response to the changing pH value [10] and temperature [11]. Iron is one of the most necessary elements for humans and living organisms [6,7]. The lack or overload of iron may lead to various physiological disorders. On the other hand, chromium is a nonbiodegradable pollutant and serious environmental pollution would be caused by the improper disposal of its compounds or products [6,12,13]. Therefore, the sensitive and selective detection of these elements especially their ionic forms such as Fe3+ and Cr2O27 is of great importance. Up to now, the detection of these ions by the lanthanide coordination compounds are commonly investigated in some nonaqueous-solutions and the studies in water systems are rarely reported [14]. It is still a challenge to obtain some stable luminescent lanthanide coordination compounds for the detection of these ions in aqueous solutions. Furthermore, the detection of nitroaromatic compounds (NACs) ⇑ Corresponding author at: State Key Laboratory of Rare Earth Resource Utilization, ERC for the Separation and Purification of REs and Thorium, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China. Fax: +86 431 85262762. E-mail address: [email protected] (W. Liao). https://doi.org/10.1016/j.poly.2019.01.067 0277-5387/Ó 2019 Elsevier Ltd. All rights reserved.
such as NB, 2,4-DNT, and TNP is also important because the leakage of NACs would lead to some respiratory diseases, anemia, methemoglobinemia and other severe health problems [15]. However, most reported lanthanide compounds have been employed for the explosive detection, and there are very few compounds that can be used for the selective detection of 2,4-DNT [16,17]. Thus, it is urgent to develop some fluorescence probes that can discriminate Fe3+, Cr2O27 and 2,4-DNT efficiently. To construct desired luminescent lanthanide materials, the rigid ligands are widely studied [18]. Among them, calixarenes are reported to be a kind of effective multidentate ligands [19–21]. Here we present a stable 1D TbIII chain of p-tert-butylthiacalix[4] arene (CIAC-239) obtained by a solvothermal synthesis. Luminescence studies showed that CIAC-239 has excellent fluorescence sensing on Fe3+, Cr2O27 , and 2,4-DNT. 2. Experimental 2.1. Materials and general methods Starting materials and solvents were obtained from commercial sources and used without further purification. p-tert-Butylthiacalix [4]arene (H4TC4A) was prepared by the literature methods [22]. Elemental analysis of C, H, and N was performed using a VarioEL instrument. Powder X-ray diffraction (XRD) patterns were recorded on a Bruker D8 Advance diffractometer. Thermogravimetric analyse (TGA) was performed on a Perkin-Elmer Thermal Ana-
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Table 1 Crystal data and structure refinement for compound CIAC-239. Formula Formula wt Crystal system space group Unit cell dimensions a (Å) b (Å) c (Å) a (°) b (°) c (°) V(Å3) Z Dcalc (g cm 3) l (mm 1) F(0 0 0) Total data Unique data GOF R1a [I > 2r(I)] wR2b (all data) a b
C89H114N2O17S8Tb4 2375.98 monoclinic C2/c 39.454(3) 13.0993(12) 22.873(2) 90 115.384(8) 90 10680.1(17) 4 1.478 14.687 4744 4532 2987 0.924 0.0808 0.2182
R1 = R||Fo| |Fc||/R|Fo|. wR2 = {R[w(Fo2-Fc2)2]/R[w(Fo2)2]}1/2.
Fig. 1. A sandwich-like Tb4-(TC4A)2 SBU (left) and a chain formed by linking these SBUs with formate ions in CIAC-239. Symmetry code: (a) 1 x, 1 y, 1 z.
lyzer under air atmosphere at a heating rate of 5 °Cmin 1. The photoluminescence (PL) excitation and emission spectra were recorded with a Hitachi F-7000 spectrophotometer with a 150 W xenon lamp as the excitation source. The luminescence decay lifetimes were measured using a Lecroy Wave Runner 6100 digital osilloscope (1 GHz) with a tunable laser (pulse width = 4 ns; gate = 50 ns) as the excitation source (Contimuum Sunlite OPO).
Fig. 3. (a) Solid-state emission spectra for CIAC-239 excited at 291 nm; (b) Emission decay curve of CIAC-239 monitored at 549 nm. The solid line represents the best fit to the data using a single-exponential function. Inset: CIE chromaticity diagram for CIAC-239 and the corresponding photographs under a UV light of k = 356 nm (x = 0.26, y = 0.59).
Fig. 2. Extended structure of CIAC-239 viewed along the c axis.
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Tb(CH3COO)36H2O (0.04 g, 0.09 mmol), CH3OH/DMF (3 ml/3 ml), triethylamine (0.1 ml) in a 20 ml Teflon-lined autoclave which was kept at 130 °C for 3 days and then slowly cooled to room temperature at about 4 °C h 1. The crystals were isolated by filtration and washed with methanol and dried in air. Yield: ca. 41% with respect to H4TC4A. Elemental Analysis (%): Calc. for C89H114N2O17S8Tb4 (excluding the disordered solvents): C, 44.95; N, 1.18; H, 4.80. Found: C, 45.32; N, 1.26; H, 4.71. FT-IR (KBr pellet, cm 1): 3529 (m), 2957(s), 2865(w), 1638(s), 1573(s), 1445(s), 1360(m), 1348 (m), 1297(s), 1253(s), 1093(m), 835(s), 747(s), 675(m), 621(m), 549(W). 2.3. X-ray crystallography
Fig. 4. Luminescence intensity at 549 nm of CAIC-239 in the solutions of different metal cations.
2.2. Preparation of {Tb4(OH)3(TC4A)2(CH3OH)2 (DMF)2(HCOO)} (CIAC239) Colorless block crystals of CIAC-239 were obtained by the reaction of a mixture of H4TC4A (0.05 g, 0.0697 mmol),
The X-ray intensity data for compound CIAC-239 (Table 1) was collected on a Bruker D8 QUEST system with Cu Ka radiation (k = 0.154178 nm) operated at 50 W (50 kv, 1 mA). The crystal structure was solved by means of direct methods and refined employing full-matrix least squares on F2 (SHELXTL-97) [23]. Solvent molecules in this structure cannot be properly modeled, whose contributions were subtracted by the ‘‘SQUEEZE” command as implemented in PLATON [24]. Based on the void_volume/count_electrons results and TG analysis, there might be four CH3OH molecules per formula unit removed by the SQUEEZE process for CIAC-239. That is, the tentative formulae are {Tb4(OH)3(TC4A)2(CH3OH)2(DMF)2 (HCOO)}(CH3OH)4 for CIAC-239. The large wR2 factor of CIAC-239 might be due to the weak high angle diffractions and
Fig. 5. (a) Emission spectra for CIAC-239 excited at 291 nm in aqueous solutions of different concentrations of Fe3+ ions; (b) dependence of the quenching efficiency on the concentration of Fe3+, estimated based on the luminescence of 5D4 ? 7F5 transition at 549 nm.; (c) Ksv curve between I0/I with the concentration of Fe3+; (d) the fitting plot of the quenching efficiency with the increasing concentration of Fe3+ in the low concentration range.
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3. Results and discussion 3.1. Crystal structure of {Tb4(OH)3(TC4A)2(CH3OH)2(DMF)2(HCOO)} (CIAC-239)
Fig. 6. Luminescence intensity at 549 nm of CAIC-239 in the solutions of various anions.
the disorder of p-tert-butyl atoms. Non-hydrogen atoms were refined anisotropically, and hydrogen atoms of the organic ligands were generated theoretically onto the specific atoms and refined isotropically with fixed thermal factors.
Single-crystal X-ray diffraction analysis reveals that compound CIAC-239 crystallizes in the monoclinic system with space group C2/c, which is characterized with some coordination chains as shown in Fig. 1. In an asymmetric unit, there are two independent crystallographic Tb sites, Tb1 and Tb2. Both Tb sites are ninecoordinated by four phenolic oxygen atoms, two sulfur bridges, one l4-OH ion, and one OH ion and one formate ion or one methanol molecule and one DMF molecule. Four adjacent Tb atoms are linked by a l4-OH ion into a planar Tb1–Tb2–Tb1A–Tb2A tetragon which is further capped by two tail-to-tail TC4A molecules into a sandwich-like Tb4-(TC4A)2 secondary building unit (SBU). And then these sandwich-like SBUs are bridged by some formate ions into the chains. It should be noted that the HCOO anions in the structure would come from the decomposition of DMF [25] and its existence was confirmed by FT-IR spectra (Fig. S1) [26]. The protonation levels of central OH were determined by bond valence sum (BVS) calculations (Table S1). The extended structure of CIAC-239 was stacked by these coordination chains in the ab plane through supramolecular interactions (Fig. 2). There would be some CAH p interactions between the phen ring of calixarene molecule and the coordinated DMF molecule of the adjacent Tb4-(TC4A)2 fragments in a same
Fig. 7. (a) Emission spectra for CIAC-239 excited at 291 nm in aqueous solutions of different concentrations of Cr2O27 ions; (b) dependence of the quenching efficiency on the concentration of Cr2O27 , estimated based on the luminescence of 5D4 ? 7F5 transition at 549 nm.; (c) Ksv curve between I0/I with the concentration of Cr2O27 ; (d) the fitting plot of the quenching efficiency with the increasing concentration of Cr2O27 in the low concentration range.
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chain. The product was stable and only the title compound was obtained with different proportions of the feeds. However, if Tb (CH3COO)36H2O was changed to TbCl36H2O, an isolated tetranuclear {Tb4-(TC4A)2} compound will be obtained as the reported [27].
3.2. Luminescent properties
Fig. 8. Luminescence intensity at 549 nm of CAIC-239 in various solvents or 0.1 mol/l concentrations of NB, TNP, 2,4-DNT in DMF solutions.
The luminescent spectra of the as-synthesized samples of CIAC239 are measured at room temperature. The H4TC4A ligand exhibits an emission band at 401 nm (kex = 279 nm), which is probably derived from the p*–p or p*–n transitions (Fig. S2) [28]. Upon excitation of CIAC-239 at 291 nm, as illustrated in Fig. 3, the emission peaks at 494, 549, 589, and 625 nm can be ascribed to the 5D4 ? 7FJ (J = 6, 5, 4, 3) transitions of the TbIII cations. The emission spectra is dominated by the 5D4 ? 7F6 and 5D4 ? 7F5 transitions, which are stronger than the others, leading to a strong green emission output. No sign of the ligand emission indicates that the TC4A ligand processes efficient energy transfer to the TbIII ion. The emission decay curve was monitored within the 5D4 ? 7F5 transition and well fitted with the single-exponential function [I = I0 exp( t/s)]. The luminescence lifetime value is 843 ms, which is comparable to other Tb or Tb/Zn complexes reported [29,30].
Fig. 9. (a) Emission spectra for CIAC-239 excited at 291 nm in DMF solutions of different concentrations of 2,4-DNT; (b) emission spectra for CIAC-239 in DMF solutions of different concentrations of NB; (c) emission spectra for CIAC-239 in DMF solutions of different concentrations of TNP; (d) comparison of the quenching efficiency for these three reagents at 10 mM DMF solution.
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(Fig. 5d), which indicates high sensing sensitivity of CIAC-239 towards Fe3+. 3.4. Sensing of Cr2O27 anion To investigate the effect of the anions on the luminescence of CIAC-239, 3 mg of CIAC-239 was dispersed in 3 ml neutral aqueous solutions of the potassium salt of different anions such as C2O24 , I , IO3 , BrO3 , Cl , CO23 , F , NO3 , SO24 , PO34 and Cr2O27 in a same concentration (0.01 mol L 1), and then the suspensions were ultrasonicated for 10 min before the luminescence analysis. As shown in Fig. 6, the luminescence is quenched obviously by the Cr2O27 anion while the luminescent intensities are slightly enhanced by the addition of other anions. To further explore CIAC-239 as a luminescent probe for Cr2O27 , the Cr2O27 concentration-dependent luminescence of CIAC-239 was studied systematically (Fig. 7a). It is found that the luminescence intensities decrease with the increasing Cr2O27 concentration and the luminescence of CIAC-239 is almost completely quenched when the Cr2O27 concentration reaches 7.5 mmol L 1 (the quenching efficiency is 97.50%). The quenching constant (Ksv) for Cr2O27 is 1.84 103 (Fig. 7c) and the detection limit of CIAC-239 for Cr2O27 is 0.21 mmol L 1 (Fig. 7d). So CIAC-239 also exhibits high sensitivity for the sensing of the Cr2O27 ions (Table S3). 3.5. Detection of small organic molecules
Fig. 10. (a) Ksv curve between I0/I with the concentration of 2,4-DNT; (b) dependence of the quenching efficiency on the concentration of 2,4-DNT in DMF solution, estimated based on the luminescence of 5D4 ? 7F5 transition at 549 nm.
3.3. Sensing of Fe3+ cation The finely ground samples of CIAC-239 (3 mg) were dispersed into the aqueous solutions (3 ml) of 0.01 mol L 1 MClx (M = Na+, K+, Ca2+, Cr3+, Co2+, Cu2+, Mn2+, Ni2+, Zn2+ or Fe3+), which were vigorously agitated by ultrasound for 10 min. As illustrated in Fig. 4, only Fe3+ cation gives a significant fluorescence quenching effect. The unusual selective quenching by Fe3+ prompted us to further study CIAC-239 as a luminescent probe for Fe3+. Therefore, a series of experiments were performed with different Fe3+ concentrations. As shown in Fig. 5a, the fluorescent intensities of CIAC-239 decline sharply with the increasing Fe3+ concentration from 0 to10 mmol L 1. When the Fe3+ concentration is 10 mmol L 1, the quenching efficiency could reach 96.84%, which is comparable to the reported fluorescence sensors for Fe3+ (Table S2). Quantitatively, the quenching efficiency was analyzed by using the Stern-Volmer equation at lower concentrations (0– 0.4 mmol L 1), I0/I = 1 + Ksv[M] (Ksv is the quenching coefficient, and [M] is the Fe3+ concentration). The Ksv value is 2.90 103 calculated from the Stern–Volmer Equation (Fig. 5c). Detailed analysis further reveals that a good linear relationship is achieved with a linear correlation (R = 0.9852) between the quenching efficiency and the amount of Fe3+ in the low concentration range of 0– 0.4 mmol L 1, and the Fe3+ detection limit is calculated to be 0.19 mmol L 1, according to 3r/k (r: standard error; k: slope) [6]
As shown in Fig. 8, the luminescence intensity of CIAC-239 is highly dependent on the solvents. Among all the solvents such as DMF, CH3OH, DMA, acetone, CH3CN, toluene, NMP, CH2Cl2, chlorobenzene, THF and H2O, the suspensions of CIAC-239 in DMF exhibited the highest luminescence intensity. So DMF was chosen as the solvent for the study on the quenching effect of the nitroaromatic compounds nitrobenzene (NB), 2,4-dinitrotoluene (2,4-DNT) and 2,4,6-trinitrophenol (TNP). All these three nitroaromatic compounds exhibit obvious quenching efficiency on the luminescence of CIAC-239. As shown in Fig. 9, the luminescence intensity of CIAC-239 decreases with the increasing concentrations of NB, 2,4-DNT and TNP. Furthermore, the change of luminescence intensity is more sensitive to the concentration of 2,4-DNT than those of NB and TNP. For instance, when the concentration of nitroaromatic compound is 10 mmol L 1, the quenching efficiency of 2,4-DNT reaches 93.05% while those of NB and TNP are only 81.05% and 47.71%, respectively. The quenching efficiency follows the order 2,4DNT > NB > TNP. The Ksv value was calculated to be 602 M 1 for 2,4-DNT (Fig. 10). To investigate the quenching mechanism of Fe3+, Cr2O27 and 2,4-DNT towards CIAC-239, the UV–Vis absorption spectra of the solutions containing different metal cations, anions or nitroaromatic compounds were recorded (Figs. S4–S6). It is found that the wide UV–Vis absorption bands for Fe3+, Cr2O27 , 2,4-DNT and NB overlap the excitation spectrum of CIAC-239, which leads to the luminescence quenching. This mechanism was consistent with those proposed by other groups [31].
4. Conclusions In summary, a Tb-p-tert-butylthiacalix[4]arene chain-like compound was obtained via a solvothermal reaction, which is featured with some sandwich-like Tb4-(TC4A)2 SBUs. The compound exhibits a characteristic emission of Tb3+. The luminescence can be quenched selectively by Fe3+, Cr2O27 , and nitroaromatic reagents such as NB, TNP and 2,4-DNT. Among these three nitroaromatic
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reagents, 2,4-DNT has the highest quenching efficiency. This compound might be a potential multi-responsive luminescent sensor. Acknowledgements This work was supported by the National Natural Science Foundation of China (no. 21571172 and 21521092) and SKLRERU Open Research Fund (RERU2018022). Appendix A. Supplementary data CCDC 1888574 contains the supplementary crystallographic data for CIAC-239. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected]. Supplementary data to this article can be found online at https://doi.org/10.1016/j.poly.2019.01.067. References [1] D.T. Tu, W. Zheng, P. Huang, X.Y. Chen, Coord. Chem. Rev. 378 (2019) 104. [2] Z. Sun, Y.G. Li, Y. Ma, L.C. Li, Dyes Pigm. 146 (2017) 263. [3] F. Pointillart, O. Cador, B. Le Guennic, L. Ouahab, Coord. Chem. Rev. 346 (2017) 150. [4] A. Karmakar, G.M. Rúbio, A. Paul, M.F.C.G. da Silva, K.T. Mahmudov, F.I. Guseinov, S.A.C. Carabineiro, A.J.L. Pombeiro, Dalton Trans. 46 (2017) 8649. [5] Y.P. Wu, G.W. Xu, W.W. Dong, J. Zhao, D.S. Li, J. Zhang, X.H. Bu, Inorg. Chem. 56 (2017) 1402. [6] M. Chen, W.M. Xu, J.Y. Tian, H. Cui, J.X. Zhang, C.S. Liu, M. Du, J. Mater. Chem. C 5 (2017) 2015. [7] S. Dang, E. Ma, Z.M. Sun, H.J. Zhang, J. Mater. Chem. 22 (2012) 16920.
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