Synthesis of a 3D lanthanum(III) MOFs as a multi-chemosensor to Cr(VI)-containing anion and Fe(III) cation based on a flexible ligand

Author’s Accepted Manuscript Synthesis of a 3D Lanthanum(III) MOFs as a Multi-Chemosensor to Cr(VI)-Containing Anion and Fe(III) Cation Based on a Flexible Ligand Yang-Min Ma, Tong Liu, Wen-Huan Huang www.elsevier.com/locate/yjssc

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S0022-4596(17)30425-5 https://doi.org/10.1016/j.jssc.2017.10.017 YJSSC19979

To appear in: Journal of Solid State Chemistry Received date: 13 September 2017 Revised date: 7 October 2017 Accepted date: 13 October 2017 Cite this article as: Yang-Min Ma, Tong Liu and Wen-Huan Huang, Synthesis of a 3D Lanthanum(III) MOFs as a Multi-Chemosensor to Cr(VI)-Containing Anion and Fe(III) Cation Based on a Flexible Ligand, Journal of Solid State Chemistry, https://doi.org/10.1016/j.jssc.2017.10.017 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Synthesis of a 3D Lanthanum(III) MOFs as a Multi-Chemosensor to Cr(VI)-Containing Anion and Fe(III) Cation Based on a Flexible Ligand Yang-Min Ma, Tong Liu, Wen-Huan Huang* College of Chemistry & Chemical Engineering, Shaanxi University of Science & Techology, Xi’an, Shaanxi 710021, China

Abstract: Based on La(NO3)3·6H2O and 4,4'-((5-carboxy-1,3-phenylene)bis(oxy))dibenzoic acid (H3cpbda), a 3D porous MOFs, [La(cpbda)(H2O)1.5]n (1), was synthesized by hydrothermal method and further characterized by single-crystal X-ray diffraction, power X-ray diffraction, IR spectroscopy, thermal-gravimetric analysis and fluorescence spectroscopy. Owing to its good stabilities and fluorescence property, the sensing experiments on sixteen cations and eleven anions were implemented. Moreover, the further titration processes show 1 can sensitively detect the Fe(III) cation and Cr(VI)-containing anions by quenching responses. Graphical abstract Based on La(NO3)3·6H2O and 4,4'-((5-carboxy-1,3-phenylene)bis(oxy))dibenzoic acid (H3cpbda), a 3D porous MOFs, [La(cpbda)(H2O)1.5]n (1), was synthesized by hydrothermal method and further characterized by single-crystal X-ray diffraction, power X-ray diffraction, IR spectroscopy, thermal-gravimetric analysis and fluorescence spectroscopy. Owing to its good stabilities and fluorescence property, the sensing experiments on sixteen cations and eleven anions were implemented. Moreover, the further titration processes show 1 can sensitively detect the Fe(III) cation and Cr(VI)-containing anions by quenching responses.

Key words: flexible ligand; MOFs; chemo-sensor; ions detection; fluorescence quenching

1. Introduction Metal-Organic Frameworks (MOFs) are considered to be a kind of excellent materials for their integration of the inorganic metal centers and functional organic building blocks, which giving fantastic structures and potential applications in gas storage[1-3], separation[4-6], catalysis[7-9], magnetism[10-12], luminescence[13-15], sensor technology[16-18], et al. Particularly, numbers of MOFs have been synthesized as the sensing materials which are of great importance for public health and environment protection for their detection abilities on heavy metal ions and toxic organic matters[19-21]. For example, iron (Fe3+) is an essential element in human body to transport and store oxygen[22-24]. Besides, compare to Cr(III), Cr(VI) is highly toxic and easily migrate in underground water[25]. The detection and adsorption of such toxicants in liquid phase become an important research topic for scientists. Compare to other organic soluble chemical probes, solid MOFs have explored as the sensing materials which possess opening pores and stable frameworks. The luminescence sensing process of MOFs probably is cooperation of chemical adsorption, framework-guest interaction and physical surface adsorption which makes MOFs are easily to separation and

recycle. Recently, lots of MOFs sensors with various molecular structures have been investigated, however, the design and construction of stable and high-sensitive MOFs chemosensors is still a great challenge in coordination chemistry materials. As we know, the selection of metal or organic units is one of the most important fact, comparing with other parameters in the construction process of MOFs, such as temperature, pH value, react time and so on. The flexibility, length, the kind and number of the coordination sites, functional groups of the organic ligands is crucial for the structures and properties of MOFs. Based on the earlier research works from our group[26-30], 4,4'-((5carboxy-1,3-phenylene)bis(oxy))dibenzoic acid H3cpbda was an excellent flexible ligand to assembly different MOFs with various structures and properties, for i) as a tridentate carboxylic ligand, it generates lots of coordination modes to combine with different number of metal ions; ii) the two ether bonds in ligand can flexibly rotate and bend and make the ligand to form different molecular configurations, “T”, “Y”, “M” shaped; iii) the electron transfer effect of protonated and deprotonated oxygen atoms and aromatic rings is important in sensing process. The possibilities and benefits of H3cpbda ligand are giving us more opportunities to search for the suitable chemo-sensors on specific ions and molecules. In this work, it reports a stable 3D porous MOFs, [La(cpbda)(H2O)1.5]n (1), which is characterized by single-crystal X-ray diffraction, IR spectroscopy, power X-ray diffraction, thermal-gravimetric analysis, luminescent properties. Considering the good stability of 1, the sensing experiments on series of cations (Ag+, Ba2+, Bi3+, Ca2+, Cd2+, Co2+, Cr3+, Cu2+, Fe3+, Mg2+, Mn2+, Na+, Ni2+, Pb2+, Sr2+, Zn2+) and anion (CO32-, Cr2O72-, CrO42-, SO42-, Br-, Cl-, ClO3-, PO43-, I-, NO3-, SCN-) are implemented, and the further titration processes of quenching responses show that 1 is highly sensitive detecting Fe(III) cation and Cr(VI)-containing anions (Cr2O72-, CrO42-).

Scheme 1 Structure of Flexible Ligand H3cpbda.

2. Experimental 2.1 Materials and measurements The reagents were used directly as supplied commercially without further purification. Elemental analyses (C, H, N) were determined with a Perkin-Elmer model 240C automatic instrument. Infrared spectra on KBr pellets were recorded on a Bruker Equinox-55 spectrometer in the range of 4000-400 cm-1. The X-ray powder diffraction pattern was recorded with a Pigaku D/Max 3III diffractometer. Thermal analysis was determined with a Netzsch STA 449C microanalyzer under flowing N2 atmosphere at a heating rate of 10 ºC /min. Luminescence spectra for the solid samples were investigated with a Hitachi F-4500 fluorescence spectrophotometer. 2.2 Preparation of [La(cpbda)(H2O)1.5] n (1) 1 was obtained by the reaction of La(NO3)3·6H2O (0.1 mmol, 43.3 mg), H3cpbda (0.05 mmol/19.7 mg), distilled water (9.0 mL) mixed in a 25mL Teflon-lined stainless steel vessel. Under hydrothermal conditions (at 160 ºC for 72 hours, and cooled to room temperature with a 5 ºC h-1 rate). Finally, the yellow crystal of 1 was collected in 50% yield. The resulting yellow crystals of 1 were isolated by washing with H2O, and dried in air. IR (KBr, cm-1) (Figure S4): 3651(vw), 3583(vw), 3076(m), 2995(m), 2881(m), 2651(w), 2538(w), 1930(vw), 1689(vs), 1591(vs), 1508(m), 1412(vs), 1300(vs), 1219(vs), 1161(s), 1128(m), 1005(m), 949(m), 854(m), 777 (m), 710(w)，629(w), 542(w), 494(w).

2.3 Preparation of luminescent complexes suspension solutions 10 mg of complexes 1 were introduced into 5mL of different M(NO3)x (M = Ag+, Ba2+, Bi3+, Ca2+, Cd2+, Co2+, Cr3+, Cu2+, Fe3+, Mg2+, Mn2+, Na+, Ni2+, Pb2+, Sr2+, Zn2+) and Kx(A) (A = CO32-, Cr2O72-, CrO42-, SO42-, Br-, Cl-, ClO3-, PO43-, I-, NO3-, SCN-), the concentration of the ion solutions is 500 ppm (5mg metal salt was dissolved into 10mL water). After the soaking of the solid crystal samples, the solutions were placed into the supersonic vibration instrument, after the 2h vibration at 40 KHz, the luminescent suspension solutions were preapared. The emission data of the solutions were recorded at the extinction wavelength of 280 nm. 2.4 Crystallographic data collection and structure determination Single-crystal X-ray diffraction analyses of the compounds 1 were carried out on a Bruker SMART APEX II CCD diffractometer equipped with a graphite monochromated Mo radiation (λ = 0.71073 Å) by using /ω scan technique at room temperature. The structures were solved using direct methods and successive Fourier difference synthesis (SHELXS-97)

[31]

, and refined using the full-matrix least-squares method on F2 with

anisotropic thermal parameters for all non-hydrogen atoms (SHELXL-97)

[32]

. All non-

hydrogen atoms were refined anisotropically. The hydrogen atoms of organic ligands were placed in calculated positions and refined using a riding on attached atoms with isotropic thermal parameters 1.2 times those of their carrier atoms. The crystallographic data for 1 are listed in Table 1, the selected bond lengths and angles are listed in Table S1. Table 1. Crystallographic data and details of diffraction experiments for complexes 1. Complex 1 Formula

La2C42H28O19

Dcalcd.[g·cm-3]

1.797

Mr

1114.46

μ [mm-1]

2.128

Crystal system

monoclinic

F [000]

2184

Space group

C2/c

θ [º]

2.86 - 26.00

a (Å)

30.212(13)

Reflections

10625 / 3999

b (Å)

9.037(4)

Rint

0.0383

c (Å)

16.369(7)

T(K)

296(2)

α (°)

90

Goof

1.084

β (°)

112.817(6)

γ (°)

90

R [I > 2σ(I)]

R1= 0.0366 wR2= 0.0946

V [Å3]

4119(3) R (all data)

Z

4

R1= 0.0503 wR2= 0.1024

R 1= Σ(|Fo|–|Fc|)/Σ|Fo|; wR2 = [Σw(Fo2 – Fc2)2/Σw(Fo2) 2]1/2

3. Results and discussion 3.1 Crystal structure of [La(cpbda)(H2O)1.5]n (1) Single crystal X-ray diffraction analysis shows that compound 1 crystallizes in a C2/c space group. The asymmetric unit contains one independent La(III) cations, one deprotonated cpbda3- ligand, and one and a half of coordinated water molecules (Figure 1). The La1 atom bonds with nine oxygen atoms from seven cpbda3- ligands and two oxygen atoms from two coordinated water molecules, forming a distorted LaO9 which adopt a nine-coordinated tricapped trigonal prismatic coordination geometry. The La-O bonds distances range from 2.402(4) (La1-O8) to 3.016(4) (La1-O5) Å, the bond angles around the La(III) cations are in the range of 45.37(13) to 154.70(11)°.

Fig.1 The coordination environment of La(III) in 1. Symmetry codes: A, 0.5+x, 0.5–y, 0.5+z; B, 1.5-x, –0.5+y, 0.5–z; C, 2-x, –y, 1–z; D, 0.5+x, 0.5+y, z; E, 1.5-x, 0.5+y, 0.5–z.

The cpbda3- ligand in 1 which bonds with six La(III) atoms, adopts “Y” shaped molecular configuration (Figure S3), forming 3D structure with opening 1D rhombus channels along the c axis (Figure 2). O1 atoms occupy the space of the 1D channels, and O2 atoms bond at opposite direction. The 3D structures of 1 along with the a and b axis are listed in SI, Figure S1-2.

Fig.2 The 3D structure of 1 constructed by La(III) ions and cpbda3- ligands, viewing along the c axis.

3.2 XRPD and TGA Results The XPRD pattern of 1 reveals that the compound is pure single phase and is also of completely identical molecular structures, corresponding to the simulated results from the single-crystal X-ray data (Figure S5). The TGA measurement is carried out in order to identify the thermal stability of 1, (Figure S6). There is a weight loss of 4.9% (calcd. 4.85 %) is observed above 192 oC, which is attribute to the loss of one and a half of coordinated water molecules. After the loss of the solvents, the framework can keep stable before 310 oC. After that, the skeleton of 1 collapses and the organic components fast break down. 3.3 Luminescence and Sensing Properties Fluorescent properties of MOFs and their potential applications as fluorescent-emitting materials becomes the most important research area in recent years. The solid-state luminescent properties of H3cpbda ligand and 1 are investigated (Figure S7). The emission peak of H3cpbda is observed at 360 (λex = 280 nm), which can be assigned to the ligandcentered electronic transitions, that is π*→π or π*→n electronic transition. Compare to the emission of H3cpbda ligand, the emission of 1 is similarly shown at 356 nm (λex = 280 nm), showing a slight blue shift of H3cpbda ligand, which is mainly due to the π→π* ligand-tometal charge transition (LMCT), the incorporation of metal-ligand coordination interaction. Compare to the pure ligands power, the increased rigidity and crystallinity of complex 1 enhances the intensity of emission peak after the metal ions bond with ligands.

To probe the sensing properties of 1 on different metal cations and anions, 10 mg of compound 1 was added into 5 mL of different M(NO3)x (M = Ag+, Ba2+, Bi3+, Ca2+, Cd2+, Co2+, Cr3+, Cu2+, Fe3+, Mg2+, Mn2+, Na+, Ni2+, Pb2+, Sr2+, Zn2+) and Kx(A) (A = CO32-, Cr2O72-, CrO42-, SO42-, Br-, Cl-, ClO3-, PO43-, I-, NO3-, SCN-) solutions, and the emission data were recorded for luminescence studies. The studies of complex 1 (Figure S8-9) showed that the Fe3+ cations (Figure 3) and the Cr2O72‒, CrO42‒ anions (Figure 4) can distinctly induce the luminescence quenching.

Fig. 3 (a) The visual change on the addition of various cations. (b) Comparison of the relative luminescence intensities of 1 suspension with sixteen metal cations.

Fig. 4 (a) The visual change on the addition of various anions. (b) Comparison of the relative luminescence intensities of 1 suspension with eleven anions.

In order to further detect the sensing sensitivities of complex 1 on this three ions, the titration experiments were conducted. The suspensions of 1 were prepared by dispersing 10 mg complexes into 3mL H2O. The concentrations of cations (Fe3+) and anions (Cr2O72‒, CrO42‒) were increased from 0 to 1667 ppm to monitor the emission responses, the analysis results of 1 suspensions are shown in Figure 5-6 and Figure S10-12. As Figure 5 shown, along with the injections of Fe3+ solution, the luminescence slowly decreases, the intensity decreases to 28.8% at 164 ppm, 9.0% at 323 ppm, 4.7% at 476 ppm. However, the Cr 2O72‒ and CrO42‒ anions give remarkable quenching effects that the ion concentration of merely 164 ppm can render the luminescence intensities to 17.7%, and 0.1% (Cr2O72‒ and CrO42‒) respectively. After that the intensities of all two Cr(VI)-containing anions decrease to 0.1% (Figure 6). The titration results of 1 are listed in Figure S10-S12, and the luminescence quenching efficiencies are listed in SI (Figure S13). Compare the processes of luminescence

intensity changes along the ionic concentration, the luminescence quenching efficiencies are totally different, showing an order of Fe3+ < Cr2O72‒ < CrO42‒. However, all the above experiments show that 1 can detect the Fe(III) metal cation and Cr(VI)-containing anions (Cr2O72‒ and CrO42‒) by the quenching responses with high sensitivities.

Fig.5 The luminescence intensities of 1 suspension with Fe(III) concentration varying from 0 to 1667 ppm.

Fig. 6 The luminescence intensities of 1 suspension with (a) Cr2O72- anions concentration varying from 0 to 769 and (b) CrO42- anions concentration varying from 0 to 476 ppm.

Generally, the two main reasons for the sensing phenomena are photo induced electron transfer or resonance energy transfer or both[33-36]. Considering the 3D porous structure of 1, the changes of fluorescence intensity should be attributed to the photo-induced electron transfers between the excited frameworks and the guest molecules. The void ratio of the LaMOF was 9.4% which was calculated by PLATON software. As we known, the flexible frameworks which can generate soft pores and selective adsorption on molecules, are giving a lot of benefits in the sensing materials. The size and polarity of the pores are crucial in sensing process. In that case, the selection of organic ligands (such as ligand length, shapes, functional groups, and so on) and structural design is significant for exploring suitable MOFs chemo-sensors.

4. Conclusions In summary, the 3D porous MOFs 1 was synthesized by reaction of La(NO3)3 and H3cpbda ligand, and the X-ray powder diffractions, thermal stability and luminescent properties have also been investigated. According to the luminescence property and sensing experiments of 1 on different ions, 1 was considered to be a multi-chemosensor which showed highly sensitive detections of Fe(III) metal cation and Cr(VI)-containing anions

(Cr2O72‒ and CrO42‒) by the quenching responses. It indicated that the flexible carboxylic acid ligand could be used as a good building block and to construct various structural and functional MOFs in future. More chemosensors based on flexible ligands are synthesizing, and the further mechanism of sensing process is analyzing. Acknowledgements This work is supported by the National Natural Science Foundation of China (21531007, 21401121), the Research Program of the Shaanxi Provincial Department of Education (16JK1108), Natural Science Foundation of Shaanxi Province (Grant 2017JQ2021), the Doctor Foundation of Shaanxi University of Science & Technology (BJ14-22), the Open Foundation of Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http: // References [1] L. J. Li, J. G. Bell, X. B. Zhao, et al. Chem. Mater., 2014, 26: 4679-4695. [2] T. L. Easun, F. Moreau, S. Yang, et al. Chem. Soc. Rev., 2017, 46: 239-274. [3] J. A. Mason, M. Veenstra, J. R. Long. Chem. Sci., 2014, 5: 32-51. [4] Z. J. Zhang, H. T. H. Nguyen, S. M. Cohen, et al. J. Am. Chem. Soc., 2016, 138: 920-925. [5] Y. Y. Zhang, S. Yuan, B. Wang, et al. J. Am. Chem. Soc., 2016, 138: 5785-5788. [6] J. Liu, G. P. Yang, W. Y. Zhang, et al. Cryst. Growth Des., 2017, 17: 2059-2065. [7] T. Zhang, K. Manna, and W. B. Lin. J. Am. Chem. Soc., 2016, 138: 3241-3249. [8] G. W. Zhan and H. C. Zeng. Adv. Funct. Mater., 2016, 26: 3268-3281. [9] Y. B. Huang, J. Liang, X. S. Wang, R. Cao. Chem. Soc. Rev., 2017, 46: 126-157. [10] Y. L. Wu, G. P. Yang, Y. Y. Wang, et al. Inorg. Chem., 2016, 55: 6592-6596. [11] M. Roy, S. Sengupta, R. Mondal, et al. Cryst. Growth Des., 2016, 16: 3170-3179. [12] X. L. Li, W. Zhang, R Li, et al. ChemCatChem., 2016, 8: 1111-1118. [13] Z. Ju, W. Yan, H. G. Zheng, et al. Cryst. Growth Des., 2016, 16: 2496-2503. [14] A. Garai, S. Sasmal, and K. Biradha. Cryst. Growth Des., 2016, 16: 4457-4466. [15] W. Dong, R. Q. Fan, Y. L.Yang, et al. Cryst. Growth Des., 2016, 16: 3366-3378. [16] H. M. Zhang, J. Yang, J. F. Ma, et al. Cryst. Growth Des., 2016, 16: 265-276. [17] H. Zhang, J. Yang, J. F. Ma, et al. Cryst. Growth Des., 2016, 16: 3244-3255. [18] Y. L. Wu, G. P. Yang, Y. Y. Wang, et al. Dalton Trans., 2015, 44, 3271-3277. [19] C. Bazzicalupi, C. Caltagirone, N. Zaccheroni, et al., Chem. Eur. J., 2013, 19: 1463914653. [20] Y. P. Zhu, T. Y. Ma, Z. Y. Yuan, et al., ACS Appl. Mater. Interfaces, 2014, 6: 1634416351. [21] S. Bhattacharyya, A. Chakraborty, T. K. Maji, et al., Chem. Commun., 2014, 50: 1356713570. [22] Z. H. Xiang, C. Q. Fang, S. H. Leng and D. P. Cao, J. Mater. Chem. A, 2014, 2: 76627665.

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