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Highly luminescent lanthanide complex as bifunctional sensor for Et2O and Fe2+
Author’s Accepted Manuscript Highly luminescent lanthanide complex bifunctional sensor for Et2O and Fe2+
as
Zhi-Peng Zhao, Ye-Fei Jiang, Yun Chen, Hao-Ran Li, Yanqiong Zheng, Cheng-Hui Zeng, Shengliang Zhong, Penghu Guo, Yong-Li Zhao www.elsevier.com/locate/jlumin
PII: DOI: Reference:
S0022-2313(18)31098-6 https://doi.org/10.1016/j.jlumin.2018.08.052 LUMIN15850
To appear in: Journal of Luminescence Cite this article as: Zhi-Peng Zhao, Ye-Fei Jiang, Yun Chen, Hao-Ran Li, Yanqiong Zheng, Cheng-Hui Zeng, Shengliang Zhong, Penghu Guo and Yong-Li Zhao, Highly luminescent lanthanide complex as bifunctional sensor for Et2O and Fe2+, Journal of Luminescence, https://doi.org/10.1016/j.jlumin.2018.08.052 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.
Highly luminescent lanthanide complex as bifunctional sensor for Et2O and Fe2+ Zhi-Peng Zhao,a Ye-Fei Jiang,a Yun Chen,a Hao-Ran Li,a Yanqiong Zheng,c Cheng-Hui Zeng,a,b,c* Shengliang Zhong,a* Penghu Guo,d* Yong-Li Zhaoa a
College of chemistry and chemical engineering, Key Laboratory of Functional Small Organic Molecule, Ministry of Education and Jiangxi’s Key Laboratory of Green Chemistry, Jiangxi Normal University, Nanchang, 330022 P. R. China. Email: [email protected]
b
Beijing National Laboratory for Molecular Sciences (BNLMS), CAS Key Laboratory of Photochemistry, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China.
c
Key Laboratory of Advanced Display and System Applications, Ministry of
Education, Shanghai University, 149 Yanchang Road, Shanghai, P. R. China. d
Laboratory of Industrial Chemistry, Ruhr University Bochum, 44801 Bochum,
Germany.
Abstract Recently,
intensively-investigated
multi-functional
sensors
and
luminescent
lanthanide detectors have become two fields of intense investigation. Functional combination of these two fields is becoming cutting edge research area. Herein, three new
dinuclear
lanthanide
complexes
[Ln2(IMBA)6(dmp)2]
(IMBA
=
4-iodo-3-methylbenzoic acid; dmp = 4,7-dimethyl-1,10-phenanthroline; Ln = Eu3+, 1a; Ln = Gd3+, 1b; Ln = Tb3+, 1c) are obtained. These complexes are fully characterized by multiple techniques such as single-crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), elemental analysis (EA) and Fourier transform infrared spectroscopy (FT-IR). Luminescence properties of 1a and 1c, including luminescence spectra, decay lifetimes and quantum yields are
discussed in detail. It is noteworthy that 1a shows ultrahigh luminescence quantum yield (QY) of 73%. Besides, it is a highly selective bifunctional sensor for diethyl ether (Et2O) and Fe2+, and the Fe2+ can be discriminated easily by the naked eye with limit of detection (LOD) of 1.0×10-6 M for Fe2+. Further in-depth research evidences that the sensing of Fe2+ would not be disturbed by Fe3+ or other species.
Graphical Abstract Three new lanthanide complexes have been prepared. Eu3+ complex shows ultrahigh luminescence QY of 73%. It is a highly selective bifunctional sensor, the sensing of Fe2+ can be discriminated by the naked eyes and would not be disturbed by other species.
Key words Highly Luminescent; Lanthanide Complex; Bifunctional Sensor; Sensing Et2O and Fe2+.
1. Introduction Environmental monitoring, especially the metal ions, chemical substances etc., is of paramount importance for the human health and society development. To monitor the pollutants, highly selective and sensitive sensors is required. Recently, the design of multi-functional probe instead of using several different probes has attracted a surge of research interest [1]. However, it is quite challenging to develop a sensor that can selectively dectcts and discriminates diverse analytes through a multi-model optical response. Furthermore, considerable efforts are still needed to design relatively simple and low-cost dual-detectors with high stability and selectivity. As part of the environmental pollutant, Fe2+ plays an important role in various biological systems [2]. Its deficiency will result in anemia, liver and kidney damages, diabetes and heart diseases[1]. Therefore, detection of Fe2+ is crucial for controlling both its concentration levels in the biosphere and impact on human health. Currently the detection of Fe2+ and Fe3+ can be achieved by using different analytical methods like mass spectroscopy[3], atomic absorption spectroscopy (AAS)[4], inductively coupled plasma spectrometry (ICP-MS) [5], colorimetric [6], electrochemical [7], electron paramagnetic resonance (EPR) [8]. But these techniques suffer from multifarious pretreatment procedures, and also to some extent the sophisticated and expensive instrumentation. In addition, it is reported that Fe2+ sensors are disturbed by Fe3+/other species, leading to unsuccessful discrimination between Fe2+ and Fe3+/other species [3, 6, 7]. To the best of our knowledge, no document about bifunctional sensor for detecting Fe2+ and Et2O is reported. To our delight, in this work, detailed investigations prove that 1a is a highly selective bifunctional detector for Fe2+ and Et2O. In recent years, lanthanide complexes have drawn increasing attention due to their structural diversity and outstanding properties [9-13]. Studies have shown that lanthanide complexes exhibit unique luminescence properties of line-like emission and long lifetime, which originate from the 4f electrons of lanthanide ions. Hence, they have a wide range of potential applications in the fields of sensing [14-17].
Unfortunately, compared to transition metal complexes, it is much more difficult to design lanthanide complexes and control the coordination environment due to their high coordination numbers and flexible geometries. Based on the above considerations and our previously reported work on lanthanide complexes sensors [18-21], in this study, dinuclear lanthanide complexes [Ln2(IMBA)6(dmp)2] (Eu3+ = 1a; Gd3+ = 1b; Tb3+ = 1c) were prepared and fully characterized. Luminescent properties of 1a and 1c were investigated in details. By further studies it is found that 1a is a bifunctional sensor for Et2O and Fe2+. It is interesting that the Fe2+ can be discriminated by the naked eyes, and the sensing isn’t disturbed by Fe3+ or other species.
2. Experimental section 2.1. Materials Eu(NO3)3·6H2O was prepared by dissolving Eu2O3 (99.9%) with concentrated HNO3 (68%) and then evaporated at 100 °C until the crystal film was observed. Gd(NO3)3·6H2O and Tb(NO3)3·6H2O were obtained from Gd2O3 and Tb4O7, respectively, with the identical method as Eu(NO3)3·6H2O. IMBA (98.0%, Mr. = 262.05), dmp (98.0%, Mr. = 360.45) and lanthanide oxides (99.9%) were purchased from Innochem. (Beijing, China) and used without further purification. Other chemicals (A.R.) are commercially available and used as received.
2.2. Physical measurements SCXRD data was collected on a Bruker SMART 1000 CCD, with graphite-monochromated Mo-K radiation (λ = 0.71073 Å) at ambient temperature. The structures were solved by direct methods and refined by full-matrix least-squares methods with SHELXL-97 crystallographic software package.[22] Anisotropic displacement parameters were applied to non-hydrogen atoms. Phase purity of the bulk samples were measured by PXRD using a DMAX2200VPC diffractometer at 30 kV and 30 mA, with the scanning speed of 5o/min. FT-IR was obtained in KBr pellets
and recorded on a Nicolet 330 FT-IR spectrometer in 4000–400 cm-1. TGA was performed on a Netzsch-Bruker TG-209 unit at a heating rate of 10 °C/min in the atmosphere, from ambient temperature to 800 °C. Emission spectra and luminescence lifetimes were measured on an Edinburgh FLS980 at ambient temperature. Luminescence QYs were also recorded by the same Edinburgh FLS980 equipped with an integrating sphere.
2.3. Synthesis of [Ln2(IMBA)6(dmp)2] (Ln = Eu3+, 1a; Ln = Gd3+, 1b; Ln = Tb3+, 1c) To a 100 mL beaker containing IMBA (132.2 mg, 0.504 mmol) and 20 mL H2O was added 0.1 M NaOH solution to adjust the pH = 6. And then the mixture was sonicated until a transparent liquid was observed. In another beaker, 70 mg dmp (0.336 mmol) dissolved in 20 mL ethanol and 150 mg Eu(NO3)3·6H2O (0.336 mmol) dissolved in 20 mL acetone were mingled together. Subsequently, the above two solutions in separate beakers were mixed together. After filtering out the white precipitate, the filtrate was transferred to a 150 mL glass bottle and sealed with Teflon lid. Finally, it is placed in a 60 °C oven and reacted for 5 days and then cooled down to room temperature. Colorless block crystals suitable for single crystal X-ray analysis were obtained by filtration and air-dried.
3. Results and discussion 3.1. Synthesis Complexes 1a-1c were synthesized under solvothermal condition by heating a mixture of Ln(NO3)3·6H2O (Ln = Eu, Gd, Tb), IMBA and dmp at a molar ratio of 1:1.5:1 at 60 oC for 5 days. All crystals were collected as colorless blocks. A few other lanthanide nitrates, including La(NO3)3·6H2O, Ce(NO3)3·6H2O, Pr(NO3)3·6H2O, Nd(NO3)3·6H2O, Yb(NO3)3·6H2O, Lu(NO3)3·6H2O, etc., were also attempted to synthesize crystals with IMBA, but unfortunately, we have not been able to get suitable crystal from them.
Table 1. Crystallographic data and structure refinement parameters for the complexes 1a-1c. Complex
1a
1b
1c
CCDC Empirical formula Formula weight Temperature / K Wavelength / Å Crystal system Space group a/Å b/Å c/Å α/° β/° γ/° V / Å3 Z Dc / mg·m-3 Μ / mm-1 F(000)
1852308 Eu2C76H60I6N4O12 2286.60 293(2) K 0.71073 Triclinic P-1 16.3777(4) 16.9699(5) 17.5384(6) 65.271(3) 80.262(2) 62.424(2) 3922.6(2) 2 1.936 4.005 2168.0 -19<=h<=19, -20<=k<=20, -20<=l<=20 0.18 x 0.16 x 0.15
1852307 Gd2C76H60I6N4O12 2297.18 293(2) K 0.71073 Triclinic P-1 16.3862(4) 16.9991(4) 17.5738(4) 65.140(2) 80.173(2) 62.393(2) 3934.13(16) 2 1.939 4.085 2172 -19<=h<=18 -20<=k<=19 -20<=l<=20 0.19 x 0.16 x 0.15
1852309 Tb2C76H60I6N4O12 2300.52 293(2) K 0.71073 Triclinic P-1 16.3716(7) 16.9358(6) 17.5775(4) 65.098(3) 80.207(3) 62.461(4) 3917.8(2) 2 1.950 4.215 2176.0 -19<=h<=16, -20<=k<=20, -20<=l<=20 0.21 x 0.12 x 0.10
Limiting indices
Crystal size / mm Theta range of data 3.38 to 25.00 /° Reflections collected / unique
49859 / 13770 [R(int) = 0.0494]
GoF 1.007 a R indices [I > 0.0556, 0.1937 2σ(I)]: R1, wR2 R indices (all data): 0.0632, 0.2083 R1, wR2 a
3.38 to 25.00
3.40 to 25.01
42880 / 13793 [R(int) = 0.0396]
29021 / 13772 [R(int) =0.0357]
1.000
1.007
0.0490, 0.1216
0.0432, 0.1081
0.0578, 0.1278
0.0537, 0.1196
R = ∑||Fo| - |Fc||/∑|Fo|, wR = [∑w(|Fo2| - |Fc2|)2/∑w(|Fo2|)2]1/2
Fig. 1. Structure analysis of 1a: a) dinuclear unit; b) dinuclear cluster constructed by Eu and the adjacent O and N atoms; c) six O and two N atoms that coordinate to Eu1 arranged in a distorted bi-capped prism mode; d) six O and two N atoms around Eu2 are in a distorted bi-capped prism mode; e) 3D cluster structure viewed along the crystallographic b axis. The hydrogen atoms are omitted for clarity.
3.2. Description of crystal structures Crystal structure data (Table 1) reveals that 1a-1c are isostructural. Therefore, 1a is selected in this discussion as representative. 1a crystallizes in triclinic space group P-1 (no. 2). Each building unit [23] contains two Eu3+ (Eu1 and Eu2), six fully deprotonated IMBA and two dmp, to form an electroneutral unit (Fig. 1a). Eu1 and Eu2 are bridged by four carboxylates, the separation of Eu1···Eu2 is 4.270 Å. Eu1, Eu2 and the coordinated O and N form a dinuclear cluster (Fig. 1b). Eu1 and Eu2 are coordinated by six carboxylate O two N and they are arranged in a distorted bi-capped prism mode (Figs. 1c, 1d). The dinuclear cluster structures are further connected by weak interactions to form a 3D framework structure (Fig. 1e). The fully deprotonated
ligands have two coordination modes (Fig. S1†), namely bridge (mode I) and chelation (mode II) [24]. Eu-O and Eu-N bond lengths are in 2.313-2.487 and 2.597-2.629 Å, respectively (Table S1†) [25], which are in line with the reported Eu-O [26, 27] and Eu-N [25, 28, 29] bond lengths of lanthanide complexes [30-32]. Selected bond lengths and angles for 1a-1c are listed in Table S1-S3†.
Fig. 2. Experimental and simulated PXRD patterns for 1a, 1b and 1c.
3.3. Thermogravimetric analysis The thermal stability of as-synthesized complexes 1a-1c was characterized by TGA from 25 to 800 °C under air atmosphere (Fig. 3). They show a very small weight loss below 302 °C, which is ascribed to the loss of lattice water. Above 302 oC, these complexes begin to decompose in three steps with about 83.9% weight losses, matching well with the calculated value of about 84.6%. TGA results indicate that 1a-1c are thermostable before 302oC.
Fig. 3. TGA of the compounds 1a-1c in the air atmosphere.
3.4. Luminescent properties of Eu3+ (1a) and Tb3+ (1c) complexes Taking the unique luminescence properties of Eu3+ and Tb3+ into consideration, luminescence spectra of 1a and 1c were investigated in solid-state at ambient temperature. Emission spectra of 1a and 1c are displayed in red and green solid line, respectively (Fig. 4). Fig. 4a shows the excitation of 1a, the broad band at 348 nm is due to antenna effect of ligand, and the sharp peak at around 396 nm is due to the transition of 7F0,1→5L6 for Eu3+.[33] Under optimal excitation at 348 nm (Fig. 4a), 1a displays the characteristic red luminescence of Eu3+ with line-like emission bands among 570-720 nm (Fig. 4c), the maximum intensities at about 579, 592, 616, 650 and 695 nm [34, 35] are ascribed to the 5D0→7FJ (J = 0-4) transitions [20, 36-39], respectively (Fig. 4a). According to the ED rule [40], the symmetry-forbidden transition of 5D0→7F0 is seen in the sites with the symmetry of Cn, Cnv and Cs [41, 42]. The presence of the 5D0→7F0 transition at 579 nm in the emission spectrum indicates that the Eu3+ centers in 1a do not have inversion symmetry [43], this is consistent with the structural analysis that the dinuclear structure is asymmetric. From the Judd-Ofelt theory [44], the intensity of electric-dipole transition (5D0→7F2) can be considered to be the sensing of the crystalline field, because the 5D0→7F2 transition is highly
sensitive to the coordination environment of Eu3+ center, while the magnetic-dipole transition of 5D0→7F1 is not. If the transition of 5D0→7F2 dominates the luminescence spectrum, the Eu3+ is located in the site without inversion symmetry [45]. The emission spectrum of 1a shows that the 5D0→7F2 transition (616 nm) is stronger than the 5D0→7F1 one, suggesting the asymmetric coordination environment of the Eu3+ center in 1a, which is in line with the single-crystal structure. Fig. 4b shows the emission spectra of 1c excited at optimal excitation 332 nm, showing characteristic emission bands of Tb3+ at about 488, 544, 586 and 621 nm, ascribing to the transitions of
5
D4→7F6,
5
D4→7F5,
5
D4→7F4 and
5
D4→7F3,
respectively [18, 46-48]. CIE coordinate diagram indicates that 1c emits green luminescence (Fig. 4c) [49, 50]. The most prominent characteristic emission peaks, 5D0→7F2 transition of Eu3+ (616 nm) and 5D4→7F5 transition of Tb3+ (544 nm), were chosen to measure the time-resolved luminescence decay lifetimes [51, 52]. The observed transient decay curves for both 1a and 1c (Fig. 4d) are well-fitted with bi-exponential functions, indicating there are two emitting centers, which is in accordance with the crystal structure analysis results. The lifetimes for 1a and 1c are 1.802 and 0.782 ms, respectively, that are longer than some reported Eu3+ and Tb3+ compounds [52, 53]. It is interesting to find that 1a and 1c show highly luminescence QY of 73% and 17%, respectively [54, 55]. This may be due to two reasons: first, the triplet state of the antenna matches better with the excited state (5D4) of Eu3+ than Tb3+ [56]; secondly, the coordinated dmp prevents H2O or other solvents from coordinating with lanthanide ions, because the energy on Ln3+ is easily get lost by oscillation effect of O-H, N-H and C-H groups on the H2O or solvents within the radius of 20 Å [57]. The luminescence QY of 1a is an ultrahigh value that is higher than some highly luminescent lanthanide complexes reported by Sigoli (luminescence QY = 50%) [55]; Bian and Wei (luminescence QY = 28%) [58]; Schlegel, Rabuffetti and Allen (luminescence QY = 47%) [59], Muller-Buschbaum (luminescence QY = 33%) [60]; but lower than the intrinsic luminescence QY of 74% documented by Kariaka [41]. In
order to obtain highly luminescent lanthanide complexes, the triplet energy level of the ligand higher than the excited level of Ln3+ about 2000-3500 cm-1 is necessary to facilitate efficient and irreversible energy transfer for lanthanide complexes, and the energy gap between the triplet energy level of the ligand and should not very high or very low [24].
Fig. 4. a) Excitation and emission spectra of 1a; b) Excitation and emission spectra of 1c; c) CIE coordinate diagram of luminescent 1a and 1c; d) luminescence decay of 1a and 1c.
3.5. Et2O and Fe2+ sensing The luminescence responses of 1a to solvents were carried out after soaked for 24 h. The 3D luminescence spectra (Fig. 5a) proved that solvents of EtOAc, EtOH, CH2Cl2,
THF, MeCN, benzene, MeOH, acetone, hexanes and DMF would not quench the Eu3+-centered luminescence, however, Et2O quenched the luminescence obviously, which is also clearly illustrated by the histogram image (Fig. 5b).
Fig. 5. a) 3D luminescence spectra show that Et2O quenches Eu-centered emission of 1a after soaking in various solvents; b) histogram shows the luminescence intensity variation (616 nm) of 1a after reacting with various solvents.
Luminescence of the sensing system (blank) at different pH was monitored to explore the sensing stability of 1a (Fig. 6). The strongest luminescence appeared under pH = 7 – 8 condition. Thus, the sensing experiments in this study were
performed at pH =7. PXRD peaks of 1a after incubation in aqueous solution for 1 h (as long as the sensing time) were in line with the as-synthesized sample and calculated data, confirming that 1a is a highly stable sensor (Fig. S3).
Fig. 6. Luminescence intensity monitoring of blank solution at pH = 1-14 (adjusted by HNO3 or NaOH). Insert: luminescence intensity comparison at 614 nm.
Stock solutions (1.0×10-3 M) of eight human necessary amino acids (Leu, Lys, Phe, Met, Trp, Val, Ile, Thr) and metal ions (MClx, M = Ba2+, Ca2+, Cd2+, Co2+, Cr3+, Fe2+, Fe3+, K+, Mg2+, Mn2+, Pb2+, Zn2+, Ni2+) (0.05 mL), 4.90 mL deionized water and 0.05 mL stock solution of 1a (1.0×10-3 M in DMF) were mixed together, forming a 5 mL mixture solution which contains 10 μM 1a, 10 μM amino acids or metal ions. Among the 21 samples, only the solution contains Fe2+ changed the color from colorless to light red immediately, indicating 1a is a highly selective detector for Fe2+ [20] and the sensing can be easily distinguished by the naked eye (Fig. 7b). After that, the mixed solutions were placed at the ambient temperature to react for 1 h. UV-Vis absorption spectrum shows obvious absorption enhancement after 1a reacted with FeCl2 (Fig. 7a), while other species displayed no absorption change. The sensing mechanism is due to the interaction between 1a and Fe2+ induced absorption at 380-600 nm (centered at
512 nm, red), and the solution was red to the naked eye. Decreasing the concentration of FeCl2 to 10-6 M, there was still absorption enhancement, however, there was no absorption enhancement observed when the concentration of FeCl2 decreased to 10-7 M (Fig. 7c). So, the above results reveal that 1a is highly sensitive to Fe2+ with LOD value of 1.0×10-6 M (0.127 mg/L).
Fig. 7. a) UV-vis spectra show that among the metal ions species (Fe2+, Fe3+, Ba2+, Ca2+, Cd2+, Co2+, Cr3+, K+, Mg2+, Mn2+, Pb2+, Zn2+, Ni2+) and amino acids (Leu, Lys, Phe, Met, Trp, Val, Ile, Thr) only Fe2+ increases the absorption (380-600 nm, centered at 512 nm) after they reacted with 1a for 1 h.
Fig. 8. a) The UV-Vis absorption spectra of solutions after 1a reacted with 1×10-5 9×10-5 M Fe2+ (insert: photograph of these solutions); b) the absorption value versus the concentration of Fe2+ (insert: the linearity relationship of Fe2+ in 2×10-5 - 8×10-5 M).
Enhancing the Fe2+ concentration from 1×10-5 M to 9×10-5 M (fix the C1a = 10 μM), UV-Vis absorption increased gradually (Fig. 8a), and it was surprising that the absorbance value at 360 nm has an excellent linear relationship versus the Fe2+ concentration in 2×10-5 - 8×10-5 M, yielding a linear equation of Y = -0.005 + 0.0127X (R2 = 0.9877) (Fig. 8b).
Fig. 9. a) UV-Vis absorption spectra of 1a reacted with metal ions and human necessary amino acids for 1 h; b) histogram shows the absorption intensity variation at 510 nm.
3.6. Specificity of the sensing system
One important factor affecting the sensing of Fe2+ is from the disturbance of Fe3+ and some other species, which make it unable to discriminate between Fe2+ and other species [6, 19]. To investigate whether the sensing of Fe2+ would be disturbed by other species [61], the UV-Vis response of this sensing system to 20 competing species of Val, Leu, Phe, Ile, Lys, Thr, Met, Fe3+, Cr3+, Pb2+, Trp, K+, Mg2+, Ba2+, Ca2+, Mn2+, Co2+, Cd2+, Zn2+ and Ni2+, which mixed with Fe2+ was monitored under the same conditions as previous procedures. As displayed in Fig. 9, Fe2+ induces a drastic absorption enhancement in the presence of 10 equiv. other species. This competing experiment result proves that Fe3+ and some other species would not disturb the Fe2+ sensing, suggesting 1a is a highly selective sensor for Fe2+.
4. Conclusion In conclusion, three new lanthanide complexes have been successfully prepared by reacting Ln3+ with two ligands IMBA and dmp. Luminescence properties of 1a and 1c complexes, including luminescence spectra, decay lifetimes and luminescence QYs have been discussed in details. It was interesting to find that 1a had ultrahigh luminescence QY of 73%, which was due to the well-matched triplet state of the antenna and excited state (5D4) of Eu3+ as well as absence of H2O or other solvents coordinate to the metal center within the radius of 20 Å. Further investigation found that 1a is a highly selective bifunctional sensor for both Et2O and Fe2+ with LOD 1.0×10-6 M for Fe2+. Besides, the sensing of Fe2+ can be distinguished easily by naked eyes and the exclusive sensing of Fe2+ can’t be disturbed by Fe3+ or other species.
Appendix A. Supplementary material Crystallographic data (excluding structure factors) for the structures in this paper have been deposited with the Cambridge Crystallographic Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies of the data can be obtained free of
charge on quoting the depository number CCDC: 1852307-1852309 (Fax: +44-1223-336-033; E-Mail: [email protected], http://www.ccdc.cam.ac.uk).
Acknowledgements This work was funded by the National Natural Science Foundation of China (Nos.21641008 and 91622105), Jiangxi Provincial Department of Science and Technology (Nos. 20151BDH80049 and 20161BAB203083).
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as
Zhi-Peng Zhao, Ye-Fei Jiang, Yun Chen, Hao-Ran Li, Yanqiong Zheng, Cheng-Hui Zeng, Shengliang Zhong, Penghu Guo, Yong-Li Zhao www.elsevier.com/locate/jlumin
PII: DOI: Reference:
S0022-2313(18)31098-6 https://doi.org/10.1016/j.jlumin.2018.08.052 LUMIN15850
To appear in: Journal of Luminescence Cite this article as: Zhi-Peng Zhao, Ye-Fei Jiang, Yun Chen, Hao-Ran Li, Yanqiong Zheng, Cheng-Hui Zeng, Shengliang Zhong, Penghu Guo and Yong-Li Zhao, Highly luminescent lanthanide complex as bifunctional sensor for Et2O and Fe2+, Journal of Luminescence, https://doi.org/10.1016/j.jlumin.2018.08.052 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.
Highly luminescent lanthanide complex as bifunctional sensor for Et2O and Fe2+ Zhi-Peng Zhao,a Ye-Fei Jiang,a Yun Chen,a Hao-Ran Li,a Yanqiong Zheng,c Cheng-Hui Zeng,a,b,c* Shengliang Zhong,a* Penghu Guo,d* Yong-Li Zhaoa a
College of chemistry and chemical engineering, Key Laboratory of Functional Small Organic Molecule, Ministry of Education and Jiangxi’s Key Laboratory of Green Chemistry, Jiangxi Normal University, Nanchang, 330022 P. R. China. Email: [email protected]
b
Beijing National Laboratory for Molecular Sciences (BNLMS), CAS Key Laboratory of Photochemistry, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China.
c
Key Laboratory of Advanced Display and System Applications, Ministry of
Education, Shanghai University, 149 Yanchang Road, Shanghai, P. R. China. d
Laboratory of Industrial Chemistry, Ruhr University Bochum, 44801 Bochum,
Germany.
Abstract Recently,
intensively-investigated
multi-functional
sensors
and
luminescent
lanthanide detectors have become two fields of intense investigation. Functional combination of these two fields is becoming cutting edge research area. Herein, three new
dinuclear
lanthanide
complexes
[Ln2(IMBA)6(dmp)2]
(IMBA
=
4-iodo-3-methylbenzoic acid; dmp = 4,7-dimethyl-1,10-phenanthroline; Ln = Eu3+, 1a; Ln = Gd3+, 1b; Ln = Tb3+, 1c) are obtained. These complexes are fully characterized by multiple techniques such as single-crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), elemental analysis (EA) and Fourier transform infrared spectroscopy (FT-IR). Luminescence properties of 1a and 1c, including luminescence spectra, decay lifetimes and quantum yields are
discussed in detail. It is noteworthy that 1a shows ultrahigh luminescence quantum yield (QY) of 73%. Besides, it is a highly selective bifunctional sensor for diethyl ether (Et2O) and Fe2+, and the Fe2+ can be discriminated easily by the naked eye with limit of detection (LOD) of 1.0×10-6 M for Fe2+. Further in-depth research evidences that the sensing of Fe2+ would not be disturbed by Fe3+ or other species.
Graphical Abstract Three new lanthanide complexes have been prepared. Eu3+ complex shows ultrahigh luminescence QY of 73%. It is a highly selective bifunctional sensor, the sensing of Fe2+ can be discriminated by the naked eyes and would not be disturbed by other species.
Key words Highly Luminescent; Lanthanide Complex; Bifunctional Sensor; Sensing Et2O and Fe2+.
1. Introduction Environmental monitoring, especially the metal ions, chemical substances etc., is of paramount importance for the human health and society development. To monitor the pollutants, highly selective and sensitive sensors is required. Recently, the design of multi-functional probe instead of using several different probes has attracted a surge of research interest [1]. However, it is quite challenging to develop a sensor that can selectively dectcts and discriminates diverse analytes through a multi-model optical response. Furthermore, considerable efforts are still needed to design relatively simple and low-cost dual-detectors with high stability and selectivity. As part of the environmental pollutant, Fe2+ plays an important role in various biological systems [2]. Its deficiency will result in anemia, liver and kidney damages, diabetes and heart diseases[1]. Therefore, detection of Fe2+ is crucial for controlling both its concentration levels in the biosphere and impact on human health. Currently the detection of Fe2+ and Fe3+ can be achieved by using different analytical methods like mass spectroscopy[3], atomic absorption spectroscopy (AAS)[4], inductively coupled plasma spectrometry (ICP-MS) [5], colorimetric [6], electrochemical [7], electron paramagnetic resonance (EPR) [8]. But these techniques suffer from multifarious pretreatment procedures, and also to some extent the sophisticated and expensive instrumentation. In addition, it is reported that Fe2+ sensors are disturbed by Fe3+/other species, leading to unsuccessful discrimination between Fe2+ and Fe3+/other species [3, 6, 7]. To the best of our knowledge, no document about bifunctional sensor for detecting Fe2+ and Et2O is reported. To our delight, in this work, detailed investigations prove that 1a is a highly selective bifunctional detector for Fe2+ and Et2O. In recent years, lanthanide complexes have drawn increasing attention due to their structural diversity and outstanding properties [9-13]. Studies have shown that lanthanide complexes exhibit unique luminescence properties of line-like emission and long lifetime, which originate from the 4f electrons of lanthanide ions. Hence, they have a wide range of potential applications in the fields of sensing [14-17].
Unfortunately, compared to transition metal complexes, it is much more difficult to design lanthanide complexes and control the coordination environment due to their high coordination numbers and flexible geometries. Based on the above considerations and our previously reported work on lanthanide complexes sensors [18-21], in this study, dinuclear lanthanide complexes [Ln2(IMBA)6(dmp)2] (Eu3+ = 1a; Gd3+ = 1b; Tb3+ = 1c) were prepared and fully characterized. Luminescent properties of 1a and 1c were investigated in details. By further studies it is found that 1a is a bifunctional sensor for Et2O and Fe2+. It is interesting that the Fe2+ can be discriminated by the naked eyes, and the sensing isn’t disturbed by Fe3+ or other species.
2. Experimental section 2.1. Materials Eu(NO3)3·6H2O was prepared by dissolving Eu2O3 (99.9%) with concentrated HNO3 (68%) and then evaporated at 100 °C until the crystal film was observed. Gd(NO3)3·6H2O and Tb(NO3)3·6H2O were obtained from Gd2O3 and Tb4O7, respectively, with the identical method as Eu(NO3)3·6H2O. IMBA (98.0%, Mr. = 262.05), dmp (98.0%, Mr. = 360.45) and lanthanide oxides (99.9%) were purchased from Innochem. (Beijing, China) and used without further purification. Other chemicals (A.R.) are commercially available and used as received.
2.2. Physical measurements SCXRD data was collected on a Bruker SMART 1000 CCD, with graphite-monochromated Mo-K radiation (λ = 0.71073 Å) at ambient temperature. The structures were solved by direct methods and refined by full-matrix least-squares methods with SHELXL-97 crystallographic software package.[22] Anisotropic displacement parameters were applied to non-hydrogen atoms. Phase purity of the bulk samples were measured by PXRD using a DMAX2200VPC diffractometer at 30 kV and 30 mA, with the scanning speed of 5o/min. FT-IR was obtained in KBr pellets
and recorded on a Nicolet 330 FT-IR spectrometer in 4000–400 cm-1. TGA was performed on a Netzsch-Bruker TG-209 unit at a heating rate of 10 °C/min in the atmosphere, from ambient temperature to 800 °C. Emission spectra and luminescence lifetimes were measured on an Edinburgh FLS980 at ambient temperature. Luminescence QYs were also recorded by the same Edinburgh FLS980 equipped with an integrating sphere.
2.3. Synthesis of [Ln2(IMBA)6(dmp)2] (Ln = Eu3+, 1a; Ln = Gd3+, 1b; Ln = Tb3+, 1c) To a 100 mL beaker containing IMBA (132.2 mg, 0.504 mmol) and 20 mL H2O was added 0.1 M NaOH solution to adjust the pH = 6. And then the mixture was sonicated until a transparent liquid was observed. In another beaker, 70 mg dmp (0.336 mmol) dissolved in 20 mL ethanol and 150 mg Eu(NO3)3·6H2O (0.336 mmol) dissolved in 20 mL acetone were mingled together. Subsequently, the above two solutions in separate beakers were mixed together. After filtering out the white precipitate, the filtrate was transferred to a 150 mL glass bottle and sealed with Teflon lid. Finally, it is placed in a 60 °C oven and reacted for 5 days and then cooled down to room temperature. Colorless block crystals suitable for single crystal X-ray analysis were obtained by filtration and air-dried.
3. Results and discussion 3.1. Synthesis Complexes 1a-1c were synthesized under solvothermal condition by heating a mixture of Ln(NO3)3·6H2O (Ln = Eu, Gd, Tb), IMBA and dmp at a molar ratio of 1:1.5:1 at 60 oC for 5 days. All crystals were collected as colorless blocks. A few other lanthanide nitrates, including La(NO3)3·6H2O, Ce(NO3)3·6H2O, Pr(NO3)3·6H2O, Nd(NO3)3·6H2O, Yb(NO3)3·6H2O, Lu(NO3)3·6H2O, etc., were also attempted to synthesize crystals with IMBA, but unfortunately, we have not been able to get suitable crystal from them.
Table 1. Crystallographic data and structure refinement parameters for the complexes 1a-1c. Complex
1a
1b
1c
CCDC Empirical formula Formula weight Temperature / K Wavelength / Å Crystal system Space group a/Å b/Å c/Å α/° β/° γ/° V / Å3 Z Dc / mg·m-3 Μ / mm-1 F(000)
1852308 Eu2C76H60I6N4O12 2286.60 293(2) K 0.71073 Triclinic P-1 16.3777(4) 16.9699(5) 17.5384(6) 65.271(3) 80.262(2) 62.424(2) 3922.6(2) 2 1.936 4.005 2168.0 -19<=h<=19, -20<=k<=20, -20<=l<=20 0.18 x 0.16 x 0.15
1852307 Gd2C76H60I6N4O12 2297.18 293(2) K 0.71073 Triclinic P-1 16.3862(4) 16.9991(4) 17.5738(4) 65.140(2) 80.173(2) 62.393(2) 3934.13(16) 2 1.939 4.085 2172 -19<=h<=18 -20<=k<=19 -20<=l<=20 0.19 x 0.16 x 0.15
1852309 Tb2C76H60I6N4O12 2300.52 293(2) K 0.71073 Triclinic P-1 16.3716(7) 16.9358(6) 17.5775(4) 65.098(3) 80.207(3) 62.461(4) 3917.8(2) 2 1.950 4.215 2176.0 -19<=h<=16, -20<=k<=20, -20<=l<=20 0.21 x 0.12 x 0.10
Limiting indices
Crystal size / mm Theta range of data 3.38 to 25.00 /° Reflections collected / unique
49859 / 13770 [R(int) = 0.0494]
GoF 1.007 a R indices [I > 0.0556, 0.1937 2σ(I)]: R1, wR2 R indices (all data): 0.0632, 0.2083 R1, wR2 a
3.38 to 25.00
3.40 to 25.01
42880 / 13793 [R(int) = 0.0396]
29021 / 13772 [R(int) =0.0357]
1.000
1.007
0.0490, 0.1216
0.0432, 0.1081
0.0578, 0.1278
0.0537, 0.1196
R = ∑||Fo| - |Fc||/∑|Fo|, wR = [∑w(|Fo2| - |Fc2|)2/∑w(|Fo2|)2]1/2
Fig. 1. Structure analysis of 1a: a) dinuclear unit; b) dinuclear cluster constructed by Eu and the adjacent O and N atoms; c) six O and two N atoms that coordinate to Eu1 arranged in a distorted bi-capped prism mode; d) six O and two N atoms around Eu2 are in a distorted bi-capped prism mode; e) 3D cluster structure viewed along the crystallographic b axis. The hydrogen atoms are omitted for clarity.
3.2. Description of crystal structures Crystal structure data (Table 1) reveals that 1a-1c are isostructural. Therefore, 1a is selected in this discussion as representative. 1a crystallizes in triclinic space group P-1 (no. 2). Each building unit [23] contains two Eu3+ (Eu1 and Eu2), six fully deprotonated IMBA and two dmp, to form an electroneutral unit (Fig. 1a). Eu1 and Eu2 are bridged by four carboxylates, the separation of Eu1···Eu2 is 4.270 Å. Eu1, Eu2 and the coordinated O and N form a dinuclear cluster (Fig. 1b). Eu1 and Eu2 are coordinated by six carboxylate O two N and they are arranged in a distorted bi-capped prism mode (Figs. 1c, 1d). The dinuclear cluster structures are further connected by weak interactions to form a 3D framework structure (Fig. 1e). The fully deprotonated
ligands have two coordination modes (Fig. S1†), namely bridge (mode I) and chelation (mode II) [24]. Eu-O and Eu-N bond lengths are in 2.313-2.487 and 2.597-2.629 Å, respectively (Table S1†) [25], which are in line with the reported Eu-O [26, 27] and Eu-N [25, 28, 29] bond lengths of lanthanide complexes [30-32]. Selected bond lengths and angles for 1a-1c are listed in Table S1-S3†.
Fig. 2. Experimental and simulated PXRD patterns for 1a, 1b and 1c.
3.3. Thermogravimetric analysis The thermal stability of as-synthesized complexes 1a-1c was characterized by TGA from 25 to 800 °C under air atmosphere (Fig. 3). They show a very small weight loss below 302 °C, which is ascribed to the loss of lattice water. Above 302 oC, these complexes begin to decompose in three steps with about 83.9% weight losses, matching well with the calculated value of about 84.6%. TGA results indicate that 1a-1c are thermostable before 302oC.
Fig. 3. TGA of the compounds 1a-1c in the air atmosphere.
3.4. Luminescent properties of Eu3+ (1a) and Tb3+ (1c) complexes Taking the unique luminescence properties of Eu3+ and Tb3+ into consideration, luminescence spectra of 1a and 1c were investigated in solid-state at ambient temperature. Emission spectra of 1a and 1c are displayed in red and green solid line, respectively (Fig. 4). Fig. 4a shows the excitation of 1a, the broad band at 348 nm is due to antenna effect of ligand, and the sharp peak at around 396 nm is due to the transition of 7F0,1→5L6 for Eu3+.[33] Under optimal excitation at 348 nm (Fig. 4a), 1a displays the characteristic red luminescence of Eu3+ with line-like emission bands among 570-720 nm (Fig. 4c), the maximum intensities at about 579, 592, 616, 650 and 695 nm [34, 35] are ascribed to the 5D0→7FJ (J = 0-4) transitions [20, 36-39], respectively (Fig. 4a). According to the ED rule [40], the symmetry-forbidden transition of 5D0→7F0 is seen in the sites with the symmetry of Cn, Cnv and Cs [41, 42]. The presence of the 5D0→7F0 transition at 579 nm in the emission spectrum indicates that the Eu3+ centers in 1a do not have inversion symmetry [43], this is consistent with the structural analysis that the dinuclear structure is asymmetric. From the Judd-Ofelt theory [44], the intensity of electric-dipole transition (5D0→7F2) can be considered to be the sensing of the crystalline field, because the 5D0→7F2 transition is highly
sensitive to the coordination environment of Eu3+ center, while the magnetic-dipole transition of 5D0→7F1 is not. If the transition of 5D0→7F2 dominates the luminescence spectrum, the Eu3+ is located in the site without inversion symmetry [45]. The emission spectrum of 1a shows that the 5D0→7F2 transition (616 nm) is stronger than the 5D0→7F1 one, suggesting the asymmetric coordination environment of the Eu3+ center in 1a, which is in line with the single-crystal structure. Fig. 4b shows the emission spectra of 1c excited at optimal excitation 332 nm, showing characteristic emission bands of Tb3+ at about 488, 544, 586 and 621 nm, ascribing to the transitions of
5
D4→7F6,
5
D4→7F5,
5
D4→7F4 and
5
D4→7F3,
respectively [18, 46-48]. CIE coordinate diagram indicates that 1c emits green luminescence (Fig. 4c) [49, 50]. The most prominent characteristic emission peaks, 5D0→7F2 transition of Eu3+ (616 nm) and 5D4→7F5 transition of Tb3+ (544 nm), were chosen to measure the time-resolved luminescence decay lifetimes [51, 52]. The observed transient decay curves for both 1a and 1c (Fig. 4d) are well-fitted with bi-exponential functions, indicating there are two emitting centers, which is in accordance with the crystal structure analysis results. The lifetimes for 1a and 1c are 1.802 and 0.782 ms, respectively, that are longer than some reported Eu3+ and Tb3+ compounds [52, 53]. It is interesting to find that 1a and 1c show highly luminescence QY of 73% and 17%, respectively [54, 55]. This may be due to two reasons: first, the triplet state of the antenna matches better with the excited state (5D4) of Eu3+ than Tb3+ [56]; secondly, the coordinated dmp prevents H2O or other solvents from coordinating with lanthanide ions, because the energy on Ln3+ is easily get lost by oscillation effect of O-H, N-H and C-H groups on the H2O or solvents within the radius of 20 Å [57]. The luminescence QY of 1a is an ultrahigh value that is higher than some highly luminescent lanthanide complexes reported by Sigoli (luminescence QY = 50%) [55]; Bian and Wei (luminescence QY = 28%) [58]; Schlegel, Rabuffetti and Allen (luminescence QY = 47%) [59], Muller-Buschbaum (luminescence QY = 33%) [60]; but lower than the intrinsic luminescence QY of 74% documented by Kariaka [41]. In
order to obtain highly luminescent lanthanide complexes, the triplet energy level of the ligand higher than the excited level of Ln3+ about 2000-3500 cm-1 is necessary to facilitate efficient and irreversible energy transfer for lanthanide complexes, and the energy gap between the triplet energy level of the ligand and should not very high or very low [24].
Fig. 4. a) Excitation and emission spectra of 1a; b) Excitation and emission spectra of 1c; c) CIE coordinate diagram of luminescent 1a and 1c; d) luminescence decay of 1a and 1c.
3.5. Et2O and Fe2+ sensing The luminescence responses of 1a to solvents were carried out after soaked for 24 h. The 3D luminescence spectra (Fig. 5a) proved that solvents of EtOAc, EtOH, CH2Cl2,
THF, MeCN, benzene, MeOH, acetone, hexanes and DMF would not quench the Eu3+-centered luminescence, however, Et2O quenched the luminescence obviously, which is also clearly illustrated by the histogram image (Fig. 5b).
Fig. 5. a) 3D luminescence spectra show that Et2O quenches Eu-centered emission of 1a after soaking in various solvents; b) histogram shows the luminescence intensity variation (616 nm) of 1a after reacting with various solvents.
Luminescence of the sensing system (blank) at different pH was monitored to explore the sensing stability of 1a (Fig. 6). The strongest luminescence appeared under pH = 7 – 8 condition. Thus, the sensing experiments in this study were
performed at pH =7. PXRD peaks of 1a after incubation in aqueous solution for 1 h (as long as the sensing time) were in line with the as-synthesized sample and calculated data, confirming that 1a is a highly stable sensor (Fig. S3).
Fig. 6. Luminescence intensity monitoring of blank solution at pH = 1-14 (adjusted by HNO3 or NaOH). Insert: luminescence intensity comparison at 614 nm.
Stock solutions (1.0×10-3 M) of eight human necessary amino acids (Leu, Lys, Phe, Met, Trp, Val, Ile, Thr) and metal ions (MClx, M = Ba2+, Ca2+, Cd2+, Co2+, Cr3+, Fe2+, Fe3+, K+, Mg2+, Mn2+, Pb2+, Zn2+, Ni2+) (0.05 mL), 4.90 mL deionized water and 0.05 mL stock solution of 1a (1.0×10-3 M in DMF) were mixed together, forming a 5 mL mixture solution which contains 10 μM 1a, 10 μM amino acids or metal ions. Among the 21 samples, only the solution contains Fe2+ changed the color from colorless to light red immediately, indicating 1a is a highly selective detector for Fe2+ [20] and the sensing can be easily distinguished by the naked eye (Fig. 7b). After that, the mixed solutions were placed at the ambient temperature to react for 1 h. UV-Vis absorption spectrum shows obvious absorption enhancement after 1a reacted with FeCl2 (Fig. 7a), while other species displayed no absorption change. The sensing mechanism is due to the interaction between 1a and Fe2+ induced absorption at 380-600 nm (centered at
512 nm, red), and the solution was red to the naked eye. Decreasing the concentration of FeCl2 to 10-6 M, there was still absorption enhancement, however, there was no absorption enhancement observed when the concentration of FeCl2 decreased to 10-7 M (Fig. 7c). So, the above results reveal that 1a is highly sensitive to Fe2+ with LOD value of 1.0×10-6 M (0.127 mg/L).
Fig. 7. a) UV-vis spectra show that among the metal ions species (Fe2+, Fe3+, Ba2+, Ca2+, Cd2+, Co2+, Cr3+, K+, Mg2+, Mn2+, Pb2+, Zn2+, Ni2+) and amino acids (Leu, Lys, Phe, Met, Trp, Val, Ile, Thr) only Fe2+ increases the absorption (380-600 nm, centered at 512 nm) after they reacted with 1a for 1 h.
Fig. 8. a) The UV-Vis absorption spectra of solutions after 1a reacted with 1×10-5 9×10-5 M Fe2+ (insert: photograph of these solutions); b) the absorption value versus the concentration of Fe2+ (insert: the linearity relationship of Fe2+ in 2×10-5 - 8×10-5 M).
Enhancing the Fe2+ concentration from 1×10-5 M to 9×10-5 M (fix the C1a = 10 μM), UV-Vis absorption increased gradually (Fig. 8a), and it was surprising that the absorbance value at 360 nm has an excellent linear relationship versus the Fe2+ concentration in 2×10-5 - 8×10-5 M, yielding a linear equation of Y = -0.005 + 0.0127X (R2 = 0.9877) (Fig. 8b).
Fig. 9. a) UV-Vis absorption spectra of 1a reacted with metal ions and human necessary amino acids for 1 h; b) histogram shows the absorption intensity variation at 510 nm.
3.6. Specificity of the sensing system
One important factor affecting the sensing of Fe2+ is from the disturbance of Fe3+ and some other species, which make it unable to discriminate between Fe2+ and other species [6, 19]. To investigate whether the sensing of Fe2+ would be disturbed by other species [61], the UV-Vis response of this sensing system to 20 competing species of Val, Leu, Phe, Ile, Lys, Thr, Met, Fe3+, Cr3+, Pb2+, Trp, K+, Mg2+, Ba2+, Ca2+, Mn2+, Co2+, Cd2+, Zn2+ and Ni2+, which mixed with Fe2+ was monitored under the same conditions as previous procedures. As displayed in Fig. 9, Fe2+ induces a drastic absorption enhancement in the presence of 10 equiv. other species. This competing experiment result proves that Fe3+ and some other species would not disturb the Fe2+ sensing, suggesting 1a is a highly selective sensor for Fe2+.
4. Conclusion In conclusion, three new lanthanide complexes have been successfully prepared by reacting Ln3+ with two ligands IMBA and dmp. Luminescence properties of 1a and 1c complexes, including luminescence spectra, decay lifetimes and luminescence QYs have been discussed in details. It was interesting to find that 1a had ultrahigh luminescence QY of 73%, which was due to the well-matched triplet state of the antenna and excited state (5D4) of Eu3+ as well as absence of H2O or other solvents coordinate to the metal center within the radius of 20 Å. Further investigation found that 1a is a highly selective bifunctional sensor for both Et2O and Fe2+ with LOD 1.0×10-6 M for Fe2+. Besides, the sensing of Fe2+ can be distinguished easily by naked eyes and the exclusive sensing of Fe2+ can’t be disturbed by Fe3+ or other species.
Appendix A. Supplementary material Crystallographic data (excluding structure factors) for the structures in this paper have been deposited with the Cambridge Crystallographic Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies of the data can be obtained free of
charge on quoting the depository number CCDC: 1852307-1852309 (Fax: +44-1223-336-033; E-Mail: [email protected], http://www.ccdc.cam.ac.uk).
Acknowledgements This work was funded by the National Natural Science Foundation of China (Nos.21641008 and 91622105), Jiangxi Provincial Department of Science and Technology (Nos. 20151BDH80049 and 20161BAB203083).
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