Article pubs.acs.org/IC
Multifunctional Luminescent Eu(III)-Based Metal−Organic Framework for Sensing Methanol and Detection and Adsorption of Fe(III) Ions in Aqueous Solution Jian Wang, Min Jiang, Ling Yan, Ren Peng, Mengjie Huangfu, Xinxin Guo, Yang Li, and Pengyan Wu* School of Chemistry and Chemical Engineering & Jiangsu Key Laboratory of Green Synthetic Chemistry for Functional Materials, Jiangsu Normal University, Xuzhou, 221116, P. R. China S Supporting Information *
ABSTRACT: A novel lanthanide−organic framework (Eu− HODA), consisting of 2,2′,3,3′-oxidiphthalic acids as efficient sensitizing units, is assembled and characterized. Eu−HODA features rare chiral helical channels despite the achiral nature of H4ODA. It is found that this MOF shows a unique luminescent response to methanol, in contrast to n-propanol and ethanol. Eu−HODA reveals a turn-off luminescence switching initiated by acetone molecules with an EC50 of 0.03 vol %, which is below the occupational exposure limit of acetone stipulated by the American Conference of Governmental Industrial Hygienists. Furthermore, it also exhibits high sensitivity (Stern−Volmer constant KSV = 2.09 × 104 L/mol) and low detection limit (6.4 ppb) for Fe3+ ions in pure water because of the existence of uncoordinated carboxyl groups within open frameworks. Eu−HODA-based test paper provides a simple and reliable detection method for Fe3+ in practical applications.
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Fe3+ in aqueous solution. Since fluorescent detection provides a simplistic method with high sensitivity and selectivity, accuracy, and economy for online monitoring and thus for selective detection of Fe3+ ions, the construction of fluorescent sensors is a good choice.7−9 However, their widespread use is still limited by their inability to be used in pure water; their cross-sensitivity toward other metal ions, like Cu2+, Al3+, and Cr3+; their bad absorbing ability; the sophisticated synthesis of probe materials; and/or the lack of a practical application model.10 Thus, developing an effective and useful fluorescent Fe3+ sensor remains a challenge. Metal−organic frameworks are a kind of crystalline framework-structured material obtained by the assembly of metal cations and organic ligands that have enjoyed wide attention for their potential applications in optical sensing/detection,15,16 gas storage/separation,11,12 catalysis,17,18 chemical separation/ purification,13,14 drug delivery,19 and so on.20 The specific pore shape and size for accommodation and/or discrimination of different substrates and incorporating specific interaction sites into a framework can both tune their functional properties by means of strategic organic chemistry. Among the various MOFs, lanthanide-based metal−organic frameworks (LnMOFs) possess lots of fascinating features, including their unique luminescent properties attributed to their diverse coordination mode, high color purity, large Stokes’ shifts, and
INTRODUCTION In recent years, more and more attention has been focused on the efficient detection of chemical pollutants, such as toxic metal ions and volatile organic compounds (VOCs), because of their threat to human health and environment. VOCs are released from a variety of point sources and diffuse sources, such as volatile solvent use, urban water, industrial wastes, and accidental leaks, and they are also emitted by a wide array of daily household products, which leads to particular difficulty in the elimination of these VOCs.1,2 For example, methanol has been widely employed, including in antifreezing agent, paints, dyes, organic synthesis, and automobiles, and even as an additive to imitation spirits and wine for illegal profit, and is an important chemical raw material. Long-term exposure to methanol is favorable for some diseases, for instance, peripheral neuropathy and visual impairment, and may possibly lead to death.3,4 Therefore, detection of methanol is very significant and necessary, especially the selective sensing of methanol over aliphatic alcohols, due to the similarity of their physical and chemical properties. Iron has experienced increasing interest and importance in biological and environmental systems owing to its significance and function in oxygen uptake and metabolic processes. A moderate concentration of Fe3+ ions is needed in living systems, and various biological disorders like hepatic cirrhosis, endotoxemia, and hereditary hemochromatosis are usually caused by its deficiency or overloading.5,6 This has prompted the development of methods to selectively detect and quantify © XXXX American Chemical Society
Received: July 29, 2016
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DOI: 10.1021/acs.inorgchem.6b01815 Inorg. Chem. XXXX, XXX, XXX−XXX
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Figure 1. (a) The distorted decahedral coordination geometry of Eu(III) in Eu−HODA. Symmetry code: A, −1 − x, 0.5 + y, 1 − z. (b) Eu ions are coordinated with the 2-, 2′-, and 3′-COO− of HODA3− to afford the Eu−HODA helical chain.
Figure 2. (a) Two-dimensional layer structure in Eu−HODA composed of helices with the same chirality together through π···π stacking. (b) Overall structure of Eu−HODA. For clarity, we omit solvent water molecules and all hydrogen atoms.
relatively long fluorescence lifetime, as well as their characteristic coordination preferences.21,22 However, it is still a challenge to get Ln-MOFs with the desired function in pure water. This is because the LnIII luminescence often can be quenched by high-energy vibrations (typically X−H oscillators, X = C, N, O); in aqueous solution, the tendency to re-form a condensed structure, as well as weak fluorecence, has limited their sensing performance to mainly be applied to mixed solvents or organic solvents.23 In this context, a rare example of chiral MOFs, Eu−HODA, comprised of europium ions and 2,2′,3,3′-oxidiphthalic acid with one carboxyl group uncoordi-
nated, is reported for size-selective methanol detection and highly selective and sensitive Fe3+ recognition in pure water.
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EXPERIMENTAL SECTION
Synthesis of Eu−HODA. 2,2′,3,3′-Oxidiphthalic acid (H4ODA) (4.5 × 10−5 mol, 15.6 mg), Eu(NO3)3·6H2O (4.5 × 10−5 mol, 20 mg), and a mixture of ethanol and water (v:v = 1:1, 4 mL) were placed in a screw-capped autoclave and then heated at 120 °C for 36 h. Through filtration and drying in the air, colorless block crystals were obtained (83% based on H4ODA). X-ray Crystallography. The X-ray diffraction data for this crystal were collected using Bruker-SAINT software on a Bruker SMART APEX CCD diffractometer equipped with a Mo Kα (λ = 0.710 73 Å) B
DOI: 10.1021/acs.inorgchem.6b01815 Inorg. Chem. XXXX, XXX, XXX−XXX
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Figure 3. (a) Fluorescence spectra of Eu−HODA (60 μM) dichloromethane emulsion as a function of the methanol concentration (from bottom: 0.0, 0.06, 0.23, 0.46, 0.83, 1.31, 1.96, and 2.60 vol %). (b) Fluorescence responses of Eu−HODA at 614 nm to the addition of alcohols (2.60 vol %) when excited at 305 nm.
through π···π stacking (spacing 3.50 Å) to form a twodimensional layered structure (Figure 2a). In Eu−HODA, the layers are further stacked parallel to the ac plane in a slipped ABAB fashion through hydrogen bonds, resulting in a threedimensional chiral network with 1D channels of 4.1 × 10.0 Å2 along the [010] direction (Figure 2b). The thermogravimetric analysis (TGA) curve of Eu−HODA showed a 3.13% weight loss between 22 and 65 °C [see the Supporting Information (SI), Figure S1], which corresponds to the loss of one guest H2O molecular (calculated as 3.08%), and upon continuing to raise the temperature up to 190 °C, another weight loss of 12.36% occurred, assigned to the four connected coordinated H2O molecules (calculated as 12.30%). To probe the structural stability, variable-temperature PXRD measurement of Eu− HODA was also performed, as shown in Figure S2 of the SI, suggesting that its crystallinity is maintained until at least 200 °C. All those results confirmed the open framework structure and demonstrated that the Eu−HODA was able to be stable in recognition conditions. Notably, colorless Eu−HODA crystals show high stability to solvents; no obvious signs of crystal dissolution/decomposition in methanol, dichloromethane, N,N′-dimethylformamide, acetone, acetonitrile, toluene, benzene, or tetrahydrofuran for 3 days are observed through visual inspection. Moreover, PXRD analyses were further performed on Eu−HODA samples after immersing in these solvents, and their patterns were nearly in accord with the original ones (see the SI, Figure S3), suggesting that Eu−HODA is stable for small-molecule sensing. Luminescent Properties and Sensing of Small Molecules. UV−vis absorption spectra of Eu−HODA solid samples showed an intense absorption band around 305 nm, which could be attributed to the π−π* transition of 2,2′,3,3′oxidiphthalic acid (see the SI, Figure S4). Since aromatic acids are efficient LnIII sensitizers, characteristic bands at 594, 614, 652, and 697 nm, arising from the transitions of 5D0 → 7F1 and 5 D0 → 7F2, 5D0 → 7F3, and 5D0 → 7F4 of the Eu(III) ions in dichloromethane (DCM) are obversed in Eu−HODA, demonstrating the efficient energy transfer from the sensitizer to the EuIII moiety, when excited at 305 nm (see the SI, Figure S5). In Eu−HODA, the electric dipole 5D0 → 7F2 transition at 614 nm is dominated due to the ambient low symmetry of the europium ion.24,25 Interestingly, the luminescent spectra of Eu−HODA are largely changed when subjected to the different solvent molecules, i.e., methanol (MeOH), dichloromethane (DCM),
graphite monochromator. Solution and refinement of this structure were performed through direct methods and full-matrix least-squares methods based on F2 values with SHELXTL version 5.1. All hydrogen atoms in backbones were placed at calculated positions geometrically. The hydrogen atoms in uncoordinated carboxylate groups were confirmed according to the difference Fourier maps, and their refinements proceeded using 1.5 times that of attaching oxygen atoms as the isotropic parameters and a fixed value of 0.85 Å for the O−H distance. The disorder of one carboxylate oxygen atom was calculated at two positions. Crystal data of Eu−HODA: C16H17O14Eu, M = 585.26, monoclinic, P2(1) space group, a = 11.020(2) Å, b = 6.9500(14) Å, c = 12.200(2) Å, α = 90.00°, β = 93.30(3)°, γ = 90.00°, V = 932.8(3) Å3, Z = 2, T = 153(2) K, Dc = 2.055 g cm−3, μ(Mo Kα) = 3.440 mm−1, 4945 unique reflections [Rint = 0.0359], final R1 [with I > 2σ(I)] = 0.0634, wR2 (all data) = 0.01984, GOOF = 1.030, CCDC number 1496239. Adsorption Ability of Eu−HODA for Fe3+. Eu−HODA (20 mg) was added to the 50 mL Fe3+ solution (5.4 μM, 0.35 ppm). After stirring the mixture for 4 h and filtering it, an inductively coupled plasma apparatus (ICP) was used to analyze the concentration of residual Fe3+ in the filtrate.
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RESULTS AND DISCUSSION Crystal Structures Description. Solvothermal reaction of H4ODA (2,2′,3,3′-oxidiphthalic acid) and Eu(NO3)3·6H2O in mixed solvents of water (H2O) and ethanol (v/v = 1/1) gave the colorless block crystal Eu−HODA {Eu(C16H 7O9 )(H2O)4(H2O)}n in a high yield (83%). Single-crystal X-ray structural data revealed that Eu−HODA crystallizes in the monoclinic structure with space group P2(1). There are one Eu atom, one HODA3− ligand, and four coordinated and one solvated water molecule in an asymmetric unit. Each europium ion is coordinated with nine oxygen atoms in distorted decahedral configuration: one oxygen atom from one dimonodentate carboxyl groups of one HODA3− ligand, four oxygen atoms from two bidentate carboxyl groups from two different HODA3− ligands, and four oxygen atoms from four different coordinated water molecules (Figure 1a). As to 2,2′,3,3′-HODA3− in Eu−ODA, the dihedral angle 75.6° of two phenyl rings and the dihedral angles 83.4°, 72.8°, 8.9° and 46.7° of four carboxylate groups (2-, 2′-, 3-, and 3′-COO−) corresponding to the planes of linked phenyl rings are measured, leaving a carboxyl group protonated and uncoordinated. EuO9 SBU units are interconnected with each other through 2-, 2′-, and 3′-carboxyl groups to afford a helical chain along the b direction, the pitch to the length is 31 Å (Figure 1b). The same chiral helical chains are connected together C
DOI: 10.1021/acs.inorgchem.6b01815 Inorg. Chem. XXXX, XXX, XXX−XXX
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Figure 4. (a) The 5D0 → 7F2 transition intensities of Eu−HODA when immersed into various pure solvents with excitation at 305 nm. (b) Family of luminescence spectra of Eu−HODA (60 μM) upon adding acetone. The inset picture exhibits the PL intensity of the Eu−HODA/DCM emulsion with the change of acetone content.
compared to that from Eu−HODA, was easy and clear to observe by the naked eye (see the SI, Figure S6). A first-order exponential decay could be well-fitted between the quenching effect of the fluorescence intensity at 614 nm and the content of acetone, indicating that the decreasing trend of Eu−HODA luminescence with acetone addition is diffusion-controlled. Since acetone shows a wide absorption from 220 to 320 nm, which overlays the absorbing band of H4ODA, it was suggested that the competitive adsorption of acetone molecules weakened the energy transfer from HODA3− sensitizer to the EuIII moiety,31 bringing about a reduction of the luminescence intensity of Eu−HODA. Furthermore, the fast/simple regeneration is the most important topic regarding the sensing performance. The solids of Eu−HODA for acetone sensing could be regenerated over many cycles after repeatedly washing with DCM. The almost complete recovery (ca. 97%) of the initial fluorescence intensity of Eu−HODA over five cycles implied their high photostability, making them potentially applicable for long-term acetone detection or environmentalmonitoring applications (see the SI, Figure S7). Luminescent Sensing of Metal Ions. Considering the uncoordinated carboxyl group in the HODA3− ligand, which can act as a potential coordination site for metal ions, we investigated the sensing properties of Eu−HODA for metal ions. In this regard, the responses of the fluorescence of Eu− HODA/water standard emulsion toward 20 different metal cationsLi+, Na+, K+, Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Zn2+, Cd2+, Fe2+, Hg2+, Co2+, Ni2+, Cu2+, Al3+, Cr3+, Fe3+, Ag+ and Pb2+in aqueous solution were studied (Figure 5b). The addition of alkali metal cations, such as K+, Na+, and Li+, resulted in nearly no obvious spectral changes of Eu−HODA. A slight fluorescence quenching was just obversed in the case of the alkaline-earth cations Mg2+, Ca2+, Sr2+, and Ba2+; the transitionmetal ion Mn2+, Zn2+, Cd2+, Fe2+, Hg2+, Co2+, Ni2+, and Cu2+; and the trivalent ions Al3+ and Cr3+. Compared with other metal ions, only addition of Fe3+ ion (1.3 mM) to Eu−HODA (60 μM) aqueous solution caused ca. 99.3% quenching of the typical Eu(III)-based fluorescence, accompanied by a remarkable luminescence quenching visible under UV radiation (see the SI, Figure S6). Further competition experiments revealed that 1 equiv of other metal ions did not affect the luminescence response induced by Fe3+; in addition, even Pb2+ and Ag+ do not cause interference of the fluorescence quenching induced
acetonitrile (MeCN), tetrahydrofuran (THF), toluene (T), benzene (B), acetone, and N,N′-dimethylformamide (DMF); particularly for methanol and acetone, the most remarkable enhancement and quenching effects are found, respectively (Figure 4a). The sensing sensitivity for methanol and acetone were further examined through fluorescence detection experiments in more detail. A 1 cm cuvette containing 3 mL of Eu− HODA/dichloromethane standard emulsion was used to monitor the emissive response to methanol by injecting different amounts of methanol into it. As shown in Figure 3a, addition of methanol leads to a gradual increase of the luminescence intensity of Eu−HODA at 614 nm up to 3.1-fold of the enhanced efficiency, indicating the potential of Eu− HODA for methanol sensing. Such turn-on luminescence switching initiated by methanol molecules is probably attributed to hydrogen-bonding interactions with the terminal water molecules in the framework, alleviating the O−H highenergy vibrations, thus leading to an increase in emission intensities.26 Interestingly, the effects of two other alcohols with different molecular sizes, i.e., ethanol (kinetic diameter 0.44 nm) and n-propanol (kinetic diameter 0.53 nm), on the fluorescent emission intensity of Eu−HODA were also studied. Consequently, a 1.5-fold increase in fluorescence was observed when the same amounts of ethanol were added to the Eu− HODA emulsion. The presence of n-PrOH left the fluorescence intensity almost unchanged under the same experimental conditions (Figure 3b). Considering that the pore size (4.1 Å) of Eu−HODA is bigger than that of methanol (kinetic diameter 3.8 nm) but smaller than that of ethanol and n-propanol, we speculate that the remarkable size selectivity for the sensing of alcohols mainly depends on the size constraint effect of the host pore and the guest analytes.27 On the other hand, the fluorescence intensities of the Eu− HODA/dichloromethane standard emulsion were gradually reduced by the gradual increase of the acetone content and almost disappeared when the acetone content was up to 0.35 vol %. Moreover, their luminescence intensity lowered to 50% (EC50) at 0.03 vol % acetone, which is much more sensitive than those obtained by other fluorescent sensors for acetone based on MOFs (0.075−0.8 vol %)28,29 and is below the occupational exposure limit of acetone (0.075 vol %) stipulated by the American Conference of Governmental Industrial Hygienists (ACGIH).30 Under UV radiation, noticeably weaker red light emission from acetone-incorporated Eu−HODA, D
DOI: 10.1021/acs.inorgchem.6b01815 Inorg. Chem. XXXX, XXX, XXX−XXX
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For Eu−HODA, the detection limit for Fe3+ is established to be at or below 0.1 μM (6.4 ppb) according to the 3δ IUPAC criteria. The high quenching effect coefficient and the low detection limit for Fe3+ demonstrated that Eu−HODA was a highly sensitive sensor for Fe3+ detection. Importantly, our system shows steady luminescence within the pH range from 6.0 to 10.5, facilitating the Fe3+ detection in aqueous media at physiological pH (see the SI, Figure S10). The further investigation of the possible sensing mechanism of Eu−HODA for Fe3+ ions has been carried out. The powder XRD was first applied to supervise the structure changes during Fe3+ solution treatment. Just as shown in Figure 6a, PXRD patterns of the Eu−HODA samples immersed in Fe3+ solution for 5 h showed several new peaks besides the original XRD pattern of Eu−HODA, and they are marked with stars. This indicates that a long immersion is likely to result in the formation of a new kind of structure; however, the main framework of Eu−HODA is maintained. Moreover, the inductively coupled plasma (ICP) measurements indicated that negligible Eu3+ content is observed in the filtrate, which excludes the following two possibilities leading to such dramatic fluorescence quenching: the MOF material is dissolved and Eu3+ in the framwork is exchanged with Fe3+. Meanwhile, FTIR spectra exhibited that the vibration bands at 1659 cm−1, assigned to the uncoordinated carboxyl groups of Eu−HODA, almost disappeared, and new vibration bands at 1142 cm−1, belonging to the bending stretching of Fe−O−H, and at 820 cm−1, belonging to the antisymmetric stretch of Fe−O, emerged for Fe3+-immersed Eu−HODA.33 All of those results demonstrate that sensing of Fe3+ by Eu−HODA was attributed to the coordination to the uncoordinated carboxyl groups of Eu−HODA, thus reducing the energy transfer efficiency from ligands to the Eu3+ ion, leading to decreased Eu(III)-based luminescence intensity. The adsorption ability of Eu−HODA in the solid−liquid phase has been also measured to evaluate its potential as a practical absorbent material for Fe3+. Eu−HODA (20 mg) was immersed into 50 mL of the Fe3+ solution (5.4 μM, 0.35 ppm). After stirring of the mixture for 4 h, it was filtered and the filtrate was subjected to ICP to analyze the concentration of residual Fe3+. The results showed that almost no Fe3+ remained. Even when adding NH4SCN solution to the above filtrate, there was no appearance of the representative sanguine species [Fe(SCN)n]3−n, further indicating that no residual Fe3+ was present in the filtrate. In the meantime, the amounts of Eu3+ in the filtrate also did not increase, demonstrating that Eu−
Figure 5. (a) The luminescence spectra of Eu−HODA (60 μM) upon adding ferric nitrate to 1.3 mM. (b) Fluorescence responses of Eu− HODA (60 μM) to various cations in H2O solution. The red bars stand for the luminescence intensities of Eu−HODA when the metal ions (1.3 mM) are present. The green ones stand for the change of the emission when continuing to add 1.3 mM Fe3+ (excitation at 305 nm).
by Fe3+, suggesting that Eu−HODA can sense Fe3+ with remarkable selectivity. To further understand the fluorescence response of Eu− HODA toward Fe3+ ions, the fluorescence spectra upon the addition of 1.3 mM Fe3+ to Eu−HODA/water suspension were collected. The Stern−Volmer equation can be used to rationalize the quenching effect: I0/I = 1 + Ksv[M], where I0 is the original fluorescence intensity and I is the fluorescence intensity upon adding Fe3+, [M] is the molar concentration (mol/L) of Fe3+, and Ksv is the Stern−Volmer constant. According to the above fluorescence data in Figure 5a, a Ksv value of 2.09 × 104 M−1 is calculated. This Ksv value is comparable to those of organic compounds for detection of Fe3+ (typical Ksv of about 104 M−1)32 (see the SI, Figure S9).
Figure 6. (a) PXRD patterns of Eu−HODA and Eu−HODA after treatment with Fe3+ solution for 5 h; stars denote the new peaks. (b) IR spectra of as-prepared Eu−HODA and Eu−HODA⊃Fe3+ [Eu−HODA after immersion in Fe(NO3)3 solution]. E
DOI: 10.1021/acs.inorgchem.6b01815 Inorg. Chem. XXXX, XXX, XXX−XXX
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Figure 7. (a) Fluorescent spectra of Eu−HODA (60 μM) in water (black line) and with 0.4 mM Fe3+ (red line) and then treatment with glutathione (10 equiv of Fe3+, green line) or EDTA/base (10 equiv of Fe3+, blue line). The inset shows part of the spectra from 608 to 616 nm and shows the photo of Eu−HODA⊃Fe3+ treated with excess NH4SCN. (b) Photographs of Eu−HODA-based test strips for visible fluorescent detection of a small amount of Fe3+ ions: (i) unused test paper and test paper treated with different concentrations of Fe3+ ions, namely, (ii) 10−7 M, (iii) 10−6 M, (iv) 10−5 M, and (v) 10−3 M (under 254 nm UV light).
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CONCLUSION In summary, we have successfully targeted the robust chiral lanthanide luminescent MOF Eu−HODA. It exhibited the sizeselective sensing of methanol over simple aliphatic alcohols in a luminescence-enhancing manner and was also a good on−off chemosensor for acetone molecule, with the especially high sensitivity of ca. 0.03 vol % (EC50). With the uncoordinated carboxyl groups within the channel as potential coordination sites for metal ions, Eu−HODA features the highly selective and ultrasensitive recognition and adsorption of Fe3+ from aqueous solution, having the potential to be a long-acting toxicide. Furthermore, a simple and portable test paper was able to detect Fe3+ ions at the picogram level by the naked eye. These remarkable results may spark real application prospects for multifunctional materials in the laboratory and in daily life in the near future.
HODA had upstanding stability and a strong adsorptivity for Fe3+. The Ministry of Environmental Protection of P. R. China has set the national standards for Fe3+ in daily drinking water to be 5.4 μM.34 Thus, we believe that Eu−HODA material has the potential ability to remove toxic metal ions from drinking water. Although electron transfer mechanisms and oxygen metabolism in the human body need the catalytic action of Fe3+ ions included in many enzymes, high levels of Fe3+ ions within the body increase the incidence of many serious deseases, such as dysfunction of pancreas, heart, and liver and certain cancers. Generally, glutathione (GSH) is one of the most common toxicides for acute iron poisoning; however, it is usually digested by an enzyme and releases these metal ions again.35 Owing to the strong coordination ability of Eu−HODA, the luminescence of the Fe3+-coordinated Eu−HODA complex cannot be recovered, even upon adding glutathione (Figure 7a). Furthermore, the mesopores are able to be protected against enzymatic digestion through the stable functional groups, and the addition of EDTA/base also cannot recover the quenching fluorescence intensity (Figure 7a). Thus, Eu−HODA should be a long-acting toxicide. In practical application, a fluorescence test paper was developed to realize simple and portable detection of Fe3+ in aqueous solution. Immersing a Whatman filter paper with the size of 2.5 × 2.5 cm2 in Eu−HODA/water emulsion and drying it affords the test papers. In order to detect Fe3+ with very small amounts, 1 μL of different concentrations of Fe3+ aqueous solutions was placed on Eu−HODA test papers. As shown in Figure 7b, the colors of different intensities, corresponding to different Fe3+ concentrations on the test papers, can be distinguished by the naked eye under UV light irradiation of 254 nm. The detectable minimum amount of Fe3+ ions was calculated to be 40.4 pg levels. All experimental data highlight the advantages of Eu−HODA as a sensor for Fe3+ ions with high efficiency, sensitivity, and selectivity.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b01815. Additional experimental details, crystal data and TGA curve of Eu−HODA, and related spectra (Figures S1− S10 and Table S1) (PDF) Crystallographic data of Eu−HODA in CIF format (CIF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest. F
DOI: 10.1021/acs.inorgchem.6b01815 Inorg. Chem. XXXX, XXX, XXX−XXX
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ACKNOWLEDGMENTS This work was financially supported by the NSFC (21401086, 21401087), the Natural Science Foundation of Jiangsu Province (BK20140234), and PAPD and TAPP of Jiangsu Higher Education Institutions.
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