Dual-Emission of Lanthanide Metal–Organic Frameworks

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Dual-Emission of Lanthanide Metal-Organic Frameworks Encapsulating Carbon Based Dots for Ratiometric Detection of Water in Organic Solvents Yongqiang Dong, Jianhua Cai, Qingqing Fang, Xu You, and Yuwu Chi Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.5b03974 • Publication Date (Web): 08 Jan 2016 Downloaded from http://pubs.acs.org on January 13, 2016

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Dual-Emission of Lanthanide Metal-Organic Frameworks Encapsulating Carbon Based Dots for Ratiometric Detection of Water in Organic Solvents Yongqiang Dong, Jianhua Cai, Qingqing Fang, Xu You and Yuwu Chi* MOE Key Laboratory of Analysis and Detection for Food Safety, Fujian Provincial Key Laboratory of Analysis and Detection for Food Safety, and College of Chemistry, Fuzhou University, Fuzhou, Fujian 350108, China *E-mail: [email protected]. Tel/Fax: +86-591-22866137

ABSTRACT: Nitrogen and sulfur co-doped CDs (N,S-CDs) with strong blue light emission are encapsulated in to red lightemitting europium metal-organic frameworks (Eu-MOFs) to form two color light-emitting nanohybrids (Eu-MOFs/N,S-CDs). In organic solvents, the encapsulated N,S-CDs are aggregated and confined in the cavities of the Eu-MOFs, exhibiting only very weak photoluminescence (PL) signal. Therefore, the nanohybrids show red light emission of the Eu-MOFs. On the contrary, as the EuMOFs/N,S-CDs are dispersed in water, the encapsulated N,S-CDs are released into solution while the red light emission of the EuMOFs are quenched due to the effect of O-H oscillators. The nanohybrids are used as the probe for the water content in organic solvents. Take ethanol as an example, as the water content is increased from 0.2% to 30%, the nanoprobe provides distinguishable PL color change. The ratio of light intensity at 420 nm to that at 623 nm (I420/I623) increases linearly with increasing water content in the range from 0.05% to 4%, with a low detection limit of 0.03%.

INTRODUCTION Microporous materials constructed by connecting organic ligands with metal clusters/cations, usually referred to metalorganic frameworks (MOFs), have received much attention in recent years.1 MOFs were found to present many unique properties including high specific surface areas, controllable pore sizes, abundant unsaturated open metal sites and predictable structures.2 Accordingly, MOFs have been proposed to be promising in many fields such as chemical catalysis,3 gas storage,4 separation,5 drug delivery & release and sensing.6-8 In particular, increasing interest has been focused on the sensing of inorganic ions and small organic molecules using functionalized MOFs.9-11 Luminescent MOFs have recently emerged to be a hot topic due to the multicolor and tunable emission properties.12 In general, two main strategies have been adopted to synthesize luminescent MOFs. One strategy is using Lanthanide ions as the coordination center to synthesize Lanthanide–MOFs (LnMOFs), which are able to generate intense visible fluorescence (PL) emission usually arising from f–f or f−d energy transfer tuned by suitable adjacent chromophores when exposed to UV light.13 Among the various Lanthanide ions, europium ion (Eu3+, red PL) and terbium ion (Tb3+, green PL) are the most widely used due to the big Stokes’ shifts and relative long lifetimes.14-16 The other strategy is encapsulating luminescent guest molecules or nanoparticles into the frameworks of non-luminescent MOFs.17 Take example, zeolitic imidazolate framework materials (ZIF-8) have been used to encapsulate some functionalized carbon based dots (CDs),18 which have been well applied in numerous applica-

tions including bioimaging,19 catalysis,20 and in particular sensing,21-23 due to the unique optical properties caused by the quantum confinement and edge effects.24-26

Scheme 1. The synthesis of Eu-MOFs/N,S-CDs and detection of water content in organic solvents.

Luminescent MOFs, especially the Ln-MOFs, have been developed as a new platform for chemical sensing in biological and environmental systems.27-31 In particular, some luminescent water sensors have been proposed based on the PL response of Ln-MOFs. Simple, fast and reliable sensors for the detection of water in organic solvents are of significance in chemical industry.32 For example, the presence of trace water often impedes not only the yield of chemical and drugs, but also their activities and uses. As a traditional method for the detection of water, Karl-Fischer titration has been used most widely. However, the requirement of specific instruments and trained personnel limits seriously its further application.33 Contrarily, luminescence-based optical sensor usually exhibits several advantages such as simple operation, low cost, and short response time.34 However, to the best of our knowledge, all the reported water sensors based on luminescent MOFs provided only single-color and intensity-

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varying PL signals, which is unfavorable for the signal analysis with naked eye. Herein, strongly blue light-emitting nitrogen and sulfur co-doped CDs (N,S-CDs) have been encapsulated in the framework of a kind of red-emitting and water-stable Eu-MOFs.35 Based on the unique PL behaviors of the dual-emission nano-hybrids (Eu-MOFs/N,S-CDs), a sensitive and visual colorimetric sensor has been developed for water contents in organic solvents (Scheme 1).

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face areas of the products were measured by Brunauer– Emmett–Teller (BET) method using nitrogen gas adsorption/desorption at 77 K (BET, Micromeritics ASAP 2020, USA). FL spectra were recorded on a F-4600 FL spectrofluorometer. UV-Vis absorption spectra were recorded by a Lambda 750 UV/Vis spectrophotometer. RESULTS AND DISCUSSION

EXPERIMENTAL SECTION Materials. Europium nitrate hexahydrate (Eu(NO3)3.6H2O, >99.9%), cyclohexanol (CP, >97%), 1,3,5benzenetricarboxylic acid (>98%), citric acid (99.9%) and Lcysteine (97.0%) were purchased from Aladdin (Shanghai, China). Ethanol and N,N-dimethylformamide (DMF) of analytical purity were obtained from Tianjin Standard Science and Technology Co. (Tianjin, China). Dibutylamine of analytical purity was obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Other chemicals were of reagent grade unless otherwise noted. All chemicals were used without further purification. Preparation of N,S-CDs. The N,S-CDs were synthesized according to a method described in a previous report. Briefly, 2 g citric acid and 1 g L-cysteine were dissolved in 2 mL DI water. Then the solution was heated at 70 °C for 24 h to form thick syrup, which was subsequently heated hydrothermally in a Teflon-equipped stainless-steel autoclave at 200 °C for 2 h with a heating rate of 10 °C min-1. The resulted black syrup product was neutralized with NaOH. The obtained solution was further dialyzed in a dialysis bag (retained molecular weight: 500 Da) for 72 h to remove the residual organics. Preparation of the bare Eu-MOFs and the N,S-CDsfunctionalized Eu-MOFs (Eu-MOFs/NS-CDs composite). The bare Eu-MOFs were synthesized according to a reported method,35 while the Eu-MOFs/NS-CDs were synthesized using the same method except for adding N,S-CDs in the precursors. Typically, Eu-MOFs/NS-CDs and the bare EuMOFs were prepared by adding Eu(NO3)3.6H2O (0.1 mmol), 1,3,5-benzenetricarboxylic acid (0.1 mmol), N,S-CDs (0.0024 g) in a mixed solvent of DMF (27 mL), water (2 mL) and cyclohexanol (2 mL), then 2 drops of dibutylamine and 3 drops of HNO3 (2 M) were added into the above mixture (the N,S-CDs were absence for the preparation of the bare Eu-MOFs). The mixed solution (pH=5) was stirred for 2 h at room temperature and later was placed in an oven at 85°C for 16 h, producing crystals. The obtained crystals were collected, washed three times in turn with DMF and ethanol, and finally dried by a vacuum oven at 80 °C for 5 h. Instrumentation. The Fourier transform infrared (FTIR) spectra were obtained on a FT-IR spectrophotometer (Thermo Nicolet 360). X-ray powder diffraction (XRD) patterns were taken using a Rigaku Miniflex X-ray diffractometer at 30 kV, 15 mA for Cu Kα (λ = 1.5406 Å) with scan speed of 0.1 sec/step and a step size of 0.01°. Transmission electron microscopic (TEM) and high resolution TEM (HRTEM) measurements were performed on a Tecnai G2 F20S-TWIN electronic microscope at operation voltage of 200 KV. The scanning electron microscopic (SEM) images were taken by a Nova Nano SEM 230 field-emission microscope. The sur-

Figure 1. (A) FTIR spectra of Eu-MOFs (a), N,S-CDs (b) and Eu-MOFs/N,S-CDs (c); (B) SEM, (C) TEM and (D) HRTEM images of the obtained Eu-MOFs/N,S-CDs composite; (E) XRD spectra obtained for Eu-MOFs (a) and Eu-MOFs/N,S-CDs (b); (F) N2 adsorption isotherm obtained for Eu-MOFs and EuMOFs/N,S-CDs composite.

The TEM image indicates that the used N,S-CDs have uniform lateral sizes range from 5 to 8 nm. The HRTEM image reveals the typical lattice spacing of ca. 0.24 nm, which corresponds to the (100) in-plane lattice spacing of graphene (Figure S1). The UV-vis spectrum of the N,S-CDs shows a broad absorption band below 450 nm, with a sharp peak centered around 343 nm. The PL spectra exhibit the excitation-dependent emission of the N,S-CDs (Figure S2). Under the excitation of 365 nm UV light, the N,S-CDs solution shows bright blue light emission. The FTIR spectra (Figure 1A) reveal that the prepared Eu-MOFs/N,S-CDs composites possess characteristic absorption bands of both Eu-MOFs and N,S-CDs, indicating that the N,S-CDs have been combined with the Eu-MOFs. The SEM, TEM and HRTEM images show that the Eu-MOFs/N,S-CDs are present as nanoscale flakes (Figure 1B, C, D). In general, the morphology of the Eu-MOFs/N,S-CDs have no obvious difference from the bare Eu-MOFs (Figure S3). XRD pattern of the EuMOFs/N,S-CDs composites agrees well with that of the parent Eu-MOFs (Figure 1E). The results of both SEM and XRD suggest that the combination with N,S-CDs has no

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effect on the main structure of the Eu-MOFs. The BET isotherms of both Eu-MOFs/N,S-CDs and Eu-MOFs at 77 K show typical type-I isotherm characteristics of microporous solid (Figure 1F). The BET surface area of the bare EuMOFs is 320.7 m2/g, while the average pore width is about 14.5 nm. In contrast, the BET surface area of the EuMOFs/N,S-CDs is decreased to 197.4 m2/g, and the average pore width is about 9.6 nm. Thus, the BET result implies that the N,S-CDs should be encapsulated in the pores of the EuMOFs.

Figure 2. PL emission spectra and UV-vis absorption spectra of 1 mg/mL Eu-MOFs/N,S-CDs dispersed in DMF (red) and water (blue). The inset shows the photos of Eu-MOFs/N,S-CDs dispersed in pure DMF solvent (left) and pure water (right) under 365nm UV light.

As shown in Figure 2, the suspension of the obtained EuMOFs/N,S-CDs materials in ethanol exhibits a broad UV-vis absorption background , with a weak peak centered at around 380 nm (red dash curve in Figure 2). The broad absorption background should result from the scattering effect of the MOF particles (Figure S4), whereas the weak peak should be ascribed to the encapsulated N,S-CDs aggregates. The PL spectrum of the Eu-MOFs/N,S-CDs suspension presents three emission bands centered at 420, 598 and 623 nm, respectively (red solid curve in Figure 2). The 420 nm band should be assigned to the encapsulated N,S-CDs, whereas the other two bands belong to the characteristic transitions of Eu3+.38 Apparently, the intensity of the blue-emission band is much weaker than those of the red-emission bands. Furthermore, the naked eye is much more sensitive to red light than to blue one. As a result, the Eu-MOFs/N,S-CDs suspension seems bright red under the excitation of 365 nm UV light (see the inset in Figure 2). As the Eu-MOFs/N,S-CDs are dispersed in water, the results are much different. The suspension shows an abvious absorption peak centered at 342 nm (blue dash curve in Figure 2), which is well consistent with the characterical absorption of the N,S-CDs (Figure S2). The PL spectrum indicates that the intensity of the blue-emission peak at 420 nm is much stronger than that in ethanol, whereas the red-emission bands at 598 and 621 nm disappear (blue solid curve in Figure 2). As the suspension is centrifuged, the supernatant keeps the bright blue emission under the excitation of 365 nm UV light (Figure S5), whereas the morphology of the precipitated MOFs has no obvious change in the SEM observation

(Figure S6). The results indicate that the increasement of the blue-emission should be related to the release of the N,SCDs. As for the quenching of the red emission, it should result from the change of chemical enviroment. It has been well known that water molecules are very efficient quencher (O-H oscillators) towards the PL of Eu3+ complexes.39,40 The mechanism of the PL response of Eu-MOFs/N,S-CDs towards water in organic solvents is shown in Scheme 1.

Figure 3. (A) PL spectra (λex = 365 nm) of 1 mg/mL EuMOFs/N,S-CDs in ethanol upon addition of aliquots of water. (B) The amplification of the red-emission peaks in (A). (C)The visual PL photos of 1 mg/mL Eu-MOFs/N,S-CDs dispersed in ethanol with various water contents(V/V) under 365 nm UV light.

Since the Eu-MOFs/N,S-CDs composite emits red light in organic solvents and blue light in water, a colorimetric sensor may be established based on the PL properties of the EuMOFs/N,S-CDs composites. As shown in Figure 3A, upon gradually increasing the water content in ethanol, the intensity of blue emission peak shows continuous enhancement. The PL intensity of the blue emission increases linearly with the water content in the range of 0% to 10% (V/V), then the growth curve bends downwards as the water content is further increased (Figure S7). At the meanwhile, the red emission peaks decrease contrarily as the water content is increased (Figure 3B). It can be seen that the PL intensity of the red emission is quite sensitive to the water content in the range of 0% to 10% (the PL intensity is directly proportional to the water content in the range from 0% to 4 %). As the water is further increased, the PL intensity of the red emission is relative insensitive to the change of the water content (Figure S6). As shown in Figure 3C, the changes in PL intensities of the emission peaks result in continuous PL color changes from red to blue. It can be seen that the color change is quite sensitive when the water content is lower than 10%. Even a slight increase of the water content in ethanol can cause obvious color change. Undoubtedly, the ratiometric PL probe is sensitive and reliable for visual detection of water in organic solvents. Under the excitation of 365 nm UV light, the intensity ratio of the two emission wavelengths (I420/I623) against the water content is shown in Figure 4. The ratio of I420/I623 increases linearly as the water content is increased

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from 0.05% to 4%. As the water content is further increased, the growth curve bends upwards. The detection limit is calculated to be 0.03% based on the ratio of signal-to-noise of 3, which is better than those of some reported methods based on Luminescent MOFs.40,41 Besides ethanol, the Eu-MOFs/N,S-CDs can also be applied to detect water content in other organics, such as DMF (Figure S8) and acetonitrile (Figure S9), etc.

Figure 4. (A) Plot of I420/I623 versus the water content in ethanol. (B) The amplification of the red region in (A). The dosage of Eu-MOFs/N,S-CDs is 1 mg/mL. The excitation wavelength was 365 nm.

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Xinqi Zhang at Instrumentation Analysis and Measurement Center of Fuzhou University for the help in TEM.

ASSOCIATED CONTENTS Supporting Information TEM and HRTEM images of the N,S-CDs (Figure S1); UV and PL spectra of the N,S-CDs (Figure S2); TEM and HRTEM images of the bare Eu-MOFs (Figure S3); UV spectra of the bare Eu-MOFs dispersed in ethanol and water (Figure S4); PL images of Eu-MOFs/N,S-CDs dispersed in water before and after centrifugation (Figure S5); SEM image of the Eu-MOFs/N,SCDs after being well soaked in water (Figure S6); Plots of I420 and I623 versus the water content in ethanol (Figure S7); The visual PL photos and the corresponding PL spectra of EuMOFs/N,S-CDs dispersed in DMF with various water contents under 365 nm UV light (Figure S8), The visual PL photos and the corresponding PL spectra of Eu-MOFs/N,S-CDs dispersed in acetonitrile with various water contents under 365 nm UV light (Figure S9). This information is available free of charge via the Internet at http://pubs.acs.org/.

REFERENCES

CONCLUSION A novel dual-emission Eu-MOFs/N,S-CDs have been synthesized. In a pure organic solvent, the N,S-CDs are aggregated and encapsulated in the chambers of Eu-MOFs. Therefore, the nano-hybrids exhibit only the red light emission of the Eu-MOFs in pure organic solvents. As the EuMOFs/N,S-CDs are dispersed in water, the N,S-CDs are released into the solution to emit strong blue light. Meanwhile, the red light emission of the Eu-MOFs is quenched due to the effect of O-H oscillators. Accordingly, the EuMOFs/N,S-CDs show strong blue light emission in water. Based on the unique PL properties of the Eu-MOFs/N,SCDs, a novel and visual PL colorimetric sensor for water contents in organic solvents has been established. As the water content in ethanol is increased gradually, the red light emission of the Eu-MOFs decreases while the blue light emission of N,S-CDs increases. The light intensity ratio, I420/I623, increases linearly with increasing water content in the range from 0.05% to 4%. The detection limit is as low as 0.03%. What is more important, the dual PL changes lead to obvious changes in color, based on which a novel, sensitive and visual sensing method for water in ethanol has been developed with a wide response range of 0.2% to 30%.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Tel: +86-591-22866137. Fax: +86-591-22866137.

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This study was financially supported by National Natural Science Foundation of China (21305017, 21375020), National Basic Research Program of China (2010CB732400), and the Program for Changjiang Scholars and Innovative Research Team in University (No. IRT1116). The authors thank Professor

(1) Zhou, H. C.; Long, J. R.; Yaghi, O. M. Chem. Rev. 2012, 112, 673-674. (2) Chen, B.; Yang, Y.; Zapata, F.; Lin, G.; Qian, G.; Lobkovsky, E. B. Adv. Mater. 2007, 19, 1693-1696. (3) Corma, A.; Garcia, H.; Llabrés i Xamena, F. Chem. Rev. 2010, 110, 4606-4655. (4) Millward, A. R.; Yaghi, O. M. J. Am. Chem. Soc. 2005, 127, 17998-17999. (5) Zornoza, B.; Martinez-Joaristi, A.; Serra-Crespo, P.; Tellez, C.; Coronas, J.; Gascon, J.; Kapteijn, F. Chem. Commun. 2011, 47, 9522-9524. (6) Horcajada, P.; Serre, C.; Maurin, G.; Ramsahye, N. A.; Balas, F.; Vallet-Regi, M.; Sebban, M.; Taulelle, F.; Férey, G. J. Am. Chem. Soc. 2008, 130, 6774-6780. (7) Kreno, L. E.; Leong, K.; Farha, O. K.; Allendorf, M.; Van Duyne, R. P.; Hupp, J. T. Chem. Rev. 2012, 112, 1105-1125. (8) Hu, Y.; Liao, J.; Wang, D.; Li, G. Anal. Chem. 2014, 86, 39553963. (9) Chen, B.; Xiang, S.; Qian, G. Acc. Chem. Res. 2010, 43, 11151124. (10) Robinson, A. L.; Stavila, V.; Zeitler, T. R.; White, M. I.; Thornberg, S. M.; Greathouse, J. A.; Allendorf, M. D. Anal. Chem. 2012, 84, 7043-7051. (11) Yang, C.-X.; Ren, H.-B.; Yan, X.-P. Anal. Chem. 2013, 85, 7441-7446. (12) Cui, Y.; Yue, Y.; Qian, G.; Chen, B. Chem. Rev. 2011, 112, 1126-1162. (13) Rocha, J.; Carlos, L. D.; Paz, F. A. A.; Ananias, D. Chem. Soc. Rev. 2011, 40, 926-940. (14) Petoud, S.; Cohen, S. M.; Bünzli, J.-C. G.; Raymond, K. N. J. Am. Chem. Soc. 2003, 125, 13324-13325. (15) Dorenbos, P. J. Lumin. 2000, 91, 91-106. (16) Werts, M. H.; Jukes, R. T.; Verhoeven, J. W. Phys. Chem. Chem. Phys. 2002, 4, 1542-1548. (17) Lu, G.; Li, S.; Guo, Z.; Farha, O. K.; Hauser, B. G.; Qi, X.; Wang, Y.; Wang, X.; Han, S.; Liu, X.; DuChene, J. S.; Zhang, H.; Zhang, Q.; Chen, X.; Ma, J.; Loo, S. C.; Wei, W. D.; Yang, Y.; Hupp, J. T.; Huo, F. Nat. Chem. 2012, 4, 310-316. (18) Lin, X.; Gao, G.; Zheng, L.; Chi, Y.; Chen, G. Anal Chem. 2014, 86, 1223-1228. (19) Yang, S.-T.; Cao, L.; Luo, P. G.; Lu, F.; Wang, X.; Wang, H.; Meziani, M. J.; Liu, Y.; Qi, G.; Sun, Y.-P. J. Am. Chem. Soc. 2009, 131, 11308-11309.

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(20) Shen, J.; Zhu, Y.; Yang, X.; Li, C. Chem. Commun. 2012, 48, 3686-3699. (21) Jacobs, C. B.; Peairs, M. J.; Venton, B. J. Anal. Chim. Acta. 2010, 662, 105-127. (22) Dong, Y.; Li, G.; Zhou, N.; Wang, R.; Chi, Y.; Chen, G. Anal Chem. 2012, 84, 8378-8382. (23) Dong, Y.; Wang, R.; Li, G.; Chen, C.; Chi, Y.; Chen, G. Anal Chem. 2012, 84, 6220-6224. (24) Li, L.; Wu, G.; Yang, G.; Peng, J.; Zhao, J.; Zhu, J. J. Nanoscale 2013, 5, 4015-4039. (25) Bacon, M.; Bradley, S. J.; Nann, T. Part. Part. Syst. Char. 2014, 31, 415-428. (26) Hola, K.; Zhang, Y.; Wang, Y.; Giannelis, E. P.; Zboril, R.; Rogach, A. L. Nano Today 2014, 9, 590-603. (27) An, J.; Shade, C. M.; Chengelis-Czegan, D. A.; Petoud, S.; Rosi, N. L. J. Am. Chem. Soc. 2011, 133, 1220-1223. (28) Li, H.; Shi, W.; Zhao, K.; Niu, Z.; Li, H.; Cheng, P. Chem. Eur. J. 2013, 19, 3358-3365. (29) Guo, Z.; Xu, H.; Su, S.; Cai, J.; Dang, S.; Xiang, S.; Qian, G.; Zhang, H.; O'Keeffe, M.; Chen, B. Chem. Commun. 2011, 47, 55515553. (30) Wu, P.; Wang, J.; He, C.; Zhang, X.; Wang, Y.; Liu, T.; Duan, C. Adv. Funct. Mater. 2012, 22, 1698-1703.

(31) Zhou, J.-M.; Shi, W.; Xu, N.; Cheng, P. Inorg. Chem. 2013, 52, 8082-8090. (32) Ruiz-Garcia, L.; Lunadei, L.; Barreiro, P.; Robla, I. Sensors 2009, 9, 4728-4750. (33) Liang, Y. Y. Anal. Chem. 1990, 62, 2504-2506. (34) Ooyama, Y.; Uenaka, K.; Matsugasako, A.; Harima, Y.; Ohshita, J. RSC Adv. 2013, 3, 23255-23263. (35) Dong, Y.; Pang, H.; Yang, H. B.; Guo, C.; Shao, J.; Chi, Y.; Li, C. M.; Yu, T. Angew. Chem. Int. Ed. 2013, 52, 7800-7804. (36) Gustafsson, M.; Bartoszewicz, A.; Martín-Matute, B.; Sun, J.; Grins, J.; Zhao, T.; Li, Z.; Zhu, G.; Zou, X. Chem. Mater. 2010, 22, 3316-3322. (37) Banks, E.; Okamoto, Y.; Ueba, Y. J. Appl. Polym. Sci. 1980, 25, 359-368. (38) Klonkowski, A. M.; Lis, S.; Pietraszkiewicz, M.; Hnatejko, Z.; Czarnobaj, K.; Elbanowski, M. Chem. Mater. 2003, 15, 656-663. (39) Yu, Y.; Ma, J.-P.; Dong, Y.-B. CrystEngComm 2012, 14, 71577160. (40) Douvali, A.; Tsipis, A. C.; Eliseeva, S. V.; Petoud, S.; Papaefstathiou, G. S.; Malliakas, C. D.; Papadas, I.; Armatas, G. S.; Margiolaki, I.; Kanatzidis, M. G. Angew. Chem. Int. Ed. 2015, 127, 1671-1676.

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