- Increasing Alkyl Chain Length in a Series of Layered Metal-Organic Frameworks Aids Ultrasonic Exfoliation to Form Nanosheets
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Metal-organic framework nanosheets (MONs) are attracting increasing attention as a diverse class of two-dimensional materials derived from metal-organic frameworks (MOFs). The principles behind the design of layered MOFs that can readily be exfoliated to form nanosheets, however, remain poorly understood. Here we systematically investigate an isoreticular series of layered MOFs functionalized with alkoxy substituents in order to understand the effect of substituent alkyl chain length on the structure and properties of the resulting nanosheets. A series of 2,5-alkoxybenzene-1,4-dicarboxylate ligands (O2CC6H2(OR)2CO2, R = methyl-pentyl, 1-5, respectively) was used to synthesize copper paddle-wheel MOFs. Rietveld and Pawley fitting of powder diffraction patterns for compounds Cu(3-5)(DMF) showed they adopt an isoreticular series with two-dimensional connectivity in which the interlayer distance increases from 8.68 ? (R = propyl) to 10.03 ? (R = pentyl). Adsorption of CO2 by the MOFs was found to increase from 27.2 to 40.2 cm3 g-1 with increasing chain length, which we attribute to the increasing accessible volume associated with increasing unit-cell volume. Ultrasound was used to exfoliate the layered MOFs to form MONs, with shorter alkyl chains resulting in higher concentrations of exfoliated material in suspension. The average height of MONs was investigated by AFM and found to decrease from 35 ± 26 to 20 ± 12 nm with increasing chain length, with the thinnest MONs observed being only 5 nm, corresponding to five framework layers. These results indicate that careful choice of ligand functionalities can be used to tune nanosheet structure and properties, enabling optimization for a variety of applications.
- Ashworth, David J.,Roseveare, Thomas M.,Schneemann, Andreas,Flint, Max,Bernáldes, Irene Dominguez,Vervoorts, Pia,Fischer, Roland A.,Brammer, Lee,Foster, Jonathan A.
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p. 10837 - 10845
(2019/08/26)
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- Novel dirhodium coordination polymers: The impact of side chains on cyclopropanation
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Seven novel dirhodium coordination polymers (Rh2-Ln) (n = 1-7) are prepared by employing bitopic ligands to connect dirhodium nodes. The formation of the framework is confirmed by attenuated total reflectance Fourier transform infrared (ATR-FTIR) and 1H → 13C cross polarization magic angle spinning nuclear magnetic resonance (CP MAS NMR) spectroscopy. Defect sites resulting from incomplete ligand substitution are revealed by 19F MAS NMR. The random stacking behavior of the frameworks in the obtained solid is analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The Rh2/O interaction in neighboring layers is investigated by diffuse reflectance ultra-violet visible light (DR-UV-vis) spectroscopy and X-ray photoelectron spectroscopy (XPS). This interaction is relevant to understand the catalytic behavior of various Rh2-Ln catalysts in the cyclopropanation of styrene with ethyl diazoacetate (EDA). In this context, the structure-reactivity relationship is discussed by taking into consideration both interlayer Rh2/O interactions and steric effects of side chains.
- Liu, Jiquan,Xu, Yeping,Groszewicz, Pedro B.,Brodrecht, Martin,Fasel, Claudia,Hofmann, Kathrin,Tan, Xijuan,Gutmann, Torsten,Buntkowsky, Gerd
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p. 5190 - 5200
(2018/10/23)
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- Zinc-1,4-benzenedicarboxylate-bipyridine frameworks - Linker functionalization impacts network topology during solvothermal synthesis
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Substitution of 1,4-benzenedicarboxylate (bdc) with additional alkoxy chains is the key to construct a family of metal-organic frameworks (MOFs) of the type [Zn2(fu-bdc)2(bipy)]n (fu-bdc = functionalized bdc; bipy = 4,4′-bipyridine) exhibiting a honeycomb-like topology instead of the default pillared square-grid topology. Both the substitution pattern of the phenyl ring of the fu-bdc linker and the chain length of the alkoxy substituents have a major impact on the structure of the derived frameworks. Substitution at positions 2 and 3 leads to the trivial pillared square-grid framework, and substitution at positions 2 and 5 or 2 and 6 yields MOFs with the honeycomb-like topology. Also, simple methoxy substituents lead to the construction of a pillared square-grid topology, whereas longer substituents like ethoxy, n-propoxy, and n-butoxy generate honeycomb-like framework structures. These honeycomb MOFs feature one-dimensional channels, which are tuneable in diameter and functionality by the choice of substituent attached to the bdc-type linker. Pure component sorption isotherms indicate that the honeycomb-like frameworks selectively adsorb CO2 over N 2 and CH4. The Royal Society of Chemistry 2011.
- Henke, Sebastian,Schneemann, Andreas,Kapoor, Shobhna,Winter, Roland,Fischer, Roland A.
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p. 909 - 918
(2012/03/27)
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- Gated channels in a honeycomb-like zinc-dicarboxylate-bipyridine framework with flexible alkyl ether side chains
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Covalent functionalization of 1,4-benzenedicarboxylate (bdc) with methoxyethoxy groups induces conformational freedom in this molecule. Applying these 2,5-disubstituted bdc derivatives in metal-organic framework synthesis together with 4,4′-bipyridine as coligand yields novel honeycomb-like structures. The cylindrical channels of these materials are populated with flexible groups, which act as molecular gates for guest molecules. This allows highly selective sorption of CO2 over N2 and CH 4.
- Henke, Sebastian,Fischer, Roland A.
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p. 2064 - 2067
(2011/04/16)
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- Synthesis and photophysical properties of polymers containing a novel class of light emitters
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The monomers derived from blue-emission chromophores were investigated. The polymethacryclate and polyester based copolymers were obtained by using free radical polymerization or the Mitsunobu reaction. It was observed that all the copolymers, incorporati
- Lederc, Nicolas,Pasareanu, Marie-Christine,Attias, Andre-Jean
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p. 1531 - 1534
(2007/10/03)
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