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| Home > Publications database > Insight into the mechanism of modulated syntheses: in situ synchrotron diffraction studies on the formation of Zr-fumarate MOF |
| Journal Article | PUBDB-2014-03547 |
; ; ; ; ; ; ;
2014
RSC
London
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Please use a persistent id in citations: doi:10.1039/c4ce01095g
Abstract: In this work, the formation of a Zr-based metal–organic framework (MOF), Zr-fumarate MOF (Zr-fumMOF), is studiedin situ by energy-dispersive diffraction. The Zr-fumMOF can be synthesised in DMF as wellas in water-based synthesis systems. In both cases, its formation requires modulation,i.e. a monocarboxylicacid which is used as the modulator has to be added to the synthesis mixture. In general, differentmechanisms of modulation are possible, for example, deprotonation of the linker molecule (deprotonationmodulation) or coordination modulation (wherein the molecules of the modulator compete with the linkermolecules for the coordination sites at the inorganic building units). Independently of the specificmechanism, modulation often improves the reproducibility of the MOF synthesis and the crystallinity of theproduct and may be used to control crystal size and morphology. This study is the first to investigate thekinetics of modulated MOF syntheses with regard to coordination modulation. According to this concept,the addition of a modulator usually decelerates the reaction. Our kinetic investigations show that this is thecase for the formation of Zr-fumMOF in the water-based synthesis with formic acid used as a modulator.On the contrary, the addition of formic acid to the DMF-based synthesis results in an accelerating effect.This unexpected effect can be attributed to a small amount of water present in formic acid. Correspondingly, the addition of water to the synthesis mixture also showed an accelerating effect. These investigations emphasise the subtle interplay of the different ingredients in a MOF synthesis. In the case of theZr-fum MOF, both the modulator formic acid and the water content strongly affect the kinetics ofcrystallisation. Quantitative evaluation of the kinetic data using the Gualtieri equation provides additionalinsight into the mechanisms of coordination-modulated MOF formation reactions and excludes the idea ofdeprotonation modulation
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