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Molecules 2019, 24(3), 641; https://doi.org/10.3390/molecules24030641

Intrinsic Flexibility of the EMT Zeolite Framework under Pressure

1
Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK
2
Department of Chemistry, University of the Western Cape, Bellville, Cape Town 7535, South Africa
3
School of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK
4
Department of Materials, Imperial College London, Kensington, London SW7 2AZ, UK
5
European Synchrotron Radiation Facility, 71 avenue des Martyrs, 38000 Grenoble, France
6
Department of Chemical Engineering, University of Bath, Claverton Down, Bath BA2 7AY, UK
*
Author to whom correspondence should be addressed.
Academic Editor: Pierandrea Lo Nostro
Received: 18 January 2019 / Revised: 2 February 2019 / Accepted: 4 February 2019 / Published: 12 February 2019
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Abstract

The roles of organic additives in the assembly and crystallisation of zeolites are still not fully understood. This is important when attempting to prepare novel frameworks to produce new zeolites. We consider 18-crown-6 ether (18C6) as an additive, which has previously been shown to differentiate between the zeolite EMC-2 (EMT) and faujasite (FAU) frameworks. However, it is unclear whether this distinction is dictated by influences on the metastable free-energy landscape or geometric templating. Using high-pressure synchrotron X-ray diffraction, we have observed that the presence of 18C6 does not impact the EMT framework flexibility—agreeing with our previous geometric simulations and suggesting that 18C6 does not behave as a geometric template. This was further studied by computational modelling using solid-state density-functional theory and lattice dynamics calculations. It is shown that the lattice energy of FAU is lower than EMT, but is strongly impacted by the presence of solvent/guest molecules in the framework. Furthermore, the EMT topology possesses a greater vibrational entropy and is stabilised by free energy at a finite temperature. Overall, these findings demonstrate that the role of the 18C6 additive is to influence the free energy of crystallisation to assemble the EMT framework as opposed to FAU. View Full-Text
Keywords: zeolite; framework materials; EMC-2; crystallization; high pressure; X-ray diffraction; flexibility window; compressibility; lattice dynamics zeolite; framework materials; EMC-2; crystallization; high pressure; X-ray diffraction; flexibility window; compressibility; lattice dynamics
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Nearchou, A.; Cornelius, M.-L.U.; Skelton, J.M.; Jones, Z.L.; Cairns, A.B.; Collings, I.E.; Raithby, P.R.; Wells, S.A.; Sartbaeva, A. Intrinsic Flexibility of the EMT Zeolite Framework under Pressure. Molecules 2019, 24, 641.

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