scholarly journals Intrinsic Flexibility of the EMT Zeolite Framework Under Pressure

2019 ◽  
Author(s):  
Antony Nearchou ◽  
Mero-Lee U. Cornelius ◽  
Jonathan M. Skelton ◽  
Zoe Jones ◽  
Andrew Cairns ◽  
...  
Keyword(s):  
Free Energy ◽  
Computational Modelling ◽  
Lattice Energy ◽  
Vibrational Entropy ◽  
Organic Additives ◽  
X Ray Diffraction ◽  
Zeolite Framework ◽  
Guest Molecules ◽  
Fau Zeolite

<p>The roles of organic additives in the assembly and crystallisation of zeolites is still not fully understood. This is important when attempting to prepare novel frameworks to produce new zeolites. We consider 18-crown-6 ether as an additive, which has previously been shown to differentiate between the EMT and FAU zeolite 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 true geometric template. This was further studied with computational modelling, using first-principles comparative periodic DFT and lattice-dynamics calculations. It is shown that the lattice energy of FAU is more stable than EMT, however this is strongly impacted by the presence of solvent/guest molecules in the framework. Furthermore, the EMT topology possesses a greater vibrational entropy, being stabilised by free energy at 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. </p>

scholarly journals Intrinsic Flexibility of the EMT Zeolite Framework Under Pressure

2019 ◽  
Author(s):  
Antony Nearchou ◽  
Mero-Lee U. Cornelius ◽  
Jonathan M. Skelton ◽  
Zoe Jones ◽  
Andrew Cairns ◽  
...  
Keyword(s):  
Free Energy ◽  
Computational Modelling ◽  
Lattice Energy ◽  
Vibrational Entropy ◽  
Organic Additives ◽  
X Ray Diffraction ◽  
Zeolite Framework ◽  
Guest Molecules ◽  
Fau Zeolite

<p>The roles of organic additives in the assembly and crystallisation of zeolites is still not fully understood. This is important when attempting to prepare novel frameworks to produce new zeolites. We consider 18-crown-6 ether as an additive, which has previously been shown to differentiate between the EMT and FAU zeolite 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 true geometric template. This was further studied with computational modelling, using first-principles comparative periodic DFT and lattice-dynamics calculations. It is shown that the lattice energy of FAU is more stable than EMT, however this is strongly impacted by the presence of solvent/guest molecules in the framework. Furthermore, the EMT topology possesses a greater vibrational entropy, being stabilised by free energy at 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. </p>

scholarly journals Intrinsic Flexibility of the EMT Zeolite Framework under Pressure

Molecules ◽  
2019 ◽  
Vol 24 (3) ◽  
pp. 641 ◽  
Author(s):  
Antony Nearchou ◽  
Mero-Lee Cornelius ◽  
Jonathan Skelton ◽  
Zöe Jones ◽  
Andrew Cairns ◽  
...  
Keyword(s):  
Free Energy ◽  
Density Functional ◽  
Computational Modelling ◽  
Lattice Energy ◽  
State Density ◽  
Vibrational Entropy ◽  
Organic Additives ◽  
X Ray Diffraction ◽  
Guest Molecules

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.

scholarly journals Pressure-induced symmetry changes in body-centred cubic zeolites

2019 ◽  
Vol 6 (7) ◽  
pp. 182158 ◽  
Author(s):  
Antony Nearchou ◽  
Mero-Lee U. Cornelius ◽  
Zöe L. Jones ◽  
I. E. Collings ◽  
Stephen A. Wells ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Organic Additive ◽  
High Symmetry ◽  
Organic Additives ◽  
X Ray Diffraction ◽  
Zeolite Framework ◽  
X Ray ◽  
Open Framework ◽  
Framework Materials

Previous work has shown a strong correlation between zeolite framework flexibility and the nature of structural symmetry and phase transitions. However, there is little experimental data regarding this relationship, in addition to how flexibility can be connected to the synthesis of these open-framework materials. This is of interest for the synthesis of novel zeolites, which require organic additives to permutate the resulting geometry and symmetry of the framework. Here, we have used high-pressure powder X-ray diffraction to study the three zeolites: Na-X, RHO and ZK-5, which can all be prepared using 18-crown-6 ether as an organic additive. We observe significant differences in how the occluded 18-crown-6 ether influences the framework flexibility—this being dependent on the geometry of the framework. We use these differences as an indicator to define the role of 18-crown-6 ether during zeolite crystallization. Furthermore, in conjunction with previous work, we predict that pressure-induced symmetry transitions are intrinsic to body-centred cubic zeolites. The high symmetry yields fewer degrees of freedom, meaning it is energetically favourable to lower the symmetry to facilitate further compression.

scholarly journals Pressure-Induced Symmetry Changes in Body-Centered Cubic Zeolites

2018 ◽  
Author(s):  
Antony Nearchou ◽  
Mero-Lee Cornelius ◽  
Zoe Jones ◽  
Ines E. Collings ◽  
Stephen A. Wells ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Organic Additive ◽  
High Symmetry ◽  
Body Centered Cubic ◽  
Organic Additives ◽  
X Ray Diffraction ◽  
Zeolite Framework ◽  
X Ray ◽  
Framework Materials

<p>Previous work has shown a strong correlation between zeolite framework flexibility and the nature of structural symmetry and phase transitions. However, there is little experimental data regarding this relationship, in addition to how flexibility can be connected to the synthesis of these open framework materials. This is of interest for the synthesis of novel zeolites, which require organic additives to permutate the resulting geometry and symmetry of the framework. Here, we have used high pressure powder X-ray diffraction to study the three zeolites: Na-X, RHO and ZK-5, which can all be prepared using 18-crown-6 ether as an organic additive. We observe significant differences in how the occluded 18-crown-6 ether influences the framework flexibility – this being dependant on the geometry of the framework. We use these differences as an indicator to define the role of 18-crown-6 ether during zeolite crystallisation. Furthermore, in conjunction with previous work we predict that pressure-induced symmetry transitions are intrinsic to body-centred cubic zeolites. The high symmetry yields fewer degrees of freedom, meaning it is energetically favourable to lower the symmetry to facilitate further compression.</p>

scholarly journals Pressure-Induced Symmetry Changes in Body-Centered Cubic Zeolites

2018 ◽  
Author(s):  
Antony Nearchou ◽  
Mero-Lee Cornelius ◽  
Zoe Jones ◽  
Ines E. Collings ◽  
Stephen A. Wells ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Organic Additive ◽  
High Symmetry ◽  
Body Centered Cubic ◽  
Organic Additives ◽  
X Ray Diffraction ◽  
Zeolite Framework ◽  
X Ray ◽  
Framework Materials

<p>Previous work has shown a strong correlation between zeolite framework flexibility and the nature of structural symmetry and phase transitions. However, there is little experimental data regarding this relationship, in addition to how flexibility can be connected to the synthesis of these open framework materials. This is of interest for the synthesis of novel zeolites, which require organic additives to permutate the resulting geometry and symmetry of the framework. Here, we have used high pressure powder X-ray diffraction to study the three zeolites: Na-X, RHO and ZK-5, which can all be prepared using 18-crown-6 ether as an organic additive. We observe significant differences in how the occluded 18-crown-6 ether influences the framework flexibility – this being dependant on the geometry of the framework. We use these differences as an indicator to define the role of 18-crown-6 ether during zeolite crystallisation. Furthermore, in conjunction with previous work we predict that pressure-induced symmetry transitions are intrinsic to body-centred cubic zeolites. The high symmetry yields fewer degrees of freedom, meaning it is energetically favourable to lower the symmetry to facilitate further compression.</p>

scholarly journals Molecular Structures Polymorphism the Role of F…F Interactions in Crystal Packing of Fluorinated Tosylates

Crystals ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 242 ◽  
Author(s):  
Dmitry E. Arkhipov ◽  
Alexander V. Lyubeshkin ◽  
Alexander D. Volodin ◽  
Alexander A. Korlyukov
Keyword(s):  
Intermolecular Interactions ◽  
Crystal Packing ◽  
Lattice Energy ◽  
Molecular Structures ◽  
X Ray Diffraction ◽  
Total Contribution ◽  
X Ray ◽  
Weak Hydrogen Bonds ◽  
Intermolecular Bonding

The peculiarities of interatomic interactions formed by fluorine atoms were studied in four tosylate derivatives p-CH3C6H4OSO2CH2CF2CF3 and p-CH3C6H4OSO2CH2(CF2)nCHF2 (n = 1, 5, 7) using X-ray diffraction and quantum chemical calculations. Compounds p-CH3C6H4OSO2CH2(CF2)nCHF2 (n = 1, 5) were crystallized in several polymorph modifications. Analysis of intermolecular bonding was carried out using QTAIM approach and energy partitioning. All compounds are characterized by crystal packing of similar type and the contribution of intermolecular interactions formed by fluorine atoms to lattice energy is raised along with the increase of their amount. The energy of intra- and intermolecular F…F interactions is varied in range 0.5–13.0 kJ/mol. Total contribution of F…F interactions to lattice energy does not exceed 40%. Crystal structures of studied compounds are stabilized mainly by C-H…O and C-H…F weak hydrogen bonds. The analysis of intermolecular interactions and lattice energies in polymorphs of p-CH3C6H4OSO2CH2(CF2)nCHF2 (n = 1, 5) has shown that most stabilized are characterized by the least contribution of F…F interactions.

scholarly journals The structure directing role of 1, 3-diaminopropane in the hydrothermal synthesis of iron(III) phosphate

2004 ◽  
Vol 69 (3) ◽  
pp. 179-186 ◽  
Author(s):  
Nevenka Rajic ◽  
Djordje Stojakovic ◽  
Darko Hanzel ◽  
Venceslav Kaucic
Keyword(s):  
Free Energy ◽  
Hydrothermal Synthesis ◽  
Layered Structure ◽  
Lattice Energy ◽  
Iron Phosphate ◽  
Free Energy Calculations ◽  
Hydrothermal Conditions ◽  
Structure Directing Agent ◽  
Energy Calculations

1,3-Diaminopropane (DAP) was used as a structure-directing agent for the hydrothermal synthesis of an organically templated iron phosphate. During crystallization at 180 ?C, iron phosphate (FePO-DAP) with a layered structure was formed after one day. Longer crystallization yielded a mixture of FePO-DAP and leucophosphite, raising the question whether a transformation of FePO-DAP to leucophosphite occurs, or whether DAP decomposes under hydrothermal conditions resulting in leucophosphite formation. Lattice energy and free energy calculations strongly support the supposition that a decomposition of DAP occurs prior to the formation of leucophosphite.

SAMPL7 TrimerTrip Host-Guest Binding Poses and Binding Affinities from Spherical-Coordinates-Biased Simulations

2020 ◽  
Author(s):  
Zhaoxi Sun
Keyword(s):  
Free Energy ◽  
Computational Modelling ◽  
Free Energy Calculations ◽  
Energy Estimates ◽  
Binding Affinities ◽  
Spherical Coordinates ◽  
Collective Variables ◽  
Guest Binding ◽  
Starting Point ◽  
Sampl Challenge

Host-guest binding remains a major challenge in modern computational modelling. The newest 7<sup>th</sup> statistical assessment of the modeling of proteins and ligands (SAMPL) challenge contains a new series of host-guest systems. The TrimerTrip host binds to 16 structurally diverse guests. Previously, we have successfully employed the spherical coordinates as the collective variables coupled with the enhanced sampling technique metadynamics to enhance the sampling of the binding/unbinding event, search for possible binding poses and predict the binding affinities in all three host-guest binding cases of the 6<sup>th</sup> SAMPL challenge. In this work, we employed the same protocol to investigate the TrimerTrip host in the SAMPL7 challenge. As no binding pose is provided by the SAMPL7 host, our simulations initiate from randomly selected configurations and are proceeded long enough to obtain converged free energy estimates and search for possible binding poses. The predicted binding affinities are in good agreement with the experimental reference, and the obtained binding poses serve as a nice starting point for end-point or alchemical free energy calculations.

Role of the Structure and Electronic Properties of Fe2O3-MoO3 Catalyst on the Dehydration of Isopropyl Alcohol

1993 ◽  
Vol 58 (7) ◽  
pp. 1591-1599 ◽  
Author(s):  
Abd El-Aziz A. Said
Keyword(s):  
Active Sites ◽  
Isopropyl Alcohol ◽  
Oxide Catalyst ◽  
Flow System ◽  
Charge Carriers ◽  
X Ray Diffraction ◽  
X Ray ◽  
Catalyst Composition ◽  
Surface Active

Molybdenum oxide catalyst doped or mixed with (1 - 50) mole % Fe3+ ions were prepared. The structure of the original samples and the samples calcined at 400 °C were characterized using DTA, X-ray diffraction and IR spectra. Measurements of the electrical conductivity of calcined samples with and without isopropyl alcohol revealed that the conductance increases on increasing the content of Fe3+ ions up to 50 mole %. The activation energies of charge carriers were determined in presence and absence of the alcohol. The catalytic dehydration of isopropyl alcohol was carried out at 250 °C using a flow system. The results obtained showed that the doped or mixed catalysts are active and selective towards propene formation. However, the catalyst containing 40 mole % Fe3+ ions exhibited the highest activity and selectivity. Correlations were attempted to the catalyst composition with their electronic and catalytic properties. Probable mechanism for the dehydration process is proposed in terms of surface active sites.

Synthesis and Structure of a Clathrated Two-Dimensional Metal-Organic Framework: [Cd(4,4'-bpy)2(H2O)2](ClO4)2·(L)2·H2O (L = Bis(1-pyrazinylethylidene)hydrazine)

2008 ◽  
Vol 73 (1) ◽  
pp. 24-31
Author(s):  
Dayu Wu ◽  
Genhua Wu ◽  
Wei Huang ◽  
Zhuqing Wang
Keyword(s):  
Metal Organic Framework ◽  
Channel Structure ◽  
Two Dimensional ◽  
X Ray Diffraction ◽  
Guest Molecules ◽  
X Ray ◽  
Square Planar ◽  
Metal Organic ◽  
Aqueous Meoh ◽  
Organic Framework

The compound [Cd(4,4'-bpy)2(H2O)2](ClO4)2·(L)2 was obtained by the reaction of Cd(ClO4)2, bis(1-pyrazinylethylidene)hydrazine (L) and 4,4'-bipyridine in aqueous MeOH. Single-crystal X-ray diffraction has revealed its two-dimensional metal-organic framework. The 2-D layers superpose on each other, giving a channel structure. The square planar grids consist of two pairs of shared edges with Cd(II) ion and a 4,4'-bipyridine molecule each vertex and side, respectively. The square cavity has a dimension of 11.817 × 11.781 Å. Two guest molecules of bis(1-pyrazinylethylidene)hydrazine are clathrated in every hydrophobic host cavity, being further stabilized by π-π stacking and hydrogen bonding. The results suggest that the hydrazine molecules present in the network serve as structure-directing templates in the formation of crystal structures.

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