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 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>

Metal-like Ductility in Organic Plastic Crystals: Role of Molecular Shape and Dihydrogen Bonding Interactions in Aminoboranes

2020 ◽  
Author(s):  
Amit Mondal ◽  
Biswajit Bhattacharya ◽  
SUSOBHAN DAS ◽  
Surojit Bhunia ◽  
Rituparno Chowdhury ◽  
...  
Keyword(s):  
Molecular Crystals ◽  
Molecular Shape ◽  
High Symmetry ◽  
Organic Crystals ◽  
X Ray Diffraction ◽  
X Ray ◽  
Plastic Crystals ◽  
Dihydrogen Bonding ◽  
Slip Planes

Ductility, which is a common phenomenon in most metals and metal-based alloys, is hard to achieve in molecular crystals. Organic crystals have been recently shown to deform plastically, but only on one or two faces, and fracture when stressed in any other arbitrary direction. Here, we report an exceptional metal-like ductility in crystals of two globular molecules, BH<sub>3</sub>NMe<sub>3</sub> and BF<sub>3</sub>NMe<sub>3</sub>, with characteristic stretching, necking and thinning with deformations as large as ~ 500%. Surprisingly, the mechanically deformed samples not only retained good long range order, but also allowed structure determination by single crystal X-ray diffraction. Molecules in these high symmetry crystals interact predominantly via electrostatic forces (B<sup>–</sup>–N<sup>+</sup>) and form columnar structures, thus forming multiple slip planes with weak dispersive forces among columns. While the former interactions hold molecules together, the latter facilitate exceptional malleability. On the other hand, the limited number of facile slip planes and strong dihydrogen bonding in BH<sub>3</sub>NHMe<sub>2</sub> negates ductility. We show the possibility to simultaneously achieve both exceptional ductility and crystallinity in solids of certain globular molecules, which may enable designing highly modular, easy-to-cast crystalline functional organics, for applications in barocalorimetry, ferroelectrics and soft-robotics.

Metal-like Ductility in Organic Plastic Crystals: Role of Molecular Shape and Dihydrogen Bonding Interactions in Aminoboranes

2020 ◽  
Author(s):  
Amit Mondal ◽  
Biswajit Bhattacharya ◽  
SUSOBHAN DAS ◽  
Surojit Bhunia ◽  
Rituparno Chowdhury ◽  
...  
Keyword(s):  
Molecular Crystals ◽  
Molecular Shape ◽  
High Symmetry ◽  
Organic Crystals ◽  
X Ray Diffraction ◽  
X Ray ◽  
Plastic Crystals ◽  
Dihydrogen Bonding ◽  
Slip Planes

Ductility, which is a common phenomenon in most metals and metal-based alloys, is hard to achieve in molecular crystals. Organic crystals have been recently shown to deform plastically, but only on one or two faces, and fracture when stressed in any other arbitrary direction. Here, we report an exceptional metal-like ductility in crystals of two globular molecules, BH<sub>3</sub>NMe<sub>3</sub> and BF<sub>3</sub>NMe<sub>3</sub>, with characteristic stretching, necking and thinning with deformations as large as ~ 500%. Surprisingly, the mechanically deformed samples not only retained good long range order, but also allowed structure determination by single crystal X-ray diffraction. Molecules in these high symmetry crystals interact predominantly via electrostatic forces (B<sup>–</sup>–N<sup>+</sup>) and form columnar structures, thus forming multiple slip planes with weak dispersive forces among columns. While the former interactions hold molecules together, the latter facilitate exceptional malleability. On the other hand, the limited number of facile slip planes and strong dihydrogen bonding in BH<sub>3</sub>NHMe<sub>2</sub> negates ductility. We show the possibility to simultaneously achieve both exceptional ductility and crystallinity in solids of certain globular molecules, which may enable designing highly modular, easy-to-cast crystalline functional organics, for applications in barocalorimetry, ferroelectrics and soft-robotics.

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>

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.

scholarly journals An investigation of polyhedral deformation in two mixed-metal diarsenates: SrZnAs2O7and BaCuAs2O7

2015 ◽  
Vol 71 (4) ◽  
pp. 330-337 ◽  
Author(s):  
Sabina Kovač ◽  
Ljiljana Karanović ◽  
Tamara Đorđević
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
General Formula ◽  
Three Dimensional ◽  
X Ray Diffraction ◽  
Hydrothermal Conditions ◽  
X Ray ◽  
Open Framework ◽  
Geometrical Characteristics ◽  
Barium Copper

Two isostructural diarsenates, SrZnAs2O7(strontium zinc diarsenate), (I), and BaCuAs2O7[barium copper(II) diarsenate], (II), have been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction. The three-dimensional open-framework crystal structure consists of corner-sharingM2O5(M2 = Zn or Cu) square pyramids and diarsenate (As2O7) groups. Each As2O7group shares its five corners with five differentM2O5square pyramids. The resulting framework delimits two types of tunnels aligned parallel to the [010] and [100] directions where the large divalent nine-coordinatedM1 (M1 = Sr or Ba) cations are located. The geometrical characteristics of theM1O9,M2O5and As2O7groups of known isostructural diarsenates, adopting the general formulaM1IIM2IIAs2O7(M1II= Sr, Ba, Pb;M2II= Mg, Co, Cu, Zn) and crystallizing in the space groupP21/n, are presented and discussed.

scholarly journals Pressure-induced Jahn-Teller Switch in the Homoleptic Hybrid Perovskite [(CH3)2NH2]Cu(HCOO)3: Orbital Reordering by Unconventional Degrees of Freedom

2021 ◽  
Author(s):  
Rebecca Scatena ◽  
Michał Andrzejewski ◽  
Roger D Johnson ◽  
Piero Macchi
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Coordination Polymer ◽  
Degrees Of Freedom ◽  
X Ray Diffraction ◽  
X Ray ◽  
Hybrid Perovskite ◽  
Jahn Teller

Through in-situ, high-pressure x-ray diffraction experiments we have shown that the homoleptic perovskite-like coordination polymer [(CH3)2NH2]Cu(HCOO)3 undergoes a pressure-induced orbital reordering phase transition above 5.20 GPa. This transition is distinct...

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