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Special Issue "High–Pressure Behaviour of Solids: From Molecular Species to 3D-Framework Materials"

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Physical Chemistry".

Deadline for manuscript submissions: closed (31 March 2019).

Special Issue Editors

Dr. Ines Collings
E-Mail Website
Guest Editor
Empa, Center for X-ray Analytics, Überland Str. 129, 8600 Dübendorf, Switzerland
Interests: structure–property relationships; high pressure; metal–organic frameworks; coordination polymers; single-crystal and powder diffraction at non-ambient conditions; phase transitions
Dr. Andrew B. Cairns
E-Mail Website
Guest Editor
Affiliation: Department of Materials, Imperial College London, London, United Kingdom
Interests: coordination polymers; high pressure; negative linear compressibility; materials engineering
Prof. Miklos Kertesz
E-Mail Website1 Website2
Guest Editor
Department of Chemistry and Institute of Soft Matter, Georgetown University, Washington DC 20057-1227, USA
Interests: conducting polymers; electronic structure; fullerenes and carbon nanotubes; aromaticity; high pressure effects in organics; vibrational spectra; carbon phases; pi-stacking; unusual pi-conjugation

Special Issue Information

Dear Colleagues,

The high-pressure behaviour of solids provides unique insight into the phase stability, mechanical and physical properties of materials. Pressure is a powerful thermodynamic parameter that can cause dramatic structural modifications to materials, giving insights into intermolecular interactions, reactivity, packing and polymorphism of molecular units, or the distortions adopted in framework materials. 

This Special Issue of Molecules aims to cover a broad range of high-pressure investigations on molecular up to three-dimensional framework materials, focusing on high-pressure behaviour and the resulting properties or chemical changes. In the case of molecular materials, high-pressure studies reveal important intermolecular interactions for maintaining stability within each phase. Zeolites, coordination polymers as well as metal–organic frameworks are increasingly studied under pressure to investigate pressure-induced distortions that are of great importance for understanding phase stability; accessing interesting properties, such as negative linear/area compressibility; and finally, studying adsorption behaviour through the inclusion of the pressure-transmitting medium. The highlighted physical properties induced by pressure include spin crossover, luminescence, and piezochromism. Pressure can also be used to synthesise new materials, for example, by triggering the polymerisation reactions of molecular species. 

We look forward to your contributions to this emerging area of high-pressure science using experimental and/or computational approaches. 

Dr. Ines Collings
Dr. Andrew B. Cairns
Prof. Miklos Kertesz
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • high pressure
  • molecules
  • framework materials
  • physical properties
  • phase stability, polymorphism
  • compressibility
  • intermolecular interactions
  • synchrotron X-ray structures
  • Raman and IR spectroscopy

Published Papers (8 papers)

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Research

Open AccessArticle
Linear, Non-Conjugated Cyclic and Conjugated Cyclic Paraphenylene under Pressure
Molecules 2019, 24(19), 3496; https://doi.org/10.3390/molecules24193496 - 26 Sep 2019
Abstract
The n-paraphenylene family comprises chains of phenylene units linked together by C-C bonds that are between single- and double-bonded, and where n corresponds to the number of phenylene units. In this work, we compare the response of the optical properties of different [...] Read more.
The n-paraphenylene family comprises chains of phenylene units linked together by C-C bonds that are between single- and double-bonded, and where n corresponds to the number of phenylene units. In this work, we compare the response of the optical properties of different phenylene arrangements. We study linear chains (LPP), cyclic systems (CPPs), and non-conjugated cyclic systems with two hydrogenated phenylenes (H4[n]CPP). Particularly, the systems of interest in this work are [6]LPP, [12]- and [6]CPP and H4[6]CPP. This work combines Raman and infrared spectroscopies with absorption and fluorescence (one- and two-photon excitations) measured as a function of pressure up to maximum of about 25 GPa. Unprecedented crystallographic pressure-dependent results are shown on H4[n]CPP, revealing intramolecular π-π interactions upon compression. These intramolecular interactions justify the H4[n]CPP singular optical properties with increasing fluorescence lifetime as a function of pressure. Full article
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Open AccessArticle
Effect of H2O on the Pressure-Induced Amorphization of Hydrated AlPO4-17
Molecules 2019, 24(16), 2864; https://doi.org/10.3390/molecules24162864 - 07 Aug 2019
Abstract
The incorporation of guest species in zeolites has been found to strongly modify their mechanical behavior and their stability with respect to amorphization at high pressure (HP). Here we report the strong effect of H2O on the pressure-induced amorphization (PIA) in [...] Read more.
The incorporation of guest species in zeolites has been found to strongly modify their mechanical behavior and their stability with respect to amorphization at high pressure (HP). Here we report the strong effect of H2O on the pressure-induced amorphization (PIA) in hydrated AlPO4-17. The material was investigated in-situ at HP by synchrotron X-ray powder diffraction in diamond anvil cells by using non- and penetrating pressure transmitting media (PTM), respectively, silicone oil and H2O. Surprisingly, in non-penetrating PTM, its structural response to pressure was similar to its anhydrous phase at lower pressures up to ~1.4 GPa, when the amorphization was observed to start. Compression of the structure of AlPO4-17 is reduced by an order of magnitude when the material is compressed in H2O, in which amorphization begins in a similar pressure range as in non-penetrating PTM. The complete and irreversible amorphization was observed at ~9.0 and ~18.7 GPa, respectively, in non- and penetrating PTM. The present results show that the insertion of guest species can be used to strongly modify the stability of microporous material with respect to PIA, by up to an order of magnitude. Full article
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Open AccessArticle
Pressure-Induced Polymorphism of Caprolactam: A Neutron Diffraction Study
Molecules 2019, 24(11), 2174; https://doi.org/10.3390/molecules24112174 - 10 Jun 2019
Abstract
Caprolactam, a precursor to nylon-6 has been investigated as part of our studies into the polymerization of materials at high pressure. Single-crystal X-ray and neutron powder diffraction data have been used to explore the high-pressure phase behavior of caprolactam; two new high pressure [...] Read more.
Caprolactam, a precursor to nylon-6 has been investigated as part of our studies into the polymerization of materials at high pressure. Single-crystal X-ray and neutron powder diffraction data have been used to explore the high-pressure phase behavior of caprolactam; two new high pressure solid forms were observed. The transition between each of the forms requires a substantial rearrangement of the molecules and we observe that the kinetic barrier to the conversion can aid retention of phases beyond their region of stability. Form II of caprolactam shows a small pressure region of stability between 0.5 GPa and 0.9 GPa with Form III being stable from 0.9 GPa to 5.4 GPa. The two high-pressure forms have a catemeric hydrogen-bonding pattern compared with the dimer interaction observed in ambient pressure Form I. The interaction between the chains has a marked effect on the directions of maximal compressibility in the structure. Neither of the high-pressure forms can be recovered to ambient pressure and there is no evidence of any polymerization occurring. Full article
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Open AccessArticle
The Effect of Pressure on Halogen Bonding in 4-Iodobenzonitrile
Molecules 2019, 24(10), 2018; https://doi.org/10.3390/molecules24102018 - 27 May 2019
Abstract
The crystal structure of 4-iodobenzonitrile, which is monoclinic (space group I2/a) under ambient conditions, contains chains of molecules linked through C≡N···I halogen-bonds. The chains interact through CH···I, CH···N and π-stacking contacts. The crystal structure remains in the same phase up [...] Read more.
The crystal structure of 4-iodobenzonitrile, which is monoclinic (space group I2/a) under ambient conditions, contains chains of molecules linked through C≡N···I halogen-bonds. The chains interact through CH···I, CH···N and π-stacking contacts. The crystal structure remains in the same phase up to 5.0 GPa, the b axis compressing by 3.3%, and the a and c axes by 12.3 and 10.9 %. Since the chains are exactly aligned with the crystallographic b axis these data characterise the compressibility of the I···N interaction relative to the inter-chain interactions, and indicate that the halogen bond is the most robust intermolecular interaction in the structure, shortening from 3.168(4) at ambient pressure to 2.840(1) Å at 5.0 GPa. The π∙∙∙π contacts are most sensitive to pressure, and in one case the perpendicular stacking distance shortens from 3.6420(8) to 3.139(4) Å. Packing energy calculations (PIXEL) indicate that the π∙∙∙π interactions have been distorted into a destabilising region of their potentials at 5.0 GPa. The structure undergoes a transition to a triclinic ( P 1 ¯ ) phase at 5.5 GPa. Over the course of the transition, the initially colourless and transparent crystal darkens on account of formation of microscopic cracks. The resistance drops by 10% and the optical transmittance drops by almost two orders of magnitude. The I···N bond increases in length to 2.928(10) Å and become less linear [<C−I∙∙∙N = 166.2(5)°]; the energy stabilises by 2.5 kJ mol−1 and the mixed C-I/I..N stretching frequency observed by Raman spectroscopy increases from 249 to 252 cm−1. The driving force of the transition is shown to be relief of strain built-up in the π∙∙∙π interactions rather than minimisation of the molar volume. The triclinic phase persists up to 8.1 GPa. Full article
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Open AccessArticle
High Pressure Crystal Structure and Electrical Properties of a Single Component Molecular Crystal [Ni(dddt)2] (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate)
Molecules 2019, 24(10), 1843; https://doi.org/10.3390/molecules24101843 - 14 May 2019
Abstract
Single-component molecular conductors form an important class of materials showing exotic quantum phenomena, owing to the range of behavior they exhibit under physical stimuli. We report the effect of high pressure on the electrical properties and crystal structure of the single-component crystal [Ni(dddt) [...] Read more.
Single-component molecular conductors form an important class of materials showing exotic quantum phenomena, owing to the range of behavior they exhibit under physical stimuli. We report the effect of high pressure on the electrical properties and crystal structure of the single-component crystal [Ni(dddt)2] (where dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate). The system is isoelectronic and isostructural with [Pd(dddt)2], which is the first example of a single-component molecular crystal that exhibits nodal line semimetallic behavior under high pressure. Systematic high pressure four-probe electrical resistivity measurements were performed up to 21.6 GPa, using a Diamond Anvil Cell (DAC), and high pressure single crystal synchrotron X-ray diffraction was performed up to 11.2 GPa. We found that [Ni(dddt)2] initially exhibits a decrease of resistivity upon increasing pressure but, unlike [Pd(dddt)2], it shows pressure-independent semiconductivity above 9.5 GPa. This correlates with decreasing changes in the unit cell parameters and intermolecular interactions, most notably the π-π stacking distance within chains of [Ni(dddt)2] molecules. Using first-principles density functional theory (DFT) calculations, based on the experimentally-determined crystal structures, we confirm that the band gap decreases with increasing pressure. Thus, we have been able to rationalize the electrical behavior of [Ni(dddt)2] in the pressure-dependent regime, and suggest possible explanations for its pressure-independent behavior at higher pressures. Full article
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Open AccessArticle
Packing Rearrangements in 4-Hydroxycyanobenzene Under Pressure
Molecules 2019, 24(9), 1759; https://doi.org/10.3390/molecules24091759 - 07 May 2019
Abstract
4-hydroxycyanobenzene (4HCB) is a dipolar molecule formed of an aromatic substituted benzene ring with the CN and OH functional groups at the 1 and 4 positions. In the crystalline state, it forms spiral chains via hydrogen bonding, which pack together through π [...] Read more.
4-hydroxycyanobenzene (4HCB) is a dipolar molecule formed of an aromatic substituted benzene ring with the CN and OH functional groups at the 1 and 4 positions. In the crystalline state, it forms spiral chains via hydrogen bonding, which pack together through π π interactions. The direct stacking of benzene rings down the a- and b-axes and its π π interactions throughout the structure gives rise to its semiconductor properties. Here, high-pressure studies are conducted on 4HCB in order to investigate how the packing and intermolecular interactions, related to its semiconductor properties, are affected. High-pressure single-crystal X-ray diffraction was performed with helium and neon as the pressure-transmitting mediums up to 26 and 15 GPa, respectively. The pressure-dependent behaviour of 4HCB in He was dominated by the insertion of He into the structure after 2.4 GPa, giving rise to two phase transitions, and alterations in the π π interactions above 4 GPa. 4HCB compressed in Ne displayed two phase transitions associated with changes in the orientation of the 4HCB molecules, giving rise to twice as many face-to-face packing of the benzene rings down the b-axis, which could allow for greater charge mobility. In the He loading, the hydrogen bonding interactions steadily decrease without any large deviations, while in the Ne loading, the change in 4HCB orientation causes an increase in the hydrogen bonding interaction distance. Our study highlights how the molecular packing and π π interactions evolve with pressure as well as with He insertion. Full article
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Open AccessArticle
Pressure-Dependent Structural and Luminescence Properties of 1-(Pyren-1-yl)but-2-yn-1-one
Molecules 2019, 24(6), 1107; https://doi.org/10.3390/molecules24061107 - 20 Mar 2019
Abstract
The crystal structure of 1-(pyren-1-yl)but-2-yn-1-one (1a, a polynuclear aromatic hydrocarbon displaying enhanced luminescence in the solid state, has been re-determined at several pressures ranging from atmospheric up to 3 GPa using a Diamond Anvil Cell (DAC). These experiments were augmented [...] Read more.
The crystal structure of 1-(pyren-1-yl)but-2-yn-1-one ( 1 a , a polynuclear aromatic hydrocarbon displaying enhanced luminescence in the solid state, has been re-determined at several pressures ranging from atmospheric up to 3 GPa using a Diamond Anvil Cell (DAC). These experiments were augmented by periodic DFT calculations at pressures up to 4.4 GPa. UV-Vis fluorescence of 1 a at non-ambient pressures has also been investigated. The crystal structure consists of infinite π -stacks of anti-parallel 1 a molecules with discernible dimers, which may exemplify aggregates formed by pyrene derivatives in solution and thin films, and is predominantly stabilized by dispersion. The average inter-planar distance between individual molecules within π -stacks decreases with pressure in the investigated range. This results in piezochromic properties of 1 a : a red-shift of sample color, as well as a bathochromic shift of fluorescence with pressure (by ca. 100 nm at 3.5 GPa). Two-component fluorescence spectra support the hypothesis that at least two types of excimers are involved in the electronic excitation processes in crystalline 1 a . Full article
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Open AccessArticle
Intrinsic Flexibility of the EMT Zeolite Framework under Pressure
Molecules 2019, 24(3), 641; https://doi.org/10.3390/molecules24030641 - 12 Feb 2019
Cited by 1
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 [...] Read more.
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. Full article
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