Compressed Arsenolite As4O6 and Its Helium Clathrate As4O6·2He

Guńka, Piotr A.; Dziubek, Kamil; Gładysiak, Andrzej; Dranka, Maciej; Piechota, Jacek; Hanfland, Michael; Katrusiak, Andrzej; Zachara, Janusz

doi:10.1021/acs.cgd.5b00390

Cited by 39 publications

(53 citation statements)

References 27 publications

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“…Helium was found to form a hydrate, form van der Waals compounds with neon and nitrogen, penetrate silica glasses and cristobalite under HP, and permeate fullerenes . We recently discovered that helium can enter nonporous crystals of cubic arsenic(III) oxide, arsenolite, and determined the crystal structure of the as‐formed As 4 O 6 ⋅ 2 He clathrate by using single‐crystal X‐ray diffraction . This was also independently found by Sans and co‐workers for powdered arsenolite samples …”

Section: Introductionsupporting

confidence: 53%

“…We noted previously that molecules of As 4 O 6 in ars undergo deformations under pressure. They consist of As and O atoms being pushed outside and inside the molecular cages, respectively . Now we define two orthonormal dimensionless symmetry coordinates that preserve the As 4 O 6 molecular symmetry of the

\overline{4} 3 m

point group to study the influence of He inclusion into the ars crystal structure on the As 4 O 6 deformations.…”

Section: Resultsmentioning

confidence: 99%

“…First, we performed potential energy surface (PES) scans along the Θ trajectory for three R values, that is, 2.746, 2.567, and 2.425 Å, for which R corresponded to the He⋅⋅⋅As distances determined from the crystal structures at 7.71(8), 17.59(5), and 29.83(5) GPa, respectively . Figure a shows the interaction energy curve for the R= 2.746 Å geometry at Hartree–Fock, MP2, and SAPT0 levels of theory (see also Figure S8).…”

Section: Resultsmentioning

confidence: 99%

“…It was found that helium atoms occupied

1 / 2

of the octahedral voids in the As ≈ fcc sublattice (Figure d). The observed diffraction pattern was interpreted as arising from a hybrid crystal composed of a pure ars core and an incl surface layer . Later, Sans et al.…”

Section: Introductionmentioning

confidence: 97%

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How and Why Does Helium Permeate Nonporous Arsenolite Under High Pressure?

et al. 2018

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Investigations into the helium permeation of arsenolite, the cubic, molecular arsenic(III) oxide polymorph As O , were carried out to understand how and why arsenolite helium clathrate As O ⋅2 He is formed. High-pressure synchrotron X-ray diffraction experiments on arsenolite single crystals revealed that the permeation of helium into nonporous arsenolite depends on the time for which the crystal is subjected to high pressure and on the crystal history. The single crystal was totally transformed into As O ⋅2 He within 45 h under 5 GPa. After release of the pressure, arsenolite was recovered and a repeated increase in pressure up to 3 GPa led to practically instant As O ⋅2 He formation. However, when a pristine arsenolite single crystal was quickly subjected to a pressure of 13 GPa, no helium permeation was observed at all. No neon permeation was observed in analogous experiments. Quantum mechanical computations indicate that there are no specific attractive interactions between He atoms and As O molecules at the distances observed in the As O ⋅2 He crystal structure. Detailed analysis of As O molecular structure changes has shown that the introduction of He into the arsenolite crystal lattice significantly reduces molecular deformations by decreasing the anisotropy of stress exerted on the As O molecules. This effect and the pΔV term, rather than any specific As⋅⋅⋅He binding, are the driving forces for the formation As O ⋅2 He.

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Section: Introductionsupporting

confidence: 53%

\overline{4} 3 m

point group to study the influence of He inclusion into the ars crystal structure on the As 4 O 6 deformations.…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

“…It was found that helium atoms occupied

1 / 2

Section: Introductionmentioning

confidence: 97%

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How and Why Does Helium Permeate Nonporous Arsenolite Under High Pressure?

et al. 2018

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“…On the other hand, the atomic structure of arsenolite and its equation of state under different pressure transmitting media (PTM) were firstly reported in Ref. [25] and later by [26]. However, the possible reaction between those PTM and arsenolite studied from a joint experimental and theoretical approach have not been studied yet.…”

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confidence: 99%

Ordered helium trapping and bonding in compressed arsenolite: Synthesis ofAs4O6·2He

et al. 2016

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Compression of arsenolite has been studied from a joint experimental and theoretical point of view. Experiments on this molecular solid at high pressures with different pressure-transmitting media have been interpreted thanks to state-of-the-art ab initio calculations. Our results confirm arsenolite as one of the most compressible minerals and provide evidence for ordered helium trapping above 3 GPa between adamantane-type As 4 O 6 cages. Our calculations indicate that, at relatively small pressures, helium establishes rather localized structural bonds with arsenic forming a compound with stoichiometry As 4 O 6 · 2He. All properties of As 4 O 6 · 2He are different from those of parent As 4 O 6 . In particular, pressure-induced amorphization, which occurs in arsenolite above 15 GPa, is impeded in As 4 O 6 · 2He, thus resulting in a mechanical stability of As 4 O 6 · 2He beyond 30 GPa. Our work paves the way to explore the formation of alternative compounds by pressure-induced trapping and reaction of gases, small atomic or molecular species, in the voids of molecular solids containing active lone electron pairs. DOI: 10.1103/PhysRevB.93.054102Molecular solids are very soft materials with openframework structures composed of molecular units, exhibiting strong covalent interatomic forces, which are linked by weak intermolecular forces, such as van der Waals interactions or hydrogen bonding forces. Pressure is a thermodynamic variable that allows tuning interatomic distances and consequently is a powerful tool to study atomic interactions and the connectivity of different molecular units -hence, the possibility of molecular solids to trap small atoms or molecules. In this sense, molecule trapping has received a lot of interest from the scientific community due to its potential industrial applications covering hydrogen storage [1] and CO 2 segregation from other organic compounds [2], among others. Recently, the small size of helium has triggered the study of pressure-induced helium trapping and how this effect affects the compressibility of host compounds. Those first studies were focused on helium trapping in silica glass [3][4][5] that is an amorphous compound with disordered interstitial voids large enough to host and trap helium. However, more studies need to be made of pressure-induced helium trapping in ordered crystallographic compounds, such as molecular solids.Helium reaction is a challenge since it is one of the most inert elements in nature [6]. Previous studies of helium trapping in glasses have not revealed the pressure-induced reactivity of helium with the glass structure. On the search of the formation of solid structures with helium, the study of * juasant2@upv.es † fjmanjon@upv.es mixtures of helium with other noble gases at high pressures has exhibited successful results. The mix of those fluids under pressure allows the formation of solid van der Waals compounds with exotic stoichiometries [7,8] [He(N 2 ) 11 , Ne(He) 2 ] given by the solubility of helium and dominated by the crystallization proces...

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Crystal Structure and Non‐Hydrostatic Stress‐Induced Phase Transition of Urotropine Under High Pressure

Guńka

Olejniczak

Fanetti

et al. 2020

Chemistry A European J

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High-pressure behavior of hexamthyleneteramine (urotropine) was studied in situ using angledispersive single-crystal synchrotron X-ray diffraction (XRD) and Fourier transform infrared absorption (FTIR) spectroscopy. Experiments were conducted in various pressure transmitting media (helium and neon for XRD, nitrogen and KBr for FTIR experiments) to study the effect of deviatoric stress on phase transformations. Contrary to As4O6 arsenolite, a material of similar cage-like molecular structure, no pressure-induced helium penetration into the crystal structure was observed. Instead, two pressure-induced structural changes are observed. The first one is suggested by the following occurrences: (i) gradual quenching of the magnitudes of atomic displacement parameters, (ii) diminishing libration contribution to the experimental C−N bond length, (iii) discontinuity in calculated IR-active vibrational modes and (iv) asymptotically vanishing discrepancy between the experimental and DFT-calculated unit cell volume. All these features reach a plateau at ~4 GPa and can be attributed to a damping of molecular librations and atomic thermal motion, pointing to the existence of a second-order isostructural phase transition. The second transformation, with an onset at ~12.5 GPa is a first-order phase transition to a tetragonal structure, characterized by sluggish kinetics and considerable hysteresis upon decompression. However, it occurs only in non-hydrostatic conditions, induced by a deviatoric stress in the sample. This behavior finds analogies in similar cubic crystals built of highly symmetric cage-like molecules and may be considered a common feature of such systems. Last but not least, it is worth noting successful Hirshfeld atom refinements, carried out for the incomplete high-pressure diffraction data up to 14 GPa, yielded more realistic C−H bond lengths than the independent atom model.

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Compressed Arsenolite As₄O₆ and Its Helium Clathrate As₄O₆·2He

Cited by 39 publications

References 27 publications

How and Why Does Helium Permeate Nonporous Arsenolite Under High Pressure?

How and Why Does Helium Permeate Nonporous Arsenolite Under High Pressure?

Ordered helium trapping and bonding in compressed arsenolite: Synthesis ofAs4O6·2He

Crystal Structure and Non‐Hydrostatic Stress‐Induced Phase Transition of Urotropine Under High Pressure

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