Crystalline Clathrate Research Articles

Amorphous-like thermal conductivity and high mechanical stability of cyclopentane clathrate hydrate.

The thermal conductivity κ of cyclopentane clathrate hydrate (CP CH) of type II was measured at temperatures down to 100 K and at pressures up to 1.3 GPa. The results show that CP CH displays amorphous-like κ characteristic of many crystalline clathrate hydrates, e.g., tetrahydrofuran (THF) CH. The magnitude of κ is 0.47 W m-1 K-1 near the melting point of 280 K at atmospheric pressure, and it is almost independent of pressure and temperature T: ln κ = -0.621-40.1/T at atmospheric pressure (in SI-units). This is slightly less than κ of type II CHs of water-miscible solvents such as THF. Intriguingly, unlike other water-rich type II clathrate hydrates of water-miscible molecules M (M·17 H2O), CP CH does not amorphize at pressures up to 1.3 GPa at 130 K and also remains stable up to 0.5 GPa at 240 K. This shows that CP CH is mechanically more stable than the previously studied water-rich type II CHs, and suggests that repulsive forces between CP and the H2O cages increase the mechanical stability of crystalline CP CH. Moreover, we show that κ of an ice-CH mixture, which often arises for CHs that form naturally, is described by the average of the parallel and series heat conduction models to within 5% for ice contents up to 22 wt%. The findings provide a better understanding of the thermal and stability properties of clathrate hydrates for their applications such as gas storage compounds.

Neon encapsulation by a hydroquinone organic crystalline clathrate under ambient conditions

The recent use of noble gases in laser devices and semiconductor lithography has greatly increased. However, there is no commercial technology for the storage of noble gases in solid materials owing to their chemical inertness and relative lightness. Here we report the simple synthesis and characteristics of a hydroquinone clathrate that stably captures neon at atmospheric pressure and room temperature. The highly flexible structure enables neon encapsulation in the one-dimensional channels of the clathrate framework despite their inter-cage migration through the hexagonal entrance of the cages. The neon uptake of as-synthesized hydroquinone clathrates is 37.3 g L−1 at 1 bar and 298 K. Increasing the temperature accelerates the release of neon from the flexible hydroquinone clathrate hydrogen-bonded organic framework, leading to guest-free clathrate formation at 1 bar and 400 K. This method represents a technological development for better storage and the controlled release of noble gases in solid structured materials.

Phonon dispersion curves in the type-I crystalline and molten clathrate compound Eu8Ga16Ge30

The dynamic structure factor , where Q and E are momentum and energy transfer, respectively, has been measured for liquid Eu8Ga16Ge30 (EGG), using inelastic x-ray scattering. The excitation energy of the longitudinal acoustic mode in the liquid was scaled to that in liquid Ba8Ga16Sn30 (BGS) with the effective mass. This result means that the local structure in both liquids are similar. The longitudinal acoustic excitation energy of type-I clathrate compound EGG disperses faster than that in the liquid, suggesting that the interatomic force is weakened on melting. The lower energy excitation was observed in both liquid EGG and liquid BGS. In comparison with the longitudinal phonon dispersion in crystalline clathrate compound EGG obtained by density functional theory-based calculations, the lower energy in the liquid was found to be near the optical mode energy. The result indicates that the lower energy mode arises from the relative motion between Eu and (Ga, Ge) atoms.

Non-destructive analysis of a mixed H2O–CO2 fluid in experimental noble-metal capsule by means of freezing and high-energy synchrotron X-ray diffraction

High-pressure high-temperature syntheses that involve volatile-bearing aqueous fluids are typically accomplished by enclosing the samples in gas-tight welded shut noble-metal capsules, from which the bulk volatile content must be extracted to be analyzed with mass spectroscopy, hence making the analysis non-replicable. Here we describe a novel non-destructive method that ensures the identification and the quantitative estimate of the volatiles directly in the sealed capsule, focusing on fluid H2O–CO2 mixtures equilibrated with graphite at conditions of geological interest (1 GPa, 800 °C). We used a high-energy (77 keV) synchrotron X-ray radiation combined with a cryostat to produce X-ray diffraction patterns and X-ray diffraction microtomographic cross-sections of the volatile-bearing samples down to –180 °C, thus encompassing the conditions at which crystalline phases-solid CO2 and clathrate (CO2 hydrate)-form. The uncertainty of the method is < 15 mol%, which reflects the difference between the volatile proportion estimated by both Rietveld refinement of the diffraction data and by image analysis of the microtomograms, and the reference value measured by quadrupole mass spectrometry. Therefore, our method can be reliably applied to the analysis of frozen H2O–CO2 mixtures and, moreover, has the potential to be extended to experimental fluids of geological interest containing other volatiles, such as CH4, SO2 and H2S.

Structural and Electrochemical Properties of the Type VIII Ba8Ga16–δ Sn30+δ (δ ≈ 1)clathrate during Lithiation

Clathrates of the Tetrel (Tt = Si, Ge, Sn) elements are host-guest structures that can undergo Li alloying reactions with high capacities. However, little is known about how the cage structure affects the phase transformations that take place during lithiation. To further this understanding, the structural changes of the type VIII clathrate Ba8Ga16–δSn30+δ (δ ≈ 1) during lithiation are investigated and compared to those in β-Sn with ex situ X-ray total scattering measurements and pair distribution function (PDF) analysis.The results show that the type VIII clathrate undergoes an alloying reaction to form Li-rich amorphous phases (Li x Ba0.17Ga0.33Sn0.67, x = 2 – 3) with local structures similar to those in the crystalline binary Li-Sn phases that form during the lithiation of β-Sn. As a result of the amorphous phase transition, the type VIII clathrate reacts at a lower voltage (0.25 V vs. Li/Li+) compared to β-Sn (0.45 V) and goes through a solid-solution reaction after the initial conversion of the crystalline clathrate phase. Cycling experiments suggest that the amorphous phase persists after the first lithiation and results in considerably better cycling than β-Sn. Density functional theory (DFT) calculations suggest that topotactic Li insertion into the clathrate lattice is not favorable due to the high energy of the Li sites, which is consistent with the experimentally observed amorphous phase transformation. The clathrate structure is hypothesized to kinetically circumvent the formation of Li-Sn or Li-Ga crystalline phases, which results in better cycling and a lower reaction voltage.The electrochemical lithiation pathway of Ba8Ga16–δSn30+δ (δ ≈ 1) is similar to that of the previously investigated type I Ba8Ge43 1 suggesting that the amorphous lithiation could be a common mechanism for guest-filled Tetrel clathrates. As amorphous phase transformations are a beneficial property for alloying anodes, Tetrel clathrates could act as precursors for obtaining amorphous phases with tunable electrochemical properties. With this assumption of a common mechanism for guest-filled clathrates, we will then discuss design rules for clathrate based alloying anodes in terms of optimizing the gravimetric capacity and reaction voltage. References (1) Dopilka, A.; Childs, A.; Bobev, S.; Chan, C. K. Understanding the Amorphous Lithiation Pathway of the Type I Ba8Ge43 Clathrate with Synchrotron X-Ray Characterization. Chem. Mater. 2020, 32, 9444–9457.

Structural and Electrochemical Properties of Type VIII Ba8Ga16-δSn30+δ Clathrate (δ ≈ 1) during Lithiation.

Clathrates of the tetrel (Tt = Si, Ge, Sn) elements are host–guest structures that can undergo Li alloying reactions with high capacities. However, little is known about how the cage structure affects the phase transformations that take place during lithiation. To further this understanding, the structural changes of the type VIII clathrate Ba8Ga16−δSn30+δ (δ ≈ 1) during lithiation are investigated and compared to those in β-Sn with ex situ X-ray total scattering measurements and pair distribution function (PDF) analysis. The results show that the type VIII clathrate undergoes an alloying reaction to form Li-rich amorphous phases (LixBa0.17Ga0.33Sn0.67, x = 2–3) with local structures similar to those in the crystalline binary Li–Sn phases that form during the lithiation of β-Sn. As a result of the amorphous phase transition, the type VIII clathrate reacts at a lower voltage (0.25 V vs Li/Li+) compared to β-Sn (0.45 V) and goes through a solid-solution reaction after the initial conversion of the crystalline clathrate phase. Cycling experiments suggest that the amorphous phase persists after the first lithiation and results in considerably better cycling than in β-Sn. Density functional theory (DFT) calculations suggest that topotactic Li insertion into the clathrate lattice is not favorable due to the high energy of the Li sites, which is consistent with the experimentally observed amorphous phase transformation. The local structure in the clathrate featuring Ba atoms surrounded by a cage of Ga and Sn atoms is hypothesized to kinetically circumvent the formation of Li–Sn or Li–Ga crystalline phases, which results in better cycling and a lower reaction voltage. Based on the improved electrochemical performance, clathrates could act as tunable precursors to form amorphous Li alloying phases with novel electrochemical properties.

Activity of the Jupiter co-orbital comet P/2019 LD2(ATLAS) observed with OSIRIS at the 10.4 m GTC

Context.The existence of comets with heliocentric orbital periods close to that of Jupiter (i.e., co-orbitals) has been known for some time. Comet 295P/LINEAR (2002 AR2) is a well-known quasi-satellite of Jupiter. However, their orbits are not long-term stable, and they may eventually experience flybys with Jupiter at very close range, close enough to trigger tidal disruptions like the one suffered by comet Shoemaker-Levy 9 in 1992.Aims.Our aim was to study the observed activity and the dynamical evolution of the Jupiter transient co-orbital comet P/2019 LD2(ATLAS) and its dynamical evolution.Methods.We present results of an observational study of P/2019 LD2carried out with the 10.4 m Gran Telescopio Canarias (GTC) that includes image analyses using a Monte Carlo dust tail fitting code to characterize its level of cometary activity, and spectroscopic studies to search for gas emission. We also presentN-body simulations to explore its past, present, and future orbital evolution.Results.Images of P/2019 LD2obtained on May 16, 2020, show a conspicuous coma and tail, but the spectrum obtained on May 17, 2020, does not exhibit any evidence of CN, C2, or C3emission. The comet brightness in a 2.6′′ aperture diameter isr′ = 19.34 ± 0.02 mag, with colors (g′−r′) = 0.78 ± 0.03, (r′−i′) = 0.31 ± 0.03, and (i′−z′) = 0.26 ± 0.03. The temporal dependence of the dust loss rate of P/2019 LD2can be parameterized by a Gaussian function having a full width at half maximum of 350 days, with a maximum dust mass loss rate of 60 kg s−1reached on August 15, 2019. The total dust loss rate from the beginning of activity until the GTC observation date (May 16, 2020) is estimated at 1.9 × 109kg. Comet P/2019 LD2is now an ephemeral co-orbital of Jupiter, following what looks like a short arc of a quasi-satellite cycle that started in 2017 and will end in 2028. On January 23, 2063, it will experience a very close encounter with Jupiter at perhaps 0.016 au; its probability of escaping the solar system during the next 0.5 Myr is estimated to be 0.53 ± 0.03.Conclusions.Photometry and tail model results show that P/2019 LD2is a kilometer-sized object, in the size range of the Jupiter-family comets, with a typical comet-like activity most likely linked to sublimation of crystalline water ice and clathrates. Its origin is still an open question. Our numerical studies give a probability of this comet having been captured from interstellar space during the last 0.5 Myr of 0.49 ± 0.02 (average and standard deviation), 0.67 ± 0.06 during the last 1 Myr, 0.83 ± 0.06 over 3 Myr, and 0.91 ± 0.09 during the last 5 Myr.

Reactivity and Controlled Redox Reactions of Salt-like Intermetallic Compounds in Imidazolium-Based Ionic Liquids.

Substituted imidazolium ionic liquids (ILs) were investigated for their reactivity towards Na12Ge17 as a model system containing redox‐sensitive Zintl cluster anions. The ILs proved widely inert for imidazolium cations with a 1,2,3‐trisubstitution at least by alkyl groups, and for the anion bis(trifluoromethylsulfonyl)azanide (TFSI). A minute conversion of Na12Ge17 observed on long‐time contact with such ILs was not caused by dissolution of the salt‐like compound, and did thus not provide dissolved Ge clusters. Rather, a cation exchange led to the transfer of Na+ ions into solution. In contrast, by using benzophenone as an oxidizer, heterogeneous redox reactions of Na12Ge17 were initiated, transferring a considerable part of Na+ into solution. At optimized conditions, an X‐ray amorphous product NaGe6.25 was obtained, which was thermally convertible to the crystalline type‐II clathrate Na24–δGe136 with almost completely Na‐filled polyhedral cages, and α‐Ge. The presented method thus provides unexpected access to Na24–δGe136 in bulk quantities.

Evolution of local motifs and topological proximity in self-assembled quasi-crystalline phases.

Using methods from the field of topological data analysis, we investigate the self-assembly and emergence of three-dimensional quasi-crystalline structures in a single-component colloidal system. Combining molecular dynamics and persistent homology, we analyse the time evolution of persistence diagrams and particular local structural motifs. Our analysis reveals the formation and dissipation of specific particle constellations in these trajectories, and shows that the persistence diagrams are sensitive to nucleation and convergence to a final structure. Identification of local motifs allows quantification of the similarities between the final structures in a topological sense. This analysis reveals a continuous variation with density between crystalline clathrate, quasi-crystalline, and disordered phases quantified by 'topological proximity', a visualization of the Wasserstein distances between persistence diagrams. From a topological perspective, there is a subtle, but direct connection between quasi-crystalline, crystalline and disordered states. Our results demonstrate that topological data analysis provides detailed insights into molecular self-assembly.

Structural Properties of Highly Doped Borazino Polyphenylenes Obtained through Condensation Reaction.

Here we describe the synthesis and spectroscopic and structural characterization of various borazine-doped polyphenylenes displaying high doping dosages (16–18%). Capitalizing on the condensation reaction approach, the desired products were formed using a mixture of p-phenylendiamine and aniline with BCl3, followed by the addition of an aryl lithium derivative. The use of mesityl lithium (MesLi) yields strained multiborazine derivatives, which proved to be unstable in the presence of moisture. However, when xylyl lithium (XylLi) was used, chemically stable multiborazines were obtained, with oligomers showing molecular weight up to 104, corresponding to 16–18 monomer units. While the dimer, trimer, and tetramer could be isolated as pure products and their structure characterized by mass and NMR analysis, higher oligomers could only be isolated as mixtures of B-hydroxy-substituted derivatives and characterized by gel permeation chromatography. The structures of the dimer and trimer derivatives were confirmed by X-ray analysis, which nicely showed the presence of the two and three borazine rings spaced by one and two 1,4-aryl bridges, respectively. Notably, the trimer forms a porous crystalline clathrate. The peripheral xylyl and phenyl moieties of each molecule intramolecularly embrace each other through C–H and π–π stacking interactions. Steady-state UV–vis absorption characterization suggested that the molecules are UV absorbers, with the extinction coefficient linearly scaling with the degree of oligomerization. On the other hand, low-emission quantum yields were obtained for all derivatives (<7%), suggesting that high BN-doping dosages dramatically affect the emission properties of the doped polyphenylenes.

Quantifying low levels (

In this feasibility study Transmission Raman spectroscopy (TRS) has been used to build quantitative models for warfarin sodium and warfarin sodium clathrate. The type of warfarin present in manufactured tablets may affect product quality. Models were used to predict warfarin sodium in commercially available tablets at extremely low dosage levels (0.5% w/w). The laboratory made calibration samples used in the modelling varied in amorphous sodium, crystalline clathrate warfarin forms, excipients and dye. This application was highly challenging due to the low level of API and high level of a Raman-active colourant which varied significantly between production batches. A photon recycling optic, known as a Beam Enhancer, was utilised to improve the signal to noise of the Raman spectra to attain a low limit of quantification of 0.19% w/w.

Trifluoroethoxy-Coated Subphthalocyanines Attract Small Arenes in Their π-Concave Cavity.

Invited for this month's cover is the group of Prof. Norio Shibata based at the Nagoya Institute of Technology, Japan. The cover picture shows the crystal structures of trifluoroethoxy-substituted subphthalocyanines which form crystalline clathrates with one small aromatic molecule, such as toluene or benzene, in their concave cavity. Twelve trifluoroethoxy substituents flexibly surround the small molecule to hold it on the 14π-electron conjugated surface of the subphthalocyanines. Read the full text of the article at 10.1002/cplu.201700508.

Managing Hydrogen Bonding in Clathrate Hydrates by Crystal Engineering.

Methanol is one of the most common inhibitors for clathrate hydrate formation. Crystalline clathrate hydrates containing methanol were synthesized and analyzed by powder X-ray diffraction and 13 C NMR spectroscopy. The data obtained demonstrate that methanol can be a helper guest for forming structure I, structure II, and structure H clathrate hydrates, as long as the lattice framework contains NH4 F. The latter acts as a lattice stabilizer by providing sites for strong hydrogen bonding of the normally disruptive methanol hydroxy group. NH4 F and methanol can be considered key materials for crystal engineering of clathrate hydrates, as the modified lattices allow preparation of hydrates of non-traditional water-soluble guests such as alcohols and diols. Methanol takes on the role of an unconventional helper guest. This extends clathrate chemistry to a realm where neither hydrophobic guests nor high pressures are required. This also suggests that more stable lattices can be engineered for applications such as gas storage.

Managing Hydrogen Bonding in Clathrate Hydrates by Crystal Engineering

AbstractMethanol is one of the most common inhibitors for clathrate hydrate formation. Crystalline clathrate hydrates containing methanol were synthesized and analyzed by powder X‐ray diffraction and 13C NMR spectroscopy. The data obtained demonstrate that methanol can be a helper guest for forming structure I, structure II, and structure H clathrate hydrates, as long as the lattice framework contains NH4F. The latter acts as a lattice stabilizer by providing sites for strong hydrogen bonding of the normally disruptive methanol hydroxy group. NH4F and methanol can be considered key materials for crystal engineering of clathrate hydrates, as the modified lattices allow preparation of hydrates of non‐traditional water‐soluble guests such as alcohols and diols. Methanol takes on the role of an unconventional helper guest. This extends clathrate chemistry to a realm where neither hydrophobic guests nor high pressures are required. This also suggests that more stable lattices can be engineered for applications such as gas storage.

Thermal expansion and magnetostriction measurements using a Quantum Design Physical Property Measurement System

Capacitive dilatometers that could be installed in a Quantum Design Physical Properties Measurements System (PPMS) were developed. Two types of dilatometers were constructed. One dilatometer was compact enough to be installed in small magnet bore of various cryostats and had a reference capacitor so that high sensitivity and stability were achieved. The other dilatometer with a movable capacitor supported by a flat spring enabled to measure large strain and exchange samples easily. We measured the thermal expansion and magnetostriction of single crystalline clathrate compound Pr3Pd20Ge6 and polycrystalline hydrogenated La(Fe0.88Si0.12)13 in the temperature range between 2 and 340 K and magnetic field up to 8 T. The dilatometers allowed to detect the strain responses with a sensitivity of 10 ppb. We could measure strain from 10−8 to 10−3 using two dilatometers.

Synthesis and optical band gaps of alloyed Si–Ge type II clathrates

Inorganic type II clathrates are low density, semiconducting allotropes of group IV elements with the potential for optoelectronic applications. This class of materials is predicted to have direct or nearly-direct band gaps, and, when Si and Ge are alloyed in the clathrate structure, the band gap is tunable in the range of 0.8–1.8 eV. In this work, we demonstrate for the first time the synthesis of alloyed Si–Ge type II clathrates. Within this alloy system, we find an amorphous region which is likely due to a miscibility gap. The optical absorptance spectra of the crystalline clathrate samples show the predicted band gap tuning with Ge content, and calculations find that the Si type II clathrate has a strong absorption coefficient for the direct interband transition. The findings in this work lay the foundation for the future use of type II clathrates in optoelectronic applications.

Structural and electrical transport properties of Mg-doped n-type Sn-based type Ⅷ single crystalline clathrate

Mg-doped Sn-based single crystalline samples Ba8Ga16-XMgXSn30(0 X 1.5) were grown from Sn flux to characterize their structural and electrical transport properties. Research results show that the prepared compounds are well indexed by the type-Ⅷ clathrate structure with a space group I43 m. With the increase in Mg content, the melting point of the corresponding compounds increases. On the contrary, the lattice constant decreases. The actual content of filling atomic Ba in doped samples is below the ideal value of 8.0, the occupancy of Ba in the dodecahedron is about 0.93 for the sample with X=1.5. All the samples show n-type conduction. The Mg atoms have an effect on the band structure of the materials, and the carrier concentrations in the doped samples are reduced. However, the absolute values of Seebeck coefficient and the resistivity of doped compounds increase, respectively. By calculation, the sample of X=1.5 obtains the maximum value of power factor 1.2610-3 Wm-1K-2 near 430 K.

Modification of the Pasynski method for determining the hydration numbers of nonelectrolytes

This paper presents a way of modifying the well known Pasynski method of calculating the solvation numbers towards more realistic assumptions concerning compressibility of the solvation shell including the non-zero value of this parameter. Assuming the compressibility of hydrates of simple non-electrolytes (methanol, tert-butanol, etc.) equal to that of solid crystalline clathrate hydrates yields hydration numbers well comparable to the stoichiometries of these hydrates deduced from the Endo theory. Applying the value of compressibility of solid hydrates close to that of ice, however, leads to hydration numbers close to those obtained from original Pasynski equation.

Growth and thermoelectric properties of Ge doped n-type Sn-based type-Ⅷ single crystalline clathrate

Single crystalline samples of type-Ⅷ Ba8Ga16-xGexSn30 (0 ≤ x ≤ 1.0) clathrates are fabricated by the Sn flux method. The structures and thermoelectric properties of the samples at temperatures ranging from 300 to 600 K are studied. Research results show that the actual content of Ge is relatively small in single crystal. The lattice parameters of the samples decrease slightly with the increase of the doping composition of Ge. The Ge doped samples have lower carrier density and higher carrier mobility than undoped samples. The Seebeck coefficients of all the doped samples are negative, and their absolute values are smaller than those of the undoped one. However, the electrical conductivity of the sample is increased by 62% after doping Ge and the sample of x=0.5 obtains a maximum value of ZT (1.25) at about 500 K.

Role of halogen bonding in clathrate formation of tetra- and hexasalicylides derived from halogenated salicylic acids

A series of oligomeric lactones, namely tetra- and hexasalicylides 1 and 2, was synthesized from various halogenated salicylic acids by a cyclocondensation reaction using POCl3. The clathrate inclusion properties of the macrocycles for some organic solvents were investigated. X-ray structures of several representative clathrates in this series were determined and the results were used to explain various features of their thermal desolvation. Halogen bonding (in particular C–I⋯OC) was found to play a significant role in the thermal stabilization of these crystalline clathrates.