Ionic Clathrate Hydrates Research Articles

2-3-1 セミクラスレートハイドレートを用いたCH_4/CO_2ガス分離に関する研究(Session 2-3 ハイドレート 2)

2-3-1 セミクラスレートハイドレートを用いたCH_4/CO_2ガス分離に関する研究(Session 2-3 ハイドレート 2)

Abnormal Proton Positioning of Water Framework in the Presence of Paramagnetic Guest within Ion-Doped Clathrate Hydrate Host

The unique host–guest interactions of ionic clathrate hydrates, as distinct from those of other nonionic clathrate hydrates, need to be investigated to understand their inherent physicochemical features, but direct observation of ionic host geometry has not yet been attempted. In this study, we first report the distortions of the water–water connection in the charged cages caused by orbital mixing between a paramagnetic guest and an ion-doped host, and by electrostatic repulsion between the cationic host and guest via the direct observation with using synchrotron high-resolution powder diffraction analysis. The present findings well explain the mechanisms of unique phenomena occurring in ionic clathrate hydrates with paramagnetic guests.

Guest-induced symmetry lowering of an ionic clathrate material for carbon capture.

We report a new lattice structure of the ionic clathrate hydrate of tetra-n-butylammonium bromide induced by guest CO2 molecules, which is found to provide high CO2 storage capacity. The structure was characterized by a set of methods, including single crystal X-ray diffraction, NMR, and MD simulations.

Hydration structures of lactic acid: characterization of the ionic clathrate hydrate formed with a biological organic acid anion.

Ionic clathrate hydrates are water-based materials that have unique properties, such as a wide range of melting temperatures and high gas capacities. In their structure, water molecules coordinate around ionic substances, which is regarded as the actual hydration structure and also linking of the hydrate clusters, giving insight into the dynamics of the water molecules and ions. This paper reports the synthesis and characterization of the ionic clathrate hydrate of tetra-n-butylammonium lactate (TBAL), the anion of which is a biological organic material. Phase equilibrium measurements and optical observations of the crystal morphology and crystal structure analysis were performed. The TBAL hydrate has a melting temperature of 284.8 K suitable for cool energy storage applications. The actual hydration patterns around a lactate anion are shown in the form of ionic clathrate hydrate structure.

Calorimetric and Structural Studies of Tetrabutylammonium Bromide Ionic Clathrate Hydrates

In the present work, characteristic properties of tetrabutylammonium bromide (TBAB) ionic clathrate hydrates structures were studied by single-crystal X-ray structure analysis. The structures of three different tetragonal TBAB ionic clathrate hydrates that were formed in our experiments were based on the same water lattice of tetragonal structure I (TS-I) differing in the ways of including bromide anions and arranging tetrabutylammonium cations. We demonstrated that (1) Br(-) can be included into the water lattice, replacing two water molecules, (2) the butyl group of the cation can be inserted not only in large T and P cavities but also in small D cavities of the water lattice TS-I, and (3) one of the reasons for polytypism of ionic clathrate hydrates on the basis of TS-I is the occurrence of alternative modes of arrangements of four-compartment cavities in adjacent layers of the water framework. The compositions of three TBAB ionic clathrate hydrates TBAB·38.1H2O, TBAB·32.5H2O, and TBAB·26.4H2O were determined by chemical analysis, and their enthalpies of fusion were measured by differential scanning calorimetry (DSC). From the obtained results, the enthalpies of the TBAB hydrate formation from TBAB and water were calculated thermodynamically.

Electric Double-Layer Capacitor Based on an Ionic Clathrate Hydrate

Herein, we suggest a new approach to an electric double-layer capacitor (EDLC) that is based on a proton-conducting ionic clathrate hydrate (ICH). The ice-like structures of clathrate hydrates, which are comprised of host water molecules and guest ions, make them suitable for applications in EDLC electrolytes, owing to their high proton conductivities and thermal stabilities. The carbon materials in the ICH Me4NOH⋅5 H2O show a high specific capacitance, reversible charge-discharge behavior, and a long cycle life. The ionic-hydrate complex provides the following advantages in comparison with conventional aqueous and polymer electrolytes: 1) The ICH does not cause leakage problems under normal EDLC operating conditions. 2) The hydrate material can be utilized itself, without requiring any pre-treatments or activation for proton conduction, thus shortening the preparation procedure of the EDLC. 3) The crystallization of the ICH makes it possible to tailor practical EDLC dimensions because of its fluidity as a liquid hydrate. 4) The hydrate solid electrolyte exhibits more-favorable electrochemical stability than aqueous and polymer electrolytes. Therefore, ICH materials are expected to find practical applications in versatile energy devices that incorporate electrochemical systems.

Single crystal X-ray diffraction study of the cubic ionic clathrate hydrate of tetrabutyl ammonium propionate (C4H9)4NC2H5COO·27.0H2O

Single crystal X-ray diffraction is used for the first time to study the structure of the ionic clathrate hydrate of tetrabutyl ammonium propionate (C4H9)4NC2H5COO·27.0H2O with the host framework based on cubic arrangement I. The structural model is characterized by a high degree of disordering in both guest and host subsystems. The structural features indicate a colocation of cations and anions in multicell 4T·nD cavities with n = 0–4; the simplest option is a pairwise location of cations and anions in combined five-cell 4T·D cavities. The positional ordering of cations leads to the formation of a 2×2×2 supercell (space group $$I\bar 43d$$ , a = 24.312(6)A). The resulting model confirms the characteristic features of ionic clathrate hydrates of tetrabutyl and tetraisoamyl ammonium carboxylates. Non-standard refinement techniques are described, which may be of interest for other structures with a high degree of disordering. The proposed structural interpretation can serve as a basis for a further investigation of this class of compounds by other methods.

Spectroscopic Observation of Na Cations Entrapped in Small Cages of sII Propane Hydrate

Although numerous studies have been conducted on various ionic clathrate hydrates, in spite of its potential importance the inclusion of metal cations in continuous water-host frameworks has not yet been clearly identified by direct spectroscopic evidence. Here, a key question arises as to whether the small alkali metals such as Na+ can be entrapped because they are considered to be too small to be stabilized in the hydrate cages. In this study, we first suggested spectroscopic evidence for the enclathration of Na+ in a small cage of sII propane hydrate. First, we checked the overall structure of sII propane hydrate incorporated with NaSO3CH3 and NaSO3NH2 with powder XRD and 13C NMR. Next, we revealed the difference of chemical shift of 23Na between Ih and sII hydrate phases with solid-state 23Na MAS NMR as direct evidence of entrapped Na+ in 512 cages. In addition, we also checked 13C MAS NMR of the CH3SO3– anion and found that Na+ cations in a small cage could be stabilized with an enclathrated CH3SO3– ...

Thermal Expansivity of Ionic Clathrate Hydrates Including Gaseous Guest Molecules

Although thermal expansion is a key factor in relation to the host-guest interaction of clathrate hydrates, few studies have investigated the thermal behavior of ionic clathrate hydrates. The existence of ionic species in these hydrates creates a unique host-guest interaction compared to that of nonionic clathrate hydrates. It was revealed that X-ray diffraction cannot be used for research of tetramethylammonium hydroxide clathrate hydrates due to damage of the cations by the X-ray, which results in abnormal thermal expansion of the ionic clathrate hydrates. Hence, in the present work, the thermal expansivities of binary sII Me(4)NOD·16D(2)O and sI DClO(4)·5.5D(2)O were measured by neutron powder diffraction (NPD) in order to shed light on their thermal behavior. General correlations for the thermal behaviors of given structures were established and lattice expansions depending on the guests were compared between ionic and nonionic clathrate hydrates. The peculiar change in the thermal expansivity of binary DClO(4)·5.5D(2)O was also considered in relation to the host-guest configuration.

Calorimetric and Structural Studies of Tetrabutylammonium Chloride Ionic Clathrate Hydrates

Three ionic clathrate hydrates of different water content are formed in the binary system tetrabutylammonium chloride-water. The data on heats of fusion of these hydrates measured by DSC are presented. Single-crystal and powder X-ray diffraction studies of ionic clathrate hydrates of tetrabutylammonium chloride have been carried out. Structural justification of the occurrence of three different ionic clathrate hydrates derived from tetragonal structure-I in the (C(4)H(9))(4)NCl-H(2)O system has been found for the first time. A novel mode of hydrophilic inclusion of the halide anion with displacement of two hydrogen-bonded host water molecules has been revealed. Structural data obtained are indicative of the possibility of location of tetrabutylammonium cations in combined cavities formed with participation of D-voids.

Double clathrate hydrates of tetrabutylammonium fluoride + helium, neon, hydrogen and argon at high pressures

Decomposition curves of double ionic clathrate hydrates of tetrabutylammonium fluoride with helium, neon, hydrogen and argon were studied at pressures up to 800 MPa. Formation of double hydrates with helium, neon and hydrogen does not lead to any significant increase of the temperatures of decomposition of these hydrates; at high temperatures the hydrates may decompose even at lower temperatures than the hydrate of pure tetraalkylammonium salt does. Decomposition temperatures of double hydrates with argon in all cases were 4–8 °C higher in comparison with the decomposition temperature of ionic clathrate hydrates of tetrabutylammonium fluoride. We suppose that this behavior is caused by simultaneous effect of three factors on hydrate decomposition temperature: (1) partial filling of the small cavities in the framework of the hydrate with water molecules, (2) weakness of the van der Waals interactions between the gas molecules and the host water molecules, and (3) dissolution of helium, hydrogen and neon in the solution of tetrabutylammonium salt causing a decrease of melting temperatures of the hydrates formed from these solutions.

Superoxide Ions Entrapped in Water Cages of Ionic Clathrate Hydrates

In the present work, we first described the stable entrapment of the superoxide ions in gamma-irradiated (Me(4)NOH + O(2)) clathrate hydrate. Owing to peculiar direct guest-guest ionic interaction, the lattice structure of gamma-irradiated (Me(4)NOH + O(2)) clathrate hydrate shows significant change of lattice contraction behavior even at relatively high temperature (120 K). Such findings are expected to provide useful information for a better understanding of unrevealed nature (such as icy nanoreactor concept, ice-based functional material synthesis and lattice tuning by specific ionic guests) of clathrate hydrate fields.

The structure of the ionic clathrate hydrate of tetrabutylammonium valerate (C4H9)4NC4H9CO2·39.8H2O

For the first time the detailed crystal structure of the ionic clathrate hydrate of tetrabutylammonium valerate (C4H9)4NC4H9CO2·39.8H2O has been determined by single crystal X-ray analysis at 150 K. The idealized water–anion host framework consists of five-compartment polyhedral cavities 4T·P and small D cavities. Butyl chains of the cation and the anion of (C4H9)4NC4H9CO2 are included in the five-compartment cavities with displacement of two “inner” host water molecules. The inclusion of the guest entities leads to the distortion of D-cavities which are partially filled by additional “guest” water molecules. The other D-cages are empty. The structure exhibits significant disordering. The adequate model of disordering and inclusion mode of the guest moieties have been obtained. Special features of the crystal structures of ionic clathrate hydrates of tetraalkylammonium carboxylates are discussed.

Physicochemical Properties of Ionic Clathrate Hydrates

Ionic clathrate hydrates are known to be formed by the enclathration of hydrophobic cations or anions into confined cages and the incorporation of counterions into the water framework. As the ionic clathrate hydrates are considered for their potential applicability in various fields, including those that involve solid electrolytes, gas separation, and gas storage, numerous studies of the ionic clathrate hydrates have been reported. This review concentrates on the physicochemical properties of the ionic clathrate hydrates and the notable characteristics of these materials regarding their potential application are addressed.

Hydrogen Gas Sensor Based on Proton‐Conducting Clathrate Hydrate

Icy detector: A simple new concept for the fabrication of amperometric H2 sensors benefits from an ionic clathrate hydrate (see picture). The physicochemical characteristics of icelike Me4NOH⋅5 H2O lead to good performance of the sensor assembly and fast response and recovery times, even at lower H2 concentrations.

Structure and magnetism of a verdazyl radical clathrate hydrate. Strong intermolecular magnetic interactions derived from π-stacking within ice-like channels

Deprotonation of 1,5-dimethyl-6-oxoverdazyl-3-carboxylic acid (2H) in acetonitrile/water affords crystals of the sodium salt of the carboxylate radial anion as a hydrated material (3). The solid state structure of 3 consists of a 2-D array of antiparallel stacked verdazyl carboxylate radical anions (2-) pillared between chains of sodium cations. These layers are separated by structurally ordered water layers. These layers consist of fused polygons based on OH⋯O hydrogen bonds that assemble into a complex 2-D hydrogen bonded network. The alternating layers are also linked via an orthogonal hydrogen bonded network. The overall structure resembles a 2-D ionic clathrate hydrate with radical stacks contained within channels. Analysis of temperature dependent magnetic susceptibility measurements reveal very strong antiferromagnetic exchange interactions (J = −290 cm−1) which can be ascribed to the 1-D stacks of radicals within the hydrate structure.

Thermal stability and ionic conductivity of the ionic clathrate hydrates incorporated with potassium hydroxide

The hydroxide clathrate hydrates exhibit high ionic conductivity even at quite low temperature because of the relatively high mobility of OH− ions in the water host framework. The unique crystalline structure of Me4NOH·10H2O facilitates a transportation of charge carriers, but its low melting temperature of −20 °C decisively hinders practical applications. We confirmed that the co-inclusion of a secondary guest, using KOH in the present study, in Me4NOH clathrate hydrate can induce a drastic increase of the melting temperature from −19.1 °C to +39.8 °C without any occurrence of structural distortion. For this ionic clathrate hydrate the ionic conductivity reaches the value of 0.20 S·cm−1, suggesting a potential super-ionic conductor. For real applications to ionic conductors the electrochemical stability region was checked by cyclic voltammetry (CV) and it was found that Me4NOH·9H2O·KOH showed a wide electrochemical window corresponding to 5.8 V. To synthesize a hydrate-based proton conductor with acceptable thermal stability and electrochemical properties, the specific anionic and cationic species have to be examined with the full consideration of the structural framework and anion/proton migration.

Discrete Magnetic Patterns of Nonionic and Ionic Clathrate Hydrates

In this communication, the charge transfer phenomenon from ionic host lattice to nonionic guest molecule was observed by magnetization and Raman spectroscopy measurements for nonionic and ionic clathrate hydrates. The present findings on the magnetic property of nonionic guest molecules in ionic hydrate might provide important information on the unrevealed nature of host-guest interaction in ionic hydrate systems. The charge transfer occurring between ionic host and nonionic guest molecules will open up interesting application fields for ionized hydrate complexes and activated secondary guest molecules.

Maximized Proton Conductivity of the HPF6 Clathrate Hydrate by Structural Transformation

The unique and specific interaction of ionic guests with the surrounding cage framework might play a key role in promoting the electrochemical properties of ionic clathrate hydrates. In this work we focus on addressing (1) structural transformation simply due to an increase of water content, (2) structure-dependent ionic conductivity, (3) the existence of maximum ionic conductivity at a specific hydration number, and (4) proton migration through channels in the crystalline hydrate matrix. The melting temperature and ionic conductivity of hexafluorophosphoric acid hexahydrate (HPF6·6.0H2O) are found to be approximately 29.5 °C and 10−1 S·cm−1, respectively, showing that HPF6·6.0H2O possesses desirable features as a solid proton conductor.

Ionic Conductivity Enhancement Due to Coguest Inclusion in the Pure Ionic Clathrate Hydrates

In this study, we present the unique role of the coguest when it is additionally included in a pure ionic clathrate hydrate. First, the ionic conductivities of xTHF·TPAOH·32H2O hydrates at various coguest THF concentrations (x = 2, 1, 0.5, 0.25, 0.13, 0) were measured in a temperature range from −40 to −10 °C and at ambient pressure. The double 2THF·TPAOH·32H2O hydrate (σ = 1.06 × 10−3 S·cm−1) exhibits ionic conductivity 2 orders of magnitude higher than that of THF-free TPAO·32H2O hydrate (σ = 6.01 × 10−6 S·cm−1) at −30 °C. This considerably different ionic conductivity behavior strongly implies that the inclusion of coguest THF induces a structural transformation via host-water lattice distortion, providing such high conductivity values for the mixed (THF + TPAOH) hydrate. We found a maximum conductivity of 0.0184 S·cm−1 at 1.49 THF mol % and −10 °C The present results provide strong evidence that THF serves as a promoter for greatly enhancing the ionic conductivity in ionic clathrate hydrates. The stru...