Clathrate Host Research Articles

Temperature-dependent influence of disorder on the thermodynamic properties of Sn20.5□3.5As20I8, a vacancy-driven superstructure of the type-I clathrate

ABSTRACT A polycrystalline sample of the Sn20.5□3.5As22I8 clathrate was synthesised by a standard ampoule method from elements. Temperature dependencies of the heat capacity Cp (T) and unit cell parameter a(T) experimentally studied at the temperatures of 2–300 K revealed abnormal behaviour of CP (T) and a(T) dependencies at the lowest (2–30 K) and elevated (200–300 K) temperatures. This was attributed to disorder in the clathrate crystal structure due to significant number of vacancies in the clathrate host matrix. The dependencies studied were analysed within the Debye–Einstein approach taking into account soft atomic potential theory, vibrations of two-level system (TLS) at the lowest temperatures, and anharmonicity of lattice vibration at elevated temperatures, which allows determining parameters of different contributions to thermodynamic characteristics of the studied clathrate. A comparison of the temperature dependence of Grüneisen parameter, which was determined from experimental data, with the temperature dependence of the calculated Grüneisen mode parameters revealed specific modes that have a decisive influence on the anomalous behaviour of the thermodynamic characteristics of the title clathrate in different parts of the studied temperature range. The dimensionless Grüneisen parameter reaches γ = 4 at moderately high temperatures, which indicates a significant degree of structural disorder and its influence on thermodynamic properties of clathrates and correlates well with low thermal conductivity of the title clathrate.

Structural studies on inclusion compounds and solvent sorption behavior of gradually elongated wheel-and-axle-type diol hosts featuring lateral benzo[b]thiophene units

Based on the wheel-and-axle design strategy, a series of six new clathrate hosts featuring two di(benzo[b]thien-2-yl)hydroxymethyl units attached to both ends of a central linear building element of varying length have been synthesized and their capability to form crystalline inclusion compounds with a fixed range of organic solvents are reported. X-ray crystal structures of relevant inclusion compounds have been determined and are comparatively discussed involving structural modification of the host molecules. Organic vapor sorption behavior of the host compounds coated as solid films on the quartz crystal of a QCM device has been studied. Significant differences in the affinities towards solvent vapors dependent both on structural and polarity properties of host and solvent are observed, indicating potential application as mass sensitive materials.

Spin-Crossover Behavior of Hofmann-Type-Like Complex Fe(4,4’-bipyridine)Ni(CN)4·nH2O Depending on Guest Species

A newly prepared metal complex Fe(4,4’-bipyridine)Ni(CN)4·nH2O, which was estimated to have a structure similar to the Hofmann-type clathrate host, changed its color from orange to deep orange and yellow on exposure to ethanol and acetone vapor, respectively, and the respective samples showed thermally induced two-step and one-step spin transitions.

Clathrate formation of Diels–Alder adduct of phencyclone and acenaphthylene. Key role of CH/π and bidentate CH/O interactions of the phenanthrene ring in construction of host framework

Two clathrate hosts (3a and 3b) were synthesized via the Diels–Alder reaction of phencyclone (1a) and tetracyclone (1b) with acenaphthylene (2), and the clathrate formation properties of these hosts towards a variety of organic guests were investigated. In the presence of aprotic solvents (i.e., aromatic, ketonic and etheric solvents), host 3a formed inclusion complexes with a 2:1 stoichiometric host/guest ratio, whereas 3b primarily formed 1:1 complexes. The desolvation temperatures of the 3a·guest complexes were extremely high in comparison to the boiling points of the pure guest liquids and were also much higher than those of the corresponding 3b·guest complexes, which contain the conformationally flexible stilbene moiety. Structural analyses of the 3a·guest complexes (i.e., 3a·benzene, 3a·toluene, 3a·1,4-dioxane, 3a·acetone and 3a·pentan-3-one) show that the aromatic CH/π (edge-to-face) interactions between phenanthrene and the acenaphthene ring as well as the interaction of the ‘bidentate’ CH/O hydrogen bond between the phenanthrene-ring hydrogen and the bridged carbonyl oxygen play a key role in the construction of the characteristic host ‘column’ structures. The guest molecule of the 3a·benzene complex is held between the stacking columns by aromatic CH/π interactions of the acenaphthene rings of adjacent host molecules. The stable clathrate formation of 3a is discussed based on X-ray structural analyses of six clathrates and PM6 molecular orbital calculations for the clathration model of 3a·benzene.

Role of edge-to-face interaction between aromatic rings in clathrate formation of 1-benzoyl-2-hydroxyindoline derivatives with benzene. X-ray crystal and PM6 analyses of the interaction

(4-Nitrophenyl- and 4-chlorophenyl)(2-hydroxy-3,3-dimethylindolin-1-yl)methanone ( 4a, b) serve as clathrate hosts for benzene guests. X-ray crystal analyses of the inclusion compounds of 4a and 4b with benzene indicate that the ‘edge-to-face interaction’ plays an important role in the formation of the inclusion complexes with benzene as well as in the host–host interactions. PM6 molecular orbital calculations were found to reproduce the characteristic structural features of both intra- and intermolecular edge-to-face interactions.

Synthesis, structures and inclusion properties of tetranaphthalides: new macrocyclic clathrate hosts

Novel tetranaphthalide host compounds 3 and 4 bearing isomeric naphthalene moieties have been synthesized and their inclusion properties were investigated. These host compounds enclathrated several kinds of ketones, cyclic ethers, amides, sulfoxides and aromatic compounds. The structures of two representative inclusion compounds containing different host molecules and a common guest (dimethyl sulfoxide) were investigated by X-ray diffraction to determine the nature of guest inclusion and to rationalize their distinctly different thermal decomposition profiles.

ChemInform Abstract: Tri-3-(2-butyl)-6-methylsalicylide (V). A Novel, Versatile Tri-o- thymotide-Based Clathrate Host Having Chiral Centers.

ChemInform Abstract: Tri-3-(2-butyl)-6-methylsalicylide (V). A Novel, Versatile Tri-o- thymotide-Based Clathrate Host Having Chiral Centers.

Supramolecular behaviour of bulky arylboranes in the crystalline state

The aromatic monoboranes 1, 2 and bisboranes 3, 4 of which 4 is a newly synthesised compound have been studied with reference to their supramolecular behaviour in the crystalline state. While the monoboranes crystallise purely, the bisboranes form channel-type solvent inclusions with m-xylene (3a) and nitrobenzene (4a) in the crystals, showing their potential as clathrate hosts in the realm of optically and electronically interesting compounds.

Decomposition Characteristics of Ethane Hydrate and Propane Hydrate by Microwave Heating

The decomposition of type I ethane hydrate and type II propane hydrate stimulated by 2.45 GHz microwave (MW) were experimentally investigated. The decomposition characteristics of the hydrates under MW heating were analyzed based on the two. step dissociation mechanism accompanied by heat and mass transfer at the crystal surface. Results show that the decomposition behavior of the gas hydrate during MW heating is coupled with the real. time electromagnetic field. Volumetric heating enhances the heat and mass transfer process at the surface layer of the hydrate particles. The time. accumulated thermal effect of MWheating promotes the destruction of the clathrate host lattice. The average decomposition rates of ethane hydrate and propane hydrate obtained in this work range from 0.109 to 0.400 mol . min(-1) . L-1 and from 0.090 to 0.222 mol . min(-1) . L-1, respectively, under incident MW power that ranges from 120 to 540 W. We conclude that the average decomposition rates of ethane hydrate and propane hydrate are faster as the MW power increases within a certain range. The decomposition rates of ethane hydrate are mainly controlled by the MW power. In contrast, the decomposition rates of propane hydrate are controlled by both the MW power and the kinetic mechanismunder relatively higher power.

Conflicting Behavior of a Versatile Host Compound: X-ray Crystal Structures Arising from Solvent-free and Solvent-Containing Crystal Formation

The X-ray crystallographic structures of four new inclusion compounds of the versatile clathrate host 2,2'-bis(9-hydroxy-9-fluorenyl)biphenyl (1) as well as the crystal structure of the unsolvated host are reported and comparatively discussed with regard to the molecular conformation and the modes of interactions the molecules make use of in the crystal packing. While the inclusion crystals demonstrate full saturation of the hydrogen bond capacity of the host molecule, 1 is only involved in weak intermolecular π-contacts in the solvent-free structure. We draw the conclusion that the well-tried strategy of coordinatoclathration, underlying the present inclusion compounds, should not be regarded as a strict rule with reference to the formation of inclusion crystals but a helpful framework in the search of new efficient clathrate hosts.

Photophysical properties of phenanthro[9,10- d]imidazole-type fluorescent hosts upon inclusion of organic solvent molecules

The crystal of phenanthro[9,10- d]imidazole-type fluorescent clathrate host ( 1) exhibits fluorescence enhancement behavior with a blue-shift of the emission maximum upon enclathration of organic solvent molecules such as 1-butanol and morpholine, whereas the crystal of 1 exhibits fluorescence enhancement behavior with a red-shift of the emission maximum upon enclathration of carboxylic acid such as acetic acid and propionic acid. The crystal structures of the guest-free and the guest-inclusion compounds of 1 have been determined by X-ray analysis. On the bases of the spectral data and the crystal structures, the effects of the enclathrated guest molecule on the solid-state photophysical properties of the guest-inclusion compounds are discussed.

Correction of Hydrate Dissociation in Shale Media via Correlation of Kim's Model

Deep-sea gas hydrates are ice-like crystalline substances in which hydrocarbon and non-hydrocarbon gases of specific molecular diameters are held by hydrogen bonding within rigid cages of water molecules. Sudden release of 1100-2100 Gt of carbon from dissociation of up to 10% of the global hydrate reservoir has been suggested as the cause of both the C-isotope excursion and coeval global atmospheric warming through an enhanced greenhouse effect. Kim's model assumed that, at a constant temperature, a two-step process could describe gas hydrate decomposition, including destruction of the clathrate host lattice at the surface of a particle and desorption of the guest molecule from the surface. In this paper, first, the thermodynamics and the kinetics of gas hydrate decomposition via Kim's model in the seafloors was reviewed; then, by a stainless steel test cell reactor and Omega Data Acquisition software, their correlation to sandy environments was formulated via numerical fitting of experimental data. The correlation of the conventional Kim's model is that the configuration of gas hydrate formation as a type of surface coating around sand grains was assumed. In the first stage of new mechanism dissociation, when the rate-controlling factor is dissociation heat, the formulation of the correlated dissociation rate was expressed. In the second stage of the mechanism, when the rate-controlling factor is mass transfer, the modified rate constant factor instead of Kim's constant factor was determined. The coefficient of correlation between the results of the estimation and experiment was more than 0.98 for both 85 and 216-μm sands.

Di-, tri-, and tetra-arylterephthalic acids as novel clathrate host compounds

Novel terephthalic acid host compounds having aromatic substituent 1– 4 have been prepared and their inclusion properties were investigated. These host compounds enclathrated several kinds of alcohols, ethers, ketones, amides, and sulfoxides. The X-ray structures of 1:1 2a/EtOH, 1:2 2b/DMF, 1:2 3/MeOH, and 1:1 4/EtOH complexes revealed complexation mode.

Solid‐State Fluorescence Changes of 2‐(4‐Cyanophenyl)‐5‐[4‐(diethylamino)phenyl]‐3H‐imidazo[4,5‐a]naphthalene upon Inclusion of Organic Solvent Molecules

AbstractNovel imidazo[4,5‐a]naphthalene‐type fluorescent clathrate host 2‐(4‐cyanophenyl)‐5‐[4‐(diethylamino)phenyl]‐3H‐imidazo[4,5‐a]naphthalene (2), with two possible tautomeric forms (A and B) of the imidazole ring, was developed. The crystal of fluorophore 2 exhibits sensitive colour change and fluorescence enhancement behaviour with a blueshift in the emission maximum upon enclathration of various kinds of organic solvent molecules. The crystal structures of the guest‐free and clathrate compounds of 2 were determined by X‐ray analysis. On the basis of spectroscopic data and crystal structures, the effects of the enclathrated guest on the solid‐state photophysical properties of the clathrate compounds are discussed.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Chemical−Clathrate Hybrid Hydrogen Storage: Storage in Both Guest and Host

Hydrogen storage from two independent sources of the same material represents a novel approach to the hydrogen storage problem, yielding storage capacities greater than either of the individual constituents. Here we report a novel hydrogen storage scheme in which recoverable hydrogen is stored molecularly within clathrate cavities as well as chemically in the clathrate host material. X-ray diffraction and Raman spectroscopic measurements confirm the formation of beta-hydroquinone (beta-HQ) clathrate with molecular hydrogen. Hydrogen within the beta-HQ clathrate vibrates at considerably lower frequency than hydrogen in the free gaseous phase and rotates nondegenerately with splitting comparable to the rotational constant. Compared with water-based clathrate hydrate phases, the beta-HQ+H2 clathrate shows remarkable stability over a range of p-T conditions. Subsequent to clathrate decomposition, the host HQ was used to directly power a PEM fuel cell. With one H2 molecule per cavity, 0.61 wt % hydrogen may be stored in the beta-HQ clathrate cavities. When this amount is combined with complete dehydrogenation of the host hydroxyl hydrogens, the maximum hydrogen storage capacity increases nearly 300% to 2.43 wt %.

Growth of Six Different Crystals of the Versatile Host Compound 1,1‘-Binaphthyl-2,2‘-dicarboxylic Acid from Solutions in 1,4-Dioxane

The six different crystals of the versatile clathrate host racemic 1,1‘-binaphthyl-2,2‘-dicarboxylic acid (BNDA) that are obtained from its solution in 1,4-dioxane at varying crystallization temperatures from 15 to 35 °C are reported. They involve four solvates (1, 2BNDA/dioxane; 2, BNDA/dioxane; 3, 2BNDA/2dioxane; 4, BNDA/2dioxane), one mixed 1,4-dioxane solvate with water (5, BNDA/3dioxane/H3O+), and one guest-free form. The framework structures are characterized by 0D associates (1, 3, and 4) that either include (3, 4) or don't include (1) guest molecules and by 1D zigzag chains with (5) or without (2) participation of guest molecules. The pseudotetramorphic solvates 1−4 are formed in accordance with a previously formulated rule for pseudopolymorphic clathrates, which is as follows: (i) the guest:host ratio decreases as the crystallization temperature increases, and (ii) the higher the formation temperature of the clathrate modification, the closer the space occupied by guest molecules.

Dynamics and equation of state of hydrogen clathrate hydrate as a function of cage occupation

The recent discovery of hydrogen clathrate hydrate with potential for efficient storage of molecular hydrogen at modest pressure has initiated significant scientific interest. Of critical importance for the amount of hydrogen that can be stored is the number of hydrogen molecules that occupy the cages in the hydrate clathrate host structure. The experimental data of cage occupancy is controversial, and the reproducibility of the initial experiment has been questioned. Therefore, in the present report we study the dynamic and thermodynamic properties of hydrogen clathrate hydrate as a function of cage occupancy using lattice dynamics calculations in order to determine the most favored occupancy at different external conditions. Lattice dynamics investigations show that all hydrogen hydrates with multiple species per cage are dynamically stable and phonon spectra strongly depend on the cage occupancy. As a result all thermodynamic functions vary significantly with cage occupancy. It is shown that quantum zero-point vibrations are of fundamental importance for the thermodynamic properties. The equation of state has been estimated as a function of temperature and cage occupancy.

Inclusion Compounds of Bulky Binaphthyl-type Bis-fluorenol Hosts

Inclusion properties of a new family of clathrate hosts (1–4) containing two 9-hydroxy-9-fluorenyl units or chloro-, bromo- and t-butyl-substituted derivatives of this group attached in the 3,3′-position to a basic 2,2′-binaphthyl construction element are reported (115 examples of clathrates). The crystal structures of six selected clathrates, involving dimethylsulfoxide, cyclopentanol, diethylether, benzylamine, chloroform and acetone as the guest, have been determined by X-ray diffraction, showing varied modes of supramolecular interaction dependent on the host and guest constitutions, while the formation of an intramolecular hydrogen bond between the hydroxy groups of the fluorenol units is a common structural feature (except in 3a) controlling twisted conformation of the host molecules.

A novel clathrate host allowing structural adjustment during the inclusion of 1,2-diaminoethanes

Dimethyl 5-hydroxy-2-oxo-4,5-diphenylcyclopent-3-ene-1,3-dicarboxylate ( 1a ) forms relatively stable inclusion complexes with compounds having 1,2-diaminoethane moiety.

Heterocyclic quinol-type fluorophores. Dramatic solid-state fluorescence enhancement behaviour of imidazoanthraquinol-type clathrate hosts upon inclusion of various kinds of organic solvent molecules

The crystals of novel imidazoanthraquinol-type clathrate hosts exhibit sensitive colour change and fluorescence enhancement behaviour upon enclathration of various kinds of organic solvent molecules. The optical changes are greatly dependent on the identity of the enclathrated guest molecules. To elucidate the enclathrated guest effects on the fluorescence properties of the crystals, the X-ray crystal structures of the guest-free and guest-inclusion compounds have been determined. On the basis of the spectral data and the crystal structures, the effects of the enclathrated guest on the solid-state photophysical properties of the clathrate compounds are discussed.