Showing papers in "Journal of Inclusion Phenomena and Macrocyclic Chemistry in 1990"
TL;DR: In this article, the authors discuss the recovery of gas from clathrate hydrates through laboratory measurement and modeling of a depressurization scheme, and provide a determination of the volume of gas produced and the position of the hydrate interface.
Abstract: D. W. Davidsonet al. [7] were among the first to recognize significant deposits of natural gas clathrate hydrates in the Western Hemisphere. This work discusses the recovery of gas from such deposits, through laboratory measurement and modeling of a depressurization scheme. The work provides a determination of the volume of gas produced and the position of the hydrate interface, as a function of time when a hydrate-containing core is depressurized. A moving boundary model is shown to provide a satisfactory fit to hydrate dissociation measurements. Qualitative information is provided concerning hydrate formation in Berea Sandstone cores.
107 citations
TL;DR: In this article, an experiment with well defined gas-water interfacial surface area was developed to study the crystallization and crystal growth of methane hydrates, and it was concluded that melting ice, which like hydrate water is hydrogen-bonded, provides a template for hydrate nucleation as well as providing a heat sink for absorbing the heat of formation during hydrate growth.
Abstract: An experiment with well defined gas-water interfacial surface area was developed to study the crystallization and crystal growth of methane hydrates. Measurable formation rates were observed only when melting ice was involved. No hydrates nucleated from liquid water or from non-melting ice. It is concluded that melting ice, which like hydrate water is hydrogen-bonded, provides a template for hydrate nucleation as well as providing a heat sink for absorbing the heat of formation during hydrate growth. The experiment was conducted in the absence of mixing so that hydrate crystals grew under quiescent conditions.
89 citations
TL;DR: The tetramethylammonium hydroxide-water system has been studied by low-temperature differential thermal analysis and X-ray powder diffraction as discussed by the authors, and the melting diagram was constructed for concentrations between 66.7 and 100 mol% H2O.
Abstract: The tetramethylammonium hydroxide-water system has been studied by low-temperature differential thermal analysis and X-ray powder diffraction. The melting diagram was constructed for concentrations between 66.7 and 100 mol% H2O. It shows the existence and stability ranges of as many as eight crystalline hydrate phases:α- andβ-Me4NOH·2H2O (phase transition at −85°C, decomposition atca. 105°C), Me4NOH·4 H2O (melting point 44°C, incongruent),α andβ-Me4NOH·5 H2O (phase transition at 42°C, melting point 68°C, congruent),α- andβ-Me4NOH·7.5 H2O (phase transition at 6°C, melting point 16°C, incongruent), and Me4NOH·10 H2O (melting point −20°C, incongruent). The structures of all these phases, except the already known one ofα-Me4NOH·5 H2O, were determined from single-crystal MoKα diffractometer data. The decahydrate and the high-temperatureβ forms of the 7.5-hydrate and the pentahydrate are genuinepolyhedral clathrate hydrates, the first ones reported of a strong base. Their mostly novel three-dimensional anionic host structures, formed by the hydrogen-bonded OH− ions and H2O molecules, arefour-connected throughout, in spite of their proton deficiency which is apparently leveled by disorder. Disorder also affects the enclosed cationic Me4N+ guest species. Like the low-temperatureα form of the pentahydrate, that of the 7.5-hydrate has a clathrate-related, but not fully polyhedral structure, some of the oxygen atoms being three-connected only. The tetrahydrate presents the rare case of both a hydrogen bond of the type OH−...OH2 and a (deprotonated) water-channel structure. This is fully ordered and apart from that can be derived from the polyhedral one of theβ-pentahydrate just by removing the appropriate number of water molecules from certain positions. The structures ofα- andβ-Me4NOH·2 H2O contain identical one-dimensionalspiro chains [HO−(HOH)/42] with the hydroxide protonnot participating in the hydrogen bonding. The Me4N+ ion is ordered in theα and disordered in theβ phase.
67 citations
TL;DR: In this paper, the authors carried out X-ray diffraction studies on single crystals of natural air-hydrate in deep ice cores recovered at Dye-3 Greenland and found that the crystallographic structure is the Stackelberg's structure II.
Abstract: We have carried out X-ray diffraction studies on single crystals of natural air-hydrate in deep ice cores recovered at Dye-3 Greenland. Integrated intensities for 470 diffracting planes were measured by an automated four-circle diffractometer. The space group determined is cubicFd3m and the lattice constant is 17.21(3) A. These results indicate that the crystallographic structure is the Stackelberg's structure II, in contrast to the previously anticipated structure. This finding agrees with the recent results on the synthetic air-hydrate by Davidsonet al. It was also found by difference Fourier synthesis for guest molecules that electron density in a 16-hedral cage has multiple maxima displaced from the center of the cage while that in the 12-hedron was approximately spherical.
61 citations
TL;DR: In this article, the temperature dependence of the unit cell parameters of two newly identified hexagonal structure clathrate hydrates of hexamethylethane (HME) and 2,2-dimethylbutane (DMB) have been measured by X-ray powder diffraction.
Abstract: The temperature dependence of the unit cell parameters of two newly identified hexagonal structure clathrate hydrates of hexamethylethane (HME) and 2,2-dimethylbutane (DMB) have been measured by X-ray powder diffraction. The thermal expansion of the two distinct crystallographic axes was found to be inequivalent. However, the coefficients of cubic expansion are comparable to that in the cubic structure I and II hydrates. The larger thermal expansivity in the clathrate hydrates relative to ice is attributed to the weakening of the host lattice due to the internal pressure generated by the rattling motions of the encaged guests.
40 citations
TL;DR: In this article, the formation and decomposition of gas hydrates is modelled as a crystallization process where two distinct processes (nucleation and growth) are involved.
Abstract: Based on our theoretical and experimental work carried out during the last decade, our understanding of the thermodynamics and the kinetics of formation and decomposition of gas hydrates is presented. Hydrate formation is modelled as a crystallization process where two distinct processes (nucleation and growth) are involved. Prior to the nucleation the concentration of the gas in the liquid water exceeds that corresponding to the vapor-liquid equilibrium. This supersaturation is attributed to the extensive structural orientation in the liquid water and is necessary for the phase change to occur. The growth of the hydrate nuclei or the decomposition of a hydrate particle are modelled as two-step procedures. Only one adjustable parameter for each hydrate forming gas is required for the intrinsic rate of formation or decomposition. In addition the inhibiting effects of electrolytes or methanol on hydrate formation are discussed and experimental data on methane gas hydrate formation in the presence of aqueous solutions of 3% NaCl and 3% NaCl + 3% KCI, are presented along with the predicted values. Finally, the relevence of the ideas to the technological implications of gas hydrates as well as areas where future research is needed are discussed.
31 citations
TL;DR: In this article, a review of charge transfer interactions in cyclophane systems is presented, where the majority of the work involves intermolecular complexation, with both donor and acceptor moieties existing within the same molecule.
Abstract: Charge-transfer interactions in cyclophane systems are reviewed. The majority of the work covered involves intermolecular complexation, with both donor and acceptor moieties existing within the same molecule. Studies have also been performed on intermolecular complexes, mainly tetracyanoethylene:cyclophane complexes. Host-guest complexes involving charge-transfer are also discussed. Other areas covered include solvent effects, substituent effects, and theoretical calculations.
25 citations
TL;DR: Complex dielectric permittivities of pure and KOH-doped tetrahydrofuran clathrate hydrates were measured in the temperature range 20-260 K and in the frequency range 20 Hz-1 MHz.
Abstract: Complex dielectric permittivities of pure and KOH-doped (x = 1.8 x 10−4) tetrahydrofuran clathrate hydrates were measured in the temperature range 20–260 K and in the frequency range 20 Hz-1 MHz. The relaxation time of the water reorientational motion was found to decrease drastically as a result of the doping; e.g., the relaxation time of the doped sample was 10−9 times shorter than that of the pure sample at 70 K. The activation enthalpy of the motion was reduced to 7.4 kJ mol−1. On cooling the crystal, the value ofɛ′ decreased suddenly at the 62 K phase transition to thee∞2 value of the pure sample and at the same timeɛ″ disappeared. No dispersion effect due to the guest reorientation was observed below the transition. These data indicate that both the host and guest molecules become ordered or, at least, change their mobility drastically. In the pure sample, a relaxation phenomenon ofe02 was found around the glass transition region. The relaxation times agreed well with those derived from the enthalpy of relaxation in a calorimetric study.
21 citations
TL;DR: In this article, a glass transition related to the proton configurational mode in the hydrogen-bonded host was observed around 90 K. This glass transition was similar to the one observed previously for the structure II tetrahydrofuran hydrate but showed a wider distribution of relaxation times.
Abstract: The heat capacity of structure I ethylene oxide clathrate hydrate EO-6.86 H2O was measured in the temperature range 6–300 K with an adiabatic calorimeter. The temperature and enthalpy of congruent melting were determined to be (284.11 ± 0.02) K and 48.26 kJ mol−1, respectively. A glass transition related to the proton configurational mode in the hydrogen-bonded host was observed around 90 K. This glass transition was similar to the one observed previously for the structure II tetrahydrofuran hydrate but showed a wider distribution of relaxation times. The anomalous heat capacity and activation enthalpy associated with the glass transition were almost the same as those for THF-hydrate.
18 citations
TL;DR: The crystal structures of four DMSO inclusion compounds with different carboxylic acid hosts, 1, 4, have been studied by single crystal X-ray analysis as mentioned in this paper, and all of them show monoclinic (P21/n) symmetry with the unit cell dimensionsa = 11.522(4),b = 18.658(2),c = 8.709(1) A and β = 98.92(2)°.
Abstract: The crystal structures of four dimethyl sulphoxide (DMSO) inclusion compounds with different carboxylic acid hosts,1–4, have been studied by single crystal X-ray analysis. Crystals of thetrans-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylic acid inclusion compound (1a), [1 · DMSO (1: 1)] show monoclinic (P21/n) symmetry with the unit cell dimensionsa = 11.522(4),b = 18.658(2),c = 8.709(1) A and β = 98.92(2)°. The clathrate of the 9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylic acid (2a), [2 · DMSO (1: 2)] is triclinic (PĪ) with the cell dimensionsa = 15.043(7),b =9.657(4),c = 8.118(7) A, α = 101.81(5), β = 96.05(4) and γ = 100.04(4)°. Triclinic (PĪ) symmetry is shown also by the inclusion compound of 9,10-dihydro-9,10-ethanoanthracene-11-monocarboxylic acid (3a) [3 · DMSO (1:1)] with the cell dimensionsa=6.3132(1),b=7.9846(2),c=17.5314(4) A, α = 96.46(2), β = 87.08(2) and γ = 106.02(2)°. The 9,9′-bianthryl-2-monocarboxylic acid clathrate (4a) [4 · DMSO (1:1)] is monoclinic (P21/n) and the cell dimensions area = 19.625(18),b = 8.817(1),c = 14.076(8) A and β = 97.92(6)°. In all these structures, the hosts show the same basic recognition pattern for the DMSO guest, involving a strong O-H ... O bond from the COON to the S=O group, and a possible C-H ... O type interaction between the carbonyl O atom of the host and a CH3 group of the guest. The crystals consist of discrete host-guest aggregates which are mainly held together by weak intermolecular interactions of the Van der Waals' type. The stoichiometries of the aggregates are, however, different.
18 citations
TL;DR: The crystal structures of 1 : 1 inclusion complexes of gossypol with tetrahydrofuran (GPTHF), cyclohexanone (GPCHN) and butanal (GPBTA) have been determined by X-ray structure analysis.
Abstract: The crystal structures of 1 : 1 inclusion complexes of gossypol with tetrahydrofuran (GPTHF), cyclohexanone (GPCHN) and butanal (GPBTA) have been determined by X-ray structure analysis. The crystals of GPTHF are triclinic, space group PĪ,a = 10.788(2),b = 10.979(3),c = 13,880(2) A, α = 80. 11(2), β = 103.87(1), γ = 77.96(2)°,V = 1517.8(6) A3,Z = 2,R = 0.052 for 2701 observed reflections. The crystals of GPCHN are triclinic, space groups PĪ,a = 10.803(4),b = 11.157(5),c = 15.428(6) A, α = 108.75(3), β = 106.93(3), γ = 103.34(3)°,V = 1573(1) A3,Z = 2,R = 0.071 for 1879 observed reflections. The crystals of GPBTA are triclinic, space group PĪ,a = 10.190(2),b = 11.335(1),c = 14.665(2) A, α = 73.04(1), β = 103.74(1), γ = 81.07(1)°,V = 1529.9(5) A3,Z = 2,R = 0.068 for 2964 observed reflections. Crystal data for another 13 isostructural inclusion complexes are given.[/p]
TL;DR: The structure I clathrate hydrate of carbon monoxide has been studied using dielectric measurements and 13C NMR spectroscopy as discussed by the authors, showing that CO molecules undergo anisotropic reorientation in the large cages and that there is still considerable mobility at 77 K.
Abstract: The structure I clathrate hydrate of carbon monoxide has been studied using dielectric measurements and13C NMR spectroscopy. Broad, weak dielectric absorption curves with maxima at 2.2–3.8 K yieldEa = 0.14 kJ mol−1 for the average Arrhenius activation energy associated with the reorientation of the low polarity guest. Except for H2S this represents the fastest reorienting polar guest known among the clathrate hydrates. The low temperature dielectric absorption curves can best be fitted with a Cole-Davidson asymmetric distribution of relaxation times and activation energies (withθ = 0.06 at 4 × 106 Hz), which at 107 Hz has been resolved into a double symmetric distribution of discrete relaxation times for CO in the small and large cages. The cross-polarization magic angle spinning13C NMR spectra indicate identical chemical shifts for CO in the small and large cages, in contrast to other hydrates. The static spectra show that the CO molecules undergo anisotropic reorientation in the large cages and that there is still considerable mobility at 77 K. One possible model for the anisotropic motion has the CO rapidly moving among sites over each of the 14 faces of the cage with the CO axis orientated towards the cage centre. The cage occupancy ratio at 220 K,θs/θL = 1.11, indicates slightly greater preference of CO for the small cage.
TL;DR: In this paper, the structural and crystal properties of host-guest compounds are explored with the use of crystal growth studies, X-ray powder patterns, and thermal analysis, and the crystal structure of the benzene cyclamer of 5-methyl-1,3-cyclohexanedione is reported.
Abstract: During crystallization 1,3-cyclohexanedione self assembles into either hydrogen-bonded chains or hexameric rings depending on the solvent conditions. The hexameric rings, called cyclamers, are the subject of this paper. These unusual structures occlude benzene as a guest molecule. The structural and crystal chemical properties of these host-guest compounds are explored here with the use of crystal growth studies, X-ray powder patterns, and thermal analysis. The crystal structure of the benzene cyclamer of 5-methyl-1,3-cyclohexanedione is reported (hexagonal,a =b = 19.19(2)A,c = 10.545(9)A,R3,Z = 18,V = 3362(6)A3; 717 unique reflections,R = 0.062). An analysis of the stereochemical implications of cyclic directionality in these cyclamers is also discussed.
TL;DR: In this paper, the steric requirement of host-guest interaction was reflected in the magnitude of the stability constants and the thermodynamic parameters of the inclusion complexes of nocloprost, a potent antiulcer prostaglandin derivative.
Abstract: Inclusion complexation of nocloprost, a potent antiulcer prostaglandin derivative, with α-, β-, and γ-cyclodextrins (CyDs) in aqueous solutions has been studied by the solubility method and13C-NMR spectroscopy. The steric requirement of host-guest interaction was reflected in the magnitude of the stability constants and the thermodynamic parameters of the inclusion complexes. Solid complexes of nocloprost with β- and γ-CyDs in a molar ratio of 1 : 2 were obtained on the basis of aBs-type phase solubility diagram. The X-ray diffraction data suggested that nocloprost is included in the cylindrical channel formed by coaxial alignment of γ-CyD molecules to give a channel type structure. Release and thermal behavior of the solid complexes was examined and compared with nocloprost itself. The results indicated that the β-CyD complex may have great utility among the three CyDs, being a rapid dissolving form of nocloprost with improved thermal stability.
TL;DR: In this article, three dimensional host lattices have been developed by forming bridges with bidentate pyrazine molecules between adjacent tetracyanonickelate polymeric layers of Ni(II) or Cd(II).
Abstract: Three dimensional host lattices have been developed by forming bridges with bidentate pyrazine molecules between adjacent tetracyanonickelate polymeric layers of Ni(II) or Cd(II). The Fourier-transform IR and Raman spectra (4000-200 cm−1) of the compounds with the general formula M(pyz)Ni(CN)4, (where M = Ni or Cd) are reported. These host lattices can include benzene molecules but it is found that aniline molecules cannot be included in these structures. They, however, form complexes with the formula M(an)2Ni(CN)4, by replacing pyrazine ligands. A monodentate pyrazine complex of Cd(II) with the formula Cd(pyz)2Ni(CN)4 has also been prepared.
TL;DR: In this paper, it was shown that the photochromic behavior of the fulgide α-2,5-dimethyl-3-furylethylidene (isopropylidenes) succinic anhydride can be modified considerably when supported on a smectite clay.
Abstract: Reversible light induced colour changes have been observed in a variety of organic and inorganic systems: the phenomenon is termed photochromism. Suitable materials have potential uses ranging from data storage to labelling. The fulgide α-2,5-dimethyl-3-furylethylidene (isopropylidene) succinic anhydride shows photochromic behaviour which is modified considerably when the fulgide is supported on a smectite clay. We have shown that Smectites cause a bathochromic shift in the fight absorption of the fulgide and the photochrome of 20 and 80 nm, respectively, relative to the values in hydrocarbon solution. Moreover, the clays catalyse several reactions on different timescales.
(1)
Z →E isomerization of the fulgide. This process is an acid catalysed interlayer reaction strongly sensitive to the presence of polar molecules even at low concentrations. The most effective catalysts were clays exchanged with trivalent interlayer cations, equilibrated at low relative humidity before use. In toluene, reflux reactions were complete in ≈ I hour. The procedure can be used in a preparative sense.
(2)
The ring closure reaction to give the photochrome (i.e.E →P). This is a surface (and interlayer) catalysed thermal reaction, taking of the order of a day in toluene reflux. The reaction does not depend to any great extent on the type of smectite used, nor, within reason, on any pretreatment of the clay.
(3)
The decomposition of the fulgide and photochrome. These reactions were found to be acid catalysed and gave at least four products. The reactions occur in the interlayer region of the clay, but at a rate slower than those listed above, taking months to reach levels at which products could be detected.
TL;DR: In this article, the crystal structure of the 2: 1 inclusion complex of gossypol with amyl acrylate has been determined by X-ray structure analysis, and the structure has been solved by direct methods and refined to the final R value of 0.059 for 5155 observed reflections.
Abstract: The crystal structure of the 2: 1 inclusion complex of gossypol with amyl acrylate has been determined by X-ray structure analysis. The crystals of (C30H30O8)2⁗C8H14O2 are triclinic, space group P\(\bar 1\),a = 14.425(2),b = 15.519(1),c = 16.409(2) A, α =97.89(1), β = 117.80(1), γ =67.01(1)° (reduced cell:a = 14.425(2),b = 15.519(2),c = 16.017(2)A, α = 92.19(1), β = 115.01(l), γ =67.01(1)°],V = 2986.7(5) A3,Z = 2,Dx = 1.31 g cm−3, μ(CuKα) = 7.40 cm−1,T = 292 K. The structure has been solved by direct methods and refined to the final R value of 0.059 for 5155 observed reflections. The gossypol molecules bonded via several hydrogen bonds form centrosymmetric tetramers. The two independent gossypol molecules, A and B, are related within the tetramer by a local noncrystallographic 2-fold axis. The host molecules in the crystal form cavities in which two guest molecules are placed. The ester molecule interacts via a pair of C-...H-O hydrogen bonds with two gossypol molecules of the same chirality and belonging to the same tetramer unit. The amyloxy group of the ester molecule shows a very large thermal motion. It adopts a non-extended conformation in which it can be fitted into the cavity formed by the host molecules.
TL;DR: The crystal structures of the inclusion compounds of trans-9,10-dihydro-9-10-ethano-anthracene-11,12-dicarboxylic acid host (1) with formic acid (1a), acetic acid(1b), and propionic acid as guests, and of the coordinatoclathrate of the 1,1′-binaphthyl-2,2′-Dicaroxyl acid host with acetic acids as guest (2b) have been studied by single crystal X-
Abstract: The crystal structures of the inclusion compounds oftrans-9,10-dihydro-9,10-ethano-anthracene-11,12-dicarboxylic acid host (1) with formic acid (1a), acetic acid (1b), and propionic acid (1c) as guests, and of the coordinatoclathrate of the 1,1′-binaphthyl-2,2′-dicarboxylic acid host (2) with acetic acid as guest (2b) have been studied by single crystal X-ray diffraction. These studies show that inclusion of small carboxylic acids by carboxylic acid hosts like1 and2 results in formation of isolated, hydrogen-bonded guest dimers. Additional H-bond contacts between host and guest carboxylic groups are only formed in cases1a and2b. The dimeric acidic guest units are sitting in the cavities of the host or host-guest framework and have no other interactions than those of a weak Van der Waals' type with the neighbouring molecules. Crystal data:1·formic acid (1:2): triclinic (PĪ),a = 11.6769(6),b = 9.4067(4),c = 9.0020(4) A,a = 81.522(4), β = 100.310(6), γ = 104.208(6)°,Z = 2,R = 0.048 for 2392 reflections;1·acetic acid (1:1): monoclinic (P21/n),a = 9.717(2),b = 14.462(2),c = 13.038(3)A, β = 104.27(1)°,Z=4,R=0.046 for 3042 observations;1·propionic acid (1:1): monoclinic (P21/n),a = 9.897(4),b = 14.671(7),c = 13.284(7) A, β = 105.92(6)°,Z = 4,R = 0.056 for 2302 reflections;2·acetic acid (2:3): triclinic (PĪ),a = 12.746(1),b = 17.781(2),c = 11.010(1) A, α = 105.606(4), β = 112.992(8), γ = 81.175(6)°,Z = 2,R = 0.067 for 4375 observations.
TL;DR: In this paper, the roof effect of a hydrate zone is defined by a positive Cl− and a negative δ18O anomaly (the opposite of the hydrate decomposition effect) and the composition ofin-situ pore waters from within hydrate zones.
Abstract: Naturally occurring gas hydrates, discovered under the deeper parts of the continental margins (generally below 500 m water depth) during the Deep Sea Drilling Project and the Ocean Drilling Program, impregnate terrigenous sediments 0.5 to 1 km thick. They form from biogenic as well as thermogenic hydrocarbon gases and are associated with characteristic chemical and isotopic anomalies in the pore waters resulting from hydrate decomposition. Typical downward trends derived from water samples squeezed on board ship show decreasing chlorinity coupled with increases in the heavy oxygen and hydrogen isotopes resulting from the combined effects of sediment compaction and salt and isotope fractionation by hydrates. Carbon isotopes can be used to differentiate between biogenic (δ13C −559‰) gas hydrates except where acetate-derived methane is involved. Smooth downward trends in the chemical and isotopic anomalies suggest steady increases in the proportion of hydrates among the pore-filling substances. Spikes are attributed to high local hydrate concentrations (or massive hydrate layers or nodules). Problems encountered in delineating the detailed relationships between hydrate occurrence and pore-water anomalies concern (i) the roof-effect of a hydrate zone which should be marked by a positive Cl− and a negativeδ18O anomaly (the opposite of the hydrate decomposition effect) (ii) the composition ofin-situ pore waters from within hydrate zones; (iii) the suppression of a positiveδ18O hydrate-decomposition anomaly due to superposition of other oxygen-isotope fractionation effects (such as volcanic glass alteration); and (iv) the non-linear correlation between Cl− depletion and18O enrichment, and the magnitude of the18O enrichment. The hydrate-decomposition mechanism still provides the most successful explanation for the chemical and isotopic porewater anomalies observed in hydrate-bearing sediments, but the problems encountered underscore the urgency for future research through deep-sea drilling in hydrate zones.
TL;DR: In this article, two aromatic rings of a phlorizin molecule form inclusion complexes with β-CD and γ-CD, and the induced circular dichroism spectra of these complexes have been measured to estimate the orientation of the 2 aromatic rings in the hydrophobic space.
Abstract: Two aromatic rings of a phlorizin molecule form inclusion complexes with β-CD and γ-CD. Induced circular dichroism spectra of these complexes have been measured to estimate the orientation of the two aromatic rings in the hydrophobic space of CDs. Apparent complex formation constants have been also estimated for each complex. It is concluded that phlorizin forms a stronger inclusion complex with β-CD than with γ-CD.
TL;DR: The crystal structures of 2:1 inclusion complexes of gossypol with methyl propionate (GPMEP and GPEAA) have been determined by X-ray structure analysis as discussed by the authors.
Abstract: The crystal structures of 2:1 inclusion complexes of gossypol with methyl propionate (GPMEP) and ethyl acetoacetate (GPEAA) have been determined by X-ray structure analysis. The crystals of GPMEP, C30H30O8⁗l/2 C4H8O2, are monoclinic, space groupC2/c,a=11.079(3),b = 30.724(7), c = 16.515(5) A, β = 90.46(2)°,V = 5621(3) A,Z = 8,Dx = 1.33 g cm−3. The structure has been refined to the finalR value of 0.059 for 1899 observed reflections. The crystals of GPEAA, C30H30O8⁗l/2 C6H10O3, are monoclinic, space groupC2/c,a=11.095(2),b=30.604(9),c = 16.955(5) A, β = 88.27(2)°,V = 5754(3) A,Z = 8,Dx = 1.35 g cm−3. The structure has been refined to the finalR value of 0.056 for 2502 observed reflections.
TL;DR: The crystal structures of the lattice inclusion complexes of gossypol with benzene and chloroform have been determined by X-ray structure analysis as mentioned in this paper, and the structure has been refined to a finalR value of 0.050 for 6146 observed reflections.
Abstract: The crystal structures of the lattice inclusion complexes of gossypol with benzene and chloroform have been determined by X-ray structure analysis. The crystals of (C30H30O8)2 · C6H6 (GPBNZ) are triclinic, space groupPI,a = 11.241(3),b = 14.986(4),c = 17.380(4) A, α = 98.89(2), β = 99.86(2), γ = 98.91(2)°,V = 2800(2) A3,Z = 2,Dx = 1.32 g cm−3, μ(CuKα) = 7.35 cm−1. The structure has been refined to a finalR value of 0.050 for 6146 observed reflections. The crystals of C30H30O8·CHCl3 (GPCLF) are monoclinic, space groupC2/c,a = 28.464(4),b = 8.948(1),c = 26.480(4) A, β = 108.93(2)°,V = 6380(2) A3,Z = 8,Dx = 1.33 g cm−3, μ(CuKα) = 30.42 cm−1. The structure has been refined to a finalR value of 0.100 for 1980 observed reflections.
TL;DR: In this article, the authors showed that both nucleation and crystal growth are faster when TEPA-Br rather than TEBA-Br is used as a template for ZSM-5 zeolite.
Abstract: Pentasil zeolites of ZSM-5 type are synthesised hydrothermally using triethyl-n-proplyammonium bromide (TEPA-Br) and triethyl-n-butylammonium bromide (TEBA-Br). The crystallization kinetics, followed by XRD, SEM and thermal analysis, clearly demonstrate the influence of size and molecular weight of the templating quaternary ammonium cation (QAC) species on the rates of nucleation and crystallization. The values of the apparent activation energies for nucleation and crystal growth indicate that both nucleation and crystal growth are faster when TEPA-Br rather than TEBA-Br is used as a template. The quantitative identification of intergrown phases characterizes both the phases to be ZSM-5 zeolite. Thermoanalytical curves for both these zeolites in as-synthesised forms exhibit two-step oxidative decomposition of the occluded organic species. This suggests that the quaternary ammonium cation may be located at two energetically different sites within the zeolite channels. The equilibrium sorption capacity, however, is found to increase in the order of size and molecular weight of the templating species in both the zeolites. The nature of acid site distribution, obtained from the temperature programmed desorption of ammonia is found to be independent of the templating species used during the synthesis.
TL;DR: Bromocalix[4]arene methyl ether as discussed by the authors is a precursor to thiocalixarene via the reagent CuSEt. The partial cone conformation is identical to that of ethylthiocyclic-aleane methyl ether, and the configuration of the calixarenes lies between the partial cone and the 1,3-altemate conformations.
Abstract: Bromocalix[4]arene methyl ether serves as a precursor in the synthesis of the title thiocalixarene via the reagent CuSEt. Ethylthiocalix[4]arene methyl ether crystallizes in the monoclinic space groupP21/c witha = 20.577(9),b, = 10.722(5),c = 20.315(9) A, β = 120.46(4)°, andDc = 1.24 g cm−3 forZ = 4. Refinement based on 1441 observed reflections led toR = 0.080. The configuration of the calixarene lies between the partial cone and the 1,3-altemate conformations. Bromocalix[4]arene methyl ether crystallizes in the triclinic space groupPI witha = 12.283(7),b = 17.658(9),c = 18.118(6) A, α = 90.25(6), β = 105.95(4), γ = 105.11(6)°, andDc = 1.68 g cm−3 forZ = 4. Refinement based on 3028 observed reflections led toR = 0.083. The unit cell also contains four CHCl3 molecules which exist pairwise enclathrated by six calixarenes. The partial cone conformation of the bromocalixarene is identical to that of ethylthiocalix[4]arene methyl ether.
TL;DR: The title complexes (1, X = F;2, X= C 1; 3 and X = Br and isomorphous with2; 4, I = I) have been prepared and characterized by X-ray crystallography as discussed by the authors.
Abstract: The title complexes (1, X = F;2, X = C 1; 3, X = Br and isomorphous with2; 4, X = I) have been prepared and characterized by X-ray crystallography. Crystal data, MoKα radiation:1, space groupCc,Z =4,a = 12.017(3),b = 14.263(5),c = 17.210(7) A,β = 103.06(2)°, andRF=0.053 for 2044 observed data;2, space groupCc,Z = 4,a = 12.817(3),b = 11.072(2),c = 16.781(5) A,β =90.74(2)°,RF = 0.044 for 2249 data;3,a = 12.873(4),b = 11. 119(2),c = 16.957(2) A,β = 89.11(2)°,RF = 0.049 for 2059 data;4, space groupP21/n,Z = 4,a = 8.858(2),b = 14.358(3),c = 15.379(3) A,β = 93.88(1)°,RF = 0.068 for 3119 data. In all four structures each thiourea molecule interacts with adjacent thiourea molecules via N-H ... S hydrogen bonds to give a ribbon-like arrangement, and also forms a pair of ‘chelating’ N-H ... X hydrogen bonds with a halide ion, resulting in an anionic framework (in1–3) or composite ribbon (in4) as a component in the crystal packing. The measured ranges of N... X distances are: 2.819(5)-2.994(7) A for1, 3.252(3)-3.291(3)A for 2, 3.353(6)-3.459(6)A for3, and 3.564(5)-3.680(5) A for 4.
TL;DR: In this article, the phonon density of states for the empty hydrate framework and for xenon hydrate have been determined; the vibrational frequencies of the guest molecules in large and small cavities have been found; and the stability of the hydrate with respect to the external pressure at low temperatures and its thermodynamic stability at temperatures around 0°C have been studied.
Abstract: Vibrational spectra and thermodynamic properties of ices and the cubic structure I (CS-I) clathrate hydrate have been studied by the lattice dynamics method. The phonon density of states for the empty hydrate framework and for xenon hydrate have been determined; the vibrational frequencies of the guest molecules in large and small cavities have been found. The stability of the hydrate with respect to the external pressure at low temperatures and its thermodynamic stability at temperatures around 0°C have been studied. It has been found that the empty hydrate framework is unstable in certain temperature and pressure regions. A definite degree of occupation of the large cavities by the guest molecules is necessary for the hydrate to become stable. It has been found that there is a maximum of the critical temperature at which the hydrate exists, which is a function of the external pressure.
TL;DR: In this article, the heat capacities of Dianin's compound (4p-hydroxypheny]-2,2, 4-trimethylchroman) and the ethanol and carbon tetrachloride adducts were measured in the 30-300k temperature range.
Abstract: The heat capacities of unsolvated (‘empty’) Dianin's compound (4p-hydroxypheny]-2,2, 4-trimethylchroman) and the ethanol and carbon tetrachloride adducts of Dianin's compound have been measured in the 30–300K temperature range. The molar heat capacities of the guest species were calculated from the experimental results and compared with molar heat capacities of bulk CCl4 and bulk C2H5OH The stoichiometry of the CCl4 adduct was determined to be six host molecules per guest CCl4, in contrast to an earlier report.
TL;DR: In this paper, two nitrogen-substituted 4,13-diaza-I8-crown-6 compounds, bearing 2-methylquinolyl and 2-miquelin-1-oxide groups, have been prepared.
Abstract: Two nitrogen-substituted 4,13-diaza-I8-crown-6 compounds, bearing 2-methylquinolyl and 2-methylquinolyl-1-oxide groups, have been prepared. Ionophore-cation selectivities with a range of inorganic divalent cations have been investigated by means of membrane techniques, demonstrating their high selectivity for the Hg(II) cation.
TL;DR: In this paper, a single crystal X-ray analysis of a 1 : 2 complex between the dinaphthopyridino-l8-crown-6 host and acetonitrile is reported.
Abstract: Single crystal X-ray analysis of a 1 : 2 complex between the dinaphthopyridino-l8-crown-6 host (1) and acetonitrile is reported. Crystals of the complex are monoclinic,P21/c witha = 12.178(5),b = 8.186(1),c = 30.873(1) A, β = 96.86(1)°, andD
c = 1.25 g cm−3 forZ = 4. The host molecule reveals an approximate mirror symmetry and exists in a so-called ‘dentist's chair’ conformation. One of the acetonitrile guest molecules is involved in possible weak interactions to two oxygen atoms of the host macroring, while the other fills free lattice space only.
TL;DR: In this article, it was shown that 1H or 2H tunnelling plays an important part in the motion of the cage molecules and the different phase behaviour of polycrystalline (CH3)4NOH·5 H2O (I and II) ion.
Abstract: Polycrystalline (CH3)4NOH·5 H2O (I) and (CH3)4NOD·5D2O (II) have been studied by1H NMR lineshapes, second moments and spin-lattice relaxation times and by2H NMR lineshapes as a function of temperature. From low temperatures the first motion to occur is reorientation of the internally rigid (CH3)4N+ ion about a uniqueC3′ axis (Eta = 8.37 kJ/mol forI,Ea = 9.00 kJ/mole forII), followed closely by pseudo isotropic reorientation of the whole ion (Ea = 18.10 kJ/mol). Motion of the cage molecules (water and hydroxide ion) occurs at higher temperatures with an apparentEa = 11.30 kJ/mol. There is some evidence of a phase transition inII but notI in the 220–230 K region.2H NMR lineshapes ofII below 220 K indicate static cage molecules. Some of the2H quadrupole coupling constants derived from these spectra correspond to O·O hydrogen-bond distances which are incompatible with the known room temperature structure ofI. Above the possible transition inII the anisotropic2H lineshapes indicate rapid motion of2H among all possible hydrogen-bond sites via transfer along the bonds and molecular reorientation. This motion persists in the high temperature phase but the lineshape becomes isotropic due to the cubic symmetry of this phase. It is possible that1H or2H tunnelling plays an important part in the motion of the cage molecules and the different phase behaviour ofI andII.