An N.M.R. study of the clathrate hydrates of SF₆, C₃H₆ and (CH₃)₂CO has been carried out to examine the type of motion a guest molecule undergoes in the clathrated cavity. ¹⁹F nuclear magnetic resonance spectra of Sulphur Hexafluoride Hydrate and Deuterate show isotropic rotation or reorientation about an axis at random of the SF₆molecule. ¹H magnetic resonance spectra of Cyclopropane Deuterate show highly restricted rotation up to 240°K, and then free rotation about C₃-axis at high temperatures. ¹H magnetic resonance spectra of Acetone Deuterate show that the CH₃-group is rotating even at 77°K, and self diffusion occurs at 172°K. The barrier hindering diffusion of the (CH₃)₂CO has been calculated and is 3.9 kcal/mole. / Science, Faculty of / Chemistry, Department of / Graduate

Includes bibliographical references. / X-ray crystallographic studies have been used to elucidate the structures of two new Werner clathrates. ... The chloroform molecule is disordered, lying on a two-fold axis. Stoicheiometric characterization of the clathrates was determined using various chemical techniques, including mass spectroscopy, proton nuclear magnetic resonance and complex iometric titration. The clathrating phase of the second clathrate was investigated by guest-loss studies on a McBain balance followed by X-ray powder photography. Host-quest non-bonded interactions of both clathrate compounds were studied using atom-pair potentials.

Le CO2 est capté par formation de clathrates hydrates sous l’action d’un promoteur de cristallisation thermodynamique. Les clathrates hydrates sont des composés d’inclusion non stœchiométriques formés de molécules d’eau organisées en réseau de cavités piégeant des molécules de gaz. Ce procédé de captage consiste à piéger de façon sélective le dioxyde de carbone dans les cavités des clathrates hydrates et à le séparer ainsi des autres gaz. Les hydrates mixtes de cyclopentane (CP) + gaz ont été étudiés dans le cadre du projet FUI ACACIA et du projet européen ICAP. Les premières expériences se sont focalisées sur l’étude des équilibres quadri phasiques (gaz CO2/N2, eau liquide, cyclopentane liquide et hydrate). Le cyclopentane est un promoteur thermodynamique qui forme des hydrates mixtes de CO2 + N2 + CP à basse pression et température modérée. La pression d’équilibre des hydrates mixtes est réduite jusqu’à 97% par rapport à la pression d'équilibre initiale des hydrates de gaz. La sélectivité de captage du CO2 dans les hydrates mixtes est augmentée et le volume de gaz stocké est de 40 m3gaz/m3hydrate. Une seconde étude expérimentale, conduite en présence d’une sonde FBRM (Focused Beam Reflectance Measurements) et d’une émulsion stable directe de CP/eau, a montré que la cinétique de cristallisation des hydrates mixtes de CP + CO2 est limitée par la diffusion du gaz à l’interface gaz/liquide. La sonde FBRM permet de détecter parfaitement l’apparition de la nucléation. Le changement de profil de la distribution en longueurs de corde (CLD) est non seulement lié à l’apparition des mécanismes de cristallisation (dont l’agglomération) mais aussi à la disparition des gouttes de CP au profit des hydrates qui cristallisent par un mécanisme à cœur rétrécissant. / CO2 separation and capture by clathrate hydrate crystallization is a non-conventional way of trapping and storing gas molecules from flue gases. Clathrates hydrates are non-stoichiometric ice-like crystalline solids consisting of a combination of water molecules and suitable guest molecules. Mixed hydrates of cyclopentane (CP) + gas have been studied in one national project (FUI ACACIA) and a European program (iCAP). Cyclopentane is an organic additive which forms mixed hydrates of CP + CO2 + N2 at low pressure and moderate temperature. The equilibrium pressure is decreasing up to 97 % (relative to the equilibrium pressure without cyclopentane). CO2 selectivity in hydrates is enhanced and gas storage capacity approaches a roughly constant value of 40 m3gas (STP) /m3hydrate. Crystallization of CP + CO2 mixed hydrates seems limited by gas diffusion through the gas / liquid interface, which gets in the way of the determination of the intrinsic kinetic constants of crystallization. Experimental studies have also been investigated in presence of a Focused Beam Reflectance Measurements (FBRM) probe in stable emulsion of CP in water. FBRM probe can successfully identify hydrate nucleation. The sharp change in the mean chord length and the spread of Chord Length Distribution (CLD) are related to the progressive disappearance of the CP droplets in favor of the CP + CO2 mixed hydrates formation. The change in the mean chord length distribution is not only related to the agglomeration phenomenon of the particles but also to the occurrence of the shrinking core crystallization of the CP droplets.

The present study aims to increase understanding of the physical processes that govern thermoelectric efficiency in Na-containing group 14 type II clathrates. This has been achieved through structural characterization and physical property measurements. Local and electronic structures of Si clathrates with the formula NaxSi136, where x = 0, 1.3, 5.5, 7.2, 8.8, 14.1, 20 and 21.5 were studied using x-ray absorption spectroscopy. Thermoelectric properties, namely Seebeck coefficient, electrical conductivity and thermal conductivity were measured from 2.5 K to 400 K. Low Na content samples, x < 8, showed reduced thermal conductivity compared to the empty clathrate, x = 0. For x > 8, increased Na content led to increased charge transfer, increased thermal conductivity and decreased magnitude of Seebeck voltages. The heat capacities of the NaxSi136 materials were measured from 2.5 K to 300 K. Analysis of the heat capacity data showed that the vibrational modes associated with Na in the Si28 cages are of sufficiently low energies to interact with heat transporting acoustic phonons, leading to reduced thermal conductivity as x is increased up to ~ 8. Increasing Na content beyond x = 8 introduces Na into the Si20 cages. This stiffens the lattice, increasing (or maintaining) phononic contributions to thermal conductivity, and increasing electronic contributions. Electronic thermal conductivity is responsible for upwards of 50 % of heat conduction when x = 21.5. Na containing type II Ge clathrates were produced using an ionic liquid reaction medium. Seebeck coefficients observed in Na9Ge136 materials, were negative but larger in magnitude than those of the NaxSi136 materials and thermal conductivities of Na9Ge136 were lower than those of the NaxSi136 materials. While both Si and Ge type II clathrates showed modest figures of merit, with maximum ZT values of 2.5 × 10-6 and 2.8 × 10-5 observed in Na20Si136 and Na¬9Ge136, of the two framework elements, type II Ge clathrates have been shown to have more favourable thermoelectric properties.

The current theoretical understanding of thermodynamics of clathrate hydrates is based on the van der Waals and Plattew (vdWP) theory developed using statistical thermodynamics approach. vdWP theory has been widely used to predict the phase equilibrium of clathrate hydrates over the decades. However, earlier studies have shown that this success could be due to the presence of a large number of parameters. In this thesis, a systematic and a rigorous analysis of vdWP theory is per-formed with the help of Monte Carlo molecular simulations for methane hydrate. The analysis revealed that long range guest-water interactions and guest-guest interactions are important, Monte Carlo integration to is superior to the spherical shell approximation for the Langmuir constant calculation and even after inclusion of all the interactions and using Monte Carlo integration for Langmuir constant, the vdWP theory still fails to regress parameters correctly. This failure of vdWP theory is attributed to the rigid water lattice approximation. To address the rigid water lattice approximation, a new method is proposed. In the proposed method, the Langmuir constant is computed in flexible water lattice, by considering the movement of water molecules. The occupancy values predicted using the proposed method are in excellent agreement with the values obtained from Monte Carlo molecular simulations for variety of hydrates, methane, ethane, carbon dioxide and tetrahydrofuran(THF) hydrates . In addition to small guest molecules like methane, ethane etc. which are mod- heled as rigid, the method is extended for large guest molecules like propane and isobutane, using configurationally bias Monte Carlo method. The phase equilib-rium and occupancy along the phase equilibrium predictions from vdWP theory are compared with the exact phase equilibrium computed from Monte Carlo molecular simulations. This comparison is done for a wide variety of hydrate systems, single hydrates , binary hydrates and quaternary hydrate. In all the cases, the vdWP theory with the flexible water lattice showed significant improvement over the rigid lattice model with significantly less absolute relative deviations in pressure. Guest-cavity interactions for hydrates are calculated using abinitio calculations. In general, these guest-cavity interaction from first principle calculations are used to develop classical force field parameters in alternative to Lorentz-Berthelot rule. In the study, comparison of guest-cavity interactions from MP2 and CCSD(T) methods revealed that less expensive MP2 method, which is generally used, is insouciant to capture the dispersion interactions accurately. These guest-cavity interactions using CCSD(T) method extrapolated to complete basis set are used to model the interaction parameters between cyclopropane and water. The potential parameters obtained from ab-initio calculations are used in the calculation of Langmuir constant using vdWP theory. Langmuir constant calculated using vdWP theory with flexible water lattice gave close agreement with the values obtained from experimental occupancy data. In addition, simulation methodology to calculate ternary hydrate phase equilibrium is extended for binary hydrates. Simulations have been successful in the prediction of sIsII and sII-sI structural transitions as observed in experiments. Predicted methane-ethane binary hydrate is also compared with the available experimental phase equilibrium data. The phase equilibrium obtained from simulations showed very good qualitative agreement with the experimental data.

Thesis. 1977. Ph.D.--Massachusetts Institute of Technology. Dept. of Chemical Engineering. / Microfiche copy available in Archives and Science. / Bibliography : leaves 414-426. / by Lucile M. Shanes. / Ph.D.

The work presented in this thesis deals with the employment of Schiff base ligands used to synthesise novel 3d-4f polynuclear coordination clusters (PCCs) and the investigation into their potential magnetic, luminescent and catalytic properties. Chapter one provides a general introduction to the chemistry described in the thesis. It includes a general overview of 3d-4f PCC chemistry and the applications of these materials and previous synthetic strategies for the preparation of Schiff base PCCs. A rationale is presented for the ligands employed in the thesis and a synthetic strategy is devised for the synthesis of specific materials. The initial chapters are focused on the synthesis of 3d-4f PCCs with novel core topologies and the study of their magnetic properties. Several novel series of 3d-4f PCCs are presented with unique core topologies which are previously unobserved in 3d-4f PCC chemistry. In addition, some of the presented PCCs display single-molecule magnet (SMM) properties or a significant magnetocaloric effect (MCE). Chapter five bridges synthetic aspects discussed in the previous chapters, with a synthetic study targeting 3d-4f PCCs with a defect dicubane core (2,3M4-1) and introduces the term “isoskeletal” to describe PCCs which possess the same topology or related organic structures with the same host framework but different guests. Chapters seven to nine are focused on the development of a well characterised isoskeletal family of 3d-4f PCCs with a defect dicubane core and the investigation of their potential catalytic properties in a range of organic reactions including Michael Addition, Friedel-Crafts alkylations and multicomponent reactions. Characterisation of the 3d-4f PCCs is emphasised and verifies the stability of the 2,3M4-1 core in solution. An attempt at understanding the catalytic system and mechanistic aspects is undertaken, which is not explored in previously reported 3d-4f PCC co-operative catalysis. Chapter ten provides an overall conclusion to the work presented in the thesis, whilst highlighting the contributions of this work to the reported literature.

Includes errata attached to first leaf. Includes bibliographical references. The complexation of a range of monovalent and divalent metal ions by the bibracchial lariat ethers has been investigated. Also investigates the complexation of metal ions and the anionic azo dye Brilliant Yellow by the diazacrown linked cyclodextrin dimers.

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (leaves 156-167).

Inhibiting the formation of ice is an essential process commercially, industrially, and medically. Compounds that work to stop the formation of ice have historically possessed drawbacks such as toxicity or prohibitively high active concentrations. One class of molecules, ice recrystallization inhibitors, work to reduce the damage caused by the combination of small ice crystals into larger ones. Recent advances made by the Ben lab have identified small molecule carbohydrate analogues that are highly active in the field of ice recrystallization and have potential in the cryopreservation of living tissue. A similar class of molecules, kinetic hydrate inhibitors, work to prevent the formation of another type of ice – gas hydrate. Gas hydrates are formed by the encapsulation of a molecule of a hydrocarbon inside a growing ice crystal. These compounds become problematic in high pressure and low temperature areas where methane is present - such as an oil pipeline. A recent study has highlighted the effects of antifreeze glycoprotein, a biological ice recrystallization inhibitor, in the inhibition of methane clathrates. Connecting these two fields through the synthesis and testing of small molecule ice recrystallization inhibitors in the inhibition of methane hydrates is unprecedented and may lead to a novel class of compounds.