No description available.

Graduation date: 1997

Thesis (Ph.D.). / Written for the Dept. of Physics. Title from title page of PDF (viewed 2009/06/08). Includes bibliographical references.

Thesis (M.S.)--Mississippi State University. Department of Chemistry. / Title from title screen. Includes bibliographical references.

No description available.

In organic-inorganic hybrid compounds an organic and an inorganic component are combined to form either a coordination or an ionic material. Relevant to the current study are hybrid materials composed of an organic part that contains one or more functional groups, for example amine, amide or carboxylic acid functional groups, and a metal halide inorganic portion. These functional materials display a range of interesting and desired properties, as evidenced from numerous literature reports on their properties. In order to utilise these properties in applications, a detailed understanding of the way that the crystal structure influences the properties of a material is required. However, before this step can be achieved, it is necessary to obtain information on the structural trends of the materials, and to use the approach of crystal engineering to identify robust supramolecular synthons that may afford structural control and prediction. The aim of the current study was to investigate the synthesis and crystal structures of hybrid materials, both ionic and coordination, composed of divalent transition metal halides and the organic components 4-aminobenzoic acid, 4-aminobenzamide and isonicotinic acid, and to identify the structural trends and crystal engineering synthons displayed by these materials. A secondary objective was the preliminary identification of properties exhibited by selected materials, in order to decide on the suitability of the materials for detailed future property investigations. Part of the work describes the investigation of the structural characteristics of coordination materials prepared by the combination of the organic and inorganic components. Five novel crystal structures of coordination materials were determined, and these are compared with six related coordination structures reported in the literature. Two of the novel structures display interesting one-dimensional coordination polymers, one of which has never been reported previously in the literature. The molecular and structural characteristics of both the novel and the literature coordination structures are presented in detail, and this discussion includes a description of the coordination geometry, the molecular geometry, packing trends, hydrogen bonding interactions and aromatic interactions. A comparison study across the three families of organic components in which the structural trends, hydrogen bonding interactions, aromatic interactions, ligand geometry and coordination modes are compared, is included. The results of the synthesis of the coordination materials by means of a mechanochemical method are presented, and the products afforded by this method are compared with those prepared via solution crystallisation. Finally, the results of preliminary studies of the thermal and electronic propertries of the materials are presented and interpreted. The combination of the hybrid components as cations and anions to form ionic materials yielded nine novel structures, and these were compared with five related ionic structures reported in the literature. The novel structures include three polar structures that contain the 4-ammoniumbenzamide cation, and to our knowledge no structures containing this cation have ever been reported in the literature, hence a significant contribution to the structural knowledge of perhalometallate salts of 4-ammoniumbenzamide is made by this study. In addition two novel structures display interesting one-dimensional and two-dimensional polymeric anions, respectively, are reported. The discussion of the novel and literature ionic structures includes a description of the molecular geometry of each of the components, the identification of packing trends, and an analysis of the hydrogen bonding and aromatic interactions occurring in the structures. The structures of all three families of organic components are compared, and trends in structural type, anion geometry, water inclusion, hydrogen bonding and functional group recognition are presented. In addition, a detailed analysis of robust crystal engineering synthons occurring in these structures is presented. Lastly the results of preliminary property investigations of the thermal and electronic properties of the materials are presented and discussed / Dissertation (MSc)--University of Pretoria, 2011. / Chemistry / unrestricted

abstract: Transition metal di- and tri-halides (TMH) have recently gathered research attention owing to their intrinsic magnetism all the way down to their two-dimensional limit. 2D magnets, despite being a crucial component for realizing van der Waals heterostructures and devices with various functionalities, were not experimentally proven until very recently in 2017. The findings opened up enormous possibilities for studying new quantum states of matter that can enable potential to design spintronic, magnetic memory, data storage, sensing, and topological devices. However, practical applications in modern technologies demand materials with various physical and chemical properties such as electronic, optical, structural, catalytic, magnetic etc., which cannot be found within single material systems. Considering that compositional modifications in 2D systems lead to significant changes in properties due to the high anisotropy inherent to their crystallographic structure, this work focuses on alloying of TMH compounds to explore the potentials for tuning their properties. In this thesis, the ternary cation alloys of Co(1-x)Ni(x)Cl(2) and Mo(1-x)Cr(x)Cl(3) were synthesized via chemical vapor transport at a various stoichiometry. Their compositional, structural, and magnetic properties were studied using Energy Dispersive Spectroscopy, Raman Spectroscopy, X-Ray Diffraction, and Vibrating Sample Magnetometry. It was found that completely miscible ternary alloys of Co(1-x)Ni(x)Cl(2) show an increasing Néel temperature with nickel concentration. The Mo(1-x)Cr(x)Cl(3) alloy shows potential magnetic phase changes induced by the incorporation of molybdenum species within the host CrCl3 lattice. Magnetic measurements give insight into potential antiferromagnetic to ferromagnetic transition with molybdenum incorporation, accompanied by a shift in the magnetic easy-axis from parallel to perpendicular. Phase separation was found in the Fe(1-x)Cr(x)Cl(3) ternary alloy indicating that crystallographic structure compatibility plays an essential role in determining the miscibility of two parent compounds. Alloying across two similar (TMH) compounds appears to yield predictable results in properties as in the case of Co(1-x)Ni(x)Cl(2), while more exotic transitions, as in the case of Mo(1-x)Cr(x)Cl(3), can emerge by alloying dissimilar compounds. When dissimilarity reaches a certain limit, as with Fe(1-x)Cr(x)Cl(3), phase separation becomes more favorable. Future studies focusing on magnetic and structural phase transitions will reveal more insight into the effect of alloying in these TMH systems. / Dissertation/Thesis / Masters Thesis Materials Science and Engineering 2020

Thesis (M.S.)--Mississippi State University. Department of Chemistry. / Title from title screen. Includes bibliographical references.

Ce travail est une contribution ab initio à la caractérisation d'halogénures diatomiques de métaux de transition. Nous avons choisi de caractériser la structure électronique des chlorures de métaux de transition du groupe Vb (NbCl et TaCl) et du fluorure de nickel car une série de spectres les concernant ont été enregistrés mais aucune donnée théorique fiable n'était disponible dans la littérature.<p><p>Pour étudier ces molécules, nous avons appliqué une procédure de calcul à deux étapes qui permet de tenir compte des effets de corrélation électronique et des effets relativistes. Dans la première étape, nous avons réalisé des calculs CASSCF/ICMRCI+Q de grande taille qui tiennent compte de l'énergie de corrélation et introduisent des effets relativistes scalaires. Dans la deuxième étape, le couplage spin-orbite est traité par la "state interacting method" implémentée dans le logiciel MOLPRO. Nous avons développé des stratégies de calcul basées sur ces méthodes de calcul et adaptées aux différentes molécules ciblées. Ainsi, pour les molécules NbCl et TaCl, nous avons utilisé des pseudopotentiels relativistes scalaires et spin-orbite, tandis que pour la molécule NiF, nous avons réalisé des calculs tous électrons.<p><p>Nous avons d'abord testé la stratégie de calcul sur les cations Nb+ et Ta+. Ensuite, nous avons calculé pour la première fois les structures électroniques relativiste scalaire et spin-orbite des molécules NbCl (de 0 à 17000 cm-1) et TaCl (de 0 à 23000 cm-1). A l'aide de ces données théoriques, nous avons interprété les spectres expérimentaux en collaboration avec Bernath et al. Nous avons proposé plusieurs attributions de transitions électroniques en accord avec l'expérience mais nos résultats théoriques ne nous ont pas permis de les attribuer toutes. Néanmoins, nous avons mis en évidence une série d'autres transitions électroniques probables qui pourraient, à l'avenir, servir à l'interprétation de nouveaux spectres mieux résolus. <p><p>Outre son intérêt expérimental, cette étude a permis de comparer les structures électroniques des molécules isovalencielles VCl, NbCl et TaCl, mettant en évidence des différences importantes.<p>L'élaboration d'une nouvelle stratégie de calcul pour décrire les systèmes contenant l'atome de nickel représentait un véritable défi en raison de la complexité des effets de corrélation électronique. Notre stratégie de calcul a consisté à introduire ces effets en veillant à réduire au maximum la taille des calculs qui devenait considérable.<p>Nous l'avons testée sur l'atome Ni et appliquée ensuite au calcul des structures électroniques relativiste scalaire et spin-orbite de la molécule NiF entre 0 à 2500 cm-1. Nous avons obtenus des résultats qui corroborent l'expérience. <p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished