Thesis (M. Phil.)--University of Hong Kong, 2000. / Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Dallas, 2007. / Includes vita. Includes bibliographical references (leaves 78-80)

M.Sc. (Chemistry) / Please refer to full text to view abstract

The structures of four compounds representing each of the organic (natural product), inorganic and organometallic classes of compounds have been determined by single-crystal X-ray diffraction, and the methods employed in solution of the structures have been discussed briefly. For all four structures, the intensity data were collected on a single-crystal diffractometer with [formula omitted] radiation and a scintillation counter. The structure of the alkaloid, daphmacrine methiodide (acetone solvate), was determined from heavy-atom Patterson and Fourier syntheses, and refined by block-diagonal least-squares methods to a final R value of 0.089 for 1834 observed reflections. The absolute configuration was determined by the anomalous dispersion method. The molecule consists of two cage-structures which are linked by a chain of two carbon atoms, and the bond lengths and valency angles do not differ from normal values. 2 4-, For both exo-tricyclo [formula omitted] silver nitrate and silver nitrate itself, the silver ion was determined from Patterson syntheses to be lying in a pseudo-special position, so that the resulting electron-density maps exhibited pseudo-symmetry. A trial-and-error method based on detailed study of the shape of the Ag-Ag Patterson peaks was adopted to find the exact location of the silver ions, and from the resulting electron-density maps the true light atom peaks could be discerned from their images. The refinement was carried out by full-matrix least-squares, and the final R for the complex of silver nitrate was 0.105 and for silver nitrate was 0.067. The structure of the complex consists of thick layers perpendicular to the a crystallographic axis, and separated by ½ a. The silver ion is coordinated roughly tetrahedrally to the double bond of the hydrocarbon (in the exo-position, [formula omitted]), and to three nitrate groups [formula omitted]. The layers are held together by van der Waals forces. The silver nitrate structure consists of layers of silver ions parallel to the b crystallographic axis, and separated by ½ b, with the nitrate groups bridging the gap between layers. Previously observed inequalities in the N—O distances have been removed, all three bond lengths in the nitrate ion being 1.26 (l)Ǻ. The anisotropic thermal motion has been described. The N,N-dimethyl(ferrocenylmethyl)ammonium tetrachlorozincate hydrate structure contains seven heavy atoms, and it was not possible to resolve the Patterson peaks because of the overlap. A direct sign-determining procedure was employed to locate the heavy atoms, and the light atoms were located from resulting electron-density maps. The structure was refined to a final R value of 0.068 for 2012 observed reflections. The mean bond distances are Fe-C = 2. 04Ǻ and C-C (cyclopentadienyl rings) = 1.43Ǻ. Groups of four cations, two anions and two water molecules (two formula units), are linked around centres of symmetry by N-H...Cl (3.11Ǻ), N-H...0 (2.76Ǻ) and 0-H...Cl (3.05, 3.17Ǻ) hydrogen bonds. / Science, Faculty of / Chemistry, Department of / Graduate

No description available.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

This dissertation describes the experimental study of the electronic-structural relationships of selected mononuclear transition-metal sulfur dioxide, cyclopentadienyl and carbonyl complexes and the application of the information gained from these to the study of quadruply-bonded dimetallic complexes. These pertinent observations result from the application of photoelectron spectroscopy (p.e.s.) as a probe into the bonding, charge-distribution and excited state effects which contribute to the specifics of the ground and excited state molecular structures. The first part of this discussion centers around a specific study of the exemplary bonding probe, SO₂, with the well characterized ArM(CO)₂ metal fragment, where Ar = Bz and Cp and M = Cr, Mn and Re. A comparison of the ionization information with the structural details and molecular orbital calculations reveals not only the surprising coordinating similarity of SO₂ and CO in these complexes, but also the electronic origin for the counter-intuitive SO₂ bonding configuration. This work then moves to a more dramatic example of electronic control of ground state molecular structure; the crystallographically determined distortion of the coordinated Cp ring in Cp*Rh(CO)₂. The electronic origin of this distortion is graphically shown with the aid of two and three dimensional experimental and theoretical electron density maps. The structural effects of removing bonding electrons from quadruply-bonded dimetallic complexes is then investigated. This study incorporates the use of high-resolution p.e.s. for the novel observations of metal-metal vibrational structure in the predominantly metal ionizations providing direct information of the bonding influence of specific metal electrons. Particular attention is focused on the delta-ionization process of MO₂(O₂CCH₃)₄. The final chapter presents a comprehensive study of the valence and core ionizations of the series of quadruply-bonded M₂(X₂CR)₄ complexes, where M₂ = Cr₂, Mo₂, MoW, and W₂, X = O and S, and R = H, CH₃, CD₃, CF₃, CH₂CH₃, CH₂CH₂CH₃ and C(CH₃)₃. The changes in the electronic structure in both the ground and excited states of these molecules is presented and, where appropriate, compared to structural changes. The study of this series not only demonstrates how p.e.s. can be used to monitor the electronic effects of specific chemical modifications, but also reveals surprising excited state features related to facile charge-reorganization processes.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, in fulfilment for the requirements for a degree in Masters of Science. November 2017, Johannesburg. / Metal complexes have a wide range of applications in fields such as medicinal, industrial, environmental and so on. Determining the formations constants for metal complexes is thus essential to gather information on complexes. Conventional methods used to study complexation include spectroscopic methods and the use of voltammetric techniques such as direct current polarography using a mercury drop electrode. In this work alternative voltammetric methods to study complex formation are investigated. Bismuth complexes have important medicinal applications but not much is known about them because of the difficulties in studying them due to extensive bismuth hydrolysis and precipitation of hydrolysis products from very low pHs. The aim of this work was to investigate whether using low concentrations of bismuth (10-6 M) would prevent precipitation in nitrate solutions as predicted in literature. Differential pulse anodic stripping voltammetry (DPASV) was the technique of choice because of its low detection limit, even though it has not been widely used in complex formation studies before. The study revealed that electrochemical response for Bi3+ was not fully reversible using this technique. Additionally, even at the low concentration precipitation was observed in the acidic region (investigated via pH titration) and was suspected to be the formation of BiONO3 species. The second alternative method investigated was the use of mercury film electrodes to replace the use of the toxic mercury drop electrodes which are being phased out worldwide. This work looked at using in situ and ex situ plated films, where the in situ measurements proved more reproducible. A number of challenges were encountered, such as film degradation, peak splitting and ligand adsorption to the film electrode. Nonetheless, formation constants of lead-glycine complexes were determined under different experimental conditions and these were found to be reasonably compared to the literature values. / LG2018

This thesis involves the design, synthesis and testing of organic hydrophobic ligands. They would act as co-collectors in froth flotation processes to enhance the recovery of sulfidic minerals which have undergone some oxidation on processing and are not efficiently collected by the commercial reagents used in froth flotation. Strong and selective binding to iron(III) oxide/hydroxide surfaces, e.g. goethite, over unwanted silicaceous material was considered essential criteria for such new cocollectors. A general overview of froth flotation processes is given in Chapter 1 as well as a description of the analytical techniques used in this thesis and the features that the ligands must have to act as co-collectors. On the basis of the strong binding to iron(III) surfaces of the organic ligand Irgacor 419®, used commercially as a corrosion inhibitor for iron, this compound was studied as a potential co-collector. Adsorption isotherms were determined by UV-Vis spectroscopy for two carboxylic acids that may also bind strongly to goethite, the results of which are discussed in Chapter 2. Chapter 3 involves the measurement of the strength of binding of one the most widely used type of collectors for sulfide ores, potassium ethyl xanthate. Complications in the analysis of materials in solution by both ICP-OES and UV-Vis spectroscopy arose due to the instability of potassium ethyl xanthate in solution, making determination and interpretation of isotherms difficult. The determination of adsorption isotherms for 2-mercaptobenzothiazole, which showed weak binding to goethite as well as to silica, and the mode of binding of 2-mercaptobenzothiazole on copper(I) surfaces is reported in Chapter 4. A crystal structure was obtained in which four units of 2-mercaptobenzothiazole bridge two nickel atoms through the nitrogen atom and the exocyclic sulfur and is considered as a model for binding to sulfidic minerals. Chapter 5 looks at the strength of binding to goethite and silica of various hydroxamic acids. Benzohydroxamic acid was initially selected for study since hydroxamates are known to act as collectors for oxidized materials. Unpredictably, benzohydroxamic acid showed strong binding to a goethite surface and did not release any iron from the surface into solution, which would have been predicted due to its known strong chelating abilities to iron(III). The X-ray structure determination of the first example of a dinuclear Fe(III) hydroxamate complex showed this to have -oxo bridge formed by the hydroxamate unit and supports multisite attachment between this ligand and the surface, as suggested by adsoption isotherms. Simple models based on this dinucleating motif provide plausible modes of multisite attachment to a goethite surface. Competitive binding studies provided a way of ranking the ability to bind to goethite of acetohydroxamic acid, which was not suitable for analyses by either ICP-OES or UV-Vis spectroscopy. Of the ligands studied in this chapter acetohydroxamic acid was found to bind most strongly to goethite followed by benzohydroxamic acid. In Chapter 6, the attachment to goethite and silica of a series of phosphonic acids is investigated. All show a very high binding strength to goethite. Froth flotation experiments at a laboratory scale are described in Chapter 7. The types of ligand that showed strong binding to goethite in adsorption isotherms experiments were tested as co-collectors in different ores and conditions. There is not a simple correlation between adsorption isotherm data and flotation performance as co-collectors because other factors, besides strength of binding, affect the system. Benzohydroxamic acid was the ligand that increased the grade/recovery of the process in all the cases studied. Irgacor 419® enhances the grade/recovery curve for Palabora ore and phenyl malonic acid for Kennecott ore. These results support the original proposition that it may be possible to increase the recovery of oxidized particles substantially by using a blend of collectors which includes a compound to target the oxidized sites.