Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2005. / In this study several potential polymerisation catalysts were synthesised. This was accomplished by coordinating α-diimine ligands such as N,N'-diferrocenyldiazabutadiene (DFDAB), N,N'-dimesityldiazabutadiene (DMDAB) as well as the bidentate amine N,N,N',N'-tetramethylethylenediamine (TMEDA), to several transition metals. The multi-step synthesis of N,N'-diferrocenyldiazabutadiene (DFDAB) from ferrocene involved the use of lithiated ferrocene, iodoferrocene, N-ferrocenylphthalimide and aminoferrocene; the latter three were characterised. This ligand was coordinated to the transition metal ions iron(II) and zinc(II) to form Fe(DFDAB)Cl2 and Zn(DFDAB)Cl2 respectively. 1H and 13C NMR, FT-IR and mass spectrometry revealed that the expected product had been synthesised in a useful form. 2,4,6-Trimethylaniline reacted with glyoxal to form N,N'-dimesityldiazabutadiene (DMDAB). The DMDAB ligand was coordinated to the transition metal ions zinc(II) and silver(I) to form Zn(DMDAB)Cl2 and Ag(DMDAB)2 respectively. Characterisation now also include molecular and crystallographic structural determinations by means of X-ray diffractometry. Another N-donor complex, Cr(CO)4(TMEDA), was also prepared by coordinating N,N,N',N'-tetramethyl ethylenediamine (TMEDA) to Cr(CO)5(THF). This was done to give an indication of the activity of low oxidation state complexes in the catalysis of olefin polymerisation. The metal-α-diimine complexes mentioned above were employed in the polymerisation of the monomers ethylene and 1-pentene probably according to a cationic mechanism. High density, high molar mass polyethylene products with narrow polydispersities were obtained. The chromium(TMEDA) complex produced polyethylene exhibiting ultra-high molar mass (> 10 000 kg/mol). The polymerisation of 1-pentene, using the Fe(DFDAB)Cl2 complex, afforded oligo-pentene with a molar mass of ~800 g/mol. After an unsuccessful attempt to prepare the (CO)5Cr=C(OZrCp2Cl)(ferrocenyl) modified Fischer-type carbene complex, the (CO)5Cr=C(OMe)(ferrocene) complex was eventually insolated. Elucidation of its molecular structure was accomplished by X-ray diffractometry. Finally, the DFDAB-ligand was coordinated to Fe2(CO)9 to generate Fe(CO)3(DFDAB) in another attempt to investigate the role of carbonyl groups and also low oxidation state metals in polymerisation reactions [compare to Cr(CO)4(TMEDA) unit above]. The sensitivity of this complex towards moisture and air prevented such action.

Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: see full text for abstract. / AFRIKAANSE OPSOMMING: Sien volteks vir die opsomming.

Thesis (MSc)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: Please refer to fulltext for abstract / AFRIKAANSE OPSOMMING: Sien asb opsomming vir volteks

Thesis (MSc)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: A thorough search through the literature as well as through the Cambridge Crystallographic Structural Database resulted in no examples of a neutral ozone acting as ligand in a complex with any metal. Ionic compounds containing ozonide as anionic species, however, are well known throughout the literature and not surprisingly the only result for 0₃ and a metal in the CCSD was an ionic rubidium ozonide compound. What follows is a systematic study into the result of placing an ozone ligand within complexing distance of a transition metal (the first transition row from titanium to copper). Due to the novelty of the system, as first approximation four different orientations of the ozone ligand relative to the metal (a metal cation in these calculations) were investigated. It was found that coordination through the terminal oxygens resulted in energy minima for all the metal cations, although not necessarily the absolute energy minimum on the potential energy surface for the specific cation. A further structural study was done by adding carbonyl and hydrogen ligands to the system, according to the 18-electron rule. For these calculations coordination through the terminal oxygens was employed. In both series the dissociation energy was also calculated. The dissociation energies for the M(CO)nHm(0₃) complexes were all positive, indicating that they are theoretically stable structures. The resulting wave functions were then analysed with the help of three techniques: Atoms in Molecules (AIM), Charge Decomposition Analysis (CDA) and Natural Bond Orbital Analysis (NBO). AIM showed that bonds were indeed formed between the ozone ligand and the transition metal and hinted that the bonding model can be interpreted with the Dewar-Chatt-Duncanson (DCD) model of σ-donation and л-back donation. CDA confirmed that this was the case. NBO results proved erroneous due to the largely delocalized electronic structure of the complexes. / AFRIKAANSE OPSOMMING: 'n Deeglike soektog deur die literatuur en die Cambridge Crystallographic Structural Database het geen resultate gelewer van komplekse waarin 'n neutrale osoonligand komplekseer met 'n metaal nie. Ioniese verbindings waarin die osonied as anioon optree, is wel bekend deur die literatuur en die enigste resultaat in die CCSD - vir 'n soektog bevattende osoon en 'n metaal - het 'n rubidiumosonied-verbinding opgelewer. Wat volg is 'n stelselmatige studie om die effek te ondersoek indien 'n osoonligand naby genoeg aan 'n oorgangsmetaal geplaas word om kompleksering te bevoordeel (metale wat gebruik is, is die eerste oorgangsreeks vanaf titanium tot koper). As gevolg van die onbekendheid van die sisteem is vier verskillende oriëntasies van die osoonligand relatied tot die metal ('n metal katioon in die geval) as beginpunt ondersoek. Daar is gevind dat koordinasie deur die terminale suurstowwe van die osoonligand vir al die metal katione lei tot energie minima, alhoewel dié minima nie noodwendig die globale minima op die potensiële energie oppervlaktes van die katione is nie. 'n Verdere studie is gedoen deur karboniel- en waterstofligande tot die sisteem te voeg, gelei deur die 18-elektron reel. Vir hierdie berekeninge is koördinasie deur die terminale suurstowwe gebruik. In beide reeks is dissosiasie-energieë bereken. Die dissosiasie energieë van die M(CO)nHm(0₃) komplekse was deurgaan positief wat aandui dat die komplekse teoreties stabiel is. Die verkrygde golffunksies is hierna analiseer deur middel van drie tegnieke: Atoms in Molecules (AIM), Charge Decomposition Analysis (CDA) en Natural Bond Orbital Analysis (NBO). AIM het getoon dat bindings inderdaad gevorm word tussen die osoonligand en die metal en bet die moontlikheid laat ontstaan dat die bindingsmodel volgens die Dewar-Chatt-Duncason (DCD) model van σ-donasie en л-terugdonasie geïnterpreteer kan word. Hierdie waarneming is bevestig deur CDA. NBO resultate kon nie suksesvol gebruik word nie as gevolg van die hoë graad van electron delokalisasie van die komplekse.

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Physics / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

In the 4d transition metal oxides, the extension of the 4d orbitals leads to comparable and thus competitive kinetic and coulomb energies. As a result, small perturbations can induce significant changes in their physical properties, giving rise to a class of exotic phenomena that are rarely found in other materials. The ruthenates materials with readily tunable parameters open an avenue to study the strong electronic correlation in the rarely explored territory: the 4d transition metal oxides. The bilayered system, Ca3Ru2O7, belongs to the Ruddlesden-Popper series in which the physical properties are intimately linked to the lattice degrees of freedom. Ca3Ru2O7, with its quasi-2D and severe structure distortion, is believed to be placed in a unique position at which the role of orbital degrees of freedom is highlighted. The system displays strikingly different behaviors when the field is applied along different crystalline axes. A ferromagnetic (FM) state with full spin polarization is achieved for B||a-axis, but colossal magnetoresistance is realized only for B||b-axis by avoiding the ferromagnetic state. In addition, for B rotating within the ac-plane, slow and strong SdH oscillations periodic in 1/B are observed for T.1.5 K in the presence of metamagnetism. For B|| [110], oscillations are also observed but periodic in B (rather than 1/B) and persist up to 15 K. These properties together with highly unusual spin-charge-lattice coupling near the Mott transition (48 K) are driven by the orbital degrees of freedom. Complex thermodynamic properties are also observed in the other ruthenates system such as Sr4Ru3O10 and Pr3RuO7. The Sr4Ru3O10 is a triple-layered system that shows a dedicate balance between fluctuations and order. Besides the anomaly at TC=102K, anomalous behavior at low temperatures are also observed in the thermal study, indicative of an unusual magnetic order in this material. The Pr3RuO7 shows one-dimensional structure with zig-zag chain of corner sharing RuO6 octahedra running in parallel with the rows of edge-shared PrO8 pseudo-cubes. Magnetic and thermal properties studies on its single crystals indicate that the exchange interaction is strongly anisotropic. A Schottky-type anomaly at low temperature suggests that the gorderedh chain Pr ions are still sensitive to a crystal field.