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Ph.D. / In order for any new useful complexes to be developed, whether of catalytic, biological or of other importance, it is very important that sufficient knowledge exists regarding the fundamental principles applying to the chemistry involved. In all chemical processes involving metal complexes, the coordinated ligands govern the reactions to a great extent. It is thus very important that the properties (solubility, reactivity, steric bulk, etc.) of various ligands of these complexes is clearly understood in order to enable intelligent adjustments to be made, inducing the effects of choice. In most catalytic cycles, basic chemical reactions like substitution, addition, oxidative addition and reductive elimination are of importance. Some of the methods used to quantify ligand properties include single crystal X-ray studies as well as investigating various reactions on model square planar complexes. Several problems are normally associated with this type of investigation and are summarized below along with the aims of this study to improve upon this. (i) Very often the Vaska type compounds crystallise on an inversion centre as is shown in a generalized structure in Figure 1.1. This creates several problems ranging from less accurate bond distances/angles to problematic refinement of single crystal data. As the disorder is ruled by symmetry, the occupancies of the disordered atoms are 50%. The example shown in Figure 1.1 is also a fortunate case where the disordered atoms do not have the same positions, making refinement of the data easier, but there are examples27 such as [Pt(Me)Cl(PCy3)2] where the disordered moieties (Me- and Cl-) occupy virtually the same positions. In examples such as these restraints have to be applied, i.e. fixing bond distances to average distances from literature. The important parameter of the ligand trans effect is then meaningless and cannot be reliably compared to data from solution studies. / Prof. A. Roodt

The regulations for water fluoridation of South African municipal waters up to the optimum fluoride (F-) concentration of 0.7 mg/L, (Government Gazette, 2001) have been legislated. Fluoridation processes need accurate analytical methodology for the determination of F- , because F- has a narrow margin of safety between beneficial and toxic levels. In this work the analytical chemistry of F- was investigated comprehensively and guidelines compiled for the accurate determination of low level F- (between 0.05 to 1 mg/L) in aqueous systems. The first part of this study focused on method validation and the evaluation of the ISE and IC methods. The analytical methodologies were applied to the analysis of natural waters such as river water (Vaal and Crocodile Rivers), dam water (Hartbeespoort Dam), and drinking water (Johannesburg municipal tap water) to evaluate the performance of the chosen methods in the analysis of real samples and to assess the effect of the sample matrix on the accuracy of F- determinations. An inter-laboratory study in collaboration with the South African Bureau of Standard (SABS) was carried out to evaluate the proficiency of South African analytical laboratories and to check the proficiency of the procedures developed in this study. In the second part of this study, the development of an IC-ICP-OES and IC-ICP-MS method was investigated for the speciation of fluoro-aluminium complexes. This work was motivated by the fact that the water fluoridation could lead to remobilisation of scale from municipal pipes. Scale may contain aluminium hydroxide or oxide precipitates that can dissolve as fluoroaluminates or hydroxofluoro aluminates. The speciation of cationic fluoro-aluminates, free Al3+, AlF2+ and, AlF2 + together with the neutral AlF3 0, was based on cation exchange Ion chromatography (IC) coupled with Inductively Coupled Plasma- Optical Emission Spectroscopy (ICP-OES) and Inductively Coupled Plasma Mass spectroscopy (ICP-MS). / Prof. P.P. Coetzee

One of the more attractive attributes of calixarenes is their wide variety of possible conformations and hence cavity shapes. However, the flexibility that allows this long-range benefit gives rise to major synthetic challenges when working with the larger members of the family. O-alkylations have proven to be the most widely employed synthetic routes to "functionalization" of the calixarenes, and these have shown a dependence upon both solvent and the metal ions present. Surprisingly, there have been no structural data presented concerning the complexes between the simple unsubstituted calix[6]arenes and the metal ions of groups 1 and 2. The structures of four complexes, containing cesium, rubidium, and calcium are reported as determined by X-ray crystallography. The solution behavior of the complexes for both representative groups is also discussed, in particular with regard to conformational stabilization of the calix[6]arenes and the role of solvent upon this stabilization. These complexes are also investigated as starting materials for the selective functionalization of the calix[6]arenes.

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