Abstract
Following an introduction on calixarene chemistry and their metal-ion complexes including some of their applications, the aims of the work are described. Thus, this thesis concerns an investigation on the solution properties of p-tert-butylcalix(4)arene tetraketone derivatives and their metal-ion complexes. Macrocycles such as 5,11,17,23-tetra-terf-butyl-25,26,27,28-tetra(benzoyl)methoxycalix(4)arene and 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetra(acetoyl)methoxy calix(4) arene are structurally (1H NMR and X-ray crystallography) and thermodynamically (solubility, calorimetry) characterised. The complexing abilities of these ligands for metal cations are investigated by a variety of techniques. To obtain information about the active sites of the ligand in its interaction with metal cations, 1H NMR studies were performed. Conductance and UV spectrophotometric measurements were used to establish the composition of the metal-ion complexes in dipolar aprotic media. Potentiometric and calorimetric measurements were carried out to derive the thermodynamic parameters of complexation of p-tert-butylcalix(4)arene tetramethyl ketone and metal-ions in acetonitrile at 298.15 K. This ligand shows the highest affinity for calcium amongst all the investigated metal cations. The medium effect on the complexation process involving metal cations and calixarene derivatives is quantitatively assessed using as an illustrative example the interaction of p-terf-butylcalix(4)arene tetraphenyl ketone and the sodium cation. Thus, detailed thermodynamics of this system is reported taking into account the solution properties of the reactants and the product in various solvents and in acetonitrile / N,N- dimethylformamide solvent mixtures. In these mixtures a linear relationship is observed between the stability constant and the solvent composition. The strength of complexation decreases from MeCN through the mixtures to pure DMF. However in terms of the enthalpy of complexation, only small variations are found between the values in different mixtures. The complexation and solution data for the reactants and the product are used to calculate the standard co-ordination enthalpies as a means of checking the reliability of the data. Based on stability constant data, two metal-ion complexes were isolated. X-ray diffraction data shows that p-tert-butylcalix(4)arene tetraphenyl ketone hosts the sodium cation in its hydrophilic cavity where it is coordinated by four ethereal oxygen atoms and four carbonyl oxygen atoms. One molecule of acetonitrile is found in the hydrophobic cavity of the ligand with the CH3 end pointing inward. The crystal structure of the cadmium and acetonitrile p-tert-butylcalix(4)arene tetramethyl ketone complex shows that the metal ion is coordinated by four ethereal oxygen atoms of the ligand and only by three carbonyl oxygens. The eight coordination site is provided by the nitrogen atom of the molecule of acetonitrile which is present in the hydrophobic cavity of calixarene derivative with the CN end pointing inward. Conclusions and suggestions for further research in this area are given.