Interactions of imidazole derived urea compounds and their transition metal complexes with selected anions.

Abstract

Anions play important roles in various chemical, biological and environmental processes, hence there is a significant interest in designing artificial anion receptors that can bind or sense anions. In this study, a range of anion receptor compounds derived from imidazole ureas has been synthesised using organic (triethylbenzene and mesitylcalixarene) and metal-organic (Ru(II), Pt(II) and Pd(II)) scaffolds and 1H NMR spectroscopy was used extensively to assess the anion binding and self-assembly properties of the receptor compounds. The cation and anion binding properties of the free imidazole urea ligands using different types of transition metals as well as anions is discussed in Chapter 2. The imidazole urea compounds bind to transition metals namely Cu(II), Co(II) and Ni(II) in unidentate fashion and show hydrogen bonding interactions with the anions at the urea NH. The self-assembly properties of these imidazole urea compounds has been studied by gelation experiments in which silver(I) complexes of these ligands, particularly the silver(I) complex of an imidazole urea bearing a dodecyl terminal group can form a gel at 2% (w/v) due to the combination of hydrogen bonding, van der Waals and solvophobic interactions.In Chapter 4, a new series of organic-based derivatives of these ligands have also been prepared using triethylbenzene and mesitylcalixarene scaffolds and they were found to show weak interactions with halide ions in a competitive solvent, DMSO and exhibit acid-base reactions with basic anions such as fluoride and acetate.In Chapters 5 and 6, the synthesis of metal-based imidazole urea derivatives using ruthenium(II), platinum(II) and palladium(II) precursors is described. During the course of the experiments, a number of interesting, and in some cases, unexpected results were found. Tripodal ruthenium(II)-based derivative in which the ruthenium(II) centre is linked to three imidazole urea ligands, have also been prepared and show interaction only with basic anions such as fluoride, acetate and benzoate. On the other hand, Pt(II) and Pd(II) complexes of imidazole ureas have shown a tendency to self-aggregate forming oligomers and also show interactions with basic anions such as fluoride and acetate through deprotonation.Finally, although the anion binding and self-assembly properties of these receptors were not fully understood, it is suggested that the complex behaviour of these organic and metal-based derivatives could be due to the multiple intramolecular and intermolecular interactions of the molecule.