An exploration of the synthesis, coordination chemistry and properties of novel thiourea ligands and their complexes

In order to highlight the presentation of this thesis and to provide more detailed investigations, the thesis was separated into five chapters according to the sequence of work. Chapter One: This chapter gives an overview of the coordination chemistry of different metal complexes focusing on Cr(III), Ni(II), Cu(II), and Zn(II) ions with common, uncommon, rare ligands and their geometric preferences. A brief introduction to magnetic susceptibility and their magnetic properties are also discussed. The cyclic voltammogram and the various types of redox processes are explained. Different electronic transitions in addition to d-d transition with the expected UV-vis. spectra bands are illustrated. HSAB theory is presented to show the stability of the metal complexes. Lastly, aims and the objectives of this thesis are shown in detail. Chapters Two and Four: These chapters focus on the preparation and full characterisation of novel molecules based upon thiourea derivatives and the subsequent synthesis of their complexes with Ni(II), Cu(II), Cu(I) and Zn(II) ions. Fully characterisation was achieved successfully by Infrared Spectroscopy (IR), Electronic transition (UV-vis.), Mass Spectrometry (MS), Magnetic Susceptibility (and Magnetic Moment), elemental analysis (CHN), Nuclear Magnetic Resonance (NMR), Cyclic voltammetry (CV) and Single Crystal X-Ray Crystallography. Many of the complexes have been crystallographically characterised to elucidate the solid state geometry. The influence of increasing the reaction temperature on the hydrolysis of amide link within thiourea was investigated to probe the ease of cleavage of the benzoyl or pivaloyl group at varying temperature. All N-benzoyl and N-pivaloyl thiourea complexes showed intramolecular H-bond (N-H.O) between the N-H of the thiourea and the oxygen of the acyl group. This result in the familiar of a six membered ring. The electrochemical studies (cyclic voltammoram) for the Cu(II), Cu(I) and Ni(II) complexes showed a quasi-reversible process in the reductive region for all the Cu(II) and Cu(I) complexes while two irreversible peaks in the reductive region are observed in the Ni(II) complexes. Chapter Three: Describes the synthesis and characterisation of thiosemicarbazone derivatives and their complexes with Ni(II), Cu(II) and Zn(II) ions. All thiosemicarbazone derivatives behave as tridentate ligands with two forms, keto (deprotonated) and enol (protonated). The hydrolysis of the thiosemicarbazone and cleavage of pivaloyl group were observed and attributed to increasing the reaction temperature. Cleavage may occur before complexation. The cyclic voltammogram showed one quasi-reversible process in the Cu(II) complexes in the reductive region whilst two irreversible peaks are observed in the Ni(II) complexes. Chapter Five: The synthesis and characterisation of the novel Cr(III) complexes with 8-hydroxyquinoline derivatives is reported in this chapter. The X-ray crystal structures and UV-vis. spectra of all Cr(III) complexes confirmed the preference for an octahedral geometry. The electrochemical studies showed two reversible peaks for all Cr(III) complexes which was attributed to a Cr(III)/Cr(II) couple and a ligand based process. The optical properties were investigated and showed one emission peak which is assigned to fluorescence based on the 8-hydroxyquinoline group. An investigation of how the electron donating and electron withdrawing effects of substituents on the 8-hydroxyquinoline effect emission wavelength and intensity was carried out. In addition, the effect of coordinating water on the emission properties of these types of complexes was all investigated.