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Synthesis and characterisation of organo-metallic complexes for use in applications in photochemistry and medicine

Tawfiq, Kinaan Mahmood (2017) Synthesis and characterisation of organo-metallic complexes for use in applications in photochemistry and medicine. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Research on sustainable technologies has accelerated during the past two decades to find alternative energy sources and combat environmental pollution, as well as to find alternative cancer treatments. One of the most intensively researched areas to achieve this, is the development of new sources of solar energy conversion and utilisation. The first chapter gives a summary of various solar cell technologies and photovoltaic conversion devices, and also highlights some potential medicinal applications of the prepared complexes described in this work. It states the aim and objectives of this investigation, and concludes with the hypothesis. Chapter 2 gives a summary of the Cu-catalysed [3+2] cycloaddition reaction between an aryl azide and aryl alkene, known as the “click reaction”. It describes work to date on various types of addition reactions, the role of Cu(I) catalysts and the use of various solvents. In Chapter 3 the literature review continues with a discussion of the dye solar cell compounds (DSSC) themselves, and focuses on the synthesis of a range of organic ligands (L1-L9). The final literature review Chapter 4 gives a summary of biological activities of bioinorganic compounds used as medicinal drugs, in particular as anticancer agents. All the ligands and organo-transition metal complexes synthesized in this investigation, were characterised comprehensively by 1H-, 13C-, DEPT, 1H- 1H COSY, 1H- 13C HQMC NMR, mass spectroscopy, FT-IR measurements, melting point determinations, UV-VIS absorbance determinations, fluorescence spectroscopy, X-ray crystallography, magnetic susceptibility and conductivity measurements, with finally quantum yield calculations. The strategy was to first synthesize a series of nine ligands of the type 1,2,3-triazol-4-yl-pyridine (PYTA) (Chapter 6), and couple them to eight different transition metals (Chapter 6). These were compared to consider the effects of electron withdrawing and electron donating substituents on the various ligands on the properties, and specifically the fluorescence yields/properties, and the geometries of the final metal complexes. Finally, the chloro ligands were replaced by isothiocyanato ones and the comparison repeated for selected complexes (Chapter 8). The investigation yielded a number of new and interesting results. In Chapter 6 a new series of PYTA ligands were readily and easily prepared through a convenient click chemistry approach. X-ray crystallography clearly indicated that the 1,2,3-triazole part had an azo-character. A novel crystal structure analysis of ligand L4 revealed that it had a unique one-dimensional zig-zag chain structure in the solid state, which was stabilised by intermolecular hydrogen bonds and stacking π-π interactions between the phenyl rings. In Chapter 7 the structural analysis indicated that complexes of the [M(L3)2(Cl)2] type were a rare example of the coexistence of two trans–coordinated Cl anions in the axial position. It was further demonstrated that the direct connection at the N8 position of the triazolyl ring of a 4-substituted phenyl substituent had a significant influence on the geometry of both the ligands and their corresponding M-complexes. The coplanarity of the organic framework led to slip-stacked π–π interactions between any two molecules of a complex. Additionally, it was shown that the nature of the pendant substituent (X = CH3, OCH3, COOH, F, Cl, CN, H, CF3) could affect the electronic properties of the organo-metallic complexes. It was demonstrated that the pyridine and triazole rings occupied the equatorial plane, whereas the metal-Cl atoms are in the axial plane, except for Mn(II) and Cd(II) complexes where the metal-Cl atoms lay in the equatorial plane. A further new contribution was that the triazole and pyridine nitrogens from each of the ligands in the equatorial plane were trans to each other. Finally, it was proven that weak intermolecular interactions via (C–H–Cl), (C–H...N) and (C–H...O) resulted in an ordered three dimensional supramolecular structure in which the molecules adopted a head-to-tail orientation stabilised by hydrogen bonding and π…π stacking. In Chapter 8, a structural analysis indicated that the complexes [Zn(L3)2(NCS)2] and [Cd(L3)2(NCS)2] were rare examples of the coexistence of two trans–coordinated NCS anions in the axial positions in the mononuclear triazole-based octahedral configuration. This is in contrast to what is found in wide band ruthenium photosensitisers (e.g. N3 and N719) that are efficient photosensitisers, where the isothiocyanato groups are cis to each other. It was also proven that the substitution of the chloro ligand by an isothiocyanato group in order to enhance the fluorescence of these complexes, failed to produce the desired effect. Finally, in Chapter 9, the remarkable structural resemblance of these novel compounds to bio-inorganic molecules with anticancer properties (such as cisplatin) indicated that compounds with the linkers bound to Co and Cu showed the maximum activity against some cancer cells, with a higher preference to target and kill colon cancer cells. This is a promising new development in the fight against cancer. Chapter 9 gives a final summary of the main findings and contributions of this work.

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