The synthesis, spectroscopic and electrochemical characterisation of ruthenium(II) and osmium(II) polypyridyl complexes containing aryl-bridged 1, 2,4-traizole ligands

The synthesis, spectroscopic and electrochemical characterisation of ruthenium(II) and osmium(II) polypyridyl mononuclear and dinuclear complexes containing arylsubstituted 5-(2-pyridyl)-l,2,4-triazoles are described. The methods of characterisation include High Performance Liquid Chromatography, ’H-NMR, UV/Visible spectroscopy, fluorimetry, electrochemistry and spectroelectrochemistry. The synthesis and characterisation of the bridging ligands used in the metal complexes are described in Chapter 3. The main chapter, Chapter 4, details the synthesis and characterisation of the mononuclear and dinuclear Ru(II) and Os(II) bipyridyl complexes of two of these ligands, 1,3- and l,4-bis(5-(2-pyridyl)-4//-l,2,4- triazol-3-yl)benzene. An examination of the electrochemical absorption and emission data for the mononuclear and dinuclear complexes reveals that the interaction between the metal centres in the dinuclear complexes is in fact very weak. Evidence for this comes from the identical first oxidation and reduction potentials and absorption and emission maxima (within experimental error) for the mononuclear and corresponding dinuclear complexes. Further confirmation of a weak metal-metal interaction comes from the observation that identical absorption spectra are exhibited by the mixed-metal Ru/Os complexes and 1:1 mixtures of their corresponding homometallic dinuclear complexes. However spectroelectrochemical studies indicate the presence of intervalence transitions in some cases for the mixed-valence species. Metal-metal interactions of 200-300 cm"1 are calculated. Furthermore, luminescence studies on the Ru/Os complexes in both their deprotonated and protonated forms suggest that an intramolecular energy transfer from the Ru-based unit to the osmium component takes place. Chapter 5 describes the synthesis and characterisation of the Ru(II) and Os(II) complexes of the 7V,iV-methylated ligand. l,2-bis(l-methyl-3-(2-pyridyl)-l,2,4- triazol-5-yl)benzene. Two isomers in which the M(bpy) 2 unit is coordinated via the pyridyl nitrogen and either the N2 or N4 site of the triazole ring are isolated for the mononuclear complexes. In the case of the dinuclear complexes, although two isomers can be distinguished using HPLC, only the N2/N2 coordinated isomers were isolated. Photophysical and electrochemical data for these complexes indicate that the substitution of N1 of the triazole ring results in the ligand having reduced adonor capacity and increased ^-acceptor capability. Finally, Chapter 6 describes the preliminary synthesis and characterisation of the ruthenium mononuclear and dinuclear complexes of the hydroquinone-substituted pyridyltriazole ligand, l,4-dihydroxy-2,5-bis(3-(2-pyridyl)-l,2,4-triazol-l-yl)benzene. The properties of these complexes are complicated by the presence of a redox-active bridge. Nevertheless it appears that the metal-metal interaction found for all the complexes used in this study is quite weak. Therefore it may be concluded that aryltype spacers are weak mediators of metal-metal interaction