The synthesis, spectroscopic and electrochemical characterisation of Ru(II) and Os(II) mononuclear complexes are described. Special attention is paid to the synthesis of a new series of terpyridine complexes capable of self-assembled on gold surfaces such as pyridine or thiol group. Chapter 1 is an introductory chapter in that the basic concepts regarding Ru(II) polypyridyl chemistry are introduced and explained. The parent complex [Ru(bpy)3]2+ is examined along with its photochemical and photophysical properties. The replacement of a bpy ligand with terpyridine is discussed, as are several examples of terpyridine systems investigated in the last few years. Chapter 2 introduces the instrumental methods and the synthetic procedures used in the preparation of all the Ru(II) and Os(II) complexes, including the synthesis of the ligands. The synthesis and purification of starting and reference materials used throughout the thesis are discussed. Having introduced Ru(II) and Os(II) complexes in the opening chapter, Chapter 3 takes a practical look at the various synthetic strategies used to synthesise such complexes. The prototypes [Ru(tpy)2]2+ and [Os(tpy)2]2+ are examined along with their synthesis and 'H-NMR measurements. The synthesis and the 'H-NMR spectra of all the Ru(II) and Os(II) complexes investigated in this thesis are compared to the archetypes before mentioned. Starting from the basic complexes [Ru(tpy>2]2+ and [Os(tpy)2]2+, photophysical and electrochemical properties are described in Chapter 4. The absorption and emission properties of the complexes investigated are described and compared to those of the two prototypes [Ru(tpy)2]2+ and [Os(tpy)2]2+. Chapter 5, takes a practical look at the various synthetic strategies attempted to synthesise Ru(II) and Os(II) terpyridine complexes with thiol group substituents. Suzuki coupling reactions used to attempt these syntheses are described. Finally, the synthesis and purification of starting and reference materials used for the Suzuki coupling reactions are discussed. Results of the work undertaken are summarised with suggestions on further possible research directions in Chapter 6. Finally three appendices are included in this thesis. In the first appendix the *HNMR spectra of the ligands and all the complexes are reported. The second appendix is a literature survey which synopsises the last five years scientific papers on metal terpyridine complexes. The third appendix shows oral presentations and posters made during the course of the research.