The synthesis, spectroscopic and electrochemical characterisation of a series of mononuclear and dinuclear ruthenium (II) and osmium (II) complexes is described. Chapter 1 provides an introduction to the area of supramolecular chemistry. The complex [Ru(bpy)3]2 , the parent complex of modem supramolecular chemistry is also introduced. Chapter 2 is a general introduction to the physical measurements of the complexes which have been synthesised. The techniques of High Performance Liquid Chromatography (HPLC), Nuclear Magnetic Resonance (NMR), UV/Visible spectroscopy, fluorimetry, spectroelectrochemistry and electrochemistry are all briefly described to provide an insight into the application of these techniques later in the thesis. Chapter 3 provides an introduction to the ligands used to synthesise the complexes described in Chapters 3, 4 and 5. The ligands all contain a fused 5 and 6 membered ring, with the 5 membered ring having an imidazo-type functionality in the case of all the ligands with the exception of one, where the 5 membered ring contains a third nitrogen and becomes a triazotype system. The ’H NMR spectra of the ligands have been assigned where possible, and die photophysics and electro chemistry of the free ligands are discussed. The synthesis of a series of novel ruthenium(II) mononuclear complexes, [Ru(bpy)2(LL)j2 is described as is the synthesis of several deuleraled analogues, [Ruic/s-bpyMLL)]2'. The characterisation of these complexes by X-Ray Crystallography and *H NMR is discussed with an isomerisation effect being discussed in detail using analysis from ’H NMR and HPLC experiments. The characterisation of the complexes is completed with an examination of the photophysical, photochemical and electrochemical properties. Chapter 4 is structured similarly. The synthesis of the osmium(II) bipyridyl complexes using the ligands discussed in Chapter 3 is described. The same isomerisation effect appears for several of the ligands and is again discussed in detail. Again, the characterisation of the complexes is completed with an examination of the photophysical, photochemical and electrochemical properties. The LL7 ligand is used to synthesise a ruthenium(II) monomer as well as a series of homonuclear and heteronuclear ruthenium(II) and osmium(n) dimers. The deuterated analogues of the Ru-Ru homonuclear dimer has also been synthesised. These complexes provide the material for discussion in Chapter 5. The photophysical and electrochemical examination of this series of complexes indicates that little or no communication exists between the metal centres, even in the case of the mixed-metal complex. The spectroelectrochemistry of the complexes agree with this supposition. Chapter 6 introduces a different type of complex and a detailed survey of previous work in this area using the bridging ligands 4,4’bipyridyl, P2P, P3P and PEP precedes the discussion of the synthesis and characterisation of the series of mononuclear ruthenium(II) and osmium(II) complexes. It proved important to understand the properties of these compounds as these monomeric species provide the starting material for the synthesis of the series of dimers discussed in Chapter 7. The synthesis and spectroscopic behaviour of this series of dinuclear complexes is presented. The dinuclear complexes have been synthesised with the intention of attaching them to surfaces. This is described for one of the complexes and a brief examination of the behaviour of the complex confined to a surface is performed. The final chapter, Chapter 8 provides a conclusion to the work carried out on the two projects that make up this thesis. The chapter also suggests further work, which may be carried out in future studies.