A series of polynuclear macrocyclic complexes has been prepared by the Schiff-base condensation of 1,5-diaminopentan-3-ol with 2,6-diformyl-4-methyl-R-phenol (where R = Me or tBu) in the presence of transition metal template ions. The (2 + 2) macrocyclic complexes, containing two or four metal ions, have been characterised by a variety of methods including microanalysis, infrared spectroscopy, cyclic voltammetry, E.I. and FAB mass spectrometry and X-ray crystallography. When the template ion is copper, tetranuclear complexes are obtained. The structures of [Cu₄(μ₄-OH)L1(CH₃CN)₃(ClO₄)₂]⋅ClO₄⋅H₂O and [Cu₄(H₂LVS)(dfmp) ₂Cl(H₂O)₂]⋅BF₄ have been determined; both complexes contain planar tetracopper cations with an exogenous hydroxo donor in the centre of the cavity, bound to all four copper ions. Under appropriate conditions the tetra copper complexes dimerise to form octacopper assemblies and the structure of one of these [{Cu₄(μ₄-O)LV5(ClO₄)}₂]⋅(ClO₄)₂⋅4H₂O is reported. Ligand binding to the exposed faces of these arrays was investigated. Tetranuclear cobalt complexes have also been prepared. The X-ray structure of [Co₄(μ₄-O)LV5(CH₃COO)₄]Cl⋅3H₂O shows that, in contrast to the copper complexes, the cation is not planar and the central exogenous donor is an oxo rather than a hydroxo ligand. Tetracobalt complexes can be obtained at various oxidation levels between Co(II)₄ and Co(III)₄. A series of dicobalt complexes has been synthesised. In contrast to the familiar Robson dinuclear complexes, the cobalt ions are not bridged by phenolate donors but are diagonally disposed in the cavity and bridged by two chloride ions. X-ray crystal structure determinations have been carried out on five of these complexes, each having a core structure of [Co₂(H₄L)Cl₂]. These complexes offer a potential route to the formation of tetra nuclear complexes containing mixed metal ions. Synthetic organic work directed towards the development of new ligands was also undertaken.