The work described in this thesis is divided into two main parts. Part I is concerned with the structural chemistry of a number of cobalt complexes; in Part II the crystallographic study of a copper(II) polymerisation catalyst is presented. The crystal structure of the Schiff base complex dicyano-5,7,7,12,12,14-hexamethyl-1,4,8,11-tetra-azacyclotetra-deca-4,14-dienecobalt(III) perchlorate, [Co(C₁₆N₄H₃₂)(CN)₂] C10₄, has shown that the quadridentate macrocycle exists in the cis-meso form, with an approximate mirror plane through the centre of the cation. The stereochemical arrangement about the central cobalt atom is approximately octahedral with cyanide groups above and below the macrocycle. The structures of the two isomers, β and α, selected from the three isomers isolated for the [Co(ethylenediamine) (dipropylenetriamine)X]²⁺ system, have been determined. These were found to possess the same topological arrangement of the ligands about the central cobalt atom, but with different conformations of the tridentate polyamine. In each of the dipropylenetriamine ligands, one of the six-membered chelate rings is found to adopt the favoured ‘chair’ conformation, while the other is constrained into a distorted ‘boat’ form by the approximately tetrahedrally coordinated secondary nitrogen atom. The preparation of suitable crystals of the highly reactive cobalt complex Co(SiF₃)(CO)₄ by vacuum line techniques is described. The structure of this complex was subsequently determined in this department. Part II presents the crystallographic studies and ultimate structure determination of a copper(II) catalyst used for initiating the graft copolymerization of monomers such as acrylonitrile inside wool fibre. The complex has been shown to possess a novel infinite, helical polymeric structure, which may have a considerable bearing on its function as a catalyst.