Chapter 2 reviews the coordination chemistry of zinc and proposes that in order to maximise the stability of the zinc complexes and to discriminate against other transition metal ions, ligands which favour tetrahedral geometry will be required. The influence of donor atom types on the stability of zinc complexes is considered in Chapter 3, based on a series of 3-substituted pyridin-2-ones. A detailed study of N-benzyl-3-hydroxy-2(1H)-pyridinethione and N-benzyl-3-hydroxyl-2(1H)-pyridinone, with OS^- and O₂^- donor sets respectively, and their complexes with Zn²⁺, Cu²⁺, Ni²⁺, Co³⁺ and Fe³⁺ reveals that a range of coodination geometries can be achieved but that the rigidity of the chelate arms force a chelate angle close to 90°C, indicating the ligands preference for O_h or D_4h geometries. This ligand type, based on a 5-membered chelate ring, is unlikely to show selectivity for Zn²⁺ ions. A range of bidentate monoanionic ligands with NS^- donor sets derived from 4-iminosubstituted 5-thiopyrazolones are described in Chapter 4. The ligands show keto-enol tautomerism and ¹H NMR spectroscopy indicate that the ligands adopt the enamine-thione tautomer in solution. The crystallographic study of four ligand derivatives and nine complexes with Zn²⁺, Co²⁺ and Ni²⁺ reveals the structural influence of the amino substituent. The zinc and cobalt complexes are isostructural and display a geometry approaching that for a perfect tetrahedron, whereas the nickel complex is highly distorted from its preferred D_4h geometry. The steric volume of the imino substituents greatly affects the stability and geometry of the complexes. In general the effectiveness of solvent extraction does not follow the Irving-Williams order but instead shows significantly better recovery of cobalt than nickel following the order Cu²⁺ > Zn²⁺ > Co²⁺ > Ni²⁺ which correlates with the propensity of the metal ions to adopt a tetrahedral geometry. Chapter 5 describes a number of di-anionic tetradentate thipyrazolone derivatives (H₂L) with a predisposition towards tetrahedral geometry, that were prepared to further increase the stability on complexation to zinc.