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Title: Design of novel tetrahedrally chelating ligands for the selective extraction of zinc
Author: Smith, Andrew G.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2000
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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 Oh or D4h 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 D4h 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.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available