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Title: Ligand self assembly to enhance the strength and selectivity of metal extraction
Author: Squires, Clare
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2001
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The strength and selectivity of commercial phenolic oxime copper extractants are thought to be due to the hydrogen-bonded pseudo-macrocycle which this ligand forms around copper. This thesis investigates the role of hydrogen-bonding of sulfonamido ligands to determine the importance of ligand association prior to and upon complexation. Chapter 2 deals with the coordination chemistry of a series of 11 relatively simple bidentate monosulfonamidodiamine ligands. The solid state structures of these ligands are difficult to predict and illustrate that a surfeit of hydrogen-bond donors and acceptors incorporated into a relatively flexible ligand leads to a variety of hydrogen-bond interactions in the solid-state and hence a range of complicated secondary structures are observed including two and three dimensional arrays. However, these ligands do form pseudo-macrocycles around copper and nickel(II) centres. These ligands were found to be quite weak (pH1/2 4-6) extractants when used in pH-swing process. Increasing the size of the chelate ring from five to six leads to even weaker extractants. In Chapter 3 the synthesis and characterisation of a series of 6 sulfonamido-oxime ligands which have a similar backbone to the commercial ortho-phenolic oximes are described. The majority of solid-state structures contain hydrogen-bonded dimers and appear to have structures which are independent of small substituent changes in the ligand. However the E, Z isomerisation of the oxime is important. The Z isomer only forms polymeric species. Complex formation by the sulfonamido-oxime ligands is less predictable than with the monosulfonamidodiamines and both 2:1 and 1:1, ligand to metal complexes are observed. In addition to the expected bonding of the sulfonamido and oximic nitrogen atoms, the bonding of the sulfonamido oxygen atoms and the deprotonated oximic oxygen atom to metal ions is also observed. Investigation of the solution chemistry of the monosulfonamidodiamine and the sulfonamido-oxime ligands are considered in Chapter 4. ESI-MS shows evidence for dimer formation and 1H nmr, VPO and IR analyses show that self-association occurs in solution and is very concentration, temperature and solvent dependent. This chapter also discusses the development of monosulfonamidodiamine and sulfonamido-oxime ligands with higher solubility in solvents of low polarity such as toluene. The possibility of developing sulfinamido ligands is also discussed covering the synthesis of sulfinyl chlorides and the attempted preparation of prototype sulfinamido ligands. Chapter 5 deals with the development of pseudo-macrocyclic and pseudo-cage structures using ternary metal/sulfonamide/amine systems. Bis- and tris-sulfonamido ligands have been synthesised and their solid state structures were investigated. The formation of metal complexes of these ligands proved difficult and no ternary complexes were isolated.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available