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Title: Kinetic and thermodynamic studies of metal complexes formed by LIX 65N and related hydroxyoxime ligands
Author: Gilmour, William Q.
ISNI:       0000 0001 3500 347X
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1980
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An investigation of some divalent transition metal complexes of the commercial liquid-liquid extractant LIX 65N (H2L) has been carried out and the results from these studies have been compared to observations found for a series of model compounds of these types of extractant. In the course of this work an improved method for obtaining pure forms of the two isomers of LIX 6SN has been developed. A 13C n.m.r. investigation has been made of LIX 65N and the model ligands and the trends observed have been compared to the results found from infra-red and electronic spectral studies. The nickel(Il) and copper(ll) bis-complexes of LIX 65N exist in a square-planar transconfiguration in non-donor and weakly donating solvents. The extremely oxygen sensitive cobalt(ll) bis-complex of LIX 65N has been isolated. The kinetics of bis-complex formation have been investigated for these complexes of LIX 65N in methanol solutions by stopped-flow spectrophotometric methods. For nickel(Il) and cobalt(ll) these reactions appear to proceed with the normal 1^ mechanism. The corresponding reaction with copper(ll) was found to be too fast to be measured with the techniques available. By comparing the complex formation rates determined for the nickel(ll) complex of LIX 65N with similar rates for a series of nickel(ll) complexes of aromatic hydroxyoxime ligands it has been found that the long alkyl chains associated with the commercial extractants have a small retarding effect on the rate of complexation. Variation of the oximino carbon substituent in these ligands by replacing hydrogen with both methyl and phenyl groups enhances the complexation rates to approximately the same extent. It is found that the outer-sphere complex formed initially in these reactions is that involving the neutral forms of the ligands. The rate determining step is believed to be formation of the first metal-to-oximino nitrogen atom bond. An investigation of the metal exchange reaction involving Ni(HL)2 and Cu(Il) by the technique of rapid scanning spectrometry (RSS) reveals that this reaction proceeds through three distinct stages. Two transient intermediate species are observed and the mechanisms involved have been investigated by single wavelength stopped-flow methods taking advantage of isosbestic points established for each stage by RSS. The overall mechanism is believed to involve dinuclear bridged intermediate species. The nickel(ll) complex of the non-alkylated model compound for LIX 65N has been found to form octahedral bis-adducts with two alkylaminc ligands. These species have been isolated and investigations of the alkylamine exchange processes have been established using 1line broadening methods. An equilibrium is found to exist between the square- planar bis-complex and the pseudo-octahedral bis-adduct, and this phenomenon has been investigated by variable temperature U.V.-visible spectrophotometry. As a continuation of previous studies from these laboratories two other systems have been investigated. The equilibrium between the trans-III isomer of [Ni(TMC)]2+(TMC = 1,4,8,11-tetramethyl- 1,4,8,11-tetra-azacyclotetradecane) and its octahedral bis-adduct with DMF has been investigated by variable temperature 1H n.m.r. methods. It has been found that this adduct exists in both the cis- and trans- isomeric forms. The equilibrium processes associated with both isomers have been investigated. An investigation of the co-ordination number and rate of exchange of methanol on [Zn(MeOH)g]2+ ion has also been studied by 1H n.m.r. methods. It has been found that the tetrafluoroborate anion has a weaker co-ordinating ability to zinc(Il) than the perchlorate anion and the activation parameters have been determined for this dynamic process using the tetrafluoroborate salt.
Supervisor: Not available Sponsor: Science Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD Chemistry