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Title: Kinetics and mechanism of the complexation of labile metal ions by macrocyclic ligands
Author: Wynn, Andrew Mark
ISNI:       0000 0001 3573 6120
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1989
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The kinetics of complexation of labile transition metal ions with three classes of macrocyclic N-donor ligands have been studied in dmso solution using pseudo-first- order conditions and employing the stopped-flow technique, with observation of U. V. / visible absorbance changes on reaction. All reactions studied displayed biphasic, consecutive first-order kinetics with an initial, rapid step which was first-order in both metal and ligand, followed by a second, slower step which was independent of the metal concentration. The unsubstituted macrocycles cyclam and [9]aneNj reacted via a dissociative interchange mechanism with the formation of an unstable intermediate which isomerises to the stable product. This intermediate is proposed to involve full co-ordination of the macrocycles to the metal ions with one or more N atoms co-ordinated in an unstable configuration. For the same macrocycles, each containing a single, pendent co-ordinating 2,2’-bipyri-dyl-6-yl-methyl arm, the complexation reactions occurred via an intermediate which involved co-ordination of the metal ions to the bipyridyl moiety, the ensuing slower reaction involving co-ordination of the macrocyclic moiety. This presents the most clear-cut evidence so far that pendent arm macrocycles react initially by coordination to the pendent arm. For N4 macrocycles, with a pyridine group substituted for a secondary amine, the reactions occur by initial attack at the secondary amines adjacent to the pyridine moiety. With the tri-methylated form of the macrocycle Ni2+ ions react more rapidly than do Co2 + ions, which is very unusual. This behaviour is explained by proposing a different reaction mechanism for each ion with Mej-PyNj as the final products are of different geometries. With Cu2+ an unstable intermediate is formed involving formation of only one Cu-N bond. The properties of silica gels modified with open-chain and macrocyclic polyamines were also studied. The less bulky and least sterically hindered polyamines were bound to the surfaces in greater quantities, although pretreatment involving heating at high temperatures significantly improved the binding of cyclam to the surfaces. An investigation of the uptake of transition metal ions from aqueous solutions illustrated the important role that the surface structure has to play on the activity of the binding sites. A gel modified with cyclam displayed a high degree of selectivity for Cu2+ over Co2+ and Ni2+ illustrating the potentially important application of such systems in ion selective waste water treatments.
Supervisor: Not available Sponsor: Science and Engineering Research Council ; Atomic Energy Establishment
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics ; QD Chemistry