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dc.contributor.advisorRoodt, A.
dc.contributor.advisorMuller, Alfred J.
dc.contributor.authorViljoen, Johannes Augustinus
dc.date.accessioned2016-01-06T09:38:36Z
dc.date.available2016-01-06T09:38:36Z
dc.date.copyright2009-04
dc.date.issued2009-04
dc.date.submitted2009-04
dc.identifier.urihttp://hdl.handle.net/11660/1984
dc.description.abstractEnglish: Hafnium and zirconium show extremely similar chemical properties and occur together in nature. Zirconium ore (commonly referred to as zircon) always contains 1 – 3% hafnium, and the separation of hafnium and zirconium is very difficult due to the similarities in chemical behaviour. The aim of this study was to investigate the chelating behaviour of hafnium with different organic bidentate ligands e.g. trifluoroacetylacetone (tfaaH), hexafluoroacetylacetone (hfaaH) and 8-hydroxyquinoline (OxH) and characterizing new compounds obtained from this by means of single crystal X-ray crystallography, NMR- and UV/Vis spectroscopy. Any differences in solution behaviour, whether it being reaction mechanism, solubility, coordination modes, equilibrium behaviour, etc., could possibly be exploited in developing novel separation techniques for the two metals. The structures of three new complexes, namely the [Hf(tfaa)4], [Hf(OH)(hfaa)3]2 and [Hf(Ox)4] were solved. This enabled the identification of products for kinetic studies and increased the available pool of these rare compounds in literature. The crystallographic characterization of these complexes are presented and compared with literature. Both [Hf(tfaa)4] and [Hf(OH)(hfaa)3]2 crystallized in a monoclinic space group, C2/c with Z = 4. [Hf(Ox)4] crystallized in a triclinic space group, Pī, with Z = 2. All three the structures include solvent molecules as part of the basic molecular unit. The co-crystallisation of the solvent molecules does not observably restrict or interfere with any significant physical properties of the solvated crystalline moieties. [Hf(tfaa)4] was coordinated to eight O atoms of the four tfaa ligands with an average Hf─O distance of 2.172(26) Å and O─Hf─O bite angle of 75.62(7)°. The hfaa ligands in [Hf(OH)(hfaa)3]2 formed three six-membered metallocycles with an average Hf—O bond distance of 2.190(21) Å and O—Hf—O bite angle of 75.3(5)°. [Hf(Ox)4] was coordinated by four O and four N atoms which formed four fivemembered metallocycles with average Hf—O and Hf—N bond distances of 2.095(13) Å and 2.399(15) Å, respectively and an O—Hf—N bite angle of 70.92(3)°. As part of the kinetic investigation the substitution reactions between HfCl4 and OxH ligands were followed by means of UV/Vis- and stopped-flow spectroscopy. Five reactions in total were observed for the stepwise coordination of OxH to the hafnium metal ion. From this the following mechanism was proposed: The first reaction (1st and 2nd observable reactions) is a two-step reaction involving the stepwise rapid formation of [Hf(LL)2Cl2] with pre-equilibrium K1 = 40(9) M-1 and rate determining second step k2 = 90(15) M-1s-1. The third observable reaction followed the usual two-term rate law, kobs3 = k3[LL'] + k-3 with k3 = 6.5(3) M-1s-1 and k-3 = 1.4(1) x 10-3 s-1 yielding an equilibrium constant K3 = 4(3) x 103 M-1. The forth reaction is proposed to be the ring closure of the five membered chelated metallocycle with K4 = 6(2) x 102 M-1 and k3 = 5.80(7) x 10-3 M-1s-1. The fifth and final reaction was concluded to be the formation of the tetrakis complex, [Hf(L,L’)4] that was isolated in the synthesis. The last process followed a normal two-term rate law, kobs5 = k5[LL'] + k-5 with k5 = 0.073(9) M-1s-1 and k-5 = 2.3(2) x 10-4 s-1 producing an equilibrium constant, K5 = 320(50) M-1.en_ZA
dc.description.abstractAfrikaans: Hafnium en sirkonium vertoon baie soortgelyke chemiese eienskappe en kom saam in die natuur voor. sirkoniumerts (oor die algemeen na verwys as sirkoon) bevat altyd 1 – 3% hafnium, en die skeiding van sirkonium en hafnium is uiters moeilik as gevolg van die ooreenkomste in hul chemiese gedrag. Die doel van hierdie studie was die ondersoek van die cheleringsgedrag van hafnium met verskillende organiese bidentate ligande bv. trifluoroasetielasetoon (tfaaH), heksafluoroasetielasetoon (hfaaH) en 8-hidroksiekinolien (OxH) en die karaterisering van nuwe verbindings is deur middel van enkel kristal X-straal kristallografie, KMRen UV/Vis spektroskopie. Enige verskil in oplossingsgedrag met betrekking tot reaksiemeganisme, oplosbaarheid, koördinasiemode, ewewigsgedrag, ens., kan moontlik gebruik word in die ontwikkeling van unieke skeidingstegnieke vir die twee metale. Die strukture van drie nuwe komplekse, naamlik [Hf(tfaa)4], [Hf(OH)(hfaa)3]2 en [Hf(Ox)4] is opgelos. Dit het die identifikasie van die produkte van kinetiese studies help verklaar en die beskikbare voorbeelde van hierdie skaars komplekse in die literatuur uitgebrei. Die kristallografiese karakterisering van hierdie komplekse is voorgelê en vergelyk met beskikbare literatuur. Beide [Hf(tfaa)4] en [Hf(OH)(hfaa)3]2 kristaliseer in die monokliniese ruimtegroep, C2/c met Z = 4. [Hf(Ox)4] kristaliseer in `n trikliniese ruimtegroep, Pī, met Z = 2. Al drie die strukture sluit oplosmiddelmolekule as deel van die basiese molekulêre eenheid in. Die kokristalisering van die oplosmiddelmolekuul beperk, of meng nie waarneembaar in met enige beduidende fisiese eienskappe van die gesolveerde kristalyne moïeteit nie. [Hf(tfaa)4] is deur agt O atome van die vier tfaa ligande gekoördineer, met `n gemiddelde Hf─O afstand van 2.172(26) Å en O─Hf─O bythoek van 75.62(7)°. Die hfaa ligande van [Hf(OH)(hfaa)3]2 vorm drie seslid metalloringe met `n gemiddelde Hf─O bindingsafstand van 2.190(21) Å en O─Hf─O bythoek van 75.3(5)°. [Hf(Ox)4] is gekoördineer deur vier O en N atome wat vier vyflid metalloringe vorm met gemiddelde Hf─O en Hf─N bindingsafstande van onderskeidelik 2.095(13) Å en 2.399(15) Å, en `n O─Hf─N byt hoek van 70.92(3)°. As deel van hierdie kinetiese studie is die substitusiereaksie tussen HfCl4 en OxH ligande deur middel van UV/Vis- en vloeistop spektroskopie gevolg. Vyf reaksies is in totaal waargeneem vir die stapsgewyse koördinasie van OxH aan die hafnium metaal kern. Hieruit word die volgende meganisme voorgestel: Die eerste reaksie (1ste en 2de waarneembare reaksies) is `n tweestap reaksie wat die stapsgewyse vinnige vorming van [Hf(LL)2Cl2] met voorekwilibrium K1 = 40(9) M-1 en tempobepalende tweede stap k2 = 90(15) M-1s-1. Die derde waarneembare reaksie volg die gewone tweeterm tempowet, kobs3 = k3[LL'] + k-3 met k3 = 6.5(3) M-1s-1 en k-3 = 1.4(1) x 10-3 s-1 wat `n ewewigskonstante van K3 =4(3) x 103 M-1 lewer. Die vierde reaksie is moontlik die ringsluiting van die vyflid chelaatmetalloring met K4 = 6(2) x 102 M-1 en k3 = 5.80(7) x 10-3 M-1s-1. Die vyfde en finale reaksie is voorgestel as die vorming van die tetrakis kompleks, [Hf(L,L’)4] wat in die sintese geïsoleer is. Hierdie laaste proses volg `n normale tweeterm tempowet, kobs5 = k5[LL'] + k-5 met k5 = 0.073(9) M-1s-1 en k-5 = 2.3(2) x 10-4 s-1 wat `n ewewigskonstante, K5 = 320(50) M-1 lewer.af
dc.description.sponsorshipAdvanced Metals Initiative (AMI)en_ZA
dc.description.sponsorshipDepartment of Science and Technology (DST)en_ZA
dc.description.sponsorshipNew Metals Development Network (NMDN)en_ZA
dc.description.sponsorshipSouth African Nuclear Energy Corporation Limited (Necsa)en_ZA
dc.description.sponsorshipUniversity of the Free Stateen_ZA
dc.description.sponsorshipen_ZA
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectDissertation (M.Sc. (Chemistry))--University of the Free State, 2009en_ZA
dc.subjectHafnium compounds -- Synthesisen_ZA
dc.subjectMechanistic studyen_ZA
dc.subjectCrystallographic characterisationen_ZA
dc.subjectKineticsen_ZA
dc.subjectSynthesisen_ZA
dc.subjectSeparationen_ZA
dc.subjectBidentate ligandsen_ZA
dc.subjectZirconiumen_ZA
dc.subjectHafniumen_ZA
dc.titleSpeciation and interconversion mechanism of mixed halo O,O' - and N,O-bidentate ligand complexes of hafniumen_ZA
dc.typeDissertationen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


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