Dissertations / Theses on the topic 'Halides. Metal halides'

The preparation of tri-n-butylstannylindene, has led to new synthetic routes to obtaining indenyl metal complexes of the Group V metal halides. Also, the fluxional behavior of tri-n-butylstannylindene has been studied by variable temperature 1H NMR spectroscopy.The interaction of the Group V metal halides with tri-n-butylstannylindene has led to the isolation and characterization of [(q5-C9H7)2TaC12] [TaC16] and [('q5-C9H7)2NbC12] [NbCl6]. Subsequent Lewis base chemistry has produced (T15-C9H7)TaC14(PMe3). The crystal structures of [(r15-C9H7)2TaCl2] [TaC16] and (15-C9H7)TaC14(PMe3) have been determined. The preparation and characterization of these compounds are discussed as well as the exploratory indenyl, Lewis base, and /or salt chemistry of vanadium, niobium, and tantalum.
Department of Chemistry

The entire set of analogous mono-indenyl metal trichlorides have been prepared for the titanium triad metals, (715-C9H7)TiC13, [(715-C9H7)ZrCI(.t-Cl)2]X, [(715-C9H7)HfCl2(µCl)]2. The interaction of (715-C9H7)TiCl3 and [(715-C9H7)HfC12(p.-Cl)]2 with A1Me3 hasled to the isolation and characterization of (715-C9H7)TiCH3C12 and [(715C9H7)HfCH3C1(µ-C1)]2, respectively. Also, the unexpected production of (715C9H7)2Ti(CH3)2 from the reaction of (715-C9H7)TiCl3 with LiMe has been examined. The reactivity of (715-C9H7)TiC13, [(715-C9H7)ZrCl(µ-Cl)2]X, and [(715-C9H7)HfC12(9-Cl)]2 with various Lewis bases has been explored and has afforded the isolation and characterization of the unusual half-sandwich phosphine complexes (C9H7)TiC13(PMe3), (715-C9H7)ZrC13(PMe3)2, (715-C9H7)HfC13(PMe3)2, and (715-C9H7)HfC13(PMe3) as well as (T15-C9H7)ZrC13(DME) and (715-C9H7)HfCI3(DME). Several examples of indenyl-metal bond cleavage have been observed. The indenyl-imido complex, [(715-C9H7)TiCI(p.NCH3)]2, has also been synthesized. The crystal structures of (715-C9H7)TiC13, [(715C9H7)HfC12(p.-Cl)]2, [(715-C9H7)HfCH3C1(µ-Cl)]2, and (715-C9H7)HfC13(PMe3) have been determined.
Department of Chemistry

Metal trihalide (MX₃) systems represent a stern challenge in terms of constructing transferable potential models. Starting from a previously published set of potentials, 'extended' ionic models are developed which, at the outset, include only anion polarization. Deficiencies in these models, particularly for smaller (highly polarizing) cations, are shown to be significant. For example, crystal structures different to those observed experimentally are adopted. The potentials are improved upon by reference to ab initio information available for alkali halides with the 'constraint' that the parameters transfer systematically in a physically transparent manner, for example, in terms of ion radii. The possible influence of anion compression ('breathing') and the relative abundance of anion-anion interactions are considered. Simulation techniques are developed to allow for the effective simulation of any system symmetry and for the study of transitions between different crystals (constant stress). The developed models are fully tested for a large range of metal trichloride (MCl₃) systems. Particular attention is paid to the comparison with recent neutron and X-ray diffraction data on the liquid state. Polarization effects are shown to be vital in reproducing strong experimental features. The excellent agreement between simulation and experiment allows for differences in experimental procedures to be highlighted. The transferability is further tested by modelling mixtures of the lanthanides with alkali halides with potentials unchanged from the pure systems. The complex evolution of the melt structure is highlighted as the concentration of MCl₃ increases. The effectiveness of the models is tested by reference to dynamical properties. Particular attention is paid to the comparison with Raman scattering data available for a wide range of systems and mixture concentrations. The simulated spectra are generated both by a simple molecular picture of the underlying vibrations and by a more complex (fluctuating polarizability) model in which the spectra are broken down into contributions from different mechanisms. This comparison allows for the validity of treating network-like systems as a series of 'isolated' molecules to be assessed. The transferability of the potentials is pushed to the limits by modelling metal tribromides, in which the parameters are obtained from the trichlorides by the same simple scaling arguments.

The interaction of TiX4 (X= Cl and Br) with 1-(trimethylsilyl) indene or 1(tributylstannyl) indene results in the formation of the crystalline trihalide complexes (rl5C9H7 )TiX3 in excellent yield. Isolation of these complexes has provided pathways for the monoalkyl complexes (TI5-C9H7 )TiX2 reaction of (r15-C9H7 )TiX3 (X = Cl and Br) withtrimethylaluminum resulted in the formation of the crystalline monomethyl complexes (Tl5C9H7 )TiX2R in good yield. Isolating these complexes free of the dimethyl derivativeproved difficult in normal alkylating solvents, but the pure monomethyl species were isolated in high yields when the reaction was performed in pentane. The chloride and bromide analogues have been stucturally characterized. Attempts to isolate thetrimethylsilylmethyl complexes (rl5-C9H7)Ti(CH2SiMe3)X2 (X = Cl and Br) as puremonoalkyl species were also successful, albeit in low yield. This set of four compounds provides a set of monoalkyl indenyl titanium species in which there are small alkyl groups or large alkyl groups as well as different halides. These complexes may prove to be excellent catalysts for the polymerization of olefins.
Department of Chemistry

The vacuum-ultraviolet (VUV) fluorescence spectroscopy of CX\(_2\)Y\(_2\) (X, Y = H, Cl or Br) has been studied following gaseous photoexcitation in the range 9-22 eV using synchrotron radiation. Fluorescence excitation, dispersed emission and action spectra have been recorded to probe the molecule in this way. Photoexcitation of these molecules has resulted in the population of Rydberg states of the neutral molecule and outer valence states of the parent ion. The study has shown that the emitters in the range 190-690 nm are due to either, neutral fragments formed by dissociation of Rydberg states of the neutral molecule or excited states of the parent ion. The identity of some of the dominant dissociation channels have also been identified via. appearance potentials extracted from action spectra. The threshold photoelectron photoion coincidence (TPEPICO) spectroscopy of CX\(_2\)Y\(_2^+\) (X, Y = H, Cl or Br), SeFe\(_6^+\), TeF\(_6^+\), SF\(_5\)CF\(_3^+\) and SF\(_5\)Cl\(^+\) has been studied following gaseous photoexcitation in the range ca. 12-27 eV using synchrotron radiation. The identity of some of the dominant dissociation channels have been identified in a similar way in which the information is extracted from action spectra in fluorescence spectroscopy. Appearance potentials extracted from ion yield plots have allowed comparison with known calculated thermochemistry. Measurement of fixed-energy TPEPICO spectra have been used to determine the decay dynamics of some two-bodied ionic dissociations. Finally, using a variation of TPEPICO spectroscopy, the kinetic energy released into certain fragments over a range of energies has been determined. Using an impulsive model, the data has been extrapolated to zero kinetic energy to obtain a value for the first dissociative ionisation energy of these molecules. From this value, more thermochemical data has been inferred.

One of the most crucial issues nowadays is the protection of the environment and the replacement of fossil fuels, which are abundantly used around the world, with more efficient and renewable sources. The highest portion of global energy demands today is used in heating and cooling purposes. One way of alleviating the fossil-based thermal energy uses is to harvest excess thermal energy using thermochemical storage materials (TCMs) for use at heating/cooling demands at different times and locations. Along this, in this master’s thesis, a bench-scale thermochemical heat storage (TCS) system is numerically designed, as a part of a collaborative project: Neutrons for Heat Storage (NHS), funded by Nordforsk. The TCS system that is designed herein employs the reversible chemical reaction of ammonia with a metal halide (MeX) for a heat storage capacity of 0.5 kWh, respectively releasing and storing heat during absorption and desorption of ammonia into and from the MeX. This system is designed for low temperature heat applications, around 40-80 °C. SrCl2 is chosen as the metal halide to be used, based on the research outcomes in determining the most suitable materials conducted by NHS project partners. In the ammonia-SrCl2 system, only the absorption and desorption between SrCl2∙NH3 and SrCl2∙8NH3 are considered. The main reason is because absorption/desorption between the last ammine and SrCl2 undergoes at a significantly higher/lower reaction pressure (for a given temperature), with a significant volume change compared to the rest of the ammines, and therefore is practically less cost effective. This thesis also includes a detailed discussion of four different thermochemical storage designs from literature, found as the most relevant to the present TCS system study, which use the reaction between ammonia and metal halides. The first system that was examined is a TCS system built by the NHS project partners at Technical University of Denmark (DTU), owing to its similarities with the desired project, regarding the design and parameters the system uses. This system works in batch mode, only allowing either absorption (i.e. heat release) or desorption (i.e. heat storage) at a given cycle. Thus, upgrading the design of this TCS system at DTU is considered as a most-likely solution to the research objectives of this current thesis project. Moreover, the TCS system at DTU uses storage conditions and desorption temperature similar to the current project’s desired low temperature range of 40-80 °C. The second system discussed herein from literature uses two reactors for cold and heat generation, which means that both charging and discharging processes occur simultaneously. This simultaneous operability is the main reason that this particular system was examined in this thesis. The next discussed system from literature also uses two reactors, for absorption and desorption processes, which work reversibly when each process is completed, like in the desired concept of this project. These two systems (i.e., the secondly and the thirdly discussed systems) use the reversible solid-gas reaction for absorption and desorption between SrCl2∙NH3 and SrCl2∙8NH3, however, the conditions of pressure and temperature between them differ. The second system from literature operates at desorption and absorption at respective conditions of 96 °C, 15 bar and 87 °C, 11 bar while the third system discussed operates at 103 °C, 16 bar and 59 °C, 3 bar during desorption and absorption respectively. The last system from literature that is discussed herein provides the same desorption temperature of 80 °C. Inaddition this particular study suggests that the reaction of solid with gaseous NH3 is better (than the solid with liquid NH3 reaction) based on results derived from several different low-pressure experiments of the reactions. The main differences between all these discussed systems from literature, as opposed to the desired TCS system design in this thesis project, concern the systems’ operating mode and the pressure and temperature-conditions. The first difference is that only one of the examined systems pumps the solid VIII powder salt around the system in contrast to the others that keep the salt static inside the reactors and pumped only the ammonia around the system, as chosen in the current system. The second difference concerns the operating conditions during absorption and desorption reactions, where these different systems operate at a widely different pressure and temperature conditions as compared to the current system expectations. Thus, there are four main lessons that were learnt via this literature analysis, to improve the TCS system at DTU to the desired new system in this work. The first lesson is related to the reactants’ transportation mechanism that should be used in this system. Regarding this, it was decided to maintain the solid salt (metal halide) stationary inside each reactor (but not pumping it instead of ammonia), similar to the majority of designs discussed from literature. According to the second and third lessons, the solid-gas reaction is the most suitable solution and only the reactions of absorption and desorption between SrCl2∙NH3 and SrCl2∙8NH3 are considered, following the experience from literature (for the reasons explained earlier). The last lesson regards the system’s suitable operating conditions and more specifically the TCS system’s temperatures that should match the district heating temperatures. Thus, the temperature point that was chosen as a priority was 80 °C, from the range 40- 80 °C set in the partner project NHS. To maintain this condition, therefore, the most suitable condition of pressure of both reactions (according to the equilibrium pressure vs temperature curve) was chosen to be at around 8 bar. This same pressure was chosen for both reactions, since the pressure difference between these reactors and the storage of ammonia (i.e. from 8 to 10 bar) should be as small as possible due to the high costs that can arise in the case of a higher pressure difference (i.e. requiring more compressors and heat exchangers). Inspired by these literature cases, firstly a conceptually suitable TCS system was proposed in this project and after that the final desired system was designed and was implemented and evaluated numerically. The numerical design and optimization of the chosen TCS system was performed herein by using the software Aspen Plus (version 9), which contains both fluids and solids in a simulation environment, using consistent physical properties. This TCS system is designed to store and release heat at around 80 °C and 8 bar through absorption and desorption by using two identical reactors respectively. Each reactor includes the amount of around 1 kg (more specifically 0.985 kg) strontium chloride salt reacting with 1.7 kg of ammonia. A verification system is also modelled in Aspen, using available experimental data from literature. Here, the modelled novel system design was adapted to this chosen other system layout from literature which uses the same reaction pair, yet at different operating conditions. This adapted system design in Aspen was then used to verify the chosen configuration and the reliability of the constructed system for the NHS project. Good agreements between the modelled results in Aspen against the available experimental data of this verification model are obtained. A sensitivity analysis is also conducted herein on the proposed novel TCS system to identify the optimum operating conditions and the behaviour of the chosen most important parameters of the system. The designed system provides an energy storage capacity of 0.5 kWh for the specific amounts (in volumetric flow rates) of ammonia and monoammine of strontium chloride, that comes from the analysis, of 1.08696 e-05 kmol/s and 1.5528 e-06 kmol/s respectively. For these specific values of the HTF, the analysis showed that the volumetric flow rates of the heat and cold external sources must be 1.56 l/min (which is decreasing with the increase of the inlet HTF temperature) and 0.42 l/min (which is increasing with the increase of the inlet HTF temperature) respectively. In conclusion, this study presents an ammonia-SrCl2 TCS benchscale system design that allows continuous heat storage and release, in an easy-to-scale up design, also suggesting optimum operating conditions.
En av de mest avgörande frågorna i dag är skyddet av miljön och utfasningen av fossila bränslen som används allmänt över hela världen för mer effektiva och förnybara resurser. Den största delen av den globala energibehovet idag avser uppvärmnings- och kylapplikationer. Ett sätt att minska fossilbaserad termiskenergianvändning är att lagra överskottsvärmeenergi genom termokemiska lagringsmaterial (TCM) och använda den för värme- och kylbehov vid olika tidpunkter och platser. I samband med detta är ett termokemiskt värmelagringssystem numeriskt utformat i detta mastersexamensprojekt, som en del av ett samarbetsprojekt Neutrons for Heat Storage (NHS) finansierat av Nordforsk. Det termokemiska lagringssystemet (TCS) som är konstruerat utnyttjar den reversibla kemiska reaktionen av ammoniak med en metallhalogenid (MeX) för en värmelagringskapacitet på 0.5 kWh, och frigör och lagrar värme respektive under absorption och desorption av ammoniak till och från MeX. Systemet är designat för lågtemperaturuppvärmningstillämpningar runt 40-80 °C. SrCl2 väljs som det mest lämpliga metallhalogeniden för systemet, baserat på studier som utförts av NHS-projektpartnerna. I ammoniak SrCl2-systemet beaktas endast absorption och desorption mellan SrCl2NH3 och SrCl28NH3. De huvudsakliga orsakerna till detta är att absorptionen/desorptionen mellan den sista aminen och SrCl2 kräver ett betydligt högre/lägre reaktionstryck (för en given temperatur), och resulterar i en betydande volymförändring jämfört med resten av aminerna, och är därför praktiskt taget mindre kostnadseffektivt. Detta mastersexamensprojekt inkluderar en detaljerad genomgång av fyra olika TCS-system från litteratur som använder reaktionen mellan ammoniak och metallhalogenider. Dessa väljs här eftersom dessa anses vara de mest relevanta (från litteratur) jämfört med det valda systemet i denna studie. Det första undersökta systemet är ett system byggt av NHS-projektpartnerna vid Danmarks Tekniska Universitet (DTU). Detta har valts på grund av likheterna med det önskade systemet i det aktuella mastersexamensprojektet, vad gäller systemdesign och parametrar. Detta system fungerar i batch-läge, vilket endast tillåter antingen absorption (dvs värmeavgivning) eller desorption (dvs värmelagring) under en specifik cykel. Således kan en uppgraderad design av detta TCS-system vid DTU möjligen vara en lämplig lösning på forskningsmålen för detta mastersexamensprojekt. Dessutom använder detta TCS-system från DTU ganska liknande driftsförhållanden (temperaturer och tryck) i nivå med det aktuella projektets önskade lågtemperaturintervall på 40-80 °C. Det andra systemet från den litteratur som diskuterats använder två reaktorer för kyla och värmeproduktion, vilket innebär att både laddningsoch urladdningsprocesser sker samtidigt. Denna samtidiga operation är främst anledningen till att systemet undersöktes, eftersom detta är en önskad funktion att uppnå i det aktuella projektet. Nästa system från den litteratur som diskuteras häri använder också två reaktorer för absorptions- och desorptionsprocesser, som fungerar reversibelt när varje process är klar, precis som önskat i detta projekt. Dessa två system (dvs det andra och det tredje diskuterade systemen) använder den reversibla fastgasreaktionen för absorption och desorption mellan SrCl2NH3 och SrCl28NH3, dock vid olika tryck- och temperaturförhållanden. Det andra systemet arbetar nämligen under kombinationer av absorption och desorption av 96 °C, 15 bar och 87 °C, 11 bar, medan det tredje systemet arbetar vid 103 °C, 16 bar respektive 59 °C, 3 bar. Det sista systemet som diskuterats från litteraturen arbetar vid samma temperatur som det önskade systemet gör (dvs. 80 ° C) och genom olika lågtrycksexperiment visar att den fasta salt-gasreaktionen är ett bättre val än reaktionen av det fasta saltet med flytande gasreaktion. De viktigaste skillnaderna mellan alla dessa diskuterade system från litteratur i motsats till det önskade TCS-system i detta mastersexamensprojekt, avser systemdriftläge samt deras tryck och X temperaturförhållanden. Den första skillnaden är att endast ett av alla undersökta system pumpar saltet i fast pulverform, till skillnad från de andra som håller saltet stillastående i reaktorerna och endast pumpar ammoniak. Den andra skillnaden gäller driftsförhållandena under absorptions- och desorptionsreaktioner där dessa system arbetar vid mycket olika tryck- och temperaturförhållanden jämfört med det nuvarande systemet. Således, från översynen av alla system, finns det fyra huvudsakliga lärdomar för att förbättra TCS-systemet vid DTU till det önskade nya systemet. Den första är relaterad till reaktanttransportmekanismen som bör användas i detta system. I detta avseende har det beslutats att hålla det fasta saltet (metallhalogenid) stillastående i varje reaktor (men inte pumpa det istället för ammoniak), till skillnad från de flesta system i litteraturen. Enligt dem andra och tredje lektionerna är den fasta gasreaktionen den mest lämpliga lösningen och endast reaktionerna på absorption och desorption mellan SrCl2∙NH3 och SrCl2∙8NH3 bör övervägas enligt erfarenheten från litteraturen (av de skäl som förklarats tidigare). Den sista lärdomen avser systemets lämpliga driftsförhållanden och mer specifikt TCS-systemets temperaturer för att matcha fjärrvärmetemperaturerna. Den temperaturpunkten valts som prioritet, från området 40-80 °C inställt av moderprojektet NHS, sattes till 80 °C. För att bibehålla detta tillstånd var det lämpligaste tryckvillkoret för båda reaktionerna (enligt jämviktstrycket kontra temperaturkurva) valdes att ligga på cirka 8 bar. Samma tryck valdes för båda reaktionerna, eftersom tryckskillnaden mellan dessa reaktorer och lagring av ammoniak (dvs. från 8 till 10 bar) borde vara så liten som möjligt på grund av de höga kostnaderna som kan uppstå vid högre tryckskillnad (dvs. fler kompressorer krävs och värmeväxlare). Inspirerad av denna litteratur föreslogs för det första ett konceptuellt lämpligt TCS-system i detta mastersexamensprojekt, varefter det slutliga systemet implementerades och utvärderades numeriskt för de önskade förhållandena. Den numeriska utformningen och optimeringen av det valda TCS-systemet utfördes här med hjälp av programvaran Aspen Plus (version 9), som innehåller både vätskor och fasta ämnen i en simuleringsmiljö, med konstant fysiska egenskaper. Detta TCS-system är utformat för att lagra och släppa värme vid cirka 80 °C och 8 bar genom absorption och desorption med användning av två identiska reaktorer respektive. Varje reaktor innefattar cirka 1 kg (närmare bestämt 0.985 kg) strontiumkloridsalt reagerande med 1.7 kg ammoniak. Ett verifieringssystem modelleras också i Aspen med hjälp av tillgängliga experimentella data från litteraturen. I detta anpassades den modellerade nya systemdesignen till denna valda andra verifieringssystemlayout från litteratur, som använder samma reaktionspar, men under olika driftsförhållanden. Denna anpassade systemdesign i Aspen användes sedan för att verifiera den valda konfigurationen och tillförlitligheten för det designade systemet för NHS-projektet. Här erhålls ett bra avtal för denna verifieringssystemdesign mellan Aspenmodellresultaten och experimentdata. Här utförs också en känslighetsanalys för det utformade TCSsystemet i det aktuella projektet för att identifiera de optimala driftsförhållandena och beteendet för de valda viktigaste parametrarna i systemet. Det konstruerade systemet ger en energilagringskapacitet på 0.5 kWh för de specifika mängderna (i volymflöde) av ammoniak och monoamin av strontiumklorid, som kommer från analysen, av 1.08696 e-05 kmol/s och 1.5528 e-06 kmol/s respektive. För dessa specifika värden på värmeöverföringsvätskan visade analysen att de volymetriska flödeshastigheterna för värme och kalla yttre källor måste vara 1.56 l/min (vilket minskar när temperaturen på värmeöverföringsvätskan ökar) och 0.42 l/min (som ökar när temperaturen på värmeöverföringsvätskan ökar). Sammanfattningsvis presenterar denna studie ett ammoniak-SrCl2 TCS-bänkskålsystem som möjliggör kontinuerlig värmelagring och frigöring, har en design som är lätt att anpassa och föreslår också optimala driftsförhållanden.

Various compounds with host structures based on geomaterials have been prepared using solid state methods (900-1200 0c), low pressure hydrothermal conditions (<220 °C, <1800 psi) or using purpose-built high pressure equipment <800°C, < 5500Opsi). Each material was characterized using various combinations of powder X-ray and neutron diffraction, single crystal X -ray diffraction, IR spectroscopy, Mossbauer spectroscopy and magnetometry. The iron end member, danalite, of the helvite family of minerals with the formula Feg[BeSi04]6S2 has been prepared for the first time. Isovalent substitution of the sulphide anion has allowed both selenide and telluride materials to be prepared. These compounds crystallize with the sodalite structure in the space group P-43n and exhibit an ordered framework constructed from alternating Be04 and Si04 tetrahedra containing a tetrahedral cluster of iron(II) ions around a central chalcogenide. Mossbauer measurements curiously show that, despite an elongated tetrahedral geometry of three oxide and one cha1cogenide around the iron ions, the valence and lattice contribution to the isomer shift oppose each other leading to zero quadrupole moment at room temperature for the sulphide material. Magnetic and polarized neutron experiments show that the interactions within the tetrahedral metal clusters of divalent ions are predominantly antiferromagnetic. In the sulphide, the clusters behave as totally isolated clusters showing no magnetic interaction across the cages. As the distance between the clusters shortens, as in the case of the selenide, threedimensional interactions between the clusters are observed. A systematic study of an extensive series of compounds in the helvite series, (Mn,Fe,Zn,Co)8[BeSi04]6X2;X = S, Se and Te has been carried out. All diffraction data of the compounds have been refmed using the Rietve1d method and very accurate structural parameters obtained. Correlations between parameters such as the beryllium and silicon tilt angles, framework bond angle and bond lengths as well as the IR absorptions have been drawn for the beryllosilicate sodalite frameworks. The theoretical maximum and minimum cell parameters for a sodalite framework, based on ordered Be04 and Si04 tetrahedra, has been determined.Transition metal boracites with the formula M3B7013X; M = Co, Zn, Mn, X = Cl, Br and I have been prepared using a borate flux. Their stoichiometries have been determined using the Mohr method and Rietveld refinement of powder X-ray diffraction data. In contrast to compounds prepared using hydrothermal methods, the halide site is not heavily substituted by hydroxide. A temperature dependant study of Mg3B7013CIo.78(OH)o.22 is also presented. Magnetic measurements have confirmed dual weak ferromagnetic and antiferromagnetic properties in the iodide materials A series of LnSF and Ln2AF4S2 materials have been synthesized using high temperature sealed tube methods. The missing member of the LnSF series, DySF, has been prepared for the first time. Precise structural data on the LnAF4S2 compounds where Ln = La, Ce, Dy and Er have been gleaned from the Rietveld refinement of powder diffraction data. . In contrast to previous studies, the lanthanide has been shown as preferentially distributed over the two LnlCa sites and the fluoride displaced from a special site to allow pseudo seven coordination for the smaller lanthanides. High-pressure methods have failed to produce the calciurnlgermanium based zeolites such as gismondine or the unusual mineral, bemalite. A new complex phosphate of the formula NaMllf;(P207 )2(P301O), containing the triphosphate unit, has been prepared at high pressure and the structure determined using single crystal methods. Using low pressure hydothermal methods, the full series of lanthanide hydroxide Ln(OH)3 have been prepared. Structure refinement has shown a contraction in the Ln-O bond distance as the series is transversed.

The work within this thesis has concentrated on the formation and isolation of titanium, vanadium, palladium, and mercury halides, with emphasis on the fluorides.TiF, TiF2, TiF3, and TiF4 have all been isolated within an argon matrix and infrared spectra obtained. From the titanium isotope splitting pattern a bond angle has been determined for TiF2 for the first time of 165o, or effectively linear. This work is also the first time that TiF has been isolated within an argon matrix. Work has also been conducted with vanadium which has lead to the isolation of VF5, VF4, VF3, and VF2, with VF4 undergoing Fermi Resonance. This is the first time that VF4 and VF2, consistent with a linear structure, have been isolated within a matrix.Work conducted upon palladium led to the isolation of numerous palladium fluorides, identified by the palladium isotope patterns in their IR spectra. Due to the similarity of the calculated stretching frequencies of PdF2, PdF3, PdF4, and PdF6 the assignment was challenging and so identification of these bands was conducted based photolysis and annealing behaviour in conjunction with computational calculations. This has allowed for the assignment of the bands present to PdF6, PdF4, PdF3, PdF2, and PdF.The bond length of molecular HgF2 has also been determined for the first time at 1.94(2) Å using the Hg L3-edge with EXAFS. Although the initial aim of this work was to isolate HgF4, using IR, UV/Vis, and XANES, no evidence could be found for oxidation states of mercury higher that HgII. The work also developed a new clean way of making HgF2 in a matrix. The identification of a new Hg…X2 complex was also discovered which when photolysed forms the HgX2 compound, this has only been proven for HgF2. This was achieved by isolating mercury atoms in an argon matrix doped matrices, photolysis of this matrix the led to the formation of HgF2 in significant amounts.

Hybrid perovskites are a new class of semiconductor which have proven to be an ideal material for making thin film solar cells. They have the advantages of flexibility, low cost, and easy processing, whilst achieving efficiencies competitive with monocrystalline silicon. Many of the properties which make them ideal for solar cells are also applicable to light emitting devices, and there is now increasing interest in their application for light emitting diodes (LEDs) and lasers. This thesis aims to use a range of novel spectroscopy techniques to investigate the origin of these favourable properties, and to exploit these properties to produce high performance distributed feedback lasers. A detailed understanding of the origins of the excellent properties of hybrid perovskites is of crucial importance in the search for new variations with improved performance or lowered toxicity. This thesis uses Kelvin probe, air photoemission, and resonant ultrasound spectroscopy to probe deeply into the underlying physics of hybrid perovskite single crystals and devices. Using these techniques, we are able to produce detailed maps of the energy levels in a common perovskite solar cell, and we also gain strong insight into the underlying strains and instabilities in the perovskite structure that give rise to their elastic properties. The strong light emission of hybrid perovskites is then exploited to produce high quality distributed feedback lasers emitting in the green and infrared part of the spectrum. These lasers are observed to have superior stability, good thresholds, and many interesting beam parameters owing to their high refractive index. We explore a wide range of processing methods in order to achieve the lowest lasing threshold and the best stability. Finally, we investigate the properties of low dimensional perovskites and investigate their potential in optoelectronic applications.

BaSIC, which stands for Bioclastic and Shape-preserving Inorganic Conversion, is shape-preserving chemical conversion process of biological (or man-made) silica structures for producing complex 3-D microscale structures. This dissertation reports the BaSIC reaction of halide gases (i.e., TiF4, ZrF4, and ZrCl4) with 3-D silica structures, (i.e., diatom frustules, silicified direct-write assembly scaffolds, and Stöber silica spheres) to produce titania and zirconia replicas of the original 3-D structures. The kinetics of reaction of silica with titanium tetrafluoride gas is analyzed by using a novel HTXRD reaction chamber, nitrogen adsorption, and transmission electron microscope (TEM). The crystal structure and the temperature-induced phase transformation (from the room temperature hexagonal R-3c structure to the higher temperature cubic Pm3m structure) of polycrystalline TiOF2 that was synthesized through metathetic reaction of silica with TiF4(g) is reported. Additionally, potential applications of the converted titania diatom frustules (i.e., as a fast micron-sized ethanol sensor, and as a pesticide hydrolyzing agent) are also demonstrated in this work.

This habilitation thesis describes the syntheses and characterizations of mostly new metal-rich cluster compounds of early transition elements. It is devided into 4 parts. The first part describes the syntheses and solid-state X-ray structures of a total of 14 mixed-halide (iodide-chloride) zirconium cluster phases, which crystallize in 9 different (some novel) structure types. All these cluster phases contain octahedral Zr6Z-units that are centered by an interstitial atom Z. Phase widths and relations between the differend structure types are discussed. The second part deals with molecular (soluble) zirconium cluster phases which are excised from solid-state precursors. It is shown that liquid mixtures of 1,3-dialkylimidazolium bromide and AlBr3 as well as molten 18-crown-6 are useful solvents for molecular zirconium cluster compounds. The syntheses and single crystal X-ray structures of 3 new materials are detailed. Furthermore, from the reaction of an iron containing Zr-cluster phase with KSCN crystals have been obtained from which a single crystal X-ray structure analysis shows that they contain a high symmetry Fe-cubane cluster. The third part of this thesis is concerned with theoretical investigations (Extended-Hckel band structure calculations) of a series of monoclinic phases which contain double-octahedral chains of rare earth metal clusters of the general formula RE3I3Z (RE = rare-earth metal atoms). The results of the electronic band structure calculations show that the observed structural variations within this series depend largely on the difference of the orbital energies of the rare earth metals and the interstitials. In the last part the phase pure synthesis of Nb21S8 and measurements of physical properties (electrical conductivity and magnetical susceptibility) as well as results from electronic band structure calculations (LMTO) are described. The property measurements show that this metal rich sulfide becomes superconducting below 3.7(2) K. The results from the electronic band structure calculations indicate the existence of an arrangement of electronic levels ("fingerprint") which favors the formation of superconducting Cooper pairs.

Trimethylamine reacts with MCl2 (M = Mn, Cd, Cu) to give mono adducts of the type MC12Nme3. Recrystallization of MnC12-Nme3 (1) from the polar solvent acetonitrile yields the anionic complexes [NMe3H] [MnCl3] (II) and [Nme3H]2 [MnCl4Δ] (III) both from the same solution. Similarly CuCl2NMe3 (IV) gives lNMe3H][CdCl3\ (V). Recrystallization of CuCliUMe3 (VI) from the chlorinated solvent CH2CI2 yields the anionic complex [Me3NCH2Cl]2 [CuC1Δ] (VII). Compounds (II). (V) and (VII) were further investigated by X-ray crystal structure determinations. The co-ordination chemistry of Group VB trichlorides with the neutral O-donor (crown ether) ligands 1,4,7,10-tetraoxacyclododecane (I2-C-4), 1,4,7,10,13- pentaoxacyclopentadecane (I5-C-5) and 1,4,7,10,13,16-hexaoxacyclooctadecane (18-C- 6) have been investigated. 12-C-4 and 15-C-5 form neutral adducts with the pyramidal MCI3 (M = As, Sb, Bi) where all oxygen atoms of the crown are co-ordinated to the metal atom in a half-sandwich structure. For I8-C-6, AsC13 does not give complex formation, instead the crown ether forms a bis-adduct (18-C-6).2CH3CN with the solvent acetonitrile. SbC13 forms a half-sandwich adduct with I8-C-6 but with an extra molecule of CH3CN trapped in the lattice and BiC13 forms a 2:1 complex which has the ionic formulation 1B2C12(18-C-6)12 + lB12CI312 Here the bismuth cation is eight co-ordinate involving all six oxygen atoms of the crown and the two chlorine atoms. The crown ethers give no simple adducts with the pentahalide SbC15. The crystals obtained from the reactions of I2-C-4 and I8-C-6 with SbC15 are the unexpected hydroniumfcrown) hexachloroantimon(V)ate salts, |H3O(12-C-4)2] (SbC1o1) and [H3O(18-C-6)] [SbC1o) respectively. I5-C-5 gives the neutral Sb(lll) adduct SbC13(l5-C-5) as the major product and the hydroniumfcrown) hexachloroantimon(V)ate salt as the minor product. A plausible mechanism for the formation of hydronium antimon(V)ate salts is presented and discussed. In the preliminary study of sterically crowded aryloxide complexes of Group VB chlorides, the reaction between SbCli and the extremely bulky 2,6-di(tertiary butyl) phenoxide has been investigated. This leads to the formation of 22' .6,6’ -tetra (tertiary butyl) diphenoquinone (A) via a redox reaction. The crystal structure of this oxidation product has been determined via an X-ray study and a plausible mechanism for the for­mation of (A) is presented and discussed.

Organic‐inorganic hybrid materials combine an inorganic component with an organic component at the nanoscale, while potentially retaining the properties of both components. In the current study the structural characteristics and magnetic properties of hybrid materials combining cations of saturated primary, secondary and tertiary amines with perchloridocuprate(II) and perbromidocuprate(II) anions, were studied. The saturated cations of cyclopentylamine, cyclohexylamine, cycloheptylamine, piperazine and 1,4‐diazoniabicyclo[2.2.2]octane were chosen since the series allows for the study of the effect of the cation size, charge and saturation on the hybrid structure and also due to the scarcity of hybrid structures containing these types of saturated cations in the literature. Perhalocuprate(II) containing hybrid materials exhibit magnetic properties due to the presence of an unpaired electron on the Cu2+ ion. At low temperatures magnetic ordering may occur via magnetic exchange pathways involving the halogeno ligands, forming ferromagnetic or antiferromagnetic materials. Identification of the magnetic exchange pathways by consideration of the crystal structure allows for the selection of a suitable theoretical quantum mechanical model to which the experimental magnetic data can be modelled, to obtain parameters like the exchange constant. A part of the work describes the preparation of crystals of the family of hybrid materials under investigation, and the experimental techniques employed to study the structural and magnetic characteristics of the materials. The crystal structures of six novel materials are discussed in detail and compared to related structures characterised in this study, or to structures previously reported in the literature, where possible. Magnetic susceptibility data is analysed for four compounds, two of which are novel and two for structures reported previously in the literature. By considering the novel structures characterised in this study, as well as structures previously reported in the literature, structural trends are identified. The role of saturation of the cation on the structure, as well as the effect of cation charge, is highlighted for related compounds. Robust hydrogen bonding motifs are identified for two sub‐families of structures, namely those containing isolated tetrahalocuprate(II) anions and those containing related polymeric perhalocuprate(II) anions. In addition, the magnetic properties of the family containing polymeric anions are compared.
Dissertation (MSc)--University of Pretoria, 2014.
Chemistry
MSc
Unrestricted

The bis 1,4,7-trithiacyclononane (1,4,7-TTCN) complexes of iron, cobalt, nickel and copper are reported in this work. Their properties have been examined using computer-controlled electrochemical and spectroscopic techniques. These TTCN complexes form readily, are unusually symmetrical and support electron transfer reactions at the metal center. The cobalt(II) complex is octahedral, low spin and symmetrical. Four oxidation states of cobalt-TTCN complex are observed; two one-electron transfer processes are reversible. Copper (II) bis 1,4,7-TTCN is unusually symmetrical evidenced by both solid phase and ambient temperature aqueous phase electron paramagnetic resonance spectra. An unusually high redox potential for the copper complex indicates extraordinary stability of the Cu(I) oxidation state but evidently not at the expense of Cu(II) stability. The complex also has a high formation constant compared to other copper-thioether complexes. This unusual strength of thioether donor is attributed to ligand geometry. The 1,4,7-TTCN molecule is the only known cyclic polythioether to have all sulfur atoms endodentate. This structure contributes to thermodynamic stability of complexes as the ground state configuration of the free ligand is maintained in the complex.

This work was motivated by the extensive research on lithium solid state materials, which have attracted increasing interest for potential applications in hydrogen storage and/or lithium ion batteries due to their extraordinary properties. In this thesis, LiBH4-derived materials, LiInBr4 and complex phases based on lithium ammonia borane with potential use as solid state electrolytes were successfully synthesised and characterised.

Heavy metals have been known to possess antimicrobial properties against bacterial, fungal, and viral pathogens. Silver and copper in particular have been used for millennia to control bacterial and fungal contamination. Metal nanoparticles (aggregations of metal atoms 1-200 nm in size) have recently become the subject of intensive study for their increased antimicrobial properties due to their increased surface area and localized release of metal ions when attached to pathogens. In the current studies, metal and metalhalide nanoparticles including silver (Ag), silver bromide (AgBr), silver iodide (AgI), and copper iodide (CuI) nanoparticles were evaluated for their antibacterial efficacy against two common bacterial pathogens. All of the nanoparticles significantly reduced bacterial numbers within 24 hours of exposure and were more effective against the Gram-negative Pseudomonas aeruginosa than the Gram-positive Staphylococcus aureus. CuI nanoparticles were found to be highly effective, reducing both organisms by >4.43 log₁₀ within 15 minutes at 60 ppm Cu. CuI nanoparticles were selected for further evaluation against a range of microorganisms to determine their broad spectrum efficacy. CuI nanoparticles formulated with different stabilizers (sodium dodecyl sulfate, SDS; PVP) were tested against representative Gram-positive and Gram-negative bacteria, Mycobacteria, a fungus (Candida albicans), and a non-enveloped virus (poliovirus). Both nanoparticles caused significant reductions in most of the Gram-negative bacteria within five minutes of exposure (>5.09-log₁₀). The Gram-positive bacterial species were more sensitive to the CuI-SDS than the CuI-PVP nanoparticles. Likewise, C. albicans was also more sensitive to the CuI-SDS than the CuI-PVP nanoparticles. In contrast, the acid-fast Mycobacterium smegmatis was more resistant to the CuI-SDS than the CuI-PVP nanoparticle solutions (2.54-log₁₀ vs. 3.80-log₁₀ after 30 minutes). Poliovirus was more resistant than the other organisms tested except for Mycobacterium fortuitum. M. fortuitum was more resistant to both CuI nanoparticle solutions than any of the other organisms tested, requiring longer exposure times to achieve comparable reductions (~4.15 log₁₀ after 24 hours). As an example of a real world antimicrobial application, polymer surface coatings with embedded CuI nanoparticles were investigated to determine their potential use as self-disinfecting surfaces. Brushed polyurethane, spincoated acrylic, and powder coated polyester-epoxy coatings containing various concentrations of CuI nanoparticles were tested for antibacterial efficacy against P. aeruginosa and S. aureus. Polyester-epoxy powder coatings were superior to the other coatings in terms of uniformity and stability under moist conditions and displayed antimicrobial properties against both organisms (>4.92 log₁₀) after six hours at 0.25% Cu. Polyester-epoxy coatings were selected for more rigorous testing under adverse conditions. These surfaces were negatively impacted when tested under dry conditions with high organic content, with organic content appearing to have a greater impact on antimicrobial efficacy. At 0.25% Cu, the antibacterial activity of the powder coatings was not impacted by washing with several commercial cleaners; however, at concentrations of 0.05% Cu, antibacterial activity was reduced by multiple washings with water, Windex®, and Pine Sol®. Additionally, ultrasonic cleaning of the coatings appeared to decrease their antimicrobial efficacy. Despite this, CuI nanoparticles were found in all studies to have great potential as a new class of fast-acting, broad-spectrum antimicrobial.

Metal halide lamp is one kind of the most compact high-performance light sources. Because of their good color rendering index and high luminous efficacy, these lamps are often preferred in locations where color and efficacy are important, such as supermarkets, gymnasiums, ice rinks and sporting arenas. Unfortunately, acoustic resonance phenomenon occurs in metal halide lamps and causes light flicker, lamp arc bending and rotation, lamp extinction and in the worst case, arc tube explosion, when the lamps are operated in high-frequency bands. This thesis takes place in the context of developing electronic ballasts with robust acoustic resonance detection and avoidance mechanisms. To this end, several envelope detection methods such as the multiplier circuit, rectifier circuit, and lock-in amplifier, are proposed to characterize fluctuations of acoustic resonance. Furthermore, statistical criteria based on the standard deviation of these fluctuations are proposed to assess acoustic resonance occurrence and classify its severity. The proposed criteria enable classifying between no acoustic resonance and acoustic resonance cases based upon either a two-dimensional plane, a histogram or a boxplot. These analyses are confirmed by the study of spectral variations (variations of the spectral irradiance and colorimetric parameters) as well. Standard deviations and relative standard deviations of these variations are also correlated with the presence of acoustic resonance. The results from this study show that whatever voltage envelope variations or spectral variations are significantly influenced by acoustic resonance phenomena. A set of metal halide lamps from different manufacturers and with different powers are tested in our experiments. We concluded that our designed multiplier and rectifier circuits for acoustic resonance detection have the same sensitivity as the lock-in amplifier, paving the way for the implementation of this function directly into the ballast circuit board.