The solid state, hydrothermal and flux methods were used for the investigation of alkaline earth and transition metal borophosphate compounds. The products and the phase relations were investigated by XRD, IR, DTA, and EDX methods. The solid state reactions of several boron compounds with different phosphating agents have been studied in the temperature range of 400-1200 oC. Hydrothermal and flux techniques were performed at 150 oC and 1200 oC, respectively. On the other hand, an attempt has been made to prepare a novel borophosphate compound MIIMIV[BPO7] (where MIV= Zr4+, Si4+, and MII= Sr2+, Ca2+) by solid state reactions and to investigate intermediate and final products. (NH4)2HPO4 and NH4H2PO4 were used as a phosphating agent. For the synthesis of these new compounds, the following reaction was predicted using the stoichiometric amount of the reactants: 2MIVO2 + 2MIICO3 + B2O3 + 2(NH4)2HPO4 &amp / #8594 / 2MIIO.MIVO2.B2O3.P2O5 + 4NH3 + 3H2O + 2CO2 (According to IUPAC formulation for the compounds composed of oxides) In the case of MIV=Zr4+ and MII=Sr2+, the formation of ZrSr[BPO7] was observed together with ZrO2 and SrBPO5. The formation of a new phase was proved by indexing the XRD pattern of the product after separating ZrO2 and SrBPO5 lines. Its crystal system was found to be orthorhombic and the unit cell parameters are a=11.85&Aring / , b=12.99 &Aring / , c=17.32 &Aring / . IR analysis shows that there is [BPO7]6- bands in the spectrum. At higher temperatures, Sr7Zr(PO4)6 was obtained. In the case of MIV=Si4+, SrBPO5 was the main product together with unreacted SiO2. At 1100 oC, Si4+ entered SrBPO5 structure and the product was indexed in orthorhombic system with a=8.9243 &Aring / , b=13.1548 &Aring / , and c=5.4036 &Aring / . Several other M:B:P ratios were tried for solid state systems. For compositions with different cations (such as Al3+, Ca2+, Na+), reactions generally pass through metal phosphates and BPO4. The X-ray diffraction powder pattern and infrared spectrum of several intermediate products obtained at different temperatures were presented and the several phase relations were investigated. The DTA and EDX analyses of some products were also reported.

In this work, alkaline earth aluminate phosphors doped with rare-earth ions and manganese were synthesized using combustion method. Several characterization techniques were used to study the structural and luminescent properties of the as-synthesized phosphors, namely X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), X-ray energy Dispersive Spectroscopy (EDS), Ultraviolet-Visible (UV-Vis) Spectroscopy, Photoluminescence (PL), and Thermoluminescence (TL). The structural properties were studied by collecting the XRD patterns of the samples using an X'Pert PRO PANalytical diffractometer with CuKα at λ = 0.15405 nm. The particle morphologies of the as-synthesized powder phosphors were investigated using a JEOL JSM-7500F field-emission scanning electron microscope (FE-SEM). The optical properties of the phosphors were studied using Perkin-Elmer Lambda 750s UV-Vis spectrometer, Jobin Yvon/SPEX FluoroLog spectrofluorometer (Model FL-1040) and Riso TL/OSL reader (Model DA-20). The as-prepared SrAl2O4:Eu 2+ ; SrAl2O4:Dy 3+; SrAl2O4:Mn 2+; phosphors were synthesized at an initiating temperature of 600 oC. The XRD patterns were consistent with the low temperature monoclinic structure of SrAl2O4 for all the as-synthesized phosphor powders. SEM measurements showed nano-rod like particles. The SrAl2O4:Eu 2+ ; SrAl2O4:Dy 3+; SrAl2O4:Mn 2+ samples were excited using a 450 W Xenon light source at 364 nm, 390 nm, and 426 nm respectively. A broad blue emission peak at 500 nm shown by the SrAl2O4:Eu 2+ sample is attributed to the 6 1 7 4f 5d 4f transition of the Eu 2+ ion. Also, the red sharp emission lines due to the 4f-4f transition of the Eu 3+ were observed. SrAl2O4:Dy3+ samples exhibited blue, green, and red emissions which can be atributed to the 4 6 9/2 15/2 F  H ,4 6 9/2 13/2 F  H , and 4 6 9 11 2 2 F  H transitions of Dy 3+ ions respectively. The two broad emissions (green at 513 nm and red at 650 nm) shown by 2+ 0.98 2 4 0.02 Sr Al O :Mn sample can be atributed to the 4 4 6 6 1 1 T ( G)  A ( S) transition of the Mn 2+ ion in the sample. The SrAl2O4:Eu 2+ , Dy 3+ ; SrAl2O4:Eu 2+, Mn 2+ ; SrAl2O4:Dy 3+, Mn 2+; and SrAl2O4:Eu 2+ ,Mn 2+, Dy 3+ phosphors were synthesized by combustion method at an initiating temperature of 600 oC. The blue emissions were observed in all the samples except SrAl2O4:Eu 2+ ,Mn 2+, Dy 3+ sample. The SrAl2O4:Eu 2+ ,Mn 2+, Dy 3+ phosphor showed the longest afterglow intensity. The BaAl2O4 doped with Eu 2+ , Mn 2+ and Dy 3+ phosphors synthesized at an initiating temperature of 600 oC using combustion method. The XRD patterns confirmed the hexagonal structure of BaAl2O4 in all the as-synthesized samples. A broad blue emission of the BaAl2O4:Eu 2+ sample at 490 nm is attributed to the 6 1 7 4f 5d 4f transition of the Eu 2+ ion in the sample. A red emission peak observed at 611 nm is due to the 4f - 4f transition of un-reduced Eu 3+ ions during the combustion reaction. A blue emission at 482 nm, a green emission at 575 nm, and a red emission at 663 nm of the BaAl2O4:Dy 3+ sample can be associated with 4 6 9/2 15/2 F  H ,4 6 9/2 13/2 F  H , and 4 6 9 11 2 2 F  H transitions of the Dy 3+ ions respectively. The green emission peaks exhibited by BaAl2O4:Mn 2+ sample at 512 nm is due to the 4 4 6 6 1 1 T ( G)  A ( S) transitions of the Mn 2+ ions. Barium aluminate phosphors doped with different concentrations of Dy 3+ ion were synthesized by combustion method at an initiating temperature of 600 oC. The XRD patterns confirmed the hexagonal structure of BaAl2O4. The emission peaks observed at 482 nm, 575 nm, and 663 nm are due to4 6 9/2 15/2 F  H ,4 6 9/2 13/2 F  H and 4 6 9 11 2 2 F  H transitions of Dy 3+ ion respectively. The PL measurements also confirmed the quenching of luminescence at higher concentrations of the Dy 3+ ion. The UV-Vis measurements has confirmed the increase in the band-gap of the BaAl2O4 sample followed by a decrease and an increase again as doping concentration of the Dy 3+ increased. The X-ray diffraction patterns of the Ca0.97M0.3Al2O4:Eu 2+ , Dy 3+ (M = Ba, Mg, and Sr) powder samples prepared by combustion method confirms the monoclinic structure of CaAl2O4 in all samples. A broad emission peak at 490 nm for both Ba 2+ and Mg 2+ substituted samples and the one for Sr 2+ substituted sample at 485nm are attributed to the 6 1 7 4f 5d 4f transition of the Eu 2+ . The decay curves confirmed that the Mg 2+ substituted sample has a longer persistence (phosphorescence) than all the other samples. / Physics / M. Sc. (Physics)

Parmi les défis que le Monde devra affronter dans les prochaines décennies, le plus difficile est l’utilisation d’énergie durable. Dans un scénario où les sociétés occidentales sont fortement dépendantes des combustibles fossiles pour garder leur niveau de bien-être (chauffage domestique, transport et production d’électricité), complété par les pays en voie de développement qui ont besoin d’alimenter leurs économies croissantes, il est nécessaire de souligner l’impact négatif sur l’environnement causé par l’utilisation de ces ressources fossiles mais aussi les problèmes géopolitiques pour les pays « non producteurs ». La collecte d’énergie provenant des sources renouvelables peut limiter la dépendance des combustibles fossiles, pourtant cette dernière ne peut remplacer les centrales électriques classiques à cause de son caractère intermittent.Les batteries sont des dispositifs qui peuvent résoudre définitivement cette limitation, puisqu’elles sont capables d’accumuler l’excès d’énergie produit afin de le délivrer au moment souhaité. De plus elles ont été envisagées comme les dispositifs principaux pour toutes les applications portables (téléphones et ordinateurs portables mais aussi véhicules). Grâces à ses excellentes performances et sa technologie bien développée, les batteries lithium-ion ont un rôle déterminant dans le support de cette nouvelle révolution énergétique. Pourtant leur usage répandu a été récemment remis en question à cause de la faible disponibilité de lithium, qui est un élément rare et concentré seulement dans certaines zones du monde. L’emploie du lithium pourrait donc engendrer les mêmes problèmes que les combustibles fossiles. De plus, cette technologie semble avoir atteint son niveau de développement maximal et ne pourrait plus être suffisante pour satisfaire des applications de plus en plus énergivores. Il est donc nécessaire d’envisager des alternatives au lithium en axant les recherches sur des ressources plus abondantes que lithium et à moindre coût mais aussi sur des systèmes plus performantes.Les batteries post-lithium, qui sont basées sur d’autres porteur de charges que le Li+, pourrait représenter des alternatives plus sécurisées, respectueuse de l'environnement et aussi plus attractifs en termes de capacité stockée. Le magnésium est un candidat prometteur pouvant remplacer le lithium dans les systèmes électrochimiques de stockage d’énergie, grâce à son abondance, son faible coût et sa capacité volumique qui est doublée par rapport à cette du lithium. Cependant, l’obstacle le plus important au développement des batteries rechargeable au magnésium est la mauvaise compatibilité entre les électrolytes classiques et le magnésium métal. Dans cette optique il est encore nécessaire d’utiliser des mélanges de sel/solvant extrêmement dangereux dans les prototypes proposés. En revanche, la recherche de possible alternatives au magnésium métal, c.-à-d. des matériaux capable de réagir à bas potentiel avec le Mg, permettrait de réaliser une véritable batterie aux ions de magnésium (MIB), compatible avec des formulations d’électrolyte classiques.Cette thèse est dédiée à l’investigation des comportements électrochimiques de plusieurs éléments du bloc p (In, Sn, Sb, Bi) qui peuvent s’allier réversiblement avec le Mg à bas potentiel. Des possibles synergies entre ces éléments ont été aussi explorées (composite Sn-Bi, phases intermétalliques BixSb1-x et InBi) qui puissent être employés comme électrodes négatives pour MIBs. Des poudres micrométriques ont été obtenues par broyage/alliage mécanique, technique de synthèse simple à mettre en œuvre. Une attention particulière a été portée à l’étude des mécanismes électrochimiques d’alliage et/ou conversion avec la diffraction des rayons X en mode operando. L’évaluation des performances électrochimiques a permis de sélectionner le meilleur candidat pour être testé comme électrode négative dans un prototype de batterie magnésium-ion. / One of the most challenging hurdles that the World has to face in the next decades is the sustainable use of energy. In a scenario where western societies are largely dependent of the fossil fuels for maintaining their wellness, i.e. for heating, automotive transportation and electricity production, and developing countries need to feed their growing economies, it is worth underlying both the major impact on the environment due to the indiscriminate use of such combustibles but also the geopolitical issues for the non-producing countries. Energy harvesting by renewable sources can help limiting the dependence on fossil fuel exploitation but cannot perfectly replace conventional power plant due to its intrinsic intermittency.Batteries are the devices that can draw a line under this situation, since they can stock the energy surplus when the plant is operating and then can squeeze it in the power grid when there is a lack of production. Moreover, they are also targeted to fulfil the even growing demand of energy for portable applications (mobile phones and computers, and nowadays cars and trucks). The excellent performance and the well-established technology of Lithium-ion batteries (LIBs) put them in a crucial position for supporting this new energy revolution. However their ubiquitous role has been recently questioned for two main reasons: i) of the low availability of Li, which is a rare and not-uniformly spread element that may lead to the similar problems caused by fossil fuels. And ii) the effective capacity to satisfy the highly energy-demanding applications, since Li-ion technology seems reaching is upper limit in terms of overall performance. Therefore cheaper and more powerful alternative to Li-based systems are needed.Post-Lithium-based batteries, based on other charge carriers than Li+ can be offer safer, more sustainable and performing alternative to LIBs. Mg is a promising candidate that can replace Li in electrochemical systems due to its abundance, low cost and a theoretical volume capacity twice higher than that of Li. Although the efforts devoted to the realization of a rechargeable Mg battery were made in the last 15 years, the major hurdle represented by the low compatibility between metallic Mg and conventional electrolytes still obliges the use of hazardous salt/solvent mixtures in research prototypes. Searching alternative negative electrodes to the Mg metal, i.e. compounds able to reversibly react with Mg at low potential, will pave the way for a veritable Magnesium-ion battery (MIB), allowing the use of conventional electrolytes.The present thesis is devoted to investigate the electrochemical behaviour of several p-block elements that can reversibly alloy with Mg at low potential (In, Sn, Sb, Bi). Possible synergies between these elements are also explored, realizing composite materials (Sn-Bi), or intermetallic phases (BixSb1-x and InBi) that could be employed as negative electrodes in MIBs. The chosen synthetic route for obtaining micrometric-sized particles is the mechanical milling/alloying, since it is simple, cost-effective and upscalable. Particular attention is put on the study of electrochemical mechanisms through the operando X-ray diffraction. Electrochemical performance evaluation allows selecting the best candidate for an effective test as negative electrode in MIB prototype.

Materiais luminescentes contendo íons terras raras (TR3+) dopados nas matrizes de tungstatos [WO4]2- têm se mostrado excelentes candidatos como fósforos. Portanto, neste trabalho os materiais MWO4:TR3+ (M: Ca2+, Sr2+, Ba2+ e TR3+: Eu, Tb) foram preparados pelo método da coprecipitação com concentração de dopantes 0,1, 1,0, 5,0 e 10 % em mol. Este método comparado aos convencionais (cerâmico, combustão etc.), apresenta vantagens por ser um método simples de operação e rápido, baixo custo, preparado a temperatura ambiente, o processo de obtenção ambientalmente é correto e também produzem-se nanopartículas. Na caracterização destes fósforos foram utilizadas as técnicas: espectroscopia de absorção no infravermelho (IV), análise termogravimétrica (TG), difração de raios X - método do pó (DRX), microscopia eletrônica de varredura (MEV) e energia dispersiva de raios X (EDS). Os picos de difração de raios X foram indexados na estrutura tetragonal scheelita. Os fósforos dopados com Eu3+ e Tb3+ apresentaram cristalitos com dimensões nanométricas. Os estados de oxidação dos íons terras raras foram investigados com a espectroscopia de absorção de raios X com radiação Síncrotron (XANES), onde indicaram a presença apenas do estado trivalente para o európio nos materiais \"como preparados\" e calcinados. No entanto, foram detectados os estados trivalente e tetravalente do térbio dopado nas matrizes CaWO4 e BaWO4, calcinados à 500 ºC. As propriedades fotoluminescentes dos compostos foram investigadas com base nas transições intraconfiguracionais 4f6 (Eu3+) e 4f8 (Tb3+). Os espectros de excitação apresentaram bandas largas na região do UV, atribuídas às bandas de transferência de carga LMCT O→W e O→Eu3+. Os espectros de excitação dos fósforos MWO4:Tb3+ apresentaram as bandas de absorção largas atribuídas transferência de carga LMCT O2-(2p)→W6+(5d) sobrepostas às transições 4f8→4f75d e também picos finos oriundos das transições 4f8 do íon Tb3+. Ademais, os seus espectros de emissão exibiram bandas finas características das transições das 5D4→7FJ do íon térbio trivalente. Os valores altos do parâmetro de intensidade experimental (Ω2 ~18 x 10-20 cm2) indicam que o sítio de simetria ocupado pelo íon Eu3+ dopado nas matrizes de tungstatos não apresentam caráter centrossimétrico, uma vez que os altos valores de Ω2 são mais influenciados pelas pequenas mudanças angulares da geometria local do íon terra rara. Os valores de eficiência quântica de emissão η do nível 5D0 dos fósforos MWO4:Eu3+ estão em torno de 30 %, sugerindo que não há variação significativa quando se altera os íons metálicos alcalinos terrosos. As coordenadas CIE (Commission Internationale l\'Eclairage) sugerem emissões multicolores dos sistemas MWO4:Eu3+ X mol-% que podem ser ajustáveis, em função das intensidades de emissão das bandas largas LMCT e dos picos finos das transições 5D0→7F0-4 e da concentração de dopagem (X mol-%) do íon Eu3+. Estes materiais luminescentes exibem cores de emissão vermelha, verde assim como cores intermediárias. / Luminescent materials containing rare earth ions (RE3 +) doped in [WO4]2- tungstate matrices have demonstrated excellent candidates as phosphors. Therefore, in this work the materials MWO4:TR3+ (M: Ca2+, Sr2+, Ba2+ e TR3+: Eu, Tb) were prepared by the coprecipitation method with doping concentration 0.1, 1.0, 5.0 and 10% mol. This method compared to conventional ones (ceramic, combustion, etc.), has advantages because it is a simple operation and fast, low cost, prepared at room temperature, the process of obtaining is environmentally correct and also make up the nanoparticles. The characterization techniques of these phosphors were investigated by infrared absorption spectroscopy (IR), thermogravimetric analysis (TG), X-ray diffraction patterns - powder method (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDS). The tungstate matrices doped with Eu3+ and Tb3+ showed crystallite sizes with nanometer dimensions. The rare earth oxidation states were investigated using absorption spectroscopy X-ray synchrotron radiation (XANES), which indicated the presence of only trivalent europium state materials \"as prepared\" and calcined. However, it was observed the trivalent and tetravalent state of terbium doped in CaWO4 and BaWO4 matrices, calcined at 500 º C. The photoluminescent properties of the compounds were investigated based on 4f6 (Eu3+) and 4f8 (Tb3+) intraconfigurational transitions. The excitation spectra showed broad bands in the UV region, assigned to the bands of charge transfer LMCT O→W e O→Eu3+. The excitation spectra of MWO4Tb3+ phosphors showed the broad absorption bands attributed charge transfer LMCT O2-(2p)→W6+(5d) overlapping with 4f8→4f75d transitions and narrow peaks arising from 4f8 transitions of Tb3+ ion. Moreover, their emission spectra exhibited narrow characteristic bands assigned to the 5D4→7FJ transitions of trivalent terbium ion. The high values of experimental intensity parameters (Ω2 ~ 18 x 10-20 cm2) indicate that the site symmetry occupied by the Eu3+ ion doped in the tungstates matrix not present centrosymmetric character, since high values of Ω2 are more affected by small angular changes of the local geometry around of rare earth ion. The values of emission quantum efficiencies (η) of the 5D0 level MWO4:Eu3+ phosphors were at around 30%, suggesting that there is no significant variation when changing the alkaline earth metal ions. The CIE coordinates (Commission Internationale l\'Eclairage) data suggest multicolored emissions for the MWO4:Eu3+ X mol-% systems can be tuneable, which depending on the emission intensities of the LMCT broad bands and 5D0→7F0-4 narrow peaks and concentration doping (X mol-%) of the Eu3+ ion. These materials exhibit luminescent emissions with red, green and intermediate colors.

No description available.

Différents phosphates ont été préparés et testés pour la déshydratation de l'acide lactique en phase gaz. La sélectivité en acide acrylique dépend fortement de la température de réaction mais peu du temps de contact. A 380°C, des valeurs de sélectivité allant de 19 à 50% ont été mesurées pour des phosphates alcalino-terreux qui sont stables sur au moins 24 h. Des mesures d'acido-basicité ont montré que ces phosphates contiennent une forte proportion de sites de même force faible. De plus, une corrélation entre la sélectivité en acide acrylique et le ratio molaire acide/base a été établie : elle atteint 50% pour un rapport proche de 1 et diminue lorsque ce ratio augmente. L'acide lactique étant thermiquement peu stable (fonction acide très réactive), nous nous sommes tournés vers la conversion du lactate d'éthyle pur. Les sélectivités en produits de déshydratation sont largement favorisées avec une sélectivité maximale de 87% à 15% de conversion. Cependant, les catalyseurs sont moins actifs et se désactivent fortement sur 24 h. La désactivation peut être inhibée par ajout d'eau dans la phase gaz. La caractérisation de surface a montré que les vitesses de réaction augmentent avec le rapport P/M et a révélé la présence d'une phase amorphe hydroxylée correspondant à des mono, dihydrogénophosphates ou des polyphosphates. Les groupements P-OH présents dans cette phase sont consommés ou modifiés en condition de réaction pour les deux réactifs suggérant qu'ils constituent des sites actifs. Enfin, le suivi DRIFT des TPD-NH3 a permis de proposer que des paires acide-base (M2+ et P-O-) sont dosées dans ce cas. Elles constitueraient le site d'adsorption de l'acide lactique conduisant ensuite à un mécanisme de déshydratation de type E2 / Various alkaline-earth phosphates were prepared and evaluated for gas phase dehydration of lactic acid. Selectivity to acrylic acid strongly depends on the reaction temperature but not on the contact time. At 380 °C, values ranging from 19 to 49% were measured for alkaline–earth phosphates catalysts that are stable for at least 24 h. Acid–base properties measurements revealed that such phosphates contain high proportion of acidic and basic sites with same weak strength. Furthermore, correlation between selectivity to acrylic acid and the acid–base balance was clearly established: it was 50% for balance close to 1 and decreased increasing this parameter. Because of poor thermal stability of lactic acid, we then focused on the ethyl lactate conversion. Selectivities in dehydration products were much higher with a maxima of 87% at 15% conversion. However, the catalysts were less active and stable. The deactivation can be inhibited adding water in the gas phase. Surface characterization of catalysts showed that catalytic activities are correlated with the P/M ratio and revealed the presence of an hydroxylated amorphous phase corresponding to mono / dihydrogenophosphates or polyphosphates. The P-OH species present in these phases are consumed or modified for both reactants suggesting that they are active sites. Finally, NH3-TPD measurements followed by DRIFT suggested that acid base pairs (M2+ and P-O-) are then probed. Such pairs would constitute the adsorption site of lactic acid which then dehydrate in acrylic acid by an E2 mechanism

Ultra-cold atoms in optical lattices provide a versatile and robust platform to study fundamental condensed-matter physics problems and have applications in quantum optics as well as quantum information processing. For many of these applications, Rydberg atoms (atoms excited to large principal quantum numbers) are ideal due to its long coherence times and strong interactions. However, one of the pre-requisite for such applications is identical confinement of ground state atoms with Rydberg atoms. This is challenging for conventionally used alkali atoms. In this thesis, I discuss the potential of using alkaline-earth Rydberg atoms for many-body physics by implementing simultaneous trapping for the relevant internal states. In particular, I consider a scheme for generating multi-particle entanglement and explore charge transport in a one dimensional atomic lattice.

The main focus of the present work was the Ge-rich part of the binary Ba – Ge system, in which by inspecting the behavior of the clathrate-I Ba8Ge43 under pressure, several new phases were found. The new phases in this system have the following compositions: BaGe3 (with two modifications), BaGe5, BaGe5.5 and BaGe6, therefore they are quite close in composition range: 75% - ~85% at. Ge. Concerning the conditions required for the synthesis of each phase, several combinations of temperature and pressure were employed in order to find a stability range. It was possible to establish such a formation range for all phases. In some cases two phases were found for a given conditions and in many other cases three or more phases were found to coexist. Thus, the stability range of pressure and temperature for single phase formation turned out to be very narrow. By inspecting of some structural features, for instance the interatomic distances, it is found that the average of the Ge – Ge distances change in line with the composition, i.e. the shorter contacts belong to BaGe6 while the longer distances are present in BaGe3 (both modification). An opposite trend is observed for the calculated density of each phase (neglecting the tI32 form of BaGe3): the lower density is found for BaGe3 and the denser compound is found to be BaGe6. Of course this is not coincidence, since due to the Ge content, BaGe6 has the largest molar mass. Similarly, by examining the density as a function of the interatomic distance. In such case, the denser compound is characterized by shorter Ge – Ge contacts, while the less dense phase holds the longest Ge – Ge contacts. This is in agreement with the building motifs within each crystal structure: columns in BaGe3 (open framework) passing through layers in BaGe5, ending in a three-dimensional network (closed framework) in BaGe6.

This Thesis describes the synthesis and characterisation of new alkaline earth- and rare earth-transition metal complexes. Experimental and computational studies were performed to investigate the structure and bonding in these complexes. Their reactivity was also studied. Chapter 1 introduces metal-metal bonded complexes and current alkaline earth- and rare earth-transition metal bonded complexes. Chapter 2 describes experimental and computational studies of new alkaline earth- and lanthanide-Fe complexes possessing the [CpFe(CO)2]- anion. Chapter 3 presents experimental studies of the reduction of Fe3(CO)12 with Ca. Chapter 4 describes experimental and computational studies of new alkaline earth- and lanthanide-Co complexes containing the [Co(CO)3(PR3)]- anion. Chapter 5 presents full experimental procedures and characterising data for the new complexes reported. Appendix describes the attempted synthesis of [Ca{CpRu(CO)2}2(THF)x]y and study by DFT of [CaRp2(THF)3]2 CD Appendix contains .cif files for all new crystallographically characterised complexes described.

This Thesis describes the synthesis and characterisation of new Main Group and Rare Earth alkyl, amide, alkoxide and borohydride complexes and their use as catalysts for the ring-opening polymerisation (ROP) of &epsilon;-caprolactone and rac-lactide. <strong>Chapter 1</strong> introduces ROP from an industrial and academic perspective, as well as polymer characterisation techniques. A literature review is given, with an emphasis placed on Main Group catalysts. <strong>Chapter 2</strong> describes the synthesis and characterisation of new homo- and hetero-scorpionate Main Group complexes. An introduction to homo- and hetero-scorpionate ligands is given, as well as a discussion of the ε-caprolactone and rac-lactide ROP activity displayed by the new complexes. <strong>Chapter 3</strong> describes the synthesis and characterisation of new neutral and cationic Main Group borohydride complexes supported by the tris(pyrazolyl)methane and tris(pyrazolyl)hydroborate ligands. A review of borohydride complexes is also given. The ε-caprolactone and rac-lactide ROP activity shown by the complexes presented is also discussed. <strong>Chapter 4</strong> describes the synthesis and characterisation of new mono- and di-cationic yttrium complexes supported by the tris(pyrazolyl)methane and triazacyclononane ligands. An introduction to the synthesis of neutral and cationic Rare Earth complexes is given. An overview of immortal ROP is also provided. The activity of the new complexes towards the immortal ROP of rac-lactide is also discussed. <strong>Chapter 5</strong> contains experimental details and characterising data for the new complexes reported in this thesis. CD Appendix</strong> contains .cif files for all of the new crystallographically characterised complexes.