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In this thesis the study of electronic, geometrical, elastic and vibrational properties of a range of prototypical iron- and lead-based materials has been addressed using the density functional theory and inter- atomic potentials. It has been proven that both quality and quantity of the correlation included in classical DFT-LSDA and -GGA func- tionals is not sufficient to treat strongly correlated materials as well as layered solids, where van der Waals' forces dominate. Owing to these considerations appears clear the need to go beyond traditional DFT to further improve the description of materials in which the correlation plays an important role. The electronic, the geometrical and the magnetic properties of the corundum-type a - Fe203 have been determined and compared within the PP-PW and the LCAO frameworks using DFT + U and HYBRID functionals. a - Fe203 is correctly described as a charge-transfer insulator, when the optimised value for the U (3.75 eV) or the 40% of HF exchange is employed. Instead B3LYP predicts a - Fe203 as a Mott insulator, in agreement with pure DFT-GGA functionals, such as PW91, PBE and BLYP. The intensities and symmetries of the Fe(3d) partial density of states, in the conduction band, of the hematite were found in agreement with with the experimental Fe K-edge XANES. spectrum. The doping of hematite with several alkali-earth metals was also investigated. All structural possibilities have been explored employing the program OASIS developed in our laboratory. Here a combinatorial inter-atomic potential strategy to confine interesting candidates from a large populations of defective solids has been also proposed. The prediction of their properties is then redirected to more accurate, but expensive, computational techniques such as DFT. With this method experimental X-ray diffraction patters for hematite doped with low concentrations of Mg were correctly reproduced. It was found that doping with low concentrations (6.25%) of Mg2+ is not a spontaneous process for hematite, i. e. magnesium is not soluble into hematite. On the other hand, the larger alkali-earth ions (Ca, Sr and Ba) all showed high solubility in a - Fe203. Several other doping mechanisms were also investigated. The description of metallic lead and its (1 1 1) Pb surface were also investigated using DFT. This latter was successfully employed to study the adsorption of S2 molecule in several configurations. According to the BE measured the tilted model is found to be far most stable than the other models: bridge ~ ccp » top ~ hcp. For the first three models the BE values ensure the incipient chemisorption of S2 involving an electron-transfer surface --> molecule. This would confirm the spontaneous formation of PbS a common lead mineral. PbO is a prototype of layered material where dispersion forces determined the stability of the layered structure. DFT has been largely shown to be inappropriate in the description of low-densities areas, responsible of dispersion forces, with traditional GGA-DFT. Here the empirical Grimme's was adapted for the description of periodic systems such as PbO. The effect of this empirical correction on the total energy as well as the gradient was employed to improve the description of the PbO geometry, IR/Raman frequencies and elastic constants which were found in excellent agreement with the experimental values found in the literature

This thesis concerns the synthesis and characterisation of new iron(II) and iron(III) complexes that exhibit spin transitions and examines their magnetic behaviour.

This thesis describes the synthesis and characterisation of a series of novel a-diimine Fe2 and Fe3 complexes and explores the controlled radical polymerisation behaviour of the Fe2 complexes.

Πολλοί από τους τομείς της επιστημονικής έρευνας, όπως χημεία, ενέργεια, βιομηχανία και ιατρική χρησιμοποιούν τη νανοτεχνολογία, με στόχο την παρασκευή υλικών, με καλύτερες και πιο εξειδικευμένες ιδιότητες σε σχέση με τα συμβατικά υλικά του μακρόκοσμου. Οι νανοσφαίρες λόγω των ποικίλων ιδιοτήτων που παρουσιάζουν, όπως οπτικές, μηχανικές, ηλεκτρικές κ.α., μπορούν να χρησιμοποιηθούν σε διάφορους τομείς της καθημερινής μας ζωής με μεγαλύτερο ενδιαφέρον στον τομέα της υγείας. Η παρούσα ερευνητική εργασία πραγματοποιήθηκε με στόχο τη σύνθεση και τη μελέτη νανοσφαιρών οξειδίων του σιδήρου. Πιο συγκεκριμένα παρασκευάσθηκαν νανοσφαίρες αιματίτη (α – Fe2O3) και μαγγεμίτη (γ – Fe2O3) και μελετήθηκαν οι μαγνητικές τους ιδιότητες. Στο πρώτο κεφάλαιο παρουσιάζεται μία εισαγωγή – ιστορική αναδρομή στο χώρο της νανοτεχνολογίας και των νανοσφαιρών. Γίνεται επίσης αναφορά στους τρόπους σύνθεσης των νανοσφαιρών και αναφέρονται εν συντομία κάποιες ιδιότητες και εφαρμογές αυτών. Στο δεύτερο κεφάλαιο αναφέρονται κάποιες βασικές έννοιες οι οποίες είναι απαραίτητες για την κατανόηση των ταχνικών που θα χρησιμοποιηθούν. Παρουσιάζονται αναλυτικά οι τρόποι με τους οποίους πραγματοποιείται η σύνθεση των νανοσφαιρών και περιγράφονται αναλυτικά, η μέθοδος λύματος – πηκτής (sol – gel) και η τεχνική του πολυμερισμού. Στο τρίτο κεφάλαιο αναφέρονται τα αντιδραστήρια καθώς επίσης και οι πειραματικές μέθοδοι που χρησιμοποιήθηκαν για το χαρακτηρισμό των νανοσφαιρών και τη μελέτη των ιδιοτήτων τους. Αναφέρονται επίσης τα όργανα που χρησιμοποιήθηκαν καθώς επίσης και οι βασικές αρχές λειτουργίας αυτών. Στο τέταρτο κεφάλαιο περιγράφεται αναλυτικά η πειραματική διαδικασία που πραγματοποιήθηκε και γίνεται συζήτηση των αποτελεσμάτων. Τέλος στο πέμπτο κεφάλαιο ανγράφονται τα συμπεράσματα και αναφέρονται μελλοντικοί στόχοι. / Nanotechnology is the study of the control of matter on an atomic and molecular scale and it’s main objective is the manufacture of new materials with better and more sophisticated properties. Nanotechnology is used in many different sciences like chemistry, physics and most of all in medicine. Nanospheres exhibit many diverse properties (electrical, optical etc) which render them the best solution for application such as drug delivery systems, Magnetic Resonance Imaging (MRI) agents, hyperthermia etc. The present work deals with the synthesis and characterization of magnetic nanospheres and more specifically in the study of magnetic properties of hematite (α – Fe2O3) and maghemite (γ – Fe2O3). The first chapter starts with a short introduction for nanospheres and nanotechnology . It reports also a quick historical review and some lines about new generation nanospheres, it’s properties and it’s applications. In the second chapter, polymerization and sol – gel techniques are described analytically. In the third chapter, reactants and experimental methods are described as well as some basic principles of the methods that were used to characterize the samples. The fourth chapter is the results and discussion session. Finally in the fifth chapter some conclusions and future targets are reported.

Les diverses perovskites de strontium-fer présentent de très fortes corrélations entre la structurecristalline et les phénomènes d’ordre de lacunes d’oxygènes, de charge, de spin et d’orbitales. Danscette thèse, nous avons réalisé une étude systématique des relations entre les ordres de charges etles ordres de spins selon les différents environnements cristallographiques rencontrés pour lescations Fe3+ et Fe4+ dans la phase Sr4Fe4O11, pour le cation Fe3+ dans les phases Sr3Fe2O6 et Sr2Fe2O10et pour le cation Fe2+ dans la phase SrFeO2. Les synthèses des phases polycristallines furent réaliséesvia des voies « solide » ou « sol-gel » en complément de la synthèse de cristaux préparés à l’aide d’unfour à image à fusion de zone verticale pour les phases Sr4Fe4O11 et Sr2Fe2O10. La qualité cristalline etchimique des oxydes fut contrôlée par diffraction de rayons X sur poudre et spectroscopieMössbauer alors que l’étude de la structure électronique de chaque phase a été réalisée à l’aide despectroscopie d’absorption de rayons X. Finalement, les structures magnétiques des phases Sr3Fe2O6et Sr4Fe4O11 sont aussi présentées. / The relationship of the crystallographic, magnetic, and electronic structure have long been of highinterest in research. Strontium iron oxides have structural, charge, spin, and orbital degrees offreedom, and thus give rich information to study for the condensed matter scientists. In this thesis,we have systematically studied the strontium iron oxides based on the freedom of the iron charge:Fe3+ and Fe4+ mixed valence compound SrFeO2,75 , Fe3+ compound Sr3Fe2O6 and SrFeO2,5 with differentcoordination around Fe3+ and Fe2+ compound SrFeO2. The synthesis of the polycrystalline compoundsare through either solid state reaction or sol-gel method. Single crystals of SrFeO2,75 and SrFeO2,5have been prepared by floating zone furnace. The purity of all the compounds is checked by lab x-raydiffraction and Mössbauer spectroscopy. Electronic structures have been studied by x-ray absorptionspectroscopy for all these compounds. Special efforts have been used to investigate the magneticstructure of SrFeO2,75 and Sr3Fe2O6 .