Investigation of Ligand Field Modifications on Lanthanide(III) Complexes: Structure, Magnetism and Optical Properties

Diese Arbeit befasst sich mit Lanthanoidkomplexen, ihrer Struktur, ihrem Magnetismus und ihren optischen Eigenschaften. Scandium, Yttrium und die Lanthanoide von Lanthan bis Lutetium sind die Elemente der Seltenen Erden. Sie weisen im Allgemeinen ähnliche chemische und physikalische Eigenschaften auf. Beginnend mit Cer und endend mit Lutetium werden die 4f-Orbitale nach und nach gefüllt. Diese Elemente nehmen im Allgemeinen eine stabile Oxidationsstufe von +3 an. Der erste Schwerpunkt dieser Arbeit liegt auf den molekularen Strukturen von Lanthanoidkomplexen. Es wurde ein Ligandensystem entworfen, das leicht modifiziert werden kann, um zu verstehen, wie sich Änderungen in der Struktur des Liganden auf die Geometrie der resultierenden Komplexe auswirken. Die Änderungen am Liganden wurden bewusst klein gehalten, um die Auswirkungen dieser Änderungen besser zu verstehen. Der zweite Schwerpunkt liegt auf den magnetischen Eigenschaften dieser Komplexe. Da Dy(III)-Ionen aufgrund ihrer Kombination aus einem starken uniaxialen magnetischen Moment und einem hohen mJ-Wert von ±15/2 am häufigsten für Lanthanoid-basierte Einzelmolekülmagnete (SMMs) verwendet werden, liegt der Schwerpunkt dieser Arbeit auf der Synthese von Dy(III)-Komplexe. Magnetische Untersuchungen von fünf zweikernigen Dy(III)-Verbindungen wurden an einem SQUID-Magnetometer durchgeführt und AC-Messungen wurden durchgeführt, um das SMM-Verhalten besser zu verstehen. Drei der vorgestellten Verbindungen zeigen schnelle Relaxationsprozesse und eine zeigt kein SMM-Verhalten. Andererseits erweist sich die Verbindung [Dy2(L2)2(CH3COO)4(CH3OH)2] (6) als ausgezeichnetes SMM. Der dritte Schwerpunkt liegt auf den optischen Eigenschaften solcher Lanthanoidkomplexe. Umfangreiche Messreihen wurden zum optischen Absorptionsverhalten des Liganden 2,6-(1-(2-(1H-Benzimidazol-2-yl)hydrazineyliden)ethyl)pyridin (HL7) und seiner Komplexe mit allen Lanthanoidionen durchgeführt

The Polytope Formalism: isomerism and associated unimolecular isomerisation

This thesis concerns the ontology of isomerism, this encompassing the conceptual frameworks and relationships that comprise the subject matter; the necessary formal definitions, nomenclature, and representations that have impacts reaching into unexpected areas such as drug registration and patent specifications; the requisite controlled and precise vocabulary that facilitates nuanced communication; and the digital/computational formalisms that underpin the chemistry software and database tools that empower chemists to perform much of their work. Using conceptual tools taken from Combinatorics, and Graph Theory, means are presented to provide a unified description of isomerism and associated unimolecular isomerisation spanning both constitutional isomerism and stereoisomerism called the Polytope Formalism. This includes unification of the varying approaches historically taken to describe and understand stereoisomerism in organic and inorganic compounds. Work for this Thesis began with the synthesis, isolation, and characterisation of compounds not adequately describable using existing IUPAC recommendations. Generalisation of the polytopal-rearrangements model of stereoisomerisation used for inorganic chemistry led to the prescriptions that could deal with the synthesised compounds, revealing an unrecognised fundamental form of isomerism called akamptisomerism. Following on, this Thesis describes how in attempting to place akamptisomerism within the context of existing stereoisomerism reveals significant systematic deficiencies in the IUPAC recommendations. These shortcomings have limited the conceptualisation of broad classes of compounds and hindered development of molecules for medicinal and technological applications. It is shown how the Polytope Formalism can be applied to the description of constitutional isomerism in a practical manner. Finally, a radically different medicinal chemistry design strategy with broad application, based upon the principles, is describe

Synthesis, crystal structures and molecular modelling of rare earth complexes with bis(2-pyridylmethyl)amine: aim topological analysis and ligand conformation search

Eight rare earth complexes with bis(2-pyridylmethyl)amine (DPA) were synthesised and recrystallised, under air-sensitive or low moisture conditions. The crystal structures were successfully determined, via SC-XRD, and the asymmetric units of five complexes (1, 3, 5, 6 and 7) were submitted for DFT molecular modelling calculations, which involved geometry optimisation and frequency calculations. The neutral complexes obtained were bis(bis(2-pyridylmethyl)amine)-trichloro-lanthanum(III) [LaCl3(DPA)2] (1), bis(bis(2-pyridylmethyl)amine)-trichloro-cerium(III)) [CeCl3(DPA)2] (2), bis(μ2-chloro)-diaqua-tetrachloro-bis(bis(2-pyridylmethyl)amine)-di-praseodymium(III) [PrCl2(μ-Cl)(DPA)(OH2)]2 (3) and bis(μ2-methoxo)-bis(bis(2-pyridylmethyl)amine)- tetrachloro-di-dysprosium(III) [DyCl2(μ-OCH3)(DPA)]2 (4). The cationic complexes obtained in this study were dichloro-bis(bis(2-pyridylmethyl)amine)- neodymium(III) chloride methanol solvate [NdCl2(DPA)2]Cl·CH3OH (5), dichloro-bis(bis(2- pyridylmethyl)amine)-dysprosium(III) chloride methanol solvate [DyCl2(DPA)2]Cl·CH3OH (6), dichloro-bis(bis(2-pyridylmethyl)amine)-yttrium(III) chloride methanol solvate [YCl2(DPA)2]Cl·CH3OH (7) and dichloro-bis(bis(2-pyridylmethyl)amine)-lutetium(III) chloride methanol solvate [LuCl2(DPA)2]Cl·CH3OH (8). The ‘Quantum theory of atoms in molecules’ approach was used to investigate the electron density topology, primarily in order to investigate the hydrogen and coordination bonds for three of the eight complexes. Two of the neutral complexes contain the ‘early’ rare earth elements lanthanum and praseodymium and one cationic complex contains the ‘late’ lanthanide element dysprosium. Noncovalent interaction analysis was also performed on the aforementioned complexes in order to gain a deeper understanding of the intra-molecular stereo-electronic interactions. Spin density analysis was used to investigate the distribution of unpaired electron density at and around the metal centres of the aforementioned paramagnetic Pr- and Dy-complexes. A ligand conformation search for DPA was undertaken and 32 low energy conformers were identified and their relative energies were determined using two DFT functionals, namely M06 and M06-2X

Functional molecular materials: supramolecular networks and coordination polymers with optical and/or magnetic properties

El camp dels materials moleculars atrau l’atenció de molts científics degut al gran potencial de la química molecular en el disseny de materials amb un ajust precís de les seues propietats. Els dos projectes tractats en aquesta tesi representen dos temes que destaquen en aquesta àrea, materials de transició d’espín i polímers de coordinació amb propietats òptiques i/o magnètiques, gràcies al seu significant progrés i ràpid desenvolupament en els últims anys. La primera part d’aquesta tesi es basa en l’ús d’enllaços d’hidrogen en el disseny de xarxes multifuncionals de ferro(II) amb transicions d’espín abruptes. El capítol 1 és una introducció a aquest tema des de la perspectiva dels complexos [Fe(bpp)2]2+ (bpp = 2,6-bis(pirazol-3-il)piridina). El capítol 2 mostra un anàlisi comparatiu de les sals [Fe(bpp)2]2+ construïdes amb l’anió flexible adipat o l’anió rígid tereftalat com acceptors d’enllaç d’hidrogen. Aquest estudi mostra la rellevància de la rigidesa dels anions en les propietats magnètiques de les xarxes resultants. A més a més, dos materials anhidres amb diferents comportaments magnètics i grau de cristal·linitat han sigut obtinguts per al derivat basat en l’anió adipat en funció del tractament tèrmic emprat. El capítol 3 descriu la incorporació d’anions acèntrics mononegatius, la qual cosa permet l’optimització de la connectivitat dels enllaços d’hidrogen. Concretament, l’ús de l’anió isonicotinat ha permés la construcció d’una xarxa cristal·lina acèntrica de tipus diamant en base a un senzill disseny per sintetitzar xarxes acèntriques. La fase anhidra d’aquest material exhibeix una transició de fase entre dos estructures ferroelèctriques en el mateix rang de temperatura en el que s’observa la transició d’espín. L’ús de l’anió isonicotinat N-òxid ha donat lloc a l’aïllament de dos sals que presenten transicions d’espín abruptes i que desencadenen noves redistribucions estructurals en resposta a l’aplicació de llum o a un canvi de temperatura: una isomerització d’un enllaç d’hidrogen que involucra a un carboxilat i un desplaçament de protó entre dos anions que formen un enllaç d’hidrogen molt fort. Experiments isotòpics i dades de difracció de neutrons revelen una gran influència dels enllaços d’hidrogen sobre les propietats de transició d’espín. Específicament, els enllaços d’hidrogen presents en la segona esfera de coordinació del ferro són més curts en l’estat de baix espín en comparació a aquelles distàncies mesurades en l’estat d’alt espín. La segona part d’aquesta tesi se centra en la síntesi i caracterització de polímers de coordinació basats en una nova família de lligands politòpics segmentats per triples enllaços. L’objectiu d’aquest treball és millorar l’estabilitat en aigua i a valors de pH extrems dels compostos de coordinació actuals mitjançant l’ús del grup funcional quelant picolinat. El capítol 4 conté un breu resum sobre les aproximacions sintètiques i aplicacions d’aquest tipus de materials. El capítol 5 descriu la síntesi (reaccions d’acoblament tipus Sonogashira) i caracterització de la nova família de lligands. La metodologia sintètica, propietats magnètiques, tèrmiques, estructurals i luminescents dels compostos cristal·lins construïts a partir d’aquests lligands i ions divalents es descriuen en el capítol 6. En canvi, el capítol 7 descriu el progrés assolit amb ions lantànids trivalents. Els experiments de detecció revelen que els derivats de Zn i Eu poden ser selectivament emprats com a sondes luminescents en medi aquós per tal de detectar ions Fe3+ i nitrobenzè gràcies a un descens dramàtic en la seua senyal luminescent. Finalment, el capítol 8 conté les conclusions generals d’aquesta tesi doctoral.The field of molecular materials attracts the interest of many scientists due to the huge potential of molecular chemistry in materials design and fine tuning of materials properties. The two different projects addressed in this thesis represent two topics that stand out in this area, spin crossover (SCO) compounds and coordination polymers with optical and/or magnetic properties, due to their significant progress and rapid development in the last years. The first part of this thesis is based on the use of hydrogen bonds in the design of multifunctional iron(II) supramolecular networks with abrupt spin transitions. Chapter 1 is an introduction to this topic from the perspective of [Fe(bpp)2]2+ complexes (bpp = 2,6-bis(pyrazol-3-yl)pyridine). Chapter 2 shows a comparative analysis of [Fe(bpp)2]2+ salts with the flexible adipate or the rigid terephthalate as hydrogen bond acceptors. This study shows the relevance of the rigidity of the anions in defining the magnetic properties. Moreover, two anhydrous materials with distinct magnetic behaviour and degree of crystallinity were obtained for the adipate derivative depending on the thermal treatment used. Chapter 3 describes the incorporation of acentric mononegative anions which enables the optimisation of the hydrogen bond connectivity. In particular, the use of the isonicotinate linker has allowed the construction of an acentric diamond-like crystal lattice, following a basic design for acentric networks. The anhydrous phase of this material exhibits a phase transition between two ferroelectric structures in the same temperature range in which the spin crossover is observed. The employment of the isonicotinate N-oxide anion has led to the isolation of two salts that present abrupt spin transitions triggering novel structural rearrangements that respond towards light irradiation or temperature change: a supramolecular linkage (H-bond) isomerisation involving a carboxylate moiety and a proton displacement between two anions that form a short strong hydrogen bond. Isotopic experiments and neutron diffraction data reveal that hydrogen bonding influences the spin crossover properties. Specifically, hydrogen bonds in the 2nd iron coordination sphere are found to be shorter for the low-spin species in comparison to those in the high-spin state. The second part of this thesis relies on the synthesis and characterisation of coordination polymers based on a novel family of ethynyl-bridged polytopic ligands. The aim of this work is to improve the stability in water and at extreme pH values of current coordination compounds through the use of the chelating picolinate functional group. Chapter 4 contains a brief summary about synthetic approaches and applications of these materials. Chapter 5 describes the synthesis (Sonogashira-type cross-coupling reactions) and characterisation of the novel family of ligands. The synthetic methodology, thermal, structural, luminescent and magnetic properties of crystalline compounds constructed from these ligands and divalent ions are described in Chapter 6. Instead, Chapter 7 gathers the progress achieved with trivalent lanthanide ions. Sensing experiments reveal that Zn and Eu derivatives can be selectively used as luminescent probes in aqueous medium towards Fe3+ and nitrobenzene detection through luminescent quenching. All these polymers are remarkably robust in water within a wide pH range. Finally, Chapter 8 compiles the general conclusions of the present dissertation

The role of heteroatoms during graphitisation: first principle calculations

Graphite is widely used in modern industry, particularly in nuclear power generation in the UK. Understanding its formation is important for economical and safety reasons. The process to turn carbon materials into graphite by heat treatment is called the graphitisation process. It is the transformation of amorphous carbon, through a 2D turbostratic carbon intermediate, into 3D ordered layers of graphite. While many manufacturing processes have been established and many authors have contributed to understanding the important stages of graphitisation, the chemistry involved is not fully understood. It appears that impurities found in precursors can have a direct impact on the final graphite obtained. The following work is an investigation of the role played by these heteroatoms during the graphitisation process. Using density functional theory (DFT), calculations on possible mechanisms involved in the graphitisation process are investigated. However, the initial stages contain complex and poorly defined chemistry, so we have chosen to avoid this area, even though factors such as the C:H:O ratios are clearly important. Instead, this work is focussed on the latter stages of graphitisation in order to better understand the ordering processes to obtain graphite (and their inverse disordering, insofar as it is relevant to radiation damage). In this way it is still possible to invoke standard concepts in the physics and chemistry of defects in crystals. If there is too much disorder, and the system is close to amorphous in nature, complexity would overwhelm the project. The descriptions of an amorphous material with a little extra order would be much more difficult than the descriptions of a crystal with some disorder. For this reason, we have focussed on the heteroatoms which endure until the later stages of graphitisation, boron and sulphur, and also on turbostratic graphite, where calculations of interlayer separation as a function of relative rotation of a layer and of its neighbours are described. We find for sulphur that it can open up folds in graphite, forming very stable sulphur decorated edges. In dislocation terms, this could be the beginning of the dissociation of a perfect prismatic edge dislocation. An edge dislocation is described as an added half plane. If the plane is a bilayer graphene terminating in a fold, the dislocation is perfect. If the plane is a single graphene the dislocation is ‘partial’. Importantly two partial dislocations have lower elastic energy than the perfect, so dissociation is important in stabilising the structure. For boron, we show how it can pin twist boundaries, preventing slip and suggest that radiation damage can achieve the same effect through vacancies. The mechanism does not appear to involve cross-linking bonds and provides a good explanation for the variations in C44 between different graphites and different methods of measurement. Furthermore, we show that B can aid in the removal of twist boundaries by pushing up their formation energy with respect to AB graphite

Structure and interaction studies of beta-amyloid in the search for new lead compounds for the treatment of Alzheimer’s disease

Alzheimer’s disease (AD) is the most devastating neurodegenerative disorder that effects the aging population worldwide. In this study three hypotheses of AD are explored, the β-amyloid cascade hypothesis, the β-amyloid metal binding hypothesis and the oxidative stress hypothesis are explored. In the first case compounds from the South African Natural Compounds Database (SANCDB) are docked to models of β-amyloid fibrils and the properties of these fibrils under pulling simulations are compared to a known small molecule disruptor of β-amyloid, wgx-50. In these simulations SANCDB compounds are identified that disrupt β-amyloid in a similar manner to wgx-50. In these simulations the disruption to the free energy of binding of chains to the fibrils is quantified. For metal binding and oxidative stress hypotheses, problems in simulation arise due to only fragments of β-amyloid being present in the Research Collaboratory for Structural Bioinformatics protein data bank (RCSB PDB), as determined from NMR experiments. In this work, β-amyloid is set up under periodic boundary conditions to simulate a fibril under reasonable computational time. Within these periodic boundary conditions, β-amyloid has been solvated in copper and zinc rich environments and diffusion of these metals around the fibrils has been explored. The localization of these metals (in simulation only using van der Waal’s and electrostatic terms) around the fibril has led us to explore other possible metal binding sites. Metal bound to the infinite fibril has been optimized at the QM/MM level and some of the reactive oxygen species in the presence of the fibril are quantified

The contemporary visualization and modelling technologies and the techniques for the design of the green roofs

The contemporary design solutions are merging the boundaries between real and virtual world. The Landscape architecture like the other interdisciplinary field stepped in a contemporary technologies area focused on that, beside the good execution of works, designer solutions has to be more realistic and “touchable”. The opportunities provided by Virtual Reality are certainly not negligible, it is common knowledge that the designs in the world are already presented in this way so the Virtual Reality increasingly used. Following the example of the application of virtual reality in landscape architecture, this paper deals with proposals for the use of virtual reality in landscape architecture so that designers, clients and users would have a virtual sense of scope e.g. rooftop garden, urban areas, parks, roads, etc. It is a programming language that creates a series of images creating a whole, so certain parts can be controlled or even modified in VR. Virtual reality today requires a specific gadget, such as Occulus, HTC Vive, Samsung Gear VR and similar. The aim of this paper is to acquire new theoretical and practical knowledge in the interdisciplinary field of virtual reality, the ability to display using virtual reality methods, and to present through a brief overview the plant species used in the design and construction of an intensive roof garden in a Mediterranean climate, the basic characteristics of roofing gardens as well as the benefits they carry. Virtual and augmented reality as technology is a very powerful tool for landscape architects, when modeling roof gardens, parks, and urban areas. One of the most popular technologies used by landscape architects is Google Tilt Brush, which enables fast modeling. The Google Tilt Brush VR app allows modeling in three-dimensional virtual space using a palette to work with the use of a three dimensional brush. The terms of two "programmed" realities - virtual reality and augmented reality - are often confused. One thing they have in common, though, is VRML - Virtual Reality Modeling Language. In this paper are shown the ways on which this issue can be solved and by the way, get closer the term of Virtual Reality (VR), also all the opportunities which the Virtual reality offered us. As well, in this paper are shown the conditions of Mediterranean climate, the conceptual solution and the plant species which will be used by execution of intensive green roof on the motel “Marković”

CHEMICAL BONDING IN METAL-ORGANIC SYSTEMS: NATURE, STRUCTURES AND PROPERTIES

The main purpose of my thesis is the application of theoretical and experimental methods for the study of the nature of the chemical bond and its effect on structures and properties in organome-tallic systems, like Metal Carbonyl Clusters and Coordination Polymers (CPs) featuring, in some of the cases under study, intrinsic porosity (in the following, PCP for Porous Coordination Polymers or MOFs for Metal-Organic Frameworks). Concerning metal clusters, we worked on high nuclearity metal carbonyl clusters, and, particularly, on those featuring semi-interstitial atoms. The chemical bonding and the related properties in these peculiar class of molecules are still a matter of discussion in the scientific community. Concerning the class of Metal-organic Frameworks, we focused our attention on azolate-based ligands as building blocks for the synthesis of MOFs, looking at their possible future application as ultra-low dielectric constant materials in electronic devices. Finally, we investigated the structural behavior of Coordination Polymers at non-ambient condition (high pressure, in the order of 0-8 GPa), to induce new interactions and attitudes like electric conductivity. This research required the application of a bunch of theoretical tools, assisted by accurate single crystal X-ray diffraction experiments in standard and not-standard conditions (low temperature and high pressure). Moreover, a protocol for comparing different energy decomposition methods was developed and successfully applied to investigate the bonding nature in simple and complex systems

The benefits of an additional practice in descriptive geomerty course: non obligatory workshop at the Faculty of Civil Engineering in Belgrade

At the Faculty of Civil Engineering in Belgrade, in the Descriptive geometry (DG) course, non-obligatory workshops named “facultative task” are held for the three generations of freshman students with the aim to give students the opportunity to get higher final grade on the exam. The content of this workshop was a creative task, performed by a group of three students, offering free choice of a topic, i.e. the geometric structure associated with some real or imagery architectural/art-work object. After the workshops a questionnaire (composed by the professors at the course) is given to the students, in order to get their response on teaching/learning materials for the DG course and the workshop. During the workshop students performed one of the common tests for testing spatial abilities, named “paper folding". Based on the results of the questionnairethe investigation of the linkages between:students’ final achievements and spatial abilities, as well as students’ expectations of their performance on the exam, and how the students’ capacity to correctly estimate their grades were associated with expected and final grades, is provided. The goal was to give an evidence that a creative work, performed by a small group of students and self-assessment of their performances are a good way of helping students to maintain motivation and to accomplish their achievement. The final conclusion is addressed to the benefits of additional workshops employment in the course, which confirmhigherfinal scores-grades, achievement of creative results (facultative tasks) and confirmation of DG knowledge adaption