Dissertations / Theses on the topic 'Ligand field theory'

The ortho metallation of some aromatic ring systems has been investigated in regard to the influence of several types of phosphorus-centred directing groups upon the reactivity, regioselectivity, and utility in later synthetic elaboration. The metallation step allows derivatisation in several useful ways, offering several routes to the synthesis of novel chiral ditertiary phosphines. Thus, an ortho lithiation of N,N,N',N'-tetramethyl-P-phenylphosphonic diamide (10) led to the interesting primary phosphine, 2-(diphenylphosphino)phenylphosphine (14), after elaboration of the phosphonic diamide directing group. This primary phosphine undergoes an unprecedented facile phenyl group exchange process between its two phosphorus atoms, upon di-lithiation of the primary phosphorus centre. The primary phosphorus centre of (14) has been elaborated in several ways to yield new ditertiary phosphines. The alkylation of this centre in the copper(I) chelate complex has been investigated in several directions. In another direction, (14) has been chemically elaborated to give a new hybrid chiral ditertiary phosphine ligand, "SemiPHOS", containing both a chiral phospholane ring and an adjacent diphenylphosphino group. SemiPHOS has been obtained in optically pure forms by a stereoselective synthesis and, independently, by a resolution procedure on its racemate. The molecular design of SemiPHOS was devised such that, when chelated to a metal atom, a subtle steric interaction appears to allow the chirality of the phospholane ring to influence the neighbouring diphenylphosphino group to adopt a complementary chiral conformation. This idea was tested and evaluated by applying SemiPHOS in catalytic asymmetric hydrogenations of (Z)-a-(Nacylamino) acrylate substrates to produce the R-amino acid precursors. Aryl species lithiated ortho to phosphorus-centred directing groups were coupled oxidatively by a convenient in situ method, to yield biaryl species that could then be elaborated to give biaryl ditertiary phosphine ligands. This method was used to make several atropisomeric chiral ditertiary phosphines.

Aquest treball presenta l’estudi teòric de l’anisotropia magnètica en complexos de metalls de transició, combinant esquemes de càlcul multiconfiguracionals relativistes amb derivacions analítiques basades en la teoria del camp del lligand, el que permet racionalitzar a través de conceptes senzills els resultats quantitatius obtinguts i interpretar les propietats estudiades. Es desenvolupa primer una metodologia per extreure els paràmetres d’anisotropia en complexos mononuclears de metalls de transició. El mètode es basa en assignar els resultats d’un càlcul ab initio d’alt nivell a un Hamiltonià model mitjançant la teoria d’Hamiltonians efectius. Aquesta metodologia s’aplica a complexos de Ni(II), Co(II) i Mn(III) i es comprova que és aplicable de forma general a complexos mononuclears. S’estén després la metodologia a complexos binuclears, pels quals l’Hamiltonià model usualment utilitzat té una base menys rigorosa. L’Hamiltonià efectiu obtingut per un complex binuclear de Ni(II) introdueix una nova parametrització amb termes addicionals de les interaccions anisotròpiques en sistemes polinuclears. Es tracta d’un procediment universal que proporciona valors precisos i a més és capaç de contrastar la consistència interna dels Hamiltonians models existents. Per racionalitzar les correlacions magnetoestructurals dels paràmetres d’anisotropia en complexos de Ni(II) i Mn(III), es descriuen els mecanismes electrònics bàsics en base a consideracions de la teoria del camp del lligand. Aquest procediment proporciona regles senzilles per augmentar l’anisotropia, que poden ser aplicades en el disseny de nous materials. Finalment, s’estudien les interaccions anisotròpiques simètriques i antisimètriques en compostos binuclears de Cu(II), interaccions de gran importància per explicar les propietats d’alguns materials d’interès tecnològic. Les interaccions antisimètriques s’extreuen a partir de càlculs ab initio d’estructura electrònica per primer cop en aquest treball. Es concentra l’atenció d’aquesta part en dos sistemes: el conegut complex binuclear de Cu(II) amb quatre ponts acetat, i l’òxid de coure en el que recentment s’ha evidenciat una fase ferroelèctrica.

Este trabalho dedica-se ao estudo de sistemas luminescentes do tipo hóspede-hopedeiro altamente emissivos. A preparação desses materiais se deu a partir da incorporação de complexos organometálicos (Eu3+ e Ir3+) em matrizes mesoporosas inorgânicas e orgâno-modificadas preparadas via sol-gel. Um complexo de európio foi imobilizado por impregnação úmida nos mesoporos de xerogéis e de materiais derivados da peneira molecular MCM-41, enquanto um complexo-surfactante de irídio foi inserido nos canais do MCM-41 como agente diretor da estrutura durante o processo de síntese. Previamente à incorporação dos centros emissores, as matrizes hospedeiras foram caracterizadas do ponto de vista estrutural, morfológico e óptico. As propriedades fotofísicas do material final foram investigadas e comparadas com aquelas apresentadas pelos complexos em solução. Para o complexo de európio foi realizado uma modelagem de suas propriedades ópticas através da teoria do campo ligante, empregando o modelo de recobrimento simples. Nesse tratamento, a geometria do estado fundamental foi obtida pelo método semi-empírico Sparkle/AM1 e confirmada a partir de um mapeamento criterioso dos fatores de carga. Observou-se que, para as amostras dopadas com o complexo de európio, a modificação da matriz hospedeira com grupos orgânicos só leva a melhoria das propriedades ópticas do material final quando a unidade orgânica substitui grupos silanol. Para o MCM-41 preparado com o complexo-surfactante de irídio, constatou-se que as propriedades fotofísicas do material final são muito superiores àquelas apresentadas pelo complexo em solução.
This work dedicates to the study of highly emissive guest-host luminescent materials prepared by the incorporation of organometallic complexes (of Eu3+ and Ir3+) in inorganic and organically-modified mesoporous hosts, obtained via sol-gel methodology. The europium complex (tris[(4 - (4\' - tert - butylbiphenyl - 4 - yl) - 2,2\' - bipyridine - κ2N,N\' - 6 - carboxylato - κO)] europium(III)) was immobilized, via wet impregnation, in the mesopores of silica xerogels and of MCM-41 derived materials. The iridium surfactant-complex (bis[1 - benzyl 4 - (2,4 - difluorophenyl) - 1H -1,2,3 - triazole](4,4\' diheptadecyl - 2,2\' - bipyridine) iridium(III)) was inserted in the channels of MCM-41 while acting as the structure driving agent (template) during the host synthesis procedure. Prior to the incorporation of the luminescent centers in the host matrices, the latter were characterized from the structural, morphological and optical points of view. The photophysical properties of the final luminescent materials were investigated and compared to those presented by the complexes in solution. Particularly, the properties of the Eu-complex were further analyzed, via ligand field theory, employing the simple overlap model. For this treatment, the geometry of the ground state was obtained by the semiempirical Sparkle/AM1 model and confirmed by mapping out the charge factors. For the Eu-complex loaded materials it was verified that the host matrix surface modification with organic groups only results in improved photophysical properties when the organic units substitute silanol groups. For the case of the MCM-41 loaded with the Ir-surfactant-complex, the photophysical properties were found to be much superior to those presented by the complex in solution.

Nous presentons un ensemble de spectres obtenus par resonance magnetique nucleaire (rmn) du proton dans la phase supraconductrice de deux supraconducteurs organiques de structure voisine : -(bedt-ttf)#2cu(ncs)#2 et -(bedt-ttf)#2cun(cn)#2br. Dans le compose -(bedt-ttf)#2cu(ncs)#2 pour un champ applique perpendiculairement aux couches conductrices nous obtenons, dans la phase mixte, des formes de raie inattendues, tres differentes de celles prevues pour un reseau de vortex abrikosov triangulaire. En particulier, au-dessous d'une temperature t* qui depend de l'intensite du champ, nous observons une raie secondaire qui traduit un ecrantage diamagnetique bien plus important que celui attendu pour un reseau de vortex triangulaire. Nous montrons que ce sont les impulsions de champ radiofrequence qui, en perturbant violemment le reseau de vortex, conduisent a des conditions d'ecrantage particulieres. Une etude de ce phenomene pour des valeurs du champ comprises entre 0. 5 et 1 t montre qu'autour de 0. 82 t l'effet des impulsions de champ radiofrequence est maximal. Nous suggerons que cette valeur correspond a celle du champ de crossover dimensionnel du reseau de vortex. Nous estimons alors l'anisotropie #c/#a#b du compose entre 145 et 160. Le comportement aux basses temperatures de la nouvelle phase suggere, a l'instar des variations de la profondeur de penetration avec la temperature, que le gap supraconducteur de -(bedt-ttf)#2cu(ncs)#2 est anisotrope avec d'eventuelles lignes de nuds. Des mesures complementaires, notamment une etude du comportement de la phase secondaire en fonction de la duree des impulsions de champ radiofrequence, sont necessaires pour une meilleure comprehension de ce phenomene, inedit a notre connaissance. Une etude systematique des formes de raie du proton pour des temperatures inferieures a 4. 2 k dans le compose voisin -(bedt-ttf)#2cun(cn)#2br, dans un champ de 0. 8 t applique perpendiculairement aux plans conducteurs, nous a permis de determiner la profondeur de penetration #a#b(0) a 4920 100 a. Les variations lineaires de #a#b(t) aux basses temperatures indiquent que l'etat fondamental de ce compose ne peut etre decrit par un couplage bcs conventionnel isotrope.

Le déploiement d'une infrastructure de supervision permet une gestion plus intelligente des réseaux de distribution d'électricité comparé à un renforcement traditionnel pour répondre aux nouveaux enjeux de la maitrise de l'énergie (Consommations, EnR, VE, ...). Pour acheminer les données, les Courants Porteurs en Ligne (CPL) possèdent un atout majeur. En effet, cette technologie permet de superposer un signal de plus haute fréquence au signal électrique 50/60 Hz. Toutefois, le support de transmission est difficile et non maîtrisable. Ces travaux de recherche ont pour objectif d'apporter une contribution à cette problématique par l'élaboration d'une plateforme de simulation des réseaux pour des fréquences allant jusqu'à 1 MHz dans un but de transmission de données. Des éléments clés des réseaux sont traités de façon séparés puis assemblés pour estimer les performances des CPL « Outdoor » actuels. La variation du comportement des réseaux en fonction du temps et de la fréquence, en particulier des perturbations en tête d'installation clients sur 24h est étudiée. Les transformateurs entre les réseaux HTA et BT sont modélisés sous la forme d'un « modèle à constantes localisées » et d'un « modèle boite noire ». Les deux modèles sont appliqués sur un transformateur H61 100 kVA. Par la suite, une modélisation des câbles de distribution est proposée sous forme d'un « modèle cascadé ». Celle-ci est appliquée sur un câble souterrain BT. Chaque modèle est obtenu à l'aide de mesures d'impédances, et validé par des mesures de transmissions. Pour compléter, une étude préliminaire sur les communications radio mobile est réalisée pour la supervision des réseaux de distribution
Establishing a supervisory infrastructure allows a better smart management than an expensive strengthening of distribution network to respond to new constraints at the energies control (Consumption, REN, EV ...). To transmit data, Power Line Communication (PLC) technologies present an advantage in this context. In fact, it enables a superposition of High Frequency (HF) signals on electrical signal 50/60 Hz. However, electric networks have not been developed to this application because of difficult propagation conditions. This research work makes a contribution to develop a simulation platform in objective to transmit data to 1 MHz. In first time, each network element is studied singly and in second time, together, to estimate "Outdoor PLC" transmission performance. The first element studied is the networks variation in function of frequency and time. Several 24h disturbance measurements on LV customers are presented. The second element is the transformers which established connection between Medium Voltage (MV) and Low Voltage (LV). The proposed modeling method is based on a "lumped model" and a "black box model". These models are applied to a 100 kVA H61 transformer most commonly used by French distribution system operator in rural and suburban networks. The third element is the power line used in MV and LV networks. The proposed modeling method is based on a "cascaded model" from the theory of transmission line. This model is applied to one power line used in LV underground network. Each model is obtained from various impedance measurements. To complete, an introductory study on mobile radio communication is performed to remote network distribution

Au cours des dernières années, les communautés virtuelles de patients se sont énormément développées sur l'Internet. Ces communautés permettent des échanges fréquents entre les patients, qui peuvent partager des informations liées à la santé dans un environnement interactif. Alors que beaucoup s'accordent sur l'opportunité représentée par ces communautés pour ses utilisateurs, les connaissances sur ce qui détermine l'action collective en ligne des patients ainsi que sur les fondamentaux de l'action collective en ligne dans ces espaces virtuels sont relativement peu développées. En conséquence, ce travail doctoral examine les raisons pour lesquelles les patients interagissent entre eux et comment ils procèdent. En nous appuyant sur le modèle du comportement orienté vers un but, la théorie de la valeur de l'attente, la théorie des forces du champ, les concepts de dons et les interviews menées, nous avons développé un modèle qui examine les interactions en ligne des patients dans un contexte d'action collective en ligne. Une approche multi-méthode, qualitative et quantitative, permet d'explorer les interactions des patients et de mesurer les déterminants de l'action collective en ligne sur ces espaces virtuels. L'analyse qualitative de 54 entretiens menés avec des patients, des proches de patients, des professionnels de la santé 2.0, des médecins et des soignants permet d'affiner le modèle de recherche, qui a ensuite été testé au travers d'une enquête quantitative auprès de 269 patients. Cette recherche contribue à la recherche en systèmes d'information en augmentant nos connaissances sur la dynamique individuelle et les interactions qui entourent les communautés de patients en ligne
Over the last few years, virtual patients’communities have been developing tremendously over the Internet. These Web 2.0 communities allow frequent interactions among patients, who can share health-related information within an interactive environment. While many agree on the opportunity represented by those communities for its users, we know very little about what determines patients’ online collective action, specifically on virtual communities as well as the fundamentals of online collective action in these virtual spaces. Accordingly, this doctoral work examines why patients interact with others and how they interact on topics related to their disease through these virtual communities. Drawing on the goal-directed behavior (MGB), the expectancy-value (EVT) theories, the field force theory, gift concepts and field interviews, we have developed a model for examining patients’ online interactions and identified gift-giving behaviors in the context of online collective action. A multi-method, qualitative and quantitative approaches, enables us to explore patients’ interactions and measures the determinants of online collective action on these virtual spaces. The qualitative analysis of 54 interviews conducted with patients, patient’s relatives, Health 2.0 professionals, doctors and caregivers allows refining the research model, which has then been tested through a survey handled with 269 patients, members of patient’s communities. This research contributes to IS research by increasing our knowledge regarding the individual dynamics and interactions that surround online patients’ communities

The aim of this work is to predict the influence of phonon modulations (Kozina et al. 2019 [1]) on the x-ray absorption near-edge fine structure of the Ti-L2,3-edge (Yamaguchi et al. 1982 [2], Thole et al. 1985 [3], De Groot 1990 [4]) in cubic SrTiO3. Employing Density Functional Theory in combination with Multiplet Ligand Field Theory (Haverkort et al. 2012 [5], Luder et al. 2017 [6]), previous experimental and theoretical data on the octahedrally symmetric structure are reproduced with good agreement. Phonon modulations with a maximum atomic displacement of 5% of the lattice parameter are shown to cause polarization-dependent changes in the x-ray absorption spectra just within reach of experimental resolution. This is suggested to reflect the strong susceptibility of the electronic structure to collective lattice excitations in SrTiO3.

In this work the electronic and magnetic structure of the crystals Sr2FeMoO6, Fe0.5Cu0.5Cr2S4, LuFe2O4 and the molecules FeStar, Mo72Fe30, W72Fe30 are investigated by means of X-ray spectroscopic techniques. These advanced materials exhibit very interesting properties like magnetoresistance or multiferroic behaviour. In case of the molecules they also could be used as spin model systems. A long standing issue concerning the investigation of these materials are contradicting results found for the magnetic and electronic state of the iron (Fe) ions present in these compounds. Therefore this work focuses on the Fe state of these materials in order to elucidate reasons for these problems. Thereby the experimental results are compared to multiplet simulations.