Nesta tese investigamos computacionalmente clusters de Aln(+,0,-), n = 2-30, com especial interesse em entender aspectos fundamentais de suas propriedades em função do número de átomos e da carga total. Clusters de Aln(+,0,-) podem variar suas propriedades completamente com a adição de um átomo ou um elétron. Essas características permitem que atuem em nanocatálise, como ácidos ou bases de Lewis ou como substrato para adsorção de compostos orgânicos e inorgânicos. Apesar das propriedades dos clusters os tornarem ótimos materiais para inúmeras aplicações, a síntese desses materiais é desafiadora, podendo ser realizada por métodos químicos ou físicos. Os métodos físicos se baseiam na vaporização a laser, e em geral é utilizado um espectrômetro de massa para segregar as partículas, enquanto os métodos químicos compreendem a síntese por meio de nucleação e banhos químicos usando agentes redutores gerando clusters passivados ou suportados por substratos. Apesar de haver muitos estudos experimentais e computacionais investigando propriedades estruturais, eletrônicas e energéticas de clusters de Alumínio como distorção janh-Teller, energia de ionização e afinidade eletrônica, poucos foram realizados priorizando a análise da estrutura eletrônica visando investigar a relação entre suas propriedades e as ligações químicas. Dessa forma, o objetivo desse trabalho foi investigar as propriedades estruturais, energéticas e eletrônicas de clusters Aln(+,0,-) , n = 2 - 30, reunindo evidências que explicam a natureza de suas ligações químicas em função do número de átomos e da carga total. As propriedades estruturais compreendem distância média, número de coordenação efetivo e distorções Janh-Teller. As propriedades energéticas envolvem energia de estabilização por átomos, energia de dissociação e função de estabilidade. As propriedades eletrônicas englobam a energia de ionização, a afinidade eletrônica, os orbitais de fronteira, a densidade de estados, além da análise da densidade eletrônica por meio da teoria de átomos em moléculas (AIM), a análise decomposição energética por interação quântica entre átomos (IQA), a análise da função de localização eletrônica (ELF), a investigação da ordem de ligação pelo índice de Mayer, a análise da ligação química pelo método de particionamento da densidade natural adaptada (AdNDP) e análise dos orbitais naturais de ligações (NBO). As estruturas iniciais dos clusters de Aln(+,0,-) foram obtidas pelo algoritmo de busca configuracional Revised Basin-Hopping Monte Carlo (RBHMC), e posteriormente otimizados pelo modelo computacional TPSSh/def2-TZVPP, esta estratégia gerou resultados de energia de ionização e afinidade eletrônica mais próximos de valores experimentais que os modelos MP2/def2-TZVPP, PBE0/def2-TZVPP, BP/def2-TZVPP e B3LYP/def2-TZVPP. Nós observamos considerável influência da carga total e do número de átomos sobre a geometria dos clusters investigados. A distância de ligação média e o número de coordenação efetivo permitiram caracterizar clusters com estrutura planar, estrutura tridimensional, e também regiões de transição entre essas geometrias por meio da simples análise do gráfico dessas propriedades em função do número de átomos. A energia de ligação por átomos revelou que a estabilização desses clusters cresce rapidamente até Al12(+,0,-) , e a partir de então, se aproxima lentamente do valor da fase bulk conforme cresce o número de átomos. A função de estabilidade revelou que a estabilização de clusters está relacionada com a sua estrutura eletrônica, revelando que alguns clusters Aln(+,0,-), n = 2 - 30, são mais estáveis que os vizinhos mais próximos, em acordo com a sugestão dos números mágicos inicialmente aplicados para clusters de sódio e potássio. A energia de ionização e a afinidade eletrônica calculadas por TPSSh/def2-TZVPP para os clusters investigados forneceram resultados muito próximo dos valores experimentais, o comportamento oscilante dessas propriedades foram associados a padrões de crescimento baseado em icosaedros, decaedros e tetraedros por alguns autores e concordam com os nossos resultados. Os orbitais de fronteira e a densidade de estados dos clusters Al13(+,0,-) indicam que o HOMO apresenta contribuição preponderante dos orbitais pi. A teoria quântica de átomos em moléculas revelou que a força das interações químicas está associada à deslocalização eletrônica nos clusters investigados que cresce na seguinte ordem Aln+ < Aln0 < Aln-. E o caráter covalente nesses clusters é maior para os cátions que para os neutros e ânions. Esses resultados conferem maior caráter metálico aos clusters Aln- que aos demais clusters carregados e neutros, confirmados pelo método ELF. O método de partição energética IQA mostrou que a contribuição energética preponderante para a estabilização das interações químicas nos clusters Aln(+,0,-), n = 2 - 7, é a energia de troca responsável pelo caráter covalente, enquanto a contribuição iônica é oriunda da energia cinética eletrônica que apresenta caráter desestabilizante ou repulsivo para os clusters Aln(+,0,-), (n = 2 - 4 e 6 - 7), por outro lado, essa contribuição é estabilizante, mesmo que muito pouco para os clusters Al5(+,0,-) e consideravelmente estabilizante para as interações nos clusters Al13(+,0,-), sendo importante para o aumento da deslocalização eletrônica confirmada pela presença de aromaticidade tridimensional investigada pelos métodos ELF, AdNDP e NICS. / In this thesis we investigate computationally Aln(+,0,-) , n = 2 - 30 clusters with special interest in understand the fundamental aspects of theirs properties in function of number of atoms and of total charge. Aln(+,0,-) clusters can vary its properties completely through the addition of an atom or an electron. These features allow them to act at nanocatalysis such as acids or basis of Lewis or such as substrate for adsorption of organic and inorganic compounds. Despite the properties of clusters become them optimal materials for numerous applications, the synthesis of these materials is challenging, it can be performed by chemical or physical methods. Physical methods are based on laser vaporization and generally used a mass spectrometer to segregate the particles, while chemical methods include comprise through nucleation and chemical baths using reducing agents generating passivated clusters or supported by substrates. Although there are many experimental and computational studies investigating structural, electronic and energetic properties of Aluminum clusters such as Jahn-Teller distortion, ionization energy and electron affinity, few were performed prioritizing the analysis of the electronic structure and to assess the relationship between its properties and the chemical bonds. This form the objective this work was investigate the structural, energetic and electronic properties of Aln(+,0,-), n = 2 - 30 clusters gathering evidence to explain the nature of their chemical bonds in function of the number of atoms and of total charge. The structural properties include average distance, effective coordination number and Janh-Teller distortions. The energetic properties involve stabilization energy of atoms, dissociation energy and stability function. The electronic properties include the ionization energy and electron affinity, frontier orbitals, density of states, as well as analysis of the electron density through the atoms in molecules (AIM) theory, the analysis by interacting quantum atoms (IQA), the analysis of electron localization function (ELF), the investigation of binding order by Mayer index, the analysis of chemical bonding by adaptive natural density partitioning method (AdNDP) and analysis of natural bond orbital (NBO). The initial structures of clusters Aln(+,0,-) were obtained by algorithm of configuracional search Revised Basin-Hopping Monte Carlo (RBHMC), and subsequently optimized by computational model TPSSh/def2-TZVPP, this strategy performed electron affinity most close of experimental values than MP2/def2-TZVPP, PBE0/def2-TZVPP, BP/def2-TZVPP e B3LYP/def2-TZVPP. We observed considerable influence of the total charge and the number of atoms on geometry of the investigated clusters. The average bond distance and effective coordination number allowed the characterization of clusters such as planar structure, three-dimensional structure, as well as transition regions between these geometries through simple graphic analysis of these properties according to the number of atoms. The bind energy by atoms revealed that the stabilization of these clusters grows rapidly until Al12(+,0,-), and from them it grows slowly approaching from bulk phase, it grows in function of number of atoms. Stability function revealed that stabilization of clusters is related to its electronic structure indicating that some clusters Aln(+,0,-), n = 2 - 30 are more stable than the nearest neighbors, in accordance with the suggestion of the magic numbers initially applied to sodium and potassium clusters. The ionization energy and the electron affinity calculated within TPSSh/def2-TZVPP for the investigated clusters provided very close results from experimental values, the oscillating behavior of these properties have been associated with growth patterns based on icosahedrons, decahedrons and tetrahedrons by some authors and agree with our results. The frontier orbitals and the density of states of the Al13(+,0,-) clusters indicate that the HOMO has dominant contribution from orbitals. Quantum theory of atoms in molecules revealed that strength of chemical interactions is associated with the electron delocalization in the investigated clusters growing in the following order Aln+ < Aln0 < Aln-. The covalent character of these clusters is higher for cations than for neutral and anions. These results provide greater metallic character to Aln- clusters than others charged and neutral clusters, such as confirmed by ELF method. IQA energy partition method revealed that dominant energetic contribution to the stabilization of chemical interactions in clusters Aln(+,0,-), n = 2 - 7 is the exchange energy responsible by covalent character, while the ionic contribution comes from the electronic kinetic energy that has destabilizing or repulsive character to the Aln(+,0,-), (n = 2 - 4 and 6 - 7) clusters. On the other hand, this contribution is stabilized to Al5(+,0,-) clusters, even though very little, and considerable stabilizing to the interactions at Al13(+,0,-) clusters. Thus, it is important to increase of the electron delocalization confirmed by presence of the three-dimensional aromaticity investigated by ELF, AdNDP and NICS methods.

O objetivo deste trabalho é descrever a estrutura eletrônica da espécie diatôrnica BeMg, utilizando métodos ab initio multiconfiguracionais. A primeira descrição teórica da espécie BeMg foi feita por Chiles e Dykstra em 1982, empregando os métodos SCF, CCD e CEPA. Naquele trabalho, os autores propuseram que a estrutura eletrônica do BeMg seria intermediária entre a apresentada pelas espécies Be2 e Mg2. Em 1994, Boldyrev et al. empregaram o método QCISD e conjuntos de bases atômicas do tipo 6 - 311 + G* para calcular a distância de equilíbrio do BeMg. Até onde sabemos, não existe nenhum outro estudo téorico, nem experimental, sobre esta espécie. Apesar dos esforços anteriores, devido à natureza dos átomos envolvidos, para descrever com maiores detalhes e precisão não somente o estado fundamental, mas também diferentes estados eletrônicos excitados, é necessário empregar métodos ab initio multiconfiguracionais, fato explicitamente reconhecido por Boldyrev et al. Em 1994. No presente trabalho, as curvas de energia potencial para os estados eletrônicos energeticamente mais baixos, que correlacionam com os primeiros quatro canais de dissociação, da espécie BeMg foram descritas teoricamente empregando conjunto de bases atômicas do tipo cc-pVQZ e funções de onda do tipo CASSCF/MRCI. Todos os orbitais de valência, além de um conjunto adicional de funções de correlação do tipo s e p foram incluídos no espaço ativo. Diversas constantes espectroscópicas também foram calculadas para os estados eletrônicos selecionados. O estado fundamental foi caracterizado como de simetria 1&#931;+ e fracamente ligado (De = 0,05 eV), possuindo consequentemente uma distância internuclear de equihbrio relativamente longa (3, 30 &#197;, &#969;e = 44, 2 cm-1). É interessante notar que nos trabalhos anteriores a distância internuclear de equilíbrio do estado fundamental foi calculada com sendo 4, 5 &#197; e 5,1 &#197;, por Chiles e Dykstra e Boldyrev et al., respectivamente. Os dois primeiros estados excitados são o a3II (Re = 2,416 &#197;, Te = 11029 cm-1) e o b3 &#931;+ (Re = 2,578 &#197;, Te = 11058 cm-1), ambos com energia de dissociação igual a 1,28 eV. / The first theoretical description of BeMg (using the SCF, CCD, and CEPA methods) was done by Chiles and Dykstra in 1982, when it was proposed that its electronic structure would be intermediate to Be2 and Mg2. In 1994, Boldyrev et al., using the QCISD method and 6 - 311+G* basis sets, presented other results on this diatomic species. To the best of our knowledge, there are no other study about this diatomic species. However, due to the nature of the atoms involved, it is necessary to employ more sophisticated theoretical methods to describe BeMg accurately. In this study, potential energy curves for the lowest-lying electronic states correlating with the first four dissociation channels were determined using the cc-p VQZ basis sets and CASSCF /MRCI wave functions. All valence orbitals plus one set of s and p correlating functions were included in the active space. A whole set of spectroscopic constants completes the characterization of each state. In its ground state (X1&#931;+) BeMg is weakly bond (De = 0.05 eV), and consequently has a long internuclear equilibrium distance (Re = 3.30 &#197;, we = 44.2cm-1). It is interesting to note that in previous theoretical works, the internuclear equilibrium distance was calculated to be around 4.5 &#197; and 5.1 &#197;. The first two excited states are an a3II (Re = 2.416 &#197;, Te= 11029 cm-1) and a b3&#931;+ (Re = 2.578 &#197;, Te= 11058 cm-1), with the same dissociation energy, 1.28 eV.

L'objectif principal de cette thèse est de parvenir, au moyen des méthodes de la chimie computationelle, à une meilleure compréhension des processus de couplages catalysés par le palladium. Une attention toute particulière a été apportée à l'étude de l'influence électronique des ligands du palladium (phosphine ou carbène N-hétérocyclique) sur les profils énergétiques des trois principales transformations: addition oxydante, transmetallation et élimination réductrice. Pour quantifier cette influence électronique, deux méthodes d'analyse différentes ont été utilisées : NBO et NOCV. La méthode NBO est classique alors que la méthode NOCV est plus récente. Il convenait pour cette dernière de tester sa pertinence pour le problème étudié.De plus, en collaboration avec différents groupes d'expérimentateurs, le mécanisme de deux réactions catalysées au Pd ont été étudiés:hydrophosphonylation du styrène et arylation directe de dérivés aromatiques fluorés. Dans chacun des cas, l'objectif principal était d'identifier les facteurs à l'origine des régiosélectivités observées. / The main objective of the present thesis is to get a better understanding of the Pd-catalyzed cross-coupling reactions, using the tools of computational chemistry. In particular, a detailed mechanistic study of all the possible reaction paths was carried out with different supporting ligands at palladium (phosphines and N-heterocyclic carbenes) in order to understand the elctronic influence of the latter on the three main steps : oxidative addition, transmetalation and reductive elimination. To probe the electronic influence of the ligands, the well-known Natural Bond orbital (NBO) analysis and the innovative Charge Displacement via Natural Orbital for Chemical Valence (NOCV) were used. In addition, two computational studies of Pd-catalyzed transformations were carried out in collaboration with some experimental groups : hydrophosphonylation of alkenes and direct arylation of fluorinated substrated aromatic rings. The main purpose of these studies was to identify the factors at the origin of the regioselectivity observed.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第14868号 / 工博第3136号 / 新制||工||1470(附属図書館) / 27290 / UT51-2009-K664 / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 榊 茂好, 教授 今堀 博, 教授 杉野目 道紀 / 学位規則第4条第1項該当

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第17065号 / 工博第3614号 / 新制||工||1548(附属図書館) / 29785 / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 佐藤 啓文, 教授 白川 昌宏, 教授 山本 量一 / 学位規則第4条第1項該当

Catalysts based on the first-row (3d) transition metals are commonly seen in chemical and biological reactions. To understand the role of the transition metal in the catalyst, the element specific technique core level spectroscopy is used to probe the electronic structure and geometric properties centered around the metal site. Different types of X-ray spectra can be applied to probe the metal 3d character orbitals involved in reactions, which make it possible to identify and characterize the reactive sites of samples in different forms. A detailed interpretation and understanding of the different X-ray spectra requires a unified method which can be used to model different types of X-ray spectra, e.g., soft and hard X-rays. In this thesis, theoretical investigations of the electronic structures of 3d transition metal complexes through X-ray spectroscopy are presented. The restricted active space method (RAS) is used to successfully reproduce different types of X-ray spectra by including all important spectral effects: multiplet structures, spin-orbit coupling, charge-transfer excitations, ligand field splitting and 3d-4p orbital hybridization. Different prototypes of molecules are adopted to test the applicability of the RAS theory. The metal L edge X-ray absorption (XAS) spectra of low spin complexes [Fe(CN)6]n and [Fe(P)(ImH)2]n in ferrous and ferric oxidation state are discussed. The RAS calculations on iron L edge spectra of these comparing complexes have been performed to fingerprint the oxidation states of metal ion, and different ligand environments. The Fe(P) system has several low-lying spin states in the ground state, which is used as a model to identify unknown species by their spectroscopic fingerprints through RAS spectra simulations. To pave the route of understanding the electronic structure of oxygen evolution complex of Mn4CaO5 cluster, the MnII(acac)2 and MnIII(acac)3 are adopted as prototypical Mn-complexes. The 3d partial fluorescence yield-XAS are employed on the Mn L-edge in solution. Combining experiments and RAS calculations, primary questions related to the oxidation state and spin state are discussed. The first application to simulate the metal K pre-edge XAS of mono-iron complexes and iron dimer using RAS method beyond the electric dipole is completed by implementing the approximate origin independent calculations for the intensities. The K pre-edge spectrum of centrosymmetric complex [FeCl6]n– ferrous state is discussed as s and a donor model systems. The intensity of the K pre-edge increases significantly if the centrosymmetric environment is broken, e:g:, when going from a six-coordinate to the four-coordinate site in [FeCl4]n. Distortions from centrosymmetry allow for 3d-4p orbital hybridization, which gives rise to electric dipole-allowed transitions in the K pre-edge region. In order to deliver ample electronic structure details with high resolution in the hard X-ray energy range, the two-photon 1s2p resonant inelastic X-ray scattering process is employed. Upon the above successful applications of one-photon iron L edge and K pre-edge spectra, the RAS method is extended to simulate and interpret the 1s2p resonant inelastic X-ray scattering spectra of [Fe(CN)6]n in ferrous and ferric oxidation states. The RAS applications on X-ray simulations are not restricted to the presented spectra in the thesis, it can be applied to the photon process of interest by including the corresponding core and valence orbitals of the sample.

The encapsulation of a small molecule inside a fullerene cage through advances in synthetic chemistry have created a new platform to study the dynamics of a freely rotating and translating quantum rotors entrapped inside a symmetric cage potential. These endohedral fullerene complexes are of great interest because the fullerene cages uniquely provide the entrapped molecules a high level of isolation, homogeneity, symmetry and stability. The endohedral fullerene complexes discussed in this thesis are the H2@C60, H2@C70 and H2O@C60. Both variants of small molecules studied in this thesis, H2 and H2O, exhibits spin isomerism, where the spins of both protons in the molecule are able to combine either symmetrically with total spin I=1 (ortho) or anti-symmetrically with total spin I=0 (para). The H2@C60 is the union between the simplest molecule and the most symmetrical molecule in the universe. This thesis discusses the temperature dependence of cold neutron scattering study in this complex to investigate the statistical distribution of the energy states. The H2@C70 is a less symmetric endohedral fullerene which has a prolate ellipsoidal symmetry cage. This thesis discusses the low temperature thermal neutron scattering and the temperature dependence of cold neutron scattering investigations in the complex to study the effect of the ellipsoidal cage on the quantum dynamics of the molecules. H2O@C60 is different to the dihydrogen variant of the small molecule endohedral fullerenes because H2O has a permanent electric dipole moment and is less symmetric than H2. The quantum dynamics of the H2O@C60 is investigated using low temperature thermal neutron scattering, temperature dependence cold neutron scattering and milli-Kelvin NMR. Unlike the dihydrogen endohedral fullerenes, the H2O@C60 also exhibits slow nuclear spin-isomer conversion at low temperatures. This low temperature ortho-H2O to para-H2O conversion process is investigated with both INS and NMR to study the conversion mechanism.

No description available.

2,2′-Bipyridine (BPy), one of the most widely used ligands in coordination chemistry, exists naturally in the s-trans conformation but must preorganize to the s-cis conformer in order to form chelating complexes. Lower stability of the s-cis conformer was mainly attributed to steric 3,3′-hydrogen clashes and nitrogen lone pair-lone pair interactions, but recent trends in the literature suggest that these clashes might be bonding interactions in similar molecules. These close contacts are also present in metal complexes with BPy and are often used as “steric repulsions” in order to explain trends in formation constants. In the present work we investigate the CH•••HC interaction in the free ligand as well as in ZnII(BPy)n(OH2)6-2n and NiII(BPy)n(OH2)6-2n complexes. We use multiple distinct advances in theoretical chemistry in order to arrive at a consistent and coherent model describing these interactions. The Quantum Theory of Atoms in Molecules (QTAIM) reveals the presence of an atomic interaction line (a bond path) for the CH•••HC interaction. Using the Interacting Quantum Atoms (IQA) energy decomposition scheme we show that the CH•••HC interaction is attractive and quantum mechanical in nature. The Extended Transition State coupled with Natural Orbitals for Chemical Valence (ETS-NOCV) energy decomposition scheme show favorable orbital mixing, and Non-Covalent Interaction (NCI) analysis reveals that no steric (Pauli) strain exists in the valence (overlap) regions of the interaction - electron density is concentrated rather than depleted in the bonding region. We also studied various other interactions, ranging from purely repulsive (N--N interaction in the s-cis conformer of BPy), purely electrostatic (CH•••N interaction in s-trans conformer of BPy), H-bonding (CH–N and CH–O bonds in complexes) to coordination bonds and covalent bonds. Using a comparative approach, we show the similarities and differences among the interactions, and conclude that the CH•••HC interaction cannot be classified as a “steric repulsion” - the interaction is similar in properties to every studied known bonding interaction and opposite in nature to the studied known repulsions. Finally, we suggest novel interpretations and understanding of the nature of intramolecular interactions and the field of theoretical chemistry, as well as representing the first work to combine and corroborate QTAIM, IQA, NCI and ETS-NOCV findings. / Dissertation (MSc)--University of Pretoria, 2013. / gm2014 / Chemistry / unrestricted

In this work, a study of a recent approach in the design of light-driven molecular motors is presented. The approach involves enabling part of the motor to obtain aromatic-like properties through photoexcitation, and is found to significantly facilitate the rotary motion by reducing the barriers normally present in the excited-state potential energy surfaces of rotary motors.