Geometry and Electronic Structure of Doped Clusters via the Coalescence Kick Method

Developing chemical bonding models in clusters is one of the most challenging tasks of modern theoretical chemistry. There are two reasons for this. The first one is that clusters are relatively new objects in chemistry and have been extensively studied since the middle of the 20th century. The second reason is that clusters require high-level quantum-chemical calculations; while for many classical molecules their geometry and properties can be reasonably predicted by simpler methods. The aim of this dissertation was to study doped clusters and explain their chemical bonding. The research was focused on three classes of compounds: aluminum clusters doped with one nitrogen atom, planar compounds with hypercoordinate central atom, partially mixed carbon-boron clusters, and transition metal clusters. The geometry of the two latter classes of compounds was explained using the concept of aromaticity, previously developed in our group

Development and Investigation of the Fluorescence of Cyclopropenium Ions

The work presented herein employs cyclopropenium ions as a central design element towards the goal of developing fluorescent, superbasic and boronium-substituted compounds. A novel guanidine-cyclopropenimine proton sponge with exceptional basicity is reported that was further utilized to develop a stable tetracoordinate boronium-substituted proton sponge. A large focus of this thesis was also placed on the development of the recently discovered fluorescence of cyclopropenium ions leading to a new class of small molecule organic fluorophores. Among this new platform of fluorescent compounds, a specific fluorophore featured an impressive photophysical profile that bodes well for future applications in fluorescent imaging techniques. Insight into the structure, electronics, bonding and photophysical properties of these derivatives is offered

The Concept of Multicenter Bonds in Chemistry and Materials Science

Chemical bonds are components of a universal and compact language of chemistry that was empirically developed before the modern concepts of quantum physics. This language explains how molecules and solids keep together. In particular, Lewis’s shared electron-pair bonding model may be considered the most successful and generally accepted theory of chemical bonding due to its simplicity and predictive power. However, there is an entire world of chemical species where the classical Lewis bonding language fails to describe the bonding pattern adequately. Those cases include but are not limited to compounds with a significant electron delocalization (where electron density spread on a region that spans more than 2 atoms) such as so-called aromatic and anti-aromatic compounds. In this dissertation, we are showing that there are some essential “words” missing in the “vocabulary” of classical Lewis’s chemical bonds language. To cover most of the chemical species, the electron-pair bonding model can be extended with the inclusion of multicenter bonds where the number of centers can reach the number of atoms in the described system. This dissertation includes six research projects, that investigate and expand the applicability of the concept of multicenter bonds in chemistry and materials science. We showed that such a developed chemical bonding model has great predictive power and can explain the structure, stability, and several physical properties of various unusual clusters and solids. Since the chemical bonding pattern can be related to reactivity, structure, and physical properties, we believe, that the concept of multicenter bonds could be developed in the future up to the level where we will be able to design novel materials with ever-wanted physical and chemical properties

Enhancement of Luminescence Properties of Cu(I) Based Materials

The purpose of this thesis is to investigate the photophysical behaviour of three distinct families of Cu(I) complexes. The distinction is done by three different type of ligands but in all cases the coordination core consists of dinuclear iodide bridged {Cu2(μ-I)2} cluster surrounded by either diimino-, phosphino- or imino-phosphino- (N^N,P,P^N) ligands. All compounds were fully characterized by spectroscopic methods, with special emphasis on their structural features revealed by X-Ray single crystal diffraction and photophysical properties supported by computational calculations. The first family consists of two new complexes bearing α-diimine (Ar-BIAN) ligands functionalized by a nitro group which were compared to the analogue non-functionalized complex. The ground state analysis clarifies the difference between the molecular structures observed within the crystals and the determining role of packing forces. TD-DFT revealed (M+X)LCT (Metal and Halide to Ligand Charge Transfer) absorption bands in the visible with some n→π* character involving stabilized π* orbitals by the presence of NO2. Dynamics of the excited state of all three complexes and of their respective free ligands were examined by Transient Absorption Spectroscopy in the femtosecond time domain allowing to probe the dark states involved in the kinetic pathways followed by excited Cu(I) complexes and the role of ligands structure in the non-radiative decays. The second family includes two new emissive dinuclear Cu(I) complexes bearing terphenyl phosphines. The photophysical behavior of these compounds in liquid solution, solid−solid Zeonex solution and powder samples were investigated at room temperature and 77 K. The steady state and time-resolved emission measurements along with group theory calculations allowed to postulate a luminescence mechanism conditioned by crystal packing. The third family comprised of two new iminophosphine-based complexes, which combine imine and phosphine properties in a sole structure supporting the suggested mechanistic pathways hypothesized for the two first compound families.A investigação científica realizada no âmbito desta tese de Doutoramento põe em foco o comportamento fotofísico de três famílias distintas de complexos de Cu(I). O que faz a distinção entre as famílias é o tipo do ligando sendo diimino-, fosfino- ou imino-fosfino- (N^N,P,P^N) respetivamente tendo todas em comum o cerne {Cu2(μ-I)2}, um fragmento binuclear de Cu(I) com Iodetos em ponte. Todos os compostos foram completamente caracterizados recorrendo às técnicas espectroscópicas com especial ênfase na Cristalografia de Raios-X para a caracterização estrutural e nos Cálculos Teóricos para melhor compreensão do comportamento fotofísico. A primeira família consiste em dois novos complexos contendo ligandos α-diimina (Ar-BIAN) funcionalizados com o grupo nitro que foram comparados com o complexo homólogo não-funcionalizado. Foram abordadas as diferenças estruturais na fase cristalina realçando o papel determinante que o empacotamento cristalino exerce na geometria que as moléculas adoptam no estado fundamental. TD-DFT revelou a natureza das bandas de absorção na região visível sendo (M+X)LCT com algum caráter n→π* com orbitais π* estabilizadas pelo grupo NO2. A dinâmica do estado excitado dos complexos bem como a dos ligandos livres foi estudada recorrendo à Espectroscopia de Absorção Resolvida no Tempo na escala de femtosecundos a fim de sondar os estados escuros envolvidos na cinética do estado excitado e a influência da estrutura dos ligandos no decaimento não radiativo. A segunda família engloba dois novos complexos com ligandos terfenilfosfina. O comportamento fotofísico em solução, em filmes de Zeonex e em pó foi investigado a 300 e 77 K. A emissão de luz no estado estacionário e resolvida no tempo juntamente com a Teoria dos Grupos permitiram postular um mecanismo de luminescência condicionada pelo empacotamento cristalino. A terceira família é composta de dois novos complexos baseados em ligandos iminofosfina que combinando as propriedades de iminas e de fosfinas na mesma estrutura irão apoiar os mecanismos sugeridos para explicar o comportamento fotofísico das duas primeiras famílias

Computational Prediction and Rational Design of Novel Clusters, Nanoparticles, and Solid State Materials

The creation of new materials is absolutely essential for developing new technologies. However, experimental efforts toward the material discovery are usually based on trial-and-error approach and thus require a huge amount of time and money. Alternatively, computational predictions can now provide a more systematic, rapid, inexpensive, and reliable method for the design of novel materials with properties suitable for new technologies. This dissertation describes the technique of theoretical predictions and presents the results on the successfully predicted and already produced (in some cases) unusual molecules, clusters, nanoparticles, and solids. The major part of scientific efforts in this dissertation was devoted to rationalizing of size- and composition-dependent properties of the materials based on understanding of their electronic structure and chemical bonding. It was shown that understanding relations between bonding and geometric structure, bonding and stability, and bonding and reactivity is an important step toward rational design of new, yet unknown materials with unusual properties. Our findings led to the discovery of the first simplest inorganic double helix structures, which can be used in the design of novel molecular devices. A significant part of this work also deals with the pseudo John-Teller effect, which potentially can be a powerful tool for rationalizing and predicting molecular and solid state structures, their deformations, transformations, and properties. Therefore, the works on the pseudo Jahn-Teller effect presented in this dissertation can be considered the steps toward further generalization and elevation of the pseudo Jahn-Teller effect to a higher level of understanding of the origin of molecular and solid state properties

From boron containing heterocycles to oxygen rich ligands for lanthanide coordination and extraction

Jusqu’à l’aube du 21e siècle, les lanthanides étaient considérés comme les métaux les plus difficiles à travailler et à manipuler. En effet, en raison de leur chimie de coordination imprévisible, la caractérisation des complexes de lanthanides représente un défi de taille pour les chimistes expérimentaux. Cependant, les dernières décennies ont vu une évolution considérable de la chimie organométallique de ces éléments du groupe f. Les orbitales-f non-perturbées contenant plusieurs éléctrons non-appariés dans certains lanthanides les ont rendu indispensables dans des applications modernes tels la catalyse, les diodes électroluminescents organiques, les luminophores, les agents de contraste en IRM et les matériaux magnétiques. La coordination de composés déficients en électrons aux lanthanides est considérée difficile en raison de l’électrophilcité de ces éléments. Malgré tout, les uniques propriétés magnétiques et optiques des lanthanides rendent importante l’étude de leurs complexes avec divers ligands, en particulier avec ceux qui possèdent un caractère acide de Lewis. Nous avons décidé de nous intéresser à ce défi en concevant des ligands hétéroaromatiques de bore capables de satisfaire les exigences électroniques et stériques des lanthanides. En plus de réaliser la coordination de ces ligands déficients en électrons à des lanthanides, nous avions pour but d’étudier leur effet sur les propriétés magnétiques de ces métaux. Premièrement, nous avons préparé un complexe monoanionique de boratabenzène et avons étudié sa coordination avec plusieurs ions de lanthanides. Un complexe inédit de tris(boratabenzène)lanthane a été isolé et caractérisé. Les composés diboratabenzènes de lanthanides, cependant, se sont révélés être difficiles à isoler. C’est pourquoi, nous avons synthétisé le 1-mesityl-4-iPr-boratabenzene comme ligand encombré stériquement. Ce dernier a révélé une réactivité riche avec l’eau et différentes bases. Nous avons aussi synthétisé une famille de diboraanthracènes dianioniques, dans le but de former des complexes « sandwich » et « triple-decker » de lanthanides. Une chimie intéressante a été observée pour ces ligands, alors que nous les avons coordonnés à plusieurs lanthanides. Un complexe « triple-decker » inverse de lanthane a été obtenu et étudié. Finalement, nous avons investigué la conception de ligands pour l’extraction sélective des lanthanides à partir de leurs minerais. Ce procédé coûteux et difficile nécessite une connaissance approfondie de la chimie de coordination des lanthanides. À cause de leur charge et de leur taille similaire, la séparation des différents lanthanides est un défi de taille. Pour cette raison, nous avons préparé des ligands polydentates qui agissent comme des donneurs « durs » d’électrons afin de lier les lanthanides. En variant l’angle de chélation, une certaine sélectivité peut être obtenue. De plus, en immobilisant ces ligands sur des supports solides, leur sélectivité et durabilité peut être améliorée pour donner une solution simple et « verte » au problème de l’extraction des lanthanides.Until the beginning of 21st century, lanthanides were considered to be the most difficult metals of the periodic table to work with. Due to the unpredictable coordination behavior of the lanthanide complexes, it was challenging for the chemists to know the exact nature of the complexes formed. However, the last decade has witnessed tremendous growth in the organometallic chemistry of these f-elements. Their unperturbed f-orbitals with large number of unpaired electrons have made them indispensable components in many modern day applications like catalysis, OLEDs, luminophores, MRI agents, magnetic materials, amongst others. The coordination of electron deficient compounds to lanthanides is considered to be challenging due to the electrophilicity of these elements. Nevertheless, the interesting magnetic and optical properties shown by lanthanides makes it of interest to investigate the effect various ligands containing Lewis acidic moieties in order to expand the scope of their properties. We decided to address this challenge by designing boron heterocyclic aromatic ligands for lanthanides that are able to satisfy both the electronic and steric requirements of these metals. Apart from achieving the coordination of these electron deficient boron compounds to lanthanides, we wanted to study their effect on the magnetic properties of the lanthanides. Initially, we synthesized a monoanionic boratabenzene ligand and studied its coordination to various lanthanide ions. A unique trisboratabenzene lanthanum complex was isolated and characterized. However, diboratabenzene lanthanide complexes were challenging to isolate and hence a sterically bulky 1-mesityl-4-iPr-boratabenzene ligand was synthesized for this purpose. This bulky ligand showed some interesting reactivity towards bases and water. We also synthesized several dianionic diboraanthracene ligands to isolate sandwich and triple-decker complexes of lanthanides. The interesting reactivity of these ligands to lanthanides was observed and the successful coordination of this electron deficient ligand to lanthanides was achieved. An inverse sandwich and triple-decker complexes of lanthanum were studied. We also investigated the design of ligands for the selective extraction of lanthanides from their ores. This is a challenging and expensive process where the knowledge of lanthanide coordination chemistry can highly profit. Due to their similar charge and size, it is difficult to separate individual lanthanides from their mixtures. We synthesized polydentate ethereal amides that act as hard donors and coordinate lanthanides. The selective extraction of smaller lanthanide ions was achieved by variation of bite angle of these ligands. The immobilization of the ligands on the solid support provided rigidity to the ligands and enhanced their selectivity and durability, thus providing an environmental friendly system for extraction

High frequency electron spin resonance spectroscopy

Elektronová spinová rezonance (ESR) je neinvazivní spektroskopická technika založená na magnetické rezonanci. Používá se v mnoha vědních oborech jako biologie, chemie a fyzika pro zkoumání systémů s nepárovými elektrony. Tato dizertační práce se věnuje spektroskopii vysokofrekvenční rezonance spinů elektronů (HF-ESR) a jejímu použití na paramagnetické koordinační sloučeniny. V první části je představen teoretický základ s rešerší literatury v této oblasti a jsou představeny aplikace HF-ESR. Dále jsou představeny metody použité ke studování těchto systémů. Zde jsou popsány doplňující metody (XPS, RS, UV-VIS, AFM, SEM) pro zkoumání vzorků a je představen návrh nové sublimační komory vysokého vakua, která byla sestavena pro tvorbu tenkých vrstech koordinačních sloučenin na površích. Následují výsledky dosažené pomocí HF-ESR na molekulárních kvantových bitech [Cu(dbm)2], jednomolekulárních magnetech [CoX2(dppf)], [Co(4MeO-L)2Cl2] a je nastíněna vize bolometrů na bázi grafenu pro detekci této třídy sloučenin. Výsledky jsou diskutovány a jejich implikace jsou shrnuty v závěru. Reference a autorské výstupy pak uzavírají celou tuto práci.Electron spin resonance (ESR) is a non-invasive magnetic-resonance-based spectroscopic technique. It is used in many scientific fields such as biology, chemistry, and physics to investigate systems with unpaired electrons. This doctoral thesis deals with high-frequency electron spin resonance (HF-ESR) spectroscopy and its use on paramagnetic coordination compounds. The first part outlines theoretical basics with literature research in this field and shows the HF-ESR applications. Afterwards, methods used to study systems of interest are presented. Herein, the complementary spectroscopic methods (XPS, RS, UV-VIS, AFM, SEM) are described, and the design of a newly built high-vacuum (HV) sublimation chamber was developed for the preparation of thin films of coordination compounds on surfaces. The next part deals with results obtained by HF-ESR on molecular quantum bits [Cu(dbm)2], single-molecule magnets [CoX2(dppf)], [Co(4MeO-L)2Cl2], and vision of graphene-based bolometers for detection of this class of compounds is outlined. The results are further discussed, and their implications are summarised in conclusions. Finally, references and the author's outputs make up the final chapters of this work.

Stable functionalized unsaturated siliconoids : from a Tetrylene / Siliconoid hybrid to application in homogeneous catalysis

Siliconoids have received tremendous attention due to the prominent role of silicon in technologies of the modern society. The presence of the partially unsubstituted cluster scaffold resembles silicon surface materials at molecular regimes. While siliconoids play important roles as presumed intermediates during chemical vapor deposition processes or in heterogeneous catalysis, the possibility to graft functional groups to the Si6 benzpolarene scaffold is a prerequisite for their incorporation as building blocks into extended systems. Main attention of this thesis is the introduction and transformation of functionalities in the periphery of Si6 siliconoids. Dichlorinated metallocenes of Group 4 are shown to be suitable reagents for the transfer of metals to the Si6 siliconoid. The electrophilic transfer of a chlorinated amidinato tetrylene to the Si6 siliconoid facilitates the coordination to transition metal fragments. As will be shown, depending on the nature of the substituents of the transition metal fragments, different and unprecedented structural motifs can be obtained. In context of the application of siliconoids in homogeneous catalysis, the reactivity of a silylene/siliconoid hybrid towards chalcogens and carbon monoxide was investigated resulting in unprecedented and unsaturated chalcogen-expanded heterosiliconoids as well as in the full cleavage of the C≡O triple bond under formation of an Si=C Enol ether bridge in the peripherie of the cluster scaffold.Silicoide erregten aufgrund der herausragenden Rolle von Silicium in den Technologien der modernen Gesellschaft eine enorme Aufmerksamkeit. Das Vorhandensein des teilweise unsubstituierten Clustergerüsts ähnelt Siliciumoberflächenmaterialien im molekularen Bereich. Während Silicoide als vermutete Zwischenprodukte bei chemischen Gasphasenabscheidungsprozessen oder bei der heterogenen Katalyse eine wichtige Rolle spielen, ist die Möglichkeit, funktionelle Gruppen auf das Si6 Benzpolarengerüst zu übertragen eine Voraussetzung für deren Einbau als Bausteine in erweiterte Systeme. Das Hauptaugenmerk dieser Arbeit liegt auf der Einführung und Transformation von Funktionalitäten in der Peripherie von Si6 Silicoiden. Es wurde gezeigt, dass dichlorierte Metallocene der Gruppe 4 geeignete Reagenzien für die Übertragung von Metallen auf das Si6 Siliciumgerüst sind. Der elektrophile Transfer eines chlorierten Amidinatotetrylens auf ein Si6 Silicoid erleichtert die Koordination an Übergangsmetallfragmente. Wie gezeigt werden wird, können unabhängig von der Art der Substituenten der Übergangsmetallfragmente unterschiedliche und beispiellose Strukturmotive erhalten werden. Im Zusammenhang mit der Anwendung von Silicoiden in der homogenen Katalyse wurde die Reaktivität eines Silylen/Silicoid Hybrids gegenüber Chalkogenen und Kohlenmonoxid untersucht, was zu beispiellosen, ungesättigten Chalkogenexpandierten Heterosilicoiden, sowie zur vollständigen Spaltung der C≡O Dreifachbindung unter Bildung einer Si=C Enoletherbrücke in der Peripherie des Clustergerüsts führte

Capabilities and Limitations of the Spin Hamiltonian Formalism in Single Molecule Magnets

The rational design of molecular magnetic materials is an ongoing effort involving physics, materials science, and chemistry. A common approach to design of complexes and interpretation of magnetic data is the spin Hamiltonian formalism. In this approach, magnetic data is interpreted through constants extracted from the parameterization of data. In design, certain structural motifs are pursued, rationalized by the minimization or maximization of terms in the spin Hamiltonian. In this work, monometallic complexes were prepared to simplify magnetic behavior and allow the examination of specific factors that influence single molecule magnetism like coordination geometry, ligand identity, symmetry, and spin-orbit coupling. A series of hydridotris(3-phenylpyrazolylborato) scorpionate compounds are presented, some of which are inadequately described by the parameterization of magnetic data, and others for which the alteration of terms within the spin Hamiltonian gives the predicted result. These discoveries and ramifications for single molecule magnetism will be discussed. A series of dmf adducts of transition metal para-toluenesulfonates is also presented