Les complexes de la famille des ansa-chromocènes sont relativement peu nombreux, mais ils ont tout de même démontré des réactivités intéressantes comme la possibilité de coordonner une molécule de monoxyde de carbone au centre métallique sans être sous pression constante de gaz, ce qui n’est pas le cas pour l’homologue chromocène. L’ansa-chromocène le plus surprenant est sans doute le Me2Si(C5Me4)2Cr, car il est le seul qui ne comporte pas de ligand autre que celui de type ansa. Cependant, ce composé a été obtenu sans que le mécanisme de la réaction ne soit compris et prouvé, seul un mécanisme proposé a été publié. Au cours de cette étude, le mécanisme proposé a tout d’abord été infirmé grâce à de nombreuses expériences qui ont mené à l’élaboration d’un nouveau mécanisme. Par la suite, la réactivité du Me2Si(C5Me4)2Cr a été approfondie en le faisant réagir avec divers réactifs. Aucun produit d’addition oxydante n’a été isolé, mais la réaction avec l’isonitrile forme un complexe asymétrique avec deux isonitriles coordonnés. La détermination du moment magnétique du composé Me2Si(C5Me4)2Cr confirme la présence de deux électrons non-pairés à la température de la pièce et évoque la possibilité d’une transition à S=2 à température plus élevée. La synthèse de nouveaux complexes de type ansachromocène insaturé a été tentée avec d’autres ligands ansa, et la réaction avec [C2H4(C9H6)2]Li2 mène à un complexe dimérique avec des ligands indényles pontés. / Only a few ansa-chromocenes complexes are known but some of them have shown interesting reactivities such as the ability to coordinate a carbon monoxide molecule to the chromium center without being under continuous gas pressure, which is not the case for the chromocene analogue. The most surprising ansa-chromocene is without doubt Me2Si(C5Me4)2Cr, because it is the only example of an ansa-chromocene lacking additional ligands. However, the compound was obtained by accident and the mechanism of its formation was neither well established nor understood. Only a tentative mechanism was published. During the course of the present study, the proposed mechanism has been disproved by a series of experiments that led to the elaboration of a new mechanism. The reactivity of Me2Si(C5Me4)2Cr has been studied by reactions with various compounds. No oxidative addition product was isolated, but the reaction with isonitrile yielded an asymmetric complex with two isonitriles coordinated to chronium. The determination of the magnetic moment of this complex confirmed two unpaired electrons at room temperature and indicated the possibility of an S=2 transition at higher temperature. The synthesis of new unsaturated ansa-chromocene complexes has been attempted with other ansa ligands, and the reaction with [C2H4(C9H6)2]Li2 led to a dimeric complex with bridged indenyl ligands.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

The diethyl ester of o-phenylenebis(oxamic acid) (opbaH2Et2) was treated with an excess of RNH2 in MeOH to cause the exclusive formation of the respective o-phenylenebis(N(R)-oxamides) (opboH4R2, R = Me 1, Et 2, nPr 3) in good yields. Treatment of 1–3 with half an equivalent of [Cu2(AcO)4(H2O)2] or one equivalent of [Ni(AcO)2(H2O)4] followed by the addition of four equivalents of [nBu4N]OH resulted in the formation of mononuclear bis(oxamidato) type complexes [nBu4N]2[M(opboR2)] (M = Ni, R = Me 4, Et 5, nPr 6; M = Cu, R = Me 7, Et 8, nPr 9). By addition of two equivalents of [Cu(pmdta)(NO3)2] to MeCN solutions of 7–9, novel trinuclear complexes [Cu3(opboR2)(L)2](NO3)2 (L = pmdta, R = Me 10, Et 11, nPr 12) could be obtained. Compounds 4–12 have been characterized by elemental analysis and NMR/IR spectroscopy. Furthermore, the solid state structures of 4–10 and 12 have been determined by single-crystal X-ray diffraction studies. By controlled cocrystallization, diamagnetically diluted 8 and 9 (1%) in the host lattice of 5 and 6 (99%) (8@5 and 9@6), respectively, in the form of single crystals have been made available, allowing single crystal ESR studies to extract all components of the g-factor and the tensors of onsite CuA and transferred NA hyperfine (HF) interaction. From these studies, the spin density distribution of the [Cu(opboEt2)]2− and [Cu(opbonPr2)]2− complex fragments of 8 and 9, respectively, could be determined. Additionally, as a single crystal ENDOR measurement of 8@5 revealed the individual HF tensors of the N donor atoms to be unequal, individual estimates of the spin densities on each N donor atom were made. The magnetic properties of 10–12 were studied by susceptibility measurements versus temperature to give J values varying from −96 cm−1 (10) over −104 cm−1 (11) to −132 cm−1 (12). These three trinuclear CuII-containing bis(oxamidato) type complexes exhibit J values which are comparable to and slightly larger in magnitude than those of related bis(oxamato) type complexes. In a summarizing discussion involving experimentally obtained ESR results (spin density distribution) of 8 and 9, the geometries of the terminal [Cu(pmdta)]2+ fragments of 12 determined by crystallographic studies, together with accompanying quantum chemical calculations, an approach is derived to explain these phenomena and to conclude if the spin density distribution of mononuclear bis(oxamato)/bis(oxamidato) type complexes could be a measure of the J couplings of corresponding trinuclear complexes. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

No description available.

One of the oldest goals across the science is to watch atoms undergo reactions in real time. However, such observations are only meaningful if the object of interest is looked at in its natural environment. For most biological and materials sciences samples, this means in solution phase or dispersed in a liquid. Unfortunately, this restriction normally prohibits either reaching atomic spatial (10-10m) or ultrafast time (10-15sec) resolution. Here, two sample preparation techniques are shown providing a natural environment for experiments with high spatial and temporal resolution: a nanofluidic cell for electron microscopy, and a chip for serial time resolved x-ray crystallography. The nanofluidic cell was implemented into different transmission electron microscopes, and in initial experiments, the key features of the sample cell are shown, namely the ability to create stable ultrathin liquid layers of tuneable thickness within the harsh electron microscope vacuum. The option to directionally flow liquid through the sample cell opens the door to high throughput electron microscopy and on-the-fly sample exchanges with the option of triggering and influencing chemical reactions with external sample control. First applications highlight the impact of the nanocell: structural disintegration of gold nanorods exemplary for materials science, and amyloid fibrils, exemplary for biomedical applications. In future applications diffractive imaging with high time resolution is planned, and will complement the range of experiments within the fields of traditional transmission electron microscopy. The second half of this thesis presents a solid target for x-ray crystallography. The chip enables the arrangement of thousands of micrometer sized protein crystals in a regular array. The ability to prepare protein crystals in such a fashion is unique and permits serial in situ crystallography. Real time crystallography requires samples to be mounted in a saturated natural environment, i.e. under ambient pressure and temperature conditions. The crystallography chip fills this need while being easily integrated into a synchrotron beam line. In a first set of experiments, the chip design was refined and could prove functionality for static in situ structure analysis of protein systems. Based on this success, future time resolved experiments are under way and will show the full capability of this device.

Multiferroic materials with a coupled ordering of electric and magnetic moments could be used to build energy-efficient, magnetic computer memory that is written with an electrical field. To understand the interaction between the magnetic and electric ordering in such materials, two examples, namely yttrium manganate YMn2O5 and neodymium iron borate NdFe3(BO3)4, are studied by means of resonant x-ray diffraction. The important role of a pure electronic contribution to the ferroelectric polarization is shown in YMn2O5. Furthermore, substitution of Fe can change the magnetic order of YMn2O5 from antiferromagnetic into ferrimagnetic, allowing the storage of easily readable magnetic information. Therefore the change of the magnetic structure upon small Fe substitution is studied. Although most of the magnetic structure of the parent compound is kept, the Fe moments have larger components along the c-direction. In NdFe3(BO3)4 the microscopic origin of the magnetoelectric coupling is addressed as the consequence of the frustration of the Fe and Nd magnetic sublattices. The application of an electrical field shifts the balance from the helical to the collinear magnetic domains, revealing again the strong magnetoelectric coupling. / Multiferroische Materialien mit einer starken magnetoelektrischen Kopplung können als energieeffizienter, magnetischer Speicher benutzt werden, welcher mit einem elektrischen Feld geschrieben wird. Um die Wechselwirkung der elektrischen mit der magnetischen Ordnung in solchen Materialien zu verstehen, werden hier zwei Beispiele, nämlich Yttriummanganat YMn2O5 und Neodymeisenborat NdFe3(BO3)4, mit resonanter Röntgenbeugung untersucht. In YMn2O5 wird die wichtige Rolle eines rein elektronischen Beitrags zur ferroelektrischen Polarisation gezeigt. Um die magnetische Struktur von YMn2O5 von antiferromagnetisch zu ferrimagnetisch zu verändern, kann Fe substituiert werden. Dies ermöglicht es, leicht zu lesende, magnetische Informationen zu speichern. Daher wurde die Änderung der magnetischen Struktur bei leichter Fe Substituierung untersucht. Auch wenn die magnetische Struktur von Fe im wesentlichen der magnetischen Struktur von Mn folgt, haben die Fe Momente größere Komponenten entlang der c-Richtung. In NdFe3(BO3)4 wird der Ursprung der starken magnetischen Kopplung als Folge der Frustration des Nd und Fe Untergitters erklärt. Das Anlegen eines elektrischen Feldes führt zur Verschiebung des Gleichgewichts von den helikalen zu den kollinearen magnetischen Domänen, welches wieder die starke magnetoelektrische Kopplung veranschaulicht.

No description available.

No description available.

Bereits kurz nach Ende des zweiten Weltkriegs, als vergleichsweise große Mengen hochreiner Seltener Erden (SE) für die Wissenschaft bereit standen, wurde erkannt, dass die SE und deren Verbindungen eine Vielzahl bis dahin nicht untersuchter bzw. gänzlich unbekannter physikalischer Phänomene bergen. Zu diesen zählen insbesondere die magnetischen Ordnungen, der KONDO-Effekt, quantenkritische Punkte, das Schwere-Fermionen Verhalten und die Supraleitung. Es konnte teilweise ein drastischer Einfluss leichter Änderungen der chemischen Zusammensetzung auf die physikalischen Eigenschaften dieser Stoffe beobachtet werden. Den Schwerpunkt der vorliegenden Arbeit bilden die detaillierte röntgenographische Aufklärung der Kristallstruktur sowie die Untersuchung des Einflusses dedizierter Variationen der chemischen Zusammensetzung auf Struktur und Eigenschaften wichtiger Vertreter dieser Substanzklasse. Ein besonderer Akzent liegt hierbei auf der Charakterisierung von modulierten Kristallen. Für die Aufklärung der Struktur wird ein breites Spektrum physikalischer Messmethoden, insbesondere die Röntgendiffraktometrie, eingesetzt. Vorgestellt werden orientierte Fremdphaseneinschlüsse im System Y-Ni-B-C, die Ausbildung inkommensurabel geordneter Vakanzen im System Ce-Si, der Einbau von Stapelfehlern sowie eine kommensurable Ordnung von Übergangsmetall-Atomen (ÜM) im System SE-ÜM-Si und eine lagenspezifische Besetzung im System Y-Mn-Fe-O, deren Aufklärung erstmals berichtet wird. Es wird gezeigt, welche Konsequenzen die strukturellen Besonderheiten für ausgewählte physikalische Eigenschaften zur Folge haben. Diese Arbeit hat das Ziel, einen Überblick über die möglichen „Antworten“ der Kristallstruktur der Seltenerd-Übergangsmetall-Verbindungen auf Variationen der chemischen Zusammensetzung zu geben. / Even shortly after World War II, as large amounts of ultrapure rare earths (RE) became available for scientific research, a large reservoir of peculiar phenomena was uncovered. These had not been investigated before or were completely unknown. Examples of these phenomena are, magnetic ordering, the KONDO effect, quantum critical points, heavy fermion behaviour, as well as superconductivity. A strong influence of small variations of the chemical composition on the physical properties had been observed. The main focus of the present thesis is the detailed elucidation of the crystal structure of fundamental representatives of this class of substances, as well as the influence of dedicated variations of the chemical composition on their structure and properties. In particular, the characterisation of modulated crystals is an important facet. A large spectrum of physical methods, especially X-ray diffraction, is employed in the investigations. Results on oriented intergrowth in the Y-Ni-B-C system, incommensurately ordered vacancies in the Ce-Si system, incorporation of stacking faults as well as commensurately ordered transition metal atoms (TM) in the RE-TM-Si system and site specific occupancy in the Y-Mn-Fe-O system are presented. Their elucidation is reported for the first time. It will be shown which consequences the structural peculiarities will have on the physical properties. An objective of this thesis is to give an overview of the possible “answers“ that can be obtained with regard to the influence of the crystal structure of rare earth transition metal compounds on deviations of the chemical composition.

Inconel 718 is a high nickel content superalloy possessing high strength at elevated temperatures and resistance to oxidation and corrosion. The non-traditional manufacturing process of wire-electrical discharge machining (EDM) possesses many advantages over traditional machining during the manufacture of Inconel 718 parts. However, certain detrimental effects are also present. The top layer of the machined surface is melted and resolidified to form what is known as the recast layer. This layer demonstrates microstructural differences from the bulk workpiece, resulting in altered material properties. An experimental investigation was conducted to determine the main machining parameters which contribute to recast layer formation in wire-EDM of Inconel 718. It was found that average recast layer thickness increased with energy per spark, peak discharge current, current pulse duration, and open-voltage time and decreased with sparking frequency and table feed rate. Over the range of parameters tested, the recast layer was observed to be between 5 and 10 μm in average thickness, although highly variable in nature. Surface roughness of the cut parts showed an increase with energy per spark. Electron Probe Microanalysis (EPMA) revealed the recast layer to be alloyed with elements from the wire electrode. X-ray diffraction testing showed the residual tensile stresses evident near the cut surface to decrease with energy per spark. Additionally, nano-indentation hardness testing indicated that the recast layer is reduced in hardness and elastic modulus compared to the bulk material. Vibratory tumbling was found to be a moderately effective post-processing tool for recast layer removal when using pre-formed ceramic abrasive media or fine grained aluminum oxide.