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Aufgrund der immer weiter voranschreitenden Miniaturisierung elektrischer Bauteile und der Limitierung Silicium-basierter Technologien ist die Suche nach neuen Materialien unausweichlich. Eine mögliche Alternative stellen hierbei molekulare Schalter auf Basis von Spin-Crossover-Verbindungen dar. Dabei handelt es sich um Materialien, welche durch äußere chemische oder physikalische Einwirkungen, beispielsweise elektromagnetische Strahlung oder Temperaturänderungen, ihre Eigenschaften verändern. Vielversprechende Materialien sind hierbei Koordinationsverbindungen mit FeIII-Zentren, welche reversibel zwischen einem sogenannten High-Spin- und Low-Spin-Zustand wechseln können. Dies geht unter anderem mit signifikanten Änderungen ihrer optischen und magnetischen Eigenschaften einher. Mögliche Anwendungsbereiche stellen hierbei die Sensorik oder die Datenspeicherung dar. Im Rahmen dieser Dissertation werden neue FeIII-Koordinationsverbindungen auf Basis von tetradentaten, pentadentaten und potentiell hexadentaten Liganden synthetisiert und charakterisiert. Die tetradentaten Verbindungen vom Salen-Typ werden mit unterschiedlichen monodentaten Liganden umgesetzt und auf potentielle Spin-Crossover-Eigenschaften untersucht. Dabei hat sich gezeigt, dass durch einen Ligandenaustausch mit Imidazol und Perchlorat als Gegenion neue molekulare Schalter erhalten werden. Bei den pentadentaten Verbindungen handelt es sich um FeIII-Komplexe mit einem Salpet-Liganden, welchen durch die Substitution mit einer pH-sensitiven Sulfonsäure-Gruppe neue, sensorische Eigenschaften hinzugefügt wurden. Dazu gehören unter anderem eine signifikante Farbänderung beim Kontakt mit Säuren oder Basen. Die letzte Gruppe bilden mit Methylpyridin- substituierte Salpet-Liganden. Das Ziel ist hier die Strukturaufklärung hinsichtlich der Koordinationssphäre des Metallzentrums. Dabei liegt das besondere Augenmerk auf der Bindung zwischen dem Eisen-Zentrum und der Methylpyridin-Gruppe. Die in dieser Arbeit vorgestellten Ergebnisse sollen neue Erkenntnisse für den Einsatz von molekularen Schaltern in sensorischen Anwendungen liefern., Due to the ever increasing demand for miniaturization of electrical components and the limitations of silicon-based technologies, the search for new materials is inevitable. Molecular switches based on spin crossover compounds represent a possible solution for these problems. Molecular switches are materials that change their properties through external chemical or physical stimuli, such as electromagnetic radiation or different temperatures. Promising materials are coordination compounds with iron(III) centres, which can reversibly switch between a so-called high spin and low spin state. This is accompanied by significant changes for example in their optical and magnetic properties. For this reason, such materials are promising candidates regarding sensor technology or data storage. In this thesis, new FeIII coordination compounds based on tetradentate, pentadentate and potentially hexadentate ligands are synthesized and characterised. The tetradentate Salen-type compounds are combined with different monodentate ligands and investigated for potential spin crossover properties. It could be shown that new molecular switches can be obtained by exchanging the monodentate ligands with imidazole and perchlorate as anion. The pentadentate compounds are FeIII complexes with Salpet ligands, to which new sensory properties, e. g. colour changes on contact with acids or bases, could be added by substitution with a pH-sensitive sulfonic acid group. The last part consists of methylpyridine-substituted Salpet ligands. The aim is to elucidate the structure with regard to the coordination sphere of the metal centre. Special attention is paid to the bonding between the iron centre and the methylpyridine group. The results presented in this thesis should provide new insights for the use of molecular switches in sensory applications.

Dissertation, RWTH Aachen University, 2020; Aachen 1 Online-Ressource (XIX, 165 Seiten) : Illustrationen, Diagramme (2020). = Dissertation, RWTH Aachen University, 2020, The present dissertation titled “Coordination compounds based on azine, thiocarbohydrazone and carbohydrazone ligands – supramolecular networks and discrete structures” focuses on the structural investigation of coordination compounds of three different Schiff base ligands with zinc(II) and with zirconium(IV). The main investigation methods used are single crystal structure analysis, nuclear magnetic resonance spectroscopy and ESI mass spectrometry. The synthesis and characterization of a novel pyridine-N-oxide-based azine ligand and the structure of two coordination compounds with known azine ligands and zinc(II) are discussed. In addition, five differently substituted salicylaldehyde-based thiocarbohydrazone ligands are structurally characterized and their coordination compounds with zinc(II)carboxylates in solution and in solid state are investigated. By self-assembly, one- and two-dimensional coordination polymers of different porosity are obtained and a discrete structure is described. In a further study with a tert-butyl-substituted thiocarbohydrazone ligand with zirconium(IV), the resulting zirconium(IV)oxo complex and a decomposition reaction of the ligand are presented. Finally, the synthesis and characterization of a novel pyridine-N-oxide-based carbohydrazone ligand is reported. As a result of the coordination of zinc(II) acetate, the structure of a circular helicate is elucidated. In total, this work contains the discussion of 19 new crystal structures., Published by Aachen

Two PhD theses (Alexander Gordienko, 1912; Johannes Angerstein, 1914) and a dissertation in partial fulfillment of a PhD thesis (H. S. French, Zurich, 1914) are reviewed that deal with hitherto unpublished UV-vis spectroscopy work of coordination compounds in the group of Alfred Werner. The method of measurement of UV-vis spectra at Alfred Werner's time is described in detail. Examples of spectra of complexes are given, which were partly interpreted in terms of structure (cis ? trans configuration, counting number of bands for structural relationships, and shift of general spectral features by consecutive replacement of ligands). A more complete interpretation of spectra was hampered at Alfred Werner's time by the lack of a light absorption theory and a correct theory of electron excitation, and the lack of a ligand field theory for coordination compounds. The experimentally difficult data acquisitions and the difficult spectral interpretations might have been reasons why this method did not experience a breakthrough in Alfred Werner's group to play a more prominent role as an important analytical method. Nevertheless the application of UV-vis spectroscopy on coordination compounds was unique and novel, and witnesses Alfred Werner's great aptitude and keenness to always try and go beyond conventional practice.

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