Spin Crossover, Charge Transfer, Valenztautomerie:Neue Mangan- und Eisenporphyrinoide mit elektronischen Besonderheiten

Gegenstand der vorliegenden Arbeit ist die Untersuchung verschiedener porphyrinoider Eisen- und Mangan-Komplexe. Schwerpunkt bildete dabei zunächst die Entwicklung einer Synthese der chronisch labilen Bidipyrrin-Komplexe, wobei die erhaltenen Verbindungen im Anschluss speziell auf ihre strukturellen...

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Bibliographic Details
Main Author: Köhler, Silke Annika
Contributors: Bröring, Martin (Prof. Dr.) (Thesis advisor)
Format: Doctoral Thesis
Published: Philipps-Universität Marburg 2007
Online Access:PDF Full Text
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The subject of this work is to investigate different porphyrinoid iron and manganese complexes. Focus is the development of a synthesis of the chronically unstable bidipyrrin complexes as well as the spectroscopic and structural analysis of the prepared compounds. Chapter 2.1.1 shows the successful preparation of the four halogene derivatives of octaethylbidipyrrin manganese (III) which were all spectroscopically and structurally characterized. The magnetic investigations of this class shows that all four compounds have a S = 2 ground state which has also been reported for the analogous porphyrin complexes. In addition to the high lability towards acids these substances show a high reactivity towards primary alcohols that lead to complete demetallation after attack of the 10,10 position. Section 2.1.2 focuses on the analogous iron complexes. These have also be characterized structurally and show to crystallize isomorphic to the corresponding manganese systems with the exception of the fluoro complex. This is an anionic hexa coordinated ferrate complex with a polymeric structure in the solid state. The investigation of the electronic properties of this new class of substances revealed a change of the spin ground state between the compound in solution and in crystalline form. All four compounds are in the high spin state in solution, while the analysis of the solid monomeric compounds clearly reveals an intermediate spin ground state. The solid samples additionally show a spin crossover from intermediate to high spin state with different intensities depending on the axial ligand. Chapter 2.2 deals with the open chain pseudohalogene complexes of manganese and iron. They show again significant differences in terms of the spin ground state and an increased reactivity of the iron complexes, which reacts rapidly in the presence of oxygen and traces of water. For the thiocyanate complex the corresponding macrocyclic oxacorrole and thiacorrole derivatives have been identified as degradation products. In the case of the analogous selenocyanate compound only the oxacorrole complex is formed, while the complexes with cyanate and azide in axial position decompose to undefined products. The electronic properties are in turn similar to those of the analogous halides. The manganese complexes are pure high spin systems showing no anomalies in the investigated temperature range. The results of the SQUID measurements of the iron complexes show a significantly greater dependence of the spin crossovers from the axial ligands than the analogous halides. The spectroscopic EPR investigations of this compound class turned out to be significantly more difficult, since the substances probably aggregate in solution. Therefore in particular the iron thiacorrole complex with NCS as axial ligand could not be analyzed by EPR spectroscopy. With the means of IR spectroscopy the change of spin ground state between solution and solid has been spectroscopically visualised. On the basis of these data a coordination mode of the ambidentate ligands via the nitrogen atom has been suggested which was confirmed by crystallographic studies of the macrocyclic manganese and the open chain iron complexes. In chapter 2.3 the synthesis and characterization of the macrocyclic halogene oxacorrole complexes of manganese and iron are presented as well as the first studies of halogene complexes of iron thiacorroles. In addition to the structural characterization of all oxacorrole compounds the iodide and chloride complexes of iron thiacorrole have also been crystallographically investigated. The spectroscopic studies show a pure intermediate spin ground state for the iodide and bromide complexes of iron, which in the past has only been described in the porphyrin literature of heavily distorted systems. Analytics of the lower homologues hint at unusual electron configurations, for which excited states or valence tautomeres seem to play a role. The manganese complexes of this series again turned out to be predictable systems with a high spin ground state. The last two chapters contain a compilation of various studies, including low spin iron(III) complexes as well as compounds with weak coordinating anions. With this diversity of compounds differences to the analogous porphyrin complexes have been brought out, which are specifically the bond strength of the axial ligands and the reactivity of the compounds. In particular, the structural characterization of the open chain m-oxo iron(III) bidipyrrin complexes provides clues on the relationship between structure and spin state and also reveales possibilities to influence the coordination sphere of the central metal by the variation of the substituents in the ligand periphery.