Synthesis and characterization of alkali-metal reduced polycyclic aromatic hydrocarbon based materials

Abstract

The reduction chemistry of polycyclic aromatic hydrocarbon (PAH) based materials is well established and has been investigated for more than a century. A frequently applied reduction method is treatment of the PAH by alkali metals, where an electron from the alkali metal is transferred to the π-system of the PAH. Recently it has been found that these reduced species can possess intriguing magnetic and electronic properties in the solid state, e.g. pentacene derivatives are excellent organic semiconductors and triphenylides are low-dimensional antiferromagnets.
This topic has also attracted considerable attention since superconductivity was reported in alkali-metal reduced PAHs synthesised by solid-state techniques. However, the unavailability of well-crystalline and single-phase materials, which would permit the unambiguous identification of the superconducting phase and disclose the origin of superconductivity, has severely hindered progress in this research direction.
In this thesis the reduction of PAHs with potassium, rubidium and caesium metals was carried out in aprotic coordinating organic solvents. Single crystalline and polycrystalline phase-pure, solvent containing- and solvent-free reduction products were successfully isolated for the first time. Crystal structures were determined with single-crystal and powder X-ray diffraction, magnetism was studied with Superconducting Quantum Interference Device (SQUID) magnetometry and electron paramagnetic resonance (EPR) spectroscopy, and charge transfer was followed with infrared (IR) and Raman spectroscopies. The synthesised materials exhibit a variety of magnetic properties, spanning canted-antiferromagnetism, ferromagnetism, low-dimensional magnetism and diamagnetism. A detailed structural analysis was performed in order to establish magnetostructural correlations. This study has expanded the family of well characterised alkali-metal reduced PAH based materials and gives an insight into the structures and magnetism of this family of compounds.