The Effects of Supramolecular Interactions on Iron(II) Spin Crossover Compounds
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Molecules with functional properties, especially ones that display spin crossover behaviour, are becoming increasingly well researched due to their potential applications as the active components in molecular memory, optical displays or sensors.1,2 To this end, a series of Fe(II) coordination compounds utilising imidazolylimine and pyridylimine based ligands have been synthesised and their spin crossover behaviour analysed through a variety of techniques including variable temperature X-ray crystallography, magnetic susceptibility, surface reflectivity and UV-Visible spectroscopy. Light-Induced Excited Spin-State Trapping (LIESST) effects have also been analysed via photomagnetic measurements. Particular attention was paid to the supramolecular interactions present within the solid-state and the effect that these interactions may have on spin crossover behaviour. Subtle changes to the complexes through counter-anion exchange, solvent effects and ligand design were explored and careful structural analysis completed. This study was separated into two distinct categories. The first describes the synthesis, structural characterisation and spin crossover behaviour of Fe(II) dinuclear triple helicates. Four dinuclear triple helicates have been synthesised, three of which display spin crossover behaviour. Weak LIESST effects were observed in two of these examples. Variation in the ligand field strength between the complexes was achieved through modification of the coordinating “head group” and differences between the flexibility of the ligand backbone were also explored. The latter part of this study describes the synthesis, structural characterisation and spin crossover behaviour of novel Fe(II) mononuclear complexes. A series of related ligands which differ in the p-substituent have been synthesised and their coordination chemistry with Fe(II) metal ions examined. Subtle changes to the counter-anion and crystallised solvent molecules were also explored during this study. Five mononuclear Fe(II) complexes were shown to undergo spin crossover and the structural changes associated with the spin-state conversion have been analysed via variable temperature X-ray crystallography and compared with magnetic susceptibility measurements. Two complexes were also analysed for LIESST behaviour and these complexes showed full photo-excitation into the high-spin state at 10 K.