The design of molecule-based storage systems and switches is an important area in modern materials chemistry. Transition metal complexes exhibiting spin crossover behaviour is one group of molecules which has potential in the development of molecular elec tronic switches and displays. Spin crossover compounds are defined as transition metal complexes that change electronic state after an external application. A temperature dependent transition is the classical example of a spin crossover, but also change i n pressure or irradiating the compound might trigger a spin crossover.
Bistability, where two different phases are stable at the same temperature, is obtained if the compound shows hysteresis effects. Cooperativity between the metal centres seems to be a n important factor in thermal hysteresis. Intermolecular effects such as solvents, anion, hydrogen bonding and pi-pi stacking can influence the cooperativitiy in a mononuclear metal complex. It is has been proposed that in polynuclear the cooperativity an d hysteresis effect should be larger. In this project I will investigate this hypothesis.
I will be working with Fe(II), Fe(III) and Co(II) complexes. The N-donor ligands that will be used are commercial available or can be synthesised through one-steps reactions. Bridging ligands that can give dinuclear and polynuclear compounds have been carefully chosen. Together with end-ligands the transition metal complexes showing spin crossover will be obtained. When the complexes undergo a spin transition a stru ctural change will also occur. This structural change will be investigated with single-crystal x-ray diffraction. Magnetic susceptibility changes will be investigated with collaborating groups in Sweden and Australia.