Multifunctional Spincrossover Compounds

Spin crossover (SC) complexes have been studied for many decades resulting in the production and investigation of a large range of substances both in solution and the solid state. However, attention is now switching from pure SC systems to those combined with other physical or chemical effects. Thus systems have been combined with other magnetic properties, liquid crystals, conductors, and non-linear optics. Research associated with SC compounds turning towards multi-functional systems seems to open a fascinating new field of research based on already available experience. This might involve the combination of SC with, for example, solvatochromism, thermochromism, or electrochromism and outlines the purpose of the present application. To attain this goal we propose to produce new multicoordinating and metal-specific ligands based on the bzimpy ligand (2,6- bis(benzimidazo-2- yl)pyridine), which shows SC behaviour when bound to iron(II). We then will coordinate these ligands with iron and transition metal ions of the first transition series in mixed-metal and mixed-valent dimers and coordination polymers in solution and solid state.

The research project `Multifunctional Spincrossover Compounds` started on 1st October 2006. Spin crossover (SC) complexes have been studied for many decades resulting in the production and investigation of a large range of substances both in solution and the solid state. In the present project attention was increasingly focused on investigations and applications of combinations of pure SC systems with other physical or chemical effects. Thus systems have been combined with other magnetic properties, liquid crystals, conductors, and non-linear optics. Our investigations included the combination of SC with, for example magnetostriction, ferroelectrics, solvatochromism, thermochromism, and magneto-chromism. To reach this target extensive synthetic work was necessary to prepare new ligands showing SC behaviour when bound to iron(II). These compounds were investigated in detail by appropriate means: T-dependent UV-Vis, IR, Far-IR Spectroscopy, X-ray diffraction, Synchrotron X-ray Powder diffractions, SQUID-magnetometer and magnetostriction, NMR, elemental analysis, etc.. The obtained ligands, however, also coordinate with other transition metal ions of the first transition series yielding a variety of new mixed-metal and mixed-valent dimers and coordination polymers. Such compounds, also showing interesting and applicable properties, have also been prepared (even when not showing Spin-Crossover) and characterised in detail in solution and solid state.