Spin crossover in the ship-in-a-bottle compound: cobalt(II) tris(bipyridyl) encapsulated in zeolite-Y

The ship-in-a-bottle compound, cobalt(II) tris(bipyridyl) complex cation encapsulated in the zeolite-Y supercage, exhibits a thermally driven interconversion between a low-spin and a high-spin state — a phenomenon not observed for this ion either in solution or in the solid state. From a study of the magnetism and optical spectroscopy of the encapsulated and unencapsulated species, supported by molecular modelling and ligand field calculations, such a spin behaviour is shown to be intramolecular in origin. The topology of the supercage forces the ion to adopt an octahedral geometry less distorted than that in its free state.