Two 3D porous lanthanide-fumarate-oxalate frameworks exhibiting framework dynamics and luminescent change upon reversible de- and rehydration.

We present two porous luminescent compounds, [Ln2(fumarate)2(oxalate)(H2O)4].4H2O (Ln = Eu, Tb), prepared by the hydrothermal method. The materials have 3D framework structure consisting of oxalate pillared lanthanide-fumarate layers with intersected channels occupied by guest water. They exhibit framework dynamics upon several cycles of dehydration and rehydration. The crystallinity of the as-prepared hydrated materials degrades completely to the amorphous dehydrated phases, while it returns upon rehydration. A mechanism for de-/rehydration is proposed on the basis of the structure and spectroscopic data. The dehydration process is accompanied by the lost of luminescence of Ln ion, but the luminescence is recovered upon rehydration, where water molecules in fact enhance the luminescence but not quench it. This is probably due to the softened environment of lanthanide ion in the dehydrated amorphous phases and the recovery of the stiffness after rehydration.