Swelling Hybrid Solids

Inorganic solids are usually rigid. Professor Hoppe , all over the years, provided a tremendous number of beautiful examples of their structural organization in oxides and fluorides. 1 His immense creativity enriched a lot this part of chemistry, and attracted many colleagues – including myself – toward solid state chemistry. A common idea, associated with the usual definition of solids, was to consider crystallized solids are rigid edifices, within which the only degrees of freedom were the thermal vibration of the atoms forming the compound and the movement of atoms during a displacive structural transition. This implied small displacements of the atoms (0.1 Å < d < 1 Å).In 2002, simultaneously with my friend Susumu Kitagawa from Kyoto university, 2 – 5 we discovered a new behavior of the crystallized solid matter: the unusually large flexibility of crystalline solids (movements of > 5–10 Å), keeping the same topology in the absence of any amorphous intermediate. Knowing your continuous curiosity toward new events in solid state chemistry, I decided to dedicate this tribute to this strange phenomenon, primitively a laboratory curiosity but which became during these last ten years a specific topic attracting chemists, physicists, and computer scientists for the academic point of view, but also companies for the applications this behavior allows. This paper will focus exclusively on the flexibility of three‐dimensional solids.