Rapid and reversible formation of a crystalline hydrate of a metal–organic framework containing a tube of hydrogen-bonded water

The flexible metal-organic framework MIL-53(Cr) undergoes a dramatic volume expansion upon immersion in water at room temperature to form a crystalline hydrate in which water is held as a hydrogen-bonded tube: the hydration is readily reversible under ambient conditions as shown by time-resolved powder X-ray diffraction.