Reversible Interpenetration in a Metal–Organic Framework Triggered by Ligand Removal and Addition

Caging cages: Crystals of a metal-organic framework, MOF-123 [Zn7O2(NBD)5(DMF)2] have a three-dimensional porous structure in which DMF ligands (see picture, pink) protrude into small channels. Removal of these ligands triggers the transformation of this MOF to the doubly interpenetrating form, MOF-246 [Zn7O2(NBD)5]. Moreover, addition of DMF into MOF-246 triggers reverse transformation to give MOF-123. NBD=2-nitrobenzene-1,4-dicarboxylate.