ALBERT

Description: Shape-memory effects are quite well-studied in general, but there is only one reported example in the context of porous materials. We report the second example of a porous coordination network that exhibits a sorbate-induced shape-memory effect and the first in which multiple sorbates, N 2 , CO 2 and CO promote this effect. The material, a new threefold interpenetrated pcu network, [Zn 2 (4,4'-biphenyldicarboxylate) 2 (1,4-bis(4-pyridyl)benzene)] n (X-pcu-3-Zn-3i), exhibits three distinct phases: the as-synthesized α phase; a denser-activated β phase; and a shape-memory phase, which is intermediate in density between the α and β phases. The phase is kinetically stable over multiple adsorption/desorption cycles and only reverts to the β phase when heated at 〉400 K under vacuum. The α phase can be regenerated by soaking the phase in N , N '-dimethylformamide. Single-crystal x-ray crystallography studies of all three phases provide insight into the shape-memory phenomenon by revealing the nature of interactions between interpenetrated networks. The β and phases were further investigated by in situ coincidence powder x-ray diffraction, and their sorption isotherms were replicated by density functional theory calculations. Analysis of the structural information concerning the three phases of X-pcu-3-Zn-3i enabled us to understand structure-function relationships and propose crystal engineering principles for the design of more examples of shape-memory porous materials.