A flexible interpenetrating coordination framework with a bimodal porous functionality

Introducing a functional part into open-framework materials that tunes the pore size/shape and overall porous activity will open new routes in framework engineering and in the fabrication of new materials. We have designed and synthesized a bimodal microporous twofold interpenetrating network {[Ni(bpe)(2)(N(CN)(2))](N(CN)(2))(5H2O)}(n) (1), with two types of channel for anionic N(CN)(2)(-) (dicyanamide) and neutral water molecules, respectively. The dehydrated framework provides a dual function of specific anion exchange of free N(CN)(2)(-) for the smaller N-3(-) anions and selective gas sorption. The N-3-exchanged framework leads to a dislocation of the mutual positions of the two interpenetrating frameworks, resulting in an increase in the effective pore size in one of the counterparts of the channels and a higher accommodation of adsorbate than in the as-synthesized framework (1), showing the first case of controlled sorption properties in flexible porous frameworks.