CCIQS-1: A Dynamic Metal-Organic Framework with Selective Guest-Triggered Porosity Switching

The synergy between porosity and soft properties in metal-organic frameworks (MOFs) can result in materials with adaptability of the pore size/shape to the adsorbate. Herein, we present a new guest-responsive flexible MOF: CCIQS-1. This material consists of threefold interpenetrated subnetworks comprising [Sc-3(mu(3)-O)(H2O)(2)(OH)(mu-O2CR)(6)] nodes interconnected by 4,4'-(9,10-anthracenediyl)dibenzoate ligands. This arrangement gives rise to the formation of hydrophilic and hydrophobic channels. Although the activated material is permanently porous, a crystal-to-crystal phase transition takes place upon solvent removal, leading to the contraction of the hydrophobic pores while 1D hydrophilic channels remain open. As a result, CCIQS-1 exhibits a higher affinity for guests with moderate polarity [tetrahydrofuran (THF), MeOH, and acetone] than for non-polar ones (toluene, cyclohexene, and hexane). X-ray diffraction studies on the contracted-pore phase (cp-CCIQS-1) after exposure to different solvents indicate that only adsorbates with a suitable polarity and molecular size trigger the recovery of the open-pore phase (op-CCIQS-1) via the combination of a breathing effect and subnetwork displacement.