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 [Sc3(μ3-O)­(H2O)2(OH)­(μ-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.