Synthesis of Type II Porous Liquids from Nonporous Metal-Organic Polyhedra Enhanced by Host-Guest Complexation

The synthesis of Type II porous liquids (PLs) from metal-organic polyhedra, a kind of excellent porous molecular sources, suffers from their strong crystallization tendency induced poor solubility. Herein, we propose a host-guest complexation enhanced dissolution strategy for constructing Type II PLs from MOPs with record-high concentration. Benefitting from host-guest interactions between pillar[5]arene and n-alkyl chains, a Type II PL (P5-PL) is developed by dissolving apolar n-dodecyl-functionalized metal-organic polyhedra (MOP-18) in polar liquid pillar[5]arene (P5-L), exhibiting solubility much higher than all MOP-based Type II PLs reported to date. MOP-18, being nonporous in the solid state because of molecular packing-induced pore blockage, displays permanent molecular porosity when molecularly and randomly dispersed in P5-L to form P5-PL, as confirmed by experimental and simulation results. P5-PL demonstrates excellent CO₂/N₂ separation capabilities, enabling the fabrication of mixed matrix membrane with superior CO₂/N₂ selectivity. This strategy can be extended to the fabrication of additional Type II PLs, showing its universality. This synergistic design concept integrating supramolecular chemistry with PLs not only overcomes traditional tedious covalent modification but also enables high compatibility between apolar cage solutes and polar solvents, affording PLs with high porosity, low volatility and viscosity, and programmable tunability.