Rational design of metal-organic frameworks featuring macrocycle and helical chain motifs for propylene/propane separation

The separation of propylene/propane is a critical process in the petrochemical industry, and the rational design of porous adsorbents is essential for efficient separation techniques. Designing metal-organic frameworks (MOFs) with supramolecular motifs could access novel structures with finely tuned pore sizes and shapes, opening up new possibilities for enhancing separation performance. Here we report the design and synthesis of three MOF structures, namely BIT-23, 24, and 25, based on a Y-shaped flexible ligand with transition metal nodes (Ni, Zn, or Cu), featuring macrocycle and helical chain motifs. Originating from the flexibility of the ligand and varying geometry of the metal nodes, the formed macrocycle or helical chain units present different conformations, leading to MOFs with distinct topologies and channels. Notably, BIT-23, possessing 1D channels with a periodic structure of wide cavities and narrow bottlenecks and an optimal pore size, could separate propylene/propane, as verified by dynamic breakthrough experiments. The kinetic separation mechanism was further validated by molecular dynamics (MD) simulations.