Tuning the Structures of Metal Organic Frameworks via a Mixed-Linker Strategy for Ethylene/Ethane Kinetic Separation

A mixed linker strategy has led to the discovery of the new metal-organic framework material, GT-18 (GT = Georgia Tech), which has no open metal sites and a chiral structure. The material includes benzotriazole (BTA) and benzimidazole (BIM) linkers. Among multiple synthesis ratios that were tested, a BTA/BIM mole ratio of 4:1 gives a material with diffusion selectivity toward ethylene over ethane. This ratio yields the largest member ring (10 MR vs 6 MR) compared to that synthesized at low mixed linker ratios (ZIF-7 like structures) and with only BIM linkers (a 2D [Zn(BTA)2](n) structure), while maintaining a narrow, but flexible, aperture size of similar to 3 angstrom. The work demonstrates tunable sorption properties, topologies, and pore shapes, in which the selectivity for an important ethylene/ethane separation is achieved via diffusion selectivity.