Ultramicroporous Lonsdaleite Topology MOF with High Propane Uptake and Propane/Methane Selectivity for Propane...

Propane (C₃H₈) is a widely used fuel gas. Metal-organic framework (MOF) physisorbents that are C₃H₈ selective offer the potential to significantly reduce the energy footprint for capturing C₃H₈ from natural gas, where C₃H₈ is typically present as a minor component. Here we report the C₃H₈ recovery performance of a previously unreported lonsdaleite, lon, topology MOF, a chiral metal-organic material, [Ni(S-IEDC)(bipy)(SCN)]_n, CMOM-7. CMOM-7 was prepared from three low-cost precursors: Ni(SCN)₂, S-indoline-2-carboxylic acid (S-IDECH), and 4,4'-bipyridine (bipy), and its structure was determined by single crystal X-ray crystallography. Pure gas adsorption isotherms revealed that CMOM-7 exhibited high C₃H₈ uptake (2.71 mmol g^-1) at 0.05 bar, an indication of a higher affinity for C₃H₈ than both C₂H₆ and CH₄. Dynamic column breakthrough experiments afforded high purity C₃H₈ capture from a gas mixture comprising C₃H₈/C₂H₆/CH₄ (v/v/v = 5/10/85). Despite the dilute C₃H₈ stream, CMOM-7 registered a high dynamic uptake of C₃H₈ and a breakthrough time difference between C₃H₈ and C₂H₆ of 79.5 min g^-1, superior to those of previous MOF physisorbents studied under the same flow rate. Analysis of crystallographic data and Grand Canonical Monte Carlo simulations provides insight into the two C₃H₈ binding sites in CMOM-7, both of which are driven by C-H···π and hydrogen bonding interactions.