Spatially Confined π‐Complexation within Pore‐Space‐Partitioned Metal–Organic Frameworks for Enhanced Light Hydrocarbon Separation and Purification

Abstract

AbstractUltramicroporous metal–organic frameworks (MOFs) are demonstrated to be advantageous for the separation and purification of light hydrocarbons such as C2H2, C2H4, and CH4. The introduction of transition metal sites with strong π‐complexation affinity into MOFs is more effective than other adsorption sites for the selective adsorption of π‐electron‐rich unsaturated hydrocarbon gases from their mixtures. However, lower coordination numbers make it challenging to produce robust MOFs directly utilizing metal ions with π‐coordination activity, such as Cu+, Ag+, and Pd2+. Herein, a series of novel π‐complexing MOFs (SNNU‐33s) with a pore size of 4.6 Å are precisely constructed by cleverly introducing symmetrically matched C3‐type [Cu(pyz)3] (pyz = pyrazine) coordinated fragments into 1D hexagonal channels of MIL‐88 prototype frameworks. Benifit from the spatial confinement combined with π‐complex‐active Cu+ of [Cu(pyz)3], pore‐space‐partitioned SNNU‐33 MOFs all present excellent C2H2/CH4, C2H4/CH4, and CO2/CH4 separation ability. Notably, the optimized SNNU‐33b adsorbent demonstrates top‐level IAST selectivity values for C2H2/CH4 (597.4) and C2H4/CH4 (69.8), as well as excellent breakthrough performance. Theoretical calculations further reveal that such benchmark light hydrocarbon separation and purification ability is mainly ascribed to the extra‐strong binding affinity between Cu+ and π‐electron donor molecules via a spatially confined π‐complexation process.