Pore-Chemistry Modulation via Ligand Functionalization in Cu−Pyrimidinecarboxylate Coordination Networks Enables High-Selectivity Recovery of n-Butane from Isobutane

The close similarity in molecular dimensions and physicochemical properties between n -butane ( n -C 4 H 10 ) and isobutane (iso-C 4 H 10 ) makes their separation a persistent industrial challenge. In this work, we employ two copper-based coordination networks, Cu-APC and Cu-MPC , constructed from amino- and methyl-functionalized pyrimidine-5-carboxylate ligands, respectively, for n -C 4 H 10 /iso-C 4 H 10 separation. The two frameworks exhibit distinct interlayer channel apertures (5.2 Å for Cu-APC and 4.1 Å for Cu-MPC ), enabling a systematic comparison of pore-chemistry effects on C4 isomer discrimination. Cu-APC exhibits a remarkable n -C 4 H 10 uptake of 33.6 cm 3 ·g −1 under the conditions of 298 K and 100 kPa, together with an adsorption ratio of 4.36 for an equimolar n -C 4 H 10 /iso-C 4 H 10 mixture. DFT calculations were performed to investigate the host−guest interactions. The results indicate that n -C 4 H 10 is preferentially stabilized within the 2D framework via synergistic C−H···π and C−H···N contacts, with measured distances of 3.42 Å and 3.15−3.68 Å, respectively. Cyclic fixed-bed breakthrough experiments further confirm the excellent stability and regenerability of Cu-APC , positioning it as a viable candidate for the energy-saving separation of n -C 4 H 10 from C4 alkane isomers.