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-C4H10) and isobutane (iso-C4H10) 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-C4H10/iso-C4H10 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-C4H10 uptake of 33.6 cm3·g-1 under the conditions of 298 K and 100 kPa, together with an adsorption ratio of 4.36 for an equimolar n-C4H10/iso-C4H10 mixture. DFT calculations were performed to investigate the host-guest interactions. The results indicate that n-C4H10 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-C4H10 from C4 alkane isomers.