Pore Contraction in an Adenine-Based Metal-Organic Framework for Light Hydrocarbon Separation

Control of pore size is a central challenge in designing porous frameworks for hydrocarbon separations. Here we report an adenine-based metal-organic framework, Zn(pip)(ad), assembled from adenine (Had) and piperidine-4-carboxylic acid (Hpip). Replacement of the planar aromatic isonicotinate (int) ligand with a saturated pip ligand subtly modifies the pore size and pore environment relative to previously reported frameworks. The resulting pore environment leads to preferential adsorption of heavier hydrocarbons over methane, following the trend C₃H₈ > C₂H₆ ≫ CH₄. Dynamic breakthrough experiments further demonstrate the stepwise separation of CH₄/C₂H₆/C₃H₈ mixtures, producing high-purity methane in the first elution stage. This work demonstrates that replacing aromatic pyridine carboxylates with saturated amine carboxylates expands the linker scope beyond int derivatives and provides new opportunities for tuning pore size and pore environment in adenine-based frameworks.