Ligand-Based Phase Control in Porous Molecular Assemblies

Functionalization of isophthalic acid ligands with linear alkoxide groups from ethoxy through pentoxy is shown to have a pronounced effect on both the synthesis of porous paddlewheel-based molecular assemblies and their resulting surface areas and gas adsorption properties. Shorter chain length is compatible with either tetragonal or hexagonal two-dimensional materials, with the hexagonal phase favored with longer chain length. Precise tuning of reaction conditions affords discrete molecular species that are soluble in a variety of organic solvents. The isolated porous molecules display BET surface areas ranging from 125 m²/g to 545 m²/g. The pentoxide-based molecular assembly shows considerable promise for the separation of hydrocarbons with average isosteric heats of adsorption of -48 and -31 kJ/mol for ethylene and ethane, respectively.