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.