Absorption Properties of a Porous Organic Crystalline Apohost Formed by a Self-Assembled Bis-Urea Macrocycle

We report herein the characterization and binding properties of a microporous crystalline host formed by the self assembly of a bis-urea macrocycle 1. Bis-urea macrocycle 1 has been designed to crystallize into stacked hollow columns. The self-assembly process is guided primarily by hydrogen bonding and aromatic stacking interactions that yield crystals of filled host 1âacetic acid (AcOH). The AcOH guests are bound in the cylindrical cavities of the crystal. The guest AcOH can be removed by heating to form a stable crystalline apohost 1. Apohost 1 displays a type I gas adsorption isotherm with CO2 that is consistent with an open framework microporous material. Apohost 1 binds a range of small molecule guests with specific stoichiometry. The formation of these inclusion complexes does not destroy the crystal framework and therefore apohost 1 can be reused, much like a zeolite. We investigated the structure of apohost 1 and its inclusion complexes by powder X-ray diffraction. The ability of guests to bind and their stoichiometry could be rationalized on the basis of the size, shape, and polarity of the guest molecules. Finally, the shape selectivity of these self-assembled porous materials was demonstrated in competition studies in which apohost 1 preferentially bound p-xylene from a mixture of xylene isomers