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

Abstract

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 1‚acetic 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 CO 2 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.

Manipulating the cavity of a porous material changes the photoreactivity of included guests

“…(316 m 2 g À1 ). 3,7 This corresponds to a total pore volume of 0.059 cm 3 g À1 for pores smaller than 6.9 Å in diameter, which was similar to the values for host 1.…”

“…2,3 We now report a similar macrocycle 2 that is synthesized from a benzophenone spacer and also forms porous crystals. The two macrocycles differ in their linking groups (ether 1 versus ketone 2).…”

“…(3)(4)(5)(6) and photoisomerization of trans-b-methylstyrene (7) in the presence of host 1 and host 2…”

Challenges and breakthroughs in recent research on self-assembly

“…Rovira and Veciana reported selfassembly of polychlorotriphenylmethyl radical derivatives substituted with six carboxylic acid groups for an investigation of its ferromagnetic properties [503]. Shimizu and corworkers synthesized porous apohost structures through self-assembly of bis-urea macrocycles and evaluated their guest inclusion properties [504]. Hydrogen-bond-based supramolecular polymers were fabricated through quadruplex-type self-assembly of ditopic guanosine macromonomers [505].…”

Short, strong halogen bonding in co-crystals of pyridyl bis-urea macrocycles and iodoperfluorocarbons

“…14 Our group utilizes bis-urea macrocycles that typically assemble through the three-centered urea hydrogen bonding motif into columnar structures and can incorporate guests within these inherently porous channels. [15][16][17][18] In contrast, the pyridyl macrocycle 2 forms columnar assemblies through two separate hydrogen bonding interactions between the urea N-H's and two different acceptors: the urea carbonyl oxygen and the pyridine nitrogen. 19 The electrostatic potential distributions of these macrocycles highlight these basic sites (shown in red) that are primarily localized on the urea oxygens and the pyridine nitrogens.…”