Cage Based Crystalline Covalent Organic Frameworks

The first two cage
based crystalline covalent organic frameworks, cage-COF-1 and cage-COF-2, were constructed from a prism-like
three-aldehyde-containing molecular cage. The cage contains two horizontal
phloroglucinol and three vertical triazine moieties forming three
identical V-shaped cavities. By reacting with p-phenylenediamine
and 4,4′-biphenyldiamine, the two cage-COFs were formed with
a hexagonal skeleton and possess a unique structure. Due to the pillared
cage nodes, the linkers are hanging with their π-surfaces but
not C–H sites exposed to the pore, and enjoy certain rotational
dynamics as suggested by 13C CP/MAS NMR. The antidirection
of the diimine linkages leads to rippled layers which pack in unique
ABC mode through alternate stacking of the cage twosided faces in
both AB and AC layers. Such packing forms trigonal channels along c axis which are interconnected in ab plane
due to the large open space created across the hanging linkers, resembling
the porous characteristics of 3D COFs. The cage-COFs have a permanent
porosity and can adsorb CO2 facilitated by the intrinsic
cage cavities that serve as prime adsorption sites. The unprecedented
cage-COFs not only merge the borderline of 2D and 3D COFs but also
bridge porous organic cages to extended crystalline organic frameworks.