Design of higher valency in covalent organic frameworks

Abstract

The valency (connectivity) of building units in covalent organic frameworks (COFs) has been primarily 3 and 4, corresponding to triangles and squares or tetrahedrons, respectively. We report a strategy for making COFs with valency 8 (cubes) and “infinity” (rods). The linker 1,4-boronophenylphosphonic acid—designed to have boron and phosphorus as an isoelectronic combination of carbon-group elements—was condensed into a porous, polycubane structure (BP-COF-1) formulated as (–B4P4O12–)(–C6H4–)4. It was characterized by x-ray powder diffraction techniques, which revealed cubes linked with phenyls. The isoreticular forms (BP-COF-2 to 5) were similarly prepared and characterized. Large single crystals of a constitutionally isomeric COF (BP-COF-6), composed of rod units, were also synthesized using the same strategy, thus propelling COF chemistry into a new valency regime.

Reticular design and crystal structure determination of covalent organic frameworks

“…71 These studies, however, draw our attention to another issue which is the generalizability-the modulator approach up to this point works well only for 3D imine-linked COFs. 72,73 Recently, Yaghi and co-workers have reported single crystals of a 2D BP-COF-6 based on boron-phosphorous linkages; 49 it is likely that the single crystals of BP-COF-6 are in situ formed under acidic conditions and are not applicable to the vast chemistry of COFs based on a variety of linkages (though the formation of BP-COF-6 paves the way for future use of specic linkers that are able to generate organic clusters in situ). At this point, it should be noted that COF chemists are still facing a great challenge with the limitation of COF crystallization, and new chemistry with impactful solutions is highly needed to open the avenue for diversifying COF chemistry.…”

Heterogeneous C–H Functionalization in Water via Porous Covalent Organic Framework Nanofilms: A Case of Catalytic Sphere Transmutation

“…Covalent organic frameworks (COFs) are a new class of crystalline materials, with highly ordered organic building blocks and discrete nano-pores. [18][19][20][21][22] The organic building units in COFs, stacked into in nite 1D columns, are ideal for docking catalysts and providing a hydrophobic microenvironment around the active site. [23][24][25] Hence, we designed a nanospherical formulation of a two-dimensional covalent organic framework with predesigned functionality.…”

Conquering the crystallinity conundrum: efforts to increase quality of covalent organic frameworks

“…In the same year, an imidazole linked COF, chemically comparable to the previously mentioned benzoaxazole linkage, could be obtained by reaction of carboxylic acids and diamines. 52 Finally, very recently the ester, 53 pyrimidazole 54 and polycubane 55 linkages were added to the ever expanding library of COF linkages. Whereas the pyrimidazole linkage was shown to be stable in both 9 M HCl and NaOH, the ester linkage was susceptible to both acids and bases but stable in aqueous environments.…”

“…Finally, the bcu net could be obtained by using the aforementioned polycubane linkage as a octahedral node. 55 The structural diversity of COFs goes beyond the underlying topologies, for example isoreticular expansion and contraction is an often studied concept which can have large implications on the structure. Some 3D structures (like dia and pts topologies) are prone to interpenetration, which can be significantly altered by expanding or contracting the used linkers.…”