Polycatenated 2D Hydrogen-Bonded Binary Supramolecular Organic Frameworks (SOFs) with Enhanced Gas Adsorption and Selectivity

Controlled assembly of two-dimensional (2D) supramolecular organic frameworks (SOFs) has been demonstrated through a binary strategy in which 1,4-bis-(4-(3,5-dicyano-2,6-dipyridyl)pyridyl)naphthalene (2), generated in situ by oxidative dehydrogenation of 1,4-bis-(4-(3,5-dicyano-2,6-dipyridyl)dihydropyridyl)naphthalene (1), is coupled in a 1:1 ratio with terphenyl-3,3',4,4'-tetracarboxylic acid (3; to form SOF-8), 5,5'-(anthracene-9,10-diyl)diisophthalic acid (4; to form SOF-9), or 5,5'-bis-(azanediyl)-oxalyl-diisophthalic acid (5; to form SOF-10). Complementary O-H···N hydrogen bonds assemble 2D 63-hcb (honeycomb) subunits that pack as layers in SOF-8 to give a three-dimensional (3D) supramolecular network with parallel channels hosting guest DMF (DMF = N,N'-dimethylformamide) molecules. SOF-9 and SOF-10 feature supramolecular networks of 2D → 3D inclined polycatenation of similar hcb layers as those in SOF-8. Although SOF-8 suffers framework collapse upon guest removal, the polycatenated frameworks of SOF-9 and SOF-10 exhibit excellent chemical and thermal stability, solvent/moisture durability, and permanent porosity. Moreover, their corresponding desolvated (activated) samples SOF-9a and SOF-10a display enhanced adsorption and selectivity for CO2 over N2 and CH4. The structures of these activated compounds are well described by quantum chemistry calculations, which have allowed us to determine their mechanical properties, as well as identify their soft deformation modes and a large number of low-energy vibration modes. These results not only demonstrate an effective synthetic platform for porous organic molecular materials stabilized solely by primary hydrogen bonds but also suggest a viable means to build robust SOF materials with enhanced gas uptake capacity and selectivity.