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.
The binding domains within a mixed matrix membrane (MMM) that is selective for CO comprising MFM-300(Al) and the polymer 6FDA-Durene-DABA have been established via in situ synchrotron IR microspectroscopy. The MOF crystals are fully accessible and play a critical role in the binding of CO, creating a selective pathway to promote permeation of CO within and through the MMM. This study reveals directly the molecular mechanism for the overall enhanced performance of this MMM in terms of permeability, solubility and selectivity for CO.
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