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

Abstract

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 (<b>2</b>), generated <i>in situ</i> by oxidative dehydrogenation of 1,4-bis-(4-(3,5-dicyano-2,6-dipyridyl)dihydropyridyl)naphthalene (<b>1</b>), is coupled in a 1:1 ratio with terphenyl-3,3',4,4'-tetracarboxylic acid (<b>3</b>; to form <b>SOF-8</b>), 5,5'-(anthracene-9,10-diyl)diisophthalic acid (<b>4</b>; to form <b>SOF-9</b>), or 5,5'-bis-(azanediyl)-oxalyl-diisophthalic acid (<b>5</b>; to form <b>SOF-10</b>). Complementary O-H···N hydrogen bonds assemble 2D 6³-<b>hcb</b> (honeycomb) subunits that pack as layers in <b>SOF-8</b> to give a three-dimensional (3D) supramolecular network with parallel channels hosting guest DMF (DMF = <i>N</i>,<i>N</i>'-dimethylformamide) molecules. <b>SOF-9</b> and <b>SOF-10</b> feature supramolecular networks of 2D → 3D inclined polycatenation of similar <b>hcb</b> layers as those in <b>SOF-8</b>. Although <b>SOF-8</b> suffers framework collapse upon guest removal, the polycatenated frameworks of <b>SOF-9</b> and <b>SOF-10</b> exhibit excellent chemical and thermal stability, solvent/moisture durability, and permanent porosity. Moreover, their corresponding desolvated (activated) samples <b>SOF-9a</b> and <b>SOF-10a</b> 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.