Discovery of Spontaneous De-interpenetration Through Charged Point-Point Repulsions

Sylvia Hanna, Northwestern University

Photo of Sylvia Hanna

Energetically driven reduction of surface area and porosity through entanglement is ubiquitous in Nature and synthetic systems. This entanglement leads to reduction of valuable internal pore space useful for applications such as catalysis, storage, sensing, and bio-molecule encapsulation. In this poster, I will describe the discovery of spontaneous de-interpenetration in a 6-fold interpenetrated uranium-based metal–organic framework (MOF), NU-1303-6. De-interpenetration transforms the small pore (14.2 Å and 19.8 Å) NU-1303-6 to its larger pore (40.7 Å) non-interpenetrated counterpart which possesses a record high 96.6% void fraction and 9.2 cm3g-1 pore volume of any MOF reported to date. Density functional theory calculations reveal that the origin of this thermodynamically favorable phenomenon stems from charged point-point repulsion between anionic, closely positioned uranium-based nodes in NU-1303-6. These repulsions compete with hydrogen-bonded water molecules that bridge together nearby networks, favoring interpenetration. Controlling the interplay between these intermolecular forces enables the reversal of omnipresent energetic equilibria, leading to thermodynamically favored open pore structures. The newly discovered phenomenon of charged point-point repulsion will likely lead to the re-evaluation of non-interpenetrated networks including their design, synthesis, and wide-reaching applications. More fundamentally, this discovery compels a re-evaluation of the thermodynamics of porosity in both uranium species and molecular network systems.

Abstract Author(s): Sylvia L. Hanna