Gate-opening Induced by C8 Aromatics in a Double Diamondoid Coordination Network

Coordination networks (CNs) that undergo guest-induced structural transformations are of topical interest thanks to their potential utility in separations and storage applications. Herein, we report a double diamondoid (ddi) topology CN, [Ni₂(bimpz)₂(bdc)₂(H₂O)] or X-ddi-2-Ni (H₂bdc = 1,4-benzenedicarboxylic acid, bimpz = 3,6-bis(imidazol-1-yl)pyridazine), that undergoes structural transformations induced by C8 isomers, i.e., xylenes (o-xylene, OX; m-xylene, MX; p-xylene, PX) and ethylbenzene (EB). X-ddi-2-Ni was characterized by single-crystal to single-crystal transformations from a nonporous phase, X-ddi-2-Ni-β, to isostructural C8-loaded phases, namely X-ddi-2-Ni-OX, X-ddi-2-Ni-MX, X-ddi-2-Ni-PX and X-ddi-2-Ni-EB. X-ddi-2-Ni accommodates two C8 isomers per Ni unit, resulting in relatively high uptake (ca. 50 wt %), but with low selectivity toward C8 isomers as found using nuclear magnetic resonance (NMR) and gas chromatography (GC). In addition, a narrow range of gate-opening pressures for each isomer was determined from dynamic vapor sorption, consistent with the nonadaptable nature of the C8-loaded phase determined crystallographically, also supported by modeling.