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)]n 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.