Collapse or capture? Guest-induced response of two structurally distinct pillared-MOFs upon exposure to pyridines and quinolines

The response of two differently entangled, Zn-containing, pillared metal-organic frameworks (MOFs) toward quinolines and pyridines was studied. The corresponding products have been defined by single crystal X-ray diffraction analysis, when possible through single-crystal-to-single-crystal transformations. These two MOFs have similar chemical compositions, each consisting of a dicarboxylate linker (4,4'-biphenyldicarboxylate or 2,6-naphthalenedicarboxylate) and the same bis-amide-bis-pyridine pillar. The flexible and interpenetrated MOF PUM168 and the rigid and polycatenated PUM210 exhibit good uptake propensity towards quinoline, although structural modelling of all the included guest molecules was successful only for PUM168. For PUM210, only one molecule of quinoline coordinated to a metal center was modeled, whereas the remaining molecules were randomly distributed along the channels. The PUM168 and PUM210 crystals rapidly degraded once in contact with liquid pyridines. The decomposition products of PUM210 in pyridine were structurally characterized, giving insights into the degradation pathway. This involves the replacement of the bis-amide-bis-pyridine pillar by pyridine with the formation of a new homoleptic 1D-coordination polymer in which Zn ions are bound to naphthalenedicarboxylate dianions and pyridine molecules. Finally, the uptake of the chelating 8-hydroxyquinoline by PUM168 led to the protonolysis of the dicarboxylate linker and the extraction of Zn ions from the framework, with formation of the bis-chelate complex Zn(8-hydroxyquinolinate)₂.