Metal-organic frameworks assembled from flexible alicyclic carboxylate and bipyridyl ligands for sensing of nitroaromatic explosives

Three new metal-organic frameworks based on flexible ligands (FL-MOFs) generally formulated as [Cd(cis-chdc)(anti-bpe)(H2O)](n) (1), [Ni(cis-chdc)(gauche-bpe)](n) (2) and [Cd-2(trans-chdc)(cis-chdc)(TG-bpp)(2)](n) (3) [H(2)chdc = 1,4-cyclohexanedicarboxylic acid, bpe = 1,2-bis(4-pyridyl)ethane and bpp = 1,3-bis(4-pyridyl) propane], have been hydrothermally synthesized and characterized. The crystal structures of the three compounds feature one-dimensional infinite chains cross-linked via flexible ligand skeletons to form three-dimensional networks. Of peculiar interest, compound 1 represents a rare self-catenated MOF with a 6(5).8-zst topology, which shows high sensitivity and quick response to the presence of trace amounts of nitroaromatic compounds. Meanwhile, the excellent ability of 1 for selective detection of 4-nitrotoluene in the presence of other nitroaromatic compounds has been demonstrated. The recyclability and reusability of 1 have also been tested based on consecutive detection reactions, in which 1 remains unchanged and detection efficiency is maintained.