Ionic liquid directed syntheses of water-stable Eu- and Tb-organic-frameworks for aqueous-phase detection of nitroaromatic explosives

Reactions of lanthanide nitrate, 1,3,5-benzenetrisbenzoic acid (H3BTB) and [RMI]Br ionic liquids (RMI = 1-alkyl-3-methylimidazolium; R = ethyl, propyl, butyl, amyl, or hexyl), gave rise to two novel lanthanide metal-organic frameworks (Ln-MOFs) [Ln(BTB)H2O], where Ln = Eu 1, Tb 2. In addition to helping solubilise the starting materials under the reaction conditions there is evidence that [RMI]Br itself can play a structure directing role and is intimately involved in template ordering in [Ln(BTB)H2O], even though neither the [RMI](+) cation nor the Br- anion is occluded into the ultimate structure. 1 and 2 are isostructural and consist of infinite rod-shaped lanthanide-carboxylate building units which are further bridged by trigonal-planar BTB ligands to give noninterpenetrated open 3D frameworks featuring a (6,6)-connected topology with the point symbol (4(4).6(7).8(4))(4(8).6(7)). Importantly, the strong emission of 1 and 2 dispersed in water prompted us to explore their application for detection of different nitroaromatics in an aquatic system. 1 and 2 show similar selectivity and sensitivity towards the presence of trace amounts of nitroaromatic analytes in the aqueous phase, showing potential as explosive sensors.