Selective Supramolecular Recognition of Nitroaromatics by a Fluorescent Metal–Organic Cage Based on a Pyridine-Decorated Dibenzodiaza-Crown Macrocyclic Co(II) Complex

Abstract

Two isomorphous fluorescent (FL) lantern-shaped metal−organic cages 1 and 2 were prepared by coordinationdirected self-assembly of Co(II) centers with a new aza-crown macrocyclic ligand bearing pyridine pendant arms (L py ). The cage structures were determined using single-crystal X-ray diffraction analysis, thermogravimetric, elemental microanalysis, FT-IR spectroscopy, and powder X-ray diffraction. The crystal structures of 1 and 2 show that anions (Cl − in 1 and Br − in 2) are encapsulated within the cage cavity. 1 and 2 bear two coordinated water molecules that are directed inside the cages, surrounded by the eight pyridine rings at the "bottom" and the "roof" of the cage. These hydrogen bond donors, π systems, and the cationic nature of the cages enable 1 and 2 to encapsulate the anions. FL experiments revealed that 1 could detect nitroaromatic compounds by exhibiting selective and sensitive fluorescence quenching toward pnitroaniline (PNA), recommending a limit of detection of 4.24 ppm. Moreover, the addition of 50 μL of PNA and o-nitrophenol to the ethanolic suspension of 1 led to a significant large FL red shift, namely, 87 and 24 nm, respectively, which were significantly higher than the corresponding values observed in the presence of other nitroaromatic compounds. The titration of the ethanolic suspension of 1, with various concentrations of PNA (>12 μM) demonstrated a concentration-dependent emission red shift. Hence, the efficient FL quenching of 1 was capable of distinguishing the dinitrobenzene isomers. Meanwhile, the observed red shift (10 nm) and quenching of this emission band under the influence of a trace amount of o-and p-nitrophenol isomers also showed that 1 could discriminate between o-and p-nitrophenol. Replacement of the chlorido with a bromido ligand in 1 generated cage 2 which was a more electron-donating cage than 1. The FL experiments showed that 2 was partially more sensitive and less selective toward NACs than 1.

Formation of an Unusual Pseudo-Square Planar-Induced Mercury(II) Dimeric Complex

“…Macrocyclic ligands play a critical role in supramolecular coordination chemistry due to their specific ability to selectively bind and self-assemble with particular metals or guest molecules [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. This selectivity is the result of their unique structure, which forms a cyclic cavity that can accommodate specific species.…”