Carboxylate ligand-directed synthesis of cucurbit[5]uril-based coordination polymers for the detection of norfloxacin

Owing to the large-scale abuse of antibiotics and their great threat to human health, developing efficient sensing materials to monitor antibiotics has attracted enormous attention in recent years. In this work, three new cucurbit[5]uril-based (Q[5]) coordination polymers (CPs) with the formulas [Ba₂(NO₃)(H₂O)₃(L1)(Q[5])]·8H₂O (1), [Ca(H₂O)₃(L2)(Q[5])_0.5] (2) and [Ba₄(H₂O)₄(L3)(Q[5])₂]·(NO₃)₄·30H₂O (3) were synthesized by employing three different aromatic carboxylate ligands, [1,1'-biphenyl]-3,4',5-tricarboxylic acid (H₃L1), 2,2'-dinitro-[1,1'-biphenyl]-4,4'-dicarboxylic acid (H₂L2), and [1,1'-biphenyl]-3,3',5,5'-tetracarboxylic acid (H₄L3), respectively. Crystal structural analysis revealed that complexes 1, 2 and 3 displayed an interesting structural variation from 1D coordination chains (1) to 2D coordination networks (2) to unique 3D coordination frameworks (3), suggesting that the substitution groups and coordination modes of the introduced second ligands have a significant effect on the structural dimensions of the formed Q[5]-based coordination polymers. More impressively, complex 2 showed a unique fluorescence ratiometric sensing capability toward norfloxacin (NFX) in aqueous media, with high selectivity, superior sensitivity and low detection limit.