Series of cadmium(II) coordination polymers based on a versatile multi-N-donor tecton or mixed carboxylate ligands: Synthesis, structure, and selectively sensing property

Abstract

Five Cd(II) metal−organic frameworks (MOFs), [Cd(HL)2] (1), [ C d (H L) 2 (H 2 O) 2 ] (2), [ C d 3 (H L) 2 (o b d a) 2 ] (3), [Cd2(HL)2(ohmbda)(DMA)(H2O)] (4), and [Cd2(HL)(btc)(H2O)2]· 3H2O (5), were prepared by reactions of Cd(NO3)2·4H2O with 1-(1H-imidazol-4-yl)-4-(4H-tetrazol-5-yl)benzene (H2L) or mixed carboxylate ancillary ligands of 1,2-benzenedicarboxylic acid (H2obda), 5-hydroxy-1,3-benzenedicarboxylic acid (H2ohmbda), and 1,3,5-benzenetricarboxylic acid (H3btc), respectively. Their structures have been characterized by single-crystal X-ray diffraction, elemental analysis, infrared spectroscopy (IR), thermogravimetric analysis, and powder X-ray diffraction. Compounds 1 and 2 are supramolecular isomeric frameworks without consideration of the solvent molecules. Complex 1 exhibits a binodal (3, 5)-connected two-dimensional (2D) layer structure with the point (Schlafl i) symbol of (52· 6)(55·64·7), while complex 2 shows a 2D + 2D → 3D (three-dimensional) framework. Complex 3 is a (3, 5, 6)-connected tetranodal 3D net with the point (Schlafl i) symbol of (4·82)2(45·6·84)2(45·65)2(48·66·8). Compound 4 is a (3, 3, 8)-connected trinodal 3D net with the point (Schlafl i) symbol based on a binuclear [Cd2N2O] subunit, while 5 is a 2-nodal (3, 4)-connected 2D V2O5-type network based on [Cd2N2(COO)2] SBU. The studies of molecular sensing properties show that the luminescent MOFs can be employed as fluorescent sensors for the detection of Fe3+ and nitro compounds. Compound 1 and 3 exhibit quenching responses for Fe3+ in dimethylformamide solution with detection limits of 2.3 × 10−6 and 8.6 × 10−7 M, respectively. Meanwhile, compound 5 can sense 4-nitrophenol with a detection limit as low as 5.75 × 10−7 M.