Series of Cadmium(II) Coordination Polymers Based on a Versatile Multi-N-Donor Tecton or Mixed Carboxylate Ligands: Synthesis, Structure, and Selectively Sensing Property

Five Cd(II) metal-organic frameworks (MOFs), [Cd(HL) 2 ] ( 1 ), [Cd(HL) 2 (H 2 O) 2 ] ( 2 ), [Cd 3 (HL) 2 (obda) 2 ] ( 3 ), [Cd 2 (HL) 2 (ohmbda)(DMA)(H 2 O)] ( 4 ), and [Cd 2 (HL)(btc)(H 2 O) 2 ]·3H 2 O ( 5 ), were prepared by reactions of Cd(NO 3 ) 2 ·4H 2 O with 1-(1 H -imidazol-4-yl)-4-(4 H -tetrazol-5-yl)benzene (H 2 L) or mixed carboxylate ancillary ligands of 1,2-benzenedicarboxylic acid (H 2 obda), 5-hydroxy-1,3-benzenedicarboxylic acid (H 2 ohmbda), and 1,3,5-benzenetricarboxylic acid (H 3 btc), 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 (Schläfli) symbol of (5 2 ·6)(5 5 ·6 4 ·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 (Schläfli) symbol of (4·8 2 ) 2 (4 5 ·6·8 4 ) 2 (4 5 ·6 5 ) 2 (4 8 ·6 6 ·8). Compound 4 is a (3, 3, 8)-connected trinodal 3D net with the point (Schläfli) symbol based on a binuclear [Cd 2 N 2 O] subunit, while 5 is a 2-nodal (3, 4)-connected 2D V 2 O 5 -type network based on [Cd 2 N 2 (COO) 2 ] SBU. The studies of molecular sensing properties show that the luminescent MOFs can be employed as fluorescent sensors for the detection of Fe 3+ and nitro compounds. Compound 1 and 3 exhibit quenching responses for Fe 3+ 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.