Mixed-ligand Zn-MOFs for highly luminescent sensing of nitro compounds.

Three Zn(II) metal-organic frameworks (Zn-MOFs), [Zn2(tib)(HL(1))(H2L(1))0.5]·2H2O (1), [Zn2(tib)(L(2))]·H2O (2) and [Zn3(tib)(L(3))2(H2O)6]·2 H2O (3), have been prepared by reactions of 1,3,5-tris(1-imidazolyl)benzene (tib), and biphenyl-3,3',4,4'-tetracarboxylic acid (H4L(1)), 4,4'-oxydiphthalic acid (H4L(2)), or benzene-1,3,5-tricarboxylic acid (H3L(3)) with corresponding Zn(II) salts, respectively. Single crystal structure analyses reveal that 1 and 2 are constructed by Zn-centered polyhedra, tib and multidentate tetracarboxylate ligands to form 3-dimensional frameworks. In contrast, when the tetracarboxylate ligands were replaced by tricarboxylate ligand, layered structure of 3 is produced. These compounds are further characterized by powder X-ray diffraction, element analyses, thermogravimetric analyses and photoluminescent spectroscopy. The luminescent properties of three Zn-MOFs dispersed in different solvents have been investigated systematically, demonstrating high sensitivity for the detection of nitro compounds via a fluorescence quenching mechanism.