Preparation, characterization and luminescence-sensing properties of two Zn MOFs with mixed 5-amino-2,4,6-tribromoisophthalic acid and bipyridyl-type ligands.

Abstract

The bromo-substituted aromatic dicarboxylic acid 5-amino-2,4,6-tribromoisophthalic acid (HATBIP), in the presence of the N-donor flexible bipyridyl-type ligands 1,3-bis(pyridin-4-yl)propane (bpp) and N,N'-bis(pyridin-4-ylmethyl)oxalamide (4-bpme) and Zn ions, was used as an O-donor ligand to assemble two novel luminescent metal-organic frameworks (MOFs), namely poly[[(μ-5-amino-2,4,6-tribromoisophthalato-κO:O)[μ-1,3-bis(pyridin-4-yl)propane-κN:N']zinc(II)] dimethylformamide monosolvate], {[Zn(CHBrNO)(CHN)]·CHNO}, (1), and poly[[(μ-5-amino-2,4,6-tribromoisophthalato-κO:O)diaqua[μ-N,N'-bis(pyridin-4-ylmethyl)oxalamide-κN:N']zinc(II)] monohydrate], {[Zn(CHBrNO)(CHNO)(HO)]·HO}, (2), using the solution evaporation method. Both (1) and (2) were characterized by FT-IR spectroscopy, elemental analysis (EA), solid-state diffuse-reflectance UV-Vis spectroscopy, and powder and single-crystal X-ray diffraction analysis. Complex (1) shows a two-dimensional (2D) corrugated layer simplified as a 2D (4,4) topological network. The supramolecular interactions (π-π stacking, hydrogen bonding and C-Br...Br halogen bonding) play significant roles in the formation of an extended three-dimensional (3D) supramolecular network of (1). Complex (2) crystallizes in the chiral space group P222 and exhibits a novel 3D homochiral framework, showing a diamond-like topology with Schläfli symbol 6. The homochirality of (2) is further confirmed by the solid-state circular dichroism (CD) spectrum. The second harmonic generation (SHG) property of (2) was also investigated. The hydrogen and C-Br...Br/O halogen bonding further stabilize the framework of (2). The central Zn ions in (1) and (2) show tetrahedral and octahedral coordination geometries, respectively. The coordinated and uncoordinated water molecules in (2) could be removed selectively upon heating. Most importantly, (1) and (2) show rapid and highly sensitive sensing for a large pool of nitroaromatic explosives (NAEs).