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

The bromo-substituted aromatic dicarboxylic acid 5-amino-2,4,6-tribromoisophthalic acid (H 2 ATBIP), 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 II 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-κ 2 O 1 : O 3 )[μ-1,3-bis(pyridin-4-yl)propane-κ 2 N : N ′]zinc(II)] dimethylformamide monosolvate], {[Zn(C 8 H 2 Br 3 NO 4 )(C 13 H 14 N 2 )]·C 3 H 7 NO} n , ( 1 ), and poly[[(μ-5-amino-2,4,6-tribromoisophthalato-κ 2 O 1 : O 3 )diaqua[μ- N , N ′-bis(pyridin-4-ylmethyl)oxalamide-κ 2 N : N ′]zinc(II)] monohydrate], {[Zn(C 8 H 2 Br 3 NO 4 )(C 14 H 14 N 4 O 2 )(H 2 O) 2 ]·H 2 O} n , ( 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 P 2 1 2 1 2 1 and exhibits a novel 3D homochiral framework, showing a diamond-like topology with Schläfli symbol 6 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 II 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).