Synthesis and characterization of two one-dimensional Cd-II coordination polymers (CPs) with 5-amino-2,4,6-tribromoisophthalic acid and flexible N-donor bipyridyl ligands

The bromo-substituted aromatic dicarboxylic acid 5-amino-2,4,6-tribromoisophthalic acid (H(2)ATBIP) was used to assemble with Cd-II ions in the presence of the N-donor flexible bipyridyl ligands 3,3'-(diazene-1,2-diyl) dipyridine (mzpy) and 1,3-bis(pyridin-3-ylmethyl) urea (3bpmu), leading to the formation of two chain coordination polymers by adopting solution methods, namely, catena-poly[[[triaqua(5-amino-2,4,6-tribromoisophthalato-kappa O)cadmium(II)]-mu-3,3'-( diazene-1,2-diyl)dipyridine-kappa N-2(1):N-1'] dihydrate], {[Cd(C8H2Br3NO4)(C10H8N4)( H2O)(3)]center dot 2H(2)O}(n) or {[Cd(ATBIP)(mzpy)(H2O)(3)]center dot 2H(2)O}(n), (1), and catenapoly[[[tetraaquacadmium(II)]-mu-1,3-bis(pyridin-3-ylmethyl)urea-kappa N-2(1):N'-[diaquabis( 5-amino-2,4,6-tribromoisophthalato-kappa O)cadmium(II)]-mu-1,3-bis(pyridin-3-ylmethyl) urea-kappa N-2(1):N-1'] octahydrate], {[Cd(C8H2Br3NO4)(C12H12N4O)(H2O)(3)]center dot 4H(2)O}(n) or {[Cd(ATBIP)(3bpmu)(H2O)(3)]center dot 4H(2)O}(n), (2). Both complexes were characterized by FT-IR spectroscopic analysis, thermogravimetric analysis (TGA), solid-state diffuse reflectance UV-Vis spectroscopic analysis, and single-crystal and powder X-ray diffraction analysis (PXRD). The mzpy and 3bpmu ligands bridge the Cd II metal centres in (1) and (2) into one-dimensional chains, and the ATBIP(2-) ligands show a monodentate coordination to the Cd II centres in both coordination polymers. A discrete water tetramer exists in (1). Within the chains of (1) and (2), there are halogen bonds between adjacent ATBIP(2-) and mzpy or 3bpmu ligands, as well as hydrogen bonds between the ATBIP(2-) ligands and the coordinated water molecules. With the aid of weak interactions, the structures of (1) and (2) are further extended into three-dimensional supramolecular networks. An analysis of the solid-state diffuse reflectance UV-Vis spectra of (1) and (2) indicates that a wide indirect band gap exists in both complexes. Complexes (1) and (2) exhibit irreversible and reversible dehydration-rehydration behaviours, respectively, and the solid-state fluorescence properties of both complexes have been studied.