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

Abstract

The bromo-substituted aromatic dicarboxylic acid 5-amino-2,4,6-tribromoisophthalic acid (H2ATBIP) was used to assemble with CdII 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-κO)cadmium(II)]-μ-3,3′-(diazene-1,2-diyl)dipyridine-κ2 N 1:N 1′] dihydrate], {[Cd(C8H2Br3NO4)(C10H8N4)(H2O)3]·2H2O} n or {[Cd(ATBIP)(mzpy)(H2O)3]·2H2O} n , (1), and catena-poly[[[tetraaquacadmium(II)]-μ-1,3-bis(pyridin-3-ylmethyl)urea-κ2 N 1:N 1′-[diaquabis(5-amino-2,4,6-tribromoisophthalato-κO)cadmium(II)]-μ-1,3-bis(pyridin-3-ylmethyl)urea-κ2 N 1:N 1′] octahydrate], {[Cd(C8H2Br3NO4)(C12H12N4O)(H2O)3]·4H2O} n or {[Cd(ATBIP)(3bpmu)(H2O)3]·4H2O} 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 CdII metal centres in (1) and (2) into one-dimensional chains, and the ATBIP2− ligands show a monodentate coordination to the CdII 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 ATBIP2− and mzpy or 3bpmu ligands, as well as hydrogen bonds between the ATBIP2− 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.