Construction of ZnII/CdII-CPs and their fluorescent detection for Fe3+, Cr2O72− and TNP in water via luminescence quenching

Abstract

Five new Zn^II/Cd^II coordination polymers (CPs) based on a flexible bis(imidazole) ligand 9,10-bis((2-methyl-1H-imidazol-1-yl)methyl)anthracene (bmima) with three different aromatic carboxylic acid ligands have been synthesized under solvothermal conditions: {[Cd(bmima)_0.5(atp)(H₂O)]·DMF·0.5H₂O} (CP 1), {[Zn(bmima)(atp)]·DMF} (CP 2), {[Cd(bmima)(bpdc)]·2DMF} (CP 3), and {[M(bmima)_0.5(oda)]·DMF·H₂O} (M = Zn for CP 4 and Cd for CP 5), (H₂atp = 2-aminoterephthalic acid; H₂bpdc = [1,1′-biphenyl]-4,4′-dicarboxylic acid and H₂oda = 4,4′-oxydibenzoic acid). CP 1 displays a 3,4-connected TiSc topology 3D framework with vertex symbols of {4²·6·10²·12}{4²·6}. CP 2 and CP 3 both feature 2D layer structures with a five-fold interpenetration framework for CP 3. CP 4 and CP 5 both show a 3D “pillar-layer” structure with pcu α-Po topology. The structural differences of the five CPs may be due to the diverse coordination modes of dicarboxylate ligands and the conformation of flexible N-donor ligands. Moreover, CP 1 and CP 3 are two good fluorescent sensors for the detection of Fe³⁺, Cr₂O₇²⁻ and TNP. The mechanism of the two sensors shows that the fluorescent sensing process toward Fe³⁺ and Cr₂O₇²⁻ is mainly attributed to the competitive absorption process, while both competitive absorption and the more efficient FRET mechanism for TNP, respectively, which indicates that CP 1 and CP 3 can serve as two fluorescence sensors to sensitively and selectively detect the presence of Fe³⁺ and Cr₂O₇²⁻ in water.