Syntheses Of Terphenylacarboxylic Acid Metal Coordination Polymers And Detection For Metal Ions

Metal-multicarboxylate supramolecular coordination polymer,as a new type of metal-organic materials,is formed by metal ions and organic ligands through self-assembly.Owing to the high surface areas,high stability and well-defined structures,supramolecular coordination polymer has been widely used in gas storage,catalysis,drug delivery and fluorescence detection and becomes a hot research topic for scientists.Especially in the field of fluorescence detection,supramolecular coordination polymer is applied in the detection of Hg²⁺,Al³⁺,Cu²⁺ ions because of its high selectivity and sensitivity to certain metal ions.In this paper,2’,5’-dimethyl-[1,1’:4’,1’’-terphenyl]-4,4’’-dicarboxylic acid was chosen as organic ligand to reacted with transition metal Zn²⁺ and Cd²⁺.Thus,two three-dimensional supramolecular coordination polymer were obtained,and the metal ions were detected by the fluorescence properties of these compounds.First of all,we chosen the 4-methoxyl carbonylphenylboronic acid and1,4-dibromo-2,5-dimethylbenzene as raw materials,to synthesize the ligand of2’,5’-dimethyl-[1,1’:4’,1’’-terphenyl]-4,4’’-dicarboxylic acid（TPDC-2CH₃）by using a Suzuki coupling reaction.Then,two highly fluorescent functionalized metal-multicarboxylate supramolecular coordination polymers crystals,[Zn（TPDC-2CH₃）（H₂O）₂]·H₂O（1）and [Cd（TPDC-2CH₃）（H₂O）₄]·H₂O（2）,were successfully designed and synthesized by diffusion method.Then the structure of the organic ligand was determined by Fourier transform infrared（FT-IR）,Nuclear magnetic resonance hydrogen spectrum（1H NMR）and Nuclear magnetic resonance carbon spectrum(¹³C NMR).The structures of compounds 1 and 2were characterized by using Fourier transform infrared,Powder X-ray diffraction patterns,X-ray diffraction analysis and UV-Vis absorption spectrum.The X-ray diffraction analysis revealed that the crystal system of compounds 1 and 2 belong to monoclinic system.Both the structures of compounds 1 and 2 are thethree-dimensional supramolecular frameworks.The results of thermogravimetric analysis show that compounds 1 and 2 can maintain the integrity of the framework at 400 ℃ and have good thermal stability.Fluorescence detection of metal ions was carried out by using these compounds materials,and its result shows that the compounds 1 and 2 exhibit high selectivity and sensitivity of detect Hg²⁺,Cu²⁺,and Fe³⁺ ions.Especially for the detection of Hg²⁺ ion,the compound 1 showed higher detection capabilities compared with the compound 2.The results of selective detection revealed that the fluorescence emission intensity of compound 1 is only related to the concentration of Hg²⁺ and is not affected by p H.Simultaneously,the detection limit of Hg²⁺ ion was calculated.The result shows that the compound 1 has higher detection ability to Hg²⁺ ions,and the detection limit can reach 3.6×10-15 mol·L^-1.