Preparation And Fluorescence Sensing Properties Of Coordination Polymers Based On Aromatic Carboxylic Acid Ligands

Aromatic carboxylic acid complexes not only have diversified structures because the carboxyl groups of the carboxylic acid can be completely deprotonated or partially deprotonated,but also generally have excellent fluorescence properties due to the existence of large conjugated π bonds.Compared with traditional detection devices,sensors based on coordination polymers have the advantages of portability,high selectivity,high sensitivity,and easy operation.In order to prepare luminescence sensors with excellent performance,we mainly select aromatic carboxylic acid ligands and pyridylamine ligands as main ligands due to their conjugated structures and multiple coordination sites.By using aromatic carboxylic acid triphenyl-3,2",5 "3 ’-tetracarboxylic acid(H4L1),3-(pyridin-3-yloxy)phthalic acid(H2L2),2-(pyridin-2-yl)-1H-benzimidazole-5-carboxylic acid(HL3),2-(4-(1H-1,2,4-triazol-1-yl)benzene)-1 H-benzimidazole-5,6-dicarboxylic acid(H2L4)and N-(2,4,4,6,6,6,8,8-heptyl(pyridin-4-ylamino))-1,3,5,7,2,4,6,8-Tetraoxanephosphate-2-yl)pyridine-4-ami ne(L5)and transition metal ions,seven coordination polymers with novel structures,[Zn2(Li)(H2O)3]n 1,[Mn3(L1)(OH)2(H2O)4]n 2,[Zn(L2)(H2O)]n 3,[Cd(L2)(H2O)2]n·nH2O4,[Cd(L3)Cl]n 5,[Co5(L4)4(OH)2]n·4nH2O 6,[Zn3(L5)(ox)3]n·nDMF.2nH2O 7 were prepared.X-ray single crystal diffraction,Fourier-infrared spectroscopy,thermal stability analysis and X-ray powder diffraction were used to characterize the constructed materials and the fluorescence sensing performance was studied.Single crystal diffraction results show that in compound 1,the binuclear Zn units are connected by the oxygen atom on the carboxyl group from two H4L1 ligands to form a one-dimensional structure which are connected to a three-dimensional network structure through the oxygen atoms of the carboxyl groups from the H4L1 ligand.In compound 2,the oxygen atom of the hydroxyl group bridges two different adjacent Mn centers to form a one-dimensional staircase chain parallel to the b axis.Adjacent one-dimensional chains are connected to each other by oxygen atoms of the carboxyl groups from the H4L1 ligand to form a three-dimensional network structure of 2.In compound 3,the H2L2 ligands connect adjacent Zn ions through carboxyl oxygen atoms and nitrogen atoms of the pyridine ring to form a one-dimensional double-stranded structure along the c axis.In compound 4,the carboxyl oxygen atom of the H2L2 ligand and the nitrogen atom of the pyridine ring connect the adjacent Cd to form a one-dimensional chain parallel to the b axis.Adjacent one-dimensional chains are connected by the oxygen atom of the other carboxyl group of the H2L2 ligand to form a two-dimensional grid structure parallel to the ab plane.In compound 5,two Cl-bridge two adjacent Cd centers to form a dimer and the HL3 ligand connects the adjacent dimer units to form a two-dimensional grid structure parallel to the be plane.In compound 6,the carboxyl oxygen atoms of L42-ligand bridge three Co centers to form a one-dimensional Co-O chain along the a axis.The adjacent one-dimensional chains are interconnected by N5 and N10 atoms on the triazole ring from two different ligands to form a three-dimensional structure with one-dimensional pores filled with solvent water molecules.In compound 7,the ox ligands bridge the adjacent Zn centers to form a one-dimensional chain structure along the a axis.In addition,the N atoms on the four pyridine rings from L5 ligands connect the adjacent one-dimensional chains respectively,and finally form a three-dimensional network structure.The X-ray powder diffraction data of 1-7 show that compounds 1-7 are all high-purity phases,further indicating that the synthesis method is mature and reliable.The thermogravimetric analysis of compounds 1-7 shows that compounds 1-7 have good thermal stability.The solid-state fluorescence properties of compound 1 were tested.The fluorescence sensing properties of compounds 2-5 and 7 were studied.It was found that compounds 2-5 and 7 have fluorescence quenching sensing capabilities for Fe3+,Cr2O72-and CrO42-ions in the solution and show higher detection sensitivity and lower detection limit.At the same time,competition and cycling experiments show that 2-5 and 7 have good anti-interference ability and recyclability for the fluorescence sensing of Fe3+,Cr2O72-and CrO42-,which indicates that 2-5 and 7 can be used as Fe3+,Cr2O72-and CrO42-fluorescent probe.At the same time,the quenching mechanism related to 2-5 and 7 was studied.