Syntheses,structures And Luminescence Properties Of Lanthanide Coordination Polymers

Coordination polymers(CPs)are constructed by metal ions or metal clusters and bridging multidentate organic ligands to form 1D,2D and 3D frameworks,and they are also synonymous with metal organic frameworks(MOFs).In the past two decades,CPs have been developed rapidly and widely used in gas storage and separation,catalysis,magnetism,conductivity,luminescence,sensing,drug delivery and other fields.This can be attributed to their simple synthetic routes and the development of X-ray crystallographic techniques.In a wide variety of CPs,the lanthanide coordination polymers(Ln-CPs)have attracted extensive attention due to their unique luminescence properties,such as high luminescence efficiency,characteristically sharp line emissions,long-lived emission and the luminescent range completely across the entire visible spectrum.Moreover,Ln-CPs can be used as the excellent candidates for luminescence tuning and white light-emission.CPs are mostly prepared by a self-assembly process,i.e.,crystallization,so the experimental conditions(e.g.,organic ligand and solvent,concentration,p H,temperature and time)employed for the synthesis of CPs significantly influence the final structure.Organic ligands with appropriate shape,functionality and symmetry play a key role in the synthesis of porous CPs.At present,bifunctional pyridine carboxylic acid organic ligands and their derivatives with the excellent coordination ability and diverse coordination modes have been widely used to construct stable porous CPs.In this work,ten Ln-CPs were synthesized based on 4-hydroxypyridine-2,6-dicarboxylic acid(H2L1)and 5-(4-pyridiyl)-isophthalic acid(H2L2)as the organic linkers under hydrothermal/solvent thermal conditions.We studied the structures and the characterizations of these Ln-CPs,and their applications in luminescence,magnetism and chemical sensing of metal ions.1.Five Ln-CPs [Ln2(L1)3(H2O)4]·2H2O(Ln = Eu(1),Tb(2),Gd(3))and [Gd2(H2O)4(L1)(C2O4)2]·3H2O(4)were synthesized based on H2L1 under hydrothermal conditions.It is worth noting that oxalic acid in the resulting framework of the compound 4 is formed in situ under hydrothermal conditions.The structural analyses reveal that the compounds 1-3 are isomorphous.A series of doped Ln-CPs [(Eu0.02-x Tbx Gd0.98)2(H2O)4(L1)3]·2H2O(x = 0,0.002,0.005,0.008,0.01,0.012,0.015,0.018,0.02)were synthesized by adjusting the co-doping ratio of Eu3+,Tb3+ and Gd3+ ions into the same framework as that of 1,the luminescent color can be tuned from green to red by changing the doping concentration of the Tb3+ ions.By increasing the amount of Gd3+,we have successfully constructed a novel doped [(Eu0.0073Tb0.0007Gd0.992)2(H2O)4(L1)3]·2H2O(5).It shows a white light emission with CIE coordinates of(0.336,0.327),which are very close to pure white light(0.333,0.333).In addition,the compound 3 shows weak ferromagnetic interactions.2.Five isomorphous two-dimensional layer Ln-CPs [Ln(H2O)2(HL2)(L2)](Ln = Eu(6),Tb(7),Gd(8)),[Tb1-x Eux(H2O)2(HL2)(L2)](9),[Gd0.998Tb0.0012Eu0.0008(H2O)2(HL2)(L2)](10)were synthesized based on H2L2 under solvent thermal conditions.By adjusting the co-doping ratio of Eu3+ and Tb3+ ions into the same framework as that of 7,we successfully designed and constructed a series of Eu3+-doped 7-Tb Ln-CPs [Tb1-x Eux(H2O)2(HL2)(L2)](x = 0,0.033,0.067,0.133,0.2,0.4,0.5,0.6,0.8,1.0)(9),the luminescent color of 9 can be tuned from green to yellow and red by varying the doping concentration of the Eu3+ ion,and the fluorescence lifetime in 9 indicates that the energy transfer from the Tb3+ center to the Eu3+ center indeed occurs.By increasing the amount of Gd3+,we have successfully constructed a novel doped [Gd0.998Tb0.0012Eu0.0008(H2O)2(HL2)(L2)](10)and it shows a white light emission with CIE coordinates of(0.327,0.329).In addition,compound 6 exhibits good luminescence sensing for the metal ions Mn+(n = 1-3)in aqueous solution.It can be found that compound 6 shows no obvious quenching for Na+,and remarkable fluorescence quenching effect toward Ni2+,Cu2+ and Cr3+.More importantly,when the concentration of Ni2+ and Cr3+ being 10-5 mol.L-1,the fluorescence quenching is still obvious.