Syntheses And Properties Of 2,4-Dichlorobenzoate-Based Lanthanide Coordination Ploymers Tuned By 4,4’-Bipyridine

In this paper,2,4-dichlorobenzoic acid（2,4-HDCB）reacted with Ln（NO₃）₃·nH₂O and NaOH under solvothermal conditions to yield five lanthanide-organiccoordinationpolymers（CPs）[Ln₂（2,4-DCB）₆（CH₃CH₂OH）₄][Ln=Sm（1）,Eu（2）]and[Ln₂（2,4-DCB）₆（H₂O）₂][Ln=Gd（3）,Tb（4）,Dy（5）].Then the second ligand4,4’-bipyridine（4,4’-bpy）was introduced into the above reaction systems to provide five lanthanide-organic CPs[Ln₂（2,4-DCB）₆（4,4’-bpy）（H₂O）₂][Ln=Sm（6）,Eu（7）,Gd（8）,Tb（9）,Dy（10）].CPs 1–10 were characterized by single-crystal X-ray diffraction,IR,PXRD,and TG analyses.Single-crystal X-ray diffraction characterization indicates that CPs 1 and2 have the same one-dimensional（1D）chain structures,and CPs 3–5 and6–10 are isostructural,respectively.In CPs 1–5,the Ln（III）ions are linked by the 2,4-DCB anions to form a 1D chain.In CPs 6–10,two Ln（III）ions are bridged by six 2,4-DCB anions into a binuclear Ln₂（2,4-DCB）₆ unit,and the Ln₂（2,4-DCB）₆ units are further connected by the 4,4’-bpy co-ligands to generate a 1D chain.The introduction of the second ligand 4,4’-bpy has an important effect on the structures of CPs 1–10.Thermogravimetric analysis shows that CPs 1–10 has a good thermal stability.The photoluminescent properties of CPs 1–2,4–7,and 9–10 were studied,and the characteristic emission of Eu/Tb（III）sensitized by the organic ligands is observed.The magnetic properties of CPs 1,3–6,and 8–10 were investigated.CPs 3 and 8 exhibit the antiferromagnetic interactions between the Gd（Ⅲ）ions,and CP 10 shows a weak slow magnetic relaxation behavior under zero dc field.