Synthesis, Structure, and Photoluminescent Properties of Metal−Organic Coordination Polymers Assembled with Bithiophenedicarboxylic Acid

Four novel metal−organic coordination polymers with the formulas Mn3(btdc)3(DMF)4 (1), Co(btdc)(DMF)3 (2), Zn(btdc)(DMF)3 (3), and Zn(btdc)(4,4′-bpy)0.5 (4), where H2btdc = 2,2′-bithiophene-5,5′-dicarboxylic acid, DMF = N,N′-dimethylformamide, and 4,4′-bpy = 4,4′-bipyridine, have been successfully synthesized. Crystal 1 with Mn2+ as the cation features a three-dimensional (3D) infinite framework built from trimanganese clusters, and crystals 2 and 3 with Co2+ and Zn2+, respectively, as the cation both have one-dimensional zigzag polymeric coordination chains. Crystal 4 synthesized using a mixture of 4,4′-bpy and H2btdc exhibits a triply interpenetrating 3D framework built from a dizinc paddlewheel second building unit with a distorted primitive cubic single net. The results of UV/vis spectra indicate that metal binding does not disturb the detailed electronic structure of the ligand. We also demonstrate that Zn2+ can greatly enhance the luminescence emission of the H2btdc ligand, and the emission intensity of crystal 4 is almost 20 times higher than that of the free H2btdc ligand. Steady-state and time-resolved spectroscopic measurement reveal that the more rigid environment of the btdc ligand can stabilize the highly excited long-lived states in metal−organic frameworks (MOFs), which thus greatly changes the emission properties of MOFs.