Structure and Luminescent Properties of A 3D Tb-MOF with Mixed Ligands of Terephthalate and Phthalate

A new three-dimensional (3D) Tb(III) metal organic framework (MOF) containing two types of carboxylic acids of terephthalic acid (1,4-benzenedicarboxylic acid) and phthalic acid (1,2-benzenedicarboxylic acid) was synthesized under hydrothermal condition at 180 °C. The formula of the 3D Tb-MOF is [Tb(1,4-bdc)0.5(1,2-bdc)(H2O)2]n (MOF-1), (1,4-H2bdc = 1,4-benzenedicarboxylic acid; 1,2-H2bdc = 1,2-benzenedicarboxylic acid). X-ray single crystal diffraction showed that the structure of Tb-MOF was 3D network. 1,2-bdc ligands coordinated with Tb(III) by oxygen atoms of the carboxyl groups and connected four Tb(III) to form 2D layers. The 1,4-bdc ligands further connected the 2D layers to construct 3D network structure. The Tb-MOF emitted the characteristic green light of Tb(III) excited by ultraviolet rays. Compared with three other similar Tb-MOFs [Tb(1,4-bdc)0.5(3,4-pdc)(H2O)2]n (MOF-2), {[Tb2(3,5-pdc)(3,4-pdc)2(H2O)4]·2H2O}n (MOF-3) and {[Tb2(3,5-pdc)(1,2-bdc)2(H2O)4]·2H2O}n (MOF-4), (3,5-H2pdc = 3,5-pyridinedicarboxylic acid; 3,4-H2pdc = 3,4-pyridinedicarboxylic acid) previously reported, it was found that MOF-1 [Tb(1,4-bdc)0.5(1,2-bdc)(H2O)2]n has the highest absolute luminescence quantum yield (Фabs) and longest luminescence lifetime in the four Tb-MOFs. The Фabs is 56% with excitation at 296 nm and the lifetime is 971 microseconds.