Two Bi-MOFs with pyridylmulticarboxylate ligands showing distinct crystal structures and phosphorescence properties

Abstract

Two Bi-MOFs, [Bi(PDC)(OH)] (Bi-PDC; H2PDC ​= ​2,4-pyridine bicarboxylic acid) and [Bi(PTC)(H2O)2] (Bi-PTC; H3PTC ​= ​2,4,6-pyridine tricarboxylic acid), have been synthesized under almost the same solvothermal condition, respectively. Both Bi-PDC and Bi-PTC were characterized by microanalysis, infrared spectra (IR), thermal gravimetric analyses (TGA), and powder X-ray diffraction (PXRD) techniques. Single-crystal structural analyses indicate that the Bi3+ ions adopt similar coordination sphere of monocapped square antiprism in Bi-PDC and Bi-PTC, while PDC2− and PTC3− ligands display distinct bridging modes through carboxylates and pyridyl groups, leading to Bi-PDC forming three-dimensional (3D) pillared-layer framework and Bi-PTC developing into two-dimensional (2D) layered structure. Two Bi-MOFs emit ligand-centered room temperature phosphorescence due to the heavy atom effect of Bi3+ ion, with lifetime and quantum yield of 0.39 ​ms and 2.49% in Bi-PDC versus 0.57 ​ms and 5.45% in Bi-PTC, and the intense green and orange phosphorescence is visible by naked eyes under ambient condition, and the long-wavelength (orange) phosphorescence Bi-based MOF is seldom reported.