Four Pb(II) metal-organic frameworks with increasing dimensions: structural diversities by varying the ligands

Three rigid, linear tigands, namely 2',5'-dimethyl-[1,1':4',1 ''-terphenyl]-4,4 ''-dicarboxylic acid (H2L1), triphenyl-6,6'-dicarboxylic acid (H2L2), and 2,2'-bipyridine-5,5'-dicarboxylic acid (H2L3), were used for constructing metal-organic frameworks (MOFs) with Pb(II). With a similar nature of solvent conditions (DMF/EtOH, with different volumes' rates), four structurally diverse MOFs, namely, [Pb(L-1)(DMF)] 1, [Pb(L-1)(DMF)] 2, [Pb(L-2)] 3, and [Pb-3(L-3)(2)(Cl-)(2)] 4, were synthesized and characterized by single-crystal X-ray diffraction, thermogravimetric analysis, elemental analysis, and powder X-ray diffraction measurements. As the numbers of the central benzene ring contained in the ligands changed from three to two, the length of the ligands varied from 15.64 angstrom to 10.89 angstrom, and steric functional groups endowed the three ligands with more variations, such as a 1D zigzag chain of 1, a 2D wave-like layer of 2, a 3D Pb-O-C-based layer of 3, and a 3D Pb-O-Cl-based chain of 4. Solid-state photoluminescence studies were carried out for all the complexes at room temperature.