Four Mixed-Ligand Zn(II) Three-Dimensional Metal-Organic Frameworks: Synthesis, Structural Diversity, and Photoluminescent Property

Assemblies of four three-dimensional (3D) mixed-ligand coordination polymers (CPs) having formulas, {[Zn-2(bdc)(2)(4-bpdh)]center dot C2H5OH center dot 2H(2)O}(n) (1), [Zn(bdc)(4-bpdh)](n) (2), {[Zn-2(bdc)(2)(4-bpdh)(2)]center dot(4-bpdh)}(n) (3), and {[Zn(bdc)(4-bpdh)]center dot C2H5OH}(n) (4) (bdc(2-) = dianion of 1,4-benzenedicarboxylic acid, 4-bpdh = 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene) have been synthesized and structurally characterized by single-crystal X-ray diffraction method. Structural determination reveals that the coordination numbers (geometry) of Zn(II) ions in 1, 2, 3, and 4 are five (distorted square-pyramidal (SP)), six (distorted octahedral (O-h)), five (trigonal-bipyramidal (TBP)), and four (tetrahedral (T-d)), respectively, and are bridged by 4-bpdh with bis-monodentate coordination mode and bdc(2-) ligands with bis-bidentate in 1, chelating/bidentate in 2, bis-monodentate and bis-bidentate in 3, and bis-monodentate in 4, to generate two-fold interpenetrating 3D cube-like metal-organic framework (MOF) with pcu topology, non-interpenetrating 3D MOF, two-fold interpenetrating 3D rectangular-box-like MOF with pcu topology and five-fold interpenetrating diamondoid-like MOF with dia topology, respectively. These different intriguing architectures indicate that the coordination numbers and geometries of Zn(II) ions, coordination modes of bdc(2-) ligand, and guest molecules play important roles in the construction of MOFs and the formation of the structural topologies and interpenetrations. Thermal stabilities, and photoluminescence study of 1-4 were also studied in detail. The complexes exhibit ligands based photoluminescence properties at room temperature.