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, {[Zn₂(bdc)₂(4-bpdh)]·C₂H₅OH·2H₂O}n (1), [Zn(bdc)(4-bpdh)]n (2), {[Zn₂(bdc)₂(4-bpdh)₂]·(4-bpdh)}n (3), and {[Zn(bdc)(4-bpdh)]·C₂H₅OH}n (4) (bdc2- = 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 (Oh)), five (trigonal-bipyramidal (TBP)), and four (tetrahedral (Td)), respectively, and are bridged by 4-bpdh with bis-monodentate coordination mode and bdc2- 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 bdc2- 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.