Carboxylate-assisted Acylamide Metal–organic Frameworks: Synthesis, Structure And Property Studies

Metal-organic frameworks (MOFs) is a popular research field in recent years, andmore and more people have paid attentions to research it, due to its extensive potentialapplications in lighting, magnetism, catalysis, separation, molecular sensing, etc. In thiswork, according to the fundament of the crystal engineering, three new neutral bi-pyridineacylamide ligands were designed and synthetized to construct metal-organic frameworksby using hydrothermal and solvothermal method with carboxylate-assisted technique.Fourteen novel d10(Zn(II)，Cd(II)) MOFs were obtained through this method. Furthermore,the structure, thermo-stability, fluorescence properties of all complexes，and gas absorptionand ferroelectric properties of some complexes were characterized. The details weresummarized under three parts:(1) We successfully synthesized five MOFs by using L1as primary ligand, aromaticdicarboxylic acids as assisted ligand with solvo/hydrothermal method. Complexes1-3were obtained through diphenyldicarboxylic acid as carboxylate-assisted ligand, andrealized the structural regulation from non-porous to porous. In the high temperature of120°C, a nonporous complex1with nine-fold interpenetrated dia topological net wasobtained, which crystalized in polar point group Cc space group, and exhibited excellentferroelectric property. In the middle temperature of100°C and low temperature of80°C,porous complex2and complex3with three-fold entanglement were obtained, and bothexhibited excellent selective adsorption property for CO2. When terephthalic acid and5-nitroisophthalic acid as carboxylate-assisted ligand, the nonporous complex4withthree-fold entanglement of2D layer structure and the porous complex5with33.6%solvent-accessible volume and two-fold interpenetrated cds topology were obtained,respectively (L1=N~1, N~3-di(pyridin-4-yl)isophthalamide).(2) Five MOFs were obtained by using L2as primary ligand, aromatic dicarboxylicacids as assisted ligand with solvothermal and hydrothermal method. Complex6exhibits polyrotaxane and polycatenane properties which based on terephthalic acid and Zn(NO3)2in hydrothermal reaction. Complex7shows unprecedented three-interpenetratednoz-4-Pcca topological property which based on4,4’-oxydibenzoic acid ascarboxylate-assisted ligand. Complex8exhibits porous structure through H-bondinteractions (N-H…O) between2D layers with36.6%solvent-accessible volume whichbased on4,4’-oxydibenzoic acid as carboxylate-assisted ligand. Complex9and10wereobtained with same reactant and different concentration. Complex9shows unusual1Dladder structure property, and through H-bond interaction between1D layers to construct a2D supermolecule. Complex10shows two-fold interpenetrated α-Po topological net.Furthermore, the fluorescence of complex6-8,10are derived from the π-π*transition ofL2ligand (L2=N~1, N~3-di(pyridin-3-yl)isophthalamide).(3) Four MOFs were obtained by using L3as primary ligand, terephthalic acid,isophthalic acid and5-hydroxyisophthalic acid as assisted ligands with hydrothermalreaction. Complex11shows2D layer structure, and has four H-bond interaction betweenfree water and2D layers which based on terephthalic acid in hydrothermal reaction.Complex12has two-fold interpenetrated dia topology feature. Complex13and14weresynthesized with5-hydroxyisophthalic acid and isophthalic acid, respectively. Complex13and14exhibits different structure property due to the different substituent group ofcarboxylate-assisted ligand. Complex13shows two-fold entanglement feature between2Dlayers. However, complex14reveals a novel infinite-fold entanglement feature between2D layers of isophthalic acid and L3ligands. The solid-state fluorescent characterization ofcomplexes11-14reveals that their fluorescence emission wavelengths were at442nm,351nm,409nm and371nm, respectively (L3=N~1, N~3-bis(pyridin-3-ylmethyl)isophthalamide).