Metal-Organic Frameworks Constructed From An Azamacrocyclic-based Tetracarboxylate Ligand And Their Properties

In recent years,metal-organic frameworks(MOFs)have received extensive attention from scientific researchers due to their rich structures and unique functionality.MOF materials not only possess high porosity and specific surface area,but also possess framework structure adjustability.Thus,they are widely used in the fields of catalysis,luminescence detection,ion exchange and electrode materials.In addition,in the process of designing MOFs,it is necessary to rationally choose organic ligands and metal ions according to the structure and function of the target MOFs.Polycarboxylic acid-based azamacrocyclic ligands combined the coordination diversity of carboxyl groups and the template characteristics of the azamacrocyclics.These types of ligands have multiple potential coordination sites and strong bridging abilities,and therefore can form different coordination modes with metal ions,which can produce some novel framework structures and functionalities.In this work,a new tetracarboxylic acid-based azamacrocyclic ligand(H4L)was designed and synthesized.Three novel MOFs,namely,[Cu3Cl(L)(H2O)2]·Cl·4DMA·8H2O(1)?[Cu2(L)(H2O)]·2DMA·3H2O(2)and[Cd3.5Cl(L1.5)(H2O)]·8DMA·10H2O(3)(H4L=1,4,8,11-tetrazacyclotetradecane-N,N?,N??,N???-tetramethylenecinnamic acid and DMA=N,N'-dimethylacetamide),were achieved by self-assembly of the H4L ligand with different metal ions under the solvothermal conditions.Single crystal X-ray diffraction was used to determine the crystal structures of 1-3.Moreover,the powder XRD diffraction,infrared spectra,elemental analysis and thermogravimetric analysis were employed to characterize these obtained MOFs.1 displays a highly porous 3D framework.Two independent nets weave each other,yielding a two-fold interpenetrating framework.In 2,the Cu(II)cation acts as the connection nodes,and the ligand L^4-extends along different directions,generating a 3D structure.In 3,each[Cd2(COO)6]dimer is linked by six L^4-ligands and every L^4-ligand bridges four[Cd2(COO)6]dimers,thus forming a 3D framework with large channels.Given the excellent stability of 1 in aqueous solution and the presence of anions in 1,we studied the capture ability of 1 for environmental toxicants Mn O4^-and Cr2O7^2-.The experimental results showed that 1 can fast and efficiently capture Mn O4^-and Cr2O7^2-via the anion exchange.Even if there are a large number of the disturbing anions,the capture process for Mn O4^-and Cr2O7^2-still remained high selectivity.1 exhibits high capture capacity and capture efficiency for toxic oxo-anions,which makes it a potential candidate for removing pollutant anions from wastewater.2 possesses Lewis acid sites(Cu(II)cations)and Lewis basic sites(O atoms),which exhibited good catalytic performance for Knoevenagel condensation reaction.Moreover,the sample of 2 is easy to be separated after the catalytic reaction.After three cycles,2 still maintained the high catalytic activity,thus 2 is an efficient heterogeneous catalyst.Finally,the luminescent performance of 3 was explored.3 featured selective and efficient detection for Mn O4^-and Fe³⁺through the fluorescence quenching effect,which has the potential to become a fluorescence detector.