Synthesis And Properties Of Cu/Cu-M Metal-Organic Frameworks Based On 2-Amino-5-sulfobenzoic Acid

Among the many porous materials,MOFs materials show an incomparable application prospect in many fields based on their advantages such as structural designability and functional adjustability.In this paper,six novel coordination polymers were designed and constructed through the assembly between Cu2+ or Cu2+/alkali metal/alkaline earth metal ion and the multifunctional ligand 2-amino-5-sulfobenzoic acid(H2asba)using the typical solution evaporation method.These complexes were characterized by single-crystal and powder X-ray diffraction analysis,FT-IR spectra,solid-state diffuse reflectance UV-Vis-NIR spectra,thermogravimetric analysis and electrochemical analysis,etc.The fluorescence sensing behaviours of these MOFs for pH,H2O2,anions,ascorbic acid and nitro-aromatic compounds were studied in detail on the basis of the structural characteristics and the fluorescence performance of these complexes in the aqueous suspensions.The electrochemical properties of these MOFs were explored.For the complex with the best electrical conductivity,the electrochemical sensing of glucose was investigated.The main work is introduced as follows:1.The self-assembly between H2asba and the d9 metal ion Cu(?)yields a novel 3D coordination polymer {[Cu2(asba)2(H2O)2]·6H2O}n(1).The asymmetric unit of complex 1 consists of two kinds of crystallographic independent asba2-ligands,one asba2-(L1)connects the adjacent Cu2+ions into 1D chains which are further linked by another crystallographic independent asba2-(L2)ligand,yielding a 2D layer.Two carboxylate oxygen atoms(O7)of L1 and two carboxylate oxygen atoms(O5)of L2 from the adjacent layers altematingly bind with Cu2 and Cu3,respectively,leading to the formation of a sandwich-like 3D framework with a 1D channel occupied by the lattice molecules(O5W,O6W,O7W and O8W).Complex 1 and the free acid H2asba show only weak fluorescence properties in the solid state.Due to the solvent polarity effect,the aqueous suspension of the as-synthesized complex 1 exhibit strong fluorescence emission.More importantly,complex 1 shows highly selective and efficient sensing for the aqueous H+.Taking advantage of this feature,we successfully used this complex to detect the pH of the aqueous solution and the simulated gastric juice by fluorescence sensing method,and obtained a good recovery rate.The fluorescence sensing mechanism was explored.In addition,the sensing behaviour of complex 1 for some nitroaromatic compounds has also been investigated in detail.2.Three heteronuclear coordination polymers were self-assembled between Cu2+,Ca2+/Sr2+/Ba2+ions and H2asba:{[CuCa(asba)2(H2O)]·5H2O}n(2),{[CuSr(asba)2(H2O)]·5H2O}n(3),{[CuBa(asba)2(H2O)6]·4H2O(4).The asymmetric unit of complexes 2 and 3 exhibit similar crystal structure.Both compounds consist of two kinds of crystallographic independent asba2-ligands.One asba2-(LI)connects the adjacent Cu2+ ions into ID chains which are further linked by another crystallographic independent asba2-(L2)ligand,yielding a 2D layer.A carboxylate oxygen atom of L1 and two carboxylate oxygen atoms of L2 from the adjacent layers bind with Ca2+/Sr2+,leading to the formation of a sandwich-like 2D layer,which further extends into a 3D supramolecular network through the hydrogen bonding.The asymmetric unit of complex 4 consists of two kinds of crystallographically independent asba2-ligands,one asba2-(L1)connects the adjacent Cu2+ ions into 1D chains which are further linked by another crystallographically independent asba2-(L2)ligand,yielding a 2D layer.The carboxylate oxygen atoms of L1 and L2 bind with Ba2+,resulting in a sandwich-like 3D framework with 1D channels occupied by the lattice molecules(O4W and O5W).Because the three coordination polymers have similar sensitivity to pH,so the complex 3 was selected as an example to perform fluorescence detection on the solution pH and the artificial simulated gastric juice.Since the other two coordination polymers can directly detect Fe3+ and Cr(?),we developed a fluorescence "on-off" detection method to indirectly detect H2O2 and ascorbic acid.Complexes 2-4 were used to perform fluorescence titration detection on various nitro aromatic compounds quantitatively in the low concentration range.The electrochemical experiment reveals that the electrochemical properties and electrical conductivity of the complexes 2?4 were better than those of complex 1.3.Cu2+ and K+/Na+ were used to construct a new 2D complex[CuNa2(asba)2(H2O)6]n(5)and a 3D complex[CuK2(asba)2(H2O)4]n(6).For complex 5,the ligand asba2-and the coordinated water(O1W)connect the adjacent Cu2+and Na+ ions alternatingly,leading to the formation of necklace-like chain.Two centrosymmetric coordinated water molecules(O2W)bridge the neighbouring Na+ of the adjacent chains,resulting in a 2D layered structure,which is further extends into a 3D supramolecular structure through hydrogen bonding.For complex 6,the sulfonate group of the asba2-ligand link the adjacent K+ ions into a centro-symmetric chain along the b-axis,which can be treated as the secondary builiding unit(SBU).The carboxylate group in the asba2-ligand and the coordinated water 01W further connect the adjacent Cu2+ ions and SBUs into a 3D framework architecture.For complex 5,direct or indirect fluorescence detection for Fe3+,H2O2,Cr(?),ascorbic acid and nitro aromatic compounds was investigated.Complex 6 exhibits the best electrical conductivity.So,we exploit this characteristic and construct a novel enzyme-free glucose electrochemical sensor through post-synthesis modifying.