Syntheses,Structures,and Properties Of Metal-organic Frameworks Based On Semi-rigid Carboxylates Ligands

Metal-organic frameworks（MOFs）,also named coordination polymers,are built from inorganic metal ions coordinated by organic linkers.Based on the geometric structure of organic ligands and coordination mode of inorganic metal ions,we can design and adjust the structure of different polymers.Because of its large specific surface area,high porosity,flexible and variable coordination mode,and the structure’s modification and adjustability,it is widely used in adsorption,separation,catalysis,and sensing.Become one of the hot research topics in today’s society.We synthesized two ligands,which are 3,3’-（2-nitro-1,4-phenylene）diacrylic acid（H₂NPDC）and 3,3’,3’’-（benzene-1,3,5-triyl）triacrylic acid（H₃BTA）.Using them as bridging-linkers,under the help of other auxiliary ligands,we synthesized eight compounds under the self-assembly with the transition metal or lanthanide in different conditions.Not only analyzed the structure of the compounds,but we also studied the practical application of some complexes in gas adsorption,magnetism,and luminescent properties.The main contents are listed as follows:1.Syntheses,structures and properties of metal-organic frameworks based on H₂NPDC ligands:The H₂NPDC ligand was synthesized by a series of chemical reactions.Then using 4,4’-bpy and bpee as the auxiliary ligand,the H₂NPDC as bridging ligands,we synthesized three 3D complexes（1-3）based on the self-assembly with Zn（Ⅱ）and Co（Ⅱ）under solvothermal method.The skeleton structure of complex1-2 is similar.These complexes consist of a 3D structure in which the nitro functionalized ligand(NPDC^2-)and bipyridine type linkers（bpee and 4,4’-bpy）coordinated to Co（Ⅱ）,leading to an fsc type 3,5-c binodal net.Its point symbol is{4;6²}{4;6⁸;8³}.Complex 3 is also a 3D structure in which the nitro functionalized ligand(NPDC^2-)and bipyridine type linkers（bpee）coordinated to Zn（Ⅱ）,leading to a simple cubic lattice double-intersected frame with pcu topology.In order to explore its behavior,we have done the following research:（1）The adsorption and desorption isotherms of complex 1 for CO₂was measured.Past studies have shown that when the ligand contains a-NO₂functional group,the ability of the complex to adsorb CO₂can be significantly improved.For complex 1,the gas adsorption properties have yet to be discovered.（2）The complex 1-2 shows fluorescent emission both in solid state and in aqueous solution.What is more,it exhibits a high selectivity for the sensing of Mn O₄^-and heavy metal ion Hg²⁺in water by quenching or enhancing luminous intensity,respectively.Naked eyes can even recognize the changes in fluorescence intensities.Moreover,the detection of Hg²⁺and Mn O₄^-indicates that the opportunities of the complexes be prominent fluorescent probes in potential applications.2.Syntheses,structures and properties of metal-organic frameworks based on H₃BTA ligands with lanthanide:With the crystal engineering strategy,we constructed four 3D isomorphic compounds（4-7）under the coordination of H₃BTA with lanthanide（Eu（ⅡI）、Tb（ⅡI）、Sm（ⅡI）、Nd（ⅡI））.We also measured the fluorescence emission spectra of the three complexes（4-6）.It was found that the complex 4 has a unique fluorescence characteristic emission spectrum of Eu（ⅡI）in the visible light range.Also,complex 4 has the highly selective sensing for nitrobenzene、Cr₂O₇^2-and Cr O₄^2-through quenching effect,which declares good advantages in fluorescence sensing detections.3.The properties of 3D metal-organic frameworks based on H₃BTA ligands and Mn ^Ⅱ:A 3D complex（8）has been synthesized using manganese acetate and organic ligand 3,3’,3’’-（benzene-1,3,5-triyl）triacrylic acid（H₃BTA）under solvothermal reactions.Single-crystal X-ray diffraction revealed that compound 1 crystallizes in the monoclinic space group C2/c.With a 6-connected Mn3 cluster as the node and a tritopic linker,it exhibits a 3D flu-（3,6）connected network with the point symbol of{4²;6}₂{4⁴;6²;8⁷;10²}.Our study of its properties shows that it has antiferromagnetic properties.