Synthesis And Properties Of Rare Earth Complexes Of Benzimidazole Carboxylic Acid

Water is the source of life,and it is especially important to protect water resources from pollution.Nowadays,the industry is vigorously developed,and water resources are heavily polluted,resulting in excessive levels of various metal ions in the water.Therefore,it is urgent to study materials with special functions that can selectively identify metal ions.Among them,multifunctional coordination polymers（CPs）are a good material.Because of its novel structure and unique properties,numerous CPs have been successfully applied in ion recognition and catalysis.In recent years,the use of rigid ligands containing heteroatoms has been widely reported.In this work,two kinds of nitrogen-containing heterocyclic carboxylic acid ligands2-（hydroxymethyl）-1H-benzo[d]imidazol-5-carboxylicacid（H₂L1）,2-（4-hydroxyphenyl）-1H-benzo[d]imidazole-5-carboxylic acid（H₂L2）were designed and synthesized.Using ligand H₂L1 with an unused rare earth metal salt Dy（Ⅲ）/Eu（Ⅲ）/Sm（Ⅲ）/Gd（Ⅲ）/Yb/（Ⅲ）/Ce（Ⅲ）self-assembly to obtain a series of three-dimensional supramolecular network coordination polymers with different structures containing hydrogen bonds,using ligand H₂L2 and unused rare earth metal salts Dy（Ⅲ）/Eu（Ⅲ）/Ho（Ⅲ）/Sm（Ⅲ）self-assembly results in a series of mononuclear complexes but can be converted into a supramolecular structure through van der Waals forces.The crystal structure was characterized by characterization means.Studies on the spectroscopic properties of the above rare earth metal coordination polymers,complexes formed by Dy（Ⅲ）/Gd（Ⅲ）/Ce（Ⅲ）with H₂L1 and H₂L2 and Dy（Ⅲ）/Ho（Ⅲ）The formed complexes were respectively tested for magnetic properties,and the electrochemical properties of the complexes 2 and 6 were tested.The main contents and conclusions of this research are as follows:1.The ligand of 2-（hydroxymethyl）-1H-benzo[d]imidazole-5-carboxylic acid（H₂L1）was synthesized and characterized by characterization method.The self-assembly synthesis of H₂L2 as ligandwascarriedout.Six Dy（Ⅲ）/Eu（Ⅲ）/Sm（Ⅲ）/Gd（Ⅲ）/Yb（Ⅲ）/Ce（Ⅲ）coordinationpolymers:{[Dy（HL1）₂（H₂O）₃]·（H₂O）₄·Cl}_n（1）,{[Eu（HL1）₂（H₂O）₃]·（H₂O）₄·Cl}_n（2）,{[Sm（HL1）₂（H₂O）₃]·H₂O}_n（3）,{[Gd（L1）₂（H₂O）₃]·Cl}_n（4）,[Yb₄（HL1）₅（H₂O）₅]·（H₂O）₆·7Cl（5）,{[Ce（HL1）（CH₃COO）₂（H₂O）₂]·H₂O}_n（6）.The structure of the above complex was determined by single crystal diffraction.The test results show that the complexes 1,2,3,4,and 6 are infinite 1D chain structures,and secondly,the 1D chain structure is expanded to 2D by weak hydrogen bonds.Eventually,the layered structure forms a 3D supramolecular structure through weak hydrogen bonds.The stability,phase purity,etc.of 1-6 were characterized.The spectroscopy properties of H₂L1 and 1-6 were tested.The magnetic properties of Dy（Ⅲ）/Gd（Ⅲ）/Ce（Ⅲ）complexes containing H₂L1 were studied and discussed.The electrochemical properties of complexes 2 and 6 were tested.2.Synthesis of 2-（4-hydroxyphenyl）-1H-benzo[d]imidazole-5-carboxylic acid（H₂L2）ligand,the ligand structure was characterized by nuclear magnetic and infrared techniques.Using H₂L2 as ligand to react with different rare earth metal salts,then four Dy（Ⅲ）/Eu（Ⅲ）/Ho（Ⅲ）/Sm（Ⅲ）coordination polymers were synthesized by reaction with different rare earth metal salts:[Dy（HL2）₂（H₂O）₆]·3Cl（7）,[Eu（HL2）₂（H₂O）₆]·（H₂O）₄·3Cl（8）,[Ho（HL2）₂（H₂O）₆]·3Cl（9）,[Sm（HL2）₂（H₂O）₆]·3Cl（10）.The structure of 7-10 was characterized by thermal stability,infrared and single crystal diffraction.The results show that the complexes7-10 are mononuclear structures.The spectroscopy properties of H₂L2 and 7-10were tested and the magnetic properties of the complexes formed by ligands H₂L2and Dy（Ⅲ）/Ho（Ⅲ）/Sm（Ⅲ）were tested.