Synthesis And Properties Of Novel Complexes Based On Derivatives Of Nitrogenous Carboxylic Acid

Nitrogen-containing carboxylic acid derivative ligands have been considered as ideal structural constructs for the synthesis of novel complexes with special structures and properties due to their various coordination patterns.In this paper,complexes 1-4 based on ligands 1,1’-bis（3,5-dicarboxybenzyl）-4,4’-bipyridine)dichloride（H₄bdcbpy·2Cl）,4,5-imidazole-dicarboxylic acid（H₂imdc）and 1,1’-bis（（4-carboxyphenyl）-4,4’-bipyridine）dibromide（H₂bpybc·2Br）were successfully synthesized by hydrothermal method.The structures and properties of 1-4 were investigated by experimental methods.The main research contents are briefly described as follows:（1）Two novel porous zinc metal-organic frameworks 1 and 2 based on 1,1′-bis（（3,5-dicarboxybenzyl）-4,4′-bipyridinium）dichloride（H₄bdcbpy·2Cl）ligand have been successfully synthesized by solvothermal reactions at different temperatures.The structures of complexes 1 and 2 were analyzed by X-ray single crystal diffraction.The result indicates that complexes 1 and 2 have the same composition but crystallize in different crystal systems.complex 1 synthesized at low temperature crystallizes in the monoclinic system,and complex2 prepared at high temperature crystallizes in the rhombohedral system.The structural differences of two complexes indicate that temperature plays an important role in the formation of the Zn-based complexes.Low temperature is more favorable to synthesize complex 1 with higher yield.The Zn²⁺ions are bridged by deprotonated formic acid moieties to form a 3D network in both complexes.H₄bdcbpy·2Cl provided an acidic environment,which led to the decomposition of DMF into a rare C₃H₂N₂²⁺cation and formic acid anion.Nitrogen adsorption measurement displays that the adsorption capacity of 1 is 711m²g^–1.The fluorescence spectra of complexes 1 shows that there is a strong emission peak at 527 nm.In addition,DMF,Acetone,dichloromethane（DCM）,methanol（Me OH）and water（H₂O）were selected to soak complex 1,and the products obtained were analyzed by powder X-ray diffraction（PXRD）.The resulting product shows an PXRD pattern similar to that of 1,indicating that the framework can remain stable after being soaked in small-sized molecules DMF and acetone.However,after soaked in large-sized molecules methanol（Me OH）,dichloromethane（DCM）and H₂O,the frameworks were distorted or collapsed,which are evidenced by the markedly changed PXRD patterns.（2）A zinc metal complex[Zn（Himdc）₂（H₂O）₂]（3）based on Zn（NO₃）₂·6H₂O and H₂imdc（H₂imdc=4,5-imidazolecarboxylic acid）was synthesized by hydrothermal method.The single-crystal X-ray diffraction analysis indicated that 3 was a mononuclear complex existed intramolecular and intermolecular hydrogen bonds.The mononuclear complexes were connected by intermolecular hydrogen bonds to form a three-dimensional hydrogen bond supramolecular network.Therefore,hydrogen bonds play an important role in the construction of supramolecular network structure.Fluorescence spectrum measurements showed that the maximum emission wavelength of complex 3 was 504 nm.（3）A photochromic compound[H₂bpybc]·[H₃btec]₂·2H₂O（4）based on 1,1’-bis（（4-carboxyphenyl）-4,4’-bipyridine）dibromide（H₂bpybc·2Br）,homophenetetraformic acid（H₄btec）and Zn（NO₃）₂·6H₂O was synthesized by self-assembly.The electron-deficient[H₂bpybc]²⁺cation and electron-donating[H₃btec]^-anion are connected by hydrogen bonds with lattice water molecules to form a three-dimensional supramolecular structure with a donor-acceptor system.[H₃btec]^-anion chains are formed by hydrogen bonds between anions,and anion chains form anion layers by hydrogen bonds with water molecules in the lattice.[H₂bpybc]²⁺cations are connected to anion chains by intermolecular hydrogen bonds,forming a amphoteric supramolecular layer containing both anions and cation.The amphoteric supramolecular layer forms a three-dimensional supramolecular network by interacting with the hydrogen bonds between the water molecules in the lattice.Complex 4has photochromic properties.Under the irradiation of 300W xenon lamp,the color changes from yellow to green.The reason is that the photoactivated electrons can be transferred from the donor unit to the recipient unit to form free radicals,resulting in a long time of charge separation state,thus showing the rapid response of photochromic.With the extension of irradiation time,the fluorescence intensity decreased,which was confirmed by fluorescence spectrum.In addition,UV-Vis absorption spectra of 4 were also studied,and the results also showed that the luminescent properties of 4 were due to the free radical generated by electron transfer.