Synthesis Characterization And Properties Of Metal Organic Frameworks Based On N-heterocyclic Carboxylic Acid Ligands

Metal-organic frameworks?MOFs?have attracted wide attention due to their potential application in the fields of gas adsorption and storage,catalysis,magnetism,luminescence,and antibacterial/anticancer.To construct serial MOFs with higher antibacterial activities,we selected small molecular organic ligands containing N-heterocyclescoordinatedwithdifferenttransitionmetalsunder hydrothermal/solvothermal conditions.We characterized the as-synthesized complexes and tested their antibacterial activities,then through comparison and analysis of the results and obtained the conclusion at last.We have done the following studies in this paper:1.we selected 4,6-bis?imidazol-1-yl?isophthalic acid ligands and four metallic ions Co?II?,Mn?II?,Ag?I?and Zn?II?and had already constructed four complexes:{[Co₂?L₁?₂?H₂O?]·EtOH}_n?1?,{[Mn₂?L₁?₂?H₂O?]·EtOH}_n?2?,{[Ag?L₁?]}_n?3?,{[Zn?L1?]}n?4?.Complexes 1 and 2 are isostructural and they are both three-dimensional framworks.The di-nuclear metallic ions are six-connected and bridged by a half occupation water molecule.The coordinated geometry is distorted octahedral geometry.3 is one-dimensional infinite chain structure,the Ag?I?ions is two-connected model.4 presents a three-dimensional framework.The variable-temperature magnetic susceptibilities measurement of 1 and 2 were performed and the result indicated that both of them display antiferromagnetic interactions.The antibacterial activities studies of 1⁴ and the H₂L₁ ligand against E.Coli strain revealed that 1,2,4 and the H₂L₁ ligand did not show obvious antibacterial activities,but 3 presented strong antibacterial activities.Further antibacterial activities studies of 3 were performed and the result indicated that 3 display strong antibacterial activities against both E.Coli and P.putida testing srains,even more active than the antibacterial agent AgNO₃.This result demonstrated the synergistic effect of the H₂L₁ligands and Ag?I?ions enhanced the antibacterial activities.2.We selected 4-?pyridine-4-yl?phthalic acid?H₂L₂?ligands and metallic ions Zn?II?and Cd?II?and had already constructed three complexes:{[Zn?L2??DMF?]}n?5?,{[Zn?L₂??H₂O?]}_n?6?,{[Cd?L₂??H₂O?]}_n?7?.In complex 5,the Zn?II?ions of is six-connected and their coordination spheres present distorted octahedral geometry.Six Zn?II?ions constructed{Zn6}“wheel type”secondary building units?SBUs?.The Zn?II?ions of 6 are five-connected and their coordination spheres present trigonal bipyramidal geometric structures,the adjacent pyridine rings existing?-?stacking effect.7 is three-dimensional framework,the di-nuclear Zn?II?ions are both half occupation and six-connected,showing a distorted octahedral geometry.The solid fluorescence studies of 5⁷ and the H₂L₂ ligand were performed at room temperature.Compared with H2L2 ligand,the fluorescence intensity of 5⁷ were significantly enhanced.The antibacterial activity studies indicated that the H2L2 ligand had no obvious antibacterial activity,but 5⁷ had different antibacterial activity.Among them,both 5 and 6 were constructed by H₂L₂ ligands and zinc ions,but the antibacterial activity of 6 much higher than 5.3.we selected 2-methyl-1-H-imidazole-4,5-dicarboxylic acid?H₃L₃?ligand to coordinate with transition metallic ions Zn?II?and lanthanide series metallic ions Tm?III?and achieved successfully a Zn-Tm heteronuclear three-dimensional framework{[Tm₃Zn₆?bipy₂?₂?mimda?₇?H₂O?₃]·?H₂O?₅}_n?8?.8 shows one-dimensional?1-D?Tm-Zn heteronuclear zigzag chain,and such chains are further linked by H₃mimda ligands into Tm-Zn heteronuclear 2-D lattice-like arrays.The 2-D heteronuclear units were connected through[Zn6?mimda?6]rings to give rise to Tm-Zn heteronuclear cages.Finally,H₃mimda ligands connected the cages into a 3-D heterometallic framework by the combination of[TmO7]n and Tm-Zn heteronuclear cages.In addition,the thermal stability and luminescent property have been investigated.