Synthesis Of Zn-Terpyridine Metal-organic Coordination Polymers And Their Recognition Of Anions And Sulfur-containing Amino Acids

Metal-organic gels (MOGs) and metal-organic frameworks (MOFs) are the members of organic-inorganic hybrid materials and both rooted from the assembly of separate organic and inorganic building unit. MOGs and MOFs have good comprehensive properties of organic materials, inorganic materials and nano materials. They display unique optical, electrochemical, catalytic and adsorption function characteristics. In addition, their morphologies and structures are well adjustable. Based on the above properties, they have been widely applied in the fields of analytical, adsorption and catalysis. In this thesis, Hcptpy(4-[2,2’:6’,2"-terpyridine]-4’-ylbenzoic acid), which with three pyridyl donors and one carboxylic group, has been chosen as the ligand to synthesis the MOGs and MOFs with Zn2+. The functions of MOGs as the anions recognition acceptor and the crystal growth medium have been studied. Moreover, the microsheets-assembled Zn-Hcptpy microflowers have been used for selective recognition of sulfur amino acid with naked eyes. The detailed results are summarized as follows:(1) The synthesis and applications of luminescent Zn(Ⅱ)-terpyridine metal-organic gel Luminescent metal-organic gels (MOGs) were prepared with zinc sulfate and Hcptpy with the assistant of triethylamine (TEA), which self-assembled through noncovalent interactions, such as hydrogen bonding, π-π interaction, van der Waals, and ionic interactions. Gelation tests for the MOGs formation showed that the gelation process depended on the reaction temperature and concentration of Zn2+, TEA and Hcptpy and the structure of the MOGs fibers. Additionally, depending on the affinity of anions to the metal ion in fuorophore-metal complexes, luminescent MOGs can effectively simultaneously recognize anions, including F-, Cl-, NO3-, Br-, I-, SCN-, N3-, PO43- and CO32-, visible with the naked eyes. The recognition mechanism has been discussed based on the theory of Hard-Soft-Acid-Base (HSAB theory) clearly.We found that the Zn-Hcptpy MOGs can be a good medium for crystal growth. Just by adding an appropriate amount of different metal ions solution, such as Cr3+[3d3], Mn2+[3d5], Fe3+[3d5], Co2+[3d7], Ni2+[3d8], Cu2+[3d9], Cd2+[4d10] and Hg2+[5d10], to the Zn-Hcptpy MOGs which comprised the MOFs precursors, they broken down in Fe3+, Co2+, Ni2+ and Cu2+ solutions in a period of time. The MOGs cracked into sol in Fe3+ and Cu2+ while transferred into octahedral Co(Ni)-MOFs crystals which self-assembled by many microparticles. The fibrous MOGs have been degradation into pure octahedral Co(Ni)-MOFs by metal ions change which characterized by scanning electron microscopy (SEM), powder X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX). The Zn2+ in MOGs was fully replaced by Co2+ or Ni2+ and the structure of MOGs was broken down and restructured for the formation of Co(Ni)-MOFs crystals. As the outer layer of Co2+ and Ni2+ comprised of unsaturated electronic state, it make them become the ideal acceptors for electrons and prefer to form stable octahedral crystals. Hence, Zn-MOGs not only as a growth medium for MOFs growth but also realized the structure transition at molecular level.(2) Controlled synthesis of hierarchical microsheet-assembled microflowers for selective recognition of sulfur amino acid Novel hierarchical metal-organic microsheet-assembled microflowers are successfully synthesized by the direct reaction of zinc sulfate and Hcptpy employing a one-pot hydrothermal process with the assistance of triethylamine (TEA) at 120℃. It is found that TEA plays a crucial role in the step-by-step changes of morphology of the Zn-Hcptpy products by controlling the pH. Investigations on the evolution of flower-like morphology as a function of hydrothermal time show that the formation dynamics involve the initial coordination nucleation followed by self-aggregation to cross-linked sheets and transformation into hierarchical microflowers. The center Zn(Ⅱ) ion in MOFs is unsaturated and thus has the capability to accept the electrons from the sulfur-containing amino acids to form the Zn-S bonds. So it is an effective sensor for selective identification of sulfur amino acids based on the fluorescence quenched of Zn-Hcptpy MOFs.