Self-assembly And Supramolecular Properties Of Metal-organic Cages Constructed From Flexible Ligands

In recent years,metal-organic cages(MOCs),as one of the important subunits,have been gradually developed,because of their well-defined hydrophobic cavities and the easy-modified organic ligand with several functional groups which endows them excellent supramolecular behavior to interact with the specific guest molecules.Moreover,the incorporation of metal ions to construct MOCs could also enrich their properties and show tremendous advantages and potential,and thus exhibit a wide application in many fields.To construct MOCs with remarkable properties,the main difficulty is relying on the rational designing of ligands,regulation of the coordinated metal ions and the choice of a suitable system.In this thesis,by the synthesis of flexiable organic ligands,incorporating of secondary amino or thiouear goups as hudrogen bonding sites,and the coordination of Co(II),Ni(II)ions,several MOCs were constructed with various structure and well-defined cavities and achieved excellent performance in RNA-nucleosides recognition,light-driven hydrogen production and organic catalysis in heterogeneous phase.(1)By incorporating the secondary amino groups reduced by C=O bond and the Co(II)ions as construction nodes,a MOC Co-TAP with pseudo-tetrahedron cavity was achieved via self-assembly.Co-TAP contains two secondary amino and six amide groups as guest-interacted sites and strongly binds the organic dye fluorescein(FI)molecules via the obvious host-guest interaction.Compared to a reference compound Co-TOP with similar structure but without secondary amino groups,they perform different selectivity to RNA-nucleosides.The experimental results indicate that Co-TAP exhibits stronger and more stable binding to FI molecules,and higher efficiency in light-driven hydrogen production than Co-TOP.(2)By incorporating the redox-active Ni(II)ions as construction nodes,a cationic hexanuclear metal-organic cylinder Ni-YL was synthtized to mimic natural enzymes for their abilities to effectively reduce proton to product hydrogen.The anionic Ru(dcbpy)3 with excellent photophysical and excited-state redox properties and suitable size was choosen as guest molecule,which could be encapsulated into the cavity of Ni-YL via hydrogen bonding,?…? interaction and static attraction to form 1:1 complexation species Ru(dcbpy)3cNi-YL.The supramolecular system enforces the proximity between the nickel-based redox catalytic sites and the photosensitizer,and allows a direct photoinduced electron transfer(PET)process from the excited state*Ru(II)to the redox catalyst in a more powerful pseudo intramolecular pathway.(3)A tetranuclear metal-organic macrocycle Ni-SPT with distorted rectangular window has been synthesized by the coordination of Ni ions and tridentate ligand SPT containing dithiourea groups that acting as both coordination sites and hydrogen-bond donors.Ni-SPT packs in a trimeric fashion and each trimeric structure is further packed into a three-dimensional network with one-dimensional channels.Fixing the catalytic thiourea groups into the skeleton of Ni-SPT could overcome the issues of self-association by intermolecular H-bonding often occurring in homogeneous system.Thus,Ni-SPT achieves the highly catalysis of Michael additions from nitrostyrenes to nitroalkanes with remarkable conversion in heterogeneous phase and size-selectivity by dragging the substrate molecule into its cavities.