Synthesis,Functionalization And Characterization Of Metal-Organic Polyhedra Of Hexanuclear Vanadium Cluster

In recent years,the field of supramolecular chemistry based on molecular assemblies and intermolecular forces has developed rapidly,with much work focusing on the synthesis of coordination-driven self-assembled metal-organic polyhedra（MOPs）and the exploration of their applications in confined nanospheres.Metal-organic polyhedra can be viewed as metal-organic coordination compounds with polyhedral configurations formed by metal ions or metal clusters bridged by organic ligands,which have flexible geometric topology and nano-sized confined cavities and have potential applications in catalysis,adsorption,and biomedicine.Compared with the widely studied metal-organic frameworks（MOFs）,metal-organic polyhedra have good solubility and chemical stability,making further functionalization possible by modifying organic linkers,metal nodes,pores or surface environments to introduce new functional groups.The topology analysis of metal-organic polyhedra reveals that 3-coordinated nodes are most widely used in the construction of metal-organic polyhedra.Therefore,in this thesis,3-coordinated hexanuclear vanadium clusters are selected as secondary building units（SBUs）to construct metal-organic polyhedra,and the structural design and functional properties are investigated from both organic bridging ligands and metal nodes.Fourteen different conformations and functions of polyoxovanadates-based metal-organic polyhedra have been successfully constructed using with 2-coordinated,3-coordinated and 4-coordinated organic ligands.And based on their unique physicochemical properties,representative metal-organic polyhedra were selected to explore their applications in adsorption,photocatalysis and organocatalysis.1.Cubes are one of the most common regular polyhedra（Platonic polyhedra）,but metal-organic polyhedra with cubic conformation are not rare due to the high symmetry of the structure.We constructed two metal-organic cubes（MOCs）（compound 1 and compound 2）by selecting large tetra-coordinated carboxylic acid ligands for self-assembly with hexanuclear vanadium clusters under solvent-thermal synthesis conditions,guided by a face-directed construction strategy.The iodine molecular adsorption properties of the cubic molecular cages were also investigated using compound 1 as a representative.（NH₂Me₂）₁₆[（V₆O₆（OCH₃）₉（SO₄））₈（PBPTA）₆]（1）（NH₂Me₂）₁₈[（V₆O₆（OCH₃）₉（VO₄））₈（PBPTA）₆]（2） PBPTA=4,4’,4’’,4’’’-（1,4-phenylenebis（pyridine-4,2,6-triyl））tetrabenzoic acid2.Endohedral functionalization of metal-organic polyhedra can confer more abundant properties and functions.However,only one example of endohedral modification of vanadium polyoxovanadate-based metal-organic polyhedra has been reported.Here,metal-organic polyhedra based on[V₆O₆（OCH₃）₉（SO₄）]（{V₆S}）of different sizes were internally modified by coordination modification strategy.The pyridine functional group was decorated inside the cage by introducing pyridine phosphonate with stronger coordination ability to replace the sulfate at the center of the{V₆S}cluster.Due to the potential steric effect,the size of the confined cavity affects the structural changes after functionalization,and smaller metal-organic polyhedra are induced to undergo structural transformation.The organic dye adsorption capacity of the metal-organic polyhedra was compared before and after the internal modification,and it was found that the internally modified structures could adsorb larger dye molecules.[NH₂Me₂]₁₂{[（V₆O₆）（OCH₃）₉（C₅NH₄PO₃）]₆（BPTC）₆[V（H₂O）]₂}·（SO₄）₂（3）[NH₂Me₂]₂₄{[（V₆O₆）（OCH₃）₉（C₅NH₄PO₃）]₈（ABTC）₆}（SO₄）₄（4）[NH₂Me₂]₁₆{[（V₆O₆）（OCH₃）₉（C₅NH₄PO₃）]₈（EBTC）₆}（5）[NH₂Me₂]₂₂{[（V₆O₆）（OCH₃）₉（C₅NH₄PO₃）]₈（TPTC）₆}（SO₄）₃（6）[NH₂Me₂]₂₂{[（V₆O₆）（OCH₃）₉（C₅NH₄PO₃）]₈（ADIP）₆}（SO₄）₃（7） BPTC=1,1’-biphenyl-3,3’,5,5’-tetracarboxylic acid ABTC=azobenzene-3,3’,5,5’-tetracarboxylic acid EBTC=1,1’-ethynebenzene-3,3’,5,5’-tetracarboxylic acid TPTC=terphenyl-3,3″,5,5″-tetracarboxylic acid ADIP=diphenylethyne-3,3’,5,5’-tetracarboxylic acid3.Based on the previous work,the modification of pyridine groups inside the cavities of metal-organic polyhedra can provide potential coordination sites for further metallization modifications.The tetrahedral configuration of metal-organic polyhedra was firstly obtained by the self-assembly of{V₆S}and H₃TPTC,and then the pyridine functional group was modified inside it.Finally,the transition metal ions were introduced to successfully obtain the heterometal-decorated metal-organic polyhedra with internal transition metal modification.Among them,the Ni-modified metal-organic polyhedra have the catalytic activity of photocatalytic reduction of CO₂[NH₂Me₂]₈{[（V₆O₆）（OCH₃）₉（SO₄）]₆（TPTC）₄}（8）[NH₂Me₂]₈{[（V₆O₆）（OCH₃）₉（C₅NH₄PO₃）]₄（TPTC）₄}（9）[NH₂Me₂]₅{[（V₆O₆）（OCH₃）₉（C₅NH₄PO₃）Zn₂（CH₃COO）]₄（TPTC）₄}（10）[NH₂Me₂]₆{[（V₆O₆）（OCH₃）₉（C₅NH₄PO₃）Co]₄（TPTC）₄}（11）[NH₂Me₂]₆{[（V₆O₆）（OCH₃）₉（C₅NH₄PO₃）Ni]₄（TPTC）₄}（12）TPTC=3,5-di（4’-carboxylphenyl）benozoic acid4.Under the guidance of hard/soft acid/base（HSAB）theories,we selected 4-pyrazolecarboxylic acid with different coordination ability functional groups as ligands and synthesized tetrahedral MOPs constructed from two SBUs,{V₆S}and trinuclear copper clusters{Cu₃Py C₃},by a one-pot method.And it can be used as the catalyst for the decomposition of H₂O₂ and the oxidation of C-H bonds of benzylic compounds.（NH₂Me₂）₈[（V₆O₆（OCH₃）₉（SO₄））₄（Py C）₆]（13）（NH₂Me₂）₈[（V₆O₆（OCH₃）₉（SO₄））₄（Cu₃Py C₃）₄]（14）PyC=4-pyrazolecarboxylic acid...