Structure,Self-assembly Synthesis And Property Study Of Novel Polyoxovanadate-based Metal–organic Polyhedra

Metal–organic polyhedra?MOPs?are a class of burgeoning porous materials after zeolites and metal–organic frameworks?MOFs?.MOPs are not infinite 3D networks,but instead they are discrete molecular entities,which are constructed from edge-sharing molecular polygons or via connections between molecular vertices.The obtained molecular polyhedra based on self-organization via metal to organic ligands are cage-like architectures at the nanoscale size,with outer and inner surfaces.Simultaneously,MOPs have flexibility in their geometrical topology,size,surface area,and porosity.By serving as host molecules,MOPs have significant applications in many fields,including catalysis,sorption,biophysical science,or as substrates for MOFs materials.As a unique branch of polyoxometalates,polyoxovanadates?POVs?have attracted continuous attention not only due to their structural diversity and remarkable properties,but also for promising applications in the fields of molecular magnetism,catalysis,redox,medical chemistry and bioactive materials.In this dissertation,we employ simple vanadium source and different carboxylate ligands to design and synthesize thirteen polyoxovanadate-based MOPs.In specific solvothermal conditions,novel polyoxovanadate-based building blocks with different coordination modes were obtained,which play significant roles in the formation of MOPs.Due to the existence of reductive vanadium in the skeletons,we explored the magnetic properties of most resulted compounds.1.Our strategy is to use polyoxovanadates and linear dicarboxylate ligands to build polyoxovanadate-based organic–inorganic hybrids.Fortunately,three isostructural{V₅O₉Cl}-based metal–organic octahedral coordination cages were obtained.These compounds were characterized by single-crystal X-ray diffraction,PXRD,IR,TGA and N2 adsorption.?NH₂Me₂?12[?V₅O₉Cl?6?BDC?12]·?DMF?17?1??NH₂Me₂?12[?V₅O₉Cl?6?BDC-NH₂?12]·?DMF?14?2??NH₂Me₂?12[?V₅O₉Cl?6?BDC-Br?12]·?DMF?8?3?BDC = 1,4-benzenedicarboxylateBDC-NH₂ = 2-amino-1,4-benzenedicarboxylateBDC-Br =2-bromo-1,4-benzenedicarboxylate2.By employing angular or extended bidentate carboxylate ligands to assemble with vanadium-oxygen clusters,we successfully obtained three novel polyoxovanadate-basedmetal–organic polyhedra,which all contain pentanuclear {V₅O₉Cl} building units.Interestingly,depending on the nature of carboxylate ligands,their structures exhibit differences including truncated triangular prism,truncated quadrangular prism and truncated octahedron.Furthermore,the magnetic investigations reveal that they show similar ferromagnetic behaviors.?NH₂Me₂?6[?V₅O₉Cl?3?TDA?6]·?DMF?1.5?CH3OH?0.5?4??NH₂Me₂?8[?V₅O₉Cl?4?m-BDC?8]·?DMF?3?CH3OH?0.5?5??NH₂Me₂?12[?V₅O₉Cl?6?NDC?12]·?DMF?8?CH3CH₂OH?0.5?6?TDA = thiophene-2,5-dicarboxylic acidm-H₂ BDC = 1,3-benzenedicarboxylic acid2,6-H₂ NDC = 2,6-naphthalenedicarboxylic aid3.We report the solvothermal synthesis and structural characterization of five unprecedented alkoxo-polyoxovanadate-based metal–organic polyhedra.Herein,the magnetic behaviors of three compounds were investigatied As a result,they all show antiferromagnetic exchange interactions.To our knowledge,this work represents a relatively rare example of integration of alkoxo-polyoxovanadates into the metal–organic materials.The discovery of {V6S} building unit not only adds a representative example to the limited family of polyoxovanadates,but also will be regarded as a 3-connected inorganic ligand which is suited for building truncated tetrahedral architectures and molecular capsules with organic linkers.?NH₂Et₂?8{[V6O6?OCH3?9?SO4?]4?BDC?6}?DEF?2?7??NH₂Et₂?8{[V6O6?OCH3?9?SO4?]4?BDC-NH₂?6}?DEF?1.5?8??NH₂Et₂?8{[V6O6?OCH3?9?SO4?]4?BDC-Br?6}?DEF?1?9??NH₂Et₂?8{[V6O6?OCH3?9?SO4?]4?BTC?4}?DEF?0.5?10??NH₂Et₂?8{[V6O6?OCH3?9?SO4?]4?BTB?4}?DEF?1.5?11?BTC = 1,3,5-benzentricarboxylateBTB = 1,3,5-tris?4-carboxyphenyl?-benzene4.Based on our previous work,when we used VCl3 instead of VOSO4·xH₂O in similar solvothermal conditions,two vanadium-based MOPs incorporated unprecedented {V₇}isopolyoxometalate clusters have been synthesized.They exhibit beautiful structures with truncated tetrahedral cages.Additionally,the {V₇} polyoxovanadate-based building unit is reported here for the first time and features the highest nuclearity of the vanadium-oxygen cluster compared with reported vanadium-based MOPs.The magnetic investigations indicate that they show similar antiferromagnetic behaviors.?NH₂Et₂?4{[V6O6?OCH3?9?VO3??H₂O?]4?BDC?6}?DEF?0.5?12??NH₂Et₂?4{[V6O6?OCH3?9?VO3??H₂O?]4?BDC-NH₂?6}?DEF?0.5?CH3OH?0.5?13?...