Synthesis And Electrochemical Behaviours Study Of ε-Keggin-Based Organic-Inorganic Hybrid Compounds

Polyoxometalates(POMs)are soluble anionic metal oxide clusters of d block transition metals in high oxidation states.And they exhibit structural features and good properties that can be exploited in many fields ranging from magnetism,medicine,photochemistry,biology and photochromism to catalysis.POMs can be connected to each other via M-O-M’(M,M’ = transition metal)linkages.Metal-organic frameworks(MOFs)also known as porous coordination polymers(PCPs),has developed rapidly driven largely by their underlying topologies in relation todesigned synthesis and good properties.As an emerging class of porous materials,MOFs assembled through coordination bonds between metal-based nodes(ions or clusters)and bridging organic linkers.Because of their structural and functional tunability,the study of MOFs has become one of the fastest growing topics in the fields of synthetic chemistry and material science.POMs can also act as important inorganic building block,the connection being ensured by transition metal complexes or bridging organic ligands(or metal-organic ligands).Such polyoxometalate-based coordination polymers are sometimes called POMOFs,which combine the nature of the moiety and the porosity of a MOF.POM-based hybrid materials have become a research hotspot in the development of polyoxometalic acid chemistry.In the work,we use Zn-ε-Keggin nodes as basic building blocks,semi-rigid organic linkers 4’-(4-carboxyphenoxy)-[1,1’-biphenyl]-4-carboxylic acid(CPBPC)and 4,4’,4"-((1,3,5-triazine-2,4,6-triyl)tris(azanediyl))tribenzoic acid)(TATAB)as organic ligands has generated two novel POM-based metal organic frameworks(POMOFs)under hydrothermal conditions.During the synthesis,the optimal reaction conditions for the preparation of target compounds was obtained by adjusting the experimental condition,such as pH values,reaction temperature and ratio of raw materials,and its properties have been characterized.Two different inorganic-organic hybrid compounds based on keggin type polyoxometalates(POMs),namely,[TBA]3[PMov8MoⅥ4O36(OH)4Zn4][CPBPC]2(1)[TBA]3[PMov8MoⅥ4O36(OH)4Zn4][PTABAB][HPTABAB].7H20(2)(PTABAB is 4,4’-((6-(phenylamino)-1,3,5-triazine-2,4-diyl)bis(azanediyl))dibenzoate)Here,a decarboxylation reaction of TATAB was observed to generate PTABAB in situ under the reaction conditions.In compound 1,Zn-s-Keggin cores were bridged by CPBPC moieties to generate a 3D dia framework with an eight-fold interpenetration,which can be described as two sets of normal fourfold nets.In compound 2,the adjacent 2D layers interlocked each other to generate a double layer,which were further packed in an AAA sequences.Under the condition of single ligand,this is the first example of Zn-ε-Keggin unit with two different types of geometric ligand.The electrochemical behaviours of these two compounds were studied,as well their diffuse reflectance performance.