Study On The Construction And Catalytic Performance Of Polyoxometalate-Based Metal-Organic Frameworks

Polyoxometalates (POM) as inorganic clusters that have particular structures and various properties have attracted many scientists and have been utilized as an important building blocks in heterogeneous catalysis, host-guest chemistry, biochemistry, nanotechnology and electricity, magnetism and light chemical materials.Metal-organic frameworks (MOFs) that have combined the characteristics of polymer composites and coordination compounds are widely used in nonlinear optical material, magnetic materials, superconducting materials and catalysis. Being different from traditional porous materials’(zeolite molecular sieve, activated carbon materials and so on) building mode, we can directly predict MOFs’ structures according to the geometry configuration of ligands.Recently, to reuse the polyoxometalates in the reaction and reduce manufacturing cost, many kinds of solid support have been used to immobilize them, however, all these supports are weakly interacted with POMs, leading to easily leaching from them which largely restrict their application in catalytic reactions. On the basis of their unusual building mode, MOFs can immobilize these POMs firmly and avoid the leaching of POMs so the POMs/MOFs can truely achieve the heterogeneous catalysis of POMs. As a consequence, it’s meaningful to study on the structural and catalytic performance of polyoxometalate-based metal-organic frameworks.We have synthesized the following six POMs/MOFs single-crystalline structures which are self-assembled by Keggin-type phosphotungstic and silicotungstic, conjugate aromatic compound4,4’-bipyridine-N,N’-dioxide and lanthanide or transition metal ions:[Er2H(μ-O)2(dpdo)4(H20)2][PW12O40]-3H2O (1),[Tm2H(μ-O)2(dpdo)4(H2O)2][PW12O40]·3H2O (2),{[Zn3Na2(μ-OH)2(dpdo)6(H2O)16][PW12O40]2}·(dpdo)3·C2H5OH·2H2O(3),[Mn3(dpdo)6(H20)4Cl2][SiW12O40]·H2O (4),[Co3(dpdo)6(H2O)4Cl2][SiW12O40]·H2O (5),[Ni3(dpdo)6(H20)4Cl2][SiW12O40]·H2O (6). We also have characterized their structures by single-crystal X-ray diffraction, IR spectra and elemental analyses.Further more, we have studied the ability of hydrolytic cleavage of an DNA-model phosphodiester BNPP catalyzed by compounds1-3and the ability of the epoxidation of styrene with hydrogen peroxide catalyzed by compounds4-6. The results indicated that compounds1- 3have high catalytic performance on hydrolytic cleavage of BNPP which is resulted from both the BrOnsted acid of POM and the Lewis acid of lanthanide metal ions, compounds4-6could catalyze the epoxidation of styrene with low selectivity and yield.