Synthesis And Properties Of Transition Metal Coordination Modified Vanadium-Capped Keggin Type Heteropolyoxoniobates

Polyoxometalates(POMs),as an important family of oxide aggregates,have potential applications in a wide range of fields such as biomedicine,sewage treatment,material science and catalysis.Polyoxoniobate is an important branch of polyoxometalate family and has attracted much attention in recent years.Compared with molybdates and tungstates,polyoxoniobates have chemical inertness and high charge density and are easy to hydrolyze under acidic conditions.Therefore,the design and synthesis of polyoxoniobates is one of the challenges in the field of POMs chemistry.In this thesis,10 new POM-based transition metal-organic frameworks 1-10 have been synthesized using vanadium-capped keggin-type heteropolyoxoniobates as building blocks.The electrochemical properties,photocatalytic degradation of dyes and organic catalytic properties of the corresponding compounds have been investigated.1.Four cases of vanadium-capped Keggin type heteropolyoxoniobates compounds 1-4 were synthesized using nitrogen containing organic ligands,K7HNb6O19· 13H20 and Cu(Ac)2 as raw materials.{[Cu(dap)2]4(AsNb10V8O46)}-(OH)3(1)H2 {[Cu(dap)2]4(AsNb9V7044)}·2H20(2){K[Cu(dap)2]4[AsNb12(VO)5040]}·(OH)4(3)H3{[Cu(phen)2]4(AsNb12V2042)}·6H20(4)In compound 1,each six-vanadium-capped polyoxoanion[AsNb10V8O46]5-links eight[Cu(dap)2]2+ to form 3D porous structure.In compound 2,each four-vanadium-capped polyoxoanion[AsNb9V7O44]10-links four[Cu(dap)2]2+.The polyoxoanion of compound 3 exhibits a five-vanadium-capped arsenic polyoxoniobate structure,which is obtained for the first time.Compound 4 exhibits a structure of bi-capped polyoxoanion[AsNb12V2O42]11-tetra-supported[Cu(phen)2]2+.The band gap values(Eg)of compounds 1-3 are 2.63,2.61 and 2.34 eV.Compound 4 has good electrocatalytic activities for H2O2 and NaN02.The photocatalytic degradation of methylene blue(MB)of compounds 1-4 has been studied.Compounds 1-4 are useful for catalytic cyanosilylation of aldehydes.The conversion rate of m-methylbenzaldehyde is 97.33%(11 h)and 93.68%(4.5 h),respectively,with compounds 2 and 4 as catalysts.2.Four cases of vanadium-capped Keggin type heteropolyoxoniobates 5-8 were synthesized with four nitrogen containing organic ligands,triethylenetetramine(teta),1,2-diaminocyclohexane(dach),trans-1,2-diaminocyclohexane,en,respectively.{[Cu(teta)]4[PNb12O40(VO)6]}·(OH)5-3H20(5){[Cu(C10H12N4)]4[PNb12O40(VO)6]}·(OH)5·3H20(6){[Cu(dach)2(H20)][Cu(dach)2]3[PNb12O40(VO)4]}·(OH)·7H20(7){[Mn(en)2]4[PNb12O40(VO)6]}·(OH)5·3H20(8)The polyoxoanions in compounds 5-8 all belong to the vanadium-capped Keggin-type polyoxoanions.The polyoxoanions in compounds 5,6 and 8 are six-vanadium-capped structures.The polyoxoanion in compound 7 is four-vanadium-capped structure.Compounds 5,6,and 8 show a three-dimensional porous structure in which each polyoxoanion act as an 8-dentate ligand to coordinate with the metal-organic fragments.Compound 7 forms a one-dimensional structure through the coordination of[PNb12O40(VO)4]7-and copper-organic fragments.The band gap value(Eg)of compounds 5-8 is 1.67,2.97,0.59 and 1.71 eV,respectively.Compounds 5-7 have good electrocatalytic activities for H2O2 and NaNO2.The heterogeneous catalysis of compounds 5-8 for the cyanohydrination of aldehydes and ketones were studied.The conversion rate of p-anisaldehyde is 93.27%for compound 6 after 22 h,and the conversion rate of m-methylbenzaldehyde reaches to 97.60%for compound 8 after 21 h.In addition,studies have shown that the hydrogen production performance of compound 5 is 1.39 times that of the original material Nb6O19.3.Two cases of vanadium-capped Keggin-type heteropolyoxoniobates compounds 9-10 were synthesized based on nitrogen containing organic ligands,1,2-dap and(1R,2R)-1,2-diaminocyclohexane(dach),respectively.{[Cu(dap)2]4[VNb,2(VO)4O40]}·(OH)(9){[Cu(dach)2][Cu(dach)2·H20]3[VNb12(VO)4O40]}·(OH)·9H20(10)There are four-vanadium-capped Keggin-type polyoxoniobates in compounds 9 and 10.[VNb12(VO)4O40]7-as building blocks bond to[Cu(dap)2]2+ or[Cu(dach)2]2+ to form a modified structure in compounds 9 and 10.The band gap value(Eg)of compound 9 is 2.51 eV.Compound 9 has good electrocatalytic activities for H2O2,NaN02,DA and AA.Studies on the catalytic performance of the acetalation reaction of aldehydes and ketones show that the conversion rate of m-methylbenzaldehyde is 97.55%for 9 at 8 h and the conversion rate of p-anisaldehyde is 95.87%for 9 at 11 h.