| The research on polyoxometalates(POMs)is mainly focused on polyoxovanadate(POV),polyoxomolybdate(POMo)and polyoxotungstate(POW),and the research on polyoxoniobate(PONb)is relatively few.In the last two decades the development of PONb has made great progress,the speed is still slowly;Especially in condition of acid,precursor K7HNb6O19·13H2O will hydrolyse and yields hydrated oxides Nb2O5·nH2O.In this paper,the design and synthesis of new PONb in acidic condition were studied.Using K7HNb6O19·13H2O and some simple compound as materials,twelve novel PONbs have been successfully synthesized and characterized.At the same time,the electrochemical,magnetic and fluorescence properties were studied.I.Using conventional aqueous methods with K7HNb6O19·13H2O,A-a-Na10SiW9O34·23H2O,transition metal salts as materials,two Keggin-type Nb/W mixed POM had been successful synthesized:1.Keggin-type Nb/W mixed POM trapping a {MnNb9} core:Cs10Na3[(SiW9Nb3O38)3Mn-O3(H2O)3]·18H2O(1)Compounds 1 is the first example of trimer Keggin-type Nb/W mixed POM,and also the first example of transition metal Mn insert PONb.The polyanion can be seen as three Keggin-{SiW9} trapping a{MnNb9} core.And,the CV behaviour of compound 1 indicates that the redox process of compound 1 is a diffusion control process.2.Keggin-type Nb/W mixed POM capping a {WNb9} core:Cs12[(SiW9Nb3O38)3WO3(OH)3]·53H2O(2)Compounds 2 and 1 are isomorphic.Compounds 2 is the first example of 4f-W atom inset in Keggin-type Nb/W mixed POM.The polyanion can be seen as three Keggin-{SiW9} trapping a {WNb9}core.Further,2 exhibits photocatalytic H2 evolution activity.II.Using conventional aqueous methods with K7HNb6O19·13H2O,K12[H2P2W12O48]·24H2O,transition metal salts as materials,two Wells-Dawson type Nb/W mixed POM had been successful synthesized:3.Dimer Wells-Dawson-type Nb/W mixed POM:K6(NH4)7H7[{P2W12Nb6O62} 2 {Co2-(H2O)8}]·17.5H2O(3)Compound 3 is the first Wells-Dawson-type Nb/W mixed POM containing transition metal cobalt.In the polyanion,the six absent sites of Wells-Dawson type K12[H2P2W12O48]·24H2O are occupied by NbO6 octahedron to form the {P2W12Nb6} unit.The two {P2W12Nb6} units are connected by NbO6 octahedron and CoO6 octahedron to form a dimeric compound having a "V" type structure.Besides,magnetic measurements show that 3 exhibits antiferromagnetic behavior.4.Tetramer Wells-Dawson-type Nb/W mixed POM:K7(NH4)14H15{P2W12Nb6O62}4 {Co6-(H2O)18}]·35H2O(4)Compound 4 is the first tetrameric Wells-Dawson type Nb/W mixed POM with transition metal cobalt.The polyanion of compound 4 are formed by Wells-Dawson type {P2W12Nb6} units which connected by NbO6 octahedron and CoO6 octahedron to form the tetrameric structures.At the same time,the study of the magnetic properties shows that the compound has an antiferromagnetic behavior.?.Using conventional aqueous methods,with K7HNb6O19·13H2O,LnCl3·nH2O as materials,eight hetero-PONb had been successful synthesized:[Eu(H2O)6]2[1H4Nb(O2)6P4O24]· 12H2O(5)[Gd(H2O)6]2[H4Nb(O2)6P4O24]· 12H2O(6)[Tb(H2O)6]2[H4Nb(O2)6P4024]·12H2O(7)[Dy(H2O)6]2[H4Nb(O2)6P4O24]· 12H2O(8)[Ho(H2O)6]2[H4Nb(O2)6P4O24]·12H2O(9)[Er(H2O)6]2[H4Nb(O2)6P4O24]·9H2O(10)[Tm(H2O)6]2[H4Nb(O2)6P4O24]·12H2O(11)[Yb(H2O)6]2[H4Nb(O2)6P4O24]·12H2O(12)Compound 5-12 are composed with[P4Nb6]and rare earth ions,and extension of a two-dimensional structure.The luminescent properties of compounds 5,7,8 were studied.And,8 exhibits ferromagnetic behavior. |
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