Syntheses,Structures And Properties Of Polyoxotungstates Constructed By Transition-Metal

The research on transition-metal-substituted polyoxometalates(POMs)is mainly focused on the sandwich structures,and the research on high-nuclearity high-nuclear metal-substituted POMs is relatively few.In this paper,eight novel POMs were isolated through the reactions of transition metal(TM)salts,some classical precursors like K8Na2[A-α-GeW9O34]25H2O,Na10[α-SiW9O34]18H2O and other reactants under appropriate conditions.In addition,compounds were fully characterized and determined by a series of conventional analysis method,like X-ray single-crystal diffraction,X-ray powder diffraction,IR,UV,thermogravimetric analyses,mass spectrometry and their magnetic properties have also been verified.1.Two novel germanotungstates transiton-metal derivatives with open Wells-Dawson structures,K10H10[Co(H2O)2]2[Co(H2O)3]2(Ge4W36O130)1-32H2O(1)and KtaH10{[Ni(H2O)2]2[Ni(H2O)3]2(Ge4W36O130)}-32H2O(2)have been successfully synthesized.This is the first time to report the tetramer germanotungstate polyanions with open Wells-Dawson structures.Compounds 1 and 2 contain the same structure of the polyoxoanions,both of which consist of the S-shaped tetrameic structure{[M(H2O)2]2[M(H2O)3]2(Ge4W36O130)}20-(M = Co,Ni).Moreover,the electrospray-ionization mass spectrometry(ESI-MS)was performed to study the stable pH value range of compounds 1 and 2 in aqueous solution.2.A giant 17-cobalt-containing silicotungstate K4Na16H13{NaCo(H2O)6[Cos(OH)6]2(CO3)g(SiW9O34)4} 34H2O(3)was isolated succesfully,and this is the most abundant polyoxotungstate containing {CO3} groups at present.The polyanion of compound 3 is a tetramer structure,which can be regarded as two{CO4SiW9} units connected by four {CO3} groups to form a dimer ｛Co4SiW9(CO3)4｝.Further,the dimer is polymerized by two disordered atoms of Co/Na to form a tetramer structure.The magnetic measurements indicate that the compound exhibits an antiferromagnetic interaction.3.Two transition-metal-sub stituted polytungstate K11Cs4H{[Cos(OH)6(H20)2](CO3)3(GeW9O34)2}·12H2O(4)and Na6K6H4｛[Nis(OH)6(H2O)2](CO3)3(SiW9O34)2}·22H2O(5),have been successfully synthesized.The polyanion of compound 4 and 5 are transition metal-substituted Keggin structural units {M4XW9},which are connected by three {CO3} groups to form dimer｛M4XW9(CO3)3}.And compounds 4 and 5 are structurally similar and the differences between them are the hetero atoms and the transition metal.Besides,magnetic measurements show that both of them exhibit antiferromagnetic behavior.4.A 9-nickel-containing silicotungstate K5.5Na5.5H3[Ni9(OH)6(H2O)6(α-SiW9O34)2(CO3)3]2OH2O(6)was isolated succesfully.The polyoxoanion structure of compound 6 can be viewed as the addition of Ni2+ to the polyoxoaion structure of compound 5.The magnetic measurements show that compound 6 exhibit antiferromagnetic behavior.5.A 6-iron-containing germanotungstate K4Na2H7{Fe6(OH)3[a-GeW9O34(OH)3]2(C5H9N2O2)2｝ 18H2O(7)was isolated succesfully.The compound 7 is a classical sandwich structure,and the magnetic measurements of compound 7 show that there are anti-ferromagnetic interactions between the iron clusters.6.A sandwich tungstobismutates NasNi(H2O)e[Bi2W20Ni2(H2O)6O70]-40H2O(8)was isolated succesfully in high yield.Different from the compound 7,the compound 8 anion has Krebs sandwich structure.