Synthesis,structures And Properties Of Keggin Polyoxometalates Modified By Lanthanide /Transition Metal

Two new transition-metal-centered Keggin-type compounds based on saturated Keggin polyoxometalates K5[Fe W12O40].12H2 O and K6[Co W12O40].16H2 O as precursors and three new lanthanide heteropolymolybdates(Ln POMs) compounds have been synthesized via conventional method by degradation and the one-pot reaction.We explored the process of the reaction condition, which includes p H in aqueous solution,temperature, concentration and ratio of mixture and so on. The FT-IR spectra, UV-Vis spectra, thermal stability, magnetic property measurements and surface photovoltage property of the compounds were also made to well characterize these novel complexes.1.Under conventional aqueous synthesis condition,begin with saturated K5[Fe W12O40].12H2 O as precursor, transition-metal cobalt salt and oxalic acid, a novel mixed-metal sandwiched trivacant tungstoferrates 1 has been synthesized by degdration:Na2K2H8[FeIII2Co2(H2O)2(FeIIIW9O34)2].27H2O(1)Compound 1 is composed of two trilvacant Keggin[B-α-Fe W9O34]11- sandwiched a mixed-metal cluster {Fe2Co2O(H2O)2}. The magnetic investigation indicates compound 1 presents strong antiferromagnetic interactions.2.In conventional aqueous,begin with saturated K6[Co W12O40]?16H2O as precursor and transition-metal nickel salt in aqueous solution produce a novel compound 2:Ni(H2O)6H4[Co W12O40].4H2O(2)X-ray single crystal diffraction analyses revealed that compound 2 is composed of the standard α-Kegging type [Co W12O40]6- polyanion,[Ni(H2O)6]2+counter ion,there is electrostatic attraction between them.The magnetic investigation indicates the presence of strong antiferromagnetic interactions between transition-metal Ni2+ and the central Co2+.3.Via aqueous solution synthesis strategy, choosing Na As O2,(NH4)6Mo7O24·4H2O and lanthanide as the starting materials in the participation of imidazole, three novel polymolybdates were obtained and structurally characterized:[C3H5N2]4[Gd(H2O)6(As Mo10O35)] ?2H2O(3)[C3H5N2]2[NH4]12[Gd4(Mo O4)(H2O)16(Mo7O24)4]·29H2O(4)[C3H5N2]2[NH4]12[Nd4(Mo O4)(H2O)16(Mo7O24)4]·71H2O(5)In compound 3,the Gd3+ ion in a eight-coordinate environment, is coordinated with two terminal oxo groups of two Mo O6 octahedron from [As Mo10O35]7– fragment with the other six sites occupied by six water molecules. Compound 3 and 4 are isostructural, 4 and 5 contain a [Ln4(Mo O4)(H2O)16(Mo7O24)4]14-{Ln=Gd3+ 4;Nd3+ 5} clusters, which are built up by a central [Ln4(Mo O4)(H2O)16]10+unit surrounded by four heptamolybdate groups. The magnetic investigation on compounds 3-5 show antiferromagnetic interaction. In addition, the surface photovoltage spectra(SPS) and electric field-induced surface photovoltage spectra(EFISPS) demonstrate that compounds 3-5 should be of p-type semiconductors.