Synthesis, Structure And Properties Of Polyoxometalates Containing Te Element

Utilization of hydrothermal synthesis provides 10 polyoxometalate compounds that have not been reported before. These compounds are characterized by elemental analyses, IR, TG and X-ray diffraction analysis.Compounds 1-9 are a series of heteropolyoxomolybdates with (3,6)-connected nets constructed from Anderson type heteropolyoxoanion [TeM₆O₂₄]^6- (M = Mo, W). Compounds 1-6 are isomorphous with the formulas (NH₄)₂{[M(H₂O)₃]₂[TeMo₆O₂₄]}H₂O (M = Mn(1), Co(2), Ni(3), Cu(4) and Zn(5)) and (NH₄)₂{[Ni(H₂O)₃]₂[TeW₆O₂₄]}H₂O (6). 1-6 are of highly symmetrical structures with pyrite-like topology constructed from [TeM₆O₂₄]^6- (M = Mo, W) and transition metals. Compounds 7-9 are isomorphous with the formulas [Ln(H₂O)₄]₂[TeMo₆O₂₄]-3H₂O (Ln = La(6), Ce(7) and Nd(8)), which crystallize in lower symmetrical space groups exhibiting rutile-like topology constructed from [TeMo₆O₂₄]^6- and rare earth metals. In these compounds Anderson type heteropolyanions act as 6-connected sites and transitional metals or rare earth metals act as 3-connected sites, which results in the unusual classical mineral structures.Compound 10 is a new vanadium tellurite templated by organic molecules, obtained under hydrothermal conditions. It exhibits a stable three-dimensional (3D) vanadium tellurite anion framework composed of vanadium, tellurium, and oxygen atoms through covalent bonds, with the [NH₃CH₂CH₂NH₃]²⁺ cations residing in the channels. Bond valence sum calculations and variable-temperature magnetic susceptibility of compound 10 both indicate that V atoms are in the +4 oxidation state. It can be concluded that ethylenediamine acts not only as a templating agent, but also as a reducing agent, which is responsible for the reduction of V⁵⁺to V⁴⁺ .