Syntheses, Structures And Properties Of Lanthanide Derivatives Based On Dawson Type Nb/W Mixed-Addendum Polyoxometalate

Polyoxometalates （POMs） are a class of discrete anionic molecular clustersformed by oxo-bridged early transition metals. They have potential applications indiverse areas such as chemical analysis, medicine, multifunctional materials andcatalysis due to their enormous structural varieties and interesting properties. In thispaper, we chose the Nb/W mixed-addendum polyoxometalate as the precursor to reactwith the lanthanide ions in acidic conditions, and successfully obtained two novelcompounds. The sythetic conditions and rules and the properties of these twocompounds are also studied. All the compounds have been fully characterized bysignal-crystal X-ray diffraction, IR spectro-scopy, thermogravimetric analysis,elemental analysis. The electrochemical photoluminescence behaviors of them havebeen discussed.Two novel isostructural polyoxotungstates have been synthesized by reaction ofsaturated Dawson-type Nb/W mixed-addendum polyoxometalate [P2W₁₅Nb₃O₆2]9–and lanthanide ions (Eu³⁺/Ce³⁺) in acidic solution.K_<sub>6Na₄H₈[Eu₆（H₂O）3₈(P₂W₁₅Nb₃O₆₂)₄]·45H₂O （1）K_<sub>6Na₄H₈[Ce₆（H₂O）3₈(P₂W₁₅Nb₃O₆₂)₄]·56H₂O （2）1and2display novel1D infinite chains with {Ln₆(P₂W₁₅Nb₃O₆₂)4} as theasymmetric subunit. The asymmetric subunit contains two identical sandwich-typefragments {Ln₃(P₂W₁₅Nb₃O₆₂)2} which are ranged in a centrosymmetry form andlinked by two Ln–O–W. All the Ln atoms bind to the NbO₆octahedra throughLn–Ot（Nb） bonds because of the high nucleophilicity of Ot（Nb）.The solid photoluminescence behavior of1has been investigated at roomtemperature, which exhibits five characteristic peaks of Eu under the excitationwavelength （394nm）. The solid emission spectra of2exhibits an emission maximumat556nm upon excitation at2₆5nm, which is assigned to the5d(²A_1g)â†'4f(²F_5/2)transition of Ce^Ш. Additionally, the cyclic voltammogram of2indicates goodelectrocatalytic activity towards the reduction of nitrite.