title: Construction of polyoxometalates from dynamic lacunary polyoxotungstate building blocks and lanthanide linkers.
abstract: A series of polynuclear metal-oxo clusters have been constructed from the dynamic polyoxometalate (POM) building block {B-α-Sb(III)W9O33} and lanthanide (Ln) linkers via a stepwise synthetic strategy with the molecular formulas of [Ln2(H2O)4{WO2(pic)}2(SbW8O30)2](10-) (Na4Li6[La-1]·28H2O, Na3Li7[Pr-2]·30H2O) and [{Ln(H2O)}{Ln(pic)}(Sb3O4)(SbW8O31)(SbW10O35)]2(24-) (K2Na6Li16[Tb-3]·63H2O, Na9Li15[Dy-4]·61H2O, Na7Li17[Ho-5]·53H2O) (Hpic = picolinic acid). The five compounds have been characterized by FT-IR, elemental analysis, TG, powder X-ray diffraction (PXRD) and single crystal X-ray diffraction. In compounds 1-5, various POM moieties, such as {B-β-SbW8O30}, {B-α-SbW8O31} and {B-α-SbW10O35}, were formed through a series of disassembling and re-assembling processes of the dynamic {B-α-SbW9O33} precursor with specific pH, reaction temperature and time. Furthermore, the use of oxytropic Ln(3+) ions as linkers, together with auxiliary organic pic ligands and/or inorganic Sb(3+) ions, led to diverse connection modes between the POM building blocks and Ln linkers and the assembly of new polynuclear metal-oxo clusters. The polyoxoanions of La-1 and Pr-2 possess the same structural feature, which can be viewed as a sandwich-type cluster composed of two {B-β-SbW8O30} units connected by two {WO2(pic)} fragments and two hydrated Ln ions. These sandwich-type polyoxoanions are further linked by the hydrated Ln ions to form a 1-D helical chain. The polyoxoanions of Tb-3, Dy-4 and Ho-5 display the same structural features, although they contain different counter-cations and lattice water molecules. In the polyoxoanions of 3-5, one {B-α-SbW8O31} POM moiety and one {B-α-SbW10O35} POM unit are connected by one {Sb3O4} fragment and one {Ln(pic)} linker, forming an asymmetric sandwich-type metal-oxo cluster. Two of these sandwich-type clusters are further fused together by extra two hydrated Ln ions, leading to an isolated polynuclear metal-oxo cluster with a size of 16.4 × 28.5 Å. The photoluminescence properties of Tb-3 and Dy-4 were investigated. Both compounds exhibit characteristic Tb(3+) and Dy(3+) luminescence. The relationship between the luminescence properties and the crystal structure of the polyoxoanion was discussed.
authors.affiliation: Key Laboratory of Polyoxometalate Science of Ministry of Education, Faculty of Chemistry, Northeast Normal University, Renmin Street No. 5268, Changchun, Jilin 130024, P. R. China. wangyh319@nenu.edu.cn zanghy100@nenu.edu.cn.
authors.forename: Lu-Lu
authors.initials: LL
authors.lastname: Li
authors.forename: Hua-Yan
authors.initials: HY
authors.lastname: Han
authors.forename: Yong-Hui
authors.initials: YH
authors.lastname: Wang
authors.forename: Hua-Qiao
authors.initials: HQ
authors.lastname: Tan
authors.forename: Hong-Ying
authors.initials: HY
authors.lastname: Zang
authors.forename: Yang-Guang
authors.initials: YG
authors.lastname: Li