pH-Controlled and Sulfite Anion-Directed Assembly of a Family of Cerium(III)-Containing Polyoxotungstates Clusters

A versatile one-pot strategy was employed to synthesize five cerium(III)-containing polyoxotungstate nanoclusters through pH-controlled and sulfite anion-directed assembly: [C2H8N](3)Na-7[Ce-2(H2O)(6)W22O72(OH)(4)]center dot 20H(2)O (1) at pH 5.0; [C2H8N](8)Na-16[Ce-4(H2O)(12)W44O144(OH)(12)]center dot 23H(2)O (2) at pH 4.5; [C2H8N](2)Na4Ce2[Ce-2(H2O)(10)W28O92(OH)(2)]center dot 27H(2)O (3) at pH 2.8-3.3; [C2H8N](2)Na-7[{alpha-SW7O28}{Ce-2(H2O)(6)}(W3O6){alpha-SW9O32}{alpha-SW9O31(OH)}]center dot 18H(2)O (4) at pH 2.5; [C2H8N](2)Na-18[Ce-2(H2O)(9)W36O110(OH)(12)](2)center dot 30H(2)O (5) at pH 1.5. These compounds were characterized by single-crystal X-ray structure analysis, IR spectroscopy, thermogravimetric (TG) analysis, X-ray photoelectron spectroscopy (XPS), and electrospray ionization mass spectrometry (ESI-MS). Moreover, their electrochemical properties were investigated. Single-crystal X-ray structure analysis revealed that 1 and 2 were di- and tetra-cerium(III)-bridged polyoxotungstates, constructed from two different types of lacunary {W-11} units. 3 composed of the well-known cerium(III)-stabilized {W-28} unit and organic aminesodiumcerium cations, was isolated in the pH range 2.83.3. In this reaction system, the SO32 anion acted as a heteroanion template at a lower pH 2.5. 4 was isolated by the combination of cerium(III) centers and SO32- heteroanion template, which is the first lanthanide-containing polyoxotungstates with sulfur heteroatoms, and the 4f metal cerium(III) centers in 4 both have eight-coordinated modes and the SO32- heteroanion templates display mu(7) and mu(9) coordination modes. At a much lower pH 1.5, the polyanion of 5 was obtained, two triangular-shaped {W-36} subunits were bridged by the cerium(III) ions, resulting in the largest lanthanide-containing iso-polyoxotungstates known to date.