Building block approach to nanostructures: step-by-step assembly of large lanthanide-containing polytungstoarsenate aggregates

Abstract

Three large cerium-containing polytungstoarsenate aggregates have been synthesized via a step-by-step assembly process. Reaction of Na₉[AsW₉O₃₃] precursors, ceric sulfate and potassium citrate in an acidic aqueous solution at pH = 3 led to the isolation of a new dimeric sandwich-type compound K₉Na₇[{Ce₂O(H₂O)₅}{WO(H₂O)}{AsW₉O₃₃}₂]₂ ·∼48H₂O (1). The presence of the citrate anion prevents precipitation of simple lanthanide salts with polyoxometalates. The reaction of compound 1 with α-alanine at pH = 2 resulted in the formation of a new alanine-decorated cryptand compound K₂Na₁₀[Ce₄As₄W₄₄O₁₅₁(ala)₄(OH)₂(H₂O)₁₀] ·∼40H₂O (2). The reaction between compound 1 and MnCl₂ at pH = 5 yielded the other inorganic cryptate Mn_0.5K₅Na₁₈[Ce₄As₄W₄₁O₁₄₉] ·∼50H₂O (3). All compounds are characterized by elemental analyses, TG analyses, IR, UV-Vis absorption spectra, X-ray photoelectron spectroscopy (XPS), single crystal X-ray diffraction and electrochemical analyses. The crystal data for these compounds: 1, triclinic, P, a = 12.314(3) Å, b = 17.953(4) Å, c = 22.355(5) Å, α = 90.18(3)°, β = 101.97(3)°, γ = 91.08(3)°, Z = 1; 2, monoclinic, P2(1)/n, a = 23.4483(15) Å, b = 21.8764(13) Å, c = 23.6930(14) Å, β = 111.0560°, Z = 2; 3, triclinic, P, a = 20.636(4) Å, b = 23.000(4) Å, c = 25.039(4) Å, α = 81.991(3)°, β = 73.333(3)°, γ = 74.835(3)°, Z = 2. Electrochemical analyses of compounds 1–3 suggest that tetravalent cerium ion can be stabilized by the polyanions with high negative charges.