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

Three large cerium-containing polytungstoarsenate aggregates have been synthesized via a step-by-step assembly process. Reaction of Na-9[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) center dot similar to 48H(2)O (1). The presence of the citrate anion prevents precipitation of simple lanthanide salts with polyoxometalates. The reaction of compound 1 with alpha-alanine at pH = 2 resulted in the formation of a new alanine-decorated cryptand compound K2Na10[Ce4As4W44O151(ala)(4)(OH)(2)(H2O)(10)] center dot similar to 40H(2)O (2). The reaction between compound 1 andMnCl(2) at pH = 5 yielded the other inorganic cryptate Mn0.5K5Na18[Ce4As4W41O149] center dot similar to 50H(2)O (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 (1) over bar, a = 12.314(3) angstrom, b = 17.953(4) angstrom, c = 22.355(5) angstrom, a = 90.18(3)degrees, beta = 101.97(3)degrees, gamma = 91.08( 3)degrees, Z = 1; 2, monoclinic, P2( 1)/ n, a = 23.4483(15) angstrom, b = 21.8764(13) angstrom, c = 23.6930(14) angstrom, beta = 111.0560 degrees, Z = 2; 3, triclinic, P (1) over bar a = 20.636( 4) angstrom, b = 23.000(4) angstrom, c = 25.039(4) angstrom, alpha = 81.991(3)degrees, beta = 73.333(3)degrees, gamma = 74.835( 3)degrees, Z = 2. Electrochemical analyses of compounds 1-3 suggest that tetravalent cerium ion can be stabilized by the polyanions with high negative charges.