New Plenary and Lacunary Polyoxotungstate Structures Assembled from Nonatungstoarsenate(III) Anions and Uranyl Cations

A new structural family of heteropolytungstate complexes containing trans-dioxo uranium (VI)(uranyl) groups has been isolated in good yield by reaction of UO22+ with (NaAs4W40O140)27- (W40) in aqueous solution. The 'lacunary' anion [(UO2)3(H2O)5As3W29O104]19- 1 is formed by the reaction of W40 with UO2(MeCO2)2 at pH 7, and the crystal structure of (NH4)19((UO2)3(H-2O)5As3W29O104)) 28H2) (orthohombic, P212121, a = 17.5626(2), b = 24.492992), c = 33.3019(3) Angstrom) is reported. The 'plenary' anion [(UO2)3(H2O)6As3W30O105]15- 2 is formed by reaction of W40 with UO2(NO3)2 at pH 4, and the crystal structure of (NH4)15[(UO2)3(H2O)6As3W30O105] ·20H2O [monoclinic, P2,/c, a = 23.63520(10), b = 18.0646(2), c = 25.32640(10) Angstrom, β=107.46o] is reported. Both heteropolyanions containg three B-AsW9O339- groups linked by uranyl cations (pentagonal bipyramids) and three (or two) additioanl corner-sharing WO6 octahedra cap the sturcure of 2 (1). A six-line 183W NMR spectrum of 2 is consistent with an effective C3v symmetry for the anion in solution. Addition of VO2- to a solution of 1 yields the V-substituted anion (3) confirmed by a structure determination of (NH4)17[(UO2)3(H2O)6As3W29O105]·44H2O) [orthohombic, Pnma, a = 31.1821(4), b = 24.9672(3) Angstrom, c = 20.3460(3) Angstrom]. The cyclic voltammogram of 3 in 0.5 M sodium acetate buffer (pH 4.7) shows the VIV/V couple at + 0.26 V (Epc) and + .040 V (Epa)