Polyoxometal cations within polyoxometalate anions.: Seven-coordinate uranium and zirconium heteroatom groups in [(UO2)12(μ3-O)4(μ2-H2O)12(P2W15O56)4]32- and [Zr4(μ3-O)2(μ2-OH)2(H2O)4 (P2W16O59)2]14-

Two new composite polyoxotungstate anions with unprecedented structural features, [(UO2)(12)(mu(3)-O)(4)(mu(2)H(2)O)(12)(P2W15O56)(4)](32-) (1) and [Zr-4(mu(3)-O)(2)(mu(2)-OH)(2)(H2O)(4) (P2W16O59)(2)](14-) (2) contain polyoxo-uranium and -zirconium clusters as bridging units. The anions are synthesized by reaction of Na-12[P2W15O56] with solutions of UO2(NO3)(2) and ZrCl4. The structure of 1 in the sodium salt contains four [P2W15O56](12-) anions assembled into an overall tetrahedral cluster by means of trigonal bridging groups formed by three equatorial-edge-shared UO7 pentagonal bipyramids. The structure of anion 2 consists of a centrosymmetric assembly of two [P2W16O59](12-) anions linked by a {Zr4O2(OH)(2)(H2O)(4)}(10+) cluster. Both complexes in solution yield the expected two-line P-31-NMR spectra with chemical shifts of -2.95, -13.58 and -6.45, -13.69 ppm, respectively. (C) 2003 Elsevier B.V. All rights reserved.