The synthesis, crystal structure, and spectroscopic characterization of [U(V)(H2O)2(U(VI)O2)2O4(OH)](H2O)4 (1), a mixed-valent U(V)/U(VI) oxide material, are reported. The hydrothermal reaction of UO2(2+) with Zn and hydrazine at 120 degrees C for three days yields 1 in the form of a dark red crystalline solid. Compound 1 has been characterized by a combination of single-crystal and powder X-ray diffraction (XRD), elemental analysis, thermogravimetric analysis, X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The structure consists of an extended sheet of edge and corner shared U(VI) pentagonal bipyramids that are further connected by edge sharing to square bipyramidal U(V) units. The overall topology is similar to the mineral ianthinite. The uranium L(III)-edge XAS revealed features consistent with those observed by single-crystal X-ray diffraction. High resolution XPS data analysis of the U4f region confirmed the oxidation states of U as originally assigned from XRD analysis and bond valence summations.

The reaction of K28Li5H7[P8W48O184].92H2O with early lanthanides under hydrothermal and conventional conditions yields novel structures of the molecular formula Ln4(H2O)28K6Li7[K subsetP8W48O184(H4W4O12)2Ln2(H2O)10] congruent with 57H2O, Ln = La (1), Ce (2, 2a), Pr (3), Nd (4), in which the central cavity of the precursor anion is occupied by lanthanide cations and H4W4O12 moieties. The new heteropolyanions were characterized by elemental analysis, infrared spectroscopy, 31P NMR, and X-ray crystallography. All of the crystals are monoclinic, space group C2/m, with lattice constants (A, Epsilon) a = 33.061(3), b = 30.986(3), c = 15.1649(13), beta = 103.607(2), (1); a = 33.0577(16), b = 31.0562(15), c = 15.2320(7), beta = 104.015(2), (2); a = 33.0577(16), b = 31.0562(15), c = 15.2320(7), beta = 104.015(2), (2a); a = 33.007(2), b = 31.060(2), c = 15.2129(10), beta = 104.0140(10), (3); a = 32.913(19), b = 31.155(18), c = 15.135(9), beta = 103.495(11), (4); and Z = 2.

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Three disulfide-containing uranyl compounds, [UO 2 (C 7 H 4 O 2 S) 3 ] 3 H 2 O (1), [UO 2 (C 7 H 4 O 2 S) 2 (C 7 H 5 O 2 S)] (2), and [UO 2 (C 7 H 4 O 2 S) 4 ] (3) have been hydrothermally synthesized. Both in situ disulfide bond formation from 3-and 4-mercaptobenzoic acid (C 7 H 5 O 2 S, MBA) to yield 3,3 0 -and 4,4 0 -dithiobisbenzoic acid (C 14 H 8 O 4 S 2 , DTBA) and direct assembly with the presynthesized dimeric ligands have been explored. While the starting materials 4-MBA and 4,4 0 -DTBA both yield 2 via in situ ligand synthesis and direct assembly, respectively, we observe the formation of 1 from the starting material 3-MBA via in situ ligand synthesis and of 3 from the direct assembly of the uranyl cation with 3,3 0 -DTBA. Concurrently with the synthesis of 1 and 2, we have observed the in situ formation of the crystalline dimeric organic species, 3,3 0 -DTBA, [(C 7 H 5 O 2 S) 2 ] (4) and 4,4 0 -DTBA, [(C 7 H 5 O 2 S) 2 ] (5). Herein we report the synthesis and crystallographic characterization of 1-5, as well as observations regarding the utility of product formation via direct assembly and in situ ligand synthesis.

Following the synthesis of pure [H 4 6− (P 2 W 18 ). Comparison of the two unsubstituted precursors revealed that the merging of the first two waves of the monophosphate occurred in a less acidic medium than for the diphosphate. The observations point to the higher basicity of the reduced forms of PW 18 compared with those of P 2 W 18 . The fingerprint pattern observed for α 2 -P 2 W 17 M derivatives in media of pH = 3 consisted of the split-

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The first examples of polyoxometalate structures that incorporate embedded chelated heteroatoms point to new possibilities for stereochemical control of applications.

Reaction of Ce(III) with lacunary versions of [H(4)XW(18)O(62)](7-) (X = P, As) yields the 1:2 complexes [Ce(H(4)XW(17)O(61)](19-) (X = As, 1; P, 2) in good yield, characterized in solution and the solid state by NMR spectroscopy and X-ray crystallographic analysis, respectively. The structures confirm a syn C(2) conformation that is analogous to that observed for [Ln(alpha(2)-P(2)W(17)O(61))(2)](17-) but with "empty" O(4) tetrahedra that are in positions remote from the cerium atom. Bond valence sum calculations for these structures show that the four protons that are required for charge balance in all salts of the XW(18) anions and their lacunary derivatives are almost certainly bound to the oxygen atoms of the empty tetrahedra.