Crystal Chemistry and Structural Complexity of Uranium(IV) Sulfates: Synthesis of U3H2(SO4)7(H2O)5·3H2O and U3(UO2)0.2(SO4)6(OH)0.4·2.3H2O with Framework Structures by the Photochemical Reduction of Uranyl.

Two uranium(IV) sulfate framework compounds were crystallized at room temperature from aqueous solutions containing uranyl ions by photochemical reduction in the presence of 2-propanol. U3H2(SO4)7(H2O)5·3H2O (1) crystallizes in space group P65 with a = 9.3052(17) Å, c = 53.515(10) Å, V = 4012.9(13) Å3, and Z = 6, and U3(UO2)0.2(SO4)6(OH)0.4·2.3H2O (2) is tetragonal, with space group P42/nmc, a = 25.624(3) Å, c = 8.9435(10) Å, V = 5872.2(11) Å3, and Z = 8. The structures of 1 and 2 are the most complex among uranium(IV) sulfates.

Structure and properties of Na5FeSi4O12 crystallized from 5Na2O-Fe2O3-8SiO2 glass.

The phase Na5FeSi4O12 [pentasodium iron(III) silicate] crystallizes readily from the Na2O-Fe2O3-SiO2 glass system in a relatively large compositional range. However, its crystal structure and properties have not been studied in detail since its discovery in 1930. In this work, the Na5FeSi4O12 phase was crystallized from a host glass with 5Na2O·Fe2O3·8SiO2 stoichiometry, and both the glass and the crystal were studied. It was found that the Na5FeSi4O12 phase crystallizes at ∼720 °C from the glass and melts at ∼830 °C when heated at a rate of 10 °C min-1. The crystal structure was solved using single-crystal X-ray diffraction and the refined data are reported for the first time for the Na5FeSi4O12 phase. It exhibits trigonal symmetry, space group R-3c, with a = 21.418 and c = 12.2911 Å. The Na atoms located between adjacent structural channels exhibit positional disorder and splitting which was only refined by using low-temperature data collection (150 K). While ∼7% of the total Fe cations occur as Fe2+ in the glass, four-coordinated Fe3+ constitutes ∼93% of the total Fe cations. However, iron in the crystal, which exhibits a paramagnetic behavior, is solely present as six-coordinated Fe3+. The magnetic and vibrational properties of the glass and crystal are discussed to provide additional insight into the structure.

Single-Crystal Time-of-Flight Neutron Diffraction and Magic-Angle-Spinning NMR Spectroscopy Resolve the Structure and 1H and 7Li Dynamics of the Uranyl Peroxide Nanocluster U60.

Single-crystal time-of-flight neutron diffraction has provided atomic resolution of H atoms of H2O molecules and hydroxyl groups, as well as Li cations in the uranyl peroxide nanocluster U60. Solid-state magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopy was used to confirm the dynamics of these constituents, revealing the transportation of Li atoms and H2O through cluster walls. H atoms of hydroxyl units that are located on the cluster surface are involved in the transfer of H2O and Li cations from inside to outside and vice versa. This exchange occurs as a concerted motion and happens rapidly even in the solid state. As a consequence of its large size and open hexagonal pores, U60 exchanges Li cations more rapidly compared to other uranyl nanoclusters.

Solution (31)P NMR Study of the Acid-Catalyzed Formation of a Highly Charged {U24Pp12} Nanocluster, [(UO2)24(O2)24(P2O7)12](48-), and Its Structural Characterization in the Solid State Using Single-Crystal Neutron Diffraction.

The first neutron diffraction study of a single crystal containing uranyl peroxide nanoclusters is reported for pyrophosphate-functionalized Na44K6[(UO2)24(O2)24(P2O7)12][IO3]2·140H2O (1). Relative to earlier X-ray studies, neutron diffraction provides superior information concerning the positions of H atoms and lighter counterions. Hydrogen positions have been assigned and reveal an extensive network of H-bonds; notably, most O atoms present in the anionic cluster accept H-bonds from surrounding H2O molecules, and none of the surface-bound O atoms are protonated. The D4h symmetry of the cage is consistent with the presence of six encapsulated K cations, which appear to stabilize the lower symmetry variant of this cluster. (31)P NMR measurements demonstrate retention of this symmetry in solution, while in situ (31)P NMR studies suggest an acid-catalyzed mechanism for the assembly of 1 across a wide range of pH values.

Structure and Reactivity of X-ray Amorphous Uranyl Peroxide, U2O7.

Recent accidents resulting in worker injury and radioactive contamination occurred due to pressurization of uranium yellowcake drums produced in the western U.S.A. The drums contained an X-ray amorphous reactive form of uranium oxide that may have contributed to the pressurization. Heating hydrated uranyl peroxides produced during in situ mining can produce an amorphous compound, as shown by X-ray powder diffraction of material from impacted drums. Subsequently, studtite, [(UO2)(O2)(H2O)2](H2O)2, was heated in the laboratory. Its thermal decomposition produced a hygroscopic anhydrous uranyl peroxide that reacts with water to release O2 gas and form metaschoepite, a uranyl-oxide hydrate. Quantum chemical calculations indicate that the most stable U2O7 conformer consists of two bent (UO2)(2+) uranyl ions bridged by a peroxide group bidentate and parallel to each uranyl ion, and a µ2-O atom, resulting in charge neutrality. A pair distribution function from neutron total scattering supports this structural model, as do (1)H- and (17)O-nuclear magnetic resonance spectra. The reactivity of U2O7 in water and with water in air is higher than that of other uranium oxides, and this can be both hazardous and potentially advantageous in the nuclear fuel cycle.

Copper(I) and copper(II) uranyl heterometallic hybrid materials.

Two copper-uranium heterometallic compounds, [(UO2)3Cu(II)O2(C6NO2)5] (1) and [(UO2)Cu(I)(C6NO2)3] (2), have been synthesized by the reaction of uranyl acetate with copper salts in the presence of isonicotinic acid. Both compounds have been characterized by single-crystal X-ray diffraction, IR, Raman, and UV-vis spectroscopy. In compound 1, interactions between copper and uranium centers occur and result in a three-dimensional pillar layered structure. Compound 1 is also the first example of a heterometallic uranyl organic framework with a trinuclear U3O18 building block. Compound 2 is the first uranyl organic framework that contains monovalent copper, which arises from the reaction of Cu(II) chloride and is assumed to be due to the oxidation of chloride at low pH.

Bis{µ-2,2'-[(butane-2,3-diylidene)bis(azanylylidene)]dibenzenethiolato}dizinc(II)-dimethyl sulfoxide-methanol (2/0.18/0.82).

The asymmetric unit in the crystal structure of the title compound, [Zn2(C16H14N2S2)2]2·0.18C2H6OS·0.82CH3OH, consists of two ordered bis{µ-2,2'-[(butane-2,3-diylidene)bis(azanylylidene)]dibenzenethiolato}dizinc(II) molecules and a disordered solvent combination at the same location which refined to 18.1 (7)% dimethyl sulfoxide and 81.9 (7)% methanol. The compound has a metallic cluster structure formed by the joining together of two zinc(II) complex molecules, forming a rhomboidal Zn2S2 arrangement. This complex was previously suggested on the basis of nonstructural evidence to be a monomer [Jadamus, Fernando & Freiser (1964). J. Am. Chem. Soc. 86, 3056-3059]. Each Zn(II) atom is five-coordinated and exhibits distorted trigonal bipyramidal geometry. The structure may be of interest with respect to zinc-thiolate bonds, the coordination chemistry of Schiff bases and the folding of proteins. The structure displays weak intermolecular C-H···S, C-H···O and C-H···N interactions, and contains a unique bonding arrangement of the ligands around the Zn2S2 rhomboid.