Hybrid Uranyl Arsonate Coordination Nanocages

Nanoscopic uranyl coordination cages have been prepared by a facile route involving self-assembly via temperature and solvent-driven, in situ ligand synthesis. The synthesis of hydrogen arsenate and pyroarsonate ligands in situ enhances flexibility, which is an important factor in producing these compounds

Ozone-Facilitated Formation of Uranyl Peroxide in Humid Conditions

Metaschoepite, [(UO2)8O2(OH)12](H2O)10, maintained in a high relative humidity (RH) environment with air initially transformed into an intermediate phase that subsequently was replaced by the peroxide phase studtite, [(UO2)(O2)(H2O)2](H2O)2, over the course of 42 days, as observed using Raman and infrared spectroscopy and powder X-ray diffraction. Addition of atmospheric ozone vastly increased the rate and extent of the transformation to studtite but only in a high-RH atmosphere. Owing to its strong affinity for peroxide, uranyl reacted with hydrogen peroxide as it formed and precipitated stable studtite. In this work, we provide a previously unidentified source of hydrogen peroxide and make a case for the re-examination of storage systems where the consequences of atmospheric ozone are not considered

Structural and Morphological Influences on Neptunium Incorporation in Uranyl Molybdates

The in situ incorporation of pentavalent neptunium has been studied in the structurally related uranyl molybdate frameworks (NH₄)₄[(UO₂)₅(MoO₄)₇]­(H₂O)₅ and (NH₄)₂[(UO₂)₆(MoO₄)₇]­(H₂O)₂ prepared under similar synthetic conditions. The presence of Np­(V) was confirmed by UV–vis–NIR spectroscopy in the first compound, whereas Np­(VI) was identified in the second based on the observation of a unit-cell contraction and the lack of a spectral signature for Np­(V). The incorporation of neptunium does not affect the overall structure of the host compound based on the crystallographic unit-cell parameters. Neptunium appears to preferentially incorporate in the structure of (NH₄)₂[(UO₂)₆(MoO₄)₇]­(H₂O)₂ due to the formation of Np­(VI) during synthesis, although higher total uptakes were observed in (NH₄)₄[(UO₂)₅(MoO₄)₇]­(H₂O)₅ due to a higher initial concentration of neptunium in solution despite maintaining the same ratio of U:Np

Structure Refinement and Thermal Stability Studies of the Uranyl Carbonate Mineral Andersonite, Na₂Ca[(UO₂)(CO₃)₃]·(5+<i>x</i>)H₂O

A sample of uranyl carbonate mineral andersonite, Na2Ca[(UO2)(CO3)3]&#183;5&#8722;6H2O, originating from the Cane Springs Canyon, San Juan Co., UT, USA was studied using single-crystal and powder X-ray diffraction at various temperatures. Andersonite is trigonal, R&#8722;3m, a = 17.8448(4), c = 23.6688(6) &#197;, V = 6527.3(3) &#197;3, Z = 18, R1 = 0.018. Low-temperature SCXRD determined the positions of H atoms and disordered H2O molecules, arranged within the zeolite-like channels. The results of high-temperature PXRD experiments revealed that the structure of andersonite is stable up to 100 &#176;C; afterwards, it loses crystallinity due to release of H2O molecules. Taking into account the well-defined presence of H2O molecules forming channels&#8217; walls that to the total of five molecules p.f.u., we suggest that the formula of andersonite is Na2Ca[(UO2)(CO3)3]&#183;(5+x)H2O, where x &#8804; 1. The thermal behavior of andersonite is essentially anisotropic with the lowest values of the main thermal expansion coefficients in the direction perpendicular to the channels (plane (001)), while the maximal expansion is observed along the c axis&#8212;in the direction of channels. The thermal expansion around 80 &#176;C within the (001) plane becomes negative due to the total release of &#8220;zeolitic&#8222; H2O molecules. The information-based structural complexity parameters of andersonite were calculated after the removal of all the disordered atoms, leaving only the predominantly occupied sites, and show that the crystal structure of the mineral should be described as complex, possessing 4.535 bits/atom and 961.477 bits/cell, which is comparative to the values for another very common natural uranyl carbonate, liebigite

Single-crystal analysis of La-doped pyromorphite [Pb5(PO4)3Cl]

Rare earth elements (REE) in calcium apatite have been widely described in the literature. Based on the investigations of minerals and their synthetic analogs, the mechanism of substitution of REE3+ for Ca2+ and their structural positions are well established. Although the presence of REE in natural pyromorphite has been reported, the structural response of substitution of REE3+ for Pb2+ is not established. A better understanding of REE-rich Pb-apatite may facilitate the potential use of this mineral in industrial processes. Two La-doped pyromorphite analogs [Pb5(PO4)3Cl] and two control pyromorphite analogs (with the absence of La) were synthesized from aqueous solutions at 25 degrees C. Na+ and K+ were used as charge-compensating ions to facilitate the incorporation of trivalent REE cations (La3+ + Na+ ↔ 2Pb2+ and La3+ + K+ ↔ 2Pb2+). Microprobe analysis, scanning electron microscopy, and Raman spectroscopy were used to confirm the purity of obtained phases. High-precision crystal structure refinements (R1 = 0.0140-0.0225) of all four compounds were performed from single-crystal X-ray diffraction data. The La content varied from 0.12(1) to 0.19(1) atoms per formula unit with the counter ions of K+ and Na+, respectively. Both substituting ions were accommodated at the Pb1 site only. By comparing the La-doped pyromorphite analogs with their control samples, it was possible to detect small changes in bond distances and polyhedral volumes caused by the La substitution. Variations in individual and mean interatomic distances reflected the cumulative effect of both the amount of substitution and ionic radii of substituting ions (La3+, Na+, and K+)

Hybrid Lanthanide–Actinide Peroxide Cage Clusters

A cage cluster consisting of 31 uranyl and 9 Sm³⁺ polyhedra self-assembles in an alkaline aqueous peroxide solution and crystallizes (U₃₁Sm₉). Trimers of Sm³⁺ polyhedra are templated by μ₃-η²:η²:η²-peroxide groups and link to oxo atoms of uranyl ions. Three such trimers link into a ring through uranyl hexagonal bipyramids, and these are attached through six polyhedra to a unit consisting of 21 uranyl hexagonal bipyramids to complete the cage. Luminescence spectra collected with an excitation wavelength of 420 nm reveal fine structure, which is not observed for a cluster containing only uranyl polyhedra

Raman Spectroscopic and ESI-MS Characterization of Uranyl Peroxide Cage Clusters

Strategies for interpreting mass spectrometric and Raman spectroscopic data have been developed to study the structure and reactivity of uranyl peroxide cage clusters in aqueous solution. We demonstrate the efficacy of these methods using the three best-characterized uranyl peroxide clusters, {U₂₄}, {U₂₈}, and {U₆₀}. Specifically, we show a correlation between uranyl–peroxo–uranyl dihedral bond angles and the position of the Raman band of the symmetric stretching mode of the peroxo ligand, develop methods for the assignment of the ESI mass spectra of uranyl peroxide cage clusters, and show that these methods are generally applicable for detecting these clusters in the solid state and solution and for extracting information about their bonding and composition without crystallization