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

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

Hybrid Uranyl-Carboxyphosphonate Cage Clusters

Two new hybrid uranyl-carboxyphosphonate cage clusters built from uranyl peroxide units were crystallized from aqueous solution under ambient conditions in approximately two months. The clusters are built from uranyl hexagonal bipyramids and are connected by employing a secondary metal linker, the 2-carboxyphenylphosphonate ligand. The structure of cluster <b>A</b> is composed of a ten-membered uranyl polyhedral belt that is capped on either end of an elongated cage by five-membered rings of uranyl polyhedra. The structure of cluster <b>B</b> consists of 24 uranyl cations that are arranged into 6 four-membered rings of uranyl polyhedra. Four of the corresponding topological squares are fused together to form a sixteen-membered double uranyl pseudobelt that is capped on either end by 2 topological squares. Cluster <b>A</b> crystallizes over a wide pH range of 4.6–6.8, while cluster <b>B</b> was isolated under narrower pH range of 6.9–7.8. Studies of their fate in aqueous solution upon dissolution of crystals by electrospray ionization mass spectrometry (ESI-MS) and small-angle X-ray scattering (SAXS) provide evidence for their persistence in solution. The well-established characteristic fingerprint from the absorption spectra of the uranium­(VI) cations disappears and becomes a nearly featureless peak; nonetheless, the two compounds fluoresce at room temperature