The physicochemical properties of aluminum trifluoromethanesulfonate in diglyme have been investigated. The spectroscopic and electrochemical properties have been examined to determine speciation, conductivity, and electrochemical stability. Gaussian calculations provide optimized molecular geometries and offer insight into the electrochemical behavior of the solutions. The ions in solution appear to exhibit very straightforward behavior, with contact ion pairs forming at very low concentrations. In addition, the electrochemical window of the electrolyte initially decreases with increasing salt concentration to a minimum value of approximately 5.5 V around 1 M and then steadily rises to a maximum value above 8 V.
Uranyl-peroxide capsules are the newestf amily of polyoxometalates. Although discovered 13 years previously with over 70 topologies reported, there is al ack in the fundamental understanding of assembly mechanisms, particularly the role of the alkali counterions.H erein, the reactionp athway anda ssembly of uranyl peroxide capsules is reported by tracking the conversion from K + uranyl triperoxide monomer to the K + uranyl-peroxide U 28 capsule by means of small-angle X-ray scattering and Raman spectroscopy.F or the first time, the K + uranyl-peroxide pentamer face is isolated and structurally characterized, giving credence to the long-held belief that these geometric faces serve as building blocks to the fully formed capsules. Once isolated and re-dissolved, the pentamer face undergoes rapid conversion to capsulef orms,u nderlining its high reactivity that challenges its isolation. Calorimetricm easurements of the studied speciesc onfirms the pentamer lies on the energy landscape between the monomer and capsule.Aqueousuranium speciation impactsall aspects of nuclear materials stewardship. These include safe storage, handling, and treatment of aqueous nuclear wastes;s torageo fs pent nuclear fuel;key steps of the cradle-to-grave nuclear fuel cycle;nuclear forensics;a nd environmental contamination. In the past 13 years, [1] uranyl-peroxide capsules have emerged as both a new molecule family akin to the transition-metalp olyoxometalates (POMs) [2] and as viable aqueous species in natural, [3] industrial, [4] and laboratory settings. Uranyl capsules have been borne out with now over 70 unique cluster topologies that have been structurally characterized, featuring variation in size (16 to 124 polyhedra), ligands (peroxide, hydroxide,o xalate, pyrophosphate) and heterometals in the capsule walls (Fe, V, W, Mo, Sm) and cavities (alkalis, alkaline earths, rare earths, Bi, Pb, Ta ,N b). [5] Peroxidei sf ormed by radiolysiso fw ater in the high radiation field of uranium ore deposits andf uel, and is stabilized by bondingt ou ranyl, forming the mineral studtite, [(UO 2 )(O 2 )(H 2 O) 2 ](H 2 O) 2 in both nature and as deposits on storednuclearf uel. [5a, 6] Peroxide is very effective for dissolving uranium in combination with am ild base or precipitating uranium in acidic to neutralc onditions.T he dissolution/precipitation behaviori so ne viable method to separateu raniumf rom other oxides (i.e. crude ore for yellowcake production).H owever,t he dichotomy of the stable uranyl-peroxideb ond deterring its controlled removal by heating,a nd the inherent tendencyo fp eroxide to disproportionatey ielding hazardouspressures of O 2 gas hasc reated dangerous scenarios with stored yellowcake [6] and other uranylp eroxide materials.With afocus on solid-state characterization and computation of uranyl peroxide capsules and related materials, we are gaining as tructural understanding of the uranyl-peroxide bond. [7] Less well-understood is its reactivity in conditions that promote the formation of soluble or precipitatedu rany...
Group V Nb‐polyoxometalate (Nb‐POM) chemistry generally lacks the elegant pH‐controlled speciation exhibited by group VI (Mo, W) POM chemistry. Here three Nb‐POM clusters were isolated and structurally characterized; [Nb14O40(O2)2H3]14−, [((UO2)(H2O))3Nb46(UO2)2O136H8(H2O)4]24−, and [(Nb7O22H2)4(UO2)7(H2O)6]22−, that effectively capture the aqueous Nb‐POM species from pH 7 to pH 10. These Nb‐POMs illustrate a reaction pathway for control over speciation that is driven by counter‐cations (Li+) rather than pH. The two reported heterometallic POMs (with UO22+ moieties) are stabilized by replacing labile H2O/HO−Nb=O with very stable O=U=O. The third isolated Nb‐POM features cis‐yl‐oxos, prior observed only in group VI POM chemistry. Moreover, with these actinide‐heterometal contributions to the burgeoning Nb‐POM family, it now transects all major metal groups of the periodic table.
Uranyl peroxide capsules are a fascinating class of polyoxometalates (POMs), discovered only in the 21st century. Understanding the reactivity between peroxide, alkali cations, and uranyl in alkaline solutions is important in nuclear science disciplines including mineralogy, nuclear energy, and legacy nuclear wastes. Here, we have developed a general procedure to isolate different fragments of the uranyl-peroxide POM capsules, using organic solvents to partially remove K+ salts from crude solids of the monomer building block UO2(O2)3 4– (K–U1 ), leading to stabilization of these reactive fragments. Higher polarity organic solvents remove more K+ salts from the crude solid, owed to higher solubility, resulting in more extensive linking of uranyl peroxide building units. By this strategy we have isolated and structurally characterized a dimer K6[(UO2)2(O2)4(OH)2]·7H2O (K–U2 ) and a hexamer face frequently observed in the capsules, K12[(UO2)6(O2)9(OH)6]·xH2O (K–U6 ). Comparing experimental and computed Raman spectra shows that these intermediates crystallize by a solid-to-solid transformation, via polymerization of the monomer building block. By small-angle X-ray scattering (SAXS), we track the conversion of the fragments to POM capsules; the reaction rate increases from K–U1 (days) < K–U2 (hours) < K–U6 (instantaneous). This study provides a general synthetic procedure to isolate metastable uranyl peroxide oligomers and control the oligomerization, which will be later applied to systems with the heavier alkalis that are even less stable.
The uranyl triperoxide anionic monomer is a fundamental building block for uranyl peroxide polyoxometalate capsules. The reaction pathway from the monomer to the capsule can be greatly altered by the counterion: both the reaction rate and the resulting capsule structure. We synthesized and characterized uranyl triperoxides Mg2UO2(O2)3·13H2O (MgUT), Ca2UO2(O2)3·9H2O (CaUT), Sr2UO2(O2)3·9H2O (SrUT), and K4UO2(O2)3·3H2O (KUT) and compared their thermodynamic stabilities. The enthalpies of formation from oxides and elements of these compounds were calculated by thermochemical cycles from measurements by high temperature oxide melt drop solution calorimetry. Their formation enthalpies from oxides become more negative linearly as a function of the increasing basicity of the respective oxides on the Smith scale. This relationship holds for previously Li and Na analogues. Further affirming the trend, ΔH f,ox of MgUT departs from linearity, due to the distinct bonding environment of Mg2+, as compared to the other alkalis and alkaline earths in the series.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.