High-nuclear polyoxovanadates assembled from pentagonal building blocks

The design and synthesis of high-nuclear polyoxometalates (POMs) constructed from pentagonal molecular building blocks (MBBs) are attractive and challenging. Herein, three new high-nuclear polyoxovanadates, including {V₂₀W₂P₂₀} (1), {V₁₈W₄P₁₄} (2), and {V₂₆W₆P₁₆} (3), have been successfully synthesized under solvothermal conditions. All these structures are assembled from pentagonal MBB {WV₅(PhPO₃)₅} with different configurations. Compound 1 exhibits efficient, stable, and versatile catalytic activity for sulfide oxidation.

Two Giant Calixarene-Like Polyoxoniobate Nanocups {Cu12 Nb120 } and {Cd16 Nb128 } Built from Mixed Macrocyclic Cluster Motifs

Cup-shaped molecules are of great interest due to their appealing architectures and properties. Compared with widely studied calixarenes, polyoxometalate-based cup-shaped molecules currently remain a virgin land waiting for exploration. In this work, we report the first discovery of two giant cup-shaped inorganic-organic hybrid polyoxoniobates (PONbs) of {Cu₁₂ Nb₁₂₀ } and {Cd₁₆ Nb₁₂₈ }. The former integrates three tricyclic Nb₂₄ clusters and a hexacyclic Nb₄₈ cluster into a cup-shaped molecule via a Cu₁₂ metallacalixarene, while the latter unifies two tricyclic Nb₂₄ clusters and a brand-new pentacyclic Nb₄₀ cluster into another cup-shaped molecule via a hybrid Cd₁₆ unit. With 132 and 144 metal centers, {Cu₁₂ Nb₁₂₀ } and {Cd₁₆ Nb₁₂₈ } show the largest two inorganic-organic hybrid PONbs known to date.

Ionothermal Synthesis of Uranyl Vanadate Nanoshell Heteropolyoxometalates

Two uranyl vanadate heteropolyoxometalates (h-POMs) have been synthesized by ionothermal methods using the ionic liquid 1-ethyl-3-methylimidazolium diethyl phosphate (EMIm-Et₂PO₄). The hybrid actinide-transition metal shell structures have cores of (UO₂)₈(V₆O₂₂) and (UO₂)₆(V₃O₁₂), which we designate as {U₈V₆} and {U₆V₃}, respectively. The diethyl phosphate anions of the ionic liquids in some cases terminate the core structures to form actinyl oxide clusters, and in other cases the diethyl phosphate oxyanions link these cluster cores into extended structures. Three compounds exist for the {U₈V₆} cluster core: {U₈V₆}-monomer, {U₈V₆}-dimer, and {U₈V₆}-chain. Tungsten atoms can partially substitute for vanadium in the {U₆V₃} cluster, which results in a chain-based structure designated as {U₆V₃}-W. Each of these compounds contains charge-balancing EMIm cations from the ionic liquid. These compounds were characterized crystallographically, spectroscopically, and by mass spectrometry.

Crystal Chemistry of Carnotite in Abandoned Mine Wastes

The crystal chemistry of carnotite (prototype formula: K2(UO2)2(VO4)2·3H2O) occurring in mine wastes collected from Northeastern Arizona was investigated by integrating spectroscopy, electron microscopy, and x-ray diffraction analyses. Raman spectroscopy confirms that the uranyl vanadate phase present in the mine waste is carnotite, rather than the rarer polymorph vandermeerscheite. X-ray diffraction patterns of the carnotite occurring in these mine wastes are in agreement with those reported in the literature for a synthetic analog. Carbon detected in this carnotite was identified as organic carbon inclusions using transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) analyses. After excluding C and correcting for K-drift from the electron microprobe analyses, the composition of the carnotite was determined as 8.64% K2O, 0.26% CaO, 61.43% UO3, 20.26% V2O5, 0.38% Fe2O3, and 8.23% H2O. The empirical formula, (K1.66 Ca0.043 Al(OH)2+ 0.145 Fe(OH)2+ 0.044)((U0.97)O2)2((V1.005)O4)2·4H2O of the studied carnotite, with an atomic ratio 1.9:2:2 for K:U:V, is similar to the that of carnotite (K2(UO2)2(VO4)2·3H2O) reported in the literature. Lattice spacing data determined using selected area electron diffraction (SAED)-TEM suggests: (1) complete amorphization of the carnotite within 120 s of exposure to the electron beam and (2) good agreement of the measured d-spacings for carnotite in the literature. Small Differences between the measured and literature d-spacing values are likely due to the varying degree of hydration between natural and synthetic materials. Such information about the crystal chemistry of carnotite in mine wastes is important for an improved understanding of the occurrence and reactivity of U, V, and other elements in the environment.

Synthesis and structural characterization of a series of uranyl-betaine coordination complexes

Trimethylglycine and betainium class ionic liquids were employed in synthesizing six uranyl-betaine coordination complexes: [(μ2-(CH3)N2C3H3(CH2COO))2 (UO2(Cl)((CH3)N2C3H3(CH2COO)))2] 2[N(SO2CF3)2] (1), [K][UO2(Cl)3((CH3)3NCH2COO)] (2), [(CH3)3NCH2COOH][UO2(Cl)3((CH3)3NCH2COO)]⋅H2O (3), [LiUO2(μ2-(CH3)3NCH2COO)4] 3[N(SO2CF3)2] (4) {(μ2-(CH3)3NCH2COO)UO2(NO3)2((CH3)3NCH2COO)}2 UO2(NO3)2, UO2(NO3)2(H2O)2⋅H2O (5), and UO2(Cl)2(H2O)(μ2-(CH3)3NCH2COO) (6). These complexes expound upon the variability of monocarboxyl-functionalized uranyl coordination complexes, providing an enhanced framework for investigations into the structural chemistry of analogous actinyl systems.

An Ultrastable Heterobimetallic Uranium(IV)/Vanadium(III) Solid Compound Protected by a Redox-Active Phosphite Ligand: Crystal Structure, Oxidative Dissolution, and First-Principles Simulation

The first heterobimetallic uranium(IV)/vanadium(III) phosphite compound, Na₂UV₂(HPO₃)₆ (denoted as UVP), was synthesized via an in situ redox-active hydrothermal reaction. It exhibits superior hydrolytic and antioxidant stability compared to the majority of structures containing low-valent uranium or vanadium, further elucidated by first-principles simulations, and therefore shows potential applications in nuclear waste management.

Captivation with encapsulation: a dozen years of exploring uranyl peroxide capsules

Uranyl peroxide cages are an extensive family of topologically varied self-assembling nanoscale clusters with fascinating properties and applications.

Recent advances in structural studies of heterometallic uranyl-containing coordination polymers and polynuclear closed species

A survey is given of recent original structural results on heterometallic species incorporating uranyl ions, particularly with carboxylate ligands.

A report on emergent uranyl binding phenomena by an amidoxime phosphonic acid co-polymer

XAFS investigations of uranyl binding by an adsorbent polymer reveal different coordination modes than anticipated from previous small molecule studies.

Structure and Solution Speciation of U(IV) Linked Phosphomolybdate (Mo(V)) Clusters

Crystals of [NaU(Mo6P4O31H7)2]·5Na·(H2O)n (NaUMo6) have been synthesized by slow evaporation of an aqueous mixture containing uranyl nitrate, sodium molybdate, phosphoric acid, and sodium dithionate. Single crystal diffraction of NaUMo6 reveals the assembly of {Mo6P4} clusters linked into one-dimensional chains with alternating Na(+) and U(4+) cations. To our knowledge, NaUMo6 is a unique example of Mo(5+) based polyoxometalate associated with actinides. With the use of similar synthesis conditions but without uranium in the aqueous solution, [Na(Mo6P4O31H10)2]·5Na·(H2PO4)·(H2O)n (NaMo6) is obtained. NaMo6 is a sandwich type cluster which is built on the assemblage of two {Mo6P4} units linked by one sodium cation. Using small-angle X-ray scattering techniques and aqueous electrolyte based dissolution strategies, we can accurately observe chains of [UNa(Mo6P4O31H7)2]n(5n), where n = 7 is the dominant soluble specie. Likewise, the dimeric form of [Na(Mo6P4O31H10)2](5-) dominates the aqueous solution, revealing the structural units observed in the crystal structure are also stable in solution, under appropriate dissolution conditions.