Superatoms are nanometer-sized molecules or particles that form ordered lattices, mimicking their atomic counterparts. Hierarchical assembly of superatoms gives rise to emergent properties in lattices of quantum dots, p-block clusters, and fullerenes. Here, we introduce a family of uranium-oxysulfate cluster anions whose hierarchical assembly in water is controlled by two parameters: acidity and the lanthanide or transition-metal countercation. In acid, larger LnIII (Ln = La–Ho) link hexamer (U6) oxoclusters into body-centered cubic frameworks, while smaller LnIII (Ln = Er–Lu and Y) promote linking of 14 U6 clusters into hollow superclusters (U84 superatoms). U84 assembles into superlattices including cubic-closest packed, body-centered cubic, and interpenetrating networks, bridged by interstitial countercations and U6 clusters. Divalent transition metals (TM = MnII and ZnII) charge-balance and promote the fusion of 10 U6 and 10 U monomers into a wheel-shaped cluster (U70). Dissolution of U70 in organic media reveals (by small-angle X-ray scattering) that differing supramolecular assemblies are accessed, controlled by TMII-linking of U70 clusters. Magnetic measurements of these assemblies reveal Curie–Weiss behavior at high temperatures, without pairing of the 5f2-electrons down to 2 K.

Organic ligands with carboxylate functionalities have been shown to affect the solubility, speciation, and overall chemical behavior of tetravalent metal ions. While many reports have focused on actinide complexation by relatively simple monocarboxylates such as amino acids, in this work we examined Th(IV) and U(IV) complexation by 4-hydroxybenzoic acid in water with the aim of understanding the impact that the organic backbone has on the solution and solid state structural chemistry of thorium(IV) and uranium(IV) complexes. Two compounds of the general formula [AnO(OH)(HO)(4-HB)]· nHO [An = Th (Th-1) and U (U-1); 4-HB = 4-hydroxybenzoate] were synthesized via room-temperature reactions of AnCl and 4-hydroxybenzoic acid in water. Solid state structures were determined by single-crystal X-ray diffraction, and the compounds were further characterized by Raman, infrared, and optical spectroscopies and thermogravimetry. The magnetism of U-1 was also examined. The structures of the Th and U compounds are isomorphous and are built from ligand-decorated oxo/hydroxo-bridged hexanuclear units. The relationship between the building units observed in the solid state structure of U-1 and those that exist in solution prior to crystallization as well as upon dissolution of U-1 in nonaqueous solvents was investigated using small-angle X-ray scattering, ultraviolet-visible optical spectroscopy, and dynamic light scattering. The evolution of U solution speciation as a function of reaction time and temperature was examined. Such effects as well as the impact of the ligand on the formation and evolution of hexanuclear U(IV) clusters to UO nanoparticles compared to prior reported monocarboxylate ligand systems are discussed. Unlike prior reported syntheses of Th and U(IV) hexamers where the pH was adjusted to ∼2 and 3, respectively, to drive hydrolysis, hexamer formation with the HB ligand appears to be promoted only by the ligand.

M IV molecular oxo-clusters (M = Zr,Hf, Ce,T h, U, Np,P u) are prolific in bottoms-up material design, catalysis, and elucidating reaction pathwaysi nn ature and in synthesis. Here we introduce Ce 70 ,awheel-shaped oxo-cluster,[ Ce IV 70-(OH) 36 (O) 64 (SO 4) 60 (H 2 O) 10 ] 4À .C e 70 crystallizes into intricate high pore volume frameworks with divalent transition metals and Ce-monomer linkers.Eight crystal-structures feature four framework types in which the Ce 70-rings are linked as propellers,i no ffset-stacks,i natartan pattern, and as isolated rings.S mall-angle X-ray scattering of Ce 70 dissolved in butylamine,w ith and without added cations (Ce IV ,a lkaline earths, Mn II), shows the metals differentiating roles in ring linking, leading to supramolecular assemblies.T he large acidic pores and abundant terminal sulfates provideion-exchange behavior, demonstrated with U IV and Nd III .Frameworks featuring Ce III/IVmonomer linkers demonstrate both oxidation and reduction. This study opens the door to mixed-metal, highly porous framework catalysts,a nd new clusters for metal-organic framework design topology of M IV-oxo clusters is the hexamer (M 6 , [M IV 6 (OH,O) 8 ]), [5] which structurally resembles the M IV O 2 fluorite-type lattice.T his molecular oxide fragment has been stabilized and isolated with carboxylate,n itrate,s ulfate,a nd polyoxometalate ligands. [6] Combining rigid bicarboxylate linkers with Zr IV 6 led to the discovery of the metal-organic framework (MOF) known as UiO-66. [5a] This compound and its derivatives comprise an extensive MOF family known for high stability and functionalizabilty,exploited in separations, storage and catalysis. [8] Not suprising,U iO-66 analogues of Hf IV , [7] Ce IV , [8] Th IV , [9] U IV , [10] Np IV , [5f] and Pu IV [11] have all been discovered. Beyond the hexamer,l arger M IV-oxo clusters are built symmetrically around the M 6 core,a nd by extension, are larger fragments of the fluorite lattice.T he largest is M 38 , synthesized from Ce IV , [12] Pu IV , [2c] U IV [13] and Np IV. [14] Ceriumoxo clusters and nanomaterials are of special relevance. [6e, 12] Owed to facile Ce III-Ce IV redox behavior and concomitant oxygen transport, ceria nanoparticles are used as automotive redox catalysts,i no xide fuel cells,a nd as photoactive solar cell materials. [15] Atomically precise cerium-oxo clusters are valuable to understand form-function relationships;and Ce 10 , Ce 20 ,C e 22 ,C e 24 ,C e 38 and Ce 40 have been isolated, some of which have distinct Ce III and Ce IV sites. [6e,12] Farha and coworkers recently demonstrated catalytic activity of Ce 38 ,owed to the high porosity and redox activity of the solid material. [16] We exploited Ln III and TM II countercations to create an ew family of giant U IV-oxo clusters including the U 84 "superatom" (with Ln III)a nd U 70 wheel (with TM II). [4b, 17] Following U 70 ,t he Zr 70 analogue was described in multiple frameworks with transition metals,Mg 2+ ,Na + and no countercations. [18] This large toroid, with external...

Aqueous solutions of polyoxometalates (POMs) have been shown to have potential as high-capacity energy storage materials due to their potential for multi-electron redox processes, yet the mechanism of reduction and practical limits are currently unknown. Herein, we explore the mechanism of multi-electron redox processes that allow the highly reduced POM clusters of the form {MO 3 } y to absorb y electrons in aqueous solution, focusing mechanistically on the Wells–Dawson structure X 6 [P 2 W 18 O 62 ], which comprises 18 metal centers and can uptake up to 18 electrons reversibly ( y = 18) per cluster in aqueous solution when the countercations are lithium . This unconventional redox activity is rationalized by density functional theory, molecular dynamics simulations, UV–vis, electron paramagnetic resonance spectroscopy, and small-angle X-ray scattering spectra. These data point to a new phenomenon showing that cluster protonation and aggregation allow the formation of highly electron-rich meta-stable systems in aqueous solution, which produce H 2 when the solution is diluted. Finally, we show that this understanding is transferrable to other salts of [P 5 W 30 O 110 ] 15– and [P 8 W 48 O 184 ] 40– anions, which can be charged to 23 and 27 electrons per cluster, respectively.

Crystallization at the solid-liquid interface is difficult to spectroscopically observe and therefore challenging to understand and ultimately control at the molecular level. The Ce70-torroid formulated [Ce IV 70(OH)36(O)64(SO4)60(H2O)10] 4-, part of a larger emerging family of M IV 70materials (M=Zr, U, Ce), presents such an opportunity. We have elucidated assembly mechanisms by X-ray scattering (small-angle scattering and total scattering) of solutions and solids, as well as crystallizing and identifying fragments of Ce70 by single-crystal X-ray diffraction. Fragments show evidence for templated growth (Ce5, [Ce5(O)3(SO4)12] 10-) and modular assembly from hexamer (Ce6) building units (Ce13, [Ce13(OH)6(O)12(SO4)14(Η2Ο)14] 6and Ce62, [Ce62(OH)30(O)58(SO4)58] 14-). Ce62, an almost complete ring, precipitates instantaneously in the presence of ammonium cations as two torqued arcs that interlock by hydrogen boding through NH4 + , which can also be replaced by other cations, demonstrated with Ce III . Room temperature rapid assembly of both Ce70 and Ce62, respectively, by addition of Li + and NH4 + , along with ionexchange and redox behavior, invite exploitation of this emerging material family in environmental and energy applications. Ce70, [Ce IV 70(OH)36(O)64(SO4)60] 4-, was described prior, and is also isostructural with Zr70 and U70. [49][50][51][52] Briefly, the Ce70 cluster can be viewed as ten Ce6-hexamers that alternate with ten Ce1-monomers. Four sulfates bridge each Ce6 and Ce1 along the outer rim, and four additional sulfates bridge only Ce6 units along the inner rim. Each fragment discussed later can be viewed in the same context. The Ce62, [Ce62(OH)30(O)58(SO4)58] 14-, consisting of ~90% of the ring, contains nine Ce6 and eight Ce1. Ce13, [Ce13(OH)6(O)12(SO4)14(Η2Ο)14] 6-, consists of two Ce6 and Ce1, and is approximately 20% of the ring. Ce5 [Ce5(O)3(SO4)12] 10-, resembles half of the Ce6 plus two flanking monomers. These clusters and their intrinsic relation to the Ce70, summarized in figure 1, serve as crystallographic snapshots of mechanistic pathways for ring formation.

Heterometallic Ce IV /M oxo clusters are underexplored yet and can benefit from synergistic properties from combining cerium and other metal cations to produce efficient redox catalysts. Herein, we designed and synthesized a series of new Ce 12 V 6 oxo clusters with different capping ligands: Ce 12 V 6 -SO 4 , Ce 12 V 6 -OTs (OTs: toluenesulfonic acid), and Ce 12 V 6 -NBSA (NBSA: nitrobenzenesulfonic acid). Single crystal X-ray diffraction (SCXRD) for all three structures reveals a Ce 12 V 6 cubane core formulated [Ce 12 (VO) 6 O 24 ] 18+ with cerium on the edges of the cube, vanadyl capping the faces, and sulfate on the corners. While infrared spectroscopy (IR), ultraviolet−visible spectroscopy (UV− vis), electrospray ionization mass spectrometry (ESI-MS), and proton nuclear magnetic resonance ( 1 H NMR) proved the successful coordination of the organic ligands to the Ce 12 V 6 core, liquid phase 51 V NMR and small-angle X-ray scattering (SAXS) confirmed the integrity of the clusters in the organic solutions. Furthermore, functionalization of the Ce 12 V 6 core with organic ligands both provides increased solubility in term of homogeneous application and introduces porosity to the assemblies of Ce 12 V 6 -OTs and Ce 12 V 6 -NBSA in term of heterogeneous application, thus allowing more catalytic sites to be accessible and improving reactivity as compared to the nonporous and less soluble Ce 12 V 6 -SO 4 . Meanwhile, the coordinated ligands also influenced the electronic environment of the catalytic sites, in turn affecting the reactivity of the cluster, which we probed by the selective oxidation of 2-chloroethyl ethyl sulfide (CEES). This work provides a strategy to make full use of the catalytic sites within a class of inorganic sulfate capped clusters via organic ligand introduction.

Two thorium­(IV) compounds, [Th­(H2O)4Cl4]·2­(HPy·Cl) (1) and (HPy)3[Th3(H2O)2Cl10(OH)5]·4­(HPy·Cl) (2) (HPy = pyridinium), were isolated from acidic aqueous solution. The compounds were synthesized at room temperature and subsequently characterized using single crystal X-ray diffraction along with Raman and IR spectroscopies. Whereas compound 1 is built from discrete mononuclear Th­(H2O)4Cl4 units, compound 2 consists of a novel hydroxo-bridged trimeric [Th3(OH)5]7+ core. Such species are largely absent from discussions of Th solution and solid-state chemistry and their isolation may be attributed to outer coordination sphere interactions that help stabilize the structural units; extensive hydrogen bonding and π–π stacking interactions are present in 1 and 2. Density functional theory calculations were performed to predict the respective vibrational frequencies of the structural units, and their relative stability was predicted at the correlated molecular theory level. Small-angle X-ray scattering analysis of [Th3(OH)5]7+ in water indicates that the trimeric structural unit remains intact and that it is indeed an important species that necessitates consideration in geochemical models and for design of Th materials from water.

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