Waste not: Actinyl nanospheres self‐assembled from alkaline solutions have been shown to be composed of 24, 28, and 32 actinyl peroxide polyhedra (for example, see picture of the uranyl peroxide polyhedra (U‐28)). The nanospheres represent a new class of polyoxometalates, and their formation in nuclear waste may have an impact on the mobility of actinides in the environment.

The coordination environment of the hydrated Cm3+ ion is probed both in the solid state and in solution. The analysis of single-crystal X-ray diffraction data from [Cm(H2O)9](CF3SO3)3 determines that the Cm species is surrounded by nine coordinating waters with a tricapped-trigonal-prismatic geometry involving six short Cm-O distances at 2.453(1) A and three longer Cm-O distances at 2.545(1) A. The Cm nona-aqua triflate is isostructural with the series of lanthanide and actinide [R(H2O)9](CF3SO3)3 (R=La-Lu, Pu) compounds. A similar nona-aqua geometry is seen for the coordination environment of Cm in aqueous solution, as probed by high-energy X-ray scattering and extended X-ray absorption fine structure spectroscopy, although the splitting in the first coordination shell is increased from 0.092(2) in the solid to 0.16(2) A in solution. This increase in splitting of the Cm-water distances in the first coordination sphere is discussed in terms of its potential relevance to the previously observed decrease in coordinating waters with decreasing ionic radius about the f-ion in solution.

Selective extraction of metal ions from a complex aqueous mixture into an organic phase is used to separate toxic or radioactive metals from polluted environments and nuclear waste, as well as to produce industrially relevant metals, such as rare earth ions. Selectivity arises from the choice of an extractant amphiphile, dissolved in the organic phase, which interacts preferentially with the target metal ion. The extractant-mediated process of ion transport from an aqueous to an organic phase takes place at the aqueous-organic interface; nevertheless, little is known about the molecular mechanism of this process despite its importance. Although state-of-the-art X-ray scattering is uniquely capable of probing molecular ordering at a liquid-liquid interface with subnanometer spatial resolution, utilizing this capability to investigate interfacial dynamical processes of short temporal duration remains a challenge. We show that a temperature-driven adsorption transition can be used to turn the extraction on and off by controlling adsorption and desorption of extractants at the oil-water interface. Lowering the temperature through this transition immobilizes a supramolecular ion-extractant complex at the interface during the extraction of rare earth erbium ions. Under the conditions of these experiments, the ion-extractant complexes condense into a two-dimensional inverted bilayer, which is characterized on the molecular scale with synchrotron X-ray reflectivity and fluorescence measurements. Raising the temperature above the transition leads to Er ion extraction as a result of desorption of ion-extractant complexes from the interface into the bulk organic phase. XAFS measurements of the ion-extractant complexes in the bulk organic phase demonstrate that they are similar to the interfacial complexes.

The formation of ion pairs in aqueous solution orchestrates vital processes in nature and engineered systems, including electron transfer [1][2][3] and other chemical reactions, [4,5] and crystallization/precipitation of synthetic and natural matter. [6][7][8][9] Polyoxometalates (POMs) have received special attention with regard to ion pairing.[10] POMs are highly charged anions with ideal topologies for binding and associating metal cations, as their assembly, [11][12][13] redox, [2] and catalytic properties [14] in aqueous solution are influenced by ion pairing. Methods for determining ion pairing [15] are largely considered to be indirect in that they observe physical changes in a solution that results from ion association. Spectroscopic methods are the exception, but these are prone to insufficient resolution, and are unable to detect solvent-separated ion pairing. Herein we show that smallangle X-ray scattering (SAXS) of the Lindqvist [Nb 6 O 19 ] 8À POM [16,17] provides a model example of direct measurement of the formation of ion pairs in aqueous solution, and reveals remarkable similarity between solution and solid-state ion contact. This study provides evidence that the structures of Lindqvist hexaniobate salts described with extreme accuracy in the solid state can be used to model the ion-pairing behavior in solution.The effectively spherical [Nb 6 O 19 ] 8À isopolyoxoanion with 25 atoms (Figure 1 a) has the greatest surface charge of all POMs.[18] High surface charge is a property noted to enhance ion pairing, both in solution [2] and in the resulting precipitates.[ . Thus, compared to tungstate, molybdate, and vanadate POMs, niobate POMs are not electrochemically reducible, they are assembled and stabilized in alkaline rather than acidic solutions, [20] they protonate rather than deprotonate in water, [21] and tend to form insoluble linked frameworks with alkali atoms [22,23] rather than soluble salts. The [Nb 6 O 19 ] 8À Lindqvist ion has been crystallized in the solid state with every alkali metal counterion, [24][25][26] and its ion 8À ion is related to its physical radius R S (blue sphere radius) by the relationship R S = ffi ffi 5 3 q R g . All the R S values presented in Table 2 were obtained directly from fitting the SAXS data with a spherical form factor model. The R SS (spherical shell radius; represented by the outermost white sphere) is the sum of the physical radius of the bare anion (fixed at 3.9 ) and the best-fit thickness of the spherical shell around the hexaniobate core.

Trivalent europium ions have been successfully incorporated in anatase TiO 2 nanocrystals via a sol-gel solvothermal synthesis, in spite of a large mismatch in ionic radius between Eu 3+ and Ti 4+ . The photoluminescence intensity of Eu 3+ :TiO 2 nanocrystals has been significantly improved, which is comparable to that of common red phosphors. Multiple sites of Eu 3+ in TiO 2 nanocrystals have been identified by the technique of site-selective spectroscopy. Eu 3+ ions at two lattice sites exhibit sharp emission and excitation peaks with site symmetries descending from D 2d to approximate C 2v and D 2 as a result of the lattice distortion, whereas Eu 3+ ions at disordered site near the surface are analogous to Eu 3+ ions located in a glasslike environment. Extended X-ray absorption fine structure is utilized for identifying the local structure and Eu 3+ coordination. The luminescence dynamics and crystal-field levels of Eu 3+ at different sites have been analyzed. A growth mechanism for the incorporation of Eu 3+ in the anatase lattice is also suggested.