Search

In efforts to study the periodic chemical properties of the rare earth elements and their structural chemistry, a hybrid double perovskite phase A

A series of actinyl(VI) nitrate salts of the form MAnO

International audience; Bent uranyl complexes can be formed with chloride ligands and 1,10-phenanthroline (phen) ligands bound to the equatorial and axial planes of the uranyl(VI) moiety, as revealed by the crystal structures, IR and Raman spectroscopy and quantum chemical calculations. With the goal of probing the influence of chloride and phenanthroline coordination enforcing the bending on the absorption and emission spectra of this complex, spin-orbit time-dependent density functional theory calculations for the bare uranyl complexes as well as for the free UO2Cl2 subunit and the UO2Cl2(phen)2 ligand were performed. The emission spectra has been fully simulated by ab initio methods and compared to experimental photoluminescence spectra, recorded for the first time for UO2Cl2(phen)2. Notably, the bending of uranyl in UO2Cl2 and UO2Cl2(phen)2 triggers excitations of the uranyl bending mode, yielding a denser luminescence spectrum.

Single-crystal X-ray diffraction (SC-XRD) structures and Raman spectra of a series of new isomorphous molecular An(IV)-oxalate compounds (Th, U, Np, and Pu) are reported. These complexes are crystallized with cobalt(III) hexamine ([Co(NH

Bent uranyl complexes can be formed with chloride ligands and 1,10-phenanthroline (phen) ligands bound to the equatorial and axial planes of the uranyl(VI) moiety, as revealed by the crystal structures, IR and Raman spectroscopy and quantum chemical calculations. With the goal of probing the influence of chloride and phenanthroline coordination enforcing the bending on the absorption and emission spectra of this complex, spin-orbit time-dependent density functional theory calculations for the bare uranyl complexes as well as for the free UO2Cl2 subunit and the UO2Cl2(phen)2 ligand we performed. The emission spectra has been fully simulated by ab initio methods and compared to experimental photoluminescence spectra, recorded for the first time for UO2Cl2(phen)2. Notably, the bending of uranyl in UO2Cl2 and UO2Cl2(phen)2 triggers vibronically induced excitations of the uranyl bending mode, yielding a denser spectrum.

International audience; The synthesis and structures of the homoleptic hexanitrato complexes of Am(III) and Cm(III), [(CH3)4N]2KAn(NO3)6 are reported. These compounds form a double perovskite structure type, A2B′BX6, crystallizing in the cubic space group Fm3m. Their electronic properties, as calculated using the Quantum Theory of Atoms in Molecules, are reported and compared to their lanthanide homologues Eu(III) and Gd(III).

The preparation of two new neptunium hydroxide compounds synthesized in concentrated potassium and rubidium hydroxide is reported. The phases K4[(NpO2)2(OH)6]·4H2O and Rb4[(NpO2)4(OH)8]·2H2O were prepared and their chemical structures determined using single-crystal X-ray diffraction. Raman spectra of the compounds are also presented. The newly synthesized phases are structurally related to Np2O5 and Na[NpO2(OH)2]. The potassium-containing phase reported here consists of infinite chains of edge-sharing neptunium hydroxide polyhedra but lacking the cation-cation interactions (CCIs) observed in Np2O5 and Na[NpO2(OH)2]. Rb4[(NpO2)4(OH)8]·2H2O is a an expanded three-dimensional framework based on NpO2+ CCIs like those observed in Np2O5 and Na[NpO2(OH)2]. Together these complexes begin to develop a structural series of neptunium(V) oxides and hydroxides of varying dimensionalities within the alkali-metal series. The potential roles of the alkali-metal cations and neptunyl(V) CCIs in directing the resulting structures are discussed.

Redox shuttle additives dissolved in the electrolyte of lithium-ion batteries provide cells with intrinsic protection against overcharge, which can induce hazardous consequences such as thermal runaway. Aromatic hydrocarbons in general, and 1,4-dimethoxybenzene (DMB) in particular, are a key family of organic redox shuttle materials, but the limited solubility (

The synthesis of a series of molecular actinyl(VI), namely, uranium(VI), neptunium(VI), and plutonium(VI), hydroxo-bridged dimers is reported. These complexes were isolated from an aqueous nitrate solution by titration with tetramethylammonium hydroxide. The solid-state structures were determined using single-crystal X-ray diffraction, revealing molecular complexes with the formula [Me4N]2[(AnO2)2(μ2-OH)2(NO3)4], where An = UVI, NpVI, and PuVI. Spectroscopic data-UV-vis-near-IR absorption, IR, and Raman-were collected on the solutions and solid-state complexes where available and compared to those of the aqueous solutions from which the crystals formed. These data provide structural evidence for higher-order polynuclear complexes of actinyl(VI) complexes upon a pH increase in the aqueous solution, confirming earlier thermodynamic models.

Gas-phase reactions of pentavalent metal dioxide cations MVO2+ with water were studied experimentally for M = V, Nb, Ta, Pr, Pa, U, Pu, and Am. Addition of two H2O can occur by adsorption to yield hydrate (H2O)2MVO2+ or by hydrolysis to yield hydroxide MV(OH)4+. Displacement of H2O by acetone indicates hydrates for PrV, UV, PuV, and AmV, whereas nondisplacement indicates hydroxides for NbV, TaV, and PaV. Computed potential energy profiles agree with the experimental results and furthermore indicate that acetone unexpectedly induces dehydrolysis and displaces two H2O from (H2O)VO(OH)2+ to yield (acetone)2VO2+. Structures and energies for several MV, as well as for ThIV and UVI, indicate that hydrolysis is governed by the involvement of valence f versus d orbitals in bonding: linear f-element dioxides are more resistant to hydrolysis than bent d-element dioxides. Accordingly, for early actinides, hydrolysis of ThIV is characteristic of a 6d-block transition metal; hydration of UV and UVI is characteristic of 5f actinyls; and PaV is intermediate between 6d and 5f. The praseodymium oxide cation PrVO2+ is assigned as an actinyl-like lanthanyl with properties governed by 4f bonding.

The synthesis and single crystal structures of Am(iii) and Cm(iii) thiocyanate complexes are reported along with an isostructural series of lanthanide thiocyanate complexes. Because the complexes are isostructural, a comparative study of the metal-thiocyanate bonds was conducted using Raman spectroscopy indicating very similar and electrostatic metal-ligand interactions.

The synthesis, structure, and vibrational properties are presented for an isostructural series of Np(VI) and Pu(VI) complexes of the form [Ph4P]2AnO2Cl4, where An = Np(VI) or Pu(VI). The reported complexes are readily synthesized in ambient laboratory conditions, and their molecular structures were determined using single crystal X-ray diffraction. Their vibrational spectra were studied using a combination of Raman and FT-IR vibrational spectroscopies. Analysis of the vibrational spectra and force constants highlight the periodic properties associated with the actinide contraction and filling of the 5f electronic shells. Additionally, we have assessed the utility of these complexes as conveniently synthesized starting materials for non-aqueous synthesis of transuranium molecules and materials.

A study of the phase transitions occurring in tetramethylammonium hexachlorometalate compounds with M = UIV, NpIV, ZrIV, SnIV, HfIV and PtIV were performed using single-crystal X-ray diffraction across the temperature range 120 - 400K. When the crystals were cooled, movement of the octahedral [MCl6]2- anions induces a phase transition from Fm¯3 m to Fd¯3 c with a doubling of the unit cell. For the actinide compounds, no correlation between the f-electron configuration and the transition temperature was observed, instead, a correlation between the transition temperatures and both the [MCl6]2- anion and the TMA cation size is highlighted. Two phase transitions were observed and characterized. The first phase transition occurs with the ordering of the TMA cation and the second from a rotation of the [MCl6]2- octahedra. A third phase transition was observed at lower temperatures and was ascribed to a tetragonal distortion of the [MCl6]2- anions. Synthesis and study of their deuterated compounds did not show a significant isotope effect. Raman spectra performed on the protonated and deuterated compounds indicate only weak hydrogen bonding interactions between the TMA cations and the [MCl6]2- octahedra.

Hydrofluxes are hydrated salts with melting points well below that of the dehydrated salt and boiling points well above that of water, affording a reaction medium, in which mild temperatures and pressures can be accessed for the synthesis of materials. Herein, the use of alkali metal hydroxide hydrofluxes for the synthesis of single crystal α-Na2 NpO4 is described, and the single crystal X-ray structure of α-Na2 NpO4 , along with its X-ray absorption spectra and vibrational spectra, is reported. The ability to synthesize complex oxides of the actinides, in particular, transuranium materials, under mild conditions will serve to advance our ability to explore the structure-property relationships of the f elements.

The synthesis of a series of molecular actinyl(VI), namely, uranium(VI), neptunium(VI), and plutonium(VI), hydroxo-bridged dimers is reported. These complexes were isolated from an aqueous nitrate solution by titration with tetramethylammonium hydroxide. The solid-state structures were determined using single-crystal X-ray diffraction, revealing molecular complexes with the formula [Me

Andreas Stihl AG is the world's leading manufacturer of chain saws and other outdoor handheld power equipment. Based on marketing challenges in its high-volume retail channel—mass merchants such as The Home Depot and Lowe's—Stihl's U.S. unit has narrowed its distribution system to a single channel: independent retail dealers specializing in yard maintenance equipment. This risky and highly publicized decision has proved extremely successful, raising profits, attracting more dealers into exclusive relationships with Stihl, and strengthening the brand's top-quality positioning. But Stihl management are concerned that this channel system may not fit tomorrow's demographics, dominated by homeowners from the so-called Generation X and Generation Y. The case outlines Stihl's business and channel systems and customer needs, then poses a series of questions that management believes must be answered to determine whether to maintain or move away from reliance on its specialty retailers and how to adapt its system.To understand issues related to retail channel strategy development in fast-changing consumer markets, as well as the challenges of adapting legacy routes-to-market systems to changing consumer service output demands.

Target Corporation is concerned that the company might be left out of one of its most lucrative and attractive product categories, video games and game players, as these products increasingly migrate to digital distribution models. What steps should the company take to maintain its relevance and build sustainable competitive advantage as these trends play out? What are the implications for the company's multi-channel online and offline format portfolio going forward?Students will develop a keen understanding of the challenges faced by contemporary retailers as consumer needs change, new product innovations emerge, market structures evolve, and format pressures escalate.

How does a mature business develop new growth markets, assuming it already has new products? That was the challenge facing The Coca-Cola Company and its global system of bottlers in the 2000s when demand for its core line of carbonated soft drinks flattened. The Australian bottler, Amatil, pinned its hopes on energy drinks, a fast-growth, youth-oriented category that was capturing headlines and share away from traditional products. To wrest control from the upstart brands that originated them, Amatil was targeting the retail context where young people congregated and formed their preferences, in pubs, nightclubs, healthclubs, and sporting events. This international case explores the challenges encountered when a mature company with considerable distribution assets, well-honed systems, and entrenched operating procedures attempts to sell into an underserved retail channel with requirements quite unlike those of the company's mainstream buyers. How does it attract market interest? How does it develop new routes-to-market without undercutting the cost efficiencies and delivery value that have earned it dominant position elsewhere? How does it win over what could be its core customers of the future without alienating today's faithful? These are just some of the questions that Amatil management was determined to solve.Understand issues related to retail channel strategy development in fast-changing international consumer markets, and the challenges of adapting legacy routes-to-market systems to changing consumer demands.

Colfax Corporation was a young, privately held collection of pump-manufacturing companies from the United States and Europe. Intending to go public, it was eager to find a story for investors of how it could grow at rates faster than its subsidiaries had historically grown in their home regions and core-customer industrial markets. This case describes a singular new-growth opportunity: selling Colfax solutions into state-owned petroleum enterprises in the Middle East at a time when these producers were straining to add capacity. Designing the optimal marketing system required Colfax to weigh a complex of issues, including global resource allocation and deployment, a process for customer-relationship building, and estimates for revenue streams versus investment outlays. The design process was, in short, far more than “sticking sales rep pins in the map.” Case readers are asked to think along with the Colfax global management team in deciding, “How much can we afford to risk our current income model in order to build new capacity in a new region in a new way?”Understanding issues related to global B2B marketing channel strategy development, as well as complexities of entering unfamiliar new international markets such as Middle East oil and gas.

The synthesis, reactivity, structures, and bonding in gas-phase binary and complex oxide anion molecules of protactinium and uranium have been studied by experiment and theory. The oxalate ions, AnVO2(C2O4)−, where An = Pa or U, are essentially actinyl ions, AnVO2+, coordinated by an oxalate dianion. Both react with water to yield the pentavalent hydroxides, AnVO(OH)2(C2O4)−. The chemistry of Pa and U becomes divergent for reactions that result in oxidation: whereas PaVI is inaccessible, UVI is very stable. The UVO2(C2O4)− complex exhibits a remarkable spontaneous exothermic replacement of the oxalate ligand by O2 to yield UO4– and two CO2 molecules. The structure of the uranium tetroxide anion is computed to correspond to distorted uranyl, UVIO22+, coordinated in the equatorial plane by two equivalent O atoms each having formal charges of −1.5 and U–O bond orders intermediate between single and double. The unreactive nature of PaVO2(C2O4)− toward O2 is a manifestation of the resistance toward oxidation of PaV, and clearly reveals the disparate chemistries of Pa and U. The uranium tetroxide anion, UO4–, reacts with water to yield UO5H2–. Infrared spectra obtained for UO5H2– confirm the computed lowest-energy structure, UO3(OH)2–.

The aqueous fluoro complexes of niobium and tantalum were studied using synchrotron based extended X-ray absorption spectroscopy (EXAFS) as model systems for comparison of the structural and coordination chemistry of the Group V metals Nb, Ta and their pseudo-homologue Pa(V). The EXAFS indicate differences in the coordination chemistry of Nb and Ta in these systems that were not intuitive based on their similar charge and ionic radii. The Ta speciation is dominated by six and seven coordinate fluoro complexes, while the chemical speciation of Nb under the same conditions is dominated by its hydrolyzed oxyfluoride complexes. Quantum chemical computations were performed to more fully describe these observations and these results were compared to our earlier study on the fluoro complexes of protactinium. Computations performed with and without the inclusion of scalar relativistic effects reveal that the differences in the chemistry among the Group V elements, and their pseudo-homologue protactinium, are due to the increasing influences of relativistic effects as Z is increased from niobium to protactinium.

The synthesis, X-ray crystal structure, vibrational and optical spectroscopy for the eight-coordinate thiocyanate compounds, [Et4 N]4 [Pu(IV) (NCS)8 ], [Et4 N]4 [Th(IV) (NCS)8 ], and [Et4 N]4 [Ce(III) (NCS)7 (H2 O)] are reported. Thiocyanate was found to rapidly reduce plutonium to Pu(III) in acidic solutions (pH

The synthesis, reactivity, structures, and bonding in gas-phase binary and complex oxide anion molecules of protactinium and uranium have been studied by experiment and theory. The oxalate ions, An

The speciation of protactinium(V) in hydrofluoric acid (HF) solutions was studied using X-ray absorption spectroscopy. Extended X-ray absorption fine structure measurements were performed on an aqueous solution of 0.05 M protactinium(V) with various HF concentrations ranging from 0.5 to 27 M in order to probe the protactinium coordination sphere with respect to the identity and number of coordinating ligands. The resulting fits to the spectra suggest the presence of an eight-coordinate homoleptic fluoro complex in highly concentrated fluoride solutions (27 M), with equilibrium between seven- and eight-coordinate fluoro complexes at moderate acidities, and in more dilute solutions, results indicate that one water molecule is likely to replace a fluoride in the first coordination sphere, at a distance of 2.54-2.57 Å. Comparisons of this chemistry with group V metals, niobium and tantalum, are presented, and the potential implications for these results on the hydrolytic behavior of protactinium in aqueous systems are discussed.

We present the structural and spectroscopic characterization of six uranyl tetrachloride compounds along with a quantified analysis showing the influence of both the crystallographic phase and the lattice solvent upon the vibrational properties of the uranyl moiety. From the uranyl symmetric and asymmetric stretching frequencies we use a valence bond potential model to calculate the stretching and interaction force constants of the uranyl moiety in each compound. Quantifying these second-sphere influences provides insight into the vibrational properties, and indirectly the electronic structure, of the uranyl ion in its ground state. These data provide a better guide for assessing the validity of future comparisons with respect to bond strength, length, and electronic properties among series of actinyl compounds where non-actinide variables may be at play.

The retrieval and purification of a macroscopic aged sample of protactinium-231 is described. The 231Pa was separated from its decay daughters using a precipitation based method. The method exploits the hydrolytic behavior and insolubility of protactinium rather than attempting to avoid it by way of concentrated hydrofluoric and sulfuric acids, which have been shown to vitiate separations using ion-exchange and solvent extraction based methods. Based on alpha spectrometry the source was previously separated in 1959–1960, consistent with the Harwell Pa separations program. The method described here achieved 98% recovery of the 231Pa with a final alpha-radiopurity of 93.75% in contrast to the 20.25% radiopurity of the starting material.

The synthesis, crystal structures, and Raman spectra of seven plutonium chloride compounds are presented. The materials are based upon Pu(VI)O2Cl4(2-) and Pu(IV)Cl6(2-) anions that are charge balanced by protonated pyridinium cations. The single crystal X-ray structures show a variety of donor-acceptor interactions between the plutonium perhalo anions and the cationic pyridine groups. Complementary Raman spectra show that these interactions can be probed through the symmetric vibrational mode of the plutonyl moiety. Unlike previously reported studies in similar uranyl(VI) systems, the facile redox chemistry of plutonium in aqueous solution has demonstrated the feasibility of using not only the An(VI)O2Cl4(2-) anion with approximate D4h symmetry but also the approximately Oh An(IV)Cl6(2-) anion in order to manipulate both the structure and dimensionality of such hybrid materials.

The formation of Pu(IV)-oxo-nanoparticles from Pu(III) solutions by a surface-enhanced redox/polymerization reaction at the muscovite (001) basal plane is reported, with a continuous increase in plutonium coverage observed in situ over several hours. The sorbed Pu extends70 Å from the surface with a maximum concentration at 10.5 Å and a total coverage of9 Pu atoms per unit cell area of muscovite (0.77 μg Pu/cm(2)) (determined independently by in situ resonant anomalous X-ray reflectivity and by ex-situ alpha-spectrometry). The presence of discrete nanoparticles is confirmed by high resolution atomic force microscopy. We propose that the formation of these Pu(IV) nanoparticles from an otherwise stable Pu(III) solution can be explained by the combination of a highly concentrated interfacial Pu-ion species, the Pu(III)-Pu(IV) redox equilibrium, and the strong proclivity of tetravalent Pu to hydrolyze and form polymeric species. These results are the first direct observation of such behavior of plutonium on a naturally occurring mineral, providing insights into understanding the environmental transport of plutonium and other contaminants capable of similar redox/polymerization reactions.

In actinide chemistry, it has been shown that equatorial ligands bound to the metal centers of actinyl ions have a strong influence on the chemistry and therefore the electronic structure of the O═An═O moiety. While this influence has received a significant amount of attention, considerably less research has been done to investigate how the identity of the actinide metal itself (U, Np, Pu, Am) affects the actinyl stretching frequencies. Herein, we present the structural and spectroscopic characterization of six actinyl tetrachloride compounds (M2AnO2Cl4: M = Rb, Cs, Me4N; An = U, Pu) as well as the stretching and interactive force constants of the actinyl moiety in each species. Our results show a decrease in the stretching force constant and a weakening of the An═O bond when traversing the actinides from uranyl to plutonyl, which is interesting because the solid state molecular structures show a slight contraction of the An═O bond length when uranium is replaced with plutonium. Additionally, the interaction force constants for both the uranyl and plutonyl compounds were found to be negative, which corresponds to a reduction of the force constant for the symmetric stretching mode.

Three uranium(VI)-bearing materials were synthesized hydrothermally using the organic ligand 4,4'-biphenyldicarboxylic acid: (UO2)(C14O4H8) (1); [(UO2)2(C14O4H8)2(OH)]·(NH4)(H2O) (2); (UO2)2(C14O4H8)(OH)2 (3). Compound 1 was formed after 1 day at 180 °C in an acidic environment (pH(i) = 4.03), and compounds 2 and 3 coformed after 3 days under basic conditions (pH(i) = 7.95). Coformation of all three compounds was observed at higher pH(i) (9.00). Ex situ Raman spectra of single crystals of 1-3 were collected and analyzed for signature peaks. In situ hydrothermal Raman data were also obtained and compared to the ex situ Raman spectra of the title compounds in an effort to acquire formation mechanism details. At pH(i) = 4.00, the formation of 1 was suggested by in situ Raman spectra. At an increased pH(i) (7.90), the in situ data implied the formation of compounds 1 and 3. The most basic conditions (pH(i) = 9.00) yielded a complex mixture of phases consistent with that of increased uranyl hydrolysis.

Adsorption of tetravalent thorium to the (0 0 1) basal surface of the phyllosilicate muscovite from an aqueous solution (1 × 10−4 mol/L Th(IV) in 1 × 10−1 mol/L NaCl, pH = 3.2) was studied by crystal truncation rod (CTR) and resonant anomalous X-ray reflectivity (RAXR) measurements. Th uptake to the muscovite surface from solutions with total Th concentrations [Th]tot = 1 × 10−6–4.88 × 10−3 mol/L and 1 × 10−1 mol/L NaCl, pH = 3.2 was quantified by alpha-spectrometry. The uptake measurements showed that Th adsorption to the muscovite surface follows a Langmuir isotherm with an apparent adsorption constant Kapp = 2 × 104 L/mol up to [Th]tot = 1.02 × 10−3 mol/L. The CTR and RAXR results identified one dominant Th species with a very broad distribution centered ∼10 A above the surface, in agreement with strongly hydrated extended outer sphere sorption. The findings indicate that the large energy of hydration (ΔGhyd = −5815 kJ/mol ( Marcus, 1991 )) for the small and highly-charged Th4+ cation is a controlling parameter in its surface speciation. The surface occupancy (0.4 Th per unit cell area, AUC) measured by RAXR exceeds the expected level for surface charge compensation by tetravalent Th (0.25 Th/AUC). However, the radiometric uptake measurements show smaller occupancies (0.21 Th/AUC) after rinsing by deionized water, indicating a partial removability of sorbed thorium. Thorium oligomerization was observed at total Th concentrations [Th]tot ⩾ 2.0 × 10−3 mol/L in presence of the surface, although solubility studies suggest that Th is soluble under these solution conditions.

Adsorption of monodisperse cubic plutonium oxide nanoparticles ("Pu-NP", [Pu(38)O(56)Cl(x)(H(2)O)(y)]((40-x)+), with a fluorite-related lattice, approximately 1 nm in edge size) to the muscovite (001) basal plane from aqueous solutions was observed in situ (in 100 mM NaCl background electrolyte at pH 2.6). Uptake capacity of the surface quantified by α-spectrometry was 0.92 μg Pu/cm(2), corresponding to 10.8 Pu per unit cell area (A(UC)). This amount is significantly larger than that of Pu(4+) needed for satisfying the negative surface charge (0.25 Pu(4+) for 1 e(-)/A(UC)). The adsorbed Pu-NPs cover 17% of the surface area, determined by X-ray reflectivity (XR). This correlates to one Pu-NP for every 14 unit cells of muscovite, suggesting that each particle compensates the charge of the unit cells onto which it adsorbs as well as those in its direct proximity. Structural investigation by resonant anomalous X-ray reflectivity distinguished two different sorption states of Pu-NPs on the surface at two different regimes of distance from the surface. A fraction of Pu is distributed within 11 Å from the surface. The distribution width matches the Pu-NP size, indicating that this species represents Pu-NPs adsorbed directly on the surface. Beyond the first layer, an additional fraction of sorbed Pu was observed to extend more broadly up to more than 100 Å from the surface. This distribution is interpreted as resulting from "stacking" or aggregation of the nanoparticles driven by sorption and accumulation of Pu-NPs at the interface although these Pu-NPs do not aggregate in the solution. These results are the first in situ observation of the interaction of nanoparticles with a charged mineral-water interface yielding information important to understanding the environmental transport of Pu and other nanophase inorganic species.

The structural chemistry of uranium(VI) in concentrated aqueous hydrobromic acid solutions was investigated using both single crystal X-ray diffraction and synchrotron-based high-energy X-ray scattering (HEXS) to reveal the structure of the uranium(VI) complexes in solution prior to crystallization. The crystal structures of a series of uranyl tetrabromide salts are reported, including Cs(2)UO(2)Br(4), Rb(2)UO(2)Br(4)·2H(2)O, K(2)UO(2)Br(4)·2H(2)O, and (NH(4))(2)UO(2)Br(4)·2H(2)O, as well as a molecular dimer of uranium(VI), (UO(2))(2)(OH)(2)Br(2)(H(2)O)(4). Limited correspondence exists between the structures observed in the solid state and those in solution. Quantitative analysis of the HEXS data show an average U-Br coordination number of 1.9(2) in solution, in contrast to the U-Br coordination number of 4 in the solid salts.

Three polynuclear thorium(IV) molecular complexes have been synthesized under ambient conditions from reactions of an amorphous Th precipitate, obtained via hydrolysis, with carboxylate functionalized ligands. The structures of Th(6)(OH)(4)O(4)(H(2)O)(6)(HCO(2))(12)·nH(2)O (1), Th(6)(OH)(4)O(4)(H(2)O)(6)(CH(3)CO(2))(12)·nH(2)O (2), Th(6)(OH)(4)O(4)(H(2)O)(6)(ClCH(2)CO(2))(12)·4H(2)O (3) each consist of a hexanuclear Th core wherein six 9-coordinate Th(IV) cations are bridged by four μ(3)-hydroxo and four μ(3)-oxo groups. Each Th(IV) center is additionally coordinated to one bound "apical" water molecule and four oxygen atoms from bridging carboxylate functionalized organic acid units. "Decoration" of the cationic [Th(6)(μ(3)-O)(4)(μ(3)-OH)(4)](12+) cores by anionic shells of R-COO(-) ligands (R = H, CH(3), or CH(2)Cl) terminates the oligomers and results in the formation of discrete, neutral molecular clusters. Electronic structure calculations at the density functional theory level predicted that the most energetically favorable positions for the protons on the hexanuclear core result in the cluster with the highest symmetry with the protons separated as much as possible. The synthesis, structure, and characterization of the materials are reported.

The chemistry of tetravalent Pu with sulfate is explored in a series of single-crystal X-ray diffraction studies of the alkali metal plutonium sulfate compounds. Five new structures of Pu(IV) sulfates are presented including the structure for the α-phase of Pu(SO(4))(2)(H(2)O)(4), Na(10)Pu(2)(SO(4))(9)(H(2)O)(4), K(8)Pu(2)(SO(4))(8)(H(2)O)(5), Rb(8)Pu(2)(SO(4))(8)(H(2)O)(4), and Cs(4)Pu(SO(4))(4)(H(2)O)(2). Changes in structure and stoichiometry are seen down the alkali-metal series despite identical reaction conditions for each of the complexes. Comparison to the other known An(IV) sulfates, Group IV sulfates, and Ce(IV) reveals limited similarity in stoichiometry and structure across the actinide series and their homologues. Marked color changes are observed down the series indicating strong interactions between the plutonium ions and the ligands in these complexes.

Pair-distribution functions (PDF)s were obtained from high-energy X-ray scattering (HEXS) data on a series of uranyl solutions as a function of chloride ion concentration. Analyses reveal that chloride forms only inner-sphere complexes with the uranyl, replacing inner-sphere waters such that the total uranyl coordination number decreases from 4.7 waters at [Cl(-)] = 0 m to 4.4 (1.7 water and 2.7 Cl(-)) at [Cl(-)] = 6.8 m. Some of the second-coordination sphere waters reorient upon uranyl inner-sphere chloride complexation in order to hydrogen bond with the bound anion. Similar data obtained on a series of solutions maintained at constant ionic strength are used to confirm structural assignments through determining stability constants for the addition of chloride to uranyl and comparison with published values. The stability constants, β(1) = 1.5(10) m(-1), β(2) = 0.8(4) m(-2), and β(3) = 0.4(1) m(-3), obtained in a series of solutions with constant ionic strength of 5.3 m, are in reasonable agreement with previously published results determined by solvent extraction. The agreement of stability constants supports our peak assignments for the PDF and thus our structural model for uranyl chloride complexes in solution. Using coordination numbers and speciation determined here as a function of chloride ion concentration, the monochloro species is found to have four coordinating waters in the uranyl equatorial plane, the dichoro species is found to be an equilibrium of three and two coordinating waters, and the trichloro species has only a single water in the equatorial plane. These values correspond to total average coordination numbers of 5, 4.3, and 4 for the mono-, di-, and trichlorouranyl complexes. From the equilibrium value of the dichloro species, it can be further estimated that ΔG = -0.5 kcal/mol for the conversion of five to four coordinate species. Overall, the HEXS data support the assertion that uranyl chloride correlations do exist and the results are not simply the result of solvent-ion effects.

The interaction of Pu3+ bearing solutions with the muscovite (0 0 1) basal plane is explored using a combination of ex-situ approaches including alpha-counting, to determine the Pu3+ adsorption isotherm, and X-ray reflectivity (XR) and resonant anomalous X-ray reflectivity (RAXR), to probe the interfacial structure and Pu-specific distribution, respectively. Pu uptake to the muscovite (0 0 1) surface from Pu3+ solutions in a 0.1 M NaClO4 background electrolyte at pH 3 follows an approximate Langmuir isotherm with an apparent adsorption constant, Kapp = 5 × 104 M−1, and with a maximum coverage that is consistent with the amount needed to fully compensate the surface charge by trivalent Pu. The XR results show that the muscovite surface reacted with a 10−3 M Pu3+ solution (at pH 3 with 0.1 M NaClO4) and dried in the ambient environment, maintains a 30–40 A thick layer, indicating the presence of a residual hydration layer (possibly including adventitious carbon). The RAXR results indicate that Pu sorbs on the muscovite surface with an intrinsically broad distribution with an average height of 18 A, substantially larger than heights expected for any specifically adsorbed inner- or outer-sphere complexes. These results are discussed in the context of recent studies of cation adsorption trends on muscovite and the possible roles of Pu hydrolysis species in controlling the Pu–muscovite interactions.

Because of the importance of probing molecular-scale chemical and physical structure of environmental samples in their natural and often hydrated state, synchrotron radiation has been a powerful tool for environmental scientists for decades. Thus, the crucial role that a highly coherent and high-brightness hard X-ray source such as the Advance Photon Source (APS) can play in addressing many of the outstanding questions in molecular environmental science (MES) was recognized even before “first light” at the facility. No single synchrotron-based technique or experimental approach can adequately address the tremendous temporal and spatial heterogeneities of the chemistry, physics, and biology of natural environmental samples. Thus, it is common at the APS that multiple X-ray techniques and experimental systems are employed to investigate environmental samples, often chosen for their ability to focus on solute species, plants, microbes, organics, interfacial species, or solids.

The ion adsorption properties of muscovite mica were exploited to prepare higher resolution alpha-spectroscopy samples of 242Pu. The samples prepared by our method are compared to those prepared using electrodeposition methods in terms of their energy resolution. The mica adsorption method results in significant increases in energy resolution vs. that of electrodeposition. Muscovite surface adsorption properties of the mica allow for monolayer adsorption of plutonium thus minimizing energy attenuation and maximizing energy resolution of the resulting spectra. The mica adsorption method allows for simplified preparation of higher-resolution alpha-spectroscopy samples useful for the isotopic analysis of alpha-emitting radionuclides.

A series of aqueous, constant ionic strength solutions containing 0.5 m Er is studied as a function of chloride/perchlorate ion concentration using high-energy X-ray scattering (HEXS) to probe the metal ion coordination environment. Perchlorate is seen to form an outer-sphere complex only in the end member (4.0 m perchlorate) of the series. Chloride ions are seen to bind as both inner- and outer-sphere complexes. A quantitative analysis of the scattering data is used to determine stability constants that depend on whether the complexation with chloride ions is assumed to add to or to replace the waters bound in the first coordination sphere. Published stability constants obtained from liquid-liquid extraction clarify the mechanism involved and, together with the HEXS data, present a consistent picture of the chemistry. The stability constants determined from the HEXS data, beta(1) = 0.38(8) and beta(2) = 0.014(9), are small, less than the available thermal energy in solution at room temperature. The combination of chemical separations and HEXS data for the analysis supports the argument that the complexes formed are real under the experimental conditions. Details of the structural correlations and interactions are discussed for applications including separations and environmental modeling.

We report the synthesis of a thorium sulfate hydrate with 11.5 A open channels that propagate through the structure. The compound crystallizes in the tetragonal space group P4(2)/nmc, a = b = 25.890(4) A, c = 9.080(2) A, Z = 8, V = 6086.3(2) A(3). The thermal stability of the compound was investigated using thermogravimetric analysis and high-energy X-ray scattering (HEXS) revealing that the compound begins to undergo decomposition near 200 degrees C with an accompanied loss in crystallinity. The immediate coordination environment about the thorium atoms remains intact through heating to 500 degrees C as demonstrated by HEXS. Further heating reveals the formation of at least two crystalline phases, Th(SO4)2 and ThO2, which ultimately decompose to ThO2.

Understanding superconductivity in PuCoGa5 presents several challenges due to the presence of local moments and self-irradiation damage. We present X-ray absorption fine-structure measurements that further establish the presence of local 5f-electrons. Moreover, these data indicate even stronger localization after the PuCoGa5 sample has aged, indicating a possible mixed valent ground state of the Pu atoms. Local structure measurements on this aged sample show an astonishing amount of damage, approximately 40% of the material after about 2 years. This amount of damage indicates that distortions around the Frenkel defects extend beyond the nearest-neighbor, and is qualitatively consistent with a percolation model for the destruction of the superconducting state after sufficient damage has accumulated.

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.

The single-crystal X-ray diffraction structure of [(CH3)4N]2PuCl6 is presented for the first time, resolving long-standing confusion and speculation regarding the structure of this compound in the literature. A temperature-dependent study of this compound shows that the structure of [(CH3)4N]2PuCl6 undergoes no fewer than two phase transitions between 100 and 360 K. The phase of [(CH3)4N]2PuCl6 at room temperature is Fd3̅c a = 26.012(3) Å. At 360 K, the structure is in space group Fm3̅m, with a = 13.088(1) Å. The plutonium octahedra and tetramethylammonium cations undergo a rotative displacement, and the degree of rotation varies with temperature, giving rise to the phase transition from Fm3̅m to Fd3̅c as the crystal is cooled. Synthesis and structural studies of the deuterated salt [(CD3)4N]2PuCl6 suggest that there is an isotopic effect associated with this phase transition, as revealed by a changing transition temperature in the deuterated versus protonated compound, indicating that the donor-acceptor interactions between the tetramethylammonium cations and the hexachloroplutonate anions are driving the phase transformation.

It is demonstrated that the gas-phase oxo-exchange of PaO2(+) with water is substantially faster than that of UO2(+), indicating that the Pa-O bonds are more susceptible to activation and formation of the bis-hydroxide intermediate, PaO(OH)2(+). To elucidate the nature of the water adduct of PaO2(+), hydration of PaO2(+) and UO2(+), as well as collision induced dissociation (CID) and ligand-exchange of the water adducts of PaO2(+) and UO2(+), was studied. The results indicate that, in contrast to UO2(H2O)(+), the protactinium oxo bis-hydroxide isomer, PaO(OH)2(+), is produced as a gas-phase species close in energy to the hydrate isomer, PaO2(H2O)(+). CID behavior similar to that of Th(OH)3(+) supports the assignment as PaO(OH)2(+). The gas-phase results are consistent with the spontaneous hydrolysis of PaO2(+) in aqueous solution, this in contrast to later AnO2(+) (An = U, Np, Pu), which forms stable hydrates in both solution and gas phase. In view of the known propensity for Th(IV) to hydrolyze, and previous gas-phase studies of other AnO2(+), it is concluded that the stabilities of oxo-hydroxides relative to oxide hydrates decreases in the order: Th(IV)Pa(V)U(V)Np(V)Pu(V). This trend suggests increasing covalency and decreasing ionicity of An-O bonds upon proceeding across the actinide series.

This work undertakes, we believe for the first time, a study of the chemistry of alkyl halides in Na 0 treated zeolites. It concludes that untreated zeolites do nucleophilic chemistry to the degree that the host is electron donating. It concludes that Na 0 treated zeolites do a mixture of nucleophilic, electron-transfer, and free radical chemistry. Zeolites NaX and NaY and their Na 0 treated forms (Na 0 /NaX and Na 0 /NaY) were exposed to linear1-haloalkanes (Cl, Br, I). NaY is inert in all cases. Framework alkoxy and halide ion are formed in NaX from the Br- and I-alkanes in an electrophilic attack of framework oxygen on the alkyl halide, while the leaving of the halide ion is assisted by the electrostatic attraction of the NaX site III or III′ Na ions. In Na 0 NaX and Na 0 /NaY direct reaction of Na 0 with the alkyl bromide or iodide yields a larger alkane and halide ion, probably via a free radical mechanism involving two Na 0 and two alkyl halides. The NaX–alkyl chloride chemistry includes exclusively or partly dehydrohalogenation, yielding 1-alkenes and chloride ion. Na 0 /NaX or Na 0 /NaY–alkyl chloride dehydrohalogenation chemistry yields chloride with 2-alkenes in low yield and alkanes in higher yields. 1-Chloropropane yields the framework propoxy and propene from NaX and yields these products plus other olefins from Na 0 /NaX. Overall the yields and reactivity fall into a pattern of Lewis basicity increasing in the order NaY 0 /NaY 0 /NaX.