Synthesis of Single Crystal Li2NpO4 and Li4NpO5 from Aqueous Lithium Hydroxide Solutions under Mild Hydrothermal Conditions.

The ternary oxides, Li2NpO4 and Li4NpO5, were synthesized under mild hydrothermal conditions using concentrated LiOH solutions containing NpO2(NO3)2. The reactions resulted in the formation of single crystals of both compounds, enabling the determination of their single crystal structures for the first time. Exploration of the synthetic phase space demonstrates that the resulting neptunate phases are dependent on the concentration of LiOH, transitioning from Li2NpO4, containing a typical octahedral neptunyl geometry with two shorter Np≡O bonds, at lower LiOH concentrations to Li4NpO5 with two long and four short Np-O bonds under saturated solution conditions. Reactions exploring the same synthetic conditions are also reported for uranyl(VI) for comparison. Raman spectra of the compounds were collected and analyzed to evaluate the Np-O bonding in these compounds.

Reactions of Neptunium(V) in Alkali-Metal Hydroxides.

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.

Thiocyanate complexes of the lanthanides, Am and Cm.

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.

Applications of Alkali Metal Hydroxide Hydrofluxes to the Synthesis of Single-Crystal Ternary Actinide Oxides.

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.