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.

Synthesis of Hydrated Ternary Lanthanide-Containing Chlorides Exhibiting X-ray Scintillation and Luminescence

A series of new ternary lanthanide-based chlorides, Cs₂EuCl₅(H₂O)₁₀, Cs₇LnCl₁₀(H₂O)₈ (Ln = Gd or Ho), Cs₁₀Tb₂Cl₁₇(H₂O)₁₄(H₃O), Cs₂DyCl₅(H₂O)₆, Cs₈Er₃Cl₁₇(H₂O)₂₅, and Cs₅Ln₂Cl₁₁(H₂O)₁₇ (Ln = Y, Lu, or Yb), were prepared as single crystals via a facile solution route. The compounds with compositions of Cs₇LnCl₁₀(H₂O)₈ (Ln = Gd or Ho) and Cs₅Ln₂Cl₁₁(H₂O)₁₇ (Ln = Y, Lu, or Yb) crystallize in a monoclinic crystal system in space groups C2 and P2₁/c, respectively, whereas Cs₂EuCl₅(H₂O)₁₀, Cs₁₀Tb₂Cl₁₇(H₂O)₁₄(H₃O), and Cs₈Er₃Cl₁₇(H₂O)₂₅ crystallize in orthorhombic space groups Pbcm, Pnma, and P2₁2₁2₁, respectively. Cs₂DyCl₅(H₂O)₆ crystallizes with triclinic symmetry in space group P1̅. All of these compounds exhibit complex three-dimensional structures built of isolated lanthanide polyhedral units that are linked together by extensive hydrogen bonds. Cs₂EuCl₅(H₂O)₁₀ and Cs₁₀Tb₂Cl₁₇(H₂O)₁₄(H₃O) luminesce upon irradiation with 375 nm ultraviolet light, emitting intense orange-red and green color, respectively, and Cs₁₀Tb₂Cl₁₇(H₂O)₁₄(H₃O) scintillates when exposed to X-rays. Radioluminescence (RL) measurement of Cs₁₀Tb₂Cl₁₇(H₂O)₁₄(H₃O) in powder form shows that the RL emission integrated in the range of 300-750 nm was ∼16% of BGO powder.

Observation of Intense X-ray Scintillation in a Family of Mixed Anion Silicates, Cs3RESi4O10F2 (RE = Y, Eu-Lu), Obtained via an Enhanced Flux Crystal Growth Technique

A new family of mixed anion cesium rare earth silicates exhibiting intense scintillation in several ranges of the visible spectrum are reported. Cs₃RESi₄O₁₀F₂ (RE = Y, Eu-Lu) have been synthesized using an enhanced flux growth method for the targeted growth of mixed anion systems. This is the first example of this method being used for the growth of oxyhalides. The compounds crystallize in the triclinic space group P1̅ with the lattice parameters a = 7.0832(2) Å, b = 7.1346(2) Å, c = 16.2121(5) Å, α = 95.8090(10)°, β = 90.0580(10)°, γ = 119.7650(10)° for the Tb analogue. The structure consists of REO₆ and REO₂F₄ polyhedra connected by Si₄O₁₀ sheets with a previously unobserved silicate sheet topology that contains the uncommon cyclic Si₃O₉ trimers. The synthesis, structure, magnetic and optical properties are reported including, notably, intense X-ray scintillation in Cs₃TbSi₄O₁₀F₂.