Solid-state syntheses and single-crystal characterizations of three tetravalent thorium and uranium silicates

Abstract

Keywords:Thorium Uranium Silicate Solid-state syntheses Single-crystal structure Raman spectroscopy a b s t r a c t Colorless crystals of ThSiO 4 (huttonite) (1) and (Ca 0.5 Na 0.5 ) 2 NaThSi 8 O 20 (2) have been synthesized by the solid-state reactions of ThO 2 , CaSiO 3 , and Na 2 WO 4 at 1073 K. Green crystals of (Ca 0.5 Na 0.5 ) 2 NaUSi 8 O 20 (3) have been synthesized by the solid-state reactions of UO 2 , CaSiO 3 , and Na 2 WO 4 at 1003 K. All three compounds have been characterized by single-crystal X-ray diffraction. Compound 1 adopts a monazitetype three-dimensional condensed structure, which is built from edge-and corner-shared ThO 9 polyhedra and SiO 4 tetrahedra. Compounds 2 and 3 are isostructural and they crystallize in a steacyite-type structure. The structure consists of discrete pseudocubic [Si 8 O 20 ] 8 À polyanions, which are connected by An 4 þ cations into a three-dimensional framework. Each An atom coordinates to eight monodentate [Si 8 O 20 ] 8 À moieties in a square antiprismatic geometry. Na þ and Ca 2 þ ions reside in the void within the framework. Raman spectra of 1, 2, and 3 were collected on single crystal samples. 1 displays more complex vibrational bands than thorite. Raman spectra of 2 and 3 are analogous with most of vibrational bands located at almost the same regions.

Comparison of Uranium(VI) and Thorium(IV) Silicates Synthesized via Mixed Fluxes Techniques

“…45,46 The Raman vibrational studies of ThSiO 4 (thorite), ThSiO 4 (huttonite), and (Ca 0.5 Na 0.5 ) 2 NaThSi 8 O 20 have been recently reported in the literature. 47,48 The Raman spectra for the novel K 2 ThSi 2 O 7 and K 2 ThSi 3 O 9 are presented in Figure 15. The bands in the range of 100−350 cm −1 for both spectra are mainly attributed to the coupling modes among O−Th−O bends and lattice vibrations (Table S8).…”

Flux Synthesis, Structure, Properties, and Theoretical Magnetic Study of Uranium(IV)-Containing A2USi6O15 (A = K, Rb) with an Intriguing Green-to-Purple, Crystal-to-Crystal Structural Transition in the K Analogue

“…13 An exception is (Ca 0.5 Na 0.5 ) 2 NaUSi 8 O 20 , which was grown using a flux-assisted solid-state synthesis, in which a small amount of Na 2 WO 4 was used to substantially reduce the temperature required for single-crystal growth. 18 Along with hydrothermal growth, the flux growth of reduced uranium oxides is desirable as the higher temperature regime available to flux growth offers the potential of stabilizing new compounds that cannot be grown at lower temperatures. However, the flux growth of uranium(IV)-containing oxides is extremely rare.…”

Structural and Spectroscopic Investigation of Novel 2D and 3D Uranium Oxo-Silicates/Germanates and Some Statistical Aspects of Uranyl Coordination in Oxo-Salts

“…Two bands at 952 and 961 cm –1 correspond to the ν 1 (SiO 4 ) 4– modes. , In the low frequency region, three bands at 576, 605, and 656 cm –1 can be assigned to the ν 4 bend modes of (SiO 4 ) 4– units. , The bands at 520 cm –1 could be attributed to the ν 1 (Si–O–Si) of 4-membered silicate rings. , The low frequenciey bands at 492, 467, and 429 may be related to the higher-membered silicate rings . The ν 3 (SiO 4 ) 4– modes are observed at 403 cm –1 . , The band at 179 cm –1 may be attributed to the translations of K cations or external modes of (SiO 4 ) 4– units . The Raman spectrum of K 4 (UO 2 ) 2 Si 8 O 20 ·4H 2 O shows three strong peaks at 2869, 2934, and 3462 cm –1 in the range of 2800–3600 cm –1 , which correspond to the antisymmetric stretching vibrations of H 2 O molecules , …”

“…35,36 The band at 179 cm −1 may be attributed to the translations of K cations or external modes of (SiO 4 ) 4− units. 43 The Raman spectrum of K 4 (UO 2 ) 2 Si 8 O 20 • 4H 2 O shows three strong peaks at 2869, 2934, and 3462 cm −1 in the range of 2800−3600 cm −1 , which correspond to the antisymmetric stretching vibrations of H 2 O molecules 22,35 For β-K 2 (UO 2 )Si 4 O 10 , the Raman spectrum presents two high intensity bands at 762 and 779 cm −1 , which correspond to the ν 1 (UO 2 ) 2+ modes. 35,36 No obvious peak for the ν 3 (UO 2 ) 2+ modes can be seen in the 800−930 cm −1 region, whereas more weak peaks for ν 2 (UO 2 ) 2+ modes are found at 217, 275, 294, and 345 cm −1 .…”