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

•Single crystal growth of three tetravalent actinide silicates from melts.•Single-crystal structures and Raman spectra of (Ca0.5Na0.5)2NaAnSi8O20 (An=Th, U).•First report of Raman spectrum of huttonite on single crystal samples.

Colorless crystals of ThSiO4 (huttonite) (1) and (Ca0.5Na0.5)2NaThSi8O20 (2) have been synthesized by the solid-state reactions of ThO2, CaSiO3, and Na2WO4 at 1073 K. Green crystals of (Ca0.5Na0.5)2NaUSi8O20 (3) have been synthesized by the solid-state reactions of UO2, CaSiO3, and Na2WO4 at 1003 K. All three compounds have been characterized by single-crystal X-ray diffraction. Compound 1 adopts a monazite-type three-dimensional condensed structure, which is built from edge- and corner-shared ThO9 polyhedra and SiO4 tetrahedra. Compounds 2 and 3 are isostructural and they crystallize in a steacyite-type structure. The structure consists of discrete pseudocubic [Si8O20]8− polyanions, which are connected by An4+ cations into a three-dimensional framework. Each An atom coordinates to eight monodentate [Si8O20]8− moieties in a square antiprismatic geometry. Na+ and Ca2+ 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.

Graphical abstractA Raman spectrum and crystal structures of (Ca0.5Na0.5)2NaAnSi8O20 (An=Th, U), which contain pseudocubic [Si8O20]8− polyanions and eight-coordinate An4+ cations.Figure optionsDownload full-size imageDownload as PowerPoint slide