Versatile Uranyl Germanate Framework Hosting 12 Different Alkali Halide 1D Salt Inclusions

Abstract

Single crystals of 13 new uranyl germanate salt-inclusion materials were grown from alkali halide fluxes: [CsCsF][(UO)(GeO)] (1), [CsAgCl][(UO)(GeO)] (2), [CsAgNaCl][(UO)(GeO)] (3), [CsAgNaCl][(UO)(GeO)] (4), [CsKCl][(UO)(GeO)] (5), [CsKAgCl][(UO)(GeO)] (6), [KKCl][(UO)(GeO)] (7), [KKBrF][(UO)(GeO)] (8), [NaRbF][(UO)(GeO)] (9), [KNaKCsClF][(UO)(GeO)] (10), [KNaKCsClF][(UO)(GeO)] (11), [KKCsF][(UO)(GeO)] (12), and [CsCsCl][(UO)O(GeO)] (13). Structures 1-12 contain the same [(UO)(GeO)] framework whose pores are filled with varied salt species selected by the choice of the specific alkali halide flux used for crystal growth. The size and identity of the salt species also influence whether the [(UO)(GeO)] framework adopts a monoclinic or orthorhombic symmetry. The 13th composition, [CsCsCl][(UO)O(GeO)] (13), crystallizes in a new structure type in the hexagonal crystal system and contains large channels. Optical characterization was performed on [CsKAgCl][(UO)(GeO)] (6) and [KKCsF][(UO)(GeO)] (12), and both exhibit UV-vis absorption and luminescence typical of the uranyl group. The fluorine-containing composition luminesces 10 times as intensely as does the chlorine-containing composition.

“Soft” Alkali Bromide and Iodide Fluxes for Crystal Growth

“…A novel intergrowth uranyl silicate, K 8 (K 5 F)U 6 Si 8 O 40 , was grown from a KF-KBr flux (Morrison et al, 2016b ), and unlike many other uranyl compounds, K 8 (K 5 F)U 6 Si 8 O 40 was found to exhibit intense luminescence behavior possibly attributable to the salt-inclusion. Similarly, a KF-KBr flux was used to prepare [KK 6 Br 0.6 F 0.4 ][(UO 2 ) 3 (Ge 2 O 7 ) 2 ] (Juillerat et al, 2018 ) in a study to explore the adaptability of the uranyl germanate SIM framework. This [(UO 2 ) 3 (Ge 2 O 7 ) 2 ] framework was found to successfully accommodate twelve different salt-inclusions that were incorporated based on the selected flux used in the synthesis.…”

Flux Growth of Uranyl Titanates: Rare Examples of TiO4 Tetrahedra and TiO5 Square Bipyramids

“…For much of their history, the focus was on the investigation of uranyl minerals and the exploration of new materials through ceramic and hydrothermal syntheses, the latter of which resembles the conditions under which most minerals form. In the past decade, the flux growth of uranyl compounds, especially using halide fluxes, has become quite prolific, resulting in many new uranyl silicates, − germanates, − phosphates, − borates, − aluminates, and others. ,, …”

Crystal Growth of Alkali Uranyl Borates from Molten Salt Fluxes: Characterization and Ion Exchange Behavior of A2(UO2)B2O5 (A = Cs, Rb, K)

“…One area of research within our group has focused on the synthesis, characterization, and investigation of structure–property relationships existing in novel complex uranium oxides with structure types conducive to the sequestration of radionuclides . Using high temperature flux growth methods, we have synthesized a number of uranium aluminates, silicates, phosphates, germanates, and aluminophosphates. − Notable examples include [Cs 3 F]­[(UO 2 )­(Si 4 O 10 )], a uranyl silicate salt-inclusion material (SIM) prepared from a CsCl/CsF eutectic mixture, characterized by a three-dimensional uranyl silicate framework containing a one-dimensional alkali halide salt lattice within the channels . Similarly, a set of highly luminescent uranyl phosphates A 6 [(UO 2 ) 7 O 4 (PO 4 ) 4 ] (A = Cs, Rb) were prepared from a CsCl flux; cation–cation interactions within the layered structure were found to induce intense luminescence in these phases .…”