Synthesis and crystal structure of [(Cs6F)(Cs3AgF)][Ge14O32] through alkali halide flux growth

Expanding the Chemistry of Salt-Inclusion Materials: Utilizing the Titanyl Ion as a Structure Directing Agent for the Targeted Synthesis of Salt-Inclusion Titanium Silicates

“…As discussed in the Introduction, the uranyl unit has proven to be an excellent structure directing agent for the formation of SIMs. Indeed, while we have to date synthesized 23 uranyl containing SIMs, we have had very limited success expanding to non-uranyl SIMs, with only [K 9 F 2 ]­[(Ln 3 Si 12 O 32 ] and [(Cs 6 F)­(Cs 3 AgF)]­[Ge 14 O 32 ] being grown. , The use of the titanyl, and potentially other transition metal -yl units, as a structure directing agent for the formation of SIMs is therefore a promising route as indicated by the formation of [Cs 3 Cs 6 Cl 0.7 F 0.3 ]­[(TiO) 4 (Si 12 O 32 )] (1) and [Cs 8 Cs 8 Cl 1.4 F 0.6 ]­[(TiO) 4 (Ti 6 Si 14 O 51 )] (2) . However, while U 6+ almost always exists as the uranyl unit in oxides, the titanyl unit is less ubiquitous, making it more challenging to utilize as a structure directing agent.…”

A Density-Functional Theory Structural Database for Discovery of Novel Actinide Waste Forms

“…The calculations for the complex waste compounds studied here yield 0 K representative formation enthalpies such that they are metastable with respect to their simpler constituent oxides, lying above the 0 K thermodynamic convex hull. ,,, Thermal entropic contributions are important for these materials and can naturally influence the relative stability of crystal structures, affecting ranking of each candidate structure. ,, While including temperature-dependent contributions could potentially change our understanding of the relative stabilities, adding thermal contributions requires several phonon calculations per structure. , Although these calculations are possible for individual studies, , the length of time to carry out these calculations on a database scale would require significant computational resources that are not available. Even the use of approximate thermal corrections would require an extensive number of calculations for each candidate crystal structure and, as such, were not attempted. , We are currently evaluating approximate methods to add thermal contributions to our calculations such that we can obtain Gibbs energies for subsets of modeled compounds and thus predict possible reaction pathways for novel waste form materials. , …”

“…The Center for Hierarchical Waste Form Materials (CHWM) has had much success in discovering new framework materials, particularly silicate- and germanate-based salt inclusion materials (SIMs), − , and is currently working to move beyond silicates to investigate other less-explored oxide frameworks. One can use crystal chemical understanding, such as oxidation-state-specific preferred coordination environments and ionic radii, to hypothesize new waste form compositions.…”

Semiconducting silicon–phosphorus frameworks for caging exotic polycations

“…AAe 6-Si 12 P 20 X compounds adopt a novel crystal structure type and exhibit exotic polycations [Ae 6 X] 11+ . Octahedral polycations such as Cs 6 F have been observed in [Cs 6 F][Cs 3 AgF][Ge 14O 32 ] as well as cesium halide uranyl silicates 24,25. However, the formal polycationic charge of Cs 6 F is +5, which is less than half of what is expected for Ba 6 Cl (+11).…”