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This paper reviews the state of the art in the structural chemistry of organically templated uranyl sulfates and selenates, which are considered as the most representative groups of U-bearing synthetic compounds. In total, there are 194 compounds known for both groups, the crystal structures of which include 84 various organic molecules. Structural studies and topological analysis clearly indicate complex crystal chemical limitations in terms of the isomorphic substitution implementation, since the existence of isotypic phases has to date been confirmed only for 24 compounds out of 194, which is slightly above 12%. The structural architecture of the entire compound depends on the combination of the organic and oxyanion parts, changes in which are sometimes realized even while maintaining the topology of the U-bearing complex. An increase in the size of the hydrocarbon part and number of charge functional groups of the organic cation leads to the formation of rare and more complex topologies. In addition, the crystal structures of two novel uranyl sulfates and one uranyl selenate, templated by isopropylammonium cations, are reported. Full article

Herein, the novel uranyl selenate and selenite compounds Rb₂[(UO₂)₂(SeO₄)₃], Rb₂[(UO₂)₃(SeO₃)₂O₂], Rb₂[UO₂(SeO₄)₂(H₂O)]·2H₂O, and (UO₂)₂(HSeO₃)₂(H₂SeO₃)₂Se₂O₅ have been synthesized using either slow evaporation or hydrothermal methods under acidic conditions and their structures were refined using single crystal X-ray diffraction. Rb₂[(UO₂)₂(SeO₄)₃] synthesized hydrothermally adopts a layered 2D tetragonal structure in space group P4₂/ncm with a = 9.8312(4) Å, c = 15.4924(9) Å, and V = 1497.38(15) Å, where it consists of UO₇ polyhedra coordinated via SeO₄ units to create units UO₂(SeO₄)₅⁸⁻ moieties which interlink to create layers in which Rb⁺ cations reside in the interspace. Rb₂[(UO₂)₃(SeO₃)₂O₂] synthesized hydrothermally adopts a layered 2D triclinic structure in space group P$\overline{1}$ with a = 7.0116(6) Å, b = 7.0646(6) Å, c = 8.1793(7) Å, α = 103.318(7)°, β = 105.968(7)°, γ = 100.642(7)° and V = 365.48(6) ų, where it consists of edge sharing UO₇, UO₈ and SeO₃ polyhedra that form [(UO₂)₃(SeO₃)₂O₂] layers in which Rb⁺ cations are found in the interlayer space. Rb₂[UO₂(SeO₄)₂(H₂O)]·2H₂O synthesized hydrothermally adopts a chain 1D orthorhombic structure in space group Pmn2₁ with a = 13.041(3) Å, b = 8.579(2) Å, c = 11.583(2) Å, and V = 1295.9(5) ų, consisting of UO₇ polyhedra that corner share with one H₂O and four SeO₄²⁻ ligands, creating infinite chains. (UO₂)₂(HSeO₃)₂(H₂SeO₃)₂Se₂O₅ synthesized under slow evaporation conditions adopts a 0D orthorhombic structure in space group Cmc2₁ with a = 28.4752(12) Å, b = 6.3410(3) Å, c = 10.8575(6) Å, and V = 1960.45(16) ų, consisting of discrete rings of [(UO₂)₂(HSeO₃)₂(H₂SeO₃)₂Se₂O₅]₂. (UO₂)₂(HSeO₃)₂(H₂SeO₃)₂Se₂O₅ is apparently only the second example of a uranyl diselenite compound to be reported. A combination of single crystal X-ray diffraction and bond valance sums calculations are used to characterise all samples obtained in this investigation. The structures uncovered in this investigation are discussed together with the broader family of uranyl selenates and selenites, particularly in the context of the role acidity plays during synthesis in coercing specific structure, functional group, and topology formations. Full article

A new organically templated uranyl molybdate [C₃H₉NH⁺]₄[(UO₂)₃(MoO₄)₅] was prepared by a hydrothermal method at 220 °C. The compound is monoclinic, Сс, a = 16.768(6), b = 20.553(8), c = 11.897(4) Å, β = 108.195(7), V = 3895(2) ų, R₁ = 0.05. The crystal structure is based upon [(UO₂)₃(MoO₄)₅]⁴⁻ uranyl molybdate layers. The isopropylammonium cations are located in the interlayer. The layers in the structure of [C₃H₉NH⁺]₄[(UO₂)₃(MoO₄)₅] are considered as modular architectures. Topological analysis of layers with UO₂:TO₄ ratio of 3:5 (T^VI = S, Cr, Se, Mo) was performed. Modular description is employed to elucidate the relationships between different structural topologies of [(UO₂)₃(TO₄)₅]⁴⁻ layers and inorganic uranyl-based nanotubules. The possible existence of uranyl molybdate nanotubules is discussed. Full article

Comparison of the natural and synthetic phases allows an overview to be made and even an understanding of the crystal growth processes and mechanisms of the particular crystal structure formation. Thus, in this work, we review the crystal chemistry of the family of uranyl selenite compounds, paying special attention to the pathways of synthesis and topological analysis of the known crystal structures. Comparison of the isotypic natural and synthetic uranyl-bearing compounds suggests that uranyl selenite mineral formation requires heating, which most likely can be attributed to the radioactive decay. Structural complexity studies revealed that the majority of synthetic compounds have the topological symmetry of uranyl selenite building blocks equal to the structural symmetry, which means that the highest symmetry of uranyl complexes is preserved regardless of the interstitial filling of the structures. Whereas the real symmetry of U-Se complexes in the structures of minerals is lower than their topological symmetry, which means that interstitial cations and H₂O molecules significantly affect the structural architecture of natural compounds. At the same time, structural complexity parameters for the whole structure are usually higher for the minerals than those for the synthetic compounds of a similar or close organization, which probably indicates the preferred existence of such natural-born architectures. In addition, the reexamination of the crystal structures of two uranyl selenite minerals guilleminite and demesmaekerite is reported. As a result of the single crystal X-ray diffraction analysis of demesmaekerite, Pb₂Cu₅[(UO₂)₂(SeO₃)₆(OH)₆](H₂O)₂, the H atoms positions belonging to the interstitial H₂O molecules were assigned. The refinement of the guilleminite crystal structure allowed the determination of an additional site arranged within the void of the interlayer space and occupied by an H₂O molecule, which suggests the formula of guilleminite to be written as Ba[(UO₂)₃(SeO₃)₂O₂](H₂O)₄ instead of Ba[(UO₂)₃(SeO₃)₂O₂](H₂O)₃. Full article