Syntheses and crystal structures of two novel alkaline uranyl chromates A2(UO2)(CrO4)2 (A=Rb, Cs) with bidentate coordination mode of uranyl ions by chromate anions

Effect of solution acidity on the crystallization of polychromates in uranyl-bearing systems: synthesis and crystal structures of Rb2[(UO2)(Cr2O7)(NO3)2] and two new polymorphs of Rb2Cr3O10

Three new rubidium polychromates, Rb2[(UO2)(Cr2O7)(NO3)2] (1), γ-Rb2Cr3O10 (2) and δ-Rb2Cr3O10 (3) were prepared by combination of hydrothermal treatment at 220 °C and evaporation of aqueous solutions under ambient conditions. Compound 1 is monoclinic, P 2 1 / c $P{2}_{1}/c$ , a = 13.6542(19), b = 19.698(3), c = 11.6984(17) Å, β = 114.326(2)°, V = 2867.0(7) Å3, R 1 = 0.040; 2 is hexagonal, P 6 3 / m $P{6}_{3}/m$ , a = 11.991(2), c = 12.828(3) Å, γ = 120°, V = 1597.3(5) Å3, R 1 = 0.031; 3 is monoclinic, P 2 1 / n $P{2}_{1}/n$ , a = 7.446(3), b = 18.194(6), c = 7.848(3) Å, β = 99.953(9)°, V = 1047.3(7) Å3, R 1 = 0.037. In the crystal structure of 1, UO8 bipyramids and NO3 groups share edges to form [(UO2)(NO3)2] species which share common corners with dichromate Cr2O7 groups producing novel type of uranyl dichromate chains [(UO2)(Cr2O7)(NO3)2]2−. In the structures of new Rb2Cr3O10 polymorphs, CrO4 tetrahedra share vertices to form Cr3O10 2− species. The trichromate groups are aligned along the 63 screw axis forming channels running in the ab plane in the structure of 2. The Rb cations reside between the channels and in their centers completing the structure. The trichromate anions are linked by the Rb+ cations into a 3D framework in the structure of 3. Effect of solution acidity on the crystallization of polychromates in uranyl-bearing systems is discussed.

Topological analysis of the layered uranyl compounds bearing slabs with UO2:TO4 ratio of 2:3

Nine new templated uranyl sulfates and selenates, [(H9O4)2(H2O)][(UO2)2(SO4)3(H2O)2] (H9US), [(C5H7 NO)2(H2O)][(UO2)2(SeO4)3(H2O)2](H2O) (OUSe), [C6H6N3][H5O2] [(UO2)2(SeO4)3(H2O)] (BH5USe), [C6H6N3][H7O3][(UO2)2(SO4)3 (H2O)](H2O) (BH7US), [C6H16N][H5O2][(UO2)2(SeO4)3(H2O)] (TeH5USe), [C6H18N2][(UO2)2(SO4)3(H2O)] (TmUS), [H5O2]2 [(UO2)2(SeO4)3(H2O)](H2O) (H5USe-1), [H5O2]2[(UO2)2(SeO4)3 (H2O)2](H2O)9 (H5USe-2), and [C4H14N2][(UO2)2(SeO4)3(H2O)](H2O) (DmUSe) have been prepared by isothermal evaporation of aqueous solutions containing extra sulfuric or selenic acid. Their crystal structures can be considered as organo-inorganic hybrids constructed of alternating [(UO2)2 (TO4)3(H2O) n ]2− slabs (T = Se6+, S6+, n = 1, 2) and layers containing templating organic moieties and/or hydronium ions and water molecules. The organic and inorganic parts of the structures are linked by multiple hydrogen bonds. Besides structure description, we offer topological analysis of the inorganic fragments with UO2:TO4 ratio of 2:3 as modular units resulting from self-assembly of fundamental chains formed by [(UO2)2(TO4)2] tetramers and TO4 tetrahedra.

Flux crystal growth: a versatile technique to reveal the crystal chemistry of complex uranium oxides

This frontier article focuses on the use of flux crystal growth for the preparation of new actinide containing materials, reviews the history of flux crystal growth of uranium containing phases, and highlights the recent advances in the field. Specifically, we discuss how recent developments in f-element materials, fueled by accelerated materials discovery via crystal growth, have led to the synthesis and characterization of new families of complex uranium containing oxides, namely alkali/alkaline uranates, oxychlorides, oxychalcogenides, tellurites, molybdates, tungstates, chromates, phosphates, arsenates, vanadates, niobates, silicates, germanates, and borates. An overview of flux crystal growth is presented and specific crystal growth approaches are described with an emphasis on how and why they - versus some other method - are used and how they enable the preparation of specific classes of new materials.

Complex Uranyl Dichromates Templated by Aza-Crowns

Three new uranyl dichromate compounds templated by aza-crown templates were obtained at room temperature by evaporation from aqueous solutions: (H2diaza-18-crown-6)2[(UO2)2(Cr2O7)4(H2O)2](H2O)3 (1), (H4[15]aneN4)[(UO2)2(CrO4)2(Cr2O7)2(H2O)] (H2O)3.5 (2) and (H4Cyclam)(H4[15]aneN4)2[(UO2)6(CrO4)8(Cr2O7)4](H2O)4 (3). The use of aza-crown templates made it possible to isolate unprecedented and complex one-dimensional units in 2 and 3, whereas the structure of 1 is based on simple uranyl-dichromate chains. It is very likely that the presence of relatively large organic molecules of aza-crown ethers does not allow uranyl chromate chain complexes to condense into the units of higher dimensionality (layers or frameworks). In general, the formation of 1, 2, and 3 is in agreement with the general principles elaborated for organically templated uranyl compounds. The negative charge of the [(UO2)(Cr2O7)2(H2O)]2−, [(UO2)2(CrO4)2(Cr2O7)2(H2O)]4− and [(UO2)3(CrO4)4(Cr2O7)2]6− one-dimensional inorganic motifs is compensated by the protonation of all nitrogen atoms in the molecules of aza-crowns.