Evgeny V. Nazarchuk

Cr(VI) Trioxide as a Starting Material for the Synthesis of Novel Zero-, One-, and Two-Dimensional Uranyl Dichromates and Chromate-Dichromates

Six different dichromate-based uranyl compounds were obtained. Their structures belong to four principally different but related structure types with different dimensionality of basic structural units. The units in Cs2(UO2)(Cr2O7)(NO3)2 (1) and (C6H11N2)2(UO2)(Cr2O7)2(H2O) (2) are unique, and these are the first “pure” uranyl-dichromates known to date. The compounds Rb2(UO2)(CrO4)(Cr2O7) (3), (C2NH8)2(UO2)(CrO4)(Cr2O7) (4), (C2NH8)2(UO2)(CrO4)2(Cr2O7)(H2O)2 (5), and (C3NH10)2(UO2)(CrO4)2(Cr2O7)(H2O)2 (6) are novel representatives of a rather small group of inorganic compounds containing both isolated CrO4 tetrahedra and dichromate Cr2O7 groups. The structures of 5 and 6 contain compositionally identical but topologically different ∞(2)[(UO2)(CrO4)2(Cr2O7)](2–) sheets (thus corresponding to different geometrical isomers), which have not been reported previously in inorganic compounds. All novel phases have been prepared with an excess of CrO3. “Pure” dichromates are formed at pH < 1.5 and with prior hydrothermal treatment of uranyl-chromate solution, whereas mixed chromate-dichromates are formed at higher pH > 2 values.

Nanoscale hemispheres in novel mixed-valent uranyl chromate(V,VI), (C3NH10)10[(UO2)13(Cr12(5+)O42)(Cr(6+)O4)6(H2O)6](H2O)6.

The structure of a novel mixed-valent chromium uranyl compound, (C(3)NH(10))(10)[(UO(2))(13)(Cr(12)(5+)O(42))(Cr(6+)O(4))(6)(H(2)O)(6)](H(2)O)(6) (1), obtained by the combination of a hydrothermal method and evaporation from aqueous solutions with isopropylammonium, contains uranyl chromate hemispheres with lateral dimensions of 18.9 × 18.5 Å(2) and a height of about 8 Å. The hemispheres are centered by a UO(8) hexagonal bipyramid surrounded by six dimers of Cr(5+)O(5) square pyramids, UO(7) pentagonal bipyramids, and Cr(6+)O(4) tetrahedra. The hemispheres are linked into two-dimensional layers so that two adjacent hemispheres are oriented in opposite directions relative to the plane of the layer. From a topological point of view, the hemispheres have the formula U(21)Cr(23) and can be considered as derivatives of nanospherical cluster U(26)Cr(36) composed of three-, four-, and five-membered rings.

Mixed-ligand coordination of the (UO2)2+ cation and apophyllite topology of uranyl chlorochromate layer in the structure of ((CH3)2CHNH3)[(UO2)(CrO4)Cl(H2O)]

Abstract Addition of the Cl-0 anions to the synthesis mixture stabilizes specific structures of uranyl complexes which results in new compounds with the unprecedented structural topologies. ((CH3)2CHNH3)[(UO2)(CrO4) · Cl(H2O)] is a new member of the small family of compounds based upon the Ur(XmOn)5 (X = Cl, Br, I) bipyramids. The structure is based upon uranyl chloride chromate layers that alternate with the layers of protonated amine molecules. The layers contain UrClO4 pentagonal bipyramids that share three of its equatorial corners with CrO4 tetrahedra. Topological analysis shows that the [(UO2)(CrO4)Cl(H2O)]-0 layer belongs to the same topology of interpolyhedral linkage as in α-UO2MoO4(H2O)2. This type of topology (linkage of 4-membered rings creating 8-membered rings) is known in silicate crystal chemistry as the topology of the [Si4O10] layers in the minerals of the apophyllite group. Their linkage via various intermediate units results in a large family of open-framework and pillared silicates.

Synthesis and crystal-chemical features of two new uranyl chromates with the structures derived from [(UO2)(T6+O4)(H2O)n]0 (T = Cr6+, S6+, Se6+, n = 0–2)

Two new chromates of hexavalent uranium, [C3H10N][(UO2)(CrO4)(NO3)] (1) and [C2H8N]2[(UO2)2· (CrO4)2(Cr2O7)](H2O)2 (2), were prepared by a combination of hydrothermal synthesis and isothermal evaporation. Compounds 1 and 2 crystallize in the triclinic system, space group

Crystal Chemistry of Uranyl Halides Containing Mixed (UO2)(XmOn)5 Bipyramids (X = Cl, Br): Synthesis and Crystal Structure of Cs2(UO2)(NO3)Cl3

P\overline 1

Formation of co-racemic uranyl chromate constructed from chiral layers of different topology

P1¯; a = 7.245(3), b = 7.329(3), c = 11.359(4) Å; α = 85.549(6)°, β = 82.547(6)°, γ = 80.174(6)° for 1; a = 7.2063(4), b = 11.5107(7), c = 16.0980(11) Å; α = 70.736(4)°, β = 80.246(4)°, γ = 71.759(4)° for 2. The structures were solved by the direct methods and refined to R1 = 0.064 [for 1495 reflections with Fo > 4σ(Fo)] and 0.047 [for 4529 reflections with Fo > 4σ(Fo)] for 1 and 2, respectively. The crystal structure of 1 is based on [(UO2)(CrO4)(NO3)]– chains between which the isopropylamine molecules are arranged. In the structure of 2, the amine and H2O molecules are localized between the [(UO2)2(CrO4)2(Cr2O7)]2– layers. The uranyl chromate complexes described are derived from [(UO2)(TO4)(H2O)n]0 chains (T = Cr6+, S6+, Se6+, n = 0–2). A brief review of uranyl compounds with tetrahedral TO42– anions (T = Cr6+, S6+, Se6+) and similar structural organization is given.

High-temperature crystal chemistry of Na6(UO2)2O(MoO4)4

[Pb10O4]Pb2(B2O5)Cl12 (1) and [Pb18O12]Pb(BO2OH)2Cl10 (2) were obtained via high-temperature high-pressure experiments. [O12Pb18](12+) and [O4Pb10](12+) oxocentered structural units of different dimensionality are excised from the ideal [OPb] layer in tetragonal α-PbO. 2 is formed with an excess of lead oxide component, and 1 is formed with an excess of borate and halide reagents. The structure of 2 can be visualized as the incorporation of {Pb(10)Cl4(BO2OH)2} clusters into alternating PbO and chloride layers, with the existence of square vacancies in both. However, the structure of 1 is described as the intrusion of [O4Pb10](12+) tetramers linked by disordered Pb(B2O5) groups into a halogen three-dimensional matrix. The structure of 2 contains 10 symmetrically independent Pb positions. The 6s(2) lone electron pair is stereochemically active on Pb(1)-Pb(9) atoms, whereas it is inert on Pb(10). All of the Pb coordinations in the structure of 2, in accordance with ECCv (volume eccentricity) parameters and the density of states (DOS), can be subdivided into three groups. The current study is the first attempt to analyze this unusual behavior in structurally complex oxyhalide material with the rare case of Pb(2+) cations, demonstrating both stereochemically active and inactive behavior of the lone pair via charge and first-principle calculations.

Open-framework sodium uranyl selenate and sodium uranyl sulfate with protonated morpholino-N-acetic acid

Single crystals of Cs2(UO2)(NO3)Cl3 were prepared by a hydrothermal method at 205 °C. The crystal structure has been solved by Direct Methods: monoclinic, P21/n, a = 10.3748(13), b = 9.4683(13), c = 12.5535(16) Å, β = 110.280(2)◦, V = 1156.7(3) Å3, R1 = 0.029. In the structure, strongly bonded linear uranyl cations UO22+ are equatorially coordinated by two O and three Cl atoms to form (UO2)Cl3O2 pentagonal bipyramids. Each bipyramid shares its O-O edge with an adjacent (NO3)− anion to form finite clusters with the chemical composition [(UO2)(NO3)Cl3]2−. The Cs+ cations provide three-dimensional connectivity of the structure by forming Cs-O and Cs-Cl contacts to the uranyl nitrate chloride complexes. Related structures of mixed-ligand uranyl halides are compared. Graphical Abstract Crystal Chemistry of Uranyl Halides Containing Mixed (UO2)(XmOn)5 Bipyramids (X = Cl, Br): Synthesis and Crystal Structure of Cs2(UO2)(NO3)Cl3