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Through the combination of low-temperature hydrothermal synthesis and room-temperature evaporation, a synthetic phase similar in composition and crystal structure to the Earth's most complex mineral, ewingite, was obtained. The crystal structures of both natural and synthetic compounds are based on supertetrahedral uranyl-carbonate nanoclusters that are arranged according to the cubic body-centered lattice principle. The structure and composition of the uranyl carbonate nanocluster were refined using the data on synthetic material. Although the stability of natural ewingite is higher (according to visual observation and experimental studies), the synthetic phase can be regarded as a primary and/or metastable reaction product which further re-crystallizes into a more stable form under environmental conditions. [ABSTRACT FROM AUTHOR]

Single crystals of four novel uranyl selenate and selenite-selenate oxysalts with protonated ethylamine molecules, (C 2 H 8 N) 2 [(UO 2 )(SeO 4 ) 2 (H 2 O)](H 2 O) ( I ), (C 2 H 8 N) 3 [(UO 2 )(SeO 4 ) 2 (HSeO 4 )] ( II ), (C 2 H 8 N)[(UO 2 )(SeO 4 )(HSeO 3 )] ( III ), and (C 2 H 8 N)(H 3 O)[(UO 2 )(SeO 4 ) 2 (H 2 O)] ( IV ) have been prepared by isothermal evaporation from aqueous solutions. Uranyl-containing 1D and 2D units have been investigated using topological approach and information-based complexity measurements that demonstrate the evolution of structural units and the increase of topological complexity with the decrease of H 2 O content. [ABSTRACT FROM AUTHOR]

Phase formation in the mixed sulfate-selenate aqueous system of uranyl nitrate and cesium nitrate has been investigated. Two types of crystalline compounds have been obtained and characterized using a number of experimental (single crystal XRD, FTIR, SEM) and theoretical (information-based complexity calculations, topological analysis) techniques. No miscibility gaps have been observed for Cs 2 [(UO 2 ) 2 ( T O 4 ) 3 ] ( T = S, Se), which crystallizes in tetragonal system, P -42 1 m , a =9.616(1)–9.856(2), c =8.105(1)–8.159(1) Å, V =749.6(2)–792.5(3) Å 3 . Nine phases with variable amount of S and Se have been structurally characterized. The structures of the Cs 2 [(UO 2 ) 2 ( T O 4 ) 3 ] ( T = S, Se) compounds are based upon the [(UO 2 ) 2 ( T O 4 ) 3 ] 2- layers of corner-sharing uranyl pentagonal bipyramids and T O 4 tetrahedra. The layers contain two types of tetrahedral sites: T 1 (3-connected, i.e. having three O atoms shared by adjacent uranyl polyhedra) and T 2 (4-connected). The Se-for-S substitution in tetrahedral sites is highly selective with smaller S 6+ cation showing a strong preference for the more tightly bonded T 2 site. Crystallization in the pure Se system starts with the formation of Cs 2 [(UO 2 )(SeO 4 ) 2 (H 2 O)](H 2 O) crystals, its subsequent dissolution and formation of Cs 2 [(UO 2 ) 2 (SeO 4 ) 3 ]. The information-based structural complexity calculations for these two phases support the rule that more topologically complex structures form at the latest stages of crystallization. [ABSTRACT FROM AUTHOR]

Crystal structures of two uranyl selenite minerals derriksite, Cu4[(UO2)(SeO3)2](OH)6, and demesmaekerite, Pb2Cu5[(UO2)2(SeO3)6(OH)6](H2O)2, which structures are based on uranyl selenite 1D structural units, were studied employing single-crystal X-ray diffraction analysis at various temperatures. The refinement of their crystal structures reveals the detailed dynamics of the interatomic interactions during the heating process, which allows describing the thermal behavior. Uranyl selenite chains and their mutual arrangement mainly provide the rigidity of the crystal structure. Thus the lowest expansion in the structure of derriksite is observed along the direction of uranyl selenite chains, while the largest expansion occurs in the direction normal to chains, with the space occupied by lone electron pairs of Se4+ atoms and low covalent bond distribution density. The maximal expansion in the crystal structure of demesmaekerite is manifested approximately along the [100], which matches the direction of chains of less strongly bonded Cu-centered octahedra, and gaps between Cu chains occupied by the Pb cations. The crystal structure of demesmaekerite undergoes contraction in the direction of the space between the U-bearing chains with the deficiency of strong covalent bonds. Contraction of the structure can also be attributed to the orthogonalization of the oblique triclinic angles of the unit cell. It is demonstrated that the assignment of U-bearing units during structure description is reasonably justified since, regardless of their dimensionality, these substructural units are one of the most stable and rigid blocks in the structural architecture, and they govern the thermal behavior of the entire structure. [ABSTRACT FROM AUTHOR]

Three novel uranyl selenate and sulfate oxysalts templated by protonated azetidine molecules, [ Az H] + , and its ring-opened counterpart 1-azetidinepropanamine, [ Az H(CH 2 ) 3 NH 3 ] 2+ , have been prepared and studied by X-ray structural analysis. Conformations of azetidinium cations were analysed by means of infrared vibrational assignments supported by the DFT calculations. Crystallization of [ Az H] 2 [(UO 2 ) 2 (SeO 4 ) 3 (H 2 O)] ( I ) from highly acidic solutions suggests that low pH does not necessarily result in the opening of azetidine ring. [ Az H(CH 2 ) 3 NH 3 ][(UO 2 ) 2 (SeO 4 ) 3 (H 2 O)](H 2 O) ( II ) and [ Az H(CH 2 ) 3 NH 3 ](H 5 O 2 )[(UO 2 ) 2 (SO 4 ) 3 (HSO 4 )] ( III ) are the first structurally characterized crystalline compounds bearing isolated ring-opened azetidine moiety. [ABSTRACT FROM AUTHOR]

Single crystals of seven novel uranyl oxysalts of selenium with protonated methylamine molecules, [C 2 H 8 N] 2 [(UO 2 )(SeO 4 ) 2 (H 2 O)] ( I ), [C 2 H 8 N] 2 [(UO 2 ) 2 (SeO 4 ) 3 (H 2 O)] ( II ), [C 4 H 15 N 3 ][H 3 O] 0.5 [(UO 2 ) 2 (SeO 4 ) 2.93 (SeO 3 ) 0.07 (H 2 O)](NO 3 ) 0.5 ( III ), [C 2 H 8 N] 3 [H 5 O 2 ][(UO 2 ) 2 (SeO 4 ) 3 (H 2 O) 2 ] 2 (H 2 O) 5 ( IV ), [C 2 H 8 N] 2 [H 3 O][(UO 2 ) 3 (SeO 4 ) 4 (HSeO 3 )(H 2 O)](H 2 SeO 3 ) 0.2 ( V ), [C 4 H 12 N] 3 [H 3 O][(UO 2 ) 3 (SeO 4 ) 5 (H 2 O)] ( VI ), and [C 2 H 8 N] 3 (C 2 H 7 N)[(UO 2 ) 3 (SeO 4 ) 4 (HSeO 3 )(H 2 O)] ( VII ) have been prepared by isothermal evaporation from aqueous solutions. Their crystal structures have been solved by direct methods and their uranyl selenate and selenite–selenate units investigated using black-and-white graphs from the viewpoints of topology of interpolyhedral linkages and isomeric variations. The crystal structure of IV is based upon complex layers with unique topology, which has not been observed previously in uranyl selenates. Investigations of the statistics and local distribution of the U–O br –Se bond angles demonstrates that shorter angles associate with undulations, whereas larger angles correspond to planar areas of the uranyl selenite layers. [ABSTRACT FROM AUTHOR]