From Order to Disorder and Back Again: In Situ Hydrothermal Redox Reactions of Uranium Phosphites and Phosphates

Abstract

Five new uranium phosphites, phosphates, and mixed phosphate-phosphite compounds were hydrothermally synthesized using H(3)PO(3) as an initial reagent. These compounds are Cs(4)[(UO(2))(8)(HPO(4))(5)(HPO(3))(5)]·4H(2)O (1), Cs[U(IV)(PO(4))(H(1.5)PO(4))](2) (2), Cs(4)[U(IV)(6)(PO(4))(8)(HPO(4))(HPO(3))] (3), Cs(10)[U(IV)(10)(PO(4))(4)(HPO(4))(14)(HPO(3))(5)]·H(2)O (4), and Cs(3)[U(IV)(4)(PO(4))(3)(HPO(4))(5)] (5). The first contains uranium(VI) and the latter four uranium(IV). Of the U(IV) structures, two have extensive disordering among the cesium cation positions, one of which also contains disordering at some of the phosphate-phosphite positions. These intermediate compounds are bookended by nondisordered phases. The isolation of these transitional phases occurred at the higher of the pH conditions attempted here. Both the starting pH and the duration of the reactions have a strong influence on the products formed. Herein, we explore the second series of in situ hydrothermal redox reactions of uranyl nitrate with phosphorous acid and cesium carbonate. The isolation of these disordered crystalline products helps to illuminate the complex reaction pathways that can occur in hydrothermal syntheses.

Crystal growth, structural characterization, cation–cation interaction classification, and optical properties of uranium(vi) containing oxychlorides, A4U5O16Cl2 (A = K, Rb), Cs5U7O22Cl3, and AUO3Cl (A = Rb, Cs)

“…In recent years, several research groups have focused on elucidating the chemical and structural complexities that uranium can adopt. As a result of their efforts, single crystals of many new compounds, including hybrid materials, 1 nitrite complexes, 2 phosphates, 3 borates, 4 oxychlorides, 5 and silicates 6 have been grown and structurally characterized.…”

Effects of ionic liquid media on the cation selectivity of uranyl structural units in five new compounds produced using the ionothermal technique

“…Each compound contains the same tetrameric group of uranyl polyhedra but contain selenite, phosphite, and phosphonate bridging ligands. [32][33][34] The selenite and phosphite compounds contain Cs + cations and interstitial water molecules, whereas the third compound contains phosphonate rings in the interlayer complex. The large BMIM cations in compound 2 presumably provide enough hydrogen bonding sites to stabilize this structural unit.…”

Structural Variations in Complex Sodium Thorium Arsenates

“…The structural chemistry of actinides is very rich due to the complex electronic structure of these elements and consequent variety of oxidation states and diversity of the actinide coordination geometries. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Thorium, whose redox chemistry, unlike most other actinides, is dominated by the +4 oxidation state, shows highly variable coordination numbers (CN) in inorganic materials ranging from 6 to 15. [17][18][19][20][21][22] Coordination chemistry of Th(IV) is similar to those of highly radiotoxic and long-live transuranic element in the oxidation state +4 (e.g.…”