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

Abstract

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.

CrVI→CrV Transition in Uranyl Chromium Compounds: Synthesis and High‐temperature X‐ray Diffraction Study of Cs2[(UO2)2(CrO4)3]

“…Both K 2 Cr 2 6+ O 7 and K 2 Cr 6+ O 4 are known to be used in various stages8,9 of nuclear fuel cycle and, in general, chromium is considered as one of the significant SNF constituents 10. Whereas there are many Cr 6+ uranyl compounds known,11–16 there are quite a few inorganic compounds of pentavalent chromium17–19 and some of them attract attention due to their possible applications 20,21. In all uranyl compounds known to date, Cr 5+ shows tetragonal pyramidal coordination,22–24 which may be stabilized in the solid state by bonding requirements of hexavalent uranium.…”

Isolated Uranyl Chromate and Polychromate Units in Crown Ether Templated Compounds

“…The [UO 2 (SO 4 ) 3 ] unit [17] with a ratio of 1:3 is the only example with exclusive bidentate edge sharing between a UO 8 hexagonal bipyramid and a SO 4 tetrahedra. A similar procedure was used previously but with small organic molecules, and it resulted in a number of new structural architectures of amine-templated [19] and also pure inorganic [20] uranyl chromates. [18] Herein, we report on the syntheses, structures, and properties of two new uranyl chromate compounds, [18crown-6] (2), obtained at room temperature from the 18-crown-6/15-crown-5-CrO 3 -(UO 2 )(NO 3 ) 2 systems by solvent evaporation from aqueous solutions.…”

Novel [(UO 2 )O 6 (NO 3 ) n ] ( n = 1, 2) based units in organically templated uranyl compounds

“…based on the structural architectures consisting of weakly bonded inorganic and organic substructures [8]. Recently we've reported a number of uranyl-chromates with amine molecules used as templates [9][10][11][12][13]. Investigation and understanding of preferable (UO 2 ) 2+ coordination environments in different chemical systems are very important for the selective complexation and separation of this ion from acid media.…”