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.

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