Complex peroxyuranates. Synthesis and structural assessment of alkali dioxoxperoxy(sulfato)aquouranates(VI), A₂[UO₂(O₂)SO₄(H₂O)] (A = NH₄, Na), and alkali dioxoperoxy(oxalato)uranate(VI) hydrates, A₂[UO₂(O₂)C₂O₄].H₂O

Abstract

Yellow microcrystalline alkali-metal and ammonium dioxoperoxy(sulfato)aquouranates(VI), A₂(UO₂(O₂)SO ₄(H₂O)) (A = NH₄, Na), and alkali-metal and ammonium dioxoperoxy(oxalato)uranate(VI) hydrates, A₂UO ₂(O₂)C₂O).H₂O (A = NH₄, Na, K), have been synthesized from the reaction of the product obtained by treating an aqueous solution of UO₂(NO₃)₂.6H₂O with alkali-metal or ammonium hydroxide, AOH, with 30% H₂O₂ and aqueous sulfuric acid and oxalic acid solution, respectively, in the mole ratio UO₂(NO₃)₂.6H₂O:H₂O₂:SO₄^{2 -} or C₂O₄^2- of 1:111:5 or 1, at pH 6 maintained by the addition of the corresponding alkali-metal or ammonium hydroxide. Precipitation was completed by the addition of ethanol. IR and laser Raman spectra suggest that the O₂^{2 -} and SO₄^{2 -} ions in (UO₂(O₂)SO₄(H₂O))^2- are bonded to the UO₂^{2 +} center in a bridging and in a monodentate manner, respectively, while both the O₂^{2 -} and C₂O₄^{2 -} ions in (UO₂(O₂)C₂O) ^{2 -} bind the uranyl center in bidentate chelated fashion. The complex peroxyuranates are diamagnetic and insoluble. The A₂(UO₂(O₂)SO₄(H₂O)) compounds, unlike A₂(UO₂(O₂)C₂O₄).H₂O, are stable up to 110°C. Whereas H₂O in A₂(UO(O₂SO₄(H₂O)) is coordinated to the UO₂²⁺ center, it occurs as a water of crystallization in the corresponding peroxy oxalato compounds.