The Role of Acidity in the Synthesis of Novel Uranyl Selenate and Selenite Compounds and Their Structures

Abstract

Herein, the novel uranyl selenate and selenite compounds Rb2[(UO2)2(SeO4)3], Rb2[(UO2)3(SeO3)2O2], Rb2[UO2(SeO4)2(H2O)]·2H2O, and (UO2)2(HSeO3)2(H2SeO3)2Se2O5 have been synthesized using either slow evaporation or hydrothermal methods under acidic conditions and their structures were refined using single crystal X-ray diffraction. Rb2[(UO2)2(SeO4)3] synthesized hydrothermally adopts a layered 2D tetragonal structure in space group P42/ncm with a = 9.8312(4) Å, c = 15.4924(9) Å, and V = 1497.38(15) Å, where it consists of UO7 polyhedra coordinated via SeO4 units to create units UO2(SeO4)58− moieties which interlink to create layers in which Rb+ cations reside in the interspace. Rb2[(UO2)3(SeO3)2O2] synthesized hydrothermally adopts a layered 2D triclinic structure in space group P1¯ with a = 7.0116(6) Å, b = 7.0646(6) Å, c = 8.1793(7) Å, α = 103.318(7)°, β = 105.968(7)°, γ = 100.642(7)° and V = 365.48(6) Å3, where it consists of edge sharing UO7, UO8 and SeO3 polyhedra that form [(UO2)3(SeO3)2O2] layers in which Rb+ cations are found in the interlayer space. Rb2[UO2(SeO4)2(H2O)]·2H2O synthesized hydrothermally adopts a chain 1D orthorhombic structure in space group Pmn21 with a = 13.041(3) Å, b = 8.579(2) Å, c = 11.583(2) Å, and V = 1295.9(5) Å3, consisting of UO7 polyhedra that corner share with one H2O and four SeO42− ligands, creating infinite chains. (UO2)2(HSeO3)2(H2SeO3)2Se2O5 synthesized under slow evaporation conditions adopts a 0D orthorhombic structure in space group Cmc21 with a = 28.4752(12) Å, b = 6.3410(3) Å, c = 10.8575(6) Å, and V = 1960.45(16) Å3, consisting of discrete rings of [(UO2)2(HSeO3)2(H2SeO3)2Se2O5]2. (UO2)2(HSeO3)2(H2SeO3)2Se2O5 is apparently only the second example of a uranyl diselenite compound to be reported. A combination of single crystal X-ray diffraction and bond valance sums calculations are used to characterise all samples obtained in this investigation. The structures uncovered in this investigation are discussed together with the broader family of uranyl selenates and selenites, particularly in the context of the role acidity plays during synthesis in coercing specific structure, functional group, and topology formations.

Advances and perspectives of actinide chemistry fromex situhigh pressure and high temperature chemical studies

“…[101][102][103] Similarly for uranium, compounds of iodate, phosphate, tungstate and selenate/selenite among others have not been reported under HT/ HP conditions, despite considerable general interest. [104][105][106][107] In the case of transuranium compounds, there are yet to be any reports of compounds from HP/HT conditions. Although, the works of Albrecht-Schönzart and co-workers have hinted at the unique bonding characteristics of transuranium compounds under pressure, unfortunately there appears to be no laboratories operating that are equipped for HP/HT experimentation with transuranium elements at this time.…”

Exploring the Valence Diversity of Uranium by Flux Growth of Uranium Silicate under Inert Atmosphere

“…Traditional glass and cementitious waste forms have been intensively studied but potentially suffer from problems of nuclide leakage and dissolution. − The necessity for the exploration of new storage media with superior physicochemical properties prompts more intensive study on new actinide-containing solid-state compounds. Crystalline actinide materials emerge as one potential storage media due to their improved water stability and load capacity as compared to glasses and cements , and of significant interest are those that can accommodate more other nonactinide nuclides from spent nuclear fuel (SNF), like the alkali metal cesium ion, which serves as one of the most representative fission products.…”