EXAFS Study of Uranyl Nitrate Dimer at High and Low Temperature

Abstract

A uranium EXAFS study of the uranyl nitrate dimer [{UO2(μ-OH)(NO3)2}2]2- at 10 and 294 K is described. Low-temperature data readily reveal the presence of the second uranium atom in the complex as well as distinguishing characteristics associated with the equatorial nitrate and bridging hydroxide groups. Observation and analysis of these critical components in EXAFS data collected at room temperature are much more difficult.

Coordination Structures of the Uranyl(VI)–Diamide Complexes: A Combined Mass Spectrometric, EXAFS Spectroscopic, and Theoretical Study

“…The experimental U–O yl (1.76/1.77 Å) and U–O carbonyl distances (2.40–2.41 Å) are consistent with those in the crystal structures of some uranyl–diamide compounds (U–O yl : 1.74–1.78 Å; U–O carbonyl : 2.36–2.40 Å). − It should be noted that the coordination mode of TMGA in the UO 2 (TMGA) 2 2+ complex is quite different from that of TBGA ( N , N , N ′, N ′-tetrabutyl­glutaramide) or TEGA ( N , N , N ′, N ′-tetraethyl­glutaramide) in the UO 2 2+ –TBGA and UO 2 2+ –TEGA crystals where two uranium atoms are bridged by two O carbonyl atoms of either TBGA or TEGA ligand. The EXAFS fitting (Figure 6 ) shows there is no peak around 4 Å which would arise from dimeric uranium species, , suggesting the amount of UO 2 2+ complexes with bridging TMGA ligands is negligible in the solution of UO 2 Cl 2 and TMGA. This is also consistent with the absence of dimeric UO 2 2+ –TMGA complexes in the ESI experiment, although the ESI results are not always valid for inferring solution speciation. , Different from the TMGA and TMTDA cases, both TMPDA and TMOGA ligands are coordinated to UO 2 2+ in tridentate fashions, which are the same as the coordination modes of similar ligands in the UO 2 2+ complexes in solutions and crystals. − , The U–O carbonyl (2.42–2.43 Å), U–O ether (2.64 Å), and U–N pyridine (2.66 Å) distances are within the range of those in the solid state (U–O carbonyl : 2.38–2.42 Å; U–O ether : 2.61 Å; U–N pyridine : 2.64 Å). − …”

Speciation of Uranyl Nitrato Complexes in Acetonitrile and in the Ionic Liquid 1‐Butyl‐3‐methylimidazolium Bis(trifluoromethylsulfonyl)imide

“…Extended X-ray absorption fine structure (EXAFS) spectroscopy measurements on uranyl nitrato compounds are rather scarce, although Thompson and co-workers have investigated the uranyl trinitrato unit in solid UO 2 (NO 3 ) 2 · 6H 2 O, [10] and the uranyl nitrate dimer in solid Him 2 [{UO 2 (µ-OH)(NO 3 ) 2 } 2 ] (Him = imidazolium) has been studied by Barnes et al [11] Solvent-extraction processes of uranyl nitrate solutions have been extensively studied because of their significance for nuclear waste treatment. [12][13][14][15][16][17][18][19][20][21] These research activities include EXAFS measurements of uranyl nitrate in trimethyl phosphate, tri-nbutyl phosphate, triisobutyl phosphate and triphenyl phosphate, which indicate a coordination of two bidentate nitrate groups and two monodentate organophosphate ligands.…”

Cation extraction by 18-crown-6 to a room-temperature ionic liquid: The effect of solvent humidity investigated by molecular dynamics simulations

“…lanthanides, uranyl cations) in the context on nuclear waste partitioning. [6][7][8][9] The low volatility and non-flammability of the ILs makes them promising alternatives over traditional ion separation techniques, provided that they are chemically stable enough. 10 Little is known about the microscopic structure of these ILs and on their solvation properties which are presumably determined by the active role of the solvent ions, by solvent impurities and by the water content of the solvent.…”