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Speciation of Uranyl Nitrato Complexes in Acetonitrile and in the Ionic Liquid 1‐Butyl‐3‐methylimidazolium Bis(trifluoromethylsulfonyl)imide
Author(s) -
Servaes Kelly,
Hennig Christoph,
Billard Isabelle,
Gaillard Clotilde,
Binnemans Koen,
GörllerWalrand Christiane,
Van Deun Rik
Publication year - 2007
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200700475
Subject(s) - uranyl , chemistry , ionic liquid , extended x ray absorption fine structure , acetonitrile , inorganic chemistry , uranyl nitrate , aqueous solution , ion , absorption spectroscopy , uranium , crystallography , organic chemistry , physics , materials science , quantum mechanics , metallurgy , catalysis
Complex formation between the uranyl ion and nitrate ions in acetonitrile and the ionic liquid 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([C 4 mim][Tf 2 N]) has been studied by absorption, magnetic circular dichroism (MCD) and uranium L III EXAFS spectroscopy. The experimental results point to the existence of a trinitrate species [UO 2 (NO 3 ) 3 ] – with D 3 h symmetry in both solvents. The atomic distances in the uranium(VI) coordination sphere for the trinitrato complex in acetonitrile are U–O ax = 1.77 ± 0.01 Å and U–O eq = 2.48 ± 0.01 Å. EXAFS data show that the uranyl ion in the ionic liquid is surrounded by six oxygen atoms in the equatorial plane at a distance of 2.49 ± 0.01 Å. The U–N distance of 2.92 ± 0.01 Å indicates a bidentate coordination of the nitrate group in both solvents. A structural comparison is made between the uranyl trinitrato complex anion [UO 2 (NO 3 ) 3 ] – and the uranyl tricarbonato complex anion [UO 2 (CO 3 ) 3 ] 4– . No evidence is found for the presence of uranyl nitrato complexes in aqueous solution. The optical absorption, MCD and EXAFS spectra resemble those of the hydrated free uranyl ion. There are two axial oxygen atoms at 1.77 ± 0.01 Å and five equatorial oxygen atoms at 2.41 ± 0.01 Å. These values agree well with structural parameters obtained for the uranyl aqua ion.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)