pubs.acs.org/IC Published on Web 06/17/2010 r 2010 American Chemical Society 6484 Inorg. Chem. 2010, 49, 6484–6494 DOI: 10.1021/ic100170t Competitive Complexation of Nitrates and Chlorides to Uranyl in a Room Temperature Ionic Liquid C. Gaillard,* ,† A. Chaumont, ‡ I. Billard, § C. Hennig, || A. Ouadi, § S. Georg, § and G. Wipff* ,‡ † Institut de Physique Nucl  eaire de Lyon, CNRS-IN2P3, 4 rue Enrico Fermi, 69622 Villeurbanne cedex, France, ‡ Laboratoire MSM, UMR 7177, Institut de Chimie, 4 rue B. Pascal, 67000 Strasbourg, France, § Institut Pluridisciplinaire Hubert Curien, DRS, Chimie Nucl  eaire, 23 rue du L!ss, 67037 Strasbourg cedex 2, France, and || Institute of Radiochemistry, Forschungszentrum Dresden-Rossendorf, P.O. Box 510119, 01314 Dresden, Germany Received January 28, 2010 By coupling EXAFS, UV-vis spectroscopy, and molecular dynamics and quantum mechanical calculations, we studied the competitive complexation of uranyl cations with nitrate and chloride ions in a water immiscible ionic liquid (IL),C 4 mimTf 2 N (C 4 mim þ : 1-butyl-3-methyl-imidazolium; Tf 2 N - = (CF 3 SO 2 ) 2 N) - : bis(trifluoromethylsulfonyl)imide). Both nitrate and chloride are stronger ligands for uranyl than the IL Tf 2 N - or triflate anions and when those anions are simultaneously present, neither the limiting complex UO 2 (NO 3 ) 3 - nor UO 2 Cl 4 2- alone could be observed. At a U/NO 3 / Cl ratio of 1/2/2, the dominant species is likely UO 2 Cl(NO 3 ) 2 - . When chloride is in excess over uranyl with different nitrate concentrations (U/NO 3 /Cl ratio of 1/2/6, 1/4/4, and 1/12/4) the solution contains a mixture of UO 2 Cl 4 2- and UO 2 Cl 3 (NO 3 ) 2- species. Furthermore, it is shown that the experimental protocol for introducing these anions to the solution (either as uranyl counterion, as added salt, or as IL component) influences the UV-vis spectra, pointing to the formation of different kinetically equilibrated complexes in the IL. Introduction Room temperature ionic liquids (ILs) are composed of an anionic and a cationic part that both influence their physi- cochemical properties like viscosity, hygroscopy, miscibility with other solvents, and electrochemical behavior. It should thus be possible to tune the physicochemical properties of ILs for a given chemical application. 1-4 Moreover, ILs are easy to handle at room temperature and display environmentally wished characteristics as they are stable under air and water and not volatile. This explains the keen interest in ILs over the past decade in many fields of chemistry. Because of their rather good radiolytic stability, 5-7 ILs emerge as interesting media for nuclear fuel reprocessing, 8 either in replacement of volatile organic solvents for liquid-liquid partitioning of actinides and lanthanides 9-11 or as complexing agents in the case of “task specific ILs” where complexing moieties are grafted on the IL anion or cation. 1,12 It was shown that uranyl chloro complexes formed in those media are the same as in other solvents like acetone or acetonitrile. 13,14 However, considering ILs as only “green” surrogates for organic solvents would be too simplistic as they have an influence on chemical processes. For instance, while Ln (III) lanthanides and An (III) actinides are generally considered as chemical homologues, they behave differently in ILs. 15 Stumpf et al. studied the interactions between Eu (III) , Am (III) , or Cm (III) with azide ions (N 3 - ) in the IL C 4 mimTf 2 N (C 4 mim þ : 1-butyl-3-methyl-imidazolium; Tf 2 N - =(CF 3 SO 2 ) 2 N) - : bis- (trifluoromethylsulfonyl)imide) and observed different kinetics of complexation for Ln (III) and An (III) ions, which *To whom correspondence should be addressed. E-mail: c.gaillard@ipnl. in2p3.fr. (1) Lee, S.-G. Chem. Commun. 2006, 1049. (2) Welton, T. Chem. Rev. 1999, 99, 2071. (3) Davis, J. H.; Fox, P. A. Chem. Commun. 2003, 1209. (4) Dupont, J.; Suarez, P. A. Phys. Chem. Chem. Phys. 2006, 8, 2441. (5) Allen, D.; Baston, G. M.; Bradley, A. E.; Gorman, T.; Haile, A.; Hamblett, I.; Hatter, J. E.; Healey, M. J.; Hodgston, B.; Lewin, R.; Lovell, K. V.; Newton, B.; Pitner, W. R.; Rooney, D. W.; Sanders, D.; Seddon, K. R.; Sims, H. E.; Thied, R. C. Green Chem. 2002, 4, 152. (6) Berthon, L.; Nikitenko, S.; Bisel, I.; Berthon, C.; Faucon, M.; Saucerotte, B.; Zorz, N.; Moisy, P. Dalton Trans. 2006, 2526. (7) Boss e, E.; Berthon, L.; Zorz, N.; Monget, J.; Berthon, C.; Bisel, I.; Legand, S.; Moisy, P. Dalton Trans. 2008, 924. (8) Cocalia, V. A.; Gutowski, K. E.; Rogers, R. D. Coord. Chem. Rev. 2006, 250, 755. (9) Dietz, M. L.; Stepinski, D. C. Talanta 2008, 75, 598. (10) Jensen, M. P.; Neuefeind, J.; Beitz, J. V.; Skanthakumar, S.; Soderholm, L. J. Am. Chem. Soc. 2003, 125(50), 15466. (11) Visser, A. E.; Rogers, R. D. J. Solid State Chem. 2003, 171, 109. (12) Ouadi, A.; Klimchuk, O.; Gaillard, C.; Billard, I. Green Chem. 2007, 9, 1160. (13) Gaillard, C.; Chaumont, A.; Billard, I.; Hennig, C.; Ouadi, A.; Wipff, G. Inorg. Chem. 2007, 46, 4815. (14) Servaes, K.; Hennig, C.; Billard, I.; Gaillard, C.; Binnemans, K.; G€ orller-Wallrand, C.; Van Deun, R. Eur. J. Inorg. Chem. 2007, No. 32, 5120. (15) Stumpf, S.; Billard, I.; Gaillard, C.; Panak, P. J.; Dardenne, K. Radiochim. Acta 2008, 96, 1.