1766 Inougan?'cC'hemistry, Vol. 9,No. 7, 1970
H. A. S w ~ r r ;J,R . .
AND
D. G.KARKAKER
and the same mechanism has been suggested for NilThe specific rates of reaction of eaQ- l 3 and Cd'EDTA (aq) and Cd1(aq).6 It is. therefore, suggested that the with NOS- are higher than those with NO*-, whereas the specific rates of reaction of H atoms,I3 Cd'(aq),j relative reactivities toirard KO3- and KOs- might be and Ni1(aqj5 with NOs- are higher than those with used as one of the guides for determining the mechanism of reduction by strong reducing agents. NOa-. The hydrated electrons are expected to be outer-sphere reducing agents, and a similar niechanisni has been suggested for Cd'EDTA. Hydrogen atoms Acknowledgments.-The authors wish to acknowlare most likely an inner-sphere reducing a g e r ~ t , ~ > l ~ - l ~ edge Dr 11 S Matheson, Professor AI Xnbar, and (13) M. Anabar and P. S e t a , 1n2. J . ApBZ. R a d i a t . i s d o p e s . 18, 483 Dr hl Faraggi for stimulating discussions lye wish (1967). (14) G . h-avon and G . S t e i n , J . P h y s . C h e n . , 69, 1391 (1965) to thank the Linac group for their careful operation and (15) M . Anbar and 11. Meyerstein, Suture, 206, 818 (196;). AIr S Petrek for maintaining the electronic equipment. 116) J. Halpern and J. Rabani, J . A m e r . Chrm. Soc., 88, 699 1966)
E.I.DE PosT
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CONTRIHCTION F R O % THE S A V A X N A H KIVERLAl3ORA'rORY, SEMOURS ASD COMPAXY, AIKEN,SOUTH CAROLINA29807
Volatile Chelates of Quadrivalent Actinides1 BY H. -4, SIVAIS,
J R , , ~A N D
D. G. KXRRAKER
ReLeived November 25, 1969 Tetrakis ,B-diketonateswere synthesized with quadrivalent thorium, uranium, neptunium, arid plutoniuni and 1,1,1,2,2,3,3heptafluoro-7,7-dimethploctane-4,6-dione (fod) and with T h 4 +and U 4 +and ',_",6,6-tetramethylheptane-3,j-dione (thd) and then characterized by elemental analysis. X-Raydiffraction data showed Th(Eod),,U(fod)4,and Xp(fod)4 were isomorphous, mm but Pu(fod)r had a different structure. T'apor pressures measured by a modified Knudsen effusion method mere ca. at 125' for all fod chelates and at 195' for both thd chelates. A H k u ~ ,increased l from 33.1 kcal/mol for Th(fod)r to 36.4 kcal/mol for Pu(fod)d. A.S~,I,I values increased nearly linearly with 2 for Th4+,G4+, and Xp*+ focl chelates; the value for A S a u ~for i Pu(fod)iwas larger than the value predicted by a linear increase with 2,probably because of the different crystal structure of Pu(fod)a.
Introduction nates of U 4 + and obtained some measure of their volatility. I n general, the substitution of fluorine for Lanthanide chelates of the sterically hindered phydrogen (-CF3 for -CHj) and replacement of nordiketones 2,2,6,6-tetra1nethylheptane-3,5-dione (thd)3 mal alkyl groups with branched alkyl groups increased 1,lj1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6and volatility. However, the most volatile of these chelates, dione ( f ~ d have ) ~ sufficient volatility to permit gas was too unstable for any pracU(CF3COCHCOCF3)4, chromatographic separation of the chelates of adjacent tical use. The greater shielding of the M4+ions by the Some lanthanide ions have been lanthanides. 3 , 4 bulky thd and fod ligands ofl'ers the possibility for both separated by fractional sublimation of Ln(thd)a cheincreased volatility and stability toward oxidation. lates. The possibility of similar separations of actinides led to the study reported in this paper. In this study, Experimental Section Th(thdj4,U(thdj4,and M(fodj4 (A1 = Th, U, Np, Pu) M(thdj4.-Th(thdjt and U(thd)r mere prepared" by mixing were prepared, and their vapor pressures and some ethanol-water solutions of the XaOH-neutralized p-diketonate other physical properties were determined. The prepand thorium nitrate or [ (CnHi)sS]2UCls.8 The chelates precipitated immediately upon mixing the solutions and were purified by aration and study of the spectra of the fod chelates of recrystallization from petroleum ether (bp 20-40') and vacuum T h 4 + and U 4 + were reportedj while this paper was in sublimation. Alnalyticaldata are given in Table I. preparation. Aittemptsto synthesize Xp(thd)4 and Pu(thd)A by the same Previous worker^^,^ have prepared over 30 B-diketoprocedure yielded products that were probably mixtures of (1) T h e information contained in this article was developed during t h e course of work under Contract AT(Oi-2)-1 with t h e U. S. Atomic Energy Commission. ( 2 ) O R A U Research Participant a t the Savannah River Laboratory, 1 8 6 i 1968. ( 3 ) K . J . Bisentl-aut and I
