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J. CHEM. SOC. DALTON TRANS. 1990 Determination by Ion Exchange of the Complexation of Europium by a Stibine an Arsine and Perchlorate in Anhydrous Aprotic Organic Solvents Gerard F. Payne,' 0. Lewin Keller jun. and Joseph Halperin Oak Ridge National Laboratory Chemistry Division P.O. Box 2008 Oak Ridge JN 37837 -6375 U.S.A. Wayne C. Wolsey Macalester College St. Paul MN 55705- 7899 U.S.A. It has been shown for the first time that a lanthanide ( Eu3+) can be complexed by a stibine or a neutral arsine. In benzonitrile (PhCN) as the solvent the predominant complexes were (1 ) [Eu( Ph,Sb)J3+ with triphenylstibine at a concentration of 0.003 mol drn-, (2) [EU(P~,A~),(CIO,)]~+ with triphenylarsine at 0.07 mol drn-, and (3) [Eu( Ph,As),(CIO,),] with Ph,As at 0.003 mol drn-,.In pure PhCN neutral and/or negative complexes of Eu3+ with CIO,- were found but in pure dimethyl sulphoxide no complexation was detected. All complexes were determined by an ion-exchange technique employing the macroreticular resin Amberlyst 1 5. Schumann and co-workers ' 7 ' have prepared salts of AsPh,H and AsBu',H with lanthanide-arsenic bonds but complexes of the neutral trialkyl- or triaryl-arsines have not been reported nor have any complexes with monodentate stibines. In a preliminary account of the present work the first complexes of a lanthanide Eu3 + with a monodentate stibine (triphenyl- antimony) and with a neutral arsine (triphenylarsine) were reported. Higher oxidation states of transition metals (such as Ni"') are known to complex arsines better than stibines.In contrast we have found that triphenylantimony (Ph,Sb) complexes more strongly than triphenylarsine (Ph,As) to Eu3 +. Also in general lanthanides prefer oxygen and nitrogen donors to those of arsenic and antimony; but under our experimental conditions Eu3+ prefers Ph3As and Ph3Sb bonding over that of benzo- nitrile (PhCN) or of perchlorate. On the other hand we found Eu3+ does not complex with C104- in dimethyl sulphoxide (Me,SO). This difference in behaviour in the two solvents is not unexpected since Me,SO solvates 6-8 cations more strongly than water whereas PhCN solvates them more weakly. identical to the solution 'outside' the resin.? This assumption is supported by the results of Pfrepper l o on macroporous resins.The tracer employed a mixture of 1 5 2 E ~ (T+ = 13.2 a) and 5 4 E ~ (T+ = 8.55 a) was produced in the Oak Ridge High Flux Isotope Reactor. All experiments were carried out at room temperature under an argon atmosphere with moisture content of less than 10 p.p.m. In all experiments the Ba(ClO,) or CsClO concentration was varied between z 0.03 and M 0.06 mol dm-3. Solutions (750 pl) containing the solvent (PhCN or Me,SO) tracer barium or caesium perchlorate and (where noted) Ph,As or Ph3Sb were first equilibrated by vibrating vigorously with a Thermolyne Maxi Mix for several hours. Then the solutions were shaken in the same manner with a weighed ( z 5 0 mg) amount of Amberlyst 15 resin. For Ba(ClO,) solutions in Me,SO our shaking tests with the resin show the same slope and log D, values for equilibration times of 17 [Figure l(a)] 25 and 45 h.Seventeen hours are therefore sufficient for the europium tracer to reach equilibrium in the resin with Ba(ClO,) as the bulk electrolyte in Me,SO. A similar time was found to be sufficient for CsClO in Me,SO. Checks with the europium tracer us. Ba(C10,) in PhCN solutions showed that a resin equilibration time of 24 h for the complexation studies with Ph,As and Ph3Sb was more than sufficient. After equilibration aliquots of 500 pl of the solution phase were counted. Also the original tube containing the remaining 250 p1 of solution and the equilibrated resin was counted. The counts attributable to the 250 p1 of solution remaining in the original tube with the resin were subtracted from the total to obtain the counts attributable to the Eu3+ actually bound to the sulphonate sites of the macroporous resin itself.All samples were counted on a Hewlett-Packard 500C auto-gamma counter to 1% statistical accuracy. The parameter DEu as calculated from these measurements is defined" as (counts Eu per gram of dry resin)/(counts Eu per cm3 of solution). Experimental Anhydrous PhCN ( > 99% water < 0.005%) Me,SO ( > 99% water <0.005%) Ph,As (9773 Ph,Sb (97%) and Ba(ClO,) (99%) were obtained from Aldrich. Caesium perchlorate (99.9%) was obtained from Alpha. Amberlyst 15 resin in the hydrogen form was supplied by Rohm and Haas. The resin was converted into the caesium form by washing with caesium hydroxide until the washings were alkaline and then with water until the washings were neutral.As a final test for total displacement of the H + ions by Cs+ a solution of caesium chloride was run through the resin. These washings were also neutral. The barium form of the resin was made by washing with a basic solution of the chloride (NH,OH-BaCl,) until the washings were alkaline then with water until neutral. Finally a solution of BaCl was run through the resin to test that all H + ions had been displaced by Ba2+. These washings were also neutral. The barium and caesium forms of the resin were dried in a vacuum at M 50 "C prior to use. Amberlyst 15 is a sulphonic acid-type macroreticular resin. It has a rigid non-swelling styrene4ivinylbenzene structure with a large average pore diameter of 288 A.Because of the large pore size coupled with a rigid network structure we assume in our experimental procedures and calculations that the solution 'inside' the resin is + Results and Discussion Ion Exchange.-Theory. The ion-exchange equilibrium3*' between a bulk displaceable ion A"' and a radioactive tracer t Our model for macroreticular resins differs from the one usually applied to gel-type resins where a non-porous elastic matrix contains the imbibed internal solution in equilibrium with the external solution.* 1993 1994 A m + v W a 0 7 0 d 3 w 0 7 d Figure 1. Exchange of Eu3 + us. Ba2 + in (a) Me2S0 and (6) PhCN + c? 3.20 -1.5 -1.4 Log ICSCL0~1 -1.2 Figure 2.Exchange of Eu3+ us. Cs+ in Me2S0 ion Eu3+ that can form complex ions with n ClO,- ions can be represented by equation (l) where R refers to the resin phase. (3 - n ) A a + ( R ) + a{(E~~+)(C10,-),}(~-")+ U{(EU~+)(C~O,-),)(~-~)+(~) + + (3 - n)A"+ (1) * The line fitted to the data in all plots was obtained by least squares. As a test of the goodness of fit we give in the text the coefficient l 5 of determination R2 for each plot. 2.85 2.75 2.65 2.55 2.45 2.35 -1. 8 -1.6 - 1.4 log I Ba(CIO& 1 3 .OO 2.80 2.60 2.40 2.20 -1.3 2.00 -1.6 1.50 1.40 1.30 J. CHEM. SOC. DALTON TRANS. 1990 For convenience we rewrite equation (1) as (2) where h = 3 - 11 (CBr(cA(R~~I(Y"B(R)ybA/Y.BYbA(R)).and B = ((Eu3+)(C104-),}. From the law of mass action the equilibrium constant for the reaction written in terms of molarities and activity coefficients is KAB = [(cB(R))"(cA)'/ con- ventions we define D B = cB(R)/cB and r A B = (yB(R)/yB)"(yA/ Y A ( R ) ) ~ . Then D'B = KAB(rAB)-l(CA(l())b(CA)-b 1.20 1.10 the or equation (3) can be written if r A B and cA(R) are constants. Since B is present only in trace concentrations the displacement of the bulk ion A from the resin is negligible; so cA(R) is a constant. The question of the constancy of r A B is determined as part of each experiment. Returning to equation (1) and specifying for our work that the slope of log D, us. log cA will be -(3 - n)/a if Eu3+ is present as a tracer the bulk displaceable ion (Cs' or Ba2+) is uncomplexed by perchlorate the applicable activity coefficient ratios r A B are constant and the formula of the europium complex (of positive charge) is the same on the resin and in the solution.1 .oo -1.2 Results. (a) Dimethyl sulphoxide as solvent. Our searches in the literature have located no references using equation (3) to study complexation in anhydrous aprotic organic solutions of electrolytes. It was therefore desirable to test the applicability of equation (3) in a solvent that inhibits complexation of perchlorate before going on to more complicated cases. Since Me2S0 solvates more strongly than water europium is unlikely to complex with perchlorate in it and equation (3) should be easy to test.For our first work then we exchanged Eu3+ with Ba2+ [Figure l(a)] and with Cs+ (Figure 2) in Me2S0 as the solvent. We found as expected that equation (3) was applicable.* The plot of log D, us. log [Ba2'] [Figure l(a)] gave a slope of - 1.49 (- 3/2) with an R2 of 0.9986 and us. log [Cs' 3 (Figure 2) gave a slope of - 2.95 ( - 3) (R2 = 0.9984) the values expected from equation (3) for an uncomplexed Eu3 + ion. The ideality of these results might be considered unexpected. For example a 'constant ionic medium' is commonly used in studies of complexation in aqueous solutions in an attempt to keep the activity coefficients of the reacting ions constant. This technique requires a constant concentration of a bulk electrolyte whose concentration is high relative to the reacting ions (whose concentrations vary).Even in aqueous solutions the use of a constant ionic medium is difficult for ion-exchange studies. ' ' The 'constant ionic medium' technique is in general not applicable to electrolyte solutions in aprotic organic solvents because of solubility limitations. Fortunately in our work there was no need for it because in the exchange of Eu3 + us. Ba2 + and Cs+ in Me2S0 the slopes [Figures l(a) and 21 are unaffected by from the 2+ to the 1 + ion as the bulk displaceable electrolyte. the large changes in ionic strength associated with switching The activity coefficient ratios r A B are constant. Otherwise the results expected theoretically from equation (3) could not appear in both plots.It is interesting to speculate that this experimentally determined constancy of r AB may be connected with the stronger solvation of cations in Me2S0 than in water.6 Also Me2S0 is larger than the H 2 0 molecule. Thus electrostatic interactions between the Eu3+ and C104- ions could be smaller and less variable than in water even though the bulk dielectric constant of Me2S0 is not as large. These results showing no complexation of Eu3 + with perchlorate are encouraging for the use of Me2S0 as an aprotic solvent in searching for new oxidation states of elements available only in trace quantities such as the heavy actinides and light transactinides.I6 1.95 - 1.85 - - h + m 1.75 1 .65 - 3 v W 4 - 1.55 - 1.45 I 1.35 1.25 1.15 1.05 0 (r h 3 v W a m c; 0 0.95 0.85 0.75 -1.6 -1.5 Figure 4.Exchange of Eu3+ us. Ba2+ in benzonitrile with triphenyl- arsine added to a concentration of (a) 0.07 and (b) 0.003 rnol dm-3 log I Ba(C10J2 1 (6) Triphenylantimony and triphenylarsenic in PhCN as solvent. We next studied the bonding of Ph,Sb and Ph3As to Eu3+. The basic idea was to use PhCN a solvent in which Eu3+ would complex with some number n of perchlorate ions to give a complex of charge 3 - n where the charge might be positive neutral or negative. Then through the addition of Ph3Sb and Ph3As to the PhCN solvent the C104- ions could be displaced with these neutral molecules thus changing n and the charge.The changes in charge would be detected by ion exchange using equation (3). The choice of PhCN as the solvent for these experiments was based on spectroscopic evidence that Eu3 + forms inner-sphere complexes with C104- ions in aceto- 1995 nitrile,".'* (MeCN) but not l 9 in Me2S0. We also made use of the order of cation solvation developed by Parker from a survey of thermodynamic and kinetic studies of electrolyte solutions in a number of solvents. In Parker's list the strength of solvation decreases from Me2S0 (highest) to water (about 1/3 down) to MeCN > PhCN (next to lowest). Since MeCN allows complexation of C104- with Eu3+ the similar PhCN will also. We chose PhCN over MeCN as a solvent for C10 - complexation because its high boiling point makes the experiments more precise and convenient to carry out.I I J -1.2 -1.4 -1.3 Bonding of triphenylantimony and triphenylarsenic to Eu3+. On the basis of Parker's survey,6 as noted above we know that C104- ions will bond to Eu3+ in pure MeCN and therefore in pure PhCN. But as seen in Figure 3 a slope of - 1.53 (- 3/2) (R2 = 0.9986) was obtained for log D, us. log[Ba2 '3 in a 0.003 mol dm-3 solution of Ph3Sb in PhCN. In this solvent as in Me,SO the slope indicates the full 3 + charge of Eu3+ so no ClO,- ions are bound to it. The Ph,Sb must have displaced all of the ClO,- ions and be bound to the Eu3+ in their places. We therefore propose that the predominant ion in this medium is [ E U ( P ~ S ~ ) ~ ] ~ + . This explanation is confirmed by the results of experiments using PhCN solutions of two different concentra- tions of Ph,As instead of Ph3Sb.The Ph3As bonds less strongly than the stibine so it is not able to displace all of the ClO,- ions from the Eu3+ and a charge different from 3 + is left on the complex ion. This effect is seen in Figure 4(a) where the slope for the exchange of europium us. Ba2 + in a 0.07 mol dm- Ph3As solution in PhCN is - 0.92 ( z - 2/2) (R2 = 0.9984). The slope of close to - 1 shows that the Eu3 + complexes with about one predominantly a complex of charge 2 + . We propose that the perchlorate ion on the average in this solvent to give predominant ion in this medium is [E~(P~,As),(C~O,)]~ +. The correctness of the interpretation that Ph3As is bonding in preference to C104- was confirmed by reducing the Ph,As concentration to 0.003 mol dm-3.The slope for the exchange of europium vs. Ba2+ [Figure 4(b)] is reduced in this medium to -0.55 (x -1/2) (R2 = 0.9994). The lower concentration of Ph,As allows two rather than one C104- ion to be retained on the Eu3 + to give predominantly a complex of total charge 1 + . We propose in this medium that the predominant complex is [Eu(Ph3As)x(C104)21+. The above explanation interprets the changes in slope as reflecting changes in the charge of europium complex ions as Ph,As and Ph,Sb displace C104- ions from the Eu3+ central changes in the activity coefficient ratio rAB and (2) changes of ion. Possible interferences with this explanation could be (1) the charge on the Ba2+ bulk displaceable ion through complexation with C104-.Changes in activity coefficients cannot be causing the changes in slope from one experiment to another (Figures 3 and 4) because the solutions only differ by the addition in low concentration of the molecular reagents Ph,As and Ph3Sb which cannot significantly alter either the ionic strength or the bulk dielectric constant of the system. Thus if any activity coefficient changes occur due to the varying concentration of Ba(ClO,) in the plots of Figures 3 and 4 they are the same in all experiments and the variations in the observed slopes cannot arise from this source. Also it is known that the alkali and alkaline-earth metals do not complex with arsines and stibines.20 In the experiments in 0.003 mol dm-3 Ph,Sb in PhCN the slope is -3/2 showing that neither the europium nor the barium ions are complexing with C104- ions.(It would be fortuitous indeed to have both the europium and barium complex with ClO,- in just the right amounts to give the theoretical slope for the bare ions.) Since the arsines and stibines have no effect on the Ba2+ the fact that barium is not complexed by ClO,- in 0.003 mol dm- Ph,Sb means that it is not complexed by C104- in any of the above experiments in PhCN and thus retains a charge of 2+ throughout. These with several resins including Nafion 1 1 7.26 1996 explanations demonstrate that ion-exchange techniques have a high enough resolution to show unequivocally that Eu3+ bonds with the arsine and the stibine.On the other hand the resolution may not be high enough to determine all the species that are present. In two of the three cases we have proposed simplistically that the Eu3+ was present predominantly in a species indicated by a theoretical slope that is near but is not exactly equal to the experimental one. In reality the solutions may be more complicated. Other species possibly present in lesser amounts can be sought by spectroscopic methods capable of supplying greater detail than ion exchange such as those applied by Bunzli and co-workers.' 7,1 Unlike ion-exchange such methods cannot in general be applied at the few atoms level required in certain areas of interest such as transeinsteinium chemistry. (c) Benzonitrile as the solvent.We also carried out exchange of europium us. Ba2+ in pure PhCN. The complexation number n of C104- with europium should equal at least two in the pure solvent since that is the value achieved with 0.003 mol dm-3 Ph3As present. Additional C104- ions could bind to the Eu3+ in pure PhCN however yielding neutral or even negatively charged complexes. The results of the ion exchange of europium us. barium perchlorate in pure PhCN are given in Figure l(b). Although the least-squares fit is not good (R2 = 0.7240) the slope of near zero makes it tempting to suggest that the europium is complexed by nearly three C104 - ions3 giving a nearly neutral complex. This interpretation based on the idea that europium is exchanging with barium according to equation (l) does not appear to be correct however because the distribution coefficient is around 200 (over 90% of the europium went into the resin).Since the exchange of europium complexes with a positive charge us. barium results in much lower distribution coefficients (of around 8-80) we must look to a mechanism other than ion exchange to explain the presence of europium in the resin. This mechanism can be seen in a discovery made by Kraus et aL2 Work of Kraus et leads us to the conclusion that in pure PhCN neutral and/or negatively charged complex ions of europium with perchlorate are invading the Amberlyst 15 ion exchanger by interacting with the organic network of the resin. In aqueous solutions using a gel type strongly acidic cation- exchange resin with a polystyrene4ivinylbenzene network (Dowex-50) Kraus et aL2' found that anionic complexes of Au"' Fe"' and Ga"' had distribution coefficients of approximately lo2 in HCl solutions and approximately lo5 in LiCl solutions.They explained these large distribution coefficients for the seeming exchange of anions into a cation exchanger as actually arising from interactions of the anions with the organic network of the ion exchanger leading to their invasion. Their interpretation was subsequently proven in extensive studies by Pfrepper'0.z2.23 who used several different ion exchangers including macroporous polystyrene- divinylbenzene-based resins without functional groups. The discovery of anion invasion into cation exchangers by Kraus et al.has been employed over the years in a number of practical Since anions can invade the polystyrene-divinylbenzene J. CHEM. SOC. DALTON TRANS. 1990 matrix of cation exchangers in aqueous electrolyte solutions it is even more likely that neutral and anionic species can invade in organic electrolyte solutions. The correspondence between our results [Figure 1(6)] and those of Kraus suggests strongly that neutral and/or anionic complexes of europium with perchlorate that are present in the PhCN-Ba(C104)2 solutions invade the organic network of the Amberlyst 15 to give a distribution coefficient of around 200. We therefore propose that the principal species present are [Eu(CIO,),]~ -" where n 2 3. Acknowledgements The authors thank Drs.R. E. Mesmer and J. S. Johnson for helpful discussions during the course of this work. This research was sponsored by the Division of Chemical Sciences Office of Basic Energy Sciences U.S. Department of Energy under contract DE-AC05-840R21400 with Martin Marietta Energy Systems Inc. 1 H. Schumann E. Palamidis J. Loebel and J. Pickardt References Organometallics 1988,7 1008. 2 H. Schumann and G-M. Frisch Z. Narurforsch. Teil B 1982,37 168. 3 G. F. Payne 0. L. Keller J. Halperin and W. C. Wolsey J. Chem. Soc. Chem. Commun. 1989,50. 4 W. Levason and C. A. McAuliffe Ace. Chem. Res. 1978,11,363. 5 C. A. McAuliffe and W. Levason 'Studies in Inorganic Chemistry,' Elsevier Amsterdam 1979 vol. 1 p. 72. 6 A. J. Parker Q. Rev. 1962,16 163.7 C. A. Fleming and A. J. Monhemius Hydrometallurgy 1979,4 159. 8 A. M. Phipps Anal. Chem. 1968,40,1769. 9 R. Kunin E. Meitzner and N. Bortnick J. Am. Chem. Soc. 1962,84 Received 13th September 1989; Paper 9/03921J 305. 10 G. Pfrepper Z. Chem. 1973,13,67. 11 Y. Marcus and A. S. Kertes 'Ion Exchange and Solvent Extraction of 12 V. S. Mlinko and T. Schonfeld Radiochim. Acta 1965,4,6. 13 K. A. Kraus in 'Trace Analysis,' eds. J. H. Yoe and H. J. Koch jun. 14 H. H. Cady and R. E. Connick J. Am. Chem. Soc. 1958,80,2646. 15 S. Dowdy and S. Wearden 'Statistics for Research,' Wiley New Metal Complexes,' Wiley-Interscience London 1969. Wiley New York 1957 p. 34. York 1983. 16 0. L. Keller Radiochim. Acta 1984,37 169. 17 J-C. G. Bunzli J-R. Yersin and C. Mabillard Inorg. Chem. 1982,21 1471. 18 J-C. G. Bunzli and C. Mabillard Znorg. Chem. 1986,25,2750. 19 J-C. G. Bunzli C. Mabillard and J-R. Yersin Inorg. Chem. 1982,21 42 14. 20 W. Levason and C. A. McAuliffe Coord. Chem. Rev. 1976,19 173. 21 K. A. Kraus D. C. Michelson and F. Nelson J. Am. Chem. SOC. 1959,81,3204. 22 G. Pfrepper and L. T. Chi J. Chromatogr. 1969,44,594. 23 G. Pfrepper J. Chromatogr. 1975,110,133. 24 F. E. Beamish Talanta 1967,14,991. 25 N. De Brucker K. Strijckmans and C. Vandecasteele Anal. Chim. Acta 1987 195 323. 26 T. Xue and K. Osseo-Asare Sep. Sci. Technol. 1988,23,1825.

ISSN:1477-9226    

DOI:10.1039/DT9900001993

出版商:RSC    

年代:1990

数据来源: RSC