Scientific paper
Application of 4,4,4-Trifluoro-1-(Biphenyl-4-yl)Butane-1,3-Dione as a Chelating Extractant in the Solvent Extraction and Separation of Light Lanthanoids in Combination
with Phosphine Oxides
Maria Atanassova,1* Stefka Kaloyanova2 and Todor Deligeorgiev2
1 University of Chemical Technology and Metallurgy, Department of General and Inorganic Chemistry,
8 Kliment Ohridski blvd.1756 Sofia, Bulgaria
2 University of Sofia, Faculty of Chemistry, 1 James Bourchier str. 1164 Sofia, Bulgaria * Corresponding author: ma@uctm.edu Received: 01-03-2010
Abstract
The 4,4,4-trifluoro-1-(biphenyl-4-yl)butane-1,3-dione(HL) has been synthesized and its complexation properties in solution was examined. Mixed ligand chelate extraction of light trivalent lanthanoids (La^Gd) from chloride medium at constant ionic strength | = 0.1 into C6H6 with HL in combination with one of the three phosphine oxide compounds trioctylphosphine oxide(TOPO), tributylphosphine oxide(TBPO) or triphenyphosphine oxide(TPPO) was studied. The composition of the extracted species was established as LnL3 with HL alone and as LnL3 2S in the presence of TOPO and TBPO or LnL3 S with the mixture of HL-TPPO. The 28 values of the overall equilibrium constants were calculated. A synergic effect up to 103-104 was observed for the extraction of the above-mentioned lanthanoid ions with binary mixtures of extractants. The change of the synergistic agent causes a significant increase of the KL,S values in the order TBPO < TPPO < TOPO. The parameters of the extraction process were determined and the separation factors between two adjacent Ln(III) were calculated.
Keywords: Extraction, lanthanoids, 4,4,4-trifluoro-1-(biphenyl-4-yl)butane-1,3-dione, TOPO, TBPO, TPPO, synergism, separation
1. Introduction
The synergistic effect was observed by Cunningham et al.1 for the extraction of Pr(III) and Nd(III) by mixtures of 2-thenoyltrifluoroacetone (HTTA) and tributylphosp-hate (TBP) in kerosene but synergism acquired its name in 1958 when a group of scientists from Oak Ridge laboratory investigated the extraction of U(VI) by combinations of organophosphorus extracting agents.2 The synergistic effect is often significant but the separation among the metal ions is poorer. A lot of efforts have been made to develop extraction systems containing reagents suitable to separate 4f elements. As the elements are so similar in size and properties, the separation is extremely difficult. Fluorinated substituents have often been introduced into extractants. The acidity of the extracting agent is increa-
sed by the electron-withdrawing effect of the fluorinated group, and the extracting agent can be used to extract metal ions from more acidic aqueous solutions.3 A popular li-gand for the solvent extraction of 4f-elements is thenoyl-trifluoroacetone used alone and in combination of various synergistic agents.3 Adduct formation constants have been determined in the thirteen diluents for two types of synergic adducts Eu(TTA)3 S and Eu(TTA)3 2S (S = TOPO) by Akiba et al.4 Irving and Edington5 have established the mi-xed-adduct complexes of the type M(TTA)2(NO3) 2TBPO (M = Am or Eu). The optimum conditions were established when Ln3+ were synergistically extracted with hexaf-luoroacetylacetone and TOPO as mixed ligand complexes with the general formula LnL3 2TOPO.6 Considering the interaction reaction between the extractants in cyclohexa-ne, Atalka and Favaro7 have identified in the organic phase the species Ln(TTA)3 TOPO and Ln(TTA)3 2TOPO for
La and Yb. The extensive study on the extraction of the whole lanthanoid series, except Pm and Lu, with HTTA and TPPO mixture in benzene from an aqueous perchlora-te medium at constant ionic strength of 0.2 M was carried out by Aly et al.8 It was found that the main extracted ad-duct contains the lanthanoid chelates together with two TPPO molecules. In the solvent extraction of metal P-di-ketonates, it is well known that the presence of a Lewis base such as TOPO enhances the extractability, because of adduct formation between the metal chelates and this Lewis base. Such synergism has been widely investigated, but steric hindrance by the terminal groups in the P-dike-tones has hardly been recognized.9 No investigations, however, have been published on the extraction of 4f-ele-ments using 4,4,4-trifluoro-1-(biphenyl-4-yl)butane-1,3-dione as well as the evaluation of its complexation properties in combination with organophosphorus extractants.
As a part of a systematic study of the synergistic solvent extraction of the lanthanoids, the present work was undertaken to investigate the extraction of light triva-lent ions of the metals of the 4f-series (La^Gd) (with exception of radioactive Pm) with a mixture of P-diketone with trifluoromethyl group, 4,4,4-trifluoro-1-(biphenyl-4-yl)butane-1,3-dione (HL) and neutral donors, the trialkyl derivatives of phosphine oxides, where alkyl is the butyl (tributylphosphine oxide, (TBPO)), octyl group (trioctylp-hosphine oxide, (TOPO)) and phenyl group (triphenylp-hosphine oxide, (TPPO)) (S) in C6H6. Our goal is to elucidate the nature of the complexes extracted into the organic phase and to determine the possibilities for separation of the light lanthanoid metals.
2. Materials and Methods
2. 1. Materials
4,4,4-trifluoro-1-(biphenyl-4-yl)butane-1,3-dione (HL) was synthesized according to modified procedure based on the Claisen condensation method10 as shown in Scheme 1.
A solution of 9.81 g (0.05 mol) 4-acetylbiphenyl and 6.65 g methyl trifluoroacetate (0.052 mol, 5.23 ml) in 70 ml benzene was added to 2.8 g sodium methoxide. The mixture was stirred about 10 minutes and left overnight. The solvent was distilled off under reduced pressure, the solid residue was acidified with HCl solution and then was neutralized with sodium acetate. The crude product
was isolated by filtration under vacuum and air dried. Yield 83%, 1H NMR (600MHz, DMSO-d6) 5 (ppm): 8.05 d (1H, ArH), 7.98 d (1H, ArH), 7.83 d (1H, ArH), 7.78-7.35 m (3H, ArH), 7.53-7.49 m (2H, ArH), 7.457.40 m (1H, ArH), 2.62 s (2H, -CH2-). Elemental analysis data: C16H11F3O2 found / (calculated) % C 65.27/ (65.56), H 3.56 /(3.79).
The commercial products trioctylphosphine oxide (TOPO), tributylphosphine oxide (TBPO) and triphenylphosphine oxide (TPPO) (Fluka, > 98%) were used as received. The diluent was C6H6 (Merck, p.a.) Stock solutions of metals with the concentration 2.5 x 10-3 mol dm-3 were prepared from their oxides (Fluka, pu-riss) by dissolving in concentrated hydrochloric acid and diluting with distilled water to the required volume. Arse-nazo III (Fluka) was of analytical grade purity as were the other reagents used.
2.	2. Methods
The experiments were carried out using 10 cm3 volumes of aqueous and organic phases. The samples were shaken mechanically (Orbital Shaker OS-20, Boeco, Germany, 120 rpm) for 55 minutes at room temperature (22 ± 2 °C) which was sufficient to reach equilibrium. After the separation of the phases, the metal concentration in the aqueous phase was determined photometrically (S-20 Spectrophotometer Boeco, Germany) using Arsenazo III.11 The concentration of the metal ion in the organic phase was calculated by subtraction of the determined amount in the aqueous phase from the total amount present. The acidity of the aqueous phase was measured by a digital pH meter (pH 211 HANNA, USA) with an accuracy of 0.01 pH units. The ionic strength was maintained at 0.1 M with (Na, H)Cl. The initial concentration of the metals was 2.5 x 10-4 mol dm-3 in all experiments.
3. Results and Discussion
3.	1. Solvent Extraction of Ln(III) with
4,4,4-trifluoro-1-(biphenyl-4-yl)butane-1,3-dione
Information about major complex for the system under study is usually obtained from the slope analysis. One assumption used in the slope analysis method is constancy
of the activity coefficients, so that concentrations can be used to describe the equilibrium involved in the extraction. The extraction process of lanthanoids with P-diketo-nes3 can be described by the equation:
Ln3+q)
+ 3HL(0) o LnL3(0) + 3H+aq)
(1)
where Ln3+ denote lanthanoid and the subscripts "aq" and "o" indicate the species in the aqueous and organic phase. The extraction constant, KL, is defined as
Kl
[LnL3](o)[H+]
[tr
[Ln3+l JHL]3
(w) — JJ 1
(o)
[HL]
(2)
(O)
where DL is the lanthanoid distribution ratio. As seen from Figs.1 and 2 the plots of logDL vs pH and log[HL] are linear, with slopes very close to 3, in accordance with eq.1.
O
BD O
Figure 1. LogDL vs. pH for the extraction of lanthanoid(III) ions with [HL] = 2 x 10-2 mol dm-3.
extraction results because of the more hydrophobic adduct formation.4-8 The synergistic solvent extraction of Ln(III) ions with mixture of HL and S can be expressed by the equation:
Lni+, + mHL,„, + nS,„, ^ LnL„ + mHL (4)
(aq)	(o)	(o)
It can be shown that
^m n(o)
(aq)
logDL,S = logKL,S + mlog[HL] + nlog[S] + mpH (5)
where DL S is the distribution ratio due to the synergistic effect and KL S is the overall equilibrium constant.
If the hydrolysis and complexation in the aqueous phase as well as the polymerization in the organic phase occur to a negligible extent only, then the double logarithmic plots of DLS vs. one of the variables [HL], [S] and
Figure 2. LogDL vs. log[HL] for the extraction of lanthanoid(III) ions at pH for La, pH = 3.50; Ce, pH = 3.30; Pr, pH = 3.35; Nd, pH = 3.15; Sm, pH = 2.95; Eu, pH = 3.05; Gd, pH = 2.75.
The equilibrium constants for the extraction of light lanthanoids with 4,4,4-trifluoro-1-(biphenyl-4-yl)butane-1,3-dione were calculated on the basis of eq. 3 and summarized in Table 1.
log^T = logDL - 3pH - 3log[HL]
(3)
The experimental data showed that the lanthanoid ions extraction with TBPO, TOPO and TPPO alone is negligible under the experimental conditions of the present study.
3. 2. Synergistic Solvent Extraction of Ln(III) with Mixtures of HL and TOPO, TBPO or TPPO
When an auxiliary reagent, such as TOPO, TBPO and TPPO (S), is added to the extraction system, enhanced
[H+] keeping the other two constant will be linear and their slopes will give the number of the ligands participating in the formation of the adduct. It can be seen from Figures 3 and 4 (plots of logDLS vs log[H+] and log[HL] at fixed S concentrations ) that three P-diketone moieties are attached to the synergistic species in all studied systems.
The plots of logDLS vs log[S] at fixed HL concentration (Fig. 5) gave slopes of one for TPPO and two for TOPO and TBPO. These results indicate the attachment of only one TPPO molecule and two TOPO or TBPO in these synergistic systems and show the extraction of the synergistic species LnL3 TPPO, LnL3 2TBPO and LnL3 2TOPO in the organic phase. The Indian researchers12 reported that two synergistic species having one and two oxo-donor molecules are simultaneously extracted (Eu(TTA)3 2S, Eu(TTA)3 S (S = TPSO, TBP and TOPO))
Figure 3. LogDLS vs. pH for the extraction of lanthanoid(III) ions with mixtures HL-TPPO(TBPO), [HL] = 1 x 10-2 mol dm 3 and HL-TOPO, [HL] = 2 x 10-2 mol dm-3 and [S] = 5 x 10-3 mol dm-3.
Figure 4. LogDLS vs. log[HL] for the extraction of lanthanoid(III) ions at [S] = 5 x 10-3 mol dm 3 and constant pH. TPPO: La, pH = 2.15; Ce, pH = 2.15; Pr, pH = 2.25; Nd, pH = 2.20; Sm, pH = 1.85; Eu, pH = 1.85; Gd, pH = 1.95. TBPO: La, pH = 3.35; Ce, pH = 3.30; Pr, pH = 3.10; Nd, pH = 3.10; Sm, pH = 3.05; Eu, pH = 3.00; Gd, pH = 2.60. TOPO: La, pH = 2.95; Ce, pH = 2.65; Pr, pH = 2.45; Nd, pH = 2.35; Sm, pH = 2.15; Eu, pH = 2.20; Gd, pH = 2.20.
Figure S. LogDLS vs log[S] for the extraction of lanthanoid(III) ions with mixtures HL-TPPO(TBPO), [HL] = 1 x 10-2 mol dm 3 and HL-TOPO, [HL] = 2 x 10-2 mol dm-3 and constant pH. TPPO: La, pH = 2.40; Ce, pH = 2.40; Pr, pH = 2.35; Nd, pH = 2.35; Sm, pH = 1.95; Eu, pH = 1.85; Gd, pH = 2.00. TBPO: La, pH = 3.60; Ce, pH = 3.30; Pr, pH = 3.50; Nd, pH = 3.20; Sm, pH = 3.05; Eu, pH = 3.10; Gd, pH = 2.95. TOPO: La, pH = 2.75; Ce, pH = 2.40; Pr, pH = 2.45; Nd, pH = 2.25; Sm, pH = 2.10; Eu, pH = 2.00; Gd, pH = 1.85.
in benzene. Kandil and Farah13 also noted on the basis of the thermodynamic studies that the coordination number of the chelate expands from 6 to 8 to accommodate direct coordination of the adduct to metal in Eu(TTA)3 2TOPO. The enhanced extraction observed during the calorimetric study by Choppin et al.14 of the adduct species Nd(TTA)3 2TOPO was attributed to the decreased hydrophilic character from the loss of water molecules Nd(TTA)3 2H2O and to the presence of hydrophobic side chains on the coordinated neutral ligand.
On the basis of the slope analysis data, the synergistic extraction of the light lanthanoids can be described by the following reactions:
Ln-3+q) + 3HL(0) + S(0)« LnL3 S<0) +	(6)
L<> + 3HL(o) + 2S(o) ~ LnL3 2S(o) + 3H+„) (7)
The overall equilibrium constant KL,S can be determined by the equations:
log^L,s = log^s - 3log[HL] - log[S] - 3pH (8)
log^L,s = log^L,S -3log[HL] - 2log[S] - 3pH (9)
The formation of mixed adducts in the organic phase can be represented by the equation:
LnL3(o) + S(o) ^ LnL3 S(o)
LnL3(o) + 2S(o) ~ LnL3 2S(o)
(10) (11)
The equilibrium constant S for the organic phase synergistic reaction can be determined as:

(12)
The values of logKL S and log^L S are given in Table 1. The equilibrium constant values mentioned here refer only to the concentration quotients which have been calculated on the assumption that the activity coefficients of
the species involved do not change significantly under the experimental conditions employed.
The data in Table 1 shown that the values of KL S increases with decreasing ionic radii of the metal ions. The variation of the equilibrium constants KL and KL,S versus the atomic number Z of the light lanthanoids is given in Fig. 6.
Figure 6. Log^L(^L S) vs. Z.
The overall equilibrium constant KLS For Ln(III) ions obtained with the synergistic mixture HL-TOPO are approximately 2 orders of magnitude smaller than those obtained with the same synergistic agent and HTTA as a chelating extractant,7 or with 1-phenyl-3-methyl-4-trifluo-roacetyl-5-pyrazolone,15 and eight kinds of ortho-substi-tuted 4-aroylpyrazol-5-ones.16 This is mainly due to the different acidity of the chelating extractants, the equilibrium constant values increase as the pKa value decrea-ses.9'17 The comparison of KLS values obtained for
Table 1. Values of the equilibrium constants KL, KL S and LS for the Ln3+ extraction with HL-S mixtures in
Ln3+	logKL	HL-TPPO	logKL,S HL-TBPO	HL-TOPO	HL-TPPO	lOg^L,S HL-TBPO	HL-TOPO
La	-6.40	0.92	-0.36	1.82	7.32	6.04	8.22
Ce	-5.59	1.09	0.32	2.57	6.68	5.91	8.16
Pr	-5.17	1.35	0.58	2.92	6.52	5.75	8.09
Nd	-4.76	1.63	1.02	3.12	6.39	5.78	7.88
Sm	-4.36	2.14	1.35	3.33	3.50	5.71	7.69
Eu	-4.06	2.34	1.62	3.50	6.40	5.68	7.56
Gd	-3.75	2.52	1.97	3.76	6.27	5.72	7.51
Note: The values of the equilibrium constants are calculated on the basis of the 39 experimental points, statistical confidence 95 % and standard deviation < ± 0.05.
HL-TPPO, HL-TBPO and HL-TOPO combinations shows that the stability of the complexes involving TOPO is higher that those involving TBPO or TPPO. A steric hindrance caused by the three phenyl groups would result in the lower stability for LnL3 TPPO adducts. The change of the synergist causes a significant increase of the KL S values in the order TBPO < TPPO < TOPO.	,
The synergistic enhancement obtained for the combination of two extractants can be evaluated calculating the synergistic coefficients (SC) as: SC = log(Dj 2/D: + D2) where D1 2, D1 and D2 denote the distribution ratio of a metal ion using mixture of extractants (D: 2) and the same extractants separately (D: and D2). The values of the synergistic coefficients of the lanthanoid ions for TPPO, TBPO and TOPO used as synergistic agent in combination with 4,4,4-trifluoro-1-(biphenyl-4-yl)butane-1,3-dio-ne are given in Table 2.
stants (Kl S(Z+1)/Kl S(Z)) are listed in Table 2. It is generally believed that the synergistic extraction makes the separation of metals worse, compared with the extraction with a chelating ligand only. Such an inclination that the addition of a synergist causes the lowering of separation efficiency is often seen in the synergistic extraction systems. The obtained SF values are higher for the three used systems. The system HL-TPPO exhibits separation for the pair Pr/La which is 3.2, 3.6 and 4.5 times smaller than that when mixtures of HL-TBPO, HPMTFP-TOPO16 (1-phenyl-3-methyl-4-(trifluoroacetyl)-5-pyrazolone) and HL-TOPO are applied. Akaiwa was also mentioned22 that the main factors controlling the selectivity in the synergi-stic extraction are the basicity of the synergist and its structure. The data for the metal separation of the same pair (Pr/La) calculated for the system HL-TOPO is analogous with that obtained by Freiser and Umetani15 when
Table 2. Values of the synergistic coefficients ([HL] = 1 X 10 2 mol dm 3, [S] = paration factors for the Ln3+ extraction with mixtures of HL-S in C6H6.
5 X 10 3 mol dm 3) and se-
Ln3+	HL-TPPO	S.C. HL-TBPO	HL-TOPO	HL	S.F. HL-TPPO	HL-TBPO	HL-TOPO
La	5.02	1.44	3.62	6.45	1.47	4.78	5.62
Ce	4.38	1.31	3.56	2.63	1.82	1.82	2.23
Pr	4.22	1.15	3.49	2.57	1.90	2.75	1.58
Nd	4.09	1.18	3.28	2.51	3.23	2.13	1.62
Sm	3.80	0.71	3.69	1.99	1.58	1.86	1.47
Eu	4.10	1.08	2.96	2.04	1.51	2.23	1.82
Gd	3.97	1.12	2.91				
It is seen that all Ln(III) ions are extracted synergi-stically (SC > 0). The addition of S to the chelating extrac-tant improves the extraction efficiency of the Ln(III) ions and produces rather large synergistic effects. The synergi-stic enhancement decreases from La to Gd for the three phosphine oxides and for a particular lanthanoid ion is larger when TPPO is used as synergistic agent. The last observation is due to the different type of extracted complexes with TPPO. The SC established in the present study are higher (2-8 times) as compared to those found by Ata-nassova and Dukov in previous investigations dealing with Ln(III) extraction with HP-DB24C8(DB18C6) (HP: 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one),18 HP(HTTA)-1-(2-pyridylazo)-2-naphtol.19 The obtained SC values for the system HL-TBPO are approximately the same as those found for the systems HTTA-DPSO (diphenylsulfoxide)17 and HTTA-phosphorus-containing calix[4]arene.20 The obtained synergistic effect of TOPO was much greater that that of TBP when complexes Eu-L3S2 have been extracted with five P-diketonate (L: fu-royltrifluoroacetone, pivaloyltrifluoroacetone, thenoyltrif-luoroacetone, benzoyltrifluoroacetone, heptafluorobuta-noylpivaloylmethane).21
The separation factors (SF) between the light Ln(III) ions, defined as a ratio of the respective equilibrium con-
these metals have been extracted with the mixture HPMTFP-CMPO (octyl(phenyl)-N,N-diisobutylcarba-moylmethylphosphine oxide) into CHCl3.The calculated SF value of the pair Eu/Nd for the system HL-TBPO (3.98) is approximately the same as those obtained when combinations of HP-phosphorus-containing calix[4]are-ne23 and H2SbBP-TOPO24 or H2SbBP-CMPO24 (H2Sb-BP, 4-acylbis(pyrazolones)) were used. In addition this value is 2 times higher that those when mixture HTTA-TPPO12 was used.
So, the addition of a neutral organophosphorous ex-tractant to the Ln3+-chelate system improves both the extraction efficiency and selectivity among the light Ln(III) ions. The donor ability of the phosphoryl oxygen is the key parameter that determines the increase extraction of lanthanoids with P-diketones in the presence of neutral oxo-donors. 24
4. Conclusions
The light trivalent ions of the metals of the lantha-noid series were extracted with binary mixtures of a che-lating extractant 4,4,4-trifluoro-1-(biphenyl-4-yl)butane-1,3-dione (HL) in combination with phosphine oxides (S
= TBPO, TOPO or TPPO) in C6H6. The composition of the extracted species was established as LnL3, LnL32S (TOPO and TBPO) and LnL3 S (TPPO). The addition of a synergist to the chelating extractant improves the extraction efficiency of the lanthanoid ions and produces rather large synergistic effect (103-104). The SF between the adjacent metals are higher for the four systems used.
5. References
1.	J. G. Cunningham, D. Scargill, H. H. Willis, Harwell, UKAEA-Research group. AERE-C/M, 1954, 215.
2.	C. A. Blake, C. F. Baes, K. B. Brown, C. F. Coleman, J. C. White, Proc. Intern. Conf. on the Peaceful Uses of Atomic Energy, Geneva, 1958, vol. 28, IAEA, Vienna, 1959, 289.
3.	K. Binnemans, Rare earth beta-diketonates. In: Handbook on the physics and chemistry of rare earths, vol. 35, Chapter 225. Eds.Elsevier Science B. V., Amsterdam, 2005, 107-272.
4.	K. Akiba, M. Wada, T. Kanno, J. Inorg. Nucl. Chem., 1981, 43, 1031-1034.
5.	H. Irving, D. N. Edgington, J. Inorg. Nucl. Chem., 1961, 21, 169-180.
6.	K. S. R. Murthy, R. J. Krupadam, Y. Aujaneyuly, Proc. Indian Acad. Sci., Chem. Sci., 1998,110(2), 83-92.
7.	D. I. T. Favaro, L. T. Atalta, J. Radioanal. Nucl. Chem. Art, 1987, 111(1), 81-94.
8.	H. F. Aly, S. M. Khalifa, N. Zakareia, Solvent Extr. Ion Exch., 1984, 2(6), 887-898.
9. K. Sasayama, S. Umetani, M. Matsui, Anal. Chim. Acta, 1983, 149, 253-258.
10.	L. Claisen, A. Claperede, Ber. 1881, 14, 2460-2468.
11.	S. B. Savvin, Arsenazo III. Atomizdat, Moskva, 1966, 177.
12.	J. N. Mathur, S. A. Pai, P. K. Khopkar, M. S. Sumramanian, J. Inorg. Nucl. Chem., 1977, 39,653-657.
13.	A. T. Kandil, K. Farah, J Inorg. Nucl. Chem., 1980, 42, 1491-1494.
14.	M. Caceci, G. R. Choppin, Q. Lin, Solvent Extr. Ion Exch., 1985, 3(5), 605-621
15.	H. Freiser, S. Umetani, Inorg. Chem, 1987, 26, 3179-3181.
16.	H. Mukai, S. Umetani, Matsui M, Solvent Extr. Ion Exch., 2003, 21(1), 73-90.
17.	M. Atanassova, I. Dukov, J. Solut. Chem., 2009, 38, 289301.
18.	I. L. Dukov, M. Atanassova, Acta Chim. Slov., 2006, 53, 457-463.
19.	I. L. Dukov, M. Atanassova, Sep. Purif. Technol., 2006, 49, 101-105.
20.	M. Atanassova, V. Lachkova, N. Vassilev, B. Shivachev, S. Varbanov, I. Dukov, Polyhedron, 2008, 27, 3306-3312.
21.	T. Taketatsu, Anal. Chim. Acta, 1985, 174, 323-326.
22.	H. Akaiwa, Int Solv Extr Conf (ISEC'90), July 16-21, Kyoto, Japan (Eds. T. Sekine), 1990, Elsevier Science Publ., 1992, 441-449.
23.	M. Atanassova, V. Lachkova, N. Vassilev, S. Varbanov, I. Dukov, J. Inclus. Phenom. Macroc. Chem., 2007, 58, 173-179.
24.	R. Pavithran, M. L. P. Reddy, Anal. Chim. Acta, 2005, 536, 219-226.
Povzetek
Sintetizirali smo 4,4,4-trifluoro-1-(bifenil-4-il)butan-1,3-dion (HL) in raziskali njegove lastnosti kompleksiranja v raztopinah. Študirali smo ekstrakcijo mešanih kelatnih ligandov lahkih trivalentnih lantanoidov (La^Gd) iz kloridnega medija pri konstantni ionski moči | = 0.1 v C6H6 s HL v kombinaciji s trioktilfosfin oksidom (TOPO), tributilfosfin oksidom (TBPO) ali trifenilfosfin oksidom (TPPO) (S). Sestava ekstrahiranih zvrsti je bila LnL3, ko smo uporabili samo HL; LnL3 • 2S, ko smo uporabili HL v kombinaciji s TOPO in TBPO in LnL3 • S v kombinaciji s TPPO. Izračunali smo 28 konstant ravnotežja. Pri ekstrakciji lantanoidnih ionov z mešanicami reagentov je prišlo do pojava sinergije z vrednostmi do 103-104. Vrednosti konstante KLS naraščajo v smeri TBPO < TPPO < TOPO. Določili smo parametre procesa ekstrakcije in izračunali separacijske faktorje za lahke Ln(III) ione.