Synergistic extraction of lanthanoids(III) with 2-thenoyltrifluoroacetone and benzoic acid: thermodynamic parameters in the complexation in organic phases and the hydration

In order to examine the reason why the magnitude of the synergistic effect observed in the extraction of lanthanoids(III) with a β-diketone and a monodentate Lewis base generally decreases along with increasing atomic number, the hydration number of the extracted species when lanthanoids(III) are extracted with TTA (2-thenoyltrifluoroacetone, HA) and benzoic acid (HB) into chloroform by Karl Fischer titration and the enthalpy change in complexation between LnA₃ and HB by calorimetric titration were determined across the lanthanoid series at 25 °C.It has been concluded that since the decrement of entropy change caused by the change in the number of released water molecules and in the coordination number of lanthanoids(III) upon complexation is larger than the increment of the enthalpy change, the values of the second formation constants of the complexes decrease with increasing the atomic number across lanthanoid series so that the magnitude of the synergistic extraction decreases with increasing the atomic number.     

Complexing Properties of Uranium and Lanthanoids With 4-(2-Thiazolylazo)-6-Chlororesorcinol

Abstract

4-(2-Thiazolylazo)-6-chlororesorcinol (TAR-Cl) reacts sensitively with uranyl(II) and lanthanoids(III), and forms reddish-brown 1:1 and 1:2 complexes. The complexing behaviors were examined spectrophotometrically. The absorption maxima of the complexes are focused near 553 nm and the optimum pH for complexation lies between 6.5–8.8. Beer's law holds up to about 2 × 10^?5 mol 1^?1, with a molar absorptivity of 3.00 × 10⁴ 1 mol^?1 cm^?1 for uranium and 6 × 10⁴ 1 mol^?1 cm^?1 level for each lanthanoid. The absorptivities are increased with the atomic number, especially in light lanthanoids, that are correlative both to the lanthanoid contraction and the basicity of ortho hydroxyl group in the resorcinol ring, but such effects are not clearly recognized in heavy lanthanoids. Effect of masking agents was also examined, and uranium could be determined selectively in the presence of lanthanoid mixtures by the addition of CyDTA.     

Dependence of the photophysical properties on the number of 2,2'-bipyridine units in a series of luminescent europium and terbium cryptates

The luminescence properties of a series of lanthanoid cryptates with an increasing number of 2,2'-bipyridine units have been investigated for the lanthanoids Eu and Tb in aqueous solution. The trends in important parameters that influence the photophysics in these complexes have been determined. With increasing bipyridine content, an increase is observed for the intersystem crossing efficiencies and the number of inner-sphere water molecules. In contrast, a decrease is found in the same direction for overall quantum yields, triplet energies, and sensitization efficiencies.     

High-energy X-ray absorption spectroscopy: a new tool for structural investigations of lanthanoids and third-row transition elements

This is the first systematic study exploring the potential of high-energy EXAFS as a structural tool for lanthanoids and third-row transition elements. The K-edge X-ray absorption spectra of the hydrated lanthanoid(III) ions both in aqueous solution and in solid trifluoromethanesulfonate salts have been studied. The K-edges of lanthanoids cover the energy range from 38 (La) to 65 keV (Lu), while the corresponding energy range for the L(3)-edges is 5.5 (La) to 9.2 keV (Lu). We show that the large widths of the core-hole states do not appreciably reduce the potential structural information in the high-energy K-edge EXAFS data. Moreover, for lanthanoid compounds, more accurate structural parameters are obtained from analysis of K-edge than from L(3)-edge EXAFS data. The main reasons are the much wider k range available and the absence of double-electron transitions, especially for the lighter lanthanoids. A comparative K- and L(3)-edge EXAFS data analysis of nonahydrated crystalline neodymium(III) trifluoromethanesulfonate demonstrates the clear advantages of K-edge analysis over conventionally performed studies at the L(3)-absorption edge for structural investigations of lanthanoid and third-row transition metal compounds. The coordination chemistry of the hydrated lanthanoid(III) ions in aqueous solution and solid trifluoromethanesulfonate salts, based on the results of both the K- and L(3)-edge EXAFS data, is thoroughly discussed in the next paper in this series (I. Persson, P. D'Angelo, S. De Panfilis, M. Sandstr?m, L. Eriksson, Chem. Eur. J. 2008, 14, DOI: 10.1002/chem.200701281).     

Lanthanoid element recognition on surface-imprinted polymers containing dioleylphosphoric acid as a functional host.

Surface-imprinted polymers have been newly developed for the separation of lanthanoid elements: i.e. La(III), Ce(III), and Dy(III). The imprinted polymers were prepared by surface template polymerization with dioleylphosphoric acid, which exhibits a high affinity to lanthanoids, as a functional host molecule. Separation behavior of La(III), Ce(III) and Dy(III) was investigated with the imprinted polymers, and the imprinting effect of the polymers was evaluated in comparison with that of the unimprinted polymers and also with a conventional solvent extraction method for the same lanthanoid ions. The results indicate that the increase of selectivity for Dy(III) compared to the rest of the ions by the surface-imprinted polymers originated from a synergistic effect of both the affinity with the functional host molecule in nature and the size exclusion by the cavity formed on the polymer surface.     

Adsorption of lanthanoid ions on calcite

The adsorption of 14 trivalent lanthanoid ions and yttrium ion (denoted by Ln3+) on calcite surfaces was investigated under various solution conditions of pH (pH = 6.8-7.8) and calcium ion concentration (pCa = -log[Ca2+]= 2.0 and 3.0), and different surface conditions of calcite crystals (well-developed and rough surfaces). The lanthanoid ions were equilibrated in a solution of ionic strength 0.1 mol dm-3(NaCl) saturated with calcite at 25.0 degrees C using excess (solid) calcite crystals suspended in solution. The concentrations of the lanthanoid ions on the calcite crystals (C(cry)/mol kg-1) and in solution (C(soln)/mol dm-3) were determined by means of inductively coupled plasma-mass spectrometry (ICP-MS). It is found that the distribution ratio (D=C(cry)/C(soln) decreases as the atomic number of the lanthanoid increases showing the so called Tetrad Effect. D values increase with increasing pH, whereas they are independent of the calcium ion concentration (i.e., carbonate ion concentration). These results indicate that lanthanoid ions are adsorbed on the calcite surface together with hydroxide ions, i.e., the adsorption of hydroxo-complexes. The heavy lanthanoid ions (Er3+ to Lu3+) are adsorbed as monohydroxo-complexes, (Ln(OH)2+), whereas those of the light lanthanoids are predominantly adsorbed as dihydroxo-complexes (Ln(OH)2+). Other lanthanoids show competitive adsorption reactions of mono- and dihydroxo complexes. Both successive adsorption constants of hydroxo complexes increase with decreasing atomic number of the lanthanoid. The rough surface of calcite is quite active and the distribution ratio of the lanthanoid ions on the rough surface is much higher than that on the well-developed crystalline surface. Rates of adsorption of lanthanide ions were measured and mechanisms are being discussed     

Mechanism for Solvent Extraction of Lanthanides from Chloride Media by Basic Extractants

The solvent extraction of lanthanides from chloride media to an organic phase containing an anion exchanger in the chloride form is known to show low extraction percentages and small separation factors. The coordination chemistry of the lanthanides in combination with this kind of extractant is poorly understood. Previous work has mainly used solvent extraction based techniques (slope analysis, fittings of the extraction curves) to derive the extraction mechanism of lanthanides from chloride media. In this paper, EXAFS spectra, luminescence lifetimes, excitation and emission spectra, and organic phase loadings of lanthanides in dry, water-saturated and diluted Aliquat 336 chloride or Cyphos IL 101 have been measured. The data show the formation of the hydrated lanthanide ion [Ln(H₂O)_8–9]³⁺ in undiluted and diluted Aliquat 336 and the complex [LnCl₆]^3? in dry Aliquat 336. The presence of the same species [Ln(H₂O)_8–9]³⁺ in the aqueous and in the organic phase explains the small separation factors and the poor selectivities for the separation of mixtures of lanthanides. Changes in separation factors with increasing chloride concentrations can be explained by changes in stability of the lanthanide chloro complexes in the aqueous phase, in combination with the extraction of the hydrated lanthanide ion to the organic phase. Finally, it is shown that the organic phase can be loaded with 107 g·L^?1 of Nd(III) under the optimal conditions.     

Rigid, perdeuterated lanthanoid cryptates: extraordinarily bright near-IR luminophores

Near-IR emissive lanthanoid cryptates have been developed with the lanthanoids Yb, Nd, Er, and Pr by designing a fully deuterated ligand environment that greatly suppresses multiphonon nonradiative deactivation pathways through avoidance of high-energy oscillators and rigidification of the ligand backbone. Strong luminescence is observed in CD(3)CN for all four lanthanoids. Luminescence lifetimes in CD(3)CN are among the highest values for molecular complexes in solution reported so far (Yb, τ(obs) = 79 μs; Nd, τ(obs) = 3.3 μs). For the ytterbium cryptate, the highest luminescence lifetime can be obtained using CD(3)OD (τ(obs) = 91 μs) and even in nondeuterated CH(3)CN the lifetime is still unusually high (τ(obs) = 53 μs). X-ray crystallography and (1)H NMR analysis of the corresponding nondeuterated lutetium cryptate suggest that the inner coordination sphere in solution is completely saturated by the octadentate cryptand and one chloride counterion. All lanthanoid cryptates remarkably show complete stability during reversed-phase HPLC measurements under strongly acidic conditions.     

Lanthanoid complexes with thenoyltrifluoroacetone and 4-tert-butylcalix[4]arene-tetraacetic acid tetraethyl ester: synergistic extraction and separation

The solvent extraction of fourteen lanthanoid ions with thenoyltrifluoroacetone (HTTA) in combination with tetraethyl 4-tert-butylcalix[4]arene-tetraacetic acid tetraethyl ester (S) from a perchlorate medium at constant ionic strength was investigated. The extracted species were identified as the Ln(TTA)₃·S complexes by slope analysis. Equilibrium constants, parameters for extraction, and the synergistic and separation factors between two adjacent Ln(III) ions were determined.

Intramolecular Sandwich Complexation of Light Lanthanoid Nitrates with Bis(benzo-12-crown-4)s: Enhanced Selectivity for Eu

Spectrophotometric titrations performed in anhydrous acetonitrile at 25°C give the complex stability constants (log Ks) and the Gibbs free energy changes (-G° for the stoichiometric 1 : 1 intramolecular sandwich complexation of light lanthanoid (III) nitrates (La Gd) with the polymethylene-bridged bis(benzo-12-crown-4)s 1, the corresponding dioxo derivative 2 and its dihydroxy analogue 3. The complex stability sequence as a function of reciprocal ionic radius of lanthanoids showed similar profiles in stability constants (log Ks) and maximum stabilities were obtained at Eu3+ for the complexation of light lanthanoids with the three bis(benzo-12-crown-4)s 1–3. The cation binding abilities and relative selectivities for the trivalent lanthanoid ions of these structurally related bis(benzo-12-crown-4)s 1–3 are discussed according to the derivatization of the bridging.     

Thermodynamic and Spectroscopic Study of the Adduct Formation of Tris(β-diketonato)lanthanoids with Heteroamines

A remarkable enhancement of the extraction of lanthanoids(Ⅲ)(Ln) with β-diketones in the presence of a Lewis base, so-called synergistic effects, would be caused by the adduct formation of the β-diketonates with the Lewis base. The trend of the variation of the adduct formation constants across the lanthanoid series may be different among β-diketones used. It has also been observed that the trend across lanthanoid series and also the values of the enthalpy change in the adduct formation of the 2-thenoyltrifluoroacetonates(TTA) with 1,10-phenanthroline(phen) are very similar to those with 2,25-bipyridyl(bpy), although the values of the adduct formation constants with the former are larger than those with the latter.     

Room temperature ionic liquid as a novel medium for liquid/liquid extraction of metal ions

Room temperature ionic liquids (RTILs) have been used as novel solvents to replace traditional volatile organic solvents in organic synthesis, solvent extraction, and electrochemistry. The hydrophobic character and water immiscibility of certain ionic liquids allow their use in solvent extraction of hydrophobic compounds. In this work, a typical room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate [C₄mim][PF₆], was used as an alternative solvent to study liquid/liquid extraction of heavy metal ions. Dithizone was employed as a metal chelator to form neutral metal-dithizone complexes with heavy metal ions to extract metal ions from aqueous solution into [C₄mim][PF₆]. This extraction is possible due to the high distribution ratios of the metal complexes between [C₄mim][PF₆] and aqueous phase. Since the distribution ratios of metal dithiozonates between [C₄mim][PF₆] and aqueous phase are strongly pH dependent, the extraction efficiencies of metal complexes can be manipulated by tailoring the pH value of the extraction system. Hence, the extraction, separation, and preconcentraction of heavy metal ions with the biphasic system of [C₄mim][PF₆] and aqueous phase can be achieved by controlling the pH value of the extraction system. Preliminary results indicate that the use of [C₄mim][PF₆] as an alternate solvent to replace traditional organic solvents in liquid/liquid extraction of heavy metal ions is very promising.     

Effect of p-tert-Butylcalix[4]arene Fitted with Phosphinoyl Pendant Arms as Synergistic Agent in the Solvent Extraction and Separation of Some Trivalent Lanthanoids with 4-Benzoyl-3-methyl-1-phenyl-5-pyrazolone

The synergistic solvent extraction of five selected lanthanoid ions (La³⁺, Nd³⁺, Eu³⁺, Ho³⁺ and Lu³⁺) with a 4-benzoyl-3-methyl-1-phenyl-5-pyrazolone(HP) and the 5,11,17,23-tert-butyl-25,26,27,28-tetrakis(dimethylphosphinoylmethoxy)calix[4]arene, (S) in CHCl₃ has been studied. It was found that in presence of this phosphorus-containing calix[4]arene the lanthanoids have been extracted as LnP₃ · S. On the basis of the experimental data, the values of the equilibrium constants have been calculated. The influence of the synergistic agent on the extraction process has been discussed. A synergistic effect of almost three orders of magnitude occurs in the extraction of Ln(III) with mixture of HP and S. The values of the separation factors (S.F.) between the adjacent elements have been evaluated. On the basis of the IR and NMR spectra the stoichiometry and the structure of the solid complexes of Eu(III) with HP and Eu(III) with HP and S were proposed.     

Ionic liquid synergistic cation-exchange system for the selective extraction of lanthanum(III) using 2-thenoyltrifluoroacetone and 18-crown-6.

A novel synergistic extraction system was investigated for the possible selective separation of light lanthanoids using an ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, as an extraction solvent and 2-thenoyltrifluoroacetone and 18-crown-6 as extractants. Trivalent lanthanum was efficiently extracted as a cationic ternary complex by the cation-exchange process, whereas europium and lutetium showed relatively low extractability without forming respective ternary complexes. This result is thought to originate in a size-fitting effect of 18-crown-6 to lanthanum and the unique nature of the ionic liquid as a chelate extraction solvent.     

Cloud point extraction and separation of copper and lanthanoids using Triton X-100 with water-soluble p-sulfonatocalix[4]arene as a chelating agent

A method is presented for the cloud-point extraction and separation of copper and lanthanoid ions. A water-soluble calixarene, p-sulfonatocalix[4]arene (C4AS), is used as the chelating agent and Triton X-100 is chosen as the surfactant. The factors affecting the extraction efficiency, such as pH, the concentrations of Triton X-100 and C4AS, equilibration time and centrifugation time, were evaluated. The results demonstrate that there are different extraction behaviors for Cu(II) and Ln(III). Cu(II) can be separated from Ln(III) using C4AS as the chelating agent under weakly acidic conditions. The method may be used to remove trace copper from the lanthanoids.     

Protonation equilibria of nitrilotris(methylenephosphonato)-and ethylenediamine-tetrakis(methylenephosphonato)-complexes of scandium,yttrium, and lanthanoids

The protonation equilibria of nitrilotris(methylenephosphonic acid) (NTMP, H₆L) and ethylenediaminetetrakis(methylenephosphonic acid) (EDTMP, H₈L) complexes of scandium, yttrium, and lanthanoids have been studied potentiometrically at 25°C and at an ionic strength of 0.1 mol-dm^–3 KNO₃. The first protonation constants of NTMP complexes of lanthanoids, K _MHL , decrease with decreasing of the ionic radius of the lanthanoid [log K _MHL =7.82 (La³⁺) –6.90 (Lu³⁺)] and show a so-called Tetrad effect. The second protonation constants, K _{MH 2}L, change very little with the lanthanoid metal ions (logK _{MH 2}L=5.3–5.7). These results suggest that, in the first protonation process in ML, the proton attacks the nitrogen of NTMP rupturing the M-N of M(ntmp)^3–. The pattern of the change in the protonation constants of the EDTMP complexes with the atomic number of the lanthanoid is quite different from that of the NTMP complexes. This fact indicates that the manner of protonation of the EDTMP complexes differs from that of NTMP complexes. The protonation constants of yttrium complexes of NTMP and EDTMP agree with those of lanthanoid complexes, whereas those of scandium complexes deviate from the values predicted from its ionic radius.     

Complexation of trivalent lanthanoid ions with 4-benzoyl-3-phenyl-5-isoxazolone and p-tert-butylcalix[4]arene fitted with phosphinoyl pendant arms in solution during synergistic solvent extraction and structural study of solid complexes by IR and NMR

The liquid extraction of 14 lanthanoids with a 4-benzoyl-3-phenyl-5-isoxazolone (HPBI) alone in CHCl₃ as a diluent from perchlorate medium at constant ionic strength μ = 0.1 is investigated. The synergistic solvent extraction of five selected lanthanoid ions (La³⁺, Nd³⁺, Eu³⁺, Ho³⁺ and Lu³⁺) with 4-benzoyl-3-phenyl-5-isoxazolone (HPBI) and 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis-(dimethylphosphinoylmethoxy)calix[4]arene, (S) in CHCl₃ has been studied too. The stoichiometry of the extracted species was characterised by a classical log–log plot analysis. It was found that the composition of the extracted species with HPBI are Ln(PBI)₃ and in the presence of the phosphorus-containing calix[4]arene the lanthanoid ions have been extracted as [Ln(PBI)₃S₂]. The values of the equilibrium constants and the separation factors have been calculated. The influence of the synergistic agent on the extraction process has been discussed.     

A Comparative Study of the Solvent Extraction of the Trivalent Elements of the Lanthanoid Series with Thenoyltrifluoroacetone and 4-Benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one Using Diphenylsulphoxide as Synergistic Agent

Solvent extraction of the trivalent lanthanoids (except Pm) with mixtures of a chelating extractant, either 1-(2-thienyl)-4,4,4-trifluoro-1,3-butanedione (thenoyltrifluoro-acetone, HTTA) or 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one (HP) and diphenylsulphoxide (S), from chloride solutions has been studied in C₆H₆. It was found that, in the presence of a diphenylsulfoxide, the lanthanoids were extracted as Ln(TTA)₃⋅S and LnP₃⋅S. The extraction data have been analyzed by a graphical method taking into account aqueous phase speciation and the plausible complex extracted into the organic phase. On the basis of the experimental data, values of the equilibrium constants have been calculated. Positive values of the synergistic coefficients show that all lanthanoids are extracted synergistically upon the addition of compound S to the chelating extractant. The separation of the lanthanoids with synergistic mixtures was, in most cases, a little higher than those obtained using HTTA or HP alone.     

Effects of pre-irradiation treatments in neutron activation analysis of rocks for measurements of their lanthanoid,thorium and uranium contents

Determination of the lanthanoids, thorium and uranium in silicate rocks has been investigated by neutron activation analysis (NAA). Seven or eight lanthanoids and thorium and uranium were determined by non-destructive instrumental NAA. The numbers of the lanthanoids determined were increased and errors on the final values were reduced by pre-irradiation treatments, which included a coprecipitation process with aluminium as collector to remove the alkali metals and halogens and a solvent extraction process to eliminate iron. The necessity of scandium removal was indicated.