Coordination Environment Of Eu Research Articles

Europium(III) Ion-Based photoluminescence complexes of Indole-Derivative β-diketone dominated by ancillary ligands

One pot reaction of β-diketone EIFD, EuCl3·6H2O and ancillary ligand yield a sequence of five luminescence β-diketone EIFD europium complexes, including Eu(EIFD)3(H2O)·CH2Cl2 (1), Eu(EIFD)3(DMSO) (2), Eu(EIFD)3(DMF)·CH2Cl2 (3), Eu(EIFD)3(phen)·CH2Cl2 (4) and Eu(EIFD)3(bpy) (5) (EIFD: 1-(1-ethyl-1H-indol-3-yl)-4,4,4-trifluorobutane-1,3-dione, phen = 1, 10-phenanthroline, bpy = 2,2′-bipyridine,). The molecular crystals reveal five mononuclear structures with the central Eu(III) ions of seven/eight coordination configuration furnished by three EIFD ligands and ancillary ligands for complexes 1–5. All the five complexes display room-temperature strong characteristic photoluminescence emissions of Eu(III) ions. The coordination environment of Eu(III) ion is a crucial factor in the optical performance of the complex. Herein, the way to introduce of oxygen and nitrogen ancillary ligands plays an important role in characteristic photoluminescence. The luminescence lifetime and quantum yields of the complexes can vary essentially by substituting the solvent molecules with oxygen and nitrogen ligands, leading to a strong luminescence intensity, as observed experimentally.

Delineating the influence of picolinic acid on Eu(iii) sorption by γ-alumina.

The present study aims at understanding the sorption mechanism of Eu(iii) by γ-alumina in the presence of picolinic acid (PA), a decontaminating agent used in the nuclear industry, through batch sorption studies, spectroscopy and surface complexation modeling. PA is weakly sorbed by γ-alumina, with the sorption increasing with pH up to 4.5 and decreasing with further increase in pH. Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR) measurements indicate that PA forms an inner sphere surface complex on γ-alumina. The presence of PA does not affect Eu(iii) sorption by γ-alumina at low [Eu(iii)], while it drastically reduces Eu(iii) sorption at high [Eu(iii)]. Similar Eu(iii) sorption profiles with different addition sequences of Eu(iii) and PA suggest identical Eu(iii) surface species for Eu(iii) sorption on γ-alumina in the presence of PA which has been validated by time resolved fluorescence spectroscopy (TRFS). TRFS measurements of Eu(iii) sorbed on γ-alumina in the absence (binary systems) and presence of PA (ternary systems) exhibited two components 1 & 2. The lifetime value of component 1 in ternary systems is enhanced compared to that in binary systems signifying the formation of new surface species containing Eu(iii), PA and the γ-alumina surface whereas the similarity of component 2 in both the binary and ternary systems reveals an almost identical coordination environment of Eu(iii) in the two types of system. Using the spectroscopic information obtained from TRFS, Eu(iii) sorption, at high [Eu(iii)], in ternary systems has been successfully modeled by considering Eu(iii) bridged PA surface species at both low and high affinity sites of γ-alumina. At low [Eu(iii)] both PA and Eu(iii) bridged ternary surface complexes only at high affinity sites of γ-alumina could describe the Eu(iii) sorption adequately.

Acid-switched Eu(III) coordination inside reverse aggregates: Insights into a synergistic liquid-liquid extraction system

Determining the structure of complex solutions bearing metal ions is challenging, but crucial for developing important technologies such as liquid-liquid extraction for metal refining and separation purposes. Herein, the structure of an organic Eu(III) solution consisting a binary mixture of lipophilic ligands di-2-ethylhexyl phosphoric acid (HDEHP) and tetraoctyl diglycolamide (TODGA) in dodecane is studied using synchrotron small angle X-ray scattering (SAXS) and X-ray absorption fine structure spectroscopy (EXAFS). This system is of technological importance in f-element separation for nuclear fuel cycle applications, where extraction is controlled by varying nitric acid concentration. Extraction is promoted at low and high concentration, but is retarded at intermediate concentration, leading to a U-shaped function; the structural origins of which we investigate. At the nanoscale, the solution is apparently comprised of reverse micelles with polar cores of approximately 1nm in size, and these remain virtually unchanged as acid concentration is varied. Inside the polar cores, the coordination environment of Eu(III) switches from a 9-coordinate [Eu(TODGA)3]3+ motif at high acid, to a 6-coordinate HDEHP-dominated complex resembling Eu(HDEHP·DEHP)3 at low acid. The results show that extraction is controlled within the coordination sphere, where it is promoted under conditions that favor coordination of either one of the two organic ligands, but is retarded under conditions that encourage mixed complexes. Our results link solution structure with ion transport properties in a technologically-important liquid-liquid ion extraction system.

Tetranuclear Heterometallic {Zn2Eu2} Complexes With 1-Naphthoate Anions: Synthesis, Structure and Photoluminescence Properties.

A series of new tetranuclear heterometallic Zn(II) -Eu(III) complexes have been synthesized, that is, (bpy)2 Zn2Eu2 (naph)10 (1), (bpy)2 Zn2Eu2 (naph)8 (NO3)2 (2), and (phen)2 Zn2Eu2 (naph)8 (NO3)2 (3), and other ones, where naph(-) is the 1-naphthoate anion, bpy=2,2'-bipyridyl, and phen=1,10-phenanthroline. The solid-phase complexes consist of large supramolecular ensembles due to stacking interactions between the aromatic ligands. Photoluminescence (PL) measurements were carried out to study PL spectra, lifetimes and quantum yields (QY) of the synthesized complexes at different temperatures. The external QY for the solid phases of complexes under UV excitation was found to exceed 20 %. It has been shown that partial replacement of naphthoate ligands in the coordination environment of Eu(3+) by NO3(-) anions influences the PL properties. To investigate the behavior of these complexes in solvent, we dissolved complex 3 in MeCN, put it on a transparent glass as a substrate, and studied the PL properties at room temperature.

Electrochemical behavior of Eu(III) in imidazolium ionic liquid containing tri- n- butyl phosphate and N,N -dihexyloctanamide ligands

Abstract The electrochemical behavior of Eu(III) in room temperature ionic liquid, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulphonyl)imide (C6mimNTf2), was studied in the presence and absence of ligands such as tri-n-butyl phosphate (TBP) and N,N-dihexyloctanamide (DHOA) by cyclic voltammetry. The cyclic voltammogram of Eu(III) in C6mimNTf2, recorded at glassy carbon electrode, exhibited a prominent quasi-reversible reduction wave occurring at the onset of − 0.25 V (Vs Fc/Fc+), culminating in a peak at − 0.84 V (Vs Fc/Fc+) was due to the reduction of Eu(III) to Eu(II). The cathodic peak current was lowered and the peak potential shifted cathodically in the presence of ligands, due to the co-ordination of Eu(III) with ligands in ionic liquid phase. The diffusion coefficient (D, cm2/s) of Eu(III) and the rate constant (ks, cm/s) for the electron transfer reaction across the electrode–electrolyte inter-phase in various systems were determined and they increased with increase of temperature. The stability constant and stoichiometry of Eu(III)–ligand complex were determined from the voltammograms recorded at various ligand concentrations. The emission spectra of Eu(III) in ionic liquid phase suggested that the coordination environment of Eu(III) in TBP was different from that in DHOA.

Laser-induced fluorescence and infrared spectroscopic studies on the specific solvation of tris(1-(2-thienyl)-4,4,4-trifluoro-1,3-butanedionato)europium(III) in an ionic liquid

The extraction constant and the two-phase stability constant ( K D,M β 3) of tris(2-thenoyltrifluoroacetonato)europium(III) between 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C 4mim][Tf 2N]) as an ionic liquid and an aqueous phase were determined by considering the extraction equilibria including anionic tetrakis(2-thenoyltrifluoroacetonato)europate(III). Specific solute–solvent interactions between the neutral Eu(III) chelate and [C 4mim][Tf 2N] molecules were revealed from the relationships between the distribution constant of the enol form of 2-thenoyltrifluoroacetone (Htta) as a proton chelate and the distribution constant ( K D,M) of the neutral Eu(III) chelate because the [C 4mim][Tf 2N] system gave the high K D,M β 3 value compared with those in conventional molecular solvents such as benzene and 1,2-dichloroethane. The coordination environment of Eu 3+ in the neutral Eu(III) chelate in [C 4mim][Tf 2N] was investigated by time-resolved laser-induced fluorescence spectroscopy and infrared absorption spectroscopy. Both methods consistently indicated that not only the Eu(III) chelate extracted but also Eu(tta) 3(H 2O) 3 synthesized as a solid crystal were almost completely dehydrated in [C 4mim][Tf 2N] saturated with water. Consequently, the higher K D,M or extractability of the neutral Eu(III) chelate in the [C 4mim][Tf 2N] system can be ascribed to the dehydration of the Eu(III) chelate, which is caused by the specific solvation with [C 4mim][Tf 2N] molecules.

Emission Enhancement through Dual Donor Sensitization: Modulation of Structural and Spectroscopic Properties in a Series of Europium Tetracyanoplatinates

The synthesis of three different europium tetracyanoplatinates all incorporating 2,2':6',2''-terpyridine (terpy) have been carried out in acetonitrile/water mixtures by reaction of Eu(3+) salts with terpy and potassium tetracyanoplatinate. The use of different Eu(3+) sources results in the isolation of Eu(C(15)H(11)N(3))(H(2)O)(2)(NO(3))(Pt(CN)(4)) x CH(3)CN (1), {Eu(C(15)H(11)N(3))(H(2)O)(3)}(2)(Pt(CN)(4))(3) x 2 H(2)O (2), or [Eu(C(15)H(11)N(3))(H(2)O)(2)(CH(3)COO)(2)](2)Pt(CN)(4) x 3 H(2)O (3) for the nitrate, triflate, or acetate salts, respectively. All three compounds have been prepared as colorless crystals, and single-crystal X-ray diffraction has been used to investigate their structural features. Crystallographic data (MoK alpha, lambda = 0.71073 A, T = 290 K): 1, monoclinic, space group P2(1)/c, a = 12.835(1), b = 15.239(1), c = 13.751(2) A, beta = 105.594(9) degrees, V = 2590.8(5) A(3), Z = 4; 2, triclinic, space group P1, a = 9.1802(8) A, b = 10.8008(9) A, c = 13.5437(9) A, alpha = 84.491(6) degrees, beta = 75.063(7) degrees, gamma = 79.055(7) degrees, V = 1272.4(2) A(3), Z = 1; 3, triclinic, space group P1, a = 12.110(3) A, b = 12.7273(11) A, c = 18.7054(16) A, alpha = 92.859(7) degrees, beta = 92.200(11) degrees, gamma = 118.057(10) degrees, V = 2534.8(7) A(3), Z = 2. Variation of the counteranions in these systems provides the opportunity to modify the structures and coordination environment of Eu(3+) for 1-3. Compounds 1 and 2 are both one-dimensional, polymeric compounds that contain Eu(3+) ions chelated by terpy and bridged by tetracyanoplatinate anions. 3 is a zero-dimensional complex salt in which Eu(3+) is coordinated by terpy, acetate, and water, but not tetracyanoplatinate. The structural differences result in varying sensitization phenomena for the three compounds. Compounds 1 and 2 display efficient donor-acceptor intramolecular energy transfer (IET) where dual donor species, terpyridine and tetracyanoplatinate, simultaneously enhance the acceptor Eu(3+) emission. In both compounds the donor species are directly coordinated to the acceptor ion, and hence a highly efficient dual-donor effect is exhibited for the IET mechanisms. In 3 where only the terpy ligand is directly coordinated to Eu(3+), the sensitization involves only one donor species. The Pt(CN)(4)(2-) unit in 3, which lacks direct bonding to Eu(3+), exhibits strong emission indicating the lack of cooperative enhancement of the lanthanide emission.

Effects of ionic strength on the coordination of Eu(III) and Cm(III) to a Gram-negative bacterium,Paracoccus denitrificans

We studied the effect of ionic strength on the interactions of Europium(III) and Curium(III) with a Gram-negative bacteriumParacoccus denitrificans. Bacterial cells grown in 0.5-, 3.5-, and 5.0% NaCl were used in adsorption experiments and laser experiments that were performed at the same ionic strengths as those in the original growth media. The distribution ratio (logKd) for Eu(III) and Cm(III) was determined at pHs 3−5. To elucidate the coordination environment of Eu(III) adsorbed onP. denitrificans, we estimated the number of water molecules in the inner sphere and strength of the ligand field by time-resolved laser-induced fluorescence spectroscopy (TRLFS) at pHs 4−6. The logKdof Eu(III) and Cm(III) increased with an increase of pH at all ionic strengths because there was less competition for ligands in cells with H+at higher pHs, wherein less H+was present in solution: cation adsorption generally occurs through an exchange with H+on the functional groups of coordination sites. No significant differences were observed in the logKdof Eu(III) and Cm(III) at each pH in 0.5-, 3.5-, and 5.0% NaCl solutions, though competition for ligands with Na+would be expected to increase at higher NaCl concentrations. The logKdof Eu(III) was almost equivalent to that of Cm(III) under all the experimental conditions. TRLFS showed that the coordination environments of Eu(III) did not differ from each other at 0.5-, 3.5-, and 5.0% NaCl at pHs 4−6. TRLFS also showed that the characteristic of the coordination environment of Eu(III) onP. denitrificanswas similar to that on a halophile,Nesterenkonia halobia, while it significantly differed from that on a non-halophile,Pseudomonas putida. These findings indicate that the number of coordination sites for Eu(III) onP. denitrificans, whose cell surface may have similar structures to that of halophiles, increased with increasing ionic strength, though their structure remained unchanged.

Association of europium(III), americium(III), and curium(III) with cellulose, chitin, and chitosan

The association of trivalent f-elements-Eu(III), Am(III), and Cm(III)--with cellulose, chitin, and chitosan was determined by batch experiments and time-resolved, laser-induced fluorescence spectroscopy (TRLFS). The properties of these biopolymers as an adsorbent were characterized based on speciation calculation of Eu(III). The adsorption study showed that an increase of the ionic strength by NaCl did not affect the adsorption kinetics of Eu(III), Am(III), and Cm(III) for all the biopolymers, but the addition of Na2CO3 significantly delayed the kinetics because of their trivalent f-element complexation with carbonate ions. It also was suggested from the speciation calculation study that all the biopolymers were degraded under alkaline conditions, leading to their masking of the adsorption of Eu(III), Am(III), and Cm(III) on the nondegraded biopolymers. The masking effect was higher for cellulose than for chitin and chitosan, indicating that of the three, cellulose was degraded most significantly in alkaline solutions. Desorption experiments suggested that some portion of the adsorbed Eu(III) penetrated deep into the matrix, being isolated in a cavity-like site. The TRLFS study showed that the coordination environment of Eu(III) is stabilized mainly by the inner spherical coordination in chitin and by the outer spherical coordination in chitosan, with less association in cellulose in comparison to chitin and chitosan. These results suggest that the association of these biopolymers with Eu(III), Am(III), and Cm(III) is governed not only by the affinity of the functional groups alone but also by other factors, such as the macromolecular steric effect. The association of degraded materials of the biopolymers also should be taken into consideration for an accurate prediction of the influence of biopolymers on the migration behavior of trivalent f-elements.

Interactions of rare earth elements with bacteria and organic ligands

We investigated the interactions of rare earth elements (REEs) Eu(III) and/or Ce(III, IV) with the common soil bacterium Pseudomonas fluorescens and organic ligands, such as malic acid, citric acid, a siderophore (DFO), cellulose, chitin, and chitosan. Malic acid formed complexes with Eu(III), but degradation of malic acid was observed when the ratio of malic acid to Eu(III) was higher than 100. Citric acid formed a stoichiometric complex with Eu(III) that was not degraded by P. fluorescens. Adsorption of Eu(III) from the DFO complex occurred as a free ion dissociated from DFO and not as the Eu(III)–DFO complex. Cerium(III) was oxidized to Ce(IV) during complexation with DFO to form the Ce(IV)–DFO complex. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) analysis showed that cellulose, chitin, and chitosan, respectively, formed a weak complex, an inner-spherical complex, and an outer-spherical complex with Eu(III). This method also demonstrated that the coordination environment of Eu(III) adsorbed on P. fluorescens possessed similar characteristics to that of chitin, and revealed that adsorption of Eu(III) on P. fluorescens was through a multidentate and predominantly inner-spherical coordination.

Sorption behavior of europium(III) and curium(III) on the cell surfaces of microorganisms

SummaryWe investigated the association of europium(III) and curium(III) with the microorganismsChlorella vulgaris,Bacillus subtilis,Pseudomonas fluorescens,Halomonassp.,Halobacterium salinarum, andHalobacterium halobium. We determined the kinetics and distribution coefficients (Kd) for Eu(III) and Cm(III) sorption at pH 3-5 by batch experiments, and evaluated the number of water molecules in the inner-sphere (NH₂O) and the degree of strength of ligand field (RE/M) for Eu(III) by time-resolved laser-induced fluorescence spectroscopy (TRLFS). Exudates fromC. vulgaris,Halomonassp., andH. halobiumhad an affinity for Eu(III) and Cm(III). The logKdof Eu(III) and Cm(III) showed that their sorption was not fully due to the exchange with three protons on the functional groups on cell surfaces. The halophilic microorganisms (Halomonassp.,Halobacterium salinarum,H. halobium) showed almost no pH dependence in logKd, indicating that an exchange with Na+on the functional groups was involved in their sorption. The Δ NH₂O(=9-NH₂O) for Eu(III) onC. vulgariswas 1-3, while that for the other microorganisms was over 3, demonstrating that the coordination of Eu(III) withC. vulgariswas predominantly an outer-spherical process. TheRE/Mfor Eu(III) on halophilic microorganisms was 2.5-5, while that for non-halophilic ones was 1-2.5. This finding suggests that the coordination environment of Eu(III) on the halophilic microorganisms is more complicated than that on the other three non-halophilic ones.

Influence of humic acid size on actinide complexation

Abstract The complexation of Am(III) and Eu(III) with humic acid of different molecular sizes was measured and the data for the ≥300kD and ≥10kD sized HA at pcH 4.0 and 6.0 was analyzed by the Charge Neutralization Model (CNM) and the Polyelectrolyte Model (PM). For the PM, solvent extraction was used to obtain the stability constants of 241Am at tracer concentration. For the CNM, ultrafiltration was used to determine the loading capacity and the stability constants for Eu(III) at macro concentrations. There was a difference of 1-2 orders of magnitude in the stability constants from the two models. The 5 D 0–7 F 0 excitation spectra of Eu(III) as a function of loading of HA was found to have a shift in wavenumbers of the peak maximum, indicating that the coordination environment of Eu(III) varied with pH, presumably due to variation in the number of functional groups of the humate bound to the metal ion.

Synthesis and structure of trisodium (ethylenediaminetetraacetato)europate(II) chloride heptahydrate

The structure of trisodium (ethylenediaminetetraacetato)europate(II) chloride heptahydrate, Na 3[Eu(C 5H 12N 2O 8)]Cl·7H 2O is polymeric and the Eu 2+ cation is octacoordinate (six carboxyl oxygen atoms and two nitrogen atoms). The Eu–O distances are similar to those observed earlier. There are no water molecules in the coordination environment of Eu 2+.

The coordination environment of Eu(III) ions in hydrated A and Y zeolites as determined by luminescence lifetime and EXAFS measurements

Luminescence lifetimes and EXAFS show that the average coordination of Eu3+ in the large-pore zeolite Y is identical to that in aqueous solution, while the coordination number in the small-pore zeolite A is lower, probably because of steric constraints.