Europium Compounds Research Articles

Spectroscopic Studies of Europium(III) and Gadolinium(III) Tris‐β‐diketonate Complexes with Diazabutadiene Ligands

AbstractAdducts of the type Ln(NTA)3·L [Ln = Eu, Gd; NTA = 1‐(2‐naphthoyl)‐3,3,3‐trifluoroacetonate; L = 1,4‐diaza‐1,3‐butadiene RN=CHCH=NR (R = p‐tolyl, o‐tolyl)] were prepared by treatment of Ln(NTA)3·2H2O with one equivalent of the chelating N−N ligand. The mixed ligand complexes were characterised by elemental analysis, thermogravimetric analysis, IR and Raman spectroscopy, and photoluminescence (PL) spectroscopy. Ab initio calculations were carried out in order to predict coordination geometries and also to interpret the vibrational spectra. For the europium(III) compounds, new Raman‐active bands at approximately 440 and 479 cm−1 are tentatively assigned to (νEu−N)sym and (νEu−N)as modes, respectively. A second band at 1185 cm−1 is associated with the symmetric stretching of the N−C(ring) and C−C (DAB) bonds, and is shifted about 20 cm−1 to a higher wavenumber relative to the corresponding band for the free ligand. The room‐temperature PL spectra of the two Eu complexes are composed of the typical Eu3+ red emission, assigned to transitions between the first excited state (5D0) and the ground multiplet (7F0−4). Based on the room‐temperature emission spectra and lifetime measurements, the quantum efficiencies of the 5D0 Eu3+ excited state were estimated and found to be quite low (e.g. 2−3%). The low efficiencies are attributed to the presence of thermally activated nonradiative channels involving ligand‐to‐metal charge‐transfer (LMCT) states. Indeed, a low‐lying LMCT band was detected for the Eu complex containing the ligand p‐tolyl‐DAB by comparison of the room‐temperature diffuse reflectance spectrum for this complex with that of the corresponding Gd analogue. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Homolysis of the Ln−N (Ln = Yb, Eu) Bond − Synthesis, Structure, and Catalytic Activity of Ytterbium(II) and Europium(II) Complexes Having (Dimethylamino)propyl‐ and (Dimethylamino)ethyl‐Functionalized Indenyl Ligands

AbstractWe have synthesized a new series of ytterbium(II) and europium(II) complexes by tandem silylamine elimination/homolysis of Ln−N (Ln = Yb, Eu) bonds. The interaction of 2 equiv. of C9H7CH2CH2CH2NMe2 (1) with [(Me3Si)2N]3Ln(μ‐Cl)Li(THF)3 (Ln = Yb, Eu) in toluene under reflux produced lanthanide(II) complexes [(η5:η1‐C9H6CH2CH2CH2NMe2)2Ln] [Ln = Yb (2), Eu(3)] in 67 and 74% yields, respectively. Treatment of 2 equiv. of Me2Si(Me2NCH2CH2C9H6)(NHtBu) with [(Me3Si)2N]3Eu(μ‐Cl)Li(THF)3 in toluene at 80 °C afforded a europium(II) complex [η5:η1‐Me2Si(Me2NCH2CH2C9H5)(NHtBu)]2Eu·(OC4H8)0.5 (4) in 46% yield. The interaction of 2 equiv. of Me2NCH2CH2C9H6SiMe3 with [(Me3Si)2N]3Eu(μ‐Cl)Li(THF)3 produced a europium(II) compound [η5:η1‐(Me2NCH2CH2C9H5SiMe3)]2Eu (5) in 49% yield. Treatment of 2 equiv. of Me2NCH2CH2C9H7 with [(Me3Si)2N]3Eu(μ‐Cl)Li(THF)3 in toluene gave a europium(II) complex (η5:η1‐Me2NCH2CH2C9H6)2Eu (6) in 57% yield. All the compounds were fully characterized by spectroscopic methods and elemental analyses. The structures of the complexes 4, 5, and 6 were determined by single‐crystal X‐ray analyses. The catalytic activities of organometallic complexes were examined; we found that all of the complexes can function as single‐component MMA polymerization catalysts with good activity. We studied the effects of solvent and temperature on the catalytic activities and the stereochemistries of the polymers. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Evaluation of the lanthanide compression by spectra of europium and terbium compounds

Comparison of the luminescence spectra of europium and terbium compounds was suggested for direct evaluation of the influence of compression of the lanthanide wavefunctions in transition from europium to terbium—‘lanthanide compression’. It is possible because the types of symmetry of the states of the Stark components of europium 7FJ energy levels determined previously could be used for assignment of corresponding components of Tb3+ energy levels. This procedure can lower the ambiguity of calculations of the crystal field parameters for terbium compounds.

Spectroscopy of europium and terbium pyridine-carboxylates

Luminescence, luminescence excitation, IR, and Raman spectra of europium and terbium isomeric pyridine-carboxylates: isonicotinates, nicotinates and picolinates were studied. The ways of the excitation energy transfer from the ligand to Ln3+ were analysed in dependence on the structure and the type of co-ordination of ligand. Intraligand charge transfer bands and Tb3+ f–d transition bands were identified in the luminescence excitation spectra of terbium and europium compounds. Co-ordination of nitrogen atom by terbium ion in picolinates (and dipicolinates) causes low-frequency shift of the f–d bands and promotes the excitation of luminescence through d-states of Tb3+.

Spectroscopy of europium and terbium pyridine-carboxylates

Luminescence, luminescence excitation, IR, and Raman spectra of europium and terbium isomeric pyridine-carboxylates: isonicotinates, nicotinates and picolinates were studied. The ways of the excitation energy transfer from the ligand to Ln 3+ were analysed in dependence on the structure and the type of co-ordination of ligand. Intraligand charge transfer bands and Tb 3+ f–d transition bands were identified in the luminescence excitation spectra of terbium and europium compounds. Co-ordination of nitrogen atom by terbium ion in picolinates (and dipicolinates) causes low-frequency shift of the f–d bands and promotes the excitation of luminescence through d-states of Tb 3+ .

Nanostructured ZnO/Y 2O 3:Eu for use as fillers in luminescent polymer electrolyte composites

Nanostructured ZnO/Eu and ZnO/Y 2O 3:Eu composites have been produced by hydrolizing a mixture of zinc acetate, yttrium acetate and europium acetate in ethanol solution, followed by mixing with lithium hydroxide. By analyzing the ICP data, XRD patterns and luminescence emission spectra we concluded that the europium and yttrium compounds appeared as coating layer on the surface of ZnO nanoparticles. Without heating, these layers were in amorphous state and transformed into crystalline state after annealing at temperatures of above 600 °C around 30 min. We observed the presence of lithium hydroxide concentration threshold below which no coating layer was formed on the surface of ZnO nanoparticles. The emission intensity of ZnO/Y 2O 3:Eu was found to increase with increasing annealing temperature, while the crystalline size of Y 2O 3 (close to 20 nm) decreased with increasing the annealing temperature. The powder produced might be used as fillers in luminescent polymer electrolyte composites, which can produce two colors, i.e., red (Eu emission) when excited using a wavelength of around 254 nm and green (emitted by ZnO nanoparticles) when excited using a wavelength of around 365 nm.

Sensitization of Luminescence of Europium Compounds on Solid Matrices by Terbium (III) Ions

The conditions of sensitization of the luminescence of Eu(III) by Tb(III) ions in complexes with inorganic (Na2WO4) and organic (nalidixic acid) ligands in sorbates on solid matrices (zeolite CaX and crystalline zirconium phosphate (ZrP)) and in coprecipitation with CaWO4 have been investigated. It has been established that the maximum sensitization of the europium luminescence is attained in the case where Eu and Tb are present in a 1:0.5 ratio. In this case, the integral intensity of luminescence of Eu(III) (the band with λmax = 612 nm) in the sorbate of its complex with nalidixic acid on ZrP accounts for more than 60% of the luminescence intensity of the industrial photoluminophor Y2O3:Eu (FL-612) possessing red luminescence, and the intensity of Tb(III) luminescence (the band with λmax = 545 nm) accounts for about 40% of the luminescence intensity of the photoluminophor Gd2O2S:Tb possessing green luminescence.

Lanthanide compounds containing a benzo-15-crown-5 derivatised [60]fullerene and the related [Tb(H2O)3(NO3)2(acac)]·C14H20O5supramolecular adduct

Novel lanthanum(III), europium(III) and terbium(III) compounds of a benzo-15-crown-5 [60]fulleropyrrolidine were isolated in the solid state and characterised using vibrational (infrared and Raman) spectroscopy and by 13C CP MAS NMR for the lanthanum(III) compound. The photoluminescence properties were investigated for the europium(III) and terbium(III) compounds. The related [Tb(H2O)3(NO3)2(acac)]·C14H20O5 [where acac− = acetylacetonate and C14H20O5 = benzo-15-crown-5] supramolecular adduct was isolated using similar synthetic conditions, in the absence of [60]fullerene, and its crystal structure used as a model for the coordination sphere of the lanthanide [60]fullerene derivatives, with further supporting evidence given by photoluminescence measurements.

Neodymium and europium complexes with amides and cyclic aminoxides

Complexes of neodymium and europium with amides and aminoxides were synthesized and characterized by complexometric analyses with EDTA, CHN microanalytical procedures, IR absorption spectra, absorption spectra of neodymium complexes, emission spectrum of europium compounds at 77 K, thermogravimetric analyses in N2 and differential scanning calorimetry (DSC) in N2. Infrared spectroscopy results revealed that the nitrate molecules are bound to the central ions as bidentate. Thermogravimetric plots indicated that the decomposition of the complexes occurs in the range 363-1163 K and resulted in the formation of Ln2O3 residues.

Europium(III) and terbium(III) trans-2-butenoates: syntheses, crystal structures, and properties

Homometallic europium(III) and terbium(III) trans-2-butenoate polymers, chemical formulas [{Eu 3(MeCHCHCO 2) 9(H 2O) 4}·H 2O·EtOH] n ( 1) and [{Tb(MeCHCHCO 2) 3(H 2O)}·MeCHCHCO 2H] n ( 2) and their dimeric 1,10-phenanthroline derivatives [Ln 2(MeCHCHCO 2) 6(phen) 2]·2H 2O, with Ln=Eu ( 3) and Tb ( 4), were prepared and characterized by single-crystal X-ray diffraction. The coordination polymers 1 and 2 adopt different carboxylate-bridged infinite chain structures. While the europium compound 1 shows three independent europium centers linked to each other by three different types and number of carboxylate bridges, the terbium polymer 2 shows one independent metal center bridged by the same type of double carboxylates along the chains. Compounds 3 and 4 are isomorphous dinuclear structures with quadruply bridged carboxylate groups, two in the η 1:η 1:μ 2 and two in the η 2:η 1:μ 2 modes. The magnetic and photophysical behaviors of the four compounds are reported in the solid state.

Homolysis of the Eu−N Bond. Synthesis, Structural Characterization, and Catalytic Activity of Novel Europium(II) Complexes

Two new indene compounds, C9H7CH2SiMe2NC4H8 (1) and C9H6-1-Me-3-CH2SiMe2NC4H8 (2), were synthesized by the reaction of C9H6RLi (R = H, Me) with ClCH2SiMe2Cl, followed by treatment with lithium pyrrolidinide C4H8NLi. The interaction of [(Me3Si)2N]3Eu(μ-Cl)Li(THF)3 with 2 equiv of 1 in refluxing toluene produced, after workup, a novel triple-decker sandwich tetranuclear europium(II) compound, [{η:5η:5η1-(C9H5CH2SiMe2NC4H8)2}Eu2(μ-Cl)]2[μ-η3:η5:η1:η3:η5:η1-(C9H5CH2SiMe2NC4H8)2]·C7H8·(C6H6)0.5 (3), with a coupled indenyl ligand through tandem silylamine elimination, reduction of Eu3+ to Eu2+, and the C−C coupling reactions. To probe the formation pathway of complex 3, the interaction of C9H6-1-Me-3-CH2SiMe2NC4H8 (3) with [(Me3Si)2N]3Eu(μ-Cl)Li(THF)3 was studied. Treatment of [(Me3Si)2N]3Eu(μ-Cl)Li(THF)3 with 2 equiv of 2 in refluxing toluene temperature or at 60 °C produced, after workup, a monomeric europium(II) complex, (η5:η1-C9H5-1-Me-3-CH2SiMe2NC4H8)2Eu (4), via tandem silylamine elimination/homolysis of...

Luminescence and photophysics of sandwich-type bis(phthalocyaninato) europium compound

Ground-state electronic absorption and fluorescence spectra of sandwich-type bis(phthalocyaninato) europium(III) compound Eu(Pc) 2 are described. The emission spectra changed dramatically under different excitation wavelength. An energy level diagram is proposed to interpret the electron and energy transition and photophysical process of the strongly coupled rare earth sandwich compound.

Physical and optical properties of the quaternary sulfides SrCu 2MS 4 and EuCu 2MS 4 ( M=Ge and Sn)

Four quaternary sulfides SrCu 2 MS 4 and EuCu 2 MS 4 ( M=Ge and Sn) were prepared from a thoroughly ground mixture of EuS or SrS, Cu, or Sn, and S in stoichiometric proportions. Electrical conductivity measurements on pressed pellets showed that all the phases are semiconductors. The optical band gaps were assessed at 2.8 eV for SrCu 2GeS 4, 2.1 eV for SrCu 2SnS 4, 2.2 eV for EuCu 2SnS 4, and 1.6 eV for EuCu 2GeS 4. Both Sr-based compounds present a temperature-independent paramagnetism, of about +135×10 −6 and +92×10 −6 emu/mol, for SrCu 2SnS 4 and SrCu 2GeS 4, respectively. In the case of the europium compounds, they follow a Curie–Weiss dependence above 1.8 K (EuCu 2GeS 4) and above 4 K (for EuCu 2SnS 4), with values of the magnetic effective moment μ eff and the Curie–Weiss temperature Θ, equal to 6.27 μ B and −2.8 K for EuCu 2GeS 4, and 6.81 μ B and +0.7 K, for EuCu 2SnS 4. The experimental magnetic moments confirm that the europium ion is in divalent state, similar to Sr in the related compounds.

The structure of ligands and effects of the europium luminescence excitation

Results of studies of the luminescence excitation spectra of europium compounds: β-diketonates, aromatic carboxylates, nitrates with sulfoxides are presented. The processes of transfer and degradation of the excitation energy are discussed. Alteration of the relative contribution of two inequivalent ligands to the luminescence excitation of europium β-diketonates with 1,10-phenanthroline derivatives upon modification of ligand radicals and variation of relative binding strength of ligands by metal ion was investigated. The participation of the ligand–metal charge transfer states both in degradation of the excitation energy and in enhancement of Eu3+ luminescence excitation was analyzed. Increase of intraligand charge transfer upon introduction of a ligand's acceptor substituent such as nitro-group, decreasing the ligand–metal charge transfer, was demonstrated. Blocking effect of methylene or oxymethylene bridges on the energy transfer from ligand to Eu3+ ion was observed. This phenomenon witnesses about the electron exchange mechanism of the interaction between the disjuncted parts of the ligand.

Electronic and Magnetic Transitions in Europium Compounds Studied by Nuclear Forward Scattering of Synchrotron Radiation

Since its observation in 1985, nuclear resonance scattering of synchrotron radiation has become an excellent tool to study hyperfine interactions as well as dynamical effects in solids. It has proven to be a complementary method to Mossbauer spectroscopy. Nuclear resonance scattering combines the advantages of both local probe experiments and scattering techniques. It gives valuable information as well on electronic and magnetic structures and on dynamics in solids. Experiments benefit from the high beam quality of third-generation synchrotron radiation sources, as the small beam size and divergence. Besides the “standard isotope” 57Fe, other Mossbauer isotopes have become more important in nuclear resonant scattering of synchrotron radiation. This article concentrates on the 151Eu isotope.

Luminescent Properties of Polyethylene Films with the Addition of Photoluminophores Based on Europium Compounds

Luminescent Properties of Polyethylene Films with the Addition of Photoluminophores Based on Europium Compounds

Energy transfer in europium and terbium compounds formed with[Cr(OH)6Mo6O18]3− and [Cr0.1Al0.9(OH)6Mo6O18]3− heteropolyanions

The new compounds Ln[M(OH)6Mo6O18]·11H2O (Ln = Tb, Eu and M = Al, Cr)were synthesized and their luminescence properties analysed and discussed.Results show that there is a very efficient energy transfer from Eu3+ (Tb3+) to Cr3+ions in Eu[Cr(OH)6Mo6O18]·11H2O and Tb[Cr(OH)6Mo6O18]·11H2O. Thetransfer strongly quenches Eu3+ (Tb3+) luminescence and greatly shortensthe lifetimes of the radiative levels. By using selective excitation at lowtemperature, the transfer mechanisms are investigated and models arepresented. Based on the above model, a rate of ET kC = 1.33 × 106s−1from Tb3+ to Cr3+ ions in Tb[Cr(OH)6Mo6O18]·11H2O at 12 K is obtained.

Absorption and emission spectroscopic investigation of the phyto-extraction of europium(III) nitrate from aqueous solutions by alfalfa biomass

Europium(III) is a common product found in nuclear wastes. Recent investigations into the use of europium compounds as cancer therapy treatments have proven promising. In this study, europium(III) nitrate binding studies were performed using unmodified and esterified alfalfa biomass. Batch experiments included pH profile studies and X-ray absorption spectroscopy (XAS) inspection to determine the functional groups responsible for the binding of europium(III) nitrate on alfalfa. Results from the pH profile study showed that approximately 80% of the europium(III) nitrate bound to the native alfalfa biomass while the esterified biomass showed approximately 40% binding at pH 5. XAS consists of two complementary components: X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The XAS experiments were performed using the europium L III edge which had an energy of 6.977 KeV. The XANES spectra showed that there were some changes in the characteristics of the europium(III) nitrate when bound to the modified and unmodified alfalfa biomass. No change in the europium(III) oxidation state was observed after europium(III) binding to the alfalfa biomass. EXAFS spectra showed that europium(III) nitrate binds to the alfalfa biomass via a nitrogen or oxygen ligand with bond lengths ranging from 2.44 to 2.49 Å. However, chemical esterification experiments show that oxygen may be the primary ligand for coordination. The coordination numbers for all samples and compounds tested were approximately 9.

Synthesis, characterization and thermal analysis of lanthanide picrate complexes with glycine

Complexes of lanthanide picrates with glycine were synthesized and characterized. Analysis of carbon, hydrogen, nitrogen and thermal analysis data suggest a general formula Ln(pic) 3·2Gly· xH 2O (Ln=La–Lu and Y; pic=picrate; Gly=glycine; x=4 for Gd–Lu, Y and x=5 for La–Eu). IR spectra indicate the presence of water molecules and suggest that glycine is coordinated to the central ion through the nitrogen of the amine group. Bands due to picrate ions also indicate that at least in part they are coordinated as bidentate through the phenoxo group and one oxygen of an ortho-nitro group. Conductance measurements in acetone show that the complexes behave as non-electrolytes. X-ray powder data show the existence of two isomorphous series. The parameters obtained from the absorption spectrum of the Nd compound indicated that the metal–ligand bonds present weak covalent character. The spectrum of the europium compound was interpreted in terms of C 2v symmetry. The thermal analyses results indicated that all the compounds present a similar behavior.

Synthesis and structure of lanthanide picrates with trans-1,3-dithiane-1,3-dioxide

Compounds with the formula [Ln(pic) 3( trans-DTSO 2) 2] (Ln=La–Lu and Y) were obtained by reaction of hydrated lanthanide picrates with trans-1,3-dithiane-1,3-dioxide ( trans-DTSO 2) in absolute ethanol. Lanthanide contents were determined by titration with EDTA; CHN were determined by microanalytical procedures. Data are in good accordance with the proposed stoichiometry. IR absorption spectra were interpreted in terms of trans-DTSO 2 and picrate anions coordinated through the oxygen atoms. The parameters obtained from the absorption spectrum of the Nd(III) compound indicate weakly covalent metal–ligand bonds. The emission spectrum obtained at 77 K for the Eu(III) compound suggests a C 2v symmetry for the coordination polyhedron. X-Ray powder patterns show that the compounds are isomorphous. The structure of europium compound was determined by single crystal X-ray analysis and showed that the crystals are triclinic, space group P 1 ̄ , a=10.771(1) Å, b=12.243(1) Å, c=16.415(2) Å, α=99.930(10)°, β=103.970(10)°, γ=106.220(10)°. The compound exhibits a polymeric structure, in which two trans-DTSO 2 are bridging the Eu(III) ions. The central ion is octacoordinated to four oxygens of trans-DTSO 2 and four oxygens of one bidentate and two monodentate picrate anions, in a bicapped trigonal prism geometry, the dihedral angle between the bases being 14.2(1) o.