Comparison of 7FJ←5DO emission spectra for Eu(III) in crystalline environments of octahedral,near-octahedral,and trigonal symmetry

Isotropic ⁷F_J←⁵D_O emission spectra are reported for Eu(III) in four different crystalline system. These systems differ with respect to Eu(III) site symmetry, coordination number, coordination geometry, and the chemical nature of the coordinated ligands. Comparison between the spectra obtained on these systems reveal major differences in the relative intensities of the ⁷F_J←⁵D_O emission, and these differences are discussed in terms of ligand modulated 4f — 4f intensity mechanism.     

Bovine α-Lactalbumin: Identification of two metal-ion-binding sites using the europium (III) luminescent probe

The luminescent Eu^III ion has been used to probe the metal-binding sites of bovine α-lactalbumin (BLA) in D₂O. Upon addition of apo-BLA to an Eu^III-containing solution, the intrinsic luminescence of the protein is quenched, and the Eu^III luminescence is enhanced. Luminescent titrations point to there being at least two different metal-binding sites in the apo-protein. Curve analysis of the high resolution ⁵D₀←⁷F₀ excitation spectra reveals the existence of three different environments for the bonded Eu^III ions. Two environments, labelled I_a and I_b, give ⁵D₀←⁷F₀ bands very close in energy; they contain four negatively charged groups and are assigned to one site we identify as the calcium-binding site. Site I is protected from solvent influences and is somewhat rigid, since it displays selectivity towards lanthanide ions. The origin of the two similar environments I_a and I_b could not be determined unambiguously. The third environment is ascribed to a nonspecific metal-binding site in which the Eu^III ion is more exposed to the solvent (site II). It is sequentially populated after saturation of site I, and its population is pH-dependent. The affinity constant of Eu^III for this site was estimated from the excitation spectra: log K₂^app ? 3.5(1). Assignment of the metal binding sites has been facilitated by comparison with model compounds, [Eu(dota)]^? (dota ? 1,4,7,10-tetraazacyclododecane N,N′,N″, N?-tetraacetate), [Eu(dtpa)]^2? (dtpa ? diethylenetriamine tetraacetate), and [Eu(bsa)] (bsa ? bovine serum albumin). The usefulness and limits of the use of curve-analysis procedures to unravel the various components of ⁵D₀←⁷F₀ excitation spectra in biological materials are also discussed.     

Study of spectroscopic properties of Europium (III) Tris(β-diketonate) complex and α-Cyclodextrin in aqueous medium

The solubilization of an europium (III) β-diketonate chelate in aqueous medium and the changes in its photophysical properties upon its inclusion into an α-cyclodextrin hydrophobic cavity are described. The complex [Eu(tta)₃·(H₂O)₂] (tta = 4,4,4-trifluoro-1-(thiophen-2-yl)butane-1,3-dione) was synthesized, characterized, and incorporated into the hydrophobic cavity by stirring in an α-cyclodextrin aqueous solution. The inclusion was confirmed by ¹H NMR, and the stoichiometry of association was obtained by the Job method. The maximum in the excitation spectrum of the α-CD inclusion compound in aqueous solution was shifted 28 nm compared with the maximum of non α-CD complex. The emission spectrum of the association is similar to that of the free solid complex and displays the characteristic ⁵D₀ → ⁷F_0-4 Eu³⁺ transitions.     

Luminescence Investigations on Eu(III) Thenoyltrifluoroacetonate Complexes with Amide Ligands

The influence of amide ligands on the photoluminescent behavior of tris(thenoyltrifluoroacetonate)- europium(III) in the solid state is reported. Elemental analysis showed that these compounds have the following formulas [Eu(TTA)₃·(ANL)₂] and [Eu(TTA)₃·PZA], where ANL = acetanilide and PZA = pyrazinamide. The photoluminescence spectra of the complexes recorded in the range 420-720 nm at 77 K show narrow bands arising from the ⁵D₀ → ⁷F _J transitions (where J = 0-4), under excitation at 394 nm. Based on the emission spectra and luminescence decay curves the intensity parameters (Ω_λ), lifetime (τ) and emission quantum efficiency (η) were determined. The Ω₂ values indicate that the Eu³⁺ion in these complexes is in a highly polarizable chemical environment. The higher value of η (60%) obtained for the complex with the ANL ligand, in comparison with the complex with the PZA ligand (30%), indicates a more efficient deactivation of the Eu³⁺ion in the [Eu(TTA)₃·PZA] complex.     

Polarographic study of Eu(III)-succinate-ethylenediamine and Eu(III)-malonate-ethylenediamine mixed systems

The mixed complexes of Eu(III) with succinate (succ^2?) and malonate (mal^2?) and ethylenediamine (en) have been studied polarographically at 25°C and at constant ionic strength, μ = 0.1 (NaNO₃) and pH 6. The reduction of the complexes in each case is quasi-reversible and diffusion-controlled. In each system three mixed complexes are formed, viz. [Eu(succ)(en)]⁺, [Eu(succ)(en)2]⁺ and [Eu(succ)₂(en)]^? with stability constants log β₁₁ = 9.2, log β₁₂ = 17.5 and log β₂₁ = 11.7; and [Eu(mal)(en)]⁺, [Eu(mal)₂(en)₂]^? and [Eu(mal)₃(en)]^3? with stability constants log β₁₁ = 11.4, log β₂₂ = 19.08 and log β₃₁ = 13.5 respectively.     

Structure and phase transitions in poly(diethylsiloxane)

The structure changes accompanying phase transitions in poly(diethylsiloxane) (PDES) have been studied by WAXS and SAXS techniques using oriented and isotropic samples. PDES may exist in two low-temperature modifications (the monoclinic α₁-form and presumably the “tetragonal” β₁-form) and two high-temperature modifications (the monoclinic α₂-form and the “tetragonal” β₂-form). In linear PDES the crystal - crystal transitions α₁–α₂ and β₁–β₂ occur near 214 and 206 K, respectively. At higher temperatures α₂ (280 K) and β₂ (290 K) forms transform into the mesomorphic phase α_m that gradually melts at 280–300 K giving an amorphous phase. According to x-ray and density data, α_m phase is also characterized by monoclinic structure slightly different from hexagonal packing.     

The Eu(III) Ion as Luminescent Probe: Investigation of the Metal-Ion Sites in a Dicyclohexyl-18-crown-6 Complex

The metal ion sites of the 3:2 complex between europium nitrate and the A -isomer of dicyclohexyl-18-crown-6, [Eu(NO₃)₂(DC18C6)]₂[Eu(NO₃)₅], have been probed by high-resolution excitation and emission spectra at 296 and 77 K. The [Eu(NO₃)₅]^2? anion gives rise to a luminescent spectrum dominated by the ⁵D₀→⁷F₂ transition. The crystal-field splitting of the ⁷F_j levels is close to that observed for (Phe₄As)₂[Eu(NO₃)₅], pointing to a structurally similar pentakis(nitrato) species. The ⁵D₀←⁷F₀ excitation spectrum of the two crystallographically independent complex cations displays five maxima. A detailed analysis of the corresponding and selectively excited emission spectra leads to the following conclusions. Well differentiated spectra are assigned to different conformations of the complex cation, in which half of the ligand atoms, including O-atoms, Present large thermal motions. The other spectra are very similar and arise from slightly unequivalent [Eu(NO₃)₂(DC18C6)]⁺ moieties differing in the conformation of their ethylene bridges. This dimonstrates the sensitivity of the Eu(III) ion as conformational probe in the solid state.     

Solid-state polymerization of long-chain vinyl compounds. I. Effect of molecular arrangement on polymerizability of octadecyl methacrylate

γ-Ray-initiated postpolymerization of octadecyl methacrylate in polymorphic crystals and melt has been investigated to clarify the effect of molecular arrangement of the monomer on polymerizability. From thermal, x-ray, and infrared (IR) analyses this long-chain monomer exhibited three crystalline modifications that we refer to as α-, sub-α, and β-forms. The β-form (mp 28.7–29.7°C), which is obtainable from solution, is a stable state with triclinic chain packing. The α-form (mp 19.5–20.0°C), which is obtained first from the melt but transforms into β-form on storing, is a metastable state with hexagonal chain packing. The sub-α-form appears transiently in α→β transition. The polymerizability of octadecyl methacrylate in the β-form is extremely low, whereas the α-form can polymerize easily and the initial polymerization rate, saturated conversion, and polymer molecular weights increase with temperature. Polymerizability in the molten state at fairly high temperature is rather low, however. Thus maximum polymerizability is obtained just above the melting point of α-form. It has been found that particular orientation and suitable packing mode with some freedom of rotational motion of the monomer molecules in layered structure accelerate the polymerization reaction.     

Synthesis and photophysical properties of new Ln(III) (Ln = Eu(III), Gd(III), or Tb(III)) complexes of 1-amidino-O-methylurea

Three new solid lanthanide(III) complexes, [Ln(1-AMUH)₃] · (NO₃)₃ (1-AMUH = 1-amidino-O-methylurea; Ln = Eu(III), Gd(III), or Tb(III)) were synthesised and characterised by elemental analysis, infrared spectra, magnetic moment measurement, and electron paramagnetic resonance (EPR) spectra for Gd(III) complex. The formation of lanthanide(III) complexes is confirmed by the spectroscopic studies. The photophysical properties of Gd(III), Eu(III), and Tb(III) complexes in solid state were investigated. The Tb(III) complex exhibits the strongest green emission at 543 nm and the Eu(III) complex shows a red emission at 615 nm while the Gd(III) complex shows a weak emission band at 303 nm. Under excitation with UV light, these complexes exhibited an emission characteristic of central metal ions. The powder EPR spectrum of the Gd(III) complex at 300 K exhibits a single broad band with g = 2.025. The bi-exponential nature of the decay lifetime curve is observed in the Eu(III) and Tb(III) complexes. The results reveal them to have potential as luminescent materials.     

(Tetracycline)europium(III) Complex as Luminescent Probe for Hydrogen Peroxide Detection

Luminescence spectra of aqueous solutions containing a fixed concentration of tetracycline (TC) and increasing concentrations of Eu³⁺ were recorded both in the absence and presence of hydrogen peroxide (H₂O₂). In H₂O₂‐free solutions in which the Eu/TC molar ratio was varied from 1 : 1 to 8 : 1, the ⁵D₀→⁷F₀ transition consisted of only one peak at 580 nm. In the presence of H₂O₂, an extra peak appeared in the spectrum at 578 nm when the Eu/TC molar ratios were above 2.5. A detailed analysis of this spectral region revealed that at lower Eu/TC molar ratios (up to 2 : 1), the ⁵D₀→⁷F₀ transition experienced a slight blue shift. This indicates that at low Eu/TC molar ratios, the presence of H₂O₂ leads to two different environments of the trivalent europium ions, which most likely form bridged peroxide complexes with hydrogen peroxide (μ‐H₂O₂ ligand). Luminescence spectra measured in the presence of molybdate ions, which catalytically decompose H₂O₂, led to the disappearance of the extra europium(III) site that was formed in the presence of H₂O₂. The intensity of the hypersensitive ⁵D₀→⁷F₂ transition did not linearly depend on the H₂O₂/TC molar ratio. For H₂O₂/TC ratios up to 10, a sharp linear increase of the peak intensity was observed, but with further increase of the H₂O₂ concentration, the intensity remained nearly constant. For H₂O₂/TC ratios above 100, the intensity of this transition even started to decrease, which limits the use of the (tetracycline)europium(III) system to quantify hydrogen peroxide in solution.     

Interaction between the buffer Tris and the eu(III) ion: Luminescence and potentiometric investigation

The interaction between the buffer 2-amino-2-(hydroxymethyl)propane-1,3-diol (Tris) and the Eu(III) ion has been studied by luminescence spectroscopy in D₂O. Emission and excitation spectra (⁵D₀←⁷F₀ transition) indicate an interaction with both [TrisH]⁺ and neutral Tris species. The former is weak and probably of the outer-sphere type. The latter is of inner-sphere type and corresponds to the formation of the [Eu(Tris)]³⁺ species (estimated logK₁ = 2.3 ± 0.3). Buffer Tris is also demonstrated to prevent the formation of an Eu-hydroxo species in the pD range of 7–8. Potentiometric measurements in H₂O allowed a more precise calculation of the stability constant: logK₁ = 2.44 ± 0.07. Comparison with the data for aliphatic amines and other metal ions lead to the conclusion that the Eu/Tris interaction is mainly achieved through the amino group. ¹H-NMR spectra in presence of Tb(III) ions confirmed both this assumption and the presence of a weak interaction with TrisH⁺. Quantitative determinations of association constants between lanthanide ions and macromolecules of biological interest performed in presence of Tris should, therefore, be corrected for the Eu/Tris interaction.     

Extraction separation of Am(III) and Eu(III) using divalent quadridentate Schiff bases-bis-salicylaldehyde ethylenediamine

For the selective extraction of Am(III) and Eu(III), quadridentate divalent phenolic Schiff bases-bis-salicylaldehyde ethylenediamine (H₂salen) was investigated as a kind of extractant. The influences of alkaline cation, inorganic anion, ionic strength, pH and the concentration of H₂salen on the distribution ratio of Am(III) and Eu(III) were investigated in detail. As a result, Am(III) and Eu(III) made anionic 1:1 complexes with the ligand (H₂salen) and could be extracted into nitrobenzene as ion-pairs with a suitable monovalent counter anion in the aqueous solution, the extracted species were possibly of the type Am(H₂salen) Eu(salen)Cl and Eu(H₂salen)Cl₃, respectively. The extractability of Eu(III) was significantly stronger than that of Am(III) and the maximum separation factor, SF_(Am/Eu), was 96 at pH 4.0. The results indicated that H₂salen had good selectivity for Am(III) and Eu(III).     

Isomerieerscheinungen an substituierten s-Trithianen und s-Triselenanen. Isolierung von α-Triselenoacetaldehyd

Isomerisations of Triple Substituted s-Trithianes and s-Triselenanes. Isolation of α-Triseleno Acetic Aldehyde α-Trithio acetic aldehyde, α-triseleno acetic aldehyde and 2.4.6-tris-(trimethylsilyl)-s-trithiane are converted to the analogous conformers if they are treated with lewis-acids. α-Triseleno acetic aldehyde has been isolated for the first time by application of a sophisticated method for the preparation of triseleno acetic aldehyde. The conversion of various α-isomers into the β-forms is shown in ¹H-NMR spectra.     

Synthesis and Spectroscopic Studies of Chosen Heteropolytungstates and Their Ln(III) Complexes

The heteropolytungstates [(Na)P₅W₃₀O₁₁₀]^4– (I), [(Na)Sb₉W₂₁O₈₆]^18– (II) and [(Na)As₄W₄₀O₁₄₀]^27– (III) and the monovacant Keggin structure of the general formula [XW_11–xMo_xO₃₉]^n– (X-Si, P; n = 7 for P and 8 for Si) (IV) as well as their europium(III) complexes were studied. The structures of I–IV as well as the europium(III) encrypted [(Eu)P₅W₃₀O₁₁₀]^12– (VI), [(Eu)Sb₉W₂₁O₈₆]^16– (VII), [(Eu)As₄W₄₀O₁₄₀]^25– (VIII) and sandwiched [Eu(XW_11–xMo_xO₃₉)₂]^n– (n =11 for P and n = 13 for Si) (V) complexes were synthesized and spectroscopically characterized. The complexes were studied using UV-Vis absorption and luminescence, as well as the laser-induced europium ion luminescence spectroscopy. Absorption spectra of Nd(III) were used to characterize the complexes formed. Excitation and emission spectra of Eu(III) were obtained for solid complexes and their solutions. The relative luminescence intensities of the Eu(III) ion, expressed as the ratio of the two strongest lines at 594 nm and 615 nm, = I₆₁₅/I₅₉₄, which is sensitive to the environment of the primary coordination sphere about the Eu(III) ion, was calculated. In the case of the sandwiched [Eu(XW_11–xMo_xO₃₉)₂]^n– complexes a linear dependence of the luminescence quantum yield of Eu(III) ion, , (calculated using [Ru(bpy)₃]Cl₂ as a standard) on the content of Mo (number of atoms, x) in the [Eu(XW_11–xMo_xO₃₉)₂]^n– structure was observed.     

Zur Elektronenstruktur hochsymmetrischer Verbindungen der f‐Elemente. 38 [1] Kristall‐, Molekül‐ und Elektronenstruktur von Tris(hydrotris(1‐pyrazolyl)borato)‐samarium(III)

Electronic Structures of Highly Symmetrical Compounds of f Elements. 38 [1] Crystal, Molecular and Electronic Structure of Tris(hydrotris(1‐pyrazolyl)borato)samarium(III) Tris(hydrotris(1‐pyrazolyl)borato)samarium(III) (SmTp₃) crystallizes in the space group P6₃/m (No. 176) with two molecules in the unit cell. The Sm³⁺ central ion is coordinated by nine N atoms in the shape of a tricapped trigonal prism, leading to an effective crystal field (CF) of D_3h symmetry. The underlying CF splitting pattern was extracted from the absorption and luminescence spectra run at room and low temperatures, and simulated by fitting the free parameters of a phenomenological Hamiltonian achieving an r.m.s. deviation of 9.4 cm^?1 for 58 assignments. The parameters used allow the estimation of the global ligand field strength experienced by the Sm³⁺ central ion, the insertion of SmTp₃ into empirical nephelauxetic and relativistic nephelauxetic series, and the set‐up of experimentally based nonrelativistic and relativistic molecular orbital schemes in the f range.     

A direct carbon-13 and nitrogen-15 NMR study of europium(III) complexation-nitrate and europium(III)-isothiocyanate complexation in aqueous solvent mixtures

A direct, low-temperature nuclear magnetic resonance spectroscopic study of europium(III)-nitrate contact ion-pairing has been completed, and preliminary results for europium(III)-isothiocyanate have been obtained. In water-acetone-Freon mixtures, at –110°C to –120°C, four¹⁵N NMR signals are observed for coordinated nitrate ion. Area evaluations of the signals and their concentration dependence indicate the formation of Eu(NO₃)²⁺, Eu(NO₃) ₂ ¹⁺ , and two higher complexes, possibly the tetra-, with either the penta-or hexanitrato. This correlates well with similar¹⁵N NMR results obtained for Ce(III), Pr(III), Nd(III), and Sm(III). As a result of a higher dielectric constant, complex formation is significantly less in water-methanol mixtures, wheein only three complexes form with Eu(NO₃) ₂ ¹⁺ dominating at the highest anion concentrations. Competitive complexing experiments in water-methanol also were made by³⁵Cl NMR chemical shift and linewidth measurements, as well as¹⁵N NMR. Initial experiments with the Eu³⁺-NCS^– system show four coordinated anion signals, displaced from the bulk anion peak by about –250 ppm and –2,500 ppm in the¹³C and¹⁵N NMR spectra, respectively. Area evaluations are consistent with the presence of Eu(NCS)²⁺ through Eu(NCS) ₄ ^1- in these solutions. A consideration of the chemical shifts identified the nitrogen atom as the site of binding in the NCS^–. A discussion of these preliminary results, as well as those for several other metal-ions, will be presented.     

Luminescent and triboluminescent properties of europium(III) complex with cinnamic acid

An intensely emitting crystalline europium(III) complex with cinnamic acid [Eu(Cin)₃] _n and exhibiting triboluminescent properties is synthesized. It is established that the measured photo- and triboluminescence spectra are identical for the above polymeric non-centrosymmetric complex and are determined by the characteristic f-f luminescence of the europium(III) ion.     

Synthesis,thermal, and photophysical properties of polymethylmethacryalte (PMMA) doped with ternary deuterated Eu(III) complexes

Two Eu(III) ternary luminescent complexes, Eu(tpb-H)₃(Tppo)₂ and Eu(tpb-H)₃(Topo)₂ (Tppo: triphenylphosphine oxide, Topo: trioctylphosphine oxide, tpb: 4,4,4-trifluoro-1-phenyl-1,3-butanedione) were synthesized using β-diketonates and phosphine oxides as ligands. Luminescent polymers were fabricated by incorporating the deuterated Eu(III) complexes in a PMMA matrix. Luminescent PMMA containing Eu(tpb-D)₃(Tppo)₂ exhibited relatively higher quantum yield, faster radiation rate, sharper red emission and larger stimulated emission cross-section and the results indicated prepared luminescent polymers including Eu(tpb-D)₃(Tppo)₂ showed promising results for applications in novel organic Eu(III) devices. Additionally, the Eu(III) complexes and luminescent PMMA showed good thermostabilization.     

Influence of the N-[methylpyridyl]acetamide ligands on the photoluminescent properties of Eu(III)-perchlorate complexes

This work reports the synthesis, characterization and spectroscopic studies of Eu(III)-perchlorate complexes with amide ligands derived from N-[x-methylpyridyl]acetamide where x=3, 4 and 6. The Eu(ClO₄)₃3(x-mpa) complexes were characterized by elemental analyses, molar conductance, TG analyses and vibrational spectroscopy. Raman and infrared data show that the perchlorate ion, (ClO₄ ⁻), is bonded to Eu(III) as a monodentate ligand and that in these three complexes water molecules are not coordinated to the rare earth ion. The profiles of the emission spectra of the complexes with 3- and 4-mpa ligands are very similar but they differ from the complex containing 6-mpa ligand. This spectroscopic behavior can be rationalized in terms of the Ω_λ (λ=2 and 4) and R₀₂ experimental intensity parameters. The values of Ω₂ (∼6.5×10⁻²⁰ cm²) in these complexes are smaller than in Eu(III)-TTA compounds (Ω₂∼35.0×10⁻²⁰ cm²), indicating that in the former case the rare earth ion is in a chemical environment less polarizable. Lifetime and emission quantum efficiency measurements for the emitting level ⁵D₀ were carried out and the results are discussed.     

COORDINATION COMPOUNDS OF LANTHANIDE PERCHLORATES WITH PYRAZINEAMIDE

Abstract

Lanthanide perchlorate complexes of the type [Ln(pyaH)₄] (ClO₄)₃ where Ln=Pr, Nd, Sm, Eu, Tb and Lu, and pyaH is pyrazinamide have been isolated. The compounds were characterized by chemical analyses, molar conductance, vibrational spectra, and electronic absorption and emission spectra. The vibrational spectra and molar conductances indicate that the perchlorate groups are ionic and that pyaH acts a bidentate ligand. The oscillator strengths of the transitions of the Nd(III) complex were determined in terms of the Judd-Ofelt theory. It was possible to use the modified Judd-Ofelt parameters, τλ, for the evaluation of the spectral intensities. In addition, a group-theoretical analysis of the emission spectrum indicates an effective site symmetry D₂ for the Eu(III) complex between 77° K and 10° K.