Europium Salts Research Articles

Charge transfer bands in the luminescence excitation spectra of isomeric pyridinedicarboxylic salts of europium

The ligand–cation charge transfer band was observed in the region of 360–400 nm of the luminescence excitation spectrum of europium salt of 3,4-pyridinedicarboxylic acid but was absent in the spectra of europium 2,6- and 2,3-pyridinedicarboxylic salts. It was due to higher efficiency of the energy transfer through the charge transfer state conditioned by increased polarizability of the ligand of the former compound. Energy transfer through the excited ligand–lanthanide charge transfer state may explain the effect of the quenching of luminescence by the redox-sensitive lanthanide ions.

Synthesis and Luminescence Properties of Monophasic Organic−Inorganic Hybrid Materials Incorporating Europium(III)

Phosphine oxides 1−5 bearing one, two, or three hydrolyzable Si(OR)3 groups have been prepared. They were treated with anhydrous europium salts [Eu(NO3)3 or EuCl3] to afford complexes 6−10, the stoichiometry of which was found to be one Eu3+ for three PO centers. The hydrolytic polycondensation of these complexes gave rise to nanostructured hybrid materials incorporating Eu3+. A solid-state 31P NMR study of these hybrid materials has shown that Eu3+ remains well encapsulated within the materials when they are prepared from europium complexes with phosphine oxides bearing one hydrolyzable Si(OR)3 group. The luminescence behavior of these materials has been investigated. At room temperature, a very strong red emission was observed. The study of the emission lines at 2 K strongly suggested that there was predominantly one Eu3+ binding site within the materials.

Hydrogen Impurity Effects. A5Tt3 Intermetallic Compounds between A=Ca, Sr, Ba, Eu and Tt=Si, Ge, Sn with Cr5B3-like Structures that are Stable Both as Binary and as Ternary Hydride and Fluoride Phases

All of the binary systems Ca, Sr, Ba, or Eu (A) with Tt (tetrel)=Si or Ge as well as Sr–Sn form both binary Cr5B3-type A5Tt3 phases and the corresponding ternary hydrides with stuffed Cr5B3- (Ca5Sn3F-) type structures. All of those tested, Ca–Si, Ba–Si, Ca–Ge, also yield the isotypic A5Tt3Fx phases. The tetragonal structures of Ca5Si3, Ca5Si3F0.42, Sr5Si3, Eu5Si3Hx, Ca5Ge3, Ca5Ge3Hx, Ca5Ge3F0.66(I4/mcm, No. 140) and of Ba5Si3F0.16 (P4/ncc, Ba5Si3-type) were refined from single-crystal X-ray diffraction data. The interstitial H, F atoms are bound in a constricted tetrahedral (A2+)4 cavity in the Cr5B3-type heavy atom structure, which can be described ideally as (A2+)5(Tt2)6−(Tt)4−. Many of 14 previous reports of the phases reported here were apparently hydrides according to lattice constant differences or, for Sr5Si3, the fractional coordinates of Sr2 about the tetrahedral site. An articulated model is developed that allows description of the relationship between the dimensions of the tetrahedral interstitial site and the cation cavity about Tt2 and for some matrix effects in this structure type. The model suggests limitations on the stability of these binary A5Tt3 compounds for the heavier tetrels, as observed. The resistivities of Ca5Ge3 and Ca5Ge3Hx are both characteristic of poor metals, and Pauli-like magnetic susceptibilities are exhibited by Ca5Ge3, Ca5Ge3Hx, Ca5Ge3F0.66, Sr5Ge3, and Sr5Sn3. The characteristic ideal Tt6−2 dimers are evidently not realistic descriptions for these phases; rather at least some of the π*4 electrons in the dimers are delocalized in a conduction band. This effect appears to be greater in two europium salts. Bond lengths of dimers in the Ca–Si and Ca–Ge families appear to shorten slightly in three instances of their oxidation to form the hydride or the fluoride, as might be expected.

Factors Affecting the Oxidative Addition of Aryl Electrophiles to 1,1‘-Bis(diphenylphosphino)ferrocenepalladium(η2-methyl acrylate), an Isolable Pd[0] Alkene Complex

The title complex 3 has been synthesized and characterized by X-ray crystallography. It undergoes oxidative addition with aryl triflates and iodides by a nondissociative mechanism in THF. The Heck addition product methyl cinnamate was detected at traces from the reaction with phenyl triflate, and from iodobenzene the direct oxidative addition product was characterized. The addition of halides or acetate salts to the system led to modest effects on the rate of oxidative addition of aryl triflates, but resulted in neutral arylpalladium(II) complexes. Addition of lithium or europium salts enhanced the reaction rate, the effect being most pronounced with Eu(OTf)3, possibly through promotion of a competing dissociative pathway.

Sodium, calcium, aluminium, zinc and europium salts of p-phenylenebis(silanetriolate). Access to a new class of organosilicates

The crystalline sodium salt of p-phenylenebis(silanetriolate), (NaO)3SiC6H4Si(ONa)3·14H2O has been prepared in quantitative yield by reaction of the corresponding alkoxysilane with NaOH. Characterization of its structure indicates two different environments for the silicon atoms (X-ray and 13C, 29Si, 1H NMR) in the solid state. Drying of the salt by thermal treatment between 20 and 180 °C (TG analysis) led to a modification of the structure without loss of the organic group. Elimination of C6H6 occurs above 200 °C and formation of the sodium silicate Na2SiO3 can be identified above 400 °C (X-ray diffraction). Quantitative replacement of the sodium cation with Al3+, Zn2+, Ca2+ and Eu3+ has been achieved resulting in the formation of the corresponding silanetriolates (EDX and elemental analyses). X-Ray diffraction analysis suggests the presence of a lamellar structure on very small domains or a short range order.

Supramolecular chemistry. Part 71.1 Evidence for hydrolytic DNA cleavage by lanthanide(III) and cobalt(III) derivatives

Double stranded plasmidic DNA, cleaved by either europium(III) salts or by the cobalt(III)–cyclen complex, is religated for the first time without the use of enzymes, showing hydrolytic mechanisms with these chemical nucleases. The same result is observed in the hydrolysis of the dinucleotide TpT by EuIII, which is achieved in 25% conversion. The only products observed by HPLC are 3′,5′-cTMP, 3′-TMP, 5′-TMP and thymidine. The nucleobase thymine itself is not detected (<1%), which demonstrates the absence of radical cleavage. The dinucleotide hydrolysis shows, with [EuIII] = 5 mM, rate enhancement factors of >107, which even exceed those observed with activated phenyl phosphates.

Stereoisomers composition of 4-[(1?-methylpropyl)-oxycarbonyl]-2-oxetanone and related compounds, as precursors of fuctional polyesters, determined by chiral gas chromatography

The configurational analysis of racemic and optically active stereoisomers of 4-[(1′-methylpropyl)oxycarbonyl]-2-oxetanone has been carried out by using chiral gas chromatography. This technique has been successful in the stereoisomers composition determination of these β-substituted β-lactones prepared by two different routes and used as monomers in the preparation of malic acid stereocopolymers. Result are in good agreement with those obtained from high resolution 1H NMR, in the presence of an Europium salt, as chiral shift reagent. This method has been extended to 3-methyl-4-[(1′,2′,2′-trimethyl propyl)oxycarbonyl]-2-oxetanone. The exact knowledge of precursors configurational structure is very important in regard to the obtention of the corresponding polystereoisomers with a strictly controlled enantiomeric or diastereoisomeric composition and consequently with predictable properties.

Electrochemical switching of fluorescence from europium ions dissolved in poly(ethylene oxide) oligomers

Europium salts were dissolved in poly(ethylene oxide) (PEO) oligomers. The europium ions were revealed to be electrochemically redox-active in PEO oligomers. Trivalent europium ions (Eu 3+) showed red fluorescence ( λ em = 614 nm) in PEO oligomers, and a new intensive blue fluorescence ( λ em = 450 nm) was obtained after reducing the Eu 3+ into Eu 2+ by giving negative potential (−0.7 V versus Ag). Reversible fluorescence switching was also carried out by changing the given potential alternately. Sufficient color change required about 20 min because of slow electrode reaction. The fluorescence intensity from europium ions was affected by the molecular weight of matrix PEO. The amount of terminal hydroxyl groups and local viscosity were revealed to affect the fluorescence as the vibrational quenching and diffusion coefficient, respectively. The PEO oligomer with average molecular weight of 600 gave the most intensive fluorescence.

Spectroscopic characterization of doped sol-gel silica gels and glasses: evidence of inner-sphere complexation of europium(III)

Eu 3+ luminescence, excitation and lifetime spectroscopy measurements have been made during the gelation and densification of Eu 3+-doped silica gels prepared by the hydrolysis and condensation of tetraethoxysilane (TEOS). Particular attention was paid to the effect of counter-ion complexation of Eu 3+ in gels prepared with different europium precursors. Precursor-dependent spectroscopic variations have been observed. The Eu 3+ probe ion was introduced in the initial stage of the sol-gel process by dissolving a hydrated europium salt in the sol. Europium precursors studied include: Eu(NO 3) 3·6H 2O, EuCl 3·6H 2O, Eu(ClO 4) 3·6H 2O. Sol, gel point and wet gel spectra and lifetimes are interpreted by analogy with spectroscopic studies of the europium salts in mixed ethanol-water solutions. In particular, the energy of the 7 F 0 → 5 D 0 excitation spectrum is used to identify complexes containing counter-ions in the inner coordination sphere of Eu 3+. Results are presented showing that the NO 3 − ions have an affinity for the inner coordination sphere of Eu 3+ which is greater than the affinity of Cl −. ClO 4 − ions retain an outer-sphere interaction with Eu 3+ throughout the sol-gel process. Thermal densification of the gels destroys the inner-sphere complexation of the counter-ions and, above 300°C, the counter-ion-dependent effects were removed. The results show that the method by which the Eu 3+ probe ion is introduced to the system significantly affects the Eu 3+ spectra.

Distribution and excretion of lanthanides: comparison between europium salts and complexes

Europium (152,154Eu) was intravenously injected into rats as: (i) the chloride salt at pH 7.4, (ii) the chloride salt at pH 3, (iii) the albumin complex and (iv) the DTPA complex, and tissue uptake was determined 24 h later. For the chlorides, the target organ for uptake was liver (about 60% of dose) whilst europium complexes were rapidly excreted in urine and were predominantly taken up into the kidney (about 0.5% of dose) and bone. Liver uptake of EuCl3, pH 7.4, corresponded to that of a colloidal material with most 152Eu present in the non-hepatocyte population; however, EuCl3, pH 3, was handled in a different manner, with significant uptake by hepatocytes. The differing tissue distributions of EuCl3 and Eu-albumin suggest that plasma albumin does not readily bind injected EuCl3. Renal uptake of europium, although a relatively low proportion of the injected dose, was associated with many subcellular fractions, including lysosomes, suggesting significant intracellular uptake and thus possible retention.

Complexation of europium using polyethylene carboxylic acid

Competitive complexation of europium(III) carboxylates by an octadecanoic carboxylate and a terminally functionalized oligomeric ethylene carboxylate ( M n = ∼ 1500–2000) showed that there was little difference between a low molecular weight alkyl carboxylate ligand and an oligomeric polyethylene carboxylate ligand in their interaction with a metal salt in a toluene solution at 105°C. The most significant difference between these two carboxylate ligands was the facility with which the oligomeric carboxylate removes europium(III) from solution when the oligomer and octadecanoate were present at comparable concentrations. Comparison of calculations and experimental values for the amount of europium left in solution after equilibration of various ratios of terminally carboxylated oligomeric polyethylene and octadecanoic acids with europium(III) was used to evaluate the relative ligating ability of a soluble macromolecular and octadecyl carboxylate for europium(III) in toluene. Use of a less well-defined oxidized polyethylene instead of well-characterized terminally carboxylated oligomers as ligands had little effect on these equilibria. Experiments also showed that the solubility of these oligomerically ligated europium salts changed significantly over a temperature range of 60–85°C.

ENERGY TRANSFER FROM COPOLYMERS OF STYRENE-MALEIC ACID TO EU(III) IONS IN TETRAHYDROFURAN

The sensitization of Eu(III) ion emission in tetrahydrofuran by copolymers of styrene-maleic anhydride, styrene-maleic acid(PSMA), and europium salt of PSMA(PSMA-Eu) was studied. When excited at 260 nm in the presence of PSMA, the emission of Eu(III) at 618 nm exhibited large enhancement compared with that in the absence of PSMA. The enhancement was even greater for PSMA-Eu and accompanied by the decrease in monomer and excimer emission of polymers, suggesting that energy is transferred from the excited polymer to Eu(III) ions

Chiral michael additions of acetamidomalonate to α-enones : Nuclear magnetic resonance and high-performance liquid chromatographic resolution of enantiomers

Solid—liquid phase transfer catalysis without addition of solvent was used to induce asymmetric Michael addition. Determinations of enantiomer ratios by chiral liquid chromatography and by NMR chiral shifts using europium salts are compared. The effect of chiral phase transfer catalyst structure, addition of solvent and addition of molecular sieves are discussed. The best enantiomeric excess are obtained with N-benzyl-N-methylephedrinium salts in the absence of solvent and in the presence of molecular sieves.

Synthesis of the hydrates of chlorinated acetates of rare earths and their thermal behaviour

The dehydration processes and their enthalpy changes for the hydrates of the monochloro- acetates, dichloroacetates and trichloroacetates of lanthanum, cerium, praseodymium, neodymium, samarium, europium and gadolinium have been investigated by means of TG, dehydration over P 2O 5 and DSC. The thermal decomposition mechanisms of the anhydrous dichloroacetates have also been studied by using elemental analysis, IR and DTA-TG-DTG techniques. The mechanisms revealed that the decompositions occur in two stages in the range from room temperature to 600° C. In the first stage the anhydrous salts decompose to form the intermediate products, Ln 2(OH)Cl 5·3H 2O (Eu 2(OH)Cl 5 · 2H 2O in the case of the europium salt) which then decompose further to the rare earth oxychlorides LnOCl (CeO 2 in the case of the cerium salt) in the second stage.

Réduction électrochimique de dérivés carbonylés en milieu non aqueux en présence de EuCl3•6H2O

The electrochemical reduction of aromatic or α,β ethylenic aromatic ketones in nonaqueous solvent (DMF) has been performed in the presence of EuCl3•6H2O. Ligand exchange between DMF and water molecules of the europium salt was first studied. A voltammetric study shows that complexation involving electrogenerated Eu(II) and ketone may occur at the electrode interface or in solution, leading respectively to [Formula: see text] and [Formula: see text] stoichiometries. The stereochemistry of hydrodimerization products is studied.

Rare‐earth‐metal‐containing polymers. 5. Synthesis, characterization, and fluorescence properties of Eu3+‐polymer complexes containing carboxylbenzoyl and carboxylnaphthoyl ligands

AbstractPartially 2‐carboxylbenzoyl (1) and 3‐carboxyl‐2‐naphthoyl (2) substituted polystyrene were prepared by the Friedel‐Crafts reaction of polystyrene with corresponding dicarboxylic anhydrides. Europium (III) salts of (1) and (2) and the copolymer of 4‐vinylbenzoyl 2′‐carboxylbenzoate‐di(2‐benzoyl benzoate) and styrene (5) were prepared. Polymer (5) was prepared by the copolymerization of the Eu3+ salt of 4‐vinylbenzoyl 2′‐benzoate and 2‐benzoylbenzoate (ratio 1:2) with styrene. The fluorescence emission intensity was measured on fine powder samples. The intensity of (5) increased linearly as the Eu content increased. However, for the 1 and 2 systems the intensity reached a maximum at a Eu content as small as 0.5 wt% and remained constant when further increases were made. This phenomenon was accounted for by steric hindrance and a decrease in the freedom of bond rotation, which prevent the formation of multiple coordination linkages between Eu3+ and the benzoate groups.

Preparation and investigation of optically active polyesters from α‐ethyl‐α‐phenyl‐β‐propiolactone, 1

Abstractα‐Ethyl‐α‐phenyl‐β‐propiolactone (7) of an optical purity up to 95% was prepared; the resolution of the two optical antipodes was carried out with the optical active precursor ethyl 2‐aminomethyl‐2‐phenylbutyrate (5), and the optical purity was determined by 1H NMR analysis using europium salt shift reagents. The solution and thermal properties of the corresponding polyesters 8, as obtained by anionic ring opening polymerization, were investigated. It was found that the inherent viscosity increased with the optical purity of the lactone. Distinct differences in the melting behaviour were found between the racemic and the optically active polymers; the ideal melting temperature TM0 for the pure enantiomeric polymer was estimated to about 535 K.

KINETICS OF TRIPLET OXIDATION OF METALLO‐PORPHYRIN COMPOUNDS TO THEIR CORRESPONDING RADICAL CATIONS

Abstract— The kinetics of photooxidation of triplets of metalloporphyrin compounds to their corresponding radical cations was investigated. Zn‐tetraphenyl porphyrin (ZnTPP) and Mg‐tetraphenylpor‐phyrin (MgTPP) triplets were oxidized by europium salt with rate constants of 4.8 × 105M‐1s‐1 and 2.1 × 106M‐1s‐1, respectively. The high rate constant of oxidation of MgTPP triplet might be related to the ground state oxidation potential, being 0.54 V (SCE) for the Mg complex and 0.71 (SCE) for the Zn complex.The rate constant of oxidation of ZnTPP excited singlet is in the order of diffusion control, i.e. ˜ 1010M ‐1 s‐1. Excitation of ferric, cupric, cobaltic, and vanadyl tetraphenylporphyrin did not result in a long‐lived triplet state that would allow oxidation studies using flash photolysis.

Photooxidation of aromatic hydrocarbons by europium(III) salts

Photooxidation of aromatic hydrocarbons by europium(III) salts

La méthoxy-12Δ 14-vincamine, nouvel alcaloïde isole du Crioceras dipladeniiflorus (Staff) K. Schumann (Apocynacées)

A new indol alkaloid has been isolated from the root barks of Crioceras dipladeniiflorus, whose structure, methoxy-12 Δ 14 vincamine, has been determined by physical methods (NMR spectra and paramagnetic shifts induced by Europium salts).