Spectroscopic study of a UV-photostable organic-inorganic hybrids incorporating an Eu3+ beta-diketonate complex.

New europium and gadolinium tris-beta-diketonate complexes have been prepared and incorporated in sol-gel-derived organic-inorganic hybrids, named di-ureasils. The general formula [Ln(btfa)3(4,4'-bpy)(EtOH)] (Ln=Eu, Gd; 4,4'-bpy=4,4'-bipyridine; btfa=4,4,4-trifluoro-1-phenyl-1,3-butanedione) for the complexes was confirmed by X-ray crystallography and elemental analysis. The ground-state geometry of the Eu3+ complex was calculated from the Sparkle/AM1 model. The calculated quantum yield obtained from the Sparkle model and from the crystal structure (both 46%) are in satisfactory agreement with the experimental value (38+/-4%). In the isolated complex the most efficient luminescence channel is S0-->S1-->T-->(5D1, 5D0)-->7F0-6, where the exchange mechanism dominates in the energy-transfer channel T-->(5D1, 5D0). For the Eu3+-based di-ureasils a 50% quantum yield enhancement compared to the Eu3+ complex is observed, which suggests an effective hybrid host-metal ion interaction and an active energy-transfer channel between the hybrid host and the Eu3+ complex. The Eu3+-based di-ureasils are photostable under UVA (360 nm) excitation, whereas under UVB (320 nm) and UVC (290 nm) photodegradation occurs.     

Polyoxometalate-supported Y- and YbIII-hydroxo/oxo clusters from carbonate-assisted hydrolysis

Carbonate-assisted hydrolysis of Y or Yb(III) ions in the presence of the trivacant Wells-Dawson polyoxoanion, alpha-[P(2)W(15)O(56)](12-), produced two polyoxometalate-supported Y- or Yb(III)-hydroxo/oxo clusters, which have been characterized by single-crystal X-ray structure determination. The structure of the Y complex consists of a distorted Y(4)(OH)(4) cubane cluster encapsulated by two lacunary alpha-[P(2)W(15)O(56)](12-) units, while the Yb cluster features a hexametallic core centered around a mu(6)-oxo atom with each Yb(3)(III) triangular face capped by an oxo or a hydroxo group. Magnetization measurements of the ytterbium(III) derivative suggested that intermolecular dipolar exchange is present at low temperatures (below 15 K). Despite its absence in the structures themselves, control experiments show that carbonate not only functions in the hydrolysis, it also influences the structure of the complexes by complexation to yttrium and the f-block elements.     

Sonoluminescence of aqueous solutions of lanthanide salts

The influence of salts (TbCl₃, Tb(NO₃)₃, PrCl₃, EuCl₃, CeCl₃, and DyCl₃) on the spectrum and intensity of multi-bubble sonoluminescence (SL) of water was observed at a frequency of 20 kHz. Luminescence bands of the lanthanide ions were detected in the SL spectra of concentrated solutions of the Ce^III, Tb^III, and Dy^III chlorides (0.1—1 mol L^–1). No luminescence was observed for solutions of the other salts, and the shape of the spectra is due to the absorption of the water SL by the lanthanide ions. Possible mechanisms of the appearance of SL of lanthanides were considered. The first mechanism is the excitation of the lanthanide aqua ions in the solution bulk due to the absorption of the short-wave portion of glow of the excited water molecules and OH radicals emitted from the cavitation gas-vapor bubbles. The second mechanism involves the transfer of the lanthanide ions to the gas phase from the liquid layer adjacent to the cavitation bubble and their excitation in the bubble volume upon collisions with other hot or electron-excited particles.     

<Emphasis Type="Italic">N,N</Emphasis>’-Bis(acylvinylated) diaza-18-crown-6 ether as a lanthanide-selective macrocyclic complex-forming agent

Nucleophilic substitution in β-chlorovinyl phenyl ketone with diaza-18-crown-6 ether resulting in displacement of the chlorine atom afforded N,N’-bis(3-oxo-3-phenylpropen-1-yl)-1,10-diaza-18-crown-6 ether. The ability of the latter to form complexes with a number of metal cations was studied. However, the complex formation occurs only with the rare-earth cations Ln³⁺ and Th⁴⁺. This fact was demonstrated by UV and ¹H NMR spectroscopy of solutions, confirmed by isolations of glassy phases of composition L₃M₂(NO₃)₆ · nH₂O (M = La, Y, n ≈ 4–7), and supported by IR spectra of these phases in KBr pellets. The formation of complexes with La³⁺ and Y³⁺ leads to an increase in fluorescence intensity of the ligand. The stability constants of the 1 : 1 complexes in methanol were evaluated by spectrophotometry. These constants increase with decreasing ionic radius of the cation.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 156–160, January, 2005.     

Sonoluminescence of aqueous solution of gadolinium chloride

A line of the Gd^III ion was detected at 311 nm in the multibubble sonoluminescence spectrum of a concentrated (1 mol L⁻¹) solution of gadolinium chloride. A comparison with the earlier studied sonoluminescence of the Ce^III and Tb^III ions shows that the Gd^III ion is excited in the volume and/or on the surface of cavitation bubbles upon collisions with “hot” particles. The efficiency of excitation of the lanthanide ions via this mechanism depends on the type of electron transition. For the same energy of the excited state, the efficiency of Gd^III excitation (f-f transition) exceeds by at least 50 times that of Ce^III excitation (f-d transition). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1341–1344, June, 2005.     

Synthesis of 1,3-bis(acetylacetonyloxy)- and 1,3-bis(benzoylacetonyloxy)benzene and their complexation with lanthanide ions

Claisen condensation of 1,3-bis(methoxycarbonylmethoxy)benzene with acetone and acetophenone afforded new chelating ligands consisting of two β-diketonate fragments, viz., 1,3-bis(acetylacetonyloxy)benzene and 1,3-bis(benzoylacetonyloxy)benzene, which are linked to each other through the resorcinol spacer. In the crystal, 1,3-bis(acetylacetonyloxy)benzene, unlike the starting ester, adopts a planar conformation and exists in the enol form. The acidities of these compounds and their complexation with lanthanide ions in aqueous ethanolic solutions were studied by pH-potentiometry. Depending on the concentration conditions and pH, the La³⁺, Gd³⁺, and Lu³⁺ ions form 1 : 1, 1 : 2, or 1 : 3 complexes with bis(β-diketones). The stability of the complexes increases as the atomic number of the lanthanide increases (La³⁺ < Gd³⁺ ≤ Lu³⁺). The complexation constants and selectivity of complexation substantially increase with increasing degree of deprotonation of the ligands, which indicates that both chelate groups of the ligands are simultaneously involved in coordination. The Ph substituents in bis(β-diketone) have a considerable effect on the composition and stability of complexes with lanthanide ions due to additional noncovalent inner-sphere interactions.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 614–622, March, 2005.     

Synthesis, characterization, and pharmacokinetic evaluation of a potential MRI contrast agent containing two paramagnetic centers with albumin binding affinity

A dinuclear gadolinium(III) complex of an amphiphilic chelating ligand, containing two diethylenetriamine-N,N,N',N',N'-pentaacetate (DTPA) moieties bridged by a bisindole derivative with three methoxy groups, has been synthesized and evaluated as a potential magnetic resonance imaging (MRI) contrast agent. Nuclear magnetic relaxation dispersion (NMRD) measurements indicate that at 20 MHz and 37 degrees C the dinuclear gadolinium(III) complex has a much higher relaxivity than [Gd(DTPA)] (6.8 vs 3.9 s(-1) mmol(-1)). The higher relaxivity of the dinuclear gadolinium(III) complex can be related to its reduced motion and larger rotational correlation time relative to [Gd(DTPA)]. In the presence of human serum albumin (HSA) the relaxivity value of the noncovalently bound dinuclear complex increases to 15.2 s(-1) per mmol of Gd3+, due to its relatively strong interaction with this protein. The fitted value of the binding constant to HSA (Ka) was found to be 10(4) M(-1). Because of its interaction with HSA, the dinuclear complex exhibits a longer elimination half-life from the plasma, and a better confinement to the vascular space compared to the commercially available [Gd(DTPA)] contrast agent. Transmetalation of the dinuclear gadolinium(III) complex by zinc(II) has been investigated. Biodistribution studies suggest that the complex is excreted by the renal pathway, and possibly by the hepatobiliary route. In vivo studies indicated that half of the normal dose of the gadolinium(III) complex enhanced the contrast in hepatic tissues around 40 % more effectively than [Gd(DTPA)]. The dinuclear gadolinium(III) complex was tested as a potential necrosis avid contrast agent (NACA), but despite the binding to HSA, it did not exhibit necrosis avidity, implying that binding to albumin is not a key parameter for necrosis-targeting properties.     

Effects of cyclodextrins on the fluorescence of Europium ion-diketone complexes

The thermodynamics of the complexation of cyclodextrins (CDs) to naphthyl, phenyl and thienyl subtituted 1,3-diketones, used as sensitizers in time-resolved fluorescence analysis of lanthanides, was studied by gel chromatography. The complexation occurs predominantly at the aromatic end of the diketones with a strength comparable to related aromatic compounds. The effects of CDs on the fluorescence of an europium (III) ion with diketones in an aqueous solution were tested for their applicability in time-resolved fluorescence analysis.     

In situ high temperature NMR and EXAFS experiments in rare-earth fluoride molten salts

The local structure in molten YF₃–LiF and LaF₃–LiF binaries has been investigated by NMR and EXAFS spectroscopy. For YF₃–LiF, the high-temperature ¹⁹F and ⁷Li NMR spectra have been recorded in situ in the molten state for compositions ranging from pure LiF to pure YF₃. The LaF₃–LiF system has been studied by ¹⁹F and ¹³⁹La NMR and EXAFS spectroscopy at the LIII edge of La. The local environment around the La³⁺ in the molten state does not depend on the composition, while ¹⁹F chemical shift evolution confirms the progressive formation of bridged species. To cite this article: A.-L. Rollet et al., C. R. Chimie 7 (2004).

Résumé

Étude in situ par spectroscopies RMN et EXAFS à haute température de fluorures de terres rares fondus. La structure locale des mélanges fondus YF₃–LiF et LaF₃–LiF a été étudiée par spectroscopies RMN et EXAFS à haute température. Pour le système YF₃–LiF, les spectres RMN à haute température de ¹⁹F et ⁷Li ont été enregistrés in situ dans le liquide pour différentes compositions variant de LiF pur à YF₃ pur. Le système LaF₃–LiF a été étudié par RMN de ¹⁹F et ¹³⁹La, et par EXAFS au seuil LIII du lanthane. L’environnement autour du La³⁺ à l’état fondu ne dépend pas de la composition, alors que les évolutions du déplacement chimique du fluor confirment la formation progressive d’espèces pontantes. Pour citer cet article : A.-L. Rollet et al., C. R. Chimie 7 (2004).     

Preparation, Spectral and Thermal Studies of Y(III) and Lanthanide(III) 1-Hydroxy-2-Naphthoates

Complexes of lanthanide(III) (La–Lu) and Y(III) with 1-hydroxy-2-naphthoic acid were obtained as crystalline compounds with a general formula Ln[C₁₀H₆(OH)COO]₃⋅nH₂O:n=6 for La–Tm and Y, n=2 for Yb and n=0 for Lu. IR spectra of the prepared complexes were recorded, and their thermal decomposition in air were investigated. Spectroscopic data suggest that in the coordination of metal-organic ligand only oxygen atoms from the carboxylate group take part. When heated, the complexes decompose to the oxides Ln₂O₃, CeO₂, Pr₆O₁₁ and Tb₄O₇ with intermediate formation of Ln(C₁₁H₇O₃)(C₁₁H₆O₃). This revised version was published online in August 2006 with corrections to the Cover Date.