Lanthanide Β-diketonates Research Articles

Mononuclear luminous β-diketonate Ln(III) complexes with heteroaromatic auxiliary ligands: synthesis and luminescence characteristics.

A series of lanthanide (samarium and terbium) β-diketonates with heteroaromatic auxiliary ligands was synthesized. The prepared complexes were characterized through electrochemical, thermal, and spectroscopic analyses. Infrared analysis revealed the binding of the respective metal ion to oxygen and nitrogen atoms of diketone and ancillary ligands. Thermogravimetry/differential thermogravimetry profiles provided thermal information and specified the high thermal stability of the prepared complexes. The complexes exhibited the sharp and structured Ln-based emission in the visible region upon irradiation in the ultraviolet range. Photophysical analysis demonstrated the green and orange-red emission due to the respective characteristic transitions of Tb3+ and Sm3+ ions. Photophysical properties affirmed the luminous behaviour of the synthesized complexes. These luminous lanthanide complexes could be used as emitting materials in the design of organic light-emitting diodes.

Bottom-Up Approach for the Rational Loading of Linear Oligomers and Polymers with Lanthanides

The adducts between luminescent lanthanide tris(β-diketonate)s and diimine or triimine ligands have been explored exhaustively for their exceptional photophysical properties. Their formation, stability, and structures in solution, together with the design of extended metallopolymers exploiting these building blocks, remain, however, elusive. The systematic peripheral substitution of tridentate 2,6-bis(benzimidazol-2-yl)pyridine binding units (Lk = L1-L5), taken as building blocks for linear oligomers and polymers, allows a fine-tuning of their affinity toward neutral [Ln(hfa)3] (hfa = hexafluoroacetylacetonate) lanthanide containers in the [LkLn(hfa)3] adducts. Two trends emerge with (i) an unusual pronounced thermodynamic selectivity for midrange lanthanides (Ln = Eu) and (ii) an intriguing influence of remote peripheral substitutions of the benzimidazole rings on the affinity of the tridentate unit for [Ln(hfa)3]. These trends are amplified upon the connection of several tridentate binding units via their benzimidazole rings to give linear segmental dimers (L6) and trimers (L7), which are considered as models for programming linear Wolf-Type II metallopollymers. Modulation of the affinity between the terminal and central binding units in the linear multitridentate ligands deciphers the global decrease of metal-ligand binding strengths with an increase in the length of the receptors (monomer → dimer → trimer → polymer). Application of the site binding model shed light onto the origin of the variation of the thermodynamic affinities: a prerequisite for the programmed loading of a polymer backbone with luminescent lanthanide β-diketonates. Analysis of the crystal structures for these adducts reveals delicate correlations between the chemical bond lengths measured in the solid state (or bond valence parameters) and the metal-ligand affinities operating in solution.

Exciton diffusion in solid solutions of luminescent lanthanide β-diketonates.

In this article, a series of luminescent lanthanide β-diketonate solid solutions, with the formula of TBAEuxM1-x(TTA)4 (TBA = tetrabutylammonium; M = La or Gd; TTA = 2-thenoyltrifluoroacetonate), are synthesized by co-precipitation. In the solid solutions, the emission efficiency of Eu3+ is significantly increased with the presence of non-luminescent chelates TBALa(TTA)4 and TBAGd(TTA)4. Low temperature luminescence spectroscopy studies indicate that the TTA- ligands in these non-luminescent chelates do emit phosphorescence with long lifetime. However, the ligand phosphorescence is strongly quenched in solid solutions with the luminescent chelate TBAEu(TTA)4, providing strong evidence for intermolecular energy transfer through the triplet excited states of the ligands. A quantitative analysis of Eu3+ emission enhancement and TTA- phosphorescence quenching reveals that each Eu3+ center may receive excitation energy from about 30 TTA- ligands, suggesting that the excitation energy has become exciton-like in the solid solutions. Based on the crystallography analysis of TBALn(TTA)4, it is discovered that TTA- ligands in neighboring Ln(TTA)4- units may form π-π stacks with intermolecular distance ≤3.5 Å, thus enabling efficient triplet exciton diffusion via exchange interaction.

Synthesis, thermogravimetric analysis and enthalpy determination of lanthanide β-diketonates

Abstract This work reports thermodynamic characterizations of lanthanide β-diketonates for use in nuclear fission product separation. Adsorption and sublimation enthalpies have been shown to be linearly correlated, therefore there is motivation to determine sublimation thermodynamics. An isothermal thermogravimetric analysis method is employed on fourteen lanthanide chelates for the ligands 2,2,6,6-tetramethyl-3,5-heptanedione and 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione to determine sublimation enthalpies. No linear trend is seen across the series; values show a cyclical nature, possibly indicating a greater influence of chemisorption for some complexes and less of a role of physisorption in dictating adsorption differences between lanthanides in the same series. This is in line with previous reports in terms of the chromatographic separation order of the lanthanides. The results reported here can be used to manipulate separations parameters and column characteristics to better separate these lanthanide chelates. Fourteen chelates of the ligand 1,1,1-trifluoro-2,4-pentanedione are also thermally characterized but found to not sublime and be undesirable for this method. Additionally, all chelates are characterized by constant heating thermogravimetric analysis coupled with mass spectrometry, melting point analysis, elemental analysis and FTIR.

MIXED-LIGAND ACETYLACETONATE COMPLEXES OF LANTANUM (III) AND GADOLINIUM (III) WITH CARBOXYLIC ACIDS AND ACETONITRILE OR DIMETHYLFORMAMIDE

This paper presents the study of mixed-ligand complexes of Ln(III), which are used as volatile precursors in CVD processes for the preparation of lanthanide-containing films and coatings. New mixed-ligand acetylacetonate complexes of lanthanides (III) with acetic (propionic) acid and acetonitrile or dimethylformamide were synthesized and investigated by physic-chemical methods of analysis (elemental analysis, differential thermal analysis, IR spectroscopy, powder X-ray diffraction). Using mixed-ligand complexation, the properties of the initial lanthanide β-diketonates (in particular, chemical and thermal stability) can be changed significantly.
 To assess the stability of the synthesized mixed-ligand complexes, their quantum-chemical modeling was performed using the semi-empirical method Sparkle/PM7. Standard changes of the Gibbs energy ∆G0298 were calculated for the solution reaction of (1) synthesis of mixed-ligand complexes and (2) substitution of one of the β-diketonate ligands in the Ln(III) tris-acetylacetonates dihydrates by an acetate ion or propionate ion. The ∆G0298 values for the syntesis reaction mainly increases with increasing donor basicity and decreasing ionic radii Ln(III) in the La>Gd>Lu series. For all mixed ligand complexes of Ln(III), the heats of formation are negative, which indicates their thermodynamic stability in solution.
 It was established that the obtained complexes have the same composition of the general formula [Ln(AA)2·L·2D], where Ln (III) = La, Gd; НАА- acetylacetonе; L - anion of acetic (HAc) or propionic (HРrop) acids, D- acetonitrile (AN), dimethylformamide (DMFA).
 The results of the thermal analysis confirm the computational data: in the case of the lanthanum mixed-ligand complexes, the carboxylic acid is coordinated to the central ion through bridging carboxylate-ions, which contributes to the formation of oligomers. The lanthanum mixed-ligand complexes are not volatile due to their oligomeric structure. On the other hand, similar gadolinium complexes are monomeric and sublimate at 180 - 350 °C.

Europium and yttrium complex formation with β-diketones and amino acids

Europium(III) and yttrium(III) complexation processes in the extraction systems with β-diketones and amino acids were studied. The increase in the lanthanide distribution ratios in these systems is caused by the formation of mixed-ligand coordination compounds of lanthanides in these systems. The formation of mixed-ligand coordination compounds of lanthanides with β-diketones and amino acids in the organic phase was confirmed by IR and luminescence spectroscopy and quantum chemical calculations of the formation energies of mixed-ligand yttrium complexes with glycine and acetylacetone or hexafluoroacetylacetone. It was found that amino acid molecules form mixed-ligand compounds with lanthanide β-diketonates by coordinating the lanthanide ion by the oxygen ion of the carboxy group with retention of the betaine structure, while the amino acid NH3+ group is hydrogen-bonded to one oxygen atom of β-diketone. The possibility of effective use of europium tris-dibenzoylmethanate as a glycine receptor is demonstrated.

Photoelectron spectroscopy of several lanthanide β-diketonates

The valence region electronic structure of Ln(acac)3 complexes (Ln=Nd, Tm, Pr; acac=acetylacetonate) is investigated using, principally, gas-phase ultraviolet photoelectron (PE) spectroscopy. Analysis of PE spectra focuses on the 7–12eV region containing the first several ionization bands which likely contain metal f-ionizations and acac-based ionizations. These correspond to oxygen 2p-type orbitals and carbon 2p-type orbitals, which are equivalent to oxygen lone pairs and electrons from the pi-bond system of the ligand.

Mechanochemical synthesis of mixed-ligand europium β-diketonates with nitrogen-containing neutral ligands

The solid-phase reaction between europium salts of β-diketones and nitrogen-containing neutral ligands in a planetary mill produces luminescent mixed-ligand compounds Eu(β-dic)3 · D, where β-dic stands for dibenzoylmethane (DBM), benzoylacetone (BA), thenoyltrifluoroacetone (TTA), or benzoyltrifluoroacetone (BTFA); and D stands for 1,10-phenanethroline (Phen), 2,2-dipyridyl (Dipy), or diphenylguanidine (DPG). The mechanosynthesis and yield of lanthanide β-diketonates are studied as affected by the treatment parameters and the nature of the reagents. Powder X-ray diffraction demonstrates a staged course of the mechanochemical synthesis. Examination of formation-rate curves shows that grinding/stirring is the rate-controlling stage of the process. Thermogravimetric analysis (TGA) shows that the mechanosynthesis can proceed in the self-propagation mode. The relative luminescence intensity is determined as a function of treatment time. Particles of the mechanically activated mixture have sizes of 10–100 μm.

Adducts of lanthanide β-diketonates with 2,4,6-tri(2-pyridyl)-1,3,5-triazine: Synthesis, structural characterization, and photoluminescence studies

Adducts of lanthanide β-diketonates of the general formula LnL 3(TPTZ) were synthesized and structurally characterized by single crystal X-ray diffraction [Ln = Eu 3+, Tb 3+, Er 3+; L is the conjugate base of dibenzoylmethane (DBM), 1-benzoylacetone (BA), thenoyltrifluoroacetone (TTA), or 4,4,4-trifluoro-1-phenyl-1,3-butanedione (BTFA); TPTZ = 2,4,6-tri(2-pyridyl)-1,3,5-triazine, a rigid Lewis base with a large π system]. The lanthanide ion in each of these complexes is nonacoordinate with six β-diketonate oxygen atoms and three TPTZ nitrogen atoms, forming a coordination polyhedron best describable as a monocapped square antiprism. Characteristic red, green, and near infrared luminescence was observed for the Eu 3+, Tb 3+, and Er 3+ complexes, respectively. All complexes showed significantly enhanced luminescence quantum yields when compared with the corresponding aqua analogues, with one of the Eu 3+ complexes displaying a quantum yield of 69.7% in chloroform.

The use of 3d-metal complexes as ligands to prepare volatile 4f–3d heterobimetallic complexes

Volatile heterobimetallic complexes can be prepared by reacting lanthanide β-diketonates, Ln(dik) 3, with Schiff base d-transition metal complexes M(SB). Complexes M(SB) behave as bidentate oxygen donor Lewis bases to react with Ln(dik) 3 Lewis acids, yielding stable heteronuclear complexes of general formula [M(SB)Ln(dik) 3]. Complexes with M=Cu, Ni, and H 2(SB) = Schiff base from ethylenediamine or other diamine and salicylic aldehyde or acetylacetone, have been synthesised. Volatility and thermal stability have been studied for some representative members of the series, in correlation with their crystal structures and thermal behaviours of the parent complexes. Some general principles for designing volatile complexes of formula [M(SB)Ln(dik) 3] may be proposed.

Synthesis of Liquid-Crystalline Adducts of Lanthanide β-Diketonates with Some Lewis Acids

Synthesis of Liquid-Crystalline Adducts of Lanthanide β-Diketonates with Some Lewis Acids

Synergism by sublimation of volatile lanthanide β-diketonates

The synergistic effect by sublimation manifests itself in an increase in the volatility of nonvolatile or slightly volatile compounds in the presence of highly volatile agents. In this study, manifestations of the synergistic effect are demonstrated by the evaporation of mixed ligand complexes, derivatives of lanthanide acetylacetonates and neutral organic ligands, and by evaporation of the following mixtures: yttrium and zirconium acetylacetonates, lanthanum and nickel dipivaloylmethanates and acetylacetonates, and lanthanum and aluminum acetylacetonates.

Water enhances the luminescence intensity of β-diketonates of trivalent samarium and terbium in toluene solutions

The influence of water on the luminescence of toluene solutions of lanthanide β-diketonates (Ln(L) 3· nH 2O, where L is benzoyltrifluoroacetone, thenoyltrifluoroacetone, acetylacetone, dipivaloylmethane) was studied. It was shown that in toluene the luminescence of dysprosium, neodymium and ytterbium β-diketonates is quenched by water while the luminescence of samarium and terbium β-diketonates is enhanced by water at [Ln(L) 3· nH 2O]>10 −4 M. The concentration quenching of the luminescence of Ln(L) 3· nH 2O in toluene was observed due to the formation of dimers [Ln(L) 3· nH 2O] 2. The quenching in dimers is caused by deactivation in both the ligand (before the energy transfer to Ln 3+ ion takes place) and by cross-relaxation in the Ln 3+ ion. It is suggested that introduction of water in toluene causes dissociation of dimers to monomers which results in the enhancement of the luminescence intensity of Sm 3+ and Tb 3+, while the quenching of Nd 3+, Dy 3+ and Yb 3+ luminescence is due to the efficient deactivation of these ions by OH-groups. Probably addition of water enhances ligand-to-Ln 3+ energy-transfer efficiency and lowers cross-relaxation efficiency of Ln 3+.

Relationship between the analytical properties of lanthanide(III) βdiketonates and the nature of ligands

The effect of the nature of β-diketones on the spectrochemical-luminescence properties of lanthanide complexes used as analytical forms for the highly sensitive determination of some rare-earth elements was examined. NMR spectroscopy, molecular mechanics, calculations, and an experimental evaluation of the hydrophobicity of the test β-diketones indicated that an increase in the intensity, quantum yield, and lifetime of luminescence of lanthanide (Ln) β-diketonates depends on the charge distribution in the chelate ring, on the spatial structure, and on the hydrophobicity of the coordinated ligand. These factors determine the efficiency of energy transfer from the β-diketone to the Ln+3 ion and the decrease in energy losses caused by the quenching action of water molecules.

Synthesis of lanthanide β-diketonates by solid state reaction at low heating temperature

Solid state reactions between β-diketones (HPMBP, HDBM) and LnAc3 · xH2O(La,Nd:x=3/2; Tb:x=4) have been investigated at low heating temperature. Pure compounds of Ln(PMBP)3 and Ln(DBM)3 are obtained by solid state reaction, and characterized by elemental analysis, infrared radiation (IR), X-ray diffraction (XRD) and photoacoustic spectra. The solid state reaction properties of β-diketones and their influences on the structures of products are discussed.

Bathochromicity of Michler’s ketone upon coordination with lanthanide(III) β-diketonates enables efficient sensitisation of Eu3+ for luminescence under visible light excitation†

The electronic absorption of Michler’s ketone (MK) and related push–pull sensitisers undergoes a strong red shift upon coordination with lanthanide(III) β-diketonates, which enables unprecedently efficient sensitisation of Eu3+ luminescence for excitation at long wavelengths extending well into the visible region to above 450 nm.

Separation of Lanthanide β-Diketonates via Organophosphorus Adduct Formation by Supercritical Fluid Chromatography

This paper describes a novel method for separation and detection of lanthanide β-diketonates by adduct formation/supercritical fluid chromatography (SFC) with an open-tubular capillary column and a FID detector. Separation of lanthanide β-diketonates cannot be achieved by SFC due to the hydration of the complexes, which exhibit strong intermolecular interactions and decomposition in the system. Formation of adducts of lanthanide β-diketonates with a neutral donor, tributylphosphine oxide (TBPO) or trioctylphosphine oxide (TOPO), alters their SFC behavior. The adduct formation approach leads to the first successful separation of lanthanide complexes of the same β-diketone ligand by SFC using neat CO2 as the mobile phase.

Gas chromatographic study of reversible adduct formation between nucleophilic solutes and stationary phases containing lanthanide β-diketonates

Complex formation between fluorinated and methylated β-diketonates of praseodymium and europium, dissolved in a polydimethylsiloxane stationary phase, and aliphatic alcohols, methyl ketones, methyl ethers and carboxylic acid methyl esters has been studied. Investigations were carried out isothermally in the range 90 to 130°C. An increase in retention values measured on the complexing stationary phase for the test solutes was the primary observation. Equilibrium constants (K) of adduct formation were determined from retention data. It was established that fluorinated lanthanide β-diketonates enhance adduct formation more selectively than the corresponding methyl compounds. Decrease in the ionic radii from praseodymium to europium gave rise to increased K values.

Effects of trivalent lanthanide complexes on the lifetimes of methylene-chain-linked biradicals in magnetic fields

Lanthanide β-diketonates and copper acetylacetonate in benzene quench the methylene-chain-linked triplet biradicals in the presence of magnetic fields. At 0.56 T, the quenching rate constant k q is in the order of 10 8 M −1 s −1 for the former complexes and 4.7×10 9 M −1 s −1 for the latter. Dipole-dipole interaction seems responsible for the quenching of the triplet biradical by the lanthanide complexes, while the Heisenberg exchange interaction is predominant in the quenching by the copper complex.

Selectivity of complexing gas chromatographic stationary phases containing lanthanide β-diketonates

The Rohrschneider—McReynolds series of organic compounds has been used to determine the polarity of gas chromatographic stationary phases containing tris-β-diketonates of praseodymium and europium, dissolved in poly(dimethylsiloxane). The selectivity of the stationary phases studied has been characterized by using the differential excess partial molar free energy of mixing within the temperature range of 90–130°C. Changes in selectivity observed with increasing temperature are discussed in the context of the proposed complexation scheme.