Synthesis, crystal structure, and luminescent properties of novel Eu3+ heterocyclic beta-diketonate complexes with bidentate nitrogen donors

New tris(heterocyclic beta-diketonato)europium(III) complexes of the general formula Eu(PBI)3.L [where HPBI = 3-phenyl-4-benzoyl-5-isoxazolone and L = H2O, 2,2'-bipyridine (bpy), 4,4'-dimethoxy-2,2'-bipyridine (dmbpy), 1,10-phenanthroline (phen), or 4,7-diphenyl-1,10-phenanthroline (bath)] were synthesized and characterized by elemental analysis, Fourier transform infrared spectroscopy (FT-IR), 1H NMR, high-resolution mass spectrometry, thermogravimetric analysis, and photoluminescence (PL) spectroscopy. Single-crystal X-ray structures have been determined for the complexes Eu(PBI)3.H2O.EtOH and Eu(PBI)3.phen. The complex Eu(PBI)3.H2O.EtOH is mononuclear, and the central Eu3+ ion is coordinated by eight oxygen atoms to form a bicapped trigonal prism coordination polyhedron. Six oxygens are from the three bidentate HPBI ligands, one is from a water molecule, and another is from an ethanol molecule. On the other hand, the crystal structure of Eu(PBI)3.phen reveals a distorted square antiprismatic geometry around the europium atom. The room-temperature PL spectra of the europium(III) complexes are composed of the typical Eu3+ red emission, assigned to transitions between the first excited state (5D0) and the multiplet (7F0-4). The results demonstrate that the substitution of solvent molecules by bidentate nitrogen ligands in Eu(PBI)3.H2O.EtOH richly enhances the quantum yield and lifetime values. To elucidate the energy transfer process of the europium complexes, the energy levels of the relevant electronic states have been estimated. Judd-Ofelt intensity parameters (Omega2 and Omega4) were determined from the emission spectra for Eu3+ ion based on the 5D0 --> 7F2 and 5D0 --> 7F4 electronic transitions, respectively, and the 5D0 --> 7F1 magnetic dipole allowed transition was taken as the reference. The high values obtained for the 4f-4f intensity parameter Omega2 for europium complexes suggest that the dynamic coupling mechanism is quite operative in these compounds.     

Synthesis and spectroscopic behavior of highly luminescent Eu(3+)-dibenzoylmethanate (DBM) complexes with sulfoxide ligands

In this paper the synthesis, characterization and photoluminescent behavior of the [RE(DBM)3L2] complexes (RE=Gd and Eu) with a variety of sulfoxide ligands; L=benzyl sulfoxide (DBSO), methyl sulfoxide (DMSO), phenyl sulfoxide (DPSO) and p-tolyl sulfoxide (PTSO) have been investigated in solid state. The emission spectra of the Eu(3+)-beta-diketonate complexes show characteristics narrow bands arising from the 5D0-->7F(J) (J=0-4) transitions, which are split according to the selection rule for C(n), C(nv) or C(s) site symmetries. The experimental Judd-Ofelt intensity parameters (Omega2 and Omega4), radiative (A(rad)) and non-radiative (A(nrad)) decay rates, and R02 for the europium complexes have been determined and compared. The highest value of Omega2 (61.9x10(-20)cm2) was obtained to the complex with PTSO ligand, indicating that Eu3+ ion is in the highly polarizable chemical environment. The higher values of the experimental quantum yield (q) and emission quantum efficiency of the emitter 5D0 level (eta) for the Eu-complexes with DMSO, DBSO and PTSO sulfoxides suggest that these complexes are promising Light Conversion Molecular Devices (LCMDs). The lower value of quantum yield (q=1%), for the hydrated complex [Eu(DBM)3H2O], indicates that the luminescence quenching occurs via multiphonon relaxation by coupling with the OH-oscillators from water molecule coordinated to rare earth ion. The pure red emission of the Eu-complexes has been confirmed by (x, y) color coordinates.     

Syntheses,Crystal Structures,and Antimicrobial Activities of N′-(5-Hydroxy-2-nitrobenzylidene)-4-dimethylaminobenzohydrazide Methanol Solvate and 2-Fluoro-N′-(5-hydroxy-2-nitrobenzylidene)benzohydrazide

Two new hydrazone compounds,N'-(5-hydroxy-2-nitrobenzylidene)-4-dimethyl-aminobenzohydrazide methanol solvate (1) and 2-fluoro-N'-(5-hydroxy-2-nitrobenzylidene)benzo-hydrazide (2),have been synthesized and characterized by elemental analysis,IR spectra,1H NMR,and single-crystal X-ray diffraction.Compound 1 crystallizes in the monoclinic space group P21/c with a=11.571(3),b=12.420(3),c=12.360(2) ?,β=97.495(2)°,V=1761.1(7) 3,Z=4,R=0.0735 and wR=0.1344.Compound 2 crystallizes in the triclinic space group P with a=7.551(3),b=8.254(3),c=11.365(2) ?,α=79.352(2),β=76.154(2),γ=71.624(2)°,V=648.2(4) 3,Z=2,R=0.0393 and wR=0.1008.The hydrazone molecules of the compounds display E configurations with respect to the C=N double bonds.In the crystal structure of 1,the hydrazone molecules are linked by methanol molecules through N-H…O,O-H…N and O-H…O hydrogen bonds,forming chains running along the c axis.In the crystal structure of 2,molecules are linked through N-H…O and O-H…O hydrogen bonds,forming ribbons running along the b axis.The preliminary antimicrobial activities were studied.     

Influence of the Nature of Carboxylic Acid on the Luminescence and Spectral Properties of (Carboxylato)bis(dibenzoylmethanato)europium(III) Complexes

A series of (carboxylato)bis(dibenzoylmethanato)europium(III) complexes containing anions of both saturated and unsaturated carboxylic acids were synthesized to compare the luminescence and spectral properties of heteroligand Eu(III) complexes. (Carboxylato)bis(dibenzoylmethanato)europium(III) complexes with unsaturated acid anions were synthesized for the first time. The compounds obtained were characterized using elemental analysis and luminescence and IR spectroscopy. These studies revealed two types of influence of the nature of an acid substituent on the luminescence spectra of (carboxylato)bis(dibenzoylmethanato)europium(III) complexes. The anomalous Stark structure of the luminescence spectra of one group of compounds is attributed to the charge transfer state at 77 K.     

Synthesis and spectroscopic properties of lanthanide nitrate complexes with a new amide-based quinoxaline-2,3-dione ligand

Solid complexes of lanthanide nitrate with 1,4-di(N,N-di-n-butyl-acetamido)-quinoxaline-2,3-dione (L), [Ln(N03)3L.H2O] (Ln=La, Nd, Eu, Gd, Tb, Er), have been prepared and characterized by elemental analysis, IR, UV-vis spectra and conductivity measurements. The fluorescence property of the europium complex in solid state and in MeCN, acetone, AcOEt and THF was studied. Under the excitation, the europium complex exhibited characteristic emissions of europium. The result indicates that the triplet state energy level of the ligand matches better to the resonance level of Eu(III) than Tb(III) ion.     

Coordination compounds of europium(III) and samarium(III) dibenzoylmethanates with 5-phenyl-2-(2′-pyridyl)-7,8-benzo-6,5-dihydro-1,3,6-triazaindolizine

Novel heteroligand europium(III) and samarium(III) complexes with dibenzoylmethane (HDBM) and 5-phenyl-2-(2??-pyridyl)-7,8-benzo-6,5-dihydro-1,3,6-triazaindolizine (L), Ln(DBM)₃L (Ln = Eu, Sm), were synthesized. The structure of the europium complex was determined by X-ray diffraction. It was shown that the use of L as an auxiliary ligand increases the luminescence intensity of lanthanides severalfold as compared with analogous complexes containing phenanthroline as the second ligand.     

Syntheses, Structures and Photoluminescence of Two New Europium（III） Coordination Polymers

Two new europium (Ⅲ) coordination polymers formulated as Eu2(H2O)2(ox)4 ]· (C5H6N)2 ·2H 2 O(1) and Eu 2(ad)3(H2O)4 ]·0.25H2O (2) (H2ox = oxalic acid, H2ad = adipic acid) have been synthesized from the self-assembly of lanthanide ions Eu 3+ with flexible oxalic and adipic acid ligands, respectively. Structural analyses revealed that complex 1 exhibits three-dimensional metalorganic frameworks, and 2 has intricate two-dimensional interpenetrated metal-organic networks. In addition, the photoluminescent properties of complexes 1 and 2 were discussed in detail, which shows strong red emission, corresponding to 5 D0 → 7 F 2 transition of Eu3+ ions.     

Synthesis and photoluminescence properties of novel europium complexes of 2'-hydroxyacetophenone and 4,6-diacetylresorcinol

Novel europium (III) complexes of the formulae Eu(OHAP)(3).2H2O, Eu(OHAP)(3)Phen, Eu2(DAR)(3).4H2O and Eu2(DAR)(3)Phen2 (HOHAP=2'-hydroxyacetophenone, H2DAR=4,6-diacetylresorcinol, Phen=1,10-phenanthroline) have been designed and synthesized in this paper. These complexes were characterized by elemental analysis, FT-IR, and UV-vis. Based on these observations, the ligands are coordinated to Eu(III) via the acetyl and phenolic oxygens, and H2DAR is concluded to be bis-bidentate donor. Photoluminescence studies showed that the several complexes emitted red luminescence. Thermo-gravimetric analysis showed that the complexes possess good thermal stability. Also, it was found that Phen as a synergic ligand, coordinated to Eu(III) in a composite system like 2'-hydroxyacetophenone and 4,6-diacetylresorcinol, could enhance the complexes luminescence intensity, quantum yield and lifetime.     

Improving the Selectivity of the Luminescence Determination of Europium(III) with the Use of a Zirconium Phosphate Solid Support

Conditions for the sorption of europium(III) ions by finely dispersed zirconium oxophosphate and for the formation of Eu complexes upon treatment of the resulting adsorbates with solutions of reagents (Na₂WO₄; oxalic, nicotinic, quinaldic, benzoic, and nalidixic acids; and benzoyltrifluoroacetone) were studied. It was found that the adsorbate of the Eu complex of nalidixic acid (the ratio of components, 1 : 2) exhibits highly intense luminescence and is characterized by the highest photostability. The use of sorption and the complexation of Eu with nalidixic acid on the sorbent improved the selectivity and lowered the detection limit for the determination of europium in high-purity samarium oxide.     

钐、铕-2,4-二氯苯氧乙酸的二元、三元配合物的合成及荧光性能

以2,4-二氯苯氧乙酸为第一配体、1,10-菲罗啉为第二配体,合成了钐、铕的二元、三元配合物。通过元素分析、EDTA络合滴定及热重分析,确定了配合物的通式为RE(DCP)3.H2O,RE(DCP)3phen(RE=Sm,Eu;DCP=2,4-二氯苯氧乙酸根;phen=邻菲罗啉);测定了配合物红外光谱、紫外光谱、荧光光谱;研究了配合物的热稳定性。结果表明,三元配合物较二元配合物稳定;Eu(DCP)3.H2O和Eu(DCP)3phen具有荧光性能。     

Reactivity of "Eu(OiPr)2" with phenols: formation of linear Eu3, square pyramidal Eu5, cubic Eu8, and capped cubic Eu9 polymetallic europium complexes

The direct reaction of europium with 2-propanol and phenols has been investigated under a variety of conditions. The reaction of europium metal with 2,6-dimethylphenol and 2,6-diisopropylphenol in 2-propanol at reflux revealed that polymetallic europium complexes could be generated by this method. Hx[Eu8O6(OC6H3Me2-2,6)12(OiPr)8], 1, and H5[Eu5O5(OC6H3iPr2-2,6)6(NCCH3)8], 2, were isolated by recrystallization in the presence of hexanes and acetonitrile, respectively, and characterized by X-ray crystallography. Complex 1 has a cubic arrangement of europium ions with face-bridging mu 4-O donor atoms, edge-bridging mu-O(phenoxide/phenol) ligands, and terminal O(isopropoxide/2-propanol) ligands. Complex 2 is mixed valent and has a square pyramidal europium core with four Eu(II) ions at the basal positions and one Eu(III) ion at the apex. Since these reactions gave complicated mixtures of products from which 1 and 2 could only be obtained in low yields, direct reactions under less forcing reaction conditions were investigated. Europium reacts slowly at room temperature to form arene-soluble divalent [Eu(OiPr)2(THF)x]n, 3. Complex 3 reacts with 2,6-dimethylphenol to form the arene-insoluble complex (H[Eu(OC6H3Me2)2(OiPr)])n, 4. Recrystallization of 4 in the presence of THF results in the crystallographically characterizable divalent trimetallic complex [Eu(OC6H3Me2-2,6)2(THF)2]3, 5, which has an unusual linear metal geometry. In the presence of HOiPr at ambient conditions in the glovebox, crystals of 5 slowly convert to the mixed valent H10[Eu8O8(OC6H3Me2-2,6)10(OiPr)2(THF)6], 6, which was found to have a cubic arrangement of europium atoms similar to 1 by X-ray crystallography. Complex 4, upon heating under vacuum, followed by reaction with THF, forms the arene-soluble divalent complex H18([Eu9O8(OC6H3Me2-2,6)10(THF)7][Eu9O9(OC6H3Me2-2,6)10(THF)6]), 7, which contains two types of capped cubic arrangements of europium ions in the solid state.     

Photoacoustic and luminescence spectra study on the effects of chlorine substituent on the energy transfer of Eu(III)-chlorobenzoic acid

The photoacoustic (PA) amplitude spectra of three complexes of Eu(III) combined with chlorobenzoic acid (Eu(o-ClC6H4CO2)3.H2O, Eu(m-ClC6H4CO2)3.H2O and Eu(p-ClC6H4CO2)3.H2O) have been measured, and the PA phase of the different complexes have been calculated. Both the PA amplitude spectra and the luminescence spectra reflect the variation of the luminescent properties, and the PA phase is directly relative to the relaxation time. Since the relaxation is the process of the intramolecular energy transfer between the ligands and the central ion, the molecular structure of ligand is the important factor to decide the energy gap between the lowest triplet state of ligand and the resonance level of central ion. The effects of chlorine substituent on the molecular structure and energy gap of the complexes have been studied by PA phase and luminescence spectra.     

Structural characterization of shielded isomeric europium complexes with metal-metal contact

New luminescent isomeric europium(III) complexes with carboxylic carbonyl group coordination (I and II) have been prepared by solvothermal synthesis using the ligand 2,2'-bipyridine-4,4'-dicarboxylic acid (bpdc), with the nonradiatively shielded Eu3+ coordination sphere completed by dimethyl sulfoxide ligands. The room temperature IR spectra and Eu3+ luminescence spectra do not provide a definitive distinction between I and II, but low-temperature luminescence can give a clear identification.     

Synthesis, structure and luminescence property of the ternary and quaternary europium complexes with furoic acid

A ternany europium complex with furoic acid (α-FURA) and 1,10-phenanthroline(phen), [Eu(α-FURA)₃phen]H₂O(I) and a quaternary europium furoate complex with 1,10-phenanthroline and nitrate, Eu(α-FURA)₂NO₃phen(II) were synthesized and characterized by X-ray diffraction. The two europium ions in each of the complexes (I) and (II) are held together by four carboxylato groups with the two modes, namely bidentate bridging and tridentate bridging, and each europium ion is further bonded to two nitrogen atoms from 1,10-phenanthroline and one chelated bidentate furoate group for the complex (I) and one chelated nitrato group for the complex (II), making a coordination number of 9. Luminescence spectra observed at 77 K show that the europium ion site in the crystals of the complexes (I) and (II) has low symmetry and lifetimes of the solid complexes (I) and (II) are 1.13 and 1.20 ms, respectively.     

Structural and thermal properties of rare earth complexes with 2,2′-biphenyldicarboxylic acid

Rare earth complexes with 2,2′-biphenyldicarboxylic acid (diphenic acid = H₂dpa) were obtained as hydrated precipitates of the general formula Ln₂(C₁₄H₈O₄)₃∙nH₂O, where n = 3 for the of Y(III) and Ce(III)–Er(III) and n = 6 for La(III), Tm(III), Yb(III) and Lu(III) complexes. On heating in air atmosphere complexes lose all water molecules in the temperature range 30–210 °C in one step and form anhydrous compounds, which are stable up to 315–370 °C. During further heating they decompose to oxides. The trihydrated compounds are crystalline powders whereas the hexahydrated are amorphous solids. The trihydrated complexes crystallize in the monoclinic (Pr(III) and Ce(III) complexes) and triclinic (Y(III) and Nd(III)–Er(III) complexes) crystal systems.     

Laser-induced fluorescence study on the interaction of Eu(III) with polycarboxylates

Laser-induced fluorescence spectroscopy was applied to obtaining hydration structure of Eu(III) complexes with synthetic polycarboxylates of poly(acrylic acid), poly(maleic acid), poly(methacrylic acid), and poly(a-hydroxyacrylic acid). Dependence of (the number of water molecules in the first coordination sphere of Eu(III) ion) on pH and supporting electrolyte concentration was obtained for these complexes. The spectroscopic results show that Eu(III) is surrounded by the “cage” of polycarboxylate ligands. The pH-induced transition in conformation of poly(methacrylic acid) ligand was clearly observed in the plot vs. pH.     

Tuning the triplet energy levels of pyrazolone ligands to match the 5D0 level of europium(III)

Three pyrazolone-based ligands, namely 1-phenyl-3-methyl-4-(1-naphthoyl)-5-pyrazolone (HL1), 1-phenyl-3-methyl-4-(4-dimethylaminobenzoyl)-5-pyrazolone (HL2), and 1-phenyl-3-methyl-4-(4-cyanobenzoyl)-5-pyrazolone (HL3), were synthesized by introducing electron-poor or electron-rich aryl substituents at the 4-position of the pyrazolone ring. Their corresponding europium complexes Eu(LX)3(H2O)2 and Eu(LX)3(TPPO)(H2O) (X = 1-3) were characterized by photophysical studies. The characteristic Eu(III) emission of these complexes with at most 9.2 x 10(-3) of fluorescent quantum yield was observed at room temperature. The results show that the modification of ligands tunes the triplet energy levels of three pyrazolone-based ligands to match the 5D0 energy level of Eu3+ properly and improves the energy transfer efficiency from antenna to Eu3+, therefore enhancing the Eu(III) emission intensity. The highest energy transfer efficiency and probability of lanthanide emission of Eu(L1)3(H2O)2 are 35.1% and 2.6%, respectively, which opens up broad prospects for improving luminescent properties of Eu(III) complexes by the modification of ligands. Furthermore, the electroluminescent properties of Eu(L1)3(TPPO)(H2O) were also investigated.     

3-Phenyl-4-benzoyl-5-isoxazolonate complex of Eu3+ with tri-n-octylphosphine oxide as a promising light-conversion molecular device

Three new europium complexes, [Eu(PBI)3.3H2O] (1), [Eu(PBI)3.2TOPO] (2), and [Eu(PBI)3.2TPPO.H2O] (3) (where HPBI, TOPO, and TPPO stand for 3-phenyl-4-benzoyl-5-isoxazolone, tri-n-octylphosphine oxide, and triphenylphosphine oxide, respectively), with different neutral ligands were synthesized and characterized by elemental analysis, Fourier transform infrared, (1)H NMR, thermogravimetric analysis, and photoluminescence (PL) spectroscopy. The coordination geometries of the complexes were calculated using the Sparkle/AM1 (Sparkle Model for the Calculation of Lanthanide Complexes within the Austin Model 1) model. The ligand-Eu3+ energy-transfer rates were calculated in terms of a model of the intramolecular energy-transfer process in lanthanide coordination compounds reported in the literature. The room-temperature PL spectra of the europium(III) complexes are composed of the typical Eu3+ red emission, assigned to transitions between the first excited state (5D0) and the multiplet (7F(0-4)). On the basis of emission spectra and lifetimes of the 5D0-emitting level, the emission quantum efficiency (eta) was determined. The results clearly show that the substitution of water molecules by TOPO leads to greatly enhanced quantum efficiency (i.e., 26% vs 92%) and longer 5D0 lifetimes (250 vs 1160 micros). This can be ascribed to a more efficient ligand-to-metal energy transfer and a less nonradiative 5D0 relaxation process. Judd-Ofelt intensity parameters (Omega2 and Omega4) were determined from the emission spectra for the Eu3+ ion based on the 5D0 --> 7F2 and 5D0 --> 7F4 electronic transitions, respectively, and the 5D0 --> 7F1 magnetic-dipole-allowed transition was taken as the reference. A point to be noted in these results is the relatively high value of the Omega2 intensity parameter for all of the complexes. This may be interpreted as being a consequence of the hypersensitive behavior of the 5D0 --> 7F2 transition. The dynamic coupling mechanism is, therefore, dominant, indicating that the Eu3+ ion is in a highly polarizable chemical environment.     

Solvation of uranyl(II), europium(III) and europium(II) cations in "basic" room-temperature ionic liquids: a theoretical study

We report a molecular dynamics study of the solvation of UO2(2+), Eu3+ and Eu2+ ions in two "basic" (Lewis acidity) room-temperature ionic liquids (IL) composed of the 1-ethyl-3-methylimidazolium cation (EMI+) and a mixture of AlCl4- and Cl- anions, in which the Cl-/AlCl4- ratio is about 1 and 3, respectively. The study reveals the importance of the [UO2Cl4]2- species, which spontaneously form during most simulations, and that the first solvation shell of europium is filled with Cl- and AlCl4- ions embedded in a cationic EMI+ shell. The stability of the [UO2Cl4]2- and [Eu(III)Cl6]3- complexes is supported by quantum mechanical calculations, according to which the uranyl and europium cations intrinsically prefer Cl- to the AlCl4- ion. In the gas phase, however, [Eu(III)Cl6]3- and [Eu(II)Cl6]4- complexes are predicted to be metastable and to lose two to three Cl- ions. This contrasts with the results of simulations of complexes in ILs, in which the "solvation" of the europium complexes increases with the number of coordinated chlorides, leading to an equilibrium between different chloro species. The behavior of the hydrated [Eu(OH2)8]3+ complex is considered in the basic liquids; the complex exchanges H2O molecules with Cl- ions to form mixed [EuCl3(OH2)4] and [EuCl4(OH2)3]- complexes. The results of the simulations allow us to better understand the microscopic nature and solvation of lanthanide and actinide complexes in "basic" ionic liquids.