Dinuclear Europium Research Articles

Dinuclear Lanthanide Compound as a Promising Luminescent Probe for Al3+ Ions.

Luminescent probes have wide applications in biological system analysis and environmental science. Here, one novel luminescent dinuclear europium compound with a crown ether analogous ligand was synthesized through a solvent-thermal reaction. Through transformation, upon the addition of Al3+ ions to the N,N'-dimethyl formamide solution of the europium compound, the luminescent intensity of the characteristic emission of Eu3+ decreased, and a new emission peak appeared at 346 nm and increased rapidly. The luminescent investigation indicated that it could act as a highly sensitive and selective luminescent probe for Al3+ ions. Moreover, mass spectrometry and single-crystal X-ray diffraction confirmed the formation of a new more stable trinuclear aluminium compound during the sensing process.

Asymmetric induction in quadruple-stranded europium(iii) helicates and circularly polarized luminescence

Chiral supramolecular lanthanide-helicates are regarded as promising chiroptical materials due to their combination of ground and excited state chirality and special luminescence properties from Ln3+, named circularly polarized luminescence (CPL). However, the sophisticated and costly asymmetric syntheses decelerate their research progress. Herein, a chiral induction strategy is employed to break the racemic equilibrium of lanthanide helicate by the formation of a compact ion pair. The synthesized chiral guanidine cation ((R/S)-HG) helps to effectively transfer chirality to anionic quadruple-stranded helicate by electrostatic, H bonds, and multiple C-H⋯F and N-H⋯F interactions. The diastereoselective control was confirmed by X-ray crystallography and CD and CPL spectroscopy, where (S)-HG prefers to bind a P (ΔΔ) helical enantiomer, in contrast a M helicate for (R)-HG. Additionally, the inconsistency of CD and CPL spectra in assessing the perturbation of a racemic equilibrium discloses their complementary advantages on monitoring molecular chirality. In the case of diastereomeric enrichment equilibrium, three pairs of helicates show high luminescence quantum yields of 42%-54%, and large |glum| with the values of 0.137-0.266. This work provides an effective strategy to synthesize excellent CPL materials based on racemic lanthanide helicate.

Single crystal X-ray structure determination and enantiomeric recognition of chiral dinuclear europium (III) complexes towards BINOL

Herein, we reported a pair of di-nuclear europium enantiomers [Eu2(PO4)6(R-/S-HL)6(MeOH)4]•2MeOH (R-complex(1a) and S-complex(1b)) constructed from chiral ligands (R)-/(S)-(+)-1,1′-binaphthyl-2,2′-diyl hydrogenphosphate (R-/S-HL) and europium (III) nitrate by solvothermal method. The structure of the complexes was characterized by single-crystal X-ray diffraction, powder X-ray diffraction and Fourier transform infrared spectroscopy. It was found that R-complex(1a) and S-complex(1b) were chiral enantiomers with a zero-dimensional chiral cluster structure. The circular dichroism studies further revealed the chiral properties of R-complex(1a) and S-complex(1b). Moreover, fluorescence sensing tests demonstrated that R-complex(1a) and S-complex(1b) possessed high enantioselectivity for axially chiral BINOL racemates.

Point Chirality Controlled Diastereoselective Self-Assembly and Circularly Polarized Luminescence in Quadruple-Stranded Europium(III) Helicates.

Aromatic β-diketones have been extensively employed as highly effective sensitizers in luminescent lanthanide complexes. However, the difficulties to make the chiral modified groups effectively participate in the frontier molecular orbital (FMO) distributions limit their applications on lanthanide circularly polarized luminescence (CPL) fields. Considering the inherent chirality of the helical structure, a pair of enantiopure dinuclear europium quadruple-stranded helicates, ΔΔ/ΛΛ-(HNEt3)2(Eu2L4) (ΔΔ/ΛΛ)-1; L = R/S-1,2-bis(4,4'-bis(4,4,4-trifluoro-1,3-dioxobutyl)phenoxyl)propane are assembled via a point chirality induced strategy. The comprehensive spectral characteristics combined with density functional theory (DFT) calculations demonstrate that the one point chirality at the spacer of the ligand successfully controls the Δ or Λ configuration around the Eu(III) ion center and the P or M helical patterns of the helicates. The mirror-image CPL and CD spectra further confirm the formation of the enantiomer pairs. As expected, the helicate presents a higher luminescence quantum yield (QY) of 68% and a large |glum| value (0.146). This study effectively combines the excellent sensitization capability of β-diketone and the helical chirality of helicates. This strategy provides an effective path for the synthesis of lanthanide material with excellent CPL performance.

Carbonate-bridged dinuclear lanthanide(III) complexes of chiral macrocycle

Mononuclear Eu(III) and Dy(III) complexes of the chiral hexaaza macrocycle L, 2(R),7(R),18(R),23(R)-1,8,15,17,24,31-hexaazatricyclo[25.3.1.1.0.0]-dotriaconta-10,12,14,26,28,30-hexaene have been obtained as chloride derivatives (1 and 2, respectively) and characterized by using spectroscopic methods. The X-ray crystal structure of 2 has been determined. The reaction of two equivalents of mononuclear 1 or 2 complexes with one equivalent of sodium carbonate results in the formation of dinuclear complexes [Eu2L2(µ2-CO3)(H2O)3]Cl43 and [Dy2L2(µ2-CO3)(H2O)3]Cl44, respectively. The X-ray crystal structure of complex 3 reveals two macrocyclic [EuL]3+ units bridged by the carbonate anion. The carbonate anion is bound to the Eu(III) ions using the η1:η2-µ2 bridging mode. The binding of carbonate anions to the [EuL]3+ or [DyL]3+ macrocyclic units has also been studied in solution using spectroscopic methods. The titration of the starting paramagnetic mononuclear chloride derivatives 1 and 2 monitored by 1H NMR spectroscopy revealed initial formation of dinuclear species, followed by the formation of complexes possessing additional carbonate ligands. The dinuclear carbonate complexes 3 and 4 are also formed in the reactions of the respective mononuclear chloride complexes with gaseous CO2. Lanthanide(III) complexes of the chiral hexaaza macrocycle L are effective for catalytic hydrolysis of bis(4-nitrophenyl) phosphate BNPP. Within the series of the studied mononuclear complexes: nitrate derivatives [LnL(NO3)(H2O)](NO3)2 (Ln = Ho, Er), [LnL(H2O)2](NO3)3 (Ln = Tm, Yb, Lu) and chloride derivatives [LnL(H2O)2]Cl3 (Ln = Tm, Yb, Lu, Y) the catalytic activity of the complexes is increased with increasing ionic size. Kinetic studies revealed that most active is the dinuclear europium(III) complex 3 which catalyzes the hydrolysis of BNPP with a rate kobs = 6.5 × 10−5 s−1 (at 0.3 mM concentration of the catalyst) at pH 8.5 and 37 °C.

Synthesis of a dinuclear europium(iii) complex through deprotonation and oxygen-atom transfer of trimethylamine N-oxide.

A dinuclear Eu(iii) complex Eu2(OCH2NMe2)2[N(SiMe3)2]4 (1) was synthesized via the reaction of Me3NO and Eu[N(SiMe3)2]3, during which the unprecedented C-H activation of Me3NO occurred along with oxygen-atom transfer. A simple Eu[N(SiMe3)2]3(OPMe3) adduct (2) was obtained when Me3PO was used, which should be due to the higher energy barrier and poorer product stability that prevent the formation of the phosphine substituted analogue of 1.

Highly sensitive and selective sensing of CH3Hg+ via oscillation effect in Eu-cluster

A new dinuclear europium cluster (Eu-cluster) is synthesized and the exact structure is determined by single-crystal X-ray diffraction. The formula of the Eu-cluster is determined to be [Eu2(4-Msal)6(phen)2(H2O)2] (4-Msal=4-methylsalicylic acid, phen=phenanthroline), it crystallizes in the triclinic space group P-1, with a=9.1193(8)Å, b=13.0855(10)Å, c=14.0981(9)Å, α=103.159(6)°, β=94.192(6)°, γ=100.632(7)°, V=1598.3(2)Å3 and Z=1. Further investigation reveals that the Eu-cluster is a highly sensitive and selective methylmercury (CH3Hg+) sensor. To the best of our knowledge, this is the first CH3Hg+ sensor based on lanthanide clusters/complexes. The responsive behavior shows the sensing has excellent linearity in 1.4–3.8μgL−1μM. The LOD for sensing CH3Hg+ is 0.8μgL−1, which meets the standard of Chinese environmental quality standard for agricultural and industrial water. Interestingly, study also reveals the sensor is applicable in real water sensing.

Mono- and dinuclear europium(III) complexes with thenoyltrifluoroacetone and 1,10-phenanthroline-5,6-dione

The N,N′-coordinated mononuclear complex Eu(TTA)3(pdn), prepared by treating 1,10-phenanthroline-5,6-dione (pdn) with Eu(TTA)3(H2O)2 (HTTA = 2-thenoyltrifluoroacetone), may be used as a benzoquinone-like ligand through the oxygen donor atoms in reaction with an additional Eu(TTA)3(H2O)2 precursor to give the dinuclear complex Eu2(TTA)6(pdn). Both the mono- and dinuclear complexes were characterized by elemental analysis, IR, TG, MS, and 1H NMR spectra. The results indicated that they both exhibited a characteristic red emission peak at 616 nm, corresponding to the 5D0 → 7F2 transition of Eu(III) ions under UV excitation. Compared with the mononuclear complex, the dinuclear complex presented better thermal stability and stronger luminescence, which makes it a promising light-conversion molecular device. .

Ratiometric luminescence thermometry based on crystal-field alternation at the extremely narrow 5D0 → 7F2 transition band of europium(iii)

A dinuclear europium(III) complex with a structure of [BP-(Eu(III))2-(ODA)3] (BP = 2,2'-bipyridine-6,6'-dicarboxylic acid bis(N-hydroxy-succinimide) ester, ODA = diglycolic acid) shows a fully reversible emission spectral change at the extremely narrow (5)D0 → (7)F2 transition band in response to temperature changes ranging from 283 K to 333 K.

Synthesis, structure and luminescent property of a new europium-based coordination polymer constructed from biphenyl-3,4′,5-tricarboxylic acid

A new 3D lanthanide metal–organic framework Eu(BPT)(DMF)(H2O)•(H2O)0.5] (1) has been synthesized by self-assembly of Eu(III) ions and ligand biphenyl-3, 4′, 5-tricarboxylate under solvothermal reaction conditions. X-ray crystallography reveals that 1 exhibits a (3, 6)-connected topology, with dinuclear europium clusters as 6-connected nodes and C2-symmetric ligands BPT as 3-connected nodes. In addition, the luminescence sensitization of 1 via excitation of the ligand is highly efficient.

Bipolar-transporting dinuclear europium(III) complexes involving carbazole and oxadiazole units: Synthesis, photophysical and electroluminescent properties

Abstract A class of bipolar-transporting dinuclear europium (III) complexes involving a carbazole and a oxadizaole fragments was synthesized and characterized by elemental analysis, infrared spectro-scopy and thermal analyses. Compared to the mononuclear europium (III) tris(dibenzoylmethane) (1,10-phenanthroline), these dinuclear europium (III) complexes presented better thermal stability, and similar UV-vis absorption and photoluminescence spectra in dichloromethane. Two intense UV-vis absorption bands at around 282 nm and 352 nm, and a characteris-tical red emission peak at 614 nm from the 5 D 0 → 7 F 2 transition of the central Eu 3+ ions were observed under photo-excitation, respectively. Using the Eu 2 (DBM) 6 (FPhOXD6CzPhen 2 ) as emitters and a blend of poly (vinylcarbazole) and 2-(4-biphenyl)-5-(4- tert -butylphenyl)-1,3,4-oxadiazole as a host matrix, the single emitting-layer polymer light-emitting devices exhibited saturated red electrolumine- scent emission from Eu 3+ ion at dopant concentrations from 1 wt % to 8 wt %.

A dinuclear europium(III) complex with thenoyltrifluoroacetonato and 1-(2-pyridylzao)-2-naphtholato ligands and its optical properties

Dinuclear lanthanide complexes of the general for Ln 2(TTA) 4(PAN) 2 (Ln = Eu, Gd, Tb, Yb; TTA and monodeprotonated thenoyltrifluoroacetone and PAN 1-(2-pyridylazo)-2-naphthol, respectively) were prepared and structurally characterized. These novel complexes, representing the first examples of crystallographically characterized lanthanide–PAN complexes, each feature a dinuclear core with the metal atoms bridged by the phenolato O atoms of the chelating-bridging PAN ligands. Electronic spectroscopic and photoluminescence studies were carried out for the Eu(III) complex, and the results are consistent with ligand-mediated energy transfer and ligand-sensitized luminescence characteristic of Eu(III). The Eu(III) complex doped into a polymeric film was shown to effectively limit a nanosecond 523-nm laser pulse, and the limiting effect is rationalized in terms of reverse saturable absorption due to the strong absorption of the metal’s excited triplet states that are populated by intersystem crossing.

Solution Chemistry of Europium(III) Aqua Ion at Micromolar Concentrations as Probed by Direct Excitation Luminescence Spectroscopy

AbstractDirect excitation europium(III) luminescence spectroscopy is used to study the speciation of aqueous europium(III) ions at micromolar concentrations and near neutral pH. The pH and concentration dependence of the europium(III) 7F0→5D0 excitation peak is consistent with the formation of both mononuclear and dinuclear europium(III) hydroxide complexes at pH 6.5. Luminescence intensity and lifetime quenching studies in the presence of NdIII at pH 5.0 and 6.5 support the formation of a dinuclear complex at pH 6.5. Steady state excitation and time‐resolved luminescence spectroscopy are consistent with the formation of innersphere nitrate and fluoride complexes, but outersphere perchlorate and chloride complexes at pH 6.5 and 5.0.

Tethered Dinuclear Europium(III) Macrocyclic Catalysts for the Cleavage of RNA

Dinuclear europium(III) complexes of the macrocycles 1,3-bis[1-(4,7,10-tris(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane]-m-xylene (1), 1,4-bis[1-(4,7,10-tris(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane]-p-xylene (2), and mononuclear europium(III) complexes of macrocycles 1-methyl-,4,7,10-tris(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane (3), 1-[3'-(N,N-diethylaminomethyl)benzyl]-4,7,10-tris(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane (4), and 1,4,7-tris(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane (5) were prepared. Studies using direct excitation ((7)F0 --> (5)D0) europium(III) luminescence spectroscopy show that each Eu(III) center in the mononuclear and dinuclear complexes has two water ligands at pH 7.0, I = 0.10 M (NaNO3) and that there are no water ligand ionizations over the pH range of 7-9. All complexes promote cleavage of the RNA analogue 2-hydroxypropyl-4-nitrophenyl phosphate (HpPNP) at 25 degrees C (I = 0.10 M (NaNO3), 20 mM buffer). Second-order rate constants for the cleavage of HpPNP by the catalysts increase linearly with pH in the pH range of 7-9. The second-order rate constant for HpPNP cleavage by the dinuclear Eu(III) complex (Eu2(1)) at pH 7 is 200 and 23-fold higher than that of Eu(5) and Eu(3), respectively, but only 7-fold higher than the mononuclear complex with an aryl pendent group, Eu(4). This shows that the macrocycle substituent modulates the efficiency of the Eu(III) catalysts. Eu2(1) promotes cleavage of a dinucleoside, uridylyl-3',5'-uridine (UpU) with a second-order rate constant at pH 7.6 (0.021 M(-1) s(-1)) that is 46-fold higher than that of the mononuclear Eu(5) complex. Methyl phosphate binding to the Eu(III) complexes is energetically most favorable for the best catalysts, and this supports an important role for the catalyst in stabilization of the developing negative charge on the phosphorane transition state. Despite the formation of a bridging phosphate ester between the two Eu(III) centers in Eu2(1) as shown by luminescence spectroscopy, the two metal ion centers are only weakly cooperative in cleavage of RNA and RNA analogues.

Efficient red organic light-emitting diodes based on a dinuclear europium complex

Pure red organic light-emitting diodes based on a dinuclear europium complex with a structure of (TTA)3Eu(PYO)2Eu(TTA)3 (TTA=thenoyltrifluoroacetonate, PYO=pyridine N-oxide) were presented. The devices showed pure red emission at a peak wavelength of 612nm with a full width at half maximum of 3nm, which is a characteristic emission from Eu3+ ion based on 5D0→7F2 transition. The maximum brightness and electroluminescent (EL) efficiency reached 340cd/m2 at a driving voltage of 19V and 2.4cd/A (0.78lm/W) at a current density of 0.14mA/cm2, respectively.

Synthesis and Characterization of the First Dinuclear Europium (II) Complex Supported by Carbon-Bridged Biphenolate Ligand

Anhydrous EuCl 3 reacted with sodium carbon-bridged biphenolate LNa 2[L = 2,2′-methylene bis(6-tert-butyl-4-methyl-phenoxo] in a 1:1 molar ratio in THF in the presence of HMPA (HMPA = hexamethylphosphoric triamide), then the product formed in situ was reduced by Na-K alloy to generate the divalent carbon-bridged biphenolate europium complex [LEu(HMPA) 2] 2(THF) 4(1) in a good isolated yield. Complex 1 was fully characterized by elemental analysis, NMR and IR spectra, and X-ray structural determination. The crystal data of complex 1 are monoclinic, P2 1/ c space group, a = 1.6521(3) nm, b = 2.8274(3) nm, c = 1.2074(2) nm, β = 111.723(6)°, V = 5.2393(14) nm 3, Z = 2, D c = 1.259 mg·m −3, μ = 1.304 mm −1, F(000) = 2092, R = 0.0815, wR = 0.1723. Complex 1 is a dimer with two Eu - 0 bridges. The coordination geometry of each europium atom can be best described as a distorted trigonal bipyramid.

Proton-assisted dissociation of a triple-stranded dinuclear europium helicate

A fruitful combination of absorption and gated luminescence spectrophotometry allowed us to gain insight into the proton-assisted dissociation of a triple-stranded dinuclear europium helicate in water. This process involves a key dimetallic double-stranded complex Eu2L2 as already observed in the self-assembly process of the triple helicate. The slow unravelling of the first strand, which is triggered by the protonation of its two carboxylate groups, dominates the whole disentangling mechanism of the supramolecular edifice. The solvolytic dissociation in water is rather slow (kD = 4(1) × 10−4 s−1) and is catalysed by H+ ions (k = 0.12(3) M−1 s−1). These lanthanide helicates, which are characterised by high kinetic inertness over a wide range of pH and high thermodynamic stability in water, are promising building blocks for the development of novel fluorescent biomarkers.

Crystal Structure and Triboluminescence Spectrum of A μ2-(ONC5H5) Bridging Dinuclear Europium(III) Complex

The crystal structure and triboluminescence spectrum of a μ2-(ONC5H5) bridging dinuclear europium(III) complex, Eu2(TTA)6(PyO)2 where HTTA=2-thenoyltrifluoroacetone, PyO=pyridine N-oxide, are reported. It is centrosymmetric and two Eu(III) atoms are bridged by two pyridine oxide oxygen atoms. The Eu……Eu distance is 4.2137(9) Å. The triboluminescence maximum is similar to that of the photoluminescence and the disorder of the thienyl rings and CF3 groups may be responsible for its triboluminescent activity. The complex crystallizes in the triclinic space group P&1macron; with cell parameters a = 12.239(1), b = 12.614(2), c = 14.048(2) Å, α = 110.31(1), β = 112.05(1), γ = 99.23(1)°, V = 1776.6(4) Å 3 and Z = 2. The strcutre was refined by full-matrix least squares methods to R = 0.0451 and R w = 0.01170.

Mono(di)nuclear Europium(III) Complexes of Macrobi(tri)cyclic Cryptands Derived from Diazatetralactams as Luminophores in Aqueous Solution

To increase the excellent light-emitting properties of the Eu3+ ion, macrobicyclic and macrotricyclic ligands 7 – 10, incorporating a 18-membered tetralactam ring (acting as a lanthanide binding site) and a sensitizer group (2,2′-bipyridine or 2,2′-bipyridine 1,1′-dioxide moiety), were synthesized. The mononuclear and dinuclear europium cryptates derived from these ligands were isolated and characterized. Their luminescent properties and those of the corresponding cryptates containing a phenanthroline group (see 11 and 12) were examined in H2O and D2O solutions at 77 and 300 K. It results that the tetralactam moiety plays a major role in the efficient shielding of the complexed Eu3+ ion from the water environment. The cryptands incorporating the bipyridine unit are the most promising labels according to their photophysical properties (excitation maxima, emission decay lifetime, relative luminescent yield). In contrast with literature data, introduction of N-oxide groups in the bipyridine chromophore weakens the luminescence properties of the cryptate.

Macrobicyclic and macrotricyclic tetralactams with 1,10-phenanthroline units. Dinuclear Eu 3+ cryptate of the macrotricyclic ligand

The synthesis of a key 18-membered diazatetralactam and of subsequent macrobicycle and macrotricycle with 1,10-phenanthroline units is described. The predominant macrotricyclic cryptand gives a dinuclear europium cryptate characterized by MS techniques and luminescence emission.