Mononuclear Eu Research Articles

Spectral Hole-Burning Studies of a Mononuclear Eu(III) Complex Reveal Narrow Optical Linewidths of the 5D0→7F0 Transition and Seconds Long Nuclear Spin Lifetimes.

Coordination complexes of rare-earth ions (REI) show optical transitions with narrow linewidths enabling the creation of coherent light-matter interfaces for quantum information processing (QIP) applications. Among the REI-based complexes, Eu(III) complexes showing the 5D0→7F0 transition are of interest for QIP applications due to the narrow linewidths associated with the transition. Herein, we report on the synthesis, structure, and optical properties of a novel Eu(III) complex and its Gd(III) analogue composed of 2,9-bis(pyrazol-1-yl)-1,10-phenanthroline (dpphen) and three nitrate (NO3) ligands. The Eu(III) complex-[Eu(dpphen)(NO3)3]-showed sensitized metal-centred emission (5D0→7FJ; J=0,1,2,3, 4, 5, or 6) in the visible region, upon irradiation of the ligand-centred band at 369 nm, with the 5D0→7F0 transition centred at 580.9 nm. Spectral hole-burning (SHB) studies of the complex with stoichiometric Eu(III) concentration revealed a narrow homogeneous linewidth (Γh) of 1.55 MHz corresponding to a 0.205 μs long optical coherence lifetime (T2opt). Remarkably, long nuclear spin lifetimes (T1spin) of up to 41 s have been observed for the complex. The narrow optical linewidths and long T1spin lifetimes obtained for the Eu(III) complex showcase the utility of Eu(III) complexes as tuneable, following molecular engineering principles, coherent light-matter interfaces for QIP applications.

Synthesis, Crystal Structure, and Optical Properties of Mononuclear Eu(III) and Tb(III) Complexes Containing a Chalcone Ligand

Chalcones are α,β-unsaturated ketones with great structural diversity and various applications. A chalcone produced by condensation of 2-acetylpyridine with 2-naphthaldehyde (L) was employed for synthesis of two mononuclear complexes: [Eu(L)(hfac)3(H2O)]·0.5CHCl3 and [Tb(L)(hfac)3], where hfac is the hexafluoroacetylacetonate anion. The chalcone and complexes were structurally characterized by single-crystal X-ray diffraction. The chalcone acts as a chelating bidentate ligand. Luminescent properties of the ligand L and the complexes were investigated in the solid state. For these heteroleptic mononuclear complexes, the emission of the Eu(III) and Tb(III) ions was influenced by the excitation wavelength.

Bright photo- and triboluminescence of centrosymmetric Eu(iii) and Tb(iii) complexes with phosphine oxides containing azaheterocycles

Novel mononuclear Eu(iii) and Tb(iii) complexes based on phosphine oxides bearing pyridine, pyrimidine or pyrazine moieties show bright photo- and triboluminescence under ambient conditions.

Steric and Electronic Control of Chiral Eu(III) Complexes for Effective Circularly Polarized Luminescence.

Circularly polarized luminescence (CPL) is characterized by the differential emission of right and left circularly polarized light by a chiral molecule. This mini-review describes the recent developments in chiral trivalent europium (Eu(III)) complexes with effective CPL. CPL has many potential applications in security tags, lasers, and three-dimensional organic electroluminescence devices, which is one of the most intensely investigated topics in molecular luminophores. Eu(III) complexes have attracted considerable attention as effective CPL luminophores for the above-mentioned applications. In this review, recent studies on the Eu(III) CPL, including the steric (dimer, tetramer, aggregates, and coordination polymers) and electronic control (mononuclear) of Eu(III) complexes for the construction of a luminophore with effective CPL, are discussed. The characteristic CPL applications employing the chiral mononuclear Eu(III) complexes are also described. Chiral Eu(III) complexes with well-designed organic ligands can result in the establishment of new research areas in the fields of photochemistry and materials science.

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.

Luminescence and anion recognition performance of mononuclear Eu(III) complexes with N- and O- donor pyridine derivatives

A series of Eu(III) complexes with pyridine-2-carboxamide (PCA), pyridine-2-carboxaldoxime (PCAO), pyridine-2,3-dicarboxylic anhydride (PDCA) or pyridine-2-methanol (PM) as primary ligands and 4,4′-dimethoxy-2,2′-bipyridine (DMBP) as ancillary ligand were synthesized. The interaction between the ligands and complexes were confirmed by FT-IR study. The complexes were abbreviated as [Eu(PCA)3DMBP].Cl3 (C1), [Eu(PCAO)3DMBP].Cl3 (C2), [Eu(PDCA)3DMBP].Cl3 (C3) and [Eu(PM)3DMBP].Cl3 (C4). Optical studies were done by UV–vis spectroscopy and PL spectroscopy. The highest intrinsic luminescent quantum yield (53.42%) and lifetime value (1456 μs) were found for C3. Lowest quantum yield was exhibited by C2. Anion sensing studies of all the complexes were done by UV–vis and PL spectroscopy and it was observed that complex C1 showed remarkable change in optical properties upon addition of F− and HSO4− ions. Thus C1 can be used as optical sensor for F− and HSO4− ions. The FQD for F− and HSO4− ions were found to be 6.55 and 3.58 respectively for C1.

Triazine based Mn (II) and Mn (II)/Ln (III) complexes: Synthesis, characterization and catecholase activities

In the current work, two triazine‐based multidentate ligands (H2L1 and H2L2) and their homo‐dinuclear Mn (II), mononuclear Ln (III) and hetero‐dinuclear Mn (II)/Ln (III) (Where Ln: Eu or La) complexes were synthesized and characterized by spectroscopic and analytical methods. Single crystals of a homo‐dinuclear Mn (II) complex {[Mn (HL1)(CH3OH)](ClO4·CH3OH}2 (1) were obtained and the molecular structure was determined by X‐ray diffraction method. In the structure of the complex, each Mn (II) ion is seven‐coordinate and one of the phenolic oxygen bridges two Mn (II) centre forming a dimeric structure. The UV–Vis. and photoluminescence properties of synthesized ligands and their metal complexes were investigated in DMF solution and the compounds showed emission bands in the UV–Vis. region. The catecholase enzyme‐like activity of the complexes were studied for 3,5‐DTBC → 3,5‐DTBQ conversion in the presence of air oxygen. Homo‐dinuclear Mn (II) complexes (1 and 4) were found to efficiently catalyse 3,5‐DTBC → 3,5‐DTBQ conversion with the turnover numbers of 37.25 and 35.78 h−1 (kcat), respectively. Mononuclear Eu (III) and La (III) complexes did not show catecholase activity.

Photosensitized Luminescence of Highly Thermostable Mononuclear Eu(III) Complexes with π-Expanded β-Diketonate Ligands

Abstract Thermostable mononuclear Eu(III) complexes with a π-expanded system, [Eu(btfa)3(DPEPO)] and [Eu(ntfa)3(DPEPO)] (DPEPO: bis[2-(diphenylphosphino)phenyl] ether oxide, btfa: benzoyltrifluoroacetonate, ntfa: 3-(2-naphthoyl)-1,1,1-trifluoroacetonate), are reported. Decomposition temperature (dp) of [Eu(btfa)3(DPEPO)] and that of [Eu(ntfa)3(DPEPO)] are estimated to be 320 °C and 318 °C, respectively. These values are higher than that of the previous [Eu(hfa)3(DPEPO)] (hfa: hexafluoroacetylacetonate, dp = 228 °C). The photosensitized emission quantum yield Φπ–π* and photosensitized energy transfer efficiency ηsens of [Eu(ntfa)3(DPEPO)] (Φπ–π* = 45%, ηsens = 77%) are larger than those of [Eu(btfa)3(DPEPO)] (Φπ–π* = 38%, ηsens = 55%). The thermostable Eu(III) complex with a π-expanded system is expected to be useful for fabrication of LED devices.

Luminescent mononuclear Eu(III) and Tb(III) complexes with bipyridyl-tetrazolate tridentate ligands

A new series of four luminescent mononuclear Eu(III) and Tb(III) complexes with bipyridyl tetrazolate tridentate chelates, [Ln(tbpy)2(DMF)(H2O)2](NO3) and [Ln(tmbpy)2(DMF)(NO3)] (Ln=Eu(III) and Tb(III), DMF=N,N-dimethylformamide, tbpy and tmbpy denote the deprotonated 6-(1H-tetrazole-5-yl)-2,2′-bipyridine and 6-(1H-tetrazole-5-yl)-4,4′-dimethyl-2,2′-bipyridine, respectively), have been synthesized and characterized. Each Ln(III) ion displays a distorted tricapped trigonal prism with two mono-anionic tridentate chelating ligands, originating from the N–H deprotonation of the tetrazolyl ring, and the introduction of two methyl groups into the 2,2′-bipyridyl ring has a significant impact on the coordination environment of the Ln(III) core, exhibiting that two coordinated water molecules are displaced by one chelating nitrate anion. Two types of Ln(III) complexes are all emissive in solution and solid states at room temperature. It is shown that the introduction of two electron-donating methyl groups into the 2,2′-bipyridyl ring has a major effect on the photoluminescence of Ln(III) complexes, and it is favorable for improving the luminescence efficiencies of Ln(III) species.

Eu3+, Yb3+ and Eu3+-Yb3+ complexes with salicylic acid and 1,10-phenanthroline: synthesis, photoluminescent properties and energy transfer.

This paper reports the synthesis of mononuclear Eu(3+), Yb(3+) and binuclear Eu(3+)-Yb(3+) complexes by solution technique, maintaining the stoichiometric ratios of salicylic acid (sal) and 1,10-phenanthroline (phen) as ligands and their structural, optical and morphological properties were demonstrated. The FTIR absorption spectra indicates that sal and phen are coordinated to the rare earth ion through the chemical bonds formed between oxygen and nitrogen atoms of the ligands and rare earth ion. The UV-vis absorption spectra of the complexes reflect the absorption spectra of the ligands and there is no significant change in the wavelength and band profiles between the spectra of the ligands and that of complexes except a slight red shift. The photoluminescent emission spectra of the complexes in visible and near-infrared (NIR) region was recorded and indicated the emission quenching in complex (2) due to the energy transfer from Eu(3+) ion to Yb(3+) ion. The morphological properties of the complexes as characterized by SEM revealed different morphologies of mononuclear and binuclear complexes.

Lanthanide(III) complexes of N4O4 Schiff base macrocycle: Luminescence and formation of heterodinuclear d–f complexes

The new macrocyclic Schiff base lanthanide(III) complexes of the formula [Ln(H4L)Cl3]·nH2O (Ln=Pr(III), Nd(III), Sm(III), Gd(III), Dy(III), Ho(III), Er(III), Tm(III), Yb(III) and Lu(III)) have been synthesized in the template condensation of 1,3-diamino-2-hydroxypropane and 2,6-diformyl-4-methylphenol in the presence of the appropriate Ln(III) chlorides. The obtained compounds have been characterized in solution by NMR spectroscopy, and the 1H and 13C NMR spectra of [Pr(H4L)Cl3]·H2O, [Nd(H4L)Cl3]·H2O, [Sm(H4L)Cl3]·H2O and [Yb(H4L)Cl3]·4H2O complexes have been assigned on the basis of COSY, NOESY and HMQC techniques. The analysis of isotropic shifts of the paramagnetic Ln(III) derivatives indicate the unsymmetrical coordination of the lanthanide(III) ions within the macrocyclic ligand H4L. 1H NMR spectroscopy has also been used to follow transformation of the [Ln(H4L)]3+ complexes into heterodinuclear derivatives, [LnCo(H2L)]3+ and [LnCo(HL)]2+. Emission and excitation spectra as well as luminescence decay time measurements (at 293 and 77K) were used to characterize the photophysical properties of the mononuclear Eu(III), Gd(III) and Yb(III) [Ln(H4L)Cl3]·nH2O complexes in solid-state. Energy transfer from the ligand to the Yb(III) ions has been proved at both room temperature and 77K. The f–f luminescence of Nd(III) and Er(III) was not observed neither by the excitation through the ligand (1π–1π∗) nor the lanthanide ion absorption transitions both at 293 and 77K. In the case of Eu(III) complex the energy transfer only occurs at 77K, while at room temperature a thermally activated back energy transfer process from 5D0 Eu(III) excited state to the ligand triplet states has been proposed. The 4f–4f emission spectrum of Eu(III) in a low site symmetry with the dominating 5D0→7F4 transition has been demonstrated for the first time.

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.

Photosensitized luminescence of thermostable polynuclear Eu(III) complexes

Tetranuclear europium(III) complexes, [Eu 4(μ-O)(L 1) 10] (L 1=2-hydroxy-4-octyloxybenzophenone, 1) and [Eu 4(μ-O)(L 2) 10] (L 2=2-hydroxy-4-dodecyloxybenzophenone, 2) were synthesized by the reaction of lanthanide nitrates with L 1 or L 2 in the presence of triethylamine in methanol. The photosensitized emission bands of the both Eu(III) complexes in THF- d 8 were observed around 579, 590, 615, 653, and 699 nm by the excitation of the ligands at 380 nm, whereas the emission from the mononuclear complex 3 containing ethanol molecules was almost quenched. The emission efficiencies were determined to be 3.1 ± 0.1 % for 1 and 3.9 ± 0.1 % for 2, respectively. The differential scanning calorimetry (DSC) measurements demonstrated that the decomposition points of 1 and 2 were 309 °C and 320 °C, respectively, indicating high thermostability of these complexes compared to the mononuclear Eu(III) complex 3 (250 °C). New strategy for designing stable rare earth compounds giving strong emission would be emphasized by introducing polynuclear complexes. Polynuclear complexes should open a wide range of molecular design for photosensitized luminescence and thermal stability.

Synthesis, Characterization, and Fluorescent Properties of Ln(III), Ln(III)–Zn(II) (Ln = Gd, Eu), and Eu(III)–Cu(II) Cryptates

The mononuclear cryptates [Ln(H3LF)(NO3)(H2O)](NO3)2 (Ln = Gd(III), Eu(III)) and the heterodinuclear cryptates [LnMLF(DMF)](ClO4)2 (Ln = Gd(III), Eu(III), M = Zn(II); Ln = Eu(III), M = Cu(II)) were synthesized and characterized. The triplet‐state energies of the cryptand (H3LF) were studied by its phosphorescence spectrum. The introduction of the Zn(II) ion into the mononuclear Eu(III) cryptate resulted in a blue‐shift of three ligand‐centered bands, the increase of its molar absorption coefficient and the increase of the luminescence intensity of Eu(III) in MeCN solution. However, the emission of the Eu(III) ion was quenched completely in the Eu–Cu cryptate.

Heterodinuclear cryptates [EuML(dmf)](ClO(4))(2)(M=Ca, Cd, Ni, Zn): tuning the luminescence of europium(III) through the selection of the second metal ion.

Four heterodinuclear cryptates [EuML(dmf)](ClO(4))(2) (M=Ca, Cd, Ni, Zn) were synthesized by a two-step method (L denotes deprotonated anionic cryptand synthesized by condensation of tris(2-aminoethyl)amine with 2,6-diformyl-4-chlorophenol). The ES-MS spectra of the four cryptates and the crystal structure of [EuNiL(dmf)](ClO(4))(2) x MeCN confirm that a strict dinuclear Eu(III)-M(II) entity exits in the cryptates. The cyclic voltammetry and luminescence spectral investigations indicate that the introduction of second metal ions into the mononuclear Eu(III) cryptate result in a negative shift of the redox potential of Eu(III) and a change in luminescence intensity of Eu(III). The cryptate [EuML(dmf)](ClO(4))(2) was shown to quench the emission of Eu(III) when M=Ni and to enhance the emission of Eu(III) when M=Ca, Cd, and Zn in the sequence: mononuclear<Eu-Ca<Eu-Cd<Eu-Zn.

NICKEL(II)-LANTHANIDE(III) COMPLEXES OF THE DINUCLEATING LIGANDN,N′-BIS(3-HYDROXYSALICYLIDENE)ETHYLENEDIAMINE

Abstract Heteronuclear nickel(II)-lanthanide(III) complexes, NiLn(dhbaen)(NO3)(H2O)2 (Ln = La, Eu or Gd), and a mononuclear Eu(III) complex, Eu(Hdhbaen)(H2O)3, were synthesized, where H4dhbaen denotes N,N′-bis(3-hydroxysalicylidene) ethylenediamine. IR spectra shows that Ni(II) and Ln(III) ions are located at the endogenous N2O2- and exogenous O4-coordination sites of ligand, respectively. Based on CD spectra, it was concluded that amino alcohols are specifically bound at the Ni(II)-Ln(III) heterometal centre, through the nitrogen to the Ni-site and through the oxygen to the Ln-site. The fluorescence intensity of the mononuclear Eu(III) complex is much greater than that of the heteronuclear Ni(II)-Eu(III) complex.

V(IV)OLn(III) complexes (Ln  La, Eu or Gd) of the compartmental ligand N,N′-bis(3-hydroxysalicylidene)ethylenediamine

Mononuclear oxovanadium(IV) complex VO(H2dhbaen) and heteronuclear oxovanadium(IV)-lanthanide(III) complexes VOLn(dhbaen)(NO3)(H2O)2.5 were synthesized, where H4dhbaen denotes N,N′-bis(3-hydroxysalicylidene)ethylenediamine. IR spectra showed that V(IV)O and Ln(III) ions are located at the endogenous N2O2- and the exogeneous O4-coordination sites of the ligand respectively. Based on circular dichroism (CD) spectra, it was suggested that amino alcohols are specifically bound at the VO-Ln heterometal center, through the nitrogen to the VO-site and through the oxygen to the Ln-site. Magnetic susceptibility measurements in the range 4.2 to 260 K revealed that the magnetic interaction between V(IV)O and Gd(III) ions is almost negligible. The fluorescence intensity of mononuclear Eu(III) complex markedly decreased on forming the heteronuclear V(IV)OEu(III) complex.

Synthesis, Characterization, and Properties of VIVO–Ln(III) (Ln = La, Pr, Eu, Gd, Tb) Complexes of N,N′-Bis(3-carboxysalicylidene)ethylenediamine

Abstract Mononuclear oxovanadium(IV) and europium(III) complexes, [VO(H2fsaen)]·2H2O and [Eu(H2fsaen)(NO3)(H2On]·(5−n)H2O, and dinuclear oxovanadium(IV)–rare earth(III) complexes, [VOLn(fsaen)(NO3)(H2O)n]·(m−n)H2O (Ln = La, Pr, Eu, Gd, Tb), of N,N′-bis(3-carboxysalicylidene)ethylenediamine (H4fsaen) have been synthesized. Oxovanadium(IV) ion and europium(III) ion in the respective mononuclear complexes is bound at the O4-site of ligand, whereas in the VIVO–Ln(III) complexes VIVO ion is bound at the N2O2-site and Ln(III) ion at the O4-site. Based on the absorption and CD spectra, it is suggested that amino alcohols are specifically bound at the VIVO–Ln(III) heterometal center, through the nitrogen to the VIVO and through the oxygen to the Ln(III). The fluorescent spectral measurements reveal that the fluorescent bands of Eu(III) for the mononuclear Eu(III) complex are significantly quenched in the dinuclear VIVO–Eu(III) complex.