Group I cation templated formation of luminescent mono- and bis-substituted thionaphthol heterobimetallic complexes of Pr, Nd, Eu and Tb

Metathesis of lanthanide tris di-tert-butyl beta-diketonates ([Ln(thd)3] Ln=Pr, Nd, Eu, Tb) with one or two equivalents of group 1 salts of the sulfur bridged binaphtholate dianion [1,1'-S(2-OC10H4But(2)-3,6)2]2-, [M2L], M=K, Li affords luminescent mono- and bis-ligand substituted complexes ML[LnL(thd)2].L; M=K, Ln=Pr , Nd , Eu and Tb (L=thf, diethyl ether or toluene) and M(thf)2[LnL2(thd)]; M=Li, Ln=Pr , Nd , Eu , Tb . The potassium salt [K2L] affords mono-L substituted complexes most cleanly, while the lithium salt [Li2L] yields the bis-L substituted complexes most cleanly. The L ligands function as antenna for the sensitised lanthanide-centred emission in Eu3+ and Tb3+ complexes. The X-ray single-crystal structures of mono- and bis-L lanthanide complexes of Nd3+ are presented.     

Visible and near-infrared intense luminescence from water-soluble lanthanide [Tb(III), Eu(III), Sm(III), Dy(III), Pr(III), Ho(III), Yb(III), Nd(III), Er(III)] complexes

The synthesis of a new ligand (1) containing a single phenanthroline (phen) chromophore and a flexibly connected diethylenetriamine tetracarboxylic acid unit (DTTA) as a lanthanide (Ln) coordination site is reported [1 is 4-[(9-methyl-1,10-phenantrol-2-yl)methyl]-1,4,7-triazaheptane-1,1,7,7-tetraacetic acid]. From 1, an extended series of water-soluble Ln.1 complexes was obtained, where Ln is Eu(III), Tb(III), Gd(III), Sm(III), Dy(III), Pr(III), Ho(III), Yb(III), Nd(III), and Er(III). The stoichiometry for the association was found 1:1, with an association constant K(A) > or = 10(7) s(-1) as determined by employing luminescence spectroscopy. The luminescence and photophysical properties of the series of lanthanide complexes were investigated in both H2O and D2O solutions. High efficiencies for the sensitized emission, phi(se), in air-equilibrated water were observed for the Ln.1 complexes of Eu(III) and Tb(III) in the visible region (phi(se) = 0.24 and 0.15, respectively) and of Sm(III), Dy(III), Pr(III), Ho(III), Yb(III), Nd(III), and Er(III) in the vis and/or near-infrared region [phi(se) = 2.5 x 10(-3), 5 x 10(-4), 3 x 10(-5), 2 x 10(-5), 2 x 10(-4), 4 x 10(-5), and (in D2O) 4 x 10(-5), respectively]. For Eu.1 and Tb.1, luminescence data for water and deuterated water allowed us to estimate that no solvent molecules (q) are bound to the ion centers (q = 0). Luminescence quenching by oxygen was investigated in selected cases.     

Preparation, Characterization and Properties of Two New Lanthanide(III)-5-(2-pyridyl)tetrazolate Complexes

Two new mononuclear lanthanide(III) complexes Ln(pytz)3(H2O)3·(H2O)3.5[Ln=Tb(1); Eu(2); Hpytz= 5-(2-pyridyl)tetrazole] were synthesized by reacting Hpytz with the corresponding lanthanide(III) ions and characterized. The single crystal X-ray diffraction analysis reveals that complexes 1 and 2 are isostructural and the lanthanide(III) ions in both complexes 1 and 2 are nine-coordinated, with three oxygen atoms of three coordination water molecules and six nitrogen atoms of three pytz ligands, forming a monocapped square antiprism. Extensive hydrogen bonds exist, resulting in a three-dimensional supramolecular network structure by hydrogen-bonds in both complexes 1 and 2, respectively. Complex 1 exhibits typical green fluorescence of Tb(III) ion and complex 2 red fluorescence of Eu(III) ion, in solid state at room temperature.     

Synthesis and luminescence properties of lanthanide complexes with a new aryl amide bifunctional bridging ligand

A new aryl amide type bifunctional bridging ligand 4,4'-bis{[(2'-benzylaminoformyl)phenoxyl]methyl}-1,1'-biphenyl (L) and its complexes with lanthanide ions (Ln=Pr, Eu, Gd, Tb, Ho, Er) were synthesized and characterized by elemental analysis, infrared spectra, conductivity measurements and thermal analysis. At the same time, the luminescence properties of the Eu and Tb complexes in acetone solutions were investigated. Under the excitation of UV light, these two complexes exhibited characteristic emission of europium and terbium ions. And the lowest triplet state energy level T1 of this ligand matches better to the lowest resonance energy level of Tb(III) than to Eu(III) ion.     

Synthesis of Eu(III) and Tb(III) complexes with novel pyridine dicarboxamide derivatives and their luminescence properties

A novel ligand, N2,N6-bis[2-(3-methylpyridyl)]pyridine-2,6-dicarboxamide (L2) and the corresponding Eu(III) and Tb(III) hydrochlorate complexes have been synthesized and characterized in detail based on elemental analysis, IR and NMR. The crystal and molecular structure of the complexes was determined by X-ray crystallography. The Eu(III) and Tb(III) ions were found to coordinate to the amido nitrogen atoms and pyridine nitrogen atoms. The luminescence properties of lanthanide complexes in solid state, in different solutions and in different pH value were investigated. The result shows that Tb(III) complexes exhibit more efficient luminescence than Eu(III) complexes, and the ligand (L2) is an excellent sensitizer to Tb(III) ion.     

Definition of an intramolecular Eu-to-Eu energy transfer within a discrete [Eu2L] complex in solution

Ligand L, based on two do3a moieties linked by the methylene groups of 6,6'-dimethyl-2,2'-bipyridine, was synthesized and characterized. The addition of Ln salts to an aqueous solution of L (0.01?M Tris-HCl, pH?7.4) led to the successive formation of [LnL] and [Ln(2)L] complexes, as evidenced by UV/Vis and fluorescence titration experiments. Homodinuclear [Ln(2)L] complexes (Ln = Eu, Gd, Tb, Yb, and Lu) were prepared and characterized. The (1)H and (13)C?NMR spectra of the Lu and Yb complexes in D(2)O solution (pD = 7.0) showed C(1) symmetry of these species in solution, pointing to two different chemical environments for the two lanthanide cations. The analysis of the chemical shifts of the Yb complex indicated that the two coordination sites present square antiprismatic (SAP) coordination environments around the metal ions. The spectroscopic properties of the [Tb(2)L] complex upon ligand excitation revealed conventional behavior with τ(H2O) = 2.05(1)?ms and ?(H2O) = 51%, except for the calculation of the hydration number obtained from the luminescent lifetimes in H(2)O and D(2)O, which pointed to a non-integer value of 0.6 water molecules per Tb(III) ion. In contrast, the Eu complex revealed surprising features such as: 1)?the presence of two and up to five components in the (5)D(0)→(7)F(0) and (5)D(0)→(7)F(1) emission bands, respectively; 2)?marked differences between the normalized spectra obtained in H(2)O and D(2)O solutions; and 3)?unconventional temporal evolution of the luminescence intensity at certain wavelengths, the intensity profile first displaying a rising step before the occurrence of the expected decay. Additional spectroscopic experiments performed on [Gd(2-x)Eu(x)L] complexes (x = 0.1 and 1.9) confirmed the presence of two distinct Eu sites with hydration numbers of 0 (site I) and 2 (site II), and showed that the unconventional temporal evolution of the emission intensity is the result of an unprecedented intramolecular Eu-to-Eu energy-transfer process. A mathematical model was developed to interpret the experimental data, leading to energy-transfer rates of 0.98?ms(-1) for the transfer from the site with q=0 to that with q=2 and vice versa. Hartree-Fock (HF) and density functional theory (DFT) calculations performed at the B3LYP level were used to investigate the conformation of the complex in solution, and to estimate the intermetallic distance, which provided F?rster radii (R(0)) values of 8.1?? for the energy transfer from site I to site II, and 6.8?? for the reverse energy transfer. These results represent the first evidence of an intramolecular energy-transfer equilibrium between two identical lanthanide cations within a discrete molecular complex in solution.     

Structural and photophysical properties of visible- and near-IR-emitting tris lanthanide(III) complexes formed with the enantiomers of N,N'-bis(1-phenylethyl)-2,6-pyridinedicarboxamide

The enantiomers of N,N'-bis(1-phenylethyl)-2,6-pyridinedicarboxamide (L), namely, (R,R)-1, and (S,S)-1, react with Ln(III) ions to give stable [LnL(3)](3+) complexes in an anhydrous acetonitrile solution and in the solid state, as evidenced by electrospray ionization mass spectrometry, NMR, luminescence titrations, and their X-ray crystal structures, respectively. All [LnL(3)](3+) complexes [Ln(III) = Eu, Gd, Tb, and Yb; L = (R,R)-1 and (S,S)-1] are isostructural and crystallize in the cubic space group I23. Although the small quantum yields of the Ln(III)-centered luminescence clearly point to the poor efficiency of the luminescence sensitization by the ligand and the intersystem crossing and ligand-to-metal energy transfers, the ligand triplet-excited-state energy seems relatively well suited to sensitize many Ln(III) ion's emission for instance, in the visible (Eu and Tb), near-IR (Nd and Yb), or both regions (Pr, Sm, Dy, Er, and Tm).     

Fully fluorinated imidodiphosphinate shells for visible- and NIR-emitting lanthanides: hitherto unexpected effects of sensitizer fluorination on lanthanide emission properties

In this paper we demonstrate that the effect of aromatic C--F substitution in ligands does not always abide by conventional wisdom for ligand design to enhance sensitisation for visible lanthanide emission, in contrast with NIR emission for which the same effect coupled with shell formation leads to unprecedented long luminescence lifetimes. We have chosen an imidodiphosphinate ligand, N-{P,P-di(pentafluorophinoyl)}-P,P-dipentafluorophenylphosphinimidic acid (HF20tpip), to form ideal fluorinated shells about all visible- and NIR-emitting lanthanides. The shell, formed by three ligands, comprises twelve fully fluorinated aryl sensitiser groups, yet no-high energy X--H vibrations that quench lanthanide emission. The synthesis, full characterisation including X-ray and NMR analysis as well as the photophysical properties of the emissive complexes [Ln(F20tpip)3], in which Ln=Nd, Sm, Eu, Gd, Tb, Dy, Er, Yb, Y, Gd, are reported. The photophysical results contrast previous studies, in which fluorination of alkyl chains tends to lead to more emissive lanthanide complexes for both visible and NIR emission. Analysis of the fluorescence properties of the HF20tpip and [Gd(F20tpip)3] reveals that there is a low-lying state at around 715 nm that is responsible for partially quenching of the signal of the visible emitting lanthanides and we attribute it to a pi-sigma* state. However, all visible emitting lanthanides have long lifetimes and unexpectedly the [Dy(F20tpip)3] complex shows a lifetime of 0.3 ms, indicating that the elimination of high-energy vibrations from the ligand framework is particularly favourable for Dy. The NIR emitting lanthanides show strong emission signals in powder and solution with unprecedented lifetimes. The luminescence lifetimes of [Nd(F20tpip)3], [Er(F20tpip)3] and [Yb(F20tpip)3] in deuteurated acetonitrile are 44, 741 and 1111 micros. The highest value observed for the [Yb(F20tpip)3] complex is more than half the value of the Yb ion radiative lifetime.     

1,5-双(1'-苯基-3'-甲基-5'-吡唑啉酮-4')-戊二酮-[1,5]和十六烷基吡啶盐的稀土配合物的合成及表征

合成了13种1,5-双(1′-苯基-3′-甲基-5′-吡唑啉酮-4′)-戊二酮-[1,5](BPMPPD)和溴化十六烷基吡啶盐(CPB)的稀土配合物.研究了配合物的红外光谱、紫外可见光谱、差热-热重谱、荧光光谱、核磁共振谱及摩尔电导等性质,发现配合物属离子型缔合物CP⁺[Ln(BPMPPD)₂]^-.Pr、Nd、Ho、Er、Tm配合物发生超灵敏跃迁.配合物的热分解温度具有"四分组"效应,Sm、Eu、Tb、Oy为线性荧光。     

Synthesis,Structures, and Luminescent Properties of Chloride and Nitrate LnIII Complexes Coordinated by tris(Pyrazolyl)methane

We report the synthesis of Ln³⁺ nitrate [Ln(Tpm)(NO₃)₃] ⋅ MeCN (Ln=Yb ( 1Yb ), Eu ( 1Eu )) and chloride [Yb(Tpm)Cl₃] ⋅ 2MeCN ( 2Yb ), [Eu(Tpm)Cl₂(μ-Cl)]₂ ( 2Eu ) complexes coordinated by neutral tripodal tris(3,5-dimethylpyrazolyl)methane (Tpm). The crystal structures of 1Ln and 2Ln were established by single crystal X-ray diffraction, while for 1Yb high resolution experiment was performed. Nitrate complexes 1Ln are isomorphous and both adopt mononuclear structure. Chloride 2Yb is monomeric, while Eu³⁺ analogue 2Eu adopts a binuclear structure due to two μ²-bridging chloride ligands. The typical lanthanide luminescence was observed for europium complexes ( 1Eu and 2Eu ) as well as for terbium and dysprosium analogues ([Ln(Tpm)(NO₃)₃] ⋅ MeCN, Ln=Tb ( 1Tb ), Dy ( 1Dy ); [Ln(Tpm)Cl₃] ⋅ 2MeCN, Ln=Tb ( 2Tb ), Dy ( 2Dy )).     

Synthesis, characterization and luminescence property of N,N'-di(pyridine N-oxide-2-yl)pyridine-2,6-dicarboxamide and corresponding lanthanide (III) complexes

A new ligand, N,N'-di(pyridine N-oxide-2-yl)pyridine-2,6-dicarboxamide (LH2) and its several lanthanide (III) complexes (La, Eu, Gd, Tb, Y) were synthesized and characterized in detail based on elemental analysis, conductivity measurements, IR, 1H NMR, MS (FAB) and UV spectra and TG-DTA studies. The results indicated that the composition of these binary complexes is [Ln(LH2)(NO3)2.H2O]NO3.nH2O (n=0-1); while the ligand has a good planar structure with strong hydrogen bonds. The fluorescence spectra exhibits that the Tb (III) complex and the Eu (III) complex display characteristic metal-centered fluorescence in solid state while ligand fluorescence is completely quenched. However, the Tb (III) complex displays more effective luminescence than the Eu (III) complex, which is attributed to especial effectivity in transferring energy from the lowest triplet energy level of the ligands (T) onto the excited state (5D4) of Tb (III) than that (5D1) of Eu (III).     

Synthesis and infrared and fluorescence spectra of rare earth complexes with a novel amide-based ligand

A novel amide-based open-chain crown ether, N,N'-1,3-propanediyl-bis[2-(benzyl -carbamoyl-methoxy)-benzamide] (L) and its solid complexes with rare earth nitrates and picrates have been prepared. The complexes were characterized by elemental analyses, molar conductivity and IR spectra. The fluorescence properties of the Eu(III) and Tb(III) complexes in solid and in organic solvents were studied. Under the excitation of ultraviolet light, these complexes exhibit characteristic emission of europium and terbium ions. The results show that the ligand favor energy transfers to the emitting energy level of Tb(III). Some factors that influence the fluorescent intensity were also discussed.     

Syntheses, structures, and luminescent and magnetic properties of novel three-dimensional lanthanide complexes with 1,3,5-benzenetriacetate

Five novel lanthanide complexes with the formulas [Nd(bta)(H2O)2.4.35H2O]n(1), [Sm(bta)(H2O)2.4.5H2O]n (2), [Eu(bta)(H2O).1.48H2O]n (3), [Tb(bta)(H2O).1.31H2O]n (4), and [Yb(bta)(H2O).H2O]n (5) (H3bta = 1,3,5-benzenetriacetic acid) have been prepared by using the corresponding lanthanide salt and H3bta. The results of an X-ray crystallographic analysis revealed that all the complexes have three-dimensional channel-like structures, in which the bta3- ligands adopt different coordination modes: monodentate and mu2-eta2:eta1-bridging coordination modes in 1, 2, and 5 and mu2-eta1:eta1-bridging and mu2-eta2:eta1-bridging coordination modes in 3 and 4, respectively. Complexes 1 and 2, as well as 3 and 4, are isostructural, respectively, in which all the Ln(III) (Ln = Nd, Sm, Eu, and Tb) atoms are nine-coordinated, while the Yb(III) atoms in complex 5 are eight-coordinated. Both complexes 3 and 4 showed strong luminescence upon excitation, and their luminescence decay curves fit well with single exponential decays of which the lifetime is 0.45 ms for 3 and 1.0 ms for 4. The magnetic properties of the complexes were investigated in the temperature range of 1.8-300 K.     

Synthesis, structure and spectroscopic properties of rare earth complexes with a new aryl amide 2,2'-bipyridine derivative

Solid complexes of rare earth nitrates and picrates with a new aryl amide ligand 3.3'-bis(benzylamido)-2,2'-bipyridine (L) were synthesized and characterized by elemental analysis, IR and molar conductivity measurements. The molecular structures of the complex [TbL(2)(NO(3))(3)H(2)O].2H(2)O have been determined by single-crystal X-ray diffraction. The fluorescent properties of the Eu(III) and Tb(III) nitrates and picrates complexes in solid state were also investigated in detail. Under the excitation, these complexes exhibited characteristic emissions of europium and terbium ions. It is worth noting that the nature of the anion has a great effect upon the composition of the complexes as well as emission properties of them.     

A water-soluble Pybox derivative and its highly luminescent lanthanide ion complexes

A new water-soluble Pybox ligand, 1, has been synthesized and found to crystallize in the monoclinic P2(1)/n space group with unit cell parameters a = 6.0936(1) ?, b = 20.5265(4) ?, c = 12.0548(2) ?, and β = 90.614(1)°. In the crystal, a water molecule is bound through hydrogen-bonding interactions to the nitrogen atoms of the oxazoline rings. This ligand was used to complex a variety of lanthanide ions, opening up new avenues for luminescence and catalysis in aqueous environment. These complexes are highly luminescent in aqueous solutions, in acetonitrile, and in the solid state. Aqueous quantum yields are high at 30.4% for Eu(III), 26.4% for Tb(III), 0.32% for Yb(III), and 0.11% for Nd(III). Er(III) did not luminesce in water, but an emission efficiency of 0.20% could be measured in D(2)O. Aqueous emission lifetimes were also determined for the visible emitting lanthanide ions and are 1.61 ms for Eu(III) and 1.78 ms for Tb(III). Comparing emission lifetimes in deuterated and nondeuterated water indicates that no water molecules are coordinated to the metal ion. Speciation studies show that three species form successively in solution and the log β values are 5.3, 9.6, and 13.8 for Eu(III) and 5.3, 9.2, and 12.7 for Tb(III) for 1:1, 2:1, and 3:1 ligand to metal ratios, respectively.     

The Formation of Luminescent Supramolecular Ternary Complexes in Water: Delayed Luminescence Sensing of Aromatic Carboxylates Using Coordinated Unsaturated Cationic Heptadentate Lanthanide Ion Complexes

The synthesis of four lanthanide ion complexes Eu?1, Eu?2, Tb?1 and Tb?2, from the heptadentate tri-arm cyclen (1,4,7,10-tetraazacyclododecane) ligands 1 and 2 that were made in one-pot syntheses is described. These coordinatively unsaturated complexes have two labile metal-bound water molecules, as demonstrated by X-ray crystallography. This was also confirmed by evaluating their hydration state (q～2) by measuring their lifetimes in D²O and H²O, respectively. The above complexes were all designed as being “photophysically silent” prior to the recognition of the anion, since they do not possess antenna that can participate in sensitisation of the Eu(III) or the Tb(III) excited state. However, the two water molecules can be displaced upon anion binding by the appropriate aromatic carboxylates to give ternary complexes in water, through either four- or six-member ring chelates (q～0), or possibly via a monodentate binding. In the case of Tb?1 and Tb?2, large luminescence enhancements were observed upon the formation of such ternary complexes with N,N-dimethylaminobenzoic acid at ambient pH. Such binding and luminescent enhancements were also observed for Tb?1 in the presence of salicylic acid. On all occasions, the anion recognition “switched” the emission “on” over two logarithmic units. At higher concentrations, the emission is reduced possibly due to quenching. In the case of aspirin, the binding was too weak to be measured, indicating that Tb?1 selectively detects salicylic acid, the active form of aspirin in water. In the case of Eu?1 and Eu?2, the affinity of these complexes towards such aromatic carboxylates was too weak for efficient ternary complex formation.     

Structural and near-IR photophysical studies on ternary lanthanide complexes containing poly(pyrazolyl)borate and 1,3-diketonate ligands

The ligands tris[3-(2-pyridyl)pyrazol-1-yl]hydroborate (L1, potentially hexadentate) and bis[3-(2-pyridyl)pyrazol-1-yl]dihydroborate (L2, potentially tetradentate) have been used to prepare ternary lanthanide complexes in which the remaining ligands are dibenzoylmethane anions (dbm). [Eu(L1)(dbm)2] is eight-coordinate, with L1 acting only as a tetradentate chelate (with one potentially bidentate arm pendant) and two bidentate dbm ligands. [Nd(L1)(dbm)2] was also prepared but on recrystallization some of it rearranged to [Nd(L1)2][Nd(dbm)4], which contains a twelve-coordinate [Nd(L1)2]+ cation (two interleaved hexadentate podand ligands) and the eight-coordinate anion [Nd(dbm)4]- which, uniquely amongst eight-coordinate complexes having four diketonate ligands, has a square prismatic structure with near-perfect O8 cubic coordination. Formation of this sterically unfavourable geometry is assumed to arise from favourable packing with the pseudo-spherical cation. The isostructural series of complexes [Ln(L2)(dbm)2](Ln = Pr, Nd, Eu, Gd, Tb, Er, Yb) was also prepared and all members structurally characterised; again the metal ions are eight-coordinate, from one tetradentate ligand L2 and two bidentate dbm ligands. Photophysical studies on the complexes with Ln = Pr, Nd, Er, and Yb were carried out; all show the near-IR luminescence characteristic of these metal ions, with longer lifetimes in CD3OD than in CH3OH. For [Yb(L2)(dbm)2], two species with different luminescence lifetimes were observed in CH3OH solution, corresponding to species with zero or one coordinated solvent molecules, in slow exchange on the luminescence timescale. For [Nd(L2)(dbm)2] a single average solvation number of 0.7 was observed in MeOH. For [Pr(L2)(dbm)2] a range of emission lines in the visible and NIR regions was detected; time-resolved measurements show a particularly high susceptibility to quenching by solvent CH and OH oscillators.     

Syntheses, structures, near-infrared and visible luminescence, and magnetic properties of lanthanide-organic frameworks with an imidazole-containing flexible ligand

Reactions of tripodal ligand 1,3,5-tris(imidazole-1-ylmethyl)-2,4,6-trimethylbenzene (L) with lanthanide metal salts and triethyl orthoformate led to the formation of six bowl-like dinuclear compounds [Ln2(L)(HL)(NO3)6(HCOO)].3CH3OH (Ln = Gd 1, Tb 2, Dy 3, Er 4, Yb 5, and Eu 6). The single-crystal X-ray diffraction analysis revealed that six complexes are isomorphous and isostructural and that the dinuclear molecules are further connected by hydrogen bonds and pi-pi interactions, resulting in 3D channel-like structures. The luminescence properties have been studied, and the results showed that the Tb(III) (2) and Eu(III) (6) complexes exhibited sensitized luminescence in the visible region and their luminescence lifetimes in powder and DMSO-d6 solution are in the range of milliseconds. The Yb(III) complex (5) emits typical near-infrared luminescence in DMSO-d6 solution. Variable-temperature magnetic susceptibility measurements of 1-6 showed that complex 1 (Gd) is nearly a paramagnet and complexes 2 (Tb), 3 (Dy), and 4 (Er) show the ferromagnetic coupling between magnetic centers, whereas the depopulation of the Stark levels in complexes 5 (Yb) and 6 (Eu) leads to a continuous decrease in (chi M)T when the sample is cooled from 300 to 1.8 K.     

Positively charged lanthanide complexes with cyclen-based ligands: synthesis, solid-state and solution structure, and fluoride interaction

The syntheses of a new cyclen-based ligand L(2) containing four N-[2-(2-hydroxyethoxy)ethyl]acetamide pendant arms and of its lanthanide(III) complexes [LnL(2)(H(2)O)]Cl(3) (Ln = La, Eu, Tb, Yb, or Lu) are reported, together with a comparison with some Ln(III) complexes of a previously reported analogue L(1) in which two opposite amide arms have been replaced by coordinating pyridyl units. The structure and dynamics of the La(III), Lu(III), and Yb(III) complexes in solution were studied by using multinuclear NMR investigations and density functional theory calculations. Luminescence lifetime measurements in H(2)O and D(2)O solutions of the [Ln(L(2))(H(2)O)](3+) complexes (Ln = Eu or Tb) were used to investigate the number of H(2)O molecules coordinated to the metal ion, pointing to the presence of an inner-sphere H(2)O molecule in a buffered aqueous solution. Fluoride binding to the latter complexes was investigated using a combination of absorption spectroscopy and steady-state and time-resolved luminescence spectroscopy, pointing to a surprisingly weak interaction in the case of L(2) (log K = 1.4 ± 0.1). In contrast to the results in solution, the X-ray crystal structure of the lanthanide complex showed the ninth coordination position occupied by a chloride anion. In the case of L(1), the X-ray structure of the [(EuL(1))(2)F] complex features a bridging fluoride donor with an uncommon linear Eu-F-Eu entity connecting two almost identical [Eu(L(1))](3+) units. Encapsulation of the F(-) anion within the two complexes is assisted by π-π stacking between the pyridyl rings of two complexes and C-H···F hydrogen-bonding interactions involving the anion and the pyridyl units.     

Photoluminescence of europium(III) dithiocarbamate complexes: electronic structure, charge transfer and energy transfer

For the first time, we observed photoluminescence in Eu(III) dithiocarbamate complexes at room temperature -- more specifically in [Eu(Et(2)NCS(2))(3)phen], [Eu(Et(2)NCS(2))(3)bpy] and the novel [Eu(Ph(2)NCS(2))(3)phen], where phen stands for 1,10-phenanthroline and bpy for 2,2'-bipyridine. Correlations between the electronic structure of the dithiocarbamate ligands on one hand, and covalency, intensity, and ligand field spectroscopic parameters on the other, could be established. Moreover, the relative values of the emission quantum efficiencies obtained for these complexes, as well as their dependence with temperature, could be satisfactorily described by a theoretical methodology recently developed.